Patent Description:
The present application claims priorities based on <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

Since an expanded molded article is good in processability and shape retainability, and has a relatively high strength, in addition to being light, it is used in various fields such as a building material, a civil engineering material, and lighting equipment, including a food tray and an automobile member. In particular, when heat resistance is not required, an expanded molded article made of a polystyrene-based resin tends to be used, and when buffering property, restorability, softness, and the like are necessary, an expanded molded article made of an olefin-based resin such as polypropylene and polyethylene tends to be used.

As a resin that has generally heat resistance higher than that of these polystyrene-based resin and olefin-based resin, there is a polycarbonate-based resin. This is a resin material that can also be utilized in places of severe weather such as an and zone and a tropical zone. This polycarbonate-based resin is not only excellent in heat resistance, but also excellent in water resistance, electric property, mechanical strength, aging resistance, and chemical resistance. For that reason, the polycarbonate-based resin has previously been used as an interior material of a building, and in recent years, use development towards an automobile member, a packaging material, various containers or the like, utilizing excellent properties thereof is also expected.

Meanwhile, as a method of producing an expanded molded article of a polycarbonate-based resin, for example, an in-die expansion molding method of expanding and fusing expanded particles in a die is known. In this method, by preparing a die having a space corresponding to a desired shape, filling expanded particles into the space, and expanding and fusing the expanded particles by heating, an expanded molded article having a complicated shape can be obtained. However, in this method, there has been a problem that an appearance of the expanded molded article is not good, and fusion between expanded particles is also not sufficient.

Therefore, the applicant of the present application has proposed the technique of providing an expanded molded article having a good appearance, by improving fusibility between expanded particles (see Patent Document <NUM>).

In addition, as an expanded molded article by an in-die expansion molding method, one comprising a polystyrene-based resin as a base resin (for example, see Patent Document <NUM>), and one comprising a polyolefin-based resin as a base resin (for example, see Patent Document <NUM>), and the like are known.

Patent Documents <NUM> and <NUM> disclose aromatic polycarbonate expanded particles and an expanded molded article obtained therefrom.

In Patent Document <NUM>, the expanded molded article having a good appearance is obtained, but provision of an expanded molded article having a further good appearance and a higher mechanical strength by further improving fusibility between expanded particles has been desired.

In addition, the expanded molded article comprising a polystyrene-based resin or a polyolefin-based resin as a base resin has a good mechanical strength around an ambient temperature (about <NUM>), but under the environment of a lower temperature or a higher temperature, a mechanical strength is sometimes reduced. For that reason, provision of an expanded molded article, a variation of a mechanical strength of which is suppressed even when an environmental temperature changes, has been desired.

In view of the above-mentioned problems, the present inventors have studied a polycarbonate-based resin to be used, and as a result, unexpectedly found out that by regulating a bulk ratio and an average cell diameter of expanded particles to specified ranges, an appearance and a mechanical strength of an expanded molded article obtained from expanded particles can be good, and at the same time, fusibility between expanded particles can be improved.

Thus, according to the present invention, there is provided expanded particles comprising a polycarbonate-based resin having an aromatic skeleton as a base resin, as defined in claim <NUM>.

Furthermore, according to the present invention, there is provided an expanded molded article obtained from the expanded particles.

According to the present invention, there can be provided an expanded molded article comprising a polycarbonate-based resin as a base resin, which is good in an appearance and a mechanical strength, and has improved fusibility, as well as expanded particles of a polycarbonate-based resin, from which an expanded molded article can be produced with good moldability.

In addition, in any of the following cases, there can be provided an expanded molded article comprising a polycarbonate-based resin as a base resin, which has better appearance and mechanical strength, and has further improved fusibility, and expanded particles of a polycarbonate-based resin, from which an expanded molded article can be produced with better moldability.

Furthermore, according to the present invention, there can be provided an expanded molded article, a variation of a mechanical strength of which is suppressed even when an environmental temperature changes.

In addition, in any of the following cases, there can be provided an expanded molded article, a variation of a mechanical strength of which is further suppressed even when an environmental temperature changes.

The expanded particles include first expanded particles, which are not part of the present invention, and second expanded particles, which are part of the present invention. In the present specification, the above-mentioned first expanded particles and second expanded particles are sometimes simply referred to as "expanded particles".

First, the first expanded particles, which are not according to the present invention, comprise a polycarbonate-based resin as a base resin, and have a specified cell density X and a specified average cell wall thickness. The present inventors have found out that by adjusting a cell density X and an average cell wall thickness, an appearance and a mechanical strength of an expanded molded article can be good, and at the same time, fusibility between expanded particles can be further improved.

In addition, the second expanded particles in the present invention comprise a polycarbonate-based resin as a base resin, and have a specified bulk ratio and a specified average cell diameter. The present inventors have found out that by adjusting a bulk ratio and an average cell diameter, an appearance and a mechanical strength of an expanded molded article can be good, and at the same time, fusibility between expanded particles can be further improved.

A cell density X can be <NUM> × <NUM><NUM> pieces/cm<NUM> or more and less than <NUM> × <NUM><NUM> pieces/cm<NUM>. When the cell density X is less than <NUM> × <NUM><NUM> pieces/cm<NUM>, increase in an expansion ratio may become difficult. When the cell density X is <NUM> × <NUM><NUM> pieces/cm<NUM> or more, a cell wall thickness becomes small, and moldability may become deteriorated. A preferable cell density X is <NUM> × <NUM><NUM> pieces/cm<NUM> or more and less than <NUM> × <NUM><NUM> pieces/cm<NUM>, and a more preferable cell density X is <NUM> × <NUM><NUM> pieces/cm<NUM> to <NUM> × <NUM><NUM> pieces/cm<NUM>.

Herein, the cell density X can be calculated by the following expression: <MAT>.

In the expression, C represents an average cell diameter (mm), ρ represents the density (kg/m<NUM>) of a polycarbonate-based resin, and D represents an apparent density (kg/m<NUM>) of expanded particles.

It is preferable that the average cell diameter C is in a range of <NUM> to <NUM>. A more preferable average cell diameter C is <NUM> to <NUM>, and a further preferable cell diameter C is <NUM> to <NUM>.

It is preferable that the density ρ of the polycarbonate-based resin is in a range of <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>. When the density ρ is less than <NUM> × <NUM><NUM> kg/m<NUM>, a heat resisting temperature may be reduced. When the density ρ is greater than <NUM> × <NUM><NUM> kg/m<NUM>, a heat resisting temperature rises, and expansion molding may become difficult. A more preferable density ρ is <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>, and a further preferable density ρ is <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>.

It is preferable that an apparent density D of the expanded particles is in a range of <NUM> to <NUM>/m<NUM>. When the apparent density D is less than <NUM>/m<NUM>, a cell film becomes thin, the cell film breaks at molding, a ratio of an open cell increases, and shrinkage and the like of the expanded particles due to buckling of a cell may be generated. When the apparent density D is greater than <NUM>/m<NUM>, a cell film becomes thick, and moldability may be reduced. A more preferable apparent density D is <NUM> to <NUM>/m<NUM>, and a further preferable apparent density D is <NUM> to <NUM>/m<NUM>.

In addition, it is preferable that a bulk density of the expanded particles is in a range of <NUM> to <NUM>/m<NUM>. When the bulk density is less than <NUM>/m<NUM>, a cell film becomes thin, the cell film breaks at molding, a ratio of an open cell increases, and shrinkage and the like of the expanded particles due to buckling of a cell may be generated. When the bulk density is greater than <NUM>/m<NUM>, a cell film becomes thick, and moldability may be reduced. A more preferable bulk density is <NUM> to <NUM>/m<NUM>, and a further preferable bulk density is <NUM> to <NUM>/m<NUM>.

An average cell wall thickness can be <NUM> to <NUM>. When the average cell wall thickness is less than <NUM>, moldability at molding, particularly fusion may be deteriorated. When the average cell wall thickness is greater than <NUM>, increase in an expansion ratio may become difficult. A preferable average cell wall thickness is <NUM> to <NUM>, and a more preferable average cell wall thickness is <NUM> to <NUM>.

A value obtained by dividing an average cell diameter of expanded particles by a bulk ratio of expanded particles shows a value within a range of <NUM> to <NUM>/times. When the value is less than <NUM>/times, a cell film becomes thin, the cell film breaks at molding, a ratio of an open cell increases, and shrinkage and the like of the expanded particles due to buckling of a cell may be generated. When the value is greater than <NUM>/times, a cell film becomes thick, and moldability may be reduced. The value is more preferably <NUM> to <NUM>/times.

The bulk ratio is in a range of <NUM> to <NUM> times. When the bulk ratio is less than <NUM> times, a cell film becomes thick, and moldability may be reduced. When the bulk ratio is greater than <NUM> times, a cell film becomes thin, the cell film breaks at molding, a ratio of an open cell increases, and shrinkage and the like of the expanded particles due to buckling of a cell may be generated. The bulk ratio is more preferably <NUM> to <NUM> times, further preferably <NUM> to <NUM> times.

The average cell diameter is in a range of <NUM> to <NUM>. When the average cell diameter is less than <NUM>, a cell film becomes thin, and the cell film breaks at molding, a ratio of an open cell increases, and shrinkage and the like of the expanded particles due to buckling of a cell may be generated. When the average cell diameter is greater than <NUM>, a cell film becomes thick, and moldability may be reduced. The average cell diameter is more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>.

It is preferable that a cell number density shows <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> pieces/cm<NUM>. When the cell number density is less than <NUM> × <NUM><NUM> pieces/cm<NUM>, increase in an expansion ratio may become difficult. When the cell number density is <NUM> × <NUM><NUM> pieces/cm<NUM> or more, a cell wall thickness becomes small, and moldability may be deteriorated. The cell number density is more preferably <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> pieces/cm<NUM>.

Herein, the cell number density can be calculated by the following expression: <MAT>.

