JP2004306567A - Pre-foaming method for obtaining pre-foamed thermoplastic resin particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a pre-foaming method for obtaining a pre-foamed particle having a good particle feeding property, a dry pre-foamed particle when fed for forming, or a pre-foamed particle showing little blocking without a big change in equipment such as a pre-foaming vessel and the like and a large extension of pre-foaming time. <P>SOLUTION: The pre-foamed particle having good the feeding property is obtained by a process of introducing dry air to the pre-foaming vessel for a predetermined period at a predetermined steam heating time. Further the temperature of the inner side of the pre-foaming vessel is kept at not lower than 80°C when the foamed thermoplastic resin particle is fed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００８３】
【発明の効果】
本発明による予備発泡粒子は、通常の予備発泡方法に比較すると、湿りが少なく、送粒時に滞留し送り難くなるような課題は発生に難くなる。またブロッキングの発生も少なくなる。また成形に供する際に金型への予備発泡粒子の充填も良好となる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for pre-expanding expandable thermoplastic particles, and without significantly extending the pre-expansion time, pre-expanded particles having good particle-feeding properties, or pre-expanded particles dried when subjected to molding, or Alternatively, the present invention relates to a method for pre-expanding pre-expanded particles with less blocking.
[0002]
[Prior art]
In molding using expandable thermoplastic resin particles of a thermoplastic resin represented by a styrene-based resin, expandable thermoplastic resin particles (hereinafter sometimes referred to as “raw material particles”) are once expanded at a predetermined magnification before molding. Then, it is general to provide for molding. A method of forming the raw material particles once into foamed particles of a predetermined magnification before molding is referred to as a prefoaming method, and the obtained foamed particles are referred to as prefoamed particles.
[0003]
This prefoaming method is roughly classified into a batch method and a continuous method. Of these, the expandable thermoplastic particles are charged into the pre-expansion tank, and the pre-expansion tank is opened under atmospheric pressure, and the mixture is opened and circulated while stirring, or steam without substantial pressurization or 0.005 to 0.005. After the pressurized steam of 0.03 MPa (gauge pressure) is circulated and heated and foamed, the foaming proceeds, and when the foamed particles reach a predetermined foaming ratio, the steam heating is stopped and air is blown to cool and dry. A batch method in which the particles to be pre-expanded particles are taken out from a pre-expansion tank is practically used as the most general method.
[0004]
Hereinafter, in the present invention, this prefoaming method is referred to as a normal prefoaming method. The pressure of the present invention is represented by a gauge pressure unless otherwise described below.
[0005]
In the batch type prefoaming method, since steam is used for heating, when the prefoamed particles are discharged from the prefoaming tank, if the coagulated water is attached to the prefoamed particles in a large amount, excessive wetness is obtained. After being discharged from the prefoaming tank, it may be difficult to send the prefoamed particles to the storage tank by, for example, pneumatic transportation using a pipe (hereinafter, this transportation is referred to as granulation).
[0006]
Usually, the pre-expanded particles are often used after being left in the storage tank for about 6 to 48 hours after being exposed to a room temperature environment (hereinafter referred to as “curing”). May not be volatilized and remain even when subjected to molding, causing a problem such as insufficient fusion between the foamed particles of the molded article.
[0007]
Furthermore, the pre-expanded particles having a high wettability tend to easily cause a blocking phenomenon in which the pre-expanded particles fuse together in the pre-expansion tank to form a lump. When blocking occurs, not only does the particle feedability deteriorate, but also a device called a filling machine that introduces pre-expanded particles into a mold during molding sometimes becomes clogged, and improvement has been demanded.
[0008]
Various attempts have been made for this. For example, the applicant of the present application has proposed a method in Patent Document 1 in which particles that have been subjected to pre-expansion are once discharged to a drying hopper, and then dried and sent.
[0009]
According to this Patent Document 1, the drying time is shortened and the granulation property is improved. However, if this is to be performed with an existing prefoaming machine, it is necessary to remodel the apparatus on a relatively large scale, and further improvement is required. Had been.
