HK1170001B - Matte finish polyimide films and methods relating thereto - Google Patents

Description

Matte finish polyimide films and methods relating thereto

Technical Field

The present invention relates generally to matte finish base films that are useful in coverlay applications and have advantageous dielectric and optical properties. More specifically, the matte finish base film of the present invention includes a relatively low concentration of pigment and matting agent in the polyimide film imidized by a chemical (as opposed to thermal) conversion process.

Background

The coverlay is broadly referred to as a barrier film, which is used to protect electronic materials, such as flexible printed circuit boards, electronic components, lead frames of integrated circuit packages, and the like. However, there is a need for coverlays that are thinner and less costly, while having acceptable electrical properties (e.g., dielectric strength) as well as acceptable structural and optical properties to prevent unwanted visual inspection and tampering of electronic components protected by the coverlay.

Summary of The Invention

The present invention relates to base films. The base film comprises a chemically converted polyimide in an amount of 71 to 96 weight percent of the base film. The chemically converted polyimide is derived from: i. at least 50 mole percent of an aromatic dianhydride, based on the total dianhydride content of the polyimide, and ii at least 50 mole percent of an aromatic diamine, based on the total diamine content of the polyimide. The base film further comprises: a low conductivity carbon black present in an amount of 2 to 9 wt% of the base film; and a matting agent, the matting agent

a. Present in an amount of 1.6 to 10 weight percent of the base film,

b. has a median particle size of 1.3 to 10 microns, and

c. having a density of 2 to 4.5 g/cc.

In one embodiment, the base film has: i.8 to 152 microns in thickness; a 60 degree gloss value of 2 to 35; an optical density greater than or equal to 2; a dielectric strength greater than 1400V/mil. The present invention also relates to coverlay films comprising a base film bonded to an adhesive layer.

Detailed Description

Definition of

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

In addition, "a" or "an" is used to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. Such description should be understood to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

As used herein, "dianhydride" is intended to include precursors or derivatives thereof, which may not be a dianhydride, strictly speaking, but may still react with a diamine to form a polyamic acid, which may in turn be converted to a polyimide.

As used herein, "diamines" are intended to include precursors or derivatives thereof, which may not be diamines, strictly speaking, but which can still react with the dianhydride to form polyamic acid, which can in turn be converted to polyimide.

As used herein, "polyamic acid" is intended to include any polyimide precursor material derived from a combination of dianhydride and diamine monomers, or functional equivalents thereof, and capable of being converted to polyimide by chemical conversion methods.

As used herein, "prepolymer" is intended to mean a relatively low molecular weight polyamic acid solution prepared using a stoichiometric excess of diamine so as to impart a solution viscosity of about 50-100 poise.

As used herein, "chemical conversion" or "chemically converted" refers to the conversion of a polyamic acid to a polyimide with a catalyst (accelerator) or dehydrating agent (or both), and is intended to include a partially chemically converted polyimide, which can then be dried at elevated temperatures to a solids content of greater than 98%.

By "final solution" herein is meant a dianhydride dissolved in a polar aprotic solvent that is added to the prepolymer solution to increase molecular weight and viscosity. The dianhydride used is typically the same dianhydride used to prepare the prepolymer (or one of them when more than one dianhydride is used).

When an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

In describing certain polymers, it should be understood that sometimes applicants refer to polymers using the monomers from which they are made or the amounts of the monomers from which they are made. Although such descriptions may not include the specific nomenclature used to describe the final polymer or may not contain terms that define the article by way, any such reference to monomers and amounts should be construed to mean that the polymer is made from those monomers, unless otherwise indicated or implied by the context.

The materials, methods, and examples herein are illustrative only and not intended to be limiting unless otherwise specified. Although methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, suitable methods and materials are described herein.

Base film

The base film of the present invention comprises a filled polyimide matrix in which the polyimide is formed by a chemical conversion process. One advantage of the chemical conversion process (as compared to the thermal conversion process alone) is that the amount of matting agent required to obtain sufficiently low gloss is at least 10%, 20%, 30%, 40% or 50% less than when the thermal conversion process is used. The generally accepted range of 60 degree gloss values is:

less than 10 extinction

10-70 matte, satin, semi-gloss (using various terms)

High light > 70

In some embodiments, the base film has a 60 degree gloss value between and optionally including any two of the following values: 2.3, 4, 5, 10, 15, 20, 25, 30 and 35. In some embodiments, the base film has a 60 degree gloss value of 2 to 35. In some embodiments, the base film has a 60 degree gloss value of 10 to 35. The 60 degree Gloss value was measured using a Micro-TRI-Gloss meter. The lower content of matting agent (which can be prepared by chemical conversion) is advantageous for the following reasons: i. the overall cost is reduced; easy dispersion of the matting agent into the polyamic acid (or other polyimide precursor material); the resulting base film has better mechanical properties (e.g., lower brittleness). Another advantage of the chemical conversion process (compared to the thermal conversion process) is the higher dielectric strength of the chemically converted base film. In some embodiments, the dielectric strength of the base film is greater than 1400V/mil (55 volts/micron).

In chemical conversion processes, the polyamic acid solution is immersed in or mixed with a conversion (imidization) chemical. In one embodiment, the conversion chemicals are a tertiary amine catalyst (accelerator) and an anhydride dehydrating material. In one embodiment, the anhydride dehydrating material is acetic anhydride, which is typically used in a molar excess over the amount of the amine acid (amic acid) groups in the polyamic acid, typically about 1.2 to 2.4 moles per equivalent polyamic acid. In one embodiment, comparable levels of tertiary amine catalyst are used.

Alternative alternatives to acetic anhydride for use as the anhydride dehydrating material include: i. other aliphatic anhydrides such as propionic acid, butyric acid, valeric acid, and mixtures thereof; anhydrides of aromatic monocarboxylic acids; mixtures of aliphatic and aromatic anhydrides; a carbodiimide; aliphatic ketenes (ketenes can be considered as carboxylic acid anhydrides obtained by the intensive dehydration of acids).

In one embodiment, the tertiary amine catalyst is pyridine and beta-picoline, typically used in amounts similar to the molar amount of anhydride dehydrating material. Depending on the desired conversion and the catalyst used, lower or higher amounts may be used. Tertiary amines having approximately the same activity as pyridine and beta-picoline may also be used. They include alpha-picoline; 3, 4-lutidine; 3, 5-lutidine; 4-methylpyridine; 4-isopropylpyridine; n, N-dimethylbenzylamine; isoquinoline; 4-benzylpyridine, N-dimethyldodecylamine, triethylamine and the like. Various other imidization catalysts (e.g., imidazoles) are known in the art and may be used in accordance with the present invention.

The conversion chemicals can typically be reacted at about room temperature or higher to convert the polyamic acid to polyimide. In one embodiment, the chemical conversion reaction occurs at a temperature of 15 ℃ to 120 ℃, wherein the reaction is very fast at higher temperatures and relatively slow at lower temperatures.

