Method for producing foamed particle molded body and foamed particle molded body

Abstract

To provide a method for producing an expanded particle molding which can shorten a molding cycle when an expanded particle molding is produced without greatly impairing physical properties of the expanded particle molding, and an expanded particle molding.SOLUTION: A method for producing an expanded particle molding in-mold molds composite resin expanded particles containing a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base material resin, and produces an expanded particle molding, wherein mixed expanded particles obtained by mixing composite resin expanded particles A having an isolated cell ratio of 10% or more and 50% or less and composite resin expanded particles B having an isolated cell ratio of 80% or more are used as the composite resin expanded particles, and a mass ratio of the composite resin expanded particles A to the composite resin expanded particles B in the mixed expanded particles is 3:97 to 30:70.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a foamed particle molded body capable of shortening the molding cycle when manufacturing the foamed particle molded body without significantly impairing the physical properties of the foamed particle molded body, and a foamed particle molded body obtained by the manufacturing method.

Background Art

[0002] A foamed particle molded body (hereinafter, also simply referred to as a molded body) formed by in-mold molding of composite resin foamed particles having a composite resin of a polystyrene-based resin component and a polyolefin-based resin component as a base resin has excellent environmental-friendly physical properties such as cushioning properties, light weight, and heat insulation properties. Therefore, the above foamed particle molded body can be used in a wide variety of applications such as the packaging field, the automotive field, and the construction and civil engineering fields, and further application development is expected.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, in the production of foamed particle molded bodies, from the viewpoint of improving productivity, it is desirable to adopt a molding method that is short in the time required for a series of steps in one in-mold molding and excellent in the molding cycle. From this perspective, there is a demand for the development of a method for manufacturing a foamed particle molded body that can shorten the time required to cool the molded body when taking out the molded body whose heating has been completed from the mold during in-mold molding. An object of the present invention is to provide a method for manufacturing a foamed particle molded body and a foamed particle molded body that can shorten the molding cycle when manufacturing the foamed particle molded body without significantly impairing the physical properties of the foamed particle molded body.

Means for Solving the Problems

[0005] The inventor has found that the above problems can be solved by adopting the following configuration, and has completed the present invention. That is, the present invention is as follows. <1> A method for manufacturing a foamed particle molded body by in-mold molding of composite resin foamed particles using a composite resin containing a polystyrene resin component and a polyolefin resin component as a base resin, wherein, as the composite resin foamed particles, a composite resin foamed particle A having a closed cell ratio of 10% or more and 50% or less and a composite resin foamed particle B having a closed cell ratio of 80% or more are mixed, and the mass ratio of the composite resin foamed particle A to the composite resin foamed particle B in the mixed foamed particles is 3:97 to 30:70. A method for manufacturing a foamed particle molded body. <2> The bulk density of the composite resin foamed particle B is 15 kg / m 3 or more and 180 kg / m 3 or less, and the ratio of the bulk density of the composite resin foamed particle A to the bulk density of the composite resin foamed particle B is 0.7 or more and 1.4 or less. The method for manufacturing a foamed particle molded body according to <1>. <3> The average bulk density of the mixed foamed particles is 15 kg / m 3 or more and 180 kg / m 3 or less. The method for manufacturing a foamed particle molded body according to <1> or <2>. <4> The average particle diameter of the composite resin foamed particle B is 2 mm or more and 8 mm or less, and the ratio of the average particle diameter of the composite resin foamed particle A to the average particle diameter of the composite resin foamed particle B is 0.7 or more and 1.4 or less. The method for manufacturing a foamed particle molded body according to any one of <1> to <3>. <5> The ratio a of the polystyrene resin component in the composite resin constituting the composite resin foamed particle A is 50% by mass or more and 90% by mass or less, and the ratio b of the polystyrene resin component in the composite resin constituting the composite resin foamed particle B is 50% by mass or more and 90% by mass or less, and the difference (a - b) between the ratio a and the ratio b is -5% or more and 5% or less. The method for manufacturing a foamed particle molded body according to any one of <1> to <4>. <6> The method for producing a foamed particle molded body according to any one of <1> to <5>, wherein the ratio of the insoluble matter when the composite resin foamed particles A are Soxhlet-extracted with xylene is 0.1% by mass or more and 40% by mass or less. <7> The method for producing a foamed particle molded body according to any one of <1> to <6>, wherein the composite resin foamed particles A are composite resin foamed particles obtained by crushing a foamed particle molded body having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin. <8> A foamed particle molded body obtained by in-mold molding of composite resin foamed particles having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin, wherein the foamed particle molded body is obtained by in-mold molding of a mixed foamed particle of composite resin foamed particles A having a closed cell ratio of 10% or more and 50% or less and composite resin foamed particles B having a closed cell ratio of 80% or more, and the total area (S B ) of the composite resin foamed particles B on the surface of the foamed particle molded body. The average value of the ratio (S A ) of the total area (S A / S B ) of the composite resin foamed particles A is 0.005 or more and 0.3 or less. <9> The foamed particle molded body according to <8>, wherein the coefficient of variation of the ratio (S A / S B ) is 40% or less. <10> The foamed particle molded body according to <8> or <9>, wherein the weight ratio of the composite resin foamed particles A to the composite resin foamed particles B in the foamed particle molded body is 3:97 to 30:70. <11> The foamed particle molded body according to any one of <8> to <10>, wherein the density of the foamed particle molded body is 15 kg / m 3 or more and 180 kg / m 3 or less.

