JP2006035680A - Polybenzazole film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polybenzazole film having high strength and high elastic modulus well-balanced in its longitudinal and lateral directions and having surface smoothness, and its manufacturing method. <P>SOLUTION: In the manufacturing method of the polybenzazole film including a process for laminating a skin layer, which is formed from an optically isotropic solution containing fine particles, on the surface of a core layer formed from an optically anisotropic polybenzazole solution, the polybenzazole film satisfies the following formulae (1): tensile elastic moduli in longitudinal and lateral directions ≥10.0 GPa, (2): tensile strengths in longitudinal and lateral directions ≥350 MPa, (3): tensile elongation at break in longitudinal and lateral directions ≥10%, (4): 0.85≤ (tensile elastic modulus in lateral direction)/(tensile elastic modulus in longitudinal direction) ≤1.20, (5):0.85≤ (tensile strength at break in lateral direction)/(tensile strength at break in longitudinal direction) ≤1.20 and (6): 0.85≤ (tensile elongation at break in lateral direction)/(tensile elongation at break in longitudinal direction) ≤1.20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polybenzazole film having a high strength and a high elastic modulus, having a surface smoothness and having a balance between mechanical properties in the longitudinal direction and the width direction, and a method for producing the same. In particular, the present invention relates to a polybenzazole-based film suitable for a magnetic recording base film and an electronic material application.

As a base film for magnetic tape, a biaxially oriented polyethylene terephthalate film is widely used in general. However, there is a limit in mechanical strength for the demand to increase the recording time and the recording capacity by thinning the base film. Therefore, development of films such as higher-strength wholly aromatic polyamides and wholly aromatic polyesters is underway. In particular, it is disclosed that polybenzazole is a rod-like polymer and its oriented film has extremely high mechanical strength (see Patent Document 1). However, when used as a magnetic tape base, the film surface must be smooth and defect-free.
The above method pays attention to the characteristic that the shear viscosity during processing is relatively low in a high concentration region where the solution of the rigid polymer exhibits optical anisotropy, that is, liquid crystallinity, and further, high orientation in the liquid crystal state. The mechanical properties of the film are improved, but when the film is formed with a solution exhibiting optical anisotropy, the mechanical properties of the film in the longitudinal direction (MD, film flow direction, machine direction) are remarkably improved. However, it is difficult to balance the mechanical properties of the longitudinal direction and the width direction (TD, direction perpendicular to MD, transverse direction). As a method for solving the problem related to the balance of mechanical properties, a film forming method is disclosed in which the process up to die extrusion is performed in an optically anisotropic phase, and after die extrusion, the phase is changed to the optically isotropic phase by composition change or temperature change. (See Patent Document 2). On the other hand, a high elasticity modulus and an appropriate elongation obtained by casting a polybenzazole solution having optical anisotropy on a support and then changing it to an optically isotropic state. A polybenzazole-based film is disclosed (see Patent Document 3).
US Pat. No. 4,973,442 JP-A-9-118758 Japanese Unexamined Patent Publication No. 2000-273214

However, in any of the above methods, it is a film formed from a liquid crystalline anisotropic solution, and because of the high orientation of the liquid crystal phase, the balance between mechanical properties in the longitudinal direction and the width direction is sufficiently solved. That's not true. Furthermore, when the liquid crystalline anisotropic solution is extruded by a T-die or the like, surface roughness is observed in the extruded sheet, but these problems have not been solved yet.
From the above points, it has been difficult to use the conventionally disclosed polybenzazole film as a practical magnetic tape. Although the improvement with respect to this is also tried, the present condition is that the film with favorable surface smoothness is not obtained (refer patent document 4, 5).
JP-T 6-503521 Japanese Patent Laid-Open No. 11-171993

  The present invention is intended to solve the above-described points, and has a high strength, a high elastic modulus, a surface smoothness, and a polybenzazole system having a balance between mechanical properties in the longitudinal direction and the width direction. It is an object to provide a film and a method for producing the film.

