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(11) | EP 0 005 948 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A transfer and process for its use in determining repeatable process conditions for transfer printing |
| (57) It is difficult to be sure that the actual conditions in a transfer printing machine
correspond to the conditions required for a desired depth of hue and shade. A transfer is provided which comprises a stable inert carrier which carries on at least a part thereof a layer containing a mixture of at least two sublimable dyes of contrasting hue and differing transfer characteristics, so chosen that a test print from the transfer will vary in hue or depth of shade with varying conditions of transfer. A standard print is also provided such that a test print from the transfer will match the standard print if the transfer printing machine was operating under the required conditions. The standard may be produced separately under carefully controlled transfer conditions or may be produced in situ with the test print. In the latter case the transfer sheet has, in an area adjacent to the two sublimable dyes of different characteristics which form the test print, a layer containing one or more dyes so chosen that the test print will match if the print is made under the pre-defined transfer conditions. |
[0001] In the sublimation transfer printing process, an inert carrier sheet, typically paper, is printed with inks containing sublimable dyes, this carrier being subsequently placed in contact with a substrate comprising a film or fabric composed of or coated or impregnated with a synthetic material and heated, whereby the dyes, which have affinity for the synthetic material, are transferred by sublimation to the said synthetic film or fabric.
[0002] In practice, the process is of particular interest for the printing of synthetic polymer textile materials. The paper or other carrier may be in the form of sheets, for which the transfer process is performed on a heated flat bed press, or in the form of a continuous roll, when the transfer process is performed continuously onto a roll of fabric using a calender with, for example, one or more heated rollers or cylinders.
[0003] In a variation of the process, transfer is made at air pressures below atmospheric which makes the process more efficient or allows dyes to be used which transfer too slowly at normal atmospheric pressure.
[0004] Typically, the transfer printing process may be carried out under reduced pressure or at atmospheric pressure. Temperatures for the process are usually from 100°C to 230°C, preferably from 160°C to 220°C and times are usually from 10 seconds to 3 minutes.
[0005] Dyes used in the process have transfer characteristics which are dependent on their individual structures. By transfer characteristics is meant the variation of transfer rate with variables of time, temperature and air pressure. For example, under the conditions of temperature, time and air pressure chosen for transferring the print to the substrate, a dye may be very sensitive to variations in these conditions, small variations resulting in large changes in the amount of dye transferred, and hence the depth of shade of the print. Another dye may be relatively insensitive to such variations. Obviously, if these two dyes having different transfer characteristics are mixed together, variation in transfer conditions may lead to variation in the hue, depth of shade, etc. of the final print. Ideally the paper printer will select dyes which will give minimum variation of hue and depth with change in transfer conditions but this is not always possible. To give reliable prints therefore, it is important for the transfer printer to control the transfer conditions, not only to ensure that they remain constant, but that they correspond to those recommended by the paper printer.
[0006] The temperature and timing controls on modern transfer printing machinery usually maintain the set temperature and time accurately but it is difficult to be sure that the actual conditions in the printing machine correspond to the pre-determined conditions required in order to obtain a desired depth of shade and hue. Where so called "vacuum" machines are used, at air pressures below atmospheric, a further variable is introduced.
[0007] We have found that it is possible to determine if a machine is actually operating under pre-determined conditions by passing through the machine a substrate in contact with a carrier which is printed with a mixture of dyes having contrasting hue and different transfer characteristics and then examining the resulting print against a suitable standard.
[0008] According to the present invention there is provided a method of monitoring the transfer conditions existing in a transfer printing machine which comprises producing a test print on a substrate in the transfer printing machine using a transfer comprising a stable inert carrier which carries on at least a part thereof of a layer containing a mixture of at least two sublimable dyes of contrasting hue and differing transfer characteristics so chosen that the test print will vary in hue and/or depth of shade with the varying conditions of transfer and comparing said test print with a standard which the test print on the substrate will match in hue and depth of shade if the machine was operating under predefined transfer conditions during the production of the print.
