Solvent resistant, aromatic polyamide films for transparent flexible substrates

Abstract

Solvent resistant, transparent films prepared from solutions of aromatic polyamides and multi-functional carboxylic acids in polar aprotic solvents are described herein. Solvent resistance is achieved by heating the films for a short time above 300 C. near the polyamide Tg. The films have CTEs less than 40 ppm/ C. and are optically clear displaying transmittance above 75% between 400 and 750 nm. The films are useful as substrates for flexible electronic devices.

Claims

1. A solvent resistant, transparent, aromatic polyamide film, comprising: a) an aromatic polyamide that is soluble in polar aprotic solvents in the absence of inorganic salts and has one or more repeat units of general formula (I): ##STR00021## wherein Ar.sub.1 is selected from the group of aromatic units as shown in the following general structures: ##STR00022## wherein p is 1 to 4, q is 1 to 3; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 are selected from the group consisting of hydrogen, halogens (fluoride, chloride, bromide and iodide), alkyls, substituted alkyls, nitro, cyano, thioalkyl, alkoxy, aryls, substituted aryls, alkyl esters, substituted alkyl esters, and combinations thereof, wherein when p is less than 1 or q is less than 3 the remaining positions on the aromatic ring are y hydrogen atoms; wherein G.sub.1 is selected from a group consisting of a covalent bond; a CH.sub.2 group; a C(CH.sub.3).sub.2 group; a C(CF.sub.3).sub.2 group; a C(CX.sub.3).sub.2 group wherein X is a halogen; a CO group; an O atom; a S atom; a SO.sub.2 group; a Si (CH.sub.3).sub.2 group; 9, 9-fluorene group; substituted 9, 9-fluorene; and an OZO group wherein Z is a aryl group or substituted aryl such as phenyl group, biphenyl group, perfluorobiphenyl group, 9, 9-bisphenylfluorene group, or substituted 9, 9-bisphenylfluorene; wherein Ar.sub.2 is selected from the group of aromatic units as shown in the following general structures: ##STR00023## wherein p is 1 to 4; R.sub.6, R.sub.7, R.sub.8, are selected from the group consisting of hydrogen, halogen (fluoride, chloride, bromide and iodide), alkyl, substituted alkyls, nitro, cyano, thioalkyl, alkoxy, aryls, substituted aryls, alkyl esters, substituted alkyl esters, and combinations thereof, wherein when p is less than 4 the remaining positions on the aromatic ring are hydrogen; wherein G.sub.2 is selected from a group consisting of a covalent bond; a CH.sub.2 group; a C(CH.sub.3).sub.2 group; a C(CF.sub.3).sub.2 group; a C(CX.sub.3).sub.2 group wherein X is a halogen; a CO group; an O atom; a S atom; a SO.sub.2 group; a Si (CH.sub.3).sub.2 group; 9, 9-fluorene group; substituted 9, 9-fluorene; and an OZO group wherein Z is a aryl group or substituted aryl such as phenyl group, biphenyl group, perfluorobiphenyl group, 9, 9-bisphenylfluorene group, or substituted 9, 9-bisphenylfluorene, wherein when p is less than 4 the remaining positions on the aromatic ring are hydrogen; and, b) a multifunctional carboxylic acid compound in an amount of about 3 wt % to about 9 wt % based on the weight of the soluble, aromatic polyamide; wherein the multifunctional carboxylic acid compound is selected from the group consisting of: trimesic acid, 2,4,6,8-naphyltetracarboxylic acid, 3,3,5,5-biphenyltetracarboxylic acid, and 2,2,4,4-biphenyltetracarboxylic acid, wherein a precursor film is formed by combining at least the aromatic polyamide and the multifunctional carboxylic acid compound and wherein the precursor film exposed to temperatures from about 300 C. to less than 350 C. for less than about one hour to form the solvent resistant film with an average coefficient of thermal expansion that is less than 40 ppm/ C. between 30 and 200 C.

2. The solvent resistant, transparent, aromatic polyamide film of claim 1, wherein Ar.sub.1 is selected from the following: ##STR00024##

3. The solvent resistant, transparent, aromatic polyamide film of claim 1, wherein Ar.sub.2 is selected from the following: ##STR00025##

4. The solvent resistant, transparent, aromatic polyamide film of claim 1, wherein the aromatic polyamide has a Tg>300 C.

