Method for manufacturing resin composite materials

Abstract

This invention provides a method for stably manufacturing high-performance resin composite materials with non-combustible and antibacterial properties, while effectively utilizing waste gypsum board, without foaming or molding defects. [Solution] Waste gypsum board is crushed to 0.3 mm or less and stirred with water at 100 rpm or more to obtain a viscous first mixture. Synthetic resin and, if necessary, fly ash are added to this to form a second mixture, which is then heated and kneaded under negative pressure degassing using a twin-screw extruder or kneader to obtain a molding material. The resulting composite material exhibits an oxygen index of 26 or higher and an antibacterial activity value of 2.0 or higher, making it suitable for use as non-combustible building materials, logistics materials, water and sewage pipes, etc.

Description

Technical Field

[0001] The present invention relates to a technology for recycling waste gypsum board, which is discharged in large quantities as construction waste, into a resin composite material excellent in formability, non-combustibility, and environmental performance by compounding it with a synthetic resin without separating the constituent components, gypsum (dihydrate gypsum) and paper fibers.

Background Art

[0002] Gypsum board is a lightweight building material with calcium sulfate dihydrate (CaSO4·2H2O) as the core material and paper liners on both sides, and is widely used in the construction field. In recent years, with the increase in demolition and renovation work, the discharge amount of waste gypsum board has increased rapidly, and from the viewpoints of environmental protection and resource circulation, its overall recycling is strongly demanded.

[0003] In conventional recycling technologies, "horizontal recycling" that separates, pulverizes, and re-fires only the gypsum component and uses it as recycled gypsum has been the mainstream. However, since the removal of paper fibers and foreign substances (nails, adhesives, paints, etc.) derived from the paper liners is a prerequisite, the equipment cost is high, and there are also problems with the stability of quality, making it difficult to recycle the entire waste gypsum board.

[0004] Technically, when paper fibers remain, foaming and carbonization occur during firing, significantly impairing the structural strength and appearance quality of the recycled gypsum board. Therefore, complete removal of paper fibers is a prerequisite, and it has been difficult to recycle the entire waste gypsum board.

[0005] Economically, even if high-quality recycled gypsum is obtained, the manufacturing cost is higher compared to natural gypsum and desulfurized gypsum, and it lacks price competitiveness. These alternative materials are distributed in large quantities and at low cost, and the market demand for recycled gypsum is limited.

[0006] Against this backdrop, a technology has been proposed to compound calcined anhydrous gypsum with thermoplastic resin (Patent Document 1). However, the extracted fine anhydrous gypsum powder has poor interfacial adhesion with the resin, making it difficult to apply to anything other than thick-walled extrusions and large injection-molded products, thus leaving challenges to its practicality. Based on the above, existing recycling methods have shown difficulty in recovering the entire waste gypsum board, including the paper fibers it contains, and have been limited to the reuse of only the gypsum component.

[0007] On the other hand, fly ash generated from biomass power plants and waste incineration facilities has traditionally been limited to treatment at controlled landfill sites due to concerns about the leaching of harmful substances. As a result, its effective utilization as a resource has been limited, and efforts to reduce the environmental burden have also been restricted. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7659337 [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a resin composite material with excellent moldability and non-combustibility by not separating the gypsum (dihydrate gypsum) and paper fibers contained in waste gypsum board, and by compounding them with a synthetic resin.

[0010] The aim is to provide a resin composite material with superior functionality while reducing environmental impact by utilizing fly ash derived from biomass power generation facilities or waste incineration facilities. [Means for solving the problem]

[0011] The resin composite material of the present invention is manufactured by crushing separated waste gypsum board, adding water to form a paste, mixing this with a synthetic resin to obtain a mixture, then heating and kneading it, and finally undergoing a degassing treatment.

