JP2012077117A - Thermoplastic liquid crystal polymer film and transmission line using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic liquid crystal polymer film which highly controls the in-plane dielectric constant.SOLUTION: The thermoplastic liquid crystal polymer film has a thermal expansion coefficient of 0-25 ppm/°C and a coefficient C (%) of variation of the dielectric constant in the plane meets formula (1): C=σ/ε×100<0.40 (wherein C is the coefficient of variation; σ is the standard deviation; and εis the average value). Further, the average value of the dielectric constant may be, for example, 3.30 or less.

Description

  The present invention relates to a film made of a thermoplastic polymer capable of forming an optically anisotropic melt phase (hereinafter referred to as a thermoplastic liquid crystal polymer film), a thermoplastic liquid crystal polymer film having a highly controlled in-plane dielectric constant, In particular, the present invention relates to a thermoplastic liquid crystal polymer film useful for millimeter wave (10 GHz to 300 GHz) antenna applications.

  In recent years, the development of information processing fields such as personal computers and wireless communication fields such as mobile phones has been remarkable. In order to improve the information processing speed in these fields, it is necessary to improve the propagation speed of the substrate and realize low transmission in the high frequency region. The signal propagation speed approaches high speed as the dielectric constant decreases. Further, since the distortion of the waveform becomes smaller as the dielectric constant is lower, development of a high-frequency circuit board having a low dielectric constant and a low dielectric loss is being studied.

  Conventionally, ceramics have been used for such applications, but the problem is that processing is difficult and expensive, and it is desired to change the material to an organic material that is easy to process and inexpensive. For example, a substrate using a fluorine resin having an excellent dielectric property as an electrical insulating layer (hereinafter referred to as a PTFE substrate) or a substrate using a polyimide having an excellent heat resistance as an organic insulating layer (hereinafter referred to as a PI substrate) is used as the organic material. It has been proposed.

  However, regarding the PTFE substrate, the fluororesin itself has excellent high-frequency characteristics and moisture resistance, but due to the influence of glass cloth or the like used to increase dimensional stability, the high-frequency characteristics and moisture resistance of the entire substrate are low. As for the PI substrate, the high frequency characteristics are significantly inferior to those of the PTFE substrate, and the hygroscopicity is large, and the high frequency characteristics are extremely deteriorated by moisture absorption.

Therefore, Patent Document 1 discloses a surface wave transmission line using a dielectric made of a thermoplastic liquid crystal polymer film as a medium.
In this document, since a thermoplastic liquid crystal polymer film, which is a low hygroscopic material, is used as a medium, it is possible to reduce deterioration of high frequency characteristics due to moisture absorption.

JP 2003-115707 A

  However, the thermoplastic liquid crystal polymer film described in Patent Document 1 has a good balance of mechanical and thermal properties between the MD and TD directions by setting the molecular orientation SOR to 1.3 or less. However, even with such a balance, liquid crystal polymers tend to exhibit dielectric anisotropy, and it is difficult to highly control variation in dielectric constant in the plane. is there.

Accordingly, an object of the present invention is to provide a thermoplastic liquid crystal polymer film having a coefficient of thermal expansion in a plane direction within a predetermined range and a very small variation in dielectric constant in the plane.
Another object of the present invention is to provide a thermoplastic liquid crystal polymer film having excellent strength and elongation properties in addition to the effects described above.

Another object of the present invention is to provide a thermoplastic liquid crystal polymer film suitable for forming a millimeter wave antenna.
Still another object of the present invention is to provide a transmission line that can reduce transmission loss.

The inventors of the present invention have made extensive studies in order to achieve the above object. As a result, (1) a very small variation in dielectric constant is required for a millimeter-wave antenna substrate. In the measurement method, it was found that the dielectric constant could not be accurately measured in the plane direction.
As a result of further research, (2) not only established a method for evaluating extremely small variations in dielectric constant, but also (3) precise heat treatment conditions according to the dielectric constant distribution of the raw film. It has been found that a thermoplastic liquid crystal polymer film having not only a very small variation in dielectric constant but also a thermal expansion coefficient within a predetermined range can be obtained by controlling to the above, and the present invention has been completed.

