Polyimide films

Abstract

To provide a filled polyimide film made using a chemical conversion process to fully imidize the film and having a reduced void concentration.SOLUTION: A polyimide film comprises: a substantially chemically converted polyimide derived from at least 10 mol%, based on the total dianhydride content of the polyimide, of an aromatic dianhydride having two or more phenyl groups, and at least 10 mol%, based on the total diamine content of the polyimide, of an aromatic diamine having two or more phenyl groups; and at least 10 vol.%, based on the total volume of the polyimide film, of an inorganic filler. The two or more phenyl groups in the aromatic dianhydride and the aromatic diamine share no carbon atoms with each other. Less than 50 vol.%, based on the total inorganic filler, of the inorganic filler has diameters less than 100 nm in all three dimensions. The void ratio of the film is 0.75 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The field of this disclosure is polyimide films. [Background technology]

[0002] Polyimide films produced using chemical imidation processes, also known as chemically converted polyimide films, are considerably less expensive than those derived from (thermally converted) thermal imidation processes. This is a result of the much higher line speeds and integrated process steps (casting and imidation) used in chemical conversion processes, which facilitate the imidation of polyamic acids to polyimides using catalysts.

[0003] However, traditionally, chemically converted films with fillers contain macroscopic voids. These voids are considered undesirable and, in terms of conductivity, they may be related to the disruption of connectivity between filler components in the composite film system, resulting in inadequate transport properties for these films compared to similar films manufactured using thermal conversion processes. Attempts to produce highly filled polyimide films using chemical imidization processes result in films with significantly lower conductivity. In addition to electrical and thermal properties, the presence of voids can play a role in the deterioration of mechanical and / or optical properties in filler-containing films.

[0004] (Patent Document 1) provides a hybrid process for filler-filled films that attempts to take advantage of the benefits of both chemical and thermal imidization processes and to avoid void formation by first partially imidizing the polyamic acid using a chemical process and then finishing the imidization using a thermal process. By limiting the chemical conversion to less than 50% imidization, the void content in the film is maintained at an intermediate but relatively low level, allowing some conductive paths to form between the conductive filler particles, resulting in conductivity observations. However, the surface resistivity of films produced using this hybrid approach is significantly higher than that of films produced using a thermal imidization process.

[0005] A polyimide film with fillers that is manufactured by completely imidizing the film using a chemical conversion process and has a reduced void concentration is highly desirable. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 4,986,946 [Patent Document 2] U.S. Patent No. 5,166,308 [Patent Document 3] U.S. Patent No. 5,298,331 [Overview of the Initiative] [Means for solving the problem]

[0007] In the first embodiment, the polyimide film comprises a substantially chemically converted polyimide and at least 10 volume percent of inorganic filler based on the total volume of the polyimide film. The substantially chemically converted polyimide is derived from at least 10 mole percent of aromatic dianhydrides having two or more phenyl groups based on the total dianhydride content of the polyimide, and at least 10 mole percent of aromatic diamines having two or more phenyl groups based on the total diamine content of the polyimide. The two or more phenyl groups in the aromatic dianhydride do not share carbon atoms with each other. The two or more phenyl groups in the aromatic diamine do not share carbon atoms with each other. The inorganic filler, less than 50 volume percent based on the total inorganic filler, has a diameter of less than 100 nm in all three dimensions. The porosity of the polyimide film is 0.75 or less.

[0008] In the second embodiment, the polyimide film comprises a substantially chemically converted polyimide and at least 10 volume percent of organic filler based on the total volume of the polyimide film. The substantially chemically converted polyimide is derived from at least 10 mole percent of aromatic dianhydrides having two or more phenyl groups based on the total dianhydride content of the polyimide, and at least 10 mole percent of aromatic diamines having two or more phenyl groups based on the total diamine content of the polyimide. The two or more phenyl groups in the aromatic dianhydride do not share carbon atoms with each other. The two or more phenyl groups in the aromatic diamine do not share carbon atoms with each other. The organic filler, less than 50 volume percent based on the total organic filler, has a diameter of less than 100 nm in all three dimensions. The porosity of the polyimide film is 1.0 or less.

[0009] Substantially chemically converted polyimide films with more than 10 volume percent fillers and low void concentrations can be produced by careful selection of dianhydride and diamine monomers used for the polyimide backbone, enabling the production of chemically converted polyimide films with transport properties such as good thermal conductivity and electrical conductivity, as well as those found in thermally converted polyimide films. [Modes for carrying out the invention]

[0010] As used herein, the term “substantially chemically converted” means that the polyimide is imidized to 75%, 80%, 85%, 90%, or 95% or more by a process that incorporates conversion chemicals (i.e., catalysts and dehydrating agents) and involves casting or coating a solvation mixture (polyamic acid casting solution) onto a support to give a partially imidized gel film, and then heating in an oven using convective and radiant heat to remove the solvent and complete the imidation. Percent imidation is measured at 1492 cm⁻¹ in Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR) spectroscopy. -1 1365 cm (for aromatic expansion and contraction used as an internal standard) -1 This can be measured by comparing the strength ratio of (polyimide CN) samples and comparing it to that of samples prepared using a standard curing method, which is defined as 100% cured.

[0011] As used herein, the term “gel film” refers to a layer of polyimide material containing volatile substances, primarily solvents, to the extent that the polyimide is gel-swollen, plasticized, and rubbery. The volatile substance content is typically in the range of 80–90 wt% of the gel film, and the polymer content is typically in the range of 10–20 wt%. The film becomes self-supporting at the gel film stage, and it can be peeled off from a cast and heated support. Gel films generally have an amide acid to imide ratio of 90:10 to 10:90. This is different from “green films,” which are either entirely polyamidic acid or have a very low polyimide content. Green films generally contain about 50–80 wt% polymer and 20–50 wt% solvent and are strong enough to be self-supporting.

[0012] As used herein, the term “void” refers to the volume of space within a solid that does not essentially contain any of the components constituting the solid. For example, in a polymer film composition having a polymer and a filler, any space within the boundaries of the film's surface and edges that does not contain the polymer or filler is a void. Voids can have any number of shapes and sizes, and an object can have any number of voids or no voids at all. Voids may be on or near the surface of a solid and may be exposed to the surrounding environment. The volume percentage of voids in a solid can be derived from the dry bulk density and theoretical void-free density of the object, as described below. The theoretical void-free density is calculated using the law of ideal mixing (see below). As used herein, the term “porosity” refers to the ratio of the total volume percentage of voids in an object divided by the total volume percentage of filler in the object, where the total volume of filler is calculated based on the weight and reported density of the filler. The voids found within the filler particles are included as part of the total volume of voids in the solid material.

[0013] Depending on the context, “diamine” as used herein is intended to mean (i) an unreacted form (i.e., a diamine monomer); (ii) a partially reacted form (i.e., a portion or more of an oligomer or other polymer precursor derived from or otherwise resulting from a diamine monomer); or (iii) a fully reacted form (a portion or more of a polymer derived from or otherwise resulting from a diamine monomer). Diamines can be functionalized in one or more portions depending on the particular embodiment selected in the implementation of the present invention.

[0014] In practice, the term “diamine” is not intended to be limited (or interpreted literally) in terms of the number of amine moieties in a diamine component. For example, (ii) and (iii) above include polymer materials that may have two, one, or zero amine moieties. Instead, diamines can be functionalized with additional amine moieties (in addition to the amine moieties at the ends of the monomer that react with the dianhydride to grow the polymer chain). Such additional amine moieties may be used to crosslink the polymer or to impart other functional groups to the polymer.

