Surface-Modification-Based Oyster Shell-Applied Plastic Composite and Method for Preparing the Same

Abstract

The present invention relates to a method for manufacturing a plastic composite using oyster shells. After removing residual organic matter and microorganisms by washing, drying, and heat-treating the oyster shells, a surface-modified oyster shell powder can be formed by spraying a silane coupling agent during the grinding process to combine the calcium component on the surface of the newly exposed oyster shell powder with the silane coupling agent. Subsequently, the surface-modified oyster shell powder can be fed into a twin-screw extruder together with a thermoplastic resin matrix and glass fibers and melt-kneaded to form a chemical bond between the organic functional group of the silane coupling agent and the reactive functional group of the resin matrix. The output from the compounding step can be obtained as a composite in the form of pellets through strand extrusion and cutting.

Description

Technology Field

[0001] The present invention relates to a surface-modified oyster shell-applied plastic composite and a method for manufacturing the same. More specifically, it relates to a method for manufacturing an oyster shell-filled thermoplastic resin composite characterized by surface-modifying oyster shell powder with a silane coupling agent and then melt-kneading and extruding it with a thermoplastic resin and glass fibers. Background Technology

[0002] Thermoplastic resin composites are widely applied in various fields, including automotive parts, electrical and electronic devices, and industrial structural materials, based on their excellent mechanical strength, heat resistance, and moldability. It is common practice to incorporate inorganic fillers or reinforcing agents into these composites to improve mechanical properties or reduce costs. Recently, active research has been conducted to simultaneously achieve resource circularity and reduce environmental burden by recycling natural mineral-derived materials—generated from industrial waste or fisheries byproducts—as fillers. Oyster shells contain a large amount of calcium carbonate as a main component, making them highly promising for use as inorganic fillers; furthermore, they are attracting attention as a sustainable material source due to their abundant production as a fisheries byproduct.

[0003] However, powder fillers derived from natural minerals, such as oyster shells, have hydrophilic surfaces, whereas thermoplastic resin matrices often have hydrophobic properties. Consequently, the interfacial affinity between the two is low, which limits the dispersibility of the filler within the composite and the bonding strength with the resin. As a result, composites simply mixed with oyster shell powder tend to fail to meet target levels for physical properties such as mechanical strength and impact resistance. Therefore, there is a need for a technology that can improve the properties of the composite by effectively forming interfacial bonds between the filler and the resin matrix. The problem to be solved

[0004] The present invention has been devised in response to the aforementioned background technology, and aims to solve the problem of deterioration in the mechanical properties of a plastic composite due to low interfacial bonding strength between inorganic oyster shell components and an organic thermoplastic resin matrix when utilizing oyster shell waste as a filler for plastic composites, and to manufacture an eco-friendly plastic composite with high physical properties in which substantial chemical bonding is formed between the filler and the resin matrix.

[0005] Furthermore, the present invention aims to increase the surface modification efficiency of oyster shell powder to economically utilize large quantities of oyster shell waste as a resource and simultaneously realize environmental and industrial value.

[0006] The technical problems of the present invention are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0007] According to one embodiment of the present invention for solving the problem described above, a method for manufacturing a plastic composite material incorporating oyster shells is disclosed.

[0008] A method for manufacturing a plastic composite material with oyster shells according to one embodiment of the present disclosure is,

[0009] A pretreatment step of removing residual organic matter and microorganisms by washing and drying oyster shells and then heat-treating them; a surface modification grinding step of forming oyster shell powder by grinding the pretreated oyster shells, wherein a silane coupling agent is sprayed onto the surface of the oyster shell powder during grinding to form surface-modified oyster shell powder in which the calcium component on the surface of the oyster shell powder newly exposed by grinding is combined with the silane coupling agent; a compounding step of feeding a thermoplastic resin matrix composed of at least one selected from polybutylene terephthalate (PBT) and polyamide (PA), glass fibers, and the surface-modified oyster shell powder into a twin-screw extruder and melt-kneading them to form a chemical bond through a reaction between the organic functional group of the silane coupling agent combined on the surface of the surface-modified oyster shell powder and the reactive functional group of the thermoplastic resin matrix; and a pelletizing step of extruding the output of the compounding step into a strand and then cutting it to form pellets. The method comprises, wherein in the pretreatment step, the heat treatment is performed at a temperature of 300°C or higher and 700°C or lower for 1 hour or more and 6 hours or less, and the pretreatment step further comprises a step of converting a portion of the calcium carbonate in the oyster shell into calcium oxide by additionally performing partial calcination at a temperature of 700°C or higher and 900°C or lower for 1 hour or more and 3 hours or less after the heat treatment, and in the surface modification grinding step, the grinding is performed by at least one selected from a fin mill, a hammer mill, and a jet mill, and the silane coupling agent is composed of a primary silane coupling agent and a secondary silane coupling agent having different functional groups, wherein the primary silane coupling agent is spray-introduced in the surface modification grinding step and the secondary silane coupling agent is introduced into the twin-screw extruder in the compounding step, and the amount of the secondary silane coupling agent introduced may be 0.10 times or more and 1.50 times or less the amount of the primary silane coupling agent introduced in the surface modification grinding step.

[0010] In addition, the ratio R_dual of the amount of the first silane coupling agent to the sum of the amount of the first silane coupling agent and the amount of the second silane coupling agent can be calculated by the following mathematical formula 1.

[0011] [Mathematical Formula 1]

[0012] R_dual = α × (φ_OS / φ_ref)^β + γ × (1 - exp(-S_BET / S_BET_ref)) (where α is a basic fractionation factor between 0.30 and 0.50, β is a content nonlinear index between 0.40 and 0.80, γ is a specific surface area correction factor between 0.10 and 0.30, φ_OS is the mass ratio (wt%) of the surface-modified oyster shell powder relative to the total mass of the composite, φ_ref is a reference content of 5 wt%, S_BET is the specific surface area (m² / g) of the oyster shell powder measured after partial calcination, and S_BET_ref is a reference specific surface area of ​​10 m² / g.)

[0013] In addition, the chemical bond formed in the compounding step may be a Ca-O-Si-RY bond (wherein R is an organic functional group of the silane coupling agent and Y is a residue derived from the reactive functional group, and the reactive functional group is an ester group of polybutylene terephthalate or an amide group of polyamide).

[0014] In addition, the first silane coupling agent is at least one selected from glycidoxysilane, aminosilane, vinylsilane, and methacryloxysilane, and may further include an aging step after the surface modification grinding step in which the surface modification oyster shell powder is maintained at a temperature of 60°C or higher and 120°C or lower for 10 minutes or more and 120 minutes or less to complete the condensation reaction between the silane coupling agent and the calcium component.

