JP7599464B2 - Method for setting in-mold molding conditions for expanded bead molding and method for manufacturing expanded bead molding - Google Patents

Description

The present invention relates to a method for setting in-mold molding conditions for foamed bead moldings and a method for manufacturing foamed bead moldings.

Polystyrene resin foamed bead molded bodies obtained by molding polystyrene resin foamed beads in a mold are lightweight and have excellent compression properties, and are therefore used in a variety of fields, including automotive materials, construction materials, and logistics materials. For molding foamed beads in a mold, a mold is used that includes a first mold and a second mold, and is configured so that a molding cavity corresponding to the shape of the desired molded body is formed between the first mold and the second mold. After filling the molding cavity of such a mold with foamed beads, steam is supplied to the first mold and the second mold in a predetermined order to heat the foamed beads in the mold, thereby obtaining a molded body with a desired shape (for example, Patent Document 1).

JP 2007-237468 A

In recent years, there has been a demand for reducing the energy required to manufacture foamed bead moldings, and from this perspective, there is a need to reduce the amount of steam used during in-mold molding without compromising the physical properties of the moldings.

The present invention has been made in view of this background, and aims to provide a method for setting in-mold molding conditions for expanded bead moldings that can easily find in-mold molding conditions that allow for a reduction in the amount of steam used during in-mold molding without impairing the physical properties of the expanded bead moldings, and a manufacturing method for expanded bead moldings that allows for a reduction in the amount of steam used during in-mold molding without impairing the physical properties of the expanded bead moldings.

One aspect of the present invention is a method for setting the in-mold molding conditions for a foamed bead molding according to the following items [1] to [6].

[1] A method for setting in-mold molding conditions for an expanded bead molding product, in order to obtain an expanded bead molding product having a fusion rate of XT [%] or more, by in-mold molding of expanded polystyrene resin beads using a molding die including a first die and a second die configured to be able to form a molding space between the first die and the second die, a first one-side heating step of supplying steam from the first die side to the molding space to heat the expanded beads in the molding space, a second one-side heating step of supplying steam from the second die side to the molding space after the first one-side heating step to heat the expanded beads in the molding space, a main heating step of supplying steam from both the first die side and the second die side to heat the expanded beads in the molding space after the second one _- side heating step, and a pressure holding step of holding the steam supplied in the main heating step in the molding die,
The setting method includes a reference condition deriving step, a steam reduction condition range deriving step, and an in-mold molding condition deriving step,
in the step of deriving the reference conditions, the steam pressure and amount of steam in the first one-way heating step, the steam pressure and amount of steam in the second one-way heating step, and the steam pressure and amount of steam in the main heating step are included as steam heating conditions, and molding conditions capable of producing an expanded bead molding having a fusion rate _X1 [%] of _XT [%] or more without substantially carrying out a pressure-holding step are derived as reference conditions;
in the step of deriving a range of steam reduction conditions, at least a part of the steam heating conditions of the standard conditions is changed so that a total steam amount, which is the sum of the steam amount in the first one-way heating step, the steam amount in the second one-way heating step, and the steam amount in the main heating step, is less than the total steam amount in the standard conditions, and a range of steam reduction conditions, which is a molding condition under which an expanded bead molding having a fusion rate _X2 [%] of 10% or more can be produced without substantially performing a pressure-holding step, is derived as a range of steam reduction conditions;
the in-mold molding condition deriving step adds a dwelling step to the first one-way heating step, the second one-way heating step, and the main heating step under each steam reduction condition derived in the steam reduction condition range deriving step such that the dwelling time _tT of the dwelling step is longer than the dwelling time under the steam reduction condition, and derives, as the in-mold molding conditions, a range of molding conditions capable of producing an expanded bead molding product having a fusion rate of _XT [%] or more.

[2] The steam reduction conditions are:
Requirement 1: the steam pressure Pa ₂ [MPa (G)] in the first one-way heating step under the steam-reducing conditions is 0.7 to 1.3 times the steam pressure Pa ₁ [MPa (G)] in the first one-way heating step under the standard conditions;
The method for setting in-mold molding conditions for an expanded bead molding product according to [1] satisfies the following four requirements: requirement 2: the steam amount _Wa2 [kg _] of the first one-side heating step under the steam reduction conditions is less than the steam amount _Wa1 [kg] of the first one-side heating step under the standard conditions; requirement 3: the steam pressure _Pb2 [MPa (G)] of the second one-side heating step under the steam reduction conditions is 0.7 to 1.3 times the steam pressure Pb1 [MPa (G)] of the second one-side heating step under the standard conditions; and requirement 4: the steam amount _Wb2 [kg] of the second one-side heating step under the steam reduction conditions is less than the steam amount _Wb1 [kg] of the second one-side heating step under the standard conditions.

[3] The method for setting in-mold molding conditions for an expanded bead molding according to [1] or [2], wherein the steam reduction conditions are configured so that a difference X1 - _X2 between a fusion rate _X1 [%] of the expanded bead molding obtained by in-mold molding under the standard conditions and a fusion rate _X2 [%] of the expanded bead molding obtained by in-mold molding under the _steam reduction conditions is 5% or more and 70% or less.
[4] The steam reduction conditions are:
The method for setting in-mold molding conditions for an expanded bead molding product according to any one of [ ₁ ] to [3], which satisfies the following two requirements: requirement 5: the steam pressure _Pm2 [MPa (G)] in the main heating step under the steam-reduced conditions is 0.7 to 1.3 times the steam pressure Pm1 [MPa (G)] in the main heating step under the standard conditions; and requirement 6: the steam amount _Wm2 [kg] in the main heating step under the steam-reduced conditions is 0.7 to 1.3 times the steam amount _Wm1 [kg] in the main heating step under the standard conditions.

[5] The steam reduction conditions are:
Requirement 7: The method for setting in-mold molding conditions for an expanded bead molding product according to any one of [1] to [4], wherein the requirement of a total steam amount [kg] under the reduced steam conditions is 0.8 times or less the total steam amount [kg] under the standard conditions is satisfied.
[6] The steam reduction conditions are:
Requirement 8: The method for setting in-mold molding conditions for an expanded bead molding product according to any one of [1] to [5], wherein the requirement that the steam amount Wm ₂ [kg] in the main heating step under the steam-reduced conditions is 0.8 to 4 times the steam amount Wa ₂ [kg] in the first one-way heating step under the steam-reduced conditions is satisfied.

Another aspect of the present invention is a method for producing an expanded molding of beads according to the following [7].
[7] A method for producing an expanded bead molding, comprising in-mold molding polystyrene-based resin expanded beads under in-mold molding conditions set by using the method for setting in-mold molding conditions for an expanded bead molding according to any one of [1] to [6] to produce an expanded bead molding.

According to the above aspect, it is possible to provide a method for setting in-mold molding conditions for an expanded bead molding (hereinafter referred to as "molded body") that can easily find in-mold molding conditions that can reduce the amount of steam used during in-mold molding without impairing the physical properties of the expanded bead molding, and a manufacturing method for an expanded bead molding that can reduce the amount of steam used during in-mold molding without impairing the physical properties of the molded body.

FIG. 1 is an explanatory diagram showing a flow chart of a method for setting molding conditions in a mold for producing an expanded bead molding. FIG. 2 is a partial cross-sectional view showing a main part of a mold used for in-mold molding of expanded beads. FIG. 3 is an explanatory diagram showing a flow chart of the in-mold molding method for expanded beads.

