JP7575310B2 - Aromatic polyester resin expanded particles, their production method, expanded molded article, and automobile component - Google Patents

Description

The present invention relates to aromatic polyester resin foam particles for in-mold foam molding, a method for producing the same, foam molded articles, and automotive components.

In-mold foam molding has been widely used as a method for producing an aromatic polyester resin foam molded article by foaming aromatic polyester resin foam particles. In-mold foam molding is a molding method that includes a step of filling a mold with resin foam particles, and a step of heating the resin foam particles filled in the mold with a heat medium such as hot water or steam to cause secondary foaming, and heat-fusing the secondary foam particles together to produce an in-mold foam molded article having a desired shape.

Aromatic polyester resin foam particles are produced by melt-kneading in an extruder, extruding and foaming through a die, and then cutting. In this process, the hot cut method, underwater cut method, etc. are used. In recent years, granulators used in the underwater cut method have dies equipped with many die holes for extruding molten resin, and it is possible to extrude the molten resin into water from multiple locations at once and form many foam particles by cutting with a cutter in one go, further improving the production efficiency of foam particles. For example, in Patent Document 1, aromatic polyester resin foam particles are produced by the underwater cut method, that is, a method in which the extruded molten kneaded resin is cut and cooled underwater.

European Patent Application Publication No. 2564799

However, in the underwater cut method, the front surface (resin discharge surface) of the mold (die) is in contact with water during the production of expanded beads, and the outlet of the die hole is opened underwater to produce resin particles. Therefore, the resin, which has become highly viscous upon cooling, may partially block or completely block (clog) the flow path of the die hole, which may excessively increase the amount of molten resin discharged from the unblocked die hole, resulting in the formation of coarse expanded beads. Therefore, if the die hole diameter is small, defective products frequently occur due to clogging, so the hole diameter could not be made small. In Patent Document 1, the hole diameter is 1.8 mm to 2.0 mm, the cooling water temperature is 20°C to 90°C, and the particle diameter of the obtained expanded beads is large, at 5 mm or more. However, if the particle diameter of the expanded beads is small, it is easy to increase the filling rate of the expanded beads in the molding die, so expanded beads with a small particle diameter are desirable. If the particle size is large, the foaming power cannot be increased, and the filling rate cannot be increased when the foam particles are filled into a molding die. As a result, it is difficult to improve the mechanical properties of the resulting foamed molded product, such as the compressive strength and compressive modulus.

One object of the present invention is to provide an aromatic polyester resin foamed molded article having excellent mechanical properties. One object of the present invention is to provide aromatic polyester resin foamed beads having a small particle size for producing the foamed molded article. One object of the present invention is to provide a method for producing the foamed beads.

The inventors discovered that by adjusting the cooling water temperature and die hole diameter within a predetermined range in the underwater cutting method, clogging is unlikely to occur even if the die hole diameter is made small, and blockage is unlikely to occur even when a die with a small hole diameter is used, expanded beads with a small particle diameter are obtained, and the expanded molded article obtained from these expanded beads has superior mechanical strength to that obtained from expanded beads with a large particle diameter, and thus completed the present invention.

The present invention typically includes the following aspects.
Item 1.
The expanded aromatic polyester resin particles have a particle diameter of 1.5 mm to 4.5 mm and a surface resin layer thickness of 5 μm to 40 μm.
Item 2.
Item 2. The expanded aromatic polyester resin particles according to item 1, wherein the average cell diameter (C) in the center of the particle and the average cell diameter (D) in the surface layer portion are both 50 μm to 300 μm, and the ratio (D/C) of the average cell diameter in the surface layer portion to the average cell diameter in the center portion is 0.75 to 0.98.
Item 3.
Item 3. The expanded aromatic polyester resin particle according to item 1 or 2, wherein the crystallinity (A) in the center portion of the particle and the crystallinity (B) in the surface portion of the particle are both 10% or less, and the ratio (B/A) of the crystallinity in the surface portion to the crystallinity in the center portion is 0.90 to 1.5.
Item 4.
4. The expanded aromatic polyester resin particle according to any one of items 1 to 3, wherein the crystallinity (A) in the center portion of the particle and the crystallinity (B) in the surface portion of the particle are both 1 to 10%.
Item 5.
Item 5. An expansion molded product of the expanded aromatic polyester resin beads according to any one of items 1 to 4.
Item 6.
Item 7. The foamed molded article according to item 6, having a density of 0.05 g/cm ³ to 0.7 g/cm ³ .
Item 7.
Item 7. An automobile component comprising the foamed molded article according to item 5 or 6.
Item 8.
A method for producing expanded aromatic polyester resin particles, comprising the steps of: supplying an aromatic polyester resin to an extruder and melt-kneading the resin in the presence of a foaming agent; cutting the melt-kneaded aromatic polyester resin extrudate from a die attached to the front end of the extruder while extruding and foaming the extrudate in cooling water to produce particulate cut products; and cooling the particulate cut products with cooling water, wherein the die has a hole diameter of 0.5 mm to 1.7 mm and the cooling water has a temperature of 55° C. to 90° C.

According to the present invention, it is possible to provide an aromatic polyester resin foam particle capable of producing a foamed molded article having excellent mechanical properties, and a method for producing the same. According to the present invention, it is possible to provide a foamed molded article having excellent mechanical properties, such as compressive strength and compressive modulus, and an automotive component containing the foamed molded article.

FIG. 2 is a schematic diagram of an underwater cutting type granulator used in one embodiment. FIG. 4 is a side cross-sectional view showing the state of a diverter valve.

In this specification, the term "comprising" is intended to encompass the terms "consisting essentially of" and "consisting of."

(Aromatic polyester resin expanded particles)
The expanded aromatic polyester resin particles contain an aromatic polyester resin as a main component. Here, the term "main component" means that the resin constituting the expanded aromatic polyester resin particles contains 80 to 100 mass %, preferably 90 to 100 mass %, of the aromatic polyester resin.