[0015] In addition, the twin-screw extruder is equipped with a main hopper, a side feeder, and a vacuum vent. In the compounding step, the thermoplastic resin matrix and the glass fiber are fed into the main hopper, and the surface-modified oyster shell powder is fed into the rear barrel of the twin-screw extruder through the side feeder. The vacuum level of the vacuum vent is maintained at -0.09 MPa or higher and -0.05 MPa or lower to suck and remove volatile matter. In the compounding step, the barrel temperature of the twin-screw extruder is 230°C or higher and 270°C or lower, the screw rotation speed is 250 rpm or higher and 500 rpm or lower, and the L / D ratio of the twin-screw extruder is 40 or higher and 52 or lower. After adding a carbodiimide-based hydrolysis inhibitor to the discharge of the compounding step in an amount of 0.2 parts by weight or higher and 1.0 parts by weight or lower per 100 parts by weight of the discharge, the pelletizing step can be performed.

[0016] Another embodiment of the present invention for solving the present problem may provide a surface-modified oyster shell-applied plastic composite comprising Ca-O-Si-RY bonds extending from the calcium component on the surface of the surface-modified oyster shell powder produced by the above-described method to the residues on the thermoplastic resin matrix side.

[0017] Other specific details of the present invention are included in the detailed description and drawings. Effects of the invention

[0018] One embodiment according to the present invention has the effect of increasing surface modification efficiency and improving interfacial bonding strength between oyster shell powder and a thermoplastic resin matrix by introducing a silane coupling agent during the grinding process so that the newly exposed surface of the oyster shell powder immediately bonds with the coupling agent.

[0019] In addition, one embodiment according to the present invention has the effect of contributing to resource recycling by utilizing oyster shells generated as waste as a filler for plastic composites, while also providing a composite material with secured mechanical properties through an excellent interfacial bonding structure.

[0020] The above effects are not limited to those mentioned in the present invention, and other unmentioned effects will be clearly understood by a person skilled in the art from the description below. Brief explanation of the drawing

[0021] Figure 1 is a flowchart illustrating the overall four-step process flow (pretreatment → surface modification grinding → compounding → pelletizing) of a method for manufacturing a plastic composite using oyster shells. Figure 2 is a diagram illustrating the heat treatment conditions performed during the pretreatment stage of oyster shells and the condition branching flow depending on whether additional partial calcination is performed. Figure 3 is a diagram illustrating the detailed process flow of the surface modification grinding step, in which oyster shells are ground while surface modification, and the aging step immediately following therefrom. FIG. 4 is a diagram illustrating the concept of dividing the input of a heterogeneous silane coupling agent into a surface modification grinding step and a compounding step in a method for manufacturing a plastic composite material using oyster shells according to one embodiment of the present disclosure, as well as the functional group differences of the two silanes and the dividing input ratio (R_dual). Figure 5 is a graph showing the parameter relationship showing how the R_dual value calculated by Equation 1 varies according to the oyster shell content (φ_OS) and specific surface area (S_BET). FIG. 6 is a block diagram illustrating the configuration of a twin-screw extruder (300) and the connection relationship between auxiliary equipment for performing compounding and pelletizing steps in a method for manufacturing a plastic composite material using oyster shells according to one embodiment of the present disclosure. Specific details for implementing the invention

[0022] Various embodiments are now described with reference to the drawings. In this specification, various descriptions are provided to facilitate an understanding of the invention. However, it is evident that these embodiments can be practiced without such specific descriptions.

[0023] As used herein, terms such as “component,” “module,” “system,” etc. refer to computer-related entities, hardware, firmware, software, combinations of software and hardware, or executions of software. For example, a component may be, but is not limited to, a procedure executed on a processor, a processor, an object, an execution thread, a program, and / or a computer. For example, both an application executed on a computing device and the computing device itself may be a component. One or more components may reside within a processor and / or an execution thread. A component may be localized within a single computer. A component may be distributed among two or more computers. Additionally, these components may be executed from various computer-readable media having various data structures stored therein. Components may communicate through local and / or remote processes, for example, according to signals having one or more data packets (e.g., data from a component interacting with another component in a local system or distributed system, and / or data transmitted through signals to other systems and networks such as the Internet).

[0024] Furthermore, the term "or" is intended to mean an implicit "or" rather than an exclusive "or." That is, unless otherwise specified or evident from the context, "X uses A or B" is intended to mean one of the natural implicit substitutions. In other words, if X uses A; if X uses B; or if X uses both A and B, "X uses A or B" may apply to any of these cases. Additionally, the term "and / or" as used herein should be understood to refer to and include all possible combinations of one or more of the enumerated related items.

[0025] Additionally, the terms “comprising” and / or “comprising” should be understood to mean that such features and / or components are present. However, the terms “comprising” and / or “comprising” should be understood not to exclude the presence or addition of one or more other features, components and / or groups thereof. Furthermore, unless otherwise specified or clearly evident from the context to indicate a singular form, the singular in this specification and claims should generally be interpreted to mean “one or more.”

[0026] Those skilled in the art should recognize that the various exemplary logical blocks, configurations, modules, circuits, means, logics, and algorithmic steps described in connection with the embodiments disclosed herein may be implemented in electronic hardware, computer software, or a combination of both. To clearly exemplify the interchangeability of hardware and software, various exemplary components, blocks, configurations, means, logics, modules, circuits, and steps have been generally described above in terms of their functionality. Whether such functionality is implemented in hardware or software depends on the specific application and design constraints imposed on the overall system. Skilled technicians may implement the described functionality in various ways for each specific application. However, such decisions regarding implementation should not be interpreted as moving out of the scope of the invention.

[0027] The description of the presented embodiments is provided to enable those skilled in the art to use or practice the present invention. Various modifications to these embodiments will be apparent to those skilled in the art. The general principles defined herein may be applied to other embodiments without departing from the scope of the present invention. Thus, the present invention is not limited to the embodiments presented herein. The present invention should be interpreted in the broadest possible scope consistent with the principles and novel features presented herein.

[0028] In this specification, oyster shell-based plastic composites may include a thermoplastic resin-based composite material containing oyster shell-derived powder as a filler or functional additive, and may include a form having any one of polybutylene terephthalate (PBT), polyamide (PA), and mixtures thereof as a matrix, a form additionally reinforced with glass fibers, or any one of pellets, sheets, or molded articles.

[0029] In this specification, a twin-screw extruder may include an extrusion facility in which two screws rotate in the same or opposite direction to convey, melt, and mix the input raw material and discharge it, and may include a form having one or more of a main hopper, a side feeder, a vacuum vent, a heating barrel, and a die.

[0030] In this specification, the discharge may include a molten mixture discharged through the die of the twin-screw extruder, and may include any one of a strand form, a sheet form, or a form in which a post-additive is additionally mixed.

[0031] In this specification, the pretreatment step may include a step of removing residual organic matter, microorganisms, or moisture by performing one or more of washing, drying, heat treatment, and partial calcination on oyster shells and processing them into a state suitable for subsequent processes.

[0032] In this specification, the compounding step may include the step of feeding raw materials, including a thermoplastic resin matrix, glass fibers, and surface-modified oyster shell powder, into the twin-screw extruder and melting and kneading them to form a homogeneous composite melt, and may additionally include the input of a secondary silane coupling agent.

[0033] In the present specification, the pelletizing step may include a step of extruding the output of the compounding step into a strand and then cutting it to form pellets of a certain size, and may include a form that includes one or more of a cooling process by water cooling or air cooling and a post-addition process of a hydrolysis inhibitor.

