GB1605098A

GB1605098A - Carrier substrate capable of use in dry transfer

Info

Publication number: GB1605098A
Application number: GB2483178A
Authority: GB
Original assignee: NAGYBACZON E N DE; Klinger AG
Current assignee: NAGYBACZON E N DE; Klinger AG
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-12-16

Description

(54) A CARRIER SUBSTRATE CAPABLE OF USE IN DRY TRANSFER (71) We, KLINGER AG, of 10 Baarerstrasse, Zug, Switzerland, a Swiss Company, and ERNO NAGY DE NAGYBACZON of Apt. 106 Rue de Bourret, Montreal, Province of Quebec, Canada, a Canadian citizen, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to a carrier substrate capable of use in dry transfer, to a dry transfer system including it and to a method of producing the said carrier substrate and the said dry transfer system.

The term "dry transfer" is conventionally used in relation to processes in which, specifically, decalcomania (i.e. adhesive transfers) are employed.

However, in the specification, "dry transfer" means any process which enables transfer of an indicium-forming material from a carrier substrate to a receiving surface to form an "indicium" (i.e. one or more letters, numerals, designs, plans, etc.) on the receiving surface, for example, the above mentioned decalcomania, copying paper or typewriter ribbons.

The term "indicium-forming material" as used herein means a material which either constitutes an indicium or is capable of forming an indicium on a receiving surface. For decalcomania the indicium-forming material conventionally includes a colouring material such as an ink and either additionally includes an adhesive or altematively the adhesive is provided on the receiving surface.

The term "dry transfer system" as used herein means a composite material including a carrier substrate (i.e. a sheet which bears the indicium-forming material), the indiciumforming material and any other layer which may be present.

Conventional dry transfer systems (of which there are a number and the most important of which are produced by silk-screen or photomechanical processes) have at least three basic elements common to them : - (a) a carrier substrate which can be paper, a polymeric film (e.g. cellulose acetate, cellulose triacetate, polystyrene, a polycarbonate, a polyester, a polyethylene or polypropylene) or a non-porous flexible sheet material, which carrier substrate either carries the preformed indicium by virtue of any of the above mentioned processes or is coated to one of its sides with a substance capable of forming an image on a receiving surface through the application of either heat or pressure, and (b) the indicium-forming material, which material includes the indicium itself or a substance, such as an ink, capable of forming it, and (c) an adhesive which is either incorporated within the indicium-forming material or is coated on the receiving surface and which, whether it is heat, pressure, moisture or solvent activated, or, for example, microrencapsulated, is capable of creating a bond between the receiving surface and the indicium (howsoever formed), which bond is greater than the bond existing between the indicium and the carrier substrate.

One problem common to such dry transfer systems is the release quality of the carrier substrate. Since every material has surface irregularities to a lesser or greater degree, the indicium-forming material which is applied to it in a liquid state enters the surface cavities of the material and forms a mechanical bond with it upon drying. The greater the bond between the indicium-forming material and the carrier substrate the more difficult is the release.To overcome this problem some well known dry transfer systems employ the following solutions: (a) by employing as the carrier substrate, a dimensionally unstable material which, on application of pressure thereto, stretches laterally, thus reducing the surface irregularities and thereby effecting release between the indiciumforming material and the carrier substrate, and/or (b) by forming the carrier substrate by coating a base sheet with, for example, a wax, a water soluble polymer (e.g. gelatin), or a lacquer, which coating serves to reduce the surface energy of the carrier substrate and thereby reduce the strength of the bond between the carrier substrate and the indiciumforming material to enable transfer of an indicium to a receiving surface.

However, the above solutions to the release difficulties present problems of their own.

Thus, when adopting solution (a), the lateral stretching of the carrier substrate tends to be accompanied by the distortion of the indicium.

Similarly, problems are encountered when using the conventional coatings referred to above when adopting solution (b). Thus, the release characteristics of wax vary with temperature and those of water soluble polymers with humidity. On the other hand, if a lacquer is employed, then although the bond between carrier substrate and indicium-forming material is reduced thereby, the mechanical bond is still too strong to enable easy release of the indicium during the transfer process.

Another disadvantage with conventional dry transfer systems is that efficient release and transfer to a receiving surface can be achieved only if an adhesive material is applied either on the carrier substrate or receiving surface as previously mentioned so that one of these surfaces must be tacky, thus presenting handling and storage problems.

In addition, the application of the adhesive requires, in the manufacture of the dry transfer system either a separate adhesive application step to provide the two separate layers of ink composition and adhesive respectively, or the incorporation of the adhesive in the ink composition to produce a single layer of indiciumforming material, which latter procedure requires still further processing steps to produce an image on the carrier substrate for transfer as later described.

A disadvantage also arises because, after transfer, an excess of adhesive tends to cover regions of the receiving surface out of register with the indicia, this being particularly so in regions immediately surrounding the indicia.

Adhesive in such regions may be unsightly and in any case tends to attract dirt and prevents further writing on the receiving surface in those regions. A similar problem arises when a waxy substance is present as a coating on the base sheet (an example of solution (b) above or as a component of the indicium-forming material.

