Method for producing porous liquid crystal polymer

Abstract

This production method includes a first step, a second step and a third step. In the first step, a liquid crystal polymer is sheet-formed to form a non-porous sheet (3). In the second step, the non-porous sheet (3) is impregnated with a supercritical fluid 15. In the third step, the pressure or temperature of the atmosphere of the non-porous sheet 3 impregnated with the supercritical fluid (15) is lowered to be less than the critical point of the supercritical fluid (3), thereby foaming the non-porous sheet 3 to produce a porous liquid crystal polymer sheet (1).

Description

Method for producing porous liquid crystal polymer

[0001] The present invention relates to a method for producing a porous liquid crystal polymer.

[0002] A foaming method using a supercritical fluid as a foaming agent is known as a method for producing a porous liquid crystal polymer (see, for example, Patent Document 1 below). In the foaming method, a liquid crystal polymer is first kneaded with a supercritical fluid to prepare a resin composition, and then the prepared resin composition is injected into a mold to foam the resin composition so that the pressure and / or temperature of the supercritical fluid is below the critical point.

[0003] Japanese Patent Application Laid-Open No. 2019-172943

[0004] Depending on the application and purpose of the porous liquid crystal polymer, a thin porous liquid crystal polymer is required. However, the foaming method described in Patent Document 1 has a drawback in that a thin porous liquid crystal polymer cannot be obtained because a resin composition is injected into a mold.

[0005] The present invention provides a method for producing a porous liquid crystal polymer, which can produce a thin porous liquid crystal polymer.

[0006] The present invention (1) includes a method for producing a porous liquid crystal polymer, comprising: a first step of preparing a liquid crystal polymer; a second step of impregnating the liquid crystal polymer with a supercritical fluid; and a third step of foaming the liquid crystal polymer by lowering at least one of the pressure and temperature of the atmosphere of the liquid crystal polymer impregnated with the supercritical fluid to a value below the critical point of the supercritical fluid, thereby producing a porous liquid crystal polymer.

[0007] In this method for producing a porous liquid crystal polymer, the liquid crystal polymer prepared in the first step is impregnated with a supercritical fluid in the second step, and then in the third step, the liquid crystal polymer impregnated with the supercritical fluid is foamed, thereby making it possible to produce a thin porous liquid crystal polymer.

[0008] The present invention (2) includes the method for producing a porous liquid crystal polymer described in (1), in which in the first step, the liquid crystal polymer is formed into a sheet to form a non-porous sheet, and in the third step, the non-porous sheet is foamed to produce a porous liquid crystal polymer sheet.

[0009] This method for producing a porous liquid crystal polymer allows the production of a thin porous liquid crystal polymer sheet.

[0010] The present invention (3) includes the method for producing a porous liquid crystal polymer according to (1) or (2), further comprising a fourth step of pressing the porous liquid crystal polymer in the thickness direction after the third step.

[0011] In this method for producing a porous liquid crystal polymer, the porous liquid crystal polymer is pressed in the thickness direction in the fourth step after the third step, so that an even thinner porous liquid crystal polymer can be produced.

[0012] The present invention (3) includes the method for producing a porous liquid crystal polymer according to any one of (1) to (3), which produces the porous liquid crystal polymer having a thickness of 25 μm or more and 200 μm or less.

[0013] This manufacturing method makes it possible to manufacture a thin porous liquid crystal polymer having a thickness of 200 μm or less.

[0014] On the other hand, since a porous liquid crystal polymer having a thickness of 25 μm or more is produced, it is possible to produce a porous liquid crystal polymer that is excellent in processability and handling.

[0015] The present invention (4) includes the method for producing a porous liquid crystal polymer according to any one of (1) to (5), wherein in the second step, the liquid crystal polymer is immersed in the supercritical fluid at a temperature higher than the melting point of the liquid crystal polymer minus 30°C.

[0016] In the second step of this method for producing a porous liquid crystal polymer, the liquid crystal polymer is immersed in a supercritical fluid at a temperature higher than the melting point of the liquid crystal polymer minus 30°C, so that the liquid crystal polymer can be sufficiently impregnated with the supercritical fluid in the second step. This makes it possible to produce a porous liquid crystal polymer with a high porosity P. As a result, a porous liquid crystal polymer with a low dielectric constant and a low dielectric loss tangent can be obtained.

[0017] According to the manufacturing method of the present invention, a thin porous liquid crystal polymer can be manufactured.