It is preferable that the density ρ of a polycarbonate-based resin is in a range of <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>. When the density ρ is less than <NUM> × <NUM><NUM> kg/m<NUM>, a heat resisting temperature may be reduced. When the density ρ is greater than <NUM> × <NUM><NUM> kg/m<NUM>, a heat resisting temperature rises, and expansion molding may become difficult. The density ρ is more preferably <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>, further preferably <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> kg/m<NUM>.

It is preferable that an apparent density D of the expanded particles is in a range of <NUM> to <NUM>/m<NUM>. When the apparent density D is less than <NUM>/m<NUM>, a cell film becomes thin, the cell film breaks at molding, a ratio of an open cell increases, and shrinkage and the like of the expanded particles due to buckling of a cell may be generated. When the apparent density D is greater than <NUM>/m<NUM>, a cell film becomes thick, and moldability may be reduced. The apparent density D is more preferably <NUM> to <NUM>/m<NUM>, further preferably <NUM> to <NUM>/m<NUM>.

It is preferable that an average cell wall thickness is in a range of <NUM> to <NUM>. When the average cell wall thickness is less than <NUM>, moldability at molding, particularly fusion may be deteriorated. When the average cell wall thickness is greater than <NUM>, increase in an expansion ratio may become difficult. The average cell wall thickness is more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>.

The open cell rate is <NUM> to <NUM>%. When the open cell rate is greater than <NUM>%, moldability of the expanded molded article may be reduced. It is more preferable that the open cell rate is <NUM> to <NUM>%.

A polycarbonate-based resin that becomes a base resin of the expanded particles may be a straight polycarbonate-based resin, or may be a branched polycarbonate-based resin.

It is preferable that the polycarbonate-based resin has a polyester structure of a carbonic acid, and a glycol or a dihydric phenol. From a view point that heat resistance is further enhanced, the polycarbonate-based resin has an aromatic skeleton. Examples of the polycarbonate-based resin include polycarbonate resins derived from bisphenol, such as <NUM>,<NUM>-bis(<NUM>-oxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-oxyphenyl)butane, <NUM>,<NUM>-bis(<NUM>-oxyphenyl)cyclohexane, <NUM>,<NUM>-bis(<NUM>-oxyphenyl)butane, <NUM>,<NUM>-bis(<NUM>-oxyphenyl)isobutane, and <NUM>,<NUM>-bis(<NUM>-oxyphenyl)ethane, and the like.

The polycarbonate-based resin may contain resins other than a polycarbonate resin. Examples of other resins include an acrylic-based resin, a saturated polyester-based resin, an ABS-based resin, a polystyrene-based resin, a polyolefin-based resin, a polyphenylene oxide-based resin, and the like. It is preferable that the polycarbonate-based resin contains <NUM>% by weight or more of the above-mentioned polycarbonate resin.

In addition, the polycarbonate-based resin has MFR of preferably <NUM> to <NUM>/<NUM>, more preferably <NUM> to <NUM>/<NUM>. Resins in this range are suitable for expansion, and more easily cause high expansion. Furthermore, the polycarbonate-based resin has MFR of preferably <NUM> to <NUM>/<NUM>, more preferably <NUM> to <NUM>/<NUM>, further preferably <NUM> to <NUM>/<NUM>. Resins in this range can suitably realize a variability rate X of the expanded molded article, described later.

A shape of the expanded particles is not particularly limited. Examples thereof include a spherical shape, a cylindrical shape, and the like. It is preferable that, among them, the shape is as close to a spherical shape as possible. That is, it is preferable that a ratio of a short diameter and a long diameter of the expanded particles is as close to <NUM> as possible.

It is preferable that the expanded particles have an average particle diameter of <NUM> to <NUM>. The average particle diameter is a value expressed by D50, obtained by classification using a Ro-Tap type sieve shaker.

Expanded particles can be obtained by impregnating a blowing agent into resin particles to obtain expandable particles, and expanding the expandable particles.

Expandable particles can be obtained by impregnating a blowing agent into resin particles made of a polycarbonate-based resin.

The resin particles can be obtained by the known method. Examples thereof include a method of granulation by melting and kneading a polycarbonate-based resin together with other additives as necessary in an extruder, and extruding the kneaded product to obtain a strand, and cutting the resulting strand in the air, in water, and while heating. As the resin particles, commercially available resin particles may be used. If necessary, additives other than the resin may be contained in the resin particles. Examples of other additives include a plasticizer, a flame retardant, a flame retardant aid, an antistatic agent, a spreading agent, a cell adjusting agent, a filler, a colorant, a weather-resistant agent, an aging preventing agent, an antioxidant, an ultraviolet absorbing agent, a lubricant, an antifogging agent, a perfume, and the like.

Next, as the blowing agent to be impregnated into the resin particles, the known volatile blowing agent or inorganic blowing agent can be used. Examples of the volatile blowing agent include an aliphatic hydrocarbon such as propane, butane, and pentane, an aromatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic alcohol, and the like. Examples of the inorganic blowing agent include a carbonic acid gas, a nitrogen gas, the air, an inert gas (helium, argon, and the like), and the like. Two or more kinds of these blowing agents may be used together. Among these blowing agents, the inorganic blowing agent is preferable, and a carbonic acid gas is more preferable.

It is preferable that the content (impregnation amount) of the blowing agent is <NUM> to <NUM> parts by weight, based on <NUM> parts by weight of the polycarbonate-based resin. When the content of the blowing agent is less than <NUM> parts by weight, an expanding power becomes low, and good expansion may be difficult. When the content exceeds <NUM> parts by weight, the plasticizing effect becomes great, shrinkage easily occurs at expansion, the productivity may be deteriorated, and at the same time, it may become difficult to stably obtain a desired expansion ratio. The more preferable content of the blowing agent is <NUM> to <NUM> parts by weight.

Examples of an impregnation method include a wet-type impregnation method of dispersing resin particles in a water system, and pressing a blowing agent therein while stirring, to thereby impregnate the blowing agent, a dry-type impregnation method substantially not using water (gaseous phase impregnation method), of placing the resin particles into a sealable container, and pressing a blowing agent therein to impregnate the blowing agent, and the like. In particular, a dry-type impregnation method by which impregnation can be performed without using water is preferable. An impregnation pressure, an impregnation time, and an impregnation temperature when the blowing agent is impregnated into the resin particles are not particularly limited.

From a view point that impregnation is effectively performed, and further good expanded particles and expanded molded article are obtained, it is preferable that an impregnation pressure is <NUM> to <NUM> MPa (gauge pressure). <NUM> to <NUM> MPa (gauge pressure) is more preferable.

It is preferable that an impregnation time is <NUM> to <NUM> hours. When the impregnation time is shorter than <NUM> hours, since an impregnation amount of the blowing agent into the resin particles is reduced, it may difficult to obtain a sufficient expanding powder. When the impregnation time is longer than <NUM> hours, the productivity may be reduced. A more preferable impregnation time is <NUM> to <NUM> hours.

It is preferable that an impregnation temperature is <NUM> to <NUM>. When an impregnation temperature is lower than <NUM>, solubility of the blowing agent in the resin is enhanced, and a more than necessary blowing agent is impregnated. In addition, diffusing property of the blowing agent in the resin is deteriorated. Hence, it may be difficult to obtain a sufficient expanding power (primary expanding power) in a desired time. When the impregnation temperature is higher than <NUM>, solubility of the blowing agent in the resin is reduced, and an impregnation amount of the blowing agent is reduced. In addition, diffusing property of the blowing agent in the resin is enhanced. Hence, it may be difficult to obtain a sufficient expanding power (primary expanding power) in a desired time. A more preferable impregnation temperature is <NUM> to <NUM>.

A surface treating agent such as a bonding preventing agent (coalescence preventing agent), an antistatic agent, and a spreading agent may be added to an impregnation product.

The bonding preventing agent has a function of preventing coalescence between expanded particles. Herein, coalescence refers to unification and integration of a plurality of expanded particles. Specific examples of the bonding preventing agent include talc, calcium carbonate, aluminum hydroxide, and the like.

Examples of the antistatic agent include polyoxyethylene alkyl phenol ether, stearic acid monoglyceride, and the like.

Examples of the spreading agent include polybutene, polyethylene glycol, silicone oil, and the like.

As a method of expanding expandable particles to obtain expanded particles (primary expanded particles), there is a method of heating expandable particles with the hot air, a heat medium such as oil, steam (water steam) or the like to expand it. In order to stably produce expanded particles, steam is preferable.

It is preferable that a sealed pressure-resistant expansion container is used in an expanding machine at expansion. In addition, a pressure of steam is preferably <NUM> to <NUM> MPa (gauge pressure), more preferably <NUM> to <NUM> MPa (gauge pressure). An expansion time is enough if it is a necessary time for obtaining a desired expansion ratio. A preferable expansion time is <NUM> to <NUM> seconds. When the expansion time exceeds <NUM> seconds, shrinkage of the expanded particles may begin, and from such expanded particles, an expanded molded article having good physical properties may not be obtained.

The above-mentioned bonding preventing agent may be removed before molding. As a removing method, it is preferable to perform washing using water, or an acidic aqueous solution such as hydrochloric acid.

By adjusting impregnation conditions (impregnation pressure, impregnation time, impregnation temperature) and primary expansion conditions (expansion pressure, expansion time) of the above-mentioned steps of producing expanded particles, a cell density X and an average cell wall thickness can be large or small.

By adjusting impregnation conditions (impregnation pressure, impregnation time, impregnation temperature) and primary expansion conditions (expansion pressure, expansion time) of the above-mentioned steps of producing expanded particles, a bulk ratio and an average cell diameter can be large or small.

An expanded molded article is obtained from a plurality of expanded particles comprising a polycarbonate-based resin as a base resin. Herein, it is preferable that expanded particles are any one selected from the group consisting of the above-mentioned first expanded particles and second expanded particles.

A cell density X is calculated from expanded particles constituting an expanded molded article. The cell density X can be calculated from the following expression: <MAT> in the same manner as the above-mentioned expanded particles. Herein, D is the density of an expanded molded article.

