JP7560282B2 - Seaweed cultivation support and its manufacturing method - Google Patents

Description

The present invention relates to a support for seaweed cultivation and its manufacturing method.

In seaweed farming, bamboo or other supports are placed at equal intervals in the sea, and nets are placed between the supports, with seaweed farming taking place on the nets. In recent years, due to the difficulty in obtaining bamboo, its uneven thickness and length, and durability issues, supports made of fiber-reinforced synthetic resin (hereafter referred to as "FRP"), which allows for uniform thickness, have come to be used.

Known methods for manufacturing FRP supports for seaweed cultivation include the so-called pultrusion method (1), in which reinforcing fibers are impregnated with an uncured thermosetting resin composition and drawn into a pipe shape using a heated ring-shaped die while being cured and continuously pulled out, and a method (2), in which reinforcing fibers impregnated with an uncured thermosetting resin composition are wound at a predetermined winding angle around a long mandrel with an outer diameter corresponding to the inner diameter of the pipe, while traversing the reinforcing fibers, forming a pipe layer while curing the resin, to form a pipe-shaped support.
Furthermore, an FRP pillar has been proposed that has a fiber-reinforced resin layer formed by winding and stacking a sheet-like fiber-reinforced resin material, in which the reinforcing fibers are made of epoxy resin as a synthetic resin, around a mandrel for forming the pillar (see, for example, Patent Document 1).

However, in the above-mentioned pultrusion molding method (1) using a mold, a high pulling force is required to pull the hardened or semi-hardened FRP pillar from the mold due to the presence of frictional resistance with the mold, which requires a large device and unavoidably increases energy consumption and equipment costs.
On the other hand, in the manufacturing method of FRP pillars described in Patent Document 1, a sheet-shaped fiber-reinforced resin material is wound and laminated around a mandrel for forming the pillars, so the maximum overall length is about 6 m due to restrictions on the length of the mandrel, etc. However, the water depth of some Nori farming fishing grounds is about 12 m, so this manufacturing method cannot be used to obtain long pillars continuously.

Furthermore, in the case of FRP supports for seaweed cultivation, the outer surface of the FRP layer is preferably coated with a thermoplastic resin or the like for the purposes of preventing injury caused by a part of the FRP layer peeling off and piercing a finger during handling, preventing hydrolysis of the FRP layer when used standing in seawater, preventing weather deterioration of the FRP layer, etc. Furthermore, it is desirable that the inner surface of the FRP layer is also coated from the viewpoint of preventing hydrolysis of the FRP layer when used standing in seawater.
The applicant has marketed an FRP post with an outer diameter of 35 to 57 mm under the product name "Compose, registered trademark" as a support for Nori cultivation, which has a three-layer structure of thermoplastic resin core layer/FRP layer/thermoplastic resin coating layer, with a core layer made of thermoplastic resin, around the periphery of the core layer, an FRP layer in which long glass fibers are bonded with a matrix resin, and a thermoplastic resin coating layer around the periphery of the FRP layer, and which satisfies these functions. The product is easy to handle, durable, and has many advantages over bamboo, and has earned a high reputation for its practical use among Nori farmers.
However, the three-layer FRP seaweed cultivation support poles described above have the following problems:
(i) Since the installation of supports for seaweed cultivation is carried out manually, the heavy weight of the supports makes the work difficult.
(ii) If the poles used for seaweed cultivation are too thick, they are difficult to grip and make work difficult. On the other hand, if the poles are simply made thinner, the rigidity of ordinary FRP will decrease, making it difficult for them to stand upright in the sea, and the nets will be more likely to be swept away.
(iii) Equipment such as aquaculture poles are usually transported to the farms by boat, but if the poles are bulky, the frequency of transportation increases and the transportation work takes more time.
(iv) In order to solve the above problems, it has been considered to use carbon fiber as an FRP material. However, if an FRP support pillar is made only from carbon fiber, it will be very expensive and not very practical.

On the other hand, Patent Document 2 discloses a fiber-reinforced thermoplastic resin composition that contains a thermoplastic resin, 5 to 25 parts by weight of carbon fiber and 20 to 70 parts by weight of glass fiber per 100 parts by weight of the thermoplastic resin, and the total amount of carbon fiber and glass fiber is 40 to 75 parts by weight per 100 parts by weight of the thermoplastic resin, and proposes application of the composition to T-shaped, L-shaped, and other connecting members such as pipe members. However, in the specific example of the invention described in Patent Document 2, when preparing a mixture containing polyethylene terephthalate resin as a thermoplastic resin, 7.7 parts by weight of carbon fiber, and 46.2 parts by weight of glass fiber (average diameter 5-20 μm, average fiber length 100-500 μm) per 100 parts by weight of PET resin, with a total fiber amount of 53.9 parts by weight, a pellet-shaped mixture in which only carbon fiber (average diameter 1-10 μm, average fiber length 100-500 μm) is blended with PET resin, a pellet-shaped mixture in which only glass fiber is blended with PET resin, and a pellet-shaped mixture made of PET resin are each prepared, and a mixture is obtained by mixing the predetermined pellet-shaped mixtures. Then, this mixture is injection molded to obtain a molded product. However, the invention described in Patent Document 2 does not refer to a technical method of ensuring bending strength and bending rigidity using continuous long fiber reinforcing fibers, such as those used in seaweed cultivation supports.

