US3298850A - Dry transfer materials - Google Patents

Dry transfer materials Download PDF

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US3298850A
US3298850A US26599663A US3298850A US 3298850 A US3298850 A US 3298850A US 26599663 A US26599663 A US 26599663A US 3298850 A US3298850 A US 3298850A
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Prior art keywords
indicia
adhesive
transfer
carrier sheet
adhesion
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Reed Kenneth James
Lythgoe Alan Lennox
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Esselte Pendaflex Corp
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Letraset International Ltd
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Assigned to ESSELTE PENDAFLEX CORPORATION reassignment ESSELTE PENDAFLEX CORPORATION MERGER (SEE DOCUMENT FOR DETAILS). MARCH 30, 1983 Assignors: LETRASET USA INC. (INTO)
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B44DECORATIVE ARTS
    • B44CPRODUCING DECORATIVE EFFECTS; MOSAICS; TARSIA WORK; PAPERHANGING
    • B44C1/00Processes, not specifically provided for elsewhere, for producing decorative surface effects
    • B44C1/16Processes, not specifically provided for elsewhere, for producing decorative surface effects for applying transfer pictures or the like
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41MPRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M3/00Printing processes to produce particular kinds of printed work, e.g. patterns
    • B41M3/12Transfer pictures or the like, e.g. decalcomanias
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B44DECORATIVE ARTS
    • B44CPRODUCING DECORATIVE EFFECTS; MOSAICS; TARSIA WORK; PAPERHANGING
    • B44C1/00Processes, not specifically provided for elsewhere, for producing decorative surface effects
    • B44C1/16Processes, not specifically provided for elsewhere, for producing decorative surface effects for applying transfer pictures or the like
    • B44C1/162Decalcomanias with a transfer layer comprising indicia with definite outlines such as letters and with means facilitating the desired fitting to the permanent base
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B44DECORATIVE ARTS
    • B44CPRODUCING DECORATIVE EFFECTS; MOSAICS; TARSIA WORK; PAPERHANGING
    • B44C1/00Processes, not specifically provided for elsewhere, for producing decorative surface effects
    • B44C1/16Processes, not specifically provided for elsewhere, for producing decorative surface effects for applying transfer pictures or the like
    • B44C1/165Processes, not specifically provided for elsewhere, for producing decorative surface effects for applying transfer pictures or the like for decalcomanias; sheet material therefor
    • B44C1/17Dry transfer
    • B44C1/1733Decalcomanias applied under pressure only, e.g. provided with a pressure sensitive adhesive
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00Stock material or miscellaneous articles
    • Y10S428/914Transfer or decalcomania
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/24Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24355Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]
    • Y10T428/24471Crackled, crazed or slit
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/24Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24752Laterally noncoextensive components
    • Y10T428/24769Cellulosic

Description

Jan. 17,'- K. J- REED ETAL 3,298,350

' DRY TRANSFER MATERIALS Filed March 18, 1963 FIGB 3,298,850 DRY TRANSFER MATERIALS Kenneth James Reed and Alan Lennox Lythgoe, London,

England, assignors to Letraset Limited, London, England, a British company v Filed Mar. 18, 1963, Ser. No. 265,996 Claims priority, application Great Britain, Mar. 21, 1962,

18 Claims. (Cl. 117-3.1)'

The invention relates to adhesive transfers (decalcomanias) and more particularly to a form of transfer material in which an image, design or printed matter (hereinafter generally referred to as indicia") may be transferred from a carrier sheet toa receiving surface. The invention includes transfer materials, their production and the processess of their use. i

It is an object of the present invention to provide a new form of dry transfer material in which the indicia can be transferred intact, without the necessity of applying any liquid to release the indicia from the carrier sheet.

Transfer may be effected in a suprisingly simple, quick and effective manner to all types of receiving surface and the adhesive strength may be designed in the range of low to very high adhesion values. The method of transfer consists in placing the transfer material on a receiving surface with the adhesive side down and applying pressure or pressure plus activating means to the back of the carrier sheet over the indicia to be transferred so that when the carrier sheet is lifted away the transferable indicia will be released and transferred intact and substantially without distortion and will be adhered by a continuous layer of adhesive beneath the indicia this layer being exactly contiguous therewith.

