JP7716451B2 - Method for producing expanded bead molded body - Google Patents

Description

The present invention relates to a method for producing foamed bead moldings.

Polystyrene-based resin expanded bead molded articles, obtained by molding expanded polystyrene-based resin beads in a mold, are lightweight and have excellent compression properties, making them useful in a variety of fields, including automotive, construction, and logistics materials. To mold expanded beads in a mold, a mold is used that includes a first and second die, with a molding cavity corresponding to the shape of the desired molded article formed between the first and second dies. After filling the molding cavity of such a mold with expanded beads, steam is supplied to the first and second dies in a predetermined order to heat the expanded beads within the mold, thereby obtaining a molded article with the desired shape (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2007-237468

In recent years, there has been a desire to reduce the energy required to produce expanded bead moldings, and from this perspective, there has been a demand to reduce the amount of steam used during in-mold molding. However, reducing the amount of steam used during in-mold molding could reduce the degree of fusion between the expanded beads in the molding, resulting in a deterioration in the physical properties of the molding. There is also a risk that the surface condition of the molding could deteriorate, resulting in a poor surface appearance of the molding.

The present invention was made in light of this background, and aims to provide a method for producing expanded bead moldings that can reduce the amount of steam used during in-mold molding while producing expanded bead moldings with good surface and fusion conditions.

One aspect of the present invention is a method for producing a foamed bead molding according to the following items [1] to [5].

[1] A method for producing a foamed bead molded article, comprising: using a molding die having a first die and a second die configured to be able to form a molding space between the first die and the second die; and molding expanded polystyrene resin beads filled in the molding space to produce a foamed bead molded article,
The method for producing the expanded bead molded article includes a filling step of filling the molding space with expanded polystyrene resin beads, a mold heating step of supplying steam into the molding space from both the first mold side and the second mold side after the filling step, a first one-side heating step of supplying steam into the molding space from the first mold side after the mold heating step, a second one-side heating step of supplying steam into the molding space from the second mold side after the first one-side heating step, a double-side heating step of supplying steam into the molding space from both the first mold side and the second mold side after the second one-side heating step, and a retaining step of retaining the steam supplied in the double-side heating step within the molding space,
a total steam amount _Wd + _f +s+b of the steam amount Wd in the mold heating step, the steam amount _Wf in the first one-side heating step, the steam amount _Ws in the second one-side heating step, and the steam amount _Wb in the double-side heating step is 0.05 kg or more and 0.5 kg or less per 1 L of the volume of the molding space,
a ratio of the amount of steam _Wd in the mold heating step to a total amount Wf+ _s +b of the amount of steam _Wf in the first one-side heating step, the amount of steam _Ws in the second one-side heating step, and the amount of steam Wb in the double-side heating step is _Wd :Wf _{+s+b =} 5:95 to 40:60;
When a total Wf _{+s+b of} the steam amounts in the first one-side heating step, the second one-side heating step, and the double-side heating step is taken as 100 mass%, a ratio of the steam amount _Wf in the first one-side heating step is 15 mass% or more and 50 mass% or less, a ratio of the steam amount _Ws in the second one-side heating step is 15 mass% or more and 50 mass% or less, and a ratio of the steam amount _Wb in the double-side heating step is 10 mass% or more and 70 mass% or less,
a ratio W _b /W _f of the amount of steam W _b in the double-side heating step to the amount of steam W _f in the first one-side heating step is 0.3 or more;
The method for producing an expanded bead molding, wherein the holding time in the holding step is 5 seconds or more .

[2] The method for producing an expanded bead molding according to [1], wherein the amount of steam _Wf in the first one-way heating step is 0.01 kg or more and 0.2 kg or less per 1 L of the volume of the molding space.
[3] The method for producing an expanded bead molding according to [1] or [2], wherein the ratio _Wd / _Wf of the amount of steam _Wd in the mold heating step to the amount of steam _Wf in the first one-side heating step is 0.2 or more and 3 or less.

[4] The method for producing an expanded bead molding according to any one of [1] to [3], wherein the ratio W _s /W _f of the amount of steam W _s in the second one-way heating step to the amount of steam W _f in the first one-way heating step is 0.6 or more and 2 or less.
[5] The method for producing an expanded bead molding according to any one of [1] to [4], wherein the holding time in the holding step is 5 seconds or more and 50 seconds or less.

This aspect provides a method for producing expanded bead moldings that can reduce the amount of steam used during in-mold molding while producing expanded bead moldings with good surface and fusion conditions.

FIG. 1 is an explanatory diagram showing a flow chart of a method for producing a foamed bead molding. FIG. 2 is a partial cross-sectional view showing the main part of a molding die used for in-mold molding of expanded beads. Figure 3(a) is a schematic diagram showing steam heating in a mold heating process, Figure 3(b) is a schematic diagram showing steam heating in a first one-side heating process, Figure 3(c) is a schematic diagram showing steam heating in a second one-side heating process, and Figure 3(d) is a schematic diagram showing steam heating in a double-side heating process. FIG. 1 is a schematic diagram of steam heating in a holding step. FIG. 1 is a schematic diagram of steam heating in the discharging process.

In this specification, "expanded polystyrene resin beads" will be referred to as "expanded beads," and "expanded bead molded articles" will be referred to as "molded articles." Furthermore, when the expression "~" is used in this specification, it is intended to include the numerical or physical values written before and after it.

Expanded bead molded articles are produced, for example, using a molding die 1 (hereinafter also referred to as mold 1) shown in Figure 2. Mold 1 comprises a first die 2 and a second die 3. At least one of first die 2 and second die 3 is configured to be movable in the opening and closing direction of mold 1. Furthermore, first die 2 and second die 3 are configured to abut against each other when mold 1 is fully closed, forming a molding space 11 between them. Molding space 11 need only have a shape corresponding to the shape of the desired molded article.

The first mold 2 and the second mold 3 each have a hollow structure, and are configured so that the internal space of each mold is in communication with the molding space 11. For example, the first mold 2 and the second mold 3 may have multiple core vents (not shown) on the inner wall portions 23, 33 facing the molding space 11, which connect the internal space of each mold with the molding space 11. This allows steam supplied to the internal space of the first mold 2 and the second mold 3 to pass through through grooves formed in the core vents of the inner wall portions 23, 33 and reach the molding space 11. The through grooves are not shown in the figure.

Expanded bead moldings are produced by molding expanded beads in a mold. As shown in Figure 1, the method for producing expanded bead moldings includes a filling step P1, a mold heating step P2, a first one-side heating step P3, a second one-side heating step P4, a double-side heating step P5, and a holding step P6. The method for producing expanded bead moldings begins with a filling step P1, in which the molding space 11 is filled with expanded polystyrene resin beads. During filling step P1, the molding space 11 of the mold 1 is filled with expanded beads.

The foamed particles filled into the molding space 11 are not particularly limited as long as they have a polystyrene-based resin as the base resin, and known polystyrene-based resin foamed particles can be used. Here, the aforementioned polystyrene-based resin refers to a resin with a styrene-derived component content of 50 mol% or more.

The expanded polystyrene resin particles can be obtained, for example, by expanding expandable polystyrene resin particles containing a polystyrene resin as a base resin and an organic physical blowing agent, such as a hydrocarbon having 3 to 6 carbon atoms.
As the expanded beads, for example, expanded beads having a bulk density of 10 kg/m ³ to 200 kg/m ³ or less can be suitably used.

