JP2011202005A - Method for producing thermoplastic resin reserved foaming particle, and device for producing thermoplastic resin reserved foaming particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for producing thermoplastic resin reserved foaming particles, as compared with conventional methods, capable of performing the cooling and drying of the reserved foaming particles in a short time, improving production efficiency and capable of reducing the consumption of electric power.SOLUTION: This method for producing the thermoplastic resin reserved foaming particles by putting-in foaming thermoplastic resin particles in a foaming vessel, heating/foaming the foaming thermoplastic resin by introducing a heating medium into the foaming vessel to form the thermoplastic resin reserved foaming particles having a desired bulk foaming magnitude, then feeding air into the foaming vessel to cool/dry the thermoplastic resin reserved foaming particles and taking out the thermoplastic reserved foaming particles is characterized by feeding the air of 3.0 to 12.0 kPa air pressure by 17.0 to 40.0 m/L/min (provided that the L is a bulk volume 1 mof the thermoplastic resin reserved foaming particles) range into the foaming vessel to perform the cooling/drying.

Description

  In the present invention, foamable thermoplastic resin particles obtained by adding a foaming agent to thermoplastic resin particles such as polystyrene resin, polyethylene resin, and polypropylene resin are heated by a pre-foaming device, and the desired bulk density (bulk foaming) is obtained. In particular, the present invention relates to a production method and a production apparatus for producing thermoplastic resin pre-foamed particles by being pre-foamed to be a multiple), and in particular, a production method capable of efficiently producing pre-foamed thermoplastic resin particles and reducing power consumption and It relates to a manufacturing apparatus.

  Conventionally, as a method for producing a foamed molded article of a thermoplastic resin such as a polystyrene resin, a polyethylene resin, or a polypropylene resin, a foamable thermoplastic resin particle containing a foaming agent in a thermoplastic resin particle is preliminarily used. A pre-foamed particle is produced by heating with a foaming device and pre-foaming so as to achieve the desired bulk density (bulk foaming multiple), and the resulting pre-foamed particle has a cavity in the shape of the desired molded product A so-called in-mold foam molding method is known, in which the pre-expanded particles in the mold are heated and foamed and then cooled to take out the foamed molded product from the mold.

In the pre-foaming, in order to produce pre-foamed particles having the desired bulk density (bulk foaming factor), when the foamable thermoplastic resin particles are placed in the foaming tank of the pre-foaming apparatus and heated by steam, the foaming tank The first level and the second level, which is the final level, are positioned along the height direction, and after supplying the foamable thermoplastic resin particles to the foaming tank, the particles are heated through steam, When the height of the foamed particle layer reaches the first level, the foaming speed is reduced by reducing the supply amount of steam or the like, and foaming to the second level is performed (for example, see Patent Documents 1 to 3). .)
Further, the pre-expanded particles obtained by pre-expansion contain a large amount of moisture on the particle surface, and in such a state, the pre-expanded particles can be bonded to each other in the expansion tank. In order to solve this problem, an air cooling process is performed in which compressed air at normal temperature is supplied into the foaming tank to cool and dry the pre-foamed particles after completion of foaming.

  In Patent Document 1, in a method of expanding and expanding foamable thermoplastic resin particles contained in a foaming tank having a stirrer with a heating medium such as heated steam to obtain pre-foamed particles, heating steam is used as a heating medium. A pre-foaming method for foamable thermoplastic resin particles, characterized in that heated air having a temperature equal to or higher than water vapor is mixed and used. Further, in this Patent Document 1, after the foamed particle layer level reaches the first level (low level), the steam supply rate is decreased to slow the foaming rate until it reaches the second level (final level). In addition, it is described that a small amount of compressed air may be mixed for the purpose of pre-foaming and further prevention of uniform foaming and coalescence of particles.

  In Patent Document 2, pre-expanded particles discharged from a pre-foaming machine to a discharge hopper are formed by providing a partition wall in the discharge hopper part or sent separately to a dry hopper part. Blowing up the standing expanded foam in a drying tower that allows moisture and air to pass but not pre-expanded particles, and sends the fallen pre-expanded particles to the ejector provided at the bottom outlet of the drying hopper. A dry granulation method for a prefoaming machine is disclosed in which the moisture of the prefoamed particles is dried and removed and heated by circulated through the drying tower and blown up into the drying tower. Has been. Further, Patent Document 2 describes a method of drying by blowing cold air, hot air or hot air into a pre-foaming machine after completion of pre-foaming.

  Patent Document 3 discloses a method in which foamable thermoplastic resin particles are heated and pre-foamed to a low magnification of 15 times or less, and two locations, a low level and a high level, are determined in the foaming tank, and the low level is set to a high level. Raw material particles were put into a foaming tank at a position of 70 to 90%, the inside of the tank was sealed and decompressed, then steam was blown into the tank, and the pressure inside the tank was maintained at atmospheric pressure or higher to heat and foam to a low level position. After that, reduce the amount of blown steam, or increase the air supply amount while keeping the steam amount as it is, lower the temperature of the blown heat medium, slow down the foaming speed to foam to a high level, and then cool and dry to foam Disclosed is a method for low-expansion pre-expansion of expandable thermoplastic resin particles, which is characterized by discharging spent particles.

JP-A 63-267513 JP-A-5-287114 Japanese Patent Laid-Open No. 3-13307

  As a pre-foaming apparatus for carrying out the pre-foaming method, currently used apparatuses are a foaming tank, a steam supply pipe for supplying steam into the foaming tank, and compressed air in the foaming tank. Compressed air supply means including a compressor for supplying air, and when pre-expanded particles obtained by steam heating in a foaming tank are cooled and dried, compressed air is supplied into the foaming tank and cooled and dried. It was the composition to do.

