JP2015044363A - Thermoplastic aromatic polyester resin pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic aromatic polyester resin pellet capable of suppressing the variation of the measuring time of a resin at injection molding.SOLUTION: An elliptic columnar thermoplastic aromatic polyester resin pellet consists of a thermoplastic aromatic polyester resin composition containing a thermoplastic aromatic polyester resin and a lubricant and satisfies the following conditions (1)-(3): (1) long diameter/short diameter>1, that is a ratio in a longitudinal direction at a vertical cross section; (2) bulk density>0.80 [g/cm]; and (3) excluded volume density<0.50 [g/cm].

Description

  The present invention relates to a thermoplastic aromatic polyester resin pellet made of a thermoplastic aromatic polyester resin composition.

Thermoplastic aromatic polyester resins have a high heat distortion temperature and are excellent in electrical properties, mechanical properties, weather resistance, water resistance, chemical resistance, etc., so they are used in various applications such as electrical / electronic parts and automobile parts. Yes.
Since the thermoplastic aromatic polyester resin is a thermoplastic resin, an injection molding method is generally employed to obtain the molded product. According to the injection molding method, for example, a resin composition containing a thermoplastic aromatic polyester resin and a lubricant is pelletized, and the pellet is put into a hopper of an injection molding machine so that the pellet is supplied to the cylinder → plasticized. After passing through the part → metering part, it is injected from the nozzle into the mold and molded into the shape of the mold. In this case, if the conveyance in the supply unit or the melting in the plasticizing unit becomes unstable for some reason, there arises a problem that the time required for measuring the resin required for one injection in the measuring unit varies. Various techniques for improving such variation in measurement time have been proposed (see, for example, Patent Documents 1 and 2). In Patent Document 1, the variation in the measurement time is improved by providing a groove of a predetermined size on the outer peripheral surface of the resin pellet, but it is necessary to prepare a special die for forming the groove at the time of producing the strand. is there. Further, in Patent Document 2, the dispersion of the measurement time is improved by mixing two different types of pellets, but the process becomes complicated, such as the need to prepare and mix the two types of pellets. .

  On the other hand, resin pellets that solve various problems by improving the shape of the pellets have been proposed (see Patent Documents 3 to 5). However, the pellets of Patent Document 3 require a special mixed ester as a release agent, and the process becomes complicated, such as transferring scratches or groove-like irregularities on the pellet surface with a roller. In addition, Patent Document 4 describes that if the diameter and height of the cylindrical pellet are excessive, the meterability is deteriorated. The improvement was not enough. In addition, the elliptical plate-shaped resin pellet of patent document 5 is for improving handleability, such as transport and storage efficiency, and is not intended to improve the above-described variation in measurement time.

JP 2000-84925 A JP 2001-247682 A JP 9-53005 A International Publication No. 2012/081381 JP 2003-266432 A

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide thermoplastic aromatic polyester resin pellets in which variation in the measurement time of the resin during injection molding can be suppressed.

The present invention for solving the above problems is as follows.
[1] An elliptic cylinder-shaped thermoplastic aromatic polyester resin pellet comprising a thermoplastic aromatic polyester resin composition containing a thermoplastic aromatic polyester resin and a lubricant,
A thermoplastic aromatic polyester resin pellet characterized by satisfying all of the following conditions (1) to (3).
(1) Ratio of major axis / minor axis of section perpendicular to longitudinal direction> 1
(2) Bulk density> 0.80 [g / cm ³ ]
(3) Excluded volume density <0.50 [g / cm ³ ]

[2] The thermoplastic aromatic polyester resin pellet according to claim 1, further satisfying the following condition (4).
(4) Aspect ratio> 1.4

[3] The thermoplastic aromatic polyester resin pellet according to [1] or [2], which satisfies the following condition (1a) instead of the condition (1).
(1a) Ratio of major axis / minor axis of section perpendicular to longitudinal direction ≧ 1.1

[4] The thermoplastic aromatic polyester resin pellet according to any one of [1] to [3], wherein the end is cut perpendicular to the longitudinal direction.

[5] The thermoplastic aromatic polyester resin pellet according to any one of [1] to [4], wherein the thermoplastic aromatic polyester resin is a polybutylene terephthalate resin.