The cell density X can be <NUM> × <NUM><NUM> pieces/cm<NUM> or more and less than <NUM> × <NUM><NUM> pieces/cm<NUM>. The reason why the cell density X was in a specified range is the same as the reason for the above-mentioned expanded particles. A preferable range and a more preferable range of the cell density X are the same as each of those for the above-mentioned expanded particles.

Furthermore, a preferable range, the reason why the range was selected, a more preferable range, and a further preferable range of each of an average cell diameter C and the density ρ of a polycarbonate-based resin are the same as each of those for the above-mentioned expanded particles.

It is preferable that density D of the expanded molded article is in a range of <NUM> to <NUM>/m<NUM>. When the density D is less than <NUM>/m<NUM>, a cell film becomes thin, the cell film breaks at molding, a ratio of an open cell increases, and this may lead to deterioration of the strength as a molded article. When the density D is greater than <NUM>/m<NUM>, a cell film becomes thick, and moldability may be reduced. A more preferable density D is <NUM> to <NUM>/m<NUM>, and a further preferable density D is <NUM> to <NUM>/m<NUM>.

An average cell wall thickness can be <NUM> to <NUM>. The reason why the average cell wall thickness was in a specified range is the same as the reason for the above-mentioned expanded particles. A preferable range and a more preferable range of the average cell wall thickness are the same as each of those for the above-mentioned expanded particles.

A value obtained by dividing an average cell diameter of an expanded molded article by a ratio of an expanded molded article shows a value within a range of <NUM> to <NUM>/times. When the value is less than <NUM>/times, a cell film becomes thin, shrinkage and the like of expanded particles due to buckling of a cell are generated, and as a result, a mechanical strength of an expanded molded article may be reduced. When the value is greater than <NUM>/times, a cell film becomes thick, moldability is reduced, and as a result, a mechanical strength of an expanded molded article may be reduced. The value is preferably <NUM> to <NUM>/times, more preferably <NUM> to <NUM>/times.

It is preferable that the ratio is in a range of <NUM> to <NUM> times. When the ratio is less than <NUM> times, a cell film becomes thick, and moldability may be reduced, or fusibility between expanded particles at molding may be reduced. When the ratio is greater than <NUM> times, a cell film becomes thin, the cell film breaks at molding, a ratio of an open cell increases, and this may lead to deterioration of the strength as a molded article. The ratio is more preferably <NUM> to <NUM> times, further preferably <NUM> to <NUM> times.

A cell number density X is calculated from expanded particles constituting an expanded molded article. The cell number density can be calculated from the following expression: <MAT> in the same manner as the above-mentioned expanded particles. Herein, D is the density of an expanded molded article.

It is preferable that the cell number density X shows <NUM> × <NUM><NUM> to <NUM> × <NUM><NUM> pieces/cm<NUM>. When the cell number density is out of the above-mentioned specified range, moldability may be deteriorated, and a mechanical strength may be reduced. A preferable range and a more preferable range of the cell number density are the same as each of those for the above-mentioned expanded particles.

It is preferable that the density D of the expanded molded article is in a range of <NUM> to <NUM>/m<NUM>. When the density D is less than <NUM>/m<NUM>, a cell film becomes thin, the film breaks at molding, a ratio of an open cell increases, and this may lead to deterioration of the strength as a molded article. When the density D is greater than <NUM>/m<NUM>, a cell film becomes thick, and moldability may be reduced, or fusibility between expanded particles at molding may be reduced. The density D is more preferably <NUM> to <NUM>/m<NUM>, further preferably <NUM> to <NUM>/m<NUM>.

It is preferable that the expanded molded article has an average cell wall thickness in a range of <NUM> to <NUM>. When the average cell wall thickness is less than <NUM>, moldability at molding, particularly fusion may be deteriorated. When the average cell wall thickness is greater than <NUM>, increase in an expansion ratio may become difficult. The average cell wall thickness is more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>.

It is preferable that an open cell rate is <NUM> to <NUM>%. When the open cell rate is greater than <NUM>%, a mechanical strength may be reduced. The open cell rate is more preferably <NUM> to <NUM>%, further preferably <NUM> to <NUM>%, particularly preferably <NUM> to <NUM>%.

It is preferable that an expansion ratio is in a range of <NUM> to <NUM> times. When the ratio is less than <NUM> times, a cell film of expanded particles becomes thick, and fusibility between expanded particles may be reduced at molding. When the ratio is greater than <NUM> times, a cell film becomes thin, the cell film breaks at expansion, a ratio of an open cell increases, and this may lead to deterioration of the strength as a molded article. The ratio is more preferably <NUM> to <NUM> times, further preferably <NUM> to <NUM> times.

When a value of a maximum point stress of a bending test at four points is measured at each temperature of -<NUM>, <NUM>, <NUM>, and <NUM>, and an average of the value of a maximum point stress of a bending test at four points is calculated, the expanded molded article shows a variability rate X of the value of a maximum point stress of a bending test at four points to the average within a range of <NUM> to <NUM>%.

In addition, when values of a maximum point stress of a bending test at four points are expressed as A, B, C, and D, the variability rate X is calculated by the following procedure. First, regarding A, an individual variability rate XA is calculated by the following expression: <MAT>.

Similarly, also regarding B, C, and D, individual variability rates XB, XC and XD are calculated. A greatest value among the resulting four individual variability rates is defined as a variability rate X.

The present inventors have found out that by showing this variability rate X by the expanded molded article, the expanded molded article can be provided in which a variation of a mechanical strength thereof is suppressed even when an environmental temperature changes. When the variability rate X is out of a range of <NUM> to <NUM>%, it is difficult to obtain the expanded molded article in which a change of a mechanical strength thereof due to a change in an environmental temperature is suppressed. The variability rate X is preferably within a range of <NUM> to <NUM>%, more preferably within a range of <NUM> to <NUM>%.

For example, it is preferable that a maximum point stress of a bending test at <NUM> is <NUM> MPa to <NUM> MPa. When the maximum point stress of a bending test is less than <NUM> MPa, the strength is deficient, and the expanded molded article may become unable to stand impact or the like. When the maximum point stress of a bending test is greater than <NUM> MPa, the expanded molded article may be easily broken at the time of impact. The maximum point stress of a bending test is more preferably <NUM> to <NUM> MPa, further preferably <NUM> to <NUM> MPa.

It is preferable that, when "maximum point stress of bending test/density" at four points is calculated by dividing the values of four points of a maximum point stress of a bending test at each temperature of -<NUM>, <NUM>, <NUM>, and <NUM> by the density of the expanded molded article, respectively, and an average of the "maximum point stress of bending test/density" at four points is calculated, the expanded molded article shows a variability rate Y of the value of "maximum point stress of bending test/density" at four points to the average within a range of <NUM> to <NUM>%. By having this variability rate, the expanded molded article that is more resistant to change in an environmental temperature can be provided. The variability rate Y is preferably within a range of <NUM> to <NUM>%, more preferably within a range of <NUM> to <NUM>%.

In addition, an average of "maximum point stress of bending test/density" at four points can be calculated by the following expression: <MAT> when a set of a maximum point stress of a bending test and the density of four points are expressed as A and a, B and b, C and c, and D and d.

A variability rate Y is calculated by the following procedure, when a set of a maximum point stress of a bending test and the density of four points are expressed as A and a, B and b, C and c, and D and d. First, regarding A and a, an individual variability rate YAa is calculated by the following expression: <MAT>.

Similarly, also regarding B and b, C and c, and D and d, individual variability rates YBb, YCc, and YDd are calculated. A greatest value among the resulting four individual variability rates is defined as a variability rate Y.

The density is preferably <NUM> to <NUM>/m<NUM>, more preferably <NUM> to <NUM>/m<NUM>.

It is preferable for the expanded molded article that "maximum point stress of bending test" at -<NUM> shows a change degree Z that changes within a range of <NUM> to <NUM>, to "maximum point stress of bending test" at <NUM>. By having this change degree, the expanded molded article that is more resistant to change in an environmental temperature can be provided. The change degree Z is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>.

In addition, the change degree Z can be calculated by the following expression: <MAT>.

In addition, it is preferable for the expanded molded article that "maximum point stress of bending test" at <NUM> shows the change degree Z' that changes within a range of <NUM> to <NUM>, to "maximum point stress of bending test" at <NUM>. By having this change degree, the expanded molded article that is more resistant to change in an environmental temperature can be provided. The change degree Z' is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>.

In addition, the change degree Z' can be calculated by the following expression: <MAT>.

As a polycarbonate-based resin, the same polycarbonate-based resin as that for the above-mentioned expanded particles can be used.

The expanded molded article can take various shapes depending on use, without particular limitation. For example, the expanded molded article can take various shapes depending on uses such as a building material (civil engineering related, housing related, and the like), a part of transportation equipment such as an automobile, an aircraft, a railway vehicle, and a ship, a structural member such as a windmill and a helmet, a packaging material, and a core material of FRP as a composite member.

From a view point that a variation of a mechanical strength is suppressed even when an environmental temperature changes, examples of the part of an automobile include, for example, parts used in the proximity of engines, exterior materials, and the like. Examples of the part of an automobile include, for example, parts such as a floor panel, a roof, a bonnet, a fender, an undercover, a wheel, a steering wheel, a container (housing), a hood panel, a suspension arm, a bumper, a sun visor, a trunk lid, a luggage box, a seat, a door, and a cowl.

The expanded molded article can be obtained, for example, by imparting a cell enlarging power to the above-mentioned expanded particles, and then, subjecting these expanded particles to a molding step.

It is preferable that before producing of the expanded molded article, a blowing agent is impregnated into the expanded particles to impart an expanding power thereto (secondary expanding power).

Examples of an impregnation method include a wet-type impregnation method of dispersing the expanded particles in a water system, and pressing a blowing agent therein while stirring, to thereby impregnate the blowing agent, a dry-type impregnation method substantially not using water (gaseous phase impregnation method), of placing the expanded particles into a sealable container, and pressing a blowing agent therein to impregnate the blowing agent, and the like. In particular, a dry-type impregnation method by which impregnation can be performed without using water is preferable. An impregnation pressure, an impregnation time, and an impregnation temperature when the blowing agent is impregnated into the expanded particles are not particularly limited.