The transfers are prepared by applying to one side of a carrier sheet by aprinting operation the transferable indicia and over which there is then applied an adhesive which completely covers the indicia (contiguous adhesive) and also overlaps onto the surrounding carrier sheet. The overlapping adhesive avoids the alternative and virtually impossible requirement of perfect registration of adhesive and indicia but introduces the serious problems of transfer of the overlapping adhesive onto the receiving surface, as free contaminating adhesive, or if the overlapping adhesive is made non-transferable the cohesive strength of the adhesive, which usually increases as the adhesive strength increases, will inhibit transfer or tear off the edges of the indicia during transfer.

The transfers of the present invention are characterised in that the overlapping adhesive is non-transferable onto the receiving surface and free adhesive will not contarninate the receiving surface even when pressure has been applied to the carrier sheet over the overlapping adhesive. Non-transference of adhesive in the overlap area is achieved partly by natural adhesion of the adhesive to the carrier sheet and also by the additional feature of carrier sheet reaction which may either increase the natural adhesion of the adhesive to the carrier sheet or preferably reduce or eliminate the adhesion of the overlapping adhesive for the receiving surface.

According to the present invention therefore, there is provided a dry transfer material which comprises a carrier sheet which has a polymer surface susceptible to solvent attack, indicia in printing ink on said carrier sheet, said indicia being resistant to said solvent attack and adhesive covering said indicia, and overlapping onto said carrier sheet, the adhesive power of the adhesive for a receiving surface determined by its peel bond adhesion ited States Patent M thereto, being less in the said overlapping areas than in usually suitable.

3,298,850 Patented Jan. 17., 1967 the areas registering with the indicia, by reason of a modification of the adhesive solely in the overlapping areas resultant on solvent action on the surface of the carrier sheet in those areas. H

The solvent action referred to may result from the presence of a solvent in the adhesive itself or the modification of the surface of the carrier sheet may be achieved by applying a solvent to the assembly of the indicia on the carrier sheet before applying the adhesive, the indicia constituting in both cases a barrier to the action of the solvent on the carrier sheet in those areas covered by the indicia. The solvent action may cause an actual weakening or shear of the adhesive layer exactly at the margins of the indicia to take place during the production of the transfer (so-called pre-shear) or the result may be so to weaken the adhesive film in the overlapping areas referred to that shear takes place at the margins of the indicia at the moment of transfer.

As noted above, the transfer materials of the present invention may employ adhesives of considerable tensile strength since, due to the deactivation of the adhesive in the areas lying outside the indicia, the danger of transferring such overlapping adhesive is eliminated. This is a factor of great importance as permitting very strong .adhesion of the indicia to the receiving surface. However, it is necessary to ensure'that the indicia do not transfer prematurely, e.g., on storage or handling. One way of achieving this is to provide a removable protective sheet which lies over the adhesiveface of the transfer and can be removed when the transfer is required for use; in this case ofcourse the protective sheet must itself have very high release properties and a silicone-treated paper is In another method it may be arranged that the adhesion of theindicia to the carrier sheet may be of sufficient strength that risk of premature transfer is thus minimised, the release of the indicia from the carrier sheet being accomplished by effecting a local stretching of the carrier sheet relative to the ink indicia. Both the aforesaid methods may be employed together. i

It will thus be appreciated that Within the scope of this invention transfer materials of variously different charac ter may be produced, care being taken in all casesso to select the. characteristics of the elements of the transfer that the desired interfacial adhesi-ons are achieved to lead to the correct end result, i.e. to the'transfe-r of the indicia and to the transfer with the indicia only of adhesive exactly coextensive with the indicia.

The desirable characteristics of the individual elements of the transfer materials of this invention will now be described in further detail.

CARRIER SHEETS To obtain accurate positioning of the transfer on the receiving surface, it is desirable that the carrier sheet and adhesive should be light transmitting, i.e. transparent or translucent, so that the receiving surface is visible through the transfer sheet at'the moment of transfer. The carrier sheet may have either a high gloss,.semi-gloss, matt or embossed finish and the indicia will transfer with a replica of the carrier sheet surface from which it has been transferred. A matt surface provides a substantially easier dry release of the indicia and an embossed surface shows easier stretch-freeing.

The thickness of the carrier sheet may bevaried between quite widelirnits determined in the thinner gauges by the difliculty of handling very thin and flimsy sheets, particularly where colour to colour register is required; in the thicker gauges the stretch-free process requires increasing localised pressures. A practical caliper range is 3 .0005.008 inch and the most useful range is .0015-.003 inch.

The carrier sheet reaction involves softening or swelling the carrier sheet surface. Consequently the carrier sheet surface may intermix with the adhesive, or it may physically occlude the adhesive. A substantial disturbance of the carrier sheet surface is desirable in order to break up the adhesive film and occlude it.