Another disadvantage is that the ink composition which provides the indicium-forming material must be specially formulated so as to be capable of forming a coating which is sufficiently strong and robust to prevent either (i) tearing or deformaticxn of the indicium-forming material during release from the carrier substrate or (ii) penetration of the indiciumforming material back into the interstices of the carrier substrate on application of pressure thereto during transfer (which penetration would increase rather than decrease the strength of the bonding between the indicium-forming material and carrier substrate thus making transfer more difficult or impossible).Thus conventional dry transfer processes can be conducted efficiently only with those ink compositions which include one or more compounds capable of forming a thick robust polymeric film imparting the required strength. In addition, to provide the necessary robustness, substantial quantities of the ink composition are generally required this being because, conventionally, increased robustness is attained by increasing the thickness of the coating of the ink composition.

A further disadvantage is that in some dry transfer systems the base sheet or coating con ventianally applied to the base sheet to reduce the surface energy of the resultant carrier substrate and thus reduce the bond between carrier substrate and indicium-forming material to enable dry transfer to take place is incompatible with many of the ink compositions which would otherwise be useful for providing the indiciumforming material. For example the base sheet or the coating thereon (when adopting solution (b) referred to above) may be either deformed (e.g. swollen) by or dissolved by the solvent of the ink composition.

A still further disadvantage with conventional dry transfer systems is that difficulties may be encountered when attempting to apply a desired image on to a carrier substrate, particularly when an intricate design or a design of accurate dimensions is to be applied. One such difficulty lies in accurately applying the large quantities of ink composition required to give a coating of sufficient robustness and another such difficulty lies in accurately applying a subsequent layer of adhesive so as to lie in register with the coating of ink composition and thus minimize the disadvantage referred to above concerning excess adhesive.These difficulties present such problems that for printing of intricate designs or designs of par ticularly high accuracy of dimension, tech niques have been employed by which the entire surface is coated with ink composition and ad hesive and thereafter with a hardenable resist material, accurately selected portions of the resist then being hardened and the remainder, together with the ink and adhesive thereunder, being washed off to leave the desired image covered with a layer of hardened resist, this layer being subsequently removed by chemical or mechanical means.

Such techniqucs have also been convention ally employed when forming, for example, dry transfer systems including a single layer of ink and adhesive combined as indicium-forming material. These techniques are, however, complicated, time consuming and expensive in both labour and wasted materials.

Yet another disadvantage is that carrier substrates bearing the indicium-forming mat erial can only be stacked one above the other if a protective interleaf is placed therebetween so as to prevent the indicium-forming material accidentally transferring from one carrier substrate surface to another.

The abo,ve mentioned problems concerning release quality can be overcome by using, in a dry transfer system, a carrier substrate within the invention which carrier substrate comprises a base sheet a surface of which is provided with a coating to produce the carrier substrate which coating can readily accept an indicium-forming material but permits efficient release of an indicium during the dry transfer process. Indeed efficient release and transfer can be effected, when using a particularly preferred carrier substrate embodying the invention, without the use of an adhesive, without a special formulation of ink composition being employed, and with much thinner layers of ink composition than are employed conventionally.

In addition, the above mentioned interleaves may be dispensed with when using certain dry transfer systems embodying the invention, as later described.

According to a first aspect of the present invention there is provided a substrate comprising a base sheet at least one surface of which has a coating thereon of a dispersion of a fluorocarbon compound (hereinafter called a fluorocarbon dispersion) which said substrate is capable of use as a carrier substrate in a dry transfer system in which indicium-forming material in face-torface contact with the said coating of fluorocarbon compound can be released from the said coating to effect the said dry transfer.

According to a second aspect of the invention there is provided a method of producing such a substrate capable of use as a carrier substrate in a dry transfer system which method includes coating at least one surface of a base sheet with a fluorocarbon compound dispersion to form a substrate and rendering the said substrate capable of said use as a carrier substrate.

In order for the substrate to be capable of said use as a carrier substrate, the coating of the fluorocarbon dispersion must be sufficiently smooth to enable efficient transfer of indiciumforming material therefrom during the transfer process. Thus, although the coated surface may be undulating it must not contain regions which are sufficiently rough as to present present crevices which would permanentiy trap the indicium-forming material thus preventing transfer or causing tearing of indicia. In general, we find that merely by coating the base sheet with a fluorocarbon dispersion a coating sufficiently smooth as to render the substrate capable of use as a carrier substrate in a dry transfer system is not produced.However, in order to render the substrate so capable, the coating of fluorocarbon dispersion can be subjected to a simple smoothing operation, for example, buffing, preferably carried out after a predetermined time interval from application of the fluorocarbon dispersion to the base sheet, after which time interval the coating has become sufficiently hard not to be damaged but is still sufficiently soft to enable removal of protruding material imparting the undesirable roughness by the buffing operation.