5. The solvent resistant, transparent, aromatic polyamide film of claim 1, wherein the aromatic polyamide film has a transmittance of about >75% between 400 nm and 750 nm.

6. The solvent resistant, transparent, aromatic polyamide film of claim 5, wherein the transmittance is >80% between 400 nm and 750 nm.

7. The solvent resistant, transparent, aromatic polyamide film of claim 1, wherein the aromatic polyamide film has a thickness that is greater than approximately 5 m.

8. The solvent resistant, transparent, aromatic polyamide film of claim 7, wherein the thickness is greater than approximately 20 m.

9. The solvent resistant, transparent, aromatic polyamide film of claim 1, wherein the solvent resistant, transparent, aromatic polyamide film is adhered to a substrate and has a thickness that is greater than approximately 5 m.

10. The solvent resistant, transparent, aromatic polyamide film of claim 9, wherein the substrate is a woven glass mat or a glass film.

11. The solvent resistant, transparent, aromatic polyamide film of claim 10, wherein the substrate has a thickness that is greater than approximately 20 m.

12. The solvent resistant, transparent, aromatic polyamide film of claim 1, wherein the average coefficient of thermal expansion of the aromatic polyamide film is less than approximately 30 ppm/ C. between 30 and 200 C.

Description

DETAILED DESCRIPTION

(1) The present invention is directed toward solvent resistant, transparent films prepared from aromatic polyamides that are soluble in organic solvents without the presence of an inorganic salt. A polyamide is prepared via a condensation polymerization of an aromatic diacid chloride with an aromatic diamine in a polar aprotic solvent at approximately 20 C. to about 40 C. The hydrochloric acid generated in the reaction is trapped by reaction with a reagent like propylene oxide (PrO) or an inorganic salt. The preferred solvent is DMAc and the preferred temperature is 0 C. If the reagent used to trap the hydrochloric acid does not form volatile products, the polymer is first isolated from the polymerization mixture by precipitation in a non-solvent and redissolved in a polar solvent (without the need for inorganic salts). The preferred non-solvent is methanol and the preferred solvent is DMAc. If the reagent forms a volatile product by reaction with hydrochloric acid, such as with PrO, films can be cast directly from the polymerization solution, and the volatile by product removed during the removal of solvent. Colorless films can be prepared by well known solvent casting procedures at temperatures below 220 C. Casting can be carried out in a batch process or continuously using a roll to roll process. By carefully manipulating the structure of the monomers, the T.sub.gs of the resulting polymers, and the CTEs and optical properties of their solution cast films can be controlled. As evident to those skilled in the art, the use of monomers containing twisted biphenyl structures such as those present in 2,2-disubstitutedbenzidines results in soluble polymers with high Tgs and low CTEs. Since such structures also result in increased transparency (U.S. Pat. No. 4,384,107, May 1983), they are preferred. The preferred diamines are PFMB and PFOMB or mixtures of these with other aromatic diamines. The use of monomers containing cardo groups such a 9,9-bis(4-aminophenyl)fluorene affords soluble polymers with very high Tgs. The use of mixtures of aromatic diacid chlorides and aromatic diamines can also be used to promote solubility. Guidelines for the preparation of soluble aromatic polyamides with high Tgs can be found in Y. S. Negi et. al. (1999), Journal of Macromolecular Science, Part C, 39:3, 391-403. The combination of monomers used to promote solubility are chosen so as to result in a polyamide with a Tg above 300 C., a CTE<40 ppm/ C., and one that can be cast into films with high transparencies between 400 and 750 nm (a minimum transmittance of 75% at 400 nm; and greater than 85% at 750 nm). It is preferred that the Tg be above 310 C., the CTE>30 ppm/ C., and the film transmittance>80% at 400 nm. The addition of a multifunctional carboxylic acid to the polymer solutions prior to casting allows the films to be made resistant to dissolution and swelling in organic solvents by heating at temperatures near the polyamide Tg. The amount of multifunctional acid added is less than approximately 10 wt %. The preferred amount is 5 wt % or less. The preferred multifunctional acid is TA. The films containing the multifunctional acid are heated above 275 C. to near the polyamide Tg under an inert atmosphere or under reduced pressure to develop solvent resistance. The time and temperature required depends on the polymer and the amount of multifunctional acid added. There parameters are easily determined for each combination of polymer and acid by holding cure time or temperature constant and varying the other parameter (Table 1).