[0010]
[Patent Document 1]
JP-A-5-287114 (page 2, claims)
[0011]
[Problems to be solved by the invention]
In order to address the above-mentioned problems, the present invention provides pre-expanded particles having good particle feedability or molding without making major changes in equipment such as a pre-expansion tank and without significantly extending pre-expansion time. An object of the present invention is to provide a method for pre-expanding pre-expanded particles that have been dried at the time or pre-expanded particles having less blocking.
[0012]
[Means for Solving the Problems]
The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems. As a result, the temperature in the pre-foaming tank at the time of charging the expandable thermoplastic resin particles is set to 80 ° C. or more every time the pre-foaming is performed. The inventors have found that the above-mentioned problem can be solved by providing a step of introducing dry air for a predetermined time for each steam heating time, and have reached the present invention.
[0013]
That is, the present invention provides a method of 1) charging foamable thermoplastic resin particles into a pre-foaming tank and foaming the same by steam heating to obtain pre-foamed particles. In the steam heating step of blowing steam into the pre-foaming tank, The present invention also relates to a method for prefoaming expandable thermoplastic resin particles, which comprises a step of temporarily stopping steam heating at predetermined intervals and introducing dry air into the prefoaming tank for a predetermined time during that time.
[0014]
Further, the present invention is characterized in that the pressure of the steam used for heating is set to be higher by 0.003 to 0.020 MPa than in the pre-foaming method without providing a step of introducing dry air during the steam heating step. The present invention relates to a method for pre-expanding expandable thermoplastic resin particles described in 1).
[0015]
Further, the present invention provides a method of 3) charging foamable thermoplastic resin particles into a pre-foaming tank and foaming by steam heating to obtain pre-foamed particles. The present invention relates to a method for pre-expanding expandable thermoplastic resin particles, wherein the temperature is set to 80 ° C. or more every time the pre-expansion is performed.
[0016]
Further, the present invention provides the foaming property according to the above item 1) or 2), wherein the temperature in the pre-foaming tank at the time of charging the foamable thermoplastic resin particles is set to 80 ° C. or more every time the pre-foaming is performed. The present invention relates to a method for pre-expanding thermoplastic resin particles.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
As the thermoplastic resin of the expandable thermoplastic particles used in the present invention, any thermoplastic resin used for in-mold foam molding can be used, and for example, a polystyrene resin or a polymethyl methacrylate resin is preferable.
[0018]
Examples of the polystyrene resin include not only general polystyrene resins but also polystyrene resins containing 50% or more of styrene or methylstyrene, high-impact polystyrene resins, styrene and butadiene, methyl methacrylate, maleic anhydride, and the like. And the like, and these may be used alone or as a combination of two or more.
[0019]
As the thermoplastic resin of the expandable thermoplastic particles that can be used in the present invention, a polystyrene resin is particularly preferable in terms of economy and appearance, and as the polystyrene resin, polystyrene resin is easily available. , And can be most preferably used in terms of price economy.
[0020]
The expandable thermoplastic particles used in the present invention contain a blowing agent. As the foaming agent, an aliphatic hydrocarbon which can be used as a normal foaming agent such as propane, normal butane, isobutane, pentane, hexane or a mixture of one or more thereof is used in an amount of 1 to 10 parts by weight per 100 parts by weight of the thermoplastic resin. Parts by weight, preferably 3 to 8 parts by weight, more preferably 4 to 7 parts by weight. Among these, normal butane, isobutane or a mixture thereof is particularly preferable from the viewpoint of the retention of the foaming agent with respect to the resin.
[0021]
In addition, the expandable thermoplastic resin particles of the present invention include fatty acid glycerides such as stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, and stearic acid monoglyceride; As a plasticizer, a substance exhibiting a plasticizing effect on a thermoplastic oil such as a volatile oil or fat, an organic hydrocarbon such as cyclohexane, toluene, or xylene, or a thermoplastic resin such as liquid paraffin can be contained, and these can be used alone or in combination. Incidentally, such a plasticizer is used for the purpose of improving the pre-foaming property and the molding fusion.
[0022]
Further, to the expandable thermoplastic particles of the present invention, other additives that can be generally used for expandable thermoplastic particles, such as a flame retardant and a nucleating agent, may be appropriately added as long as the object of the present invention is not impaired. Can be.
