JP2023014887A - Foamed bead and method for producing foamed bead - Google Patents

Abstract

To provide a foamed bead that can suppress deformation during foaming and molding, and can be molded into a resin foamed molding having excellent sound absorbing property.SOLUTION: Provided is a foamed bead that has at least one through hole and/or at least one concave, and in which the maximum wall thickness is 100 μm or more and less than 1000 μm, the sum of the through hole opening ratio and the concave opening ratio is 10% or more, and the average gap ratio is 10% or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to expanded beads and methods for producing expanded beads.

Resin foam materials are used as materials for replacing conventional solid resin materials and metal materials, as members of automobiles and electronic devices, and as structural materials for containers. These resin foam materials are characterized by low density, high heat insulation, and cushioning properties, and these properties are mainly used effectively. On the other hand, properties expected of resin foam materials include sound absorbing properties and sound insulating properties, but their range of application has been limited in the past.

The reason for this is that sound absorption and sound insulation are not characteristics that are expressed in foams in general, but rather depend on the cell structure. The body has excellent rigidity and mechanical strength, but its sound absorption and sound insulation performance is very low. Each property tends to contradict each other, such as being inferior in mechanical strength, and it is difficult to achieve both of them.

Examples of open-cell resin foams include urethane resins and melamine resins, which are mainly used as sponges that absorb fluids and cushioning materials that utilize flexibility and shock absorption. Because of their excellent sound absorption properties, they are widely used as sound absorbing materials that are lighter than inorganic materials. used as a constituent layer.

The main methods of manufacturing foams include the bead foam molding method and the extrusion foam molding method. In the bead foam molding method, granular foam beads obtained by pre-expanding resin particles are molded into a desired shape. After being filled in a mold, the foamed beads are thermally expanded and fused to form a molded product. It is possible to manufacture body products with high productivity, that there is no material loss that occurs in cutting, and that molding dies can be manufactured at low cost. This method is particularly preferable as a molding method.
However, in the foam molding process of the bead foam molding method, the foam cells are closed cells separated by a resin film, and the mechanism of mutual fusion between the foam particles due to the expansion of the bubbles is used. Since the cell structure of is basically a closed cell structure, it is generally inferior in sound absorption performance.

On the other hand, as exemplified below, a foam having a continuous pore structure, that is, a continuous pore structure in the foam by the bead foam molding method, and a method for producing the same have been proposed, and it is also known that it can be used as a sound absorbing foam material. ing.

In the method described in Patent Document 1, a molded body having excellent sound absorption in a wide frequency range is obtained by in-mold expansion of hollow cylindrical resin expanded particles having a specific range of porosity and bulk density of the molded body. It states that it is possible.

In the method described in Patent Document 2, the relationship between the density of the raw material resin before foaming, the bulk density of the expanded resin particles, and the true density satisfies specific conditions, and the C-shaped cross-sectional partial cylindrical shape (substantially cylindrical shape with a C-shaped cross section) is obtained. It is described that by foaming the expanded resin particles in the mold, it is possible to obtain a resin expanded molded article which is excellent in sound absorbing performance and also excellent as a structural material.

JP-A-10-329220 JP 2018-131620 A

However, in the method described in Patent Document 1, the walls of the expanded resin beads are thick, and a sufficient structure of interconnected pores cannot be ensured when formed into a molded article, so further improvement is desired.
Further, in the method described in Patent Document 2, if the gap portion of the C-shaped cross section is increased in order to increase the open area ratio of the foamed resin beads in order to improve the sound absorption performance, the gap portion opens further during foaming or molding. However, there is a problem that the cross-sectional shape changes from C-type to I-type.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a foamed bead that is suppressed in deformation during foaming and molding, and that can be used to form a foamed resin article having excellent sound absorption performance.

As a result of intensive studies to solve the problem, the present inventors have found that they have through holes and/or recesses, and the maximum wall thickness, the sum of the through hole opening ratio and the recess opening ratio, and the average gap ratio are within specific ranges. The inventors have found that the above problems can be solved by using expanded beads, and have completed the present invention.

That is, the present invention is as follows.
[1]
A foamed bead having at least one through hole and/or at least one recess,
The maximum wall thickness Tmax is 100 μm or more and less than 1000 μm,
For each of the at least one through-hole, the ratio of the through-hole area to the area surrounded by the outer circumference of the foamed bead (peripheral area) in the orthogonal projection image in which the area of the through-hole (through-hole area) is maximized The opening ratio represented by (through hole area/peripheral area) is obtained, and the total value is taken as the through hole opening ratio,
For each of the at least one concave portion, in the orthogonal projection image including the deepest portion of the concave portion, the area (envelope area) of the portion surrounded by the line (envelope line) connecting the vertices of the convex portions of the foam beads, Aperture ratio represented by a ratio (area S _A /enveloping area) of the area (area S _A ) of the region A surrounded by the line segment B circumscribing the recess at least at two points and the outer surface of the foam bead. are calculated and the total value is taken as the opening ratio of the concave portion,
The sum of the aperture ratio of the through holes and the aperture ratio of the concave portions is 10% or more,
For each of the at least one concave portion, the length of the line segment B (length L A foamed bead characterized in that the gap ratio represented by the ratio of _B ) (length L _B /envelope perimeter) is calculated and the average gap ratio is 10% or less.
[2]
The expanded bead according to [1], wherein the ratio of the maximum outer diameter Dmax to the maximum wall thickness Tmax (Dmax/Tmax) is 2.2 or more and 4.2 or less.
[3]
expanded particles having only the through holes,
The maximum outer diameter Dmax is 4 mm or less,
The expanded bead according to [1] or [2], having a maximum pore diameter dmax of 1.5 mm or less.
[4]
Having at least one node portion whose wall thickness is 80% or less of the maximum wall thickness Tmax,
The expanded bead according to any one of [1] to [3], wherein the ratio of minimum wall thickness Tmin to maximum wall thickness Tmax (Tmin/Tmax) is 0.4 or more and less than 1.0.
[5]
A resin pellet having at least one through-hole and/or at least one concave portion is produced by discharging a resin vertically from a ring-shaped nozzle and then cooled with a coolant, and the resin pellet is foamed. A method for producing expanded beads, comprising:

ADVANTAGE OF THE INVENTION According to this invention, the deformation|transformation at the time of foaming and molding is suppressed, and it can provide the foaming bead which can shape|mold the resin foam molding excellent in sound absorption performance.

It is a figure which shows an example of the cross section of the expanded bead of this embodiment. 1 is a perspective view showing an example of a foamed bead having recesses according to the present embodiment; FIG. The shape of the outlet of the profile extrusion die used in Examples and Comparative Examples ((a1) to (e1)), the cross-sectional shape of the obtained foamed beads ((a2) to (e2)), and the shape of the obtained foamed beads It is a figure which shows the line segment B ((b3), (d3), (e3)) in the orthogonal projection image containing the deepest part of a recessed part.

