JPH0365203B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is a filtration method that can efficiently filter a molten thermoplastic polymer high viscosity substance without abnormally retaining it. It relates to a filtration method using a filtration device that can be used for a long period of time, and the filter media can be easily regenerated.It is especially effective for removing foreign substances and impurities from melted thermoplastic polymer materials such as polyamide and polyester. The present invention relates to a method for filtering highly viscous substances suitable for filtering.

[Conventional technology]

In the manufacturing process of thermoplastic polymers, a filtration process for removing foreign substances from reaction products has been considered to be an extremely important process. In particular, in the case where the polycondensation reaction of a polymer is carried out over a long period of time, for example, in continuous polymerization, a filtration step is essential because foreign substances such as polymer deterioration products increase over time, and an efficient filtration means is required.

In other words, if foreign matter is present in the reaction product, this will lead to an increase in nozzle back pressure and single fiber breakage when the polymer is melt-spun and drawn, resulting in problems with fiber drawability, fine deniering, and high-speed spinning. Moreover, when extrusion molding into a film, abnormal protrusions are generated, which impairs the surface uniformity and yield of the film. Therefore, it is extremely important to provide a filtration step as a means for removing foreign substances at the final stage of the polymer production process.

Various types of devices have been known for filtering molten thermoplastic polymers with high viscosity, but there is still room for improvement in the quality of the filtrate obtained and in the maintenance of the devices. Ta.

For example, FIG. 3 is a cross-sectional explanatory view of a typical conventional filtering device for high viscosity substances, which is a vertical filtration system in which ring-opening filter media 3 are arranged in parallel in a casing 1 via a filtration mounting tube plate 2. Show the device. In this conventional example, a high viscosity substance represented by a molten polymer is introduced from an inlet 5 and rises in the direction of arrow A.
Filtration is performed by press-fitting into each closed-ring type filter medium 3. The filtered high-viscosity substance then rises in the direction of arrow B from the upper opening 3' of the closed ring filter medium 3 and is discharged from the discharge port 6. Further, 9 is a jacket, which heats the inside of the casing with a heating medium.

[Problem that the invention seeks to solve]

However, in the conventional filtering device for high viscosity substances shown in FIG. 3, due to its structure, the flow velocity of high viscosity substances decreases in the downstream flow direction within the casing 1, particularly near the inner wall surface of the casing and near the filter medium mounting tube plate 2. Therefore, the time for replacing the high viscosity substance in this part becomes infinite, resulting in abnormal retention called a so-called dead space. Therefore, when a highly viscous substance that is particularly susceptible to heat, such as a molten polymer, is applied to this device, the high viscosity substance rises to near the temperature of the heating medium in the above-mentioned abnormal retention section, causing heat to be applied to the polymer. This causes deterioration and turns into foreign matter, which quickly clogs the nearby filter surface. As the filter surface is blocked, the casing 1 becomes more
The flow velocity in the downstream flow direction decreases, the dead space expands, the abnormal retention area (the dotted area in Figure 3) increases, and the effective filtration area decreases, causing a sudden increase in filtration pressure. cause.

If the filtration pressure becomes high, the polymer gelled by the heat will slip through, making it impossible to stably obtain a product of excellent quality. In addition, thermally degraded polymers adhere to the filter media attachment tube plate 2 as carbides, gelled substances, highly crystallized substances, etc., making it difficult to remove the ring-closed filter media 3 from the filter media attachment tube plate 2 during repairs. In addition to causing maintenance troubles, there is a problem in that it is extremely difficult to regenerate the ring-closed filter medium 3 to which such heat-degraded substances are adhered.

Therefore, conventional filtration devices for high viscosity substances using closed-ring filter media cannot be used for long periods of time, have to be replaced frequently, are complicated to handle, and cannot be used to filter uniform high viscosity substances. It was difficult to obtain it stably.

[Purpose of the invention]

The purpose of the present invention is to process a molten thermoplastic polymer with high viscosity without causing thermal deterioration or abnormal retention.
The object of the present invention is to obtain a filtration method using a filtration device that can increase the effective filtration area, can be used for a long period of time, and allows easy regeneration of the filter medium.

[Structure of the invention]

As a result of intensive studies to achieve the above object, the present inventors have developed a method for filtrating a thermoplastic polymer molten high viscosity substance using a closed-ring type filter medium by dividing the flow path of the high viscosity substance and directing the flow upward from the conventional lower inlet. Separately from the flow, it is guided to the upper part via the central inflow pipe to create a downward flow, and the baffle plate strengthens the flow near the inner wall of the casing and near the tube plate where the filter medium is attached, and evenly distributed opposing flow. The inventors have discovered that an effect that meets the above objectives can be obtained by following this flow, and have arrived at the present invention.

