JP2017069369A - Partition plate for ic tag erroneous recognition prevention, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent erroneous recognition of an IC tag and to improve read accuracy by providing a partition plate for IC tag erroneous recognition prevention which has a radio wave shield performance substantially equal to that of a metal plate and is capable of reducing and avoiding radio wave interference by smoothly changing a phase of a reflection radio wave within a layer without considerably absorbing radio waves.SOLUTION: A partition plate 1 for IC tag erroneous recognition prevention is a tabular body which is configured by composing conductive fibers 2, non-conductive fibers 3 and a binder 4 for binding the fibers and of which the thickness ranges from 2 to 30 mm. An average fiber length of the conductive fibers 2 ranges from 25 to 200 mm and the conductive fibers are dispersed in a three-dimensional manner in a surface direction and a thickness direction of the partition plate. A transmission attenuation amount of the partition plate 1 at 920 MHz ranges from -21 to -53 dB and a reflection attenuation amount ranges from 0.3 to -3.6 dB. A surface material 5 may also be stuck to one surface or both surfaces.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an IC tag erroneous recognition preventing partition plate.

  RFID (Radio Frequency IDentification) used in a logistics facility such as a warehouse is a non-contact type that manages people and goods by a reader / writer, an antenna, and a wireless IC tag (simply referred to as “IC tag” in this specification). Information recognition technology. The reader / writer includes a type having a built-in antenna and a type in which an external antenna is connected via a cable. In this specification, the term “antenna” includes both a built-in antenna and an external antenna. The reader / writer unit other than the antenna is assumed. In the RFID system, radio waves having a frequency of 915 to 950 MHz in the UHF band (simply referred to as “920 MHz band” in this specification) are mainstream, and the communication distance is usually adjusted to several meters.

  However, communication failure due to radio wave interference between the antennas and reflected radio waves from the wall may occur, and the IC tag may be misrecognized, and measures to increase the reading accuracy of the IC tag are urgently needed. When reading an IC tag, even if the antenna and the IC tag can communicate with each other, a position where the reading is impossible (referred to as a null point) is likely to occur. On the other hand, the radio wave emitted from the antenna and the reflected radio wave have the same phase and strengthen each other, and it is easy to erroneously read an IC tag in a place that cannot be normally read only by the radio wave of the antenna.

  Therefore, conventionally, a metal plate radio wave shielding material and a partition plate made of radio wave absorbing material have been used, but it has been difficult to prevent erroneous recognition.

Patent Document 1 describes a non-contact IC tag classification method in which radio waves are absorbed by an electromagnetic wave absorbing cloth to prevent erroneous recognition. In this prior art, a conductive resin layer containing carbon black, graphite, or carbon fiber milled fiber is provided in a range of 30 to 120 g / m ^{2 on} at least one surface of the base fabric, and the transmission attenuation at 1 GHz is −3 to −. Radio waves are absorbed by an electromagnetic wave absorbing cloth for non-contact radio wave recognition within a range of 20 dB. However, according to the study of the present inventor, erroneous recognition could not be prevented with this amount of transmission attenuation.

  In addition, a technique for preventing erroneous recognition by installing a plurality of antennas or adjusting the output of a reader / writer is known, but there is no technique for adjusting the position, angle, and thickness of a partition plate as a recognition system. When the type and arrangement of the IC tag are changed, the frequency of adjusting the position, distance, and output of the reader / writer and the antenna is high.

Japanese Patent No. 5262341

  Therefore, an object of the present invention is to have a radio wave shielding performance similar to that of a metal plate, and reduce and avoid radio wave interference by gently changing the phase of the reflected radio wave in the layer without significantly absorbing the radio wave. An IC tag misrecognition prevention partition plate is provided to prevent misrecognition of an IC tag and to improve reading accuracy.

  A radio wave is a wave, and its frequency per second is a frequency. The distance that the wave propagates during an amplitude is called wavelength (λ). The wavelength with a frequency of 1 GHz is approximately 30 cm. Here, for example, in the case of a polyester plate, since the relative dielectric constant is about 3.2, the wavelength of the radio wave in the layer is about 17 cm (= 30 / √3.2). If the relative permittivity is about 10 by mixing carbon fibers, the wavelength in the layer is about 9.5 cm, and the thickness of the λ / 4 type wave absorber is 2.4 cm. It is considered to be.

