Single-layer polymer film and electronic device

Abstract

In a first aspect, a single-layer polymer film comprises 60 to 99 wt% of a crosslinked polyimide having a gel fraction of 20% to 100% and a refractive index of 1.74 or less, and 1 to 40 wt% of a colorant. The surface of the single-layer polymer film has been textured and has a maximum roughness (S pv ) of 6 μm or greater, an L* color of 30 or less, and a 60° glossiness of 15 or less. In a second aspect, a cover layer for a printed circuit board comprises the single-layer polymer film of the first aspect. In third and fourth aspects, methods for forming a single-layer polymer film comprising a crosslinked polyimide film are disclosed, the crosslinked polyimide film comprising a dianhydride and a diamine.

Description

FIELD OF THE TECHNOLOGY

[0001] The field of the present disclosure is single-layer polymer films, overcoats, and electronic devices, and methods of forming the same. BACKGROUND OF THE DISCLOSURE

[0002] Industry increasingly desires that polyimide films for electronic applications be matte in appearance, have a specific color, be durable to handling and circuit processing, and when used as an overcoat, provide security against unwanted visual inspection of the electronic components protected by the overcoat. Single-layer matte-glossy films do not have an L* color less than 30, providing the deep, rich, saturated colors desired by industry. Typically, as the amount of the matting agent increases, the color of the film weakens. The effect of the increased surface roughness from the matting agent is the dilution of the pigment color, making it appear lighter and less saturated. This is caused by the dilution of the diffuse reflection (in the case of perceiving the pigment color) by the increased scattering of specular reflection (white light). The rougher the surface, the lower the gloss, and the greater the scattering of specular reflection. Thus, as the gloss decreases, the L* (brightness) typically increases. Adding more colorants does not reduce the L* color. Therefore, it is difficult to achieve both low gloss and low L* color simultaneously. To overcome these challenges, U.S. Patent Nos. 9,469,781, 9,481,150, and 9,481,809 use a multilayer structure in which a thin polyimide layer incorporating a blend of a matting agent, carbon black, and submicron particles is adhered to a thicker base polyimide layer, such that the multilayer film can achieve the desired combination of both low L* color and low gloss.

[0003] The success of multilayer overcoats in circuit production depends on the etch thickness during pumice, desmear, and plasma processes. For the very thin outer layer of a multilayer film, there is a risk of etching the outer layer of the film and exposing the base layer during these processes, which can lead to significant gloss and color changes. Thus, the outer layer must be thick enough to withstand removal during these processes.

[0004] As electronic devices and their electronic components become thinner and more compact, the challenge of forming an overcoat with both low gloss and low color becomes even more difficult. In some cases, the need for a thinner overcoat limits the use of matting agents (which may have a particle size on the order of the film thickness), and limits the total thickness of the layers in a multilayer overcoat. There is a need for a single-layer polymer film that is matte in appearance, has deep, rich, saturated colors, and when used as an overcoat, provides sufficient optical density to provide visual security, while having acceptable electrical properties (e.g., dielectric strength), mechanical properties, and durability to handling and circuit processing. This film should also be more tolerant to post-treatment etching processes. SUMMARY OF THE INVENTION

[0005] In a first aspect, a single-layer polymer film comprises 60 to 99 wt% of a crosslinked polyimide having a gel fraction of 20% to 100% and a refractive index of 1.74 or less, and 1 to 40 wt% of a colorant. The surface of the single-layer polymer film has been textured and has a maximum roughness (S pv ) of 6 μm or greater, an L* color of 30 or less, and a 60° gloss of 15 or less.

[0006] In a second aspect, a cover layer for a printed circuit board comprises the single-layer polymer film of the first aspect.

[0007] In a third aspect, a method for forming a single-layer polymer film comprising a crosslinked polyimide film is disclosed, the crosslinked polyimide film comprising a dianhydride and a diamine. The dianhydride, the diamine, or both the dianhydride and the diamine comprise an alicyclic monomer, an aliphatic monomer, or both an alicyclic monomer and an aliphatic monomer. The polymer film has an L* color of 30 or less and a 60° gloss of 15 or less. The crosslinked polyimide film is formed by:

[0008] (a) polymerizing the dianhydride and the diamine in the presence of a solvent to obtain a polyamic acid solution;

[0009] (b) imidizing the polyamic acid solution to form a substantially imidized solution;

[0010] (c) adding a crosslinking agent and a colorant to the substantially imidized solution;

[0011] (d) casting the substantially imidized solution onto a removable substrate to form a film, the removable substrate having a textured surface with a maximum roughness (S pv ) of 6 μm or greater;

[0012] (e) crosslinking the polyimide while drying the film; and

[0013] (f) removing the single-layer polymer film from the textured substrate.

[0014] In a fourth aspect, a method for forming a single-layer polymer film comprising a crosslinked polyimide film is disclosed, the crosslinked polyimide film comprising a dianhydride and a diamine. The dianhydride, the diamine, or both the dianhydride and the diamine contain an alicyclic monomer, an aliphatic monomer, or both an alicyclic monomer and an aliphatic monomer. The polymer film has an L* color of 30 or less and a 60° gloss of 15 or less. The crosslinked polyimide film is formed by:

[0015] (a) Polymerize the dianhydride and the diamine in the presence of a first solvent to obtain a polyamic acid solution;

[0016] (b) Imidize the polyamic acid solution to form a first substantially imidized solution;

[0017] (c) Precipitate the first substantially imidized solution with an anti-solvent;

[0018] (d) Filter and dry the first substantially imidized solution to obtain a solid polyimide resin;

[0019] (e) Dissolve the solid polyimide resin in a second solvent, and add a crosslinking agent and low-conductivity carbon black to form a second substantially imidized solution;

[0020] (f) Cast the second substantially imidized solution onto a removable substrate to form a film, the removable substrate having a textured surface with a maximum roughness (S pv ) of 6 μm or greater;

[0021] (g) Crosslink the polyimide while drying the film; and

[0022] (h) Remove the single-layer polymer film from the textured substrate.

[0023] The foregoing general description and the following detailed description are exemplary and explanatory only and do not limit the invention as defined by the appended claims. Detailed Description

[0024] In a first aspect, the single-layer polymer film comprises 60 to 99 wt% of a crosslinked polyimide having a gel fraction of 20% to 100% and a refractive index of 1.74 or less, and 1 to 40 wt% of a colorant. The surface of the single-layer polymer film has been textured and has a maximum roughness (S pv ) of 6 μm or greater, an L* color of 30 or less, and a 60° gloss of 15 or less.

[0025] In an embodiment of the first aspect, the single-layer polymer film further comprises a matting agent.

[0026] In another embodiment of the first aspect, the crosslinked polyimide comprises a dianhydride selected from the group consisting of aromatic dianhydrides, aliphatic dianhydrides, and mixtures thereof. In a specific embodiment, the dianhydride is selected from the group consisting of: 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), cyclobutanedicarboxylic anhydride (CBDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), bisphenol A dianhydride (BPADA), 4,4'-oxydiphthalic anhydride (ODPA), bis(3,4-dicarboxyphenyl)sulfone dianhydride (DSDA), and hexahydro-4,8-ethano-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetrone (BODA), and mixtures thereof.

[0027] In yet another embodiment of the first aspect, the crosslinked polyimide comprises a diamine selected from the group consisting of aromatic diamines, aliphatic diamines, and mixtures thereof. In a specific embodiment, the diamine is selected from the group consisting of: 1,6-hexamethylenediamine (HMD), trans-1,4-diaminocyclohexane (CHDA), 3-(4-aminophenyl)-1,1,3-trimethyl-5-aminoindane (PIDA), isophoronediamine (IPDA), metaxylenediamine (MTB), 2,2'-bis(trifluoromethyl)benzidine (TFMB), m-phenylenediamine (MPD), 1,3-bis-(4-aminophenoxy)benzene (RODA), 2,2-bis-(4-[4-aminophenoxy]phenyl)propane (BAPP), and 3,4'-diaminodiphenyl ether (3,4-ODA), and mixtures thereof.

[0028] In still another embodiment of the first aspect, the single-layer polymer film has a thickness of 2 to 125 μm.

[0029] In still yet another embodiment of the first aspect, the crosslinked polyimide has a refractive index of 1.69 or less.

[0030] In another embodiment of the first aspect, the colorant comprises low-conductivity carbon black.

[0031] In a second aspect, a cover layer for a printed circuit board comprises the single-layer polymer film of the first aspect.

[0032] In a third aspect, a method for forming a single-layer polymer film comprising a crosslinked polyimide film is disclosed, the crosslinked polyimide film comprising a dianhydride and a diamine. The dianhydride, the diamine, or both the dianhydride and the diamine comprise an alicyclic monomer, an aliphatic monomer, or both an alicyclic monomer and an aliphatic monomer. The polymer film has an L* color of 30 or less and a 60° gloss of 15 or less. The crosslinked polyimide film is formed by:

[0033] (a) Polymerize the dianhydride and the diamine in the presence of a solvent to obtain a polyamic acid solution;

[0034] (b) Imidize the polyamic acid solution to form a substantially imidized solution;

[0035] (c) Add a crosslinking agent and a colorant to the substantially imidized solution;

[0036] (d) Cast the substantially imidized solution onto a removable substrate to form a film, the removable substrate having a textured surface with a maximum roughness (S pv ) of 6 μm or greater;

[0037] (e) Crosslink the polyimide while drying the film; and

[0038] (f) Remove the single-layer polymer film from the textured substrate.