In one embodiment, the chemically treated polyamic acid solution can be cast or extruded onto a heated conversion surface or substrate. In one embodiment, the chemically treated polyamic acid solution can be cast onto a belt or drum. The solvent can be evaporated from the solution and the polyamic acid can be partially chemically converted to polyimide. The resulting solution then takes the form of a polyamic acid-polyimide gel. Alternatively, the polyamic acid solution can be extruded into a bath of conversion chemicals consisting of an anhydride component (dehydrating agent), a tertiary amine component (catalyst), or both, with or without a diluent solvent. In either case, a gel film is formed in which the percentage of conversion of amic acid groups to imide groups is dependent upon contact time and temperature, but is typically about 10 to 75 percent complete. To cure to solids greater than 98%, the gel film must generally be dried at elevated temperatures (about 200 ℃ C., up to about 550 ℃ C.), which tends to drive the imidization reaction to completion. In some embodiments, it is preferred to use both a dehydrating agent and a catalyst, which facilitates the formation of a gel film and achieves the desired conversion.

Gel films are generally self-supporting, regardless of how high the solvent content is. Typically, the gel film is then dried to remove water, residual solvent, and residual conversion chemicals, during which the polyamic acid is substantially completely converted to polyimide (i.e., greater than 98% imidized). Drying may be carried out under relatively mild conditions, in which case the polyamic acid is not completely converted to polyimide, or drying and conversion may be carried out simultaneously using a higher temperature.

Because the gel contains a large amount of liquid that must be removed during the drying and converting steps, the gel must typically be restrained during drying to avoid undesirable shrinkage. In continuous production, the base film may be held at the edges with tenter clips and pins having a restraining action, for example in a tenter frame.

The gel film can be converted to a polyimide-based film in the same step by drying the base film for a short time using a high temperature and inducing further imidization. In one embodiment, the base film is heated to a temperature of 200 ℃ to 550 ℃. Generally, thinner films require less heat and time than thicker films.

During such drying and conversion (from polyamic acid to polyimide), the base film can be prevented from over shrinking and can in fact be stretched up to 150% of its original dimension. In the manufacture of the film, stretching can be performed in the machine direction or the transverse direction or in both directions simultaneously. The constraints can also be adjusted to allow a limited degree of shrinkage, if desired.

Another advantage is that the chemically converted base film of the present invention is matte on both sides even when cast on smooth surfaces. If both sides of the base film are matte, any additional layers may be applied to either side of the base film. In contrast, when a similarly filled polyimide precursor film is only thermally converted and cast onto a smooth surface, the cast side tends to be glossy and the opposite side tends to be matte.

Another advantage is that the chemically converted base film has a higher dielectric strength than the base film that is only thermally converted. In general, the dielectric strength decreases with increasing matting agent content. Therefore, although lower 60 degree gloss values (only to the bare surface) can be obtained by increasing the amount of matting agent in a separate thermal conversion process, the dielectric strength will be reduced.

In one embodiment, the polyamic acid is prepared by the steps of: approximately equimolar amounts of dianhydride and diamine are dissolved in a solvent and the resulting solution is then stirred under controlled temperature conditions until polymerization of the dianhydride and diamine is complete. Molecular weight and viscosity are usually initially controlled with a slight excess of one of the monomers (usually a diamine) and can then be increased by adding a small further amount of the deficient monomer. Examples of dianhydrides suitable for use in the polyimide of the present invention include aromatic dianhydrides, aliphatic dianhydrides, and mixtures thereof. In one embodiment, the aromatic dianhydride is selected from:

pyromellitic dianhydride;

3,3 ', 4,4' -biphenyltetracarboxylic dianhydride;

3,3 ', 4,4' -benzophenone tetracarboxylic dianhydride;

4,4' -oxydiphthalic anhydride;

3,3 ', 4,4' -diphenylsulfone tetracarboxylic dianhydride;

2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane;

bisphenol A dianhydride; and

mixtures and derivatives thereof.

In another embodiment, the aromatic dianhydride is selected from:

2, 3, 6, 7-naphthalene tetracarboxylic dianhydride;

1, 2, 5, 6-naphthalene tetracarboxylic dianhydride;

2,2 ', 3, 3' -biphenyltetracarboxylic dianhydride;

2, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride;

bis (3, 4-dicarboxyphenyl) sulfone dianhydride;

3,4, 9, 10-perylenetetracarboxylic dianhydride;

1, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride;

1, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride;

bis (2, 3-dicarboxyphenyl) methane dianhydride;

bis (3, 4-dicarboxyphenyl) methane dianhydride;

oxydiphthalic anhydride;

bis (3, 4-dicarboxyphenyl) sulfone dianhydride;

mixtures and derivatives thereof.

Examples of aliphatic dianhydrides include:

cyclobutane dianhydride;

[1S^*，5R^*，6S^*]-3-oxabicyclo [3.2.1]Octane-2, 4-dione-6-spiro-3- (tetrahydrofuran-2, 5-dione); mixtures thereof.

Examples of diamines suitable for use in the polyimides of the present invention include aromatic diamines, aliphatic diamines, and mixtures thereof. In one embodiment, the aromatic diamine is selected from:

3, 4' -diaminodiphenyl ether;

1, 3-bis (4-aminophenoxy) benzene;

4,4' -diaminodiphenyl ether;

1, 4-diaminobenzene;

1, 3-diaminobenzene;

2, 2' -bis (trifluoromethyl) benzidine;

4,4' -diaminobiphenyl;

4,4' -diaminobiphenyl sulfide;

9, 9' -bis (4-amino) fluoro;

mixtures and derivatives thereof.

In another embodiment, the aromatic diamine is selected from the group consisting of:

4,4' -diaminobiphenylpropane;

4,4' -diaminobiphenylmethane;

p-diaminobiphenyl;

3, 3' -dichlorobenzidine;

3, 3' -diaminodiphenyl sulfone;

4,4' -diaminodiphenyl sulfone;

1, 5-diaminonaphthalene;

4,4' -diaminodiphenyldiethylsilane;

4,4' -diaminodiphenylsilane;

4,4' -diaminodiphenylethylphosphine oxide;

4,4' -diaminodiphenyl N-methylamine;

4,4' -diaminodiphenyl-N-phenylamine;

1, 4-diaminobenzene (p-phenylenediamine);

1, 2-diaminobenzene;

mixtures and derivatives thereof.

Examples of suitable aliphatic diamines include:

1, 6-hexanediamine;

dodecanediamine;

cyclohexane diamine;

and mixtures thereof.

In one embodiment, the chemically converted polyimide is derived from pyromellitic dianhydride ("PMDA") and 4,4' -oxydianiline ("4, 4 ODA"). In one embodiment, the polyimide of the present invention is a copolyimide derived from any of the above diamines and dianhydrides. In one embodiment, the copolyimide is derived from 15 to 85 mole% of biphenyltetracarboxylic dianhydride, 15 to 85 mole% of pyromellitic dianhydride, 30 to 100 mole% of p-phenylenediamine and optionally comprises 0 to 70 mole% of 4,4 '-diaminodiphenyl ether and/or 4,4' -diaminodiphenyl ether. Such copolyimides are further described in U.S. patent 4,778,872 and U.S. patent 5,166,308.

In one embodiment, the polyimide dianhydride component is pyromellitic dianhydride ("PMDA") and the polyimide diamine component is a combination of 4,4' -oxydianiline ("4, 4 ODA") and p-phenylenediamine ("PPD"). In one embodiment, the polyimide dianhydride component is pyromellitic dianhydride ("PMDA") and the polyimide diamine component is a combination of 4,4' -oxydianiline ("4, 4 ODA") and p-phenylenediamine ("PPD"), wherein the ratio of ODA to PPD (ODA: PPD) is any one of the following molar ratios: i.20-80: 80-20; ii.50-70: 50-30; or iii.55-65: 45-35. In one embodiment, the polyimide dianhydride component is PMDA and the diamine component is ODA and PPD in a molar ratio (ODA: PPD) of about 60: 40.