  ADVANTAGE OF THE INVENTION According to this invention, the thermoplastic aromatic polyester resin pellet which can suppress the dispersion | variation in the measurement time of resin at the time of injection molding can be provided.

The thermoplastic aromatic polyester resin pellet of the present invention is an elliptic cylindrical thermoplastic aromatic polyester resin pellet made of a thermoplastic aromatic polyester resin composition containing a thermoplastic aromatic polyester resin and a lubricant. It is characterized by satisfying all of the conditions (1) to (3).
(1) Ratio of major axis / minor axis of section perpendicular to longitudinal direction> 1
(2) Bulk density> 0.80 [g / cm ³ ]
(3) Excluded volume density <0.50 [g / cm ³ ]
The thermoplastic aromatic polyester resin pellets of the present invention satisfy all of the above conditions (1) to (3), thereby suppressing variation in the resin measurement time when molding by injection molding.
Below, the thermoplastic aromatic polyester resin composition which comprises the thermoplastic aromatic polyester resin pellet of this invention is demonstrated first.

[Thermoplastic aromatic polyester resin composition]
The thermoplastic aromatic polyester resin composition according to the present invention includes a thermoplastic aromatic polyester resin and a lubricant, and includes other components as necessary. Below, each component is demonstrated one by one.

(Thermoplastic aromatic polyester resin)
The thermoplastic aromatic polyester resin is a reaction between a dicarboxylic acid component mainly composed of a dicarboxylic acid compound and / or an ester-forming derivative thereof and a diol component mainly composed of a diol compound and / or an ester-forming derivative thereof. Is a thermoplastic polyester resin obtained by the above-mentioned method, and contains an aromatic compound in at least one of a dicarboxylic acid component or a diol component.

Examples of the dicarboxylic acid component include aliphatic dicarboxylic acids (for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecane dicarboxylic acid, dodecane dicarboxylic acid, hexadecanedicarboxylic acid, dimer, and the like. Dicarboxylic acids of about C _4-40 such as acids, preferably dicarboxylic acids of about 4 to 14 carbon atoms, alicyclic dicarboxylic acids (for example, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, highmic acid) C _4-40 dicarboxylic acid, preferably C _8-12 dicarboxylic acid), aromatic dicarboxylic acid (eg, phthalic acid, isophthalic acid, terephthalic acid, methyl isophthalic acid, methyl terephthalic acid, 2,6 -Naphthalene dicarboxylic acid such as naphthalene dicarboxylic acid 4,4′-biphenyl dicarboxylic acid, 4,4′-diphenoxy ether dicarboxylic acid, 4,4′-dioxybenzoic acid, 4,4′-diphenylmethane dicarboxylic acid, 4,4′-diphenyl ketone dicarboxylic acid, etc. _C8-16 dicarboxylic acid), or derivatives thereof (for example, derivatives capable of forming an ester such as lower alkyl esters, aryl esters, and acid anhydrides). These dicarboxylic acid components can be used alone or in combination of two or more. Preferred dicarboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid (particularly terephthalic acid and 2,6-naphthalenedicarboxylic acid). The dicarboxylic acid component preferably contains, for example, 50 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more of aromatic dicarboxylic acid. Furthermore, you may use together polyvalent carboxylic acid, such as trimellitic acid and a pyromellitic acid, or its ester formation derivative (alcohol ester etc.) etc. as needed. When such a polyfunctional compound is used in combination, a branched thermoplastic polyester resin can also be obtained.

