Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-01-24
2002-07-23
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C527S313000, C527S314000
Reexamination Certificate
active
06423775
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 03 979.8, filed on Jan. 25, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a starch-based graft polymer, a process for its preparation, and the use thereof in printing inks and overprint varnishes.
2. Discussion of Background Information
Currently used binders for printing inks and overprint varnishes are usually based on polymer dispersions having a solids content of 40-50% by weight of styrene and its derivatives, which are used as copolymers with acrylic acid. This requires neutralization with high concentrations of ammonia or amines, resulting in undesirably high amounts of volatile components in the product. Synthetic starting materials are used for the preparation.
On the other hand, many starch-based products are known in the prior art. Natural or modified starch has many uses in the food, paper, textile, adhesive and other industries. Starch can be modified by physical and chemical action as well as by introducing foreign groups and by grafting reactions.
SUMMARY OF THE INVENTION
The invention provides an improved graft polymer by partial or complete employment of renewable raw materials or modifications thereof, which improved graft polymer is suitable for preparing polymer dispersions that have a negligible content of volatile components and can be used advantageously as binders in printing inks or overprint varnishes. At the same time, the property profile of the currently used binders is changed as little as possible. In particular, properties such as gloss, storage stability, compatibility, water resistance and processibility are at a comparable level.
The present invention relates to a graft polymer based on derivatized starch or derivatized starch product as the graft substrate. The starch or starch product is derivatized by one or more bifunctional monomers and is grafted, at sites of derivatization, with one ore more ethylene derivatives.
The present invention also relates to a process for preparing the graft polymers according to the present invention. The process includes providing an aqueous medium containing dissolved or dispersed starch or dissolved or dispersed starch product. This dissolved or dispersed starch or dissolved or dispersed starch product is subjected to derivatization with one or more bifunctional monomers to prepare a derivatized starch or a derivatized starch product. The derivatized starch or derivatized starch product then is graft-polymerized, at sites of derivatization, with one ore more ethylene derivatives.
The resulting graft polymer can be incorporated, for example, as a polymer dispersion, in a printing ink or an overprint varnish. Consequently, the present invention also relates to printing inks and overprint varnishes which include the graft polymer.
Finally, the present invention also relates to an aqueous dispersion containing the graft polymer. A corresponding aqueous dispersion is obtainable, for example, by the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The process for preparing such a polymer dispersion proceeds in multiple steps. The first step (i) comprises providing (preparing) a solution or dispersion of starch or starch product and water.
Starch or starch products within the meaning of this invention are natural starches from various sources as further described below as well as modified starches such as partially degraded starches, intermediate starch products and the like. Therefore, in the following, the recited terms are used synonymously, that is, the following examples, although primarily relating to starch, also apply correspondingly to the starch products employed in the present invention.
The water-soluble or water-dispersible starch can be obtained from grains, such as corn, wheat, millet or rice as well as from tubers and roots, such as potatoes and tapioca, fruit, or legumes and other natural products. Starch products, such as dextrins or modified dextrins, can also be used advantageously. In particular, hydrolyzed starches may be used. For example, the so-called desiccated dextrins, such as yellow potato dextrin of high or average viscosity, octenyl-succinate-waxy-maize starch and/or oxidized waxy-maize starch may be used. Combinations of the aforesaid starches may also be used.
Preferred for use are one or more of the most water-soluble starches that are available, for example, in hydrolyzed form. Dissolution takes place generally in a suitable reactor provided with a heat source, a stirrer, a cooling device and a thermometer. Dissolution is accelerated by heating to about 85-95° C. The dissolution step generally lasts about 1 to 2 hours. The degree of dissolution is monitored visually on samples withdrawn from the reactor at suitable time intervals. Sixty-micron coatings are made from these samples with a doctor blade and a glass plate. Monitoring is limited to the size and content of specks in the dried film. Dissolution or dispersion is considered complete only when the 60-micron film is almost speck-free and free of gel particles.
The second process step (ii) comprises making a derivative of the dissolved or dispersed starch with bifunctional monomers. The bifunctional monomers used for this purpose contain a vinyl group and a functional group that can be condensed with the free hydroxyl groups in the starch.
The bifunctional monomers N-methylolacrylamide, N-methylolmethacrylamide, hydroxyethyl methacrylate, hydroxypropyl methacrylate or mixtures thereof are preferred for use in the condensation reaction.
It is important to use specific catalyst systems and temperature ranges for successful condensation and later polymerization.
Examples of useful catalysts include aluminum chloride, aluminum zirconium acetate, ammonium chloride, ammonium phosphate, magnesium chloride, organic acids, such as lactic acid, citric acid, para-toluenesulfonic acid, sodium chlorate or sodium perchlorate, in combination with magnesium or zinc salts, zinc nitrate, or zinc perchlorate.
The second process step is conducted generally at a temperature of about 80 to about 100° C., preferably about 90 to about 100° C. and in particular, at about 90° C. Reaction time is generally about 1 to 5, preferably about 2 to 4 and in particular, about 3 hours. For example, the condensation can be conducted at about 90°
0
C. and for a period of about 3 hours. However, varying reaction times may be required, depending on the production equipment and the reactor type and size. Adapting reaction times appropriately is a matter for the skilled artisan's judgment.
The condensation reaction in the aqueous phase generally does not proceed to completion. For example, the reaction may be conducted to about 20% conversion of the bifunctional monomers. The remaining unreacted monomer will then be incorporated in the graft polymer during the subsequent radical polymerization and thus also contribute to the stability and the most favorable properties of the polymers.
The result of this process step can be followed analytically. The analysis may relate, for example, to the product of the condensation reaction involving the dissolved starch and N-methylolacrylamide. For this purpose, the condensate, for example, is precipitated with an about 7-fold quantity of ethanol and washed several times with a 50% ethanol solution. Then nitrogen is analyzed by the Kjeldahl method (according to DIN EN ISO 3188). After evaluation of the samples and blanks, the Kjeldahl nitrogen analysis generally shows that the condensation has proceeded to an extent of about 20%.
After the condensation reaction, the radical reaction with the ethylene derivative(s) can proceed as the third step (iii).
The resulting graft polymer is graft-polymerized with ethylene derivatives essentially through the starch sites derivatized by the bifunctional monomers. Therefore, the present invention also r
Brune Dirk
Von Eben-Worlée Reinhold
Greenblum & Berstein P.L.C.
Mullis Jeffrey
Worlée-Chemie GmbH
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