JPH0645721B2 - Method for producing pre-expanded thermoplastic resin particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing pre-expanded thermoplastic resin particles.

[Conventional technology]

BACKGROUND ART In-mold foam moldings obtained by foam molding synthetic resin pre-expanded particles into a predetermined shape in a molding mold are widely used as heat insulating materials, cushioning materials, soundproofing materials, packaging materials, and the like. The pre-expanded particles used in the production of the in-mold expanded molded article can be obtained by, for example, heat-foaming by adding a foaming agent to resin particles, but to obtain pre-expanded particles having a higher expansion ratio and excellent physical properties. A two-stage foaming method has been proposed in which pre-expanded particles obtained by foaming resin particles are given a foaming ability and then again heat-expanded (JP-A-54-31475 and JP-A-59).
-133233 publication).

[Problems to be solved by the invention]

Conventionally, in the two-stage foaming method, the pre-expanded particles are pressurized with an inorganic gas or the like to increase the internal pressure of the particles to give the pre-expanded particles a foaming ability, and then the pre-expanded particles are stored in a storage tank or the like.
If necessary, extract the pre-expanded particles that have been given a foaming ability from a storage tank or the like into a hopper, and measure the pre-expanded particles required for one-time two-stage expansion from the hopper, fill the foaming tank, and heat. It is foaming. However, the pre-expanded particles are exposed to the atmospheric pressure while they are stored in a storage tank or when they are taken out into a hopper, so that the internal pressure of the particles decreases (foaming time) as the foaming time elapses. There is a problem in that it is difficult to obtain the pre-expanded particles with the desired high expansion ratio, and in order to apply the internal pressure of particles that can compensate for the decrease in internal pressure during storage in a storage tank, etc. The expanded particles have to be pressurized at a higher pressure for a long time, which requires a device capable of withstanding the high pressure and causes a decrease in work efficiency. Further, in the conventional method, when the pre-expanded particles are filled from the hopper into the foaming tank, there is no pressure difference between the hopper and the foaming tank, so that the filling takes a long time, and therefore the filling time in the foaming cycle is long. There was a problem.

[Means for solving problems]

As a result of intensive studies to solve the above problems, the present inventors have found that
We have found a method of holding the pre-expanded particles with expanding ability under pressure in a pressure tank until the pre-expanded particles are heated and re-expanded. When measuring and taking out, the pressure difference between the pressure inside the pressure tank and the measuring device is large, and the pre-expanded particles are extruded rapidly from the inside of the pressure tank. There is a problem that it is difficult to accurately take out the particles.

Therefore, as a result of further intensive research, the inventors of the present invention pressure-charged and filled the pre-expanded particles in a metering tank having a predetermined internal volume to dispense a predetermined amount of the pre-expanded particles into the metering tank and pre-foam in the metering tank. All the above problems are solved by pressurizing the particles and then pre-expanding the pre-expanded particles in the metering tank that is in a pressurized state to the foaming tank for foaming, and it is easy to obtain pre-expanded particles with a higher expansion ratio. The present invention has been completed and the present invention has been completed.

According to the present invention, the thermoplastic resin pre-expanded particles to which the foaming ability is applied are kept under pressure in a pressure tank, and then the pre-expanded particles are pressure-fed into a measuring tank having a predetermined internal volume to fill a predetermined amount of the pre-expanded particles. The foamed particles are collected in a measuring tank, and the pre-foamed particles are pressurized in the measuring tank, and then the pre-foamed particles in the measuring tank which are in a pressurized state are pressure-fed to the foaming tank, and in the foaming tank. This is a method for producing pre-expanded thermoplastic resin particles having a higher expansion ratio than the original expansion ratio by heat-expanding the pre-expanded particles.

The present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 is a pressure tank in which pre-expanded thermoplastic resin particles having a foaming ability are held under pressure.

Examples of the base material of the thermoplastic resin pre-expanded particles used in the present invention include styrene resin, ethylene resin, propylene resin, and the like. Among them, ethylene resin,
Polyolefin such as propylene-based resin is preferable, and propylene-based resin such as polypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer (all 50% by weight or more of propylene component) is particularly preferable.

The pre-expanded particles include thermoplastic resin particles, for example, aliphatic hydrocarbons such as propane, butane, n-pentane and isopentane, halogens such as dichlorodifluoromethane, tetrafluoroethane, trichlorofluoromethane, methyl chloride and ethyl chloride. Foaming agents such as volatile hydrocarbons and inorganic gases such as air, nitrogen, carbon dioxide, argon, helium, etc., and one or more kinds of foaming agents used for ordinary foaming, and then heat foaming A product obtained by a method such as caulking is used, but a foaming ratio of 4 to 40 is preferable.

