Cylindrical foam molded body and method for producing cylindrical foam molded body

Abstract

To provide a cylindrical foam molded body (regenerated float) that has undergone a molding treatment for restoring buoyancy of a used foam float previously discarded, and to provide a method for producing the cylindrical foam molded body (regenerated float).SOLUTION: A cylindrical foam molded body (regenerated float) 1 according to the present invention has a layered structure in which an inner-layer foam molded body (used float 2) and an outer-layer foam molded body 3 covering the inner-layer foam molded body are integrally molded, and has a cylindrical shape having a diameter (D) of 100 mm or more and 800 mm or less and a length (L) of 100 mm or more and 1500 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cylindrical foam molded article and a method for producing the same. [Background technology]

[0002] While environmental pollution, including global warming, is being pointed out, marine pollution, primarily caused by plastic waste, is becoming increasingly serious, and the possibility that the amount of plastic waste discarded in the ocean may exceed the total amount of marine resources is being discussed as a realistic issue. On the other hand, there are also concerns that marine organisms may prey on microplastics that have been denatured by marine plastic waste, which cannot be digested in the body and can have life-or-death effects, and that microplastics, which are essentially microplastics that have been broken down to an invisible level, may enter the ecosystem at the cellular level through the food chain, causing genetic effects such as mutations.

[0003] According to statistics published by the Ministry of the Environment for fiscal year 2018, an estimated 32,000 tons of driftwood was counted along Japan's coastlines, with approximately 60 vol% being plastic waste and approximately 40 vol% originating from fishing gear. Foam float waste generated from foam floats used in marine aquaculture, etc., is the second largest source of waste after fishing nets and ropes, and is estimated to account for 10 vol% of the total. Legal interpretation requires fishermen to dispose of foam floats used in marine aquaculture as industrial waste at their own risk. Meanwhile, active efforts are encouraged to reuse reusable fishing gear, and the same is recommended for foam floats.

[0004] In marine aquaculture, the role of foam floats as fishing gear is to provide buoyancy (see, for example, Patent Document 1). Nets used in marine aquaculture have a box-like structure, with five surfaces (four walls and a bottom) made of netting. Marine aquaculture involves raising fish from juvenile to adult within these net bags in the ocean. The open tops of these nets must be kept at a certain height above the sea surface, otherwise the fish will escape. To prevent this, the upper edges of the net bags are typically secured with iron frames made of metal pipes. The iron frames of the net bags, which are integrated with the iron frames, are then fastened together with the foam floats to form a marine aquaculture net. The weight of the iron frames and nets is generally estimated to be around 6 tons. For example, taking the commonly used #300 float as an example, #300 floats are designated by their size #300 because they have a volume of approximately 300 L, but they are also known to generate approximately 300 kg of buoyancy in the ocean. Regarding the marine aquaculture nets, which have a total weight of 6 tons, it is said that in order to stably maintain the opening above the waterline at the sea surface, 20 #300 foam floats should be fastened to an iron frame to ensure a stable aquaculture fishing ground.

[0005] When first installed, these aquaculture farms function without any problems, but as time passes, it is often observed that it becomes difficult to maintain buoyancy due to erosion caused by the natural environment, such as damage and destruction by birds and animals from the outer periphery of the foam floats, powdering due to ultraviolet rays, and the attachment of shellfish such as barnacles and seaweed.

[0006] As fishermen observe and manage these changes, they will need to carry out tasks such as replacing foam floats to maintain the aquaculture grounds. Floats that are replaced for some reason are often disposed of as industrial waste, but because disposal also incurs costs, they are sometimes stored in open piles on coastlines for the purpose of efficient disposal. However, there are times throughout the year when the sea is rough, and unfortunately, foam floats stockpiled on coastlines can be swept away by the waves. Such spills occur frequently, and it is said that some cases may even be intentional. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-171721 Summary of the Invention [Problem to be solved by the invention]

[0008] One of the reasons for these types of outflow accidents is the fact that fishermen are responsible for disposing of used floats as industrial waste. Foam floats must be replaced when they lose buoyancy, but if it were possible to repair them, restore their original buoyancy, and offer them for reuse, floats that have been considered used until now would not lose their asset value, and outflow accidents would decrease.

[0009] Therefore, the present invention aims to provide a cylindrical foam molded body (recycled float) that has been subjected to a molding process to restore the buoyancy of used foam floats that have previously been discarded, and to provide a manufacturing method for producing a cylindrical foam molded body (recycled float). [Means for solving the problem]

[0010] The present invention has a layer structure in which an inner layer foam molded body and an outer layer foam molded body covering the inner layer foam molded body are integrally molded, It is cylindrical with a diameter (D) of 100 mm or more and 800 mm or less, and a length (L) of 100 mm or more and 1500 mm or less. It is a cylindrical foam molded body.

[0011] The present invention also provides a method for producing the cylindrical foamed molded article of the present invention, comprising: After the inner layer foam molded body is set in a mold that seals and opens, repair foam particles are filled into the gap between the mold and the inner layer foam molded body, and then the molded body is heated to form the outer layer foam molded body so as to cover the inner layer foam molded body. This is a method for producing a cylindrical foamed molded article. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a cylindrical foam molded body (recycled float) that has been subjected to a molding process to restore the buoyancy of a used foam float that has previously been discarded, and it is also possible to provide a manufacturing method for manufacturing a cylindrical foam molded body (recycled float). [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an example of an embodiment of a cylindrical foam molded article of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing another embodiment of the cylindrical foam molded article of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, preferred embodiments of the cylindrical foam molded article (recycled float) of the present invention and its manufacturing method will be described in detail. Fig. 1 is a cross-sectional view showing one embodiment of the cylindrical foam molded article of the present invention, and Fig. 2 is a cross-sectional view showing another embodiment of the cylindrical foam molded article of the present invention. As shown in FIG. 1, the cylindrical foam molded body (recycled float) 1 according to this embodiment has a cylindrical shape and a layered structure in which an inner layer foam molded body (used float) 2 and an outer layer foam molded body 3 that covers the inner layer foam molded body 2 are integrally molded. The recycled float 1 is preferably used as a net end (float). The recycled float 1 has a cylindrical shape with a diameter (D) of 100 mm or more and 800 mm or less, and a length (L) of 100 mm or more and 1500 mm or less. Furthermore, the bulk density of the recycled float 1 is preferably 60 g / L or less, and more preferably 50 g / L or less. The replacement of used floats 2 with reduced buoyancy is often determined by the experience and intuition of fishermen managing the aquaculture site. Generally, the threshold for replacement is considered to be when the buoyancy falls below 85%, assuming 100% buoyancy at the time of installation. As long as foamed molded articles with an expansion ratio of over 20 are used as floats, buoyancy generally correlates with the volume of the molded article. In other words, the buoyancy retention rate (or buoyancy recovery rate after regeneration) can be defined as (current buoyancy of the foamed molded article) / (buoyancy at the time of installation). However, if measuring buoyancy is difficult, (current volume of the foamed molded article) / (volume of the molded article at the time of installation) can be used as an approximation. Maintaining and restoring buoyancy is important for the performance of recycled floats 1. Therefore, the buoyancy of recycled floats 1 is preferably 90% or more, and more preferably 95% or more, of the buoyancy at the time of installation. A buoyancy below 90% is undesirable because it may shorten the time until replacement.

[0015] In this embodiment, the method for producing a recycled float 1 (cylindrical foam molded product) involves setting a used float 2 (inner layer foam molded product) in a mold that seals and opens, filling the gap between the mold and the used float 2 with repair foam particles described below, and then heat molding to form an outer layer foam molded product 3 so as to cover the used float 2. That is, the method for producing a recycled float 1 (cylindrical foam molded product) includes the steps of setting a used float 2 (inner layer foam molded product) in a mold that seals and opens, and filling the gap between the mold and the used float 2 with repair foam particles described below, and then heat molding, whereby an outer layer foam molded product 3 is formed so as to cover the used float 2, and a recycled float 1 is obtained.

