JP2009125975A - Method of removing foreign substance contained in thermoplastic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce, in melting a thermoplastic resin containing foreign substances and removing foreign substances by passing it through a filter to filtrate, the load applied to the filter and prolong the lifetime of the filter. <P>SOLUTION: The first extruder E1 is a twin-screw extruder. The thermoplastic resin containing foreign substances that is supplied from the supply port 2 through the weight-type feeder 9 is molten in the plasticization zone 4a, sent to supercritical fluid mixing, kneading and impregnating zone 4b for the supercritical fluid to be impregnated, and is lowered in its viscosity. Subsequently, the resin is sent to the second extruder E2 after the removal of the foreign substances by filtration by passing it through the filter 18. By decompressing the resin in the second extruder E2 the inner pressure is reduced and the impregnated supercritical fluid is evaporated and removed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for removing foreign matter contained in a thermoplastic resin, which can produce a thermoplastic resin having excellent physical properties and optical properties by removing the foreign matter from a thermoplastic resin containing foreign matter. Is.

  The thermoplastic resin may contain foreign substances such as an unreacted substance and an agglomerate of fillers due to impurities in the manufacturing process and the recycling process. If the thermoplastic resin contains a foreign substance, it causes a decrease in physical properties such as a decrease in strength and a decrease in optical properties such as a decrease in transmittance. Therefore, in order to produce a thermoplastic resin having excellent characteristics, a method for removing foreign substances contained in the thermoplastic resin has been developed.

  For example, in JP 2001-293723 A (Patent Document 1), a flake polyester obtained by pulverizing a recycle bottle is used as a raw material, and melted in an extruder and filtered through a filter to remove mixed foreign matters. A method for producing a regenerated polyester resin pellet which is extruded as a strand and cut into pellets is disclosed.

Japanese Patent Laid-Open No. 2000-219737 (Patent Document 2) discloses a method for removing foreign substances by filtering molten polycarbonate through a filter having a retention particle diameter of 20 μm or less with a differential pressure of 20 kg / cm ² or more. It is disclosed.

JP 2001-293723 A JP 2000-219737 A

  However, in the method of filtering the molten thermoplastic resin through a fine filter, the molten resin pressure on the upstream side of the filter becomes high when the viscosity of the molten resin is high. For this reason, the apparatus cannot be operated unless the discharge amount is extremely reduced, or the filter needs to be frequently replaced. In some cases, the filter is broken and continuous operation for a long time cannot be performed. Moreover, since it receives a high shearing force when passing through the filter, the temperature of the molten resin rises, leading to deterioration. Furthermore, since the molten resin pressure on the upstream side of the filter becomes high, there is a problem that the molten resin leaks from a movable part such as a filter changer.

  The present invention has been made to solve the above problems, and when a thermoplastic resin containing foreign substances is melted and filtered through a filter, the load on the filter is reduced and the life of the filter is extended. It is an object of the present invention to provide a method for removing foreign substances contained in a thermoplastic resin, which has improved productivity.

In order to achieve the above object, the method for removing foreign matter contained in the thermoplastic resin according to the present invention comprises:
The melted thermoplastic resin is melted, a supercritical fluid is added to the molten thermoplastic resin, and mixing and kneading at a critical temperature or higher and a critical pressure or higher is performed to reduce the viscosity of the molten thermoplastic resin. Then, after removing the foreign matter by filtering through a filter, the impregnated supercritical fluid is vaporized and removed by lowering the resin pressure.

  Since this invention is comprised as mentioned above, there exists an effect as described below.

  When the foreign material is removed by melting the thermoplastic resin containing the foreign material and filtering through the filter, the molten resin easily passes through the filter, and the pressure difference between the upstream side and the downstream side of the filter is reduced. Therefore, the lifetime of the filter can be extended.

  An embodiment of a method for removing foreign matter contained in a thermoplastic resin according to the present invention will be described.

  FIG. 1 is an explanatory view showing an example of an apparatus used for carrying out the present invention.

  The first extruder E1 is a twin screw extruder, and a thermoplastic resin containing foreign matters is supplied from a supply port 2 provided at the upstream end of the cylinder 1 through a weight feeder 9 at a constant rate. Is done.

