Volume reduction method of resin foam

Abstract

To reduce the volume of a resin foam by simple treatment.SOLUTION: A method for reducing the volume of a resin foam includes a volume reduction step of heating a resin foam stored in a storage body in a state in which a pressure in the storage body is lower than an atmospheric pressure at a temperature equal to or higher than a glass transition temperature.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a technique for reducing the volume of a resin foam. [Background technology]

[0002] Resin foams are used in various applications, such as containers for agricultural, forestry and fishery products, cushioning materials, food containers, heat insulating materials and building materials. As described above, resin foams are used in many applications, and therefore a large amount of used resin foams are discarded. Therefore, in recent years, there has been an active movement to recycle used resin foams as resources.

[0003] However, resin foams are usually produced by expanding the volume of the raw resin several to several tens of times. In other words, resin foams have a very large volume relative to their weight. Therefore, if resin foams are to be recycled as is, the cost of transporting them as is would be enormous. Therefore, when recycling resin foams, they are often subjected to a process to reduce their volume (volume reduction process).

[0004] As a method for reducing the volume, for example, there is a method of reducing the volume by dissolving the resin foam using a solvent (e.g., Patent Documents 1 to 3). However, the solvent used to dissolve the resin foam has environmental concerns and requires careful handling.

[0005] Therefore, a method has been proposed for reducing the volume of a resin foam by melting it using frictional heat generated when the resin foam is crushed, without using a solvent (for example, Patent Document 4). Specifically, a molten material is obtained by melting the resin foam using frictional heat generated when the resin foam is crushed using a crusher. This molten material is extruded, for example, into a plate shape, and then cooled to become an ingot. The ingot is then made into, for example, a pellet shape, and reused as a recycled raw material in various products. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2002-128949 A [Patent Document 2] JP 2002-069230 A [Patent Document 3] Japanese Patent Application Publication No. 07-113089 [Patent Document 4] Japanese Patent Application Publication No. 11-300743 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the method of reducing the volume by using frictional heat, it is necessary to crush and melt the resin foam, and then extrude the molten material to form an ingot, which requires many steps before the resin foam can be reused, which is troublesome. In consideration of the above circumstances, the present invention has an object to reduce the volume of a resin foam by a simple process. [Means for solving the problem]

[0008] [1] A method for reducing the volume of a resin foam, comprising a volume reduction step of heating the resin foam contained in a container at a temperature above the glass transition temperature while the pressure inside the container is lower than atmospheric pressure.

[0009] [2] The volume reduction method according to [1], wherein the volume reduction step includes a decompression step of reducing the pressure inside the container to a target pressure lower than atmospheric pressure.

[0010] [3] The volume reduction method according to [1] or [2], wherein the volume reduction step includes a pressurization step of increasing the pressure inside the container from a target pressure lower than atmospheric pressure.

[0011] [4] The volume reduction method according to either [2] or [3], wherein the target pressure is 0.1 MPa or less.

[0012] [5] A volume reduction method according to any one of [1] to [4], wherein in the volume reduction step, the resin foam is heated at a temperature equal to or lower than the melting point. Effect of the Invention

[0013] According to the volume reduction method of the present invention, the volume of a resin foam can be reduced by a simple process. [Brief description of the drawings]

[0014] [Figure 1] 4 shows a change in pressure inside a container according to an embodiment. [Diagram 2] This is 3D data obtained using a 3D digitizer for an unreduced fish box and a reduced fish box. [Diagram 3] This is a photograph of the fish box before and after reduction in volume. [Figure 4] This is a photo of the lid before and after volume reduction. [Diagram 5] Electron microscope images of the lid before and after volume reduction. [Figure 6] This is a photo of interior goods in which the powder after reduction is reused as artificial sand. [Figure 7] Photographs of cushioning material before and after volume reduction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The volume reduction method according to the present invention is a method for reducing the volume of a resin foam (i.e., reducing the volume). The resin foam is, for example, a molded body formed by foaming a base resin, and has a large number of bubbles (cells). Examples of the base resin include, but are not limited to, polystyrene-based resins, polyolefin-based resins, polyester-based resins, and polycarbonate-based resins. The resin foam is used in various applications such as containers for agricultural, forestry, and fishery products, cushioning materials, food containers, heat insulating materials, and building materials.

