JP2023118117A - Crystalline thermoplastic resin foam particle molding, and method for producing the same - Google Patents

Abstract

To provide a crystalline thermoplastic resin foam particle molding which has a desired shape even in the case of omitting a curing step, and is excellent in appearance and rigidity, and a method for producing the same.SOLUTION: A crystalline thermoplastic resin foam particle molding is obtained by mutually fusing crystalline thermoplastic resin foam particles having no through holes and having a columnar shape. The molding magnification of the crystalline thermoplastic resin foam particle molding is 15 times or more and 90 times or less. The isolated cell ratio of the crystalline thermoplastic resin foam particle molding is 90% or more. The open air bubble ratio of the crystalline thermoplastic resin foam particle molding is 2% or more and 7.5% or less.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a crystalline thermoplastic resin expanded bead molded article and a method for producing the same.

Polypropylene-based resin expanded particle molded articles are used in various applications because they are lightweight and excellent in shock-absorbing properties, rigidity, and the like. Polypropylene-based resin expanded bead molded articles are produced by, for example, a method called an in-mold molding method in which expanded polypropylene-based resin particles are filled into a mold and then heated by supplying steam into the mold. In the in-mold molding method, when steam is supplied into the molding die, the foamed particles are secondary foamed and the surface is melted. As a result, the foamed particles in the mold are fused together, and a molded article having a shape corresponding to the shape of the cavity of the mold can be obtained. Since the molded article immediately after molding tends to swell due to secondary foaming, it is released from the molding die after being cooled with water, air, or the like in the molding die.

In the manufacturing process of the above-mentioned molded article, if the expanded bead molded article after being released from the mold is stored at room temperature, the steam that has flowed into the cells of the expanded bead molded article during molding in the mold will condense in the cells. , the inside of the bubble becomes negative pressure. As a result, volumetric shrinkage occurs in the expanded bead molded article, and the molded article may be greatly deformed. In order to suppress the deformation of the molded article after such release, after the expanded bead molded article is released from the mold, it is allowed to stand still for a predetermined time in a high-temperature atmosphere adjusted to a temperature of, for example, about 60°C to 80°C. A curing step is carried out to restore the shape of the expanded bead molded article.

However, in the in-mold molding of expanded polypropylene resin beads, the curing process requires capital investment and is time-consuming. It is desired that For example, Patent Literature 1 discloses a technique of fusing foamed particles each composed of a foam layer and a fusible layer while maintaining gaps between the particles. Further, Patent Document 2 discloses a technique for in-mold molding of foamed particles using a polypropylene-based resin whose melting point, melt flow index, Z-average molecular weight, etc. are adjusted to specific ranges.

JP-A-2003-39565 JP-A-2000-129028

However, in the technique described in Patent Document 1, although the curing step can be omitted, a large number of voids are formed between the expanded particles of the molded article, so that the appearance of the expanded bead molded article is remarkably poor, and depending on the application, the rigidity is increased. was insufficient. In the technique described in Patent Document 2, although the curing process can be shortened, the curing process is still required. If the curing process is omitted, the foamed bead molded article will shrink and deform significantly, and will have the desired shape. It was difficult to obtain an expanded bead molded article.

The present invention has been made in view of such a background, and provides a crystalline thermoplastic resin expanded bead molded article which has a desired shape and is excellent in appearance and rigidity even if the curing step is omitted, and a method for producing the same. is trying to provide.

One aspect of the present invention resides in a crystalline thermoplastic resin expanded bead molded article according to the following [1] to [3].

[1] A crystalline thermoplastic resin foamed particle molded article having a molding magnification of 15 times or more and 90 times or less, wherein columnar crystalline thermoplastic resin expanded particles having no through-holes are fused to each other. There is
The molded body has a closed cell ratio of 90% or more,
A crystalline thermoplastic resin foamed particle molded product, wherein the molded product has an open cell rate of 2% or more and 7.5% or less.

[2] The crystalline thermoplastic resin expanded bead molded article according to [1], wherein the number of the expanded particles per unit area on the surface of the molded article is 3/cm ² or more and 30/cm ² or less.

[3] Molding of crystalline thermoplastic resin expanded particles according to [1] or [2], wherein the ratio of 50% compressive stress σ ₅₀ to the density of the molded body is 7.5 kPa/(kg/m ³ ) or more. body.

Another aspect of the present invention resides in a method for producing a crystalline thermoplastic resin expanded bead molded product according to the following [4] to [10].

[4] Filling the crystalline thermoplastic resin expanded particles into the mold,
After that, by supplying steam into the mold and performing in-mold molding, a crystalline thermoplastic having a molding magnification of 15 times or more and 90 times or less and an open cell ratio of 2% or more and 7.5% or less A method for producing a crystalline thermoplastic resin expanded bead molded article for obtaining an expanded resin bead molded article, comprising:
The foamed particles have a foamed layer with a crystalline thermoplastic resin as a base resin,
The foamed beads have a columnar shape with no through holes and at least one groove on the side peripheral surface thereof,
The ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads on the cut surface obtained by cutting the expanded beads at the center in the axial direction along a plane perpendicular to the axial direction is is 0.01 or more and 0.25 or less, and the ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads is 0.02 or more and 0.75 or less, and the average outer diameter of the expanded beads is The diameter D is 0.5 mm or more and 10 mm or less,
A method for producing a crystalline thermoplastic resin expanded bead molded product, wherein the ratio L/D of the average length L in the axial direction of the expanded beads to the average outer diameter D of the expanded beads is 0.5 or more and 2.0 or less.

[5] The crystalline thermoplastic resin expanded bead molding according to [4], wherein the average cross-sectional area Ca per groove in the cut surface of the expanded bead is 0.05 mm ² or more and 2.0 mm ^{2 or} less. body manufacturing method.
[6] The ratio H/D of the average depth H per groove to the average outer diameter D of the expanded beads on the cut surface of the expanded beads is 0.35 or less, [4] or [5] ].

[7] A ratio A/B of the average cross-sectional area A of the expanded beads to the area B of the virtual perfect circle having the average outer diameter D of the expanded beads is 0.35 or more and 0.90 or less; ] to [6].
[8] Any one of [4] to [7], wherein the ratio L/D of the average length L in the axial direction of the expanded beads to the average outer diameter D of the expanded beads is more than 0.7 and less than 1.3. 3. A method for producing a crystalline thermoplastic resin expanded particle molded product according to claim 1.

[9] The foamed particles have a coating layer covering the foamed layer, and the base resin of the coating layer is a thermoplastic resin having a lower melting point or lower softening point than the melting point of the crystalline thermoplastic resin. The method for producing a crystalline thermoplastic resin expanded bead molded product according to any one of [4] to [8].
[10] without applying an internal pressure to the expanded beads, or after applying an internal pressure of 0.1 MPa (G) or less to the expanded beads, the expanded beads are filled in the mold, [4] to [ 9].

According to the above aspect, even if the curing step is omitted, the crystalline thermoplastic resin expanded bead molded article (hereinafter referred to as "expanded bead molded article" or "molded article") has a desired shape and is excellent in appearance and rigidity. ) and its manufacturing method can be provided.

FIG. 1 is a perspective view of columnar expanded beads having a cross-shaped cross section. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 (a plan view of a cut surface of the expanded beads). FIG. 3 is a perspective view of a cylindrical foamed particle. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 (a plan view of a cut surface of the expanded beads). FIG. 5 is a perspective view of triangular prism-shaped expanded particles. 6 is a cross-sectional view taken along line VI-VI in FIG. 5 (a plan view of a cut surface of the expanded beads). FIG. 7 is a perspective view of square prism-shaped expanded particles. FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 7 (a plan view of a cut surface of expanded beads). FIG. 9 is an explanatory diagram showing a method of calculating the area of the high temperature peak. 10 is a perspective view of expanded beads in Example 1. FIG. 11 is a cross-sectional view taken along the line XI-XI in FIG. 10 (a plan view of a cut surface of the expanded beads).

(Expanded particle molding)
The foamed bead molded product is obtained by in-mold molding columnar crystalline thermoplastic resin foamed beads (hereinafter referred to as "expanded beads") having no through-holes. In-mold molding of foamed particles having no through-holes makes it possible to obtain a molded article having excellent surface properties, and to easily adjust the value of the open cell ratio of the molded article within the specific range. can be done.

The molded body has an open cell structure. The open cell structure is a minute space portion communicating with the outside of the molded article. The open-cell structure is formed by intricately connecting voids formed by communicating voids between foamed particles, open-cell portions of foamed particles constituting a molded article, and the like. In addition, when a molded article is produced using expanded beads having grooves on the side peripheral surfaces as described later, voids formed by interconnecting grooves of a plurality of expanded beads and grooves of expanded beads are expanded. Voids and the like formed in communication with voids formed between particles can also have an open cell structure.

The molded product has an open cell ratio of 2% or more and 7.5% or less. By setting the open cell ratio of the molded article to the specific range, it is possible to suppress significant shrinkage, deformation, etc. of the molded article and improve the appearance and rigidity of the molded article even if the curing step is omitted. This is because the molded article has an open-cell structure at the above-mentioned specific ratio, so that air can quickly flow into the cells inside the molded article after the mold is released, increasing the internal pressure of the entire molded article. This is thought to be because

If the open cell ratio of the molded article is too low and the curing step is omitted, the molded article may shrink and deform significantly, making it impossible to obtain a molded article having a desired shape. Even if the curing step is omitted, the open cell ratio of the molded body is set to 2% or more from the viewpoint of further suppressing significant shrinkage, deformation, etc. of the molded body. From the same point of view, the open cell ratio of the molded product is preferably 2.5% or more, more preferably 3% or more, and even more preferably 4% or more. On the other hand, if the open cell ratio of the molded article is too high, the appearance of the molded article may deteriorate and the rigidity may decrease. In addition, depending on the application, the water leakage prevention property of the molded product may be insufficient. The open cell ratio of the molded article is set to 7.5% or less from the viewpoint that the appearance, rigidity and water leakage prevention property of the molded article can be further improved. From the same point of view, the open cell ratio of the molded article is preferably 7% or less, more preferably 6.5% or less, and even more preferably 6% or less.

The open cell ratio of the molded body conforms to ASTM-D6226-10, and according to procedure 2 described in Supplement X1.3 of the same standard, corrects the influence of closed cells that are destroyed when the measurement sample is cut out. measured. Specifically, first, the molded article is allowed to stand at a temperature of 23° C. for 12 hours to adjust the state of the molded article. Next, a first cubic test piece measuring 2.5 cm long x 2.5 cm wide x 2.5 cm high was cut out from the center of the compact, and its geometric volume Va (unit: cm ³ ), that is, The product of the vertical dimension (unit: cm), the horizontal dimension (unit: cm) and the height dimension (unit: cm) is calculated. Next, the true volume V1 (unit: cm ³ ) of the first test piece is measured using a dry automatic densitometer (specifically, Accupic II1340 manufactured by Shimadzu Corporation). At this time, the pressure applied in the purging step and the testing step is set to 5 kPa. Also, in steps 9.13 and 9.14, wait until the pressure change rate becomes 0.100 kPa/min or less, and record the pressure.

After that, the first test piece is divided into 8 equal parts to prepare a second cubic test piece of 1.25 cm length×1.25 cm width×1.25 cm height. Then, the true volume (unit: cm ³ ) of each second test piece is measured by the same method as the method for measuring the true volume V1 of the first test piece. The true volumes of the individual second specimens are then summed to determine the true volume V2 of the second specimen.

Using the geometric volume Va of the first test piece thus obtained, the true volume V1 of the first test piece, and the true volume V2 of the second test piece (unit: cm ³ ), the following The open cell ratio (unit: %) of the first test piece is calculated based on the formula (1). The open cell ratio measured in this manner is a value corrected for the influence of closed cells destroyed when cutting out the second test piece from the first test piece, and is also called a corrected open cell ratio.
Open cell ratio = (Va-2V1+V2) x 100/Va (1)

The above operation is performed for the five first test pieces, and the open cell ratio of each first test piece is calculated. Then, the arithmetic mean value of the open cell ratios in the five first test pieces is taken as the open cell ratio Co of the compact.

In addition, the open cell ratio Co in this specification is a physical property value measured in accordance with ASTM-D6226-10 as described above, correcting the influence of cutting out the sample according to procedure 2 described in Supplement X1.3. , ASTM-D6226-10, which cannot be calculated based on the closed cell content of the molded product. That is, the open cell ratio Co of the molded body measured by the above method has the relationship shown in the following formula (2) with the closed cell ratio Bp of the molded body measured according to ASTM-D6226-10. are doing.
Co≠100−Bp (2)

The open cell ratio Co measured by the above method is corrected for the effect of closed cells destroyed when the test piece is cut, while it is measured according to the method described in ASTM-D6226-10. The closed cell ratio Bp of the molded product obtained is not corrected for the influence of closed cells that are destroyed when the test piece is cut out. Therefore, the open cell rate Co of the molded body is a physical property value having a concept different from the closed cell rate Bp. In addition, the ratio of closed cells destroyed when the test piece is cut out depends on the shape of the expanded beads (that is, the presence or absence of grooves, the cross-sectional area of the grooves, etc.) and the closed cell ratio of the expanded beads. greatly affected. Furthermore, the proportion of closed cells destroyed when a test piece is cut out is also affected by the molding conditions of the expanded bead molded article (that is, the molding pressure, the internal pressure of the expanded bead, the filling method, etc.). Therefore, it is also difficult to estimate the value of the open cell ratio Co based on the value of the closed cell ratio of the molded body measured according to ASTM-D6226-10. The closed cell content of the molded body measured in accordance with ASTM-D2856-70 procedure C is technically equivalent to the closed cell content Bp of the molded body measured in accordance with ASTM-D6226-10. Therefore, it is also difficult to estimate the value of the open cell ratio Co based on the value of the closed cell ratio of the molded article measured according to ASTM-D2856-70 procedure C.

