GB2063766A - Transfer lettering system - Google Patents

Abstract

A dry transfer lettering system comprising a release carrier sheet bearing indicia formed by screen- printing a pigmented adhesive composition, the indicia optionally being protected by a release liner. Screen-printable pigmented adhesives which may be used to prepare the dry transfer lettering system comprise (i) a pressure sensitive adhesive composition comprising an organic polymer adhesive, a tackifier resin and a mixture of aliphatic and aromatic solvents, the composition having a solids content of from 30 to 51% by weight, and (ii) 10 to 40% by weight of the pigmented composition of a pigment, e.g. carbon, the pigment composition having a solids content of 35 to 65% by weight.

Description

SPECIFICATION Transfer lettering system This invention relates to a transfer lettering system, to its application in the production of car number plates and to components for use therein.

The concept of dry transfer lettering is known and is disclosed, for example, in British Patent Specification Nos. 954459 and 959670. Such dry transfer lettering systems normally consist of: 1) carrier film, 2) a transferable ink film, 3) a high pressure sensitive adhesive, 4) optionally a semi-release or protective film which may be laid down on the carrier film, and 5) an interleaving protective liner.

The ink film may be transferred to a substrate by removing the protective liner, placing the ink film with its adhesive coating against the substrate and applying pressure to the ink film through the carrier film. The ink film adheres to the substrate and the carrier sheet is peeled away from the transferred ink film. The transfer lettering system has found wide application in signing and also in the manufacture of acrylic car number plates.

An exemplary method presently used in the manufacture of these plates consists of: 1) lamination of a sheet of clear acrylic polycarbonate, glass, etc., with a transparent adhesive, 2) transfer of dry transfer indicia onto the reflective sheeting, 3) lamination of the reflective sheet and adhesive coated acrylic, 4) lamination of adhesive coated protective sheeting on the back of the reflective sheeting, (aluminium, pvc, etc.).

This method of fabrication results in the production of gloss lettering with a reflective background behind a transparent, easy-to-clean, weatherable material.

It is an object of the present invention to provide an alternative transfer lettering system suitable for preparing acrylic car number plates and materials for use therein.

Therefore according to the invention there is provided a transfer lettering system comprising a release carrier sheet bearing an indicia formed by screen-printing a screen-printable (as defined herein) pigmented adhesive composition.

The invention provides a simplified transfer lettering system in which the transferable ink film is itself a pressure-sensitive adhesive and accordingly a separate layer of pressure-sensitive adhesive is not required as in the prior art systems. The indicia of the transfer lettering system is formed by screen-printing a pigmented pressure-sensitive adhesive. The indicia may be transferred to a substrate in the conventional manner.

The term "transfer lettering system" has been used generically herein to refer to transfer systems for indicia which indicia may be in the form of letters, numbers, lines, patterns and any other symbols.

The screeen-printable pigmented adhesive compositions useful for preparing the transfer lettering system of the invention are new as are the screen-printable adhesive compositions from which they are prepared.

Therefore according to one embodiment of the invention there is provided a screen-printable (as defined herein) pressure-sensitive adhesive composition comprising an organic polymer adhesive, a tackifier resin and a mixture of aliphatic and aromatic solvents, the composition having a solids content of from 30 to 51 % by weight.

Generally, printable pressure sensitive adhesive compositions have a solids content of less than 25%. However, the screen-printable pressure sensitive adhesive compositions of the invention have a high solids content in the range 30 to 51% and preferably about 46% by weight.

The term "screen-printable" used herein refers to compositions which will pass through a 77 threads per centimetre polyester monofilament screen of 33.5% open area under standard hand screen printing conditions onto a 44 to 55 gram/25 mm strip release paper to give an essentially continuous film when examined by the naked eye, the film possessing a visually sharp edge and being substantially free from pinholes or mottle.

The present invention also provides a pigmented screen-printable (as defined herein) pressure sensitive adhesive composition comprising: (i) a pressure sensitive adhesive composition as defined above, and (ii) 10 to 40% by weight based on the pigmented composition of a pigment, the pigmented composition having a solids content of 35 to 65% by weight, preferably 47 to 53% by weight.

