This invention relates to screen printing and more particularly to new, or at least much improved, screen printing frame. BACKGROUND ART

In the screen printing process, an essential factor is a frame which is of rectangular configuration and made of a suitable material, often wood. To this frame is attached a tensioned mesh, the degree and eveneεs of the tension of which is of vital importance to the production of high quality screen printing.

In the infancy of the screen printing art, the mesh was of woven silk and the proceεε of producing prints from 5 original stencils was known as εerigraphy; in recent years silk mesh has been supplanted by meshes fabricated from woven plastic filamentε or woven εtainleεε εteel wire. The oldeεt and simplest method of attaching the mesh to the frame is as follows:- _Q a piece of the selected mesh is fixed into a mechanical tenεioning device which iε able to stretch the mesh in both directions until the required tension is achieved. A rigid, rectangular frame is positioned so as to underlie the tensioned piece of mesh and be in contact with it. 5 The stretched mesh is now attached to the frame by various means. In the case of wooden frames, a large number of wire staples is driven through the mesh and into the frame, while in the case of metal frames, cover strips are attached by glueing and/or screwing so as to 'sandwhich' the margins of the 0 mesh between frame and cover strips. A coat of liquid fixative, such aε polyeεter reεin, iε then applied to the mesh at the regions in which it is in contact with the frame, allowed to soak through so as to contact the frame below and left to set or cure. This procedure assists with the retention 5 of the tension and also prevents tearing of the mesh where it has been penetrated by staples or screws.

Attempts have been made to overcome the problems inherent in stretching mesh over a rigid frame by the provision of so-called "floating bar" frames, two kinds of which are illustrated in Figures A and B, now to be briefly deεcribed.

Figure A shows a two-floating bar frame comprising a rectangular frame and an unconnected pair of floating bars, all components being generally wooden. Figure B shows a similar device but having four unconnected floating bars. Usually, the mesh is stretched by initially affixing it to the frame by the above-described means; the mesh is then similarily affixed to the floating bars. By tightening the wing nuts down onto the machine screws, the meεh is thereby stretched, folds of its being formed between frame and floating bars.

The above-noted methods have been in use for many years and all have numerous shortcomingε, some of which are liεted below:-

1. All non-metal meεheε (by far the moεt commonly used kind) suffer from a phenomenon known as "cold creep and flow" which causes a loss of tension over a period of time. A mesh of good quality could be retensioned a number of times before having to be discarded. In the prior art systems, because the mesh is permanently attached to the frame and to the floating bars, if these latter are employed, means that expensive mesh - with the potential for much longer use - has to be dicarded due to loss of tension.

2. In order to re-mesh a prior art frame, all εtapleε and fixativeε must be removed and wooden frames sanded smooth. This is a time consuming and expensive procedure.

3. The mechanical tensioning devices referred to previously are expensive to purchase and require the mesh to be substantially larger than the frame. This extraneous material iε trimmed off when the meshing or re-meshing is completed. As mesh of good quality is expensive, this waste is of considerable consequence. 4. Even with the most sophisticated mechanical tensioning devices, the tension attainable in the mesh is below

the optimum. The lower the mesh tension, the more off-contact distance is necessary between the mesh and the material being printed. The lower and more uneven the tension, the less accurate the registration of different colours will be. 5. "Cold creep and flow" starts in a meshed frame immediately it is released from the tensioning device, up to 20% of the initial tension may well be lost in the first twenty minutes after tensioning. After eighteen hours, more than 28% of its original tension will have been lost and this will continue to drop each successive day.

According to my earlier Australian Patent Application No. 21158/88, the contents of which are intended to be included herein by way of cross-reference, there is disclosed a screen printing frame comprising a rectangular, expandible inner frame and a rectangular, rigid outer frame adapted to surround said inner frame in the same plane thereas; the inner frame being such as to be able to be expanded in both directions of its horizontal plane, to thereby tension a sheet of mesh εcreen printing fabric attachable thereto, without losing the essentially rigid rectangular form thereof.

