GB1578099A

GB1578099A - Film transport means for a contact printing machine

Info

Publication number: GB1578099A
Application number: GB1967078A
Authority: GB
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1977-06-06
Filing date: 1978-05-15
Publication date: 1980-10-29
Also published as: DE2823590A1; JPS541622A; DE2823590C3; DE2823590B2

Description

(54) A FILM TRANSPORT MEANS FOR A CONTACT PRINTING MACHINE (71) We, DAINIPPON SCREEN SEIZO KABUSHIKI KAISHA, a Japanese Corporation, of 1--1 Tenlin-kitamachi, Teranouchi-agaru 4-chome, Horikawa-dori, Kamigyo-ku, Kyoto-shi, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a film transport means for a contact printing machine for printing from an original picture to a photosensitive material such as a photographic film, with particular application to contact printing machines applied to industrial photography in the photo-printing or metal processing fields.

A suction printing frame, as shown in Fig. 1 of the accompanying drawings, conventional contact printing machine is well known. In this case, there are provided a cover glass 1 and a soft sheet 2 made of rubber or the like, below it, and the soft sheet 2 has a packing strip 3 around its periphery. An original picture 4 is placed over a photo-sensitive film 5 and the two are inserted between the cover glass 1 and the soft sheet 2, and sealed by contacting the packing strip 3 with the cover glass 1.

Then, the sealed space is evacuated by a vacuum means so as to contact the soft sheet 2 tightly to the cover glass 1, thereby contacting the original picture 4 with the film 5. The original picture 4 is printed onto the film 5 by applying light through the cover glass 1.

Such a suction printing frame is used widly, but has disadvantages. Because the cover glass and the soft sheet are necessarily separated from each other when loading or unloading the original picture and the photo-sensitive film, and because the space between the cover glass and the soft sheet must be alternately evacuated and ventilated, this method involves much time labour and its operational efficiency is low.

Furthermore, the dimensions of the original picture are limited to those of the cover glass or the soft sheet.

A cylinder-type continuous printing means widely used in an office reproducers and the like, is also well-known. In this case, the original picture and the photo-sensitive film are passed around the outer surface of a transparent cylinder which has a light source inside, and the printing is performed continuously during their passage. The dimension of the original picture in the direction of travel is not restricted, but, since the photo-sensitive film is exposed in such a way that the original picture and the photo-sensitive film are wound one on another around the outer surface of the transparent cylinder, some dimensional error of the reproduction on the film in the direction of travel is unavoidable.

Accordingly, this method is unsuitable for precise applications.

For an industrial photographing machine such as a phototype plate-making camera, a machine has been developed and constructed so that a long rolled film is used as a photo-sensitive material and is continuously supplied to the printing surface, thereby reducing the loading and unloading time of the film.

In Fig. 2, there is shown a film transport means for such a plate-making camera, which comprises a suction box 6 having many suction openings, a pair of rollers 7 and 8 positioned in the front and the rear ends of the suction box 6, and an endless belt 9 having many perforations, which is stretched between the rollers 7 and 8 and is moved over the suction box 6 in contact with its outer surface where the suction openings are located.

The film 10 is placed on the belt 9 and is held by evacuating the inside of the suction box 6, and accordingly the film 10 is transported by and with the belt 9.

This transport means has many advantages: for example, its construction is relatively simple, and the film is held easily and transported positively. Thus, this means may be conveniently used for a platemaking camera using roll film.

Fig. 3 is a side view of an example of a contact printing machine suitable for application of the present invention. It includes the film transport means with a perforated endless belt described above, and will now be described in more detail.

At the front and rear ends of a suction box 11, a pair of drive rollers 12 and 13 are arranged, and a tension roller 14 is also disposed under the suction box 11. A perforated endless belt 15 is supported by the rollers 12, 13 and 14.

A pair of support shafts 16 and 17 for supporting and rolling both ends of a transparent cover sheet belt 18 having the same width as the endless belt 15, are arranged above the suction box 11. The transparent cover sheet belt 18 is contacted to the endless belt 15 by a pair of supplementary rollers 19 and 20 positioned at front and rear portions of the suction box 11.

Between the supplementary rollers 19 and 20, the transparent cover sheet 18 contacts with and is moved by the perforated endless belt 15. During transport of the belt 15, the transparent sheet 18 is sucked via the perforations of the belt 15 and the openings of the suction box 11 by evacuating the inside of the suction box 11.

