Patent Description:
In the related art, for example in <CIT>, such a flat membrane element includes, for example, a sheet-type filtration membrane <NUM> bonded to a surface of a filter plate <NUM> as illustrated in <FIG> and <FIG>. The outer edge of the filtration membrane <NUM> of such a flat membrane element <NUM> is thermally welded over the circumference of the surface of the filter plate <NUM> by a thermal welding part <NUM>. The thermal welding part <NUM> is formed into square meshes. This provides sealing between the filtration membrane <NUM> and the filter plate <NUM> along the outer edge of the filtration membrane <NUM>.

In a known method for producing the flat membrane element <NUM>, as illustrated in <FIG>, the filtration membrane <NUM> is disposed on the surface of the filter plate <NUM>, and then as illustrated in <FIG>, a hot projection <NUM> provided on a hot plate <NUM> is pressed onto the filter plate <NUM> from above of the outer edge of the filtration membrane <NUM>. This forms the thermal welding part <NUM> so as to thermally weld the filtration membrane <NUM> to the filter plate <NUM>.

As illustrated in <FIG>, the hot projection <NUM> is shaped like the thermal welding part <NUM>, that is, meshes. Thus, a plurality of recesses <NUM> (hollows) surrounded by the hot projection <NUM> are formed on the hot plate <NUM>.

The flat membrane element is illustrated with reference to <CIT>.

<CIT> discloses a flat membrane element and a method for producing a flat membrane element according to the preamble of claim <NUM> and claim <NUM>, respectively.

In the configuration of the related art, as illustrated in <FIG>, the hot projection <NUM> of the heated hot plate <NUM> comes into contact with the filter plate <NUM> or the filtration membrane <NUM> during the production of the flat membrane element <NUM>. This may generate gas or cause burning (hereinafter, referred to as burnt bits) on the resin of the filter plate <NUM> or the filtration membrane <NUM>.

The hot projection <NUM> is shaped like meshes and surrounds the recesses <NUM>, so that the generated burnt bits are likely to be retained in the recesses <NUM> of the hot plate <NUM>. When burnt bits are retained in the recesses <NUM> of the hot plate <NUM>, the burnt bits in the recesses <NUM> may stick to the flat membrane element <NUM> during thermal welding and cause a poor appearance or low waterproofness.

Cleaning of the hot plate <NUM> may be a solution to the sticking of burnt bits. However, burnt bits in the recesses <NUM> may be hard to remove in cleaning because the hot projection <NUM> is shaped like meshes and the recesses <NUM> are surrounded by the hot projection <NUM>. Thus, cleaning of the hot plate <NUM> requires a lot of time and effort.

An object of the present invention is to provide a flat membrane element and a method for producing the same, by which burnt bits are hardly retained on a hot plate and the hot plate is easily cleaned even if burnt bits stick to the hot plate, so that burnt bits are prevented from sticking to the hot plate.

The invention relates to a flat membrane element according to claim <NUM>.

With this configuration, when the flat membrane element is produced, the filtration membrane is disposed on the surface of the filter plate, and then a hot projection provided on a hot plate is pressed onto the filter plate from above of the outer edge of the filtration membrane. Thus, the thermal welding part is formed and the filtration membrane is thermally welded to the filter plate in the thermal welding part.

The hot projection used for producing the flat membrane element is identical in shape to the thermal welding part, unlike the mesh-type projection in the related art. Thus, recesses formed on the hot plate are not surrounded by the hot projection and are opened in an outward direction. Hence, the hot plate is cleaned so as to easily remove burnt bits, thereby preventing burnt bits from sticking to the flat membrane element during thermal welding.

According to the invention, the outer edge of the filtration membrane is disposed inside the outer end of the projected portion of the thermal welding part and outside the inner end of the recessed portion of the thermal welding part.

With this configuration, in the production of the flat membrane element, even if the filtration membrane is displaced from the filter plate or a production error appears in the dimensions of the filtration membrane, the thermal welding part provides firm sealing between the filter plate and the filtration membrane as long as the outer edge of the filtration membrane is disposed inside the outer end of the projected portion and outside the inner end of the recessed portion.

According to an advantageous embodiment, the outer boundary line is wavy.

