Method for producing preform and preform

Abstract

A preform is produced more efficiently and at lower cost from resin flakes obtained by crushing recovered polyester resin molded articles into flakes. Resin flakes obtained by crushing recovered polyester resin molded articles into flakes are prepared, and the resin flakes are plasticized after heat treatment under reduced pressure. While removing foreign matter from the molten resin obtained by plasticizing the resin flakes, the molten resin is supplied to an injection molding device, and a preform is injection molded.

Description

Preform manufacturing method and preform

[0001] The present invention relates to a method for manufacturing a preform and a preform.

[0002] Conventionally, synthetic resin containers have been used in a wide range of fields as containers for various beverages, seasonings, etc., by producing a bottomed cylindrical preform from a polyester resin such as polyethylene terephthalate and then molding this preform into a bottle by biaxial stretch blow molding or the like. This type of container is generally known as a PET bottle, and in recent years, in response to social demand, a recycling technology known as "bottle-to-bottle" has been considered, in which used PET bottles are collected and reused as recycled material to manufacture PET bottles.

[0003] For example, Patent Document 1 discloses a technology in which recovered polyester resin molded articles are crushed into flakes to produce resin flakes, which are decontaminated, melted to produce resin pellets, and then solid-state polymerized and transported to an injection molding device to produce preforms.

[0004] Japanese Patent Application Publication No. 2021-98350

[0005] In view of the above background art, the present inventors have conducted extensive research to enable preforms to be produced more efficiently and at lower cost from resin flakes obtained by crushing recovered polyester resin molded articles into flakes, and as a result, have completed the present invention.

[0006] The method for manufacturing a preform according to the present invention involves preparing resin flakes by crushing recovered polyester resin molded articles into flakes, heat-treating the resin flakes under reduced pressure conditions and then plasticizing them, and then removing any foreign matter from the molten resin obtained by plasticizing the resin flakes, while supplying the molten resin to an injection molding device to injection-mold a preform.

[0007] Furthermore, the preform according to the present invention is a preform manufactured by the above manufacturing method, and is configured so that 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 ppm or less.

[0008] According to the present invention, preforms can be produced more efficiently and at lower cost from resin flakes obtained by crushing recovered polyester resin molded articles into flakes.

[0009] 1 is an explanatory diagram conceptually showing an entire apparatus in which an embodiment of the present invention can be suitably carried out. FIG. 2 is an explanatory diagram showing an example of an apparatus for subjecting resin flakes to a heat treatment in an embodiment of the present invention.

[0010] Preferred embodiments of the present invention will now be described.

[0011] In this embodiment, first, resin flakes are prepared by crushing recovered polyester resin molded articles into flakes.

[0012] When preparing such resin flakes, it is preferable to wash them by any washing means such as alkaline washing or hot water washing in order to remove stains such as residues of contents remaining on the surface and foreign matter mixed in. "Recovered polyester resin molded products" can include polyester resin molded products such as used PET bottles that have been collected separately as recyclable waste, as well as scrap materials generated in the process of manufacturing polyester resin molded products.

[0013] Examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene furanoate, and copolymers thereof. These polyester resins may be polyester resins with an increased biomass content, for example, by using ethylene glycol or a derivative thereof derived from plant-derived bioethanol as a diol component, or terephthalic acid or a derivative thereof derived from plant-derived bioparaxylene as a dicarboxylic acid component, or furandicarboxylic acid or a derivative thereof derived from plant-derived fructose as a dicarboxylic acid component.

[0014] When polyester resin molded articles such as used PET bottles are collected and reused as recycled materials by so-called mechanical recycling to manufacture recycled products, a decrease in intrinsic viscosity due to deterioration of the resin caused by the thermal history of the collected articles during production can cause problems in the manufacturing process of the recycled products. Furthermore, if a large amount of low-molecular-weight impurities such as acetaldehyde (AA) produced by thermal decomposition of polyester resins, oligomers such as bishydroxyethyl terephthalate (BHET), monohydroxyethyl terephthalate (MHET), and cyclic trimer (CT) produced by depolymerization of polyester resins, and limonene derived from the contents remain in the recycled materials, they not only affect the quality of the recycled products but also cause productivity reduction by fouling the manufacturing equipment.

