Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2000-11-27
2002-01-15
Nutter, Nathan M. (Department: 1711)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S384000, C427S385500, C427S388100, C427S389900, C427S391000, C427S392000, C427S393000
Reexamination Certificate
active
06338875
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to aqueous compositions of copolymers and to their use as printing vehicles. More particularly, it relates to alkyl acrylate copolymers and their use in printing inks or varnishes particularly suited for use flexographic or gravure printing processes.
BACKGROUND OF THE INVENTION
The use of aqueous alkyl methacrylate and alkyl acrylate ester polymers as printing ink vehicles, overprint varnishes and lacquers is generally known in the art. However, several problems still exist, for example heat resistance of the dried films is low. Heat resistance is needed for many applications in inks and overprint varnishes. A major use is for printing preprint linerboard, where a high degree of hot rub resistance is needed. Another significant use is heat sealing of foil to form airtight seals (metallized balloons, coffee pouches, etc). Overprints are often used in preprint and some heat seal applications as a protective coating over standard inks. It is known that heat resistance can be improved by adding large quantities (about 4-10 wt. %) of zinc compounds such as zinc oxide or zinc ammonium carbonate (ZAC). However, the high pH of these zinc compounds leads to strong ammonia smell and large amounts of zinc can be toxic.
SUMMARY OF THE INVENTION
The invention is a high temperature emulsion composition comprising borax and a substantially water-insoluble polymer prepared by aqueous suspension polymerizing a blend of monomers, said blend comprising a plasticizing amount by weight of at least one plasticizing alkyl acrylate monomer, a hardening amount by weight of at least one hardening alkyl acrylate monomer and a crosslinking amount by weight of at least one multi-ethylenically unsaturated monomer, in an aqueous suspension comprising a water-soluble polymer component comprising at least one acrylic polymer having carboxylate functionality, its method of use and coated substrates made therewith.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to novel aqueous dispersions of polymers, to printing ink vehicles that contain these novel aqueous suspensions, and to methods that employ these novel aqueous suspensions. The aqueous dispersions of polymers are heat resistant emulsion resins that form high gloss films upon drying without the need for zinc addition.
An outline of how this is done may best be understood by starting with the formulation of a control: a water-insoluble acrylic polymer comprising a plasticizing monomer (such as 2-ethylhexyacrylate) and a hardening monomer (such as methylmethacrylate) is polymerized in an aqueous stabilizer. The stabilizer comprises at least one water-soluble acrylic polymer with carboxyl or carboxylate groups (such as polystyreneacrylic acid or polystyrenemaleic acid) and, optionally, a surfactant. Zinc is then added as zinc oxide or zinc ammonium carbonate as well as biocides, coalescents (such as glycol ether solvents), defoamers and the like. This is then used as a base for formulating printing inks, lacquers and the like.
In the absence of zinc, or when zinc is low, the heat resistance of the ink is low. The present invention eliminates the need for zinc, while maintaining, and even improving, gloss. This is done by adding multi-ethylenically unsaturated monomers (such as allylmethacrylate and triallyl cyanurate) to the plasticizing/hardening monomer mixture and then by adding borax instead of zinc compounds. Zinc compounds may, however, be added in smaller quantities than used in the past, on the order of about 0.6 wt. % if desired to achieve formulations with synergistic benefits of both approaches. As an alternative to zinc additions, zirconium ammonium carbonate, aziridine and aziridine polymers may be employed. Note that hereinafter all, quantities, except in the examples, are understood to be modified by “about.”
Note that the dried film comprises at least two polymers: the initially water-soluble acrylic; and the initially water-insoluble acrylic. The initially water soluble acrylic is soluble by virtue of its being supplied as a salt of a fugitive amine such as aminomethylpropanol or ammonia, and it also becomes insoluble upon loss of the amine.
