Printing compositions

A printing medium comprises a thermoplastic resin and a rheology-controlling diluent, the medium having a melting point of between 40.degree. and 80.degree. C., and being non-tacky at room temperature. The diluent is preferably selected from liquid resins, high molecular weight esters, fatty alcohols and saturated fatty acids. The medium is used in a method of decorating an article comprising forming an image of the decoration in a flowable ink composition on a heated support, picking up the image from the support on a silicone transfer member at a lower temperature to form a flexible film on the transfer member in a semi-fluid condition, and applying the film to an article to be decorated within a period of time during which the composition remains semi-fluid whereby the composition solidifies immediately on contact with the surface of the article to form a non-tacky coating thereon.

This invention relates to printing compositions and is especially, but not 
exclusively, applicable to compositions for use in printing or decorating 
heat resistant substrates such as glass, ceramics, including tiles and 
tableware, or enamelled metals. 
Off-set printing techniques are known in which a printed image is 
transferred by a flexible pad or other carrier member from a printing 
station to a decorating station where the image is applied to an article 
to be decorated. Hitherto pads formed from gelatine were widely employed, 
but more recently silicone pads have been employed and the decorating 
compositions or inks used for such purposes must be compatible with the 
silicone pad and hitherto have been designed to dry on the decorated 
article by solvent evaporation or by a combination of solvent evaporation 
and oxidation. 
Various problems are encountered in utilising decorating inks of this kind. 
While such inks are generally suitable for relatively low printing speeds 
and for single colour printing, they are not entirely satisfactory when 
used for high speed multi-colour printing. Moreover, such inks do not 
always give 100% transfer from the pad to the article being decorated and 
hence, when used for multi-colour printing there is a tendency for the ink 
retained on the transfer pad at one decorating stage to be transferred to 
the article during subsequent stages thereby resulting in reject items. 
Moreover, inks of this type are subject to changes in rheological and 
printing properties throughout the printing run due to the volatilisation 
of solvents. This necessitates frequent adjustment of ink and machine 
settings to ensure colour consistency which is time consuming and 
inconvenient. Many such inks also have a limited shelf life. 
It is an object of the present invention to obviate or mitigate at least 
some of these disadvantages. 
According to one aspect of the invention there is provided a printing 
medium comprising a thermoplastic resin and a rheology-controlling 
diluent, the medium having a melting point of between 40.degree. and 
80.degree. C. and being non-tacky at room temperature. 
Preferably the rheology-controlling diluent comprises a liquid resin, a 
high molecular weight ester, a fatty alcohol or a saturated fatty acid. 
The term "high molecular weight ester" is used herein to refer to esters 
having molecular weights greater than 200. 
Preferably the medium comprises from 30% to 98% of thermoplastic resin and 
from 2% to 70% of diluent. Advantageously the thermoplastic resin 
component may comprise two or more resins to extend the thermo-plasticity 
of the medium, one of the resins being a film forming resin such as an 
acrylic resin. 
The medium may be used to form a printing ink composition by the addition 
of suitable quantities of a pigment, flux or other required constituent. 
According to a further aspect of the invention there is provided a printing 
composition which is fluid at temperatures between 40.degree. and 
80.degree. C., will form a coherent film on a silicone transfer member and 
will release completely therefrom and solidify immediately on contact with 
the surface of an article to be decorated, to form a non-tacky coating 
thereon. 
The invention also provides a method of decorating an article comprising 
forming an image of the decoration in a flowable ink composition on a 
heated support, picking up the image from the support on a silicone 
transfer member at a lower temperature to form a flexible film on the 
transfer member in a semi-fluid condition, and applying the film to an 
article to be decorated within a period of time during which the 
composition remains semi-fluid whereby the composition solidifies 
immediately on contact with the surface of the article to form a non-tacky 
coating thereon. 
The term "complete release" is used herein to refer to a degree of release 
or transfer of the film leaving no visible or readily ascertainable trace 
thereof remaining on the transfer member. 
The term "immediate" is used herein to refer to solidification which takes 
place instantaneously or within a few seconds. 
The term "silicone" as used herein in relation to transfer members or pads 
is to be construed as referring to transfer members or pads at least the 
working surface of which consists of or incorporates a major proportion of 
silicone. 
Any thermoplastic resin having the required thermoplasticity and thermal 
decomposition properties may be employed. Preferably, however, the resin 
is selected from cellulose ethers, styrenes, terpenes, methacrylates, 
rosins, modified rosins and rosin esters. 
Suitable liquid resin diluents include triethylene glycol ester of rosin, 
hydrogenated methyl ester of rosin, low molecular weight (300-400) styrene 
resin and polyterpene derived from alpha-pinene. 