According tQ a third aspect of the invention there is provided a dry transfer system comprising a base sheet at least one surface of which has a coating thereon of a fluoro carbon dispersion to thereby define a carrier substrate, at least a portion of the said coating of fluorocarbon dispersion on the said one coated surface bearing an indicium-forming material and being capable of allowing release from the said coating of the said carrier substrate of the indicium-forming material to effect transfer of an indicium.

According to a fourth aspect of the present invention there is provided a method of producing a dry transfer system which includes the steps of coating at least one surface of a base sheet with a fluorocarbon dispersion to form a substrate, rendering the said substrate capable of use as a carrier substrate in a dry transfer system and thereafter applying to the carrier substrate on at least a portion of the said one coated surface an indicium-forming material capable of release from the carrier substrate from which indicium-forming material in contact with the said coating of fluorocarbon dispersion can be released to effect the said dry transfer.

Preferably, in a carrier substrate embodying the invention or dry transfer system including such a carrier substrate, both surfaces of the base sheet are coated with a fluorocarbon dispersion. In this case, at least a portion of the said one surface bears the indicium-forming material and the other surface may serve as a protective layer to prevent accidental transfer of an indicium from another said dry transfer system when placed in face-to-face relation therewith (it being usually unnecessary to subject this other coated surface to a smoothing operation).

According to a fifth aspect of the present invention there is provided, in combination, (a) a dry transfer system comprising a base sheet at least one surface of which is coated with a fluorocarbon dispersion to thereby define a carrier substrate, at least a portion of the said one coated surface bearing an indicium-forming material and being capable of allowing release from the carrier substrate of the indicium-forming material to effect transfer of an indicium and (b) a protective sheet having at least one surface thereof coated with a fluorocarbon dispersion and in juxtaposed relation with the said dry transfer system so that the or one said coated surface of the protective sheet and the said one coated surface of the base sheet at least a portion of which coated surface bears the indicium-forming material are in face-to-face relation with one another, the protective sheet thereby serving to prevent accidental transfer of indicium-forming material from the carrier substrate.

The dry transfer system (a) and the protective sheet (b) of such a combination may be separate sheets between which binding may be provided along the adjacent edges of such sheets to hold them together.

Alternately, the combination may consist of a single sheet material coated on one surface with a fluorocarbon dispersion and folded about itself so as to provide two leaves joined together along a common edge so as to lie in face-to-face relation and having their respective mutually facing surfaces coated with the fluorocarbon dispersion, one leaf being provided on at least a portion of the coated surface thereof with indicium-forming material to produce the dry transfer system (a) and the other leaf con stituting the protective sheet (b).

The fluorocarbon compound is preferably a polymer and/or telomer, which more preferably contains units derived from tetrafiuoro- ethylene, and a particularly preferred fluorocarbon dispersion is a polytetrafluoroethylene homopolymer and!or homotelomer dispersion, hereinafter called a PTFE dispersion.

The fluorocarbon compound is preferably dispersed in at least one organic liquid and the dispersion is preferably in non-coagulated form.

Commercially available PTFE products which are particularly preferred are Klinger flown (a Registered Trade Mark for a material which has been previously used as a release coating for moulds in the plastics industry) and Vydax AR (Vydax is a Registered Trade Mark) manufactured by Du Pont de Nemours, a dispersion of PTFE in trichlorotrifluoroethylene, CCl2FCClF2 and a "Freon" (a Registered Trade Mark), in which at least some of the PTFE is in telomeric form.

The coating of the fluorocarbon dispersion should be sufficiently smooth to reduce the bonding forces between the indicium-forming material and the carrier substrate to a degree enabling easy release and should be of a structure sufficiently compact to prevent penetration of the indicium-forming material (preferably even the thinnest layers thereof) back into the carrier substrate on application of a pressure.

A further advantage to be achieved by employing a fluorocarbon dispersion is that the coating thus produced can be used with a wide variety of ink compositions. For example, it is not dissolved by solvents present in most con ventional ink compositions.

The base sheet material of the transfer system may take the form af a sheet, film, web, strip, tape or ribbon and may be made from paper or a polymeric film. It should be of a material which is dimensionally stable so as to resist stretching, especially during the transfer process. This stability is particularly desirable because stretching greatly limits accuracy of transfer, increases the risk of accidental release, and may cause breakage of indicia carried thereby. In addition, again for greater accuracy of transfer it is preferable that the carrier substrate be transparent to enable inspection of the indicium therethrough.By reason of such pro potties being desired, the base sheet is most preferably a film of a polyester homopolymer or copolymer, for example Melinex (a Registered Trade Mark for a commercially available polyethylene terephthalate produced by ICI).

The indicium-forming material may be any material which either constitutes an indicium (as in the case of many decalcomania) or is capable of forming an indicium on a receiving surface (for example, as in the case of copying paper or typewriter ribbons). For the reasons given below the indicium-forming material need not contain an adhesive and such an adhesive need not be present either on the carrier substrate nor on a receiving surface for the indicium thus reducing expense. In addition the ink composition of the indicium-forming material need not be specially formulated.