[0016] The volume reduction method of the present invention includes a volume reduction step in which the resin foam contained in a container is heated at a temperature equal to or higher than the glass transition temperature in a state in which the pressure inside the container (i.e., the environment in which the resin foam is placed) is lower than atmospheric pressure. In the volume reduction step, for example, a volume reduction device capable of controlling both temperature and pressure (e.g., a reduced pressure thermostatic chamber or a vacuum drying device) is used. The internal space of such a volume reduction device (a space capable of controlling temperature and pressure) is an example of the container.

[0017] As described above, the temperature to which the resin foam is heated in the volume reduction step (target heating temperature) is equal to or higher than the glass transition temperature of the resin foam, and is preferably equal to or higher than 100° C., more preferably equal to or higher than 120° C., and further preferably equal to or higher than 130° C. The upper limit of the target heating temperature is not particularly limited as long as the volume of the resin foam can be reduced, and may be appropriately changed depending on the type of resin foam, but is assumed to be 180° C., for example.

[0018] In this embodiment, the volume reduction process is performed by performing a first process and a second process for the pressure of the container. The heating target temperature (preset temperature) of the resin foam is typically constant at a temperature equal to or higher than the glass transition temperature throughout the first process and the second process.

[0019] Fig. 1 is a diagram showing the pressure change inside the container in the first process and the second process. The first process is a process for lowering the pressure inside the container from atmospheric pressure (normal pressure) to a pressure lower than atmospheric pressure (hereinafter referred to as "target pressure"). In other words, the first process is a process for creating a negative pressure inside the container. Fig. 1 illustrates an example in which the pressure inside the container is changed in the first process so that the pressure decreases continuously from atmospheric pressure to the target pressure.

[0020] The second process is a process for increasing the pressure inside the container from a target pressure to atmospheric pressure (normal pressure). In other words, the second process is a process for increasing the pressure inside the container so that the pressure approaches a positive pressure. FIG. 1 illustrates an example in which the pressure inside the container is changed in the second process so that the pressure increases continuously from the target pressure to atmospheric pressure.

[0021] The period during which the first process is performed (i.e., the time it takes to reach the target pressure from atmospheric pressure) is, for example, about 1 to 15 minutes. Similarly, the period during which the second process is performed (i.e., the time it takes to reach the target pressure from the target pressure) is, for example, about 1 to 15 minutes. From the viewpoint of bringing the pressure inside the container to the target pressure in a short period of time, it is preferable to start the first process after the resin foam has reached the glass transition temperature or higher.

[0022] The volume reduction process is realized by controlling the pressure of the contained body through the first process and the second process. In the first process and the second process, the section in which the pressure of the contained body is lower than atmospheric pressure (the section not including the state where the pressure is atmospheric pressure) on the timeline of Fig. 1 corresponds to the volume reduction process.

[0023] In other words, the volume reduction process of this embodiment includes a depressurization process for reducing the pressure inside the container to a target pressure, and a pressurization process for increasing the pressure inside the container from the target pressure. The depressurization process is a process in the first process in a section where the pressure inside the container is lower than atmospheric pressure (a section that does not include a state where the pressure is at atmospheric pressure). The pressurization process is a process in the second process in a section where the pressure inside the container is lower than atmospheric pressure (a section that does not include a state where the pressure is at atmospheric pressure).

[0024] The target pressure (absolute pressure, the same applies below) is, for example, 0.1 MPa or less, preferably 0.05 MPa or less, more preferably 0.03 MPa or less, even more preferably 0.02 MPa or less, particularly preferably 0.015 MPa or less, and most preferably 0.011 MPa or less. By setting the target pressure within the above range, the volume reduction rate can be increased. The lower limit of the target pressure is not particularly limited, and may be the limit pressure that can be reached in the specifications of the volume reduction device used in the volume reduction step.