Such disturbance is best achieved by using a molecularly orientated organic polymer either as a self supporting sheet or as a layer on another support. An orientated self supporting polymer sheet has a stressed surface and can be identified by heating at or above the softening point and measuring the heat retraction in sheet dimensions. Sheet orientated by monoaxial stretching will retract in one dimension; sheet orientated by biaxial stretching will retract equally in two dimensions and sheet which has triaxial orientation will contact unequally in two dimensions. If the polymer is orientated non uniformly or locally, or is supported on another support sheet, orientation may be measured by birefringence or by X-ray diffraction or infra-red dichroism.

Orientated i.e. stressed, carrier sheet reaction to the adhesive is visible as a stresscracked, etched or reticulated effect. It appears that in an extreme case the surface breaks up into a laminar or scale-like effect which may further curl over and effectively mask the adhesive. Such carrier sheet reaction therefore is most easily distinguished by a difference in surface finish, i.e. gloss value, of the carrier sheet in the reacted and non reacted regions. If the adhesive has caused the reaction, rather than a solvent applied before the adhesive, the difference in surface finish is usually still visible but if necessary, an adhesive unmodified chemically by the carrier sheet may be removed by extraction with a solvent inert towards the carrier sheet. Since the carrier sheet does not react (i.e. change in surface finish from its original condition) beneath the indicia, by removal of one element of indicia, and by comparing the carrier sheet surface finish beneath this element of indicia and in the adjacent overlapping region, the carrier sheet reaction may be visually observed.

INDICIA The indicia must be composed of a material which acts as a barrier and prevents reaction of the carrier sheet with the adhesive in the areas of indicia. Generally, the indicia itself, or the printing ink from which the indicia are derived, should not itself react with the carrier sheet, although a very mild etching of the carrier sheet may be permitted, this degree of reaction being very slight compared to the overlapping adhesive reaction. Strong reaction of the carrier sheet with the indicia would be shown as a marked change in surface finish beneath the indicia and almost always in disintegration of the indicia film which will no longer transfer intact. Such disintegration of the overlapping adhesive film is of course, highly desirable in order to provide the pre-shear characteristics. Barrier properties are generally obtained by selection of dry indicia films which are not dissolved by the liquid adhesive solvents. Continuous indicia, free from pinholes, and with sufficient film thickness are required. It is perhaps surprising that an indicia in the form of a dot or a line .002 inch Wide may still provide a fully satisfactory barrier and will transfer perfectly even when a very strong pressure sensitive adhesive is used and explains why the finest detail may be produced in the transfers of this invention. The adhesive contiguous with the indicia usually has a smooth, highly gloss appearance and contrasts sharply with the overlapping, reacted adhesive.

The indicia should have suflicient tensile strength and flexibility to transfer without breaking and without distortion even when transfer pressure is applied as lines or bands leaving small gaps. Generally the tensile strength is measured by the force necessary to break a one inch 4 wide strip of indicia and the lower limit must exceed the peel bond of the indicia to the carrier sheet and withstand the forces involved in stretching the carrier sheet. A tensile strength of at least 20 grams per inch is normally required (which equals about psi. for .0003 inch thick indicia) and tensile strength values of 200' grams may be achieved. The flexibility of the indicia, measured by elongation at yield and break points must be sufiicient to withstand handling stresses but must not be so high as to prevent the stretch-freeing mechanism if that is to be employed.

ADHESIVE Substantial shearing of the overlapping adhesive, during preparation of the transfer will usually occur. If shear is inadequate, then on transfer the edges of the indicia will be torn or transfer will be inhibited, or the adhesive itself will transfer. The greater the film or cohesive strength of the adhesive, the greater must be the pre-shear, which is believed to be caused by disintegration of the overlapping adhesive by the severe surface stresscracking of the carrier sheet. A smaller proportion of adhesive post-shear may occur at the moment of transfer. Pre-shear may be measured by comparing the force necessary to peel a long thin element of indicia off the transfer sheet compared. to the force when the long edges of such element have been cut.

It is highly desirable that there should be a considerable difference in tack between the adhesive in the area of the indicia and in the overlapping area, since otherwise a powerful adhesive will tear a receiving surface such as paper in the overlapping regions when the carrier sheet is pulled away. Using sufficiently large indicia, e.g. as strips one inch wide, the tack differential may be measured by applying the indicia to a receiving surface and then peeling off and comparing this (high) value with the force necessary to peel off a one inch wide strip of carrier sheet with overlapping adhesive when applied to the receiving surface with the same force as the indicia.

