Porous resin molded body

Abstract

The present invention provides a porous resin molded body having a gradient foam structure in which a polyolefin resin is used as a base resin and the porosity changes in a graduated manner in the thickness direction. Provided is a porous resin molded body 1 in which the porosity changes in a graduated manner in the thickness direction, wherein a polyolefin resin is formed as a base resin, and the base resin has a propylene fraction of less than 14 mol% in the monomer unit ratio as measured by 13C-NMR, the base resin being prepared such that there are at least seven tertiary carbons per 1,000 carbon atoms as measured by 13C-NMR .

Description

Porous resin molded body

[0001] The present invention relates to a porous resin molded body having a porosity that changes gradually in the thickness direction.

[0002] For example, Patent Document 1 discloses a gradient foam plastic sheet that is produced by dissolving a gas that is gaseous at room temperature and pressure in plastic at high temperature and pressure, exposing the plastic to an atmosphere of pressure lower than the pressure at which the gas was dissolved, and then exposing both sides of the sheet to atmospheres of different temperatures.

[0003] Japanese Patent Application Laid-Open No. 2002-363324

[0004] The present inventors have conducted extensive research focusing on this background art, and have come to the following findings. Specifically, in Patent Document 1, a sheet is foamed by extrusion foam molding. Because foaming occurs immediately after extrusion from a die, even if both sides of the sheet are subsequently exposed to atmospheres with different temperatures, it is difficult to gradually change the foam content, i.e., it is difficult to increase the degree of the gradient. Furthermore, Patent Document 1 also shows an example in which both sides of the sheet are passed through temperature-controllable rolls to expose them to atmospheres with different temperatures, but sandwiching the sheet between the rolls makes it difficult to achieve high foaming. In addition, the bubbles formed in the sheet tend to be large and elongated in the extrusion direction (plane direction). Furthermore, due to the difference in foam content, i.e., the expansion coefficient of the material, between the two sides of the sheet, the sheet is prone to undulations and wrinkles. This makes it difficult to ensure flatness, and defects such as undulations and wrinkles become more pronounced when high foaming is achieved.

[0005] Therefore, in view of the above-mentioned background art, the present inventors have conducted further intensive studies in order to provide a porous resin molding using a polyolefin-based resin as a base resin and having a favorable gradient foam structure in which the porosity changes gradiently in the thickness direction, and as a result have completed the present invention.

[0006] The gradient foam molded article according to the present invention is a porous resin molded article in which the porosity changes gradiently in the thickness direction, and the base resin is a polyolefin-based resin, and the base resin is １３ In the monomer unit ratio measured by CNMR, the propylene fraction is less than 14 mol%,１３ The number of tertiary carbon atoms measured by CNMR is 7 or more per 1000 carbon atoms.

[0007] According to the present invention, it is possible to provide a porous resin molded body in which a gradient foam structure in which the porosity changes gradually in the thickness direction is well formed.

[0008] FIG. 1 is an explanatory diagram schematically showing a porous resin molded body according to an embodiment of the present invention; FIG. 2 is an explanatory diagram showing a manufacturing example of a porous resin molded body according to an embodiment of the present invention; FIG. 3 is a cross-sectional CT image of Example 1; FIG. 4 is a surface SPM image of Example 1; FIG. 5 is a cross-sectional CT image of Example 2; FIG. 6 is a cross-sectional CT image of Example 3; FIG. 7 is a cross-sectional CT image of Example 4; FIG. 8 is a cross-sectional CT image of Example 5; FIG. 9 is a cross-sectional CT image of Example 6; FIG. 10 is a cross-sectional CT image of Example 7; FIG. 11 is a cross-sectional CT image of Comparative Example 1; FIG. 12 is a cross-sectional CT image of Comparative Example 2; FIG. 13 is a surface SPM image of Comparative Example 2; FIG. 14 is a cross-sectional CT image of Comparative Example 3; FIG. 15 is a cross-sectional CT image of Comparative Example 4; FIG. 16 is a cross-sectional CT image of Comparative Example 5.