Preferably, the inner frame includes four hollow side members able to be joined together, so as to constitute the said rectangular inner frame, by four right-angled corner members, the limbs of which are telescopically receivable in respective co-acting ends of the side members to thereby permit the inner frame to be expanded in the previously mentioned directions. DISCLOSURE OF INVENTION

It will be clear to the reader that my earlier invention is concerned with the development of the four floating bar frame, whereas the present invention relates to an equivalent development of the two floating bar frame embodiment.

Therefore, in accordance with this present invention there is provided a screen printing frame comprising an expandible, L-shaped inner part-frame and a rectangular.

rigid outer frame adapted to surround said inner part-frame in the same plane thereas; said inner part-frame being such as to be able to be expanded in both directions of its horizontal plane, to thereby tension a sheet of mesh screen printing fabric attachable thereto, and to two co-acting sideε of said rigid outer frame, without losing the L-shaped integrity of the said inner part-frame.

Preferably, the inner part-frame includes two hollow side members able to be joined together, so as to constitute the L-shaped, inner part-frame, by a right-angled corner member, limbs of which are telescopically receivable in respective co-acting ends of the hollow side members to thereby permit said inner part-frame to be expanded in the said directions. Ideally, anchoring means may be provided on the outwardly-facing surface of each side member and of each co-acting side of the rigid outer frame, to enable reεpective margins of said sheet of mesh screen printing fabric to be removably attached to the side members and to the said co-acting sides.

Advantageously, means may be provided to tenεionally couple these side members to corresponding sides of the rigid outer frame, the tensioning means being operable to individually displace the two side members of the L-shaped, inner part-frame towards the rigid outer frame to thereby tension the mesh.

Each anchoring means may well include a channel disposed upon the above-noted outwardly-facing surface and extending therealong, and also a co-acting locking strip receivable within the channel; this arrangement being such that, when a said margin is folded about a said locking strip and the latter then wedged into a co-acting channel of a said side member, the greater the degree of outward displacement thereof, the firmer the grip of the channel on the locking strip becomes.

Preferably, the tensioning means comprises a number

of threaded bolts each insertable through a hole in the rigid outer frame, across the εpace between the latter and the part-frame, and on into a correεpondingly internally-threaded meanε aεsociated with the inner part-frame; thus, by screwing the threaded bolts into the internally-threaded meanε, the two εide memberε of the L-shaped, inner part-frame are able to be displaced towards corresponding sides of the rigid outer frame

The right-angled corner member may comprise a pair of right-angled sub-members having a resilient insert strip

10 diεpoεed therebetween. BRIEF DESCRIPTION OF DRAWINGS

In order that a better understanding of the present invention may be gained, hereinafter will be described a preferred embodiment thereof, by way of example only and with _._ reference to the accompanying drawingε in which:-

Figure .l is a fragmental plan view of a screen printing frame according to the invention; and

Figure 2 is a fragmental cross-section taken on the line II - II of Figure 1.

Throughout the drawings, like integers are 0 referenced by the same numeral. BEST MODE FOR CARRYING OUT THE INVENTION

A screen printing frame in accordance with the present invention comprises a rigid rectangular outer frame, 5 generally indicated 1 and ideally made from tubular metal stock of subεtantially rectangular cross-section. Outer frame 1 is conventionally constructed with fixed right-angled corner inserts 2, and is of such dimensions as to be able to surround an inner, L-shaped part-frame - to be later described - in the 0 same plane thereas. The parent discloses a screen printing frame having a rectangular outer frame composed of four sides of identical cross-section; however, the rectangular, rigid outer frame 1 according to the present invention is composed of two sides 3 and 4 of simple rectangular cross-section and two sides 5 and 6 of a modified rectangular cross-section as best 5 to be seen in Figure 2.

The inner "frame", better defined as an L-shaped part-frame, is of such a construction that is able to be expanded in both directions "A" and "B", indicated by the appropriate arrows, to thereby tension a sheet of mesh screen printing fabric - indicated at 7 - attachable to the L-shaped inner part-frame and to sides 5 and 6 of the rigid rectangular outer frame 1, without losε of the L-εhaped integrity of the inner part-frame.

