JP2023160500A - Inclined porous sheet - Google Patents

Abstract

To provide an inclined porous sheet with reduced undulations and wrinkles.SOLUTION: An inclined porous sheet 1 has a porosity changing in an inclined manner in one direction in its thickness direction. The porous forms extend in the thickness direction. A degree of inclination, B/b, is 1.3 or more, where B denotes a porosity of the high porosity side in the surface-adjacent region and b denotes a porosity of the low porosity side in the surface-adjacent region. A degree of flatness F defined by the following formula (1) is 3 or less. F=H/t (1), where H denotes the maximum height when cutting the sheet into a 5 cm square and placing on a flat surface and t denotes the thickness of the sheet.SELECTED DRAWING: Figure 1

Description

The present invention relates to an inclined porous sheet in which the porosity changes in a gradient manner in one direction in the thickness direction.

For example, in Patent Document 1, after dissolving a gaseous gas at room temperature and pressure into plastic at high temperature and high pressure, and then exposing the plastic to a pressure atmosphere lower than the pressure at which the gas was dissolved, both sides of the sheet are Oblique foam plastic sheets are disclosed that are produced by exposing each to atmospheres of different temperatures.

Japanese Patent Application Publication No. 2002-363324

The inventors of the present invention have made extensive studies focusing on such background technology, and have come to the following findings. That is, in Patent Document 1, the sheet is foamed by an extrusion foam molding method, and since the sheet foams immediately after being extruded from a die, even if both sides of the sheet are subsequently exposed to atmospheres with different temperatures, the porosity (porosity) rate) is difficult to change in a gradient manner, that is, it is difficult to increase the degree of gradient. Furthermore, Patent Document 1 shows an example in which the sheet is passed through temperature-controllable rolls and exposed to atmospheres with different temperatures on both sides of the sheet, but it is difficult to achieve high foaming when the sheet is sandwiched between the rolls. In addition, the air bubbles (pores) formed within the sheet tend to have a large horizontally elongated shape in the extrusion direction (in-plane direction), and the porosity, that is, the expansion rate of the material, differs on both sides of the sheet. As a result, undulations and wrinkles are likely to occur in the sheet. For this reason, it is difficult to ensure flatness, and defects such as waviness and wrinkles become more noticeable when the foam is highly foamed.

Therefore, in view of the above-mentioned background art, the present inventors conducted further intensive studies in order to provide an inclined porous sheet in which waviness, wrinkles, etc. are suppressed, and as a result, the present invention was completed.

The inclined porous sheet according to the present invention is an inclined porous sheet in which the porosity changes in a gradient manner in one direction in the thickness direction, and the pore shape extends in the thickness direction, and the porosity on the high porosity side When the porosity in the near-surface region is B, and the porosity in the near-surface region on the low porosity side is b, the slope B/b is 1.3 or more and is determined by the following formula (1). The flatness F is 3 or less.
F=H/t... (1)
However, H is the maximum height when the sheet is cut into 5 cm square pieces and placed on a flat surface, and t is the thickness of the sheet.

Further, the inclined porous sheet according to the present invention is an inclined porous sheet in which the porosity changes in a gradient manner in one direction in the thickness direction, and the pore shape extends in the thickness direction, and the pore diameter is The aspect ratio is 1.3 or more, and when the porosity in the near-surface region on the high porosity side is B, and the porosity in the near-surface region on the low porosity side is b, the slope B/b is It is also possible to adopt a configuration in which the ratio is 1.3 or more.

According to the present invention, it is possible to provide an inclined porous sheet in which waviness, wrinkles, etc. are suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram schematically showing an inclined porous sheet according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing an example of manufacturing a tilted porous sheet according to an embodiment of the present invention. 1 is a cross-sectional CT image of Example 1. It is a cross-sectional CT image of Example 2. It is a cross-sectional CT image of Example 3. 3 is a cross-sectional CT image of Comparative Example 1.

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

FIG. 1 is an explanatory diagram schematically showing an inclined porous sheet according to this embodiment, and FIG. 2 is an explanatory diagram showing an example of manufacturing the inclined porous sheet according to this embodiment. As shown in these figures, the inclined porous sheet 1 is formed by obliquely foaming a sheet-like foaming agent-impregnated sheet 2 impregnated with a foaming agent, and the porosity changes in a gradient in one direction in the thickness direction. ing.

