Plastic filter for a photograph developing apparatus

Liquid purification or separation – Processes – Separating

Reexamination Certificate

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Details

C210S497010, C210S510100, C210S496000

Reexamination Certificate

active

06180015

ABSTRACT:

The present invention relates to a plastic filter for a photograph developing apparatus, particularly a plastic filter for a photograph developing apparatus, which is useful for effectively separating, by filtration, foreign matters in various treating tanks of the photograph developing apparatus.
An automated developing apparatus for developing treatment of photographic sensitive materials such as photographic films or photographic printing papers, comprises treating tanks for treating liquids such as a developing solution, a fixing solution and washing water, transporting means which sequentially pass the photographic sensitive materials to be treated through the respective treating tanks, treating liquid circulating systems connected to the respective treating tanks, and liquid temperature controlling apparatus disposed in the circulating systems.
Such treating liquid circulating systems are provided with pipings and electromagnetic valves for circulating the respective treating liquids by circulating pumps, and they are also provided with filters for photograph-developing apparatus, as filtration means to remove foreign matters, such as various sludges formed by chemical reactions, fine contaminants and scales.
As such a filter, a plastic filter is available which is molded by a so-called sintering method wherein a polyolefin type material such as a low density or high density polyethylene or polypropylene is filled in a mold, and the mold is heated to a level close to the melting point of the resin to fuse only the surface of particles.
However, such a material undergoes an abrupt deterioration of the elastic modulus at a temperature higher than the melting point, and yet no rubber-like flat portion is observed. Accordingly, if the material constituting the filter is fine particles, clogging of the spaces among particles is likely to take place by the Laplace principle, and it will be difficult to control the porosity and the pore diameter.
Accordingly, commercially available plastic filters for photograph developing apparatus are those obtained by sinter-forming materials having relatively large particle sizes. Such plastic filters have had a problem that the pore sizes are large, and fine foreign matters in the treating tanks can not be separated by filtration, and a problem that the production costs tend to be high since the molding method is a batch system.
Further, there has been a filter for a photograph developing apparatus which is prepared by winding non-woven fabrics or yarn fibers on the outer circumference of a cylindrical plastic support. However, such a filter has had a problem that filamentous contaminants are likely to result from itself due to e.g. fuzzing of fibers during its use, thus leading to an increase of foreign matters in the treating tanks.
As a result of extensive studies, the present inventors have found a plastic filter for a photograph developing apparatus having a good filtration precision, which is capable of solving the above problems. Namely, the present invention provides a) plastic filter for a photograph developing apparatus, which is obtained by sinter-forming a thermoplastic material and which has a porosity of from 30 to 60 vol %, a filtration precision of a level capable of capturing foreign matters of at least 30 &mgr;m, and a pressure loss of at most 20 mmAq at a dry air flow rate of 1 m
3
/m
2
·min, b) the plastic filter for a photograph developing apparatus, wherein the thermoplastic material is an ultrahigh molecular weight polyethylene and it is in the form of a hollow cylinder having a radial crushing strength of at least 5 kg/cm
2
, and c) the plastic filter for a photograph developing apparatus, wherein the average particle size of the ultrahigh molecular weight polyethylene is from 50 to 700 &mgr;m.
Now, the present invention will be described in detail with reference to the preferred embodiments.
The plastic filter for a photograph developing apparatus of the present invention, which is obtained by sinter-forming a thermoplastic material, is required to have a porosity of from 30 to 60 vol %, a filtration precision of a level capable of capturing foreign matters of at least 30 &mgr;m, and a pressure loss of at most 20 mmAq at a dry air flow rate of 1 m
3
/m
2
·min. Preferably, the thermoplastic material is an ultrahigh molecular weight polyethylene, and the radial crushing strength is at least 5 kg/cm 2. More preferably, the average particle size of the ultrahigh molecular weight polyethylene is from 50 to 700 &mgr;m.
The thermoplastic material constituting the plastic filter for a photograph developing apparatus of the present invention, is not particularly limited so long as it is a material having a small melt flow rate and whereby a porous body can relatively easily be obtained, among polyolefin resins such as polyethylene and polypropylene, polyvinyl chloride resins, polyester resins, polyamide resins, polystyrene resins, polyacrylic resins, fluorine resins, etc. Among them, particularly preferred is an ultrahigh molecular weight olyethylene having a melt flow rate (MFR) as small as at most 1.0, preferably at most 0.01, since a rubber-like flat portion is observed in a stress-strain curve within a wide temperature range of at least the melting point, clogging of spaces among particles scarcely takes place, and a plastic film for a photograph developing apparatus, having a uniform pore diameter, can be obtained.
The thermoplastic material is preferably in the form of a powder, and its average particle size may be within a range of from 50 to 700 &mgr;m, preferably from 60 to 500 &mgr;m, which brings about good results. Namely, if the average particle size is smaller than 50 &mgr;m, the filtration precision may be improved, but the pressure loss during passage of a fluid, tends to be high, such being undesirable. If the average particle size exceeds 700 &mgr;m, no adequate filtration precision tends to be obtained, such being undesirable.
The porosity of the plastic filter for a photograph developing apparatus of the present invention, is required to be within a range of from 30 to 60 vol %, preferably from 35 to 55 vol %, which brings about good results. Namely, if the porosity is less than 30 vol %, the pressure loss during passage of a fluid, tends to be high, such being practically unsuitable. On the other hand, if the porosity is more than 60 vol %, the mechanical strength tends to be inadequate, for example, the radial crushing strength tends to be small, such being practically unsuitable.
In the present invention, the porosity is calculated by the following formula.
Porosity (vol %)=[(A−B)/A]×100
where A is the true density (g/cm 3) of the thermoplastic material constituting the plastic filter, and B is the apparent density (g/cm
3
) of the plastic filter.
Here, the apparent density B of the plastic filter is obtained by measuring the mass and the volume of a test specimen cut out from the filter, by the respective conventional methods and dividing the mass value (g) by the volume value (cm
3
). Further, when the filter is of a predetermined shape such as a hollow cylinder, the volume value can be obtained also by measuring its outer diameter, inner diameter and length, so that the volume can be calculated. On the other hand, the true density A of the thermoplastic material constituting the plastic filter can be obtained also by measurement with respect a sample obtained by remelting the filter, followed by cooling for solidification.
The filtration precision of the plastic filter for a photograph developing apparatus of the present invention, is required to be a filtration precision of a level capable of capturing foreign matters of at least 30 &mgr;m. Namely, particle sizes of various foreign matters (such as various sludges, fine contaminants and scales) to be removed for the development treatment, are roughly from about 50 to 200 &mgr;m except for special foreign matters. On the other hand, pore diameters of the filter obtained by sinter-forming a thermoplastic material have a

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