[0025] Here, for example, in a method of reducing the volume of a resin foam by melting it with frictional heat generated when the resin foam is pulverized (hereinafter referred to as a "Comparative Example"), a melting step using frictional heat generated by pulverization and a step of extruding the molten material to form an ingot are required, which causes problems such as time-consuming work and scattering of resin foam powder. In contrast, the volume reduction method of the present embodiment can reduce the volume of a resin foam by a volume reduction step in which the resin foam is heated at a pressure lower than atmospheric pressure and at or above the glass transition temperature. That is, compared to the Comparative Example, the resin foam can be reduced in volume by a simple method. However, the volume reduction method of the present embodiment may also reduce the volume of the resin foam after pulverizing it.

[0026] The reason why volume reduction proceeds in the volume reduction method of this embodiment will be explained. In the resin foam manufacturing process (process of foaming the base resin), the air bubbles can become negative pressure. Over time, the inside of the air bubbles approaches atmospheric pressure. However, it is believed that the air bubbles in the resin foam do not become completely at atmospheric pressure (normal pressure) and are in a state of negative pressure to some extent. In the volume reduction method of this embodiment, the negative pressure in the air bubbles in the resin foam is believed to be one of the factors that causes a large volume reduction.

[0027] First, in the depressurization step, it is believed that the volume reduction influenced by thermal shrinkage due to heating becomes significant. Specifically, the gas in the independent cells of the resin foam expands due to heating, causing the cells (walls) to break (i.e., the cells become interconnected or communicate with the outside air). In addition to the bubbles breaking, the resin foam heated to the glass transition temperature or higher easily deforms, so that thermal shrinkage becomes significant. On the other hand, in the pressurization step, it is believed that the negative pressure state bubbles that did not break and maintained an independent state in the depressurization step and the mutually interconnected but still negative pressure state bubbles are compressed due to the increase in pressure inside the container.

[0028] As described above, the volume reduction method of the present embodiment has a remarkable effect of reducing the volume of the resin foam by including both the depressurization step and the pressurization step. However, the volume reduction method may include either the depressurization step or the pressurization step.

[0029] Moreover, in the comparative example, in order to reduce the volume of the resin foam, it is necessary to use a large volume reduction machine including a pulverizer and an extruder. Therefore, there is a problem that it is not easy to introduce at the site where the resin foam is discharged. In contrast, in the volume reduction method of the present embodiment, as long as both temperature and pressure can be controlled, the resin foam can be reduced in volume even with a volume reduction device (e.g., a reduced pressure thermostatic chamber or a vacuum drying device) that is not equipped with a pulverizer or an extruder. In other words, compared to the comparative example, the resin foam can be reduced in volume with a simple volume reduction device. Therefore, the volume reduction device can be easily introduced. EXAMPLES

[0030] The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

[0031] [Example 1] An EPS (Expanded Polystyrene, bead-method polystyrene foam) fish box (external dimensions: 580 mm x 370 mm x 231 mm) with an expansion ratio of 60 times was decompressed. The glass transition temperature of the fish box was measured using a DSC (differential scanning calorimeter DSC-60, Shimadzu Corporation) and found to be 95 ° C. The volume of the fish box was reduced using a reduced pressure thermostatic bath (MZT-11H-H, Espec Corporation). First, the tank containing the fish box was heated from 120 ° C to 130 ° C under normal pressure. Next, the pressure in the tank was reduced to 0.0107 MPa over about 7 minutes. Then, the tank was returned to normal pressure (0.1013 MPa) over about 2 minutes. The volume of two EPS fish boxes of the same type was reduced. Figure 2 shows 3D data obtained using a 3D digitizer (FLARE Pro 16M, Tokyo Boeki Technosystems Co., Ltd.) for the unreduced fish box (Box-o) and the reduced fish boxes (Box-T1, Box-T7). Table 1 shows the mass, volume, density, and reduction rate for the unreduced fish box (Box-o) and the reduced fish boxes (Box-T1, Box-T7). The dimensions and volume of the fish boxes were measured using the 3D digitizer. The mass of the fish boxes was measured using a general-purpose scale.

