High-strength filled films containing polymers having imidazole groups

Abstract

1. A filled polymer film comprising a polymer and an inorganic dielectric constant enhancing additive, the filled polymer film having 12 to 75 weight percent of the inorganic dielectric constant enhancing additive, based on the combined weight of the polymer and the inorganic dielectric constant enhancing additive in the filled polymer film; the polymer comprises imidazole groups; and the filled polymer film has a filled film strength that is 70 to 100 percent of the neat film strength of a polymer film of the same thickness made from the same polymer but without the inorganic dielectric constant enhancing additive.

Description

[Technical Field]

[0001] The present invention relates to polymer films with improved voltage resistance that are more suitable for handling higher voltage requirements in automobiles, electronic devices, and other applications. Specifically, the present invention relates to polymer films with high dielectric constants (also known as relative permittivity), and methods for making such films. [Background technology]

[0002] The present invention relates to a polymer film made from a polymer produced by polymerizing a diamine and a diacid, preferably a polymer film having residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and an aromatic diamine and an aromatic diacid chloride. Various publications have disclosed that films and other articles can be produced with residues of paraphenylenediamine (PPD), 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI), and terephthaloyl dichloride (TDC). These include, for example, U.S. Patent Nos. 8,497,344 to Bos and 8,362,192 to De Vos et al.; Longbo et al. High Performance Polymers 2017, Vol. 29(I), pp. 58-67; and U.S. Patent No. 9,193,841 to Lee.

[0003] Furthermore, it is known that the addition of particulate matter to polymer films can dramatically reduce the film tenacity of the films they are loaded with. The particles are not believed to provide film reinforcement because they are simply encapsulated in the film, creating a Swiss cheese-like film structure similar to a voided film, significantly reducing strength compared to a polymer film of the same thickness but without particles or voids.

[0004] The dielectric constant of insulating materials, such as films, is important in the design of thin-film capacitors and other devices where the film may be expected to introduce capacitance into a circuit. Capacitance refers to the ability of a component or circuit to collect and store energy in the form of an electric charge. The dielectric constant or relative permittivity of an insulating material, such as a film, is a measure of the insulating material's or film's ability to store electrical energy in an electric field. Films used for electrical insulation typically have low dielectric constants, but films used for their capacitance, such as in capacitors, desirably have high dielectric constants so that the films used in capacitors can be made thinner. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, polymer films with high dielectric constants are highly desirable by manufacturers of automobiles and electronic devices because their value per unit weight increases, which leads to space savings for component miniaturization. Therefore, any increase in the dielectric constant of such a polymer film is highly valuable, especially when the dielectrically reinforced film is a filled film with a film strength that is 70 to 100 percent of the film strength of a neat film of the same thickness and made from the same polymer. [Means for solving the problem]

[0006] The present invention provides a filled polymer film comprising a polymer and an inorganic dielectric constant enhancing additive, wherein the polymer comprises imidazole groups; the filled polymer film having 12 to 75 weight percent of said inorganic dielectric constant enhancing additive, based on the combined weight of polymer and said inorganic dielectric constant enhancing additive in the filled polymer film; and The filled polymer film has a filled film strength that is 70 to 100 percent of the neat film strength of a polymer film having the same thickness made from the same polymer but without said inorganic dielectric constant enhancing additive. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a graph of capacitance versus dielectric constant dK for films of various thicknesses. [Figure 2] 1 is a graph showing that the relative level of in-plane dielectric constant (or dielectric constant dK) is affected by the electronic state of the imidazole groups in the polymer, and that dK is relatively stable over a wide range of frequencies. [Figure 3] Chemical structure of a 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeat unit in a polymer chain, where the nitrogen in the benzimidazole is fully protonated in the form of a benzimidazolium salt. [Figure 4] Chemical structure of a 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeat unit in a polymer chain, where the nitrogens in the benzimidazole are considered to be in a "neutral" state, i.e., there is no salt designation, so one of the imidazole nitrogens contains a proton and the other imidazole nitrogen has a double bond. [Figure 5] The chemical structure of a 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeat unit in a polymer chain, where the nitrogen in the benzimidazole is considered to be in a deprotonated state, forming a benzimidazolide. Specifically, as used herein, a benzimidazolide is understood to be a salt, where one of the nitrogens in the imidazole residue is an anion that provides a negative charge (-) to the salt, and some other species is a cation that provides a positive charge to the salt. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention relates to filled films with high loadings of dielectrically enhancing particles that unexpectedly retain much of the strength of neat films of the same thickness and made from the same polymer. By neat film, we mean that the film is made from a polymer and does not contain a particulate inorganic dielectric constant enhancing additive. By filled film, we mean that the film is made from a polymer and further contains a particulate inorganic dielectric constant enhancing additive.

[0009] Specifically, the present invention relates to a filled polymer film comprising a polymer and an inorganic dielectric constant enhancing additive, wherein the polymer contains imidazole groups for high temperature stability. The filled polymer film has 12 to 75 weight percent of the inorganic dielectric constant enhancing additive, based on the total weight of the polymer and the inorganic dielectric constant enhancing additive in the filled polymer film. The filled polymer film has a filled film strength of 70 to 100 percent of the neat film strength. A neat film is a polymer film having the same thickness and made from the same polymer, but without any inorganic dielectric constant enhancing additive.

