Method for producing nanofoamed polymers and nanofoamed polymers

Abstract

To provide a new method for producing a resin foam, and a resin foam produced by the method.SOLUTION: A method for producing a nano foamed polymer includes: arranging a first resin where first gas is dissolved under atmosphere containing first gas and second gas reducing surface tension of the first resin (step S10); then performing pressurization of raising a partial pressure of the first gas and a partial pressure of the second gas in the above-described atmosphere (step S20); and then lowering the partial pressure of the first gas and the partial pressure of the second gas in the above-described atmosphere (step S30). In the step S20, for example, the pressure of the atmosphere is raised, and in the step S30, for example, the pressure of the atmosphere is lowered.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a nano-foamed polymer and a nano-foamed polymer.

Background Art

[0002] Foams of resins such as polymers have excellent properties in terms of light weight, heat insulation, sound insulation, and insulation. Therefore, foams of various polymers are used in a wide range of technical fields.

[0003] One method for producing a resin foam is a physical foaming method. In this foaming method, a foaming gas is dissolved in a polymer at high pressure, and then the solubility of the gas in the polymer is reduced by depressurization or heating to form bubbles.

[0004] For example, Patent Document 1 describes using a mixed gas of nitrogen and carbon dioxide in a physical foaming method of a lactic acid-based polymer. Also, Patent Document 2 describes using a mixed gas mainly composed of nitrogen in a method for producing polypropylene-based resin foam particles.

[0005] Further, in Non-Patent Document 1, in the foaming process of polystyrene, the application of a foaming gas in which supercritical carbon dioxide having a high solubility and a high plasticizing effect and supercritical nitrogen having a high nucleation effect are mixed is examined. This document reports that a high bubble density and bubble growth density can be obtained by using a gas in which carbon dioxide and nitrogen are mixed at 75% and 25%, respectively, under saturated temperature conditions of 100°C to 180°C.

[0006] Non-patent document 2 also investigates batch foaming methods for polycaprolactone, a semicrystalline polymer, comparing the use of supercritical carbon dioxide as a foaming agent with the use of a supercritical carbon dioxide-ethanol mixture as a foaming agent. This document reports that, under saturated conditions of 35°C to 45°C and 12.3 MPa to 20.5 MPa, using supercritical carbon dioxide results in a non-uniform pore structure, while using a supercritical carbon dioxide-ethanol mixture improves the uniformity of the bubble structure.

[0007] Furthermore, HFC-134a is slightly more soluble than carbon dioxide, making it a more effective plasticizer. Under similar processing conditions, HFC-134a produces foam samples with a higher nucleation density than carbon dioxide. Non-patent document 3 reports that blending carbon dioxide and HFC-134a may cause the mixed gas to affect the interdiffusion coefficient, significantly influencing the final foam morphology.

[0008] Furthermore, Non-Patent Document 4 describes the determination of vapor-liquid equilibrium data from bubble point measurements in an HCFC-22 / carbon dioxide mixed system at temperatures ranging from 30°C to 70°C. In addition, this document uses the Peng-Robinson equation of state to correlate vapor-liquid equilibrium data.

[0009] Furthermore, Non-Patent Document 5 describes the measurement of phase behavior data for chlorodifluoromethane, difluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroethane, and polylactic acid at temperatures of 303.15K to 373.15K and pressures of 3MPa to 85MPa.

[0010] Furthermore, Non-Patent Document 6 describes the measurement of phase behavior data for a mixed system of dichloromethane and carbon dioxide, as well as polylactic acid.