A mode for carrying out the present invention (hereinafter referred to as "this embodiment") will be specifically described below. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

[Foam beads]
The expanded bead of this embodiment has at least one through hole and/or at least one recess.
In this specification, having a through hole and/or a recess means that there is a direction in which an orthogonal projection image of a concave figure is obtained. In this specification, a concave figure means that at least a part (preferably, the whole line segment) of a line segment connecting two points on the outer surface of the orthogonal projection image figure to be a concave figure defines the external region of the foam bead. It means that it is possible to choose two points that will be a line segment that passes through. However, among the concave shapes confirmed in the orthogonal projection image that becomes a concave figure, the maximum value of the distance to the intersection of the perpendicular line of the straight line that circumscribes the concave shape at least at two points or more and the outer surface of the concave shape is foamed. It is assumed that an orthographic image larger than the maximum bead wall thickness Tmax can be obtained.
The through-holes and recesses have structures different from those of foamed cells formed during foaming.
In this embodiment, whether or not the expanded beads have through-holes and/or recesses can be confirmed by observing and judging transmission images of the expanded beads with an optical microscope while changing the observation direction of the particles.

There may be one or more through-holes and recesses, respectively, or only one or more through-holes connecting the surfaces of the foam beads, or one or more recesses that do not penetrate the foam beads. There may be only one, or one or more through-holes and one or more recesses may be mixed. Here, the through hole may be a cavity connecting two holes formed on the outer surface of the foam bead, and in the orthogonal projection image of the cavity, the cavity is surrounded by the foam bead. (Orthographically projected images in which the cavities form isolated cavities within the foam beads) may be obtained.

In the foamed beads of the present embodiment, the sum of the aperture ratio of through holes and the aperture ratio of concave portions is 10% or more, preferably 20% or more, and more preferably 25% or more. The sum of the aperture ratio of through holes and the aperture ratio of concave portions is preferably 65% or less, more preferably 55% or less, and even more preferably 45% or less. When the sum of the aperture ratio of the through holes and the aperture ratio of the concave portions of the foam beads is within the above range, the communicating voids (continuous voids, communicating voids) are formed satisfactorily, and a resin foam molded article having excellent sound absorption performance can be molded. be able to.
In this specification, the through-hole aperture ratio refers to the area surrounded by the outer periphery of the foamed bead ( The opening ratio represented by the ratio of the through-hole area to the outer peripheral area (through-hole area/peripheral area) is calculated and summed, and is the average value of 20 or more expanded beads. The through-hole area and the outer peripheral area are measured using a general microscope (for example, a digital microscope VHX-2000 manufactured by Keyence Corporation), and the foam beads placed on a transparent petri dish are measured from the lens in the opposite direction across the foam beads. In the orthogonal projection image obtained by applying light from and observing, it can be measured with image analysis software (for example, mounted on Keyence Digital Microscope VHX-2000), and each of 20 or more foam beads Average value. Specifically, it can be measured by the method described in Examples below.
In addition, the recess opening ratio is the area (envelope area), the ratio of the area (area S _A ) of the area A surrounded by the line segment B circumscribing the recess at least at two points and the outer surface of the foam bead (area S _A /enveloping area) The open area ratio is calculated and totaled, and is the average value of 20 or more expanded beads. Area S _A and the enveloping area are measured using a general microscope (for example, Keyence Digital Microscope VHX-2000), the foam beads placed on a transparent petri dish, from the lens in the opposite direction across the foam beads. In the orthogonal projection image obtained by applying light from and observing, it can be measured with image analysis software (for example, mounted on a digital microscope VHX-2000 manufactured by Keyence Corporation). Specifically, the implementation described later It can be measured by the method described in the examples.
Here, the deepest part of the recess may be the part where the distance to the intersection of the straight line perpendicular to the recess at least at two points or more and the outer surface of the recess is the longest.
An envelope curve means a line connecting the vertexes of the convex portions of the foamed beads with the shortest distance in the orthogonal projection image so that there are no dents. The enveloping area is the area of the portion surrounded by the enveloping line. In the orthogonal projection image, the area of the shape obtained when the vertices of the convex portions of the foam beads are connected at the shortest distance so that there are no dents. means.

The expanded beads of the present embodiment have an average gap rate of 10% or less, preferably 8% or less, and more preferably 5% or less. Due to the average gap ratio being within the above range, foamed beads that have a thin wall thickness and a high degree of opening (the sum of the opening ratio of through-holes and concave portions) have suppressed deformation during foaming and molding. can be realized.
In this specification, the average gap ratio is defined as the ratio of the circumference of the portion surrounded by the envelope (envelope circumference) in the orthographic projection image including the deepest part of the concave portion of each concave portion of the foamed bead to the concave portion. The gap rate represented by the ratio of the length (length L _B ) of the line segment B circumscribing at least two points (length L _B /envelope perimeter) is calculated and averaged. It is the average value of foamed beads. The length L _B of the line segment B and the envelope perimeter length are measured using a general microscope (for example, a digital microscope VHX-2000 manufactured by Keyence Corporation). The orthographic projection image obtained by observing the beads sandwiched by light from the opposite direction can be measured with image analysis software (for example, mounted on a digital microscope VHX-2000 manufactured by Keyence Corporation). can be measured by the method described in Examples below.
The envelope perimeter is the length of the envelope, and means the perimeter of the shape obtained by connecting the vertexes of the convex portions of the foamed beads at the shortest distance in the orthogonal projection image so as not to have any dents.

In the foamed beads of the present embodiment, the length LB of the line segment _B is preferably 1.5 mm or less, more preferably 1.0 mm or less, and still more preferably 1.0 mm or less in an orthogonal projection image including the deepest part of each recess. is 0.7 mm or less. When the length LB of the line segment _B is within the above range, deformation during foaming and molding is suppressed even if the wall thickness is thin and the degree of opening is high (the sum of the opening ratio of the through holes and the opening ratio of the concave portions). foamed beads can be realized.

The foamed beads of the present embodiment have a maximum wall thickness Tmax of 100 μm or more and less than 1000 μm, preferably 250 to 950 μm, more preferably 350 to 900 μm. When the maximum wall thickness Tmax is within the above range, good communication gaps are formed, and a foamed resin article having excellent sound absorption performance can be obtained.
The foamed beads of the present embodiment preferably have a minimum wall thickness Tmin of 40 to 1000 μm, more preferably 100 to 950 μm, still more preferably 140 to 900 μm. When the minimum wall thickness Tmin is within the above range, a resin foam molded article having high mechanical strength can be produced, and the foaming agent and expansion agent are prevented from scattering outside the foamed beads during foaming and molding. Foaming and molding can be performed efficiently.
Further, in the foamed beads of the present embodiment, the ratio of the minimum wall thickness Tmin to the maximum wall thickness Tmax (Tmin/Tmax) is preferably 0.4 or more and less than 1.0, more preferably 0.45 to 0.45. 98, more preferably 0.5 to 0.95. When Tmin/Tmax is 0.4 or more, breakage of the wall portion of the foamed beads tends to be suppressed during foaming and molding. Further, when Tmin/Tmax is less than 1.0, clogging of the through-holes and recesses during foaming and molding is suppressed, and even when foamed beads having a small pore diameter and outer diameter are used, the communicating voids in the molded product are obtained. The structure tends to be easily retained, and the sound absorption performance tends to be excellent.
In addition, the maximum wall thickness Tmax and the minimum wall thickness Tmin are obtained by image analysis software (for example, Keyence Digital Microscope VHX -2000) are the largest and smallest values obtained, respectively, and are taken as the average of 20 or more expanded beads.

