JPS60219015A - Prefoaming process of foamed heat-melting resin particles - Google Patents

Abstract

PURPOSE:To obtain heat-melting resin particles foamed at entirely uniform prefoaming multiplication factor by mixing compressed air into a heating medium and heating the mixture at higher than softening point temperature under pressure. CONSTITUTION:A compressed air pipe 25 branches off and connects with any proper spot at the outlet side of an electromagnetic steam valve 22 on steam supply piping 19. The amount of compressed air controlled by an electromagnetic compressed air valve 26 is compressed and mixed from the compressed air pipe 25 into the steam supply pipe 19 through a needle valve and other means. The mixing of compressed air to a heating medium takes place prior to the supply of the heating medium into a can 1, thus enabling the mixing with less dispersion. Temperature distribution in the can becomes uniform and the prefoaming multiplication factor becomes ever constant.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for pre-foaming expandable thermoplastic resin particles, and particularly to a batch pre-foaming process in which the resin particles are pressurized and heated in a can. In addition to stabilizing the temperature distribution inside the can to obtain a uniform expansion ratio, it also prevents the occurrence of blocking, improves yield and elasticity, and produces homogeneous pre-expanded particles with low adhesion moisture and high commercial value. It relates to a method of manufacturing.

(Prior Art) Conventionally, expandable plastic resin particles, such as beads of expandable polystyrene or polyolefin, which are subjected to foam molding, are usually pre-expanded to a magnification of several tens of times. In order to perform such pre-foaming, conventionally, a certain amount of expandable thermoplastic resin particles are loaded into a vertical cylindrical can with a built-in stirrer, and while stirring, a heating medium such as heated steam is introduced into the can. By supplying the atmosphere 1] 3 or more LE
heating the resin particles under direct force to a temperature above their luster point;
Batch type 1 is generally used, in which the foam is cooled and taken out from the can when a predetermined expansion ratio is reached. In this process, it is necessary to adjust the expansion ratio to a level of a predetermined volume of the can.

For this reason, various attempts have been made to control the heating medium inlet (ffi) by detecting changes in the pressure inside the can as the total volume increases due to foaming of resin particles inside the can. Adjusting the expansion ratio using the control method does not sufficiently uniformize the temperature inside the can, resulting in variations in the expansion ratio at the bottom of the can, and the so-called blocking phenomenon in which resin particles fuse together in lumps. accompany,
This was also a factor in deteriorating the quality of foam molded products obtained using I''L.

In order to promote uniformity of pre-expanded particles, an auxiliary screw is provided on the stirring shaft inside the RiJ vertical commercial can to promote mixing and stirring of the resin particles and eliminate non-uniformity of stirring. Japanese Utility Model Publication No. 5-42908 (Japanese Patent Publication No. 53-42-42908), an attempt to uniformly heat the inside of the can using a heating medium inlet pipe placed parallel to the stirring blades between the stirring blades (Japanese Patent Publication No. 53-42-789) Alternatively, a device that aims to improve the stirring efficiency by rotating the stirring shaft within the foaming tank and rotating the body of the foaming tank, which is equipped with blades corresponding to the stirring blades on the inside t7, instead of the stirring shaft. (Special IJF1 Publication No. 57-L49538) has been proposed.

However, these proposed devices; t, fl!
Since it has a special structure, it not only causes an increase in installation costs and maintenance costs, but also leaves you at an economic disadvantage.
Between the resin particles that come into contact with the steam and undergo rapid heating near the steam vent, and the resin particles that undergo mild heating at a location remote from the steam vent. However, it cannot be excluded that there is a difference in the expansion rate of foam, and the problem of blocking has not yet been fundamentally solved.

(Problems to be Solved by Komei) In order to overcome the above-mentioned problems in the prefliiii foaming technology, the present inventors have improved the performance of the heating medium itself + f! (The present invention was completed as a result of intensive research focusing on the method and efficiency of addition.)

An object of the present invention is to provide thermoplastic resin particles having a uniform pre-foaming rate of 1 throughout. The purpose is to modify Equation 1 without requiring a particularly large investment in equipment and obtain uniform pre-foamed particles economically.Another object is to prevent the occurrence of blocking phenomena in the pre-foaming process. The purpose is to prevent fJ2 and increase the yield of pre-foamed resin particles.The ultimate objective is to provide a foamed resin molded product that is homogeneous and has high commercial value.

(Another means to solve the problem) The above-mentioned purpose is to heat the expandable thermoplastic resin particles housed in the can by supplying a heating medium into the can.
In the step of pre-foaming by pressurizing to a pressure above and heating to a temperature above the softening point of the resin particles,
This is achieved by a method for pre-foaming expandable thermoplastic resin particles, which is characterized by mixing compressed air into the heating medium.