However, in the conventional pre-foaming apparatus, when pre-foamed particles obtained by pre-foaming are cooled and dried with compressed air, it takes a long time to sufficiently cool and dry the pre-foamed particles. There was a problem that the production cycle of the product became longer and the production efficiency deteriorated.
In addition, it is necessary to drive the compressor for a long time for cooling and drying, and there is a problem that the power consumption for the increase increases and the manufacturing cost increases.

  The present invention has been made in view of the above circumstances, and can cool and dry the pre-foamed particles in a short time compared to the case of using a conventional pre-foaming apparatus, and can increase production efficiency and reduce power consumption. It aims at providing the manufacturing method and manufacturing apparatus of a thermoplastic resin pre-expanded particle.

In order to achieve the above-mentioned object, the present invention puts foamable thermoplastic resin particles in a foaming tank, introduces a heating medium into the foaming tank, heat-foams the foamable thermoplastic resin particles, and obtains a desired bulk foaming factor. In the production method of producing the thermoplastic resin pre-expanded particles, and then supplying air into the foaming tank to cool and dry the thermoplastic resin pre-expanded particles, and then removing the thermoplastic resin pre-expanded particles, When the foamed particles are cooled and dried, air with a wind pressure of 3.0 to 12.0 kPa is supplied with an air volume of 17.0 to 40.0 m ³ / L / min (where L is a volume of 1 m ³ of the pre-foamed thermoplastic resin particles). The method for producing thermoplastic resin pre-expanded particles is provided by supplying into the foaming tank within the range of

  In the method for producing the thermoplastic resin pre-expanded particles of the present invention, the cooling drying is preferably performed so that the temperature in the foaming tank when the foamable thermoplastic resin is charged is less than 80 ° C. every time pre-foaming is performed.

  The present invention also includes a foaming tank that heats the foamable thermoplastic resin particles to produce thermoplastic resin pre-foamed particles, a steam supply pipe that supplies a heating medium into the foaming tank, and a wind pressure in the foaming tank. An apparatus for producing pre-expanded thermoplastic resin particles comprising a cooling air supply means including a blower for supplying air of 3.0 to 12.0 kPa is provided.

In the apparatus for producing the thermoplastic resin pre-expanded particles of the present invention, the blower has an air volume of 17.0 to 40.0 m ³ / L / min (where L is a bulk volume of the thermoplastic resin pre-expanded particles). It is preferable that 1 m ³ of air can be supplied.

In the method for producing the thermoplastic resin pre-expanded particles of the present invention, the foamable thermoplastic resin particles are heated and foamed in a foaming tank to produce thermoplastic resin pre-expanded particles having a desired bulk expansion ratio, and then in the foaming tank. When air is supplied to cool and dry the thermoplastic resin pre-expanded particles, air with a wind pressure of 3.0 to 12.0 kPa is supplied with an air volume of 17.0 to 40.0 m ³ / L / min (where L is a thermoplastic resin) Preliminary foamed particles are supplied into the foaming tank in the range of 1 m ³ in volume) and cooled and dried, so that the spare air can be spared in a shorter time than the conventional technique in which compressed air is supplied into the foaming tank. The expanded particles can be sufficiently cooled and dried, the production cycle of the pre-expanded particles can be shortened, and the production efficiency can be improved.
In addition, the ability to use a blower that can blow a large amount of low-pressure air to cool and dry can greatly reduce power consumption and reduce manufacturing costs compared to the conventional technology that supplies compressed air to the foaming tank. be able to.

An apparatus for producing pre-expanded thermoplastic resin particles according to the present invention includes a foaming tank that heats expandable thermoplastic resin particles to produce pre-expanded thermoplastic resin particles, and a steam supply pipe that supplies a heating medium into the foaming tank. Compared with the conventional apparatus for supplying compressed air into the foaming tank, because it is provided with a cooling air supply means including a passage and a blower for supplying air with a wind pressure of 3.0 to 12.0 kPa in the foaming tank, The pre-expanded particles can be sufficiently cooled and dried in a shorter time, the production cycle of the pre-expanded particles can be shortened, and the production efficiency can be improved.
In addition, the ability to use a blower that can blow a large amount of low-pressure air for cooling and drying can greatly reduce power consumption and reduce manufacturing costs compared to conventional devices that supply compressed air into the foaming tank. it can.

It is a schematic block diagram which shows an example of the manufacturing apparatus of the thermoplastic resin pre-expanded particle of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of a production apparatus for thermoplastic resin pre-expanded particles (hereinafter referred to as pre-expanded particles) of the present invention.
This manufacturing apparatus includes a foaming tank 2 that heats foamable thermoplastic resin particles to produce pre-foamed particles 1, a steam supply pipe 4 that supplies steam 3 as a heating medium into the foaming tank 2, and foaming The tank 2 is provided with a cooling air supply means 6 including a blower 5 for supplying air having a wind pressure of 3.0 to 12.0 kPa.

