Method for producing preform and preform

Abstract

A preform is manufactured more efficiently and at lower cost from a resin sheet obtained by pulverizing a recovered polyester resin molded article into flakes. Resin flakes obtained by pulverizing the recovered polyester resin molded article into flakes are prepared, the resin flakes are plasticized after heat treatment under reduced pressure conditions, foreign matter is removed from molten resin obtained by plasticizing the resin flakes, and the molten resin is supplied to an injection molding device to injection-mold a preform.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a prefabricated part and the prefabricated part. Background Art

[0002] Conventionally, synthetic resin containers obtained by forming a bottomed cylindrical preform using a polyester resin such as polyethylene terephthalate into a bottle shape by biaxial stretch blow molding or the like have been used in a wide range of fields as containers for various beverages, various seasonings, etc. Such containers are generally considered to be PET bottles, and in recent years, in response to social demands, a recycling technology called "bottle-to-bottle" has been studied, in which used PET bottles are collected and reused as recycling materials to manufacture PET bottles.

[0003] For example, Patent Document 1 discloses a technique in which resin flakes obtained by crushing recovered polyester resin molded products into flakes are decontaminated, resin pellets produced by melting the flakes are solid-phase polymerized, and then conveyed to an injection molding device to produce a preform.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-98350 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In view of the above background art, the present inventors have conducted intensive studies to produce preforms more efficiently and at lower cost from resin flakes obtained by pulverizing recycled polyester resin molded products into flakes, and have completed the present invention.

[0009] Means for solving problems

[0010] The manufacturing method of the preform of the present invention is set as the following method: preparing a resin sheet obtained by crushing a recycled polyester resin molded product into a flake shape; plasticizing the resin sheet after heating it under reduced pressure conditions; and removing foreign matter from the molten resin obtained by plasticizing the resin sheet, and supplying the molten resin to an injection molding device to injection mold a preform.

[0011] In addition, the preform of the present invention is a preform manufactured by the above manufacturing method, wherein the residual amount of acetaldehyde is 1 to 15 ppm, the residual amount of bishydroxyethyl terephthalate is 1 to 35 ppm, the residual amount of monohydroxyethyl terephthalate is 1 to 35 ppm, and the residual amount of cyclic trimer is 6000 pm or less.

[0012] Effects of the Invention

[0013] According to the present invention, a preform can be manufactured more efficiently and at a lower cost from resin flakes obtained by pulverizing a recovered polyester-based resin molded product into flakes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is an explanatory diagram conceptually showing the entire device for preferably carrying out the embodiment of the present invention.

[0015] Figure 2 This is an explanatory diagram showing an example of an apparatus for performing a heat treatment on a resin sheet in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] Hereinafter, preferred embodiments of the present invention will be described.

[0017] In the present embodiment, first, a resin flake is prepared by pulverizing a recovered polyester resin molded product into flakes.

[0018] When preparing the resin sheet, it is preferably washed by any washing method such as alkali washing, warm water washing, etc., in order to remove dirt such as residues of the contents remaining on the surface, foreign matter mixed in, etc. The "recovered polyester resin molded products" may include waste materials generated in the process of manufacturing polyester resin molded products in addition to used PET bottles and other polyester resin molded products collected separately as resource waste.

[0019] Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene furandicarboxylate, and copolymers thereof. These polyester resins may be polyester resins having a high biomass content by using ethylene glycol or its derivatives derived from plant-derived bioethanol as a diol component, terephthalic acid or its derivatives derived from plant-derived bio-paraxylene as a raw material, furandicarboxylic acid or its derivatives derived from plant-derived fructose as a raw material, and the like as a dicarboxylic acid component.

[0020] When used polyester resin molded products such as PET bottles are collected and reused as recycling materials based on so-called mechanical recycling to produce recycled products, the reduction in intrinsic viscosity caused by the degradation of the resin due to the thermal history etc. during the production of the recycled products becomes a cause of malfunctions in the production process of the recycled products. Furthermore, if a large amount of acetaldehyde (AA) generated by thermal decomposition of the polyester resin, oligomers such as bis(hydroxyethyl) terephthalate (BHET), mono(hydroxyethyl) terephthalate (MHET), and cyclic trimer (CT) generated by depolymerization of the polyester resin, and low molecular weight impurity components such as limonene derived from the content remain in the recycled materials, not only the quality of the produced recycled products is affected, but also the production equipment is contaminated, which becomes a cause of reduced productivity.