[0016] The used float 2 to be recycled is a foam molded body that is exposed after removing the surface protective cover that covers the outer periphery and the resin molded product that covers the surface when it is pulled up from the water body. In the case of a foam molded body that does not have a resin molded product or sheet-like cover for surface protection, it can be used in the recovered state. The used float 2 to be recycled can be used in the recovered state and does not need to maintain its shape as a single unit. However, it is preferable to retain it as a single unit with a volume of approximately 30% or more of the float before recycling. A single unit is preferable because it facilitates retention in the center of the molding cavity of the recycling mold. Maintaining this state in the center of the molding cavity makes it easy to mold the recycled float 1 by filling the outer periphery of the block with repair foam particles and molding it into a single unit. Even if the float is broken into multiple pieces, recycling is possible without any problems if the float can be accommodated in the mold and uniformly filled with repair foam particles. However, if the used float is broken into multiple pieces during recovery and cannot be accommodated in the mold, it can be preliminarily connected using connecting means 4 to make it possible to accommodate it, as shown in Figure 2, and then placed in the mold for recycling. Preliminary connecting means may be any method necessary for accommodating the float in the mold, such as using adhesives, pressure-sensitive adhesives, strings, or wires.

[0017] Used floats 2 that are recovered and reused are often eroded from the outer periphery of the molded product. The eroded surface has a non-uniform appearance, with the skin of the foam particles peeling off and air bubbles exposed. Some floats tend to be powdered by ultraviolet light, soiled with sediment or sand, or have barnacles and other shellfish attached, or seaweed and algae growing on them. Because the float's primary purpose is to maintain buoyancy at the aquaculture site, as long as the final recycled float 1 is a single piece, it can be recycled using foam particles to restore the outer periphery to its original shape, regardless of dirt or foreign matter. However, if dirt or foreign matter is mixed into the recycled product and could impair buoyancy, or if excessive open-cell formation could cause problems with the recycled mold, it is preferable to clean or remove foreign matter, or to cut or grind the surface before recycling.

[0018] When regeneration molding is performed, the used float 2 must be sufficiently dried. Regarding the degree of drying, the weight change between the weight W0 of the used float before regeneration molding and the weight Wd of the used float after drying in a 40°C oven for 30 minutes is preferably 30% or less, and more preferably 10% or less. A weight change of 30% or more is undesirable because the moisture contained in the used float, primarily water, can affect the heating during regeneration molding, causing temperature variations inside the mold and potentially resulting in molding defects. The closer the weight change rate is to zero, the more stable the conditions for regeneration molding become. However, considering the costs spent on molding management, it is not necessarily required to be zero; a weight change rate of 10% or less is preferable because it allows regeneration molding to be performed without any problems.

[0019] The 90°C weight loss rate of the used float 2 (inner layer foam molded article) is preferably 2.5% or less. Also, the 90°C volume shrinkage rate of the used float 2 (inner layer foam molded article) is preferably 10% or less. Here, the 90°C weight loss rate and the 90°C volume shrinkage rate are measured by the following procedure. 1. Measure the weight (W1) and volume (V1) of a portion (sample) of used float 2 cut out at random from the used float 2, approximately 1 L in volume. (Note that volume measurement is performed by the submersion method. The same applies below.) 2. Next, place the sample in a hot air circulating dryer heated to 90°C and leave it for 24 hours. 3. After 24 hours, remove the sample from the hot air circulating dryer and leave it for about 30 minutes. 4. Next, measure the weight (W2) and volume (V2) of the sample. 5. Then, calculate the 90°C weight loss rate and 90°C volume shrinkage rate using the following formulas. 90℃ weight loss rate=(W1-W2) / W1×100 Volumetric shrinkage at 90°C = (V1 - V2) / V1 x 100

[0020] The material of the used float 2 is not particularly limited, but may be a polystyrene-based expanded particle molded body, a polypropylene-based expanded particle molded body, a polyethylene-based expanded particle molded body, a polyethylene terephthalate-based expanded particle molded body, a polymethyl methacrylate-based expanded particle molded body, a polylactic acid-based expanded particle molded body, a polyglycolic acid-based expanded particle molded body, a poly(β-hydroxybutyric acid)-based expanded particle molded body, or a poly(β-hydroxybutyric acid-co-β-hydroxyvaleric acid) Preferred examples of the resins include expanded bead molded bodies, poly-β-propiolactone-based expanded bead molded bodies, poly-ε-caprolactone-based expanded bead molded bodies, polyethylene succinate-based expanded bead molded bodies, polybutylene succinate-based expanded bead molded bodies, poly(butylene succinate-co-butylene adipate)-based expanded bead molded bodies, poly(β-hydroxybutyrate-co-3-hydroxyhexanoate)-based expanded bead molded bodies, and expanded bead molded bodies made by blending two or more of these resins. The density of the used float 2 is preferably 100 g / L or less. A density exceeding 100 g / L is undesirable because not only does the recycled product tend to lack buoyancy, but the center of gravity of the recycled product tends to become unstable. It is preferable to collect and reuse used floats 2 that have been installed for at least three months. More preferably, the density is six months or more, and preferably one year or more. Those that are less than three months old are not preferred because the molding range of the regenerated mold tends to be narrow.

[0021] The outer foam molded body 3 is preferably made of repair foam particles. There are no particular limitations on the material of the repair foam beads (material of the outer foam molded body 3) as long as they are regenerative foam beads that can be integrated with the used float 2 and restore buoyancy. Therefore, there are no particular restrictions on the material, but for example, polystyrene-based expanded particles, polypropylene-based expanded particles, polyethylene-based expanded particles, polyethylene terephthalate-based expanded particles, polymethyl methacrylate-based expanded particles, polylactic acid-based expanded particles, polyglycolic acid-based expanded particles, poly(β-hydroxybutyric acid)-based expanded particles, poly(β-hydroxybutyric acid-co-β-hydroxyvaleric acid)-based expanded particles, poly-β-propiolactone-based expanded particles, poly-ε-caprolactone-based expanded particles, polyethylene succinate-based expanded particles, polybutylene succinate-based expanded particles, poly(butylene succinate-co-butylene adipate)-based expanded particles, poly(β-hydroxybutyric acid-co-3-hydroxyhexanoic acid)-based expanded particle molded bodies, or expanded particles made by mixing two or more of these expanded particles can be used. Among these, it is preferable that the outer layer foamed molding 3 is composed of one or more types selected from the group consisting of polystyrene-based foamed particles, polylactic acid-based foamed particles, poly(β-hydroxybutyric acid)-based foamed particles, and poly(β-hydroxybutyric acid-co-3-hydroxyhexanoic acid)-based foamed particles.

[0022] There are no particular restrictions on the repair foam particles, as long as they are regenerative and can be integrated with the used float 2 and restore buoyancy, so they can be used regardless of whether the resin is crosslinked or not. Crosslinking is defined as a state in which the resin is crosslinked when repair foam particles or resin made by reducing the volume of repair foam particles by heat or other means are used as a test specimen and boiled in boiling toluene for one hour, and then the test specimen is placed in the solution and 5 wt% or more of the weight of the test specimen is detected as insoluble matter. Furthermore, if 5 wt% or less of insoluble matter is detected, the resin is defined as being in an uncrosslinked state. While the state of the resin in repair foam particles (crosslinked or not) does not matter, it is desirable that the secondary foaming temperature in the regenerative type does not exceed the shrinkage temperature of the used float.