  The foaming tank 2 has a rotating shaft 7 inserted into the tank, a stirrer 8 provided in multiple stages along the longitudinal direction of the rotating shaft 7, and one end on the inner wall of the tank so as not to contact the stirrer 8. A baffle rod 9 fixed in multiple stages, a hatch 10 for taking out pre-expanded particles to the outside of the tank, a wire mesh 11 provided at the bottom of the foam tank 2, and the height of the pre-expanded particles generated in the tank A first level meter 12 for detecting that the first level is lower than the final level corresponding to the bulk expansion ratio of the target pre-expanded particles, and the layer height of the pre-expanded particles is the final level. And a second level meter 13 for detecting that the second level is reached.

The steam supply line 4 has a steam pressure control valve 15 and a header 16 interposed in order from the upstream side to the downstream side in the steam line 14 through which the steam 3 flows, and further branches into two on the downstream side of the header 16. The first steam line 14a and the second steam line 14b merge at the downstream side of the valves 17 and 18 provided in the respective lines, and the subsequent line 19 is connected to the bottom side of the foaming tank 2. Has been. This steam supply line 4 adjusts the amount of steam supplied from the bottom side of the foaming tank 2 by opening and closing the valves 17 and 18 of the first steam line 14a and the second steam line 14b. It can be done.
The configuration of the steam supply pipe 4 shown in FIG. 1 is merely an example, and the present invention is not limited to this, and the arrangement of each valve, the type of valve, the presence or absence of branching, and the like can be changed as appropriate. .

The cooling air supply means 6 supplies air into the air pipe 21 on one end of the air pipe 21 connected to the pipe 19 via a valve 20 and the other end of the air pipe 21. And a blower 5 connected so as to be supplied. When cooling the inside of the foaming tank 2, the cooling air supply means 6 drives the blower 5 so as to allow air to flow through the air pipe 21, and opens the valve 21 (at this time, from the steam supply pipe 4. By stopping the steam supply), the cooling air can be blown into the tank from the bottom side of the foaming tank 2 through the pipe line 19.
The configuration of the cooling air supply means 6 shown in FIG. 1 is merely an example, and the present invention is not limited to this. The arrangement of the valve, the type of the valve, the configuration of the connection pipe line to the foaming tank 2, and the like. Can be appropriately changed.

Next, an embodiment of the method for producing pre-expanded particles of the present invention will be described.
The production method of the pre-expanded particles of the present invention is applicable to the production of various pre-expanded particles for producing a foamed molded article of a thermoplastic resin such as polystyrene resin, polyethylene resin, polypropylene resin, etc. Therefore, it is suitable for the production method of pre-expanded polystyrene resin particles used for the production of polystyrene resin foam moldings that are currently produced in large quantities and widely used.

As the expandable thermoplastic resin particles used for manufacturing the polystyrene resin pre-expanded particles, the foaming properties manufactured by various known manufacturing methods such as the following (1) to (3) manufacturing methods are known. Polystyrene resin particles can be used.
(1) Polymerization is carried out by dispersing a polymerizable monomer containing a styrene monomer as a main component in an aqueous suspension, and a foaming agent is added during the polymerization or after completion of the polymerization to expand the polystyrene resin particles. So-called suspension polymerization method,
(2) After dispersing the polystyrene resin seed particles in the aqueous suspension, the seed particles are allowed to absorb the polymerizable monomer and polymerize, and during the polymerization, A so-called seed polymerization method in which a foaming polystyrene resin particle is obtained by adding a foaming agent after completion of the polymerization,
(3) A polystyrene resin is charged into an extruder, melted by heating, mixed with a foaming agent in the middle of moving to the discharge side while kneading, and the small die having a large number of small holes attached to the discharge side of the extruder A so-called melt extrusion method (also referred to as an underwater cutting method or the like) is obtained by extruding a foaming agent mixed resin from a hole, immediately after cutting it in water, and rapidly cooling to obtain expandable polystyrene resin particles.

Examples of the styrene monomer used in the above (1) suspension polymerization method and (2) seed polymerization method include styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromo. The main component is a styrene monomer such as styrene, and the styrene monomer is usually contained in an amount of 50% by mass or more, preferably 80% by mass or more. Of these styrene monomers, styrene is particularly preferable.
Further, the polymerizable monomer that can be used in combination with the styrene monomer is not particularly limited as long as it is copolymerizable with the styrene monomer, and divinylbenzene, alkylene glycol dimethacrylate, acrylonitrile, methyl methacrylate, and the like. Is mentioned.

  (2) When producing expandable polystyrene resin particles by the seed polymerization method, the polystyrene resin particles obtained by the suspension polymerization method are used as seed particles, or the polystyrene resin is obtained in advance by an extruder. After adjusting to the diameter, it may be used as seed particles. (2) When seed particles are produced using an extruder in the seed polymerization method, or (3) polystyrene resins used in the melt extrusion method are commercially available ordinary polystyrene resins, suspension polymerization methods, etc. In addition to using polystyrene resins that are not recycled materials (virgin polystyrene), such as newly produced polystyrene resins by the method, use recycled materials obtained by reprocessing used polystyrene resin foam moldings. Can do. Examples of this recycled material include recycled polystyrene resin foam molded products such as fish boxes, household appliance cushioning materials, food packaging trays, etc., and recycled by the limonene dissolution method or heating volume reduction method. It is done.

  The particle diameter of the expandable polystyrene resin particles is not particularly limited, but is usually about 0.3 to 2.0 mm from the viewpoint of filling of the pre-expanded particles into the mold cavity at the time of molding. 3-1.4 mm is preferable.

  As for the molecular weight of the polystyrene resin in the expandable polystyrene resin particles, the mass average molecular weight (Mw) by GPC method is preferably 170,000 to 700,000. If the molecular weight of the styrenic resin particles is less than 170,000, the strength of the foamed molded product is lowered, and if it exceeds 700,000, it is difficult to obtain sufficient foamability, which is not preferable.