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0010] Fig. 1 is an explanatory diagram showing a schematic diagram of a porous resin molded body according to this embodiment, and Fig. 2 is an explanatory diagram showing a manufacturing example of a porous resin molded body according to this embodiment. As shown in these figures, the porosity of the porous resin molded body 1 changes gradually in one direction of the thickness direction.

[0011] In this embodiment, the porous resin molding 1 uses a polyolefin resin as a base resin, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), homopolypropylene (hPP), etc. These resins are appropriately blended together to form the base resin of the porous resin molding 1. １３ In the monomer unit ratio measured by CNMR, the propylene fraction is less than 14 mol%, １３The porous resin molding 1 made of the base resin thus prepared is prepared so that the number of tertiary carbon atoms measured by CNMR is 7 or more per 1000 carbon atoms. The porous resin molding 1 made of the base resin thus prepared can have a good gradient foam structure in which preferably 50% or more of the pores, more preferably 90% or more of the pores are formed as independent pores, as will be described later.

[0012] The porous resin molded body 1 can be produced, for example, by preparing a foaming-agent-impregnated molded body 2 impregnated with a foaming agent and subjecting it to gradient foaming. The foaming-agent-impregnated molded body 2 is preferably in the form of a sheet having a thickness of 0.3 to 10 mm, more preferably 0.5 to 3 mm, but is not limited thereto. Depending on the application of the porous resin molded body 1, it can also be molded into a film having a thickness thinner than the above range or into a plate having a thickness thicker than the above range.

[0013] The blowing-agent-impregnated molded body 2 can be produced, for example, by dissolving a blowing agent in a base resin that is melt-kneaded in a plasticizing unit of an injection molding machine, injection-molding the base resin into a predetermined shape while applying a holding pressure to suppress foaming, and removing the base resin from the mold after cooling to a temperature that is at least lower than the cooling and solidification temperature of the base resin. Alternatively, the blowing-agent-impregnated molded body 2 may be produced, for example, by preforming the base resin into a predetermined shape, placing the preform in an autoclave, and dissolving the blowing agent in the base resin under high pressure.

[0014] Examples of foaming agents include physical foaming agents such as carbon dioxide and nitrogen, organic thermal decomposition type chemical foaming agents such as azodicarbonamide, or inorganic thermal decomposition type chemical foaming agents such as sodium bicarbonate, as well as thermally expandable capsules containing foaming components. However, the foaming agent can be selected appropriately without being limited to these, depending on the solubility in the base resin, etc.

[0015] When producing the porous resin molded body 1, the foaming-agent-impregnated molded body 2 does not have to be prepared in a state in which foaming is completely suppressed. A small amount of foaming may occur during the process of producing the foaming-agent-impregnated molded body 2, resulting in a micro-foamed state. As long as foaming is suppressed to an extent that gradient foaming can be controlled as described below, the foaming-agent-impregnated molded body 2 may be in an unfoamed or micro-foamed state.

[0016] To cause gradient foaming of the foaming-agent-impregnated molded body 2, for example, as shown in Fig. 2, the foaming-agent-impregnated molded body 2 formed into a predetermined shape is placed on a mounting table 10, and radiant heat is irradiated toward the foaming-agent-impregnated molded body 2 from a heat source 20 disposed above the mounting table 10. This heats the foaming-agent-impregnated molded body 2, and foaming begins in the heated area. At this time, the size and number of bubbles C change so that they are relatively large on the high-temperature side closer to the heat source 20 and relatively small on the low-temperature side farther from the heat source 20. As a result, gradient foaming can be progressed so that the porosity changes gradiently in one direction in the thickness direction in accordance with the temperature gradient in the thickness direction.

[0017] When subjecting the foaming-agent-impregnated molded body 2 to tilt foaming, it is preferable to restrain one of the opposing main surfaces of the foaming-agent-impregnated molded body 2 (the side in contact with the mounting table 10 in the illustrated example). In the illustrated example, the one side is restrained by carving suction grooves 11 in the top surface of the mounting table 10 according to the shape and size of the foaming-agent-impregnated molded body 2 and vacuum-suctioning the entire periphery of the foaming-agent-impregnated molded body 2 using a vacuum pump P, but this is not limitative. As long as one of the opposing main surfaces of the foaming-agent-impregnated molded body 2 can be restrained so as to restrict movement of the foaming-agent-impregnated molded body 2 in the planar direction (the direction perpendicular to the thickness direction), the foaming-agent-impregnated molded body 2 may be releasably adhered to the top surface of the mounting table 10, for example.

