WO2013133316A1

WO2013133316A1 - Porous resin sheet and method for manufacturing same

Info

Publication number: WO2013133316A1
Application number: PCT/JP2013/056117
Authority: WO
Inventors: 紘子池永; 笠置　智之; 須藤　剛; 請井　博一
Original assignee: 日東電工株式会社
Priority date: 2012-03-09
Filing date: 2013-03-06
Publication date: 2013-09-12
Also published as: JP2013213198A

Abstract

Provided is a porous resin sheet that is a thick film having a thickness of at least 1 mm, has a low dielectric constant and dielectric loss tangent, and has a high elastic modulus, and a method for manufacturing same. The single-layered porous resin sheet that includes a thermoplastic resin has a thickness of at least 1.0 mm, a relative permittivity of 2.00 or less at 1 GHz, a dielectric loss tangent of 0.0050 or less, and a tensile modulus of at least 200 MPa. Also, the method for manufacturing the porous resin sheet comprises a gas impregnation process in which a non-reactive gas is impregnated under increased pressure into a thermoplastic resin composition containing at least the thermoplastic resin, and a foaming process in which the thermoplastic resin composition is foamed by decreasing the pressure after the gas impregnation process. The porous resin sheet is employed as a patch antenna used particularly in a mobile phone antenna.

Description

Porous resin sheet and manufacturing method thereof

The present invention relates to a porous resin sheet having a low relative dielectric constant and a dielectric loss tangent and a method for producing the same. This porous resin sheet is used as a wide range of substrate materials such as low dielectric constant materials used in high-frequency circuits such as circuit boards and antennas for band phones, electromagnetic wave control materials such as electromagnetic wave shields and electromagnetic wave absorbers, and heat insulating materials. Is possible.

As a high-frequency circuit board such as an antenna for a mobile phone, a circuit board using a low dielectric material is required to reduce signal transmission loss. For example, a circuit board using ceramics is used.

As the ceramic substrate, an alumina substrate made of alumina is used and has heat resistance against solder reflow. However, there is a problem that the substrate is heavy and easily broken, and replacement with a resin is progressing. Furthermore, use in a high frequency region is desired for improving signal transmission. At that time, a circuit board using a low dielectric material is required for reducing transmission loss. In general, the dielectric loss becomes smaller as the relative dielectric constant and the dielectric loss tangent are smaller as shown in the following equation, which is effective in reducing transmission loss.
Ad = 27.3 × f / C × tan δ × √ε _r
Ad: Dielectric loss
f: Frequency (Hz)
ε _r : relative dielectric constant C: speed of light tan δ: dielectric loss tangent

Also, patch antennas used for mobile phone antennas and the like are becoming important antennas for communication and engineering applications because they are multifunctional, lightweight, compact, and inexpensive to manufacture. Currently, there is a need for a multi-frequency antenna that uses several applications with a single antenna, and this multi-frequency antenna can be realized by widening the bandwidth of the frequency band. Antennas generally have a drawback that their frequency characteristics are narrow.

For this reason, patch antennas have a configuration in which a parasitic radiating patch element is arranged and coupled to the upper part of the microstrip radiating element, or a method of adding a broadband matching circuit to the feeder line is a means to increase the bandwidth. It is being considered. In addition, the substrate material used for the patch antenna can also be widened, and there are a method of increasing the substrate thickness and a method of using a low dielectric substrate. However, when the substrate thickness is increased, there is a problem that the dielectric loss is large in a high dielectric substrate such as a ceramic substrate, and the bandwidth is narrowed because the Q value representing the sharpness of resonance becomes high. On the other hand, a fluorine substrate having excellent dielectric characteristics as a high-frequency substrate is useful as a substrate material for patch antennas, but has a high material cost and has problems in workability such as using special chemicals in circuit processing such as plating. Therefore, there has been a demand for a low dielectric and low loss substrate material to replace the fluorine substrate.

On the other hand, in order to maintain low dielectric properties, it is known to lower the dielectric constant by making the substrate film porous. There is a porous film using a thermoplastic resin such as polypropylene or polyethylene as a film having pores, which achieves low dielectric constant and thick sheet, but has insufficient heat resistance and insufficient strength. Moreover, although the porous film using a high heat-resistant polymer is examined, although the dielectric constant is low enough, it was difficult to increase the thickness of the sheet (see Patent Document 1 and Patent Document 2). That is, in Patent Document 1, after impregnating a heat-resistant polymer with a non-reactive gas such as carbon dioxide in a supercritical state, the pressure is reduced, and then the foam is heated and heated at a temperature exceeding 120 ° C. Although a method for producing a body is disclosed, foaming to the extent that a film thickness of 1 mm or more is realized is not achieved because the temperature during impregnation is low. Patent Document 2 discloses that an open-cell porous body is obtained by a wet coagulation method, but there is no disclosure that a porous body having a thickness of 1 mm or more is obtained.

