WO2004026947A1 - Polybenzazole film and process for producing the same - Google Patents

Abstract

Production of a heat-resistant polymer film of high peel strength that excels in a balance of lengthwise and crosswise strengths. In particular, a polybenzazole film is produced through a process comprising extruding a rigid polymer solution of 1 to 1.3 times the optically anisotropic lower limit solution concentration C2 through irrotational die, subsequently effecting biaxial drawing of the resultant film-shaped rigid polymer solution, solidifying the same in a coagulation bath, removing the solvent with a washing liquid, and removing the washing liquid.

Description

 Description Polybenzazole film and method for producing the same

 The present invention relates to a high-strength, high-modulus or high-heat-resistant polymer film and a technique for producing the same. Background art

 A rigid polymer solution, a so-called liquid crystalline polymer, has molecular chains oriented in the direction of flow, and once oriented, it takes a long time for the molecular chains to change to random orientation. Molded articles can be manufactured. Furthermore, the rigid polymer has a high glass transition temperature, melting point and thermal decomposition temperature, so that a heat-resistant molded article can be obtained.

Rigid polymers, especially boribenzazol polymers, are soluble only in limited mineral acids such as methanesulfonic acid and polyphosphoric acid. Conventionally, such polymers are generally formed from either a low-concentration solution of mineral acid of 2% or less or a high-concentration solution of mineral acid of 14% or more as described in Examples of Patent Document 1. It was a target. In the case of processing into a fiber / film of polybenzazole alone, it is formed from a high-concentration liquid crystal dope as described in Patent Documents 2 and 3. When making a polybenzazole film from such a high-concentration liquid crystal dope, the molecules are oriented in the discharge direction and the draw-down direction, so that there is a problem that the film is easily torn when pulled in the horizontal direction. Therefore, Patent Document 4 describes a technique for producing a thin film by biaxial stretching by blow molding, and Patent Document 5 further improves the anisotropy of mechanical properties by orienting the film in different directions on the front and back. Attempts have been made to do so. However, even if the problem of rupture in the lateral direction can be improved by these methods, the peel strength in the thickness direction cannot be improved, but rather tends to be deteriorated, and a practical improvement is strongly desired. Ma Also, attempts have been made to obtain a thin transparent film by spin-coating a low-concentration solvent. For example, Non-Patent Document 1 describes the optical characteristics of a polybenzazole thin film formed on a silicon wafer using a methanesulfonic acid solution of 0.5% polyparaphenylenebenzenezobisthiazole polymer. However, forming from a low-concentration solution requires a large amount of mineral acid to make the product, which is not suitable for industrial processes. Alternatively, there has been studied a method of forming a polymer starting from a blend of a rigid high molecule and a flexible polymer such as a polyamide or polyether ketone as a starting material. However, in this method, a high-performance material utilizing the characteristics of the rigid polymer has not been put into practical use.

 [Patent Document 1]

 Japanese Patent Application Laid-Open No. Sho 63-3210

 [Patent Document 2]

 U.S. Pat.No. 5,555,2221

 [Patent Document 3]

 U.S. Patent No. 5,366,702

 [Patent Document 4]

 U.S. Pat.No. 2,898,924

 [Patent Document 5]

 U.S. Pat.No. 4,939,239

 [Non-Patent Document 1]

 L. A. Cmtavey et al., Journal of Applied Polymer Science, Vol. 76, ppl448-1456 (2000) Disclosure of Invention

That is, the present invention is directed to a biaxially stretched film using a solution of 1 to 1.3 times as high as the optically anisotropic lower limit solution concentration C2 of the rigid polymer and having a peel strength of 100 mNZcm or more. A polymer film and a method for producing the same, wherein the solution is a mineral of a boribenzazol polymer. The polymer film described above, which is an acid solution, and a method for producing the same.

 Hereinafter, the present invention will be described in detail.