[0039] In a fourth aspect, a method for forming a single-layer polymer film including a crosslinked polyimide film is disclosed, the crosslinked polyimide film including a dianhydride and a diamine. The dianhydride, the diamine, or both the dianhydride and the diamine include an alicyclic monomer, an aliphatic monomer, or both an alicyclic monomer and an aliphatic monomer. The polymer film has an L* color of 30 or less and a 60° glossiness of 15 or less. The crosslinked polyimide film is formed by:

[0040] (a) Polymerize the dianhydride and the diamine in the presence of a first solvent to obtain a polyamic acid solution;

[0041] (b) Imidize the polyamic acid solution to form a first substantially imidized solution;

[0042] (c) Precipitate the first substantially imidized solution with an anti-solvent;

[0043] (d) Filter and dry the first substantially imidized solution to obtain a solid polyimide resin;

[0044] (e) Dissolve the solid polyimide resin in a second solvent, and add a crosslinking agent and low-conductivity carbon black to form a second substantially imidized solution;

[0045] (f) Cast the second substantially imidized solution onto a removable substrate to form a film, the removable substrate having a textured surface with a maximum roughness (S pv ) of 6 μm or greater;

[0046] (g) Crosslink the polyimide while drying the film; and

[0047] (h) Remove the single-layer polymer film from the textured substrate.

[0048] In one embodiment of the method of the fourth aspect, after (e) and before (f), the second substantially imidized solution is filtered to remove insoluble components of the solution.

[0049] In another embodiment of the method of the fourth aspect, the first and second solvents are the same or different.

[0050] Numerous aspects and embodiments have been described above and are merely exemplary and non-limiting. After reading this specification, those skilled in the art will understand that other aspects and embodiments are possible without departing from the scope of the invention. Other features and advantages of the invention will be apparent from the following detailed description and from the claims.

[0051] In one embodiment, a single-layer polymer film having a crosslinked polyimide enables the formation of a very thin cover layer that is more resistant to etching than a film using a conventional cover layer material. Using a soluble polyimide that is crosslinked after film formation results in a single-layer polymer film having improved chemical resistance, which retains the low L* color and low gloss characteristics required for these films.

[0052] As used herein, "diamine" is intended, depending on the context, to mean: (i) in an unreacted form (i.e., a diamine monomer); (ii) in a partially reacted form (i.e., one or more moieties of an oligomer or other polymer precursor derived from or otherwise attributable to a diamine monomer) or (iii) in a fully reacted form (one or more moieties of a polymer derived from or otherwise attributable to a diamine monomer). Depending on the specific embodiment selected in the practice of the present invention, the diamine may be partially functionalized with one or more moieties.

[0053] In fact, the term "diamine" is not intended to be limited (or literally interpreted) to the number of amine moieties in a diamine component. For example, (ii) and (iii) above include polymeric materials that may have two, one, or zero amine moieties. Alternatively, the diamine may be functionalized with additional amine moieties (in addition to the amine moieties at the monomer termini that react with dianhydrides to extend the polymer chain). Such additional amine moieties may be used to crosslink the polymer or to provide other functional groups to the polymer.

[0054] Similarly, as used herein, the term "dianhydride" is intended to mean a component that reacts (cooperates) with a diamine and the combination is capable of reacting to form an intermediate which can then be cured into a polymer. Depending on the context, as used herein, "anhydride" can mean not only the anhydride moiety itself but also 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 acyl halide (e.g., chloride) ester moiety (or any other moiety known or developed in the future) capable of being converted to an anhydride functional group.

[0055] Depending on the context, "dianhydride" can mean: (i) the unreacted form (i.e., the dianhydride monomer, whether the anhydride functional group is in the true anhydride form or the precursor anhydride form as discussed in the preceding paragraph); (ii) the partially reacted form (i.e., one or more portions of an oligomer or other partially reacted precursor polymer composition resulting from or otherwise attributable to the dianhydride monomer) or (iii) the fully reacted form (one or more portions of a polymer derived from or otherwise attributable to the dianhydride monomer).

[0056] Depending on the specific embodiments selected in the practice of the present invention, the dianhydride can be partially functionalized with one or more. In fact, the term "dianhydride" is not intended to be limited (or literally interpreted) to the number of anhydride moieties 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 moieties depending on whether the anhydride is in the precursor state or the reacted state. Alternatively, the dianhydride component can be functionalized with additional anhydride-type moieties (in addition to the anhydride moieties that react with the diamine to provide the polymer). Such additional anhydride moieties can be used to crosslink the polymer or to provide other functional groups to the polymer.

[0057] Any one of many polyimide manufacturing processes can be used to prepare the single-layer polymer film. It is not possible to discuss or describe all possible manufacturing processes useful in the practice of the present invention. It should be understood that the monomer systems of the present invention are capable of providing the above advantageous properties in various manufacturing processes. The compositions of the present invention can be made as described herein and can be readily made in any of many (possibly countless) ways by those of ordinary skill in the art using any conventional or unconventional manufacturing techniques.

[0058] Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

[0059] When an equivalent, concentration, or other value or parameter is given as a range, a preferred range, or a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not those ranges are separately disclosed. When a numerical range is described herein, unless otherwise stated, the range is intended to include its endpoints, as well as all integers and fractions within the range. The scope of the invention is not intended to be limited to the specific values recited when defining the range.

[0060] When describing certain polymers, it should be understood that sometimes the applicant refers to a polymer by the monomers used to make the polymer or the amounts of monomers used to make the polymer. Although such a description may not include a specific name for the final polymer or may not contain terms that define the product by the process, any such reference to monomers and amounts should be construed to mean that the polymer is made from those monomers or that amount of monomers, and their corresponding polymers and compositions.

[0061] Unless otherwise specified, the materials, methods, and examples herein are illustrative only and not intended to be limiting.

[0062] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof are intended to cover non-exclusive inclusion. For example, a method, process, article, or apparatus that includes a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such method, process, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not an exclusive or. For example, condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and both A and B are true (or present).

[0063] Additionally, the use of “a / an” is used to describe elements and components of the present invention. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one, and the singular form also includes the plural, unless it is obvious that it means otherwise.

[0064] organic solvent

[0065] Useful organic solvents for synthesizing the polymers of the present invention preferably can dissolve the polymer precursor materials. Such solvents should also have a relatively low boiling point, such as below 225 °C, so that the polymers can be dried at moderate (i.e., more convenient and lower-cost) temperatures. Boiling points less than 210 °C, 205 °C, 200 °C, 195 °C, 190 °C, or 180 °C are preferred.

[0066] The solvents of the present invention can be used alone or in combination with other solvents (i.e., co-solvents). Useful organic solvents include: N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetramethylurea (TMU), diethylene glycol diethyl ether, 1,2-dimethoxyethane (monoglyme), diethylene glycol dimethyl ether (diglyme), 1,2-bis-(2-methoxyethoxy)ethane (triglyme), bis[2-(2-methoxyethoxy)ethyl)]ether (tetraglyme), γ-butyrolactone, and bis-(2-methoxyethyl) ether, tetrahydrofuran. In one embodiment, preferred solvents include N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc).

[0067] Co-solvents can generally be used in about 5 to 50 weight percent of the total solvent, and useful such co-solvents include xylene, toluene, benzene, "cellosolve" (ethylene glycol monoethyl ether), and "acetocellosolve" (ethylene glycol monoacetate).

[0068] diamine

[0069] In one embodiment, suitable diamines for forming polyimides can include aliphatic diamines such as 1,2-diaminoethane, 1,6-diaminohexane (HMD), 1,4-diaminobutane, 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), isophorone diamine (IPDA), bicyclo[2.2.2]octane-1,4-diamine, and combinations thereof. Other aliphatic diamines suitable for practicing the present invention include those having six to twelve carbon atoms or combinations of longer-chain and shorter-chain diamines, so long as both developability and flexibility are maintained. Longer-chain aliphatic diamines increase flexibility.

[0070] In one embodiment, suitable diamines for forming polyimide may further include fluorinated aromatic diamines such as 2,2'-bis(trifluoromethyl)benzidine (TFMB), trifluoromethyl-2,4-diaminobenzene, trifluoromethyl-3,5-diaminobenzene, 2,2'-bis-(4-aminophenyl)-hexafluoropropane, 4,4'-diamino-2,2'-trifluoromethyldiphenyl ether, 3,3'-diamino-5,5'-trifluoromethyldiphenyl ether, 9,9'-bis(4-aminophenyl)fluorene, 4,4'-trifluoromethyl-2,2'-diaminobiphenyl, 4,4'-oxy-bis-[(2-trifluoromethyl)aniline] (1,2,4-OBABTF), 4,4'-oxy-bis-[(3-trifluoromethyl)aniline], 4,4'-thio-bis-[(2-trifluoromethyl)aniline], 4,4'-thiobis[(3-trifluoromethyl)aniline], 4,4'-sulfoxyl-bis-[(2-trifluoromethyl)aniline], 4,4'-sulfoxyl-bis-[(3-trifluoromethyl)aniline], 4,4'-keto-bis-[(2-trifluoromethyl)aniline], 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'-bis(trifluoromethyl)phenyl]benzene, 1,4-bis[2'-cyano-3'-(4-aminophenoxy)phenoxy]-2-[(3',5'-bis(trifluoro-methyl)phenyl]benzene (6FC-diamine), 3,5-diamino-4-methyl-2',3',5',6'-tetrafluoro-4'-trifluoromethyldiphenyl ether, 2,2-bis[4'(4”-aminophenoxy)phenyl]phthalide-3',5'-bis(trifluoromethyl)aniline (6FADAP), and 3,3',5,5'-tetrafluoro-4,4'-diamino-diphenylmethane (TFDAM). In a specific embodiment, the fluorinated diamine is 2,2'-bis(trifluoromethyl)benzidine (TFMB). In one embodiment, the fluorinated aromatic diamine may be present at 40 to 95 mole percent based on the total diamine content of the polyimide. In a more specific embodiment, the fluorinated aromatic diamine may be present at 50 to 75 mole percent based on the total diamine content of the polyimide.