[0018] 1A to 1D are process diagrams of one embodiment of the method for producing a porous liquid crystal polymer of the present invention. Fig. 1A is the first process. Fig. 1B is the second process. Fig. 1C is the third process. Fig. 1D is the fourth process. Fig. 2 is a cross-sectional view of a printed circuit board provided with a porous liquid crystal polymer sheet.

[0019] <One embodiment of the method for producing a porous liquid crystal polymer> A method for producing a porous liquid crystal polymer sheet, which is one embodiment of the method for producing a porous liquid crystal polymer of the present invention, will be described with reference to Figures 1A to 1D. The method for producing a porous liquid crystal polymer sheet 1 includes a first step, a second step, and a third step as essential steps. The method for producing a porous liquid crystal polymer sheet 1 further includes a fourth step as an optional step. In the method for producing a porous liquid crystal polymer sheet 1 of this embodiment, steps 1 to 4 are carried out in order.

[0020] <First Step> As shown in FIG. 1A, in the first step, a liquid crystal polymer is formed into a sheet to form a non-porous sheet 3.

[0021] <Liquid Crystal Polymer> The liquid crystal polymer is not limited. The liquid crystal polymer is a liquid crystalline thermoplastic resin. Examples of the liquid crystal polymer include liquid crystal polyester, preferably aromatic liquid crystal polyester. Liquid crystal polymers are specifically described in, for example, JP 2020-147670 A and JP 2004-189867 A. Commercially available liquid crystal polymers can be used. Examples of commercially available products include UENO LCP (registered trademark, the same applies hereinafter) 8100 series (low melting point type, manufactured by Ueno Pharmaceutical Co., Ltd.) and UENO LCP 5000 series (high melting point type, manufactured by Ueno Pharmaceutical Co., Ltd.). Preferably, the UENO LCP 8100 series is used.

[0022] The melting point of the liquid crystal polymer is not limited. The melting point of the liquid crystal polymer is, for example, 200°C or higher, preferably 220°C or higher, and for example, 400°C or lower, preferably 370°C or lower. The melting point of the liquid crystal polymer is determined by differential scanning calorimetry. In differential scanning calorimetry, the temperature is increased at a rate of 10°C / min, scanning the range from 25°C to 400°C, and the liquid crystal polymer is heated in a nitrogen atmosphere. If the liquid crystal polymer is a commercially available product, the catalog value of the commercially available product can be used as is. If the melting point of the liquid crystal polymer is below the above-mentioned upper limit, the porous liquid crystal polymer sheet 1 has excellent handleability and processability. If the melting point of the liquid crystal polymer is above the above-mentioned lower limit, the porous liquid crystal polymer sheet 1 has excellent heat resistance.

[0023] Furthermore, additives can be added to the liquid crystal polymer. Examples of additives include fillers. Examples of fillers include hollow spheres. Hollow spheres include, for example, glass balloons. Hollow spheres are described, for example, in JP 2004-189867 A. Preferably, no additives are added to the liquid crystal polymer. If no additives are added to the liquid crystal polymer, the porous liquid crystal polymer sheet 1 can be prevented from becoming brittle.

[0024] <Sheet Formation> To form a sheet from a liquid crystal polymer, for example, first, the liquid crystal polymer provided in a bulk or particulate form is kneaded, and then the kneaded product is formed into a sheet. The kneading conditions are not limited. The kneading temperature is, for example, 200°C or higher, preferably 210°C or higher, and, for example, 300°C or lower, preferably 270°C or lower, more preferably 250°C or lower.

[0025] The kneaded mixture is formed into a sheet to produce the nonporous sheet 3. Examples of methods for forming the kneaded mixture into a sheet include pressing, extrusion, and injection. Pressing is preferred, and heat pressing is more preferred. Vacuum pressing is also preferred, and vacuum heat pressing is particularly preferred.

[0026] The pressing temperature is, for example, 200° C. or more and 300° C. or less. The pressing pressure is, for example, 1 MPa or more, preferably 4 MPa or more, and for example, 20 MPa or less, preferably 10 MPa or less. The pressure of the pressing atmosphere is, for example, 0.05 MPa or less, preferably 0.01 MPa or less.

[0027] There are no limitations on the thickness of the nonporous sheet 3. Specifically, the thickness of the nonporous sheet 3 is, for example, 1000 μm or less, preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less, and for example, 10 μm or more, preferably 50 μm or more.