 The rigid polymer according to the present invention is a polymer in which the entire molecular chain is composed of a rigid unit, a product obtained by copolymerizing a flexible monomer between rigid units, or a product obtained by combining a rigid unit with a crank type. A material in which a spacer is provided on the side chain of the rigid main chain can be used. Examples of preferred rigid polymers include polyparaphenylene terephthalamide, polybenzimid, polyparaphenylene and polybenzazole. Polybenzazole (PBZ) refers to polybenzoxazole (PBO) homopolymer, polybenzotic 7zol (PBT) homopolymer and polybenzimidazole (PBI) homopolymer, or their PBO, PBT , PBI means random, sequential or block copolymer. Here, borenzoxazole, polybenzothiazole and their random, sequential or block copolymers are described, for example, in Wolfe et al., Ijuiquid Crystalline Polymer Compositions, Process and Products J U.S. Pat. No. 4,730,103. (October 27, 1987), "Liquid Crystalline Polymer Compositions, Process and Products J U.S. Pat. No. 4,533,692 (August 6, 1985)", "Liquid Crystalline Poly ( (2,6-j3enzothiazole) Composition, Process and Products J U.S. Pat.No. 4,533,732 (August 6, 1985), Liquid Crystalline Polymer Compositions, Process and Products J U.S. Pat. No. 693 (August 6, 1985), Evers "Thermo oxidatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole PolymresJ U.S. Pat. January 16), Tasi et al. “Method ior making Jtieterocychc Block Copolymer” Katatoku thousand ^! 4 5 7 8 4 3 No. 2 (1 9 8 6 March 2, 5 days), are described in the equal.

The structural unit contained in the polybenzazole polymer is preferably selected from a lyotropic liquid crystal polymer. The monomer unit is a structural formula It consists of the monomer units described in (a) to (n), and more preferably consists essentially of one monomer unit selected from structural formulas (a) to (c).

 [Formula 1]

(h)

【化 2】

[Formula 2]

これらの、 剛直性高分子の溶液は転相濃度 c *を越えると光学異方性 溶液を形成する。光学異方性溶液を形成するための好適な溶媒としては、 クレゾ一ルやそのポリマーを溶解し得る非酸化性の酸が含まれる。 特に 好適な酸溶媒の例としては、 ポリ リン酸、 メタンスルホン酸および高濃 度の硫酸等の鉱酸あるいはそれらの混合物が挙げられる。 光学異方性を 発現す る 転相濃度 C * は、 温度 に依存す る 。 こ の事実は、 Picken(Macromolecules 第 2 2卷、 頁 1766.1771、 1 9 8 9年）にも記 載されている。 本発明では、 溶液の調整から成形までの最高温度での等 方相を含まない異方相を形成する濃度が重要である。 転相濃度 C *では 液晶相と等方相がともに存在する。 このような相では流動性が非常に悪 く、 成形加工ができない。 等方相と液晶相が共存する領域の下限濃度を C 1 , 上限濃度を C 2 と定義する。 本発明は、 溶液の調整から成形まで の最高温度での等方相が現れない下限濃度 C 2から C 2の 1 . 3倍の濃 度の溶液を成形することを特徴とする。 より好ましい濃度範囲は C 2か ら C 2の 1 . 2倍さらに好ましくは C 2から C 2の 1 . 1倍である。 濃度 C 2の決定は、 偏光顕微鏡観察で実施する方法が簡便である。 ほ かに、 流体粘度を測定する方法 （例えば、 H.FISCHER J.A.ODELL A.KELLER M.MURRAYらの J. Materials Science, 第 2 9巻 頁 1025) がある。 偏光顕微鏡観察では、 試料をスライ ドグラスの間でおよそ 5 0 L m以下の厚みに潰して加熱ステージ上で観察する。 溶融温度以上で溶 液調整から加工温度までの温度範囲で光学的異方性による模様が消えな い濃度組成を検討する。 溶媒の種類や、 溶媒の水分率さらにはポリマー 重合度により下限濃度 C 2は変化する。 例えば、 極限粘度数 2 5のポリ パラフエ二レンべンズビスォキサゾールの 1 1 6 %ポリ燐酸溶液の場合 2 0 0 °Cでの液晶形成下限濃度 C 2はおよそ 8重量％である。