[0021] In this embodiment, in order to avoid such undesirable conditions, the prepared resin sheet is subjected to a heat treatment in an atmosphere with a reduced pressure of preferably less than 1000 Pa and a temperature of preferably 160 to 240°C, so that a solid phase polymerization reaction of the polyester resin that forms the resin sheet is carried out while the resin sheet is kept in a sheet-like form without melting, and crystallization is promoted.

[0022] By carrying out a solid phase polymerization reaction, the terminal groups of the polyester resin whose molecular chains are cut due to degradation and whose polymerization degree is reduced are repolymerized, and thus, as the polymerization degree is restored, the intrinsic viscosity corresponding to the molecular weight can be restored. Furthermore, by heating the resin sheet under reduced pressure conditions, especially by exposing it to a temperature atmosphere of 160 to 240°C under reduced pressure conditions, the hydrolysis of the polyester resin can be suppressed, and the crystallization can be well promoted by the melting point depression effect. As a result, the free volume between the molecular chains of the polyester resin is reduced (the amorphous phase is reduced), and the low molecular weight impurity components (organic impurity components) and the water adsorbed on the resin sheet as described above contained in the free volume part of the resin sheet are selectively exuded to the surface layer of the resin sheet, so that they are volatilized or evaporated, or washed with warm water, steam, organic solvents, etc. as needed, so that they can be efficiently removed.

[0023] In this embodiment, the specific method of heat treating the resin sheet is not particularly limited. For example, it is preferred to use Figure 2 The processing apparatus 100 shown in the figure performs a heat treatment, and includes at least one preheating chamber 102 and a processing chamber 103 capable of adjusting the internal atmosphere to a temperature and pressure suitable for the heat treatment.

[0024] Here, it is explained Figure 2 The processing device 100 shown in FIG. 1 is preferably provided with a 7 to 18 m 3A closed container 101 is constructed in a manner to have an internal volume of . In addition, a processing chamber 103 is provided in the closed container 101, and two preheating chambers 102 are provided above the closed container 101. The two preheating chambers 102 are connected to the closed container 101 via an opening and closing mechanism such as a sliding gate (not shown) so as to be able to communicate with the processing chamber 103 while maintaining airtightness with the outside of the system.

[0025] In addition, Figure 2 In the figure, illustration of a heating device, a decompression device, and incidental equipment such as pipes for adjusting the internal atmosphere of the processing chamber 103 is omitted.

[0026] When the resin sheet is subjected to heat treatment using such a treatment apparatus 100, it is preferred that, before the heat treatment, the resin sheet is placed in the preheating chamber 102 and the preheating chamber 102 is sealed, the temperature of the resin sheet is raised to a predetermined temperature, and the pressure in the preheating chamber 102 is reduced to a predetermined pressure. At this time, for example, it is preferred that a heated gas (for example, an inert gas such as N2 gas) is ejected into the preheating chamber 102 through an ejection hole or the like provided at an opening on the inner wall surface of the preheating chamber 102, and the ejection direction and ejection amount are appropriately adjusted to generate an airflow in the preheating chamber 102, the temperature of the resin sheet is raised while the resin sheet is stirred, and the preheating chamber 102 is depressurized and sucked, thereby dispersing at least a part of the impurity components and the like contained in the resin sheet and removing them to the outside of the system.

[0027] Thus, when the temperature of the resin sheet is raised, it is preferable to appropriately adjust the final temperature and pressure in the preheating chamber 102 in consideration of the internal atmosphere of the processing chamber 103. Furthermore, it is preferable to open the opening and closing device, and to drop the resin sheet in the preheating chamber 102 by its own weight while maintaining airtightness with the outside of the system, so as to supply the resin sheet into the processing chamber 103 without damaging the internal atmosphere of the processing chamber 103 adjusted to a temperature and pressure suitable for the heat treatment.

[0028] exist Figure 2 In the processing device 100 shown, the resin sheets are sequentially introduced into two preheating chambers 102, and the preheating treatment of heating the resin sheets is performed alternately, and the resin sheets are sequentially dropped from the preheating chamber 102 where the introduced resin sheets have been heated to a predetermined temperature to the processing chamber 103, but the present invention is not limited thereto. According to the processing capacity of the processing device 100, that is, the total amount of resin sheets that can be subjected to heat treatment per unit time, the number of preheating chambers 102 can be one or more than three. In short, it is preferred to repeatedly perform the operation of dropping the resin sheets from the preheating chamber 102 to the processing chamber 103, while stacking them sequentially for each set of dropped sheets. Moreover, it is preferred that the resin sheets be exposed to the internal atmosphere of the processing chamber 103 while being deposited in the processing chamber 103, so that the resin sheets can be subjected to heat treatment.