  The inventor makes the conductive fiber and the non-conductive fiber have different dielectric constants, mixes the fiber diameter and fiber length with different materials, or uses a conductive powder, ferrite, etc. as a binder. It was thought that by mixing magnetic powder and powder of a compound having a high dielectric constant, radio wave interference can be further suppressed and it can be expected to prevent misrecognition, and further investigations were made to arrive at the present invention.

(1) The IC tag erroneous recognition preventing partition plate of the present invention is
A partition plate for preventing erroneous recognition of an IC tag, comprising a composite of conductive fibers, non-conductive fibers, and a binder that binds these fibers, and having a thickness in the range of 2 to 30 mm,
The conductive fiber has an average fiber length in the range of 25 to 200 mm, and is three-dimensionally dispersed in the surface direction and the thickness direction of the partition plate,
The transmission attenuation amount at 920 MHz is in the range of −21 to −53 dB, and the reflection attenuation amount is in the range of −0.3 to −3.6 dB.

(2) The manufacturing method of the IC tag misrecognition prevention partition plate of the present invention mixes non-conductive fibers and conductive fibers having an average fiber length in the range of 25 to 200 mm, and forms a nonwoven fabric by the needle punch method. After heating, it is cold-pressed to form a partition plate having a thickness in the range of 2 to 30 mm.

[Action]
The mechanism of the IC tag misrecognition prevention partition plate of the present invention is that the radio wave of the frequency 920 GHz band transmitted from the antenna is diffusely reflected by the conductive fibers contained in the partition plate, so that the measurement space of the IC tag is passed through. A cushion that can transmit radio waves, and the wavelength shift and reflection direction due to the time lag of the reflected radio waves become random due to the three-dimensional fiber orientation and fiber dispersion of the conductive fibers contained in the partition plate. That can improve the reading accuracy of IC tags by suppressing the excessive fluctuation of radio waves due to in-phase and anti-phase due to radio waves transmitted from the antenna and reflected waves from the partition plate. This is new knowledge. Since these effects are obtained, the present invention has been found to provide a partition plate having moderately high radio wave shielding properties and high radio wave absorption properties.

  In other words, the antenna reception may read IC tags outside the desired range if the radio wave shielding is too low, and if the radio wave absorption is too high, the radio wave cannot be sent as soon as possible, and a low value is detected. Is likely to occur.

  A conductive fiber having an average fiber length of 25 mm or more and 200 mm or less in the layer is three-dimensionally dispersed in the thickness direction of the plate, thereby causing a phase change in the reflected radio wave and suppressing radio wave interference (reader / writer (By suppressing the null point, which is the “facing” in which the radio waves from and the opposite-phase radio waves due to reflection cancel each other), erroneous recognition can be prevented. The reading accuracy of the internal IC tag can be increased by covering the distance between the reader / writer and the IC tag with the partition plate for prevention of the present invention within a communicable distance. In other words, the conventional problem is solved by using the IC tag erroneous recognition preventing partition plate having the radio wave shielding performance similar to that of a metal plate and having the radio wave absorption performance controlled to be low.

When the average fiber length of the conductive fibers is less than 25 mm, the fibers fall more during needle punching, and when the average fiber length exceeds 200 mm, the fibers are easily clogged.
When the thickness of the conductive fiber is less than 2 mm, the phase change of the radio wave is less likely to occur, and when the thickness exceeds 30 mm, a space similar to a 1 / λ type radio wave absorber is formed and erroneous recognition is likely to occur.
By including non-conductive fibers, the contact points of the conductive fibers are reduced, and appropriate radio wave absorption can be obtained.
By performing needle punching, the conductive fibers are entangled three-dimensionally, the directionality of reflection of radio waves is reduced, and radio wave interference can be suppressed.

If the transmission attenuation is less than -21 dB, radio waves cannot be shielded, the adjacent IC tag is erroneously recognized, and if it exceeds -53 dB, total reflection of the metal plate tends to occur. Preferably it is −40 to −53 dB, and more preferably −50 to −53 dB.
When the return loss is less than −0.3, almost no radio wave absorption can be expected, and when it exceeds −3.6 dB, the radio wave absorption becomes extremely high, and the radio wave sensitivity for detecting the IC tag decreases. It is preferably −0.4 to −2.4 dB, more preferably −0.6 to −1.8 dB.