The polymers are prepared by suspension polymerization and are at least copolymers of two different alkyl acrylates and/or methacrylates and a multi-ethylenic compound. Thus, important starting materials for preparing the novel polymers of this invention are alkyl esters of acrylic acid and methacrylic acid. Such esters are described in “Acrylic and Methacrylic Ester Polymers”,
Encyclopedia of Polymer Science and Engineering
, vol. 1, pp. 234-299 (John Wiley & Sons, Inc., N.Y., N.Y., 1985), the disclosure of which is incorporated herein by reference. The precise identity of each monomer and the amount of each monomer affect properties of the polymer which are important to its utility in a printing ink vehicle.
A measure of the plasticizing effect of a monomer can be found by examining the glass transition temperature of a homopolymer of the monomer. Generally, a plasticizing monomer will be such that a homopolymer of the monomer will exhibit a glass transition temperature (Tg) of less than about −30° C. Thus, acrylates of a straight chain alkyl group having from 3 to 11 carbon atoms or a branched chain alkyl group having from 5 to 11 carbon atoms will generally be useful for plasticizing the polymer. Examples of such acrylate esters that will be useful include the n-propyl, n-butyl, isobutyl, n-hexyl, 2-ethylbutyl, 2-heptyl, and 2-ethylhexyl. (Because of the relatively high T
g
of poly(t-butyl acrylate), the use of a monomer t-butyl acrylate is unlikely to be advantageous as a plasticizer. 2-Ethylhexylacrylate (2-EHA) is preferred.
The other alkyl acrylate or methacrylate monomer is a hardening monomer. As discussed above, a measure of the hardening effect of the monomer can be found by examining the glass transition temperature of a homopolymer of the monomer. Generally, the monomer will be selected such that a homopolymer of the monomer will exhibit a glass transition temperature (T
g
) of greater than about 50° C. Thus, methacrylates having short chain alkyl groups, e.g. from 1 to about 4 carbon atoms, e.g. branched chain alkyl groups having from 3 or 4 carbon atoms, will generally be useful for hardening the polymer. Examples of alkyl methacrylates that will be useful include methyl, ethyl, isopropyl, sec-butyl, isobutyl, and t-butyl. Typically, the polymer will be prepared from a blend comprised of from about 35% to about 55% by weight (and preferably from about 40% to about 50%) of one or more hardening monomers. Methylmethacrylate (MMA) is preferred. The preferred ratio of 2-EHA to MMA is 95/5 to 50/50.
In addition to mono-ethylenically unsaturated monomers, the blend from which the water-insoluble polymer is prepared will also be comprised of an ethylenically unsaturated monomer having at least two sites of ethylenic unsaturation, i.e. a di- or higher multi-ethylenically unsaturated monomer. Examples of multi-ethylenic monomers include alkenyl acrylates or methacrylates (e.g. allyl methacrylate), other allyl vinyl monomers such as dially maleate and fumarate, di-alkenyl arenes, particularly di-alkenyl benzenes (e.g. divinyl benzene), di-alkenyl ethers (e.g. ethylene glycol di-allyl ether and pentaerythritol di-allyl ether), di-acrylamides (e.g. methylene-bis-acrylamide, trimethylene-bis-acrylamide, hexamethylene-bis-acrylamide, N,N′-diacryloylpiperazine, m-phenylene-bis-acrylamide, and p-phenylene-bis-acrylamide), di- or higher multi-(meth)acrylates (e.g. diethylene glycol diacrylate, propylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, bis(4-acryloxypolyethoxyphenyl)propane, 1,5-pentanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol acrylate, and polypropylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, ethyleneglycol dimethacrylate and triethylene glycol dimethacrylate). Also useful are allyl
Boucher Steve
Feng Ching
Sinka Joseph
Smith George A
Taipale Brenda
Cook Composites and Polymers Co.
Nutter Nathan M.
Whyte Hirschboeck Dudek SC
Whyzmuzis Carol
LandOfFree
Heat resistant emulsion resins does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat resistant emulsion resins, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat resistant emulsion resins will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2825919