JP3316119B2 - Filtration method of thermoplastic polymer - Google Patents

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 a method for reducing the flow velocity distribution of a molten polymer in a filter housing to avoid thermal degradation of the polymer due to stagnation and to form a gelled polymer. The present invention relates to a method for filtering a thermoplastic polymer, in which the filtration is suppressed.

[0002]

2. Description of the Related Art As a filter for filtering and refining a molten thermoplastic polymer, a cylindrical filter or a leaf disk filter in which two filter media are stacked and a support is included is usually used. In general, the latter is more expensive than the former, but because it has pressure resistance, it is suitable for high-viscosity polymer filtration or microfiltration, and a large filtration area can be secured for its volume. It is suitable for filtration of a thermoplastic polymer which can shorten the passage time and is liable to be thermally degraded.

However, along with the diversification of products manufactured by melt-molding polymers, the polymers have also diversified, and those having low fluidity, low heat resistance, and those having a high melting point, which are liable to undergo thermal deterioration. There is a need to perform melt molding and molding of products in which tolerance for defects caused by polymer degradation is extremely severe, and there is a need for a filtration device or a filtration method with a higher degree of thermal degradation.

Conventionally, at least two means have been proposed as means for solving these problems.
The first is an improvement that eliminates the filter's own stagnant area.
For example, Japanese Utility Model Application Laid-open No. Sho 60-86426 and Japanese Utility Model Application Laid-Open No. 61-175.
No. 418, Japanese Utility Model Application Laid-Open No. 60-179308,
No. 15009, No. 4-126705, No. 4-
No. 70112 and Japanese Utility Model Laid-Open No. 3-47007 are proposed. The second is an improvement that eliminates polymer stagnation that occurs at the boundary between the filter and the housing or flange that are stacked in multiple layers. In the latter case, for example, when a filter set actually used for long-time filtration of polyester is pulled out of the housing and the state of thermal deterioration of the polymer is observed, in the conventional filtration device (FIG. 3), the filter at the most downstream side of the polymer flow is Polymer degradation is particularly severe at the filter / flange interface, followed by polymer degradation at the most downstream filter / housing interface. As a method of avoiding the stagnation deterioration, Japanese Patent Application Laid-Open No. 60-90017 discloses a method in which an inner cross-sectional area of a housing is measured by a fluid (polymer)
To reduce the flow velocity gradually at the interface with the housing at the downstream of the filter. Although this method is effective in reducing the stagnation at the interface between the filter and the housing at the downstream portion of the filter, the stagnation suppressing effect at the interface between the filter and the flange at the most downstream portion is poor. In addition, there is a problem that extraction and disassembly work of the filter set becomes complicated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the retention of polymer at the boundary between a multi-layered leaf disk filter and a housing or flange in the filtration of a thermoplastic polymer, and to prevent deterioration of the polymer compared with the prior art. An object of the present invention is to broaden the range of effects and to reduce the complexity of work.

[0006]

According to the present invention, a plurality of leaf disk filters are stacked and housed in a housing through a center shaft, and the molten polymer introduced into the housing is leafed. In a method of filtering a thermoplastic polymer by passing through a disc filter and moving to a polymer flow path of a center shaft, at least one or more and five or less leaf disc filters from the most downstream side of the polymer flow in the housing, 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 a structure in which an inner surface of a flange connected to the housing keeps a substantially constant distance from the filter having the outer diameter. Achieved by a method of filtering a thermoplastic polymer, characterized in that It is.

Examples of the thermoplastic polymer in the present invention include polyolefins such as polypropylene, polyamides such as nylon 6 and nylon 66, aromatic polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polycarbonates. Of these, aromatic polyesters are particularly preferred.

In the filtering device of the present invention, three or more leaf disk filters are stacked and housed in a housing through a center shaft, and the molten polymer introduced into the housing is passed through the leaf disk filter to form a center shaft. It has a structure to move to the polymer channel.

In the leaf disk filter, the filter medium is a non-woven sintered body of metal fibers or a sintered body of metal powder, ceramic powder, or the like. If necessary, two filter media are stacked via a filter material reinforcing material. The filter includes a support that forms a polymer flow path on the secondary side of the filter, is laminated, and has a hub ring that passes a hollow shaft in the center. Such filters are conventionally widely known and used.

In the present invention, at least one and at most five leaf disk filters from the most downstream side of the polymer flow in the housing are filters having a smaller outer diameter than other filters and do not become larger toward the downstream side. Are arranged as follows. At this time, it is preferable to adopt a structure in which the inner diameter of the housing is reduced in accordance with the outer diameter of the filter on the downstream side. Since a filter having a small outer diameter has a small filtration area, stacking more than five sheets unnecessarily reduces the overall filtration area, which is not preferable.

The arrangement of the filters is such that their outer diameter does not increase towards the downstream of the molten polymer, but preferably decreases progressively downstream. The inner surface of the flange connected to the housing has a structure that maintains a substantially constant interval with the filter having the small outer diameter. Therefore, in particular, 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 the flow velocity from decreasing at the interface with the housing at the downstream portion of the filter.

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

In order to further improve the flow of the molten polymer downstream of the filter, a filter having a small outer diameter at the downstream portion has a smaller pressure loss than other large diameter filters, in other words, a filter having a smaller filtration resistance. Is preferred. Specifically, a pressure loss of 5% or more,
It is preferable to make it 0% or less. This upper limit is 50
%, More preferably 40%.

As a method of reducing the pressure loss of the leaf disk filter, there are a method of reducing the pressure loss of the filter medium and a method of reducing the flow path resistance on the filter secondary side.