Advantages of the Invention

[0006] According to the present invention, it is possible to provide a method for producing a foamed particle molded body and a foamed particle molded body capable of shortening the molding cycle when producing the foamed particle molded body without significantly impairing the physical properties of the foamed particle molded body.

Embodiments for Carrying Out the Invention

[0007] In the present invention, except for using mixed foamed particles obtained by mixing composite resin foamed particles A having a specific closed cell ratio (hereinafter, also simply referred to as foamed particles A) and composite resin foamed particles B having a specific closed cell ratio (hereinafter, also simply referred to as foamed particles B), well-known apparatuses and manufacturing techniques described in JP-A-2011-42718, JP-A-2011-256244, JP-A-2012-72225, JP-A-2016-180073, JP-A-2017-105881, JP-A-2017-105882, etc. can be adopted.

[0008] The foamed particles A and the foamed particles B used in the present invention are each composite resin foamed particles having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin. Such a composite resin can be obtained, for example, by impregnating and polymerizing a styrene-based monomer into seed particles having a polyolefin-based resin as a base resin. Further, composite resin foamed particles can be obtained by foaming resin particles having such a composite resin as a base resin or the like.

[0009] The ratio a of the polystyrene-based resin component in the composite resin constituting the foamed particles A and the ratio b of the polystyrene-based resin component in the composite resin constituting the foamed particles B are each preferably 50% by mass or more and 90% by mass or less. Further, from the viewpoint of obtaining a foamed particle molded body having higher rigidity while maintaining toughness, the ratio a and the ratio b are each preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. From the viewpoint of easily obtaining a foamed particle molded body in which the reduction in physical properties of the obtained molded body is suppressed while shortening the molding cycle, the difference (a - b) between the ratio a and the ratio b is preferably -5% or more and 5% or less, and more preferably -3% or more and 3% or less.

[0010] As the polyolefin resin constituting the polyolefin resin component in the composite resin, a polyethylene resin or a polypropylene resin can be used, and a polyethylene resin can preferably be used. As the polyethylene resin, for example, linear low-density polyethylene, branched low-density polyethylene, high-density polyethylene, ethylene-acrylic acid copolymer, ethylene-alkyl acrylate copolymer, ethylene-alkyl methacrylate copolymer, etc. can be used. In addition, examples of the polypropylene resin include a propylene homopolymer and a polypropylene copolymer in which the structural unit derived from propylene is 50% by mass or more. Examples of the copolymer include copolymers of propylene and ethylene or an α-olefin having 4 or more carbon atoms such as ethylene-propylene copolymer, propylene-butene copolymer, propylene-ethylene-butene copolymer, and propylene-acrylic acid copolymer, propylene-maleic anhydride copolymer, etc. These copolymers may be any of block copolymers, random copolymers, and graft copolymers. The above-mentioned resin may be a single polymer or a mixture of two or more polymers.

[0011] The polystyrene resin component in the composite resin has a styrene component unit in the styrene resin of 50% by mass or more, and preferably 80% by mass or more, and more preferably 90% by mass or more.

[0012] Examples of the styrenic monomers that constitute the styrenic resin component in the composite resin include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, p-n-butylstyrene, p-t-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, styrenesulfonic acid, sodium styrenesulfonate, and the like. Also, within the range where the intended object of the present invention can be achieved, monomers copolymerizable with styrene may be used. Examples of monomers copolymerizable with styrene include acrylic monomers such as methyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.

[0013] From the viewpoint of enhancing the foamability of the composite resin particles, it is preferable to use styrene alone or in combination with an acrylic monomer as the styrenic monomer. From the viewpoint of further enhancing the foamability, it is particularly preferable to use styrene and butyl acrylate as the styrenic monomer. In this case, the blending amount of butyl acrylate is preferably adjusted so that the proportion of the butyl acrylate component in the composite resin is 0.5 to 10% by mass, more preferably adjusted to 1 to 8% by mass, and even more preferably adjusted to 2 to 5% by mass.

[0014] The composite resin may or may not be crosslinked. More specifically, the foamed particles or foamed particle molded body may or may not contain xylene-insoluble matter measured by Soxhlet extraction with xylene. Foamed particles and foamed particle molded bodies using a crosslinked composite resin as the base resin generally tend to be difficult to recycle and reuse. On the other hand, in the present invention, as described later, even when using recycled particles derived from a foamed particle molded body formed in a mold using crosslinked foamed particles, a good foamed particle molded body can be produced. Therefore, it is possible to reduce the resources used in the production of the foamed particle molded body. From this perspective, when the foamed particles (specifically, foamed particle A or foamed particle B) or the foamed particle molded body is subjected to Soxhlet extraction with xylene, the proportion of the insoluble matter may be 0.1% by mass or more and 40% by mass or less, may be 1% by mass or more and 30% by mass or less, may be 3% by mass or more and 20% by mass or less, or may be 5% by mass or more and 10% by mass or less, respectively.

[0015] The closed cell ratio of the foamed particle A is 10% or more and 50% or less. Also, the closed cell ratio of the foamed particle B is 80% or more. By using the foamed particles A and B with the closed cell ratio within the above range to form the mixed foamed particles, it is possible to shorten the molding cycle when manufacturing the foamed particle molded body while suppressing the deterioration of the physical properties of the obtained molded body during in-mold molding. From the perspective of more easily suppressing the deterioration of the physical properties of the obtained molded body while shortening the molding cycle, the closed cell ratio of the foamed particle A is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. Also, from the perspective of enhancing the in-mold moldability of the mixed foamed particles and stably suppressing the deterioration of the physical properties of the obtained molded body, the closed cell ratio of the foamed particle B is preferably 85% or more, and more preferably 90% or more.

