JP4135958B2 - Apparatus and method for measuring bulk density of pre-expanded particles and method for producing pre-expanded particles - Google Patents

Description

  The present invention relates to an apparatus and method for automatically measuring the bulk density of pre-expanded particles of a foamable thermoplastic resin to be foamed by a pre-foaming apparatus, and the foaming conditions in the pre-foaming apparatus are automatically measured using this measuring method. It is related with the method for manufacturing the pre-expanded particle | grains with constant bulk density by adjusting.

  In order to produce a foamed resin product from a foamable thermoplastic resin, first, foamable thermoplastic resin particles (raw material particles) as a raw material are prefoamed to a predetermined bulk density by a prefoaming device, and further foamed by a molding machine. Let the molded body be molded. In the production of foamed resin products, it is important to make the bulk density of the pre-foamed particles constant in order to stabilize the amount of pre-foamed particles supplied to the molding machine and to stabilize the quality of the molded body. It is.

  In general, the step of producing the pre-foamed particles includes supplying a predetermined amount of raw material particles made of a foamable thermoplastic resin to a pre-foaming pressure vessel of a pre-foaming apparatus and performing predetermined foaming with a heating medium such as water vapor. Foaming up to a magnification, or raw material particles are introduced together with a dispersing aid such as water, a dispersing agent or a surfactant from a charging port of a prefoaming pressure vessel, and a foaming agent is charged with a pressure setting device. The inside of the pressurized container is adjusted to a predetermined pressure, steam is passed through a jacket attached to the pressurized container, the mixture in the pressurized container is adjusted to a predetermined temperature, and if the predetermined temperature and pressure are reached, the pressure is increased. Foaming is performed by opening the container discharge valve and discharging from the pressurized container through the nozzle. The pre-expanded particles thus obtained are separated from water by a separator and sent to a pre-expanded particle storage tank.

As a method for adjusting the bulk density of the pre-foamed particles, the pre-foamed particles are collected, the bulk density is measured, and the operating conditions of the pre-foaming device based on the deviation from the target value (for example, pre-foaming) What is necessary is just to change the supply amount of the raw material particle | grains to a pressurization container, the pressure of a pre-foaming pressurization container, temperature, etc.). The bulk density of the pre-expanded particles is determined by dehydrating the pre-foamed particles wetted with water vapor or water after pre-foaming with the pre-foaming apparatus, and measuring this with a bulk density measuring apparatus. For example, after completion of the pre-foaming, a predetermined amount of pre-foamed particles wetted with water is sampled, sent to the drying container and dried in about 10 to 30 seconds by dry air blown from the dry air supply device in the drying container, A method has been proposed in which this is sent to an automatic magnification measuring device to automatically measure the expansion ratio (Patent Document 1: Japanese Patent Laid-Open No. 6-80816).
In this method, an automatic magnification measuring device is attached to a batch-type pre-foaming device, and the supply amount of raw material particles for the production of pre-foamed particles in the next batch is changed from the difference between the foaming magnification obtained by the calculation and the target foaming magnification. Thus, the expansion ratio of the pre-expanded particles is automatically adjusted.
Japanese Patent Laid-Open No. 6-80816

  The previously known automatic magnification measuring apparatus for pre-expanded particles is applied to a batch-type foaming operation, and the change of the foaming conditions (feeding amount of raw material particles) based on the measurement result is performed at the production stage of the pre-expanded particles of the next batch. It has been implemented. However, in this method, when the batch size is small, the foaming time is short, and even if the expansion ratio of the pre-expanded particles can be measured during foaming, the foaming may end before adjusting the conditions during foaming, When the foaming time is short, the fluctuation of the bulk density during that time is not large, so that the conditions have not been adjusted during foaming. On the other hand, if the batch capacity is increased for the purpose of increasing productivity, the foaming time becomes longer, and the foaming ratio varies within the foaming time. As a method for solving this problem, it is conceivable to measure the bulk density, adjust the foaming conditions by looking at the measurement result, and adjust the foaming ratio to the target. One of the problems to be solved by the present invention is to provide an apparatus and method for measuring the bulk density of wet pre-expanded particles after pre-expansion in a short time. Another problem is to produce pre-expanded particles having a uniform bulk density, that is, a stable expansion ratio, by adjusting the expansion conditions during the expansion time based on the measurement result of the bulk density of the pre-expanded particles. It is.