[0015] In this embodiment, in order to avoid such problems, the prepared resin flakes are subjected to a heat treatment, preferably in a reduced pressure atmosphere of 1000 Pa or less and at a temperature of preferably 160 to 240°C, so that the solid-state polymerization reaction of the polyester resin that forms the resin flakes proceeds and crystallization is promoted while the resin flakes remain in their flake form without melting the resin flakes.

[0016] By allowing the solid-state polymerization reaction to proceed, the end groups of the polyester resin, whose degree of polymerization has decreased due to scission of molecular chains caused by degradation, recondense, thereby restoring the degree of polymerization and restoring the intrinsic viscosity corresponding to the molecular weight. Furthermore, by subjecting the resin flakes to heat treatment under reduced pressure, particularly by exposing them to a temperature atmosphere of 160 to 240°C under reduced pressure, hydrolysis of the polyester resin can be suppressed while effectively promoting crystallization by utilizing the melting point lowering effect. This reduces the free volume between the molecular chains of the polyester resin (reducing the amorphous phase), and selectively bleeds out the low-molecular-weight impurities (organic impurities) that were included in the free volume of the resin flakes and the moisture sorbed by the resin flakes to the surface layer of the resin flakes, where they can be efficiently removed by volatilization or evaporation, or by washing with hot water, steam, organic solvents, or the like, as needed.

[0017] In this embodiment, the specific method for subjecting the resin flakes to the heat treatment is not particularly limited. For example, it is preferable to subject the resin flakes to the heat treatment using a treatment device 100 as shown in FIG. 2, which includes at least one preheating chamber 102 and a treatment chamber 103 capable of adjusting the internal atmosphere to a temperature and pressure suitable for the heat treatment.

[0018] Here, the outline of the processing apparatus 100 shown in FIG. 2 will be explained. The processing apparatus 100 is preferably 7 to 18 m ３ The system includes a sealed container 101 constructed to have an internal volume of 100 psi. A processing chamber 103 is provided within the sealed container 101, and two preheating chambers 102 are provided above the sealed container 101. The preheating chambers 102 are connected to the sealed container 101 via opening / closing mechanisms such as sliding shutters (not shown) so as to be able to communicate with the processing chamber 103 while maintaining airtightness from the outside of the system. Note that Fig. 2 does not show incidental equipment such as a heating device, a decompression device, and associated piping for adjusting the internal atmosphere of the processing chamber 103.

[0019] In order to heat-treat resin flakes using such a treatment device 100, it is preferable to first put the resin flakes into the preheating chamber 102, seal the preheating chamber 102, heat the resin flakes to a predetermined temperature, and reduce the pressure in the preheating chamber 102 to a predetermined level. ２ It is preferable to spray an inert gas (such as a gas) into the preheating chamber 102, and appropriately adjust the direction and amount of spray to generate an air flow within the preheating chamber 102, stirring and heating the resin flakes, and also to apply a reduced pressure and suction to the preheating chamber 102 to disperse at least some of the impurity components contained in the resin flakes and remove them from the system.

[0020] In this way, when raising the temperature of the resin flakes, it is preferable to appropriately adjust the final temperature and pressure in the preheating chamber 102 taking into consideration the internal atmosphere of the processing chamber 103. Then, it is preferable to open the opening and closing device, maintain airtightness from the outside of the system, and allow the resin flakes in the preheating chamber 102 to fall by their own weight, so that the resin flakes are supplied into the processing chamber 103 without damaging the internal atmosphere of the processing chamber 103, which has been adjusted to a temperature and pressure suitable for the heat treatment.

