JP2022176131A - Polyamide-imide composition - Google Patents

Abstract

To provide a polyamide-imide (PAI) composition which can be formed into a CB-containing PAI film which satisfies both of high stiffness and high toughness.SOLUTION: Provided is a polyamide-imide (PAI) composition which comprises polyamide-imide (PAI-1) having a different acid value from PAI-1, polyamide-imide (PAI-2), carbon black (CB) and a solvent and which satisfies the following 1) to 4): 1) both PAI-1 and PAI-2 are a PAI obtained using trimellitic anhydride (TMA) and o-tolidine diisocyanate (TODI); 2) an acid value of PAI-1 is 10 mg-KOH/g or less and an acid value of PAI-2 is more than 10 mg-KOH/g and 20 mg-KOH/g or less; 3) CB is acidic CB having a pH of less than 7; and 4) a solid content ratio of PAI (a ratio of (a total mass of PAI-1 and PAI-2) to (a total mass of PAI-1, PAI-2 and the solvent)) is more than 15 mass% and 22 mass% or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a polyamide-imide (PAI) composition that can be molded into a film, for example, and suitably used as an intermediate transfer belt, a fixing belt, or the like for copiers, printers, and the like.

Films made of polyimide-based materials such as PAI, which are excellent in heat resistance, mechanical properties, and dimensional stability, are widely used as intermediate transfer belts and fixing belts of copiers and printers that require high speed.
These belts can be obtained, for example, by applying a composition (solution) consisting of PAI, carbon black (CB), and a solvent to a mold and drying it. It is used as a seamless belt.

As a CB-containing PAI film obtained from such a PAI solution, a PAI film using trimellitic acid (TMA) as an acid component and o-tolidine diisocyanate (TODI) as an isocyanate component is known. . Patent Documents 1 to 3 disclose that a PAI belt made of a PAI film having such a chemical structure is excellent in dimensional stability, heat resistance and mechanical properties (particularly rigidity). Here, CB mixed with PAI is often used as a filler for adjusting the charging characteristics of the belt when the PAI film is used as an intermediate transfer belt.
As a composition comprising PAI using TMA and TODI, and CB, Patent Document 4 discloses a solution composition containing two types of PAI with different logarithmic viscosities. PAI films are described as having a high tensile modulus.

Japanese Patent Application Laid-Open No. 2003-261768 JP 2005-25586 A JP 2009-237364 A JP 2008-266430 A

However, the CB-containing PAI composition described in Patent Document 4 had points to be improved. That is, the CB used here is "basic CB", and this CB does not have good dispersibility in the PAI solution, and the CB tends to aggregate during storage of the solution. When the CB is aggregated and formed into a belt-like film, although high rigidity of the film is ensured, there is a problem that it becomes difficult to obtain high toughness of the film, that is, high tensile elongation. When such a belt is attached to a copier and used for a long period of time, breakage or cracking may occur. For this reason, there has been a demand for a PAI solution that has good dispersibility of CB and that can ensure both high rigidity and high toughness when made into a film. In addition, the PAI concentration of the PAI solution composition described in the example of Patent Document 4 is as low as 15% by mass, and from the viewpoint of the productivity of the PAI solution, the PAI solid content concentration of the PAI solution should be higher. was desired to do. That is, it was necessary to increase the PAI solid content concentration of the PAI solution while ensuring good dispersibility of CB.

Therefore, the present invention solves the above problems, and can be a CB-containing PAI film that has both high rigidity and high toughness, and even if the PAI concentration is high, the PAI has good CB dispersibility. It is intended to provide a composition.

As a result of intensive research to solve the above-mentioned problems, the above-mentioned problems have been solved by preparing a solution-like PAI composition in which a specific CB is blended with two or more types of PAI having a specific chemical structure and acid value. The inventors have found that the present invention has been completed.