(Aromatic polyester resin)
The aromatic polyester resin is a polyester containing an aromatic dicarboxylic acid component and a diol component, and examples thereof include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexane dimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc., with polyethylene terephthalate being preferred. The aromatic polyester resin may be used alone or in combination of two or more kinds.

In addition to the aromatic dicarboxylic acid component and diol component, the aromatic polyester resin may contain, as a constituent, for example, a tricarboxylic acid such as trimellitic acid, a tetracarboxylic acid such as pyromellitic acid, or a polyvalent carboxylic acid having three or more valences, or anhydrides thereof, a triol such as glycerin, or a polyhydric alcohol having three or more valences, such as a tetraol such as pentaerythritol, etc.

Aromatic polyester resins can be made not only from petroleum-derived products, but also from plant-derived products and recycled products recovered and regenerated from used PET bottles, etc.

The intrinsic viscosity (IV value) of the aromatic polyester resin is preferably 0.7 to 1.1, more preferably 0.75 to 1.05, since it has excellent extrusion foamability and excellent secondary foamability of the resulting foamed beads.

The intrinsic viscosity (IV value) of the aromatic polyester resin is a value measured in accordance with JIS K7367-5 (2000). Specifically, the aromatic polyester resin is dried at a vacuum of 133 Pa at 40°C for 15 hours.

Take 0.1000 g of the aromatic polyester resin as a sample and place it in a 20 mL measuring flask, then add approximately 15 mL of a mixed solvent (phenol 50% by weight, 1,1,2,2-tetrachloroethane 50% by weight) to the measuring flask. Place the sample in the measuring flask on a hot plate and heat to approximately 130°C to melt it. After melting the sample, cool it to room temperature and adjust the volume to 20 mL to prepare a sample solution (sample concentration: 0.500 g/100 mL).

8 mL of the sample solution is supplied to the viscometer using a whole pipette, and the temperature of the sample is stabilized using a water bath filled with water at 25°C, after which the flow time of the sample is measured. The concentration of the sample solution is changed by sequentially adding 8 mL of the mixed solvent to the viscometer, mixing and diluting the solution to prepare a diluted sample solution. The flow time of the diluted sample solution is then measured. The flow time of the mixed solvent is measured separately from the sample solution.

The intrinsic viscosity of the aromatic polyester resin was calculated based on the following formula: The following was calculated from the flow time (t ₀ ) of the mixed solvent and the flow time (t) of the sample solution.
Relative viscosity (η _r ) = t/t ₀
Specific viscosity (η _sp )=(t−t ₀ )/t ₀ =η _r −1
Reduced viscosity = η _sp /C
From the measurement results of diluted sample solutions in which the concentration C (g/100 mL) of the sample solution was variously changed, a graph was created with the reduced viscosity on the vertical axis and the concentration C of the sample solution on the horizontal axis, and the intrinsic viscosity [η] was calculated from the vertical intercept obtained by extrapolating the obtained linear relationship to C = 0.

The aromatic polyester resin constituting the aromatic polyester resin foam particles may be a modified aromatic polyester resin crosslinked by a crosslinking agent. As the crosslinking agent, a known agent may be used, for example, an acid dianhydride such as pyromellitic anhydride, a polyfunctional epoxy compound, an oxazoline compound, an oxazine compound, etc. The crosslinking agent may be used alone or in combination of two or more kinds.

When modifying an aromatic polyester resin by crosslinking with a crosslinking agent, the aromatic polyester resin and the crosslinking agent are supplied to an extruder during the production of aromatic polyester resin foam particles, and the aromatic polyester resin is crosslinked in the extruder with the crosslinking agent. The amount of crosslinking agent supplied to the extruder is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 1 part by mass, per 100 parts by mass of aromatic polyester resin, from the viewpoint of performing extrusion foaming well.

The mass average molecular weight of the aromatic polyester resin constituting the expanded beads of the present invention is preferably 45,000 to 100,000, and more preferably 60,000 to 90,000, in order to provide excellent extrusion foamability and excellent secondary foamability of the resulting expanded beads.
When the aromatic polyester resin constituting the expanded beads is a modified aromatic polyester resin, the mass average molecular weight of the aromatic polyester resin means the mass average molecular weight of the modified aromatic polyester resin.

The mass average molecular weight (Mw) of the aromatic polyester resin constituting the expanded beads of the present invention means the mass average molecular weight in terms of polystyrene (PS) measured using gel permeation chromatography (GPC).
Specifically, the mass average molecular weight is measured as follows. 0.5 mL of hexafluoroisopropanol (HFIP) and 0.5 mL of chloroform are added to 5 mg of sample in this order to dissolve the sample (immersion time: 6.0±1.0 hr (complete dissolution)) to obtain a sample solution. After confirming that the sample is completely dissolved in the solution, chloroform is added to the sample solution to dilute the volume to 10 mL, and the solution is shaken and mixed. The sample solution is filtered through a non-aqueous 0.45 μm syringe filter manufactured by Shimadzu GLC Co., Ltd. to obtain a filtrate. The filtrate is measured using a chromatograph under the following measurement conditions. The mass average molecular weight (Mw) is determined from a standard polystyrene calibration curve prepared in advance.
Equipment used: Tosoh Corporation's "HLC-8320GPC EcoSEC" gel permeation chromatograph (with built-in RI and UV detectors)

(GPC measurement conditions)
Columns Sample side Guard column = TSK guardcolumn HXL-H (6.0 mm x 4.0 cm) x 1, manufactured by Tosoh Corporation Measurement column = TSKgel GMHXL (7.8 mm ID x 30 cm) x 2, manufactured by Tosoh Corporation, in series Reference side Resistance tube (inner diameter 0.1 mm x 2 m) x 2, in series

Column temperature = 40 ° C.
Mobile phase = chloroform Mobile phase flow rate Sample side pump = 1.0 mL/min
Reference pump = 0.5 mL/min
Detector: UV detector Wavelength: 254 nm
Injection volume: 15 μL
Measurement time: 10 min - 32 min
Runtime: 20 min
Sampling pitch: 500 msec