JP 2007-259838 A JP 2019-214694 A

The applicant has conducted extensive research into the above problems (i) to (iv), i.e., FRP seaweed cultivation supports that are easy to handle manually, lightweight, and highly rigid, and are relatively inexpensive and highly practical, and has previously filed a patent application under the title JP 2019-063246 (filed March 31, 2020). The invention of this application arranges carbon fiber on the outer periphery side and glass fiber on the inner periphery side of an FRP layer formed on the outer periphery of a core layer made of thermoplastic resin. Arranging the carbon fiber on the outer periphery side was effective in terms of improving handleability and workability, as it was possible to narrow the outer diameter and ensure rigidity. However, when arranging the carbon fiber bundles, the number of which is naturally limited due to the constraints of material costs, on the outer periphery of the FRP layer, it is difficult to arrange the carbon fiber bundles at uniform intervals in the circumferential direction, and uneven distribution of the carbon fibers is observed. Therefore, when bending stress is applied to the support, the bending strength varies greatly depending on the circumferential position (direction) to which the stress is applied, which makes it difficult to set up the support in the sea, and when the seaweed net is stretched and used in the sea, the amount of displacement between each support due to waves in the row of support columns for seaweed cultivation is uneven. On the other hand, in order to solve this problem, it is also possible to arrange the carbon fibers uniformly in the circumferential direction by lowering the fineness (average fiber diameter) of the carbon fibers and increasing the number of carbon fibers used. However, since the price per weight of carbon fibers with small fineness is higher than that of carbon fibers with large fineness, the problem of an increase in the product price of the support columns for seaweed cultivation is a problem.
Therefore, the inventors of the present invention have conducted extensive research into arranging carbon fibers uniformly in the circumferential direction in order to achieve uniform bending strength depending on the location (direction) in the circumferential direction, and have completed the present invention.

That is, the present invention provides the following inventions [1] to [4].
[1] A seaweed cultivation support pole having a composite structure including a core layer made of a thermoplastic resin, an FRP layer formed on the outer periphery of the core layer, and a covering layer formed on the outer periphery of the FRP layer, the core layer being made of a thermoplastic resin having chemical affinity with a thermosetting resin which is a matrix component constituting the FRP layer at least on its outer periphery, the FRP layer having an FRP inner layer and an FRP outer layer, the FRP inner layer being made of a main body of reinforcing fibers made of long fiber-like carbon fibers on the outer periphery in the longitudinal direction of the core layer. a carbon fiber outer layer is bonded longitudinally to the outer periphery of the FRP inner layer with a matrix component, the FRP outer layer is bonded longitudinally to the outer periphery of the FRP inner layer with a matrix component and is mainly made of long glass fibers as reinforcing fibers, the cross-sectional area ratio of the glass fibers to the carbon fibers in the cross section of the FRP layer is 60:40 to 90:10, and at least the inner periphery of the coating layer is composed of a thermoplastic resin having chemical affinity with the thermosetting resin which is the matrix component constituting the FRP layer.
[2] A seaweed cultivation support as described in [1], in which a plurality of carbon fiber bundles are arranged circumferentially and symmetrically along the central axis in the FRP inner layer, and the carbon fiber bundles are arranged adjacent to each other.
[3] The seaweed cultivation support according to [1], wherein the cross-sectional area ratio of glass fiber to carbon fiber in the FRP layer is 70:30 to 80:20.
[4] A method for producing a Nori cultivation support pole according to any one of [1] to [3] above, comprising the following steps (i) to (vii):
(i) preparing a required number of carbon fiber bundles and glass fiber bundles as long fiber reinforcing fibers, inserting the carbon fiber bundles and the glass fiber bundles into predetermined guide holes in a collection guide, and arranging them in parallel to each other so that the reinforcing fiber bundles can be taken through an impregnation operation guide in an impregnation tank, a drawing die for longitudinally aligning the bundles in a predetermined arrangement around the outer periphery of the core layer, an extruder for a coating layer, and a production line;
(ii) injecting a liquid curable resin composition containing a thermosetting resin and a thermosetting agent into an impregnation tank;
(iii) a core layer production step in which a thermoplastic resin forming the core layer is continuously extruded from a melt extruder into a cylindrical shape of a predetermined dimension and continuously withdrawn through a production line;
(iv) a step of lowering an impregnation operation guide into an impregnation tank while taking up the reinforcing fiber bundle prepared in (i) above, impregnating the reinforcing fiber bundle with a curable resin composition, and vertically attaching the bundle to the outer periphery of a central core layer running through the center of a hole in a drawing die, and gradually squeezing out the excess resin composition by the drawing die to form an uncured tubular article having a reinforcing fiber bundle vertically attached to the central core layer;
(v) a melt-coating step of passing the uncured tubular article through a crosshead of a melt extruder to extrude the uncured tubular article into a circular shape with a thermoplastic resin for a coating layer, and then cooling the coating layer;
(vi) guiding the coated uncured tubular article into a heat curing tank to heat cure the uncured thermosetting resin composition inside, and withdrawing the tightly integrated composite tubular article; and (vii) cutting the withdrawn tubular article to a predetermined length for use as a seaweed cultivation support.

The Nori cultivation support of the present invention is a composite structure having a core layer made of a thermoplastic resin, an FRP layer formed on the outer periphery of the core layer, and a covering layer formed on the outer periphery of the FRP layer, and the FRP layer has an FRP inner layer and an FRP outer layer, the FRP inner layer has long fiber carbon fiber reinforced fibers on the outer periphery of the core layer in the longitudinal direction, and the FRP outer layer has long fiber glass fiber reinforced fibers on the outer periphery of the FRP inner layer, and the cross-sectional area ratio of the glass fiber to the carbon fiber is within a predetermined range, so that a Nori cultivation support that can eliminate variations in bending strength caused by carbon fibers not being uniformly arranged in the circumferential direction can be provided. And, the Nori cultivation support of the present invention can be made more rigid and lighter at the same outer diameter than a conventional FRP layer made only of glass fiber. Also, if it is desired to have the same rigidity as the conventional one, the outer diameter can be made thinner, which can reduce weight and improve handling due to the thinner diameter.
In addition, the method for manufacturing the Nori cultivation support pole of the present invention can reproducibly, stably, and economically produce the Nori cultivation support pole of the present invention, which is easy to handle by hand, is lightweight yet highly rigid, and is relatively inexpensive and highly practical.