The pigmented composition of the invention is capable of being screen-printed onto a suitable release carrier sheet to provide a dry transfer lettering system.

The high solids content of the pressure-sensitive adhesive minimizes shrinkage on drying and the high level of pigment also assists in minimizing shrinkage and modifying the adhesive, altering the tack and release properties. The solvent content of the adhesive and pigmented composition is selected to provide suitable physical properties for screen printing, i.e. the composition must have a suitable viscosity and rheology to pass through the meshes of the screens to form a clean adhesive film. The solvent mixture comprises a blend of aromatic (good) and aliphatic (poor) solvents. The solvents preferably have similar boiling point. A narticularly preferred blend of solvents is based on xylene and Clarisol 330 solvents.

Suitable pressure sensitive adhesives for use in the invention are knowxn and consist of a tacky resin or polymer, e.g. natural rubber, vulcanised rubber, synthetic rubber and polymers or copolymers selected from isobutylene, choroprene, butadiene, acrvlonitrile, acrylic monomers, methacrylic monorners, polyethers, styrene or styrene homologues. Preferred polymers include polyethers, in particular polyvinyl isobuty! ather..

Suitable tacky and tackifying resins include rosin and rosin denvatives such as hydrogenated rosin, esters and alcohols.

It has been found that high solids screen-printable adhesive composi*,3ions based on polyvinyl isobutyl ether (BASF hutanol 160) and hydrogenated rosin ether are carticularly effective.

Stabilizers may also be incorporated and are normally at a sufficiently low level to have minimal effect on tensile strength, elongation and adhesion, etc.

Pigments, dyes and filler may be incorporated into 'he adhesive by milling to give any desired coloured, opaque, metallic or transparent effect. Suitable pigments include carbon, s,g. carbon black having a particle size of about 20 nm. It has been found that to obtain a repositionable and workable pigmented adhesive which affords a gloss image on transfer to a clear substrate, much higher levels than normal of pigment must be used. For example, using carbon black it has been found that the addition of 10 to 40% by weight, generally 15 to 25% by weight based on the total weight of pigmented adhesive composition is required. Tack and release can be modified by varying the carbon content.

The pigmented adhesive composition preferably has a viscosity in the range 30,000 to 70,000 cP more preferably from 40,000 to 50,000 Cp.

The indicia can be printed onto the carrier sheet by screen-printing. Direct, indirect or direct/indirect screens can be used, the selection of mesh size and screen type in part controlling the final thickness of the ink film. Effective drying of the ink can be achieved in conventional batch ovens at 80 to 90"C. A wide range of screens may be used, e.g. within the range 10 to 100 threads per centimetre, preferably 68 to 77 threads per centimetre.

The indicia are preferably printed at a dry coating weight of 14 g/m2 + 35%, more preferably 14 g/m2 + 25%.

Suitable release carrier sheets for use in the transfer lettering system of the invention include dimensionally stable paper or polymer film coated with a suitable release agent, e.g. fluorocarbon, high alkyl acrylate or silicone. Good release properties have been obtained from silicone coated surfaces. Preferably the release value of the surface of the sheet is from 40 to 50 9/25 mm strip.

The release value for the surface of the carrier sheet is determined as follows.

Strips of AT. 160 adhesive tape, commercially available from Samuel iones n td 25 mm wide, are placed on the release paper. The strips are placed on -op ot eacil other, in-terlçaved with filter paper and between two smooth flat metal plates under a weight of 32 Lobs, in an oven at 80"C for 10 minutes (weight equivalent to 4 psi). The laminated release paper is cooled for at least 10 minutes and then stripped at a rate of 12 inches per minute and the force required measured using a spring balance. The release value is calculated as the average reading ignoring the first one inch.

The transter lettering system of the invention preferably has a release liner positioned over the indicia. The protective liners may comprise similar materials to the carrier sheets although ideally the release value of the protective liner should be lower than that for the carrier sheet.