The foaming agent-impregnated sheet 2 is produced, for example, by dissolving a foaming agent in a resin material that is melt-kneaded in a plasticizing unit of an injection molding machine, and injection-molding it into a sheet while applying holding pressure to suppress foaming. It is produced by cooling the resin material to a temperature lower than the cooling solidification temperature and then removing it from the mold, or by putting the resin material preformed into a sheet into an autoclave and adding a blowing agent into the resin material under high pressure. It can be produced by dissolving it in

Examples of resin materials include polyethylene, polypropylene, polystyrene, polyester, polyamide, polyvinyl chloride, polyvinylidene chloride, polybutene, polyacetal, polyphenylene oxide, polymethyl methacrylate, polysulfone, polyether sulfone, polyether ketone, and polyether ether. Examples include ketone, polyamideimide, polycarbonate, polyarylate, polyimide, fluororesin, ethylene-propylene resin, ethylene-ethyl acrylate, epoxy resin, urethane resin, imide resin, acrylic resin, and norbornene resin. These may be used alone or in combination, and may be a polymer alloy or a composite material of a resin matrix and a filler, but the use of the inclined porous sheet 1 is not limited to these. It can be selected as appropriate depending on the situation.

Foaming agents include physical foaming agents such as carbon dioxide and nitrogen, organic thermal decomposition type foaming agents such as azodicarbonamide, or inorganic thermal decomposition type chemical foaming agents such as sodium bicarbonate, as well as foaming components. An example is a thermally expandable capsule, but the capsule is not limited to these and can be appropriately selected depending on the solubility in the resin material.

In order to foam the foaming agent-impregnated sheet 2 at an angle, as shown in FIG. Radiant heat is irradiated toward the foaming agent-impregnated sheet 2. As a result, the foaming agent-impregnated sheet 2 is heated, and foaming starts at the heated portion. Then, the bubbles C grow so that they are relatively large on the high temperature side near the heat source 20 and relatively small on the low temperature side far from the heat source 20, and the size of the bubbles C and the bubble ratio ( Gradient foaming can be performed so that the porosity (porosity) changes in a gradient manner.

At that time, the entire circumference of the foaming agent-impregnated sheet 2 is vacuum-suctioned by a vacuum pump P through a suction groove 11 carved on the top surface of the mounting table 10, thereby forming foam on the mounting table 10. By restraining the agent-impregnated sheet 2, the shape change due to oblique foaming can be prioritized in the thickness direction. As a result, the growth of the bubbles C in the plane direction (direction perpendicular to the thickness direction) is suppressed, and the bubbles (pores) C become elongated in the thickness direction, and in the process of progressing oblique foaming, Waviness and wrinkles are less likely to occur. At this time, by controlling the progress of inclined foaming so that the aspect ratio of the pore diameter (the average value of the ratio of the pore diameter in the thickness direction to the pore diameter in the surface direction) is 1.3 or more, undulations and wrinkles can be eliminated. It is possible to produce the inclined porous sheet 1 in which the pores are more suppressed.

In addition, when irradiating radiant heat toward the foaming agent-impregnated sheet 2, as shown in FIG. can be adjusted. In this way, by selectively heating the areas of the foaming agent-impregnated sheet 2 other than the peripheral edge, non-foaming or low-foaming areas are formed in the peripheral edge 1a of the inclined porous sheet 1. It is preferable that the

By doing this, the heated region of the foaming agent-impregnated sheet 2 is surrounded by non-foamed or low-foamed regions and the tilted foaming progresses while being more restrained in the plane direction. The shape change becomes more prioritized in the thickness direction. As a result, the growth of the bubbles C in the planar direction is more appropriately suppressed, and it becomes possible to control the progress of oblique foaming so that undulations, wrinkles, etc. are less likely to occur.

In the inclined porous sheet 1 according to the present embodiment, by controlling the progress of the inclined foaming and foaming the foaming agent-impregnated sheet 2 in an inclined manner, the porosity in the region near the surface on the high porosity side is reduced to B. , the porosity in the near-surface region on the high-porosity side is made larger so that the slope B/b is 1.3 or more, where b is the porosity in the near-surface region on the low-porosity side. However, although the porosity of the entire pore region is preferably slanted foamed to have a high porosity of 50% or more, the shape of the pores extends in the thickness direction. , undulations, wrinkles, etc. can be suppressed.

