GB2054876A - Contact printing using copying material in web form - Google Patents

Abstract

Where a copy of a high resolution original 63, such as a master video- disc is to be produced by contact printing, it is essential that the copying material 16 and the original 63 be brought into intimate contact. This contact can be prevented by foreign matter at the interface, by differential movements and thermal expansion during exposure, and, where a diazo copying material is used, by the gas released during the exposure. Removal of the foreign matter is assisted by operating in a vacuum, with separate supply 10, exposure 56, and take-up 100 chambers. The take- up chamber 100 is isolated from the exposure chamber 56 to reduce the loss of vacuum by a seaport 102 comprising inflatable rubber tubing (112, Figs. 5a and 5b). Cleaning is aided by a contra-moving cleaning material 31 in the supply chamber 26 and an inflatable pressure pad 59 assists contact between the original 63 and the copying material 16. Isolation from forces causing differential movement is provided by a planar isolating member (150 Fig. 11) between the pressure-pad 59 and the copying material 16, and differential thermal expansion is minimised by use of an optical filter having an appropriate pass-band to modify the light-source 90. <IMAGE>

Description

SPECIFICATION Copying apparatus The present invention relates to the copying of information from a master record carrier onto a receiving material by optical contact printing and, more particularly, to apparatus and method useful for such copying.

A master record carrier, for example a master video-disc, is a high quality recording of a video programme. From the master disc, it is desirable to mass produce copies for consumer use. One known method for copying a video-disc uses a master disc comprising a thin metal film evaporated onto an optically polished plate-glass disc. Video information is recorded on the master disc by using a laser beam to selectively melt the metal coating. The master disc is then coated with a photoresist material which is exposed through the rear of the glass disc. After processing, an array of bumps remains which coincides with the initial array of information holes. This bumpy surface is used to produce a metal stamper, or mould, by much the same techniques as are used in audio record manufacture.Discs are mass produced from the mould by thermoform copying which generally takes one of three forms: (1 ) In compression moulding, a soft "patty" of warm plastic is placed between the open halves of a mould cavity. The mould is heated and the halves are pressed together forcing the plastic to assume the shape of the cavity. (2) In injection moulding, the halves of the mould cavity are first clamped shut, and then hot plastic is injected at high pressure to fill the cavity. (3) In embossing, a preformed sheet of plastic such as polyvinyl chloride is placed in a press and the metal stamper is pressed against the surface of the plastic sheet to transfer the video information.

The above process can be simplified by using a photoresist master comprising a glass disc-shaped blank coated with a thin, uniform layer of positive (or negative) photoresist. The photoresist is directly exposed with a laser recording beam, and processing produces an array of pits (or bumps) corresponding to the video information. A metal stamper, or mould, is made from the processed photoresist master and thermoform copying is used to produce replicas.

It is apparent that thermoform copying is a relatively complex technique, whether one uses a metal master or a photoresist master. An alternative -- and attractive -- copying process is optical contact printing. A conventional metal master is used, without modification by photoresist coating, etc., as an optical mask through which a contact print exposure is made. In general, however, optical contact printing is not well suited to the copying of video-discs for two major reasons: (1) Video information recorded on a video-disc is commonly in the form of an array of elliptical apertures only a few wavelengths of light in size; diffraction by such apertures causes contact between the master disc and the copy receiving material to be extremely critical.Even a slight separation occurring between the master disc and the copy receiving material during exposure will result in a large decrease in the fidelity of the recorded image, the size of which should preferably be preserved to within a few percent, i.e., about 20 to 40 angstroms. (2) The standard video-disc is about 30 cm (twelve inches) in diameter and has literally billions of micron-sized apertures covering the disc, thereby making it necessary to maintain uniform and intimate master-to-copy contact over the entire image surface, which contact is made difficult to achieve due to the presence of dust, dirt, disc imperfections, etc.

French Patent 2,310,586 and corresponding German Offenlegungsschrift 2,620,283 disclose apparatus for copying video-discs onto a diazo material by optical contact printing. In accordance with that teaching, a web of copying material comprising a diazo compound on a support is unwound at constant speed. A transparent cylinder rotates on the copying material as the material is unwound. A flexible master record carrier having video information recorded in the form of spaced apertures is wrapped around the transparent cylinder. A monochromatic, ultraviolet lamp is disposed inside the cylinder along its longitudinal axis and emits radiation through the apertures of the master to expose the diazo layer of the copying material.French Patent 2,310,586 apparently fails to recognize that the copying process is critically sensitive to the presence of foreign particles because no provision for cleaning the copying material of such particles is described.

In addition, the copying material is at least partially wrapped around the cylinder to drive the cylinder and to contact the master record carrier during the contact print exposure. Such wrapping gives rise to compressive strain along the inside radius of the copying material that will tend to distort the material as well as causing the material to abrade the master, thereby degrading the image and also causing wear of the master record carrier.

Because of the exacting requirements for videodisc copying, designing and constructing a machine suitable for the mass production of video-discs by contact printing is a formidable problem. Such a machine would have to include apparatus for thoroughly cleaning the copying material of virtually all foreign particles. Means would also have to be provided for rapidly bringing the master disc into close contact with the copying material for successive contact print exposures. Further, it has been found that the contacting process must be highly uniform since variations in the intimacy of contact cause objectionable quality variations in the copy.Still further, the copying of video-discs by optical contact printing is critically sensitive to numerous factors, at least some of which are either not completely understood or are uncontrollable, thereby making the process somewhat unpredictable. It is, therefore, highly desirable that means be provided to enable an operator to remove a portion of the exposed copying material for purposes of monitoring the quality of the process, preferably without disturbing the operating conditions in the machine.