Preferably the high molecular weight ester diluent is selected from 
materials within the melting point range 25.degree.-50.degree. C. and 
comprising the palmitates, stearates and laurates. Methyl palmitate 
(Melting Point 24.degree. C.), methyl stearate (MP 36.degree. C.), 
propylene glycol monostearate (MP 38.degree. C.), stearyl laurate (MP 
41.degree. C.) and diethylene glycol monostearate (MP 44.degree. C.) have 
been found particularly suitable. Other suitable esters include the 
phthalates such as diethoxyethyl phthalate (MP 34.degree. C.) and dibenzyl 
phthalate (MP 42.degree. C.), and the benzoates such as neopentyl glycol 
dibenzoate (MP 49.degree. C.) and triethylene glycol dibenzoate (MP 
47.degree. C.). 
Preferably the fatty alcohol diluents are selected from fatty alcohols 
having from 12 to 18 carbon atoms in the chain, including myristyl alcohol 
(MP 39.degree. C.), cetyl alcohol (MP 49.degree. C.) and stearyl alcohol 
(MP 58.degree. C.). 
The fatty acid diluents are preferably selected from those having 10 to 18 
carbon atoms in the chain, including capric acid (MP 31.5.degree. C.), 
lauric acid (MP 44.degree. C.) and myristic acid (MP 58.degree. C.). 
The diluent must be compatible with the resin at elevated temperature since 
in the molten state (that is at operating temperature) it acts to reduce 
the melt viscosity of the resin to the required level for good printing 
performance. 
Generally, two or more thermoplastic resins will be employed in combination 
to extend the thermoplasticity of the ink composition. Preferably one 
resin has a softening point within the range 105.degree.-170.degree. C. 
and the other a softening point within the range 5.degree.-90.degree. C. 
It is particularly advantageous that one of the resins used should be a 
true film former in order to impart high internal cohesion to the ink film 
and to assist in maintaining its integrity during the transfer operation 
from the silicone surface to the article being printed. 
The viscosity of the composition may be altered to suit desired 
requirements. Relatively low viscosity compositions are desirable when 
dealing with patterns or decorations having fine detail, whereas higher 
viscosity can be used in other cases. The viscosity can be controlled by 
means of the proportion of resin to diluent utilised without substantially 
affecting the physical performance of the composition. Suitable 
viscosities are those within the range 1-60 poises at a shear rate of 615 
sec.sup.-1 within the operational temperature range of 
40.degree.-80.degree. C.

The following are examples, given by way of illustration only, of 
decorating mediums according to the invention, all proportions being by 
weight. 
EXAMPLE 1 
Underglaze Medium for printing on to porous earthenware at a temperature of 
65.degree. C.-70.degree. C. 
______________________________________ 
Methacrylate Resin (softening point 120.degree.-140.degree. C.) 
20% 
Styrene Resin (softening point 50.degree. C.) 
20% 
Diethylene Glycol Monostearate (melting point 44.degree. C.) 
60% 
______________________________________ 
EXAMPLE 2 
Underglaze medium for printing on to vitrified earthenware at a temperature 
of 55.degree.-60.degree. C. 
______________________________________ 
Methacrylate Resin (softening point 150.degree.-160.degree. C.) 
30% 
Terpene Resin (softening point 25.degree. C.) 
20% 
Stearyl Laurate (melting point 41.degree. C.) 
50% 
______________________________________ 
EXAMPLE 3 
Onglaze pottery medium for printing at a temperature of 55.degree. 
C.-60.degree. C. 
______________________________________ 
Methacrylate Resin (softening point 130.degree.-140.degree. C.) 
28% 
Styrene Resin (softening point 75.degree. C.) 
5% 
Propylene Glycol Monostearate (melting point 38.degree. C.) 
67% 
______________________________________ 
EXAMPLE 4 
Inglaze pottery medium for printing at a temperature of 50.degree. 
C.-55.degree. C. 
______________________________________ 
Methacrylate Resin (softening points 130.degree.-140.degree. C.) 
40% 
Styrene Resin (softening point 5.degree. C.) 
2% 
Methyl Stearate (melting point 36.degree. C.) 
58% 
______________________________________ 
EXAMPLE 5 
Borosilicate or soda glass medium for printing at a temperature of 
60.degree. C.-65.degree. C. 
______________________________________ 
Ethyl Cellulose (softening point 150.degree.-160.degree. C.) 
12% 
Terpene Resin (softening point 10.degree. C.) 
78% 
Methyl Palmitate (melting point 25.degree. C.) 
10% 
______________________________________ 
EXAMPLE 6 
Medium for printing on to enamelled iron or enamelled aluminium at a 
temperature of 45.degree. C.-50.degree. C. 
______________________________________ 
Methacrylate Resin (softening point 105.degree.-115.degree. C.) 
10% 
Terpene Resin (softening point 25.degree. C.) 
30% 
Methyl Stearate (melting point 36.degree. C.) 
60% 
______________________________________ 
EXAMPLE 7 
Underglaze medium for printing on to porous earthenware at 50.degree. 
C.-55.degree. C. 
______________________________________ 
Glycerol Rosin Ester (softening point 73.degree.-78.degree. C.) 
50% 
Isobutyl Methacrylate (softening point 105.degree.-115.degree. C.) 