[0034] In this specification, the input of oyster shell raw materials may include the operation of supplying oyster shells generated during the oyster farming or processing process as input raw materials for the pretreatment step, and may include the operation of supplying oyster shells in any form among classified or unclassified oyster shells, or oyster shells before or after washing.

[0035] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0036] Each step described in this specification is described as being performed by a computer, but the subject of each step is not limited thereto, and depending on the embodiment, at least some of each step may be performed on different devices.

[0037] FIG. 1 is a flowchart illustrating the overall four-step process flow (pretreatment → surface modification grinding → compounding → pelletizing) of a method for manufacturing a plastic composite using oyster shells. Referring to FIG. 1 according to one embodiment of the present disclosure, the method for manufacturing a plastic composite using oyster shells may include a series of processes starting from the input of raw materials for oyster shells (S110), sequentially passing through a pretreatment step (S120), a surface modification grinding step (S130), a compounding step (S140), and a pelletizing step (S150), leading to the production of pellets (S160).

[0038] First, in the oyster shell raw material input (S110) step, waste oyster shells discharged from an oyster farm or oyster processing plant can be provided as input raw materials for the process. For example, the received oyster shells can be managed in lot units with attached metadata such as origin, date of receipt, and moisture content, and can be transferred to a subsequent pre-processing step (S120) in quantitative units (e.g., 50 kg per lot) via a hopper or conveyor line. In addition, the lot identifier, input time, and input amount of the raw material provided in the oyster shell raw material input (S110) are loaded as records in the format (lot_id, timestamp, weight_kg, moisture_pct) in the raw material history table of the process management system, and can be utilized to ensure traceability in subsequent steps.

[0039] In the pretreatment step (S120), the oyster shells supplied from the oyster shell raw material input (S110) can be washed, dried, and then heat-treated to remove organic matter and microorganisms remaining on the surface and inside the oyster shells. For example, washing can be performed by immersing the oyster shells in room temperature water or alkaline water and stirring to separate surface deposits such as sand, mud, and salt, and drying can be performed by placing the oyster shells inside a hot air dryer for a certain period of time to remove residual moisture. Heat treatment can be performed by loading the oyster shells into the internal chamber of an electric furnace or gas furnace and maintaining them according to a preset temperature and time profile, and the temperature profile at this time can be managed by receiving the thermocouple signal installed inside the furnace through a PID control loop and reflecting it in the heating output. In one embodiment, as a result of the pretreatment step (S120), organic matter such as proteins and chitin and microorganisms on the surface of the oyster shell can be removed by oxidation and thermal decomposition, and the product can be transferred to the surface modification grinding step (S130) in the form of primary powder or granules.

[0040] In the surface modification grinding step (S130), oyster shells transferred from the pretreatment step (S120) are ground to form oyster shell powder, and a silane coupling agent may be sprayed onto the surface of the oyster shell powder during the grinding process. For example, while a grinding means such as a pin mill, hammer mill, or jet mill is operating inside the grinder, a spray nozzle positioned at the top or side of the grinding chamber may continuously spray the silane coupling agent in the form of fine droplets or spray it in the form of pulses synchronized with the grinding load signal. Additionally, as the oyster shell particles are crushed by grinding, the calcium (Ca) component of the newly exposed surface immediately comes into contact with and reacts with the hydrolyzed silanol group of the sprayed silane coupling agent, thereby forming surface-modified oyster shell powder in which the surface is modified with silane. In one embodiment, the surface modification grinding step (S130) can be performed in an in-situ surface modification form in which grinding and surface modification proceed simultaneously within the same chamber by controlling the silane spray amount and grinding speed to balance the new surface exposure speed, and the surface modification oyster shell powder, which is the product, can be transferred to the compounding step (S140) through a quantitative supply hopper.

[0041] In the compounding step (S140), a thermoplastic resin matrix composed of at least one selected from polybutylene terephthalate (PBT) and polyamide (PA), glass fibers, and surface-modified oyster shell powder formed in the surface-modification grinding step (S130) can be fed into a twin-screw extruder and melt-mixed. For example, raw material input can be performed in such a manner that resin pellets of PBT or PA are supplied in a fixed quantity through the main hopper of the twin-screw extruder, and glass fibers and surface-modified oyster shell powder are supplied in a fixed quantity separately through a side feeder. The supply amount of each raw material can be measured by a load cell-based gravimetric feeder and loaded into a process control system as a log record in the form of (time, type of raw material, supply amount). The co-rotating screw inside the extruder can perform melt-mixing while heating, shearing, and conveying the raw materials, and during this process, the organic functional group (R) of the silane coupling agent bonded to the surface of the surface-modified oyster shell powder can react with the reactive functional group on the thermoplastic resin matrix side. Here, the reactive functional group corresponds to an ester group in the case of PBT and an amide group in the case of PA, and as a result of the reaction, a Ca-O-Si-RY bond can be formed from the calcium on the surface of the oyster shell powder to the matrix-side residue (Y). In one embodiment, the interfacial bonding force between the oyster shell powder and the matrix is ​​strengthened by this covalent interfacial crosslinking, thereby improving the mechanical properties of the composite material, such as tensile strength, flexural strength, and impact strength.

[0042] In the pelletizing step (S150), the output from the compounding step (S140) can be extruded into a strand and then cut to form a pellet. For example, the molten output can be extruded in the form of multiple strands through a strand die placed at the outlet of a twin-screw extruder, and the extruded strands can be cooled and solidified while passing through a water bath or an air-cooled conveyor, and then cut into a certain length (e.g., 2 to 5 mm) by a rotary cutting blade of a pelletizer to produce a pellet. Additionally, the diameter, length, and weight of the pellets produced in the pelletizing step (S150) can be measured through an inline vision sensor or sampling inspection and stored as a quality record in the format (batch ID, time of measurement, diameter_mm, length_mm).

[0043] Finally, in the pellet production (S160) step, oyster shell-applied plastic composite pellets can be secured as the final product, and the produced pellets can be packaged and shipped as raw materials for subsequent molding processes such as injection molding or extrusion molding. In one embodiment, the result of pellet production (S160) can be provided in the form of a composite material that has enhanced interfacial bonding strength with a PBT / PA matrix while recycling a fishery byproduct called oyster shells.

[0044] FIG. 2 is a diagram illustrating the heat treatment conditions performed during the pretreatment step of oyster shells and the condition branching flow depending on whether partial calcination is additionally performed. Referring to FIG. 2 according to an embodiment of the present disclosure, the pretreatment step (S120) may proceed in the order of washing and drying (S210), heat treatment (S220), determination of whether to perform partial calcination (S230), partial calcination (S240), and output of pretreated oyster shells (S250). Depending on the result of the determination of whether to perform partial calcination (S230), either a path passing through partial calcination (S240) or a path bypassing it and branching directly to the output of pretreated oyster shells (S250) may be selected.