Examples of the diol component include aliphatic alkanediols (for example, ethylene glycol, trimethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, hexanediol, octanediol, and decanediol. An aliphatic diol of about C _2-12 , preferably an aliphatic diol of about C _2-10 , and the like, a polyoxyalkylene glycol (a glycol having an alkylene group of about C _2-4 and having a plurality of oxyalkylene units, For example, diethylene glycol, dipropylene glycol, ditetramethylene glycol, triethylene glycol, tripropylene glycol, polytetramethylene glycol, etc.), alicyclic diol (for example, 1,4-cyclohexanediol, , 4-cyclohexanedimethanol, and hydrogenated bisphenol A), and the like. In addition, aromatic diols such as hydroquinone, resorcinol, bisphenol, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis- (4- (2-hydroxyethoxy) phenyl) propane, and xylylene glycol are used in combination. May be. These diol components can be used alone or in combination of two or more. Preferred diol components include C _2-10 alkylene glycol (linear alkylene glycol such as ethylene glycol, trimethylene glycol, propylene glycol, 1,4-butanediol) and the like. The diol component preferably contains, for example, 50 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more of _C2-10 alkylene glycol. Furthermore, if necessary, a polyol such as glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, or an ester-forming derivative thereof may be used in combination. When such a polyfunctional compound is used in combination, a branched thermoplastic polyester resin can also be obtained.

  Examples of the thermoplastic aromatic polyester resin include a copolyester obtained by combining two or more of the above-described dicarboxylic acid component and diol component, and another copolymerizable monomer (hereinafter sometimes referred to as a copolymerizable monomer). Copolyesters that combine carboxylic acid components, lactone components, and the like can also be used.

Examples of the oxycarboxylic acid (or oxycarboxylic acid component or oxycarboxylic acid) include oxycarboxylic acids such as oxybenzoic acid, oxynaphthoic acid, hydroxyphenylacetic acid, glycolic acid, oxycaproic acid, and derivatives thereof. . Lactones include C _3-12 lactones such as propiolactone, butyrolactone, valerolactone, caprolactone (eg, ε-caprolactone, etc.), and the like.

  In the copolyester, the proportion of the copolymerizable monomer can be selected, for example, from the range of about 0.01 mol% to about 30 mol%, and is usually about 1 mol% to about 30 mol%, preferably 3 mol%. It is about 25 mol% or less, more preferably about 5 mol% or more and 20 mol% or less. Further, when the homopolyester and the copolyester are used in combination, the proportion of the homopolyester and the copolyester is such that the proportion of the copolymerizable monomer is 0.1 mol% or more and 30 mol% or less with respect to the total monomers (Preferably about 1 mol% to 25 mol%, more preferably about 5 mol% to 25 mol%), usually the former / the latter = 99/1 to 1/99 (mass ratio), Preferably, it can be selected from the range of about 95/5 to 5/95 (mass ratio), more preferably about 90/10 to 10/90 (mass ratio).

Preferred thermoplastic aromatic polyester resins include homopolyesters or copolyesters having an alkylene arylate unit such as alkylene terephthalate or alkylene naphthalate as the main component (for example, about 50 to 100 mol%, preferably about 75 to 100 mol%) [ for example, polyalkylene terephthalate (e.g., polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), poly _{C 2-4} alkylene terephthalate such as polybutylene terephthalate (PBT)), 1,4-cyclohexane dimethylene terephthalate (PCT) , polyalkylene naphthalate (e.g., polyethylene naphthalate, polypropylene naphthalate, poly C _2-4 alkylene naphthalate and polybutylene naphthalate), such as Mo polyester; main component an alkylene terephthalate and / or alkylene naphthalate unit (e.g., more than 50 mol%) includes copolyesters] containing as may be used in combination thereof singly or two or more.

Particularly preferred thermoplastic aromatic polyester resins are 80 mol% or more (especially 90 mol% or more) of _C2-4 alkylene arylate units such as ethylene terephthalate, trimethylene terephthalate, tetramethylene terephthalate, and tetramethylene-2,6-naphthalate. Homopolyester resin or copolyester resin (for example, polyethylene terephthalate resin, polytrimethylene terephthalate resin, polybutylene terephthalate resin, polytetramethylene-2,6-naphthalenedicarboxylate resin, etc.).

  Among these, polyethylene terephthalate resin and polybutylene terephthalate resin are preferable, and polybutylene terephthalate resin is particularly preferable.

  The amount of terminal carboxyl groups of the thermoplastic aromatic polyester resin is not particularly limited as long as the effects of the present invention are not impaired. The amount of terminal carboxyl groups of the thermoplastic aromatic polyester resin is preferably 30 meq / kg or less, and more preferably 25 meq / kg or less.