[0028] The non-porous sheet 3 made of the liquid crystal polymer can be used as is. Specifically, a commercially available non-porous sheet 3 can be used as is.

[0029] <Second Step> In the second step, as shown in FIG. 1B , the nonporous sheet 3 is impregnated with the supercritical fluid 15. Specifically, the nonporous sheet 3 is brought into contact with the supercritical fluid 15. A supercritical apparatus 10 is used to impregnate the nonporous sheet 3 with the supercritical fluid 15. The supercritical apparatus 10 includes a pressure vessel 11, a circulation device (not shown), and a temperature adjustment device (not shown). The pressure vessel 11 is capable of circulating the supercritical fluid 15 while storing it therein. The circulation device circulates the supercritical fluid 15 through the pressure vessel 11. The temperature adjustment device is capable of adjusting the temperature of the pressure vessel 11.

[0030] <Supercritical fluid 15> There is no limitation on the type of supercritical fluid 15. Examples of the supercritical fluid 15 include supercritical carbon dioxide and supercritical nitrogen. From the viewpoint of production costs, the supercritical fluid 15 is preferably supercritical carbon dioxide (critical temperature 31°C, critical pressure 7.4 MPa).

[0031] In the second step, the nonporous sheet 3 is placed in the pressure vessel 11. Then, in the supercritical device 10, the supercritical fluid 15 is introduced into the pressure vessel 11. Then, the supercritical fluid 15 is circulated by a circulation device (not shown). As a result, the supercritical fluid 15 comes into contact with the nonporous sheet 3.

[0032] Then, first, the supercritical fluid 15 outside the nonporous sheet 3 is impregnated into the nonporous sheet 3. In other words, the supercritical fluid 15 penetrates into the nonporous sheet 3. In this way, the supercritical fluid 15 is impregnated into the nonporous sheet 3.

[0033] The conditions for the second step are not limited. Specifically, the temperature of the supercritical fluid 15 is, for example, higher than the melting point of the liquid crystal polymer minus 30°C. If the temperature of the supercritical fluid 15 is higher than the melting point of the liquid crystal polymer minus 30°C, the nonporous sheet 3 can be sufficiently impregnated with the supercritical fluid 15 in the second step. Therefore, a porous liquid crystal polymer sheet 1 having a high porosity P can be produced. As a result, a porous liquid crystal polymer sheet 1 having a low dielectric constant and a low dielectric loss tangent can be obtained. Specifically, the temperature of the supercritical fluid 15 is, for example, 150°C or higher, preferably 175°C or higher, more preferably 200°C or higher, and, for example, 370°C or lower, preferably 340°C or lower, more preferably 300°C or lower, even more preferably 275°C or lower, and particularly preferably 230°C or lower.

[0034] The pressure of the supercritical fluid 15 is, for example, 5 MPa or more, preferably 10 MPa or more, and for example, 50 MPa or less, preferably 30 MPa or less. The impregnation time is not limited. The impregnation time is, for example, 20 minutes or more, preferably 1 hour or more, and for example, 100 hours or less, preferably 24 hours or less.

[0035] <Third Step> In the third step, as shown in Figure 1C, at least one of the pressure and temperature of the atmosphere around the nonporous sheet 3 impregnated with the supercritical fluid is reduced to below the critical point of the supercritical fluid. In this embodiment, the pressure of the atmosphere around the nonporous sheet 3 impregnated with the supercritical fluid is reduced to below the critical pressure of the supercritical fluid. The critical point corresponds to the lower limit of the pressure and the lower limit of the temperature at which the fluid can be maintained as a supercritical fluid.

[0036] Specifically, the pressure inside the pressure vessel 11 is reduced so that the pressure of the atmosphere around the nonporous sheet 3 becomes atmospheric pressure (0.1 MPa). The pressure inside the pressure vessel 11 is reduced while removing the supercritical fluid 15 from inside the pressure vessel 11. The reduced pressure inside the pressure vessel 11 is adjusted so as to promote foaming by the supercritical fluid 15 impregnated in the nonporous sheet 3. Specifically, the time required to reduce the pressure from the pressure when the supercritical fluid 15 is present inside the pressure vessel 11 to atmospheric pressure (0.1 MPa) is set to, for example, 5 minutes or less, preferably 1 minute or less, more preferably 10 seconds or less, and even more preferably 3 seconds or less. The lower limit of the time is not limited. The lower limit of the time is, for example, 0.1 seconds. The average pressure reduction rate is, for example, 1 MPa / second or more, preferably 10 MPa / second or more, more preferably 15 MPa / second or more, and even more preferably 20 MPa / second or more. The upper limit of the average pressure reduction rate is not limited. The upper limit of the average pressure drop rate is, for example, 100 MPa / sec.