Expandable polystyrene-based resin particles can be produced by a conventionally known method, such as suspension polymerization. Furthermore, conventionally known methods can be used to expand the expandable polystyrene-based resin particles. For example, the expandable polystyrene-based resin particles can be expanded by supplying a heating medium such as steam to the expandable polystyrene-based resin particles and heating the expandable polystyrene-based resin particles. More specifically, the expandable polystyrene-based resin particles can be expanded by heating the expandable polystyrene-based resin particles with steam or the like using, for example, a cylindrical expansion machine equipped with a stirrer.

The polystyrene-based resin may be a homopolymer of a styrene-based monomer or a copolymer containing a styrene-based monomer. More specifically, the polystyrene-based resin may be polystyrene (GPPS), a styrene-acrylic acid copolymer containing styrene as the main component, a styrene-methyl acrylate copolymer, a styrene-ethyl acrylate copolymer, a styrene-butyl acrylate copolymer, a styrene-methacrylic acid copolymer, a styrene-methyl methacrylate copolymer, a styrene-ethyl methacrylate copolymer, a styrene-butyl methacrylate copolymer, a styrene-maleic anhydride copolymer, a styrene-acrylonitrile copolymer, a styrene-acrylonitrile-butadiene copolymer, a styrene-methylstyrene copolymer, a styrene-dimethylstyrene copolymer, a styrene-ethylstyrene copolymer, or a styrene-diethylstyrene copolymer.
From the viewpoint of being able to stably obtain expanded beads that have good in-mold moldability and can be used to mold expanded bead moldings with good mechanical properties, the content of components derived from styrene in the polystyrene-based resin is preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more.

Figure 3 illustrates the mold heating step P2, the first one-side heating step P3, the second one-side heating step P4, and the double-side heating step P5. While the details of the configuration of the mold 1 are omitted in Figure 3, the mold 1 may have the same configuration as that shown in Figure 2. In Figure 3, arrows indicate an example of the flow of steam within the mold. The same applies to Figures 4 and 5.
For the terms mold heating process, one-side heating process, and double-side heating process in this disclosure, reference can be made to the contents of the Collection of Well-Known and Commonly Used Techniques (Foam Molding) published by the Japan Patent Office (August 1982).

As shown in FIG. 3(a), in the mold heating process P2 performed after the filling process P1, steam is supplied to the molding space 11 from both the first mold 2 side and the second mold 3 side to heat the mold and the expanded beads within the molding space 11. In the mold heating process P2, for example, the steam supply valves 21, 31 and drain valves 22, 32 of each mold are all opened, and steam is supplied from the steam supply valves 21, 31. This allows the air within the molding space 11 to be evacuated and replaced with steam, while also heating the expanded beads within the molding space 11 and the molding mold. Furthermore, this mold heating process P2 efficiently preheats the expanded beads and molding mold for the double-sided heating process P5 described below, efficiently raising the temperatures of the expanded beads and molding mold. This prevents the amount of steam required in the first one-sided heating process P3 or the second one-sided heating process P4 described below from becoming excessively large, and allows the formation of a molded body to proceed with a relatively small amount of steam in the double-sided heating process P5.

After the mold heating step P2 is completed, the first one-side heating step P3 is performed, in which steam is supplied from the first mold 2 side to the molding space 11 to heat the expanded beads in the molding space 11. In the first one-side heating step P3, the first steam supply valve 21 of the first mold 2 and the second drain valve 32 of the second mold 3 are opened, and the other valves (specifically, the second steam supply valve 31 and the first drain valve 22) are closed while supplying steam from the first steam supply valve 21, thereby allowing steam to flow from the first mold 2 side to the second mold 3 side (see Figure 3(b)). This primarily heats the first mold 2 side of the molding mold 1, and also heats the expanded beads in the molding space 11, mainly on the first mold 2 side of the molding mold 1. This also allows the foamed beads and mold to be efficiently preheated for the double-sided heating step P5 described below, preventing the amount of steam required in the second one-sided heating step P4 described below from becoming excessively large, and allows the formation of a molded body to proceed in the double-sided heating step P5 with a relatively small amount of steam.

After the first one-side heating step P3 is completed, the second one-side heating step P4 is performed, in which steam is supplied from the second mold 3 side to the molding space 11 to heat the expanded beads within the molding space 11. In the second one-side heating step P4, the second steam supply valve 31 of the second mold 3 and the first drain valve 22 of the first mold 2 are opened, and the other valves (specifically, the first steam supply valve 21 and the second drain valve 32) are closed. Steam is supplied from the second steam supply valve 31, allowing steam to flow from the second mold 3 side to the first mold 2 side (see Figure 3(c)). This primarily heats the second mold 3 side of the molding mold 1, and heats the expanded beads within the molding space 11, primarily around the second mold 3 side of the molding mold 1. This also allows the expanded beads and molding mold to be efficiently preheated for the double-side heating step P5, described below, allowing the formation of a molded body to proceed with a relatively small amount of steam in the double-side heating step P5.

After the second one-sided heating process P4 is completed, the double-sided heating process P5 is performed, in which steam is supplied to the molding space 11 from both the first mold 2 side and the second mold 3 side to heat the expanded beads within the molding space 11. In the double-sided heating process P5, the first steam supply valve 21 of the first mold 2 and the second steam supply valve 31 of the second mold 3 are opened, and the first drain valve 22 and the second drain valve 32 of each mold are closed while supplying steam, thereby increasing the pressure within the molding space 11 (see Figure 3(d)). This allows the expanded beads within the molding space 11 to be heated while increasing the pressure within the molding space 11. As a result, the expanded beads within the molding space 11 are fused together, filling the gaps between the expanded beads and forming the surface of the molded body.

After the double-sided heating step P5 is completed, a holding step P6 is performed, as shown in Figure 1, in which the steam supplied in the double-sided heating step P5 is held within the mold 1. In the in-mold molding method for producing molded articles, the heating performed up to the holding step P6 causes the foamed beads in the molding space 11 to undergo secondary expansion and fuse together, forming a molded article in which the foamed beads are fused together. In the holding step P6, the steam supply valves 21, 31 and drain valves 22, 32 of each mold are all closed, which slows the decrease in the temperature and pressure in the molding space 11 that was increased in the double-sided heating step P5. This allows the temperature and pressure in the molding space 11 to be maintained high for a certain period of time without the need to supply new steam (see Figure 4). This further heats the foamed beads in the molding space 11 without the need for new steam. In this way, by carrying out steps P2 to P6 in order and supplying steam in each step in a specific relationship as described below, the fusion of the expanded beads within the molding space 11 can be further promoted, filling the gaps between the expanded beads and improving the fusion and surface condition of the molded product. Note that, as long as the temperature and pressure within the molding space after the double-sided heating step can be maintained high for a certain period of time and the intended purpose of the present invention can be achieved, some of the steam within the molding space may be vented to the outside of the molding space during the holding step P6.

In the manufacturing method of the present disclosure, the expanded bead molding is manufactured by controlling the amount of steam _Wd in the mold heating step P2, the amount of steam _Wf in the first one-side heating step P3, the amount of steam _Ws in the second one-side heating step P4, and the amount of steam _Wb in the double-side heating step P5. The relationship between the amounts of steam in each step will be described below.