Hereinafter, specific embodiments of the method of the present invention will be further described in detail with reference to Figure 1m.

FIG. 1 is a schematic elevational view showing an example of a conventionally known apparatus used for pre-foaming expandable plastic resin particles.

FIG. 2 shows an example of a prefoaming apparatus adapted to carry out a preferred embodiment of the method of the invention (in schematic elevational view).

FIG. 3 is a chart 1 showing the valve opening/closing procedure at each stage of the process of carrying out the present invention using the apparatus shown in FIG. 2.

In Fig. 1, the vertical cylindrical can (1) forming the main body of the pre-foaming machine has a rotating shaft (
A stirrer (4) consisting of a rotating shaft (3) and a power source (5) such as a motor via an ID reducer etc. are installed concentrically.
It is rotated by a drive device η(6) connected to the drive unit η(6).

Below the raw material bopper (7) provided above the can body (1), a steam chamber (10) is installed at the bottom of the foaming hot UJ plastic discharged from the raw material bopper (7). The perforated disc (11) is provided with small slits and the like that are sized to allow gas to pass through but prevent resin particles from passing through.The top of the can body (1) has , exhaust valve (12
), the trip valve (13) for upward adjustment, and the exhaust port (15) that is combined with the emergency valve (l → There is a level meter (16) at the bottom of the can, and at the bottom of the side there is an F-equipped foam granule discharge port (18) equipped with an opening/closing mechanism (17) that uses a reciprocating motion such as a plunger. The bottom steam chamber θ0) is provided with a steam supply pipe (+9), a compressed air supply pipe (20), and a drain discharge pipe (21), respectively. These pipings are connected to a steam solenoid valve (22), an air solenoid valve (23+), and a drain solenoid valve (23+), respectively.
4) Equipped with a mechanism that opens and closes manually and automatically according to the detected pressure inside the can.

In the conventionally known method of performing pre-foaming using such an apparatus, first, a constant amount of 1 ftkgl of foamable resin particles is dropped into a funnel-shaped receiver (9) through a feed valve (8), and then the feed valve (8)
The liquid is then supplied to the can body (1). At that time, the exhaust valve (threshold and drain solenoid valve (24) is opened, and the can body (1) is kept open to the outside air.The amount of resin particles supplied is determined by Calculate the volume of the can body from the height at which it reaches level meter 06) and measure the predetermined pre-expansion ratio.

It is set in advance to be corrected.

After finishing the supply and charging of the raw material resin particles, the stirrer (4)
While operating , -order addition ρL is performed. -6 (Heating is done by preheating to a temperature just before reaching the resin softening temperature to loosen the temperature gradient in the next secondary heating step and to avoid as much as possible unevenness in the expansion ratio due to local heating. This is done by opening the steam solenoid valve (22j) with the exhaust valve (12) open and passing a heating medium such as heated steam into the can.
In the case of 1,50 seconds to 1,50 minutes at a temperature of about 75 DEG to 80 DEG C. under an atmosphere of 110 DEG C., it is generally considered sufficient.

The resin particles then proceed to a secondary heating stage. The heating at this stage is performed by closing the exhaust valve ((2) to create a closed system.
A heating medium from the steam supply pipe (19) is heated to a temperature above the plasticizing temperature, that is, the softening point, and at a suitable temperature above atmospheric pressure in order to control the rapid expansion action of the blowing agent. Pressure is applied 1. For example, in the case of polystyrene beads, the temperature should be 90 - 0°C, preferably 95 - 98°C, the internal pressure of one can 02 - 0.8 G (gauge pressure), preferably 0.2 - 0. Processing 1 [j for 40 seconds to 80 seconds under the condition of 5 (to) G is normal. At this time, the pressure inside the can is regulated by the operation of the trip valve (13), while the pressure inside the can is detected and converted into an electrical signal, and the steam electromagnetic valve (22) is actuated thereby.
The supply 1d of the heating medium is automatically controlled, and the humidity is normally adjusted while maintaining the pressure.

After completing the above secondary addition, the pre-expanded resin particles are then subjected to a cooling process. At this stage, first, the steam solenoid valve (z2) is closed to stop the supply of the heating medium, and the exhaust valve (12) is opened to gently reduce the pressure inside the can to atmospheric pressure, and the air solenoid valve C23 is closed. )'x opens to supply compressed air. At this early stage, the pre-foaming has completely stopped, and when heated steam was used as a medium in the preceding process, the condensed water that had adhered to the resin particles was vaporized and removed over the course of the night. dry.

