JPH04161210A - Filter - Google Patents

Abstract

PURPOSE:To provide a filter excellent in the filtering of foreign matter and suppressed in the generation of a gel by coating the surface of a sintered filter material with a chromium oxide film formed by liquid phase reaction. CONSTITUTION:The surface of a sintered filter material is coated with a chromium oxide film formed by liquid phase reaction. The chromium oxide film may be heat-treated after liquid phase reaction. Further, in the same way as the surface of the sintered filter material, the surface of a perforated support plate or that of a filtrate discharge auxiliary material is pref. coated with a chromium oxide film. It is necessary to form the chromium oxide film by a liquid phase reaction method. For example, a filter is dipped for 1-30min in a solution prepared by adding lead oxide and ferric hydroxide to an aqueous solution with pH of about 12 containing 13-15% of caustic soda and several % of a sodium salt of sulfuric acid, nitric acid or phosphoric acid as an oxidizing catalyst and heated to 104-106 deg.C. By this method, the thermal deterioration of a polymer can be suppressed.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a filter used for filtration of molten polymer, and more specifically, a long-life molten polymer filtration filter that is excellent in filtering out foreign substances and suppresses gel formation. Regarding.

[Conventional technology] Thermoplastic polymers such as polyester, boria.

When manufacturing films and sheets by melting Robylene, polycarbonate, etc., foreign substances and gel-like substances in the polymer,
It is necessary to remove coarse particles and the like derived from additives such as fillers, and filters made of sintered metal particles or thin metal wires have conventionally been used. When the viscosity of the molten polymer is high and the amount of filtration is large,
A filter in which so-called leaf disk-shaped filters are stacked in multiple stages, as described in Japanese Patent No. 5210, is used. The surface layer of such a leaf disc-shaped filter is a filtration layer, and the inner layer is a reinforcing element for the filtration layer.

In the production of films and sheets, how efficiently and reliably filter out the foreign substances, gel-like substances, coarse particles, etc. mentioned above also influences productivity, quality, etc.

For example, in the case of magnetic recording media, the demand for which has recently been growing rapidly, the base film has a moderate level of cleanliness and has a flat surface, and the smoother the surface coated with magnetic material, the higher the quality of the recording medium. becomes. Therefore, although it is desirable that the additives dispersed and contained in the base film be fine particles, even if the particles are extremely fine, if the particles have the property of agglomerating, they will form agglomerates of secondary particles, resulting in the formation of fine particles. Characteristics are lost. If the filtration of these secondary particles is not sufficient, the secondary particles will eventually have the same adverse effects as foreign substances. In addition, foreign substances contained in the polymer are
It forms abnormal protrusions on the film surface and causes dropouts in magnetic recording media.

In addition, ultra-thin films (thickness 5 μm or less), which have recently been in high demand as bases for capacitors and thermal transfers, are so thin that if foreign matter like the one described above is present in the film, it is difficult to , when stretched in the transverse direction, this serves as a starting point for breakage, greatly reducing productivity.

[Problems to be Solved by the Invention] The above-mentioned sintered filter is used to filter out these foreign substances, but it has been found that in conventional filters, the filter itself is a source of foreign substances and gel.

For example, in a filter configured with a filter medium and a punching plate as a support plate, the filtrate tends to stay in the non-opening portion of the punching plate, resulting in gel formation. As a solution to this problem, it has been proposed in Utility Model Application Publication No. 60-86426 to replace the punching plate with a sintered plate made of metal particles. There are problems such as difficulty in completely removing foreign substances present inside the device.

Also, among the foreign substances that can be generated from filters, metal elements dissolved in polymers such as polymer catalysts and stabilizers precipitate on the metal surface of the filter, and these precipitates are peeled off due to some action. There is. If this peeling phenomenon occurs near the secondary side of the filter, the peeled off material will not be captured by the filter and will become foreign matter in the film. One possible solution to this problem is to reduce the amount of catalysts and stabilizer additives that can be the source of foreign substances, but this method has disadvantages such as lowering the polymerization rate and impairing the thermal stability of the polymer. There is.

(Means for Solving Eight Problems) The present invention aims to improve these problems and provide a long-life filter in which the filter itself suppresses foreign matter and gel, which is a source of generation, which has been difficult with the conventional technology. The filter is equipped with a sintered filter medium made of stainless steel, a porous support plate, and a filtrate discharge aid, and the surface of the sintered filter medium is formed by a liquid phase reaction, and if necessary, heat-treated after the liquid phase reaction. , because it is coated with a chromium oxide film.

In the present invention, the filter is equipped with a sintered filter medium made of stainless steel, a porous support plate, and a filtrate drainage aid, and the sintered filter medium, porous support plate, and filtrate discharge aid are conventionally known. can be used. As the sintered filter medium, for example, a filter medium obtained by sintering particles made of stainless steel or IN nonwoven fabric can be used. The porous support plate is a porous support plate made of stainless steel having a large number of through holes that supports the sintered filter medium against the filtration pressure, and is usually called a punching plate. It also includes those that have the same effect. The filtrate discharge aid forms, for example, a gap between two filter media to help the filtrate flow smoothly to the discharge section, and is usually a wire mesh made of stainless steel. It also includes those that have the same effect.