  The supplied thermoplastic resin containing the foreign matter is melted in the plasticizing zone 4a, and then sent to the supercritical fluid mixing / kneading / impregnation zone 4b to be injected from the supercritical fluid injection nozzle 12. And mixed and kneaded. The supercritical fluid injection nozzle 12 is connected to a supercritical fluid supply device 10 capable of supplying a constant amount of supercritical fluid via a pipe line 11 in which a stop valve 11a is interposed.

  The gear pump 13, the diverter pump 14, and the filter changer 15 are sequentially connected to the downstream side of the first extruder E1, and the outlet side of the filter changer 15 is connected to the supply port 17 of the second extruder E2. 16 is connected.

  The second extruder E2 is a twin-screw or single-screw extruder having a decompression vent port 19. One end of a decompression conduit 24 with a decompression trap 20 interposed is connected to the decompression vent port 19, and melting is performed by decompressing via a vacuum pump 22 disposed at the other end of the decompression conduit 24. The impregnated supercritical fluid is vaporized and removed by lowering the resin pressure.

  Further, downstream of the second extruder E2, a die 25 for extruding the molten thermoplastic resin from which foreign matters have been removed in the shape of a strand, a strand bath 21 for cooling the strand, and cutting the strand into a pellet form Strand cutters 23 are sequentially installed.

  FIG. 2 is an explanatory view showing another example of an apparatus used for carrying out the present invention. As shown in FIG. 2, the thermoplastic resin containing foreign substances is plasticized and compressed in the plasticizing zone by the screw rotation of the first extruder E1, and then injected with a supercritical fluid into the molten resin. In order to impregnate the supercritical fluid, the groove depth is deeply processed to mix and knead the supercritical fluid with the supercritical fluid injection nozzle 12 and the supercritical fluid in which the pressure in the cylinder 1 and the pressure in the cylinder 1 is kept above the critical pressure. The first extruder El equipped with a supercritical fluid mixing / kneading / impregnation zone is introduced. A stop valve 11 a for turning on / off the supply of the supercritical fluid and a supercritical fluid supply device 10 for quantitatively supplying the supercritical fluid are installed upstream of the supercritical fluid injection nozzle 12.

  On the downstream side of the first extruder El, a diverter pump 14, a filter changer 15 provided with a filter (screen) 18 in sequence, and a second extruder E2 are connected. A decompression pipe 24 in which a decompression trap 20 and a vacuum pump 22 are sequentially interposed is connected to the decompression vent port 19 of the second extruder E2. Moreover, the die | dye 25, the strand bath 21, and the strand cutter 23 are installed in the downstream of the 2nd extruder E2.

  An embodiment of a method for removing foreign matter contained in a thermoplastic resin according to the present invention will be described in detail.

  In the present invention, the thermoplastic resin may be either hard or soft and is not particularly limited. Examples of thermoplastic resins include polypropylene, polyethylene, polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, polybutylene terephthalate, polystyrene, ABS (acrylonitrile butadiene styrene copolymer), AS (acrylonitrile styrene copolymer), Polymethyl methacrylate, polyamide, polyacetal, polycarbonate, polyphenylene sulfide, polyphenylene ether, polyether ether ketone, polysulfone, polyether sulfone, polyamideimide, polyetherimide, thermoplastic polyimide, natural rubber, isoprene rubber, chloroprene rubber, styrene rubber , Nitrile rubber, ethylene propylene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, epipyrrolol Ringomu, acrylic rubber, urethane rubber, fluorine rubber, mixed and kneaded material of two or more such as silicone rubber (ethylene-propylene copolymer, etc.), a graft polymer, such as maleic anhydride grafted polypropylene. These thermoplastic resins may be a single product or a mixture of a plurality of types. In addition, an unused material may be used, but a used recycled thermoplastic resin material may also be used.

  In addition, the foreign material contained in the thermoplastic resin is a gel-like substance produced as a starting material, such as a low molecular weight oligomer or an unreacted residual monomer reactant, an agglomerated or re-agglomerated filler, or a recycled material. Examples include metals, minerals, and thermosetting resins.