[0029] In addition, the treatment time for heat treatment of the resin flakes is usually more than 30 minutes. In order to suppress the hue degradation of the resin and perform solid phase polymerization reaction, it is preferably adjusted appropriately within the range of 1 to 8 hours. Preferably, after the resin flakes accumulated in the treatment chamber 103 have passed the treatment time, the amount equal to the amount dropped from the preheating chamber 102 is taken out from the treatment chamber 103 in order from the lower layer side formed and accumulated as described above to manage its treatment time. At this time, the time required for the preheating treatment in the preheating chamber 102 also depends on the water content, shape, etc. of the resin flakes, and the intervals of the operation of repeatedly dropping the resin flakes may cause deviations, so it is preferred to manage the treatment time for each set of resin flakes dropped.

[0030] In this way, in order to properly manage the processing time when the resin sheet is heated, Figure 2 In the processing device 100 shown, an opening and closing mechanism 104 is provided on the bottom side in the sealed container 101. The opening and closing mechanism 104 is configured to form the bottom surface of the processing chamber 103 and to be a partition with a take-out portion 105 provided at the bottom in the sealed container 101. Thus, when the opening and closing mechanism 104 is opened, the resin flakes are scattered on the take-out portion 105, and by appropriately adjusting the timing of opening and closing the opening and closing mechanism 104, the resin flakes in an amount equal to the amount dropped from the preheating chamber 102 can be taken out, and although there is some mixing, the resin flakes are taken out for each set dropped from the preheating chamber 102.

[0031] In addition, as described above, by performing the heat treatment under reduced pressure, impurities can be removed efficiently, but it is not preferable that the volatilized or evaporated impurities remain in the processing chamber 103. Figure 2 The processing device 100 shown in the figure is provided with a circulation flow path 106, which can circulate the gas phase components in the processing chamber 103, and includes a catalyst tank 107 in the path for decomposing low molecular weight impurity components from the polyester resin, and the circulation flow path 106 is configured to be connected to the processing chamber 103. Preferably, the processing device 100 is configured such that, for example, an inert gas such as N2 gas is used as a carrier gas, and the gas phase components in the processing chamber 103 are guided to the circulation flow path 106 and circulated without damaging the internal atmosphere of the processing chamber 103, thereby reducing the impurity components and the like retained in the processing chamber 103.

[0032] In addition, when cleaning the impurity components that selectively seep into the surface layer of the resin sheet, although not specifically shown in the figure, the resin sheet taken out from the processing chamber 103 can be liquid cleaned using a rotary or convection liquid cleaning machine, or a pressurized water vapor convection cleaning machine can be used for steam cleaning. In the case of liquid cleaning, it is necessary to dry the cleaned resin sheet, but in this drying process, the resin sheet can be heated again in the same atmosphere as the internal atmosphere of the processing chamber 103, or it can be dried using a hot air circulation drying device. Furthermore, the drying of the resin sheet can also use two jacketed rollers with spiral grooves on the surface, and the shear heat generated by the rotation of the rollers is used to make the surface layer of the resin sheet semi-fused and pressed, and the organic impurities and water of the resin sheet are further removed by a rotating forward drying device (open twin-screw extruder). In this case, the resin sheet that has been dried using an open roller twin-screw extruder is simply separated and dispersed into sheets by the pressing roller of the roller rear cooling section.

[0033] In this embodiment, as described above, the resin flakes are heat-treated under reduced pressure to remove low molecular weight impurities (decontamination) and then plasticized. At this time, the heat-treated resin flakes are fed into the extruder 200, and the heat from the heating cylinder and the shear heat based on the screw are used to melt-mix and plasticize the flakes, but preferably a twin-screw extruder is used for plasticization. The twin-screw extruder has a high mixing effect, can plasticize the resin flakes more uniformly, and can also shorten the time required for plasticization, so it is also preferred in terms of suppressing degradation, thermal decomposition, and depolymerization of the resin.