That is, the present invention is a film made of a thermoplastic polymer capable of forming an optically anisotropic melt phase (hereinafter referred to as a thermoplastic liquid crystal polymer film),
The thermal expansion coefficient is 0 to 25 ppm / ° C.
The in-plane dielectric constant variation coefficient C (%) is a thermoplastic liquid crystal polymer film satisfying the following formula (1).
C = σ / ε _ave × 100 <0.40 (1)
(Here, C: coefficient of variation, σ: standard deviation, ε _ave : average value)

  The average value of the dielectric constant of the thermoplastic liquid crystal polymer film may be, for example, 3.30 or less. The dielectric loss tangent at 15 GHz of the thermoplastic liquid crystal polymer film may be 0.005 or less.

  Such a thermoplastic liquid crystal polymer film can be usefully used as a high-frequency circuit board material, and can be particularly suitably used as a film for a millimeter wave antenna.

Further, the present invention is a transmission line including at least one conductor and at least one insulator,
The insulator is formed of the above-described thermoplastic liquid crystal polymer film, and a ratio (ΔY / ΔX) of a difference between transmission loss Y (dB / cm) and frequency X (GHz) at frequencies of 15 GHz and 40 GHz is −0. The transmission line which is 020 to -0.010 is also included.

According to the present invention, it is possible to obtain a thermoplastic liquid crystal polymer film having a thermal expansion coefficient in the plane direction within a predetermined range and an extremely small variation in dielectric constant within the plane.
Such a thermoplastic liquid crystal polymer film is excellent in dielectric properties and also in strong elongation properties derived from the thermoplastic liquid crystal polymer.

Since the thermoplastic liquid crystal polymer film of the present invention has very little variation in dielectric constant, it can be suitably used for forming a millimeter wave antenna.
Further, in the present invention, a transmission line capable of reducing transmission loss can be obtained by using a thermoplastic liquid crystal polymer film having very little variation in dielectric constant in the plane.

The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and description and should not be used to define the scope of the present invention. The scope of the invention is defined by the appended claims.
(A) is a schematic sectional drawing for demonstrating the process of producing the transmission line of the Example of this invention, (b) is a schematic sectional drawing which shows the transmission line produced by this process.

The present invention is a thermoplastic liquid crystal polymer film having a thermal expansion coefficient of 0 to 25 ppm / ° C. and an in-plane dielectric constant variation coefficient C (%) satisfying the following formula (1).
C = σ / ε _ave × 100 <0.40 (1)
(Here, C: coefficient of variation, σ: standard deviation, ε _ave : average value)

[Thermoplastic liquid crystal polymer]
The thermoplastic liquid crystal polymer film is formed from a liquid crystalline polymer that can be melt-molded. The thermoplastic liquid crystal polymer is not particularly limited as long as it has a chemical structure as long as it is a liquid crystalline polymer that can be melt-molded. , Thermoplastic liquid crystal polyester, or thermoplastic liquid crystal polyester amide having an amide bond introduced therein.

  The thermoplastic liquid crystal polymer may be a polymer in which an isocyanate-derived bond such as an imide bond, a carbonate bond, a carbodiimide bond, or an isocyanurate bond is further introduced into an aromatic polyester or an aromatic polyester amide.

  Specific examples of the thermoplastic liquid crystal polymer used in the present invention include known thermoplastic liquid crystal polyesters and thermoplastic liquid crystal polyester amides derived from the compounds (1) to (4) listed below and derivatives thereof. Can be mentioned. However, it goes without saying that there is an appropriate range of combinations of various raw material compounds in order to form a polymer capable of forming an optically anisotropic melt phase.

