Title of Invention

"A FRAME FOR SUPPORTING A PRINTING SCREEN AND A PRINTING SCREEN UNIT THEREOF"

Abstract

A frame for supporting a printing screen comprising a sheet having two pairs of opposite edges, at least sections of which include attachment elements, the frame comprising: first and second pairs of interface members attachable to the attachment elements at each of the pairs of opposite edges of the sheet, wherein the interface members each include an attachment section which provides for attachment to the attachment element at a respective edge of the sheet, and an engagement section for engagement to a tensioning mechanism; and corner pieces coupling adjacent ends of each of the interface members, such as to define a frame which is substantially rigid when handled, but allows for outward movement of the respective pairs of interface members by a tension applied by tensioning mechanisms to the engagement sections of the interface members.

Full Text

The present invention relates to a frame for supporting a printing screen and a printing screen unit thereof. The present invention relates to printing screens, often alternatively referred to as stencils or masks, for use in the screen printing of workpieces, typically electronic substrates, such as circuit boards and components, frames therefor, and printing screen units. In one known printing screen unit, the printing screen comprises a thin, stiff . metal sheet, typically of stainless steel or brass, which includes a plurality of printing apertures which define a pattern for the printing of a printing medium, typically solder paste. The printing screen is mounted to a rectangular frame by a flexible, perforate sheet, typically a woven mesh of polypropylene or stainless steel strands, which acts to tension the printing screen. Whilst the above-described printing screen unit has been well used, the unit does have a number of drawbacks, notably in being expensive to fabricate, and not allowing for the printing screen to be detached from the frame without permanently damaging the perforate sheet. In another, more recent printing screen unit, the printing screen is a demountable printing screen which comprises a thin, stiff metal sheet, typically of stainless steel, which includes a plurality of printing apertures which define a pattern for the printing of a printing medium, typically solder . paste, and a plurality of fixing apertures at opposite edges thereof. The printing screen is mounted to a frame by mechanical tensioning mechanisms which engage the fixing apertures in the printing screen and act to tension the printing screen, with the tensioning force typically being provided by hydraulic, pneumatic or spring means. WO-A-93/25061 discloses one such printing screen unit in which the printing screen includes a plurality of elongate slots, as the fixing apertures, along each of opposite edges thereof, and the tensioning mechanisms each Include a sol: of tooth which engage the slots at respective ones of the opposite edges of the printing screen to tension the printing screen, with the tensioning mechanisms being configured to draw respective ones of the opposite edges of the printing screen over respective supporting edges of the frame. GB-A--2364(J61. discloses another such printing screen unit in which the printing screen includes n plurality of first, fixing apertures along each of opposite edges thereof which arc engaged by respective tensioning mechanisms, and a plurality of second, Hexing apertures along each of the opposite edges thereof which extend inwardly of the respective fixing apertures and provide for regions of increased flexibility, with the tensioning mechanisms being configured to draw respective ones of the opposite edges of the printing screen over respective supporting edges of the frame. These printing screen units, in not: requiring the permanent attachment of a printing screen to a frame, advantageously allow for printing screens to be stored separately and mounted on frames as and when required, (.'hereby being cheaper and facilitating use. Those printing screen units do, however, still suffer from a number of significant drawbacks. In particular, the edges of the printing screens are required to be more flexible than the main body thereof, and, as such, are more prone to damage during handling and mounting. This is particularly the case as the printing screens are stored as unsupported sheets. Also, as the printing screens are very thin, typically having a thickness of from about 0.1 to 0.25' mm, the edges thereof arc razor sharp, which can lead to personal injury to a user If not handled with utmost care. Further, the printing screens are restricted to being fabricated from materials which have the necessary strength to allow for direct tensioning by tensioning mechanisms. Yet: further, the printing screens require specific manufacturing techniques, such as etching, electroforming and punching, and thereby limit: thr scope for mass fabrication. It is therefore an aim of the present invention to provide a printing screen unit: which at: least: partially overcomes the above-mentioned problems associated with existing printing screen units, and printing screens and frames for such printing screen units. In one aspect:, it is an aim of the present invention to provide a demountable printing screen which provides improved resistance to damage during handling and mounting. In another aspect, it is an aim of the present invention to provide a demountable printing .screen which is safer to handle. In a further aspect:, it: is an aim of the present invention to provide a printing screen unit which allows for use of printing screens from a wide range of materials, including plastics. In a yet further aspect, it is an aim of the present invention to provide a printing screen unit which can he manufactured cheaply and simply. In one aspect the present invention provides a printing screen, comprising a sheet, at least sections of at least one pair of opposite edge;; of which are folded such as to define attachment: elements. Preferably, the attachment elements are each folded inwardly such as to enclose an acute angle with a major surface of the sheet. In one embodiment at least ones of the attachment elements each comprise a plurality of projections spaced along a length thereof. Preferably, the projections comprise rectangular projections. Preferably, the projections of ouch attachment clement define- a castellated structure!. In another embodiment at least ones of the attachment elements each comprise a single, continuous, attachment element, and the sheet includes a plurality of flexing apertures in spaced relation along each of tho opposite edges thereof in zones overlapping fold lines of the respective folds. In one embodiment the sheet has two pairs; of opposite edges, and at least sections of each of the pairs of opposite edges of the sheet are folded such as to define attachment elements. In one embodiment at least ones of the edges of the sheet have an attachment element extending along substantially the length thereof. In another embodiment at least ones of the edges of the sheet have an attachment element extending along part of the length thereof. Preferably, the part comprises n mid part. In a further embodiment al: least ones of the edges of the sheet have attachment elements extending along parts of the length thereof. Preferably, the parts comprise end parts. In one embodiment the sheet includes a pattern of printing apertures which define a pattern of deposits to be printed thereby. In another embodiment the sheet is n blank and includes no printing apertures therein. In one embodiment the sheet comprises a metal sheet. In anotherr embodiment the shoot comprises a plastics shod:. In another aspect the present invention provides a printing screen, comprising n sheet, at: least sections of at least one pair or opposite edges of which comprise a plurality of projections spaced along a length thereof. Preferably, the projections comprise rectangular projections. Preferably, the projections define a castellated structure. In one embodiment the sheet, includes a pattern of printing apertures which define a pattern of deposits to be printed thereby. In another embodiment the sheet is a blank and includes no printing apertures therein. In one embodiment the shoot comprises a metal sheet. In tinothor embodiment, the sheet comprises a