[0034] When a twin-screw extruder is used to plasticize a resin sheet, the twin-screw extruder is configured to have an exhaust port. For example, it is preferred that the exhaust port provided through the heating barrel is used to decompress and suction the gas phase components containing low molecular weight impurity components from the polyester resin retained in the twin-screw extruder and discharge them to the outside of the system. In this way, the impurity components remaining in the plasticized polyester resin can be further reduced. At this time, in particular, circulating oligomers and the like are generated in the equilibrium reaction during hot melting, so circulating oligomers are generated when polyethylene terephthalate is melted. Therefore, it is important to use the exhaust port of the twin-screw extruder to perform decompressive suction and removal. The optimal conditions (temperature, pressure) for gas-liquid separation of circulating oligomers are estimated. The melting point of circulating oligomers is 319°C, which is sublimable. When the resin melting temperature of polyethylene terephthalate at the exhaust port of the twin-screw extruder is assumed to be 300°C, the reduced vacuum pressure at which the circulating oligomer can sublimate (convert into gas) is approximately 0.1 KPa (100 Pa) or less, so it is necessary to adjust the pressure to a relatively high vacuum degree. Therefore, the possibility of molten resin being discharged (vented up) at the exhaust port also increases. In order to avoid discharge, in terms of the screw rotation direction of the twin-screw extruder used, it is preferred to use a twin-screw extruder of the reverse (different direction) type compared to a twin-screw extruder of the same (same direction) type.

[0035] In addition, the resin flakes taken out from the processing chamber 103 as described above may be directly put into the extruder 200 for plasticization, or may be stored in the buffer tank 300 and then put into the extruder 200 for plasticization. As described above, in the case of managing the processing time when the resin flakes are heated, the resin flakes are taken out from the processing chamber 103 intermittently according to the interval of the operation of repeatedly dropping the resin flakes from the preheating chamber 102 to the processing chamber 103, and the amount of the resin flakes taken out each time also depends on the processing amount in the preheating chamber 102. In such a case, especially when there is a deviation in the interval of the operation of repeatedly dropping the resin flakes, the amount of the resin flakes taken out per unit time is not constant. Therefore, if the resin flakes are stored in the buffer tank 300 in advance and taken out from the buffer tank 300 quantitatively at an arbitrary interval each time, the input amount of the resin flakes can be easily adjusted according to the processing capacity of the extruder 200 so that the amount of the resin plasticized in the extruder 200 can always be maintained constant.

[0036] When the buffer tank 300 is provided, it is preferable to appropriately adjust the internal volume of the buffer tank 300 in advance so that more resin sheets can be stored. Thus, even if a malfunction occurs in a subsequent process after the process of plasticizing the resin sheet and the subsequent process is stopped, the heating process of the resin sheet can be continued without stopping, and the portion that is not sent to the subsequent process can be stored in the buffer tank 300.

[0037] In addition, in anticipation of such a failure, or changes in the situation such as the processing speed of the subsequent process speeding up or slowing down, a safety tank 400 (relief tank) may be provided in advance in the middle of the conveying path for conveying the resin sheet taken out of the processing chamber 103 to the buffer tank 300. Furthermore, it is preferable that the resin sheet in the middle of conveying can be conveyed to the buffer tank 300 by retreating to the safety tank 400.

[0038] Thus, for example, when the subsequent process is stopped, the resin sheet taken out from the processing chamber 103 can be evacuated to the safety tank 400, and the transfer to the buffer tank 300 can be restricted. When the processing speed of the subsequent process is accelerated, in addition to the resin sheet taken out from the processing chamber 103, the resin sheet evacuated to the safety tank 400 can also be transferred to the buffer tank 300. When the processing speed of the subsequent process is slowed down, part of the resin sheet taken out from the processing chamber 103 can be evacuated to the safety tank 400, and the amount of the resin sheet transferred to the buffer tank 300 can be appropriately adjusted. In this way, when the resin sheet is evacuated to the safety tank 400 as needed, the internal atmosphere of the safety tank 400 is preferably set to 100° C. or more to prevent the resin sheet from containing water.

[0039] In the present embodiment, after the above-mentioned steps, foreign matter is removed from the molten resin obtained by plasticizing the resin sheet, and the molten resin is supplied to the injection molding device 500 to injection-mold the preform. In order to remove foreign matter from the molten resin obtained by plasticizing the resin sheet, for example, a filter 600 for removing foreign matter may be provided on the discharge port side of the extruder 200. In addition, the specific structure of the injection molding device 500 is not particularly limited. For example, the preform can be injection-molded using the injection molding device 500 having at least one injection cylinder (pot) and a preform molding mold, and the at least one injection cylinder is configured to meter the supplied molten resin and then inject a certain amount of the molten resin.