[0015] Similarly, the term “dianhydride,” as used herein, is intended to mean a component that reacts with (and is complementary to) a diamine and, in combination, can react to form an intermediate (which can then be cured into a polymer). Depending on the context, “anhydride,” as used herein, can also mean a precursor of the anhydride moiety, such as (i) a pair of carboxylic acid groups (which can be converted to an anhydride by dehydration or a similar type of reaction); or (ii) an acid halide (e.g., acid chloride) ester functional group (or any other functional group currently known or to be developed in the future) that can be converted to an anhydride functional group.

[0016] Depending on the context, "dianhydride" can mean (i) an unreacted form (i.e., a dianhydride monomer, regardless of whether the anhydride functional group is in the true anhydride form or the precursor anhydride form as discussed in the preceding paragraph above); (ii) a partially reacted form (i.e., an oligomer reacted from a dianhydride monomer or other part or parts of a partially reacted or precursor polymer composition otherwise resulting from a dianhydride monomer), or (iii) a fully reacted form (a part or parts of a polymer derived from a dianhydride monomer or otherwise resulting from a dianhydride).

[0017] The dianhydride can be functionalized in one or more parts depending on the particular embodiment selected in the practice of the present invention. In fact, the term "dianhydride" is not intended to be limiting (or literally interpreted) with respect to the number of anhydride parts in the dianhydride component. For example, (i), (ii), and (iii) in the above paragraph include organic substances that can have two, one, or zero anhydride parts depending on whether the anhydride is in a precursor state or a reacted state. Instead, the dianhydride component can be functionalized with additional anhydride-type parts (in addition to the anhydride parts that react with diamine to give a polymer). Such additional anhydride parts could be used to crosslink the polymer or to give other functional groups to the polymer.

[0018] Any one of a number of polyimide manufacturing processes can be used to prepare a polymer film. It would be impossible to discuss or describe all possible manufacturing processes useful in the practice of the present invention. It should be fully understood that the monomer systems of the present invention can provide the above advantageous properties in various manufacturing processes. The compositions of the present invention can be manufactured as described herein and can be readily manufactured in any one of many (presumably countless) ways by those skilled in the art using any conventional or non-conventional manufacturing technique.

[0019] Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein.

[0020] Where a quantity, concentration, or other value or parameter is shown as a range, preferred range, or list of upper and lower preferred values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper limit range or preferred value and any lower limit range or preferred value, whether or not the ranges are individually disclosed. When numerical values of a range are recited herein, unless otherwise specified, the range is intended to include its endpoints, as well as all integers and fractions within that range. The scope of the present invention is not intended to be limited to the specific values recited when defining a range.

[0021] When describing a particular polymer, it should be understood that the Applicant may refer to the polymer in terms of the monomers used to produce the polymer or the amounts of monomers used to produce the polymer. Such a description may not include the specific nomenclature used to describe the final polymer or may not contain product-by-process terminology, but any such reference to monomers and amounts is to be construed as meaning that the polymer is made from those monomers or amounts of monomers, and the corresponding polymer and its composition.

[0022] The materials, methods, and examples herein are illustrative only and are not intended to be limiting except as specifically stated.

[0023] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof are intended to have non-exclusive inclusion. For example, a method, process, article, or apparatus that includes a list of elements may not necessarily be limited to those elements alone, and may include other elements that are not explicitly listed or that are inherent to such method, process, article, or apparatus. Furthermore, unless explicitly stated otherwise, “or” means comprehensive or not, not exclusive or. For example, condition A or B is satisfied by either one of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); and both A and B are true (or exist).

[0024] Furthermore, the use of “one (a)” or “one (an)” is used to describe the elements and components of the present invention. This is done solely for convenience and to illustrate the general meaning of the present invention. This description should be read as including one or at least one, and the singular also includes the plural unless it is clear that it does not.

[0025] The terms First, Second, Third, etc., may be used herein to describe various elements, components, regions, layers, and / or areas, but it will be understood that these elements, components, regions, layers, and / or areas should not be limited by these terms. These terms are used merely to distinguish one element, component, region, layer, and / or area from another element, component, region, layer, and / or area. Thus, a First element, component, region, layer, and / or area may be referred to as a Second element, component, region, layer, and / or area without departing from the teachings of the present invention. Similarly, the terms "top" and "bottom" are merely relative to each other. It will be understood that when an element, component, layer, etc., is inverted, what was the "bottom" before inversion will be the "top" after inversion, and vice versa. When an element is said to be "on top of" or "placed on top of" another element, it means that it is located above or below a part of an object, but it does not inherently mean that it is located above the part of the object based on the direction of gravity; it could be directly above the other element, or an intervening element could be present between them. In contrast, when an element is said to be "directly on top of" or "placed directly on top of" another element, no intervening element is present.

[0026] Furthermore, when one element, component, region, layer, and / or area is said to be "between" two elements, components, regions, layers, and / or areas, it will also be understood that it can be the sole element, component, region, layer, and / or area between the two elements, components, regions, layers, and / or areas, or there may be one or more intervening elements, components, regions, layers, and / or areas.

[0027] Organic solvents A useful organic solvent for the synthesis of the polyimide of the present invention is preferably capable of dissolving the polyimide precursor material. Such a solvent should also have a relatively low boiling point, such as below 225°C, so that the polymer can be dried at a moderate (i.e., more convenient and less costly) temperature. Boiling points below 210, 205, 200, 195, 190, or 180°C are preferred.

[0028] Useful organic solvents include N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), methyl ethyl ketone (MEK), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetramethylurea (TMU), glycol ethyl ether, diethylene glycol diethyl ether, 1,2-dimethoxyethane (monoglym), diethylene glycol dimethyl ether (diglym), 1,2-bis-(2-methoxyethoxy)ethane (triglycerim), gamma-butyrolactone, and bis-(2-methoxyethyl) ether, tetrahydrofuran (THF), ethyl acetate, hydroxyethyl acetate glycol monoacetate, acetone, and mixtures thereof. In one embodiment, preferred solvents include N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc).

[0029] Diamine In one embodiment, an aromatic diamine having two or more phenyl groups can be used to form a polyimide, where the two or more phenyl groups in the aromatic diamine do not share carbon atoms with each other. These flexible bonds provide more conformational degrees of freedom to the polyimide skeleton formed from the diamine, thereby limiting the formation of voids in the polyimide derived from these monomers.Aromatic diamines having two or more phenyl groups linked by flexible bonds include 2,2'-bis(trifluoromethyl)benzidine (TFMB), 2,2'-bis-(4-aminophenyl)hexafluoropropane, 4,4'-diamino-2,2'-trifluoromethyldiphenyl oxide, 3,3'-diamino-5,5'-trifluoromethyldiphenyl oxide, 9,9'-bis(4-aminophenyl)fluorene, 4,4'-trifluoromethyl-2,2'-diaminobiphenyl, and 4,4'-oxy-bis[2-trifluoromethyl [(1,2,4-OBABTF), 4,4'-oxy-bis[3-trifluoromethyl)benzeneamine], 4,4'-thiobis[(2-trifluoromethyl)benzeneamine], 4,4'-thiobis[(3-trifluoromethyl)benzeneamine], 4,4'-sulfoxyl-bis[(2-trifluoromethyl)benzeneamine], 4,4'-sulfoxyl-bis[(3-trifluoromethyl)benzeneamine], 4,4'-keto-bis[(2-trifluoromethyl)benzeneamine], 1,1-bis[4'-(4"- [amino-2"-trifluoromethylphenoxy)phenyl]cyclopentane, 1,1-bis[4'-(4"-amino-2"-trifluoromethylphenoxy)phenyl]cyclohexane, 2-trifluoromethyl-4,4'-diaminodiphenyl ether; 1,4-(2'-trifluoromethyl-4',4"-diaminodiphenoxy)benzene, 1,4-bis(4'-aminophenoxy)-2-[(3',5'-ditrifluoromethyl)phenyl]benzene (6F-amine), 1,4-bis[2'-cyano-3'("4-aminophenoxy Examples of fluorinated aromatic diamines include c)phenoxy]-2-[(3',5'-ditrifluoromethyl)phenyl]benzene (6FC-diamine), 3,5-diamino-4-methyl-2',3',5',6'-tetrafluoro-4'-trifluoromethyldiphenyl oxide, 2,2-bis[4(4-aminophenoxy)phenyl]phthalein-3',5'-bis(trifluoromethyl)anilide (6FADAP), and 3,3',5,5'-tetrafluoro-4,4'-diamino-diphenylmethane (TFDAM).