[0023]
As the pre-foaming tank used in the present invention, a pre-foaming tank used in an ordinary pre-foaming method can be used. In addition, equipment attached to the prefoaming tank used in the present invention, for example, a steam valve, an air valve, a measuring device, and the like can be used as long as the range to be used or measured conforms to the usage range of the equipment. .
[0024]
However, usually, for example, only the heating of the steam purge described below is performed, and the structure is reinforced in the case of a pre-foaming tank having a relatively low pressure resistance design because the pressure does not substantially exceed the atmospheric pressure, or in the case where there is no resistance to the reduced pressure. Of course, it is preferable. In the case of prefoaming by automatic operation, a program such as a control device generally called a sequencer or a programmable controller is changed to a portion different from a normal prefoaming method, and the process according to the procedure of the present invention is changed. Naturally, it must be changed or newly established so that it can be selected and implemented. Furthermore, the object of the present invention is also realized in that it is necessary to install a thermometer and a pressure gauge capable of sending a control signal or measurement data to the sequencers as needed to realize a predetermined temperature and pressure. It is only natural to complete.
[0025]
As a basic flow of the prefoaming method in the present invention, a usual batch type prefoaming method can be used.
[0026]
The ordinary batch type prefoaming method will be described again. The expandable thermoplastic particles are charged into the prefoaming tank, and the inside of the prefoaming tank is connected to the atmosphere such as an exhaust valve while stirring the inside by rotating the stirring blade. The steamed valve is opened to open the prefoaming tank substantially at atmospheric pressure, and the steam valve is opened to allow steam to flow through the prefoaming tank to heat and foam, or 0.005 to 0.03 MPa ( (Gauge pressure) The foam is heated and foamed by pressurized steam heating to distribute the pressurized steam. When the foaming progresses and the foamed particles reach a predetermined foaming ratio, the steam is stopped, and air is blown to cool and dry. This is a pre-expansion method in which the particles to be pre-expanded particles are taken out from a pre-expansion tank.
[0027]
When charging the expandable thermoplastic particles into the prefoaming tank, the pressure in the prefoaming tank may be reduced before the charging, and the raw material charging valve may be opened and charged in that state.
[0028]
Further, for the heating, it is also possible to adopt a pre-expansion by a combination in which the expandable thermoplastic particles are slightly expanded by steam purge heating, and then expanded to a predetermined expansion ratio by pressurized steam heating.
[0029]
In pressurized steam heating, the opening degree of each of the exhaust valve and the steam valve is adjusted so that the inside of the pre-foaming tank is kept in a pressurized state, and heating is performed until the foamed particles reach a predetermined expansion ratio. The steam valve can be opened with the exhaust valve closed, steam can be introduced into the prefoaming tank, and when the pressure in the prefoaming tank reaches a predetermined pressure, the steam valve is closed and the exhaust valve is opened to open the prefoaming tank. The process of lowering the internal pressure and, when the pressure drops to a predetermined pressure, closing the exhaust valve again, opening the steam valve, and introducing steam into the preliminary foaming tank can be repeated until the foamed particles reach a predetermined expansion ratio. . Further, both can be implemented in combination.
[0030]
The prefoaming method of the present invention is achieved by incorporating one or both of the following two steps into the above-mentioned ordinary batch type prefoaming method.
[0031]
The first point is to control the temperature in the pre-expansion bath when the expandable thermoplastic resin particles are charged into the pre-expansion bath.
[0032]
In a normal batch type pre-expansion step, except for pre-heating the pre-expansion tank at the start of production, other than in the pre-expansion tank when charging the expandable thermoplastic resin particles into the pre-expansion tank for each production batch. The temperature is not controlled, and after the pre-expanded particles produced in the previous batch are discharged from the pre-expansion tank, the next batch starts production at the expected temperature.
[0033]
On the other hand, in the method of the present invention, when the expandable thermoplastic resin particles are charged into the prefoaming tank, the temperature is preferably set to 80 ° C. or higher, preferably 83 ° C. or higher for each prefoaming. The upper limit temperature is not important because it is unlikely that the temperature will rise excessively in operation, which is excessive. However, if the temperature is to be specified, the upper limit temperature is controlled to 110 ° C. or lower, preferably 90 ° C. or lower. .
[0034]
If the temperature is lower than 80 ° C., the effect of the present invention tends to be difficult to obtain. When the temperature exceeds 110 ° C., it takes a long time to raise the temperature of the pre-expansion tank before charging the expandable thermoplastic resin particles, so that a problem is likely to occur in productivity.