Further, as a method of thickening a thin sheet, it is known to laminate the sheet via an adhesive layer (see Patent Document 3). As a result, the laminated sheet is thicker than the dielectric constant and dielectric loss tangent of the porous film alone, resulting in higher values of the dielectric constant and dielectric loss tangent, but the dielectric constant of the adhesive is that of the polymer. If the difference is significantly different from the above, there is a problem that the transmission characteristics in the high-frequency region vary due to thickness variations caused by pressurization at the time of lamination, and a defect that the elastic modulus is weak due to the lamination and is easily deformed during substrate processing.

JP 2001-55464 A Japanese Patent Application Laid-Open No. 2004-87638 JP 2000-269616 A

An object of the present invention is to provide a single-layer porous resin sheet having a thick film, a low relative dielectric constant and a dielectric loss tangent, and a high tensile elastic modulus, and a method for producing the same.

That is, the present invention is a single-layer porous resin sheet containing a thermoplastic resin, having a thickness of 1.0 mm or more, a relative dielectric constant at 1 GHz of 2.00 or less, and a dielectric loss tangent of 0.0050 or less. And providing a porous resin sheet characterized by a tensile elastic modulus of 200 MPa or more.

The porous resin sheet of the present invention preferably has bubbles having an average cell diameter of 5.0 μm or less, a porosity of 40% or more, and a thickness variation of 10 μm or less. It is.

The thermoplastic resin constituting the porous resin sheet of the present invention is preferably polyimide or polyetherimide, and the thermoplastic resin is preferably amorphous.

The present invention is also a method for producing the porous resin sheet,
A porous resin comprising a gas impregnation step of impregnating a thermoplastic resin composition containing at least a thermoplastic resin with a non-reactive gas under pressure, and a foaming step of foaming the thermoplastic resin composition by reducing the pressure after the gas impregnation step A method for manufacturing a sheet is provided.

In the method for producing a porous resin sheet of the present invention, it is preferable to provide a heating step of heating the porous resin sheet at a temperature of 150 ° C. or higher after the foaming step.

In the method for producing a porous resin sheet of the present invention, it is preferable to use carbon dioxide as a non-reactive gas.

In the method for producing a porous resin sheet of the present invention, it is preferable to impregnate a non-reactive gas in a supercritical state.

The present invention also provides a porous substrate in which a metal foil layer is provided on at least one surface of the porous resin sheet.

The porous resin sheet of the present invention is a low dielectric constant used for high-frequency circuits such as circuit boards and band-phone antennas, taking advantage of the properties of thick film, low relative dielectric constant and dielectric loss tangent, and high tensile elastic modulus. It can be used as a wide range of substrate materials such as materials, electromagnetic wave control materials such as electromagnetic wave shields and electromagnetic wave absorbers, and heat insulating materials. The porous resin sheet of the present invention can be used as a patch antenna element substrate material having a particularly wide bandwidth and high antenna characteristics.

FIG. 1 shows a side view of an analysis model for performing a simulation when the porous resin sheet of the present invention is applied to a patch antenna. FIG. 2 shows a three-dimensional view of the analysis model shown in FIG.

Hereinafter, embodiments of the present invention will be described. The porous resin sheet of the present invention is a single-layer porous resin sheet containing a thermoplastic resin, has a thickness of 1.0 mm or more, a relative dielectric constant at 1 GHz of 2.00 or less, and a dielectric loss tangent. It is 0.0050 or less, and the tensile elastic modulus is 200 MPa or more.

Although the thermoplastic resin used in the present invention is not particularly limited, it is preferably a thermoplastic resin having heat resistance, and in particular, a resin having a glass transition temperature of 150 ° C. or more is preferably used. Examples of such thermoplastic resins include polyamide, polycarbonate, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, polyarylate, polysulfone, polyethersulfone, polyetheretherketone, polyamideimide, polyimide, and polyetherimide. A thermoplastic resin can be used individually or in mixture of 2 or more types.