  Examples of the gel-like substance include a crosslinked product produced in the resin production process, a low molecular weight organic material produced by thermal degradation, and a metal compound.

  The filler is not particularly limited as long as it has properties that affect the properties of the resin composition by the method of the present invention. Examples of fine fillers include cationic layered compounds such as layered alkali metal silicates and layered titanates, layered double hydroxide salts, vermiculite, halosite, calcium carbonate, calcium carbonate whiskers, magnesium sulfate, sulfuric acid Examples thereof include barium, magnesium hydroxide, dolomite, wollastonite, spherical silicon oxide particles, sericite, carbon black, carbon fiber, carbon nanotube, carbon whisker, glass fiber, and aramid fiber. Among these, examples of layered alkali metal silicates include natural products such as montmorillonite, magnesia montmorillonite, iron montmorillonite, iron magnesia montmorillonite, hectorite, sabonite, stevensite, beidellite, nontronite, and soconite, chemically. Synthesized synthetic sukumenite, synthetic mica, etc. are listed. These may be used alone or in combination. These fine fillers may be partially substituted with organic compounds such as fatty acids or derivatives. Further, an untreated fine filler that has not been treated at all may be used.

  Examples of the metal include iron, copper, silver, gold, lead, aluminum, magnesium, and alloys thereof.

  Examples of the thermosetting resin include a phenol resin, a melanin resin, and an epoxy resin.

  The thermoplastic resin containing these foreign substances is plasticized in the plasticizing zone 4a of the first extruder E1 to be in a molten state, and the critical pressure and critical temperature of the supercritical fluid are determined by the thrust of the screw and the seal portion 5. It is adjusted to the condition exceeding. At this time, the pressure may be adjusted to a pressure lower than the critical pressure, but the pressure is preferably set to a critical pressure after the supercritical fluid is injected.

  In the present invention, the means for melting the thermoplastic resin containing foreign substances and adjusting the temperature to the critical temperature or higher and the critical pressure or higher is not particularly limited as long as it has the same function as the above-described extruder. . For example, the molten resin is sealed in a pressure-resistant container with a stirring function that can be heated, and the atmosphere of an inert gas such as nitrogen gas is pressurized while heating to a temperature higher than the critical temperature of the fluid to be injected, and the critical pressure of the fluid to be injected There is a method of applying pressure as described above. In addition, a solid or molten thermoplastic resin is introduced into an extruder such as a single-screw extruder or a twin-screw extruder, and the temperature is adjusted to be higher than the critical temperature and higher than the critical pressure of the fluid to be injected by the driving force of the heater and screw. and so on. Among them, the method using an extruder is most desirable from the viewpoint of productivity and quality maintenance because it can be continuously performed from plasticization of a thermoplastic resin to temperature rise and pressure increase. Further, when a single-screw extruder is used, the tip pressure of the extruder can be increased, which is advantageous for filtration.

  The supercritical fluid added to the thermoplastic resin is a third fluid that has an intermediate property between gas and liquid above the critical temperature and above the critical pressure, and has a larger diffusion coefficient than liquid. ing. Carbon dioxide, methane, nitrogen, etc. are listed as materials that can make a supercritical fluid relatively easily. In the present invention, those capable of becoming a supercritical fluid in a temperature range from the melting temperature of the thermoplastic resin to the decomposition temperature are preferred. Moreover, what can impregnate in a thermoplastic resin and can reduce the viscosity of molten resin is preferable. The supercritical fluid used in the present invention is most preferably carbon dioxide, which has the greatest effect, is inert, has little adverse effect on the thermoplastic resin, and is easy to handle.

  Supercritical carbon dioxide refers to carbon dioxide in a supercritical state controlled at a pressure of 31 ° C. or higher and 7.4 Mpa or higher. Since supercritical carbon dioxide has a density close to that of liquid and a diffusion coefficient close to that of gas, a larger amount of carbon dioxide can coexist with other substances faster than liquid carbon dioxide as compared with gaseous carbon dioxide.

