Alkylenebisnaphtol derivative and charge control agent which consists of the same

1. An alkylenebisnaphthol derivative represented by formula [I]:

wherein Y 1 , Y 2 , Y 1 ′ and Y 2 ′ may be same or different and each of them is selected from the group consisting of a carboxyl group, an esterified carboxyl group, a group of —(CONH)n-X (wherein X is an optionally branched and optionally substituted hydrocarbon group which may have an unsaturated bond, an optionally substituted aromatic group and a heterocyclic group having conjugated double bonds, n is an integer of 1 or 2);

k is an integer of 1–12;

R and R′ are selected from the group consisting of hydrogen atom, an alkaline metal, an optionally branched and optionally substituted alkyl or acyl group of 1–6 carbon atoms and a phenylalkyl group;

Q and Q′ are selected from the group consisting of an optionally branched alkyl or alkoxy group of 1–6 carbon atoms, a halogen atom, nitro group, nitroso group, amino group and sulfo group; and

m and m′ each represents an integer of 0–3

or a salt thereof.

2. The alkylenebisnaphthol derivative or a salt thereof of claim 1 , wherein k is 1.

3. The alkylenebisnaphthol derivative or a salt thereof of claim 1 , wherein said derivative is negatively chargeable and the absolute value of the triboelectric charge is equal to or greater than 1.3 μC/g.

4. A charge control agent consisting of an alkylenebisnaphthol derivative represented by formula [I]:

wherein Y 1 , Y 2 , Y 1 ′ and Y 2 ′ may be same or different and each of them is selected from the group consisting of a carboxyl group, an esterified carboxyl group, a group of —(CONH)n-X (wherein X is an optionally branched and optionally substituted hydrocarbon group which may have an unsaturated bond, an optionally substituted aromatic group and a heterocyclic group having conjugated double bonds, n is an integer of 1 or 2);

k is an integer of 1–12;

R and R′ are selected from the group consisting of hydrogen atom, an alkaline metal, an optionally branched and optionally substituted alkyl or acyl group of 1–6 carbon atoms and a phenylalkyl group;

Q and Q′ are selected from the group consisting of an optionally branched alkyl or alkoxy group of 1–6 carbon atoms, a halogen atom, nitro group, nitroso group, amino group and sulfo group; and

m and m′ each represents an integer of 0–3

or a salt thereof;

provided that said derivative is negatively chargeable and the absolute value of the triboelectric charge is equal to or greater than 1.3 μC/g.

5. A method of using an alkylenebisnaphthol derivative,

comprising providing an alkylenebisnaphthol derivative as defined in claim 1 or a salt thereof as a charge control agent, provided that said derivative is negatively chargeable and the absolute value of the triboelectric charge is equal to or greater than 1.3 μC/g.

6. An electrophotographic toner, comprising at least a binder resin, a colorant and an alkylenebisnaphthol derivative of formula [I]:

wherein Y 1 , Y 2 , Y 1 ′ and Y 2 ′ may be same or different and each of them is selected from the group consisting of a carboxyl group, an esterified carboxyl group, a group of —(CONH)n-X (wherein X is an optionally branched and optionally substituted hydrocarbon group which may have an unsaturated bond, an optionally substituted aromatic group and a heterocyclic group having conjugated double bonds, n is an integer of 1 or 2);

k is an integer of 1–12;

R and R′ are selected from the group consisting of hydrogen atom, an alkaline metal, an optionally branched and optionally substituted alkyl or acyl group of 1–6 carbon atoms and a phenylalkyl group;

Q and Q′ are selected from the group consisting of an optionally branched alkyl or alkoxy group of 1–6 carbon atoms, a halogen atom, nitro group, nitroso group, amino group and sulfo group; and

m and m′ each represents an integer of 0–3

or a salt thereof;

provided that said derivative is negatively chargeable and the absolute value of the triboelectric charge is equal to or greater than 1.3 μC/g.