(Method of Setting In-Mold Molding Conditions for Expanded Bead Molded Product)
The method for setting in-mold molding conditions includes a step S1 for deriving a reference condition, a step S2 for deriving a steam reduction condition range, and a step S3 for deriving in-mold molding conditions, as shown in Fig. 1. The setting method is configured to perform these steps to set in-mold molding conditions for obtaining a molded body having a desired fusion rate _XT (unit: %) or more while reducing the amount of steam used in in-mold molding of expanded polystyrene resin beads (hereinafter referred to as "expanded beads"). The in-mold molding conditions set by the setting method can be applied to, for example, the following in-mold molding methods.

The mold used for in-mold molding comprises a first mold 2 and a second mold 3, as shown in FIG. 2, for example. At least one of the first mold 2 and the second mold 3 is configured to be movable in the opening and closing direction of the mold 1. The first mold 2 and the second mold 3 are configured to abut against each other when the mold 1 is completely closed, forming a molding space 11 between them. The molding space 11 may have any shape that corresponds to the shape of the desired molded body.

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 communicates with the molding space. For example, the first mold 2 and the second mold 3 may have a plurality of core vents (not shown) on the inner wall parts 23, 33 facing the molding space 11, which communicate between the internal space of each mold and the molding space 11. This allows steam supplied to the internal space of the first mold 2 and the second mold 3 to reach the molding space 11 through through grooves formed in the core vents of the inner wall parts 23, 33.

As shown in FIG. 3, the in-mold molding method for foamed beads includes a filling process P1, a first one-side heating process P3, a second one-side heating process P4, and a main heating process P5.

In the filling step P1, the molding space 11 of the mold 1 is filled with foamed particles. The foamed particles to be filled in the molding space are not particularly limited as long as they are foamed particles whose base resin is polystyrene resin, and known polystyrene resin foamed particles can be used. Here, the above-mentioned polystyrene resin refers to a resin whose content of components derived from styrene monomers exceeds 50 mol%. From the viewpoint of improving the moldability and mechanical properties of the polystyrene resin in a well-balanced manner, the content of components derived from styrene monomers in the polystyrene resin is preferably 80 mol% or more, and more preferably 90 mol% or more.

In addition, the polystyrene resin expanded particles can be obtained, for example, by using a polystyrene resin as a base resin and expanding expandable polystyrene resin particles containing an organic physical blowing agent. Examples of the organic physical blowing agent include hydrocarbons having 3 to 6 carbon atoms.

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

As the polystyrene-based resin, a homopolymer of a styrene-based monomer and a copolymer containing a styrene-based monomer can be used. More specifically, the polystyrene-based resin may be polystyrene (GPPS), a styrene-acrylic acid copolymer mainly composed of styrene, 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, an acrylonitrile-butadiene-styrene copolymer, a styrene-methylstyrene copolymer, a styrene-dimethylstyrene copolymer, a styrene-ethylstyrene copolymer, a styrene-diethylstyrene copolymer, or the like.

In the in-mold molding method, after the filling step P1 is completed, and before the first one-sided heating step P3 is performed, an exhaust step P2 (see FIG. 3) may be performed as necessary to exhaust the air in the mold 1 to the outside of the mold 1. In the exhaust step P2, for example, a method may be adopted in which steam is supplied to the molding space 11 from both the first mold 2 side and the second mold 3 side to replace the air in the mold 1 with steam.

When performing the exhaust process P2, for example, the pressure 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 exhaust process P2, it is preferable to supply steam at the aforementioned pressure for, for example, 1 to 5 seconds.

After the filling step P1 or the exhaust step P2, which is performed as necessary, 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 foamed particles in the molding space 11. In the first one-side heating step P3, the degree of heating of the foamed particles in the molding space 11 can be controlled by controlling the steam pressure Pa and steam amount Wa of the steam supplied to the first mold 2. In the first one-side heating step P3, for example, as described below, the steam supply valve of the first mold 2 and the drain valve of the second mold 3 can be opened, and the other steam supply valves and drain valves can be closed, so that steam can flow from the first mold 2 side to the second mold 3 side. This allows the foamed particles in the molding space 11 to be heated.

After the first one-sided heating process P3 is completed, the second one-sided heating process P4 is performed in which steam is supplied from the second mold 3 side to the molding space 11 to heat the foamed beads in the molding space 11. In the second one-sided heating process P4, the degree of heating of the foamed beads in the molding space 11 can be controlled by controlling the steam pressure Pb and steam amount Wb of the steam supplied to the second mold 3. In the second one-sided heating process P4, for example, as described below, the steam supply valve of the second mold 3 and the drain valve of the first mold 2 are opened, and the other steam supply valves and drain valves are closed, so that steam can flow from the second mold 3 side to the first mold 2 side. This allows the foamed beads in the molding space 11 to be heated.

After the second one-sided heating step P4 is completed, the main heating step P5 is performed to supply steam to the molding space 11 from both the first mold 2 side and the second mold 3 side to heat the foamed beads in the molding space 11. In the main heating step P5, the steam pressure Pm and steam amount Wm of the steam supplied to the first mold 2 and the second mold 3 can be controlled to control the degree of heating of the foamed beads in the molding space 11 and the degree of pressure (surface pressure) applied to the inner wall of the molding mold 1. In addition, in the main heating step P5, for example, as described below, the steam supply valve of the first mold 2 and the steam supply valve of the second mold 3 can be opened and the drain valves of each mold can be closed to increase the pressure in the molding space 11. This makes it possible to increase the surface pressure applied to the molding mold 1 while heating the foamed beads in the molding space 11.

After the main heating step P5 is completed, a pressure holding step P6 is performed to hold the steam supplied to the mold 1 in the main heating step P5 within the mold 1. In the pressure holding step P6, the degree of heating of the foamed beads in the molding space 11 can be controlled by controlling the pressure holding time t (unit: seconds), that is, the time for which the steam supplied to the mold 1 is held. In the pressure holding step P6, for example, as described below, the steam supplied to the molding space 11 can be held within the molding space 11 by closing the steam supply valves and drain valves of each mold. This allows the reduction in the surface pressure applied to the mold 1 to be gradual, and the foamed beads in the molding space 11 to be heated under the desired pressure for a long period of time without supplying steam to the mold 1.

In the in-mold molding method, the heating performed up to the pressure holding step P6 causes the foamed particles in the molding space 11 to undergo secondary foaming while fusing together to form a molded body. After the pressure holding step P6 is completed, a cooling step P7 may be performed as necessary to cool the molded body in the mold 1. After the shape of the molded body in the mold 1 has been stabilized to a certain extent, the mold 1 can be opened to obtain the molded body.

Next, we will explain each step in the method for setting the in-mold molding conditions in more detail.

[Reference condition derivation step S1]
In the reference condition derivation step S1, the molding conditions that can produce a molded body having a fusion rate _X1 (unit: %) equal to or greater than the target fusion rate _XT without substantially performing the pressure holding step P6 in the above-mentioned in-mold molding method are derived as reference conditions. Here, the molding conditions that "substantially do not perform the pressure holding step P6" include molding conditions in which the pressure holding step P6 is not performed (i.e., the pressure holding time t is 0 seconds) and molding conditions in which the pressure holding time t is greater than 0 seconds and is equal to or less than a value that does not significantly affect the improvement of the fusion rate of the molded body. More specifically, the molding conditions that "substantially do not perform the pressure holding step P6" include molding conditions in which the pressure holding time t is, for example, 0 seconds or more and less than 5 seconds. In addition, the target fusion rate _XT can be a value required depending on the application, shape, etc. of the molded body. For example, the target fusion rate _XT may be 80%, 85%, or 90%.