In the manufacturing method, the total steam amount _Wd + _f +s+b, which is the amount of steam Wd in the mold heating step P2, the amount of steam Wf in the first one-side heating step P3, the amount of steam _Ws in the second one-side heating step P4 _, and the amount of steam _Wb in the double-side heating step P5, is set to 0.05 kg or more and 0.5 kg or less per 1 L of the molding space 11 volume. In the manufacturing method of the present disclosure, a foamed bead molded body with a good surface condition and fusion state can be obtained with a relatively small total steam amount within the above range. If the total steam amount Wd _+f+s+b per 1 L of the molding space 11 volume is too small, the fusion state and surface condition of the molded body may deteriorate. On the other hand, if the total steam amount Wd _+f+s+b per 1 L of the molding space 11 volume is too large, the amount of steam used to obtain the molded body increases, making it impossible to reduce energy consumption. From this viewpoint, the total amount of steam W _d+f+s+b per liter of the volume of the molding space 11 is preferably 0.06 kg or more and 0.4 kg or less.

In the present disclosure, the amount of steam in each step generally refers to the amount of steam supplied to the interior space of the casting mold in each step from a steam supply valve provided for supplying steam to the interior space of the casting mold. This amount of steam can be determined, for example, by attaching a flow meter configured to be able to measure the cumulative flow rate of steam to a steam pipe connected to the steam supply valve and measuring the cumulative flow rate of steam supplied in each step.
In in-mold molding, the amount of steam required to obtain a good molded body is affected by the size of the mold. Furthermore, since there is a correlation between the size of the mold and the volume of the molding space, in this disclosure, the amount of steam supplied in each process is specified as the amount of steam per 1 L of the volume of the molding space 11. This makes it easier to determine the appropriate amount of steam required to obtain a good molded body while reducing the influence of the size of the mold used (the size of the molded body to be obtained).
On the other hand, the volume of the molding space 11 is preferably approximately 5 L or more and 100 L or less, more preferably 10 L or more and 90 L or less, and even more preferably 15 L or more and 80 L or less.
The volume of molding space 11 can be determined, for example, from the dimensions of the inner wall of mold 1 used to form molding space 11, by calculating the volume of the space enclosed by the inner wall of each mold when the mold is closed. Furthermore, if the mold has multiple molding spaces and is capable of molding multiple molded bodies in a single molding run (specifically, for example, a multi-cavity mold), the volume of the molding space is the sum of the volumes of the multiple molding spaces. The dimensions of the inner wall may be measured or calculated from drawings of the mold, etc.

The ratio of the steam amount _Wd in the mold heating step P2 to the total amount Wf+ _s +b of the steam amount _Wf in the first one-side heating step P3, the steam amount _Ws in the second one-side heating step P4, and the steam amount Wb in the double-side heating step P5 is _Wd :Wf _+s+b = 5:95 to 40:60. In other words, when the total steam amount Wd+ _{f +s+b of the steam amounts Wd, Wf, Ws , and Wb} is taken as 100% by mass, the proportion of the steam amount _Wd is 5% by mass or more and 40% by mass or less. By controlling the steam amount in this manner, a relatively large amount of steam _Wd in the mold heating step P2 can be ensured. This allows the molding space 11 to be sufficiently heated at the beginning of molding. If the ratio of the steam amount _{Wd to the total steam amount Wd+f+s+b} is 100% by mass, the air in the molding space ₁₁ will not be sufficiently exhausted, making it difficult to sufficiently heat the molding space 11 in the mold heating step P2 and subsequent steps, which may result in a deterioration in the fusion state and surface condition of the resulting molded body. Furthermore, the molding space 11 may not be heated efficiently, which may increase the overall amount of steam used. On the other hand, if the ratio of the steam amount _Wd to the total steam amount Wd _+f+s+b is 100% by mass, the amount of steam available for other steps under conditions of reduced overall steam use will be reduced, which may result in a decrease in the fusion rate of the molded body or a deterioration in the surface condition of the molded body. From this viewpoint, the ratio of the amount of steam _Wd to the total amount _{Wf +s+} b of the amount of steam _Wf , the amount of steam _Ws, and the amount of steam Wb is preferably _Wd :Wf _+s+b = 10:90 to 40:60, and more preferably _Wd :Wf _+s+b = 15:85 to 35:65.

When the sum Wf _+s+b of the steam amounts in the first one-side heating step P3, the second one-side heating step P4, and the double-side heating step P5 is taken as 100% by mass, the proportion of the steam amount _Wf in the first one-side heating step P3 is 15% by mass or more and 50% by mass or less, the proportion of the steam amount _Ws in the second one-side heating step P4 is 15% by mass or more and 50% by mass or less, and the proportion of the steam amount _Wb in the double-side heating step P5 is 10% by mass or more and 70% by mass or less. Furthermore, the ratio _Wb / _Wf of the steam amount _Wb in the double-side heating step P5 to the steam amount Wf in the first one-side heating step _P3 is 0.3 or more. By controlling the amount of steam in this manner, under conditions where the total amount of steam used is reduced, a predetermined amount of steam is used in the double-sided heating step P5, and steam is supplied so as not to excessively unbalanced between the amount of steam in the first one-sided heating step P3 and the amount of steam in the second one-sided heating step P4. This allows the molding space 11 to be preheated evenly, and then the expanded beads in the molding space 11 to be sufficiently heated by main heating. Furthermore, by setting the ratio of the amount of steam in the double-sided heating step P5 to the amount of steam in the first one-sided heating step P3 to be equal to or greater than a predetermined value, the expanded beads in the molding space are sufficiently heated and a sufficiently high pressure can be created in the molding space at the end of the double-sided heating step P5. By performing the holding step P6 after such a double-sided heating step P5, the temperature and pressure in the molding space after the double-sided heating step P5 can be maintained at a sufficiently high level for a long period of time, and the foamed particles can be sufficiently fused together without the need to supply new steam, while filling the gaps between the foamed particles.This reduces the amount of steam used during molding in the mold, and allows for the production of a molded product with good fusion and surface condition.

If the ratio of the steam amount _Wf in the first one-side heating step P3 is excessively low, the temperature in the molding space 11 is likely to be uneven, which may result in some areas of poor fusion between the expanded beads. If the ratio of the steam amount _Wf in the first one-side heating step P3 is excessively high, the difference between the steam amount _Wf in the first one-side heating step P3 and the steam amount in the second one-side heating step P4 will be large, which may result in uneven preheating in the molding space 11 before the double-side heating step P5. This may result in a decrease in the fusion rate of the molded body or a deterioration in the surface condition of the molded body. From this perspective, as described above, when the total steam amount Wf+s+b of the steam amounts in the first one-side heating step P3, the second one-side heating step P4, and the double-side heating step P5 is taken as 100% by mass, the ratio of the steam amount _Wf in the first one-side heating step P3 is set to 15 _% by mass or more and 50% by mass or less.
For example, the aforementioned Patent Document 1 describes that, while steam is supplied for a predetermined time or longer in the first one-sided heating step, which has the highest steam flow rate per unit time and requires the most steam, the total amount of steam used can be reduced by establishing a specific relationship between the steam supply time in the one-sided heating step and the holding time in the holding step and shortening the steam supply time in the one-sided heating step. However, it has been found that if the total amount of steam used is further reduced, even if the holding step is performed, there is a risk of a decrease in the fusion rate of the molded body and a deterioration in the surface condition of the molded body, as described above. In the present disclosure, by supplying steam in each step and performing a holding step so that the amount of steam supplied in each step satisfies a predetermined relationship, it is possible to mold a molded body with a good surface condition and fusion state while reducing the amount of steam used to produce the molded body.
The total amount of steam W supplied to the mold in the mold heating step, the first one-side heating step, the second one-side heating step, and the double-side heating step (i.e., the total amount of steam W) is preferably 8 kg or less, more preferably 7 kg or less. The total amount of steam W is preferably 2 kg or more, more preferably 3 kg or more, and even more preferably 4 kg or more.