[0030] Other useful diamines having two or more phenyl groups linked by flexible bonds include 4,4'-diaminobiphenyl, 4,4''-diaminoterphenyl, 4,4'-diaminobenzanilide (DABA), 4,4'-diaminophenylbenzoate, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), and 4,4' Examples include -bis(4-aminophenoxy)biphenyl (BAPB), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 4,4'-isopropylidenedianiline, 2,2'-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4-aminophenyl-3-aminobenzoate, bis(p-beta-amino-t-butylphenyl) ether, and p-bis-2-(2-methyl-4-aminopentyl)benzene. In one embodiment, the diamine is a triamine such as N,N-bis(4-aminophenyl)-n-butylamine, N,N-bis(4-aminophenyl)methylamine, or N,N-bis(4-aminophenyl)aniline.

[0031] Other useful diamines having two or more phenyl groups linked by flexible bonds include 1,2-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene (RODA), 1,2-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1-(4-aminophenoxy)-4-(3-aminophenoxy)benzene, 2,2-bis(4-[4-aminophenoxy]phenyl)propane (BAPP), and 2,2'-bis(4-phenoxyaniline)isopropylidene. In one embodiment, the substantially chemically converted polyimide can be derived from an aromatic diamine having at least 10 mol%, at least 20 mol%, at least 30 mol%, at least 40 mol%, or at least 50 mol% of two or more phenyl groups, where the two or more phenyl groups in the aromatic diamine do not share carbon atoms with each other.

[0032] In one embodiment, additional diamines for forming a polyimide include monomers that do not have two or more phenyl groups and are linked by flexible bonds. Examples of these additional diamines include p-phenylenediamine (PPD), m-phenylenediamine (MPD), 2,5-dimethyl-1,4-diaminobenzene, 2,5-dimethyl-1,4-phenylenediamine (DPX), 1,4-naphthalenediamine, 1,5-naphthalenediamine, 1,5-diaminonaphthalene, m-xylylenediamine, and p-xylylenediamine.

[0033] Other useful additional diamines for forming polyimides include aliphatic diamines such as 1,2-diaminoethane, 1,6-diaminohexane (HMD), 1,4-diaminobutane, 1,5-diaminopentane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane (DMD), 1,11-diaminoundecane, 1,12-diaminododecane (DDD), 1,16-hexadecamethylenediamine, 1,3-bis(3-aminopropyl)-tetramethyldisiloxane, trans-1,4-diaminocyclohexane (CHDA), isophoronediamine (IPDA), bicyclo[2.2.2]octane-1,4-diamine, and combinations thereof. Other suitable aliphatic diamines for carrying out the present invention include those having 6 to 12 carbon atoms, or combinations of long-chain and short-chain diamines, as long as both polymer developmentability and flexibility are maintained. Long-chain aliphatic diamines can enhance flexibility.

[0034] Other useful additional diamines for forming polyimides include alicyclic diamines (which may be fully or partially saturated), such as cyclobutanediamines (e.g., cis- and trans-1,3-diaminocyclobutane, 6-amino-3-azaspiro[3.3]heptane, and 3,6-diaminospiro[3.3]heptane), bicyclo[2.2.1]heptane-1,4-diamine, isophoronediamine, and bicyclo[2.2.2]octane-1,4-diamine. Other alicyclic diamines include cis-1,4-cyclohexanediamine, trans-1,4-cyclohexanediamine, 1,4-bis(aminomethyl)cyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methyl-cyclohexylamine), and bis(aminomethyl)norbornane.

[0035] dianhydride In one embodiment, aromatic dianhydrides having two or more phenyl groups can be used to form polyimides, where the two or more phenyl groups in the aromatic dianhydride do not share carbon atoms with each other. As described above for diamines, these flexible bonds provide more conformational freedom to the polyimide skeleton formed from the dianhydrides, thereby limiting the formation of voids in the polyimides derived from these monomers. Dianhydrides can be used in their tetraacid form (or as mono, di, tri, or tetraesters of tetraacids) or as their diesteric acid halides (chlorides). However, in some embodiments, the dianhydride form may be preferred because it is generally more reactive than the acid or ester.

[0036] Suitable aromatic dianhydrides having two or more phenyl groups linked by flexible bonds include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzimidazole dianhydride, 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzoxazole dianhydride, 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzothiazole dianhydride, and 2,2',3,3'-benzophenone dianhydride. Tracarboxylic acid dianhydride, 2,3,3',4'-benzophenonetetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA), 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 4,4'-thio-diphthalic acid anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfoxide dianhydride (DSDA), bis(3,4-dicarboxyphenyl) Nyloxadiazole-1,3,4)-p-phenylene dianhydride, bis(3,4-dicarboxyphenyl)-2,5-oxadiazole-1,3,4-dianhydride, bis(3',4'-dicarboxydiphenyl ether)-2,5-oxadiazole-1,3,4-dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), bis(3,4-dicarboxyphenyl)thioether dianhydride, bisphenol A dianhydride (BPADA), bisphenol S dianhydride, bis-1,3-isobenzofrandione, 1 Examples include 4-bis(4,4'-oxyphthalic anhydride)benzene, bis(3,4-dicarboxyphenyl)methane dianhydride, perylene-3,4,9,10-tetracarboxylic acid dianhydride, 1,3-bis(4,4'-oxydiphthalic anhydride)benzene, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic acid dianhydride.In one embodiment, the substantially chemically converted polyimide can be derived from an aromatic dianhydride having at least 10 mol%, at least 20 mol%, at least 30 mol%, or at least 50 mol%, of two or more phenyl groups, where the two or more phenyl groups in the aromatic dianhydride do not share carbon atoms with each other.

[0037] In one embodiment, additional dianhydrides for forming a polyimide include monomers that do not have two or more phenyl groups linked by flexible bonds. These additional dianhydrides include 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, bicyclo-[2,2,2]-octen-(7)-2,3,5,6-tetracarboxylic acid-2,3,5,6-dianhydride, cyclopentadienyltetracarboxylic acid dianhydride, ethylenetetracarboxylic acid dianhydride, pyromellitic acid dianhydride (PMDA), tetrahydrofurantetracarboxylic acid dianhydride, 2, Examples include 6-dichlorophthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, phenanthrene-1,8,9,10-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, and thiophene-2,3,4,5-tetracarboxylic dianhydride.