[0035]
As a method of raising the temperature of the pre-expansion tank to a predetermined temperature when charging the expandable thermoplastic resin particles, for example, a heating steam is introduced into the pre-expansion tank before charging the expandable thermoplastic resin particles. After raising the temperature about 10 ° C higher than the desired temperature, open the air valve and drain valve that can blow dry air into the prefoaming tank, and discharge the coagulated water stored in the prefoaming tank out of the prefoaming tank It is easy to reduce the temperature to the desired temperature while performing the heating.
[0036]
According to this method, the coagulated water present in the pre-foaming tank can be discharged before the foamable thermoplastic resin particles are charged, so that the inside of the pre-foaming tank can be substantially dried, and the pre-foaming tank can be relatively uniformly and easily formed. The temperature inside can be adjusted. The coagulated water present in the pre-expanded foaming tank before the foamable thermoplastic resin particles are charged is likely to cause the wetness of the obtained pre-expanded particles. It is more preferable to discharge the coagulated water.
[0037]
The second point is to provide a step of introducing dry air into the preliminary foaming tank for a predetermined time at predetermined time intervals when heating the foamed particles in the preliminary foaming tank with steam.
[0038]
That is, every time heating is performed for a predetermined time, the steam valve is closed, the exhaust valve and the drain valve are opened, the air valve is opened, and the foaming particles in the preliminary foaming tank are exposed to air, preferably dry air. Until the particles reach a predetermined magnification, the process is repeatedly performed for a predetermined time every predetermined heating time.
[0039]
The predetermined heating time cannot be unconditionally determined because it is determined by various factors such as the expandable thermoplastic resin particles to be used, the volatile content thereof, and the pressure of the steam to be introduced, but is preferably approximately 5 to 30 seconds. For example, if the predetermined expansion ratio is about 60 times with polystyrene resin particles, and the pressure of the used steam is about 0.011 MPa on average, about 15 seconds, if the pressure of the used steam is about 0.017 MPa on average, Preferably, it is about 10 seconds.
[0040]
If the heating time is lengthened, the foamed particles tend to be moistened, and the effect of the present invention tends to be weakened. When the length is shortened, foaming does not progress easily, and the productivity tends to decrease.
[0041]
Similarly, the flow time of the air introduced for each predetermined heating time cannot be determined unconditionally, but is preferably about 0.5 to 5 seconds. For example, if the predetermined expansion ratio is about 60 times with polystyrene resin particles and the pressure of the used steam is about 0.011 to 0.017 MPa, it is preferably about 3 seconds.
[0042]
If the air circulation time is lengthened, the productivity tends to decrease probably because the foamed particles cool. If the length is too short, sufficient moisture cannot be obtained, and the effect of the present invention tends to be weakened.
[0043]
Open the air valve to introduce the air into the pre-foaming tank for the air flow, but depending on the pre-foaming tank, valves such as steam, air, and drain were separated from the chamber with the foamed particles by a mesh wire mesh. It may be provided in a chamber called a chamber below the preliminary foaming tank. In this case, when the air valve is opened, the drain water remaining in the chamber flows back to the chamber containing the foamed particles together with the air, or the chamber is weakly pressurized by the air, so that the water from the chamber containing the foamed particles is released. There is a tendency for the drain to fall naturally into the chamber. In this case, the effect of the present invention tends to be weakened. In such a case, only the drain valve is opened without opening the air valve in the chamber, and air is introduced using another air valve provided in the chamber where the foamed particles are present, for example, a cleaning air valve in the pre-foaming tank. Is preferred.
[0044]
When the air is circulated, the foamed particles in the prefoaming tank may rise, and a sensor called a level sensor provided in the prefoaming tank and detecting the end of foaming may be in a detection state. In order to avoid this, it is preferable to provide a waiting time of 0.5 to 2 seconds after the end of the air circulation time and before starting the next heating. That is, from the viewpoint of stable production, it is preferable to move to the next process after the soared foamed particles fall and the erroneous detection state of the level sensor is eliminated.