[0011] Furthermore, Non-Patent Document 7 describes the measurement of three-phase equilibrium data for hydrochlorofluorocarbon (HCFC) / carbon dioxide / polymethyl methacrylate resin (PMMA). [Preliminary Technology Documents] [License]

[0012] [License 1] Special Announcement No. 2001-342279 [License 2] Special Announcement No. 58-76230 [Non-licensed literature]

[0013] [Non-licensed Document 1] Wong, LH Mark, MM Hasan, CB Park, The synergy of supercritical CO2 and supercritical N-2 in foaming of polystyrene for cell nucleation, J. Supercrit. Fluids, 90 (2014) 35-43. [Non-licensed Document 2] I. Tsivintzelis, E. Pavlidou, C. Panayiotou, Biodegradable polymer foams prepared with supercritical CO2-ethanol mixtures as blowing agents, J. Supercrit. Fluids, 42 (2007) 265-272. [Non-licensed Document 3] C. Vachon, R. Gendron, Foaming polystyrene with mixtures of carbon dioxide and HFC-134a, Cellular Polymers, 22 (2003) 75-87. [Non-licensed Document 4] J.M. Lee, B.C. Lee, C.H. Cho, Measurement of bubble point pressures and critical points of carbon dioxide and chlorodifluoromethane mixtures using the variable - volume view cell apparatus, Korean J. Chem. Eng., 17 (2000) 510 - 515.

Non - Patent Document 5

Non - Patent Document 6

Non - Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0014] Depending on the use of the resin foam, it is necessary to lower the average cell diameter while setting the expansion ratio of the resin foam to a certain value or more. In order to achieve this, it is necessary to consider a new manufacturing method for the resin foam.

[0015] An object of the present invention is to provide a novel method for producing a resin foam and a resin foam produced by this method.

Means for Solving the Problems

[0016] According to the present invention, a preparation step of disposing a first resin in which a first gas is dissolved in an atmosphere containing the first gas and a second gas that reduces the surface tension of the first resin with respect to the first gas; A pressurization step of increasing the partial pressure of the first gas and the partial pressure of the second gas in the atmosphere; A depressurization step of reducing the partial pressure of the first gas and the partial pressure of the second gas in the atmosphere; A method for producing a nano-foamed polymer comprising the above is provided.

[0017] Further, according to the present invention, a preparation step of disposing a first resin in which a first gas is dissolved in an atmosphere containing the first gas and a second gas having a solubility in the first resin higher than that of the first gas; A pressurization step of increasing the partial pressure of the first gas and the partial pressure of the second gas in the atmosphere; A depressurization step of reducing the partial pressure of the first gas and the partial pressure of the second gas in the atmosphere; A method for producing a nano-foamed polymer comprising the above is provided.

Advantages of the Invention

[0018] According to the present invention, a novel method for producing a resin foam and a resin foam produced by this method can be provided.

Brief Description of the Drawings

[0019] [Figure 1] This is a flowchart showing the method for producing a resin foam according to the embodiment. [Figure 2] This figure shows an example of an apparatus for performing the processing shown in Figure 1. [Figure 3] The images shown are low-magnification SEM images of the cross-sections of the resin foams according to Examples 1-4 and the Comparative Example. [Figure 4] The image in Figure 3 shows the result of first blackening the cross-section of the resin foam, and then whiteening the bubbles with a diameter of 100 μm or more. [Figure 5] The results of taking cross-sectional images in the x, y, and z directions using 3D X-ray CT for Examples 1, 2, and 3 are shown. [Figure 6] The images shown are high-magnification photographs of the cross-sections of the resin foams relating to Examples 1-4 and the Comparative Example, specifically the portions without air bubbles larger than 100 μm. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described below with reference to the drawings. In all drawings, similar components are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0021] (Embodiment) Figure 1 is a flowchart illustrating a method for producing a resin foam (nano-foamed polymer) according to this embodiment. The resin foam production method shown in this figure is an example of a physical foaming method and includes a preparation step (step S10), a pressurization step (step S20), and a depressurization step (step S30). Details of the preparation step, pressurization step, and depressurization step will be described later, but according to this embodiment, a resin foam consisting of a single resin and having fine bubbles (for example, an average foam diameter of 1 μm or less, and even 120 nm or less) can be produced. Furthermore, according to this embodiment, a resin foam with an average bubble diameter of 120 nm or less and a porosity of 38% or more can be produced. The bubble density (nucleation density) of this resin foam is 1 × 10⁻⁶ 13 pieces / cm 3This can be achieved. Furthermore, in the cross-section of the resin foam, the density of bubbles with a diameter of 100 μm or more is 0.5 bubbles / 1 mm. 2 The following can be done:

[0022] Furthermore, if the majority of the bubbles in the resin foam are around 100 nm in size, the resin foam will have light-transmitting properties.

