^(S queegee and stencil move in mutually opposite directions ₎

TECHNICAL FIELD

The present invention relates to a silk screen printer and more particularly to a silk screen printer of the kind which comprises a printing table, a frame-held stencil, and a squeegee which can be displaced relative to the stencil frame, such that a first pattern formed on the stencil can be applied to print material regis¬ tered in a printing position on said table and therewith form a second pattern on said material, by forcing ink, paste, lacquer or varnish through a pattern of holes formed in the stencil and corresponding to said first pattern, with the aid of said squeegee.

The invention is concerned particularly with silk screen printers of the kind in which the printing table is flat and functions to support thin material to which the second pattern is to be applied.

Although the printer is constructed to print thin mate- rial, it will be understood that the printer is also able to print thick and stiff material, provided that said material can be held firmly by grippers provided therefor.

BACKGROUND ART

Various silk screen printer of this kind are known to the art. In addition to endeavours to increase the printing speed of such printers, endeavours have also been made constantly to enable the second pattern to be applied to print material with no positional discrepancy or with only a small positional discrepancy.

The demand for high printing speeds, e.g. speeds in excess of 1500 prints per hour, is normally counter¬ active to the demand for small positional discrepancies,

An example of one known printer equipped with a flat printing table with which a high printing speed is desired and where discrepancies can be kept low is described and illustrated in U.S. Patent Specification 4,516,495.

In view of the measures taken in the development of the present invention, mention should perhaps also be made to U.S. Patent Specification No. 3,874,289, and particu¬ larly to Figures 8 and 9 of this specification, which teaches a silk screen printer which lacks a flat print¬ ing table but in which measures have been taken to cause the squeegee to move over the stencil and relative to the stencil frame in a first direction during an actual printing sequence while the stencil and stencil-frame are arranged to move in a second direction opposite to said first direction. The second direction coincides with the speed and direction of the movement of a flat and/or an angled object. It can be assumed that the speed of the object in relation to a stand which forms

_* part of the silk screen printer is synchronized with the speed of the stencil frame relative to said stand.

SUMMARY OF THE INVENTION

TECHNICAL PROBLEMS A study of the present standpoint of techniques as described above will show that in the case of a silk screen printer equipped with a flat printing table, a frame-carried stencil, and a squeegee which can be moved relative to the stencil-frame, a qualified technical problem resides in the ability to create, with the aid of simple means, conditions which will enable movement

of the squeegee, the length of squeegee movement, and the length of stencil or stencil-frame movement to be reduced, so as to enable the printing speed of the printer to be increased drastically as a result of these shorter distances.

It will also be seen that a technical problem resides in the provision of a silk screen printer equipped with a flat printing table and intended for printing relatively thin material with which the aforesaid problem has been solved and therewith provide a simple gripping arrange¬ ment and a simple movement of print material from a laying-on position to a printing position and from a printing position to a laying-off.

Another technical problem associated with a silk screen printer of the aforesaid kind equipped with a flat printing table is one of realizing the advantages that can be gained when the printing table is able to move reciprocatingly in synchronism with the stencil and stencil-frame, and also of realizing that the gripper means need not be registered relative to the printing table solely in a known manner, but can accompany the printing table in its direction of movement during the printing sequence, and in other respects adapt the path of movement and speed of the gripping means to the aforesaid conditions.

It will also be seen that a further qualified technical problem associated with a silk screen printer having a flat printing table and intended to solve one or more of the aforesaid technical problems is one of realizing the significance of utilizing a printing table which can be raised and lowered, in a manner known per se, and which during a printing sequence can be moved to an upper position such as to bring a gripper in a registered

position when raised.

It will also be seen that a qualified technical problem is one of realizing the advantage of using known rais- able and lowerable grippers, of which one gripper is intended to take an upper position when print material is intended to pass over the printing material to a material and gripper registering position, and then lowered to a registering position in coaction with the printing table.

