US2226871A - Apparatus for drying - Google Patents

Description

H. l. NICHOLAS APPARATUS FOR DRYING Filed April 9, 1938 Rfl O FREQUENCY oscmgnraza Dec. 31,

/lgi ATTORNEY.

BY I

Patented Dec. 31,1940

PATENT OFFICE APPARATUS FOR DRYING Harold I. Nicholas, Chicago, Ill., assignor to W. F.

Hall Printing Company, Chicago, 111., a corporation of Illinois Application April 9, 1938, Serial No. 201,140

1 Claim. ((31. 34-48) This invention relates to an improvement in the apparatus for drying, and is more particularly concerned with the drying of webs, sheets, textiles and photographic films as well as inks or 5 colors applied thereon.

One of the'objects of my invention is to provide a method and apparatus for quickly and efi'ectively drying inks used in printing and the like.

Another object is to provide a method and apparatus for drying webs of paper or textile materials.

Another object is to provide a method and apparatus for drying photographic films and lithographed plates.

Another object is to provide a method and apparatus employing either an electrostatic field, an electromagnetic, or a radio field to effect dry- A still further object is to eliminate the expensive and inemcient methods and apparatus now employed in the printing and textile industries for the drying of inks and colors.

It will be understood that the term drying as used herein is intended to cover evaporation, oxidation, hardening, molecular redistribution or colloidal thickening.

As is well known in the printing art the prevention of offset is an important problem which prior to this invention was not satisfactorilycontrol of the heat. Because of the highspeeds at which present day printing presses operate, the

above means in order effectively to dry the ink,

must of necessity employ high temperatures.

(5 Consequently when the linear speed of the printed web is at a reduced point below the normal operating speed, as when the press is started or when it is slowed down to attach a new roll of paper,

the heating elements must be correspondingly adjusted in anticipation of this reduced speed. During these intervals the ink is not adequately dried and spoilage due to ofiset results.

As a result of these difliculties experienced in the art, the tendency has been to use paper which is in itself of an absorbent character and which the ink and not merely on the surface as is done to some extent obviates the necessity of using the inefficient and expensive means above described. This paper obviously is of a poor quality and is frequently undesirable for use as a base for printed material.

In my invention I make use of the peculiar physical properties of printing inks. Generally, printing inks, particularly black inks, are composed of carbon particles dispersed in a medium such as oil or varnish. Since they are colloidal in 10 character it is seen that each carbon particle which is an electric conductor is completely enclosed by the dispersing phase or surrounding medium which is dielectric in characten, In effect the ink serves to function as a series of con- 15 densers. By exposing said ink to short wave radiations the ink is caused to be heated and thereby dried. It will be seen that no electrodes are in contact with the ink, only the field is used which penetrates uniformly through all strata o and independently influences all particles within the range of the field. In this way a heating effect is accomplished from within the body of in direct heat radiation. V 7

Since a variety of ink compositions' is generally used, some of which are not as responsive to the wave radiations as others, I have found it desirable, in order to accelerate the heating action, to add to said inks certain agents having electrical conductivity as for example tri-ethanolamine oleate, metallic soaps, graphite, finely divided metals or conducting emulsifying agent. It is known that for every electrolytic substance with a definite conductivity and dielectric constant there is a definite wave length in the case of which the heating'of the substance in relation to others is especially pronounced. It is therefore possible by the selection of a suitable wave 46 length to achieve the desired drying effect with every type of ink.

In view of the foregoing, the novel method and means which I employ to accomplish the drying of inks on printed material either on a fast moving web or on separate sheets will be fully brought out in the following description when read in connection with the accompanying drawing.

It will be understood that with this invention sheets, textiles and photographic films can be 50 dried in the same manner as that shown with respect to the drying of inks.

Figure 1 is a diagrammatic view showing my invention in its application to the drying of ink or the like on one side of a web.

Figure 2 is an enlarged view of my drying apparatus.

Figure 3 is a perspective view of the electrode element.

Figure 4 is a perspective view of the electrode.

Figure 5 is a fragmentary perspective view partly in cross section of a modified form of construction in which two webs or the opposite sides of the same web are acted upon simultaneously.

Figure 6 shows a modified form of electrode element.

Figure 'l is a plan view of another type of elec- I trode element capable of being used.

Referring to the drawing, a drying mechanism comprises a metal cage I0 within which is positioned the electrode element generally indicated at H. Said electrode element comprises a bed l2 preferably of material having a high dielectric constant such as glass or porcelain, into which are fused two parallel electrodes l3 and I4 each connected to respective electrical conducting rods i5 and IS. The conducting rods I5 and ii are imbedded in the bed I! and are bent L shaped to terminate as at Na and Ma on one end of the bed. The rods connect by suitable conducting wires lib and I6b to a radio frequency oscillator II. By having said rods terminate in the manner shown the loss through leakage of any radio waves is minimized.

The electrode members I: and H are spacedly positioned in the bed I: slightly below the surface and have part of the top-portions exposed. Said electrodes as more clearly shown in Figure 4 are substantially circular in cross section and are provided with rounded blunt ends Ba and Ida and one squared edge l3b and ilb. This type of electrode element serves to concentrate the radiation of the waves from the electrodes at one line and thus prevent leakage at other points.