[0037] In the third step, the nonporous sheet 3 is foamed to obtain a porous liquid crystal polymer sheet 1 containing a plurality of pores 2. This porous liquid crystal polymer sheet 1 is larger in the thickness direction and the surface direction than the nonporous sheet 3 before foaming. In other words, the nonporous sheet 3 expands to become the porous liquid crystal polymer sheet 1.

[0038] <Fourth Step> In the fourth step, the porous liquid crystal polymer sheet 1 obtained in the third step is thinned. Methods for thinning the porous liquid crystal polymer sheet 1 include, for example, pressing, stretching, and rolling. Pressing is preferred from the viewpoint of precision in adjusting the thickness of the porous liquid crystal polymer sheet 1 obtained as a product.

[0039] Specifically, the porous liquid crystal polymer sheet 1 is pressed in the thickness direction. More specifically, the porous liquid crystal polymer sheet 1 is heat-pressed. In the heat press, for example, a press device equipped with two press plate members 30 is used. In the heat press, a spacer member 35 can be disposed between the two press plate members 30 and around the porous liquid crystal polymer sheet 1. In the heat press, the thickness of the spacer member 35 is adjusted to adjust the thickness of the porous liquid crystal polymer sheet 1 to be manufactured. The conditions for the heat press are not limited.

[0040] By carrying out the above-mentioned first to fourth steps, the porous liquid crystal polymer sheet 1 is manufactured.

[0041] <Porous Liquid Crystal Polymer Sheet 1> The porous liquid crystal polymer sheet 1 has a thickness and a sheet shape. The sheet shape includes a film shape. The porous liquid crystal polymer sheet 1 extends in a planar direction. The planar direction is perpendicular to the thickness direction. The porous liquid crystal polymer sheet 1 has a large number of fine pores (voids) 2. Examples of the cell structure of the porous liquid crystal polymer sheet 1 include a closed cell structure, an open cell structure, and a semi-closed semi-open cell structure. A closed cell structure is preferred.

[0042] <Thickness> The thickness of the porous liquid crystal polymer sheet 1 is, for example, preferably 10 μm or more, more preferably 30 μm or more, and for example, 1000 μm or less, preferably 500 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less. If the thickness of the porous liquid crystal polymer sheet 1 is not less than the above-mentioned lower limit, the porous liquid crystal polymer sheet 1 has excellent processability and handleability. If the thickness of the porous liquid crystal polymer sheet 1 is not more than the above-mentioned upper limit, the porous liquid crystal polymer sheet 1 can be made thinner.

[0043] <Porosity P> The porosity P of the porous liquid crystal polymer sheet 1 is, for example, 1% or more, preferably 1.5% or more, more preferably 10% or more, even more preferably 20% or more, and even more preferably 22% or more, 30% or more, even 35% or more, even 40% or more, even 50% or more, and even 55% or more. The upper limit of the porosity P of the porous liquid crystal polymer sheet 1 is not limited. The upper limit of the porosity P of the porous liquid crystal polymer sheet 1 is, for example, 95%, and preferably 90% from the viewpoint of ensuring the mechanical strength of the porous liquid crystal polymer sheet 1. The porosity P of the porous liquid crystal polymer sheet 1 can be determined using a nonporous liquid crystal polymer film corresponding to the porous liquid crystal polymer sheet 1. Specifically, the specific gravity G1 of the porous liquid crystal polymer sheet 1 and the specific gravity G0 of the nonporous liquid crystal polymer sheet are each measured, and the porosity P of the porous liquid crystal polymer sheet 1 is calculated using the following formula:

[0044] P=100×(1-G1 / G0)

[0045] P: porosity P of the porous liquid crystal polymer sheet 1 G1: specific gravity of the porous liquid crystal polymer sheet 1 G0: specific gravity of the non-porous liquid crystal polymer film

[0046] <Dielectric Constant> The dielectric constant of the porous liquid crystal polymer sheet 1 at 10 GHz is, for example, less than 3.10, preferably 2.60 or less, more preferably 2.50 or less, even more preferably 2.20 or less, further preferably 2.10 or less, 2.00 or less, or 1.90 or less. If the dielectric constant of the porous liquid crystal polymer sheet 1 is equal to or less than the above-mentioned upper limit, the porous liquid crystal polymer sheet 1 has low dielectric constant. The lower limit of the dielectric constant of the porous liquid crystal polymer sheet 1 at 10 GHz is not limited. For example, the dielectric constant of the porous liquid crystal polymer sheet 1 at 10 GHz is 1.00. A method for measuring the dielectric constant of the porous liquid crystal polymer sheet 1 will be described later in the Examples.