In one embodiment, the polyimide dianhydride component is 3,3 ', 4,4' -biphenyl tetracarboxylic dianhydride ("BPDA") and the polyimide diamine component is a combination of 4,4' -diaminodiphenyl ether ("4, 4 ODA") and p-phenylenediamine ("PPD"). In one embodiment, the polyimide dianhydride component is BPDA and the polyimide diamine component is a combination of 4, 4ODA and PPD, wherein the ratio of ODA to PPD (ODA: PPD) is any one of the following molar ratios: i.20-80: 80-20; ii.50-70: 50-30; or iii.55-65: 45-35. In one embodiment, the polyimide dianhydride component is BPDA and the diamine component is ODA and PPD in a molar ratio (ODA: PPD) of about 60: 40.

In one embodiment, the polyamic acid solvent must dissolve one or both of the polymerization reactants, and in one embodiment, will dissolve the polyamic acid polymerization product. The solvent should not substantially react with all of the polymerization reactants and the polyamic acid polymerization product.

In one embodiment, the polyamic acid solvent is a liquid N, N-dialkylcarboxamide, e.g., a low molecular weight carboxamide, especially N, N-dimethylformamide and N, N-diethylacetamide. Other useful solvent compounds of this type are N, N-diethylformamide and N, N-diethylacetamide. Other useful solvents are sulfolane, N-methyl-2-pyrrolidone, tetramethylurea, dimethylsulfone, and the like. The solvents may be used alone or in combination with each other. The solvent is preferably used in an amount ranging from 75 to 90% by weight of the polyamic acid.

The polyamic acid solution is generally prepared by: diamine is dissolved in anhydrous solvent, and dianhydride is slowly added under the conditions of stirring and temperature control in an inert atmosphere.

Pigment (I)

Almost any pigment (or combination of pigments) can be used in the practice of the present invention. In some embodiments, useful pigments include, but are not limited to, the following pigments: barium lemon yellow, cadmium light yellow, cadmium middle yellow, cadmium orange yellow, scarlet lake, cadmium red, cadmium vermilion, mauve, durably mauve, iron oxide brown, raw ochre green, or burnt ochre color. In some embodiments, useful black pigments include: cobalt oxide, iron-manganese-bismuth black, iron-manganese oxide spinel black, (Fe, Mn)2O3 black, copper chromite black spinel, lampblack, bone char, bone ash, bone black, hematite, black iron oxide, mica iron oxide, black Composite Inorganic Color Pigment (CICP), CuCr2O4 black, (Ni, Mn, Co) (Cr, Fe)2O4 black, aniline black, perylene black, anthraquinone black, chromium green-black hematite, ferrochrome oxide, pigment green 17, pigment black 26, pigment black 27, pigment black 28, pigment brown 29, pigment black 30, pigment black 32, pigment black 33, or mixtures thereof.

In some embodiments, low conductivity carbon black is used. The amount of low conductivity carbon black and the thickness of the base film generally affect the optical density. If the content of the low conductivity carbon black is too high, the base film is conductive even in the case of using the low conductivity carbon black. If too low, the base film may not achieve the desired optical density and color. For the purposes of the present invention, low conductivity carbon black is used to impart black color to the base film, and to achieve the desired optical density of the base film, wherein the thickness of the base film is between and optionally includes any two of the following values: 8. 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, and 152 microns. In some embodiments, the base film has a thickness of 8 to 152 micrometers. In some embodiments, the base film thickness is 8 to 127 micrometers. In another embodiment, the base film has a thickness of 10 to 40 microns. Low conductivity carbon black is intended to mean channel black or furnace black. In some embodiments, bone char may be used to impart a black color. In one embodiment, the low conductivity carbon black is present in an amount between and optionally including any two of the following values: 2, 3,4, 5, 6, 7, 8 and 9 wt% of the base film. In some embodiments, the desired optical density (opacity) (e.g., no wires in the flex circuit are visible) is greater than or equal to 2. An optical density of 2 is intended to mean 1X 10^-2Or 1% of the light is transmitted through the base film.

In some embodiments, the low conductivity carbon black is a surface oxidized carbon black. One way to assess the degree of oxidation of the (carbon black) surface is to measure the volatile content of the carbon black. The volatile content can be measured by calculating the weight loss at 950 ℃ for 7 minutes of calcination. Generally, carbon black (high volatile content) with a highly oxidized surface can be easily dispersed in a polyamic acid solution (polyimide precursor), and then imidized into (well-dispersed) filled polyimide-based polymer of the present invention. It is generally believed that if the 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 of 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 carbon blacks may be surface treated to increase the volatile content.

The uniform dispersion of the individual particles (aggregates) separated not only reduces conductivity, but also tends to produce uniform color intensity. In some embodiments, the low conductivity carbon black is milled. In some embodiments, the average particle size of the low conductivity carbon black is between (and optionally includes) any two of the following values: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 microns. The thickness of the base film can be tailored to suit a particular application.

In some embodiments, dyes may be used. Examples of dyes that can be used are, but are not limited to, nigrosine, monoazo chromium complex black, or mixtures thereof. In some embodiments, mixtures of dyes and pigments may be used.

Matting agent

Polymeric materials typically have an inherent surface gloss. To control gloss (and thus produce matte surface features), dull, low-gloss surface features can be obtained by a variety of additive methods. In a broad sense, the additive approach is based on the same underlying physics, namely the formation of (micron-scale) rough and irregularly shaped modified surfaces, thereby reflecting less light back to distant (e.g., greater than 50 cm) observers. When multiple light rays are irradiated onto a bright surface, most of the light is reflected at similar angles, so that a relatively high level of light reflectivity can be observed. When the same light source illuminates a non-light (i.e. irregular) surface, the light is scattered in many different directions and much more light is absorbed. Thus, on rough surfaces, light tends to scatter diffusely in all directions, and the image formation quality is greatly reduced (the reflected object appears no longer bright but dim).

The gloss meter used to characterize the gloss of a particular surface is based on this same principle. Generally, a light source irradiates a surface at a fixed angle, and after reflection, the amount of reflected light is read by a light sensor. Multiple angles of reflection can be read. The maximum gloss performance of an extremely shiny surface tends to show 100% reflection, while a completely dull surface tends to show 0% reflection.

Silica is an inorganic particle that can be milled and sieved to a specific particle size range. The very irregular shape and porosity of the silica particles and the low cost make them a common matting agent. Other potential matting agents may include: i. other ceramics such as borides, nitrides, carbides, and other oxides (e.g., alumina, titania, etc.); organic particles provided that the organic particles can withstand the processing temperatures of the chemically converted polyimide (processing temperatures of about 250 ℃ to about 550 ℃, depending on the particular polyimide process selected). On matting agents useful in polyimide applications that can withstand the thermal conditions of polyimide synthesis are polyimide particles.

The amount, median particle size and density of matting agent must be sufficient to produce the desired 60 degree gloss value. In some embodiments, the 60 degree gloss value of the base film is between and optionally includes any two of the following values: 2. 5, 10, 15, 20, 25, 30 and 35. In some embodiments, the 60 degree gloss value of the base film is from 10 to 35.