[0045]
The air used for the distribution of the air may be ordinary compressed air used for industrial compressed air equipment, but dry air is more preferable in order to ensure the effect of the invention. For example, dry air that has passed through a freeze dryer to remove the wetness of the air itself can be used favorably.
[0046]
Note that the predetermined heating time, the predetermined time for introducing air, and the time required for stabilization do not necessarily have to be strictly constant, and may be slightly changed for each repetition depending on the expansion stage of the expanded particles.
[0047]
In carrying out the present method, the pressure of the steam used may be the same as the pressure of the steam used in the ordinary batch type prefoaming, but in that case, the time required for the prefoaming tends to be long. Although the reason is unknown, it is presumed that the pre-expanded particles are likely to cool down due to the flow of air and to require reheating time.
[0048]
In the present invention, if the pre-expansion time can be long, the same pressure as in the ordinary batch type pre-expansion method may be used. It is preferably set higher by 0.003 to 0.020 MPa, preferably 0.005 to 0.015 MPa.
[0049]
Although the reason is not clear, in the method of the present invention, in particular, when the step of introducing dry air into the prefoaming tank for a predetermined time at a predetermined time in the steam heating step is provided, blocking hardly occurs.
[0050]
Accordingly, the steam pressure can be further increased, but since the foaming speed becomes too fast and the foaming ratio tends to partially vary, it is preferable not to excessively increase the steam pressure.
[0051]
When the method of the present invention is used, when the level sensor is provided at the same height and the detection stabilization time of the level sensor is the same as compared with the case of the normal pre-foaming method, the foamable thermoplastic resin to be charged is used. In some cases, it is necessary to reduce the amount of resin particles by about 10% by the input weight. Although the detailed cause is unknown, this is because when the prefoaming method of the present invention is used, the foamed particles are likely to be in a dry state even in the prefoaming tank, so that the foamed particles are lifted up by the operation of the stirring blade in the prefoaming tank, It is considered that the level sensor is detected earlier than in the case of the normal prefoaming method.
[0052]
In this case, the present invention can be implemented without reducing the input amount by performing an easy countermeasure such as delaying the detection by elevating the position of the level sensor or taking a long detection time of the level sensor. .
[0053]
In the present invention, it is preferable to carry out both of these two steps in combination, as compared with the case where each of them is carried out alone, because the particle feedability is further improved.
[0054]
The pre-expanded particles according to the present invention have less wetness compared to the ordinary pre-expanded method, and the problem that the pre-expanded particles stay at the time of granulation and become difficult to send becomes difficult to occur. Also, the occurrence of blocking is reduced. In addition, the filling of the pre-expanded particles into the mold during the molding is improved.
[0055]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to only these Examples.
[0056]
In this example and comparative examples, preliminary foaming was performed using a BHP-110 type preliminary foaming machine manufactured by Daikai Kogyo Co., Ltd. The sequencer program of the prefoaming machine was changed every time based on the operation method of each example, and a series of steps were performed by automatic operation.
[0057]
Kanepal MKM (manufactured by Kaneka Chemical Industry Co., Ltd.) using polystyrene resin as a resin component as raw material particles which are expandable thermoplastic resin particles (the volatile matter measured by a pre-expanded particle volatile measurement method described later is about 5 vol. 0.7%).
[0058]
In Examples and Comparative Examples, after the raw materials were charged, pre-expanded particles were obtained in accordance with the steps of each example described later, and then the following evaluation items were evaluated.
1) Expansion ratio
Specific gravity of raw material particles is 1.04 g / cm ³ The expansion ratio was calculated based on the following equation.
(Expansion ratio) = (Bulk specific gravity of obtained pre-expanded particles) /1.04
[0059]
2) Amount of blocking occurrence
After taking out the pre-expanded particles from the foaming tank, the whole amount was put into a wire mesh positive basket having an opening of 10 mm, and sieving was performed. Then, the blocking mass in which the pre-expanded particles remaining on the wire mesh were fused was collected. The weight was measured, divided by the weight of the expandable thermoplastic resin particles charged, and calculated as a percentage.
[0060]
3) Evaluation of particle feedability
The particle-feeding property was evaluated using the angle of repose, and the smaller the angle of repose, the better the particle-feeding property.
