JPH08244033A - Method and apparatus for producing polyester chips - Google Patents

Abstract

PURPOSE: To obtain polyester chips low in water content by transporting cut chips while holding them to a reduced pressure state or a pressurized state to store them in a first storage tank and to dry the polyester chips at low temp. without lowering productivity. CONSTITUTION: Polyethylene terephthalate produced by polycondensation reaction is extruded from a cap in a strand shape at a speed of 5 ton/hr by applying pressure to a polycondensation vessel and the extruded polymer is cooled and solidified by water and cut by a cutter to form chips. The chips are discharged from the cutter to be supplied to a centrifugal separation type dehydrator to remove a part of bonded moisture and the dehydrated chips are transported over a distance of 30m by pressure feed type transport equipment having capacity of 6 ton/hr to be charged in a chip storage tank to be stagnated for one hr. By this constitution, the chips are dried at low temp. and the moisture content of the chips supplied to a drying process is reduced without lowering productivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing polyester chips. More specifically, the present invention relates to a method and apparatus for manufacturing polyester chips having a low water content.

[0002]

2. Description of the Related Art Polyester is industrially produced by a two-step process including an esterification reaction using terephthalic acid as a raw material or a transesterification reaction using dimethyl terephthalic acid as a raw material and a polycondensation reaction, when polyethylene terephthalate is used as an example. Has been done. The polymer whose viscosity has been increased to a predetermined level by the polycondensation reaction is extruded from the polycondensation reaction tank in the form of a strand or film, cooled, and then made into chips by a cutting device. Was stored in The quality of the chips stored in the storage tank is confirmed. If there is no problem, the chips are transferred to a larger chip storage tank as normal products and sent to the spinning process.

When a chip is spun or molded and injected, a step of melting the chip is carried out, but if the moisture content of the chip is high in this step, the viscosity is lowered due to the decomposition of the polymer, which causes a trouble in the spinning and molding. Before melting, the polymer is dried under normal pressure or reduced pressure to reduce the water content in the chips to prevent the melt viscosity of the polymer from decreasing. The chip drying is generally one in which hot air is passed through the chips inside the drier, but in order to prevent fusion of the chips inside the drier, it must be dried at a temperature 50 to 150 ° C. lower than the melting point of the polymer, Requires a long drying time. Particularly for a polyester having a melting point of 200 ° C. or lower, it is necessary to set the drying temperature to 100 ° C. or lower, and it may take 50 hours or more to dry the polyester. There is also a method of reducing the pressure inside the dryer in order to shorten the drying time, but such a dryer can only perform batch-type drying, which complicates the process.

On the other hand, as a method of previously reducing the moisture content of chips to be put into a dryer in order to improve the drying efficiency,
It is known that the chips discharged from the chipping equipment can be prevented from adsorbing moisture by using a dehydrator to reduce moisture absorption in the chips and reduce the moisture content of the chips. For example, the attached water cannot be removed sufficiently.

A method is also known in which the chip is preliminarily dried by passing a dry inert gas through the chip storage tank. However, even with this method, the limit is to maintain the moisture content of the chips at the time of adding them to the chip storage tank. Can not supply low chips.

Therefore, there has been a demand for a method of supplying chips having a low water content in the drying step by reducing the water content of the chips in advance and introducing them into a chip storage tank or the like.

[0007]

Conventionally, there is no technique for reducing the moisture content in the chip in advance as a technique for eliminating the decrease in productivity in the drying process and enabling the downsizing of equipment, and an improvement in this respect is desired. It had been.

In order to solve the above problems, it is an object of the present invention to provide a method of drying at a low temperature and reducing the water content of chips to be supplied to the drying step in advance so as not to reduce the productivity. .

[0009]

The method for producing a polyester chip of the present invention has the following constitution in order to solve the above problems. That is, a method for producing a polyester chip in which molten polyester is extruded from a discharge mouthpiece, solidified by water cooling while moving a guide device, cut into chips, and accumulated, and the cut chips are depressurized or pressed. A method for producing a polyester chip, characterized in that the polyester chip is transported while being kept in a pressure state and is retained in a first storage tank.

The polyester chip manufacturing apparatus of the present invention has the following constitution in order to solve the above problems. That is, it is a polyester chip manufacturing apparatus including a transportation device and a storage tank, wherein at least the first storage tank is directly connected to the suction type or compressed air type transportation device.

The raw material glycol of the polyester used in the production method of the present invention is ethylene glycol (hereinafter referred to as E
G), 1,4-butanediol, neopentyl glycol, hexamethylene glycol, decamethylene glycol, cyclohexanediol, polyoxyethylene glycol, polyoxytetramethylene glycol, etc. may be used alone or in combination of two or more. Can be selected arbitrarily. Further, as a bifunctional component mainly composed of an aromatic dicarboxylic acid used for a reaction with a glycol component or an ester-forming derivative thereof, terephthalic acid (hereinafter,
TPA), isophthalic acid (hereinafter referred to as IPA), naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, oxybenzoic acid, adipic acid, sebacic acid and the like, and alkyl derivatives of these acid components are exemplified. Alternatively, one or more of these may be mixed.

The chip forming means used in the method of the present invention is such that the strands of molten polyester extruded from the polycondensation tank are extruded from the discharge nozzle and are water-cooled and solidified while moving in the guide device, and are cut into chips by the cutting device. Any material may be used as long as it is cut and stored in a storage tank such as a chip bunker, or may be chips that are solidified before being completely solidified and then cooled and solidified.