  The polymerization initiator used in the above (1) suspension polymerization method and (2) seed polymerization method is not particularly limited as long as it is usually used in suspension polymerization of styrene. For example, a radical generating polymerization initiator is used. Can be used. Specifically, benzoyl peroxide, lauryl peroxide, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t-butylperoxide Organic peroxides such as oxybutane, t-butylperoxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate, azobisisobutyronitrile, azobisdimethylvaleronitrile, etc. Of the azo compound. These polymerization initiators can be used alone or in combination of two or more.

In the polymerization described above, in order to reduce the styrene monomer remaining in the polystyrene resin particles, it is preferable to use a high temperature decomposition type polymerization initiator and set the final polymerization temperature to 115 ° C. or higher. Examples of the high-temperature decomposition type polymerization initiator include t-butyl peroxybenzoate, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t-butyl peroxy. Examples include butane having a temperature of 100 to 115 ° C. for obtaining a half-life of 10 hours. An excessive addition of a high temperature decomposition type polymerization initiator is not preferable because alcohols as decomposition byproducts are generated.
In the polymerization, the decomposition temperature for obtaining a half-life of 10 hours is in the range of 80 to 120 ° C. in terms of adjusting the molecular weight of the polystyrene resin particles and reducing the residual amount of monomer. It is preferable to use a combination of two or more polymerization initiators.

In carrying out the (1) suspension polymerization or (2) seed polymerization, a suspending agent may be used to disperse styrene monomer droplets or seed particles in an aqueous medium. Examples of the suspending agent include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinyl pyrrolidone, and poorly water-soluble inorganic compounds such as tricalcium phosphate and magnesium pyrophosphate. In addition, when using a slightly water-soluble inorganic compound, it is preferable to use an anionic surfactant together.
Examples of the anionic surfactant include fatty acid soaps, N-acyl amino acids or salts thereof, carboxylates such as alkyl ether carboxylates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, dialkylsulfosuccinates, alkylsulfates. Sulfates such as acetates and α-olefin sulfonates; sulfates such as higher alcohol sulfates, secondary higher alcohol sulfates, alkyl ether sulfates, polyoxyethylene alkylphenyl ether sulfates; alkyls And phosphoric acid ester salts such as ether phosphoric acid ester salts and alkyl phosphoric acid ester salts. Expandable polystyrene resin particles can be produced by impregnating the polystyrene resin particles obtained as described above with a foaming agent and a plasticizer by a suspension polymerization impregnation method or a post-impregnation method.

  Examples of the foaming agent used in the present invention include aliphatic hydrocarbons having 5 or less carbon atoms, such as n-butane, isobutane, n-pentane, isopentane, and neopentane, which are used in the production of general thermoplastic resin foams. Can be mentioned.

  The content of the foaming agent is preferably in the range of 5 to 9% by mass, more preferably 5 to 8% by mass with respect to the thermoplastic resin particles. When the content ratio is less than 5% by mass, not only is it difficult to reduce the density, but the effect of increasing the secondary foaming power during molding cannot be obtained, so that the appearance of the foamed molded product is deteriorated. On the other hand, if the content ratio exceeds 9% by mass, the shrinkage during foam molding, the delay in adjusting the residual gas in the pre-expanded particles, and the molding cycle become longer, which is not preferable from the viewpoint of productivity.

  The foamable thermoplastic resin particles are used in the production of foamable polystyrene resin particles, as long as they do not impair the physical properties. Plasticizers, foamed cell nucleating agents, fillers, flame retardants, flame retardants. Auxiliaries, lubricants, colorants and the like may be used as necessary. In addition, if powder metal soaps such as zinc stearate are applied to the surface of the expandable styrene resin particles, the bonding between the polystyrene resin pre-expanded particles is reduced in the pre-expanding step of the expandable polystyrene resin particles. This is preferable.

  In order to produce the pre-foamed particles by the production method of the present embodiment, the foaming thermoplastic resin particles are put into the foaming tank 2 using the production apparatus having the configuration shown in FIG. The steam 3 is introduced and the foamable thermoplastic resin particles are heated and foamed to produce pre-expanded particles 1 having a desired bulk expansion ratio.

  The expandable thermoplastic resin particles heated by the supplied steam 3 start to foam, and the pre-expanded particles 1 in which the particles are independent from each other without being bonded to each other by stirring with the stirring rod 8 in the foaming tank 2. Become. As the pre-foaming progresses (increase in the bulk foaming factor), the layer height of the pre-foamed particles 1 increases.

In this pre-foaming, the layer height of the pre-foamed particles 1 generated in the foaming tank 2 has reached the first level which is lower than the final level corresponding to the bulk foaming factor of the target pre-foamed particles 1. The first level meter 12 for detecting this and the second level meter 13 for detecting that the second level, which is the final level, has been installed, and the layer height of the pre-expanded particles has reached the first level 25. Thereafter, either the first steam line 14a or the second steam line 14b of the steam supply line 4 is stopped, the amount of steam supplied to the bottom of the foaming tank 2 is reduced, and heating and foaming to the second level are performed. .
The first level meter 12 is preferably installed so as to have a detection height of 70 to 90% of the detection height of the second level meter 13.

