GB2356599A

GB2356599A - Screen printing apparatus

Info

Publication number: GB2356599A
Application number: GB0028514A
Authority: GB
Inventors: Stuart Mcanulty
Original assignee: ALDRIDGE PLASTICS Ltd
Current assignee: ALDRIDGE PLASTICS Ltd
Priority date: 1999-11-23
Filing date: 2000-11-23
Publication date: 2001-05-30
Anticipated expiration: 2020-11-23
Also published as: GB2356599B; GB9927516D0; GB0028514D0

Description

2356599 SCREEN PRINTING APPARATUS This invention relates to screen

printing apparatus, and particularly to such apparatus for printing on contoured articles.

Screen printing is a versatile and widely used method of printing. A stencil is formed from a mesh screen, traditionally made of silk, to which a design has been applied. A variety of processes may be used to apply the design to the mesh screen to form a stencil; the effect is to make some areas of the mesh impervious to ink. The screen is brought into close proximity to an article that is to be printed with the design. Ink is then applied to the screen and prints selectively onto the article through the pervious areas of the mesh. The mesh screen is generally either stretched in a frame, or the screen may be wrapped around a cylinder for rotary printing.

As the design is applied to the screen rather than being printed on or in the article directly, screen printing can be used with a variety of different materials, and can be used to print onto a wide range of articles. A problem arises, however, in matching the contours of the article to a substantially planar stretched screen.

A variety of techniques have been developed in an attempt to address this problem. One approach is to convey an article past a screen printing station to print one portion of a surface thereof; rotate the article and then convey it once more past the screen printing station to print another portion of the surface. Cylindrical articles may be printed on by iterating this approach. Each time that the article is moved, however, it must be re-registered with respect to the screen or screens. Therefore each movement of the article must be repeatable and precise. Such screen 2 printers tend to be highly mechanically complex and expensive. Additionally the screen printing process using these printers is multi-stage and therefore not particularly robust.

Another approach is to form the frame holding the screen with a corresponding curvature to that of the article to be printed on. Historically, this has been done either by custom making a curved holding frame or bending the frame to shape in a custom-made rigid holder.

A particular problem, not addressed by either of the above approaches, is printing on surfaces with double-curvature such as an egg has. This is impractical with the first approach outlined above also due to the mechanical complexity of rotating the article in three dimensions. It is impractical with the second approach outlined above due to the difficulty of holding the silk screen taut in double curvature.

The present invention is directed at these problems.

According to the present invention there is provided a screen printing apparatus comprising a screen for applying a design on a surface of an article, a support which acts to hold the screen, and a platform mounted in relation to the support such that one is capable of being pivoted with respect to the other during application of the design.

By pivotal movement of the support, and therefore the screen, about the platform or vice versa the orientation of the screen with respect to the article is varied, allowing the design to be applied to different portions of a contoured article.

3 The support or platform may be pivoted with respect to the platform or support respectively in two or more directions. The support or platform may be pivoted with respect to the platform or support respectively about at least one pair of substantially orthogonal directions. Preferably, during pivotal movement, there is no, or substantially no, translational movement between the support and the platform.

Using this apparatus, there is no need to move the article during printing to achieve double curvature printing. The screen can simply be pivoted with respect to the article, or the article may be pivoted with respect to the screen, in a number of directions as ink is applied to the screen.

The platform may act to hold the article. This may facilitate pivotal movement of the screen with respect to the article, with little or no translational movement therebetween. The article may be attached to a mount. The platform may register with the mounted article. This may facilitate pivotal movement of the screen with respect to the article, with little or no translational movement therebetween. The platform may be attached to the mount.

In a preferred embodiment the article is fixed to a mount, the platform is attached to the mount and comprises a frame-like structure, the platform seats around the article and the support is pivotally movable with respect to the platform allowing the screen to pivot with respect to the article to apply a design thereto.

The support may be suspended over the platform. It may then be pivoted around the point of suspension to change its orientation with respect to the platform.

4 One or more mounting members may be provided between the support and the platform, to mount the platform in relation to the support. The or each mounting member may be attached to the platform. Alternatively, the or each mounting member may be attached to the support. When a plurality of mounting members are provided, some may be attached to the platform and some to the support. Preferably, the mounting members are positioned around the circumference of the platform and/or support.