That is, the present invention has an inlet for a molten thermoplastic polymer high viscosity substance at the bottom and an outlet for taking out the high viscosity substance after filtration at the top. A mounting tube plate having a large number of through holes is provided on one side, and a cylindrical closed-ring type filter medium having a filtration surface on the circumferential surface is hung and installed in each of the through holes of the mounting tube plate. A high viscosity substance introducing dispersion pipe having a window for guiding the viscous substance to the ceiling and dispersing the flow radially in the horizontal direction immediately below the above-mentioned installed tube plate is provided, and the pipe is installed at least in two locations above and below each of the closed ring type filter media arranged in the forest. By providing a baffle plate that adjusts the flow of high-viscosity substances, the high-viscosity substances that flow into the casing from the high-viscosity substance inlet are divided into a flow that ascends through the introduction dispersion pipe and a flow that ascends near the direct ring-closed filter medium. After ascending through the introduction dispersion tube and being dispersed horizontally and radially from the upper window, a flow is created that flows downward and a flow that ascends near the directly closed ring type filter medium, thereby strengthening the flow near the inner wall surface of the casing. , provides a method for filtering a molten thermoplastic polymer high viscosity substance, characterized in that the above-mentioned downstream flow and upward flow are opposed to each other.

A typical closed ring filter medium used in the present invention is a cylindrical closed ring filter medium as shown in a perspective view in FIG. In each of these closed ring type filter media 3, filtration is performed when high viscosity substances enter the inside from the outside through the surrounding filter portion, and the filtered high viscosity substances are discharged from the upper opening 3' of the filter media 3. It's becoming like that. Candle-shaped filter media are particularly preferred as the type of closed-ring filter media, and it is preferable to arrange the number of filter media corresponding to the required filtration area in an optimal arrangement to minimize the volume around the filter media.

The high-viscosity thermoplastic polymer melt that can be applied to the present invention is a material that flows in a laminar state in various parts of the casing, and usually has a flow rate of 1000 poise or more, especially
It is most effective for polymers with a temperature of 1000 poise or more that easily deteriorate due to heat, and polycondensation melt polymers such as polyamide and polyester are typical examples.

[Effect]

In the method of the present invention, the high viscosity substance flowing into the casing from the high viscosity substance inlet is divided into a flow ascending through the introduction dispersion pipe and a flow ascending near the direct ring-opening type filter medium, and the high viscosity substance flows upward through the introduction dispersion pipe. By opposing the flow that flows downward after being dispersed horizontally and radially from the upper window and the flow that rises near the directly closed ring type filter media, the flow near the inner wall surface of the casing and near the tube plate where the filter media is attached is reduced. In addition, the height of each filter medium is shifted at the part where the flow collides, so there is no dead space.

In particular, by strengthening the flow near the inner wall surface of the casing, which is easily heated by the heating jacket, deterioration of the thermoplastic polymer is prevented, gel is less likely to form, and as a result, filter media is less likely to be clogged.

Hereinafter, the apparatus used in the present invention will be explained based on the drawings.

FIG. 1 is an explanatory cross-sectional view of the apparatus including the method of the present invention, in which 1 is a casing, 2 is a filter medium attachment tube plate, 3 is a closed-ring filter medium, 4 and 4' are butt-full plates,
5 is an inlet, 6 is an outlet, 7 is an inflow pipe, 8 is an introduction/dispersion pipe, 9 is a jacket, and the arrows indicate the flow paths of the high-viscosity substances.

In the apparatus shown in FIG. 1, a large number of closed ring filter media 3
Buff-full plates 4, 4' are provided above and below the casing 1, and these are fixed in the casing 1 by the mounting tube plate 2, and a tubular high-viscosity substance inflow pipe 7 is provided at an intermediate position of the filter medium 3.
By providing this, a flow path is formed around the filter medium 3 in which highly viscous substances flow in countercurrent directions.

For example, when filtrating a thermoplastic molten polymer using the apparatus shown in FIG. 1 (arrow B), the gap between the inflow pipe 7 and the filter medium 3 via the gap between the buttful plate 4 and the filter medium 3 (arrow C), and the inflow pipe 7 (arrow D). Flows in the direction of each arrow. The molten polymer that has flowed into the inflow pipe 7 in the direction of arrow D flows out uniformly in the outer circumferential direction (arrow d) from the dispersion pipe 8 having a window around the upper end of the inflow pipe 7, and flows out into the filter medium attachment pipe. It flows near the plate, further hits the buff-full plate 4', is distributed, passes through the gap between the buff-full plate 4' and the filter medium 3, and connects to the gap between the inflow pipe 7 and the filter medium 3 (arrow c) and the outer periphery of the buff-full plate 4'. Gap with casing (arrow b)
Forms a downward flow.

