Strong, flexible dry transfers

A decalcamania or pressure-sensitive dry transfer is described in which a transferable design or indicium is supported on a heat-resistant flexible carrier sheet. The design is formed, at least in part, from a heat-fused plastisol ink and has a pressure-sensitive adhesive coating covering the design and extending onto the carrier sheet. An intrinsically low tack adhesive is employed which is susceptible to plasticiser migration from the plastisol, so that the adhesive tack level is increased only in the part of the adhesive which is in contact with the plastisol. In an alternative embodiment, the adhesive coating is applied first to the carrier sheet and the design printed onto the adhesive coating, the design being releasable by manipulation of the carrier sheet.

This invention relates to dry transfers having a pressure-sensitive 
adhesive layer on the indicia. 
The need to have informative, decorative, or advertising matter on glass or 
other substrates has hitherto been solved by a variety of means originally 
by hand painting which is relatively crude and labour intensive, by using 
printed self adhesive materials which either have unsightly background or 
the obvious shape of the cut plastic or require tedious registration if 
punched to shape for example or by the use of pressure sensitive decals. 
In the case of the latter the need to apply the adhesive in precise 
register with the graphics has always been a problem particularly where 
the graphics are extremely intricate. In the case of the most intricate 
small graphic elements there exists several problems with conventional 
self adhesive decals. With for example nitrocellulose inks used commonly 
for inks for such decals the strength of the ink is very limited and it is 
not possible to build sufficient strength in fine lines to enable the ink 
to be transferred easily without rupturing. If again the adhesive is 
printed overall and requires that the adhesive shears to enable the fine 
detail to be transferred without any unsightly traces of adhesive then the 
adhesive must be of very low tack enabling the shearing process to work. 
This in turn makes the receptivity to glass very poor and transfer of 
complex patterns very difficult indeed. The reason for the limitations 
found with screen process printed nitrocellular transfer is that the mesh 
required to print fine definition graphics is necessarily fine and the low 
solids content of nitrocellulose screen printing inks exacerbates the 
problem of getting sufficiently thick deposits of ink to give the strength 
required for ease of transfer and to overcome the cohesion of the adhesive 
coating so that the adhesive shears accurately. Increasing the tack of the 
adhesives to improve transfer increases the adhesive cohesion, thus 
preventing effective adhesive shearing. Also, increasing the subsequent 
adhesion of the graphics makes removal difficult. Altogether the 
limitations of conventional nitrocellulose decalcamania and transfers 
restrict the ease of use and the graphic qualities and make ease of 
removal also a problem. Such decals are describe din U.S. Pat. No. 
5,571,557 for use as a simulated glass etch. 
Among other solutions proposed for this problem are the methods disclosed 
in U.S. Pat. No. 4,820,559 in which a graphic design is printed and 
activated by solvent to make transfer of the design possible. In this 
particular example of the prior art, the difficulties of working with 
solvents to activate the transfer process, the time required to release 
solvents from between the carrier material and glass in order to develop 
bond of sufficient strength to overcome the bond between graphics and the 
carrier web, makes the process difficult, tedious and time consuming. 
It is the object of the present invention to overcome the problems hitherto 
associated with means of decorating, marking, or providing advertising 
images by transfer onto a range of materials, including glass, plastics, 
metals, wood and painted surfaces. 
According to one aspect of the present invention there is provided a 
decalcamania which comprises a heat-fused plastisol ink supported on a 
heat resistant carrier sheet and having an adhesive layer on the sheet, 
the adhesive being in contact with the plastisol ink and the ink 
consisting a plasticiser capable of migrating into the adhesive layer and 
interacting therewith to form a tacky adhesive layer in those parts of the 
plastisol ink in contact with the adhesive layer. 
The invention also includes a method of preparing such transfers, said 
method comprising forming a design in a plastisol ink onto a 
heat-resistant flexible carrier sheet, curing the ink by heating and 
applying a pressure-sensitive adhesive layer over the design, said 
adhesive having a low intrinsic tack but being capable of interacting with 
plasticiser migrating from the cured plastisol ink to increase the level 
of tack in areas where the adhesive layer is in contact with the plastisol 
ink. 