Among the above polymers, polyimide or polyetherimide is preferably used. The reason why polyimide or polyetherimide is used as the thermoplastic resin in the present invention is that the dimensional stability at high temperature is good. Polyimide can be obtained by a known or conventional method. For example, a polyimide can be obtained by reacting an organic tetracarboxylic dianhydride and a diamino compound (diamine) to synthesize a polyimide precursor (polyamic acid) and dehydrating and ring-closing the polyimide precursor.

Examples of the organic tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and 2,2-bis (2,3-dicarboxyl). Phenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexa Fluoropropane dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone A dianhydride etc. are mentioned. These organic tetracarboxylic dianhydrides may be used alone or in admixture of two or more.

Examples of the diamino compound include m-phenylenediamine, p-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, and 3,3'-diaminodiphenyl. Sulfone, 2,2-bis (4-aminophenoxyphenyl) propane, 2,2-bis (4-aminophenoxyphenyl) hexafluoropropane, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 2,4-diaminotoluene, 2,6-diaminotoluene, diaminodiphenylmethane, 4,4'-diamino-2,2'-dimethylbiphenyl, 2,2'-bis (trifluoromethyl) ) -4,4'-diaminobiphenyl and the like.

As the polyimide used in the present invention, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is used as the organic tetracarboxylic dianhydride, p-phenylenediamine and / or 4 is used as the diamino compound. 4,4'-diaminodiphenyl ether is preferably used.

The polyimide precursor can be obtained by reacting approximately equimolar organic tetracarboxylic dianhydride and a diamino compound (diamine) usually in an organic solvent at 0 to 90 ° C. for about 1 to 24 hours. Examples of the organic solvent include polar solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, and dimethyl sulfoxide.

The dehydration ring-closing reaction of the polyimide precursor is performed, for example, by heating to about 300 to 400 ° C. or by acting a dehydration cyclizing agent such as a mixture of acetic anhydride and pyridine. In general, polyimide is a polymer that is insoluble in organic solvents and difficult to mold. Therefore, when producing a porous body made of polyimide, it is common to use the above polyimide precursor as a polymer for the preparation of the polymer composition having the microphase separation structure.

In addition to the above method, the polyimide can be obtained by a method in which a polyamic acid silyl ester obtained by reacting an organic tetracarboxylic dianhydride and an N-silylated diamine is heated and cyclized.

The polyetherimide can be obtained by a dehydration ring-closing reaction between the diamino compound and an aromatic bisether anhydride such as 2,2,3,3-tetracarboxydiphenylene ether dianhydride. For example, Ultem resin (manufactured by SABIC), Superior resin (manufactured by Mitsubishi Plastics) or the like may be used.

The thermoplastic resin used in the present invention is preferably amorphous. By using an amorphous thermoplastic resin, it is possible to obtain a porous resin sheet excellent in impact resistance and workability and excellent in flexural elasticity in a high temperature range. The amorphous thermoplastic resin is a resin that does not substantially contain a crystalline portion in the thermoplastic resin, and its crystallinity is preferably 2% or less, more preferably 0%. is there. Amorphous thermoplastic resin is also judged from having only a glass transition point and no melting point.

In the present invention, the porous resin sheet may contain an additive as required in addition to the thermoplastic resin. The kind of additive is not particularly limited, and various additives that are usually used for foam molding can be used.

For example, examples of the additive include a cell nucleating agent, a crystal nucleating agent, a plasticizer, a lubricant, a colorant, an ultraviolet absorber, an antioxidant, a filler, a reinforcing material, a flame retardant, and an antistatic agent. The kind and addition amount are not particularly limited, and can be used as long as the characteristics of the porous resin sheet of the present invention are not impaired.

The single layer of the present invention having a thickness of 1.0 mm or more, a relative dielectric constant at 1 GHz of 2.00 or less, a dielectric loss tangent of 0.0050 or less, and a tensile elastic modulus of 200 MPa or more. In order to manufacture this porous resin sheet, it can be manufactured by using a thermoplastic resin layer containing the thermoplastic resin and making it porous. In particular, by using a porous resin sheet having bubbles with an average bubble diameter of 5.0 μm or less and a porosity of 40% or more, the dielectric constant or dielectric constant is reduced without lowering the insulation or mechanical strength. The tangent can be reduced without variation.

In the method for producing a porous resin sheet of the present invention, a thermoplastic resin composition containing at least a thermoplastic resin is impregnated with a non-reactive gas under pressure, a gas impregnation step, and after the gas impregnation step, the pressure is reduced to reduce the thermoplasticity. A foaming step of foaming the resin composition is included.