  In order to achieve the above object, an apparatus for measuring the bulk density of pre-expanded particles according to the present invention is an apparatus for automatically measuring the bulk density of pre-expanded particles of a foamable thermoplastic resin. In order to sample the pre-foamed particles from the pipe for sending the pre-foamed foamed thermoplastic resin pre-foamed particles from the pre-foaming device to the pre-foamed particle storage tank, a sample collecting pipe branched from the middle of the pipe; , One end side is connected to the sampling pipe, the other end has a structure that allows water and gas to permeate but does not allow the pre-expanded particles to permeate, a sample collection container having a blower connected to the other end side, and A dryer connected to the one end side of the sample collection container; and a bulk density measuring machine connected to the dryer.

  The method for measuring the bulk density of pre-expanded particles according to the present invention is a method for measuring the bulk density of pre-expanded particles of a foamable thermoplastic resin, which is pre-foamed by a pre-foaming device and pre-expanded from the pre-foaming device. Part of the pre-expanded particles of the foamable thermoplastic resin sent to the expanded particle storage tank is collected in a sample collection container through the sample collection pipe, and the collected pre-expanded particles are discharged from the sample collection container to the dryer by a blower. Then, after the pre-expanded particles are air-dried, the bulk density of the dried pre-expanded particles is automatically measured by a bulk density measuring machine.

  In the measurement method of the present invention, the amount of water dehydrated and / or dried from the pre-expanded particles is stabilized by discharging the pre-expanded particles from the sampling container to the dryer by the dry air supplied from the blower. Can do.

  In addition, the sample collection pipe, the sample collection container and the dryer are connected to a three-way valve, and pre-expanded particles are collected in the sample collection container via the sample collection pipe by switching the direction of the three-way valve. The pre-expanded particles may be discharged from the sample collection container to the dryer.

  A heater for heating the air supplied from the blower to the sample collection container may be provided, and the dry air when the pre-expanded particles are discharged from the sample collection container to the dryer by the blower may be heated.

  Furthermore, it is preferable to connect a bulk density comparison calculation device to the bulk density measuring device.

  In addition, the method for producing pre-expanded particles having a predetermined bulk density according to the present invention automatically measures the bulk density using the method and apparatus of the present invention, and sets the measurement result as a target bulk density with the bulk density arithmetic unit. The result of the comparison is fed back to the pre-foaming device so that the bulk density of the pre-foamed particles produced is constant, the foaming conditions are automatically adjusted, and the raw material particles are pre-foamed by the pre-foaming device. Is.

  The foaming conditions are preferably adjusted by adjusting the set pressure of the preliminary foaming device by feedback from the bulk density comparison arithmetic device.

  As a preferred method for producing pre-expanded particles according to the present invention, expandable thermoplastic resin particles are introduced together with water, a dispersing agent, and the like from an inlet of a pre-expanded pressure vessel of a pre-expanding device, and pre-foamed with a pressure setting device. A foaming agent is introduced into the pressure vessel, the inside of the prefoaming pressure vessel is adjusted to a predetermined pressure and temperature, and foamed through a nozzle, and the result of comparison with a target value by the bulk density comparison calculation device is compared with the prefoaming device. There is a method of adjusting the pressure in the pre-foaming pressurized container by feeding back to the pressure setting device.