[0009] The at least two sublimable dyes are chosen so that the test print obtained will vary in hue and/or depth of shade with varying conditions of transfer and this may be achieved by selecting at least two dyes which transfer at rates considerably different from each other.
[0010] The standard print or prints may be produced separately, or in situ with the printed substrate, hereinafter referred to as the test print, in one of the following ways:-
(i) By separately transfer printing or otherwise colouring a suitable substrate to a hue and depth which will match the test print when the latter is produced under the required pre-defined conditions.
(ii) In situ, by means of the stable carrier, which, on an area adjacent to the two sublimable dyes of different characteristics which form the test print, additionally carries a layer containing one or more dyes so chosen that they will produce a print on the chosen substrate, which the test print matches only when the print is made with the machine set to give the required, pre-defined transfer conditions.
[0011] The invention also includes a transfer for use in the method of the invention, comprising a stable inert carrier carrying on at least a part thereof, a layer containing a mixture of at least two sublimable dyes of contrasting hue, and different transfer characteristics so chosen that the test print will vary in hue and/or depth of shade with varying conditions of transfer.
[0012] The invention further includes a transfer for use in the method of the invention comprising a stable inert carrier carrying on part thereof a layer containing a mixture of at least two sublimable dyes of contrasting hue and different transfer characteristics, chosen such that the print obtained varies in hue with variation in the conditions of transfer, and on an adjacent part thereof, carries a layer containing one or more sublimable dyes so chosen that when subsequently heat transfer printed according to the method of the invention, the latter dye or dyes produce a print which the former layer matches in hue and depth of shade if the transfer printing machine used was operating under predefined conditions.
[0013] The method by which the transfer test sheet is prepared can be any that is normally used for producing transfers for the heat transfer printing process. The dyes used are applied to the transfer substrate in the form of an ink or inks which may be based on a non-aqueous, aqueous or partially aqueous system using typical printing processes such as gravure, flexo, litho, off-set litho, and screen or may in some cases simply be applied by a coating machine. Each dye may be applied separately to the transfer but it is preferably to make one ink containing a mixture of the two or more dyes involved.
[0014] It has been found that the choice of dyes is not important provided that they are sufficiently different in transfer characteristics and hue and/or depth of shade to give a mixture which when transferred gives a print which varies in hue with the conditions of transfer. The sensitivity of the system to variations in transfer conditions can be controlled by the choice of dyes. The further apart they are in hue and transfer characteristics, the greater the sensitivity obtained. The dyes must be chosen so that under the conditions of transfer, all show some degree of transfer. They must, of course, be dyes which have affinity for the substrate to be transfer printed. Examples of such dyes may be found amongst those classified as Disperse Dyes and Solvent Dyes in the Colour Index (Colour Index, 3rd Edition, published 1971 by the Society of Dyers and Colourists, Bradford, BD1 2JB).
[0015] The transfer sheet of the invention is used by applying it to a typical substrate using the transfer press or continuous transfer printing machine under test and then comparing the depth and hue of the print so obtained with a standard. When the press or transfer machine is operating under these same standard conditions, then the test print will match that of the standard.
[0016] The standard may be prepared simply by transfer printing from a sample of' the transfer sheet of the invention under very carefully controlled conditions ' onto a suitable substrate. Alternatively, it may be produced using other dyes which have similar transfer characteristics to one another and so chosen that they produce a print which matches that produced when the transfer of the invention is transferred under specified standard conditions. It would also be possible to produce a standard by other methods of coloration such as dyeing or conventional textile printing methods. It may even be possible by careful choice of dyes to use only one in preparation of the standard.
[0017] Another way to obtain a standard print is for it to be produced in situ by the machine under test at the same time as the test print is produced.