(1) Aromatic or aliphatic dihydroxy compounds (see Table 1 for typical examples)

(2) Aromatic or aliphatic dicarboxylic acids (see Table 2 for typical examples)

(3) Aromatic hydroxycarboxylic acids (see Table 3 for typical examples)

(4) Aromatic diamine, aromatic hydroxyamine or aromatic aminocarboxylic acid (see Table 4 for typical examples)

  Representative examples of the liquid crystal polymer obtained from these raw material compounds include copolymers having the structural units shown in Tables 5 and 6.

  Of these copolymers, a polymer containing at least p-hydroxybenzoic acid and / or 6-hydroxy-2-naphthoic acid as a repeating unit is preferable, and in particular, (i) p-hydroxybenzoic acid and 6-hydroxyoxy- A polymer containing a repeating unit with 2-naphthoic acid, (ii) at least one aromatic hydroxycarboxylic acid selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and 4,4 ′ A repeating unit of at least one aromatic diol selected from the group consisting of dihydroxybiphenyl and hydroquinone and at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid Polymers containing are preferred.

  For example, in the polymer (i), when the thermoplastic liquid crystal polymer contains at least repeating units of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the repeating unit (A) of p-hydroxybenzoic acid is used. And the molar ratio (A) / (B) of the repeating unit (B) to 6-hydroxy-2-naphthoic acid is (A) / (B) = about 10/90 to 90/10 in the liquid crystal polymer. Desirably, it is desirable that (A) / (B) = about 50/50 to 85/15, and more preferably (A) / (B) = 60/40 to 80/20. It may be a degree.

  In the case of the polymer (ii), at least one aromatic hydroxycarboxylic acid (C) selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and 4,4′-dihydroxy At least one aromatic diol (D) selected from the group consisting of biphenyl and hydroquinone, and at least one aromatic dicarboxylic acid (E) selected from the group consisting of terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid. The molar ratio of each repeating unit in the liquid crystal polymer is about aromatic hydroxycarboxylic acid (C): aromatic diol (D): aromatic dicarboxylic acid (E) = about 30-80: 35-10: 35-10. More preferably, (C) :( D) :( E) = 35 to 75: 32.5 to 12.5: 3 May be about .5～12.5, more preferably, (C) :( D) :( E) = 40~70: it may be about 30 to 15: 30-15.

  Moreover, it is preferable that the molar ratio of the repeating structural unit derived from aromatic dicarboxylic acid and the repeating structural unit derived from aromatic diol is (D) / (E) = 95 / 100-100 / 95. Outside this range, the degree of polymerization does not increase and the mechanical strength tends to decrease.

  The optical anisotropy at the time of melting referred to in the present invention can be recognized by, for example, placing a sample on a hot stage, heating and heating in a nitrogen atmosphere, and observing the transmitted light of the sample.

  The thermoplastic liquid crystal polymer preferably has a melting point (hereinafter referred to as Mp) in the range of 260 to 360 ° C, more preferably Mp of 270 to 350 ° C. Mp is determined by measuring the temperature at which the main endothermic peak appears with a differential scanning calorimeter (Shimadzu Corporation DSC).

  The thermoplastic liquid crystal polymer may include a thermoplastic polymer such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyarylate, polyamide, polyphenylene sulfide, polyester ether ketone, and fluororesin within a range not impairing the effects of the present invention. It may be added.

[Method for producing thermoplastic liquid crystal polymer film]
The raw material of the thermoplastic liquid crystal polymer film used in the present invention (hereinafter sometimes referred to as the raw material film) is obtained by extrusion molding of the thermoplastic liquid crystal polymer. As long as the direction of the rigid rod-like molecule of the thermoplastic liquid crystal polymer can be controlled, any extrusion method can be applied, but not only in the mechanical axis direction of the film (hereinafter abbreviated as MD direction) by forming into a cylindrical shape, Since stress is also applied in a direction perpendicular to this (hereinafter abbreviated as TD direction) and the film can be uniformly stretched in the MD direction and TD direction, the inflation method is used to obtain a film having a small variation in dielectric constant. Is preferred.

