High dielectric constant pure polymer film

Abstract

Disclosed is a polymeric membrane and a method of making the same, the membrane comprising residues of 5 (6)-amino-2-(p-aminophenyl) benzimidazole, aromatic diamine and aromatic diacyl chloride in the form of a polymer having a polymer chain comprising a salt of formula I wherein C + is a sodium, potassium or calcium cation, and C + is a sodium, potassium or calcium cation, the film has a thickness of about 1 to 50 microns, and a dielectric constant of 4.5 or greater at 2 GHz in the absence of any particulate additive that increases the dielectric constant of the film.

Description

Background Art

[0001] FIELD OF THE INVENTION The present invention relates to polymer films having improved voltage resistance, which are additionally suitable for addressing higher voltage requirements in automotive, electronic devices, and other applications. In particular, the present invention relates to polymer films having a high dielectric constant (also known as relative permittivity) and methods for making such films.

[0002] Description of Related Art. The dielectric constant or relative permittivity of an insulating material (such as a film) is a measure of the ability of the insulating material or film to store electrical energy in an electric field. The dielectric constant of a film is important in the design of thin film capacitors and in other devices where it is expected that the film may introduce capacitance into a circuit. Films used for electrical insulation typically have a low dielectric constant, while films used for their capacitance (such as in capacitors) are desired to have a high dielectric constant, thereby allowing thinner films to be used in capacitors.

[0003] The present invention relates to polymer films made from polymers made by polymerizing diamines and diacids; specifically polymer films having residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and one or more aromatic diamines and one or more aromatic diacid chlorides. Various publications disclose that films and other articles can be made having residues of: p-phenylenediamine (PPD), 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI); and terephthaloyl dichloride (TDC). These include, for example, such publications as: U.S. Pat. Nos. 8,497,344 to Bos and 8,362,192 to De Vos et al.; Longbo et al. in High Performance Polymers [High Performance Polymers] 2017, Vol. 29(I), pp. 58-67; and U.S. Pat. No. 9,193,841 to Lee.

[0004] However, none of these references disclose or provide guidance regarding polymer residues of DAPBI wherein the imidazole is in a deprotonated state, thereby forming a salt with a cation. It has been found that polymer films comprising polymers containing residues or repeating units of DAPBI wherein the imidazole is in a deprotonated state have an increased dielectric constant. Polymer films having a high dielectric constant are highly desirable to manufacturers of automobiles and electronic devices due to their increased value per unit weight, and therefore any increase in the dielectric constant of such polymer films is of high value. Summary of the invention

[0005] The present invention relates to a polymer film comprising residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine and an aromatic diacid chloride, said residues being in the form of a polymer having a polymer chain comprising a salt of formula I, wherein C+ is a sodium, potassium or calcium cation, said film having a thickness of from about 1 to 50 microns and a dielectric constant of 4.5 or greater at 2 GHz in the absence of any particulate additives that increase the dielectric constant of the film.

[0006]

[0007] The present invention also relates to a method for manufacturing a polymer film comprising residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine and an aromatic diacid chloride, said residues being in the form of a polymer having a polymer chain comprising a salt of formula I, wherein C+ is a sodium, potassium or calcium cation,

[0008]

[0009] The method comprises the following steps:

[0010] a) forming an isotropic casting solution of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine and an aromatic diacid chloride in an organic solvent in the presence of a solubilizing salt, said isotropic casting solution having a polymer concentration of from 1 to 5 weight percent based on the total amount of polymer, solvent and solubilizing salt in the isotropic casting solution,

[0011] b) casting the isotropic casting solution in a laminar flow onto a surface to form a cast film,

[0012] c) removing the solvent from the cast film at a temperature of from 35 °C to 280 °C, said removal comprising the step of washing the cast film with an aqueous solution of a base having a pH of 13.8 or greater to deprotonate the imidazole and form a polymer film having a polymer chain comprising a polymer imidazole salt having a base cation,

[0013] d) optionally, rinsing the film with water in a second washing step, and

[0014] e) further removing liquid from the film in a tension drying step, wherein the film is restricted from shrinking at a temperature of from 35 °C to 280 °C to form the film. Description of the Drawings

[0015] Figure 1 is a graph showing the relationship between the capacitance and the dielectric constant dK of films of various thicknesses.

[0016] Figure 2A graph showing the relative level of the in-plane permittivity (or dielectric constant dK) affected by the electrical state of imidazole groups in the polymer, and dK being relatively stable over a wide frequency range.

[0017] Figure 3 The chemical structure of the 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeating unit in the polymer chain, where the nitrogen in benzimidazole is fully protonated into the form of benzimidazolium salt.

[0018] Figure 4 The chemical structure of the 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeating unit in the polymer chain, where the nitrogen in benzimidazole is considered to be in a "neutral" state; that is, one of the imidazole nitrogens contains a proton and the other imidazole nitrogen has a double bond as it has no salt label.