More specifically, in the reference condition derivation step S1, the steam pressures Pa, Pb, Pm and the steam amounts Wa, Wb, Wm in the in-mold molding method shown in Figure 3 are variously changed to perform steps P1 to P5, and in-mold molding is performed without substantially performing the pressure retention step P6. In this case, the pressure retention time t may vary within the range described above, but from the viewpoint of making it easier to derive suitable reference conditions, it is preferable that it be a constant value.

The fusion rate of the molded article thus obtained is measured, and molding conditions under which a molded article having a fusion rate equal to or higher than the target fusion rate _XT can be produced are set as candidates for the reference conditions.

The fusion rate can be measured, for example, as follows. First, the molded body is folded into roughly equal parts and broken. At this time, the molded body may be cut in advance to make it easier to break. Then, 100 or more foamed beads are randomly selected from those exposed on the fractured surface of the molded body and visually observed to determine whether the foamed beads have broken from the inside (i.e., material failure) or at the interface between the foamed beads (i.e., interfacial failure). The ratio of the total number of foamed beads with material failure to the total number of foamed beads visually observed, expressed as a percentage, is taken as the fusion rate of the molded body (unit: %).

The candidates for the standard conditions may include molding conditions under which a fusion rate X1 equal to or greater than the target fusion rate _XT can be achieved based on molding conditions that have been experimentally confirmed to be capable of achieving a fusion rate equal to or greater than the target fusion rate _XT , in addition to molding conditions under which a molded _body was actually produced and the fusion rate was measured. That is, the candidates for the standard conditions may include molding conditions under which the fusion rate has not actually been measured. For example, the fusion rate of a molded body generally tends to increase as the amount of heat applied to the expanded beads increases. Therefore, if a fusion rate _X1 equal to or greater than the target fusion rate _XT can be achieved under two molding conditions with the same steam pressure and different steam amounts, it can be estimated that a fusion rate _X1 equal to or greater than the target fusion rate _XT can also be achieved under a molding condition with an intermediate steam amount between the steam amounts under these two molding conditions.

One molding condition selected from the candidates for the reference condition obtained as described above is derived as the reference condition. The reference conditions thus derived include at least six steam heating conditions: steam pressure _Pa1 (unit: MPa (G)) and steam amount _Wa1 (unit: kg) in the first one-way heating step P3, steam pressure _Pb1 (unit: MPa (G)) and steam amount _Wb1 (unit: kg) in the second one-way heating step P4, and steam pressure _Pm1 (unit: MPa (G)) and steam amount _Wm1 (unit: kg) in the main heating step P5. There is no particular limitation on the method of selecting the reference conditions from the candidate reference conditions, but from the viewpoint of efficiently performing the steam reduction condition range derivation step S2 performed later, it is preferable to derive as the reference conditions the molding conditions having the smallest total steam amount _W1 (unit: kg), that is, the sum of the steam amount _Wa1 in the first one-way heating process P3, the steam amount _Wb1 in the second one-way heating process P4, and the steam amount _Wm1 in the main heating process P5, assuming that a predetermined fusion rate is satisfied.

[Step S2 for Derivation of Steam Reduction Condition Range]
In the steam reduction condition range derivation step S2, at least some of the steam heating conditions of the standard conditions are changed to derive a range of steam reduction conditions, which are molding conditions under which a molded body having a fusion rate _X2 (unit: %) of 10% or more can be produced with a total steam amount _W2 (unit: kg) less than _the total steam amount W1 under the standard conditions without substantially performing the pressure holding process P6.

More specifically, in the steam reduction condition range derivation step S2, one or more steam heating conditions among the steam amount _Wa1 in the first one-way heating step P3, the steam amount _Wb1 in the second one-way heating step P4, and the steam amount _Wm1 in the main heating step P5 under the standard conditions are changed so that the total steam amount _W2 is less than the total steam amount _W1 under the standard conditions, and in-mold molding is performed. Also, in the steam reduction condition range derivation step S2, in addition to the steam amounts _Wa1 , _Wb1 , and _Wm1 , one or more steam heating conditions among the steam pressures _Pa1 , _Pb1 , and pressure _Pm1 under the standard conditions may be changed to perform in-mold molding.

The molding conditions in which the dwelling process P6 is not substantially performed mentioned above include molding conditions in which the dwelling process P6 is not performed (i.e., the dwelling time t is 0 seconds). More specifically, the molding conditions in which the dwelling process P6 is not substantially performed include molding conditions in which the dwelling time t is, for example, 0 seconds or more and less than 5 seconds. Similarly to the reference condition derivation step S1, the dwelling time t in the steam reduction condition range derivation step S2 may vary within the aforementioned range, but from the viewpoint of making it easier to derive suitable steam reduction conditions, it is preferable that the dwelling time t be a constant value.

The fusion rate of the molded body thus obtained is measured, and the range of steam reduction conditions capable of producing a molded body having a fusion rate _X2 of 10% or more is derived as the steam reduction condition range. From the viewpoint of making it easier to derive the in-mold molding conditions capable of achieving the target fusion rate _XT , the fusion rate _X2 is preferably 20% or more, more preferably 30% or more, and even more preferably 50% or more. In addition to the steam reduction conditions under which a molded body is actually produced and the fusion rate is measured, the steam reduction condition range may include steam reduction conditions that are estimated to be capable of achieving the fusion rate in the specific range based on steam reduction conditions that have been experimentally confirmed to be capable of achieving the fusion rate in the specific range. In other words, the steam reduction condition range may include steam reduction conditions under which the fusion rate has not actually been measured.

The steam reduction condition range derived in this manner is composed of one or more steam reduction conditions having at least six steam heating conditions: steam pressure _Pa2 (unit: MPa (G)) and steam amount _Wa2 (unit: kg) in the first one-way heating process P3, steam pressure _Pb2 (unit: MPa (G)) and steam amount _Wb2 (unit: kg) in the second one-way heating process P4, and steam pressure _Pm2 (unit: MPa (G)) and steam amount _Wm2 (unit: kg) in the main heating process P5.

The steam reduction conditions are:
Requirement 1: The steam pressure _Pa2 in the first one-side heating step P3 under the steam reduction condition is 0.7 to 1.3 times the steam pressure _Pa1 in the first one-side heating step P3 under the standard condition.
Requirement 2: The steam amount _Wa2 in the first one-side heating step P3 under the steam reduction condition is smaller than the steam amount _Wa1 in the first one-side heating step P3 under the standard condition.
It is preferable that the following four requirements are satisfied: requirement 3: the steam pressure _Pb2 in the second one-side heating step P4 under the reduced steam conditions is 0.7 to 1.3 times the steam pressure _Pb1 in the second one-side heating step P4 under the standard conditions; and requirement 4: the steam amount _Wb2 in the second one-side heating step P4 under the reduced steam conditions is less than the steam amount _Wb1 in the second one-side heating step P4 under the standard conditions.

The steam supplied to the first mold 2 in the first one-side heating process P3 usually passes through the molding space 11 and is led from the second mold 3 to the outside of the molding die 1. Similarly, the steam supplied to the second mold 3 in the second one-side heating process P4 usually passes through the molding space 11 and is led from the first mold 2 to the outside of the molding die 1. Therefore, the in-mold molding method has a problem in that the amount of steam Wa used in the first one-side heating process P3 and the amount of steam Wb used in the second one-side heating process P4 tend to be large.