[0012] The technical features of this invention are as follows: - By mixing waste gypsum board with water to form a paste, the gypsum components (dihydrate gypsum) and paper fibers become plasticized, improving interfacial adhesion with synthetic resins. - Hydrogen-bonded water molecules impart clay-like plasticity, significantly improving dispersibility and moldability with thermoplastic resins, while also providing flame retardancy. - The paper fibers are dispersed three-dimensionally, functioning as a fiber reinforcement material and also contributing to improved flame retardancy through carbonization. - When mixed with dihydrate gypsum, fly ash does not scatter or aggregate, but is finely dispersed three-dimensionally, functioning as a reinforcing, flame retardant, and antibacterial agent.

[0013] Conventional fly ash derived from coal-fired power plants becomes spherical crystalline particles through high-temperature firing and tends to aggregate without becoming finely atomized during mixing. On the other hand, the fly ash derived from biomass power generation facilities or incineration facilities used in this invention becomes plate-like or flattened particles through low-temperature firing, which easily disperses three-dimensionally during mixing and functions effectively as a reinforcing material.

[0014] The fly ash used in this invention consists of inorganic fine particles derived from biomass power generation facilities or incineration facilities, and mainly contains silicon dioxide (SiO2), aluminum oxide (Al2O3), calcium oxide (CaO), etc. These components do not decompose when heated, have low thermal conductivity, and function as a thermal barrier layer, thereby suppressing the spread of combustion in the resin composite material. Furthermore, the three-dimensional dispersion of fly ash within the resin promotes the formation of a carbonized layer during combustion and acts as a physical barrier that blocks oxygen supply. This has resulted in an improvement in the oxygen index.

[0015] The fly ash used in this invention is derived from biomass combustion residue and contains a large amount of alkaline oxides such as calcium oxide (CaO), magnesium oxide (MgO), and potassium oxide (K2O). When dispersed in the resin composite material, these components increase the pH of the surface and interior, creating an environment that suppresses the growth of microorganisms. Potassium oxide, in particular, readily reacts with water to form a strongly alkaline environment, which is known to have a destructive effect on the cell membranes of bacteria and fungi. This promotes the expression of antibacterial activity. [Effects of the Invention]

[0016] According to the present invention, by compounding the gypsum (dihydrate gypsum) and paper fibers contained in waste gypsum board with synthetic resin without separating them, it becomes possible to recycle the entire waste gypsum board, which was previously considered difficult. This eliminates processes such as sorting, firing, and recycling, thereby reducing equipment costs and improving the resource recycling rate.

[0017] Dihydrate gypsum releases crystalline water when heated, forming a heat-insulating layer within the resin, thereby exhibiting flame retardancy that suppresses the spread of combustion. In particular, hydrogen-bonded water molecules contained in dihydrate gypsum are gradually dehydrated when heated, inducing a slow carbonization reaction accompanied by heat absorption, and promoting the formation of a homogeneous carbonized layer within the resin. This carbonized layer acts as a physical barrier that blocks oxygen supply, suppressing the persistence of combustion.

[0018] Furthermore, the paper fibers are dispersed three-dimensionally together with dihydrate gypsum, functioning as a fiber reinforcement and assisting in the formation of the carbonized layer, thereby contributing to improved flame retardancy. The carbonization behavior of the paper fibers is also controlled by the presence of hydrogen-bonded water molecules, forming a stable carbonized structure while avoiding rapid thermal decomposition. These synergistic effects result in an improved oxygen index, significantly enhancing the non-flammability of the resin composite material.

[0019] Furthermore, the fly ash used in the present invention is low-temperature calcined ash derived from a biomass power generation facility or an incineration facility. Since it has a plate-like or flat particle shape, it is easily microdispersed three-dimensionally in the resin and has high functionality as a reinforcing material. As a result, the mechanical strength and dimensional stability of the molded product are improved.

[0020] Inorganic components such as silicon oxide (SiO2), aluminum oxide (Al2O3), and calcium oxide (CaO) contained in the fly ash do not thermally decompose during heating and have low thermal conductivity, so they function as a heat insulation layer and suppress the spread of combustion of the resin composite material. In addition, by promoting the formation of a carbonized layer, it contributes to further improvement of flame retardancy.