By configuring the inclined porous sheet 1 in this way, it can be applied to a wider range of applications, but in this embodiment, the porosity in the region near the surface of the high porosity side HV is 50%. It is preferable that the porosity is above, and it is preferable that the porosity of the region near the surface of the low porosity side LV is 40% or less. Further, it is preferable that the average pore diameter of the entire inclined porous sheet 1 is 20 to 500 μm.

Here, the near-surface region refers to the region from the surface to a depth of 20% of the thickness of the inclined porous sheet 1, and the thickness of the inclined porous sheet 1 is preferably 0.5 to 20 mm, and 1 to 20 mm. More preferably, it is 10 mm.

Further, from the viewpoint of improving surface smoothness, the inclined porous sheet 1 preferably has no bubbles broken on the sheet surface, and the thickness of the skin layer formed on the sheet surface is preferably 500 μm or less.

Further, it is preferable that the flatness F of the inclined porous sheet 1, which is determined by the following formula (1) as an index of its flatness, is 3 or less.
F=H/t... (1)
However, H is the maximum height when the inclined porous sheet 1 is cut into 5 cm square pieces and placed on a flat surface, and t is the thickness of the sheet.

The inclined porous sheet 1 according to this embodiment can be applied to a wide range of applications in various fields. In addition to being applicable to civil engineering and construction materials, automobile materials, packaging materials, etc. that utilize properties such as heat insulation, shock absorption, and sound absorption, the porosity changes gradually in one direction in the thickness direction. By taking advantage of the fact that its dielectric constant changes in a gradient manner, it can be applied, for example, to a sheet that adjusts the transmission of millimeter waves in order to improve the stability of radar systems that use millimeter waves. You can also do it.

When used as a sheet for adjusting the transmission of millimeter waves, for example, the sheet surface of the high porosity side HV is used as the incident surface, and the dielectric constant ε of the high porosity side HV is 1. 8 or less, and the pores in the region near the surface of the high porosity side HV are adjusted such that the relative permittivity ε changes in a gradient manner toward the low porosity side LV at a rate of change of Δε<0.3/100 μm. It is preferable to set the ratio B, the porosity b of the region near the surface of the low porosity side LV, and the slope B/b.

Hereinafter, the present invention will be explained in more detail by giving specific examples.
[Example 1]
Polyethylene terephthalate was used as the resin material and nitrogen was dissolved therein as a blowing agent to prepare a blowing agent-impregnated sheet that was injection molded into a sheet having a length of 90 mm, a width of 90 mm, and a thickness of 1.25 mm.

Next, the foaming agent-impregnated sheet is placed on a temperature-controlled mounting table, and radiant heat is irradiated from a heat source placed above the mounting table so that the peripheral edge of the foaming agent-impregnated sheet is not heated. The parts of the foaming agent-impregnated sheet except for the peripheral edges were heated so that there was a temperature difference between the opposing main surfaces of the foaming agent-impregnated sheet. At that time, one side of the opposing main surfaces of the foaming agent-impregnated sheet that was in contact with the mounting table was restrained. As a result, inclined foaming was progressed, and then the foam was cooled and solidified to stop the growth of bubbles.

FIG. 3 shows a CT image of a cross section of the inclined porous sheet manufactured in this manner. From this CT image, the aspect ratio of the pore diameters (the average value of the ratio of the pore diameters in the thickness direction to the pore diameters in the surface direction) was found to be 1.92. You can confirm that you are doing so.

Furthermore, the porosity B of the near-surface region on the high-porosity side is 57.3%, the porosity b of the near-surface region on the low-porosity side is 3.2%, and the slope B/b is 18. It was .1.
Further, the porosity of the entire pore area was 50.6%.
In addition, the maximum height H when the produced inclined porous sheet was cut into 5 cm square pieces and placed on a flat surface was determined, and the ratio H/t to the thickness t of the produced inclined porous sheet was evaluated as an index of flatness. However, the value was 1.08.

[Example 2]
A tilted porous sheet was produced in the same manner as in Example 1, except that the amount of heat when heating the foaming agent-impregnated sheet was increased by 7.5 times. A CT image of the cross section is shown in FIG. From this CT image, the aspect ratio of the pore diameter was determined to be 1.44, confirming that the pores were foamed at an angle so that the pores extended in the thickness direction.