plastics sheet. In a further aspect: the present invention provides a printing screen unit, comprising: a printing screen, comprising a shect> at: least: sections of at least one pair of opposite edges of which include attachment elements; and at least one pair of interface members attachable to the attachment, elements at the at least one pair of opposite edges of the sheet. Preferably, the at least sections of the at least one pair of opposite edges of the shoot are folded such as to define attachment elements. More preferably, the attachment: elements are each folded inwardly such as to enclose an acute angle with a major surface of the sheet. In one embodiment at least ones of the attachment elements each comprise: a plurality of projections spaced along n length thereof. Preferably, the projections comprise rectangular projections. Preferably, the projections of each attachment, element define a castellated structure. In another embodiment at least ones of the attachment elements each comprise a single, continuous attachment element, and the sheet includes a plurality of flexing apertures in spaced relation along each of the opposite edges thereof in zones overlapping fold lines of the respective folds. In one embodiment at least ones of the edges of the sheet have an attachment element extending along substantially the length thereof. In another embodiment at least one:; of the edges of the sheet; have an attachment element extending along part of the length thereof. Preferably, the part comprises a mid part. In a further embodiment at least ones of the edges of the sheet have attachment elements extending along parts of the length thereof. Preferably, the parts comprise end parts. In one embodiment the printing screen unit comprises: a pair of interface members attachable to the attachment elements at one pair of opposite edges of the sheet. In another embodiment the sheet has two pairs of opposite edges; and the printing screen unit comprises: a pair of interface members attachable to the attachment elements at one pair of opposite edges of the sheet; and further comprises: a pair of'support members attachable l:o l.lio other pair ol1 opposite* edges of the sheet. In a further embodiment the sheet has two pairs of opposite edges, at least sections of which include attachment elements; and the printing screen unit comprises: first and second pairs of Interface members attachable to l.ho attachment elements at each of the pairs of opposite edges of the sheet. Preferably, the printing screen unit further comprises: corner pieces coupling adjacent ends of each of the interface! members such as to define a frame. More preferably, the e:orner piece!!-; each comprise one of first: and second recesses or projectie>ns and the ends of the; interface member!,: each include the other of recesses or projections, which projections and recesses are engaged such as to provide for coupling of the interface members. Yet more! preferably, the realises and projections of the corner pieces and the interlace membeirs are configured such as to provide for relative! movement: e>f the interface members on being tensioned by a tensioning mechanism. More preferably, at least one of the corner pieces comprises at least first and second coupling members which are configured such as to enable assembly thereof with the projections and recesses of the! at least one corner piece) arid interface! members in engagement, thereby enabling assembly ol" the frame with the Interface members thereof attached to the respective! edges of the sheet. In one embodiment the sheet includes a pattern of printing apertures which define a pattern of deposits to be printed thereby. In another embodiment the shoot is a blank and includes no printing apertures therein. In one embodiment the sheet comprises a metal sheet. In another embodiment the sheet comprises a plasties sheet. In one embodiment: the interface members each include sin attach merit: section which provides for attachment to the at least one attachment clement: at a respective edge of the shoot, and an engagement; section for engagement to a tensioning mechanism. Preferably, the attachment section of each interface member includes an attachment surface which in use is attached to the at least one attachment element at a respective edge of the sheet. More preferably, the attachment surface of each interface member is inclined inwardly from a free edge of the attachment surface relative to the respective edge of the sheet. More preferably, the attachment surface of each interface member is defined by a continuous surface. Preferably, the engagement section of each interface member includes an engagement surface for engagement to a tensioning mechanism. More preferably, the engagement surfaces of each interface member is inclined outwardly from a free edge of the engagement surface relative to the respective edge of the sheet. More preferably, the engagement surface of each interface member is defined by a continuous surface. In yet another aspect the present invention provides a frame for supporting a printing screen comprising a sheet having (.wo pairs of opposite edges, at: least: sections of which include attachment elements, the frame comprising: first and second pairs of interface members attachable to l:ho attachment, elements at each of the pairs of opposite edges of the; shoot; and corner pieces coupling adjacent: ends of each of the interface members such as to define the frame. Preferably, the corner pieces each comprise one of first and second recessos or projections and the ends of the interface members each include the other of recesses or projection}.., which projections and recesses are engaged such as to provide for coupling of the interlace members. More preferably, the recesses and projections of the corner pieces and the interface members; are configured such as; to provide for relative movement of the interface members on being tensioned by a tensioning mechanism. Preferably, at: least one of the corner pieces; comprises at least first and second coupling members which are configured such as to enable assembly thereof with the projections and recesses of the at least one comer piece and intorfaco members in engagement, thereby enabling assembly of the frame with the interface members thereof attached to the respective edges of the sheet. In one embodiment the interface members each include an attachment section which provides for attachment to the at least one attachment element: at a respective edge of the sheet, and an engagement section for engagement to a tensioning mechanism. Preferably, the attachment section of each interface member includes an attachment: surface which in use is attached to the at least one attachment element at: a respective edge of the sheet. More preferably, the attachment surface of each Interface member is inclined inwardly (torn a free edge of the attachment surface relative to the respective! edge of the sheet. More preferably, the attachment surface of each interface member is defined by a continuous surface. Prefer-ably, the engagement section of each interface member includes an engagement: surface for engagement to a tensioning mechanism. More preferably, the engagement surface of each interface member is inclined outwardly from a free edge of the engagement surface relative to the. respective edge of the sheet. More preferably, the engagement, surface of each interface member is defined by a continuous surface. In a yet further aspect the present invention provides a printing screen unit, comprising: a printing screen, comprising a sheet:; and at least one pair of interface members attached lo at least one pair of opposite edges of the sheet. In one embodiment the interface members are bonded to the printing screen. Preferably, each interface member includes an engagement surface for engagement to a tensioning mechanism. More preferably, the engagement surface of each interface member is inclined outwardly from a free edge of the engagement surface relative to the respective edge of the sheet. More preferably, the engagement surface of each interface member is defined by a continuous; surface. In one embodiment the engagement surface is disposed outwardly of the respective edge of the sheet. In another embodiment the engagement .surface is disposed Inwardly of the respective edge of the sheet. In one embodiment the interface; members each comprise a plurality of interface elements spaced along a length of the respective edge of the sheet. In another embodiment the interface member's; each comprise first and .