An increased efficiency of transfer is attained when using a carrier substrate embodying the invention; this is because the surface of the carrier substrate coated with a fluorocarbon dispersion has (i) a degree of smoothness such that the strength of the mechanical bond between the indicium-forming material and the carrier substrate is sufficiently strong to hold the material thereon prior to use in a dry transfer process and yet sufficiently weak to enable easy release of the indicium during transfer and (ii) a sufficiently compact structure that penetration of even the thinnest layer of indicium-forming material back into the carrier substrate on application of pressure is prevented thus maintaining the said mechanical bond sufficiently weak during transfer to enable easy release of the indicium.Because of this increased efficiency, the coating of ink composition (however thin) is not held too firmly by the interstices of the smooth and compact fluorocarbon dispersion coating of the carrier substrate and there is therefore no need to ensure that the indicium-forming material forms a particularly robust and therefore thick coating.

Thus since the indicium-forming material need not be thick, it can take the form of a film which is sufficiently thin, pliable and extensible as to be deformable in conformation with surface irregularities in the receiving surface and so become readily accepted and permanently held by the relatively larger interstices of the receiving surface with which the indicium-forming material forms a mechanical key. Indeed, it is found that, again contrary to conventional dry transfer systems, the thinner the coating of ink composition of a dry transfer system embodying the invention the more efficient the transfer; this is because as mentioned above a thinner coating will more readily be accepted and permanently held by the interstices within the receiving surface thus achieving greater ease of transfer and minimising breakage of indicia during transfer or in subsequent use.With particularly thin films of indicium-forming material comes the advantage that, in contrast to conventional dry transfer systems, the presence of an adhesive is not required and, in an especially preferred dry transfer system embodying the invention, the indicium-forming material takes the form of a single layer consisting of a thin pliable and extensible film of ink. A preferred thickness is less than 10 microns more preferably less than 5 microns. This contrasts with the conventional dry transfer system in which the thickness of the indicium-forming material is usually from 15 to 40 microns.

The improved bonding between the indicium of smaller thickness and the receiving surface provides a much more permanent and durable image thereon enabling a more robust use of the resultant transferred image; when using especially preferred dry transfer systems em bodying the invention, the transferred indicium is sQ strongly secured by the previously men tioned mechanical key to the receiving surface that a substantial disturbance of the receiving surface (e.g. by hard rubbing) is necessary to remove the indicium.

Such a dry transfer system embodying the invention has the following further advantages: (i) since neither the dry transfer system nor the receiving surface need be provided with an adhesive or waxy substance then neither surface need be tacky either before or after transfer. This eliminates the handling and storage problems associated with this tackiness.

(ii) Again in contrast to conventional dry transfer systems, since it is not necessary, when using a dry transfer system embodying the invention, to employ a particularly thick coat ing of ink composition as the indicium-forming material to attain efficient transfer, the amount of material required can be reduced.

(iii) Since it is unnecessary to build up the thickness of the coating of ink compcsition, it is not essential for the ink composition to be specially formulated; for example, although the presence of a compound capable of form ing a polymeric film does indeed impart a degree of strength to the coating its presence is not absolutely essential.

Elimination of the requirement that the ink composition be specially formulated has, of course, quite far-reaching advantages. Thus many types of colouring composition can be used and this far greatly increases the practical applications of a carrier substrate embodying the invention and dry transfer system including it. Thus, many colouring compositions can be employed as indicium-forming material, for example, many standard printing inks and certain photo-copying inks, (the so-called "liquid toners", which form a thin, pliable extensible film) paints, for example, poster paint, and conventional inks, for example, those used in felt-tipped pens.

Since a much wider variety of ink compositions can be employed as indicium-forming materials than in conventional dry transfer systems a much wider variety of methods can be employed for their application to the carrier substrate.

Thus, for example, an image can be applied to the carrier substrate by merely printing (by any of a large number of methods), writing, painting or drawing on it.

When a printing method is employed, this may be carried out by any conventional printing technique, for example, letterpress, gravure or screen printing, but an offset printing technique, especially a "dry", offset letterpress technique is most preferred since this gives the thinnest layer of ink.

Since certain photo-copying inks can be efficiently transferred, photo-copying provides a very efficient commercial method of producing a dry transfer system embodying the invention, it being necessary merely to pass a plu rality of carrier substrate successively through a photo-copying machine supplied with a "liquid toner". Such a dry transfer system thus produced is ready for use.

The layer of indicium-forming material so produced may take the form of a single, thin, pliable and extensible film as previously described and by applying the methods described above the ink composition producing this film may be applied directly on to the carrier substrate to define a preformed image thereon.

The preformed image is thus applied by a single (e.g. printing or writing) operation and is defined by a single layer of indicium-forming material. Although the ink composition may contain an oil or plasticizer it need not, and preferably does not, contain an adhesive. Such dry transfer systems differ from conventional dry transfer systems which either have two separate layers of indicium-forming material, one of ink and one of adhesive or have a single layer of ink and adhesive combined but require image formation by the previously mentioned complicated technique of removing selected regions of ink from a carrier substrate coated entirely with ink.