  The thermoplastic liquid crystal polymer film may be stretched as necessary after extrusion. The stretching method itself is known, and either biaxial stretching or uniaxial stretching may be adopted, but biaxial stretching is preferred because it is easier to control the degree of molecular orientation. For stretching, a known uniaxial stretching machine, simultaneous biaxial stretching machine, sequential biaxial stretching machine or the like can be used.

  In the present invention, the most important point is that the heat treatment conditions for the film are controlled in order to reduce the variation in the dielectric constant of the raw film. That is, the present inventors have not only found that the dielectric constant of the raw film varies in the plane direction, but accurately measured the dielectric constant to a level that was impossible in the past, and the dielectric constant is Since it has also been found that the temperature changes depending on the heat treatment conditions, a thermoplastic liquid crystal polymer film having a reduced variation in dielectric constant in the plane direction can be newly produced.

The heat treatment is not limited as long as the variation of the thermal expansion coefficient and dielectric constant of the film can be controlled. For example, the obtained raw film has a plurality of blocks (for example, 2 to 5 blocks) in the width direction (that is, TD direction). (Preferably 3 blocks), and the dielectric constant in the MD direction and the TD direction in each block is measured.
Here, the dielectric constants in the MD direction and the TD direction are values measured by the method described in Examples described later.

  More specifically, for example, when the original film is divided into three blocks in the width direction (that is, the TD direction), the film is divided into three blocks: a left block, a center block, and a right block. Then, a sample is cut out for each of the left block, the central block, and the right block, and the dielectric constants in the MD direction and the TD direction are determined.

  The width of the block can be set as appropriate according to the type of film and the like, but the width of each block is preferably uniform.

Next, the ratio of the dielectric constant between the MD direction and the TD direction of each block (P _MD / P _TD ) is taken. If P _MD / P _TD <1, the heat treatment temperature of the block is set to P _MD / P _TD ≧ By setting the temperature lower than the heat treatment temperature of the block being 1 (for example, about 0.5 to 5 ° C., preferably about 1 to 4 ° C.), variation in the dielectric constant of the entire thermoplastic liquid crystal polymer film can be reduced. it can.

  Various methods can be used for such heat treatment, and the heat treatment conditions can be performed by adjusting the temperature of the ripening roll, the temperature of the heating furnace, and the like.

For example, when a heating roll is used, the thermoplastic liquid crystal polymer film can be subjected to heat treatment for each block using a heating roll with at least one surface superimposed on a support.
Further, in the heating furnace, the thermoplastic liquid crystal polymer film alone or as a laminate of the thermoplastic liquid crystal polymer film and the support may be subjected to heat treatment for each block in a heating furnace set at an appropriate temperature. it can.

  The heat treatment temperature can be appropriately set according to the thermal expansion coefficient of the material used as the support. For example, the heat treatment temperature ranges from (melting point of film −10 ° C.) to (melting point of film + 10 ° C.). Preferably, it may be (melting point of film −5 ° C.) to (melting point of film + 5 ° C.).

  That is, in the present invention, by first controlling the heat treatment temperature, the thermal expansion coefficient of the thermoplastic liquid crystal polymer film can be controlled, and furthermore, the heat treatment temperature can be changed relatively between the blocks in the original film. Thus, variation in dielectric constant within the film plane can be controlled.

  The heat treatment time can be appropriately set according to the heat treatment temperature, the thickness of the support, the thickness of the film, etc., but may be, for example, about 5 to 60 seconds, preferably 10 to 30 seconds. It may be a degree.

[Thermoplastic liquid crystal polymer film]
The thermoplastic liquid crystal polymer film thus heat-treated is not only highly controlled in variation in dielectric constant, but also can be adjusted to a suitable range in terms of thermal expansion coefficient.