  According to the apparatus and method for measuring the bulk density of pre-expanded particles according to the present invention, the pre-expanded particles to be dehydrated and dried by once collecting the wet pre-expanded particles collected from the pre-expanded apparatus in a sample collection container. The moisture amount is stabilized, and the drying time is shortened by sending it to a drier and air-drying it. Thereby, accurate bulk density measurement can be performed in a short time. Therefore, it is possible to produce pre-expanded particles having a predetermined bulk density by feeding back the measurement result of the bulk density to the operating conditions of the pre-expanding device.

  In addition, the sample collection pipe, the sample collection container and the dryer are connected to a three-way valve, and pre-expanded particles are collected in the sample collection container via the sample collection pipe by switching the direction of the three-way valve. If the pre-expanded particles are discharged from the sample collection container to the dryer, the configuration and operation of the bulk density measuring device can be simplified.

  In addition, if a heater for heating the air supplied from the blower to the sample collection container is provided and the dry air when the pre-foamed particles are discharged from the sample collection container to the dryer by the blower is heated, The pre-expanded particles can be dried in a shorter time.

  Further, by connecting a bulk density comparison calculation device to the bulk density measuring device, it becomes easy to feed back the measurement result of the bulk density to the preliminary foaming device.

  Further, according to the method for producing pre-expanded particles according to the present invention, the bulk density of the pre-expanded particles expanded by the pre-expanding device can be measured in a short time and fed back to the pre-expanding device. By adjusting the foaming conditions, it is possible to produce pre-foamed particles having a uniform bulk density, that is, a stable foaming ratio.

As the adjustment of the foaming conditions, by adjusting the set pressure of the preliminary foaming device by feedback from the bulk density comparison calculation device, the foaming conditions can be quickly adjusted, and the fluctuation of the bulk density of the preliminary foamed particles can be adjusted. Can be small.

FIG. 1 is an overall flow diagram of a pre-foamed particle manufacturing apparatus in which an automatic bulk density measuring apparatus according to an embodiment of the present invention is applied to a pre-foaming apparatus. FIG. 2 shows the bulk density of the pre-foamed particles of Examples produced by adjusting the bulk density of the foamed particles during foaming based on the measurement results of the automatic bulk density measuring apparatus of the present invention, and the foamed particles being foamed by the conventional method. It is a graph which shows the bulk density of the pre-expanded particle of the comparative example manufactured while measuring the bulk density.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pre-foaming pressurization container 2 Input port 3 Pressure setting device 4 Pressurization container discharge valve 5 Nozzle 6 Separator 7 Drain pump 8 Piping 9 Sample collection piping 10 Prefoaming device 11 Three-way valve 12 Sample collection container 13 Blower 14 Heater 15 Dryer 16 Bulk density measuring device 17 Bulk density comparison calculation device 18 Dryer discharge valve 20 Automatic bulk density measuring device 30 Pre-foamed particle storage tank

  Hereinafter, the present invention will be described with reference to FIG. FIG. 1 schematically shows the flow of the entire pre-expanded particle manufacturing apparatus in which an automatic bulk density measuring apparatus 20 is connected to the pre-expanding apparatus 10. The preliminary foaming apparatus 10 includes a preliminary foaming pressurized container 1, a nozzle 5, and a separator 6. The pre-foamed pressurized container 1 includes an input port 2, a pressure setting device 3, and a pressurized container discharge valve 4. The separator 6 includes a drain pump 7.

  The process of producing the pre-foamed particles by the pre-foaming apparatus 10 is as follows. First, expandable thermoplastic resin particles (raw material particles) made of, for example, a polyolefin resin such as polyethylene or polypropylene, or a polystyrene resin such as polystyrene, and the like are used to disperse water, a dispersant, a surfactant, and the like from the inlet 2. The pre-foaming pressure vessel 1 is charged together with the agent, and then the charging port 2 is closed, and the foaming agent is charged by the pressure setting device 3 and adjusted to a predetermined pressure. Next, steam is passed through a jacket (not shown) attached to the pre-foamed pressurized container 1 to adjust the mixture in the pre-foamed pressurized container 1 to a predetermined temperature and pressurize if the predetermined temperature and pressure are reached. The container discharge valve 4 is opened and foamed through the nozzle 5. The pre-expanded particles thus obtained are separated from water by the separator 6. The separated water is discharged by the drainage pump 7, and the pre-foamed particles are sent to the pre-foamed particle storage tank 30 through the pipe 8 connecting the separator 6 and the pre-foamed particle storage tank 30.