In contrast, as described above, by setting the ranges of the steam pressure _Pa2 in the first one-side heating step P3 and the steam pressure _Pb2 in the second one-side heating step P4 to the ranges specified in the requirements 1 and 3, it is possible to produce a molded body that satisfies a predetermined fusion rate _X2 , while easily deriving the ranges in which the steam amount _Wa2 in the first one-side heating step P3 and the steam amount _Wb2 in the second one-side heating step P4 can be reduced, and the addition of the pressure holding step P6 makes it easier to derive the condition range in which the target fusion rate _XT can be achieved. Furthermore, by reducing the amount of steam in the first one-side heating step P3 and the second one-side heating step P4, which tend to use a relatively large amount of steam, the total steam amount _W2 can be reduced more effectively.

From the viewpoint of more reliably obtaining the above-mentioned effects, in requirement 1, the steam pressure _Pa2 in the first one-side heating step P3 under the steam-reduced condition is more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times, the steam pressure Pa1 in the first one-side heating step P3 under the standard condition. Also, in requirement 3, the steam pressure _Pb2 in the second one-side heating step P4 under the steam _- reduced condition is more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times, the steam pressure _Pb1 in the second one-side heating step P4 under the standard condition.

The steam reduction conditions are preferably configured so that the difference X1 _-X2 between the fusion rate X1 of the molded body obtained by in-mold molding under the standard conditions and the fusion rate _X2 of the molded body obtained by in-mold molding under the steam reduction conditions is 5% or more and 70% or less. By setting the difference _{X1 - X2} in the fusion rates to the specific range, it is possible to more easily derive a steam reduction condition range in which the target fusion rate _XT can be achieved by adding the pressure holding process _P6 while reducing the total amount of steam.

From the viewpoint of further reducing the total amount of steam, the difference in the fusion rates X ₁ -X ₂ is more preferably 7% or more, even more preferably 10% or more, particularly preferably 15% or more, and most preferably 20% or more. On the other hand, from the viewpoint of more easily deriving the in-mold molding conditions capable of achieving the target fusion rate _XT , the difference in the fusion rates X ₁ -X ₂ is more preferably 70% or less, even more preferably 60% or less, particularly preferably 50% or less, and most preferably 40% or less.

In determining the preferred range of the difference in fusion rates X ₁ -X ₂ , the upper limit and the lower limit of the difference in fusion rates X ₁ -X ₂ can be combined in any manner. For example, the preferred range of the difference in fusion rates X ₁ -X ₂ may be 7% or more and 70% or less, 10% or more and 60% or less, 15% or more and 50% or less, or 20% or more and 40% or less.

The steam reduction conditions are as follows:
It is preferable to satisfy the following two requirements: Requirement 5: the steam pressure _Pm2 in the main heating step P5 under the steam reduction condition is 0.7 to 1.3 times the steam pressure _Pm1 in the main heating step P5 under the standard condition, and Requirement 6: the steam amount _Wm2 in the main heating step P5 under the steam reduction condition is 0.7 to 1.3 times the steam amount _Wm1 in the main heating step P5 under the standard condition. In this way, by bringing the steam pressure and steam amount in the main heating step P5 under the steam reduction condition closer to the steam pressure and steam amount in the main heating step P5 under the standard condition, it becomes easier to derive suitable steam reduction conditions, and the addition of the pressure holding step P6 makes it easier to derive the condition range in which the target fusion rate _XT can be achieved.

From the viewpoint of more reliably obtaining the above-mentioned effects, in requirement 5, the steam pressure _Pm2 in the main heating step P5 under the steam-reduced condition is more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times, the steam pressure Pm1 in the main heating step _P5 under the standard condition. Also, in requirement 6, the steam amount _Wm2 in the main heating step P5 under the steam-reduced condition is more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times, the steam amount _Wm1 in the main heating step P5 under the standard condition.

The steam reduction conditions are:
Requirement 7: It is preferable that the requirement that the total steam amount _W2 under the steam reduction condition is 0.8 times or less the total steam amount _W1 under the standard condition is satisfied. In this case, the total steam amount can be reduced more reliably.

The steam reduction conditions are:
Requirement 8: It is preferable that the steam amount _Wm2 in the main heating step P5 under the reduced steam conditions is 0.8 to 4 times the steam amount _Wa2 in the first one-way heating step P3 under the reduced steam conditions. In this case, it is possible to more easily derive the range of reduced steam conditions in which the target fusion rate _XT can be achieved by adding the pressure holding step P6 while reducing the total steam amount.

[Step S3 for deriving in-mold molding conditions]
In the in-mold molding condition derivation step S3, a pressure dwell step P6 is added to the first one-way heating step P3, the second one-way heating step P4, and the main heating step P5 under each steam reduction condition derived in the steam reduction condition range derivation step so that the pressure dwell time _tT (unit: seconds) of the pressure dwell step P6 is longer than the pressure dwell time _t2 (unit: seconds) under the steam reduction condition, and a range of molding conditions capable of producing a molded body having a fusion rate of _XT or more is derived as the in-mold molding condition.

More specifically, in the in-mold molding condition derivation step S3, the steam pressures Pa ₂ , Pb ₂ , Pm ₂ and the steam amounts Wa ₂ , Wb ₂ , Wm ₂ under the steam reduction condition are adopted as the steam pressure and steam amount in each process P3 to P5, and the pressure retention time t is variously changed to a value longer than the pressure retention time t ₂ under the steam reduction condition to perform in-mold molding. The fusion rate of the molded body thus obtained is measured, and a range of molding conditions capable of producing a molded body having a fusion rate equal to or higher than the target fusion rate _XT is derived as the in-mold molding condition. From the viewpoint of stably obtaining a molded body with a high fusion rate without excessively lengthening the molding cycle of the molded body, the pressure retention time t of the in-mold molding condition in the in-mold molding condition derivation step S3 is preferably 5 seconds or more and 30 seconds or less, more preferably 8 seconds or more and 25 seconds or less.

The number of steam reduction conditions used in deriving the in-mold molding conditions may be one or more. From the viewpoint of more easily deriving the in-mold molding conditions that can obtain a good molded body with a smaller amount of steam, it is preferable to derive the in-mold molding conditions in the in-mold molding condition derivation step S3 using steam reduction conditions in which the total steam amount W2 of the steam reduction conditions is 0.8 times or less than the total steam amount _W1 under the standard conditions. From the same viewpoint, the total steam amount _W2 of the steam reduction conditions used in the in-mold molding condition derivation step _S3 is more preferably 0.75 times or less, and even more preferably 0.7 times or less, of the total steam amount _W1 under the standard conditions.

From the viewpoint of increasing the fusion rate of the obtained molded body, it is preferable to derive the in-mold molding conditions in the in-mold molding condition derivation step S3 using steam reduction conditions that can achieve a fusion rate _X2 of 0.5 times or more the target fusion rate _XT . From the same viewpoint, it is more preferable that the steam reduction conditions used in the in-mold molding condition derivation step S3 are configured so as to achieve a fusion rate _X2 of 0.6 times or more the target fusion rate _XT, and even more preferable that they are configured so as to achieve a fusion rate _X2 of 0.7 times or more.