The foamed beads of the present embodiment preferably have a maximum outer diameter Dmax of 4 mm or less, more preferably 3.5 mm or less, and even more preferably 3.0 mm or less. When the maximum outer diameter Dmax is within the above range, the molded article has excellent surface precision and an excellent balance between ease of foaming and sound absorption performance.
The foamed beads of the present embodiment preferably have a minimum outer diameter Dmin of 1 mm or more, more preferably 1.5 mm or more, and still more preferably 1.75 mm or more. When the minimum outer diameter Dmin is within the above range, even if foamed beads having a small pore size are used, the structure of communicating voids is likely to be maintained when formed into a molded product, resulting in excellent sound absorbing performance.
In addition, the maximum outer diameter Dmax and the minimum outer diameter Dmin are obtained by image analysis software (for example, Keyence Digital Microscope VHX -2000) is used to measure the outer diameter of the foam beads, and the average value of 20 or more foam beads is the largest and smallest measured value obtained.

The foamed beads of the present embodiment preferably have a maximum pore diameter dmax of 1.5 mm or less, more preferably 1.25 mm or less, and even more preferably 1.0 mm or less. When the maximum pore diameter dmax is within the above range, complex communicating voids are favorably formed in a molded article, and a resin foam molded article having excellent sound absorbing performance can be obtained.
The foamed beads of the present embodiment preferably have a minimum pore diameter dmin of 0.35 mm or more, more preferably 0.45 mm or more, and still more preferably 0.6 mm or more. When the minimum pore diameter dmin is within the above range, clogging of the through holes during foaming and molding tends to be suppressed.
The maximum pore diameter dmax and the minimum pore diameter dmin are obtained by using image analysis software (for example, mounted on a digital microscope VHX-2000 manufactured by Keyence Corporation) in the orthogonal projection image with the maximum through-hole area. When measuring the diameter, it is the largest value and the smallest value among the obtained measured values, and is taken as the average value of 20 or more expanded beads.

In the expanded beads of the present embodiment, the ratio of the maximum outer diameter Dmax to the maximum wall thickness Tmax (Dmax/Tmax) is preferably 2.2 or more and 4.2 or less, more preferably 2.4 to 3.7. It is more preferably 2.6 to 3.2. When Dmax/Tmax is 2.2 or more, clogging of through holes and recesses during foaming and molding tends to be suppressed. Further, when Dmax/Tmax is 4.2 or less, breakage of the wall portion of the foamed beads tends to be suppressed during foaming and molding.

The expanded bead of the present embodiment may have a knot portion (constricted portion) having a wall thickness of 80% or less of the maximum wall thickness Tmax. The number of knot portions is preferably 1-8, more preferably 1-6, still more preferably 2-5. By having at least one knot portion, expansion of the wall portion during foaming and molding escapes to the knot portion, which tends to suppress clogging of the through holes and recesses, which is preferable.
The knot portion is formed by, for example, ejecting resin using a nozzle having a gap portion for air inflow, which will be described later, and fusing the ejected resin so as to close the gap when producing resin pellets. be.

A particularly excellent shape as the shape having the recesses includes a structure in which groove-shaped recesses are provided in the foam beads, and the foam beads in which the groove-shaped recesses are adjacent when the foam beads are heat-sealed during the production of the resin foam molded product. are joined in a filled state in which the foam beads are partially engaged to form a resin foam molding having a large joining area between the foam beads and high strength, and at the same time, the adjacent foam beads are joined in a form where the grooves are connected. Voids extending between the expanded beads, ie, interconnecting voids, are formed in some cases.

As the groove-shaped concave portion, for example, a shape (FIG. 2) obtained by overlapping a cross section (FIG. 1) of a shape (C type) obtained by cutting a part of a hollow substantially circle, a hollow substantially polygonal shape (substantially triangular, substantially quadrangular, etc.) etc.), and a shape obtained by stacking a cross section (FIG. 1) obtained by cutting a part thereof. Here, the hollow in the hollow substantially circle and the hollow substantially polygon may be substantially circular or substantially polygonal, but preferably has the same shape as the shape surrounding the hollow. . Moreover, it is preferable that the center of the hollow shape overlaps with the center of the shape surrounding the hollow (for example, a concentric circle).

Examples of the recess include, for example, a saddle-shaped shape formed by bending a disk shape having a certain thickness, a shape formed by bending or bending a disk in the out-of-plane direction, and a single or multiple recesses on the outer surface of a cylindrical shape. structure provided with a concave portion. Among the particle shapes, an example of a particle shape that is particularly preferable in terms of ease of production, excellent productivity, and easy control of the shape is a cylindrical shape having a common axis with an outer diameter smaller than the outer diameter. Examples include a shape (FIG. 2) obtained by cutting out and cutting out a portion within a certain angle when viewed from the axial direction of a cylinder obtained by cutting a column of height. Hereinafter, this shape will be referred to as a C-shaped cross-sectional partial cylindrical shape, and even if it is substantially the same shape that is slightly deformed based on this shape, it is possible to form the same voids in the resin foam molding. Therefore, if the above conditions are satisfied, it can be used within the scope of the present invention. FIG. 2 shows a preferred example of a C-shaped cross-sectional partial cylindrical shape.

It is preferable that the recesses have the same shape when the cross section is continuously formed in one specific direction of the foamed beads. For example, as shown in FIG. 2, the shape of the concave portion in a cross section in one direction (vertical direction in FIG. 2, extrusion direction) of the foamed bead and the shape of the concave portion in a different cross section shifted in the one direction are the same. is preferred.
The foamed beads may have the same shape or different shapes when the cross section is continuously formed in one specific direction, and preferably have the same shape.

In the foamed beads of the present embodiment, the ratio ρ ₀ /ρ ₁ between the density ρ ₀ of the resin contained in the foamed beads and the true density ρ ₁ of the foamed beads is preferably 2.0 to 20, more preferably 2. .2 to 18, more preferably 2.5 to 15. When ρ ₀ /ρ ₁ is less than 2.0, the sound absorbing performance is not sufficiently developed, and when it exceeds 20, the mechanical strength is lowered, which is not preferable.

In the expanded beads of the present embodiment, the ratio ρ ₁ /ρ ₂ between the true density ρ ₁ of the expanded beads and the bulk density ρ ₂ of the expanded beads is preferably 1.5 to 4.0, more preferably 1.5. 8 to 3.5, more preferably 2.0 to 3.0. If ρ ₁ /ρ ₂ is less than 1.5, the sound absorbing performance is not sufficient, and if it exceeds 4.0, the mechanical strength is lowered, which is not preferable.

