US3041203A - Quick dry vehicle and method of drying same - Google Patents

Description

3,041,203 QUICK DRY VEHICLE AND WTHOD OF DRYING SAME Benjamin L. Sites, Elmhurst, and Meyer S. Agruss, Chi- This invention relates to the art of coating materials. It has particular reference to an improved quick-drying vehicle of the drying oil type for various coatings, and to an improved method for rapidly indurating or drying such a vehicle after the coating operation.

The invention is applicable generally to coating materials utilizing a drying oil type of vehicle, where quickdrying of the vehicle is desired. The term coating materials is intended to cover such vehicles or materials which embrace the characteristics of the subject invention and which may have applications in fields other than those specifically mentioned herein, such as, for example, photosensitive resists for use in the graphic arts, plugging materials for use in the drilling operations encountered in the petroleum industries, and the like. However, for illustrative purposes, and with no intent to limit its field of use, the invention will be described with particular reference to printing, wherein the coat-forming material is applied by a conventional printing plate.

Printing inks as made heretofore consist mainly of a non-aqueous vehicle, namely a drying oil, pigmented to the desired color. The drying oils commonly used for printing inks, such as tung oil, linseed oil, rape seed oil, and oiticica oil, have by nature a drying rate which is slow compared to the potential operating speeds of printing presses, even when the usual driers (e.g. cobalt) are added to the oils. Particularly with the advent of the higher speed presses and multiple color printing, the avoidance of smudges and off-set on the successive sheets coming from the printing press has presented a serious problem.

While numerous attempts have been made to solve this problem, none of them, as far as we are aware, can be regarded as satisfactory. For example, the use of heat-set inks and steam-set inks, which were developed for this purpose, require the addition of large and expensive accessory equipment to the printing press in order to utilize the full productivity of the press; and the heat or steam tend to impair the dimensional stability of the paper and therefore thequality of the finished printed matter. The use of fine powder sprays or a transparent protective coating over the freshly printed surface (see Costello Patent No. 2,696,168, dated December 7, 1954), also requires considerable accessory equipment and is generally inconvenient.

It has also been proposed to increase the drying rate of printing'inks by employing a catalyst or polymerization promoter for speeding up the drying of the vehicle, sometimes in conjunction with heat or radiation of certain light energy. These proposals likewise involve objectionable features which have barred or greatly limited their commercial use. For example, a printing ink containing a diacyl peroxide as the catalyst will undergo skinning and livering even after a short period of storage under ordinary conditions, due to the strong oxidizing effect of this peroxide on the eleostearin of the drying oil, asdisclosed in Hooft Patent No. 2,109,774, dated March 1, 1938. Thus, Hooft proposed to apply the diacyl peroxide to the paper separately from the ink, which entails obvious disadvantages in commercial printing. Wendt Patents Nos. 2,453,769 and 2,453,77- disclose printing inks containing certain methane derivatives for promoting polymerization of the drying oil, and irradiation of the printed material with ultra violet light of certain wave lengths;

' tat 3,6,23 Patented June 26, 1962 operate at maximum speed with no smudging or ofi-setting on the successively printed sheets, and without impairing the dimensional stability of the paper. Further objects are to provide a quick-drying ink containing a polymerization promoter activated by ultra-violet light, alpha rays, or other forms of cold energy, and to provide an ink of this character which is stable in that it can be stored for a long period of time under ordinary conditions without livering. (While we have referred in the above to sheet-fed presses, it will be understood that the invention is also applicable to web-fed presses.)

By a vehicle of the drying oil type we mean a vehicle containing a drying-oil binder having a conjugated system of double bonds. By quick-drying We mean that when the vehicle containing the ink pigment or other material is applied in a thin film (about 2 to 4 microns in thickness) as in printing, it will dry or set in a matter of seconds; that is, the surface of the film when irradiated for about l-3 seconds with the cold energy, preferably ultra-violet light, becomes sufliciently dry so that in the .case of a printing ink, for example, it will not off-set on succeeding sheets coming from the press. However, the drying action does not stop after the ultra-violet light or activating energy is removed. On the contrary, in the practice of the present invention we have found that Within about 10-30 seconds after such removal of the activating energy, the polymerization or drying action has penetrated the entire film to provide a film which is hard throughout. On the other hand, a film ofthe same thickness consisting of the vehicle alone, when irradiated for the same period of time with the ultraviolet light, will dry through the entire depth of the film in this short period of irradiation, there being no inert pigment in the vehicle to slow down the polymerization rate.

