JP3937235B2 - Polyimide benzoxazole film - Google Patents

Description

  The present invention relates to a polyimide benzoxazole film, in particular, a polyimide benzoxazole film that is suitable as a base material for high frequency electronic components and has excellent heat resistance.

  Conventionally, ceramic has been used as a base material for electronic components such as information communication equipment (broadcast equipment, mobile radio equipment, portable communication equipment, etc.), radar, high-speed information processing devices, and the like. A base material made of ceramic has heat resistance, and can cope with a recent increase in the frequency band of information communication equipment (reaching the GHz band). However, ceramics are not flexible and cannot be thinned, so the fields that can be used are limited.

  For this reason, studies have been made to use a film made of an organic material as a base material for an electronic component, and a film made of polyimide and a film made of polytetrafluoroethylene have been proposed. A film made of polyimide is excellent in heat resistance and has the advantage that the film can be thin because it is tough, but there are concerns about problems such as a decrease in signal strength and a delay in signal transmission in application to high-frequency signals. . A film made of polytetrafluoroethylene can handle high frequencies, but it has a low elastic modulus, so the film cannot be made thin, the adhesion to metal conductors and resistors on the surface is poor, and the linear expansion coefficient is low. The problem is that it is not suitable for the production of a circuit having a fine wiring due to a large dimensional change due to a temperature change, and the usable fields are limited. As described above, a film for a substrate having both heat resistance, high frequency compatibility and flexibility has not been obtained.

Moreover, the polyimide benzoxazole film which consists of a polyimide which has a benzoxazole ring in the principal chain is proposed as a polyimide film which raised the elasticity modulus (refer patent document 1). A printed wiring board using the polyimide benzoxazole film as a dielectric layer has also been proposed (see Patent Document 2 and Patent Document 3).
JP-A-6-56992 Japanese National Patent Publication No. 11-504369 Japanese National Patent Publication No. 11-505184

  However, the use of a base material made of a polyimide benzoxazole film, which has been reported in the past, is inferior to the use of a base material made of a ceramic in dealing with ultra-high frequencies reaching the millimeter wave region. Specifically, since the transmission efficiency of the high-frequency signal is low and the response speed is slow (the rise of the pulse signal is poor), it is difficult to increase the operation speed of the circuit using the polyimide benzoxazole film. An object of the present invention is to provide a film made of an organic material that achieves higher levels of heat resistance, high frequency response, and flexibility.

As a result of intensive studies, the present inventors have made it possible to lower the dielectric loss tangent of a polyimide benzoxazole film by forming a polyimide benzoxazole film so that a specific density is exhibited. The present invention was completed by finding that the benzoxazole film has both heat resistance, high frequency compatibility and flexibility.
That is, this invention consists of the following structures.
1. Amino a film composed mainly of (aminophenyl) benzoxazole and polyimide benzoxazole obtained by reacting pyromellitic acid dianhydride, an amino (aminophenyl) benzoxazole and pyromellitic dianhydride A polyamic acid solution obtained by reacting is obtained, and then the polyamic acid solution is coated on a support and dried to obtain a green film, and then the green film is heated at 0.5 to 3 ° C./second. A polyimide benzoxazole film having a film density of 1.47 to 1.55 g / cm ³ obtained by heating and annealing at 120 to 150 ° C. for 1 to 10 minutes and then subjecting to heat treatment .
2. 2. The polyimide benzoxazole film according to 1 above, wherein the film has a plane orientation coefficient of 0.79 to 0.89 as measured by an X-ray diffraction method.
3. The film as measured by the cavity resonance perturbation method has a relative permittivity of 1 GHz of 2.7 to 3.1 and a relative permittivity of 100 GHz of 2.6 to 3.0. Polyimide benzoxazole film.
4). The film measured in the frequency range of 1 to 100 GHz by the cavity resonance perturbation method has a relative permittivity of 1 GHz of 2.7 to 3.1, a relative permittivity of 100 GHz of 2.6 to 3.0, and 1 The polyimide benzoxazole film film according to any one of 1 and 2 above, wherein a relative dielectric constant in a frequency range of ˜100 GHz is not less than a smaller value of a relative dielectric constant at the two frequencies and not more than a larger value.

