JPH0959314A - Treatment of vinyl chloride-based polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating a vinyl chloride-based polymer by which a product of the vinyl chloride-based polymer to be shipped can be classified into required grain sizes and mixed foreign materials can completely be removed before the shipping. SOLUTION: A granular vinyl chloride-based polymer taken out of a silo is fed to a secondary oscillating screen having a screen net having <=4000μm mesh size in the method for treating the vinyl chloride-based polymer comprising a step for drying the vinyl chloride-based polymer prepared by the suspension polymerization, a step for subsequently feeding the granular vinyl chloride-based polymer after drying to a primary oscillating screen, classifying the polymer and selecting the vinyl chloride-based polymer having a prescribed grain size or below, and a step for subsequently transferring the selected granular vinyl chloride-based polymer to a silo for shipping and storing the transferred polymer in the silo, and a step for taking out the vinyl chloride-based polymer in order to ship the polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a classifier consisting of a vibrating sieve after the outlet of a silo for shipping a granular vinyl chloride polymer product to exceed a certain particle size mixed in the product to be shipped. The present invention relates to a method for improving the quality of shipped products by removing coarse vinyl chloride polymer particles and foreign substances.

[0002]

BACKGROUND OF THE INVENTION Vinyl chloride polymers are produced by suspension polymerization, emulsion polymerization, solution polymerization and bulk polymerization. In the case of suspension polymerization, the vinyl chloride polymer obtained by the polymerization is dried, the obtained polymer particles are passed through a vibrating screen, and the excessive particles are removed and then transferred to a shipping silo. The polymer stored in the shipping silo is appropriately taken out and shipped. To specifically explain the case of suspension polymerization, a slurry of a vinyl chloride polymer produced by polymerization in a polymerization vessel is extracted from the polymerization vessel and dehydrated by a centrifuge,
Next, the product is dried by a dryer to obtain a vinyl chloride polymer dried product, which is then subjected to a vibrating screen. Here, excess particles are removed and then stored in silos until they are shipped. At the time of shipping, the polymer is extracted from the silo shipping port, transferred to a tank truck, and shipped.

In the case of a vinyl chloride polymer obtained by suspension polymerization, particles having a size of about 400 to 500 μm or less are usually selected by a vibrating screen according to the intended product specifications. This is because coarse particles exceeding this amount cause a product defect called fish eye during molding. A vibrating sieve for removing such coarse particles out of product specifications is not provided at the product outlet from the shipping silo. For example, in order to completely remove coarse particles of 420 μm or more, it is necessary to use a mesh having an opening of 400 μm. Such vibrating sieves having such a relatively fine opening and a currently available vibrating screen have a processing capacity of at most 10 tons / hour. But at least 30 at the exit of the shipping silo
This is because a processing capacity of ton / hour is required.

[0004]

Even if the above-mentioned vibrating screen is provided after the drying step and before the shipping silo, coarse particles and foreign matters of the vinyl chloride polymer are still present in the product as follows. May get in. (1) The solidified product of the vinyl chloride polymer product adhered to the inner surface of the air transportation pipe between the vibrating screen and the shipping silo is separated and mixed into the product. (2) Fragments are mixed due to breakage of the screen of the vibrating screen, or cleaning balls for preventing clogging of the screen are dropped and mixed into the product. (3) The weight of the weight level meter installed in the shipping silo falls and mixes into the product. Further, when the manhole on the upper part or the side part of the shipping silo is opened and closed, the bolts and nuts for opening and closing the manhole fall and are mixed in the product. These coarse particles and foreign substances are different from the coarse particles (particle size 420 to 1000 μm) generated during the production of the vinyl chloride polymer in that the particle size or size is large, usually 4000 μm or more.

An object of the present invention is to provide a treatment method for removing coarse particles and relatively large foreign substances mixed in a vinyl chloride polymer product after a vibrating screen provided between a drying process and a shipping silo. Especially.

