JPH09150018A - Filtration method for thermoplastic polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a molten polymer from becoming thermally deteriorated due to its residence and eliminate an operating complicacy by decreasing the outer diameter of a leaf disc filter on the extreme downstream side of a polymer flow in a housing than the outer diameter of another filter, and arranging the leaf disc filter in such a manner that its outer diameter does not enlarge toward the downstream side. SOLUTION: The outer diameters of 1 to 5 pieces of lead disc filter 31', 31"... from the extreme downstream side of a polymer flow in a housing 1 are smaller than those of other filters. In addition, the leaf disc filters are arranged in such a manner that their outer diameters do not enlarge toward the downstream side. In this case, it is preferred that the inner diameter of the housing 1 be reducible in compliance with the outer diameters of the filters on the downstream side. Further, the leaf disc filters 31', 31"... should be arranged so that their outer diameters do not enlarge toward the downstream side of a molten polymer flow, and preferably become gradually smaller toward the downstream side. Besides, the inner surface of a flange connected to the housing 1 is spaced almost constantly with the filters of smaller outer diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for filtering a thermoplastic polymer, and more particularly, to reduce the flow rate distribution of the molten polymer in the filter housing to avoid thermal deterioration of the polymer due to retention and to produce a gelled polymer. The present invention relates to a method for filtering a thermoplastic polymer in which the temperature is suppressed.

[0002]

2. Description of the Related Art As a filter for filtering and refining a melted thermoplastic polymer, a cylindrical filter or a leaf disc filter in which two filters are stacked and a support is included is usually used. Generally, the latter is more expensive than the former, but because it has pressure resistance, it is suitable for filtration or microfiltration of high-viscosity polymers, and since a large filtration area can be secured for its volume, the molten polymer can be used for the filtration process. It is suitable for filtration of thermoplastic polymers that can be passed through in a short period of time and is prone to thermal deterioration.

However, along with the diversification of products produced by melt-molding polymers, the polymers are also diversified and have low fluidity, low heat resistance, or high melting points, which easily cause thermal deterioration. It is necessary to carry out melt molding and molding of products having extremely strict criteria for accepting defects caused by polymer deterioration products, and there is a demand for a filtration device or filtration method in which thermal deterioration is highly reduced.

Conventionally, at least two means have been proposed as means for solving these problems.
The first is the improvement to eliminate the retention part of the filter itself,
For example, Japanese Utility Model No. 60-86426, Japanese Utility Model No. 61-175.
No. 418, Japanese Utility Model Laid-Open No. 60-179308, JP-A No. 2-1.
No. 15009, No. 4-126705, No. 4-126
No. 70112 and Jitsukaihei 3-47007 are proposed. The second is an improvement to eliminate polymer retention that occurs at the boundary between the multi-layered filter and the housing or flange. In the latter case, for example, when the filter set used for actual filtration of polyester for a long time is taken out from the housing and the state of thermal deterioration of the polymer is observed, in the conventional filtration device (FIG. 3), the most downstream side of the polymer flow is detected. Polymer degradation at the filter-flange interface is particularly severe, followed by polymer degradation at the most downstream filter-housing interface. As a method for avoiding this retention deterioration, in JP-A-60-90017, the inner cross-sectional area of the housing is defined by the fluid (polymer).
It is proposed that the flow velocity be gradually reduced along the flow direction to prevent the flow velocity at the interface with the housing downstream of the filter from decreasing. This method is effective in reducing retention at the boundary surface with the housing at the downstream part of the filter, but is poor in retaining effect at the boundary surface between the filter and the flange at the most downstream part. In addition, there is a problem that extraction and disassembly work of the filter set becomes complicated.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to reduce the polymer retention occurring at the boundary between the leaf disc filter and the housing or the flange which are laminated in multiple stages in the filtration of the thermoplastic polymer, and prevent the deterioration from the prior art. It is to broaden the range of effects and to eliminate the complexity of work.

[0006]

According to the present invention, an object of the present invention is to store a plurality of leaf disc filters in a housing by stacking them through a center shaft and introducing the molten polymer introduced into the housing into leaves. In a method of filtering a thermoplastic polymer by passing it through a disc filter and moving it to a polymer channel of a center shaft, at least one leaf disc filter and at least one leaf disc filter from the most downstream side of the polymer flow in the housing are: A filter having an outer diameter smaller than that of the other filters and arranged so as not to become larger toward the downstream side, and the inner surface of the flange connected to the housing maintains a substantially constant distance from the filter having the smaller outer diameter. Achieved by a method of filtering thermoplastic polymers characterized by It is.

Examples of the thermoplastic polymer in the present invention include polyolefin such as polypropylene, polyamide such as nylon 6 and nylon 66, aromatic polyester such as polyethylene terephthalate and polyethylene naphthalate, polycarbonate and the like. Of these, aromatic polyesters are particularly preferable.

