GB2142210A - Method and apparatus for curing magnetic tape coatings - Google Patents

Abstract

A method for curing the coating on a magnetic tape comprises passing the tape with the uncured coating through an electron beam by means of one or more temperature controlled rollers made of a medium to high atomic numbered material which rebounds a portion of the electron beam back through the tape to increase the total dosage. In one embodiment the uncured web (10) is continuously passed through an electron beam (16) provided by an electron source (18) by engagement of the web with the periphery of a rotating cylindrical drum (14). The latter is formed of copper or equivalent metal so that a proportion of the electrons of the electron beam which pass through the web rebound and pass back through the web again.The temperature of the drum is controlled by admitting water to the inside surface of the drum. Meams (50-58) are provided for controlling the temperature of the drum. Preferably the temperature of the cooling water is measured after it has contact the drum and hot or cold water is admixed with the cooling water, dependent upon what adjustment is found necessary. In a second embodiment the web follows a serpentine path through the beam of electrons by being passed successively over the peripheries of the rollers of two staggered arrays of roller (26-38). The rollers are hollow, preferably formed of copper, and cooling water is admitted to their interiors so as to control the temperature of the web during curing. As before, means (60-68) are provided for controlling the temperature of the rollers by adding hot or cold water to the cooling water. <IMAGE>

Description

SPECIFICATION Method and apparatus for curing magnetic tape coatings The present invention relates to a method and apparatus for curing coatings on moving web materials and, more particularly, for a method and appar atus for curing the resin coating on magnetic tape by means of electron bombardment.

Magnetictape media utilizes a polymer base tape such as MYLAR, a polyethylene terephthalate available from E.l. duPont Nemours & Co. with a resin coating thereon in which magnetic particles are embedded. It is necessary, during the manfuacture of such tape, to cure the coating either by heating it or by bombarding it with electrons. This particular invention relates to the lattertypeoftapecoating curing.

The problem in the past has been thatthe tape coating must absorb a sufficient amount of energy from the electron beam to producethe curing while at the same time not becoming overheated. A single exposure of a magnetic bindertapeto a high power electron beam has been recognised as not feasible as a ameans of curing the binder structure.It was found that either the binder would not cure because the electron beam was of insufficient power or, alternatively, if the power was high enough to cure, the tape would overheat- possibly exceeding the glass transition temperature of the Mylar support, which is approximately 80 C. This difficulty could conceivably be alleviated by passing thetapeseveral times through a low power electron beam, however, the time required to cure the tape would adversely impact upon the production capacity of the process and would not permit control of the temperature ofthe tape.

The above and other disadvantages ofthe prior art methods and apparatus for curing magnetictape coatings are overcome by the present invention which comprises means for generating an electron beam, rotatable web handling means positioned within the electron beam, such web handling means being made of a medium to high atomic number material, and means for internally controlling the temperature of the web with sufficient accuracy to prevent overheating without prohibiting the curing process from going forward.

There are two preferred embodiment ofthe invention. In the first embodiment, a single, relatively large diameter roller which is hollow and which is provided with an internal cooling medium is rotatably mounted within the electron beam. The magnetic tape to be cured is rotatably supported on the roller within the electron beam. Electrons passing through the material strike the roller, which is preferably made of material such as copper or steel, and then rebound back through the tape to increase the dosage level.

In a second embodimentofthe invention, a plurality of cooled rollers are rotatably mounted parallel to each otherwithin the electron beam and the tape is festooned about the rollers to follow a serpentine path through the electron beam. Again, the rollers are preferably made of a moderate to high atomic numbered material, such as copper or steel, and are provided with internal cooling. The same electron rebounding effect takes place in the second embodiment.

It is therefore an object of the present invention to provide improved apparatus for curing magnetic tape coatings by electron bombardmentwhilesimultaneously cooling the tape.

It is yet another object of the invention to provide for a magnetictape coating cured by electron bombardment in which the electrons are rebounded back throughthetapeto be cured.

It is yet another object of the present invention to control the temperature of the web to prevent overheating while simultaneously allowing the curing to go forward.

The novel features which are believed to be characteristic of the invention, both asto organization and method of operation, together with further advantages thereof, will be better understood from the following drawings, in which two preferred embodiments of the invention are illustrated byway of example.

Figure 1 is a vertical view, partly in section, illustrating a first embodiment ofthe invention; and Figure 2 is a perspective view of the second embodiment of the invention.