The support and/or platform may be moveably mounted on the or each mounting member. Alternatively, or additionally, one or more of the mounting members may be adjustable in height, for example by comprising a spring or damper. This may allow the spacing between the platform and the support to be varied, and to pivot in relation to the article.

The or each, or some, of the mounting members may be provided with, or may comprise, resilient biasing means. This may allow the support and/or platform to return automatically to an inoperative position after a driving force applied to cause pivoting is removed. Preferably the or each mounting member is so resiliently biased.

In a preferred embodiment four mounting members are provided attached to the platform. Each mounting member comprises a rigid support surrounded by a helical spring. The support is slideably mounted with respect to the rigid supports and is supported on the helical springs. The spacing between the platform and the support may therefore be varied without varying other aspects of their relative positions. This equipment is relatively easy and inexpensive to manufacture and assemble.

Alternatively the screen may be supported on fluid filled dampers. These may be automatically driven in order to pivot the support with respect to the platform.

The screen printing apparatus may have one or more stops. The or each, or some, of the mounting means may be provided with a stop. These limit the amount of travel of the support in relation to the platform. The support may comprise a frame-like structure. The screen may be 10 mounted within or beneath the support in use. The frame may be curved in one direction. This makes printing on articles with such a predominant curvature faster, more accurate and easier. It has a similar effect when the articles have double curvature. The frame may be curved in more than one direction. The screen may be substantially flat. Alternatively, 15 the screen may be contoured. For example, the screen may be provided with one or more facets. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a first embodiment of a screen printing apparatus according to the invention; Figure 2 is a perspective view of the screen printing apparatus of Figure 1, with an article attached to it; Figure 3 is a top perspective view of the screen printing apparatus of Figures 1 and 2; 6 Figure 4 is a side view of the screen printing apparatus of Figures 1 to 3; Figure 5 is an exploded perspective view of part of a second embodiment of a screen printing apparatus according to the invention; Figure 6 is a perspective view of an article to be printed using the screen printing apparatus of Figure 5; Figure 7 is a perspective view of the screen printing apparatus of Figure 5, and Figure 8 is a side view of the screen printing apparatus of Figures 5 and 7.

Figures 1 to 4 illustrate a first embodiment of a screen printing apparatus 1. This consists of a screen 2, a support 3, a platform 4 and a mount 5 for an article 6 (Figure 2). In this embodiment the article 6 is a rigid moulding of a plastics material, is substantially rectangular and is curved in both its longitudinal and transverse directions.

As shown best in Figure 1 the mount 5 is in the form of a printing table which has a base plate 7 and a jig 8 to which the article 6 is attached.

The base plate 7 and jig 8 are custom made and shaped to correspond to the shape and size of the contoured, moulded article 6. This enables the article to be held steadily on the base plate 7 despite any contours on the underside of the article 6.

7 The platform 4 consists of a frame having a circumferential outline of a rectangle with an outer edge that conforms to the outer edge of the base plate 7 and an inner edge somewhat larger than the outer edge of the article 6. The base plate and the frame are hinged together along a longer 5 side of the rectangle.

An elongate prop 9 is pivotally attached at one of its ends to the frame of the platform 4, and shaped at its other end to abut a prop support 10 that is formed in, or attached to, the base plate 7.

Cylindrical mounting members 11 are positioned at each corner of the platform 4. A helical spring 12 surrounds a bottom portion of each mounting member 11, as shown. The spring 12 is easily slideable along the mounting member 11.

The support 3 comprises an upper frame 13. This has substantially the same dimensions as the frame of the platform 4. The screen 2 is stretched onto a holding frame 14, which is fixed beneath the upper frame 13. The screen 2 is made from a conventional "silk screen" meshed material such as nylon or silk.

In order to start the printing process the support 3 is mounted on the mounting members 11, as shown in Figure 2. The upper frame 13 is slid onto the mounting members 11 on the platform 4 through respective holes in the frame 13 until it comes to rest on the helical spring 12. The upper frame is then secured to the platform by screwing a cap nut 11' (Figure 4) onto an externally screw-threaded outer end portion of each mounting member 11, a washer being located on the mounting member between the upper frame 13 and the nut.

8 The prop 9 is subsequently detached from the prop stop 10, allowing the platform 4 to be brought into registration with the mount 5 and the article 6 by lowering the frame of the platform 4 until it comes to rest on the base plate 7. The screen 2 is thus positioned just above the article.