[0010] The filled polymer film preferably has a thickness of 1 to 50 micrometers. Films thicker than 50 micrometers typically present manufacturing challenges in that the film is cast from a solution that has a high percentage of solvent that must be removed. Films thinner than 1 micrometer are very difficult to manufacture; thin films are difficult to handle and can easily tear. In some embodiments, the filled polymer film has a thickness of 1 to 12 micrometers, while in some other embodiments, the filled polymer film has a thickness of 1 to 5 micrometers. In still other embodiments, the filled polymer film has a thickness of 2 to 25 micrometers, 2 to 15 micrometers, or 2 to 5 micrometers.

[0011] The filled polymer film has a dielectric constant of 5.5 or greater at 2 GHz, preferably 5.8 or greater at 2 GHz, which is advantageous because a higher dielectric constant means the film has a higher capacitance. In some embodiments, the filled polymer film has a dielectric constant of at least 6.2 at 2 GHz. In some embodiments, the dielectric constant is 10 or less at 2 GHz.

[0012] The relationship between the dielectric constant of a film and its capacitance per area is given by the following equation:

number

[0013] Figure 1 is a graphical representation of the relationship of capacitance per area to dielectric constant dK for various thicknesses of an idealized film, using the above equation. For any particular film with a particular dK, thinner films have higher capacitance than thicker films.

[0014] The dielectric constant (dK) of any film is conveniently measured on a 25 micrometer thick film sample, but the dielectric constant does not vary substantially over the claimed thickness range of about 1 to 50 micrometers.

[0015] In some embodiments, the filled polymer film has a resistance of at least 15 nF / inch. 2In some preferred embodiments, the filled polymer film has a capacitance of at least 20 nF / inch. 2 As can be seen from Figure 1, to achieve a thin film with a higher capacitance, the dK of the material must be increased.

[0016] The filled polymer film contains an inorganic dielectric constant-enhancing additive. By inorganic dielectric constant-enhancing additive, we mean an inorganic material, typically in powder or particle form, having a high dielectric constant. Examples of inorganic dielectric constant-enhancing additives include various titanates, including barium titanate, lead zirconium titanate, barium strontium titanate, and lead lanthanum zirconium titanate. In some embodiments, the inorganic dielectric constant-enhancing additive comprises barium titanate. In some embodiments, the inorganic dielectric constant-enhancing additive is a single inorganic additive, and in some embodiments, the single inorganic dielectric constant-enhancing additive is barium titanate. Additional additives that improve other properties may be added as long as they do not adversely affect the tensile properties of the film.

[0017] In some embodiments, the inorganic dielectric constant enhancing additive has a particle size range of 0.1 to 3.0 microns. In some embodiments, a particle size range of 0.1 to 1.5 microns may be preferred, and in other embodiments, a particle size range of 0.1 to 1.0 microns may be preferred. In yet other embodiments, a particle size range of 0.1 to 0.7 microns may be preferred.

[0018] As used herein, the term "particle size" refers to the average particle size assigned to the particles by the particle manufacturer / supplier; the average particle size may also be determined using visual inspection of a magnified image of the particles, for example, using scanning electron microscopy (SEM) techniques.

[0019] In some embodiments, the filled polymer film comprises 30 to 75 weight percent of the inorganic dielectric constant enhancing additive, hi some preferred embodiments, the filled polymer film comprises 40 to 75 weight percent of the inorganic dielectric constant enhancing additive, and in some other embodiments, the filled polymer film comprises 50 to 75 weight percent of the inorganic dielectric constant enhancing additive.

[0020] In some embodiments, the filled polymer film has a filled film strength that is 75 to 100 percent of the neat film strength of a polymer film of the same thickness made from the same polymer but without the inorganic dielectric constant-enhancing additive. In yet other preferred embodiments, the filled polymer film has a filled film strength that is 80 to 100 percent of the neat film strength of a polymer film of the same thickness and made from the same polymer but without said inorganic dielectric constant-enhancing additive.

[0021] The polymer of the polymer film contains imidazole groups in the polymer chain; in some preferred embodiments, the polymer of the polymer film has residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride. Although DAPBI-containing polymers are exemplified, the polymers useful in the polymer film extend, without limitation, to any polymer film made from a polymer containing imidazole groups.

[0022] As used herein, the term "residue" of a chemical species refers to a moiety that is a resulting product of a chemical species in a particular reaction scheme or subsequent formulation or chemical product, regardless of whether the moiety is actually derived from the chemical species. Thus, a copolymer containing residues of paraphenylenediamine has the formula: [ka] It refers to a copolymer having one or more units of:

[0023] The copolymer having residues of terephthaloyl dichloride has the formula: [ka] It contains one or more units of:

[0024] Similarly, copolymers containing residues of DAPBI contain one or more units as shown in Figures 3-5, with the exact structure depending on the state of the imidazole group. For example, Figure 3 shows residues of DAPBI in which the nitrogens in the benzimidazole are fully protonated in the form of a benzimidazolium salt. Specifically, as used herein, a benzimidazolium salt is understood to be a salt in which one of the nitrogens in the imidazole residue is a cation, providing a positive charge (+) to the salt, and some other species is an anion (A-), providing a negative charge to the salt. This is generally the case when an imidazole polymer is treated with acid to protonate the benzimidazole and form a benzimidazolium salt.

[0025] This is also the chemical structure of the polymer immediately after polymerization of 5(6)-amino-2-(p-aminophenyl)benzimidazole and an aromatic diamine with an aromatic diacid chloride, since the polymerization produces an acid by-product. Because the diacid chloride is usually a monomer, the acid by-product is typically hydrochloric acid (HCl). Therefore, immediately after polymerization, the DAPBI residue has the chemical structure shown in Figure 3, where the anion "A-" is a chloride ion (Cl-) ionically bonded to the imidazole ring. Washing the film with water can reduce the amount of ionically bonded chloride, but it cannot remove it. This chemical structure also exists when the polymer is recovered and then dissolved in a stronger acid, such as sulfuric acid, and then cast into a film. In this case, the "A-" anion is a sulfate ion (HSO4-) ionically bonded to the imidazole ring. Washing the film with water can reduce the amount of ionically bonded sulfate, but it cannot remove it.

