JP7365928B2 - Expanded polyamide resin particles and method for producing expanded polyamide resin particles - Google Patents

Description

The present invention relates to expanded polyamide resin particles and a method for producing expanded polyamide resin particles.

Polyamide resins are known as plastics with excellent heat resistance, abrasion resistance, chemical resistance, and the like. In addition, a foamed molded product obtained by foaming this polyamide resin has the above-mentioned properties and is a lightweight molded product, so it is expected to be used in automobile parts, electrical products, and the like.

For example, Patent Document 1 describes an invention of amide-based foamed resin particles (hereinafter also referred to as conventional particles 1) for improving the recovery properties, resilience, and strength of a foamed molded article using amide-based foamed resin particles. ) are disclosed. Specifically, the same document proposes conventional particles 1, which are amide foam resin particles whose surface crystallinity is lower than the internal crystallinity, as amide foam resin particles for obtaining a foam molded product by in-mold molding. has been done.
This document describes that the conventional particles 1 are formed by impregnating pellet-shaped polyamide resin with a blowing agent such as carbon dioxide under pressure, and then foaming the resin under high pressure steam.

Further, Patent Document 2 proposes polyamide particles (hereinafter also referred to as conventional particles 2) containing closed cells having an average cell diameter within a predetermined range, with the aim of providing a polyamide foam with a high expansion ratio. There is. This document describes that as a method for molding polyamide foam, polyamide foam particles suitable for molding a foam molded product with a high expansion ratio are provided by using secondary foaming or high-order foaming. There is. The conventional particles 2 are manufactured by heating pellet-shaped polyamide resin impregnated with carbon dioxide with high-temperature air.

Patent Document 3 also proposes an invention of polyamide pre-expanded particles (hereinafter also referred to as conventional particles 3). According to the same document, conventional particles 3, which are polyamide pre-expanded particles whose density, heat distortion temperature, etc. are specified, are proposed.
In the same document, polyamide resin particles and a blowing agent are dispersed in an aqueous dispersion medium in a closed container, one end of the container is opened while maintaining the temperature and pressure inside the closed container in an appropriate range, and the blowing agent is dispersed in an airtight container. It is described that Conventional Particles 3 were obtained by taking out resin particles containing the following under a low pressure atmosphere.

Japanese Patent Application Publication No. 2016-188342 Japanese Patent Application Publication No. 2011-105879 Publication No. 61-268737

However, it has been difficult to obtain foamed particles with high heat resistance, as conventional foamed polyamide resin particles tend to deform when a compressive load is applied in a high-temperature environment.
In addition, in general resin foam particle technology, in order to increase the expansion ratio, the manufactured foam particles are heated and subjected to multi-stage foaming (two-stage foaming, three-stage foaming, etc.) to further expand the foaming ratio. may be realized. However, when the above-mentioned multi-stage foaming was carried out using expanded polyamide-based resin particles, a phenomenon called blocking, in which the expanded particles were fused to each other and formed into lumps, was likely to occur during the multi-stage foaming. Therefore, it has been difficult to obtain expanded polyamide resin particles with a high expansion ratio.

The present invention has been made in view of the above-mentioned problems, and the present invention has been made to provide foamed polyamide resin particles that have excellent heat resistance and can suppress the blocking phenomenon of the foamed particles when the foamed particles are expanded in multiple stages. The present invention also relates to a method for producing expanded polyamide resin particles that can produce the above-mentioned expanded polyamide resin particles.

The expanded polyamide resin particles of the present invention are expanded particles made of a polyamide resin, and the polyamide resin constituting the expanded particles has a flexural modulus of 1000 MPa or more, and the following resin absorbance ratio R is as follows: Foamed polyamide resin particles characterized in that the ratio I/R, which is the ratio of surface absorbance ratio I, is 1.0 or more.
Resin absorbance ratio R: Maximum absorbance Dr _B at wave numbers 1320 to 1400 cm ^-1 and wave numbers 3250 to 3350 cm ^- in the infrared absorption spectrum of the polyamide resin constituting the expanded particles, measured by total reflection absorption infrared spectroscopy. It is the absorbance ratio Dr _A /Dr _B with the maximum absorbance Dr _A at ¹ .
Surface absorbance ratio I: Maximum absorbance Ds _B at wave numbers 1,320 to 1,400 cm ^-1 and maximum absorbance at wave numbers 3,250 to 3,350 cm ^-1 in the infrared absorption spectrum of the surface of the foamed particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with Ds _A is Ds _A /Ds _B.

The method for producing foamed polyamide resin particles of the present invention is a method for producing foamed polyamide resin particles of the present invention, in which the polyamide resin particles are heat-treated to form crystals in the surface layer of the polyamide resin particles. The present invention is characterized by comprising a crystallization promotion step of promoting crystallization, and a foaming step of foaming the polyamide resin particles that have undergone the crystallization promotion step to obtain expanded polyamide resin particles.

Further, the method for producing expanded polyamide resin particles of the present invention is a method for producing expanded polyamide resin particles of the present invention, which includes a foaming step of foaming polyamide resin particles to obtain expanded polyamide resin particles; The method is characterized by including a crystallization promoting step of promoting crystallization of the surface layer portion of the expanded polyamide resin particles by heat-treating the expanded polyamide resin particles.

The foamed polyamide resin particles of the present invention have a surface absorbance ratio I of 1.0 or more with respect to a resin absorbance ratio R constituting the foamed particles, and the crystallinity of the surface of the foamed particles is high. By having such a configuration, the polyamide system has excellent heat resistance and suppresses the blocking phenomenon of the foamed particles even when the foamed particles are foamed in multiple stages to increase the expansion ratio of the foamed particles. Resin foam particles are provided.

Further, according to the method for producing expanded polyamide resin particles of the present invention, the above-mentioned expanded polyamide resin particles of the present invention can be sufficiently produced using a general manufacturing apparatus.

It is a graph for explaining the second manufacturing method in the manufacturing method of the present invention. It is a graph for explaining a modification of the second manufacturing method in the manufacturing method of the present invention. 7 is a graph for explaining a temperature increase pattern in Example 2. It is a DSC curve measured based on the heat flux differential scanning calorimetry method of the polyamide resin foam particle of a present Example.

Below, the polyamide resin foam particles of the present invention and the method for producing the polyamide resin foam particles will be explained in order. For technical details such as terms, measurement methods, and materials used that are duplicated in the following description, the respective descriptions can be referred to as appropriate.
In the following description, preferred numerical ranges of the present invention may be indicated as appropriate. In this case, preferred ranges, more preferred ranges, particularly preferred ranges regarding the upper and lower limits of the numerical range can be determined from all combinations of the upper and lower limits.

[1] Polyamide Resin Foamed Particles The polyamide resin foamed particles of the present invention have a ratio I/R, which is the ratio of the surface absorbance ratio I to the resin absorbance ratio R, of 1.0 or more.
Here, the resin absorbance ratio R is the maximum absorbance Dr B at a wave number of 1320 to 1400 cm ^-1 and the maximum absorbance Dr _B at a wave number of 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the polyamide resin, measured by total reflection absorption infrared spectroscopy. It is the absorbance ratio Dr _A /Dr _B with the maximum absorbance Dr _A at .
In addition, the surface absorbance ratio I is the maximum absorbance Ds B at wave numbers 1320 to 1400 cm- ¹ and the maximum absorbance Ds _B at wave numbers 3250 to 3350 cm- ¹ in the infrared absorption spectrum of the surface of the foamed particles, measured by total reflection absorption infrared spectroscopy. is the absorbance ratio Ds _A /Ds _B with the maximum absorbance Ds _A of .
The inherent flexural modulus of the polyamide resin constituting the expanded particles according to the present invention is 1000 MPa or more.

The expanded polyamide resin particles of the present invention have the above-mentioned ratio I/R of 1.0 or more. This means that crystallization of the surface layer portion of the expanded polyamide resin particles progresses sufficiently, and the heat resistance is excellent. As described above, the expanded polyamide resin particles of the present invention have a ratio I/R of 1.0 or more, and a flexural modulus of the polyamide resin constituting the expanded particles is a specific value or more. Therefore, the expanded polyamide resin particles of the present invention can exhibit excellent heat resistance, such as being difficult to deform when a compressive load is applied, for example, in a high-temperature environment. Further, in the expanded polyamide resin particles of the present invention, since crystallization of the surface layer portion of the expanded particles has sufficiently progressed, blocking phenomena are unlikely to occur during multi-stage foaming. Therefore, the expanded polyamide resin particles of the present invention can achieve a high expansion ratio, and the fusion properties of the expanded particles are not impaired even during in-mold molding.
Therefore, according to the present invention, it is possible to provide excellent polyamide resin foam particles and a foam particle molded article (hereinafter also simply referred to as an expanded particle molded article) formed by molding the polyamide resin foam particles in a mold. .
The structure of the expanded polyamide resin particles of the present invention will be explained in more detail below.

[Polyamide resin]
Examples of the polyamide resin in this specification include polyamide and polyamide copolymers, with polyamide copolymers being preferred.
Examples of the polyamide include poly(6-aminohexanoic acid) also known as poly(caprolactam) (polycaproamide, nylon 6), poly(laurolactam) (nylon 12), poly(hexamethyleneadipamide) (nylon 66), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid) (nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(11-aminoundecanoic acid) (nylon 11), poly(hexamethylene sebaamide) (nylon 610), poly(decamethylene sebaamide) (nylon 1010), poly(hexamethylene azeramide) ) (nylon 69), poly(tetramethylene adipamide) (nylon 46), poly(tetramethylene sebacamide) (nylon 410), poly(pentamethylene adipamide) (nylon 56), and poly(pentamethylene Examples include homopolymers such as sebacamide (nylon 510).
The above-mentioned polyamide copolymer means one having two or more types of monomer components (constituent units) and having an amide bond in at least a part of each of the constituent units.
Examples of the polyamide copolymer include polycaproamide/polyhexamethylene adipamide copolymer (nylon 6/66), caprolactam/hexamethylene diamino adipic acid/lauryllactam (nylon 6/66/12), and caprolactam/polyhexamethylene adipamide copolymer (nylon 6/66/12). Examples include lauryl lactam copolymer (nylon 6/12).
As the polyamide resin, one type of these polyamides and polyamide copolymers may be used alone, or two or more types may be used in combination. Among the above polyamide resins, polyamide resins that are a combination of one or more selected from nylon 6, nylon 66, and nylon 6/66 are preferable, and nylon 6/66 is more preferable. preferable.

The polyamide copolymer may be a block copolymer in which a certain amount of an amide of the same repeating unit is followed by a certain amount of a different type of amide, or a random copolymer in which different types of amides are repeated randomly. It may be a combination. In particular, the polyamide copolymer is preferably a random copolymer. If the polyamide copolymer is a random copolymer, it becomes possible to mold the expanded polyamide resin particles in a mold at a relatively low molding pressure.

The polyamide-based resin foam particles may be composed of one type of polyamide-based resin alone, or may be composed of a combination of two or more types of polyamide-based resins.
Further, the expanded polyamide resin particles may contain other components other than the polyamide resin, such as thermoplastic resins and elastomers, as long as the objects and effects of the present invention are not impaired. Other resins include thermoplastic resins, such as polyethylene resins, polypropylene resins, polystyrene resins, vinyl acetate resins, thermoplastic polyester resins, acrylic ester resins, and methacrylic ester resins. . The content of other components in the expanded polyamide resin particles is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

In addition to polyamide resin, foamed polyamide resin particles contain commonly used cell regulators, antistatic agents, conductivity imparting agents, lubricants, antioxidants, ultraviolet absorbers, flame retardants, and metal deactivators. , colorants (pigments, dyes, etc.), crystal nucleating agents, fillers, and other various additives may be appropriately blended as needed. Examples of foam regulators include inorganic foam regulators such as talc, sodium chloride, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, aluminum hydroxide, alum, and carbon, phosphoric acid compounds, and amine compounds. , and organic cell regulators such as polytetrafluoroethylene (PTFE). The amount of these various additives added varies depending on the purpose of use of the expanded particle molded product, but it is preferably approximately 0.1 to 30 parts by weight based on 100 parts by weight of the resin component constituting the expanded polyamide resin particles. . More preferably 0.5 to 20 parts by weight, still more preferably 1 to 15 parts by weight.

Regarding the present invention, the melting point of the polyamide resin constituting the polyamide resin particles and expanded polyamide resin particles is preferably 180° C. or higher, for example, from the viewpoint of providing a foamed particle molded product with excellent heat resistance. , more preferably 185°C or higher, more preferably 188°C or higher, even more preferably 190°C or higher. On the other hand, from the viewpoint of easy temperature control in the foaming process, the melting point is preferably 280°C or lower, more preferably 260°C or lower, even more preferably 240°C or lower, and 230°C or lower. It is more preferable that the temperature is below ℃.
In addition, the melting point of the polyamide-based resin foam particles mentioned above refers to the melting point of the polyamide-based resin when the resin constituting the foamed particles is one type of polyamide-based resin alone. When the foamed polyamide resin particles are composed of a mixture of two or more types of polyamide resins, or when they are composed of a mixture of a polyamide resin and another resin, the foamed polyamide resin particles described above are used. The melting point of refers to the melting point of a kneaded product that has been kneaded in advance using an extruder or the like.