It will also be seen that a technical problem associated with the use of a number of grippers related to one another via endless movement-transmission means, such as chains or the like, is one of realizing the advantage that can be gained by using said grippers and said transmission means in a known manner, such that said grippers and transmission means will move intermittently and therewith enable simultaneous registration of a first gripper in the laying-on position and registration of a second gripper relative to the printing table or stand in the printing position, and to afford coaction between grippers and printing table such that the grip¬ per will finally be registered when the printing table is raised to its upper position.

Finally, it will be seen that a qualified technical problem is one of realizing the advantage that is gained when the movement path of the squeegee relative to the stand and the movement paths of the stencil-frame rela¬ tive to said stand are of equal length and adapted particularly to the length dimension of the printed pattern in the movement or transport direction.

SOLUTION

The present invention affords a solution to one or more

of the aforesaid technical problems and said qualified technical deliberations, departing from a silk screen printer which incorporates a printing table, a frame- held stencil, and a squeegee which is movable in rela- tion to said stencil-frame, such as to enable a first pattern formed on the stencil to be transferred, in the form of a second pattern, onto print material registered in position on the printing table, said material being so thin as to make it preferable for said material to rest on the printing table during the actual printing sequence.

The invention utilizes the principles applied in another basic silk-screen printer construction, namely that the squeegee shall be arranged for movement over the stencil and relative to the stencil-frame in a first direction during the actual printing sequence, while the stencil and stencil-frame are arranged to move in another direction opposite to the first direction.

With the aforesaid combination of features taken from a silk screen printer having a flat printing table and a silk screen printer adapted to print directly onto flat or right-angled objects, the present invention provides a unique coordination of printer features where the printing table is a flat printing-table and is recipro- catingly movable synchronously with the frame, and where grippers which collect print material from a laying-on position are registered with the printing table or printer stand for movement common therewith during the printing sequence.

According to one further embodiment of the invention, the printing table is capable of being raised and lowered and is intended to take an upper position during the printing sequence.

It is also proposed that the grippers can be raised and lowered and arranged to take an upper position when print material is intended to pass over the printing table to a material-and-gripper registering position.

According to a further embodiment of the invention, the speed at which the squeegee is able to move in relation to the stencil is twice as fast as its movement relative to a printer stand.

It also lies within the concept of the invention to relate a plurality of grippers one to the other, via endless movement-transmission means, such as chains, and to move the same intermittently, therewith enabling simultaneous registration of a first gripper in the laying-on position and registration of a second gripper in the printing table, this latter registration prefer¬ ably being effected when the printing table is raised to its upper position.

Finally, the movement path of the squeegee relative to the printer stand and the movement path of the stencil- frame relative to said stand are of equal distance and are preferably adapted to the length extension of the printed pattern in the transport direction.

ADVANTAGES Those advantages primarily afforded by an inventive silk screen printer reside in the possibilities of enabling a silk screen printer having a flat printing table to produce print at a speed which considerably exceeds the speed normally attainable with conventional silk screen printers having flat printing tables. It is expected, in this regard, to achieve an increase in printing speeds of more than 30%, and with normal printer sizes generat¬ ing prints in the order of 70 x 100 cm, the inventive

printer is able to achieve a printing capacity of above 2000 prints per hour.

Theoretical calculations indicate that the printing speed can be increased to values of between 50 and 80 %.

The primary characteristic features of an inventive silk screen printer are set forth in the characterizing clause of the following Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to two exemplifying embodiments at present preferred and lying within the scope of the present invention, and also with reference to the accompanying drawings, in which

Figure 1 illustrates highly schematically a first embodiment and illustrates the end of a printing sequence, with stencil, print material, gripper and printing table in a terminal position of a printing sequence; Figure 2 illustrates subsequent and necessary raising of the squeegee;

Figure 3 illustrates subsequent and necesary raising of the squeegee, frame and stencil in the form of a unit, and simultaneous lowering of the printing table; Figure 4 illustrates a later position or state, in which print-material placed in the laying-on position by means of a gripper has been displaced between stencil and printing table, which have been caused to carry out a return movement during displacement of

said print material; Figure 5 illustrates a following position of the squeegee, frame and stencil in positions coacting with the print material and with with the printing table in an upper posi¬ tion so as to enable a printing sequence to commence; Figure 6 illustrates an operational state during an ongoing printing sequence immediately before reaching the operational state illustrated in Figure 1; and