[0019] Figure 5 The chemical structure of the 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeating unit in the polymer chain, where the nitrogen in benzimidazole is considered to be in a deprotonated state, and this structure forms benzimidazolide. Detailed Description

[0020] The present invention relates to polymer films having residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and one or more aromatic diamines and one or more aromatic diacyl chlorides, and these polymer films have unexpectedly high dielectric constants achieved without adding inorganic dielectric enhancing particles. The increase in the dielectric constant of the film is achieved by the nitrogen in benzimidazole being in a deprotonated state (this structure forms benzimidazolide). Specifically, as used herein, benzimidazolide should be understood as a salt in which one nitrogen in the imidazole residue is the anion providing the negative charge (-) for the salt, and some other substance is the cation providing the positive charge (C+) for the salt. The salt preferably contains sodium, potassium or calcium cations.

[0021] The polymer film preferably has a thickness of 1 to 50 microns. Films thicker than 50 microns have manufacturing problems because typically these films are cast from solutions with a high percentage of solvent, and the solvent has to be removed. Films thinner than 1 micron become very difficult to manufacture; thin films may be difficult to handle and may be prone to tearing. In some embodiments, the polymer film has a thickness of 1 to 12 microns, and in some other embodiments, the polymer film has a thickness of 1 to 5 microns. In still other embodiments, the polymer film has a thickness of 2 to 25 microns, 2 to 15 microns or 2 to 5 microns.

[0022] It is advantageous for the polymer film to have a dielectric constant of 4.5 or greater at 2 GHz, preferably 5.0 or greater at 2 GHz, because a higher dielectric constant means the film has a higher capacitance. In some embodiments, the polymer film has a dielectric constant of at least 6.0 at 2 GHz. In some embodiments, the dielectric constant does not exceed 8 at 2 GHz.

[0023] The relationship between the dielectric constant of the film and its capacitance per area is represented by the following equation:

[0024]

[0025] where C is the capacitance in nF / in 2 , the dielectric constant dK is dimensionless, A is the area of the film under test in square inches, 0.2248 is a constant with the unit nF / in, and the capacitor film thickness D is measured in inches. If desired, the capacitance in SI units (nF / cm 2 ) can be obtained by the following relationship: (nF / cm 2 ) = (nF / in 2 ) / 6.45. The dielectric constant dK is dimensionless because it is the ratio of the permittivity of the material to the permittivity of free space (air) equivalent.

[0026] Figure 1 is a plot of the capacitance versus the dielectric constant dK for idealized films of various thicknesses using the above equation. For any particular film with a given dK, a thinner film has a higher capacitance than a thicker film. It can be recognized from Figure 1 that in order to achieve a thin film with a higher capacitance, the dK of the material must be increased.

[0027] The dielectric constant (dK) of any film is conveniently measured on a 25-micron-thick film sample; however, the dielectric constant does not vary significantly over the thickness range of about 1 to 50 microns required.

[0028] The polymer of the polymer film contains residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and one or more aromatic diamines and one or more aromatic diacyl chlorides.

[0029] As used herein, the term "residue" of a chemical substance refers to the portion of the product obtained from the chemical substance in a particular reaction scheme or subsequent formulation or chemical product, regardless of whether the portion is actually obtained from the chemical substance. Thus, a copolymer containing residues of p-phenylenediamine refers to a copolymer having one or more units of the following formula:

[0030]

[0031] And the copolymer having a residue of terephthaloyl dichloride contains one or more units having the following formula:

[0032]

[0033] Similarly, the copolymer containing a residue of DAPBI contains one or more units as shown in Figures 3 to 5 , and the exact structure depends on the state of the imidazole group. For example, Figure 3 shows the residue of DAPBI, in which the nitrogen in benzimidazole is fully protonated to the form of benzimidazolium salt. Specifically, as used herein, benzimidazolium salt should be understood as such a salt in which one of the nitrogen atoms in the imidazole residue is the cation providing the positive charge (+) for the salt, and some other substance is the anion (A-) providing the negative charge for the salt. This is usually the case when an imidazole polymer is treated with an acid to protonate benzimidazole and form a benzimidazolium salt.

[0034] This is also the chemical structure of the polymer directly after the polymerization of 5(6)-amino-2-(p-aminophenyl)benzimidazole and one or more aromatic diamines with one or more aromatic diacyl chlorides, because the polymerization produces acidic by-products. Typically, the acidic by-product is hydrochloric acid (HCl), since the diacyl chloride is usually one of these monomers. Thus, directly after the polymerization, the DAPBI residue has the Figure 3 chemical structure, where the anion "A-" is the chloride ion (Cl-) ionically bonded to the imidazole ring. Washing the membrane with water can reduce but not eliminate the amount of ionically bonded chloride ions. If the polymer is recovered and then dissolved in a stronger acid such as sulfuric acid and then formed into a membrane, this chemical structure also exists. In this case, the "A-" anion is the sulfate ion (HSO4-) ionically bonded to the imidazole ring. Washing the membrane with water can reduce but not eliminate the amount of ionically bonded sulfate.