[0047] <Dielectric loss tangent> The dielectric loss tangent of the porous liquid crystal polymer sheet 1 at 10 GHz is, for example, 0.00129 or less, preferably 0.00100 or less, more preferably 0.00080 or less, even more preferably 0.00070 or less, and particularly preferably 0.00060 or less. If the dielectric loss tangent of the porous liquid crystal polymer sheet 1 is equal to or less than the above-mentioned upper limit, the porous liquid crystal polymer sheet has low dielectric constant. The lower limit of the dielectric loss tangent of the porous liquid crystal polymer sheet 1 at 10 GHz is not limited. For example, the dielectric loss tangent of the porous liquid crystal polymer sheet 1 at 10 GHz is 0.00000. A method for measuring the dielectric loss tangent of the porous liquid crystal polymer sheet 1 will be described in the Examples below.

[0048] <Uses of Porous Liquid Crystal Polymer Sheet 1> There is no limitation on the uses of the porous liquid crystal polymer sheet 1. Examples of uses of the porous liquid crystal polymer sheet 1 include an insulating layer of a wiring circuit board and an antenna substrate for wireless communication.

[0049] Next, an example of a wiring circuit board having a porous liquid crystal polymer sheet 1 as an insulating layer is shown in FIG.

[0050] 2, the wired circuit board 21 extends in a planar direction. The wired circuit board 21 has a sheet shape. The wired circuit board 21 includes an insulating layer 12 and a conductor layer 13 arranged in this order toward one side in a thickness direction.

[0051] The insulating layer 12 is made of the porous liquid crystal polymer sheet 1 described above.

[0052] The conductor layer 13 is in contact with one surface in the thickness direction of the insulating layer 12. The conductor layer 13 has a predetermined wiring pattern 14.

[0053] To obtain the wired circuit board 21, for example, a laminate 16 including an insulating layer 12 and a conductive sheet 25 is prepared. The conductive sheet 25 is depicted by a virtual line in Fig. 2. For example, a nonporous laminate (shown by the virtual line in Fig. 1A) including the nonporous sheet 3 and the conductive sheet 25 is prepared, and the nonporous sheet 3 in the nonporous laminate is made porous using the manufacturing method described above (steps 1 to 4), thereby obtaining the laminate 16.

[0054] Thereafter, the conductive sheet 25 in the laminate 16 is patterned to form the conductive layer 13. For example, etching is used for the patterning.

[0055] <Effects> In one embodiment of the manufacturing method of the porous liquid crystal polymer sheet 1, the non-porous sheet 3 formed into a sheet in the first step is impregnated with the supercritical fluid 15 in the second step, and then in the third step, the non-porous sheet 3 impregnated with the supercritical fluid 15 is foamed, so that a thin porous liquid crystal polymer sheet 1 can be manufactured.

[0056] In this manufacturing method of the porous liquid crystal polymer sheet 1, in the fourth step after the third step, the porous liquid crystal polymer sheet 1 is pressed in the thickness direction, so that an even thinner porous liquid crystal polymer sheet 1 can be manufactured.

[0057] This manufacturing method makes it possible to manufacture a thin porous liquid crystal polymer sheet 1 having a thickness of 200 μm or less.

[0058] On the other hand, since the porous liquid crystal polymer sheet 1 having a thickness of 25 μm or more is produced, the porous liquid crystal polymer sheet 1 can be produced with excellent processability and handling properties.

[0059] In the second step of the manufacturing method of this porous liquid crystal polymer sheet 1, the nonporous sheet 3 is immersed in the supercritical fluid 15 at a temperature higher than the melting point of the liquid crystal polymer minus 30°C, thereby allowing the nonporous sheet 3 to be sufficiently impregnated with the supercritical fluid 15. This makes it possible to manufacture a porous liquid crystal polymer sheet 1 having a high porosity P. As a result, a porous liquid crystal polymer sheet 1 having a low dielectric constant and a low dielectric loss tangent can be obtained.