Preferably, the release liner has a release value of 1 to 20 9/26 mm strip.

The pigmented adhesive composition of the invention is generally low in tack and may be insufficiently tacky to hold the protective liner in place. Accordingly, it may be necessary to include additional means to retain the protective liner in place over the indicia. A suitable method of retaining the protective liner in place is to print an additional bar of pigmented adhesive composition above or below the indicia and crimp the carrier sheet and Drotent ve liner together through the adhesive. The protective liner and carrier sheet rnay be pe.rfraea in order to permit removal of the adhesive bar before the lettering system is used.

Figures 1 and 2 of the accompanying drawings illustrate such a lettering systems. Fia I represents an exploded view of the lettering system and Fig. 2 represents an end view of the lettering system of Fig. 1. Figs. 1 and 2 show the carrier film 2 bearing an indicia 4 which comprises a dried film of adhesive composition of the invention. A bar of adhesive 6 is printed below the indicia to assist in the attachment o, Çhe protective liner 8 to the carrier film. 7he attachment is effected by crimping the carrier film and protective liner together through the adhesive bar at 10.The liner and carrier are perforated at 1 2 to permit removal of the adhesive bar before use.

The transfer lettering system of the invention is particularly useful for the preparation of car number plates. The lettering system is formed with the individual indicia printed on the carrier sheet and protected by the liner, the sheet and liner being cut into tiles. The protective liner is removed and the tiles can simply be laid directly onto a transparent substrate, the size of the tile giving automatic spacing, and then passed through high pressure rollers, e.g. metal and rubber, to effect transfer. The carrier backing is then peeled away and the imaged material laminated with reflective or retroreflective sheeting.

It is also possible to apply the indicia direct to the reflective or retroreflective sheeting and thereafter laminate the transparent substrate. The car number plates prepared in accordance with the invention possess black glossy characters and good weathering properties. The glossy appearance of the indicia on number plates and the like is far superior to that of many prior art products. This is believed to be due to efficient wetting of the substrate by the pigmented pressure-sensitive composition.

The transfer lettering system of the invention is also useful for the preparation of street signing and the like in which case lamination may be undertaken with reflective, retroreflective, transparent, translucent or opaque backing.

The invention will now be illustrated by the following Example in which all parts are by weight.

Example (i) Preparation of a screen-printable high solids pressure-sensitive adhesive Formulation parts polyvinyl isobutyl ether (Lutanol 160 BASF) 43.3 aliphatic solvent blend (Clairsol 330) 41.2 xylene 12.4 hydrogenated rosin 2.9 2, 2'-methylene-bis-(4-methyl-6-cyclohexyl phenol) (antioxidant) 0.2 2-hydroxy-4-methoxy-benzophenone (u.v. absorber) 0.2 Total solids 46.4% All the components were batched and stirred until dissolved, then filtered.

(ii) Pigmented adhesive parts high solids adhesive from (i) above 73 carbon black (Raven 1255) 16 aromatic solvent blend (Caromax 20) 11 Total solids 50% Clairsol 330 is commercially available from Carless Solvents Limited, London, and comprises a blend of aliphatic solvents having an initial boiling point of 1 80 C and an aromatic content of 0.05% v/v.

Raven 1 255 is commercially available from Columbian International (GB) Limited.

Caromax 20 is commercially available from Carless Solvents Limited, London, and comprises a blend of aromatic solvents having an initial boiling point of 183"C and an aromatic content of 98% v/v.

The pigmented adhesive was made up by addition of the carbon black and aromatic solvent to the adhesive stock (i) and the whole passed through a triple roll mill to disperse the carbon. The viscosity of the resulting pigmented adhesive was found to be 48,500 cP using a number 5 spindle at 4 rpm at 70"F on a Brookfield RVF viscometer. The specific gravity was 0.93.