[0018] When inclined foaming is performed with one of the opposing main surfaces of the foaming-agent-impregnated molded body 2 constrained and the other unconstrained, shape change due to inclined foaming is prioritized in the thickness direction. This allows the inclined foaming to be controlled so that bubbles extend in the thickness direction while suppressing bubble growth in the planar direction. As a result, undulations and wrinkles are less likely to occur during the inclined foaming process, making it possible to produce a porous resin molded body 1 with excellent flatness. In this case, it is preferable to control the inclined foaming so that the cross-sectional shape of the independent pores is preferably circular or elliptical, more preferably elliptical with the major axis in the thickness direction.

[0019] Furthermore, when heating the foaming-agent-impregnated molded body 2, it is preferable to selectively heat the area other than the peripheral edge of the foaming-agent-impregnated molded body 2. To achieve this, for example, as shown in Fig. 2, a shielding member 30 may be provided around the heat source 20 to appropriately adjust the irradiation range of the radiant heat from the heat source 20.

[0020] By doing so, the peripheral portion of the foaming-agent-impregnated molded body 2 can be a non-foamed portion that remains unfoamed, or a low-foamed portion (including an extremely low-foamed portion) that has unexpectedly foamed due to heat conduction from the heated portion. As a result, the heated portion of the foaming-agent-impregnated molded body 2 is surrounded by the non-foamed or low-foamed portion, and the inclined foaming proceeds while being more constrained in the planar direction. Therefore, the shape change due to the inclined foaming is prioritized in the thickness direction. As a result, the growth of bubbles in the planar direction is more effectively suppressed, and the inclined foaming can be controlled so as to make it less likely for swells and wrinkles to occur. This improves the planarity of the porous resin molded body 1 produced.

[0021] In the illustrated example, radiant heat is irradiated from the heat source 20 disposed on the other of the opposing main surfaces of the foaming-agent-impregnated molded body 2 toward the foaming-agent-impregnated molded body 2 to heat only the other side, but this is not limiting. For example, a resistance heating element or a temperature control circuit in which a temperature control medium circulates may be disposed inside the mounting table 10 so that the foaming-agent-impregnated molded body 2 can be heated or cooled from the mounting table 10 side. This makes it possible to further widen the range in which the temperature difference between the main surfaces can be adjusted.

[0022] Furthermore, it is preferable to adjust the temperature difference between the main surfaces so that foaming does not occur in the surface layer portion on one side (lower temperature side) of the opposing main surfaces of the foaming-agent-impregnated molded body 2. This forms a non-foamed layer in the surface layer portion on that side, making it more difficult for undulations and wrinkles to occur as the inclined foaming progresses, and making it possible to produce a porous resin molded body 1 with better flatness.

[0023] After the gradient foaming is performed at a desired bubble rate, the process is terminated by cooling and solidifying the product to stop the bubble growth. When the process is terminated, after the bubble growth is stopped by cooling and solidifying the product, the product may be subjected to secondary processing into a product shape by thermoforming or the peripheral portion may be trimmed depending on the application of the porous resin molded body 1.

[0024] When controlling the gradient foaming as described above and forming a gradient foam structure in the porous resin molding 1, the viscoelastic behavior of the base resin significantly affects the formation of the gradient foam structure. For example, when a polyethylene resin is heated from a temperature below its melting point, its elastic modulus (storage modulus) drops sharply at temperatures above its melting point, causing cells to break with even a slight increase in temperature, making it difficult to form a satisfactory gradient foam structure.

[0025] Therefore, in order to enable the base resin to exhibit good viscoelastic behavior over the temperature range in which gradient foaming progresses, the present inventors blended the above-mentioned polyolefin resins, such as LDPE (melting point: 100 to 115°C) and LLDPE (melting point: 122 to 124°C), which have relatively low melting points, as the low-melting component, with HDPE (melting point: 130 to 137°C) and hPP (melting point: 160 to 165°C), which have relatively high melting points, as the high-melting component, and attempted to examine the viscoelastic behavior of the blend.