The overlapping adhesive may have high natural adhesion to the carrier sheet; the non-transfer properties are, however, further enhanced by the carrier sheet reaction which increases the adhesive bond to the carrier sheet. and also by the tack differential.

Initially the indicia will adhere to the carrier sheet with a measurable peel bond. Whereas this peel bond may only be about 4 grams per inch width, it has been found that there is also an edge effect on each of the indicia which increases the force required to remove the indicia to many times the peel bond value (which is measured with the edge of the indicia already separated from the carrier sheet). This edge adhesion is a useful feature in preventing premature transfer. There is a possibility that the perfect contact between indicia and carrier sheet owes its edge adhesion to atmosphere pressure. Irrespective of the theory of adhesion, a positive means of ensuring transfer instantly when required is achieved by the stretch-freeing mechanism. In practice, to test this feature, the indicia are applied to the carrier sheet which is then supported at its ends and then strokes with a stylus or serrated bar are applied through the carrier to the indicia which are not in contact with any surface. The same test may be applied after the adhesive has been applied. Freeing of the indicia is visible as small spots of different colour or tone occuring (due to air entering between indicia and carrier sheet) or a complete change of tone, showing the whole indicia has been released, may be observed. The freed indicia clings to the carrier sheet by static electricity forces. It only requires that a small amount of such freed points occur at the edge of the indicia to break the edge adhesion bond and permit easy and reliable transfer. Apart from visual changes, the stretch-freeing may be identified by determining the percentage transfer before and afterstretching by the pre-stretch process, Data, which refers to certain of the examples which follow later herein, are set out in the following Table 1:

TABLE 1 Transfer at- Example Stretched p.s.i. p.s.i. 50 p.s.i. 110

r Y 1 p.s.1. 1

High Tack Adhesive,. 0% Example 1, 10% 100% 100% 100% Low Tack Adhesive, 0% 0% 25% Example 3, 0% 100% 100% 100% The specification'of the physical and chemical prop I erties of a carrier sheet and indicia combination which will exhibit stretch-freeing involve a number of complicated measurements and calculations and suitable materials are best selected by the visual andtransfer characteristics described above. terials is assisted by a knowledge of the importance 'of the elongation characteristics of the materials used. The basic requirement for stretch-freeing is that when the carrier sheet is stretched, the indicia should resist stretching (and not fracture) to anextent sufli-cient to break some or all the bonds of adhesion. Obviously'the stronger the bonds of adhesion, the greater must be the resistance of the indicia. As an approximation, the percentage elongation of the carrier sheet at break point, usually a known or easily determined value, and the elongation of the indicia at break-point which is readily determined, are correlated whereby the carrier sheet elongation should exceed the elongation of the indicia with the limitation that the indicia should preferably not exceed 50% elongation otherwise an impractical amount of carrier stretching is required. Values for actual examples which show and do not show stretch-free relationships are given in Table 2. e

TABLE 2 Property Example 1 Example 2 Example 3 Example 4 Stretch-free Good Good Excellent Nil Carrier Sheet Elongation, percent 10 10 100 100 Indieia Elongation,

percent 5-6 5-6 15 55 Adhesion values and their inter-relationships are very important physical properties in the three element assembly and its ancillary protective cover and receiving surface. There are eight adhesion properties identified as follows:

Adhesion values are conveniently estimated by peel bond values which are determined by applying a long However selection of ma- 1 test strip, one inch wide to a standard surface, such as matt polyester drawing film under specified pressures and then measuring the force in grams required to peel off the strip again at right angles at a rate of peel of one foot per minute.

Adhesion 1 and 2.-Adhesion 1 is measured by a direct 90% pull and not as a peel bond, the test procedure serving to measure the force necessary to break the edge adhesion of the indicia. Very high forces are required to overcome edge adhesion but once an edge has yielded, the subsequent force (-peel bond) to completely remove the indicia may be a small fraction of the edge value. The edge value may be 2,500 grams per sq. inch of indicia with a corresponding peel bond of only 4 grams i per inch width. The stretch-free mechanism is perfectly able to overcome the high edge adhesion, which explains its importance. Adhesion No. 2 must be lower than Adhesion 5 since it is the latter value which pulls the indicia off the carrier sheet after it has been stretchfreed, unless 100% stretch-freeing is used.