  The automatic bulk density measuring device 20 of the present invention is provided with a sample collecting pipe 9 for sampling pre-foamed particles, which is branched from the middle of a pipe 8 connecting the separator 6 and the pre-foamed particle storage tank 30, and one end of the pipe A fixed-volume sample collection container 12 having a structure that does not allow the pre-expanded particles to pass therethrough and a dryer 15 are provided, and these are connected to the three-way valve 11. The sample collection container 12 includes a blower 13 including a heater 14. The dryer 15 is connected to a bulk density measuring machine 16 provided with a bulk density comparison calculation device 17.

  The measurement of the pre-expanded particles by the automatic bulk density measuring device 20 is performed as follows. During the pre-foaming, the three-way valve 11 causes the sample collecting pipe 9 and the sample collecting container 12 to communicate with each other, the sample collecting pipe 9 and the dryer 15 are disconnected, and the pipe between the separator 6 and the pre-foamed particle storage tank 30. The pre-expanded particles are collected from the sample collection pipe 12 through the sample collection pipe 9 and the three-way valve 11.

  The three-way valve 11 can be a commonly used three-way ball valve. There are two types of commercially available three-way ball valves, an L port type and a T port type. In the present invention, it is preferable to use an L port type. This is a ball valve for changing the direction of fluid in three directions. By rotating a ball with an L-shaped flow path by 90 degrees, instead of using three two-way valves, The direction can be switched by one. The diameter of the three-way valve only needs to be large enough to prevent the pre-expanded particles from being blocked. If the diameter of the pre-expanded particles is about 2 mm, the diameter of the pre-expanded particles is about 10 mm or more. , 50A (inner diameter approximately 50 mm) or more, can be collected without clogging. Three-way ball valves include a type in which the diameter of the ball portion is smaller than the diameter of the pipe, and a type in which both have the same diameter (referred to as a full bore). Either type can be used as long as the pre-expanded particles are not blocked.

  A mesh m is provided on the other end side of the sample collection container 12 (the side opposite to the side where the three-way valve 11 is connected). As long as mesh m captures pre-expanded particles but can pass water and gas, the wire diameter and mesh size are not limited. Due to the internal pressure of the pre-foaming device 10 (pre-foaming pressure vessel 1), the pre-foamed particles, water and gas pass through the three-way valve 11 and flow into the sample collection container 12, and the pre-foamed particles that flow in are captured by the mesh m. A part of the water and the gas pass through the mesh m, and further flow backward through the heater 14 and the blower 13 to be discharged to the outside. In this way, a predetermined amount of pre-expanded particles are filled into the space A in the sample collection container 12 partitioned by the mesh m by the internal pressure of the pre-expanding device 10. When the internal pressure of the pre-foaming device 10 is insufficient to fill the pre-expanded particles into the sample collection container 12, the pressure inside the sample collection container 12 is reduced through the mesh m to enter the sample collection container 12. The pre-expanded particles can be filled smoothly. The capacity of the sample collection container 12, that is, the volume of the space A partitioned by the mesh m is about 10 to 0.05L, more preferably about 3 to 0.3L. If the capacity of the sample collection container 12 is too large, it becomes difficult to quickly dry the pre-expanded particles, and the bulk density may not be measured during the foaming time and the measurement results may not be fed back. If it is too small, the measurement accuracy of the bulk density decreases, which is not preferable.