In addition, the open cell ratio Co in this specification is a physical property value having a concept different from that of the porosity of the molded body. The porosity of the compact is measured and calculated, for example, as follows. Specifically, first, a rectangular parallelepiped test piece (for example, 20 mm long×100 mm wide×20 mm high) is cut out from the center of the compact. Next, the test piece is submerged in a graduated cylinder filled with ethanol, and the true volume Vc (unit: L) of the test piece is determined from the rise in the liquid level of ethanol. Also, the apparent volume Vd (unit: L) is obtained from the external dimensions of the test piece. The porosity (unit: %) of the compact is expressed by the following formula (3) using the true volume Vc and the apparent volume Vd of the test piece obtained above.
Porosity = [(Vd-Vc) / Vd] × 100 (3)

Thus, the measurement of the porosity of the molded body also does not consider the closed cells that are broken when the test piece is cut out. In addition, this method differs from the method for measuring the open cell ratio Co in that a liquid such as ethanol is used as a medium for measurement. Therefore, it is also difficult to estimate the value of the open cell ratio Co based on the value of the porosity of the compact. In addition, the porosity of the molded body is always a value larger than the open cell ratio Co.

The molded article has a closed cell ratio of 90% or more. By setting the closed cell ratio of the molded body to 90% or more, the appearance and rigidity of the molded body can be improved. From the viewpoint of further improving the appearance and rigidity of the molded article, the closed cell ratio of the molded article is preferably 91% or more, more preferably 92% or more.

The closed cell content of the molded body is measured according to ASTM-D6226-10. Specifically, first, a specimen of 25 mm length × 25 mm width × 25 mm height is cut out from the center of the molded body, and the geometric volume Va (unit: cm ³ ) of the specimen, that is, the vertical dimension (unit: cm), the horizontal dimension (unit: cm) and the height dimension (unit: cm). Next, according to the procedure described in ASTM-D6226-10, an air comparison type hydrometer (specifically, Accupic II1340 manufactured by Shimadzu Corporation) is used to measure the true volume value Vx of the specimen. . At this time, the pressure applied in the purging step and the testing step is set to 5 kPa. Also, in steps 9.13 and 9.14, wait until the pressure change rate becomes 0.100 kPa/min or less, and record the pressure. The true volume value Vx obtained by the air-comparative hydrometer is the sum of the volume of the resin constituting the measurement sample and the total bubble volume of the closed-cell portion in the measurement sample (unit: cm ³ ). is.

The closed cell ratio (unit: %) of the test piece is obtained by the weight W (unit: g) of the test piece, the density ρ (unit: g/cm ³ ) of the resin constituting the expanded beads, and the method described above. Using the geometric volume Va of the specimen and the true volume Vx of the specimen, it is represented by the following formula (4).
Closed cell ratio = (Vx-W/ρ) x 100/(Va-W/ρ) (4)

The above operation is performed for five specimens, and the closed cell ratio of each specimen is calculated. Then, the arithmetic average value of the closed cell ratios in these five specimens is taken as the closed cell ratio of the molded body.

From the viewpoint that dimensional change can be more sufficiently suppressed even if the curing step is omitted, the porosity of the molded body is preferably 4% or more, more preferably 4.5% or more. % or more is more preferable. On the other hand, from the viewpoint of further improving rigidity and appearance, the porosity of the molded body is preferably 12% or less, more preferably 10% or less, and even more preferably 8% or less. The porosity of the molded body can be measured by the measuring method described above.

The molding magnification of the molded body is set to 15 times or more and 90 times or less. A molded article having a molded article magnification within the specific range is lightweight and has excellent rigidity. In addition, by setting the open cell ratio and closed cell ratio of the molded body to the specific ranges, even when the curing step is omitted in the range of the molded body magnification of 15 times or more and 90 times or less, shrinkage of the molded body and Deformation can be suppressed. If the molding magnification is too low, it is difficult to obtain a lightweight molding. From the viewpoint of avoiding such problems more easily, the molding magnification is preferably 20 times or more, more preferably 25 times or more, and even more preferably 30 times or more.

On the other hand, if the molding magnification is too high, the rigidity of the molding may be lowered. From the viewpoint of avoiding such problems more easily, the molding magnification is preferably 75 times or less, more preferably 55 times or less. If the molding magnification is too low, the rigidity of the molding becomes high, so there is no need to perform a curing step for the purpose of recovering dimensional changes due to shrinkage and deformation of the molding after molding in the mold.

The molding magnification is a value obtained by dividing the density (unit: kg/m ³ ) of the crystalline thermoplastic resin constituting the molding by the molding density (unit: kg/m ³ ). The density of the molded article is calculated by dividing the mass (unit: g) of the molded article by the volume (unit: L) determined from the outer dimensions of the molded article and converting the unit. For example, when the molded body has at least a partially complicated shape and it is difficult to determine the volume from the external dimensions of the molded body, the volume of the molded body can be determined by the submersion method.

The compact density is preferably 10 kg/m ³ or more and 60 kg/m ³ or less. In this case, it is possible to improve the lightness and rigidity of the molded body in a well-balanced manner. From the viewpoint of further improving the rigidity of the molded article, the density of the molded article is more preferably 15 kg/m ³ or more, further preferably 20 kg/m ³ or more. From the viewpoint of further improving the lightness of the molded article, the density of the molded article is more preferably 50 kg/m ³ or less, and even more preferably 45 kg/m ³ or less.

Conventionally, when producing a compact with a low density (that is, a compact with a high molding ratio), it has been particularly difficult to omit the curing step because the compact is likely to be remarkably deformed after demolding. On the other hand, even if the density of the expanded bead molded article is low, the curing process can be omitted, and even without curing, the molded article has a desired shape and is excellent in appearance and rigidity. Also from the viewpoint of effectively exhibiting this effect, it is preferable to set the density of the compact within the above range.

The number of foamed particles per unit area on the surface of the molded article is preferably 2/cm ^{2 or} more and 50/cm 2 or less, and is preferably 3/cm ^{2 or} more and 30/cm ² or less. More preferably, it is 4/cm ² or more and 20/cm ² or less. In this case, the effect of suppressing shrinkage and deformation of the molded body can be more reliably obtained even when the curing step is omitted in the range of the molded body magnification of 15 times or more and 90 times or less.

The number of expanded particles per unit area on the surface of the molded article can be measured by the following method. First, five or more square-shaped evaluation regions each having a side of 100 mm are set on the surface of the molded body, excluding the end portions. Then, the number of foamed particles present in each evaluation area is counted. At this time, it is assumed that the foamed particles existing on the boundary line of the evaluation area also exist within the evaluation area. By dividing the number of foamed particles in the evaluation area thus obtained by the area of the evaluation area, the number of foamed particles per unit area (that is, 1 cm ² ) in each evaluation area is calculated. By arithmetically averaging the number of expanded particles per unit area (that is, 1 cm ² ) obtained in a plurality of evaluation areas, the number of expanded particles per unit area on the molded body surface can be calculated.

The 50% compressive stress σ ₅₀ of the compact is preferably 185 kPa or more, more preferably 200 kPa or more, and even more preferably 220 kPa or more. In this case, the rigidity of the molding can be further increased. The 50% compressive stress σ ₅₀ of the compact can be obtained based on JIS K6767:1999.

Also, the ratio of the 50% compressive stress σ ₅₀ to the density of the compact is preferably 7.5 kPa/(kg/m ³ ) or more. In this case, the rigidity per unit mass of the molded body can be further increased, and the balance between lightness and rigidity of the molded body can be further improved.

Molded articles are also used as sound absorbing materials, impact absorbing materials, cushioning materials, etc. in various fields such as the field of vehicles such as automobiles and the field of construction.

(Manufacturing method of foamed bead molding)
In producing the expanded bead molded article, for example, after filling the expanded crystalline thermoplastic resin particles into a molding die, steam is supplied into the molding die to carry out molding in the mold. Specifically, first, foamed particles are filled into a mold having a cavity corresponding to the shape of a desired molded article.

The foamed particles to be filled in the mold have a foamed layer with a crystalline thermoplastic resin as a base resin, have a columnar shape without through-holes, and have at least one have grooves. The ratio Ca/ A is 0.01 or more and 0.25 or less, and a ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads is 0.02 or more and 0.75 or less, The average outer diameter D is 0.5 mm or more and 10 mm or less. The ratio L/D of the average length L of the expanded beads in the axial direction to the average outer diameter D of the expanded beads is 0.5 or more and 2.0 or less. A more detailed configuration of the expanded beads will be described later.

After filling the mold with such expanded particles, steam is supplied into the mold to heat the expanded particles. The foamed particles in the molding die are heated by steam and are fused together while undergoing secondary foaming. As a result, the expanded particles in the mold can be integrated to form a molded product.

After the heating of the expanded particles is completed, the molded body in the mold is cooled to stabilize its shape. After that, the in-mold molding is completed by removing the molded body from the molding die. In the manufacturing method, if necessary, a curing step may be performed in which the molded article after mold release is allowed to stand in a high temperature atmosphere adjusted to a temperature of about 60° C. to 80° C. for a predetermined period of time. Shrinkage and deformation of the molded body can be suppressed even when the molded body is not subjected to a curing step in a high-temperature atmosphere after molding. When the curing step is omitted, the shape of the molded article can be stabilized by, for example, leaving the molded article after release from the mold in an environment of 23° C. for 12 hours.

In the production method, the open cell ratio of the molded product can be adjusted within the range of 2% or more and 7.5% or less, for example, by the following method.

First, as the expanded beads, expanded beads having the specific shape and a closed cell ratio within the specific range are used. The expanded beads used in the manufacturing method have a columnar shape with no through holes. Since the expanded particles do not have through-holes inside, the expanded particles easily expand outward by secondary expansion during molding in the mold, and the secondary expandability is high. Therefore, by not forming through-holes in the foamed particles, the open cell ratio of the molded article can be easily adjusted within the above range. In addition, the expanded beads have grooves on their side peripheral surfaces. If the foamed particles do not have grooves, it is difficult to set the open cell ratio of the molded article to 2% or more. A specific aspect of the grooves provided in the expanded beads will be described later.

In addition, the open cell ratio of the molded product is determined by the ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads, and the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads. The higher the ratio Ct/A, the greater the tendency. Therefore, when the ratio Ca/A and/or the ratio Ct/A is too low, the open cell ratio tends to be less than 2%, and when the ratio Ca/A and/or the ratio Ct/A is too high, the open cell ratio is It tends to be higher than 7.5%.

The open cell ratio of the molded article tends to increase as the ratio L/D of the average length L of the expanded beads in the axial direction to the average outer diameter D of the expanded beads increases. Therefore, even when the ratio L/D is too high, the open cell ratio tends to be higher than 7.5%.

Furthermore, when the foamed beads have a low closed cell ratio, the foamed beads themselves contain a large number of open cells, so that the molded article tends to have a high open cell ratio. Therefore, by performing in-mold molding using expanded particles having a closed cell ratio of 90% or more, an excessive increase in the open cell ratio of the molded article can be easily avoided.

In addition to the in-mold molding using such specific foamed particles, for example, by controlling the conditions in the in-mold molding as follows, the open cell ratio of the molded product can be increased to 2% or more7. It can be more easily adjusted within the range of 5% or less.

When internal pressure is applied to the foamed particles before being filled into the mold, secondary foaming tends to occur during molding, and the open cell ratio tends to decrease. In addition, when the internal pressure of the foamed beads is increased, the foamed beads tend to swell more easily during molding, so that the open cell ratio tends to decrease. From the viewpoint of more easily avoiding the open cell rate becoming too small and more stably producing a molded article having an open cell rate of 2% or more, and from the viewpoint of the production efficiency of the molded article, it is recommended to fill the mold. The internal pressure of the expanded beads is preferably 0.1 MPa (G) (G: gauge pressure) or less, more preferably 0.05 MPa (G) or less, and 0.03 MPa (G) or less. More preferably, 0 MPa (G), that is, molding without applying an internal pressure to the expanded beads is particularly preferable. The pressure (internal pressure) inside the bubble can be measured by the method described in Japanese Patent Application Laid-Open No. 2003-201361, for example.

Further, if the filling is performed so that the foamed particles in the mold are in a compressed state when the filling is completed, the gaps between the foamed particles are easily filled. For example, when the filling rate of the expanded particles filled in the mold at the completion of filling is increased, the open cell rate tends to decrease, and when the filling rate is decreased, the open cell rate tends to increase. Therefore, the open cell ratio can be adjusted within a desired range by adjusting the filling rate of the expanded particles.

As a method of compressing the foamed particles, for example, a cracking filling method can be adopted. The cracking filling method is a molding method that prevents the mold from being completely closed in order to efficiently fill the foamed particles in an amount exceeding the volume inside the mold when filling the mold with foamed particles. This is a method of providing an opening. This open portion is called cracking, and the ratio of the volume of the open portion to the volume inside the mold (unit: %) is called the amount of cracking. The cracking is finally closed when steam is introduced after the mold is filled with foamed particles, and as a result, the filled foamed particles are mechanically compressed. When the foamed particles are filled into the molding die by the cracking filling method, the cracking amount is generally preferably in the range of 5% to 35%, more preferably in the range of 8% to 30%. , more preferably in the range of 10% to 25%.

Instead of the cracking filling method described above, a compression filling method (for example, the method described in JP-B-4-46217), etc., in which foamed particles that have been pre-compressed by pressurized gas or the like are filled into a mold. method can also be adopted.

In particular, the ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads is more than 0.20 and 0.25 or less, or the total number of grooves to the average cross-sectional area A of the expanded beads. When performing in-mold molding using expanded beads having relatively large grooves, such as expanded beads having a cross-sectional area Ct ratio Ct/A of more than 0.20 and 0.75 or less, An open cell structure is easily formed. In this case, the filling rate of the foamed particles in the molding die is, for example, 30% or more, preferably 40% or more, thereby suppressing the formation of an excessive open-cell structure in the molded body and improving the appearance and rigidity. An excellent molded article can be obtained. In this case, it is preferable to fill the mold with the foamed particles by a compression filling method.

The filling rate (unit: %) of the expanded particles is defined by the mass a (unit: kg) of the expanded particles filled in the mold, the bulk density b (unit: kg/m ³ ) of the expanded particles, and the internal volume of the mold. It is represented by the following formula (5) using c (unit: m ³ ).
Filling rate = [{a/(bxc)}-1]x100 (5)

In addition, when the molding temperature (specifically, the molding pressure) during molding in the mold is increased, the open cell ratio tends to decrease, and when the molding temperature (specifically, the molding pressure) is lowered, the open cell ratio tends to increase. However, from the viewpoint of production efficiency of the molded body, it is preferable to perform molding at a low molding pressure. From this point of view, the molding pressure is, for example, preferably in the range of 0.18 MPa (G) or more and 0.30 MPa (G) or less in gauge pressure, and in the range of 0.22 MPa (G) or more and 0.28 MPa (G) or less. is more preferable.