In order to make the pressure loss smaller than that of other filters without changing the foreign matter collecting performance of the filter medium, when the filter medium is made of a sintered metal powder or a sintered ceramic powder,
It can be achieved by selecting 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 sintered nonwoven fabric 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 path resistance on the filter secondary side, there is a method of increasing the flow path cross-sectional area on the filter secondary side or the hub ring secondary side.

Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a filtration apparatus showing one embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of a filtration apparatus showing another embodiment of the present invention, and FIG. 3 is a conventional filtration apparatus. FIG.

In FIG. 3 showing a conventional system, a molten polymer 2 introduced into a housing 1 is diverted to leaf disk filters 3, 31 and the like, and passes through respective filter media 4.
The polymer enters the polymer channel 7 of the center shaft 6 through the channel 5 on the secondary side of each filter, and merges with the polymer that has passed through each filter in the process of moving the polymer channel 7 to the end 8 of the filtering device. Reach. Although 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 filter, the leaf disk filter of the lowermost stage 31 of the filter set has an adjacent surface such as the flange 9. In general, the retention 10 and 11 of the polymer tend to occur because of the blocking surface.

In FIG. 1 showing an embodiment of the present invention, the outermost diameter of the leaf disc filter at the most downstream stage 31 'of the filter set is 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. It is designed to form a smooth flow path together.

In the conventional method, a filter having a small outer diameter is used for the most downstream stage filters located at the portions 10 and 11 where polymer retention is likely to occur, and a smooth polymer flow path is formed between the flange and the filter. In addition, an appropriate polymer flow is generated in the lower portion of the filter set, so that the retention can be reduced.

Further, by changing the filter having a small outer diameter to a filter having a smaller pressure loss per unit filtration area than the other filters, the pressure distribution of each polymer flow path in the filter device is changed, and the lower stage of the filter set is changed. The flow rate of the polymer in the portion can be further increased, and the retention prevention effect can be further improved. It is also effective to stack filters having a small outer diameter so as to increase the filter interval as compared with stacking other filters.

FIG. 2 showing another embodiment of the present invention is a case where the filter diameter at the downstream stage of the filter set is reduced in two stages, 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 disc filter The filter to be measured is sandwiched between the both sides of the filter to the hub ring of the filter by a plate having the same outer diameter as the filter via the primary side spacer (spacer to be incorporated when the filter is laminated). Attached suction port and pressure detecting end are attached, and a vacuum pump is connected to the suction port to suction from the hub ring. Running the vacuum pump In the apparatus, by adjusting the intake air flow rate by measuring the degree of vacuum at that time, and the pressure loss of the filter intake flow rate per filter media 1 cm ² is with a degree of vacuum of 1 liter / sec I 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 used as shown in FIG.
In the apparatus described above, 50 sheets were stacked on a center shaft having a hollow polymer flow path and stored in a housing. However, a filter having an outer diameter of 127 mm was used as the filter at the lowermost stage 31 'of the filter set. The inner surface of the flange is designed to create a smooth polymer flow path to match the outer diameter of the filter.

The molten polyethylene terephthalate was extruded into a sheet at 305 ° C. after passing through the filtration device.
Even after 0 days, generation of gel due to polymer deterioration was not observed. After stopping the extrusion and cooling, the flange of the filtration device was removed and the interface with the filter was observed. As a result, coloring due to polymer deterioration was slight.

Comparative Example 1 Extrusion was performed under the same conditions as in Example 1 except that the filter at the lowermost 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 was caused due to the gel which was deteriorated by the polymer. The boundary between the filter and the flange at the lowermost stage 31 of the filter set was markedly colored by polymer deterioration.

Example 2 A 305 mm outer diameter leaf disk filter made by sintering a stainless steel fiber into a non-woven fabric was stacked on a center shaft having a hollow polymer flow channel in the apparatus shown in FIG. Stored in. However, the outer diameter of the downstream stage of the filter set is 222
1 mm and 149 mm filters are incorporated so that the outer diameter decreases toward the downstream, and the inner surface of the flange is designed 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 path on the secondary side is increased by 30% as compared with the other filters.
The pressure loss of the filter is 30% lower.

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

[Comparative Example 2] Evaluation was performed under the same extrusion conditions as in Example 2 except that the filter at the lowermost stage of the filter set was the same as the other filters and the apparatus shown in FIG. 3 was used. On the day there was a drawback due to the gel of polymer degradation.

[0033]

According to the present invention, it is possible to provide a filtration method capable of reducing the retention of the polymer, expanding the range of the effect, and reducing the complexity of the operation.

[Brief description of the drawings]

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

FIG. 2 is a schematic 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]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Flow of molten polymer 3 Filter 4 Filter medium 5 Filter secondary flow path 6 Center shaft 7 Polymer flow path 8 Termination 9 Flange 10, 11 Polymer retention section 31 The most downstream filter 31 'The outermost downstream with a small outer diameter Step filter 31 "Small diameter filter

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-9017 (JP, A) JP-A 52-52781 (JP, U) JP-B-46-16872 (JP, B1) 505669 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 29/39 B01D 35/02 C08J 3/00 B01D 63/08

Claims (2)

(57) [Claims] 1. A plurality of leaf disk filters are stacked and housed in a housing through a center shaft, and a molten polymer introduced into the housing is passed through the leaf disk filter and moved to a polymer flow path of the center shaft. In the method for filtering a thermoplastic polymer by the above 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 provided with a filter having an outer diameter smaller than that of the other filters and on the downstream side. A method for filtering a thermoplastic polymer, characterized in that the flanges connected to the housing are arranged so as not to increase in size, and the inner surface of the flange is maintained at a substantially constant distance from the filter having a small outer diameter. 2. The method for filtering a thermoplastic polymer according to claim 1, wherein the filtration resistance of at least one or more and five or less leaf disks having smaller outer diameters than the other filters from the most downstream side is smaller than that of the other filters.