An operator then uses one hand to apply ink to the screen, e.g. using a sponge. This is conveniently done by several sweeping motions along the longitudinal axis of the screen. Meanwhile the operator uses his or her other hand to apply pressure to the upper frame 13 of the support 3. The position and magnitude of the manual pressure may be varied to pivot the screen 2 with respect to the article 6. The screen may therefore be moved over and into close proximity with an area of the article to which ink should be applied. It may even touch and be stretched over the article 6 itself in this process. If so, this enlarges the area of contact between the screen 2 and the article 6 and ensures that the printed design closely follows the contours of the article 6.

The support 3, and thus the screen 2, can be pivoted to any desired angle of orientation with respect to the article 6. Ink may therefore be applied through the screen to any point along the top surface of the article.

By applying manual pressure at an appropriate portion of the upper frame 13 of the support, the screen 2 is pivoted transversely in relation to the article 6. This enables printing on the transverse curvature of the article.

By applying manual pressure at an appropriate portion of the upper frame 13 the screen is pivoted longitudinally in relation to the article 6. This enables printing on the longitudinal curvature of the article. Double curvature printing may thus be easily and quickly accomplished.

9 The manual pressure applied to the upper frame 13 of the support compresses helical springs 12 of the mounting members 11, along the portions of the frame to which pressure is applied. The springs 12 are resilient and, on release of the manual pressure, the frame 13 returns to 5 its inoperative position, wherein the screen 2 is held away from the article 6.

An adjustable stop 15 (Figure 4) may be provided next to one of the mounting members 11. This prevents over travel of the upper frame 13 of the support towards the platform 4, and prevents compression of the screen 2 against the article 6.

Figures 5, 7 and 8 illustrate a second embodiment of a screen printing apparatus. This apparatus is similar in construction and operation to that of the first embodiment, and like reference numerals have been used to describe like features. The apparatus 1 consists of a screen 2, a support 3, a platform 4 and a mount 5 for an article 6 (Figure 8). The mount 5 is again in the form of a printing table which has a base plate 7 and a jig to which the article 6 is attached. The base plate 7 and jig are again custom made and shaped to correspond to the shape and size of the article 6.

The platform 4 consists of a frame as in the first embodiment of the apparatus. The base plate 7 and the frame of the platform 4 are hinged together along longer sides thereof. Again, cylindrical mounting members 11 are positioned at each corner of the platform 4, and a helical spring 12 surrounds the bottom portion of each mounting member 11.

The support 3 comprises an upper frame 13, as before. The screen 2 is stretched onto a holding frame 14, which is fixed beneath the upper frame 13. The screen 2 is made from a conventional "silk screen" meshed material such as nylon or silk.

The screen 2 in this embodiment is not substantially flat, as in the first embodiment. The screen is itself contoured, and is provided with two facets 20 and 21 (Figure 5). This is achieved by appropriate bending and shaping of the holding frame 14, and the provision of two ribs 22 and 23 which extend between members of the frame as shown in Figure 5. The ribs allow the screen material comprising each facet to be held taut in the frame. The upper frame 13 may be contoured on its screen side, to match the contouring of the screen. The screen 2 thus comprises three parts. The first part 24 in use lies, at least initially, substantially parallel to the frame 13 and the platform 4. The second part, comprising the first facet 20, is bent out of the plane of the first part 24 towards the platform 4, and the third part, comprising the facet 21, is bent still further out of the plane of the first part 24 towards the platform 4.

Such a screen facilitates printing on double-curvature articles of complex form, such as that shown in Figure 6. As can be seen this article essentially comprises three portions 26, 27 and 28. Each portion lies in a different plane, but, due to the contouring of the screen, a part thereof may be brought into proximity with or into contact with each portion of the article for printing thereon.

To start the printing process the support 3 is mounted on the mounting members 11 as before. The screen 2 is thus positioned just above the article. An operator then uses one hand to apply ink to the screen, whilst using his or her other hand to apply pressure to the upper frame 13 of the support. The position and magnitude of the manual pressure may be varied to pivot the screen 2 with respect to the article 6. The screen may therefore be moved over and into close proximity with an area of the article to which ink should be applied. As the screen is contoured, the facets 20 and 21 can be moved into close proximity with, or indeed into contact with, the portions 27 and 28 respectively of the article. A handle 29 may be provided on the upper frame 13 to facilitate movement of the facets of the screen into proximity or contact with the article. Thus an double-curvature article which is also of complex form may be printed.