  Since the film of the present invention has lower loss with respect to high frequency and faster response speed than the conventionally known polyimide film (the rise of the pulse signal is good), the polyimide benzoxazole film of the present invention is used. This circuit can be expected to operate at higher speeds. At the same time, since it has higher rigidity, strength, and heat resistance than conventional polyimide films, it is suitable for use in high frequency electronic devices and other electronic devices. It is particularly useful as a base material for flexible electronic circuit boards.

  The polyimide benzoxazole film of the present invention comprises a polyimide benzoxazole obtained by reacting an aromatic diamine having a benzoxazole structure with an aromatic tetracarboxylic acid anhydride, and has a specific higher order structure (described later). ). In the “reaction” described above, first, a diamine and a tetracarboxylic acid anhydride are subjected to a ring-opening polyaddition reaction in a solvent to obtain a polyamic acid solution, and then, from this polyamic acid solution, a green acid is obtained as necessary. This is done by forming a film or the like and then performing dehydration condensation (imidization).

<Aromatic diamines>
Specific examples of the aromatic diamine having a benzoxazole structure used in the present invention include the following, and it is preferable to use an aromatic diamine having a benzoxazole structure of 70 mol% or more in the total diamine.

  Among these, amino (aminophenyl) benzoxazole isomers are preferable from the viewpoint of ease of synthesis. Here, “each isomer” refers to each isomer in which two amino groups of amino (aminophenyl) benzoxazole are determined according to the coordination position (eg, the above “formula 1” to “formula 4”). Each compound described in the above. These diamines may be used alone or in combination of two or more.