FIG. 4 is a schematic cross-sectional view of a seaweed cultivation support according to Example 2 of the present invention. FIG. 2 is a schematic cross-sectional view of a Nori cultivation support pole according to Comparative Example 2 of the present invention. FIG. 1 is an explanatory diagram of an example of a production line used in the method for producing seaweed cultivation supports of the present invention.

The following describes preferred embodiments of the present invention. Note that the embodiments shown in the attached drawings are intended to illustrate one example of a representative embodiment of the present invention, and the dimensions and other details are not to scale, and the scope of the present invention should not be interpreted narrowly based on these drawings.

The seaweed cultivation support pole of the present invention is a seaweed cultivation support pole of a tightly integrated composite structure having a core layer made of a thermoplastic resin, an FRP layer formed on the outer periphery of the core layer, and a covering layer formed on the outer periphery of the FRP layer, at least the outer periphery of the core layer is made of a thermoplastic resin that has chemical affinity with the thermosetting resin that is the matrix component constituting the FRP layer, the FRP layer has an FRP inner layer and an FRP outer layer, and the FRP inner layer has long fiber-like carbon fiber on the outer periphery of the longitudinal direction of the core layer. The FRP outer layer is made of long glass fibers that are mainly reinforcing fibers and are bonded vertically with a matrix component to the outer periphery of the FRP inner layer, the cross-sectional area ratio of the glass fibers to the carbon fibers in the cross section of the FRP layer is 60:40 to 90:10, and at least the inner surface of the coating layer is made of a thermoplastic resin that has chemical affinity with the thermosetting resin that is the matrix component that constitutes the FRP layer.

As shown in Figure 1, which shows an example of a layer structure in a cross section perpendicular to the longitudinal direction, the seaweed cultivation support 4 of the present invention is formed from a core layer 1 made of thermoplastic resin, an FRP inner layer 21 in which carbon fiber bundles (commonly called "carbon fiber tows") 2a and glass fiber bundles (commonly called "glass fiber rovings") 2b having a predetermined cross-sectional area ratio as reinforcing fibers are bound together with a cured thermosetting resin 2c as a matrix component, and a coating layer 3 made of thermoplastic resin formed on the outer periphery of the FRP outer layer 22.
The Nori cultivation pole 4 of the present invention has an outer diameter of approximately 35 mm to 60 mm, due to the rigidity required to support the Nori net and to withstand waves when erected in the sea, and this outer diameter is used as the main part erected on the seabed. There is a cone-shaped tip at the end facing the seabed, and a tip called an antenna with an outer diameter of 10 to 20 mm and a length of 1 to 2.0 m is connected via a joint to the sea surface side, to ensure that the net rope is held in place at high tide. The present invention relates to the main part of the Nori cultivation pole, and its length is approximately 4 to 15 m due to the relationship with the sea depth of the fishing ground.

(Thermoplastic resin of the core layer)
In the present invention, the core layer is produced by melt extrusion of a thermoplastic resin. At least the outer periphery of the core layer must be in close contact (bonded) with the interface of the FRP inner layer through chemical affinity. For this reason, the thermoplastic resin used for the core layer is selected from thermoplastic resins that have chemical affinity with the thermosetting resin that is the matrix component constituting the FRP layer, such as ABS (acrylonitrile-butadiene-styrene resin), AES (acrylonitrile-ethylene-propylene-rubber-styrene resin), AS (acrylonitrile-styrene resin), AAS (acrylonitrile-acrylic-styrene resin), PS (polystyrene resin), PC (polycarbonate resin), PPE (modified polyphenylene ether resin; graft copolymer of polyphenylene and polystyrene), polyvinyl chloride resin, etc.
The inner diameter of the core layer is about 30.5 to 50.5 mm, and the layer thickness is about 1.5 to 3.0 mm. At least the outer peripheral surface of the core layer needs to have chemical affinity with the thermosetting resin that is the matrix component constituting the FRP layer, and the outer peripheral surface may be formed by multi-layer extrusion of the above-mentioned thermoplastic resin that is compatible with the matrix component or a thermoplastic resin copolymer modified to improve adhesion.

[FRP layer]
The FRP layer of the seaweed cultivation support of the present invention has an FRP inner layer and an FRP outer layer, the inner FRP layer being mainly made of long fiber carbon fibers as reinforcing fibers bonded longitudinally to the outer periphery of the longitudinal direction of the core layer with a matrix component, and the outer FRP layer being mainly made of long fiber glass fibers as reinforcing fibers bonded longitudinally to the outer periphery of the FRP inner layer with a matrix component, and the cross-sectional area ratio of the glass fibers to the carbon fibers in the cross section of the FRP layer is 60:40 to 90:10.
In relation to the manufacturing method of the seaweed cultivation support of the present invention described above, the FRP layer is first formed by impregnating long carbon fiber bundles and glass fiber bundles assembled in a predetermined cross-sectional area ratio as reinforcing fibers with a curable resin composition and attaching them vertically to the outer periphery of a continuously extruded core layer, and then gradually squeezing out the excess resin composition using a squeezing die to form an uncured tubular product consisting of two layers: an FRP inner layer with carbon fiber as the reinforcing fiber on the side in contact with the core layer, and an FRP outer layer with glass fiber attached vertically as the reinforcing fiber on the outer periphery, and then proceeding to the next process.
Next, (v) the uncured tubular product is passed through the crosshead of a melt extruder to be extruded and coated in a circular shape with a thermoplastic resin for the coating layer, and the coating layer is cooled in a melt coating process, and (vi) the coated uncured tubular product is introduced into a heat curing tank to heat cure the uncured thermosetting resin composition consisting of two inner layers, and a tubular product having a composite structure in which the core layer, the FRP layer consisting of an inner FRP layer and an outer FRP layer, and the coating layer are tightly integrated is drawn off.