In this specification, the bulk density ρ ₂ is the value M/V ₂ obtained by dividing the foamed beads of a predetermined weight M by the bulk volume V ₂ of the foamed beads at that weight M, and the true density ρ ₁ is It is the value M _/ V1 obtained by dividing the foam bead by the true volume _V1 of the foam bead at its weight M. _The bulk volume V2 refers to the value obtained by filling a graduated cylinder with expanded beads of the predetermined weight M, vibrating the graduated cylinder, and reading the scale when the volume reaches a constant weight. _The true volume V1 is the volume of the liquid increased when the foamed beads of the predetermined weight M are submerged in a measuring cylinder containing a liquid that does not dissolve the foamed beads.
The density ρ ₀ of the resin is the density of the raw material resin before foaming, and is the density measured by the submersion method using a weighing scale.
In this specification, ρ ₀ , ρ ₁ , and ρ ₂ all mean values obtained by measurement under an environment of 20° C. and 0.10 MPa.

[Method for producing expanded beads]
In the method for producing expanded beads of the present embodiment, a resin pellet having at least one through-hole and/or at least one recess is formed by discharging a resin vertically from a ring-shaped nozzle and then cooling it with a coolant. and foaming the resin pellets.
Preferably, the resin is melted in an extruder, extruded vertically through a ring-shaped nozzle (a die having a ring-shaped cross section), cooled by water cooling or the like, and then cut into a predetermined length by a pelletizer. , a method of producing a resin pellet having at least one through hole and/or at least one recess, impregnating the resin pellet with a foaming agent, and heating to foam at a predetermined expansion ratio.

The screw diameter of the extruder is preferably 20 mm or more and 200 mm or less. It is more preferably 30 mm or more and 125 mm or less, and most preferably 40 mm or more and less than 100 mm.
The L/D of the extruder is preferably 20 or more and less than 60, more preferably 30 or more and less than 60, and most preferably 40 or more and less than 60. L/D here is a value obtained by dividing the length [L] of the screw of the extruder by the diameter [D] of the screw.

The molten resin temperature is affected by factors such as the set temperature of the cylinder, the number of screw revolutions, and the amount of resin supplied. is preferably +250° C. or less with respect to its glass transition point. It is more preferably +180° C. or lower, and still more preferably +130° C. or lower.
By adjusting the temperature of the molten resin to this temperature range, the generation of carbides and precipitates called die buildup is suppressed, and deformation of the resin after ejection is suppressed. Appropriate tension is applied to the resin, and good-shaped resin pellets can be produced.
The molten resin temperature at this time is the temperature of the molten resin extruded from the die of the extruder actually measured by a thermometer such as a contact thermocouple.
The melting point of the crystalline resin refers to a value measured by differential scanning calorimetry (DSC) according to JIS K7121. The endothermic peak appearing in the measurement is taken as the resin melting peak, and the temperature at the endothermic peak appearing on the highest temperature side is taken as the melting point.
As a measuring device, a commercially available differential scanning calorimeter may be used, and examples thereof include DSC7 manufactured by PerkinElmer. As the measurement conditions, normal conditions may be used, for example, in an inert gas atmosphere, temperature conditions: the resin is held at a temperature above its melting point, then rapidly cooled to about room temperature at 20 ° C./min, and then A condition such as raising the temperature at 20° C./min to a temperature above the melting point can be mentioned.

The ring-shaped nozzle is not particularly limited, and includes nozzles (profile extrusion dies) having a cross-sectional shape such as a ring-shaped or polygonal ring-shaped (triangular ring, square ring, hexagonal ring, etc.).
The ring-shaped nozzle preferably has a gap portion for air inflow. The gap portions for air inflow are preferably arranged at regular intervals in the cross section of the ring-shaped nozzle.
The number of gap portions for air inflow is preferably 1-8, more preferably 1-6, and still more preferably 2-5. When the number of gap portions is within the above range, sufficient air flows into the hollow portions (or substantially hollow portions) of the discharged resin to suppress deformation and tend to stabilize the shape. If the number of gap portions exceeds 8, the die swell effect necessary to fuse the resin pellets at the gap portions tends to be insufficient, resulting in insufficient fusion.
When the resin is ejected vertically from the ring-shaped nozzle, deformation of the ejected resin is suppressed, and the shape of the resin pellet tends to be stabilized.

In addition, regarding the discharge amount per nozzle hole, the discharge amount per unit opening area of the nozzle hole and unit time expressed by the following formula is 4 kg/hr·cm ² to 50 kg/hr·cm ² . It is preferable to select an appropriate die and extruder discharge rate corresponding to the extrusion discharge rate of the extruder. The discharge rate per unit opening area per nozzle hole per unit time is more preferably 5 kg/hr·cm ² to 40 kg/hr·cm ² , and still more preferably 6 kg/hr·cm ² to 35 kg/hr. - ^cm2 .
O(hole)=O(total)/(N(die)×A(die))
(Here, O (hole) is the discharge amount per unit opening area per nozzle hole/unit time [kg/hr cm ² ], O (total) is the discharge amount of all extruders [kg/ hr], N (die) is the number of extruder die holes [pieces], and A (die) is the cross-sectional area per nozzle hole [cm ² ].)
By setting the discharge amount per nozzle hole within the above range, the pressure inside the die becomes appropriate, surging and excessive heat generation during extrusion are suppressed, and a more stable production method can be achieved.

In the method for producing foamed beads of the present embodiment, the drawdown ratio represented by the ratio of the outer diameter of the ring-shaped nozzle to the outer diameter of the resin pellet (nozzle outer diameter/resin pellet outer diameter) is 1.5 to 9. preferably 2 to 8, and still more preferably 3 to 7. When the drawdown ratio is within the above range, deformation of the discharged resin is suppressed, and the shape of the resin pellet tends to be stabilized.

In addition, the ratio R of the take-up speed R (draw) [m/min] of the pelletizer to the discharge speed R (hole) [m/min] per unit opening area per nozzle hole per unit time represented by the following formula: (draw)/R(hole) is preferably 2-28, more preferably 8-25, still more preferably 12-22.
R(hole)=O(hole)/(ρ(melt)×6)
(Here, R (hole) is the unit opening area per nozzle hole/discharge speed per unit time [m/min], O (hole) is the unit opening area/unit time per nozzle hole. Discharge rate [kg/hr·cm ² ], ρ (melt) is density of molten resin [g/cm ³ ].)
By setting the ratio of the take-up speed to the discharge speed within the above range, an appropriate tension is applied to the molten resin after discharge, deformation is suppressed, and a more stable manufacturing method can be achieved.

In addition, in the method for producing foamed beads of the present embodiment, the distance from the discharge port of the annular nozzle to the refrigerant (HD: hot distance) is preferably 50 to 350 mm, more preferably 85 to 250 mm, and more preferably 85 to 250 mm. It is preferably 95 to 200 mm. When the hot distance is within the above range, fusion of the resin in the gap portion is promoted, and the wall thickness of the fused portion can be increased.

