Polyolefin-based resin foamed particles, polyolefin-based resin foam molded body, and production method for polyolefin-based resin foam molded body

Abstract

The present invention addresses the problem of providing polyolefin-based resin foamed particles capable of providing a polyolefin-based resin foam molded body having excellent sound absorption performance and compression strength. The present invention provides polyolefin-based resin foamed particles wherein: when the cross-sectional area of a cross-section perpendicular to the thickness direction of a polyolefin-based resin foamed particle is indicated by A1, and the area of a region surrounded by an envelope connecting each end of the polyolefin-based resin foamed particle in the cross-section is indicated by A2, A2 / A1 ≥ 1.20; and L / D is 0.10 or more and less than 0.70.

Description

Polyolefin resin expanded particles, polyolefin resin expanded molded article, and method for producing polyolefin resin expanded molded article

[0001] The present invention relates to expanded polyolefin resin beads, a polyolefin resin foam molded article, and a method for producing a polyolefin resin foam molded article.

[0002] Polyolefin resin foam molded articles are used in a variety of applications, including automotive interior components, core materials for automotive bumpers, heat insulation materials, cushioning packaging materials, returnable containers, etc. In particular, for automotive interior materials, molded articles with sound-absorbing properties are required.

[0003] Molded articles having sound-absorbing properties are described, for example, in Patent Document 1 and Patent Document 2. Patent Document 1 describes a molded article made of columnar expanded polyolefin resin beads having a predetermined average L / D, etc. Patent Document 2 also describes a molded article made of expanded beads having through holes, the ratio of the maximum length of the through holes in the penetration direction to the maximum diameter of the cross section perpendicular to the length being a predetermined value.

[0004] Japanese Unexamined Patent Publication No. 2007-45979 Japanese Unexamined Patent Publication No. 10-329220

[0005] However, even if the expanded beads described in the above-mentioned prior art have no problem in sound absorption performance of the molded article, there is room for improvement in terms of achieving both sound absorption performance and compressive strength of the molded article. That is, the expanded beads described in the above-mentioned prior art are not sufficient from the viewpoint of providing expanded beads that can provide a molded article excellent in sound absorption performance and also excellent in compressive strength, and there is room for further improvement.

[0006] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide expanded polyolefin resin particles that can provide expanded polyolefin resin molded articles having excellent sound absorption performance and compressive strength.

[0007] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by controlling the shape of expanded polyolefin resin beads to a predetermined shape, and have thus completed the present invention.

[0008] That is, the expanded polyolefin resin beads according to one embodiment of the present invention are expanded polyolefin resin beads, in which, when A1 is the cross-sectional area of ​​a section perpendicular to the thickness direction of the expanded polyolefin resin beads and A2 is the area of ​​a region enclosed by an envelope connecting each end of the expanded polyolefin resin beads in the cross section, A2 / A1≧1.20, and L / D of the expanded polyolefin resin beads is 0.10 or more and less than 0.70: where D is the diameter of the smallest circle among circles that have all of the cross-sectional shapes in the cross section inside and inscribe at least two of the end portions in the circle, and L is the length of the longest part in the thickness direction of the expanded polyolefin resin beads in the cross section parallel to the thickness direction.

[0009] According to one aspect of the present invention, it is possible to provide expanded polyolefin resin beads that can provide expanded polyolefin resin molded articles that are excellent in sound absorption performance and compressive strength.

[0010] 1 is a view from one direction of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 2 is a view from one direction of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 3 is a view from one direction of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 4 is a view from one direction of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 5 is a view from one direction of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 6 is a view from one direction of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 7 is a view from the front of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 8 is a view from one direction of an expanded polyolefin resin bead according to one embodiment of the present invention. FIG. 8 is a view from one direction of an example of polyolefin-based resin particles produced using a discharge hole whose cross section perpendicular to the extrusion direction has the shape shown in FIG. 7.

[0011] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent literature described in this specification is incorporated herein by reference.

[0012] Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)."

[0013] In this specification, "polyolefin resin particles" may be simply referred to as "resin particles," and "expanded polyolefin resin particles" may be simply referred to as "expanded particles." Furthermore, "expanded polyolefin resin particles according to one embodiment of the present invention" may be simply referred to as "expanded particles," and "expanded polyolefin resin molded article" may be simply referred to as "molded article." Furthermore, "expanded polyolefin resin particles according to one embodiment of the present invention" may be simply referred to as "molded article."

[0014] [1. Technical Concept of an Embodiment of the Invention] Patent Document 1 describes a molded article made of columnar expanded polyolefin resin beads having a predetermined average L / D, etc. Patent Document 2 describes a molded article made of expanded beads having through holes, in which the ratio of the maximum length of the through holes in the penetration direction to the maximum diameter of the cross section perpendicular to the length is a predetermined value. These molded articles have sound absorption performance, but there is room for improvement in terms of compressive strength. After extensive research by the present inventors into the cause, it was found that the expanded beads described in Patent Documents 1 and 2 have insufficient compressive strength due to their shape.

[0015] Therefore, the present inventors have conducted extensive research into the shape of expanded polyolefin resin beads that can provide molded articles with excellent sound-absorbing performance and also have excellent compressive strength, and have found that the above-mentioned problems can be solved by forming expanded polyolefin resin beads so that the cross-sectional shape of the expanded polyolefin resin beads and the longest and shortest parts in the thickness direction of the cross section parallel to the thickness direction of the expanded polyolefin resin beads satisfy predetermined requirements.

[0016] 2. Expanded Polyolefin Resin Beads Expanded polyolefin resin beads according to one embodiment of the present invention are polyolefin resin expanded beads, wherein, when A1 is the cross-sectional area of ​​a cross section perpendicular to the thickness direction of the expanded polyolefin resin beads and A2 is the area of ​​a region enclosed by an envelope line connecting each end of the expanded polyolefin resin beads in the cross section, A2 / A1 is 1.20 or more, and the L / D of the expanded polyolefin resin beads is 0.10 or more but less than 0.70, where D is the diameter of the smallest circle among circles that contain the entire cross-sectional shape in the cross section and inscribe at least two of the end portions in the circle, and L is the length of the longest part in the thickness direction of the expanded polyolefin resin beads in the cross section parallel to the thickness direction.

[0017] The present expanded beads have the above-mentioned structure, and therefore can provide a polyolefin resin expansion molded article having excellent sound absorption properties and compressive strength.

[0018] (2-1) Polyolefin Resin Particles The expanded polyolefin resin particles are preferably expanded particles obtained by expanding polyolefin resin particles. The polyolefin resin particles contain a polyolefin resin as a base resin. The "base resin" refers to a resin that accounts for 50% by weight or more of 100% by weight of the resin contained in the resin particles.

[0019] In this specification, the term "resin contained in the resin particles" refers to the polyolefin resin contained in the resin particles, as well as thermoplastic resins and elastomers other than the polyolefin resin that may be contained in the resin particles.

[0020] In this specification, the term "polyolefin resin particles" refers to a resin having the highest content of olefin units among all the structural units constituting the resin. The polyolefin resin contains, for example, 50 mol% or more of olefin units out of 100 mol% of all structural units. The polyolefin resin preferably contains 60 mol% or more of olefin units out of 100 mol% of all structural units, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more.

[0021] The polyolefin resin particles contain 50% by weight or more of polyolefin resin, preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, of 100% by weight of resin contained in the resin particles.

[0022] The polyolefin resin is not particularly limited as long as it is a polymer compound synthesized using an olefin as a monomer, and examples thereof include polyethylene resins, polypropylene resins, etc. These polyolefin resins may be used alone or in combination of two or more.

[0023] In this specification, the term "polyethylene resin" refers to a resin having the highest content of ethylene units among all structural units constituting the resin. For example, the polyethylene resin contains 50 mol % or more of ethylene units out of 100 mol % of all structural units.

[0024] Examples of polyethylene resins include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, styrene-modified polyethylene resin, ethylene / vinyl acetate copolymer, ethylene / propylene copolymer, ethylene / 1-butene copolymer, ethylene / 1-butene / propylene copolymer, ethylene / hexene copolymer, ethylene / 4-methyl-1-pentene copolymer, etc. These may be used alone or in combination of two or more.

[0025] In this specification, the term "polypropylene resin" refers to a resin having the highest content of propylene units among all the structural units constituting the resin. For example, the polypropylene resin contains 50 mol % or more of propylene units out of 100 mol % of all structural units.

[0026] Examples of polypropylene resins include polypropylene homopolymers, ethylene / propylene random copolymers, 1-butene / propylene random copolymers, ethylene / 1-butene / propylene random copolymers, ethylene / propylene block copolymers, 1-butene / propylene block copolymers, propylene / chlorinated vinyl copolymers, propylene / maleic anhydride copolymers, etc. These may be used alone or in combination of two or more.

[0027] The base resin of the expanded polyolefin resin beads preferably contains a polypropylene resin containing three structural units including a propylene unit. In this specification, a "polypropylene resin containing three structural units including a propylene unit" is sometimes referred to as a "ternary polypropylene resin." The greater the amount of ternary polypropylene resin in the base resin, the lower the foaming temperature during the production of the expanded beads and the lower the water vapor pressure during in-mold molding, thereby enabling energy-saving processing and reducing steam costs. Furthermore, the greater the amount of ternary polypropylene resin in the base resin, the greater the advantage of being able to obtain a foamed molded article with excellent strength. The amount (content) of the ternary polypropylene resin in the base resin is preferably 50% by weight or more, more preferably 60% by weight or more, more preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more, based on 100% by weight of the base resin. The amount (content) of the ternary polypropylene resin in 100% by weight of the base resin may be 100% by weight, in other words, the base resin may be composed solely of the ternary polypropylene resin.

[0028] The following describes a copolymer, such as an ethylene / propylene copolymer, that contains, as structural units, structural units derived from ethylene monomers (also referred to as ethylene units) and structural units derived from propylene monomers (also referred to as propylene units). In this case, a copolymer containing more ethylene units than propylene units is called a polyethylene-based resin, and a copolymer containing more propylene units than ethylene units is called a polypropylene-based resin.

[0029] The polyolefin resin may contain a thermoplastic resin component other than the polyolefin resin and / or an elastomer component, as long as the effects of the present invention are not impaired.

[0030] Examples of thermoplastic resins other than polyolefin resins include vinyl acetate resins, thermoplastic polyester resins, acrylic ester resins, styrene resins, polyamide resins, etc. These thermoplastic resins may be used alone or in combination of two or more.