In some embodiments, the matting agent is present in an amount between and optionally including any two of the following values: 1.6, 2, 3,4, 5, 6, 7, 8, 9 and 10 wt% of the base film. In some embodiments, the median particle size of the matting agent is between and optionally includes any two of the following values: 1.3, 2, 3,4, 5, 6, 7, 8, 9 and 10 microns. The matting agent particles should have an average particle size of less than (or equal to) about 10 microns and greater than (or equal to) about 1.3 microns. Larger matting agent particles can negatively impact the mechanical properties of the final base film. In some embodiments, the density of the matting agent is between and optionally includes any two of the following values: 2.3, 4 and 4.5 g/cc. In some embodiments, when the amount of matting agent is less than 1.6 weight percent of the base film, the desired 60 degree gloss value is not achieved even if the median particle size and density of the matting agent are within the desired ranges. In some embodiments, when the median particle size is below 1.3 microns, the desired 60 degree gloss value is not achieved even if the amount and density of matting agent is within the desired range. In some embodiments, the matting agent is selected from silica, alumina, barium sulfate, and mixtures thereof.

The base film may be prepared by any method known in the art for preparing a chemically converted filled polyimide layer. In one such embodiment, a slurry comprising a low conductivity carbon black is prepared, and a matting agent slurry is prepared. The slurry may or may not be milled to the desired particle size using a ball mill. The slurry may or may not be filtered to remove any residual 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 a low conductivity carbon black slurry and a matting agent slurry with a high shear mixer. When a slight excess of diamine is used to prepare the polyamic acid solution, additional dianhydride solution may or may not be added to increase the viscosity of the mixture to the level required for film casting. The amounts of polyamic acid solution, low conductivity carbon black slurry, and matting agent slurry can be adjusted to achieve the desired level in the cured base film. In some embodiments, the mixture is cooled below 0 ℃ and mixed with a conversion chemical prior to casting onto a heated drum or belt in order to produce a partially imidized gel film. The gel film is stripped from the drum or belt, placed on a tenter frame, and then cured in an oven with convection and radiant heat to remove solvent and complete the imidization reaction to greater than 98% solids.

Adhesive agent

In some embodiments, the base film is a multilayer film comprising a base film and an adhesive layer. The base film of the present invention may include an adhesive layer to hold the base film in place after application. In one embodiment, the adhesive is comprised of an epoxy resin and a hardener, and optionally further comprises additional components such as elastomers, cure accelerators (catalysts), hardeners, fillers, and flame retardants.

In some embodiments, the adhesive is an epoxy. In some embodiments, the epoxy resin is selected from:

bisphenol F type epoxy resin,

Bisphenol S type epoxy resin,

Phenol novolac epoxy resin,

Biphenyl type epoxy resin,

Biphenyl aralkyl type epoxy resin,

Aralkyl type epoxy resin,

Dicyclopentadiene type epoxy resin,

A multifunctional epoxy resin,

Naphthalene type epoxy resin,

Rubber-modified epoxy resin, and

mixtures thereof.

In another embodiment, the adhesive is an epoxy resin selected from the group consisting of: bisphenol a type epoxy resins, cresol novolac type epoxy resins, phosphorous epoxy resins, and mixtures thereof. In some embodiments, the binder is a mixture of two or more epoxy resins. In some embodiments, the adhesive is a mixture of the same epoxy resins having different molecular weights.

In some embodiments, the epoxy adhesive comprises a hardener. In one embodiment, the hardener is a phenolic compound. In some embodiments, the phenolic compound is selected from:

phenolic phenol resin,

Aralkyl type phenol resin,

Biphenyl aralkyl type phenol resin,

A multifunctional phenol resin,

A nitrogen-containing phenol resin,

A dicyclopentadiene type phenol resin,

A phosphorus-containing phenol resin, and

a triazine phenol novolac-containing epoxy resin.

In another embodiment, the hardener is an aromatic diamine compound. In some embodiments, the aromatic diamine compound is a diaminobiphenyl compound. In some embodiments, the diaminobiphenyl compound is 4,4' -diaminobiphenyl or 4,4' -diamino-2, 2 ' -dimethylbiphenyl. In some embodiments, the aromatic diamine compound is a diaminodiphenylalkane compound. In some embodiments, the diaminodiphenylmethane compound is 4,4 '-diaminodiphenylmethane or 4,4' -diaminodiphenylethane. In some embodiments, the aromatic diamine compound is a diaminodiphenyl ether compound. In some embodiments, the diaminodiphenyl ether compound is 4,4' -diaminodiphenyl ether or bis (4-amino-3-ethylphenyl) ether. In some embodiments, the aromatic diamine compound is a diaminodiphenyl sulfide compound. In some embodiments, the diaminodiphenyl sulfide compound is 4,4' -diaminodiphenyl sulfide or bis (4-amino-3-propylphenyl) sulfide. In some embodiments, the aromatic diamine compound is a diamino diphenyl sulfone compound. In some embodiments, the diamino diphenyl sulfone compound is 4,4' -diamino diphenyl sulfone or bis (4-amino-3-isopropylphenyl) sulfone. In some embodiments, the aromatic diamine compound is a phenylenediamine. In one embodiment, the hardener is an amine compound. In some embodiments, the amine compound is guanidine. In some embodiments, the guanidine is Dicyandiamide (DICY). In another embodiment, the amine compound is an aliphatic diamine. In some embodiments, the aliphatic diamine is ethylene diamine or diethyl diamine.

In some embodiments, the epoxy adhesive comprises a catalyst. In some embodiments, the catalyst is selected from the group consisting of imidazole-type, triazine-type, 2-ethyl-4-methyl-imidazole, triazine-containing phenol novolac-type, and mixtures thereof.

In some embodiments, the epoxy adhesive comprises an elastomeric toughener. In some embodiments, the elastic toughening agent is selected from the group consisting of ethylene-acryl based rubbers, acrylonitrile-butadiene rubbers, carboxyl terminated acrylonitrile-butadiene rubbers, and mixtures thereof.

In some embodiments, the epoxy adhesive comprises a flame retardant. In some embodiments, the flame retardant is selected from the group consisting of aluminum hydroxide, melamine polyphosphate, condensed polyphosphate, other phosphorus containing flame retardants, and mixtures thereof.

In some embodiments, the adhesive layer is selected from:

polyimide, polyimide,

Butyral phenolic resin,

Polysiloxane, and,

Polyimide siloxane,

Fluorinated ethylene propylene copolymer,

A perfluoroalkoxy copolymer,

Ethylene-vinyl acetate copolymer,

Ethylene-vinyl acetate-glycidyl acrylate terpolymer,

Ethylene-vinyl acetate-glycidyl methacrylate terpolymer,

Ethylene-alkyl acrylate copolymer with tackifier,

Ethylene-alkyl methacrylate copolymers with tackifiers,

Ethylene glycidyl acrylate,

Ethylene glycidyl methacrylate,

Ethylene-alkyl acrylate-glycidyl acrylate terpolymer,

Ethylene-alkyl methacrylate-glycidyl acrylate terpolymer,

Ethylene-alkyl acrylate-maleic anhydride terpolymer,

Ethylene-alkyl methacrylate-maleic anhydride terpolymer,

Ethylene-alkyl acrylate-glycidyl methacrylate terpolymer,

Ethylene-alkyl methacrylate-glycidyl methacrylate terpolymer,

Acrylic acid alkyl ester-acrylonitrile-acrylic acid terpolymer,

Acrylic acid alkyl ester-acrylonitrile-methacrylic acid terpolymer,

Ethylene acrylic acid copolymers (including salts thereof),

Ethylene methacrylic acid copolymers (including salts thereof),

Acrylic acid alkyl ester-acrylonitrile-glycidyl methacrylate terpolymer,

Alkyl methacrylate-acrylonitrile-glycidyl methacrylate terpolymer,

Acrylic acid alkyl ester-acrylonitrile-acrylic acid glycidyl ester terpolymer,

Alkyl methacrylate-acrylonitrile-glycidyl acrylate terpolymer,

Polyvinyl butyral,

Ethylene-alkyl acrylate-methacrylic acid terpolymer and salts thereof,

Ethylene-alkyl methacrylate-methacrylic acid terpolymer and salt thereof,

Ethylene-alkyl acrylate-acrylic acid terpolymer and salt thereof,

Ethylene-alkyl methacrylate-acrylic acid terpolymer and salts thereof,

Ethylene maleic acid monoethyl ester,

Ethylene alkyl acrylate maleic acid monoethyl ester,

Ethylene alkyl methacrylate maleic acid monoethyl ester,

And mixtures thereof.

In some embodiments, the multilayer film is a coverlay film.

In the following examples, all parts and percentages are by weight unless otherwise indicated.

Examples

The invention will be further described in the following examples, which are not intended to limit the scope of the invention as set forth in the claims.

Optical density was measured with a Macbeth TD904 densitometer. The average of 5 to 10 individual measurements was recorded.

The 60 degree Gloss values were measured using a Micro-TRI-Gloss glossmeter (Gardner USA, Columbia, Md.). The average of 5 to 10 individual measurements was recorded.

Surface resistivity was measured at 1000 volts using an ultra high resistance meter model Advanter 8340 with UR type concentric ring probes. The average of 3 to 5 individual measurements was recorded.

Dielectric strength was measured according to ASTM D149 using a Beckman Industrial AC dielectric breakdown tester. The average of 5 to 10 individual measurements was recorded.

Median particle size was measured using a Horiba LA-930 particle size analyzer (Horiba, Instruments, Inc., Irvine CA). DMAC (dimethylacetamide) was used as the carrier liquid.

When the sample was prepared using the continuous film casting method, the matting agent content in the film was determined by the ashing method. The film ashing step was as follows: all of the polymer and low conductivity carbon black were burned off by heating in a furnace at 900 ℃ leaving only a white residue of matting agent. The matting agent content in the film can be obtained by comparing the weights before and after ashing.

The viscosity of the polyamic acid was measured on a Brookfield programmable DV-II + viscometer with either the RV/HA/HB #7 spindle or the LV #5 spindle. The viscometer speed was varied between 5 to 100rpm to provide acceptable percent torque values. The readings were corrected to a temperature of 25 ℃.

Examples 1-5 show that chemical conversion achieves lower 60 degree gloss values (matte appearance) on both sides of the base film with low amounts of matting agent, while also achieving high dielectric strength.

Example 1

A carbon Black slurry was prepared consisting of 80 wt.% DMAC, 10 wt.% polyamic acid prepolymer solution (20.6 wt.% polyamic acid solids in DMAC), and 10 wt.% low conductivity carbon Black powder (Special Black 4 from Evonik Degussa). The above ingredients were thoroughly mixed in a rotor stator high speed dispersion mill. The slurry is then processed in a ball mill to disperse any large agglomerates and to achieve the desired particle size. The median particle size of the slurry was 0.3 microns.

A solution of 75.4 wt% DMAC, 9.6 wt% polyamic acid prepolymer solution (20.6 wt% polyamic acid solids in DMAC), and 15.0 wt% silica powder (Syloid) was preparedC803 from w.r.grace Co.) slurry. The ingredients were thoroughly mixed in a high shear rotor-stator type mixer. Median particle size is 3.3-3.6 microns.

16.4kg of the carbon black slurry was mixed in a 50 gallon (189.3 liter) tank into 158kg of PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise). Three independently controlled agitator shafts were mounted to the tank: low speed anchor agitators, high speed disk dispersers, and high shear rotor-stator emulsifiers. Approximately 7kg of a 5.8 wt% PMDA solution in DMAC was added incrementally and mixed to complete the preparation of the mixture to increase the molecular weight and reach a viscosity of about 3000 poise. The speed of the anchor stirrer, disperser, and emulsifier are adjusted as needed to ensure effective mixing and dispersion without overheating the mixture. The temperature of the mixture was further adjusted by flowing cooled ethylene glycol through the mixing tank jacket. The final solution was filtered through a 20 micron filter and the entrapped air was removed by vacuum degassing.

Metered amounts of the silica slurry were added to a metered stream of the final polymer/carbon black mixture and thoroughly mixed with a high shear rotor-stator mixer. The combined stream is cooled to about 6 ℃ and metered conversions are addedChemical acetic anhydride (0.14 cm)³/cm³Polymer solution) and 3-methylpyridine (0.15 cm)³/cm³Polymer solution) and mixed and cast into a film using a slot die on a heated rotating drum at 90 c. The resulting gel film was peeled from the drum and fed to a tenter oven for drying and curing by convection and radiation heating to a solids content of greater than 98%. The base film comprised 5 wt% carbon black and 3.5 wt% silica.

The results are shown in Table 1.

Example 2

An alumina slurry was prepared consisting of 41.7 wt.% DMAC, 23.3 wt.% polyamic acid prepolymer solution (20.6 wt.% polyamic acid solids in DMAC), and 35.0 wt.% alpha alumina powder having a median particle size of about 2.2 microns. The above ingredients were thoroughly mixed in a rotor stator high speed dispersion mill.

A metered amount of alumina slurry was added to a stream of cooled (-7 deg.C.) metered final polymer/carbon black mixture of example 1 along with conversion chemicals and a polyimide film was cast and cured in substantially the same manner as in example 1. The resulting base film comprised 5 wt% carbon black and 7 wt% alumina.

The results are shown in Table 1.

Example 3

Carbon black and silica slurries were prepared as described in example 1. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount such that the cured film yielded 5 wt% carbon black and 2 wt% silica. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 2250 poise. The final polymer mixture was degassed under vacuum. The polymer mixture was hand cast onto Mylar adhered to a glass plate using cast stainless steel rodsPolyethylene terephthalate sheet. Will comprise the Mylar of the wet cast filmThe polyethylene terephthalate sheets were immersed in a bath consisting of 50/50 mixtures of 3-methylpyridine and acetic anhydride. The bath was gently stirred for 3 to 4 minutes to allow imidization to occur and the film to gel. Removing the gel film from MylarThe polyethylene terephthalate sheet was peeled off and placed on a needle plate rack to confine the film and prevent shrinkage. After the residual solvent in the film was drained, the needle plate frame containing the film was placed in a 120 ℃ oven. The furnace temperature was gradually raised to 320 ℃ over 60 to 75 minutes, held at 320 ℃ for 10 minutes, then transferred to a 400 ℃ furnace, held for 5 minutes, and then removed from the furnace and cooled.

The results are shown in Table 1.

Example 4

The base film was prepared as described in example 3, wherein the cured film comprised 3 wt% silica.

The results are shown in Table 1.