[0045] In washing and drying (S210), preparatory treatment may be performed to remove residual organic matter, moisture, and microorganisms attached to the surface of the oyster shell supplied from the oyster shell raw material input (S110). For example, washing and drying (S210) may be performed by immersing the oyster shell in fresh water or a weakly alkaline washing solution to first remove surface salt and attached foreign matter, and then evaporating the moisture in a hot air dryer at approximately 80°C until the moisture content drops to a certain level (e.g., 1% by weight or less). Additionally, to stably secure the efficiency of the subsequent heat treatment (S220), the immersion time and drying temperature may be applied differentially according to the size and thickness of the oyster shell, and process variables such as the moisture content and residual salt concentration of the dried oyster shell obtained in this process may be stored in the log table of the process control system as a record in the format (batch ID, time of measurement, moisture content, salt concentration).

[0046] Next, in the heat treatment (S220), the oyster shells output from the washing and drying (S210) can be heated in a temperature range of 300°C to 700°C for 1 hour to 6 hours, thereby oxidizing and decomposing the organic matter and microorganisms remaining in the oyster shells to remove them. For example, the heat treatment (S220) can be performed by loading the oyster shells into a muffle furnace or a rotary electric furnace, and then raising the internal temperature of the furnace to a set value within the range of 300°C to 700°C according to a preset temperature increase profile (e.g., 5 to 10°C per minute) by a process control unit, and maintaining the set value for 1 to 6 hours. In one embodiment, for batches in which the thickness of the oyster shells is relatively thick or the amount of residual organic matter is high, the holding temperature of the heat treatment (S220) can be raised to 500°C or higher and the holding time to 4 hours or higher so that the residual organic matter, such as collagen and chitin, is sufficiently decomposed. Meanwhile, if the temperature of the heat treatment (S220) is less than 300℃ or the holding time is less than 1 hour, the decomposition of residual organic matter is insufficient and may cause dust and gas generation in the subsequent compounding step (S140), and if the temperature exceeds 700℃ or exceeds 6 hours, unintended extensive decomposition of calcium carbonate may occur, making it difficult to control the specific surface area in the subsequent step.

[0047] When the heat treatment (S220) is completed, the determination of whether to perform partial calcination (S230) may determine whether to additionally perform subsequent partial calcination (S240). For example, the determination of whether to perform partial calcination (S230) may be performed by querying the partial calcination application flag (e.g., JSON format {"batch_id": ..., "partial_calcination": true / false}) entered by the user through the operator input interface of the process control terminal, or the value of the 'partial_calcination_flag' column in the batch-specific process recipe table registered in the storage unit in advance, and branching to the partial calcination (S240) path if the value is true, and to the pre-processed oyster shell output (S250) path if it is false. In one embodiment, the determination of whether to perform partial calcination (S230) may automatically determine the branch based on the result of comparing the measured values, such as the specific surface area and thermal weight loss of oyster shells sampled from the batch immediately after heat treatment (S220), with reference values.

[0048] In the determination of whether to perform partial calcination (S230), if it is determined that partial calcination is to be performed (Yes path), in partial calcination (S240), the oyster shell that has undergone heat treatment (S220) may be further heat-treated at a temperature of 700°C or higher and 900°C or lower for 1 hour or more and 3 hours or less, thereby performing an operation to convert a portion of the calcium carbonate (CaCO3) in the oyster shell into calcium oxide (CaO). For example, partial calcination (S240) may be performed in the same furnace used in heat treatment (S220) while maintaining the furnace atmosphere gas as air or a low-oxygen atmosphere, by further raising the temperature to a set value (e.g., 800°C) within the range of 700°C to 900°C, and maintaining the set value for 1 to 3 hours, so that the calcium carbonate on the surface layer of the oyster shell is partially decomposed to form a porous calcium oxide layer. As a result of this partial calcination (S240), micropores may develop on the surface of the oyster shell particles, increasing the specific surface area, and the number of active sites to which a silane coupling agent can penetrate and bind may increase in the subsequent surface modification grinding step (S130). In one embodiment, the holding temperature and time of the partial calcination (S240) may be determined according to the amount of residual organic matter and calcium carbonate content of the oyster shells at the end of the heat treatment (S220). For example, for batches in which organic matter is sufficiently removed during the heat treatment (S220), the holding temperature of the partial calcination (S240) may be set to 800°C or higher to increase the calcium oxide conversion rate, and for batches in which it is not, it may be held for a longer period at a relatively low temperature of around 750°C to suppress excessive decomposition of calcium carbonate. Meanwhile, if the temperature of partial calcination (S240) exceeds 900℃, the decomposition of calcium carbonate proceeds excessively, which may lower the mechanical strength of the oyster shell powder, and if it is below 700℃, conversion to calcium oxide hardly occurs, so the effect of introducing partial calcination (S240) may be negligible.

[0049] Oyster shells that have undergone partial calcination (S240), or oyster shells that are determined not to undergo partial calcination in the determination of whether to perform partial calcination (S230), can be transferred to a subsequent process through the pre-treated oyster shell output (S250). For example, in the pre-treated oyster shell output (S250), the pre-treated oyster shells are discharged into a quantitative hopper and can be transferred to the pre-treated oyster shell input (S310) of the surface modification grinding step (S130) shown in FIG. 3. In addition, at the time of the output of the pre-processed oyster shell (S250), process result data such as the heat treatment (S220) conditions (temperature and time) of the batch, whether and conditions of partial calcination (S240) are applied, and the measured specific surface area and residual calcium carbonate ratio can be stored in the database of the process management system as a record in the format (batch ID, step, condition, measured value), and the record can be used as reference data for determining the silane input amount of the subsequent step and setting the process conditions of the compounding step (S140).

[0050] FIG. 3 is a diagram illustrating the detailed process flow of a surface modification grinding step in which oyster shells are ground while surface modification, and an aging step immediately thereafter. Referring to FIG. 3 according to one embodiment of the present disclosure, the surface modification grinding step may sequentially include a step of introducing pre-treated oyster shells into a grinding facility (S310), a step of performing grinding by selecting a grinding method (S320), a step of spraying a silane coupling agent during grinding (S330), a step of forming surface modification oyster shell powder (S340), a step of aging the formed powder at a certain temperature and time (S350), and a step of transferring the powder after aging is completed to the next process (S360).

[0051] In the pre-processed oyster shell input (S310) step, oyster shell lumps or coarse crushed particles output from the preceding pre-processing process (e.g., the step completed up to the heat treatment and partial calcination of FIG. 2) may be input into the hopper of the crushing equipment. For example, the pre-processed oyster shell input (S310) step may be performed by measuring a predetermined input amount with an automatic meter based on a batch record of the upper process management system (e.g., a record in the form of (batch ID, time of completion of pre-processing, input mass)) and then supplying it to the crusher via a conveyor or vibrating feeder.

[0052] In the step of selecting a grinding method (S320), oyster shells can be ground into fine powder using at least one grinder selected from a pin mill, a hammer mill, and a jet mill. For example, a hammer mill may be selected if relatively large particles are to be processed quickly, and a pin mill or a jet mill may be selected alone or in combination if a more uniform and fine particle size distribution is to be obtained. In one embodiment, the selection of the grinding method may be determined based on target particle size information entered by an operator (e.g., user input value via an HMI screen) or the results of querying a mapping table (target particle size, throughput, grinder type) predefined in a storage unit.