[0018] For example, a transfer test sheet, printed according to the invention, so as to carry on part of its area a print comprised of two or more sublimable dyes of contrasting hue and different transfer characteristics may be also printed in an adjacent area with one sublimable dye or a mixture of sublimable dyes with very similar transfer characteristics to one another. This latter will show comparatively little variation in hue or depth over a wide range of transfer conditions. It can be compounded so as to give a standard hue over a range of transfer conditions, for comparison against the hue of the mixture producing the test print. The two mixtures of dyes which are printed on adjacent areas of the transfer test sheet are chosen so that under pre-defined operating conditions of a transfer printing machine, the prints produced by the two mixtures will be of the same hue and depth of shade. The transfer printing machine can thus be tested using such a transfer sheet to ascertain whether or not it is operating under the required conditions.
[0019] In a further extension of the above, a carrier printed with dyes having similar transfer characteristics may be divided into several seperate areas, each area varying in dye content from the next so as to produce a stepwise variation in hue on the substrate when subsequently transfer printed. This can be used as a multistep standard against which to compare the print obtained from the mixture of dyes of different transfer rates. This will allow transfer conditions to be quantified rather than just compared against one standard set of conditions. It will also allow transfer machine operators to set their machines to one of several possible predetermined conditions. As a further alternative, several different mixtures of the dyes of differing transfer rate may be printed onto the carrier in adjacent areas so as to give on transfer, according to the transfer conditions used, a range of hues which may be compared with a standard produced in one of the various ways described above. In a further variation, adjacent areas of a transfer may be printed with two different inks both based on mixtures of dyes having different transfer rates but so chosen that the subsequent transfer print of the two areas will only match if printed under standard conditions. For example, one ink may contain a mixture of two dyes, a slow transferring yellow and a rapid transferring blue, whilst the other may contain a slow transferring blue and a rapid transferring yellow. Only under pre determined standard transfer conditions would the two adjacent parts of print on the textile substrate match. Either or both of these inks may contain extra shading colours to ensure that a match in hue is obtained under the standard conditions.
Example 1
[0021] A gravure printing ink was prepared containing:
10.5 part of the yellow dye of formula(1)
3.6 parts of C.I. Solvent Blue 36 (CI 61551)
4 parts ethyl cellulose (Grade N7)
81.9 parts toluene
[0022] This ink was used on a gravure printing machine to print blocks of colour 2"x3" onto a stable paper substrate in roll form.
[0024] These pieces were then used to print polyester fabric using a flat bed press under the following conditions:
[0025] If the first print (30 sec. at 210°C) is considered as a "standard", then the hues of the other prints when compared to it were as described in column 3 of the above table.
[0026] By using the papers printed as described above on a second flat bed press which was known to have an inaccurate thermometer, it was found possible to set its thermostat to consistently produce 30 second prints which matched the "standard".
Example 2
[0027] The above example was repeated, but substituting the following yellow dye for dye (I).
The results were much the same, except that the hue variation with change in transfer conditions was less marked. This is because the yellow dye of formula (II) is less sensitive to variations in transfer conditions than is dye of general formula (1).
Example 3
[0028] A gravure ink was produced based on a similar formula to that used in Example 1 except that the following dyes were used:
C.I. Disperse Blue 14 (CI 61500)
C.I. Disperse Yellow 54 (CI 47020)
and for shading C.I. Disperse Red 60 (CI 60756)
[0029] The amounts of these were adjusted so that when printed onto paper using the same gravure roller used in Example 1 and subsequently transfer printed onto polyester fabric for 30 seconds at 210°C, the resultant print matched the "standard" print from Example 1 for both hue and depth.
[0030] A roll of paper was then printed using a gravure machine fitted with two printing rollers so etched and set as to print two equal blocks of colour side by side each block 3"x4", the whole surrounded by white. One block of colour was produced using the ink described above and one using the ink from Example 1.
[0031] It was found that when pieces of this paper were used to transfer print and polyester fabric for 30 seconds at a range of temperatures, the two adjacent areas of colour only matched when the transfer was made at 210°C.