The quick-drying vehicle of the present invention is non-aqueous and consists essentially of a drying oil binder having a conjugated system of double bonds, and a compound selected from the group consisting of titanates, and diisocyanates, such compound being soluble in the binder. We have found that compounds in this group act as a photopolymen'zation catalyst to promote a rapid polymerization of the binder when a film or coating of the vehicle is irradiated with ultra-violet light. The latter thus constitutes an activating means for triggering a reaction in which the catalyst readily absorbs ultra-violet light to form free radicals which, in turn form free radicals with the binder of the vehicle. This provides a rapid reaction which completes the polymerization or drying of the vehicle in a matter of a few seconds.

We have further found that these compounds will not cause skinning or livering of the vehicle. Accordingly, the invention makes possible the formulation of vehicles having a long shelf life.

The binder may be any of the drying oils commonly used in printing inks and containing conjugated unsaturation, or a mixture of two or more such oils. Bodied tung oil is preferred as the conjugatedly unsaturated drying oil. As indicated above, however, the binder may comprise a conjugatedly unsaturated drying oil, such as, tung oil and a portion of non-conjugatedly unsaturated drying oil. If the binder contains less than about 30% conjugated unsaturation, the vehicle will not undergo the rapid and complete polymerization which is preferred for the purpose of the invention.

The proportions of catalyst and drying oil binder in the vehicle are not critical, but we have found that for best results the catalyst should be present in an amount which is roughly 2% by weight of the binder.

The ultra-violet light used to trigger the polymerization reaction is preferably a full spectrum of ultra-violet, including 1800 A. to 4000 A., as we have found that isolated bands of the spectrum do not provide as rapid a polymerization as the full spectrum. An example of such a light source is a high pressure electronic discharge quartz mercury arc tube having an active length of about 1% inches and drawing about 100 watts, the ultra-violet intensity of radiations of 3130 A. and shorter, measured at 20 inches distance, being over 250 microwatts per square centimeter.

The method of the invention comprises essentially the rapid induration of the drying oil binder by (1) forming a non-aqueous solution of the binder and a catalyst compound selected from the group consisting of titanates and diisocyanates, (2) forming a film of the resulting vehicle, and (3) irradiating the film with cold energy (preferably ultra-violet light) adapted to activate the catalyst to form free radicals.

In the preferred practice of the invention, the vehicle containing a pigment in the desired proportion is applied in any suitable manner in a film to the material to be coated such as a paper, and is then irradiated with the ultra-violet light to trigger the polymerizing reaction.

In the case of printing, the printing ink comprises the vehicle and the desired pigment suspended in the vehicle. The ink is applied in the usual manner by the printing press, and the source of ultra-violet light is positioned to irriadiate the printed surfaces of the successive sheets coming from the press.

In the following examples, a few drops of the vehicle in each case were placed upon a glass microscope slide and spread out to a thin film with an accurately honed steel depth gate, so that the thickness of the various films were substantially uniform for comparative purposes; and in each case, the thin film on glass was placed one inch away from the ultra-violet source previously described and timed for complete polymerization to take place. The number of seconds required for the vehicle to polymerize or dry to a hard film, starting with the inception of the irradiation, is given for each vehicle. For comparative purposes, it was found that a similar film of bodied tung oil by itself required 95 seconds of similar irridation before polymerizing to a hard film. All percentages in these examples are on a weight basis.

TITANATES Thin Film,

Vehicle Composition, Wt. Percent Seconds (l2ril8% Bodied Tung Oil, 2% Isopropyl Titannte (C ILOh DIISOCYANATES (8) 96.5% Bodied Tung Oil, 1.0% Polyvinyl Alcohol, 2.0%

2,4-Toluene Diisocyanate, CHs-OnHs-(NCOM (9) 987 Bodied Tung Oil, 2% Diphenyl methane diisocyana'e (10) 95% Bodied Tung Oil, 2% 3,3-Dlto1ylene-4,4-diisoeyand e (11) 96% Bodied Tung Oil, 4% Toluene-2,4-dilsoeyanate..

In each of the foregoing examples, the vehicle dried to a hard film during the specified period of irradiation, the titanate giving a clear film and the diisocyanate giving a matte film in each case. None of these vehicles exhibited any tendency to skin or liver during storage under ordinary conditions after several weeks.

Additional vehicles were made in which butyl titanate,

isobutyl titanate, 2-ethyl butyl titanate, and 2-ethyl hexyl titanate, respectively, were blended with bodied tung oil, the vehicle in each case containing 4% of the titanium ester and 96% of the bodied tung oil. Each of these vehicles polymerized to a hard clear film in approximately 4 seconds, under the conditions described in connection with the preceding examples. None of these additional vehicles exhibited any tendency to skin or liver when stored under ordinary conditions after several weeks.