When these rigid polymer solutions exceed the phase inversion concentration c *, they form an optically anisotropic solution. Suitable solvents for forming the optically anisotropic solution include non-oxidizing acids that can dissolve cresol and its polymers. Examples of particularly suitable acid solvents include mineral acids such as polyphosphoric acid, methanesulfonic acid and highly concentrated sulfuric acid, or mixtures thereof. The phase inversion concentration C * that develops optical anisotropy depends on the temperature. This fact is also described in Picken (Macromolecules Vol. 22, p. 1766.1771, 1989). In the present invention, the concentration that forms an anisotropic phase that does not include an isotropic phase at the highest temperature from preparation of a solution to molding is important. At the phase inversion concentration C *, both the liquid crystal phase and the isotropic phase exist. Such a phase has very poor fluidity and cannot be processed. The lower limit concentration of the region where the isotropic phase and the liquid crystal phase coexist is defined as C 1, and the upper limit concentration is defined as C 2. The present invention covers from solution preparation to molding The solution is characterized by forming a solution having a lower concentration of C 2 to 1.3 times the concentration of C 2 at which the isotropic phase does not appear at the highest temperature. A more preferred concentration range is from C2 to 1.2 times C2, more preferably from 1.1 to 1.1 times C2 to C2. The method of determining the concentration C2 by observation with a polarizing microscope is simple. In addition, there is a method of measuring fluid viscosity (for example, J. Materials Science of H. FISCHER JAODELL A. KELLER M. MURRAY et al., Vol. 29, p. 1025). In polarization microscope observation, the sample is crushed to a thickness of about 50 Lm or less between slide glasses and observed on a heating stage. Investigate the concentration composition where the pattern due to optical anisotropy does not disappear in the temperature range from the solution adjustment to the processing temperature above the melting temperature. The lower limit concentration C 2 varies depending on the type of the solvent, the water content of the solvent, and the degree of polymerization of the polymer. For example, in the case of a 116% polyphosphoric acid solution of polyparafuzenylenebenzbisoxazole having an intrinsic viscosity of 25, the lower limit concentration C2 of liquid crystal formation at 200 ° C. is about 8% by weight.

 Another advantage of reducing solution concentration is that it reduces intermolecular interactions in the solution. Even in optically anisotropic solutions having different concentrations, the higher the concentration, the higher the intermolecular interaction. The optically anisotropic solution is derived from the polydomain structure of the nematic liquid crystal. When the solution concentration is high, the repulsion between molecules in the domain becomes strong, so the elasticity of the domain itself increases, and the interaction between domains (academically called long-range order) increases. Such a solution is rich in elasticity, and tends to cause unstable flow at the time of molding, and it is easy to form irregularities on the surface of the molded body. Therefore, it is preferable to form a solution having a concentration of C1 or more and a concentration as low as possible.

 In the present invention, an isotropic phase does not appear at the highest temperature from the preparation of the solution to the molding. is important. A non-rotating die is a type in which the contacting die wall is not driven during extrusion just before the dope is discharged to obtain a free surface.

By optimizing the film-forming conditions at the lower concentration of C2, which is 1.3 times the concentration of C2, at which the isotropic phase does not appear at the highest temperature from solution preparation to molding, Stable film formation becomes possible, and when a thin film is manufactured, it can be stretched through the stretching process, which expands the processing range.In addition, the molecular orientation by stretching makes the film strength, elastic modulus, and thermal dimension. Stability control is also possible. Furthermore, the obtained films show excellent peel strength. The reason why the peel strength is improved by the present invention is not clear, but it is presumed that as a result of being superior in moldability as compared with the case of using a high-concentration solution, the number of defects serving as starting points of peeling is reduced.

 Next, a process of stretching the dope extruded from the die will be described. Non-rotating dies are dies that are not driven during die extrusion. A relatively simple process is a method of extruding from a circumferential slit die and subjecting it to professional stretching. For example, a method as described in U.S. Pat. No. 4,889,924 is suitable. The first method is to extrude from a circumferential slit die. In this blow stretching method, the biaxial stretching is achieved by the drawdown in the discharge direction and the circumferential expansion of the discharged tube. At this time, it is more preferable to form a film by adding a coagulating liquid also inside the tube. It is more preferable to add a coagulating liquid also on the inner side, since coagulation can be performed from both sides.

 As a second stretching method, there is a method in which a dope extruded from a slit die and a supporting film are integrated with a flexible polymer as a supporting film, and the supporting film is sandwiched between tenter clips and stretched. In this case, the supporting film may be integrated on both sides of the dope, or may be bonded on only one side. If both sides are laminated, it is necessary to peel off the flexible fillem on one side before solidification. Suitable flexible polymers for this method include polyesters such as polyethylene terephthalate, polyethylene isophthalate, and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; and fluorine-based resins such as polytetrafluoroethylene. , And these multilayer molded films can be used.

The stretched dope solidifies upon contact with the non-solvent. The non-solvent may be in a liquid phase or a gas phase. Further, the solvent may be coagulated by evaporation or extraction. The medium used for coagulation and extraction is An inorganic aqueous solution or an organic solvent such as alcohol or dalicol can be used. A preferred coagulant is water or a mixture of water and a mineral acid.