  There is no restriction | limiting in particular about the manufacturing method of supercritical carbon dioxide. For example, liquid carbon dioxide that has been sufficiently cooled with a chiller is pressurized with a plunger-type or diaphragm-type pump and heated at the same time to bring the temperature and pressure to a supercritical state of 31 ° C. or higher and 7.4 MPa or higher, respectively. Pressurization method or gas pressurization method that uses pressurized nitrogen gas or air to pressurize gaseous carbon dioxide to bring the temperature and pressure to 31 ° C or higher and 7.4 MPa or higher, respectively. It has been known.

  In the liquid pressurization method, the fluid before pressurization must be liquid, and a cooling mechanism is always required to keep the liquid between the carbon dioxide cylinder and the pump, and cavitation occurs in the pump. In addition, since the pressurization capacity may be reduced, a method of producing a supercritical fluid by a gas pressurization method is more preferable when supplying a small amount of supercritical fluid. On the other hand, in the case of supplying a large amount of supercritical fluid, a method of producing a supercritical fluid by a liquid pressurization method that can control the supply amount widely and with high accuracy and requires less frequent maintenance is more preferable.

  The coexistence amount of the supercritical fluid in the present invention is 0.5 to 50 parts by weight, preferably 1.0 to 20 parts by weight, more preferably 2.0 to 15 parts by weight based on the total amount of the resin composition of the present invention. Part. The supercritical fluid coexisting with the thermoplastic resin diffuses into the thermoplastic resin and swells to lower the viscosity of the molten resin. For example, when 3 wt% of carbon dioxide in a supercritical state is added to polypropylene resin, the shear viscosity of the molten resin is reduced by 1.1 to 14%, and when 7 wt% is added, it is reduced by 11 to 44%. The resin pressure can be reduced.

  However, if the coexistence amount is less than 0.5 parts by weight, the viscosity and density of the molten resin do not change, so the resin pressure on the upstream side of the filter cannot be reduced. Further, if the addition amount is more than 50% by mass, the viscosity and density of the molten resin are excessively lowered, and it becomes difficult to keep the pressure in the coexisting place above the critical pressure, or the thermoplastic resin composition and the supercritical dioxide. This is not preferable because not only carbon is separated but also the molten resin is entrained and ejected from the vent port, or released without contributing to lowering the viscosity of the molten resin.

  In the present invention, a low molecular organic compound can be added as an auxiliary agent together with supercritical carbon dioxide. Since the auxiliary agent shown here has an action of changing the polarity of supercritical carbon dioxide, the structure of the resulting thermoplastic resin composition can be controlled over a wider range or / and finely, and the properties can be controlled over a wide range or / In addition, fine control is possible.

  The low molecular organic compound used in the present invention is preferably at least one low molecular organic compound having 1 to 10 carbon atoms selected from alcohols, ethers, ketones, and saturated hydrocarbons. Specifically, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol as alcohols, diethyl ether, methyl ethyl ether, ethyl butyl ether, ethyl propyl ether, methyl propyl ether as ethers, acetone as ketones Examples of methyl ethyl ketone and saturated hydrocarbons include hexane, heptane, pentane and the like. Among these, ethanol is most preferable because it has an effect of changing the polarity of supercritical carbon dioxide and has little harmfulness.

  Low molecular organic compounds may be used alone or in combination of two or more. The combination of two or more kinds of low-molecular organic compounds is more preferable because the polarity can be controlled more finely.

  The addition amount of the low molecular organic compound is 0.1 to 50% by mass, preferably 2.0 to 30% by mass, more preferably 3.0 to 20% by mass, based on the total amount of the thermoplastic resin composition obtained in the present invention. %. The low molecular weight organic compound in the above range is most effective in changing the polarity of the supercritical carbon dioxide, and as a result, the characteristics of the thermoplastic resin composition of the present invention can be controlled in a wider range.