20% 
Myristyl Alcohol (melting point 39.degree. C.) 
30% 
______________________________________ 
EXAMPLE 8 
Borosilicate or sodaglass medium for printing at a temperature of 
70.degree. C.-75.degree. C. 
______________________________________ 
Isobutyl Methacrylate (softening point 130.degree.-140.degree. C.) 
13.5% 
Styrene resin (softening point 5.degree. C.) 
76.5% 
Cetyl alcohol (melting point 49.degree. C.) 
34.5% 
______________________________________ 
EXAMPLE 9 
Underglaze medium for printing on to vitrified earthenware at a temperature 
of 60.degree. C.-65.degree. C. 
______________________________________ 
Rosin maleic pentaerythritol ester 
55% 
(softening point 123.degree. C.-127.degree. C.) 
Methyl ester of hydrogenated rosin (liquid) 
5% 
Stearyl Alcohol (melting point 58.degree. C.) 
40% 
______________________________________ 
EXAMPLE 10 
Inglaze pottery medium for printing at a temperature of 75.degree. 
C.-80.degree. C. 
______________________________________ 
Isobutyl Methacrylate (softening point 105.degree.-115.degree. C.) 
12% 
Terpene resin (liquid) 88% 
______________________________________ 
EXAMPLE 11 
Medium for printing on to enamelled iron at a temperature of 55.degree. 
C.-60.degree. C. 
______________________________________ 
Isobutyl Methacrylate (softening point 130-140.degree. C.) 
25% 
Styrene resin (softening point 5.degree. C.) 
37.5% 
Lauric acid (melting point 44.degree. C.) 
37.5% 
______________________________________ 
Decorating compositions can be prepared from the carrier mediums set out in 
Examples 1-11 by dispersing in the medium a proportion of an appropriate 
colouring material or pigment to suit the article to be printed. In the 
case of underglaze decoration of pottery, underglaze colours would be 
utilised and likewise onglaze colours would be adopted in respect of 
mediums intended for use in the onglaze decoration of pottery. Generally 
the ink composition will consist of 40-80% colouring material and 60-20% 
carrier medium. 
Decorating compositions according to the invention may be applied using a 
variety of different printing techniques. In one arrangement the 
composition may be applied to a heated intaglio plate on which the pattern 
to be applied to the article is engraved or etched, the transfer pad 
serving to pick up the inked image from the plate and transfer it to the 
article. In an alternative arrangement the decorating ink may be applied 
through a heated screen on to a heated flat plate, the image being 
subsequently picked up from the flat plate by means of the silicone 
transfer member. In a further arrangement, the pattern may be screened on 
to a heated silicone or silicone coated diaphram, the diaphram then being 
used as a carrier to transfer the screened pattern to a position above the 
ware where it is pressed into contact with the ware by the silicone pad or 
a similar conforming pressure member. Other forms of apparatus may also be 
used in association with decoration compositions according to the 
invention. 
The operating conditions require to be such that the ink is fluid when the 
initial image is formed and will adhere satisfactorily to the transfer 
member or pad when picked up from the plate or the like on which the image 
is supported. A coherent film in a semi-fluid state is formed on the pad 
during transfer to the article but care is necessary to ensure that the 
film does not dry or solidify on the pad. This may be controlled by 
varying the proportion of diluent to resin. 
The operating temperatures may be varied dependent on the composition of 
the medium, the article to be decorated and the apparatus utilized. In 
general however the plate or the like on which the image is supported will 
be at a temperature of 40.degree.-80.degree. C., and the pad will operate 
at a temperature of the order of 25.degree.-50.degree. C., due to the heat 
imparted to the pad by contact with the decorating composition and the 
plate, the article being at ambient temperature of the order of 
16.degree.-28.degree. C. The time the composition remains on the pad may 
also vary considerably to suit individual circumstances but will generally 
be of the order of 0.01-30 seconds. 
Decorating compositions of the kind described above have the advantage that 
once machine operating conditions are set there is little or no need for 
further adjustment throughout the production run. Furthermore, the 
physical properties of the composition do not change during the printing 
operation irrespective of the length of time for which printing is carried 
out. A multiplicity of colours may be printed one following the other 
without the problem of decorating ink remaining on the silicone transfer 
member and subsequently causing spoilage of the final decoration. 
Ink compositions according to the invention also have a superior capability 
for resolving fine image detail compared with conventional decorating 
means. This is due to the fact that when the silicone transfer surface 
contacts the ink in its fluid state, the lower surface temperature of the 
silicone results in an instantaneous change in state of the ink rheology 
from fluid to semi-solid. Consequently, the ink does not flow or spread 
and the most minute image detail is maintained virtually in its original 
form. 
Various modifications may be made without departing from the invention. For 
example, other compositions having the desired physical properties may be 
utilised and though principally evolved for the decoration of heat 
resistant substrates by means of silicone transfer members, ink 
compositions according to the invention may be used for the decoration of 
articles made of other materials such as plastics materials and using 
different forms of equipment.