[0060] <Modifications> In the modification, the same components and steps as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the modification can achieve the same effects as those in the first embodiment unless otherwise specified. Furthermore, the first embodiment and its modification can be combined as appropriate.

[0061] In one embodiment, the pressure inside the pressure vessel 11 is reduced in the third step, but in a modified example, the temperature inside the pressure vessel 11 is reduced to below the critical temperature. Furthermore, both the pressure and the temperature inside the pressure vessel 11 can be reduced to below the critical points (critical pressure and critical temperature, respectively).

[0062] The manufacturing method of the modified example does not include the fourth step.

[0063] The method for producing the porous liquid crystal polymer sheet 1 preferably includes a fourth step. If the production method includes the fourth step, a thinner porous liquid crystal polymer sheet 1 can be produced.

[0064] On the other hand, from the viewpoint of producing a porous liquid crystal polymer sheet 1 having a high porosity P, the method for producing the porous liquid crystal polymer sheet 1 preferably does not include the fourth step. In other words, if the production method does not include the fourth step, it is possible to suppress the narrowing of the pores 2 caused by thinning the porous liquid crystal polymer sheet 1 in the fourth step. Therefore, it is possible to obtain a porous liquid crystal polymer sheet 1 having a low dielectric constant and a low dielectric loss tangent.

[0065] The modified printed circuit board includes a conductor layer, an insulating layer, and another conductor layer in this order toward one side in the thickness direction.

[0066] In the present invention, it is sufficient to produce a porous liquid crystal polymer, for example, a bulk porous liquid crystal polymer. In this case, in the first step, a bulk liquid crystal polymer is prepared. In the second step, the bulk liquid crystal polymer is immersed in a supercritical fluid. In the third step, the bulk liquid crystal polymer is foamed to produce a bulk porous liquid crystal polymer.

[0067] On the other hand, in one embodiment, a thin porous liquid crystal polymer sheet 1 can be produced.

[0068] The present invention will be described in more detail below with reference to examples. Note that the present invention is not limited to these examples. Specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than" or "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the above "Modes for Carrying Out the Invention."

[0069] First, the liquid crystal polymer used will be described in detail below.

[0070] <Types of liquid crystal polymers> A5000: UENO LCP (registered trademark) A5000, high melting point type (catalog value: melting point 280°C), manufactured by Ueno Pharmaceutical Co., Ltd. A8100: UENO LCP (registered trademark) A8100, low melting point type (catalog value: melting point 220°C), manufactured by Ueno Pharmaceutical Co., Ltd.

[0071] Example 1

[0072] First step: UENO LCP A5000 manufactured by Ueno Pharmaceutical Co., Ltd. was kneaded as a liquid crystal polymer using a Laboplastomill (model number: 100C100) manufactured by Toyo Seiki Co., Ltd., and then a non-porous sheet 3 having a thickness of 100 μm was produced using a manual hydraulic vacuum press (model number: 11FD) manufactured by Imoto Manufacturing Co., Ltd. (FIG. 1A). The kneading temperature was 300° C., and the rotation speed was 30 min. －１ The temperature in the press was 300° C., the press pressure was 4 to 10 MPa, and the atmospheric pressure was 0.1 MPa.

[0073] Step 2: Using an AKICO "CO2 Supercritical Fluid Experimental Apparatus," supercritical carbon dioxide as a supercritical fluid was impregnated into the non-porous sheet 3 (FIG. 1B). In Step 5, the temperature of the supercritical carbon dioxide was 263°C, the pressure of the supercritical carbon dioxide was 25.0 MPa, and the impregnation time (extraction time) was 60 minutes.

[0074] Step 3: While removing the supercritical carbon dioxide from the pressure vessel 11, the pressure in the pressure vessel 11 was reduced to atmospheric pressure (0.1 MPa) over 1 second (FIG. 1C). The average pressure reduction rate was 25 MPa / second. By the third step, a porous liquid crystal polymer sheet 1 having a thickness of 200 μm and a plurality of pores 2 was obtained.

[0075] Examples 2 to 5 A porous liquid crystal polymer sheet 1 was produced using the same production method as in Example 1. However, the conditions for the foaming method were changed as shown in Table 1.

[0076] Example 6 A porous liquid crystal polymer sheet 1 was produced using the same production method as in Example 1. After the third step, the fourth step (vacuum hot pressing) was carried out.