As the blowing agent to be used, a blowing agent at production of the expanded particles, for example, the known volatile blowing agent or inorganic blowing agent can be used. Examples of the volatile blowing agent include an aliphatic hydrocarbon such as propane, butane, and pentane, an aromatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic alcohol, and the like. Examples of the inorganic blowing agent include a carbonic acid gas, a nitrogen gas, the air, an inert gas (helium, argon, and the like), and the like. Among them, the inorganic blowing agent is preferably used. In particular, it is preferable to use one of a nitrogen gas, the air, an inert gas (helium, argon), and a carbonic acid gas, or use two or more of them together.

It is desirable that a pressure for imparting an internal pressure is a pressure to an extent that the expanded particles do not collapse, and is in such a range that an expanding power can be imparted. Such a pressure is preferably <NUM> to <NUM> MPa (gauge pressure), more preferably <NUM> to <NUM> MPa (gauge pressure). Impregnation of the blowing agent into the expanded particles in this manner is defined as internal pressure impartation.

It is preferable that an impregnation time is <NUM> to <NUM> hours. When the impregnation time is shorter than <NUM> hours, an impregnation amount of the blowing agent into the expanded particles is too small, and it may be difficult to obtain a necessary secondary expanding power at molding. When the impregnation time is longer than <NUM> hours, the productivity may be reduced. A more preferable impregnation time is <NUM> to <NUM> hours.

It is preferable that an impregnation temperature is <NUM> to <NUM>. When the impregnation temperature is lower than <NUM>, it may be difficult to obtain a sufficient secondary expanding power in a desired time. When the impregnation temperature is higher than <NUM>, it may be difficult to obtain a sufficient secondary expanding power in a desired time. A more preferable impregnation temperature is <NUM> to <NUM>.

The expanded particles with an internal pressure imparted thereto are taken out from the container at impregnation, and supplied to a molding space formed in a molding die of an expansion molding machine, thereafter, a heat medium is introduced therein, and thereby, the expanded particles can be in-die molded into a desired expanded molded article. As the expansion molding machine, an EPS molding machine that is used when the expanded molded article is produced from the expanded particles made of a polystyrene-based resin, and a molding machine with high-pressure specification, which is used when the expanded molded article is produced from the expanded particles made of a polypropylene-based resin and the like can be used. Regarding the heat medium, when a heating time becomes long, since shrinkage or deterioration in fusion may be generated in the expanded particles, the heat medium that can give the high energy in a short time is desired, and therefore, as such a heat medium, water steam is suitable.

It is preferable that a pressure of water steam is <NUM> to <NUM> MPa (gauge pressure). In addition, a heating time is preferably <NUM> to <NUM> seconds, more preferably <NUM> to <NUM> seconds.

In addition, for adjusting a cell density X and an average cell wall thickness, by adjusting impregnation conditions (impregnation temperature, impregnation time, impregnation pressure), and primary expansion conditions (expansion pressure, expansion time) of steps of producing the expanded molded article, in addition to using the expanded particles having the above-mentioned specified cell density X and specified average cell wall thickness, a cell density X and an average cell wall thickness can be large or small.

Additionally, for adjusting a bulk ratio and an average cell diameter, by adjusting impregnation conditions (impregnation temperature, impregnation time, impregnation pressure), and primary expansion conditions (expansion pressure, expansion time) of steps of producing the expanded molded article, in addition to using the expanded particles having the above-mentioned specified bulk ratio and specified average cell diameter, a bulk ratio and an average cell diameter can be large or small.

In addition, for adjusting a maximum point stress and the density of a bending test, by adjusting impregnation conditions (impregnation temperature, impregnation time, impregnation pressure), and molding conditions (expansion pressure, expansion time) of steps of producing the expanded molded article, a maximum point stress and the density of a bending test can be large or small.

The expanded molded article may be used as a reinforced composite by laminating and integrating a skin material on the surface of the expanded molded article. When the expanded molded article is an expanded sheet, it is not necessary that the skin material is laminated and integrated on both sides of the expanded molded article, and it is sufficient if the skin surface is laminated and integrated on at least one side of both sides of the expanded molded article. Lamination of the skin material may be decided depending on uses of the reinforced composite. Among others, in view of a surface hardness and a mechanical strength of the reinforced composite, it is preferable that the skin material is laminated and integrated on each of both sides in a thickness direction of the expanded molded article.

The skin material is not particularly limited, but examples thereof include a fiber-reinforced plastic, a metal sheet, a synthetic resin film, and the like. Among them, a fiber-reinforced plastic is preferable. The reinforced composite using a fiber-reinforced plastic as the skin material is called fiber-reinforced composite.

Examples of a reinforcing fiber constituting the fiber-reinforced plastic include: inorganic fibers such as a glass fiber, a carbon fiber, a silicon carbide fiber, an alumina fiber, a tyranno fiber, a basalt fiber, and a ceramic fiber; metal fibers such as a stainless fiber and a steel fiber; organic fibers such as an aramid fiber, a polyethylene fiber, and a polyparaphenylenebenzoxazole (PBO) fiber; and a boron fiber. As the reinforcing fiber, one kind may be used alone, or two or more kinds may be used together. Among them, a carbon fiber, a glass fiber, and an aramid fiber are preferable, and a carbon fiber is more preferable. These reinforcing fibers have the excellent mechanical properties, in spite of being light.

It is preferable that the reinforcing fiber is used as a reinforcing fiber base material that has been processed into a desired shape. Examples of the reinforcing fiber base material include a woven fabric, a knitted fabric, and a non-woven fabric using a reinforcing fiber, a plane material in which a fiber bundle (strand) obtained by arranging reinforcing fibers in one direction is bound (sutured) with a yarn, and the like. Examples of a method of weaving a woven fabric include plain weaving, twill weaving, sateen weaving, and the like. In addition, examples of the yarn include a synthetic resin yarn such as a polyamide resin yarn and a polyester resin yarn, and a stitch yarn such as a glass fiber yarn.

As the reinforcing fiber base material, only one reinforcing fiber base material may be used without lamination, or a plurality of reinforcing fiber base materials may be used as a laminated reinforcing fiber base material by laminating them. As the laminated reinforcing fiber base material obtained by laminating a plurality of reinforcing fiber base materials, (<NUM>) a laminated reinforcing fiber base material obtained by preparing a plurality of reinforcing fiber base materials of only one kind, and laminating these reinforcing fiber base materials, (<NUM>) a laminated reinforcing fiber base material obtained by preparing a plurality of kinds of reinforcing fiber base materials, and laminating these reinforcing fiber base materials, (<NUM>) a laminated reinforcing fiber base material obtained by preparing a plurality of reinforcing fiber base materials in which a fiber bundle (strand) obtained by arranging reinforcing fibers in one direction is bound (sutured) with a yarn, stacking these reinforcing fiber base materials so that fiber directions of a fiber bundle are directed to mutually different directions, and integrating (suturing) stacked reinforcing fiber base materials with a yarn, and the like are used.

The fiber-reinforced plastic is one in which a synthetic resin is impregnated into a reinforcing fiber. Reinforcing fibers are bound and integrated with an impregnated synthetic resin.

A method of impregnating the synthetic resin into the reinforcing fiber is not particularly limited, but examples thereof include, for example, (<NUM>) a method of immersing the reinforcing fiber in the synthetic resin, (<NUM>) a method of coating the synthetic resin on the reinforcing fiber, and the like.

As the synthetic resin to be impregnated into the reinforcing fiber, any of a thermoplastic resin or a thermosetting resin can be used, and a thermosetting resin is preferably used. The thermosetting resin to be impregnated into the reinforcing fiber is not particularly limited, but examples thereof include an epoxy resin, an unsaturated polyester resin, a phenol resin, a melamine resin, a polyurethane resin, a silicone resin, a maleimide resin, a vinyl ester resin, a cyanic acid ester resin, a resin obtained by pre-polymerizing a maleimide resin and a cyanic acid ester resin, and the like, and since heat resistance, shock absorbability or chemical resistance is excellent, an epoxy resin and a vinyl ester resin are preferable. An additive such as a curing agent and a curing accelerator may be contained in the thermosetting resin. In addition, the thermosetting resin may be used alone, or two or more kinds may be used together.

In addition, the thermoplastic resin to be impregnated into the reinforcing fiber is not particularly limited, but examples thereof include an olefin-based resin, a polyester-based resin, a thermoplastic epoxy resin, an amide-based resin, a thermoplastic polyurethane resin, a sulfide-based resin, an acrylic-based resin, and the like, and since adhesive property with the expanded molded article or adhesive property between reinforcing fibers constituting the fiber-reinforced plastic is excellent, a polyester-based resin and a thermoplastic epoxy resin are preferable. In addition, the thermoplastic resin may be used alone, or two or more kinds thereof may be used together.

Examples of the thermoplastic epoxy resin include a polymer that is a polymer or a copolymer of epoxy compounds, and has a straight-chain structure, and a copolymer that is a copolymer of an epoxy compound and a monomer polymerizable with this epoxy compound, and has a straight-chain structure. Specifically, examples of the thermoplastic epoxy resin include, for example, a bisphenol A-type epoxy resin, a bisphenol fluorene-type epoxy resin, a cresol novolak-type epoxy resin, a phenol novolak-type epoxy resin, a cyclic aliphatic-type epoxy resin, a long chain aliphatic-type epoxy resin, a glycidyl ester-type epoxy resin, a glycidyl amine-type epoxy resin, and the like, and a bisphenol A-type epoxy resin and a bisphenol fluorene-type epoxy resin are preferable. In addition, the thermoplastic epoxy resin may be used alone, or two or more kinds may be used together.

Examples of the thermoplastic polyurethane resin include a polymer having a straight-chain structure, which is obtained by polymerizing a diol and a diisocyanate. Examples of the diol include, for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, and the like. The diol may be used alone, or two or more kinds may be used together. Example of the diisocyanate, include, for example, an aromatic diisocyanate, an aliphatic diisocyanate, and an alicyclic diisocyanate. The isocyanate may be used alone, or two or more kinds may be used together. In addition, the thermoplastic polyurethane resin may be used alone, or two or more kinds may be used together.