[0031] Examples of elastomers other than polyolefin-based resins include ethylene / propylene rubber and ethylene / propylene / butadiene rubber. These elastomers may be used alone or in combination of two or more. In this specification, "thermoplastic resin components and / or elastomer components other than polyolefin-based resins" may also be referred to as "other resins."

[0032] The polyolefin resin particles may contain various additives in addition to the polyolefin resin, if necessary.

[0033] In this specification, the additives contained in the polyolefin-based resin particles, in other words, the additives kneaded into the polyolefin-based resin particles, are also referred to as "resin particle additives." The "resin particle additives" can also be said to be components in the resin particles other than the resin (polyolefin-based resin, thermoplastic resin other than polyolefin-based resin, and elastomer).

[0034] Examples of resin particle additives include hydrophilic compounds, antioxidants, heat stabilizers, ultraviolet absorbers, flame retardants, antistatic agents, metal deactivators, carbon black, pigments, dyes, nucleating agents, and cell regulators.

[0035] The amount of these resin particle additives, in total, of all the resin particle additives is preferably 25 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, per 100 parts by weight of the resin contained in the resin particles. When the total amount of the resin particle additives is 25 parts by weight or less per 100 parts by weight of the resin contained in the resin particles, the following advantages (a) to (d) are obtained: (a) there is no risk of the dispersibility of the polyolefin resin particles in the dispersion being deteriorated in the process for producing expanded beads using the obtained resin particles; (b) the average cell diameter of the obtained expanded beads does not become too small; (c) the expanded beads can provide a good molded article in the molding process; and (d) the mechanical strength of the obtained molded article is not reduced.

[0036] (2-2. Shape of Expanded Polyolefin Resin Beads) In the expanded beads, when the cross-sectional area of ​​a cross section perpendicular to the thickness direction of the expanded beads is A1 and the area of ​​a region enclosed by an envelope line connecting each end of the expanded polyolefin resin bead in the cross section is A2, A2 / A1≧1.20. A1 and A2 will be described with reference to FIG.

[0037] Fig. 1 is a view of an expanded polyolefin resin bead according to one embodiment of the present invention as seen from one direction. Fig. 2 is a cross-sectional view taken along line A-A' in Fig. 1. That is, Fig. 2 is a view showing a cross section perpendicular to the thickness direction of the expanded polyolefin resin bead shown in Fig. 1. Line A-A' passes through the center in the thickness direction. Fig. 3 is a view showing the region surrounded by an envelope line connecting each end of the expanded polyolefin resin bead in the cross section shown in Fig. 2.

[0038] In this case, the cross-sectional area A1 of the cross section shown in Figure 2 and the area A2 of the region shown in Figure 3 satisfy the relationship A2 / A1 ≥ 1.20. An example of a shape that satisfies this relationship is a shape in which the cross section perpendicular to the thickness direction of the expanded beads has two or more end portions. The end portions refer to the tips of the convex portions that constitute the cross-sectional shape. The convex portions refer to protruding portions in the cross section. In the case of the shape shown in Figure 2, the convex portions are five protruding portions that form a star shape.

[0039] In this specification, a shape having a convex portion and its end portion is also referred to as a “baseline shape.” For example, a star-shaped shape has five convex portions and their end portions, and is therefore also referred to as a “five-baseline shape.”

[0040] The shape having two or more ends can form a recess between a convex portion and another adjacent convex portion. Examples of such shapes include a U-shape, an L-shape, and a V-shape, which have two convex portions and their ends; a Y-shape, which has three convex portions and their ends; an X-shape, which has four convex portions and their ends; and a star shape and a W-shape, which have five convex portions and their ends.

[0041] The end portion is a tip of the expanded particle and therefore has a curved shape, i.e., the end portion is not an intersection of two straight lines but has a rounded shape.

[0042] Here, when the cross-sectional shape is a circle or an ellipse, A2 / A1 = 1. Also, when the cross-sectional shape is a polygon such as a rectangle, which has vertices but does not have recesses formed between adjacent protrusions, A2 / A1 = 1, and the relationship A2 / A1 ≥ 1.20 is not satisfied.

[0043] The larger the A2 / A1 ratio, the higher the porosity and sound absorption coefficient of the molded article obtained from the expanded beads. Therefore, A2 / A1 is preferably 1.30 or more, more preferably 1.40 or more, more preferably 1.50 or more, even more preferably 1.60 or more, even more preferably 1.70 or more, and particularly preferably 1.80 or more. While the upper limit of A2 / A1 is not particularly limited, since the end portions of the expanded beads are less likely to have a narrow shape, the compressive strength of the molded article is likely to be high, it is preferably 2.20 or less, more preferably 2.10 or less, and even more preferably 2.00 or less. The above A1 and A2 can be measured by imaging a cross section perpendicular to the thickness direction of the expanded beads using a digital microscope or the like and measuring the area using the obtained image.

[0044] In the present expanded beads, the L / D of the expanded polyolefin resin beads is 0.10 or more and less than 0.70.

[0045] D is the diameter of the smallest circle among circles that have all of the cross-sectional shapes of the polyolefin resin foam beads in a cross section perpendicular to the thickness direction and in which at least two of the end portions are inscribed.

[0046] 4 is a diagram showing an example of a circle having all of the above-described exemplary cross-sectional shapes inside, where two of the end portions in the cross section are inscribed in the circle (points 1 and 2 in the diagram), and the other three end portions are not inscribed in the circle, but are inside the circle, and where the circle has the smallest diameter. The circle having two of the end portions inscribed in the circle and the other three end portions not inscribed in the circle, but is inside the circle, may have a larger diameter than the circle shown in FIG. However, in this specification, D, which will be described later, is determined based on the circle with the smallest diameter among the circles.

[0047] In FIG. 4 , there are two end points inscribed in the circle (points 1 and 2), but the number of end points inscribed in the circle is not limited to this. For example, in the case of a star-shaped cross-sectional shape as shown in FIG. 4 , the number of end points inscribed in the circle may be 2, 3, 4, or 5. In a star-shaped cross-sectional shape, if five end points are inscribed in the circle, there will be no end points not inscribed in the circle. In other words, if all end points of a cross-section having two or more end points can form a circle inscribed in the circle, there will be no end points not inscribed in the circle. If not all of the end points can form a circle inscribed in the circle, when at least two of the end points are inscribed in the circle, at least one end point will be inside the circle that is not inscribed in the circle. In this case, D, described below, is determined based on the circle that has the shortest possible distance between at least one of the end points that is inside the circle but not inscribed in the circle and the circumference of the circle. This distance is the length of the shortest straight line drawn from the vertex of the end point inscribed in the circle to the circumference. For example, in the case of Figure 4, it is the length of the shortest straight line drawn from point 3 that is not inscribed in the circle to the circumference. The diameter of the circle set for the expanded polyolefin resin particles in this way is defined as D.

[0048] FIG. 5 is a view of a cross section of the expanded polyolefin resin beads parallel to the thickness direction, viewed from one direction. The thickness direction is the direction of L shown in FIG. 1. L in FIG. 5 corresponds to L shown in FIG. 1. In the figure, L is the length of the longest part in the thickness direction in the above plane. As shown in FIG. 5, the expanded beads have the longest thickness direction length at the center in a direction perpendicular to the thickness direction in the above plane. As a result, as shown in FIG. 5, the expanded beads have a curved center. In the course of extensive research, the present inventors expanded polyolefin resin beads prepared under specific conditions using an extruder, as described below. Surprisingly, the present inventors independently discovered that expanded polyolefin resin beads having a curved center can be obtained in this case, as shown in FIG. 5. Note that when the expanded polyolefin resin beads are expanded by expanding polyolefin resin beads obtained using an extruder, the thickness direction of the expanded polyolefin resin beads can also be referred to as the extrusion direction of the polyolefin resin beads.

[0049] Since a molded article having excellent compressive strength and sound absorption properties can be obtained, D is preferably 2.0 mm to 12.0 mm, more preferably 3.0 mm to 10.0 mm, more preferably 4.0 mm to 9.0 mm, even more preferably 5.0 mm to 8.0 mm, even more preferably 6.0 mm to 8.0, and particularly preferably 7.0 mm to 8.0.

[0050] Since L can provide a molded product having excellent compressive strength and sound absorption properties, it is preferably 0.5 mm to 7.0 mm, more preferably 1.0 mm to 6.0 mm, even more preferably 1.5 mm to 5.0 mm, even more preferably 2.0 mm to 4.0 mm, and particularly preferably 2.0 mm to 3.5 mm.

[0051] The above L / D is preferably 0.20 to 0.60, more preferably 0.24 to 0.55, even more preferably 0.27 to 0.50, and particularly preferably 0.30 to 0.45, since a molded product having excellent compressive strength and sound absorption properties can be obtained.

[0052] The D can be determined by measuring the diameter of the circle set on the prepared expanded beads. The D is preferably the average value of the D of a plurality of particles. For example, 10 expanded beads are randomly selected, and the average value calculated based on the D of the 10 particles can be used as the D.

[0053] The L can be determined by measuring the length of the longest part in the thickness direction of the prepared expanded beads in a cross section parallel to the thickness direction. The L is preferably the average value of the L of a plurality of beads. For example, the L can be determined by randomly selecting 10 expanded beads and calculating the average value based on the L of the 10 beads.

[0054] The present expanded beads satisfy all of the requirements of A2 / A1≧1.20 and L / D of 0.10 or more and less than 0.70. When the expanded beads have a common shape such as a spherical shape, they have excellent compressive strength, but their sound absorption performance is superior to so-called irregularly shaped beads, such as those with two or more edges as described above. However, irregularly shaped beads have problems with compressive strength. Because the present expanded beads are irregularly shaped particles, they satisfy all of the above requirements, and therefore have the advantage of being able to provide molded articles that have voids and excellent structural strength, i.e., molded articles that are excellent not only in sound absorption performance but also in compressive strength.

[0055] The expanded beads of the present invention can be produced by the method for producing expanded polyolefin resin beads described below. In this method, the cross-sectional shape and diameter of the discharge holes, and the shape of the polyolefin resin particles obtained in the chopping step are controlled as described below, thereby producing the expanded beads of the present invention that satisfy the above requirements. This will be described in detail later.

[0056] The expanded beads preferably have 4 to 8 end portions in a cross section perpendicular to the thickness direction of the expanded polyolefin resin beads. This configuration allows the expanded beads to have a number of end portions that is favorable for improving sound absorption performance. This allows for the production of expanded beads with excellent sound absorption performance and compressive strength.