Next, air is supplied into the foaming tank 2 to cool and dry the pre-expanded particles 1. In the production method of the present invention, when the pre-foamed particles 1 are cooled and dried, air with a wind pressure of 3.0 to 12.0 kPa is supplied with an air volume of 17.0 to 40.0 m ³ / L / min (where L is a thermoplastic resin). It is characterized in that it is supplied into the foaming tank 2 within a range of (bulk volume of 1 m ³ of the pre-foamed particles) and cooled and dried.

The blower 5 is preferably a blower that can blow a large amount of low-pressure air having a wind pressure of 3.0 to 12.0 kPa.
If the wind pressure is less than 3.0 kPa, sufficient air does not reach the pre-expanded particles 1 in the foaming tank 2 and cooling and drying of the pre-expanded particles 1 becomes insufficient. In order to send the cooling air whose wind pressure exceeds 12.0 kPa, the normal specification blower 5 alone is not sufficient, and other air compression means must be provided, the blower 5 becomes expensive, and the blower Therefore, the effect of reducing the power consumption required for cooling and drying the pre-expanded particles 1 cannot be obtained.

Moreover, when the said air volume is less than 17.0 m < ³ > / L / min, sufficient air will not spread over the pre-expanded particle 1 in the foaming tank 2, and cooling drying of the pre-expanded particle 1 will become inadequate. In order to send the cooling air whose air volume exceeds 40.0 m ³ / L / min, a large blower 5 is required, and power consumption for blowing increases, so that the pre-foamed particles 1 are cooled and dried. The effect of reducing the required power consumption cannot be obtained.

  Although the temperature of the air supplied in the said foaming tank is not specifically limited, Since it takes time to dry when it is too low temperature, it is preferable that it is 5 degreeC or more. Moreover, if the temperature of the air is high and the humidity is low, the drying efficiency of the pre-fermented particles 1 can be improved and the drying can be performed in a shorter time. It is not desirable to use heated air from the viewpoint that the supply air needs to be heated, etc., and the energy cost increases. In addition, when inexpensive heating air can be obtained by using waste heat of other devices, the heating air can also be used.

This cooling and drying is desirably performed so that the temperature in the foaming tank when the foamable thermoplastic resin is charged is less than 80 ° C. every time the preliminary foaming is performed.
When the temperature in the foaming tank when the foamable thermoplastic resin is charged is 80 ° C. or higher, the prefoamed particles are not sufficiently cooled and dried, the moisture content of the prefoamed particles is increased, and the prefoamed particles are coalesced with each other. It becomes easy to cause blocking in the foaming tank, and it may be difficult to smoothly feed the pre-foamed particles.

Further, this cooling and drying is desirably performed so that the moisture content of the pre-expanded particles is in the range of 8 to 4%, preferably in the range of 7 to 5%.
If the water content of the pre-expanded particles exceeds 8%, the pre-expanded particles are likely to coalesce with each other, blocking may occur in the foaming tank, and smooth granulation of the pre-expanded particles may be difficult.
On the other hand, when the water content of the pre-expanded particles is less than 4%, static electricity is likely to be generated, and there is a problem that the pre-expanded particles adhere to the inside of the pipe or the tank wall and are difficult to handle.

The pre-expanded particles are pre-expanded so as to have a bulk density equivalent to the density of the thermoplastic resin foam molding to be produced. In the present invention, the bulk density is not limited, but in the production of polystyrene resin pre-foamed particles, it is usually in the range of 0.0125 to 0.2 g / cm ³ (5 to 80 times as the bulk foaming factor), and 0.02 A range of ˜0.10 g / cm ³ (10 to 50 times as a bulk foaming factor) is preferable, and a range of 0.02 to 0.05 g / cm ³ (20 to 50 times as a bulk foaming factor) is more preferable.

  The pre-foamed particles obtained by performing the pre-foaming treatment described above are taken out from the hatch 10 of the foaming tank 2, pulverized by a foam granulating machine, transferred to a large pre-foamed particle storage tank by an ejector or the like, and stored. If necessary, it is allowed to stand for a predetermined number of days for aging, and if necessary, the pre-foamed particles are transferred from the pre-foamed particle storage tank to the foam molding apparatus and used for the production of a foam molded article by the in-mold foam molding method. .

In the method for producing pre-expanded particles according to the present embodiment, the foamable thermoplastic resin particles are heated and foamed in the foaming tank 2 to generate the pre-expanded particles 1 having a desired bulk expansion factor, and then air is supplied into the foaming tank 2. When the pre-expanded particles 1 are supplied and cooled and dried, air with a wind pressure of 3.0 to 12.0 kPa is supplied with an air volume of 17.0 to 40.0 m ³ / L / min (where L is the pre-expanded particles of the thermoplastic resin) Pre-expanded particles 1 in a shorter time than the conventional technique in which compressed air is supplied into the foaming tank by supplying the foamed tank 2 to the foaming tank 2 within a range of (bulk volume 1 m ³ ) and cooling and drying. Can be sufficiently cooled and dried, the production cycle of the pre-expanded particles 1 can be shortened, and the production efficiency can be improved.
In addition, the ability to use a blower 5 that can blow a large amount of low-pressure air to cool and dry can significantly reduce power consumption and reduce manufacturing costs compared to the conventional technology that supplies compressed air to the foaming tank. Can be planned.