[0053] In the step of spraying and injecting a silane coupling agent (S330), the silane coupling agent may be injected into the grinding chamber in the form of a spray through a spray nozzle while grinding is in progress. At this time, the amount of silane coupling agent injected may be set in a range of 1.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of oyster shell powder. For example, when the hourly throughput of oyster shell powder is measured in real time by a load cell of a metering feeder and transmitted to the control unit as a time series in the form of (time, throughput), the control unit can calculate the spray flow rate (g / min) by multiplying the measured throughput by a ratio corresponding to 1.5 to 5 parts by weight and adjust the rotational speed of the spray pump. In one embodiment, the injected silane coupling agent may be at least one selected from glycidoxysilane, aminosilane, vinylsilane, and methacryloxysilane. For example, if the polymer matrix is ​​an ester resin such as polybutylene terephthalate (PBT), a glycidoxy silane with high affinity for epoxy rings may be selected, and if compatibility with amide additives is to be increased, an amino silane may be selected. If the spray input amount is less than 1.5 parts by weight, the surface of the newly exposed calcium component may not be sufficiently covered, resulting in insufficient improvement in interfacial bonding strength, and if it exceeds 5 parts by weight, unreacted silane may act as a plasticizer within the polymer matrix, thereby degrading mechanical properties.

[0054] In the step of forming surface-modified oyster shell powder (S340), oyster shell particles are crushed by grinding, and the alkoxy group of the sprayed silane coupling agent comes into contact with the surface of the newly exposed calcium component, thereby causing primary adsorption and hydrolysis / condensation reactions, and thus oyster shell powder with a surface modified with silane can be formed. For example, the step of forming surface-modified oyster shell powder (S340) can be carried out by collecting the powder in a cyclone or bag filter at the rear end of the grinding chamber, and a portion of the collected powder can be recorded in a storage unit as a log in the form of (time, specific surface area, peak intensity) by monitoring the specific surface area and Si-O-Ca bond peaks through an inline BET analyzer or FT-IR analyzer to check the progress of surface modification.

[0055] In the aging (S350) step, the surface-modified oyster shell powder is maintained at a temperature of 60°C or higher and 120°C or lower for 10 minutes or more and 120 minutes or less, so that the condensation reaction between the silanol group of the silane coupling agent and the calcium component on the surface of the oyster shell can be completed. For example, the aging (S350) step can be performed with the powder loaded in a constant temperature oven or a jacketed silo, and the temperature value measured by the thermocouple inside the oven is collected in a time series (timestamp, measured temperature) in the control unit, and if the measured temperature deviates from the set range (60~120°C), the heater output can be adjusted through a PID control loop. In one embodiment, if the aging temperature is less than 60°C or the holding time is less than 10 minutes, the condensation reaction does not proceed sufficiently, and volatile unreacted materials may generate gas during the subsequent compounding process; if the aging temperature exceeds 120°C or the holding time exceeds 120 minutes, the silane layer may self-condense excessively, and the crosslinking density between the oyster shell surface and the polymer may actually decrease. For example, when using a general glycidoxy-based silane, aging of about 60 minutes at around 80°C may be selected, and when using an amino-based silane, aging of about 30 minutes at around 100°C may be selected.

[0056] In the step of transfer to the compounding stage (S360), the surface-modified oyster shell powder, which has completed maturation, can be transferred to the next process, the compounding stage (e.g., the melt mixing stage using the twin-screw extruder of FIG. 1 or FIG. 6). For example, the step of transfer to the compounding stage (S360) can be performed by supplying a quantitative amount of powder through a rotary valve at the bottom of the maturation silo and a vacuum transfer line, and the powder temperature and moisture content during transfer can be monitored in the form of (time, temperature, moisture) and recorded in a storage unit. Additionally, the step of transfer to the compounding stage (S360) can maintain the mixing ratio of the powder and the polymer resin within the extruder to a preset recipe (e.g., X parts by weight of oyster shell powder relative to 100 parts by weight of polymer) by controlling the flow rate of the powder supplied to the main hopper or side feeder of the subsequent process.

[0057] FIG. 4 is a diagram illustrating the concept of dividing the input of a heterogeneous silane coupling agent into a surface modification grinding step and a compounding step in a method for manufacturing an oyster shell-applied plastic composite according to one embodiment of the present disclosure, as well as the functional group differences of the two silanes and the split input ratio (R_dual). Referring to FIG. 4 according to one embodiment of the present disclosure, a primary silane coupling agent (110) can be supplied in a spray form to a grinder (200) to form a surface-modified oyster shell powder (210), and a secondary silane coupling agent (310) can be additionally input through a separate path to a twin-screw extruder (300) to contribute to the formation of Ca-O-Si-RY bonds in the extruded material (400).

[0058] Specifically, the primary silane coupling agent (110) is a silane compound having a functional group R₁ and can be selected to preferentially bind to the calcium component on the surface of the oyster shell powder. For example, the primary silane coupling agent (110) can be selected from the group of trialkoxysilanes having amino, epoxy, or methacryloxy functional groups (e.g., 3-aminopropyltriethoxysilane) and can be sprayed in the form of fine droplets in a range of 1.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of oyster shell through a spray nozzle installed at the inlet of the grinder (200) or inside the grinding chamber. The grinder (200) can be configured as a pin mill, a hammer mill, or a jet mill, and the silanol group generated by the hydrolysis of the alkoxy group of the primary silane coupling agent (110) at the active site of the oyster shell surface newly exposed by grinding can be immediately adsorbed and condensed to form a chemical bond of the Ca-O-Si-R₁ type. By this simultaneous grinding and spraying method, surface-modified oyster shell powder (210) can be produced without losing the activity of the newly formed surface created by grinding.

[0059] Next, the surface-modified oyster shell powder (210) can be transported to a compounding area along with a thermoplastic resin matrix (e.g., polybutylene terephthalate or polyamide) and glass fibers through the main hopper or side feeder path of the twin-screw extruder (300). At this time, the secondary silane coupling agent (310) can be selected as a silane compound having a functional group R₂ different from the functional group R₁ of the primary silane coupling agent (110), such that the relationship R₁≠R₂ is satisfied. For example, if the primary silane coupling agent (110) has an amino functional group, the secondary silane coupling agent (310) may be a trialkoxysilane having an epoxy, isocyanate, or vinyl functional group, and can be continuously supplied to a metering pump through a liquid injection port located at the rear end of the plasticization area of ​​the twin-screw extruder (300). The functional group R₂ of the secondary silane coupling agent (310) can react with the terminal group of the molten thermoplastic resin matrix (e.g., the carboxyl group of polybutylene terephthalate or the amine group of polyamide) to form a Y-side bond, and as a result, the Ca-O-Si-R₁ bond starting from the surface of the surface-modified oyster shell powder (210) and the Si-R₂-Y bond formed on the matrix side are connected to form a cross-linked structure of the Ca-O-Si-RY type within the extruded product (400).