In the above methods of application, the desired image is applied directly onto the carrier substrate. For producing alternative dry transfer systems embodying the invention, however, the entire carrier substrate may be coated with an ink composition and the resultant dry transfer system employed as, for example, copying paper or a typewriter ribbon.

In conventional copying papers indiciumforming material is particulate (e.g. carbon paper) rather than in the form of a film, and usually contains an adhesive such as a wax.

These suffer from the disadvantage that only a portion of the ink is transferred from a selected region of the dry transfer system. It is not therefore possible to produce an indicium with a predetermined opacity nor a predetermined depth of shade. In addition the presence of the adhesive renders the copying paper subject to the previously mentioned disadvantage associated with this presence. A preferred dry transfer system embodying the invention and con stituting a copying paper contains indiciumforming material in the form of a film thus enabling 100% transfer of ink from a selected region of the copying paper, it therefore being possible to produce an indicium with a predetermined opacity and depth of shade. The preferred dry transfer system contains no adhesive thus overcoming the disadvantages associated therewith.

Thus such a dry transfer system may be placed with a coating of ink composition adjacent to a receiving surface, and all of the ink from a selected portion of the dry transfer system transferred merely by the application of a burnishing instrument, for example, a writing instrument, to the rear surface of the carrier substrate. This is possible because, in such a dry transfer systems embodying the invention, the adhesive force of the ink film is greater than the adhesive force binding the ink film to the carrier substrate.

Carrier substrates embodying the invention are particularly useful when formation and transfer of an intricate design or a design of accurate dimensions is desired. Thus, since only a fine coating of ink composition need be applied, since accurate registration of a subsequent layer of adhesive is not required and since the base sheet can conveniently be of a transparent and dimensionally stable material, then a design of precise dimensions can be easily applied to the carrier substrate and this can thereafter be accurately transferred to a receiving surface.

In stark contrast to this, a further use to which a carrier substrate embodying the invention can be applied is a children's game it being possible to apply to the carrier substrate many colours of, for example, poster paint which can, at will, be transferred by children wishing to consuuct drawings, this being achieved merely by rubbing or writing on selected areas of the reverse side of the carrier substrate.

A preferred carrier substrate embodying the present invention and dry transfer system including it will now be described in greater detail by way of example with reference to the accompanying drawing, wherein the sole figure is a diagrammatic enlarged cross sectional view showing the relative dispositions of the various layers in the dry transfer system.

Referring to the drawing, the dry transfer system includes a base sheet comprising a polyester film 2 coated on each side thereof with respective PTFE dispersion layers 4, 5 to define a carrier substrate. One of the PTFE dispersion layers 4 has been buffed and carries a single thin, pliable and extensible film 6 of ink covering a portion thereof, and the other PTFE dispersion layer 5 constitutes a rear surface of the carrier substrate.

The dry transfer system is manufactured by coating both sides of the polyester film 2 with a PTFE dispersion to form the dispersion layers 4,5 and thus produce a carrier substrate.

A typical PTFE dispersion composition is : - 200 g Vydax AR (a dispersion of PTFE in a mixture of tri chlorotrifluoroethylene, CCl2FCClF2, and a "Freon") 720 g Freon TF (solvent) 80 g acetone (solvent) Each PTFE dispersion layer 4 may be formed by applying one or two coatings, but howsoever applied, the total thickness of each layer 4,5 is preferably from 3-5 microns this being sufficient to ensure complete covering of the polyester film with PTFE dispersion and not so thick as to affect the tarnsparency of the carrier substrate. The coatings of PTFE dispersion may be applied using a Mayer equalizing bar, preferably wound with a 100 micron diameter stainless steel wire, this giving both the required thickness and degree of smoothness.The coatings are then dried by passing the film through an oven at 503C at a rate of 35 ft/min, the oven drying from 15 to 20ft. of film at a time.

In the Vydax AR dispersion at least some of the PTFE is in telomeric form and at least some of the telomer is soluble in the organic solvent mixture. It is believed that on drying of the coated dispersion the dissolved telomer may form a film which acts as a matrix for the remaining solid particles thus increasing the smoothness of the resultant coating.

The dispersion layer 4 is then immediately subjected to a buffing operation using brushes in order to further increase the smoothness by removing any protruding material (which would otherwise present crevices in which the ink composition to be applied would run and be permanently trapped therein, thus preventing transfer or causing tearing of indicia). This buffing operation is carried out after a predetermined time interval has been allowed to elapse from application of the PTFE dispersion to the polyester film 2 during which time interval (from say 25-35 seconds) the coating has become sufficiently hard not to be damaged but is still sufficiently soft to enable removal of the material imparting the undesirable roughness.