[0016] The closed cell ratio of the foamed particles can be measured as follows. First, a group of foamed particles with a bulk volume of about 20 cm 3 is immersed in water to measure the apparent volume Va of the group of foamed particles. Next, after sufficiently drying the group of foamed particles whose apparent volume Va has been measured, in accordance with Procedure C described in ASTM-D2856-70, the value Vx of the true volume (the sum of the volume of the resin constituting the foamed particles and the total bubble volume of the closed cell portions within the foamed particles) of the group of foamed particles is measured. For the measurement of this true volume Vx, an air comparison type specific gravity meter "930" manufactured by Toshiba Beckman Co., Ltd. or the like can be used. Then, the closed cell ratio is calculated by the following formula (1), and the arithmetic mean value of the measurement results of 5 times using different groups of foamed particles is obtained. Independent bubble rate (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (1) Vx: True volume of the foamed particle group measured by the above method (cm 3 ) Va: Apparent volume of the foamed particle group measured from the rise in the water level when the foamed particle group is submerged in water in a graduated cylinder (cm 3 ) W: Mass of the foamed particle group (g) ρ: Density of the resin constituting the foamed particles (g / cm 3 )

[0017] In the above mixed foamed particles, the mass ratio of the foamed particle A to the foamed particle B is 3:97 to 30:70. By mixing the foamed particle A and the foamed particle B at the above mass ratio, it is possible to shorten the molding cycle when manufacturing the foamed particle molded body while suppressing a decrease in the physical properties of the obtained molded body. From the viewpoint of further suppressing a decrease in the physical properties of the obtained molded body, the mass ratio of the foamed particle A to the foamed particle B is preferably 3:97 to 20:80, more preferably 3:97 to 15:85, and even more preferably 3:97 to 10:90.

[0018] As the foamed particle A, foamed particles (recycled particles) derived from a foamed particle molded body having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin can be preferably used. In this case, since the foamed particle molded body can be manufactured using mixed foamed particles containing recycled foam derived from a foamed particle molded body once molded in a mold, such as a foamed particle molded body used in various applications, efficient recycling of the foamed particle molded body becomes possible. Further, according to the present invention, even when the composite resin constituting the foamed particle molded body is crosslinked, a good foamed particle molded body can be manufactured. Therefore, since the present invention can reduce the resources used in the production of the foamed particle molded body, it also has great technical significance as an environmental response technology.

[0019] As the foamed particles A (recycled particles), it is more preferable to use composite resin foamed particles obtained by crushing a foamed particle molded body having the composite resin as a base resin. Such foamed particles are those in which the foamed particle molded body is crushed into particles. For example, by crushing, the vicinity of the interface between the foamed particles constituting the foamed particle molded body is destroyed, and the molded body is separated into particles. As described above, the foamed particles A (recycled particles) can be obtained by crushing the foamed particle molded body or the like. The crushing of the molded body can be performed using a crushing device such as "Mini In-A-Box" manufactured by KBM. As the crushing device, a device including a crusher (such as a jaw crusher) for roughly crushing the molded body and a screen (such as punching metal) for making the size of the roughly crushed molded body uniform can be preferably used.

[0020] For example, when obtaining recycled particles by crushing a foamed particle molded body made of a polystyrene-based resin such as polystyrene, fine powder of the molded body was likely to be generated during crushing. Therefore, when molding is performed using the foamed particles containing the recovered recycled particles, the physical properties of the obtained molded body may deteriorate, or the yield of the recycled particles that can be used for molding may decrease. On the other hand, when obtaining recycled particles by crushing a foamed particle molded body having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin, presumably due to the properties of the composite resin, during crushing, the foamed particles are likely to separate near the interface between the foamed particles in the molded body, and the foamed particles are not easily crushed by crushing, and there is a tendency that fine powder of the molded body is not easily generated. Therefore, by crushing a foamed particle molded body having a composite resin as a base resin to obtain recycled particles, even when using mixed foamed particles containing the recycled particles, it is possible to stably manufacture a foamed particle molded body having good physical properties. In addition, clogging of the steam holes (vent holes) of the mold is less likely to occur during in-mold molding, and a molded body can be manufactured with good productivity.

[0021] As the foamed particles B, it is preferable to use unformed foamed particles (non-recycled particles) obtained by foaming resin particles having a composite resin as a base resin. As a method for obtaining the non-recycled particles by foaming the resin particles, a method of heating the resin particles impregnated with a volatile foaming agent with steam, hot air, etc. to foam the resin particles, or a sealable container such as a pressure-resistant container, An aqueous medium, resin particles, and a volatile foaming agent are put in, adjusted to a predetermined temperature and pressure, and then the content of the container is released into a pressure atmosphere lower than the pressure in the container to foam the resin particles. A method or the like can be adopted. As the foaming agent to be used, organic foaming agents such as butane, pentane, and propane, or inorganic foaming agents such as carbon dioxide, air, and nitrogen can be used. As the foamed particles B, it is preferable to use foamed particles foamed using an inorganic foaming agent. In this case, the amount of the foaming agent remaining in the foamed particles B is reduced. Therefore, when molding the mixed foamed particles, it becomes easy to suppress the foamed particles B from excessively secondarily foaming with respect to the foamed particles A, and it becomes easy to obtain a molded body having good physical properties. In addition, the molding cycle of the mixed foamed particles can be easily shortened.