[0026] Figure 4 illustrates the residue of DAPBI, where the benzimidazole nitrogens are considered to be in a "neutral" state; that is, one of the imidazole nitrogens contains a proton and the other imidazole nitrogen lacks a salt designation and therefore has a double bond. This is the chemical structure of the polymer after the acid by-products generated during polymerization have been neutralized with a typical base.

[0027] Figure 5 illustrates residues of DAPBI in which the nitrogen in the benzimidazole also forms a salt; in this case, the nitrogen is considered deprotonated, forming a benzimidazolide. Specifically, as used herein, a benzimidazolide is understood to be a salt in which one of the nitrogens in the imidazole residue is an anion, providing a negative charge (-) to the salt, and some other species is a cation (C+), providing a positive charge to 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. A very high pH of 13.8 or preferably higher is required to generate a negative charge on the imidazole. The strong base is typically sodium hydroxide, potassium hydroxide, calcium hydroxide, or a mixture thereof, so the cation (C+) on any one repeating unit can be either sodium, potassium, or calcium. Neat or unfilled benzimidazole films, such as those made from the polymers in Figure 5, were found to have dielectric constants 15-20% higher than neat or unfilled neutral benzimidazole films with neutralized imidazole states, such as those shown in Figure 4.

[0028] The term "polymer," as used herein, refers to a material prepared by polymerizing monomers, end-functionalized oligomers, and / or end-functionalized polymers, whether of the same or different types. The term "copolymer," as used herein, refers to a polymer prepared from at least two different monomers. For clarity, it is understood that the use of the term "polymer" as used herein can be used interchangeably with "copolymer" unless otherwise indicated. In some embodiments, all monomers can be combined and reacted at once to form a polymer. In some embodiments, monomers or varying amounts of monomers can be reacted sequentially to form an oligomer, which can be further reacted with additional monomers or oligomers to form a polymer. "Oligomer" refers to a polymer or species eluting at less than 3000 MW using a column calibrated with polyparaphenylenediamine terephthalamide homopolymer.

[0029] As used herein, "stoichiometric amount" refers to the amount of a component theoretically required to react with all of 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 the amine components (paraphenylenediamine and DAPBI). Those skilled in the art will appreciate that the term "stoichiometric amount" refers to a range of amounts that are 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 of the amine groups of paraphenylenediamine and DAPBI.

[0030] The term "organic solvent" as used herein is understood to include a single organic solvent or a mixture 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, an inorganic salt solubility enhancer is added in an appropriate amount before or during polymerization to improve 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 to liberate a halogen atom ion. In some embodiments, a preferred inorganic salt is potassium chloride (KCl), zinc chloride (ZnCl), lithium chloride (LiCl), or calcium chloride (CaCl). In certain preferred embodiments, the inorganic salt is LiCl or CaCl. The amount of inorganic salt added to the solvent to enhance the solubility of the polymer is preferably removed by washing from the film and therefore does not substantially contribute to increasing the dielectric constant of the polymer, and therefore, for purposes of this specification, it is understood that dielectric constant enhancing additive does not include any inorganic salt added as a polymer solubility enhancer. "Solids" as used in connection with a polymer solution means the ratio of the mass of polymer (on a neutral basis) to the total mass of the solution, i.e., the mass of polymer and solvent.

[0031] In a preferred embodiment, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, and residues of an aromatic diamine and an aromatic diacid chloride. In some embodiments, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, where the imidazole forms a salt with a sodium, potassium, or calcium cation; and residues of an aromatic diamine and an aromatic diacid chloride.

[0032] Suitable aromatic diamines include paraphenylenediamine, 4,4'-diaminobiphenyl, 2-methyl-paraphenylenediamine, 2-chloro-paraphenylenediamine, 2,6-naphthalenediamine, 1,5-naphthalenediamine, and 4,4'-diaminobenzanilide. In some embodiments, the preferred organic solvent is paraphenylenediamine.

[0033] Suitable aromatic diacid chlorides include terephthaloyl dichloride, 4,4'-benzoyl dichloride, 2-chloroterephthaloyl dichloride, 2,5-dichloroterephthaloyl chloride, 2-methylterephthaloyl dichloride, 2,6-naphthalenedicarboxylic acid chloride, and 1,5-naphthalenedicarboxylic acid chloride. In some embodiments, the preferred aromatic diacid is terephthaloyl dichloride.

[0034] In one preferred embodiment, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, and residues of paraphenylenediamine and terephthaloyl dichloride. In another preferred embodiment, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, in which the imidazole forms a salt with a sodium, potassium, or calcium cation; and residues of paraphenylenediamine and terephthaloyl dichloride.

[0035] In some embodiments, with respect to the residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and the residues of aromatic diamine in the polymer film, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is 30 / 70 to 85 / 15. In some embodiments, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is 45 / 55 to 85 / 15. In still other embodiments, 5(6)-amino-2-(p-aminophenyl)benzimidazole represents 50 mole percent or more of the total moles of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromatic diamine residues present in the polymer and film. Preferably, the aromatic diamine is paraphenylenediamine.