  In the present invention, in addition to the above-mentioned auxiliary for adjusting the polarity of supercritical carbon dioxide, an antioxidant, a hydrochloric acid absorbent, a heat stabilizer, a light stabilizer, and an ultraviolet absorber as long as the object of the present invention is not impaired. , Internal lubricants, external lubricants, antistatic agents, flame retardants, pigments, dyes, dispersants, copper damage inhibitors, neutralizers, plasticizers, foaming agents, antifoaming agents, crosslinking agents, peroxides and other additives Can be added.

  The supercritical fluid supplied from the supercritical fluid supply device is injected into the molten resin whose pressure has been increased to near the critical temperature and critical pressure in the extruder through a supercritical fluid injection nozzle. The injected fluid is mixed and kneaded by a screw rotating in the cylinder of the extruder, and the supercritical fluid finely and uniformly dispersed in the molten resin gradually diffuses into the resin, and eventually all or part of the fluid melts. Impregnate resin.

  In the present invention, there is no particular limitation on the means for injecting the supercritical fluid into the thermoplastic resin, mixing, kneading, and impregnation, but it is possible to melt the thermoplastic resin continuously and to mix and knead efficiently. An extruder such as a single screw extruder or a twin screw extruder may be used. In that case, raise the internal pressure of the extruder above the critical pressure of the supercritical fluid, inject the supercritical fluid through an injection nozzle with a backflow prevention mechanism, and use the screw dispersion / thinning function. The resin is impregnated with all or part of the supercritical fluid.

  When injecting a supercritical fluid, an injection nozzle is installed at one or a plurality of locations in the cylinder of the extruder, or a nozzle having many fine holes as shown in US Pat. No. 6,169,122. If the supercritical fluid is quickly distributed and dispersed in the molten resin, for example, by installing, the time until the resin is impregnated is shortened.

  As mixing and kneading conditions, it is possible to impregnate the molten resin with the supercritical fluid more reliably by increasing the residence time in the extruder and increasing the screw rotation speed to increase the mixing and kneading ability. However, since the energy received by the molten resin is increased, deterioration and the like are likely to occur, so that appropriate conditions are preferable.

  As another example, there is a method in which a batch type pressure vessel is filled with a molten resin, a fluid is injected into the pressure vessel, and the fluid is held for a certain period of time as a condition above the critical pressure / temperature, and impregnated with a supercritical fluid. However, the processing amount per unit time is smaller than when an extruder is used. Due to the supercritical fluid impregnated in the molten resin, the viscosity of the molten resin is lowered and becomes easy to flow. Then, the molten resin having the reduced viscosity is passed through a filter having an opening size smaller than the size of the foreign material to be removed with a small resistance, thereby removing the foreign material.

  In the present invention, the means for filtering and removing foreign substances contained in the molten resin is not particularly limited. For example, a filter is placed between an upstream extruder that functions to plasticize a thermoplastic resin and impregnate the supercritical fluid, and a downstream extruder that removes the impregnated supercritical fluid from the molten resin. In general, a method of sandwiching an installed breaker plate and filtering foreign matter in the molten resin with the filter is widely used. The breaker plate is plate-shaped or cylindrical to increase the filtration area, but is preferably cylindrical to increase the efficiency of filtration. In addition, it is more preferable that a filter changer is provided that can replace the filter without stopping the flow of the molten resin when the opening area of the filter has decreased due to the accumulation of foreign matter. Further, when the filter has a fine mesh, a high pressure is generated on the upstream side of the filter and the flow of the molten resin is deteriorated. Therefore, it is more preferable to provide a pressure increasing means such as a gear pump on the upstream side of the filter. Further, it is more preferable to provide a diverter pump or the like between the gear pump and the filter so that the extruder is not stopped when the filter is blocked.

  When installing a filter on the breaker plate, in order to prevent the filter from being broken, install a filter with coarse and high strength upstream and downstream of the finest filter, and a molten resin between the filter and breaker plate. In order to prevent a short path between them, it is preferable to install a filter in which these filters are unitized without any gap. The molten resin from which foreign matter has been removed through the filter is decompressed by the pressure adjusting means.