[0006]

According to the present invention, a step of drying a vinyl chloride polymer obtained by suspension polymerization,
Next, the granular vinyl chloride polymer after drying is subjected to a primary vibrating sieve and classified to select a vinyl chloride polymer having a certain particle size or less, then a first sieving step, and then the granular vinyl chloride polymer thus selected. In a method for treating a vinyl chloride-based polymer, which comprises a step of transferring the vinyl chloride-based polymer to a silo for shipping and storing it in the silo, and then a step of extracting the vinyl chloride-based polymer from the silo for shipping. There is provided a method for treating a vinyl chloride-based polymer, which comprises subjecting the discharged granular vinyl chloride-based polymer to a secondary vibrating sieve having a sieve mesh with an opening of 4000 μm or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Drying Step After completion of polymerization, the vinyl chloride polymer in a slurry state taken out from the polymerization vessel is sent to a dehydrator. A known dehydrator can be used, and examples thereof include a centrifugal separator and a filter. The water content of the slurry is usually removed to 25% by weight or less with a centrifuge or the like to obtain a wet polymer cake. The polymer cake is sent to the dryer. A well-known dryer can be used, and examples thereof include a fluid dryer, a rotary dryer, and a wind tube dryer. The water content in the cake is usually removed to 0.1% by weight or less with a fluidized dryer to obtain a granular vinyl chloride polymer. First sieving process

In the first sieving process and the second sieving process described later, a vibrating screen is used as a classifying means. The structure of the vibrating screen is known, and for example, as shown in FIG. 1, a screen screen 1 is stretched over the bottom of a screen frame 2 made of wood or the like. For convenience of description, a part of the screen 1 and the screen frame 2 is cut out. When the sieve frame 2 is vibrated, the particles of the vinyl chloride polymer hit the sieve screen 1 while repeatedly jumping. Then, the particles are sorted into fine particles that can pass through the mesh (standard product) and coarse particles that cannot pass through the mesh (nonstandard product). In order to prevent clogging of the sieve screen 1, another stage and a frame 3 are provided on the lower side of the sieve frame 2, a mesh 4 having a larger opening than the sieve screen 1 is stretched, and a synthetic white rubber is placed between both meshes. It is effective to place a cleaning ball 5 made of polyurethane, silicone rubber or the like. Frame 3
When the frame 3 that is fixed to the lower end of the screen frame 2 and vibrates as a unit during movement is in use, the cleaning ball 5 is
Frequently hits the back side of the screen 1 while jumping up on the screen 4, and prevents the particles of the vinyl chloride polymer from clogging the screen of the screen 1.

As the driving mechanism of the vibrating screen, for example, a mechanism can be used in which the driving force of a motor that is a power source is transmitted to the vibrating screen through a cam, an electromagnet, an eccentric shaft, an unbalanced weight, and the like. . There are circle, ellipse, up and down, tilting methods and the like as the motion method of the vibrating screen, and any method may be adopted. The optimum number of movements and amplitude may be determined according to the opening of the screen of the vibrating screen. For example, in the vibrating screen of the first screening process,
Number of movements: 1000 to 7,000 times / min, amplitude: 1 to 5 mm, and in the vibrating sieve of the second sieving process, number of movements: 60 to 300
Times / minute, amplitude: 10-100 mm.

The primary vibrating screen is subjected to a drying step in order to completely remove nonstandard coarse particles contained in the dried vinyl chloride-based polymer and scale small pieces separated from the wall surface in the polymerization vessel. It is provided between shipping silos. Since it is preferable that the classification treatment is performed at a low speed and is as uniform as possible, it is appropriate to install the classification treatment continuously at the outlet of a continuous operation device such as a continuous drying device that performs the treatment at a constant speed.