The pre-expanded particles are filled in a cavity of a mold using a well-known apparatus and technique in the manufacturing field of thermoplastic resin foam-molded articles such as polystyrene resins, and heated by steam heating or the like. In-mold foam molding is performed to produce a thermoplastic resin foam molded body (hereinafter referred to as a foam molded body).
The density of the foamed molded product of the present invention is not particularly limited, but in the production of a polystyrene-based resin foam molded product, it is usually in the range of 0.0125 to 0.2 g / cm ³ (5 to 80 times as the expansion factor). The range of 02 to 0.10 g / cm ³ (10 to 50 times as the expansion factor) is preferable, and the range of 0.02 to 0.05 g / cm ³ (20 to 50 times as the expansion factor) is more preferable.

  In the present invention, the bulk density / bulk foaming factor of the pre-expanded particles and the density / foaming factor of the foamed molded product indicate values measured as follows.

<Bulk density / bulk expansion ratio of pre-expanded particles>
The mass (a) of about 5 g of pre-expanded particles is weighed in the second decimal place. Next, weighed pre-expanded particles in a 500 cm ³ graduated cylinder with a minimum scale unit of 5 cm ³ , and a circular resin plate slightly smaller than the caliber of the graduated cylinder, about 1.5 cm wide in the center, A pressure tool in which a rod-shaped resin plate having a length of about 30 cm was fixed upright was applied, the volume (b) of the pre-expanded particles was read, and the bulk density and the bulk expansion factor of the pre-expanded particles were determined by the following equations.
Bulk density (g / cm ³ ) = (a) / (b)
Bulk foaming factor = 1 / bulk density (g / cm ³ )

<Density and expansion ratio of foam molding>
A test piece of 50 cm ³ or more (100 cm ³ or more in the case of semi-rigid and soft materials) was cut so as not to change the original cell structure of the material, its mass was measured, and calculated by the following formula.
Density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
Test piece condition adjustment and measurement test pieces were cut out from samples that had passed 72 hours or more after molding, and were subjected to atmospheric conditions of 23 ° C. ± 2 ° C. × 50% ± 5% or 27 ° C. ± 2 ° C. × 65% ± 5%. It has been left for more than an hour.
Further, the expansion factor of the foamed molded product is a numerical value calculated by the following equation.
Foaming multiple (times) = 1 / density (g / cm ³ )

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited by these Examples.

(Pre-expanded particle production equipment)
As a manufacturing apparatus, a pre-foaming machine “PSX / 850” (trade name) manufactured by Kasahara Kogyo Co., Ltd. is used as a base, and as shown in FIG. 1, a pipeline 19 (thickness 1.5B) for supplying steam and cooling air is used. A branch part is formed in the middle of the ring, and as the blower 5, a ring blower (200 V × 1.3 kWh) manufactured by Fuji Electric Systems Co., Ltd., a connecting air pipe 21 (thickness 1 B), and provided in the middle of the air pipe 21 The cooling air supply means 6 formed by a ball valve (valve 20) was connected.
In the foaming tank of this apparatus, a first level meter 12 for detecting that the volume of the pre-foamed particles has reached 770 L, and a second level meter 13 for detecting that the volume of the pre-foamed particles has reached 870 L; Until the first level gauge is reached during steam heating, steam is supplied from both the first steam line 14a and the second steam line 14b, and when the first level gauge reaches the first steam line 14a The second steam line 14b is controlled to be closed when the second level meter is reached.

(Pre-foaming process)
As expandable polystyrene resin particles as raw materials, expandable polystyrene beads “Eslen Beads HDMA” (trade name) manufactured by Sekisui Plastics Co., Ltd. were used, and pre-expanded particles were produced by pre-expanding them to a bulk expansion ratio of 60 times. . The outline of the process is as follows.
(1) Hatch closed (2) Feeding raw materials; 14.8 kg of raw foam beads are put into the foaming tank.
(3) Steam supply; the first steam line 14a and the second steam line 14b are opened. When the first level meter is reached, the first steam line 14a is closed.
(4) Steam supply stop; when the second level meter is reached, the second steam line 14b is closed.
(5) Cooling and drying; the ring blower is driven and cooling air is supplied into the foaming tank.
(6) Removal of pre-expanded particles: The pre-expanded particles are transferred from the foaming tank to a pulverizer and transferred to an aging silo after pulverization.
(7) Air discharge In each of the following tests, the operation mode of the preliminary foaming machine was “high temperature”. The room temperature during the test was about 35 ° C.

<Test 1: Cooling air volume>
When the pre-expanded particle manufacturing apparatus is used, the air volume of the ring blower is appropriately adjusted during cooling and drying (cooling time is constant at 45 seconds), and the resulting pre-expanded particles (hereinafter referred to as expanded particles) Water content, foam flow in the granulator, and static electricity of the foam. These measurement methods and criteria were as follows.

(Foamed grain moisture content)
The mass of the taken-out foam particles is determined, the mass of the foam particles after drying at 105 ° C. for 1 hour (the mass after complete drying) is measured, and the moisture content (%) is calculated by the following formula.
Water content (%) = (mass of taken-out foam particles−mass after complete drying) ÷ (mass after complete drying) × 100

(Flow of foam particles in a granulator)
The taken-out foamed particles were transferred to a pulverizer, and when pulverized, the behavior of the foamed particles when the foamed particles passed through a wire mesh having an opening of 10 mm was visually observed. If the water content of the foamed particles is large, the foamed particles are difficult to drop from the wire mesh, and if the water content of the foamed particles is too small, static electricity is generated and the foamed particles easily adhere to the wire mesh.