[0060] Additionally, the amount of the secondary silane coupling agent (310) added can be controlled to a range of 0.10 times or more and 1.50 times or less compared to the amount of the primary silane coupling agent (110). If the amount of the secondary silane coupling agent (310) added is less than 0.10 times the amount of the primary silane coupling agent (110), the formation of matrix-side bonds is insufficient, so the effect of improving interfacial bonding strength may be negligible, and if it exceeds 1.50 times, unreacted silane remains and acts like a plasticizer, which may reduce the stiffness of the composite material.

[0061] Meanwhile, in one embodiment of the present disclosure, the ratio R_dual of the amount of the primary silane coupling agent (110) to the sum of the amount of the primary silane coupling agent (110) and the amount of the secondary silane coupling agent (310) can be calculated by the following [Equation 1].

[0062] [Mathematical Formula 1]

[0063] R_dual = α × (ϕ_OS / ϕ_ref)^β + γ × (1 - exp(-S_BET / S_BET_ref))

[0064] Here, α is a basic division factor of 0.30 or more and 0.50 or less, β is a content non-linear index of 0.40 or more and 0.80 or less, γ is a specific surface area correction factor of 0.10 or more and 0.30 or less, φ_OS is the mass ratio (wt%) of surface-modified oyster shell powder (210) relative to the total mass of the composite material, φ_ref is a reference content of 5 wt%, S_BET is the specific surface area (m² / g) of the oyster shell powder measured after partial calcination, and S_BET_ref is a reference specific surface area of ​​10 m² / g.

[0065] For example, the φ_OS value required for the calculation of R_dual can be obtained through an SQL query from the `os_wt_pct` column of a formulation table (e.g., `compound_recipe`) in a process database that manages the formulation recipe of the compounding stage, and the S_BET value can be loaded into a storage unit as a time series record in the form of (batch ID, measurement time, S_BET[m² / g]) by parsing a measurement log file (e.g., `bet_log.csv` in CSV format) output from a BET specific surface area analyzer immediately after partial calcination, and then retrieved on a batch basis. The calculated R_dual value is converted into a JSON record in the form of (batch ID, φ_OS, S_BET, R_dual, primary silane input amount, secondary silane input amount) and can be transmitted in real time to the spray nozzle control unit of the grinder (200) and the liquid injection pump control unit of the twin screw extruder (300), and each control unit can adjust the spray amount and pump flow rate according to the received input amount instruction value.

[0066] In another embodiment, when the content φ_OS of the surface-modified oyster shell powder (210) is greater than the reference content φ_ref of 5 wt%, the (φ_OS / φ_ref)^β term may be evaluated as greater than 1, and the R_dual value may increase, and accordingly, the specific gravity of the primary silane coupling agent (110) may increase, and splitting may be performed in a direction that preferentially saturates the active sites on the surface of the oyster shell. Meanwhile, when the specific surface area S_BET measured after partial calcination is sufficiently large compared to the reference specific surface area S_BET_ref of 10 m² / g, the (1 - exp(-S_BET / S_BET_ref)) term may be close to 1, and a correction amount of γ may be added, and when the specific surface area is small, the term may be close to 0, and the correction amount may be reduced. For example, under conditions where α = 0.40, β = 0.60, γ = 0.20, φ_OS = 10wt%, and S_BET = 15m² / g, R_dual ≈ 0.40 × (10 / 5)^0.60 + 0.20 × (1 - exp(-15 / 10)) ≈ 0.61 + 0.155 ≈ 0.77 can be calculated, and in this case, about 77% of the total input amount of the primary silane coupling agent (110) and the secondary silane coupling agent (310) can be input during the surface modification grinding stage, and the remaining about 23% can be input during the compounding stage.

[0067] Additionally, as shown in FIG. 4, the primary silane coupling agent (110) is connected to the grinder (200) via a spray path, the surface-modified oyster shell powder (210) is transferred from the discharge side of the grinder (200) to the twin-screw extruder (300), and the secondary silane coupling agent (310) is connected to the twin-screw extruder (300) via a separate liquid input path, so that finally, an output (400) with Ca-O-Si-RY bonds formed can be produced at the discharge port of the twin-screw extruder (300).

[0068] FIG. 5 is a graph illustrating the parameter relationship showing how the R_dual value calculated by Equation 1 varies according to the oyster shell content (φ_OS) and specific surface area (S_BET). Referring to FIG. 5 according to one embodiment of the present disclosure, a low specific surface area curve (530), a reference specific surface area curve (540), and a high specific surface area curve (550) can be shown together on a coordinate plane defined by the horizontal axis (510) of φ_OS and the vertical axis (520) of R_dual, and through this, the behavior of R_dual, which is the distribution ratio of the input amount between the primary silane coupling agent (110) and the secondary silane coupling agent (310), can be visually understood.

[0069] The φ_OS horizontal axis (510) is an axis that displays the mass ratio (wt%) of the surface-modified oyster shell powder (210) relative to the total mass of the composite material in a range of 0 wt% or more and 30 wt% or less, and a reference line in the form of a dotted line may be displayed on the φ_OS horizontal axis (510) at a position corresponding to the reference content φ_ref=5 wt%. For example, the oyster shell content displayed on the φ_OS horizontal axis (510) can be calculated from the weighing values ​​of the polymer and the surface-modified oyster shell powder (210) fed into the main hopper (800) and side feeder (120) of the twin-screw extruder (300) during the compounding step (S140), and can be stored in a process control database as a record in the format (batch ID, φ_OS_wt%, measurement time).

[0070] The R_dual vertical axis (520) may be an axis that displays R_dual, which is the ratio of the amount of the primary silane coupling agent (110) to the sum of the amount of the primary silane coupling agent (110) and the amount of the secondary silane coupling agent (310), in a range of 0 to 1.5. In one embodiment, the R_dual value may be calculated in the form of R_dual = m_1 / (m_1 + m_2) and mapped to a value on the R_dual vertical axis (520) after obtaining the mass of the primary silane coupling agent (110) sprayed in the surface modification grinding step (S130) and the mass of the secondary silane coupling agent (310) fed into the twin-screw extruder (300) in the compounding step (S140) as an integrated value of a flow meter or metering pump, respectively.

[0071] In one embodiment of the present disclosure, the low specific surface area curve (530), the reference specific surface area curve (540), and the high specific surface area curve (550) may all be the result of plotting the R_dual value calculated according to the following [Equation 1] against the change in the φ_OS horizontal axis (510).

[0072] [Mathematical Formula 1]

[0073] R_dual = α × (ϕ_OS / ϕ_ref)^β + γ × (1 - exp(-S_BET / S_BET_ref))

[0074] Here, α is a basic division factor selected from a range of 0.30 to 0.50, β is a content nonlinear index selected from a range of 0.40 to 0.80, γ is a specific surface area correction factor selected from a range of 0.10 to 0.30, φ_OS is the mass ratio (wt%) of surface-modified oyster shell powder (210) relative to the total mass of the composite material, φ_ref is a reference content of 5 wt%, S_BET is the specific surface area (m² / g) of the oyster shell powder measured after partial calcination (S240), and S_BET_ref may be a reference specific surface area of ​​10 m² / g. For example, the low specific surface area curve (530), the reference specific surface area curve (540), and the high specific surface area curve (550) are all results calculated under conditions where the median values ​​of α=0.40, β=0.60, and γ=0.20 are applied, and each curve data is loaded into a process control storage unit as a time series or lookup table in the form of (S_BET, φ_OS, R_dual) and can be referenced to determine the amount of secondary silane coupling agent (310) to be added in the compounding step (S140).