The in-mold molding conditions derived in the in-mold molding condition derivation step S3 may include one molding condition, or may include two or more molding conditions. In addition to the molding conditions under which a molded body was actually produced and the fusion rate was measured, the in-mold molding conditions may include molding conditions that are estimated to be capable of achieving a fusion rate of the target fusion rate _XT or more based on molding conditions that have been experimentally confirmed to be capable of achieving a fusion rate of the target fusion rate _XT or more. That is, the in-mold molding conditions may include molding conditions under which the fusion rate has not actually been measured. For example, if a fusion rate _X1 of the target fusion rate _XT or more can be achieved under two molding conditions with different dwell times _tT , it can be estimated that a fusion rate of the target fusion rate _XT or more can also be achieved under molding conditions with a dwell time intermediate between the dwell times of these two molding conditions.

The in-mold molding conditions derived in the in-mold molding condition derivation step are preferably configured such that the maximum surface pressure F _max applied to the mold 1 in the main heating step P5 in the in-mold molding condition derivation step is 0.09 MPa (G) or more and 0.12 MPa (G) or less, and the time during which the surface pressure applied to the mold 1 becomes F _max -0.01 MPa or more in the pressure holding step P6 in the in-mold molding condition derivation step is 4 seconds or more and 20 seconds or less. In this case, the target fusion rate X _T can be more easily achieved while reducing the total amount of steam. In addition, the molding cycle of the molded body can be easily shortened, so that the productivity of the molded body can be further increased.

The surface pressure applied to the mold 1 is obtained by measuring the pressure generated during in-mold molding near the center of the molding surface (inner wall) when looking from one mold to the other along the mold clamping direction. A surface pressure gauge can be used to measure the surface pressure. The surface pressure gauge may be provided in the first mold 2 or in the second mold 3.

(Method for producing expanded bead molded article)
In producing a foamed bead molding, it is preferable to produce a foamed bead molding by in-mold molding the foamed beads under the in-mold molding conditions set by the in-mold molding condition setting method. As described above, the in-mold molding condition setting method can derive in-mold molding conditions that can reduce the amount of steam used compared to the standard conditions and obtain a molding having a fusion rate comparable to that of a molding obtained by in-mold molding under the standard conditions. Therefore, by performing in-mold molding using the in-mold molding conditions, a molding having good physical properties can be easily obtained while reducing the amount of steam used. In addition, the in-mold molding conditions set by the setting method can perform in-mold molding in a molding cycle equivalent to the molding cycle of the standard conditions set in the standard condition derivation step, or a molding cycle shorter than the molding cycle of the molding conditions set in the standard condition derivation step, and thus the productivity is excellent.

When the in-mold molding conditions including a plurality of molding conditions are derived in the method for setting the in-mold molding conditions, any one of the plurality of molding conditions may be used to perform in-mold molding in the manufacturing method. From the viewpoint of reducing the amount of steam used, it is preferable to perform in-mold molding using the molding conditions that have the smallest total amount of steam among the molding conditions included in the in-mold molding conditions.

Example 1
An example of the method for setting the in-mold molding conditions will be described below. In this example, the in-mold molding conditions were derived for producing a flat plate-shaped molded body having a length of 1000 mm, a width of 600 mm, and a thickness of 50 mm using expanded polystyrene beads.

The specific configuration of the mold 1 used in this example will be described with reference to FIG. 2. As shown in FIG. 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 so that it can move relative to the first mold 2 in the opening and closing direction of the mold 1. Between the first mold 2 and the second mold 3, there is provided a molding space 11 in which a molded body having the above-mentioned shape can be molded.

The first mold 2 has a hollow structure. The first mold 2 also has a first steam supply valve 21 configured to be able 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 be able to lead steam 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 a plurality of core vents that communicate between the internal space of the first mold 2 and the molding space 11.

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

In addition, a surface pressure gauge (not shown) configured to be able to measure the pressure (i.e., surface pressure) applied to the inner wall 23 is attached to the inner wall 23 of the first mold 2. The surface pressure gauge is provided near the center of the inner wall 23 when the first mold 2 is viewed from the second mold 3 along the mold clamping direction. More specifically, the surface pressure gauge is provided at a position on the inner wall 23 corresponding to the center of a surface of the molded body that is 1000 mm long and 600 mm wide. The foamed particles heated during the in-mold molding process fuse together while undergoing secondary expansion to become a molded body. Therefore, by providing the surface pressure gauge on the inner wall 33, the progress of the in-mold molding can be easily grasped through the change in surface pressure accompanying the secondary expansion of the foamed particles. The surface pressure gauge may be attached to the inner wall 33 of the second mold 3.

Although not shown in the figure, the steam pipe connected to the first steam supply valve 21 is equipped with a pressure gauge configured to measure the steam pressure and a flow meter configured to measure the steam flow rate. This makes it possible to measure the pressure and amount of steam supplied from the first steam supply valve 21 to the first mold 2.

The second mold 3 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 die 1 to the internal space of the second mold 3, and a second drain valve 32 configured to be able to lead steam from the internal space of the second mold 3 to the outside of the molding die 1. Although not shown in the figure, the inner wall portion 33 facing the molding space 11 in the second mold 3 has multiple core vents drilled therein 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, the steam pipe connected to the second steam supply valve 31 is equipped with a pressure gauge configured to measure the steam pressure and a flow meter configured to measure the steam flow rate. This makes it possible to measure the pressure and amount of steam supplied from the second steam supply valve 31 to the second mold 3.

In this example, the in-mold molding of the expanded beads is carried out according to the procedure shown in FIG. 3. That is, first, a filling step P1 is carried out to fill the molding space 11 of the mold 1 with the expanded beads (step P1). The expanded beads used in this example are polystyrene-based resin expanded beads with polystyrene as the base resin. The expanded beads have a bulk magnification of 60 times. 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 on the floor several times to stabilize the filling height of the expanded particles in the measuring cylinder. After that, the bulk volume (unit: L) of the expanded particles is read from the graduations on the measuring cylinder. The mass (unit: g) of the expanded particles in the measuring cylinder is divided by the aforementioned bulk volume, and the value is converted into a unit to obtain the bulk density (unit: kg/ ^m3 ) of the expanded particles.

After the filling step P1 is completed, an exhaust step P2 is performed in which the air in the mold 1 is pushed out of the mold 1 by steam. In the exhaust step P2 of this example, with the first steam supply valve 21, the first drain valve 22, the second steam supply valve 31, and the second drain valve 32 shown in FIG. 2 open, steam is supplied from the first steam supply valve 21 to the first mold 2, and steam is supplied from the second steam supply valve 31 to the second mold 3. This allows the air that has been stagnating in the internal space of the first mold 2 and the internal space of the second mold 3 to be replaced with steam.

After the exhaust process P2 is completed, as shown in FIG. 3, the first one-side heating process P3 is carried out to supply steam from the first mold 2 side to the molding space 11. In the first one-side heating process P3 of 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 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 through the core vent provided on the inner wall portion 23 of the first mold 2. This heats the foamed particles in the molding space 11. After that, the steam in the molding space 11 is led to the internal space of the second mold 3 through the core vent provided on the inner wall portion 33 of the second mold 3, and is led out of the molding mold 1 from the second drain valve 32.

