Method for producing polyester resin pellet

Abstract

To suppress the generation of curved pellets when crystalline polyester resin pellets are produced by an underwater cutter method.SOLUTION: A method for producing a polyester resin pellet, comprising a step of extruding a molten resin of a crystalline polyester resin from a die hole of an underwater cutter facility into cooling water and cutting the molten resin into a predetermined length with a cutter to obtain a pellet, wherein a temperature of the cooling water is 35 to 100 °C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyester resin pellets. [Background technology]

[0002] Polyester resins occupy an important position industrially due to their excellent mechanical and chemical properties. For example, crystalline polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are resins with excellent hygienic, heat, and chemical resistance. Due to their ease of processing and economic efficiency, they are widely used in extrusion molding applications, including various industrial sheets and films, as well as injection molding applications for food packaging, electrical and electronic components, automotive parts, and precision instrument parts.

[0003] Polyester resin is obtained by melt polycondensation of a dicarboxylic acid component, such as terephthalic acid, with a diol component, such as ethylene glycol or 1,4-butylene glycol. After the melt polycondensation is complete, the resin is usually processed into granules known as pellets.

[0004] A commonly used method for producing these resin pellets is a strand cutting method in which molten resin is extruded in the form of a strand, brought into contact with cooling water using a slider or the like to cool the resin to below its glass transition point, and then cut.

[0005] For resins that are difficult to harden into strands due to reasons such as a low glass transition temperature, an underwater cutting method (hereinafter sometimes referred to as the "underwater cutting method") is known, in which molten resin is directly extruded into cooling water through a die hole in underwater cutting equipment and simultaneously cut into pellets on the spot (Patent Document 1). Molten resin cut underwater typically deforms into a spherical shape due to surface tension, and the pellet shape is then fixed by crystallization. However, in the case of Patent Document 1, the cooling water used during cutting is a mixture of water and an organic solvent, and the temperature of the cooling liquid is high, at 100 to 190°C, which is undesirable from the standpoint of safety, the equipment cost of the high-pressure equipment, and the subsequent solvent removal process.

[0006] On the other hand, when the cooling water temperature is around normal room temperature, resins with a relatively slow crystallization rate, such as polyethylene terephthalate, produce pellets that are perfectly spherical. However, resins with a fast crystallization rate produce pellets that are bent in a V-shape (hereinafter, this shape may be referred to as "curved"). Pellets that are curved are less stable when fed to a molding machine. For example, in the case of extrusion molding, this can cause production problems due to fluctuations in discharge pressure and torque, and in the case of injection molding, it can result in reduced productivity due to longer metering times. It is believed that the reason for the curved pellets is that the cooling water flow impinges on the polyethylene resin extruded from the die hole from the side (approximately perpendicular to the extrusion direction). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-349811 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to suppress the occurrence of curved pellets when crystalline polyester resin pellets are produced by an underwater cutter method. [Means for solving the problem]

[0009] As a result of extensive research into solving the above-mentioned problems, the inventors have found that the problems can be solved by setting the cooling water temperature in the underwater cutting method to 35° C. or higher and 100° C. or lower. The present invention is based on this finding and is summarized as follows.

[0010] [1] A method for producing polyester resin pellets, comprising the steps of extruding molten crystalline polyester resin through a die hole of underwater cutter equipment into cooling water and cutting it to a predetermined length with a cutter to form pellets, wherein the temperature of the cooling water is 35 to 100°C.

[0011] [2] The method for producing polyester resin pellets according to [1], wherein the temperature of the cooling water is 45 to 65°C.

[0012] [3] The method for producing polyester resin pellets according to [1] or [2], wherein terephthalic acid, 1,4-butanediol, and polyether polyol are polymerized to produce a crystalline polyester resin, which is then extruded through the die hole into cooling water.

[0013] [4] The method for producing polyester resin pellets according to [3], wherein the polyether polyol is polytetramethylene glycol.

[0014] [5] The method for producing polyester resin pellets according to [4], wherein the content of polytetramethylene glycol in the terephthalic acid, 1,4-butanediol, and polytetramethylene glycol is 30% by mass or less. [Effects of the Invention]

[0015] According to the method for producing polyester pellets of the present invention, it is possible to obtain pellets that are more stably supplied to a molding machine, thereby improving the productivity in producing various molded articles. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below, but the explanation of the constituent elements described below is a representative example of an embodiment of the present invention, and the present invention is not limited to these contents.

