MARKER ASSEMBLY

Abstract: Replacing silicone paper release sheet of known adhesive-backed roll-feed 50 micron polyester curable marker product with 90+ (pref. 100) micron plastics release sheet (12) enables A4 sheets to be printed in sheet-fed printers with reduced curling or multi-sheet feeding and enables release sheet to be made from economically desirable non-stress-relieved plastics, whereas thinner plastics release sheets (and the polyester marker backing (10)) need stress relief to survive heat-curing of the printed material without unacceptable distortion. Preferred versions have spacing means (14), preferably a strip of adhesive tape, projecting from the surface of the release sheet (12) facing away from the printable marker (10) to facilitate separation of sheets from a stack thereof by maintaining air gaps between adjacent sheets in the stack.

Description: MARKER ASSEMBLY This invention relates to marker assemblies comprising a support sheet having a surface provided with a porous coating of latent curable material capable of receiving printed indicia, which coating is capable of being subsequently cured to render the indicia substantially indelible. Such marker assemblies are described in our EP-B-0237258, and one commercially successful form thereof comprises a 50-micrometre-fhick polyester support sheet having a layer of adhesive on the surface not carrying the porous coating and having a silicone- coated release paper removably adhering to the adhesive. These known assemblies are very successful for use with roll-fed printers, but have unexpectedly proved at times to be unsuitable for sheet-fed printers requiring a supply of sheets in the A3 to A5 size- range, preferably A4. The present invention provides sheets in that size-range using a new construction of marker assembly for improved sheet-fed printing. The invention accordingly provides a marker assembly in substantially rectangular form of edge dimensions not greater than A3 sheet size and not less than A5 sheet size, comprising (i) a support sheet having a surface provided with a porous coating of latent curable material capable of receiving printed indicia, which coating is capable of being subsequently cured to render the indicia substantially indelible, the porous coating preferably being in particulate and/or filamentary form, (ii) a layer of adhesive on the surface of the support sheet not carrying the porous coating, and (iii) a plastics release sheet of at least 90 micrometres thickness removably adhered to and covering at least part of the adhesive layer. The specified construction may be adapted to promote a number of commercially attractive features in the aforementioned sheet sizes. The plastics release sheet of 90 micrometres or more thickness tends to resist curling, which has been found to be a problem with the known silicone release papers in A4 size sheets. It is well adapted to die cutting of individual markers from the printable sheet, being less prone to accidental through-cutting of the release sheet, which has been found to occur when the curling problem was addressed by using certain release papers coated on both sides with silicone release agent. It tends to resist multi-sheet feedings, which can be caused by electrostatic attraction when thinner plastics release sheets are used, for example 50- micrometre-thick polyester sheet similar to that used for the known support sheet. And most unexpectedly, at 90 micrometres or more thickness it can be, and preferably is, made from economically-advantageous plastics sheet which has not been stress-relieved, unlike the preferred support sheet which is stress-relieved to render it heat-stable under at least some conditions subsequently used to cure heat-curable porous coatings. Thinner release sheets made from non-stress-relieved plastics (e.g. polyester) sheet of 50 or 75 micrometres thickness have been found to become unacceptably distorted during such curing. The upper thickness limit of the release sheet is not critical, provided that the resulting assembly remains suitable for the sheet-fed printers in question, but it will generally be economically preferable to use thicknesses near the specified minimum, for example widiin the range from 90 to 120 or 90 to 110 micrometres, thicknesses of 95 to 105, preferably close to 100, micrometres being convenient for polyester release sheets, which are preferred, especially in conjunction with polyester support sheets. The release sheet may be made of an inherently non-adherent plastics material, but will preferably have a surface coating of a known release material, for example polysiloxane (silicone) release coatings, since d is allows greater freedom of choice for the release sheet material to suit sheet feeding and economic requirements. The components of the assembly other than d e release sheet may be as described in EP-B-0237258, the disclosure of which is incorporated herein by reference. The release sheet may be made of plastics selected from to those described for the support sheet in EP-B-0237258, but polyesters are preferred, especially when the support sheet is made of polyester. As a specific example to illustrate the invention, an A4-sized marker assembly according to the invention may be made using known assembly methods from a support sheet of 50-micrometres-thick heat-stabilised (stress-relieved) white Melanex ST529 (Trademark) polyester sheet from ICI, coated on one side with a curable porous layer as described in EP-B-0237258, and coated on the other side with a solvent-based pressure- sensitive acrylic adhesive available from National Starch and Chemical Ltd. under the Trademark Durotak 180-1197, the solvent being removed after coating. The dry adhesive coating is overlaid