Production of a Stencil

TECHNICAL FIELD

The present invention relates primarily to a method of producing a stencil for use in stencil printing machines for applying to print material a print pattern which corresponds to a pattern formed in the stencil, or for producing an offset plate consisting of electrically insulating material, such as a polyester plate, adapted for use in an offset printer so as to be able to apply to print material a print pattern which corresponds to a pattern formed in the offset plate.

For the sake of simplicity, reference is solely made to a "stencil" in the following description, although the person skilled in this art will be aware of the procedures that are required to enable the invention to be applied adequately in producing a stencil or an offset plate.

The present invention thus relates to a method and apparatus for producing a stencil or the like.

Stencils of the kind to which the present invention refers consist of a stencil frame and a carrier substrate, in the form of a cloth, which is stretched in the frame and which incorporates a pattern.

The invention is effected with the aid of digital information relating to positioning of the pattern and its form on the stencil and stored in computer equipment.

Also used are means connected to said computer equipment and functioning to transfer said pattern-related digital informa¬ tion to a light-sensitive layer applied to the carrier substrate.

BACKGROUND ART

Several different methods of producing a stencil for use in stencil printing machines and different methods for producing offset plates for offset machines are known to the art.

With regard to stencil printing machines, it is known to produce a stencil on the basis of a carrier substrate, such as a cloth stretched in a stencil frame and coated with a special layer of emulsion which forms a light-sensitive layer.

Exposure is effected by illuminating the emulsion layer with a projected image, wherewith illuminated parts of the emulsion layer harden and non-illuminated and non-hardened parts form the pattern, and wherein the non-illuminated and non-hardened parts of the emulsion layer are washed away in a subsequent developing process.

The resultant stencil thus includes exposed pattern-associat¬ ed parts through which printing paste is able to pass during the printing sequence.

It will be apparent that a method of the aforedescribed kind requires the use of projector equipment, a film as the original, and strong lighting, and that a stencil-producing method of this kind is time-consuming and its associated equipment expensive.

However, the use of large projector equipment enable large stencils to be produced, such as stencils in the order of 2 x 3 metres.

It is also known when producing stencils to illuminate a carrier substrate onto which a light-sensitive layer or a layer of emulsion has been applied with laser beams generated by laser equipment and to produce the pattern concerned by

guiding movement of the laser beams along the cloth.

Practical application indicates that the laser method is well-suited for smaller stencils with limited print patterns, small dimensions with regard both to cloth and pattern image, although the requisite laser equipment and control (guide) unit demands a relatively high investment.

With regard to the production of polyester offset plates in particular it is known to coat the polyester material with a light-sensitive emulsion and to expose the emulsion with a pattern in essentially the same way as that described above with reference to stencils for stencil printing machines, and to develop the thus exposed plate so as to form the pattern.

SUMMARY OF THE INVENTION

TECHNICAL PROBLEMS

When considering the present standpoint of techniques, it will be seen that a technical problem resides in providing with the aid of simple means conditions whereby large stencils can be produced in a simpler manner, i.e. more quickly and with good resolution without requiring the use of relatively large projector equipment or laser equipment.

A technical problem also resides in using to this end a unit which is associated with its use in another technical field and to realize the minor constructional changes that are required to adapt said unit for application in the manner intended here.

When considering the present standpoint of techniques as described above, it will also be seen that a technical problem resides in realizing the possibilities that are afforded when a modified laser printing unit is used as a means for transferring digitally stored pattern-related

information to a light-sensitive layer applied to a carrier substrate.

It will also be seen that a technical problem is one of realizing those advantages that are afforded in the manufac¬ ture of large stencils when the pattern is divided into different mutually parallel sections, each having a width corresponding to the effective width of one (or more) laser printing units, and to therewith produce section after section until the whole of the pattern has been produced on the carrier substrate.

It will also be seen that another technical problem is one of realizing the significance of and the advantages associat- ed with allowing the laser printing unit to be movable backwards and forwards over a light-sensitive layer of emulsion, and by transferring section by section of the complete pattern digitally with the aid of computer equipment as a light-absorbent layer, for instance by applying a thin layer of carbon powder over the emulsion layer.

It will also be seen that a technical problem resides in realizing the advantages that are associated with the application of carbon powder subsequent to requisite exposure and fixation, and by washing away the non-hardened emulsion located beneath the carbon powder without soiling the surroundings to any significant extent.

A technical problem also resides in the provision of means which will enable carbon powder to be removed after fixing with the aid of subpressure prior to washing away solely non- hardened emulsion.

It will also be seen that a technical problem is one of realizing the significance of using an earlier known laser printing unit for the aforesaid purpose and for solving one or more of the aforesaid technical problems, and to modify

this laser printing unit so that, to this end, a heating device normally used with the laser printer can be discon¬ nected and an electrifying wire or roller applied to the opposite side of the carrier substrate or the cloth in relation to the laser printer in general.