(2) Representative and illustrative examples of the useful aromatic diacid dichlorides in the invention are:

(3) Terephthaloyl dichloride (TPC);

(4) ##STR00008##

(5) Isophthaloyl dichloride (IPC);

(6) ##STR00009##

(7) 2, 6-naphthaloyl dichloride (NDC);

(8) ##STR00010##

(9) 4, 4-Biphenyldicarbonyl dichloride (BPDC);

(10) ##STR00011##

(11) Representative and illustrative examples of the useful aromatic diamines in the invention are:

(12) 4, 4-Diamino-2, 2-bistrifluoromethylbenzidine (PFMB);

(13) ##STR00012##

(14) 4,4-Diamino-2,2-bistrifluoromethoxylbenzidine (PFMOB);

(15) ##STR00013##

(16) 4,4-Diamino-2,2-bistrifluoromethyldiphenyl ether (6FODA);

(17) ##STR00014##

(18) Bis-(4-amino-2-trifluoromethylphenyloxyl)benzene (6FOQDA);

(19) ##STR00015##

(20) Bis-(4-amino-2-trifluoromethylphenyloxyl)biphenyl (6FOBDA).

(21) ##STR00016##

(22) Representative and illustrative examples of the useful multifunctional aromatic acid in the invention are:

(23) Trimesic acid (TA)

(24) ##STR00017##

(25) 2, 4, 6, 8-Naphthyl tetracarboxylic acid (TTNA)

(26) ##STR00018##

(27) 3, 3, 5, 5-Biphenyltetracarboxylic acid (BPTA 1)

(28) ##STR00019##

(29) 2, 2, 4, 4-Biphenyltetracarboxylic acid (BPTA 2)

(30) ##STR00020##

EXAMPLES

Example 1

(31) This example illustrates the general procedure used to prepare a polyamide solution for film casting directly from monomers.

(32) A polymer solution was prepared from TPC/IPC and PFMB (70/30/100 mol ratio) containing 5% TA (weight ratio to the polymer) in the following manner: To a 250 ml, three necked, round bottom flask, equipped with a mechanical stirrer, a nitrogen inlet, and outlet, was added PFMB (3.2024 g, 0.01 mol) and dried DMAc (45 ml). After the PFMB dissolved completely, the solution was cooled to 0 C. and IPC (0.6395 g 0.003 mol) was slowly added. The flask wall was washed with DMAc (1.5 ml) to insure all of the IPC was transferred to the solution. After 15 minutes, TPC (1.4211 g, 0.007 mol) was slowly added and the flask wall was again washed with DMAc (1.5 ml). The solution quickly became quite viscous and formed a gel. After PrO (1.4 g, 0.024 mol) was added, the gel slowly broke up to form a viscous, homogenous solution. The polymerization mixture was stirred for another 4 hours at 0 C. After TA (0.45 g) was added, the mixture was allowed to warm to room temperature and stirred for another two hours.

Example 2

(33) This example illustrates the general procedure used to prepare polyamide solutions for film casting from preformed polymer.

(34) The polymer solution in Example 1 was added to methanol prior to the addition of TA. The fibrous precipitate that formed was collected by filtration, washed with methanol, and dried. A 10% solids solution was then prepared by dissolving the polymer in DMAC. After 0.45 g of TA was added, the solution was stirred for 1 hr at room temperature.

Example 3

(35) The polymerization described in Example 1 was carried out using 2,6-naphthaloyl dichloride (NDC) in place of TPC. In this case, the mol ratio of NDC/IPC/PFMB was 50/50/100.

Comparative Example 1

(36) The copolymer solution in Example 1 was prepared, but no TA was added.

Comparative Example 2

(37) The copolymer solution in Example 3 was prepared, but no TA was added.