The present invention is characterized by the following: "A PAI composition comprising a polyamideimide (PAI-1), a polyamideimide (PAI-2) having an acid value different from that of PAI-1, CB, and a solvent. ”.
1) Both PAI-1 and PAI-2 are PAIs using TMA as an acid component and TODI as an isocyanate component.
2) The acid value of PAI-1 is 10 mg-KOH/g or less, and the acid value of PAI-2 is more than 10 mg-KOH/g and 20 mg-KOH/g or less.
3) CB is an acidic CB with a pH of less than 7.
4) PAI solid content ratio (ratio of "total mass of PAI-1 and PAI-2" to "total mass of PAI-1, PAI-2 and solvent") is more than 15% by mass and 22% by mass or less is.

The PAI composition of the present invention has good dispersibility of CB in spite of its high PAI concentration. In this case, high rigidity and high toughness of the film can be ensured at the same time.

The present invention will be described in detail below.

The composition of the present invention comprises polyamideimide (PAI-1), polyamideimide (PAI-2) having an acid value different from that of PAI-1, carbon black (CB), and a solvent. Here, both PAI-1 and PAI-2 must be PAI using TMA as an acid component and TODI as an isocyanate component. The acid value of PAI-1 should be 10 mg-KOH/g or less, and the acid value of PAI-2 should be more than 10 mg-KOH/g and 20 mg-KOH/g or less. The acid value of PAI-1 is preferably 8 mg-KOH/g or less, and the acid value of PAI-2 is preferably 12 mg-KOH/g or more and 16 mg-KOH/g or less. Here, the acid value is a numerical value that is mainly measured depending on the terminal carboxylic acid concentration of PAI. Dispersibility can be ensured.
The acid value is determined by diluting about 1.0 g of the PAI solution with N-methyl-2-pyrrolidone (NMP) so that the PAI concentration is about 1% by mass, based on the provisions of JIS K0070 (1992), and adding bromothymol blue ( BTB) is used as an indicator, titration is performed with potassium hydroxide (KOH), and the number of mg of KOH consumed for neutralization can be confirmed as a value converted per 1 g of PAI.

PAI-1 or PAI-2 of the present invention can be obtained as a solution, for example, by the following method.
That is, it can be obtained by polymerizing approximately equimolar amounts of TMA and TODI in a solvent.
Here, in the PAI of the present invention, part of TODI is preferably replaced with 4,4'-diphenylmethane diisocyanate (MDI) and/or tolylene diisocyanate (TDI). As tolylene diisocyanate (TDI), 2,4-TDI, 2,6-TDI or mixtures thereof can be used. As the mixture, for example, one having a molar ratio of 2,4-TDI/2,6-TDI=70 to 100/0 to 30 can be used. As for the substitution ratio, 5 to 70 mol % of TODI is preferably substituted with MDI and/or TDI, more preferably 10 to 60 mol %. By doing so, an optically uniform PAI solution can be obtained. Whether or not it is optically uniform can be visually determined. That is, the solution is observed, and if white turbidity is observed, it is optically heterogeneous, and if no white turbidity is observed, it is optically uniform.
PAI-1 and PAI-2 may have the same or different monomer compositions, but are preferably the same.

Also, in the PAI of the present invention, part of TMA may be substituted with other acid components. Other acid components include, for example, tricarboxylic anhydrides, alicyclic dicarboxylic acids, and aliphatic dicarboxylic acids. The substitution rate is preferably 20 mol % or less.
Specific acid components that substitute for TMA include tricarboxylic anhydrides such as cyclohexanetricarboxylic anhydride, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dimer acid, and the like. and the like. Among the aliphatic dicarboxylic acids, dimer acid (DA) is preferred for ensuring high toughness. Here, the dimer acid (DA) is a fatty acid mainly composed of dibasic acid of C36 dicarboxylic acid produced by dimerization of C18 unsaturated fatty acid using vegetable oil as a raw material, Croda Japan Co., Ltd., Tsuno It can be obtained as a commercial product from Shokuhin Kogyo Co., etc.