[0057] The number of ends of the cross section is not limited to this, and the cross section may have 9 or more ends. On the other hand, from the viewpoint of (i) obtaining a molded article having superior sound absorption performance and compressive strength, and (ii) facilitating the preparation of expanded beads, it is preferable that the cross section have 4 to 8 ends.

[0058] The expanded beads having a cross section with 4 to 8 ends can be obtained, for example, by forming a cross section perpendicular to the extrusion direction of a discharge hole in a die in a shape having 4 to 8 ends in a method for producing expanded polyolefin resin beads described below.

[0059] (2-3. DSC Curve) The present expanded beads have two melting peaks in a DSC curve obtained by differential scanning calorimetry, and when the heat of fusion of the low-temperature peak is Ql (J / g) and the heat of fusion of the high-temperature peak is Qh (J / g), it is preferable that the DSC ratio = {Qh / (Ql+Qh)} x 100 is 20.0% to 45.0%.

[0060] The DSC curve can be obtained by heating 5 to 6 mg of expanded polyolefin resin beads from 40° C. to 220° C. at a heating rate of 10° C. / min using a differential scanning calorimeter.

[0061] Figure 6 shows an example of a DSC curve obtained by subjecting the expanded beads to DSC, raising the temperature from 40°C to 220°C at a heating rate of 10°C / min. In Figure 6, the horizontal axis represents temperature and the vertical axis represents heat quantity. The upward direction of the vertical axis represents heat generation, and the downward direction represents endothermic reaction. The DSC curve shown in Figure 6 can also be considered as the DSC curve during the first heating. The DSC curve shown in Figure 6 has two peaks. These two peaks are a melting peak and an endothermic peak.

[0062] FIG. 6 shows two melting peaks. The lower-temperature peak is referred to as the lower-temperature melting peak, and the peak temperature of this peak is referred to as the lower-temperature peak temperature. The higher-temperature peak is referred to as the higher-temperature melting peak, and the peak temperature of this peak is referred to as the higher-temperature peak temperature. Each point on the DSC curve of the expanded beads shown in FIG. 6 during the first heating cycle will be described. Point A represents the endotherm at a temperature of 100°C. Point B represents the endotherm at the temperature at which the higher-temperature melting ends. Point B can also be considered the intersection of the line extending from the higher-temperature melting peak toward the higher temperature and the higher-temperature baseline (which is also the melting end baseline). Point C represents the point at which the endotherm between the lower-temperature melting peak and the higher-temperature melting peak is smallest. Point D represents the point at which a line parallel to the Y-axis drawn from point C toward line segment AB intersects with this line. The heat quantity based on the range enclosed by the low-temperature melting peak and line segments AD and CD is referred to as the low-temperature melting heat (Ql). The heat quantity based on the range enclosed by the high-temperature melting peak and line segments BD and CD is referred to as the high-temperature melting heat (Qh). The sum of the low-temperature melting heat (Ql) and the high-temperature melting heat (Qh) is the heat quantity of the entire melting peak.

[0063] (2-4. DSC Ratio) The ratio of the high temperature heat of fusion (Qh) to the total heat of the melting peak is called the DSC ratio or high temperature heat ratio. The DSC ratio is expressed by the following formula (3): DSC ratio (%) = (Qh / (Ql+Qh)) x 100 Formula (3).

[0064] The DSC ratio of the present expanded beads is preferably 20.0% to 45.0%, more preferably 21% to 35%, more preferably 22% to 33%, even more preferably 23% to 32%, even more preferably 23% to 31%, and particularly preferably 24% to 30%. When the DSC ratio is within this range, molding using the present expanded beads (e.g., in-mold foam molding) has the advantage of allowing a wide range of molding conditions to be selected. In a molded article produced using the present expanded beads, the structure of the polyolefin resin expanded beads changes, but the composition does not. Therefore, the DSC ratio of a polyolefin resin expanded molded article can be considered to be the same as the DSC ratio of the polyolefin resin expanded beads that are the raw material for the molded article. The DSC ratio of a polyolefin resin expanded molded article can be determined from a DSC curve obtained by the same DSC as that of the polyolefin resin expanded beads (specifically, the DSC curve at the first heating time).

[0065] (2-5. Bulk Density) The expanded beads preferably have a bulk density of 10.0 g / L to 300.0 g / L. This configuration has the advantage of providing expanded beads with little variation in expansion ratio and good moldability. In view of this advantage, the bulk density is more preferably 12.0 g / L to 100.0 g / L, even more preferably 14.0 g / L to 60.0 g / L, even more preferably 16.0 g / L to 50.0 g / L, and particularly preferably 20.0 g / L to 40.0 g / L. The method for measuring the bulk density of expanded beads will be described in detail in the Examples below.

[0066] (2-6. Average Cell Diameter) The present expanded beads preferably have an average cell diameter of 100 μm to 350 μm. Cell diameter is synonymous with cell diameter. This configuration has the advantage that, when preparing a molded article, it is easy to firmly fuse the expanded beads together, and the porosity of the molded article can be maintained high. In view of these advantages, the average cell diameter is more preferably 150 μm to 300 μm.

[0067] The average bubble diameter can be adjusted to a desired value by using a nucleating agent (inorganic nucleating agent) during the production of polyolefin resin particles. Examples of nucleating agents include talc, titanium oxide, silica (silicon dioxide), silicates, alumina, diatomaceous earth, calcium carbonate, magnesium oxide, magnesium carbonate, magnesium sulfate, calcium phosphate, feldspar apatite, barium sulfate, and zinc borate. Examples of silicates include talc, magnesium silicate, kaolin, halloysite, dickite, aluminum silicate, and zeolite. Only one nucleating agent may be used, or two or more nucleating agents may be used in combination.

[0068] The amount of nucleating agent added varies depending on the type of polyolefin resin and the type of cell nucleating agent used and cannot be generally determined, but is generally 0.001 to 2 parts by weight per 100 parts by weight of polyolefin resin.

[0069] The method for measuring the average cell diameter will be described in detail in the Examples below.

[0070] [3. Method for producing expanded polyolefin resin beads] The method for producing expanded polyolefin resin beads is not particularly limited, and known methods can be used. Examples of the method for producing expanded polyolefin resin beads include a method (hereinafter also referred to as method A) comprising the following steps: an extrusion step of extruding a polyolefin resin composition containing a polyolefin resin through one or more discharge holes provided in a die of an extruder; a cooling step of solidifying the extruded polyolefin resin composition by cooling it using a cooling device equipped with a cooling medium; a take-up step of taking up the solidified polyolefin resin composition into a gas phase using a take-up machine; a chopping step of chopping the taken-up polyolefin resin composition to obtain polyolefin resin particles; a dispersion preparation step of mixing the polyolefin resin particles with a dispersion medium and a blowing agent in a container to prepare a dispersion; and a release step of releasing the dispersion into a pressure region lower than the internal pressure of the container to obtain expanded polyolefin resin beads. According to Method A, it is possible to provide expanded polyolefin resin particles that can provide expanded polyolefin resin molded articles that are excellent in sound absorption performance and compressive strength.

[0071] The "polyolefin resin composition containing a polyolefin resin" is a blend containing a polyolefin resin and, if necessary, the other resins and resin particle additives described above. The polyolefin resin composition can be produced by melt-kneading the blend. Method A may further include a resin composition preparation step of heating and melting the blend in an extruder and kneading it to prepare a polyolefin resin composition.

[0072] The apparatus for melt-kneading the blend (melt-kneading apparatus) may be, for example, an extruder as described below, with a twin-screw extruder being more preferred.

[0073] The temperature at which the blend is melt-kneaded (hereinafter, sometimes referred to as "resin temperature") can also be said to be the temperature of the molten kneaded product (polyolefin resin composition) immediately before the molten kneaded product is extruded from a discharge hole provided in a die of an extruder.

[0074] The temperature is not particularly limited, but may be the melting point of the polyolefin resin [Tm １ (°C)], Tm １ +40℃ or more Tm １ It may be +110°C or lower. The melting point of the polyolefin resin referred to here is the value obtained by differential scanning calorimetry (DSC) using a differential scanning calorimeter. The specific operating procedure is as follows: (1) 4 to 6 mg of polyolefin resin is heated from 40°C to 220°C at a heating rate of 10°C / min to melt it; (2) the temperature is lowered from 220°C to 40°C at a heating rate of 10°C / min to crystallize it; and (3) the temperature is further increased from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (melting peak) of the DSC curve obtained during the second heating (i.e., during (3)) can be determined as the melting point of the polyolefin resin.

[0075] In expanded polyolefin resin beads produced using polyolefin resin particles containing a polyolefin resin, the structure of the polyolefin resin particles changes, but the composition of the polyolefin resin particles does not. Furthermore, in expanded polyolefin resin molded articles produced using expanded polyolefin resin particles produced using polyolefin resin particles, the structure of the expanded polyolefin resin particles changes, but the composition of the expanded polyolefin resin particles does not change. Therefore, the melting point value obtained by analyzing the expanded polyolefin resin beads or the expanded polyolefin resin molded articles can be considered to be the melting point value of the polyolefin resin contained in the polyolefin resin particles, which are their raw material.

[0076] In this specification, the melting point of the expanded polyolefin resin particles or the expanded polyolefin resin molded article is a value obtained by measuring in the same manner (DSC) as the melting point of the polyolefin resin, except that expanded polyolefin resin particles or expanded polyolefin resin molded article, respectively, are used instead of the polyolefin resin.

[0077] (3-1. Extrusion Step) In this step, the polyolefin resin composition is extruded from one or more discharge holes provided in a die equipped in an extruder. The polyolefin resin composition, which is a melt-kneaded product, can be extruded, for example, in the form of strands, from one or more discharge holes provided in a die attached to the tip of an extruder (for example, a melt-kneading device). "Extruding" the polyolefin resin composition from the discharge hole may also be referred to as "discharging."

[0078] The number of discharge holes provided in the die is not particularly limited as long as it is one or more. The cross-sectional area of ​​the discharge hole perpendicular to the extrusion direction can be adjusted by changing the cross-sectional shape and cross-sectional diameter of the discharge hole. The extrusion direction is the direction in which the polyolefin resin composition (melt-kneaded product) is extruded.

[0079] Here, when the area of ​​a cross section perpendicular to the extrusion direction of the one or more discharge holes is A3 and the area of ​​a region in the cross section enclosed by an envelope connecting each end of the discharge holes is A4, it is preferable that A4 / A3 ≥ 1.2. When there are two or more discharge holes, it is preferable that each discharge hole satisfies the requirement of A4 / A3 ≥ 1.2.

