Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-10-04
2003-10-14
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S272000, C525S048000, C525S517500
Reexamination Certificate
active
06632859
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to alkyd-based resins for improving the wetting and drying properties of ink vehicles and ink compositions containing such vehicles, and to ink vehicles and ink compositions containing the resins.
BACKGROUND
In conventional lithographic printing processes, image and non-image areas are created on printing plates by a combination of photo-mechanical and photo-chemical processes which make the image area ink receptive and the non-image area water receptive. The image areas are oleophilic and hydrophobic whereas the non-image areas are hydrophilic and oleophobic.
Accordingly, in principle the image areas accept only ink while the non-image areas accept only water so that the ink is limited to the image areas of the plate. The ink composition is applied to the plate by first wetting the plate with water to cause the non-image areas to become saturated, and the ink is then applied over the plate surface adhering only to the image areas.
After coating the image areas of the plate with ink, the plate then transfers ink from the image areas to a blanket or intermediate roller which, in turn, transfers the ink to a substrate or media to be printed in the desired pattern. This method of printing is used in most commercial lithographic printing processes and is typically referred to as “offset” printing.
In order to promote drying, ink film toughness and lower volatiles once an image is printed, lithographic inks generally contain from about 1 to about 30 wt. % alkyd resin, a modified vegetable oil component or a combination of the two. Conventional alkyd components used to promote drying are made from vegetable oils such as soy and linseed oils which possess a relatively high amount of nonconjugated unsaturated compounds. These components dry or become solid by an oxidation process which is relatively slow, thereby limiting the speed of the printing and finishing process.
Another problem with conventional lithographic ink formulations stems from their tendency to have a “bronze” appearance on the surface of the printed ink film. This phenomena varies with different pigments and is related to how well the pigment particles are wet by the other components of the vehicle.
In addition to vegetable oil-derived alkyd resins which promote drying, ink film toughness, lower volatiles, and pigment wetting, lithograph ink formulations typically contain primary resins such as phenolic or maleic modified rosin esters for improving the gel structure of the ink in order to improve the print quality and reduce misting of the finished ink during printing. In some cases, hydrocarbon-based resins of varying compositions may be used as the primary resin component. It is also common to include with the primary resin a secondary or co-resin to further modify the ink properties such as the ink transfer and ink oil solubility of the primary resin component. Typical co-resins include hydrocarbon-based resins and rosin ester resins.
Accordingly, it is an object of the invention to provide an improved vehicle for ink formulations.
Another object of the invention is to provide a method for making ink vehicles for lithographic ink formulations which exhibit improved drying properties, especially increased drying rates.
Yet another object of the invention is to provide environmentally friendly ink vehicles for lithographic ink formulations.
Still another object of the invention is to provide an ink vehicle and an ink formulation containing the vehicle which exhibits improved pigment wetting properties thereby reducing the bronze appearance on the printed ink surface.
A further object of the invention is to provide an ink vehicle and an ink formulation containing the vehicle which exhibits an improved gel structure for improved performance on modem, high-speed printing machines.
SUMMARY OF THE INVENTION
With regard to the above and other objects, the invention provides an improved lithographic ink vehicle which comprises a primary resin which is preferably a phenolic or maleic modified rosin ester, an ink solvent and from about 1 to about 30% by weight of an alkyd resin comprising the reaction product of a mono-unsaturated cyclic diacid anhydride, a polyol and a fatty acid. The vehicle may also contain a metallic cross-linking agent and a secondary or co-resin, such as a base- or acid-catalyzed rosin ester as described in commonly assigned application Ser. No. 08/975,585, filed Nov. 21, 1997, the disclosure of which is incorporated herein by reference.
Another aspect of the invention involves providing an improved lithographic ink formulation containing a flushed pigment and from about 45 to about 65% by weight of an ink vehicle which includes a primary resin, ink solvents and from about 1 to about 30% by weight of an alkyd resin comprising the reaction product of a mono-unsaturated cyclic diacid anhydride, a polyol and a tall oil fatty acid. The formulation may also contain a metallic drying agent and a wax or wax compound and a secondary or co-resin along with a metallic cross-linking agent to assist in gellation of the formulation.
According to another aspect of the invention, an improved method is provided for making an ink vehicle especially well suited for use in lithographic inks which comprises reacting a mono-unsaturated cyclic diacid anhydride, a polyol and a tall oil fatty acid under conditions sufficient to produce an alkyd resin and mixing from about 1 to about 30 wt. % of the alkyd resin with a primary resin, an ink solvent and, optionally, a secondary or co-resin and a metallic cross-linking agent for gellation.
Ink vehicles incorporating alkyd resins according to the invention enable the production of lithographic inks which exhibit significantly improved drying rates and pigment wetting properties as compared to known ink vehicles and inks containing conventional vegetable oil-derived alkyd components. The improvement is especially evident with rubine red inks. When included with ink vehicles in ink compositions, alkyd resins according to the invention also have been found to confer improved gel structures, thereby limiting the need for costly metallic gellants.
Ink vehicles according to the invention are also environmentally friendly in that they may be formulated with naturally-derived materials such as rosin esters and with alkyds derived from tall oil fatty acids (TOFA), both of which are by-products of wood, a renewable resource, and these materials also generate considerably decreased volatiles considered harmful to the environment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention provides improved ink vehicles for lithographic printing ink compositions. A key feature of the invention lies in the use in ink vehicles containing an alkyd resin derived from a reaction mixture containing a diacid anhydride with cyclic monounsaturation. The preferred anhydride is 1,2,3,6-tetrahydrophthalic anhydride (THPA). However, C
1
-C
6
alkyl or alkenyl ring substituted diacid anhydrides with cyclic monounsaturation may also be used.
Another key component in the reaction mixture is a tall oil fatty acid (TOFA) derived from the fractionation of crude tall oil (CTO), a by-product of the wood pulping process. Of significance to this invention, TOFA characteristically contains significantly less nonconjugated polyunsaturation than soy and linseed oils. These oils are commonly used to produce alkyd resins due to the faster dry times which result from the oxidative crosslinking of their higher linoleic and linolenic acid contents as compared to the content of linoleic and linolenic acid in TOFA. A suitable TOFA may be selected from tall oil fatty acids available from Arizona Chemical Company of Panama City, Florida under the tradenames SYLFAT FA-2, SYLFAT FA-1 Special and SYLFAT FA-1. It has been discovered, quite surprisingly, that the use of THPA in combination with TOFA in an alkyd formulation results in faster dry times than those for soy- or linseed-based alkyds. Without being bound by theoretical considerations, it is believed that the faster dry times
Jones Raymond H.
Jordan Thomas C.
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