Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-05-24
2003-07-22
Tarazano, D Lawrence (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S520000, C428S522000, C524S801000, C524S804000, C524S812000, C503S227000
Reexamination Certificate
active
06596379
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to novel cationic polymeric coatings and plastic substrates comprising such coatings, as well as methods for preparing same.
BACKGROUND OF THE INVENTION
Typically, in the production of emulsion polymers by free-radical polymerization, it has been a common practice to use nonionic or anionic materials to stabilize the emulsions. Alternatively, others have used protective colloids like poly(vinyl alcohol) [PVOH], hydroxyethyl cellulose, or derivatives thereof, either singly or in combination, to stabilize aqueous emulsion polymers. These stabilizers produce emulsion particles that are electrically neutral or negatively charged in an aqueous environment.
Commercially produced emulsions that contain positively charged particles (that is, cationic emulsions) are known, but are far fewer in number. U.S. Pat. No. 5,521,266 to Lau discloses the synthesis of cationic emulsions, but requires complexation of water-insoluble monomers with macromolecular carbohydrates (for example, cyclodextrin, cyclodextrin derivative, cycloinulohexose, cycloinuloheptose, cycloinuloctose, calyxarene and cavitand) having a hydrophobic cavity.
U.S. Pat. No. 4,308,189 to Moritani et al. reviews many conventional techniques for producing cationic emulsions using low-molecular-weight cationic emulsifiers such as laurylamine salt, octadecylamine salt, laurylpyridinium chloride, and others that are toxic and subject to stringent regulations. The '189 patent also describes the use of cationic initiators and monomers to create cationic emulsions. Moreover, one can add materials like alkylaminopolyoxyethylene to nonionic and anionic emulsions to render emulsion particles cationic. Furthermore, the '189 patent unfavorably described the potential for using protective colloids made from cationic derivatives of carbohydrates (for example, starch and cellulose) and polyamide-polyamine epichlorohydrin, which according to U.S. Pat. No. 2,926,154 to Keim is the reaction product of epichlorohydrin with polyamides containing the following recurring groups:
—NH(C
n
H
2n
HN)
x
—COR
3
CO—
where n and x are each 2 or more and R
3
is the divalent organic radical of a dicarboxylic acid. According to Moritani et al., these materials are poor stabilizers and usually used in combination with nonionic surfactants.
Moritani et al. disclosed an improved class of protective colloids based on cationic group-modified PVOH. While these materials improve fixation affinity for pulp and improved bonding affinity for glass, sand, and concrete, they are not suggested to disclose improved adhesion to plastic film, especially after prolonged exposure to water. Indeed, PVOH and its water-soluble derivatives are prone to swell and release from plastic upon prolonged exposure to water.
U.S. Pat. No. 5,254,631 to Yamamoto et al. discloses cationically electrodepositable, finely divided gelled polymers (that is, internally cross-linked polymer particles that do not coalesce into a film upon drying) having a core-sheath structure obtained by emulsion polymerization. They used water-soluble or water-dispersible cationic resins as a stabilizer in their emulsion-polymerization process. The resin used in their process has, in the molecule, a cationic functional group capable of imparting positive charges and hydrophilicity when neutralized with an acid. They created this water-soluble cationic resin by by reacting a polyphenol with epichlorohydrin to form a polyglycidyl compound compound having a number-average molecular weight between 800 and 2000 and then reacting the epoxy group of the polyglycidyl compound with a cationizing agent.
The polyphenols that they described include bis(4-hydroxyphenyl)-2,2-propane, 4,4′-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxy-tertbutylphenyl-2,2-propane, bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene, bis(2,4-dihydroxyphenyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxydiphenylsulfone, phenol novolac and cresol novolac.
They selected cationizing agents from a list of relatively small amine-containing molecules such as ammonia, hydroxylamine, hydrazine, hydroxyethylhydrazine, N-hydroxyethylimidazoline compound and
(1) Primary amines such as methylamine, ethylamine, n- or isopropylamine, monoethanolamine, n- or isopropanolamine and the like.
(2) Secondary amines such as diethylamine, diethanolamine, di-n- or di-isopropanolamine, N-methylethanolamine, N-ethylethanoilamine and the like.
(3) Polyamines such as ethylenediamine, diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, dimethylaminoethylamine, dimethylaminopropylamine and the like.
Therefore the number-average molecular weight of the water-soluble cationic resin will not be significantly more than 2,000 and probably less than about 3,000, especially since Yamamoto et al. teach that content of the cationic group in their water-soluble or water-dispersible cationic resin should be kept as low as possible.
So, there are few processes that yield stable emulsions and none that offer satisfactory performance properties in applications that require film formation on and adhesion to plastic film or adhesion to inks after prolonged exposure to water or solvents like isopropyl alcohol (IPA).
For example, U.S. Pat. No. 4,214,039 to Steiner et al. discloses a cationic polymer as a primer for vinylidene chloride polymers used as coatings for oriented polypropylene packaging films. The primer comprises an epoxy resin composition comprising a) a liquid epoxy resin, e.g., one based on Bisphenol A, preferably emulsified or dissolved in water, and b) a water-soluble, amine-modified acrylic resin. This system, also employed at higher coating weights in U.S. Pat. No. 6,025,059 to McGee et al., has limited shelf stability. Once the ingredients are mixed, the ingredients start to react. The useful pot life of the mixture of the '059 patent is no more than about 3 days. After this, the mixture gels or agglomerates, with precipitation of components. Moreover, undesired blocking can occur at coating weights below 0.25 grams/1000 in
2
(g/msi). In addition, ink adhesion problems can occur during printing with black UV-curable screen ink. Finally, the formulation may contain amounts of up to 10-20 wt. % propylene glycol monomethyl ether, which may require certain precautions in handling and use on a commercial scale.
Typically, films prepared for use as label facestock are coated on the printing side with a coating, which enhances ink adhesion. For instance, U.S. Pat. No. 5,380,587 to Musclow et al. discloses a multilayer packaging or label stock film having excellent printability and non-blocking characteristics. The film is first primed and then coated with copolyester coating.
Another ink adhesion enhancing coating is described in U.S. Pat. No. 5,382,473 to Musclow et al. which discloses a multilayer film structure with a prime coating which is the reaction product of acidified aminoethylated vinyl polymer and epoxy resin, top coated with polyester ink base to eliminate blocking.
U.S. Pat. No. 5,662,985 to Jensen et al. discloses a two-side coated label which comprises a polymeric film substrate having on a first surface thereof (A) an adhesive anchor layer and on a second surface thereof (B) an ink base layer, the (A) and (B) layers being selected from the group consisting of: (i) a prime coating having on an external surface a functional coating of an interpolymer of (a) an alpha, beta-monoethylenically unsaturated carboxylic acid; and (b) a neutral monomer ester comprising an alkyl acrylate ester and an alkyl methacrylate ester; and (ii) an iminated polymer; or the (A) adhesive anchor layer being selected from the group consisting of: (iii) a mixture of the functional coating of (i) and the iminated polymer of (ii); (iv) a linear water dissipatable polyester condensation product; and (v) a polyester; or the (B) ink base layer being selected from the group consisting of:
Bell Keith A.
ExxonMobil Oil Corporation
James Rick F.
Tarazano D Lawrence
LandOfFree
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