[0071] In one embodiment, any number of additional diamines can be used to form the polyimide, including p-phenylenediamine (PPD), m-toluidine (MTB), m-phenylenediamine (MPD), 3-(4-aminophenyl)-1,1,3-trimethyl-5-aminoindane (PIDA), 2,5-dimethyl-1,4-diaminobenzene, 2,5-dimethyl-1,4-benzenediamine (DPX), 2,2-bis-(4-aminophenyl)propane, 1,4-naphthalenediamine, 1,5-naphthalenediamine, 4,4'-diaminobiphenyl, 4,4''-diaminotriphenyl, 4,4'-diaminobenzanilide, 4,4'-diaminophenyl benzoate, 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), 4,4'-bis-(aminophenoxy)biphenyl (BAPB), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether (3,4-ODA), 4,4'-diaminobenzophenone, 4,4'-isopropylidenedianiline, 2,2'-bis-(3-aminophenyl)propane, N,N-bis-(4-aminophenyl)-n-butylamine, N,N-bis-(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, m-aminobenzoyl-p-aminobenzanilide, 4-aminophenyl-3-aminobenzoate, N,N-bis-(4-aminophenyl)aniline, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,6-diaminotoluene, 2,4-diamino-5-chlorotoluene, 2,4-diamino-6-chlorotoluene, 2,4-bis-(β-amino-tert-butyl)toluene, bis-(p-β-amino-tert-butylphenyl)ether, p-bis-2-(2-methyl-4-aminopentyl)benzene, m-xylylenediamine, and p-xylylenediamine.

[0072] Other useful diamines 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), 2,2'-bis-(4-phenoxyaniline) isopropylidene, 2,4,6-trimethyl-1,3-diaminobenzene, and 2,4,6-trimethyl-1,3-diaminobenzene.

[0073] diacid anhydride

[0074] In one embodiment, any number of suitable dianhydrides can be used to form the polyimide. The dianhydride can be used in its tetraacid form (or as the mono-, di-, tri-, or tetraester of the tetraacid), or as its diester acyl halide (chloride). However, in some embodiments, the dianhydride form may be preferred because it is generally more reactive than the acid or ester.

[0075] Examples of suitable dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2-(3',4'-dicarboxyphenyl)5,6-dicarboxybenzimidazole dianhydride, 2-(3',4'-dicarboxyphenyl)5,6-dicarboxybenzoxazole dianhydride, 2-(3',4'-dicarboxyphenyl)5,6-dicarboxybenzothiazole dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, bicyclo-[2,2,2]-octene-(7)-2,3,5,6-tetracarboxylic-2,3,5,6-dianhydride, 4,4'-thio-diophthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfoxide dianhydride (DSDA), bis(3,4-dicarboxyphenyl)oxadiazole-1,3,4)terephthalic anhydride, bis(3,4-dicarboxyphenyl)2,5-oxadiazole 1,3,4-dianhydride, bis 2,5-(3',4'-dicarboxydiphenylether)1,3,4-oxadiazole dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), bis(3,4-dicarboxyphenyl)sulfide dianhydride, bisphenol A dianhydride (BPADA), bisphenol S dianhydride, bis-1,3-isobenzofurandione, 1,4-bis(4,4'-oxydiphthalic anhydride)benzene, bis(3,4-dicarboxyphenyl)methane dianhydride, cyclopentadienyltetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, ethylenetetracarboxylic dianhydride, perylene 3,4,9,10-tetracarboxylic dianhydride, pyromellitic dianhydride (PMDA), tetrahydrofurantetracarboxylic dianhydride, 1,3-bis-(4,4'-oxydiphthalic anhydride)benzene, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,6-dichloronaphthalene-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.

[0076] In one embodiment, suitable dianhydrides can include alicyclic dianhydrides such as cyclobutane dianhydride (CBDA), cyclohexane dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), hexahydro-4,8-endoethylidene-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetrone (BODA), 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic 1,4:2,3-dianhydride (TCA), and meso-butane-1,2,3,4-tetracarboxylic dianhydride.

[0077] In one embodiment, suitable dianhydrides for forming polyimide can include fluorinated dianhydrides such as 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride.

[0078] crosslinking agent

[0079] In one embodiment, a crosslinking agent is used in the polymer film. By crosslinking the polyimide, the polymer film can have improved mechanical properties and improved chemical resistance. The crosslinking agent can include polyetheramines such as D-230, D-400, D-2000, D-2010, D-4000, ED-600, ED-900, D-2003, EDR-148, THF-100, THF-170, SD-2001, D-205 and RFD-270, secondary amines such as piperazine, N,N'-diisopropylethylenediamine, N,N'-diisopropyl-1,3-propanediamine, and N,N'-dimethyl-1,3-propanediamine, and triamines such as 2,4,6-triaminopyrimidine (TAP), melamine, diethylenetriamine, T-403, T-3000, T-5000. Additionally, many of the diamines that can be used as diamine monomers for polyimide as described above can also be used as crosslinking agents.

[0080] colorant

[0081] In one embodiment, the polymer film contains from about 1 to about 40 wt% of a colorant, such as a pigment or a dye. In some embodiments, the polymer film contains a mixture of from about 1 to about 40 wt% of a pigment and a dye. In some embodiments, the polymer film contains a colorant between and including any two of: 1, 5, 10, 15, 20, 25, 30, 35, and 40 wt%.

[0082] Virtually any pigment (or combination of pigments) can be used to practice the present invention. In some embodiments, useful pigments include, but are not limited to, the following: barium lemon yellow, cadmium lemon yellow, cadmium lemon yellow, cadmium pale yellow, cadmium medium yellow, cadmium orange yellow, scarlet lake, cadmium red, cadmium vermilion, deep alizarin red, fast garnet, Van Dyke brown, green raw sienna, or burnt sienna. In some embodiments, useful black pigments include: cobalt oxide, Fe-Mn-Bi black, Fe-Mn oxide spinel black, (Fe,Mn) 2 O 3 black, copper chromite black spinel, lamp black, bone black, bone ash, bone char, hematite, black iron oxide, mica iron oxide, black composite inorganic color pigment (CICP), (Ni,Mn,Co)(Cr,Fe) 2 O 4 black, aniline black, perylene black, anthraquinone black, chromium green-black hematite, chromium iron oxide, pigment green 17, pigment black 26, pigment black 27, pigment black 28, pigment brown 29, pigment brown 35, pigment black 30, pigment black 32, pigment black 33, or mixtures thereof.

[0083] In some embodiments, the pigment is lithopone, zinc sulfide, barium sulfate, cobalt oxide, yellow iron oxide, orange iron oxide, red iron oxide, brown iron oxide, hematite, black iron oxide, mica iron oxide, chromium(III) green, ultramarine blue, ultramarine violet, ultramarine pink, Prussian blue, cadmium pigments, or lead chromate pigments.

[0084] In some embodiments, the pigment is a composite inorganic color pigment (CICP), such as a spinel pigment, a rutile pigment, a zircon pigment, or bismuth vanadate yellow. In some embodiments, useful spinel pigments include, but are not limited to: Zn(Fe,Cr) 2 O 4 brown, CoAl 2 O 4 blue, Co(AlCr) 2 O 4 blue green, Co 2 TiO 4 green, CuCr 2 O 4 black or (Ni,Mn,Co)(Cr,Fe) 2 O 4Black. In some embodiments, useful rutile pigments include, but are not limited to: Ti-Ni-Sb yellow, Ti-Mn-Sb brown, Ti-Cr-Sb light yellow, zircon pigments, or bismuth vanadate yellow.

[0085] In another embodiment, the pigment is an organic pigment. In some embodiments, useful organic pigments include, but are not limited to: aniline black (Pigment Black 1), anthraquinone black, monoazo type, diazo type, benzimidazolone, benzidine yellow, monoazo yellow salt, diphenylamine orange, pyrazolone orange, azo red, naphthol red, azo condensation pigments, lake pigments, copper phthalocyanine blue, copper phthalocyanine green, quinacridone, diaryl pyrrolo pyrrole, amino anthraquinone pigments, dioxazine, isoindolinone, isoindoline, quinophthalone, phthalocyanine pigments, indanthrone pigments, Pigment Violet 1, Pigment Violet 3, Pigment Violet 19, or Pigment Violet 23. In yet another embodiment, the organic pigment is a vat dye pigment such as, but not limited to: perylene, perylene black, violanthrone, or thioindigo. The uniform dispersion of the isolated individual pigment particles (aggregates) tends to produce a uniform color intensity. In some embodiments, the pigment is ground. In some embodiments, the average particle size of the pigment is between any two of the following sizes (and optionally includes either of these two): 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 μm. In some embodiments, luminescent (fluorescent or phosphorescent) or pearlescent pigments can be used alone or in combination with other pigments or dyes.

