POLYAMIC ACID VARNISH

Abstract

The present application provides a polyimide powder in which a conductive filler is uniformly dispersed within particles, and a polyamic acid varnish that is prepared from the powder and capable of implementing a polyimide molded article that not only has excellent moldability and processability, but also has excellent conductivity, tensile strength, elongation, and elastic modulus.

Claims

1. A polyamic acid varnish comprising: a polyamic acid including a diamine monomer and a dianhydride monomer as polymerization units; a conductive filler; and an organic solvent.

2. The polyamic acid varnish of claim 1, wherein the conductive filler is included in an amount of 0.1 to 50% by weight based on the total polyamic acid varnish.

3. The polyamic acid varnish of claim 1, wherein the conductive filler includes one or more selected from the group consisting of carbon black, conductive carbon, graphite, a conductive metal, and a conductive metal oxide.

4. The polyamic acid varnish of claim 1, wherein the dianhydride monomer includes at least one compound represented by Chemical Formula 1 below: ##STR00005## in Chemical Formula 1, .Math. is a tetravalent aliphatic ring group, a tetravalent heteroaliphatic ring group, a tetravalent aromatic ring group, or a tetravalent heteroaromatic ring group, and the carbon atom of the carbonyl group of Chemical Formula 1 is connected to the ring constituent atom of the aliphatic ring group, the heteroaliphatic ring group, the aromatic ring group, or the heteroaromatic ring group, and the aliphatic ring group, the heteroaliphatic ring group, the aromatic ring group, or the heteroaromatic ring group is a monocyclic ring or a condensed ring; or linked by a linking group including one or more divalent substituents selected from the group consisting of a single bond, a substituted or unsubstituted alkylene group, a substituted or unsubstituted alkylidene group, a substituted or unsubstituted alkenylene group, a substituted or unsubstituted alkynylene group, a substituted or unsubstituted arylene group, O, S, C(?O), S(?O).sub.2, and Si(R.sub.b).sub.2, wherein R.sub.b is hydrogen or an alkyl group.

5. The polyamic acid varnish of claim 4, wherein X is ##STR00006## or an aliphatic ring group, and M is at least one selected from the group consisting of a single bond, an alkylene group, an alkylidene group, O, S, C(?O), and S(?O).sub.2.

6. The polyamic acid varnish of claim 1, wherein the diamine monomer includes at least one compound represented by Chemical Formula 2 below: ##STR00007## in Chemical Formula 2, any one of B.sub.1 to B.sub.5 is an amino group (NH.sub.2), RNH.sub.2, or ORNH.sub.2, and R is a substituted or unsubstituted alkylene group, a substituted or unsubstituted alkylidene group, a substituted or unsubstituted alkenylene group, a substituted or unsubstituted alkynylene group, or a substituted or unsubstituted arylene group, and the others are hydrogen; a halogen; a hydroxyl group; a carboxyl group; or a halogen-substituted or unsubstituted alkyl group.

7. A particle-like polyimide powder comprising a cured product of the polyamic acid varnish of claim 1.

8. The polyimide powder of claim 7, wherein a conductive filler is dispersed within the particles.

9. A polyimide molded article comprising the polyimide powder of claim 7.

10. The polyimide molded article of claim 9, having a surface resistance ranging from 1.0?10.sup.2 to 1.0?10.sup.13?, as measured according to an ASTM D-257 method.

11. The polyimide molded article of claim 9, having an elongation of 3% or more, as measured according to an ASTM D-1708 method.

12. The polyimide molded article of claim 9, having a tensile strength of 65 MPa or more, as measured according to an ASTM D-1708 method.

13. A method of preparing a polyamic acid varnish, comprising: dispersing a conductive filler in an organic solvent; and polymerizing a diamine monomer and a dianhydride monomer in the organic solvent in which the conductive filler is dispersed.

14. The method of claim 13, wherein the dispersion is performed by sonication.

15. A method of preparing a polyimide powder, comprising: dispersing a conductive filler in an organic solvent; polymerizing a diamine monomer and a dianhydride monomer in the organic solvent in which the conductive filler is dispersed; and thermally curing a polymer produced in the polymerization to obtain a polyimide powder.

16. The method of claim 15, wherein the thermal curing is performed at a temperature of 150 to 300? C. for 1 to 10 hours.

17. A method of manufacturing a polyimide molded article, comprising: dispersing a conductive filler in an organic solvent; polymerizing a diamine monomer and a dianhydride monomer in the organic solvent in which the conductive filler is dispersed; thermally curing a polymer produced in the polymerization to obtain a polyimide powder; and molding the obtained polyimide powder to manufacture a polyimide molded article.

Description

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0092] Hereinafter, the present invention will be described in more detail through examples according to the present invention and comparative examples not according to the present invention, but the scope of the present invention is not limited by the examples presented below.

Example 1

[0093] A Dean-Stock trap was installed in a 1000 ml reactor equipped with a stirrer and a nitrogen inlet and outlet tube, and while injecting nitrogen, 10% by weight of carbon black (based on the total polyamic acid varnish) as a conductive filler was added to a solvent in which N-methyl-2-pyrrolidone (NMP) and m-cresol were mixed at a weight ratio of 8:2, and dispersed by sonication. The solvent in which the conductive filler was dispersed was heated to 75? C., and then 100 molar parts of 4,4-diaminodiphenyl ether (ODA) was added and completely dissolved. Afterwards, pyromellitic dianhydride (PMDA) was added at 80 molar parts to the 100 molar parts of ODA, oxydiphthalic dianhydride (OPDA) was added at 20 molar parts to the 100 molar parts of ODA, and this mixture was reacted at 75? C. for 2 hours to prepare a polyamic acid varnish in which the conductive filler was uniformly dispersed. Afterwards, the temperature of the polyamic acid varnish was raised to 200? C. while stirring, and the mixture was heated for an additional 2 hours to precipitate a polyimide powder.