The melting points of the polyamide resin constituting the expanded polyamide resin particles and the polyamide resin constituting the polyamide resin particles are measured based on JIS K 7121-1987. More specifically, it is measured by a method similar to the method described in Examples described later.

The method for producing the polyamide resin particles of the present invention is not particularly limited, and can be produced by any known method. For example, polyamide resin particles can be produced by a method selected from a strand cut method, a hot cut method, an underwater cut method (UWC method), and the like. In the above strand cutting method, a polyamide resin and additives such as a cell regulator and a coloring agent are put into an extruder and kneaded to form a melt-kneaded product. This is a method to obtain granules by extruding the melt-kneaded material in the form of strands through small holes and cutting the extruded strand-like melt-kneaded material with a pelletizer to a predetermined mass. The hot cut method is a method in which a molten kneaded material is extruded into a gas phase, and the extruded molten kneaded material is cut in the gas phase to obtain granules. The underwater cutting method (UWC method) is a method in which a melt-kneaded product is extruded into water, and the extruded melt-kneaded product is cut in water to obtain granules.

In addition, since the resin particles produced by the above method are cooled when cutting and granulating the molten mixture, the surface layer portion of the resin particles after granulation is particularly susceptible to rapid cooling. As a result, crystallization of the surface layer portion of the resin particles is difficult to proceed sufficiently, resulting in a low absorbance. Such resin particles tend to cause blocking between resin particles during foaming, and foamed particles obtained using such resin particles tend to cause blocking between foamed particles during two-stage foaming. On the other hand, the present invention provides that even when polyamide resin particles manufactured by the method described above are used, blocking between resin particles is unlikely to occur, and
It is possible to satisfactorily prevent the occurrence of blocking between the foamed particles while maintaining the fusion properties of the resulting foamed particles.

Next, the crystallinity of the expanded polyamide resin particles of the present invention will be explained.
According to the studies conducted by the present inventors, polyamide resin particles are less likely to undergo crystallization on the surface of the resin particles when heated, compared to resin particles made of other crystalline resins such as polypropylene resins. Understood. Therefore, for example, when attempting to produce foamed polyamide resin particles by the direct foaming method, the temperature inside the closed container is raised to the foaming temperature at a relatively fast rate without sufficient crystallization of the surface layer. When the temperature is increased, blocking between resin particles tends to occur in the closed container, and the resin particles cannot be appropriately released together with the dispersion medium, so that expanded particles cannot be stably obtained. In the description of the present invention, the surface layer portion of a resin particle or foamed particle includes the surface of the resin particle or foamed particle and the vicinity of the surface.
Further, in order to prevent the above-mentioned blocking, it is possible to add an antiblocking agent during the manufacturing process of the expanded polyamide resin particles. However, if the amount of anti-blocking agent added to the sealed container is increased to the extent that blocking between resin particles can be suppressed, blocking between resin particles can be suppressed. When multistage foaming was performed on the foamed beads obtained in the above steps, a blocking phenomenon occurred in the foamed beads, making it impossible to obtain good foamed beads. In addition, in this case, the state of fusion between the expanded particles during in-mold molding tended to deteriorate.
Furthermore, by further increasing the amount of antiblocking agent added into the container, it is possible to prevent not only blocking within the closed container but also blocking during multistage foaming. However, in this case, the state of fusion between the expanded particles during in-mold molding is significantly reduced.
Heretofore, although there are techniques for suppressing crystallization on the surface of particles, such as in Patent Document 1, none have paid attention to increasing the crystallinity of polyamide resin particles or expanded polyamide resin particles.
To solve this problem, the expanded polyamide resin particles of the present invention are configured such that the ratio I/R, which is the ratio of the surface absorbance ratio I to the resin absorbance ratio R, is 1.0 or more.

Although the method for adjusting the ratio I/R is not particularly limited, for example, it is preferable to carry out the crystallization promotion step described below before or after the foaming step of foaming the polyamide resin particles. A preferred example of the method for producing expanded polyamide resin particles of the present invention in which the ratio I/R is 1.0 or more will be described later.

The resin absorbance ratio R is the absorbance ratio Dr _A /Dr _B between the maximum absorbance Dr _B and the maximum absorbance Dr _A , which is measured by total reflection absorption infrared spectroscopy.
Further, the surface absorbance ratio I is the absorbance ratio Ds _A /Ds _B between the maximum absorbance Ds _B and the maximum absorbance Ds _A , which is measured by total reflection absorption infrared spectroscopy.
Here, the maximum absorbance Dr _B is the maximum value of absorbance observed in the infrared absorption spectrum of the polyamide resin constituting the expanded particles in a wave number range of 1320 cm ^-1 to 1400 cm ^-1 . The maximum absorbance Dr _A is the maximum value of absorbance observed in the infrared absorption spectrum of the polyamide resin constituting the expanded particles in the range of wave numbers from 3250 cm ^-1 to 3350 cm ^-1 .
The maximum absorbance Ds _B is the maximum value of absorbance observed in the infrared absorption spectrum of the surface of the foamed particles in the range of wave numbers from 1320 cm ^-1 to 1400 cm ^-1 . Further, the maximum absorbance Ds _A is the maximum value of absorbance observed in the infrared absorption spectrum of the surface of the expanded particles in the range of wave numbers from 3250 cm ^-1 to 3350 cm ^-1 .
Absorbance and the like related to the present invention can be measured by the method described in Examples described later.

In the infrared absorption spectrum measured by total internal reflection absorption infrared spectroscopy, a peak that appears near 3280 cm ^-1 that is observed in the wave number range of 3250 cm ^-1 to 3350 cm ^-1 such as maximum absorbance Dr _A and maximum absorbance Ds _A The maximum value of the absorbance is a peak that changes depending on the crystal state of the polyamide resin, and is a peak derived from the stretching movement of NH in the amide bond.
Note that as the degree of crystallinity increases, the ratio of stretching motion of N--H derived from hydrogen bonds between amide groups increases, and the values of maximum absorbance Dr _A , maximum absorbance Ds _A , etc. become higher. Therefore, the values of the maximum absorbance Dr _A and the maximum absorbance Ds _A are suitable as indicators of the crystalline state of the polyamide resin.
On the other hand, ^the maximum value of the absorbance of the peak that appears around 1370 cm -1, which is observed in the wave number range of 1320 cm ^-1 to 1400 cm ^-1 such as maximum absorbance Dr _B and maximum absorbance Ds _B , depends on the crystalline state of the polyamide resin. It is a peak that does not change.
By specifying the ratio of these maximum absorbances, it becomes possible to appropriately evaluate the degree of crystallization of the expanded particles.

The resin absorbance ratio R (absorbance ratio Dr _A /Dr _B ) is determined by melting the polyamide resin constituting the foamed particles and removing the thermal history of the resin, under an atmosphere substantially free of water such as a vacuum condition. This is a value measured on a film made of a polyamide resin that has been heat-treated to sufficiently promote crystallization of the resin. Therefore, this value is an index of the absorbance ratio normally exhibited by the polyamide resin constituting the expanded particles. More specifically, it can be measured by the method described in Examples below.
On the other hand, the larger the value of the surface absorbance ratio I (absorbance ratio Ds _A /Ds _B ), the more advanced the crystallization of the polyamide resin on the surface of the expanded polyamide resin particles is.
Therefore, polyamide resin foam particles whose ratio I/R, which is the ratio of the surface absorbance ratio I to the resin absorbance ratio R, is 1.0 or more indicate that crystallization of the polyamide resin in the surface layer has sufficiently progressed. means.
Therefore, in the foamed polyamide resin particles of the present invention, the foamed particles are difficult to fuse to each other during two-stage foaming, and the blocking phenomenon is difficult to occur.
The heat treatment of the film is preferably carried out at a temperature of -70°C or higher, the melting point of the polyamide resin, and -40°C or lower, the melting point of the polyamide resin.

In the present invention, an antiblocking agent may be used as an auxiliary agent, but it is sufficient to use a small amount that does not impair the fusion properties of foamed particles during in-mold molding. Therefore, even when an antiblocking agent is used in the present invention, it is not necessary to remove the antiblocking agent attached to the expanded particles in order to maintain the above-mentioned fusion properties.
In addition, the foamed particles of the present invention have a high expansion ratio and are resistant to deformation even when a compressive load is applied in a high-temperature environment, resulting in foamed particles with sufficiently enhanced heat resistance. Therefore, for example, by heating a mixture of expanded particles and a thermosetting resin in a mold and curing the thermosetting resin, a composite molded body whose main structural material is a cured thermosetting resin can be produced. When forming, the foamed particles are not easily deformed, and a composite molded article having a desired structure can be formed. Therefore, the expanded particles of the present invention can be suitably used in applications that are used in high-temperature environments, such as composite molded products and applications that are exposed to high-temperature conditions such as sterilization.
From this viewpoint, the ratio I/R is more preferably 1.1 or more. In addition, the above ratio I/R is preferably approximately 1.4 or less, more preferably 1.3 or less, from the viewpoint of further increasing the fusion state of foamed particles during in-mold molding, and 1.3 or less. More preferably, it is .2 or less.

Further, in the present invention, the ratio II/R, which is the ratio of the cross-sectional absorbance ratio II below to the resin absorbance ratio R, is preferably 1.0 or more.
The above cross-sectional absorbance ratio II is the maximum absorbance Dc B at wave numbers 1320 to 1400 cm ^-1 and the maximum absorbance Dc _B at wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the central cross section of the expanded particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with the maximum absorbance Dc _A is Dc _A /Dc _B.
A large value of the cross-sectional absorbance ratio II (absorbance ratio Dc _A /Dc _B ) means that crystallization of the polyamide resin inside the expanded polyamide resin particles is progressing. Therefore, when the ratio II/R satisfies the above range, the foamed particles will have sufficiently advanced crystallization in the center of the foamed particles. Thereby, even when in-mold molding is performed under high-temperature conditions, thermal shrinkage of the expanded particle molded product can be easily suppressed, and expanded beads with better in-mold moldability can be obtained.
From the above viewpoint, the ratio II/R is more preferably 1.1 or more. Further, the ratio II/R is preferably approximately 1.4 or less, more preferably 1.3 or less, and even more preferably 1.2 or less.
From the viewpoint of being able to stably increase the cross-sectional absorbance ratio II, as will be described later, the foaming step involves dispersing the polyamide resin particles in an aqueous medium in a closed container, and dispersing the polyamide resin particles at a temperature of 80% higher than the melting point of the polyamide resin particles. It is preferable to discharge the contents of the sealed container into a pressure range lower than the internal pressure of the sealed container within a temperature range from 50° C. lower than the melting point.

Further, in the present invention, it is preferable that the ratio I/II, which is the ratio of the surface absorbance ratio I to the cross-sectional absorbance ratio II, is 0.90 or more.
The polyamide resin foam particles satisfying the above ratio I/II mean that the crystallization of the polyamide resin in the surface layer portion has progressed to approximately the same extent as the crystallization inside the foam particles. Therefore, in addition to being excellent for in-mold molding, the heat resistance of the foamed particles is further improved, and blocking phenomenon is stably suppressed when the foamed particles are subjected to multi-stage foaming through a multi-stage foaming process such as two-stage foaming. can do.
From the viewpoint of more fully suppressing the blocking phenomenon during two-stage foaming of the amide resin expanded particles, the ratio I/II is preferably 0.92 or more, and preferably 0.93 or more. More preferably, it is 0.95 or more.
Further, the ratio I/II is preferably approximately 1.2 or less, preferably 1.1 or less, and more preferably 1.0 or less.

(flexural modulus)
The flexural modulus of the polyamide resin constituting the expanded polyamide resin particles of the present invention is 1000 MPa or more. By setting the flexural modulus of the polyamide resin within the above range, even if the foamed particles have a high expansion ratio, they will not easily shrink after foaming and will have excellent heat resistance. In addition, by increasing the secondary foaming power of the expanded particles during in-mold molding and improving the in-mold moldability of the expanded particles, even if the crystallinity of the surface layer of the expanded particles is increased, a good fusion state can be achieved. A foamed particle molded article can be obtained.
From the viewpoint of increasing the mechanical strength of the obtained expanded particles and expanded particle molded articles, the flexural modulus is preferably 1100 MPa or more, and more preferably 1200 MPa or more.
Further, from the viewpoint of stably obtaining expanded particles with a high expansion ratio, the bending elastic modulus of the polyamide resin is preferably approximately 3000 MPa or less, more preferably 2500 MPa or less, and preferably 2000 MPa or less. More preferred.
Note that the flexural modulus of the amide elastomer as described in Patent Document 1 is approximately 600 MPa or less.

