Method for manufacturing porous liquid crystal polymers

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

Technical Field

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

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

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

Means for Solving the Problems

[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 producing a porous liquid crystal polymer by foaming the liquid crystal polymer by lowering at least one of the pressure and temperature of the atmosphere surrounding the liquid crystal polymer impregnated with the supercritical fluid to below the critical point of the supercritical fluid.

[0007] In this method for producing porous liquid crystal polymers, a liquid crystal polymer prepared in the first step is impregnated with a supercritical fluid in the second step, and then the liquid crystal polymer impregnated with the supercritical fluid is foamed in the third step, thereby enabling the production of thin porous liquid crystal polymers.

[0008] The present invention (2) includes a method for producing a porous liquid crystal polymer as described in (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 produce a porous liquid crystal polymer sheet.

[0009] This method for manufacturing porous liquid crystal polymers allows for the production of thin porous liquid crystal polymer sheets.

[0010] The present invention (3) includes a 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 manufacturing porous liquid crystal polymers, the porous liquid crystal polymer is pressed in the thickness direction in the fourth step, following the third step, making it possible to manufacture even thinner porous liquid crystal polymers.

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

[0013] This manufacturing method makes it possible to produce thin porous liquid crystal polymers with a thickness of 200 μm or less.

[0014] On the other hand, since porous liquid crystal polymers with a thickness of 25 μm or more are manufactured, porous liquid crystal polymers with excellent processability and handling properties can be produced.

[0015] The present invention (4) includes a method for producing a porous liquid crystal polymer according to any one of (1) to (5), wherein the second step involves immersing the liquid crystal polymer in a 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 porous liquid crystal polymer manufacturing method, the liquid crystal polymer is immersed in a supercritical fluid at a temperature higher than 30°C below the melting point of the liquid crystal polymer. This allows the liquid crystal polymer to be sufficiently impregnated with the supercritical fluid in the second step. As a result, a porous liquid crystal polymer with a high porosity P can be manufactured. Consequently, a porous liquid crystal polymer with a low dielectric constant and a low dielectric loss tangent can be obtained. [Effects of the Invention]

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

[0018] [Figure 1] Figures 1A to 1D are process diagrams of one embodiment of the method for producing a porous liquid crystal polymer according to the present invention. Figure 1A is the first step. Figure 1B is the second step. Figure 1C is the third step. Figure 1D is the fourth step. [Figure 2] Figure 2 is a cross-sectional view of a wiring circuit board comprising a porous liquid crystal polymer sheet. [Modes for carrying out the invention]

[0019] <One embodiment of a method for manufacturing porous liquid crystal polymer> A method for manufacturing a porous liquid crystal polymer sheet, which is an embodiment of the method for manufacturing a porous liquid crystal polymer of the present invention, will be described with reference to FIGS. 1A to 1D. The method for manufacturing the porous liquid crystal polymer sheet 1 includes, as essential steps, a first step, a second step, and a third step. The method for manufacturing the porous liquid crystal polymer sheet 1 further includes, as an optional step, a fourth step. In the method for manufacturing the porous liquid crystal polymer sheet 1 of the present embodiment, the first step to the fourth step are sequentially performed.

[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. The liquid crystal polymer is specifically described in, for example, JP-A-2020-147670 and JP-A-2004-189867. Commercially available products can be used as the liquid crystal polymer. 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 LCP8100 series is mentioned.

[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 heating rate is 10 °C / min, the range from 25 °C to 400 °C is scanned, and the liquid crystal polymer is heated in a nitrogen atmosphere. Also, if the liquid crystal polymer is a commercially available product, the catalog value of the commercially available product can be directly adopted. If the melting point of the liquid crystal polymer is below the above-mentioned upper limit, the porous liquid crystal polymer sheet 1 is excellent in 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 is excellent in heat resistance.

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

[0024] <Sheet formation> To form the liquid crystal polymer into a sheet, for example, first, the liquid crystal polymer provided in a bulk shape or a particle shape 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] By forming the kneaded product into a sheet, a non-porous sheet 3 is produced. To form the kneaded product into a sheet, examples include pressing, extrusion, and injection. Pressing is preferably used, more preferably hot pressing. Vacuum pressing is also preferable. Most preferably, vacuum hot pressing is used.

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

[0027] The thickness of the non-porous sheet 3 is not limited. Specifically, the thickness of the non-porous 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 also, for example, 10 μm or more, preferably 50 μm or more.