A light means comprising a rod light source 21, and a light source cover 22 having a slit 23 in its bottom, is suitably positioned above the suction box 11, the light from the light source 21 radiating the suction surface of the belt 15 through the slit 23.

In this case, the original picture and the photo-sensitive film are superimposed and inserted between the perforated belt 15 and the transparent cover sheet 18. The original picture and the photo-sensitive film are held in contact and transported by the perforated belt 15 and the transparent sheet 18, and the printing is effected as they pass under the slit 23 of the light source cover 22.

Such a contact printing machine described above has not been inplemented yet, for the following reasons.

If the transparent sheet 18 is sucked under the vacuum pressure required in the contact printing operation, the contact surface of the perforated belt 15 with the suction box 11 is subjected to the same pressure as the vacuum pressure. The friction at the contact surface becomes excessive making it impossible or extremely difficult for the perforated belt 15 to move.

In the film transport means of the platemaking camera of Fig. 2, the suction pressure required is maximum when a contact screen is placed onto the film during photographing. In this case, a suction pressure of approximately 0.1 kg/cm2 (1000 mm Hg) is enough. Moreover, the film is exposed by light in the static state, and thus this machine can be implemented relatively readily by increasing the suction when exposing and decreasing the suction when transporting.

On the other hand, for the contact printing of an original picture with a film, the contact pressure should usually be at least 0.8 kg'cm2 (600 mm Hg). If the contact pressure is inefficient, a so-called "print gradation" is caused, resulting in the disappearance or enlargement of lines, distortion, and blurring. In a contact printing machine with a suction box and a perforated endless belt using the same construction as for the plate-making camera, under such a high suction pressure the belt cannot be moved at all.

However, a contact printing machine, as shown in Fig. 3, has many advantages over the conventional suction frame of Fig. 1.

For example, it increases the operational efficiency of printing, and the dimension of the original picture in the direction of travel is not restricted. Furthermore, its efficiency may readily be further increased by the provision of a film processing means as a directly following step. Accordingly, the need for a contact printing machine of this kind has been strongly felt in the field.

One solution which has been considered in order to remove the defects described above, is as follows. So as to improve the transmission of the driving force to the perforated belt from the drive rollers, the outer surfaces of the drive rollers and the inner surface of the perforated belt are made rough, thereby increasing the coefficient of friction therebetween.

However, if the inner surface of the perforated belt is roughened, tight contact cannot be obtained at the contact surfaces between the suction box and the perforated belt, and air may enter the suction box through the contact surface. Thus, the degree of vacuum in the suction box drops, and the desired suction pressure cannot be obtained.

Another solution is as follows. A pair of sprocket chains are attached along the sides of the perforated belt, sprocket wheels are mounted on the drive rollers, and thereby the belt is positively driven. However, in this case, since the perforated belt is sucked into contact with the suction box, the friction therebetween is high, and the front and rear portion of the belt move faster than the central portion, thereby causing wrinkles in the belt. Thus, air enters the suction box and the degree of vacuum falls.

The present invention seeks to provide a film transport means for a contact printing machine free from the abovementioned defects, in which sufficient vacuum contact pressure between an endless belt and a transparent cover sheet is maintained, the friction between the belt and a suction box is reduced, and an original picture and a photo-sensitive material are contacted tightly under the desired pressure and are moved by a relatively small driving force.

According to the present invention, there is provided a film transport means for a contact printing machine, comprises: a suction box adapted to be evacuated and having a substantially flat upper surface; an endless belt having an upper run adapted to move in sliding contact with the upper surface of the suction box; and a cover belt adapted to move in contact with the upper surface of the upper run of the endless belt at the same velocity at least over a portion of the upper surface of the suction box, characterized in that at least one groove is disposed in the upper surface of the suction box, substantially parallel to the direction of motion of the belts, and at least one hole is provided to communicate between the groove and the inside of the suction box, and in that a plurality of suction grooves are disposed in the upper surface of the endless belt substantially at right angles to its direction of movement, and at least one suction hole is provided in each suction groove to communicate between the suction groove in the endless belt and the groove in the suction box.