The flexural modulus of the polyamide resin constituting the expanded polyamide resin particles can be determined by preparing a resin test piece of the polyamide resin and measuring the flexural modulus of the resin test piece based on JIS K7171:2016. It is determined by
More specifically, it is measured by a method similar to the method described in Examples described later.

(Density of polyamide resin)
The density of the polyamide resin is preferably 1.05 g/cm ³ or more, more preferably 1.1 g/cm ³ or more. Note that the density of the amide elastomer is approximately less than 1.05 g/cm ³ . Density can be determined based on the method described in ISO 1183-3.

(high temperature peak)
The foamed polyamide resin particles of the present invention were measured by heat flux differential scanning calorimetry in accordance with JIS K7122-1987, and the foamed polyamide resin particles were heated at a heating rate of 10°C/min from 30°C to the end of the melting peak. The first DSC curve measured when melting by heating to a temperature higher than 30 degrees Celsius shows a melting peak (specific peak) specific to the polyamide resin, and a peak temperature that appears on the higher temperature side than the peak temperature of the specific peak. It is preferable that a peak (high temperature peak) appears. The total heat of fusion of all high-temperature peaks whose peak temperatures appear on the higher temperature side than the peak temperature of the characteristic peak is preferably 5 J/g or more, more preferably 6 J/g or more, and 8 J/g or more. It is more preferable that Further, the total heat of fusion is preferably 50 J/g or less, more preferably 30 J/g or less, and even more preferably 20 J/g or less. In addition, when two or more of the above-mentioned high-temperature peaks appear, the heat of fusion of the high-temperature peaks means the total heat of all the high-temperature peaks.
When the heat of fusion at the high temperature peak is within the above range, the heat resistance of the expanded beads can be improved, and the in-mold moldability of the expanded beads can be further improved.
Further, the total heat of fusion (total heat of fusion of the unique peak heat of fusion and the high temperature peak) in the first DSC curve is preferably 40 g/J or more, more preferably 45 g/J or more. preferable. Further, the total heat of fusion is preferably approximately 70 J/g or less, more preferably 60 g/J or less.
By setting it as the above range, it is possible to obtain expanded particles that have better heat resistance and are also better in molding in a mold.
Note that the melting peak (unique peak) specific to polyamide resin is determined by maintaining the temperature for 10 minutes at a temperature 30°C higher than the end of the melting peak after the first DSC curve measurement, and then cooling at a cooling rate of 10°C/ Melting that appears in the DSC curve (second DSC curve) measured when cooling to 30°C at a heating rate of 10°C/min and melting by heating to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C/min. This is a melting peak derived from the crystal structure indicated by the peak. The apex temperature of the characteristic peak roughly matches the apex temperature of the melting peak appearing in the second DSC curve.
A specific method for measuring the heat of fusion at the high temperature peak and the total heat of fusion in the first DSC curve will be described in Examples.

(Crystallinity)
The degree of crystallinity of the entire expanded polyamide resin particles is preferably 20 to 50%. By setting it as the above range, foamed particles with better heat resistance can be obtained. Furthermore, such expanded particles have excellent in-mold moldability, and even when in-mold molding is performed under high temperature conditions, thermal shrinkage of a foamed particle molded article formed using the expanded particles can be suppressed. Furthermore, by using such expanded particles, it is possible to stably obtain a foamed particle molded article having excellent heat resistance.
From the above viewpoint, the degree of crystallinity of the entire expanded polyamide resin particles is preferably 25 to 45%, more preferably 30 to 40%.
From the viewpoint of being able to stably increase the degree of crystallinity of the entire foamed polyamide resin particles, as described below, the foaming step involves dispersing the polyamide resin particles in an aqueous medium in a closed container. It is carried out by releasing the contents of the sealed container into a pressure range lower than the internal pressure of the sealed container at a temperature ranging from 80°C lower than the melting point of the particles to a temperature 50°C lower than the melting point. is preferred.
The degree of crystallinity of the entire foamed polyamide resin particles can be determined by performing XRD measurement on the foamed polyamide resin particles using an X-ray diffraction device, and from the obtained X-ray diffraction profile, the area of the diffraction peak derived from crystals and the amorphous It can be determined by calculating the ratio of the area of the diffraction peak derived from the crystal to the total area of the diffraction peak derived from the crystal.
A more specific measuring method will be explained in the Examples described later.

(Crystallinity x ratio I/II)
In the present invention, the value obtained by multiplying the degree of crystallinity of the foamed polyamide resin particles by the ratio I/II, which is the ratio of the surface absorbance ratio I to the cross-sectional absorbance ratio II of the foamed polyamide resin particles, is 29% or more. is preferable, and more preferably 30% or more. It is considered that the above value pseudo-indicates the degree of crystallinity of the surface layer portion of the expanded polyamide resin particles. When the above value falls within the above range, the heat resistance of the foamed particles is increased, and blocking during two-stage foaming and the like can be stably suppressed.
From the viewpoint of enhancing in-mold molding of expanded particles, the above value is preferably approximately 50% or less, more preferably 45% or less, and even more preferably 40% or less.

The apparent density of the expanded amide resin particles of the present invention is not particularly limited. For example, from the viewpoint of being able to mold a foamed particle molded product that is sufficiently foamed and exhibits high strength, the apparent density of the foamed particles is preferably 10 kg/m ³ or more, and should be 30 kg/m ³ or more. is more preferable, and even more preferably 50 kg/m ³ or more. On the other hand, from the viewpoint of providing foamed amide resin particles with sufficient expansion and a high expansion ratio, the above apparent density is preferably 300 kg/m ³ or less, more preferably 200 kg/m ³ or less. It is preferably 150 kg/m ³ or less, more preferably 120 kg/m 3 or less, and particularly preferably 120 kg/m ³ or less.
In addition, when the apparent density is 10 kg/m ³ or more and 300 kg/m ³ or less, the foamed amide resin particles and the foamed particle molded product made of the foamed particles are difficult to shrink, which is preferable.
In addition, it is possible to provide multistage foamed particles that can be subjected to multistage foaming, have a high expansion ratio, and have good mechanical properties, and can also be used to form a foamed particle molded product by in-mold molding using the multistage foamed particles. From the viewpoint of being able to obtain stably, the apparent density of the foamed particles for multistage foaming is preferably 50 to 300 kg/m ³ , more preferably 55 to 200 kg/m ³ , and 60 to 150 kg /m ³ is more preferable, and 60 to 120 kg/m ³ is particularly preferable.
In addition, in this specification, the foamed particles used for multistage foaming (foamed particles for multistage foaming) refer to the foamed particles that are supplied to a closed container or the like and pressurized with a gas such as air, so that the pressure inside the foamed particles ( These are foamed particles that are used to increase the internal pressure (internal pressure) and impart expandability to the foamed particles, and then heat the foamed particles with a heating medium such as water vapor to expand them to produce foamed particles with a lower density. In multi-stage foaming, the first multi-stage foaming is usually called two-stage foaming, the second multi-stage foaming is called three-stage foaming, and the third multi-stage foaming is called four-stage foaming. It is. Further, the number of times of multistage foaming is usually 1 to 3 times.
The apparent density of the expanded polyamide resin particles is measured by the method described in the Examples below.

The foamed polyamide resin particles of the present invention may be single-layer foamed particles, or may have a core layer in a foamed state formed by foaming polyamide resin particles, and a sheath-core layer that covers the core layer. It may be a structure.

[2] Method for producing expanded polyamide resin particles Next, a method for producing expanded polyamide resin particles will be described. The manufacturing method described below shows a preferred example of the method for manufacturing the expanded polyamide resin particles of the present invention described above, but does not limit the method for manufacturing the expanded polyamide resin particles of the present invention. The manufacturing method described below is appropriately referred to as the manufacturing method of the present invention.

[First embodiment]
A first embodiment of the manufacturing method of the present invention will be described. The first embodiment includes a crystallization promotion step and a foaming step performed after the crystallization promotion step.
In the first embodiment, the crystallization promotion step is a step of promoting crystallization of the surface of the polyamide resin particles by heat-treating the polyamide resin particles. The foaming step is a step of foaming the polyamide resin particles that have undergone the crystallization promotion step at a foaming temperature to obtain expanded polyamide resin particles. In the first embodiment, a blowing agent impregnation step of impregnating the polyamide resin particles with a blowing agent is performed before the foaming step.
By including the crystallization promotion step, the manufacturing method of the present invention can sufficiently promote crystallization of the surface of the polyamide resin particles. Thereby, it is possible to provide expanded polyamide resin particles in which the occurrence of blocking phenomenon is suppressed.

Crystallization promotion process:
The heat treatment in the crystallization promotion step is not particularly limited as long as it can promote crystallization of the surface of the polyamide resin particles. The heating temperature in the heat treatment is preferably lower than the melting point temperature of the polyamide resin particles. Further, when producing expanded particles by a direct foaming method, the heating temperature is more preferably lower than the foaming temperature in the foaming step.
By sufficiently promoting crystallization of the surface of the polyamide resin particles before the foaming process, a polyamide resin having a ratio I/R, which is the ratio of the surface absorbance ratio I to the resin absorbance ratio R mentioned above, is 1.0 or more. It is possible to produce resin foam particles.

From the viewpoint of suppressing blocking between resin particles when foaming resin particles and stably obtaining foamed particles satisfying the ratio I/R, in the crystallization promotion step, the following surface absorbance with respect to the following resin absorbance ratio r is used. The ratio i/r, which is the ratio of ratio i, can be adjusted so that the ratio i/r of the polyamide resin particles after heat treatment is larger than the ratio i/r of the polyamide resin particles before heat treatment. preferable. Here, the ratio i/r of the polyamide resin particles after the heat treatment is preferably 0.97 or more, more preferably 0.98 or more.
More specifically, from the above-mentioned viewpoint, by heat-treating polyamide-based resin particles having a ratio i/r of less than 0.97, the ratio i/r of the polyamide-based resin particles after heat treatment is increased to 0.97 or more. It is preferable to heat-treat polyamide-based resin particles having a ratio i/r, which is the ratio of the following surface absorbance ratio i to the following resin absorbance ratio r, of less than 0.98, so that the heat-treated polyamide-based resin particles It is more preferable that the ratio i/r is 0.98 or more.
In addition, when it is difficult to measure the ratio i/r of the polyamide resin particles after the heat treatment in the crystallization promotion step, the resin absorbance ratio R measured using foamed particles obtained by foaming the resin particles, If the ratio I/R, which is the ratio of the surface absorbance ratio I, is 1.0 or more, it is assumed that the ratio i/r after the heat treatment is a predetermined value or more.
Here, the resin absorbance ratio r is the maximum absorbance Drp _B at a wave number of 1320 to 1400 cm ^-1 in the infrared absorption spectrum of the polyamide resin constituting the resin particles measured by total reflection absorption infrared spectroscopy and the wave number 3250. The absorbance ratio with the maximum absorbance Drp _A at ~3350 cm ^-1 is Drp _A /Drp _B.
Furthermore, the surface absorbance ratio i is the maximum absorbance Dsp B at a wave number of 1320 to 1400 cm ^-1 in the infrared absorption spectrum of the surface of the resin particle measured by total reflection absorption infrared spectroscopy and the maximum absorbance Dsp _B at a wave number of 3250 to 3350 cm ^-1 . The absorbance ratio between the maximum absorbance Dsp _A and the maximum absorbance Dsp A is Dsp _A /Dsp _B.
The resin absorbance ratio r (absorbance ratio Drp _A /Drp _B ) is determined by melting the polyamide resin constituting the resin particles, removing the thermal history of the resin, and then under an atmosphere substantially free of water such as a vacuum condition. This is a value measured on a film made of a polyamide resin that has been heat-treated to sufficiently promote crystallization of the resin. Therefore, this value is an index of the absorbance ratio normally exhibited by the polyamide resin constituting the resin particles.
The heat treatment of the film is preferably carried out at a temperature of -70°C or higher, the melting point of the polyamide resin, and -40°C or lower, the melting point of the polyamide resin.

The crystallization promotion step may be performed before the blowing agent impregnation step of impregnating the polyamide resin particles with the blowing agent, may overlap with part or all of the blowing agent impregnation step, or may be performed before the blowing agent impregnation step. It may be carried out after the process.

The amide resin particles subjected to the crystallization promotion step are the same as the method for manufacturing the polyamide resin particles described above, so a description thereof will be omitted here. The shape of the polyamide resin particles is not particularly limited, as long as it is granular. Note that the resin particles include pellet-like particles.