The above-described manufacturing conditions are only an example, and if the foamed beads are molded so that the open cell ratio of the finally obtained molded product is 2% or more and 7.5% or less, the desired It is possible to produce a molded article having a shape and excellent appearance and rigidity.

The molded body obtained by the above manufacturing method is less likely to shrink or deform even when the curing step is not performed. The reason why this effect is obtained is, for example, the following reasons. Since the expanded particles have grooves extending along their axial direction, it is thought that when steam is supplied into the mold, the steam can pass through the grooves. It is believed that this makes it easier for the steam to reach the inside of the mold, so that the entire foamed particles in the mold can be easily heated. Therefore, even if the molding heating temperature is low during in-mold molding, it is possible to obtain a molded article that is excellent in fusion bondability and has a good appearance.

In addition, as a result of the steam reaching the inside of the mold more easily, the amount of heat received by the foamed particles due to the steam during molding in the mold can be kept low. Moreover, the internal temperature of the molded body after mold release is prevented from becoming excessively high. As a result of these factors, it is believed that the dimensions of the molded body after in-mold molding are easily stabilized at an early stage.

In addition, as described above, the molded article after in-mold molding has an open-cell structure consisting of open cells, that is, has minute space portions communicating with the outside of the molded article. Therefore, it is thought that when the molded body is removed from the mold after in-mold molding, air quickly flows into the air bubbles inside the molded body through the open cells, and as a result, the internal pressure of the molded body stabilizes at an early stage. As a result, it is considered that the manufacturing method can suppress significant shrinkage and deformation of the compact even when the curing step is not performed.

(Crystalline thermoplastic resin expanded particles)
The foamed beads used in the manufacturing method have a columnar shape with no through-holes, and have at least one groove on the side peripheral surface thereof. For example, as shown in FIG. 1, the expanded bead 1 includes a bottom surface 11, a top surface 12 disposed above the bottom surface 11 and having substantially the same shape as the bottom surface 11, and an edge of the bottom surface 11 and the top surface 12. It has a side peripheral surface 13 that connects the edge of the In the expanded bead 1 having such a columnar shape, at various positions on the line connecting the center of the bottom surface 11 and the center of the top surface 12 (that is, the central axis of the expanded bead 1), The cross-sectional shape obtained by cutting the foamed beads 1 along a vertical plane is generally the same.

Further, the aforementioned "groove" refers to a concave portion provided on the side peripheral surface of the expanded bead and extending along the axial direction of the expanded bead. More specifically, when the grooves 3 of the expanded beads 1 are cut along a plane perpendicular to the axial direction of the expanded beads 1 as shown in FIG. observed as part.

The foamed bead 1 can have various shapes as long as it has a columnar shape with no through-holes and has one or more grooves 3 on its side peripheral surface. For example, as shown in FIGS. 1 and 2, the expanded beads 1 may have a columnar shape with a cross section perpendicular to the axial direction. The expanded bead 1 having such a shape has four grooves 3 on its side peripheral surface 13 . The cross-sectional shape of the foamed beads 1 in the cross section perpendicular to the axial direction is not limited to the shape shown in FIGS. , a shape based on a triangle as shown in FIG. 6, a shape based on a quadrangle as shown in FIGS. 7 and 8, and the like.

The number of grooves 3 provided in the expanded bead 1 may be one as shown in FIGS. 3 and 4, or two or more as shown in FIGS. 1, 2 and 5 to 8. There may be. Further, the cross-sectional shape of the grooves 3 in the cross section perpendicular to the axial direction of the expanded bead 1 is not limited to the V-shape shown in FIGS. Various forms such as a shape (see FIGS. 5 and 6) and a U shape (see FIGS. 7 and 8) are possible. When the expanded bead 1 has two or more grooves 3, all the grooves 3 may have the same cross-sectional shape, or may have different cross-sectional shapes.

It is preferable that the expanded beads have 2 or more and 6 or less grooves. In this case, an open cell structure, which will be described later, is more likely to be formed in the molded body. Therefore, even when the curing step is omitted, the compact is less likely to deform.

Moreover, when the expanded bead has two or more grooves, these grooves are preferably arranged at equal intervals on the side peripheral surface of the expanded bead. In other words, when the expanded bead has a plurality of grooves, these grooves are preferably arranged at symmetrical positions with respect to the center axis of the expanded bead. In-mold molding of such expanded particles facilitates formation of a more uniform open cell structure in the molded product. Therefore, shrinkage and deformation of the compact can be more reliably suppressed even when the curing step is omitted.

The ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads on the cut surface obtained by cutting the expanded beads at the center in the axial direction along a plane perpendicular to the axial direction is is 0.01 or more and 0.25 or less, and the ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads is 0.02 or more and 0.75 or less, and the average outer diameter of the expanded beads is The diameter D is 0.5 mm or more and 10 mm or less. Also, the ratio L/D of the average length L in the axial direction of the expanded beads to the average outer diameter D of the expanded beads is 0.5 or more and 2.0 or less. Furthermore, the foamed beads have a closed cell ratio of 90% or more.

In this way, the open cell rate of the molded product is within the predetermined range by using the foamed particles having a shape in which the dimensions of each part satisfy the above-described specific range and the closed cell rate is within the above-described specific range. By performing molding in a mold, even if the curing step is omitted, significant shrinkage, deformation, etc. can be suppressed, and a molded product having a desired shape and excellent appearance and rigidity can be produced.

The reason why such an effect can be obtained from the expanded beads is considered to be, for example, as follows. That is, when the foamed particles are molded in a mold, an open-cell structure composed of open cells, that is, a minute space communicating with the outside of the molded body is formed in the molded body. Specifically, the open cell structure includes voids formed by mutually communicating grooves of a plurality of foamed particles, voids formed by grooves of foamed particles communicating with voids formed between foamed particles, and foamed particles. Voids formed by connecting voids between them, open-cell portions of foamed particles constituting the molded article, and the like are connected in a complicated manner.

Since the open-cell structure communicates with the outside of the molded body, it is thought that when a molded body having an appropriate open-cell ratio is released from the mold, outside air will quickly flow into the air bubbles inside the molded body through the open-cell structure. . Then, by allowing outside air to flow into the air bubbles inside the molded body, the internal pressure of the entire molded body tends to quickly balance with the pressure of the atmosphere outside the molded body. As a result of the above, it is believed that the dimensions of the molded body can be stabilized at an early stage, and significant shrinkage and deformation of the molded body can be suppressed even when the curing step is not performed.

In addition, since the foamed particles have grooves extending along the axial direction, it is considered that steam can pass through the grooves when steam is supplied into the molding die. It is believed that this makes it easier for the steam to reach the inside of the mold, so that the entire foamed particles in the mold can be easily heated. Therefore, even if the molding heating temperature is low during in-mold molding, it is possible to obtain a molded article that is excellent in fusion bondability and has a good appearance. As a result, the amount of heat received by the foamed particles due to steam during in-mold molding can be reduced. Moreover, the internal temperature of the molded body after mold release is prevented from becoming excessively high. As a result of these factors, it is believed that the dimensions of the molded body after in-mold molding are easily stabilized at an early stage.

The expanded beads used in the manufacturing method have a columnar shape with no through holes. Since the expanded particles do not have through-holes inside, the expanded particles easily expand outward by secondary expansion during molding in the mold, and the secondary expandability is high. Therefore, by not forming through-holes in the foamed particles, it is possible to easily suppress an excessive increase in the open cell ratio of the molded article described later, and to easily produce a molded article excellent in appearance and rigidity.

When the ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads and/or the ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads is too low In the case of in-mold molding, it becomes difficult for steam to spread in the mold, which may lead to deterioration of moldability. Moreover, in this case, it becomes difficult to form an open cell structure in the molded body, and there is a possibility that a curing step is required in order to suppress significant shrinkage or deformation of the molded body. By setting the ratio Ca/A to 0.01 or more and the ratio Ct/A to 0.02 or more, these problems can be easily avoided, and significant shrinkage or deformation of the molded body can be achieved even when the curing step is not performed. It is possible to obtain expanded particles capable of suppressing the Moreover, by using such expanded particles, the water cooling time during in-mold molding can be shortened. From the viewpoint of obtaining these effects more reliably, the ratio Ca/A is preferably 0.02 or more, more preferably 0.03 or more. From the same point of view, the ratio Ct/A is preferably 0.05 or more, more preferably 0.08 or more, and even more preferably 0.10 or more.

On the other hand, when the ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads and/or the ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads is too high. However, there is a risk that the rigidity of the molded product will be reduced and the appearance will be deteriorated. Moreover, in this case, the open cell ratio of the molded article may become excessively high. By setting the ratio Ca/A to 0.25 or less and the ratio Ct/A to 0.75 or less, these problems can be easily avoided, and the rigidity and appearance of the molded product can be improved. From the viewpoint of obtaining such effects more reliably, the ratio Ca/A is preferably 0.20 or less, more preferably 0.15 or less, and even more preferably 0.10 or less. From the same viewpoint, the ratio Ct/A is preferably 0.70 or less, more preferably 0.50 or less, further preferably 0.30 or less, and 0.20 or less. is particularly preferred.

A method for calculating the average cross-sectional area A of the expanded beads described above is as follows. First, the expanded beads 1 are cut at the center in the axial direction along a plane perpendicular to the axial direction to expose a cut surface as shown in FIG. The cross-sectional area of the expanded beads 1 on this cut surface is measured. For example, as shown in FIG. 2, when the foamed bead 1 consists of only the foamed layer 2, the cross-sectional area of the foamed bead 1 is equal to the cross-sectional area of the foamed layer 2 on the cut surface. Further, as shown in FIG. 11, when the foamed bead 1 has the foamed layer 2 and the coating layer 4 covering the foamed layer 2, the cross-sectional area of the foamed bead 1 is equal to the cross-sectional area of the foamed layer 2 on the cut surface. It is the sum with the cross-sectional area of layer 4 . The cross-sectional area of the expanded beads 1 on the cut surface can be measured, for example, by taking a photograph of the cut surface of the expanded beads and analyzing the image.

The above operation is performed for 100 or more expanded beads, and the arithmetic average value of the cross-sectional areas of the obtained expanded beads is defined as the average cross-sectional area A of the expanded beads on the cut surface.

The method for calculating the average cross-sectional area Ca per groove and the total cross-sectional area Ct of the grooves is as follows. As shown in FIG. 2 and the like, a tangent line L1 is drawn outside the individual grooves 3 on the cut surface of the foamed bead 1, which contacts the outline of the foamed bead 1 at two points P1 and P2 and does not pass through the inside of the foamed bead 1. As shown in FIG. Then, the area of the region surrounded by the outline of the foamed bead 1 and the tangent line L1 is calculated, and this area is defined as the cross-sectional area C of each groove 3 . That is, the cross-sectional area C of each groove 3 is the area of the shaded area in FIG. The above operation is performed for all the grooves 3, and the sum of the cross-sectional areas C of the grooves 3 in each foamed bead 1 is calculated. Further, the total cross-sectional area C of the grooves 3 thus obtained is divided by the number of the grooves 3 to calculate the cross-sectional area per groove in each expanded bead 1 .

The above operation is performed for 100 or more foamed beads, and the arithmetic average value of the total cross-sectional areas of the obtained grooves is defined as the total cross-sectional area Ct of the grooves. The obtained average value of the cross-sectional area per groove is defined as the average cross-sectional area Ca per groove.

If the average outer diameter D of the expanded particles at the cut surface is too small, the molded product is likely to be deformed or shrunk when the curing step is omitted, which may lead to a decrease in dimensional stability. Such problems can be easily avoided by setting the average outer diameter D of the expanded beads to 0.5 mm or more, preferably 1.0 mm or more, and more preferably 2.0 mm or more.

On the other hand, if the average outer diameter D of the expanded particles is too large, there is a risk of deterioration in the fillability into the mold. Such problems can be easily avoided by setting the average outer diameter D of the expanded beads to 10 mm or less, preferably 8.0 mm or less, and more preferably 5.0 mm or less.

If the ratio L/D of the average length L of the expanded beads in the axial direction to the average outer diameter D of the expanded beads is too high, the open cell ratio of the molded article may become too large. Moreover, in this case, there is a possibility that the surface property of the molded body is deteriorated and the rigidity is lowered. In addition, depending on the application, the water leakage prevention property of the molded product may be insufficient. These problems can be easily avoided by setting the value of the ratio L/D to 2.0 or less. From this point of view, the ratio L/D of the average length L of the expanded beads in the axial direction to the average outer diameter D of the expanded beads is preferably 1.5 or less, more preferably less than 1.3. preferable.

On the other hand, if the ratio L/D of the average length L of the expanded beads in the axial direction to the average outer diameter D of the expanded beads is too low, the water cooling time during in-mold molding may become longer. Moreover, as a result of the excessively low open cell ratio of the molded article, it may become difficult to suppress deformation of the molded article when the curing step is omitted. Such a problem can be easily avoided by setting the value of the ratio L/D to 0.5 or more. From the same point of view, the ratio L/D of the average length L of the expanded beads in the axial direction to the average outer diameter D of the expanded beads is preferably 0.7 or more, and more preferably exceeds 0.7. .

A method for calculating the average outer diameter D of the expanded beads described above is as follows. First, the expanded bead 1 is cut at the center in the axial direction along a plane perpendicular to the axial direction to expose the cut surface of the expanded bead 1 as shown in FIG. 2 and the like. Two points P3 and P4 are defined on the contour of the expanded bead 1 on the cut surface so that the distance between them is the longest, and the distance between these two points (that is, the maximum outer diameter of the expanded bead on the cut surface) is determined. The outer diameter of each expanded bead 1 is defined as d. Then, the average outer diameter D of the expanded beads is defined as the arithmetic average value of the measured outer diameters d of 100 or more expanded beads 1 . The outer diameter of the expanded beads 1 on the cut surface can be measured, for example, by taking a photograph of the cut surface of the expanded beads and analyzing the image.