[0021] In the processing apparatus 100 shown in FIG. 2 , resin flakes are sequentially fed into two preheating chambers 102, and preheating treatments for raising the temperature of the resin flakes are alternately performed. The resin flakes are then dropped into the processing chamber 103 in the order from the preheating chamber 102 in which the fed resin flakes have been heated to a predetermined temperature. However, this is not limited to this configuration. Depending on the processing capacity of the processing apparatus 100, i.e., the total amount of resin flakes that can be heat-treated per unit time, the number of preheating chambers 102 can be one, or three or more. In either case, it is preferable to repeatedly drop the resin flakes from the preheating chamber 102 into the processing chamber 103, so that each dropped group forms a layer and is stacked in order. It is then preferable to expose the resin flakes, once they have been deposited in the processing chamber 103, to the internal atmosphere of the processing chamber 103, so that the resin flakes can be heat-treated.

[0022] The treatment time for heat-treating the resin flakes is typically 30 minutes or more, and is preferably adjusted appropriately within the range of 1 to 8 hours to promote the solid-state polymerization reaction while suppressing deterioration of the resin's color. It is preferable to manage the treatment time by sequentially removing the resin flakes deposited in the treatment chamber 103 from the treatment chamber 103 after the treatment time has elapsed, starting from the lower layer of the deposited layers as described above, in amounts equal to the amount dropped from the preheating chamber 102. Since the time required for the preheating treatment in the preheating chamber 102 depends on the water content and shape of the resin flakes, and variations may occur in the intervals between repeated dropping operations of the resin flakes, it is preferable to manage the treatment time for each group of dropped resin flakes.

[0023] In this way, in order to suitably manage the processing time when heat-treating resin flakes, the processing apparatus 100 shown in Figure 2 is provided with an opening / closing mechanism 104 on the bottom side of the sealed container 101. The opening / closing mechanism 104 forms the bottom surface of the processing chamber 103 and is configured to serve as a partition between the processing chamber 103 and the removal section 105 provided at the bottom of the sealed container 101. This allows the resin flakes to spill into the removal section 105 when the opening / closing mechanism 104 is opened, and by appropriately adjusting the timing of opening and closing the opening / closing mechanism 104, it is possible to remove an amount of resin flakes equal to the amount dropped from the preheating chamber 102. Although there will be some mixing, the resin flakes can be removed in groups dropped from the preheating chamber 102.

[0024] As mentioned above, impurity components can be efficiently removed by performing heat treatment under reduced pressure conditions, but it is undesirable for volatilized or evaporated impurity components to remain in the treatment chamber 103. For this reason, the treatment apparatus 100 shown in FIG. 2 is configured to circulate the gas phase components in the treatment chamber 103, and is equipped with a circulation flow path 106 including a catalyst tank 107 in the path that decomposes low-molecular-weight impurity components derived from polyester-based resins, and the circulation flow path 106 is connected to the treatment chamber 103. By configuring the treatment apparatus 100 in this way, for example, N ２It is preferable to reduce impurity components remaining in the processing chamber 103 by using an inert gas such as a gas as a carrier gas and circulating the gas phase components in the processing chamber 103 through the circulation flow path 106 without damaging the internal atmosphere of the processing chamber 103.

[0025] Furthermore, when cleaning the impurity components selectively bled out from the surface layer of the resin flakes, the resin flakes removed from the treatment chamber 103 can be liquid washed using a rotary or convection liquid washer, or steam washed using a pressurized steam convection washer, although not shown. When liquid washing is applied, the resin flakes after washing must be dried. For this drying process, the resin flakes may be subjected to a heat treatment again in an atmosphere equivalent to the internal atmosphere of the treatment chamber 103, or may be dried using a hot air circulation dryer. Furthermore, the resin flakes can be dried using two jacketed rolls with spiral grooves on their surfaces, utilizing the shear heat generated by the roll rotation to semi-weld and press-bond the surface layer of the resin flakes, and then further removing organic impurities and moisture from the resin flakes using a rotary forward drying device (open roll twin-screw extruder). In this case, the resin flakes dried in the open-roll twin-screw extruder are easily separated and dispersed into flakes by the pressure of the pressure rolls in the cooling section downstream of the rolls.