That is, the present invention comprises a core layer formed from an optically anisotropic polybenzazole solution and a skin layer formed from an optically isotropic polybenzazole solution on both surfaces of the core layer. The polybenzazole film is characterized by satisfying the following formulas (1) to (6).
(1) Tensile elastic modulus in the longitudinal direction and the width direction ≧ 10.0 GPa,
(2) Tensile breaking strength in the longitudinal direction and the width direction ≧ 350 MPa,
(3) Tensile breaking elongation in the longitudinal direction and the width direction ≧ 10%,
(4) 0.85 ≦ (tensile modulus in the width direction) / (tensile modulus in the longitudinal direction) ≦ 1.20,
(5) 0.85 ≦ (tensile breaking strength in the width direction) / (tensile breaking strength in the longitudinal direction) ≦ 1.20,
(6) 0.85 ≦ (tensile elongation at break in the width direction) / (tensile elongation at break in the longitudinal direction) ≦ 1.20.
The core layer formed from an optically anisotropic polybenzazole solution is 25 to 75% of the total thickness of the film, and the polybenzazole film is a polybenzazole film. The polybenzazole-based film is paraphenylene benzobisoxazole.
The present invention also includes a step of laminating a skin layer formed from an optically isotropic polybenzazole-based solution on both surfaces of a core layer formed from an optically anisotropic polybenzazole-based solution. In the method for producing the polybenzazole-based film, a more preferable aspect is that the polymer concentration of the optically anisotropic polybenzazole-based polymer solution is 8.0 to 16.0% by mass, In this method, the concentration of the optically isotropic polybenzazole polymer solution is 0.5 to 5% by mass.

  The polybenzazole-based film of the present invention can correct and improve the defects of the film produced only from the anisotropic polymer solution by adopting the configuration as described in the claims, and the film The balance of physical properties such as the strength and elongation in the longitudinal direction (MD) and the width direction (TD) is good, the slipperiness is good, the handling property of the film and the running property such as a magnetic tape are good. Also, since the surface is smooth and does not have coarse protrusions, the magnetic recording characteristics are good. Furthermore, since it has a very high tensile modulus, it can be used as a thin film substrate film. In particular, it is useful as a thin film substrate film for magnetic recording.

  The polybenzazole-based polymer in the present invention is a polybenzoxazole (PBO) homopolymer, a polybenzothiazole (PBT) homopolymer and a polybenzimidazole (PBI) homopolymer, or PBO, PBT and / or PBI. Random copolymer, alternating copolymer or block copolymer. Here, polybenzoxazole, polybenzothiazole and their random, alternating or block copolymer may be exemplified by US Pat. No. 4,703,103, US Pat. No. 4,533,692, US Pat. No. 4,533,724, US Pat. No. 4, U.S. Pat. No. 4,578,432, and the like.

  The structural unit contained in the polybenzazole polymer is preferably selected from lyotropic liquid crystal polymers. The structural unit is composed of structural units described in structural formulas (a) to (n), and more preferably is a structural unit selected from structural formulas (a) to (f). Particularly preferred is a PBO polymer comprising monomer units selected from structural formulas (a) to (b).

  In the present invention, the above-described polybenzazole-based polymer preferably contains 80% by mass or more, and less than 20% by mass may contain other polymers such as aromatic polyimide. In order to obtain a polybenzazole film having more excellent mechanical properties, the content of the polybenzazole polymer is desirably 90% by mass or more.

  In the present invention, as described in claim 4, it is a preferred embodiment that the polybenzazole-based polymer is polyparaphenylene benzobisoxazole. By using the polymer, better heat resistance and mechanical properties can be obtained.

As a preferred embodiment of the present invention, there is a polybenzazole film characterized in that the polybenzazole film satisfies all of the formulas (1) to (6).
(1) Tensile elastic modulus in the longitudinal direction and the width direction ≧ 10.0 GPa,
(2) Tensile breaking strength in the longitudinal direction and the width direction ≧ 350 MPa,
(3) Tensile breaking elongation in the longitudinal direction and the width direction ≧ 10%,
(4) 0.85 ≦ (tensile modulus in the width direction) / (tensile modulus in the longitudinal direction) ≦ 1.20,
(5) 0.85 ≦ (tensile breaking strength in the width direction) / (tensile breaking strength in the longitudinal direction) ≦ 1.20,
(6) 0.85 ≦ (tensile elongation at break in the width direction) / (tensile elongation at break in the longitudinal direction) ≦ 1.20.