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

[0029] <Second process> In the second step, as shown in Figure 1B, the supercritical fluid 15 is impregnated into the non-porous sheet 3. Specifically, the non-porous sheet 3 is brought into contact with the supercritical fluid 15. A supercritical apparatus 10 is used to impregnate the non-porous sheet 3 with the supercritical fluid 15. The supercritical apparatus 10 comprises a pressure vessel 11, a circulation device (not shown), and a temperature control device (not shown). The pressure vessel 11 is capable of circulating the supercritical fluid 15 while containing it. The circulation device circulates the supercritical fluid 15 in the pressure vessel 11. The temperature control device can adjust the temperature of the pressure vessel 11.

[0030] <Supercritical fluid 15> The type of supercritical fluid 15 is not limited. Examples of supercritical fluids 15 include supercritical carbon dioxide and supercritical nitrogen. From the viewpoint of manufacturing cost, supercritical carbon dioxide (critical temperature 31°C, critical pressure 7.4 MPa) is preferred as the supercritical fluid 15.

[0031] In the second step, the non-porous sheet 3 is placed in the pressure vessel 11. Next, the supercritical fluid 15 is introduced into the pressure vessel 11 in the supercritical device 10. Subsequently, the supercritical fluid 15 is circulated by a circulation device (not shown). Through these steps, the supercritical fluid 15 comes into contact with the non-porous sheet 3.

[0032] First, the supercritical fluid 15 on the outside of the non-porous sheet 3 is impregnated into the non-porous sheet 3. In other words, the supercritical fluid 15 penetrates into the interior of the non-porous sheet 3. This impregnates the non-porous sheet 3 with the supercritical fluid 15.

[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 non-porous sheet 3 can be sufficiently impregnated with the supercritical fluid 15 in the second step. As a result, a porous liquid crystal polymer sheet 1 having a high porosity P can be manufactured. Consequently, a porous liquid crystal polymer sheet 1 with 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 also, 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 also, 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 also, for example, 100 hours or less, preferably 24 hours or less.

[0035] <3rd process> In the third step, as shown in Figure 1C, the pressure and temperature of the atmosphere surrounding the non-porous sheet 3 impregnated with the supercritical fluid are lowered so that at least one of them falls below the critical point of the supercritical fluid. In this embodiment, the pressure of the atmosphere surrounding the non-porous sheet 3 impregnated with the supercritical fluid is lowered so that it falls below the critical pressure of the supercritical fluid. The critical point corresponds to the lower limit of pressure and 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 atmospheric pressure of the non-porous sheet 3 becomes atmospheric pressure (0.1 MPa). The pressure inside the pressure vessel 11 is lowered while removing the supercritical fluid 15 inside the pressure vessel 11. The pressure reduction inside the pressure vessel 11 is adjusted so as to promote foaming by the supercritical fluid 15 impregnated into the non-porous sheet 3. Specifically, the time taken to lower the pressure inside the pressure vessel 11 from the pressure when the supercritical fluid 15 is present 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. For example, the lower limit of the time is 0.1 seconds. The average pressure drop 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 drop rate is not limited. The upper limit of the average rate of pressure drop is, for example, 100 MPa / second.

[0037] In the third step, the non-porous sheet 3 foams up, yielding a porous liquid crystal polymer sheet 1 containing multiple pores 2. This porous liquid crystal polymer sheet 1 is larger in both the thickness and planar directions compared to the non-porous sheet 3 before foaming. In other words, the non-porous sheet 3 expands to become the porous liquid crystal polymer sheet 1.

[0038] <4th process> 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. Preferably, from the viewpoint of the accuracy of adjusting the thickness of the porous liquid crystal polymer sheet 1 obtained as a product, pressing is used.

[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 hot-pressed. For hot pressing, for example, a press device equipped with two press plate members 30 is used. In hot pressing, a spacer member 35 can be placed between the two press plate members 30 and around the porous liquid crystal polymer sheet 1. In hot pressing, the thickness of the manufactured porous liquid crystal polymer sheet 1 is adjusted by adjusting the thickness of the spacer member 35. The conditions for hot pressing are not limited.

[0040] By carrying out the above-described steps 1 through 4, a porous liquid crystal polymer sheet 1 is manufactured.

