Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-08-30
2003-07-15
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C264S004100, C264S004300, C264S004330, C264S004600, C264S004700, C428S402220, C428S500000, C430S109500, C430S110100, C522S013000
Reexamination Certificate
active
06592990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cross-linkable adhesive. It more particularly relates to microencapsulated adhesives and products containing such microencapsulated adhesive.
2. Description of Related Art
Microencapsulated adhesives are known in the art and are often conveniently classified based upon mode of activation, extent of component microencapsulation, adhesive chemistry, or suitability for various surfaces.
Microencapsulated adhesives can involve solvent-based systems or reactive and curable resin systems. Solvent-based systems rely on adhesive reactivation through solvent delivery. Sometimes microcapsules are used as the vehicle to retain the solvent until needed. Other activatable systems rely on the plasticizer or UV initiator being encapsulated in place of solvent in order to tackify the resin at the time of use.
Capsules containing a solvent for the adhesive are typically dispersed throughout a nontacky adhesive coating on a substrate. Upon rupture of the capsules, a solvent is released making the adhesive tacky. A plasticizer can similarly be encapsulated and used in place of or in conjunction with a solvent to tackify the adhesive. Solvent systems relying primarily on organic solvents are increasingly disfavored for environmental considerations.
Reactive resin systems typically involve an encapsulated curing system. Either the total formulation or one component can be encapsulated. The reactive components however must be isolated or kept separate until use. Typically two separate encapsulations are required. Reactive systems typically employ epoxy resins, isocyanates, polyesters and the like.
Another form of encapsulated adhesive is the self-contained capsule. Typically the curing agent is adhered to the capsule surface. Upon rupture of the capsule wall, the resin flows to contact the curing agent. Curing agents can include boron trifluouride complexes, nitrile or aniline type calatysts, acid chlorides, hexamethylenetetramine, various oxides, dibutyltin dilaurate and the like.
Capsule release mechanisms can involve pressure, heat or dissolution of the capsule wall. Heat activated systems thermally cure upon heating above the activation temperature.
DETAILED DESCRIPTION.
The present invention provides a novel and improved adhesive comprising an encapsulated adhesive of monomers polymerized in situ within a microcapsule to form the adhesive. More particularly, the present invention provides a microcapsule and process for forming a microcapsule that benefically provides for in situ polymerization within the capsule to form a microencapsulated pressure sensitive or flowable adhesive. The adhesive is formed inside the microcapsule incident to or following capsule formation.
The microencapsulated adhesive comprises a capsule wall material composed of a polymeric composition enclosing an adhesive core material composed of a polymeric composition. The polymeric composition comprising capsule wall material is formed of monomers which polymerize at a lower temperature than monomers which form the polymeric composition of the adhesive core material.
The microencapsulated adhesive can be made pressure sensitive or responsive to other known means of capsule rupture in addition to impact, such as heat, friction, sonic energy or other energy input making the microcapsule permeable or fractured. The adhesive can be pressure sensitive or flowable. Rupture of the capsule by any of the above recited means makes the adhesive available.
Unlike solvent based adhesive reactivation systems, the invention teaches a new adhesive system. The invention is a microcapsule containing adhesive (or microencapsulated adhesive) wherein the adhesive is formed in situ in the microcapsule. The composition comprises a substantially water insoluble adhesive-forming core material. The core material comprises at least a first addition polymerizable pre-polymer material whose homopolymer has a Tg of less than about 0° C. a flash point of at least 75° C., and a boiling point of at least 175° C. A solvent for the adhesive-forming core material is optionally included. The solvent is substantially water insoluble and nonreactive with the pre-polymer material. Rather than adhesive reactivation, the solvent provides a medium for the various pre-polymer materials in which to undergo polymerization and adhesive formation. Useful solvents include petroleum oils, vegetable oils, vegetable oil esters, liquid hydrocarbon resins, liquid plasticizers and blends thereof.
A catalytically effective amount of a substantially water insoluble free radical initiator is also included along with the addition polymerizable pre-polymer and solvent. The free radical initiator is selected to have a half-life of at least 10 hours at 25° C., and more preferably at least 1 hour at 25° C. The free radical initiator needs to be soluble in the polymerizable pre-polymer material and solvent. The free radical initiator can be selected from the group of initiators comprising an azo initiator, peroxide, dialkyl peroxide, alkyl peroxide, peroxyester, peroxycarbonate, peroxyketone and peroxydicarbonate. More particularly the free radical initiator is selected from 2, 2′-azobis (isobutylnitrile), 2,2′-azobis(2,4-dimethylpentanenitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis(2-methylpropanenitrile), 2,2′-azobis (methylbutyronitrile), 1,1′-azobis (cyclohexanecarbonitrile), 1,1′-azobis(cyanocyclohexane), benzoyl peroxide, decanoyl peroxide; lauroyl peroxide; benzoyl peroxide, di(n-propyl) peroxydicarbonate, di(sec-butyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, 1,1-dimethyl-3-hydroxybutyl peroxyneodecanoate, &agr;-cumyl peroxyneoheptanoate, t-amyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-amyl peroxypivalate, t-butyl peroxypivalate, 2,5-dimethyl 2,5-di (2-ethylhexanoyl peroxy) hexane, t-amyl peroxy-2-ethyl-hexanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxyacetate, di-t-amyl peroxyacetate, t-butyl peroxide, di-t-amyl peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexyne-3, cumene hydroperoxide, 1,1-di-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane, 1,1-di-(t-butylperoxy)-cyclohexane, 1,1-di-(t-amylperoxy)-cyclohexane, ethyl-3,3-di-(t-butylperoxy)-butyrate, t-amyl perbenzoate, t-butyl perbenzoate and ethyl 3,3-di-(t-amylperoxy)-butyrate.
The microcapsules are obtained by providing an aqueous mixture containing 5 a colloidal dispersion of hydrophillic wall-forming material for forming microcapsules.
High shear agitation is applied to the aqueous mixture to achieve a particle size of the core material of about 0.1 to 250 &mgr; (250 microns), preferably 0.1 to 100 microns and more preferably 0.1 to 50 microns. Smaller capsules of 10 &mgr; or less can be produced for specialized applications. Stirring at a first temperature effects microcapsule wall formation of the microcapsule wall-forming material. Heating to a second temperature which could be substantially the same as the first temperature, although usually higher, polymerizes the monomer of the core material to form an adhesive in situ in the formed microcapsules.
With gelatin-based wall-forming materials, the first temperature heating step would entail relatively low temperatures such as 5° C. for the wall forming step and 25° C. or more, more typically 60° C. to 90° C. for the adhesive-forming or adhesive-polymerizing step. With alkyl acrylate acrylic acid copolymer wall materials, the wall forming temperature is typically around 60° C. and the adhesive-forming step at about 90° C. The respective temperatures of the wall-forming step and adhesive-forming step relate to the temperature of polymerization of the selected wall-forming material and adhesive pre-polymers. The first and second temperature can be substantially similar with appropriate materials selection, though this is not preferred. Some temperature separation of at least 2-3 degrees is preferred to minimize adhesive occlusion in the wall material. In addition to stirring at a first temperature, the pH ca
Acquah Samuel A.
Appleton Papers Inc.
Mieliulis Benjamin
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