Example 5

A carbon black slurry was prepared as described in example 1. A slurry of synthetic barium sulfate (Blanc Fixe F from Sachtleben Chemie GmbH) was prepared consisting of 51.7 wt% DMAC, 24.1 wt% prepolymer solution (20.6 wt% polyamic acid solids in DMAC) and 24.1 wt% barium sulfate powder. The ingredients were thoroughly mixed in a high shear rotor-stator type mixer. Median particle size was 1.3 microns.

The slurry was mixed with a PMDA/4, 4' ODA polyamic acid solution (20.6% polyamic acid solids, viscosity about 50 poise) in an amount to allow inclusion in the cured filmContaining 7% by weight of carbon black and 10% by weight of barium sulphate. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 2400 poise. The final polymer mixture was degassed under vacuum. The polymer mixture was cast onto Mylar as described in example 3Polyethylene terephthalate sheet and chemically imidized and cured.

The results are shown in Table 1.

Comparative example 1

Comparative example 1 shows that thermal conversion with an equal amount of matting agent as in example 5 results in a higher (undesirable) 60 degree gloss value on both sides of the base film and a low dielectric strength.

A carbon black slurry was prepared as described in example 1. A synthetic barium sulfate (Blanc Fixe F, available from Sachtleben Chemie GmbH) slurry was prepared consisting of 51.7 wt.% DMAC, 24.1 wt.% polyamic acid prepolymer solution (20.6 wt.% polyamic acid solids present in DMAC), and 24.1 wt.% barium sulfate powder. The ingredients were thoroughly mixed in a high shear rotor-stator type mixer. Median particle size was 1.3 microns.

The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 7 wt% carbon black and 10 wt% barium sulfate in the cured film. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 1500 poise. The final polymer mixture was degassed under vacuum. The film was hand cast onto glass plates using a stainless steel casting bar. The glass plate containing the wet cast film was placed on a hot plate at 80 to 100 ℃ for 30 to 45 minutes to form a partially dried, partially imidized "green" film. The green film was peeled from the glass plate and placed on a needle plate holder. The needle bar frame containing the green film was placed in a 120 ℃ oven. The furnace temperature was gradually raised to 320 ℃ over 60 to 75 minutes, held at 320 ℃ for 10 minutes, then transferred to a 400 ℃ furnace, held for 5 minutes, and then removed from the furnace and cooled.

The results are shown in Table 1.

Comparative example 2

Comparative example 2 shows that thermal conversion with 4 wt% matting agent results in a higher (undesirable) 60 degree gloss value on both sides of the base film and has low dielectric strength.

Carbon black and silica slurries were prepared as described in example 1. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount such that the cured film yielded 5 wt% carbon black and 4 wt% silica. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 2250 poise. The final polymer mixture was degassed under vacuum. The film was hand cast onto glass plates using a stainless steel casting bar. The glass plate containing the wet cast film was placed on a hot plate at 80-100 ℃ for 30-45 minutes to form a partially dried, partially imidized "green" film. The green film was peeled from the glass plate and placed on a needle plate holder. The needle bar frame containing the green film was placed in a 120 ℃ oven. The furnace temperature was gradually raised to 320 ℃ over 60 to 75 minutes, held at 320 ℃ for 10 minutes, then transferred to a 400 ℃ furnace, held for 5 minutes, and then removed from the furnace and cooled.

The results are shown in Table 1.

Comparative example 3

Comparative example 3 shows that thermal conversion requires the use of higher levels of matting agent to produce a lower 60 degree gloss value on the voided side (matte appearance), but the other side (non-voided side) still has an undesirable 60 degree gloss value.

A carbon black slurry was prepared as described in example 1. An alumina slurry was prepared consisting of 51.72 wt.% DMAC, 24.14 wt.% polyamic acid prepolymer solution (20.6 wt.% polyamic acid solids in DMAC), and 24.14 wt.% alpha alumina powder with a median particle size of 2.3 microns. The ingredients were thoroughly mixed in a rotor stator high speed dispersion mill. The slurry is then ground in a ball mill to break up the large agglomerates. The carbon black and alumina slurry is filtered to remove any remaining large particles or agglomerates.

The formulation of the PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) was accomplished by mixing with 5.8 weight percent PMDA in DMAC in a high shear mixer to increase the molecular weight and bring the viscosity to about 1500 poise. The final solution was filtered and mixed with a low conductivity carbon black and alumina slurry in a high shear mixer, with additional PMDA final solution and a small amount of a tape stripper (which allows the cast green film to be easily peeled from the casting tape). The amount of PMDA final solution was adjusted to obtain a viscosity of 1200 poise. The desired carbon black and alumina loading levels and the desired pressure at the casting die are obtained by adjusting the relative amounts of polymer, slurry and final solution. The final polymer/slurry mixture was pumped through a filter to a slot die where the streams were separated in a manner that formed the outer layers of the three layer coextruded film.

The second PMDA/4, 4' ODA prepolymer polymer solution stream was formulated to a viscosity of 1500 poise in a high shear mixer and then pumped through a filter to a casting die to form the middle unfilled polyimide core layer of the three layer coextruded film. The flow rates of the outer layer and unfilled polyimide core layer solutions were adjusted to achieve the desired layer thicknesses.

Three-layer coextruded films were prepared from the above components by casting from a slot die onto a moving stainless steel ribbon. The belts were passed through a convection oven to evaporate the solvent and partially imidize the polymer, resulting in a "green" film. The green film had a solids content (measured by weight loss after heating to 300 ℃) of 72.6%. The green film was peeled off the cast tape and rolled up. The green film was then passed through a tenter oven to obtain a cured polyimide film. Shrinkage is controlled by constraining the film along the edges during tentering. The solid content (measured by weight loss after heating to 300 ℃) of the cured film was 98.8%.

The middle unfilled layer comprises 33% or 1/3 of the total thickness of the multilayer film, and the outer layers comprise alumina and low conductivity carbon black of equal thickness. The outer layer comprised 7 wt% of low conductivity carbon black and 30 wt% of alumina. The total thickness of the film was 0.49 mils.

The results are shown in Table 1.

Comparison of examples 4 and 5 shows that a certain amount of matting agent is required to obtain a lower 60 degree gloss value (matte appearance) on both sides of the base film, and that matting agents with a particle size below 1.3 microns result in glossy base films.

Comparative example 4

A carbon black slurry having a median particle size of 0.3 microns was prepared as described in example 1. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount such that the cured film yielded 7 weight percent carbon black. While mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 1900 poise. The final polymer mixture was degassed under vacuum. The polymer mixture was cast to Mylar as described in example 3Polyethylene terephthalate sheet and chemically imidized and cured.

The results are shown in Table 1.

Comparative example 5

To the metered final polyamic acid/carbon black mixture stream of example 1 was added a metered amount of additional carbon black slurry to increase the carbon black content in the cured film to 7 wt%, and the two streams were thoroughly mixed using a high shear rotor stator mixer. A chemically imidized base film was prepared as described in example 1.

The results are shown in Table 1.

Comparative example 6

Comparative example 6 shows that with 10 wt.% BaSO₄Chemical conversion of example 5 with 30 wt.% BaSO₄The chemical conversion carried out did not show the desired reduction in dielectric strength. But surprisingly with 10 wt.% BaSO₄Comparison with comparative example 1 with 30% by weight of BaSO₄The chemical conversion is carried out with higher dielectric strength.