In the present invention, which uses the apparatus shown in FIG. Further, opposing flows are formed around the filter medium 3 and are introduced into the filter medium 3 one after another while colliding with each other. The filtered molten polymer is then discharged from the upper end opening 3' of the filter medium 3 through the discharge port 6.
is discharged to.

Therefore, there is no abnormal accumulation of molten polymer near the filter media mounting tube plate 2, and the dead space, which was a major problem in the structure of conventional filter devices, is eliminated. Not only can efficient filtration be achieved without deterioration, but the filtration area of the device can be increased, the device can be used for a long period of time, and the filter medium can be easily regenerated.

Here, there was a concern that abnormal retention would be formed in the central part where the opposing polymers collide, but the colliding parts are not at exactly the same height on each filter medium,
Because there is a slight misalignment, it becomes easier to mix like a vortex, making it difficult to cause abnormal stagnation, and because it is located in the center of the casing, which is less likely to be heated by the heating medium, it is less susceptible to thermal deterioration, and the thermal deterioration that occurs here The actual filtration life is very long because there are fewer foreign substances and the filter material is less likely to become clogged.

Note that in the above-mentioned device, the pressure ratio of the high viscosity substance flow above and below the casing of the filtration device can be arbitrarily changed by selecting the pressure loss ratio such as the diameter and length of each flow path. , a pressure ratio of 1:1 is most preferred.

〔Example〕

The present invention will be specifically described below with reference to Examples.

Example 1 and Comparative Example 1 The high viscosity substance filtration apparatus shown in FIG. 1 (Example) and FIG. 3 (Comparative Example) was used as the apparatus. In order to be able to observe the inside of the device, the material was made of transparent PVC (casing capacity 7000ml).
30 closed type filter media 14mmφ). Polyalkylene glycol (Nitsun Unilube 70DE−
2620: Nippon Oil & Fats Co., Ltd.), red ink (Pilot: Absorbance 5.8 at 0.5 wt% in Unilube) was used as a coloring dye. Due to equipment issues, the viscosity has been reduced to 60~70Poise.
In order to carry out this experiment, 0.5 wt% of red ink was added to polyalkylene glycol mixed with 28 wt% of water, and the mixture was stirred until the color became uniform. This red liquid was injected into the casing, and closed-type filter media (30 pieces of 14 mm diameter) were gently inserted from above, and the filter was allowed to stand overnight to remove air bubbles within the filter media. A transparent fluid (polyalkylene glycol: water content 28wt%) without red ink is added at a specified amount of 40Kg/hr and a discharge pressure of 1.15Kg/hr.
Using a snake pump at ^cm2・G, we observed the exchange status inside the feeding casing, and
Coloring was carried out at specified time intervals, and the red dye concentration and substitution rate were determined from the absorbance.

The results are as shown in the graph of FIG. 4, and compared to Comparative Example 1 (conventional type), the red dye concentration of the collected fluid remained at a high position for a longer period of time in the example immediately after the start. This is because the transparent fluid has only one inlet at the bottom and the outlet channel is at the top, so the transparent fluid
It is thought that this was because the red fluid that had been injected earlier was pushed out. However, after about 10 minutes, the concentration reversed. At this point, in the example, the red fluid was already present only near the center of the casing, and more was being replaced than in the conventional type. In the end, in the conventional type, a small amount of red ink remained in the sampled liquid forever, but in the example, it disappeared after 30 minutes. As for the replacement rate, in the case of the example, all the red fluid was replaced, whereas
In the conventional model, replacement stopped at 96%, and 4% was stored in the upper corner of the casing and stopped moving. This revealed that in the conventional type, abnormal accumulation occurred at the upper corner of the casing.