[0036] Similarly, in some embodiments, with respect to the residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromatic diamine in the polymer film, where the imidazole forms a salt with sodium, potassium, or calcium cation, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is 30 / 70 to 85 / 15. In some embodiments, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is 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 paraphenylenediamine.

[0037] Figure 2 shows that the relative levels of in-plane dielectric constant, or dK, of neat DABPI-containing films are unexpectedly affected by the electronic state of the imidazole groups in the polymer, and that dK is relatively stable over a wide range of frequencies. Figure 2 shows that the highest in-plane dielectric constants are achieved when the polymer film contains DAPBI residues that are benzimidazolides having the structure shown in Figure 5, and that the lowest in-plane dielectric constants are achieved when the polymer film contains DAPBI residues that are benzimidazolium salts having the structure shown in Figure 3. Figure 2 also shows the in-plane dielectric constants of two other sets of data for polymer films containing DAPBI residues in the neutral state, i.e., those with the structure shown in Figure 4. Two sets of data provide the in-plane dielectric constant for a polymer film having a 70 / 30 molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine (neutral 70 / 30) and a 50 / 50 molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine (neutral 50 / 50). As shown, the in-plane dielectric constant, or dK, does not change appreciably over this range of molar ratios.

[0038] The polymerization reaction of 5(6)-amino-2-(p-aminophenyl)benzimidazole, aromatic diamines, and aromatic dichlorides can be achieved 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 acid chlorides and one or more aromatic diamines are reacted in a polar amide solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, or dimethylimidazolidinone. In some embodiments, N-methyl-2-pyrrolidone is preferred.

[0039] In some embodiments, an appropriate amount of an inorganic salt solubilizer, such as lithium chloride or calcium chloride, is added before or during polymerization to improve the solubility of the resulting polymer in the amide polar solvent. After the desired degree of polymerization is achieved, the polymer exists in the form of unneutralized solid crumbs. By "crumb," we mean that the polymer is in the form of a brittle material or gel that easily separates into distinct, identifiable chunks when sheared. The unneutralized crumbs contain the polymer, polymerization solvent, solubilizer, and the by-product acid from the condensation reaction, typically hydrochloric acid (HCl). In the presence of the HCl by-product, the DAPBI residues in the polymer chain have the chemical structure shown in Figure 3, in which the imidazole is protonated.

[0040] After the polymerization reaction is complete, the unneutralized crumbs can optionally be contacted with a base, which can be a basic inorganic compound such as sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, or ammonium hydroxide. The basic inorganic compound can be used in aqueous solution to neutralize the HCl by-product. Optionally, the basic compound can be an organic base such as diethylamine, tributylamine, or other amines. Typically, the unneutralized copolymer crumbs are contacted with the aqueous base by washing, which converts the acidic by-products to salts (generally, sodium chloride salts when sodium hydroxide is the base and HCl is the acidic by-product) and removes a portion of the polymerization solvent. If necessary, the unneutralized copolymer crumbs can be optionally first washed one or more times with water before contacting with the basic inorganic compound to remove excess polymerization solvent. Once the acidic by-products in the polymer crumbs have been neutralized, additional water washes can be used to remove the salts and polymerization solvent. After this wash, the DAPBI residues in the polymer chains have the chemical structure shown in Figure 4, in which the imidazole is neutralized. In some embodiments, the film is cast from a polymer solution in which the imidazole is in a neutralized state.

[0041] The molecular weight of a polymer is typically monitored and correlated with one or more dilute solution viscosity measurements. Thus, the relative viscosity ("V") is typically used. rel " or "η rel " or "n rel ") and intrinsic viscosity ("V inh " or "η inh " or "n inh ") are used to monitor polymer molecular weight. The relative viscosity and intrinsic viscosity of dilute polymer solutions are related according to the following equation: V inh =ln(V rel ) / C where ln is the natural logarithm function and C is the concentration of the polymer solution. rel is a unitless ratio, so V inh is typically expressed in units of inverse concentration 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 greater. In some embodiments, the intrinsic viscosity can be 6 dl / g or greater.

[0042] A polymer film comprising an inorganic dielectric constant enhancing additive and a polymer having residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride is a) forming an isotropic casting solution comprising an inorganic dielectric constant enhancing additive and a polymer 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, wherein the isotropic casting solution has 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 a layer of an isotropic casting solution onto a surface to form a cast film; c) removing the solvent and solubilized salts from the cast film; The composition can be produced by a process comprising:

[0043] Films can also be made in a similar manner from an isotropic casting solution containing a polymer containing imidazole groups and an inorganic dielectric constant enhancing additive.

[0044] In some embodiments, the isotropic casting solution of step 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 (a preferred solvent is DMAc). In other words, in this embodiment, preferably, 5(6)-amino-2-(p-aminophenyl)benzimidazole, para-phenylenediamine, and terephthaloyl dichloride are polymerized at a high solids content (7 weight percent or greater) in NMP / CaCl or DMAC / CaCl, followed by isolating and optionally washing the polymer crumbs, which are then dissolved in an organic solvent to form a low-solids isotropic casting solution. In some cases, using polymer crumbs in which the by-product HCl has been neutralized can reduce bubble formation when the polymer is subsequently dissolved in a strong acid such as sulfuric acid. However, neutralization of the polymer crumbs is optional. Preferably, the polymer is cast from a polymer solution that leaves no sulfur residue in the film; i.e., the final film has only trace amounts of sulfur (less than 0.05 weight percent sulfur). Preferably, the film is produced without contact with sulfuric acid or any other sulfur-containing compound.