In accordance with the present invention there is provided apparatus for use in the photographic copying of information from a master record carrier onto a copying material in web form, the apparatus comprising: an exposure chamber; means for bringing copying material and a master record carrier into contact within the exposure chamber for a contact print exposure; means for evacuating the exposure chamber; a ported takeup chamber arranged to receive the exposed copying material from the exposure chamber; and means for selectively closing the port between the exposure chamber and the takeup chamber.

In accordance with a second aspect of the invention, a supply chamber is provided that is arranged to receive a material in web form. A web cleaning device is disposed in the supply chamber for cleaning foreign particles from the web material. Means are provided for evacuating the supply chamber to prevent foreign particles removed from the material from drifting about under the influence of air currents are recontaminating the material.

There is further provided a method of photographically copying information from a master record carrier onto a copying material comprising the steps of: degassing the copying material in a vacuum environment; treating to remove foreign particles from the surface of the copying material while in a vacuum environment; and photographically exposing the copying material to the master record carrier while in intimate contact in a vacuum environment.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front sectional view of a video-disc copying machine embodying the present invention; Figure 2 is a side sectional view of the videodisc copying machine of Figure 1; Figure 3 is a top view of the video-disc copying machine of Figure 1; Figure 4a is a drawing to a larger scale showing part of an exposure station in the video-disc copying machine of Figure 1; Figure 4b is a perspective view of the exposure station of Figure 4a; Figure 5a is a drawing to a larger scale showing a seal port device used in the video-disc copying machine of Figure 1; Figure Sb is a view showing a section on the line A-A of Figure 5a;; Figure 6 is a block diagram of a logic circuit for controlling the operation of the video-disc copying machine of Figure 1; Figure 7 shows a master record carrier, the size of the images being greatly exaggerated; Figure 8 shows the result of contact printing the master record carrier of Figure 7 on tb a diazo copying material, the size of the images again being greatly exaggerated; Figures 9 and 10 are views of the exposure station shown in Figure 4a to illustrate the mechanism of the distortions occurring when using a diazo copying material; Figure 11 is a view of the exposure station shown in Figure 4a showing a first embodiment for reducing the distortions occurring when using a diazo copying material;; Figure 1 2a is a perspective view of a pressure platen for use in the exposure station of Figure 4a in a second embodiment for reducing the distortions occurring when using a diazo copying material; and Figures 1 3a and 1 3b show a filter for use with the light source of the apparatus shown in Figure 1.

A video-disc copying machine as shown in the drawings generally includes three major sections: (1) a supply chamber 10 wherein copying material 1 6 is degassed and its photosensitive surface cleaned of foreign particles, (2) an exposure station 51 including an exposure chamber 56 (which can be evacuated) containing a pressure platen 57 or other means for bringing the material 1 6 and a master record carrier 63 into close contact for the contact print exposure, and (3) a takeup chamber 100 for storing exposed material, the takeup chamber being separated from the exposure chamber 56 by a sealport 102 device which, when activated, permits the takeup chamber-100 to be brought up to atmospheric pressure without substantially affecting the operating conditions in the remainder of the machine.

Referring to Figure 1, the supply chamber 10 contains a spindle 12 for receiving a supply reel 14 of a copying material 16. The spindle 12 is driven by a torque motor 18 through a belt ?0 and pulleys 22, 24 as shown in Figure 3. A surface of the material 1 6 will ultimately be pressed into contact with a master record carrier for the purpose of contact printing the information on the master to the material 1 6. This surface will be referred to as the contacting surface and will usually, but not necessarily, be the photosensitive surface of the material 1 6. The quality of the contact printing process is dependent, inter alia, upon the closeness of contact maintained between the master device and the material during the contact print exposure. Close and uniform contact is especially important when contact printing high frequency information (such as video information carried in the form of micronsized apertures). For this reason, it is desirable that the contacting surface of the material 1 6 be cleaned of foreign particles.

To this end, the material 1 6 passes through a web cleaning device 26. The web cleaning device 26 comprises a spindle 28 which receives a supply reel 30 of open mesh rayon paper 31, or other suitable web cleaning material. The paper web 31 passes over guide rollers 32, 34 and is wound onto a takeup reel 36 mounted on a spindle 38. A motor 40 drives the spindle 38 through a belt 42 and pulleys 44, 46 shown most clearly in Figure 2. The material 1 6 passes over a guide roller 48 and contacts the paper web 31.

The paper web 31 advances in a direction opposite to that of the material 1 6 to effect cleaning of its photosensitive surface by a rubbing action. Alternatively, a brush-type cleaner having bristles which have been treated to attract foreign particles could also be used to clean the web surface. Most foreign particles on the material 1 6 become embedded in the paper web 31. Some foreign particles, however, do not become so embedded and fall toward a collection tray 50.

These falling particles present a problem because even slight air currents within the supply chamber 10 can cause the particles to drift around in the chamber 10 and ultimately land back on the material 1 6. This problem is especially serious if the foreign particles land on that portion of the material 1 6 that has already passed through the web cleaning device 26 and is being advanced to the exposure station.

The supply chamber 10 is provided with a vacuum port 52 which is connected to a vacuum pump 53 (see Figure 3) for evacuating the chamber 10. Were the atmosphere within the chamber 10 maintained at a perfect vacuum, each foreign particle dislodged from the material 1 6 which did not become embedded in the web 31 would fall directly onto the collection tray 50 like a "dead weight", i.e., the particle would fall with an acceleration equal to the acceleration due to gravity (ignoring any electrostatic attraction between the material 1 6 and the foreign particles). Since it is not possible economically to maintain a perfect vacuum in the chamber 10, some amount of gas pressure will be present.

