GB2034638A - A stencil printing machine - Google Patents

Abstract

A printing machine uses stencils 66 stacked one above the other from which the bottom stencil can be moved into a printing position. To speed up the working speed, the stencils 66 are divided into two stacks 6,6' one at each of two printing stations 2 and 2' respectively. In the region of each station 2,2' the bottom stencil 66 in each case can be moved into a printing position so that inwardly facing printing edges of the two stencils 66 to be printed are arranged one pattern repeat or a multiple of a pattern repeat away from one another. The machine is particularly suited for multi-colour printing, each stencil being associated with a different ink, and the web 3 only being advanced once the complete batch of stencils have printed at both stations 2 and 2', the stencils being transferred between the stacks 6,6' during each cycle. <IMAGE>

Description

SPECIFICATION A planographic machine This invention relates to a planographic machine, for use with stencils stacked one above the other from which the bottom stencil can be moved into a printing position.

Machines of this type are known per se. The stencils in such machines are either stacked vertically or arranged in a magazine, and the bottom stencil in each case is let down onto the web of material by lowering means, impressed and returned to the stack.

The invention aims to provide an improved machine of this type with improved working speed, having two stencils operating simultaneously except for the beginning and end of the batch.

According to the invention, there is provided a planographic machine, for use with stencils stacked one above the other from which the bottom stencil can be moved into a printing position, in which the number of stencils to be impressed is divided into two stacks, in which two printing stations are provided, in the region of which the bottom stencil in each case can be moved into a printing position and in which inwardly facing printing edges of the two stencils to be printed are arranged one pattern repeat or a multiple of a pattern repeat away from one another.

With this apparatus the entire batch generally operates with two stencils simultaneously, so that the output of the machine is almost doubled. The only part of the cycle which is not doubled is the first print and the final one.

An example of the invention is illustrated in the accompanying single figure drawing, which is a side view of a planographic machine of the invention in a working position.

It will be seen from the drawing that the planographic machine firstly comprises a machine frame 1, which is known per se and in which two printing stations 2 and 2' are provided. The printing stations 2 and 2' may be of any construction. In the example illustrated they are provided with suction boxes 20, so that the ink impressed through the stencils can be drawn into the incoming web of material. A web of material 3 is carried by an endlessly revolving conveyor belt or screen belt 4. The material 3 passes discontinuously through the machine and out of the end of it to apparatus for further processing, e.g. a steamer.

A supporting frame 5 for holding two stacks of stencils 6 and 6' is provided above the printing stations 2 and associated with them. All the stencils 66 to be impressed are divided into two stacks, the lower most stencil 66 in each stack being moved into the printing position. This can be done by providing lowering means in a known manner, e.g. pressure cylinders with their rams carrying the stencils. In the examples shown the stencils comprise a mother frame 60, which in each case engages around an actual stencil frame 61. However, simple stencils of appropriate construction may equally be used.

The stencils 66 in the stack are held by the frame 5 using appropriate supporting means. The stencil in the lower part is picked up and lowered onto the surface of the printing table in the appropriate printing station 2, 2', as illustrated in the drawing.

The two stacks 6 and 6' operate jointly but in different directions, so that they can form a common printing design. Where two stacks are provided one moves downwardly and the other upwardly. The stack of stencils 6' may move downwardly in the direction of the arrow A, i.e. the stencils are lowered one by one within the stack. The stacks 6 moves upwardly, i.e. after the lowering movement of the stencil 66 onto the printing position the stencil 66 is raised, whereupon the entire stack is lifted and the top stencil transferred to the stack 6'. This is done by conveying means such as conveyor belts 7. If there is an uneven number of inks, the second stack, e.g. the stack 6, is simply lifted slightly above the height of the rear stack 6'.

In order to understand the printing sequence it is important to know that the front stack 6 is associated with the front printing station 2 and the rear printing station 2' is associated with the rear stack 6'. The terms 'front' and 'rear' refer to the movement of material.

Individual stencils are defined as I to VIII..

Assuming e.g. that there are eight inks, stencils I to IV would be located above the rear printing table.

Stencil Twill be at the bottom and stencil IV at the top. Stencil I is lowered and prints in the rear table in station 2', in such a way that here e.g. an application of ink (not shown) is produced by reciprocating movement of a wiper box, wiper roller or the like, and the ink is drawn into the material by means of a suction box 20, which e.g. may have a reciprocating movement. The ink may be fed to the stencil through tubes (also not shown). The ink reservoir may be located in a wiper box within the stencil frame 61, which is replenished from time to time. These are secondary points which can be varied.