[0022] From the viewpoint of increasing the mechanical strength of the obtained foamed particle molded body, the bulk densities of the foamed particles A and B are each preferably 15 kg / m 3 or more, more preferably 16 kg / m 3 or more, and even more preferably 18 kg / m 3 or more. On the other hand, from the viewpoint of increasing the lightness of the obtained foamed particle molded body, the bulk densities of the foamed particles A and B are each preferably 180 kg / m 3 or less, more preferably 120 kg / m 3 or less, even more preferably 100 kg / m 3 or less, still more preferably 80 kg / m 3 or less, even more preferably 60 kg / m 3 or less, and particularly preferably 60 kg / m The bulk density of the foamed particles can be determined, for example, as follows. First, about 500 cm3 Fill the foam particle group into the female cylinder, and gently tap the floor surface several times at the bottom surface of the female cylinder to stabilize the filling height of the foam particle group in the female cylinder. Next, read the bulk volume of the foam particle group indicated by the scale of the female cylinder, and let this be V1 (L). Next, measure the mass of the foam particle group, and let this be W1 [g]. Divide the mass W1 [g] of the foam particles by the volume V1 (W1 / V1) and convert the unit to [kg / m 3 , and the bulk density of the foam particles can be obtained.

[0023] In the case of the mixed foam particles, the ratio of the bulk density of the foam particles A to the bulk density of the foam particles B is preferably 0.7 or more and 1.4 or less. When the above ratio is within the above range, in the mixed foam particles, each foam particle is easily mixed homogeneously, and a foam particle molded body having good mechanical physical properties can be stably obtained. Further, when the above ratio is within the above range, the effect of shortening the molding cycle by using the mixed foam particles can be stably exhibited. From such a viewpoint, the ratio of the bulk density of the foam particles A to the bulk density of the foam particles B is preferably 0.8 or more, more preferably 0.9 or more, further preferably 1.0 or more, and particularly preferably 1.1 or more.

[0024] From the viewpoint of obtaining a foam particle molded body having an excellent balance between lightness and mechanical strength, the average bulk density of the mixed foam particles is 15 kg / m 3 or more and 180 kg / m 3 or less, preferably 16 kg / m 3 or more and 120 kg / m 3 or less, more preferably 18 kg / m 3 or more and 100 kg / m 3 or less, further preferably 18 kg / m 3 or more and 60 kg / m 3 or less is particularly preferable. The average bulk density of the mixed foamed particles can be determined as a weighted average value of the bulk density of the foamed particles A and the bulk density of the foamed particles B, taking into account the mass ratio of the foamed particles A and the foamed particles B in the mixed foamed particles.

[0025] From the viewpoint of facilitating improvement of in-mold formability, the average particle diameters of the foamed particles A and the foamed particles B are preferably 2 mm or more and 8 mm or less, and more preferably 3 mm or more and 6 mm or less, respectively. Further, in the mixed foamed particles, from the viewpoint of facilitating uniform mixing of each foamed particle, the ratio of the average particle diameter of the foamed particles A to the average particle diameter of the foamed particles B is preferably 0.7 or more and 1.4 or less, and more preferably 0.8 or more and 1.2 or less. The average particle diameter of the foamed particles is the value of the cumulative 63% diameter (that is, d63) calculated based on the particle size distribution on a volume basis of the foamed particles. The particle size distribution on a volume basis of the foamed particles can be obtained using a particle size distribution measuring device (for example, "Millitrack JPA" manufactured by Nikkiso Co., Ltd.).

[0026] The foamed particle molded body in the present invention can be manufactured by a known in-mold molding method such as steam heating. Specifically, by introducing a heating medium such as steam into a molding die filled with mixed foamed particles, the mixed foamed particles are heated and expanded (secondary foaming), and at the same time, they are fused to each other, so that a foamed particle molded body having the shape of the molding space imparted thereto can be obtained. When filling the molding die with the mixed foamed particles, the foamed particles A and the foamed particles B may be mixed in advance and then the mixed foamed particles may be filled into the molding die. Alternatively, the foamed particles A and the foamed particles B may be simultaneously supplied into the molding die, and filled while mixing the foamed particles A and the foamed particles B in the molding die.

[0027] By the production method of the present invention, a foamed particle molded body satisfying the following aspects can be obtained. A foamed particle molded body obtained by in-mold molding of composite resin foamed particles having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin, The foamed particle molded body is formed by in-mold molding of mixed foamed particles of composite resin foamed particles A having a closed cell ratio of 10% or more and 50% or less and composite resin foamed particles B having a closed cell ratio of 80% or more. On the surface of the foamed particle molded body, the total area (S B ) of the foamed particles A with respect to the total area (S A ) of the foamed particles B, the ratio (S A / S B ) has an average value of 0.005 or more and 0.3 or less. The foamed particle molded body satisfying the above aspect enables in-mold molding with a short molding cycle and becomes a foamed particle molded body having good physical properties. Regarding the foamed particles A and B for constituting the foamed particle molded body, reference can be made to the description of the foamed particles A and B used for in-mold molding.