[0026] In this embodiment, the resin flakes are heat-treated under reduced pressure conditions to remove (decontaminate) low-molecular-weight impurities, and then plasticized. The heat-treated resin flakes are fed into the extruder 200 and melt-kneaded and plasticized by the heat from the heating cylinder and the shear heat of the screw. However, a twin-screw extruder is preferred for plasticization. Twin-screw extruders have a high kneading effect, can plasticize the resin flakes more uniformly, and can also shorten the time required for plasticization. Therefore, they are also preferred for suppressing resin degradation, thermal decomposition, and depolymerization.

[0027] When plasticizing resin flakes using a twin-screw extruder, it is preferable to configure the twin-screw extruder with a vent port. For example, it is preferable to vacuum-suction and discharge gaseous components containing low-molecular-weight impurities derived from the polyester resin that remain in the twin-screw extruder through a vent port provided through the heating cylinder. This can further reduce the impurities remaining in the plasticized polyester resin. In particular, cyclic oligomers are generated during equilibrium reactions during thermal melting, so cyclic oligomers are generated when polyethylene terephthalate is melted. Therefore, it is important to perform vacuum absorption and removal at the vent port of the twin-screw extruder. The optimal conditions (temperature and pressure) for gas-liquid separation of cyclic oligomers are estimated. The melting point of cyclic oligomers is 319°C and they are sublimable. Assuming that the resin melt temperature at the vent port of a twin-screw extruder for polyethylene terephthalate is 300°C, the reduced vacuum pressure at which cyclic oligomers can sublimate (transform into gas) is generally 0.1 KPa (100 Pa) or less, so it is necessary to adjust the pressure to a relatively high vacuum. This increases the possibility of the molten resin venting up at the vent port. To avoid venting up, it is preferable to use a twin-screw extruder with counter-rotating (counter-rotating) screws rather than one with the same (co-rotating) screw rotation direction.

[0028] Furthermore, the resin flakes removed from the treatment chamber 103 as described above may be directly fed into the extruder 200 for plasticization, or may be stored in the buffer tank 300 and then fed into the extruder 200 for plasticization. When managing the treatment time for heat-treating the resin flakes as described above, the removal of the resin flakes from the treatment chamber 103 is performed intermittently according to the interval at which the operation of dropping the resin flakes from the preheating chamber 102 into the treatment chamber 103 is repeated, and the amount of resin flakes removed each time also depends on the amount of resin processed in the preheating chamber 102. In such a case, particularly if there is variation in the interval at which the operation of dropping the resin flakes is repeated, the amount of resin flakes removed per unit time will not be constant. Therefore, if the resin flakes are stored in the buffer tank 300 and can be removed from the buffer tank 300 in fixed amounts at any interval, the amount of resin flakes added can be easily adjusted according to the processing capacity of the extruder 200 so that the amount of resin plasticized in the extruder 200 can always be maintained constant.

[0029] When installing the buffer tank 300, it is preferable to appropriately adjust the internal volume of the buffer tank 300 so that a larger amount of resin flakes can be stored. By doing so, even if a problem occurs in a subsequent process after the process of plasticizing the resin flakes, causing the subsequent process to be stopped, the heating treatment of the resin flakes can be continued without interruption, and the amount that cannot be sent to the subsequent process can be stored in the buffer tank 300.

[0030] Furthermore, in anticipation of such trouble occurring or changes in circumstances such as an increase or decrease in the processing speed of the subsequent process, a relief tank 400 can be installed midway along the transport path that transports the resin flakes removed from the processing chamber 103 to the buffer tank 300. It is preferable to transport the resin flakes to the buffer tank 300 while allowing them to be evacuated to the relief tank 400 during transport.

[0031] By doing so, for example, when the subsequent process is stopped, the resin flakes removed from the process chamber 103 can be evacuated to the relief tank 400, and their transport to the buffer tank 300 can be limited. When the processing speed of the subsequent process increases, the resin flakes evacuated to the relief tank 400 can be transported to the buffer tank 300 together with the resin flakes removed from the process chamber 103. When the processing speed of the subsequent process decreases, some of the resin flakes removed from the process chamber 103 can be evacuated to the relief tank 400, and the amount of resin flakes transported to the buffer tank 300 can be adjusted appropriately. In this way, when evacuating the resin flakes to the relief tank 400 as needed, the internal atmosphere of the relief tank 400 is preferably set to 100°C or higher to prevent the resin flakes from absorbing moisture.