(Coefficient of thermal expansion)
The thermoplastic liquid crystal polymer film of the present invention thus obtained has a thermal expansion coefficient of 0 to 25 ppm / ° C. as described above, and the thermal expansion coefficient is preferably about 5 to 22 ppm / ° C. There may be. In addition, a thermal expansion coefficient is a value measured by the method described in the Example mentioned later.
In general, ceramics, Teflon (registered trademark), and the like are used as dielectrics used in the millimeter wave and high frequency bands, and their thermal expansion coefficient is 0 ppm / ° C. for ceramics, and Teflon containing glass cloth. (Registered Trademark) is 18 ppm / ° C., and the problem is that the thermal expansion coefficient varies greatly depending on the dielectric used. On the other hand, in the present invention, as described above, since the thermal expansion coefficient can be changed according to the heat treatment, a wide range of thermal expansion coefficient can be obtained. It is possible to match the thermal expansion coefficient of the material.

(Dielectric constant)
The dielectric constant of the thermoplastic liquid crystal polymer film, for example, the dielectric constant in the TD direction of the thermoplastic liquid crystal polymer film at 15 GHz may be 3.30 or less (for example, about 1.8 to 3.28), preferably May be about 2.5 to 3.25. In addition, a dielectric constant is a value measured by the method described in the Example mentioned later.

The special point in the present invention is that a specific manufacturing method is used. Therefore, in the thermoplastic liquid crystal polymer film of the present invention, the coefficient of variation C (%) of the in-plane dielectric constant satisfies the following formula (1). Yes.
C = σ / ε _ave × 100 <0.40 (1)
(Here, C: coefficient of variation, σ: standard deviation, ε _ave : average value)

C may be preferably less than 0.30, more preferably less than 0.20.
Here, what is important in evaluating the variation in the dielectric constant is to accurately measure the film thickness and appropriately adjust the sample acquisition method according to the overall size of the film to be evaluated.

That is, it is necessary to calculate the average value and the standard deviation for the dielectric constant of the cut sample based on the sample cut by the predetermined method described below.
(1) How to cut out in the TD direction First, the cutting out method in the TD direction is performed separately for (a) when the film has a total width of 28 cm or more and (b) when the film has a total width of less than 28 cm.

(A) When the total width of the film is 28 cm or more After dividing the film equally into 7 rows, the center 4 cm of each row is sampled.
For example, when the total width is W (cm), the sampling interval w (cm) is determined from w = (W−4 × 7) / 7.

Next, based on this w, from one end to the other in the TD direction,
First sample: wx1 / 2-4 + wx1 / 2 (cm)
Second sample: 4 + wx3 / 2 to 8 + wx3 / 2 (cm)
Third sample: 8 + wx5 / 2 to 12 + wx5 / 2 (cm)
Fourth sample: 12 + wx7 / 2 to 16 + wx7 / 2 (cm)
5th sample: 16 + wx9 / 2 to 20 + wx9 / 2 (cm)
Sixth sample: 20 + wx11 / 2 to 24 + wx11 / 2 (cm)
Seventh sample: 24 + wx13 / 2 to 28 + wx13 / 2 (cm)
In this order, the cutout width of the sample is determined.

Specifically, for example, when the total width W = 56 cm, the sampling interval w = (56−4 × 7) / 7 = 4 cm.
Then, the sample is cut out at locations of 2 to 6 cm, 10 to 14 cm, 18 to 22 cm, 26 to 30 cm, 34 to 38 cm, 42 to 46 cm, and 50 to 54 cm from one end to the other end in the TD direction.

(B) When the total width of the film is less than 28 cm In the TD direction of the film, samples having a width of 4 cm are collected at equal intervals. For example, when the total width W ′ (W ′ <28) is assumed and the maximum value of a sample capable of collecting a sample having a width of 4 cm from the full width W ′ is s (1 ≦ s ≦ 6), the sampling interval w ′ is w ′ = ( W'-4xs) / s.
Specifically, for example, when the full width W = 15 cm, the maximum value s of samples that can be collected is 3, and when the full width W = 18 cm, the maximum value s of samples that can be collected is 4.
(2) How to cut out in the MD direction Regarding how to cut out in the MD direction, (a) when the total length of the film is 100 cm or more and (b) when the total length of the film is less than 100 cm, it is performed separately.