It was found that as the molecular weight of the titanium compound is increased, the dried film acquires a greasy feel similar to a tale or soapstone. It was further found that the titanate imparts a non-spreading characteristic to the vehicle when applied to paper. Inks formed by pigmenting such a vehicle give more'clearly defined edges to the printed matter and thus improve the quality of the printing. Apparently, the amphoteric nature of titanium causes a fixing of the vehicle on the paper fibers so that the vehicle does not spread out due to capillary action or surface tension. The vehicle will penetrate the paper Without enlarging the surface area of the vehicle.

The titanates provide a rapid polymerization of the tung oil under the action of the irradiated energy, resulting in a clear, hard, glassy film. In addition, the alkyl titanates react with active hydrogen materials to produce titanium hydrate and the released ester. The members of the alkyl titanates of higher molecular weights hydrolyze 1 very slowly, and the hydrolysis rate for the lower members can be controlled by the proper choice of solvent. In the case of inks made from the new vehicle containing an alkyl titanate, the latter apparently reacts with the active hydrogen in the cellulose molecules in the paper to prevent spreading of the ink film by capillary action.

The use of a diisocyanate as the photopolymerization catalyst is particularly advantageous for dry-offset printing where no moisture comes into contact with the ink. The diisocyanates have the property of polymerizing in the presence of materials containing active hydrogen (glycols, alcohols, esters, water, etc.).

We claim:

1. A method of rapidly indurating a polymerizable binder of the drying oil type having a conjugated system of double bonds, which comprises forming a non-aqueous solution of said binder and a soluble photopolymerization catalyst selected from the group consisting of saturated organic titanates and diisocyanates, forming a film of said solution, and irradiating said film with actinic rays adapted to activate the catalyst.

2. A method according to claim 1, in which said actinie rays are ultra-violet light.

3. A method according to claim 1, in which said actinic rays are the full spectrum of ultra-violet light.

4. A method according to claim 1, in which said binder has a conjugated unsaturation of at least about 30%.

5. In the art of printing a sheet, the improvement which comprises forming a non-aqueous solution of a polymerizable binder of the drying oil type and a soluble photopolymerization catalyst selected from the group consisting of saturated organic titanates and diisocyanates, the binder having a conjugated system of double bonds, said solution containing a pigment in suspension to form an ink, printing the sheet with said ink, and irradiating the printed surface of the sheet with actinic rays adapted to activate the catalyst, thereby rapidly indurating the ink.

6. The improvement according to claim 5, in which said binder has a conjugated unsaturation of at least about 30%.

7. The improvement according to claim 5, in which said actinic rays are ultra-violet light.

8. The improvement according to claim 5, in which said actinic rays are the -full spectrum of ultra-violet light.

9. A stable non-aqueous quick-drying vehicle for coating materials which comprises a drying oil binder having a conjugated system of double bonds and an oil-soluble saturated organic titana-te photopolymerization catalyst, said drying oil and organic titanate being in substantially unreacted form and adapted to quickly dry when exposed in a thin film to actinic rays.

10. A vehicle according to claim 9, in which the binder has a conjugated unsaturation of at least about 30%.

11. A vehicle according to claim 9, in which the catalyst is present in an amount in the order of 2% by weight of the 'binder.

12. A stable quick-drying printing ink comprising a drying oil binder having a conjugated system of double bonds, a pigment suspended in the binder and a soluble saturated organic titanate photopolymerization catalyst, said drying oil and titanate being in substantially unreacted form and adapted to quickly dry when exposed in a thin film to actinic rays.

13. A printing ink according to claim 12, in which the binder has a conjugated unsaturation of at least about References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Grant, 1.: Hackhs Chemical Dictionary, McGraw-Hill Book Co., Inc., N.Y., 1944, page 17.

Claims (1)

1. A METHOD OF RAPIDLY INDURATING A POLYMERIZABLE BINDER OF THE DRYING OIL TYPE HAVING A CONJUGATED SYSTEM OF DOUBLE BONDS, WHICH COMPRISES FORMING A NON-AQUEOUS SOLUTION OF SAID BINDER AND A SOLUBLE PHOTOPOLYMERIZATION CATALYST SELECTED FROM THE GROUP CONSISTING OF SATURATED ORGANIC TITANATES AND DIISOCYANATES, FORMING A FILM OF SAID SOLUTION, AND IRRADIATING SAID FILM WITH ACTINIC RAYS ADAPTED TO ACTIVATE THE CATALYST.