US2588811A - Process of drying gelatine layers - Google Patents

Description

March 11, 1952 Q, DlpPEL Er AL 2,588,811

PROCESS OF DRYING GELATINE LAYERS Filed May 2, 1947 Patented Mar. 11, 1952 PROCESS OFDRYIN G GELATINE LAYERS Cornelis `Johannes Dippel, J an 4Anthony Lely, vand Johannes Aloysius Maria Dikhoi, Eindhoven,

Netherlands, assignors to .Hartford National Bank and Trust Company, Hartford, Conn., :as

ktrustee .Application Mayz2, 1947, Serial-No. 745,396 `.In the Netherlands .J une -1, 1946 :4 Claims.

In drying gelatine layers, for example in manufacturing photographic material, great diiiculty is encountered in nthat gelatine can only lbedried very slowly. Theinstallations for makingphotolgraphic material in which a photo-sensitive gelatine emulsion is provided on a substratum thus become of very large size and hence very expensive. The avoidance of the formation of dust in vsuch large spaces of several tens of meters in length, which is absolutely necessary for making good photographic material, increases lthe cost to a considerable extent. Furthermore, the usual heating by means of heated dry air has a poor emciency. Similar ldiiculties `arise in manufacturing gelatine layers which Ido not comprise photosensitive compounds such, forexample, as gelatine layers which are intended for recording sound by mechanical means, for example by cutting a sound track lm or record.

vThe present invention relates to a process of drying gelatine layers which permits drying to beteffectedfat aconsiderably .greater speed with thense o'f equipment of verysmall size.

According to .the invention, gelatine layers are dried by heating in an electric field of high frequency.

Whereas indrying a coagulated gelatine emulsion .by means of heated dry air, as has been usual hitherto, drying may take place only very slowly since otherwise the gelatine melts and inhomogeneous layers .are obtained. It has been found that theuseof high-frequency drying .permits the temperature of the .gelatine layer -to exceed its melting vpoint Without any harmful consequences for the homogeneityof the .gelatine layer .being involved.

This vaiords vthe k1possibility of .greater speed in the .drying process. According to the invention yan aqueous gelatine `layer which, after drying,

has a thicknessof 100 microns at the most issubjected to an electric field while passing a stream oigas over the gelatine for dissipating the water vapour produced, said field being of ysuch irequency .and strength that the Water is removed within veminutes. .A treatment of five minutes at the most means that .any point .of the layer is subject `tothe .eld fornve minutes at the most.

.Fora better understanding of the .invention it is V,pointed out that the reason why melting of the glatine layer need not necessarily result in any unevenness is probably due to the fact that the Water which is at rst evaporated .is rapidly removedso that partly dried gelatine of low water .content .follows almost immediately. This gelatine upon melting yields amass .of such viscosity that flows or the like which might lead to troublesome unevennesses no longer occur in it. Since the gelatine treated according to the invention is dried,.at least initially, in the molten state it .is not necessary for the gelatine emulsion, after being poured out on a substratum to form a layer, to coagulate before drying, contrary to the drying methods which have been usual hitherto. It is further pointed out that a gelatine emulsion of the kind utilized for pouring Aout a layer of uniform thickness usually contains irom180% to A% by weight of water. If such an emulsion is caused tc coagulate by cooling and subsequently heated up, it melts below a temperature of '30 C. to forma thin iiuid mass. The water content decreases as the melting point increases. An emulsion which has been dried te a water content of about '50% produces .a vmolten mass which exhibits -at 50 C. a viscosity such that no troublesome flaws occur in it. Gelatine layers of photographic films are dried to a water content of `about 15%. With such a water content the layers are about ten times thinner than in the freshly-coagulated undried state.

It is evident that the speed of drying is dependent on the thickness of the gelatine layer. Layers of a thickness of about 50microns, such as are used .for cutting mechanical sound records, for example sound iilm records exhibiting so-called variations in width, Vrequire a drying time longer than that for layers of from l5 to 20 microns such as are used for the ordinary photographic silver halide gelatine material. According to the invention, the last-mentioned layers are adapted to be dried within half a minute.