Accordingly, the term vacuum as used herein is intended to encompass a partial vacuum condition.

The maximum permissible amount of gas pressure in the chamber 10 depends upon the maximum size of foreign particle which can be tolerated on the contacting surface of the material 16, which, in turn, depends upon factors such as the desired quality of reproduction, frequency of information to be copied. This is because for a given gas pressure within the chamber 10, the larger and heavier particles, affected less by air currents, fall more readily onto the collection tray 50 than do the smaller and lighter particles. As the gas pressure is decreased (the vacuum increased), smaller and lighter particles fall onto the collection tray 50.In the case of copying video information in the form of micron sized data bits, virtually all foreign particles having a maximum dimension of the order of a micron or more should be removed from the material 1 6. (It has been found that foreign particles which have a maximum dimension in the sub-micron range do not adversely interfere with the contact printing process when the material 1 6 has a photosensitive surface comprised of a diazotype film emulsion. As disclosed in U.S. Patent Application Serial No. 891,865 on which a Continuation-in-Part U.S. Patent Application No.

11 2,250 was filed, and which was published in Research Disclosure Vol. 1 88 December 1 979 Item 18854, however, the use of a diazotype material, as well as other types of materials disclosed therein, allows acceptable quality videodisc copies to be made with less than perfect contact between the master device and the copying material. It may be the case, therefore, that higher conditions of cleanliness are required when copying onto a material that is not of a type referred to above. Through experimentation it has been determined that a vacuum in the chamber 10 of about 50 to 100 microns Hg is sufficient to permit most particles having a dimension of a micron or more to fall onto the collection tray 50.

It will be apparent that this finding is dependent upon many factors such as the type of foreign particles (in particular, the ratio of particle mass to surface area), the configuration of the supply chamber 10 itself, the threading configuration of the material 1 6, the positioning of the web cleaning device 26, and so on. For any particular supply chamber configuration, and any particular application, the appropriate vacuum level to be maintained in the supply chamber can be determined readily by trial runs at various vacuum levels.

An additional advantage obtained by evacuating the supply chamber is that the photographic speed of the copying material 16 is made more uniform. Depending upon the history of the material 1 6, the moisture content of the material 16 may vary considerably, thus affecting certain properties of the sensitized material (e.g., photographic speed). By evacuating the supply chamber, the web of material 1 6 is caused to outgas, thereby removing substantially all of the free moisture therein irrespective of the initial moisture content. Evacuating the supply chamber, therefore, eliminates a potentially troublesome variable in the process, especially for high contrast materials for which exposure is critical.

The material 1 6 leaves the supply chamber 10 and enters an exposure station through a port 54.

At this point, the surface of the material 1 6 has been generally cleaned of foreign particles and its moisture content has been normalized. It will be apparent that the web cleaning device 21 does not have to be physically located inside the supply chamber 10; alternatively, it may be located inside the exposure chamber, or elsewhere, so long as the material 1 6 is cleaned of foreign particles before the contact print exposure.

The exposure station 51 comprises three main components: (1) a source of radiation 55, (2) the exposure chamber 56 and (3) the pressure platen device 57. The material 1 6 enters the exposure chamber 56 through a port 54 and is guided over the pressure platen device 57 by a pair of guide rollers 58, 60. The exposure chamber 56 is connected to the supply chamber 10, via the port 54, and is thus maintained at a vacuum level approximately equal to that in the chamber 10.

The pressure platen device 57 shown in Figures 1, 4a and 4b has a pressure pad assembly 59 which is generally disc shaped, having a diameter of about 35 cm. This configuration matches a master record carrier 63 laminated on a glass support disc 62 that faces the pressure pad assembly 59. The support disc 62 is glued to a metal mounting ring 65 to securely hold the disc 62 in place. An "O" ring 65a provides a seal between the mounting ring 65 and the machine frame. The present invention is not limited to a particular type of master record carrier, or to a particular configuration of pressure pad or pressure platen device. The only requirement is that the pressure platen device, of whatever type, bring the copying material 1 6 and the master record carrier 63 into close contact.

The particular form of pressure platen device 57 used in the copying machine of Figures 1,2 and 3 is shown most clearly in Figures 4a and 4b.

The pressure pad assembly 59 has a fabricreinforced rubber diaphragm 66 clamped at the edge to a disc-shaped plate 68. The disc-shaped plate 68 has a port 70 which is connected by a supply hose 72 to an external air source 73. A linkage mechanism comprising four links 74, 76, 78 and 80, joined by a pair of crosslinks 81 and 83, supports the pressure pad assembly 59. The linkage mechanism is actuated by rotation of a drive shaft 82 by means of a drive arm 84 connected to an air cylinder 86. As shown most clearly in Figure 1 , the air cylinder 86 and the drive arm 84 are external to and mounted on the housing of the copying machine.In response to actuation of the air cylinder 86, rotation of the drive shaft 82 causes the four links 74, 76, 78 and 80 to drive the pressure pad assembly 59 toward the master record carrier 63. Linear guiding of the pressure pad assembly 59 is provided by a linear guide device 88. The linkage mechanism is arranged to drive the pressure pad assembly 59 to touch the underside of the copying material 16 and to urge it almost against, or in light contact with, the master record carrier 63. The rubber diaphragm 66 is then inflated by air from the source 73 to press the photosensitive surface of the material 1 6 into close contact with the information bearing surface of the master record carrier 63. The vacuum condition maintained in the exposure chamber 56 facilitates such contact.

A source of radiation 55 is then flashed to expose the material 1 6 through the master record carrier 63 with actinic radiation. The particular radiation source 55 shown in Figures 1,3 and 4a is the subject of U.S. Patent Application Serial No.