[0032] [Table 1]

[0033] As shown in Figure 2, the fish box was reduced in volume while maintaining the original shape to some extent, though not completely. As shown in Table 1, the volume of the fish box after reduction was greatly reduced and the density increased, with the reduction rate (%) ((1-volume after reduction / volume before reduction) x 100) being approximately 97%. Note that the volume before reduction was approximately the volume of Box-o.

[0034] [Example 2] A fish box with a pattern was reduced in volume under the same conditions as in Example 1. Figure 3 shows a photograph of the fish box with a pattern before reduction and the fish box after reduction (within the frame). For comparison, the reduced fish box was placed on top of an unreduced fish box of the same type as the reduced fish box and photographed. As shown in Figure 3, it can be confirmed that the pattern is not significantly distorted before and after reduction.

[0035] [Example 3] The lid of an EPS (Expanded Polystyrene, bead-processed polystyrene foam) fish box was reduced in volume under the same conditions as in Example 2. FIG. 4 shows photographs of an unreduced lid (Lid-o) and a reduced lid (Lid-T). FIG. 5 shows SEM images of the surfaces and cross sections of the unreduced lid (Lid-o) and the reduced lid (Lid-T) taken with an SEM (scanning electron microscope JSM-6390LV, JEOL Ltd.). As shown in FIG. 5, it can be seen that after volume reduction, the spherical beads are deformed to the point where there are no gaps, and the air bubbles are crushed and dense.

[0036] For comparison, SEM images of the surface and cross section of the same type of lid heated at 130°C for 15 minutes under normal pressure using the above-mentioned reduced pressure thermostatic chamber are also shown in Figure 5. As can be seen from Figure 5, even if the lid is heated at 130°C for a long time (15 minutes) at normal pressure, a certain volume reduction effect is obtained, but the air bubbles in the spherical beads are hardly crushed, and gaps can be seen between the beads. As can be understood from the above explanation, according to the volume reduction method of the present invention, which reduces pressure while heating and returns to normal pressure, a higher volume reduction rate can be obtained compared to a heating only treatment method for a similar treatment time.

[0037] Table 2 shows the flexural modulus, maximum stress (flexural strength), and breaking strain measured by a universal testing machine (Autograph AG-10TD, Shimadzu Corporation) for test pieces cut out from the unreduced lid and the reduced lid. As shown in FIG. 4, all the lids are not flat but have a shape with a concave-convex pattern, so the test pieces were cut out from parts with a relatively uniform thickness. The bending test conditions were set with reference to JIS K 7171 (ISO 180). For the unreduced lid (Lid-o), a test piece with dimensions of approximately 380 mm x 20 mm x 18 mm was cut out and tested under conditions of a support distance of 220 mm and a test speed of 5 mm / min. On the other hand, for the reduced lid (Lid-T), a test piece with dimensions of approximately 140 mm x 15 mm x 6 mm was cut out and tested under conditions of a support distance of 96 mm and a test speed of 2 mm / min.

[0038] [Table 2]

[0039] As can be seen from Table 2, after reduction, the flexural modulus was more than 20 times higher and the maximum point stress (flexural strength) was more than twice as high as before reduction. As mentioned above, the shape of the test piece is special, so the measured values ​​are for reference only.

[0040] As shown in Examples 1-3 above, it was confirmed that the volume of a resin foam can be significantly reduced by the volume reduction method according to the present invention. The ingots produced by the volume reduction method of the comparative example are, for example, pelletized and reused as recycled raw materials in various products. In contrast, the resin foam reduced in volume by the present invention has the advantage that it can be manufactured as it is without going through recycled raw materials, since it is likely to maintain its shape before volume reduction. For example, when a box-shaped resin foam is reduced in volume, it may be used as a product such as a small item holder or a stationery holder.

[0041] In the examples 1-3, the case where the fish box and the lid of the fish box are reduced in volume is exemplified, but for example, a powdered resin foam (for example, a powder generated during the manufacture of a resin foam) may be reduced in volume. Also, a volume reduction device other than the reduced pressure thermostatic bath may be used for volume reduction.