  Next, the three-way valve 11 is switched to shut off the sample collection pipe 9 and the sample collection container 12, and the sample collection container 12 and the dryer 15 are communicated with each other. The pre-expanded particles collected and filled in the space A are extruded with dry air obtained by heating the air flow with the heater 14, sent to the dryer 15, and dehydrated and dried. The heater 14 may be a commonly used air heater. Examples of the heater 14 include a shell-type heater, a duct heater, a screw heater, and the like. Depending on the air volume and temperature required to send the pre-foamed particles from the sample collection container 12 to the dryer 15 for dehydration and drying. Select the one with the appropriate method and ability. The amount of air from the blower 13 used for drying and the temperature of the drying air adjusted by the heater 14 are the moisture content on the surface of the pre-foamed particles, the humidity of the dry air, the resin composition of the pre-foamed particles, and the type and amount of the foaming agent. What is necessary is just to set according to etc. Since drying time will become long if drying temperature is low, it is good to increase the air volume from the air blower 13 in this case. Depending on the resin composition, if the drying temperature is low, the particles shrink, and the correct bulk density may not be measured. In such a case, the drying temperature may be increased as long as the pre-expanded particles do not shrink.

  As the dryer 15 to which the pre-expanded particles are sent from the sample collection container 12, a dryer of a system generally used for drying powder particles can be used. The residence time of the pre-expanded particles in the dryer 15 may be a time required for drying. When the drying speed is fast and the pre-expanded particles are dried in a few seconds from the sample collection container 12 to the dryer 15, a dryer called air flow drying or flash drying can be used. When the drying speed is low, a cyclone dryer or a fluidized bed dryer can be used. If the dryer 15 has a structure in which dry air and pre-expanded particles rotate inside, such as a cyclone dryer, the pre-expanded particles stay in the dryer as long as the air is blown, and the drying is completed. The necessary residence time can be secured freely. However, when excessively dried, the pre-expanded particles whose surface has no moisture are charged inside the dryer 15 and the particles repel at the time of measuring the bulk density described later, so that the correct bulk density may not be measured. In this case, the bulk density can be measured normally by adding (spraying) an antistatic agent to the pre-expanded particles and grounding the device before drying. As the antistatic agent, commercially available antistatic agents, surfactants and the like can be used. As a countermeasure against electrification of dry particles, it is also effective to humidify the air used for drying.

The dried pre-expanded particles are put into the bulk density measuring device 16 from the discharge valve 18 at the bottom of the dryer 15. The bulk density measuring device 16 can calculate the bulk density by collecting a sample in a container having a constant volume and measuring the weight of the sample. Further, the bulk density measuring device 16 includes a mechanism for discharging the measured sample to the outside. The measurement result of the bulk density is calculated by the bulk density comparison calculation device 17. The bulk density comparison calculation device 17 inputs the electrical signal of the measurement result of the bulk density output from the bulk density measuring device 16 into a personal computer or a sequencer, and performs a comparison calculation with the target value. When it is calculated by the bulk density comparison calculation device 17 and is different from the target bulk density, a signal for setting a new pressure set value is sent to the pressure setting device 3 of the preliminary foaming device 10. Known devices can be used for the bulk density measuring device 16 and the bulk density comparison calculation device 17.

(Example 1)
EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. In the following examples, “part” represents “part by weight”.

The example which applied this invention to manufacture of polyolefin resin pre-expanded particle is given. For 100 parts of ethylene-propylene random copolymer (density 0.91 g / cm ³ , ethylene content 3%, melting point 145 ° C., MI = 5.5 g / 10 min, flexural modulus 1000 MPa) which is a polyolefin resin, Add 0.1 part of talc (average particle size 7 μm) as an inorganic filler, supply it to a 50 mmφ single screw extruder, melt knead, extrude from a cylindrical die with a diameter of 1.5 mmφ, cut with a cutter after water cooling, Resin particles (pellets) (1.8 mg / particle) were obtained from the columnar polyolefin-based resin composition. The obtained resin particles had a melting point of 145 ° C. and a density of 0.90 g / cm ³ measured according to JIS K 7112.