[0023] <Preparation process (Step S10)> The preparation step (step S10) is a step in which the first resin, which will become a resin foam, is placed in an atmosphere containing a first gas and a second gas that reduces the surface tension (interfacial tension) of the first resin relative to the first gas. The atmosphere in the preparation step preferably consists of a first gas, a second gas, and unavoidable impurities. In the preparation step, the first resin may first be placed in an atmosphere in which the second gas is the main component (for example, 50% or more, preferably 80% or more), and then the first gas may be introduced into the atmosphere.

[0024] The first resin contains, for example, polymethyl methacrylate resin (PMMA). Here, the first resin preferably has PMMA as its main component (for example, 50% or more, preferably 80% or more, and more preferably 90% or more). More preferably, it is, for example, PMMA. However, the first resin may be another resin that can dissolve the first gas, such as polystyrene, polypropylene, or polylactic acid. Also, the first resin may be a single resin, excluding unavoidable impurities.

[0025] The first gas is a gas that dissolves in the first resin, for example, carbon dioxide. However, the first gas may be another gas, for example, nitrogen.

[0026] The second gas, as described above, reduces the surface tension of the first resin. Specifically, when the first resin is placed in an atmosphere containing the second gas, the surface tension of the first resin is reduced by 10% or more compared to the state without the second gas by adjusting the temperature and partial pressure. As an example, the second gas is a substance that has a higher solubility in the first resin than the first gas. For example, if the first resin contains PMMA, examples of the second gas are at least one of chlorofluorocarbons (e.g., chlorodifluoromethane (HCFC-22)) and hydrofluoroolefins (e.g., trans-1,3,3,3-tetrafluoropropene (HFO-1234ze-(E))). When the second gas is present in the atmosphere, the concentration of the second gas in the atmosphere is, for example, 1 mol% or more, preferably 5 mol% or more, and more preferably 10 mol% or more. Note that if the partial pressure of the second gas is increased too much, the first resin will completely dissolve. Therefore, the partial pressure of the second gas should be such that the first resin does not completely dissolve. Ma It needs to be below a certain value. For example, if the first gas is carbon dioxide, the second gas is HCFC-22, the atmosphere consists of the first and second gases and unavoidable impurities, the ambient temperature is 80°C, and the ambient pressure is 40M P In case a, the upper limit of the partial pressure of the second gas is 20 mol. % That is the case.

[0027] <Pressurization process (Step S20)> The pressurization step (step S20) is a step in which the partial pressure of the first gas and the partial pressure of the second gas are increased in the atmosphere described above, and is performed after the preparation step (step S10), for example, after the preparation step. An example of the pressurization step is a step in which the pressure of the atmosphere itself is increased. When increasing the pressure of the atmosphere, it is preferable that the pressure of the atmosphere be, for example, 20 MPa or more, preferably 40 MPa or more. It is preferable that the state in which the partial pressure of the first gas and the partial pressure of the second gas are increased is maintained for 1 hour or more, preferably 10 hours or more, and more preferably 20 hours or more. As a result, the first gas dissolves in the first resin, and the second gas also dissolves in the first resin.

[0028] <Depressurization process (Step S30)> The depressurization step (step S30) is a step in which the partial pressures of the first gas and the second gas in the atmosphere are reduced, and is performed after the pressurization step (step S20), for example, after the pressurization step. In order to reduce the partial pressures of the first gas and the second gas, for example, the atmosphere is depressurized. In this depressurization step, the solubility of the first gas and the second gas in the first resin decreases, so that bubbles or their nuclei are formed in the first resin by the first gas and the second gas. By including this step, a resin foam is produced. In the depressurization step, it is preferable that the rate of depressurization of the partial pressure of the first gas is 1 GPa / second or more. In this way, the first resin foams sufficiently.

