Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2000-11-13
2004-04-20
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C523S160000, C524S031000, C524S315000, C524S503000, C524S589000, C524S773000, C524S874000, C156S277000, C156S384000, C156S385000, C156S386000, C156S387000
Reexamination Certificate
active
06723820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a poly(urethane) urea resin and to its use in printing ink compositions. More particularly, the present invention relates to a poly(urethane/urea) resin useful as a binder for formulating printing inks and coatings used in laminating plastic films.
2. Description of Related Art
Recent diversification in package bags or containers has required a high degree of performance for printing inks or coating agents used for the ornamentation or surface protection. Such inks or coating agents should exhibit excellent adhesiveness for various kinds of plastic films and blocking resistance, and excellent adaptability for boiling or retorting treatment. For instance, printing inks for plastic films are needed to provide more excellent printability, adhesion to a wider range of films, and more excellent blocking resistance and gloss than conventional ones.
In the field of food packaging, bags or containers made of laminated film materials are used for the reasons that they are sanitary and their contents do not come in direct contact with the ink and to provide a satisfactory appearance as high grade printed products. Generally there are two methods for producing such laminated film materials: One is an extrusion laminating method, wherein a plastic film substrate is printed with an ink, and if necessary, a primer is applied onto the inked surface; then a molten resin such as polyolefin is extruded onto the inked surface. Another method is an adhesive laminating method, wherein an adhesive is applied onto the inked surface of the plastic film substrate, and a plastic film is then laminated onto the same surface. Accordingly, laminating inks must posses excellent adhesion to the printing substrate as well as adhesiveness (lamination strength) to the film to the laminated. When the laminated film materials further undergo boiling or retorting treatment in which packages are immersed in hot water for the purpose of cooking or sterilization of the contents, such film laminates should not undergo delamination through the retorting treatment. Most of these performance requirements for the printing ink or coating mainly depend upon the performance of the binder resin used. Accordingly, in the case of printing inks for plastic film, one or more of various binder resins are selected so as to meet the performance required for individual printing inks. In general, however, when a binder resin in a film hardens, there is a tendency for the resulting film to have blocking resistance but with reduced adhesion to the plastic film and lamination strength. For instance, when binder resins are used, such as acrylic resins, polyamide resins and polyester resins, an aromatic ring or a highly polar functional group is introduced in the molecule which hardens the resin film. However, such rings and functional groups invite the reduction of adhesion and lamination strength. Accordingly, such resins typically are unsuitable as a binder for a laminating inks and coatings to be applied to a wide variety of films.
Polyurethane resins can be improved both in hardness of the coated film and in adhesion to plastic films by increasing the concentration of urethane bonds in the molecule. An ink containing a polyurethane resin of this type provides good adhesiveness and lamination strength, as compared with inks containing other resins providing ink films having the same hardness. For this reason, polyurethane resins in which the concentration of urethane bond is increased as highly as possible, have been used as binders for printing inks and coatings for use in laminates of plastic films. However, polyurethane resins wherein the concentration of urethane bond is increased highly, fail to give sufficient adaptability for boiling or retorting treatment. To eliminate this problem a two-component reaction type resin system is used composed of one component containing a polyurethane resin and the other component containing a polyisocyanate compound as a curing agent. Nevertheless, the two-component reaction type resin system has various problems as well. Since the main component must be mixed with the curing agent immediately before being used, it is inconvenient in handling, the pot life is short and the remaining ink or coating after printing is unstable. Further, the use of expensive curing agent raises substantially costs of packaging bags or containers.
Plastic film substrates such as those used in laminates, typically are printed using flexographic printing or gravure printing. In flexographic printing, the flexographic ink or coating is applied to the surface of a resilient letter-press image, and the image is then transferred to the plastic print stock. Flexographic inks, for example, typically contain a polar organic solvent such as an alkanol, which dissolves ink binder components but which does not swell or otherwise deteriorate the resilient letter-press image. In gravure printing, the gravure ink is deposited in image wells in the flat surface of a gravure plate, and the deposited ink image is then transferred to the print stock. Since gravure printing typically is carried out at high speeds, the gravure ink typically contains volatile organic solvents such as alkyl esters, which dissolve ink binder components and must be rapidly removed during the drying process. Accordingly, flexographic ink and gravure ink each have specific performance requirements dictated by the distinctly different methods of printing. As a result, the inks and coatings for each application are formulated to meet those requirements including specific binder components designed specifically for flexographic inks or for gravure inks. Such specific binder components which are specifically designed for one ink type, have been found to be incompatible in solvent systems of the other ink type, which has necessitated the preparation and storage of two distinct ink systems with there attendant expense.
While there continues to be a need for an improved laminating ink and coating in general, there also is a clear industry need for a single binder resin system which can be used to formulate inks and coatings useful for both flexographic and gravure printing applications.
SUMMARY OF THE INVENTION
The above mentioned industry needs are met by the solvent-soluble poly(urethane/urea) resin of this invention which is derived from a polyurethane prepolymer being the reaction product of: a diisocyanate component; and, a diol component having (i) a first diol having a molecular weight below 2000; and (ii) a polymeric diol having a molecular weight below 3000; wherein the —NCO/—OH ratio is less than 2; the polyurethane prepolymer contains 1.3 to 6.0 wt. % of unreacted —NCO groups; and 80 to 120% of a diamine, based on the equivalents of the unreacted —NCO groups; whereby the resulting poly(urethane/urea) resin is soluble in organic solvent.
An added embodiment of this invention is an improved method of producing a poly(urethane/urea) resin involving the steps of: (a) preparing a polyurethane prepolymer solution by reacting a diisocyanate component, a diol component, and a condensation polymerization catalyst in an organic solvent; wherein the polyurethane prepolymer contains unreacted —NCO groups; and (b) reacting the polyurethane prepolymer with a diamine; wherein the improvement comprises:
preparing a diamine solution comprised of diamine and a solvent mixture having an alcohol solvent and a second organic solvent; and adding, at a controlled rate, the polyurethane prepolymer solution into the diamine solution to form a poly(urethane/urea) resin.
A further embodiment of this invention is a solvent-based laminating ink useful in flexographic and/or gravure printing comprising: (A) a solvent-soluble poly(urethane/urea) resin which is derived from a polyurethane prepolymer being the reaction product of: a diisocyanate component; and, a diol component having (i) a first diol having a molecular weight below 2000; and (ii) a polymeric diol having a molecular weight below 3000;
Arcurio Ralph
Rocco Mark
Schneider Mark
Slavinski David J.
Gorr Rachel
Persley Sidney
Sun Chemical Corporation
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