The content of the synthetic resin in the fiber-reinforced plastic is preferably <NUM> to <NUM>% by weight. When the content is less than <NUM>% by weight, binding ability between reinforcing fibers, or adhesive property between the fiber-reinforced plastic and the expanded molded article becomes insufficient, and the mechanical properties of the fiber-reinforced plastic or a mechanical strength of the fiber-reinforced composite may not be sufficiently improved. When the content is more than <NUM>% by weight, the mechanical properties of the fiber-reinforced plastic are reduced, and a mechanical strength of the fiber-reinforced composite may not be sufficiently improved. The content is more preferably <NUM> to <NUM>% by weight.

A thickness of the fiber-reinforced plastic is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>. The fiber-reinforced plastic having a thickness within this range is excellent in the mechanical properties in spite of being light.

A basis weight of the fiber-reinforced plastic is preferably <NUM> to <NUM>/m<NUM>, more preferably <NUM> to <NUM>/m<NUM>. The fiber-reinforced plastic having a basis weight in this range is excellent in the mechanical properties in spite of being light.

Then, a method of producing the reinforced composite will be described. A method of laminating and integrating a skin material on the surface of the expanded molded article to produce the reinforced composite is not particularly limited, but examples thereof include, for example, (<NUM>) a method of laminating and integrating the skin material on the surface of the expanded molded article via an adhesive agent, (<NUM>) a method of laminating, on the surface of the expanded molded article, a fiber-reinforced plastic forming material in which a thermoplastic resin is impregnated into a reinforcing fiber, and laminating and integrating the fiber-reinforced plastic forming material as a fiber-reinforced plastic, on the surface of the expanded molded article, using a thermoplastic resin impregnated into a reinforcing fiber as a binder, (<NUM>) a method of laminating, on the surface of the expanded molded article, a fiber-reinforced plastic forming material in which an uncured thermosetting resin is impregnated into a reinforcing fiber, and laminating and integrating, on the surface of the expanded molded article, a fiber-reinforced plastic formed by curing a thermosetting resin, using a thermosetting resin impregnated into a reinforcing fiber as a binder, (<NUM>) a method of disposing, on the surface of the expanded molded article, a skin material that has become softened by heating, and laminating and integrating the skin material on the surface of the expanded molded article, if necessary, while deforming the skin material along the surface of the expanded molded article, by pressing the skin material on the surface of the expanded molded article, (<NUM>) a method that is generally applied in molding of the fiber-reinforced plastic, and the like. From a view point that the expanded molded article is excellent in the mechanical properties such as load resistance under the high temperature environment, the above-mentioned method (<NUM>) can also be suitably used.

Examples of a method that is used in molding of the fiber-reinforced plastic include, for example, an autoclave method, a hand lay-up method, a spray up method, a PCM (Prepreg Compression Molding) method, a RTM (Resin Transfer Molding) method, a VaRTM (Vacuum assisted Resin Transfer Molding) method, and the like.

The thus obtained fiber-reinforced composite is excellent in heat resistance, a mechanical strength, and lightness. For that reason, the composite can be used in a wide range of uses such as the transportation equipment field such as an automobile, an aircraft, a railway vehicle, and a ship, the home electric appliance field, the information terminal field, and the field of household furniture.

For example, the fiber-reinforced composite can be suitably used as a part of transportation equipment, and a part for constituting transportation equipment including a structural part constituting a body of transportation equipment (particularly, a part of an automobile), a windmill blade, a robot arm, a buffering material for a helmet, an agricultural box, a transportation container such as a heat/cold insulating container, a rotor blade of an industrial helicopter, and a part packaging material.

According to the present invention, there is provided a part of an automobile constituted of the fiber-reinforced composite of the present invention, and examples of the part of an automobile include, for example, parts such as a floor panel, a roof, a bonnet, a fender, an undercover, a wheel, a steering wheel, a container (housing), a hood panel, a suspension arm, a bumper, a sun visor, a trunk lid, a luggage box, a seat, a door, and a cowl.

The present invention will be specifically described below by way of Examples, but the present invention is not limited thereto. First, methods of measuring various physical properties in Examples will be described below.

The density of the polycarbonate-based resin was measured by a method defined in ISO1183-<NUM>:<NUM>, or ASTM D-<NUM>.

An impregnation amount of blowing agent is defined as a value calculated by the following expression.

An average particle diameter is defined as a value expressed by D50.

Specifically, using a Ro-Tap type sieve shaker (manufactured by SIEVE FACTORY IIDA Co. ), about <NUM> of a sample was classified with JIS standard sieves (JIS Z8801-<NUM>:<NUM>) having a sieve aperture of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> for <NUM> minutes, and the weight of the sample on a sieve mesh was measured. From the obtained results, an accumulated weight distribution curve was prepared, and a particle diameter at which the accumulated weight becomes <NUM>% (median diameter) was defined as an average particle diameter.

A central part of a cross section obtained by dividing, at a central part, expanded particles extracted from expanded particles obtained by primary expansion roughly into two parts was magnified <NUM> to <NUM> times and photographed using a scanning electron microscope. A photographed image was printed on an A4 paper. On an expanded particle cross-sectional image, three parallel arbitrary straight lines (length <NUM>) were drawn in a longitudinal direction and a transverse direction, and when there was a cell having an extremely large cell diameter, each three of arbitrary straight lines were drawn in each direction away from the cell.

In addition, an arbitrary straight line was drawn so that a cell comes in contact only at a tangent point as little as possible, and when it comes in contact, this cell was also added to the number. The cell numbers counted regarding three arbitrary straight lines in each direction of a longitudinal direction and a transverse direction were arithmetically averaged, and this was defined as the cell number.

An average chord length t of a cell was calculated from an image magnification at which the cell number was counted, and this cell number, by the following expression.

The image magnification was obtained by the following expression by measuring a scale bar on an image with "Digimatic Caliper" manufactured by Mitsutoyo Corporation to <NUM>/<NUM>.

Then, a cell diameter was calculated by the following expression.

Length <NUM> × width <NUM> × thickness <NUM> was excised from a central part of a molded article of length <NUM> × width <NUM> × thickness <NUM>, a cross section in a thickness direction of the excised molded article piece was magnified <NUM> to <NUM> times and photographed using a scanning electron microscope. A photographed image was printed on an A4 paper. On an expanded molded article cross-sectional image, three parallel arbitrary straight lines (length <NUM>) were drawn in a longitudinal direction and a transverse direction, and when there was a cell having an extremely large cell diameter, each three of arbitrary straight lines were drawn in each direction away from the cell.

In addition, arbitrary straight lines were drawn so that a cell comes in contact only at a tangent point as little as possible, and when it comes in contact, this cell was also added to the number. The cell numbers counted regarding three arbitrary straight lines in each direction of a longitudinal direction and a transverse direction were arithmetically averaged, and this was defined as the cell number.

The image magnification was obtained by the following expression, by measuring a scale bar on an image with "Digimatic Caliper" manufactured by Mitsutoyo Corporation to <NUM>/<NUM>.

Then, an average cell diameter was calculated by the following expression.

About <NUM><NUM> of expanded particles were filled into a measuring cylinder up to a graduation of <NUM><NUM>. In addition, the measuring cylinder was visually seen from a horizontal direction, and if any one of expanded particles had reached a graduation of <NUM><NUM>, filling of expanded particles into the measuring cylinder was completed at that time point. Then, the weight of expanded particles filled into the measuring cylinder was weighed with significant figures to a second decimal place, and the weight was defined as W (g). Then, the bulk density of the expanded particles was obtained by the following expression.

A bulk ratio was defined as a value obtained by multiplying an inverse number of a bulk density by the density (kg/m<NUM>) of a polycarbonate-based resin.

The weight A (g) of about <NUM><NUM> of expanded particles was measured. Subsequently, an empty wire net container, from which placed expanded particles are not slopped in the state where the container is closed with a lid, was immersed in water, and the weight B (g) of the empty wire net container in the state of being immersed in water was measured. Then, the expanded particles at the whole quantity were placed into this wire net container, thereafter, this wire net container was immersed in water, the container was swung a few times to remove cells attached to the container and the expanded particles, thereafter, the weight C (g) that is the sum of the weight of the wire net container in the state of being immersed in water, and the whole quantity of the expanded particles placed in this wire net container was measured. Then, an apparent density D (kg/m<NUM>) of the expanded particles was calculated by the following expression.

An apparent ratio was defined as a value obtained by multiplying an inverse number of an apparent density by the density (kg/m<NUM>) of a polycarbonate-based resin.

The density (kg/m<NUM>) of the expanded molded article was obtained by the expression (a)/(b), by measuring the weight (a) and the volume (b) of a test piece (width <NUM> × length <NUM> × thickness <NUM>) excised from the expanded molded article (that had been dried at <NUM> for <NUM> hours or longer after molding), each to <NUM> or more significant figures (condition A), or the density was obtained by the expression (a)/(b), by measuring the weight (a) and the volume (b) of a test piece (width <NUM> × length <NUM> × thickness <NUM>) excised from the expanded molded article (that had been dried at <NUM> for <NUM> hours or longer after molding), each to <NUM> or more significant figures (condition B). Measurement was performed under a temperature of <NUM>.

As an expansion ratio was defined as a value obtained by multiplying an inverse number of the density by the density (kg/m<NUM>) of a polycarbonate-based resin.