[0026] LDPE and LLDPE, which are low-melting point components, are blended with the assumption that they will foam in the molten state because their molecular chains are highly branched and the entanglement of molecular chains results in a relatively high melt tension when melted.HDPE and hPP, which are high-melting point components, are blended with the assumption that they will foam in the solid state because they have excellent crystallinity and exhibit strain hardening properties.

[0027] Blending these low-melting and high-melting components is expected to provide favorable viscoelastic behavior across the temperature range in which gradient foaming occurs. However, gradient foaming tends to be hindered as the proportion of hPP in the high-melting component increases. This is thought to be due to a decrease in compatibility with the low-melting components LDPE and LLDPE, which increases the likelihood of cell breakage at the sea-island interface. Gradient foaming also tends to be hindered when the proportion of HDPE in the high-melting component increases. This is thought to be due to a decrease in the proportion of LDPE and LLDPE in the low-melting components, which reduces the melt tension and places a heavy load on the crystalline components that cannot adapt to deformation during foaming.

[0028] In view of this tendency, the present inventors have conducted extensive research focusing on the proportion of polypropylene contained in the base resin and the number of branches of the resin contained in the base resin, i.e., the number of tertiary carbons to which branched chains are bonded. １３ In the monomer unit ratio measured by CNMR, the propylene fraction is less than 14 mol%, １３ It was confirmed that a good gradient foam structure can be formed by appropriately selecting the low-melting point component and the high-melting point component and appropriately adjusting the blending ratio of these components so that the number of tertiary carbons measured by CNMR is 7 or more per 1,000 carbon atoms.

[0029] To form a better gradient foam structure, the base resin forming the porous resin molding 1 is preferably a polyethylene-based resin. More specifically, it is preferable to prepare the porous resin molding 1 so that it contains at least one of LDPE and LLDPE as a low-melting point component and HDPE as a high-melting point component, but other resin components may also be contained as long as a good gradient foam structure can be formed. The base resin may also be a copolymer based on these polyethylene-based resins.

[0030] Furthermore, in the resin temperature range of 80 to 120°C where foaming begins to occur, if the storage modulus is extremely low, the cells will break, whereas if the storage modulus is extremely high, foaming will not occur and heating to near the melting point will be necessary. Taking this into consideration, the base resin forming the porous resin molded body 1 preferably has a storage modulus of 10 to 120 MPa at 100°C as determined by dynamic viscoelasticity measurement.

[0031] Furthermore, in order to prevent a dramatic decrease in elastic modulus due to melting in the resin temperature range of 80 to 120°C where foaming begins to occur, the base resin forming the porous resin molding 1 preferably has a melting peak at 120°C or higher in the first DSC curve obtained by differential scanning calorimetry at 10°C / min, and the heat of fusion calculated from the area of ​​the melting peak is preferably 10 J / g or higher.

[0032] The present invention will be described in more detail below with reference to specific examples.

[0033] [Example 1] A base resin having the following composition was used, and nitrogen was dissolved therein as a blowing agent. The resin was injection-molded into a sheet having a length of 90 mm, a width of 90 mm, and a thickness of 1.25 mm to prepare a blowing-agent-impregnated molded article. LLDPE (MFR (190°C) 3.6 g / 10 min (ASTM D-1238), density 0.885 g / cm) ３ (ASTM D-1505)): 50% by weight HDPE (MFR (190°C) 12g / 10min (JIS K6922-2), density 0.960g / cm ３ (JIS K7112): 50% by weight

[0034] Next, the foaming-agent-impregnated molded body was placed on a flat table, and the entire periphery of the foaming-agent-impregnated molded body was vacuum-suctioned to restrain one of the opposing main surfaces of the foaming-agent-impregnated molded body that was in contact with the table. Next, radiant heat was irradiated toward the foaming-agent-impregnated molded body from a heat source located on the other of the opposing main surfaces of the foaming-agent-impregnated molded body, heating the foaming-agent-impregnated molded body so that there was a temperature difference between the main surfaces. This allowed gradient foaming to proceed, and the foam was then cooled and solidified to stop the growth of bubbles.