  According to the present invention, an IC tag that has radio wave shielding performance equivalent to that of a metal plate and can reduce and avoid radio wave interference by gently changing the phase of reflected radio waves within a layer without significantly absorbing radio waves. By providing a partition plate for preventing erroneous recognition, it is possible to prevent erroneous recognition of the IC tag and improve the reading accuracy.

FIG. 4A is a cross-sectional view, FIG. 4B is an enlarged cross-sectional view, and FIG. 4C is a diagram for explaining characteristics of an IC tag erroneous recognition preventing partition plate (with a face material) according to the present invention. It is the schematic which shows the usage example of the partition plate. It is a schematic diagram of the structural example which changes the position or angle of the partition plate. It is a schematic diagram of the example of a structure which changes the thickness of the partition plate.

  As shown in FIG. 1, the IC tag erroneous recognition preventing partition plate 1 includes conductive fibers 2 (for example, carbon fibers), non-conductive fibers 3 (for example, core material of core-sheath structure polyester fibers) and these fibers. It is a plate-like body that is composed of a composite with a binding material 4 (for example, a sheath-welded portion of a core-sheath polyester fiber) and has a thickness in the range of 2 to 30 mm. The conductive fibers 2 have an average fiber length in the range of 25 to 200 mm, and are three-dimensionally dispersed in the surface direction and the thickness direction of the partition plate. A face material 5 (for example, a low melting point polyethylene film) may be attached to one side or both sides of the partition plate 1 for preventing erroneous recognition of the IC tag. The transmission attenuation amount at 920 MHz of the IC tag erroneous recognition preventing partition plate 1 is in the range of -21 to -53 dB, and the reflection attenuation amount is in the range of -0.3 to -3.6 dB.

  An example of use is shown in FIG. For example, as shown in FIG. 2A, the IC tag erroneous recognition preventing partition plate 1 can be installed so as to surround an antenna disposed within a communicable distance and an IC tag to be recognized. . As described above, the function of sending radio waves through the measurement space by diffuse reflection by the IC tag misrecognition prevention partition plate 1 and the function of suppressing excessive radio wave fluctuation due to the same phase or opposite phase can be obtained. Accuracy can be increased. It is possible to adjust the angle and sensitivity of the antenna, and to improve the reading rate by using a plurality of antennas and reader / writers.

  Further, as shown in FIG. 2 (b), the IC tag erroneous recognition preventing partition plate 1 includes a reader / writer provided so that an article with an IC tag passes, a first gate having an antenna, and a second gate. A partition plate can be installed between the two so as to partition them. In addition to the above operation, the reading range is controlled to be narrowed by the IC tag erroneous recognition preventing partition plate 1 so that IC tags passing through different gates are not recognized.

1. Conductive fiber Although it does not specifically limit as a conductive fiber, Carbon fiber, a metal fiber, the fiber coat | covered with the metal, etc. can be illustrated, 1 type, or 2 or more types chosen from these can be used. In addition, the flame resistant fiber by a low temperature process is substantially nonelectroconductive, and is not contained in the conductive fiber in this invention.
In the case of carbon fiber, there are pitch type, PAN type and the like depending on the production method, but it is not particularly limited. In the case of carbon fiber, the content is preferably 25 g / m ² or more, and more preferably 130 g / m ² or more. When it is less than 25 g / m ² , shielding shortage is likely to occur due to dispersion unevenness, and when it is 130 g / m ² or more, shielding properties are particularly high.

2. Non-conductive fiber The non-conductive fiber is not particularly limited, but is an inorganic fiber such as glass fiber, mineral fiber, ceramic fiber, silica fiber, polyester fiber (polyethylene terephthalate (PET) fiber, polybutylene terephthalate (PBT) fiber) Etc.), polyolefin fibers (polyethylene (PE) fibers, polypropylene (PP) fibers, etc.), vinylon fibers, rayon fibers, nylon fibers, polycarbonate fibers, polyacetal fibers, acrylic fibers, etc., cotton, Natural fibers such as bamboo and hemp can be exemplified, and one or more selected from these can be used. Among these, glass fiber, polyester fiber, and polyolefin resin fiber are preferable. Polyester fibers are particularly preferable because they are lightweight, have no tingling sensation, are self-extinguishing, have a relatively high dielectric constant, and are inexpensive.
Further, the non-conductive fiber is a core material after only the sheath material of the core-sheath structure fiber composed of the core material having a relatively high melting point and the sheath material having a relatively low melting point is thermally melted. Also good.