[0021] Also, alkaline oxides such as calcium oxide (CaO), magnesium oxide (MgO), and potassium oxide (K2O) contained in the fly ash, when dispersed in the resin composite material, raise the pH of the surface and interior, forming an environment that suppresses the growth of microorganisms. In particular, potassium oxide is known to easily form a strongly alkaline environment by reacting with moisture and has a destructive effect on the cell membranes of bacteria and fungi, contributing to the expression of antibacterial properties.

[0022] As described above, the present invention recycles materials such as waste gypsum board and fly ash, which were conventionally treated as waste, into a resin composite material excellent in moldability, non-combustibility, antibacterial properties, and environmental performance, and is expected to be applied to building materials, interior materials, civil engineering materials, etc. This contributes to the construction of a sustainable resource circulation-type society that achieves both effective utilization of waste and reduction of environmental load.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a flowchart showing the manufacturing process of the resin composite material of the present invention. It shows the process of adding water to the pulverized powder of waste gypsum board to make it into a paste, mixing this with a synthetic resin, and then performing extrusion kneading, degassing, molding, cooling, and cutting.

Embodiments for Carrying Out the Invention

[0024] The following describes in more detail embodiments of the method for manufacturing a resin composite material and its structure according to the present invention. While the method for manufacturing a resin composite material and the details of the resin composite material can be applied to the present invention as described in Japanese Patent Publication No. 7061239, the invention is not limited thereto.

[0025] The waste gypsum board used in this embodiment is construction waste that has been separated and discharged. After primary crushing at a recycling facility, it is processed into a powder with a particle size of 0.5 mm or less, preferably 0.3 mm or less, using a secondary pulverizer. When pulverizing, it is desirable to pulverize the gypsum core material and paper fibers together without separating the paper layer. This allows the paper fibers to act as fillers, improving interfacial dispersibility when kneading with the synthetic resin described later.

[0026] To the obtained powder, water is added in an amount of approximately 30-80% by weight, and the mixture is stirred using a stirrer (e.g., a blade mixer, a paddle mixer, etc.). In this process, the gypsum powder and paper fibers absorb the water, and a viscous, homogeneous paste-like substance (hereinafter referred to as the first mixture) is obtained. The viscosity of the paste is due to the formation of a network by hydrogen bonding between the gypsum and cellulose fibers, which have an affinity for water, and is important for achieving both plasticity and retention properties of the material.

[0027] The rotational speed during this stirring is preferably 100 rpm or higher, and is set within a range that ensures the shear energy necessary for mixing uniformity and structure formation. There is no particular upper limit, and it is adjusted as appropriate according to the viscosity of the material and the torque characteristics of the stirrer. Excessively high rotational speeds may cause frictional heat buildup and molding defects due to air entrapment, so in practice, a medium-speed stirring (for example, up to about 300 rpm) is often considered a stable operating range.

[0028] The paste-like mixture of the present invention is preferably made with sufficient plasticity and viscosity to retain moisture while not being dehydrated when subjected to a centrifugal dehydrator. This corresponds to a state in which the gypsum powder and paper fibers retain water by forming hydrogen bonds, and a stable viscous structure is maintained even in subsequent molding and degassing processes.

[0029] To this first mixture, granular or powdered thermoplastic synthetic resin (e.g., polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), etc.) is added and mixed using a mixer at approximately 60-150 rpm for 10 minutes or more. The amount of synthetic resin added is preferably set so that its weight percentage in the final composite material is 30-49 wt%, resulting in a mixture in which the resin particles are uniformly dispersed.

