Ferromagnetic pigments

Details Ferromagnetic pigments Ferromagnetic pigments

1998-07-13

2000-02-15

Koslow, C. Melissa

Compositions

Magnetic

Iron-oxygen compound containing

252 6255, 252 6256, 252 6259, 252 626, 252 6257, 252 6264, 428403, 428404, 428692, 428570, 106403, 106457, 106459, H01F 106, G11B 5706

Patent

active

060248904

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to phosphorus-containing ferromagnetic pigments containing in particular a core comprising essentially iron and cobalt, a process for their preparation, their use in magnetic recording materials and magnetic recording materials which contain such pigments.
With increasing storage density of magnetic recording materials, the pigments to be used in these materials are having to meet higher and higher requirements. Owing to the higher specific magnetization compared with oxide materials, metallic iron particles, which may also be doped with nickel or cobalt, have become established for high-density magnetic recording (for example in the V8 system). However, in addition to good magnetic properties, in particular the length and the volume of the pigment particles are of primary importance. The signal
oise ratio of the magnetic recording material increases in proportion to the square root of the number of particles contained in a volume element (Finn Jorgensen, The complete Handbook of Magnetic Recording, 3rd Ed., Tob Books Inc., Summit 1988). It is also known that the average particle length of the particles used in a magnetic recording material may not exceed one third of the recording wavelength without signal losses occurring (Auweter et al., IEEE, Vol. 27(1991), 4669-4671). Magnetic particles for the 8 mm video system having a recording wavelength of 0.58 .mu.m therefore may on average be no longer than 195 nm, while those for the Hi8 system (0.4 .mu.m recording wavelength) may not be longer than 130 nm. Particles having a length of from 50 to 100 nm are required for novel, digital video systems for high-density recording. Thus, finely divided and short magnetic particles which nevertheless must have a high coercive force and be readily dispersible are required for high-density magnetic recording. However, the more finely divided magnetic particles there are, the more difficult is homogeneous dispersing (Jorgensen, loc cit, page 310). It is very important that the particles are not agglomerated by sintering or that the particle surface has many anchor groups for the dispersants, permitting homogeneous dispersion of the particles in the binder system.
Ferromagnetic iron pigments are known and are obtained, inter alia, if acicular iron oxide compounds, for example the oxides or oxide hydroxides, in particular iron(III) oxide hydroxides, such as .alpha.-FeOOH, coated with a cobalt compound, are reduced with hydrogen or other gaseous reducing agents.
The good magnetic properties of such pigments are based essentially on the anisotropic shape of the particles, i.e. the acicular shape of the particles. To minimise the loss of shape occurring during conversion of the acicular iron oxide compounds coated with a cobalt compound and to avoid sintering, the particles are provided with a shape-stabilizing coating prior to this conversion.
For example, acicular cobalt-containing, ferromagnetic iron pigments can be obtained according to DE-A 39 11 039, but said iron pigments disadvantageously have a length of from 250 to 500 .mu.m and cannot be used for high-density magnetic recordings.
The synthesis of .alpha.-FeOOH can be carried out by the acidic process (DE-A 36 03 431). The starting material used here is an aqueous iron(II) salt solution, to which further ions are added if required (DE-A 32 43 868). The geometry of the FeOOH particles can be influenced by the addition of these foreign ions. Some of the iron(II) ions are precipitated with alkali at the beginning of the synthesis. This is followed by oxidation, for example by passing in air, to give .alpha.-FeOOH. The protons thus liberated are first trapped by the dissolving iron(II) hydroxide precipitate so that the pH does not fall below 5. Once the iron(II) hydroxide precipitate has completely dissolved, the pH decreases sharply and the formation of .alpha.-FeOOH comes virtually to a stop. This first part is referred to as the nucleation phase. The iron(II) ions present in solution are then oxidized with an oxidizing agent, e.g. air,

REFERENCES:
patent: 2879154 (1959-03-01), Campbell
patent: 4050962 (1977-09-01), Koester et al.
patent: 4133677 (1979-01-01), Matsui et al.
patent: 4165232 (1979-08-01), Jaeckh et al.
patent: 4305753 (1981-12-01), French
patent: 4560544 (1985-12-01), Nakata et al.
patent: 4933004 (1990-06-01), Hoppe et al.
patent: 5151115 (1992-09-01), Tamai
patent: 5466306 (1995-11-01), Mishima et al.
patent: 5645652 (1997-07-01), Okinaka et al.
Jorgensen, "The Complete Handbook of Magnetic Recording", 3rd. Ed., 1988, pp. 310-311. no month.
Auweter et al., IEEE Transactions on Magnetics, vol. 27, No. 6, Nov. 1991, pp. 4669-4671.
Williams et al., AIP Conf. Proc. 5, pp. 738-742, 1971. no month.

Affiliated with

Also associated with

Rating

Ferromagnetic pigments does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ferromagnetic pigments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ferromagnetic pigments will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1903174