In addition, as an acid component, a part of TMA may be may be substituted with a tetracarboxylic dianhydride such as a compound. The substitution rate from TMA is preferably 10 mol % or less. If this substitution rate exceeds 5 mol %, it may become difficult to ensure good dispersibility. Therefore, for example, as disclosed in WO 2003/072639, "trimellitic anhydride/3,3',4,4'-benzophenonetetracarboxylic dianhydride/3,3' as an acid component ,4,4′-biphenyltetracarboxylic dianhydride=70 to 90/5 to 25/5 to 25 (mol %), and 3,3′-dimethyl-4,4′-biphenyl diisocyanate as a diisocyanate component. "Including" PAI or the like cannot be said to be an effective method from the viewpoint of ensuring a high tensile modulus and a high tensile elongation at the same time.

The molar ratio between the acid component and the isocyanate component is preferably 1/0.95 to 1.05.
By adjusting the molar ratio of the isocyanate component to the acid component in this manner, a PAI-1 solution or PAI-2 solution having the acid value specified in the present invention can be obtained.
Furthermore, during the polymerization reaction, basic compounds such as 1,8-diazabicyclo[5.4.0]undecene-7 (DBU) and triethylenediamine (DABCO) are used as catalysts, and 0.01 to 1 mol% of TMA is blended. can do.
By using such a basic catalyst, a PAI solution with a lower acid value can be obtained.

Although the solvent used for the polymerization reaction is not limited, it is preferable to use an amide solvent. Specific examples of amide solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc) and the like. These solvents can be used alone or as a mixture. Among these, NMP, DMAc, and mixtures thereof are preferred. These polymerization solvents are preferably dehydrated to a moisture content of 100 ppm or less.

The reaction temperature for the polymerization reaction is preferably 100 to 200°C, more preferably 120 to 180°C. In this reaction, the order of addition of the monomers and solvent is not particularly limited, and any order may be used.

The PAI concentration of the PAI solution obtained as described above is preferably more than 15% by mass and less than 22% by mass for both the PAI-1 solution and the PAI-2 solution, and is 16% by mass or more and 21% by mass or less. is more preferable.
By doing so, the PAI solid content ratio ("total mass of PAI-1 and PAI-2", "total mass of PAI-1 and PAI-2 and solvent ) can be more than 15% by mass and 22% by mass or less.
More preferably, the PAI solid content ratio is 16% by mass or more and 22% by mass or less.
Here, the PAI solid content ratio is obtained by, for example, removing CB by filtration as necessary, collecting about 5 g of the PAI solution on a petri dish, and treating it at 300 ° C. for 120 minutes in a nitrogen stream to volatilize the solvent. It can be confirmed by measuring the mass of the solid content of.

The PAI composition of the present invention can be obtained by mixing CB with the PAI solution obtained as described above.
Here, the CB must be an acidic CB with a pH of less than 7, preferably 5 or less, more preferably 4 or less.
Here, the pH of CB can be confirmed by preparing an aqueous suspension of CB (concentration of about 0.05% by mass) and measuring with a glass electrode.

Specific examples of acidic CB having a pH of less than 7 include Degussa's "Printex 150T" (pH 4.5, volatile content 10.0%) and "Special Black 350" (pH 3.5, volatile content 2 .2%), the same "Special Black 100" (pH 3.3, volatile content 2.2%), the same "Special Black 250" (pH 3.1, volatile content 2.0%), the same "Special Black 5" ( pH 3.0, volatile content 15.0%), "Special Black 4" (pH 3.0, volatile content 14.0%), "Special Black 4A" (pH 3.0, volatile content 14.0%), "Special Black 550" (pH 2.8, volatile content 2.5%), "Special Black 6" (pH 2.5, volatile content 18.0%), "Color Black FW200" (pH 2.5, volatile minute 20.0%), the same "Color Black FW2" (pH 2.5, volatile content 16.5%), the same "Color Black FW2V" (pH 2.5, volatile content 16.5%), "MONARCH 1000" manufactured by Cabot Corporation ” (pH 2.5, volatile content 9.5%), Cabot “MONARCH 1300” (pH 2.5, volatile content 9.5%), Cabot “MONARCH 1400” (pH 2.5, volatile content 9.0% ), the same “MOGUL-L” (pH 2.5, volatile content 5.0%), the same “REGAL400R” (pH 4.0, volatile content 3.5%), and the like. These CBs can be used alone or as a mixture.

