JP7627019B2 - Filter media for improving filtrate passage and treatment method for improving filtrate passage - Google Patents

Description

The present invention relates to a filter material (or sieve) used for filtering liquid or paste-like objects, and to a technology for reducing the resistance to passage (filter material resistance) when the object passes through.

As proposed in Patent Document 1, the present applicants have proposed a technology that can suppress the adhesion of powder by forming countless irregular (random) microscopic irregularities on the surface of a member that comes into contact with powder (hereinafter also referred to as a powder contact member) through a fine particle projection process (e.g., fine particle peening), which is a type of shot material projection process in which shot material is projected.

Patent No. 6416151

Here, the applicants have been taking various approaches to confirm new effects in various fields that can be achieved by forming countless micro-convexities and concaves on the surface of a component, in order to explore the possibility of applying surface modification technology that uses countless randomly formed micro-convexities and concaves to various fields. In the process, the inventors have obtained new knowledge that was not known before.

Up until now, the effects that have been known to result from forming multiple (innumerable) micro recesses include suppressing adhesion of powders and sticky substances, and forming countless micro irregularities on the sliding surface to function as oil reservoirs, reducing sliding resistance and suppressing wear. The effect discovered this time is a completely different effect that could not be predicted from these.

The finding is that by randomly forming a countless number (multiple) of minute depressions on the surface of a filter medium, the resistance of the filter medium is reduced, and the resistance to passage of the object to be filtered (especially the filtrate) passing through it can be reduced.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a filter medium with improved filtrate permeability and a treatment method for improving filtrate permeability, which reduces the resistance to filtrate passage by randomly forming countless minute irregularities on the surface of the filter medium.

For this reason, the filtrate permeability improving filter medium according to the present invention has the following features:
The filter is characterized in that, on at least a portion of the surface that comes into contact with the filtrate , there are formed countless random micro-irregularities based on a shot projection process, the micro-irregularities having a minimum irregularity pitch of 0.5 μm or more and a maximum irregularity pitch of 40 μm or less, and a minimum concave depth of 0.03 μm or more and a maximum concave depth of 2.0 μm or less, thereby making the kurtosis value (Pku) of the surface greater than 3 and reducing the filter material resistance to the filtrate.

The filtrate permeability improving filter material according to the present invention is
The filter is characterized in that, on at least a portion of the surface that comes into contact with the filtrate , there are formed countless random micro-irregularities based on a shot projection process, the micro-irregularities having a minimum irregularity pitch of 0.5 μm or more and a maximum irregularity pitch of 10 μm or less, and a minimum concave depth of 0.3 μm or more and a maximum concave depth of 2.0 μm or less, thereby making the kurtosis value (Pku) of the surface greater than 3 and reducing the filter material resistance to the filtrate.

In the present invention, the surface on which the micro-roughness is formed may have a water contact angle of 65° or less.

In the present invention, the filtrate can be characterized as being a food liquid or paste-like substance containing water, oil, and other raw materials in any proportion, a pharmaceutical liquid or paste-like substance containing water, oil, and other raw materials in any proportion, or a cosmetic liquid or paste-like substance containing water, oil, and other raw materials in any proportion.

The method for improving filtrate passing property according to the present invention comprises the steps of:
The present invention is characterized in that by forming countless random micro-irregularities on at least a portion of the surface that comes into contact with the filtrate based on a shot material projection process, the micro-irregularities have an irregularity pitch of at least 0.5 μm and a maximum of at most 40 μm, and the depth of the recesses is at least 0.03 μm and a maximum of at most 2.0 μm, thereby making the kurtosis value (Pku) of the surface greater than 3 and reducing the filter material resistance to the filtrate.

The method for improving filtrate passing property according to the present invention comprises the steps of:
The filter is characterized in that, on at least a portion of the surface that comes into contact with the filtrate , there are formed countless random micro-irregularities based on a shot projection process, the micro-irregularities having a minimum irregularity pitch of 0.5 μm or more and a maximum irregularity pitch of 10 μm or less, and a minimum concave depth of 0.3 μm or more and a maximum concave depth of 2.0 μm or less, thereby making the kurtosis value (Pku) of the surface greater than 3 and reducing the filter material resistance to the filtrate.

The present invention can be characterized in that the water contact angle of the surface on which the micro-roughness is formed is 65° or less.

In the present invention, the filtrate can be characterized as being a food liquid or paste-like substance containing water, oil, and other raw materials in any proportion, a pharmaceutical liquid or paste-like substance containing water, oil, and other raw materials in any proportion, or a cosmetic liquid or paste-like substance containing water, oil, and other raw materials in any proportion.

According to the present invention, it is possible to provide a filter medium for improving filtrate permeability and a treatment method for improving filtrate permeability, in which the resistance to the passage of filtrate is reduced by randomly forming countless minute irregularities on the surface of the filter medium.