  If the tensile modulus is less than 10.0 GPa, the post-processing speed cannot be increased, or film deformation occurs due to high tension and tension during high-speed winding at the time of use. It becomes difficult. The tensile modulus of the polyobenzazole film of the present invention is more preferably 12.0 GPa or more. Further, if the tensile strength at break is less than 350 MPa, it is not preferable that the film is broken when post-processing is performed at a high speed and high tension. The tensile elongation at break is preferably 10% or more. If the tensile elongation at break is less than this, not only is handling difficult during processing, but the film becomes brittle during use, which is not preferred.

  Furthermore, in the polybenzazole film of the present invention, the relationship between the tensile modulus in the longitudinal direction, the tensile breaking strength and the tensile breaking elongation and the tensile modulus in the width direction, the tensile breaking strength and the tensile breaking elongation is the above (4). It is necessary to satisfy the formula (6) at the same time. By satisfying the above equations (4) to (6) at the same time, the mechanical properties of the film in the longitudinal direction and the width direction can be balanced, so that the film can be obtained by a conventionally known production method that is easy to tear in a specific direction. Can be improved and can be suitably developed for various uses.

  Although the thickness of the polybenzazole film used in the present invention is not particularly limited, for example, when used as a high-density magnetic tape, 0.5 to 10 μm is preferable. When the film is thick, it is often unnecessary to use the high-strength film of the present invention. In general, a thickness of 0.5 μm or more is suitable because it is necessary to withstand the tension during the processing step and tape running.

  In the present invention, in order to exhibit the above-described properties, as described in the claims, the optically isotropic polycrystal is formed on both surfaces of the core layer formed from the optically anisotropic polybenzazole-based solution. It is necessary to laminate and form a skin layer formed from a benzazole-based solution. By forming the film by this method, the polymer molecular chain is oriented in the flow direction generated when the film is formed using only the optically anisotropic polybenzazole polymer solution, and is expressed by the orientation of this molecular chain. The disadvantage of the prior art that the balance between the mechanical properties of the film in the longitudinal direction and the width direction of the film is lost and the roughness of the film surface that occurs during die extrusion are remarkably improved.

  Whether or not the polybenzazole-based solution is optically isotropic is confirmed by observing a preparation prepared by thinly extending the solution on a slide glass and sandwiching the solution with a cover glass under a crossed Nicol. In other words, if the liquid crystal state is optically anisotropic, when the sample stage is rotated, a domain structure derived from the liquid crystal structure is observed and a bright field is obtained. For example, even if the sample stage is rotated, the dark field remains, and the difference between the two can be distinguished.

  In the present invention, the polybenzazole film is formed from the above optically isotropic solution and the optically anisotropic solution. An optically anisotropic solution and an optically isotropic solution may be laminated by coextrusion to form a thin film. The skin layer may be formed by thinning and then applying an optically isotropic solution to both surfaces of the core layer. A laminated polybenzazole-based film can be obtained by coagulating, washing, drying and the like for the obtained thin film laminate. In the process of forming into a thin film, it can be formed by a known method such as a T-die method or a circular die method. However, in terms of control of mechanical properties, stretching treatment in the longitudinal direction and / or the width direction is performed before solidification. May be applied.

  The following method can be illustrated when performing a extending | stretching process. That is, a co-extrusion method is used to form a laminate comprising a polybenzazole solution exhibiting optical anisotropy in the core layer and a polybenzazole solution exhibiting optical isotropy in both skin layers, followed by a counter roll, rolling A composite laminate structure of a support and a laminated polybenzazole film precursor is formed by sandwiching the laminate between at least two supports via an apparatus or a press apparatus. The obtained sandwich composite laminate is guided to a coagulation bath, and the support is peeled off and coagulated in the coagulation bath. The configuration and arrangement of the facing roll, the rolling device, the pressing device, and the like can be variously combined. Desirably, a polybenzazole film precursor sandwiched between at least two supports is sandwiched between at least a pair of opposing rolls, and the opposite rolls are rotated in the opposite direction to provide a support / polybenzazole film precursor / This is a system for forming a sandwich-like composite laminate of the support.