[0032] In this embodiment, after the above-described steps are performed, the molten resin obtained by plasticizing the resin flakes is supplied to the injection molding apparatus 500 to injection mold a preform while removing any foreign matter from the molten resin obtained by plasticizing the resin flakes. To remove foreign matter from the molten resin obtained by plasticizing the resin flakes, for example, a filter 600 for removing foreign matter may be provided on the discharge port side of the extruder 200. Furthermore, the specific configuration of the injection molding apparatus 500 is not particularly limited. For example, the preform can be injection molded using the injection molding apparatus 500 that includes at least one injection pot configured to measure the supplied molten resin and then inject a predetermined amount of the molten resin, and a preform mold.

[0033] Furthermore, when supplying the molten resin obtained by plasticizing the resin flakes to the injection molding apparatus 500, it is undesirable for the resin to deteriorate (particularly, its color) during transportation. To this end, in order to shorten the time the molten resin remains in the transportation path, it is preferable to set the transportation distance from the time the molten resin is supplied to the injection molding apparatus 500 after removing foreign matter to 1 to 7 m, more specifically, the distance from the outlet of the gear pump 700 installed downstream of the filter 600 to the inlet of the injection pot provided in the injection molding apparatus 500. In this case, the transportation rate of the molten resin is preferably 900 to 1500 kg / h.

[0034] According to the present embodiment as described above, preforms can be produced more efficiently and at lower cost from resin flakes obtained by crushing recovered polyester resin molded articles into flakes. In particular, according to the present embodiment, even though the preforms are produced by recycling recovered polyester resin molded articles, 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 bishydroxyethyl terephthalate is 1 to 35 ppm, preferably 1 to 30 ppm, more preferably 1 to 20 ppm, the residual amount of monohydroxyethyl terephthalate is 1 to 35 ppm, preferably 1 to 30 ppm, more preferably 1 to 20 ppm, and the residual amount of cyclic trimer is 6000 ppm or less, preferably 4000 ppm or less, more preferably 3000 ppm or less, and preferably, when the mass of the preform is 14 to 50 g, L ＊ a ＊ b ＊ L in color system ＊ Value 70-90, b ＊ Preforms with values ​​between 2 and 18 can be successfully produced.

[0035] Here, the residual amounts of acetaldehyde, bishydroxyethyl terephthalate (BHET), monohydroxyethyl terephthalate (MHET), and cyclic trimer (CT), and the intrinsic viscosity can be determined, for example, as follows.

[0036] <Residual Amount of Acetaldehyde> A piece cut from a preform is used as a sample. 1.0 g of the sample is weighed into a glass bottle, and 5.0 mL of pure water is added and sealed. This suspension is heated for 60 minutes in an oven controlled at 120°C, and then cooled in ice water. 1.0 mL of the supernatant of the suspension is sampled, to which 0.2 mL of a 0.1% 2,4-dinitrophenylhydrazine / phosphate solution is added. The mixture is left to stand for 30 minutes and then measured by high-performance liquid chromatography. A standard solution is also measured at the same time, and the acetaldehyde content is calculated based on the obtained calibration curve.

[0037] <Residual Amounts of BHET, MHET, and CT> A piece cut from a preform was used as a sample. 0.2 g of the sample was weighed, and 1 mL of a mixed solvent of hexafluoroisopropanol and chloroform (weight ratio 1 / 1) was added to completely dissolve the sample. 4 mL of chloroform was added to the solution, and then 5 mL of acetonitrile was gradually added. The solution was left for 3 hours to precipitate the PET polymer. 1 mL of the suspension was sampled and filtered through a membrane filter with a pore size of 0.45 μm, and the filtrate was measured by high-performance liquid chromatography. Measurements of standard solutions were also performed at the same time, and the contents of MHET, BHET, and CT in the pellets were calculated based on the obtained calibration curve.