[0038] In one embodiment, additional dianhydrides for forming polyimides include alicyclic dianhydrides such as cyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (CBDA), 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, 1,2,3,4-cyclohexanetetracarboxylic acid dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride (CPDA), hexahydro-4,8-ethano-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetron (BODA), 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride (TCA), and meso-butane-1,2,3,4-tetracarboxylic acid dianhydride.

[0039] In one embodiment, the substantially chemically converted polyimide has a weight-average molecular weight (M) of 100,000 daltons or more, 150,000 daltons or more, 200,000 daltons or more, or 250,000 daltons or more. w ) can have.

[0040] Imidation catalyst In one embodiment, an imidation catalyst (sometimes called an "imidation accelerator") can be used as a conversion chemical that can help lower the imidation temperature and shorten the imidation time for forming polyimides. The polyamic acid casting solution of the present invention comprises both a polyamic acid solution combined with a certain amount of a conversion chemical. Conversion chemicals found to be useful in the present invention include, but are not limited to, (i) one or more dehydrating agents and / or co-catalysts, such as aliphatic acid anhydrides (acetic anhydride, trifluoroacetic anhydride, propionic anhydride, monochloroacetic anhydride, bromoadipic anhydride, etc.) and aromatic acid anhydrides; and (ii) one or more imidation catalysts, such as aliphatic tertiary amines (triethylamine, etc.), aromatic tertiary amines (dimethylaniline, N,N-dimethylbenzylamine, etc.) and heterocyclic tertiary amines (pyridine, alpha, beta, gamma, picoline, 3,5-lutidine, 3,4-lutidine, isoquinoline, etc.) and guanidines (e.g., tetramethylguanidine). In one embodiment, the imidation catalyst does not contain diazole. Other useful dehydrating agents include diacetyl oxide, butyryl oxide, benzoyl oxide, 1,3-dichlorohexylcarbodiimide, N,N-dicyclohexylcarbodiimide, benzenesulfonyl chloride, thionyl chloride, and phosphorus pentoxide. In some embodiments, the dehydrating agent can also function as a catalyst to increase the reaction rate for imidation. The anhydride used to dehydrate the material is typically used in a slightly molar excess of the amount of amide acid groups present in the polyamic acid solution. In one embodiment, the amount of dehydrating agent used is typically about 2.0 to 4.0 moles per equivalent of the polyamic acid formula unit. Generally, the same amount of tertiary amine catalyst is used. The ratio of these catalysts in the polyamic acid solution and their concentrations will affect the imidation reaction rate and film properties. A polyimide film having substantially chemically converted polyimide may have an imidation catalyst present in the polyimide film in amounts ranging from parts per billion (ppb) to 1 wt%, 10 ppb to 0.1 wt%, or 100 ppb to 0.01 wt%.

[0041] filling material In one embodiment, fillers for polyimide films include inorganic fillers, organic fillers, or mixtures thereof. In some embodiments, the fillers are spherical, rectangular, needle-shaped, or plate-shaped. Examples of inorganic fillers include thermally conductive fillers, metal oxides, inorganic nitrides, and metal carbides, as well as conductive fillers such as metals (e.g., gold, silver, copper, etc.). In one embodiment, examples of inorganic fillers include metal oxides such as diamond, clay, talc, sepiolite, mica, dicalcium phosphate, magnetic metal oxides, transparent conductive oxides, and fumed metal oxides. In one embodiment, examples of inorganic fillers include inorganic oxides such as silicon, aluminum, and titanium oxides, hollow (porous) silicon oxide, antimony oxide, zirconium oxide, indium tin oxide, antimony tin oxide, mixed titanium / tin / zirconium oxide, and binary, ternary, quaternary, and higher-order oxides of one or more cations selected from silicon, titanium, aluminum, antimony, zirconium, indium, tin, zinc, niobium, and tantalum. In one embodiment, particle composite materials (e.g., one or more core / shell structures) can be used in which one oxide encapsulates another oxide within a single particle.

[0042] In one embodiment, examples of inorganic fillers include other ceramic compounds such as boron nitride, aluminum nitride, ternary or more compounds containing boron, aluminum and nitrogen, gallium nitride, silicon nitride, aluminum nitride, zinc selenide, zinc sulfide, zinc telluride, silicon carbide, and combinations thereof, or higher-order compounds containing multiple cations and multiple anions.

[0043] In one embodiment, examples of organic fillers include polyaniline, polythiophene, polypyrrole, polyphenylene vinylene, polydialkylfluorene, carbon black, graphite, graphene, multi-walled and single-walled carbon nanotubes, other nanotube structures, and carbon nanofibers. In one embodiment, low-coloring organic fillers such as polydialkylfluorene can also be used.

[0044] In one embodiment, the filler for the polyimide film has a median particle size in the range of 0.1 to 10 μm, 0.1 to 5 μm, 0.2 to 5 μm, or 0.2 to 3 μm, d 50 It may have the following characteristics. The filler size can be measured using a laser particle size analyzer when the filler is dispersed in an organic solvent (optionally with the help of a dispersant, adhesion promoter, and / or coupling agent). Median particle size, d 50This is the equivalent spherical diameter based on the median volume distribution of the particles. If the median particle size is smaller than 0.1 μm, the filler particles may tend to aggregate or become unstable in the organic solvent used in the production of the polyimide. If the median particle size of the aggregated particles exceeds 10 μm, the dispersion system of the filler components in the polyimide film may be too heterogeneous (or unusually large relative to the film thickness). In one embodiment, the ratio of the median particle size of the filler to the thickness of the polyimide film in which the filler is contained is less than 0.30, less than 0.29, less than 0.28, less than 0.27, less than 0.26, less than 0.25, or less than 0.20 to 1. A relatively non-homogeneous dispersion system of filler components in the film may result in insufficient mechanical elongation of the film, insufficient flex life of the film, and / or low dielectric strength. In one embodiment, the filler may require extensive milling and filtration to break up undesirable particle aggregation, which is typical when attempting to disperse several fillers in a polymer matrix. Such milling and filtration can be costly and may not remove all undesirable aggregates. In one embodiment, the average aspect ratio of the packing material can be 1 or greater. In some embodiments, the packing material is selected from the group consisting of acicular packing material, fibrous packing material, plate-like packing material, polymer fibers, and mixtures thereof. In one embodiment, the packing material can have an aspect ratio of at least 1, at least 2, at least 4, at least 6, at least 8, at least 10, at least 12, at least 15, at least 25, at least 50, at least 100, at least 200, or at least 300 to 1. In some embodiments, the d is less than 100 nm in all three dimensions. 50 One or more additional fillers having the same properties can be used in blends of different fillers.

[0045] In one embodiment, examples of electrically insulating thermally conductive fillers include metal oxides such as diamond, clay, talc, sepiolite, mica, dicalcium phosphate, magnetic metal oxides, transparent conductive oxides, and fumed metal oxides. In one embodiment, examples of inorganic fillers include inorganic oxides such as oxides of silicon, aluminum, zinc, and titanium, hollow (porous) silicon oxide, antimony oxide, zirconium oxide, and binary, ternary, quaternary, and higher-order oxides of one or more cations selected from silicon, titanium, aluminum, antimony, zirconium, indium, tin, zinc, niobium, and tantalum. In one embodiment, particle composite materials (e.g., one or more core / shell structures) can be used in which one oxide encapsulates another oxide within a single particle.