[0017] [Crystalline polyester resin] The polyester resin of the present invention is a crystalline polyester, which refers to any polyester having crystallinity. That is, it is a polyester resin obtained by polycondensation of a dicarboxylic acid component and a diol component, and crystallizes at any temperature above the glass transition point. In the present invention, the resin preferably has a fast crystallization rate when crystallized from a molten state. Specifically, when the resin is melted and then measured at 180°C using a differential scanning calorimeter (DSC), the resin preferably has a half-crystallization time of 1 second to 200 seconds, more preferably 30 seconds to 100 seconds.

[0018] Examples of dicarboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, phthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; and aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These dicarboxylic acid components can be introduced into the polymer backbone as dicarboxylic acids or using dicarboxylic acid derivatives such as dicarboxylic acid esters and dicarboxylic acid halides as raw materials. Terephthalic acid or dimethyl terephthalate is particularly preferred as the main component. The main component refers to a component that is contained in the dicarboxylic acid component in an amount of 50 mol % or more, preferably 80 mol % or more.

[0019] Examples of diol components include aliphatic diols such as ethylene glycol, diethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, and 1,8-octanediol; alicyclic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, and 1,4-cyclohexanedimethylol; aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone; and polyether polyols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, which are obtained by polymerizing these diols.

[0020] Among these, aliphatic diols and polyether polyols are preferred as the diol component. 1,4-butanediol is preferred as the aliphatic diol, and polyethylene glycol and polytetramethylene glycol are preferred as the polyether polyol. When the polyether polyol is polytetramethylene glycol, one having a number average molecular weight of 650 to 2000, particularly 800 to 1500, is preferred due to its good reactivity.

[0021] In the polyester obtained by polycondensing terephthalic acid, 1,4-butanediol, and polyether polyol, where the polyether polyol component is polytetramethylene glycol, it is preferable that the terephthalic acid, 1,4-butanediol, and polyether polyol contain polytetramethylene glycol in an amount of 30% by mass or less, particularly 25% by weight or less, and especially 0.1 to 10% by weight.

[0022] The crystalline polyester used in the present invention can be produced by a conventional method, either continuously or batchwise. Polytetramethylene glycol copolymerized polybutylene terephthalate can be produced by, for example, the method disclosed in JP 2017-160359 A.

[0023] Resin extruded from a crystalline polyester manufacturing facility is usually transferred to a die plate through direct piping by a pump such as a gear pump at a temperature above its melting point. The transferred molten resin passes through die holes in the die plate and is extruded into cooling water.

[0024] The equipment used for the process from polyester production to underwater cutter may be an extruder that melts and pelletizes crystalline polyester in a molten or solid state as a raw material, instead of a polyester resin production equipment that performs polycondensation from a monomer.

[0025] The resin extruded from the die holes into water is immediately cut to a predetermined length by a cutter that rotates facing the die plate to form pellets, which are then transferred to a dehydrator together with cooling water, where the cooling water and the pellets are separated.The cooling water then passes through a temperature regulator to be adjusted to an appropriate temperature, and is then transferred again to the underwater cutter.

[0026] [Underwater cutter method] The equipment used in the underwater cutter method of the present invention may be of any type, size, or structure as long as it can extrude molten resin directly into cooling water from a die plate having die holes and cut the molten resin.

[0027] In the present invention, the cooling water temperature is set to 35 to 100° C., preferably 45 to 70° C., more preferably 50 to 65° C., and particularly preferably 55 to 65° C. If the cooling water temperature is lower than this range, the resin pellets will be significantly curved, and if it is higher than this range, the equipment costs and heating costs will increase.

[0028] The pellet size can be adjusted appropriately by controlling the die hole diameter, extrusion pressure of the molten resin, viscosity, cutter rotation speed, etc., but is preferably 0.1 g / 100 pellets or more and 5 g / 100 pellets or less, more preferably 1 g / 100 pellets or more and 3 g / 100 pellets or less. If the pellet size is below this range, blockage due to rapid cooling inside the die hole is likely to occur, while if it exceeds this range, it becomes difficult to melt the pellets during molding, resulting in reduced productivity during molding. The die hole diameter is preferably 0.1 to 10 mm, and more preferably 1.0 to 5 mm. [Example]

[0029] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The methods for measuring physical properties and evaluation items used in the following examples are as follows.

[0030] <Pellet weight> 100 pellets were collected and weighed to determine the weight per pellet.