[0023] Generally, expanded beads for in-mold molding undergo a secondary expansion phenomenon when heated during in-mold molding, resulting in an increase in expansion ratio compared to the original expanded beads. Subsequently, as heating continues, the secondary expansion stops and the beads transition to a shrinkage mode. The repair expanded beads used in the regeneration mold also undergo a similar secondary expansion phenomenon, and as heating continues, the secondary expansion stops and the beads transition to a shrinkage mode. This phenomenon occurs not only in expanded beads, but also in the inner layer foam molded article (used float 2) of the present invention, which transitions to a shrinkage mode after a slight secondary expansion occurs due to heating during in-mold molding. The temperature during this process, during which the expansion ratio increases, is called the secondary expansion temperature, and the temperature at which the shrinkage mode is observed is called the shrinkage temperature. If the secondary expansion temperature during the regeneration mold exceeds the shrinkage temperature of the used float 2, as the temperature difference increases, uncontrollable shrinkage, known as unequal shrinkage, occurs first, making it difficult to obtain a molded product, which is undesirable. The secondary expansion temperature of the repair expanded beads during the regeneration mold can be measured using the mold used for the regeneration mold. The expansion ratio is determined by filling a mold with a small amount of expanded beads that does not fill the mold under the heating conditions for regeneration molding, heating and cooling under the regeneration molding conditions, and then comparing the expansion ratios before and after. Usually, the ratio of the expansion ratios before and after secondary expansion of expanded beads confirmed to have undergone secondary expansion is preferably 1.3 to 2.0, and must be at least 1.1. Specifically, the secondary expansion temperature of the repair foam beads (outer layer foam molded article 3) is preferably 105 to 150°C, more preferably 110 to 145°C, and even more preferably 115 to 140°C.

[0024] Similarly, the shrinkage temperature of the used float 2 during regeneration molding can be measured using the mold used for regeneration molding. The used float 2 is placed in a mold under the heating conditions for regeneration molding, and heated and cooled under regeneration molding conditions without filling it with repair foam particles. The expansion ratio before and after the heating and cooling is then compared to determine the shrinkage. Typically, the ratio of the expansion ratios before and after the used float 2 is preferably 1.1 to 0.8, and must be at least 0.8 or greater. A value of 0.8 or less can be defined as shrinkage. When molding a recycled float 1 by maintaining the used float 2 in the center of the molding cavity and filling the outer periphery of the mass with repair foam particles and molding it integrally, the secondary expansion force of the repair foam particles may increase, causing in-mold foaming to proceed in a way that crushes the used foam float placed in the center. However, this does not constitute shrinkage due to heating and is not defined as shrinkage.

[0025] It is preferable that the density of the repair foam particles be foam particles that can maintain the bulk density of the recycled float 1 at 60 g / L or less, but if foam particles with a bulk density of more than 80 g / L are used, they may have to be avoided because they may cause an extreme shift in the center of gravity of the recycled float 1. If the position of the center of gravity of the recycled float 1 is extremely shifted from the center of the molded product, this is not preferable because when the recycled float 1 is attached at an aquaculture site, the shifted center of gravity may cause unexpected movement such as violent rotation, which may cause injury to workers who attach the recycled float 1 to aquaculture ponds at sea.

[0026] The particle size of the repair foam beads is not particularly limited as long as it does not interfere with filling the mold with the foam beads in the regenerated mold, but an average particle size of 1 mm to 15 mm is preferred. A particle size of 1 mm or less is undesirable because it may clog the core vent through which the heating medium passes when heating the mold, while a particle size of more than 15 mm is undesirable because it may require an extremely large filling gun when filling the mold with the beads. The recycled float 1 of the present invention must be integrally molded with an inner foam molded body smaller than the recycled float 1, positioned at a position at least 5 mm from the surface of the cylinder toward the center. In the regeneration mold, the inner foam molded body, which is smaller in size than the recycled float 1, is often a used float 2. However, just before filling with the repair foam particles, the used float 2 is placed in the center of the mold so that its minimum distance from the inner wall of the mold is 5 mm or more. By filling with the repair foam particles and regenerating the mold, the used float 2, which is smaller than the recycled float 1, is placed at a position 5 mm or more from the surface of the recycled float 1 toward the center, achieving integral molding. It is more preferable that the used float 2 is placed at a position 10 mm or more from the surface of the recycled float 1 toward the center, and even more preferable that the used float 2 is placed at a position 15 mm or more from the surface of the recycled float 1. In other words, the shortest distance C from the surface of the recycled float 1 to the used float 2 is preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more.

[0027] The particle size of the repair foam particles is also determined by the distance from the surface of the recycled float 1 to the used float 2 toward the center. It is preferable for three or more foam particles to be arranged between the filling and the regenerated mold. Therefore, if the distance from the surface of the recycled float 1 to the used float 2 toward the center is 5 mm, the particle size of the repair foam particles is preferably approximately 1.7 mm or less. Similarly, if the distance is 10 mm, the particle size is preferably 3.3 mm or less. If the distance from the surface of the molded body to the used float toward the center is 15 mm, the particle size of the repair foam particles is preferably 5 mm or less. A distance of 5 mm or less from the surface of the recycled float 1 to the used float 2 toward the center is undesirable because it makes filling the regenerated mold difficult. A distance of 5 mm or more from the surface of the recycled float 1 to the used float 2 toward the center and less than 150 mm allows for easy regeneration. However, a distance of more than 150 mm is undesirable because it reduces the amount of used float 2 used.

[0028] The combination of the used float 2 and the repair foam beads depends on the combination of the secondary expansion temperature and shrinkage temperature described above, and is not determined by the base resin or expansion ratio. However, in light of recent environmental awareness, when regenerating a used float made of, for example, a polystyrene-based foam bead molded body, the desired horizontal recycling can be achieved by selecting polystyrene-based foam beads as the repair foam beads from the perspective of horizontal recycling.

[0029] On the other hand, for customers with a higher level of environmental awareness, foam floats made from polylactic acid-based expanded beads are often desired, but currently, price issues make it difficult to provide them as inexpensive floats, which has hindered their widespread use. One way to solve these issues has been to develop a recycled float 1, which uses used floats 2 made from polystyrene-based expanded bead molded bodies as used floats 2 and polylactic acid-based expanded beads as repair foam beads. In this case, the amount of expensive polylactic acid-based expanded beads used can be significantly reduced, making it possible to offer them at a lower price. Even in a structure in which a used float 2 made of a polystyrene-based expanded particle molded body is used as the used float 2 and polylactic acid-based expanded particles are used as the repair expanded particles, as time passes after installation at the aquaculture fishery farm, the foam float becomes difficult to maintain its buoyancy due to erosion caused by the natural environment, such as damage and destruction by birds and animals from the outer periphery, powdering by ultraviolet rays, and the attachment of shellfish such as barnacles and seaweed.However, because erosion occurs from the outer periphery, the base resin that is eroded away from the recycled float 1 is generally polylactic acid, and therefore it is possible to achieve the same effect as a foam float molded from polylactic acid-based expanded particles alone. Similarly, when the used float 2 is a polylactic acid-based expanded particle molded body, it is possible to select polylactic acid-based expanded particles as the repair expanded particles and carry out the recycled float 1, making it possible to offer it at a low price.