1 is a table showing the measurement results of the contact angle of water of each test piece according to one embodiment of the present invention. 13 is an image showing the contact angle of water measured for each test piece according to the embodiment of the present invention. 1 is a table showing the measurement results of the contact angle of oil (salad oil) of each test piece according to the embodiment of the present invention, and contact angle measurement images. FIG. 2 is a diagram showing an example of the surface properties (concave-convex pitch and concave depth) of the projection-treated surface of a test piece (sample A) according to the embodiment of the present invention. FIG. 2 is a diagram showing an example of the surface properties (concave-convex pitch and concave depth) of the projection-treated surface of a test piece (sample B) according to the embodiment of the present invention. 1 is an enlarged image of the surface of a test piece (Reference) according to the embodiment of the present invention. 1 is an enlarged image of the surface of a test piece (sample B) according to the embodiment of the present invention. 13 is an image showing the results of network passability verification of a medium-thick sauce according to the embodiment of the present invention. 13 is an image showing the results of verification of the mesh-penetrability of chocolate syrup according to the embodiment of the present invention. FIG. 13 is a diagram showing the size of the mesh of the filter medium used in each actual production line and the size of the minute projections and recesses formed on the filter medium by the projection treatment. FIG. 1 is a diagram showing an example of the surface characteristics (roughness pitch and recess depth) formed by projection treatment on a filter material used in a production line for food sauce 1. FIG. 1 is a diagram showing an example of the surface characteristics (pitched and concave portions and depth of concave portions) formed by a projection treatment performed on a filter material used in a production line for food sauce 2. FIG. 1 is a diagram showing an example of the surface characteristics (pitched and concave portions and depth of concave portions) formed by a projection treatment performed on a filter medium used in an emulsion production line. 1A is a graph showing the time reduction (time difference) of the projection treatment (sample B) compared to the untreated sample (Reference), and FIG. 1B is a photograph of the exterior of the liquid passage experimental device (Experimental Method 1). 1A is a graph showing the time reduction (time difference) of the projection treatment (sample B) compared to the untreated sample (Reference), and FIG. 1B is a photograph of the exterior of the liquid passage experimental device (Experimental Method 2). 1 is a graph showing the Kurtosis value (Pku) on the horizontal axis and the contact angle of water (°) on the vertical axis for the projection treatment performed on each test piece according to the embodiment of the present invention. FIG. 2A is a diagram for explaining the contact angle of water on a surface, and FIG. 2B is a diagram for explaining the kurtosis value (Pku). FIG. 4 is a diagram showing measurement conditions for the kurtosis value according to the embodiment of the present invention. 11 is a cross-sectional SEM image of a single minute recess formed experimentally by one-shotting the media used in the fine particle peening process according to the embodiment of the present invention. 1 is a SEM image of a cross section of a recess formed by laser processing.

One embodiment of the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited to the embodiment described below.

Here, we will explain in detail the finding obtained by the inventors that "if a countless number (multiple) micro recesses are randomly formed on the surface of a filter medium, the resistance of the filter medium is reduced, and the resistance to passage of the object to be filtered (especially the filtrate) passing therethrough can be reduced."

Liquid raw materials, one example of a material that requires filtration, are used in a variety of situations, including at food, pharmaceutical, and cosmetic manufacturing sites. To prevent foreign matter from entering these liquid raw materials, they are filtered using filter media such as nets or mesh.

Among these, there were many calls for shortening the filtration process time to improve work efficiency. When performing liquid filtration, the liquid to be filtered is generally poured into the top of the screen (upstream side of the liquid flow), and the liquid that passes through the screen is collected in a container placed below the screen (downstream side of the liquid flow) (or sent to the next process downstream).

When trying to shorten the time required for such filtration work, for example, the filtration device itself could be enlarged to increase the filtration capacity and shorten the time, but this creates problems such as securing work space, so there is a need to shorten the time by using existing equipment.

Increasing the mesh size of the net or mesh used will improve the liquid permeability, but this will reduce the filtering capacity and will not be effective in preventing foreign matter from entering the filter. Factors that determine the permeability of liquid filtration, or the filtering speed, include the filtering pressure, filter material resistance (the resistance of the filter material itself), and the clogging resistance of the filter material.

For this reason, the inventors believed that in order to improve the passage of liquids while maintaining filtering capacity, it would be beneficial to reduce the resistance of the filter material to the flow of the material being filtered, and that a surface modification technique that randomly creates countless minute irregularities could contribute to this.

Furthermore, the inventors considered that in order to improve the permeability of the liquid (e.g., water), which is one of the objects to be filtered, imparting hydrophilicity to the filter medium would improve the affinity between the filter medium and the object to be filtered (filtrate, e.g., water in this case), and therefore hydrophilicity would be related to reducing the filter medium resistance.
Therefore, a test was conducted to confirm whether hydrophilicity is improved by randomly forming an innumerable (plural) minute irregularities on the surface of a member.

Tables 1 and 2 in Figure 1 show the results of measuring the contact angle of water (purified water) 1 hour and 50 hours after a test piece (here a flat plate) was washed with water, dried by air blowing, and then exposed to the atmosphere. Note that when the contact angle of water is simply mentioned without indicating the drying time, it refers to the value after 50 hours (or the value when sufficient drying time has been given).

FIG. 2 shows images of the contact angles measured when water was placed on each test piece.
The contact angle of water is one of the indicators of "wettability" and "hydrophilicity". The smaller the contact angle of water, the higher the "wettability" and "hydrophilicity", and the larger the contact angle of water, the lower the "wettability" and "hydrophilicity" (see Figure 17 (A)).
In this embodiment, the water contact angle of the surface of the test piece was obtained (measured) using a portable contact angle meter PCA-11 manufactured by Kyowa Interface Science Co., Ltd.

For the untreated test piece (SUS304 #700 flat plate: Reference), the contact angle was around 70° both after 1 hour and after 50 hours, and there was no difference in the contact angle with time.
The untreated test piece (SUS304 #700 flat plate: Reference: Comparative example) was a stainless steel plate made of SUS304, the surface of which was polished with a P700 buff.

On the other hand, for sample A, the contact angle after 1 hour was 31.2 to 35.3°, and after 50 hours was 56.1 to 59.7°. This indicates that the sample was more hydrophilic than the untreated test piece, and that the contact angle varied over time.
Sample A was prepared by subjecting an untreated test piece (a flat plate of SUS304 #700: Reference) to a projection treatment (Ni) to randomly form countless minute projections and recesses on the surface.