Figure 7 illustrates a second embodiment of a silk screen printer with stencil-frame, print material and printing table in the opera tional position shown in Figure 1.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED The following description is primarily intended to illustrate the function of a silk screen printer having a flat printing table and operating in accordance with the principles of the present invention, said descrip¬ tion being made with reference to Figures 1-6 of the accompanying drawings. In order to simplify the draw- ings, the devices and constructional elements required for moving the squeegee, raising and lowering the frame, raising and lowering the printing table in respective displaced gripper-bars and for registering the same in respective registrering positions have not been shown.

Mention will be made, however, in the following to those publications in which examples of such devices and constructional elements are illustrated.

Thus, as illustrated in Figure 1, the present invention is based on a silk screen printer 1 which comprises a

flat printing table 2, a stencil 4 stretched in a frame 3, and a squeegee 5 which is movable in the direction of arrow "A" relative to the frame 3 and the stencil 4, such as to transfer a first pattern on the stencil onto print material 6 registered in a printing position on the printing table 2, so as to form a second pattern on said print material. The frame 3 and the stencil 4 are arranged for movement in the direction of the arrow "R".

Figure 1 also illustrates a first gripper 7 which is operative to hold the print material 6 during a printing sequence and which, in the illustrated position, is registered relative to a printer stand 9 or to the printing table 2.

In the position illustrated in Figure 1, a second grip¬ per 8 is operative to grip print material 6a located in the laying-on station.

The grippers 7 and 8 can be moved in unison to the left in Figure 1, in the direction of the arrow "C", by an endless movement-transmission means, in the form of a chain 10. The gripper 8 is also registered relative to the stand 9 in the position illustrated in Figure 1.

Any appropriate arrangement can be used for effecting movement of the grippers and for registering said grip¬ pers in position. An example of one such arrangement is described and illustrated in U.S. Patent Specification 4,221,165, Figures 1 and 1A.

Figure 1 illustrates the mutual positions of the print¬ ing table 2, the frame 3, the squeegee 5, the print material 6 and 6a, and the grippers 7 and 8 at the end of a printing sequence, and the direction arrows "A", "B" and "C" indicate the movement of these printer

members prior to the operational state of the printer illustrated in Figure 1.

It should be noted that the various operational states of the printer illustrated in Figures 1-7 have been shown in a following sequence, so as to provide a clear¬ er understanding of the mutual positions of displacement of the printer members.

As illustrated in Figure 2, at the end of a printing sequence the squeegee 5 is raised, so as to release coaction of the stencil 4 with the print material 6, thereby enabling the print material 6 to be removed from the printing position and also to enable the print material 6a located on the laying-on station to be moved to the printing position by means of the gripper 8.

Figure 3 illustrates the operational state of the prin¬ ter immediately after the operational state illustrated in Figure 2, and the arrow "D" indicates that the frame 3, together with the stencil 4, and the squeegee 5 have been raised to a position in which print material and gripper are able to pass freely therebeneath.

The reference sign "E" indicates that the flat printing table 2 is, at the same time, caused to take a lower position, so as to enable free passage of the gripper 8 and further print material 6a immediately above the printing table, to the material printing position.

With particular reference to the positions of the print¬ er members illustrated in Figures 1 to 3, Figure 4 shows that the frame 3, together with the stencil 4, is then displaced horizontally in the direction of the arrow "F", somewhat to the right, at the same time as the squeegee 5 is displaced horizontally to the left through

an equally long distance for refilling purposes, as indicated by the arrow "G".

The arrow "H" illustrates that the flat printing table 2 is also displaced horizontally to the right. This dis¬ placement of the printing table 2 and the frame 3 (to¬ gether with the stencil 4) takes place synchronously through the intermediary of an arrangement not shown.

At the same time as the frame 3 and the printing table 2 are displaced horizontally to the right, the gripper 8 is displaced to the left, so as to take the position illustrated in Figure 4 and therewith place the print material 6a in the printing position.