  The intrinsic viscosity (IV) of the thermoplastic aromatic polyester resin is not particularly limited as long as the effects of the present invention are not impaired. The intrinsic viscosity of the thermoplastic aromatic polyester resin is preferably 0.60 to 1.30 dL / g. From the viewpoint of preventing cracking and improving toughness for improving heating and cooling durability, it is more preferably 0.70 to 1.20 dL / g. When a thermoplastic aromatic polyester resin having an intrinsic viscosity in such a range is used, the resulting thermoplastic aromatic polyester resin composition has particularly excellent moldability. It is also possible to adjust the intrinsic viscosity by blending thermoplastic aromatic polyester resins having different intrinsic viscosities. For example, by blending a thermoplastic aromatic polyester resin having an intrinsic viscosity of 1.0 dL / g and a thermoplastic aromatic polyester resin having an intrinsic viscosity of 0.8 dL / g, a thermoplastic aromatic having an intrinsic viscosity of 0.9 dL / g A polyester resin can be prepared. The intrinsic viscosity (IV) of the thermoplastic aromatic polyester resin can be measured, for example, in o-chlorophenol at a temperature of 35 ° C.

  As the thermoplastic aromatic polyester resin, a commercially available product may be used, and a dicarboxylic acid component or a reactive derivative thereof, a diol component or a reactive derivative thereof, and a monomer that can be copolymerized, if necessary, are used in a conventional manner. You may use what was manufactured by copolymerization (polycondensation) by a method, for example, transesterification, the direct esterification method, etc.

(Lubricant)
As the lubricant, those used for ordinary thermoplastic resins can be used. Specifically, fatty acid, fatty acid metal salt, oxy fatty acid, paraffin, low molecular weight polyolefin, fatty acid amide, alkylene bis fatty acid amide, aliphatic ketone, fatty acid partial saponified ester, fatty acid lower alcohol ester, fatty acid polyhydric alcohol ester, fatty acid Examples include polyglycol esters and modified silicones.

  Fatty acids having 6 to 40 carbon atoms are preferred. Specifically, oleic acid, stearic acid, lauric acid, hydroxystearic acid, behenic acid, arachidonic acid, linoleic acid, linolenic acid, ricinoleic acid, palmitic acid, montan Examples thereof include acids and mixtures thereof. The fatty acid metal salt is preferably an alkali metal salt or alkaline earth metal salt of a fatty acid having 6 to 40 carbon atoms, and specific examples include calcium stearate, sodium montanate, calcium montanate, and the like.

  Examples of the oxy fatty acid include 1,2-oxystearic acid. Paraffin having 18 or more carbon atoms is preferable, and examples thereof include liquid paraffin, natural paraffin, microcrystalline wax, petrolactam and the like.

  As the low molecular weight polyolefin, for example, those having a molecular weight of 5,000 or less are preferable, and specific examples include polyethylene wax, maleic acid-modified polyethylene wax, oxidized type polyethylene wax, chlorinated polyethylene wax, and polypropylene wax.

  Fatty acid amides having 6 or more carbon atoms are preferred, and specific examples include oleic acid amide, erucic acid amide, and behenic acid amide.

  The alkylene bis fatty acid amide is preferably one having 6 or more carbon atoms, and specifically includes methylene bis stearic acid amide, ethylene bis stearic acid amide, N, N-bis (2-hydroxyethyl) stearic acid amide and the like.

  As the aliphatic ketone, those having 6 or more carbon atoms are preferable, and examples thereof include higher aliphatic ketones.

  Examples of the fatty acid partial saponified ester include a montanic acid partial saponified ester.

  Examples of the fatty acid lower alcohol ester include stearic acid ester, oleic acid ester, linoleic acid ester, linolenic acid ester, adipic acid ester, behenic acid ester, arachidonic acid ester, montanic acid ester, isostearic acid ester and the like. These may be mixed esters using a plurality of types of fatty acids and / or lower alcohols.

  Examples of fatty acid polyhydric alcohol esters include (poly) glycerin tristearate, (poly) glycerin distearate, (poly) glycerin monostearate, (poly) pentaerythritol tetrastearate, (poly) pentaerythritol Examples include tristearate, (poly) pentaerythritol distearate, (poly) pentaerythritol monostearate, (poly) pentaerythritol adipate stearate, sorbitan behenate, and the like. These may be mixed esters using a plurality of types of fatty acids and / or polyhydric alcohols.