It will also be seen that a technical problem resides in the ability to realize the significance and the simplicity of using two or more such modified laser printing units simulta- neously, said units being conveniently laterally related and arranged for common movement relative to the layer-coated carrier-substrate.

It will also be seen that a technical problem is one of realizing the significance of supplementing the laser printing unit with position-determining means and allocating position-determining means to said unit so as to enable positioning in relation to registration to be controlled by a controlling unit, such as registration and positioning in relation to an adjacent part-pattern.

It will also be seen that a technical problem resides in realizing the significance of enabling the carrier substrate to move for registration between an already applied-related part-pattern and a part-pattern which is to be applied.

SOLUTION

With the intention of solving one or more of the aforesaid technical problems, the present invention relates to a method and to apparatus for producing a stencil or an offset plate which is adapted to enable a pattern on the stencil to be transferred to print material as a print pattern by means of a printing process, wherein the stencil comprises initially a carrier substrate with a carrier-substrate associated pattern, while using digital information relating to the pattern and stored in computer equipment and while using

means for transferring said digital information to a light- sensitive layer applied on the carrier substrate.

With a starting point from this known technique, it is proposed in accordance with the present invention that the computer equipment is connected to at least one modified laser printing unit, and that the printing unit is moved relative to the layer-coated carrier substrate while said unit applies to the light-sensitive layer a light-absorbent layer corresponding to said pattern, whereafter an exposure and a developing process may be carried out in a known manner to form said stencil.

According to preferred embodiments, two or more modified laser printing units are mutually coordinated and arranged side-by-side for common movement relative to the layer-coated carrier substrate.

It is also proposed that at least one laser printing unit shall be assigned position-determining means so as to provide precise positioning and registration, for instance relative to a part-pattern, through the medium of a position-regulat¬ ing means or control unit.

In this regard, it is proposed that the carrier substrate can be moved by the position-regulating means so as to obtain precise registration between a part-pattern that has already been applied and a part-pattern which is to be applied.

It is also proposed that the laser printing unit can be moved in a horizontal direction.

ADVANTAGES

Those advantages that are primarily afforded by an inventive method and inventive apparatus reside in the provision of conditions whereby a large stencil (or a large offset plate)

can be produced in a simple and inexpensive manner and also above all relatively quickly with a resolution of about 600 dpi, with the aid of a principly known, but slightly modified laser printing unit for applying to a carrier substrate coated with light-sensitive material a light-absorbing and pattern-forming layer by enabling the laser printing unit to move along the carrier substrate and therewith apply the complete pattern image in consecutive sections or part- images, said completed pattern image being exposed and developed after all pattern sections have been applied and a complete pattern has been formed.

The primary characteristic features of an inventive stencil- producing method are set forth in the characterizing clause of the following Claim 1, and the primary characteristic features of inventive apparatus are set forth in the charac¬ terizing clause of the following Claim 6.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of a stencil-producing apparatus according to an embodiment at present preferred and having features significant of the present invention will now be described in more detail with reference to the accompanying drawing, in which

Figure l is a perspective view of a horizontal stencil which includes a cloth stretched in a frame and coated with a light-sensitive layer, said stencil being shown in the process of a part-pattern allocated light-absorbing layer being applied by a modified laser printing; and

Figure 2 is a sectional view of a schematically illustrated laser printing unit used in the procedure illus¬ trated in Figure 1.

DESCRIPTION OF AN EMBODIMENT AT PRESENT PREFERRED

Figure 1 is thus a perspective view of an inventive arrange¬ ment which includes a horizontally positioned stencil frame 1 and equipment for applying a light-absorbing, pattern- forming layer section-by-section onto a light-sensitive layer.

Although the following description refers to the application of the light-absorbing, pattern-forming layer section-by- section until the complete pattern has been formed, it will be understood that when pattern images have a width which is smaller than the width of the laser printing unit used, the entire pattern can be accommodated in one single section.

In producing printed articles with the aid of a stencil that can be used in a stencil printing machine, the stencil comprises a frame 1 in which there is stretched a cloth 2 serving as a carrier substrate and a pattern 4 (A, A) formed in the cloth 2.

The characteristic features of the invention are illustrated in the following description with reference to a large frame and to a large pattern (A, A).

The cloth 2 is first coated with a light-sensitive layer or a layer of emulsion 3 of earlier known composition with the aid of means not shown.

It is also necessary to apply a pattern image (A, A), referenced 4, which can be created by coating the surface areas applicable to the actual pattern image 4 with a light- absorbing layer 5 and by allowing the surface regions 5'

around said pattern image 4 to remain exposed in relation to the underlying layer 3.