[0031] <Crystallization half time> The sample was cut into pieces of approximately 0.1 mg size and placed in an aluminum pan. The pan was then introduced into a Perkin-Elmer differential scanning calorimeter (DSC 8000). The sample was heated to 300°C and held there for 3 minutes to melt, then rapidly cooled to 180°C and held isothermal while continuously detecting the heat release. The time when the temperature reached 180°C was defined as zero seconds, and the time it took for the crystallization heat release to reach half its value after 10 minutes was defined as the half-crystallization time.

[0032] <Pellet shape> 10 g of pellets were sampled and visually observed for shape using a magnifying glass, and the pellets were evaluated as follows: x if 50% by weight or more were curved, o if 20% by weight or more but less than 50% by weight, and ⊚ if less than 20% by weight. The criteria for determining whether or not a pellet was curved was that it had a dent and was entirely bent.

[0033] <Molding evaluation> The pellets were placed into an injection molding machine FE-80S (manufactured by Nissei Plastic Industrial Co., Ltd.) equipped with a mold for producing a 2 mm thick, 110 mm square molded plate, and injection molding was performed under the following conditions, and the metering time was measured. The cylinder temperatures were set to 245°C, 250°C, 240°C, and 210°C, starting from the hopper, respectively; the mold temperature was 20°C; the screw rotation speed was 75 rpm; and the screw back pressure was 10 kgf / cm. 2 Injection molding was performed with an injection time of 10 seconds and a cooling time of 20 seconds.

[0034] [Example 1] 195 parts by weight of dimethyl terephthalate, 104 parts by weight of 1,4-butylene glycol, 24 parts by weight of polytetramethylene glycol (average molecular weight 1000 DA), and 0.71 parts by weight of tetrabutoxytitanium were weighed and charged into an ester exchange reactor. While removing methanol from the system using a rectification column equipped with an attached column, the temperature was raised from 150°C to 210°C over 4 hours and then maintained at 210°C for 30 minutes. The reaction product was then transferred to a polycondensation reactor, and 0.94 parts by weight of tetrabutoxytitanium, 0.86 parts by weight of magnesium acetate tetrahydrate, and 2.4 parts by weight of Adeka STAB AO-60 (manufactured by Adeka) were charged. The temperature was raised from 210°C to 238°C over 1 hour and 30 minutes, while the pressure was reduced to 1 Torr over 110 minutes, completing the polycondensation.

[0035] The obtained polycondensate was continuously discharged from the bottom of the polycondensation tank and pelletized with an underwater cutter (Nordson BKG AHD190). The die hole diameter was 3.2 mm and the number of die holes was 100. The die plate temperature was 255°C, and the cooling water flow rate was 30 m / h. 3 Pellets were produced at a cutter rotation speed of 1580 rpm, an extrusion rate of 3.5 tons per hour, and a cooling water temperature of 60° C. Table 1 shows the pellet properties and the weighing time for molding evaluation.

[0036] [Comparative Example 1] Pellets were produced in the same manner as in Example 1, except that the cooling water temperature was set to 30° C. Table 1 shows the pellet properties and the weighing time for molding evaluation.

[0037] [Table 1]

[0038] <Consideration> As shown in Table 1, according to Example 1, pellets with good pellet shape are produced.

Claims

1. A method for producing polyester resin pellets, comprising the steps of extruding a molten crystalline polyester resin through a die hole of underwater cutter equipment into cooling water and cutting the molten resin into pellets of a predetermined length with a cutter, The crystalline polyester resin is a resin having a crystallization half time of 1 second or more and 200 seconds or less, as measured by the following method using a differential scanning calorimeter (DSC), The method for producing polyester resin pellets, wherein the temperature of the cooling water is 45 to 65°C. <Method for measuring crystallization half time> The sample is heated to 300°C and held there for 3 minutes to melt, then rapidly cooled to 180°C and held isothermally while continuously detecting the amount of heat generated. The time when the temperature reaches 180°C is defined as zero seconds, and the time 10 minutes later until the amount of heat generated by crystallization reaches half its value is defined as the half-crystallization time.

2. 2. The method for producing polyester resin pellets according to claim 1, wherein terephthalic acid, 1,4-butanediol, and polyether polyol are polymerized to produce a crystalline polyester resin, which is then extruded through the die hole into cooling water.

3. 3. The method for producing polyester resin pellets according to claim 2, wherein the polyether polyol is polytetramethylene glycol.

4. 4. The method for producing polyester resin pellets according to claim 3, wherein the content of polytetramethylene glycol in the terephthalic acid, 1,4-butanediol, and polytetramethylene glycol is 30% by mass or less.

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