The projection treatment (Ni) performed on sample A is one of the surface treatments (also referred to as shot material projection treatment, micro-dimple treatment, fine particle projection treatment, etc.; the same applies below) that form countless tiny irregularities, and is a surface modification treatment in which media (abrasive material (product name "Nickel (Ni) Powder", particle number #200-350) from Fukuda Metal Foil and Powder Co., Ltd. (product name: "Nickel (Ni) Powder", particle number #200-350)) together with compressed air of about 1/several (e.g., 0.3) MPa) is sprayed from a spray nozzle onto the surface to be processed (surface of a sample, surface of a component) which has been polished with a P700 buff (Reference: comparison control).
FIG. 4 shows an example of the surface shape data of sample A.

The 3D images, surface shapes, and surface shape data in this embodiment, including those described below, were acquired using a shape measuring laser microscope VK-X1000 manufactured by KEYENCE Corporation.

FIG. 4 shows an example of the surface shape and surface shape data of sample A.
FIG. 4 shows a portion of the surface of sample A, and countless minute irregularities are randomly formed on the surface of sample A, with an irregularity pitch (diameter of the entrance to the irregularities) of about 20 to 60 μm and a irregularity depth of about 1.5 μm.
The unevenness pitch can be expressed as the distance between protrusions, the width of the entrance of a recess, the width of an opening, or the diameter of an opening.

For sample B, the contact angle after 1 hour was 15.0 to 18.3°, and the contact angle after 50 hours was 37.1 to 39.2°. Sample B was therefore more hydrophilic than the untreated test piece and sample A, and like sample A, there was a difference in the contact angle over time.
Sample B was prepared by subjecting an untreated test piece (a flat plate of SUS304 #700: Reference) to projection treatment (C400) to randomly form countless minute projections and recesses on the surface.

The projection treatment (C400) applied to sample B is one of the surface treatments that creates countless minute irregularities, and is a surface modification treatment in which media (SiC (silicon carbide) with particle number #400 (maximum particle diameter 75 μm or less, particle diameter at 50% of cumulative height 30.0 ± 2.0 μm) of "Fuji Random (Carborundum) C" manufactured by Fuji Manufacturing Co., Ltd.)) is sprayed from a spray nozzle along with compressed air of about 1/several (e.g. 0.3) MPa onto the surface of a plate material (comparison control) made of SUS304 stainless steel that has been polished with a P700 buff, and the projection treatment is performed on the processed surface (surface of the sample, surface of the component).

FIG. 5 shows an example of the surface shape and surface shape data of sample B.
5 shows a portion of the surface of Sample B, in which countless minute irregularities are randomly formed on the surface of Sample B, with the irregularity pitch (inlet diameter of the irregularities) ranging from about 4.0 to 20.0 μm and the irregularity depth ranging from about 0.4 to 2.0 μm. The minute irregularities formed on the surface of Sample B have a smaller irregularity pitch than those formed on the surface of Sample B.
In addition, when indicating a range for the size of the unevenness pitch (spacing between convex parts, entrance width of the concave part, opening width, opening diameter) and the depth of the concave part, the range of minimum and maximum values of the unevenness pitch and the depth of the concave part is indicated.

The reason why the contact angle differed over time for Samples A and B is that even though the test pieces appear dry at first glance, a small amount of moisture (water molecules) is physically adsorbed on the surface immediately after washing with water, and the residual moisture causes the test pieces to exhibit hydrophilic properties with a smaller contact angle immediately after washing. It is then exposed to air for 50 hours, causing the small amount of moisture (water molecules) on the test piece surface to desorb, increasing the contact angle.

This phenomenon is thought to be due to the fact that the projection process, in which the shot material is projected, creates minute (microscopic) irregularities on the surface of the test piece, and these microscopic recesses temporarily hold trace amounts of moisture (water molecules). Supporting this, no difference in contact angle over time was observed in the untreated test piece. Furthermore, the fact that there was no difference in the untreated test piece also supports the idea that there were no effects of contamination due to exposure to the atmosphere during this verification experiment.

Based on the above, the inventors believed that when a liquid to be filtered is passed through a filter medium with countless randomly formed minute projections and recesses on its surface, the liquid components are retained in the minute recesses. When the same liquid passes over the filter medium, the liquid and the filter medium become more compatible, reducing the resistance of the filter medium and improving the liquid permeability.

Similarly, we also measured the contact angle of salad oil (see Table 3 in Figure 3 and the contact angle measurement image). As with the contact angle measurement of water, the order of contact angle was untreated test piece > sample A > sample B.

Many of the liquids used in the food, pharmaceutical, and cosmetic markets contain a mixture of water and oil. Therefore, for sample B, which had a large hydrophilic and lipophilic effect for both components, a similar treatment was applied to a screen (or filter material, sieve, etc.) and the liquid permeability was compared with that of an untreated screen.

An untreated net made of SUS304 (Reference: Comparative control) and a net of the same specifications that had been subjected to the same projection treatment as Sample B were prepared, and a comparative experiment was conducted in which food sauce was poured onto these nets.
The nets used in the experiment were an untreated SUS304 net (Reference) with a mesh size of approximately 500 μm and a wire diameter of approximately 180 μm, which is a kitchen sieve sold at general home improvement stores, and a net that had been subjected to the same projection treatment as sample B. Verification tests were conducted using these nets.

FIG. 6 shows an enlarged image of an untreated SUS304 net (Reference), and FIG. 7 shows an enlarged image of a net that has been subjected to the same projection treatment (C400) as sample B.
These enlarged images were taken using a digital microscope VHK-7000 manufactured by KEYENCE.