If the ratio of the steam amount _Ws in the second one-side heating step P4 is excessively low, the temperature in the molding space 11 is likely to become uneven, which may result in some areas of poor fusion between the expanded beads. If the ratio of the steam amount _Ws in the second one-side heating step P4 is excessively high, the difference between the steam amount _Wf in the first one-side heating step P3 and the steam amount in the second one-side heating step P4 will become large, which may result in uneven preheating in the molding space 11 before the double-side heating step P5. This may result in a decrease in the fusion rate of the molded body or a deterioration in the surface condition of the molded body. From this perspective, as described above, when the total steam amount Wf+s+b of the steam amounts in the first one-side heating step P3, the second one-side heating step P4, and the double-side heating step P5 is taken as 100% by mass, the ratio of the steam amount _Ws in the second one-side heating step P4 is set to 15% by _mass or more and 50% by mass or less.

If the proportion of the steam amount _Wb in the double-side heating step P5 is excessively low, the pressure in the molding space 11 cannot be sufficiently increased and the molding space 11 cannot be sufficiently heated, which may result in a decrease in the fusion rate of the molded body and a deterioration in the surface condition of the molded body. If the proportion of the steam amount _Wb in the double-side heating step P5 is excessively high, the amount of steam in other steps may be insufficient under conditions where the overall amount of steam used is reduced. If the amount of steam in the first one-side heating step P3 or the second one-side heating step P4 is insufficient, the temperature in the molding space 11 is likely to become uneven, which may result in partial areas where the foamed beads are poorly fused together. Furthermore, if the amount of steam in the mold heating step P2 is insufficient, the air in the molding space 11 is not sufficiently exhausted, making it difficult to sufficiently heat the molding space 11 in the subsequent steps, which may result in a deterioration in the fusion condition and surface condition of the molded body obtained under conditions where the overall amount of steam used is reduced. From this viewpoint, as described above, when the total amount of steam Wf _+s+b of the first one-side heating step P3, the second one-side heating step P4, and the double-side heating step P5 is taken as 100 mass%, the proportion of the amount of steam _Wb in the double-side heating step P5 is set to 10 mass% or more and 70 mass% or less.

The ratio _Wb / _Wf of the amount of steam Wb in the double-side heating step _P5 to the amount of steam _Wf in the first one-side heating step P3 is preferably 0.4 or more, more preferably 0.5 or more, from the viewpoint of more stably obtaining a molded product with a good surface condition. Furthermore, from the viewpoint of more stably obtaining a molded product with a good fusion state, the ratio _Wb / _Wf is preferably 4 or less, more preferably 3 or less, and even more preferably 2 or less.

Furthermore, the ratio _Wd / _Wf of the amount of steam _Wd in the mold heating step P2 to the amount of steam _Wf in the first one-side heating step P3 is preferably 0.2 or more and 3 or less. In this case, while reducing the amount of steam, it becomes easier to achieve a state in which the molding space 11 is sufficiently heated in the early stages of molding, making it easier to prevent deterioration in surface appearance and deterioration in the fusion state. As a result, it becomes easier to obtain a molded body with good surface appearance and fusion properties. From this perspective, _Wd / _Wf is more preferably 0.3 or more and 2 or less, and even more preferably 0.4 or more and 2 or less.

Furthermore, the ratio _Ws / _Wf of the amount of steam _Ws in the second one-side heating step P4 to the amount of steam _Wf in the first one-side heating step P3 is preferably 0.6 or more and 2 or less. In this case, the amount of steam used in in-mold molding is reduced, while the molding space 11 is easily preheated evenly before the main heating in the double-side heating step P5, and molded bodies with good surface appearance and fusion state can be consistently obtained. From this perspective, _Ws / _Wf is more preferably 0.7 or more and 2 or less, and even more preferably 0.8 or more and 2 or less.

The preferred amount of steam and steam conditions for each step when carrying out the manufacturing method of the present disclosure are described below. The amount of steam for each step can be controlled, for example, by adjusting the steam pressure and steam supply time for each step. For example, the amount of steam can be increased by increasing the steam pressure or lengthening the supply time. On the other hand, the amount of steam can be reduced by decreasing the steam pressure or shortening the supply time.

The amount of steam _Wd in the mold heating step P2 is preferably 0.005 kg or more and 0.2 kg or less, and more preferably 0.01 kg or more and 0.1 kg or less, per 1 L of the volume of the molding space 11. In this case, the pressure Pd of the steam supplied to the first mold 2 and the second mold 3 is preferably 0.02 MPa (G) or more and 1 MPa (G) or less, and more preferably 0.03 MPa (G) or more and 0.06 MPa (G) or less. In addition, in the mold heating step P2, steam at the aforementioned pressure is preferably supplied for, for example, 1 to 5 seconds. In this specification, the "(G)" attached to the unit of pressure means that the pressure is gauge pressure.

The amount of steam _Wf in the first one-side heating step P3 is preferably 0.01 kg or more and 0.2 kg or less per 1 L of the volume of the molding space 11. In this case, the amount of steam used in the first one-side heating step P3 can be reduced and the steam ratio in other steps can be increased while stably heating the molding space 11. From the viewpoint of being able to sufficiently heat the first one-side heating step while further increasing the steam ratio in other steps, the amount of steam _Wf in the first one-side heating step P3 per 1 L of the volume of the molding space 11 is more preferably 0.015 kg or more and 0.1 kg or less.

In the first one-side heating step P3, the steam pressure _Pf of the steam supplied to the first mold 2 is preferably 0.02 MPa (G) or more and 1 MPa (G) or less, and more preferably 0.03 MPa (G) or more and 0.8 MPa (G) or less. In the first one-side heating step P3, it is preferable to supply steam at the above-mentioned pressure for, for example, 1 to 10 seconds.

The amount of steam _Ws in the second one-side heating step P4 is preferably 0.01 kg or more and 0.2 kg or less, and more preferably 0.02 kg or more and 0.1 kg or less, per 1 L of the volume of the molding space 11. In this case, the steam pressure _Ps of the steam supplied to the second mold 3 is preferably 0.02 MPa(G) or more and 1 MPa(G) or less, and more preferably 0.03 MPa(G) or more and 0.8 MPa(G) or less. In the second one-side heating step P4, steam at the aforementioned pressure is preferably supplied for, for example, 1 to 10 seconds.

The amount of steam _Wb in the double-side heating step P5 is preferably 0.01 kg or more and 0.2 kg or less, and more preferably 0.02 kg or more and 0.1 kg or less, per 1 L of the volume of the molding space 11. In this case, the steam pressure _Pb of the steam supplied to the first mold 2 and the second mold 3 is preferably 0.02 MPa(G) or more and 1 MPa(G) or less, and more preferably 0.03 MPa(G) or more and 0.8 MPa(G) or less. In the second one-side heating step P4, steam at the aforementioned pressure is preferably supplied for, for example, 5 to 20 seconds.