Foaming process:
In the manufacturing method according to the first embodiment, the foaming step is performed after the crystallization promotion step is performed.
The foaming step is not particularly limited as long as it is a method that can foam the polyamide resin particles obtained through the crystallization promotion step to a predetermined expansion ratio. Before the foaming step, a foaming agent impregnation step is appropriately carried out, and expandable polyamide resin particles are used in the foaming step.
For example, the foaming process includes an impregnation foaming method, a direct foaming method, and the like.
In the impregnation foaming method, resin particles are impregnated with a foaming agent in a closed container to produce foamable resin particles, and then the foamable resin particles are supplied to a device for producing foamed particles, which is heated and foamed. This is a method to obtain expanded particles.
In addition, in the direct foaming method, resin particles are dispersed in an aqueous medium such as water in a closed container, and the resin particles are impregnated with a foaming agent in the closed container to produce foamable resin particles, and then a predetermined pressure is applied. This is a method of obtaining foamed particles by releasing the contents of a sealed container into a pressure region lower than the pressure inside the sealed container at a low temperature to foam the foamable resin particles.
In particular, it is one of the preferred embodiments of the production method of the present invention that the foaming step is performed by a direct foaming method.

The foaming temperature in the above-mentioned foaming step is the temperature at which the foamed polyamide resin particles containing the foaming agent foam. In addition, the foaming temperature in the direct foaming method means the temperature of the dispersion liquid immediately before releasing the contents of the closed container such as expandable resin particles (a dispersion liquid in which resin particles are dispersed in an aqueous medium). In other words, in direct foaming, the temperature of the dispersion liquid immediately before releasing the contents of a closed container such as expandable resin particles (a dispersion liquid of resin particles dispersed in an aqueous medium) is set to a temperature suitable for foaming (a dispersion liquid in which resin particles are dispersed in an aqueous medium). temperature).
In the foaming step, after the resin particles start foaming at the foaming temperature, the temperature of the dispersion may be maintained at a constant temperature, or may be increased or decreased as appropriate.
Regarding the first embodiment, a first manufacturing method and a second manufacturing method will be described below as more specific examples of manufacturing methods.

(First manufacturing method)
The first manufacturing method, which is one implementation pattern of the first embodiment, will be described below. The first manufacturing method is a method in which a crystallization promotion step described below is first carried out, and the polyamide resin particles obtained thereby are subjected to a foaming step. Before the foaming step, arbitrary steps such as a dispersion liquid preparation step and a blowing agent impregnation step, which will be described later, are performed as appropriate.

Crystallization promotion process:
Polyamide-based resin particles manufactured by a known resin particle manufacturing method are prepared, and a crystallization promotion step is performed. The crystallization promotion step in the first production method is characterized in that it is carried out in a gas phase.
More specifically, in the first production method, the crystallization promotion step is carried out in a gas phase at a temperature ranging from 100°C lower than the melting point temperature of the polyamide resin particles to 20°C lower than the melting point temperature. It is preferable to carry out the heat treatment of the polyamide resin particles. By performing the heat treatment in the gas phase in the above temperature range, crystallization of the surface of the polyamide resin particles can be sufficiently promoted.
In addition, from the viewpoint of efficiently promoting crystallization on the surface of the polyamide resin particles while suppressing discoloration due to heating, the above heat treatment is performed from a temperature 80°C lower than the melting point temperature to a temperature lower than the melting point temperature. It is more preferable to conduct the melting at a temperature of 30°C lower than the above melting point temperature, and from a temperature 70°C lower than the above melting point temperature.
It is more preferable to perform the heat treatment at a temperature that is 40° C. lower than the melting point temperature.
By performing the crystallization promotion step, it is possible to satisfactorily suppress the occurrence of a blocking phenomenon during the foaming step of the polyamide resin particles and during the multistage foaming of the expanded polyamide resin particles obtained by the foaming step.

The above heat treatment is performed using a heating device that can heat the polyamide resin particles within a predetermined temperature range. Examples of the heating device include, but are not limited to, an oven. It is more preferable that the heat treatment is performed in an atmosphere where the polyamide resin is not easily affected by water, such as a vacuum atmosphere or a nitrogen atmosphere.
The heating time of the heat treatment is not particularly limited as long as the desired expanded particles can be obtained, but for example, based on the results of preliminary experiments, polyamide resins having each structure specified in the present invention It can be adjusted and set appropriately so that expanded particles can be obtained.
Although it depends on the temperature of the heat treatment, from the viewpoint of promoting crystallization of the surface layer of the resin particles with good productivity, the heating time is preferably about 5 to 50 hours, and 10 to 30 hours. is more preferable.

The foamed particles of the present invention can be obtained by performing the above-described foaming step on the resin particles that have undergone the crystallization promotion step.
Hereinafter, a method for obtaining expanded particles by the direct foaming method will be explained.

Dispersion preparation process:
After carrying out the crystallization promotion process mentioned above, it is good to carry out a dispersion liquid preparation process.
The dispersion preparation step is a step of preparing a dispersion containing polyamide resin particles that have undergone a crystallization promotion step.

Specifically, the dispersion preparation step is a step in which the polyamide resin particles that have undergone the crystallization promotion step are dispersed in an aqueous medium such as water in a container to obtain a dispersion.
The method for dispersing polyamide resin particles in water is not particularly limited, and any known method can be used. For example, a dispersion can be obtained by using a closed container equipped with a stirrer, adding polyamide resin particles while stirring an aqueous medium charged in the container, and further stirring. The amount of the aqueous medium added is preferably 200 parts by mass or more and 5000 parts by mass or less, more preferably 250 parts by mass or more and 4000 parts by mass or less, based on 100 parts by mass of the resin particles.
In addition, if necessary, dispersants such as inorganic substances such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, talc, and smectite, sodium dodecylbenzenesulfonate, and sodium alkanesulfonate may be added to the dispersion liquid. A dispersion aid such as an anionic surfactant such as the following may be added.
The amount of the dispersant added is preferably 0.1 parts by mass or more and 10 parts by mass or less based on 100 parts by mass of the resin particles. In addition, the above-mentioned dispersant also functions as an anti-blocking agent that suppresses blocking between foamed particles in the multi-stage foaming process by adhering to the surface of the resin particles. From the viewpoint of suppressing the blocking phenomenon while maintaining the fusion properties of the expanded particles during in-mold molding, the amount of dispersant (antiblocking agent) added is 0 to 100 parts by mass of the polyamide resin particles. .1 parts by mass or more and 3 parts by mass or less, more preferably 0.1 parts by mass or more and 2 parts by mass or less, even more preferably 0.1 parts by mass or more and 1 part by mass or less, It is particularly preferable that the amount is .2 parts by mass or more and 0.5 parts by mass or less. It is preferable to use kaolin as the dispersant. In particular, if the amount of the dispersant (anti-blocking agent) added is in the range of 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the polyamide resin particles in a closed container, the dispersant (anti-blocking agent) agent) can be attached to the foamed particles in an amount that does not impair the fusion properties of the foamed particles during in-mold molding.
As mentioned above, in the present invention, since the absorbance, which reflects the degree of crystallinity of the expanded particles, is desirably adjusted, even by using a small amount of a dispersant (anti-blocking agent), blocking between resin particles and expansion particles can be prevented. It is possible to effectively prevent blocking between the two.
The amount of the antiblocking agent attached to the foamed polyamide resin particles is preferably 0.01 parts by mass or more and 1 part by mass or less, based on 100 parts by mass of the foamed polyamide resin particles to which the antiblocking agent is attached. It is more preferably 0.05 parts by mass or more and 0.5 parts by mass or less, and even more preferably 0.10 parts by mass or more and 0.30 parts by mass or less. As mentioned above, the amount of the antiblocking agent attached to the foamed particles can be determined not only by adding a dispersant (antiblocking agent) in a closed container, but also by adding an antiblocking agent to the foamed particles produced through the foaming process. It can also be adjusted by attaching it.
Further, the mass ratio of the above-mentioned dispersant and dispersion aid (dispersant/dispersion aid) is preferably 1 to 500, more preferably 1 to 100.

Foaming agent impregnation process:
It is preferable to carry out the blowing agent impregnation step using the dispersion obtained by the above-mentioned dispersion preparation step.
The blowing agent impregnation step is a step of impregnating the polyamide resin particles in the dispersion with a blowing agent. The method of impregnating the polyamide resin particles with the blowing agent is not particularly limited, but it is preferable to impregnate the polyamide resin particles dispersed in a dispersion liquid with the blowing agent in a pressurized airtight container such as an autoclave. . In addition, from the viewpoint of sufficiently impregnating the blowing agent into the polyamide resin particles in a short time, the blowing agent is impregnated into the polyamide resin particles by applying pressure under moderate pressure (hereinafter also referred to as impregnation pressure). It is preferable to include an impregnating and holding step of heating and impregnating at an appropriate temperature (hereinafter also referred to as impregnating temperature).

In order to perform the above-mentioned pressurization, it is preferable to add a foaming agent to the closed container containing the dispersion liquid to adjust the pressure inside the closed container. From the viewpoint of sufficiently impregnating the polyamide resin particles with the foaming agent in a short time, the impregnation pressure in the closed container in the impregnation holding step is preferably 1.5 MPa (G) or higher, and 2.5 MPa (G) or higher. It is more preferable to set it to be 7.0 MPa (G) or less, and more preferably to set it to 5.0 MPa (G) or less. Note that, for example, "1.5 MPa (G)" means 1.5 MPa in gauge pressure.

In addition, the impregnation temperature in the impregnation holding step is preferably 50°C or higher, more preferably 80°C or higher, from the viewpoint of sufficiently impregnating the polyamide resin particles with the foaming agent in a short time, and preferably 80°C or higher. It is below the melting point (Tm (°C)), more preferably below (Tm (°C) - 20 (°C)), even more preferably below (Tm (°C) - 40 (°C)).

Further, from the viewpoint of sufficiently impregnating the polyamide resin particles with the foaming agent, the time period of the impregnation holding step is preferably 5 minutes or more. On the other hand, from the viewpoint of productivity of expanded polyamide resin particles, the above-mentioned time is preferably 50 minutes or less, more preferably 30 minutes or less. The time for the impregnation and holding process is the time from when the temperature of the impregnation and holding process is reached and the blowing agent is added until the contents of the sealed container (a dispersion of resin particles dispersed in an aqueous medium) are released. means time.

As the foaming agent, for example, a physical foaming agent can be used. Examples of physical blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, chlorofluoromethane, trifluoromethane, Halogenated hydrocarbons such as 1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride, and dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, etc. Can be mentioned. Examples of inorganic physical foaming agents include carbon dioxide, nitrogen, helium, argon, and air.
Among the physical foaming agents, inorganic physical foaming agents are preferred, carbon dioxide or nitrogen is more preferred, and carbon dioxide is even more preferred, from the viewpoint of having little impact on the environment, being non-flammable, and being excellent in safety.

Although the dispersion liquid preparation step and the blowing agent impregnation step are described as independent steps in the above description, these steps may be performed in duplicate as appropriate.

Foaming process:
The foaming step is a step in which the polyamide resin particles that have undergone the crystallization promotion step are foamed at a foaming temperature to obtain expanded polyamide resin particles. The above-described dispersion liquid preparation step and blowing agent impregnation step may be performed between the crystallization promotion step and the foaming step.
The method for foaming the polyamide resin particles is not particularly limited, but from the viewpoint that the polyamide resin particles can be foamed at a low foaming temperature by plasticizing the polyamide resin particles by water absorption, the foaming agent is used in a closed container. The impregnated polyamide resin particles are dispersed in an aqueous medium, and a closed container is heated to around the foaming temperature of the resin particles, and the polyamide resin particles are dispersed together with the aqueous medium in the closed container under a predetermined pressure and temperature. Foaming is preferably carried out by discharging into a pressure atmosphere lower than the pressure (usually under atmospheric pressure).

The foaming temperature in the foaming step is not particularly limited, and can be appropriately determined within a range that does not depart from the spirit of the present invention.
The foaming temperature is generally around the melting point of the polyamide resin. However, in the blowing agent impregnation step, the polyamide resin particles that have been plasticized by absorbing water can be foamed at a lower foaming temperature than the polyamide resin before plasticization.

(Second manufacturing method)
Next, a second manufacturing method, which is another pattern of the first embodiment, will be explained. FIGS. 1 and 2 will be used as appropriate to explain the second manufacturing method. FIG. 1 is a graph for explaining the second manufacturing method. FIG. 2 is a graph for explaining a modification of the second manufacturing method.
The second manufacturing method includes a crystallization promotion step 10 and a foaming step 20, and both steps are performed in a closed container. In the second production method, the blowing agent impregnation step may be performed during the crystallization promotion step 10 or before or after the crystallization promotion step 10, and the crystallization promotion step 10 and the foaming step 20 are performed in a closed container. May be performed consecutively.
In the following explanation, an example will be explained in which the dispersion liquid preparation step is started before the start of the crystallization promotion step 10, the blowing agent impregnation step is performed after the crystallization promotion step 10, and then the foaming step 20 is performed. do.