3. Binding material The binding material may be inorganic or organic. The inorganic system is not particularly limited, and examples thereof include silica sol, alumina sol, zirconia sol, titania sol, aluminum phosphate system, aluminum sulfate system, sodium silicate, ceramic adhesive, mineral clay, and cements. The organic type is not particularly limited, but vinyl acetate type, polyvinyl alcohol type, polyvinyl acetal type, vinyl chloride type, acrylic type, polyethylene type, polypropylene type, cellulose type, polyester type, urea type, resorcino -Rule, melamine, phenol, epoxy, polyurethane, polyimide, polyaromatic resin, chloroprene, nitrile rubber, SBR, polysulfide, butyl rubber, silicone rubber elastomer, starch , Natural examples of casein, chicken, asphalt and tar. These binders may be used alone or in combination of two or more. These can be impregnated and applied in a liquid state or sprayed with a powder to obtain a drying and heating step to bind the fibers.
The binding material may be one in which the sheath material of the core-sheath structure fiber described above is melted and heat-sealed between the fibers, or is relatively lower than the non-conductive fiber mixed in the non-conductive fiber. A synthetic fiber having a melting point may be melted and heat-welded between the fibers. These binders are preferable because they can be bonded between the fibers in the heating step, and are easy to manufacture.

4). Face Material A sheet-like face material may be laminated on one side or both sides of the partition plate. Although it does not specifically limit as a material of a face material, The polyolefin resin, the moisture-permeable film for building materials, wallpaper, etc. can be illustrated. Polyolefin resins are preferred because they do not generate toxic gases such as chlorine gas and hydrogen chloride gas during combustion, are not related to environmental hormones, and do not generate dioxins even when incinerated at about 800 ° C. or lower. Moreover, flameproofness and a flame retardance can be improved by adding the flameproof flame-retardant compound which does not contain halogen elements, such as a metal hydroxide, for example in polyolefin resin.

5. Structure for changing the position or angle of the partition plate It is preferable to add a structure for changing one or both of at least a part of the position or angle to the partition plate. By changing and adjusting the position or angle of the partition plate, even if the type or arrangement of the IC tag is changed, the reading environment can be shortened without adjusting the output of the reader / writer or the position or distance of the antenna. Can be provided in time.

Although it does not specifically limit as a structure which changes the position or angle of a partition plate, The following aspect can be illustrated.
(1) As shown in FIG. 3A, a structure in which the partition plate 1 is pivotally attached to a stand 10 that can be displaced by a caster 15, and the partition plate 1 having a predetermined tilt angle is stopped by a knob 11.
(2) As shown in FIG. 3B, a base 21 that can be displaced by a caster 25, a column 22 that is pivotally attached to the caster 25, and a column 22 that has a predetermined tilt angle are connected to the base 21. The structure which attached the partition plate 1 to the pillar part 22 using the adjuster 20 which consists of the arm 23 to stop.
In addition to these, a partition plate is attached to the three-dimensional frame, a structure in which the front / rear feed and angle adjustment of the partition plate can be arbitrarily designed manually or automatically by driving a ball screw, replacement mounting of a fixing jig, etc. Can be illustrated.

  In the present invention, since the average fiber length of the conductive fibers is 25 mm or more, it is possible to effectively use the phenomenon in which the return loss changes depending on the incident angle of the partition plate due to the radio wave. Although there is no clear law for these angles, even if the type of IC tag changes, a high reading sensitivity can be obtained by processing determination with a plurality of data based on the difference in incident angles.

6). Structure for changing thickness of partition plate It is preferable to add a structure for changing the thickness of at least a part of the partition plate. By changing and adjusting the thickness of the partition plate, a higher reading environment can be achieved in a short time without adjusting the output of the reader / writer or the position or distance of the antenna even if the type or arrangement of the IC tag is changed. Can be provided at.