•second strips attached to opposite sides; of the respective edge of the sheet. In a further embodiment the interface members each comprise first and second strips; attached to opposite sides of the respective edge of the sheet., and include a plurality of engagement apertures for engagement to a tensioning mechanism spaced along a length thereof. Preferably, the sheet liar, two pairs of opposite edges, at least sections of which include attachment elements; and the printing screen unit comprises: first and second pairs of interface members attached to the at least one attachment element at each of the pairs of opposite edges of the sheet. The present invention provides an improved printing screen unit which is compatible with existing support frame systems, with the interface members protecting edges of the printing screen from damage during handling and mounting, thereby increasing the life of the printing screen. Further, sharp edges of the printing screen arc enclosed, making the printing screen safer to handle. In addition, the interface members confer structural support, reducing the flex in the printing screen during storage. Significantly, the provision of interface members allows plastic shed: to be used as the primary material of printing screens for mounting on tonsionablo support frames. Still further, thn attachment of a printing .screen to interface members further simplifies the manufacture of the printing screen unit as a whole, in obviating the need for an adhesive bond. Preferred embodiments of the present: invention will now be described horeinbolow by way of example only with reference to the accompanying drawings, in which: Figure 1(a) illustrate!)' a perspective view of a printing screen unit in accordance with a first embodiment ol the present invention; Figure 1(b) illustrates one corner region of the printing screen unit of figure 1(a); Figure 1(c) illustrates a vertical sectional view through an edge region of the printing screen unit of Figure 1(a); Figure 2(a) illustrates one corner region of a printing screen unit in accordance with a second embodiment of the present Invention; Figure 2(b) illustrates a vertical sectional view through an edge region of the printing screen unit of Figure 2(a); Figure 3(a) illustrates one corner region of a printing screen unit in accordance! with a third embodiment of the present invention; Figure 3(b) illustrates a vertical sectional view through an edge region of the printing screen unit: of Figure 3(a); Figure 4(a) illustrates one comer region of a printing screen unit in accordance with a fourth embodiment of the present invention; Figure 4(b) illustrates a verticr.il sectional view through an edge region of the printing screen unit of Figure 4(a); Figure 5(a) illustrator, a perspective; view of a printing screen unit in accordance with a fifth embodiment of the present invention; Figure 5(b) illustrates one corner region of the printing screen unit of Figure 5(a); Figure 5(c) illustrates a vertical sectional view through an edge region of the printing screen unit of Figure 5(a); Figure 6(a) illustrates a perspective view of a printing screen unit In accordance with a sixth embodiment of the present invention; Figure 6(b) illustrates one corner region of the printing screen unit of Figure 6(H); Figure G(c) illustrates a vertical sectional view through an edge region of the printing screen unit of Figure G(a); Figure 7(a) illustrates a perspective view of a printing screen unit in accordance with a seventh embodiment of the present invention; Figure 7(b) illustrates one corner region of the printing screen unit of Figure 7(a); Figure 7(c) illustrates a vertical sectional view through an edge region of the printing screen unit of Figure 7(a); Figure.! 8(a) illustrates a perspective; view of a printing screen unit in accordance with an eighth embodiment of the present invention; Figure 8(b) illustrates one corner region of the printing screen unit, of Figure H(a); Figure 0(c) illustrates a vertical sectional view through an edge region of the printing screen unit of Figure 8(a); Figure 9(a) illustrates a perspective view of a printing screen in accordances with a ninth embodiment of the present invention; Figure 9(b) illustrates one corner region of the printing screen of Figures 9(a); Figure 9(c) illustrates a vortical sectional view through an edge region of this printing screen of Figure,! 9(a); Figure .10(a) illustrates a perspective view of a printing screen unit: in accordance with a tenth embodiment of the present invention; Figure 1.0(b) illustrates the upper side of ones corner region ol the printing semen unit of Figure 10(a); Figure 10(c) illustrates the under side of the one corner region of the printing screen unit of Figure 10(a); Figure J.t)(e:l) illustrates an exploded perspective view of the one corner region of the printing screesn unit of Figure 10(a); Figure .10(e) illustrates a vertical sectional view through an edge region of the printing screen unit of Figure 10(a); Figure 10(f) illustrates an exploded perspective view of one corner piece of the printing screen unit of Figure 10(a); Figure 1:1 illustrates one corner region of an alternative printing screen for the printing screen unit of Figure 10(a), with the attachment elements being partially cut away for purposes of illustration; and Figure :12 illustrates an alternative corner piece for the printing screen unit of Figure 10(a). Figures 1(a) to (<: illustrate a printing screen unit :i in accordance with first embodiment of the present invention.> The printing screen unit 10 comprises a printing screen .12, in this embodiment of rectangular shape, a pair of interface members 16, 1G which are attached to one pair of opposite edges of the printing screen .1.2, and a pair of support members 10, 15.5 which are attached to the other pair of opposite edges of the printing screen 12. The printing screen 12 includes a pattern of apertures 20 which define the pattern of deposits to be printed. The pattern of apertures 20 can be formed, for example, by laser cutting or etching, as is well known in the art. In preferred embodiments the printing screen 12 comprises a sheet of a metal, such as stainless steel, or a plastic. The interface members 16, 16 each comprise an elongate member which extends along the length of the respective edge of the printing screen 12. The interface member's J 6, 16 each include an attachment section '?.?. which extends inwardly of the respective free edge of the printing screen 12, us Illustrated in Figure 1(c), and is In this embodiment bonded to the printing screen 12. The bonding of the interface members 16, 16 to the printing screen 1.2 may be by any suitable adhesive or curing technique;, us would be known l;o a person skilled in tlie att. The interface members 10, 10 each further include an engagement section 24 which, relative Lo the printing screen .12, is disposed outwardly of the attachment section 22 and provides for engagement to a tensioning mechanism. The engagement section 24 includes an inwardly-facing engagement surface 28, in this embodiment defined by a continuous channel, which extends along the length of the respective interface member J.G. The engagement surface 28 is outwardly inclined from the free edge thereof relative to the; printing screen 12, such as to define a hook arrangement: which provides for captive engagement with a tensioning meichanism. As will be appreciated, the engagement surface 28, in being defined by a continuous channel, allows for fabrication by a wide variety of manufacturing techniques, such as machining, routing and extrusion, which are much simpler and cheaper techniques than the fabrication techniques required in fabricating the; printing screen:; of the prior art printing screen units. The support members .1.8, 18 each comprise an elongate strip which extends along the length of the respective edge of the printing screen 12. The support: members 10, 18 provide both that no free, sharp edges of the printing screen 1.2 are exposed, thereby preventing the risk of injuiy during handling, and also further support, the printing screen 12, rendering the printing screen .1.2 loss prone to Hexing when being handled and stored. Furthermore, in providing the printing