(Cross-sectional area ratio of reinforcing fiber and FRP layer)
In the present invention, the reinforcing fibers are mainly carbon fibers in the inner FRP layer and mainly glass fibers in the outer FRP layer. In the present invention, "mainly reinforcing fibers" means that other functional fibers may be mixed into the carbon fibers or glass fibers depending on the purpose as long as the reinforcing function of the fibers is not impaired. The reinforcing fibers constituting the FRP layer can be fiber bundles of 1,000 to 50,000 reinforcing fibers having an average diameter of 5 to 10 μm. The specific strength of the reinforcing fibers is preferably 1,000 kN·m/kg or more and the specific elastic modulus is preferably 20,000 kN·m/kg or more.
The long fiber reinforcing fibers used in the FRP layer consisting of the inner FRP layer and the outer FRP layer of the Nori cultivation support of the present invention are carbon fiber in the inner FRP layer and glass fiber in the outer FRP layer, with the glass fiber ratio being high. The cross-sectional area ratio of glass fiber to carbon fiber in the FRP layer cross section in the longitudinal direction of the Nori cultivation support is 60:40 to 90:10, more preferably 65:35 to 85:15, and even more preferably 70:30 to 80:20. If the cross-sectional area ratio of glass fiber to carbon fiber in the cross section of the FRP layer is 60:40 to 90:10, i.e., if carbon fiber accounts for 40% or less in area ratio, it is possible to provide a seaweed cultivation support that is inexpensive enough to tolerate the increase in raw material costs due to the carbon fiber and that can exhibit the effects of improving bending strength, bending rigidity, light weight, and workability. If the cross-sectional area ratio is 90:10, i.e., if carbon fiber accounts for 10% or more in area ratio, it is possible to provide a seaweed cultivation support that can exhibit the effects of improving bending strength, bending rigidity, light weight, and workability due to the carbon fiber, and it is easy to evenly arrange the carbon fiber circumferentially in the FRP inner layer, thereby providing a seaweed cultivation support with little variation in bending strength.
By setting the cross-sectional area ratio of glass fiber to carbon fiber in the cross section of the FRP layer at 70:30 to 80:20, it is possible to provide a seaweed cultivation support that is less expensive and has sufficient bending strength and bending rigidity for practical use.
The cross-sectional area ratio of the reinforcing fibers in the cross section of the FRP layer can be determined by calculating the cross-sectional areas of the glass fibers and carbon fibers used in the FRP layer from the number, fineness and density of each fiber used.

Furthermore, the carbon fiber used in the FRP inner layer is preferably arranged such that a plurality of carbon fiber bundles are arranged symmetrically about the central axis on the outer periphery of the core layer, and the carbon fiber bundles are arranged adjacent to each other. "Adjacent" means that the carbon fiber bundles are adjacent to each other, preferably forming a circumferential layer, as shown in the schematic cross-sectional view of Figure 1.
Furthermore, by arranging the carbon fibers (bundles) symmetrically in the FRP inner layer at approximately the same central angle θ with respect to the center of the support, the high elastic modulus carbon fibers are evenly distributed around the circumference, so that the support does not become distorted in the longitudinal direction or have anisotropy during use, and straightness and straightness recovery to a degree necessary for practical use are maintained.
From the viewpoint of reducing the amount of carbon fiber and maintaining strength, the flatness of the carbon fiber bundle is preferably 0.33 to 0.83, and the aspect ratio is preferably 3:2 to 6:1.

Examples of glass fibers that can be used as reinforcing fibers for the outer FRP layer of the seaweed cultivation support of the present invention include E glass fiber (for electrical use), C glass fiber (for corrosion resistance), S glass fiber, T glass fiber, etc. As for the fiber form, glass roving, which is a bundle of glass fibers (filaments), is suitable for use in the FRP layer. Examples of glass fibers that can be used include products manufactured by Nitto Boseki Co., Ltd. under the names RS110QL-533AH, RS220RL-510AH, and RS440RR-531AH; products manufactured by Central Glass Co., Ltd. under the names ERS2200-820/LX and ERS4400-820/LX; products manufactured by Chongqing International Composite Materials Co., Ltd. (CPIC) under the names ER469-4400 and ER469-2200; and products manufactured by Jishi Group Co., Ltd. under the names EDR17-1150-386T and Jishi Group Co., Ltd. EDR22-2200-312T.

Carbon fibers that can be used as reinforcing fibers for the inner layer of the FRP of the seaweed cultivation support of the present invention include, for example, polyacrylonitrile (PAN)-based carbon fibers made from PAN fibers, pitch-based carbon fibers made from petroleum tar or petroleum pitch, cellulose-based carbon fibers made from viscose rayon or cellulose acetate, vapor-grown carbon fibers made from hydrocarbons, and graphitized fibers of these. Of these carbon fibers, PAN-based carbon fibers are preferred because of their excellent balance between strength and elastic modulus. Examples of carbon fibers that can be obtained and used include Mitsubishi Chemical Corporation's TRW40 50L 3750tex and Zoltek Companies, Inc.'s PX35 (50K).

(Matrix component)
The matrix components of the inner and outer FRP layers of the seaweed cultivation support of the present invention are formed by curing a thermosetting resin composition, such as unsaturated polyester resin, unsaturated carboxylic acid-modified vinyl ester resin, epoxy resin, etc.
Among these, unsaturated polyester resins are preferably used because they are thermosetting and from the viewpoints of versatility, economy, etc.
In addition, the unsaturated polyester resin contains styrene as a monomer component, and can be selected to have chemical affinity with the thermoplastic resin of the core layer and the coating layer, and these three layers can be tightly integrated after heat curing.
The thermosetting resin is prepared as a thermosetting resin composition by mixing a thermosetting catalyst (curing agent), calcium carbonate for viscosity adjustment, and, if necessary, a thixotropic agent such as Aerosil (trade name), which is ultrafine silica particle, and is impregnated into the reinforcing fibers and finally heat-cured to form the matrix component.