  Examples of fatty acid polyglycol esters include polyethylene glycol fatty acid esters and polypropylene glycol fatty acid esters.

  Examples of the modified silicone include polyether-modified silicone, higher fatty acid alkoxy-modified silicone, higher fatty acid-containing silicone, higher fatty acid ester-modified silicone, methacryl-modified silicone, and fluorine-modified silicone.

  Preferred lubricants include, for example, fatty acid metal salts, low molecular weight polyolefins, alkylene bis fatty acid amides, fatty acid partial saponified esters, fatty acid lower alcohol esters, fatty acid polyhydric alcohol esters, and the like. Of these, low molecular weight polyolefins, fatty acid polyhydric alcohol esters, and alkylene bis fatty acid amides are more preferred. Among these, polyethylene wax, adipic acid ester, montanic acid ester, behenic acid ester, stearic acid ester, glycerin fatty acid ester, pentaerythritol fatty acid ester, trimethylolpropane fatty acid ester, sorbitan fatty acid ester, and ethylenebisstearic acid amide are more preferable, and trimethylol. Particularly preferred are mixed esters of propane, montanic acid and adipic acid, glycerin stearate, and pentaerythritol stearate.

  The addition amount of the lubricant in the present invention is from 0 to 100 parts by mass with respect to 100 parts by mass of the thermoplastic aromatic polyester resin from the viewpoint of suppressing leaching while providing good metering stability and releasability during molding. It is preferable to set it as 01-5.0 mass parts, and it is more preferable to set it as 0.1-3.0 mass parts.

(Other ingredients)
The thermoplastic aromatic polyester resin composition according to the present invention may contain other components as necessary. Other ingredients include inorganic fillers, anti-dripping agents, antioxidants such as hindered phenols, phosphorus secondary antioxidants, thioether secondary antioxidants, inorganic crystal nucleating agents, colorants, and the like. Can be contained.

[Thermoplastic aromatic polyester resin pellets]
The thermoplastic aromatic polyester resin pellet of the present invention is composed of the above thermoplastic aromatic polyester resin composition, the shape thereof is an elliptic cylinder, and satisfies all of the following conditions (1) to (3).
(1) Ratio of major axis / minor axis of section perpendicular to longitudinal direction> 1
(2) Bulk density> 0.80 [g / cm ³ ]
(3) Excluded volume density <0.50 [g / cm ³ ]

The condition (1) “ratio of major axis / minor axis of the elliptical section perpendicular to the longitudinal direction” is the ratio of the major axis to the minor axis (flatness) of the elliptical section of the thermoplastic aromatic polyester resin pellet of the present invention. It is a condition that prescribes. The reason why the meterability is advantageous due to the high flatness ratio is not clear, but if the ratio value is greater than 1, the surface area of the pellet increases, so the contact probability between the pellets increases, It is presumed that idling due to the sliding of the pellets in the plasticizing part is suppressed, effective shearing heat generation occurs, and the measuring time is shortened. The ratio value is preferably 1.1 or more (condition (1a)).
In order to increase the flatness ratio, in addition to making the dies for discharging the strands into a flat elliptical shape, even when using a perfect circular die, the time to immerse in the water bath after discharging is shortened, or the cutter is For example, the pellets may be deformed into a flat shape at the time of cutting by arranging them at a short distance from each other and cutting them before cooling and solidification of the strands proceed.
The “elliptical shape” in the present application includes shapes close to an ellipse such as an oval or a rounded rectangle.

The bulk density under the condition (2) is obtained by dropping the pellet into a 50 ml graduated cylinder to the 50 ml scale and measuring the weight of the charged pellet. When the bulk density is larger than 0.80 [g / cm ³ ], the thermoplastic aromatic polyester resin pellets are densely present, and the feeding and transport to the molding machine are efficiently performed, thereby shortening the measuring time. It is inferred that The bulk density is preferably 0.81 [g / cm ³ ] or more, and more preferably 0.82 [g / cm ³ ] or more. The upper limit of the bulk density is not particularly defined, but does not exceed the density of the thermoplastic aromatic polyester resin composition itself.
In order to increase the bulk density, the major axis or the minor axis of the thermoplastic aromatic polyester resin pellet may be reduced, and the degree should be set appropriately in consideration of satisfying the conditions (1) to (3). Can do.