  The obtained support / polybenzazole film precursor / support sandwich composite laminate is stretched by a longitudinal stretching machine and / or a transverse stretching machine such as a tenter. Thereafter, the polybenzazole-based solution is solidified by being guided to a coagulation bath and peeling the support in the coagulation bath. As the support, a plastic film such as a polyester film typified by a PET film or a polyolefin film such as a polypropylene (also referred to as PP) film can be used. Further, a porous film, fabric or nonwoven fabric having moisture permeability as a support may be used as it is or in combination with the plastic film support. When the plastic film is used as a support, the solidification time after the support is peeled off. When the porous film is used as a support alone, the time until the support is peeled off after the sandwich composite laminate is immersed in the coagulation bath and This is important because it affects the film structure and physical properties of the coagulated wet film that provides the time for immersion in the coagulation bath after peeling off the support.

  In the polybenzazole film of the present invention, it is important that the thickness of the core layer formed from the optically anisotropic polybenzazole-based solution is 25 to 75% of the total film thickness (the thickness of the entire laminate). . When the thickness of the core layer is less than 25% with respect to the total thickness of the laminate, the mechanical properties in the longitudinal direction and the width direction are excellent, but the mechanical strength is reduced. On the other hand, when the thickness of the core layer is greater than 75% of the total thickness of the laminate, the mechanical properties in the longitudinal direction are improved, but the balance between the mechanical properties in the longitudinal direction and the width direction is lost. Problem arises.

  In the present invention, in order to obtain the above optically anisotropic solution, the polymer concentration is desirably 8.0 to 16.0% by mass. When the content is less than 8% by mass, optical anisotropy is hardly exhibited, and when the content exceeds 16% by mass, the viscosity of the solution increases and molding processing becomes difficult. In order to obtain an optically isotropic solution, the concentration of the polybenzazole-based polymer is preferably 0.5 to 5% by mass. More preferably, it is 3 mass% or less. On the other hand, when the concentration is less than 0.5% by mass, the viscosity of the polymer solution becomes small, and the applicable film forming methods are limited. In addition, the resulting polybenzazole-based film has a tensile elastic modulus, tensile breaking strength, and tensile breaking elongation. It is not preferable because mechanical properties such as the above become small. Since it becomes economically disadvantageous, 0.5 mass% or more is preferable. If the solution concentration exceeds 5% by mass, the optical anisotropy of the solution tends to be developed, and the solution viscosity increases and the moldability becomes difficult.

  In order to adjust the concentration of the polybenzazole polymer solution to the range shown above, the following method can be used. That is, a method in which a polymer solid is once separated from a polymerized polybenzazole-based polymer solution, and the concentration is adjusted by adding a solvent again and dissolving. Furthermore, the method of adjusting the concentration by adding a solvent to the polymer solution and diluting the polymer solution without separating the polymer solid from the polymer solution that has been subjected to condensation polymerization in polyphosphoric acid. Furthermore, there is a method of directly obtaining a polymer solution in the above concentration range by adjusting the polymerization composition of the polymer.

  Preferable solvents used for adjusting the concentration of the polymer solution include methanesulfonic acid, dimethylsulfuric acid, polyphosphoric acid, sulfuric acid, trifluoroacetic acid and the like, or a mixed solvent combining these solvents can also be used. Of these, methanesulfonic acid and polyphosphoric acid are particularly preferable.

  The degree of polymerization of the polymer in the polybenzazole-based polymer solution used for obtaining the polybenzazole-based film of the present invention is represented by an intrinsic viscosity. The intrinsic viscosity is preferably 15 dl / g or more and 35 dl / g or less, and more preferably 20 dl / g or more and 30 dl / g or less. If it is less than this range, the mechanical properties of the resulting polybenzazole-based film will decrease, and if it exceeds this range, the viscosity of the solution will be high and processing will be difficult.

  The coagulating liquid is not limited as long as it is compatible with the solvent forming the above solution and is a poor solvent for the polymer. For example, water, aqueous metal salt solution, polyhydric alcohol, Examples include protic polar solvents and protic polar solvents.

  Since the coagulated film contains an acid that is a solvent of the polymer solution, it is necessary to wash and remove the acid. Water is usually used as the cleaning liquid, but it may be washed with warm water as necessary, or may be washed with water after neutralizing and washing with an aqueous alkali solution. Cleaning includes, for example, a method of running the film in the cleaning liquid or spraying the cleaning liquid.