Although it does not specifically limit as a structure which changes the thickness of a partition plate, The following aspect can be illustrated.
(1) As shown in FIG. 4, a structure in which the partition plate 1 is sandwiched between both sides by a non-conductive resin plate 30 and the like and is tightened and compressed by screws 32. The resin plate 30 may be a plate having no holes as shown in FIGS. 4 (a1) and (a2), or a plate having a plurality of holes 31 (in the illustrated example, a lattice arrangement) as shown in FIGS. 4 (b1) and (b2). Good. When the partition plate 1 is compressed with a plate having a plurality of holes 31, the partition plate 1 bites into the holes 31, and thus the thickness of the partition plate 1 changes.
(2) A structure in which the partition plate is stopped by being compressed with staples.

By setting the bulk density to 10 to 100 kg / m ³ , a partition plate having flexibility and compression recovery property can be obtained, and the thickness can be adjusted. If the thickness is compressed, the transmission attenuation increases and the reflection attenuation decreases. If the thickness is increased, the opposite performance is obtained. When partition plates are laminated and a core material with excellent cushioning properties such as urethane foam is put in, even if it is a non-flexible partition plate with high bulk density, the gap distance of the partition plates can be changed. The effect is obtained.

  Hereinafter, an IC tag erroneous recognition preventing partition plate according to an embodiment of the present invention will be described. Table 1 shows the composition of the materials of the examples and comparative examples. Note that the materials, configurations, and numerical values described in the examples are examples and can be changed as appropriate.

In Examples 1 to 8 and Comparative Example 1, the conductive fiber is a carbon fiber, the non-conductive fiber is a core material after only the sheath material of the core-sheath structure PET fiber is thermally melted, and the binding material is the sheath. The material is melted and the fibers are thermally welded. The carbon fiber is a PAN fiber having a fiber length of 50 mm and an average fiber diameter of 6 μm. The core-sheath structure PET fiber has a fiber length of 38 mm and a fineness of 2 denier, the core material is PET having a melting point of 253 ° C., and the sheath material is PET having a melting point of 130 ° C.
In Examples 9 and 10, the conductive fiber is a metal fiber, the non-conductive fiber is a PET fiber, and the binder is a material in which PP fibers are melted and heat-bonded between the fibers. The metal fiber is a stainless steel (SUS316) fiber having a fiber length of 50 mm and an average fiber diameter of 12 μm. The PET fiber has a fiber length of 50 mm, a fineness of 4 denier, and a melting point of 255 ° C. The PP fiber has a melting point of 158 ° C. and contains 0.5% by mass of carbon powder.
In Examples 1, 2, 3, and 8, face materials are attached to both surfaces of the partition plate. The face material is a polyethylene film having a thickness of 35 μm and a melting point of 120 ° C.

In Comparative Example 2, the conductive fiber is the same carbon fiber as in Example 1 and the like, there is no non-conductive fiber, and the binder is a material in which PP fibers having a melting point of 158 ° C. are melted and the fibers are thermally welded.
Comparative Example 3 is a simple copper plate having a thickness of 2 mm.
Comparative Example 4 is a case where no partition plate is used.
Comparative Example 5 is a radio wave absorber for building materials (trade name “Solaton ST12-ES-600” manufactured by Nitto Boseki Co., Ltd.).

  The partition plates of Examples 1 to 10 and Comparative Examples 1 and 2 are a mixture of conductive fibers, non-conductive fibers, and binder fibers, dry blended by a needle punch method to form a nonwoven fabric, and dried at 190 ° C. After heating in a furnace for 5 minutes to melt the low melting sheath material or binder fiber, it was formed into a plate shape by pressing to a constant pressure with a cold press (FIG. 1). See). The face material was laminated on the non-woven fabric, and was integrally pasted by pressure molding at the same time.

The following measurement / test was performed on the partition plates of the examples and comparative examples. The results are shown in Table 1.
(1) Transmission attenuation The transmission attenuation is measured according to the Kansai Electronics Industry Promotion Center method (KEC method) at a frequency of 920 MHz and n = 3, and the average value of the transmission attenuation (dB) of the electric field at a frequency of 920 MHz. It was adopted.
(2) Return loss The return loss was measured at a frequency of 920 MHz using a low frequency μ stripline radio wave return loss measuring device. The size of the test body was 1000 mm × 300 mm.
(3) IC tag recognition test As shown in FIG. 2 (b) above, between a stationary reader / writer compatible with the 920 MHz band, a first gate having two antennas, and a second gate, When the partition plates of each example and comparative example are installed so as to partition, and a cart in which three cardboard boxes containing 12 articles with IC tags are stacked is passed through each gate at the same time, the number of each IC tag is determined. As the reading accuracy, the case where all were correctly read was evaluated as ◎, the case where one was impossible, ◯, and the case where two or more were impossible, was evaluated as ×.