The cage in completely encloses the electrode unit and serves as a shield to prevent the radiation of waves into the surrounding atmosphere. Said cageis preferably rectangular in plan and is provided with slot openings Illa and Illb which 48 permit passage of a web therethrough. The roof portion lllc is provided with an exhaust port l8 which is adapted to accommodate a pipe l9 leading to an exhaust fan which serves to remove vapors which may collect in the cage. Means are provided as at 2| for grounding the cage.

The modified embodiment of my invention as illustrated in Fig. 5 provides for the passage of two separate webs through my device at the same time, or the return of the same web travelling in the opposite direction. Referring to Fig. 5 the electrode element indicated generally as at 22 is enclosed in the metal cage 23 which is provided with two pairs of opposing slots 23a, 23b, 23c, 23d

00 to permit passage of the webs, 9 and 9a. Exhaust ports 24 and 25 are provided at the top and bottom portions of said cage and are adapted to be connected to exhaust fans as previously described.

The electrode element 22 is positioned within the cage so as to permit the passage of both webs 9 and 9a and is constructed substantially similar to the electrode element i2 hereinbefore described. In this case, however, the electrodes 22a and 22b are substantially semicircular in cross section and are oppositely positioned having their straight edges exposed.

In the case where it is desired to print on both sides of the web, the web 9 is first passed through my device with printed matter on the underside of the web to dry said ink. The web is then printed on its opposite side and returned to my device through the opening 23b as at in to dry the web as shown.

Referring to Fig. 1 the web or sheet is passed between the printing cylinder 8 and platen roll 81: where the ink is deposited and then through the slot openings Ma and llib provided in the cage i0. It is desirable to have the printed surface nearest the electrode element for best results.

When the oscillator I1 is in operation a radio field is set up and is most concentrated along the sharp edges I31; and Ila of the electrodes. The portion of the web 9 which is in the field at the time, is permeated by the radio waves which act to heat the ink and cause it'to dry. It will be remembered that the occurrence of this phenomena is instantaneous, therefore the ink can be heated far above the kindling point of the web without any apparent ill effects on the web.

In the modified embodiment illustrated in Fig. 5 the web 9 after the first printing impression, passes through the upper slots 23a and 230 of the cage 23 where the ink is dried sufiiciently to avoid offset. The moving web 8 then passes through a second printing cylinder and platen roll (not shown) where a printing operation is performed on the other side of the web. The web then passes through the lower slots 23b and 23d of the cage 23 where the ink is dried and the web thus prepared for subsequent operations. It is sometimes desirable to cool the web surface after the first drying and before the second printing. This is easily accomplished by passing the web over a cold roller preferably of a material having a high dielectric constant.

The most effective results are obtained when the moving web is led parallel to the direction of the electrostatic waves in the field.

In the operation of my device I find it highly desirable to employ a radio frequency current of a large output in a range between 20 and meters. The short wave band is preferred since more efficient heating is accomplished, although shorter waves than those indicated above can be used, their use however is discouraged because of the increased cost attached to producing same. The use of wave lengths longer than those indicated above is found highly ineificient.

When the waves are modulated preferably by an audio frequency between 500 and 15,000 cycles an increased efficiency in drying per wattage output is effected.

A rhombic antenna as is used in radio wave transmission can be substituted and used in lieu of the electrodes previously described which perform the same function. The rhombic antenna shown in Figure 6 is formed of two bars of oppositely positioned electrodes 28 imbedded in a base of dielectric material 29. Said electrodes are preferably semi-elliptical in plan and are positioned so that the major axes of each pair of electrodes are at 58 degrees with respect to each other. This creates a field that is concentrated along the line bisecting said angle. By passing the web or sheet through said field the desired drying is effected.

In lieu of the electrode constructions i l and 22 shown in Figs. 1 to 5 inclusive, I can make use of the modified form shown in Fig. '7. In this case the coil 21 which is connected to a radio frequency oscillator such as H, is supported on a suitable frame member 26 and is positioned so that the web 8 is caused to pass over the partoi the coil at which the field is most concentrated.

It will be understood that the method and apparatus described in the application can be used very effectively in drying webs or sheets ot'materiais which are saturated with or which have deposited upon them a substance conductive to high frequency radio waves. This method can be used most efficiently in the manufacture 01' paper for the drying of the paper web as well as in the textile industry for the drying of cloth and the like. It also finds application in the drying of photogr: phic films and other related articles. The method is equally applicable for drying prints lithographed on metal plate.

The term web wherever used in this application is intended to designate paper, sheets, textiles, films and the like.

It will be understood that various changes and modifications can be made without departing from the spirit and scope of my invention.

I claim: In an apparatus for drying webs of relatively great width and length as compared to thickness 5 which comprises, a dielectric base member, said base member being provided with relatively elongated parallel slots which open to the upper surface of said base member, a relatively elongated electrode positioned in each slot, each electrode having a relatively sharp longitudinal edge, the distance from the edge of one electrode to the edge of the other electrode through an air path being substantially the shortest distance between said electrodes via an air path, means for creating a field of continuous radio waves between said electrodes, and means for moving a web over said base in a direction substantially coincident to a portion of said field.

mom I. NICHOLAS.

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