The foamed beads of this embodiment contain a resin. Examples of the resin include thermoplastic resins.
Examples of the thermoplastic resin include polystyrene, polyα-methylstyrene, styrene maleic anhydride copolymer, blend or graft polymer of polyphenylene oxide and polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene terpolymer, styrene-butadiene. Copolymers, styrenic polymers such as high impact polystyrene, polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, post-chlorinated polyvinyl chloride, vinyl chloride polymers such as copolymers of ethylene or propylene and vinyl chloride, polyvinylidene chloride Copolymer resins, nylon-6, nylon-6,6, homo- and copolymer polyamide resins, polyethylene terephthalate, homo- and copolymer polyester resins, modified polyphenylene ether resins (phenylene ether-polystyrene alloy resins), polycarbonate resins, methacrylimide Resins, polyphenylene sulfides, polysulfones, polyethersulfones, polyester resins, phenol resins, urethane resins, polyolefin resins, and the like can be used.

Examples of the polyolefin resin include polypropylene polymerized using a Ziegler catalyst or metallocene catalyst, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene. Polypropylene resins such as terpolymers, low density polyethylene, medium density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, high density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl Polyethylene-based resins such as methacrylate copolymers and ionomer resins may be used alone or in combination.

The resin preferably has a surface tension of 37 to 60 mN/m at 20° C., more preferably 38 to 55 mN/m. If the surface tension is within the above range, a sound-absorbing foamed resin article having high mechanical strength can be obtained, which is particularly preferable.
As the surface tension of the resin, the value measured by the method described in JIS K6768 "Plastics-Film and Sheet-Wet Tension Test Method" with the temperature changed to 20°C is used.

Examples of thermoplastic resins included in the preferable surface tension range include polyamide resins, polyester resins, polyether resins, methacrylic resins, modified polyether resins (phenylene ether-polystyrene alloy resins), etc., and the surface tension is within the above range. A thermoplastic resin is mentioned. Among them, polyamide resin has excellent heat resistance, chemical resistance, and solvent resistance, and is suitable for use as a highly heat-resistant foam structure material. Modified polyether resin (phenylene ether-polystyrene alloy resin).

By setting the surface tension of the resin within the above range, especially when the foamed resin is thermally expanded and fused by superheated steam, the affinity between the water vapor and the surface is increased, and as a result, a uniform resin foam molded article with high fusion bonding strength can be obtained. can get. Incidentally, the surface tension of the resin may be the surface tension of the mixed resin of all the resins constituting the foamed beads, and the surface tension of at least one of all the resins constituting the foamed beads satisfies the above range. More preferably, the surface tension of all resins satisfies the above range.

The resin preferably has a glass transition temperature of −10° C. or higher and 280° C. or lower.
As the glass transition temperature of the resin, a value measured by the DSC method in accordance with JIS K7121:1987 "Method for measuring transition temperature of plastics" is used. That is, after conditioning for at least 24 hours at 23±2° C. and 50±5% relative humidity, the specimen was placed in the container of the DSC instrument and, if amorphous, was treated at a temperature at least about 30° C. above the end of the glass transition. to at least about 30° C. above the end of the melting peak, if crystalline, and held at each temperature for 10 minutes, followed by quenching to about 50° C. below the glass transition temperature. The heating rate is maintained at a temperature about 50° C. lower than the transition temperature until the device stabilizes, and then heated at a heating rate of 20° C. per minute to a temperature about 30° C. higher than the end of the transition, and a DSC curve is drawn.

The lower limit of the glass transition temperature of the resin raw material is more preferably 0°C, still more preferably 10°C. By making the glass transition temperature equal to or higher than the above lower limit, it is possible to suppress deterioration of the sound absorbing performance due to long-term compressive force applied to the molded product, and it is preferable in that it can be used for sound absorbing members to which stress is applied.

The upper limit of the glass transition temperature is more preferably 260°C, still more preferably 240°C. When the glass transition temperature is not higher than the above upper limit, the temperature for foam molding can be set low, and the foam can be manufactured with high productivity, which is particularly preferable.

Examples of thermoplastic resins included in the preferred glass transition temperature range include polyamide resins, polyester resins, polyether resins, methacrylic resins, modified polyether resins (phenylene ether-polystyrene alloy resins), etc., and the glass transition temperature is the above. Included are thermoplastic resins that are within the scope.
Among them, polyamide resin has excellent heat resistance, chemical resistance, and solvent resistance, and is suitable for use as a highly heat-resistant foam structure material. Modified polyether resin (phenylene ether-polystyrene alloy resin).
The glass transition temperature of the resin may be the glass transition temperature of the mixed resin of all resins constituting the foamed beads, and the glass transition temperature of at least one resin among all the resins constituting the foamed beads is within the above range. It is preferable that the glass transition temperature of all the resins satisfy the above range.

The above thermoplastic resin may be used in an uncrosslinked state, or may be used after being crosslinked by peroxide, radiation, or the like.

The foamed beads of the present embodiment may optionally contain conventional compounding agents such as antioxidants, light stabilizers, ultraviolet absorbers, flame retardants, coloring agents such as dyes and pigments, plasticizers, lubricants, and crystallization agents. Inorganic fillers such as nucleating agents, talc, and calcium carbonate may be included depending on the purpose.
As the flame retardant, a bromine-based, phosphorus-based, etc. flame retardant can be used, and as the antioxidant, a phenol-based, phosphorus-based, sulfur-based, etc. antioxidant can be used. Hindered amine-based and benzophenone-based light stabilizers can be used as the agent.
If it is necessary to adjust the average cell diameter of the expanded beads, a cell control agent may be added. Inorganic nucleating agents include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, sodium bicarbonate, alumina, barium sulfate, aluminum oxide, bentonite, and the like. The amount to be used is usually 0.005 to 2 parts by mass based on the total amount of raw materials for foamed beads.

A volatile foaming agent or the like may be used as the foaming agent used in producing the foamed beads of the present embodiment. Examples of the volatile blowing agent include chain or cyclic lower aliphatic hydrocarbons such as methane, ethane, propane, butane, isobutane, pentane, isopentane, neopentane, hexane, heptane, cyclopentane, cyclohexane, and methylcyclopentane; Halogenated hydrocarbons such as dicyclodifluoromethane, trichloromonofluoromethane, 1-chloro-1,1-difluoroethane, 1-chloro-2,2,2-trifluoroethane; inorganics such as nitrogen, air, and carbon dioxide; A gas-based foaming agent and the like are included.

[Resin foam molding]
The foamed resin article of the present embodiment is a molded article in which the foamed beads are fused to each other. That is, the resin foam molded article of the present embodiment is a molded article having at least a portion in which at least two foam beads are fused to each other. There are fused portions and voids between the fused expanded beads. The resin foam molded article of the present embodiment can be used as a member that shields various noises, such as a soundproof member for vehicles such as automobiles. The soundproof member preferably contains the foamed resin article of the present embodiment, and may consist of the foamed resin article of the present embodiment only.
In addition, the resin foam molded article of the present embodiment has continuous voids between the fused foamed beads, and preferably has a porosity of 15 to 80%, more preferably 30 to 70%. preferable.
In addition, the said porosity can be calculated|required from the following formulas.
Porosity (%) of resin foam molding = [(BC) / B] × 100
(B is the apparent volume (cm ³ ) of the resin foam molding, C is the true volume (cm ³ ) of the resin foam molding, and the apparent volume B is the volume calculated from the external dimensions of the molded body, the true volume C means the actual volume of the molded article excluding voids, and the true volume C is obtained by measuring the increased volume when the resin foam molded article is submerged in a liquid (eg, alcohol). )

In the resin foam molded article of the present embodiment, if the foam beads account for 98% by weight or more of the entire resin foam molded article, the performance of the foam beads having through holes and/or recesses can be substantially obtained. preferable.