(38) Preparation and Characterization of the Polymer Films

(39) The polyamide solution containing TA prepared in the Examples were used to prepare films. For the preparation of small films in a batch process, the solution is poured on a flat glass plate or other substrate, and the film thickness is adjusted with a doctor blade. After drying on the substrate under reduced pressure at 60 C. for several hours, the film is further dried at 200 C. under a dry nitrogen stream for 1 hour. The film is made solvent resistant by heating at or near the polymer T.sub.g under vacuum or in an inert atmosphere for several minutes. It is to be understood that the film can be heated at any temperature between approximately 10% lower than the Tg and approximately 10% higher than the T.sub.g. Mechanical removal from the substrate yields a transparent, free standing film with a thickness greater than approximately 10 m. The thickness of the free standing film can be increased to as large as approximately 125 m by adjusting the solids content and the viscosity of the polymer solution. In some instances, the film is cast on a thin substrate such as a woven glass mat or a glass film and not removed, so as to form an polymer impregnated mat or a laminate. The thickness of the substrate is typically approximately 25 m thick or greater and the thickness of the polyamide film is approximately 5 m or greater. It is also understood that the batch processes described herein can be modified so that it can be carried out continuously using a roll-to-roll process by techniques known to those skilled in the art.

(40) The film CTE and polyamide T.sub.g are measured with a thermal mechanical analyzer (TA Q 400 TMA) with a load strain of 0.05N. Film samples with a thickness of approximately 20 m are normally used. In one aspect, the CTE is less than approximately 40 ppm/ C., but it is understood that in other aspects, the CTE is less than approximately 30 ppm/ C. The experimentally derived CTEs are the average of the CTEs obtained from 30 C. to 200 C. The Tg is taken as the extrapolated point at which the CTE undergoes a dramatic increase.

(41) Film transparency is measured by determining the transmittance of a 10 m thick film from 400 to 750 nm with a UV-Visible spectrometer (Shimadzu UV 2450).

(42) The solvent resistance of the film is determined by immersing it in DMF, DMAC, and NMP for 30 minutes at room temperature. The film is considered solvent resistant if it is substantially free of surface wrinkles, swelling, or any other visible damage after immersion in all three solvents.

(43) The properties of films obtained from the polyamide solutions of Examples 1 and 3 before and after heat treatment are given in Tables 2 and 3, respectively. For comparison purposes, the properties of the films prepared from polyamide solutions not containing TA (Comparative Examples 1 and 2) are also given in Tables 2 and 3.

(44) TABLE-US-00001 TABLE 1 Effect of TA Concentration on Cure Temperature at Constant Cure Time (0.5 hr).sup.1 Cure Temp TA Added (wt %) 250 C. 300 C. 350 C. 9% No.sup.2 Yes.sup.3 Yes 8% No Yes Yes 7% No Yes Yes 6% No Yes Yes 5% No No Yes 4% No No Yes 3% No No Yes .sup.1Film of polymer from Example 1; TPC/IPC/PFMB = 70/30/100. .sup.2No: soluble or swellable in polar aprotic solvents. .sup.3Yes: solvent resistant to polar aprotic solvents.

(45) TABLE-US-00002 TABLE 2 Properties of Film Prepared from Polymer Solutions Obtained in Example 1 and Comparative Example 3. TPC/IPC/PFMB 70/30/100 w/o TA w/5% TA Heat treatment None.sup.1 Yes.sup.2 None Yes Tg, C. 322 309 308 313 CTE, ppm/ C., 0.65 0.6 0.38 26.9 30-200 C. T% @ 400 nm 83.4 81.6 86.1 80.4 T% @ 750 nm 88.9 88.9 88.7 87.9 Dn 0.1045 0.1091 0.0942 0.0466 Solvent Resistant No No No Yes .sup.1No heat treatment. .sup.2Yes means film was heated at 330 C. for 10 minutes under reduced pressure.

(46) TABLE-US-00003 TABLE 3 Properties of Film Prepared from Polymer Solutions Obtained in Example 3 and Comparative Example 4 NDC/IPC/PFMB 50/50/100 w/o TA w/5% TA Heat treatment None Yes None Yes Tg, C. 316 319 303 313 CTE, ppm/ C., 7.6 9.3 3.4 39.7 30-200 C. T% @ 400 nm 85.2 72.1 85.1 77.1 T% @ 750 nm 88.7 86.8 89.2 87.7 Dn 0.1024 0.0854 0.0955 0.0941 Solvent Resistant No No No Yes .sup.1No heat treatment. .sup.2Yes means film heated at 330 C. for 10 minutes under reduced pressure.

(47) The embodiments have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. Although the description above contains much specificity, this should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the embodiments of this invention. Various other embodiments and ramifications are possible within its scope.

(48) Furthermore, notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.