[0077] In the fourth step, the porous liquid crystal polymer sheet 1 obtained in the third step was further thinned by vacuum heat pressing (FIG. 1D). The temperature was 245°C, the pressing pressure was 2.0 MPa, and the atmospheric pressure was 0.1 MPa. A spacer member 35 with a thickness of 0.1 mm was used in the vacuum heat pressing. This resulted in a porous liquid crystal polymer sheet 1 with a thickness of 100 μm.

[0078] <Evaluation> The porous liquid crystal polymer sheets 1 of Examples 1 to 6 were evaluated for the following items. The results are shown in Table 1.

[0079] <Porosity P> The specific gravity G1 of the porous liquid crystal polymer sheet 1 and the specific gravity G0 of the non-porous sheet 3 made of a liquid crystal polymer corresponding to the porous liquid crystal polymer sheet 1 were measured using an electronic hydrometer (model number: EW300SG) manufactured by Alpha Mirage, Inc. Then, the porosity P of the porous liquid crystal polymer sheet 1 was calculated using the following formula.

[0080] P=100×(1-G1 / G0)

[0081] P: porosity P of the porous liquid crystal polymer sheet 1 G1: specific gravity of the porous liquid crystal polymer sheet 1 G0: specific gravity of the non-porous sheet 3

[0082] <Dielectric Constant and Dielectric Loss Tangent> The dielectric constant and dielectric loss tangent of the porous liquid crystal polymer sheet 1 at 10 GHz were measured using a "10 GHz SPDR resonator" manufactured by QWED Inc. according to the SPDR method in accordance with ASTM D150.

[0083]

[0084] The above invention is provided as an exemplary embodiment of the present invention, but it is merely an example and should not be interpreted as being limiting. Modifications of the present invention that are obvious to those skilled in the art are included in the scope of the following claims.

[0085] The porous liquid crystal polymer sheet of the present invention is used as an insulating layer for a wiring circuit board and an antenna substrate for wireless communication.

[0086] 1 Porous liquid crystal polymer sheet 3 Non-porous sheet 15 Supercritical fluid

Claims

1. A method for manufacturing a porous liquid crystal polymer, comprising: a first step of preparing a liquid crystal polymer; a second step of impregnating the liquid crystal polymer with a supercritical fluid; and a third step of foaming the liquid crystal polymer by reducing at least one of the pressure and temperature of the atmosphere of the liquid crystal polymer impregnated with the supercritical fluid to be less than the critical point of the supercritical fluid, thereby manufacturing a porous liquid crystal polymer.

2. The method for manufacturing a porous liquid crystal polymer according to claim 1, wherein in the first step, the liquid crystal polymer is formed into a sheet to form a non-porous sheet, and in the third step, the non-porous sheet is foamed to manufacture a porous liquid crystal polymer sheet.

3. The method for manufacturing a porous liquid crystal polymer according to claim 1 or 2, further comprising a fourth step of pressing the porous liquid crystal polymer in the thickness direction after the third step.

4. The method for manufacturing a porous liquid crystal polymer according to claim 1 or 2, wherein the porous liquid crystal polymer having a thickness of 25 μm or more and 200 μm or less is manufactured.

5. The method for manufacturing a porous liquid crystal polymer according to claim 3, wherein the porous liquid crystal polymer having a thickness of 25 μm or more and 200 μm or less is manufactured.

6. The method for manufacturing a porous liquid crystal polymer according to claim 1 or 2, wherein in the second step, the liquid crystal polymer is immersed in the supercritical fluid at a temperature higher than the temperature obtained by subtracting 30°C from the melting point of the liquid crystal polymer.

7. The method for manufacturing a porous liquid crystal polymer according to claim 3, wherein in the second step, the liquid crystal polymer is immersed in the supercritical fluid at a temperature higher than the temperature obtained by subtracting 30°C from the melting point of the liquid crystal polymer.

8. The method for manufacturing a porous liquid crystal polymer according to claim 4, wherein in the second step, the liquid crystal polymer is immersed in the supercritical fluid at a temperature higher than the temperature obtained by subtracting 30°C from the melting point of the liquid crystal polymer.

9. The method for manufacturing a porous liquid crystal polymer according to claim 5, wherein in the second step, the liquid crystal polymer is immersed in the supercritical fluid at a temperature higher than the temperature obtained by subtracting 30°C from the melting point of the liquid crystal polymer.

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