The foamed resin article of the present embodiment is a molded article obtained by fusion-bonding aggregates of the foamed beads, and is required to have continuous voids between the foamed beads.
As used herein, the term “continuous voids” refers to the formation of mutually continuous voids between the fused foam beads, resulting in the ), which means that continuous voids are generated and the fluid can flow. The resin foam molded article of the present embodiment preferably has voids continuous in at least one direction, and preferably has voids continuous in the thickness direction. In the present embodiment, a plate-shaped resin foam molded sample with a thickness of 10 mm is used as the communicating void, and the unit length flow resistance measured in the thickness direction by the AC method specified in the international standard ISO 9053 is 1. ,000,000 N·s/m ⁴ or less, more preferably 500,000 N·s/m ⁴ or less.

The foamed resin article of the present embodiment is produced by filling the foamed beads into a closed mold and foaming them. You may adopt the method of making it wear. A general-purpose in-mold foaming automatic molding machine can be used depending on the type of resin and molding conditions.

In the present embodiment, foamed beads having through holes and/or recesses and particles having general shapes as foamed beads such as oval spheres, cylinders, and polygonal columns without through holes and/or recesses are mixed at an arbitrary ratio. By using it to produce a resin foam molded article, a desired balance between sound absorption performance and mechanical strength can be adjusted.

In addition to being used as a single molded article, the resin foam molded article of the present embodiment is obtained by laminating other inorganic and organic woven fabrics, nonwoven fabrics, and other fiber assembly layers, inorganic and organic porous layers in an arbitrary form. can be used The layer to be laminated is used as a skin material to improve the surface appearance and surface characteristics of the product.In addition to laminating and bonding with the resin foam molding, foam beads are placed in a state where the skin material is set inside the mold when molding foam beads. It is also possible to use a method of heat sealing by filling and performing foam molding.

The embodiments of the present invention are illustrated by the following examples. However, the scope of the present invention is not limited by the examples.

Evaluation methods used in Examples and Comparative Examples are described below.

(1) Through hole opening ratio and recess opening ratio of expanded beads Twenty expanded beads were randomly extracted from an aggregate of expanded beads, and the through hole opening ratio (%) and recess opening ratio of each expanded bead were determined as follows. A rate (%) was obtained.
The through-holes of the foam beads were observed using a microscope (Digital Microscope VHX-2000 manufactured by Keyence Corporation), and the foam beads placed on a transparent petri dish were illuminated from the opposite direction with the foam beads sandwiched from the lens. By doing so, an orthogonal projection image with the maximum through-hole area was obtained. Using image analysis software (installed in a digital microscope VHX-2000 manufactured by Keyence Corporation), the through-hole area and the peripheral area of the expanded beads were measured. The aperture ratio (through-hole area/peripheral area) was calculated, and when there were a plurality of through-holes, the aperture ratio was totaled to obtain the through-hole aperture ratio (%) of each expanded bead.
For recesses of foam beads, using a microscope (Digital Microscope VHX-2000 manufactured by Keyence Corporation), foam beads placed on a transparent petri dish are illuminated from the opposite direction with the foam beads sandwiched from the lens and observed. An orthographic projection image including the deepest part of the recess was obtained. The enveloping area was measured using image analysis software (installed in a digital microscope VHX-2000 manufactured by Keyence Corporation). In addition, a line segment B that circumscribes the concave portion at least at two points is designated on the orthographic projection image, and the area S _A of the region A surrounded by the line segment B and the outer surface of the foam bead is measured using the above image analysis software. bottom. The opening ratio (area S _A /enveloping area) was calculated, and when there were a plurality of concave portions, the opening ratios were totaled to obtain the concave opening ratio (%) of each foamed bead.
Table 1 shows the sum of the aperture ratio of through holes and the aperture ratio of recessed portions of each foamed bead, and averaged for 20 foamed beads.

(2) Average Gap Ratio of Expanded Beads Twenty expanded beads were randomly extracted from an aggregate of expanded beads, and the average gap ratio (%) of each expanded bead was determined as follows.
For recesses of foam beads, using a microscope (Digital Microscope VHX-2000 manufactured by Keyence Corporation), foam beads placed on a transparent petri dish are illuminated from the opposite direction with the foam beads sandwiched from the lens and observed. An orthographic projection image including the deepest part of the recess was obtained. The envelope perimeter was measured using image analysis software (installed in a digital microscope VHX-2000 manufactured by Keyence Corporation). In addition, both ends of the line segment B that circumscribes the concave portion at least at two points on the orthogonal projection image are specified, and the length LB of the line segment _B is measured using the image analysis software (FIG. 3 (b3), 3(d3), see segment B at 3(e3)). The average gap ratio (%) of each expanded bead was obtained by calculating the gap ratio (length _LB /envelope perimeter) and averaging the gap ratios when there were a plurality of concave portions.
Table 1 shows the average gap ratio obtained for 20 expanded beads.

(3) Maximum wall thickness Tmax and minimum wall thickness Tmin of expanded beads
In the orthogonal projection image of each foamed bead obtained in (1) above, the wall thickness is obtained using image analysis software (mounted on a digital microscope VHX-2000 manufactured by Keyence Corporation), and the largest value is the maximum wall thickness Tmax ( mm), and the smallest value was taken as the minimum wall thickness Tmin (mm).
Table 1 shows the values averaged for 20 expanded beads.

(4) Maximum outer diameter Dmax and minimum outer diameter Dmin of expanded beads
In the orthogonal projection image of each foamed bead obtained in (1) above, the outer diameter of the foamed bead is obtained using image analysis software (mounted on a digital microscope VHX-2000 manufactured by Keyence Corporation), and the largest value is the maximum outside diameter. The diameter Dmax (mm) and the smallest value was taken as the minimum outer diameter Dmin (mm).
Table 1 shows the values averaged for 20 expanded beads.

(5) Maximum pore diameter dmax and minimum pore diameter dmin of expanded beads
In the orthogonal projection image of each foamed bead obtained in (1) above, the diameter of the through-hole is obtained using image analysis software (mounted on a digital microscope VHX-2000 manufactured by Keyence Corporation), and the largest value is the maximum hole diameter dmax. (mm), and the smallest value was taken as the minimum pore diameter dmin (mm).
Table 1 shows the values averaged for 20 expanded beads.