[0030] On the other hand, for example, if a polystyrene-based foamed bead molded body is used for the used float 2 and polypropylene-based foamed beads are used for the repair foamed beads, the shrinkage temperature of the used float 2 will be significantly lower than the secondary expansion temperature of the polypropylene-based foamed beads, so this is not a desirable combination for implementing the regeneration type. Even when a polystyrene foam bead molded body is used for the used float 2 and polystyrene foam beads are used for the repair foam beads, it is necessary to maintain the relationship in which the shrinkage temperature of the used float 2 is higher than the secondary expansion temperature of the repair foam beads. Polystyrene-based foam beads typically use a volatile blowing agent with plasticity to polystyrene resin as a blowing agent. They are pre-expanded by heating before being molded. Volatile blowing agents effectively affect pre-expansion and can be controlled with the minimum amount of energy required to achieve the desired expansion ratio. While some of the blowing agent dissipates during the pre-expansion and molded-in process, some remains. The secondary expansion temperature of foam beads and molded products tends to be highly dependent on the amount of residual blowing agent. As the amount of residual blowing agent decreases over time, the secondary expansion temperature increases, leading to a higher shrinkage temperature. Furthermore, the higher the amount of residual blowing agent in repair foam beads, the lower the secondary expansion temperature. Therefore, even when comparing used float 2 and repair foam beads, both of which are based on the same polystyrene resin, it is possible to maintain a relationship in which the shrinkage temperature of used float 2 is higher than the secondary expansion temperature of repair foam beads.

[0031] For example, even if the used float 2 is made of a polystyrene-based expanded bead mold and the repair foam is made of polylactic acid-based expanded beads, the shrinkage temperature of the used float 2 must be higher than the secondary expansion temperature of the repair foam. Generally, polylactic acid-based expanded beads are made from polymers polymerized primarily from L-type monomers. While polylactic acid resin can be given a relatively high melting point through crystallization, it is known that the melting point and crystal content can be adjusted by adding D-type lactic acid to the polymerization monomer and performing random polymerization. Polylactic acid-based expanded beads made primarily from polylactic acid resin containing 0.5% or more D-type lactic acid monomers tend to have a lower melting point and a slower crystallization rate than polylactic acid-based expanded beads made primarily from 100% L-type polylactic acid resin. This allows for a lower secondary expansion temperature when used as repair foam. As long as the shrinkage temperature of the used float is kept higher than the secondary expansion temperature of the repair foam particles, the D-body ratio has no particular effect, but from the perspective of ease of processing, a D-body ratio of 0.5% to 8% is preferred. A D-body ratio of 0.5% or less is undesirable because it tends to accelerate crystallization, while a D-body ratio of 8% or more is undesirable because it becomes difficult to crystallize the polylactic acid layer after repair molding, making it difficult to achieve practical heat resistance.

[0032] Furthermore, a strategy for lowering the secondary expansion temperature of polylactic acid-based expanded beads can be achieved by storing the expanded beads after pre-expansion in a state that does not increase their crystallinity. Polylactic acid resins generally have a glass transition temperature of around 70°C, which is lower than that of polystyrene resins, which have a glass transition temperature of around 90°C. This allows the secondary expansion temperature to be maintained lower than that of polystyrene-based resin expanded beads. Meanwhile, crystallization may progress during pressure treatments such as heat treatment or internal pressure application, and as crystallization progresses, the secondary expansion temperature tends to rise rapidly. The progression of crystallization can be delayed by maintaining a stable storage environment, preferably at 40°C or below. More preferably, expanded beads with a bulk density of 10 g / L to 80 g / L and a D-isomer ratio of 0.5% to 8% as the main raw material are preferably stored at 40°C or below to suppress crystallization.

[0033] In a recycled float 1 using the recycled method, the inner foam molded body, which is primarily used for used floats 2, and the outer foam molded body 3, which is composed of repair foam particles covering the inner foam molded body, do not necessarily need to be bonded together as long as the recycled float 1 does not affect the buoyancy of the float. However, if the distance from the surface of the recycled float 1 to the used float 2 toward the center is 15 mm or less and the interlayer adhesion is poor, this is undesirable because, when installed in an aquaculture site, water may seep between the layers, causing repeated freezing and thawing in winter, leading to damage. If interlayer adhesion is not actively performed, it is preferable that the distance from the surface of the recycled float 1 to the used float 2 toward the center be 15 mm or more. If the distance from the surface of the recycled float 1 to the used float 2 toward the center is 15 mm or less, it is preferable to implement a method to actively maintain interlayer adhesion.

[0034] For example, interlayer adhesion can be achieved by applying an adhesive or the like to the surface of the used float 2 (covering the surface of the used float 2 with an interlayer adhesive), setting it in a mold, and then regenerating it with repair foam particles. The adhesive must be selected to achieve interlayer adhesion without dissolving the used float 2 or the repair foam particles. As long as the adhesive meets the requirements, both thermoplastic and thermosetting resins can be used, regardless of their liquid or solid state. Examples of thermosetting resins include unsaturated polyester resins, epoxy resins, vinyl ester resins, phenolic resins, polyamide resins, urea resins, melamine resins, polyimide resins, diallyl phthalate resins, and urethane resins. These resins are generally provided in liquid form, and one or a combination of two or more types can be used. Solid thermosetting resins can be provided primarily in a state known as the B-stage. They are used in a substantially uncured state, exhibiting a solid or semi-solid state at room temperature.

[0035] The thermosetting resin preferably contains a curing agent capable of reacting with the thermosetting resin to form a cured product. The curing agent is not particularly limited as long as it can react with the thermosetting resin to solidify and form a cured product. For example, curing agents for epoxy resins include linear aliphatic amines, cyclic aliphatic polyamines, aliphatic aromatic polyamines, aromatic amines, acid anhydrides such as methylhexahydrophthalic anhydride, phenolic resins such as novolac phenolic resins and cresol novolac epoxy resins, phthalic anhydride derivatives, dicyandiamide, imidazole compounds, aluminum chelates, 2-ethyl-4-methylimidazole, and amine complexes of Lewis acids such as BF3. These can be used alone or in combination. When an unsaturated polyester resin is used as the thermosetting resin, it is preferable to use a peroxide as a curing agent (polymerization initiator). As the peroxide, organic peroxides such as benzoyl peroxide, lauroyl peroxide, methyl ethyl ketone peroxide, peroxyperbenzoate, peroxyketal, and dicumyl peroxide can be preferably used. These peroxides can be used alone or as a mixture of two or more. A chain transfer agent may be used in addition to the peroxide. From the viewpoint of efficiently curing the thermosetting resin, the amount of the curing agent added is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and preferably 20 parts by weight or less, more preferably 10 parts by weight or less, relative to 100 parts by weight of the thermosetting resin.

[0036] Liquid thermoplastic resins are generally provided as solutions in which the thermoplastic resin is dissolved in a solvent. Examples of thermoplastic resins include general-purpose resins such as butadiene homopolymer, ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, acrylonitrile-styrene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate, and methyl methacrylate-styrene copolymer; rubbers such as nitrile rubber, hydrogenated nitrile rubber, acrylic rubber, urethane rubber, chloroprene rubber, ethylene-propylene rubber, chlorosulfonated polyethylene, butadiene rubber, epichlorohydrin rubber, natural rubber, isoprene rubber, styrene-butadiene rubber, butyl rubber, butadiene rubber, polysulfide rubber, norbornene rubber, thermoplastic elastomers, and latex; and elastomers such as styrene-based elastomers, olefin-based elastomers, vinyl chloride-based elastomers, urethane-based elastomers, ester-based elastomers, and amide-based elastomers. These resins can be used alone or in combination. Among these, styrene-ethylene-butylene block copolymer, styrene-ethylene-butadiene block copolymer, styrene-butadiene block copolymer, styrene-isoprene block copolymer, 1-2 polybutadiene, polyurethane-polyester block copolymer, polyurethane-polyether block copolymer, polypropylene-ethylene propylene diene block copolymer, etc. are preferred.