The gas impregnation step is a step of impregnating a thermoplastic resin composition containing at least a thermoplastic resin with a nonreactive gas under pressure. Examples of the nonreactive gas include carbon dioxide, nitrogen gas, and air. . These gases may be used alone or in combination.

Of these non-reactive gases, it is particularly preferable to use carbon dioxide which has a large amount of impregnation into the thermoplastic resin composition used as a material for the porous resin sheet and has a high impregnation rate.

The pressure and temperature when impregnating the non-reactive gas depend on the type of non-reactive gas, the type of thermoplastic resin or thermoplastic resin composition, and the average cell diameter and porosity of the target porous resin sheet. It is necessary to adjust accordingly. For example, when carbon dioxide is used as a non-reactive gas and polyimide is used as a thermoplastic resin, in order to produce a porous resin sheet having an average cell diameter of 5.0 μm or less and a porosity of 40% or more, The pressure is about 7.4 to 100 MPa, preferably 20 to 50 MPa, and the temperature is about 120 to 350 ° C., preferably about 120 to 300 ° C. For example, when carbon dioxide is used as a non-reactive gas and polyetherimide is used as a thermoplastic resin, a porous resin sheet having an average cell diameter of 5.0 μm or less and a porosity of 40% or more is produced. The pressure is about 7.4 to 100 MPa, preferably 20 to 50 MPa, and the temperature is about 120 to 260 ° C., preferably about 120 to 220 ° C.

Further, from the viewpoint of increasing the impregnation rate into the thermoplastic resin composition, the non-reactive gas is preferably in a supercritical state. For example, in the case of carbon dioxide, when the critical temperature is 31 ° C., the critical pressure is 7.4 MPa, and the temperature is 31 ° C. or higher and the pressure is 7.4 MPa or higher, the solubility of carbon dioxide in the thermoplastic resin composition Is significantly increased, and high concentration can be mixed. In addition, when the gas is impregnated in the supercritical state, the gas concentration in the thermoplastic resin composition is high. Therefore, when the pressure is suddenly lowered, a large amount of bubble nuclei are generated, and the bubble nuclei grow and the bubble nuclei grow. Even if the density is the same as the porosity, the density increases, and very fine bubbles can be obtained.

In the present invention, the foaming step is a step of foaming the thermoplastic resin composition by reducing the pressure after the gas impregnation step. By reducing the pressure, a large amount of bubble nuclei are generated in the thermoplastic resin composition. The degree of pressure reduction (pressure reduction rate) is not particularly limited, but is about 5 to 400 MPa / second.

In the present invention, a heating step of heating a porous resin sheet made of a thermoplastic resin composition in which cell nuclei are formed by a foaming step at a temperature of 150 ° C. or higher may be provided. By heating the porous resin sheet in which bubble nuclei are generated, the bubble nuclei grow and bubbles are formed. The heating temperature is preferably 180 ° C. or higher, more preferably 200 ° C. or higher. When the heating temperature is less than 150 ° C., it may be difficult to obtain a porous resin sheet having a high porosity. Note that after the heating step, the porous resin sheet may be rapidly cooled to prevent the growth of bubbles or the shape of the bubbles may be fixed.

In the present invention, a gas impregnation step of impregnating a non-reactive gas under pressure into a thermoplastic resin composition containing at least a thermoplastic resin, and a foaming step of foaming the thermoplastic resin composition by reducing the pressure after the gas impregnation step The batch method or the continuous method may be used.

According to the batch method, for example, the foam can be produced as follows. That is, a sheet containing a thermoplastic resin as a base resin is formed by extruding a thermoplastic resin composition containing at least a thermoplastic resin using an extruder such as a single screw extruder or a twin screw extruder. Alternatively, a thermoplastic resin composition containing at least a thermoplastic resin is uniformly kneaded using a kneading machine provided with blades such as a roller, a cam, a kneader, a banbari type, etc. A sheet containing a thermoplastic resin as a base resin is formed by press molding to a predetermined thickness. The non-foamed sheet thus obtained is put in a high-pressure vessel, and a non-reactive gas composed of carbon dioxide, nitrogen, air, etc. is injected, and the non-reactive gas is impregnated in the non-foamed sheet. When the non-reactive gas is sufficiently impregnated, the pressure is released (usually up to atmospheric pressure), and bubble nuclei are generated in the base resin. And after growing a bubble by heating this bubble nucleus, it cools rapidly with cold water etc., prevents the growth of a bubble, or a heat resistant polymer foam is obtained by fixing a shape.