  In this invention, if it is less than 30 mol% of all the diamines, you may use together the diamine which does not have the benzoxazole structure illustrated below 1 type, or 2 or more types. Examples of such diamines include 4,4′-bis (3-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, and bis [4- (3-aminophenoxy) phenyl]. Sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 3,3′-diamino Diphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-dia Nodiphenyl sulfide, 3,3′-diaminodiphenyl sulfoxide, 3,4′-diaminodiphenyl sulfoxide, 4,4′-diaminodiphenyl sulfoxide, 3,3′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone, 4 , 4′-diaminodiphenylsulfone, 3,3′-diaminobenzophenone, 3,4′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 4, 4′-diaminodiphenylmethane, bis [4- (4-aminophenoxy) phenyl] methane, 1,1-bis [4- (4-aminophenoxy) phenyl] ethane, 1,2-bis [4- (4-amino) Phenoxy) phenyl] ethane, 1,1-bis [4- 4-aminophenoxy) phenyl] propane, 1,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,1-bis [4- (4-aminophenoxy) phenyl] butane, 1,3-bis [4- (4-aminophenoxy) phenyl] butane, , 4-bis [4- (4-aminophenoxy) phenyl] butane, 2,2-bis [4- (4-aminophenoxy) phenyl] butane, 2,3-bis [4- (4-aminophenoxy) phenyl] Butane, 2- [4- (4-aminophenoxy) phenyl] -2- [4- (4-aminophenoxy) -3-methylphenyl] propane, 2,2-bis [4- (4-amino) Nophenoxy) -3-methylphenyl] propane, 2- [4- (4-aminophenoxy) phenyl] -2- [4- (4-aminophenoxy) -3,5-dimethylphenyl] propane, 2,2- Bis [4- (4-aminophenoxy) -3,5-dimethylphenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexa Fluoropropane, 1,4-bis (3-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4 -Aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenyl) Noxy) phenyl] sulfoxide, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 1, 3-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (3-aminophenoxy) benzoyl] Benzene, 4,4′-bis [(3-aminophenoxy) benzoyl] benzene, 1,1-bis [4- (3-aminophenoxy) phenyl] propane, 1,3-bis [4- (3-aminophenoxy) ) Phenyl] propane, 3,4'-diaminodiphenyl sulfide, 2,2-bis [3- (3-aminophenoxy) phenyl] 1,1,1,3,3,3-hexafluoropropane, bis [4- (3-aminophenoxy) phenyl] methane, 1,1-bis [4- (3-aminophenoxy) phenyl] ethane, 1, 2-bis [4- (3-aminophenoxy) phenyl] ethane, bis [4- (3-aminophenoxy) phenyl] sulfoxide, 4,4′-bis [3- (4-aminophenoxy) benzoyl] diphenyl ether, 4 , 4′-bis [3- (3-aminophenoxy) benzoyl] diphenyl ether, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [ 4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, bis [4- {4- (4-aminophenoxy) phenoxy} pheny ] Sulfone, 1,4-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl Benzene, 1,3-bis [4- (4-amino-6-trifluoromethylphenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-fluorophenoxy) ) -Α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-methylphenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4- Amino-6-cyanophenoxy) -α, α-dimethylbenzyl] benzene, 3,3′-diamino-4,4′-diphenoxybenzophenone, 4,4′-diamino-5,5′-diphenoxy Benzophenone, 3,4'-diamino-4,5'-diphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4 -Phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 4,4'-diamino-5,5'-dibiphenoxybenzophenone, 3, 4,4′-diamino-4,5′-dibiphenoxybenzophenone, 3,3′-diamino-4-biphenoxybenzophenone, 4,4′-diamino-5-biphenoxybenzophenone, 3,4′-diamino-4- Biphenoxybenzophenone, 3,4'-diamino-5'-biphenoxybenzophenone, 1,3-bis (3-amino-4-phenoxybenzoyl) benzene, 1,4-bis (3-amino-4-phenoxybenzoyl) benzene, 1,3-bis (4-amino-5-phenoxybenzoyl) benzene 1,4-bis (4-amino-5-phenoxybenzoyl) benzene, 1,3-bis (3-amino-4-biphenoxybenzoyl) benzene, 1,4-bis (3-amino-4-biphenoxy) Benzoyl) benzene, 1,3-bis (4-amino-5-biphenoxybenzoyl) benzene, 1,4-bis (4-amino-5-biphenoxybenzoyl) benzene, 2,6-bis [4- (4 -Amino-α, α-dimethylbenzyl) phenoxy] benzonitrile and some or all of the hydrogen atoms on the aromatic ring of the aromatic diamine are halogen atoms, carbon Substitution with a C1-C3 halogenated alkyl group or alkoxyl group in which some or all of the hydrogen atoms of the prime alkyl group, alkoxyl group, cyano group, alkyl group or alkoxyl group are substituted with halogen atoms Aromatic diamines made and the like.

<Aromatic tetracarboxylic acid anhydrides>
The tetracarboxylic acid anhydrides used in the present invention are aromatic tetracarboxylic acid anhydrides. Specific examples of the aromatic tetracarboxylic acid anhydrides include the following, and it is preferable to use the aromatic tetracarboxylic acid anhydrides in an amount of 70 mol% or more based on the total tetracarboxylic dianhydrides.

  These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  In the present invention, one or two or more non-aromatic tetracarboxylic dianhydrides exemplified below may be used in combination as long as they are less than 30 mol% of the total tetracarboxylic dianhydrides. Examples of such tetracarboxylic acid anhydrides include butane-1,2,3,4-tetracarboxylic dianhydride, pentane-1,2,4,5-tetracarboxylic dianhydride, and cyclobutanetetracarboxylic acid. Acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, cyclohexane-1,2,4,5-tetracarboxylic dianhydride, cyclohex-1-ene-2,3 5,6-tetracarboxylic dianhydride, 3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohexane-3 -(1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride 1-ethylcyclohexane -(1,2), 3,4-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane- 1- (2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ′, 4′-tetracarboxylic dianhydride, bicyclo [2.2.1] Heptane-2,3,5,6-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane-1 -(2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ', 4'-tetracarboxylic dianhydride, bicyclo [2.2.1] heptane -2,3,5,6-tetracarboxylic dianhydride, Cyclo [2.2.2] octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2,3,5,6-tetracarboxylic acid A dianhydride etc. are mentioned. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  The solvent used when polymerizing diamines and tetracarboxylic acid anhydrides to obtain polyamic acid is not particularly limited as long as it dissolves both the raw material monomer and the polyamic acid to be produced. Organic solvents are preferred, such as N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphos Examples include hollic amide, ethyl cellosolve acetate, diethylene glycol dimethyl ether, sulfolane, and halogenated phenols. These solvents can be used alone or in combination. The amount of the solvent used may be an amount sufficient to dissolve the monomer as a raw material. As a specific amount used, the mass of the monomer in the solution in which the monomer is dissolved is usually 5 to 40% by mass, The amount is preferably 10 to 30% by mass.