The specifications of the screen used for the primary vibrating screen are selected according to the particle size of the polymer particles to be treated. Normally open
400 to 500 μm is preferable, and generally 400 to 500 μm
It is possible to remove coarse particles and foreign matter exceeding the above. The mesh opening ratio is preferably 55% or more from the viewpoint of processing capacity, and the mesh wire diameter depends on the material, but it depends on the material.
It is preferably 0 μm or more. There is a contradictory relationship between the mesh opening ratio and the mesh wire diameter. For practical purposes, it is preferable that the opening ratio is 55 to 65% and the mesh wire diameter is 100 to 160 μm. Examples of the material of the screen include stainless steel, nylon, tetron and the like, and preferably stainless steel. This primary vibrating screen is required to have a processing capacity of about 4 to 8 tons / hour. Shipping silo

The structure of the shipping silo may be a known one.
There is no particular limitation. Also, the equipment specifications such as the capacity of the shipping silo and the size of the product outlet can be determined as necessary. Second sieving process

The vibrating sieve in the second sieving step is provided after the product outlet of the shipping silo. The opening of the screen of the vibrating screen is selected according to the size of coarse particles or foreign matter to be removed, and is usually 4000 μm or less, preferably 1000 to 2500 μm.
m, and more preferably 1500-2500 μm. Depending on the size of the openings, it is possible to remove coarse particles and foreign substances having a size of 1500 to more than 3000 μm. Since the size of foreign matter mixed in after passing through the primary vibrating screen is usually 4000 μm or more,
It can be completely removed by such openings.

Since a large processing capacity is required for the secondary vibrating screen, a larger opening ratio of the screen is more desirable. But,
The fact that a large processing capacity is required also means that a large amount of strength is required for the screen wire of the screen. Therefore, the mesh opening ratio and the mesh wire diameter are in a trade-off relationship. Usually, the mesh opening ratio is preferably 55% or more, more preferably 60% or more, and practically 55 to 70% in relation to the mesh wire diameter. The net wire diameter is practically in the range of 400 to 1000 μm, and more preferably in the range of 450 to 650 μm.

If necessary, a plurality of secondary vibrating screens may be provided, and the total processing capacity is 30 tons / hour or more, preferably 80 tons.
Tons / hour or more. Generally, a range of 30 to 150 tons / hour is practical.

The material of the screen is stainless steel, nylon,
Polyester or the like can be used, and stainless steel is preferable.

Specific embodiments of the present invention will be described below with reference to examples and comparative examples.

【Example】

Example 1 Using the apparatus shown in FIG. 2, a vinyl chloride polymer produced by suspension polymerization was dried, classified, stored in a silo, and shipped. First, a vinyl chloride polymer cake (water content 24% by weight) produced by suspension polymerization was placed in a fluid dryer 21.
And dried in the dryer to a water content of 0.1% by weight. The average particle size of the vinyl chloride polymer particles obtained by drying was 160 μm. The particle size distribution was measured by classifying with a sieve (JIS Z8801). Table 1 shows the results.

[0018]

[Table 1]

Next, the dried vinyl chloride polymer product, together with the air sucked from the intake pipe 23 by the suction blower 22,
Transferred to the cyclone 26 through the pipes 24 and 25. And
The cyclone 26 separated the dried product from the air, and the dried product was sent to the primary vibrating screen 28 through the pipe 27. Primary vibrating screen
28 has the structure shown in FIG. 1, and its specifications are as shown in Table 2.

[0020]

[Table 2] The primary vibrating screen 28 captured polymer particles having a particle size of more than 420 μm, scale particles, etc. on the screen, and then collected in a collecting container 29.

Next, the vinyl chloride polymer product passing through the primary vibrating screen 28 was sent to a rotary valve 31 through a pipe 30. Then, the polymer product is taken in through the air intake port 32 and is piped together with the air pressurized by the blower blower 33.
Guided to cyclone 35 through 34. The vinyl chloride polymer product was separated from air by a cyclone 35, and the recovered polymer product was transferred to the shipping silo 36. The maximum storage capacity of the shipping silo 36 was 150 tons. A secondary vibrating screen 38 is provided immediately below the vinyl chloride polymer product outlet 37 of the shipping silo 36. For this vibrating screen, a mesh material made of stainless steel and having a mesh area of 2.3 m ² was used. Specifications other than these are shown in Table 3. The cleaning ball was made of neoprene and had a diameter of 35 mm. The frequency of this sieve was 250 rpm. By the secondary vibrating screen 38, 2030
Coarse particles with a particle size of more than μm and foreign substances are captured on the sieve,
It was collected in the collection container 39.