The standard polystyrene samples used for the calibration curve were "STANDARD SM-105" and "STANDARD SH-75" manufactured by Showa Denko K.K. and had mass average molecular weights of 5,620,000, 3,120,000, 1,250,000, 442,000, 151,000, 53,500, 17,000, 7,660, 2,900, and 1,320.
The above-mentioned standard polystyrene for calibration curve is grouped into A (5,620,000, 1,250,000, 151,000, 17,000, 2,900) and B (3,120,000, 442,000, 53,500, 7,660, 1,320), and then A (2 mg, 3 mg, 4 mg, 4 mg, 4 mg) is weighed and dissolved in 30 mL of chloroform, and B (3 mg, 4 mg, 4 mg, 4 mg) is also weighed and dissolved in 30 mL of chloroform. The standard polystyrene calibration curve is obtained by injecting 50 μL of each of the prepared A and B solutions and creating a calibration curve (cubic equation) from the retention time obtained after measurement. The mass average molecular weight is calculated using the calibration curve.

(Method for producing expanded aromatic polyester resin particles)
The expanded beads of the present invention can be produced by a production method that includes, for example, a step of feeding an aromatic polyester resin to an extruder and melt-kneading it in the presence of a foaming agent, a step of cutting the melt-kneaded aromatic polyester resin extrudate from a die attached to the front end of the extruder while extruding and foaming it in cooling water to produce particulate cut pieces, and a step of cooling the particulate cut pieces with cooling water, in which the hole diameter of the die is 0.5 mm to 1.7 mm and the temperature of the cooling water is 55° C. to 90° C. Such a production method is also one aspect of the present invention. Note that, although this production method will be described below, the production method of the expanded aromatic polyester resin beads of the present invention is not limited to the following method.

First, an example of a production apparatus used for producing expanded aromatic polyester resin beads will be described. The production apparatus shown in Fig. 1 is a so-called underwater cutting type granulator T, which is commonly used in the field of expanded bead production.
The granulation device T includes an extruder 2 having a granulation die 1 attached to its tip, and a cutter 3 for cutting the molten aromatic polyester resin 20 (aromatic polyester resin in a molten state containing a foaming agent) discharged from the die hole 15 of the granulation die 1 shown in FIG. 2, and a chamber 4 for bringing a cooling water flow into contact with the resin discharge surface 10f, which is the front surface of the granulation die 1.
A pipe 5 for circulating cooling water is connected to the chamber 4 , and one end of the pipe 5 (upstream of the chamber 4 ) is connected to a water tank 7 via a water pump 6 .
At the other end of the pipe 5 (downstream of the chamber 4), a dehydration treatment section 8 is provided which separates the expandable resin particles from the cooling water and dehydrates and dries them.
The expandable resin particles separated, dehydrated and dried in the dehydration treatment unit 8 are sent to a container 9, and the cooling water is returned to the water tank 7.
Reference numeral 21 denotes a hopper, 22 denotes a blowing agent supply port, and 23 denotes a high-pressure pump.
In the granulating device T and the granulating die 1, the side from which the resin is extruded is referred to as the "front" or "front end", and the opposite side is referred to as the "rear" or "rear end", and these terms are used consistently in the following description.

As shown in FIG. 2, the granulation die 1 is composed of a die body 10 (also called a die plate) and a die holder 11 fixed to the tip side (right side in the figure) of the extruder 2. The die body 10 is fixed to the tip side of the die holder 11 by a number of bolts, and a portion of the tip side of the die holder 11 to which the die body 10 is fixed is movable and functions as a diverter valve 13.

The die holder 11 is connected to the cylinder of the extruder 2, and has a rear end flow passage 11a and a tip end flow passage 11b formed in that order from the rear end to the tip end. The diverter valve 13 has a first flow passage 11c that penetrates from the rear end to the tip end and a second flow passage 11d that passes from the rear end to the side of the die holder 11, and relays the rear end flow passage 11a, the tip end flow passage 11b, and the first flow passage 11c.

The die body 10 has a cone-shaped protrusion 10 protruding rearward at the center of the rear end face.
With the die body 10 and the die holder 11 connected, the conical protrusion 10a is inserted into the tip side flow passage 11b of the die holder 11 with a predetermined gap therebetween.
That is, the molten aromatic polyester resin 20 that passes through the rear end side flow passage 11a of the die holder 11 flows along the circumferential surface of the conical convex portion 10a in the tip end side flow passage 11b, and passes through multiple resin flow passages 14 to communicate with multiple die holes 15 that open into the tip end surface of the die body 10.

The die body 10 is roughly configured to include a resin discharge surface 10f whose tip surface is in contact with the cooling water flow, a plurality of resin flow paths 14 for transporting the molten aromatic polyester resin 20 extruded from the extruder 2 toward the resin discharge surface 10f, a plurality of die holes 15 provided at the tips of the plurality of resin flow paths 14 and opening into the resin discharge surface 10f, a heat insulating material 16 provided at the center position of the resin discharge surface 10f, a cartridge heater 17 for heating the resin discharge surface 10f and the resin flow paths 14 at a position closer to the extruder 2 than the resin discharge surface 10f, and a short heater 18 for heating the die body 10.

The resin discharge surface 10f of the die body 10 has a heat insulating material 16 with a circular cross section arranged in the center, and a plurality of die holes 15 are provided radially outside the heat insulating material 16 with their openings lined up in the circumferential direction.
The central portion of the resin discharge surface 10 f , on which the heat insulating material 16 is arranged and on which the multiple die holes 15 are formed, is adapted to come into contact with cooling water inside the chamber 4 .