[0038] <Intrinsic Viscosity> A piece cut out from the preform is used as a sample, and this sample is vacuum dried at 150°C for 1 hour and weighed out at 0.2 g. A mixed solvent of 1,1,2,2-tetrachloroethane and phenol (weight ratio 1:1) is added to this to adjust the concentration to 1.00 g / dL, and the mixture is stirred at 120°C for 20 minutes to completely dissolve it. The dissolved solution is cooled to room temperature, and the relative viscosity is measured using a relative viscometer temperature-controlled at 30°C to determine the intrinsic viscosity.

[0039] Also, L ＊ a ＊ b ＊ L in color system ＊ value, b ＊ The value is measured at the body of the preform using a spectrophotometer under the measurement conditions of a D65 light source and a 2° field of view.

[0040] The present invention will be described in more detail below with reference to specific examples.

[0041] [Example 1] 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 these resin flakes were determined in the same manner as described above. The intrinsic viscosity was 0.803 dL / g, and the residual acetaldehyde content was 6.0 ppm.

[0042] The prepared resin flakes 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 subjected to a heat treatment. The treatment time was 2 hours. The intrinsic viscosity and the amount of residual acetaldehyde of the heat-treated resin flakes were measured, and the intrinsic viscosity was 0.826 dL / g, and the amount of residual acetaldehyde was 5.7 ppm.

[0043] After the resin flakes were heat-treated, they were fed into a twin-screw extruder and plasticized. During this process, gaseous components, including low-molecular-weight impurities derived from the polyester resin, remaining in the twin-screw extruder were evacuated to the outside of the system by venting. The vacuum level during venting was 1 kPa.

[0044] While removing foreign matter using a filter installed on the discharge port side of the extruder, the plasticized molten resin was supplied to an injection molding machine and injection molded at a production rate of 750 28 g preforms per minute. At this time, the distance from the outlet of the gear pump installed downstream of the filter to the inlet of the injection pot equipped with the injection molding machine was 6 m, the residence time of the molten resin in the transport path was 260 seconds, and the transport rate of the molten resin was 1260 kg / h.

[0045] For preforms manufactured by controlling the temperature of the molten resin supplied to the injection molding machine to the temperatures shown in Table 1, the decrease rate of intrinsic viscosity relative to the raw material, the amount of acetaldehyde (AA) remaining, and L ＊ value, b ＊ The values ​​obtained are shown in Table 1.

[0046]

[0047] In this example, the amount of residual acetaldehyde was less than 15 ppm at all temperatures, and in particular, it was less than 5 ppm at 280° C. The rate of decrease in intrinsic viscosity was only 3.0% even at a temperature of 300° C.

[0048] [Example 2] 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 to plasticize the heat-treated resin flakes, and no venting was performed.

[0049] For preforms manufactured by controlling the temperature of the molten resin supplied to the injection molding machine to the temperatures shown in Table 2, the decrease rate of intrinsic viscosity relative to the raw material, the amount of acetaldehyde (AA) remaining, and L ＊ value, b ＊ The values ​​obtained are shown in Table 2.

[0050]

[0051] In this example, the amount of remaining acetaldehyde was below 15 ppm at all temperatures.

[0052] Example 3 A preform was produced in the same manner as in Example 2, except that the distance from the outlet of the gear pump installed downstream of the filter to the inlet of the injection pot provided in the injection molding machine was set to 8 m.

[0053] For preforms manufactured by controlling the temperature of the molten resin supplied to the injection molding machine to the temperatures shown in Table 3, the decrease rate of intrinsic viscosity relative to the raw material, the amount of acetaldehyde (AA) remaining, and L ＊ value, b ＊ The values ​​obtained are shown in Table 3.

[0054]

[0055] In this example, the amount of remaining acetaldehyde at 280°C and 285°C was below 15 ppm.

[0056] A comparison between Example 2 and Example 3 confirms that the rate of decrease in intrinsic viscosity and the amount of residual acetaldehyde are reduced by shortening the transport distance from when the plasticized molten resin is removed from foreign matter until it is supplied to the injection molding machine. Furthermore, a comparison between Example 1 and Example 2 confirms that the rate of decrease in intrinsic viscosity and the amount of residual acetaldehyde are further reduced by feeding the heat-treated resin flakes into a twin-screw extruder to plasticize them and then performing a venting process. Furthermore, the methods described in these examples can be considered environmentally friendly in that they involve little thermal history and emit little carbon dioxide.