  In the present invention, the pressure adjusting means for reducing the pressure of the molten resin from the critical pressure to a predetermined pressure is not particularly limited as long as it causes a pressure difference between upstream and downstream. For example, an orifice having a narrow flow path, a gear pump, an extruder and the like can be mentioned. Among them, a gear pump and an extruder are preferable because the pressure difference can be finely adjusted by the rotation speed of the gear and screw. The extruder is preferable because even if the molten resin is foamed by decompression, the gas in the foam can be quickly discharged to the outside, and further, the thermoplastic resin can be processed into a desired shape on the downstream side thereof. Among them, the twin screw extruder is most preferable because of its high ability to discharge the gas in the foam.

  The pressure difference to be adjusted is not particularly limited, but if the pressure difference is large before and after the filter, the filter will be easily broken by the differential pressure and the life will be shortened. Therefore, the differential pressure should be as small as possible while maintaining the throughput. It is preferable to adjust to.

  In addition, when the pressure is reduced to a pressure lower than the critical pressure, the supercritical fluid changes to bubbles, and the volume rapidly expands, making it difficult to handle.

  Next, the molten resin is further depressurized and finally adjusted to a normal pressure or a depressurized state, and the supercritical fluid impregnated in the thermoplastic resin is removed from the system in a gaseous state.

  In the present invention, as a means for removing the supercritical fluid mixed and / or impregnated in the thermoplastic resin, the supercritical fluid may be removed by leaving the thermoplastic resin in a molten state. Therefore, it is preferable to forcibly remove the supercritical fluid by reducing the atmosphere. Further, it is more preferable to reduce the thickness of the thermoplastic resin using an extruder and then to reduce the pressure because the supercritical fluid is efficiently removed. In particular, it is most preferable to use a twin screw extruder having a high surface renewal performance because the supercritical fluid can be removed most efficiently.

  The thermoplastic resin after the supercritical fluid is removed is discharged out of the extruder through a die. As for the shape imparting method after discharging, for example, it may be cooled in the form of a strand through a die and cut into pellets using a strand cutter, or may be pelletized by mounting an underwater hot cutter. Moreover, after connecting a gear pump, you may shape | mold into a sheet | seat or a film through a T die or a round die.

  A device similar to that shown in FIG. 1 is used. A twin screw extruder TEX44αIIL / D77 (first extruder E1) made by Nippon Steel Works, which can inject supercritical carbon dioxide, and a gear pump, a diverter pump, and a filter changer are arranged downstream, and further downstream A twin screw extruder TEX30L / D42 (second extruder E2) manufactured by Nippon Steel Works for removing carbon dioxide from the molten resin was disposed.

  Recycled polycarbonate pellets containing particles with a particle size of about 20μm to 150μm are put into a twin screw extruder TEX44αIIL / D77 at 50kg / h, and after plasticization, manufactured with a supercritical fluid supply device (Showa Carbon Dioxide) Carbon dioxide in the supercritical state was quantitatively injected into a twin screw extruder through an injection nozzle. And after adjusting the discharge amount and the pressure in an extruder with a gear pump in the state which opened the diverter pump, the diverter pump was closed, molten resin was passed through the filter in the filter changer, and the time until the filter was broken was measured. Further, the molten resin that passed through the filter was further introduced into the downstream twin screw extruder TEX30L / D42, and after removing carbon dioxide in a reduced-pressure atmosphere, it was discharged in the form of a strand from the die and cooled by a strand bath. Then, it processed into the pellet with the strand cutter.

  Treat the polycarbonate under the conditions shown in Table 1, measure the pressure upstream of the filter and the time until the filter breaks, and the proportion of particles of 100 μm or more and the proportion of particles less than 100 μm contained in the obtained pellets Were observed and weighed with a microscope. The obtained results are shown in Table 2, Table 3 and FIG.

(Comparative example)
The conditions for not injecting the supercritical fluid as shown in Table 1 in the same manner as in the examples were used as comparative examples. The obtained results are shown in Table 2 and FIG.