[0040] In addition, when the molten resin obtained by plasticizing the resin sheet is supplied to the injection molding device 500, it is not preferable that the resin deteriorates (especially the color phase deteriorates) during the conveying process. Therefore, in order to shorten the time that the molten resin stays in the conveying path, it is preferable to set the conveying distance from the removal of foreign matter to the supply to the injection molding device 500, more specifically, the distance from the outlet of the gear pump 700 provided on the downstream side of the filter 600 to the inlet of the injection cylinder provided in the injection molding device 500, to 1 to 7 meters. At this time, the conveying amount of the molten resin is preferably 900 to 1500 kg / h.

[0041] According to the present embodiment described above, preforms can be manufactured more efficiently and at lower cost from resin flakes obtained by pulverizing the recycled polyester resin molded article into flakes. In particular, according to the present embodiment, although it is manufactured by recycling the recycled polyester resin molded article, the residual amount of acetaldehyde is 1 to 15 ppm, preferably 1 to 10 ppm, more preferably 1 to 5 ppm, the residual amount of bis(2-hydroxyethyl) terephthalate is 1 to 35 ppm, preferably 1 to 30 ppm, more preferably 1 to 20 ppm, the residual amount of 2-hydroxyethyl terephthalate is 1 to 35 ppm, preferably 1 to 30 ppm, more preferably 1 to 20 ppm, the residual amount of cyclic trimer is 6000 ppm or less, preferably 4000 ppm or less, more preferably 3000 ppm or less. Preferably, when the mass of the preform is 14 to 50 g, a preform having an L* value of 70 to 90 and a b* value of 2 to 18 in the L*a*b* colorimetric system can be manufactured well.

[0042] Here, the residual amounts of acetaldehyde, bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl terephthalate (MHET), cyclic trimer (CT), and intrinsic viscosity can be determined as follows.

[0043] <Residual amount of acetaldehyde>

[0044] Using the slice cut out from the preform as a sample, weigh 1.0 g of this sample in a glass bottle, add 5.0 mL of pure water, and seal it. After heating this suspension in an oven adjusted to 120 °C for 60 minutes, cool it in ice water. Collect 1.0 mL of the supernatant of the suspension, add 0.2 mL of a 0.1% 2,4-dinitrophenylhydrazine-phosphoric acid solution thereto, let it stand for 30 minutes, and measure it by high performance liquid chromatography. At the same time, measure the standard solution, and calculate the acetaldehyde content based on the obtained standard curve.

[0045] <Residual amounts of BHET, MHET, and CT>

[0046] Using the slice cut out from the preform as a sample, weigh 0.2 g of this sample, add 1 mL of a mixed solvent of hexafluoroisopropanol and chloroform (weight ratio 1 / 1) thereto, and dissolve it completely. After adding 4 mL of chloroform to the solution, slowly add 5 mL of acetonitrile, and let it stand for 3 hours to precipitate the PET polymer. Take 1 mL from this suspension, filter it through a membrane filter with a pore size of 0.45 μm, and measure the filtrate by high performance liquid chromatography. At the same time, measure the standard solution, and calculate the contents of MHET, BHET, and CT in the pellets based on the obtained standard curve.

[0047] <Intrinsic viscosity>

[0048] The slices cut from the preform were used as samples, and the samples were vacuum dried at 150°C for 1 hour, and 0.2 g was weighed. A mixed solvent of 1,1,2,2-tetrachloroethane and phenol (weight ratio 1:1) was added to adjust the concentration to 1.00 g / dL, and stirred at 120°C for 20 minutes to completely dissolve. The dissolved solution was cooled to room temperature, and the relative viscosity was calculated using a relative viscometer adjusted to 30°C to determine the intrinsic viscosity.

[0049] The L* value and b* value in the L*a*b* colorimetric system are values ​​measured using a spectrocolorimeter under the measurement conditions of a D65 light source and a 2° viewing field with the main body of the preform as the measurement site.

[0050] Example

[0051] The present invention will be described in more detail below with reference to specific examples.