[0086] In one embodiment, the colorant can include low-conductivity carbon black. In some embodiments, the colorant contains low-conductivity carbon black between any two of the following and including either of these two: 1, 5, 10, 15, and 20 wt%. In yet another embodiment, the colorant includes from about 2 to about 9 wt% of low-conductivity carbon black.

[0087] Low conductivity carbon black is intended to mean channel type carbon black, furnace black, or lamp black. In some embodiments, the low conductivity carbon black is surface oxidized carbon black. One method for evaluating the degree of surface oxidation (of carbon black) is to measure the volatile content of the carbon black. The volatile content can be measured by calculating the weight loss upon calcination at 950 °C for 7 minutes. Generally speaking, highly surface oxidized carbon black (high volatile content) can be easily dispersed into a polyamic acid solution (a polyimide precursor), and can then be imidized into the filled polyimide base polymer of the present disclosure with good dispersion. It is believed that if carbon black particles (aggregates) do not contact each other, electron tunneling, electron hopping, or other electron flow mechanisms are generally inhibited, resulting in lower conductivity. In some embodiments, the low conductivity carbon black has a volatile content greater than or equal to 1%. In some embodiments, the low conductivity carbon black has a volatile content greater than or equal to 5%, 9%, or 13%. In some embodiments, furnace black can be surface treated to increase the volatile content. Typically, the low conductivity carbon black has a pH less than about 6.

[0088] The uniform dispersion of separated carbon black particles (aggregates) not only reduces conductivity but also tends to produce a uniform color intensity. In some embodiments, the low conductivity carbon black is ground. In some embodiments, the average particle size of the low conductivity carbon black is between any two of the following sizes (and optionally includes either of these two): 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 μm.

[0089] matting agent

[0090] In one embodiment, the polymer film contains from about 0.5 to about 20 wt% of a matting agent selected from the group consisting of silica, alumina, zirconia, boron nitride, barium sulfate, polyimide particles, calcium phosphate, talc, or mixtures thereof. In some embodiments, the polymer film contains a matting agent between any two of the following and including either of these two: 0.5, 1, 5, 10, 15, and 20 wt%. In one embodiment, the matting agent has a particle size of from about 2 to about 10 μm, or from about 3 to about 9 μm, or from about 5 to about 7 μm.

[0091] submicron particle

[0092] In one embodiment, the polymer film contains up to about 39 wt% of at least one submicron particle, such as a submicron vapor-phase metal oxide (also known as a pyrolytic metal oxide) or a submicron colloidal metal oxide or a mixture thereof. In some embodiments, the submicron vapor-phase metal oxide is vapor-phase alumina, vapor-phase silica, or a mixture thereof. The addition of the submicron vapor-phase metal oxide unexpectedly reduces the amount of colorant (such as submicron carbon black) required to produce a film having an L* color of less than about 30 in the polymer film. The submicron vapor-phase alumina and vapor-phase silica in the PI film are sometimes white or hazy by themselves, so it is unpredictable that their addition actually reduces the amount of colorant required to produce a deep, rich, saturated color. It is also unexpected that other submicron metal oxides do not have the same effect. In one embodiment, the polymer film comprises up to about 20 wt% or up to about 10 wt% of at least one submicron particle. In one embodiment, the submicron particle has a particle size of less than about 1 μm. In one embodiment, the submicron particle has a particle size of about 0.01 to about 1 μm, or about 0.05 to about 0.5 μm.

[0093] A particle size analyzer, such as LA-930 (Horiba, Instruments, Inc., Irvine CA), Mastersizer 3000 (Malvern Instruments, Inc., Westborough, MA), or LS-230 (Beckman Coulter, Inc., Indianapolis, IN), can be used to measure the particle sizes of the submicron particles, carbon black, and the matting agent in the slurry by laser diffraction. However, due to the tendency of the submicron particles to flocculate, it is sometimes more accurate to measure the particle sizes of these ground slurries by optical microscopy observation.

[0094] single-layer polymer film

[0095] As used herein, the term "single-layer polymer film" refers to a polymer film layer having a substantially uniform composition throughout the layer such that monomers for forming the polymer are present throughout the layer thickness and any fillers such as matting agents, carbon black, and submicron particles are also distributed throughout the layer thickness. A single-layer polymer film, while substantially uniform, may exhibit some gradation in the composition over certain regions or over its entire thickness and especially on the surface of the film. In contrast, a polymer film having distinct compositional variations throughout a region or thickness of the film will not be a single-layer polymer film. For example, a polyimide film having a core layer of one composition and a thin outer layer of a different composition (such as different monomers for forming the outer layer polymer or different fillers in the outer layer) will not be a single-layer polymer film.

[0096] In one embodiment, the single-layer polymer film may comprise polyimide, which can be produced by combining a diamine and a dianhydride (in monomer or other polyimide precursor form) with a solvent to form a polyamic acid (also referred to as polyamide acid) solution. The dianhydride and diamine can be combined in a molar ratio of about 0.90 to about 1.10. The molecular weight of the polyamic acid formed therefrom can be adjusted by regulating the molar ratio of the dianhydride and diamine.

[0097] Useful methods for producing a polymer film containing polyimide include:

[0098] (a) A method in which the diamine component and the dianhydride component are premixed together and then the mixture is added batchwise to the solvent while stirring.

[0099] (b) A method in which the solvent is added to a stirred mixture of the diamine and dianhydride components. (Contrary to (a) above)

[0100] (c) A method in which the diamine is dissolved in the solvent alone and then the dianhydride is added thereto at a rate that allows control of the reaction rate.

[0101] (d) A method in which the dianhydride component is dissolved in the solvent alone and then the amine component is added thereto at a rate that allows control of the reaction rate.

[0102] (e) A method in which the diamine component and the dianhydride component are dissolved in the solvent separately and then these solutions are mixed in a reactor.

[0103] (f) A method in which a polyamic acid having an excess amine component and another polyamic acid having an excess dianhydride component are preformed and then made to react with each other in a reactor, especially in such a way as to produce a non-random or block copolymer.

[0104] (g) The following method, in which the amine component and the dianhydride component of a specific part are first reacted, and then the remaining diamine component is reacted, or vice versa.

[0105] (h) The following method, in which these components are added, in part or in whole, in any order to part or all of the solvent, and in addition, part or all of any component can be added as a solution in part or all of the solvent.

[0106] (i) The following method, in which one of the dianhydride components is first reacted with one of the diamine components to obtain a first polyamic acid. Then another dianhydride component is reacted with another amine component to obtain a second polyamic acid. Then the polyamic acids are combined in any of a number of ways.

[0107] In one embodiment, the polyamic acid solution can be combined with conversion chemicals such as: (i) one or more dehydrating agents such as aliphatic acid anhydrides (acetic anhydride, etc.) and / or aromatic acid anhydrides; and (ii) one or more catalysts such as aliphatic tertiary amines (triethylamine, etc.), aromatic tertiary amines (dimethylaniline, etc.), and heterocyclic tertiary amines (pyridine, α, β, and γ methylpyridines (2-methylpyridine, 3-methylpyridine, 4-methylpyridine), isoquinoline, etc.). The acid anhydride dehydrating materials are often used in a molar excess compared to the amount of amic acid groups in the polyamic acid. The amount of acetic anhydride used is typically about 2.0 to about 4.0 moles / equivalent (repeat unit) of the polyamic acid. Generally, a comparable amount of the tertiary amine catalyst is used.

[0108] In one embodiment, the conversion chemical can be an imidization catalyst. Using an imidization catalyst can help reduce the imidization temperature and shorten the imidization time. The range of typical imidization catalysts can be bases such as imidazole, 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole, 2-phenylimidazole, benzimidazole, isoquinoline, or substituted pyridines such as methylpyridine, dimethylpyridine, and trialkylamines. Combinations of tertiary amines and acid anhydrides can be used. These dehydrating agents that can act as co-catalysts include acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, etc. The ratio of these catalysts and their concentration in the polyamic acid solution will affect the imidization kinetics.

[0109] In one embodiment, the polyamic acid solution can be heated, optionally in the presence of an imidization catalyst, to partially or completely imidize the polyamic acid and convert it to a polyimide. The temperature, time, and the concentration and selection of the imidization catalyst may affect the degree of imidization of the polyamic acid solution. Preferably, the solution should be substantially imidized. In one embodiment, for a substantially polyimide solution, as determined by infrared spectroscopy, greater than about 85%, greater than about 90%, or greater than about 95% of the amic acid groups are converted to polyimide.

[0110] In one embodiment, a substantially polyimide solution is formed using monomers (diamines or dianhydrides) having structural features important for solubility, the structural features including flexible linkages such as, but not limited to, aliphatic spacers, ethers, thioethers, substituted amines, amides, esters, and ketones, weak intermolecular interactions, bulky substitutions, non-coplanarity, non-linearity, and asymmetry. Examples of diamines that incorporate some of these features are aliphatic diamines such as HMD, CHDA, and IPDA, and aromatic diamines such as MTBTFMB, MPD, RODA, BAPP, and 3,4-ODA. Examples of dianhydrides that incorporate some of these features are 6FDA, BPADA, ODPA, DSDA, and BODA.