(A) When the total length of the film is 100 cm or more When the total length is 100 cm or more, an arbitrary 100 cm is selected in the MD direction, and after dividing equally into 10 lines, the center 5 cm of each line is sampled.
(B) When the total length of the film is 50 cm or more and less than 100 cm After dividing the film into 10 lines evenly in the MD direction, the center 5 cm of each line is sampled.
(C) Total length of film less than 50 cm In the MD direction of the film, samples as wide as 5 cm are collected at equal intervals.

  From the viewpoint of ensuring implementation on an industrial scale, the film size is usually 12 cm or more in width and 30 m or more in length, and preferably 30 cm or more in width and 50 m or more in length. In such a case, since the number of samples is 3 to 7 columns in width and 6 to 10 rows in length, measurement is performed on 18 to 70 samples.

(Dielectric loss tangent)
In the preferred thermoplastic liquid crystal polymer film, the dielectric loss tangent of the thermoplastic liquid crystal polymer film at 15 GHz is 0.005 or less (for example, about 0.0001 to 0.0045), preferably about 0.0005 to 0.004. Also good.
The lower the dielectric loss tangent, the smaller the transmission loss. Although the transmission loss varies depending on the conductor loss and the shape of the circuit used, the transmission circuit is generally 0.8 dB / cm or less as the S21 parameter in the 15 GHz band. Is preferable, and 0.3 dB / cm is more preferable. When the dielectric loss tangent at 15 GHz of the thermoplastic liquid crystal polymer film is 0.005 or less, it can be suitably used for such a transmission circuit, and low power and low noise can be achieved. In addition, a dielectric constant is a value measured by the method described in the Example mentioned later.

(Strong elongation)
In addition, in the preferred thermoplastic liquid crystal polymer film, it is possible to ensure a uniform dielectric constant in the plane without reducing the excellent strength and elongation of the thermoplastic liquid crystal polymer film, for example, thermoplastic liquid crystal The tensile breaking strength of the polymer film may be, for example, at least 5 kg / mm ² (for example, 5 to 50 kg / mm ² ), preferably 10 kg / mm ² or more.
Further, the tensile elongation at break of the thermoplastic liquid crystal polymer film may be, for example, at least 10% (for example, 10 to 60%), preferably 15% or more. The strength and elongation are values measured according to JIS C 2318.

(Thickness)
The thermoplastic liquid crystal polymer film used in the present invention may have any thickness, and includes a plate or sheet of 5 mm or less. However, when it is used for a high-frequency transmission line, the transmission loss decreases as the thickness increases, so it is necessary to increase the thickness as much as possible. However, when a thermoplastic liquid crystal polymer film is used alone as the electrical insulating layer, the film thickness is preferably in the range of 10 to 500 μm, and more preferably in the range of 15 to 200 μm. When the thickness of the film is too thin, the rigidity and strength of the film are reduced. Therefore, a method of obtaining an arbitrary thickness by laminating films having a film thickness in the range of 10 to 200 μm may be used.

  In particular, the film of the present invention can be suitably used as a film for a millimeter wave antenna. In millimeter-wave antenna applications, if the dielectric constant varies, it causes propagation speed fluctuations and frequency fluctuations, and the antenna performance is significantly reduced. In recent years, materials with extremely low dielectric constant variations have been desired. Since C <0.40 can be achieved in the film of the present invention, design constraints can be cleared and the film can be used as a practical millimeter-wave antenna film.

[Transmission line]
The transmission line of the present invention includes at least one conductor and at least one insulator, and the form thereof is not particularly limited as long as the thermoplastic liquid crystal polymer film is used as an insulator. Various transmission lines such as, for example, , A coaxial line, a strip line, a microstrip line, a coplanar line, a parallel line, and the like can be used as well-known or conventional transmission lines.