[0035] Figure 4 shows the residue of DAPBI, in which the nitrogen in benzimidazole is considered to be in a "neutral" state; that is, one of the imidazole nitrogens contains a proton and the other imidazole nitrogen has a double bond because it has no salt label. This is the chemical structure of the polymer after neutralizing the acidic by-products generated during the polymerization with a typical base.

[0036] Figure 5Shows the residues of DAPBI, where the nitrogen in benzimidazole also forms a salt, but in this case the nitrogen is considered to be in a deprotonated state, and this structure forms a benzimidazolide. Specifically, as used herein, a benzimidazolide should be understood as a salt in which one of the nitrogens in the imidazole residue is the anion providing the negative charge (-) for the salt, and some other substance is the cation (C+) providing the positive charge for the salt. This is the case when an imidazole polymer is treated with a very strong base having a very high pH to deprotonate the benzimidazole and form a benzimidazolide. To generate a negative charge on the imidazole, a very high pH of 13.8 or preferably greater is required. Since strong bases are typically sodium hydroxide, potassium hydroxide, calcium hydroxide, or mixtures thereof, the cation (C+) on any one repeating unit can be sodium, potassium, or calcium. It has been found that, as shown by Figure 5 the dielectric constant of a benzimidazole film made from a polymer is 15% to 20% higher than that of a neutral benzimidazole (control) film having a neutralized imidazole state as shown in Figure 4 .

[0037] As used herein, the term "polymer" means a material prepared by polymerizing monomers, end-functionalized oligomers, and / or end-functionalized polymers, whether of the same type or different types. As used herein, the term "copolymer" refers to a polymer prepared from at least two different monomers. For clarity, it should be understood that, unless otherwise indicated, the use of the word "polymer" as used herein can be used interchangeably with "copolymer". In some embodiments, all monomers can be combined and reacted all at once to form a polymer. In some embodiments, monomers or different amounts of monomers can be reacted sequentially to form oligomers, which can further react with one or more additional monomers or one or more oligomers to form a polymer. "Oligomer" means a polymer or substance eluting at <3000 MW on a column calibrated with poly(p-phenylenediamine terephthalamide) homopolymer.

[0038] As used herein, "stoichiometric amount" means the amount of a component theoretically required to react with all the reactive groups of a second component. For example, "stoichiometric amount" refers to the number of moles of terephthaloyl dichloride required to react with substantially all of the amine groups of an amine component (p-phenylenediamine and DAPBI). Those skilled in the art will understand that the term "stoichiometric amount" refers to a range of amounts typically within 10% of the theoretical amount. For example, the stoichiometric amount of terephthaloyl dichloride used in a polymerization reaction can be 90% - 110% of the amount of terephthaloyl dichloride theoretically required to react with all the p-phenylenediamine and DAPBI amine groups.

[0039] The term "organic solvent" as used herein shall be understood to include single-component organic solvents or mixtures of two or more organic solvents. In some embodiments, the organic solvent is dimethylformamide, dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), or dimethyl sulfoxide. In some preferred embodiments, the organic solvent is NMP or DMAc. In some embodiments, a solubility enhancer for inorganic salts is added in a suitable amount before or during polymerization to enhance the solubility of the resulting polymer in the amide polar solvent. The term "inorganic salt" refers to a single inorganic salt or a mixture of two or more inorganic salts. In some embodiments, the inorganic salt is sufficiently soluble in the solvent and releases halogen atom-containing ions. In some embodiments, preferred inorganic salts are potassium chloride (KCl), zinc chloride (ZnCl2), lithium chloride (LiCl), or calcium chloride (CaCl2). In certain preferred embodiments, the inorganic salt is LiCl or CaCl2. "Solid" as used with the polymer solution means the ratio of the mass of the polymer (on a neutral basis) to the total mass of the solution (i.e., the mass of the polymer plus the solvent).

[0040] The polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, which forms a salt with sodium, potassium, or calcium cations; and residues of an aromatic diamine and an aromatic diacyl chloride.

[0041] Suitable aromatic diamines include p-phenylenediamine, 4,4'-diaminobiphenyl, 2-methyl-p-phenylenediamine, 2-chloro-p-phenylenediamine, 2,6-naphthalenediamine, 1,5-naphthalenediamine, and 4,4'-diaminobenzanilide. In some embodiments, the preferred aromatic diamine is p-phenylenediamine.

[0042] Suitable aromatic diacyl chlorides include terephthaloyl dichloride, 4,4'-benzoyl dichloride, 2-chloroterephthaloyl dichloride, 2,5-dichloroterephthaloyl chloride, 2-methylterephthaloyl dichloride, 2,6-naphthalene dicarboxylic acid chloride, and 1,5-naphthalene dicarboxylic acid chloride. In some embodiments, the preferred aromatic diacid is terephthaloyl dichloride.

[0043] In a preferred embodiment, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and residues of p-phenylenediamine and terephthaloyl dichloride, and the imidazole forms a salt with sodium, potassium, or calcium cations.