For de one flops solvent extraction is stretched to proceed in the dope is to prevent the film defect occurring _c when the cause volume change, as described in U.S. Patent No. 5 3 0 2 3 3 4 No. In addition, it is necessary to apply tentering and limited shrinkage while coagulation progresses. Subsequent to coagulation, it is preferable to sufficiently extract the solvent. It is also possible to add a base, such as caustic soda, for the purpose of neutralizing the residual solvent mineral acid.

 In the polybenzazole molded article obtained in the above step, the third component is introduced at least from the coagulated product of a high-concentration solution as disclosed in Japanese Patent No. 2522828. It is also possible. That is, it is suitable as a method for producing an open-cell network structure for an impregnated polymer film. The film obtained by the film forming method of the present invention is very suitable as a substrate of the patent and can be used for producing a homogeneous composite.

 Washing with water, washing with water, neutralization, and drying the non-solvent from the resin-impregnated complex involves more volume change than solvent extraction. Therefore, it is preferable to use a fixing method as disclosed in US Pat. No. 5,445,779. Drying may be performed with dry air at room temperature, but in an industrial process, a hot air method is preferable. In addition, if the material is rapidly dried with a high-temperature gas, fine crack defects may occur inside, so it is preferable to dry the material over time.

 By the above film formation, a film having a thickness of 0.05 to 20 and preferably 1 to 10 / im was obtained. The homogeneity was ± 0.3 m with respect to the film thickness of 5 / m, and a homogeneous film was obtained.

Although the film obtained by drying as described above becomes a strong film with a high elastic modulus, it can be heat-treated at a temperature of 350 ° C or more to further arrange the internal molecules. is there. When heat treated, packing between polymer molecules improves, increasing density, increasing elastic modulus, and increasing equilibrium moisture content. Changes in film physical properties such as a decrease occur.

 As means for modifying the polybenzazole film obtained by the present invention, dyeing, addition of inorganic particles, stabilizers, antioxidants, and ultraviolet absorbers can be used in addition to the impregnation method. Furthermore, it is possible to modify the surface properties of the film by corona treatment, plasma treatment, and application of an anchoring agent.

The polybenzazole film produced by the present invention is excellent in mechanical properties, heat resistance, thermal dimensional stability, gas barrier properties, electrical insulation properties, and the like. Utilizing these properties, magnetic recording films, electronic circuit boards, substrates for mounting electronic components, composite material reinforcing materials, structural surface protective films, flame-resistant heat-resistant electric wire coating materials for aircraft, window materials for vacuum vessels, optical control It can be used as an application material. When used in these applications, the peel strength of the film is desirably at least 10 OmNZcm or more, and below this, peeling occurs during secondary processing such as formation of an adhesive layer and a magnetic layer. Not only that, but also products that have low durability in actual use environments can be obtained. More preferably, a peel strength of 500 OmNZcm or more, more preferably 200 OmN / cm or more is desirable from the viewpoint of durability in an actual use environment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a method for testing a peeling force according to the present invention. (Schematic diagram of test method) Adhesive tape

 Film under test

 Pull up and down (stress (mN / cm))

Determination of the peel force according to the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION

 Examples are shown below, but the present invention is not limited to these examples.

<Measurement method>

 (Intrinsic viscosity number) It was measured at 25 using a methanesulfonic acid solvent.

 (Strength)

 The dried film is cut into strips with a length of 100 mm and a width of 10 mm in the machine direction (MD direction) and the transverse direction (TD direction), respectively, to obtain test pieces. Tensile), a tensile test was performed at a tensile speed of 50 mm Z and a distance between chucks of 40 mm, and tensile strength and elastic modulus were measured.

 (Thickness)

 A micrometer was used to measure the homogeneity. In addition, homogeneity was measured at every four corners and the center point where the diagonal line of the obtained square film intersects with a micrometer, and the average was calculated.

Peeling force test>

An E-31B tape (manufactured by Nitto Denko Corporation) was attached to the dried film with a rubber roller, and the film was reciprocated once from above with a 20 N rubber roller to make close contact. The sample was allowed to stand for 30 minutes under the conditions of a temperature of 23 ° C and a humidity of 55 ± 5% RH, and then cut into a strip having a width of 25 mm. Tapes shall be applied in the machine direction (MD direction) and the transverse direction (TD direction) in parallel, and five test pieces shall be prepared. However, if only one direction of the test piece can be obtained due to the shape of the film to be tested, measure only the direction that can be manufactured. Using a tensile tester (Orientec Tensilon), the film under test and the adhesive tape are each checked as shown in Fig. 1 and pulled at a tensile speed of 30 O mrnZ in the manner of T-type peeling, and the peeling force is used. (Unit: mNZ cm) was measured. The peel force is defined as the average stress during peel propagation after the yield stress, as shown in Figure 2. Obtained from each test piece The value obtained by averaging the obtained peeling forces is defined as the peeling strength of the film under test.