[0028] In a preferred aspect of the foamed particle molded body as described above, on the surface of the foamed particle molded body, the total area (S B ) of the foamed particles A with respect to the total area (S A ) of the foamed particles B, the ratio (S A / S B ) has an average value of 0.005 or more and 0.3 or less. By the average value of the ratio (S A / S B ) being within the above range, the action of the foamed particles A and the action of the foamed particles B can be expressed in a well-balanced manner. Therefore, the molding cycle during molding can be shortened, and a foamed particle molded body having good physical properties can be obtained. From the viewpoint of further enhancing the balance between the molding cycle and the physical properties, the average value of the ratio (S A / S B ) is preferably 0.006 or more and 0.2 or less, more preferably 0.008 or more and 0.1 or less, and even more preferably 0.01 or more and 0.08 or less.

[0029] In addition, from the viewpoint that the distribution of the foamed particles A and the foamed particles B in the molded body becomes more homogeneous, the effects of the foamed particles A and the effects of the foamed particles B can be stably exhibited, and it becomes easier to obtain a molded body having good physical properties, the ratio (S A / S B ) preferably has a coefficient of variation of 40% or less, more preferably 30% or less, still more preferably 25% or less, even more preferably 22% or less, and particularly preferably 20% or less.

[0030] The method for calculating the value, the average value, and the coefficient of variation of S A / S B described above is specifically as follows. First, on the surface of a randomly selected molded body, a square measurement region with a length of 50 mm and a width of 50 mm is set, and the total area S A of the foamed particles A and the total area S B of the foamed particles B occupying the measurement region are calculated. In this measurement, the area of each foamed particle can be obtained based on the boundary between the foamed particles. Next, by dividing S A by S B , the value of the ratio S A / S B is obtained. Next, the above-described measurement is performed on 20 or more randomly selected measurement regions, and the value of the ratio S A / S B in each measurement region is obtained in the same manner. The average value of the ratio S A / S B can be calculated by arithmetically averaging the measured multiple ratios S A / S B . In addition, based on the values of the multiple ratios S A / S B described above, the unbiased standard deviation of the ratio S A / S B is calculated, and the unbiased standard deviation of the ratio S A / S B is divided by the average value of the ratio S A / S B to obtain the coefficient of variation of the ratio S A / S BThe coefficient of variation can be calculated. Note that the ratio S A / S B The unbiased standard deviation σ of is specifically represented by the following formula (2).

Equation

[0031] From the viewpoint of enabling in-mold molding with a short molding cycle and stably and easily obtaining a foamed particle molded body having good physical properties, the mass ratio of the foamed particles A to the foamed particles B in the foamed particle molded body is preferably 3:97 to 30:70. Further, from the viewpoint of easily increasing the mechanical strength of the foamed particle molded body, the mass ratio of the foamed particles A to the foamed particles B is preferably 3:97 to 20:80, more preferably 3:97 to 15:85, and even more preferably 3:97 to 10:90.

[0032] From the viewpoint of obtaining a foamed particle molded body having an excellent balance between lightness and mechanical strength, the density of the foamed particle molded body is preferably 15 kg / m 3 or more and 180 kg / m 3 or less, more preferably 16 kg / m 3 or more and 120 kg / m 3 or less, even more preferably 18 kg / m 3 or more and 100 kg / m 3 or less, and particularly preferably 18 kg / m 3 or more and 60 kg / m 3 or less. The density of the foamed particle molded body can be obtained by dividing the mass of the foamed particle molded body by the volume calculated based on the dimensions of the foamed particle molded body.

[0033] From the viewpoint of easily enhancing the mechanical properties of the resulting foamed particle molded body, the closed cell ratio of the foamed particle molded body is preferably 70% or more, more preferably 80% or more, and even more preferably 85% or more. Further, from the viewpoint of easily shortening the molding cycle during in-mold molding, the closed cell ratio of the foamed particle molded body is preferably 98% or less, more preferably 96% or less, and even more preferably 95% or less. The closed cell ratio of the foamed particle molded body can be measured as follows. First, from the foamed particle molded body, a rectangular parallelepiped-shaped measurement sample having outer dimensions of 30 × 25 × 25 mm is cut out so as not to include the skin of the molded body, and the volume Vb of the measurement sample is measured from the outer dimensions. Next, after the measurement sample whose apparent volume Vb has been measured is sufficiently dried, in accordance with Procedure C described in ASTM-D2856-70, the true volume value Vy of the measurement sample is measured. For this measurement of the true volume Vy, an air comparison type specific gravity meter "930" manufactured by Toshiba Beckman Co., Ltd. or the like can be used. Then, the closed cell ratio is calculated by the following formula (3), and the arithmetic mean value of the five measurement results using different measurement samples is obtained. Closed cell ratio (%) = (Vy - W / ρ) × 100 / (Vb - W / ρ) ··· (3) Vy: True volume of the measurement sample measured by the above method (cm 3 ) Vb: Volume obtained from the outer dimensions of the measurement sample (cm 3 ) W: Mass of the measurement sample (g) ρ: Density of the resin constituting the foamed particle molded body (g / cm 3 )

Example

[0034] <Production of Foamed Particles A, Foamed Particles B, Reference Examples 1 and 2> First, by the method shown below, foamed particles B and a foamed particle molded body B (Reference Example 1) formed by in-mold molding of foamed particles B were produced.