[0045] In some other embodiments, the isotropic casting solution of step a) comprises: 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; ii) optionally adjusting the amount of solvent in the polymer solution by either 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; It can be formed by:

[0046] 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. Polymer concentrations below 1 weight percent require more solvent than is typically desirable or practical in commercial processes, while polymer concentrations above 5 weight percent are considered to be at or near the upper limit of the polymer's solubility in DMAc and risk the formation of undesirable gels that are difficult to cast into films. In a preferred embodiment, the isotropic casting solution has a polymer concentration of 2 to 4 weight percent based on the amount of polymer, solvent, and solubilizing agent in the isotropic casting solution. In some preferred embodiments, the isotropic casting solution is prepared by dissolving the polymer in a DMAc / CaCl or DMAc / LiCl solvent system, with the solubilizing agent (CaCl or LiCl) having a concentration of 0.5 weight percent or greater in the solvent system. In some embodiments, a solubilizing agent concentration of 1.5 weight percent or greater in the solvent system is desirable. In some embodiments, the concentration of the solubilizing salt in the solvent system is between 2 and 5 percent by weight.

[0047] The inorganic dielectric constant-enhancing additive is preferably added to the polymer solution via a stock solution. For example, a dilute solution of 0.5 to 1.0 weight percent polymer in a solvent or solvent system (preferably DMAc / CaCl) is first prepared, and a certain amount of inorganic dielectric constant-enhancing additive is added, preferably with high shear mixing, to form a stock solution. The desired amount of stock solution can then be added to a polymer solution having a solids content of about 3 to 4 weight percent to form a casting solution having a solids content, where the solids content is about 2 to 4 weight percent solids of the combination of polymer and inorganic dielectric constant-enhancing additive. The final solids concentration of the casting solution should have a viscosity that pours well and casts as a film. If the viscosity of the casting solution is too high, additional solvent can be added.

[0048] The isotropic casting solution may further contain additives such as antioxidants, lubricants, UV filters, colorants, and the like.

[0049] Step a) of forming an isotropic casting solution is then followed by step b) of casting a layer of the isotropic casting solution onto a surface to form a film. Casting the isotropic casting solution to produce a film can be achieved by a number of processes. For example, the film can be produced by casting the casting solution onto a polished metal surface and calendering it. In some methods, the film can be produced continuously, for example, by casting through a film casting die or doctor blade, or by casting the solution onto a surface such as a belt or rotating roll (or glass plate), and then optionally further doctoring the casting solution to form a cast film of desired or uniform thickness on the surface.

[0050] Once the cast film is produced, in step c), the solvent and solubilizing salts are removed from the cast film. There are many methods for removing the solvent and solubilizing salts from the film, and the method and rate of solvent removal can determine the final film structure. For commercial production, the solvent removal rate needs to be as fast as practical without damaging the film. If the solvent is removed too quickly, voids may form in the film, resulting in defects and actual pinholes. These defects and holes can reduce the strength and / or breakdown voltage of the film.

[0051] The rate of removal of the solvent and solubilizing salt depends on factors such as the amount of solvent and solubilizing salt present, the thickness of the film, and the driving force imposed on the film. It has been found desirable to control the rate of solvent removal in step c) to avoid creating voids in the film. The rate of solvent removal can be controlled, for example, by removing the solvent in two or more steps, where the driving force of any one step does not create voids in the film.

[0052] In addition, it may be advantageous to restrain the cast film during removal of the solvent in step c), for example, by using a frame that sandwiches the cast film between the frame and the surface to prevent shrinkage of the film during this step.

[0053] Removal of the solvent and solubilizing salts from the cast film in step c) can be accomplished by a number of processes: The solvent and solubilizing salts can be removed from the cast film by washing the film with an aqueous liquid in one or more steps, or by using a combination of washing and drying steps, each of which includes one or more steps.

[0054] The solvent and solubilizing salts can be removed from the cast polymer film in step c) by submerging the cast polymer film in one or more aqueous baths and / or by applying aqueous liquids to the film surface using various applicators (spray bars, troughs, etc.), preferably by washing the cast film in a countercurrent washing process using water with increasingly dilute solvent solution (less solvent in the wash water) in each stage.

[0055] Alternatively, if the solvent can be removed from the cast polymer film in step c), the drying step involves exposing the film to heat to remove the solvent from the film. In the drying step, the cast film can be exposed to heat in an oven or heated gas in a plenum chamber, each of which provides energy to remove the solvent from the cast film.

[0056] Whether the solvent is removed by washing or by the application of heat, solvent removal from the cast film can be accomplished over a wide range of temperatures, depending on how quickly the solvent needs to be removed. For example, in one embodiment of a washing process, the solvent can be removed by exposing the cast film to temperatures ranging from room temperature (20°C) or slightly above to the boiling point of the washing liquid. Alternatively, in one embodiment, the solvent can be removed from the cast polymer film by exposing the cast film to a drying step maintained at a temperature of about 35-280°C. In some embodiments, the drying step is maintained at a temperature of 80-150°C. In other embodiments, it may be desirable to perform the drying step at a temperature of 35-80°C, or to perform drying in multiple stages, each stage having a higher temperature than the previous stage.

[0057] If a drying step is used to remove the solvent, the process should further include a washing step to remove any solubilized salts left behind, as salts are undesirable in the final film.