[0052] [Example 1]

[0053] PET bottles collected from the market were washed and crushed to prepare resin flakes as raw materials. The intrinsic viscosity and residual acetaldehyde content of the resin flakes were determined in the same manner as above. The intrinsic viscosity was 0.803 dl / g and the residual acetaldehyde content was 6.0 ppm.

[0054] The prepared resin sheets were piled up in a treatment chamber whose internal atmosphere was adjusted to a temperature of 202° C. and a pressure of 400 Pa, and heat-treated. The treatment time was 2 hours. The intrinsic viscosity and the residual amount of acetaldehyde of the heat-treated resin sheets were determined, and the intrinsic viscosity was 0.826 dl / g, and the residual amount of acetaldehyde was 5.7 ppm.

[0055] After the resin sheet is heated, it is put into a twin-screw extruder for plasticization. At this time, the gas phase components including low molecular weight impurities derived from the polyester resin retained in the twin-screw extruder are decompressed and sucked through the exhaust port by venting, and discharged to the outside of the system. The vacuum degree of the venting treatment is 1 kPa.

[0056] Foreign matter was removed by a filter provided at the discharge port side of the extruder, and the plasticized molten resin was supplied to the injection molding device, and a 28 g preform was injection molded at a production rate of 750 pieces per minute. At this time, the distance from the outlet of the gear pump provided at the downstream side of the filter to the inlet of the injection cylinder provided in the injection molding device was 6 m, the molten resin stayed in the conveying path for 260 seconds, and the conveying amount of the molten resin was 1260 kg / h.

[0057] For the preforms produced by controlling the temperature of the molten resin supplied to the injection molding device to the temperature shown in Table 1, the reduction rate of the intrinsic viscosity of the raw material, the residual amount of acetaldehyde (AA), the L* value, and the b* value were determined. The results are shown in Table 1.

[0058]

[0059] In this example, the residual amount of acetaldehyde was less than 15 ppm at any temperature, and particularly less than 5 ppm at 280° C. The reduction rate of the intrinsic viscosity was also as small as 3.0% at a temperature of 300° C.

[0060] [Example 2]

[0061] A preform was produced in the same manner as in Example 1 except that a single-screw extruder was used instead of a twin-screw extruder when plasticizing the heat-treated resin sheet and that the degassing treatment was not performed.

[0062] For the preforms produced by controlling the temperature of the molten resin supplied to the injection molding device to the temperature shown in Table 2, the reduction rate of the intrinsic viscosity of the raw material, the residual amount of acetaldehyde (AA), the L* value, and the b* value were determined. The results are shown in Table 2.

[0063]

[0064] In this embodiment, the residual amount of acetaldehyde is lower than 15 ppm at any temperature.

[0065] [Example 3]

[0066] A preform was produced in the same manner as in Example 2 except that the distance from the outlet of the gear pump provided on the downstream side of the filter to the inlet of the injection cylinder provided in the injection molding device was changed to 8 m.

[0067] For the preforms produced by controlling the temperature of the molten resin supplied to the injection molding device to the temperature shown in Table 3, the reduction rate of the intrinsic viscosity of the raw material, the residual amount of acetaldehyde (AA), the L* value, and the b* value were determined. The results are shown in Table 3.

[0068]

[0069] In this embodiment, the residual amount of acetaldehyde at 280° C. and 285° C. is less than 15 ppm.

[0070] By comparing Example 2 with Example 3, it can be confirmed that the reduction rate of the intrinsic viscosity and the residual amount of acetaldehyde can be reduced by shortening the conveying distance of the plasticized molten resin until it is supplied to the injection molding device after the foreign matter is removed. Furthermore, by comparing Example 1 with Example 2, it can be confirmed that the reduction rate of the intrinsic viscosity and the residual amount of acetaldehyde can be further reduced by feeding the resin sheet subjected to the heat treatment into the twin-screw extruder for plasticization and performing the exhaust treatment.

[0071] Furthermore, the methods described in these Examples can be said to be environmentally friendly methods from the viewpoint of less thermal history and less carbon dioxide emission.

[0072] As mentioned above, although the present invention was described by showing the preferred embodiment, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made within the scope of the present invention.

[0073] Description of reference numerals:

[0074] 100 Processing Device

[0075] 101 Processing Room

[0076] 102 Preheating Room

[0077] 107 Catalyst Tank

[0078] 200 Extruder (twin screw extruder)

[0079] 300 Buffer tank

[0080] 400 Safety Cans

[0081] 500 Injection molding device

[0082] 600 Filters

[0083] 700 gear pump.