A carbon black slurry was prepared as described in example 1. A slurry of synthetic barium sulfate (Blanc Fixe F from Sachtleben Chemie GmbH) was prepared consisting of 51.7 wt% DMAC, 24.1 wt% prepolymer solution (20.6 wt% polyamic acid solids in DMAC) and 24.1 wt% barium sulfate powder. The ingredients were thoroughly mixed in a high shear rotor stator type mixer. Median particle size was 1.3 microns.

The slurry was mixed with a PMDA/4, 4' ODA polyamic acid solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 7 wt% carbon black and 30 wt% barium sulfate in the cured film. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 2400 poise. The final polymer mixture was degassed under vacuum. The polymer mixture was cast onto Mylar as described in example 3Polyethylene terephthalate sheet and chemically imidized and cured.

The results are shown in Table 1.

Examples 6-7 show that by chemical conversion, even with lower amounts of matting agent, lower 60 degree gloss values (matte appearance) can be obtained on both sides of the base film, and higher dielectric strength can be obtained.

Example 6

A chemically imidized black polyimide-based film was prepared as described in example 1, except that the stoichiometric ratio of the silica slurry was reduced by 37%. The base film contains 2.2 wt% silica, as analyzed by ash.

The results are shown in Table 1.

Example 7

Carbon black and silica slurries were prepared as described in example 1. The formulation of the PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) was accomplished by mixing with 5.8 weight percent PMDA in DMAC in a high shear mixer to increase the molecular weight and bring the viscosity to about 2500 poise. A metered stream of the final polyamic acid solution was cooled to about-10 ℃. A similarly cooled conversion chemical, acetic anhydride (0.18 cm) was stirred with a high shear stirrer³/cm³Polymer solution) and 3-methylpyridine (0.17cm3/cm3 polymer solution) and carbon black (0.095cm³/cm³Polymer solution) and silica slurry (0.029 cm)³/cm³Polymer solution) is mixed into the polyamic acid solution. The cooled mixture was filtered and immediately cast into a film using a slot die on a hot drum at 105 ℃. The resulting gel film was peeled from the drum and fed to a tenter oven for drying and curing by convection and radiation heating to a solids content of greater than 98%. The base film comprises about 5.5 wt% carbon black. The film contained 1.8 wt% silica, as analyzed by ash.

The results are shown in Table 1.

Example 8

A carbon black slurry was prepared as described in example 1. Prepared as described in comparative example 3An alumina slurry. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 5% by weight carbon black and 10% by weight alumina in the cured film. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 1900 poise. The final polymer mixture was degassed under vacuum. The polymer mixture was cast onto Mylar as described in example 3Polyethylene terephthalate sheet and chemically imidized and cured.

The results are shown in Table 1.

Comparative example 7

Comparative example 7 shows that thermal conversion using an equal amount of matting agent as in example 8 results in a higher (undesirable) 60 degree gloss value on both sides of the base film and has low dielectric strength.

A carbon black slurry was prepared as described in example 1. Alumina slurry was prepared as described in comparative example 3. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 5% by weight carbon black and 10% by weight alumina in the cured film. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 1900 poise. The final polymer mixture was degassed under vacuum. The film was cast and heat imidized as described in comparative example 2.

The results are shown in Table 1.

Comparative examples 8 and 9 show that the content of matting agent must be higher than 1.5% by weight in order to obtain a lower value of 60 degrees gloss (matt appearance) on both sides of the base film.

Comparative example 8

A base film was prepared as described in example 3, wherein the cured film contained 1 wt% silica.

The results are shown in Table 1.

Comparative example 9

A base film was prepared as described in example 3, wherein the cured film contained 1.5 wt% silica.

The results are shown in Table 1.

Comparative examples 10 and 11 show that the median particle size of the matting agent has a lower limit in order to obtain a lower 60 degree gloss value.

Comparative example 10

A carbon black slurry was prepared as described in example 1. An alumina slurry was prepared consisting of 81.4 wt.% DMAC, 8.3 wt.% PMDA/BPDA//4, 4' -ODA/PPD prepolymer solution (14.5 wt.% polyamic acid solids in DMAC), 0.1 wt.% dispersant, and 10.2 wt.% fumed alumina powder. The above ingredients were thoroughly mixed in a rotor stator high speed dispersion mill. The slurry was then milled in a media mill to break up the large agglomerates and to achieve a median particle size of about 0.35 μm. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 5% by weight carbon black and 2% by weight alumina in the cured film. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 2150 poise. The final polymer mixture was degassed under vacuum. The polymer mixture was cast to Mylar as described in example 3Polyethylene terephthalate sheet and chemically imidized and cured.

The results are shown in Table 1.

Comparative example 11

Preparation of anhydrous calcium Hydrogen phosphate (CaHPO)₄) A slurry consisting of 11.5 wt.% dibasic calcium phosphate, 64.7 wt.% polyamic acid prepolymer solution (20.6 wt.% polyamic acid solids in DMAC), and 23.8 wt.% DMAC. The ingredients were thoroughly mixed in a high shear rotor stator type mixer. Median particle size was 1.25 microns.

A metered slurry of dibasic calcium phosphate was added to and mixed with a metered stream of the cooled (-8 deg.C.) final polymer/carbon black mixture of example 1 along with a conversion chemical, and then a polyimide film was cast and cured in substantially the same manner as in example 1. The resulting base film comprised 5 wt% carbon black and 2.8 wt% dibasic calcium phosphate.

The results are shown in Table 1.

Comparative example 12

Comparative example 12 shows that a high density matting agent will produce a higher (undesirable) 60 degree gloss value on both sides of the base film.

A carbon black slurry was prepared as described in example 1. A barium titanate (Sakai, BT-05) slurry was prepared consisting of 75 wt.% DMAC, 10 wt.% polyamic acid prepolymer solution (20.6 wt.% polyamic acid solids in DMAC) and 15 wt.% barium titanate powder. The ingredients were thoroughly mixed in a high shear rotor stator type mixer and then sonicated to a median particle size of 1.5 microns.

The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 5 wt% carbon black and 2 wt% barium titanate in the cured film. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 1500 poise. The final polymer mixture was degassed under vacuum. The polymer mixture was cast onto Mylar as described in example 3Polyethylene terephthalate sheet and chemically imidized and cured.

The results are shown in Table 1.

Examples 9, 10 and 11

A base film was prepared as described in example 3, except that the amount of the silica slurry was adjusted to include 5 wt%, 7.5 wt%, and 10 wt% of silica in the cured film, respectively.

The results are shown in Table 1.

Examples 12 and 13

Membranes were prepared as described in example 1. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 5% by weight carbon black and 2.2% by weight silica in the cured film. Compounding of the mixture, casting to form a film, chemical imidization and curing were performed as described in example 1. The conditions were adjusted to give 2 mil and 5 mil thick base films.

The results are shown in Table 1.

Examples 14 and 15

Treating silica powder (Syloid) in air classifierC803) In order to remove a fraction of the largest particles. Slurries were prepared with air-classified silica as described in example 1. Median particle size was 2.1 microns. A carbon black slurry was prepared as described in example 1. The carbon black and silica slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount to yield 5% by weight carbon black and 2% and 4% by weight silica in the cured film. This was done as described in example 3Preparing a mixture, and preparing a basement membrane.

The results are shown in Table 1.

Example 16

Example 16 shows that chemical conversion with different low conductivity carbon blacks can still achieve lower 60 degree gloss values (matte appearance) on both sides of the base film and high dielectric strength.