[0058] One particularly useful process for producing films is c-1) removing at least a portion of the solvent from the cast film using heat to form an intermediate film; c-2) rinsing the intermediate film with water in a second washing step; c-3) In the tension drying process, shrinkage of the intermediate film is suppressed and liquid is further removed from the intermediate film to form a film. It has been found that a step c) comprising:

[0059] Step c-1) can be carried out as previously described; i.e., the solvent can be removed from the cast polymer film by exposing the cast film to a drying step maintained at a temperature of about 35-280° C. In some embodiments, the drying step is maintained at a temperature of 80-150° C. In other embodiments, it may be desirable to carry out the drying step at a temperature of 35-80° C. or to carry out drying in multiple stages, each stage having a higher temperature than the previous stage.

[0060] Step c-1) is then followed by step c-2), in which the intermediate film is rinsed, typically by using an aqueous liquid as the rinse solution. It is contemplated that the rinse solution can be effective over a wide temperature range; the rinse solution can have a temperature ranging from room temperature (20°C) or slightly above to the boiling point of the rinse solution. In some embodiments, the rinse solution is maintained at a temperature of 80-150°C. In other embodiments, it may be desirable for the rinse solution to have a temperature of 35-80°C.

[0061] The amount of washing is determined by the process used. If it is desired to simply remove the solubilizing salts, the amount of washing is determined by the desired amount of residual solubilizing salts that will remain in the intermediate film after washing.

[0062] The result of step c-2) is a wet film, which is then followed by step c-3) of removing liquid from the washed intermediate film in a tension drying step, in which the intermediate film is subjected to temperatures ranging from room temperature (20°C) to 280°C while shrinkage is suppressed to form the final film. In some embodiments, it may be desirable to expose the intermediate film to temperatures of 80 to 150°C in this tension drying step. In other embodiments, it may be desirable to expose the intermediate film to temperatures of 35 to 80°C in this tension drying step. In the tension drying step, the intermediate film may be exposed to heat, for example, in an oven or to heated gas in a plenum chamber.

[0063] Optionally, after or during step c-3), the method for producing a polymer film can further include an optional step in which the film is further mechanically stretched either axially or biaxially. In some embodiments, the film is stretched so that the stretch ratio cross-sectional area of ​​the film is 1.2 to 8.0 percent, preferably 1.2 to 4 percent, in the axial or one direction; in some other embodiments, the film is biaxially stretched 1.2 to 8.0 percent in both directions, preferably 1.2 to 4 percent in both directions.

[0064] Neat polymer films comprising polymers containing residues or repeat units of 5(6)-amino-2-(p-aminophenyl)benzimidazole, where the imidazole is in the deprotonated state as shown in Figure 5, have increased dielectric constants in the neat form prior to the addition of any inorganic dielectric constant-enhancing additive as shown in Figure 2. Such films have dielectric constants 15 to 20 percent higher than control films having the imidazole in the neutralized state as shown in Figure 4. Thus, filled polymer films in which the imidazole is in the deprotonated state, in combination with inorganic dielectric constant-enhancing additives, provide polymer films exhibiting even higher dielectric constants.

[0065] Preferably, filled polymer films comprising both an inorganic dielectric constant enhancing additive and a polymer comprising residues or repeat units of 5(6)-amino-2-(p-aminophenyl)benzimidazole, where the imidazole is in a deprotonated state as shown in Figure 5, have a dielectric constant of 6.3 or greater at 2 GHz, preferably 6.7 or greater at 2 GHz, which is advantageous because a higher dielectric constant means a higher capacitance for the film. In some embodiments, the filled polymer film has a dielectric constant of at least 7.1 at 2 GHz. In some embodiments, the dielectric constant is 12 or less at 2 GHz.

[0066] Such loaded films having residues or repeating units of 5(6)-amino-2-(p-aminophenyl)benzimidazole, in which the imidazole is in a deprotonated state as shown in Figure 5, can be prepared by washing the film in step c) using an aqueous base wash solution to deprotonate the imidazole using any of the processes described herein to form a polymer film having polymer chains comprising polymeric imidazole salts with a cation (C+) determined by the type of base, e.g., sodium hydroxide, potassium hydroxide, calcium hydroxide, etc. The aqueous base wash solution should have a pH of 13.8 or greater. Preferably, the aqueous base wash solution has a pH of 14 or greater; the aqueous base solution is preferably an aqueous solution containing sodium hydroxide, potassium hydroxide, calcium hydroxide, or mixtures thereof or a buffer. A base wash solution having a pH of 13.8 or greater can be prepared by dissolving an appropriate amount of base in water.

[0067] 5 is desired, the wash solution should contact the film for a sufficient time to achieve the desired chemical structure, i.e., a sufficient time to deprotonate one of the nitrogens so that the benzimidazole is in a deprotonated state and form a benzimidazolide salt with the sodium, potassium, or calcium cation. Preferably, one of the nitrogens on at least 90 percent of the imidazole residue repeat units in the polymer is deprotonated, and most preferably one of the nitrogens on at least 95 percent of the imidazole residue repeat units in the polymer is deprotonated, with the anion providing the negative charge (-) to the salt, while some other species are cations providing the positive charge (C+) to the salt.

[0068] Specifically, at least 90 percent, preferably at least 95 percent, of the DAPBI residue repeat units in the polymer are salts having a structure as shown in FIG.

[0069] The films are used in electronic devices requiring higher frequencies, lower voltages, and higher currents, particularly in applications requiring smaller form factors and lower costs. It is believed that the films can provide improved electrical performance to devices, including reduced substrate size. The films have particular application in embedded capacitance applications, as well as slot liners.

[0070] Test Method The dielectric constant (relative permittivity or dK) and dissipation factor (Df or tan delta) were determined from 2 to 10 GHz (or the frequency provided using a rectangular cavity resonator according to ASTM 2520C, IPC-TM-650 2.5.5.3).