[0044] In some embodiments, for the residue of 5(6)-amino-2-(p-aminophenyl)benzimidazole in the polymer film, the imidazole forms a salt with sodium, potassium, or calcium cations; and for the residue of the aromatic diamine, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to the aromatic diamine is from 30 / 70 to 85 / 15. In some embodiments, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to the aromatic diamine is from 45 / 55 to 85 / 15. In still other embodiments, 5(6)-amino-2-(p-aminophenyl)benzimidazole is 50 mole percent or more of the total moles of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromatic diamine present. Preferably, the aromatic diamine is p-phenylenediamine.

[0045] Figure 2 It is shown that the relative level of the in-plane permittivity or dK of the pure DABPI-containing film is unexpectedly affected by the electrical state of the imidazole groups in the polymer, and dK is relatively stable over a wide frequency range. Figure 2 It is shown that when the polymer film contains DAPBI residues that are benzimidazolides having the structure as shown in Figure 5 highest relative in-plane permittivity is achieved; and when the polymer film contains DAPBI residues that are benzimidazolium salts having the structure as shown in Figure 3 the lowest relative in-plane permittivity is achieved. Figure 2 It is further shown the in-plane permittivities of two additional sets of data, which are polymer films containing DAPBI residues in the neutral state; i.e., having the structure as shown in Figure 4 These two sets of data provide the in-plane permittivities of a polymer film in which the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to the aromatic diamine is 70 / 30 (neutral 70 / 30) and a polymer film in which the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to the aromatic diamine is 50 / 50 (neutral 50 / 50). As shown, the in-plane permittivity or dK does not vary significantly within this molar ratio range.

[0046] The polymerization reaction of 5(6)-amino-2-(p-aminophenyl)benzimidazole, aromatic diamine, and aromatic dichloride can be accomplished by means known in the art. See, for example, PCT patent application No. 2005 / 054337 and U.S. patent application No. 2010 / 0029159. Typically, one or more acyl chlorides and one or more aromatic diamines are reacted in an amide polar solvent (such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethylimidazolinone, etc.). In some embodiments, N-methyl-2-pyrrolidone is preferred.

[0047] In some embodiments, prior to or during polymerization, a solubility agent for an inorganic salt (such as lithium chloride or calcium chloride, etc.) is added in a suitable amount to enhance the solubility of the resulting polymer in an amide polar solvent. After the desired degree of polymerization has been reached, the polymer exists in the form of unneutralized solid debris. "Debris" means that the polymer is in the form of a friable material or gel that easily separates into recognizable individual chunks upon shearing. The unneutralized debris contains the polymer, the polymerization solvent, the solubility agent, and the by-product acid (typically hydrochloric acid (HCl)) from the condensation reaction. In the presence of the HCl by-product, the DAPBI residue in the polymer chain has Figure 3 a chemical structure in which the imidazole is protonated.

[0048] After completion of the polymerization reaction, the unneutralized debris can optionally be contacted with a base, which can be an alkaline inorganic compound such as sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, ammonium hydroxide, etc. The alkaline inorganic compound can be used in an aqueous solution to carry out the neutralization reaction of the HCl by-product. If desired, the basic compound can be an organic base such as diethylamine or tributylamine or other amines. Typically, the unneutralized copolymer debris is contacted with an aqueous solution of the base by washing to convert the acidic by-product into a salt (usually sodium chloride salt if sodium hydroxide is the base and HCl is the acidic by-product) and also to remove some of the polymerization solvent. If desired, the unneutralized copolymer debris can optionally be washed with water one or more times prior to contact with the alkaline inorganic compound to remove the excess polymerization solvent. Once the acidic by-product in the polymer debris is neutralized, additional water washing can be employed to remove the salt and the polymerization solvent. After this washing, the DAPBI residue in the polymer chain has Figure 4 a chemical structure in which the imidazole is in a neutral state. In some embodiments, the membrane is cast from a polymer solution in which the imidazole is in a neutral state.

[0049] The molecular weight of the polymer is typically monitored by one or more dilute solution viscosity measurements and is related to the one or more dilute solution viscosity measurements. Thus, typically the relative viscosity ("V rel " or "η rel " or "n rel ") and the intrinsic viscosity ("V inh " or "η inh " or "n inh ") of dilute solution measurements are used to monitor the polymer molecular weight. The relative viscosity and the intrinsic viscosity of the dilute polymer solution are related according to the following expression

[0050] V inh = ln(V rel ) / C,

[0051] where ln is the natural logarithm function and C is the concentration of the polymer solution. V rel is a unitless ratio, and thus V inh is expressed in units of reciprocal concentration, typically expressed as deciliters per gram ("dl / g"). The polymer typically has an intrinsic viscosity of at least 3 dl / g, preferably at least 5 dl / g or higher. In some embodiments, the intrinsic viscosity can be 6 dl / g or greater.

[0052] A polymer film comprising residues of a polymer having 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride can be made by a method comprising the steps of:

[0053] a) forming an isotropic casting solution of a polymer comprising 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride in an organic solvent in the presence of a solubilizing salt, the isotropic casting solution having a polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution,

[0054] b) casting the isotropic casting solution in a laminar flow onto a surface to form a cast film, and

[0055] c) removing the solvent and the solubilizing salt from the cast film.