(6) Sound Absorption Characteristics of Resin Foam Moldings Based on JIS A1405-2, normal incident sound absorption coefficients at 23° C. were measured. A disk with a diameter of 41 mm and a thickness of 30 mm is cut from a flat resin foam molded product (thickness: 30 mm), and the normal incidence sound absorption coefficient is measured at frequencies of 200 to 5000 Hz using a normal incidence sound absorption measurement system WinZac MTX manufactured by Nippon Onkyo Engineering Co., Ltd. bottom. The measurement is performed by measuring the average sound absorption coefficient of the 1/3 octave band with 11 points of 200Hz, 250Hz, 315Hz, 400Hz, 500Hz, 630Hz, 800Hz, 1000Hz, 1250Hz, 1600Hz, and 2000Hz as the center frequencies. If there are 5 or more frequencies with a sound absorption rate of 30% or more, the sound absorption characteristics are excellent (◎), 3 to 4 points are good sound absorption characteristics (○), and 2 points or less are sound absorption characteristics. It was evaluated as inferior (×).

(7) Sound insulation properties of resin foam molding A disk with a diameter of 41 mm and a thickness of 10 mm is cut from a flat resin foam molding (thickness 10 mm). The sound insulation was evaluated by determining the transmission loss at 1000 Hz. By placing the sound source on the foam layer side and placing the microphone on the non-breathable outer layer side, the attenuation of the sound transmitted through the sample was measured.

[Example 1]
Polyamide 6 resin (UBE nylon "1022B", manufactured by Ube Industries, surface tension at 20 ° C. 46 mN / m, melting point 226 ° C.) is melted using an extruder (screw diameter: 40 mm, L / D: 48) (melting Resin temperature: 330 ° C.), three gaps for air inflow arranged at equal intervals. was quenched in water and then pelletized with a pelletizer to obtain pellets with an average outer diameter of 1.5 mm. The distance (HD) from the nozzle outlet to the water surface is 155 mm, the discharge rate O (hole) per nozzle hole is 18 kg/hr·cm ² , and the pelletizer take-up speed R ( The ratio R(draw)/R(hole) of draw) was 18.1.
The obtained pellets were put into a pressure cooker at 10° C., and carbon dioxide gas of 4 MPa was blown into them for absorption for 3 hours. Next, the mini-pellets impregnated with carbon dioxide gas were transferred to a foaming device, and air at 240° C. was blown for 20 seconds to obtain aggregates of foamed beads. The expanded beads had a cross-sectional shape shown in FIG. 3(a2) and had through holes.
The resulting foamed bead assembly was placed in the pressure cooker again and allowed to absorb 4 MPa of carbon dioxide gas at 10° C. for 3 hours. Next, the foamed beads impregnated with carbon dioxide gas are filled into a flat plate mold of an in-mold foam molding device, and air at 230° C. is blown in for 30 seconds to form a flat resin foam molded product ( A thickness of 30 mm and an expansion ratio of 7.5 were obtained.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

[Example 2]
Polyamide 6 resin (UBE nylon "1022B", manufactured by Ube Industries, surface tension 46 mN / m at 20 ° C.) is melted using an extruder (screw diameter: 40 mm, L / D: 48) (molten resin temperature: 310 ° C), a strand discharged vertically from a profile extrusion die (outer diameter 4 mm) having a cross-sectional shape shown in FIG. to obtain pellets with an average outer diameter of 1.5 mm. The distance (HD) from the nozzle outlet to the water surface is 155 mm, the discharge rate O (hole) per nozzle hole is 9 kg/hr·cm ² , and the pelletizer take-up speed R ( The ratio R(draw)/R(hole) of draw) was 18.1.
The obtained pellets were put into a pressure cooker at 10° C., and carbon dioxide gas of 4 MPa was blown into them for absorption for 3 hours. Next, the mini-pellets impregnated with carbon dioxide gas were transferred to a foaming device, and air at 240° C. was blown for 20 seconds to obtain aggregates of foamed beads. The expanded beads had a cross-sectional shape shown in FIG. 3(b2) and had recesses.
The resulting foamed bead assembly was placed in the pressure cooker again and allowed to absorb 4 MPa of carbon dioxide gas at 10° C. for 3 hours. Next, the foamed beads impregnated with carbon dioxide gas are filled into a flat plate mold of an in-mold foam molding device, and air at 230° C. is blown in for 30 seconds to form a flat resin foam molded product ( A thickness of 30 mm and an expansion ratio of 7.5 were obtained.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

[Example 3]
Polyamide 6 resin (UBE nylon "1022B", manufactured by Ube Industries, surface tension 46 mN / m at 20 ° C.) is melted using an extruder (screw diameter: 40 mm, L / D: 48) (molten resin temperature: 350 ℃), the strand discharged in the vertical direction from a profile extrusion die (outer diameter 4 mm) having a cross-sectional shape shown in FIG. Pellets with an average outer diameter of 1.5 mm were obtained. The distance (HD) from the nozzle outlet to the water surface is 155 mm, the discharge rate O (hole) per nozzle hole is 18 kg/hr·cm ² , and the pelletizer take-up speed R ( The ratio R(draw)/R(hole) of draw) was 18.1.
The obtained pellets were put into a pressure cooker at 10° C., and carbon dioxide gas of 4 MPa was blown into them for absorption for 3 hours. Next, the mini-pellets impregnated with carbon dioxide gas were transferred to a foaming device, and air at 240° C. was blown for 20 seconds to obtain aggregates of foamed beads. The expanded beads had a cross-sectional shape shown in FIG. 3(c2) and had through holes.
The resulting foamed bead assembly was placed in the pressure cooker again and allowed to absorb 4 MPa of carbon dioxide gas at 10° C. for 3 hours. Next, the foamed beads impregnated with carbon dioxide gas are filled into a flat plate mold of an in-mold foam molding device, and air at 230° C. is blown in for 30 seconds to form a flat resin foam molded product ( A thickness of 30 mm and an expansion ratio of 7.5 were obtained.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

[Example 4]
The screw diameter of the extruder is 30 mm, HD is 90 mm, the discharge rate O (hole) is 23 kg/hr cm ² , the ratio R (draw) / R (draw) / R ( Hole) was changed to 4.3 to obtain pellets (average outer diameter 1.5 mm), foamed beads and resin foamed moldings in the same manner as in Example 1.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

[Example 5]
The screw diameter of the extruder is 30 mm, the discharge rate O (hole) is 9.4 kg/hr·cm ² , and the ratio R (draw)/R (hole) of the take-up speed R (draw) of the pelletizer to the discharge speed R (hole). Pellets (average outer diameter: 1.5 mm), foamed beads, and resin foamed articles were obtained in the same manner as in Example 1, except that the was changed to 10.8.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