with a 100-micrometres-thick clear Melanex (Trademark) Type S polyester sheet from ICI having a silicone release coating pre-applied to the surface facing the adhesive. Sheets of A4 size cut from this assembly by known mediods have been found satisfactory for sheet-fed printing in known ink-jet printers. The invention includes a method of producing markers comprising printing indicia on the porous coating of one or more of the novel assemblies hereinbefore described by means of a sheet-fed printer, preferably an ink-jet printer, and preferably including the step of curing, preferably heat-curing, the printed porous coating to render the indicia substantially indelible . The substantial indelibility of the indicia may be determined as described in EP-B- 0237258, the disclosure of which is incorporated herein by reference. The present invention includes a feature for advantageously reducing sheet-to-sheet adhesion, which adhesion may hinder feeding of the sheets individually from a stack diereof owing to electrostatic attraction and/or vacuum suction and/or frictional forces between successive sheets in the stack. The invention accordingly provides a marker assembly as hereinbefore described, wherein the exposed surface of the said plastics release sheet facing away from the remainder of the assembly has spacing means projecting therefrom capable of maintaining one or more air gaps between the said release sheet and the adjacent porous coating of an adjacent similar assembly when in a stack of such assemblies, the said spacing means being arranged to provide the said air gap(s) at least in an edge region of the assembly which will be the leading edge region when fed from a stack of such assemblies to sheet handling equipment in use, diereby facilitating separation of individual assemblies from the stack. The advantages of marker assemblies having a reduced tendency to stick together in a stack will be self-explanatory, regardless of whether the individual assemblies (hereinafter sheets) from the stack are fed to the sheet handling equipment by means external to that equipment, or are pulled into the equipment by means incorporated therein. A single air gap may be envisaged extending around the edges of a centrally-placed spacing means or extending in and out between a relatively large number of small projecting spacing means in the form of pads or "islands". In theory, such discrete projecting spacing means could become more numerous and smaller progressively until something approaching a coating of minute glass beads on the sheet surface might be achieved. However, such small projections may be less satisfactory than larger projecting surfaces from the point of view of friction against the adjacent porous coating of an adjacent sheet when one sheet slides over the other during the feeding operation. The sheet handling equipment will usually be a sheet-fed printer, for example an ink jet printer, or heating equipment used for curing the indica-bearing coating after printing, or other devices such as die cutters, conveyor belts etc. It is preferred that die spacing means comprises at least one strip of plastics material adhered to the said release sheet. Whether adhered to the release sheet or formed integrally with it, d e spacing means preferably comprises a single strip of material substantially centrally aligned with the intended direction of feed of die assembly in use. It will be understood that a single straight strip of material running more or less down the centre of the sheet in die direction of feed will often be the most economical form of spacing means. However, the shape of the spacing means is not necessarily limited to straight-edged rectangular strips. When a single spacing strip is used as aforesaid, it is preferred that d e widdi of the single spacing strip is at least 25 mm, preferably at least 50 mm, more preferably at least one third and not more than two thirds of the total widdi of the assembly, and preferably not more than 125 mm. Dimensions widiin diese ranges may be selected so as to spread the effect of the two air gaps running down die opposed edges of fhe spacing strip to the most effective positions across the widdi of fhe sheets in d e stack. Single spacing strips are not however essential, and the spacing means may comprise two or more strips of material, preferably substantially symmetrically aligned widi the intended direction of feed of fhe assembly in use. In some cases, it may be sufficient to provide the spacing means and air gaps only in the region of the leading edge of the sheets, or extending only part way from the leading edge towards the opposite trailing edge of the assembly. However, it will usually be preferable that die spacing means and die air gap(s) extend continuously from the leading edge of the assembly to die opposite trailing edge of the assembly. In such a structure, the sheet-to-sheet adhesion-reducing effect of fhe air gaps will be felt over the entire length of the sheet instead of just a leading portion. It is preferred that the spacing means has a substantially sheet-like smooth exterior surface facing away from the remainder of the assembly, since this will tend to reduce sliding friction between adjacent sheets as diey are fed one by one from the stack. It is unnecessary to quantify exactly the degree of smoothness of the spacing means exposed surface, but it is clearly a case of "the smoother the better" and coherent polymer films will usually be more satisfactory than rough or corrugated surfaces such as the back of crepe paper masking tape. It is very much preferred that the spacing means is adhered to the said release sheet by an adhesive that permits movement of the spacing means along the surface of fhe