Adhesion 3.This should exceed other values, so that the adhesive never parts from the indicia.

' Adhesion 4.-When accurate positioning is required this value should be lower than No. 1 unless pre-stretching is used when No. 4 should be lower than No. 2.

Adhesion 5 .This determines the final adhesion of the indicia to the receiving surface after transfer by the correct transfer process. A range of very high values to very low values may be designed. For example on paper surfaces 2. value below 100' grams e.g. 50 grams is de sirable if it is required to subsequently remove the indicia without tearing the surface.

Adhesion 6.-T his must exceed the forces tending to cause removal of the adhesive that is adhesion to the receiving surface, i.e. Adhesion 7.

Adhesion 7 must in turn be less than Adhesion 5 to give the required tack differential and in fact No. 7 is frequently zero.

Adhesion 8 should be as low as possible and less than Adhesion l and preferably less than Adhesion 2.

By way of example, some of the above adhesion values are given in Table 3:

TABLE 3 0. 100 at C.

Selected indicia may be permanently fixed to the receiving surface by the application of a fixing liquid after transfer. indicia are selected so that they may be softened by the application of a liquid which causes the indicia to become soft and tacky and makes direct contact with the receiving surface. The liquid should not however cause the indicia to soften to such an extent that it flows and loses its shape. The combination of an active solvent, which softens the indicia but causes it to flow, and an inert liquid which prevents the flow, provides a suitable composition. The correct proportions are determined by gradually adding the inert solvent to the active solvent until flow is controlled and the indicia still makes full contact with the receiving surface. The fixing liquid may contain a polymer to provide an additional protective film over the indicia (see Example 5).

The stretching process as noted above, may be used as an important additional feature to provide positive protection against premature transfer. The necessity for such protection is best understood by considering the confiicting requirements of the transfer assembly when using a pressure sensitive adhesive. It is necessary to store and transport very large quantities of the transfers even under adverse conditions, with the protective cover in situ but when the latter is removed prior to transfer, the indicia must be completely from transfer onto the protective cover. Furthermore, during transfer it is necessary to position the transfer accurately onto the receiving surface and several contacts may be made under light finger or hand pressure, in which no trans-fer must occur. Nevertheless when the final position is achieved, instant transfer must be possible. In a transfer constructed so that the adhesive pulls the indicia off the carrier sheet it is difficult to achieve positive protection from accidental transfer, particularly as the adhesion of a transfer varies according to the roughness and type of the receiving surface and according to the indicia area.

When the stretching process is to be employed it is preferred to provide a three element transfer assembly in which transfer will positively not occur under light finger pressure /2 p.s.i.) and preferably no transfer will occur up to a pressure of 15 or even 50 psi. However, if the carrier sheet under the indicia is stretched, reversibly or irreversibly, the indicia is partly or completely freed from adhesion to the carrier sheet and will completely and instantly transfer at a low pressure such as 50 or 15 p.s.i. Stretching may be carried out manually by applying a series of strokes of a small radiused rod, ball pen or pencil and a pressure of at least 50 p.s.i. must be applied to cause such stretch-freeing of the indicia. In practice a pressure of 500 or even 1500 psi. is used, the latter being achieved by applying light Writing load of 2 ounces to a ball pen having a .04 inch diameter ball.

Naturally such stretching pressure in addition to freeing the indicia, will simultaneously transfer the indicia. Stretching and transfer in two separate stages may also be practiced and is particularly valuable when either the heavy stretching pressure must not be applied to a delicate receiving surface, or in mechanised application of the transfer. For example the carrier sheet may be pulled over a serrated bar to cause local stretch release at 500 p.s.i. at the tips of the serrations and then applied by a 15 p.s.i. pressure of a rubber roller.

Bearing in mind the requirements in terms of'physical characteristics discussed in detail above, the materials employed may be selected from the following, which are by way of example.

CARRIER SHEET The carrier sheets may consist of individual sheets or reels of a polymer or co-polymer which may be a selfsupporting film or may be applied to a support such as paper, regenerated cellulose, foil or other polymer. Suitable polymers and copolymers are as followspo lystyrene and polystyrene homologues and substituted polystryrene polymers including high impact polystyrene, polystyrenes with rubbery additives such as butadiene as comonomer, polystyrene-butadiene-acrylontrile copolymers; acrylic polymers such as polymethylmethacrylate, and other alkymethacrylates, acrylic polymers with other polymers or co-monomers such as butadiene, and acrylonitrile; vinyl polymers including vinyl-halides, -esters, -acetals and -alcohols and copolymers and with other polymers and co-monomers, cellulose esters and ethers, polycarbonates, rubber hydrochloride, polyolefins such as polyethylene of normal and high density and polypropylene; polyesters; polyamides; gelatin.