The average length L of the expanded beads described above is the arithmetic mean value of the maximum length in the axial direction of the expanded beads measured for 100 or more expanded beads. The maximum length of the expanded beads in the axial direction can be measured using, for example, a vernier caliper.

The closed cell ratio of the expanded beads is preferably 90% or more, preferably 92% or more, and more preferably 95% or more. In this case, even if the filling rate of the mold is relatively low, it is possible to form an appropriate open-cell structure in the molded article and more easily obtain a molded article having excellent surface properties and rigidity. can.

The closed cell content of the expanded beads can be measured using an air-comparative hydrometer based on ASTM-D6226-10. Specifically, it is measured as follows. First, the expanded beads are allowed to stand in an environment of 50% relative humidity, 23° C. temperature, and 1 atm atmospheric pressure for 24 hours or longer to adjust the state of the expanded beads. After collecting a measurement sample so that the bulk volume of the foamed particles after conditioning, that is, the value of the marked line when naturally deposited in a graduated cylinder is about 20 cm ³ , the apparent volume of the measurement sample is measured. Measure. The apparent volume of the measurement sample is specifically the volume corresponding to the amount of rise in the liquid level when the measurement sample is submerged in a graduated cylinder containing ethanol at a temperature of 23°C.

After sufficiently drying the measurement sample whose apparent volume was measured, according to the procedure described in ASTM-D6226-10, the value of the true volume of the measurement sample measured by Accupic II 1340 manufactured by Shimadzu Corporation to measure. In the measurement of the true volume Vx, the pressure applied in the purging step and the testing step is 5 kPa. Also, in steps 9.13 and 9.14, wait until the pressure change rate becomes 0.100 kPa/min or less, and record the pressure. Then, using these volume values, the closed cell ratio (unit: %) of the measurement sample is calculated based on the following formula (6).
Closed cell ratio = (Vx-W/ρ) x 100/(Va-W/ρ) (6)

However, Vx (unit: cm ³ ) in the above formula (6) is the true volume of the expanded bead (that is, the sum of the volume of the resin constituting the expanded bead and the total volume of the closed cells in the expanded bead). where Va (unit: cm ³ ) is the apparent volume of the foamed beads (that is, the volume measured from the rise in liquid level when the foamed beads are submerged in a measuring cylinder containing ethanol), and W (unit: : g) is the mass of the measurement sample, and ρ (unit: g/cm ³ ) is the density of the crystalline thermoplastic resin forming the foam layer.

The above operation is performed five times using different measurement samples, and the arithmetic average value of the closed cell ratios obtained by these five measurements is taken as the closed cell ratio of the expanded beads.

The bulk ratio of the expanded beads is preferably 15 times or more and 90 times or less. By performing in-mold molding using expanded particles having a bulk ratio within the above range, it is possible to easily obtain a molded article that is lightweight and has excellent rigidity. In addition, the foamed particles have the specific shape and the closed cell ratio is set in the specific range, so that even when the curing process is omitted in the range of the bulk magnification of 15 times or more and 90 times or less, the foamed beads can shrink or deform. can more easily obtain a compact with a small .

The bulk ratio of the expanded beads is a value obtained by dividing the density (unit: kg/m ³ ) of the crystalline thermoplastic resin forming the expanded layer by the bulk density (unit: kg/m ³ ) of the expanded beads. A method for calculating the bulk density of the expanded beads is as follows. First, the expanded beads are allowed to stand in an environment of 50% relative humidity, 23° C. temperature, and 1 atm atmospheric pressure for 24 hours or longer to adjust the state of the expanded beads. Next, the foamed particles after conditioning are filled in a graduated cylinder so that they naturally accumulate, and the bulk volume (unit: L) of the foamed particles is read from the scale of the graduated cylinder. Then, the bulk density of the expanded particles (unit: kg/m ³ ) can be obtained by converting the value obtained by dividing the mass (unit: g) of the expanded particles group in the graduated cylinder by the bulk volume described above. .

It is preferable that the average cross-sectional area Ca per groove on the cut surface of the expanded beads is 0.05 mm ² or more and 2.0 mm ² or less. After setting the ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads as the specific range, the average cross-sectional area Ca per groove is set within the specific range. By doing so, the above-described effect of the grooves can be obtained more reliably. From the same point of view, the average cross-sectional area Ca per groove is more preferably 0.1 mm ² or more and 1.8 mm ² or less.

It is preferable that the ratio H/D of the average depth H per groove to the average outer diameter D of the expanded beads on the cut surface of the expanded beads is 0.35 or less. In this case, an open-cell structure is likely to be appropriately formed in the molded body, and shrinkage and deformation of the molded body when the curing step is omitted can be more effectively suppressed. Furthermore, in this case, in addition to the effects described above, the rigidity of the molded body can be increased. From the viewpoint of enhancing such effects, the ratio H/D of the average depth H per groove to the average outer diameter D of the expanded beads is more preferably 0.30 or less, more preferably 0.25 or less. is more preferable.

From the same point of view, the average depth H per groove on the cut surface of the expanded beads is preferably 1.5 mm or less, more preferably 1.2 mm or less, and 1.0 mm or less. is more preferred.

In addition, from the viewpoint of suppressing an excessive decrease in the open cell ratio of the molded article, the ratio of the average depth H per groove to the average outer diameter D of the expanded beads on the cut surface of the expanded beads H/D is preferably 0.02 or more, more preferably 0.05 or more. From the same point of view, the average depth H per groove on the cut surface is preferably 0.1 mm or more, more preferably 0.2 mm or more.

A method for calculating the average depth H per groove on the cut surface is as follows. First, the expanded bead 1 is cut at the center in the axial direction along a plane perpendicular to the axial direction to expose the cut surface of the expanded bead as shown in FIG. 2 and the like. Next, a tangent line L1 is drawn outside the individual grooves 3 on the cut surface, which contacts the outline of the foamed bead 1 at two points P1 and P2 and does not pass through the inside of the foamed bead 1 . The maximum value h of the distance from the tangent line L1 to the peripheral edge of the groove 3 (that is, the contour of the expanded bead) in the direction perpendicular to the tangent line L1 is measured. Then, the maximum value h of the distance described above is measured for all the grooves 3, and the arithmetic mean value of these values is taken as the depth of the groove of each foamed bead. The depth of the grooves of the individual expanded beads on the cut surface can be measured, for example, by taking a photograph of the cut surface of the expanded beads and analyzing the image.

The arithmetic average value of the groove depths measured for 100 or more expanded beads 1 is defined as the groove depth H of the expanded beads.

The ratio A/B of the average cross-sectional area A of the expanded beads to the area B of the virtual perfect circle having the average outer diameter D of the expanded beads is preferably 0.35 or more and 0.90 or less. In this case, the open cell ratio of the molded body can be more easily adjusted to an appropriate range, the rigidity and appearance of the molded body can be improved more easily, and shrinkage and deformation of the molded body can be suppressed when the curing step is not performed. effect can be obtained more reliably. From the viewpoint of easily improving the rigidity and appearance of the molded article, the ratio A/B is more preferably 0.40 or more, more preferably 0.55 or more, and more preferably 0.70 or more. is particularly preferred. From the viewpoint of more reliably obtaining the effect of suppressing shrinkage and deformation of the molded body, the ratio A/B is more preferably 0.85 or less, and even more preferably 0.80 or less.

The ratio of the apparent density to the bulk density of the expanded beads is preferably 1.7 or more and 1.9 or less. In this case, the open cell ratio of the molded body can be more easily adjusted to an appropriate range, the rigidity and appearance of the molded body can be improved more easily, and shrinkage and deformation of the molded body can be suppressed when the curing step is not performed. effect can be obtained more reliably.

From the viewpoint of the balance between lightness and rigidity of the molded article, the apparent density of the foamed particles is preferably 10 kg/m ³ or more and 150 kg/m ³ or less, and 15 kg/m ³ or more and 100 kg/m ³ or less. is more preferably 20 kg/m ³ or more and 80 kg/m ³ or less, and particularly preferably 25 kg/m ³ or more and 45 kg/m ³ or less. In this way, by performing in-mold molding using foamed particles having a low apparent density, it is possible to easily obtain a lighter molded body. In addition, conventionally, in the case of producing a molded body with a particularly low density (that is, a molded body with a high molded body magnification), the molded body tends to be significantly deformed after releasing from the mold, and it has been difficult to omit the curing step. . On the other hand, since the foamed particles can omit the curing step even when the apparent density is low, a lightweight molded body having a desired shape can be produced without curing.

A method for calculating the apparent density of the expanded beads is as follows. First, the foamed beads are allowed to stand for one day in an environment of 50% relative humidity, 23° C. temperature, and 1 atm atmospheric pressure to adjust the state of the foamed beads. After measuring the mass (unit: g) of the foamed particles, immerse them in a graduated cylinder filled with alcohol (e.g., ethanol) at 23°C using a wire mesh or the like. Unit: L). Thereafter, the apparent density (unit: kg/m ³ ) of the expanded beads can be calculated by converting the value obtained by dividing the mass of the expanded beads by the volume of the expanded beads.

The foamed beads have a foamed layer with a crystalline thermoplastic resin as a base resin. A crystalline thermoplastic resin is a thermoplastic resin having crystallinity, and examples thereof include polypropylene-based resins, polyethylene-based resins, polyamide-based resins, and crystalline polyester-based resins. In this specification, the polypropylene-based resin refers to a homopolymer of a propylene monomer and a propylene-based copolymer containing 50% by mass or more of structural units derived from propylene. Further, the polyethylene-based resin refers to homopolymers of ethylene monomers and ethylene-based copolymers containing 50% by mass or more of constitutional units derived from ethylene.

As used herein, the term "having crystallinity" refers to "when heat of fusion is measured after performing a certain heat treatment" described in JIS K7122 (1987) (heating rate and cooling rate in condition adjustment of test piece are all 10 ° C./min.), using a heat flux differential scanning calorimeter, the endothermic peak heat quantity accompanying the melting of the resin based on the DSC curve obtained at a heating rate of 10 ° C./min is 5 J / g or more. The endothermic peak heat quantity is preferably 15 J/g or more, more preferably 30 J/g or more.

The foam layer may contain a polymer other than the crystalline thermoplastic resin as long as it does not impair the above effects. Examples of other polymers include amorphous thermoplastic resins such as polystyrene resins, elastomers, and the like. The content of the other polymer in the foam layer is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. It is particularly preferred that the layer contains substantially only crystalline thermoplastic resin as polymer.

In addition, the crystalline thermoplastic resin, which is the base resin of the foam layer, contains a cell control agent, a crystal nucleating agent, a flame retardant, a flame retardant aid, a plasticizer, and an antistatic agent within a range that does not impair the effects described above. Additives such as agents, antioxidants, UV inhibitors, light stabilizers, conductive fillers, antibacterial agents, colorants and the like may also be included. The content of the additive in the foam layer is preferably, for example, 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the crystalline thermoplastic resin.

The crystalline thermoplastic resin forming the foam layer is preferably a polypropylene-based resin, more preferably a propylene-based copolymer obtained by copolymerizing propylene with another monomer. Propylene-based copolymers include propylene and α-olefins having 4 to 10 carbon atoms, such as ethylene-propylene copolymers, butene-propylene copolymers, hexene-propylene copolymers, and ethylene-propylene-butene copolymers. A copolymer with is preferably exemplified. These copolymers may be, for example, random copolymers or block copolymers, but random copolymers are preferred. The foam layer may contain one type of polypropylene resin, or may contain two or more types of polypropylene resin.

Among these polypropylene-based resins, the crystalline thermoplastic resin constituting the foam layer is particularly preferably an ethylene-propylene random copolymer containing 0.5% by mass or more and 3.5% by mass or less of an ethylene component. According to the foamed beads having such a foamed layer, it is possible to more easily obtain a molded article which has excellent in-mold moldability, excellent rigidity and surface properties, and which can suppress deformation and shrinkage even when the curing step is omitted. be able to.

From the viewpoint of obtaining a molded article that is more excellent in rigidity and has less deformation and shrinkage when the curing step is omitted, the content of the ethylene component contained in the ethylene-propylene random copolymer is 0.5% by mass or more. It is preferably less than 2.0% by mass. On the other hand, from the viewpoint of improving the moldability of the expanded beads and obtaining a molded article having excellent energy absorption characteristics, the content of the ethylene component contained in the ethylene-propylene random copolymer is 2.0% by mass or more3. It is preferably 0.5% by mass or less.

The above-mentioned "ethylene component" and "propylene component" respectively mean an ethylene-derived structural unit and a propylene-derived structural unit in an ethylene-propylene copolymer. Moreover, the content of the ethylene component is the mass ratio of the ethylene component when the total of the ethylene component and the propylene component is 100% by mass. The content of each component in the ethylene-propylene copolymer can be determined based on the results of IR spectrum measurement.

When the base resin of the foam layer is a polypropylene-based resin, the melting point Tmc of the polypropylene-based resin is preferably 155° C. or less. In this case, a molded article having excellent appearance and rigidity can be molded at a lower molding temperature (that is, a lower molding pressure). From the viewpoint of improving this effect, the melting point Tmc of the polypropylene-based resin forming the foam layer is preferably 152° C. or lower, more preferably 148° C. or lower. On the other hand, from the viewpoint of further improving the heat resistance, mechanical strength, etc. of the molded product, the melting point Tmc of the polypropylene resin constituting the foam layer is preferably 135° C. or higher, more preferably 138° C. or higher. More preferably, the temperature is 140° C. or higher.

The melting point of the crystalline thermoplastic resin forming the foam layer can be determined based on the obtained DSC curve by performing differential scanning calorimetry (that is, DSC) based on JIS K7121-1987. Specifically, first, the condition of the test piece is adjusted according to "(2) When measuring the melting temperature after a certain heat treatment". A DSC curve was obtained by heating the conditioned test piece from 30°C to 200°C at a heating rate of 10°C/min. Let Tmc. When a plurality of melting peaks appear in the DSC curve, the apex temperature of the melting peak with the largest area is taken as the melting point Tmc.