The steps involved in this new method involve the following: 
A very strong and flexible ink is provided, which can be printed by screen 
process printing such that the ink is highly cohesive even when printed in 
fine lines. An ink which can provide these properties is described in GB 
Patent No. 1488487 and is a plastisol or organosol. In basic terms, the 
first advantages of a plastisol ink is that it contains little or no 
solvent so that the actual deposit printed is not significantly reduced in 
thickness on drying. This must be contrasted with nitrocellulose inks, for 
example, which normally will contain only 25-35% solids and therefore the 
deposit of ink possible for the same definition is only one third or one 
quarter of that obtainable by the plastisol ink. Hence the use of a 
plastisol ink provides a high solids ink (up to 100% solids) and this 
gives immediately three to four times the thickness of deposit compared to 
say nitrocellulose inks given the same screen mesh of equivalent 
definition. The additional strength of a plastisol ink compared to 
nitrocellulose inks is much higher and the elasticity considerably better. 
Combined with the fact that a fully cured plastisol can inherently be 
formulated to give many times more cohesive strength than a nitrocellulose 
ink the advantage of this type of ink is very evident. The plastisol inks 
are formulated from vinyl resins by mixing the vinyl resin powder with a 
suitable plasticiser. The choice of plasticiser is dependent on a number 
of factors, for example: 
(a) some plasticisers dissolve the vinyl powders more readily than others 
and in some cases the plasticisers are such good solvents that some form 
of dissolution occurs even at room temperature. In such cases the inks are 
relatively unstable and after mixing, the solution of the vinyl polymer 
powder can cause the ink to increase in viscosity giving a relatively 
short pot life. When made and used in situ this is not necessarily a 
disadvantage if the process can be controlled in the production of the 
product. On the other hand some plasticisers do not dissolve the vinyl 
polymer powder so readily so that the pot life of the ink is better but 
higher temperatures are required for the plasticiser to dissolve the vinyl 
polymer and form the plastisol film. The plastisol inks employed in the 
present invention typically contain from 45 to 100 parts of plasticiser 
per 100 parts by weight of the vinyl polymer. Suitable plasticisers are 
alkyl phthalates, e.g. dialkyl phthalates wherein the alkyl group contains 
from 4 to 10 carbon atoms, e.g. dioctyl phthalate. Other types of pvc 
plasticisers may be employed such as tricresyl phosphate, or an alkyl 
sulfonic acid ester of phenol (available from Bayer under the trade mark 
Mesamoll). One may also use in conjunction with alkyl phthalates 
dibutyrate esters of polyhydric alcohols, e.g. 2,2,4-trimethyl-1,3-pentyl 
diisobutyrate, which is available from Eastman Chemicals under the trade 
name Eastman TXIB plasticiser. The vinyl polymer is preferably polyvinyl 
chloride but copolymers of vinyl chloride with other vinyl or vinylidene 
monomers can be employed. Normally, a dispersion of finely divided pvc 
particles is formed by mixing or milling the vinyl polymer particles into 
the plasticiser. The plastisol ink, which may be pigmented or clear, is 
deposited on the heat-resistant carrier sheet, preferably by a printing 
process. Screen painting is convenient because thick films can be readily 
formed. After forming the design on the carrier, the ink is cured by heat 
fusing to form a homogeneous plastisol layer. Typical curing conditions 
are 160 to 180.degree. C. for 20 seconds to 5 minutes. 
After curing the ink, a low tack pressure sensitive is deposited onto the 
cured design. The adhesive may be printed in register but this is 
unnecessary as will be explained below. 
It is an observed fact that the plasticisers used to make the plastisol 
inks can be readily absorbed into pressure sensitive adhesives. This has 
been regarded in the past as a serious disadvantage, for example, in 
reducing the kinds of adhesives which may be selected for use in contact 
with highly plasticised pvc films, since the character of the adhesive is 
entirely changed as it picks up plasticiser from the pvc film. 
Consequently, adhesives of choice for application have been those 
unaffected by such migration, e.g. cross-linking, water-based acrylic 
adhesives. 
The plasticiser migration from the vinyl plastisol to the adhesive can be 
accelerated if the adhesive contains solvents which are mutual solvents 
for the adhesive system and the plasticisers used. The temperature of 
processing is also a contributory factor. Under normal temperature 
conditions the migration of plasticiser from the plastisol to the adhesive 
reaches a stable balance after about three days of storage. The effect of 
the plasticiser on the adhesive is to reduce its cohesion and increase its 
tack. With a basically sticky adhesive used on a very compatible 
plasticised plastisol the result can be to turn the adhesive into a messy 
fluid. 