That is, the pre-expanded particles immediately after the pre-expansion are collected and put into a pair of a styrene foam box having a length of 450 mm, a width of 350 mm, a height of 250 mm (inner dimensions) and a thickness of 30 mm, the upper surface of which is released and the short side surface is detachable. . At the time of loading, the box is thrown in while shaking. After throwing in so that there is no gap, the cutting is performed on the open surface at the top of the box. Thereafter, the detachable short side surface was promptly removed without taking a short time, and the inclination angle of the propelled particles inside the collapsed box was measured to obtain the angle of repose.
[0061]
4) Pre-expansion cycle
The opening time of the raw material charging valve into the pre-foaming tank was set to 0, the pre-foaming step was completed, and the time until the discharge door of the pre-foaming tank was closed was defined as the pre-foaming cycle.
[0062]
(Example 1)
The exhaust valve and the steam valve of the prefoaming tank of the BHP-110 type prefoaming machine were opened, and steam heating was performed until the temperature of the thermometer attached to the prefoaming tank reached 95 ° C. When the temperature of the thermometer reaches 95 ° C., the steam valve is closed, the cleaning valve in the can and the drain valve are opened to cool the inside of the prefoaming tank, and the coagulated water is discharged from the prefoaming tank. The cooling and discharging were performed until the temperature indicated by the thermometer dropped to 85 ° C.
[0063]
When the temperature of the thermometer reaches 85 ° C., the raw material charging valve is opened to feed the raw material particles into the pre-foaming tank. Vacuum purged for seconds.
[0064]
Thereafter, pressurized steam heating was performed at a lower limit pressure of 0.015 MPa to an upper limit pressure of 0.020 MPa. In this pressurized steam heating, the steam valve is opened and the steam is introduced into the prefoaming tank while the exhaust valve is closed until the inside of the prefoaming tank reaches the upper limit pressure. The heating operation of opening the exhaust valve and reducing the pressure in the preliminary foaming tank to the lower limit pressure was repeatedly performed until the level sensor detection described later.
[0065]
When performing the pressurized steam heating, the steam valve is closed, the exhaust valve, the drain valve, and the cleaning valve in the can are opened every 10 seconds after the operation (referred to as a heating unit time) to open the prefoaming tank. After introducing air for 3.5 seconds (referred to as a unit cooling time), a step of taking a level sensor stabilizing time (referred to as a unit stabilizing time) of 1.5 seconds was inserted every time.
[0066]
In the pressurized steam heating, the pressurized steam heating is terminated when the level sensor provided in the preliminary foaming tank continuously detects for 2 seconds or more, the steam valve is closed to cool the foamed particles in the preliminary foaming tank, the exhaust valve, The operation was performed for 30 seconds by opening the drain valve and the cleaning valve in the can.
[0067]
After cooling was completed, the discharge door was opened and the pre-expanded particles were discharged to an external hopper to obtain pre-expanded particles.
[0068]
Table 1 shows the evaluation items of the obtained pre-expanded particles.
[0069]
Although the obtained pre-expanded particles had the same initial cycle as the pre-expanded particles obtained by the ordinary pre-expanded method shown in Comparative Example 1, no blocking occurred, and the angle of repose was about It was extremely small, ie, 1/4 or less, and the particle feedability was also good.
[0070]
(Example 2)
Prefoaming was performed in the same manner as in Example 1 except that the temperature adjustment of the prefoaming tank before the raw material particles were put into the prefoaming tank was eliminated, to obtain prefoamed particles. In this example, the measurement was carried out five times by the same method, and the fifth measurement was carried out. At this time, the temperature of the pre-expansion bath at the time of charging the raw material particles into the pre-expansion bath was 75 ° C.
Table 1 shows the evaluation items of the obtained pre-expanded particles.
[0071]
Although the obtained pre-expanded particles did not have a small angle of repose as in Example 1, the pre-expansion cycle was equivalent to that of the pre-expanded particles obtained by the normal pre-expansion method shown in Comparative Example 1. Nevertheless, blocking did not occur, the angle of repose was extremely reduced to about 1/3 or less, and the particle feedability was also improved.
[0072]
(Example 3)
Pre-expansion was performed in the same manner as in Comparative Example 1 described below, except that the temperature of the pre-expansion tank before charging the raw material particles into the pre-expansion tank was set to 85 ° C. in the same manner as in Example 1. Particles were obtained.