In such a transmission line, the ratio (ΔY / ΔX) of the difference between transmission loss Y (dB / cm) and frequency X (GHz) at frequencies of 15 GHz and 40 GHz is −0.020 to −0.010, preferably − It can be set to 0.018 to -0.008.
Here, ΔY = (40 GHz transmission loss) − (15 GHz transmission loss), and ΔX = 40−15. The unit of (ΔY / ΔX) is dB / (cm × GHz).

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by this Example. In the following examples and comparative examples, various physical properties were measured by the following methods.

[Film thickness]
For an area 6 mm square from the center point of the dielectric constant measurement, the average value measured at nine cylinders at equal intervals was taken as the film thickness of the sample, and the measurement was performed using a contact linear gauge (HS3412 manufactured by Ono Sokki).

[Dielectric constant measurement]
Using a molecular orientation meter “MOA6015” manufactured by Oji Scientific Instruments Co., Ltd., the dielectric constant and dielectric loss tangent at 15 GHz in the TD direction and MD direction were measured for each sample collected in each of the TD direction and MD direction. Moreover, the film thickness mentioned above was employ | adopted for the film thickness input in the case of a measurement.

[Mature expansion coefficient (CTE)]
Using a thermomechanical analyzer (TMA), the temperature was raised from 25 ° C. to 200 ° C. at a rate of 5 ° C./min, cooled to 30 ° C. at a rate of 20 ° C./min, and again at a rate of 5 ° C./min. It measured between 30 degreeC and 150 degreeC when it heated up. The film was measured in both the TD direction and the MD direction, and the average value was defined as the thermal expansion coefficient of the film.

[Mechanical properties (tensile breaking strength and tensile breaking elongation)]
The tensile breaking strength and tensile breaking elongation were measured according to JIS C 2318 using a tensile tester.

[Transmission loss]
A vector network analyzer (HP8753D, manufactured by Agilent Technologies) was used, and transmission loss was measured in a frequency range of 15 to 40 GHz under a temperature of 20 ° C. and a humidity of 65% RH.

(Examples 1 to 4 and Comparative Examples 1 and 2)
(1) Production of Raw Antithermoplastic Liquid Crystal Polymer Film A thermoplastic liquid crystal polymer having a melting point of 280 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (molar ratio: 73/27). Was kneaded with a single-screw extruder and melt extruded from an annular inflation die (die diameter 46.0 mm, die slit interval 800 μm) to produce a raw film having a melting point of 280 ° C. and a film thickness of 100 μm. The obtained raw film had different dielectric constants due to Lot. Table 7 shows the dielectric constant of the original film in the MD direction and the TD direction.

(2) Heat treatment A 50 μm thick aluminum foil is used as a support, a heat-resistant rubber roll (hardness of 90 degrees) and a heated metal roll are attached to a continuous hot roll press machine, and the thermoplastic liquid crystal polymer film original fabric is mounted on the heat-resistant rubber roll surface. However, it is supplied between the rolls so that the aluminum foil is in contact with the heated metal roll surface, and is pressure-bonded at a pressure of 10 kg / cm ² in a heated state at 260 ° C. to produce a laminate having a structure of thermoplastic liquid crystal polymer film / aluminum. did. Subsequently, in the furnace, the laminated plate was heated at a rate of 3 m / min in a hot air circulation type heat treatment furnace having a furnace length of 1.5 m in which the left side, the center, and the right side were precisely controlled to the predetermined temperatures shown in Table 7, respectively. It processed and the laminated board after heat processing was obtained. In the obtained laminated plate, the film was peeled off at an angle of 180 ° with respect to the support, and a thermoplastic liquid crystal polymer film with controlled dielectric constant and thermal expansion coefficient (TD direction width: 530 mm, MD direction length: 100 m, thickness: 100 μm, tensile breaking strength: 30 kg / mm ² , tensile breaking elongation: 45%). Table 7 shows other physical properties of the obtained film.