[0035] <Manufacture of Foamed Particle B1> (1) Preparation of Core Particles As the polyethylene resin, linear low-density polyethylene (specifically, "Nipolon Z HF 210K" manufactured by Tosoh Corporation) polymerized using a metallocene polymerization catalyst was prepared. The melting point Tm of this polyethylene resin was 103°C. Also, as the antioxidant masterbatch, "TMB113" manufactured by Toho Co., Ltd. was prepared. Further, as the foaming nucleating agent masterbatch, "CE-7335" manufactured by Polyol Co., Ltd. was prepared. "CE-7335" manufactured by Polyol Co., Ltd. had a zinc borate (bubble regulator) content of 10% by mass and a linear low-density polyethylene ("Nipolon Z HF 210K") content of 90% by mass. 8.57 kg of the polyethylene resin, 0.09 kg of the antioxidant masterbatch, and 1.34 kg of the bubble regulator masterbatch were supplied to a Henschel mixer and mixed for 5 minutes to obtain a resin mixture. Next, the resin mixture was melt-kneaded using a 50 mmφ single-screw extruder and cut into an average of 0.35 mg / particle by the underwater cutting method to obtain core particles.

[0036] (2) Preparation of Composite Resin Particles 1000 g of deionized water was put into an autoclave with an internal volume of 3 L equipped with a stirring device, and 6.0 g of sodium pyrophosphate was further added. Then, 12.9 g of powdery magnesium nitrate hexahydrate was added and stirred at room temperature for 30 minutes. Thereby, a magnesium pyrophosphate slurry as a suspending agent was prepared. Next, 2.0 g of sodium lauryl sulfonate (10% by mass aqueous solution) as a surfactant, 0.2 g of sodium nitrite as a water-soluble polymerization inhibitor, and 75 g of core particles were added to this suspending agent. Next, two types of organic peroxides were prepared as polymerization initiators. Specifically, as organic peroxide A, t-butylperoxy-2-ethylhexyl monocarbonate ("Perbutyl E" manufactured by NOF Corporation) was prepared, and as organic peroxide B, t-hexyl peroxybenzoate (specifically, "Perhexyl Z" manufactured by NOF Corporation) was prepared. Further, as a chain transfer agent, α-methylstyrene dimer ("Nofmer MSD" manufactured by NOF Corporation) was prepared. Then, 1.72 g of t-butylperoxy-2-ethylhexyl monocarbonate, 0.86 g of t-hexyl peroxybenzoate, and 0.63 g of α-methylstyrene dimer were dissolved in the first monomer (styrenic monomer). And the solution was added into the above-mentioned autoclave to which nucleating particles etc. were added while stirring at a rotation speed of 500 rpm. As the first monomer, a mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used. Next, after replacing the air in the autoclave with nitrogen, the temperature increase was started, and the temperature inside the autoclave was raised to 100°C over 1 hour and 30 minutes. After the temperature increase, it was held at this temperature of 100°C for 1 hour. Then, the stirring speed was lowered to 450 rpm and held at a temperature of 100°C for 7.5 hours. The temperature at this time (specifically 100°C) is the polymerization temperature. Also, 350 g of styrene as the second monomer (styrenic monomer) was added into the autoclave over 5 hours 1 hour after reaching the temperature of 100°C. Next, the temperature inside the autoclave was raised to 125°C over 2 hours and held at the temperature of 125°C as it was for 5 hours. Then, the autoclave was cooled and the content (resin particles (composite resin particles) with a composite resin as the base resin) was taken out. Next, nitric acid was added to dissolve magnesium pyrophosphate adhering to the surface of the composite resin particles. Then, dehydration and washing were performed with a centrifuge, and the moisture adhering to the surface was removed with an air flow drying device, thereby obtaining composite resin particles with a ratio (mass ratio) of polystyrene-based resin to polyethylene-based resin of 85:15. This ratio of polystyrene-based resin to polyethylene-based resin is obtained from the blending ratio (mass ratio) of the styrenic monomer and the ethylene-based resin used during production.

[0037] (3) Production of Expanded Particles 500 g of composite resin particles were charged into a 5 L pressure-resistant sealed container equipped with a stirrer together with 3500 g of water as a dispersion medium. Subsequently, 5 g of kaolin as a dispersant and 0.5 g of sodium alkylbenzene sulfonate as a surfactant were further added to the dispersion medium in the pressure-resistant sealed container. Next, while stirring the inside of the pressure-resistant sealed container at a rotation speed of 300 rpm, the temperature inside the container was raised to a foaming temperature of 165°C. Then, carbon dioxide, which is a physical foaming agent, was injected into the pressure-resistant sealed container so that the pressure inside the pressure-resistant sealed container became 3.2 MPa (G: gauge pressure), and it was held at the same temperature for 15 minutes. Thereby, carbon dioxide was impregnated into the composite resin particles to obtain expandable composite resin particles. Next, the expandable composite resin particles were discharged from the sealed container to atmospheric pressure together with the dispersion medium, and the bulk density was 37 kg / m 3 Expanded particles (Expanded Particles B1) having a composite resin with a density of were obtained using the composite resin as a base resin. Using the method described above, each physical property of the obtained expanded particles was measured. The results are shown in Table 1. The proportion of the polystyrene-based resin component in the composite resin constituting the expanded particles is 85% by mass.