A suitable coating of an ink composition is then applied over selected portions of the upper PTFE dispersion layer 4 and this is allowed to dry to form a single thin, pliable and extensible film 6 of ink which defines a preformed image on the carrier substrate and thus produces a dry transfer system, the preformed image being capable of release therefrom onto a receiving surface.A typical ink composition for application by gravure printing is: carbon black (colouring component) ethyl cellulose N22 - a commercially available ethyl cel lulose (film-form ing component) diisooctyl phthalate (plasticizer) methyl ethyl ketone (solvent) Where a particularly intricate design or design of accurate dimensions is to be applied, however, the coating is preferably effected by an offset-printing technique, more preferably offset letterpress this being because an ink coating of minimum thickness, i.e. 4 microns or less, can be achieved by this method.

The dry transfer system embodying the invention described above, in which a design having precise dimensions and capable of accurate transfer has been applied, is particularly useful for providing images of components to be displayed in technical literature and, in particular, they may bear architects plans, engineering drawings or component parts thereof.

In order to effect transfer using the dry transfer system described above it is neccessary merely to place it with the film 6 of ink defining the desired preformed image in face-toface relation with a receiving surface and apply a pressure to the rear surface 5 of the carrier substrate in such a way that forces tending to deform the film 6 of ink and so release it from the carrier substrate and push it into the interstices of the receiving surface to achieve a mechanical key therewith are transmitted through the carrier substrate. This can be achieved by burnishing or, for example, with a typewriter key.

By this method the thin, pliable and extensible film 6 of ink can be transferred efficiently and held permanently by many types of receiving surface, for example, polyester drafting film, tracing paper and conventional paper; unlike conventional dry transfer systems it is not necessary in order to achieve efficient transfer to carefully select a given ink composition as indicium-forming material in dependence of the nature of the receiving surface which is to accept the image.

Although the carrier substrate specifically described above and constituting a preferred embodiment of the invention carries an indicium-forming material which takes the form of a single thin, pliable extensible film 6 this need not, of necessity, be the case. Indeed a carrier substrate embodying the invention may carry any of the conventionally employed indicium-forming materials and still achieve a more efficient transfer by virtue of the nature of the carrier substrate as previously described.

A plurality of dry transfer systems embodying the invention can be stored until required for use in stacks in which they are placed on top of one another, and can be so stacked without the requirement for interleaves between respective dry transfer systems. With known dry transfer systems, if two or more sheets were placed on top of one another without the interleaf therebetween then if pressure were accidentally applied to the top sheet, transfer would take place from one sheet to, the next in the area where the accidental pressure was applied. Such accidental transfer is satisfactorily prevented when stacking the abovementioned dry transfer systems embodying the invention by the provision of the rear PTFE dispersion layer 5 on the polyester film 2.

WHAT WE CLAIM IS:- 1. A substrate comprising a base sheet at least one surface of which has a coating thereon of a dispersion of a fluorocarbon compound which said substrate is capable of use as a carrier substrate in a dry transfer system in which indicium-forming material in face-to-face contact with the said coating of fluorocarbon compound can be released from the said coating to effect the said dry transfer.

2. A substrate according to claim 1, wherein the or one of said coated surfaces has been buffed to render the said substrate capable of use as a said carrier substrate.

3. A substrate according to, claim 1 or claim 2, wherein the fluorocarbon compound is a polymer and/or telomer.

4. A substrate according to claim 3 wherein the polymer and/or telomer contains units derived from tetrafluoroethylene.

5. A substrate according to claim 4, wherein the said polymer and/or telomer is a polytetrafluoroethylene homopolymer and/or homotelomer.

6. A substrate according to any one of the preceding claims wherein the fluorocarbon compound is dispersed in at least one organic liquid.

7. A substrate according to any one of the preceding claims wherein the said dispersion is in non-coagulated form.

8. A substrate according to any one of the preceding claims wherein the base sheet is dimensionally stable so as to resist stretching thereof.

9. A substrate according to any one of the preceding claims which is transparent.

10. A substrate according to claim 8 or claim 9 wherein the base sheet is a film of a polyester homopolymer or copolymer.

11. A substrate according to any one of the preceding claims wherein the base sheet has opposed said surfaces each of which is coated