The resin flow paths 14 have a circular cross section, extend in a direction perpendicular to the resin discharge surface 10f, and are arranged at regular intervals along a circumference (a circumference drawn on the resin discharge surface 10f) centered on the central axis of the die body 10. In this embodiment, eight resin flow paths 14 are provided, and the central angle between adjacent resin flow paths 14 in the circumferential direction of the circumference is 45°.
As described above, each resin flow path 14 is connected to the tip side flow path 11b of the die holder 11 and is configured to allow the molten polystyrene-based resin 20 to flow to the die hole 15 through the first flow path 11c of the diverter valve 13.

The die holes 15 are arranged at a predetermined interval along a circumference drawn on the resin discharge surface 10f, and the heat insulating material 16 is provided on the resin discharge surface 10f inside the circumference on which the die holes 15 are arranged, and is provided to prevent heat from the die body 10 from escaping to the cooling water in the chamber 4, thereby suppressing a drop in temperature of the die body 10.

The cartridge heater 17 and the short heater 18 each have a rod-like heater shape, and the cartridge heater 17 is located closer to the resin discharge surface 10 f side than the short heater 18 in the direction of the front and rear ends of the granulating die 1 .
The cartridge heaters 17 are arranged on both circumferential sides of the circumference of the resin flow path 14, and are arranged with their longitudinal direction extending radially across the circumference, and have the function of heating the resin discharge surface 10f, the die hole 15, and the resin flow path 14 in the vicinity of the resin discharge surface 10f.
In this embodiment, eight cartridge heaters 17 are provided, each at a predetermined central angle (here, an angle of 45°) in the circumferential direction.
In other words, each die hole 15 is arranged so as to be sandwiched between two cartridge heaters 17 in the circumferential direction of the circumference.

The short heaters 18 are arranged at a predetermined distance from each cartridge heater 17 on the rear side, and the same number (8) of short heaters 18 are arranged as the number of cartridge heaters 17, and have the function of heating the rear end side of the resin flow path 14. The length dimension of the short heaters 18 is shorter than that of the cartridge heaters 17.

The granulating die 1 is also provided with temperature measuring devices 19A and 19B for measuring the temperature of the die body 10 and the temperature of the molten resin.
The first temperature measuring element 19A measures the temperature at the center of the die body 10 (temperature of the die body: die holding temperature).
The second temperature measuring element 19B is for measuring the temperature and resin pressure of the molten aromatic polyester resin 20 flowing inside the die holder 11 .

The extruder 2 used in the granulation apparatus T shown in FIG. 1 is not particularly limited as long as it is a conventionally used extruder. For example, a single screw extruder, a twin screw extruder, or a tandem extruder in which multiple extruders are connected together can be used.
The chamber 4 housing the cutter 3 may be a conventional one used in the hot cutting method.

In the manufacturing method of the present invention, the diameter of the die hole is 0.5 mm to 1.7 mm, and preferably 0.5 mm to 1.6 mm.
In the production method of the present invention, the temperature of the cooling water is 55°C to 90°C, and preferably 60°C to 90°C.
By setting the pore size and water temperature within the above ranges, the pores are less likely to be blocked by the resin, and expanded beads having a particle size of 1.5 mm to 4.5 mm and a surface resin layer thickness of 5 μm to 40 μm can be produced.

As the blowing agent, a conventionally widely used one is used. Examples of the blowing agent include chemical blowing agents such as azodicarbonamide, dinitrosopentamethylenetetramine, hydrazoyldicarbonamide, and sodium bicarbonate; saturated aliphatic hydrocarbon-based blowing agents such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; ether-based blowing agents such as dimethyl ether; fluorocarbon-based blowing agents such as methyl chloride, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, and monochlorodifluoromethane; and inorganic blowing agents such as carbon dioxide and nitrogen. Dimethyl ether, propane, normal butane, isobutane, and carbon dioxide are preferred, propane, normal butane, isobutane, and carbon dioxide are more preferred, and normal butane, isobutane, and carbon dioxide are particularly preferred. The blowing agents may be used alone or in combination of two or more.

The amount of foaming agent supplied to the extruder is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, and particularly preferably 0.5 to 4 parts by mass, per 100 parts by mass of aromatic polyester resin, in order to easily achieve an appropriate expansion ratio for the foamed particles.

It is preferable that a bubble control agent is supplied to the extruder. Examples of such bubble control agents include polytetrafluoroethylene powder, polytetrafluoroethylene powder modified with acrylic resin, and talc.

The amount of the bubble control agent supplied to the extruder is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and particularly preferably 0.1 to 2 parts by mass, per 100 parts by mass of aromatic polyester resin, in order to keep the bubble diameter of the foamed particles within an appropriate range.

The expanded aromatic polyester resin particles obtained by the manufacturing method of the present invention have a sufficiently small particle diameter, which allows a high filling rate when filling a molding die. Furthermore, the manufacturing method of the present invention allows the thickness of the resin layer of the expanded beads to be in a range suitable for expansion, for example, 5 μm to 40 μm, so the expansion power is high. Therefore, the in-mold foamed article obtained from these expanded beads has excellent mechanical properties, such as compressive strength or compressive elastic modulus.

The expanded aromatic polyester resin particles have a bulk density of preferably 0.05 g/cm ³ to 0.7 g/cm ³ , more preferably 0.07 g/cm 3 to 0.6 g/cm ^{3 , and particularly preferably 0.08 g/cm 3 to} 0.5 g/cm ³ , from the viewpoints of improving the expanding power and the fusion power of ^the secondary expanded particles.

The bulk density of the aromatic polyester resin foam particles is measured in accordance with JIS K6911: 1995 "General testing method for thermosetting plastics." More specifically, it is determined by the method described in the examples.

When the aromatic polyester resin foam particles have a high degree of crystallinity, the heat resistance of the foamed molded article is improved, but the fusion strength of the secondary foamed particles does not increase, and as a result, it is difficult to improve the mechanical strength of the foamed molded article. For this reason, it is preferable that the crystallinity (A) at the center of the particle and the crystallinity (B) at the surface layer of the particle are both 10% or less, more preferably 1 to 10%, and particularly preferably 2 to 8%.