According to this embodiment, the hot projection used for producing the flat membrane element is wavy, and identical in shape to the thermal welding part, unlike the mesh-type projection in the related art. Thus, recesses formed on the hot plate are not surrounded by the hot projection, hardly leaving burnt bits. The hot projection provided on the hot plate is opened in the outward direction. Hence, even if burnt bits stick to the projection, the hot plate is cleaned so as to easily remove burnt bits, thereby preventing burnt bits from sticking to the flat membrane element during thermal welding.

According to an advantageous embodiment, the inner boundary line has a plurality of projected portions and recessed portions that are alternately formed in a consecutive manner,.

According to an advantageous embodiment, the inner boundary line is wavy.

According to an alternative advantageous embodiment, the inner boundary line is a straight line.

According to an advantageous embodiment, the outer edge of the filtration membrane is thermally welded to the surface of the filter plate by the first thermal welding part thermally welded to the surface of the filter plate and a second thermal welding part that is different from the first thermal welding part, and
the first thermal welding part is disposed between the second thermal welding part and the outer edge of the filter plate.

With this configuration, the outer edge of the filtration membrane is thermally welded to the surface of the filter plate by the first thermal welding part and the second thermal welding part. This can more reliably prevent the outer edge of the filtration membrane from peeling from the surface of the filter plate.

According to an advantageous embodiment, the outer boundary line and the inner boundary line of the second thermal welding part are straight lines that are parallel with each other.

The invention also relates to a method for producing a flat membrane element according to claim <NUM>.

With this configuration, the hot projection is identical in shape to the thermal welding part, unlike the mesh-type projection in the related art. Thus, recesses formed on the hot plate are not surrounded by the hot projection, hardly leaving burnt bits. The hot projection provided on the hot plate is opened in an outward direction. Hence, even if burnt bits stick to the projection, the hot plate is cleaned so as to easily remove burnt bits, thereby preventing burnt bits from sticking to the flat membrane element during thermal welding.

According to the invention, the filtration membrane is bonded to the filter plate while the outer edge of the filtration membrane is disposed inside the outer end of the projected portion of the thermal welding part and outside the inner end of the recessed portion of the thermal welding part.

According to an advantageous embodiment, the inner boundary line of the thermal welding part is linearly formed.

According to an advantageous embodiment, the hot projection is entirely shaped like a rectangular loop.

According to an advantageous embodiment, the outer edge of the filtration membrane is pressed by a first hot projection and a second hot projection of the hot plate so as to form a first thermal welding part and a second thermal welding part that is different from the first thermal welding part, and the filtration membrane is bonded to the filter plate while the first thermal welding part is disposed between the second thermal welding part and the outer edge of the filter plate.

According to an advantageous embodiment, each of the first hot projection and the second hot projection is entirely shaped like a rectangular loop.

As has been discussed, the present invention hardly leaves burnt bits on the hot plate. Even if burnt bits stick to the hot plate, the hot plate is cleaned so as to easily remove burnt bits, thereby preventing burnt bits from sticking to the flat membrane element during thermal welding.

In the first embodiment, as illustrated in <FIG>, reference numeral <NUM> denotes a submerged membrane separator used for a membrane-separation activated sludge process. The membrane separator <NUM> is configured such that a plurality of flat membrane elements <NUM> and an air diffuser <NUM> for blowing air from the bottom are provided in a case <NUM>. The case <NUM> can be separated into an upper membrane case <NUM> and a lower air diffusion case <NUM>. The flat membrane elements <NUM> are disposed at predetermined intervals in the membrane case <NUM>. The air diffuser <NUM> is disposed in the air diffusion case <NUM>.

As illustrated in <FIG> and <FIG>, the flat membrane element <NUM> includes a filter plate <NUM> made of a thermoplastic resin, e.g., ABS resin and sheet-type organic filtration membranes <NUM> bonded to the respective sides of the filter plate <NUM>.

A permeate passage is formed between the filter plate <NUM> and the filtration membrane <NUM> and in the filter plate <NUM>, and a permeate outlet <NUM> in communication with the permeate passage is provided on the upper end of the filter plate <NUM>. Permeate having passed through the filtration membrane <NUM> is collected from the permeate outlet <NUM> through the permeate passage.

