Method for individually encapsulating magnetic particles

• US 4,419,383 A
• Filed: 04/11/1983
• Issued: 12/06/1983
• Est. Priority Date: 12/26/1979
• Status: Expired due to Fees

• Current Assignee: Magnavox Electronic Systems Company
• Original Assignee: Magnavox Government and Industrial Electronics Company
• Inventors: Lee, Lawrence L.
• Primary Examiner(s): Pianalto, Bernard D.
• Application Number:
  US06/483,668
• Time in Patent Office: 239 Days
• Field of Search: 427/47, 427/128
• US Class Current: 427/550
• CPC Class Codes: B01J 13/04 by physical processes, e.g. drying, spraying
• CPC Class Codes: G09F 9/375 the position of the elements being controlled by the application of a magnetic field
• CPC Class Codes: H01F 1/44 of magnetic liquids, e.g. ferrofluids particles in a bonding agent H01F1/28, H01F1/36, H01F1/37

Abstract

A method for encapsulating magnetic particles by enclosure within oil drops, mixing in an aqueous solution and dispersing the oil drops with the enclosed particles by application of an alternating magnetic field. The dispersed and oil covered particles are microencapsulated with at least one type of polymer.

Claims

1. A method for dispersing a preselected average number of magnetized particles, the particles being enclosed in a discrete amount of internal phase, comprising the following steps:

immersing the particles in a liquid internal phase;

suspending internal phase drops containing the immersed particles in a liquid continuous phase;

mechanically agitating the continuous phase to provide initial dispersing of said particles and forming smaller drops with a reduced number of particles in each drop;

applying a varying magnetic field to said suspension for further dispersing of said particles into smaller drops with a reduced number of particles in each drop, the frequency of said field variations being selected according to the desired number of particles in individual drops;

microencapsulating individual ones of said drops to form capsules containing drops in which said particles are rotatable.

2. The method of claim 1 including the step of mechanically agitating the continuous phase after the microencapsulating step, to keep the capsules separated while the capsule shell walls become smooth.

3. The method of claim 1 wherein said mechanical agitating step comprises stirring said continuous phase.

4. The method of claim 1 wherein said microencapsulation step comprises injecting an acidic composition into said continuous phase to form a two phase mixture, one phase being a first solution of the capsule shell forming material and a second phase being a coacervation of a more concentrated solution than said first solution of a capsule shell forming material.

8. The method of claim 1 including the step of flowing said internal phase drops suspended in the continuous phase through a magnetic field of increasing frequency.

9. The method of claim 1 wherein said internal phase comprises by weight 4 parts of paraffin oil and 1 part kerosene, with 5% trimesoyl chloride and 4% Alrosperse 100 by weight added, and the continuous phase comprises 60 gm of 2% solution of 290 Bloom, pig-skin gelatin and 0.15 cc of 40% sodium hexameta phosphate.

10. The method of claim 1 wherein the step of applying a varying magnetic field comprises the continuous flow step of flowing said internal phase drops suspended in the continuous phase through an elongated tube and applying a separate varying magnetic field to each of a plurality of longitudinally spaced portions of said tube, the magnetic field frequency applied to said portions sequentially downstream of said tube being correspondingly sequentially increasing.

11. The method of claim 10 wherein said continuous flow step includes increasing the magnetic field frequency of each of said portions to the next successive of said portions downstream of said tube by a factor of less than two.

12. The method of claim 1 wherein said step of mechanically agitating the continuous phase continues throughout the steps of applying a varying magnetic field and microencapsulating.

5. A method for dispersing a preselected average number of magnetized particles, the particles being enclosed in a discrete amount of internal phase, comprising the following steps:

immersing the particles in a liquid internal phase;

suspending internal phase drops containing the immersed particles in a liquid continuous phase;

controlling at least one of the temperature, pH, and concentrations of the continuous phase in order to initiate formation of the capsule shell walls;

varying the magnetic field to said suspension for further dispersing of said particles into smaller drops with a reduced number of particles in each drop, the frequency of said field variations being selected according to the desired number of particles in individual drops;

microencapsulating individual ones of said drops to form capsules containing drops in which said particles are rotatable;

strengthening the capsule walls.

6. The method of claim 5 wherein said step of varying the magnetic field comprises applying an initial field frequency and strength and after the microencapsulation step, applying a second field of reduced frequency and reduced field strength.

7. The method of claim 6 wherein said initial frequency is about 430 Hz and said initial field strength is about 400 gauss and said second frequency is less than 100 Hz and said second field strength is less than 100 gauss.

13. The method of claim 5 wherein the controlling step comprises reducing the temperature of the continuous phase from an initial temperature to a lower second temperature prior to suspending the internal phase drops in the continuous phase.

14. The method of claim 13 wherein said initial temperature is in the range of 50°

C. to 55°

C., said second temperature is approximately 41°

C., and said final temperature is about 10°

C.

15. The method of claim 13 wherein said strengthening step comprises quenching the continuous phase containing the drops from said second temperature to a final temperature lower than said second temperature whereby the coacervate capsule shell walls become a gel.