Crystallization promotion process:
In the crystallization promotion step 10 in the second production method, the polyamide resin particles are dispersed in an aqueous medium in a closed container, and the temperature is lowered by 50°C than the melting point T3 of the polyamide resin particles. This is carried out by heat-treating the polyamide-based resin particles at temperatures as low as .degree. Note that the blowing agent may be added in any order and timing; for example, in the heating step of raising the temperature to a predetermined temperature, the blowing agent may be added all in a sealed container at the start of heating, or it may be added multiple times. It may be added separately.

From the viewpoint of better preventing the occurrence of the blocking phenomenon, it is preferable to add the above-mentioned antiblocking agent (dispersant) to the closed container together with the polyamide resin.

In this embodiment, a dispersion preparation step is performed before the crystallization promotion step 10, and a blowing agent impregnation step is performed after the crystallization promotion step 10 (the dispersion preparation step and the blowing agent impregnation step are omitted from illustration in FIG. 1). . By performing the blowing agent impregnation step, expandable polyamide resin particles are obtained.
The dispersion liquid preparation step in the second production method is the same as the first method except that resin particles before the crystallization promotion step are used instead of resin particles that have been subjected to the crystallization promotion step in the gas phase. The description of the dispersion liquid preparation process regarding one manufacturing method is referred to as appropriate. Further, for the description of the blowing agent impregnation step in the second manufacturing method, the description of the dispersion liquid preparation step in the first manufacturing method is appropriately referred to. Therefore, a detailed explanation of these descriptions will be omitted here.

In the second production method, the crystallization promotion step is performed by changing the temperature in the closed container to which the polyamide resin particles and the aqueous medium are added from a temperature 80°C lower than the melting point T3 of the polyamide resin particles to a temperature lower than the melting point T3. The temperature is raised to the foaming temperature T1, which is 50 °C lower than the above temperature, and the time from the start of the temperature increase to the foaming temperature T1-30 °C (T2 in FIG. 1) is defined as the required time t2, and the temperature increase is When the time from the start of the process until the foaming temperature T1 is reached is the required time t1, it is preferable that the difference between the required time t1 and the required time t2 is adjusted to be 15 minutes or more and 50 minutes or less. .
Note that the temperature range from the foaming temperature T1 to 30° C. (T2 in FIG. 1) to the foaming temperature T1 is a temperature range in which crystallization of the polyamide resin tends to proceed in the presence of water. In view of the characteristics of the polyamide resin, by maintaining the dispersion liquid within this temperature range, crystallization of the surface of the polyamide resin can be promoted.
In the second manufacturing method, the difference between the required time t1 and the required time t2 is large, and the time required to reach the foaming temperature T1 can be secured relatively long, so that the dispersion can be heated slowly. This allows the crystallization of the surface layer of the resin particles to proceed sufficiently before reaching the foaming temperature T1, so that blocking between resin particles occurs due to the surface layer becoming too soft during temperature rise. can be further suppressed. Further, since the foamed particles obtained in this way have sufficiently advanced crystallization in the surface layer portion, it is possible to further suppress the blocking phenomenon between the foamed particles during multistage foaming such as two-stage foaming.

It is preferable that the crystallization promotion step 10 includes a holding step in which the temperature increase rate becomes zero between T1-30° C. (T2 in FIG. 1) and the foaming temperature T1. The holding process may be carried out once, or as shown in FIG. 1, a plurality of temperature patterns such as a first holding 210 and a second holding 220 may be performed. Below, an example in which holding steps are performed twice, first holding 210 and second holding 220, will be specifically described.
In the first holding 210, the temperature increase rate of the dispersion liquid is first adjusted to zero for a certain period of time. That is, in the first holding 210, the first holding temperature Th (for example, the foaming temperature T1-10° C.) is maintained. After the first holding 210, the temperature increase rate is increased again to adjust the temperature of the dispersion liquid to a predetermined temperature (for example, foaming temperature T1) higher than the first holding temperature Th.
Thereafter, in the second holding 220, the temperature increase rate of the dispersion liquid is adjusted to zero for a certain period of time. That is, in the second holding 220, the predetermined temperature is maintained. Specifically, FIG. 1 shows an embodiment in which the predetermined temperature is the foaming temperature T1, so after the second holding 220 is performed, the foaming step 20 can be performed at an appropriate timing. As a modification not shown, for example, if the predetermined temperature at the second holding 220 is lower than the foaming temperature T1, the second holding 220 may be performed again as after the first holding 210. The temperature of the dispersion liquid may be raised by increasing the heating rate, and finally the temperature may be raised to the foaming temperature T1.
In this way, in the crystallization promotion step 10, by providing a period of zero temperature increase rate (a holding step in which the temperature is held constant) once or multiple times in the temperature range up to the foaming temperature T1, the required time t1 and the required time The difference from time t2 can be adjusted within a predetermined range, and crystallization of the surface of the expanded polyamide resin particles can be favorably promoted. After the temperature of the dispersion liquid is finally raised to the foaming temperature T1, the foaming step can be carried out at an appropriate timing.

A modification of the second manufacturing method is shown in FIG. In the second production method, as shown in FIG. 2, after reaching a predetermined temperature Th in the heating step, the heating rate may be slowed down and the dispersion liquid may be heated slowly until it reaches the foaming temperature T1. .

In the crystallization promotion step 10 of the second manufacturing method, from the viewpoint of efficiently promoting crystallization of the surface layer portion of the resin particles, the temperature in the closed container is kept within a certain range at a temperature below the foaming temperature T1. It is preferable to include a holding step. In this case, the temperature of the holding step is preferably carried out in a temperature range of not less than the foaming temperature T1-30°C (T2 in FIG. 2) and not more than the foaming temperature T1; It is more preferable to carry out the foaming temperature in a temperature range of −3° C. or lower, and even more preferably to carry out the foaming temperature in a range of T1-20° C. or higher and T1-5° C. or lower. Further, the holding step time is preferably 3 to 30 minutes, more preferably 5 to 20 minutes.
Furthermore, from the viewpoint of manufacturing expanded particles with good productivity, promoting crystallization of the surface layer of the resin particles, suppressing hydrolysis of the resin, and further suppressing the deterioration of the physical properties of the obtained expanded particles, the heating step The time is preferably 40 to 80 minutes, more preferably 50 to 70 minutes. In addition, the time of the temperature raising step means the time from when the temperature of the closed container is started until the foaming temperature is reached. Further, the temperature at which the temperature rise of the closed container is started is not particularly limited as long as the intended purpose of the present invention can be achieved, but it is preferably approximately 10 to 50°C.

Foaming process:
After the temperature of the contents (dispersion liquid) in the closed container reaches the foaming temperature T1 in the crystallization promotion step 10 described above, the contents are at an appropriate timing under a pressure atmosphere lower than the internal pressure of the closed container. A foaming step 20 is started in which the foam is discharged (usually under atmospheric pressure) and foamed.
Immediately before the foaming step 20, the temperature inside the closed container is lowered to the foaming temperature T1 in order to promote crystallization of the resin particles as a whole, promote the formation of a high temperature peak, and improve the in-mold moldability of the resulting foamed particles. It is preferable to have a holding step (second holding 220) of holding at a constant temperature. In this case, the holding step time is preferably 3 to 20 minutes, more preferably 5 to 15 minutes. Note that the holding step time refers to the time from when the foaming temperature T1 is reached until the contents of the closed container (a dispersion of resin particles dispersed in an aqueous medium) are released.

In the temperature raising step of the second production method, it is preferable to select an aqueous medium such as water as the dispersion medium added to the closed container. By dispersing the polyamide resin particles in an aqueous medium and absorbing water, the polyamide resin particles can be plasticized. As a result, the foaming temperature T1 of the polyamide resin particles can be substantially lowered.
The foaming temperature T1 may be set at a high temperature around the melting point temperature T3 of the polyamide resin particles unless the above-mentioned plasticization is taken into consideration. However, when such high-temperature conditions are set, it may be difficult to stably produce expanded polyamide resin particles using a general direct foaming device.
In the present invention, when foaming the plasticized polyamide resin particles as described above, the foaming temperature T1 ranges from 80°C lower than the melting point temperature T3 of the polyamide resin particles to 50°C lower than the melting point temperature T3. It can be set in a low temperature range up to a low temperature. Therefore, it is possible to produce foamed particles with good productivity and sufficiently advanced internal crystallization and surface layer crystallization.

Although the manufacturing method of the present invention has been described above using the first manufacturing method and the second manufacturing method, the manufacturing method of the present invention is not limited thereto. For example, the manufacturing method of the present invention includes embodiments in which elements of the first manufacturing method and the second manufacturing method are appropriately combined. Specifically, for example, the crystallization promotion step in the first production method may be carried out, and the polyamide resin particles obtained thereby may be subjected to the second production method. In this case, the crystallization of the surface of the polyamide resin particles before being impregnated with the blowing agent is promoted, and the crystallization of the surface can be further promoted in the crystallization promotion step in the second production method.

[Second embodiment]
Next, a second embodiment of the manufacturing method of the present invention will be described. The second embodiment includes a foaming step of foaming polyamide resin particles to obtain foamed polyamide resin particles, and a heat treatment of the foamed polyamide resin particles obtained through the foaming step. The method includes a crystallization promotion step of promoting crystallization of the surface layer portion of the particles.
In the second embodiment, a dispersion liquid preparation step, a blowing agent impregnation step, etc. may be carried out as appropriate before the foaming step. The above-mentioned foaming step, dispersion liquid preparation step, blowing agent impregnation step, etc. are omitted here because the explanation in the first embodiment is referred to as appropriate, except for using resin particles that have not undergone a crystallization promotion step. do.

The second embodiment is characterized in that crystallization is achieved by heating expanded particles instead of resin particles. The heating method in the crystallization promotion step is not particularly limited, and for example, the heating method using an oven or the like in the first manufacturing method described above can be employed.
By performing the crystallization promotion step on the expanded particles in this way, the above-mentioned ratio I/R can be made 1.0 or more, and the desired effect of the present application can be achieved.

A polyamide resin expanded particle molded article (hereinafter also simply referred to as a molded article) can be produced using the polyamide resin expanded particles of the present invention described above. The manufacturing method is not particularly limited, and conventionally known methods can be employed. For example, an in-mold molding method is preferred for producing the molded article. In particular, according to the in-mold molding method using steam, the steam plasticizes the polyamide resin constituting the expanded polyamide resin particles, so it is possible to lower the molding pressure during in-mold molding. By drying the obtained molded product, it becomes possible to exhibit the physical properties inherent to the polyamide resin, resulting in a molded product having high heat resistance.
The above-mentioned molded product has high heat resistance, and is also excellent in abrasion resistance, chemical resistance, etc., and is also excellent in molded product fusion adhesion and tensile strength. Therefore, the above-mentioned molded body can be well used for automobile parts, electrical products, etc.

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto.

(Example 1)
[Manufacture of pellet-shaped polyamide resin particles]
An extruder with an inner diameter of 65 mm was prepared, and the extruder was equipped with a die capable of extruding a large number of strand-shaped molten mixtures on the exit side (downstream side) of the extruder.
"UBE Nylon 5033B; polyamide 6/66 copolymer (nylon 6/66), polyamide 6/polyamide 66 = 85/15" (manufactured by Ube Industries, Ltd.) was supplied to the extruder, and "Talcan Powder PK" was added as a bubble regulator. -S" (manufactured by Hayashi Kasei Co., Ltd.) was supplied so that its content was 8000 ppm by mass, and "Stabaxol P" (manufactured by Rhein Chemie Co., Ltd.) was supplied as an end-blocking agent so that it was 1 part by mass. Melted and kneaded.
Thereafter, the melt-kneaded product obtained by the above-mentioned melt-kneading is extruded as a strand with a circular cross section through the pores of the mouthpiece attached to the downstream end of the extruder, and after cooling the extruded strand with water, it is mass-produced using a pelletizer. The particles were cut into pieces weighing about 2.0 mg each, and dried to obtain polyamide resin particles.
Note that the density (catalog value) of the polyamide resin was 1.14 g/cm ³ .

[Manufacture of expanded polyamide resin particles]
The foamed polyamide resin particles in Example 1 were produced according to the second production method described above, using the temperature increase pattern shown in FIG. 1. Further, the first holding temperature Th was set as the foaming temperature T1-10°C.
First, 1 kg of the polyamide resin particles produced as described above and 3 liters of water as an aqueous medium were charged into a 5 liter autoclave equipped with a stirrer, and further, for 100 parts by mass of the polyamide resin particles, 0.3 parts by mass of kaolin as a dispersant (antiblocking agent) and 0.004 parts by mass of sodium alkylbenzenesulfonate as a surfactant were added to the dispersion (dispersion preparation step).
Then, while stirring the contents in the autoclave, carbon dioxide was pressurized as a blowing agent until the pressure inside the autoclave reached 1.0 MPa (G), and the temperature was raised from room temperature T0 (23°C). The first holding temperature Th shown was reached (temperature raising step). At this time, the time required to reach the first holding temperature Th shown in Table 1 from room temperature T0 (23°C) was 47 minutes.

