High heat-resistant polyamic acid solution and polyimide film

Abstract

This invention relates to a highly heat-resistant polyamic acid solution and a polyimide film having improved thermal dimensional stability, wherein the polyamic acid solution includes a polymer of a diamine compound, containing 1 to 10 mol % of a carboxylic acid functional group-containing diamine compound based on the total amount of diamine, and a dianhydride compound, and the polyimide film includes polyimide, which is an imidized product of the polyamic acid solution and is configured such that main chains thereof are crosslinked through an amide bond (CONH).

Claims

1. A polyimide film, comprising a polyimide, which is an imidized product of a polyamic acid solution and is configured such that main chains thereof are crosslinked through an amide bond (CONH), wherein the polyamic acid solution comprises a polymer of a diamine compound and a dianhydride compound, wherein the diamine compound includes 1 to 10 mol % of a carboxylic acid functional group-containing diamine compound based on a total molar amount of the diamine compound, and wherein the polyimide film has a coefficient of thermal expansion (CTE) of 5 ppm/ C. or less at a temperature ranging from 50 to 500 C. and a CTE increase index of 10 or less, as defined by Equation 1 below:
CTE increase index=2nd CTE/1st CTE<Equation 1> wherein 1st CTE is a coefficient of thermal expansion first measured in a temperature range of 50 to 500 C. according to a TMA (thermomechanical analyzer) method and 2nd CTE is a coefficient of thermal expansion obtained by cooling a first measured sample to room temperature and performing second measurement under the same conditions as in a first measurement, in which 1st CTE2nd CTE is satisfied.

2. The polyimide film of claim 1, wherein the polyimide film has a tensile strength of 250 to 350 MPa, an elastic modulus of 7.0 to 10.0 GPa, and an elongation of 13 to 15%, according to ASTM D882.

Description

MODE FOR INVENTION

Examples

(1) A better understanding of the present invention may be obtained through the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

Example 1

(2) While nitrogen was passed through a 1 L reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller and a condenser, 715 g of N,N-dimethylacetamide (DMAc) was added to the reactor, the temperature of the reactor was set to 35 C., 43.92 g of p-phenylenediamine (p-PDA), corresponding to 99 mol % based on the total molar amount of diamine (0.405 mol, which is identically applied to Examples 2 and 3 and Comparative Examples 1 to 3), was dissolved therein, and the resultant solution was maintained at 35 C.

(3) Furthermore, the solution was added with 1.02 g of 4,4-diaminobiphenyl-3,3-dicarboxylic acid, corresponding to 1 mol % based on the total molar amount of diamine, and 36.18 g of biphenyl tetracarboxylic dianhydride (BPDA), corresponding to 30 mol % based on the total molar amount of dianhydride, reacted for 2 hr, added with 62.60 g of 1,2,4,5-benzene tetracarboxylic dianhydride (PMDA), corresponding to 67 mol % based on the total molar amount of dianhydride, and stirred for 12 hr and thus dissolved and allowed to react. As such, the temperature of the solution was maintained at 35 C., thus yielding a polyamic acid solution having a solid content of 17 wt % and a viscosity of 140 ps.

(4) The solution obtained after termination of the reaction was applied on a support, cast to a thickness of 20 m, thermally treated using hot air at 200 C. for 30 min to primarily remove the solvent, additionally dried using hot air at 300 C. for 1 hr and at 500 C. for 2 min, and slowly cooled to separate the resulting film from the support, thus obtaining a polyimide film having a thickness of 12 m.

Example 2

(5) A polyimide film was manufactured in the same manner as in Example 1, with the exception that 42.12 g of p-PDA, corresponding to 95 mol % based on the total molar amount of diamine, and 5.69 g of DATA, corresponding to 5 mol % based thereon, were used. The polyamic acid solution obtained during the manufacturing process of Example 2 had a solid content of 17 wt % and a viscosity of 135 ps.