Embodiments of the present invention will now be described, by way of example, with respect to the accompanying drawings, in which: Fig. 1 is a sectional side view of a conventional suction frame; Fig. 2 is a side view, partly in section, of a conventional film transport means used in a plate-making camera; Fig. 3 is a side view of a contact printing machine suitable for application of the present invention; Fig. 4 is a fragmentary perspective view of the film transport means of the present invention; and, Figs. 5A and SB are fragmentary plan views of alternative embodiments of the endless belt having suction grooves, used in the present invention.

The present invention will now be described in terms of an embodiment applied to the contact printing machine shown in Fig. 3, which has already been described.

Referring to Fig. 4, a hollow suction box 11 is provided with a suction pipe 25 which leads to a vacuum source (not shown). The upper surface 26 of the suction box 11 is flat.

A pair of parallel longitudinal grooves 27 (only one groove is shown in Fig. 4) are formed in the side portions of the upper surface 26 of the suction box 11, though the number of the longitudinal grooves 27 may be increased if the width of the suction box 11 makes it desirable. The longitudinal grooves 27 extend between the two supplementary rollers 19 and 20 and in the longitudinal grooves 27 are provided openings 28 at appropriate intervals.

The endless belt 15, made of an airtight flexible material such as rubber, is provided with a plurality of parallel suction grooves 31 perpendicular to the direction of travel of the belt 15 at suitable intervals in the outer surface of the belt 15, the ends of each suction groove 31 leading to suction holes 32 which are arranged to connect with the longitudinal grooves 27.

The transparent cover sheet 18 is held in contact with the endless belt 15 by the supplementary rollers 19 and 20, due to their weight alone or assisted by other means such as springs. The supplementary rollers 19 and 20 are placed in the fork-like bearings 37 secured to the sides of the suction box 11 and are movable up and down.

When the air in the suction box 11 is evacuated via the suction pipe 25 by the vacuum pump, the air between the belt 15 and the transparent cover sheet 18 is exhausted via the suction grooves 31, the suction holes 32, the longitudinal grooves 27 and the openings 28, with the result that the transparent sheet 18 is drawn into contact with the belt 15 by the resulting vacuum pressure.

However, the vacuum pressure does not act to press the belt 15 against the upper surface 26 of the suction box 11 except in the vicinity of the longitudinal grooves 27, so the area of contact pressure between the suction box 11 and the belt 15 is small, and hence the friction is also small.

Consequently, the belt 15 can be readily moved by a relatively small driving force. An anti-friction surface treatment such as a coating of tetrafluoroethylene resin or the like may preferably be applied to the upper surface 26 of the suction box 11.

When the drive roller 12 is rotated by a drive means not shown, the belt 15 is moved in contact with the upper surface 26 of the suction box 11 and the transparent sheet 18 moves with it.

As the belt is moved, the suction grooves 31 and the suction holes 32 pass over the upper surface 26 of the suction box 11 in such a way that some of them always lead to the longitudinal grooves 27 thereby maintaining the vacuum pressure between the belt 15 and the transparent cover sheet 1'8.

An original picture 38 and a photo sensitive film 39 are superimposed and inserted between the belt 15 and the transparent sheet 18, and are held in tight contact and moved under the slit 23 of the light source, and thus the printing is performed accurately.

The following are details of a particular example of a contact printing machine using the film transport means of the present invention.

Width of the endless belt: 600 mm Length of the suction box: 700 mm Width and depth of the suction grooves in the belt: 1 mm Interval between the suction grooves of the belt: 50 mm Number of longitudinal grooves: 2 Suction rate of the vacuum pump: 40 1/mien Drive motor: D.C. motor 100W In a test, when two superimposed lithographic films of a polyester base 0.1 mm in thickness were used, the resulting contact vacuum pressure was at least 620 mm Hg, thereby obtaining a satisfactory contact.

Although the invention has been described with respect to the preferred embodiment shown in Figs.3 and 4, it should be understood by those skilled in the art that various modifications can be made, and therefore the scope of the invention is not to be limited by the particular embodiment described, or by the drawings.

For example, the transparent cover sheet 18 which is supported by the support shafts 16 and 17 and the supplementary rollers 19 and 20, may be an endless belt. In this case, the dimension of the original picture in the direction of travel is not restricted at all.

Also, the upper path of the transparent cover sheet 18 may conveniently be moved above the light source.