[0035] A CT image of the cross section of the gradient foam molded article thus produced is shown in Figure 3. This CT image confirms the formation of a favorable gradient foam structure. Furthermore, an SPM image of the surface of the gradient foam molded article is shown in Figure 4, which shows no sea-island structure. The CT images were taken using a Tesco TXS90-ACTIS microscope with a 4 mm diameter field of view. The SPM images were taken using a Hitachi High-Tech AFM5300E microscope with a 20 μm × 20 μm field of view, a scanning speed of 2 to 20 μm / sec, a cantilever spring constant of 2 N / m, and a phase-modulated (PM) field of view.

[0036] <Dynamic viscoelasticity measurement> A test piece was cut out from the produced gradient foam molded article and subjected to dynamic viscoelasticity measurement, which revealed that the storage modulus at 100°C was 49 MPa. The dynamic viscoelasticity measurement was carried out using a measuring device: DMS6100 manufactured by Seiko Instruments Inc. The measurement was carried out at a temperature rise rate of 3°C / min, with a strain amplitude of 10 µm, a tensile / compressive force gain of 1.2, and a frequency of 1 Hz.

[0037] < １３ CNMR Measurement> A test piece was cut out from the produced gradient foam molded article to prepare a sample. １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and it was found that no propylene was detected and the number of tertiary carbon atoms per 1000 carbon atoms was 27.2. １３ The CNMR measurement was carried out using a JNM-ECA measuring device manufactured by JEOL Ltd. The measurement temperature was 130°C and the number of accumulations was 10,000. The sample solvent was benzene-d6 / ortho-dichlorobenzene-d4 = 1 / 3 (v / v), adjusted to 60 mg sample / 600 μL. - Method for quantifying monomer components The ethylene / propylene monomer ratio of the polyolefin component was quantified using the following formula: E = k{1 / 2(S βδ +S δδ +S αγ +S αδ ) + 1 / 4 (S γδ )} P = k {S αα +1 / 2 (S αγ +S αδ)} Propylene ratio (mol%) = P / (P+E) Quantitative method for tertiary carbon １３ The ratio of tertiary carbon was determined by dividing the total integrated value T of the peaks derived from the four tertiary carbons shown below among the carbon peaks obtained by CNMR by the sum of the total peaks derived from the carbons of the main chain skeleton and side chains that are secondary or lower and T. δδ (Butene) = T δδ (B): 39.8ppm T δδ (Hexene) = T δδ (H): 38.3ppm T βδ (Propylene) = T βδ (P): 31ppm T ββ (Propylene) = T ββ (P): 28.9ppm T=T δδ (B) + T _δδ (H) + T βδ (P) + T ββ (P)

[0038] <Differential Scanning Calorimetry> A test piece was cut from the produced gradient foam molded article and subjected to differential scanning calorimetry. In the first DSC curve obtained by differential scanning calorimetry at 10°C / min, a melting peak appeared at 129.5°C. The heat of fusion at 120°C or higher, calculated from the area of ​​the melting peak, was 72.2 J / g. The differential scanning calorimetry was performed using a TA Instruments Discovery DSC2500 measurement device, and measurements were made in the range of 0°C to 200°C at 10°C / min. The melting enthalpy at 120°C or higher was determined by connecting the two points from 120°C where the melting peak returns to the baseline with a straight line, which served as the reference line, and calculating the area between this line and the spectrum.

[0039] Example 2 A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LLDPE (same as in Example 1): 70% by weight HDPE (same as in Example 1): 30% by weight

[0040] A gradient foamed molded article was produced in the same manner as in Example 1, except that the amount of heat used to heat the foaming-agent-impregnated molded article was 0.75 times that of Example 1. A CT image of the cross section of the foamed article is shown in Figure 5. This CT image confirms that a good gradient foamed structure was formed.

[0041] <Dynamic Viscoelasticity Measurement> Dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, and the storage modulus at 100°C was found to be 17 MPa.