Next, as shown in FIG. 1, after the temperature of the dispersion liquid reached the first holding temperature Th, a first holding 210 was performed. Specifically, as the first holding 210, the temperature increase rate was set to zero, and the temperature of the dispersion liquid was held at the first holding temperature Th for 10 minutes.
Thereafter, the temperature of the dispersion liquid was raised to the foaming temperature T1.
A required time t1 that is the time from the start of the temperature increase until reaching the foaming temperature T1, and a required time t2 that is the time from the start of the temperature increase until the foaming temperature T1-30°C (T2) is reached. The difference was 21 minutes.
After implementing the crystallization promotion step 20, a second holding 220 was performed. That is, after the temperature of the dispersion liquid reaches the foaming temperature T1, carbon dioxide is pressurized into the autoclave until the pressure within the autoclave reaches 4.0 MPa (G), and while maintaining that pressure, the foaming temperature is set as the second holding 220. The dispersion was held at T1 for 5 minutes. After that, foaming step 10 was carried out. That is, polyamide resin particles impregnated with a blowing agent were discharged together with a dispersion medium (water) under atmospheric pressure (0.1 MPa). The obtained expanded polyamide resin particles were cured in an oven at 60° C. for 24 hours, and then slowly cooled to obtain expanded polyamide resin particles.
In addition, after the expanded polyamide resin particles obtained by the above method were placed in a closed container, the inside of the closed container was pressurized with air to adjust the pressure inside the closed container to 0.4 MPa (G). . Thereafter, the foamed particles that have been pressurized and given an internal pressure are taken out, and the foamed particles are brought into contact with water vapor of 0.07 MPa (G) to carry out two-stage foaming, resulting in two-stage foamed polyamide resin particles. I got it.

[Manufacture of polyamide resin expanded particle molded product]
Next, a polyamide resin expanded particle molded article was produced using the polyamide resin expanded particles.
First, the obtained expanded polyamide resin particles were filled into a flat molding mold of 200 mm long x 65 mm wide x 40 mm thick, and molded in the mold by steam heating to obtain a plate-shaped expanded particle molded product. The heating method is to preheat (exhaust process) by supplying steam (0.1 MPa (G)) for 5 seconds with the drain valves of the molds on both sides open, and then supply steam (0.10 MPa (G)) from the moving mold. G)) was supplied for 5 seconds, and then steam (0.14 MPa (G)) was supplied from the fixed side mold for 5 seconds, and then heated to molding heating steam pressure (molding pressure = molding steam pressure). Note that the molding heating steam pressure was 0.18 MPa (G), and heating was performed for 3 seconds.
After heating, the pressure was released and the molded product was cooled with water until the surface pressure due to the foaming force of the molded product decreased to 0.02 MPa, and then the mold was opened and the molded product was taken out from the mold. The obtained molded body was cured in an oven at 80° C. for 12 hours, and then slowly cooled to room temperature. In this way, a polyamide resin expanded particle molded article was obtained.
Further, a polyamide resin foamed particle molded article was produced using the polyamide resin two-stage expanded particles under the same molding conditions. The obtained molded body was cured in an oven at 80° C. for 12 hours, and then slowly cooled to room temperature. In this way, a polyamide-based resin expanded particle molded article consisting of two-stage expanded polyamide-based resin particles was obtained.

(Example 2)
Example 2 was carried out in accordance with the first manufacturing method described above. Specifically, using polyamide-based resin particles produced in the same manner as in Example 1, the polyamide-based resin particles were placed in an oven and heat-treated at 140°C for 20 hours to form crystals. A process to promote

Subsequently, using the polyamide resin particles that had been heated through the crystallization promotion step, a temperature raising step was carried out according to the temperature raising pattern shown in FIG. 3 .
Specifically, first, 1 kg of polyamide resin particles taken out from the oven and 3 liters of an aqueous medium (water) were placed in a 5 liter autoclave equipped with a stirrer, and then 1 kg of polyamide resin particles were added to 100 parts by mass of the polyamide resin particles. Then, 0.3 parts by mass of kaolin as a dispersant (antiblocking agent) and 0.004 parts by mass of sodium alkylbenzenesulfonate as a surfactant were added to the dispersion.
Then, while stirring the contents in the autoclave, carbon dioxide as a blowing agent was pressurized until the pressure inside the autoclave reached 1.0 MPa (G), and the temperature was increased at a constant rate (2 The temperature was started to increase at a rate of .2° C./min) to reach the foaming temperature T1. In Example 2, the required time t1 is the time from the start of the temperature increase until the foaming temperature T1 is reached, and the time from the start of the temperature increase until the foaming temperature -30°C (T2) is reached. The difference from a certain required time t2 was 12 minutes.
Subsequently, after the temperature of the dispersion liquid reaches the foaming temperature T1, carbon dioxide is pressurized into the autoclave until the pressure within the autoclave reaches 4.0 MPa (G), and while maintaining that pressure, the temperature of the dispersion liquid reaches the foaming temperature. After holding at T1 for 15 minutes (second holding 220), the expandable resin particles were foamed in the same manner as in Example 1 to obtain expanded polyamide resin particles. Further, in the same manner as in Example 1, the expanded particles were expanded (two-stage foaming) to obtain two-stage expanded polyamide resin particles. In Example 2, the temperature was not maintained at the first holding 210 before reaching the foaming temperature T1, but only at the second holding 220 after reaching the foaming temperature T1.
Using the polyamide resin foam particles and two-stage polyamide resin foam particles produced as described above, a polyamide resin foam particle molded article and a polyamide resin foam particle consisting of the polyamide resin two-stage foam particles were prepared in the same manner as in Example 1. A molded body was produced.

(Example 3)
Using polyamide resin particles produced in the same manner as in Example 1, the resin particles were crystallized in an oven in the same manner as in the crystallization promotion step of Example 2.
The temperature raising step, the crystallization promotion step 10, and the foaming step 20 were carried out in the same manner as in Example 1, except that the polyamide resin particles that had undergone the crystallization promotion step as described above were used, and the expanded polyamide resin particles were Obtained. Further, in the same manner as in Example 1, the expanded particles were expanded (two-stage foaming) to obtain two-stage expanded polyamide resin particles.
Using the polyamide resin foam particles and the polyamide resin two-stage expanded particles, a polyamide resin foam particle molded article and a polyamide resin expanded particle molded body consisting of the polyamide resin two-stage expanded particles were produced in the same manner as in Example 1. .

(Comparative example 1)
An attempt was made to produce foamed polyamide resin particles in the same manner as in Example 2, except that the crystallization promotion step was not carried out and the foaming temperature T1 was set at 136.6°C, but the resin particles blocked each other during foaming. However, expanded particles could not be obtained.
In addition, in Comparative Example 1, the crystallization promotion step was not performed, and the foaming step was performed by raising the temperature from room temperature T0 to foaming temperature T1 at a constant temperature increase rate (2.2°C/min). It was inferred that the resin particles were not sufficiently crystallized.

(Comparative example 2)
Expanded polyamide resin particles and expanded polyamide resin particle molded articles were produced in the same manner as in Comparative Example 1, except that the amount of the dispersant (antiblocking agent) added was 3 parts by mass. Further, in the same manner as in Example 1, the expanded particles were expanded (two-stage foaming) to obtain two-stage expanded polyamide resin particles, and a molded article of expanded polyamide resin particles made of the two-stage expanded polyamide resin particles was obtained.

(Comparative example 3)
Expanded polyamide resin particles and expanded polyamide resin particle molded articles were produced in the same manner as in Comparative Example 1, except that the amount of the dispersant (antiblocking agent) added was 0.6 parts by mass.
Further, in the same manner as in Example 1, when an attempt was made to obtain two-stage expanded polyamide resin particles by foaming (two-stage foaming) the expanded beads, blocking of the expanded polyamide resin particles occurred. Therefore, it was not possible to obtain a molded article made of two-stage expanded polyamide resin particles.

Measurement and evaluation of various physical properties of the polyamide resin particles, expanded polyamide resin particles, and expanded polyamide resin particle molded articles of each Example and each Comparative Example obtained as described above were carried out as follows. The measurement results and evaluation results are shown in Table 1 or Table 2.

[Evaluation of polyamide resin particles]
<Melting point (℃)>
The melting points of the polyamide resin particles and foamed polyamide resin particles were measured by heat flux differential scanning calorimetry in accordance with JIS K7121-1987. Under conditions of a nitrogen flow rate of 30 mL/min, heat melting at a heating rate of 10 °C/min from 30 °C to a temperature 30 °C higher than the end of the melting peak (first temperature rise), and then increase the temperature to that temperature. After holding for 10 minutes at a cooling rate of 10°C/min to 30°C, the DSC curve obtained by heating and melting at a heating rate of 10°C/min again to a temperature 30°C higher than the end of the melting peak. It was determined as the peak apex temperature of the melting peak. As a measuring device, a highly sensitive differential scanning calorimeter "EXSTAR DSC7020" (manufactured by SII Nanotechnology) was used. In addition, polyamide resin particles and foamed polyamide resin particles are placed in a desiccator under a nitrogen atmosphere to avoid hydrolysis by avoiding high temperature and high humidity conditions, and then vacuumed to reduce the moisture content to 1000 mass ppm or less for 24 hours. The stored sample was used for melting point measurements.
The melting point of the polyamide resin particles and foamed polyamide resin particles obtained in Examples and Comparative Examples was 193°C.
<Bending elastic modulus (MPa)>
The flexural modulus of the polyamide resin constituting the expanded polyamide resin particles was determined by measuring in accordance with JIS K7171:2016. The flexural modulus was determined by preparing a resin test piece with a thickness of 4 mm, a width of 10 mm, and a length of 80 mm. After leaving the test piece for 72 hours at a room temperature of 23°C and a humidity of 50%, the distance between the supporting points was 64 mm, and the indenter was Values calculated by measuring with an Autograph AGS-10kNG (manufactured by Shimadzu Corporation) testing machine under the conditions of radius R 15.0 mm, support base radius R 25.0 mm, test speed 2 mm/min, room temperature 23 ° C, and humidity 50%. The average value of (5 points) was adopted.
The flexural modulus of the polyamide resin constituting the expanded polyamide resin particles obtained in Examples and Comparative Examples was 1260 MPa.