 (Example 1, Comparative Examples 1 and 2)

A 6-, 8-, and 14-percent poly-paraffinylene-cis-benzbisoxazolyl polymer solution with a concentration of 116% polyphosphoric acid as a solvent was polymerized in a 2 L flask. The concentration of phosphoric anhydride at the time of charging was adjusted to equalize the concentration of the solvent. The resulting dope was sandwiched between slide glasses, the temperature was adjusted with a linker hot stage, and observed using a polarizing microscope (Nikon ECLIPSE E600 POL) in a crossed Nicol field of view. At a concentration of 6%, it was confirmed that the anisotropic phase partially disappeared at 140 ° C and became a mixed phase with the isotropic phase.- At a concentration of 8% or more, the temperature was raised to 300 ° C. However, most of the field of view remained optically anisotropic. A solution of these concentrations was discharged vertically downward at 180 ^ from a slit die with a width of 120 mm and a gap of 0.8 mm, and a thickness of 140 / m was obtained at a position of 300 mm from the die. It was sandwiched between polypropylene unstretched films, stretched 3 times in the MD direction by a stretching roll, and then 3 times in the TD direction by a heating tenter at 13.5, and one bit was cut and wound with a slitter. . One side of the stretched polypropylene film was peeled off in cold water at 5 ° C, and a Tyvek sheet made by DuPont was sandwiched and wound up in water. Peel off the polypropylene film and Tyvek sheet from both sides of the sheet immersed in water for 6 hours, run the washing tank for 2 minutes, and then run at 180 ° C for 3 minutes while running in a drying oven with built-in rollers. And dried under tension.

【table 1 】

液晶形成下限濃度 C 2未満の 6 %ドープ'を用いたフィルムでは、 ド一 プの加工時に流動性が乏しく成形体に空孔欠点が多数発生し、 低い強度 のフィルムしか得られない。 液晶形成下限濃度 C 2の 1 . 3倍を超えた 濃度 1 4 %では、 スリッ トノズルょり吐出される際に流動不安定現象が 発生しフィルム表面に著しい凹凸が発生した。 また、 その剥離強度は著 しく低い値となり、 本発明の効果は明らかである。

In the case of a film using a 6% dope having a liquid crystal formation lower limit concentration of less than C 2, the fluidity is poor at the time of doping, and a large number of void defects are generated in the molded product, so that only a low strength film can be obtained. At a concentration of 14%, which exceeds 1.3 times the lower limit concentration C2 of liquid crystal formation, a flow instability phenomenon occurred when ejected from the slit nozzle, and marked irregularities occurred on the film surface. Further, the peel strength is extremely low, and the effect of the present invention is clear.

Industrial applicability

 As described above, the present invention provides a high-strength, high-modulus, and high-heat-resistant polymer film that satisfies both moldability and economic efficiency and has excellent peel strength. · It is possible to industrially produce a film having a good balance of mechanical properties in the lateral direction and excellent heat resistance and a high elastic modulus, and the industrial applicability of the present invention is great.

Claims

The scope of the claims 1. A biaxially stretched film made of a solution that is 1 to 1.3 times the lower limit of the optical anisotropy solution concentration C2 of the rigid polymer, with a peel strength of 100 mN / cm or more. A polymer film, comprising:  2. The polymer film according to claim 1, wherein the polymer film is coagulated in a coagulating solution after biaxial stretching, and the solvent is removed with a washing solution.  3. The polymer film according to claim 1, wherein the solution is a mineral acid solution of a polybenzazole polymer.  A solution of 1 to 1.3 times the optical anisotropy lower limit solution concentration of the rigid polymer, C 1, is extruded from a non-rotating die, and then the film-like rigid polymer solution is biaxially stretched. A method for producing a polymer film, comprising coagulating with a washing solution and removing a solvent with a washing liquid. 5. The method for producing a polymer film according to claim 4, wherein the solution is a mineral acid solution of a polybenzazole polymer.