914,105 [U.K. Patent Application No. 7,919,951 (Serial No. 2,026,707)]. Briefly, referring to Figure 1, the radiation source 55 includes a reflector 89 comprised of a pyramidal arrangement of generally planar reflective surfaces formed, for example, from sheet aluminium. A source such as a xenon flash lamp 90 is disposed within the reflector 89 and positioned so that the reflective surfaces form a spherical array of virtual images of the source. It has been found that such a'radiation source satisfactorily exposes a standard 30 cm diameter master video-disc. Other sources of radiation are also useful with the copying machine as long as they adequately illuminate the particular master record carrier 63 that is to be copied.

To facilitate cooling of the radiation source 55, an air cap 92 is provided which fits over, but is spaced from, the apex region of the pyramidal reflector 89. Air is forced under pressure through an inlet port 94. Part of the air flows around the outer surface of the reflector and part provides direct cooling of the envelope of the lamp 90.

After the contact print exposure has been made, the rubber diaphragm 66 is deflated and the air cylinder 86 is actuated to lower the pressure pad 59 to its original position. The exposed material 1 6 is then advanced through a port 49 into a takeup chamber 100.

The takeup chamber 100 is isolated from the exposure chamber 56 by the sealport device 102.

Referring to Figures 5a and Sb, the sealport device 102 comprises a housing 104 having a passageway 106 through which the material 1 6 passes. The passageway 106 includes a cylindrical region 108 extending through the width of the housing and having its longitudinal axis generally perpendicular to the direction of web advancement through the passageway 106.

The outer periphery of the cylindrical region 108 is a tangent to a lower surface 110 of the passageway 106, as shown by the dotted lines in Figure 5a. A length of rubber tubing 112 is stretched inside the cylindrical region 108 and is fastened at both ends to cylindrical plugs 114, 16. The rubber tubing 112, in its uninflated state, is smaller in diameter than the cylindrical region 108 so that the web of material 1 6 does not touch the rubber tubing 112. The cylindrical plug 114 has an air port 120 through which air under pressure flows by way of an air tube 121 connected to an air source 125 to inflate the rubber tubing 112.The inflated rubber tubing 112 fills the cylindrical region 108 and presses the material 1 6 against the lower surface 110 of the passageway 106 with sufficient force and over a sufficient area to effectively seal the takeup chamber 100 from the exposure chamber 56, thereby providing vacuum isolation of the two chambers.

The purpose of the sealport device 102 is two fold. First, it is often desired to open the takeup chamber 100 in order to monitor the quality of the copied video information. To do this, a selection of the exposed material 1 6 is removed from the takeup chamber 100, processed and examined.

Without the sealport device 102, opening of the takeup chamber 100 would cause the vacuum in the exposure and supply chambers 56 and 10 respectively to be lost. In addition the material 1 6 in the exposure and supply chambers 56, 10 would absorb moisture from the air. When the takeup chamber 100 is reclosed it would then be necessary to re-evacuate the supply, exposure and takeup chambers 10, 56 and 1 00. Because of the relatively large volumes involved, and because of outgassing, the re-evacuation would consume considerable time, depending upon the capacity of the pumping system. The sealport device 102 permits the takeup chamber 100 to be isolated from the exposure chamber 56 (and thus the supply chamber 10).The takeup chamber 100 can thus be opened, material 1 6 removed, and the takeup chamber closed without substantially affecting the vacuum condition in the remainder of the machine. Then, before the sealport device 102 is reopened, the takeup chamber 100 is reevacuated through a vacuum port 122 connected to a vacuum pump 123 (see Figure 3).

Alternatively, the takeup chamber 100 could be evacuated through the port 52 in the supply chamber 10, although this procedure could be more time consuming because of path length, and could introduce dirt into the exposure chamber 56 and supply chamber 10.

The second purpose of the sealport device 102 is to prevent foreign particles which enter the takeup chamber 100 during repressurization from contaminating other sections of the machine. By evacuating the takeup chamber 100 before opening the sealport device 102, any foreign particles which have entered the takeup chamber 100 are removed or fall to the floor 1 00a of the chamber 100. Foreign particles in the takeup chamber 100 are not nearly so undesirable as in the supply or exposure chambers, however, because the contact print exposure has already been made, and subsequent processing is generally not critically sensitive to foreign particles.

Upon passing through the sealport device 102, the material 16 passes over a roller 103. A wheel 105 contacts the roller 103 and is rotated thereby.

The wheel 105 is used to drive a web footage indicator 107 (Figure 3) to allow accurate positioning of an exposure on the material 1 6.

The material 1 6 is wound onto a reel 130 mounted on a takeup reel spindle 1 32. A torque motor 19 drives the spindle 132 by a belt 21 and pulleys 23, 25 as shown in Figure 3. To advance the material 16 from the supply reel 14 to the takeup reel 130, the torques of the supply and takeup spindle drive motors 1 8 and 19 are adjusted to produce a net positive torque on the takeup spindle 132, so as to accelerate the takeup spindle 132 and takeup reel 130 while maintaining web tension constant. The web tension and the torque of the supply spindle motor 1 8 together accelerate the supply reel 14.To stop advancement of the material 1 6 while maintaining web tension at the same level, the torque of the supply spindle drive motor 1 8 is increased to decelerate the supply reel 14, and the torque of the takeup motor 1 9 is decreased.

The various machine functions may be automatically controlled by a microprocessor.

Referring to Figure 6, the machine operator enters the desired web tension, the web thickness, and the takeup and supply reel diameters. From these parameters, the microprocessor calculates the initial torque settings of the motors 1 8, 1 9 to produce the desired web tension.