In the present invention, the foaming ability is given to the pre-expanded particles by pressurizing the pre-expanded particles with an inorganic gas, a volatile foaming agent or a mixed gas of an inorganic gas and a volatile foaming agent similar to those used for foaming resin particles. Done by processing 0.
It is preferable to apply an internal pressure of 5 to 10 kg / cm ² (G).
The above pressure treatment may be performed in the pressure tank 1 or in a separate process.

The pressure tank 1 is configured so that the pre-expanded particles can be kept under a predetermined pressure by the pressure regulator 2. The pressure for holding the pre-expanded particles in the pressure tank 1 under pressure is preferably 0.5 to ¹⁰ kg / cm ² (G). Further, it is preferable to pressurize and heat the pre-expanded particles in the pressure tank 1, which is usually 0.5 to 1.7 kg / cm.
It is preferable to use steam of about ² (G).

The pre-expanded particles held under pressure in the pressure tank 1 are pressure-fed and filled into the first measurement tank 4 and / or the second measurement tank 5 to collect the pre-expanded particles. The amount of pre-expanded particles required for one expansion according to the internal volume of the second measuring tank 5 is measured. Whether the pre-expanded particles are pumped and filled only in the first weighing tank 4 or sorted, or only the second weighing tank 5 is pumped and filled in and collected, or the first weighing tank 4 and the second weighing tank Whether or not both of the tanks 5 are pressure-fed and filled is selected according to the expansion ratio of the pre-expanded particles in the foaming tank 3. That is, when the foaming tank 3 is to be expanded to a high expansion ratio, the first measuring tank 4 having a small internal volume is selected, and when the expansion ratio is low, the second measuring tank 5 having a large internal volume is selected. When the expansion ratio is lower, the pre-expanded particles are pressure-filled and collected in both the first measuring tank 4 and the second measuring tank 5. Each of the measuring tanks 4 and 5 is provided with a filling detecting means such as a pressure sensor, and when the filling is completed, the opening / closing valve 6 of the pressurizing tank 1 is closed so that the pre-expanded particles from the pressurizing tank 1 are fed under pressure. finish.

The pre-expanded particles filled in the measuring tanks 4 and / or 5 are pressurized in the measuring tanks 4 and / or 5. This pressurization is preferably performed at 0.5 to 10 kg / cm ² (G).

The pre-expanded particles that have been separated and pressurized in the measurement tank 4 and / or the measurement tank 5 are, for example, the first pre-expanded particles.
When it is collected only in the measuring tank 4, the first measuring tank opening / closing valve 7 and the second measuring tank opening / closing valve 8 are opened, and the pre-expanded particles pass through the second measuring tank 5 into the foaming tank 3. Pumped. At this time, since there is a pressure difference between the first measuring tank 4 and the foaming tank 3 (the internal pressure of the foaming tank 3 is equal to the atmospheric pressure), the pre-foamed particles are transferred to the foaming tank 3 in a short time. .
When the pressure-feeding of the pre-expanded particles to the foaming tank 3 is completed, the first measuring tank opening / closing valve 7 and the second measuring tank opening / closing valve 8 are closed.

In the foaming tank 3, the pre-expanded particles are heated with stirring and have a higher expansion ratio than the original expansion ratio, preferably 1.
It can be foamed 5 to 7 times. The pre-expanded particles in the foaming tank 3 are usually heated by heating steam, and the steam pressure is preferably about 0.5 to ² kg / cm ² (G).

In FIG. 1, 13 is a three-way valve, 14 is a silencer,
Reference numeral 15 is a steam pipe for supplying heating steam to the foaming tank 3.

In the above manufacturing apparatus, the case where two weighing tanks having different internal volumes are connected in series has been described, but the number of measuring tanks may be one or three or more, and a plurality of measuring tanks may be connected in parallel. As shown in FIG. 2, the measuring tank 9 is composed of a fixed tank 10 and a movable tank 11 which can be moved up and down. By moving the movable tank 11 up and down, the internal volume of the measuring tank 9 is required for one foaming. It may be configured to be adjustable according to the amount of such pre-expanded particles. When the measuring tank 9 having a variable inner volume is used, it is possible to easily deal with the case of manufacturing pre-expanded particles having different expansion ratios.

In FIG. 2, reference numeral 12 is an internal volume display scale.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

Examples 1 to 4 First, pre-expanded particles shown in Table 1 were pressurized with air in a pressure tank by using a device in which a pressure tank, a variable inner volume measuring tank, and 500 foaming tanks were connected. After the treatment and application of the internal pressure shown in Table 1, the pressure was held in the pressure tank for 2 days under the pressure shown in the same table. Next, set the internal volume of the measuring tank to the size shown in Table 1, pressure-feed the pre-expanded particles to the measuring tank from the pressure tank, and collect the pre-expanded particles. The pre-expanded particles in the measuring tank were pressure-fed to the foaming tank and heated with steam having the pressure shown in Table 1 to obtain the pre-expanded particles having the bulk expansion ratio shown in the same table. Table 1 shows the time required to transfer the pre-expanded particles from the measuring tank to the foaming tank. This operation 1
The results of measurement of the bulk expansion ratio of the first pre-expanded particles and the tenth pre-expanded particles repeated 0 times are also shown in Table 1.