Example 3

(6) A polyimide film was manufactured in the same manner as in Example 1, with the exception that 39.92 g of p-PDA, corresponding to 90 mol % based on the total molar amount of diamine, and 10.20 g of DATA, corresponding to 10 mol % based thereon, were used. The polyamic acid solution obtained during the manufacturing process of Example 3 had a solid content of 17 wt % and a viscosity of 138 ps.

Comparative Example 1

(7) A polyimide film was manufactured in the same manner as in Example 1, with the exception that 44.40 g of p-PDA, corresponding to 99.1 mol % based on the total molar amount of diamine, and 0.93 g of DATA, corresponding to 0.9 mol % based thereon, were used. The polyamic acid solution obtained during the manufacturing process of Comparative Example 1 had a solid content of 17 wt % and a viscosity of 136 ps.

Comparative Example 2

(8) A polyimide film was manufactured in the same manner as in Example 1, with the exception that 39.48 g of p-PDA, corresponding to 89 mol % based on the total molar amount of diamine, and 11.22 g of DATA, corresponding to 11 mol % based thereon, were used. The polyamic acid solution obtained during the manufacturing process of Comparative Example 2 had a solid content of 17 wt % and a viscosity of 140 ps.

Comparative Example 3

(9) In order to obtain a polyimide film, the same procedure as that of Example 1 was performed, with the exception that 39.90 g of p-PDA, corresponding to 85 mol % based on the total molar amount of diamine, and 11.398 g of DATA, corresponding to 15 mol % based thereon, were used, but the DATA was not dissolved in the solvent, and thus a polyamic acid solution could not be obtained.

Comparative Example 4

(10) A polyimide film was manufactured in the same manner as in Example 1, with the exception that 727 g of N,N-dimethylacetamide (DMAc), 43.14 g of p-PDA, corresponding to 95 mol % based on the total molar amount of diamine (0.398 mol, which is identically applied to Comparative Example 5), 4.62 g of 4,4-diamino biphenyl (DABP), corresponding to 5 mol % based thereon, 37.07 g of BPDA, corresponding to 30 mol % based on the total molar amount of dianhydride, and 61.37 g of PMDA, corresponding to 67 mol % based thereon, were used. The polyamic acid solution obtained during the manufacturing process of Comparative Example 4 had a solid content of 17 wt % and a viscosity of 148 ps.

Comparative Example 5

(11) A polyimide film was manufactured in the same manner as in Example 1, like Comparative Example 4, with the exception that 738 g of N,N-dimethylacetamide (DMAc), 40.87 g of p-PDA, corresponding to 90 mol % based on the total molar amount of diamine, and 9.24 g of DABP, corresponding to 10 mol % based thereon, were used. The polyamic acid solution obtained during the manufacturing process of Comparative Example 5 had a solid content of 17 wt % and a viscosity of 125 ps.

(12) Evaluation of Properties

(13) The films of Examples 1 to 3 and Comparative Examples 1 to 5 were measured for CTE and mechanical properties as follows. The results are shown in Tables 1 and 2 below.

(14) (1) CTE (Coefficient of Thermal Expansion)

(15) CTE was measured two times using a TMA (Diamond TMA, made by PerkinElmer) through a TMA method, and the heating rate was 10 C./min and a load of 100 mN was applied. Here, the sample to be measured had a width of 4 mm and a length of 23 mm. In the measurement of 1.sup.st CTE, the CTE was measured in a manner in which a temperature of 50 C. was maintained for 1 min and then increased to 500 C. at a heating rate of 10 C./min under a load of 100 mN (which is defined as the coefficient of thermal expansion of the film, and is referred to as a 1.sup.st CTE based on the measurement sequence). The sample was cooled to room temperature at a rate of 5 C./min after the completion of measurement of the 1.sup.st CTE. Also, the measurement of the 2nd CTE was performed under the same conditions as in 1.sup.st CTE, and the 2.sup.nd CTE was measured in a manner in which a temperature of 50 C. was maintained for 1 min and then increased to 500 C. at a heating rate of 10 C./min under a load of 100 mN.

(16) In the foregoing and following description, the CTE indicates a coefficient of linear thermal expansion.