Furthermore, the holding time t _h in the holding step P6 is preferably 5 seconds or more and 50 seconds or less. In this case, the fusion of the expanded beads within the molding space 11 can be sufficiently promoted and the gaps between the expanded beads can be sufficiently filled while preventing the molding cycle from becoming excessively long. As a result, molded articles with good fusion and surface conditions can be consistently obtained. Note that if the holding step P6 is not performed, the fusion rate of the molded article may decrease or the surface condition of the molded article may deteriorate, even if the amount of steam supplied in each step satisfies the specified relationship.
Furthermore, from the viewpoint of improving the molding cycle and stably obtaining molded bodies with good fusion and surface conditions, the ratio th/(td _+tf +ts+tb) of the holding time th in the holding step P6 to the sum of the steam supply time _td in the mold heating step P2, the steam supply time _tf in the first one-side heating step _P3 , the steam supply time ts in the second one-side heating step P4, and the steam supply _{time tb in the} double _- side heating step _P5 is preferably 0.1 or more and 3 or less, and more preferably 0.2 or more and 2 or less.

After the holding step P6 is completed, the discharge step P7 can be carried out, as shown in Figure 1, to discharge the steam from the molding space 11. In the discharge step P7, the steam supply valves 21 and 31 of each mold are closed, and the drain valves 22 and 32 of each mold are opened, thereby discharging the steam from the molding space 11 through the drain valves 22 and 32 and depressurizing (see Figure 5). Furthermore, after the discharge step P7 is completed, a cooling step P8 can be carried out, if necessary, to cool the molded body in the forming mold 1. After the shape of the molded body has been stabilized to a certain extent in the forming mold 1, the forming mold 1 can be opened to obtain the molded body.

In the manufacturing method described above, the amount, ratio, and distribution of steam used in the mold heating step P2, first one-side heating step P3, second one-side heating step P4, and double-side heating step P5 are adjusted within specific ranges while the holding step is carried out. This allows for a sufficient reduction in the amount of steam used during in-mold molding, while still producing foamed bead moldings with good fusion and surface conditions.

(Example 1-1)
An example of a method for producing an expanded bead molding is described below. In this example, expanded beads having a styrene-butyl acrylate copolymer as the base resin are used to produce a box-shaped molding having a length of 410 mm, a width of 410 mm, a height of 410 mm, and side and bottom wall thicknesses of 20 mm.

The specific configuration of the mold 1 used in this example will be described with reference to Figure 2. Note that in Figure 2, the shape of the molding space has been omitted for ease of drawing. As shown in Figure 2, the mold 1 has a first mold 2 and a second mold 3. The first mold 2 is fixed, and the second mold 3 is configured to be able to move relative to the first mold 2 in the opening and closing direction of the mold 1. A molding space 11 is provided between the first mold 2 and the second mold 3, which is capable of molding a molded body of the shape described above.

The first mold 2 has a hollow structure. The first mold 2 also has a first steam supply valve 21 configured to supply steam from the outside of the molding die 1 to the internal space of the first mold 2, and a first drain valve 22 configured to allow steam to be discharged from the internal space of the first mold 2 to the outside of the molding die 1. Although not shown in the figure, the inner wall portion 23 of the first mold 2 facing the molding space 11 is provided with multiple core vents that connect the internal space of the first mold 2 and the molding space 11.

A first watering nozzle 24 configured to spray water onto the inner wall portion 23 is provided in the internal space of the first mold 2.

The inner wall 23 of the first mold 2 is fitted with a surface pressure gauge (not shown) that is capable of measuring the pressure (i.e., surface pressure) applied to the inner wall 23. The surface pressure gauge is located near the center of the inner wall 23 when viewing the first mold 2 from the second mold 3 along the mold clamping direction. More specifically, the surface pressure gauge is located at a position on the inner wall 23 that corresponds to the center of a surface of the molded body that is 410 mm long and 410 mm wide. The expanded beads heated during the in-mold molding process undergo secondary expansion and fuse together to form the molded body. Therefore, by providing the surface pressure gauge on the inner wall 33, the progress of in-mold molding can be easily monitored through changes in surface pressure associated with the secondary expansion of the expanded beads. The surface pressure gauge may also be attached to the inner wall 33 of the second mold 3.

Although not shown in the figure, a flow meter (Spirax Sarco TVA steam flow meter) capable of measuring the cumulative flow rate of steam is attached to the steam pipe connected to the first steam supply valve 21 near the supply valve 21. This makes it possible to measure the cumulative flow rate of steam supplied from the first steam supply valve 21 to the first mold 2.

The second mold 3 also has a hollow structure, similar to the first mold 2. The second mold 3 also has a second steam supply valve 31 configured to be able to supply steam from the outside of the molding mold 1 to the internal space of the second mold 3, and a second drain valve 32 configured to be able to discharge steam from the internal space of the second mold 3 to the outside of the molding mold 1. Although not shown in the figure, the inner wall portion 33 of the second mold 3 facing the molding space 11 is provided with multiple core vents that connect the internal space of the second mold 3 to the molding space 11.

A second watering nozzle 34 is provided in the internal space of the second mold 3, and is configured to spray water onto the inner wall portion 33.

Although not shown in the figure, a flow meter (Spirax Sarco TVA steam flow meter) capable of measuring the cumulative flow rate of steam is attached near the steam pipe connected to the second steam supply valve 31. This allows the amount and pressure of steam supplied from the second steam supply valve 31 to the second mold 3 to be measured. Specifically, the molding machine used was a "VS1300-DeCo" manufactured by Daisen Kogyo Co., Ltd., which was used to control the pressure and supply time of the steam supplied in each process. The mold was capable of molding four of the box-shaped molded bodies (volume approximately 16 L) in one molding run, and the volume (total volume) of its molding space was 64 L. The amount of steam supplied in each process was calculated by measuring the cumulative flow rate of steam supplied in each process using the flow meter attached to the steam pipe.

In this example, the in-mold molding of expanded beads is carried out according to the procedure shown in Figure 1. That is, first, a filling step P1 is carried out in which the molding space 11 of the molding die 1 is filled with expanded beads. The expanded beads used in this example are expanded polystyrene-based resin beads whose base resin is a styrene-butyl acrylate copolymer. Specifically, the expanded beads are obtained by expanding expandable polystyrene-based resin beads whose base resin is a styrene-butyl acrylate copolymer containing 0.5% by mass of a component derived from butyl acrylate. The bulk density of the expanded beads is 25 kg/ ^m3 . The bulk density of the expanded beads can be measured by the following method.

First, the expanded particles are filled into a measuring cylinder, and the bottom of the measuring cylinder is lightly tapped against the floor several times to stabilize the filling height of the expanded particles in the measuring cylinder. The bulk volume (unit: L) of the expanded particles is then read from the scale on the measuring cylinder. The mass (unit: g) of the expanded particles in the measuring cylinder is then divided by the bulk volume, and the resulting value is converted into a unit to obtain the bulk density (unit: kg/ ^m3 ) of the expanded particles.

After the filling process P1 is completed, the mold heating process P2 is carried out, in which steam is supplied to the molding space 11 from both the first mold 2 side and the second mold 3 side to heat the expanded beads within the molding space 11. In the mold heating process P2 of this example, with the first steam supply valve 21, first drain valve 22, second steam supply valve 31, and second drain valve 32 shown in FIG. 2 open, steam is supplied to the first mold 2 from the first steam supply valve 21 and steam is supplied to the second mold 3 from the second steam supply valve 31. This replaces the air that has been stagnating in the internal spaces of the first mold 2 and second mold 3 with steam, and heats the molding mold 1 and the expanded beads within the molding space 11.