[0057] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0058] REFERENCE SIGNS LIST 100 Processing device 101 Processing chamber 102 Preheating chamber 107 Catalyst tank 200 Extruder (twin-screw extruder) 300 Buffer tank 400 Relief tank 500 Injection molding device 600 Filter 700 Gear pump

Claims

1. The recovered polyester resin molded articles are pulverized into flakes to prepare resin flakes; The resin flakes are heat-treated under reduced pressure and then plasticized; A method for producing a preform, comprising the steps of: removing foreign matter from a molten resin obtained by plasticizing the resin flakes; supplying the molten resin to an injection molding machine; and injection-molding a preform.

2. The method for producing a preform according to claim 1, wherein the heat-treated resin flakes are fed into a twin-screw extruder to be plasticized.

3. The method for producing a preform according to claim 2, wherein the twin-screw extruder is provided with a vent port, and gas phase components containing low-molecular-weight impurity components derived from the polyester resin remaining in the twin-screw extruder are sucked under reduced pressure through the vent port and discharged outside the system.

4. 2. The method for producing a preform according to claim 1, wherein the transport distance of the plasticized molten resin after removing foreign matter is 1 to 7 m until it is supplied to the injection molding device.

5. The method for producing a preform according to claim 1, wherein the resin flakes are heat-treated in an atmosphere reduced in pressure to 1000 Pa or less and at a temperature of 160 to 240°C.

6. A method for manufacturing a preform as described in claim 5, wherein the resin flakes are placed in a preheating chamber, heated to a predetermined temperature, and then the pressure inside the preheating chamber is reduced to a predetermined level, and then the resin flakes are dropped from the preheating chamber into a processing chamber whose internal atmosphere is adjusted to a predetermined temperature and pressure while maintaining airtightness from the outside of the system, and the resin flakes are deposited in the processing chamber and subjected to a heat treatment.

7. A method for manufacturing a preform as described in claim 6, wherein the heat-treated resin flakes are sequentially removed from the treatment chamber in amounts equal to the amount dropped from the preheating chamber, starting from the bottom layer deposited in the treatment chamber, and plasticized.

8. A method for manufacturing a preform as described in claim 6, wherein the heat-treated resin flakes are sequentially removed from the treatment chamber in amounts equal to the amount dropped from the preheating chamber, starting from the bottom layer deposited in the treatment chamber, stored in a buffer tank, and then plasticized.

9. A method for manufacturing a preform as described in claim 8, wherein a relief tank is installed midway along the transport path for transporting the resin flakes removed from the processing chamber to the buffer tank, so that the resin flakes can be evacuated to the relief tank during transport while being transported to the buffer tank.

10. The resin flakes are sequentially fed into a plurality of preheating chambers, and the resin flakes are dropped into the processing chambers in the order of the preheating chambers in which the fed resin flakes have been heated to a predetermined temperature. A method for manufacturing a preform according to any one of claims 6 to 9.

11. The method for manufacturing a preform according to any one of claims 6 to 9, wherein heated gas is ejected into the preheating chamber to heat the resin flakes while stirring them, and the inside of the preheating chamber is suctioned under reduced pressure.

12. A method for manufacturing a preform according to any one of claims 6 to 9, wherein a treatment chamber in which the resin flakes are subjected to a heat treatment is connected to a circulation flow path that allows the gas phase components in the treatment chamber to circulate and includes a catalyst tank in the path that decomposes low molecular weight impurity components derived from polyester-based resins, and the gas phase components in the treatment chamber are guided and circulated through the circulation flow path, thereby reducing the impurity components remaining in the treatment chamber.

13. A preform manufactured by the preform manufacturing method according to any one of claims 1 to 9, A preform characterized in that 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 ppm or less.

14. When the mass of the preform is 14 to 50 g, L ＊ a ＊ b ＊ L in color system ＊ Value 70-90, b ＊ A preform according to claim 13, wherein the value is 2 to 18.