Although it is the torque differential which advances the web 16, the absolute torque settings and systems inertia control the web tension. If the web tension is too low, indexing problems may occur because the advancing material 1 6 may not drive the roller 103 which, via the wheel 105, drives the web footage indicator 107. If the torque settings are too high, the web tension will be too great, with the result that the web 1 6 may slip on the supply and takeup reels causing cinch marks on the photosensitive surface of the replicate material 1 6.

Upon application of the calculated torques, the state of motion of the web is sensed (by wheel 105, for example). If the web is moving, a parameter N, hereinafter referred to as the "copy count", is decreased or increased depending upon whether the direction of web advancement is toward the takeup reel 130 or the supply reel 14, respectively. (Although the copy count N does not affect the change in torque settings at this point, it will be taken into account by the microprocessor to determine the new torque settings after a contact print exposure has been made.) The torque settings are then adjusted by a fixed, incremental value and the web motion is again sensed.This process is repeated until the web 16 is stationary. (Unless unforeseen system perturbations are present, the initial torque settings calculated by the microprocessor are such that the web 1 6 will be stationary without the need for adjusting the initial torque settings.) The copying process is now ready to begin.

The cleaner motor 40 is activated and the torque motors are unbalanced to advance the web 1 6 from the supply reel 14 to the takeup reel 130.

The duration of web advancement, and thus the length of advancement, can be determined by counting clock pulses, or monitoring edge perforations, or using the web footage indicator, etc. To stop web advancement, the torque motors are first unbalanced against the direction of web advancement and then balanced as the web comes to rest. The web portion is then sensed to determine if the web is in proper position for exposure. If not, the torque motors are again unbalanced to advance the web one way or the other to the proper position. A time delay, on the order of 100 msec, is provided after final advancement of the material 1 6 to permit the system to stabilize.

The air cylinder 86 is then activated to move the pressure pad assembly 59 toward the material 1 6. A position switch (not shown) senses when the pressure pad assembly 59 is in proper position for inflation of the rubber diaphragm 66. The diaphragm 66 is then inflated and a time delay of about 0.5 seconds is provided to permit the system to stabilize. The contact print exposure is now made by activating the flashlamp 90. A sensor may be provided to determine if the lamp has flashed. If not, the machine is automatically shut down. After the contact print exposure, the diaphragm 66 is deflated and the air cylinder 86 is deactivated to return the pressure pad assembly 59 to its initial position. After the pressure pad assembly 59 reaches its initial position, a time delay of about 0.5 seconds is provided to allow the system to stabilize.Upon sensing that the pressure pad assembly 59 has returned to its initial position, the copy count N is incremented.

The new copy count tells the microprocessor that a certain length of material 1 6 has been advanced from the supply reel 1 4 to the takeup reel 130, ,and thus allows the microprocessor to calculate the new torque settings required to maintain the desired web tension. (It will be recalled that the copy count N was incremented if the web was moving after application of the initial torque settings. Since the new torque settings calculated after advancement of the replicate material depend upon the copy count N, any unforseen system perturbations are compensated.) The invention has been described in detail with particular reference to preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the scope of the claims.For example, the web cleaning device 26 shown in Figure 1 removes foreign particles from the photosensitive (contacting) surface of the material 1 6. The web cleaning device 26 could also be arranged to remove foreign particles from the opposite surface of the material 1 6. By adding a second web cleaning unit, or by providing a different type of web cleaning unit, both surfaces of the material 16 can be cleaned. Further, depending upon the number, size and type of foreign particles in the supply roll of material 16, it may be desirable to increase the cleaning action of the web cleaning device 26. This may be done by increasing the tension of the web cleaning material.

Still further, in some applications it may be desirable to isolate the exposure chamber 56 from the supply chamber 10 as well as the takeup chamber 100 by means of a sealport device. In this case, only the exposure chamber 56 need be evacuated. In operation, the material 1 6 is advanced to the exposure station for a contact print exposure. Both sealport devices are then actuated to provide vacuum isolation of the exposure chamber 56 from the supply 10 and takeup 100 chambers. The exposure chamber 56 is then evacuated, the material 1 6 and the master record carrier 63 are brought into close contact, and the contact print exposure is made. The sealport devices are deactivated to permit the material 1 6 to be advanced for the next contact print exposure.

Where a copy of a video-disc was made using apparatus as above with a diazo copying material, the resultant copy had been found, when played back on a video monitor, to produce an unstable picture that had a low signal-to-noise ratio and that was devoid of high frequency information.

Microscopic examination of the disc revealed that the apertures, which were well-defined and generally circular or elliptical in shape on the master video-disc, had been distorted during the copying process into ill-defined, tadpole shaped images with tails, or streaks, many times the length of the original image. Moreover, the tails were generally, although not uniformly, disposed toward the centre of the copy video-disc.

It was found that relative movement of the master and the material during the contact print exposure caused the observed distortion. The cause of such movement was determined to be the result of several interactive factors. Initially, an inflated rubber diaphragm presses the master and copying material into close contact. During the contact print exposure, however, the diazo copying material emits nitrogen gas, the pressure of which counteracts the applied force pressing the master and copying material together, thereby causing the master and material to separate. Even though the amount of released gas is small, and the separation is thus only slight, the nitrogen gas acts as an efficient lubricant of the master copying material interface.While not completely understood, it is believed that the lubricated master copying material interface permits tensional and compressional forces in the rubber diaphragm to cause the replicate material to stretch and/or shrink, thereby giving rise to a major portion of the observed distortion pattern.

The above described copying machine produces satisfactory results when used with a variety of copying materials. When using a diazo copying material, however, a distortion pattern was observed in the copied image. Figure 7 shows an image array in the form of micron-sized apertures 63' on an original master record carrier 63'. The apertures 63' are greatly exaggerated in size and only one ring of such apertures is shown.