The central portion and the surface portion of the expanded beads are determined as follows.
The expanded bead is divided into approximately two equal parts at the center using a razor blade, and the portion of the exposed cross section ranging from the center of the bead to 20% of the expanded bead in the radial direction is defined as the central portion, and the portion of the exposed cross section ranging from the surface of the bead to 20% of the expanded bead in the radial direction is defined as the surface portion.

The crystallinity of the expanded beads is determined by the method described in JIS K7122:1987 and JIS K7122:2012, and more specifically by the method described in the Examples.

The ratio (B/A) of the crystallinity (B) in the surface layer to the crystallinity (A) in the center of the expanded aromatic polyester resin particles is preferably 0.90 to 1.5, more preferably 0.95 to 1.4, and particularly preferably 0.95 to 1.3, from the viewpoint of improving the expansion power or the fusion power of the secondary expanded particles.

From the viewpoint of improving the expansion power or the fusion power of the secondary foamed particles, the thickness of the resin layer on the surface of the aromatic polyester resin foamed particles is preferably 5 μm to 40 μm, and more preferably 10 μm to 35 μm. Here, the thickness of the resin layer on the surface of the foamed particles is determined from an image of the surface layer of a cross section of the foamed particle roughly divided into two at the center, taken at 500 times magnification using a scanning electron microscope, and in detail is determined by the method described in the examples.

From the viewpoint of improving the expansion power or the fusion power of the secondary expanded particles, it is preferable that the average bubble diameter (C) at the particle center and the average bubble diameter (D) at the particle surface layer of the aromatic polyester resin expanded particles are both 50 μm to 300 μm.

It is preferable that the bubble diameter of the surface layer of the expanded aromatic polyester resin particles is slightly smaller than that of the center, because this leads to good expansion and high fusion strength of the secondary expanded particles. For this reason, the ratio (D/C) of the average bubble diameter (D) in the surface layer to the average bubble diameter (C) in the center of the expanded beads is preferably 0.75 to 0.98, more preferably 0.77 to 0.96, and particularly preferably 0.79 to 0.95.

The aromatic polyester resin foam particles of the present invention are filled into the cavity of a mold, heated, and expanded. The secondary foam particles obtained by expanding the aromatic polyester resin foam particles are thermally fused together by their expansion pressure, thereby obtaining an in-mold foamed article having a desired shape and excellent mechanical properties. The heating medium for the aromatic polyester resin foam particles filled in the mold is not particularly limited, and examples thereof include hot air, warm water, and the like, in addition to steam.

The present invention also includes a foamed molded article made from the expanded aromatic polyester resin beads of the present invention. This foamed molded article is obtained by in-mold foaming of the expanded beads of the present invention.

From the viewpoints of light weight and mechanical strength, the density of the aromatic polyester resin foam molded article is preferably 0.05 g/cm ³ to 0.7 g/cm ³ , more preferably 0.07 g/cm ³ to 0.6 g/cm ³ , and particularly preferably 0.08 g/cm ³ to 0.5 g/cm ³ .

Furthermore, immediately before in-mold foaming, the aromatic polyester resin foam particles may be impregnated with an inert gas to improve the foaming power of the aromatic polyester resin foam particles. By improving the foaming power of the aromatic polyester resin foam particles in this way, the thermal fusion between the aromatic polyester resin foam particles during in-mold foaming is improved, and the resulting in-mold foamed article has even better mechanical strength. Examples of the inert gas include carbon dioxide, nitrogen, helium, and argon, with carbon dioxide being preferred.

As a method for impregnating the aromatic polyester resin foam particles with an inert gas, for example, there is a method in which the aromatic polyester resin foam particles are placed in an inert gas atmosphere having a pressure equal to or higher than normal pressure, thereby impregnating the aromatic polyester resin foam particles with an inert gas. In such a case, the aromatic polyester resin foam particles may be impregnated with an inert gas before being filled into a mold, or the aromatic polyester resin foam particles may be impregnated with an inert gas by placing the mold and the aromatic polyester resin foam particles in an inert gas atmosphere after being filled into a mold.

The temperature when impregnating the aromatic polyester resin foam particles with an inert gas is preferably 5°C to 40°C, more preferably 10°C to 30°C.

The pressure when impregnating the aromatic polyester resin foam particles with an inert gas is preferably 0.2 to 2.0 MPa, more preferably 0.25 MPa to 1.5 MPa. When the inert gas is carbon dioxide, the pressure is preferably 0.2 MPa to 1.5 MPa, more preferably 0.25 MPa to 1.2 MPa.

The time for impregnating the aromatic polyester resin foam particles with the inert gas is preferably 10 minutes to 72 hours, more preferably 15 minutes to 64 hours, and particularly preferably 20 minutes to 48 hours.

The aromatic polyester resin foam particles impregnated with an inert gas are expanded (pre-expanded) by heating, for example, to 55°C to 90°C to produce pre-expanded particles.

A composite structural member can be made by using a foamed molded body as a core material and laminating and integrating a skin material onto the surface of the foamed molded body. A composite structural member including a foamed molded body and a skin material laminated and integrated onto the surface of the foamed molded body can also be one aspect of the present invention. The thickness of the foamed molded body used as the core material in the composite structural member is preferably 1 mm to 40 mm in terms of strength, weight, and impact resistance.

The skin material is not particularly limited, and examples include fiber-reinforced synthetic resin sheets, metal sheets, and synthetic resin sheets. Fiber-reinforced synthetic resin is preferred as the skin material because it has excellent mechanical strength and light weight.

A fiber-reinforced synthetic resin sheet is a sheet in which fibers are bonded together with a matrix resin. The fibers constituting the fiber-reinforced synthetic resin sheet are not particularly limited, and examples include carbon fiber, glass fiber, aramid fiber, boron fiber, and metal fiber. As the fibers have excellent mechanical strength and heat resistance, carbon fiber, glass fiber, and aramid fiber are preferred, and carbon fiber is more preferred.