[0056] In some embodiments, the isotropic casting solution of a) can be formed by dissolving pre-formed polymer crumbs made from 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride in a suitable organic solvent, and the preferred solvent is DMAc. In other words, in this embodiment, it is preferred to polymerize 5(6)-amino-2-(p-aminophenyl)benzimidazole, p-phenylenediamine, and terephthaloyl dichloride at a high solids content (7 weight percent or greater) in NMP / CaCl2 or DMAC / CaCl2, then separate and optionally wash the polymer crumbs, and then dissolve them in an organic solvent to form a low-solids isotropic casting solution. In some cases, if the polymer is later dissolved in a strong acid (such as sulfuric acid), using polymer crumbs in which the by-product HCl has been neutralized can reduce bubble formation. However, the neutralization of the polymer crumbs is optional. Preferably, the polymer is cast from a polymer solution that does not leave sulfur residues in the film; that is, the final film has at most a trace amount of sulfur (less than 0.05 weight percent sulfur). Preferably, the film is made without contact with sulfuric acid or any other sulfur-containing compound.

[0057] In some other embodiments, the isotropic casting solution of a) can be formed

[0058] i) Polymerize 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacyl chloride in an organic solvent in the presence of a solubilizing salt to form a polymer solution, and

[0059] ii) Optionally, adjust the amount of solvent in the polymer solution by adding or removing solvent to form an isotropic casting solution having a polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution.

[0060] Regardless of the source of the polymer, the isotropic casting solution has a solid polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution. It is believed that a polymer concentration of less than 1 weight percent requires more solvent than is typically desired or practical in commercial processes, while a polymer concentration of greater than 5 weight percent is at or near the upper limit of the solubility of the polymer in DMAc, thus risking the formation of an undesirable gel that is difficult to cast into a film. In a preferred embodiment, the isotropic casting solution has a polymer concentration of 2 to 4 weight percent based on the amounts of polymer, solvent, and solubilizer in the isotropic casting solution. In some preferred embodiments, the isotropic casting solution is made by dissolving the polymer in a DMAc / CaCl2 or DMAc / LiCl solvent system, where the solubilizer (CaCl2 or LiCl) has a concentration of 0.5 weight percent or greater in the solvent system. In some embodiments, a solubilizer concentration of 1.5 weight percent or greater in the solvent system is desired. In some embodiments, the concentration of the solubilizing salt in the solvent system is 2 to 5 weight percent.

[0061] The isotropic casting solution may further contain additives such as antioxidants, lubricants, UV blockers, colorants, etc.

[0062] Following the step a) of forming the isotropic casting solution is the step b) of casting the isotropic casting solution as a layer onto a surface to form a film. Casting the isotropic casting solution to make a film can be accomplished by a variety of methods. For example, the film can be made by casting the casting solution onto a polished metal surface and calendering. In some methods, the film can be made continuously by, for example, casting via a film casting die head or a knife coater; or casting the solution onto a surface such as a belt or a rotating roll (or a glass plate), and then optionally additionally doctoring the casting solution to produce a casting film having a desired or uniform thickness on the surface.

[0063] Once the cast film is made, the solvent and solubilizing salt are removed from the cast film, and this step includes washing the film with an alkaline aqueous solution in step c) to deprotonate the imidazole.

[0064] There are many methods for removing solvents and solubilized salts from the membrane; however, the method and rate of solvent removal can determine the final structure of the membrane. For commercial production, the solvent removal rate needs to be actually as fast as possible without damaging the membrane. If the solvent is removed too quickly, voids will be generated in the membrane, and cracks and actual pinholes may form. These cracks and holes can reduce the toughness of the membrane and / or reduce the breakdown voltage of the membrane.

[0065] The rate of solvent and solubilized salt removal depends on matters such as the amount of solvent and solubilized salt present, the thickness of the membrane, and the driving force applied to the membrane. It has been found that if a mostly transparent or light-transmissive membrane is desired, it is desirable to control the solvent removal rate in step c) to avoid generating voids in the membrane, which will lead to objectionable opacity. The solvent removal rate can be controlled, for example, by removing the solvent in more than one step, where the driving force in any one step does not generate voids in the membrane.

[0066] The pure membrane typically has a golden color. Specifically, on the L*, a*, b* scale, the approximate coloring values of the membrane fit within the following ranges: L* (88 - 92); a* (-7 to -11); b* (23 - 37). In addition, it has been found that by controlling the removal of the solvent (such as by removing the solvent in more than one step), a light-transmissive or transparent (non-turbid) membrane with a golden color can be made. The light-transmissive or transparent (non-turbid) membrane typically has a D65 / 10 haze percentage of 5% or less, preferably 2% or less, as measured according to ASTM D1003, section 8, procedure B. Compared with higher numbers, lower numbers indicate lower haze or higher transparency.

[0067] In addition, it may be advantageous to restrict the cast film during solvent removal in step c); for example, using a frame that sandwiches the cast film between the frame and a surface to prevent the film from shrinking during this step.