When the base resin of the foam layer is a polypropylene resin, the melt mass flow rate (that is, MFR) of the polypropylene resin is preferably 5 g/10 minutes or more, more preferably 6 g/10 minutes or more. More preferably, it is 7 g/10 minutes or more. In this case, foamability and moldability can be further enhanced. On the other hand, the MFR of the polypropylene-based resin is preferably 12 g/10 minutes or less, more preferably 10 g/10 minutes or less, from the viewpoint of increasing the rigidity of the molded article. The MFR of a polypropylene resin is a value measured under conditions of a test temperature of 230° C. and a load of 2.16 kg based on JIS K7210-1:2014.

When the base resin of the foam layer is a polypropylene-based resin, the bending elastic modulus of the polypropylene-based resin is preferably 800 MPa or more and 1600 MPa or less. From the viewpoint of increasing the rigidity of the molded body and from the viewpoint of more reliably suppressing dimensional changes when the curing step is omitted, the flexural modulus of the polypropylene-based resin constituting the foam layer is preferably 800 MPa or more. It is more preferably 850 MPa or more, still more preferably 900 MPa or more, and most preferably 1200 MPa or more. On the other hand, from the viewpoint of being able to mold a molded article with excellent appearance and rigidity at a lower molding temperature (i.e., low molding pressure) and from the viewpoint of obtaining a molded article with expanded particles having excellent energy absorption characteristics, the polypropylene constituting the foam layer The flexural modulus of the system resin is preferably less than 1200 MPa, more preferably 1100 MPa or less, and even more preferably 1000 MPa or less. The flexural modulus of polypropylene resin can be determined according to JIS K7171:2008.

Conventionally, when foamed particles made of a polypropylene resin having a bending elastic modulus of less than 1200 MPa are molded in a mold, the resistance to shrinkage and deformation after mold release is small, and if the curing process is omitted, the There was a tendency for the molded product to shrink and deform significantly. On the other hand, according to the above-described method for manufacturing a molded body, even when foamed particles made of a polypropylene-based resin having a flexural modulus of less than 1200 MPa are used, the curing step can be omitted. .

The expanded beads may have a multi-layer structure having a foam layer and a coating layer covering the foam layer. In this case, the covering layer may cover the entire surface of the foam layer, or may cover a portion of the foam layer. The base resin of the coating layer is preferably a thermoplastic resin having a melting point or softening point lower than that of the crystalline thermoplastic resin, which is the base resin of the foam layer. Further, when the base resin of the coating layer is a crystalline thermoplastic resin of the same kind as the base resin of the foam layer, the base resin of the coating layer is the crystalline thermoplastic resin that is the base resin of the foam layer. It is preferred to have a crystallinity lower than the crystallinity. By coating the foam layer with such a thermoplastic resin, the foamed particles can be fused at a lower molding temperature (that is, a lower molding pressure) during in-mold molding. As a result, it is possible to more reliably suppress deformation and shrinkage of the compact when the curing step is omitted.

The thermoplastic resin forming the coating layer may be a crystalline thermoplastic resin or an amorphous thermoplastic resin. As the crystalline thermoplastic resin used for the coating layer, for example, the same kind of crystalline thermoplastic resin as the crystalline thermoplastic resin forming the foam layer can be used. Examples of non-crystalline thermoplastic resins used for the coating layer include polystyrene-based resins and non-crystalline polyester-based resins. When the foam layer is composed of a polypropylene resin, the base resin of the coating layer is preferably a polyolefin resin from the viewpoint of adhesion to the foam layer, and is selected from the group consisting of polyethylene resins and polypropylene resins. It is more preferably one or more selected resins, more preferably a polypropylene-based resin. Examples of the polypropylene resin used as the base resin of the coating layer include ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-propylene-butene copolymers and propylene homopolymers. Among these, it is particularly preferable to use one or more copolymers selected from the group consisting of ethylene-propylene copolymers and ethylene-propylene-butene copolymers as the base resin of the coating layer.

When the thermoplastic resin constituting the coating layer is a crystalline thermoplastic resin, the difference between the melting point Tmc of the crystalline thermoplastic resin constituting the foam layer and the melting point Tms of the crystalline thermoplastic resin constituting the coating layer is Tmc−. Tms is preferably 5°C or higher, more preferably 6°C or higher, and even more preferably 8°C or higher. In this case, the meltability of the foamed particles can be further improved, and the molding temperature can be further lowered. On the other hand, from the viewpoint of suppressing peeling between the foam layer and the coating layer and mutual adhesion between foam particles, the difference Tmc−Tms between the melting point Tmc and the melting point Tms is preferably 35° C. or less, and 20° C. or less. is more preferably 15° C. or lower. The melting point of the crystalline thermoplastic resin used for the coating layer is obtained based on JIS K7121:1987. More specifically, the melting point of the crystalline thermoplastic resin used for the coating layer can be obtained under the same conditions and method as those for the polypropylene-based resin constituting the foamed layer.

Further, when the thermoplastic resin constituting the coating layer is an amorphous thermoplastic resin, the melting point Tmc of the crystalline thermoplastic resin constituting the foam layer and the softening point Tss of the amorphous thermoplastic resin constituting the coating layer The difference Tmc−Tss from the temperature is preferably 5° C. or more, more preferably 6° C. or more, and even more preferably 8° C. or more. In this case, the meltability of the foamed particles can be further improved, and the molding temperature can be further lowered. On the other hand, from the viewpoint of suppressing peeling between the foam layer and the coating layer and mutual adhesion between foam particles, the difference Tmc−Tss between the melting point Tmc and the softening point Tss is preferably 35° C. or less, and 20° C. The following are more preferable. The softening point of the amorphous thermoplastic resin used for the coating layer is the Vicat softening point measured by the A50 method based on JIS K7206:1999.

In the thermoplastic resin constituting the coating layer, crystal nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, ultraviolet inhibitors, light Additives such as stabilizers, conductive fillers, antimicrobial agents, colorants and the like may also be included. The content of the additive in the coating layer is preferably, for example, 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin.

The coating layer of expanded particles may be in a foamed state or in a non-foamed state, but is preferably in a substantially non-foamed state. The term "substantially non-foamed" includes a state in which the coating layer is not foamed and contains no cells, and a state in which the cells disappear after foaming, and means that the coating layer has almost no cell structure. . The thickness of the coating layer is, for example, 0.5 μm or more and 100 μm or less. Further, an intermediate layer may be further provided between the foam layer and the covering layer.

The mass ratio (mass% ratio) of the resin constituting the foam layer and the resin constituting the coating layer is, from the viewpoint of improving the moldability while maintaining the rigidity of the molded body, the foam layer: coating layer = 99.5. : 0.5 to 80:20, more preferably 99:1 to 85:15, even more preferably 97:3 to 88:12.

The foamed particles show an endothermic peak due to melting unique to the crystalline thermoplastic resin constituting the foamed layer and an endothermic peak from the endothermic peak in the DSC curve obtained when heated from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min. It preferably has a crystal structure that exhibits one or more melting peaks located on the high temperature side. Expanded beads having such a crystal structure are excellent in mechanical strength and moldability. In the following description, the endothermic peak due to melting specific to the crystalline thermoplastic resin appearing in the DSC curve is referred to as "resin specific peak", and the melting peak appearing on the higher temperature side than the resin specific peak is referred to as "high temperature peak". The resin-specific peak is generated by endothermic heat absorption during melting of crystals inherent in the crystalline thermoplastic resin forming the foam layer. On the other hand, it is presumed that the high-temperature peak is caused by the melting of secondary crystals formed in the crystalline thermoplastic resin forming the foam layer during the manufacturing process of the expanded beads. That is, when a high-temperature peak appears in the DSC curve, it is presumed that secondary crystals are formed in the crystalline thermoplastic resin.

Whether or not the expanded beads have the crystal structure described above can be determined based on a DSC curve obtained by performing differential scanning calorimetry (DSC) under the conditions described above in accordance with JIS K7121:1987. In performing DSC, 1 to 3 mg of foamed particles may be used as a sample.

In addition, after heating from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min as described above (that is, the first heating), the temperature is cooled from 200 ° C. to 23 ° C. at a cooling rate of 10 ° C./min. In the DSC curve obtained when cooling and then heating again from 23 ° C. to 200 ° C. at a heating rate of 10 ° C./min (that is, the second heating), the crystalline heat constituting the foam layer Only the endothermic peak due to melting inherent to plastic resins is observed. Therefore, by comparing the DSC curve obtained during the first heating and the DSC curve obtained during the second heating, the resin-specific peak and the high-temperature peak can be distinguished. The temperature at the top of this resin-specific peak may slightly differ between the first heating and the second heating, but the difference is usually within 5°C.

The amount of heat of fusion at the high-temperature peak of the expanded beads is preferably 5 J/g or more and 40 J/g or less, from the viewpoint of further improving the moldability of the expanded beads and obtaining a molded article having excellent rigidity, and is preferably 7 J/g. g or more and 30 J/g or less, more preferably 10 J/g or more and 20 J/g or less.

The heat of fusion at the high-temperature peak mentioned above is a value obtained as follows. First, 1 to 3 mg of expanded beads after condition adjustment are used as a sample, and differential scanning calorimetry is performed under the condition of heating from 23° C. to 200° C. at a heating rate of 10° C./min to obtain a DSC curve. An example of a DSC curve is shown in FIG. When the expanded beads have a high temperature peak, the DSC curve shows a resin-specific peak ΔH1 and a high-temperature peak ΔH2 having a peak on the high temperature side of the peak of the resin-specific peak ΔH1, as shown in FIG.

Next, a straight line L2 is drawn connecting the point α corresponding to 80° C. on the DSC curve and the point β corresponding to the final melting temperature T of the expanded beads. Note that the melting end temperature T is the end point on the high temperature side of the high temperature peak ΔH2, that is, the intersection of the high temperature peak ΔH2 and the baseline on the higher temperature side than the high temperature peak ΔH2 in the DSC curve.

After drawing the straight line L2, a straight line L3 parallel to the vertical axis of the graph is drawn through the maximum point γ existing between the resin-specific peak ΔH1 and the high-temperature peak ΔH2. The straight line L3 divides the resin-specific peak ΔH1 and the high-temperature peak ΔH2. The amount of heat absorbed by the high temperature peak ΔH2 can be calculated based on the area of the portion surrounded by the portion forming the high temperature peak ΔH2, the straight line L2, and the straight line L3 in the DSC curve.

(Method for producing expanded beads)
The foamed particles are produced by, for example, dispersing crystalline thermoplastic resin particles having a crystalline thermoplastic resin as a base resin (hereinafter referred to as "resin particles") in a dispersion medium and impregnating the resin particles with a foaming agent. After that, the resin particles containing the foaming agent are discharged under low pressure together with the dispersion medium. Such a foaming method is sometimes called a "direct foaming method".

Resin particles can be produced, for example, by a strand cut method. In the strand cut method, first, a crystalline thermoplastic resin that serves as the base resin of the foam layer and additives such as cell nucleating agents that are supplied as necessary are supplied into an extruder, heated and kneaded to form a resin. It is considered as a melt-kneaded product. Thereafter, the resin melt-kneaded material is extruded through a small hole of a die attached to the tip of the extruder to form a columnar extrudate having grooves. After cooling the extrudate, the extrudate is cut to a desired length to obtain resin particles having a single-layer structure comprising a core layer of a crystalline thermoplastic resin as a base resin.

In order to obtain foamed particles having a multi-layered structure comprising a foam layer and a coating layer, a core layer-forming extruder, a coating layer-forming extruder, and a co-connector connected to these two extruders are used. A co-extrusion device equipped with an extrusion die may be used to produce resin particles having a multilayer structure. In this case, in the core layer-forming extruder, a crystalline thermoplastic resin, which is the base resin of the foam layer, and optional additives are melt-kneaded to form a melt-kneaded core layer-forming resin. to make. In addition, in the extruder for forming the coating layer, a thermoplastic resin serving as the base resin of the coating layer and additives and the like added as necessary are melt-kneaded to prepare a resin melt-kneaded product for forming the coating layer. .

These melt-kneaded resins are co-extruded and combined in a die to form a multi-layer structure composite consisting of a non-foamed columnar core layer and a non-foamed coating layer covering the outer surface of the core layer. to form The composite is extruded through the perforations of a die to form a fluted columnar extrudate. After cooling the extrudate, it is cut to a desired length to obtain resin particles having a multilayer structure. The method for producing the resin particles is not limited to the method described above, and a hot cutting method, an underwater cutting method, or the like may be employed.

In the direct foaming method, the resin particles are foamed while the shape of the resin particles is generally maintained. Therefore, the shape of the expanded beads obtained by the direct foaming method generally has a shape obtained by enlarging the shape of the resin beads. Therefore, for example, in the case of obtaining expanded beads having a cross-shaped cross-sectional shape at the cut surface, the cross-sectional shape at the cut surface generated when the resin bead is cut along a plane perpendicular to the axial direction is cross-shaped. It suffices to expand the columnar resin particles. Such a resin particle having a cross-shaped cross-sectional shape at the cut surface can be obtained, for example, by using a die having a cross-shaped small hole corresponding to the shape of the desired cut surface of the resin particle in the strand cut method described above. can be manufactured by In this case, the direction of extrusion during production of the resin particles corresponds to the axial direction of the expanded particles.

After producing the resin particles as described above, the resin particles are dispersed in a dispersion medium. The operation of dispersing the resin particles in the dispersion medium may be performed in a closed container used in the foaming step described later, or may be performed in a container separate from the closed container used in the foaming step. From the viewpoint of simplification of the manufacturing process, it is preferable to carry out the dispersing process in a closed container used in the foaming process.

As the dispersion medium, an aqueous dispersion medium containing water as a main component is used. In addition to water, the aqueous dispersion medium may contain hydrophilic organic solvents such as ethylene glycol, glycerin, methanol and ethanol. The proportion of water in the aqueous dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

It is preferable to add a dispersant to the dispersion medium. By adding a dispersant to the dispersion medium, it is possible to suppress fusion between the resin particles heated in the container in the foaming step. The amount of the dispersant added is preferably 0.001 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the resin particles. As the dispersing agent, an organic dispersing agent or an inorganic dispersing agent can be used, but it is preferable to use a fine particulate inorganic material as the dispersing agent because of ease of handling. More specifically, the dispersant includes, for example, clay minerals such as amsnite, kaolin, mica, and clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide, and the like. can be used. These dispersants may be used alone, or two or more dispersants may be used in combination. Among these, it is preferable to use a clay mineral as a dispersant. Clay minerals may be natural or synthetic.