[Evaluation of expanded polyamide resin particles]
<In-pot fusion evaluation>
In-pot fusion (blocking during the foaming process) was evaluated based on the following criteria.
None: The polyamide resin particles can be discharged from the autoclave in the foaming step 20 described above, and no lumps formed by blocking of resin particles remain in the autoclave.
Yes: In the above-mentioned foaming step 20, polyamide resin particles cannot be discharged from the autoclave due to the generation of lumps caused by blocking of resin particles, or lumps are observed in the autoclave after discharge.
<Measurement of total heat of fusion and high temperature peak heat of fusion (J/g)>
The total heat of fusion and the high temperature peak were determined from the DSC curve measured by heat flux differential scanning calorimetry when heating and melting from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C/min. The heat of fusion was determined. As a measuring device, a highly sensitive suggestive scanning calorimeter "EXSTAR DSC7020" (manufactured by SII Nanotechnology) was used.
As shown in FIG. 4, a straight line was drawn connecting point I at 150° C. on the DCS curve and point II indicating the melting end temperature on the DSC curve. Next, pass through point III on the DSC curve, which is the valley between characteristic peak a and high temperature peak b, and cross the line perpendicular to the temperature on the horizontal axis of the graph with the line connecting point I and point II. was set as point IV. The area surrounded by the straight line connecting point IV and point II, the straight line connecting point III and point IV, and the DSC curve connecting point III and point II was determined as the heat of fusion of the high temperature peak. Further, the area of the portion surrounded by the straight line connecting point I and point II and the DSC curve was determined as the total heat of fusion.
<Crystallinity (%)>
Using an X-ray diffraction device "SmartLab SE" (manufactured by Rigaku Corporation), the expanded polyamide resin particles were subjected to XRD measurement using a transmission method. Note that during the measurement, the foamed particles were spread on a measuring table so that the foamed particles did not overlap each other. Thereafter, peak separation of the obtained X-ray diffraction profile was performed using analysis software attached to the apparatus. In peak separation, a Gaussian function was assumed as the peak shape, and the peaks were separated into a crystal-derived diffraction peak and an amorphous-derived diffraction peak.
By calculating the area of each peak obtained by peak separation and substituting the area into the following formula (1), the crystal The degree of crystallinity (%) of the expanded particles, which is the ratio of the area of the derived diffraction peak, was calculated.
[Number 1]
Crystallinity X (%) = ΣAci/(ΣAci+ΣAai)×100...(1)
Here, ΣAci (i = 1 to n) is the total area of diffraction peaks derived from n crystals obtained when peak separation is performed, and ΣAai (i = 1 to n) is the sum of the areas of diffraction peaks derived from n crystals obtained when peak separation is performed. This is the area of the resulting amorphous-derived diffraction peak.
The conditions during the measurement were as follows.
slit:
Incoming solar slit 1: Slit for parallel beam Incoming solar slit 2: 5.0°
Longitudinal limit slit: 10mm
Light receiving optical element: 0.0228°
Detector:
D/teX Ultra250
Measurement condition:
Measurement range: 5~35°
Step: 0.04°
Speed: 2°/min
X-ray wavelength: 0.154nm
<Apparent density (kg/m ³ )>
Prepare a graduated cylinder containing water at a temperature of 23°C, and measure the mass W1 of about 500 cm ³ of foamed polyamide resin particles that were left in the graduated cylinder for 2 days at a relative humidity of 50%, 23°C, and 1 atm. and submerged it using wire mesh. Considering the volume of the wire mesh, measure the volume V1 [cm ³ ] of the foamed polyamide resin particles, which can be read from the rise in the water level, and divide the mass W1 [g] of the foamed polyamide resin particles by the volume V1 (W1 /V1), and the apparent density of the expanded particles was determined by converting the unit into [kg/m ³ ].
<Total reflection absorption infrared spectroscopy>
The maximum absorbance at a predetermined wave number of the foamed polyamide resin particles (hereinafter also simply referred to as foamed particles) of each Example and each Comparative Example was measured by total internal reflection absorption infrared spectroscopy as follows. In addition, details of the abbreviated expressions regarding Examples and Comparative Examples are shown below.
Maximum absorbance Dr _A : Maximum absorbance of the polyamide resin constituting the foam particles at a wave number of 3250 to 3350 cm ^-1 Maximum absorbance Dr _B : Maximum absorbance of the polyamide resin constituting the foam particles at a wave number of 1320 to 1400 cm ^-1 Resin absorbance ratio R: ratio of maximum absorbance Dr _A to maximum absorbance Dr _B (Dr _A /Dr _B )
Maximum absorbance Drp _A : Maximum absorbance of the polyamide resin constituting the resin particles at wave numbers 3250 to 3350 cm ^-1 Maximum absorbance Drp _B : Maximum absorbance of the polyamide resin constituting the resin particles at wave numbers 1320 to 1400 cm ^-1 Resin absorbance ratio r: ratio of maximum absorbance Drp _A to maximum absorbance Drp _B (Drp _A /Drp _B )
Maximum absorbance Ds _A : Maximum absorbance of the surface of foamed particles at wave numbers of 3250 to 3350 cm ^-1 Maximum absorbance Ds _B : Maximum absorbance of the surface of foamed particles at wave numbers of 1320 to 1400 cm ^-1 Surface absorbance ratio I: Maximum absorbance Ds Ratio of maximum absorbance Ds _A to _B (Ds _A /Ds _B )
Maximum absorbance Dc _A : Maximum absorbance of the central cross section of the expanded particle at a wave number of 3250 to 3350 cm ^-1 Maximum absorbance Dc _B : Maximum absorbance of the central cross section of the expanded particle at a wave number of 1320 to 1400 cm ^-1 Cross-sectional absorbance ratio II: Maximum Ratio of maximum absorbance Dc _A to absorbance Dc _B (Dc _A /Dc _B )
Half-value width Xs: Value of the peak width at the midpoint of the height from the baseline to the peak top of the maximum peak confirmed at a wave number of 3250 to 3350 cm ^-1 on the surface of the foamed particle. Half-value width , the value of the peak width at the midpoint of the height from the baseline to the peak top of the maximum peak confirmed at wavenumbers 3250 to 3350 cm ^-1 Surface absorbance half-width ratio III: ratio of half-width Xs to maximum absorbance Ds _A (Xs / _DsA )
Cross-sectional absorbance half-width ratio IV: Ratio of half-width Xc to maximum absorbance Dc _A (Xc/Dc _A )
Maximum absorbance Dsp _A : Maximum absorbance of the surface of a resin particle at a wave number of 3250 to 3350 cm ^-1 Maximum absorbance Dsp _B : Maximum absorbance of the surface of a resin particle at a wave number of 1320 to 1400 cm ^-1 Surface absorbance ratio i: Maximum absorbance Dsp Ratio of maximum absorbance Dsp _A to _B (Dsp _A /Dsp _B )

Specifically, the maximum absorbance of the polyamide resin constituting the expanded particles was measured using a total reflection absorption measuring device based on the Attenuated Total Teflection (ATR method) in the IR measurement method. As the total reflection absorption measurement device, an infrared spectrophotometer “FT/IR-4600” manufactured by JASCO Corporation and a total reflection absorption measurement device “ATR PRO 450-S” manufactured by the same company were used. The measurement conditions of the total internal reflection absorption measurement device are as follows: prism: ZnSe (PKS-ZnSe), incident angle: 45°, measurement method: single-time ATR method, measurement wavenumber range: 4000 to 650 cm ^-1 , wavenumber dependence on measurement depth. Characteristics: with correction, resolution: 4 cm ⁻¹ , number of integrations: 16 times. In addition, after correcting the infrared absorption spectrum so that 3800 cm ^-1 and 2500 cm ^-1 pass through the zero point of absorbance, each absorbance was determined.
The test piece (resin film) used for measuring absorbance was measured as follows.
First, the foamed particles were supplied into a hot press mold, and then preheated for 5 minutes at a temperature of 30°C (223°C) above the melting point of the polyamide resin particles to melt the foamed particles. Next, hot press molding was performed while holding the mold at this temperature for 1 minute, followed by slow cooling. In this way, a resin film with a thickness of about 100 μm was produced.
Next, the produced resin film was placed in an oven that can be evacuated and heated at 140° C. for 6 hours under vacuum conditions to perform heat treatment on the resin film. In this way, a polyamide resin film was produced in which crystallization was sufficiently promoted. Next, the polyamide resin film in which crystallization had been sufficiently promoted was pressed against the prism of a total reflection absorption measuring device at a pressure of 340 kg/cm ² and the maximum absorbance was measured. An infrared absorption spectrum (with ATR correction) was obtained. Next, the maximum absorbance Dr _A and the maximum absorbance Dr _B obtained from the infrared absorption spectrum were measured. Then, the resin absorbance ratio R was calculated from these. In addition, in the measurement of absorbance, measured values affected by peaks that are clearly distinguished from absorption peaks derived from resin components, such as absorption peaks derived from antiblocking agents, etc., were not measured.
In addition, a polyamide resin film was produced in the same manner as above except that resin particles were used instead of expanded particles, and the resin film was heat-treated to sufficiently promote crystallization. Created. This resin film was subjected to infrared absorption spectrum measurement in the same manner as above, the maximum absorbance Drp _A and the maximum absorbance Drp _B were measured, and the resin absorbance ratio r was calculated. In calculating the resin absorbance ratio R and the resin absorbance ratio r, similar measurements were performed on 10 test pieces, and the average of the eight absorbance ratios, excluding the maximum and minimum values, was calculated. The value was determined, and this value was defined as the resin absorbance ratio R and the resin absorbance ratio r. In Examples and Comparative Examples, the resin absorbance ratio r (Drp _A /Drp _B ) of the polyamide resin constituting the resin particles and the resin absorbance ratio R (Dr _A /Dr _B ) of the polyamide resin constituting the expanded particles are 3. It was .21. The maximum absorbance of the foamed particle surface and cross section was measured using a total reflection absorption measuring device based on the Attenuated Total Teflection (ATR method) in the IR measurement method. As the total reflection absorption measurement device, an infrared spectrophotometer “FT/IR-4600” manufactured by JASCO Corporation and a total reflection absorption measurement device “ATR PRO 450-S” manufactured by the same company were used. The measurement conditions of the total internal reflection absorption measurement device are as follows: prism: ZnSe (PKS-ZnSe), incident angle: 45°, measurement method: single-time ATR method, measurement wavenumber range: 4000 to 650 cm ^-1 , wavenumber dependence on measurement depth. Characteristics: with correction, resolution: 4 cm ⁻¹ , number of integrations: 16 times. In addition, after correcting the infrared absorption spectrum so that 3800 cm ^-1 and 2500 cm ^-1 pass through the zero point of absorbance, each absorbance etc. was determined. In the measurement, expanded particles were used which had been dried in an oven at 50° C. for 24 hours after removing the dispersant attached to the expanded particles.
To measure the maximum absorbance on the surface of foamed particles, first, press the foamed particles against the prism of a total reflection absorption measurement device at a pressure of 340 kg/cm ² and measure the absorbance, and then measure the infrared absorption spectrum ( However, with ATR correction) was obtained. Next, the maximum absorbance Ds _A and the maximum absorbance Ds _B obtained from the infrared absorption spectrum were measured. Then, the surface absorbance ratio I was calculated from these.
On the other hand, to measure the maximum absorbance of the center cross section of the foamed particles, first, the foamed particles were cut into approximately two equal parts through the center using a razor to form a cut surface. Next, an infrared absorption spectrum (with ATR correction) at the center cross section of the foamed particles was obtained in the same manner as described above, except that the cut surface was pressed against a prism of a total reflection absorption measuring device. Next, the maximum absorbance Dc _A and the maximum absorbance Dc _B obtained from the infrared absorption spectrum were measured. Then, the cross-sectional absorbance ratio II was calculated from these.
Next, the ratio I/R of the surface absorbance ratio I to the resin absorbance ratio R, the ratio II/R of the cross-sectional absorbance ratio II to the resin absorbance ratio R, and the ratio I/II of the surface absorbance ratio I to the cross-sectional absorbance ratio II. Calculated.
Further, from the above measurements, the half-width Xs of the surface of the foamed particles and the half-width Xc of the center cross section of the foamed particles were determined. Then, the surface absorbance half-width ratio III and the cross-sectional absorbance half-width ratio IV were calculated. Next, the ratio III/IV of the surface absorbance half-width ratio III to the cross-sectional absorbance half-width ratio IV was calculated.
In addition, the absorbance was measured by pressing the resin particles into close contact with the prism of the total reflection absorption measuring device: ZnSe (PKS-ZnSe) at a pressure of 340 kg/cm ² , and the infrared absorption spectrum on the surface of the resin particles (ATR (with corrections). Next, the maximum absorbance Dsp _A and the maximum absorbance Dsp _B obtained from the infrared absorption spectrum were measured. Then, the surface absorbance ratio i was calculated from these. In addition, after correcting the infrared absorption spectrum so that 3800 cm ^-1 and 2500 cm ^-1 pass through the zero point of absorbance, each absorbance was determined. In addition, in calculating the above-mentioned surface absorbance ratio I, cross-sectional absorbance ratio II, surface absorbance half-width ratio III, cross-sectional absorbance half-width ratio IV, and surface absorbance ratio i, similar measurements were performed on 10 foamed particles and resin particles. Among the measured values such as the absorbance ratio obtained, the average value of eight measured values excluding the maximum and minimum values was determined, and this value was adopted as the absorbance ratio etc.
In addition, the measurement of infrared absorption spectra on the surface of the expanded particles and the surface of the resin particles was performed on a surface other than the edge surface of the expanded particles or resin particles (a surface other than the surface perpendicular to the extrusion direction of the strand during resin particle production). Measurements were made for.

<Amount of dispersant (anti-blocking agent) attached>
The amount of the dispersant (antiblocking agent) adhering to the surface of the one-stage foamed particles (the foamed particles before two-stage foaming) was measured as follows.
First, the foamed polyamide resin particles were vacuum dried in an oven at 60° C. for 24 hours, and then immediately placed in a desiccator and left under a nitrogen atmosphere for 72 hours. Next, the weight of 100 g of the expanded beads taken out from the desiccator was accurately measured to three decimal places to determine the weight (F) of the expanded beads in g.
Next, the entire amount of the foamed particles used in the above measurement was immersed in 5L of 1N hydrochloric acid solution to wash the foamed particles, then immersed in 5L of ion-exchanged water to wash off the hydrochloric acid solution, and then 5L of 1N hydroxide solution. After washing the expanded particles by immersing them in a sodium aqueous solution, they were immersed in 5 L of ion-exchanged water to wash off the sodium hydroxide. After repeating this operation twice, the entire amount of the foamed particles was vacuum-dried in an oven at 60° C. for 24 hours, and then immediately placed in a desiccator and left to stand under a nitrogen atmosphere for 72 hours. Subsequently, the weight (S) g of the washed expanded particles was determined in the same manner as above.
The difference between the weight (F) and the weight (S) was taken as the amount of dispersant attached to the surface of the foamed particles, and this was converted into the amount (parts by mass) of the dispersant attached per 100 parts by mass of the foamed particles.
<Blocking evaluation during two-stage foaming>
The presence or absence of blocking of the two-stage expanded particles was evaluated based on the following criteria.
None: When 300 g of two-stage foamed particles are passed through a 3.5 mesh (5.6 mm) screen, the weight of the two-stage foamed particles remaining on the screen is the weight of the two-stage foamed particles placed on the screen. less than half of
Yes: When 300 g of two-stage foamed particles are passed through a 3.5 mesh (5.6 mm) screen, the weight of the two-stage foamed particles remaining on the screen is the weight of the two-stage foamed particles placed on the screen. more than half of
<Apparent density of two-stage expanded particles>
The apparent density of the two-stage expanded particles was measured in the same manner as the method for measuring the apparent density in the evaluation of the polyamide resin expanded particles described above, except that the two-stage expanded particles were used.
<Heat resistance evaluation of expanded particles>
Using a razor, the single-stage expanded particles were cut into approximately two equal parts through the center. One of the expanded particles (measured The sample) was compressed with its cross section facing down under high temperature conditions. Specifically, when the initial load was 500 mN and the temperature of the probe was raised from 30°C to 200°C at a rate of 5°C/min, the probe indentation depth (displacement amount) was monitored, and the The thickness (Ta) of the sample at 30°C) and the thickness (Tb) of the sample at 130°C were determined.
These values were substituted into the following equation (2) to determine the dimensional change rate of the expanded particles.
[Number 2]
Dimensional change rate (%) = 100 x (1-Tb/Ta)...(2)

[Evaluation of polyamide resin expanded particle molded product]
Both a foamed particle molded article molded using expanded particles that were not multi-stage expanded and a foamed particle molded article molded using two-stage expanded beads were evaluated.
<Apparent density of expanded particle molded product>
The value obtained by dividing the mass of the expanded particle molded object obtained by in-mold molding by the apparent volume calculated based on the external dimensions was defined as the apparent density of the expanded particle molded object.
<Fusionability evaluation>
The foamed particle molded product obtained by in-mold molding was fractured, the fractured surface was observed, and the number of foamed particles whose material was fractured and the number of foamed particles separated at the interface were counted.
Next, the ratio of the foamed particles with material destruction to the total number of foamed particles with material destruction and foamed particles separated at the interface was calculated, and the value expressed as a percentage was taken as the fusion rate (%).
The case where the fusion rate was 80% or more was marked as "○", and the case where it was less than 80% was marked as "x".