When a PAI solution is mixed with an acidic CB to form the composition of the present invention, first, a CB dispersion is prepared by dispersing CB in a PAI-2 solution at a high concentration, and this dispersion is mixed with a PAI-1 solution. is preferably mixed to obtain a composition of PAI, CB and a solvent.
By doing so, good dispersibility can be ensured.

In order to mix the PAI-2 solution and the CB, the PAI-2 solution is blended with the CB, premixed with a stirrer or the like, and then dispersed with a ring mill, ball mill, sand mill or the like.
In order to mix the PAI-2 solution in which CB is dispersed and the PAI-1 solution, a stirrer or the like may be used for mixing.

As described above, in this dispersion step, the final dispersion, that is, the PAI concentration after making the composition of the present invention is more than 15% by mass and 22% by mass or less. This is extremely important from the viewpoint of ensuring
Even if the acid value of PAI is a predetermined acid value, if the PAI concentration is 15% by mass or less or more than 22% by mass, CB aggregation is likely to occur, and as a result, good dispersion stability cannot be secured. It may become difficult.

The content of CB in the PAI composition is not limited, but it is preferably 10% by mass or more and 80% by mass or less, and 15% by mass or more and 60% by mass or less with respect to the total solid content of the composition. is more preferable.

The mixing ratio of the PAI-2 solution and the PAI-1 solution is not limited, but the amount of the PAI-2 solution used is preferably 50 to 500% by mass of the PAI-1 solution in terms of PAI solid content. It is more preferable to make it to 300% by mass.

The composition of the present invention may further contain a dispersant in order to further enhance the dispersibility of CB.
Such a dispersant may have a low molecular weight or a high molecular weight, and may be cationic, anionic, nonionic, or the like, but nonionic polymers are preferred.

The PAI composition of the present invention obtained as described above can be coated on a substrate and dried to form a CB-containing PAI film.
The substrate to be used is not limited, but metal foil such as copper foil, organic polymer film such as polyester film and polyimide film can be preferably used.
Moreover, a seamless belt made of a PAI film can be obtained by applying the solution containing the PAI of the present invention to a cylindrical mold, drying it, and removing it from the mold.
As drying conditions for obtaining a film from the PAI solution, it is preferable to pre-dry at a temperature of 50 to 180°C and then dry at 200 to 300°C.
Although the thickness of the molded PAI film is not limited, it is usually about 1 to 200 μm.

The film obtained from the PAI composition of the present invention preferably has a tensile modulus of 4.5 GPa or more, more preferably 5.5 GPa or more.
Also, the tensile elongation is preferably 15% or more, more preferably 25% or more.
By doing so, it can be used, for example, as a tough film for CB-containing copier belts.
The tensile modulus and tensile elongation of the PAI film can be confirmed by measuring according to JIS-K7127 (1999). Specifically, the PAI film was cut into a width of 1.0 mm and a length of 100 mm, and was measured using an Intesco Precision Universal Material Testing Machine Model 2020 manufactured by Intesco, with a chuck distance of 50 mm and a tensile speed of 20 mm/min. .

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited by these examples.

<Example 1>
TMA: 1.00 mol, TODI: 0.81 mol, MDI: 0.20 mol, DABCO: 0.0005 mol in a glass reaction vessel under a nitrogen atmosphere so that the solid content concentration is 25% by mass, After charging with dehydrated NMP (water content 80 ppm), heating to 150 ° C. with stirring and reacting for 5 hours, by diluting with NMP, a PAI-1 solution having a PAI solid content concentration of 16% by mass was obtained. Obtained.
Next, the polymerization reaction was carried out in the same manner as the PAI-1 solution in this example, except that TMA was 1.03 mol, to obtain a PAI-2 solution with a PAI solid content concentration of 16% by mass. .
Add 12 parts by mass of "Special Black 4" (pH 3.0), an acidic CB, manufactured by Degussa, to 100 parts by mass of PAI-2 solution, pre-mix with a stirrer, and then use a ball mill for 20 hours at 25 ° C. A PAI solution in which CB was uniformly dispersed was obtained by the dispersion treatment.
To 160 parts by mass of the obtained CB dispersion, 200 parts by mass of PAI-1 solution was added and mixed with a stirrer to obtain a PAI composition (solution) having a PAI solid content concentration of 16% by mass in which CB was dispersed. got
Next, the resulting PAI solution was applied onto a polyester film, dried at 80° C. for 10 minutes and at 130° C. for 10 minutes, and then the coating film was peeled off from the polyester film. Thereafter, this coating film was sandwiched between metal frames and dried at 260° C. for 60 minutes in a nitrogen gas atmosphere to obtain a PAI film with a thickness of 50 μm.
The tensile modulus and tensile elongation of this PAI film were measured by the method based on JIS described above and evaluated according to the following criteria.
<Tensile modulus>
A: 5.5 GPa or more (excellent)
B: less than 5.5 GPa, 4.5 GPa or more (no practical problem)
C: less than 4.5 GPa (practical problem)
<Tensile elongation>
A: 25% or more (excellent)
B: less than 25%, 15% or more (practically no problem)
C: less than 15% (practical problem)