On the surface of the wire of the net that was subjected to the same projection treatment as sample B (Figure 7), it can be seen that countless tiny irregularities were formed by the projection treatment, giving it a matte appearance, while on the surface of the wire of the untreated SUS304 net (Reference) (Figure 6) there are some areas that resemble contact scratches, but overall it is a surface that shines almost like a mirror, with streak-like processing marks from the drawing process, etc.

Figure 8 shows images taken from the back of the net (the side through which the sauce passes and comes out) after food sauce was poured onto each of the two nets mentioned above, in order to confirm the difference in the permeability (degree of passage) of the food sauce due to the difference in the nets.
The food sauce used was a medium-thick sauce manufactured by Company K, which is easily available in supermarkets and the like, and the amount of each drop was 5 ml.

Looking at the image in Figure 8, it can be seen that the sauce on the untreated mesh in Figure 8 (A) has multiple areas over a wide area that have not passed through to the back side, while the sauce on the mesh that has been treated in the same way as sample B in Figure 8 (B) has the entire surface of the sauce dripped onto the front side passing through the mesh to the back side.

As mentioned above, this is thought to be because a net (filter material) with countless randomly formed minute projections and recesses on the surface of the wire that makes up the net (filter material) is more compatible with the object to be filtered, resulting in improved permeability compared to an untreated net (or filter material).

Similarly, a comparative experiment was conducted by preparing a SUS304 #700 net (Reference) and a net of the same specifications that was subjected to the same projection treatment as Sample B, and dripping chocolate syrup onto these nets. Chocolate syrup has a higher viscosity than food sauces and the like, and can be used as an example of a paste-like object to be filtered.
In addition, the term "paste-like" refers to a soft, viscous, glue-like or kneaded material, or may refer to a material that has been ground up and processed into a semi-solid material with fluidity.

Figure 9 shows images taken from the back of the screen (the side where the syrup passes through and comes out) after chocolate syrup was poured onto each of the two screens mentioned above, in order to confirm the difference in how the chocolate syrup passes through due to the differences in the screens.
The chocolate syrup used was manufactured by M Company, which is sold in supermarkets and is easily available, and the amount dropped was 7 ml each.

Looking at Figure 9, the chocolate syrup on the untreated wire mesh in Figure 9(A) does not pass through the wire over the entire surface, but remains entirely on the top (front side) of the wire. On the other hand, the chocolate syrup on the wire mesh that was treated in the same way as sample B in Figure 9(B) has some areas that have passed through to the back side of the wire, and the chocolate syrup has also permeated the inside of the wire mesh (the gaps between the wires).

As mentioned above, a net (filter material) with countless randomly formed minute projections and recesses on the surface of the wire that makes up the net (filter material) is thought to have better compatibility with the object to be filtered, and therefore better permeability than an untreated net (or filter material).

In addition, SUS304 filter media used in the production lines of food sauce 1 (food manufacturer A), food sauce 2 (food manufacturer B), liquid chocolate 1 (food manufacturer C), liquid chocolate 2 (food manufacturer D), and milky lotion (cosmetics manufacturer E) were subjected to projection treatment (C3000, B400, C400, C400, C1000) and the filter media was used in the production lines. It was confirmed that the filtration time could be shortened by about 30% to 50% compared to conventional untreated filter media, and that there was an improvement in permeability (reduction in filter media resistance).

FIG. 10 shows the size of the openings of the filter media used in each actual production line and the size of the minute projections and recesses formed by the projection treatment on the filter media.
In the experiment for food sauce 1, a filter medium (mesh size of about 63 μm) that had been subjected to projection treatment (C3000) was used, and on the surface of the filter medium that had been subjected to this treatment, countless minute irregularities were randomly formed with an irregularity pitch (diameter of the inlet of the recess) size in the range of about 0.05 to 2.0 μm and a recess depth in the range of about 0.03 to 0.1 μm. An example of the surface shape of a test piece (flat plate) of SUS304 that had been subjected to projection treatment (C3000) is shown in FIG. 11.

For the food sauce 2 experiment, a filter medium (mesh size of about 10,000 μm) that had been subjected to projection treatment (B400) was used, and on the surface of the filter medium that had been subjected to this treatment, countless minute irregularities were randomly formed with an irregularity pitch (diameter of the inlet of the recess) size in the range of about 20 to 40 μm and a recess depth in the range of about 1.0 to 2.0 μm. An example of the surface shape of a test piece (flat plate) of SUS304 that had been subjected to projection treatment (B400) is shown in Figure 12.

The experiments on Liquid Chocolate (liquid chocolate used in chocolate products, etc.) 1 and Liquid Chocolate 2 used filter media (mesh size approximately 259 μm) that had been subjected to projection treatment (C400), and on the surface of the filter media that had been subjected to this treatment, countless minute projections and recesses were randomly formed with an irregularity pitch (diameter of the recess entrance) size ranging from approximately 4.0 to 20 μm and a recess depth ranging from approximately 0.4 to 2.0 μm. An example of the surface shape of a SUS304 test piece (flat plate) that had been subjected to projection treatment (C400) is similar to that shown in Figure 5.

For the emulsion experiment, a filter medium (mesh size of 100 μm or more) that had been subjected to projection treatment (C1000) was used, and on the surface of the filter medium that had been subjected to this treatment, countless minute irregularities were randomly formed with an irregularity pitch (diameter of the inlet of the recess) size ranging from 0.5 to 2.5 μm and a recess depth ranging from 0.3 to 1.0 μm. An example of the surface shape of a test piece (flat plate) of SUS304 that had been subjected to projection treatment (B400) is shown in Figure 13.

From the above, it has been found that filter media that has been treated to randomly create countless tiny irregularities has the effect of improving permeability (reducing filter media resistance), and can reduce filtration time by approximately 30 to 50% on an actual production line (production site), which in turn can contribute to improving production efficiency.