[0046] In one embodiment, examples of thermally conductive fillers include other ceramic compounds such as boron nitride, aluminum nitride, ternary or more compounds containing boron, aluminum and nitrogen, gallium nitride, silicon nitride, aluminum nitride, zinc selenide, zinc sulfide, zinc telluride, silicon carbide, and combinations thereof, or higher-order compounds containing multiple cations and multiple anions, as well as oxycarbides and oxynitrides.

[0047] In one embodiment, the conductive filler may be a metal (e.g., gold, silver, copper, etc.), a conductive mixed metal oxide (e.g., copper oxide, oxide superconductor, indium tin oxide, antimony tin oxide, mixed titanium / tin / zirconium oxide, etc.), an organic filler such as polyaniline, polythiophene, polypyrrole, polyphenylene vinylene, polydialkylfluorene, carbon black, graphite, graphene, multi-walled and single-walled carbon nanotubes, and other nanotube structures, as well as carbon nanofibers. In one embodiment, a low-coloring organic filler such as polydialkylfluorene may also be used. In one embodiment, a particle composite material (e.g., one or more core / shell structures) may be used in which one type of filler encapsulates another type of oxide in one particle. For example, an electrically insulating thermal conductive material may be used as the core, and the conductive material may form the shell of the composite particle.

[0048] In one embodiment, the conductive filler is carbon black. In one embodiment, the conductive filler is selected from the group consisting of acetylene black, ultra-abrasive furnace black, conductive furnace black, conductive channel-type black, carbon nanotubes, carbon fibers, fine thermal black, and mixtures thereof. As described above for low-conductivity carbon black, the oxygen composite on the surface of the carbon particles functions as an electrical insulating layer. Therefore, low volatility is generally desirable for high conductivity. However, it is also necessary to consider the difficulty of dispersing carbon black. Surface oxidation increases the deaggregation and dispersion of carbon black. In some embodiments, when the conductive filler is carbon black, the carbon black has a volatility of 1% or less.

[0049] In some embodiments, the filler may include a mixture or blend of fillers having any number of particle types, particle sizes and particle shapes, wherein the mixture or blend may be of the same type or different types of fillers. In some embodiments, the filler may include submicron fillers having a particle size of 100 nm or less in all three dimensions, in less than 50 volume percent of the total amount of filler in the polyimide film. In other embodiments, the filler may include submicron fillers having a particle size of 100 nm or less in all three dimensions, in less than 40, less than 30, less than 20, or less than 10 volume percent of the total amount of filler in the polyimide film. In one embodiment, the submicron filler may include colloidal nanoparticles. The submicron filler may include compositions and particle shapes as described above for inorganic or organic fillers.

[0050] In one embodiment, the filler can be coated with a coupling agent. For example, filler particles can be coated with an acrylic or methacrylic coupling agent derived from aminosilane, phenylsilane, or the corresponding alkoxysilane. A trimethylsilyl surface capping agent can be introduced to the particle surface by reaction of the filler with hexamethyldisilazane. In one embodiment, the filler can be coated with a dispersant. In one embodiment, the filler can be coated with a combination of a coupling agent and a dispersant. Alternatively, the coupling agent, dispersant, or a combination thereof can be incorporated directly into the polymer film and not necessarily coated on the filler.

[0051] Polyimide film In one embodiment, a polyimide film can be produced using a chemical conversion process in which a diamine and a dianhydride (monomer or other polyimide precursor form) are chemically bonded together with a solvent to form a polyamic acid (also called polyamic acid) solution. The dianhydride and diamine can be chemically bonded in a molar ratio of about 0.90 to 1.10. The molecular weight of the polyamic acid formed therefrom can be adjusted by adjusting the molar ratio of the dianhydride to the diamine.

[0052] In one embodiment, the polyamic acid casting solution is derived from the polyamic acid solution. The polyamic acid casting solution and / or the polyamic acid solution is combined with (i) one or more dehydrating agents, such as fatty acid anhydrides (e.g., acetic anhydride) and / or aromatic acid anhydrides; and (ii) one or more transforming chemicals, such as catalysts, such as aliphatic tertiary amines (e.g., triethylamine), aromatic tertiary amines (e.g., dimethylaniline), and heterocyclic tertiary amines (e.g., pyridine, picoline, isoquinoline). The anhydride dehydrating agent is often used in molar excess relative to the amount of amidic acid groups in the polyamic acid. The amount of acetic anhydride used is typically about 2.0 to 4.0 moles per equivalent (repeating unit) of polyamic acid. Generally, the same amount of tertiary amine catalyst is used. The filler, dispersed or suspended in the solvent as described above, is then added to the polyamic acid solution.

[0053] In one embodiment, the polyamic acid solution is dissolved in an organic solvent at concentrations ranging from about 5.0 or 10 percent to 15, 20, 25, 30, 35, or 40 weight percent. In one embodiment, a slurry containing a filler is prepared, having a solid content in the range of 0.1–70, 0.5–60, 1–55, 5–50, or 10–45 volume percent. The slurry may or may not be ground using a ball mill to reach a desired particle size. The slurry may or may not be filtered to remove any remaining large particles. The polyamic acid solution can be prepared by methods well known in the art. The polyamic acid solution may or may not be filtered. In some embodiments, the solution is mixed with the filler slurry in a high-shear mixer. If the polyamic acid solution is prepared using a slightly excess of diamine, an additional dianhydride solution may or may not be added to increase the viscosity of the mixture to a desired level for film casting. The amounts of polyamic acid solution and filler slurry can be adjusted to achieve the desired loading level in the cured film. In some embodiments, the mixture is cooled below 10°C and mixed with the conversion chemical before casting.

[0054] A solvation mixture (polyamic acid casting solution) can then be cast or coated onto a support, such as an endless belt or a rotating drum, to obtain a partially imidized film. Alternatively, it can be cast onto a polymer support such as PET, other forms of Kapton® polyimide film (e.g., Kapton® HN or Kapton® E film), or other polymer supports. The gel film can be peeled from the drum or belt, placed on a tenter frame, and cured in an oven using convection and radiant heat to remove the solvent and complete imidization to a solids content level of over 98%. The film can then be separated from the support and oriented by tentering or the like while continuing to heat (dry and cure) to provide a substantially chemically converted polyimide film.

[0055] Useful methods for producing polyimide films using chemical conversion methods can be found in (Patent Document 2) and (Patent Document 3), all of which are incorporated herein by reference. (a) A method in which the diamine component and the dianhydride component are mixed together beforehand, and then the mixture is gradually added to the solvent while stirring. (b) The solvent is added to a stirred mixture of the diamine component and the dianhydride component (contrary to (a) above). (c) A method in which a diamine is exclusively dissolved in a solvent, and then a dianhydride is added thereto in a ratio that allows control of the reaction rate. (d) A method in which a dianhydride component is exclusively dissolved in a solvent, and then an amine component is added thereto in a ratio that allows control of the reaction rate. (e) A method in which the diamine component and the dianhydride component are dissolved separately in a solvent, and then these solutions are mixed in a reactor. (f) A method in which a polyamic acid having an excess amine component and another polyamic acid having an excess dianhydride component are formed in advance and then reacted with each other in a reactor, in particular in a manner that produces a non-random copolymer or a block copolymer. (g) A specific portion of the amine component is reacted first with the dianhydride component, and then the remaining diamine component is reacted, or vice versa. (h) A method of forming a polyamic acid casting solution by mixing a conversion chemical (catalyst) with a polyamic acid, and then casting it to form a gel film. (i) A method in which components are added to any part or all of a solvent, either partially or as a whole, in any order, and any part or all of any component is added as a solution of any part or all of the solvent. (j) A method for obtaining a primary polyamic acid by first reacting one of the dianhydride components with one of the diamine components. Numerous other modifications are also possible. Next, another dianhydride component is reacted with another amine component to obtain a second polyamic acid. Then, the amidic acid is combined using one of several methods before film formation.