Referring now more particularlyto Figure 1, a coated polymer foil web 10, which is approximately 66 cm in width and .005 cm in thickness, is received for curing by the apparatus ofthe invention. The web or tape 10 can be made of any of a variety of polymer materials, such as a polyethyleneterephthalate (Mylar) or the like. The magnetic media coating can be any of a variety of types which are well-known in the trade and which are curable either by the application of heat or by electron bombardment. See for example U.S.

Patent No.4,004,997.

The tape 10 travels in a horizontal position from the coating application station (notshown)andpasses into shielded housing 24 over a first roller 12, then around a second, large diameter roller 14, preferably ofcopperor steel where it travels in a vertical direction through an electron beam 16 produced by an electron beam generator 18. While passing through the beam 16, the coating is cured on the tape. The tape ultimately leaves contact with the surface of the drum or roller 14 and passes around still another roller 20 to resume a horizontal direction. The cylinder 14 is rotated by a motor drive (not shown) at a rate which causes the web 10 to move at a predetermined speed ~for example at approximately 254 cm per second.

Ideally, for most applications, an exposure of approximately 4000 megarads perfoot per minute is sought.

The electron beam radiation 16 passes through the tape 10 and the coating thereon and rebounds to some extent (approximately 20%) offthe cylinder 14to pass back through the tape 10, thereby adding to the total dose of radiation sustained bythetape. The electron bombardment causes the cylinder 14to heat up and, thus, it is necessary to provide a meansforcontrollably cooling the drum and in turn the tape in contact therewith.

As previously stated, the present invention is primarily concerned with controlling the temperature of the tape structure during curing. It is recognised thatthereisa limited amount of energy that can be deposited on the binder structure before the tape overheats to the point of distortion. Conversely, too low a temperature level of the tape can preventthe curing process from going forward. The actual temperatures of operation would depend upon the chemical nature of the binder being employed, as well as the specific support or substrate chosen. The curing temperature, as well as the distortion temperature, in any particularcasewould be parameters well known to anyone of ordinary skill in the art.The present invention deals with providing a device for enabling the practitionerto controllably select a temperature rangeforthe particular binder systemisupport to allow curing without distortion.

In furthering the goal advanced above, annular space 57 is provided with a cooling medium which can bewateroranyotherliquid capable of dissipating heat energy. The annular space can either be rigidly connected to drum 14 and thus rotate with said drum or alternatively annular space 57 can be free floating or rigidly attached to frame 24. In the later embodi ment,the annular ring and drum would be slidably engaged. In either case, a provision is made for measuring the temperature of liquid in annular space 57 shown schematically at 56.By way of example, liquid is passed through sensor 50, which measures thetemperatureofthe liquid.Asignal is then sent to controller 51 which compares the sensor signal to a presetvalue which the operator determines based upon the specific tape formulation being cured. The controller next sends a signal to actuator52which provides for the addition of either heated liquid through valve 54 or cold liquid through valve 53 depending upon the signal being received from the controller. In the alternative, if it is determined that the liquid is too cold, no further liquid addition can be made to allowthe heating action ofthe electron beams to heatthe liquid 57 and drum 14.

Itwill be well recognized that as additional heated or cooled liquid is fed into annularspace 57 at 55, there must consequently be a liquid overflow provision, shown schematically at 58. The placement of the liquid entry and liquid removal ports have been arbitrarily drawn in Fig. 1 as the only important consideration is that the overall temperature of the liquid in annular space 57 and thus the temperature of drum 14 be capable of being controlled. It is further noted that annular space 57 can be provided with means for increasing the liquid velocity by, for example, the placement of baffles, in aiding energy transfer between drum 14 and the cooling liquid.

Instead of providing an annular space, the device of the present invention could alternatively be provided with a water spray mechanism within hollow cylinder 14. As in the previous embodiment, the temperature of the spray could be controlled by sampling the accumulated liquid within the drum by means of a sensor and passing the information through a controllerand actuatorto raise or lowerthe liquid sprayfeed temperature orto turn on the spray only when cooling is desired. In fact, virtually any means of providing contact between a liquid and the innersurface of rotating drum 14while controlling thetemperature thereof is considered to be within the scope of the present invention.

Referring now more particularly to Figure 2, basical lythesamecuring apparatus is illustrated exceptthat, instead of passing around a single large diameter water cooled drum 14, the tape 10 serpentines about a series of parallel rollers 26,28,30,32,34,36 and 38 which are disposed within the electron beam 16 generated bythe electron beam generator 18. Thus, the tape passes first around a rol ler 26 and then back around a second roller 28, which is mounted parallel to the roller 26, but slightly below it and further away from the electron generator 18, as viewed in Figure 2.