After the mold heating step P2 is completed, as shown in FIG. 1, a first one-side heating step P3 is performed, in which steam is supplied from the first mold 2 side to the molding space 11 to heat the expanded beads within the molding space 11. In this example, the first steam supply valve 21 and the second drain valve 32 shown in FIG. 2 are opened, and the other valves are closed. In this state, steam is supplied from the first steam supply valve 21 to the first mold 2, thereby introducing the steam into the internal space of the first mold 2. The steam introduced into the internal space of the first mold 2 flows into the molding space 11 via a core vent provided in the inner wall portion 23 of the first mold 2 (see FIG. 3(b)). This heats the expanded beads within the molding space 11. The steam within the molding space 11 is then guided into the internal space of the second mold 3 via a core vent provided in the inner wall portion 33 of the second mold 3 and discharged to the outside of the molding mold 1 through the second drain valve 32.

After the first one-side heating step P3 is completed, as shown in FIG. 1, the second one-side heating step P4 is carried out, in which steam is supplied from the second mold 3 side to the molding space 11 to heat the expanded beads in the molding space 11. In this example, the second one-side heating step P4 involves opening the second steam supply valve 31 and the first drain valve 22 shown in FIG. 2, while closing the other valves. In this state, steam is supplied from the second steam supply valve 31 to the second mold 3, thereby introducing the steam into the internal space of the second mold 3. The steam introduced into the internal space of the second mold 3 flows into the molding space 11 via a core vent provided in the inner wall 33 of the second mold 3 (see FIG. 3(c)). This heats the expanded beads in the molding space 11. The steam in the molding space 11 is then guided into the internal space of the first mold 2 via a core vent provided in the inner wall 23 of the first mold 2, and then discharged to the outside of the molding mold 1 through the first drain valve 22.

After the second one-side heating step P4 is completed, as shown in FIG. 1, a double-side heating step P5 is carried out in which steam is supplied to the molding space 11 from both the first mold 2 side and the second mold 3 side to heat the expanded beads within the molding space 11. In this example, in the double-side heating step P5, the first steam supply valve 21 and the second steam supply valve 31 shown in FIG. 2 are opened, while the other valves 22 and 32 are closed. In this state, steam is supplied from the first steam supply valve 21 to the first mold 2 and from the second steam supply valve 31 to the second mold 3, thereby introducing steam into the internal spaces of the first mold 2 and the second mold 3. The steam introduced into the internal spaces of these molds flows into the molding space 11 through core vents provided in the inner wall portions 23 and 33 (see FIG. 3(d)). This increases the pressure within the molding space 11 and heats the expanded beads.

After the double-sided heating step P5 is completed, as shown in Figure 1, a holding step P6 is carried out to hold the steam supplied to the first mold 2 and the second mold 3 in the double-sided heating step P5 within the molding die 1. In this example, during the holding step P6, all valves 21, 22, 31, and 32 shown in Figure 2 are closed to hold the steam within the molding die 1. This allows the pressure applied to the molding surface of the molding die 1 to decrease gradually, and the expanded beads in the molding space 11 can be heated under high pressure for a long period of time without supplying steam to the molding die 1 (see Figure 4).

After the holding step P6 is completed, as shown in Figure 1, the discharge step P7 is performed to discharge the steam from the molding space 11. In this example, in the discharge step P7, the steam supply valves 21 and 31 of each mold are closed, and the drain valves 22 and 32 of each mold are opened. This allows the steam from the molding space 11 to be discharged through the drain valves 22 and 32, thereby depressurizing the molding space 11 (see Figure 5).

After the ejection process P7 is completed, the cooling process P8 is carried out to cool the molded body in the mold 1, as shown in Figure 1. In this example, the cooling process P8 includes a water cooling process in which water is sprayed onto the inner wall portions 23, 33 from the first water spray nozzle 24 and the second water spray nozzle 34 shown in Figure 2, and a vacuum cooling process in which the internal space of the first mold 2 and the internal space of the second mold 3 are depressurized after the water cooling process is completed.

In the water cooling process, water is sprayed onto the inner walls 23, 33 from the first water spray nozzle 24 and the second water spray nozzle 34. This lowers the temperature of the inner walls 23, 33 and cools the molded body in contact with the inner walls 23, 33.

In the vacuum cooling process, the vacuum valve (not shown) on the mold 1 is opened, and the other valves are closed. In this state, the pressure inside the mold 1 is reduced by forcibly evacuating the gas inside the mold 1 through the vacuum valve using a vacuum pump. When the pressure inside the mold 1 is reduced, the water sprayed inside the mold 1 during the water cooling process becomes more likely to evaporate. As the water evaporates, heat inside the mold 1 is taken away as latent heat of evaporation, so by reducing the pressure inside the mold 1, the mold 1 and the molded body can be cooled more quickly. After the vacuum cooling process is completed, the vacuum state inside the mold 1 is released by opening the exhaust valve (not shown) on the mold 1.

After the cooling step P8 is completed, the mold 1 can be opened to obtain the molded body.

In this example, the steam pressures _Pd , Pf, Ps, Pb, the steam amounts Wd, _Wf , _Ws , _Wb , and the steam supply times _td , _{tf, ts ,} and _tb in the mold heating step _P2 , the first one- _side heating step P3, the _second one-side heating step P4, and the double-side heating step _P5 were adjusted as shown in Table 1. The holding time _th in the holding step was also adjusted as shown in Table 1. By adjusting the molding conditions in this manner, an expanded bead molding was produced.

The fusion rate, surface condition, number of voids, and molding cycle of the molded bodies obtained as described above were examined as follows. Note that these evaluations were performed on molded bodies molded in the molding space located farthest from the first steam supply valve 21 and the second steam supply valve 31.

Fusion rate: First, the molded body was folded into roughly equal parts and broken. To facilitate the breaking of the molded body, slits may be made in the molded body beforehand. Then, 100 or more expanded beads exposed on the fracture surface of the molded body were randomly selected and visually observed to determine whether the expanded beads had broken internally (i.e., material failure) or at the interface between the expanded beads (i.e., interfacial failure). The ratio of the total number of expanded beads with material failure to the total number of visually observed expanded beads, expressed as a percentage, was taken as the fusion rate (unit: %) of the molded body. The results are shown in Table 1.
The fusion rate of the molded article is preferably 40% or more, which can be considered to be an expanded bead molded article in which the expanded beads are fused together.

Number of voids For a box-shaped foamed bead molding, a 100 mm x 100 mm square was drawn in the center of the outer surface of one of the side walls facing each other in the left-right direction of the molding mold. Then, the number of voids present within the square, i.e., voids with a size of 0.5 ^mm2 or more when viewed from above among the gaps formed between the foamed beads, was counted. The number of measured voids was divided by the measured area and converted to a unit to calculate the number of voids per unit area ( ^cm2 ). The results are shown in Table 1. The fewer the number of voids per unit area, the better the surface condition of the molded body.

Molding cycle: The time required from the start of mold clamping to the release of the mold during in-mold molding was measured. The mold was opened when the pressure (surface pressure) applied to the inner wall of the mold in the cooling step P8 reached a gauge pressure of 0.02 MPa (G).

(Example 1-2)
The molding conditions were changed as shown in Table 1, and the rest were the same as in Example 1-1.

(Examples 1-3)
The molding conditions were changed as shown in Table 1, and the rest were the same as in Example 1-1.