(17) The 1.sup.st CTE and 2.sup.nd CTE values thus obtained were substituted into Equation 1 below to thus calculate a CTE increase index.
CTE increase index=2.sup.nd CTE/1.sup.st CTE<Equation 1>

(18) In Equation 1, the 1.sup.st CTE is the coefficient of thermal expansion, first measured in the temperature range of 50 to 500 C. according to a TMA method, and the 2.sup.nd CTE is the coefficient of thermal expansion obtained by cooling the first measured sample to room temperature and performing second measurement under the same conditions as in the first measurement (in which 1.sup.st CTE2.sup.nd CTE is satisfied).

(19) (2) Mechanical Properties

(20) Tensile strength, elastic modulus and elongation were measured based on ASTM D882 using Instron 5967. Each sample had a size of 13 mm100 mm, a load cell was 1 KN, a tension rate was 50 mm/min, and the individual properties thereof were measured seven times, and the average value thereof, excluding the maximum and the minimum, was determined.

(21) TABLE-US-00001 TABLE 1 CTE Molar ratio Viscosity 1.sup.st CTE 2.sup.nd CTE increase Composition (mol %) (Ps) (ppm/ C.) (ppm/ C.) index (%) Ex. 1 pPDA + DATA + BPDA + PDMA 99:1:30:67 140 0.75 3.87 5.16 Ex. 2 95:5:30:67 135 1.23 2.59 2.10 Ex. 3 90:10:30:67 145 2.37 2.89 1.21 C. Ex. 1 pPDA + DATA + BPDA + PDMA 99.1:0.9:30:67 138 0.35 5.15 14.71 C. Ex. 2 89:11:30:67 136 1.38 15.66 11.34 C. Ex. 3 85:15:30:67 Not evaluated C. Ex. 4 pPDA + DABP + BPDA + PMDA 95:5:30:67 148 0.37 5.98 16 C. Ex. 5 99:10:30:67 125 0.26 6.53 25

(22) Based on the results of measurement of properties, as is apparent from Table 1, when the amount of DATA having a carboxylic acid functional group was 1 to 10 mol % based on the total molar amount of the diamine compound, 2.sup.nd CTE was lower than Comparative Examples 1 to 3, in which the amount of DATA fell out of the range of the invention, and thus the CTE increase index was remarkably low.

(23) In Comparative Examples 4 and 5, using DABP having no carboxylic acid functional group compared to DATA as the diamine monomer, 2.sup.nd CTE was high and thus the CTE increase index was remarkably high.

(24) Therefore, the polyimide film of the present invention was concluded to have thermal dimensional stability.

(25) TABLE-US-00002 TABLE 2 Tensile Elastic Molar ratio Thickness strength modulus Elongation Composition (mol %) (m) (MPa) (GPa) (%) Ex. 1 pPDA + DATA + BPDA + PDMA 99:1:30:67 13 260 7.3 15 Ex. 2 95:5:30:67 12 310 8.5 14 Ex. 3 90:10:30:67 15 330 9.5 13 C. Ex. 1 pPDA + DATA + BPDA + PDMA 99.1:0.9:30:67 11 258 7.2 10 C. Ex. 2 89:11:30:67 13 333 9.6 11 C. Ex. 3 85:15:30:67 Not evaluated C. Ex. 4 pPDA + DABP + BPDA + PMDA 95:5:30:67 13 270 7.2 12 C. Ex. 5 99:10:30:67 14 280 7.3 11

(26) Based on the results of measurement of mechanical properties, as is apparent from Table 2, the degree of crosslinkage between chains was increased with an increase in the molar amount of DATA, which enables the crosslinking reaction, whereby both tensile strength and elastic modulus were high. Also, as the amount of diamine having a carboxylic acid functional group increases, the film may become slightly brittle due to the biphenyl structure of diamine, thus decreasing the elongation thereof, which is however regarded as superior compared to when using diamine having no carboxylic acid functional group. If the amount thereof falls out of the range of the present invention, the elongation is drastically decreased, thus deteriorating mechanical properties.