On the other hand, according to the continuous method, for example, a non-reactive gas is injected while kneading a thermoplastic resin composition containing at least a thermoplastic resin using an extruder such as a single screw extruder or a twin screw extruder, After sufficiently impregnating the non-reactive gas in the resin, the pressure is released by extrusion (usually up to atmospheric pressure) to generate bubble nuclei. And after making a bubble grow by heating, it cools rapidly with cold water etc., the growth of a bubble is prevented or a porous resin sheet can be obtained by fixing a shape.

According to the method for producing a porous resin sheet of the present invention, a non-porous layer (skin layer) substantially free of bubbles may be formed on the outermost surfaces on both sides of the produced porous resin sheet. This non-porous layer is formed in the pressure release process after impregnation with the non-reactive gas. The nonporous layer may be removed by slicing to form a porous resin sheet consisting of only a porous portion, or a porous resin sheet having a nonporous layer may be left leaving the nonporous layer. By using a porous resin sheet having a non-porous layer, there is an advantage that mechanical strength and heat resistance can be improved.

In the present invention, the porous resin sheet is a single layer and has a thickness of 1.0 mm or more. In the present invention, the single-layer porous resin sheet is composed of the same thermoplastic resin composition throughout the thickness direction of the sheet, and, for example, a plurality of sheets are bonded together with an adhesive or an adhesive sheet made of different materials. Things are not included.

The thickness of the porous resin sheet of the present invention is 1.0 mm or more, preferably 1.2 mm or more, more preferably 1.3 mm or more (usually 3.0 mm or less). If the thickness of the porous resin sheet is 1.0 mm or more, for example, when used for an antenna for a band telephone, there is an advantage that the reflection characteristic shifts to a lower direction in the antenna characteristic and the band is broadened. If so, the reflection characteristics cannot be increased and the bandwidth cannot be increased.

In the present invention, the variation in the thickness of the porous resin sheet is preferably 10 μm or less, and more preferably 8 μm or less. When the variation in the thickness of the porous resin sheet exceeds 10 μm, the porous resin sheet may be easily warped or distorted.

In the present invention, the thickness of the porous resin sheet is determined by measuring the film thickness with a dial gauge at 25 points divided in 1 cm ² in the surface of a 50 mm × 50 mm sample, and taking the average value as the thickness. The difference between the value and the minimum value is taken as variation.

The porous resin sheet of the present invention is characterized in that the relative dielectric constant at 1 GHz is 2.00 or less. If the relative dielectric constant of the porous resin sheet is 2.00 or less, there is an advantage that the broadband width is widened with the same low dielectric thickness, and if it exceeds 2.00, the broadband width is narrowed, so the sheet thickness is increased. Need to do. In the present invention, the dielectric constant at 1 GHz of the porous resin sheet is preferably 1.90 or less, more preferably 1.85 or less (usually 1.40 or more).

The porous resin sheet of the present invention is characterized in that the dielectric loss tangent is 0.0050 or less. If the dielectric loss tangent of the porous resin sheet is 0.0050 or less, there is an advantage that the dielectric loss in the high frequency region can be reduced, and if it exceeds 0.0050, the dielectric loss becomes larger than that of a single resin. In the present invention, the dielectric loss tangent of the porous resin sheet is preferably 0.0045 or less, more preferably 0.0042 or less.

In the present invention, the relative dielectric constant of the porous resin sheet was measured by measuring the complex dielectric constant at a frequency of 1 GHz by the cavity resonator contact method, and the real part (εr ′) was defined as the relative dielectric constant. The dielectric loss tangent (tan δ) was obtained from the ratio (εr ″ / εr ′) of the real part (εr ′) and the imaginary part (εr ″). The measuring instrument uses a strip-shaped sample (sample size 2 mm × 70 mm length) by a cylindrical cavity resonator (“Network Analyzer N5230C” manufactured by Agilent Technologies, “Cavity Resonator 1 GHz” manufactured by Kanto Electronics Application Development Co., Ltd.). Can be measured.

The porous resin sheet of the present invention is characterized by a tensile elastic modulus of 200 MPa or more. There exists a malfunction that it is easy to deform | transform at the time of board | substrate processing that a tensile elasticity modulus is less than 200 Mpa. In the present invention, the tensile elastic modulus of the porous resin sheet is preferably 220 MPa or more, and more preferably 240 MPa or more (usually 400 MPa or less).