[0042] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and it was found that no propylene was detected and the number of tertiary carbon atoms per 1000 carbon atoms was 35.8.

[0043] <Differential Scanning Calorimetry> Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10°C / min, a melting peak appeared at 128.5°C. The heat of fusion at 120°C or higher calculated from the area of ​​the melting peak was 45.1 J / g.

[0044] [Example 3] A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LDPE (MFR (190°C) 23 g / 10 min (JIS K6922-2), density 0.918 g / cm ３ (JIS K7112)): 50% by weight HDPE (same as in Example 1): 50% by weight

[0045] In addition, a gradient foam molded article was produced by heating the foaming-agent-impregnated molded article in the same manner as in Example 1. A CT image of the cross section is shown in Figure 6. This CT image confirms the formation of a favorable gradient foam structure. Furthermore, an SPM image of the surface of the gradient foam molded article is shown in Figure 7, in which no sea-island structure was observed.

[0046] <Dynamic Viscoelasticity Measurement> When dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, the storage modulus at 100°C was 69 MPa.

[0047] < １３CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and it was found that no propylene was detected and the number of tertiary carbon atoms per 1000 carbon atoms was 9.0.

[0048] <Differential Scanning Calorimetry> Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10°C / min, a melting peak appeared at 129.6°C. The heat of fusion at 120°C or higher calculated from the area of ​​the melting peak was 77.3 J / g.

[0049] [Example 4] A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that the base resins used were the following: LLDPE (same as in Example 1): 47.5 wt % HDPE (same as in Example 1): 47.5 wt % hPP (MFR (230°C) 13 g / 10 min (JIS K6921-2), density 0.9 g / cm ３ (JIS K6921-2): 5% by weight

[0050] Furthermore, a gradient foamed molded article was produced by heating the foaming-agent-impregnated molded article in the same manner as in Example 1. A CT image of the cross section is shown in Figure 8. From this CT image, it can be confirmed that a good gradient foamed structure was formed.

[0051] <Dynamic Viscoelasticity Measurement> Dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, and the storage modulus at 100°C was found to be 57 MPa.

[0052] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and the propylene fraction was found to be 4.6 mol % and the number of tertiary carbon atoms per 1000 carbon atoms was found to be 43.7.

[0053] <Differential scanning calorimetry> Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10°C / min, a melting peak derived from PE appeared at 129.2°C. The heat of fusion at 120°C or higher, calculated from the area of ​​the melting peak derived from PE, was 61.6 J / g.

[0054] [Example 5] A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LLDPE (same as in Example 1): 45% by weight; HDPE (same as in Example 1): 45% by weight; hPP (same as in Example 4): 10% by weight.

[0055] Furthermore, a gradient foamed molded article was produced by heating the foaming-agent-impregnated molded article in the same manner as in Example 1. A CT image of the cross section is shown in Figure 9. From this CT image, it can be confirmed that a good gradient foamed structure was formed.

[0056] <Dynamic Viscoelasticity Measurement> When dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, the storage modulus at 100°C was 61 MPa.

[0057] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and the propylene fraction was found to be 7.9 mol % and the number of tertiary carbon atoms per 1000 carbon atoms was found to be 61.3.

[0058] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10°C / min, a melting peak derived from PE appeared at 129.1°C. The heat of fusion at 120°C or higher, calculated from the area of ​​the melting peak derived from PE, was 56.5 J / g.

[0059] Example 6 A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LLDPE (same as in Example 1): 49.5% by weight; HDPE (same as in Example 1): 49.5% by weight; Additive (Metablen MZE-4, manufactured by Mitsubishi Chemical Corporation): 1% by weight.

[0060] The foaming-agent-impregnated molded article was heated to produce a gradient foamed molded article in the same manner as in Example 1. A CT image of the cross section is shown in Figure 10. From this CT image, it can be confirmed that a good gradient foam structure was formed.

[0061] <Dynamic Viscoelasticity Measurement> Dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, and the storage modulus at 100°C was found to be 57 MPa.

[0062] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and it was found that no propylene was detected and the number of tertiary carbon atoms per 1000 carbon atoms was 24.9.