  As shown in FIG. 3, when a filter in which a 1400 mesh filter was simply sandwiched between backup filters was used, the effect of the addition of supercritical carbon dioxide on the internal pressure upstream of the filter did not appear clearly. However, it is clear that the time until the filter breaks is extended by the addition of supercritical carbon dioxide. When the amount of supercritical carbon dioxide added is 3 parts by weight, the time until the filter breaks is shorter than when 1 part by weight is added. This is due to Shutaro Kawabe, Taku Saito, Molding '07 As shown in Proceedings of the 18th Annual Conference P93 (2007), the amount of supercritical carbon dioxide dissolved in the molten resin increases, the number of entanglement points of the polymer chain decreases and the friction between the polymer chain and the filter It can be inferred that the time until tearing has shortened.

  As shown in FIG. 4, when a 300-mesh filter and a 1400-mesh filter are stacked and sandwiched between backup filters, the internal pressure on the upstream side of the filter is 14 minutes later in a system without adding supercritical carbon dioxide. Over 38 MPa, the operation could not be continued due to danger.

  In the system to which supercritical carbon dioxide was added, the ultimate pressure decreased, and the filter was not broken during the test period. Moreover, when addition of supercritical carbon dioxide was stopped on the way, the internal pressure increased and the filter was broken after 15 minutes. From this, it is clear that the addition of supercritical carbon dioxide reduces the pressure difference between the upstream side and the downstream side of the filter and increases the lifetime of the filter.

  Fig. 5 shows the internal pressure (pre-filter pressure) on the upstream side of the filter when a thermoplastic resin having a different viscosity is used with a 300-mesh filter and a 1400-mesh filter overlapped with each other in the same way as in Fig. 1. The relationship of filtration time is shown. The resins with MFR = 40 and MFR = 120 showed an effect of extending the filter life by adding supercritical carbon dioxide, but the resins with MFR = 15 showed no effect of extending the life.

  Table 3 shows the change in the ratio of foreign matters of 100 μm or more before and after filtration. In any system using any raw material, it was confirmed that the ratio of foreign matters having a size of 100 μm or more decreased in the molten resin after filtration to which supercritical carbon dioxide was added.

It is explanatory drawing which shows an example of the apparatus used for implementation of this invention. It is explanatory drawing which shows the other example of the apparatus used for implementation of this invention. It is a graph which shows the influence which the addition of a supercritical carbon dioxide has on the internal pressure and filter lifetime of the upstream of a filter at the time of using the filter which pinched | interposed the filter of 1400 mesh with the backup filter. It is a graph which shows the influence which the addition of a supercritical carbon dioxide has on the internal pressure and filter lifetime of the upstream of a filter at the time of using it, putting a 1400 mesh filter on a 300-mesh filter, and putting it between backup filters. The effect of the addition of supercritical carbon dioxide on the internal pressure on the upstream side of the filter and the filter life when a 300-mesh filter and a 400-mesh filter are used with a different viscosity resin sandwiched between backup filters is shown. It is a graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Supply port 3 Rotation drive machine 4a Plasticization zone 4b Supercritical fluid mixing, kneading | mixing, impregnation zone 5 Seal part 9 Heavy feed feeder 10 Supercritical fluid supply apparatus 11 Pipe line 11a Stop valve 12 Supercritical fluid injection nozzle 13 Gear pump 14 Diverter Pump 15 Filter Changer 16 Discharge Line 17 Supply Port 18 Filter 19 Depressurization Hent Port 20 Decompression Trap 21 Strand Bath 22 Vacuum Pump 23 Strand Cutter 24 Decompression Pipeline

Claims (3)

  The melted thermoplastic resin is melted, a supercritical fluid is added to the melted thermoplastic resin, and mixing and kneading at a critical temperature or higher and a critical pressure or higher is performed to reduce the viscosity of the molten thermoplastic resin. And then removing the foreign matter by filtering through a filter, and then evaporating and removing the impregnated supercritical fluid by lowering the resin pressure. Foreign matter removal method.   A method for removing foreign matter contained in a thermoplastic resin, wherein the amount of supercritical fluid added is within a range of 0.5 to 15 parts by weight with respect to 100 parts by weight of the thermoplastic resin.   The method for removing foreign substances contained in a thermoplastic resin according to claim 1 or 2, wherein the supercritical fluid is supercritical carbon dioxide.

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