(Covering layer)
The covering layer of the seaweed cultivation support of the present invention can also be configured such that the thermoplastic resin constituting at least the inner peripheral surface of the covering layer is selected from thermoplastic resins containing styrene as a component, and the thermosetting resin constituting the matrix component of the FRP layer comes into contact with an unsaturated polyester resin containing a styrene monomer as a monomer component in an uncured state, and the FRP layer/covering layer are bonded and integrated with each other after the thermosetting resin hardens due to chemical affinity.

[Method for manufacturing seaweed cultivation supports]
The method for producing a Nori seaweed cultivation pole of the present invention is characterized by comprising the following steps (i) to (vii). Each step will be described below in order.

As shown in FIG. 3, in this step, a required number of carbon fiber bundles 2a for the FRP inner layer and glass fiber bundles 2b for the FRP outer layer are prepared in a creel 12 and a creel 13, respectively, as fibrous reinforcing fibers. Taking into consideration the arrangement in the FRP layer, an impregnation tank 11a is prepared for the carbon fiber for the FRP inner layer, and an impregnation tank 11b is prepared for the glass fiber for the FRP outer layer. The carbon fiber bundles and the glass fiber bundles are inserted into predetermined guide holes (not shown) in the respective assembly guides (battens) (not shown). These are then arranged in parallel and passed through the impregnation operation guides (not shown) of the impregnation tanks 11a and 11b. During steady running, these are vertically aligned in a predetermined arrangement along the outer periphery of the core layer 1, and prepared so as to be able to be taken up through a squeezing die 7 for squeezing out excess thermosetting resin, a coating layer extruder 8, and the subsequent (downstream) production lines. At this stage of the reinforcing fiber preparation process, the extrusion of the core layer 1, the resin impregnation operation of the reinforcing fiber bundle in the thermosetting resin impregnation tank 11, the squeeze molding, and the coating in the coating extruder 8 are not performed, but rather, this is a process for preparing the reinforcing fibers so that they can be placed on the production line during steady-state operation.

(ii) Preparation of curable resin composition This is a step of injecting a liquid curable resin composition containing a thermosetting resin and a thermosetting agent into the impregnation tanks 11a and 11b. The thermosetting resin is selected from the above-mentioned ones, and the thermosetting resin is stirred and mixed with a predetermined amount of a thermosetting catalyst (curing agent), calcium carbonate for viscosity adjustment, and a thixotropic agent such as Aerosil (trade name) which is ultrafine silica, if necessary, and then stirred and mixed as a thermosetting resin composition, which is then injected into the impregnation tanks 11a and 11b. The stirring and mixing may be performed in advance, or after the transition to a steady production state, a predetermined amount of each of the substances constituting the thermosetting resin composition may be measured and mixed in a mixing device, and the materials may be continuously injected into the impregnation tank in accordance with the consumption of the thermosetting resin composition.

(iii) Core Layer Manufacturing Process The thermoplastic resin forming the core layer 1 is continuously extruded from the melt extruder 5 into a cylindrical shape of specified dimensions while controlling the inner diameter with a mandrel or the outer diameter with a mold, cooled in a cooling tank 6, and continuously drawn off through the subsequent production line in the core layer manufacturing process. Afterwards, the uncured resin composition impregnated into the long reinforcing fibers is squeezed to a specified outer diameter so that it can be coated in the coating melt extruder 8.

(iv) Manufacturing process of uncured tubular section While pulling out the reinforcing fibers prepared in (i) above, an impregnation operation guide (not shown) is lowered toward the impregnation tanks 11a, 11b to impregnate the reinforcing fiber bundle with the curable resin composition, and this is vertically aligned to the outer periphery of the core layer 1 running through the center of the hole of the drawing die 7. The excess resin is gradually squeezed out by the drawing die, to produce an uncured tubular article 14 in which carbon fibers are vertically aligned to the outer periphery of the core layer and glass fibers are further vertically aligned to the outer periphery of the carbon fibers as reinforcing fibers.

(v) Step of Melt Coating and Cooling of Uncured Tubular Article In this melt coating and cooling step, the uncured tubular article 14 is passed through the crosshead of the coating melt extruder 8 to be extruded and coated in an annular shape with a thermoplastic resin for the coating layer, and the coating layer is immediately cooled and solidified in a cooling tank 9 to obtain an uncured tubular article 15 with a coating layer.

(vi) Heat curing and taking-up process of the uncured tubular article with coating layer In this process, the uncured tubular article with coating layer 15 is introduced into a heat curing tank 10 to heat cure the uncured thermosetting resin composition inside, and the composite structure tubular article (composite tubular article) 16 in which the core layer 1, FRP inner layer 21, FRP outer layer 22, and coating layer 3 are tightly integrated is taken up by a rubber belt type or caterpillar type take-up machine (not shown) or the like.

(vii) Step of cutting the composite tubular product to a predetermined length Since the composite tubular product 16 thus taken up has high rigidity and is difficult to wind on a drum or the like, it is cut to a predetermined length according to the length required for use.

(Other processes)
Although detailed description is omitted since it is not the main part of the present invention, the cut composite tubular object obtained as described above is used as the main part of a support for Nori cultivation, with one end connected to a conical tip member (not shown) for piercing the seabed, and the other end connected to a thin composite tubular object of a predetermined length as a tip member (so-called "antenna") via a connecting member, to serve as a support for Nori cultivation. It is efficient to connect these members on a line that is continuous with the cutting process.

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. The following description will also refer to the drawings.