[0037] The solvent for dissolving the thermoplastic resin is not limited to a specific type or structure, as long as it maintains the ability to uniformly dissolve the dissolved thermoplastic resin and does not dissolve the used float 2 or the repair foam particles. However, in order to improve workability, it is preferable that the solvent evaporates quickly after application. Examples of solvents include ethanol, butyl alcohol, propyl alcohol, acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, dimethyl ether, diethyl ether, toluene, xylene, cyclopentane, chlorobenzene, hexane, chloroform, methylene chloride, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide. These can be used alone or in combination.

[0038] There are no particular restrictions on the shape of the solid thermoplastic resin, as long as it can be set in a mold while uniformly covering the surface of the used float 2, but it is generally provided as a film, sheet, mesh net, or powder. Of these, provision in the form of a mesh net is preferable. On the other hand, powder is easy to use as long as it maintains the property of remaining on the surface of the used float 2 by itself, but in many cases it must be dispersed in an incompatible solvent before being applied and adhered, making it difficult to achieve an effect greater than that achieved with a liquid thermoplastic resin, and therefore is not a method that is actively adopted.

[0039] Furthermore, even when provided as a film or sheet, if the surface of the used float 2 can be uniformly covered and set in the mold, it is preferable to obtain a recycled float 1 that maintains interlayer adhesion with the repair foam particles. However, covering the used float 2 with a film or sheet can result in slack between the film or sheet and the recycled float 1, leaving a clear gas space, which is undesirable. Depending on the material, venting can be time-consuming, making this method difficult to adopt. When provided as a solid thermoplastic resin, it is most preferable to provide it in the form of a mesh net. Furthermore, a net with excellent elasticity is preferred, and it is preferable to select a mesh size smaller than the diameter of the foam particles so that the foam particles do not pass through. Specifically, the stretchability of the net in any uniaxial direction is preferably 30% or more, more preferably 50% or more, and preferably 100% or more. A stretch rate of 30% or less is undesirable because it may cause slack between the used float 2, as with films and sheets. There are no particular restrictions on the opening size or shape as long as the opening size is smaller than the diameter of the expanded beads, but the opening size is preferably 80% or less, and more preferably 50% or less, of any projected area of ​​the expanded beads. If the opening size is 80% or more, the expanded beads may exceed the projected area of ​​any expanded beads when the net is stretched, which is undesirable because they may slip through the meshes of the net.

[0040] Examples of solid thermoplastic resins include general-purpose resins such as butadiene homopolymer, ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, acrylonitrile-styrene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate, and methyl methacrylate-styrene copolymer; rubbers such as nitrile rubber, hydrogenated nitrile rubber, acrylic rubber, urethane rubber, chloroprene rubber, ethylene propylene rubber, chlorosulfonated polyethylene, butadiene rubber, epichlorohydrin rubber, natural rubber, isoprene rubber, styrene-butadiene rubber, butyl rubber, butadiene rubber, polysulfide rubber, norbornene rubber, thermoplastic elastomer, and latex; and elastomers such as styrene-based elastomer, olefin-based elastomer, vinyl chloride-based elastomer, urethane-based elastomer, ester-based elastomer, and amide-based elastomer. These may be used alone or in combination. Among these, styrene-ethylene-butylene block copolymer, styrene-ethylene-butadiene block copolymer, styrene-butadiene block copolymer, styrene-isoprene block copolymer, 1-2 polybutadiene, polyurethane-polyester block copolymer, polyurethane-polyether block copolymer, polypropylene-ethylene propylene diene block copolymer, etc. are preferred.

[0041] There is no limit to the amount of net used, as long as it does not affect the buoyancy of the recycled float 1. Since the amount used increases in proportion to the surface area of ​​the used float 2, it is preferable to select a net with a small basis weight. On the other hand, if the mesh size is too large, the covering adhesive area will be insufficient, which is not desirable, so the basis weight of the net should be 50 g / m 2 More than 900g / m 2 It is preferable that the thickness is 100 g / m or less. 2 More than 500g / m 2 Less than 50g / m 2 If the adhesive strength is less than 900 g / m, it becomes difficult to maintain effective adhesive strength. 2 If it exceeds this value, it is not desirable because it will have a significant effect on buoyancy.

[0042] The density of the recycled float 1 after regeneration is closely related to buoyancy, and is therefore the most important control item. Buoyancy and expansion ratio are also closely related, but buoyancy tends to change easily when the expansion ratio is around 20 times. That is, when the expansion ratio exceeds 20 times, the change in buoyancy is gradual, but when the expansion ratio is below 20 times, buoyancy tends to decrease rapidly. Similarly, in the recycled float 1 of the present invention, it is preferable to maintain an expansion ratio of 20 times or more, with about 20 times as a guideline.

[0043] For example, even if the used float 2 is a polystyrene resin foam bead molded body, the expansion ratio required for aquaculture, etc., is 20 times or more. Naturally, repair foam beads used to repair a 50 to 80 times used float 2 are preferably 50 to 80 times. However, the repair foam beads do not necessarily need to have a high expansion ratio. In particular, to maintain the relationship between the shrinkage temperature of the used float 2 and the secondary expansion temperature of the repair foam beads in a regenerated form, using foam beads of 20 times or less makes it easier to adjust the conditions, thereby broadening the range of molding conditions and making the regenerated form easier. On the other hand, for example, when repairing a used float with an expansion ratio of 50 to 80 times with polylactic acid foam beads, there is a high possibility that the secondary expansion temperature of the polylactic acid foam beads will exceed the shrinkage temperature of the used polystyrene float 2. It has been confirmed that the secondary expansion temperature of general polyester-based expanded particles tends to increase when the expansion ratio exceeds an appropriate level. Therefore, it is preferable to select an expansion ratio of 15 to 30 times for polylactic acid-based expanded particles for repair, as this tends to make it easier to prevent the secondary expansion temperature from exceeding the shrinkage temperature of the used polystyrene-based float 2.

[0044] The repair foam beads are not limited by the manufacturing method of the foam beads, and any foam beads manufactured by the extrusion foaming method, the foaming agent impregnation pre-expansion method, the direct foaming method, or the like can be used as long as they are capable of undergoing secondary expansion in a mold and mutual fusion between the foam beads.

[0045] For example, it is possible to use pre-expanded expanded particles obtained by a direct expansion method in which expandable polylactic acid resin particles are dispersed in a pressure-resistant vessel together with a dispersion medium under heated conditions in the presence of a foaming agent, and then released together with the dispersion medium from the pressure-resistant vessel to a pressure lower than that of the vessel. Because a pressure-resistant vessel is used, it is generally more difficult to design a high-pressure-resistant vessel than an extruder. Therefore, the pre-expansion pressure applied to the resin particles immediately before expansion in direct expansion tends to be lower than the pre-expansion pressure that can be applied by an extruder. Based on the common principle of foaming, a foam is obtained by transferring resin particles containing high-pressure gas to a low pressure to generate bubbles. Therefore, considering only this principle, foaming using an extruder would appear to be superior to foaming using a pressure vessel for obtaining a high expansion ratio product. However, it is known that foaming using a pressure vessel can produce a higher expansion ratio for some products.

[0046] Direct foaming tends to require an extremely large instantaneous output volume for foaming, generally requiring a release rate of 500 kg / hr to 2000 kg / hr or more. In other words, by shortening the time required to transfer resin particles from a high-pressure state to a low-pressure state compared to the time required in an extruder, it is possible to increase the rate of pressure drop within the resin particles, thereby increasing the efficiency of foaming agent use and compensating for the disadvantage of lower pre-foaming pressure compared to an extruder.

[0047] However, direct foaming is known to have drawbacks arising from its extremely fast instantaneous discharge speed, and is generally known to be unsuitable for foaming so-called hard resin particles, which tend to have a high elastic modulus. In particular, it is unsuitable for resins classified as brittle materials with a high elastic modulus. For example, when foamed particles made of resin particles such as polystyrene resin, thermosetting resins that tend to be brittle, ABS resins, and polymethyl methacrylate resins are produced by direct foaming, the foamed particles are likely to be damaged due to collisions between the foamed particles during foaming, and the closed cell ratio is likely to decrease, which is undesirable.

