Method of manufacturing discontinuous pattern on a support material

Discontinuous transferable adhesive layers have been proposed for manufacture by printing or by coating and subsequent stripping of a matrix to leave a plurality of individual areas of adhesive. Such processes are slow and difficult to effect leading to increased cost. According to the invention, a coating composition is continuously coated on to a release substrate, the composition and drying thereof being selected that, at the end of drying, the adhesive composition is present as a plurality of discrete areas. This may be effected, e.g. by coating an emulsion and drying down appropriately.

FIELD OF INVENTION 
This invention relates to transfer adhesives. 
BACKGROUND OF THE INVENTION 
It is known to use adhesives to prepare artwork for photography or client 
approval by sticking the various components such as photographs, 
headlines, etc. into their desired positions on a layout board. The 
adhesives used in this application should be simple to use allowing the 
components to be re-positioned as desired but providing sufficient 
adhesion between the components and the layout board so that the 
components do not come off during handling. Furthermore, the adhesive 
should be easily cleaned off the layout board without leaving a stain when 
a component has been initially deposited in an incorrect position. 
Solvent based rubber adhesives have been used for this purpose but they are 
messy and difficult to spread uniformly over a surface. Water based 
adhesives are also messy and produce the additional problem of paper curl. 
Spray adhesives require spray areas and adequate ventilation when being 
applied. Hot melt and thermal adhesives require special applicators, the 
applicator for the former being expensive and its use involving a 
time-delay in which the adhesive is heated up. In the latter case, the 
artwork components cannot be repositioned. 
Transfer adhesives have been proposed which overcome the above problems. In 
these adhesives, an adhesive coating is applied to a release substrate and 
then a protective cover sheet is applied to the coating to form a transfer 
sheet. In use, an area corresponding to the size of the component to be 
adhered is cut out from the sheet, the cover sheet removed and the 
adhesive is pressed onto the surface of the component. The substrate is 
then removed leaving the component with an adhesive layer. However, 
problems may be encountered if the adhesive is not correctly positioned 
relative to the component surface and not correctly cut to size. If the 
adhesive is too small and/or incorrectly positioned, edges or corners may 
be left with no adhesive and will be prone to lifting. 
Alternatively, the cover sheet can be removed, the component placed in 
contact with the exposed adhesive, and then the component and its adhesive 
are separated from the remainder of the adhesive sheet by cutting around 
the edge of the component. This is problematic as the cutting has to be 
done with the adhesive exposed, which can be messy and the adhesive may 
not be correctly applied. 
One approach to overcome the problems mentioned associated with the use of 
transfer adhesive sheets is to make the adhesive coating shearable. In 
such an arrangement, the component is pressed on to the adhesive once the 
cover sheet has been removed and as the component is pulled away, the 
adhesive shears to provide the surface of the component with a complete 
covering of adhesive which extends to the edges of the component. However, 
the additives which have to be used to make the adhesive shearable, for 
example, silica, tend to reduce the cohesiveness and tack of the adhesive. 
This results in the adhesive smearing instead of being removed when the 
component to which it is adhered is deposited initially in the wrong 
position and has to be repositioned. 
British Patent Specification 1384423 discloses a further approach to 
overcome the problems mentioned above. In this document, substantially 
non-contiguous adhesive segments are disclosed which are formed on a 
release substrate, the adhesivity between each segment and the substrate 
being less than the adhesivity between the segment and the surface to 
which it is to be affixed. As each segment is substantially non-contiguous 
with adjacent segments, a surface pressed on to the adhesive coating will 
only pick up adhesive on that surface and each segment will be easily 
separated from any other. 
Adhesive transfer sheets according to British Patent Specification 1384423 
can be produced by printing. However, in order to form an eventual strong 
adhesive bond (supplying sufficient adhesive) it is necessary to form a 
coarse pattern of the adhesive segments. This makes such transfer sheets 
unsuitable for use in adhering small items, for example a single line of 6 
point type being stripped into text. Furthermore, printing processes which 
are used to produce such transfer sheets are both slow and expensive when 
compared with web coating processes. 