The cooled and dried resin particles are discharged from the pre-expanded particle outlet (18) which is opened by the action of the opening/closing mechanism (17). Careful attention was paid to making the temperature distribution uniform, such as by continuing to stir the whole process from the initial stage of foaming to the next stage of heating and discharging, and also heating in two stages. !
/1. Although many improvement efforts have been made, such as distributing the distribution of heating medium supply pipes, asymmetry in the T' f+iif irrigation ratio is still observed. . However, according to the method of the present invention, in the heating step of the conventional method, particularly in the secondary heating step, a force of 11
It is truly surprising that by mixing 11E compressed air into the heat medium and supplying it into the can, we were able to achieve a uniform temperature distribution inside the can and a uniform expansion ratio all at once. It is.

In other words, the non-inventive method θ; is the heating medium LA person from the steam supply pipe (19) and the compressed air 1+1 person L from the compressed air supply pipe (20) in the addition stage in the conventional method described in 111j. should be done at the same time.

The heating medium and compressed air are combined in the steam chamber (]O), passed through the slit of the perforated plate (ll), and into the can body (1). : Heat the resin particles using RJS8. On this occasion,
The original specific force of the compressed air is 4 to 6% G, and the blowing pressure is adjusted to 0.1 to 0.05 G by a needle valve.

Table 1 compares the effects of the conventional method and the method of the present invention in pre-foaming polystyrene.

However, in this table, the blowing pressure of steam and air are both 0.557.
(). In addition, the humidity inside the can is not the initial state, but the results obtained when the initial 5 batches are discarded and the results are repeated after the 6th batch.

As shown in the table above, the method of the present invention not only almost eliminates the variations in can temperature and expansion ratio difference caused by the conventional method, but also has the remarkable effect of completely preventing the occurrence of the blocking phenomenon. There is no doubt that such remarkable effects are due to the excellent action of the method of the present invention, but the physicochemical function when compressed air is mixed with the heating medium is not known in detail, and it is likely that Due to the increased fluidity of the heating medium and the change in thermodynamic properties,
This is thought to be due to the fact that the propagation speed of thermal energy increases, the temperature distribution inside the can becomes uniform, and the entire can is heated stably and slowly.

FIG. 2 shows a conventionally known pre-foaming device modified to provide a most suitable embodiment for applying the method of the present invention. In the figure, steam (J): supply lJL! Pipe (1
9) At an appropriate location on the outlet side of the upper steam solenoid valve (22), (E
The line trachea (25) is branched and connected, and the [E line trachea (25)
), if the compressed air from the vat controlled by the compressed air solenoid valve (2G) flows, the mixing of compressed air into the heating medium will be as follows.
Compared to the case where the heating medium is mixed in the steam chamber 00) prior to the supply of the heating medium into the can, more even and complete mixing is achieved, and the temperature distribution is stabilized and made more uniform. It becomes even easier.

Therefore, in such a preferred embodiment of the method of the present invention, if compressed air' is mixed with the jJII heat medium only in the secondary heating stage, the objective can be sufficiently achieved and the process can be simplified.

The valve opening/closing procedure at each stage of the process of carrying out the method of the present invention using the apparatus shown in FIG. 2 will be explained with reference to FIG. The feeding step and the subsequent heating step are the same as described above regarding the known method.

Regarding primary heating, compressed air can be mixed into the heating medium by operating the compressed air solenoid valve (26), but it may be omitted as in the conventional method.

In the secondary heating stage, compressed air solenoid valve (2G + f
When the compressed air is mixed with the heating medium in the steam supply pipe α8), the uniformly mixed heating medium is supplied under pressure to the resin particle layer through the steam chamber 00).

In the cooling stage, the conventional method of opening the exhaust valve (12) and the air solenoid valve (23) was shown, but the compressed air solenoid valve t26+
k opening, which can promote cooling and drying action, and
If only the compressed air pipe (25) is provided without the compressed air supply pipe (20), step f: This step (①) is performed by operating the compressed air solenoid valve (26).

The stage of discharging the pre-expanded particles is different from the conventional method. Example 1: Expandable polystyrene beads (manufactured by Kanebuchi Kagaku Co., Ltd., trade name: Nepal GM) f: The can body 8 eyes shown in Fig. 2 was used. 1
Pre-foaming was carried out using a 600 t pre-foaming device according to the procedure shown in FIG. The process conditions are as follows: - next heating;
Add secondary heating! 1-1: Linear air was mixed with A steam.