screen 12 with additional structural support, the printing screen .1.2 advantageously allows more readily for use of a plastic sheet. The ur,a of plastic sheets has many advantages, in being cheaper, easier to fabricate, and lighter. As described hereinabove, metal shoots, such as stainless steel sheets, necessarily have to be used for existing printing screens which are mounted directly to tensionable support frames, as the design of those existing printing screens is not such as l:o withstand the tension applied thereto by tensionable support: frames. In one alternative embodiment: the support members 18, 18 can bo omitted from the printing screen unit 10. In another alternative embodiment the printing screen unit 10 could include a second pair of interface members 16, 16 attached to respective ones of the other pair of opposite edges of the printing screen .12. Figures 2 (a) and (b) illustrate! a printing screen unit 10 in accordance with a second embodiment of the present invention. The printing screen unit 10 of this embodiment is very similar to the printing screen unit 10 of the above-described first: embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like pari:: being designated by like reference signs. The printing screen unit .1.0 of this embodiment differs from that of the first-described embodiment only in the manner of attachment of the printing screen 12 to the interface members 16, ,1,6. In this embodiment the interface members 16, 16 each include an elongate cover strip 1J0 which is bonded over the respective free edge of the printing screen :I2 such as to enclose the same. The bonding of the printing screen 12 to the main bodies and the cover strips 30 of the Interface members 16, .16 can be by any suitable adhesive or curing technique, as would be known to a person skilled in the art. Figures 3(n) and (b) illustrate a printing screen unit 10 in accordance with a third embodiment of the present Invention. The printing screen unit: 1.0 of this embodiment is quite similar to the printing screen unit .1.0 of the above-described final ombodimont; unci thus, in order to avold unnecessary duplication of description, only the differences will be described in detail, with like parts being designated by like reference signs. The printing .screen unit ,1.0 of this ombodimont differs from that of the first-described embodiment only in the manner of attachment of the printing screen .12 to the interface members 16, 16. In this embodiment the edges of the printing screen 12 to which the interface members 10, 16 are attached are folded to define attachment elements 32, 32, and the attachment section 22 of each interface member 1G includes a narrow, attachment slot 34 which extends along the length thereof and in which a respective one of the attachment elements 32, 32 is a I'rictional fit. In this embodiment the edges of t:he printing screen 12 are folded such thai: the attachment, elements 32, 32 defined thereby enclose an acute angle with the main body of the printing screen 12, and the attachment slots 34 in the interface members 16, 16 are inclined inwardly towards the respective inner edges thereof. In this embodiment the interface members 1.6, 16 are slid onto the respective attachment: elements 32, 32 of the printing screen 12 and field thereto by the factional engagement therebetween, with there being no bonding thereof. In one embodiment the interlace members .1.6, :J6 could be bonded to the attachment elements 32, 32 of the printing screen 12. With this configuration, the attachment elements 32, 32 become more firmly engaged in the attachment slots 34 in the respective interface members 16, .1.6 on tensioning the printing screen unit 10. Figures 4(a) and (b) illustrate a printing screen unit 10 in accordance with a fourth embodiment of the present invention. The printing screen unit 10 of this embodiment is quite similar to the printing screen unit 1.0 of the above-described first embodiment:, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like parts being designated by like reference signs. The printing screen unit 1.0 of this embodiment differs from that of the first-described embodiment in the manner of attachment of the printing screen 12 to the interlace members if), .1,6 and by the omission of the support members 18,18. Tn this embodiment the edges of the printing screen 12 to which the Interface members 10, .10 are attached are folded to define attachment elements 32, 32, and the attachment section 22 of each interface member 16 includes an attachment groove 30 which extends along the length thereof, in this embodiment defined by a continuous channel, in which a respective one of the attachment elements 32, 32 is located. In this embodiment the edges of the printing screen 12 are folded such that the attachment elements 32, 32 defined thereby enclose an acute angle with the main body of the printing screen 12. Tn this embodiment the attachment groove 36 in the attachment section 27, of each interface member 10 defines an attachment surface 3fi at the inner edge thereof relative to the printing screen 12. The attachment surface! 38 is inwardly inclined from the free edge thereof relative to the printing screen 12, such as to define a hook arrangement which provides for attachment with a respective one of the attachment elements 32 of the printing screen 1.2. In being inwardly inclined, the attachment: surface 38 of each attachment groove 30 provides for Lire captive attachment of the respective attachment element 32 of the printing screen 12 on tensioning the printing screen unit .1.0. Figures 5(a) to (c) illustrate a printing screen unit 40 in accordance with a fifth embodiment: of the present: invention. he printing screen unit: 40 comprises a printing screen 42, in this embodiment of rectangular .shape, and a pair of interface members 46, 46 which are attached to one pair of opposite edges or the printing screen 42. The printing screen 42 includes a pattern of apertures 50 which define the pattern of deposits to be printed. The pattern of apertures 50 can bo formed, for example, by laser cutting or etching, as is well known in the art. In preferred embodiments the printing screen 42 comprises a sheet of a metal, such as stainless steel, or a plastic. The edges of the printing screen 42 to which the interface members 46, 46 are attached are folded to define attachment elements 52, 52. In this embodiment the edges of the printing screen 47. are folded such that the attachment elements 52, 52 defined thereby enclose an acute angle with tho main body of tho printing screen '12. The Interface members 46, 46 each comprise an elongate member which extends along the length of the respective edge of the printing screen 42. The interface members 4G, 46 each include an attachment section 54 which includes an attachment slot 56 which extends along tho length thereof and in which a respective one of tho attachment elements 52, 52 of the printing screen 42 is located. The attachment slot 56 comprises a first, support slot: part: 5Ga, in this embodiment of linear section, which extends inwardly into the attachment section 54 from the inner edge of the respective interface member 46, and receives the region of the printing screen 42 which is inwardly adjacent the respective* attachment element 52 of the printing screen 42 and acta to support: the respective interface member 46 in tho required orient relative to tho printing screen 41. The attachment slot 56 further comprises a second, attachment slot part 56b which extends inwardly and backwardly from the distal end of the support: slot pari: 56a such as to define a hook arrangement which provides for attachment with the respective attachment element 52 of the printing screen 42. In being inwardly inclined, the attachment slot part 561) of the attachment: slot 56 provides for the captive attachment of the respective attachment element 52 of the printing screen 42.. The interface members 46, 46 each further include an engagement section 58 which provides for engagement to a tensioning mechanism. The engagement section 58 includes an inwardly-facing engagement surface; 59, in this embodiment defined by a continuous rebate, which extends along the length of the respective interface member 46. The engagement surface 59 is outwardly inclined from the free edge thereof relative to the printing screen 42, such as to define a hook arrangement which provides for