Furthermore, the porosity B of the near-surface region on the high-porosity side is 51.2%, the porosity b of the near-surface region on the low-porosity side is 35.6%, and the slope B/b is 1. It was .4.
Further, the porosity of the entire pore area was 61.1%.
In addition, the maximum height H when the produced inclined porous sheet was cut into 5 cm square pieces and placed on a flat surface was determined, and the ratio H/t to the thickness t of the produced inclined porous sheet was evaluated as an index of flatness. However, the value was 1.28.

[Example 3]
A tilted porous sheet was produced in the same manner as in Example 1, except that an olefin resin was used as the resin material and the amount of heat when heating the foaming agent-impregnated sheet was reduced by 50%. A CT image of the cross section is shown in FIG. From this CT image, the aspect ratio of the pore diameter was determined to be 2.68, confirming that the pores were foamed at an angle so that the pores extended in the thickness direction.

Furthermore, the porosity B of the near-surface region on the high-porosity side is 50.2%, the porosity b of the near-surface region on the low-porosity side is 5.1%, and the slope B/b is 9. It was .9.
Further, the porosity of the entire pore area was 43.2%.
In addition, the maximum height H when the produced inclined porous sheet was cut into 5 cm square pieces and placed on a flat surface was determined, and the ratio H/t to the thickness t of the produced inclined porous sheet was evaluated as an index of flatness. However, the value was 2.02.

[Comparative example 1]
Example 1 was performed, except that one side of the opposing main surfaces of the foaming agent-impregnated sheet in contact with the mounting table was not restrained, and both main surfaces were unrestrained, and the entire surface of the foaming agent-impregnated sheet was irradiated with radiant heat. A tilted porous sheet was produced in the same manner.
The inclined porous sheet thus produced was largely distorted as a whole, and the value of the ratio H/t determined in the same manner as in Example 1 was 5.17.
The porosity B of the near-surface region on the high porosity side is 60.3%, the porosity b of the near-surface region on the low porosity side is 43.7%, and the slope B/b is 1. It was .4.
Further, the porosity of the entire pore area was 57.5%.
Further, a CT image of the cross section is shown in FIG. 6, and the aspect ratio of the pore diameter determined from the CT image is 1.25, which indicates that the growth of the pores in the plane direction is smaller than in Examples 1 to 4. We can confirm that it has not been suppressed.

Although the present invention has been described above by showing preferred embodiments, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the present invention. Nor.

1 Slanted porous sheet 1a Periphery HV High porosity side LV Low porosity side

Claims (9)

An inclined porous sheet in which the porosity changes in a gradient manner in one direction in the thickness direction,
The pore shape extends in the thickness direction,
When the porosity in the near-surface region on the high porosity side is B, and the porosity in the near-surface region on the low porosity side is b, the slope B/b is 1.3 or more,
An inclined porous sheet characterized in that a flatness F determined by the following formula (1) is 3 or less.
F=H/t... (1)
However, H is the maximum height when the sheet is cut into 5 cm square pieces and placed on a flat surface, and t is the thickness of the sheet. The inclined porous sheet according to claim 1, wherein the aspect ratio of the pore diameters is 1.3 or more. An inclined porous sheet in which the porosity changes in a gradient manner in one direction in the thickness direction,
The pore shape extends in the thickness direction,
The aspect ratio of the pore diameter is 1.3 or more,
When the porosity in the near-surface region on the high porosity side is B, and the porosity in the near-surface region on the low porosity side is b, the gradient B/b is 1.3 or more. Slanted perforated sheet. The inclined porous sheet according to any one of claims 1 to 3, wherein the porosity of the entire pore region is 50% or more. The porosity according to any one of claims 1 to 3, wherein the porosity of the near-surface region on the high porosity side is 50% or more, and the porosity of the near-surface region on the low porosity side is 40% or less. Slanted perforated sheet. The inclined porous sheet according to any one of claims 1 to 3, wherein no bubbles are broken on the surface of the sheet. The inclined porous sheet according to claim 3, wherein the flatness F determined by the following formula (1) is 3 or less.
F=H/t... (1)
However, H is the maximum height when the sheet is cut into 5 cm square pieces and placed on a flat surface, and t is the thickness of the sheet. The inclined porous sheet according to any one of claims 1 to 3, and 7, wherein a non-foamed or low-foamed area is formed in the peripheral edge. An inclined porous sheet obtained by secondary processing the inclined porous sheet according to any one of claims 1 to 3 and 7.

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