The shape of the suction grooves 31 of the belt 15 shown in Fig. 4 may also be changed, for instance, as shown in Fig. 5(a) and (b), to zig-zag suction grooves 31a or wave-form suction grooves 3lib. In these cases, the belt 15a or 1 sub moves more smoothly around the drive rollers 12 and 13 and its durability may be increased.

WHAT WE CLAIM IS: 1. A film transport means for a contact printing machine, comprising: a suction box adapted to be evacuated and having a substantially flat upper surface; an endless belt having an upper run adapted to move in sliding contact with the upper surface of the suction box; and a cover belt adapted to move in contact with the upper surface of the upper run of the endless belt at the same velocity at least over a portion of the upper surface of the suction box, characterized in that at least one groove is disposed in the upper surface of the suction box, substantially parallel to the direction of motion of the belts, and at least one hole is provided to communicate between the groove and the inside of the suction box, and in that a plurality of suction grooves are disposed in the upper surface of the endless belt substantially at right angles to its direction of movement, and at least one suction hole is provided in each suction groove to communicate between the suction groove in the endless belt and the groove in the suction box.

2. A film transport means according to claim I, wherein the cover belt is held in contact with the endless belt by supplementary rollers, by their weight alone or assisted by spring means, at front and rear portions of its contact portion with the endless belt.

3. A film transport means according to claim 1 or claim 2, wherein the cover belt is a transparent endless belt.

4. A film transport means according to any preceding claim, wherein the suction grooves of the endless belt are arranged as regularly spaced parallel straight lines.

5. A film transport means according to any of claims 1 to 3, wherein the suction grooves of the endless belt are arranged as regularly spaced zig-zag lines running parallel to each other.

6. A film transport means according to any of claims 1 to 3, wherein the suction grooves of the endless belt are arranged as regularly spaced wavy lines running parallel to each other.

7. A film transport means for a contact printing machine, substantially as hereinbefore described with reference to Figures 3 to 5B of the accompanying drawings.

8. A contact printing machine incorporating a film transport means according to any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sensitive film 39 are superimposed and inserted between the belt 15 and the transparent sheet 18, and are held in tight contact and moved under the slit 23 of the light source, and thus the printing is performed accurately. The following are details of a particular example of a contact printing machine using the film transport means of the present invention. Width of the endless belt: 600 mm Length of the suction box: 700 mm Width and depth of the suction grooves in the belt: 1 mm Interval between the suction grooves of the belt: 50 mm Number of longitudinal grooves: 2 Suction rate of the vacuum pump: 40 1/mien Drive motor: D.C. motor 100W In a test, when two superimposed lithographic films of a polyester base 0.1 mm in thickness were used, the resulting contact vacuum pressure was at least 620 mm Hg, thereby obtaining a satisfactory contact. Although the invention has been described with respect to the preferred embodiment shown in Figs.3 and 4, it should be understood by those skilled in the art that various modifications can be made, and therefore the scope of the invention is not to be limited by the particular embodiment described, or by the drawings. For example, the transparent cover sheet 18 which is supported by the support shafts 16 and 17 and the supplementary rollers 19 and 20, may be an endless belt. In this case, the dimension of the original picture in the direction of travel is not restricted at all. Also, the upper path of the transparent cover sheet 18 may conveniently be moved above the light source. The shape of the suction grooves 31 of the belt 15 shown in Fig. 4 may also be changed, for instance, as shown in Fig. 5(a) and (b), to zig-zag suction grooves 31a or wave-form suction grooves 3lib. In these cases, the belt 15a or 1 sub moves more smoothly around the drive rollers 12 and 13 and its durability may be increased. WHAT WE CLAIM IS:

1. A film transport means for a contact printing machine, comprising: a suction box adapted to be evacuated and having a substantially flat upper surface; an endless belt having an upper run adapted to move in sliding contact with the upper surface of the suction box; and a cover belt adapted to move in contact with the upper surface of the upper run of the endless belt at the same velocity at least over a portion of the upper surface of the suction box, characterized in that at least one groove is disposed in the upper surface of the suction box, substantially parallel to the direction of motion of the belts, and at least one hole is provided to communicate between the groove and the inside of the suction box, and in that a plurality of suction grooves are disposed in the upper surface of the endless belt substantially at right angles to its direction of movement, and at least one suction hole is provided in each suction groove to communicate between the suction groove in the endless belt and the groove in the suction box.