[0071] The capacitance of the film was determined with a Hioki IM3536 LCR meter using the method provided with the meter.

[0072] The breakdown voltage of the films was determined according to ASTM D-149.

[0073] Film thickness was measured using a Solartron® thickness gauge model number DR600.

[0074] Film tensile properties (film strength, modulus, and elongation at break) were measured according to ASTM D-882.

[0075] Reference Example The polymer was prepared as follows. The monomers 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI) and paraphenylenediamine (PPD) were combined with a stoichiometric amount of terephthaloyl dichloride (TC1) in a solvent system containing N-methyl-2-pyrrolidone (NMP) solvent and 4.5 wt. % calcium chloride (CaCl) as a solubility enhancer in amounts appropriate to form a copolymer with a 70 / 30 DAPPI / PPD monomer ratio. The monomers polymerized to form the copolymer. After polymerization was complete, the copolymer crumbs were collected, 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. [Example]

[0076] Example 1 Films were prepared from solutions containing a polymer, an inorganic dielectric constant-enhancing additive, and a solvent system. The polymer was the copolymer of the reference example. The inorganic dielectric constant-enhancing additive was barium titanate. The specific barium titanates used in the examples were Bespa BTC-4FB and Bespa BTC-5B, available from Nippon Chemical Industry Co., Ltd. Bespa BTC-4FB contains barium titanate particles having a particle size of approximately 0.5 micrometers, while Bespa BTC-5B contains barium titanate particles having a particle size of approximately 1.0 micrometers. The solvent system was dimethylacetamide (DMAc) with 4 wt. % lithium chloride.

[0077] Nine solutions were prepared by weighing each component listed in Table 1 into a 250 mL glass bottle. Item A was a control that contained no inorganic dielectric constant-enhancing additive and was made into a neat film. Items 1-4 were made using 0.5 μm particles, while items 5-8 were made using 1.0 μm particles.

[0078] The glass bottles were then placed in an industrial paint shaker and mixed until a uniform mixture was observed (approximately 2-8 hours). Each of these solutions was then cast onto a glass plate using a drawdown bar set to a 381 μm gap. The cast solutions were then heated in a nitrogen-purged oven at 90°C for 45 minutes to remove the solvent. After removal from the oven, the glass plate with the cast prefilm was immersed (washed) in a deionized water bath at room temperature for 60 minutes to remove the lithium chloride solubility enhancer. The cast prefilm was then removed from the glass plate and clamped to a clamping frame. Once clamped, it was immediately placed in a vacuum oven at 120°C for 60 minutes to allow the film to fully form, then cooled. After the film and frame had cooled to room temperature, the film was removed from the clamping frame. The films were trimmed and measured. All films were approximately 7 inches by 7 inches square, with a thickness of approximately 9 μm. The properties of the resulting films are shown in Tables 2 and 3.

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] The filled films retained greater than 90% of the strength of the neat film when compared to the control neat film. Specifically, across particle loadings of 13 to 30 weight percent of barium titanate particles having a particle size range of approximately 0.5 to 1.0 micrometers in the filled films, the filled films unexpectedly retained strength in the range of 93.1 to 96.9 percent of the neat film. The filled films also had improved dielectric constants (dielectric constants).

[0083] Example 2 This example illustrates the properties of filled films with widely varying particle loadings. Filled films containing 0.5μ barium titanate particles were fabricated by preparing a dispersion of the desired amounts of polymer, solvent system, and inorganic dielectric constant-enhancing additive, and then casting the dispersion onto a glass substrate. A polymer stock solution was formed by first dissolving the polymer in a solvent system of dimethylacetamide (DMAc) and 4.5 wt% calcium chloride (CaCl). The relative amounts of solvent and polymer were used to obtain a polymer stock solution containing 2.5 wt% polymer in DMAc.

[0084] A number of polymer dispersions for casting films with different concentrations of barium titanate were then prepared by combining the polymer stock solution, additional DMAc solvent, and 0.5μ barium titanate particles. To ensure homogeneous dispersions, even at high particle concentrations, a high-shear mixer was used to mix 50 wt% DMAc, 40 wt% polymer stock solution, and 10 wt% barium titanate particles. This pre-dispersion was then combined with additional amounts of polymer stock solution, followed by further mixing, to form polymer dispersions (casting solutions) with a nominal 3.5 wt% polymer and additive barium titanate particle concentrations for producing films that varied from 30 to 80 wt%.

[0085] Each casting solution was cast onto a glass plate using a drawdown bar. The casting solution on the glass plate was then heated on a large hot plate at 80°C for 5 minutes to remove the solvent and form a cast film on the glass plate. The glass plate and cast film were then removed from the oven, allowed to cool to room temperature, and subsequently washed in a deionized water bath at room temperature for 60 minutes to remove the solubility enhancer. The cast film was then removed from the glass plate and secured to a stationary frame. Once secured, the film and frame were placed in a nitrogen-purged oven at 120°C for 60 minutes. The film and frame were then allowed to cool to room temperature, after which the filled film was removed from the frame. The filled film was then trimmed to form a square film sample approximately 12 inches by 12 inches. The properties of the resulting filled films are shown in Tables 4 and 5. Item A, the neat film from Example 1, was used as a control.

[0086] Filled films with particle loadings of 30 to 75 wt. % unexpectedly retained strength in the range of 76 to 98 percent of the neat film when compared to the neat film control. The filled films also had improved dielectric constants (dielectric constants).