[0042] [Example 4] The powdered resin foam produced by the conventional volume reduction method using frictional heat was placed in a vacuum dryer (AVO-250N, AS ONE Corporation) that was heated from room temperature to 130°C under normal pressure, and the pressure inside the machine was reduced to -0.1 MPa (gauge pressure) over a period of about 3 minutes. The pressure inside the machine was then returned to normal pressure of 0 MPa (gauge pressure) over a period of about 1 minute. The reduced powdered resin foam has a higher density and is less likely to scatter, making it suitable for a variety of uses. For example, as shown in Figure 6, the powdered resin foam after volume reduction can be used as artificial sand to be spread on interior goods.

[0043] [Example 5] A PE (Polyethylene) foam cushioning material was reduced in volume under the same conditions as in Example 4 using a vacuum dryer (AVO-250N, AS ONE Corporation). Figure 7 shows photographs of the unreduced PE cushioning material and the reduced PE cushioning material. As shown in Figure 7, the cushioning material was reduced in volume while maintaining the original shape to some extent, though not completely. It was also confirmed that not only EPS foam but also PE foam can be reduced in volume.

[0044] <Modification> The above-mentioned exemplary embodiments can be modified in various ways. Specific modified embodiments are exemplified below. Two or more embodiments selected from the following examples can be appropriately combined.

[0045] (1) The target temperature for heating the resin foam is typically constant throughout the volume reduction process (the first and second processes). However, the target temperature for heating the resin foam may be changed during the volume reduction process as long as it is equal to or higher than the glass transition temperature.

[0046] (2) A process of maintaining the target pressure for a predetermined period of time may be included between the first process and the second process.

[0047] (3) In the depressurization step (first process), it is not essential to continuously reduce the pressure inside the container. For example, in the depressurization step, the pressure inside the container may be reduced stepwise. Note that the depressurization step may include a section in which the pressure increases or a section in which the pressure is maintained, as long as the pressure is ultimately reduced to the target pressure.

[0048] (4) In the pressurizing step (second process), it is not essential to continuously increase the pressure inside the container. For example, in the pressurizing step, the pressure inside the container may be increased in stages. Note that the pressurizing step may include a section in which the pressure decreases or a section in which the pressure is maintained, as long as the pressure is ultimately increased to approach atmospheric pressure. Also, as long as the pressurizing step is a step of increasing the pressure inside the container in a direction approaching atmospheric pressure, it is not essential to increase the pressure from the target pressure. In other words, the pressurizing step may be a step of increasing the pressure inside the container from a pressure higher or lower than the target pressure to approach atmospheric pressure.

[0049] (5) If the resin foam can be heated to the glass transition temperature or higher while the pressure inside the container is lower than atmospheric pressure, it is not essential that the volume reduction method includes a depressurization step and a pressurization step. For example, the volume reduction step may include either a depressurization step or a pressurization step, or the volume reduction step may include a step of maintaining the pressure inside the container constant at a pressure (target pressure) lower than atmospheric pressure.

[0050] (6) The volume reduction method may include a step other than the volume reduction step. For example, the volume reduction method may include a step of heating the resin foam at normal pressure before the volume reduction step. The volume reduction method may also include a step of assembling a plurality of resin foams before the volume reduction step. Furthermore, the volume reduction method may include a step of shaping the resin foam after volume reduction using a jig, a mold, or the like.

Claims

1. A method for reducing the volume of a resin foam, comprising the steps of: The method includes a volume reduction step of heating the resin foam contained in the container at a temperature equal to or higher than the glass transition temperature in a state in which the pressure inside the container is lower than atmospheric pressure. Volume reduction processing method.

2. The volume reduction step includes a decompression step of reducing the pressure inside the container to a target pressure lower than atmospheric pressure. The volume reduction method according to claim 1.

3. The volume reduction step includes a pressurization step of increasing the pressure inside the container from a target pressure lower than atmospheric pressure. The volume reduction method according to claim 1.

4. The target pressure is 0.1 MPa or less. The volume reduction method according to claim 2 or 3.

5. In the volume reduction step, the resin foam is heated at a temperature equal to or lower than the melting point. The volume reduction method according to claim 1.

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