The flat membrane element <NUM> is in communication with a water collecting pipe <NUM> via a tube <NUM> connected to the permeate outlet <NUM>. A permeate delivery pipe <NUM> for delivering permeate is connected to the water collecting pipe <NUM>.

As illustrated in <FIG>, the outer edge of the filtration membrane <NUM> is thermally welded over the circumference of the surface of the filter plate <NUM> by a first thermal welding part <NUM>. This provides sealing between the filtration membrane <NUM> and the filter plate <NUM> along the outer edge of the filtration membrane <NUM>. In the thermal welding part, at least one of the filtration membrane and the filter plate is pressed by a hot projection on a hot plate.

The first thermal welding part <NUM> includes an outer boundary line <NUM> disposed inside an outer edge 11a of the filter plate <NUM> and an inner boundary line <NUM> disposed inside the outer boundary line <NUM>. Thermal welding is performed over an area between the outer boundary line <NUM> and the inner boundary line <NUM>. The inner boundary line <NUM> is shaped like a straight line.

The outer boundary line <NUM> is wavy with a plurality of first projected portions <NUM> and a plurality of first recessed portions <NUM> that are alternately formed in a consecutive manner. The first projected portion <NUM> is shaped like an arc projecting toward the outer edge 11a of the filter plate <NUM> and is equivalent to a portion having a large welding area. The first recessed portion <NUM> is formed between the first projected portions <NUM>, is U-shaped so as to retract in an inward direction A opposite to the outer edge 11a of the filter plate <NUM>, and is equivalent to a portion having a small welding area.

An outer edge 12a of the filtration membrane <NUM> is disposed inside outer ends 25a of the first projected portions <NUM> and outside inner ends 26a of the first recessed portions <NUM>. The first thermal welding part <NUM> is slightly lower than the surface of the filter plate <NUM> surrounding the first thermal welding part <NUM>.

As illustrated in <FIG>, a hot plate <NUM> is used for thermally welding the outer edge of the filtration membrane <NUM> to the surface of the filter plate <NUM>. The hot plate <NUM> includes a first hot projection <NUM>. The first hot projection <NUM> is entirely shaped like a square (rectangular) loop and is wavy like the first thermal welding part <NUM>. Specifically, the first hot projection <NUM> includes a plurality of projected portions <NUM> and recessed portions <NUM>, which are wavy, and identical in shape to the first projected portions <NUM> and the first recessed portions <NUM> of the first thermal welding part <NUM>, on the outer edge of the first hot projection <NUM>.

A method for producing the flat membrane element <NUM> will be described below.

First, as illustrated in <FIG>, the filtration membrane <NUM> is disposed on the surface of the filter plate <NUM>. Subsequently, as illustrated in <FIG>, the first hot projection <NUM> of the hot plate <NUM> is pressed to the filter plate <NUM> from above of the outer edge of the filtration membrane <NUM>. Thus, the first thermal welding part <NUM> is formed and the outer edge of the filtration membrane <NUM> is thermally welded to the surface of the filter plate <NUM> in the first thermal welding part <NUM>.

Thereafter, the hot plate <NUM> is lifted so as to remove the first hot projection <NUM> upward from the flat membrane element <NUM>.

As illustrated in <FIG>, the first hot projection <NUM> is wavy like the first thermal welding part <NUM>, unlike the mesh-type projection in the related art. Thus, recesses <NUM> formed on the hot plate <NUM> are not surrounded by the first hot projection <NUM>, hardly leaving burnt bits. The first hot projection <NUM> is opened in an outward direction B. Thus, even if burnt bits stick to the projection, the hot plate <NUM> is cleaned so as to easily remove burnt bits, thereby preventing burnt bits from sticking to the flat membrane element <NUM> during thermal welding.

In the production of the flat membrane element <NUM>, even if the filtration membrane <NUM> is displaced from the filter plate <NUM> or a production error appears in the dimensions of the filtration membrane <NUM>, the first thermal welding part <NUM> provides firm sealing between the filter plate <NUM> and the filtration membrane <NUM> as long as the outer edge 12a of the filtration membrane <NUM> is disposed inside the outer ends 25a of the first projected portions <NUM> of the first thermal welding part <NUM> and outside the inner ends 26a of the first recessed portions <NUM> of the first thermal welding part <NUM> as illustrated in <FIG>.

