EP1157832A1

EP1157832A1 - Impression device for silk-screen printing machines

Info

Publication number: EP1157832A1
Application number: EP00110347A
Authority: EP
Inventors: Nickolas Bizzio
Original assignee: TECNO-ITALIA Srl
Current assignee: TECNO-ITALIA Srl
Priority date: 2000-05-15
Filing date: 2000-05-15
Publication date: 2001-11-28

Abstract

The impression device (1; 21; 41) for so-called continuous silkscreen printing machines for ceramic tiles (9) comprises a drum (2; 22; 42) which carries screens (3; 23; 43) and in the interior of which there is mounted a blade distributor unit (4; 24; 44) for enamels (S). The drum (2; 22; 42) is motor-driven to rotate in both directions of rotation (A, B) through arcs of predefinable width, means (8; 28) being provided to support and vertically position the blade distributor unit (4; 24; 44) within the drum (2; 22; 42) at at least three predefined levels, namely an inactive first position (q₁) in which it is raised from the screens (3; 23; 43), a decorating second position in which it is in sliding contact with the screens (3; 23; 43), and an intermediate third position (q₂) in which it spreadingly dispenses the enamel onto the screens.

Description

This invention relates to an impression device for so-called continuous silk-screen printing machines, particularly for ceramic tiles.
Silk-screen printing machines of the continuous decoration type consist essentially of a frame which supports a headpiece supporting one or more screens which are either directly shaped into a drum or are mounted on a drum-shaped support structure, the drum being positioned above a conveying line along which the products to be decorated continuously advance.
The axis of said drum is horizontal and lies transverse to the direction in which the conveying line for the elements to be decorated advances. Means are provided to set the drum position in a vertical direction and in the direction of the drum axis in order to adjust the contact between the screen and the surfaces to be decorated.
To rotate said drum there is provided a motor unit activated by signals originating from a photoelectric cell or an equivalent sensing member, to synchronize the drum rotation with the passage of the products to be decorated along the underlying conveyor.
Continuous silk-screen printing machines are especially used in the ceramics sector for producing tiles, they operating with satisfactory efficiency and functional capacity.
In currently known continuous silk-screen printing machines, the drums rotate in a direction determined only by the direction of advancement of the elements to be decorated, so that the drum rotates always in the same direction. During the passage of time, with continuous use this can result in serious damage to the screens. Even if only one of the screens is damaged, the entire drum has to be replaced, even if its other screens are still usable, as the single screen cannot be reused.
Such a situation evidently affects production costs to a considerable degree.
A further problem lies in the fact that the image transferred to the surfaces to be decorated using drums with a single direction of rotation has a degree of precision which can differ from one screen to another of the same drum. In this respect, small screen mounting inaccuracies are inevitable, so that the image produced by one screen can be slightly displaced in the axial direction of the drum or be slightly rotated in the horizontal plane relative to that of another screen of the same drum, leading to evident problems especially if the same tiles, whether unfired or fired, have to be silk-screen printed several times to obtain the required decoration.
An object of this invention is to solve the aforesaid problems presented by known drum impression devices for silk-screen printing machines.
These and further objects are attained by an impression device for so-called continuous silk-screen printing machines, comprising a screen-carrying drum, in the interior of which there is mounted a blade distributor unit for enamels, characterised in that the drum is motor-driven to rotate in both directions of rotation through arcs of predefinable width, the blade distributor unit being supported such that its position can be adjusted vertically within the drum to at least three predefined levels, namely an inactive first position in which it is raised from said screens, a decorating second position in which it is in sliding contact with the screens, and an intermediate third position in which it spreadingly dispenses the enamel onto the screens.
Further characteristics and advantages will be more apparent from the description of a preferred embodiment of an impression device of the invention, illustrated by way of non-limiting example on the accompanying drawings, on which:
Figures 1a to 1d show a ceramic tile decorating cycle using a device of the invention in the single bladed version;
Figures 2a to 2d show a tile decorating cycle using a device of the invention in a first double bladed version;
Figures 3 and 4 show a decorating cycle using a device of the invention in a second double bladed version.
With reference to the figures, an impression device 1 for so-called continuous silk-screen printing machines comprises a drum 2 carrying screens 3 and having a blade distributor unit 4 for enamels S mounted in its interior.
The drum 2 is motor-driven (by relative means of known type, not shown) to rotate in both directions of rotation (as indicated by the arrows A and B) through arcs of predetermined width.
The blade distributor unit 4 is supported inside the drum and can be positioned vertically, by relative support and positioning means 8, at at least three predefined levels, namely an inactive first position, indicated by q₁ (Figure 1c), in which the blade distributor unit 4 is raised from the screens 3, a decorating second position (Figures 1a and 1b) in which it is in sliding contact with the screens 3, and an intermediate third position, indicated by q₂ (Figure 1d), in which it spreadingly dispenses the enamel S onto the screens 3.
The blade distributor unit 4 consists of at least one crosspiece 6 which is lowerly provided with a blade 7 and is supported on the frame of the silk-screen printing machine by way of a series of parallel hydraulically operated actuator cylinders 8.
In another possible version (Figures 2a-2d) of the device, indicated by 21, the blade distributor unit 24 consists of two parallel crosspieces 26a and 26b provided lowerly with respective blades 27a, 27b which are alternately moved into their utilization position. The two blades 27a and 27b have different moduli of elasticity because one blade, namely the blade 27a in this specific case, is used for the actual decoration and is hence more rigid, whereas the other, namely the blade 27b in this case, has merely to spread the enamel S over the screens, and hence is less rigid.
The operation of the device is described hereinafter firstly for the single bladed version 1 (Figures 1a-1d) and then for the double bladed versions 21 and 41 (Figures 2a-2d and 3 respectively), all relating to a decorating line for ceramic tiles 9 carried by a conveyor 10.
With reference to Figures 1a-1d, each tile 9 arriving on the conveyor 10 is sensed by a sensor 11 (normally a photoelectric cell) which feeds a pulse to the motor unit to synchronously rotate the drum 2 such that the speed at which the lateral surface of this latter moves is equal to the traversing speed of the conveyor 10. Said rotation commences (Figure 1a) when the front edge of the tile 9 coincides with the corresponding edge of the appropriate screen 3a of the drum 2. This latter then undergoes a rotation corresponding to the surface extension of the tile 9 in the direction in which the conveyor 10 moves, with the result that the upper face of the tile 9 is decorated, after which the drum 2 reverses its direction of rotation (arrow B of Figure 1d) to return to its starting position.
During the aforedescribed decoration stage (between the Figures 1a and 1b) the blade 7 is maintained in sliding contact with the inner face of the screen 3a, so accumulating excess enamel indicated by S₁ (Figure 1b). At this point, while the drum 2 continues to rotate in the direction of the arrow A, the cylinders 8 are operated to raise the blade 7 such that its lower edge lies at the level q₁. By virtue of this rotation of the drum 2 in the direction A, the excess enamel is able to pass beyond the blade, as shown in Figure 1c in which the enamel is indicated by S.
During the subsequent return of the drum 2 (the commencement of which is shown in Figure 1d), the blade 7, operated by the cylinders 8, is lowered to the intermediate level q₂, so that as the drum 2 now rotates in the direction of the arrow B, the excess enamel S is redistributed by being spread over the inner surface of the drum and hence also of the screen 3, so preparing it for the next cycle.
Likewise, for that version of the device, indicated by 21 (Figures 2a-2d, in which elements identical or similar to those of the device 1 of Figures 1a-1d are indicated by the same reference numerals plus 20), which comprises two alternately operating blades 27a and 27b (Figures 2a-2d), the blade 27a acts as the decorating blade and the blade 27b acts as the spreading blade.
More specifically, the blade 27a impresses the decoration through the screen 23a during the first arc of rotation of the drum 22 by pressing against this latter (stage between Figure 2a and Figure 2b), then, before the rotation of the drum 22 is reversed, the cylinders 28 rotate the unit 4 about the hinge point 32 (shown only in Figure 2a for simplicity) so as to deviate the blade 27a (Figure 2b), however the blade 27b also moves simultaneously rigid therewith to become positioned on the vertical diameter of the drum 22 but slightly raised in order to be able to spread the enamel S over the same screen 23a during the return arc of rotation of the drum 22.
In the second and preferred version 41 of the device of the invention (Figures 3 and 4 in which elements identical or similar to those of the device 21 are indicated by the same reference numeral plus 20), each blade 47a and 47b is operated independently by its own cylinder 48a and 48b, to be raised and lowered in the aforedescribed operating manner, to alternate in applying the decoration to the tiles 9 (blade 47a) and in spreading the enamel S (blade 47B).
From the aforegoing it is apparent that the described invention attains the stated objects. It is susceptible to modifications and variants, where falling within the same inventive concept. In particular, all details can be replaced with other technically equivalent elements.
In the practical implementation of the invention, the materials used and the forms and dimensions can be chosen at will, according to requirements, without thereby leaving the scope of protection of the following claims.