After the first one-side heating process P3 is completed, as shown in FIG. 3, the second one-side heating process P4 is carried out to supply steam from the second mold 3 side to the molding space 11. In the second one-side heating process P4 of this example, the second steam supply valve 31 and the first drain valve 22 shown in FIG. 2 are opened, and the other valves are closed. In this state, steam is supplied from the second steam supply valve 31 to the second mold 3, thereby introducing 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 through the core vent provided on the inner wall portion 33 of the second mold 3. This heats the foamed particles in the molding space 11. After that, the steam in the molding space 11 is led to the internal space of the first mold 2 through the core vent provided on the inner wall portion 23 of the first mold 2, and is led out to the outside of the molding mold 1 through the first drain valve 22.

After the second one-sided heating step P4 is completed, as shown in FIG. 3, the main heating step P5 is carried out to supply steam to the molding space 11 from both the first mold 2 side and the second mold 3 side. In this example, the first steam supply valve 21 and the second steam supply valve 31 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 and from the second steam supply valve 31 to the second mold 3, thereby introducing steam into the internal space of the first mold 2 and the internal space of the second mold 3. The steam introduced into the internal spaces of these molds flows into the molding space 11 through the core vents provided in the inner walls 23 and 33. This increases the pressure in the molding space 11 and heats the foamed particles.

After the main heating step P5 is completed, as shown in FIG. 3, a pressure holding step P6 is carried out to hold the steam supplied to the first and second molds 2 and 3 in the main heating step P5 within the mold 1. In this example, the pressure holding step P6 closes all the valves shown in FIG. 2 to hold the steam within the mold 1. This allows the pressure applied to the molding surface of the mold 1 to decrease slowly, and the foamed particles within the molding space 11 to be heated under the desired pressure for a long period of time without supplying steam to the mold 1.

After the pressure holding step P6 is completed, a cooling step P7 is performed to cool the molded body in the mold 1, as shown in FIG. 3. The cooling step P7 in this example includes a water cooling step in which water is sprayed onto the inner walls 23, 33 from the first watering nozzle 24 and the second watering nozzle 34 shown in FIG. 2, and a vacuum cooling step 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 step 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 reduces 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 discharging 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 in the water cooling process becomes more likely to evaporate. When 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 P7 is completed, the mold 1 can be opened to obtain the molded body.

In this example, the in-mold molding conditions applicable to the in-mold molding method having the above-mentioned steps P1 to P7 were derived using the in-mold molding condition setting method (see FIG. 1) that includes the above-mentioned step S1 of deriving the reference conditions, step S2 of deriving the steam reduction condition range, and step S3 of deriving the in-mold molding conditions.

First, in the reference condition derivation step S1, the filling step P1, the exhaust step P2, the first one-side heating step P3, the second one-side heating step P4, the main heating step P5, and the cooling step P7 were performed under three types of molding conditions shown in the condition numbers A1 to A3 in Table 1, and a molded body was produced without performing the pressure holding step P6. The target fusion rate _XT in this example was set to 80%. In addition, the "total steam amount W" shown in Table 1 is the sum of the steam amount Wa in the first one-side heating step P3, the steam amount Wb in the second one-side heating step P4, and the steam amount Wm in the main heating step P5, and the "maximum surface pressure _Fmax " is the maximum value of the surface pressure applied to the inner wall portion 33 of the second mold 3 in the main heating step P5. In the reference condition derivation step S1, the pressure holding step P6 was not performed as described above, so the symbol "-" was entered in the "pressure holding step" column in Table 1.

The fusion rate of the molded body obtained by performing in-mold molding under each molding condition is as shown in Table 1. The method for measuring the fusion rate is as described above. That is, first, the molded body was folded so that the molded body broke near the longitudinal center of the molded body, and the molded body was broken into roughly equal parts. Then, 100 or more foamed beads were randomly selected from the foamed beads exposed on the fracture surface of the molded body and visually observed, and the ratio of the total number of foamed beads that had broken material to the total number of foamed beads visually observed was expressed as a percentage to calculate the fusion rate of the molded body. As shown in Table 1, among the condition numbers A1 to A3, the molding conditions under which the fusion rate X is equal to or greater than the target fusion rate _XT are two, condition numbers A1 and A2. Therefore, in the reference condition derivation step S1, these two molding conditions were set as candidates for the reference condition. Then, among the condition numbers A1 and A2, the condition number A2 with the smallest total steam amount W was set as the reference condition.

In addition, in the in-mold molding under condition number A2, the molding cycle was evaluated by measuring the time from when the mold clamping started to when the molded body was released from the mold. The mold was opened when the pressure (surface pressure) applied to the inner wall of the mold in the cooling process P7 reached a gauge pressure of 0.02 MPa (G). As a result, the time required from the start of mold clamping to mold release was 205 seconds. The shorter this time, the more efficient the in-mold molding of the foamed bead molding can be performed, which means a better molding cycle.

In step S2 of deriving the steam reduction condition range, at least some of the steam heating conditions of the standard condition (condition number A2) were changed, and the filling process P1, exhaust process P2, first one-side heating process P3, second one-side heating process P4, main heating process P5 and cooling process P7 were performed under the four molding conditions shown in condition numbers B1 to B4 in Table 1, and a molded body was produced without performing the pressure holding process P6. In condition numbers B1 and B2, the steam amount Wa in the first one-side heating process P3 and the steam amount Wb in the second one-side heating process P4 were changed from the standard conditions. In condition number B3, the steam amount Wa in the first one-side heating process P3 and the steam amount Wb in the second one-side heating process P4 were changed from the standard conditions. In addition, in condition number B4, the amount of steam Wa in the first one-way heating step P3, the amount of steam Wb in the second one-way heating step P4, and the amount of steam Wm in the main heating step P5 are changed from the standard conditions.

The fusion rates of the molded bodies obtained by performing in-mold molding under each molding condition are as shown in Table 1. The "fusion rate difference X ₁ -X ₂ " column in Table 1 lists the value obtained by subtracting the fusion rate under each molding condition from the fusion rate of the molded body under the standard condition. The "requirement 1: Pa ₂ /Pa ₁ " column lists the value of the ratio of the steam pressure Pa ₂ of the steam supplied in the first one-side heating step P3 under each of condition numbers B1 to B4 to the steam pressure Pa 1 of the steam supplied in the first one-side heating step P3 under the standard condition. The "requirement 2: Wa ₂ < Wa ₁ " column lists "OK" when the amount of steam Wa ₂ used in the first one-side heating step P3 under each of condition numbers B1 to B4 is less than the amount of steam Wa ₁ in the first one-side heating step _P3 under the standard condition, and "NG" when Wa ₁ or more.

The "Requirement 3: _Pb2 / _Pb1 " column lists the ratio of the steam pressure Pb2 of the steam supplied in the second one-way heating step _P4 in each of the condition numbers B1 to B4 to the steam pressure _Pb1 of the steam supplied in the second one-way heating step P4 under the standard conditions. The "Requirement 4: _Wb2 < _Wb1 " column lists "OK" if the amount of steam _Wb2 used in the second one-way heating step P4 in each of the condition numbers B1 to B4 is less than the amount of steam _Wb1 used in the second one-way heating step P4 under the standard conditions, and "NG" if it is equal to or greater than _Wb1 . The "Requirement 5: _Pm2 / _Pm1 " column lists the ratio of the steam pressure Pm2 of the steam supplied in the main heating step _P5 in each of the condition numbers B1 to B4 to the steam pressure _Pm1 of the steam supplied in the main heating step P5 under the standard conditions.