  100 parts (3000 kg) of the obtained resin particles, 1.5 parts of tribasic calcium phosphate as a dispersing agent and 0.03 part of sodium n-paraffin sulfonate as a dispersing aid, together with 300 parts of water, the prefoaming apparatus 10 shown in FIG. Then, 12 parts of butane was press-fitted from the pressure setting device 3 and heated to 140 ° C. while stirring the aqueous dispersion in the pre-foaming pressure vessel 1. At this time, the pressure in the pre-foamed pressurized container 1 was about 1.3 MPa. After that, while maintaining the pressure in the pre-foamed pressurized container 1 with butane so that the bulk density is 45 to 55 g / L, the pressurized container discharge valve 4 is opened and the mixture of the resin particles and the aqueous dispersion medium is removed from the nozzle 5. To obtain pre-expanded particles having a closed cell structure. The foamed pre-expanded particles were separated from water by the separator 6 and sent to the pre-expanded particle storage tank 30 through the pipe 8 of 250A.

  At this time, the pre-expanded particles were sampled through the 50 A sample collection pipe 9 connected in the middle of the pipe 8 connecting the separator 6 and the pre-foamed particle storage tank 30. The sampled pre-expanded particles pass through the sample collection pipe 9 and the three-way valve 11 when the 50A three-way valve 11 is opened to the sample collection pipe 9 and the sample collection container 12, and the sample collection container 12 having a capacity of 1.5L. The space A was filled. After 10 seconds, the pre-expanded particle filling was complete.

Next, the blower 13 was operated, the heater 14 was heated to 50 ° C., and the three-way valve 11 was opened to the dryer 15 and the sample collection container 12. Dry air of 5.0 m ³ / min and static pressure of 4.0 kPa is discharged from the blower 13, and the pre-expanded particles filled in the sample collection container 12 with static pressure pass through the three-way valve 11 and pass through the dryer 15. Sent to. 60 seconds after the start of air blowing, the air blower 13 was stopped, the discharge valve 18 at the bottom of the dryer 15 was opened, and the dried pre-expanded particles were dropped and put into the bulk density measuring device 16 having a known structure. In the bulk density measuring device 16, the pre-expanded particles were put into a measuring cup having a capacity of 1.0 L, and a certain volume was collected. Excess pre-expanded particles 0.5 L overflowed from the measuring cup and discharged to the outside. The measuring cup was suspended by a measuring instrument, the weight W (g) of the pre-expanded particles was measured, and the bulk density of the pre-expanded particles was determined as W / 1.0 = W (g / L). .

  The pre-expanded particles that had been measured were discharged to the outside from a discharge valve provided at the bottom of the measuring cup, and the measurement of the bulk density was completed. Two minutes after sampling of the pre-expanded particles, measurement of the bulk density was completed 30 seconds after the sample pre-expanded particles were put into the bulk density measuring device 16. Next, the measurement result and the target value were compared by a known bulk density comparison calculation device 17 composed of a personal computer with a built-in analog signal input / output terminal. The measured value of the bulk density in the first 2 minutes was 48 g / L, which is smaller than 50 g / L, which is the target median value of 45 to 55 g / L. Therefore, a signal for increasing the set pressure was sent to the pressure setter 3. Thereafter, the bulk density of the pre-foamed particles was measured every 2 minutes, and the adjustment was continued so as to bring the bulk density closer to the target median value. Table 1 and FIG. 2 show the measurement results of the bulk density measured during foaming for 65 minutes. As shown in Table 1 and FIG. 2, the bulk density of the pre-expanded particles was within the target 45 to 55 g / L.