[0080] The above A3 is set to 1.0 mm in order to optimize the size of the expanded particles in consideration of the filling property into the mold. ２ ~6.0mm ２ From this viewpoint, it is preferable that A3 is 1.2 mm. ２ ~5.0mm ２ More preferably, it is 1.6 mm ２ ~4.0mm ２ It is more preferable that:

[0081] Here, Fig. 7 is a front view showing an example of the configuration of one discharge hole provided in a die. That is, Fig. 7 shows a cross section perpendicular to the extrusion direction of the discharge hole. The discharge hole is a discharge hole for obtaining star-shaped resin particles that are the raw material for star-shaped expanded beads. The polyolefin resin composition discharged from the discharge hole can be subjected to each step after the cooling step to obtain, for example, the present expanded beads shown in Fig. 1.

[0082] Fig. 8 is a diagram showing a region surrounded by an envelope line connecting each end of the discharge hole shown in Fig. 7. In this case, the cross-sectional area A3 of the cross section shown in Fig. 7 and the area A4 of the region shown in Fig. 8 preferably satisfy the relationship A4 / A3 ≥ 1.2. By satisfying this relationship, the expanded beads of the present invention satisfy the aforementioned relationship A2 / A1 ≥ 1.20.

[0083] An example of a shape that satisfies the relationship A4 / A3≧1.2 is a shape in which the cross-sectional shape has two or more ends. The ends refer to the tips of the convex portions that constitute the cross-sectional shape of the discharge hole. The convex portions refer to the portions that protrude in the cross section. For example, in the case of the shape shown in FIG. 7, the convex portions are five protruding portions that form a star shape. Examples of shapes that have two or more ends include the U-shape, L-shape, V-shape, Y-shape, X-shape, star shape, and W-shape described in (2-2. Shape of expanded polyolefin resin beads).

[0084] The larger the ratio A4 / A3, the higher the porosity and sound absorption coefficient of the molded article obtained from the expanded beads, so A4 / A3 is preferably 1.2 or more. While the upper limit of A4 / A3 is not particularly limited, it is preferably 4.0 or less, since the end of the expanded beads is less likely to be narrowed, and the compressive strength of the molded article is likely to be high. As mentioned above, A4 and A3 can be adjusted to satisfy the relationship A4 / A3≧1.2 by changing the cross-sectional shape and cross-sectional diameter of the discharge hole.

[0085] The discharge hole preferably has a slit width of 0.05 mm to 0.80 mm. The slit width refers to the width of the convex portion in a cross section perpendicular to the extrusion direction of the discharge hole. For example, in the cross section shown in FIG. 7, this corresponds to the width of the portion indicated as "slit width." In the cross section shown in FIG. 7, the slit width is constant for all convex portions, but if the slit width varies depending on the convex portion, it is preferable that the average slit width of all convex portions is 0.05 mm to 0.80 mm. Furthermore, if the slit width varies depending on the location of one convex portion, the average slit width can be found for each convex portion and used to calculate the average slit width of all convex portions.

[0086] The slit width is more preferably 0.15 mm to 0.60 mm, and even more preferably 0.25 mm to 0.50 mm, from the viewpoint of (i) enhancing sound absorption properties and (ii) preventing nozzle clogging when foreign matter gets mixed in.

[0087] The discharge hole preferably has 4 to 8 slits. The number of slits refers to the number of convex portions in a cross section perpendicular to the extrusion direction of the discharge hole. For example, in the cross section shown in Figure 7, the number of slits is 5. Having 4 to 8 slits has the advantage that the discharge hole can easily satisfy the requirement A4 / A3 ≥ 1.2. From this perspective, the number of slits is more preferably 4 to 7, and even more preferably 5 to 6.

[0088] (3-2. Cooling Step) In this step, the extruded polyolefin resin composition is solidified by cooling it using a cooling device equipped with a cooling medium.

[0089] The cooling medium may be water, air, or the like, and is preferably water from the viewpoint of cooling efficiency. The cooling device may be, for example, a water tank or a water channel containing water as the cooling medium.

[0090] The temperature of the cooling medium may be referred to as the water temperature when a water tank containing water is used as the cooling medium. The temperature of the cooling medium is not particularly limited, but may be Tm １ -150℃ or moreTm １ It may be −90° C. or lower, and Tm １ -150℃ or more Tm １ A temperature of −110° C. or lower is preferred.

[0091] When the polyolefin resin composition is discharged from the cooling device into the gas phase for the later-described take-off process, the cooling time may affect the surface temperature of the polyolefin resin composition discharged from the cooling device into the gas phase. The surface temperature is not particularly limited, but may be Tm １ It may be -70°C or lower, Tm １ A temperature of −100° C. or lower is preferred.

[0092] (3-3. Take-up step) In this step, the solidified polyolefin resin composition is taken up into the gas phase from the cooling medium (cooling device) using a take-up machine. Examples of the take-up machine include a roller-type take-up machine that performs take-up using rollers, and can be used to take up the polyolefin resin composition extruded from one or more discharge holes provided in the die.

[0093] (3-4. Shredding Step) In this step, the taken-out polyolefin resin composition is shredded to obtain polyolefin resin particles.

[0094] The shredding speed of the polyolefin resin composition that has undergone the above-mentioned take-up step can be changed as appropriate. The shredding speed refers to the shredding speed when the polyolefin resin composition taken up by a take-up machine or the like is shredded by a shredding device. When a shredding device equipped with a blade such as a cutter is used, the shredding speed can also be said to be the rotation speed of the blade.

[0095] In a preferred embodiment of the present invention, the shredding step is a step of shredding the taken-up polyolefin resin composition to obtain polyolefin resin particles having an LP / DP ratio of preferably 0.1 to 1.3, more preferably 0.2 to 1.2, even more preferably 0.3 to 1.1, and particularly preferably 0.4 to 1.0. The LP is the length of the longest part in the thickness direction of the polyolefin resin particle in a cross section parallel to the thickness direction, and the DP is the diameter of the smallest circle among circles that have the entire cross-sectional shape of the polyolefin resin particle in a cross section perpendicular to the thickness direction and inscribe at least two of the ends of the polyolefin resin particle. When the taken-up polyolefin resin composition is shredded in the shredding step so that the LP / DP of the polyolefin resin particles falls within the above range, method A has the advantage of easily obtaining expanded polyolefin resin particles having an L / D ratio of 0.10 or more and less than 0.70.

[0096] (3-5. Dispersion Preparation Step) This step can be carried out by adding polyolefin resin particles, a dispersion medium, a foaming agent, and optionally a dispersant, a dispersion aid, etc. to a container and mixing them. The order in which these are added to the container is not particularly limited. The manner in which the added raw materials are mixed is not particularly limited, and examples include a method in which the raw materials are stirred using a stirring blade or the like provided in the container.

[0097] The container is preferably one that can withstand the expansion temperature and expansion pressure during the production of expanded beads, and is more preferably a pressure-resistant container. Examples of the container include an autoclave-type pressure-resistant container. The expansion temperature and expansion pressure will be described in detail later.

[0098] The dispersion medium is not particularly limited. The dispersion medium is preferably an aqueous dispersion medium, and it is preferable to use only water as the dispersion medium. In Method A, a dispersion medium obtained by adding methanol, ethanol, ethylene glycol, glycerin, or the like to water can also be used as the dispersion medium. Only one type of dispersion medium may be used, or two or more types may be used in combination.

[0099] The amount of the dispersion medium used is preferably 200 parts by weight or more, more preferably 300 parts by weight or more, relative to 100 parts by weight of the polyolefin resin particles. When the amount of the dispersion medium used is 200 parts by weight or more relative to 100 parts by weight of the polyolefin resin particles, the dispersibility of the polyolefin resin particles in the dispersion liquid improves as the amount of the dispersion medium used increases.

[0100] In Method A, when a hydrophilic compound is contained in the polyolefin resin particles and the dispersion medium contains water, the water in the dispersion medium can act as a blowing agent, thereby improving the expansion ratio of the resulting expanded beads.

[0101] Examples of the blowing agent include aliphatic hydrocarbons, halogenated hydrocarbons, and inorganic gases. Examples of aliphatic hydrocarbons include propane, butane, isobutane, pentane, and isopentane. Examples of halogenated hydrocarbons include monochloromethane and hydrofluoroolefins. Examples of inorganic gases include air, nitrogen, and carbon dioxide. For example, water contained in the dispersion medium can be used as the blowing agent. These blowing agents may be used alone or in combination of two or more. In Method A, inorganic gases and / or water are preferred as the blowing agent because they do not adversely affect the environment. The blowing agent is preferably air and / or carbon dioxide gas, and more preferably carbon dioxide gas.

[0102] The amount of the foaming agent used cannot be generally specified, as it varies depending on the type of polyolefin resin used, the type of foaming agent, the desired expansion ratio, etc. The amount of the foaming agent used is preferably, for example, 2 parts by weight or more and 60 parts by weight or less per 100 parts by weight of the polyolefin resin particles.

[0103] A dispersant may be used in Method A. When a dispersant is used in the dispersion preparation step, (a) coalescence of polyolefin resin particles in the dispersion can be prevented, and / or (b) coalescence of polyolefin resin particles after the dispersion is released can be prevented.

[0104] Examples of dispersants include, but are not limited to, inorganic dispersants such as tricalcium phosphate, trimagnesium phosphate, calcium pyrophosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, and silicates. Examples of silicates include clay minerals such as kaolin, talc, and clay. These dispersants may be used alone or in combination of two or more.

[0105] The amount of the dispersant used is not particularly limited and can be appropriately changed depending on the type of dispersant. The amount of the dispersant used is preferably, for example, 0.01 parts by weight or more and 3.00 parts by weight or less per 100 parts by weight of the polyolefin resin particles.

[0106] In Method A, a dispersing aid may be used. When a dispersing aid is used in the dispersion preparation step, (a) coalescence of polyolefin resin particles in the dispersion can be prevented, and / or (b) coalescence of polyolefin resin particles after the dispersion is released can be prevented. The dispersing aid is preferably used together with the dispersant.

[0107] The dispersing aid may be, but is not limited to, an anionic surfactant. The dispersing aid may be used alone or in combination of two or more.

[0108] The amount of the dispersing aid used is, for example, preferably 0.001 to 0.300 parts by weight, more preferably 0.010 to 0.200 parts by weight, and more preferably 0.020 to 0.150 parts by weight, per 100 parts by weight of the polyolefin resin particles.