[0075] The low specific surface area curve (530) may be a curve representing the R_dual behavior under the condition of S_BET=5m² / g, that is, under the condition of oyster shell powder where partial calcination (S240) is not applied or the specific surface area is maintained relatively low by only heat treatment (S220). For example, in the low specific surface area curve (530), the γ × (1 - exp(-S_BET / S_BET_ref)) term of [Equation 1] contributes only slightly to the level of approximately γ × (1 - exp(-0.5)) ≈ 0.20 × 0.393 ≈ 0.079, so the R_dual value may be calculated to be lower than the reference specific surface area curve (540) and the high specific surface area curve (550) at the same φ_OS value, and this may be indicated in the form of a dotted line located at the bottom of the drawing.

[0076] The reference specific surface area curve (540) is a curve representing the R_dual behavior under the condition S_BET=S_BET_ref=10m² / g, and can be plotted to have a value of approximately α + γ × 0.632 ≈ 0.40 + 0.126 ≈ 0.526 by the (1-exp(-1)) term at the reference point where φ_OS=φ_ref=5wt%. In one embodiment, the reference specific surface area curve (540) can be used as a design reference line reflecting the standard partial calcination (S240) results of oyster shell powder, and can also be referenced as an interpolation reference curve when determining the amount of secondary silane coupling agent (310) to be added during the compounding step (S140).

[0077] The high specific surface area curve (550) may be a curve representing the R_dual behavior under the condition of S_BET=30m² / g, that is, under the condition of oyster shell powder where some of the CaCO3 is converted to CaO by partial calcination (S240) and the specific surface area is greatly increased. For example, in the high specific surface area curve (550), the γ × (1 - exp(-S_BET / S_BET_ref)) term approaches saturation at a level of approximately 0.20 × (1 - exp(-3)) ≈ 0.20 × 0.950 ≈ 0.190, so even if the specific surface area increases further, a saturation behavior may appear in which the increment on the R_dual vertical axis (520) gradually slows down, which can be represented by a point-diamond shaped curve located at the top of the figure.

[0078] In addition, the low specific surface area curve (530), the reference specific surface area curve (540), and the high specific surface area curve (550) may all show a pattern in which the (φ_OS / φ_ref)^β term increases non-linearly as the value of the φ_OS horizontal axis (510) increases beyond φ_ref=5wt%, and the R_dual value increases together. Meanwhile, in the region where the φ_OS value is close to 0wt%, the (φ_OS / φ_ref)^β term converges to 0, and the R_dual value may converge to a small amount mainly determined by the γ × (1 - exp(-S_BET / S_BET_ref)) term.

[0079] A computing device or process control unit according to one embodiment of the present disclosure may calculate [Equation 1] in real time using the oyster shell content φ_OS value of the batch and the specific surface area S_BET value measured after partial calcination (S240) as input variables immediately before proceeding with the surface modification grinding step (S130) and the compounding step (S140), and convert the calculated R_dual value into a command for quantitative pump control and transmit it to the spray nozzle of the primary silane coupling agent (110) and the side feeder (120) of the secondary silane coupling agent (310) quantitative supply device. For example, among the low specific surface area curve (530), reference specific surface area curve (540), and high specific surface area curve (550) of FIG. 5, the curve corresponding to the measured S_BET value may be stored in the storage unit as a key-value pair (φ_OS_bin, R_dual) in the form of a lookup table, and the process control unit can automatically adjust the distribution of the input amounts of the primary silane coupling agent (110) and the secondary silane coupling agent (310) by determining the R_dual value within a period of several seconds for each batch through SQL query or in-memory interpolation.

[0080] FIG. 6 is a block diagram illustrating the configuration of a twin-screw extruder (300) and the connection relationship between auxiliary equipment for performing compounding and pelletizing steps in a method for manufacturing a plastic composite material using oyster shells according to one embodiment of the present disclosure. Referring to FIG. 6 according to one embodiment of the present disclosure, the twin-screw extruder (300) is equipped with a main hopper (800) at the front end, a side feeder (120) coupled to a barrel at the rear end, and a vacuum vent (130) at the top of the barrel, so that a polybutylene terephthalate (PBT) or polyamide (PA) thermoplastic resin matrix, glass fiber, and surface-modified oyster shell powder (210) can be melt-kneaded to form an extruder (400) having Ca-O-Si-RY bonds formed therein.

[0081] The main hopper (800) is positioned at the front upper end of the twin-screw extruder (300) to gravity feed a thermoplastic resin matrix and glass fibers into the extruder. For example, the main hopper (800) can feed resin in the form of PBT or PA pellets and chopped glass fibers at a preset mixing ratio through a loss-in-weight feeder, and the feed data can be stored in a storage unit as a log record in the form of (time, type of raw material, cumulative amount of feed) to be used for real-time correction of mixing deviations. Additionally, the side feeder (120) is coupled to the rear end barrel side along the longitudinal direction of the twin-screw extruder (300) to force-feed surface-modified oyster shell powder (210) in a lateral direction. As the side feeder (120) is positioned in the rear barrel, the surface-modified oyster shell powder (210) can be introduced into a resin matrix that has already reached a molten state, thereby allowing the silane coupling agent on the surface of the powder to form Ca-O-Si-RY bonds at the interface with the matrix without receiving excessive thermal history.

[0082] A vacuum vent (130) is connected to the upper part of the barrel of a twin-screw extruder (300) to suck and remove volatile substances generated during compounding. For example, the vacuum vent (130) is connected to a vacuum pump so that the vacuum level can be maintained in a range of -0.09 MPa or higher and -0.05 MPa or lower. The vacuum level measurement is collected in real-time (e.g., at 1-second intervals) from a pressure transducer as a time-series record in the form of (time, vent port number, vacuum level) and can be input into a PID control loop that automatically corrects the drive output of the vacuum pump when it deviates from the set range. Meanwhile, if the vacuum level is weaker than -0.05 MPa, the suction of residual moisture and volatile by-products is insufficient, and pores may occur in the pellet (430). If it is stronger than -0.09 MPa, some of the low molecular weight additive or surface-modified oyster shell powder (210) itself may be sucked in, resulting in loss.

[0083] Additionally, the twin-screw extruder (300) can be operated during the compounding stage under conditions of a barrel temperature of 230°C or higher and 270°C or lower, a screw rotation speed of 250 rpm or higher and 500 rpm or lower, and an L / D ratio of 40 or higher and 52 or lower. For example, the barrel temperature can be divided into multiple zones, and a thermocouple sensor can be attached to each zone. The temperature measurement value of each zone can be collected as a time series record in the form of (time, zone number, measured temperature) at a interval of 1 to 5 seconds, and the output of the heater can be corrected based on the deviation from the set range of 230°C to 270°C. Additionally, the screw rotation speed can be obtained from the rotation speed signal of the inverter motor. If the rotation speed is less than 250 rpm, the dispersion of the surface-modified oyster shell powder (210) may be insufficient, and if it exceeds 500 rpm, the cutting of the glass fiber may proceed excessively, thereby reducing the reinforcing effect. If L / D is less than 40, the residence time is insufficient and the formation of Ca-O-Si-RY bonds may be incomplete, and if it exceeds 52, thermal decomposition of the resin may proceed due to excessive shear heat.