[0041] <Porous liquid crystal polymer sheet 1> The porous liquid crystal polymer sheet 1 has thickness and a sheet shape. The sheet shape includes a film shape. The porous liquid crystal polymer sheet 1 extends in the 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 (vacancies) 2. Examples of the cellular structure of the porous liquid crystal polymer sheet 1 include a closed-cell structure, a continuous-cell structure, and a semi-closed / semi-continuous-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 also, 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 greater than or equal to the lower limit described above, the porous liquid crystal polymer sheet 1 has excellent processability and handling properties. If the thickness of the porous liquid crystal polymer sheet 1 is less than or equal to the upper limit described above, 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 more preferably 22% or more, 30% or more, even more preferably 35% or more, even more preferably 40% or more, even more preferably 50% or more, and even more preferably 55% or more. There is no upper limit to the porosity P of the porous liquid crystal polymer sheet 1. The upper limit of the porosity P of the porous liquid crystal polymer sheet 1 is, for example, 95%, and from the viewpoint of ensuring the mechanical strength of the porous liquid crystal polymer sheet 1, preferably 90%. The porosity P of the porous liquid crystal polymer sheet 1 can be determined by using a non-porous 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 non-porous liquid crystal polymer sheet are measured, and the porosity P of the porous liquid crystal polymer sheet 1 is determined by the following formula.

[0044] P = 100 × (1 - G1 / G0)

[0045] P: Porosity P of porous liquid crystal polymer sheet 1 G1: Specific gravity of porous liquid crystal polymer sheet 1 G0: Specific gravity of non-porous liquid crystal polymer film

[0046] <Dielectric constant> The dielectric constant of the porous liquid crystal polymer sheet 1 at 10 GHz is preferably less than 3.10, more preferably 2.60 or less, more preferably 2.50 or less, even more preferably 2.20 or less, and even more 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 below the above upper limit, the porous liquid crystal polymer sheet 1 is low dielectric. 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. The method for measuring the dielectric constant of the porous liquid crystal polymer sheet 1 will be described in a later example.

[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 below the upper limit described above, the porous liquid crystal polymer sheet is considered to have low dielectric properties. 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. The method for measuring the dielectric loss tangent of the porous liquid crystal polymer sheet 1 will be described in a later example.

[0048] <Applications of Porous Liquid Crystal Polymer Sheet 1> The applications of the porous liquid crystal polymer sheet 1 are not limited. Examples of applications for the porous liquid crystal polymer sheet 1 include insulating layers for wiring circuit boards and antenna substrates for wireless communication.

[0049] Next, Figure 2 shows an example of a wiring circuit board that includes a porous liquid crystal polymer sheet 1 as an insulating layer.

[0050] As shown in Figure 2, the wiring circuit board 21 extends in the planar direction. The wiring circuit board 21 has a sheet shape. The wiring circuit board 21 is provided with an insulating layer 12 and a conductive layer 13 in order toward one side in the 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 side of the insulating layer 12 in the thickness direction. The conductor layer 13 has a predetermined wiring pattern 14.

[0053] To obtain the wiring circuit board 21, for example, a laminate 16 comprising an insulating layer 12 and a conductor sheet 25 is prepared. The conductor sheet 25 is depicted by a dashed line in Figure 2. For example, a non-porous laminate (dashed line in Figure 1A) comprising the non-porous sheet 3 and the conductor sheet 25 is prepared, and the non-porous sheet 3 in the non-porous laminate is made porous using the manufacturing method described above (steps 1 to 4) to obtain the laminate 16.

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

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

[0056] In this method for manufacturing the porous liquid crystal polymer sheet 1, the porous liquid crystal polymer sheet 1 is pressed in the thickness direction in the fourth step after the third step, making it possible to manufacture an even thinner porous liquid crystal polymer sheet 1.

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

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

[0059] In the second step of the method for manufacturing the porous liquid crystal polymer sheet 1, immersing the non-porous sheet 3 in a supercritical fluid 15 at a temperature higher than 30°C below the melting point of the liquid crystal polymer allows the non-porous sheet 3 to be sufficiently impregnated with the supercritical fluid 15. As a result, a porous liquid crystal polymer sheet 1 having a high porosity P can be manufactured. Consequently, a porous liquid crystal polymer sheet 1 with a low dielectric constant and a low dielectric loss tangent can be obtained.

[0060] <Variation> In the modified examples, components and processes similar to those in the first embodiment are given the same reference numerals, and their detailed descriptions are omitted. Furthermore, the modified examples can achieve the same effects and advantages as the first embodiment, unless otherwise specified. Moreover, the first embodiment and its modified examples 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 temperature inside the pressure vessel 11 can be reduced to below the critical point (critical pressure and critical temperature, respectively).

[0062] The method for manufacturing the modified form does not include a fourth step.

[0063] The method for manufacturing the porous liquid crystal polymer sheet 1 preferably includes a fourth step. If the manufacturing method includes a fourth step, an even thinner porous liquid crystal polymer sheet 1 can be manufactured.

[0064] On the other hand, from the viewpoint of producing a porous liquid crystal polymer sheet 1 with a high porosity P, it is preferable that the method for producing the porous liquid crystal polymer sheet 1 does not include a fourth step. In other words, if the manufacturing method does not include a fourth step, the narrowing of pores 2 caused by thinning the porous liquid crystal polymer sheet 1 in the fourth step can be suppressed. As a result, a porous liquid crystal polymer sheet 1 with a low dielectric constant and a low dielectric loss tangent can be obtained.