  Conventionally known conditions may be applied for the polymerization reaction for obtaining the polyamic acid (hereinafter also simply referred to as “polymerization reaction”). As a specific example, in a temperature range of 0 to 80 ° C., 10 Stirring and / or mixing continuously for minutes to 30 hours. If necessary, the polymerization reaction may be divided or the temperature may be increased or decreased. In this case, the order of adding both monomers is not particularly limited, but it is preferable to add aromatic tetracarboxylic acid anhydrides to the solution of aromatic diamines. The mass of the polyamic acid in the polyamic acid solution obtained by the polymerization reaction is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, and the viscosity of the solution is measured with a Brookfield viscometer (25 ° C.). From the viewpoint of the stability of liquid feeding, it is preferably 10 to 2000 Pa · s, and more preferably 100 to 1000 Pa · s.

  Vacuum defoaming during the polymerization reaction is effective for producing a high-quality polyamic acid organic solvent solution. Moreover, you may perform superposition | polymerization by adding a small amount of terminal blockers to aromatic diamines before a polymerization reaction. Examples of the end capping agent include compounds having a carbon-carbon double bond such as maleic anhydride. The amount of maleic anhydride used is preferably 0.001 to 1.0 mol per mol of aromatic diamine.

  In order to form a polyimide film from the polyamic acid solution obtained by the polymerization reaction, a green film is obtained by applying the polyamic acid solution on a support and drying, and then subjecting the green film to a heat treatment. A method of imidization reaction may be mentioned.

  The support on which the polyamic acid solution is applied needs only to have smoothness and rigidity sufficient to form the polyamic acid solution into a film, and a drum or belt whose surface is made of metal, plastic, glass, porcelain, etc. And the like. Among them, the surface of the support is preferably a metal, more preferably stainless steel that does not rust and has excellent corrosion resistance. The surface of the support may be plated with metal such as Cr, Ni, or Sn. The surface of the support can be mirror-finished or processed into a satin finish as required. Application of the polyamic acid solution to the support includes, but is not limited to, casting from a slit base, extrusion through an extruder, squeegee coating, reverse coating, die coating, applicator coating, wire bar coating, etc. Conventionally known solution coating means can be appropriately used.

  There are no particular limitations on the conditions for drying the polyamic acid coated on the support to obtain a green film. The temperature is exemplified by 70 to 150 ° C, preferably 80 to 120 ° C, and the drying time is 5 to 5 ° C. 180 minutes is exemplified, preferably 10 to 120 minutes, more preferably 30 to 90 minutes. A conventionally known drying apparatus that satisfies such conditions can be applied, and examples thereof include hot air, hot nitrogen, far infrared rays, and high frequency induction heating. Subsequently, in order to obtain the target polyimide benzoxazole film from the obtained green film, an imidization reaction is performed. In general, the imidization reaction proceeds by treatment at a higher temperature than the above drying, and a polyimide benzoxazole film can be obtained. In addition to being able to influence the plane orientation coefficient of the film obtained by imidation reaction conditions, the present inventors control the density by annealing the green film peeled off from the support before imidization treatment. New knowledge that it is possible was obtained (described later).

<Flat orientation coefficient>
The film of the present invention has a plane orientation coefficient measured by an X-ray diffraction method of 0.79 to 0.89. When the plane orientation coefficient of the film is less than 0.79, the dielectric loss tangent of the film becomes large and it is not suitable for use at a high frequency.
The plane orientation coefficient is a parameter that expresses the higher order structure of molecules constituting the film. Among the molecules constituting the film, a specific lattice having a crystal lattice that is a structural unit in a crystal part having high order. The degree to which the surface is oriented with respect to the film surface is quantified. The higher this value, the smaller the difference between the orientation of the specific lattice plane and the orientation of the film plane. The “certain specific lattice plane” in the polyimide benzoxazole film of the present invention is a lattice plane that gives a diffraction peak near 2θ = 21.8 °. The specific measurement operation of the plane orientation coefficient of the film is described in the Examples section.