The projection treatment (C3000) applied to the filter media used in the Food Sauce 1 experiment is one of the surface treatments that creates countless minute irregularities, and is equivalent to a surface modification treatment in which media (product name "Fuji Random C (Carborundum)", SiC (silicon carbide) with particle number #3000 (maximum particle size 13 μm or less, particle size at 50% of cumulative height 4.0±0.5 μm)) is sprayed from a spray nozzle along with compressed air of about 1/several (e.g. 0.3) MPa onto the surface of a plate (control) made of stainless steel made of SUS304 that has been polished with a P700 buff, performing a projection treatment (projection processing) on the processed surface.

The projection treatment (B400) applied to the filter media used in the Food Sauce 2 experiment is one of the surface treatments that creates countless minute irregularities, and is equivalent to a surface modification treatment in which the surface of a stainless steel plate made of SUS304 (control) is polished with a P700 buff, and media (shot material) with grain number 400 (median grain size ≦53μm) of abrasive FGB (Fuji Glass Beads) made by Fuji Manufacturing Co., Ltd. is sprayed from a spray nozzle along with compressed air of about 1/several (e.g. 0.3) MPa to perform a projection treatment (projection processing) on the processed surface.

Here, food sauce refers to a liquid or paste-like seasoning that is served with other foods or used in cooking, such as a liquid seasoning made by adding salt, sugar, vinegar, and spices to vegetable or fruit juice or puree, and adjusting and maturing it.

The projection treatment (C400) applied to the filter media used in the experiments with Liquid Chocolate 1 and 2 was the same as the treatment applied to Sample B described above.

The projection treatment (C1000) applied to the filter media used in the emulsion experiment is a type of surface treatment that creates countless minute irregularities, and is equivalent to a surface modification treatment in which media (SiC (silicon carbide) with particle number #1000 (maximum particle size 32 μm or less, particle size at 50% of cumulative height 11.5±1.0 μm) of product name "Fuji Random C (Carborundum)")) is sprayed from a spray nozzle along with compressed air of about 1/several (e.g. 0.3) MPa onto the surface of a plate (control) made of stainless steel made of SUS304, which has been polished with a P700 buff, to perform projection treatment (projection processing) on the processed surface.

According to the above experiments, if the unevenness pitch (diameter of the inlet of the recess, distance between adjacent protrusions) of the micro-irregularities formed on the surface of the filter medium is in the range of 0.5 μm to 40 μm, and the depth of the recess is in the range of 0.03 μm to 2.0 μm, there is an effect of reducing the resistance of the filter medium (i.e., an effect of improving the passability of the object to be filtered).
In particular, filter media that have been subjected to projection processing (C400, C1000) have a relatively large effect in reducing filter material resistance, and if the concave-convex pitch of the micro-convexities (concave entrance diameter, spacing between adjacent convexities) is in the range of 0.5 to 10 μm and the concave depth is in the range of 0.3 μm to 2.0 μm, it is possible to further reduce the filter material resistance.

<Experimental Method 1>
In addition, using an apparatus as shown in FIG. 14(B), the time required for the liquid (filter object) in the cylinder to pass through the net and be discharged by free fall (passing time) was measured.
Specifically, a SUS304 #700 mesh (Reference) and a mesh (filter material) of the same specifications that had been subjected to projection treatment (C1000) were prepared, and these meshes were set in the mesh installation location of the liquid passage experimental device to confirm the difference in liquid passage time due to the difference in mesh.
As shown in Fig. 14(B), the liquid passage experimental device is a cylinder made of acrylic (diameter about 100 mm) arranged almost vertically, with a plug (drain plug) below the net installation location closed, and liquid (here, water) is poured into the cylinder up to a predetermined starting height (about 5 L), and from that state, the plug (drain plug) below the net installation location is opened to start discharging the liquid inside. After that, the time until the height of the liquid (height of the water column) in the cylinder passed point A (top point), the time until it passed point B (middle point), and the time until it passed point C (bottom point) are measured. Here, the experimental results when water was used as the liquid are shown.

Here, the difference in water permeability depending on whether or not projection processing is performed is measured by measuring the time difference. The measurement method is to use a high-speed camera to capture the falling water and measure the time difference it takes for it to pass through each point. The high-speed camera used is a MEMRECAM HX-6 manufactured by NAC Image Technology Co., Ltd. The same applies to Experimental Method 2 described below.

Figure 14 (A) is a graph comparing the time (X) it takes for the liquid surface to pass through each point when a SUS304 #700 net (Reference) is set, and the time (Y) it takes for the liquid surface to pass through each point when a net that has been subjected to the same projection treatment as Sample B is set, and showing the difference (Y-X: time reduction for Sample B compared to the Reference).

From Figure 14 (A), it was confirmed that at all points A, B, and C, when a net with a projection treatment to form micro-irregularities on the surface was set, the passage time was faster (faster discharge speed, falling speed, etc.) and the filter resistance was smaller.
In this experimental device, experiments were conducted using approximately 5 L of water; however, since actual production lines handle several tons to tens of tons of liquid, the time required for filtration on the production line can be reduced by several thousand to tens of thousands of times, for example, 1 to 4 ms.

In other words, by using a net (filter material) that has been subjected to a projection treatment to form minute irregularities on its surface, it is possible to reduce the resistance of the filter material to the flowing object to be filtered while maintaining the same filtering capacity with the same mesh size (opening size, wire diameter, etc.), thereby improving the pass-through of the object to be filtered.
This has been confirmed to enable shortening of filtration time, realizing more efficient filtration operations, and ultimately contributing to improved production efficiency in a variety of situations, such as food, pharmaceutical, and cosmetics manufacturing sites.