[0111] In one embodiment, a solvated mixture (substantially imidized solution) can be mixed with a crosslinker and a colorant such as a pigment or a dye, and then cast to form a single-layer polyimide film. In one embodiment, the colorant can be low-conductivity carbon black. In another embodiment, the solvated mixture (first substantially imidized solution) can be precipitated with an anti-solvent such as water or an alcohol (e.g., methanol, ethanol, isopropanol). In one embodiment, the precipitate can be washed to remove the catalyst. After washing, the precipitate can be substantially dry, but does not have to be completely dry. The polyimide precipitate can be redissolved in a second solvent such as methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), tetrahydrofuran (THF), cyclopentanone, ethyl acetate, acetone, DMAc, NMP, and mixtures thereof, to form a second substantially imidized solution (casting solution). A crosslinker and a colorant can be added to the second substantially imidized solution, which can then be cast to form a single-layer polymer film. In one embodiment, the single-layer polymer film contains from about 80 to about 99 wt% of crosslinked polyimide. In some embodiments, the polymer film contains crosslinked polyimide between and including any two of: 80, 85, 90, 95, and 99 wt%. In yet another embodiment, the polymer film contains from about 91 to about 98 wt% of crosslinked polyimide.

[0112] The crosslinking of the polyimide can be determined by various methods. In one embodiment, the gel fraction of the polyimide can be determined by using the equilibrium swelling method and comparing the weights of the dry film before and after crosslinking. In one embodiment, the crosslinked polyimide can have a gel fraction of from about 20% to about 100%, or from about 40% to about 100%, or from about 50% to about 100%, or from about 70% to about 100%, or from about 85% to about 100%. In one embodiment, the crosslinked network can be identified using rheological methods. Oscillatory time sweep measurements at specific strain, frequency, and temperature can be used to confirm the formation of the crosslinked network. Initially, the loss modulus (G”) value is higher than the storage modulus (G’) value, indicating that the polyimide solution behaves like a viscous liquid. Over time, the formation of the crosslinked polyimide network is evidenced by the crossing of the G’ and G” curves. The crossing, called the “gel point”, indicates when the elastic component predominates over the viscous component and the polymer begins to behave like an elastic solid.

[0113] In one embodiment, a substantially imidized polyimide solution can be cast or applied onto a support (such as an endless belt or a drum) to form a film. Alternatively, it can be cast onto a polymer carrier such as a polyethylene terephthalate (PET) film, other forms of polyimide film (e.g., HN or OL film) or other polymer carriers. In one embodiment, the support or carrier layer can be textured, such as a textured PET substrate. Next, the substantially imidized solution can be converted into a film by heating to crosslink the polyimide and partially or completely remove the solvent. The film is heated at a low temperature to initiate polyimide crosslinking and partially dry the polyimide film. Typically, a temperature below about 100 °C is used for the initial drying and crosslinking. Next, the film is heated to a higher temperature up to about 300 °C to complete polyimide crosslinking and further remove the solvent. In some aspects of the present invention, the film is separated from the carrier before drying is complete. The final drying step can be carried out with the film dimensionally supported. In other aspects, the film is heated directly on the carrier.

[0114] In one embodiment, the single-layer polymer film comprises a polyimide having a low refractive index, such as less than about 1.74, or less than about 1.69, or less than about 1.60. Reducing the refractive index of the polyimide enables the formation of a single-layer polymer film having both low L* and gloss. Conventional polyimides exhibit significantly higher refractive indices (RIs) due to the high content of aromatic rings and imide structures compared to other common optical polymers. However, their poor transparency in the visible region is a severe light-trapping obstacle, increasing the reflection at the film surface. The light absorption of polyimides in the visible region is mainly caused by intramolecular and intermolecular charge transfer (CT) interactions between electron-donating diamines and electron-accepting dianhydride moieties. In one embodiment, the average refractive index n of a material can be estimated by the Lorentz-Lorenz equation av :

[0115]

[0116] where α av is the average molecular polarizability, V int is the intrinsic volume of the repeating unit, ρ is the density, N A is Avogadro's number, and M is the molecular weight. The equation can be simplified to:

[0117]

[0118] where K p is the molecular packing coefficient and V vdw is the molecular van der Waals volume (see Y. Terui and S. Ando, J Polym Sci: Part B Polymer Physics, 42, 2354-2366 (2004)). Based on this equation, a method for minimizing the refractive index of a polymer formulation is to minimize the contribution of the α av / V vdw ratio. The variables of this ratio can be calculated empirically, semi-empirically, or from ab initio principles. Using the calculated ratio, monomers can be selected or removed to achieve a low refractive index. The aim is to reduce the polarizability of the polyimide molecular chains, thereby reducing the refractive index of the polymer. The polarizability of the polymer can be reduced by introducing electron-withdrawing fluorine atoms or fluorinated substituents, incorporating alicyclic moieties, and modifying the molecular backbone with meta-substituted structures and bulky side-chain groups.

[0119] In one embodiment, the single-layer polymer film may have an L* of about 30 or less and a 60° gloss (60GU) of about 15 or less. In one embodiment, the single-layer polymer film may have an L* of about 25 or less or about 20 or less. In one embodiment, the single-layer polymer film may have a 60° gloss of about 10 or less, or about 8 or less, or about 6 or less.

[0120] The thickness of the single-layer polymer film can be adjusted according to the intended purpose of the film or the final application specifications. In one embodiment, the single-layer polymer film has a total thickness of about 2 to about 125 μm, or about 4 to about 50 μm, or about 5 to about 20 μm.

[0121] In one embodiment, the single-layer polymer film can be textured using mechanical or chemical means. In one embodiment, mechanical texturing may include a process of physically removing portions of the film surface, such as sandblasting or laser ablation. In one embodiment, for sandblasting, the single-layer polymer film can be textured by spraying the surface of the film with fine sand in an abrasive jet (centrifugal jet) process where an impeller rotates therein to utilize centrifugal force for sandblasting. In one embodiment, texturing can be provided by embossing or imprinting a texture on the film surface. In one embodiment, for imprinting, the single-layer polymer film can be textured by casting the film onto a textured surface, where the texture is transferred onto the polymer film surface. In one embodiment, chemical texturing can be provided by photolithography.

[0122] In one embodiment, even if the film does not contain a matting agent, the textured film can have both a low L* color and a low gloss. In one embodiment, the single-layer polymer film having a textured surface may have a maximum roughness (S pv ) of about 6 μm or greater, an L* of about 30 or less, and a 60° gloss (60GU) of about 15 or less. In one embodiment, the single-layer polymer film having a textured surface may have an S pv of about 7 μm or greater or about 8 μm or greater. In one embodiment, the single-layer polymer film having a textured surface may have an L* of about 25 or less or about 20 or less. In one embodiment, the single-layer polymer film having a textured surface may have a 60° gloss of about 10 or less, or about 8 or less, or about 6 or less. In one embodiment, both sides of the single-layer polymer film may have a textured surface.

[0123] application

[0124] In one embodiment, a single-layer polymer film can be used in electronic device applications, such as for a cover layer of a printed circuit board or other electronic components in an electronic device, thereby providing protection against physical damage, oxidation, and other contaminants that may adversely affect the functionality of the electronic components. A very thin cover layer of a single-layer polymer film using cross-linked polyimide is more chemical resistant and can withstand etching during the grinding, decontamination procedures, and plasma processes used in circuit production while maintaining good optical properties.

[0125] The advantageous properties of the present invention can be observed by reference to the following examples that illustrate but do not limit the invention. All parts and percentages are by weight unless otherwise indicated.

[0126] example

[0127] test method

[0128] CIE L*, a*, b* color

[0129] Using A XE double-beam spectrophotometer (Hunter Associates Laboratory, Inc., Reston, VA) was used to perform color measurements in the reflectance (including specular reflectance) mode. The instrument was standardized before each use. Color data from the instrument was reported as L*, a*, b* in the CIELAB 10° / D65 system. An L* value of 0 is pure black, while an L* value of 100 is pure white. Typically, a difference in L* value of 1 unit is distinguishable to the eye.

[0130] refractive index

[0131] Using A Model 2010 prism coupler (Metricon Corporation, Pennington, NJ) was used to measure the refractive index using a laser wavelength of 633 nm (632.8 nm). The instrument was benchmarked before each use. Refractive index measurements were made in the transverse electric mode to report the refractive index in the plane of the film.

[0132] gel fraction

[0133] The polyimide gel fraction was measured using the Soxhlet extraction method. The polymer film sample was placed in a glass thimble, which was placed in the main chamber of a Soxhlet extractor located above a nitrogen-purged, solvent-filled round-bottom flask. The extraction solvent (DMAc) was continuously circulated through the sample by boiling and condensation. After applying sufficient heat to the round-bottom flask, the solvent in vapor form was transferred to the main chamber of the Soxhlet extractor and condensed. After reaching the overflow level, the solvent was drained back into the round-bottom flask via a siphon tube.

[0134] A polymer film of approximately 2 × 3 inches was used. The film sample was wiped clean with acetone, air-dried, weighed, and crumpled before being placed in the glass thimble. The temperature of DMAc (approx. 300 ml) was set at 165 °C to 175 °C and extraction was carried out over a period of at least 7 hours. After that, the sample was removed from the apparatus, dried on a hot plate at 50 °C for up to 1 hour, and placed in an oven at 120 °C. The oven was heated from 120 °C to 250 °C (16 °C / min) and then held at 250 °C for 20 minutes. The film was removed “hot” from the oven after heating at 250 °C for 20 minutes and allowed to cool in air, and the sample was weighed again. Fresh solvent was used for each sample.