A sample cup of "Air Comparison Pycnometer <NUM> type" manufactured by Tokyo Science Co. was prepared, and a total weight A (g) of expanded particles at such an amount that fills around <NUM>% of this sample cup was measured. The volume B (cm<NUM>) of the whole of the expanded particles was measured by a <NUM>-<NUM>/<NUM>-<NUM> air pressure method using an air comparison pycnometer, and the pycnometer was corrected with standard spheres (large <NUM><NUM>, small <NUM><NUM>). Subsequently, an empty wire net container, from which placed expanded particles are not slopped in the state where the container is closed with a lid, was immersed in water, and the weight C (g) of the empty wire net container in the state of being immersed in water was measured. Then, the expanded particles at the whole quantity were placed into this wire net container, thereafter, this wire net container was immersed in water, the container was swung a few times to remove cells attached to the container and the expanded particles, thereafter, the weight D (g) that is the sum of the weight of the wire net container in the state of being immersed in water, and the whole quantity of the expanded particles placed in this wire net container was measured. Then, an apparent volume E (cm<NUM>) of the expanded particles was calculated by the following expression. An open cell rate of the expanded particles was calculated by the following expression, based on this apparent volume E (cm<NUM>) and the volume B (cm<NUM>) of the whole of the expanded particles. <MAT> <MAT>.

An expanded article was excised so that all six surfaces of a molded article do not have a molded surface skin, and further, the cut section surface was finished with "FK-4N" Bread Slicer manufactured by Fujishima Koki Co. , to prepare five cubic test pieces of width <NUM> × length <NUM> × thickness <NUM>. An external dimension of the resulting test piece was measured to <NUM>/<NUM> using "Digimatic Caliper" manufactured by Mitsutoyo Corporation, and an apparent volume (cm<NUM>) was obtained. Then, using "<NUM> type" Air Comparison Pycnometer manufactured by Tokyo Science Co. , the volume (cm<NUM>) of the test piece was obtained by a <NUM>-<NUM>/<NUM>-<NUM> air pressure method. An open cell rate (%) was calculated by the following expression, and an average of an open cell rate of five test pieces was obtained. Test pieces had been stored for <NUM> hours in advance under the environment of Symbol <NUM>/<NUM>, <NUM>-Class of JIS K7100:<NUM>, thereafter, measurement was performed under the same environment. In addition, the air comparison pycnometer was corrected with standard spheres (large <NUM><NUM>, small <NUM><NUM>).

An average cell wall thickness of the expanded particles was calculated as follows. The thickness was calculated by the following expression, using an average cell diameter and an apparent ratio of the expanded particles, obtained by the above-mentioned measuring method.

An average cell wall thickness of the expanded molded article was calculated as follows. The thickness was calculated by the following expression, using an average cell diameter and a ratio of the expanded molded article, obtained by the above-mentioned measuring method.

The load, the stress, the displacement, and the energy of a maximum point were measured by a method conforming to JIS K7221-<NUM>:<NUM> "Rigid cellular plastics - Determination of flexural properties - Part <NUM>: Basic bending test". That is, from the expanded molded article, a rectangular parallelepiped test piece of width <NUM> × length <NUM> × thickness <NUM> was excised. For measurement, a Tensilon universal testing machine ("UCT-10T" manufactured by Orientec Co. ) was used. A bending maximum point stress of the bending strength was calculated using a universal testing machine data processing system ("UTPS-<NUM> Ver, <NUM>" manufactured by SOFTBRAIN Co.

A strip-shaped test piece was placed on a support stand, and a bending maximum point stress was measured under the conditions of a load cell <NUM> N, a test speed <NUM>/min, a tip jig of a support stand 5R, and an opening width <NUM>. The number of test pieces was <NUM> or more, the state was adjusted over <NUM> hours under the standard environment of Symbol "<NUM>/<NUM>" (temperature <NUM>, relative humidity <NUM>%), <NUM>-Class of JIS K7100:<NUM>, and thereafter, measurement was performed under the same standard environment. After the state was regulated over <NUM> hours in a thermostatic bath set at each test temperature of -<NUM>, <NUM>, and <NUM>, the test piece was set on a jig in a thermostatic bath attached to an apparatus, which had been rapidly set at each designated temperature, and measurement was performed after <NUM> minutes. An arithmetic mean of a bending maximum point stress of each test piece was defined as a bending maximum point stress of the expanded molded article, respectively.

Additionally, a bending maximum point stress per unit density was calculated by dividing a bending maximum point stress by the density of the expanded molded article.

In addition, the density (kg/m<NUM>) of the expanded molded article was obtained by the expression (a)/(b), by measuring the weight (a) and the volume (b) of a test piece excised from the expanded molded article.

The bending elastic modulus was measured by a method conforming to JIS K7221-<NUM>:<NUM> "Rigid cellular plastics - Determination of flexural properties - Part <NUM>: Basic bending test". That is, from the expanded molded article, a rectangular parallelepiped test piece of width <NUM> × length <NUM> × thickness <NUM> was excised. For measurement, a Tensilon universal testing machine ("UCT-10T" manufactured by Orientec Co. ) was used. The bending elastic modulus was calculated by the following expression, using a universal testing machine data processing system ("UTPS-<NUM> Ver, <NUM>" manufactured by SOFTBRAIN Co. The number of test pieces was <NUM> or more, the state was adjusted over <NUM> hours under the standard environment of Symbol "<NUM>/<NUM>" (temperature <NUM>, relative humidity <NUM>%), <NUM>-Class of JIS K7100:<NUM>, and thereafter, measurement was performed under the same standard environment. An arithmetic mean of the compression elastic modulus of each test piece was defined as the bending elastic modulus of the expanded molded article, respectively.

The bending elastic modulus was calculated by the following expression using an initial straight portion of a load-deformation curve.

In addition, the bending elastic modulus per unit density was calculated by dividing the bending elastic modulus by the density of the expanded molded article.

A <NUM>% compression stress, a <NUM>% compression stress, a <NUM>% compression stress, and a <NUM>% compression stress of the expanded molded article were measured by a method described in JIS K7220:<NUM> "Rigid cellular plastics - Determination of compression properties". That is, using a Tensilon universal testing machine ("UCT-10T" manufactured by Orientec Co. ) and a universal testing machine data processing system ("UTPS-<NUM> Ver, <NUM>" manufactured by SOFTBRAIN Co. ), the compression strength (<NUM>% deformation compression stress, <NUM>% deformation compression stress, compression elastic modulus) was measured under a test specimen size cross section <NUM> × <NUM> and thickness <NUM>, and a compression speed of <NUM>/min. The number of test pieces was <NUM> or more, the state was adjusted over <NUM> hours under the standard environment of Symbol "<NUM>/<NUM>" (temperature <NUM>, relative humidity <NUM>%), <NUM>-Class of JIS K7100:<NUM>, and thereafter, measurement was performed under the same standard environment. An arithmetic mean of the compression strength (<NUM>% deformation compression stress, <NUM>% deformation compression stress, <NUM>% deformation compression stress, <NUM>% deformation compression stress) of each test piece was defined as a <NUM>% compression stress, a <NUM>% compression stress, a <NUM>% compression stress, and a <NUM>% compression stress of the expanded molded article, respectively.

A <NUM>% (<NUM>%, <NUM>%, <NUM>%) deformation compression stress was calculated by the following expression. In addition, the inside of ( ) was defined as the condition for calculating a <NUM>% deformation compression stress, a <NUM>% deformation compression stress, or a <NUM>% deformation compression stress.

The compression elastic modulus of the expanded molded article was measured by a method described in JIS K7220:<NUM> "Rigid cellular plastics - Determination of compression properties". That is, using a Tensilon universal testing machine ("UCT-10T" manufactured by Orientec Co. ), and a universal testing machine data processing system ("UTPS-<NUM> Ver, <NUM>" manufactured by SOFTBRAIN Co. ), the compression elastic modulus was calculated by the following expression under a test specimen size cross section <NUM> × <NUM> and thickness <NUM>, and a compression speed of <NUM>/min. The number of test pieces was <NUM> or more, the state was adjusted over <NUM> hours under the standard environment of Symbol "<NUM>/<NUM>" (temperature <NUM>, relative humidity <NUM>%), <NUM>-Class of JIS K7100:<NUM>, and thereafter, measurement was performed under the same standard environment. An arithmetic mean of the compression elastic modulus of each test piece was defined as the compression elastic modulus of the expanded molded article.

The compression elastic modulus was calculated by the following expression using an initial straight portion of a load-deformation curve.

In addition, the compression elastic modulus per unit density was calculated by dividing the compression elastic modulus by the density of the expanded molded article.

Examples of first expanded particles (not according to the invention).

Polycarbonate-based resin particles (Panlite L-1250Y manufactured by Teijin Limited, density <NUM> × <NUM><NUM> kg/m<NUM>) were dried at <NUM> for <NUM> hours. The resulting dried product was supplied to a single screw extruder having a bore diameter of <NUM> at a ratio of <NUM>/hr per hour to melt and knead the product at <NUM>. Subsequently, the kneaded product was extruded into a chamber accommodating cooling water at about <NUM>, from die holes (four nozzles having a diameter of <NUM> are arranged) of a die (temperature: <NUM>, inlet side resin pressure: <NUM> MPa) mounted to a tip portion of a single screw extruder, a rotating shaft of a rotary blade having four cutting blades was rotated at a rotation number of <NUM> rpm to cut the extruded product into particles, and thereby, the particles were cooled with the cooling water to prepare resin particles (average particle diameter <NUM>).

<NUM> parts by weight of the above-mentioned resin particles were closed in a pressure vessel, the inside of the pressure vessel was substituted with a carbonic acid gas, and thereafter, a carbonic acid gas was pressed therein to an impregnation pressure of <NUM> MPa. The pressure vessel was left at rest under the environment at <NUM>, and after a lapse of an impregnation time of <NUM> hours, the inside of the pressure vessel was slowly depressurized over <NUM> minutes. In this way, the resin particles were impregnated with a carbonic acid gas to obtain expandable particles. In addition, an impregnation amount of blowing agent at this time was <NUM>% by weight.

Immediately after depressurization in the above-mentioned impregnation step, the expandable particles were taken out from the pressure vessel, and thereafter, the above-mentioned impregnation product was expanded with water steam in an expansion tank at a high pressure, while stirring at an expansion temperature of <NUM> for <NUM> seconds using water steam. After expansion, drying was performed with an airstream drying machine to obtain expanded particles. When a bulk density of the resulting expanded particles was measured by the above-mentioned method, the bulk density was <NUM>/m<NUM> (expansion ratio <NUM> times).