<Experimental Method 2>
In addition, using an apparatus as shown in FIG. 15(B), the time (passing time) required for the liquid (filter object) in the cylinder to pass through the net and be discharged by free fall was measured.
Specifically, a SUS304 #700 mesh (Reference) and a mesh (filter material) of the same specifications that had been subjected to projection treatment (C1000) were prepared, and these meshes were set in the mesh installation location of the liquid passage experimental device to confirm the difference in liquid passage time due to the difference in mesh.
As shown in FIG. 15B, in this liquid passage experimental device, a liquid (here, water) is poured into an acrylic cylinder (diameter about 100 mm) arranged almost vertically with a plug (drain plug) installed below the net installation location closed, up to a predetermined starting height position (about 5 L). In that state, the top end is plugged, and then the plug (drain plug) installed below the net installation location is opened. From that state, the plug at the top end is removed, and the liquid inside begins to be discharged from the plug (drain plug) installed below the net installation location. After that, the time until the height of the liquid (height of the water column) in the cylinder passed point A (top point), the time until it passed point B (middle point), and the time until it passed point C (bottom point) were measured. Here, the experimental results when water was used as the liquid are shown.

Figure 15 (A) is a graph showing the difference (Y-X: time reduction for sample B compared to the Reference) between the time (X) it takes for the liquid surface to pass through each point when a SUS304 #700 net (Reference) is set and the time (Y) it takes for the liquid surface to pass through each point when a net that has been subjected to the same projection treatment as sample B is set.

From Figure 15 (A), it can be confirmed that at all points A, B, and C, when a net with a projection treatment to form micro-irregularities on its surface was set, the passage time was faster (faster discharge speed, falling speed, etc.) and the filter material resistance was smaller.
In this experimental device, experiments were conducted using approximately 5 L of water; however, since actual production lines handle several tons to tens of tons of liquid, the time required for filtration on the production line can be reduced by several thousand to tens of thousands of times, for example, 1 to 7.5 ms.

In other words, by using a net (filter material) that has been subjected to a projection treatment to form minute irregularities on its surface, it is possible to reduce the resistance of the filter material to the flowing object to be filtered while maintaining the same filtering capacity with the same mesh size (opening size, wire diameter, etc.), thereby improving the pass-through of the object to be filtered.
This has been confirmed to enable shortening of filtration time in a variety of situations, such as food, pharmaceutical, and cosmetics manufacturing sites, thereby contributing to the realization of more efficient filtration operations and ultimately improved production efficiency.

Furthermore, by forming minute irregularities on at least a portion of the surface that comes into contact with the object to be filtered, the resistance of the filter material to the object to be filtered can be reduced, thereby improving the passage of the object to be filtered.

In addition, the contact angle of water (wettability) of the surface on which the micro-roughness was formed and the kurtosis value (value indicating the sharpness of the roughness), which is closely related to the hydrophilicity of the surface on which the micro-roughness was formed, were also examined. The conditions for measuring the kurtosis value are as shown in FIG. 18.
The kurtosis value (Pku) is one of the indices that indicate the sharpness or peakedness of the height distribution (see FIG. 17B).
Pku = 3: The height distribution is normal. Pku > 3: There are many sharp peaks and valleys on the surface. Pku < 3: There are few sharp peaks and valleys on the surface.
A kurtosis value (Pku) of less than 3 indicates a water-repellent surface, whereas a kurtosis value of more than 3 indicates a hydrophilic surface.

The results are shown in Figure 16. The contact angle on the surface of the test piece for "hydrophilic treatment 1 (sample A)" (= projection treatment (Ni)) was 57.7°, and the kurtosis value (Pku) was 3.37.

In addition, the contact angle on the surface of the test piece for "hydrophilic treatment 2 (sample B)" (= projection treatment (C400)) was 38.4°, and the kurtosis value (Pku) was 4.17.

In addition, the contact angle on the surface of the test piece subjected to "hydrophilic treatment 3" (= projection treatment (C1000)) was 64.9°, and the kurtosis value (Pku) was 4.13.

From FIG. 16, it is considered that if the contact angle of water on the surface on which minute irregularities are formed is 65° or less, there is an effect of reducing the resistance of the filter medium.
In addition, from Fig. 16, if the kurtosis value (Pku) of the surface that forms micro unevenness is greater than 3, it is considered that there is an effect of reducing filter resistance.In addition, from Fig. 16, if the kurtosis value (Pku) is 3.3 or more, or 4.0 or more, it is considered that there is a higher effect of reducing filter resistance.

As explained above, a filter medium with countless randomly formed micro-irregularities on the surface that comes into contact with the liquid or paste-like object to be filtered can reduce the resistance of the filter medium to the flowing object, thereby improving the liquid permeability (reducing the resistance of the filter medium) while maintaining the filtering capacity.

In this way, we have discovered that forming countless micro-irregularities (micro-depressions) randomly on the surface of a filter medium (mesh elements, sieves) reduces the filter medium resistance and therefore the resistance to passage of the object being filtered, which can contribute to shortening the filtration time. However, this discovery relates to a previously unknown effect of a component having countless micro-irregularities (micro-depressions) formed on its surface, and is unpredictable based on previous knowledge.

Based on this new knowledge, the present invention uses a filter medium with a randomly arranged micro-irregularities (micro-concave portions) on its surface for use as a filter medium with improved liquid permeability (filter medium with reduced resistance to passage).

As described above, according to the present invention, by randomly forming countless minute irregularities on the surface through which the liquid or paste-like filter object passes, it is possible to provide a filter medium with improved liquid permeability (filter medium with reduced passage resistance) that reduces the passage resistance of the filter object.