(Comparative Example 1-1)
The molding conditions were changed as shown in Table 1, and the rest were the same as in Example 1-1.

(Comparative Example 1-2)
The molding conditions were changed as shown in Table 1, and the rest were the same as in Example 1-1.

(Comparative Examples 1-3)
The molding conditions were changed as shown in Table 1, and the rest were the same as in Example 1-1.

(Comparative Examples 1-4)
The molding conditions were changed as shown in Table 1, and the rest were the same as in Example 1-1.

As can be seen from Table 1, the manufacturing conditions of Examples 1-1 to 1-3 produce molded articles with good fusion and surface conditions while reducing the total amount of steam used during in-mold molding compared to the manufacturing conditions of Comparative Example 1-1, which does not include a holding step. This is because the manufacturing methods of Examples 1-1 to 1-3 include a mold heating step, a first one-side heating step, a second one-side heating step, a double-side heating step, and a holding step, and the total steam amount Wd _+f+s+b is set to 0.05 kg or more and 0.5 kg or less per 1 L of the volume of the molding space 11, while the steam amounts in the mold heating step P2, the first one-side heating step P3, the second one-side heating step P4, and the double-side heating step P5 have a specific relationship. Specifically, this is because the _{ratio Wd} :Wf _+s+b = 5:95 to 40:60 is satisfied, and when the total amount of steam, Wf _+s+b , is 100% by mass, the amount of steam _Wf is 15% by mass or more and 50% by mass or less, the amount of steam _Ws is 15% by mass or more and 50% by mass or less, the amount of steam _Wb is 10% by mass or more and 70% by mass or less, and further _Wb / _Wf is 0.3 or more.

Comparative Example 1-1 is an example in which in-mold molding was performed under conditions that allowed for the production of molded articles with good fusion and surface conditions without performing a holding step. In Comparative Example 1-1, molded articles with good fusion and surface conditions similar to those of Examples 1-1 to 1-3 were obtained, but the amount of steam used was greater. When the total steam amount of Comparative Example 1-1 was taken as 100%, the reduction rates of the total steam amount of Example 1-1, Example 1-2, and Example 1-3 relative to the total steam amount of Comparative Example 1-1 were 36%, 41%, and 33%, respectively.
The molding cycle of Comparative Example 1-1 was 185 seconds, while the molding cycle of Example 1-1 was 184 seconds, so that both had equivalent molding cycles. The molding cycles of Examples 1-2 and 1-3 were 176 seconds and 187 seconds, respectively.

In Comparative Example 1-2, the holding step was not performed and the total amount of steam was reduced to the same level as in Example 1-1. In this case, the surface condition of the molded body deteriorated.

In Comparative Example 1-3, the total amount of steam was reduced to the same extent as in Example 1-1, and the holding step was performed, but the allocation of the amount of steam _Wf in the first one-side heating step P3 was excessively increased. In this case, the surface condition of the compact was deteriorated.

In Comparative Example 1-4, the total amount of steam and the amount of steam in the mold heating step were set to the same levels as in Example 1-1, but the proportion of the amount of steam _Wf in the first one-side heating step P3 was excessively increased, resulting in a deterioration in the surface condition.

As can be seen from a comparison between the Examples and Comparative Examples, by implementing a holding process and ensuring that the steam amounts used in each process satisfy a specific relationship, it is possible to reduce the amount of steam used during in-mold molding while maintaining good surface and fusion conditions for the molded body.

Example 2
In this example, expanded beads with polystyrene as the base resin were used to produce a block-shaped molded body measuring 800 mm in length, 200 mm in width, and 150 mm in height. Specifically, the expanded beads used in this example were obtained by expanding Styrodia (registered trademark) "XJ251N," an expandable polystyrene bead manufactured by JSP Corporation. The bulk density of the expanded beads was 17 kg/ ^m3 . The molding machine used was a "VS1300-DeCo," as in Example 1-1. The mold was capable of molding two of the block-shaped molded bodies (volume approximately 24 L) at a time, and the volume of the molding space was 48 L.

In this example, a molded body was produced by in-mold molding in the same manner as in Example 1-1, except that the molding conditions for in-mold molding were changed as shown in Table 2. The same evaluations as in Example 1-1 were then carried out. The results are shown in Table 2. The number of voids was calculated in the same manner as in Example 1-1, except that a 100 mm x 100 mm square was drawn in the center of the main surface of the molded body (a surface measuring 800 mm long x 200 mm wide).

(Comparative Example 2-1)
The molding conditions were changed as shown in Table 2, but the other conditions were the same as in Example 2.

(Comparative Example 2-2)
The molding conditions were changed as shown in Table 2, but the other conditions were the same as in Example 2.

As can be seen from Table 2, the manufacturing conditions of Example 2 reduce the total amount of steam used during in-mold molding compared to the manufacturing conditions of Comparative Example 2-1, which does not include a holding step, while producing molded bodies with good fusion and surface conditions. This is thought to be because, like Example 1-1, Example 2 performs a holding step and sets a specific relationship between the amount of steam used in each step. Furthermore, Example 2 produces large, block-shaped molded bodies. Even in this case, by performing a holding step and controlling the amount of steam used in each step, it is possible to reduce the amount of steam used during in-mold molding and obtain molded bodies with good fusion and surface conditions.

Comparative Example 2-1 is an example in which in-mold molding was performed under conditions that allowed for the production of a molded product with good fusion and surface conditions without performing a holding step. In Comparative Example 2-1, a molded product with good fusion and surface conditions similar to those of Example 2 was obtained, but the amount of steam used was greater. Note that when the total steam amount of Comparative Example 2-1 was taken as 100%, the reduction rate of the total steam amount of Example 2 relative to the total steam amount of Comparative Example 2-1 was 34%.
Furthermore, the molding cycle in Comparative Example 2-1 was 158 seconds, whereas the molding cycle in Example 2 was 158 seconds, and both had equivalent molding cycles.

In Comparative Example 2-2, the holding step was performed while reducing the total steam amount to the same level as in Example 2, but the allocation of the steam amount _Wf in the first one-side heating step P3 was excessively increased. In this case, the surface condition of the molded body deteriorated, and the fusion rate of the molded body also decreased.

Example 3
In this example, a plate-shaped molded body measuring 910 mm in length, 595 mm in width, and 40 mm in thickness was produced using expanded beads containing a flame retardant and polystyrene as the base resin. Specifically, the expanded beads used in this example were obtained by expanding Styrodia (registered trademark) "FA201," an expandable polystyrene bead manufactured by JSP. The bulk density of the expanded beads was 25 kg/ ^m3 . The molding machine used was a "VS2800S-S1" manufactured by Daisen Kogyo Co., Ltd. The volume of the molding space was 22 L.

In this example, a molded body was produced by in-mold molding in the same manner as in Example 1-1, except that the molding conditions for in-mold molding were changed as shown in Table 3. The same evaluations as in Example 1-1 were then carried out. The results are shown in Table 3. The number of voids was calculated in the same manner as in Example 1-1, except that a 100 mm x 100 mm square was drawn in the center of the main surface of the molded body (a surface measuring 910 mm long x 595 mm wide).

(Comparative Example 3-1)
The molding conditions were changed as shown in Table 3, but the other conditions were the same as in Example 3.

(Comparative Example 3-2)
The molding conditions were changed as shown in Table 3, but the other conditions were the same as in Example 3.