(Were the master record carrier 142 a video recording, for example, the record carrier 142 would be covered with thousands of millions of such micron-sized apertures.) Figure 8 shows the result of using the above described copying machine to contact print the information on the master record carrier 142 onto a copying material 16 in web form which is of the diazo type. The copying material 1 6 has a polyethylene terephthalate support. As can be seen, a peculiar distortion pattern has appeared which has been found to be repeatable from print-to-print.

It has been discovered that the distortion pattern is caused by relative movement of the master record carrier 142 and the diazo copying material 16 during the contact print exposure.

Such relative movement is not a simple sliding since the streaks do not extend in the same direction. Based upon the streak pattern, the relative movement is much more complicated, apparently involving both a radial component of movement and at least two non-colinear components. Moreover, the density of a copied aperture 140' is not uniform. Each copied aperture appears to be comprised of a generally circular image (corresponding to the original image on the master) having a streak, or tail, extending therefrom of greater density (assuming transparent apertures in the master and a positive diazo film system).

The observed distortion is greatly reduced by placing an isolating member between the rubber diaphragm 66 and the copying material 16.

The contact printing process begins by bringing a master record carrier 63 into close contact with a diazo copying material 16, as shown in Figure 9.

The diazo copying material 1 6 comprises a support material (e.g., polyethylene terephthalate) and a diazo emulsion. The diazo emulsion contains a diazonium salt that is highly absorptive to actinic radiation, usually in the 400 nm range. See, for example, Glafkides, Photographic Chemistry (1960), Vol. 2, at 715-726. Upon exposure to actinic radiation, nitrogen gas is formed. The diazo copying material 16, therefore, emits nitrogen gas during the contact print exposure. The released nitrogen gas forces the master record carrier 63 and the copying material 1 6 to separate slightly as shown in Figure 9. Even though this separation is slight, the nitrogen gas forms a gas bearing that acts as an efficient lubricant of the master copying material interface.

Two sources are believed to be responsible for causing relative movement of the master record carrier 63 and the copying material 1 6. First, tension forces and compression forces in the rubber diaphragm 66 are believed to be transmitted to the copying material 1 6 and to cause it to stretch or shrink relative to the master record carrier 63. Since the rubber diaphragm is disc-shaped, the tension and compression forces tend to be generally radially disposed, thereby accounting for the major part of the radial component of relative movement between the master record carrier 63 and the copying material 16.This effect would not occur when the copying material 1 6 that does not emit gas during the contact print exposure is used because the master record carrier 63 and the copying material 16 are tightly pressed together and remain so during the contact print exposure. As a result, tension or compression forces transmitted from the diaphragm 66 to the copying material 16 have little, if any, effect because frictional engagement of the master record carrier 63 and the copying material 1 6 inhibit its stretching or shrinking.

Further, the tension or compression forces are transmitted through the copying material 1 6 to the master record carrier 63, so both stretch or shrink together.

The second source of relative movement between the master record carrier 63 and the copying material 1 6 is believed to be relative thermal expansion of the copying material 1 6 and the master record carrier 63. Such thermal expansion occurs during the contact print exposure as the master 63 and copying material 1 6 absorb thermal energy from the exposing source of radiant energy. It is believed that the anisotropic nature of the polyethylene terephthalate support (due to biaxial crystal structure) of the copying material 16 causes nonuniform thermal expansion and gives rise to a major portion of the nonradial components of relative movement. Other support materials, such as cellulose acetate, may exhibit different thermal expansion properties and thus produce a different distortion pattern.

To assist in preventing relative movement of the master record carrier 63 and the copying material 1 6 caused by strain forces in the rubber diaphragm 66, an isolating member 150 (see Fig.

11) is disposed between the rubber diaphragm 66 and the master copying material sandwich. The isolating member 1 50 is flexible in the direction of the arrow 152, yet stiff (resists stretch and shrinkage due to applied strain forces) in the direction of the arrow 1 54. Being flexible in the direction of the arrow 1 52, the isolating member 150 conforms to the contour of the master copying material sandwich during the contact printing process, thereby producing uniform contact of the master 63 and the copying material 16.

Because it is stiff in the direction of the arrow 154, the isolating member 150 isolates the copying material 1 6 from tension and compression forces in the rubber diaphragm 66.

The stiffness of the isolating member 1 50 required for a particular application is believed to depend upon a combination of several factors: (1) the amount of relative movement that can be tolerated between the master record carrier 63 and the copying material 1 6, (2) the rigidity of the copying material 16 itself (a more rigid material resists stretch and shrinkage better), (3) the amount of frictional engagement between the isolating member 1 50 and the rubber diaphragm 66, and (4) the amount of frictional engagement between the isolating member 1 50 and the copying material 16.

It is believed that, at least under certain conditions, the use of an isolating member 1 50 also inhibits relative movement of the master record carrier 63 and the copying material 1 6 due to relative thermal expansion. Since the master record carrier 63 is laminated to a glass disc 62, it undergoes little thermal expansion. And since during the contact print exposure the isolating member 150 is pressed into contact with the copying material 1 6, frictional engagement of the copying material 16 and the isolating member 150 also inhibits thermal expansion of the copying material 16.

As an example of a specific material suitable for use as the isolating member 150, a sheet of brass having a modulus of elasticity of 10.3 x 1010 newtons per square metre and a thickness of 0.025 cm was cut to a circle 30 cm in diameter and attached to the rubber diaphragm 66 with a piece of double sided tape. This isolating member satisfactorily isolated a diazo copying material 1 6 from tension and compression forces in the rubber diaphragm 66.