(Comparative Example 1)
Foaming was carried out by the same method as in the Examples except that the bulk density was measured by the method described in JP-A-6-80816. In this method, since it took 8 minutes to dry all the collected samples of pre-expanded particles with a dryer, it took 10 minutes to measure the bulk density. As a result of adjusting the preliminary foaming conditions every 10 minutes in response to the measurement result of the bulk density, the time change of the bulk density was as shown in Table 1 and FIG. Since it took 10 minutes from the sample collection to the completion of measurement, the bulk density was adjusted later and adjustment with high accuracy was not possible. As a result, three points out of the six measurement points were out of the target range of 45 to 55 g / L.

Claims (11)

  An apparatus for automatically measuring the bulk density of pre-expanded particles of an expandable thermoplastic resin, wherein the pre-expanded particles of the expandable thermoplastic resin pre-expanded by the pre-expand apparatus are stored in the pre-expanded particle storage tank. A sample collection pipe branched from the middle of the pipe for feeding to the pipe, and one end side is connected to the sample collection pipe and water and gas are permeated to the other end side but the pre-expanded particles are not permeated. A sample collecting container having a blower connected to the other end, a dryer connected to the one end of the sample collecting container, and a bulk density measuring machine connected to the dryer Bulk density measuring device.   The automatic bulk density measuring apparatus according to claim 1, wherein the sample collection pipe, the sample collection container, and the dryer are connected to a three-way valve.   The automatic bulk density measuring apparatus according to claim 1 or 2, further comprising a heater for heating air supplied from the blower to the sample collection container.   The automatic bulk density measuring device according to any one of claims 1 to 3, wherein the bulk density measuring device includes a bulk density comparison operation device.   A method for measuring the bulk density of pre-expanded particles of an expandable thermoplastic resin, wherein the pre-expanded particles of the expandable thermoplastic resin are pre-expanded by a pre-expanding device and sent from the pre-expanding device to a pre-expanded particle storage tank. The sample is collected in a sample collection container through a sample collection pipe, and the collected pre-expanded particles are discharged from the sample collection container to the dryer by a blower, and the pre-expanded particles are air-dried, and then the pre-expanded particles are dried. A method of automatically measuring the bulk density with a bulk density measuring machine.   6. The amount of water dehydrated and / or dried from the pre-expanded particles is stabilized by discharging the pre-expanded particles from the sampling container to the dryer with the dry air supplied from the blower. Measuring method.   One of the three-way valves is connected to the sample collection pipe, the other is connected to the sample collection container, the other one is connected to the dryer, and the direction of the three-way valve is switched to change the sample collection pipe. The measurement method according to claim 5 or 6, wherein pre-expanded particles are collected in a sample collection container, and the pre-expanded particles are discharged from the sample collection container to the dryer.   The measurement method according to any one of claims 5 to 7, wherein dry air is heated when the pre-expanded particles are discharged from the sample collection container to the dryer by the blower.   While continuously discharging the pre-expanded particles from the pre-expanding device, the bulk density of the discharged pre-expanded particles is measured by the method according to any one of claims 5 to 8, The measurement result is compared with the target value by the bulk density comparison calculation device, and the result is fed back to the pre-foaming device to adjust the foaming conditions of the pre-foamed particles pre-foamed by the pre-foaming device. A method for producing pre-expanded particles.   The manufacturing method according to claim 9, wherein the set pressure of the pre-foaming device is adjusted by feedback from the bulk density comparison calculation device.   The foamable thermoplastic resin particles are introduced together with water, a dispersing agent, etc. from the inlet of the prefoaming pressurization container of the prefoaming device, and the foaming agent is put into the prefoaming pressurization container with the pressure setting device, and prefoaming pressurization is performed. The inside of the container is adjusted to a predetermined pressure and temperature and foamed through a nozzle, and the result of comparison with a target value by the bulk density comparison calculation device is fed back to the pressure setting device of the preliminary foaming apparatus, and the prefoaming pressure container The manufacturing method according to claim 10, wherein the internal pressure is adjusted.

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