As can be seen from Table 3, the manufacturing conditions of Example 3 reduce the total amount of steam used during in-mold molding compared to the manufacturing conditions of Comparative Example 3-1, which does not include a holding step, while producing molded articles with good fusion and surface conditions. This is thought to be because, in Example 3, like Examples 1-1 to 1-3 and Example 2, a holding step is performed and the steam amounts used in each step are set to a specific relationship. Furthermore, Example 3 produces plate-shaped molded articles with a different shape from Example 2. Even in this case, by performing a holding step and controlling the amount of steam used in each step, it is possible to reduce the amount of steam used during in-mold molding and obtain molded articles with good fusion and surface conditions.

Comparative Example 3-1 is an example in which in-mold molding was performed under conditions that allowed for the production of a molded product with good fusion and surface conditions without performing a holding step. In Comparative Example 3-1, a molded product with good fusion and surface conditions similar to those of Example 3 was obtained, but the amount of steam used was greater. Note that when the total steam amount of Comparative Example 3-1 was taken as 100%, the reduction rate of the total steam amount of Example 3 relative to the total steam amount of Comparative Example 3-1 was 39%.
Furthermore, the molding cycle in Comparative Example 3-1 was 740 seconds, while the molding cycle in Example 3 was 735 seconds, and both had equivalent molding cycles.

In Comparative Example 3-2, the holding step was performed while reducing the total steam amount to the same extent as in Example 3, but the allocation of the steam amount _Wf in the first one-side heating step P3 was excessively increased. In this case, the surface condition of the molded body deteriorated, and the fusion rate of the molded body also decreased.

Example 4
In this example, expanded beads with polystyrene as the base resin were used to produce a box-shaped molded body measuring 350 mm in length, 660 mm in width, 250 mm in height, with a side wall thickness of 30 mm and a bottom wall thickness of 25 mm. Specifically, the expanded beads used in this example were obtained by expanding Styrodia (registered trademark) "JQ250NX," an expandable polystyrene bead manufactured by JSP Corporation. The bulk density of the expanded beads was 17 kg/ ^m3 . The molding machine used was a "VS1300-MCJ" manufactured by Daisen Kogyo. The molding die was capable of molding two box-shaped molded bodies (volume approximately 18 L) at a time, and the volume (total volume) of the molding space was 36 L.

In this example, a molded body was produced by in-mold molding in the same manner as in Example 1-1, except that the molding conditions for in-mold molding were changed as shown in Table 4. The same evaluations as in Example 1-1 were then carried out. The results are shown in Table 4. The number of voids was calculated in the same manner as in Example 1-1, except that a 100 mm x 100 mm square was drawn in the center of the outer surface of one of the side walls facing each other in the left-right direction of the mold.

(Comparative Example 4-1)
The molding conditions were changed as shown in Table 4, but the other conditions were the same as in Example 4.

(Comparative Example 4-2)
The molding conditions were changed as shown in Table 4, but the other conditions were the same as in Example 4.

As can be seen from Table 4, the manufacturing conditions of Example 4 reduce the total amount of steam used during in-mold molding compared to the manufacturing conditions of Comparative Example 4-1, which does not include a holding step, while producing molded articles with excellent fusion and surface conditions. This is thought to be because, in Example 4, like Examples 1-1 to 1-3, 2, and 3, a holding step is performed and the steam amounts used in each step are set to a specific relationship. Furthermore, Example 4 produces box-shaped molded articles with thicker side walls and bottom walls than the box-shaped molded articles of Examples 1-1 to 1-3. Even in this case, by performing a holding step and controlling the amount of steam used in each step, it is possible to reduce the amount of steam used during in-mold molding and obtain molded articles with excellent fusion and surface conditions.

Comparative Example 4-1 is an example in which in-mold molding was performed under conditions that allowed for the production of a molded product with good fusion and surface conditions without performing a holding step. In Comparative Example 4-1, a molded product with good fusion and surface conditions similar to those of Example 1-1 was obtained, but the amount of steam used was greater. Note that when the total steam amount of Comparative Example 4-1 is taken as 100%, the reduction rate of the total steam amount of Example 4 relative to the total steam amount of Comparative Example 4-1 was 28%.
Furthermore, the molding cycle in Comparative Example 4-1 was 451 seconds, while the molding cycle in Example 4 was 456 seconds, and both had equivalent molding cycles.

In Comparative Example 4-2, the holding step was performed while reducing the total steam amount to the same extent as in Example 4, but the allocation of the steam amount _Wf in the first one-side heating step P3 was excessively increased. In this case, the surface condition of the molded body deteriorated, and the fusion rate of the molded body also decreased.

1 Mold 11 Mold space 2 First mold 3 Second mold

Claims (5)

A method for producing an expanded bead molded article, comprising: using a molding die having a first die and a second die configured to be able to form a molding space between the first die and the second die; and in-mold molding expanded polystyrene resin beads filled in the molding space to produce an expanded bead molded article,
The method for producing the expanded bead molded article includes a filling step of filling the molding space with expanded polystyrene resin beads, a mold heating step of supplying steam into the molding space from both the first mold side and the second mold side after the filling step, a first one-side heating step of supplying steam into the molding space from the first mold side after the mold heating step, a second one-side heating step of supplying steam into the molding space from the second mold side after the first one-side heating step, a double-side heating step of supplying steam into the molding space from both the first mold side and the second mold side after the second one-side heating step, and a retaining step of retaining the steam supplied in the double-side heating step within the molding space,
a total steam amount _Wd + _f +s+b of the steam amount Wd in the mold heating step, the steam amount _Wf in the first one-side heating step, the steam amount _Ws in the second one-side heating step, and the steam amount _Wb in the double-side heating step is 0.05 kg or more and 0.5 kg or less per 1 L of the volume of the molding space,
a ratio of the amount of steam _Wd in the mold heating step to a total amount Wf+ _s +b of the amount of steam _Wf in the first one-side heating step, the amount of steam _Ws in the second one-side heating step, and the amount of steam Wb in the double-side heating step is _Wd :Wf _{+s+b =} 5:95 to 40:60;
When a total Wf _{+s+b of} the steam amounts in the first one-side heating step, the second one-side heating step, and the double-side heating step is taken as 100 mass%, a ratio of the steam amount _Wf in the first one-side heating step is 15 mass% or more and 50 mass% or less, a ratio of the steam amount _Ws in the second one-side heating step is 15 mass% or more and 50 mass% or less, and a ratio of the steam amount _Wb in the double-side heating step is 10 mass% or more and 70 mass% or less,
a ratio W _b /W _f of the amount of steam W _b in the double-side heating step to the amount of steam W _f in the first one-side heating step is 0.3 or more;
The method for producing an expanded bead molding, wherein the holding time in the holding step is 5 seconds or more . 2. The method for producing an expanded bead molded article according to claim 1, wherein the amount of steam _Wf in the first one-way heating step is 0.01 kg or more and 0.2 kg or less per 1 L of the volume of the molding space. 3. The method for producing an expanded bead molded article according to claim 1, wherein a ratio _Wd / _Wf of the amount of steam _Wd in the mold heating step to the amount of steam _Wf in the first one-side heating step is 0.2 or more and 3 or less. 3. The method for producing an expanded bead molding according to claim 1, wherein a ratio _Ws / _Wf of the amount of steam _Ws in the second one-way heating step to the amount of steam _Wf in the first one-way heating step is 0.6 or more and 2 or less. The method for producing a foamed bead molding according to claim 1 or 2, wherein the holding time in the holding step is from 5 seconds to 50 seconds.