[0030] Furthermore, fly ash derived from biomass power generation facilities or incineration facilities can be added as needed. The timing of fly ash addition is not particularly limited; it can be added at any stage of the process, such as before mixing with the synthetic resin, after mixing, or immediately before melting and kneading. Fly ash with alkalinity (pH 8-11) and an average particle size of 10-50 μm is preferable. By adding 10-40 wt% of the total composite material, it is possible to improve heat resistance and non-flammability while exhibiting its function as an inorganic filler.

[0031] The resulting mixture (hereinafter referred to as the second mixture) is fed into a closed-type kneading apparatus equipped with a vent, preferably a twin-screw extruder, and kneaded while being heated to a temperature above the melting point of the synthetic resin (PE: approximately 130°C, PP: approximately 170°C, PVC: approximately 150-180°C). At this time, the heating zone of the extruder is set to 3 to 4 stages, and stable melt kneading is achieved by gradually increasing the temperature.

[0032] During mixing, degassing is performed in the vent section under negative pressure (-0.05 to -0.1 MPa) to efficiently remove excess moisture and volatile components. This reduces the moisture content at the thermal fluid temperature to 1 wt% or less, preventing molding defects such as foaming and surface roughness during molding. As a result, a resin composite material with excellent dimensional stability, surface quality, and mechanical strength can be obtained. Details of the extruder, the venting device for the extruder, and the venting method for the extruder can be applied to the present invention as described in Japanese Patent Publication No. 7532705, but are not limited thereto.

[0033] For example, it can be used as an extruded material with an irregular cross-section (e.g., furring strips), a thin-walled hollow structure (e.g., hollow sheets, T-die molded products), or a strip-shaped fibrous molded product such as flat yarn produced by slitting and stretching a film obtained by inflation molding or T-die molding.

[0034] As a non-combustible building material, it can be molded into interior panels, flooring, ceiling materials, etc., exhibiting excellent fire resistance and dimensional stability. Furthermore, as an infrastructure material, it can be molded into water supply pipes (internal pressure-resistant straight pipes) and sewer corrugated pipes (corrugated structural material with ring rigidity), and depending on the intended use, it can be labeled as a material with antibacterial or hydrogen sulfide resistance (functionality labeling).

[0035] Furthermore, the carbonization behavior of the paper fibers in this invention is controlled by the presence of hydrogen-bonded water molecules contained in dihydrate gypsum, forming a stable carbonized structure while avoiding rapid thermal decomposition. As a result, a homogeneous carbonized layer is formed on the surface of the molded product, acting as a physical barrier that blocks oxygen supply during combustion. Furthermore, the potassium oxide (K2O) contained in fly ash reacts with moisture on the surface of molded products, creating a strongly alkaline environment. This has a destructive effect on the cell membranes of bacteria and fungi, resulting in antibacterial activity. In particular, it has been confirmed that the antibacterial activity persists even in humid environments. <Examples>

[0036] The following are specific examples of the manufacturing of the resin composite material according to the present invention. However, the present invention is not limited to these examples. <Example 1>

[0037] (1) Preparation of waste gypsum board powder Waste gypsum board (with gypsum core and paper liner) recovered from construction demolition work was crushed into a powder with a particle size of 0.3 mm or less using a primary crusher (jaw crusher) and a secondary pulverizer (hammer mill). No drying treatment was performed, and the material was used in its naturally moist state.

[0038] (2) Preparation of the first mixture (paste) To 100 parts by weight of the powder, 50 parts by weight of pure water was added and stirred for 10 minutes using a blade-type mixer (stirring speed 200 rpm) to obtain a homogeneous paste-like mixture. The obtained paste showed no separation of water even after treatment with a centrifugal dehydrator and exhibited a stable viscous structure.

[0039] (3) Mixing with synthetic resin 100 parts by weight of polyethylene (PE) pellets were added and mixed for 15 minutes in a blade-type mixer (rotation speed 120 rpm). The resulting second mixture was subjected to an extrusion and kneading process. The PE used was Novatec LL® UF420 manufactured by Nippon Polyethylene Co., Ltd.