Example 1
The composite tubular body of the support for seaweed cultivation was made using the materials shown below.
[Material composition]
(Thermoplastic resin for core layer)
ABS resin: Toyolac (registered trademark) 600-309N, manufactured by Toray Industries, Inc.
(Thermosetting resin composition)
100 parts by mass of unsaturated polyester resin: U-PICA (registered trademark) 3464, manufactured by Japan U-PICA Corporation
Calcium carbonate 10 parts by mass: LW350, manufactured by Shimizu Kogyo Co., Ltd.
Organic peroxide-1 4 parts by mass: Kayaester (registered trademark) O-50E, manufactured by Kayaku Nouryon Co., Ltd.
Organic peroxide-2 1 part by mass: Trigonox (registered trademark) 117, manufactured by Kayaku Nouryon Co., Ltd.
(Reinforced Fiber)
Carbon fiber tow 16 pieces: PYROFIL (registered trademark), TRW40 50L, manufactured by Mitsubishi Chemical Corporation
Glass fiber roving 114 strands: RS220RL-510AH (2200tex), manufactured by Nitto Boseki Co., Ltd.
(Thermoplastic resin for coating)
ABS resin: Toray Industries, Inc., Toyolac (registered trademark) 600-309N, FB-1682 (black colored masterbatch)
(Preparation of Uncured Thermosetting Resin Composition)
As the uncured thermosetting resin composition to be impregnated into the reinforcing fibers constituting the inner and outer layers of the FRP, the above-mentioned unsaturated polyester resin, organic peroxide, and calcium carbonate as a filler were each measured in predetermined amounts, stirred and mixed in a mixing tank equipped with a stirrer, and then injected into the impregnation tanks 11a and 11b.

As shown in FIG. 3, the above ABS resin was continuously extruded from a melt extruder 5 for the core into a pipe shape having an outer diameter of 37.6 mm and an inner diameter of 33.6 mm as the core layer 1 .
The FRP layer formed on the outer periphery of the core was formed by forming an inner layer and an outer layer based on a two-stage reinforcing fiber squeezing method. Carbon fiber was used for the FRP inner layer, and in order to arrange it on the inner periphery of the FRP layer, the carbon fiber bundles arranged on a creel 12 (details not shown) were bundled and impregnated with the thermosetting resin composition of the impregnation layer 11a, and then guided stepwise to a plurality of drawing die devices 7 so that the fiber density [fiber volume/(fiber volume+thermosetting resin volume] when only the carbon fiber was arranged was 48 volume %. Glass fiber was used for the FRP outer layer, and in order to arrange it on the outer periphery of the FRP layer, the glass fiber bundles arranged on a creel 13 (details not shown) were bundled and impregnated with the thermosetting resin composition of the impregnation layer 11b, and then guided along the outer periphery side of the already squeezed carbon fiber, and finally guided to a plurality of drawing die devices 7 where the inner diameter gradually converges to the outer diameter of the FRP layer, 41.5 mm.
That is, a layer formed of carbon fiber and a curable resin composition impregnated therein was attached to the outer periphery of the core layer, and glass fiber and a curable resin composition impregnated therein were arranged on the outer periphery of the core layer and were then molded in a final drawing die to obtain an uncured tubular product 14 having an outer diameter of 41.5 mm. This was then introduced into the crosshead of the melt extruder 8 for the coating layer to obtain an uncured tubular product 15 with a coating layer.
The uncured tubular product 15 with the coating layer was then introduced into a thermal curing bath 10 using hot water as a heat medium to thermally cure the uncured FRP layer inside, and cooled in a cooling water bath (not shown) to obtain a three-layered composite tubular product 16 consisting of a core layer, an inner layer, an outer layer, an FRP layer, and a coating layer, which was then cut into a length of 10 m by a cutting device (not shown). The outer diameter of the resulting support (composite tubular product) was 42.8 mm, and the FRP layer thickness was 2.0 mm. The cross-sectional area ratio of glass fiber/carbon fiber, bending strength, etc. of the resulting support are summarized in Table 1.

Example 2
In Example 1, a core having an outer diameter of 41.0 mm and an inner diameter of 37.0 mm was extruded into a pipe shape, and the carbon fiber tows and glass fiber rovings were changed to 16 and 150, respectively, and the FRP layer outer diameter was changed to 45.1 mm, the FRP layer thickness to 2.1 mm, and the coating layer outer diameter to 46.2 mm. A 10 m long pillar sample was obtained in the same manner as in Example 1. The outer diameter of the obtained pillar was 46.2 mm. A schematic cross-sectional view of the obtained pillar is shown in FIG. 1. In the FRP inner layer 21, 16 carbon fibers (bundles) 2a were arranged adjacent to each other.

Example 3
A 10 m long pillar sample was obtained in the same manner as in Example 2, except that the number of carbon fiber tows was changed to 24 and the number of glass fiber rovings was changed to 114. The outer diameter was 46.2 mm.

Example 4
A 10 m long pillar sample was obtained in the same manner as in Example 2, except that the carbon fiber tows were changed to 12 and the glass fiber roving was changed to 78 strands of RS440RR-531AH (4400 tex) manufactured by Nitto Boseki Co., Ltd. The outer diameter was 46.2 mm.

Comparative Example 1
In Example 1, 114 glass fiber rovings were prepared in creel 12, and 16 carbon fiber tows were prepared in creel 13. These were impregnated with a curable resin composition, and the order of longitudinally aligning them in the longitudinal direction of the core layer was reversed to that in Example 1. A 10 m long support sample was obtained in the same manner. The outer diameter was 42.8 mm.

Comparative Example 2
In Example 2, 150 glass fiber rovings were prepared in creel 12, and 16 carbon fiber tows were prepared in creel 13. These were impregnated with a curable resin composition, and the order of longitudinally aligning the core layer was reversed from that in Example 2. A 10 m long support sample was obtained in the same manner. The outer diameter was 46.2 mm.
As shown in the schematic cross-sectional view of FIG. 2, the carbon fibers in the cross section were in a state where the carbon fiber bundles were not adjacent to each other on the outermost peripheral side of the FRP layer, but had gaps therebetween.