[0029] Figure 2 shows an example of an apparatus 10 for performing the process shown in Figure 1. The apparatus 10 shown in this figure is an extrusion apparatus that can continuously produce resin foam.

[0030] Specifically, the apparatus 10 has a container 110. The container 110 has a certain length, with a shared port 112 at one end and a discharge port 114 at the other end. The first resin is supplied from the shared port 112 and discharged to the outside from the discharge port 114.

[0031] The container 110 is connected to a first gas supply unit 130 and a second gas supply unit 140 via piping. The first and second gases are introduced into the container 110 from multiple locations. In this process, the first gas supply unit 130 can control the supply amount of the first gas, and the second gas supply unit 140 can control the supply amount of the second gas. Furthermore, the pressure inside the container 110 is controllable. The pressure inside the container 110 becomes the pressure required for, for example, the pressurization process (step S20 in Figure 1).

[0032] A mixing shaft 120 is provided inside the container 110. Although not shown in the diagram, the shaft 120 is screw-shaped and rotated by a motor 122. This rotation moves the first resin from the shared port 112 towards the discharge port 114, and it is eventually pushed out to the outside from the discharge port 114.

[0033] The supply of the first resin from the shared port 112 into the container 110 corresponds to the preparation step (step S10 in Figure 1). The movement of the first resin from the shared port 112 to the discharge port 114 inside the container 110 corresponds to the pressurization step (step S20 in Figure 1). The discharge of the first resin from the discharge port 114 corresponds to the depressurization step (step S30 in Figure 1). In this way, using the apparatus 10, resin foam can be continuously manufactured according to the manufacturing method shown in Figure 1.

[0034] As described above, according to this embodiment, a novel method for manufacturing resin foam makes it possible to lower the average cell diameter while maintaining a foaming ratio above a certain value. For this reason, this resin foam is suitable for use as a thermal insulation material, a lightweight structural material, and a cushioning material.

[0035] Furthermore, in conventional manufacturing methods, a skin layer is formed on the surface of the first resin where the first gas escapes quickly, resulting in an excess of the first gas being retained inside the first resin. In this case, a coarse foam structure (i.e., large-diameter bubbles) is formed inside the resin foam, significantly impairing the homogeneity and functionality of the resin foam. In contrast, according to this embodiment, the surface tension of the first resin is lowered using a second gas, thereby suppressing the formation of the aforementioned skin layer. As a result, a coarse foam structure is less likely to form inside the resin foam.

[0036] Furthermore, while nucleating agents, polymer copolymers, and polymer blends have generally been used in the production of resin foams, this embodiment allows for the production of resin foams using only one type of resin (e.g., PMMA).

[0037] (Examples) The following describes a specific method for producing a resin foam using PMMA as the first resin, but the method for producing the resin foam of the present invention is not limited to the method described below.

[0038] In this example, resin foams according to Examples 1 to 4 and resin foams according to the comparative example were manufactured. Carbon dioxide was used as the first gas in these manufacturing processes.

[0039] In detail, first, PMMA (manufactured by Sigma Aldrich, molecular weight 350,000) was hot-pressed into a disc with a diameter of 8 mm and a thickness of 1 mm. After vacuum-drying this disc, it was wrapped in a metal mesh to prevent fusion and placed in a volume of 24 cm³. 3 The mixture was introduced into a pressure vessel. The ambient temperature inside the pressure vessel was set to 80°C, and a second gas, which has a higher solubility in PMMA than carbon dioxide (the first gas), was introduced. Subsequently, carbon dioxide was introduced to pressurize the mixture to 40 MPa. In this state, the atmosphere inside the vessel was a mixture of carbon dioxide and the second gas. After leaving it in this state for 24 hours, the PMMA was foamed by rapidly depressurizing it.