[0048] In the production of foamed beads by direct foaming, it is suitable for foamed beads made of resins classified as ductile materials with a relatively low elastic modulus, and it is preferable to use it to obtain foamed resin beads such as polyethylene-based resins and polypropylene-based resins. For resin particles such as polylactic acid, which are intermediate between ductile and brittle materials, resin foam particles can be produced by restricting the foaming conditions. Examples of restricting the foaming conditions include lowering the modulus of elasticity somewhat by adding a small amount of D-lactic acid to L-lactic acid in the monomer structure of polylactic acid, suppressing the pre-foaming pressure to 3 MPa or less to slightly reduce the release rate, increasing the particle weight per resin particle to reduce the number of foam particles released and reduce the collision probability of resin particles during foaming, and pre-mixing a plasticizing component or adding a low-molecular-weight component to the dispersion medium to reduce the modulus of elasticity of polylactic acid resin particles. Combining these methods makes it possible to produce resin foam particles.

[0049] In direct foaming production methods, blowing agents can be inorganic gases such as air, nitrogen, helium, carbon dioxide, and water; volatile blowing agents such as aliphatic hydrocarbons (e.g., propane, normal butane, isobutane, normal pentane, isopentane, and hexane); alicyclic hydrocarbons (e.g., cyclopentane and cyclobutane); ethers (e.g., dimethyl ether, diethyl ether, and methyl ethyl ether); and alcohols (e.g., methanol and ethanol). Chemical blowing agents, including thermally decomposing blowing agents such as sodium bicarbonate, azodicarbonamide, and dinitrosopentamethylenetetramine, can be used alone or in combination. Two or more of inorganic gases, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, alcohols, and chemical blowing agents including thermally decomposing blowing agents can be used in combination, and the mixing ratio can be adjusted as desired.

[0050] The repair foam beads can be produced by, for example, an extrusion foaming method in which a resin containing a foaming agent is extruded from an extruder through a nozzle die, and the extrudate is cut with a rotary blade while being foamed. Specifically, a resin composition containing a resin and optional additives is melted in a manufacturing device using an extruder, a foaming agent is dissolved in the resin composition, and a molten resin containing the resin composition and the foaming agent is prepared.The molten resin is then cooled before being extruded into a low-pressure region so that the resin viscosity and resin temperature are within appropriate ranges, and the molten resin is then extruded into a low-pressure region.The expanded strand-like foam is then cut so that the L / D ratio is 0.6 to 1.5, thereby producing resin foam particles. As for the equipment for cooling the molten resin, detailed classification is not a particular issue as long as it can maintain a sufficiently and uniformly cooled state of the molten resin, but generally, a single-screw extruder with a large L / D ratio, a melt cooler, or a static mixer can be used. The extruded molten resin can be shredded using a strand cutting method or a die face cutting method. The strand cutting method involves foaming a molten resin containing a foaming agent extruded from a die, cooling it through a water tank, collecting a strand-like foam, and then cutting it with a pelletizer or the like. The die face cutting method involves cutting the molten resin extruded from a die hole with a rotating cutter while in contact with the surface of the die or while leaving a small gap between them.

[0051] The die face cutting method allows for the selection of different cooling methods depending on the state of the molten resin. Specifically, if the viscosity of the molten resin when extruded is low and cooling is deemed necessary, the underwater cutting (hereinafter sometimes referred to as UWC) method is used. On the other hand, if it is deemed that little cooling is required, the hot cutting (hereinafter sometimes referred to as HC) method is used. If the resin viscosity state is deemed to be between the above two, the watering cutting (hereinafter sometimes referred to as WRC) method can also be used.

[0052] The UWC method is a method in which a chamber attached to the tip of a die is filled with cooling water adjusted to a predetermined pressure so that it contacts the resin discharge surface of the die, and the molten resin extruded from the die hole is cut underwater. The WRC method is a method in which a cooling drum connected to the die is placed downstream from the die, through which cooling water flows along the inner surface of the cooling drum, and the molten resin cut by the cutter is cooled in the cooling water while foaming in the air or after foaming. The HC method is a method in which the molten resin is cut by the cutter in the air, and the cut molten resin is cooled in the air while foaming in the air or after foaming. Examples of the HC method include a mist cut method, which further includes a step of spraying a mixed mist of water and air. When producing expanded resin beads, the foam extruded into strands is generally extruded at a relatively high resin viscosity due to the effect of adiabatic expansion, so in many cases the HC method is used for production. Compared to the UWC and WRC methods, this method has the advantage of reducing the amount of equipment required and the amount of equipment assembly work required, making it a preferred method for producing expanded beads.

[0053] Resins suitable for extrusion foaming include polystyrene resins, polypropylene resins, polyethylene resins, polyethylene terephthalate resins, polymethyl methacrylate resins, and aliphatic polyester resins. Furthermore, examples of aliphatic polyester resins that can be used include polylactic acid resins, polyglycolic acid resins, poly(β-hydroxybutyric acid) resins, poly(β-hydroxybutyric acid-co-β-hydroxyvaleric acid) resins, poly-β-propiolactone resins, poly-ε-caprolactone resins, polyethylene succinate resins, polybutylene succinate resins, poly(butylene succinate-co-butylene adipate) resins, and poly(β-hydroxybutyric acid-co-3-hydroxyhexanoic acid) resins. Two or more of these suitable resins can be mixed to obtain expanded particles.

[0054] Examples of blowing agents that can be used in extrusion foaming include inorganic gases such as air, nitrogen, helium, carbon dioxide, and water; volatile blowing agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; alicyclic hydrocarbons such as cyclopentane and cyclobutane; ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; and alcohols such as methanol and ethanol. Chemical blowing agents, including thermally decomposing blowing agents such as sodium bicarbonate, azodicarbonamide, and dinitrosopentamethylenetetramine, can be used alone or in combination. Two or more of these inorganic gases, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, alcohols, and chemical blowing agents including thermally decomposing blowing agents can be used in combination, and the mixing ratio can be adjusted as desired.

[0055] As a manufacturing method of the expanded repair beads, for example, a foaming agent impregnation pre-expansion method can be adopted. The expanded beads obtained by the foaming agent impregnation pre-expansion method are generally called expandable resin beads, but essentially, expandable resin beads are unexpanded resin beads containing a volatile foaming agent and, if necessary, resin particles having a coating agent applied to the surface thereof. The expandable resin particles can be expanded by a conventional method, such as by using a cylindrical pre-expansion device and heating the expandable resin particles with a heating medium such as steam to expand them. The device used for expanding the expandable resin particles and the expansion conditions are not particularly limited and may be appropriately set depending on the composition of the expandable resin particle body and / or the desired expansion ratio, etc.

[0056] The method for producing expandable resin particles is not limited to the structure or composition of the equipment, as long as the resin particles can be brought into contact with a volatile blowing agent under heating and pressure, and the particles can be stably stored in an impregnated state. However, from the viewpoints of preventing the resin particles from adhering to each other under heating and pressure, and of ease of temperature control, it is preferable to produce expandable resin particles by dispersing the resin particles in an aqueous medium in a pressure vessel while stirring, and bringing the particles into contact with a volatile blowing agent.