When a dispersant is used, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylbenzenesulfonate, sodium laurylsulfate, sodium oleate, etc. as a dispersing aid. The amount of the dispersion aid added is preferably 0.001 parts by mass or more and 1 part by mass or less per 100 parts by mass of the resin particles.

After dispersing the resin particles in the dispersion medium, the resin particles are impregnated with a foaming agent in a closed vessel. The foaming agent with which the resin particles are impregnated is preferably a physical foaming agent. Physical blowing agents include inorganic physical blowing agents such as carbon dioxide, air, nitrogen, helium and argon; aliphatic hydrocarbons such as propane, butane and hexane; cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; Halogenated hydrocarbons such as fluoromethane, trifluoromethane, 1,1-difluoromethane, 1-chloro-1,1-dichloroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc. organic physical blowing agents. These physical foaming agents may be used alone, or two or more physical foaming agents may be used in combination. Moreover, an inorganic physical foaming agent and an organic physical foaming agent can be mixed and used. From the viewpoint of environmental load and handleability, inorganic physical blowing agents are preferably used, and carbon dioxide is more preferably used.

The amount of the foaming agent added to 100 parts by mass of the resin particles is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 0.5 parts by mass or more and 15 parts by mass or less.

As a method for impregnating the resin particles with the foaming agent in the production process of the expanded beads, the foaming agent is supplied into a closed container, and the pressure inside the closed container is increased to impregnate the resin particles in the dispersion medium with the foaming agent. method can be adopted. At this time, by heating the resin particles together with the dispersion medium, the impregnation of the foaming agent into the resin particles can be further promoted.

The pressure in the sealed container during foaming is preferably 0.5 MPa (G) or more in gauge pressure. On the other hand, the pressure in the sealed container is preferably 4.0 MPa (G) or less in gauge pressure. Within the above range, the foamed beads can be produced safely without causing damage to the sealed container, explosion, or the like.

In addition, when the dispersion medium is heated, the temperature during foaming can be kept within an appropriate range by increasing the temperature of the dispersion medium at a rate of 1 to 5° C./min.

After impregnation of the resin particles with the blowing agent is complete, the contents of the closed container are released into an environment having a lower pressure than the closed container. As a result, the core layer of the resin particles is expanded to form a cell structure, and the resin particles are cooled by the outside air to stabilize the cell structure, thereby obtaining expanded beads.

When the base resin of the core layer is a polypropylene-based resin, it is preferable to perform heating and foaming in the following manner when impregnating the foaming agent. That is, first, (melting point of polypropylene resin −20° C.) or higher and below (melting end temperature of polypropylene resin) is performed for a sufficient time, preferably about 10 to 60 minutes, for a one-stage holding step. The temperature is adjusted from (melting point of polypropylene resin −15° C.) to below (melting end temperature of polypropylene resin +10° C.). Then, if necessary, a two-stage holding step is performed in which the temperature is maintained for a sufficient time, preferably about 10 to 60 minutes. After that, it is preferable to release the contents of the closed container to the outside while the temperature inside the closed container is set to (the melting point of the polypropylene-based resin -10°C) or higher to expand the resin particles. It is more preferable that the temperature in the sealed container during foaming is from (the melting point of the polypropylene resin) to (the melting point of the polypropylene resin +20° C.) or less. By heating and foaming the resin particles in this manner, secondary crystals are formed in the polypropylene-based resin constituting the foam layer, and foamed particles having excellent mechanical strength and excellent moldability can be easily obtained. be able to.

The expanded particles obtained as described above may be used as they are for the production of the molded article. Further, the foamed particles obtained by the above-described direct foaming method can be further expanded to produce a molded article using the expanded particles having an increased bulk ratio. When the resin particles are expanded in two stages as described above, the first-stage expansion process is referred to as a one-stage expansion process, and the expanded particles obtained by the one-stage expansion process are referred to as one-stage expanded particles. Moreover, the foaming process of the second stage is called a two-stage foaming process. The expanded beads obtained by the two-step expansion process are sometimes called two-step expanded beads.

A method for increasing the bulk ratio of expanded particles by two-stage expansion is, for example, as follows. First, resin particles are expanded by the above-described direct expansion method as the one-step expansion step to obtain one-step expanded beads. After that, internal pressure is applied to the single-stage expanded beads. More specifically, after the single-stage expanded particles are placed in a pressure vessel, the inside of the pressure vessel is pressurized with an inorganic gas such as air or carbon dioxide to impregnate the expanded particles with the inorganic gas. As a result, the pressure inside the cells of the single-stage expanded particles is made equal to or higher than the atmospheric pressure. After that, the single-stage expanded beads taken out from the pressure vessel are heated using a heating medium such as steam or heated air in an environment having a lower pressure than the pressure inside the bubbles, thereby further expanding the single-stage expanded beads.

Examples of the foamed beads, the foamed beads molded article, and the manufacturing method thereof will be described.

(polypropylene resin)
Table 1 shows the properties of the polypropylene-based resin as the crystalline thermoplastic resin used for producing the expanded beads. Both the ethylene-propylene copolymer and the ethylene-propylene-butene copolymer used in this example are random copolymers. The densities of PP1 and PP2 shown in Table 1 are 900 kg/m ³ .

<Monomer component content of polypropylene resin>
The content of the monomer component of the polypropylene resin (specifically, ethylene-propylene copolymer, ethylene-propylene-butene copolymer) was obtained by a known method of determining by IR spectrum. Specifically, Polymer Analysis Handbook (Edited by Japan Society for Analytical Chemistry Polymer Analysis Research Round-table Conference, publication date: January 1995, publisher: Kinokuniya Bookstore, page numbers and item names: 615-616 "II. 2.3 2.3.4 Propylene/Ethylene Copolymers”, 618-619 “II.2.3 2.3.5 Propylene/Butene Copolymers”), i.e. ethylene and butene It was obtained by a method of quantifying from the relationship between the absorbance corrected by a predetermined coefficient and the thickness of the film-like test piece.

More specifically, first, a polypropylene-based resin was hot-pressed in an environment of 180° C. to form a film, and a plurality of test pieces having different thicknesses were produced. Next, by measuring the IR spectrum of each test piece, the absorbance at 722 cm ^-1 and 733 cm ^-1 derived from ethylene (A ₇₂₂ , A ₇₃₃ ) and the absorbance at 766 cm ^-1 derived from butene (A ₇₆₆ ) were read. Ta. Next, for each test piece, the ethylene component content (unit: mass %) in the polypropylene resin was calculated using the following formulas (7) to (9). The value obtained by arithmetically averaging the ethylene component contents obtained for each test piece was defined as the ethylene component content (unit: mass %) in the polypropylene resin.

(K' ₇₃₃ ) _c = 1/0.96 {(K' ₇₃₃ ) _a −0.268 (K' ₇₂₂ ) _a } (7)
(K' ₇₂₂ ) _c = 1/0.96 {(K' ₇₂₂ ) _a −0.150 (K' ₇₃₃ ) _a } (8)
Ethylene component content = 0.575 {( _K'722 ) _c + ( _K'733 ) _c } (9)

However, K _{' a} in formulas (7) to (9) is the apparent extinction coefficient at each wavenumber (K _{' a} = A/ρt), K' _c is the corrected extinction coefficient, and A is the absorbance. where ρ is the density of the resin (unit: g/cm ³ ) and t is the thickness of the film-like test piece (unit: cm). The above formulas (7) to (9) can be applied to random copolymers.

For each test piece, the butene component content (unit: % by mass) in the polypropylene-based resin was calculated using the following formula (10). The value obtained by arithmetically averaging the butene component contents obtained for each test piece was defined as the butene component content (unit: mass %) in the polypropylene resin.
Butene component content = 12.3 (A ₇₆₆ /L) (10)
However, A in the formula (10) is the absorbance, and L is the thickness (unit: mm) of the film-like test piece.

<Flexural modulus of polypropylene resin>
A polypropylene resin was heat-pressed at 230° C. to prepare a 4 mm sheet, and a test piece of 80 mm length×10 mm width×4 mm thickness was cut out from this sheet. The flexural modulus of this test piece was determined according to JIS K7171:2008. The radius R1 of the indenter and the radius R2 of the support are both 5 mm, the distance between fulcrums is 64 mm, and the test speed is 2 mm/min.

<Melting point of polypropylene resin>
The melting point of the polypropylene resin was obtained based on JIS K7121:1987. Specifically, first, the condition of a test piece made of a polypropylene resin was adjusted according to JIS K7121:1987, "(2) In the case of measuring the melting temperature after a certain heat treatment". A DSC curve was obtained by heating the conditioned specimen from 30°C to 200°C at a heating rate of 10°C/min. The apex temperature of the melting peak appearing on the DSC curve was taken as the melting point. A heat flux differential scanning calorimeter (manufactured by SII Nanotechnology Co., Ltd., model number: DSC7020) was used as a measuring device.

<Melt mass flow rate of polypropylene resin>
The melt mass flow rate (that is, MFR) of the polypropylene resin was measured according to JIS K7210-1:2014 under the conditions of a temperature of 230° C. and a load of 2.16 kg.

Next, the structure and manufacturing method of the expanded beads used in this example will be described.

(Expanded particles A)
As shown in Table 2, the foamed beads A consist of a foamed layer using PP1 (see Table 1) as a base resin and a non-foamed coating covering the foamed layer using PP3 (see Table 1) as a base resin. It has a multi-layer structure with layers. As shown in FIGS. 10 and 11, the expanded bead A has a cross-sectional shape perpendicular to its axial direction, that is, the direction connecting the bottom surface 11 and the top surface 12 (that is, the shape of the cut surface of the expanded bead). has a cross-shaped columnar shape. The side peripheral surface 13 of the foamed bead A is covered with the coating layer 4 , and the inside of the coating layer 4 is composed of the foamed layer 2 . Four grooves 3 are arranged at equal intervals on the side peripheral surface 13 of the expanded bead A. As shown in FIG. The grooves 3 of the expanded beads A have a V-shaped cross section. The expanded beads A do not have through-holes.

In producing the expanded beads A, first, using a coextrusion device equipped with a core layer forming extruder, a coating layer forming extruder, and a coextrusion die connected to these two extruders, The extrudate extruded from the co-extrusion device was cut by a strand cut method to prepare multilayer resin particles. Specifically, PP1 as a base resin and zinc borate as a cell control agent were melt-kneaded in an extruder for forming a core layer to obtain a melt-kneaded resin for forming a core layer. The maximum set temperature in the core layer-forming extruder was 245° C., and the amount of zinc borate was 500 mass ppm with respect to the mass of the polypropylene resin. In parallel with this, in the extruder for forming the coating layer, PP3 as the base resin was melt-kneaded at a maximum set temperature of 245° C. to obtain a melt-kneaded resin material for forming the coating layer.

These melt-kneaded resins were co-extruded and combined in a die to form a composite consisting of a non-foamed core layer and a non-foamed coating layer covering the side peripheral surface of the core layer. After extruding this composite from a die, the extrudate is cooled in water while being taken out, and cut into an appropriate length using a pelletizer, so that the cross-sectional shape of the cross section perpendicular to the extrusion direction is cross-shaped, and the core A multilayer resin particle comprising a layer and a coating layer covering the side peripheral surface of the core layer was obtained. The mass ratio of the core layer to the coating layer in the multilayer resin particles was set to core layer:coating layer=95:5 (that is, the mass ratio of the coating layer was 5%). Also, the mass per multilayer resin particle was set to about 1.5 mg.

Next, expanded beads A were obtained by expanding the multilayered resin beads by a direct expansion method. Specifically, 1 kg of multi-layered resin particles was put into a 5 L airtight container together with 3 L of water as a dispersion medium. Next, 0.3 parts by mass of a dispersing agent and 0.004 parts by mass of a dispersing aid are added to 100 parts by mass of the multilayered resin particles in a sealed container to disperse the multilayered resin particles in the dispersion medium. Ta. Kaolin was used as a dispersant. A surfactant (sodium alkylbenzenesulfonate) was used as a dispersing aid.

Then, after adding carbon dioxide as a foaming agent into the closed container, the closed container was sealed and heated to the foaming temperature shown in Table 2 while stirring the inside of the closed container. The internal pressure of the container (also referred to as impregnation pressure or carbon dioxide pressure) at this time was as shown in Table 2. After maintaining the foaming temperature shown in Table 2 for 15 minutes, the contents of the container were released to atmospheric pressure to form a foamed core layer and a non-foamed coating layer covering the foamed layer. A foamed particle A was obtained. The bulk magnification of the expanded beads A was 36.7 times. A method for measuring the bulk ratio will be described later.

(Expanded particles B)
The method for producing expanded beads B is the same as the method for producing expanded beads A, except that PP2 is used as the base resin of the core layer, and the expansion temperature and the internal pressure of the container during expansion are changed to the values shown in Table 2. . The bulk magnification of the expanded beads B was 36.0 times.

(Expanded particles C)
In producing the expanded beads C, resin particles similar to the resin particles used in producing the expanded beads A were expanded in two stages. Specifically, resin particles were produced under the same conditions as in the production of expanded beads A. These resin particles were expanded by a direct expansion method under the conditions shown in Table 2 to obtain single-stage expanded particles having a bulk ratio of 15.0. After that, the single-stage expanded particles were dried at 23° C. for 24 hours.

Next, the single-stage expanded beads after drying were placed in a pressure container, and the inside of the pressure container was pressurized with air to impregnate the air into the cells and increase the internal pressure in the cells of the expanded beads. Table 2 shows the pressure inside the cells in the single-stage expanded beads taken out of the pressure vessel. After putting the single-stage expanded particles taken out from the pressure vessel into a metal drum, steam having a pressure shown in the "drum pressure" column of Table 2 was supplied into the drum to heat the single-stage expanded particles under atmospheric pressure. As described above, the single-stage expanded beads were further expanded to obtain expanded beads C (two-stage expanded beads). The bulk magnification of the expanded particles C was 36.7 times.

(Expanded particles D)
The ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads in the expanded beads D and the ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads are shown in Table 2. is larger than the foamed particles A as shown in FIG. The method for producing expanded beads D was the same as the method for producing expanded beads A, except that the shape of the die was changed to increase the cross-sectional area of the grooves of the resin particles, and the expansion conditions were changed as shown in Table 2. is.