[0109] (3-6. Releasing Step) This step is a step of releasing the dispersion obtained in the dispersion preparing step into a pressure region lower than the internal pressure of the container used in the dispersion preparing step to obtain expanded polyolefin resin beads.

[0110] The discharging step may be carried out, for example, by increasing the pressure inside the container to a pressure higher than atmospheric pressure in advance and discharging the dispersion under atmospheric pressure to obtain expanded polyolefin resin beads having an expansion ratio of 10 times or more. The pressure lower than the pressure inside the container is preferably atmospheric pressure. The expansion ratio of the resulting expanded beads is preferably 60 times or less.

[0111] The temperature and pressure inside the container when the dispersion is released into a pressure region lower than the pressure inside the container are also referred to as the foaming temperature and foaming pressure, respectively. Method A may further include a heating step of increasing the temperature inside the container to the foaming temperature and / or a pressurizing step of increasing the pressure inside the container to the foaming pressure.

[0112] The foaming temperature varies depending on the type of polyolefin resin used, the type and / or amount of resin particle additive kneaded (used) into the polyolefin resin, and the type and / or amount of foaming agent, and cannot be generally defined. The foaming temperature is calculated by dividing the melting point of the polyolefin resin particles by [Tm ２ (°C)], Tm ２ -30 (℃) or more Tm ２ Preferably, it is +10°C or lower.

[0113] In this specification, the melting point Tm of the polyolefin resin particles ２ The melting point Tm of the polyolefin resin is the same as that of the polyolefin resin except that polyolefin resin particles are used instead of the polyolefin resin. １ The value is obtained by measuring by the same method (DSC) as above.

[0114] In polyolefin-based resin particles produced using a polyolefin-based resin, although the resin particle additive is present, the physical properties of the polyolefin-based resin are not changed. Therefore, in one embodiment of the present invention, the melting point Tm ２ is the melting point Tm of the polyolefin resin used to produce the polyolefin resin particles １ can be the same as

[0115] The expansion pressure varies depending on the desired expansion ratio of the expanded polyolefin resin beads and cannot be generally defined. The expansion pressure is preferably 0.50 MPa·G or more and 6.0 MPa·G or less, and more preferably 1.0 MPa·G or more and 4.5 MPa·G or less. In this specification, "G" written after the pressure unit indicates that the pressure is a gauge pressure. In other words, "MPa·G" can also be rewritten as "MPa (gauge pressure)."

[0116] When a dispersion liquid containing polyolefin resin particles is released from a container into a pressure region lower than the container internal pressure, the dispersion liquid may be released through an orifice having an opening of 2 mm to 10 mm in diameter for the purposes of adjusting the release amount (flow rate) and reducing the expansion rate variation of the resulting expanded beads. A "pressure region lower than the container internal pressure" is also referred to as a low-pressure atmosphere. In Method A, when the dispersion liquid in the container is released into a low-pressure atmosphere for the purpose of increasing the expansion rate, the temperature of the low-pressure atmosphere may be adjusted.

[0117] The dispersion prepared in the vessel may be heated to the foaming temperature and pressurized to the foaming pressure under stirring, and then maintained at the foaming temperature and pressure for a certain period of time. The certain period of time is typically 5 to 180 minutes, and preferably 10 to 60 minutes. The dispersion maintained at the foaming temperature and pressure for the certain period of time is then released into a low-pressure atmosphere (usually atmospheric pressure) by opening a valve provided at the bottom of the vessel, thereby producing expanded polyolefin resin beads.

[0118] [4. Polyolefin-based resin foam molded article] The polyolefin-based resin foam molded article according to one embodiment of the present invention is preferably a molded article obtained by molding (e.g., in-mold foam molding) the polyolefin-based resin foam beads described in the above section [2. Polyolefin-based resin foam beads]. As described above, the polyolefin-based resin foam beads according to one embodiment of the present invention can provide a polyolefin-based resin foam molded article having excellent sound absorption performance and compressive strength.

[0119] The present molded article is preferably a molded article obtained by molding (for example, in-mold foam molding) expanded beads produced by the production method described in the above section [3. Production method of expanded polyolefin resin beads].

[0120] A mold may be used to produce the molded article. The amount of cracking during molding of the molded article is preferably 10% to 50%, more preferably 20% to 50%. A cracking amount within the above range has the advantage of making it easier to obtain a molded article with a high specific strength and a high sound absorption coefficient in the low frequency range. In this specification, "cracking" refers to the distance between the movable and fixed molds in the molding space of the mold while the foamed beads are being filled; in other words, the degree of mold opening width, when the average thickness of the resulting foamed molded article (the thickness of the foamed molded article calculated by dividing the volume of the foamed molded article by the projected area when light is irradiated on the foamed molded article from the direction of movement of the movable mold) is taken as 100%.

[0121] The porosity of the molded body is not particularly limited, but is preferably 20% to 50%, more preferably 21% to 45%, even more preferably 22% to 40%, and particularly preferably 24% to 32%. This configuration has the advantage of excellent sound absorption in the low and medium frequency ranges of 3000 Hz or less. The method for measuring the porosity of the molded body will be explained in detail in the Examples below.

[0122] The specific strength of the molded body is not particularly limited, but is preferably 7.5 kPa / (kg / m ３ )~11.0kPa / (kg / m ３ ) and 7.7 kPa / (kg / m ３)~10.5kPa / (kg / m ３ ), and more preferably 8.0 kPa / (kg / m ３ )~10.0kPa / (kg / m ３ ), and more preferably 8.5 kPa / (kg / m ３ )~9.5kPa / (kg / m ３ ) is particularly preferred. This configuration has the advantage of providing excellent structural strength even in the case of a foamed molded article having a high porosity and being lightweight. The method for measuring the specific strength of the molded article will be described in detail in the following examples.

[0123] [5. Method for producing a polyolefin resin foam molded article] A method for producing a polyolefin resin foam molded article according to one embodiment of the present invention (hereinafter also referred to as "the present production method") includes a molding step of molding the expanded polyolefin resin beads described in the above section [2. Expanded polyolefin resin beads], and in the molding step, the amount of cracking of the mold is preferably 10% to 50%.

[0124] Hereinafter, a method for producing a polyolefin resin foam molded article according to one embodiment of the present invention will be described. However, except for the matters detailed below, the description in [4. Polyolefin resin foam molded article] will be used as appropriate.

[0125] In another embodiment of the present invention, the method for producing the molded article includes a molding step of molding the expanded polyolefin resin beads produced by the method described in the above section [3. Method for producing expanded polyolefin resin beads], and in the molding step, the amount of cracking of the mold is preferably 10% to 50%.

[0126] The present production method has the above-mentioned features, and therefore can provide a polyolefin resin foam molded article that is excellent in sound absorption performance and compressive strength.

[0127] (5-1. Molding Step) This step is a step of molding the expanded polyolefin resin beads described in the above section [2. Expanded Polyolefin Resin Beads] to obtain a polyolefin resin foam molded article. The method for molding the expanded beads is not particularly limited, and any known method can be used, for example, an in-mold foam molding method using an in-mold foam molding machine equipped with a mold can be mentioned.

[0128] Examples of in-mold foam molding methods include, but are not limited to, the following methods (1) to (6) in order: (1) A mold consisting of a fixed mold that cannot be driven and a movable mold that can be driven is mounted on an in-mold foam molding machine. Here, the fixed and movable molds can be formed inside the fixed and movable molds by driving the movable mold toward the fixed mold (this operation is sometimes referred to as "mold closing"); (2) driving the movable mold toward the fixed mold so that the fixed and movable molds are not completely closed, in other words so that cracking (gaps) are formed between the fixed and movable molds; (3) filling the molding space formed inside the fixed and movable molds with foamed particles, for example, through a filling machine; (4) driving the movable mold so that the fixed and movable molds are completely closed (i.e., completely closing the mold); (5) after preheating the mold with steam, one-sided heating and reverse-sided heating of the mold with steam are performed, and the mold is further heated on both sides with steam, thereby performing in-mold foam molding; (6) removing the in-mold foam-molded product from the mold and drying (for example, drying at 75°C) to obtain a foam-molded product.

[0129] In the above (2), the amount of cracking is preferably 10% to 50%, and more preferably 20% to 50%, of the average thickness of the foamed molded article to be obtained, which is 100%. If the amount of cracking is within the above range, there is an advantage that a molded article having a smooth and beautiful surface can be easily obtained.

[0130] In the above (3), the following methods (3-1) to (3-3) can be mentioned as methods for filling the molding space with the expanded beads: (3-1) A method in which the expanded beads (including the above-mentioned two-stage expanded beads, the same applies hereinafter) are pressurized with an inorganic gas in a container to impregnate the expanded beads with the inorganic gas, and after applying a predetermined internal pressure (expanded bead internal pressure), the expanded beads are filled into the molding space; (3-2) A method in which the expanded beads are compressed by gas pressure and filled into the molding space; (3-3) A method in which the expanded beads are filled into the molding space without any particular pretreatment.

[0131] The present production method uses the present expanded beads for molding, and since the amount of cracking is 10% to 50%, it is possible to provide a polyolefin resin foam molded article that has excellent sound absorption properties and compressive strength.

[0132] The polyolefin resin foam molded article according to one embodiment of the present invention is suitable for applications such as automobile interior materials. Examples of applications for automobile interior materials include sound insulation of engine compartment noise, shock absorbing materials (tibia pads) for protecting the lower legs of passengers, shock absorbing materials (knee pads) for protecting the knees of passengers, floor pads for reducing road noise, trunk boxes and trunk lids for insulating rear motor noise, and shock absorbing materials (side impact pads) for protecting passengers in side collisions. In these applications, sound-insulating films and plates can be laminated onto the foam molded article to create a structure in which the foam of the present invention absorbs noise and then provides sound insulation (i.e., improves sound insulation).

[0133] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0134] An embodiment of the present invention may have the following configuration.

[0135] [1] Expanded polyolefin resin beads, wherein A2 / A1≧1.20, where A1 is the cross-sectional area of ​​a section perpendicular to the thickness direction of the expanded polyolefin resin beads and A2 is the area of ​​a region enclosed by an envelope connecting each end of the expanded polyolefin resin beads in the cross section, and L / D of the expanded polyolefin resin beads is 0.10 or more and less than 0.70, where D is the diameter of the smallest circle among circles that contain all of the cross-sectional shapes in the cross section and inscribe at least two of the end portions in the circle, and L is the length of the longest part in the thickness direction of the expanded polyolefin resin beads in the cross section parallel to the thickness direction.