[0068] Removing the solvent and solubilized salt from the cast film of step c) can be accomplished by a variety of methods. The solvent and solubilized salt can be removed from the cast film by washing the film with an aqueous liquid in one or more stages; or using a combination of washing and drying steps, where each of the washing and drying steps includes one or more stages.

[0069] The solvent and solubilized salt can be removed from the cast polymer film in step c) by immersing the cast polymer film in one or more water baths and / or applying an aqueous liquid to the film surface with various applicators (spray bars, troughs, etc.), preferably washing the cast film in a countercurrent washing process using water, where each stage has a gradually diluted solvent solution (less and less solvent in the washing water).

[0070] Alternatively, the solvent can be removed from the cast polymer film in step c) by a drying step that exposes the film to heat to drive off the solvent from the film. In the drying step, the cast film can be exposed to the heat in an oven or to heated gas in an inflation chamber, each providing energy to strip the solvent from the cast film.

[0071] Regardless of whether the solvent is removed via washing or by applying heat, the removal of the solvent from the cast film can be accomplished over a wide temperature range, depending on how quickly the solvent needs to be removed. For example, in an embodiment of the washing process, the solvent can be removed by exposing the cast film to a temperature ranging from room temperature (20 °C) or slightly higher up to the boiling point of the washing liquid. Alternatively, in one embodiment, the solvent can be removed from the cast polymer film by a drying step that maintains the film at a temperature of about 35 °C to 280 °C. In some embodiments, the drying step is maintained at a temperature of 80 °C to 150 °C. In other embodiments, it may be desirable for the drying step to be carried out at a temperature of 35 °C to 80 °C; or for the drying to be carried out in multiple stages, where each stage has a higher temperature than the previous stage.

[0072] If a drying stage is used to remove the solvent, the process should additionally include a washing step to remove any solubilized salts that remain, as the salt is undesirable in the final film.

[0073] It has been found that a method particularly useful for manufacturing a film utilizes step c) that includes the following steps:

[0074] c-1) removing at least a portion of the solvent from the cast film by heating to form an intermediate film, c-2) rinsing the intermediate film with water in a second washing step, and

[0075] c-3) further removing liquid from the intermediate film in a tension drying step, where the intermediate film is restricted from shrinking to form the film.

[0076] Step c-1) can be carried out as previously described; that is, the solvent can be removed from the cast polymer film by a drying step that maintains the film at a temperature of about 35 °C to 280 °C. In some embodiments, the drying step is maintained at a temperature of 80 °C to 150 °C. In other embodiments, it may be desirable for the drying step to be carried out at a temperature of 35 °C to 80 °C; or for the drying to be carried out in multiple stages, where each stage has a higher temperature than the previous stage.

[0077] Following step c-1) is a step c-2) of rinsing the intermediate film, which is typically carried out by using an aqueous liquid as the rinsing liquid. It is believed that the rinsing liquid can be effective over a wide temperature range; the rinsing liquid can have a temperature ranging from room temperature (20 °C) or slightly higher to the boiling point of the rinsing liquid. In some embodiments, the rinsing liquid is maintained at a temperature of 80 °C to 150 °C. In other embodiments, it may be desirable for the rinsing liquid to have a temperature of 35 °C to 80 °C.

[0078] The amount of this washing is determined by the method used. If it is desired to simply remove the solubilized salt, the amount of washing is determined by the desired amount of residual solubilized salt remaining in the intermediate film after washing.

[0079] Since the result of step c-2) is a wet film, step c-3) is then carried out to remove the liquid from the washed intermediate film in a tension drying step, where the intermediate film is restricted from shrinking while being exposed to a temperature ranging from room temperature (20 °C) to 280 °C to form the final film.

[0080] In some embodiments, it may be desirable to expose the intermediate film to a temperature of 80 °C to 150 °C in this tension drying step. In other embodiments, it may be desirable to expose the intermediate film to a temperature of 35 °C to 80 °C in this tension drying step. In the tension drying step, the intermediate film can be exposed to the heat in an oven or the heated gas in an inflation chamber, for example.

[0081] If desired, after or during step c-3), the method for manufacturing the polymer film can further include an optional step in which the film is additionally mechanically stretched axially or biaxially. In some embodiments, the film is stretched at a certain draw ratio. The cross-sectional area of the film is stretched axially or in one direction by 1.2% to 8.0%, preferably 1.2% to 4%; in some other embodiments, the film is biaxially stretched by 1.2% to 8.0% in two directions, preferably biaxially stretched by 1.2% to 4% in two directions.