captive engagement with a tensioning mechanism. As will bo appreciated, the engagement section 515, in being defined by a continuous rebate, allows for fabrication by a large variety of manufacturing techniques, such as machining, routing and extrusion, which are much simpler and cheaper techniques than the fabrication techniques required in fabricating the printing screens of the prior art printing screen units. In an alternative embodiment the printing screen unit 40 could include a second pair of Interlace members 46,46 attached to respective oner, of the other pair of opposite; edges of the printing screen 42. Figures 6(a) to (c) illustrate a printing screen unit 00 in accordance with a sixth embodiment of the present invention. The printing screen unit 60 comprises a printing screen 62, in this embodiment of rectangular shape, and a pair of interface members 66, 66 t hich are attached to one; pair of opposite edges of the: printing screen 62 and extend inwardly thereof. The printing seroon 62 include;-, a pattern of apertures 70 which define the pattern of deposits to be printed. The pattern of apertures; 70 am be formed, for example, by laser cutting or etching, as is well known in the art In preferred embodiment'; the printing .screen 62 compiles a sheet of a metal, such as stainless steel, or n plastic. The interface member; 66, 66 each comprise an elongate member which extends along the length of the respective edge of the printing screen .1.2. The interface members 66, 66 each include an attachment section 72 which is located at the respective free edge of the printing screen 67, as illustrated in l-iguie 6(c), and is in this embodiment bonded to the printing screen 62. The bonding of the interlace members 66, 66 to the printing screen 62 may be by any suitable adhesive or curing technique, as would be known to a person skilled in the art. The interface members 66, 66 each further include an engagement section 7'l which provide*; for engagement to a tensioning mechanism. The engagement section 74 includes an inwardly-facing engagement surface 78, in this embodiment defined by a continuous surface, which extends along the length of the respective interface; member 66. The engagement surface 78 is outwardly inclined from the free edge thereof relative to the printing screen 62, such as to define a hook arrangement which provides for captive engagement with a tensioning mechanism. As will he appreciated, the engagement surface 7K, in being defined by a continuous surface, allows for fabrication by a wide variety of manufacturing techniques, such as machining, routing and extrusion, which are much simpler and cheaper techniques than the fabrication techniques required in fabricating tho printing screens of the prior art printing screen units. In one alternative embodiment the printing screen unit 60 could include a second pair of Interface members 66,66 attached to respective ones of the. other pair of opposite edges of the printing screen 62. In another alternative embodiment the interface members 66, 66 can be configured such as to extend beyond the respective edges of the printing screen 62 to which the interface members; 66, 66 are attached. In one embodiment the interface members 66,66 can each include, as in the second-described embodiment, an elongate cover strip which Is bonded over the respective free edge of tins printing screen 62 such as to enclose the same. l-lgurcs 7(a) and (b) illustrate a printing) screen unit 60 in accordance with a seventh embodiment of the present: invention. "I'he printing screen unit 60 of (his embodiment is quite similar to the printing screen unit GO of the above-described sixth embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like parts being designated by like reference signs. The printing screen unit 60 of this embodiment differs from that of the sixth-described embodiment only in the construction of the interface members 66,66. In this embodiment the interface members 60 66 each comprise a plurality of block elements 66' which are spaced along the lengths of the respective edges of the printing screen 62 to which the interface members 66,66 arc attached. In one embodiment, whore the printing screen G2 is formed of a plastics material the block elements GG' of the interface members 66, 66 could be machined or formed into a uniform thick plastic .sheet. Figures 0(a) to (c) illustrate a printing screen unit 00 in accordance with an eighth embodiment: of the present invention. The printing screen unit 00 comprises n printing screen 02, in this embodiment of rectangular shape, and first nnd second pairs of interface; members 06, OG, 07, 07 which are attached to the respective pairs of opposite edges of the printing screen 02 and together define a supporting frame. The printing screen 02 includes a pattern of apertures 90 which define the pattern of deposits to be printed. The pattern of apertures 90 can be formed, for example, by laser cutting or etching, as is well known in the art. In preferred embodiments the printing screen 02 comprises n sheet of n metal, such as stainless steel, or a plastic. The interface members 0G, 0G, 07, 07 each comprise a pair of elongate strips 06a, 0Gb, 07a, 07b which extend along the length of the ro.spectivo edge of the printing screen 02, with the strips 06a, 0Gb, 87a, 07b being disposed on opposite sides of the printing screen 02 and overlapping the respective edge of the printing screen 02 so as to sandwich the same. The interface members 86, 86, 07, 07 each include an attachment section 92 which extends inwardly of the respective free edge of the printing screen 02, as illustrated in Figure 0(c), and is in this embodiment bonded to the printing screen 02. The bonding of the interface members 06, 0G, 07, 07 to the printing screen 02 may bo by any suitable adhesive or curing technique, as would be known to a person skilled in the art. Tho interface members 86, 86, 87, 87 ouch 1url-.hc.jr include an engagement suction 94 which provides for engagement to a tensioning mechanism. The engagement .suction 94 includes a plurality of engagement: apertures 96 which are spaced along the length of the respective interface member 86, 8f>, 87, 87 and provide for engagement to a tensioning mechanism. In this embodiment the printing .screen unit 80 includes interface members 86, 86, 87, 87 which extend along each of the edges of tho printing screen 82 and together define a frame which .support:;; the printing screen 82, but in an alternative embodiment the printing screen unit 80 can include only a single pair of interface members 86, 86 which extend along one pair of opposite edges of the printing screen 87. As mentioned hereinabove, in providing the printing screen 82 with structural support through tho provision of interface members 86, 80, 87, 87, the printing screen 82 advantageously allows more readily for use of a plastic sheet. The use of plastic sheets lias many advantages, in being cheaper, easier to fabricate, and lighter'. As again mentioned hereinabove, metal wheels, such as stainless steel sheets, have to date necessarily boon used for existing printing screens which are mounted directly to tensionable support frames, as the design of those existing printing screens is not such as to withstand the tension applied thereto by tensionable support frames. Figures 9(a) to (c) illustrate a printing screen .1.02 in accordance with a ninth embodiment of the present invention. The printing screen 1.02, in this embodiment of rectangular shape, includes a pattern of apertures 1.04 which define tho pattern of deposits to be printed. The pattern of apertures 104 can be formed, for example, by laser culling or etching, as is well known in the art. fn a preferred embodiment the printing screen 3.02 comprises a shoot of a metal, such as stainless steel. The edges of the printing screen 1.02 l:o which tensioning mechanisms are to be attached each comprl.sc a plurality of spaced projection:? J.0G along the length thereof which defino a castellated structure, and are folded lo define attachment elements 1.08, 108. In thlr> embodiment the edges of the printing screen 1.02 are each folded along a line intersecting the projections 106, here at substantially a mid point of the length of the projections .1.06, with each of projections 106 defining a hook element:. In this embodiment the edges of the printing screen 102 are (bided such that: the attachment