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. PTFE dispersion layer 4 and this is allowed to dry to form a single thin, pliable and extensible film 6 of ink which defines a preformed image on the carrier substrate and thus produces a dry transfer system, the preformed image being capable of release therefrom onto a receiving surface.A typical ink composition for application by gravure printing is: carbon black (colouring component) ethyl cellulose N22 - a commercially available ethyl cel lulose (film-form ing component) diisooctyl phthalate (plasticizer) methyl ethyl ketone (solvent) Where a particularly intricate design or design of accurate dimensions is to be applied, however, the coating is preferably effected by an offset-printing technique, more preferably offset letterpress this being because an ink coating of minimum thickness, i.e. 4 microns or less, can be achieved by this method. The dry transfer system embodying the invention described above, in which a design having precise dimensions and capable of accurate transfer has been applied, is particularly useful for providing images of components to be displayed in technical literature and, in particular, they may bear architects plans, engineering drawings or component parts thereof. In order to effect transfer using the dry transfer system described above it is neccessary merely to place it with the film 6 of ink defining the desired preformed image in face-toface relation with a receiving surface and apply a pressure to the rear surface 5 of the carrier substrate in such a way that forces tending to deform the film 6 of ink and so release it from the carrier substrate and push it into the interstices of the receiving surface to achieve a mechanical key therewith are transmitted through the carrier substrate. This can be achieved by burnishing or, for example, with a typewriter key. By this method the thin, pliable and extensible film 6 of ink can be transferred efficiently and held permanently by many types of receiving surface, for example, polyester drafting film, tracing paper and conventional paper; unlike conventional dry transfer systems it is not necessary in order to achieve efficient transfer to carefully select a given ink composition as indicium-forming material in dependence of the nature of the receiving surface which is to accept the image. Although the carrier substrate specifically described above and constituting a preferred embodiment of the invention carries an indicium-forming material which takes the form of a single thin, pliable extensible film 6 this need not, of necessity, be the case. Indeed a carrier substrate embodying the invention may carry any of the conventionally employed indicium-forming materials and still achieve a more efficient transfer by virtue of the nature of the carrier substrate as previously described. A plurality of dry transfer systems embodying the invention can be stored until required for use in stacks in which they are placed on top of one another, and can be so stacked without the requirement for interleaves between respective dry transfer systems. With known dry transfer systems, if two or more sheets were placed on top of one another without the interleaf therebetween then if pressure were accidentally applied to the top sheet, transfer would take place from one sheet to, the next in the area where the accidental pressure was applied. Such accidental transfer is satisfactorily prevented when stacking the abovementioned dry transfer systems embodying the invention by the provision of the rear PTFE dispersion layer 5 on the polyester film 2. WHAT WE CLAIM IS:-

1. A substrate comprising a base sheet at least one surface of which has a coating thereon of a dispersion of a fluorocarbon compound which said substrate is capable of use as a carrier substrate in a dry transfer system in which indicium-forming material in face-to-face contact with the said coating of fluorocarbon compound can be released from the said coating to effect the said dry transfer.

with a said dispersion, one said coated surface being capable of use as a surface bearing an indicium-forming material and capable of allowing release therefrom of an indiciumforming material in a dry transfer process and the other said coated surface being capable of serving as a protective layer to prevent accidental transfer of an indicium from a dry transfer system when placed in face-to-face relation therewith.

12. A substrate according to any one of the preceding claims substantially as herein described with reference to and as illustrated in the accompanying drawing.

13. A dry transfer system comprising a base sheet at least one surface of which has a coating thereon of a dispersion of a fluorocarbon compound to thereby define a carrier substrate, at least a portion of the said coating of fluorocarbon compound on the said one coated surface bearing an indicium-forming material and capable of allowing release from the said coating of the said carrier substrate of the indiciumforming material to effect transfer of an indicium.

14. A dry transfer system according to claim 13 wherein the base sheet has opposed said surfaces each of which is coated with a said dispersion, at least a portion of one said coated surface bearing the indicium-forming material and the other said coated surface being capable of serving as a protective layer to prevent accidental transfer of an indicium from another dry transfer system when placed in face-to-face relation therewith.

15. A dry transfer system according to claim 13 or claim 14 wherein the said indiciumforming material comprises a thin, pliable and extensible film capable of deformation during transfer to a receiving surface so as to confirm with surface irregularities in the receiving surface and achieve a mechanical key between interstices of the receiving surface and the said film of indicium-forming material.

16. A dry transfer system according to claim 15 which is capable of use in a dry transfer process without the presence of an adhesive on either of the carrier substrate or receiving surface for the indicium.

17. A dry transfer system according to claim 15 or claim 16 wherein the said indiciumforming material comprises a single layer consisting of the said thin, pliable and extensible film.

18. A dry transfer system according to any one cf claims 15 to 17 wherein the thickness of the said thin pliable and extensible film of indicium-forming material is less than 10 microns.

19. A dry transfer system according to claim 18 wherein the thickness of the said thin, pliable and extensible film of indicium-forming material is less than 5 microns.

20. A dry transfer system according to any one of claims 17 to, 19 wherein the said film of indicium-forming material defines an image capable of transfer to a receiving surface.

21. A dry transfer system according to claim 20 wherein the image is preformed on the carrier substrate.

22. A dry transfer system according to claim 21 wherein the said image is preformed from a printing ink composition applied by printing onto the carrier substrate.

23. A dry transfer system according to claim 22 wherein the said image is preformed by an offset printing technique.

24. A dry transfer system according to claim 23 wherein the said image is preformed by offset letterpress.

25. A dry transfer system according to claim 22 wherein the printing ink composition is a phcsto-copying ink composition capable of forming the said thin, pliable and extensible film of indicium-forming material.

26. A dry transfer system according to any one of claims 13 to 19 wherein the said indicium-forming material is coated on the entire said one surface of the carrier substrate, selected portions thereof being transferable by the application of pressure to correspondingly selected regions of the said other surface of the carrier substrate when the or the said one surface bearing the said indicium-forming material is disposed in face-tcrface relation with a receiving surface for an indicium.