The matrix resins constituting the fiber-reinforced synthetic resin include thermosetting resins and thermoplastic resins. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, and phenolic resins. Thermosetting resins may be used alone or in combination of two or more. Examples of thermoplastic resins include polyamides (nylon 6, nylon 66, etc.), polyolefins (polyethylene, polypropylene, etc.), polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polystyrene, ABS, and copolymers of acrylonitrile and styrene. Thermoplastic resins may be used alone or in combination of two or more.

The thickness of the fiber-reinforced synthetic resin sheet is preferably 0.2 mm to 2.0 mm in terms of strength, weight, and impact resistance.

The method for producing the composite structural member is not particularly limited, and examples of the method include a method in which a skin material is laminated and integrated onto the surface of a foamed molded body that serves as a core material using an adhesive, and a method generally used in molding fiber-reinforced synthetic resin sheets. Examples of the method used in molding fiber-reinforced synthetic resin sheets include the autoclave method, the hand lay-up method, the spray-up method, the PCM (Prepreg Compression Molding) method, the RTM (Resin Transfer Molding) method, and the VaRTM (Vacuum assisted Resin Transfer Molding) method.

Such composite structural members are useful for applications such as automobile components, aircraft components, railroad vehicle components, and building materials. Examples of automobile components include door panels, door inners, bumpers, fenders, fender supports, engine covers, roof panels, trunk lids, floor panels, center tunnels, and crash boxes. For example, when composite structural members are used for door panels that were previously made of steel plates, the door panels have roughly the same rigidity as steel door panels, but the weight can be significantly reduced, resulting in a significant reduction in the weight of the automobile.

Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these.
The methods for determining various physical properties in the examples are described below.

(Bulk density)
The bulk density was measured in accordance with JIS K6911:1995 "General testing method for thermosetting plastics" using an apparent density measuring device in accordance with JIS K6911.
Bulk density of expanded beads (g/cm ³ )=[mass of measuring cylinder containing sample (g)−mass of measuring cylinder (g)]/[volume of measuring cylinder (cm ³ )]

(Particle size)
The average particle size of the resin particles was measured by the following method. First, a plurality of types of sieves having different openings as specified in JIS (opening 6.70 mm, opening 5.60 mm, opening 4.75 mm, opening 4.00 mm, opening 3.35 mm, opening 2.80 mm, opening 2.36 mm, opening 2.00 mm, opening 1.70 mm, opening 1.40 mm, opening 1.18 mm, opening 1.00 mm, opening 0.850 mm, opening 0.710 mm, opening 0.600 mm, opening 0.500 mm) were prepared, and 50 g of the expanded particles were sieved through the sieves from the larger openings to the smaller openings. Then, the expanded particles were unable to pass through the sieves with the predetermined openings according to the particle size of each particle, and remained on each sieve. The average particle size of the expanded particles remaining on each sieve is determined based on the size of the mesh size of the sieve, as shown in the following table. For example, the particle size of the expanded particles remaining on a sieve with a mesh size of 1.70 mm is set to 1.85 mm.

The average particle size of the expanded beads remaining on each sieve was determined as the arithmetic mean value of the mesh size of the sieve and the mesh size of the sieve with the next largest mesh size after the sieve with the mesh size of 1.70 mm. In the case of a sieve with an opening size of 1.70 mm, the arithmetic mean value of the mesh size of the sieve with the next largest mesh size after the sieve with the mesh size of 2.00 mm specified by JIS was used.
Next, the weight W of the expanded beads remaining on the sieve was measured for each sieve, and the weight ratio R (wt%) of the expanded beads remaining on the sieve to the total expanded beads was calculated for each sieve. The particle diameter D of the expanded beads for each sieve was multiplied by the weight ratio R of the expanded beads to calculate the average particle diameter (mm) of the expanded beads.
Average particle size=Σ(particle size D of expanded particles on each sieve × weight ratio R of expanded particles/100)

(Crystallization degree)
The crystallinity was measured by the method described in JIS K7122:1987 and JIS K7122:2012. However, the sampling method and temperature conditions were as follows. Samples were taken from the surface and center of the expanded beads. The surface layer sample was taken from a portion that was approximately bisected at the center of the expanded beads using a razor blade and was located within 20% of the expanded bead surface in the radial direction. Similarly, the center sample was taken from a portion that was approximately 20% of the expanded bead center in the radial direction.
5.5±0.5 mg of sample was packed into an aluminum measuring container so that there were no gaps at the bottom, and then an aluminum lid was placed on it. Differential scanning calorimetry was then carried out using a Hitachi High-Tech Science DSC7000X, AS-3 differential scanning calorimeter. The sample was heated in the following steps under a nitrogen gas flow rate of 20 mL/min to obtain a DSC curve.
(Step 1)
Hold at 30°C for 2 minutes.
(Step 2)
The temperature was raised from 30°C to 290°C at a rate of 10°C/min. Alumina was used as the reference material. The difference between the heat of fusion (J/g) calculated from the area of the melting peak and the heat of crystallization (J/g) calculated from the area of the crystallization peak was calculated. The ratio calculated by dividing this difference by the theoretical heat of fusion of 140.1 J/g of polyethylene terephthalate perfect crystal was taken as the degree of crystallization. The heat of fusion and the heat of crystallization were calculated using the analysis software attached to the device. Specifically, the heat of fusion was calculated from the straight line connecting the point where the DSC curve leaves the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the part surrounded by the DSC curve. The heat of crystallization was calculated from the straight line connecting the point where the DSC curve leaves the low-temperature baseline and the point where the DSC curve returns to the high-temperature side, and the area surrounded by the DSC curve. In other words, the degree of crystallization was calculated from the following formula.
Crystallinity (%) = (heat of fusion (J/g) - heat of crystallization (J/g))/140.1 (J/g) x 100

(Crystallization ratio)
The crystallinity ratio was calculated by the following formula.
Crystallinity ratio = Crystallinity (%) of the surface layer of the expanded bead / Crystallinity (%) of the center of the expanded bead