<Example 2>
The PAI solid content concentration of the PAI-1 solution and the PAI-2 solution in Example 1 was changed to set the PAI solid content concentration of the PAI-1 solution and the PAI-2 solution to 20% by mass. In the same manner as above, a PAI composition (solution) having a PAI solid content concentration of 20% by mass in which CB was dispersed was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Example 3>
TMA: 1.00 mol, TODI: 0.61 mol, TDI: 0.40 mol, DABCO: 0.0004 mol in a glass reaction vessel under a nitrogen atmosphere so that the solid content concentration is 20% by mass, After charging with dehydrated NMP (water content 80 ppm), heating to 150 ° C. with stirring and reacting for 5 hours, by diluting with NMP, a PAI-1 solution having a PAI solid content concentration of 16% by mass was obtained. Obtained.
Next, the polymerization reaction was carried out in the same manner as the PAI-1 solution in this example, except that TMA was 1.03 mol, to obtain a PAI-2 solution with a PAI solid content concentration of 16% by mass. .
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Example 4>
The PAI solid content concentrations of the PAI-1 solution and the PAI-2 solution in Example 3 were changed to set the PAI solid content concentrations of the PAI-1 solution and the PAI-2 solution to 18% by mass. In the same manner as in 1, a PAI composition (solution) having a PAI solid content concentration of 18% by mass in which CB was dispersed was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Example 5>
The PAI-1 solution was the PAI-1 solution in Example 1 (PAI solid content concentration: 16% by mass), and the PAI-2 solution was the PAI-2 solution in Example 3 (PAI solid content concentration: 16% by mass). A PAI composition (solution) having a PAI solid content concentration of 16% by mass in which CB was dispersed was obtained in the same manner as in Example 1, except for the above.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Example 6>
TMA: 0.985 mol, DA: 0.015 mol, TODI: 0.81 mol, MDI: 0.20 mol, DABCO: 0.0005 mol in a glass reaction vessel under a nitrogen atmosphere. It was charged with dehydrated NMP (moisture content of 80 ppm) so as to be 16% by mass, heated to 150 ° C. with stirring, reacted for 5 hours, and then diluted with NMP, so that the PAI solid content concentration was 16 mass. % PAI-1 solution was obtained.
Next, the polymerization reaction was carried out in the same manner as the PAI-1 solution in this example except that TMA: 1.015 mol and DA: 0.015 mol, and the PAI solid content concentration was 16% by mass. of PAI-2 solution was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Example 7>
TMA: 0.90 mol, DA: 0.1 mol, TODI: 0.81 mol, MDI: 0.20 mol, DABCO: 0.0005 mol in a glass reaction vessel under a nitrogen atmosphere. It was charged with dehydrated NMP (moisture content of 80 ppm) so as to be 16% by mass, heated to 150 ° C. with stirring, reacted for 5 hours, and then diluted with NMP, so that the PAI solid content concentration was 16 mass. % PAI-1 solution was obtained.
Next, the polymerization reaction was carried out in the same manner as the PAI-1 solution in this example except that TMA: 0.93 mol and DA: 0.1 mol, and the PAI solid content concentration was 16% by mass. of PAI-2 solution was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Comparative Example 1>
Example 1 except that the PAI solid content concentrations of the PAI-1 solution and the PAI-2 solution in Example 1 were changed to 23% by mass. In the same manner as above, a PAI composition (solution) having a PAI solid content concentration of 23% by mass in which CB was dispersed was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Comparative Example 2>
The PAI solid content concentrations of the PAI-1 solution and the PAI-2 solution in Example 1 were changed to set the PAI solid content concentrations of the PAI-1 solution and the PAI-2 solution to 12% by mass. In the same manner as in 1, a PAI composition (solution) having a PAI solid content concentration of 12% by mass in which CB was dispersed was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Comparative Example 3>
The PAI solid content concentrations of the PAI-1 solution and the PAI-2 solution in Example 7 were changed to set the PAI solid content concentrations of the PAI-1 solution and the PAI-2 solution to 12% by mass. In the same manner as in 1, a PAI composition (solution) having a PAI solid content concentration of 12% by mass in which CB was dispersed was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Comparative Example 4>
CB was dispersed in the same manner as in Example 1 except that the PAI solid content concentration of the PAI-2 solution in Example 1 was changed to 10% by mass. , to obtain a PAI composition (solution) having a PAI solid content concentration of 14% by mass.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Comparative Example 5>
The PAI-1 solution was the PAI-2 solution (PAI solid content concentration: 16% by mass) in Example 1, and the PAI-2 solution was changed to 10 by changing the PAI solid content concentration of the PAI-2 solution in Example 1. A PAI composition (solution) containing CB dispersed therein and having a PAI solid content concentration of 14% by mass was obtained in the same manner as in Example 1, except that the concentration was changed to % by mass.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