[Comparative Example 1]
Polyamide 6 resin (UBE nylon "1022B", manufactured by Ube Industries, surface tension 46 mN / m at 20 ° C.) is melted using an extruder (screw diameter: 30 mm, L / D: 48) (molten resin temperature: 360 ° C.), a strand discharged vertically from a profile extrusion die (outer diameter 2.2 mm) having a cross-sectional shape shown in FIG. to obtain pellets with an average outer diameter of 1.5 mm. The distance (HD) from the nozzle outlet to the water surface is 60 mm, the discharge rate O (hole) per nozzle hole is 18.7 kg/hr·cm ² , and the take-up speed of the pelletizer relative to the discharge speed R (hole). The ratio R(draw)/R(hole) of R(draw) was 4.2.
The obtained pellets were put into a pressure cooker at 10° C., and carbon dioxide gas of 4 MPa was blown into them for absorption for 3 hours. Next, the mini-pellets impregnated with carbon dioxide gas were transferred to a foaming device, and air at 240° C. was blown for 20 seconds to obtain aggregates of foamed beads. The expanded beads had a cross-sectional shape shown in FIG. 3(d2) and had recesses.
The resulting foamed bead assembly was placed in the pressure cooker again and allowed to absorb 4 MPa of carbon dioxide gas at 10° C. for 3 hours. Next, the foamed beads impregnated with carbon dioxide gas are filled into a flat plate mold of an in-mold foam molding device, and air at 230° C. is blown in for 30 seconds to form a flat resin foam molded product ( A thickness of 30 mm and an expansion ratio of 7.5 were obtained.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

[Comparative Example 2]
Polyamide 6 resin (UBE nylon "1022B", manufactured by Ube Industries, surface tension 46 mN / m at 20 ° C.) is melted using an extruder (screw diameter: 30 mm, L / D: 48) (molten resin temperature: 360 ° C), a strand discharged vertically from a profile extrusion die (outer diameter 2.8 mm) having a cross-sectional shape shown in FIG. to obtain pellets with an average outer diameter of 1.5 mm. The distance (HD) from the nozzle outlet to the water surface is 45 mm, the discharge rate O (hole) per nozzle hole is 12.1 kg/hr·cm ² , and the take-up speed of the pelletizer relative to the discharge speed R (hole). The ratio R(draw)/R(hole) of R(draw) was 6.8.
The obtained pellets were put into a pressure cooker at 10° C., and carbon dioxide gas of 4 MPa was blown into them for absorption for 3 hours. Next, the mini-pellets impregnated with carbon dioxide gas were transferred to a foaming device, and air at 240° C. was blown for 20 seconds to obtain aggregates of foamed beads. The expanded beads had a cross-sectional shape shown in FIG. 3(e2) and had recesses.
The resulting foamed bead assembly was placed in the pressure cooker again and allowed to absorb 4 MPa of carbon dioxide gas at 10° C. for 3 hours. Next, the foamed beads impregnated with carbon dioxide gas are filled into a flat plate mold of an in-mold foam molding device, and air at 230° C. is blown in for 30 seconds to form a flat resin foam molded product ( A thickness of 30 mm and an expansion ratio of 7.5 were obtained.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

[Comparative Example 3]
Polyamide 6 resin (UBE nylon "1022B", manufactured by Ube Industries, surface tension 46 mN / m at 20 ° C.) is melted using an extruder (screw diameter: 30 mm, L / D: 48) (molten resin temperature: 360 ℃), the strand discharged in the vertical direction from a profile extrusion die (outer diameter 4 mm) having a cross-sectional shape shown in FIG. Pellets with an average outer diameter of 1.5 mm were obtained. The distance (HD) from the nozzle outlet to the water surface is 45 mm, the discharge rate O (hole) per nozzle hole is 18 kg/hr·cm ² , and the pelletizer take-up speed R ( The ratio R(draw)/R(hole) of draw) was 18.1.
The obtained pellets were put into a pressure cooker at 10° C., and carbon dioxide gas of 4 MPa was blown into them for absorption for 3 hours. Next, the mini-pellets impregnated with carbon dioxide gas were transferred to a foaming device, and air at 240° C. was blown for 20 seconds to obtain aggregates of foamed beads. The expanded beads had a cross-sectional shape shown in FIG. 3(c2) and had through holes.
The resulting foamed bead assembly was placed in the pressure cooker again and allowed to absorb 4 MPa of carbon dioxide gas at 10° C. for 3 hours. Next, the foamed beads impregnated with carbon dioxide gas are filled into a flat plate mold of an in-mold foam molding device, and air at 230° C. is blown in for 30 seconds to form a flat resin foam molded product ( A thickness of 30 mm and an expansion ratio of 7.5 were obtained.
Table 1 shows the measurement and evaluation results of the foamed beads and the resin foamed molded product.

Since the foamed beads of the present invention undergo little deformation during foaming and molding, it is possible to produce a foamed resin article having excellent sound absorbing properties.
Examples of applications of the resin foam molded product produced from the foamed beads of the present invention include members used for driving noise reduction in vehicles such as automobiles, electric trains, trains, etc., and aircraft, etc. where lightness and noise reduction are required. In particular, it can be suitably used for sound absorbing members such as automobile engine covers, engine capsules, engine room hoods, transmission casings, sound absorbing covers, motor casings for electric vehicles, and sound absorbing covers.
Furthermore, the resin foam molded article produced from the foamed beads of the present invention can be used in air conditioning equipment such as air conditioners, refrigerators, heat pumps, etc., parts that form air passages such as ducts, washing machines, dryers, etc., where noise reduction is required. , various household electric appliances such as refrigerators and vacuum cleaners, OA equipment such as printers, copiers and facsimiles, and building materials such as core materials for wall materials and core materials for floor materials.

Claims (5)

A foamed bead having at least one through hole and/or at least one recess,
The maximum wall thickness Tmax is 100 μm or more and less than 1000 μm,
For each of the at least one through-hole, the ratio of the through-hole area to the area surrounded by the outer circumference of the foamed bead (peripheral area) in the orthogonal projection image in which the area of the through-hole (through-hole area) is maximized The opening ratio represented by (through hole area/peripheral area) is obtained, and the total value is taken as the through hole opening ratio,
For each of the at least one concave portion, in the orthogonal projection image including the deepest portion of the concave portion, the area (envelope area) of the portion surrounded by the line (envelope line) connecting the vertices of the convex portions of the foam beads, Aperture ratio represented by a ratio (area S _A /enveloping area) of the area (area S _A ) of the region A surrounded by the line segment B circumscribing the recess at least at two points and the outer surface of the foam bead. are calculated and the total value is taken as the opening ratio of the concave portion,
The sum of the aperture ratio of the through holes and the aperture ratio of the concave portions is 10% or more,
For each of the at least one concave portion, the length of the line segment B (length L A foamed bead characterized in that the gap ratio represented by the ratio of _B ) (length L _B /envelope perimeter) is calculated and the average gap ratio is 10% or less. 2. The expanded bead according to claim 1, wherein the ratio of the maximum outer diameter Dmax to the maximum wall thickness Tmax (Dmax/Tmax) is 2.2 or more and 4.2 or less. expanded particles having only the through holes,
The maximum outer diameter Dmax is 4 mm or less,
3. The expanded bead according to claim 1, wherein the maximum pore diameter dmax is 1.5 mm or less. Having at least one node portion whose wall thickness is 80% or less of the maximum wall thickness Tmax,
The expanded bead according to any one of claims 1 to 3, wherein the ratio of minimum wall thickness Tmin to maximum wall thickness Tmax (Tmin/Tmax) is 0.4 or more and less than 1.0. A resin pellet having at least one through-hole and/or at least one concave portion is produced by discharging a resin vertically from a ring-shaped nozzle and then cooled with a coolant, and the resin pellet is foamed. A method for producing expanded beads, comprising:

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