[0057] The resin particles used for the expandable resin particles can be resin particles prepared in advance by the UWC method, WRC method, HC method, etc. Resin particles prepared by the strand cutting method, in which resin extruded in strand form from an extruder is cooled in water and cut into cylindrical resin particles with a rotary blade, or a method in which a dispersion medium, dispersant, monomer, and polymerization initiator are added to a pressure vessel used for producing expandable resin particles, resin particles are prepared by polymerization reaction, and then a volatile blowing agent is introduced into the pressure vessel to produce expandable resin particles in one step can also be used. However, when using a seed suspension polymerization method as a resin particle preparation method, seed resin particles can be prepared in advance in a pressure vessel with a dispersion medium, dispersant, and seed resin particles, and then the monomer and polymerization initiator are added, and the volatile blowing agent is introduced just in time to complete the seed polymerization in the seed resin, thereby producing expandable resin particles.

[0058] Resins suitable for the resin particles used in the expandable resin particles include polystyrene-based resins, polypropylene-based resins, polyethylene-based resins, polyethylene terephthalate-based resins, polymethyl methacrylate-based resins, and aliphatic polyester-based resins. Furthermore, examples of aliphatic polyester-based resins that can be used include polylactic acid-based resins, polyglycolic acid-based resins, poly(β-hydroxybutyric acid)-based resins, poly(β-hydroxybutyric acid-co-β-hydroxyvaleric acid)-based resins, poly-β-propiolactone-based resins, poly-ε-caprolactone-based resins, polyethylene succinate-based resins, polybutylene succinate-based resins, and poly(butylene succinate-co-butylene adipate)-based resins. Expanded particles can be obtained by kneading two or more of these suitable resins.

[0059] The particle weight of the resin particles used in the expandable resin particles is preferably 20 mg or less, more preferably 10 mg or less, and even more preferably 5 mg or less per resin particle. If it exceeds 20 mg, the impregnation state of the volatile blowing agent in the resin particles is likely to be lost uniformly, and problems such as foaming on the periphery but difficulty in forming bubbles inside are likely to occur, which is not preferable. In addition, a method of polymerizing resin particles in a pressure vessel and introducing a volatile blowing agent to produce expandable resin particles is characterized by the ease of obtaining resin particles of 1 mg or less.

[0060] The blowing agents used in the expandable resin particles include volatile blowing agents such as aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane, alicyclic hydrocarbons such as cyclopentane and cyclobutane, ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and alcohols such as methanol and ethanol. While inorganic gases such as air, nitrogen, helium, carbon dioxide, and water are not preferred when used alone because it is difficult to retain the blowing agent in the resin, they can be used in combination within a range of 30 wt% or less relative to the volatile blowing agent. The combined use of a volatile blowing agent and an inorganic gas has the effect of reducing the bubble diameter of the expanded particles.

[0061] For the polystyrene-based expanded beads that are often used as repair expanded beads, it is preferable to use expanded beads obtained by pre-expanding expandable resin beads. In order to maintain the secondary expansion temperature of the repair expanded beads lower than the shrinkage temperature of the used float, a high closed cell ratio tends to be preferable, and in order to maintain a high closed cell ratio, it is preferable to use expanded beads obtained by pre-expanding expandable resin beads compared to methods such as direct foaming and extrusion foaming, so it is preferable to use expanded beads obtained by pre-expanding expandable resin beads. When using polylactic acid-based expanded beads as repair beads, the manufacturing method of the expanded beads is not superior or inferior in terms of achieving a regenerated form. However, in order to lower the secondary expansion temperature as much as possible, it is preferable to use expanded beads obtained by extrusion foaming using the HC method, followed by expanded beads obtained by pre-expanding expandable resin beads, and even more preferable to use expanded beads obtained by direct foaming. When producing polylactic acid-based expanded beads with the aim of lowering the secondary expansion temperature as much as possible, it is best to keep the ambient temperature as low as possible when forming the expanded beads, and it tends to be preferable to use expanded beads obtained by extrusion foaming using the HC method because it is easy to rapidly cool the outer surface of the expanded beads. Aliphatic polyester resins containing polylactic acid generally tend to have a slow crystallization acceleration, and polylactic acid resins also tend to have a slow crystallization acceleration. In other words, it is preferable to use an ambient temperature below the glass transition temperature of the polylactic acid resin at the moment of foaming, because it is possible to foam while relatively suppressing crystallization of the outer surface of the expanded beads. On the other hand, expanded beads obtained by direct foaming or methods using expandable resin beads tend to be exposed to temperatures above the glass transition point for a longer period of time than expanded beads obtained by extrusion foaming using the HC method, and this is undesirable because crystallization tends to progress, even if only slightly.

[0062] The expanded polylactic acid resin particles can be selected regardless of whether they are crystalline or amorphous, but it is preferable to use expanded particles that tend to be crystalline in order to impart heat resistance after molding. The constituent monomers may be derived from either the L-form or the D-form, and a mixed resin of so-called amorphous and crystalline resins is also acceptable, but it is preferable to use expanded polylactic acid resin particles that have a heat of crystalline fusion of 5 J / g or more in differential scanning calorimetry (DSC) measurement from 30°C to 200°C. The heat of crystalline fusion is measured by subjecting test pieces prepared using a measuring pan containing 1 mg to 20 mg of expanded particles to DSC, measuring at a heating rate of 10°C / min in the range of 30°C to 200°C (first melting point measurement), then lowering the temperature from 200°C to 30°C at 10°C / min (first crystallization temperature measurement), and then raising the temperature from 30°C to 200°C at 10°C / min (second melting point measurement). The heat of crystalline fusion is obtained from the DSC curve and used.

[0063] For expanded polylactic acid resin beads, the value of the heat of crystallization appearing between the glass transition temperature and the melting point is preferably measured in the first melting point measurement of the DSC measurement. It is preferably 3 J / g or more, more preferably 10 J / g or more, and more preferably 15 J / g or more. The heat of crystallization is understood to be a value indicating the amorphous crystalline components that have not yet crystallized among the crystallizable crystalline components of the expanded beads, and is considered to be the heat that affects the secondary foaming temperature.

[0064] Generally, it is believed that the secondary foaming temperature is correlated with the difference between the heat of fusion obtained in the second melting point measurement and the heat of crystallization obtained in the first melting point measurement, and for repair polylactic acid resin foam particles, the difference between the heat of fusion obtained in the second melting point measurement and the heat of crystallization obtained in the first melting point measurement is preferably 3 J / g or more, more preferably 10 J / g or more, and even more preferably 15 J / g or more.

[0065] In the measurement of the heat of fusion observed in the first melting point measurement of expanded polylactic acid resin beads, double or multiple peaks may be observed. This phenomenon reflects the thermal history that occurs during the manufacturing process of the expanded beads, and is known to have the effect of raising the shrinkage temperature of expanded repair beads. However, since it also tends to raise the secondary expansion temperature, the value of the heat of fusion obtained by subtracting the peak heat of fusion that appears on the low-temperature side in the measurement of the heat of fusion observed in the first melting point measurement is preferably 10 J / g or less, and more preferably 3 J / g or less.

[0066] The second heat of fusion of the expanded polylactic acid resin beads is preferably 5 J / g or more, more preferably 15 J / g or more, and even more preferably 25 J / g or more. If it is 5 J / g or less, it is not preferable because it does not provide substantial heat resistance. On the other hand, if it is 50 J / g or more, it is not preferable because it tends to be difficult to adjust the amount of crystallization on the outer surface of the expanded beads.

[0067] When recycling used floats 2 using repair foam particles, there is no particular preference for the region of the molding base, but as for the method of implementation, recycling can be carried out by bringing it into the factory equipment. However, if used floats 2 are brought to a recycling factory, recycled, and then transported the return distance for delivery, the cost of shipping would be incurred for both the return trip, which is not expected to be efficient. If possible, if a system could be established in which the repair foam particles used in the recycling are pre-expanded on-site and recycling is carried out on-site, it would be possible to reduce the round-trip shipping costs of the floats, and the price of recycled floats 1 could be reduced.