(3) Production of Strip Line Using the thermoplastic liquid crystal polymer film obtained in (2) and a central conductor having a thickness of 18 μm, a strip line having a length of 50 mm and a width of 200 μm was produced by the method described below. The wiring width was designed so that the characteristic impedance (Z0) was 50 ± 2Ω from the thickness and dielectric constant of the insulating layer.

  Specifically, first, as shown in FIG. 1 (a), the two thermoplastic liquid crystal polymer films 11, 11 are aligned so that the TD direction of each film is the longitudinal direction of the strip line. The center conductor (conductor as a signal line) 13 is sandwiched between the thermoplastic liquid crystal polymer films 11 and 11 in such a manner that the longitudinal direction of the center conductor 13 coincides with the longitudinal direction of the strip line. The planar ground conductors 14 and 14 as ground planes were disposed outside the liquid crystal polymer films 11 and 11 to produce an assembly.

  Next, this assembly was placed between the metal plates 15 and 15 of the hot press apparatus and thermocompression bonded under the conditions of the surface temperature of the metal plate of 300 ° C. and the surface pressure of 4 MPa, and the strip line shown in FIG. The strip line has a linear insulator 12 having a substantially rectangular axial cross section, a strip-shaped central conductor 13 as a signal line disposed inside the insulator 12, and the insulator 12 interposed therebetween. The planar ground conductors 14 and 14 are arranged on both sides. Table 7 shows the physical properties of the obtained strip line.

  As shown in Table 7, variations in dielectric constant cannot be controlled in Comparative Example 1 and Comparative Example 2 in which heat treatment was not performed on the raw film in post-processing. On the other hand, in Examples 1 to 4, variation in the dielectric constant in the plane direction is suppressed to an extremely low level by performing heat treatment. Further, in Examples 1 to 3, since the heat treatment is performed at different temperatures, the thermal expansion coefficient of each film can be changed, and the thermoplastic liquid crystal polymer film having a wide range of thermal expansion coefficients. Can be obtained.

  The thermoplastic liquid crystal polymer film of the present invention can be used as a circuit board material, and can be usefully used as a high-frequency circuit board material by taking advantage of the uniformity of the dielectric constant.

  As described above, the preferred embodiments of the present invention have been described. However, various additions, modifications, or deletions are possible without departing from the spirit of the present invention, and such modifications are also included in the scope of the present invention. It is.

DESCRIPTION OF SYMBOLS 11 ... Thermoplastic liquid crystal polymer film 12 ... Insulator 13 ... Center conductor 14 ... Planar ground conductor 15 ... Metal plate

Claims (5)

A film comprising a thermoplastic polymer capable of forming an optically anisotropic melt phase (hereinafter referred to as a thermoplastic liquid crystal polymer film),
The thermal expansion coefficient is 0 to 25 ppm / ° C.
A thermoplastic liquid crystal polymer film having an in-plane dielectric constant coefficient of variation C (%) satisfying the following formula (1).
C = σ / ε _ave × 100 <0.40 (1)
(Here, C: coefficient of variation, σ: standard deviation, ε _ave : average value)   The thermoplastic liquid crystal polymer film according to claim 1, wherein an average value of dielectric constant is 3.30 or less.   The thermoplastic liquid crystal polymer film according to claim 1 or 2, wherein the dielectric loss tangent at 15 GHz is 0.005 or less.   The thermoplastic liquid crystal polymer film according to claim 1, which is used as a millimeter wave antenna film. A transmission line comprising at least one conductor and at least one insulator,
The said insulator is formed from the thermoplastic liquid crystal polymer film as described in any one of Claims 1-4, and the difference of the transmission loss Y (dB / cm) and the frequency X (GHz) in frequency 15GHz and 40GHz. A transmission line having a ratio (ΔY / ΔX) of −0.020 to −0.010.

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