27. A dry transfer system according to claim 26 which is in the form of a copying paper.

28. A dry transfer system according to claim 26 which is in the form of a typewriter ribbon.

29. A dry transfer system according to any one of claims 13 to 28 in combination with a protective sheet having at least one surface thereof coated with a said dispersion and in juxtaposed relation with the said dry transfer system so that the or one said coated surface of the protective sheet and the said one coated surface of the base sheet at least a portion of which coated surface bears the indiciumforming material are in face-to-face relation with one another, the protective sheet thereby serving to prevent accidental transfer of indicium-forming material from the carrier substrate.

30. A combination according to claim 29 which comprises a single sheet material coated on one surface with a said dispersion and folded to bring two coated leaves of the single sheet material into juxtaposed relation with one another so that respective coated surfaces of the said leaves are brought into face-to-face relation with one another, one said leaf of the folded said single sheet being capable of use as a carrier substrate in a said dry transfer system and being provided on at least a portion of the said coated surface thereof with the indicium-forming material to produce the said dry transfer system and the other said coated leaf of the folded said single sheet constituting the said protective sheet.

31. A combination according to claim 29 wherein the said dry transfer system and the said protective sheet are constituted by respective sheets bound together along respective adjacent portions thereof.

32. A dry transfer system according to any one of claims 13 to 31 substantially as herein described with reference to and as illustrated in the accompanying drawings.

33. A method of producing a substrate capable of use as a carrier substrate in a dry transfer system which method includes coating at least one surface of a base sheet with a dispersion of a fluorocarbon compound to form a substrate and rendering the said substrate capable of said use as a carrier substrate from which indicium-forming material in contact with the said coating of fluorocarbon compound can be released to effect the said dry transfer.

34. A method according to claim 33 wherein the said step of rendering the said substrate capable of said use as a carrier substrate is carried out by buffing the or one of said coated surfaces.

35. A method according to claim 34 wherein the buffing is carried out after a predetermined time interval from coating.

36. A method according to claim 33, claim 34 or claim 35 both said surfaces of the base sheet are coated with the said dispersion.

37. A method according to any one of claims 33 to 36 substantially as herein described with reference to and as illustrated in the accompanying drawing.

38. A substrate whenever produced by a method according to any one of claims 33 to 37.

39. A method of producing a dry transfer system which includes the steps of coating at least one surface of a base sheet with a dispersion of a fluorocarbon compound to form a substrate, rendering the said substrate capable of use as a carrier substrate in a dry transfer system and thereafter applying to the carrier substrate on at least a portion of the said one coated surface an indicium-forming material capable of release from the carrier substrate.

40. A method according to claim 38 wherein both said surfaces of the base sheet are coated with the said dispersion.

41. A method according to claim 39 or claim 40 wherein the said step of applying the indicium-forming material carried out so as ta form, on at least a portion of the said one coated surface of the carrier substrate, a thin, pliable and extensible film of the said indiciumforming material, which said film is capable of deformation during transfer to a receiving surface sa as to conform with surface irregularities in the receiving surface and achieve a mechanical key between interstices of the receiving surface and the said film of indicium-forming material.

42. A method according to claim 41 wherein the said step of applying the indicium-forming material consists of applying on to at least a portion of the said one coated surface of the carrier substrate an ink composition capable of forming a single said thin, pliable and extensible film.

43. A method according to claim 42 wherein the ink composition is applied by coating and allowing the ink composition to dry to form the said single thin pliable extensible film.

44. A method according to claim 41, claim 42 or claim 43 wherein the thickness of the said applied thin, pliable and extensible film of indicium-forming material is less than 10 microns.

45. A method according to claim 44 wherein the thickness of the said applied thin, pliable and extensible film of indicium-forming material is less than 5 microns.

46. A method according to any one of claims 39-45 wherein the said step of applying to the carrier substrate an indicium-forming material is carried out so as to apply, on the said carrier substrate, a desired preformed image capable of transfer to a receiving surface.

47. A method according to claim 46 wherein the said step of applying to the carrier substrate an indicium-forming material is carried out by printing.

48. A method according to claim 47 wherein the said printing is carried out by an offset printing technique.

49. A method according to claim 48 wherein the offset printing technique is offset letterpress.

50. A method according to claim 47 wherein the printing is carried out by passing the carrier substrate through a photo-copying machine to deposit thereon an image formed by a photocopying ink composition capable of forming the said thin, pliable and extensible film of indicium-forming material.

51. A method according to any one of claims 39 to 45 wherein the indicium-forming material is applied to the entire surface of the or the said one coated surface, a desired image being uansferable therefrom by application of pressure to selected portions of the said other sur face of the carrier substrate when the or the said one coated surface bearing the indiciumforming material is disposed in face-to-face relation with a receiving surface for an indicium.

52. A method according to any one of claims 39 to 51 substantially as herein described with reference to. and as illustrated in the accompanying drawing.

53. A dry transfer system whenever produced by a method according to any one of claims 39 to 52.