Heating of the gelatine layer is preferably effected by means of an electric field generated between filamentary or rod-shaped electrodes which are arranged parallel to the surface of the layer vand along which the gelatin layer is guided in such manner that the lines of -force of the eld extend through the material substantiallyin the direction of movement. With such an arrangement of the electrodes the lines of force extend over a comparatively long distance through the layer itself and over only small distance through the medium, for example air, between the electrodes and the material to be dried. This results in an increase of the efflciency of the eld so that a great amount ci heat may be generated in the gelatine layer by means of small equipment and a high-frequency generator of low power. Although with the .said arrangement of the electrodes the strength of the iield in the direction of movement of the material is not constant, the result of the treatment in this direction is homogeneous provided that the movement takes place at constant speed. The homogeneity in the transverse direction, normal to the direction of movement, may be controlled by the use of electrodes the length of which is greater than the width of the material. Y

The arrangement of the electrodes is preferably such that, on passing the electrodes, the gelatine layer is subjected to a field of gradually decreasing strength, since as the drying process is proceeding and the gelatine contains less water, the watel` is driven out of the gelatine more slowly, probably due to the fact'that a thin layer of poor transmitting capacity forms on the surface of the gelatine layer. Consequently, the risk of undue heating of the gelatine increases. Although the gelatine in this drying stage exhibits a viscosity such that flows in the gelatine need practically not be feared, there is in this case a risk of the formation of vapour and hence of bubbles in the gelatine layer. A gradually decreasing eld may be obtained by a gradual increase of the distances between the electrodes between which the field is generated, by a, decrease of voltage, and

so on.

As an alternative, weaker heating in the last stage of the drying process may be obtained by treating the gelatine layer in this stage with cold air.

Local overheating as a result of locally greater intensity of the field isr avoided by control of the rate at which the gelatine layer is guided through the iield so that the layer is subject to these points of higher-field intensity for a short time only. The rate which is preferably used is about 0.5 metre per minute. y

The gelatine layer may be guided between the electrodes in the horizontal position, or in the inclined, for example vertical, position. Any guide rollers or guide paths which may be provided in the electric field are required to consist of material of low dielectric losses so that they are not unduly heated. There need be no fear of combustion of the substratum, e. g. nitrocellulose for the gelatine due to electrostatic charges generated by friction on the rollers, since with the use of the invention the atmosphere in the drying space is not required to be as dry as in the usual processes, in which heating and drying take place by means of heated dry air. i

The amount of gas, for example air, which is guided along the gelatine `layerfor the dissipationof the water vapour is preferably such as to be just sufficient for the absorption of the eX- pelled water vapour without becoming oversaturated. This aiiords the advantage that the amount of air that is directed over the gelatine may be as small as possible so that the risk of y contamination of the gelatine layer by dust particles is reduced. The amount of air is preferably 100% more than that which is required for the dissipation of the water vapour.

In the usual process of drying gelatine the amount of air owing along is considerable in order to enhance as much as possible the vaporisation of water brought about -by the slightly heated and very dry air. With such large Vamounts of air flowing along the gelatine the risk of contamination by dust particles is very great. `According to the invention, the'air is preferably guided along the material in the same direc- 4 tion as that in which the material is moved. The air thus first comes into contact with the moistest gelatine from which a great amount of water is required to be absorbed quickly and at which the temperature is'required to be lowest. During flowing through the heating device the temperature of the air increases. This is not objectionable since the melting point of the gelatine with which it is in contact also rises as the Water is driven out and the viscosity of the melted and partly dried gelatine is such that unevenness due to iiaws in the gelatine do not arise. On the contrary, this heating of the air is advantageous since the capacity of air to absorb water vapour increases as the temperature rises. The air thus remains capable of absorbing water vapour from the gelatine, which is advantageous since the water vapour may thus be absorbed by a small amount of air.

. It is further pointed out that in drying gelatine layers in an electric field the heat is largely generated in the gelatine and the substratum is hardly heated due to the fact that the dielectric losses of a dry substratum-are considerably lower than those of a wet gelatine layer. Y

The invention is advantageously applicable not only to drying gelatine layers that are freshly applied but also to drying gelatine layers which, after drying, are moistened again, for example photographic material which is developed, fixed and rinsed. f Y

The invention will be described in connection with the following example and the accompanying drawing in which:

Fig. 1 shows one form of apparatus for drying film; and

Fig. 2 shows another form of apparatus for drying film.