<Comparative Example 6>
In the same manner as in Example 1, except that the CB was a basic CB, “Denka Black” (pH 10) manufactured by Denki Kagaku Kogyo Co., Ltd., CB was dispersed and PAI solid content concentration was 16% by mass. A PAI composition (solution) was obtained.
Next, a PAI film was obtained in the same manner as in Example 1 from this PAI solution.

Table 1 shows the acid value of each PAI obtained in Examples and Comparative Examples, and the evaluation results of films obtained from each PAI composition.

As shown in the examples, the PAI composition (solution) of the present invention has a high PAI solid content concentration, and from this solution, a PAI film having both a high tensile modulus and a high tensile elongation can be obtained. .
On the other hand, each comparative example had the following problems.
In Comparative Example 1, since the PAI solid content ratio was high, a film having sufficient tensile elongation could not be obtained. In Comparative Examples 2 and 3, since the PAI solid content ratio was low, a film having both high tensile modulus and tensile elongation could not be obtained. In Comparative Example 4, although a high tensile modulus was obtained, a sufficient tensile elongation was not obtained. It is considered that this is because the PAI solid content ratio is low. In Comparative Example 5, since the acid value of PAI-1 was high, a film having both high tensile modulus and tensile elongation could not be obtained. Since basic CB was used in Comparative Example 6, dispersibility was lowered, and a film having both high tensile modulus and tensile elongation could not be obtained.

A film obtained from the PAI composition of the present invention can be suitably used as a seamless PAI belt, as an intermediate transfer belt or fixing belt for copiers and printers.

Claims (1)

A composition comprising polyamideimide (PAI-1), polyamideimide (PAI-2) having an acid value different from PAI-1, carbon black (CB), and a solvent, characterized by the following: Polyamideimide (PAI) composition.
1) Both PAI-1 and PAI-2 are PAIs using trimellitic anhydride (TMA) as an acid component and o-tolidine diisocyanate (TODI) as an isocyanate component.
2) The acid value of PAI-1 is 10 mg-KOH/g or less, and the acid value of PAI-2 is more than 10 mg-KOH/g and 20 mg-KOH/g or less.
3) CB is an acidic CB with a pH of less than 7.
4) PAI solid content ratio (ratio of "total mass of PAI-1 and PAI-2" to "total mass of PAI-1, PAI-2 and solvent") is more than 15% by mass and 22% by mass or less is.