[0038] <Production of Expanded Particle Molded Body B1 (Reference Example 1)> The expanded particles B1 obtained as described above were filled into a mold having a cavity in the shape of a flat plate with a length of 250 mm, a width of 200 mm, and a thickness of 50 mm. Next, steam was introduced into the mold and heated at the molding pressure (steam pressure) shown in Table 1 for a predetermined time to fuse the expanded particles to each other. The above molding was performed at a molding pressure (minimum molding pressure) at which good fusion of the expanded particles to each other, no excessive sink marks occurred in the molded body, and there were few gaps on the surface of the molded body, enabling the acquisition of a good molded body. Then, after cooling the inside of the mold by water cooling, the expanded particle molded body was taken out of the mold. Further, the expanded particle molded body was placed in an oven adjusted to a temperature of 60°C for 12 hours to perform drying and curing. In this way, an expanded particle molded body B1 (Reference Example 1) was obtained. Regarding the foamed particle molded body, the "cooling time", "fusion rate", "dimensional change rate of the foamed particle molded body with respect to the mold dimensions", and "50% deformation compression stress of the foamed particle molded body" were evaluated as follows. Table 2 shows the evaluation results and each physical property of the foamed particle molded body measured by the above-described method.

[0039] [Cooling time (molding cycle evaluation)] During the in-mold molding of the foamed particles, the time (cooling time) from the point when the heating by steam ended to the point when the pressure (surface pressure) generated on the inner surface of the mold of the molding die reached 0.02 MPa (G: gauge pressure) was measured. The shorter this cooling time, the shorter the time required for cooling the molded body, and the more efficiently the in-mold molding of the foamed particle molded body can be performed, resulting in an excellent molding cycle. [Fusion rate] The foamed particle molded body after curing was bent and broken, and the number of foamed particles (C1) present on the fracture surface and the number of broken foamed particles (C2) were determined. The ratio (C2 / C1×100) of the broken foamed particles to the above foamed particles was calculated as the material fracture rate. Note that the higher the value of the above fusion rate, the better the fusion state of the foamed particles with each other. The above fusion rate is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. [Dimensional change rate of the foamed particle molded body with respect to the mold dimensions] The longitudinal dimension (L B ) of the foamed particle molded body after curing was measured. The ratio ([L A - L A / L B ×100) of the difference between the longitudinal dimension of the molding die and the longitudinal dimension of the foamed particle molded body with respect to the longitudinal dimension (L A ) of the molding die was calculated and used as the dimensional change rate of the foamed particle molded body with respect to the mold dimensions. Note that the smaller the value of the above dimensional change rate, the less the shrinkage of the molded body, which means that a good molded body close to the dimensions of the molding die is obtained. The above dimensional change rate is preferably 2.0% or less, more preferably 1.5% or less, and even more preferably 1.2% or less. [50% deformation compressive stress of the expanded particle molded body] From the obtained molded body, a test piece with a length of 5 cm × width of 5 cm × height of 2.5 cm was taken, and the test piece was compressed at a compression rate of 10 mm / min to measure the stress at 50% strain. Further, the stress at 50% strain obtained was divided by the density of the molded body to calculate the specific strength. The higher the stress, the better the compression physical properties of the expanded particle molded body.

[0040] [Production of Expanded Particle B2] In the production of the expanded particles, except that carbon dioxide, which is a physical foaming agent, was injected into the pressure-resistant closed container so that the pressure in the pressure-resistant closed container became 3.8 MPa (G: gauge pressure), the expanded particles were produced in the same manner as the expanded particles B1. The physical properties of the obtained expanded particles B2 are shown in Table 1.

[0041] [Production of Expanded Particle B3] In the production of the expanded particles, except that carbon dioxide, which is a physical foaming agent, was injected into the pressure-resistant closed container so that the pressure in the pressure-resistant closed container became 2.1 MPa (G: gauge pressure), the expanded particles were produced in the same manner as the expanded particles B1. The physical properties of the obtained expanded particles B3 are shown in Table 1.

[0042] [Production of Expanded Particle Molded Body B3 (Reference Example 2)] An expanded particle molded body B3 (Reference Example 2) was obtained in the same manner as the production of the expanded particle molded body B1, except that in-mold molding was performed using the expanded particles B3. The physical properties of the obtained expanded particle molded body are shown in Table 2.

[0043] Next, expanded particles A were produced by the method shown below. [Production of Expanded Particle A1] By crushing the expanded particle molded body B1 obtained by the above method, expanded particles A1 were obtained. Note that this expanded particle molded body B1 is a plate-shaped molded body (length 250 mm, width 200 mm, thickness 50 mm), and its apparent density is 39 kg / m 3 and it was. More specifically, the molded body B1 was crushed as follows using a crushing device (manufactured by KBM: Mini In-A-Box). The crushing device includes a crusher (jaw crusher) for roughly crushing the molded body and a screen (punching metal: hole diameter 6 mm) for aligning the size of the roughly crushed molded body. The crushing device was operated and the molded body B1 was fed into the crushing device. The molded body B1 was roughly crushed by the crusher and dropped onto the punching metal installed below the crusher. Next, the crushed pieces remaining on the punching metal were pressed against the punching metal with the teeth of the rotating crusher to further crush the crushed pieces and pass them through the punching metal. At this time, a powder separator (gas cyclone) was operated to separate the powder generated during crushing and the like. The crushed particles that passed through the punching metal were collected and used as the foamed particles A1. The physical properties of the obtained foamed particles A1 were measured by the method described above. The results are shown in Table 1. The proportion of the polystyrene resin component in the composite resin constituting the foamed particles is 85% by mass.

[0044] <Production of Foamed Particles A2> In the production of the foamed particles A1, after collecting the crushed particles that passed through the punching metal, they were sieved with a sieve having a mesh size of 5.6 mm, and the crushed particles that passed through the sieve were collected. The crushed particles thus obtained were used as the foamed particles A2. The physical properties of the obtained foamed particles A2 are shown in Table 1.