[0135] 60° glossiness

[0136] The 60° gloss (60GU) was measured using a Micro-TRI-gloss glossmeter (BYK-Gardner USA, Columbia, MD). This instrument was calibrated before each use.

[0137] particle size

[0138] The particle size of the filler particles in the slurry was measured by laser diffraction using a particle size analyzer (Mastersizer 3000, Malvern Instruments, Westborough, MA). DMAc was used as the carrier fluid.

[0139] surface roughness

[0140] ZeGage TM Pro 3D optical profiler (Zygo Corp., Middlefield, CT) was used to measure the surface roughness over an area of 167 × 167 μm (0.28 mm 2 ). The maximum roughness (S pv , S z or R z ) is the maximum peak height of the measured surface (S p) and the maximum valley depth (S v ), and S pv = S p + S v .

[0141] carbon black with low conductivity

[0142] Prepare a carbon black solution consisting of 90 wt% DMAc and 10 wt% carbon black powder (Special Black 4, SB4, Orion Engineered Carbons LLC, Kingwood, TX). Mix the components well using a handheld high-shear mixer.

[0143] Compare Comparative Example 1 and Example 1

[0144] For Comparative Example 1 and Example 1 (CE1 and E1), a soluble thermoplastic polyimide with a monomer composition of 3,3',4,4'-benzophenone tetracarboxylic dianhydride / / 3-(4-aminophenyl)-1,1,3-trimethyl-5-aminoindane (BTDA 1.0 / / PIDA 1.0) 9725, Huntsman Corp., The Woodlands, TX was used as a dry powder.

[0145] For CE1, 5 g of the dry polymer resin was added to 17.4 g of dimethylacetamide (DMAc, HPLC grade) and mixed in a centrifugal planetary mixer (THINKY USA, Laguna Hills, CA) to obtain a solution. The solution was degassed using the centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. A 10 wt% solution of 2.5 g of SB4 carbon (Orion Engineered Carbons) in DMAc, along with a release agent, was added to the polyimide solution to facilitate the removal of the film from the casting substrate. The solution was mixed at 2200 rpm for 2 minutes using the centrifugal planetary mixer and then degassed at 2000 rpm for 5 minutes.

[0146] The solution was cast onto a matte PET substrate at 25 °C (Kaisei Industries, Inc., Japan) to produce a 1 - 2 mil cured film. The film on the matte PET substrate was heated to 80 °C for 15 minutes and then lifted from the matte PET surface and mounted onto an 8×12 inch frame. The mounted film was placed in an oven. The oven was heated from 120 °C to 250 °C (16 °C / min), then held at 250 °C for 20 minutes. The film was removed “hot” from the oven after heating at 250 °C for 20 minutes and allowed to cool in air.

[0147] For E1, a polyimide solution with carbon black was prepared as described above for CE1. Before the final degassing step, 1.04 g of a 10 wt% solution of D - 230 (Huntsman) in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed for 30 seconds at 2200 rpm using a centrifugal planetary mixer, and then degassed at 2000 rpm for 5 minutes while kept at low temperature.

[0148] The solution was cast onto a matte PET substrate at 25 °C to produce a 1 - 2 mil cured film. The film on the matte PET substrate was heated to 80 °C for 10 minutes and then lifted from the matte PET surface and mounted onto an 8×12 inch frame. The mounted film was placed in an oven and heated as described above for CE1.

[0149] Compare Comparative Example 2 and Example 2

[0150] For the polyamic acid (PAA) solution with a monomer composition of BPADA 1.0 / / PIDA 1.0 for Comparative Example 2 and Example 2 (CE2 and E2), 6.77 g of 3 - (4 - aminophenyl)-1,1,3 - trimethyl - 5 - aminoindane (PIDA, Changzhou Sunlight Pharmaceutical Co., Ltd., China) was added to a 300 ml beaker inside a nitrogen - purged glove box together with 180 g of DMAc. 13.20 g of 4,4’ - bisphenol A dianhydride (BPADA, Sabic, Riyadh, Saudi Arabia) was added in three equal portions at three 5 - 10 minute intervals. The reaction mixture was kept at 40 °C during these additions. The reaction was held at 40 °C overnight until the weight - average molecular weight M w = 284,000 g / mol, with a dispersity of 1.85.

[0151] For CE2 and E2, to prepare a substantially imidized polyimide solution (polyimide amic acid solution), 9.47 g of β-methylpyridine (Sigma Aldrich, Milwaukee, WI) and 10.38 g of acetic anhydride (Sigma Aldrich) were combined with the PAA solution. The reaction mixture was stirred at 40 °C for 30 minutes and then heated to 80 °C for 3 hours to imidize the solution. 200 g of the room temperature polymer solution was poured into 600 ml of methanol (Sigma Aldrich) in a blender and rapidly stirred to crush the polymer solids. The crushed polymer solids were stirred in the blender for 10 minutes and then collected by filtration. The polymer was air dried overnight and then further dried under vacuum at 35 °C overnight.

[0152] For CE2, a polyimide solution with carbon black was prepared as described above for CE1 and cast and heated to form a film.

[0153] For E2, a polyimide solution with carbon black was prepared as described above for CE1. Before the final degassing step, 0.77 g of a 10 wt% solution of D-230 in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed at 2200 rpm for 30 seconds using a centrifugal planetary mixer and then degassed at 2000 rpm for 5 minutes while maintaining at low temperature.

[0154] The solution was cast onto a matte PET substrate at 25 °C to produce a cured film of approximately 2.5 mils. The film on the matte PET substrate was heated to 80 °C for 15 minutes and then lifted from the matte PET surface and mounted onto an 8×12 inch frame. The mounted film was placed in an oven and heated as described above for CE1.

[0155] Table 1 summarizes the properties of E1 - E2 and CE1 - CE2. As confirmed by gel fraction measurements, while all of E1 - E2 and CE1 - CE2 exhibit good color and gloss properties, the crosslinked films (E1 and E2) have excellent chemical resistance. Additionally, the 60 GU of the crosslinked films is lower than that of their non-crosslinked counterparts.

[0156] Table 1

[0157]

[0158] Comparative Example 3

[0159] For Comparative Example 3 (CE3), as used in CE1 and E1, used as a dry powder 9725 Polymer.

[0160] For CE3, 2.5 g of the dry polymer resin was added to 8.7 g of DMAc and mixed in a centrifugal planetary mixer to obtain a solution. The solution was degassed using the centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. A 2.5 wt% solution of triphenyl phosphite release agent in DMAc and a 10 wt% solution of SB4 carbon in DMAc, 1.25 g, were added to the polyimide solution. The solution was mixed at 2200 rpm for 2 minutes using the centrifugal planetary mixer and then degassed at 2000 rpm for 10 minutes. 1.04 g of a 10 wt% solution of D - 230 in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed at 2200 rpm for 30 seconds using the centrifugal planetary mixer and then degassed at 2000 rpm for 5 minutes while maintaining at low temperature.

[0161] The solution was cast onto a polyester film (DuPont Teijin Films USA, Chester, VA) substrate at 25 °C to produce a 1 - 2 mil cured film. The film on the substrate was heated to 80 °C for 15 minutes and then lifted from the polyester film surface and mounted onto an 8×12 inch frame. The mounted film was placed in an oven and heated as described above for CE1. The polyimide was cast on the smooth surface of the polyester film (low S pv ) resulting in a polymer film with high gloss, despite its high degree of cross - linking (see Table 1).

[0162] Example 3

[0163] For the polyamic acid (PAA) solution of Example 3 (E3) having a monomer composition of CBDA 0.6 / 6FDA 0.4 / / TFMB 1.0, 2.268 kg of trifluoromethyl-benzidine (TFMB, Seika Corp., Wakayama Seika Kogyo Co., Ltd., Japan) together with 32.191 kg of DMAc were added to a 72 L resin kettle purged with nitrogen. 1.252 kg of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA, Daikin America Incorporated, Decatur, AL) and 0.829 kg of cyclobutanedicarboxylic anhydride (CBDA, Wilshire Technologies, Princeton, NJ) were added in three equal portions at three 60-minute intervals. The reaction mixture was maintained at 40 °C during these additions. The polymer was polymerized ("processed") to 12 poise using a small addition of 6FDA powder.

[0164] For E3, to prepare a substantially imidized polyimide solution (polyimide amic acid solution), an additional 2.787 kg of DMAc was added and stirred for 60 minutes. 1.65 kg of β-methylpyridine and 1.808 kg of acetic anhydride were combined with the PAA solution. The reaction mixture was heated to 80 °C for 2 hours to imidize the solution. 1,000 g of the room temperature polymer solution was poured into 2 L of methanol in a blender and rapidly stirred to crush the polymer solids. The crushed polymer solids were stirred in the blender for 10 minutes and then collected by filtration. The polymer was air dried overnight and then further dried under vacuum at 50 °C overnight.

[0165] For E3, 2.5 g of the dried polymer was added to 21.2 g of DMAc and mixed in a centrifugal planetary mixer to obtain a solution. The solution was degassed using the centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. A 2.5 wt% solution of triphenyl phosphite release agent in DMAc and a 10 wt% solution of SB4 carbon in DMAc were added to the polyimide solution. The solution was mixed using the centrifugal planetary mixer at 2200 rpm for 2 minutes. 0.5 g of A 10 wt% solution of D-230 in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed at 2200 rpm for 30 seconds using the centrifugal planetary mixer, followed by degassing at 2000 rpm for 5 minutes while maintaining at low temperature.