Claims

An impression device (1; 21; 41) for so-called continuous silk-screen printing machines for ceramic tiles (9), comprising a drum (2; 22; 42) which carries screens (3; 23; 43) and in the interior of which there is mounted a blade distributor unit (4; 24; 44) for enamels (S), characterised in that the drum (2; 22; 42) is motor-driven to rotate in both directions of rotation (A, B) through arcs of predefinable width, means (8; 28) being provided to support and vertically position the blade distributor unit (4; 24; 44) within the drum (2; 22; 42) at at least three predefined levels, namely an inactive first position (q₁) in which it is raised from the screens (3; 23; 43), a decorating second position in which it is in sliding contact with the screens (3; 23; 43), and an intermediate third position (q₂) in which it spreadingly dispenses the enamel onto the screens.
An impression device (1; 21; 41) as claimed in claim 1, characterised in that the means for supporting and positioning the blade distributor unit comprise hydraulically operated actuator cylinders (8; 28; 48a; 48b).
An impression device (1) as claimed in claim 1, characterised in that the blade distributor unit (4) comprises a single blade (7).
An impression device (21; 41) as claimed in claim 1, characterised in that the blade distributor unit (24; 44) comprises two blades (27a, 27b; 47a, 47b), one of which (27a; 47a) is used for the decoration and the other (27b; 47b) for spreading the enamel (S).
An impression device (21; 41) as claimed in claim 4, characterised in that the blade (27a; 47a) used for the decoration is more rigid than the other blade (27b; 47b).
An impression device (21) as claimed in claim 4, characterised in that means are also provided to rotate the two blades (27a, 27b), rigidly joined together to form a contained angle, through a determined angle about an axis (32) parallel to the axis of rotation of the drum (22).
An impression device (41) as claimed in claim 4, characterised in that the two blades (41a, 41b) are mutually independent, each having its own support and positioning means (48a, 48b).