This expandible L-shaped inner part-frame is made up of two hollow side members 8 and 9 able to be joined together, so as to constitute the said L-shaped part-frame, by a right-angled corner member 10. Side members 8 and 9 are ideally made from tubular aluminium stock of rectangular cross-section and the two limbs of corner member 10 are telescopically receivable in respective ends of side members 8 and 9. The corner member 10 is also of rectangular cross-εection and of a εize which iε a snug, sliding fit inside members 8 and 9. Thus, the two hollow side members are not able to rotate about their longitudinal axes. The limbs, or legs of corner member 10 are of a length which will allow sufficient telecoping action without disengaging from the side members.

Thus it will be appreciated that the two hollow side members 8 and 9 can be moved apart, to the extent permitted by the lengths of the limbs of right-angled corner member 10. As previously stated, the rectangular croεs-εections of both side members and corner member prevent any tendency of the side members to rotate on the corner member. The configuration of corner member 10 is just as has been described in relation to Figure 4 of the drawings forming part of the specification relating to the parent. That is to say, the corner member is comprised of an overlying pair of right-angled εub-memberε having 'sandwiched' between them a strip of some suitable resilient material such as hard rubber,

The sub-members are guillotined from suitable

aluminium angle stock. This construction (although a solid, one-piece corner member is also envisaged) allows the εide members to be moved through different distanceε without cauεing a "toggle", or "torque" on the telescoping action. Such a requirement arises if the εheet of meεh is not cut exactly square. When one side member is moved out of its perpendicular relationship with the other, the two sub-members which make up the corner member 10 are able to move against the resilient insert to thus compensate for the "out-of-true" situation.

Figure 2 is a fragmental cross-section on line II - II of Figure 2. To enable the mesh to be removable attached to the side members 8 and 9 of the expandible L-shaped inner part-frame and to εides 5 and 6 of the rigid outer frame, the outwardly-facing surface 11 of each side member 8 and 9, and the outwardly facing surface 12 of each frame side 5 and 6 is provided with mesh-anchoring means. This anchoring meanε includeε a ridged channel 13,14 on the outwardly-facing εurface 11 and 12 respectively, and co-acting locking strips 15 and 16 receivable within channelε 13 and 14 respectively; the locking strips are the same length as their aεsociated channelε and are made of a suitable material.

When a margin of the sheet of meεh to be fitted iε folded about a locking strip and the latter then wedged into a co-acting channel, the greater the degree of outward displacement of the side member, tovard the outer frame, the firmer the grip of the channel's ridges on the locking strip becomes. Tensioning means are provided to couple side members 8,9 to corresponding sides 3,4 of outer frame 1.

A series of holes is provided in side members 8 and 9 and in frame sides 3 and 4 so that, when the L-shaped inner frame iε laid upon a flat work-surface, within outer frame 1, and spaces 17 and 18 made equal, these holes are in register. Threaded bolts 19 are inserted through the outer frame holes, across the spaces 17,18 and on into ferrules 20 loosely journalled within side members 8,9. Ferrules 20 are partially internally-threaded to take threaded bolts 19, and have

hexagonal headε 21 and a groove to receive a circlip 22; thuε are the ferrules held in place within the side members. To prevent the ferrule from rotating aε threaded bolt 19 iε εcrewed into it, side member 8,9 haε a pair of εpaced-apart landε or beads 23 on its inwardly-facing surface, between which head 21 is immobilised. On completion of aεεembly, a flexible strip of adhesive tape 24 may be placed over head 21.

It will now be appreciated that, by tightening bolts 19 into ferrules 20, side members 8 and 9 will be pulled towards respective sideε 3 and 4 of outer frame 1, this being made possible because of the teleεcoping movement ^' of the limbε of corner member 10 out of εide memberε 8 and 9.