This pattern is repeated through rollers 30,32,34,36 and, lastly, roller38. After leaving the roller 38, the web 10 passes around the roller 20 outside of the enclosure 24 to travel on to a finishing station (not shown). The rollers 26,30,34 and 38 are arranged in a first column and the rollers28,32 and 36 are arranged in a second column. The first column is closestto the electron beam generator 18. The rollers 26, 30, 34and 38 are vertically spaced apart by distances that are less than the diameter of the rollers ofthe second column so that substantially all of the electron beam impinges uponthetapesurface.

The rate of tape travel and electron bombardment are approximatelythe same asinthe embodiment of Figure 1. The rollers 26 through 38, although of a smallerdiameterthanthe rollerl4,arealsowater cooled and preferably made of copper or other moderately high atomic numbered material. Again, the electron beam passed through the tape 10 is rebounded bythe rollers 26 through 38 through the tape 10 to increase the effective dosage for curing the coating onthetape.

Like the embodiment described above, means are provided forcontrolling the temperature ofthe liquid to in turn control the temperature of support rollers 26, 28,30,32,34,36 and 38, which enables one to control the temperature of the magnetictapewhile being cured. As illustrative of this embodiment, cooling liquid such as water iswithdrawn from the interior of roller 38, shown schematically as 60, and is passed to sensor 61 where its temperature is determined. The temperature information is then passed to controller 62 which determines whether the temperature is higher or lowerthan that determined as optimum by the operator ofthe system. This information is then passed to actuator 63 which applies either hot or cold fluid from taps 64 and 65, which in turn feed the proper fluid via lines 66 and 67 to enter the system at 68.

The terms and expressions which have been employed here are used as terms of description and not of limitation and there is no intention, in the use of such terms and expressions, of excluding equivalents ofthefeatures shown and described, or portions thereof, it being recognized that various modifications are possible within the scope ofthe invention as

Claims (12)

1. claimed.

   CLAIMS 1. Apparatus for curing a resin composition on a moving web comprising meansforgenerating an electron beam, web transport means for passing the web through the electron beam and a housing for enclosing the electron beam generator and the web transport means, and furtherwherein the web trans port means comprises at least one roller having a peripheral surface which supports the web within the electron beam which is provided with meansfor controlling the temperature of the roller.
2. 2. Web coating apparatus as recited in Claim 1 wherein thewebtransport apparatus comprises a plurality of rollers whose peripheral surfaces support the tape within the electron beam and which are impinged upon bythe electron beam,the rollers being rotatably mounted and parallel to each other and wherein the web is serpentined about the rollers within the electron beam.
3. 3. Apparatus as recited in Claim 2 wherein a plurality of rollers are arranged in two columns with respectto the electron beam, the column of rollers closest to the electron beam generator having its rollers vertically spaced apart by a distance which is less than the diameter of the rollers in the other column.
4. 4. Apparatus as recited in Claims 1 or 2 wherein the web transport means receives and outputs the web in a horizontal direction.
5. 5. Apparatus as recited in Claims 1 or2wherein the web transport means comprises a material having an atomic number at least as high as that of copper.
6. 6. Apparatus as recited in claim 1 wherein said roller receives electron beam radiation through the web and reflects a substantial portion ofthe electron beam backthrough the web.
7. 7. Apparatus of claims 1 or 2 wherein said rollers are composed of a metal selected from the group consisting of copper and steel.
8. 8. Apparatus ofclaims 1 or2whereinsaidmeans for controlling the temperature ofthe rollers compris escontacting a liquid with the interior surfaces of said rollers.
9. 9. Apparatus of claim 8 wherein said liquid is entrapped within an annular space defined bythe inner surface of said rollers.
10. 10. Apparatus of claims 1 or 2 wherein the temperature of the roller is controlled by providing a liquid proximate to the interior of said roller, the temperature of which is raised or lowered by sampling said liquid by a sensor and determining whether its temperature is higher or lower than a preset value by use of a controller which, in turn, passes a signal to an actuator which provides forthe addition of heated or cooled liquidtothe remaining liquid located proximate the roller.
11. 11. A method of curing a resin coating on a moving web comprising the steps of passing the web with the uncured coating thereon through an electron beam while in contactwith a supporting roller having a liquid in contact with the interior surface thereof, measuring the temperature of said liquid by a sensor and supplying the temperature information to a controller which compares the temperature to a presel temperature value and, in turn, passing a signal to an actuatorwhich raises or lowers the liquid tempera ture.
12. 12. Apparatus for curing a resin composition on a moving web substantially as described herein with reference to Figure 1 or Figure 2 of the accompanying drawings.