elements 1.08, 1.08 defined thereby enclose an acute angle with the main body of the printing screen 102. The projections 106 which define the castellated structures can, for example, be formed using a press tool or laser. Alternatively, the projections 1.06 could be Conned by electro-discharge machining (EDM) or water jet: milling, which fabrication techniques would allow several printing screens .102 to bo fabricated simultaneously. The edges of lite printing screen .102 can be folded by using, for example, a roll or press tool. In this embodiment, the configuration of the folded projections 106, which define the castellated structures, advantageously provides for the application of a uniform tension over the main body of the printing screen .1.02 in taking up Hits shape of the tensioning mechanisms, and thereby prevents distortion of the main body of the printing screen 102, which typically has to be maintained flat. Figures 1.0(a) to (f) illustrate a printing screen unit 110 in accordance with a tenth embodiment of the present invention. The printing screen unit 110 comprises a printing screen 11.2, in this embodiment of rectangular shape, and first and second pairs of interface members 116, 1.16, 1.1.7, 1.17 which are attached to the respective pairs of opposite! edge;; of the printing screen and coupled by corner pieces 11.8a-d such as to define a supporting frame. The printing screen 112 include; a pattern of apertures J20 which define l.he pattern of deposits to ho printed. The pattern of apertures 120 can be formed, for example, by laser cutting or etching, as is well known in the art. In preferred embodiments the printing screen .1.1.2 comprises a .sheet of a metal, such as stainless steel, or a plastic. The edges of the printing screen 1.12 to which tensioning mechanisms are to bo attached each comprise a plurality of spaced projections 122 along the length thereof which define a castellated structure, and are folded l:o define attachment, elements .1.24, 124. In this embodiment: the edges of the printing screen :1.1.2 are each folded along a line intersecting the projections I 22, hero at substantially a mid point of the length of the projections 122, with each of projections .122 defining a hook element. In this embodiment the edges of the printing screen 112 are folded such that: the attachment: elements .1.24, 124 defined thereby enclose an acute angle with the main body of the printing screen 112. The projections 1.22 which define the castellated structures can, for example, bo formed using a press tool or laser. Alternatively, the projections 122 could be formed by electro-discharge machining (EDM) or water jet milling, which fabrication techniques would allow several printing screens 112 to be fabricated simultaneously. The edges of the printing screen 112 can be folded by using, for example, a roll or press tool. In this embodiment, the configuration of the folded projections 122, which define the castellated structures, advantageously provides for the application ol a uniform tension over the main body of the printing screen 112 in taking up the shape of the tensioning mechanisms, and thereby prevents distortion of the main body of the printing screen .1.12, which typically has to bo maintained flat. The interface members 116, 1.1.6, .1.17, 1.17 each comprise an elongate member which extends along the length of the respective edge of the printing screen 112. The interface members 116, 116, 117, 1.17 each Include an attachment section 126 which comprises a first, lower body part 1.2ft and a second, upper body part 130 and together define an attachment Riot .13?. which extend?; along the length thereof and in which a respective one of the attachment elements 124 of the printing .screen 112 is located. The attachment slot 132 comprise.'; a first, support slot part 134, In this embodiment of linear section, which extends inwardly into the attachment section 12G from the inner edge of the respective interface member .1.16, 116, .1.1/, 11/, and receives the region of the printing scrren 112 which is inwardly adjacent the respective attachment element 124 of the printing screen .1.1.2 and acts to support the respective interface member .1.1.6, 116, 117, 117 in the required orient relative to the printing screen 1.1,2. The attachment slot :I32 further comprises a second, attachment slot: pari: 136 which includes an attachment surface .13H which extends inwardly and backwardly from the distal end of the support slot part .134 such as to define a hook arrangement which provides for attachment: with the respective attachment element 12/1 of the printing screen 112. In being inwardly inclined, the attachment surface 138 provides for the captive attachment of the respective attachment element 124 of the printing screen 112. The interface members 116, 116, 117, 117 each further include an engagement: section 140 which, relative to the printing screen 112, is disposed outwardly of the attachment section 126 and provides for engagement: to a tensioning mechanism. The engagement section 140 includes an inwardly-facing engagement surface 1.4?., in this embodiment, defined by a continuous surface, which extends along the length of the respective Interface member 116, 11(5, 117, 1.1.7. The engagement surface 142 is outwardly inclined from the free edge thereof relative to the printing .screen 112, such as to define a hook arrangement which provides for captive engagement with a tensioning mechanism. As will be appreciated, the engagement section 140, in being defined by a continuous surface, allows for fabrication by a wide variety of manufacturing techniques, such as machining, routing and extrusion, which are much simpler- and cheaper techniques than the fabrication techniques required in fabricating the printing screens of the prior art printing screen units. The Interface members 116, 116, 117, 117 each further include! recesses 144, 146, in this embodiment of substantially rectangular section, at the distal ends thereof for receiving the tongue elements ,1.00, 1.61 of respective corner pieces I 18a-d, as will be described in more detail horoinbolow. In this embodiment the corner pieces :118a-d each comprise first and second coupling members 152, 1.54, which lock together to define the respective corner pieces 1.1.fin-d. In this embodiment the first coupling member 152 comprises a body element 156 which includes a slot 15W, hero of the same rectangular section as the recesses 144, 146 in the distal ends of the interface members 116, 116, 1.1.7, :117, which extends in a first direction therethrough, and a tongue element 160 for fitting in a respective one of the recesses 144, 146 in the distal ends of the interface members .1:1.6, 116, 1:1.7, J. 17 which extends from the body element 156 in a second direction orthogonal to the first direction of the slot 1S8 therein. In this embodiment the second coupling member 154 comprises a body element 16?., and a tongue element 164 for fitting in an adjacent one of the recesses .1.44, 146 in the distal ends of the interface members :116, 116, 117, 1.1.7 which extends from the body element 162. The body element 162 of the second coupling member 15-1 is configured to be a tight, snap-lit in the slot: 1.58 In the body element .1.56 of the first coupling member :I54 such that, when inserted therein, the tongue elements .160, .161 of the coupling members .152, 154 are locked in a coupling configuration. In one embodiment the coupling members 1.52, 154 could be bonded together. With this configuration, the coupling members .1.52, 154 allow for the in situ assembly of the last of the corner pieces 118a-d to be fitted, in enabling the tongue elements 160, 1.64 of the respective pair of the coupling members 152, .154 to be inserted into respective recesses 144, 146 in the distal ends of the interlace members 1.16, .1.16, .11.7, .11,7 in assembling the last corner piece 118a-d. It will be appreciated thai, three of the corner1 pieces 118a-d can bo pro-assembled and need not be assembled In situ. Indeed, in one embodiment three of the corner pieces l.l.8a-d can be fabricated as an integral unit, typically as a moulding or casting. In this embodiment the tongue elements 160, .1.64 of the coupling members 1.52, .154 are configured such as to be a tight fit in the. recesses .144, ,146 in the distal ends of the interface members 1:1,6, 1:16, 1,17, 1.1.7, but such as to allow for movement of the