(Average bubble diameter)
The surface layer and the central portion of a cross section of an expanded bead roughly divided in two at the central portion were photographed at 100 times magnification using a scanning electron microscope "SU1510" manufactured by Hitachi High-Technologies Corp. The surface layer was taken as a portion within 20% of the expanded bead surface in the radial direction, and the central portion was taken as a portion within 20% of the expanded bead surface in the radial direction.
The captured microscopic images were arranged side by side on one A4 sheet of paper in landscape orientation and printed on A4 paper.
For each printed image of the cross section of the expanded beads, three arbitrary straight lines (60 mm long) parallel to the vertical and horizontal directions were drawn. That is, for each of two microscopic images, six arbitrary straight lines were drawn in the vertical direction and six arbitrary straight lines were drawn in the horizontal direction. The lines were drawn so that they did not come into contact with the bubbles only at their contact points as much as possible. The number of bubbles that the straight lines passed through was then counted. If a bubble came into contact with the line only at its contact point, this bubble was also included in the count. The number of bubbles counted for the six arbitrary straight lines in each of the vertical and horizontal directions was calculated as the number of bubbles in each direction. The average chord length t of the bubbles was calculated from the magnification of the image where the number of bubbles was counted and the number of bubbles using the following formula.
Average chord length t (mm) = 60/(number of bubbles x image magnification)

The image magnification was calculated by measuring the scale bar on the image to the nearest 1/100 mm using a "Digimatic Caliper" manufactured by Mitutoyo Corporation and using the following formula:
Image magnification = actual scale bar value (mm) / scale bar display value (mm)

The bubble diameters in the vertical and horizontal directions were calculated using the following formula.
Vertical or horizontal bubble diameter D (mm) = t/0.616

Furthermore, the square root of the product of the cell diameter D in the vertical direction and the cell diameter D in the horizontal direction was defined as the cell diameter.
Bubble diameter (μm) = 1000 x (D length x D width) ^1/2

The above operation was carried out for each of the surface layer and the central portion with an N number of 10, and the average value was taken as the average cell diameter.

(Average bubble diameter ratio)
The average cell diameter ratio was calculated by the following formula.
Average bubble diameter ratio = average bubble diameter (μm) of the surface layer of the expanded particle / average bubble diameter (μm) of the center of the expanded particle

(Thickness of surface resin)
The surface layer of the cross section of the expanded bead, roughly divided in two at the center, was photographed at 500x magnification using a Hitachi High-Technologies Corporation "SU1510" scanning electron microscope. At any position on the expanded bead surface in the microscope image, five straight lines perpendicular to the tangent line were drawn in the radial direction of the expanded bead, and the distance from the surface to the first air bubble that came into contact with each straight line was measured. That is, five such distances were measured for one cross-sectional image. The above procedure was carried out with an N number of 10, and the average value was taken as the thickness (μm) of the surface resin.

(Formability evaluation)
The moldability was evaluated according to the following criteria.
○: The expanded particles were strongly bonded to each other by thermal fusion and were integrated. ×: The expanded particles were not bonded to each other and easily fell off.

(Density of foamed molded body)
The mass (a) and volume (b) of a rectangular parallelepiped test piece (e.g., 75 mm x 300 mm x 30 mm) cut out from a foam molded product (dried at 55°C for 20 hours or more after molding) were measured to have three or more significant digits, and the density (g/ ^cm3 ) of the foam molded product was calculated using the formula (a)/(b).

(Compression test: 5% compression strength and compression modulus)
The 5% compression strength and compression modulus were measured in accordance with JIS K6767:1999. That is, the 5% compression strength was measured using a Shimadzu Corporation "Autograph AG-X plus 100kN" universal testing machine and a Shimadzu Corporation "TRAPEZIUM X" universal testing machine data processing software. The test piece size was 50mm x 50mm x thickness 25mm, and the number of test pieces was 3. The test pieces were conditioned for 16 hours under the standard atmosphere of JIS K 7100:1999 "23/50" (temperature 23°C, relative humidity 50%), class 2, and then used for measurement under the same standard atmosphere. The compression speed was 2.5mm/min. From the obtained graph, the load region with the maximum slope was set, and the compression modulus was obtained using the universal testing machine data processing software. The intersection point of this elastic modulus straight line and the stroke was set as the origin of elongation, and the compressive strength at 5% compression was automatically calculated.

(Evaluation of mechanical properties of molded products)
The mechanical properties of the molded product were evaluated according to the following criteria.
Good: 5% compressive strength is 0.80 MPa or more and compressive modulus is 30 MPa or more.
×: 5% compressive strength is less than 0.80 MPa or compressive modulus is less than 30 MPa.

Example 1
(Expanded Bead Manufacturing Process)
An underwater cutting type granulator was used, which has a diverter valve as shown in Figure 2, a die with 38 die holes (diameter 0.6 mm, land length 2.0 mm), and a diverter valve set so that the molten resin supplied from the extruder to the die through the resin flow path on the outside discharge side of the diverter valve is discharged outside the machine. In addition, a single screw extruder with a hole diameter of 65 mm and an L/D ratio of 34 was used as the extruder that supplies the molten resin to this granulator.

First, the temperature of the die hole of the die was adjusted to 300° C. by using a heater, and the temperature of the extruder was also adjusted. Specifically, the upstream extruder was set at a higher temperature than the downstream extruder to increase the solubility of the foaming agent, and the extruder temperature was set so that the molten resin was finally supplied to the die at a resin temperature of 290° C.
A polyethylene terephthalate composition containing 100 parts by weight of plant-derived polyethylene terephthalate (intrinsic viscosity: 0.80, density: 1,400 kg/ ^m3 , melting point: 247.2°C, glass transition temperature 78.7°C, mass average molecular weight 74,000, plant content: 30%), 1.8 parts by weight of a master batch containing polyethylene terephthalate and talc (polyethylene terephthalate content: 60% by weight, talc content: 40% by weight, intrinsic viscosity of polyethylene terephthalate: 0.82) and 0.22 parts by weight of pyromellitic anhydride was supplied to this extruder at a rate of 30 kg/h and melt-kneaded.