The "Requirement 6: _Wm2 / _Wm1 " column lists the ratio of the amount of steam _Wm2 used in the main heating step P5 under each of condition numbers B1 to B4 to the amount of steam _Wm1 used in the main heating step P5 under the standard conditions. The "Requirement 7: _W2 / _W1 " column lists the ratio of the total amount of steam _W2 under each of condition numbers B1 to B4 to the total amount of steam _W1 under the standard conditions. The "Requirement 8: _Wm2 / _Wa2 " column lists the ratio of the amount of steam Wm2 used in the main heating step P5 to the amount of steam _Wa2 used in the first one-way heating step P3 under each of condition numbers B1 to _B4 .

As shown in Table 1, among condition numbers B1 to B4, the molding conditions for which the fusion rate X is 10% or more are condition numbers B1 and B2. Therefore, in step S2 of deriving the steam reduction condition range, these two molding conditions are set as the steam reduction conditions, and the range including condition numbers B1 and B2 is set as the steam reduction condition range.

In the in-mold molding condition derivation step S3, among the steam reduction conditions derived in the steam reduction condition range step S2, the pressure holding step P6 was added to the condition number B2 with the smallest total steam amount _W2, and three molding conditions shown as condition numbers C1 to C3 in Table 1 were set. Then, under these three molding conditions, the filling step P1, the exhaust step P2, the first one-side heating step P3, the second one-side heating step P4, the main heating step P5, the pressure holding step P6, and the cooling step P7 were performed to produce a molded body. For the condition numbers C1 to C3, the time at which the surface pressure reached the maximum surface pressure F _max -0.01 MPa (G) or more in the pressure holding step P6 was measured and listed in Table 1.

The fusion rates of the molded bodies obtained by performing in-mold molding under each molding condition are as shown in Table 1. As shown in Table 1, all of condition numbers C1 to C3 are configured to obtain molded bodies having a fusion rate equal to or higher than the target fusion rate _XT . In addition, the total steam amount W under these in-mold molding conditions is all less than the total steam amount W ₁ under the standard conditions (i.e., 6.8 kg). Therefore, in the in-mold molding condition derivation step S3, condition numbers C1 to C3 were derived as the in-mold molding conditions.

As described above, in the method for setting the in-mold molding conditions, the in-mold molding conditions are derived in three steps: in step S1, the reference conditions are derived; in step S2, the steam reduction condition range is derived, which allows a molded body to be produced with a smaller amount of steam than the reference conditions; and in step S3, the steam reduction condition range is added to the steam reduction condition, and a pressure holding process P6 is added. By deriving the in-mold molding conditions in these three steps, it is possible to easily find in-mold molding conditions that allow a reduction in the amount of steam used during in-mold molding while obtaining a foamed bead molded body with a good fusion rate. Furthermore, according to the in-mold molding conditions obtained by the method for setting the in-mold molding conditions, it is possible to produce a molded body with a good fusion rate while reducing the amount of steam.

Furthermore, when the molding cycle was evaluated for in-mold molding under condition numbers C1 to C3, the time required from the start of mold clamping to demolding under these molding conditions was 152 seconds, 161 seconds, and 157 seconds, respectively. From these results, it was found that condition numbers C1 to C3, which were derived as the in-mold molding conditions, enable in-mold molding to be performed with a faster molding cycle than condition number A2, which was used as the reference condition, and are therefore superior in productivity.

(Comparative Example 1)
In this example, a method for setting the in-mold molding conditions when the molding conditions in which the first one-side heating step P3 and the second one-side heating step P4 are not performed are derived as the steam reduction conditions in the steam reduction condition derivation step S2 will be described. More specifically, in this example, the condition number B3 in Example 1, that is, the molding conditions in which the first one-side heating step P3 and the second one-side heating step P4 are not performed and the main heating step P5 is performed, is set as the steam reduction condition. Then, in the in-mold molding condition derivation step S3, in-mold molding was performed under molding conditions (Table 2, condition numbers D1 to D2) in which the pressure holding step P6 was added to the steam reduction conditions, and the fusion rate of the obtained molded body was measured. Table 2 shows the fusion rates of the molded bodies obtained by in-mold molding under condition numbers D1 to D2.

As shown in Table 2, when the first one-way heating process P3 and the second one-way heating process P4 were not performed, a molded body having the desired fusion rate could not be obtained even if the pressure holding process P6 was added after the main heating process P5.

Example 2
In this example, a method for setting molding conditions in a mold when a box-shaped molded body is produced using polystyrene-based resin foamed beads having a styrene-butyl acrylate copolymer as a base resin will be described. The base resin of the foamed beads used in this example is a styrene-butyl acrylate copolymer containing 0.5% by mass of a butyl acrylate component. The bulk ratio of the foamed beads is 60 times. The mold 1 in this example has a molding space 11 capable of producing a box-shaped molded body having dimensions of 550 mm in length, 350 mm in width, 110 mm in height, and 25 mm in thickness, and is configured so that the inner wall portion on the first mold 2 side in the mold clamping direction corresponds to the bottom surface of the box-shaped molded body (i.e., the surface with a length of 550 mm and a width of 350 mm). The surface pressure gauge is provided near the center of the inner wall portion of the first mold 2 when the first mold 2 is viewed from the second mold 3 along the mold clamping direction.

Using such expanded beads and mold 1, step S1 for deriving a reference condition and step S2 for deriving a range of steam reduction conditions were carried out in the same manner as in Example 1. The molding conditions (condition number E1 and condition numbers F1 to F3) under which in-mold molding was carried out in these steps are shown in Table 3. The target fusion rate _XT in this example was set to 90%.

As shown in Table 3, in this example, condition number E1 was set as the reference condition, and some of the steam heating conditions in the reference condition were changed to derive a steam reduction condition range including condition numbers F1 and F2. In addition, in the in-mold molding condition derivation step S3, a pressure dwell process P6 was added to condition number F2, which has the smallest total steam amount among condition numbers F1 and F2 shown in Table 3. As a result, two in-mold molding conditions, condition numbers G1 and G2 shown in Table 3, were derived.

As shown in Table 3, according to the in-mold molding conditions (condition numbers G1 to G2) derived in this example, a molded body having a fusion rate equal to or higher than the target fusion rate _XT could be obtained with a total steam amount less than that of the standard condition (condition number E1).

Furthermore, when the molding cycle was evaluated for in-mold molding under condition number E1 and condition numbers G1-G2, the time required from the start of mold clamping to demolding under these molding conditions was 134 seconds, 141 seconds, and 115 seconds, respectively. From these results, it was found that condition numbers G1-G2, which were derived as the in-mold molding conditions, are capable of in-mold molding with a molding cycle equal to or faster than condition number E1, which was used as the reference condition, and are therefore highly productive.

Example 3
In this example, a method for setting molding conditions in a mold when a flat molded body is produced using expanded polystyrene resin beads having a base resin of styrene-acrylonitrile copolymer is described. The base resin of the expanded beads used in this example is a styrene-acrylonitrile copolymer containing 26% by mass of acrylonitrile component. The bulk ratio of the expanded beads is 60 times. The mold 1 has a molding space 11 capable of producing a flat molded body having dimensions of 1000 mm in length, 600 mm in width, and 25 mm in thickness.

Using such expanded beads and mold 1, step S1 for deriving a reference condition and step S2 for deriving a range of steam reduction conditions were carried out in the same manner as in Example 1. The molding conditions (condition numbers H1 to H3 and condition numbers I1 to I2) under which in-mold molding was carried out in these steps are shown in Table 4. The target fusion rate _XT in this example was set to 80%.

