Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Identified reactant isolating material or capsule wall...
Reexamination Certificate
2001-10-11
2003-04-08
Acquah, Samuel A. (Department: 1711)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Identified reactant isolating material or capsule wall...
C264S004100, C264S004320, C264S004330, C264S004400, C264S004700, C264S005000, C264S007000, C428S402210, C428S403000, C427S372200, C427S374100, C430S109500, C430S111400, C503S218000
Reexamination Certificate
active
06544926
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of microcapsules having a nucleus material encased within a double shell material, where an inner shell comprises polymeric material and an outer shell comprises cross-linked complex colloid material, particularly formaldehyde capsules encased within gelatin, with glutaraldehyde having been used as a cross-linker for the gelatin. The invention also contemplates use of such microcapsules in printing processes, resulting in good printability and improved efficiency in the amount of microcapsule material used to obtain a specified level of print definition on paper stock.
BACKGROUND OF THE INVENTION
As used herein, a microcapsule is defined as having a diameter of about 1 micron to about 300 microns, preferably about 5-100 microns. Microcapsules have many applications, such as in manufacture of pharmaceuticals, pesticides, paints, adhesives, and many other chemical products. Microcapsules are especially useful where it is desired to provide controlled release of an enclosed and contained nucleus material, namely the substance being encapsulated. In one example of controlled release, the product known as “carbonless paper” is made by providing at least one component of a two-component colorant as the nucleus material in such microcapsules.
When the two components are mixed, such as when the encapsulated component is released from the capsule, the color-producing material is released and thus enabled to provide the desired coloration. In such carbonless paper, a layer of capsules of one or both components of a 2-component color-generating system may be coated onto a surface of paper or other fibrous web or sheet, or onto facing surfaces of facing sheets of paper or other fibrous web or sheet. When the capsules are broken, such as by pressure on the paper, the encapsulated colorant component is released, whereby the color-producing activity is enabled.
In one well known process, known by the term coacervation, the microcapsules can comprise an e.g. oil-containing nucleus material, and oil-impermeable shells formed of gelled complex polymerized materials. Principles of coacervation are taught by e.g. U.S. Pat. No. 2,800,457, and in the Kirk-Othmer Encyclopedia of Chemical Technology, Volume 13, John Wiley & Sons, 1967, Chapter on Microencapsulation, pages 436-456.
Coacervation comprises the phenomenon of phase separation in certain liquid polymer compositions leading to formation of two or more liquid phases, and deposition of polymerizable liquid shell material onto dispersed particles of liquid nucleus material. The cooperative formation of disperse particles, each having two such distinctly different liquid phases, distinguishes coacervation from precipitation of polymer solute in solid form in a liquid solvent. Coacervation can be activated by e.g. adjusting pH of the mixture. Both the gellable shell material and the nucleus material must be ionizable; and the combination of nucleus material and shell material must exist in the mixture, under certain conditions, with opposite ionic charges simultaneously existing on respective ones of the nucleus material and the shell material such that the respective particles of nucleus material and shell material are attracted to each other. Such opposite charges can be achieved by proper selection of the nucleus material and the shell material, and by adjusting pH or other physical property where one or both of the shell material and nucleus material are amphoteric, so as to effect polarity change. After the microcapsules are formed, the gelled or otherwise polymerized shell material can be hardened, optionally separated from the e.g. solvent liquid, dried, and if desired, comminuted to a desired particle size.
A liquid carrier such as oil can be used as the primary nucleus material, to carry one or more dispersed acting materials, either solid or liquid acting materials, including materials which can evaporate or degrade due to exposure to air. Additionally the carrier, itself, can be the material of interest in the nucleus, such as, for example, a perfume or marking fluid.
This invention relates to processes for en masse manufacturing of minute capsules, referred to herein as microcapsules, in a liquid manufacturing medium. The processes of the invention involve liquid-liquid phase separation of a relatively concentrated solution of polymeric material to be used in the formation of shells for the minute capsules. The processes of this invention involve, for example, the polymerization of urea and formaldehyde, monomeric or low molecular weight polymers of dimethylol urea or methylated dimethylol urea, melamine formaldehyde, monomeric or low molecular weight polymers of methylol melamine or methylated methylol melamine, in an aqueous vehicle wherein the reaction is conducted in the presence of certain acrylic acid-alkyl acrylate copolymers.
The sizes of microcapsules can suitably be chosen depending upon the expected end use. Where microcapsules are employed in e.g. pressure sensitive recording sheets, preferred microcapsule size is about 5 microns to about 30 microns in order to enable creating sharply defined images using the chromogenic nucleus material contained in such microcapsules. Where the microcapsules are to be coated onto a fibrous or otherwise porous sheet or web, such individual microcapsules may be so small as to become significantly recessed below the surface of the sheet or web, and accordingly cushioned from a crushing force directed toward the surface of such sheet or web. As a result, a normal activation pressure on the sheet or web is ineffective to rupture and thus activate, such individual microcapsules. Such recess of the microcapsule into the web or sheet can be overcome by employing relatively larger size microcapsules, but the resulting images created using such microcapsules exhibit relatively less clarity and sharpness of edge definition because of the larger size microcapsules. Yet a larger size particle is highly desirable in order to retain the particle at the surface of the sheet where such particle can more readily be broken by mechanical force applied at the surface of the sheet. Such larger size particle which can be retained at the surface of the sheet, while providing excellent image definition, is achieved in the invention by providing aggregates of the desirably small size microcapsules.
A method of encapsulation by in situ polymerization including a reaction between urea and formaldehyde or polycondensation of monomeric or low molecular weight polymers of dimethylol urea or methylated dimethylol urea in an aqueous vehicle conducted in the presence of negatively-charged, carboxyl-substituted linear aliphatic hydrocarbon polyelectrolyte material dissolved in the vehicle, is disclosed in U.S. Pat. Nos. 4,001,140; 4,087,376; and 4,089,802.
A method of encapsulating by in situ polymerization, including a reaction between melamine and formaldehyde or polycondensation of monomeric or low molecular weight polymers of methylol melamine or etherified methylol melamine in an aqueous vehicle conducted in the presence of negatively-charged, carboxyl-substituted, linear aliphatic hydrocarbon polyelectrolyte material dissolved in the vehicle, is disclosed in U.S. Pat. No. 4,100,103.
A method of encapsulating by polymerizing urea and formaldehyde in the presence of gum arabic is disclosed in U.S. Pat. No. 4,221,710. This patent further discloses that anionic high molecular weight electrolytes can also be employed with the gum arabic. Examples of the anionic high molecular weight electrolytes include acrylic acid copolymers and under specific examples of acrylic acid copolymers are listed copolymers of alkyl acrylates and acrylic acid including methyl acrylate-acrylic acid copolymers, ethyl acrylate-acrylic acid copolymers, butyl acrylate-acrylic acid copolymers and octyl acrylate-acrylic acid copolymers.
An exemplary method of preparing microcapsules by polymerizing urea and formaldehyde in the presence of an anionic polyelectrolyte and an ammonium salt of
Bodmer Jerome Robert
Patel Chandrakant Bhailalbhai
Schwantes Todd Arlin
Seehafer Troy Ronald
Acquah Samuel A.
Appleton Papers Inc.
Wilhelm Thomas D.
Wilhelm Law Service
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