Method for manufacturing polyester resin pellets

Abstract

To provide a method for producing polyester resin pellet in which generation of curved pellet is suppressed when producing crystalline polyester resin pellet by an underwater cutter method.SOLUTION: Provided is a method for producing polyester resin pellet, which is a method for producing polyester resin pellet that includes a step of extruding molten resin of crystalline polyester resin from a die hole of underwater cutter equipment into cooling water and cutting it into a predetermined length with a cutter to make it into pellet, and in which the 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 Art

[0002] Polyester resins occupy an important position industrially due to their excellent mechanical and chemical properties. For example, among them, crystalline polyesters typified by polyethylene terephthalate (hereinafter sometimes abbreviated as PET) and polybutylene terephthalate (hereinafter sometimes abbreviated as PBT) are resins excellent in hygiene, heat resistance, chemical resistance, etc., and due to the ease of molding processing and economy, they are widely used in fields such as extrusion molding applications including various industrial sheets and films, or injection molding applications such as food packaging applications, electrical and electronic parts, automotive parts, and precision equipment parts.

[0003] Polyester resins are obtained by melt polycondensing a dicarboxylic acid component typified by terephthalic acid and a diol component typified by ethylene glycol, 1,4-butylene glycol, etc. After the melt polycondensation is completed, it is usually processed into a granular form called pellets.

[0004] As a method for producing these resin pellets, the strand cutting method in which the molten resin is extruded in a strand shape, brought into contact with cooling water by a slider or the like, cooled below the glass transition point, and then cutting is performed is commonly used.

[0005] For resins that are difficult to cure as strands due to reasons such as a low glass transition temperature, an underwater cutting method (hereinafter sometimes referred to as the "underwater cutter method") is known, in which molten resin is directly extruded from a die hole of an underwater cutter into cooling water, and at the same time the molten resin is cut on the spot to obtain pellets (Patent Document 1). Molten resin cut underwater is usually deformed into a spherical shape by surface tension, and then crystallizes to fix the pellet shape. However, in the case of Patent Document 1, the composition of 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 a safety standpoint, in terms of equipment costs for high-pressure equipment, and because it requires a subsequent solvent removal process.

[0006] On the other hand, when the cooling water temperature is around normal room temperature, resins with relatively slow crystallization rates, such as polyethylene terephthalate, produce perfectly spherical pellets without any problems. However, with resins that have a fast crystallization rate, the pellets become bent into a "V" shape (hereinafter, this shape may be referred to as "bent"). Pellets deformed into a bent shape have poor supply stability to the 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 leads to a decrease in productivity due to longer metering times. It is presumed that the reason why pellets deform into a bent shape is that the cooling water flow hits 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 Publication No. 2005-349811 [Overview of the project] [Problems that the invention aims to solve]

[0008] The objective of the present invention is to suppress the generation of curved pellets when manufacturing crystalline polyester resin pellets by the underwater cutter method. [Means for solving the problem]

[0009] The inventors of this invention have conducted extensive research to solve the above problems and have found that the problem can be solved by setting the cooling water temperature in the underwater cutter method to between 35°C and 100°C. This invention is based on this finding and is summarized below.

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

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

[0012] [3] A method for producing polyester resin pellets according to [1] or [2], comprising polymerizing terephthalic acid, 1,4-butanediol, and a polyether polyol to produce a crystalline polyester resin and extruding it from a die hole into cooling water.

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

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

[0015] The present invention provides a method for producing polyester pellets that offers improved supply stability to the molding machine. This improves productivity when producing various molded products. [Modes for carrying out the invention]

[0016] The present invention will be described in detail below, but the following descriptions of constituent elements are representative examples of embodiments 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, and refers to all polyesters that possess crystalline properties. That is, it is a polyester resin obtained by polycondensation of a dicarboxylic acid component and a diol component, and which crystallizes at a temperature above its glass transition temperature. In the present invention, it is preferable that the resin has a fast crystallization rate when crystallized from a molten state. Specifically, when the resin is melted and then the semi-crystallization time at 180°C is measured using a differential scanning calorimeter (DSC), it is preferable that the resin has a semi-crystallization time of 1 second or more and 200 seconds or less, and more preferably 30 seconds or more and 100 seconds or less.

[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 the component that is present in the dicarboxylic acid component at a concentration 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 polymers of these diols.

[0020] Among the diol components, aliphatic diols and polyether polyols are preferred. 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, a number-average molecular weight of 650 to 2000, particularly 800 to 1500, is preferred due to its good reactivity.

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

[0022] The crystalline polyester used in this invention can be produced by conventional methods, either continuous or batch. Polytetramethylene glycol copolymerized polybutylene terephthalate can be produced, for example, by the method disclosed in Japanese Patent Application Publication No. 2017-160359.

[0023] The resin extruded from the production equipment of crystalline polyester is usually transferred directly through a pipe to a die plate by a pump such as a gear pump at a temperature above the melting point. The transferred molten resin passes through the die holes provided in the die plate and is extruded into cooling water.