A carbon black slurry was prepared consisting of 80 wt% DMAC, 10 wt% prepolymer solution (20.6 wt% polyamic acid solids in DMAC) and 10 wt% channel carbon black with 6% volatile content (Printex U from Evonik Degussa). The ingredients were thoroughly mixed in a rotor stator disperser. The slurry was then treated with an ultrasonic processor (sonic & Materials, inc., model VCX-500) to depolymerize the carbon black. A silica slurry was prepared as described in example 1. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 50 poise) in an amount such that the cured film yielded 5 wt% carbon black and 2 wt% silica. Upon mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to complete the formulation of the mixture to give a final viscosity of about 2250 poise.

A base film chemically imidized was prepared by the procedure described in example 3.

The results are shown in Table 1.

Comparative example 13

Comparative example 13 shows that thermal conversion with an equal amount of matting agent as in example 16 results in a higher (undesirable) 60 degree gloss value on both sides of the base film, as well as a low dielectric strength.

Slurries were prepared as described in example 16. The final polymer mixture was hand cast onto a glass plate using a stainless steel casting bar. The glass plate containing the wet cast film was placed on a hot plate at 80-100 ℃ for 30-45 minutes to form a partially dried, partially imidized "green" film. The green film was peeled from the glass plate and placed on a needle plate holder. The needle bar frame containing the green film was placed in a 120 ℃ oven. The furnace temperature was gradually raised to 320 ℃ over 60-75 minutes, held at 320 ℃ for 10 minutes, then transferred to a 400 ℃ furnace and held for 5 minutes, and then removed from the furnace and cooled.

The results are shown in Table 1.

Example 17

Example 17 shows that chemical conversion with different low conductivity carbon blacks can still achieve lower 60 degree gloss values (matte appearance) on both sides of the base film and high dielectric strength.

Base films were prepared as described in example 16, except that the carbon Black slurry was prepared from furnace Black (Special Black 550, from Evonik Degussa) having a volatile content of 3.5%.

The results are shown in Table 1.

Comparative example 14

Comparative example 14 shows that thermal conversion with an equal amount of matting agent as in example 17 results in a higher (undesirable) 60 degree gloss value on both sides of the base film, as well as a low dielectric strength.

Base films were prepared as described in comparative example 13, except that the carbon Black slurry was prepared from furnace Black (Special Black 550, from Evonik Degussa) having a volatile content of 3.5%.

The results are shown in Table 1.

Example 18

Example 18 shows that chemical conversion with different low conductivity carbon blacks can still achieve lower 60 degree gloss values (matte appearance) on both sides of the base film and high dielectric strength.

A base film was prepared as described in example 16, except that the carbon black slurry was prepared from furnace carbon black (Printex 55, available from Evonik Degussa) having a volatile content of 1.2%.

The results are shown in Table 1.

Comparative example 15

Comparative example 15 shows that thermal conversion with an equal amount of matting agent as in example 18 results in a higher (undesirable) 60 degree gloss value on both sides of the base film, as well as a low dielectric strength.

A base film was prepared as described in comparative example 13, except that the carbon black slurry was prepared from furnace carbon black (Printex 55, available from Evonik Degussa) having a volatile content of 1.2%.

The results are shown in Table 1.

Comparative example 16

Comparative example 16 shows that thermal conversion using a high amount (30 wt%) of matting agent can achieve the desired 60 degree gloss value on the open side of the base film, but the other side of the base film has a higher (undesirable) 60 degree gloss value and lower dielectric strength.

Carbon black and silica slurries were prepared as described in example 1. The slurry was mixed with a PMDA/4, 4' ODA prepolymer solution (20.6% polyamic acid solids, viscosity of about 4500 poise) in an amount to yield 5 wt% carbon black and 30 wt% silica in the cured film. While mixing, a 6 wt% solution of PMDA in DMAC was added incrementally to adjust the viscosity of the mixture to 300 poise. The final polymer mixture was degassed under vacuum. The film was hand cast onto glass plates using a stainless steel casting bar. The glass plate containing the wet cast film was placed on a hot plate at 80-100 ℃ for 30-45 minutes to form a partially dried, partially imidized "green" film. The green film was peeled from the glass plate and placed on a needle plate holder. The needle bar frame containing the green film was placed in a 120 ℃ oven. The furnace temperature was gradually raised to 320 ℃ over 60-75 minutes, held at 320 ℃ for 10 minutes, then transferred to a 400 ℃ furnace and held for 5 minutes, and then removed from the furnace and cooled.

The results are shown in Table 1.

It is noted that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that other activities may be performed in addition to those described. Further, the order in which each of the acts is listed is not necessarily the order in which they must be taken. After reading this specification, one of ordinary skill in the art will be able to ascertain the specific needs and desired actions available to them.

In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. All the elements disclosed in this specification may be replaced by alternative elements serving the same, equivalent or similar purpose.

Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention.

Claims (8)

1. A base film, comprising:

A. a chemically converted polyimide in an amount of 71 to 96 weight percent of the base film, the chemically converted polyimide derived from:

a. at least 50 mole percent of an aromatic dianhydride, based on the total dianhydride content of the polyimide, and

b. at least 50 mole percent of an aromatic diamine based on the total diamine content of the polyimide;

B. a low conductivity carbon black present in an amount of 2 to 9% by weight of the base film, the low conductivity carbon black being selected from channel carbon black, furnace carbon black, or carbon black having a volatile content of greater than or equal to 1%; and

C. a matting agent, the matting agent:

a. present in an amount of 1.6 to 10 weight percent of the base film,

b. has a median particle size of from 1.3 to 10 microns, and

c. has a density of 2 to 4.5 g/cc;

the base film has a 60 degree Gloss value of 2 to 35 and both sides of the base film are matte as measured with a Micro-TRI-Gloss meter.

2. The base film according to claim 1, wherein:

a. the aromatic dianhydride is selected from:

pyromellitic dianhydride,

3,3 ', 4,4' -biphenyltetracarboxylic dianhydride,

3,3 ', 4,4' -benzophenone tetracarboxylic dianhydride,

4,4' -oxydiphthalic anhydride,

3,3 ', 4,4' -diphenylsulfone tetracarboxylic dianhydride,

2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane,

Bisphenol A dianhydride, and

mixtures thereof; and is

b. The aromatic diamine is selected from:

3, 4' -diaminodiphenyl ether,

1, 3-di- (4-aminophenoxy) benzene,

4,4' -diaminodiphenyl ether,

1, 4-diaminobenzene,

1, 3-diaminobenzene,

2, 2' -bis (trifluoromethyl) benzidine,

4,4' -diaminobiphenyl,

4,4' -diaminobiphenyl sulfide,

9, 9' -bis (4-amino) fluoro, and

mixtures thereof.

3. The base film according to claim 1, wherein the chemically converted polyimide is derived from pyromellitic dianhydride and 4,4' -oxydianiline.

4. The base film according to claim 1, wherein the matting agent is selected from the group consisting of silica, alumina, barium sulfate and mixtures thereof.

5. The base film according to claim 1, wherein the base film has a thickness of 8 to 152 microns.

6. A multilayer film comprising an adhesive layer and the base film of any one of claims 1-5.

7. The multilayer film according to claim 6, wherein the adhesive layer is an epoxy resin selected from the group consisting of: bisphenol a type epoxy resins, cresol novolac type epoxy resins, phosphorous epoxy resins, and mixtures thereof.

8. The multilayer film of claim 6, wherein the multilayer film is a coverlay film.