In the filter of the present invention, three or more leaf disc filters are housed in the housing by stacking them through the center shaft, and the molten polymer introduced into the housing is passed through the leaf disc filters to pass through the center shaft. It is composed of a structure that is moved to the polymer channel.

In the leaf disk filter, the filter medium is a non-woven fabric-like sintered body of metal fibers or a sintered body of metal powder, ceramic powder or the like. If necessary, two filter mediums are superposed with a reinforcing material of the filter medium interposed therebetween. It has a hub ring that passes through a hollow shaft in the center and is laminated by including a support that forms a polymer channel on the secondary side of the filter. Such filters have been widely known and used in the past.

In the present invention, at least one and no more than 5 leaf disk filters from the most downstream side of the polymer flow in the housing are filters having an outer diameter smaller than that of the other filters, and do not become larger toward the downstream side. Are arranged as follows. At that time, it is preferable that the inner diameter of the housing is reduced according to the outer diameter of the downstream filter. Since a filter having a small outer diameter has a small filtration area, stacking more than five filters undesirably reduces the overall filtration area.

The arrangement of the filters is such that the outside diameter of the filter does not increase toward the downstream side of the molten polymer, and preferably, it decreases gradually toward the downstream side. The inner surface of the flange connected to the housing has a structure in which the inner surface of the flange has a substantially constant distance from the filter having the small outer diameter. Therefore, it is not necessary to gradually reduce the gap between the housing and the filter along the flow direction of the molten polymer in order to prevent a decrease in the flow velocity at the interface with the housing downstream of the filter.

The reason is that at least a part of the molten polymer existing in the gap between the downstream filter and the housing and the flange flows to the filter having a smaller outer diameter, so that the flow rate is lowered in the conventional filter system. This is because a smooth polymer flow is generated in the gap in the downstream portion and stagnation is avoided.

In order to further improve the flow of the molten polymer in the downstream part of the filter, the filter having a smaller outer diameter in the downstream part is used as a filter having a smaller pressure loss than the other filters having a larger outer diameter, in other words, a filter having a smaller filtration resistance. It is preferable. Specifically, the pressure loss is 5% or more, and further 1
It is preferable to reduce it by 0% or more. This upper limit is 50
%, And more preferably 40%.

Methods for reducing the pressure loss of the leaf disc filter include a method of reducing the pressure loss of the filter medium and a method of reducing the flow path resistance on the secondary side of the filter.

In order to make the pressure loss smaller than other filters without changing the foreign matter collecting performance of the filter medium, when the filter medium is made of a metal powder sintered body or a ceramic powder sintered body,
This can be achieved by selecting the sintering conditions so that the particle size distribution of the powder and the porosity of the sintered body meet the purpose. When the filter medium is made of a non-woven fabric sintered body of metal fibers, it can be achieved by selecting a combination of fiber diameter, basis weight, porosity and the like.

On the other hand, in order to reduce the flow passage resistance on the secondary side of the filter, there is a method of increasing the flow passage cross sectional area on the secondary side of the filter or the flow passage cross sectional area on the secondary side of the hub ring.

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

FIG. 1 is a schematic sectional view of a filtering device showing an example of an embodiment of the present invention, FIG. 2 is a schematic sectional view of a filtering device showing another embodiment of the present invention, and FIG. 3 is a conventional type filtering device. FIG.

In FIG. 3 showing the conventional system, the molten polymer 2 introduced into the housing 1 is split into the leaf disc filters 3, 31, etc., and passed through the respective filter media 4,
In the process of moving in the polymer flow path 7 of the center shaft 6 through the flow path 5 on the secondary side of each filter, and in the process of moving through the polymer flow path 7, the polymer that has passed through each filter is merged to form the end 8 of the filtration device. Reach The flow rate of the polymer is inversely proportional to the pressure loss of each flow path from the inlet to the end of the filtration device, but the leaf disc filter at the most downstream stage 31 of the filter set has the adjacent surface like the flange 9. Since it is a blocking surface, polymer retention 10 and 11 are generally likely to occur.

In FIG. 1 showing an embodiment of the present invention, the leaf disc filter at the most downstream stage 31 'of the filter set has an outer diameter smaller than that of the adjacent upper stage filter 3, and the inner surface of the flange 9 has the outer diameter of the filter. Together they are designed to form a smooth flow path.

In the conventional method, a filter having a small outer diameter is used for the most downstream filters located in the portions 10 and 11 where polymer retention is likely to occur, and a smooth polymer channel is formed between the flange and the filter. , A proper polymer flow is generated in the lower part of the filter set, and the retention can be reduced.