In a third embodiment (not shown) the support 3 is mounted on the platform 4 by mounting means that comprise compressed air dampers.

These may be independently driven by a pneumatic controller in response to instructions from a computer, as part of an automated screen printing process. An appropriate software package on the computer may be used to design the contours of the article. Alternatively, these contours could be scanned in using a suitable scanner.

The computer may then automatically derive a programming sequence detailing the different positions of the dampers necessary during the printing sequence. Alternatively these positions could be manually programmed in. In this case the computer may instruct the pneumatic controller to drive each damper to a position in which a certain area of the screen 2 is in close proximity to the article 6. Ink may then be applied by an automatic printing head. The dampers are thereafter driven to another position, and the process repeated.

This screen printing apparatus allows quick, convenient and repeatable printing of single or double curvature articles. It is also useful for printing on articles with irregular contours.

Claims

12 CLAIMS

1. A screen printing apparatus comprising a screen for applying a design on a surface of an article, a support which acts to hold the screen, and a platform mounted in relation to the support such that one is capable of being pivoted with respect to the other during application of the design.

2. An apparatus according to claim 1 in which the support pivots with respect to the platform in two or more directions.

3. An apparatus according to claim 1 in which the platform pivots with respect to the support in two or more directions.

4. An apparatus according to claim 2 in which the support pivots with respect to the platform about at least one pair of substantially orthogonal directions.

5. An apparatus according to claim 3 in which the platform pivots with respect to the support about at least one pair of substantially orthogonal directions.

6. An apparatus according to any of claims 2 to 5 in which during pivotal movement, there is no, or substantially no, translational movement between the support and the platform.

7. An apparatus according to any preceding claim in which the platform acts to hold the article.

13

8. An apparatus according to any preceding claim in which the article is attached to a mount.

9. An apparatus according to claim 8 in which the platform registers 5 with the mounted article.

10. An apparatus according to claim 8 in which the platform is attached to the mount.

11. An apparatus according to any preceding claim in which the article is fixed to a mount, the platform is attached to the mount and comprises a frame-like structure, the platform seats around the article and the support is pivotally movable with respect to the platform allowing the screen to pivot with respect to the article to apply a design thereto.

12. An apparatus according to any preceding claim in which the support is suspended over the platform.

13. An apparatus according to any preceding claim in which one or more mounting members are provided between the support and the platform, to mount the platform in relation to the support.

14. An apparatus according to claim 13 in which the or each mounting member is attached to the platform.

15. An apparatus according to claim 13 in which the or each mounting member is attached to the support.

14

16. An apparatus according to any of claims 13 to 15 in which the mounting members are positioned around the circumference of the platform and/or support.

17. An apparatus according to any of claims 13 to 16 in which the support and/or platform are moveably mounted on the or each mounting member.

18. An apparatus according to any of claims 13 to 17 in which one or 10 more of the mounting members is adjustable in height.

19. An apparatus according to any of claims 13 to 18 in which the or each, or some, of the mounting members are provided with, or may comprise, resilient biasing means. 15

20. An apparatus according to any of claims 13 to 19 in which four mounting members are provided attached to the platform, each mounting member comprises a rigid support surrounded by a helical spring, and the support is slideably mounted with respect to the rigid supports and is 20 supported on the helical springs.

21. An apparatus according to any of claims 1 to 12 in which the screen is supported on fluid filled dampers. 25

22. An apparatus according to claim 21 1 which the dampers are automatically driven in order to pivot the support with respect to the platform.

23. An apparatus according to any preceding claim in which the screen 30 printing apparatus has one or more stops.

24. An apparatus according to any preceding claim in which the support comprises a frame.

25. An apparatus according to any preceding claim in which the screen is mounted within or beneath the support in use.

26. An apparatus according to any preceding claim in which the screen is substantially flat. 10

27. An apparatus according to any of claims 1 to 25 in which the screen is contoured.

28. An apparatus according to claim 27 in which the screen is provided 15 with one or more facets.

29. An apparatus substantially as described herein with reference to Figures 1 to 4 of the accompanying drawings.

30. An apparatus substantially as described herein with reference to Figures 5 to 8 of the accompanying drawings.