The excluded volume density of the condition (3) is the volume of a sphere having a diameter of “the length of the diagonal of the rectangle with the major axis of the pellet and the major axis of the cross section” (the volume that can eliminate the surrounding pellets). The value is obtained by dividing the mass of the pellet. That is, it means the density obtained by assuming that the volume that can be taken to the maximum when any one thermoplastic aromatic polyester resin pellet rotates freely is the volume. Similar to the bulk density, it is considered that the higher the excluded volume density, the shorter the measurement time. However, in reality, the opposite is true, and the lower one is advantageous. The reason for this is not clear, but if the excluded volume density is less than 0.50 [g / cm ³ ], the degree of freedom of the position where the pellets can be taken increases, and the feeding time is more efficiently supplied. It is inferred that The excluded volume density is preferably 0.49 [g / cm ³ ] or less, and more preferably 0.48 [g / cm ³ ] or less. The lower limit of the excluded volume density is 0.40 [g / cm ³ ].
In order to reduce the excluded volume density, the length of the thermoplastic aromatic polyester resin pellet (in the height direction of the elliptic cylinder) may be increased, and the degree satisfies the conditions (1) to (3). It can be set as appropriate while taking into consideration.

  The thermoplastic aromatic polyester resin pellets of the present invention are preferably those whose ends are cut perpendicular to the longitudinal direction from the viewpoint of further shortening the measuring time. That is, when the strand formed by melt-molding the thermoplastic aromatic polyester resin composition is cut into pellets, it is preferable to cut the strands vertically rather than obliquely.

The thermoplastic aromatic polyester resin pellet of the present invention preferably satisfies the condition (4) aspect ratio> 1.40 from the viewpoint of further shortening the measuring time.
The aspect ratio of the condition (4) means a value obtained by dividing the length of the pellet by the average value of the major axis and minor axis of the pellet cross section. From the viewpoint of bulk density, it is considered that the smaller the aspect ratio, the more easily the pellets are densely packed, which is advantageous for efficient transportation. However, the larger the aspect ratio, the shorter the measuring time, and the excluded volume of (3) above. As with density, the trend is the opposite of what is expected. The aspect ratio is more preferably 1.45 or more.
In order to increase the aspect ratio, the length of the thermoplastic aromatic polyester resin pellet may be increased, or the major axis and / or the minor axis of the cross section may be decreased, and the degree thereof is determined by conditions (1) to (3). It can be set as appropriate in consideration of satisfying the above.

  The size of the thermoplastic aromatic polyester resin pellet of the present invention is not particularly limited as long as all of the above conditions (1) to (3) are satisfied. For example, the length is 2.0 to 5.0 mm. The major axis of the ellipse on the top and bottom surfaces can be 1.5 to 4.0 mm, and the minor axis can be 1.0 to 3.5 mm.

  The thermoplastic aromatic polyester resin pellet of the present invention can be obtained, for example, as follows. That is, first, a thermoplastic aromatic polyester resin composition constituting the thermoplastic aromatic polyester resin pellet to be produced is melt-molded to obtain a strand. At this time, the shape of the die is set to a shape satisfying the major axis / minor axis ratio of the condition (1) (for example, an elliptical shape) while considering the conditions (2) and (3). Next, the strand is cut so as to satisfy the conditions (2) and (3).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Examples 1-2, Comparative Examples 1-7]
In each of the examples and comparative examples, the thermoplastic aromatic polyester resin and the lubricant in the number of parts shown in Table 1 below were blended, and a twin-screw extruder having a 30 mmφ screw (TEX-30 manufactured by Nippon Steel Works) was used. The mixture was melt kneaded at 260 ° C. and extruded to obtain a strand. Thereafter, the obtained strand was cut to obtain thermoplastic aromatic polyester resin pellets. In each of the examples and comparative examples, the shape of the thermoplastic aromatic polyester resin pellet is changed to that shown in Table 1 by changing the shape of the die used for the twin-screw extruder and the cutting method (length, angle) for the strand. The shape is as shown.
Details of each of the above components are as follows.
Thermoplastic aromatic polyester resin: manufactured by Wintech Polymer Co., Ltd., polybutylene terephthalate resin lubricant with intrinsic viscosity of 0.84 1: manufactured by Clariant Japan Co., Ltd., Licolub WE40
Lubricant 2: Pentaerythritol tetrastearate