Claims

1. A method for manufacturing a prefabricated part, characterized in that: The manufacturing method of the prefabricated part is as follows: preparing resin flakes obtained by crushing the recovered polyester resin molded product into flakes; Plasticizing the resin sheet after heating it under reduced pressure; as well as Foreign matter is removed from molten resin obtained by plasticizing the resin sheet, and the molten resin is supplied to an injection molding device to injection-mold a preform.

2. The method for manufacturing a preform according to claim 1, wherein: The resin sheet subjected to the heat treatment is fed into a twin-screw extruder for plasticization.

3. The method for manufacturing a preform according to claim 2, wherein: The twin-screw extruder includes a vent port, through which a gas phase component including low-molecular-weight impurity components from the polyester-based resin retained in the twin-screw extruder is decompressed and sucked to be discharged to the outside of the system.

4. The method for manufacturing a preform according to any one of claims 1 to 3, wherein: The conveying distance of the plasticized molten resin from the removal of foreign matter to the supply to the injection molding device is set to 1 m to 7 m.

5. The method for manufacturing a preform according to any one of claims 1 to 4, wherein: The resin sheet is heat-treated in an atmosphere at a temperature of 160° C. to 240° C. with a reduced pressure of 1000 Pa or less.

6. The method for manufacturing a preform according to any one of claims 1 to 5, wherein: The resin sheet is placed in a preheating chamber, the temperature of the resin sheet is increased to a specified temperature, and the pressure in the preheating chamber is reduced to a specified pressure. Thereafter, the resin sheet is repeatedly dropped from the preheating chamber into a treatment chamber whose internal atmosphere is adjusted to a specified temperature and a specified pressure while maintaining airtightness with the outside of the system, and the resin sheet is accumulated in the treatment chamber to be subjected to a heat treatment.

7. The method for manufacturing a preform according to claim 6, wherein: The resin sheets subjected to the heat treatment are sequentially taken out from the treatment chamber in an amount equal to the amount dropped from the preheating chamber from the lower layer side where the resin sheets subjected to the heat treatment are accumulated in the treatment chamber and plasticized.

8. The method for manufacturing a preform according to claim 6, wherein: The resin sheets subjected to the heat treatment are sequentially taken out from the treatment chamber in an amount equal to the amount dropped from the preheating chamber from the lower layer side where the resin sheets subjected to the heat treatment are accumulated in the treatment chamber, stored in a buffer tank, and then plasticized.

9. The method for manufacturing a preform according to claim 8, wherein: A safety tank is provided in the middle of a conveyance path for conveying the resin sheet taken out from the processing chamber to the buffer tank, so that the resin sheet in the middle of conveyance can be conveyed to the buffer tank while being evacuated to the safety tank.

10. The method for manufacturing a preform according to any one of claims 6 to 9, wherein: The resin sheet is sequentially placed in a plurality of preheating chambers, and the resin sheet is sequentially dropped from the preheating chambers where the temperature of the placed resin sheet is raised to a predetermined temperature into the processing chamber.

11. The method for manufacturing a preform according to any one of claims 6 to 10, wherein: The heated gas is jetted into the preheating chamber to raise the temperature of the resin sheet while stirring the resin sheet, and the preheating chamber is decompressed and evacuated.

12. The method for manufacturing a preform according to any one of claims 1 to 11, wherein: A circulation flow path is connected to the treatment chamber for performing heat treatment on the resin sheet. The circulation flow path can circulate the gas phase components in the treatment chamber, and the path of the circulation flow path includes a catalyst tank for decomposing low molecular weight impurity components from the polyester resin. The gas phase components in the treatment chamber are circulated by guiding them to the circulation flow path, thereby reducing the impurity components retained in the treatment chamber.

13. A preform manufactured by the method for manufacturing a preform according to any one of claims 1 to 12, characterized in that: The residual amount of acetaldehyde is 1 ppm to 15 ppm, the residual amount of bis(hydroxyethyl) terephthalate is 1 ppm to 35 ppm, the residual amount of mono(hydroxyethyl) terephthalate is 1 ppm to 35 ppm, and the residual amount of cyclic trimer is less than 6000 ppm.

14. The preform according to claim 13, wherein: When the mass of the preform is 14 g to 50 g, the L* value in the L*a*b* colorimetric system is 70 to 90, and the b* value is 2 to 18.

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