release sheet at temperatures experienced by the spacing means during curing of the indicia-receiving porous coating in use. For this purpose, fhe spacing means preferably comprises a low-tack pressure-sensitive adhesive protective tape, for example that available under die trademark "Flowstrip FL205" from Flowstrip Limited of Scunfhorpe, England. This is especially relevant when the spacing means comprises a polymeric film material which may undergo some longitudinal shrinkage at elevated temperatures. The movement permitted by the preferred adhesive allows such shrinkage to occur without curling to an unacceptable extent die release sheet to which the tape adheres. It has been found that shrinkage of 2 - 3 mm at each end of the preferred pressure-sensitive adhesive tape can thus be accommodated without curling the assembly as a whole. The mickness of the spacing means is not critical, but it may be preferable that the spacing means projects from the release sheet to a distance widiin die range from 25 to 100 micrometres. Pressure-sensitive adhesive tapes of such thickness are accordingly preferred, the aforementioned tape FL205 being approximately 50 micrometres thick. The marker assemblies according to this invention are especially useful in mediods of feeding fhe assemblies one at a time from a stack thereof to sheet handling equipment, wherein means are provided for reducing static charge on the assemblies during such feeding. Such static reduction means, for example known anti-static bars, enhance the adhesion-reducing effect of the aforementioned air gaps and have been found to enable trouble-free feeding of a stack of up to 25 A4-size sheets into a desk top inkjet printer. It is understood diat references in the original co-pending application and herein to sheet sizes in the A3 to A5 size range do not restrict the sheets to "A" proportions. U.S. quarto, foolscap and other sizes, and the standard sizes of other countries may all be included within die overall dimensional range from A3 to A5. Specific embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings wherein Figure 1 shows schematically in end view a single marker assembly according to the invention; Figure 2 shows schematically a stack of three such marker assemblies in a (sectioned) feed tray; Figure 3 shows in magnified greater detail an end view of two possible structures for a marker assembly according to the invention; and Figures 4 to 6 show schematically in plan view different arrangements of the spacing means on d e surface of the aforementioned release sheet. Referring to the drawings, Figure 1 shows the coated A4 support sheet 10 adhered by a layer of adhesive (not shown) to a plastics release sheet 12 of at least 90 micrometres thickness as described in die aforementioned co-pending application, with a 75mm wide strip of the aforementioned FL205 low tack protective tape 14 adhered to the release sheet 12 in a substantially central position with respect to the widdi of fhe assembly as shown in this end view. When sheets such as that shown in Figure 1 are stacked in use for feeding dirough a printer, as shown in Figure 2, the 50 micrometres thickness of the projecting tape 14 will result in air gaps 16 between the release sheet 12 carrying the tape and the porous coating of the carrier sheet 10 of the adjacent assembly in fhe stack. The proportions and shape of the air gaps 16 have been exaggerated for clarity in this diagram. The structure of the assemblies according to this aspect of fhe invention is shown in more detail in die schematic end view of figure 3. The marker assembly comprises the porous coating (30) of latent curable material capable of receiving printed indica, which coating is carried on the support sheet (32), the opposite surface of which carries the layer of adhesive (34) to which is adhered the plastics release sheet (36), all as described in the aforementioned co-pending application. This A4 assembly is approximately 210 mm in widdi and the various layers constituting it may for example be 60 micrometres thick curable coating (30), 50 micrometres thick Melinex (trademark) ST 529 support sheet (32), 10 micrometres thick pressure-sensitive adhesive (34), and 100 micrometres thick Melinex (trademark) type S release sheet (36). The 50 micrometres thick FL 205 low tack protective tape (38) is adhered to the exposed surface of the release sheet (36) by its low tack adhesive layer (40) and produces air gaps (42), corresponding to air gaps (16) of Figure 2 as schematically indicated by broken lines in Figure 3. In an alternative embodiment of fhe invention, the tape (38) of 75 mm widdi could be replaced by diree strips (44) of similar tape of 25 mm widdi evenly spaced across the width of fhe assembly and extending from the leading edge all the way to die trailing edge as aforementioned. In such an arrangement, diere would be four air gaps (46) as schematically indicated by the broken lines associated with die three strips of tape (44). Figure 4 illustrates schematically the preferred arrangement of a single strip of spacing tape (14) positioned substantially centrally and extending all die way from the leading edge to the trailing edge of fhe release sheet (12) of a strucmre similar to Figure 1 as viewed from below. Figure 5 shows possible alternative strucmres having three strips of tape (44) extending only part way from the leading edge towards d e trailing edge, widi possible further short strips (45) indicated in broken lines to extend the spacing effect over more of the sheet area. Figure 6 shows another possible, though generally less preferred, alternative having a number of smaller round portions of spacing tape (50) distributed over the surface of the release sheet (51).