[0056] In one embodiment, a solvation mixture (polyamic acid casting solution) can be mixed with a coloring agent, such as a crosslinking precursor and / or a pigment or dye, and then cast to form a polymer film. In one embodiment, the coloring agent may be low-conductivity carbon black. In one embodiment, the polymer film contains crosslinking polymer in the range of 80-99 wt%. In some embodiments, the polymer film contains crosslinking polymer between any two of the following: 80, 85, 90, 95, and 99 wt%, and any two of those. In yet another embodiment, the polymer film contains 91-98 wt% crosslinking polymer.

[0057] In one embodiment, the crosslinking reaction includes a compound, such as a highly reactive amine, that can participate in a crosslinking reaction that crosslinks polymer chains in the film. In one embodiment, the polymer can be crosslinked using heat. In one embodiment, the polymer can be crosslinked by a photoinitiation process using irradiation with a light source. In one embodiment, the polymer can be crosslinked using additional highly reactive chemical species. In one embodiment, the polymer can be crosslinked using any combination of these processes.

[0058] Polymer crosslinking can be determined by various methods. In one embodiment, the gel fraction of the polymer can be determined by using an equilibrium swelling method that compares the weights of the dried film before and after crosslinking. In one embodiment, the crosslinked polymer can have gel fractions in the range of 20-100%, 40-100%, 50-100%, 70-100%, or 85-100%. In one embodiment, the crosslinked network can be identified using a rheological method. The formation of the crosslinked network can be confirmed using vibration time sweep measurements at specific strains, frequencies, and temperatures. Initially, the loss modulus (G'') value is higher than the storage modulus (G') value, indicating that the polymer solution behaves like a viscous liquid. Over time, the formation of the crosslinked polymer network is demonstrated by the intersection of the G' and G'' curves. The intersection, called the "gel point," represents the point where the elastic component is dominant over the viscous component.

[0059] In one embodiment, the filler is first dispersed in a solvent to form a slurry. The slurry is then dispersed in a polyamic acid solution. In one embodiment, the filler-to-polyimide concentration (in the final film) is in the range of 10-50 vol%, 15-45 vol%, 15-40 vol%, 20-35 vol%, or 25-30 vol%. In one embodiment, the filler-to-polyimide concentration (in the final film) is at least 10, at least 15, at least 20, or at least 25 vol%. The composition of the cured film can be calculated from the composition of the components in the mixture, excluding the DMAc solvent (which is removed during curing) and taking into account the removal of water during the conversion of polyamic acid to polyimide. When using a thermally conductive and / or conductive filler, the conductivity of the polyimide film also increases as the concentration of the filler increases. In one embodiment, the thermally conductive polyimide film may have a thermal conductivity in the range of 0.1 to 100 watts per meter-kelvin (W / mK), 0.1 to 50 W / mK, 0.15 to 10 W / mK, 0.2 to 5 W / mK, 0.25 to 1 W / mK, 0.25 to 0.8 W / mK, or 0.3 to 0.6 W / mK. In one embodiment, the thermally conductive film may have a dielectric strength in the range of 1000 to 9000, 2000 to 8000, 3000 to 8000, 5000 to 8000, or 6000 to 8000 V / mil. In one embodiment, the conductive polyimide film can have a surface resistivity in the range of 0.5 ohms / m² to 2 megaohms / m², 2 to 10,000 ohms / m², 5 to 5,000 ohms / m², 10 to 1,000 ohms / m², or 20 to 500 ohms / m².

[0060] In one embodiment, the polyamic acid casting solution with filler is a blend of polyamic acid solution and filler. In this casting solution, the filler is present in a concentration range of 0.1–70 vol%, 1–60 vol%, 2–50 vol%, 5–45 vol%, or 5–40 vol%. In one embodiment, the filler is first dispersed in an aprotic solvent of the same polarity (e.g., DMAc) used to prepare the polyamic acid solution. Optionally, a small amount of polyamic acid solution may be added to the filler slurry to increase the viscosity of the slurry. Optionally, a dispersant or dispersing agent may be added to aid in dispersion or to alter the rheology of the slurry.

[0061] In one embodiment, the blending of the filler slurry and the polyamic acid solution to form a filler-containing polyamic acid casting solution is performed using high-shear mixing. In this embodiment, if the filler is present in more than 50 volume percent of the final film, the film may be too brittle and not flexible enough to form a self-supporting, mechanically robust, flexible sheet. Furthermore, if the filler is present at a level of less than 10 volume percent, the film formed therefrom may not be sufficiently conductive.

[0062] In one embodiment, the casting solution may further contain one of a number of additives, such as processing aids (e.g., oligomers), antioxidants, light stabilizers, flame retardant additives, antistatic agents, heat stabilizers, ultraviolet absorbers, or various reinforcing agents.

[0063] In some embodiments, a co-extrusion process can be used to form a multilayer polyimide film in which an inner core layer is sandwiched between two outer layers. In this process, the finished polyamic acid solution is filtered and pumped to a slot die, where the flow is divided in such a way that it forms the first and second outer layers of the three-layer co-extruded film. In some embodiments, the second flow of polyimide is filtered and then pumped to a casting die in such a way that it forms the central polyimide core layer of the three-layer co-extruded film. The flow rate of the solution can be adjusted to achieve the desired layer thickness.

[0064] In some embodiments, the multilayer film is prepared by simultaneously extruding a first outer layer, a core layer, and a second outer layer. In some embodiments, the layers are extruded through a single-cavity or multi-cavity extrusion die. In another embodiment, the multilayer film is manufactured using a single-cavity die. When a single-cavity die is used, the laminar flow should have a viscosity high enough to prevent flow mixing and to provide uniform lamination. In some embodiments, the multilayer film is prepared by casting a partially imidized multilayer gel film from a slot die onto a moving stainless steel belt. The gel film can be peeled from a drum or belt placed on a tenter frame and cured in an oven using convective and radiant heat to remove the solvent and complete imidization to a solids content level of over 98%. The multilayer film can then be separated from the support and oriented by tentering or the like while continuing to heat (dry and cure) to provide a multilayer substantially chemically converted polyimide film.

[0065] The thickness of the polyimide film can be adjusted depending on the intended purpose or end-use specifications of the film. In one embodiment, the polyimide film has a total thickness in the range of 2-300 μm, 5-200 μm, 10-150 μm, 20-100 μm, or 20-80 μm.

[0066] By reducing the concentration and volume of voids in filler-filled polyimide films, films with good electrical and / or thermal conductivity can be manufactured. Void reduction can also result in improved mechanical, optical, and mass transfer properties of the polyimide film. By using a chemical conversion process to produce substantially imidized filler-filled polyimide films with low void concentrations, the films can be manufactured at a lower cost than their thermally imidized counterparts.