In Comparative Example 1, it is considered that erroneous recognition could not be prevented because the radio wave reflectivity was high as in the case of a metal plate and a sufficient phase change was not obtained.
In Comparative Example 2, since there were too many binders, it was not a plate having a uniform thickness. Particularly, the carbon fibers on the surface were in two-dimensional surface contact, and the intersections of the carbon fibers increased, so that there was a sufficient phase change. It is thought that it was not obtained, and misrecognition was not prevented.
In Comparative Example 3, since it is a metal plate, it is considered that radio wave reflectivity is high, the null point cannot be suppressed, and erroneous recognition cannot be prevented.
In Comparative Example 4, since there is no partition plate, it is considered that the erroneous recognition that radio waves pass through and the adjacent tag is read cannot be prevented.
In Comparative Example 5, it is considered that the sensing performance of the IC tag is lowered because the radio wave absorber has high radio wave absorption performance.

In addition, this invention is not limited to the said Example, For example, as follows, it can change suitably in the range which does not deviate from the meaning of invention, and can be embodied.
(1) A metal foil or a metal thin plate may be attached to the back surface of the partition plate, or an air layer may be provided.
(2) In addition to a flat surface, the partition plate can be used as a curved surface or an uneven surface, or can be assembled into a three-dimensional molded product, a polyhedron, or a box shape.
(3) The partition plate can be bent or folded by providing a groove on the flat plate.

1 IC tag erroneous recognition prevention partition plate 2 Conductive fiber 3 Non-conductive fiber 4 Binding material 5 Face material

Claims (9)

A partition plate for preventing erroneous recognition of an IC tag, comprising a composite of conductive fibers, non-conductive fibers, and a binder that binds these fibers, and having a thickness in the range of 2 to 30 mm,
The conductive fiber has an average fiber length in the range of 25 to 200 mm, and is three-dimensionally dispersed in the surface direction and the thickness direction of the partition plate,
A partition plate for preventing erroneous recognition of an IC tag, wherein the transmission attenuation at 920 MHz is in the range of -21 to -53 dB and the reflection attenuation is in the range of -0.3 to -3.6 dB. . The partition plate for preventing erroneous recognition of an IC tag according to claim 1, wherein the conductive fiber is a carbon fiber and is contained in an amount of 130 g / m ² or more.   The non-conductive fiber is a core material after only the sheath material of the core-sheath structure fiber composed of a core material having a relatively high melting point and a sheath material having a relatively low melting point is thermally melted. Or the partition plate for IC tag misrecognition prevention of 2 description.   4. A partition plate for preventing erroneous recognition of an IC tag according to claim 3, wherein the binding material is obtained by melting the sheath material and thermally welding the fibers.   The binding material according to any one of claims 1 to 4, wherein a synthetic fiber having a relatively low melting point is melted with respect to the non-conductive fiber mixed in the non-conductive fiber and the fibers are heat-welded. The partition plate for preventing erroneous recognition of the IC tag according to one item.   The IC tag erroneous recognition prevention partition plate according to any one of claims 1 to 5, wherein a sheet-like face material is laminated on one side or both sides of the partition plate.   The IC tag erroneous recognition preventing partition plate according to any one of claims 1 to 6, wherein a structure for changing at least one of the position and angle of the partition plate or one or both of the angles is added to the partition plate.   The IC tag erroneous recognition preventing partition plate according to any one of claims 1 to 7, wherein a structure for changing the thickness of at least a part of the partition plate is added.   Non-conductive fibers and conductive fibers having an average fiber length in the range of 25 to 200 mm are mixed, made into a nonwoven fabric by the needle punch method, heated and then cold pressed, and the thickness is in the range of 2 to 30 mm. A manufacturing method of a partition plate for preventing erroneous recognition of an IC tag, characterized in that the partition plate is molded into an inner partition plate.

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