Subsequently, butane consisting of 35% by weight of isobutane and 65% by weight of normal butane was pressurized into the molten polyethylene terephthalate composition midway through the extruder in an amount of 3.0 parts by mass per 100 parts by mass of polyethylene terephthalate as a foaming agent, and uniformly dispersed in the polyethylene terephthalate.
Then, a molten polyethylene terephthalate composition was supplied to the die and discharged to the outside of the machine through the resin flow path of the diverter valve.
When the temperature of the extruder, the pressure of the foaming agent, etc. became stable, a cutter was operated in the chamber attached in front of the die, the flow path of the molten polyethylene terephthalate composition was switched by the diverter valve, and granulation was started by circulating 90°C cooling water with a water pressure of 0.3 MPa in the chamber at 12 ^m3 /h.

The molten polyethylene terephthalate extrudate extruded while foaming in the cooling water was cut with a rotary blade to produce foamed particles. The particulate cut material was foamed in the cooling water to produce polyethylene terephthalate foamed particles. The cooling water containing the foamed particles was transported from the chamber to a dehydration treatment section, where the cooling water was removed from the foamed particles.

(Molding process)
The obtained foamed beads were left at 23° C. under atmospheric pressure for 30 days, then filled into a molding die of 30 mm×300 mm×400 mm, heated with water vapor of 0.05 MPa for 180 seconds and with water vapor of 0.10 MPa for 30 seconds, and then cooled until the maximum surface pressure of the foamed molded product decreased to 0.01 MPa, thereby obtaining a foamed molded product.

Example 2
Polyethylene terephthalate expanded beads and expanded molded products were obtained in the same manner as in Example 1, except that a die having 22 die holes with a diameter of 0.8 mm and a land length of 2.0 mm was used and the cooling water temperature was set to 80°C.

Example 3
Polyethylene terephthalate expanded beads and expanded molded products were obtained in the same manner as in Example 1, except that a die having 10 die holes with a diameter of 1.2 mm and a land length of 2.0 mm was used and the cooling water temperature was set to 70°C.

Example 4
Polyethylene terephthalate expanded beads and expanded molded products were obtained in the same manner as in Example 1, except that a die having seven die holes with a diameter of 1.5 mm and a land length of 2.0 mm was used and the cooling water temperature was set to 70°C.

(Comparative Example 1)
Polyethylene terephthalate expanded beads were obtained in the same manner as in Example 1, except that a die having five die holes with a diameter of 2.0 mm and a land length of 2.0 mm was used and the cooling water temperature was set to 80° C. The obtained expanded beads were molded in the same manner as in Example 1, but the expanded beads were not bonded to each other and easily fell off, and no expanded molded product was obtained.

(Comparative Example 2)
Polyethylene terephthalate expanded beads and expanded molded products were obtained in the same manner as in Example 1, except that a die having seven die holes with a diameter of 1.5 mm and a land length of 2.0 mm was used and the cooling water temperature was set to 50°C.

(Comparative Example 3)
Polyethylene terephthalate expanded beads and expanded molded products were obtained in the same manner as in Example 1, except that a die having seven die holes with a diameter of 1.5 mm and a land length of 2.0 mm was used and the cooling water temperature was set to 95°C.

(Comparative Example 4)
Polyethylene terephthalate expanded beads were produced in the same manner as in Example 1, except that a die having seven die holes with a diameter of 1.5 mm and a land length of 2.0 mm was used and the cooling water temperature was set to 25° C. However, blockage of the die holes occurred and expanded beads could not be obtained.

The physical properties measured for the expanded beads and expanded molded articles obtained in the above examples and comparative examples are shown in Table 2.

By setting the pore size to about 0.5 mm to 1.7 mm and the cooling water temperature to about 55°C to 90°C, expanded beads with particle diameters of about 1.5 mm to 4.5 mm and resin layers on the particle surfaces with thicknesses of about 5 μm to 40 μm were obtained. The expanded molded articles obtained by in-mold expansion molding of these expanded beads had excellent compressive strength and compressive elastic modulus.

Claims (8)

Aromatic polyester resin foam particles with a particle diameter of 1.5 mm to 4.5 mm and a surface resin layer thickness of 5 μm to 40 μm. The expanded aromatic polyester resin particles according to claim 1, wherein the average cell diameter (C) in the center of the particle and the average cell diameter (D) in the surface layer are both 50 μm to 300 μm, and the ratio (D/C) of the average cell diameter in the surface layer to the average cell diameter in the center is 0.75 to 0.98. The expanded aromatic polyester resin particles according to claim 1 or 2, wherein the crystallinity (A) in the center of the particle and the crystallinity (B) in the surface layer are both 10% or less, and the ratio (B/A) of the crystallinity in the surface layer to the crystallinity in the center is 0.90 to 1.5. The expanded aromatic polyester resin particles according to any one of claims 1 to 3, wherein the crystallinity (A) in the center of the particle and the crystallinity (B) in the surface layer are both 1 to 10%. A foamed molded product made from the expanded aromatic polyester resin particles according to any one of claims 1 to 4. The foamed molded article according to claim 5 , having a density of 0.05 g/cm ³ to 0.7 g/cm ³ . An automotive component containing the foamed molded article according to claim 5 or 6. 5. The method for producing expanded aromatic polyester resin particles according to claim 1, comprising the steps of: supplying an aromatic polyester resin to an extruder and melt-kneading the resin in the presence of a foaming agent; cutting the melt-kneaded aromatic polyester resin extrudate from a die attached to the front end of the extruder while extruding and foaming the extrudate in cooling water to produce particulate cut pieces; and cooling the particulate cut pieces with cooling water, wherein the die has a hole diameter of 0.5 mm to 1.7 mm and the cooling water has a temperature of 55° C. to 90° C.

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