[0067] Purpose In one embodiment, an electrically insulating thermally conductive polyimide film is useful as a substrate (dielectric) in electronic devices that require good thermal conductivity of the dielectric material. Examples of such electronic devices include (but are not limited to) thermal interface materials (TIMs), thermoelectric modules, thermoelectric coolers, DC / AC and AC / DC inverters, DC / DC and AC / AC converters, power amplifiers, voltage regulators, ignition devices, light-emitting diodes, IC packages, etc. In one embodiment, to improve conformability to mating surfaces and reduce the thermal contact resistance of the TIM assembly, a soft thermal interface layer (having a hardness less than the core of the polyimide film) may be coated or laminated onto a substantially chemically converted polyimide and a thermally conductive polyimide film having low porosity. In one embodiment, the soft thermal interface may be part of the outer layer of a multilayer polyimide film.

[0068] In one embodiment, conductive polyimide films can be useful for flexible or rigid applications and are particularly suitable as thin, flexible heaters for high-voltage, high-temperature applications over large areas, such as wind turbine blades, aircraft wing tips, and helicopter blades, where prevention of snow and / or ice accumulation is desired. While high-voltage, high-temperature applications are particularly suitable for these film-based heating devices, those skilled in the art may envision using these heating devices for other heating applications, such as low-voltage, low-temperature applications, low-voltage, high-temperature applications, and high-voltage, low-temperature applications. Other examples of high-temperature applications include clothing irons, hair straighteners, and industrial heater applications. In one embodiment, film-based heating devices may also be useful as wall heaters, floor heaters, roof heaters, and sheet heaters. In one embodiment, conductive polyimide films can also be used in a variety of applications requiring good antistatic properties, such as copier belts, space blankets, and flexible circuit boards. In one embodiment, conductive polyimide films can also be used as electromagnetic interference (EMI) shielding layers.

[0069] The advantageous characteristics of the present invention can be seen by referring to the following examples, which illustrate but do not limit the present invention. All parts and percentages are by weight unless otherwise specified. [Examples]

[0070] Test method porosity Porosity is defined as the ratio of the total volume percentage of voids in the film to the total volume percentage of the filler material in the film (i.e., porosity = [void percentage] / [volume percentage of filler]). (It can also be called percentage voids, void percentage, or percentage porosity.) The total volume percentage of voids in the film is calculated using the following formula:

[0071]

number

[0072] It is determined by

[0073] Density without theoretical voids The density without theoretical voids of the film is calculated using the ideal mixing assumption: the total volume of the mixture (film) is equal to the sum of the individual volumes of each component in the mixture, and the total mass is equal to the sum of the masses of each individual component, and the following relationship for the density without theoretical voids:

[0074]

Equation

[0075] is shown. In the formula, ρ = the density of the film, n = an integer of the component, m i = the mass of the i-th component, v i = the volume of the i-th component.

[0076] The individual volume of each component is calculated from the known final solid content mass input and the known individual component density as follows: v i = m i / ρ i

[0077] The density for the solid content discussed in the examples is as follows:

[0078]

Table 1

[0079] The polyimide film density is calculated as the dry bulk density as described below, and the filler density is from the literature and supplier documentation. [[ID=5…]]

[0080] Dry bulk density The dry bulk density of the films was determined by measuring their physical dimensions. The point thickness was measured at five locations according to standard ASTM D3716 for a 4-inch × 6-inch sample (a sample manufactured using a precision die cutter, giving a known sample area with an accuracy of less than 1%) and averaged. The mass of the sample was measured using a laboratory balance with an accuracy of 0.0001 g. The dry bulk density was then calculated using the following formula:

[0081]

number

[0082] The calculation was performed in grams per cubic centimeter.

[0083] particle size The median particle size of the filler particles in the slurry, d 50 The equivalent spherical diameter (based on the central volume distribution of the particles) was measured by laser diffraction using a particle size analyzer (Mastersizer 3000, Malvern Instruments, Inc., Westborough, MA). DMAc was used as the dispersion medium.

[0084] Thermal conductivity Thermal conductivity was measured according to standard ASTM D5470-17 using a thermal interface material (TIM 1400, Analysis Tech Inc., Wakefield, MA) testing apparatus. Polyimide films were treated as Type III materials and run at a sample pressure of 150 psi using silicone oil as the thermal grease.

[0085] Dielectric strength Dielectric strength was measured in air at 23°C and 50% relative humidity, at 60 Hz with a rise time of 500 V / s, using a dielectric breakdown test apparatus (730-1 A, Hiptronics Inc, Brewster, NY) according to standard ASTM D149-20, Method A, with a brass electrode (1 / 4-inch diameter opposing rod with a 1 / 32 edge radius). The average of 5 to 10 individual measurements was reported.

[0086] surface resistivity In accordance with ASTM D257, surface resistivity was measured at 15 locations uniformly spread across approximately 12-inch x 12-inch pieces of film using a Loresta AX MCP-T370 equipped with a PSP Linear 4-point probe (Mitsubishi Chemical Analytec Co., Ltd., Kanagawa, Japan). The surface resistivity of the film was determined by averaging the 15 measurements.

[0087] (Examples) Examples 1 and 2 For Examples 1 and 2 (E1-E2), 27.67 kg of 1,3-bis(4-aminophenoxy)benzene (RODA) and 229.06 kg of dimethylacetamide (DMAc) were added to an 80-gallon reactor, which was nitrogen-purged with stirring. The solution was stirred to completely dissolve RODA in the DMAc solvent, and stirring was continued throughout all subsequent steps. The reaction mixture was heated to approximately 40°C for this procedure. Approximately 23 kg of 4,4'-oxydiphthalic anhydride (ODPA) and approximately 2.2 kg of pyromellitic dianhydride (PMDA) were added in four separate aliquots over 3 hours. An additional aliquot of approximately 0.45 kg of PMDA was added to the reaction mixture over approximately 1 hour. The viscosity of the polyamic acid solution was approximately 367 poise at 29°C.

[0088] Examples 3-6 For Examples 3-6 (E3-E6), 26.13 kg of 4,4'-oxydianiline (ODA) and 212.28 kg of DMAc were added to an 80-gallon reactor, which was nitrogen-purged with stirring, along with a monomer composition of PMDA 0.46 / BPDA 0.54 / / ODA. The solution was stirred to completely dissolve the ODA in the DMAC solvent, and stirring was continued throughout all subsequent steps. The reaction mixture was heated to approximately 40°C for this procedure. Approximately 5 kg of biphenyltetracarboxylic dianhydride (BPDA) and approximately 3 kg of pyromellitic dianhydride (PMDA) were added in four separate aliquots over 2 hours. An additional aliquot of approximately 0.68 kg of PMDA was added to the reaction mixture over approximately 1 hour. The viscosity of the polyamic acid solution was approximately 78 poise at 21°C.

[0089] Comparative Examples 1-3 For Comparative Examples 1-3 (CE1-CE3), polyamic acid solutions in DMAc were prepared using conventional methods with a monomer composition of PMDA / / ODA and an excess of diamine to a viscosity in the range of 50-100 poise. The polyamic acid solutions had a solid content of 20.6%.

[0090] Alpha Alumina Rally In some embodiments, an alpha-alumina (α-Al2O3) slurry was prepared consisting of 37-50 wt% α-Al2O3 powder (Martoxid® MZS-1, Huber Engineered Materials, Atlanta, GA), 3-8 wt% polyamic acid solids, and 47-58 wt% DMAc. The raw materials were thoroughly mixed in a high-speed disk-type disperser. In some embodiments, the slurry was then processed in a bead mill to disperse any aggregates and achieve the desired particle size. Median particle size, d 50 The size was 1.4–2.2 μm.