A similar result can be achieved by an isolating member 1 50 of other materials as well, each material having a thickness inversely dependent upon the materials' modulus of elasticity. A material having a higher modulus of electricity will thus permit the use of a thinner isolation member 1 50 for a given stiffness. Use of a thin isolating member 1 50 is advantageous because a thinner isolating member 1 50 will have a better ability to conform to local thickness variations of the master copying material sandwich.For example, the brass sheet material described above, with a modulus of elasticity of 10.3 x 1010 newtons per square metre and a thickness of 0.025 cm, may be replaced by a stainless steel sheet about 0.014 cm in thickness having a modulus of elasticity of 19.3 x 1010 newtons per square metre, or a sheet of beryllium 0.009 cm in thickness having a modulus of eleasticity of 29 x 10'0 newtons per square metre. Relative to the brass isolating member, the stainless steel isolating member, because it is thinner, will have greater flexibility by a factor of about 3.5, and the beryllium will have a greater flexibility by a factor of about 7.8.

An alternative embodiment of the invention obviates the necessity for a separate isolating member 1 50 and pressure pad. Referring to Figures 1 2a and 1 2b, a pressure pad 59' includes a diaphragm 66' of material having the physical properties of the isolating member 150. The pressure pad 59' can be incorporated into the above described copying machine as a replacement for the pressure pad 59. The diaphragm 66' is fastened at the periphery of a disc-shaped plate 68' shaped to provide a fluid chamber 166. Upon the introduction of fluid into the chamber 1 66 through a port 70', the diaphragm 66' is urged outwardly to press the master record carrier 63 and the copying material 16 into close and uniform contact.Because the sheet is flexible normal to the diaphragm 66' it conforms to the contour of the master copying material sandwich thereby ensuring close and uniform contact. Because the diaphragm 66' is stiff, in the plane of the diaphragm 66' there are only insubstantial amounts of tension and compression forces transmitted to the copying material 1 6.

The result of using an isolating member having the described properties is that the distortion pattern is still present but the lengths of the streaks have been greatly reduced (to about 7 percent of the original length). Regarding the remaining streaks, it is believed that the gas bearing formed during the contact print exposure is so effective in lubricating the master copying material interface that a supersensitivity to relative thermal expansion occurs.Although it is known to filter out the infrared wavelengths of a radiation source to prevent damage from overheating, the present invention recognizes that the remainder of the streaks can be virtually eliminated by removing those wavelength ranges of the radiation source that cause relative thermal expansion of the master record carrier 63 and the copying material 1 6. Preferably, all wavelengths emitted by the source 55 that are absorbed by the master record carrier 63 or the copying material 16, apart from the radiation used for exposure, and which give rise to relative thermal expansion of the master record carrier 63 and the copying material 1 6 are filtered out.

Figures 1 3a and 1 3b show a filter 1 60 suitable for removing such radiation from a high intensity xenon flashlamp 90' mounted in the pyramidal reflector 89'. The filter 160 is of a liquid type and contains an aqueous solution of 30 gm CuSo4-5H20 and 400 ml of 15 molar NH4OH per litre of solution. Such a filter 0.6 cm in thickness has a transmission of 95 percent in the wavelength band (400 nm range) actinic to the diazo copying material, and blocks the remainder of the visible and near infrared to 1 micron with a transmission of less than 10 percent.There is an infrared leak from 1 to 1.4 microns that can be blocked with a heat-absorbing glass, although this has been found to be unnecessary when using a xenon flashlamp 90' as the exposing source 50' because of the absence of radiation in this band. It will be apparent that for other applications the aqueous solution used in the liquid filter will depend upon the wavelength range actinic to the photosensitive layer of the copying material 1 6 and upon those wavelength ranges that give rise to relative thermal expansion of the master record carrier 63 and the copying material 16. The type of filter-exposing source combination used will also depend upon the quality with which it is desired to copy information.In the case of the copying of video information, all wavelengths should be filtered out that give rise to relative thermal expansion of the master record carrier 63 and the copying material 1 6 by such an amount as to cause appreciable distortion. In less stringent applications, the amount of relative thermal expansion that can be tolerated can be greater, so long as it does not become significant.

The liquid filter 1 60 has several distinct advantages over other types of filters. By using a pump 1 63 to circulate the liquid solution through a cooling unit 1 62, even a high intensity xenon flashlamp 90' can be used without overheating the filter. Further, conventional glass heat absorbing filters have a gradual cut-off in the infrared and pass (with an attenuation of 10 to 1 5 percent) all of the visible radiation. As a result, much of the exposing radiation is not effective for the diazo exposure and is absorbed by the master record carrier 63 and the copying material 16, causing relative thermal expansion and thus image degradation. A gelatin filter (a 'Wratten' No. 34, for example ('Wratten' is a Trade Mark of Kodak Limited)) can be added to the glass heat absorber so that the combination passes only that radiation effective for diazo exposure; however, peak transmission is only about 50 percent in the actinic wavelength range, thereby resulting in an inefficient exposure. Another problem with glass heat-absorbers is that they are generally not available in sizes large enough to cover the entire exposure plane for a 30 cm diameter video-disc.

Use of a liquid filter alone reduced the streak length to about 30 percent of the original value.

Use of the isolating member 1 50 in combination with the liquid filter 1 60 substantially eliminated the streaks.

Claims (27)

1. Apparatus for use in the photographic copying of information from a master record carrier onto a copying material in web form, the apparatus comprising: an exposure chamber; means for bringing copying material and a master record carrier into contact within the exposure chamber for a contact print exposure; means for evacuating the exposure chamber; a ported takeup chamber arranged to receive the exposed copying material from the exposure chamber; and means for selectively closing the port between the exposure chamber and the takeup chamber.