In this embodiment, experiments on the passage resistance were conducted on water, salad oil, food sauce, chocolate syrup, liquid chocolate, and milky lotion, but the filter can be applied to filter liquid or paste-like objects such as liquid or paste-like seasonings (soy sauce, ketchup, mayonnaise, etc.), food, liquid or paste-like cosmetics, and liquid or paste-like fats and oils such as oil, grease, petroleum, and kerosene.

In the present embodiment, the minute concaves and convexes are formed randomly by shot projection processing, but the minute concaves and convexes can also be formed randomly by subjecting the surface of the member to chemical polishing (chemical etching) or plasma processing (e.g., argon bombardment processing), etc. However, the present invention is not limited to this, and the minute recesses according to the present invention can also be formed by at least one of chemical etching, plasma processing, shot projection processing, etc., or by a suitable combination of these.
For chemical polishing (chemical etching), it is assumed that an aqueous solution of, for example, acidic chemicals such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, or iron (III) chloride is prepared in any ratio and used.

In addition, forming micro-irregularities (micro-depressions) on the surface of a filter medium also includes forming a composite irregular shape (composite dimples) on the surface of the filter medium by, for example, transfer using a mold having micro-irregularities (micro-depressions) on its surface formed based on (using) chemical etching, plasma treatment, shot projection treatment, etc.

The effect of improving the passability of the filter material (the effect of reducing the resistance of the filter material) due to the formation of minute irregularities according to this embodiment is believed to be equivalent for any stainless steel material, particularly non-magnetic austenitic stainless steel (SUS303, 304, 316, etc.), regardless of the surface finish specifications such as #700 for the base material before the projection treatment. The present invention is also applicable to metal materials other than stainless steel (for example, in the case of iron, metals or alloys such as steel (SS400, etc.), aluminum, titanium, etc.).

The filter medium according to the present invention can be, for example, a reticulated member (mesh member) or a punched metal member (member with punched openings) (including resin) with multiple openings, but is not limited to these, and there are no particular limitations on the structure, shape, size, etc., as long as it is a filter medium.

In the present invention, the object to be filtered is not particularly limited as long as it is a substance that can be filtered, but can be, for example, a liquid or paste-like substance for food containing water, oil, and other raw materials in any ratio, a liquid or paste-like substance for pharmaceutical use containing water, oil, and other raw materials in any ratio, or a liquid or paste-like substance for cosmetics containing water, oil, and other raw materials in any ratio.

In addition, in the present invention, the subject to be filtered may also be a liquid or a paste-like substance in which solids, powders, etc. are dispersed.

In addition, the micro-roughness forming process (shot projection process, micro-dimple process) according to this embodiment can obtain the desired processed product (Ni, B400, C400, C1000, C3000, etc.) with different surface shapes (surface textures) by using a known injection device to inject media (shot material, abrasive particles) with different specifications (material, size, shape, etc.) as described above while adjusting the conditions and colliding them against the surface of the component to be surface treated.

For example, a blasting device can be used as the injection device. An example of a blasting device that can be used is the "PNEUMA BLASTER" (models: SC series, SG series, etc.) manufactured by Fuji Manufacturing Co., Ltd. In addition, for example, a device described in JP 2019-25584 A can be used.

More specifically, the injection device that injects the injection particles toward the surface of the component can be a known blast processing device (blast processing device) that injects abrasives (fine particles) together with compressed gas (air, argon, nitrogen, etc.).

As blast processing equipment (blast processing devices), there are commercially available suction type blast processing equipment that uses negative pressure generated by the injection of compressed gas to inject abrasives, gravity type blast processing equipment that injects abrasives dropped from an abrasive tank by carrying them on the compressed gas, direct pressure type blast processing equipment that introduces compressed gas into a tank containing abrasives and combines the abrasive flow from the abrasive tank with the compressed gas flow from a separately provided compressed gas supply source and injects the abrasives, and blower type blast processing equipment that injects the direct pressure type compressed gas flow by carrying it on a gas flow generated by a blower unit, and all of these can be used to inject the aforementioned injection particles.
Alternatively, a water jet can be used, which sprays a shot at high pressure with a liquid such as water.

Here, in the present invention, in order to specify from the shape or structure of an uneven surface formed by (or based on) a shot material projection process known as a micro-roughness forming process, micro-dimple process, fine particle projection process, etc., a specifying method is used in which countless dimple-shaped micro-roughnesses (micro-depressions and ridge-like convestibules around the depressions, each with its own shape, pitch and depth) are formed randomly, which is completely different from the geometrical and regular uneven shapes formed according to pre-designed drawings by laser processing or the like.
In other words, instead of using the expression "micro-depressions are formed on the surface by (or based on) the shot projection process," a specific method (expression) such as "countless micro-convexities (or micro-depressions) are randomly formed on the surface of the filter material" is used.
However, in comparison with prior art, it is anticipated that there will be cases in which it will be difficult to adopt the uneven surface formed by the shot projection process as a distinctive identifying method (expression) that distinguishes it from others with the above-mentioned identifying method (expression).

For this reason, it is conceivable that there will be a situation in which it will be necessary to specify the uneven surface formed by (or based on) shot material projection processing using the specification method (expression) of "forming micro-irregularities on the surface by (or based on) shot material projection processing."
Therefore, at the time of filing this application, there were circumstances that made it impossible or unrealistic to specify the shape, structure, characteristics, etc. of the micro-irregularities formed by the shot material projection process, and there are cases in which it is unavoidable to use the expression "by forming micro-irregularities on the surface by (or based on) the shot material projection process (taking into account cases such as transfer)", as will be explained below.