[0084] The extruded material (400) extruded through the die of the twin-screw extruder (300) can be transferred to a hydrolysis inhibitor post-addition unit (420), and the hydrolysis inhibitor post-addition unit (420) can post-add a carbodiimide-based hydrolysis inhibitor in a range of 0.2 parts by weight or more and 1.0 parts by weight or less per 100 parts by weight of the extruded material (400). For example, the hydrolysis inhibitor post-addition unit (420) is connected to a metering pump or a powder metering feeder, receives time-series data (time, extruded amount) in real time from a mass flow meter of the immediate extruded line, and can calculate the input amount of the carbodiimide-based hydrolysis inhibitor per unit time through the formula post-addition amount = extruded amount × R_carb / 100 (where R_carb is a value of 0.2 or more and 1.0 or less) and quantitatively input it. In one embodiment, if the amount of post-addition is less than 0.2 parts by weight, the hydrolysis resistance of the pellet (430) may not be sufficiently secured, and if it exceeds 1.0 part by weight, unreacted carbodiimide may remain, and the color or mechanical properties may be degraded.

[0085] The extruded material (400) to which a hydrolysis inhibitor has been added afterwards can be transferred to a strand extrusion and cutting process to form a pellet (430), and the pellet (430) can be formed by cooling a strand extruded from the die of a twin-screw extruder (300) in a water-cooling bath and then cutting it with a pelletizer. For example, the cutting cycle and take-up speed of the pelletizer can be collected as a time-series record in the form of (time, take-up speed, cutting cycle) and used to control the diameter and length deviation of the pellet (430) within a certain range, and the formed pellet (430) can be recorded in a storage unit as batch history data in the form of (batch number, production time, cumulative production amount, post-addition rate, vacuum level, barrel temperature) and used for subsequent processes and quality tracking.

[0086] Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention may be implemented in other specific forms without altering its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 A method for manufacturing a surface-modified oyster shell-applied plastic composite, comprising: a pretreatment step of washing and drying oyster shells and then heat-treating them to remove residual organic matter and microorganisms; a surface-modifying grinding step of grinding the pretreated oyster shells to form oyster shell powder, wherein a silane coupling agent is sprayed onto the surface of the oyster shell powder during grinding to form surface-modified oyster shell powder in which the calcium component on the surface of the oyster shell powder newly exposed by grinding is combined with the silane coupling agent; a compounding step of feeding a thermoplastic resin matrix composed of at least one selected from polybutylene terephthalate (PBT) and polyamide (PA), glass fibers, and surface-modified oyster shell powder into a twin-screw extruder and melt-kneading them to form a chemical bond through a reaction between the organic functional group of the silane coupling agent combined on the surface of the surface-modified oyster shell powder and the reactive functional group of the thermoplastic resin matrix; and a pelletizing step of extruding the output of the compounding step into a strand and then cutting it to form pellets. A method for manufacturing a surface-modified oyster shell-applied plastic composite, comprising: a pretreatment step in which the heat treatment is performed at a temperature of 300°C or higher and 700°C or lower for 1 hour or more and 6 hours or less; a pretreatment step further comprising a step of converting a portion of the calcium carbonate in the oyster shell into calcium oxide by additionally performing partial calcination at a temperature of 700°C or higher and 900°C or lower for 1 hour or more and 3 hours or less after the heat treatment; wherein the silane coupling agent is composed of a primary silane coupling agent and a secondary silane coupling agent having different functional groups, wherein the primary silane coupling agent is spray-introduced in the surface-modifying grinding step and the secondary silane coupling agent is introduced into the twin-screw extruder in the compounding step, and the amount of the secondary silane coupling agent introduced is 0.10 times or more and 1.50 times or less the amount of the primary silane coupling agent introduced in the surface-modifying grinding step. Claim 2 A method for manufacturing a surface-modified oyster shell-applied plastic composite according to claim 1, wherein the ratio R_dual of the amount of the first silane coupling agent to the sum of the amount of the first silane coupling agent and the amount of the second silane coupling agent is calculated by the following mathematical formula 1. [Mathematical Formula 1] R_dual = α × (φ_OS / φ_ref)^β + γ × (1 - exp(-S_BET / S_BET_ref)) (where α is a basic fractionation factor between 0.30 and 0.50, β is a content nonlinear index between 0.40 and 0.80, γ is a specific surface area correction factor between 0.10 and 0.30, φ_OS is the mass ratio (wt%) of the surface-modified oyster shell powder relative to the total mass of the composite, φ_ref is a reference content of 5 wt%, S_BET is the specific surface area (m² / g) of the oyster shell powder measured after partial calcination, and S_BET_ref is a reference specific surface area of ​​10 m² / g.) Claim 3 A method for manufacturing a surface-modified oyster shell-applied plastic composite according to claim 2, wherein the chemical bond formed in the compounding step is a Ca-O-Si-RY bond (wherein R is an organic functional group of the silane coupling agent and Y is a residue derived from the reactive functional group, and the reactive functional group is an ester group of polybutylene terephthalate or an amide group of polyamide). Claim 4 In claim 3, the first silane coupling agent is at least one selected from glycidoxysilane, aminosilane, vinylsilane, and methacryloxysilane, and further comprises an aging step in which the surface-modified oyster shell powder is maintained at a temperature of 60°C or higher and 120°C or lower for 10 minutes or more and 120 minutes or less after the surface-modifying grinding step to complete the condensation reaction between the silane coupling agent and the calcium component, and the twin-screw extruder is equipped with a main hopper, a side feeder, and a vacuum vent, and in the compounding step, the thermoplastic resin matrix and the glass fiber are fed into the main hopper, and the surface-modified oyster shell powder is fed into the rear barrel of the twin-screw extruder through the side feeder, and the vacuum level of the vacuum vent is maintained at -0.09 MPa or higher and -0.05 MPa or lower to suction and remove volatile matter, and in the compounding step, the barrel temperature of the twin-screw extruder is 230°C or higher A method for manufacturing a surface-modified oyster shell-applied plastic composite, wherein the temperature is 270℃ or lower, the screw rotation speed is 250 rpm or higher and 500 rpm or lower, the L / D of the twin-screw extruder is 40 or higher and 52 or lower, and a carbodiimide-based hydrolysis inhibitor is subsequently added to the discharge of the compounding step in an amount of 0.2 parts by weight or higher and 1.0 parts by weight or lower per 100 parts by weight of the discharge, and then the pelletizing step is performed. Claim 5 A surface-modified oyster shell-applied plastic composite material manufactured by the method of any one of claims 1 to 4, comprising Ca-O-Si-RY bonds extending from the calcium component on the surface of the surface-modified oyster shell powder to the residue on the thermoplastic resin matrix side.

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