After the resulting expanded particles were allowed to stand at room temperature (<NUM>) for one day, and thereafter, was closed in a pressure vessel, the inside of the pressure vessel was substituted with a nitrogen gas, and thereafter, a nitrogen gas was pressed therein to an impregnation pressure (gauge pressure) of <NUM> MPa. The pressure vessel was left at rest under the environment at <NUM>, and pressure aging was carried out for <NUM> hours. After taken out, the expanded particles were filled into a <NUM> × <NUM> × <NUM> molding die, heated with water steam at <NUM> MPa for <NUM> seconds, and then, cooled until a maximum surface pressure of an expanded molded article dropped to <NUM> MPa, and thereby, an expanded molded article having an expansion ratio of <NUM> times (density <NUM>/m<NUM>) was obtained.

In the same manner as that of Example 1a except that a carbonic acid gas was pressed therein to an impregnation pressure of <NUM> MPa, an impregnation amount of a blowing agent was <NUM>% by weight, and an expansion time was <NUM> seconds, expanded particles having a bulk ratio of <NUM> times (bulk density <NUM>/m<NUM>) and an expanded molded article having an expansion ratio of <NUM> times (density <NUM>/m<NUM>) were obtained.

In the same manner as that of Example 1a except that a carbonic acid gas was pressed therein to an impregnation pressure of <NUM> MPa, an impregnation amount of a blowing agent was <NUM>% by weight, Panlite Z-<NUM> (density <NUM> × <NUM><NUM> kg/m<NUM>) manufactured by Teijin Limited was used as a polycarbonate-based resin, an expansion temperature was <NUM>, and an expansion time was <NUM> seconds, expanded particles having a bulk ratio of <NUM> times (bulk density <NUM>/m<NUM>) and an expanded molded article having an expansion ratio of <NUM> times (density <NUM>/m<NUM>) were obtained.

In the same manner as that of Example 1a except that a carbonic acid gas was pressed therein to an impregnation pressure of <NUM> MPa, an impregnation amount of a blowing agent was <NUM>% by weight, Panlite Z-<NUM> manufactured by Teijin Limited was used as a polycarbonate-based resin, an expansion temperature was <NUM>, and an expansion time was <NUM> seconds, expanded particles having a bulk ratio of <NUM> times (bulk density <NUM>/m<NUM>), and an expanded molded article having an expansion ratio of <NUM> times (density <NUM>/m<NUM>) were obtained.

In the same manner as that of Example 1a except that a carbonic acid gas was pressed therein to an impregnation pressure of <NUM> MPa, an impregnation amount of a blowing agent was <NUM>% by weight, and an impregnation time was <NUM> seconds, expanded particles having a bulk ratio of <NUM> times (bulk density <NUM>/m<NUM>) and an expanded molded article having an expansion ratio of <NUM> times (density <NUM>/m<NUM>) were obtained.

In the same manner as that of Example 1a except that a carbonic acid gas was pressed therein to an impregnation pressure of <NUM> MPa, an impregnation amount of a blowing agent was <NUM>% by weight, Panlite Z-<NUM> manufactured by Teijin Limited was used as a polycarbonate-based resin, an expansion temperature was <NUM>, and an expansion time was <NUM> seconds, expanded particles having a bulk ratio of <NUM> times (bulk density <NUM>/m<NUM>) and an expanded molded article having an expansion ratio of <NUM> times (density <NUM>/m<NUM>) were obtained.

An average cell diameter C, a bulk ratio, a bulk density, an apparent ratio, an apparent density D, a cell number density, and an average cell wall thickness of primary expanded particles, as well as an average cell diameter C, an open cell rate, an expansion ratio, a density D, a cell density X, an average cell wall thickness, and bending test results, and compression test results assessment of expanded molded articles, of Examples 1a to 6a and Comparative Examples 1a to 3a, are shown in Tables <NUM> and <NUM>.

In addition, photographs obtained by magnifying cut sections of expanded particles and expanded molded articles of Examples 1a to 6a and Comparative Examples 1a to 3a <NUM> to <NUM> times with a scanning electron microscope are shown in <FIG>.

From the above-mentioned Tables <NUM> and <NUM>, it is seen that by regulating a cell density X and an average cell wall thickness to specified ranges, an expanded molded article having a high mechanical strength is obtained. Specifically, when Examples 1a to 4a and Comparative Examples 1a to 2a using the same L1250Y as a polycarbonate-based resin are compared, it is seen that a maximum point stress and the elastic modulus per unit density in a bending test, and the elastic modulus per unit density in a compression test are further improved in Examples than in Comparative Examples. Furthermore, when Examples 5a to 6a and Comparative Example 3a using the same Z-<NUM> as a polycarbonate-based resin are compared, it is seen that a maximum point stress and the elastic modulus per unit density in a bending test, and the elastic modulus per unit density in a compression test are further improved in Examples than in Comparative Examples.

In addition, from <FIG>, it is seen that since in expanded molded articles of Comparative Examples 1a to 3a, fusion between expanded particles is insufficient, and many gaps exist between expanded particles, an appearance is deteriorated, while in expanded molded articles of Examples 1a to 6a, there are little gaps between expanded particles, and an appearance is good.

Examples of second expanded particles (according to the invention).

Immediately after depressurization in the above-mentioned impregnation step, the expandable particles were taken out from the pressure vessel, and thereafter, the above-mentioned impregnation product was expanded with water steam in an expansion tank at a high pressure, while stirring at an expansion temperature of <NUM> for <NUM> seconds using water steam. After expansion, drying was performed with an airstream drying machine to obtain expanded particles. When a bulk density of the resulting expanded particles was measured by the above-mentioned method, the bulk density was <NUM>/m<NUM> (bulk ratio <NUM> times).

The resulting expanded particles were allowed to stand at room temperature (<NUM>) for one day, and thereafter, closed in a pressure vessel, the inside of the pressure vessel was substituted with a nitrogen gas, and thereafter, a nitrogen gas was pressed therein to an impregnation pressure (gauge pressure) of <NUM> MPa. The pressure vessel was left at rest under the environment at <NUM>, and pressure aging was carried out for <NUM> hours. After taken out, the expanded particles were filled into a <NUM> × <NUM> × <NUM> molding die, heated with water steam at <NUM> MPa for <NUM> seconds, and then, cooled until a maximum surface pressure of an expanded molded article dropped to <NUM> MPa, and thereby, an expanded molded article having an expansion ratio of <NUM> times (density <NUM>/m<NUM>) was obtained.

In the same manner as that of Example 1b except for the following conditions, expanded particles and an expanded molded article were obtained.

In the same manner as that of Example 1b except for the following conditions, expanded particles were obtained.

In addition, in the same manner as that of Example 1b except that, as a molding step, a nitrogen gas was pressed therein to an impregnation pressure (gauge pressure) of <NUM> MPa, an expanded molded article was obtained.

Various physical properties of expanded particles and expanded molded articles of Examples 1b to 9b and Comparative Examples 1b to 3b are shown in Tables <NUM> to <NUM>.

In addition, photographs obtained by magnifying cut sections of expanded particles and expanded molded articles of Examples 1b to 9b and Comparative Examples 1b to 3b <NUM> to <NUM> times with a scanning electron microscope are shown in <FIG>.

From the above-mentioned Tables <NUM> to <NUM>, it is seen that by regulating a bulk ratio and an average cell diameter to specified ranges, an expanded molded article having a high mechanical strength is obtained.

In addition, from <FIG>, it is seen that since in expanded molded articles of Comparative Examples 1b to 3b, fusion between expanded particles is insufficient, and many gaps exist between expanded particles, an appearance is deteriorated, while in expanded molded articles of Examples 1b to 9b, there are little gaps between expanded particles, and an appearance is good.

Polycarbonate-based resin particles (Panlite L-1260Y manufactured by Teijin Limited, density <NUM> × <NUM><NUM> kg/m<NUM>) were dried at <NUM> for <NUM> hours. The resulting dried product was supplied to a single screw extruder having a bore diameter of <NUM> at a ratio of <NUM>/hr per hour to melt and knead the product at <NUM>. Subsequently, the kneaded product was extruded in a chamber accommodating cooling water at about <NUM>, from die holes (four nozzles having a diameter of <NUM> are arranged) of a die (temperature: <NUM>, inlet side resin pressure: <NUM> MPa) mounted to a tip portion of a single screw extruder, a rotating shaft of a rotary blade having four cutting blades was rotated at a rotation number of <NUM> rpm to cut the extruded product into particles, and thereby, the particles were cooled with the cooling water to prepare resin particles (average particle diameter <NUM>).

<NUM> parts by weight of the above-mentioned resin particles were closed in a pressure vessel, the inside of the pressure vessel was substituted with a carbonic acid gas, and thereafter, a carbonic acid gas was pressed therein to an impregnation pressure of <NUM> MPa. The pressure vessel was left at rest under the environment at <NUM>, and after a lapse of an impregnation time of <NUM> hours, the inside of the pressure vessel was slowly depressurized over <NUM> minutes. In this way, the resin particles were impregnated with a carbonic acid gas to obtain expandable particles.

Immediately after depressurization in the above-mentioned impregnation step, the expandable particles were taken out from the pressure vessel, and thereafter, the above-mentioned impregnation product was expanded with water steam in an expansion tank at a high pressure, while stirring at an expansion temperature of <NUM> for <NUM> seconds using water steam. After expansion, drying was carried out in an airstream drying machine to obtain expanded particles.

The resulting expanded particles were allowed to stand at room temperature (<NUM>) for one day, and thereafter, closed in a pressure vessel, the inside of the pressure vessel was substituted with a nitrogen gas, and thereafter, a nitrogen gas was pressed therein to an impregnation pressure (gauge pressure) of <NUM> MPa. This was left at rest under the environment at <NUM>, and pressure aging was carried out for <NUM> hours. After taken out, the expanded particles were filled into a <NUM> × <NUM> × <NUM> molding die, heated with water steam at <NUM> MPa for <NUM> seconds, and then, cooled until a maximum surface pressure of an expanded molded article dropped to <NUM> MPa, and thereby, an expanded molded article having an expansion ratio of about <NUM> times was obtained.