(Expanded particles E)
The expanded beads E have a cylindrical shape with no through-holes and no grooves on the side peripheral surfaces. In preparing the expanded beads E, first, columnar resin particles (see Table 2) having a core layer with PP1 as the base resin and a coating layer with PP3 as the base resin were prepared. The resin particles were subjected to a single-stage expansion process under the conditions shown in Table 2 to obtain single-stage expanded particles having a bulk ratio of 15.0. Then, the single-stage expanded beads were subjected to a two-stage expansion process under the conditions shown in Table 2 to further expand the single-stage expanded beads to obtain expanded beads E (two-stage expanded beads). The bulk magnification of the expanded particles E is 35.7 times.

(Expanded particles F)
The expanded bead F has a cylindrical shape with no grooves on the side peripheral surface and a through hole provided along the central axis. The cross-sectional shape of the through-holes in the cross-section perpendicular to the axial direction of the expanded beads F is substantially circular, and the average hole diameter is 1.55 mm. In preparing expanded beads F, first, cylindrical resin particles (see Table 2) having a core layer with PP1 as the base resin and a coating layer with PP3 as the base resin were prepared. These resin particles were foamed under the conditions shown in Table 2. The bulk magnification of the expanded particles F is 36.2 times.

(Expanded particles G)
The method for producing the expanded beads G was the same as the method for producing the expanded beads F, except that the resin beads were prepared using PP2 as the base resin of the core layer, and the resin beads were expanded under the conditions shown in Table 2. It is the same. The bulk magnification of the expanded particles G is 36.0 times.

(Expanded particles H)
The foamed particles H have a columnar shape with no through holes. Further, the cross section of the expanded bead H perpendicular to the axial direction is cross-shaped. The ratio L/D of the average length L in the axial direction of the expanded beads to the average outer diameter D of the expanded beads H is larger than that of the expanded beads A as shown in Table 2. The method for producing expanded beads H was the same as the method for producing expanded beads A, except that the resin particles were cut so that the ratio L/D in the resin particles was increased, and the expansion conditions were changed as shown in Table 2. .

Next, using the expanded beads A to H described above, molded articles were produced by the following method.

(Examples 1 to 3, Example 5, Comparative Examples 1 to 3 and Comparative Examples 5 to 7)
First, the foamed particles shown in Tables 3 and 4 were dried at 23° C. for 24 hours, and then impregnated with air to reduce the internal pressure, that is, the pressure inside the cells, to the value shown in the column "Particle internal pressure" in Tables 3 and 4. heightened. The internal pressure of the expanded beads is a value measured as follows. The mass Q (unit: g) of the expanded bead group under increased internal pressure immediately before filling the mold and the mass U (unit: g) of the expanded bead group after 48 hours were measured. The difference from U was defined as the increased air amount W (unit: g). Using these values, the internal pressure (unit: MPa (G)) of the expanded beads was calculated based on the following formula (11).
P=(W/M)×R×T/V (11)

However, in the above formula (11), M is the molecular weight of air, R is the gas constant, T is the absolute temperature, and V is the volume of the base resin occupying the expanded bead group from the apparent volume of the expanded bead group. is the volume (unit: L) after subtracting In this example, M=28.8 (g/mol), R=0.0083 (MPa·L/(K·mol)), and T=296 (K).

Next, the expanded particles were filled into a flat plate mold of 300 mm long×250 mm wide×60 mm thick by a cracking filling method. The amount of cracking during filling, that is, the ratio of the mold opening amount to the inner dimension in the thickness direction is the value shown in Tables 3 and 4, and after filling is completed, the mold is clamped in the thickness direction. The expanded particles were mechanically compressed.

Tables 3 and 4 show the filling rate of the foamed particles filled in the mold in this example. The filling rate (unit: %) of the expanded particles is determined by the mass a (unit: kg) of the expanded particles filled in the mold, the bulk density b (unit: kg/m ³ ) of the expanded particles, and the density of the mold. Using the internal volume c (unit: m ³ ), it is represented by the following formula (5).
Filling rate = [{a/(bxc)}-1]x100 (5)

After the mold was clamped, an exhaust process was performed in which steam was supplied from both sides of the mold for 5 seconds to preheat. After that, steam was supplied from one side of the mold until the pressure reached a pressure lower than the molding pressure during main heating shown in Tables 3 and 4 by 0.08 MPa (G), and one side heating was performed. Next, steam was supplied from the other side of the mold until the pressure reached 0.04 MPa (G) lower than the molding pressure during main heating, and one heating was performed. After that, steam was supplied from both sides of the mold until the molding pressure shown in Tables 3 and 4 was reached, and main heating was performed. After the main heating was completed, the pressure in the mold was released, and the molded product was cooled in the mold until the surface pressure due to the foaming force of the molded product reached 0.04 MPa (G). After that, the molded body was taken out from the mold.

(Example 4)
The method for producing the molded article of Example 4 was the same as the method for producing the molded article of Example 1, except that no internal pressure was applied to the expanded particles A and that the amount of cracking was changed to the value shown in Table 3. It is the same.

(Example 6 and Comparative Example 4)
The methods for producing the molded bodies of Example 6 and Comparative Example 4 consisted of filling the mold with the expanded particles shown in Tables 3 and 4 by compression filling instead of the cracking filling method, and filling the mold with the expanded particles. Except for changing the filling rate and the molding pressure to the values shown in Table 3, the molding method was the same as that of Example 1. The procedure for filling the foamed particles by the compression filling method is specifically as follows. First, the expanded particles to which the internal pressure was applied were put into the filling hopper. Thereafter, compressed air was used as pressurized gas to pressurize the inside of the filling hopper, the inside of the molding die, and the inside of the transfer path connecting the two, thereby compressing the expanded particles in the filling hopper. After that, the foamed particles compressed in the filling hopper were supplied into the mold through the transfer path while maintaining the compressed state, and the mold was filled with the foamed particles. In this example, since the foamed particles were filled with the mold closed, "-" is indicated in the cracking amount column of Table 4.

Tables 2 to 4 show various properties of the expanded particles and molded articles used in Examples and Comparative Examples. Evaluation methods for various properties shown in Tables 2 to 4 are as follows.

(Evaluation of expanded particles)
For the measurement and evaluation of the physical properties of the expanded beads, the expanded beads were used after being left still for 24 hours under the conditions of 50% relative humidity, 23° C., and 1 atm.

<Ratio L/D between average outer diameter D and average length L>
First, for 100 expanded beads randomly selected from the group of expanded beads after conditioning, the maximum length in the axial direction was measured using a vernier caliper. The height was L (unit: mm). These foamed beads were cut at the center position in the axial direction along a plane perpendicular to the axial direction to expose the cut surface of the foamed beads illustrated in FIG. 11 . Next, a photograph of the cut surface of the foamed beads was taken, and the outer diameter d of each foamed bead was measured by image analysis. Specifically, two points P3 and P4 are set on the outline of the foamed beads on the cutting plane so that the distance between them is the longest, and the distance between these two points is the distance between the individual foamed beads on the cutting plane. The outer diameter is d. Then, the arithmetic average value of the outer diameters d of 100 expanded beads was defined as the average outer diameter D (unit: mm) of the expanded beads on the cut surface. Table 2 shows the average outer diameter D of the expanded beads, the average length L of the expanded beads and the ratio L/D of the two obtained above.

<Bulk magnification/bulk density>
The foamed particles after conditioning were filled in a graduated cylinder so that they were deposited naturally, and the bulk volume (unit: L) of the foamed particles was read from the scale of the graduated cylinder. After that, the mass (unit: g) of the expanded particles in the graduated cylinder was divided by the bulk volume described above, and the unit was converted to calculate the bulk density (unit: kg/m ³ ) of the expanded particles. Further, the bulk ratio of the expanded beads was calculated by dividing the density (unit: kg/m ³ ) of the polypropylene-based resin forming the foamed layer by the bulk density of the expanded beads.

<Apparent density>
After measuring the mass of the foamed particles after conditioning, they were submerged in a graduated cylinder containing ethanol at a temperature of 23° C. using a wire mesh. Then, considering the volume of the wire mesh, the volume of the foamed particles read from the water level rise was measured. After dividing the mass (unit: g) of the group of expanded particles thus obtained by the volume (unit: L), the units are converted to give the apparent density (unit: kg/m ³ ) of the expanded particles. Calculated. In addition, the column "Apparent Density/Bulk Density" in Table 2 shows the ratio of the apparent density to the bulk density obtained by the method described above.

<Closed cell rate>
The closed cell content of the expanded beads was measured using an air comparison type hydrometer based on ASTM-D6226-10. Specifically, it was obtained as follows. The foamed particles having a bulk volume of about 20 cm ³ after conditioning were used as a measurement sample, and the apparent volume Va was accurately measured by the ethanol immersion method. After sufficiently drying the measurement sample whose apparent volume Va was measured, according to the procedure described in ASTM-D6226-10, the true volume of the measurement sample measured by Accupic II 1340 manufactured by Shimadzu Corporation. A value Vx was measured. In addition, in the measurement of the true volume Vx, the pressure applied in the purging step and the testing step was 5 kPa. In steps 9.13 and 9.14, the pressure was recorded after waiting until the pressure change rate became 0.100 kPa/min or less. Using these volume values Va and Vx, the closed cell ratio (unit: %) of the measurement sample was calculated based on the following formula (6).
Closed cell ratio = (Vx-W/ρ) x 100/(Va-W/ρ) (6)

The above operation was performed five times using different measurement samples, and the arithmetic average value of the closed cell ratios obtained from these five measurements was taken as the closed cell ratio of the expanded beads.

The meanings of the symbols in the formula (6) are as follows.
Vx: The true volume of the measurement sample measured by the above method, that is, the sum of the volume of the resin constituting the expanded bead and the total volume of the closed cells within the expanded bead (unit: cm ³ ).
Va: Apparent volume of the measurement sample measured from the water level rise when the measurement sample is submerged in a graduated cylinder containing ethanol (unit: cm ³ )
W: Mass of measurement sample (unit: g)
ρ: Density of the resin constituting the expanded beads (unit: g/cm ³ )

<High-temperature peak heat quantity of expanded beads>
A DSC curve was obtained by performing differential scanning calorimetry in accordance with JIS K7121:1987 using one expanded bead after conditioning. In DSC, the measurement start temperature was 23° C., the measurement end temperature was 200° C., and the heating rate was 10° C./min. As a measuring device, "DSC.Q1000" manufactured by TA Instruments was used. The area of the high temperature peak in the DSC curve obtained by the method described above was calculated. The above measurement was performed on five expanded beads, and the arithmetic average value of the areas of the obtained high-temperature peaks was taken as the high-temperature peak heat quantity.

<Average Cross-sectional Area A of Expanded Beads at Cut Surface>
100 expanded beads were randomly selected from the group of expanded beads after conditioning, and these expanded beads were cut at the central position in the axial direction along a plane perpendicular to the axial direction to expose the cut surface of the expanded beads. Ta. Next, a photograph of the cut surface of the foamed beads was taken, and the cross-sectional area of each foamed bead was measured by image analysis. Then, the arithmetic average value of these values was taken as the average cross-sectional area A of the expanded beads.

<Area B of virtual perfect circle having average outer diameter D>
Using the average outer diameter D of the expanded beads on the cross section obtained by the method described above, the area B of a virtual perfect circle having the average outer diameter D was calculated based on the following formula (12). Table 2 also shows the ratio A/B of the average cross-sectional area A of the expanded beads on the cut surface to the area B of the virtual perfect circle having the average outer diameter D.
B=πD ² /4 (12)

<Total cross-sectional area Ct of grooves, average cross-sectional area Ca per groove>
100 expanded beads were randomly selected from the group of expanded beads after conditioning, and these expanded beads were cut at the central position in the axial direction along a plane perpendicular to the axial direction to expose the cut surface of the expanded beads. Ta. Next, a photograph of the cross section of the foamed beads was taken, and the cross-sectional area C of the grooves of the individual foamed beads was measured by image analysis. Specifically, as exemplified in FIG. 11, a tangent line L1 was drawn outside each groove 3, contacting the outline of the expanded bead at two points P1 and P2 and not passing through the inside of the expanded bead. The area of the region surrounded by the contour of the expanded bead and the tangent line L1 (that is, the area of the hatched portion in FIG. 11) was calculated, and this area was defined as the cross-sectional area C of each groove 3 . Then, the total cross-sectional area C of the grooves 3 was calculated for each foamed bead. Also, the total cross-sectional area C of the grooves 3 was divided by the number of grooves 3 formed in the expanded bead to calculate the cross-sectional area per groove.

The above operation was performed on 100 expanded beads, and the arithmetic average value of the total cross-sectional area of the grooves obtained was taken as the total cross-sectional area Ct of the grooves, and the average value of the cross-sectional areas per groove was calculated as Ct. The average cross-sectional area was taken as Ca. Table 2 also shows the ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads on the cut surface and the ratio Ca of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads /A was described.

<Average groove depth H>
100 expanded beads were randomly selected from the group of expanded beads after conditioning, and these expanded beads were cut at the central position in the axial direction along a plane perpendicular to the axial direction to expose the cut surface of the expanded beads. Ta. Next, a photograph of the cut surface of the foamed beads was taken, and the depth h of the grooves of the individual foamed beads was measured by image analysis. Specifically, as exemplified in FIG. 11, a tangent line L1 was drawn outside each groove 3, contacting the outline of the expanded bead at two points P1 and P2 and not passing through the inside of the expanded bead. The maximum value of the distance from the tangent line L1 to the peripheral edge of the groove 3 (that is, the contour of the expanded bead) in the direction perpendicular to the tangent line L1 was defined as the depth h of each groove. Then, the groove depth h was measured for all the grooves, and the arithmetic average value of these groove depths h was taken as the average groove depth H of the foamed particles. Table 2 also shows the ratio H/D of the average depth H of the grooves to the average outer diameter D of the expanded beads on the cut surface.

(Evaluation of compact)
For the measurement and evaluation of the physical properties of the molded body, the molded body was molded without being subjected to a curing step after being released from the molding die. Specifically, in the above-described method for producing a molded body, the molded body after release from the mold was left to stand for 12 hours under the conditions of 50% relative humidity, 23 ° C., and 1 atm, and the molded body was used. .