[0063] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10° C. / min, a melting peak appeared at 130.2° C. The heat of fusion at 120° C. or higher calculated from the area of ​​the melting peak was 75.6 J / g.

[0064] Example 7 A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LLDPE (same as in Example 1): 47.5% by weight; HDPE (same as in Example 1): 47.5% by weight; and additive (Metablen MZE-4, manufactured by Mitsubishi Chemical Corporation): 5% by weight.

[0065] The foaming-agent-impregnated molded article was heated to produce a gradient foamed molded article in the same manner as in Example 1. A CT image of the cross section is shown in Figure 11. From this CT image, it can be confirmed that a good gradient foam structure was formed.

[0066] <Dynamic Viscoelasticity Measurement> Dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, and the storage modulus at 100° C. was found to be 48 MPa.

[0067] < １３ CNMR Measurement> In the same manner as in Example 1, １３The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and it was found that no propylene was detected and the number of tertiary carbon atoms per 1000 carbon atoms was 24.3.

[0068] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10° C. / min, a melting peak appeared at 129.7° C. The heat of fusion at 120° C. or higher, calculated from the area of ​​the melting peak, was 70.6 J / g.

[0069] Comparative Example 1 A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: HDPE (same as in Example 1): 100% by weight

[0070] A gradient foamed molded article was produced in the same manner as in Example 1, except that the amount of heat applied to the foaming-agent-impregnated molded article was doubled. A CT image of the cross section is shown in Figure 12. This CT image confirms that the cells had broken and a gradient foam structure had not been formed.

[0071] <Dynamic Viscoelasticity Measurement> Dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, and the storage modulus at 100° C. was found to be 232 MPa.

[0072] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbons per 1000 carbon atoms were determined by CNMR, and neither propylene nor tertiary carbon was detected.

[0073] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10° C. / min, a melting peak appeared at 130.6° C. The heat of fusion at 120° C. or higher calculated from the area of ​​the melting peak was 122.6 J / g.

[0074] Comparative Example 2 A foaming agent-impregnated molded article was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LLDPE (same as in Example 1): 50% by weight; hPP (same as in Example 4): 50% by weight.

[0075] A gradient foam molded article was produced in the same manner as in Example 1, except that the amount of heat used when heating the foaming-agent-impregnated molded article was 0.25 times that of the conventional foam molded article. A CT image of the cross section is shown in Figure 13. This CT image confirms that the cells had broken and a gradient foam structure had not been formed. An SPM image of the surface of the gradient foam molded article is shown in Figure 14, revealing a sea-island structure that appears to be phase separation between LLDPE and hPP.

[0076] <Dynamic Viscoelasticity Measurement> When dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, the storage modulus at 100°C was 140 MPa.

[0077] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and the propylene fraction was found to be 44.4 mol % and the number of tertiary carbon atoms per 1000 carbon atoms was found to be 200.9.

[0078] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10° C. / min, a melting peak derived from PP appeared at 166.9° C. The heat of fusion at 120° C. or higher, calculated from the area of ​​the melting peak, was 45.3 J / g.

[0079] Comparative Example 3 A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that the base resins used were the following: LDPE (Novatec LD LJ8041 manufactured by Japan Polyethylene Corporation): 40% by weight HDPE (Novatec HD HJ580N manufactured by Japan Polyethylene Corporation): 60% by weight

[0080] A gradient foamed molded article was produced in the same manner as in Example 1, except that the amount of heat used to heat the foaming-agent-impregnated molded article was increased by 1.5 times. A CT image of the cross section is shown in Figure 15. From this CT image, it can be seen that the cells had broken and a gradient foam structure had not been formed.

[0081] <Dynamic Viscoelasticity Measurement> When dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, the storage modulus at 100°C was 94 MPa.

[0082] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and it was found that no propylene was detected and the number of tertiary carbon atoms per 1000 carbon atoms was 6.5.

[0083] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10° C. / min, a melting peak appeared at 131.4° C. The heat of fusion at 120° C. or higher calculated from the area of ​​the melting peak was 84.3 J / g.