[0068] The business model of this invention involves loading a 4-ton Unic truck with molding dies, a simple boiler, a generator, and a small compressor, making it possible to complete repair molding on-site. Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this. [Example]

[0069] Example 1 The #300 float, which had been used for marine aquaculture for approximately two years, was collected, the polyethylene cover was removed, and the polystyrene foam molded body was left exposed in an indoor warehouse for approximately three months. The dried polystyrene foam molded body weighed 2.8 kg and had a density of 13 kg / m at the time of purchase. 3 The volume was 213 L. From these figures, it was confirmed that the buoyancy at the time of recovery was 210 kg and the buoyancy retention rate was 74%, and it was used as an inner layer foam molded product (used float 2). The buoyancy of a new float (#300 float) was 280 kg and the volume was 284 L. Polystyrene resin foam particles were used as the repair foam particles. The bulk density was 20 kg / m 3 The secondary foaming temperature was 118°C. The regeneration mold has a structure that can be opened and closed and sealed, and has a structure that allows steam, air, and cooling water to be passed through the mold, which is the molding space, through slits. After the inner layer foam molded body is set in the mold, repair foam particles are filled into the space between the inner layer molded body and the mold using a filling feeder, and then a pressure of 0.8 kgf / cm is applied. 2 After introducing steam of 1000 kJ / min and cooling with water, the mold was opened and the regenerated product was removed. After drying for 24 hours in a drying room at 40°C, the molded product (regenerated float) was measured and found to have a diameter of 600 mm, a length of 1050 mm, a volume of 284 L, and a weight of 4.2 kg. The buoyancy was 280 kg, meaning that the buoyancy recovery rate was 100%.

[0070] Example 2 Bulk density of 40 kg / m as foam particles for repair 3 A molded product (recycled float) was produced in the same manner as in Example 1 above, except that the polystyrene foam beads were used and the secondary expansion temperature of the repair foam beads was 120°C.

[0071] Example 3 A molded product (recycled float) was produced in the same manner as in Example 1 above, except that polylactic acid-based expanded beads were used as the repair expanded beads.

[0072] Example 4 A molded product (recycled float) was produced in the same manner as in Example 3 above, except that an inner layer foam molded article whose base resin was polylactic acid was used.

[0073] Example 5 The floats that had been used for marine aquaculture for about a year were collected, the polyethylene covers were removed, and the polypropylene foam molded body was left exposed in an indoor warehouse for about three months. The dried polypropylene foam molded body weighed 0.12 kg and had a density of 30 kg / m at the time of purchase. 3The volume was 4.1 L. From these figures, it was confirmed that the buoyancy at the time of recovery was 4.0 kg and the buoyancy retention rate was 73%, and it was used as an inner layer foam molded product (used float 2). The buoyancy of a new float was 5.3 kg and the volume was 5.5 L. The foamed repair particles used were polypropylene resin foamed particles. The bulk density was 42 kg / m 3 The secondary foaming temperature was 140°C. The regeneration mold has a structure that can be opened and closed and sealed, and has a structure that allows steam, air, and cooling water to be passed through the mold, which is the molding space, through slits. After the inner layer foam molded body is set in the mold, repair foam particles are filled into the space between the inner layer molded body and the mold using a filling feeder, and then a pressure of 3.8 kgf / cm is applied. 2 After introducing steam of 1000 kJ / min and cooling with water, the mold was opened and the regenerated product was removed. After drying for 24 hours in a drying chamber at 60°C, the molded product (regenerated float) was measured and found to have a diameter of 600 mm, a length of 1050 mm, a volume of 5.5 L, and a weight of 0.18 kg. The buoyancy was 5.3 kg, indicating a buoyancy recovery rate of 97%.

[0074] (Comparative Example 1) An unused #200 float (different only in size from the #300 float) that had not been used for marine aquaculture was used as the inner foam molded body. This molded body had a diameter of 560 mm, a length of 900 mm, a weight of 2.6 kg, a volume of 203 L, and a buoyancy of 200 kg. The foamed particles used for repair were polystyrene resin foamed particles. The bulk density was 13 kg / m 3 The secondary foaming temperature was 124°C. The regeneration mold has a structure that can be opened and closed and sealed, and has a structure that allows steam, air, and cooling water to be passed through the mold, which is the molding space, through slits. After the inner layer foam molded body is set in the mold, repair foam particles are filled into the space between the inner layer molded body and the mold using a filling feeder, and then 1.4 kgf / cm 2After introducing steam at 1000 kJ / min and cooling with water, the mold was opened and the regenerated molded product was removed. After drying for 24 hours in a drying room at 40°C, the molded product was measured and found to have a diameter of 570 mm, a length of 1020 mm, a volume of 249 L, and a weight of 3.2 kg. The buoyancy was 246 kg, indicating a buoyancy recovery rate of 88%.

[0075] (Comparative Example 2) A molded product was produced in the same manner as in Comparative Example 1, except that polylactic acid-based expanded beads were used as the repair expanded beads. Various data on the cylindrical foam molded body (recycled float 1), inner layer foam molded body (used float 2), and repair foam particles (outer layer foam molded body 3) of each Example and Comparative Example are shown in Table 1. The values ​​for the "new float" in Comparative Example 1 and Comparative Example 2 are the values ​​for the #300 float, which is the standard for calculating the buoyancy recovery rate.

[0076] [Table 1]

[0077] In the table, PS stands for polystyrene, PLA stands for polylactic acid, and PP stands for polypropylene. As can be seen from Table 1, the regenerated float of the example was evaluated as being good. [Explanation of symbols]

[0078] 1. Recycled float (cylindrical foam molding) 2 Used float (inner layer foam molding) 3. Outer layer foam molded body 4 Connection means

Claims

1. It has a layer structure in which an inner layer foam molded body and an outer layer foam molded body covering the inner layer foam molded body are integrally molded, It has a cylindrical shape with a diameter (D) of 100 mm or more and 800 mm or less, and a length (L) of 100 mm or more and 1500 mm or less. Cylindrical foam molding.

2. The end of the net (float) The cylindrical foam molded article according to claim 1.

3. The weight loss rate of the inner foamed molded body at 90°C is 2.5% or less, and the volume shrinkage rate of the inner foamed molded body at 90°C is 10% or less. The cylindrical foam molded article according to claim 1.

4. The outer layer foam molded product is an aliphatic polyester foam bead molded product. The cylindrical foam molded article according to claim 1.

5. The outer layer foamed molded article is composed of one or more types selected from the group consisting of polystyrene-based expanded particles, polylactic acid-based expanded particles, poly(β-hydroxybutyric acid)-based expanded particles, and poly(β-hydroxybutyric acid-co-3-hydroxyhexanoic acid)-based expanded particles. The cylindrical foam molded article according to claim 1.

6. Bulk density is 60g / L or less The cylindrical foam molded article according to claim 1.

7. The inner layer foam molded article is a used float. The cylindrical foam molded article according to claim 1.

8. The secondary foaming temperature of the outer foamed molded body is 105 to 150°C. The cylindrical foam molded article according to claim 1.

9. A method for producing the cylindrical foamed molded article according to claim 1, After the inner layer foam molded body is set in a mold that seals and opens, repair foam particles are filled into the gap between the mold and the inner layer foam molded body, and then the molded body is heated to form the outer layer foam molded body so as to cover the inner layer foam molded body. A method for producing a cylindrical foamed molded article.

10. When the inner layer foam molded body is set in the mold, the surface of the inner layer foam molded body is covered with an interlayer adhesive layer. A method for producing the cylindrical foam molded article according to claim 9.

11. The secondary expansion temperature of the repair foam particles is 105 to 150°C. A method for producing the cylindrical foam molded article according to claim 9.

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