The method of the present invention does not employ the conventional technique of dropping chips having a large amount of water adhered after cutting by cooling with water and solidifying them, and retaining them in the first storage tank. When it is retained in the first storage tank, it is transported while being kept in a depressurized or pressurized state by a pressure-fed or suction-type transportation device. If the atmosphere during this transportation is atmospheric pressure, the water adhering to the chips cannot be effectively reduced. In addition, similarly, the water adhering to the chips cannot be effectively reduced unless the water is transported under such conditions when the water is retained in the first storage tank.

At this time, it is more preferable to carry out a dehydration step by a centrifugal separation method or the like before transporting the chips to which water adheres.

It is preferable that the distance of transportation while maintaining the reduced pressure or the pressurized state is 3 meters or more, and more preferably 20 meters or more from the viewpoint of effectively reducing the water adhering to the chips. Further, the chip transportation capacity needs to be equal to or more than the chip forming capacity of the chip forming equipment, and one having a capacity of 1.5 to 2.5 times the chip forming capacity is preferable.

The inside of the chip transportation pipe may be in an outside air atmosphere, but it is more preferable that the inside of the pipe is in a dry inert gas atmosphere such as dry air or nitrogen for the purpose of strengthening dehumidification in the pipe.

The chips transported while being kept under reduced pressure or pressure are first retained in the first storage tank.
It is also preferable to preliminarily ventilate and replace dry air or a dry inert gas such as nitrogen in the storage tank so as to retain the chips in a dehumidifying atmosphere and further strengthen the moisture absorption prevention.

An apparatus for producing such polyester chips is an apparatus for producing polyester chips having a transportation device and a storage tank, and at least the transportation device directly connected to the first storage tank is of a suction type or a pneumatic type. Is. If all of the transportation devices are in a system in which atmospheric pressure is maintained,
It is not possible to effectively reduce the water adhering to the chips. Further, at least the first chip storage tank is directly connected to the suction type or compressed air type transportation device. If the transportation device and the first storage tank are not directly connected, even if the water is removed, it tends to absorb moisture before entering the first storage tank, making it difficult to achieve the object of the present invention.

Further, as described above, it is preferable that the storage tank directly connected to the transportation device can be kept under a dehumidifying atmosphere because the prevention of moisture absorption can be further enhanced.

[0020]

The present invention will be described in more detail with reference to the following examples.

Example 1 Polyethylene terephthalate produced by the polycondensation reaction was pressed into a polycondensation can to extrude the polymer in a strand form at a rate of 5 tons / hour from a spinneret, and the polymer was water-cooled and solidified into chips. It was made into chips with a chemical cutter.

After the chips are discharged from the cutter, they are subjected to a centrifugal dehydrator to remove a part of attached water, and then 6 tons /
Transport by 30 meters with a time-controlled pumping facility,
It was put in the chip reservoir.

After the chips placed in the chip reservoir were retained for 1 hour, the moisture content of the chips was measured and found to be 200 ppm ± 50 ppm.

Comparative Example After polyethylene terephthalate was water-cooled and solidified into chips by the same method as in Example 1, the same method as in Example 1 was applied to a centrifugal dehydrator to remove a part of attached water. , Without using transportation equipment,
It was dropped into the chip reservoir.

After the chips charged in the chip reservoir were retained for 30 minutes, the moisture content of the chips was measured and found to be 2000 ppm ± 500 ppm.

Example 2 A polyethylene terephthalate chip was treated in the same manner as in Example 1 and charged into a chip reservoir, and then 10 m ³ / min of dry air having a temperature 20 ° C. lower than the dew point was introduced into the chip reservoir. After allowing the chips to stay for 1 hour, the water content in the chips was measured and found to be 150 ppm ± 50 ppm.

Example 3 After the chips were retained for 30 days in the same manner as in Example 3, the moisture content of the chips was measured and found to be 120 ppm ± 50 ppm.

Example 4 Chips were treated in the same manner as in Example 1 and charged into a chip tank, and then dry air at a temperature lower than the dew point by 20 ° C. was charged into the chip tank at 1 m ³ / min to chip the chips. After staying for 1 hour, the moisture content of the chips was measured and found to be 200 ppm ± 50 ppm.

[0029]

Industrial Applicability According to the present invention, it is possible to obtain a polyester chip having a low water content, and to provide a method and an apparatus for producing polyester which can be dried at a low temperature without lowering productivity.

Claims (4)

[Claims] 1. A method for producing a polyester chip in which molten polyester is extruded from a discharge mouthpiece, solidified by water cooling while moving a guide device, and cut into chips to retain the cut chips. A method for producing polyester chips, characterized in that the polyester chips are transported while being kept in a reduced pressure or a pressurized state and are retained in a first storage tank. 2. The method for producing polyester chips according to claim 1, wherein the chips are retained in the first storage tank under a dehumidifying atmosphere. 3. A polyester chip manufacturing apparatus comprising a transportation device and a storage tank, wherein at least the first storage tank is directly connected to the suction type or compressed air type transportation apparatus. 4. The polyester chip manufacturing apparatus according to claim 3, wherein the first storage tank can be kept in a dehumidifying atmosphere.