[0065] The modified wiring circuit board comprises a conductor layer, an insulating layer, and another conductor layer, arranged in sequence toward one side in the thickness direction.

[0066] In this invention, a porous liquid crystal polymer can be manufactured, for example, a bulk-shaped porous liquid crystal polymer can be manufactured. In this case, the first step is to prepare a bulk-shaped liquid crystal polymer. In the second step, a supercritical fluid is immersed in the bulk-shaped liquid crystal polymer. In the third step, the bulk-shaped liquid crystal polymer is foamed to produce a bulk-shaped porous liquid crystal polymer.

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

[0068] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numbers defined as "less than or equal to" or "less than") or lower limits (numbers defined as "greater than or equal to" or "greater than or equal to") of the blending ratios (content ratios), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0069] First, the details of the liquid crystal polymer used are described 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] 1st step UENO LCP A5000, manufactured by Ueno Pharmaceutical Co., Ltd., was kneaded using a Laboplast Mill (model: 100C100) manufactured by Toyo Seiki Co., Ltd., and then a 100 μm thick non-porous sheet 3 was fabricated using a manual hydraulic vacuum press (model: 11FD) manufactured by Imoto Seisakusho Co., Ltd. (Figure 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 4-10 MPa, and the ambient pressure was 0.1 MPa.

[0073] 2nd process Using the AKICO "CO2 Supercritical Fluid Experiment Apparatus," supercritical carbon dioxide was impregnated into a non-porous sheet 3 as a supercritical fluid (Figure 1B). 2 The temperature of the supercritical carbon dioxide during the process was 263°C, the pressure of the supercritical carbon dioxide was 25.0 MPa, and the impregnation time (extraction time) was 60 minutes.

[0074] 3rd process While removing supercritical carbon dioxide from inside the pressure vessel 11, the pressure in the pressure vessel 11 was reduced to atmospheric pressure (0.1 MPa) in 1 second (Figure 1C). The average pressure drop rate was 25 MPa / second. In the third step, a porous liquid crystal polymer sheet 1 with a thickness of 200 μm and having multiple pores 2 was obtained.

[0075] <Examples 2 to 5> A porous liquid crystal polymer sheet 1 was manufactured using the same manufacturing 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 manufactured using the same manufacturing method as in Example 1. After the third step, the fourth step (vacuum hot pressing) was performed.

[0077] In the fourth step, the porous liquid crystal polymer sheet 1 obtained in the third step was further thinned by vacuum heat pressing (Figure 1D). The temperature was 245°C, the pressing pressure was 2.0 MPa, and the ambient 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] <Rating> The following aspects were evaluated for the porous liquid crystal polymer sheets 1 of Examples 1 to 6. 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, which is made of the 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 Co., Ltd. Subsequently, the porosity P of the porous liquid crystal polymer sheet 1 was determined using the following formula.

[0080] P = 100 × (1 - G1 / G0)

[0081] P: Porosity P of porous liquid crystal polymer sheet 1 G1: Specific gravity of porous liquid crystal polymer sheet 1 G0: Specific gravity of non-porous sheet 3

[0082] <Dielectric constant and dielectric loss tangent> Using the SPDR method compliant with ASTMD150, the dielectric constant and dielectric loss tangent of porous liquid crystal polymer sheet 1 at 10 GHz were measured using a "10 GHz SPDR resonator" manufactured by QWED Corporation.

[0083] [Table 1]

[0084] The above invention is provided as an illustrative embodiment of the present invention, but this is merely illustrative and should not be interpreted restrictively. Modifications of the present invention that are obvious to those skilled in the art are included in the claims below. [Industrial applicability]

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

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

Claims

1. The first step involves forming a non-porous sheet by creating a sheet from a liquid crystal polymer, A second step involves impregnating the liquid crystal polymer with a supercritical fluid, A method for producing a porous liquid crystal polymer, comprising: a third step of foaming the non-porous sheet by lowering at least one of the pressure and temperature of the atmosphere of the liquid crystal polymer impregnated with the supercritical fluid to below the critical point of the supercritical fluid, thereby producing a porous liquid crystal polymer.

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

3. A method for producing a porous liquid crystal polymer according to claim 1 or 2, wherein the porous liquid crystal polymer has a thickness of 25 μm or more and 200 μm or less.

4. The method for producing 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 melting point of the liquid crystal polymer minus 30°C.

5. The method for producing 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 melting point of the liquid crystal polymer minus 30°C.

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