  In the present invention, the drying step is desirably performed under tension and by restricting shrinkage of the film under constant tension. When the film is dried by free shrinkage, partial shrinkage occurs, resulting in uneven thickness, and further, the flatness of the film may be impaired. In order to dry the film while restricting the shrinkage, for example, a tenter dryer or a metal frame can be used for drying. Other conditions related to drying are not particularly limited, and examples include a drying method using a heated gas such as air or nitrogen or a room temperature gas, a drying method using a heater or an infrared lamp, and the like.

  The film forming step, the coagulation step, the washing step, the drying step, and the like may be performed continuously or in a batch manner. Furthermore, you may add another special process between each process.

  The polybenzazole-based film used in the present invention may be applied with an anchor agent or subjected to chemical etching treatment, corona treatment, plasma treatment, etc. in order to increase the adhesive strength with a magnetic recording layer or a metal vapor deposition layer. Good.

The film of the present invention may contain known additives such as ultraviolet absorbers, heat stabilizers, stretching aids, lubricants and the like.
In the present invention, the same polybenzazole polymer may be used for the core layer and the skin layer, or different polybenzazole polymers may be used. In the polybenzazole-based polymer, the core layer is formed from an anisotropic solution of one kind of polybenzazole-based polymer selected from polyoxazole-based polymer, polythiazole-based polymer, and polyimidazole-based polymer. A skin layer is laminated from an isotropic solution of a kind of polybenzazole polymer selected from polyoxazole polymer, polythiazole polymer, and polyimidazole polymer to form the polybenzazole film of the present invention. I can do it.

Hereinafter, the contents and effects of the present invention will be described with reference to examples, but the present invention is not limited to the following examples. In addition, the measurement / evaluation method in an Example is as follows.
1. Intrinsic viscosity The viscosity of a polymer solution adjusted to a concentration of 0.5 g / l using methanesulfonic acid as a solvent was measured in an oven at 30 ° C. using an Ostwald viscometer and calculated.

2. Evaluation of optical isotropy of polymer solution The solution was placed on a slide glass, sandwiched between cover glasses and stretched thinly, and observed under crossed Nicols using a polarizing microscope. Even when the sample stage was rotated, it was a dark field, and when the domain structure was not observed, it was judged as an optically isotropic solution. When a domain structure changing from a dark field to a bright field was observed by rotating the sample stage, the solution was judged to be an optically anisotropic solution.

3. Tensile modulus, tensile strength at break, and tensile elongation at break The dried film was cut into strips of length 100 mm and width 10 mm in the longitudinal direction (MD direction) and width direction (TD direction), respectively, and used as a test piece. Using a machine (Shimadzu Corporation Autograph (R), model name AG-5000A), measured at a tensile speed of 50 mm / min and a distance between chucks of 40 mm, the tensile modulus, tensile breaking strength and tensile breaking elongation were measured. Asked.

4). 3D surface roughness of film Using a stylus type 3D surface roughness meter (SE-3AK, manufactured by Kosaka Laboratories), the film surface was measured under the conditions of a needle radius of 2 μm and a load of 30 mgf. A cut-off value of 0.25 mm in the direction was measured over a measurement length of 1 mm, divided into 500 points at a pitch of 2 μm, and the height of each point was taken into a three-dimensional roughness analyzer (SPA-11). The same operation was performed 150 times continuously at intervals of 2 μm in the width direction of the film, that is, over 0.3 mm in the width direction of the film, and the data was taken into the analyzer. Then, the analyzer was made to calculate the three-dimensional average surface roughness SRa.

(Preparation of polybenzazole solution)
(1) Preparation of polymer solution (solution A) After adding 14.49 kg of diphosphorus pentoxide to 43.86 kg of polyphosphoric acid 116 mass% per batch under a nitrogen stream, 4,6-diaminoresorcinol dihydrochloride per batch 9.10 kg and 7.10 kg of terephthalic acid pulverized to an average particle size of 2 μm were stirred and mixed at 80 ° C. in a tank reactor. The mixture was further heated and mixed at 150 ° C. for 10 hours and then polymerized using a biaxial extruder heated to 200 ° C. to obtain a 14% by mass solution of polyparaphenylenebenzoxazole (PBO) through a nominal aperture 50 μm filter. The color of the polymer solution was yellow, and the intrinsic viscosity measured with a methanesulfonic acid solution was 27 dl / g.
(2) Production of polymer solution (solution B) Polyphosphoric acid was added to the solution (A) and diluted to prepare a polymer solution for film formation having a PBO concentration of 1.0% by mass. This film-forming polymer solution was optically isotropic.