  In general, examples of means for controlling the plane orientation coefficient of the film include means for adjusting a temperature rising profile at the time of forming a green film, and means for stretching at the time of imidization. Can be applied. For example, in order to increase the plane orientation coefficient of a polyimide benzoxazole film, there are means for reducing the amount of heat applied to the green film and for stretching the film in the longitudinal direction, the transverse direction, or both the longitudinal and transverse directions during the imidization reaction. Can be mentioned. On the contrary, in order to reduce the plane orientation coefficient of the polyimide benzoxazole film, a means for increasing the amount of heat applied to the green film can be mentioned. Moreover, the present inventors can control the plane orientation coefficient of the film obtained by the heating conditions at the time of imidizing the polyimide precursor (polyamic acid). A preferable means for controlling the plane orientation coefficient of the film includes heating conditions during imidization.

<Density>
The film of the present invention has a density of 1.47 to 1.55 g / cm ³ measured by a density gradient tube method. If the density of the film is less than 1.47, the dielectric constant of the film becomes large and it is not suitable for use at high frequencies. The specific measurement operation of the film density is described in the Examples section.

  Examples of means for controlling the density of the film include means for increasing the residual solvent amount of the green film and for stretching during imidization. The above means can also be applied to the film of the present invention. For example, in order to increase the density of the polyimide benzoxazole film, means for reducing the amount of heat applied to the green film or stretching the film in the longitudinal direction, the lateral direction, or both the longitudinal and lateral directions during the imidization reaction can be mentioned. . Conversely, in order to reduce the density of the polyimide benzoxazole film, means for increasing the amount of heat applied to the green film can be mentioned. The present inventors have also found a new finding that the density of the resulting film can be controlled by annealing the polyimide precursor (polyamic acid) before imidization treatment. A preferable means for controlling the plane orientation coefficient of the film includes annealing before imidization treatment.

<Heating conditions for imidization reaction>
As described above, a polyimide film is generally obtained by heating a green film obtained by drying a polyamic acid solution to cause an imidization reaction. The following imidization is mentioned from the point that the obtained film becomes easy to exhibit the above-mentioned plane orientation coefficient.

Imidization method: two-stage heat treatment by thermal ring closure method,
First stage heat treatment: treatment at 150 to 250 ° C. for 1 to 10 minutes,
Second stage heat treatment: treatment at 400-600 ° C. for 0.1-15 minutes,
Temperature rising conditions from the end of the first stage heat treatment to the start of the second stage heat treatment: 2 to 7 ° C./second.

  The thermal ring closure method is a method in which polyamic acid is imidized by heating. The polyamic acid solution may contain a ring closing catalyst and a dehydrating agent, and the imidization reaction may be promoted by the action of the ring closing catalyst and the dehydrating agent. In this method, after the polyamic acid solution is applied to the support, the imidization reaction is partially advanced to form a film having self-supporting property, and then imidization can be performed completely by heating.

  The timing for adding the ring-closing catalyst to the polyamic acid solution is not particularly limited, and may be added in advance before the polymerization reaction for obtaining the polyamic acid. Specific examples of the ring-closing catalyst include aliphatic tertiary amines such as trimethylamine and triethylamine, and heterocyclic tertiary amines such as isoquinoline, pyridine, and betapicoline. Among them, heterocyclic tertiary amines are mentioned. At least one amine selected from is preferred. Although the usage-amount of a ring-closing catalyst with respect to 1 mol of polyamic acids does not have limitation in particular, Preferably it is 0.5-8 mol.