[0082] Comprising residues or repeating units containing 5(6)-amino-2-(p-aminophenyl)benzimidazole, where the imidazole is in the form as Figure 5A polymer in the deprotonated state shown in [figure] can be made into a pure polymer film with an increased dielectric constant by washing the film in step c) with an alkaline aqueous solution using any of the steps described herein to deprotonate the imidazole and form a polymer film having polymer chains containing a polymer imidazolium salt (where the cation (C+) is determined by the type of base (such as sodium hydroxide, potassium hydroxide, calcium hydroxide, etc.)). The alkaline aqueous solution should have a pH of 13.8 or greater. Preferably, the alkaline aqueous solution has a pH of 14; the alkaline water is preferably an aqueous solution containing sodium hydroxide, potassium hydroxide, calcium hydroxide, or a mixture thereof. Such a suitable alkaline washing solution with a pH of 13.8 or greater can be made by dissolving an appropriate amount of base in water. The washing solution should be in contact with the film for a sufficient time to achieve the desired chemical structure, i.e., to deprotonate one benzimidazole nitrogen so that the benzimidazole is in the deprotonated state to form a benzimidazolide salt with sodium, potassium, or calcium cations. Preferably, at least 90% of the imidazole residue repeating units in the polymer are deprotonated at one nitrogen, and most preferably at least 95% of the imidazole residue repeating units in the polymer are deprotonated at one nitrogen. The anion provides the negative charge (-) for the salt, while some other substance is the cation that provides the positive charge (C+) for the salt.

[0083] Specifically, at least 90%, and preferably at least 95%, of the DAPBI residue repeating units in the polymer are salts having the structure shown in [figure]. Figure 5 in [figure].

[0084] These films are used in electronic devices that require higher frequencies, lower voltages, and greater currents, specifically in applications that require smaller form factors and lower costs. It is believed that these films can provide improved electrical performance in the device, including reduced board size. These films have particular uses in embedded capacitance applications and slot linings.

[0085] Test Methods

[0086] The dielectric constant (relative permittivity or dK) and dissipation factor (Df or tan δ) are determined using a rectangular cavity resonator at 2 to 10 GHz (or the provided frequency) in accordance with ASTM2520C, IPC-TM-650 2.5.5.3.

[0087] The capacitance of the film is determined using a Hioki IM3536 LCR meter using the method provided with the meter.

[0088] The breakdown voltage of the film is determined in accordance with ASTM D-149.

[0089] The film thickness is measured using a thickness gauge model DR600.

[0090] The film tensile properties (film toughness, modulus, and elongation at break) were measured according to ASTM D - 882.

[0091] The film color and transparency (haze) were determined by following Procedure B of Section 8 of ASTM D1003, using a Hunter Lab Vis spectrophotometer, along with QC and SensorManager, and software. The Commission Internationale de l'Eclairage (CIE) designates D65 as the standard daylight illuminant. The observer angle is measured at 10 degrees to obtain the name "D65 / 10" haze. Compared to higher haze numbers, lower numbers indicate lower haze or higher transparency.

[0092] Example 1

[0093] A polymer was made as follows. The monomers 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI) and p-phenylenediamine (PPD) were combined in amounts suitable for forming a copolymer with a DABPI / PPD monomer ratio of 70 / 30 with a stoichiometric amount of terephthaloyl dichloride (TCl) in a solvent system that included the N-methyl-2-pyrrolidone (NMP) solvent and 4.5 weight percent calcium chloride (CaCl2) as a solubility enhancer. These monomers were polymerized to form the copolymer. After polymerization was complete, the copolymer crumbs were recovered, ground, and washed with sodium hydroxide to neutralize the by-product hydrochloric acid. The crumbs were then filtered and dried. The copolymer had an intrinsic viscosity of approximately 6.4 dl / g.

[0094] A polymer solution was then made from the dried polymer flakes by mixing 3 weight percent of the polymer, 3 weight percent of the CaCl2 solubility enhancer, 2 weight percent of water, and 92 weight percent of dimethylacetamide (DMAc). A film approximately 6” × 8” was cast onto a glass plate using a doctor blade equipped with a micrometer set to approximately 20 times the target dry thickness. The glass plate with the cast film was then placed in an oven operating at 100 °C to 120 °C until approximately 50% of the DMAc was removed.

[0095] For the first control film, a sample of the partially dried and unwashed film on glass was placed in a first wash bath containing 3 liters of water for 30 minutes. For the comparative benzimidazolium salt film, a sample of the partially dried and unwashed film on glass was placed in a first wash bath containing 3 liters of water adjusted to pH 3 with HCl. For the benzimidazolide film of the present invention, the film on glass was placed in a first wash bath containing 3 liters of water adjusted to pH 14 with NaOH. Each sample was loosened from the glass and placed in separate second and third water wash baths for one hour each; each wash bath contained 1 liter of water. Each wet film was placed on a tensioning frame and restricted in the frame while the film was dried in an oven operating at 100 °C for one hour. The film was cooled to room temperature before being removed from the frame. The chloride ion level in the control film was measured to be below 100 ppm. In a similar manner, a second control film was made from a copolymer having a 50 / 50 DAPBI / PPD monomer ratio using a polymer solution having 2 weight percent polymer, 6 weight percent CaCl2, 2 weight percent water, and 90 weight percent DMAc. Then the thickness and dielectric constant of each film sample were determined at 68 - 69 degrees Fahrenheit and 40 - 42 relative humidity. The data are summarized in Tables 1 and 2 and Figure 2 in.