[0166] Cast the solution onto a matte PET substrate at 25 °C as described above for CE1 to produce a 1-2 mil cured film.

[0167] Example 4

[0168] For the polyamic acid (PAA) solution of Example 4 (E4) with a BPADA 1.0 / / 3,4-ODA 1.0 monomer composition, add 5.56 g of 3,4-oxydianiline (3,4-ODA, Seika Corp., Wakayama Seika Kogyo Co., Ltd., Japan) along with 180 g of DMAc to a 300 ml beaker in a nitrogen-purged glove box. Add 14.415 g of BPADA in three equal portions at three 5-10 minute intervals. Keep the reaction mixture at 40 °C during these additions. Hold the reaction at 40 °C overnight until the weight-average molecular weight M w = 184,000 g / mol, with a dispersity of 2.00.

[0169] For E4, to prepare a substantially imidized polyimide solution (polyimide amic acid solution), combine 10.34 g of β-methylpyridine and 11.33 g of acetic anhydride with the PAA solution. Stir the reaction mixture at 40 °C for 30 minutes, then heat to 80 °C for 3 hours to imidize the solution. Pour 200 g of the room-temperature polymer solution into 600 ml of methanol in a blender and stir rapidly to crush the polymer solid. Stir the crushed polymer solid in the blender for 10 minutes, then collect by filtration. Air-dry the polymer overnight and then further dry it under vacuum at 35 °C overnight.

[0170] For E4, add 2.5 g of the dried polymer to 8.7 g of DMAc and mix in a centrifugal planetary mixer to obtain a solution. Degas the solution using the centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. Add a 2.5 wt% solution of triphenyl phosphite release agent in DMAc and a 10 wt% solution of SB4 carbon in DMAc to the polyimide solution. Mix the solution using the centrifugal planetary mixer at 2200 rpm for 2 minutes. Add a 10 wt% solution of D-230 in DMAc to the polymer solution. While cooling in a cold cup, mix the solution using the centrifugal planetary mixer at 2200 rpm for 30 seconds, then degas at 2000 rpm for 5 minutes, keeping it at low temperature.

[0171] Cast the solution onto a matte PET substrate at 25 °C as described above for CE1 to produce a 1-2 mil cured film.

[0172] Example 5

[0173] For the polyamic acid (PAA) solution of Example 5 (E5) having a BPADA 1.0 / / RODA 1.0 monomer composition, 8.647 g of 1,3-bis(4-aminophenoxy)benzene (RODA) together with 180 g of DMAc were added to a 300 ml beaker in a nitrogen-purged glove box. 8.630 g of BPADA was added in smaller aliquots and stirred until completely dissolved. The reaction mixture was maintained at 40 °C during these additions. The reaction was maintained at 40 °C overnight until the weight-average molecular weight M w w = 184,000 g / mol, with a dispersity of 2.00.

[0174] For E5, to prepare a substantially imidized polyimide solution (polyimide amic acid solution), an additional 17.0 g of DMAc together with 10.31 g of β-picoline and 11.31 g of acetic anhydride were added to the PAA solution. The reaction was stirred at room temperature for approximately two hours. During this time, the solution viscosity increased slightly and an additional 50 ml of DMAc was added. The solution was stirred overnight.

[0175] 200 g of the polymer solution was mixed with approximately 600 ml of methanol and mixed in a laboratory blender until fine powder solid particles were produced. The resulting suspension was then filtered, air-dried at room temperature overnight, and vacuum-dried at 50 °C overnight.

[0176] For E5, 2.5 g of the dried polymer was added to 12.9 g of DMAc and mixed in a centrifugal planetary mixer to obtain a solution. The solution was degassed using the centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. A 2.5 wt% solution of triphenyl phosphite as a release agent in DMAc and a 10 wt% solution of SB4 carbon in DMAc were added to the polyimide solution. The solution was mixed using the centrifugal planetary mixer at 2200 rpm for 2 minutes. 0.42 g of a 10 wt% solution of D-230 in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed using the centrifugal planetary mixer at 2200 rpm for 30 seconds, followed by degassing at 2000 rpm for 5 minutes while maintaining at low temperature.

[0177] The solution was cast onto a 25 °C matte PET substrate as described above for CE1 to produce a 1 - 2 mil cured film.

[0178] Example 6

[0179] For Example 6 (E6), as used in CE1 and E1, used as a dry powder 9725 polymer.

[0180] For E6, 2.5 g of the dry polymer resin was added to 8.7 g of DMAc and mixed in a centrifugal planetary mixer to obtain a solution. The solution was degassed using a centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. A 2.5 wt% solution of 0.05 g of triphenyl phosphite release agent in DMAc and a 10 wt% solution of 1.25 g of SB4 carbon in DMAc were added to the polyimide solution. The solution was mixed at 2200 rpm for 2 minutes using a centrifugal planetary mixer, followed by degassing at 2000 rpm for 10 minutes. 2.08 g of A 10 wt% solution of D-230 in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed at 2200 rpm for 30 seconds using a centrifugal planetary mixer, followed by degassing at 2000 rpm for 5 minutes while maintaining at low temperature.

[0181] The solution was cast onto a matte PET substrate at 25 °C as described above for CE1 to produce a 1 - 2 mil cured film.

[0182] Example 7

[0183] For Example 7 (E7), as used in CE1 and E1, used as a dry powder 9725 polymer.

[0184] For E7, 2.5 g of the dry polymer resin was added to 8.7 g of DMAc and mixed in a centrifugal planetary mixer to obtain a solution. The solution was degassed using a centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. A 2.5 wt% solution of 0.05 g of triphenyl phosphite release agent in DMAc and a 10 wt% solution of 1.25 g of SB4 carbon in DMAc were added to the polyimide solution. The solution was mixed at 2200 rpm for 2 minutes using a centrifugal planetary mixer, followed by degassing at 2000 rpm for 10 minutes. 0.66 g of A 10 wt% solution of T - 403 (Huntsman Corporation) in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed at 2200 rpm for 30 seconds using a centrifugal planetary mixer, followed by degassing at 2000 rpm for 5 minutes while maintaining at low temperature.

[0185] Cast the solution onto a matte PET substrate at 25 °C as described above for CE1 to produce a 1-2 mil cured film.

[0186] Example 8

[0187] For Example 8 (E8), as used in CE1 and E1, use the 9725 polymer as a dry powder.

[0188] For E8, add 2.5 g of the dry polymer resin to 8.7 g of DMAc and mix in a centrifugal planetary mixer. Degas the solution using the centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. Add a 2.5 wt% solution of 0.05 g of triphenyl phosphite release agent in DMAc and a 10 wt% solution of 1.25 g of SB4 carbon in DMAc to the polyimide solution. Mix the solution at 2200 rpm for 2 minutes using the centrifugal planetary mixer, then degas at 2000 rpm for 10 minutes. Add a 10 wt% solution of 0.31 g of m-xylenediamine (MXD, Sigma-Aldrich, Milwaukee, WI) in DMAc to the polymer solution. While cooling in a cold cup, mix the solution at 2200 rpm for 30 seconds using the centrifugal planetary mixer, then degas at 2000 rpm for 5 minutes while maintaining at low temperature.

[0189] Cast the solution onto a matte PET substrate at 25 °C as described above for CE1 to produce a 1-2 mil cured film.

[0190] Example 9

[0191] For Example 9 (E9), as used in CE1 and E1, use the 9725 polymer as a dry powder.

[0192] For E9, add 2.5 g of the dry polymer resin to 4.95 g of DMAc and mix in a centrifugal planetary mixer to obtain a solution. Degas the solution using the centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. Add a 2.5 wt% solution of 0.05 g of triphenyl phosphite release agent in DMAc and a 10 wt% solution of 5 g of perylene black ( Black L 0086, BASF SE, Germany) in DMAc to the polyimide solution. Mix the solution at 2200 rpm for 2 minutes using the centrifugal planetary mixer, then degas at 2000 rpm for 10 minutes. Add 1.04 g of A 10 wt% solution of D-230 in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed for 30 seconds at 2200 rpm using a centrifugal planetary mixer, and then degassed for 5 minutes at 2000 rpm while maintaining at a low temperature.

[0193] The solution was cast onto a 25 °C matte PET substrate as described above for CE1 to produce a 1-2 mil cured film.

[0194] Example 10

[0195] For Example 10 (E10), as used in CE1 and E1, 9725 polymer was used as a dry powder 9725 polymer.

[0196] For E10, 2.5 g of the dry polymer resin was added to 7.45 g of DMAc and mixed in a centrifugal planetary mixer to obtain a solution. The solution was degassed using a centrifugal planetary mixer to force the gas out of the polymer at 2000 rpm for 10 minutes. A 2.5 wt% solution of triphenyl phosphite release agent in DMAc, a 10 wt% solution of SB4 carbon in DMAc, and a 10 wt% solution of silica matting agent ( C807, W.R. Grace & Co., Columbia, MD) in DMAc were added to the polyimide solution. The solution was mixed for 2 minutes at 2200 rpm using a centrifugal planetary mixer, and then degassed for 10 minutes at 2000 rpm. A 10 wt% solution of D-230 in DMAc was added to the polymer solution. While cooling in a cold cup, the solution was mixed for 30 seconds at 2200 rpm using a centrifugal planetary mixer, and then degassed for 5 minutes at 2000 rpm while maintaining at a low temperature.