<Mold density>
After dividing the mass (unit: g) of the molded body by the volume (unit: L) obtained from the external dimensions of the molded body, the density of the molded body (unit: kg/m ³ ) was calculated by unit conversion.

<Closed cell rate>
The closed cell content of the molded body was measured according to ASTM-D6226-10. Specifically, first, a specimen of 25 mm length × 25 mm width × 25 mm height is cut out from the center of the molded body, and the geometric volume Va (unit: cm ³ ) of the specimen, that is, the vertical dimension (unit: cm), the horizontal dimension (unit: cm) and the height dimension (unit: cm). Next, according to the procedure described in ASTM-D6226-10, the true volume Vx of the specimen was measured with an air comparison type hydrometer (specifically, Accupic II1340 manufactured by Shimadzu Corporation). At this time, the pressure applied in the purging step and the testing step was set to 5 kPa. In steps 9.13 and 9.14, the pressure was recorded after waiting until the pressure change rate became 0.100 kPa/min or less. The geometric volume Va and the true volume Vx of the specimen obtained as described above, the mass W (unit: g) of the specimen, and the density ρ (unit: g/cm ³ ) of the resin constituting the expanded beads was used to calculate the closed cell ratio (unit: %) of the specimen based on the following formula (4).
Closed cell ratio = (Vx-W/ρ) x 100/(Va-W/ρ) (4)

The above operation was performed for five specimens, and the closed cell ratio of each specimen was calculated. Then, the arithmetic average value of the closed cell ratios in these five test pieces was taken as the closed cell ratio of the molded body.

<Open cell ratio Co>
In accordance with ASTM-D6226-10, the open cell ratio Co was measured by correcting for the influence of closed cells destroyed during cutting out the measurement sample according to procedure 2 described in Supplement X1.3 of the same standard. Specifically, first, the molded article was allowed to stand at a temperature of 23° C. for 12 hours to adjust the state of the molded article. Next, a first cubic test piece measuring 2.5 cm long x 2.5 cm wide x 2.5 cm high was cut out from the center of the compact, and its geometric volume Va (unit: cm ³ ), that is, The product of the vertical dimension (unit: cm), the horizontal dimension (unit: cm) and the height dimension (unit: cm) was calculated. Next, the true volume V1 (unit: cm ³ ) of the first test piece was measured using a dry automatic densitometer (specifically, Accupic II1340 manufactured by Shimadzu Corporation). At this time, the pressure applied in the purging step and the testing step was set to 5 kPa. In steps 9.13 and 9.14, the pressure was recorded after waiting until the pressure change rate became 0.100 kPa/min or less.

After that, the first test piece was divided into 8 equal parts to prepare a second cubic test piece measuring 1.25 cm long×1.25 cm wide×1.25 cm high. Then, the true volume (unit: cm ³ ) of each second test piece was measured by the same method as the method for measuring the true volume V1 of the first test piece. The true volumes of the individual second specimens were then summed to calculate the true volume V2 of the second specimen.

Using the geometric volume Va of the first test piece obtained above, the true volume V1 of the first test piece, and the true volume V2 of the second test piece (unit: cm ³ ), the following formula ( 1), the open cell ratio (unit: %) of the first test piece was calculated.
Open cell ratio = (Va-2V1+V2) x 100/Va (1)

The above operation was performed for five first test pieces, and the open cell ratio of each first test piece was calculated. The arithmetic mean value of the open cell ratios of the five first test pieces was taken as the open cell ratio Co of the molded body.

<Porosity of compact>
A test piece having a rectangular parallelepiped shape of 20 mm long×100 mm wide×20 mm high was cut out from the center of the compact. The test piece was submerged in a graduated cylinder filled with ethanol, and the true volume Vc (unit: L) of the test piece was obtained from the rise in the liquid level of ethanol. Also, the apparent volume Vd (unit: L) of the test piece was obtained from the external dimensions of the test piece. Using the true volume Vc and apparent volume Vd of the test piece obtained above, the porosity (unit: %) of the compact was calculated based on the following formula (3).
Porosity = [(Vd-Vc) / Vd] × 100 (3)

<Number of expanded particles per unit area on surface of molded article>
On the surface of the molded body, five square evaluation areas each having a side of 100 mm were set at equal intervals on the part excluding the end portions. Then, the number of foamed particles present in each evaluation area was counted. At this time, the foamed particles existing on the boundary line of the evaluation area were also assumed to exist within the evaluation area. By dividing the number of foamed particles in the evaluation area thus obtained by the area of the evaluation area, the number of foamed particles per unit area (that is, 1 cm ² ) in each evaluation area was calculated. Then, the number of expanded particles per unit area (that is, 1 cm ² ) obtained in a plurality of evaluation areas was arithmetically averaged to calculate the number of expanded particles per unit area on the molded article surface.

<50% compressive stress σ ₅₀ >
A test piece having a prismatic shape of 50 mm long x 50 mm wide x 25 mm thick was cut out from the center of the molded body, and did not include the skin surface, that is, the surface that was in contact with the inner surface of the mold during in-mold molding. . Based on JIS K6767:1999, a compression test was performed at a compression rate of 10 mm/min to determine the 50% compressive stress σ ₅₀ (unit: kPa) of the compact. Tables 3 and 4 also show the values obtained by dividing the 50% compressive stress σ ₅₀ of the molded body by the density of the molded body (σ ₅₀ /density of the molded body).

<Surface properties (appearance)>
The surface of the molded article was visually observed, and the surface properties of the molded article were evaluated based on the following criteria.
A: The surface of the molded product has few gaps between particles, and shows a good surface condition in which irregularities caused by grooves, through holes, etc. are not conspicuous.
B: The surface of the molded article is slightly uneven due to inter-particle gaps and/or grooves and through-holes.
C: A relatively large number of irregularities due to gaps between particles and/or grooves and through holes are observed on the surface of the molded product.
D: Remarkable irregularities due to inter-particle gaps and/or grooves and through-holes are observed on the surface of the molded product.

<Recoverability>
In a plan view of the molded body in the thickness direction, the thickness of the molded body at four positions located 10 mm inward from each vertex toward the center and the thickness of the molded body at the central portion were measured. Next, the ratio (unit: %) of the thickness of the thinnest portion to the thickness of the thickest portion among the measured portions was calculated. In the "Restoration" column of Tables 3 and 4, "Good" was written when the thickness ratio was 95% or more, and "Poor" was written when it was less than 95%.

<Water leakage prevention test>
By the same method as the above-described molded body manufacturing method, the outer dimensions are 200 mm long, 150 mm wide, and 50 mm high, the inner dimensions are 180 mm long, 130 mm wide, and 40 mm high, and the thickness of the side wall and bottom wall is Box-shaped moldings measuring 10 mm were produced. 0.9 L of water was added to this box-shaped compact, and the compact was allowed to stand under an environment of 23° C., 50% RH, and 1 atm for 24 hours. In the "water leakage prevention test" column of Tables 3 and 4, "Good" is indicated when water leakage from the compact is not observed, and "Poor" is indicated when water leakage is observed.

<Permeability coefficient>
The water permeability coefficient of the molded article was measured by conducting a constant water permeability test according to JIS A1218 using an expanded bead molded article as a test piece. Specifically, two cylinders having a base circle diameter of 105 mm and a height of 50 mm were cut out from the compact, and these cylinders were overlapped to prepare a test piece for the constant water permeability test. The shape of the test piece was a cylinder with a bottom circle diameter of 105 mm and a height of 100 mm. In the "permeability coefficient" column of Tables 3 and 4, when the permeability coefficient is 0 cm / sec or more and less than 0.001 cm / sec, the symbol "N" is used. The symbol "M" is indicated, and the symbol "P" is indicated in the case of 0.008 cm/sec or more.

As shown in Table 2, the expanded beads A to D used in Examples 1 to 6 had a columnar shape with no through holes and four grooves on the side peripheral surface. In addition, the bulk ratio, closed cell ratio, ratio Ca/A, ratio Ct/A, average outer diameter D and ratio L/D of these expanded beads are within the above-mentioned specific ranges. In Examples 1 to 6, such foamed particles were used to produce molded articles having an open cell ratio within a predetermined range. Therefore, even if the curing step was omitted, the molded body obtained was free from significant shrinkage and deformation, and was excellent in appearance and rigidity.

On the other hand, the expanded beads E used in Comparative Example 1 are conventional polypropylene-based resin expanded beads having a columnar shape as shown in Table 2 and having no grooves on the side peripheral surfaces thereof. Such expanded particles are less likely to form passages for steam during in-mold molding. In addition, almost no open-cell structure is formed in the molded article obtained. Therefore, as shown in Table 4, when the molded article of Comparative Example 1 was not subjected to the curing step after being released from the mold, the molded article significantly shrunk and deformed, and the recoverability failed. .

The expanded beads F used in Comparative Example 2 and the expanded beads G used in Comparative Example 3 had a cylindrical shape with through holes. As shown in Table 4, when such expanded beads were molded in a mold, an open cell structure derived from the through holes was formed, resulting in an excessively high open cell ratio of the molded product. Therefore, the appearance of the molded article was poor, and the rigidity was also lowered. In addition, the molded bodies of these comparative examples could not pass the water leakage prevention test.

Comparative Example 4 is an example in which, in order to reduce the open cell ratio of the molded article of Comparative Example 2, the internal pressure of the particles was further increased and the filling rate of the foamed particles F into the mold was further increased. As shown in Table 4, in Comparative Example 4, the open cell ratio of the molded article was excessively small, and the molded article significantly shrunk and deformed when the molded article released from the mold was not subjected to the curing step. Recoverability failed.

Comparative Example 5 is an example in which the same foamed particles D as in Example 6 were used, but the molding conditions were changed to produce a molded article. The molded article of Comparative Example 5 had an excessively open cell structure. As a result, the appearance of the molded article deteriorated. It also failed the leak prevention test.

Comparative Example 6 is an example in which a molded article was produced using expanded particles H having a large L/D ratio. In Comparative Example 6, the resulting molded article had a large open cell ratio, poor appearance, and reduced rigidity. It also failed the water leakage test.

Comparative Example 7 is an example in which the same expanded beads A as in Example 1 were used, but the molding conditions were changed to produce a molded article. In Comparative Example 7, the open cell ratio of the obtained molded article was excessively small, and when the molded article released from the mold was not subjected to the curing step, the molded article significantly shrunk and deformed, resulting in failure in recoverability. became.

Specific aspects of the crystalline thermoplastic resin expanded beads, the crystalline thermoplastic resin expanded beads molded article, and the method for producing the same according to the present invention have been described above based on the examples. Specific aspects of the expanded resin particles and the like are not limited to the aspects of the examples, and the configuration can be changed as appropriate within the scope of the present invention.

REFERENCE SIGNS LIST 1 foamed particles 2 foamed layer 3 grooves

Claims (10)

A crystalline thermoplastic resin expanded bead molded article formed by mutually fusing columnar crystalline thermoplastic resin expanded particles having no through-holes and having a molded article magnification of 15 times or more and 90 times or less,
The molded body has a closed cell ratio of 90% or more,
A crystalline thermoplastic resin foamed particle molded product, wherein the molded product has an open cell rate of 2% or more and 7.5% or less. 2. The crystalline thermoplastic resin expanded bead molded article according to claim 1, wherein the number of said expanded particles per unit area on the surface of said molded article is 3/cm ² or more and 30/cm ² or less. 3. The molded article of crystalline thermoplastic resin expanded particles according to claim 1 or 2, wherein a ratio of 50% compressive stress _σ50 to density of said molded article is 7.5 kPa/(kg/ ^m3 ) or more. Filling the mold with crystalline thermoplastic resin foam particles,
Thereafter, steam is supplied into the mold for in-mold molding to obtain a molded product having a molded product magnification of 15 times or more and 90 times or less and an open cell ratio of 2% or more and 7.5% or less. , a method for producing a crystalline thermoplastic resin expanded particle molded product,
The foamed particles have a foamed layer with a crystalline thermoplastic resin as a base resin,
The foamed beads have a columnar shape with no through holes and at least one groove on the side peripheral surface thereof,
The ratio Ca/A of the average cross-sectional area Ca per groove to the average cross-sectional area A of the expanded beads on the cut surface obtained by cutting the expanded beads at the center in the axial direction along a plane perpendicular to the axial direction is is 0.01 or more and 0.25 or less, and the ratio Ct/A of the total cross-sectional area Ct of the grooves to the average cross-sectional area A of the expanded beads is 0.02 or more and 0.75 or less, and the average outer diameter of the expanded beads is The diameter D is 0.5 mm or more and 10 mm or less,
A method for producing a crystalline thermoplastic resin expanded bead molded product, wherein the ratio L/D of the average length L in the axial direction of the expanded beads to the average outer diameter D of the expanded beads is 0.5 or more and 2.0 or less. 5. The production of the crystalline thermoplastic resin expanded bead molded article according to claim 4, wherein the average cross-sectional area Ca per groove in the cut surface of the expanded bead is 0.05 mm ² or more and 2.0 mm ² or less. Method. 6. The crystal according to claim 4, wherein the ratio H/D of the average depth H per groove to the average outer diameter D of the expanded beads is 0.35 or less on the cut surface of the expanded beads. A method for producing a flexible thermoplastic resin expanded particle molded product. 6. A ratio A/B of the average cross-sectional area A of the expanded beads to the area B of the virtual perfect circle having the average outer diameter D of the expanded beads is 0.35 or more and 0.90 or less. 3. The method for producing the crystalline thermoplastic resin expanded bead molded product according to 1. 6. The crystalline thermoplastic according to claim 4, wherein the ratio L/D of the average length L in the axial direction of the expanded beads to the average outer diameter D of the expanded beads is more than 0.7 and less than 1.3. A method for producing an expanded resin bead molded product. The foamed particles have a coating layer covering the foamed layer, and the base resin of the coating layer is a thermoplastic resin having a lower melting point or a lower softening point than the melting point of the crystalline thermoplastic resin. 6. The method for producing the crystalline thermoplastic resin expanded bead molded article according to claim 4 or 5. 6. The mold according to claim 4 or 5, wherein the expanded beads are filled into the mold without applying an internal pressure to the expanded beads or after applying an internal pressure of 0.1 MPa (G) or less to the expanded beads. A method for producing a crystalline thermoplastic resin expanded particle molded product.

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