[0040] In Examples 1 and 2, HCFC-22 was used as the second gas. The concentration of the second gas in Example 1 was 2.6 mol%, and in Example 2, it was 14.2 mol%. In Examples 3 and 4, HFO-1234ze-(E) was used as the second gas. The concentration of the second gas in Example 3 was 1.7 mol%, and in Example 4, it was 9.0 mol%.

[0041] Furthermore, in the comparative example, the second gas was not introduced.

[0042] Table 1 shows the manufacturing conditions for the resin foams related to Examples 1 to 4 and the comparative examples described above.

[0043] [Table 1]

[0044] Figure 3 shows images of cross-sections of resin foams according to Examples 1-4 and the comparative example, taken with a low-magnification SEM. Figure 4 shows the result of blacking out the cross-section of the resin foam in the image shown in Figure 3, and then blackening out the bubbles with a diameter of 100 μm or more. Figure 5 shows the results of taking cross-sections in the x, y, and z directions for Examples 1, 2, and 3 using 3D X-ray CT.

[0045] Table 2 shows the percentage of bubbles 100 μm or larger in the cross-section of the resin foams for Examples 1-4 and the Comparative Example. This percentage (%) is calculated as (area of ​​cross-section of bubbles 100 μm or larger / area of ​​sample cross-section) × 100.

[0046] [Table 2]

[0047] As shown in Table 2, the proportion of bubbles 100 μm or larger in the cross-section of the resin foams in Examples 1 to 4 was 5.0%, 0.1%, 6.4%, and 0.9%, respectively. In contrast, the proportion of bubbles 100 μm or larger in the cross-section of the resin foam in the comparative example was 17.8%. These values ​​indicate that the formation of a coarse foam structure was suppressed in the examples. This effect was particularly pronounced in Examples 2 and 4, where the molar concentration of the second gas was 5% or higher. Specifically, in Example 2, the density of bubbles with a diameter of 100 μm or larger was 0.3 bubbles / 1 mm. 2 In Example 4, the density of bubbles with a diameter of 100 μm or more was 0.4 bubbles / 1 mm. 2 That was the case.

[0048] Figure 6 shows high-magnification images of the cross-sections of the resin foams according to Examples 1-4 and the Comparative Example, specifically the portion without bubbles larger than 100 μm. Table 3 shows the porosity, the average foam diameter in the portion without bubbles larger than 100 μm, and the nucleation density for the resin foams according to Examples 1-4 and the Comparative Example. Here, the porosity was calculated using the Archimedes method (specific gravity measurement before and after foaming). The average foam diameter was calculated by processing the images shown in Figure 6 with the image processing software Image J. The nucleation density was calculated using specific gravity measurement and the images shown in Figure 6.

[0049] [Table 3]

[0050] As shown in Table 3, the porosity of the resin foams in Examples 1 to 4 was equal to or better than that of the comparative examples, despite the low number of bubbles larger than 100 μm. In particular, in Examples 1 and 2, the porosity was high at 45% or more because HCFC-22 was used as the second gas, and in Example 2, the porosity was especially high because the concentration of the second gas was increased to 10 mol% or more.

[0051] Furthermore, as shown in Table 3, the average foam diameter in the areas without bubbles larger than 100 μm in the resin foams of Examples 1 to 4 was equivalent to that of the comparative examples. In particular, in Examples 1, 3, and 4, this average value was 120 nm or less.

[0052] Furthermore, as shown in Table 3, in the resin foams of Examples 1 to 4, the nucleation density of bubbles was 4 × 10⁻⁶. 13 cm -3 The results were as described above, and were higher than those of the comparative example. In particular, the nucleation densities of Examples 1 and 4 were more than five times higher than those of the comparative example.

[0053] The embodiments and examples of the present invention have been described above with reference to the drawings, but these are merely examples of the present invention, and various other configurations can also be adopted.