Comparative Examples 1 to 4 Pre-expanded particles similar to those in Examples 1 to 4 were pressure-treated in a pressure tank to give the same internal pressure as in the above Examples, and then the pressure in the pressure tank was released. It was atmospheric pressure. Then, the pre-expanded particles were transferred to a storage tank by a blower and kept at atmospheric pressure for 2 days, and then transferred from the storage tank to a measuring tank similar to those in Examples 1 to 4 having the internal volume shown in Table 1 by a blower. After filling, a predetermined amount of pre-expanded particles was collected. Next, the pre-expanded particles in the measuring tank were transferred to the foaming tank without pressurization and heated with the steam having the pressure shown in Table 1 to obtain the pre-expanded particles having the bulk expansion ratio shown in the same table. Table 1 shows the time required to fill the pre-expanded particles from the measuring tank into the foaming tank. Repeat this operation 10 times, the first time and 10
The first measurement result of the bulk expansion ratio of the pre-expanded particles
Shown according to the table.

EFFECTS OF THE INVENTION The present invention provides a foaming ability in a method for producing pre-expanded particles having a higher expansion ratio than the original expansion ratio by imparting expansion ability to thermoplastic resin pre-expanded particles and then heat-expanding the mixture. The pre-expanded particles are kept under pressure in the pressure tank until just before foaming, and then pressure-filled from the pressure tank to a measuring tank having a predetermined internal volume to collect a predetermined amount, and then pressure is applied in the measuring tank. After that, a method was adopted in which the pre-expanded particles in the weighing tank placed under pressure were sent to the foaming tank to cause them to expand.
There is no risk of the pre-expanded particles being reduced before foaming. Therefore, it is possible to easily obtain pre-expanded particles with a high expansion ratio and a small expansion ratio variation without applying a high internal pressure that can compensate for the decrease in internal pressure in advance. You can In addition, since the pre-expanded particles collected in a predetermined amount in the measuring tank are pressurized in the measuring tank, the pressure difference between the measuring tank and the foaming tank when transferring the pre-expanded particles from the measuring tank to the foaming tank is large. Therefore, the pre-expanded particles can be transferred to the foaming tank in a short time, and the production can be efficiently performed.

[Brief description of drawings]

The drawings show an embodiment of the present invention, FIG. 1 is a schematic view showing an example of a manufacturing apparatus for carrying out the manufacturing method of the present invention, and FIG. 2 is a longitudinal sectional view showing another embodiment of a weighing tank. 1 ... Pressurized tank, 3 ... Foaming tank 4, 5, 9 ... Measuring tank

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-51-147567 (JP, A) JP-B-53-42789 (JP, B2) JP-B-55-42909 (JP, Y2) JP-B-59- 3870 (JP, Y2)

Claims (8)

[Claims] 1. A thermoplastic resin pre-expanded particle having a foaming ability is held under pressure in a pressure tank, and then the pre-expanded particle is pressure-fed and filled into a measuring tank having a predetermined internal volume to obtain a predetermined amount. Of the pre-expanded particles in the measuring tank and pressurize the pre-expanded particles in the measuring tank, and then the pre-expanded particles in the pressurized tank in a pressurized state are pressure-fed to the foaming tank. A method for producing pre-expanded particles of a thermoplastic resin, characterized in that the pre-expanded particles are heated therein to expand at a higher expansion ratio than the original expansion ratio. 2. The production method according to claim 1, wherein the base resin of the thermoplastic resin pre-expanded particles is polyolefin. 3. The method according to claim 2, wherein the polyolefin is a propylene resin. 4. The method according to claim 1, wherein the pre-expanded thermoplastic resin particles having the foaming ability have an internal pressure of 0.5 to 10 kg / cm ² (G). 5. The expansion ratio of the thermoplastic resin pre-expanded particles to which the foaming ability has been given is 4 to 40 times.
The manufacturing method described in the item. 6. The method according to claim 1, wherein the thermoplastic resin pre-expanded particles are pressurized and held in a pressure tank at a pressure of 0.5 to 10 kg / cm ² (G). 7. The thermoplastic resin pre-expanded particles are pressurized to 0.5 to 10 kg / cm ² (G) in a measuring tank.
The manufacturing method described in the item. 8. The production method according to claim 1, wherein the thermoplastic resin pre-expanded particles having the foaming ability are expanded to 1.5 to 7 times the original expansion ratio.