Claims: ________ 1. A marker assembly in substantially rectangular form of edge dimensions not greater than A3 sheet size and not less than A5 sheet size, comprising (i) a support sheet having a surface provided with a porous coating of latent curable material capable of receiving printed indicia, which coating is capable of being subsequently cured to render the indicia substantially indelible, me porous coating preferably being in particulate and/or filamentary form, (ii) a layer of adhesive on d e surface of fhe support sheet not carrying the porous coating, and (iii) a plastics release sheet of at least 90 micrometres thickness removably adhered to and covering at least part of the adhesive layer. 2. An assembly according to claim 1, wherein the porous coating is heat-curable and the support sheet material is stress-relieved so that the support sheet is heat-stable under at least some conditions capable of heat curing the porous coating. 3. An assembly according to claim 2, wherein the plastics release sheet material is not stress-relieved and/or is not heat-stable under any commercially-acceptable conditions capable of heat curing the porous coating. 4. An assembly according to any preceding claim, wherein the support sheet and/or die release sheet comprise polyester material. 5. An assembly according to any preceding claim, wherein the release sheet carries a release coating, preferably comprising polysiloxane material. 6. An assembly according to any preceding claim of substantially A4 sheet size. 7. A method of producing markers comprising printing indicia on the porous coating of one or more assemblies according to any preceding claim by means of a sheet- fed printer, preferably an ink-jet printer. 8. A method according to claim 7, including die step of curing, preferably heat- curing, the printed porous coating to render the indicia substantially indelible. 9. A marker assembly according to any of claims 1 to 6, wherein the exposed surface of the said plastics release sheet facing away from the remainder of the assembly has spacing means projecting therefrom capable of maintaining one or more air gaps between the said release sheet and the adjacent porous coating of an adjacent similar assembly when in a stack of such assemblies, fhe said spacing means being arranged to provide die said air gaps at least in an edge region of the assembly which will be the leading edge region when fed from a stack of such assemblies to sheet handling equipment in use, diereby facilitating separation of individual assemblies from the stack. 10. An assembly according to claim 9, wherein the spacing means comprises at least one strip of plastics material adhered to the said release sheet. 11. An assembly according to claim 9 or 10, wherein the said spacing means comprises a single strip of material substantially centrally aligned widi the intended direction of feed of fhe assembly in use. 12. An assembly according to claim 11, wherein the width of fhe said single spacing strip is at least 25 mm, preferably at least 50 millimetres, more preferably at least one third and not more than two diirds of the total widdi of fhe assembly, and preferably not more than 125 millimetres. 13. An assembly according to claim 9 or 10, wherein the said spacing means comprises two or more strips of material, preferably substantially symmetrically aligned with the intended direction of feed of fhe assembly in use. 14. An assembly according to any of claims 9 to 13, wherein the spacing means and the air gap(s) extend from the leading edge of the assembly to die opposite trailing edge of fhe assembly. 15. An assembly according to any of claims 9 to 14, wherein the spacing means has a substantially smooth sheet-like exterior surface facing away from e remainder of the assembly. 16. An assembly according to any of claims 9 to 15, wherein the spacing means is adhered to the said release sheet by an adhesive which permits movement of the spacing means along the surface of the release sheet at temperamres experienced by the spacing means during curing of the indicia-receiving porous coating in use. 17. An assembly according to claimlό, wherein the spacing means comprises a low- tack pressure-sensitive adhesive protective tape. 18. An assembly according to anyof claims 9 to 17, wherein the spacing means projects from the release sheet to a distance widiin die range from 25 to 100 micrometers. 19. A method of feeding assemblies according to any of claims 1 to 6 and 9 to 18 one at a time from a stack of such assemblies to sheet handling equipment, wherein means are provided for reducing static charge on the assemblies during such feeding.

Inventors: STEADMAN STUART, STEADMAN, STUART
Applicants: RAYCHEM LTD, STEADMAN STUART, RAYCHEM LIMITED, STEADMAN, STUART
Application year: 1996
Main classification: G09F3
IPC codes: G09F3