It should be noted that the gripper 12 does not grip print material in this position, since new print- material shall be gripped by the gripper 12 when the gripper is registered.

The arrow "J" in Figure 5 illustrates that the frame 3, together with the stencil 4, and the squeegee 5 adopt a lower position in which the squeegee 5 urges the stencil 4 against the print material 6a, while the arrow "K" illustrates that the flat printing table 2 is now in its upper position, the same position as that shown in Figure 1, in which it supports the print material.

It will also be seen that the print material 6 has been transported to a laying-off position, by the gripper 7, the reference 13 illustrating a laying-off table.

As will also be seen from Figure 5, a registered gripper 12 now grips new print-material 6b located in the lay- ing-on station and intended for print.

Finally, Figure 6 illustrates that during an actual printing sequence, the gripper 8, the print-material 6a, the table 2 and the frame 3 are moved in unison, i.e. together, to the left, while maintaining registration between gripper 8 and the table 2, at the same time as the squeegee 5 is moved horizontally to the right in the direction of the arrow "A". The printing speed is the sum of these movements.

It should be noted in particular that during the time period in which the frame 3 and the printing table 2 are displaced from the position illustrated in Figure 3 to the position illustrated in Figure 4, at the same time as the squeegee is moved from the position shown in Figure 3 to the position shown in Figure 4, the gripper 8 will move the print material 6a from the Figure 3 position to the Figure 4 position, which means that movement of the gripper 8 and the print material 6a will take place at a greater speed from the Figure 3 position to the Figure 4 position than the events occurring during the printing sequence in Figure 6. Thus, the endless movement-transmission means shall be capable of being driven at mutually different speeds at mutually different times, determined by the positions of the frame and the table 2.

Figure 7 illustrates a modified embodiment, in which the grippers 7', 8' can be raised and lowered by means of a link-arm arrangement 15, 16, and in which the endless movement-transmission means 10' has a slightly modified configuration than the movement-transmission means described with reference to Figures 1-6.

It will be obvious that the printing table 2 is station- ary relative to the stand and that movement of the gripper 8' takes place over the printing table 2 when

the frame 3 is in its upper position, illustrated in Figure 3. This will ensure that a sufficiently large space is obtained between the frame 3 and the uppermost surface of the printing table 2, so as to enable the gripper 8 with print material 6a held thereby to pass over the printing table 2.

The operational state illustrated in Figure 7 corre¬ sponds to the operational state illustrated in Figure 1. It is evident that the embodiment illustrated in Figure 7 can take positions which conform to the positions illustrated in Figures 2-5, and also in Figure 6, al¬ though such positions are not shown, since they are considered to be obvious.

Thus, in the case of both embodiments, the printing table comprises a flat printing-table 2 which can be moved reciprocatingly in synchronism with the frame 3, and that during a printing sequence a gripper 8 opera- tive to collect print material 6a from the laying-on station is registered in the printing table for common movement therewith.

Furthermore, the squeegee 5, during a printing sequence, is arranged to move in relation to the stencil at twice the speed that it moves relative to the stand 9 of the printer. Furthermore, the grippers are related to one another via endless movement-transmission means (chains) and are moved intermittently, via machinery not shown. This enables simultaneous registration of a first grip¬ per in the laying-on station and registration of a second gripper in the printing table, when said table is raised to its upper position or the gripper is lowered to its lower position. The gripper may conveniently be provided with pins intended for coaction with holes in the printing table.

The movement path of the squeegee in relation to the printer stand and the movement path of the frame rela¬ tive to said stand are mutually equal and adapted to the length extension of the print pattern in the transport direction.

A silk screen printer provided with a raisable and lowerable gripper is described and illustrated in Euro¬ pean Patent Specification 0 109 598.

A silk screen printer having a raisable and lowerable printing table is illustrated and described in U.S. Patent Specification 3,384,010.

It will be understood that the invention is not restric¬ ted to the aforedescribed exemplifying embodiments thereof and that modifications can be made within the scope of the following claims.