In the present embodiment, the outer boundary line <NUM> has, but is not limited to, a wavy shape of curves. The outer boundary line <NUM> may be formed in a zigzag pattern of straight lines (see <FIG>) or a pattern of rectangular projections and recesses (see <FIG>).

In a second embodiment, as illustrated in <FIG>, the outer edge of a filtration membrane <NUM> is thermally welded to the surface of a filter plate <NUM> by a first thermal welding part <NUM> and a second thermal welding part <NUM> that is different from the first thermal welding part <NUM>. The first thermal welding part <NUM> is disposed between the second thermal welding part <NUM> and an outer edge 11a of the filter plate <NUM>.

The second thermal welding part <NUM> is shaped like a straight line having a predetermined width W and is disposed inside the first thermal welding part <NUM>. An outer boundary line <NUM> and an inner boundary line <NUM> of the second thermal welding part <NUM> are straight lines that are parallel with each other.

With this configuration, the outer edge of the filtration membrane <NUM> is thermally welded to the surface of the filter plate <NUM> by the first thermal welding part <NUM> and the second thermal welding part <NUM>. This can more reliably prevent the outer edge of the filtration membrane <NUM> from peeling from the surface of the filter plate <NUM>.

As illustrated in <FIG>, a hot plate <NUM> includes a first hot projection <NUM> for forming the first thermal welding part <NUM> and a second hot projection <NUM> (an example of another hot projection) for forming the second thermal welding part <NUM>. The first hot projection <NUM> and the second hot projection <NUM> are entirely shaped like square (rectangular) loops. The second hot projection <NUM> is identical in shape to the second thermal welding part <NUM>, that is, the second hot projection <NUM> is linearly formed with the predetermined width W.

First, as illustrated in <FIG>, the filtration membrane <NUM> is disposed on the surface of the filter plate <NUM>. Subsequently, as illustrated in <FIG>, the first hot projection <NUM> and the second hot projection <NUM> of the hot plate <NUM> are pressed to the filter plate <NUM> from above of the outer edge of the filtration membrane <NUM>. Thus, the first thermal welding part <NUM> and the second thermal welding part <NUM> are formed and the outer edge of the filtration membrane <NUM> is thermally welded to the surface of the filter plate <NUM> in the first thermal welding part <NUM> and the second thermal welding part <NUM>.

Thereafter, the hot plate <NUM> is lifted so as to remove the first hot projection <NUM> and the second hot projection <NUM> upward from the flat membrane element <NUM>.

This configuration can achieve the same operations and effects as in the first embodiment.

Claim 1:
A flat membrane element (<NUM>) comprising a sheet-type filtration membrane (<NUM>) bonded to a surface of a filter plate (<NUM>) made of thermoplastic resin,
the flat membrane element (<NUM>) including a first thermal welding part (<NUM>) in which an outer edge (12a) of the filtration membrane (<NUM>) is bonded to the surface of the filter plate (<NUM>) by thermal welding,
wherein the thermal welding part (<NUM>) is formed over the entire area between an outer boundary line (<NUM>) inside an outer edge (11a) of the filter plate (<NUM>) and an inner boundary line (<NUM>) located further inside than the outer boundary line (<NUM>),
the outer boundary line (<NUM>) has a plurality of projected portions (<NUM>) and recessed portions (<NUM>) that are alternately formed in a consecutive manner,
the projected portion (<NUM>) projects toward the outer edge (11a) of the filter plate (<NUM>), and
the recessed portion (<NUM>) is formed between the projected portions (<NUM>) and retracts in an inward direction (A) opposite to the outer edge (11a) of the filter plate (<NUM>),
characterized in that the outer edge (12a) of the filtration membrane (<NUM>) is disposed inside an outer end (25a) of the projected portion (<NUM>) of the thermal welding part (<NUM>) and outside an inner end (26a) of the recessed portion (<NUM>) of the thermal welding part (<NUM>).