tongue elements .1.60, 164 in the respective recesses 144, 146 in the direction of a tension as applied to the printing screen .1:12. With this configuration, the Interface members 116, 1:1.6, 117, 117 present a substantially rigid frame when handled, but allow for relative movement of respective pairs of the interface members 116, .1.16, 117, 1.1.7 on being tonsioned by tensioning mechanisms. In allowing for relative movement of the interface members 116, 1.16, J17, .1.1.7, design tolerances can be accommodated in order to provide for uniform tensioning of the printing screen 112. In one alternative embodiment., as illustrated in Figure 1.1, the printing screen 112 can include single, continuous attachment elements 124 along each of the edges thereof, with the printing screen 112 including a plurality of flexing apertures 166 in spaced relation along each of the fold linns of the folds. This configuration, .similarly to the castellated structures, advantageously provides for the application of a uniform tension over the main body of the printing screen 112 and yet allows for flexing of the printing screen 112 in taking up the shape of the tensioning mechanisms. Tn another alternative embodiment, as illustrated in Figure ,1.2, the corner pieces ]:18n-d each comprise first and second coupling members 172, 174, which each comprise a tongue element 17(5 for fitting in a respective one of the recesses "Ml, .MG in Hie distal ends of the interface members I. IG, I.1G, 117, 1:17 and a keying structure 178 which provides for the locking of Lite coupling members 172, 174 in a coupling configuration, first and second capping members 100, in?, which are disposed to opposite sides of the coupling members ,1.72, 174, and lixing pins .1,84 for fixing the capping members .180, 1152 to the coupling members 172, 174 such as to fix the coupling members 172, 174 in the coupling configuration, In this embodiment: the capping members IfJ0r 182 are also bonded to the coupling members 1.72, .1.74. In this embodiment the coupling members 172, 1.74 are fabricated from a sheet material and are of such a thickness as to allow for the in situ assembly of the last of the corner pieces ,1.18u-d, in enabling the tongue elements 17G of a respective pair of the coupling members 172, 174 to be inserted into respective recesses 144, 146 in the distal ends of the interface members 116, 116, 1.17, 1.1.7 in overlapping relation and subsequent keying together of the keying structures 178 thereof in the manner of a jigsaw. Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without: departing from the scope of the invention as defined by the appended claims. For example, in one: modification, t:ho folded edges of the printing screens 12, 42 of the third to filth embodiments could utilize the castellated edge structures of the ninth-described embodiment. Also, in the described embodiments; which utilize interface members 10, 46, GG, 86, the interface members !G, 4G, GG, 8G are described as extending along substantially the complete length of the respective edges of the printing screens 12, 42, G2, 82. In other embodiments the interface members 16, 4G, GG, 86 can bo attached only to part or parts of the respective edges of the printing screens 12, 42, G2, 02, for example, a mid part, or end parts, with the interlace members !G, 4G, GG, 86 merely extending along the other parts or part such as to protect both the edges of the printing screens 12, 42, 62, 82 from damage and a user from the sharp edges of the printing screens .12, 42, G2, 82. We Claim: 1. A frame for supporting a printing screen (12) comprising a sheet having two pairs of opposite edges, at least sections of which include attachment elements (32, 32), the frame comprising: first and second pairs of interface members (16, 16) attachable to the attachment elements (32, 32) at each of the pairs of opposite edges of the sheet, wherein the interface members (16, 16) each include an attachment section (22) which provides for attachment to the attachment element (32) at a respective edge of the sheet, and an engagement section (24) for engagement to a tensioning mechanism; and corner pieces coupling adjacent ends of each of the interface members, such as to define a frame which is substantially rigid when handled, but allows for outward movement of the respective pairs of interface members (16, 16) by a tension applied by tensioning mechanisms to the engagement sections (24) of the interface members. 2. The frame as claimed in claim 1, wherein the corner pieces each comprise one of first and second recesses or projections and the ends of the interface members each include the other of recesses or projections, which projections and recesses are engaged such as to provide for coupling of the interface members. 3. The frame as claimed in claim 2, wherein the recesses and projections of the corner pieces and the interface members are configured such as to provide for relative movement of the interface members on being tensioned by a tensioning mechanism. 4. The frame as claimed in any of claims 1 to 3, wherein at least one of the corner pieces comprises at least first and second coupling members which are configured such as to enable assembly thereof with the projections and recesses of the at least one corner piece and interface members in engagement, thereby enabling assembly of the frame with the interface members thereof attached to the respective edges of the sheet. 5. The frame as claimed in any of claims 1 to 4, wherein the attachment section of each interface member includes an attachment surface which in use is attached to the attachment element at a respective edge of the sheet. 6. The frame as claimed in claim 5, wherein the attachment surface of each interface member is inclined inwardly from a free edge of the attachment surface relative to the respective edge of the sheet. 7. The frame as claimed in any of claims 4 to 6, wherein the engagement section of each interface member includes an engagement surface for engagement to a tensioning mechanism. 8. The frame as claimed in claim 7, wherein the engagement surface of each interface member is inclined outwardly from a free edge of the engagement surface relative to the respective edge of the sheet. 9. A printing screen unit, comprising: a printing screen, comprising a sheet having two pairs of opposite edges, at least sections of which include attachment elements; and the frame of any of claims 1 to 8, wherein the first and second pairs of interface members are attached to the attachment elements at each of the pairs of opposite edges of the sheet. 10. The printing screen unit as claimed in claim 9, wherein the at least sections of each pair of opposite edges of the sheet are folded such as to define the attachment elements. 11. The printing screen unit as claimed in claim 10, wherein the attachment elements are each folded inwardly such as to enclose an acute angle with a major surface of the sheet. 12. The printing screen unit as claimed in claim 10 or 11, wherein at least ones of the attachment elements each comprise a plurality of projections spaced along a length thereof. 13. The printing screen unit as claimed in claim 12, wherein the projections comprise rectangular projections. 14. The printing screen unit as claimed in claim 12 or 13, wherein the projections of each attachment element define a castellated structure. 15. The printing screen unit as claimed in any of claims 10 to 14, wherein at least ones of the attachment elements each comprise a single, continuous attachment element, and the sheet includes a plurality of flexing apertures in spaced relation along each of the opposite edges thereof in zones overlapping fold lines of the respective folds. 16. The printing screen unit as claimed in any of claims 9 to 15, wherein at least ones of the edges of the sheet have an attachment element extending along substantially the length thereof. 17. The printing screen unit as claimed in any of claims 9 to 16, wherein at least ones of the edges of the sheet have an attachment element extending along part of the length thereof. 18. The printing screen unit as claimed in any of claims 9 to 17, wherein the sheet includes a pattern of printing apertures which define a pattern of deposits to be printed thereby. 19. The printing screen unit as claimed in any of claims 9 to 17, wherein the sheet is a blank and includes no printing apertures therein.

