Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
1999-03-08
2003-03-04
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S508000, C427S496000, C427S500000, C427S511000, C427S504000, C427S393500
Reexamination Certificate
active
06528127
ABSTRACT:
BACKGROUND INFORMATION
1. Field of the Invention
The present invention relates to the printing of thermoplastic packaging materials, particularly to printing techniques involving the use of radiation curable coatings used to protect underlying layers of printed markings.
2. Background of the Invention
Although printing techniques have become quite specialized and well-defined over the years, the printing of thermoplastic packaging films has remained a bit of a black art. Not until recently have packagers required film manufacturers to provide packaging films bearing photograph quality printed images. This is a significant challenge by itself, but the uses to which some packagers put those films often make a difficult situation even worse.
Packaging applications that require heat shrinkable films present especially challenging problems to film manufacturers. This is due to the need for the printing ink(s) to exhibit sufficient flexibility so as not to crack or flake off once the film has undergone heat shrinking. Those heat shrink applications involving significant amounts of heat, friction, and/or film-to-metal contact magnify the problem all the more. Films intended for cook-in applications can undergo all of these strenuous conditions and provide film manufacturers and converters with some of their greatest printing challenges.
To prevent cracking and/or flaking of printed images, film manufacturers have developed several strategies. Most often, these involve the use of new ink formulations. Standard inks used in the printing of thermoplastic films involve pigments carried in a resin (e.g., nitrocellulose, polyamide, etc.) which is soluble in a carrier solvent (e.g., an alcohol). Once the ink is applied to the film, the solvent evaporates, leaving behind the resin-pigment combination. Newer, more exotic formulations have involved two-part polyurethane resin systems as well as solvent-free systems in which the resin(s) can be cured by means of ultraviolet (UV) light. These new approaches are not without drawbacks, however, due primarily to concerns regarding operator exposure (due to the components causing short term effects such as nausea, headaches, nosebleeds, etc.) and the need to assure that the components have crosslinked to a degree sufficient to ensure that the system complies with applicable governmental food safety regulations. The components used in the two-part system of the former often are not approved for use with food packaging films while the latter requires the presence of photoinitiators which migrate into the packaged product. Both of these are unacceptable to the conscientious film manufacturer.
That which the art has not taught and which remains desirable is a printing technique which allows the use of standard ink formulations but which avoids the cracking and/or flaking problems which those types of ink have exhibited under the strenuous conditions presented by heat shrink applications.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a printed thermoplastic flexible packaging material which includes a coating of a material that protects the printed image. The packaging material includes at least two primary surfaces. On at least one of those surfaces, a printed image is applied. The image includes at least one pigment-containing marking derived from a solvent-based ink and a pigment-free coating overlying the outermost pigment-containing marking. The coating includes one or more polymerizable materials, each of which can be cured by ionizing radiation. When the printed packaging material is exposed to ionizing radiation, the coating hardens to form a protective layer over the pigment-containing markings of the printed image.
In another aspect, the present invention provides a method of printing a packaging material. That method involves (a) applying one or more solvent-based inks to a thermoplastic flexible packaging material and allowing or causing the applied ink(s) to become affixed to the packaging material so as to create a pigment-containing marking on the packaging material; (b) applying to the marked packaging material, in a manner which substantially completely covers all of the pigment-containing markings, a pigment-free coating which includes one or more polymerizable materials; and (c) exposing the marked packaging material to ionizing radiation so as to polymerize and, optionally, crosslink the one or more polymerizable materials in the pigment-free coating. Where more than one ink is applied to the packaging material, each ink preferably is applied only after the previous one(s) have become sufficiently affixed to the packaging material that smearing and smudging are avoided.
The method of the present invention provides a distinct and significant advantage over previously described printing methods in that allows for the use of standard solvent-based inks, even where the end use of the printed film involves significant physical and/or chemical abuse. By employing an extremely tough coating over such inks, those inks are protected even through severe handling and processing conditions. This avoids the need for exotic ink systems and/or a tempering of the handling and processing conditions.
The following definitions apply herein throughout unless a contrary intention is expressly indicated:
“comprising” means including at least, but not limited to, the named materials (in relation to an article or composition), parts (in relation to a machine), or steps (in relation to a method);
“disposed on,” with respect to the location of an ink in relation to the surface layer of the printed film, means coated on or applied to such that it is in intimate contact with a primary surface of the film;
“flexible” means capable of deformation without catastrophic failure;
“package” means one or more packaging materials (e.g., a film) configured around a product;
“polymer” means the polymerization product of one or more monomers and is inclusive of homopolymers, copolymers, and interpolymers as well as blends and modifications thereof;
“mer unit” means that portion of a polymer derived from a single reactant molecule; for example, a mer unit from ethylene has the general formula —CH
2
CH
2
—;
“homopolymer” means a polymer consisting essentially of a single type of repeating mer unit;
“copolymer” means a polymer that includes mer units derived from two reactants (normally monomers) and is inclusive of random, block, segmented, graft, etc., copolymers;
“interpolymer” means a polymer that includes mer units derived from at least two reactants (normally monomers) and is inclusive of copolymers, terpolymers, tetrapolymers, and the like;
“polyolefin” means a polymer in which some mer units are derived from an olefinic monomer which can be linear, branched, cyclic, aliphatic, aromatic, substituted, or unsubstituted (e.g., olefin homopolymers, interpolymers of two or more olefins, copolymers of an olefin and a non-olefinic comonomer such as a vinyl monomer, and the like);
“(meth)acrylic acid” means acrylic acid and/or methacrylic acid;
“(meth)acrylate” means an ester of (meth)acrylic acid;
“anhydride-grafted” means a group containing an anhydride moiety, such as that derived from maleic acid, fumaric acid, etc., has been chemically attached to or affiliated with a given polymer;
“permeance” (in the packaging industry, “permeance” often is referred to as “transmission rate”) means the volume of a gas (e.g., O
2
) that passes through a given cross section of film (or layer of a film) at a particular temperature and relative humidity when measured according to a standard test such as, for example, ASTM D 1434 or D 3985;
“curable” means capable of polymerization and/or crosslinking;
“photoinitiator” means a substance which, when exposed to specific wavelengths (e.g., polymerization) or actinic radiation, forms a reactive species that initiates a reaction in one or more other substances in its vicinity;
“solvent-based ink” means an ink in which a pigment is dispersed in a polymeric carrier which, in turn, is solvated in a liquid medium such as, for examp
Edlein Marc A.
Kyle David Ray
Cryovac Inc.
Padgett Marianne
Ruble Daniel B.
LandOfFree
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