Example 1
Using a multi-manifold type two-layer three-layer laminated T-die extruder, create a laminated PBO film precursor with solution A as the core layer and solution B as the skin layer, and pulling it at a rate of 0.30 m / min. And introduced into a 20 ° C. coagulation water bath. The residence time in the coagulation water tank was about 2 minutes, and the solidified laminated PBO film was wound up at 0.31 m / min. The coagulated film was sufficiently washed with water, and then heat fixed at 150 ° C. for 30 seconds while holding both ends with a tenter to obtain a PBO film having a thickness of 5.0 μm. At this time, the discharge amounts of various solutions and the lip gap were adjusted so that the total thickness of the completed film was about 5.0 μm for the core layer and 2.5 μm for the core layer. The solution temperature at the time of extrusion was set to 170 ° C.

(Example 2)
A PBO film having a thickness of 4.9 μm was obtained in the same manner as in Example 1 except that the thickness of the core layer was 1.3 μm.

(Comparative Example 1)
A PBO film having a thickness of 5.0 μm was obtained in the same manner as in Example 1 except that only the solution (A) was used. At this time, remarkable surface roughness was observed on the surface of the PBO film precursor extruded from the T-die.
For this reason, the three-dimensional surface roughness is not measured.

(Comparative Example 2)
A 5.1 μm thick PBO film was prepared in the same manner as in Example 1 except that the thickness of the core layer was 4.5 μm. In addition, although the surface roughness of the film was improved as compared with Comparative Example 1, it was determined that the three-dimensional surface roughness was not at a level for evaluation, and SRa was not measured.

(Comparative Example 3)
A laminated PBO film having a thickness of 5.1 μm was prepared in the same manner as in Example 1 except that the thickness of the core layer was 1.0 μm.
Table 1 shows the results of evaluating the films obtained in each of the above Examples and Comparative Examples.

  The polybenzazole-based film of the present invention adopts the configuration as described in the claims, so that the slipperiness is good, so that the film is easy to handle and has a running property such as a magnetic tape, It is useful as a thin film base film for magnetic recording or as an electronic material. Further, since it has a very high tensile modulus and can be used as a thin film, it is particularly useful as a base film for a high-capacity magnetic recording medium.

Claims (6)

  A polybenzazole comprising a core layer formed from an optically anisotropic polybenzazole-based solution and a skin layer formed from an optically isotropic polybenzazole-based solution on both surfaces of the core layer Film. The polybenzazole film according to claim 1, which satisfies the following formulas (1) to (6).
(1) Tensile elastic modulus in the longitudinal direction and the width direction ≧ 10.0 GPa,
(2) Tensile breaking strength in the longitudinal direction and the width direction ≧ 350 MPa,
(3) Tensile breaking elongation in the longitudinal direction and the width direction ≧ 10%,
(4) 0.85 ≦ (tensile modulus in the width direction) / (tensile modulus in the longitudinal direction) ≦ 1.20,
(5) 0.85 ≦ (tensile breaking strength in the width direction) / (tensile breaking strength in the longitudinal direction) ≦ 1.20,
(6) 0.85 ≦ (tensile elongation at break in the width direction) / (tensile elongation at break in the longitudinal direction) ≦ 1.20.   The polybenzazole film according to any one of claims 1 and 2, wherein the thickness of the core layer formed from the optically anisotropic polybenzazole solution is 25 to 75% of the total film thickness.   The polybenzazole film according to claim 1, wherein the polybenzazole is polyparaphenylene benzobisoxazole.   It includes a step of laminating a skin layer formed from an optically isotropic polybenzazole-based solution on both surfaces of a core layer formed from an optically anisotropic polybenzazole-based solution. Production method of polybenzazole film.   The optically anisotropic polybenzazole polymer solution has a polymer concentration of 8.0 to 16.0% by mass, and the optically isotropic polybenzazole polymer solution has a concentration of 0.5 to 5% by mass. The method for producing a polybenzazole film according to claim 5.