On the other hand, the major axis / minor axis ratio, the bulk density, and the excluded volume density of the elliptical cross section of the thermoplastic aromatic polyester resin pellet were measured as follows.
(1) Major axis / minor axis ratio of elliptical cross section The major axis and minor axis of the pellet were measured with a digital caliper manufactured by Mitutoyo Corp. and obtained by calculation.
(2) Bulk density The pellet was naturally dropped into a 50 ml graduated cylinder up to a 50 ml scale, and the weight of the charged pellet was measured and determined by calculation.
(3) Excluded volume density In the same manner as in (1) above, the major axis and length of the pellet are measured, and the length of the diagonal of the rectangle that makes each vertical and horizontal and the volume of the sphere assuming that the length of the diagonal is the diameter. Obtained by dividing the weight of the pellet.
(4) Aspect ratio The long diameter, short diameter, and length of the pellet were measured in the same manner as in (1) above, and the length was divided by the average value of the long diameter and the short diameter.

  The thermoplastic aromatic polyester resin pellets of Examples and Comparative Examples obtained as described above were put into an injection molding machine (EC40 manufactured by Toshiba), and a 65 mm × 55 mm × 2 mm flat plate was continuously molded. During 200 shots, the weighing time for each shot was measured. In addition, in order to remove the influence of the initial instability, the first 20 shots were discarded, and 200 shots after 20 shots were taken as the measurement object, and the average weighing time and the maximum weighing time were obtained. The results are shown in Table 1.

From Table 1 above, it can be seen that the measurement time becomes unstable when either the bulk density or the excluded volume density is outside the range defined in the present invention.
Moreover, Example 1 and Example 2 are the same numerical values for the bulk density and the excluded volume density, and only the major axis / minor axis ratio of the elliptical cross section is different, but the metering time of Example 2 is more stable. From this, it is understood that the measuring time is stabilized when the major axis / minor axis ratio is larger. That is, it is presumed that the measurement time can be stabilized when an elliptical shape in which the cross-sectional shape of the thermoplastic aromatic polyester resin pellet is higher in flatness than a perfect circle can be stabilized.
Furthermore, Comparative Example 2 and Comparative Example 3 have the same numerical values for the bulk density and the excluded volume density, and the aspect ratio is changed depending on the major axis, minor axis, and length. Since it is getting worse, it is presumed that the aspect ratio is more advantageous.

Claims (5)

An elliptic cylinder-shaped thermoplastic aromatic polyester resin pellet comprising a thermoplastic aromatic polyester resin composition containing a thermoplastic aromatic polyester resin and a lubricant,
A thermoplastic aromatic polyester resin pellet characterized by satisfying all of the following conditions (1) to (3).
(1) Ratio of major axis / minor axis of section perpendicular to longitudinal direction> 1
(2) Bulk density> 0.80 [g / cm ³ ]
(3) Excluded volume density <0.50 [g / cm ³ ] Furthermore, the thermoplastic aromatic polyester resin pellet of Claim 1 which satisfies the following conditions (4).
(4) Aspect ratio> 1.4 The thermoplastic aromatic polyester resin pellet according to claim 1 or 2, which satisfies the following condition (1a) instead of the condition (1).
(1a) Ratio of major axis / minor axis of section perpendicular to longitudinal direction ≧ 1.1   The thermoplastic aromatic polyester resin pellet according to any one of claims 1 to 3, wherein the end portion is cut perpendicular to the longitudinal direction.   The thermoplastic aromatic polyester resin pellet according to any one of claims 1 to 4, wherein the thermoplastic aromatic polyester resin is a polybutylene terephthalate resin.