(Static foam foam)
The static electricity amount (kV) of the foamed particles was measured using a static electricity measuring device STATILON M (trade name) manufactured by Sind electrostatic.
In addition, it is considered dangerous if the amount of static electricity foamed is 20 kV or more. This amount of static electricity is a measured value for the foamed particles immediately after foaming, and the foamed particles are pneumatically transported after being pulverized and supplied to an aged silo. At this time, the amount of static electricity is further promoted, and there is a high possibility of entering a hazardous atmosphere. Therefore, the static electricity amount of the foamed particles after the foaming force is preferably 10 kV or less.

[Example 1]
At the time of cooling and drying, the air volume of the ring blower was set to 27.5 m ³ / L / min, and the moisture content of the foamed particles, the flow of the foamed particles in the granulator and the static electricity of the foamed particles were examined. The results are shown in Table 1.

[Example 2]
At the time of cooling and drying, the air volume of the ring blower was set to 19.0 m ³ / L / min, and the moisture content of the foam particles, the flow of the foam particles in the granulator, and the static electricity of the foam particles were examined. The results are shown in Table 1.

[Example 3]
At the time of cooling and drying, the air volume of the ring blower was set to 38.0 m ³ / L / min, and the moisture content of the foam particles, the flow of the foam particles in the granulator and the static electricity of the foam particles were examined. The results are shown in Table 1.

[Comparative Example 1]
The air volume of the ring blower at the time of cooling and drying is set to 15.0 m ³ / L / min which is equal to or lower than the lower limit (17.0 m ³ / L / min) of the air volume in the present invention. The flow and the static electricity of the foam particles were examined. The results are shown in Table 1.

[Comparative Example 2]
At the time of cooling and drying, the air volume of the ring blower is set to 42.0 m ³ / L / min which is equal to or higher than the upper limit value (40.0 m ³ / L / min) of the air volume in the present invention. The flow and the static electricity of the foam particles were examined. The results are shown in Table 1.

From the results of Table 1, in Examples 1 to ^{3 in} which the air volume of the ring blower was within the range of 17.0 to 40.0 m ³ / L / min during cooling and drying, the moisture content of the taken-out foam particles was 4.0 to 4.0. The foamed particle flow in the pulverizer was smooth. In addition, the foamed particles of Examples 1 to 3 were good because the static electricity amount was less than 10 kV.
On the other hand, in Comparative Example 1, the air volume of the ring blower was set to be equal to or lower than the lower limit value (17.0 m ³ / L / min) of the air volume in the present invention. The amount was high, and it was difficult to flow the foamed particles with a granulator, which was not preferable.
In Comparative Example 2, the air volume of the ring blower was set to be equal to or higher than the upper limit (40.0 m ³ / L / min) of the air volume in the present invention. It became easy to adhere to the wire mesh. Furthermore, static electricity tends to be promoted during pneumatic transportation to the aging silo, and when stored in the silo, it may exceed the dangerous range of 20 kV, which is not preferable.
In addition, if the air volume increases, the foam particles rise strongly in the foaming tank, and the foam particles adhere to the top plate in the foaming tank. There is a risk that. Foamed grains that have been exposed to steam many times become a hard solid, and if mixed, it causes poor quality of the foamed molded product.
From the results of Test 1, it is understood that the air volume of the cooling air is preferably in the range of 17.0 to 40.0 m ³ / L / min.

<Test 2: Cooling air pressure>
The foamed granules were produced in the same manner as in Test 1 except that cooling drying was performed by appropriately changing the air pressure of the cooling air (the air cooling time was constant at 45 seconds). The foam flow in the machine, the static electricity of the foam and the inside of the foaming tank were investigated. The measurement of the moisture content of the foamed particles, the flow of the foamed particles with a pulverizer, and the static electricity of the foamed particles was performed in the same manner as in Test 1.

(Internal situation of foaming tank)
During the cooling and drying, the movement of the foam particles in the tank, particularly the presence or absence of soaring, was visually observed from the observation window of the foam tank.

[Example 1]
The wind pressure was set to 6.9 kPa at the time of cooling and drying, and the moisture content of the foam particles, the flow of the foam particles in the pulverizer, the static electricity of the foam particles, and the internal state of the foam tank were examined. The results are shown in Table 2.

[Example 4]
At the time of cooling and drying, the wind pressure was set to 4.0 kPa, and the water content of the foam particles, the flow of the foam particles in the pulverizer, the static electricity of the foam particles, and the internal state of the foam tank were examined. The results are shown in Table 2.

[Example 5]
The wind pressure was set to 11.0 kPa at the time of cooling and drying, and the water content of the foamed particles, the flow of the foamed particles in the pulverizer, the static electricity of the foamed particles, and the internal state of the foaming tank were examined. The results are shown in Table 2.

[Comparative Example 3]
At the time of cooling and drying, the wind pressure was set to 2.0 kPa, and the water content of the foamed particles, the flow of the foamed particles in the pulverizer, the static electricity of the foamed particles, and the state inside the foaming tank were examined. The results are shown in Table 2.

[Comparative Example 4]
At the time of cooling and drying, the wind pressure was set to 13.0 kPa, and the water content of the foam particles, the flow of the foam particles in the pulverizer, the static electricity of the foam particles, and the internal state of the foam tank were examined. The results are shown in Table 2.