The structure of the filter can be a conventionally known structure. For example, in a leaf disk filter, two sheets of thin sintered m material with an opening in the center are stacked, a gap is formed between these filter materials, and a hole is formed in the center opening. A filtrate discharge aid for discharging the filtrate is disposed, a porous support plate is disposed between the filter medium and the filtrate discharge aid for supporting the filter against filtration pressure, and It is possible to adopt a structure in which the parts are connected directly to each other or to the outer periphery or the outer periphery of the metal porous support plate.

In the present invention, the surface of the sintered filter medium is coated with a chromium oxide film formed by a liquid phase reaction. This oxidized chromic acid may be heat-treated after the liquid phase reaction. Further, it is preferable that the surfaces of the porous support plate and the filtrate discharge aid are coated with the chromium oxide film, similar to the surface of the sintered filter medium.

The chromium oxide film that coats the filter surface is inert to molten polymers, such as aromatic polyester, and prevents thermal deterioration (gelation or lower molecular weight) of the polymer.
It has been confirmed through research by the present inventors that the effect of promoting gelation is low, and it exhibits excellent effects in suppressing gelation of polymers. Furthermore, in order to prevent the generation of foreign matter, it is sufficient to prevent the metal elements etc. dissolved in the polymer from precipitating on the metal surface of the filter, but since this precipitation phenomenon is generally thought to occur due to electrochemical action, Precipitation can be prevented by coating the surface of the filter metal with a material with low conductivity. However, the chromium oxide film is a material with low conductivity, and can solve the problems of polymer gelation and foreign substances at the same time.

The chromium oxide film must be formed by a liquid phase reaction method.

There are two methods for forming a film: a gas phase method and a liquid phase method. For example, Japanese Patent Laid-Open No. 2-35907 proposes formation by a chemical vapor phase reaction method. Although this method has the flexibility to choose various ceramic compositions depending on the purpose, it is difficult to form a uniform coating on every corner of the filter medium, and the method itself is generally quite expensive. Therefore, it was difficult to put it into practical use.

The liquid phase reaction of the present invention is a liquid phase method in which 11 materials are immersed in chemicals to form a film, so it is possible to avoid the occurrence of unformed parts when forming a film on filter media, etc. .

As a method for forming a chromium oxide film, for example, the method described in "Metal" No. 28 (1958> No. 6.434-436), the method described in Japanese Patent Publication No. 33-4957, etc. can be used. .

For example, 13-15% caustic soda and a few percent sulfuric acid.

Lead oxide and ferric hydroxide were added as oxidation catalysts to an aqueous solution of pl-(12) coexisting with soda salts such as nitric acid and vA acid, and the filter was heated to 104-106°C. This method forms a thin black chromium oxide film on the non-spun steel surface of the filter.The treatment effect may vary depending on the material of the non-stainless steel, so It is preferable to select the composition of the treatment liquid, the treatment conditions, and the treatment conditions.Furthermore, if the filter is heat treated in an oxidizing atmosphere after this treatment, the adhesion of the film will be improved.

Stability is further improved.

[Examples of actual pus Next, the present invention will be explained by examples.

Examples and comparative examples Caustic soda 15%, sodium phosphate 3%, sodium nitrite 2%
, a mixed aqueous solution of 0.1% ferric hydroxide and 2% lead peroxide is kept in a boiling state, and stainless steel 316L and wire diameter 8μ are added to it.
A leaf disk type filter with an outer diameter of 178IIII and made of a nonwoven fabric of 300 mL as a filter medium was immersed for 15 minutes. Then remove the filter and wash it with water.

A filter with chromic acid oxide formed on the surface was obtained by drying.

A chromium oxide film with a thickness of about 0.05 μm was formed on the metal surface of the filter.

A set of 10 of these filters was set in a filter housing to form a polymer filter. A die is connected to this polymer filter, and polyethylene terephthalate at 300°C is extruded at a rate of 50k (]/hour.
A 100 μm sheet was formed. Even after 96 hours from the start of extrusion, almost no degraded polymer (gel) or foreign matter was observed.

On the other hand, when the filter was formed in the same manner as in the above example without being coated with chromium oxide, a gel-like polymer was observed approximately 55 hours after the start of extrusion, and further fine black foreign matter became apparent.

Analysis of the black foreign matter revealed that it was an sb compound used as a catalyst during polymerization.

After dissolving the polymer of the used filter with a solvent, disassembling it, and observing the secondary side under magnification, it was found that an sb compound similar to the black foreign matter in the sheet was deposited on the metal surface of the filter.

[Effects of the Invention] In the filter coated with a chromium oxide film by the liquid phase reaction method of the present invention, thermal deterioration of the polymer is suppressed due to the chromium oxide film, and furthermore, precipitation of dissolved metals such as sb in the polymer is prevented. As a result, the usage time of the filter can be significantly extended.

Patent applicant Teijin Kaisha Ltd.

Claims (1)

[Scope of Claims] 1. A filter comprising a sintered filter medium made of stainless steel, a porous support plate, and a filtrate discharge aid, the surface of the sintered filter medium being formed by a liquid phase reaction, if necessary. A filter characterized by being coated with a chromium oxide film that has been heat-treated after a phase reaction. 2. Claim 1, characterized in that the surface of the porous support plate and/or the filtrate discharge aid is coated with a chromium oxide film formed by a liquid phase reaction, and optionally heat-treated after the liquid phase reaction.
Filters listed.