[0045] <Production of Foamed Particles A3> In the production of the foamed particles A1, after collecting the crushed particles that passed through the punching metal, they were sieved with a sieve having a mesh size of 4.75 mm, and the crushed particles that passed through the sieve were collected. The crushed particles thus obtained were used as the foamed particles A3. The physical properties of the obtained foamed particles A3 are shown in Table 1.

[0046] <Production of Foamed Particles A4> Instead of the foamed particle molded body B1, foamed particles A4 were obtained in the same manner as the foamed particles A1, except that the foamed particle molded body B3 was used. The physical properties of the obtained foamed particles A4 are shown in Table 1.

[0047] Using the foamed particles A and the foamed particles B obtained by the above method, a foamed particle molded body was manufactured. <Examples 1 to 7> A foamed particle molded body was manufactured in the same manner as in the production method of Reference Example 1, except that the foamed particles A and the foamed particles B shown in Table 1 were used and the mixed foamed particles obtained by mixing the foamed particles A and the foamed particles B were filled into a mold so as to have the mixing ratio shown in Table 1. Regarding the foamed particle molded body, the "cooling time", "fusion rate", "dimension change rate of the foamed particle molded body with respect to the mold dimension", and "50% deformation compression stress of the foamed particle molded body" were evaluated by the above method. The evaluation results and the physical properties of each foamed particle molded body measured by the above method are shown in Table 2.

[0048]

Table 1

[0049]

Table 2

[0050] As described above, by mixing the foamed particles A and the foamed particles B having the closed cell ratio within the above range in the above mass ratio to form mixed foamed particles and molding these mixed foamed particles in a mold, it was possible to shorten the molding cycle when manufacturing the foamed particle molded body while suppressing the deterioration of the physical properties of the molded body. Further, even when the mixed foamed particles are composed of the recycled particles derived from the foamed particle molded body using the composite resin as the base resin as the foamed particles A, the decrease in the compression physical properties with respect to the foamed particle molded body molded using only the unformed foamed particles (non-recycled particles) is suppressed, and it was possible to obtain a foamed particle molded body having good mechanical physical properties. Therefore, it was shown that the present invention enables efficient recycling of the foamed particle molded body.

Claims

1. A method for manufacturing a foamed particle molded body by in-mold molding of composite resin foamed particles having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin, As the composite resin foamed particles, Composite resin foamed particles A having a closed cell ratio of 10% or more and 50% or less, and Using mixed foamed particles obtained by mixing composite resin foamed particles B having a closed cell ratio of 80% or more, A method for manufacturing a foamed particle molded body, wherein the mass ratio of the composite resin foamed particles A to the composite resin foamed particles B in the mixed foamed particles is 3:97 to 30:

70.

2. The bulk density of the composite resin foam particles B is 15 kg / m ３ or more and 180 kg / m ３ or less, and the ratio of the bulk density of the composite resin foam particles A to the bulk density of the composite resin foam particles B is 0.7 or more and 1.4 or less. The method for producing a foam particle molded body according to claim 1.

3. The average bulk density of the mixed foamed particles is 15 kg / m ３ or more and 180 kg / m ３ or less. The method for producing a foamed particle molded body according to claim 1 or 2.

4. The average particle diameter of the composite resin foamed particles B is 2 mm or more and 8 mm or less, The ratio of the average particle diameter of the composite resin foamed particles A to the average particle diameter of the composite resin foamed particles B is 0.7 or more and 1.4 or less. The method for manufacturing a foamed particle molded body according to any one of Claims 1 to 3.

5. The ratio a of the polystyrene-based resin component in the composite resin constituting the composite resin foamed particles A is 50% by mass or more and 90% by mass or less, The ratio b of the polystyrene-based resin component in the composite resin constituting the composite resin foamed particles B is 50% by mass or more and 90% by mass or less, The difference (a - b) between the ratio a and the ratio b is -5% or more and 5% or less. The method for manufacturing a foamed particle molded body according to any one of Claims 1 to 4.

6. The ratio of the insoluble matter when the composite resin foamed particles A are subjected to Soxhlet extraction with xylene is 0.1% by mass or more and 40% by mass or less. The method for manufacturing a foamed particle molded body according to Claims 1 to 5.

7. The composite resin foamed particles A are composite resin foamed particles obtained by crushing a foamed particle molded body having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin. The method for manufacturing a foamed particle molded body according to any one of Claims 1 to 6.

8. A foamed particle molded body obtained by in-mold molding of composite resin foamed particles having a composite resin containing a polystyrene-based resin component and a polyolefin-based resin component as a base resin, The foamed particle molded body is formed by in-mold molding of mixed foamed particles of composite resin foamed particles A having a closed cell ratio of 10% or more and 50% or less and composite resin foamed particles B having a closed cell ratio of 80% or more, The total area (S Ｂ of the composite resin foamed particles A with respect to the total area (S Ａ of the composite resin foamed particles B on the surface of the foamed particle molded body, and the ratio (S Ａ / S Ｂ ) has an average value of 0.005 or more and 0.3 or less, a foamed particle molded body.

9. The coefficient of variation of the ratio (S Ａ / S Ｂ ) is 40% or less. The expanded particle molded article according to claim 8.

10. In the foamed particle molded body, the weight ratio of the composite resin foamed particles A to the composite resin foamed particles B is 3:97 to 30:

70. The foamed particle molded body according to Claim 8 or 9.

11. The density of the foamed particle molded body is 15 kg / m ３ or more and 180 kg / m ３ or less. The foamed particle molded body according to any one of claims 8 to 10.

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