<Tensile test> (Tensile maximum point load)
From the expanded particle molded bodies obtained in Example 1, Comparative Example 2, and Comparative Example 3, samples with a thickness of 10 mm with a dumbbell-like No. 1 shape specified in JIS K6251 (2010) were cut out, and samples with a thickness of 10 mm were cut out according to JIS K6767 (1999). The measurement was carried out in accordance with the method for measuring tensile elongation. Note that the above sample was cut out so as not to include the skin layer of the expanded particle molded product.
For the measurement, the sample was left for 24 hours under conditions of 23° C. and 50% humidity, and then a tensile test was performed at a test speed of 500 mm/min to measure the maximum point stress. The above measurement was performed five times, and the arithmetic average value of the obtained values was adopted as the tensile strength.
As a result of the tensile test, the tensile strength of the expanded particle molded article in Example 1 was 0.99 MPa, and the tensile strength of the polyamide resin expanded particle molded article consisting of two-stage expanded particles was 0.49 MPa. Further, in Comparative Example 2, the tensile strength of the expanded particle molded product was 0.34 MPa, and the tensile strength of the polyamide resin expanded particle molded product made of two-stage expanded particles was 0.24 MPa. Further, the tensile strength of the expanded particle molded article in Comparative Example 3 was 0.83 MPa.
From these results, the expanded particle molded product obtained in Example 1 showed superior tensile strength to the expanded particle molded products obtained in Comparative Examples 2 and 3.

The above embodiment includes the following technical ideas.
(1) Polyamide resin foam particles,
The flexural modulus of the polyamide resin constituting the expanded particles is 1000 MPa or more,
Foamed polyamide resin particles characterized in that the ratio I/R, which is the ratio of the surface absorbance ratio I below to the resin absorbance ratio R below, is 1.0 or more.
Resin absorbance ratio R: maximum absorbance Dr _B at wave numbers 1320 to 1400 cm ^-1 and wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the polyamide resin constituting the expanded particles, measured by total reflection absorption infrared spectroscopy The absorbance ratio Dr _A /Dr _B with the maximum absorbance Dr _A at
Surface absorbance ratio I: Maximum absorbance Ds _B at wave numbers 1320 to 1400 cm ^-1 and maximum absorbance at wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the surface of the expanded particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with Ds _A is Ds _A /Ds _B.
(2) is the ratio of the surface absorbance ratio I to the cross-sectional absorbance ratio II below,
The polyamide resin foam particles according to (1) above, wherein the ratio I/II is 0.90 or more.
Cross-sectional absorbance ratio II: Maximum absorbance Dc B at wave numbers 1320 to 1400 cm ^-1 and maximum absorbance Dc _B at wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the central cross section of the expanded particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with absorbance Dc _A is Dc _A /Dc _B.
(3) is the ratio of the cross-sectional absorbance ratio II to the resin absorbance ratio R;
The expanded polyamide resin particles according to (2) above, wherein the ratio II/R is 1.0 or more.
(4) The expanded polyamide resin particles according to any one of (1) to (3) above, wherein the expanded particles have a crystallinity of 20% or more and 50% or less.
(5) The expanded polyamide resin particles according to any one of (1) to (4) above, wherein the expanded particles have an apparent density of 10 kg/m ³ or more and 300 kg/m ³ or less.
(6) A method for producing expanded polyamide resin particles according to any one of (1) to (5) above, comprising:
a crystallization promotion step of heating the polyamide resin particles to promote crystallization of the surface layer of the polyamide resin particles;
A method for producing expanded polyamide resin particles, comprising the step of foaming the polyamide resin particles that have undergone the crystallization promotion step to obtain expanded polyamide resin particles.
(7) In the crystallization promotion step, polyamide resin particles having a ratio i/r of less than 0.97, which is the ratio of the following surface absorbance ratio i to the following resin absorbance ratio r, are heat-treated. The method for producing expanded polyamide resin particles according to (6) above, wherein the ratio i/r of the polyamide resin particles is 0.97 or more;
The resin absorbance ratio r is the maximum absorbance Drp B at a wave number of 1320 to 1400 cm ^-1 and the maximum absorbance Drp _B at a wave number of 3250 to 3350 cm ^- in the infrared absorption spectrum of the polyamide resin constituting the resin particles, which is measured by total reflection absorption infrared spectroscopy. The absorbance ratio Drp _A /Drp _B with the maximum absorbance Drp _A at ¹ is
Surface absorbance ratio i: Maximum absorbance Dsp _B at wave numbers 1320 to 1400 cm ^-1 and maximum absorbance at wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the surface of the resin particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with Dsp _A is Dsp _A /Dsp _B.
(8) In the crystallization promotion step, the polyamide resin particles are heat-treated in a gas phase at a temperature ranging from 100°C lower than the melting point of the polyamide resin particles to 20°C lower than the melting point. The method for producing expanded polyamide resin particles according to (6) or (7) above, which is carried out by:
(9) The crystallization promotion step involves dispersing the polyamide resin particles in an aqueous medium in a closed container, and increasing the temperature from 80°C lower than the melting point of the polyamide resin particles to 50°C lower than the melting point. The method for producing foamed polyamide resin particles according to (6) or (7) above, which is carried out by heat-treating the polyamide resin particles within the range of (6) or (7).
(10) In the foaming step, the polyamide resin particles that have undergone the crystallization promotion step are dispersed in an aqueous medium in a closed container, and the temperature ranges from a temperature 80° C. lower than the melting point of the polyamide resin particles to a temperature lower than the melting point. According to any one of (6) to (9) above, the method is performed by releasing the contents of the sealed container into a pressure range lower than the internal pressure of the sealed container at a temperature up to 50°C lower. A method for producing expanded polyamide resin particles.
(11) an antiblocking agent is added together with the polyamide resin particles in the airtight container;
The expanded polyamide resin particles according to (9) or (10) above, wherein the amount of the antiblocking agent added is 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the polyamide resin particles. Production method.
(12) A method for producing expanded polyamide resin particles according to any one of (1) to (5) above, comprising:
a foaming step of foaming polyamide resin particles to obtain expanded polyamide resin particles;
A method for producing expanded polyamide resin particles, comprising the step of promoting crystallization of the surface layer portion of the expanded polyamide resin particles by heat-treating the expanded polyamide resin particles.

10... Crystallization promotion step 20... Foaming step 210... First holding 220... Second holding T0... Room temperature T1... Foaming temperature T3... Melting point temperature t1, t2...・Required time

Claims (12)

Polyamide resin foam particles,
The flexural modulus of the polyamide resin constituting the expanded particles is 1000 MPa or more,
Foamed polyamide resin particles characterized in that the ratio I/R, which is the ratio of the surface absorbance ratio I below to the resin absorbance ratio R below, is 1.0 or more.
Resin absorbance ratio R: Maximum absorbance Dr _B at wave numbers 1320 to 1400 cm ^-1 and wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the polyamide resin constituting the expanded particles, measured by total reflection absorption infrared spectroscopy. It is the absorbance ratio Dr _A /Dr _B with the maximum absorbance Dr _A at .
Surface absorbance ratio I: Maximum absorbance Ds _B at wave numbers 1320 to 1400 cm ^-1 and maximum absorbance at wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the surface of the foamed particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with Ds _A is Ds _A /Ds _B. The foamed polyamide resin particles according to claim 1, wherein the ratio I/II, which is the ratio of the surface absorbance ratio I to the cross-sectional absorbance ratio II below, is 0.90 or more.
Cross-sectional absorbance ratio II: Maximum absorbance Dc B at wave numbers 1320 to 1400 cm ^-1 and maximum absorbance Dc _B at wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the central cross section of the expanded particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with absorbance Dc _A is Dc _A /Dc _B. The foamed polyamide resin particles according to claim 2, wherein the ratio II/R, which is the ratio of the cross-sectional absorbance ratio II to the resin absorbance ratio R, is 1.0 or more. The expanded polyamide resin particles according to any one of claims 1 to 3, wherein the expanded particles have a crystallinity of 20% or more and 50% or less. The expanded polyamide resin particles according to any one of claims 1 to 4, wherein the expanded particles have an apparent density of 10 kg/m ³ or more and 300 kg/m ³ or less. A method for producing expanded polyamide resin particles according to any one of claims 1 to 5, comprising:
a crystallization promotion step of heating the polyamide resin particles to promote crystallization of the surface layer of the polyamide resin particles;
A method for producing expanded polyamide resin particles, comprising the step of foaming the polyamide resin particles that have undergone the crystallization promotion step to obtain expanded polyamide resin particles. In the crystallization promotion step, polyamide resin particles having a ratio i/r, which is the ratio of the following surface absorbance ratio i to the following resin absorbance ratio r, is less than 0.97 are heat-treated, so that the polyamide resin after the heat treatment is The method for producing expanded polyamide resin particles according to claim 6, wherein the ratio i/r of the particles is 0.97 or more.
Resin absorbance ratio r: Maximum absorbance Drp _B at wave numbers 1320 to 1400 cm ^-1 and wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the polyamide resin constituting the resin particles, measured by total reflection absorption infrared spectroscopy. Drp _A /Drp _B is the absorbance ratio with the maximum absorbance Drp _A at .
Surface absorbance ratio i: Maximum absorbance Dsp _B at wave numbers 1320 to 1400 cm ^-1 and maximum absorbance at wave numbers 3250 to 3350 cm ^-1 in the infrared absorption spectrum of the surface of the resin particles, measured by total reflection absorption infrared spectroscopy. The absorbance ratio with Dsp _A is Dsp _A /Dsp _B. In the crystallization promotion step, the polyamide resin particles are heat-treated in a gas phase at a temperature ranging from 100° C. lower than the melting point of the polyamide resin particles to 20° C. lower than the melting point. The method for producing expanded polyamide resin particles according to claim 6 or 7, wherein the method is carried out. The crystallization promotion step involves dispersing the polyamide resin particles in an aqueous medium in a closed container at a temperature ranging from 80°C lower than the melting point of the polyamide resin particles to 50°C lower than the melting point. The method for producing expanded polyamide resin particles according to claim 6 or 7, which is carried out by heat-treating the polyamide resin particles. In the foaming step, the polyamide resin particles that have undergone the crystallization promotion step are dispersed in an aqueous medium in a closed container, and the temperature ranges from 80° C. lower than the melting point of the polyamide resin particles to 50° C. lower than the melting point. The foamed polyamide resin particles according to any one of claims 6 to 9, which is carried out by releasing the contents of the closed container into a pressure region lower than the internal pressure of the closed container, Production method. An antiblocking agent is added together with the polyamide resin particles in the airtight container,
The method for producing expanded polyamide resin particles according to claim 9 or 10, wherein the amount of the antiblocking agent added is 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the polyamide resin particles. A method for producing expanded polyamide resin particles according to any one of claims 1 to 5, comprising:
a foaming step of foaming polyamide resin particles to obtain expanded polyamide resin particles;
A method for producing expanded polyamide resin particles, comprising the step of promoting crystallization of the surface layer portion of the expanded polyamide resin particles by heat-treating the expanded polyamide resin particles.

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