[0087] [Table 4]

[0088] [Table 5]

[0089] Example 3 This embodiment requires that the filled film has a capacitance of at least 15 nF / inch. 2This shows that the filled film samples can have a capacitance of 50 and 60 weight percent of 0.5 micrometer barium titanate particles in a manner similar to Example 2. The filled films had a nominal thickness of 2 micrometers. Three-inch diameter circles were cut from the film samples and then sputter-coated on both sides with gold palladium (AuPd) and then tested for capacitance. The properties of the filled films are shown in Table 6.

[0090] [Table 6]

[0091] Example 4 This example further illustrates the capacitance and breakdown voltage characteristics of several filled film samples. Film samples with 50 weight percent barium titanate particles were prepared and tested according to Example 3, except that three different film samples were made from barium titanate particles with three different particle diameters: 0.6 micrometers, 0.3 micrometers, and 0.15 micrometers. The filled films had a nominal thickness of 2 micrometers. Film properties are shown in Table 7.

[0092] [Table 7]

[0093] Example 5 This example illustrates a filled polymer film in which an inorganic dielectric constant-enhancing additive is added to a polymer having imidazole groups in a deprotonated state. Example 2 is repeated, but rather than washing the film with deionized water, the film is washed with an aqueous sodium hydroxide wash solution at a pH of 14. This provides a polymer film in which the nitrogen in the benzimidazole is believed to be in a deprotonated state, forming a benzimidazolide structure in which at least 95% of the imidazole residue repeat units in the polymer are salts, as shown in Figure 5. In this particular example, the benzimidazolide is a salt, and one of the nitrogens in the imidazole residue is an anion that provides a negative charge (-) to the salt, while the positive charge to the salt is provided by a sodium cation. Table 8 compares the dK values ​​of the neutralized imidazole film (labeled Ex. 2) neutralized in Example 2 and having the neutral structure shown in Figure 4 with the predicted dK values ​​of the benzimidazolide film (labeled Ex. 5), demonstrating the improved dielectric constant (dielectric constant) of the filled film made with benzimidazolide.

[0094] [Table 8]

Claims

1. 1. A filled polymer film comprising a polymer and an inorganic dielectric constant enhancing additive, the polymer comprises imidazole groups; the filled polymer film having 12 to 75 weight percent of the inorganic dielectric constant enhancing additive, based on the combined weight of the polymer and the inorganic dielectric constant enhancing additive in the filled polymer film; and A filled polymer film, wherein the filled polymer film has a filled film strength that is 70 to 100 percent of the neat film strength of a polymer film having the same thickness made from the same polymer but without the inorganic dielectric constant enhancing additive.

2. 10. The filled polymeric film of claim 1 comprising 30 to 75 weight percent of said inorganic dielectric constant enhancing additive.

3. 3. The filled polymeric film of claim 2 comprising 40 to 75 weight percent of said inorganic dielectric constant enhancing additive.

4. 4. The filled polymeric film of claim 3 comprising 50 to 75 weight percent of said inorganic dielectric constant enhancing additive.

5. 5. The filled polymer film of any one of claims 1 to 4, wherein the filled film strength is 75 to 100 percent of the neat film strength of a polymer film having the same thickness made from the same polymer but without the inorganic dielectric constant enhancing additive.

6. 6. The filled polymer film of claim 5, wherein the filled film strength is 80 to 100 percent of the neat film strength of a polymer film having the same thickness made from the same polymer but without the inorganic dielectric constant enhancing additive.

7. The filled polymer film of any one of claims 1 to 6, wherein the filled polymer film has a thickness of from 2 to 25 micrometers.

8. 8. The filled polymeric film of claim 7, wherein the filled polymeric film has a thickness of 2 to 10 micrometers.

9. 9. The filled polymeric film of claim 8, wherein the filled polymeric film has a thickness of 2 to 5 micrometers.

10. 10. The filled polymer film of any one of claims 1 to 9, wherein the filled polymer film has a dielectric constant of at least 5.8 or greater at 2 GHz for a 25 micrometer thick sample.

11. 11. The filled polymer film of claim 10, wherein the filled polymer film has a dielectric constant of at least 6.2 or greater at 2 GHz for a 25 micrometer thick sample.

12. The filled polymeric film of any one of claims 1 to 11, wherein the inorganic dielectric constant enhancing additive comprises barium titanate.

13. The filled polymeric film of any one of claims 1 to 12, wherein the inorganic dielectric constant enhancing additive is a single inorganic additive.

14. 14. The filled polymeric film of any one of claims 1 to 13, wherein the polymer comprising imidazole groups comprises 5(6)-amino-2-(p-aminophenyl)benzimidazole.

15. 15. The filled polymer film of claim 14, wherein the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride.

16. 16. The filled polymeric film of claim 15, wherein the aromatic diamine is para-phenylenediamine.

17. 17. The filled polymeric film of claim 15 or 16, wherein the aromatic diacid chloride is terephthaloyl dichloride.

18. 18. The filled polymeric film of any one of claims 15 to 17 having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of from 30 / 70 to 85 / 15.

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

20. The filled polymeric film of any one of claims 14 to 18 comprising 50 mole percent or more of 5(6)-amino-2-(p-aminophenyl)benzimidazole.

21. 21. The filled polymeric film of any one of claims 14 to 20, wherein the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacid chloride in the form of a polymer having polymer chains comprising a salt of Formula I, where C+ is a sodium, potassium, or calcium cation. 【Chemical 1】

22. 22. The polymer film of claim 21, wherein at least 90% of the imidazole residue repeat units in the polymer are the salt of Formula I.

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