[0197] The solution was cast onto a 25 °C matte PET substrate as described above for CE1 to produce a 1-2 mil cured film. E3-E10, as summarized in Table 2, show a series of crosslinked polymers with low refractive indices, which have low color and gloss for films with sufficient surface roughness.

[0198] Comparative Example 4

[0199] For the polyamic acid solution of Comparative Example 4 (CE4) having a BPDA 1.0 / / PPD 1.0 monomer composition, 10.95 g of p-phenylenediamine (PPD) together with 160.17 g of anhydrous DMAc were added to a 300 ml nitrogen-purged reaction vessel. 28.89 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) were added over a period of several minutes. The reaction mixture was stirred until all monomers had reacted. The total stoichiometric ratio of dianhydride to diamine was approximately 0.97:1. The mixture reached a polymer viscosity of 75 - 250 poise at approximately 20% polyamic acid solids. The polymer was polymerized ("processed") using a solution of PMDA in a small amount of added DMAc to increase the molecular weight and provide the desired viscosity. The polymer solution was stored in a freezer until use.

[0200] A solution was prepared by adding an 8.42 g, 10 wt% solution of SB4 carbon in DMAc to 91.58 g of the polymer solution and mixing it in a centrifugal planetary mixer. The solution was cast onto a matte PET substrate at 25 °C to produce a 1 - 2 mil cured film. The film on the matte PET substrate was heated at 90 °C for 20 minutes and then lifted from the matte PET surface and mounted onto an 8 x 12 inch frame. The mounted film was placed in an oven. The oven was heated from 120 °C to 320 °C (16 °C / min), then the film was "hot" removed from the oven and placed in another oven at 400 °C for 5 minutes, then removed and dried in air.

[0201] Comparative Example 5

[0202] For the polyamic acid solution of Comparative Example 5 (CE5) having an ODPA 0.5 / PMDA 0.5 / / MPD 0.5 / BAPP 0.5 monomer composition, 20.48 g of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) and 5.40 g of m-phenylenediamine (MPD) together with 148.2 g of DMAc were added to a 300 ml nitrogen-purged reaction vessel. 10.45 g of pyromellitic dianhydride (PMDA) and 15.48 g of 4,4'-oxydiphthalic anhydride (ODPA) were added over a period of several minutes. The reaction mixture was stirred until all monomers had reacted. The total stoichiometric ratio of dianhydride to diamine was approximately 0.98:1. The mixture reached a polymer viscosity of 75 - 250 poise at approximately 26% polyamic acid solids. The polymer was polymerized ("processed") using a solution of PMDA in a small amount of added DMAc to increase the molecular weight and provide the desired viscosity. The polymer solution was stored in a freezer until use.

[0203] A solution was prepared by adding an 11.84 g solution of SB4 carbon in DMAc at 10 wt% to 88.64 g of a polymer solution and mixing it in a centrifugal planetary mixer. The solution was cast onto a matte PET substrate at 25 °C to produce a 1 - 2 mil cured film. The film on the matte PET substrate was heated at 90 °C for 20 minutes and then lifted from the matte PET surface and mounted onto an 8×12 inch frame. The mounted film was placed in an oven. The oven was heated from 120 °C to 350 °C (16 °C / min), and then the film was removed "hot" from the oven and allowed to cool in air. As shown by CE4 and CE5 summarized in Table 2, there are challenges in achieving both low color and low gloss in a single - layer polymer film when the refractive index is too high (CE4) or the surface roughness is too low (CE5).

[0204] Table 2

[0205]

[0206] It should be noted that not all of the activities described above in the general description are necessary, some specific activities may not be necessary, and other activities may be carried out in addition to those described. Also, the order in which each activity is listed need not be the order in which they are implemented. After reading this specification, those skilled in the art will be able to determine which activities are applicable to their specific needs or expectations.

[0207] In the foregoing specification, the invention has been described with reference to specific embodiments. However, those of ordinary skill in the art understand that various modifications and changes can be made without departing from the scope of the invention as defined in the following claims. All features disclosed in this specification may be replaced by alternative features serving the same, equivalent, or similar purpose.

[0208] Accordingly, this specification should be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the invention.

[0209] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, a benefit, an advantage, a solution to a problem, and any element or elements that may cause any benefit, advantage, or solution to occur or become more apparent are not to be construed as a critical, necessary, or essential feature or element of any or all of the claims.

Claims

1. A single-layer polymer film, comprising: 60 to 99 wt% of a crosslinked polyimide having a gel fraction of 20% to 100% and a refractive index of 1.74 or less; and 1 to 40 wt% of a colorant, wherein the surface of the single-layer polymer film has been textured and has a maximum roughness (S pv ) of 6 μm or greater, an L* color of 30 or less, and a 60° gloss of 15 or less, The crosslinked polyimide is crosslinked by a crosslinking agent selected from polyetheramines, secondary amines, and triamines.

2. The single-layer polymer film according to claim 1, further comprising a matting agent.

3. The single-layer polymer film according to claim 1, wherein, The crosslinked polyimide comprises a dianhydride selected from the group consisting of aromatic dianhydrides, aliphatic dianhydrides, and mixtures thereof.

4. The single-layer polymer film according to claim 3, wherein, The dianhydride is selected from the group consisting of: 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), cyclobutanedicarboxylic anhydride (CBDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), bisphenol A dianhydride (BPADA), 4,4'-oxydiphthalic anhydride (ODPA), bis(3,4-dicarboxyphenyl)sulfone dianhydride (DSDA), and hexahydro-4,8-ethano-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetrone (BODA) and mixtures thereof.

5. The single-layer polymer film according to claim 1, wherein, The crosslinked polyimide comprises a diamine selected from the group consisting of aromatic diamines, aliphatic diamines, and mixtures thereof.

6. The single-layer polymer film according to claim 5, wherein, The diamine is selected from the group consisting of: 1,6-hexamethylenediamine (HMD), trans-1,4-diaminocyclohexane (CHDA), 3-(4-aminophenyl)-1,1,3-trimethyl-5-aminoindane (PIDA), isophoronediamine (IPDA), m-xylylenediamine (MTB), 2,2'-bis(trifluoromethyl)benzidine (TFMB), m-phenylenediamine (MPD), 1,3-bis-(4-aminophenoxy)benzene (RODA), 2,2-bis-(4-[4-aminophenoxy]phenyl)propane (BAPP), and 3,4'-diaminodiphenyl ether (3,4-ODA) and mixtures thereof.

7. The single-layer polymer film according to claim 1, wherein, The single-layer polymer film has a thickness of 2 to 125 μm.

8. The single-layer polymer film according to claim 1, wherein, The crosslinked polyimide has a refractive index of 1.69 or less.

9. The single-layer polymer film according to claim 1, wherein, The colorant comprises low-conductivity carbon black.

10. A cover layer for a printed circuit board, the cover layer comprising the single-layer polymer film according to claim 1.

11. A method for forming a single-layer polymer film, the single-layer polymer film comprising a crosslinked polyimide film containing a dianhydride and a diamine, wherein: The dianhydride, the diamine, or both the dianhydride and the diamine contain alicyclic monomers, aliphatic monomers, or both alicyclic monomers and aliphatic monomers; The polymer film has an L* color of 30 or less and a 60° glossiness of 15 or less; and The crosslinked polyimide film is formed by the following method: (a) Polymerizing the dianhydride and the diamine in the presence of a solvent to obtain a polyamic acid solution; (b) Imidizing the polyamic acid solution to form a substantially imidized solution; (c) Adding a crosslinking agent and a colorant to the substantially imidized solution, the crosslinking agent being selected from polyetheramine, secondary amine, and triamine; (d) Cast the substantially imidized solution onto a removable substrate to form a film, the removable substrate having a textured surface with a maximum roughness (S pv ) of 6 μm or greater; (e) Crosslinking the polyimide while drying the film; and (f) Removing the single-layer polymer film from the textured substrate.

12. A method for forming a single-layer polymer film, the single-layer polymer film comprising a crosslinked polyimide film containing a dianhydride and a diamine, wherein: The dianhydride, the diamine, or both the dianhydride and the diamine contain an alicyclic monomer, an aliphatic monomer, or both an alicyclic monomer and an aliphatic monomer; The polymer film has an L* color of 30 or less and a 60° glossiness of 15 or less; and The crosslinked polyimide film is formed by the following method: (a) Polymerizing the dianhydride and the diamine in the presence of a first solvent to obtain a polyamic acid solution; (b) Imidizing the polyamic acid solution to form a first substantially imidized solution; (c) Precipitating the first substantially imidized solution with an anti-solvent; (d) Filtering and drying the first substantially imidized solution to obtain a solid polyimide resin; (e) Dissolving the solid polyimide resin in a second solvent, and adding a crosslinking agent and low-conductivity carbon black to form a second substantially imidized solution, the crosslinking agent being selected from polyetheramine, secondary amine, and triamine; (f) Cast the second substantially imidized solution onto a removable substrate to form a film, the removable substrate having a textured surface with a maximum roughness (S pv ) of 6 μm or greater; (g) Crosslinking the polyimide while drying the film; and (h) Removing the single-layer polymer film from the textured substrate.

13. The method according to claim 12, wherein, After (e) and before (f), the second substantially imidized solution is filtered to remove the insoluble components of the solution.

14. The method according to claim 12, wherein, The first solvent and the second solvent are the same or different.

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