Screen printing of indicia was effected using a 1 96 mesh (77 threads/cm) direct screen, the indicia being printed onto a siliconised paper (101 g/m2). A bar of adhesive may also be printed at the same time as the indicia (the bar subsequently being used to key the protective liner and the carrier film together). After printing the printed stock was dried in a batch oven at 70 to 90"C for 2.5 hours. Interleaving with siliconised vegetable parchment was followed by die stamping individual tiles. During this operation the interleaf and carrier was also crimped together through the adhesive bar.

Claims (51)

1. A transfer lettering system comprising a release carrier sheet bearing an indicia formed by screen-printing a screen-printable (as defined herein) pigmented adhesive composition.

2. A transfer lettering system as claimed in Claim 1 in which the release value of the carrier sheet is from 40 to 50 9/25 mm strip (as defined herein).

3. A transfer lettering system as claimed in Claim 1 or Claim 2 in which the indicia is formed by printing the pigmented composition at a dry coating weight of 14 g/m2 + 35%.

4. A transfer lettering system as claimed in Claim 3 in which the indicia is formed by coating the pigmented composition at a dry coating weight of 14 g/m2 + 25%.

5. A transfer lettering system as claimed in any preceding claim in which the pigmented adhesive composition has been printed through a 68 to 77 threads/cm screen.

6. A transfer lettering system as claimed in any preceding claim in which the release carrier sheet is siliconised paper.

7. A transfer lettering system as claimed in any preceding claim which additionally comprises a release liner over the indicia.

8. A transfer lettering system as claimed in Claim 7 in which the release value of the liner is in the range of 10 to 20 9/25 mm strip (as defined herein).

9. A transfer lettering system as claimed in Claim 7 or Claim 8 in which the release liner is siliconised vegetable parchment.

10. A transfer lettering system as claimed in any one of Claims 7 to 9 in which the release liner is attached to the release carrier sheet by crimping the release carrier sheet and release liner through a bar of pigmented adhesive printed simultaneously with the indicia.

11. A transfer lettering system as claimed in Claim 10 in which the release liner is perforated adjacent said adhesive bar to facilitate removal of the release liner protecting the indicia.

1 2. A transfer lettering system as claimed in any preceding claim in which the pigmented screen-printable (as defined herein) pressure-sensitive adhesive composition comprises: (i) a screen-printable pressure-sensitive adhesive composition, and (ii) 10 to 40% by weight based on the pigmented composition of a pigment, the pigmented composition having a solids content of 35 to 65% by weight.

1 3. A transfer lettering system as claimed in Claim 1 2 in which the screen-printable (as defined herein) pressure sensitive adhesive composition comprises an organic polymer adhesive, a tackifier resin and a mixture of aliphatic and aromatic solvents, the composition having a solids content of from 30 to 51 % by weight.

14. A transfer lettering system as claimed in Claim 1 3 in which the pressure sensitive adhesive composition has a solids content of about 46% by weight.

1 5. A transfer lettering system as claimed in Claim 1 3 or Claim 14 in which the organic polymer adhesive is selected from natural rubber and polymers or copolymers of one or more of isobutylene, chloroprene, butadiene, acrylonitrile, acrylic monomers, methacrylic monomers, polyethers, styrene and styrene homologues.

1 6. A transfer lettering system as claimed in Claim 1 5 in which the organic polymer adhesive is polyvinyl isobutyl ether.

1 7. A transfer lettering system as claimed in any one of Claims 1 3 to 1 6 in which the tackifier resin is a rosin or a rosin derivative.

18. A transfer lettering system as claimed in Claim 1 7 in which the tackifier resin is an hydrogentated rosin.

1 9. A transfer lettering system as claimed in any one of Claims 1 3 to 18 in which the mixture of solvent comprises xylene and Clairsol 330.

20. A transfer lettering system as claimed in any one of Claims 1 3 to 1 9 in which the pressure-sensitive adhesive composition additionally comprises an antioxidant.

21. A transfer lettering system as claimed in any one of Claims 1 3 to 20 in which the pressure-sensitive adhesive composition additionally comprises an ultra violet absorber.

22. A transfer lettering system as claimed in any preceding claim in which the pigmented adhesive composition has a solids conent of 47 to 53% by weight.

