Method of making underwater marker

To make an underwater marker with indicia on it, an uncured or partcured base material of one color is prepared with the shape of the desired indicia cut out of it. The indicia are cut from uncured or partcured material of different color and are fitted into the cut-out in the base material to form a single layer. A transfer material bearing antifouling material is placed over the face of the layer and the assembly is pressed together to embed the antifouling material into the layer and to cure the contrasting materials together with each other and with an optionally underlying reinforcing layer. A backing sheet of the transfer material is stripped off to expose the particles.

The marking of structures underwater is a problem. Ordinary painted or 
embossed signs will very soon be corroded away or hidden by growth. The 
making of markers with an antifouling surface however presents 
difficulties in the preservation at the same time of the antifouling 
properties and of contrast in the surface by which symbols can be 
recognised. 
The present invention is concerned with a particularly attractive and 
economical solution of this problem. 
In this invention an underwater marker is made with an antifouling surface 
by using part-cured or uncured sheets of elastomer of contrasting colours, 
by making a positive shape of a desired symbol from a sheet of one colour, 
making a negative outline of the same symbol from a sheet of a colour 
contrasting with the one colour, the positive and negative outlines being 
closely conforming. 
fitting the positive into the negative outline to form a single-thickness 
sheet, 
placing on the surface of the single-thickness sheet which is exposed and 
which shows the contrasting symbol a transfer material bearing antifouling 
particles, with the particles contacting that surface, 
moulding the layers together to embed the particles in the said surface and 
to cure together the sheets the particles and a reinforcing backing sheet, 
if provided, and 
stripping off a backing web of the transfer material to leave exposed a 
cured surface of a reinforced marker laminate in which the desired symbol 
is visible and over the area of which the antifouling particles are 
distributed. 
The method may include assembling the single-thickness sheet on a part 
cured or uncured reinforcing sheet (the fitting together of the two 
contrasting sheets may be done at the same time as or later than the 
assembly with the reinforcing sheet). 
The moulding is preferably done within a moulding frame to the dimensions 
of which both the elastomer and reinforcing sheets are carefully cut, 
whereby moulding pressure is prevented from causing any substantial 
sideways escape of the laminate or of its elements. 
If the moulding is carried out under controlled conditions of temperature 
and pressure, readily found by empirical trial, it will be found that an 
effectively jointless uniform sheet is formed by the curing together of 
the materials of contrasting colours but without any substantial running 
or blurring at the interface between them, that the particles are firmly 
embedded, that a firm lamination is achieved and that there is no run off 
at the edges. 
In particular it is desirable to carry out the moulding in a moulding frame 
which constrains the edges of the sheets as mentioned and of which an 
uppermost surface is of the order of 0.5 mm lower than the exposed surface 
of the sheets of contrasting colours. 
The transfer material may be that claimed in and made by the method of 
copending European application No. 86302149 now European patent 
publication No. 0196207, published Oct. 1, 1986, equivalent to U.S. 
application No. 843,739 (Turner) filed on 25 Mar. 1986 now U.S. Pat. No. 
4,753,701, issued June 28, 1988.