In the same manner as that of Example 1c except that an expansion time of an expansion step was <NUM> seconds, and an expansion ratio of an expanded molded article was about <NUM> times, expanded particles and an expanded molded article were obtained.

In the same manner as that of Example 1c except that polycarbonate-based resin particles (Panlite Z-<NUM> manufactured by Teijin Limited, density <NUM> × <NUM><NUM> kg/m<NUM>) were used, an expansion temperature of an expansion step was <NUM>, an expansion time was <NUM> seconds, an impregnation pressure (gauge pressure) of a molding step was <NUM> MPa, and an expansion ratio of an expanded molded article was about <NUM> times, expanded particles and an expanded molded article were obtained.

In the same manner as that of Example 1c except that polycarbonate-based resin particles (LEXAN <NUM> manufactured by SABIC Company, density <NUM> × <NUM><NUM> kg/m<NUM>) were used, an expansion temperature of an expansion step was <NUM>, an expansion time was <NUM> seconds, and an expansion ratio of an expanded molded article was about <NUM> times, expanded particles and an expanded molded article were obtained.

In the same manner as that of Example 1c except that polycarbonate-based resin particles (LEXAN 101R manufactured by SABIC Company, density <NUM> × <NUM><NUM> kg/m<NUM>) were used, an expansion temperature of an expansion step was <NUM>, an expansion time was <NUM> seconds, and an expansion ratio of an expanded molded article was about <NUM> times, expanded particles and an expanded molded article were obtained.

In the same manner as that of Example 1c except that polycarbonate-based resin particles (Panlite K-1300Y manufactured by Teijin Limited, density <NUM> × <NUM><NUM> kg/m<NUM>) were used, an expansion temperature of an expansion step was <NUM>, an expansion time was <NUM> seconds, an impregnation pressure (gauge pressure) of a molding step was <NUM> MPa, and an expansion ratio of an expanded molded article was about <NUM> times, expanded particles and an expanded molded article were obtained.

In the same manner as that of Example 1c except that polycarbonate-based resin particles (Wonderlite PC-<NUM> manufactured by Chimei Corporation, density <NUM> × <NUM><NUM> kg/m<NUM>) were used, an expansion temperature of an expansion step was <NUM>, an expansion time was <NUM> seconds, and an expansion ratio of an expanded molded article was about <NUM> times, expanded particles and an expanded molded article were obtained.

In the same manner as that of Example 1c except that polycarbonate-based resin particles (Panlite L-1250Y manufactured by Teijin Limited, density <NUM> × <NUM><NUM> kg/m<NUM>) were used, an expansion temperature of an expansion step was <NUM>, an expansion time was <NUM> seconds, and an expansion ratio of an expanded molded article was about <NUM> times, expanded particles and an expanded molded article were obtained.

According the same manner as that of Example 1c except that polycarbonate-based resin particles (LEXAN <NUM> manufactured by SABIC Company, density <NUM> × <NUM><NUM> kg/m<NUM>) were used, an impregnation pressure of an impregnation step was <NUM> MPa, <NUM> part by weight of calcium carbonate as a bonding preventing agent was mixed based on <NUM> parts by weight of a polycarbonate-based resin immediately after taking out of expandable particles, an expansion time of an expansion step was <NUM> seconds, and heating was performed for <NUM> seconds at a water steam pressure of <NUM> MPa in a molding step, expanded particles and an expanded molded article were obtained.

<NUM>% by weight of a polyethylene terephthalate (PET) resin (MITSUI PET SA-<NUM> manufactured by Mitsui Chemicals, Inc. ), <NUM>% by weight of a polyethylene naphthalate (PEN) resin (Teonex TN8050SC manufactured by Teijin Limited), <NUM> % by weight of a cell adjusting agent (PET-F40-<NUM> manufactured by TERABO LTD. ), and <NUM>% by weight of a crosslinking agent (pyromellitic dianhydride manufactured by Daicel Corporation) were supplied to a single screw extruder having a bore diameter of <NUM> and a LID ratio of <NUM>, to melt and knead them at <NUM>. Subsequently, butane consisting of <NUM>% by weight of isobutane and <NUM>% by weight of normal butane was pressed into a resin composition in the melted state, from the middle of an extruder, so that an amount thereof became <NUM> part by weight relative to a total amount of <NUM> parts by weight of the PET resin and the PEN resin, and uniformly dispersed in the resin composition. Thereafter, at a front end part of the extruder, the resin composition in the melted state was cooled to <NUM>, and thereafter, the resin composition was extruded from each nozzle of a multi-nozzle die attached to a front end of the extruder, and expanded.

An in-die expansion molding machine provided with a die (male die and female die) was prepared. In the state where the male die and the female die were clamped, a rectangular parallelepiped cavity having an internal dimension of length <NUM> × width <NUM> × height <NUM> was formed between female and male dies.

Then, expanded particles were filled into the die in the state where the die cracking was taken by <NUM>, thereafter, water steam was introduced from the female die for <NUM> minutes so that a pressure of the inside of the cavity became <NUM> MPa (gauge pressure), then, water steam was introduced from the male die for <NUM> seconds so that a pressure of the inside of the cavity became <NUM> MPa (gauge pressure), then, water steam was supplied from both male and female dies for <NUM> seconds so that a pressure of the inside of the cavity became <NUM> MPa (gauge pressure), and the expanded particles were heated and secondarily expanded to thermally fuse and integrate secondary expanded particles. Thereafter, this was retained for <NUM> seconds in the state where introduction of water steam into the cavity was stopped (heat-retaining step), finally, cooling water was supplied into the cavity to cool an expanded molded article in the die, and thereafter, the cavity was opened to take out an expanded molded article. At that time, the time required for obtaining an expanded molded article from a step of filling expanded particles into the die (molding cycle time) was <NUM> seconds.

<NUM> parts by weight of an ethylene-propylene random copolymer and <NUM> part by weight of a zinc borate powder (cell adjusting agent) were supplied to an extruder, and heated, melted, and kneaded to form a first melted resin for forming a core layer. At the same time, an ethylene-propylene random copolymer was supplied to another extruder, and heated, melted, and kneaded to form a second melted resin for forming a covering layer.

Next, the first melted resin for forming a core layer and second melted resin for forming a covering layer were supplied to a coextrusion die, and in the die, the second melted resin was laminated on the first melted resin so that the second melted resin covered the periphery of a strand of the first melted resin.

Next, the laminated melted resin was extruded in the shape of a strand from the coextrusion die, and cut so that a diameter was about <NUM>, and a length became approximately <NUM> times of a diameter, to obtain multilayer resin particles having an average weight per one particle of <NUM>.

Using the multilayer resin particles, expanded particles were produced as described below.

<NUM> parts by weight (<NUM>) of the multilayer resin particles, <NUM> parts by weight of water, <NUM> part by weight of sodium dodecylbenzenesulfonate (surfactant), and <NUM> part by weight of kaolin (dispersant), and a carbonic acid gas (blowing agent) were added to a <NUM> liters autoclave, a temperature was raised to a temperature that is lower than an expansion temperature by <NUM>, while stirring, and this was retained at that temperature for <NUM> minutes. Then, a temperature was raised to an expansion temperature, and this was retained at the same temperature for <NUM> minutes. Then, one end of the autoclave was opened to discharge the autoclave content under an atmospheric pressure, to obtain expanded particles.

In addition, discharge was carried out while a carbonic gas was supplied into the autoclave, so that a pressure in the autoclave kept a pressure in the autoclave immediately before discharge, during discharge of the multilayer resin particles from the autoclave.

Using the resulting expanded particles, an expanded particle molded article was molded as described below. Using, as a molding machine, a small scale molding machine that can stand a saturated water steam pressure of <NUM> MPa (G), the expanded particles were filled into a die having a molding space of <NUM> × <NUM> × <NUM>, in the state where the die was not completely closed, and a gap (about <NUM>) was provided, then, the die was completely clamped, the air in the die was discharged by a water steam pressure, thereafter, water steam at <NUM> MPa was supplied into the die, and thereby, heating and molding were performed. After heating and molding, this was cooled with water until a surface pressure of a molded article in the die became <NUM> MPa, thereafter, an expanded molded article was taken out from the die, aged at <NUM> for <NUM> hours, and thereafter, cooled to room temperature.

Various physical properties of expanded molded articles of Examples 1c to 8c and Comparative Examples 1c to 3c are shown in Table <NUM>. In Table <NUM>, PC represents a polycarbonate-based resin, PET represents a polyester-based resin, and PP represents a propylene-based resin.

From the above-mentioned Table <NUM>, it is seen that in expanded molded articles of Examples 1c to 8c, a variation of a mechanical strength is further suppressed even when an environmental temperature changes. On the other hand, it is seen that in expanded molded articles of Comparative Examples 1c to 3c, a variation is large, or the expanded molded articles themselves are melted or deformed.

In addition, regarding a maximum point stress of a bending test, a value obtained by calculating stress change between at -<NUM> and <NUM> is shown in Table <NUM>. Stress change means [(maximum point stress of bending test at -<NUM>) - (maximum point stress of bending test at <NUM>)] ÷ (maximum point stress of bending test at <NUM>).

In addition, regarding a maximum point stress of a bending test, a value obtained by calculating stress change between <NUM> and <NUM> is shown in Table <NUM>. Stress change means [(maximum point stress of bending test at <NUM>) - (maximum point stress of bending teat at <NUM>)] ÷ (maximum point stress of bending test at <NUM>).

Claim 1:
Expanded particles comprising a polycarbonate-based resin having an aromatic skeleton as a base resin,
wherein when an average cell diameter of said expanded particles is divided by a bulk ratio of said expanded particles, said expanded particles have a value within a range of <NUM> to <NUM>/times, and
said expanded particles have a bulk ratio of <NUM> to <NUM> times, an average cell diameter of <NUM> to <NUM>, and an open cell rate of <NUM> to <NUM>%,
wherein the average cell diameter, the bulk ratio and the open cell rate are determined as indicated in the description.