During the first printing process no printing takes place in the front station 2. Only the stencil I prints in the rear station 2'. The stencil I is the lifted out and transported to the front printing station 2: this can be done in known manner, e.g. by means of laterally arranged conveyor belts or the like. The stencil lis lowered there, and the stencil II is simultaneously lowered in the region of the rear printing station 2'.

Stencil I prints in the front portion and stencil II in the rear printing station 2', with the stencils 66 in fact printing simultaneously.

After this second printing process two stencils are lifted out; stencil II is of course only lifted high enough to enable it to be transported to the front printing mechanism 2 in the opposite direction to the material, and stencil I high enough for the stack 6 to be raised and for stencil V to be picked up by the upper chain guide 7, moved in the same direction as the material, and deposited above the stack 6', which is located above the rear printing station 2'. As already mentioned, stencil II, which has been im pressed in the rear printing station 2', has been moved to the front station 2, and stencil Ill is lowered in the rear printing station 2'. This cycle is repeated until the printing batch has been completed.The last impression is then provided by the last stencil 66 to print, namely stencil VIII; this is the last in the printing batch to be conveyed from the front station 2 to the rear station 2' and back to the front station 2.

It then prints alone, in the front station 2 only, while the rear station 2' is inoperative, in a position for waiting for recommencement of the cycle when the web of material has been moved up.

The inwardly facing edges of the two operative stencils in the stacks 6, 6' are at least one pattern repeat or a multiple of a repeat away from each other. If the repeat is e.g. 3 metres, then the movement of material is controlled so that the web 3 is advanced 3 metres the first time, 9 metres the next time, then 3 metres again, and so on alternately.

That is to say, two repeats are normally printed with the repeat between them omitted, then when the web 3 has been moved forward one repeat, the omitted piece is printed by the rear station 2' and an adjoining piece by the front station 2. Thus there are then three successive fully printed repeat portions on the web of material, so that when the web is advanced for the first time it had to be moved forward exactly the length of one repeat, so that the intermediate piece between the already printed repeats can be brought below the rear station 2' while a fresh piece of web 3 is guided below the front station 2; these pieces of web then enclose between them a repeat which has already been printed by the front station 2. Each time this printing process is completed the web has to be advanced 3 repeats, that is to say 9 metres in the example illustrated.

It is also possible to arrange the two stacks 6, 6' further away from one another, e.g. leaving 3 repeats between the printing stations. In this case, when a printing batch has been carried out, e.g.

when all 8 stencils have been impressed, the web of material is moved forward the length of one repeat 3 times. The reason for moving it forward 3 times in this way is that the gap between the printing stations 2, 2' is completely filled. The web 3 is the moved foward 5 repeats, since the large gap between the printing stations, i.e. between the stacks of stencils, has closed and an advance of the whole web is necessary so that the whole cycle can be started.

The advantage of the apparatus is in the great saving of time: there are generally always two stencils printing simultaneously, and it is only at the beginning and end of a printing batch that only one stencil is in use.

As a means of taking the entire stencils to the cleansing station, there is a possibility of carrying these away and taking them to the cleansing bath using a crane arrangement 8, and bringing a fresh set of stencils to the planographic machine.

Claims (6)

1. A planographic machine, for use with stencils stacked one above the other from which the bottom stencil can be moved into a printing position, in which the number of stencils to be impressed is divided into two stacks, in which two printing stations are provided, in the region of which the bottom stencil in each case can be moved into a printing position, and in which inwardly facing printing edges of the two stencils to be printed are arranged one pattern repeat or a multiple of a pattern repeat away from one another.

2. A machine according to claim 1, in which the printing mechanism is arranged to be under each stack when in the printing station, so that two stencils can be printed simultaneously.

3. A machine according to claim 1 or claim 2, including means whereby stencils can be moved in opposite directions within a stack operative so that one stack lowers its stencils and stencils in the other stack are raised.

4. A machine according to any one of claims 1 to 3, in which transporting means such as chain guides, conveyor belts or the like are arranged between the stacks.

5. A machine according to any one of claims 1 to 4, including means whereby web of material to be printed can be moved forward intermittently.

6. A planographic machine substantially as hereinbefore described with reference to the accompanying drawing.