Examples 2 to 6

[0094] Polyimide powder was precipitated in the same manner as in Example 1, except that the monomer components, solvent, and conductive filler were adjusted as shown in Table 1 below.

Comparative Examples 1 to 4

[0095] Polyimide powder was precipitated in the same manner as in Example 1, except that the conductive filler was not used and the monomer components, solvent, and catalyst were adjusted as shown in Table 1 below.

[0096] In Table 1 below, to explain the mixing method of the conductive filler, the dispersion mixing of Examples 1 to 7 refers to a method of mixing the conductive filler in the solvent through sonication in the polyamic acid polymerization as in Example 1. The dry mixing of Comparative Examples 1 to 4 refers to a method of polymerizing polyamic acid without using a conductive filler, imidizing it to precipitate polyimide powder, and then mechanically mixing the precipitated polyimide powder and the conductive filler.

TABLE-US-00001 TABLE 1 Dianhydride Conductive filler Molar Solvent Content (% Mixing Classification Type 1 Type 2 ratio Diamine (weight ratio) Type by weight) method Example 1 PMDA OPDA 8:2 ODA NMP/m-cresol CB 10 Dispersion (8:2) mixing Example 2 PMDA OPDA 8:2 ODA NMP/m-cresol CB 1 Dispersion (8:2) mixing Example 3 PMDA OPDA 8:2 ODA NMP/m-cresol CB + 15 + 5 Dispersion (8:2) rGO mixing Example 4 PMDA OPDA 8:2 ODA NMP/m-cresol MWCNTs 5 Dispersion (8:2) mixing Example 5 PMDA OPDA 8:2 ODA NMP/m-cresol MWCNTs 10 Dispersion (8:2) mixing Example 6 PMDA OPDA 8:2 ODA NMP/m-cresol rGO + 10 + 5 Dispersion (8:2) MWCNTs mixing Comparative PMDA OPDA 8:2 ODA NMP/m-cresol CB 10 Dry mixing Example 1 (8:2) Comparative PMDA OPDA 8:2 ODA NMP/m-cresol rGO 10 Dry mixing Example 2 (8:2) Comparative PMDA OPDA 8:2 ODA NMP/m-cresol Graphite 15 Dry mixing example 3 (8:2) Comparative PMDA OPDA 8:2 ODA NMP/m-cresol MWCNTs 5 Dry mixing Example 4 (8:2) CB: Carbon black rGO: Reduced graphene oxide MWCNTs: Multi-walled carbon nanotubes

Experimental Example 1Processability

[0097] Molded articles obtained by HCM molding the polyimide powder of the Examples and Comparative Examples were processed into a dogbone shape to prepare each of samples, and the exterior of the sample was observed with the naked eye to check whether cracks had occurred and the number of cracks. Specifically, samples were divided into cases where no cracks occurred and cases where cracks occurred in an area of 10 cm?10 cm, and when cracks occurred, they were classified into few cracks and many cracks depending on the number of cracks, as shown below. [0098] O: No cracks [0099] ?: 1 to 5 cracks (few cracks) [0100] X: more than 5 cracks (many cracks)

Experimental Example 2Surface Resistance

[0101] The surface resistance of molded articles obtained by HCM molding the polyimide powder of the Examples and Comparative Examples was measured according to ASTM D-257 using Advanced Energy/Trek 152-1. The measurement temperature was set to 23?3? C., and the source voltage was set to 10 V.

Experimental Example 3Elongation and Tensile Strength Measurement

[0102] The polyimide powder of the Examples and Comparative Examples was HCM-molded, processed into a dogbone shape with a length of 38 mm and a width of 15 mm, and then elongation and tensile strength were measured according to the ASTM D-1708 method using Instron UTM equipment from Instron.

TABLE-US-00002 TABLE 2 Surface Tensile resistance strength Elongation Classification Processability (?) (MPa) (%): Example 1 ? 1.8 ? 10.sup.12 102 7.5 Example 2 ? 1.3 ? 10.sup.12 90 6.2 Example 3 ? 1.8 ? 10.sup.10 80 5.1 Example 4 ? 1.0 ? 10.sup.5 93 6.3 Example 5 ? 1.0 ? 10.sup.4 80 4.8 Example 6 ? 1.0 ? 10.sup.3 78 5.9 Comparative X 1.2 ? 10.sup.10 55 2.8 Example 1 Comparative X 1.1 ? 10.sup.9 53 1.9 Example 2 Comparative X 1.0 ? 10.sup.12 40 1.5 Example 3 Comparative ? 1.0 ? 10.sup.9 60 2.4 Example 4

Advantageous Effects

[0103] The present application provides a polyimide powder in which a conductive filler is uniformly dispersed within particles, and a polyamic acid varnish that is prepared from the powder and capable of implementing a polyimide molded article that not only has excellent moldability and processability, but also has excellent conductivity, tensile strength, elongation, and elastic modulus.