The timing of adding the dehydrating agent to the polyamic acid solution is not particularly limited, and may be added in advance before the polymerization reaction for obtaining the polyamic acid. Specific examples of the dehydrating agent include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride. Among them, acetic anhydride, benzoic anhydride, etc. Acids or mixtures thereof are preferred. Moreover, the usage-amount of the dehydrating agent with respect to 1 mol of polyamic acids is not particularly limited, but is preferably 0.1 to 4 mol. When a dehydrating agent is used, a gelation retarder such as acetylacetone may be used in combination.
The polyimide film precursor (green sheet, green film) formed on the support may be peeled off from the support before being completely imidized, or may be peeled off after imidization.

<Annealing conditions before imidation reaction treatment>
Before performing the imidation treatment as described above, a polyimide film having a higher density can be obtained by heating a green film obtained by drying the polyamic acid solution under the annealing conditions described below. The following annealing treatment is mentioned from the point that the obtained film becomes easy to exhibit the above-mentioned density.
Annealing method before imidation: One-stage annealing treatment Annealing treatment: treatment at 120-150 ° C. for 1-10 minutes Temperature rising condition: 0.5-3 ° C./second

<Relative permittivity>
Since the film of the present invention as described above exhibits a small relative dielectric constant with respect to high frequency, it is suitable for high frequency applications. Here, the relative dielectric constant of the film is defined with respect to a signal entering the film surface direction. From the viewpoint of high frequency response, it is preferable that the relative dielectric constant of the film is small. The lower limit of the relative permittivity is preferably as small as possible from the viewpoint of high-frequency characteristics. However, if the relative permittivity of the polyimide benzoxazole film is not more than a predetermined range, other physical properties, particularly mechanical properties, are significantly deteriorated, which is not preferable in practice. . The relative dielectric constant at 100 GHz of the film of the present invention measured by the cavity resonance perturbation method is 2.60 to 3.00. Preferably it is 2.65 to 2.90, and more preferably 2.70 to 2.80. The relative dielectric constant at 1 GHz of the film of the present invention measured by the cavity resonance perturbation method is preferably 2.70 to 3.10. Preferably it is 2.75-3.00, More preferably, it is 2.80-2.90.
The film of the present invention preferably has a smaller dielectric loss tangent at 100 GHz, preferably 0.01 or less, more preferably 0.003 or less, and still more preferably 0.001 or less. Although the lower limit of the dielectric loss tangent is not particularly defined, 0.0001 is exemplified from the viewpoint of film production. In the present invention, the relative dielectric constant and dielectric loss tangent of the film are measured by the cavity resonance vibration method. Specific measurement operations are described in the Examples section.

  The present inventors have newly found that the relative permittivity of the film can be controlled by controlling the density and the plane orientation coefficient of the polyimide benzoxazole film. As another means for controlling the relative dielectric constant of the film, there is a method of adjusting the ratio of the compound remaining in the film as polyamic acid without imidization (hereinafter, also referred to as “ratio of unreacted polyamic acid”). It is done. For example, in order to increase the relative dielectric constant of the polyimide benzoxazole film, means for increasing the proportion of unreacted polyamic acid can be mentioned. On the contrary, in order to reduce the relative dielectric constant of the polyimide benzoxazole film, means for reducing the proportion of unreacted polyamic acid can be mentioned.

The thickness of the polyimide benzoxazole film of the present invention is not particularly limited, but is usually 1 to 150 [mu] m, preferably 3 to 50 [mu] m in consideration of use as a base material for an electronic substrate. This thickness can be easily controlled by the amount of the polyamic acid solution applied to the support and the concentration of the polyamic acid solution.
The polyimide benzoxazole film of the present invention is usually an unstretched film, but may be uniaxially or biaxially stretched. Here, the unstretched film refers to a film obtained without intentionally applying a mechanical external force in the surface expansion direction of the film by tenter stretching, roll stretching, inflation stretching, or the like.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited by a following example. In addition, the evaluation method of the physical property in the following examples is as follows.
1. Reduced viscosity of polyamic acid (ηsp / C)
A solution dissolved in N-methyl-2-pyrrolidone so that the polymer concentration was 0.2 g / dl was measured at 30 ° C. using an Ubbelohde type viscosity tube.