In the case of a negative pattern image, it will be under- stood that the image 4 may be exposed while remaining surfaces 5' are covered with the light-absorbent layer 5.

The light-absorbing layer 5 is thus intended to prevent hardening of the underlying emulsion 3 within and beneath those surface regions in which the light-absorbing layer is located and to cause hardening of said layer within those surface regions that lack a covering light-absorbent layer, in a subsequent exposure process effected with the aid of lighting.

In a following developing process, the layer 5 is washed away together with the non-hardened emulsion 3 located therebe- neath so as to produce the pattern image 4 (A, A), which is surrounded by hardened emulsion sections, wherein in a subsequent printing process ink paste is able to pass through the cloth within those regions thereof in which the meshes of the cloth are open, i.e. outwardly of (or inwardly of) the pattern image 4 (A, A).

In accordance with the present invention, a stencil is produced with the aid of computer equipment 10 and with the aid of digital information relating to the pattern and stored in the computer equipment principly in a known manner. The computer equipment 10 is connected by a cable 11 to means which enable the digital information to be transferred to form a light-absorbent layer 5 over the light-sensitive layer 3 earlier applied to the carrier substrate or to the cloth 2.

According to the invention, the computer equipment 10 is connected to at least one modified laser printer unit 20.

The laser printer unit 20 is fixed to a frame part 30 and can be moved reciprocatingly in the direction of the arrow P with the aid of movement transmitting means not shown. Movement of the laser printer unit to the left in Figure 1 will result in application of the light-absorbing layer, whereas movement in the opposite direction is merely a return movement.

The laser printer unit 20 can thus be moved relative to the layer-coated 3 carrier substrate 2 through the medium of a frame part 30 and a stand part 31 while each movement to the left will result in the laser printer unit applying to the surface of the light-sensitive layer or to the surface of the carrier substrate a section of a light-absorbent layer relating to the complete pattern.

The means and procedures that follow in order to expose and develop the stencil are well known to the person skilled in this art and have not therefore been shown.

The invention also enables two or more similarly modified laser printer units 20, 20' to be mounted side-by-side in said frame part 30 for common movement in the direction P relative to the layer-coated carrier substrate.

The laser printer unit 20' is shown in broken lines in Figure 1.

According to the present invention, at least one laser printer unit, such as the laser printer unit 20, at least when this unit is to apply the light-absorbent layer 5 on its own, is provided with an edge-related device which functions to position the laser printer unit 20 in relation to an earlier applied part-pattern for instance, this positioning being effected with the aid of a sensor 22 connected to the computer equipment 10 by a cable 11a.

In this way, the left-hand edge of the laser printer unit 20

for an applied part-section can be positioned precisely adjacent the right-hand edge of the adjacent part-section that has already been applied.

It is especially proposed that the carrier substrate 2 is capable of being moved into registration by a movement generating arrangement 41, 42, 43, 44, such as into regis¬ tration between an already applied part-section and a part- section which is to be applied. Alternatively the laser printer unit 20 may be arranged for movement in the frame part 30 or in the stand part 31 both horizontally and transversely to the direction of the arrow P.

Another alternative is to allow the stand part 31 to coact with a movement generating means 51 or 52.

The arrangement can be controlled with the aid of circuits in the computer equipment 10.

The laser printer unit used may be a laser printer marketed by Texas Instruments, U.S.A., under the trademark "micro¬ Laser" Pro 600.

The modification or supplementation required to enable such a printer unit to be used in accordance with the invention resides in connecting or removing a heating coil intended for burning or baking-in powdered carbon.

It is also necessary to remove a de-electrifying roller, although measures may be taken to place this roller on the opposite side of the carrier substrate.

The thus modified laser printer unit is placed in the frame part 30.

If not removed, the de-electrifying roller is placed in the frame part 30' on the opposite side of the carrier substrate

in relation to the laser printer unit 20.

Although not described in detail, means are provided for moving the laser printer unit 20 and the de-electrifying roller (or the wire) in unison.

Figure 2 is a schematic sectional view of the laser printer unit 20 in the position shown in Figure 1.

Shown in Figure 2 is a drum 25, a cleaning roller 26, a charge indicator 27, a pattern image exposing region 28, a developing region 29, and a region 25a in which the pattern is transferred to the layer 3, and a de-electrifying roller or wire 25b placed beneath the cloth 2.

Since the principle of a laser printer unit is known to the art, the unit will not be described in more detail here.

By laser printer unit is meant any type of unit which utilizes photo-electrographics and/or is based on the ability of producing a pattern with the aid of electromagnetic fields.

Such "laser printer units" may also include light-emitting diodes.

By light-absorbing layer is also meant light-reflecting layers or other means which provide the function of a photomask.

It will be understood that the invention is not restricted to the aforedescribed and illustrated embodiment and that modifications can be made within the scope of the inventive concept as defined in the following Claims.