Further, by changing the filter having the smaller outer diameter to a filter having a smaller pressure loss per unit filtration area than the other filters, the pressure distribution of each polymer passage in the filtration device is changed, and the lower stage of the filter set. The flow rate of the polymer in the part can be further increased to further improve the retention preventing effect. Further, it is also effective to stack the filters having a small outer diameter so that the filter intervals are wider than those of other filters.

FIG. 2, which shows another embodiment of the present invention, is a case in which the diameter of the filter at the downstream stage of the filter set is reduced in two steps and is suitable for a filter set having a large outer diameter.

The physical properties of the present invention are measured and defined as follows. 1. Pressure loss of leaf disk filter Insert the filter to be measured into the hub ring of the filter from both sides with a plate of the same outer diameter as the filter through the primary side spacer (spacer incorporated when the filter is stacked), and place the flow controller in the center of the plate. An attached intake port and a pressure detection end are attached, and a vacuum pump is connected to the intake port to suck from the hub ring. The vacuum pump is operated in the device, the suction flow rate is adjusted and the degree of vacuum at that time is measured, and the vacuum degree at the time when the suction flow rate per 1 cm ^{2 of} the filter medium is 1 liter / sec. To do.

[0025]

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

[Example 1] A leaf disk filter having an outer diameter of 178 mm formed by sintering stainless particles was prepared as shown in FIG.
In the above apparatus, 50 sheets were laminated on a center shaft having a hollow polymer passage and housed in a housing. However, a filter having an outer diameter of 127 mm was used as the filter of the most downstream stage 31 'of the filter set. The inner surface of the flange is designed to match the outer diameter of the filter to create a smooth polymer channel.

Molten polyethylene terephthalate was extruded into a sheet at 305 ° C. after passing through the filtration device.
No generation of gel due to polymer deterioration was observed even after 0 day. After stopping this extrusion and cooling, the flange of the filtration device was removed and the boundary surface with the filter was observed. As a result, coloring due to polymer deterioration was slight.

[Comparative Example 1] Extrusion was carried out under the same conditions as in Example 1 except that the filter at the most downstream stage of the filter set was the same as the other filters and the apparatus shown in Fig. 3 was used. As a result, on the 8th day from the start of extrusion, a defect caused by a polymer-degraded gel was generated. The boundary surface between the filter and the flange of the most downstream stage 31 of the filter set was markedly colored due to polymer deterioration.

[Embodiment 2] In the apparatus of FIG. 2, 60 leaf disk filters having an outer diameter of 305 mm formed by sintering stainless fibers into a non-woven fabric are laminated on a center shaft having a hollow polymer passage to form a housing. Stored in. However, the outer diameter of the downstream stage of the filter set is 222.
mm and 149 mm filters are incorporated so that the outer diameter becomes smaller toward the downstream side, and the inner surface of the flange is designed so as to form a smooth polymer flow path according to the outer diameter of the filter.

This filter is designed so that the cross-sectional area of the flow passage on the secondary side is increased by 30% as compared with other filters.
The pressure loss of the filter is 30% lower.

Molten polyethylene-2,6-naphthalate was extruded into a sheet at 318 ° C. after passing through the filtration device, but no gel was formed due to polymer deterioration even after 8 days.

[Comparative Example 2] As a result of evaluation under the same extrusion conditions as in Example 2 except that the filter at the most downstream stage of the filter set was the same as the other filters and the apparatus shown in FIG. 3 was used, extrusion start 5 On the day, it caused defects due to polymer-degraded gels.

[0033]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a filtration method that reduces polymer retention, expands the range of its effect, and eliminates the complexity of work.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a filtration device according to the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of the filtration device according to the present invention.

FIG. 3 is a schematic sectional view of a conventional filtration device.

[Explanation of symbols]

 1 Housing 2 Flow of Molten Polymer 3 Filter 4 Filter Material 5 Filter Secondary Side Flow Path 6 Center Shaft 7 Polymer Flow Path 8 End 9 Flange 10, 11 Polymer Retention Area 31 Downstream Stage Filter 31 'Downstream of Small Outer Diameter Multi-stage filter 31 ″ Small outer diameter filter

Claims (2)

[Claims] 1. A plurality of leaf disc filters are stacked in a housing by passing them through a center shaft, and the molten polymer introduced into the housing is passed through the leaf disc filters and moved to a polymer channel of the center shaft. In the method for filtering a thermoplastic polymer by means of such a method, at least one or more and five or less leaf disk filters from the most downstream side of the polymer flow in the housing are filters having an outer diameter smaller than that of other filters, and the downstream A method for filtering a thermoplastic polymer, characterized in that the inner surface of a flange connected to the housing is arranged so as not to become large toward the outside and has a structure in which the flange has a substantially constant distance from the filter having a small outer diameter. 2. The method of filtering a thermoplastic polymer according to claim 1, wherein at least one and no more than 5 leaf disk filters having an outer diameter smaller than the others from the most downstream side have a filtration resistance smaller than that of the other filters.