[0040] (4) Melt mixing and degassing The second mixture was heated and kneaded (melt-kneaded) using a twin-screw extruder with heating zone settings: Zone 1: 120°C, Zone 2: 140°C, Zone 3: 170°C, and Zone 4: 160°C. Degassing treatment was performed in the vent section of Zone 4 under negative pressure of -0.08 MPa, and the moisture content at the thermal fluid temperature of 140°C was reduced to 0.1 wt%.

[0041] (5) Molding The resulting molten mixture was removed from the extrusion die in strand form, cooled, cut, and pelletized. The resulting resin composite material had an oxygen index of 27.5 and a flexural modulus of 1200 MPa. Furthermore, it was confirmed that it could be subjected to inflation molding and that it was suitable for processing as a flat yarn. <Comparative Example 1>

[0042] As a comparative example, 100 parts by weight of the same powder as in Example 1 (particle size 0.3 mm or less) was mixed with 50 parts by weight of pure water and stirred at a stirring speed of 20 rpm for 5 minutes. However, due to insufficient energy from stirring, it did not become a paste, and residual powder and separation of water were observed. When this mixture was kneaded with synthetic resin and an extrusion process was attempted, the free water turned into steam, causing a rapid increase in pressure inside the extruder, resulting in the contents being ejected from the extrusion die and making molding impossible. <Example 2>

[0043] To confirm the effect of fly ash, steps (1) to (3) were carried out similarly under conditions in which the amount of mixture in (2) of Example 1 was halved. Specifically, 75 parts by weight of the second mixture was obtained by adding 25 parts by weight of pure water to 50 parts by weight of the powder.

[0044] (3) Addition of fly ash To 75 parts by weight of the second mixture, 75 parts by weight of fly ash (average particle size 25 μm, pH 11.0) derived from a biomass power generation facility was added and mixed for a further 10 minutes. The blending ratio of the synthetic resin was the same as in Example 1 (40 wt%).

[0045] The subsequent steps were carried out in the same manner as in Example 1. The resulting resin composite material exhibited an oxygen index of 26.7 and a flexural modulus of 1100 MPa, and was capable of inflation molding and flat yarn processing. Furthermore, an antibacterial activity value of 2.0 or higher was confirmed for an 80 μm thick film through antibacterial testing in accordance with JIS Z 2801. <Example 3>

[0046] To confirm the effect of different synthetic resin blending ratios on rigidity, 50 parts by weight of PE and 50 parts by weight of PP were used in the same procedure as in Example 2. The PP used was Novatec® PP MA3 manufactured by Nippon Polypropylene Co., Ltd.

[0047] We were able to obtain good quality pellets. The resulting resin composite material exhibited an oxygen index of 26.4 and a flexural modulus of 2900 MPa, and was suitable for pipe molding and corrugated pipe molding by extrusion. Antimicrobial activity values ​​of 2.0 or higher were confirmed in antimicrobial tests conducted in accordance with JIS Z 2801 for the molded products. <Example 4>

[0048] A test was conducted using polyvinyl chloride (PVC) as the synthetic resin. The mixing ratio was waste gypsum board powder:water:fly ash:PVC = 40:20:10:30, and Shin-Etsu Chemical's GR 2500S was used as the PVC. Mixing was carried out in a kneader with a vent, and the resulting mixture was in flake form.

[0049] These flakes and a foaming agent were fed into an extruder, and foam extrusion molding was performed. The dimensions of the molded product were 500 mm in width and 30 mm in thickness. This material was cut into 300mm squares and subjected to a 20-minute heating test using a heating furnace method compliant with JIS A 1321. The results confirmed that it exhibited excellent non-flammability, low smoke emission, and gas suppression, meeting the requirements for non-combustible materials under the Building Standards Act. In addition, an antibacterial activity value of 2.0 or higher was confirmed in an antibacterial test.