[0136] [2] Expanded polyolefin resin particles according to [1], which have two melting peaks in a DSC curve obtained by differential scanning calorimetry, and have a DSC ratio of 20.0% to 45.0% when the heat of fusion of the lower-temperature peak is Ql (J / g) and the heat of fusion of the higher-temperature peak is Qh (J / g): DSC ratio = {Qh / (Ql + Qh)} x 100.

[0137] [3] The expanded polyolefin resin particles according to [1] or [2], having a bulk density of 10.0 g / L to 300.0 g / L.

[0138] [4] The expanded polyolefin resin beads according to any one of [1] to [3], wherein the shape of a cross section perpendicular to the thickness direction of the expanded polyolefin resin beads is one or more shapes selected from the group consisting of U-shape, L-shape, V-shape, Y-shape, X-shape, star-shape, and W-shape.

[0139] [5] The expanded polyolefin resin beads according to any one of [1] to [4], wherein a cross section perpendicular to the thickness direction of the expanded polyolefin resin beads has 4 to 8 ends.

[0140] [6] Expanded polyolefin resin particles according to any one of [1] to [5], having an average cell diameter of 100 μm to 350 μm.

[0141] [7] The expanded polyolefin resin beads according to any one of [1] to [6], wherein the base resin of the expanded polyolefin resin beads comprises a polypropylene resin containing three types of structural units including a propylene unit.

[0142] [8] The expanded polyolefin resin beads according to any one of [1] to [7], wherein D of the expanded polyolefin resin beads is 2.0 mm to 12.0 mm.

[0143] [9] The expanded polyolefin resin beads according to any one of [1] to [8], wherein L of the expanded polyolefin resin beads is 0.5 mm to 7.0 mm.

[0144]

[10] The expanded polyolefin resin particles according to any one of [1] to [9], wherein the expanded polyolefin resin particles are formed by expanding polyolefin resin particles, and the polyolefin resin particles contain 25 parts by weight or less of a resin particle additive per 100 parts by weight of the polyolefin resin contained in the polyolefin resin particles.

[0145]

[11] The expanded polyolefin resin beads according to any one of [1] to

[10] , wherein the base resin of the expanded polyolefin resin beads contains at least one selected from the group consisting of polypropylene homopolymer, ethylene / propylene random copolymer, 1-butene / propylene random copolymer, ethylene / 1-butene / propylene random copolymer, and ethylene / propylene block copolymer.

[0146]

[12] A polyolefin resin foam molded article obtained by molding the expanded polyolefin resin beads according to any one of [1] to

[11] .

[0147]

[13] The polyolefin resin foam molded article according to

[12] , wherein the amount of cracking during molding is 10% to 50%.

[0148]

[14] The polyolefin resin foam molded article according to

[12] or

[13] , wherein the amount of cracking during molding is 20% to 50%.

[0149]

[15] The polyolefin resin foam molded article according to any one of

[12] to

[14] , having a porosity of 20% to 50%.

[0150]

[16] Specific strength is 7.5 kPa / (kg / m ３ )~11.0kPa / (kg / m ３

[16] The polyolefin resin foam molded article according to any one of

[12] to

[15] ,

[0151]

[17] A method for producing a polyolefin resin foam molded article, comprising a molding step of molding the expanded polyolefin resin beads according to any one of [1] to

[11] , wherein the amount of cracking of the mold in the molding step is 10% to 50%.

[0152]

[18] A method for producing the expanded polyolefin resin beads according to any one of [1] to

[11] , comprising: an extrusion step of extruding a polyolefin resin composition containing a polyolefin resin through one or more discharge holes provided in a die of an extruder; a cooling step of solidifying the extruded polyolefin resin composition by cooling it using a cooling device equipped with a cooling medium; a take-up step of taking up the solidified polyolefin resin composition into a gas phase using a take-up machine; a shredding step of shredding the taken-up polyolefin resin composition to obtain polyolefin resin particles; a dispersion preparation step of mixing the polyolefin resin particles with a dispersion medium and a blowing agent in a container to prepare a dispersion; and a release step of releasing the dispersion into a pressure region lower than the internal pressure of the container to obtain expanded polyolefin resin beads.

[0153]

[19] The method for producing expanded polyolefin resin beads according to

[18] , wherein the discharge hole satisfies the requirement of A4 / A3≧1.2: wherein A3 is the area of ​​a cross section perpendicular to the extrusion direction of the discharge hole, and A4 is the area of ​​a region enclosed by an envelope line connecting each end of the discharge hole in the cross section.

[0154]

[20] The method for producing expanded polyolefin resin beads according to

[19] , wherein the cross-sectional shape has two or more ends.

[0155]

[21] The method for producing expanded polyolefin resin particles according to any one of

[18] to

[20] , wherein the shredding step is a step of shredding the taken-up polyolefin resin composition to obtain polyolefin resin particles having an LP / DP ratio of 0.1 to 1.3. Here, the LP is the length of the longest part in the thickness direction of the polyolefin resin particle in a cross section parallel to the thickness direction, and the DP is the diameter of the smallest circle among circles that have the entire cross-sectional shape of the polyolefin resin particle in a cross section perpendicular to the thickness direction and inscribe at least two of the ends of the polyolefin resin particle in the circle.

[0156]

[22] The method for producing expanded polyolefin resin beads according to any one of

[18] to

[21] , wherein the cooling medium is water.

[0157]

[23] The method for producing expanded polyolefin resin beads according to any one of

[18] to

[22] , wherein the amount of the dispersion medium used is 200 parts by weight or more per 100 parts by weight of the polyolefin resin beads.

[0158]

[24] The method for producing expanded polyolefin resin beads according to any one of

[18] to

[23] , wherein the foaming agent is one or more foaming agents selected from the group consisting of aliphatic hydrocarbons, halogenated hydrocarbons, inorganic gases, and water.

[0159]

[25] The method for producing expanded polyolefin resin beads according to any one of

[18] to

[24] , wherein a dispersant is used in the dispersion preparation step.

[0160]

[26] The method for producing expanded polyolefin resin beads according to any one of

[18] to

[25] , wherein in the discharging step, the dispersion is passed through an orifice having a diameter of 2 mm to 10 mm and discharged into a pressure region lower than the internal pressure of the container.

[0161]

[27] The method for producing expanded polyolefin resin beads according to any one of

[18] to

[26] , wherein the polyolefin resin particles contain 25 parts by weight or less of a resin particle additive per 100 parts by weight of the polyolefin resin contained in the polyolefin resin particles.

[0162] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0163] [Materials] The materials used in the examples and comparative examples are as follows.

[0164] <Polyolefin-based resin> A 1-butene / ethylene / propylene random copolymer (melting point 149°C, 1-butene content 3.8 wt%, ethylene content 0.5 wt%, melt index (MI) = 10.1 g / 10 min), which is a polypropylene-based resin, was used as the polyolefin-based resin.

[0165] <Additives> Glycerin: Refined glycerin D (manufactured by Lion Corporation) Talc: Talc Powder (registered trademark) PK-S (manufactured by Hayashi Kasei Co., Ltd.).

[0166] [Measurement Methods] Evaluations in the examples and comparative examples were carried out by the following methods.

[0167] <Melting point Tm of polyolefin resin １Measurement> The melting point of the polyolefin resin was determined by measurement using a differential scanning calorimeter (DSC6200 model, manufactured by Seiko Instruments Inc.). The specific operating procedures were as follows (1) to (4): (1) the temperature of 5 mg to 6 mg of polyolefin resin was raised from 40.0°C to 220.0°C at a heating rate of 10.0°C / min to melt the polyolefin resin; (2) the temperature of the molten polyolefin resin was then lowered from 220.0°C to 40.0°C at a heating rate of 10.0°C / min to crystallize the polyolefin resin; (3) the temperature of the crystallized polyolefin resin was then further raised from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (4) the temperature of the peak (melting peak) of the DSC curve of the polyolefin resin obtained during the second heating (i.e., during (3)) was taken as the melting point of the polyolefin resin. In addition, when there are multiple peaks (melting peaks) in the DSC curve of the polyolefin resin obtained during the second heating by the above-mentioned method, the temperature of the peak (melting peak) with the maximum heat of fusion was taken as the melting point of the polyolefin resin.

[0168] The MI of the polyolefin resin was measured using an MI measuring device described in JIS K7210:1999 under the following conditions: orifice diameter: 2.0959±0.005 mmφ, orifice length: 8.000±0.025 mm, load: 2.16 kgf, and temperature: 230°C (230±0.2°C).

[0169] <Measurement of Average Cell Diameter of Expanded Polyolefin Resin Beads> The average cell diameter of expanded beads was measured by the following methods (1) to (5): (1) Using a razor (high-stainless double-edged blade manufactured by Feather Corporation), the expanded beads were cut so that the cut surface passed through the center of the expanded beads; (2) The cut surface of the obtained expanded beads was observed using an optical microscope (VHX-5000 manufactured by Keyence Corporation) at a magnification of 50 times; (3) In the image obtained by observation, a straight line passing through the center or approximately the center of the cut surface of the expanded beads was drawn; (4) (4-1) the number n of cells present on the line was measured, and (4-2) the length of the line segment cut from the line at the intersection of the line with the surface of the expanded beads was measured and defined as the expanded bead diameter L; (5) The average cell diameter of expanded beads ("average cell diameter" in Tables 1 and 2) was calculated using the following formula: average cell diameter (μm) = L / n

[0170] <Measurement of DSC Ratio> The DSC ratio = {Qh / (Ql+Qh)} × 100(%) was measured using a differential scanning calorimeter (DSC6200, manufactured by Seiko Instruments Inc.) Specifically, the DSC ratio ("high-temperature DSC ratio" in Tables 1 and 2) was calculated from the DSC curve (see FIG. 6) obtained during the first temperature rise when 5 to 6 mg of expanded polyolefin resin beads were heated from 40°C to 220°C at a heating rate of 10°C / min.

[0171] <LP / DP of Polyolefin Resin Particles> The LP was determined by measuring the thickness direction length of a cross section of a polyolefin resin particle parallel to the thickness direction using an optical microscope (Keyence VHX-8000) at 40x magnification and measuring the distance between two points on a still image. Hereinafter, the same measuring function was used for measuring length and area. The DP was determined as the diameter of the smallest circle among circles that contain the entire cross-sectional shape of a polyolefin resin particle in a cross section perpendicular to the thickness direction, and in which at least two of the ends of the polyolefin resin particle are inscribed.