2. The thickness of the polyimide benzoxazole film was measured using a micrometer (Finereuf, Millitron 1245D).

3. Tensile modulus, tensile breaking strength and tensile breaking elongation of polyimide benzoxazole film The polyimide benzoxazole film to be measured was cut into strips of 100 mm × 10 mm in the flow direction (MD direction) and the width direction (TD direction), respectively. A test piece was used. Using a tensile tester (manufactured by Shimadzu Corp., Autograph (R), model name AG-5000A) under the conditions of a tensile speed of 50 mm / min and a distance between chucks of 40 mm, the tensile modulus and tension in each of the MD and TD directions. The breaking strength and tensile breaking elongation were measured.

4). Linear expansion coefficient (CTE) of polyimide benzoxazole film
About the polyimide benzoxazole film to be measured, the stretch rate in the MD direction and the TD direction was measured under the following conditions, and the stretch rate at intervals of 30 ° C. to 45 ° C., 45 ° C. to 60 ° C.,. / The temperature was measured, this measurement was performed up to 300 ° C., and the average value of all measured values was calculated as CTE. The meanings of the MD direction and the TD direction are the same as in the measurement of “3.” above.
Device name: TMA4000S manufactured by MAC Science
Sample length; 20mm
Sample width: 2 mm
Temperature rise start temperature: 25 ° C
Temperature rising end temperature: 400 ° C
Temperature increase rate: 5 ° C / min
Atmosphere: Argon

5). Melting point and glass transition temperature of polyimide benzoxazole film The polyimide benzoxazole film to be measured is subjected to differential scanning calorimetry (DSC) under the following conditions, and the melting point (melting peak temperature Tpm) and glass transition point (Tmg) are set according to JIS K 7121. Sought in accordance with.
Device name: DSC3100S manufactured by MAC Science
Pan ： Aluminum pan (non-airtight)
Sample mass: 4mg
Temperature rising start temperature: 30 ° C
Temperature rising end temperature: 600 ° C
Temperature increase rate: 20 ° C / min
Atmosphere: Argon

6). Thermal Decomposition Temperature of Polyimide Benzoxazole Film Using a sufficiently dried polyimide benzoxazole film to be measured as a sample, thermobalance measurement (TGA) is performed under the following conditions, and the temperature at which the mass of the sample decreases by 5% is defined as the thermal decomposition temperature. I saw it.
Device name: TG-DTA2000S manufactured by MAC Science
Pan ： Aluminum pan (non-airtight)
Sample mass: 10 mg
Temperature rising start temperature: 30 ° C
Temperature increase rate: 20 ° C / min
Atmosphere: Argon

7). Plane orientation coefficient of polyimide benzoxazole film A polyimide benzoxazole film to be measured is mounted on a measurement jig, and X-ray diffraction measurement is performed under the following conditions. I asked for a figure.
Device name: RINT 2100PC manufactured by Rigaku Co., Ltd., multipurpose sample base Voltage, current value; 40 kV, 40 mA
Measurement method; reflection method and transmission method scanning range; reflection method α; 15 to 90 ° / 2.5 ° interval
β: 0 to 360 ° / 5 ° interval
Reflection method α: 0-15 ° / 2.5 ° interval
β: 0-360 ° / 5 ° interval slit; DS 0.1 mm, SS 7 mm, RS 7 mm,
Vertical divergence limit slit 1.2mm
Scanning speed: Continuous (360 ° / min)
Detector: Scintillation counter

FIG. 1 schematically shows this pole figure. In the figure, peak half widths (HMD and HTD) were determined from diffraction intensity profiles at two broken lines, and the average value of HMD and HTD was defined as Ha (unit: °). The peak half-value width was obtained using a Rigaku analysis program. From the thus obtained Ha, the plane orientation coefficient of the polyimide benzoxazole film was calculated by the following formula.
Plane orientation coefficient = (180 °-Ha) ÷ 180 °

8). Volume resistivity of polyimide benzoxazole film Volume resistivity was measured by a method according to JIS C2318.

9. Dielectric breakdown voltage of polyimide benzoxazole film The dielectric breakdown voltage was measured by a method according to JIS C2318.