It is, therefore, normal practice to formulate adhesives for plastisols or 
highly plasticised pvc films such that the plasticisers are, as far as 
possible, incompatible with the plasticisers used, water based adhesives 
are used in preference to solvent-based adhesives, and cross-linking 
polymers are preferred as adhesives to non-cross-linked, solvent-soluble 
adhesives. 
However, the underlying concept of the present invention is to capitalise 
on those factors which have hitherto been regarded as major problems and 
to use the effects which can be so disadvantageous to very considerable 
benefit. 
When formulating an adhesive for use in conjunction with a nitrocellulose 
ink the adhesive can be designed without reference to the formulation of 
the ink since no migration of materials occurs from the ink to the 
adhesive. This means that if the adhesive is coated outside the area 
coated by the ink the same physical characteristics of the adhesive are 
maintained. A tacky adhesive which might be required to give very good 
adhesion to say a glass surface would therefore be tacky not only over the 
ink area but also outside the area of the indicia. This is undesirable 
since a sheet say of a number of individual designs would grab the 
substrate and be very difficult to manipulate. Further, the adhesive would 
have a comparatively high cohesive nature and would be more difficult to 
shear around the perimeter of the ink. 
However, with a plastisol ink which provides a migratable plasticiser, the 
adhesive can be so designed to accommodate the migration of adhesive to 
change the nature of the adhesive only in the area where the adhesive is 
in contact with the plastisol. In this case the adhesive is formulated 
such that outside the indicia area it is low tack and does not grab say a 
glass surface and can be readily moved and manipulated on the surface 
whilst on the indicia. Since the indicia is exactly in register with the 
adhesive surface, the latter will be effectively changed to give a more 
tacky adhesive which adheres well to the glass or other substrate. 
Furthermore the adhesive being intrinsically of low tack can be formulated 
to shear very easily. 
The result effectively of combining the use of a low tack shearable 
adhesive with a plastisol such that the plastisol provides a migratable 
component or components which can suitably modify the tack and cohesion of 
the adhesive is that the product has a high tack only where it is required 
that is in complete registration with the indicia. By manipulating the 
types and quantities of various plasticisers having poor to good solvency 
for the vinyl polymer and poor to good migratory properties together with 
poor to good compatibility with the dry adhesive layer the proper degree 
of tack and cohesion can be imparted to the adhesive. 
Since the migration of plasticisers into the adhesive takes a significant 
period of time (approx. 3 days) the exact properties of the stabilised 
product cannot be immediately determined. However, having established the 
formulations, bearing in mind the change occurring the final formulations 
take the changes into consideration. 
Control over the level of adhesive tack by the manipulation of both ink 
formulation and adhesive formulations is broadly achieved as follows: 
Adhesives which are based on vinyl polymers may be selected for the 
purposes of the invention, since the plasticisers employed in plastisols 
migrate effectively into vinyl polymer films. An adhesive coated layer 
consisting of, say, a polyvinyl isobutyl or butyl ether, will vary in tack 
and cohesiveness according to the average molecular weight of the layer. 
Below 30,000 average mol wt the layer will be tacky and low in cohesion. 
Between 30,000 and 70,000 average molecular weight the tack becomes less 
aggressive and the cohesion becomes much higher. 
Over 70,000 average molecular weight the tack becomes much lower and the 
layer is extremely cohesive. 
Without altering the cohesiveness of the adhesive the tack can be further 
altered by adding finely divided extenders such as silica or talc which 
reduce the intrinsic tack further. 
The migratory plasticisers used in the plastisol will migrate relative to 
their molecular weight into the adhesive layer and thus reduce the average 
molecular weight of the adhesive layer. 
The balance required is achieved by increasing the average molecular weight 
of the adhesive layer when the plastisol contains low molecular weight 
plasticisers and reducing the average molecular weight of the adhesive 
when the higher molecular weight plasticisers are used in the plastisol 
ink. 
An average molecular weight of say 40,000 will give a very acceptable 
medium tack cohesive adhesive suitable for pressure-sensitive dry 
transfers. A level of tack similar to that exhibited by such an adhesive 
would be achieved in accordance with this invention by selecting one or 
more polyvinyl isobutyl ethers of average molecular weight above 60,000, 
and using low molecular weight plasticisers in the plastisol ink which 
will migrate into the adhesive to give in the final decalcamania an 
adhesive having an average mol weight of about 40,000. 