Comparative Example 3
In Example 3, 114 glass fiber rovings were prepared in creel 12, and 24 carbon fiber tows were prepared in creel 13. These were impregnated with the curable resin composition, and the order of longitudinally aligning them in the longitudinal direction of the core layer was reversed to that in Example 3. A 10 m long support sample was obtained in the same manner. The outer diameter was 46.2 mm.

Comparative Example 4
In Example 4, 78 glass fiber rovings were prepared in creel 12, and 12 carbon fiber tows were prepared in creel 13. These were impregnated with a curable resin composition, and the order of longitudinally aligning the core layer was reversed to that in Example 4. A 10 m long support sample was obtained in the same manner. The outer diameter was 46.2 mm.

Comparative Example 5
A 10 m long support sample was obtained in the same manner as in Example 2, except that the number of glass fiber rovings was changed to 188 and no carbon fiber tow was used. The outer diameter was 46.2 mm.

<Evaluation of seaweed cultivation support samples obtained in the Examples and Comparative Examples>
(Cross-sectional dimensions of the support sample)
The specimen was cut perpendicular to the longitudinal direction with a circular saw-type tipped saw cutter, and the inner and outer diameters of the core layer, the outer diameter of the FRP layer, and the outer diameter of the coating layer in the cross section were measured with a vernier caliper (CD-20CPX, manufactured by Mitutoyo Corporation). The number of measurements, n, was 5, and the average was used.
(Volume content of reinforcing fibers in FRP layer, and cross-sectional area ratio of glass fibers to carbon fibers in cross section of FRP layer)
The cross-sectional area Sf of the FRP layer is calculated from the above cross-sectional dimensions. The cross-sectional area Sg of the glass fiber and the cross-sectional area Sc of the carbon fiber are calculated from the number of glass fiber rovings and carbon fiber tows used in each Example and Comparative Example, and their respective fineness and density, and the calculation is performed using [(Sg + Sc) / Sf] x 100.
The cross-sectional area ratio of the glass fibers to the carbon fibers in the cross section of the FRP layer was expressed using the cross-sectional area Sg of the glass fibers and the cross-sectional area Sc of the carbon fibers.
The calculation was made assuming a density of 2.54 g/ ^cm3 for the glass fiber roving (RS220RL-510AH and RS440RR-531AH: E glass, manufactured by Nitto Boseki Co., Ltd.) and a density of 1.81 g/ ^cm3 for the carbon fiber tow (PYROFIL (registered trademark), TRW40 50L, manufactured by Mitsubishi Chemical Corporation).

(Bending strength)
With reference to JIS K 7074:1988, measurements were performed in a three-point bending test (n=10) under the following conditions.
Bending direction: A sample of a composite tubular object (fiber-reinforced resin tubular body) used as the main support for seaweed cultivation was bent perpendicular to the longitudinal direction and in the direction in which the diameter of the fiber-reinforced resin tubular body was shortest (the direction perpendicular to the parallel portion).
Diameter D of test piece: The width of the fiber reinforced resin tubular body in the load direction directly under the indenter was measured with a vernier caliper (n = 1).
- Support radius: 2.0 mm
Indenter radius: 5.0 mm
Distance between supports _Lm : (40±8)×D mm (JIS requires calculation based on the thickness H of the solid body, but this was calculated based on the diameter D of the test piece)
Test piece length l _m : L _m + 660 mm
Test speed: 20 mm/min (JIS: 0.01 _L/m2 ^/ 6H)
・Flexural strength (N): Maximum bending stress applied to the test piece

(Variation in bending strength)
Using the above method, measurements were taken for n=10 samples of seaweed cultivation supports from the Examples and Comparative Examples, and the minimum, maximum, average and standard deviation of bending strength (N) were calculated. The standard deviation was then divided by the average to obtain the coefficient of variation (%) expressed as a percentage.

Table 1 shows the outer diameter and thickness of the FRP layer of the seaweed cultivation support samples of each Example and Comparative Example, the fineness (tex) and number of glass fiber bundles and carbon fiber bundles (tows) used, the volume content (%) of reinforcing fibers in the FRP layer, the cross-sectional area ratio of glass fiber to carbon fiber in the FRP layer, the outer diameter of the support, the location of the carbon fiber in the FRP layer, and the bending strength.

As shown in Table 1, Example 1 and Comparative Example 1 use the same number of glass fiber rovings, 114 and carbon fiber tows, 16, and while Example 1 uses carbon fiber in the inner layer of the FRP, Comparative Example 1 places the carbon fiber on the outside (outermost layer) of the FRP layer. Comparing the two, Comparative Example 1 has a larger standard deviation of bending strength than Example 1, with a coefficient of variation of 15.1%, more than double the 7.3% of Example 1.
In Example 2, in which the volume content of the reinforcing fibers in the FRP layer was 58.8 volume % and the carbon fibers were arranged in the inner FRP layer, and in Comparative Example 2, in which the carbon fibers were arranged on the outside of the FRP layer, the coefficients of variation were 6.0% and 11.9%, respectively, a difference of approximately two times.
In addition, in Example 3 and Comparative Example 3, in which the cross-sectional area ratio of the carbon fiber was increased to 33.5, the coefficient of variation in Example 3, in which the carbon fiber was arranged in the inner layer of the FRP, was 4.7%, while in Comparative Example 3, in which the carbon fiber was arranged on the outside of the FRP layer, the coefficient of variation was 9.2%, a difference of approximately two times.
On the other hand, in Example 4 and Comparative Example 4, in which the cross-sectional area ratio of the carbon fiber was 15.6, the coefficient of variation was 7.3% and 13.6%, respectively, a difference of about 1.9 times, due to the difference in the arrangement position of the carbon fiber as described above.