10. Relative permittivity of polyimide benzoxazole film (preparation of test piece)
The polyimide benzoxazole film was piled up to the required thickness, and a pressure of 300 kgf / cm ² was applied and pressed to prepare a 1.6 mm × 1.5 mm × 75 mm prismatic test piece.
(Measurement of specimen)
Using the N5250A millimeter wave PNA series network analyzer manufactured by Agilent Technologies, the above samples were measured and recorded for the dielectric constant and dielectric loss tangent in the range of 1 GHz to 100 GHz by the cavity resonance perturbation method.

11. Density of polyimide benzoxazole film A polyimide benzoxazole film was cut into a size of 5 mm x 5 mm and subjected to density measurement. This cut sample was put into a density gradient tube prepared with an aqueous calcium nitrate solution, and the density was measured from the standard float position and density calibration curve with a known density and the sample position after 5 hours. The liquid temperature of the density gradient tube is 30 ° C.

(Preparation of polyamic acid solution)
After the inside of a reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod was purged with nitrogen, 500 parts by mass of 5-amino-2- (p-aminophenyl) benzoxazole was added. Next, 5000 parts by mass of N-methyl-2-pyrrolidone was added and completely dissolved, and then 485 parts by mass of pyromellitic dianhydride was added and stirred at 25 ° C. for 50 hours. A polyamic acid solution was obtained. The reduced viscosity (ηsp / C) was 4.6.

(Manufacture of polyamic acid green film)
This polyamic acid solution was coated on a stainless steel belt (squeegee / belt gap was 650 μm) and dried at 90 ° C. for 60 minutes. The polyamic acid film that became self-supporting after drying was peeled from the stainless steel belt to obtain a green film having a thickness of 40 μm.

(Production of polyimide benzoxazole film)
The obtained green film was passed through a continuous heat treatment furnace purged with nitrogen, and heated in two stages under the conditions shown in Table 1 to advance the imidization reaction. Then, the polyimide benzoxazole film of Examples 1-4 and Comparative Examples 1-3 which show brown was obtained by cooling to room temperature in 5 minutes. Table 1 shows the measurement results of the obtained polyimide benzoxazole films.

  Since the film of the present invention has a lower loss with respect to high frequency and faster response speed than a conventionally known polyimide film (the rise of the pulse signal is good), the circuit using the film of the present invention is Expect faster operation. At the same time, since it has higher rigidity, strength, and heat resistance than conventional polyimide films, it is useful as a base material for flexible electronic circuit boards used in high-frequency electronic devices and other electronic devices.

The X-ray diffraction pole figure of a polyimide benzoxazole film is typically represented.

Claims (4)

Amino a film composed mainly of (aminophenyl) benzoxazole and polyimide benzoxazole obtained by reacting pyromellitic acid dianhydride, an amino (aminophenyl) benzoxazole and pyromellitic dianhydride A polyamic acid solution obtained by reacting is obtained, and then the polyamic acid solution is coated on a support and dried to obtain a green film, and then the green film is heated at 0.5 to 3 ° C./second. A polyimide benzoxazole film having a film density of 1.47 to 1.55 g / cm ³ obtained by heating and annealing at 120 to 150 ° C. for 1 to 10 minutes and then subjecting to heat treatment .   The polyimide benzoxazole film according to claim 1, wherein the film has a plane orientation coefficient of 0.79 to 0.89 as measured by an X-ray diffraction method.   The relative dielectric constant of 1 GHz of the film measured by the cavity resonance perturbation method is 2.7 to 3.1, and the relative dielectric constant of 100 GHz is 2.6 to 3.0. The polyimide benzoxazole film film as described.   The film measured in the frequency range of 1 to 100 GHz by the cavity resonance perturbation method has a relative permittivity of 1 GHz of 2.7 to 3.1, a relative permittivity of 100 GHz of 2.6 to 3.0, and 1 The polyimide benzoxazole film film according to any one of claims 1 and 2, wherein a relative dielectric constant within a frequency range of -100 GHz is not less than a smaller value of a relative dielectric constant at the two frequencies and not more than a larger value. .

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