[0084] Comparative Example 4 A foaming agent-impregnated molded body was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LDPE (same as in Example 3): 30% by weight HDPE (same as in Example 1): 70% by weight

[0085] A gradient foamed molded article was produced in the same manner as in Example 1, except that the amount of heat used to heat the foaming-agent-impregnated molded article was increased by 1.5 times. A CT image of the cross section is shown in Figure 16. This CT image confirms that the cells had broken and a gradient foam structure had not been formed.

[0086] <Dynamic Viscoelasticity Measurement> Dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, and the storage modulus at 100° C. was found to be 121 MPa.

[0087] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and it was found that no propylene was detected and the number of tertiary carbon atoms per 1000 carbon atoms was 6.3.

[0088] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10° C. / min, a melting peak appeared at 133.1° C. The heat of fusion at 120° C. or higher calculated from the area of ​​the melting peak was 42.3 J / g.

[0089] Comparative Example 5 A foaming agent-impregnated molded article was prepared in the same manner as in Example 1, except that a base resin having the following composition was used: LLDPE (same as in Example 1): 40% by weight; HDPE (same as in Example 1): 40% by weight; hPP (same as in Example 4): 20% by weight.

[0090] Furthermore, a graded foamed molded article was produced by heating the foaming-agent-impregnated molded article in the same manner as in Example 1. A CT image of the cross section is shown in Figure 17. From this CT image, it can be confirmed that the cells had broken and a graded foam structure had not been formed.

[0091] <Dynamic Viscoelasticity Measurement> When dynamic viscoelasticity measurement was carried out in the same manner as in Example 1, the storage modulus at 100° C. was 104 MPa.

[0092] < １３ CNMR Measurement> In the same manner as in Example 1, １３ The monomer unit ratio and the number of tertiary carbon atoms per 1000 carbon atoms were determined by CNMR, and the propylene fraction was found to be 14.2 mol %, and the number of tertiary carbon atoms per 1000 carbon atoms was found to be 86.3.

[0093] Differential scanning calorimetry was performed in the same manner as in Example 1. In the first DSC curve obtained by differential scanning calorimetry at 10° C. / min, a melting peak derived from PE appeared at 129.2° C. The heat of fusion at 120° C. or higher, calculated from the area of ​​the melting peak derived from PE, was 50.2 J / g.

[0094] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0095] The porous resin molded article according to the present invention can be used in a wide range of applications in various fields. In addition to being applicable to applications such as civil engineering and construction materials, automotive materials, and packaging materials, which utilize its properties such as heat insulation, impact absorption, and sound absorption, the porous resin molded article can also be used as a millimeter wave low reflection sheet for improving the stability of radar systems using millimeter waves, taking advantage of the fact that the dielectric constant also changes gradually as a result of the porosity changing gradually between the opposing main surfaces.

[0096] 1. Porous resin molded body

Claims

1. A porous resin molded body having a porosity that changes gradually in the thickness direction, the base resin being a polyolefin resin, １３ In the monomer unit ratio measured by CNMR, the propylene fraction is less than 14 mol%, １３ A porous resin molded article, characterized in that the number of tertiary carbon atoms measured by CNMR is 7 or more per 1,000 carbon atoms.

2. The porous resin molded article according to claim 1, wherein 50% or more of the pores are independent pores.

3. The porous resin molded product according to claim 2, wherein the cross-sectional shape of the independent pores is circular or elliptical.

4. The porous resin molded product according to claim 2, wherein the cross-sectional shape of the independent pores is an ellipse having a major axis in the thickness direction.

5. A porous resin molded body according to any one of claims 1 to 4, wherein the base resin has a storage modulus of 10 to 120 MPa at 100°C as determined by dynamic viscoelasticity measurement.

6. A porous resin molding according to any one of claims 1 to 5, wherein the base resin exhibits a melting peak at 120°C or higher in a first DSC curve obtained by differential scanning calorimetry at 10°C / min.

7. The porous resin molding according to claim 6, wherein the heat of fusion calculated from the area of ​​the fusion peak is 10 J / g or more.

8. A porous resin molded body according to any one of claims 1 to 7, wherein the base resin is a polyethylene resin.

9. The porous resin molded article according to claim 8, which contains at least one of low density polyethylene and linear low density polyethylene, and high density polyethylene.

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