[0050] <Effects of the Example> According to the present invention, by compounding inorganic fine particles such as waste gypsum board powder and fly ash with a thermoplastic resin at a high concentration, and forming a viscous structure that suppresses the release of free water, foaming and separation during heating and melting can be avoided, and a stable resin composite material can be obtained. Such composite materials are inexpensive, yet offer the advantage of excellent formability, as they allow for inflation molding and sheet processing using T-dies, which were difficult with conventional high-filler composite materials.

[0051] In particular, films obtained by inflation molding and sheets produced by T-dies can be processed into flame-retardant and antibacterial flat yarns and honeycomb structured products, enabling a wide range of applications such as agricultural and construction materials, logistics materials, packaging materials, and cushioning materials. Furthermore, by compounding chemical-resistant resins such as PE with the alkaline inorganic components of gypsum and fly ash, it is possible to provide materials with high hydrogen sulfide resistance for sewage applications where corrosion by hydrogen sulfide is serious. In addition, since rigidity is greatly improved by high filling, it can be applied to structural materials for infrastructure, such as large-diameter, high-rigidity corrugated pipes, which were not possible with conventional PE alone.

[0052] Furthermore, when polyvinyl chloride (PVC) is used as the base material, it can be effectively utilized as a non-combustible building material through foam extrusion, and is lightweight and has excellent dimensional stability. In particular, compared to ALC (autoclaved lightweight concrete) and concrete structures, it has superior waterproofing and resistance to frost damage, making it suitable for a wide range of building applications, including interior and exterior panel materials, flooring materials, and ceiling materials. This makes it possible to provide a new non-combustible composite material that can complement or replace the functions of gypsum and concrete-based building materials. [Industrial applicability]

[0053] The resin composite material according to the present invention uses industrial waste such as waste gypsum board and fly ash as its main raw materials, and by compounding these with resin at a high density while achieving both high moldability and functionality, it has the potential for a wide range of applications as an innovative upcycled material in the fields of building materials, infrastructure materials, and packaging materials.

[0054] Specifically, to address the serious issue of hydrogen sulfide corrosion of concrete structures in sewage treatment facilities, the formation of large-diameter corrugated pipes with corrosion resistance, high rigidity, and antibacterial properties can be put into practical use as long-life, low-maintenance piping system materials. Furthermore, this material, which excels in film and sheet molding, can also be processed into flat yarn by inflation molding and honeycomb structures by T-die molding. As a lightweight, flame-retardant, and antibacterial high-value-added product, it is expected to be widely used in fields such as logistics, packaging, agriculture, and building materials.

[0055] Furthermore, when combined with PVC resin, it can be used as a non-combustible building material that can replace ALC and concrete building materials through foam extrusion. It can compensate for the lack of waterproofing and resistance to water absorption and frost damage that were issues with ALC, while ensuring lightness and ease of installation. As a next-generation functional building material that addresses social issues such as environmental protection, resource recycling, and disaster countermeasures, it has extremely high industrial significance.

Claims

1. A step of crushing waste gypsum board into powder, The process involves adding water to the aforementioned powder and stirring it at a rotation speed of 100 rpm or more to obtain a paste. The process involves mixing the paste and the synthetic resin to obtain a mixture. The process involves placing the mixture inside a sealed container equipped with a vent, heating and kneading it at a temperature at which the synthetic resin melts, and forming a molten kneaded body. A method for producing a resin composite material, comprising the step of degassing the molten mixture under negative pressure in the vent section.

2. In the method for producing a resin composite material according to claim 1, A method for producing a resin composite material, further comprising the step of adding fly ash derived from a biomass power generation facility or incineration facility to the mixture and mixing to obtain the mixture.

3. In the method for producing a resin composite material according to claim 1 or claim 2, The sealed container is a twin-screw extruder, which is a method for manufacturing resin composite materials.

4. In the method for producing a resin composite material according to claim 1 or claim 2, A method for producing a resin composite material, wherein the synthetic resin is one of polyethylene, polypropylene, or polyvinyl chloride.

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