Magnetic recording medium

Abstract

An aspect of the present invention relates to a magnetic recording medium comprising a nonmagnetic layer comprising a nonmagnetic powder and a binder and a magnetic layer comprising a ferromagnetic powder and a binder in this order on a nonmagnetic support, wherein the magnetic layer and/or nonmagnetic layer comprises organic acid A and organic acid B below, with an acid strength pKa(A) of organic acid A and an acid strength pKa(B) of organic acid B satisfying a relation of pKa(A)<pKa(B); organic acid A: an unsaturated bond-containing organic acid comprising one substituent selected from the group consisting of a carboxyl group, a phosphoric acid group, and a phosphonic acid group per molecule; organic acid B: an aliphatic or alicyclic organic acid in which two or more substituents substituted onto adjacent carbon atoms within the molecule are present per molecule, and at least one of the substituents is a carboxyl group.

What is claimed is: 
     
         1 . A magnetic recording medium comprising a nonmagnetic layer comprising a nonmagnetic powder and a binder and a magnetic layer comprising a ferromagnetic powder and a binder in this order on a nonmagnetic support, wherein
 the magnetic layer comprises organic acid A and organic acid B below, with an acid strength pKa(A) of organic acid A and an acid strength pKa(B) of organic acid B satisfying a relation of pKa(A)<pKa(B);   organic acid A: an unsaturated bond-containing organic acid comprising one substituent selected from the group consisting of a carboxyl group, a phosphoric acid group, and a phosphonic acid group per molecule;   organic acid B: an aliphatic or alicyclic organic acid in which two or more substituents substituted onto adjacent carbon atoms within the molecule are present per molecule, and at least one of the substituents is a carboxyl group.   
     
     
         2 . The magnetic recording medium according to  claim 1 , wherein at least one of the substituents comprised in organic acid B is a hydroxyl group. 
     
     
         3 . The magnetic recording medium according to  claim 1 , wherein the unsaturated bond comprised in organic acid A is comprised in an aromatic heterocyclic ring or a benzene ring. 
     
     
         4 . The magnetic recording medium according to  claim 1 , wherein the binder comprises an aromatic ring component. 
     
     
         5 . The magnetic recording medium according to  claim 1 , wherein the binder comprises a sulfonic acid (salt) group-containing binder. 
     
     
         6 . The magnetic recording medium according to  claim 1 , wherein the binder comprises a polyurethane having a glass transition temperature ranging from 75° C. to 150° C. 
     
     
         7 . The magnetic recording medium according to  claim 1 , wherein the binder comprises a polyester polyurethane in the form of a reaction product of polyester polyol (A) comprising structural components in the form of a dibasic acid and a glycol component, aromatic isocyanate (B), and compound (C) with a molecular weight of less than 1,000 having two or more functional groups per molecule that are capable of reacting with an isocyanate group and having a branching side chain. 
     
     
         8 . The magnetic recording medium according to  claim 7 , wherein the glycol component is a glycol component denoted by general formula (I) or (II):
   HO—CH 2 —CR 1 R 2 —CH 2 —OH  (I)
   wherein, in general formula (I), each of R 1  and R 2  independently denotes a methyl group or ethyl group;
   HO—CHR 3 —CH 2 —OH  (II)
 
   wherein, in general formula (I), R 3  denotes a methyl group or ethyl group.   
     
     
         9 . The magnetic recording medium according to  claim 8 , wherein equal to or greater than 80 mole percent of the structural components in polyester polyol (A) is an aromatic dibasic acid, and 60 to 100 mole percent of the glycol component is a glycol denoted by general formula (I) or (II). 
     
     
         10 . The magnetic recording medium according to  claim 1 , wherein at least one of the magnetic layer and the nonmagnetic layer further comprises at least one of a fatty acid and fatty acid ester.