In the present invention, the tensile elastic modulus of the porous resin sheet is calculated based on IPC-TM-650, Number 2.4.18.3, and is calculated from the slope of the stress curve at a tensile speed of 50 mm / min.

The average bubble diameter of the bubbles contained in the porous resin sheet of the present invention is preferably 5.0 μm or less, more preferably 4.0 μm or less (usually 0.01 μm or more). If the average cell diameter of the porous resin sheet is 5.0 μm or less, there is an advantage that the relative permittivity and the dielectric loss tangent can be lowered without lowering the insulation and mechanical strength. Insulation and mechanical strength may decrease.

The average cell diameter of the bubbles contained in the porous resin sheet of the present invention is determined by observing the cut surface of the porous resin sheet with a scanning electron microscope (SEM) (“S-3400N” manufactured by Hitachi, Ltd.) Was binarized with image processing software (“WinROOF” manufactured by Mitani Shoji Co., Ltd.), separated into a bubble portion and a resin portion, and the maximum vertical chord length of the bubbles was measured. The average value of 50 bubbles from the larger bubble diameter was taken as the average bubble diameter.

Further, the porosity of the porous resin sheet of the present invention is preferably 40% or more, more preferably 50% or more, and particularly preferably 60% or more (usually 80% or less). If the porosity of the porous resin sheet is 40% or more, there is an advantage that uniform pores exist in the sheet and there is no variation in dielectric characteristics. If it is less than 40%, the pore formation state is uneven. In some cases, variations in dielectric characteristics are likely to occur.

The porosity of the porous resin sheet of the present invention is calculated by the following formula by measuring the specific gravity of the thermoplastic resin composition before foaming and the porous resin sheet after foaming.
Porosity (%) = [1− (specific gravity of the porous resin sheet after foaming / specific gravity of the thermoplastic resin composition before foaming)] × 100

In addition, the porous resin sheet of the present invention desirably has a tensile strength (breaking strength) of 8 to 20 MPa, preferably 10 to 15 MPa. If the tensile strength is in the range of 8 to 20 MPa, the porous resin sheet of the present invention has sufficient strength and stability when used for circuit boards, band phone antennas, electromagnetic wave control materials, heat insulating materials, etc. Dielectric properties can be obtained. On the other hand, if the tensile strength is less than 8 MPa, sufficient strength may not be obtained when used in the above applications, and the dielectric properties may vary due to the increased bubble diameter. On the other hand, if the tensile strength exceeds 20 MPa, pores are not sufficiently formed, and a low relative dielectric constant and dielectric loss tangent may not be obtained.

Further, the porous resin sheet of the present invention has a tensile elongation (breaking elongation) of 2.0 to 4.0%, preferably 2.5 to 3.5%. If the tensile elongation is in the range of 2.0 to 4.0%, when the porous resin sheet of the present invention is used for a circuit board, an antenna for a band phone, an electromagnetic wave control material, a heat insulating material, etc., deformation, etc. It has no sufficient shape stability and stable dielectric properties can be obtained. If the tensile elongation is less than 2.0%, pores are not sufficiently formed, and a low relative dielectric constant and dielectric loss tangent may not be obtained. On the other hand, if the tensile elongation exceeds 4.0%, there is a risk of deformation or the like when used in the above applications, and the dielectric properties may vary due to the increased bubble diameter.

In the present invention, the tensile strength and tensile elongation of the porous resin sheet were determined based on IPC-TM-650, Number 2.4.18.3, and obtained from the strength and elongation at the breaking point at a tensile speed of 50 mm / min.

The porous resin sheet of the present invention can have solder heat resistance by using a thermoplastic resin having heat resistance. Solder heat resistance is evaluated by observing the presence or absence of a change by floating a porous resin sheet for 30 seconds in a solder reflow heated to 260 ° C.

The porous resin sheet of the present invention can be made into a porous substrate by forming a metal foil layer on at least one surface thereof. The porous substrate is used as an electromagnetic wave control material such as an antenna for a mobile phone or an antenna substrate, a high-frequency circuit board, an electromagnetic wave shield, or an electromagnetic wave absorber. In particular, it is used as a patch antenna used for mobile phone antennas.