[0172] In the examples and comparative examples, a die having discharge holes with a star-shaped cross section was used to produce polyolefin resin particles with a star-shaped cross section (five-baseline shape) in a cross section perpendicular to the thickness direction.

[0173] The diameter of the smallest circle among circles that have the entire cross-sectional shape of the produced polyolefin resin particle in a cross section perpendicular to the thickness direction and inscribe at least two ends of the polyolefin resin particle in the circle was determined using an image obtained by capturing the particle at a magnification of 50 times using an optical microscope (Keyence VHX-8000).

[0174] Fig. 9 is a view from one direction of an example of polyolefin resin particles produced using an extrusion hole having a cross section perpendicular to the extrusion direction with the shape shown in Fig. 7. For the polyolefin resin particles shown in Fig. 9, a circle can be set in which five ends are inscribed in a circle, and therefore the DP shown in Fig. 9 is the DP. When it is not possible to obtain a circle in which all ends are inscribed in a circle, the DP was set as explained in (2-2. Shape of expanded polyolefin resin beads) using Fig. 5. In this way, the LP / DP of 10 polyolefin resin particles was determined, and the average value thereof was taken as the LP / DP of the polyolefin resin particles.

[0175] <A4 / A3 of Discharge Holes> (Examples 1 to 6 and Comparative Examples 1 and 2) The shape shown in FIG. 7 has five slits, and the nozzle area per hole is 3.1 mm ２ A die having five discharge holes with a slit width of 0.4 mm was used. A3 is the area of ​​the cross section of the discharge hole perpendicular to the extrusion direction, and the above 3.1 mm ２ A4 corresponds to this. A4 is the area of ​​the region surrounded by an envelope connecting each end of the discharge hole in the cross section. The envelope was set by connecting the ends with tangent lines. The A4 was determined by area measurement using an image obtained by photographing with an optical microscope (Keyence VHX-8000). The determined A4 was multiplied by the 3.1 mm ２ The A4 / A3 ratio for all five holes was the same, 2.6.

[0176] (Comparative Examples 3 and 4) The shape shown in FIG. 7 has five slits, and the nozzle area per hole is 3.1 mm ２ A die having five discharge holes with a slit width of 0.65 mm was used. A3 is the area of ​​the cross section of the discharge hole perpendicular to the extrusion direction, and the above 3.1 mm ２ A4 corresponds to this. A4 is the area of ​​the region surrounded by an envelope connecting each end of the discharge hole in the cross section. The envelope was set by connecting the ends with tangent lines. The A4 was determined by area measurement using an image obtained by photographing with an optical microscope (Keyence VHX-8000). The determined A4 was multiplied by the 3.1 mm ２ The A4 / A3 ratio for all five holes was the same, 1.9.

[0177] Comparative Example 5 In Comparative Example 5, the nozzle has a four-baseline (cross) shape and the nozzle area per hole is 5.2 mm ２ A die having six discharge holes with a slit width of 0.82 mm was used. A3 is the area of ​​the cross section of the discharge hole perpendicular to the extrusion direction, and the above 5.2 mm ２ A4 corresponds to this. A4 is the area of ​​the region surrounded by an envelope connecting each end of the discharge hole in the cross section. The envelope was set by connecting the ends with tangent lines. The A4 was determined by area measurement using an image obtained by photographing with an optical microscope (Keyence VHX-8000). The determined A4 was multiplied by the 5.2 mm ２ The A4 / A3 ratio for all five holes was the same, 1.7.

[0178] <L / D of Expanded Polyolefin Resin Beads> The L was determined by measuring the length of the longest part in the thickness direction of the expanded polyolefin resin beads in a cross section parallel to the thickness direction by measuring the dimension between two points using an optical microscope (Keyence VHX-8000). When it was possible to set a circle in which all the cross-sectional shapes in a cross section perpendicular to the thickness direction of the expanded polyolefin resin beads were inside and all the end portions were inscribed in the circle, the D of the circle was used as the D. On the other hand, when it was not possible to set a circle in which all the end portions were inscribed in the circle, the D was set as explained in (2-2. Shape of Expanded Polyolefin Resin Beads) using FIG. 5. The L / D of 10 expanded polyolefin resin beads was determined in this way, and their arithmetic mean value was used as the L / D of the expanded polyolefin resin beads.

[0179] <A2 / A1 of Expanded Polyolefin Resin Beads> A1 is the cross-sectional area of ​​a cross section perpendicular to the thickness direction of the expanded polyolefin resin bead, and A2 is the area of ​​the region enclosed by an envelope connecting each end of the expanded polyolefin resin bead in the cross section. As shown in Figure 1, the area A1 of a cross section (Figure 2) obtained by cutting the expanded polyolefin resin bead along line A-A' passing through the center of the expanded polyolefin resin bead in the thickness direction of the expanded polyolefin resin bead was determined by area measurement using an image obtained by capturing an image using an optical microscope (VHX-8000, manufactured by Keyence Corporation). In addition, an envelope was defined by connecting each end of the expanded polyolefin resin bead with a tangent (straight line) in the cross section, and the area A2 of the region enclosed by the envelope (Figure 3) was determined by area measurement using an image obtained by capturing an image using an optical microscope (VHX-8000, manufactured by Keyence Corporation), to calculate A2 / A1. In this way, A2 / A1 of 10 expanded polyolefin resin beads was determined, and the average value was taken as A2 / A1 of the expanded polyolefin resin beads.

[0180] <Bulk Density of Expanded Polyolefin Resin Beads> The bulk density of expanded polyolefin resin beads was measured by the following methods (1) to (3): (1) The expanded polyolefin resin beads were conditioned at room temperature and normal pressure for 4 hours or more, and the volume V1 (cm ３(2) The powder surface (top end) of the container was scraped off, and the weight W1 (g) of the expanded beads in the container was measured. (3) The bulk density of the expanded beads was calculated using the following formula: Bulk density of expanded beads (g / L) = Weight W1 (g) of expanded beads / {Volume of container V1 (cm ３ ) / 1000}.

[0181] <Amount of Cracking> A mold consisting of a fixed mold and a movable mold was mounted on an in-mold foam molding machine, and the amount of cracking was adjusted by driving the movable mold toward the fixed mold (i.e., closing the mold).

[0182] <Density of Polyolefin-Based Resin Foam Molded Article> First, a test piece measuring 50 mm long, 50 mm wide, and 25 mm thick was cut out from the center of the obtained polyolefin-based resin foam molded article (370 mm long, 320 mm wide, and 50 mm thick). However, 12.5 mm long, including the surface layer in the thickness direction of the in-mold foam molded article, was cut off to obtain a 25 mm thick test piece.

[0183] The weight W (g) of the test piece was measured, and the length, width, and thickness of the test piece were measured with a vernier caliper to determine the volume V (cm ３ ) was calculated, and the density of the polyolefin resin foam molded article ("Molded article density" in Tables 1 and 2) was calculated: Density of foam molded article (g / L) = (W / V) / 1000.

[0184] <Porosity of Polyolefin-Based Resin Foam Molded Article> A Φ29 x 40 mm test piece was cut out from a polyolefin-based resin foam molded article (length 370 mm x width 320 mm x thickness 50 mm) prepared for porosity measurement to measure normal incident sound absorption coefficient. For the test piece, Vc was measured according to the method described in Procedure C of ASTM D2856-87, and the porosity (%) was calculated according to the following formula: Porosity (%) = {(Va - Vc) x 100} / Va.

[0185] Here, the volume Vc (cm ３ ) is the volume of the test piece (Φ29 × 40 mm) obtained by measurement using an air comparison type hydrometer Model 1000 manufactured by Tokyo Science Co., Ltd. Also, the volume Va (cm ３) is the apparent volume calculated by measuring the diameter D (cm) and height H (cm) of the test piece (Φ29 × 40 mm) with a vernier caliper after measuring Vc with the air comparison type hydrometer, using the following formula: Volume Va (cm ３ ) = πD ２ H / 4.

[0186] <Sound Absorption Performance of Polyolefin-Based Resin Foam Molded Articles> Normal incidence sound absorption coefficients were measured at 500 Hz to 6,400 Hz using 40.0 mm thick samples in accordance with JIS A1405. A 29 mm diameter, 50.0 mm thick sample was cut from a polyolefin-based resin foam molded article (370 mm long x 320 mm wide x 50 mm thick). Both skin surfaces of this sample were cut to a thickness of 40.0 mm to prepare a normal incidence sound absorption coefficient measurement sample. The normal incidence sound absorption coefficient was measured in a state where the sample was in close contact with a rigid wall that reflects sound waves, i.e., in a state where there was no air behind it. The normal incidence sound absorption coefficient was measured using an SR-4100 normal incidence sound absorption coefficient measuring device manufactured by Ono Sokki Co., Ltd. From the obtained frequency-normal incidence sound absorption coefficient curve, the normal incidence sound absorption coefficient (maximum sound absorption coefficient α) at ​​the frequency f at which the normal incidence sound absorption coefficient was maximized was read.

[0187] The sound absorption performance was evaluated based on the maximum sound absorption peak frequency f and the maximum sound absorption coefficient α according to the following criteria. When the sound absorption performance of a molded article was rated as "excellent," "good," or "fair," it was determined that the sound absorption performance of the molded article was good, and when the sound absorption performance of the molded article was "fail," it was determined that the sound absorption performance of the molded article was bad: Excellent: α≧0.7 and f<1000 Hz Good: α≧0.7 and 1000≦f<1300 Hz Fair: α≧0.7 and 1300 Hz≦f Fail: α<0.7.

[0188] <Compressive Strength of Polyolefin Resin Foam Molded Article> The compressive strength of the foam molded article was determined at 50% strain using a tension and compression tester (TG-50kN manufactured by Minebea Co., Ltd.) in accordance with JIS K 6767 for the test piece on which the molded article density had been measured. The compressive strength at 50% strain was then divided by the molded article density to determine the specific strength. Based on the specific strength obtained, the compressive strength was evaluated according to the following criteria. When the compressive strength of the molded article was evaluated as "good" or "fair", the compressive strength of the molded article was deemed to be good, and when the compressive strength of the molded article was evaluated as "poor", the compressive strength of the molded article was deemed to be poor: Good: Specific strength was 8.0 kPa / (kg / m ３ ) Over 7.5kPa / (kg / m ３ ) or more than 8.0 kPa / (kg / m ３ ) or less Unacceptable: Specific strength is 7.5 kPa / (kg / m ３ ) Less than Example 1 (Preparation of Polyolefin-Based Resin Particles) 100 parts by weight of polyolefin-based resin, 0.2 parts by weight of glycerin, and 0.1 parts by weight of talc were weighed out and dry-blended using a small tumbler manufactured by O-N Machine Co., Ltd. to obtain a mixture. The mixture was then melt-kneaded at a resin temperature of 200°C using a twin-screw extruder (TEM26-SX manufactured by Toshiba Machine Co., Ltd.). Next, a strand was extruded at 3 kg / Hr per hole from a die having six discharge holes with a shape shown in FIG. 7, with five slits attached to the tip of the twin-screw extruder. The area and slit width of the discharge holes were as described above.

