Plastic and nonmetallic article shaping or treating: processes – Encapsulating normally liquid material – Liquid encapsulation utilizing an emulsion or dispersion to...
Reexamination Certificate
1992-11-17
2002-04-23
Lovering, Richard D. (Department: 1712)
Plastic and nonmetallic article shaping or treating: processes
Encapsulating normally liquid material
Liquid encapsulation utilizing an emulsion or dispersion to...
C264S004100, C264S004300, C264S004700, C411S258000, C428S402200, C428S402210, C428S402220, C428S402240, C523S176000
Reexamination Certificate
active
06375872
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to microencapsulated adhesives and processes for producing such microencapsulated adhesives. More particularly, the invention relates to a process for microencapsulating acrylate-based or methacrylate-based adhesives to produce an adhesive composition that is initially non-tacky but exhibits tacky properties upon application of external forces, such as shearing.
Adhesive compositions are generally tacky and gluey. However, there are numerous applications where it would be beneficial to mask the tacky nature of the adhesive prior to its use. Examples of such applications include adhesive materials for stamps or envelopes.
One potential way of rendering adhesives non-tacky is to microencapsulate the adhesive. Various attempts have been made to encapsulate adhesives such as hot melt ethylene/vinyl acetate copolymers and styrene/isoprene/styrene-type block copolymers. However, due to their high molecular weight and high viscosity, these copolymers tend to be solids at room temperature and precipitate when emulsified, and thus are very difficult to microencapsulate.
It is an object of the present invention to produce an adhesive composition that is initially non-tacky but can be made tacky when desired.
Another object of the present invention is to provide an adhesive compound that can be microencapsulated.
A further object of the present invention is to provide a monomer compound that is capable of being microencapsulated and is also capable of being polymerized inside the microcapsules to form a polymer adhesive.
The present inventor has found that acrylate or methacrylate monomers can be microencapsulated by well-known microencapsulation techniques, and then these monomers can be polymerized inside the microcapsules to form adhesives. These microencapsulated adhesives are initially non-tacky, but when external forces such as shearing are applied, the capsules break and the tacky adhesive is exposed.
SUMMARY OF THE INVENTION
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a method of producing a microencapsulated adhesive by providing a mixture containing as a major component, an alkyl acrylate or alkyl methacrylate monomer, or a mixture thereof, along with a free radical initiator. This mixture of monomer and initiator is microencapsulated. The microencapsulated monomer and initiator is heated for a time and a temperature sufficient to cause the monomer to polymerize inside the microcapsules.
In another aspect of the present invention, there is provided a microencapsulated adhesive composition containing an adhesive produced from a monomer including as a major component an alkyl acrylate or methacrylate, or a mixture thereof, encapsulated in microcapsules. This composition functions as an adhesive that is initially non-tacky but exhibits tacky properties upon application of external forces, such as shearing. Specifically, upon application of an external force, such as shearing, at least some of the microcapsules are broken and the adhesive is exposed.
In a further aspect of the present invention, there is provided a microencapsulated adhesive composition produced by microencapsulating a mixture containing as a major component, an alkyl acrylate or methacrylate monomer having about 4 to about 12 carbon atoms, or a mixture thereof, along with a free radical initiator. The microencapsulated monomer and initiator are heated for a time and at a temperature sufficient to cause the monomer to polymerize inside the microcapsules. The adhesive that is formed is initially non-tacky but exhibits tacky properties upon the application of external forces, such as shearing.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, microencapsulated adhesives are produced from monomers having as a major component an alkyl acrylate or methacrylate monomer, or a mixture thereof. The acrylate or methacrylate monomers used as a major component of the adhesives of the invention generally have very low viscosity and thus are capable of being encapsulated. Preferably, the monomer of the invention is a C
4
-C
12
alkyl acrylate or methacrylate. It is to be understood, however, that any acrylate-based or methacrylate-based monomer that is capable of being polymerized inside microcapsules and is useful as an adhesive is within the scope of the present invention. In addition, other monomers such as vinyl acetate, styrene, acrylonitrile, methacrylonitrile, and the like can be present in the invention as a minor component. Following encapsulation, the monomers can be polymerized in the microcapsules by heating.
Examples of the acrylate and methacrylate monomers that can be used as the major component in accordance with the invention include, but are not limited to: isobutyl acrylate, isobutyl methacrylate, isodecyl acrylate, isodecyl methacrylate, isooctyl acrylate, 2-ethyl hexyl acrylate, isobornyl acrylate, 4-methyl-2-pentyl acrylate, 2-methyl butyl acrylate, isoamyl acrylate, isononyl acrylate and the like. Preferred monomers are isodecyl methacrylate and a mixture of ethyl hexyl acrylate and isobornyl acrylate.
In accordance with the invention, the monomers may be polymerized in the microcapsule by heating to a temperature sufficient to cause a reaction exotherm to be observed. After the reaction exotherm is reached, the microcapsule solution is preferably further heated to a temperature of about 5 degrees greater than the exotherm temperature for a period preferably ranging from about 4 to about 6 hours to complete the free radical polymerization.
In accordance with the invention, the adhesive can be microencapsulated by those techniques known in the art, including interfacial polymerization, gelatin/gum arabic coacervation and melamine/formaldehyde encapsulation. A preferred encapsulation technique is interfacial polymerization. The walls of the microcapsules are preferably comprised of polyamide or polyurea.
The interfacial polymerization method that may be used in accordance with the invention involves mixing the adhesive monomer or monomers to be microencapsulated together with a free radical initiator and either an acid chloride or an isocyanate. The resultant mixture is emulsified in an emulsification agent to obtain an oil-in-water emulsion. A polyfunctional amino compound is then added into the emulsion, whereby microcapsule walls are formed around each microparticle of oil. In accordance with the invention, when an acid chloride is mixed with the monomer and initiator, a polyamide microcapsule is produced—when an isocyanate is mixed with the monomer and initiator, polyurea capsules are formed. After the monomer or monomers and initiator are microencapsulated, the entire composition is heated to thermally polymerize the monomer or monomers inside the microcapsules.
The gelatin/gum arabic coacervation encapsulation method that may be used in accordance with the present invention involves first emulsifying the core material into a gelatin solution to obtain an oil-in-water emulsion. The emulsion is mixed with a gum arabic solution. The system is then pH adjusted or diluted to cause the gelatin/gum arabic to coacervate. Thereafter, the capsules are post-treated with a crosslinking agent, such as formaldehyde, glutaldehyde, or other similar known compounds.
The melamine-formaldehyde encapsulation method that may be used in accordance with the present invention involves first emulsifying the core material into a carboxyl methyl cellulose solution or a poly(styrene-maleic anhydride) solution to obtain an oil-in-water emulsion. The emulsion is then mixed with a m
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Lovering Richard D.
Moore Business Forms
LandOfFree
Microencapsulated adhesive does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Microencapsulated adhesive, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Microencapsulated adhesive will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2892863