GENERAL DESCRIPTION OF THE INVENTION 
According to the present invention, there is provided a method of 
manufacturing a discontinuous adhesive product consisting of a substrate 
having a release surface and a plurality of areas of adhesive composition 
distributed on the surface, each such area being removable from the 
surface by the application of a receptor to the exposed faces of the 
individual areas of adhesive composition and peeling apart the receptor 
and release surfaced substrate, the areas of adhesive composition 
adhering, preferentially, to the receptor, which method comprises applying 
a coating composition to the release surface in liquid form, and drying 
the liquid coating composition to semi-solid form, the composition and 
drying conditions being so selected that, during drying, the continuous 
layer of coating composition breaks up into a plurality of discrete areas. 
It has been found that this method enables a discontinuous adhesive pattern 
covering a release substrate to be formed easily and without the 
disadvantages associated with the printing or coating and stripping 
systems proposed in British Patent 1384423. 
In order to carry out the process of the invention, care must be taken to 
formulate the coating composition to ensure that, after coating on to the 
substrate, it breaks up to discontinuous form. A preferred way of 
achieving this is to formulate the adhesive as a conventional water based 
polymer emulsion and then further emulsify this with an immiscible 
hydrocarbon solvent. When such a double emulsion is coated onto a 
water-repelling release surface and then dried, a discontinuous layer of 
adhesive polymer in a fine pattern results. The size of the pattern is 
determined by the size of the hydrocarbon droplets and competition for the 
release surface. The adhesive polymer has a cohesive strength and enough 
tack to make it adequately adhesive for the purpose intended. Acrylic 
polymers are particularly suitable and silicone release surfaces are 
preferred. 
The tack/adhesion of the final discontinuous layer can be adjusted by 
changing the acrylic polymer emulsion from which it is made. Similarly, it 
can be influenced by the dry coat weight, and by the dot size and 
distribution of the dried adhesive. This itself is influenced by the 
concentration of the hydrocarbon solvent and the application viscosity of 
the applied adhesive. 
It may be convenient to blend the acrylic or similar pressure sensitive 
aqueous emulsion with an aqueous polymer emulsion of high cohesive 
strength, e.g. a styrene butadiene acrylonitrile copolymer. This high 
cohesive strength polymer increases the overall cohesive strength of the 
final adhesive significantly. This allows for the easy removal of the 
adhesive from the surface of the card after use, by rubbing with a finger 
or eraser, by causing the adhesive to "ball up" on rubbing. It also 
reduces the risk of contamination on repositioning or on subsequent 
removal of the adhesive. 
It may also be convenient to colour the discontinuous adhesive layer so 
that the user can ascertain whether the adhesive has been picked up from 
the silicone release surface, determine what areas of adhesive on the 
release surface have been used and to show up any areas of contamination 
during use so that they can be easily removed. This can be simply achieved 
by the use of aqueous dyes or aqueous pigment dispersions. Care should be 
taken not to use too high a level of colourant or else "show through" of 
the adhesive will occur when used on thin substrates. 
As noted in British Patent 1384423, it is convenient to be able to roll up 
or stack the adhesive material, and in order for this to be done, the 
adhesion between the individual areas of adhesive and the back of the 
release coated substrate must be less than the adhesion between them and 
the front of that substrate. British Patent 1384423 suggests using a 
substrate with differential release properties on its two sides. This may 
be done in practising the present invention, with the emulsion being 
applied on the less releasing side. However, an alternative approach is to 
incorporate a small quantity of a silicone adhesive into the coating 
emulsion to "key" the adhesive polymer onto the release surface. This 
reduces the amount of set-off onto the back of a release substrate having 
the same release properties on both sides. Without this "keying" 
mechanism, there would be considerably more set-off when the substrate is 
rolled up or when sheets are pressed together in pad form. Obviously, the 
"keying" should not be overdone, otherwise the adhesive will not release 
adequately from the substrate when in use. 
The following Examples will serve to illustrate the invention.