Table 1 shows the evaluation items of the obtained pre-expanded particles.
[0073]
Although the obtained pre-expanded particles did not have a small angle of repose as in Examples 1 and 2, the pre-expansion cycle was equivalent to that of the pre-expanded particles obtained by the normal pre-expansion method shown in Comparative Example 1. Despite this, blocking did not occur, the angle of repose was reduced by about 20%, and the particle feedability was improved.
[0074]
(Comparative Example 1)
The raw material input valve of the BHP-110 type prefoaming machine is opened to feed the raw material particles into the prefoaming tank. After the raw material particles are charged, the exhaust valve and the steam valve of the prefoaming tank of the prefoaming machine are opened, and the steam is purged for 30 seconds. .
[0075]
Thereafter, pressurized steam heating was performed at a lower limit pressure of 0.008 MPa to an upper limit pressure of 0.013 MPa. In this pressurized steam heating, the steam valve is opened and the steam is introduced into the prefoaming tank while the exhaust valve is closed until the inside of the prefoaming tank reaches the upper limit pressure. The heating operation of opening the exhaust valve and reducing the pressure in the preliminary foaming tank to the lower limit pressure was repeatedly performed until the level sensor detection described later.
[0076]
In the pressurized steam heating, the pressurized steam heating is terminated when the level sensor provided in the preliminary foaming tank continuously detects for 2 seconds or more, the steam valve is closed to cool the foamed particles in the preliminary foaming tank, the exhaust valve, The operation was performed for 30 seconds with the drain valve and the cooling valve opened.
[0077]
After cooling was completed, the discharge door was opened and the pre-expanded particles were discharged to an external hopper to obtain pre-expanded particles.
[0078]
In this example, the measurement was carried out five times by the same method, and the fifth measurement was carried out. At this time, the temperature of the pre-expansion bath at the time of charging the raw material particles into the pre-expansion bath was 75 ° C.
Table 1 shows the evaluation items of the obtained pre-expanded particles.
[0079]
In this comparative example, a normal prefoaming method was used. However, the obtained prefoamed particles produced blocking as compared with Example 1. In addition, the angle of repose was three times that of Example 1, and the particle feedability was inferior to that of Example 1.
[0080]
(Comparative Example 2)
Prefoaming was carried out in the same manner as in Example 1 except that pressurized steam heating was carried out at a lower limit pressure of 0.015 MPa to an upper limit pressure of 0.020 MPa to obtain prefoamed particles.
Table 1 shows the evaluation items of the obtained pre-expanded particles.
[0081]
This comparative example is also a normal prefoaming method, but the obtained prefoamed particles have a blocking as compared with the example 1. In addition, the angle of repose was three times that of Example 1, and the particle feedability was inferior to that of Example 1. Further, as compared with Comparative Example 1, the blocking was increased, and the cycle time of the preliminary foaming was shorter than that of Comparative Example 1, but the productivity was lowered.
[0082]
[Table 1]

[0083]
【The invention's effect】
The pre-expanded particles according to the present invention have less wetness compared to the ordinary pre-expanded method, and the problem that the pre-expanded particles stay at the time of granulation and become difficult to send becomes difficult to occur. Also, the occurrence of blocking is reduced. In addition, the filling of the pre-expanded particles into the mold during the molding is improved.

Claims (4)

A method in which expandable thermoplastic resin particles are charged into a pre-foaming tank and foamed by steam heating to obtain pre-expanded particles. And a step of introducing dry air into the pre-foaming tank for a predetermined time during the pre-foaming. The foaming heat according to claim 1, wherein the pressure of the steam used for heating is set to be higher by 0.003 to 0.020 MPa than in the prefoaming method in which a step of introducing dry air is not provided in the steam heating step. Preliminary foaming method for plastic resin particles. A method in which expandable thermoplastic resin particles are charged into a pre-expansion tank and foamed by steam heating to obtain pre-expanded particles. A method for prefoaming expandable thermoplastic resin particles, wherein the temperature is 80 ° C. or higher. 3. The method for prefoaming expandable thermoplastic resin particles according to claim 1, wherein the temperature in the prefoaming tank at the time of charging the expandable thermoplastic resin particles is set to 80 ° C. or more every time the prefoaming is performed.