Documents:

3349-DELNP-2004-Abstract-(10-02-2012).pdf

3349-delnp-2004-Abstract-(22-10-2013).pdf

3349-delnp-2004-abstract.pdf

3349-DELNP-2004-Claims-(10-02-2012).pdf

3349-delnp-2004-Claims-(22-10-2013).pdf

3349-delnp-2004-claims.pdf

3349-DELNP-2004-Correspondence Others-(10-02-2012).pdf

3349-delnp-2004-Correspondence Others-(22-10-2013).pdf

3349-DELNP-2004-Correspondence-Others-(16-11-2010).pdf

3349-delnp-2004-correspondence-others.pdf

3349-DELNP-2004-Description (Complete)-(10-02-2012).pdf

3349-delnp-2004-description (complete).pdf

3349-DELNP-2004-Drawings-(10-02-2012).pdf

3349-delnp-2004-drawings.pdf

3349-DELNP-2004-Form-1-(10-02-2012).pdf

3349-delnp-2004-form-1.pdf

3349-delnp-2004-form-18.pdf

3349-DELNP-2004-Form-2-(10-02-2012).pdf

3349-delnp-2004-form-2.pdf

3349-DELNP-2004-Form-3-(10-02-2012).pdf

3349-delnp-2004-form-3.pdf

3349-delnp-2004-form-5.pdf

3349-DELNP-2004-GPA-(10-02-2012).pdf

3349-delnp-2004-gpa.pdf

3349-delnp-2004-pct-101.pdf

3349-delnp-2004-pct-105.pdf

3349-delnp-2004-pct-210.pdf

3349-delnp-2004-pct-301.pdf

3349-delnp-2004-pct-304.pdf

3349-delnp-2004-pct-308.pdf

3349-delnp-2004-pct-332.pdf

3349-delnp-2004-pct-409.pdf

3349-DELNP-2004-Petition-137-(10-02-2012).pdf

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