[0096] As can be seen from the figures and tables, the benzimidazolide film samples of the present invention (benzimidazolide examples) have a higher dielectric constant than the control or benzimidazolium salt film samples (benzimidazolium salt comparisons). Unexpectedly, the dielectric constant of the film can be altered by changing the state of the imidazole groups in the polymer film. In the case of the comparative example where the imidazole is in the protonated state, the dielectric constant is reduced by 0.5 relative to the control; while when the imidazole is in the deprotonated state as in the examples of the present invention, the dielectric constant is increased by a whole unit relative to the control. This effect can be used to modulate the dielectric constant for applications requiring low dK or high dK. As can be seen from the control examples, the relative amounts of the monomers do not appear to have a significant effect on the dielectric constant, while the state of the imidazole groups does.

[0097] Table 3 summarizes the percentage differences in dielectric constant from the control samples for both the benzimidazolide examples of the present invention and the comparative benzimidazolium salt examples, showing an unexpectedly large increase in the dielectric constant for the examples of the present invention. The benzimidazolide examples of the present invention show a consistent increase in dK of 16% to 20% compared to the control samples, while the comparative benzimidazolium salt examples have dK values that are always less than the control samples.

[0098] Table 1

[0099]

[0100]

[0101] Table 2

[0102]

[0103] Table 3

[0104]

Claims

1. A polymer film comprising residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride, said residues being in the form of a polymer having a polymer chain comprising a salt of formula I, wherein C+ is a sodium, potassium, or calcium cation, The film has a thickness of about 1 to 50 microns and a dielectric constant of 4.5 or greater at 2 GHz in the absence of any particulate additives that increase the dielectric constant of the film.

2. The polymer film according to claim 1, wherein, The dielectric constant is 5.0 to 6.0 at 2 GHz.

3. The polymer film according to claim 1 or 2, having a thickness of about 1 to 12 microns.

4. The polymer film according to any one of claims 1 to 3, wherein, The aromatic diamine is p-phenylenediamine.

5. The polymer film according to any one of claims 1 to 4, wherein The aromatic diacid chloride is terephthaloyl dichloride.

6. The polymer film according to any one of claims 1 to 5, having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of 30 / 70 to 85 / 15.

7. The polymer film according to claim 6, having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of 45 / 55 to 85 / 15.

8. The polymer film according to any one of claims 1 to 7, wherein, 5(6)-Amino-2-(p-aminophenyl)benzimidazole is 50 mole percent or more of the total moles of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromatic diamine present.

9. The polymer film according to any one of claims 1 to 8, wherein, At least 90% of the imidazole residue repeating units in the polymer are salts of formula I.

10. A method for manufacturing a polymer film comprising residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride, said residues being in the form of a polymer having a polymer chain comprising a salt of formula I, wherein C+ is a sodium, potassium, or calcium cation, The method comprises the following steps: a) forming an isotropic casting solution of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride in an organic solvent in the presence of a solubilizing salt, said isotropic casting solution having a polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution, b) casting the isotropic casting solution in a laminar flow onto a surface to form a cast film, c) removing the solvent from the cast film at a temperature of 35°C - 280°C, said removing including the step of washing the cast film with an aqueous base solution having a pH of 13.8 or greater to deprotonate the imidazole and form a polymer film having a polymer chain comprising a polymer imidazole salt having a base cation, d) optionally, rinsing the film in a second washing step with water, and e) further removing liquid from the film in a tension drying step, wherein the film is restricted from shrinking at a temperature of 35°C to 280°C to form a film.

11. The method according to claim 10, wherein, The isotropic casting solution of a) is formed by i) polymerizing 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride in an organic solvent in the presence of a solubilizing salt to form a polymer solution, and ii) Optionally, the amount of solvent in the polymer solution is adjusted by adding or removing solvent to form an isotropic casting solution having a polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution.

12. The method according to claim 10 or 11, wherein In step c), the solvent is removed from the film at a temperature of 80°C to 150°C.

13. The method according to any one of claims 10 to 12, wherein The aqueous alkali solution in step c) has a pH of 14 or greater.

14. The method according to any one of claims 10 to 13, wherein, The tension drying in step e) is carried out at a temperature of 80°C to 150°C.

15. The method according to any one of claims 10 to 14, wherein, The film is additionally mechanically stretched during or after step e).

16. The method according to any one of claims 10 to 15, wherein, The aromatic diamine is p-phenylenediamine.

17. The method according to any one of claims 10 to 16, wherein, The aromatic diacyl chloride is terephthaloyl dichloride.

18. The method according to any one of claims 10 to 17, having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of 30 / 70 to 85 / 15.

19. The method according to claim 18, having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of 45 / 55 to 85 / 15.

20. The method according to any one of claims 10 to 19, wherein 5(6)-Amino-2-(p-aminophenyl)benzimidazole is 50 mole percent or more of the total moles of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromatic diamine present.

21. The method according to any one of claims 10 to 20, wherein, At least 90% of the imidazole residue repeating units in the polymer of the film are salts having formula I.

Images