Carrier sheets which are soluble or swell or are stress cracked in selective solvents or are reactive towards adhesive liquids are all useable.

The above carrier sheets are characterised in that they soften, swell or etch in selective reactive liquids such as organic solvents, water, acids, which may also be present in the adhesive composition, to provide a reactive adhesive and indicia may be selected from the following list to resist particular liquids and act as the barrier layer.

In the preferred form of the invention, the above polymers are additionally molecularly orientated. Orientation by biaxial stretching is particularly useful and polystyrene and polystyrene containing polymers, polyvinylhalides and copolymers, preferably unplasticised, and polypropylene and polyethylene are particularly useful.

INDICIA The dry indicia preferably consists of an organic polymer which may also contain plasticizers, dyes, pigments, stabilisers and fillers. Suitable polymers are cellulose nitrate; cellulose acetate; cellulose acetobutyrate; ethyl cellulose; ethylhydroxyethyl cellulose; dry oils and dry oil varnishes; alkyds and alkyds modified or copolymerized with a drying oil, styrene, urethane, vinyl, silicone or acrylic resin; polyvinyl-halides, -esters -acetals and alcohols; polyurethanes; epoxy polymers, epoxy-phenolic, epoxy-polyamide and catalysed epoxy resins and copolymers; urea-, melamine-, and benzoguanamine-formaldehyde polymers; chlorinated and isonerised rubber; polystyrene and polyvinyl toluene; polysiloxanes and silicone containing polymers; polyacrylates, polymethacrylates and thermosetting acrylic resins; gelatin; zein; casein, starch or modified starch.

The above polymersare applied to the carrier sheet preferably in the form of a layer of viscous liquid such as a lacquer, i.e. a solution in organic solvents, or an aqueous emulsion, hot melt, plastisol, organosol or as a liquid monomer or liquid polymer containing catalyst. Various printing processes may be used such as screen process, fiexographic or gravure printing. The liquid indicia are then dried or set. If the lacquer contains a solvent this must not react with the carrier sheet under the particular drying conditions and coating thickness, to damage it mechanically or to cause distintegration of the indicia film or increase the adhesion of the indicia past the acceptable limits.

The dry indicia is formulated to provide the necessary specifications of barrier properties, tensile strength, elongation and adhesion to the carrier sheet. Tensile strength is mainly determined by the polymer used and to a less extent on the plasticizer concentration; elongation is also determined mainly by the polymer and the amount of plasticizer; mutual adhesion between carrier sheet and indicia is determined by the polymers used for both the carrier sheet and indicia and also by the plasticizer concentration of the latter, a high plasticizer concentration giving more adhesion than a'low plasticizer concentration by reducing the stretch-free properties. The same chemical class of polymer is preferably not used for the carrier sheet and the indicia since strong specific adhesion forces may be produced.

The pigments, dyes, fillers and stabilisers which may be incorporated in the transferable layer have a moderate effect on tensile strength, elongation and adhesion which must be allowed for. The tensile strength of the indicia is dependent on its thickness and this is also controlled.

PRESSURE SENSITIVE ADHESIVES These consist of a tacky resin or polymer. Alternative- 1y an intrinsically tacky polymer or elastomer may be tackified by the addition of a tacky or non tacky resin or plasticiser. Suitable polymers and tackifying materials are as follows: natural unvulcanised rubber, vulcanised rubber, synthetic rubber such as polyisobutylene, polychloroprene, polybutadiene, polyacrylonitrile and copolymers of these and with styrene and styrene homologues and acrylic monomers; polyvinyl alkyl ethers such as methyl, ethyl and butyl ethers; acrylic and methacrylic polymers such as polybutylacrylate and copolymer with polybutylmethacrylate. Tacky and tackifying resins conv non blocking at room temperature.

. taken place.

sist ofrosin and rosin derivatives such as hydrogenated rosin, esters and alcohols; liquid polymeric styrenes and styrene homologues; polymerised terpenes such as pinene; ketone resins; low molecular weight polyisobutylenes and other olefins.

If required, a tack controlling agent may be added preferably in the form of a soft or easily deformable material to allow good flow and contact with the receiving surface. Particularly suitable