As shown in Table 4, in this example, condition number H2 was set as the reference condition, and some of the steam heating conditions in the reference condition were changed to derive a steam reduction condition range including condition number I1. In this example, in-mold molding condition derivation step S3, a pressure holding process P6 was added to condition number I1 shown in Table 4. As a result, condition number J1 shown in Table 4 was derived as the in-mold molding condition.

As shown in Table 4, according to the in-mold molding conditions (condition number J1) derived in this example, a molded body having a fusion rate equal to or higher than the target fusion rate _XT could be obtained with a smaller total amount of steam than the standard condition (condition number H2).

In addition, when the molding cycle was evaluated for in-mold molding under condition numbers H2 and J1, the time required from the start of mold clamping to demolding was 218 seconds and 125 seconds, respectively. From these results, it was found that the in-mold molding condition under condition number J1 allows for in-mold molding with a faster molding cycle than the standard condition under condition number H2, and is therefore superior in productivity.

Based on the above results, it can be seen that in Examples 2 and 3 as well, by deriving the in-mold molding conditions in the three steps described above, it is possible to easily find in-mold molding conditions that enable a reduction in the amount of steam used during in-mold molding without impairing the physical properties of the foamed bead molding, just as in Example 1.

(Comparative Example 2)
In this example, a method for setting the in-mold molding conditions when molding conditions under which the fusion between the expanded beads is insufficient are adopted as the steam-reduced conditions is described. More specifically, in this example, the steam-reduced conditions were the molding conditions under which the fusion rate of the molded body was less than 10%, i.e., the condition number I2 in Example 3. Then, in the in-mold molding condition derivation step S3, in-mold molding was performed under molding conditions (Table 5, condition numbers K1 to K2) in which a pressure-holding process P6 was added to the steam-reduced conditions, and the fusion rate of the obtained molded body was measured. Table 5 shows the fusion rates of the molded bodies obtained by in-mold molding under condition numbers K1 to K2.

As shown in Table 5, when molding conditions that result in insufficient fusion between the foamed particles are used as steam reduction conditions, a molded body with the desired fusion rate cannot be obtained even if the pressure holding process P6 is added to those molding conditions.

Above, the method for setting the in-mold molding conditions for the expanded bead molding product and the method for manufacturing the expanded bead molding product according to the present invention have been explained based on Examples 1 to 3. However, the specific aspects of the method for setting the in-mold molding conditions for the expanded bead molding product and the method for manufacturing the expanded bead molding product according to the present invention are not limited to those described in the examples, and the configurations can be changed as appropriate within the scope of the present invention.

1 Mold 11 Mold space 2 First mold 3 Second mold

Claims (7)

A method for setting in-mold molding conditions for an expanded bead molding product, in order to obtain an expanded bead molding product having a fusion rate of X T [%] or more, by in-mold molding of expanded polystyrene resin beads 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, the method including: a first one-side heating step of supplying steam into the molding space from the first die side to heat the expanded beads in the molding space; a second one-side heating step of supplying steam into the molding space from the second die side after the first one-side heating step to heat the expanded beads in the molding space; a main heating step of supplying steam into the molding space from both the first die side and the second die side after the second one _- side heating step to heat the expanded beads in the molding space; and a pressure holding step of holding the steam supplied in the main heating step in the molding die,
The setting method includes a reference condition deriving step, a steam reduction condition range deriving step, and an in-mold molding condition deriving step,
in the step of deriving the reference conditions, the steam pressure and amount of steam in the first one-way heating step, the steam pressure and amount of steam in the second one-way heating step, and the steam pressure and amount of steam in the main heating step are included as steam heating conditions, and molding conditions capable of producing an expanded bead molding having a fusion rate _X1 [%] of _XT [%] or more without substantially carrying out a pressure-holding step are derived as reference conditions;
in the step of deriving a range of steam reduction conditions, at least a part of the steam heating conditions of the standard conditions is changed so that a total steam amount, which is the sum of the steam amount in the first one-way heating step, the steam amount in the second one-way heating step, and the steam amount in the main heating step, is less than the total steam amount in the standard conditions, and a range of steam reduction conditions, which is a molding condition under which an expanded bead molding having a fusion rate _X2 [%] of 10% or more can be produced without substantially performing a pressure-holding step, is derived as a range of steam reduction conditions;
the in-mold molding condition deriving step adds a dwelling step to the first one-way heating step, the second one-way heating step, and the main heating step under each steam reduction condition derived in the steam reduction condition range deriving step such that the dwelling time _tT of the dwelling step is longer than the dwelling time under the steam reduction conditions, and derives, as the in-mold molding conditions, a range of molding conditions capable of producing an expanded bead molding product having a fusion rate of _XT [%] or more. The steam reduction conditions are:
Requirement 1: the steam pressure Pa ₂ [MPa (G)] in the first one-way heating step under the steam-reducing conditions is 0.7 to 1.3 times the steam pressure Pa ₁ [MPa (G)] in the first one-way heating step under the standard conditions;
2. The method for setting in-mold molding conditions for an expanded bead molding body according to claim 1, which satisfies the following four requirements: requirement 2: the amount of steam _Wa2 [kg] in the first one-side heating step under the steam reduction conditions is less than the amount of steam _Wa1 [ _kg ] in the first one-side heating step under the standard conditions; requirement 3: the steam pressure _Pb2 [MPa (G)] in the second one-side heating step under the steam reduction conditions is 0.7 to 1.3 times the steam pressure Pb1 [MPa (G)] in the second one-side heating step under the standard conditions; and requirement 4: the amount of steam _Wb2 [kg] in the second one-side heating step under the steam reduction conditions is less than the amount of steam _Wb1 [kg] in the second one-side heating step under the standard conditions. 3. The method for setting in-mold molding conditions for an expanded bead molding according to claim 1 or 2, wherein the steam reduction conditions are configured so that a difference X1 - _X2 between a fusion rate _X1 [%] of the expanded bead molding obtained by in-mold molding under the standard conditions and a fusion rate _X2 [%] of the expanded bead molding obtained by in-mold molding under the _steam reduction conditions is 5% or more and 70% or less. The steam reduction conditions are:
3. The method for setting in-mold molding conditions for an expanded bead molding body according to claim 1 or 2, which satisfies two requirements: requirement 5: the steam pressure _Pm2 [MPa (G)] in the main heating process under the reduced steam conditions is 0.7 to 1.3 times the steam pressure _Pm1 [MPa (G)] in the main heating process under the standard conditions; and requirement 6: the steam amount _Wm2 [kg] in the main heating process under the reduced steam conditions is 0.7 to 1.3 times the steam amount _Wm1 [kg] in the main heating process under the standard conditions. The steam reduction conditions are:
3. The method for setting in-mold molding conditions for an expanded bead molding product according to claim 1 or 2, wherein the following requirement is satisfied: Requirement 7: The total steam amount [kg] under the reduced steam conditions is 0.8 times or less the total steam amount [kg] under the standard conditions. The steam reduction conditions are:
3. The method for setting in-mold molding conditions for an expanded bead molding product according to claim 1 or 2, wherein the following requirement is satisfied: Requirement 8: The steam amount _Wm2 [kg] of the main heating step under the steam reduction condition is 0.8 to 4 times the steam amount _Wa2 [kg] of the first one-way heating step under the steam reduction condition. A method for producing an expanded bead molding, comprising molding expanded polystyrene resin beads in a mold under the in-mold molding conditions set using the method for setting in-mold molding conditions for an expanded bead molding according to claim 1 or 2, to produce an expanded bead molding.

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