Escample A band of nitrocellulose having a width of 16 mms. and a thickness of microns has applied to it a gelatine layer by treatment with a solution containing 20% of gelatineat about 35 C. and by coagulation of the emulsion. Subsequently, the layer is guided in the vertical direction from below to above, at a speed of 0.7 meter per minute, through van electric field having a frequency of 15 megacycles/sec. and a power of 80 watts, the layer being dry within 15 seconds. About 35 liters of air per minute at the ambient temperature is directed along the layer. The thickness of the layer in the dried state is about 25 microns. The electrode System used for generating the electric field is shown diagrammatically in the accompanying drawing. Reference numeral l indicates the nitrocellulose band'which is provided with a gelatine layer and which is moved from below to above. which are varranged. to be mutually shifted are rod-shaped and have a diameter of 3.5 mms. and a length of 20 mms. All the electrodes on the same side of the band are interconnected in a conductive manner and are energized by an r-f oscillator 3. The lowermost seven electrodes are at a distance of 2 mms. from the band and exhibit a mutual spacing of 10 mms. The remaining electrodes are at a distance of 4 mms. from the band and exhibit mutual distances of 30 mms. The electrode system is arranged in a tube 4 consisting of material of low dielectric losses through which a stream of air is passed by means of an exhaust fan 5 in Fig. l or by means of a blower system comprising an intake fari 0 and an exhaust The electrodes 2 What we claim is:

1. A process of drying gelatine layers, having a thickness when dried of less than approximately 100 microns comprising the steps of subjecting the gelatine layer containing Water to an alternating electric eld of high frequency having an intensity at which the gelatine is heated to a temperature at which it melts and the Water removed therefrom within ve minutes, and passing a gas stream over the gelatine layer to remove the water vapor expelled from the Wet gelatine layer.

2. A process of drying gelatine layers, having a thickness when dried of less than approximately 20 microns comprising the steps of subjecting the gelatine layer containing water to an alternating electric eld of high frequency having an intensity at which the gelatine is heated to a temperature at which it melts and the Water removed therefrom Within one-half a minute, and passinga gas stream over the gela tine layer to remove the Water vapor expelled from the Wet gelatine layer.

3. A process of drying gelatine layers, having a ,A

thickness when dried of less than approximately 100 microns comprising the steps of passing the gelatine layer containing water through an alterf hating electric eld of high frequency having an intensity at which the gelatine is heated to a temperature at which it melts and the water removed therefrom Within ve minutes at a speed exceeding one-half meter per minute, and passing a gas stream over the gelatine layer to remove the Water vapor expelled from the Wet gelatine layer.

4. A process or drying gelatine layers, having a thickness when dried of less than approximately 100 microns comprising the steps of passing the gelatine layer containing Water through an alternating electric eld of high frequency having lines of force extending substantially parallel to the direction of motion of the layer and having an intensity at which the gelatine is heated to a temperature at which it melts and the water removed therefrom within five minutes at a speed of at least one-half meter per minute, and passing a gas stream over the gelatine layer to remove the water vapor expelled from the wet gelatine layer.

CORNELIS JOHANNES DIPPEL.

JAN ANTHONY LELY.

J OHANNES ALOYSIUS MARIA DIKHOFF.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,042,145 Darrah May 26, 1935 2,226,871 Nicholas Dec. 31, 1940 2,231,457 Stephen Feb. 11, 1941 2,291,807 Hart, Jr. Aug. 4, 1942 2,402,609 Brabander June 25, 1946 2,459,623 Cohoe et al Jan. 18, 1949 2,473,251 Hsu June 14, 1949 FOREIGN PATENTS Number Country Date 691,038 Germany May l5, 1940

Claims (1)

1. A PROCESS OF DRYING GELATINE LAYERS, HAVING A THICKNESS WHEN DRIED OF LESS THAN APPROXIMATELY 100 MICRONS COMPRISING THE STEPS OF SUBJECTING THE GELATINE LAYER COMTAINING WATER TO AN ALTERNATING ELECTRIC FIELD OF HIGH FREQUENCY HAVING AN INTENSITY AT WHICH THE GELATINE IS HEATED TO A TEMPERATURE AT WHICH IT MELTS AND THE WATER REMOVED THEREFROM WITHIN FIVE MINUTES, AND PASSING A GAS STREAM OVER THE GELATINE LAYER TO REMOVE THE WATER VAPOR EXPELLED FROM THE WET GELATINE LAYER.

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