A wax may be included in the adhesive formulations to modify the tack level 
of the adhesive. 
Plastisol inks require to be cured at temperatures between 120-180.degree. 
C., preferably 140 to 180.degree. C., for between 20 seconds and 5 
minutes, preferably from 30 seconds to 1 minute. Because of this high 
temperature requirement it is necessary to use temporary supports which 
withstand this kind of temperature. Whilst it may be possible to use 
supports like paper or "Teflon"-coated fabric etc. it is most practical to 
use polyester film. 
The polyester film used would normally be between 50 and 100 microns thick 
to allow for ease of use during sheet fed printing operations but could be 
thinner, e.g. 20 to 40 or 50 microns, for reeled printing operations. 
The ease of release of plastisol inks from polyester films varies depending 
on the characteristics of the ink and the surface of the polyester. In 
order to improve the release qualities of the inks the polyester film can 
be coated with a release agent. 
It is possible to use modified silicone release agents for this purpose, 
but normally this is not always satisfactory since the print qualities are 
affected and the release of adhesive outside the indicia area is also 
possible. A more acceptable release coating can be produced using 
"Quillon" (a product of DuPont Corp.). Even this is usually too good a 
release coating and gives rise to problems through poor adhesion of the 
adhesive coating. Much more superior results are obtained by using release 
coatings based on cross linked epoxy polyamides or similar highly 
cross-linked enamel type resins such as urea or melamine formaldehyde 
resins. Other very satisfactory release coatings can be made from water 
soluble resins such as polymethyl vinyl ether/maleic anhydride resins and 
cellulose derivatives. 
The release coating is applied to the heat-resistant flexible film using 
very dilute solutions of the resins to give coating weights of 0.1-2 
microns. Whilst curing the polyester may mean heating the sheets or reels 
to temperatures in excess of 140.degree. C., this process can be 
beneficially used to heat shrink the polyester to maintain more precise 
dimensional stability at the printing stage should this be required. 
Instead of printing the adhesive over the plastisol ink design; the 
sequence may be reversed and an adhesive layer printed first, followed by 
the plastisol ink. In such an embodiment, a flexible, heat-resistant 
carrier sheet is coated with a release agent, e.g. the carrier sheet is a 
silicone treated paper. The carrier sheet, which may be in the form of a 
web or continuous strip, is printed overall with a low tack adhesive and 
dried. Indicia in a plastisol ink are then printed onto the dried adhesive 
layer and cured by heat fusing the plastisol. The resulting web can be 
coiled immediately without an intervening release sheet because neither 
the adhesive nor the surfaces of the indicia have any significant tack. 
After storage for about 2-3 days, the adhesive under the indicia will have 
increased in tack level because of migration of plasticiser into the 
portion of the adhesive coating which is sandwiched between the indicium 
and the siliconised paper. The indicia can then be transferred to a 
receptor surface, e.g. by pulling the web around an edge or corner. 
Because of the thickness and stiffness of the indicia, this will cause 
them to lift from the carrier paper, when their tacky under-surface is 
exposed and can be pressed onto a receptor surface. Because the adhesive 
outside the areas covered by the indicia has a low tack, and is relatively 
thin, it remains adhered to the siliconised paper surface. This embodiment 
is particularly suitable for printing labels. 
The invention is illustrated in FIG. 1 of the accompanying drawings which 
is a section through a dry transfer in accordance with the invention. 
Referring to the drawing, a flexible carrier sheet 1 of heat resistant 
polymer film is preferably transparent or translucent and is coated with 
an adherent thin release layer 2. On the surface of the release layer one 
or more indicium or other design 5 is printed in a heat-fused plastisol 
ink. Coated over the indicium 5 and extending over the surface of the 
release layer is a coating of a pressure sensitive adhesive 3. This 
adhesive has an intrinsically low tack so that it forms a bond of low 
strength with a substrate. The adhesive is susceptible to plasticiser 
migration from the plastisol ink 5 so that, after several days storage 
following manufacture, the portion 4 of adhesive develops increased tack. 