2. Apparatus as claimed in claim 1 further comprising means forming a supply chamber for the copying material and having a port through which the copying material passes into the exposure chamber, and means for evacuating the supply chamber.

3. Apparatus as claimed in claim 1 or 2 further comprising a web cleaning device for cleaning foreign particles from the copying material prior to contact with the master record carrier.

4. Apparatus as claimed in claim 3 wherein the web cleaning device includes a cleaning material and means for rubbing the surface of the copying material with the cleaning material to remove foreign particles therefrom.

5. Apparatus as claimed in claim 3 or 4 wherein the web cleaning device comprises means for advancing a web cleaning material relative to, and in contact with, a surface of the copying material to remove foreign particles from such surface.

6. Apparatus as claimed in any preceding claim wherein the selective closing means comprises: a housing having a passageway which interconnects the exposure chamber and the takeup chamber and through which the copying material passes; and an inflatable element arranged to seal upon inflation the copying material against the housing and to thereby close the passageway.

7. Apparatus as claimed in claim 6 wherein the passageway includes a substantially cylindrical region having its longitudinal axis generally perpendicular to the direction of advancement of the copying material through the passageway, and wherein the inflatable element comprises an inflatable rubber tube disposed within the cylindrical region of the passageway.

8. Apparatus as claimed in claim 7 and further comprising plugs mounted in the opposed ends of the tube to seal the tube against leakage and wherein one of the plugs has a port for the admission of an inflating fluid.

9. Apparatus as claimed in any preceding claim further including means for evacuating the takeup chamber after cleaning, and before opening the selective closing means.

10. Apparatus as claimed in any preceding claim wherein means for bringing the copying materials and the master record carrier into contact comprise: a pressure pad for engaging the copying material; and mounting means for selectively moving the pressure pad into contact with the copying material to press the copying material against the master record carrier.

11. Apparatus as claimed in claim 10 wherein the pressure pad comprises an inflatable diaphragm and means are provided for inflating said diaphragm.

1 2. Apparatus as claimed in any preceding claim further comprising a planar isolating member resistant to stretch and compression in the plane thereof disposed so as to be sandwiched between the contacting means and the material to isolate the material from strain forces from the contacting means.

1 3. Apparatus as claimed in any preceding claim for use in contact printing information from a master record carrier onto a copying material that emits gas during a contact print exposure, including means for bringing the master record carrier and the copying material into contact to form a master copying material sandwich, wherein the contacting means includes an isolating member which is flexible to conform to the contour of the sandwich, yet resistant to stretch and shrinkage so that substantial tension and compression forces are not transmitted to the sandwich.

14. Apparatus as claimed in claim 12 or 13 wherein the isolating member is a thin sheet of metal.

1 5. Apparatus as claimed in claim 12, 13 or 14 wherein said isolating member is a sheet of brass about 0.025 cm in thickness.

1 6. Apparatus as claimed in any preceding claim for use in contact printing information from a master record carrier onto a copying material that emits a gas during the contact print exposure, the apparatus further comprising a source of radiation for making the contact print exposure that does not expose the master record carrier and copying material to radiation of a type that would cause significant relative thermal expansion of the master record carrier and the copying material.

1 7. Apparatus as claimed in claim 16 wherein the source of radiation comprises a primary source of radiation and an optical filter, the optical filter passing radiation actinic to a diazo copying material and absorbing those wavelengths of radiation emitted by the primary source of radiation that give rise to significant relative thermal expansion of the master record carrier and the diazo copying material.

1 8. Apparatus as claimed in claim 1 7 wherein the filter is a liquid filter containing a liquid solution consisting essentially of 30 gm CuSO45H2O and 400 ml of 1 5 molar NH4OH per litre of solution.

19. Apparatus as claimed in claim 1 8 wherein the filter is a liquid filter approximately 0.6 cm in thickness.

20. Apparatus as claimed in claim 1 and substantially as hereinbefore described, with reference to and as illustrated in Figs. 1 to 6, or Figs. 1 to 6, 1 1, 12a and 12b,orFigs. 1 to6and 11 to 13b, or Figs. 1 to6, 13a and 13b.

21. A method of removing foreign particles from the surface of a web material comprising the step of rubbing the web material with a cleaning material while in a vacuum environment.

22. A method of photographically copying information from a master record carrier onto a copying material comprising the steps of; degassing the copying material in a vacuum environment; treating to remove foreign particles from the surface of the copying material while in a vacuum environment; and photographically exposing the copying material to the master record carrier while in intimate contact in a vacuum environment.

23. The method of claim 22 wherein the copying material is maintained in a vacuum environment at all times between degassing and completion of the photographic exposure.

24. A method as claimed in claim 22 or 23 wherein the copying material and the master record carrier are brought into contact to form a master copying material sandwich by applying pressure to the sandwich through an intermediate contact member which is flexible enough to conform generally to the sandwich and which is resistant to stretch and shrinkage to prevent tension and compression forces from being transmitted to the sandwich.

25. A method as claimed in claim 22 substantially as hereinbefore described.

26. Apparatus for use in the photographic copying of information from a master record carrier onto a copying material in web form, the apparatus comprising means for bringing the copying material and a master record carrier into contact for a contact print exposure, and a planar isolating member resistant to stretch and compression in the plane thereof disposed so as to be sandwiched between the contacting means and the material to isolate the material from strain forces within the contacting means.

27. Apparatus for use in the photographic copying of information from a master record carrier onto a copying material that emits a gas during exposure, the apparatus comprising means for bringing the copying material and a master record carrier into contact for a contact print exposure, and a source of radiation for making the exposure that does not expose the master record carrier and the copying material to radiation of a type that would cause significant relative thermal expansion of the master record carrier and the copying material.