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

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

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

[0027] In the present invention, the cooling water temperature is set to 35 - 100°C, preferably 45 - 70°C, more preferably 50 - 65°C, and particularly preferably 55 - 65°C. When the cooling water temperature is lower than this range, the warping of the resin pellets is significant, and when it is higher than this range, the equipment cost and heating cost increase.

[0028] The pellet size can be adjusted as appropriate by controlling the die hole diameter, molten resin extrusion pressure, viscosity, cutter rotation speed, etc., but is preferably 0.1 g / 100 pellets or more, 5 g / 100 pellets or less, and 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, and if it exceeds this range, it becomes difficult to melt during molding, and the productivity during molding decreases. The die hole diameter is preferably 0.1 to 10 mm, particularly 1.0 to 5 mm. [Examples]

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

[0030] <Pellet weight> We collected 100 pellets, measured their weight, and determined the weight of each pellet.

[0031] <Semi-crystallization time> The sample was cut into pieces approximately 0.1 mg in size, placed in an aluminum pan, and introduced into a PerkinElmer differential operating calorimetry system (DSC 8000). The temperature was raised to 300°C and held for 3 minutes to melt the sample, then rapidly cooled to 180°C, and the heat generation was continuously detected while maintaining isothermal temperature. The point at which the temperature reached 180°C was defined as zero seconds, and the time until the crystallization heat generation reached half of the original value after 10 minutes was defined as the semi-crystallization time.

[0032] <Pellet shape> A 10g pellet was taken and its shape was visually observed with a magnifying glass. It was evaluated as follows: × if 50% or more by weight were curved pellets, ○ if 20% or more by weight were less than 50% by weight, and ◎ if less than 20% by weight were curved pellets. The criteria for determining whether a pellet was curved was that it had a concave shape and the entire pellet was bent.

[0033] <Molding Evaluation> Pellets were fed into an injection molding machine FE-80S (manufactured by Nissei Plastic Industrial Co., Ltd.) equipped with a mold to produce molded plates with a thickness of 2 mm and a square diameter of 110 mm. Injection molding was performed under the conditions shown below, and the weighing time was measured. The cylinder temperatures were set to 245°C, 250°C, 240°C, and 210°C in order from the hopper, the mold temperature was 20°C, the screw rotation speed was 75 rpm, and the screw back pressure was 10 kgf / cm². 2 Injection molding was performed with an injection time of 10 seconds and a cooling time of 20 seconds.

[0034] [Example 1] After weighing 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, the mixture was placed in a transesterification reactor and heated from 150°C to 210°C over 4 hours while removing the mixture from the system using a rectification column with methanol, and then held at 210°C for 30 minutes. Subsequently, the reaction product was 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 stub AO-60 (manufactured by Adeka) were added. The mixture was then heated from 210°C to 238°C over 1 hour and 30 minutes, while the pressure was reduced to 1 Tor over 110 minutes to complete the polycondensation.

[0035] The resulting polycondensate was continuously withdrawn from the bottom of the polycondensation vessel and pelletized using 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 m³ / h. 3 Pellets were produced using a cutter rotation speed of 1580 rpm, an extrusion speed of 3.5 tons per hour, and a cooling water temperature of 60°C. Table 1 shows the pellet properties and weighing times during molding evaluation.

[0036] [Comparative Example 1] Pellets were manufactured 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 weighing times during molding evaluation.

[0037] [Table 1]

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

Claims

1. A method for manufacturing polyester resin pellets, comprising the step of extruding molten crystalline polyester resin from a die hole of an underwater cutter into cooling water and cutting it to a predetermined length with a cutter to form pellets, A method for producing polyester resin pellets by polymerizing terephthalic acid, 1,4-butanediol, and a polyether polyol to produce the crystalline polyester resin, and extruding the resulting pellets from a die hole into cooling water, wherein A method for producing polyester resin pellets, characterized in that the temperature of the cooling water is 45 to 65°C.

2. A method for producing polyester resin pellets according to claim 1, wherein the polyether polyol is polytetramethylene glycol.

3. A method for producing polyester resin pellets according to claim 2, wherein the content of polytetramethylene glycol in terephthalic acid, 1,4-butanediol, and polytetramethylene glycol is 30% by mass or less.

4. The method for producing polyester resin pellets according to any one of Claims 1 to 3, wherein the crystalline polyester resin is a resin whose semi-crystallization time, as measured by differential scanning calorimeter (DSC) using the following method, is 1 second or more and 200 seconds or less. <Method for measuring semi-crystallization time> The sample is heated to 300°C and held for 3 minutes to melt, then rapidly cooled to 180°C and kept isothermal while continuously detecting the heat generation. The point at which the temperature reaches 180°C is defined as zero seconds, and the time until the temperature reaches half of the heat generation for crystallization after 10 minutes is defined as the semi-crystallization time.

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