Amount of raw material beads input: 1700 Nori Steam blowing pressure °0.5 shell G Air source pressure °5.0 Ground air blowing pressure ° 0.2 G -Second heating time °48 seconds Primary heating setting temperature: 78℃ Expansion ratio Setting value: 64 times Comparative Example 1 For comparison, preliminary foaming was carried out under all the same conditions as in Example 1, except that the steam pressure was 1 o 75 G and no compressed air was mixed.

Example 2 Using expandable polystyrene beads (manufactured by Kanebuchi Kagaku Co., Ltd., trade name: Nepal GM), the can body capacity was 1600 as shown in Fig. 2.
7! Pre-foaming was carried out using the pre-foaming device of , according to the procedure shown in FIG. The process conditions were as follows, and compressed air was mixed with heated steam only in the secondary heating stage.

Amount of raw material beads input; 17. soKg Blowing steam pressure: 05 (to) G - Secondary heating set temperature: 80°C Expansion ratio set value: 60 times Comparative Example 2 All the same as in Example 2 above except that compressed air was not mixed in the secondary heating stage. Foaming was carried out under the following conditions.

Each of the above Examples and Comparative Examples are carried out consecutively,
The first 5 batches were discarded and the situation was observed in 4 batches after the 6th batch, and the results are shown in Table 2.

(Hereinafter, blank space) - As is clear from Table 2, according to the method of the present invention,
Compared to the known method as a comparative example, the temperature inside the can is significantly uniformized, and therefore the expansion ratio of the resin particles is also uniformized to such an extent that there is almost no difference between the upper and lower layers of Norkulu. In addition, it can be seen that the formation of pronking was not observed at all, which produced an extremely good anal effect.

Furthermore, at the end of the secondary heating, although the wetness level is approximately the same as that of the secondary heating, the time required to reach the foaming ratio set value by the two-blow JJII heat, that is, the secondary heating In batch pre-foaming of plastic Ik resin particles, the heating time required is longer in the method of the present invention because the heating action proceeds slowly and does not cause sudden local temperature rises. The stable uniformization of the temperature distribution inside the can, which was considered difficult to solve in the past, and the equalization of the envelope magnification (preliminary generation) can be achieved using existing equipment or by making minimal modifications to it. Therefore, it can be realized industrially easily and economically, and it greatly contributes to improving the quality of pre-expanded resin particles and, by extension, to improving the accuracy and quality of foam molded products using them.

In addition, the present invention beautifully prevents the blocking phenomenon that has been a hindrance in the conventional pre-foaming process and foam molding process, resulting in an unexpected by-product effect of improving the yield. His contributions to this field are enormous.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram 1m showing an example of a conventionally known apparatus used for pre-foaming expandable thermoplastic resin particles, and FIG. FIG. 2 is an elevational view schematically showing an example of the device. Third
The figure is a chart showing the valve opening/closing means at each stage of the process of carrying out the present invention using the apparatus of FIG. 2. (K)・・・Can body, (2)・・・Finger stirrer. (3)... Rotating shaft 9. (4)... Stirrer. (5)...Power source, (6)...Drive device. (7)... Raw material hopper, (8)...
Supply valve. (9)・・・Benefit, (1o)・・・Steam room. (11)・・・・・・Perforated plate, 02)・・・Exhaust valve. α needle: Trip valve, θ→: Emergency valve. (+5)...II"fi, 0, (16)・
...Level il. 07)...Opening/closing mechanism, 08)...Pre-expanded grain outlet. (19)...Steam supply piping, 00)...
...Compressed air supply piping. (21)...Drain discharge piping, (22)・
...Steam solenoid valve. (23)...Air solenoid valve, /24+...
...Drain solenoid valve. (25)...[E-line trachea, (2G)...
...H:, linear solenoid valve. (27)...Steam pressure it, (28)...
・Air Y] Sanriki iil' + (29) ...... Riki Kanuchida 81° Patent applicant Kanebuchi Chemical Industry Co., Ltd., -1
Agent Patent Attorney Yasushi Miyamoto −゛(′、blank)Figure f

Claims (1)

[Claims] ■. Expandable thermoplastic resin particles housed in the can body,
In the step of supplying a heating medium into the can body to pressurize it to a pressure higher than atmospheric pressure and heating it to a temperature higher than the softening point of the resin particles to cause pre-foaming, compressed air is mixed into the heating medium. Characteristic method for pre-foaming expandable thermoplastic resin particles. 2. The method for pre-foaming expandable thermoplastic resin particles according to claim 1, wherein the heating medium is mixed with compressed air prior to supplying the heating medium into the can body. 3. Claim 1 which adjusts the flow rate of 1f compressed air
A method for pre-foaming expandable thermoplastic resin particles according to item 1 or 2.