Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Finishing or perfecting composition or product
Reexamination Certificate
2000-11-13
2003-07-15
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Finishing or perfecting composition or product
Reexamination Certificate
active
06593068
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a concentrated dampening water composition useful for lithographic printing, and more specifically, to a concentrated dampening water composition which provides a dampening water composition useful for offset printing using a lithographic printing plate.
2. Description of the Prior Art
Lithographic printing technique makes the best use of the properties of water and an oil such that they are essentially incompatible with one another. The printing surface of a lithographic printing plate comprises areas which receive water and repel an oil ink and those which repel water and receive an oil ink, the former serving as non-image areas and the latter serving as image areas. The non-image areas become damp with damping water used in lithographic printing to thus enhance the difference in surface chemical properties between the image areas and the non-image area and hence to increase both the ink repellency of the non-image areas and the ink receptivity of the image areas.
As such dampening water, there have generally been known conventionally aqueous solutions containing alkali metal salts or ammonium salt of bichromic acid, phosphoric acid or salts thereof such as ammonium salt, and such a colloidal substance as gum arabic or carboxymethyl cellulose (CMC). However, it is difficult to uniformly dampen the non-image areas of lithographic printing plates with the above dampening water, and for this reason, the resultant printed matters are sometimes contaminated and a substantial skill in controlling the feed rate of the dampening water is required.
To overcome such disadvantages, there has been proposed the Dahlgren dampening system in which an aqueous solution containing about 20 to 25% of isopropyl alcohol is used as a dampening water. This method provides a variety of advantages concerning workability and accuracy of printed matters, such that the wettability of the non-image areas is improved that the amount of the dampening water can be reduced, that it is easy to control the balance between feed rates of printing ink and dampening water, that the amount of water emulsified into the printing ink is lowered and that the transfer of printing ink to the blanket is improved.
However, isopropyl alcohol is apt to evaporate, and therefore, the use of a special device is required for keeping the concentration thereof constant. This is unfavorable from the economical point of view. Moreover, isopropyl alcohol gives out bad smell and is toxic and thus the use thereof is not favorable in view of the pollution of working atmosphere.
In addition, even if the dampening water containing isopropyl alcohol is applied to offset printing in which a dampening molleton roller is commonly used, isopropyl alcohol evaporates from a roller surface and the printing plate surface. Therefore, it cannot show its own effects.
Moreover, the pollution with industrial waste has recently become a matter of great concern, the regulation with respect to discharge of chromium ions in waste water becomes much severer and there is a tendency of controlling the use of organic solvents such as isopropyl alcohol from the viewpoint of safety and hygiene. For this reason, it has been desired to develop a dampening water free of such a compound.
Under such circumstances, Japanese Patent Publication for Opposition Purpose (hereunder referred to as “J.P. KOKOKU”) Nos. 55-25075. 55-19757 and 58-5797 disclose compositions containing a variety of surfactants which can only slightly reduce the surface tension of water. In general, the dampening water should have a surface tension ranges from 35 to 50 dyn/cm. Therefore, if these compositions are used as dampening water, it is necessary to substantially increase the concentration of surfactants in a dampening water. Furthermore, water is adhered to an ink film or an ink spreads over the surface of water because of vigorous movement of ink and/or water existing below an ink roll, a printing plate and a roll for supplying dampening water which rotate at a high speed, during the practical lithographic printing. However, combinations of surfactants disclosed in the foregoing methods explained above are insufficient to completely solve these problems. Besides, these dampening water containing such surfactants easily cause foaming during pumping and/or stirring thereof.
In addition, U.S. Pat. No 3,877,372 discloses a solution containing a mixture of ethylene glycol monobutyl ether and at least one of hexylene glycol and ethylene glycol. U.S. Pat. No. 4,278,467 discloses a dampening water containing at least one member selected from the group consisting of n-hexoxyethylene glycol, n-hexoxydiethylene glycol, 2-ethyl-1,3-hexanediol, n-butoxyethylene glycol acetate, n-butoxydiethylene glycol acetate and 3-butoxy-2-propanol. Japanese Patent Un-examined Publication (hereunder referred to as “J.P. KOKAI”) No. 57-199693 (U.S. Pat. No. 4,560,410) discloses dampening water containing 2-ethyl-1,3-hexanediol and at least one member selected from the group consisting of completely water-soluble propylene glycol, ethylene glycol, dipropylene glycol, diethylene glycol, hexylene glycol, triethylene glycol, tetraethylene glycol, tripropane glycol and 1,5-pentanediol. As these dampening water compositions do not contain isopropyl alcohol, they are preferable in view of safety and hygiene. However, when an organic solvent having a low solubility in water such as 2-ethyl-1,3-hexanediol is used, it is unfavorable to obtain a concentrated dampening water or an additive for dampening water having high concentration.
In order to solve this problem, the use of surfactant is necessary, and on the other hand, the use of surfactant causes the problem of foaming and deterioration of printing properties.
Accordingly, it is desired to obtain a stable concentrated damping water composition which does not cause the problem of foaming or deterioration of printing properties.
SUMMARY OF THE INVENTION
Accordingly an object of the present invention is to provide a concentrated dampening water composition which is stably solubilized in spite of the use of an organic solvent having a low solubility in water therein, and which is free of the problem of foaming and deterioration of printing properties.
Under such circumstances, the inventors of this invention have conducted various studies on a concentrated dampening water composition for lithographic printing, and have found that maleic acid and a salt thereof exhibit an excellent solubilizing effect. Thus the inventors have completed the present invention.
Consequently, the present invention is directed to a concentrated dampening water composition for lithographic printing comprising an organic solvent having a solubility of 1 to 10% in water at 20° C., which composition comprises at least one selected from the group consisting of maleic acid and a salt thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in more detail below.
In the concentrated dampening water composition according to the present invention, at least one selected from the group consisting of maleic acid and a salt thereof (component (a)) is used. The examples of the salt of maleic acid used in the present invention include a lithium salt, a potassium salt, an ammonium salt, a monoethanol amine salt, a diethanol amine salt, a triethanol amine salt and the like.
Maleic anhydride can be used in the concentrated dampening water composition to exhibit the same effect as those of maleic acid or a salt thereof.
In the concentrated dampening water composition according to the present invention, the amount of at least one selected from the group consisting of maleic acid and a salt thereof suitably ranges from 0.5 to 10% by weight, and more preferably from 1 to 5% by weight. If the amount is less than 0.5% by weight, sufficient solubilizing effect on the organic solvent having a water-solubility of 1 to 10% is not obtained. On the other hand, if the amount is more than 10% by weight, the conc
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