On the other hand, in Comparative Example 5, no carbon fiber was used, and only glass fiber was used as the reinforcing fiber, with a glass fiber volume content of 58.7%, which is similar to that of Example 2 and Comparative Example 2 in terms of the volume content of the reinforcing fiber. However, the coefficient of variation for Comparative Example 5 was 5.0%, for Example 2 it was 6.0%, and for Comparative Example 2 it was 11.9%, and it was confirmed that Example 2 had the same variation in bending strength as the support sample of Comparative Example 5, which is a seaweed cultivation support made of conventional glass fiber reinforced FRP.
In addition, in the other examples, the coefficient of variation was 4.7 to 7.3%, which was confirmed to be approximately the same variation in bending strength as that of conventional glass fiber reinforced FRP seaweed cultivation supports.

The Nori cultivation support of the present invention has carbon fiber arranged in the inner FRP layer, so it can naturally be used as a Nori cultivation support that is more rigid and lighter than the conventional FRP layer that is constructed only of glass fiber for the same outer diameter. In addition, it is possible to uniform the bending strength at the circumferential part in the longitudinal cross section where stress is applied, which improves the efficiency of installation in the sea. Furthermore, there is no variation in the function of the support when stretching the Nori net and cultivating Nori, so it can be effectively used as a Nori cultivation support that is suitable for management during the cultivation work.
Furthermore, if it is desired to achieve the same level of rigidity as conventional FRP pillars that use only glass fiber as the reinforcing fiber, the outer diameter can be made thinner, allowing the pillars to be used as seaweed cultivation pillars that are lighter in weight and easier to handle due to the thinner diameter.
In addition, the method for manufacturing a seaweed cultivation support of the present invention can achieve more uniform bending strength at circumferential parts in the longitudinal cross section to which stress is applied, and therefore can be used as a method for reproducibly, stably, and economically manufacturing the seaweed cultivation support of the present invention, which is easy to handle by hand, lightweight, and highly rigid, and is relatively inexpensive and highly practical.

1 Core layer 2 FRP layer 2a Carbon fiber bundle (glass fiber in the comparative example)
2b Glass fiber bundle (carbon fiber in the comparative example)
2c Thermosetting resin cured material (matrix component)
3 Thermoplastic resin coating layer 4 Support for seaweed cultivation (composite tubular object)
5 Melt extruder for core 6 Cooling tank for core 7 Drawing die device 8 Melt extruder for covering layer 9 Cooling tank 10 Heat curing tank 11 Impregnation tank 11a Impregnation tank for FRP inner layer 11b Impregnation tank for FRP outer layer 12 Creel (for reinforcing fiber bundles for FRP inner layer)
13 Creel (for reinforcing fiber bundles for the outer layer of FRP)
14 Uncured tubular article 15 Uncured tubular article with coating layer 16 Composite tubular article 21 FRP inner layer 22 FRP outer layer

Claims (4)

A seaweed cultivation support pole having a tightly integrated composite structure including a core layer made of a thermoplastic resin, an FRP layer formed on the outer periphery of the core layer, and a covering layer formed on the outer periphery of the FRP layer,
the core layer is made of a thermoplastic resin having chemical affinity with the thermosetting resin, which is a matrix component constituting the FRP layer, at least on its outer peripheral surface;
The FRP layer has an inner FRP layer and an outer FRP layer,
The FRP inner layer is bonded to the outer periphery of the core layer in the longitudinal direction with a matrix component, with long fiber carbon fibers as the main reinforcing fibers, and the FRP outer layer is bonded to the outer periphery of the FRP inner layer with a matrix component, with long fiber glass fibers as the main reinforcing fibers,
a cross-sectional area ratio of the glass fibers to the carbon fibers in a cross section of the FRP layer is 60:40 to 90:10;
The covering layer is characterized in that at least its inner surface is made of a thermoplastic resin that has chemical affinity with the thermosetting resin that is the matrix component constituting the FRP layer. The seaweed cultivation support pole according to claim 1, in which a plurality of carbon fiber bundles are arranged symmetrically around the central axis on the circumference of the FRP inner layer, and the carbon fiber bundles are arranged adjacent to each other. The seaweed cultivation support according to claim 1, wherein the cross-sectional area ratio of glass fiber to carbon fiber in the FRP layer is 70:30 to 80:20. A method for producing a Nori cultivation support pole according to any one of claims 1 to 3, characterized in that it comprises the following steps (i) to (vii):
(i) preparing a required number of carbon fiber bundles and glass fiber bundles as long fiber reinforcing fibers, inserting the carbon fiber bundles and the glass fiber bundles into predetermined guide holes in a collection guide, and arranging them in parallel to each other so that the reinforcing fiber bundles can be taken through an impregnation operation guide in an impregnation tank, a drawing die for longitudinally aligning the bundles in a predetermined arrangement around the outer periphery of the core layer, an extruder for a coating layer, and a production line;
(ii) injecting a liquid curable resin composition containing a thermosetting resin and a thermosetting agent into an impregnation tank;
(iii) a core layer production step in which a thermoplastic resin forming the core layer is continuously extruded from a melt extruder into a cylindrical shape of a predetermined dimension and continuously withdrawn through a production line;
(iv) a step of lowering an impregnation operation guide into an impregnation tank while taking up the reinforcing fiber bundle prepared in (i) above, impregnating the reinforcing fiber bundle with a curable resin composition, and vertically attaching the bundle to the outer periphery of a central core layer running through the center of a hole in a drawing die, and gradually squeezing out the excess resin composition by the drawing die to form an uncured tubular article having a reinforcing fiber bundle vertically attached to the central core layer;
(v) a melt-coating step of passing the uncured tubular article through a crosshead of a melt extruder to extrude the uncured tubular article into a circular shape with a thermoplastic resin for a coating layer, and then cooling the coating layer;
(vi) guiding the coated uncured tubular article into a heat curing tank to heat cure the uncured thermosetting resin composition inside, and withdrawing the tightly integrated composite tubular article; and (vii) cutting the withdrawn tubular article to a predetermined length for use as a seaweed cultivation support.