In the shot projection process, projected particles (media) are collided with the surface of the workpiece using compressed air at speeds of several tens to over a hundred meters per second, forming irregular, roughly spherical, micron-sized micro-depressions with convex edges over almost the entire surface of the workpiece without significant dimensional change. When the media collides to form the micro-depressions in the shot projection process, the periphery of the micro-depressions rises in a crater-like manner to form convexities (see Figure 19). When other media collides with these raised convexities, they become depressed, resulting in irregular convexities.

In contrast, mechanical processes such as laser processing and cutting create regular recesses and do not create protrusions because they are removal processes (there is no protrusion associated with the formation of recesses). For this reason, the height of the protrusions around minute recesses in mechanical processes such as laser processing and cutting matches the height of the surface (original material surface) of the workpiece (the component being laser processed) (see Figure 20).

In addition, since the minute irregularities formed by the shot projection process are formed in an infinite number of irregular (random) patterns, the surface texture (shape) formed by the shot projection process differs from the surface shape (texture) formed by processes such as polishing and grinding that scrape the surface and create scratches (grooves such as streaks). However, when measured with a surface roughness meter, the two end up with similar numerical values, so it is not possible to distinguish between the two based on surface roughness, etc.

However, the effects obtained by the surface texture (shape) formed by the shot projection process (such as improving the passability of the object to be filtered and reducing the resistance of the filter material) are exceptional and cannot be predicted from the surface shape (texture) formed by processes such as polishing and grinding, which scratch the surface by scraping it.
Furthermore, shot peening, which involves colliding media of the order of a few millimeters to impart residual stress and improve the fatigue limit, makes it impossible to predict that a surface that has been subjected to shot projection treatment would have the effect of improving the passability of the object to be filtered or the effect of reducing the resistance of the filter media.

In this way, the micro-convexities and concaves formed by the shot material projection process are formed in an countless irregular (random) manner, the shapes of the micro-concave portions and the convex portions surrounding them are irregular, and in light of this irregularity being the source of the effects achieved by the present invention, it is not possible to specify the surface formed by the shot material projection process other than by using the expression "formed by (or based on) the shot material projection process" as a term for specifying the surface texture (shape) formed by the shot material projection process.
As described above, at the time of filing this application, there are circumstances that make it impossible or unrealistic to specify the shape, structure, characteristics, etc. of the minute irregularities formed by the shot projection process.

However, the present invention is not limited to the above-described embodiment of the invention, and various modifications can be made without departing from the spirit of the invention.

The present invention provides a filter medium and a processing method for improving the passability of a filter object by randomly forming countless microscopic irregularities on the surface of the filter medium, thereby reducing the resistance to the passage of the filter object, and is useful and usable in industries that involve filtration work.

Claims (8)

A filter medium with improved filtrate permeability, characterized in that at least a portion of the surface that comes into contact with the filtrate has minute irregularities formed randomly by a shot projection process, the minute irregularities having a minimum irregularity pitch of 0.5 μm or more and a maximum irregularity pitch of 40 μm or less, and a minimum concave depth of 0.03 μm or more and a maximum concave depth of 2.0 μm or less, thereby making the kurtosis value (Pku) of the surface greater than 3 and reducing the resistance of the filter medium to the filtrate. A filter medium with improved filtrate permeability, characterized in that at least a portion of the surface that comes into contact with the filtrate has minute irregularities formed randomly by a shot projection process, the minute irregularities having a minimum irregularity pitch of 0.5 μm or more and a maximum irregularity pitch of 10 μm or less, and a minimum concave depth of 0.3 μm or more and a maximum concave depth of 2.0 μm or less, thereby making the kurtosis value (Pku) of the surface greater than 3 and reducing the filter medium resistance to the filtrate. 3. The filter medium for improving filtrate permeability according to claim 1, wherein the surface on which the minute projections and recesses are formed has a water contact angle of 65° or less. The filtrate is a liquid or paste-like substance for food containing water, oil and other raw materials in any proportion, a liquid or paste-like substance for pharmaceutical use containing water, oil and other raw materials in any proportion, or a liquid or paste-like substance for cosmetics containing water, oil and other raw materials in any proportion. The filtrate permeability improving filter medium according to any one of claims 1 to 3, characterized in that the filtrate is a liquid or paste-like substance for pharmaceutical use containing water, oil and other raw materials in any proportion. A treatment method for improving filtrate permeability, characterized in that by forming, on at least a portion of a surface that comes into contact with the filtrate , minute irregularities, the minimum irregularity pitch of which is 0.5 μm or more and the maximum of which is 40 μm or less, and the minimum concave depth of which is 0.03 μm or more and the maximum of which is 2.0 μm or less, randomly by shot material projection treatment, the kurtosis value (Pku) of the surface is greater than 3 and the filter material resistance to the filtrate is reduced. A treatment method for improving filtrate permeability, characterized in that by forming, on at least a portion of a surface that comes into contact with the filtrate , minute irregularities, the minimum irregularity pitch of which is 0.5 μm or more and the maximum of which is 10 μm or less, and the minimum concave depth of which is 0.3 μm or more and the maximum of which is 2.0 μm or less, randomly by shot material projection treatment, the kurtosis value (Pku) of the surface is greater than 3 and the filter material resistance to the filtrate is reduced. 7. The method for improving filtrate passing property according to claim 5 or 6 , wherein the surface on which the minute projections and recesses are formed has a contact angle of water of 65° or less. The method for improving filtrate passability according to any one of claims 5 to 7, characterized in that the filtrate is a liquid or paste-like substance for food containing water, oil, and other raw materials in any proportion, a liquid or paste-like substance for pharmaceutical use containing water, oil, and other raw materials in any proportion, or a liquid or paste - like substance for cosmetics containing water, oil, and other raw materials in any proportion.

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