The metal foil is not particularly limited, but stainless steel foil, copper foil, aluminum foil, copper-beryllium foil, phosphor bronze foil, iron-nickel alloy foil, etc. are usually used. The method for forming the metal foil layer is not particularly limited, but (1) a method in which a resin layer to be foamed is formed on a base made of metal foil and foamed, and (2) the foamed resin layer is first formed. And a method of metallizing by a known method such as sputtering, electrolytic plating, and electroless plating. Also, two or more techniques can be used in combination.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

[Measurement and evaluation method]
(Relative permittivity, dielectric loss tangent)
As for the relative dielectric constant, the complex dielectric constant at a frequency of 1 GHz was measured by the cavity resonator contact method, and the real part (εr ′) was defined as the relative dielectric constant. The dielectric loss tangent (tan δ) was obtained from the ratio (εr ″ / εr ′) of the real part (εr ′) and the imaginary part (εr ″). The measuring instrument uses a strip-shaped sample (sample size 2 mm × 70 mm length) by a cylindrical cavity resonator (“Network Analyzer N5230C” manufactured by Agilent Technologies, “Cavity Resonator 1 GHz” manufactured by Kanto Electronics Application Development Co., Ltd.). Measured.

(Thickness, thickness variation)
A sample of 50 mm × 50 mm was taken from the porous resin sheet, and the film thickness was measured with a dial gauge (“R1-205” manufactured by Ozaki Mfg. Co., Ltd.) at 25 points divided in 1 cm ² within the surface. The value was the thickness, and the difference between the maximum value and the minimum value was regarded as variation.

(Average bubble diameter)
The porous resin sheet was cooled with liquid nitrogen and cut perpendicularly to the sheet surface using a blade to produce an evaluation sample. The cut surface of the sample was subjected to Au vapor deposition, and the cut surface was observed with a scanning electron microscope (SEM) (“S-3400N” manufactured by Hitachi, Ltd.). The image was binarized with image processing software (“WinROOF” manufactured by Mitani Corporation), separated into a bubble portion and a resin portion, and the maximum vertical chord length of the bubbles was measured. The average value of 50 bubbles from the larger bubble diameter was taken as the average bubble diameter.

(Porosity)
The specific gravity of the thermoplastic resin composition before foaming and the porous resin sheet after foaming was measured with a hydrometer (“MD-300S” manufactured by Alfa Mirage), and the porosity was calculated by the following formula.
Porosity (%) = [1− (specific gravity of the porous resin sheet after foaming / specific gravity of the thermoplastic resin composition before foaming)] × 100

(Mechanical properties)
The mechanical properties (elastic modulus, tensile strength, tensile elongation) of the porous resin sheet are determined according to IPC-TM-650, 2.4.18.3 using a tensile / compression tester ("Technograph TG-100kN" manufactured by Minebea). It was calculated from a stress curve obtained at a speed of 50 mm / min.

(Solder heat resistance)
For solder heat resistance, the porous resin sheet was floated for 30 seconds in a solder reflow heated to 260 ° C., and the presence or absence of change was observed.
○: No change ×: Appearance and external shape change such as shrinkage and melting

Example 1
A polyetherimide resin (manufactured by SABIC, trade name “Ultem 1000”, Tg: 217 ° C., specific gravity: 1.27, amorphous) was formed into a single-layer sheet having a thickness of 0.8 mm by a twin screw extruder. The unfoamed single layer sheet was put into a 500 cc pressure vessel, and the inside of the tank was kept in a carbon dioxide atmosphere at 120 ° C. and 25 MPa for 5 hours to impregnate carbon dioxide. Thereafter, the sheet was returned to atmospheric pressure at 300 MPa / second, then continuously passed through an oil bath at 210 ° C. for 60 seconds to grow bubbles, quickly removed, and then rapidly cooled with water containing ice. A porous resin sheet made of polyetherimide having a thickness of 1.81 mm was obtained. The surface of the obtained porous resin sheet had a non-porous layer having a thickness of 1 μm.

Example 2
A polyetherimide resin (manufactured by SABIC, trade name “Ultem 1000”, Tg: 217 ° C., specific gravity 1.27, amorphous) was formed into a single-layer sheet having a thickness of 0.8 mm by a twin screw extruder. The unfoamed single layer sheet was put in a 500 cc pressure vessel, and the tank was impregnated with carbon dioxide by holding it in a carbon dioxide atmosphere at 210 ° C. and 25 MPa for 1 hour. Then, after returning this sheet | seat to atmospheric pressure at 300 Mpa / sec, the porous resin sheet which consists of a polyetherimide with a thickness of 1.55 mm was obtained. The surface of the obtained porous resin sheet had a non-porous layer having a thickness of 1 μm.