Assembly of the invention is as follows:- a piece of mesh screen printing fabric is cut sufficiently large to accommodate the locking strips. The meεh iε laid on a flat work-εurface and the outer rigid frame laid on top of it. A locking strip 16 corresponding to one of the εideε 5,6 of outer frame 1 is placed on the extreme edge of protruding margin of mesh. The locking strip 16 and the meεh are now rolled together towardε the outer face 12 of the frame εide 5,6 thuε wrapping or folding the mesh about the locking strip. When this iε a εuitable diεtance from outer face 12, locking εtrip 16, together with the meεh folded about it, are wedgingly inserted into the co-acting channel 14. Thiε procedure is repeated for the other one of the frame sides 5 or 6, resulting in the mesh being attached to the outer frame on two adjacent sides.

Inner L-shaped part-frame is now positioned inεide outer frame 1 and the two unattached adjacent sides of the mesh similarly attached to side members 8 and 9 by means of locking strips 15 and channels 13, the part-frame being in telescopically pushed-in condition.

Threaded bolts 19 are inserted through the aligned holes and on into the pre-placed ferrules 20. As the bolts are screwed in to draw side members 8 and 9 outwardly, the mesh - wrapped about its locking strips - tightens progressively and

as this occurs, the grip of the locking stripε in their associated channels becomes intenser, eliminating all possibility of the mesh's pulling free. The tautening procedure is continued until the required tension of a set of such frames can be achieved by a final tightening of the boltε with a pre-εet torεion wrench.

The εcreen printing frame according to the preεent invention iε intended to complement that of my earlier invention, giving even better reεultε in certain applications. The preεent invention provideε a lighter, cheaper and εimpler screen print"ng frame which neverthelesε poεεesses all those advantages over and above the prior art and those conventional systems as are enumerated in respect of my earlier invention.

1. Mesh can be continually re-tensioned throughout its working life and need only to be discarded when it iε physically damaged.

2. Mesh can be tensioned to much higher levels, this giving greater registration accuracy and requiring less off-contact distance.

3. Very little more than the exact measurement of mesh is required, thus avoiding the waste of surpluε meεh required by previouε methodε.

4. The invention incorporates its own integral tensioning device, eliminating the need for costly separate mechanical tensionerε.

5. All εcreens can be tensioned to exactly the same degree for greater accuracy in multi-colour work.

6. Re-meshing is quick, clean and easy, and does not involve removing stapleε, glues and the sanding of wooden frames.

7. As the mesh iε at optimum tenεion, the meεh and squeegees will last longer as less friction is created.

8. Frames can be pre-assembled, meshed and re-meshed without the neceεεity for removing the boltε, making the task of meshing a frame more rapid.

INDUSTRIAL APPLICABILITY

The proceεεing of a mesh to make screen printing possible is achieved by many methods. All constitute attaching to the mesh a resist of ink impervious material which is open only where it is required ink will pass through the mesh, thus making the print.

All reεiεtε muεt be as flexible as the meεh itself to allow intimate contact with the subεtrate being printed. Moεt resists are extremely tough and durable. The method of attaching the mesh to the invention is obviously reversible and the mesh can, therefore, be removed from the frame as easily as it can be inserted. This is of particular value to small organisations which require only small quantities of screen printing at any one time but have a requirement to repeat that item at intervals. Hitherto, these organisations had to either retain a complete screen frame complete with its mesh and resist, which involves high cost, or remove the resist from the meεh, involving replacing it each time the same print is required.

This invention means that the low cost mesh only can be removed and retained, allowing other mesheε to be inεerted into a single frame. The removed mesh, complete with its resist can be stored and re-used as required without extra cost.

The quatity of the print after removal and replacement is equal to the original print.

This feature of the invention also enables the end user to have mesheε made by others at a distance and receive a new mesh, complete with imaged resists for immediate installation in the frame.

From the abovegoing, it will be readily appreciated by those εkilled in the art that numerous variations and modifications may be made to the invention without departing from the spirit and scope thereof as set out in the following claims.