The apparatus was operated for the above treatment for 3 months.
Table 3 shows the total treatment amount on the primary vibrating screen, the total amount removed, the total amount removed from the shipping silo, the total amount removed on the secondary vibrating screen, and the average hourly processing rate on the secondary vibrating screen during that period. It was

The vinyl chloride polymer product thus passed through the secondary vibrating screen 38 was molded and processed, and the number of fish eyes generated on the molded sheet was measured to determine whether the product passed or failed. The fisheye measurement method and the acceptance criteria are as follows. Table 3 shows the results.

Fisheye measurement method 100 parts by weight of vinyl chloride polymer, 1 part by weight of tribasic lead sulfate, 1.5 parts by weight of lead stearate, 0.2 parts of titanium oxide.
Parts by weight, 0.1 parts by weight of carbon black and 50 parts by weight of dioctyl phthalate were mixed. The obtained mixture was kneaded with a roll at 145 ° C. for 5 minutes, and the thickness was adjusted to 0.
The sheet was molded into a 2 mm sheet, and the number of fish eyes contained in 100 cm ^{2 of} the sheet was counted.

[ Fisheye acceptance criteria ] Pass: 10 pieces / 100 cm ² or less Fail: 11 pieces / 100 cm ² or more

Table 3 shows the measured values / judgment of the fish eyes, the number of test days and the treatment amount. The result of this example is that
Both fisheye value and processing speed meet the specifications.

[Examples 2 and 3 and Comparative Examples 1 and 2] In each example, suspension was performed under the same conditions as in Example 1 except that the specifications and operation period of the secondary vibrating screen shown in Table 3 were changed. The vinyl chloride polymer obtained by the polymerization was treated. Table 3 shows the total throughput of the primary vibrating screen, the total removal amount, the total withdrawal amount from the shipping silo, the total removal amount of the secondary vibrating screen, and the average hourly processing rate of the secondary vibrating screen in each example. The fish eye of the treated polymer product was measured in the same manner as in Example 1.
Table 3 shows the results.

In Example 2, the total throughput of the primary vibrating screen was 28,0.
At 50 tons, I found that the screen of the primary vibrating screen was broken and repaired it. Fragments of the sieve screen were captured by the secondary vibrating screen when the total throughput of the primary vibrating screen was 28,100 tons.

[0029]

[Table 3]

[0030]

As described above, according to the treatment method of the present invention, the vinyl chloride polymer product to be shipped is classified to the required particle size, and the foreign substances mixed in are completely removed before shipping. Therefore, the quality of the shipped polymer product is kept high and the reliability is high.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a vibrating screen.

FIG. 2 is an explanatory view schematically showing an apparatus for carrying out the processing method of the present invention.

[Explanation of symbols]

 21 Fluid Dryer 28 Primary Vibrating Sieve 29 Top Sieve Repair Container 36 Silo for Shipping 38 Secondary Vibrating Sieve

Claims (1)

[Claims] 1. A step of drying a vinyl chloride-based polymer obtained by suspension polymerization, and then the dried granular vinyl chloride-based polymer is subjected to a primary vibrating screen for classification to classify the vinyl chloride-based polymer having a certain particle size or less. Selecting a polymer, then transferring the granular vinyl chloride-based polymer thus selected to a shipping silo and storing it in the silo, then from the silo for shipping the vinyl chloride-based polymer A method for treating a vinyl chloride polymer comprising a step of extracting, wherein the granular vinyl chloride polymer extracted from the silo is subjected to a secondary vibrating screen having a sieve screen with an opening of 4000 μm or less. A method for treating a vinyl polymer.