EXAMPLE 1 
A coating emulsion was made up of the following composition (parts by 
weight): 
______________________________________ 
Acrylic ester copolymer emulsion 
30 parts 
(Revecryl 396 ex Harlow Chemicals) 
Water 10 parts 
Hydrocarbon solvent 20 parts 
(Exsol 145/160 ex Esso Chemicals) 
______________________________________ 
This emulsion was made by first diluting the acrylic emulsion with the 
water using a planetary mixer. After 10 minutes mixing, the hydrocarbon 
solvent was added, 5 parts at a time, using the slowest speed compatible 
with the incorporation of the solvent. After all the solvent had been 
absorbed, stirring was continued for a further 15 minutes. 
The resulting mixture was then coated onto a web of differential release 
paper (Quicklease 40/804 ex Jointine Ltd). The coating was applied using a 
Meyer bar (size 8, wire diameter 0.2 mm) at a speed of about 10 m/min. 
After drying at 90.degree. C. for 5 minutes the coating was found to have 
broken up into a random pattern of discontinuous adhesive segments 
generally less than 2 mm across at their maximum dimension and separated 
by gaps of less than 1 mm. 
The adhesive could be picked up by an applied piece of card using pressure 
and no shearing of the adhesive was observed, whilst each segment of the 
adhesive was removed cleanly, when the card was lifted from the substrate. 
The card holding the adhesive adhered firmly to artwork but could be 
removed and repositioned as necessary and any adhesive left behind on the 
artwork could be removed by rubbing it off. Additional layers of adhesive 
could be picked up onto the card prior to adhering the card in position. 
The adhesive transfer to the card could be achieved either way up, i.e. 
pressing the card onto the adhesive pattern or placing the release paper, 
adhesive side down, on to the card, pressing down, and peeling away. 
EXAMPLE 2 
A coating composition was made up of the following components (parts by 
weight): 
______________________________________ 
Acrylic copolymer emulsion (Crodafix 27-017 
80 parts 
ex Croda Adhesives Ltd.) 
Styrene butadiene acrylonitrile copolymer 
20 parts 
emulsion (Revinex 34D10 ex Doverstrand Ltd.) 
Silicone adhesive solution (2.2% by weight 
66 parts 
solution of DC 282 ex Dow Corning Ltd in 
hydrocarbon solvent (Exsol 145/160)) 
Water 33 parts 
______________________________________ 
The two copolymer emulsions were mixed together for 10 minutes using a 
planetary stirrer. The silicone solution was then added and the mixture 
was stirred for a further 45 minutes. Finally, the mixture was diluted 
with the water. 
45 Gsm white greaseproof paper (ex Union Paper Co Ltd) was coated with the 
mixture using an 8 Bar at 10 m/min. The coating was dried at 90.degree. C. 
for 5 minutes. The resultant web was sheeted, stacked, and left for 24 
hours. 
On inspection of the stack, it was found that there was little tendency for 
the coating to offset onto the back of similar sheets, it being 
preferentially held to the coated side by the silicone adhesive. 
EXAMPLE 3 
A coating emulsion was made up of the following composition (parts by 
weight): 
______________________________________ 
(Revacryl 491 high tack/adhesion acrylic 
80 parts 
pressure sensitive adhesive emulsion ex 
Harlow Chemicals) 
Styrene butadiene acrylonitrile copolymer 
20 parts 
emulsion (as in Example 2) 
Colouring agent (30% Monastral Blue BG (ex 
0.1 parts 
ICI) in 6% Gelvatol 40-20 polyvinyl alcohol 
(ex Monsanto) solution 
Silicone adhesive solution (3.1% by weight 
66 parts 
solution of DC 282 ex Dow Corning in Exsol 
145/160) 
Water 41.5 parts 
______________________________________ 
The emulsions and the colouring agent were mixed together until homogeneous 
using a paddle stirrer. The silicone adhesive solution was added while 
continuing stirring with the paddle stirrer and stirring continued until 
all the solution had been incorporated. The water was added while sturring 
to dilute the mixture to its coating viscosity. 
41 gsm white siliconised greaseproof paper (ex Union Paper Co Ltd) was 
coated with the mixture using a 10 meyer bar at around 10 m/min and dried 
at 60.degree. C. for 10 minutes. 
The resultant adhesive when picked up on to card or paper in the way 
previously described had a higher degree of surface tack, higher adhesion 
to surfaces and was more permanent than that of Examples 1 and 2.