We describe first how to make a transfer material which may be the material 
applied in the present invention: 
FIGS. 1 and 2 of the drawings illustrate apparatus for the application of 
cupro nickel granules to adhesive tape. The apparatus should be capable of 
applying granules to adhesive strip or sheet of widths between about 0.3 
and 1 m. 
A backing web 1 of material with an adhesive surface 1 is pulled off a roll 
2 of tape by means of a knurled roller 3 driven through a belt 4 by an 
electric motor 5. A suitable web is available from Adhesive Tapes and 
Conversions Limited, Crowborough, Sussex, England, under the name PPI 
1022. The web passes over an idler roller 6 downwardly into a dip 7 before 
rising at 8 to a roller 9 which is driven by belt 10 from the motor 5 via 
belt 4. Photo electric sensors 11,12 detect if the base of the dip reaches 
a level below sensor 11 or above sensor 12, and stop the drive if it does. 
End plates 13 are similar to the guides on a mill roll and can be set to 
accommodate the width of the web with a minimum or zero gap between the 
edges of the web and themselves. A trough 14 is below the dip. A bank of 
granules 15 such as the chopped copper or copper wire as described above 
is placed on the adhesive web 1 in the dip 7 and is held on it by the end 
plates 13. It has been found that, when the strip is pulled through by the 
roller 9, the weight of the granules is sufficient to preserve the dip 7 
and the granules roll, providing excellent coverage of the tape by an 
adhered layer 16 of granules. Granules which are not adhering to the tape 
will roll back down the incline 8. The only escape for the granules is 
that some will fall over the edges and these are caught in the tray 14. 
These can be led back to the bank 15. Guide surfaces (not shown) may be 
provided especially behind the rise run 8 to help form the dip and prevent 
bulging or swinging. 
The web with granules on its surface passes between the driven roller 9 and 
a pressure roller 17 to consolidate the adhered layer 16 and then a 
variable loop 18 to a main conveyor 19 which includes a spraying zone 20. 
There need to be sufficient spraying guns to ensure coverage of the 
complete width of the strip. The number of spray guns can be activated 
according to the required width and spray beyond the edges of the web can 
be blanked off. 
The first row 21 of spray guns would be spraying a primer such as Chemlok 
Primer 205 and the second row 22 an adhesive such as Chemlok Adhesive 
CH47. Extraction and hot air driers are provided and, if necessary, 
infra-red heating. 
At the moment, anti-fouling material is required in lengths of about 4 m. 
In this case the total length of the run of the main conveyor 19 should be 
1 m. in the region 23 before the spraying zone, 2 m. in the spray zone 20 
and 5 m. in the region 24. This will provide room for material to be cut 
to length and removed sideways from the conveyor 19. This main conveyor 5 
(as also the web drives) can be hand driven but preferably will be 
powered. 
It is moved intermittently to allow further actions (to be described) or 
cutting and removal to occur in the region 24. Since the web 1 is in 
principle being moved continuously, the loop 18 varies in its extent 
between the limits shown. Photo electric sensors 25,26 detect these limits 
and may indeed control the drive of the conveyor 19 in a repetitive run. 
To make an underwater marker a positive image 30 is made of a desired 
symbol, here the Arabic numeral 3. This is made from a sheet of uncured 
elastomer material of one colour for example yellow. 
Another sheet of the same or a compatible uncured or part-cured material is 
meanwhile prepared as seen at 31 with a negative image 32 cut from it in 
the appropriate place, which of course need not be central in the manner 
as shown here, but could be anywhere on the sheet. Furthermore, more than 
one symbol may be let into the sheet 31 and these may be of the same or 
respectively different colours contrasting with the colour of the sheet 
31. 
The outer dimensions of the sheet 31 are known. The positive and negative 
images of the symbol are made very precisely to conform exactly to each 
other. 
In a next step the two sheets are assembled together and with an uncured or 
partly cured reinforcing layer 33 in a mould frame 34. It is clear that 
the positive image 30 of the symbol may be inserted into the sheet 31 
before they are placed together upon the pre-placed reinforcing layer 33 
or the two layers may be assembled together before being placed in the 
mould or (as is probably most convenient) the reinforcing layer 33 may be 
placed first in the mould followed by the layer 31 and the positive image 
30 of the symbol being placed in last. In whichever order the steps are 
carried out, the assembly of 30 and 31 results in a sheet of single 
thickness--that of the sheet 31. 
The moulding frame 34 may have a base and walls 35 as shown or may simply 
be an open-bottomed frame with walls 35 only. It is dimensioned to fit 
exactly the outer dimensions of the sheet 31 and the reinforcing layer is 
cut equally to fit. 
The nature of the reinforcement in the layer 33 may be conventional cord 
layers or the like and its matrix is part cured or uncured and is 
compatible with the materials used in sheets 30 and 31. 
Transfer material to be taken from or still at the region 24 is now cut to 
the same size to form sheet 36. It is placed on the exposed face of the 
sheets 30,31 with the metal particles 37 in contact with that face. 
Then as seen in FIG. 5 a heated press mould plate 38 is applied to at least 
one face of the laminate to press together the sheets 30,31 and 33 and 36, 
to cure them together i.e. to cure together both the sheets 30 and 31 
around the boundaries of the symbol and to cure both of those sheets 
together with the reinforcing layer 33. 
At the same time the particles 37 are forced into and embedded in the 
exposed surface of the sheets 30,31 over the whole of that surface and are 
cured into it. 
The conditions of pressure and temperature are to be regulated in such a 
way as not to cause undue distortion of the sheets which would cause 
distortion of the symbol and perhaps a spread or flow of the material at 
its edge leading to some indistinctness or confusibility. Furthermore the 
complete laminate should be contained within the walls 35 of the frame so 
that there is no opportunity for heated material to escape and flow from 
the edges of the laminate since this would cause decrease of the particle 
density in that area and thus possible encroachment of marine growth upon 
the marker when it is in use. 
A particularly useful rule of thumb method of limiting the pressure applied 
is to construct the mould frame in such a way that the walls 35 are 0.5 mm 
less high than the uncured assembly including the thickness of the uncured 
elastomer sheets plus reinforcing sheet, see FIG. 4. 
Then as best seen in FIG. 6 the backing web 39 of the transfer material 36 
is stripped off leaving the metal particles embedded in a substantially 
uniform but random distribution over the whole of the face of the finished 
article 40. If necessary, the particles may be polished or buffed in that 
surface.