[0091] Carbon black slurry In some embodiments, a carbon black slurry was prepared consisting of 10-18 wt% carbon black powder (Conductex® 7055U, Aditya Birla Group, Marietta, GA), 3 wt% polyamic acid solids, and 63-73 wt% DMAc. The raw materials were thoroughly mixed in a high-speed disk-type disperser. In some embodiments, the slurry was then processed in a bead mill to disperse any aggregates and achieve the desired particle size. The median particle size was 0.3-5.0 μm. In some embodiments, a dispersant was used for improved processing.

[0092] For E1-E6 and CE1-CE3, viscosity was adjusted by controlling the amount of dianhydride in the polyamic acid composition. A filler slurry in a ratio appropriate to produce the desired composition after curing was then added to the polyamic acid solution and mixed using a high-shear mixer. The polymer mixture was cooled to approximately 6°C, and the conversion chemical acetic anhydride (approximately 0.14 cm³) was added. 3 / cm 3 Polymer solution) and beta-picoline (approximately 0.15 cm) 3 / cm 3 A polymer solution was added and mixed. A film was cast from the polyamic acid solution onto a rotating drum at approximately 90°C using a slot die. The resulting gel film was peeled from the drum and supplied to a tenter oven, where it was dried and cured to a solids content level of over 98% using convection and radiant heating. The composition of the cured film was calculated from the composition of the components in the mixture, excluding the DMAc solvent (which is removed during curing) and considering the removal of water during the conversion of polyamic to polyimide.

[0093] Examples are summarized in Tables 1 and 2.

[0094] [Table 2]

[0095] Polyimide films E1 to E5 all contain polyimides derived from aromatic dianhydrides having two or more phenyl groups at a rate of at least 10 mole percent based on the total dianhydride content of the polyimide, and from aromatic diamines having two or more phenyl groups at a rate of at least 10 mole percent based on the total diamine content of the polyimide. Even with a filler loading of 39 vol% (E5), the porosity remains relatively low and the thermal conductivity remains good. In contrast, CE1, which contains polyimides not derived from aromatic dianhydrides having two or more phenyl groups at a rate of at least 10 mole percent based on the total dianhydride content of the polyimide, and not derived from aromatic diamines having two or more phenyl groups at a rate of at least 10 mole percent based on the total diamine content of the polyimide, exhibits higher porosity and lower thermal conductivity despite a filler loading of only 21 vol%. In addition, the dielectric strength of E1 to E5 remains good even at higher filler loading levels.

[0096] [Table 3]

[0097] Polyimide film E6 contains polyimide derived from aromatic dianhydrides having two or more phenyl groups at a rate of at least 10 mol percent based on the total dianhydride content of the polyimide, and polyimide derived from aromatic diamines having two or more phenyl groups at a rate of at least 10 mol percent based on the total diamine content of the polyimide. With a 29 vol% filler loading, it has extremely low porosity and low surface resistivity. In contrast, CE2-CE3, which contain both aromatic dianhydrides having two or more phenyl groups at a rate of at least 10 mol percent based on the total dianhydride content of the polyimide, and polyimide not derived from aromatic diamines having two or more phenyl groups at a rate of at least 10 mol percent based on the total diamine content of the polyimide, have much higher porosity and higher surface resistivity with comparable filler loading.

[0098] Comparative Examples 4 and 5 For Comparative Examples 4 and 5 (CE4-CE5), a polyamic acid solution in DMAc, along with the PMDA / / ODA monomer composition, was prepared to a viscosity of approximately 2000 poise by conventional means using excess diamine. The polyamic acid solution had a solid content of approximately 20%. Next, a carbon slurry was added to the polyamic acid solution and mixed using a rotation-and-revolution agitator. The polymer mixture was cast onto a Mylar® PET sheet. The sheet was immersed in a 1:1 mixture of acetic anhydride and beta-picoline for 8 minutes. The web was then peeled from the Mylar and fixed onto a frame. Next, CE4 was placed in an oven and heated at 300°C for 30 minutes to dry. For CE5, a hybrid water extraction process was used, which attempts to take advantage of the benefits of both chemical and thermal imidization processes and avoid void formation by first partially imidizing the polyamic acid using a chemical process and then finishing the imidization using a thermal process. The CE5 was fixed onto a frame and then immersed in a mixture of 1 part by volume of DMAc in 9 parts distilled water. After immersion for 10 minutes, the CE5 was removed, drained, placed in an oven, and heated at 300°C for 30 minutes to dry.

[0099] Based on the total dianhydride content of the polyimide, CE4 to CE5, which contain both at least 10 mole percent of aromatic dianhydrides having two or more phenyl groups and at least 10 mole percent of polyimides not derived from aromatic diamines having two or more phenyl groups, based on the total diamine content of the polyimide, have very high porosity. Table 3 summarizes the film properties of CE4 to CE5.

[0100] [Table 4]

Claims

1. a substantially chemically converted polyimide derived from at least 10 mole percent aromatic dianhydrides having two or more phenyl groups, based on the total dianhydride content of the polyimide, and at least 10 mole percent aromatic diamines having two or more phenyl groups, based on the total diamine content of said polyimide; At least 10 volume percent of an inorganic filler, based on the total volume of the polyimide film; A polyimide film comprising: the two or more phenyl groups in the aromatic dianhydride do not share carbon atoms with each other; the two or more phenyl groups in the aromatic diamine do not share carbon atoms with each other; less than 50 volume percent of the inorganic fillers, based on the total inorganic fillers, have diameters of less than 100 nm in all three dimensions; The porosity of the polyimide film is 0.75 or less. Polyimide film.

2. 2. The polyimide film of claim 1, further comprising an imidization catalyst selected from the group consisting of aliphatic acid anhydrides, aromatic acid anhydrides, aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines.

3. 2. The polyimide film according to claim 1, wherein the aromatic dianhydride having two or more phenyl groups is selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)sulfoxide dianhydride, 4,4'-oxydiphthalic anhydride, bisphenol A dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, 1,3-bis-(4,4'-oxydiphthalic anhydride)benzene, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride, and mixtures thereof.

4. The aromatic diamine having two or more phenyl groups may be 2,2'-bis(trifluoromethyl)benzidine, 2,2'-bis-(4-aminophenyl)hexafluoropropane, 9,9'-bis(4-aminophenyl)fluorene, 2,2-bis[4(4-aminophenoxy)phenyl]phthalein-3',5'-bis(trifluoromethyl)anilide, 4,4'-diaminobiphenyl, 4,4'-diaminobenzanilide, 4,4'-diaminobenzophenone, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis(4-amino 2. The polyimide film according to claim 1, wherein the bis(4-aminophenyl)aminobenzophenone is selected from the group consisting of 4,4'-isopropylidenedianiline, 2,2-bis(4-aminophenyl)propane, 1,2-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2-bis(4-[4-aminophenoxy]phenyl)propane, and mixtures thereof.

5. The polyimide film according to claim 1 , wherein the inorganic filler comprises a metal oxide, an inorganic nitride, or a metal carbide.

6. 10. The polyimide film of claim 1, having a dielectric strength in the range of 1000 to 9000 volts per mil (V / mil).

7. 10. The polyimide film of claim 1, having a thermal conductivity in the range of 0.2 to 5 watts per meter-Kelvin (W / mK).

8. 10. The polyimide film of claim 1 having a surface resistivity in the range of 0.5 ohms / square to 2 megaohms / square.