[0054] Furthermore, while the flowcharts used in the above description show multiple steps (processes) in sequence, the execution order of the steps performed in each embodiment is not limited to the order in which they are described. In each embodiment, the order of the illustrated steps can be changed to the extent that it does not impede the content. Also, the above embodiments can be combined to the extent that their contents do not conflict. [Explanation of symbols]

[0055] 10 equipment 110 Container 112 Supply port 114 Discharge port 120 shaft 122 Motor 130 First Gas Supply Unit 140 Second Gas Supply Unit

Claims

1. A preparation step involves placing a first resin in which a first gas dissolves in an atmosphere containing the first gas and a second gas that reduces the surface tension of the first resin relative to the first gas. A pressurization step to increase the partial pressure of the first gas and the partial pressure of the second gas in the aforementioned atmosphere, A depressurization step to reduce the partial pressure of the first gas and the partial pressure of the second gas in the aforementioned atmosphere, Equipped with, The first gas is carbon dioxide. A method for producing a nanofoamed polymer, wherein the second gas contains at least one of chlorofluorocarbons and hydrofluoroolefins, and the first resin can be dissolved by increasing the partial pressure.

2. A preparation step involves placing a first resin in which a first gas dissolves in an atmosphere containing the first gas and a second gas having a higher solubility in the first resin than the first gas. A pressurization step to increase the partial pressure of the first gas and the partial pressure of the second gas in the aforementioned atmosphere, A depressurization step to reduce the partial pressure of the first gas and the partial pressure of the second gas in the aforementioned atmosphere, Equipped with, The first gas is carbon dioxide. A method for producing a nanofoamed polymer, wherein the second gas contains at least one of chlorofluorocarbons and hydrofluoroolefins, and the first resin can be dissolved by increasing the partial pressure.

3. In the method for producing a nanofoamed polymer according to claim 1 or 2, The first resin is a method for producing a nanofoamed polymer containing polymethyl methacrylate (PMMA).

4. In a method for producing a nanofoamed polymer according to any one of claims 1 to 3, The method for producing a nanofoamed polymer, wherein the chlorofluorocarbon is chlorodifluoromethane (HCFC-22).

5. In a method for producing a nanofoamed polymer according to any one of claims 1 to 3, The hydrofluoroolefins are trans-1,3,3,3-tetrafluoropropene (HFO-1234ze-(E)). A method for producing a nanofoamed polymer.

6. In a method for producing a nanofoamed polymer according to any one of claims 1 to 5, In the cross-section of the aforementioned nanofoamed polymer, the density of bubbles with a diameter of 100 μm or more is 0.5 bubbles / 1 mm. ２ The following is a method for producing nanofoamed polymers.

7. In a method for producing a nanofoamed polymer according to any one of claims 1 to 6, The bubble density of the aforementioned nanofoamed polymer is 1 × 10 １３ pieces / cm ３ The above describes a method for producing nanofoamed polymers.

8. In a method for producing a nanofoamed polymer according to any one of claims 1 to 7, A method for producing a nanofoamed polymer, wherein the average foam diameter of the nanofoamed polymer is 1 μm or less.

9. In a method for producing a nanofoamed polymer according to any one of claims 1 to 8, A method for producing a nanofoamed polymer, wherein at least the reduced pressure step is an extrusion step in an extruder.

10. In a method for producing a nanofoamed polymer according to any one of claims 1 to 9, A method for producing a nanofoamed polymer, wherein the partial pressure of the second gas in the aforementioned atmosphere is less than the value at which the first resin completely dissolves in the pressurization step.

11. It contains multiple air bubbles, The average foam diameter is 1 μm or less. In the cross-section, the density of the bubbles with a diameter of 100 μm or more is 0.5 bubbles / 1 mm ２ The following: The density of the aforementioned bubbles is 1 × 10 １３ pieces / cm ３ The above describes the nanofoamed polymer.

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