Comparative Example 2 A conventional filtration device of the same type as that used in Comparative Example 1, made of heat-resistant stainless steel, was installed in a polyester straight-line heavy equipment and a field test was conducted.
The experiment was conducted using 210 filter media with an effective filtration area of 0.0498 m ² . Here, the temperature was maintained at 280 to 300°C, and polyethylene terephthalate with a viscosity of 2000 to 3000 Poise was fed at a specified rate of 1 to 2 T/hr, and the increase in filtration pressure and the amount of foreign matter increased were measured. Note that the number of foreign substances was measured by the number of fish eyes. (The obtained polymer was made into a biaxially stretched film and was
The above foreign matter was counted and converted into the number of foreign matter per gram of polymer, which was determined as the number of foreign matter. ) Example 2 A filtration device with a flow path in which highly viscous substances flow in countercurrents around a filter medium of the same type as that used in Example 1 was incorporated into a polyester straight-connection equipment using heat-resistant stainless steel. We conducted a practical test.
The experiment was conducted using 200 filter media with an effective filtration area of 0.0498 m ² . Here, the temperature is kept at 280 to 300℃ and the viscosity is
Polyethylene terephthalate of 2000 to 3000 Poise was fed at a specified rate of 1 to 2 T/hr, and the increase in filtration pressure and increase in foreign matter was measured. The results were as follows.

First, regarding the increase in filtration pressure, Comparative Example 2 (conventional type)
Immediately after the start of the test, the discharge pressure rose rapidly as shown in the graph in Figure 5, and exceeded 150 kg/cm ² G in just 22 days, requiring the filter medium to be replaced. When I tried to replace the filter and removed the tube plate to which the filter was attached, carbide etc. adhered to the vicinity of the tube plate, making it impossible to remove the filter. Also,
The filtration pressure rose too quickly to regenerate the filter material in time, and the plant had no choice but to operate without the filter material. This is thought to be because, as observed in Comparative Example 1, abnormal retention of molten polymer occurred in the upper corner of the casing, which was carbonized by the heat of the filter medium attachment tube plate and gradually grew, resulting in adhesion of carbide.

On the other hand, in Example 2, the rate of change was small for 50 days immediately after the start, and although it rapidly increased after that, it took 70 days to reach the filter medium replacement standard of 150 kg/cm ² ·G. When the exchange was carried out, no carbide was observed as in Comparative Example 2, and the exchange could be carried out smoothly. Also, since there was more time available for regeneration, it became possible to replace the filter earlier at a filtration pressure of 120 to 130 kg/cm ² G. Next, regarding the amount of foreign matter (graph in Figure 6), in Comparative Example 2 (conventional type), the amount of foreign matter rapidly increased from 10 days after the start, whereas in Example 2, 58
The number remains between 0 and 2 pieces/g until a few days later. This also shows that in the conventional type, foreign matter slips through the filter medium as soon as it starts.

〔Effect of the invention〕

As explained above, according to the method of the present invention,
High viscosity substances such as molten polymers can be efficiently filtered without causing abnormal retention and thermal deterioration due to the heat medium in the jacket.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an apparatus for carrying out the method of filtering a molten thermoplastic polymer high viscosity substance of the present invention, and FIG.
The figure is a perspective view of a closed-ring type filter medium, Figure 3 is a sectional view showing a device for carrying out a conventional filtration method for high viscosity substances, Figure 4 is a graph showing the relationship between elapsed time, substitution rate, and red paint concentration. FIG. 5 is a graph showing the relationship between the number of elapsed days and discharge pressure, and FIG. 6 is a graph showing the relationship between the number of elapsed days and the number of foreign objects. 1... Casing, 2... Filter medium mounting tube plate, 3...
...closed tube type filter medium, 3'...opening of closed tube type filter medium, 4,
4'...Spacer, 5...High viscosity substance inlet,
6... High viscosity substance outlet, 7... High viscosity substance inflow pipe, 8... Dispersion pipe, 9... Jacket.

Claims (1)

[Claims] 1 The bottom part has an inlet for the molten high-viscosity substance of thermoplastic polymer, and the top part has an outlet for taking out the high-viscosity substance after filtration, and a large number of through holes are provided in the ceiling of the casing whose outer wall surface is heated with a heating medium. A cylindrical closed-ring type filter medium having a filtration surface around the periphery is installed by hanging down into each through hole of the mounting tube plate, and the high viscosity substance is placed in the ceiling of the central part of the casing. A high viscosity substance introducing dispersion pipe having a window for dispersing the flow radially in the horizontal direction is provided directly below the above-mentioned attached tube plate, and the flow of the high viscosity substance is at least two places above and below each of the closed ring filter media arranged in a forest. By providing a buffer plate to adjust the high viscosity substance, the high viscosity substance flowing into the casing from the high viscosity substance inlet is divided into a flow rising through the introduction dispersion pipe and a flow rising near the direct ring-closed filter medium. After rising and being dispersed horizontally and radially from the upper window, a flow that flows downward and a flow that rises directly near the closed ring type filter medium are created, thereby strengthening the flow near the inner wall surface of the casing, and also strengthening the flow near the inner wall of the casing. A method for filtrating a molten thermoplastic polymer with high viscosity, characterized by opposing upward flows.