Comparative Example 1
A porous resin sheet made of polyetherimide having a thickness of 0.065 mm was obtained in the same manner as in Example 1 except that a single-layer sheet having a thickness of 0.035 mm was used. Ten porous resin sheets were laminated with an epoxy adhesive sheet (“B-EL10 # 40” manufactured by Nitto Shinko Co., Ltd.), treated with an autoclave at 150 ° C. under conditions of 15 kg / cm ² for 3 hours. A 01 mm laminated sheet was produced. The surface of the obtained porous resin sheet had a non-porous layer having a thickness of 1 μm.

In Examples 1 and 2, since it is a single-layer porous resin sheet without an adhesive layer, it has a low dielectric constant of 2.00 or less and a dielectric loss tangent of 0.0050 or less, and has high rigidity ( (Elastic modulus) and thickness are not varied, and further, characteristics such as maintaining solder heat resistance can be achieved. On the other hand, in Comparative Example 1, although the dielectric constant is small, it is inferior in rigidity and dielectric loss tangent by being laminated through an adhesive layer.

(Antenna characteristics simulation)
A simulation analysis by “MW STUDIO” manufactured by CST was performed on the bandwidth and antenna characteristics when the porous resin sheet of the present invention was applied to a patch antenna. The analysis model of the patch antenna was performed with the configuration shown in FIGS. FIG. 1 is a side view, and is an explanatory view when the configuration of a simulated patch antenna is viewed from the side. FIG. 2 is a three-dimensional view, and is a perspective view of the configuration of the simulated patch antenna as viewed obliquely from above, and is an image diagram that is divided at the porous resin sheet portion and floated upward for easy understanding of the positional relationship of the slots. As shown.

In order to make the influence of the power feeding part as similar as possible, the patch antenna of the simulation model has a two-layer structure through the slot 3, and the power feeding to the antenna is performed not by direct power feeding but by electromagnetic coupling through the slot 3. . The thickness of the substrate 5 on the microstrip line 4 forming side was 1.2 mm, the relative dielectric constant was 4.3, and the dielectric loss tangent was zero. The conductor of each layer was made of Cu, and its thickness T _Cu was 10 μm.
The analysis of bandwidth and antenna characteristics by simulation was performed by changing the substrate material on the patch antenna element 2 side. With respect to the substrate material on each antenna element side, each size is adjusted as follows so that the patch antenna resonates in the vicinity of 2.4 GHz (see Table 2). For reference, simulation results for fluororesins and ceramics conventionally used for patch antenna substrates are also shown.

The bandwidth at −6 dB obtained from the return loss by simulation and the antenna radiation characteristics (directivity gain at 1 m, absolute gain) at each resonance frequency were analyzed. The results are shown in Table 3.

As a result, it can be seen that a patch antenna having a wide bandwidth and high antenna characteristics can be manufactured by applying the porous resin sheet of the present invention to a patch antenna element.

DESCRIPTION OF SYMBOLS 1 Porous resin sheet 2 Patch antenna element 3 Slot 4 Microstrip line 5 Substrate

Claims

A single-layer porous resin sheet containing a thermoplastic resin, having a thickness of 1.0 mm or more, a relative dielectric constant at 1 GHz of 2.00 or less, a dielectric loss tangent of 0.0050 or less, and tensile elasticity A porous resin sheet characterized by a rate of 200 MPa or more.
2. The porous resin sheet according to claim 1, wherein the porous resin sheet has bubbles having an average cell diameter of 5.0 μm or less and a porosity of 40% or more.
The porous resin sheet according to claim 1, wherein the thickness variation is 10 μm or less.
The porous resin sheet according to claim 1 or 2, wherein the thermoplastic resin is polyimide or polyetherimide.
The porous resin sheet according to claim 1 or 2, wherein the thermoplastic resin is amorphous.
It is a manufacturing method of the porous resin sheet according to claim 1,
A porous resin comprising a gas impregnation step of impregnating a thermoplastic resin composition containing at least a thermoplastic resin with a non-reactive gas under pressure, and a foaming step of foaming the thermoplastic resin composition by reducing the pressure after the gas impregnation step Sheet manufacturing method.
The method for producing a porous resin sheet according to claim 6, further comprising a heating step of heating the porous resin sheet at a temperature of 150 ° C or higher after the foaming step.
The method for producing a porous resin sheet according to claim 6 or 7, wherein the non-reactive gas is carbon dioxide.
The method for producing a porous resin sheet according to claim 6 or 7, wherein the non-reactive gas is impregnated in a supercritical state.
A porous substrate provided with a metal foil layer on at least one surface of the porous resin sheet according to claim 1 or 2.