From the results of Table 2, in Examples 1, 4 and 5 in which the wind pressure was in the range of 3.0 to 12.0 kPa, the moisture content of the taken-out foamed particles was 4.0 to 6.0%, and the granulator The foam flow was smooth. In addition, the foamed particles of Examples 1 to 3 were good because the static electricity amount was less than 10 kV. Further, the foamed grains in the foaming tank were stable during cooling and drying, and no soaring was observed.
On the other hand, Comparative Example 3 in which the wind pressure was 2.0 kPa was not preferable because drying of the foamed particles was insufficient, the moisture content of the taken-out foamed particles was high, and the foamed particles were difficult to flow with a granulator.
Further, in Comparative Example 4 in which the wind pressure was 13.0 kPa, the moisture content of the foamed particles was reduced, static electricity was generated, and it was easy to adhere to the wire mesh with a granulator. Furthermore, the foamed grains in the tank rose to the top plate during cooling and drying, and a part of the particles adhered to the top plate.
From the results in Table 2, it can be seen that the wind pressure in the cooling and drying is preferably in the range of 3.0 to 12.0 kPa.

<Test 3: Comparison with current pre-foaming machine>
In the present preliminary foaming machine, compressed air having a wind pressure of 5000 kPa is supplied from a 55 kWh screw compressor to the foaming tank through a pipe having a thickness of 1B.
The current cooling drying with compressed air (hereinafter referred to as air cooling) of the preliminary foaming machine was compared with the air cooling with blower air in Example 1 described above.
The air cooling with compressed air and the air cooling with blower air have the same pressure at the time of air cooling, but the compressed air is reduced to 3 / 8B by 1B piping to light oil in the steam chamber and blown into the foaming chamber. The air volume at this time is 1.86 m ³ / min per foaming tank. On the other hand, in the air cooling with blower air, the wind pressure is as low as 6.9 kPa, but the air volume is about 13 times as high as 24 m ³ / min per foaming tank.
The air cooling with the compressed air and the air cooling with the blower air were performed, respectively, and the relationship between the air cooling time and the foamed grain moisture content was examined. The results are shown in Table 3.
From the results of Tests 1 and 2, the preferable foamed grain moisture content at the end of air cooling was set to 5%, and the air cooling was stopped when the foamed grain moisture content reached 5%.

From the results in Table 3, the air cooling time to reach a preferred foamed grain water content of 5% is shorter for the blower air of Example 1 by 20 seconds, and the shortened time is one cycle time of the pre-foaming step. As a result, according to the present invention, the production efficiency of foamed particles can be increased.
In addition, in the case of compressed air, a 55 kWh screw compressor is used, whereas in the case of blower air, a 1.3 kWh ring blower is sufficient. According to the present invention, power consumption in the preliminary foaming process is reduced. can do.
The compressed air supplied from the screw compressor has a high wind pressure and speed, but the air piping is narrowed from 1B to 3 / 8B. Therefore, the moment the compressed air is blown into the steam chamber, the wind speed and air volume drop sharply. If the air cooling time is the same, the water content of the foamed particles becomes high.

  In the present invention, foamable thermoplastic resin particles obtained by adding a foaming agent to thermoplastic resin particles such as polystyrene resin, polyethylene resin, and polypropylene resin are heated by a pre-foaming device, and the desired bulk density (bulk foaming) is obtained. In particular, the present invention relates to a production method and a production apparatus for producing thermoplastic resin pre-foamed particles by being pre-foamed to be a multiple), and in particular, a production method capable of efficiently producing pre-foamed thermoplastic resin particles and reducing power consumption and It relates to a manufacturing apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Pre-expanded particle, 2 ... Foaming tank, 3 ... Steam, 4 ... Steam supply line, 5 ... Blower, 6 ... Air supply means for cooling, 7 ... Rotating shaft, 8 ... Stirring rod, 9 ... Baffle rod, 10 ... hatch, 11 ... wire mesh, 12 ... first level meter, 13 ... second level meter, 14 ... steam line, 14a ... first steam line, 14b ... second steam line, 15 ... steam pressure regulating valve, 16 ... header, 17 ... valve, 18 ... valve, 19 ... conduit, 20 ... valve, 21 ... air conduit.

Claims (4)

Put foamable thermoplastic resin particles in the foaming tank, introduce a heating medium into the foaming tank and heat foam the foamable thermoplastic resin particles to produce thermoplastic resin pre-foamed particles with a desired bulk foaming factor, Next, in the production method of supplying air into the foaming tank, cooling and drying the thermoplastic resin pre-expanded particles, and then taking out the thermoplastic resin pre-expanded particles,
When the thermoplastic resin pre-expanded particles are cooled and dried, air with a wind pressure of 3.0 to 12.0 kPa is supplied with an air volume of 17.0 to 40.0 m ³ / L / min (where L is the volume of the thermoplastic resin pre-expanded particles A method for producing thermoplastic resin pre-expanded particles, wherein the foamed tank is supplied in the range of 1 m ³ and cooled and dried.   The method of producing thermoplastic resin pre-expanded particles according to claim 1, wherein the cooling and drying is performed such that the temperature in the foaming tank when the foamable thermoplastic resin is charged is less than 80 ° C every time pre-foaming is performed.   A foaming tank that heats the foamable thermoplastic resin particles to produce thermoplastic resin pre-foamed particles, a steam supply line that supplies a heating medium into the foaming tank, and a wind pressure of 3.0 to 12 in the foaming tank An apparatus for producing pre-expanded thermoplastic resin particles, comprising: a cooling air supply means including a blower for supplying 0.0 kPa of air. The blower is capable of supplying air having an air volume of 17.0 to 40.0 m ³ / L / min (where L represents a bulk volume of 1 m ³ of pre-foamed thermoplastic resin particles) into the foaming tank. 3. The apparatus for producing pre-expanded thermoplastic resin particles according to 3.

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