23. A transfer lettering system as claimed in Claim 22 in which the pigmented adhesive composition contains 1 5 to 25% by weight of pigment.

24. A transfer lettering system as claimed in any preceding claim in which the pigmented adhesive composition has a viscosity in the range of 30,000 to 70,000 cP.

25. A transfer lettering system as claimed in Claim 24 in which the pigmented adhesive composition has a viscosity in the range of 40,000 to 50,000 cP.

26. A transfer lettering system as claimed in any preceding claim in which the pigmented adhesive composition contains carbon as a pigment.

27. A transfer lettering system as claimed in any preceding claim in which the pigment has a particle size of about 20 nm.

28. A transfer lettering system substantially as herein described with reference to the Example.

29. A transfer lettering system substantially as herein described with reference to the accompanying drawing.

30. A method of forming an indicia on a surface which comprises: (i) providing a transfer lettering system as claimed in any preceding claim, (ii) removing the release liner if present, (iii) placing the indicia supported on the release carrier sheet in face-to-face contact with the said surface, (iv) applying pressure to the indicia through the release carrier sheet sufficient to adhere the indicia to the said surface, and (v) removing the release carrier sheet.

31. A method of forming an indicia on a surface as claimed in Claim 30 substantially as herein described.

32. A method of preparing a car number plate, street sign and the like which comprises applying to a surface of a transparent substrate the desired indicia by a method as claimed in Claim 30 and thereafter laminating a backing sheeting to the transparent substrate over said indicia.

33. A car number plate prepared by a method as claimed in Claim 32 in which the backing sheet is reflective or retroreflective.

34. A screen-printable (as defined herein) pressure sensitive adhesive composition comprising an organic polymer adhesive, a tackifier resin and a mixture of aliphatic and aromatic solvents, the composition having a solids content of from 30 to 51% by weight.

35. A composition as claimed in Claim 34 having a solids content of about 46% by weight.

36. A composition as claimed in Claim 34 or Claim 35 in which the organic polymer adhesive is selected from natural rubber and polymers or copolymers of one or more of isobutylene, chloroprene, butadiene, acrylonitrile, acrylic monomers, methacrylic monomers, polyethers, styrene and styrene homologues.

37. A composition as claimed in Claim 36 in which the organic polymer adhesive is polyvinyl isobutyl ether.

38. A composition as claimed in any one of Claims 34 to 37 in which the tackifier resin is a rosin or rosin derivative.

39. A composition as claimed in Claim 38 in which the tackifier resin is an hydrogenated rosin.

40. A composition as claimed in any one of Claims 34 to 39 in which the mixture of solvent comprises xylene and Clairsol 330.

41. A composition as claimed in any one of Claims 34 to 40 which additionally comprises an antioxidant.

42. A composition as claimed in any one of Claims 34 to 41 which additionally comprises an ultra violet absorber.

43. A screen-printable pressure sensitive adhesive composition substantially as herein described with reference to the Example.

44. A pigmented screen-printable (as defined herein) pressure sensitive adhesive composition comprising (i) a pressure sensitive adhesive composition as claimed in any one of Claims 34 to 43, and (ii) 10 to 40% by weight based on the pigmented composition of a pigment, the pigmented composition having a solids content of 35 to 65% by weight.

45. A pigmented composition as claimed in Claim 44 which has a solids content of 47 to 53% by weight.

46. A pigmented composition as claimed in Claim 44 or Claim 45 which contains 1 5 to 25% by weight of pigment.

47. A pigmented composition as claimed in any one of Claims 44 to 46 having a viscosity in the range of 30,000 to 70,000 cP.

48. A pigmented composition as claimed in Claim 47 having a viscosity in the range of 40,000 to 50,000 cP.

49. A pigmented composition as claimed in any one of Claims 44 to 48 in which the pigment is carbon.

50. A pigmented composition as claimed in any one of Claims 44 to 49 in which the pigment has a particle size of about 20 nm.

51. A pigmented screen-printable pressure sensitive adhesive composition substantially as herein described with reference to the Example.