[0032] Pieces of paper produced as above were then used to set up a transfer printing machine, by adjusting its temperature until it produced prints on the polyester fabric in which the two adjacent areas of colour matched.
Example 4
[0033] A gravure ink was produced in the same way as in . Example 1 except that it contained the following dyes:
together with a small amount of CI Disperse Red 60 (CI 60756) as a shading dye. The amounts of the three dyes in the ink were adjusted so that when printed onto paper and subsequently transfer printed onto a polyester fabric for 30 seconds at 210°C the resultant print was an exact match to the "standard" print form Example 1.
[0034] Dye (III) is a slow transferring blue and dye(IV) is a rapidly transferring yellow which is the opposite of the combination in Example 1 of a rapid transferring . blue with a slow transferring yellow.
[0035] It was found that if the ink described above was gravure printed in an area adjacent to the ink from Example 1, in the same way as in Example 4, then on subsequently transfer printing onto polyester at a range of temperatures, the two adjacent areas of colour only matched when printed under the "standard conditions" of 30 seconds at 210°C.
1. A method of monitoring the transfer"conditions existing in a transfer printing machine which comprises producing a test
print on a substrate in the transfer printing machine using a transfer comprising
a stable inert carrier which carries on at least a part thereof a layer containing
a mixture of at least two sublimable dyes of contrasting hue and differing transfer
characteristics so chosen that the test print will vary in hue and/or depth of shade
with the varying conditions of transfer and comparing said test print with a standard
which the test print on the substrate will match in hue and depth of shade if the
machine was operating under predefined transfer conditions during the production of
the print.
2. A method of monitoring transfer conditions as claimed in Claim 1 in which the standard
is produced separately from the test print by transfer printing or otherwise colouring
a suitable substrate to a hue and depth which the print on the substrate will match
if produced under the required pre-defined conditions.
3. A method of monitoring transfer conditions as claimed in Claim 1 or 2 in which
the standard is produced by transfer printing a suitable substrate with a sample of
the s-table, inert carrier as described in claim 1 under pre-defined and very carefully
controlled transfer conditions.
4. A method of monitoring transfer conditions as claimed in Claim 1 in which the standard
is produced in situ with the test print, by means of the transfer sheet which in an
area adjacent to the two sublimable dyes of different characteristics which form the
test print, additionally carries a layer containing dye or dyes so chosen that they
will produce a print on the chosen substrate which the test print will match if the
print is made under the required pre-defined transfer conditions.
5. A method of monitoring transfer conditions as claimed in Claim 4 in which the dyes
used to print the standard are dyes with similar transfer characteristics and which
show comparatively little variation in hue or depth over a wide range of transfer
conditions.
6. A method of monitoring transfer conditions as claimed in Claim 4 in which only
one dye is used to print the standard, which dye shows comparatively little variation
in hue or depth over a wide range of transfer conditions.
7. A method of monitoring transfer conditions as claimed in Claim 4 in which the dyes
used to print the standard differ in hue and transfer characteristics, but in a way
which is opposite to those forming the test print, such that only under the pre-defined
transfer conditions will the test print match that of the standard in hue and depth.
8. A method of monitoring transfer conditions as claimed in Claim 4, 5, 6 or 7 in
which several different standards are produced with each test print, each corresponding
in depth and hue to that obtained with the test print at different pre-defined transfer
conditions.
9. A transfer for use according to the method claimed in claim 1 comprising a carrier
carrying on at least a part thereof, a layer containing a mixture of at least two
sublimable dyes of contrasting hue and different transfer characteristics so chosen
that the test print will vary in hue and/or depth of shade with varying conditions
of transfer.
10. A transfer as claimed in claim 9 together with a standard which is produced by
transfer printing or otherwise colouring a suitable substrate and which is applicable
according to the method claimed in claim 2.
11. A transfer as claimed in claim 9 which additionally carries adjacent to the layer
containing the two sublimable dyes of different characteristics, a layer comprising
dyes which will produce a standard during transfer, and which is applicable according
to the method claimed in claim 4.