When the surface of the portion 4 of adhesive is pressed into contact with 
a receptor surface, a strong bond is developed which, on manipulating the 
carrier sheet 1, causes the adhesive to shear around the periphery of the 
indicium. Thus, the indicium 5 is lifted from the carrier sheet leaving 
the remaining adhesive 3 attached to the carrier sheet.

EXAMPLES 
EXAMPLE 1 
1. Polyester film 75 microns thick (e.g. Melinex film) 
The film was coated with a release coating of poly methyl vinyl 
ether/maleic anhydride and cured at 160.degree. C. on a conveyorised belt. 
Indicia were printed on the release coating of a film thickness of about 20 
microns using a black vinyl plastisol ink having the following formula and 
cured by heating to a temperature of about 180.degree. C. in a tunnel oven 
for 60 seconds: 
______________________________________ 
Vinyl chloride homopolymer 
62.65 
Dioctyl phthalate (plasticiser) 
22.50 
Tin based stabiliser 2.00 
Carbon black 2.65 
Ezsol D40 (aliphatic hydrocarbon solvent) 
9.70 
______________________________________ 
The indicia were letters and numerals suitable for vehicle licence plates. 
An adhesive was prepared having the following formulation: 
______________________________________ 
Polyvinyl isobutyl ether average mol wt 100,000 
3.00 
Polyvinyl isobutyl ether average mol wt 60,000 
12.00 
Hydrogenated ester resin (tackifier) 
8.0 
Finely divided Silica 2.4 
Ethylene glycol mono ethyl ether 
12.00 
Xylene 20.00 
White Spirit 42.6 
______________________________________ 
The above adhesive was coated over the entire printed sheet by 
screen-printing and then oven dried at about 100.degree. C. 
The adhesive after drying had a very low tack but the tack developed after 
three days in the precise region of the indicia to give a highly tacky and 
cohesive film over the plastisol indicia and a low tack in the areas 
outside the indicia. 
The indicia were protected with a silicone coated protective paper for 
storage prior to use. The indicia could be transferred to a glass sheet, 
the indicia adhering strongly to the sheet and the adhesive shearing 
precisely around the periphery of the indicia so that there was no border 
of transferred adhesive around the periphery of the transferred indicia. 
EXAMPLE 2 
A carrier sheet consisting of 75 micron polyester was coated with polyvinyl 
vinyl ether/maleic anhydride solution and heated to 150-180.degree. C. to 
form a release layer on the carrier sheet. 
The coated sheet was printed with graphics using heat set inks by the 
offset litho process. 
A clear plastisol layer was screen printed in register with the offset 
litho print using the plastisol ink described in Example 1, except that 
the carbon black pigment was ommitted and heat-fused as described in 
Example 1. 
A pressure sensitive adhesive of non-cross-linking acrylic type was printed 
over the entire sheet covering the printed graphics. After 3 days storage, 
the adhesive developed a differential tack, being of high tack in the area 
of the printed graphics but of low tack outside. The adhesive surface was 
protected with siliconised paper during storage. 
EXAMPLE 3 
A polyester sheet of 75 micron thickness was given an epoxy polyamide 
release coating having a dry film thickness of approximately 0.5 micron. 
A design in a clear plastisol ink containing mica and silica extender was 
printed on the release coating to give an etched glass appearance. The 
plastisol ink was cured as described in Example 1. 
An adhesive as described in Example 1 was applied over the sheet so that it 
covered the design. A differential adhesive tack was developed with the 
adhesive on the plastisol ink exhibiting a high surface tack and the 
surrounding adhesive having a very low surface tack. The resulting 
decalcamania could be used to transfer lettering or other design to a 
window, and simulated the appearance of an etched glass design. The 
adhesive sheared precisely around the design and no adhesive transferred 
with the design. 
Other variations may be made in the preparation of transfers in accordance 
with the invention. For example, other release coatings may be used such 
as melamine-formaldehyde coatings. A variety of effects may be achieved, 
e.g. by screen printing normal vinyl or other inks over the plastisol ink. 
Interesting effects may be secured where the plastisol ink is formulated 
to give an etched glass appearance (as in Example 30 or is a white 
pigmented plastisol ink and additional designs are overprinted. Tinted 
clear plastisol inks may also be employed. 
Any of the conventional printing methods can be used to apply the plastisol 
or other inks, including using digital laser printers. 
There are many uses for the transfers of this invention, including for 
application to glass as a resist for sand-blasting and for manufacture of 
number plates.