[0189] The extruded product (strand) was water-cooled in a 2-m-long water tank. The distance from the surface of the discharge hole to the water surface facing the surface was 20 mm, and the water-cooled strand in a water tank with a water temperature of 30°C was taken up and chopped using a pelletizer (manufactured by Ishinaka Iron Works) (chopping process). The distance between all six discharge holes was 20 mm. The strand was taken up so that the take-up speed / resin linear speed = elongation ratio was 0.9, and cut using a pelletizer to produce polyolefin resin particles with an LP / DP of 0.5. This procedure yielded polyolefin resin particles (weight per particle: 2.5 mg) having the shape shown in Figure 1 (star-shaped, five-baseline shape).

[0190] (Preparation of expanded polyolefin resin particles) A ​​10 L pressure vessel was charged with 100 parts by weight of the obtained polyolefin resin particles, 475 parts by weight of water as an aqueous dispersion medium, 0.50 parts by weight of kaolin as a dispersant, 0.18 parts by weight of sodium dodecylbenzenesulfonate as a dispersing aid, 0.10 parts by weight of citric acid as a pH adjuster, and carbon dioxide as a foaming agent, in amounts according to the foaming pressure, to prepare a dispersion containing a foaming agent.

[0191] The obtained dispersion was heated to a foaming temperature (temperature inside the pressure vessel) of 153.0° C. while being stirred. After the temperature and pressure inside the pressure vessel reached the predetermined foaming temperature (153.0° C.) and foaming pressure (2.8 MPa (gauge pressure)) (heating step and pressurizing step), the temperature and pressure inside the pressure vessel were maintained at the predetermined foaming temperature and foaming pressure for an additional 30 minutes (maintaining step).

[0192] Next, carbon dioxide was introduced, and the pressure inside the pressure vessel was maintained at the expansion pressure of 2.4 MPa (gauge pressure). The valve at the bottom of the pressure vessel was opened, and the dispersion inside the pressure vessel was released to atmospheric pressure through a 4.0 mm diameter orifice to obtain expanded polyolefin resin beads (release step). The expanded polyolefin resin beads were dried at 75°C for 15 hours. The DSC curve of the expanded polyolefin resin beads measured using the DSC method showed two peaks derived from the polyolefin resin. The bulk density of the expanded polyolefin resin beads was evaluated. Furthermore, the L and D of the expanded polyolefin resin beads were 2.3 mm and 7.6 mm, respectively. The L / D ratio of the expanded polyolefin resin beads was evaluated. The results are shown in Tables 1 and 2.

[0193] (Preparation of polyolefin resin foam molded article) The obtained polyolefin resin foam beads were filled into a mold for a box-shaped molded article (length 370 mm × width 320 mm × thickness 50 mm) using a polyolefin in-mold foam molding machine (filling step). The polyolefin resin foam beads were heat-fused with steam at 0.34 MPa (gauge pressure), then water-cooled and demolded to obtain an in-mold foam molded article. The obtained in-mold foam molded article was left at room temperature for 1 hour, then cured and dried in a thermostatic chamber at 75 ° C for 15 hours (drying step), and again left at room temperature for 4 hours to obtain a plank foam molded article.

[0194] The maximum sound absorption peak frequency f, maximum sound absorption coefficient α, and specific strength of the obtained foamed molded article were measured. The maximum sound absorption peak frequency f was 1140 Hz, and the maximum sound absorption coefficient α was 0.95, indicating good sound absorption performance. The specific strength was 7.8 kPa / (kg / m ３ The compressive strength was good. The results are shown in Tables 1 and 2.

[0195] Examples 2 to 6 and Comparative Examples 1 to 5 Expanded beads and foamed molded articles were obtained in the same manner as in Example 1, except that the discharge holes, the production conditions for polyolefin resin beads, and the expansion conditions for expanded polyolefin resin beads were changed as shown in Tables 1 and 2. The physical properties of the resulting expanded beads and foamed molded articles were measured and evaluated. The results are shown in Tables 1 and 2.

[0196] The expanded polyolefin resin beads obtained in Examples 1 to 6 were expanded beads produced by the present production method and correspond to the present expanded beads. As shown in Table 1, the expanded polyolefin resin beads have good sound absorption properties and compressive strength.

[0197] On the other hand, the expanded polyolefin resin beads of Comparative Examples 1 and 2 were obtained by a method in which the L / D ratio did not satisfy the requirements of the present production method, and the sound absorption performance and compressive strength of the expanded polyolefin resin beads did not satisfy the requirements of the present invention.

[0198] The expanded polyolefin resin beads of Comparative Examples 3 and 4 were obtained by a method in which the L / D and A2 / A1 ratios did not satisfy the requirements of the present production method, and the sound absorption performance of the expanded polyolefin resin beads did not satisfy the requirements of the present expansion beads.

[0199] The expanded polyolefin resin beads of Comparative Example 5 were obtained by a method in which the A2 / A1 ratio did not satisfy the requirements of the present production method, and the sound absorption performance of the particles did not satisfy the requirements of the expanded beads of the present invention.

[0200] The expanded polyolefin resin beads obtained in the comparative examples did not satisfy any of the requirements for the expanded polyolefin resin beads, and therefore, either the sound absorption performance or the compressive strength was "unacceptable." In other words, the expanded polyolefin resin beads obtained in the comparative examples could not provide a molded article excellent in both sound absorption performance and compressive strength.

[0201] As described above, the results of the Examples and Comparative Examples show that by satisfying the requirements of the present expanded beads, expanded polyolefin resin beads having excellent sound absorption performance and compressive strength can be obtained. Furthermore, it is clear that the above-mentioned expanded polyolefin resin beads can be produced by a production method that satisfies the requirements of the present production method.

[0202] One embodiment of the present invention can provide expanded polyolefin resin particles having excellent sound absorption properties and compressive strength, and therefore, can be suitably used in a variety of applications, such as cushioning packaging materials, logistics materials, heat insulation materials, civil engineering and construction materials, and automotive components.

Claims

1. Expanded polyolefin resin beads, wherein A2 / A1≧1.20, where A1 is the cross-sectional area of ​​a cross section perpendicular to the thickness direction of the expanded polyolefin resin beads and A2 is the area of ​​a region enclosed by an envelope connecting each end of the expanded polyolefin resin beads in the cross section, and L / D of the expanded polyolefin resin beads is 0.10 or more and less than 0.70, where D is the diameter of the smallest circle among circles that contain all of the cross-sectional shapes in the cross section and inscribe at least two of the end sections in the circle, and L is the length of the longest part in the thickness direction of the expanded polyolefin resin beads in the cross section parallel to the thickness direction.

2. The expanded polyolefin resin particles according to claim 1, which have two melting peaks in a DSC curve obtained by differential scanning calorimetry, and have a DSC ratio of 20.0% to 45.0%, where Ql (J / g) is the heat of fusion of the lower-temperature peak and Qh (J / g) is the heat of fusion of the higher-temperature peak: DSC ratio = {Qh / (Ql+Qh)} x 100.

3. The expanded polyolefin resin particles according to claim 1, having a bulk density of 10.0 g / L to 300.0 g / L.

4. The expanded polyolefin resin beads according to claim 1, wherein the cross section perpendicular to the thickness direction of the expanded polyolefin resin beads has 4 to 8 ends.

5. The expanded polyolefin resin particles according to claim 1, wherein the average cell diameter is 100 μm to 350 μm.

6. The expanded polyolefin resin particles according to claim 1, wherein the base resin of the expanded polyolefin resin particles comprises a polypropylene resin containing three types of structural units including a propylene unit.

7. The expanded polyolefin resin beads according to claim 1, wherein D of the expanded polyolefin resin beads is 2.0 mm to 12.0 mm.

8. The expanded polyolefin resin beads according to claim 1, wherein the L of the expanded polyolefin resin beads is 0.5 mm to 7.0 mm.

9. The expanded polyolefin resin particles according to claim 1, wherein the expanded polyolefin resin particles are formed by expanding polyolefin resin particles, and the polyolefin resin particles contain 25 parts by weight or less of a resin particle additive per 100 parts by weight of the polyolefin resin contained in the polyolefin resin particles.

10. A polyolefin resin foam molded article obtained by molding the polyolefin resin foam beads according to any one of claims 1 to 9.

11. The polyolefin resin foam molded article according to claim 10, wherein the amount of cracking during molding is 10% to 50%.

12. The polyolefin resin foam molded article according to claim 10, wherein the amount of cracking during molding is 20% to 50%.

13. A method for producing a polyolefin resin foam molded article, comprising a molding step of molding the polyolefin resin foam beads described in any one of claims 1 to 9, wherein the amount of cracking of the mold during the molding step is 10% to 50%.

14. A method for producing expanded polyolefin resin beads according to any one of claims 1 to 9, comprising the steps of: an extrusion step of extruding a polyolefin resin composition containing a polyolefin resin through one or more discharge holes provided in a die of an extruder; a cooling step of solidifying the extruded polyolefin resin composition by cooling it using a cooling device equipped with a cooling medium; a take-up step of taking up the solidified polyolefin resin composition into a gas phase using a take-up machine; a shredding step of shredding the taken-up polyolefin resin composition to obtain polyolefin resin particles; a dispersion preparation step of mixing the polyolefin resin particles with a dispersion medium and a blowing agent in a container to prepare a dispersion; and a release step of releasing the dispersion into a pressure region lower than the internal pressure of the container to obtain expanded polyolefin resin beads.

15. A method for producing expanded polyolefin resin beads as described in claim 14, wherein the discharge hole satisfies the requirement of A4 / A3≧1.2, where A3 is the area of ​​a cross section of the discharge hole perpendicular to the extrusion direction, and A4 is the area of ​​a region enclosed by an envelope connecting each end of the discharge hole in the cross section.

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