Heat sensitive inked element for high speed thermal printers

The inked element which is preferably in ribbon form comprises a flexible plastics carrier of a thickness of from 5 to 15.mu., covered with a thermotransferable coating which is 2 to 6.mu. in thickeness. The mixture of the coating comprises a blend of thermoplastic resins of non-polymeric type with natural or synthetic waxes with a melting point of between 60.degree. and 80.degree. C. The waxes and the resins are so selected as to be compatible with each other and to provide a melting point of between 60.degree. and 80.degree. C. and a melt viscosity of between 50 to 1000 cps. The ribbon makes it possible to print at a printing rate of 40 to 120 characters/sec on papers having a Bendtsen roughness of 10 to 100 ml/min. The ribbon can be prepared with bands of different colors for multi-color printing.

BACKGROUND OF THE INVENTION 
The present invention relates to a heat-sensitive inked element for 
high-speed printers, comprising a plastics material base carrier covered 
on one side with a coating of a mixture which is transferable to a 
printing carrier when it is subjected to heat and pressure, the mixture 
comprising a pigment and/or colouring agent and a binder formed by a blend 
of thermoplastic resins and natural or synthetic waxes with a melting 
point of between 60.degree. and 80.degree. C. 
Various inked elements in the form of single-use ribbons are known. In a 
known ribbon, the resin requires a high melting temperature and is 
accordingly relatively rigid and fragile at room temperature, whereby it 
has a tendency to crack. 
To overcome that disadvantage, a ribbon has already been proposed, in which 
the mixture comprises a polymeric resin and a plasticising agent to 
increase adhesion to the paper, but, because of the viscosity in the 
molten state, it does not permit a high printing rate. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide an inked element of the 
above-indicated type, which is suitable for high-speed printing. 
The inked element according to the invention is characterised in that the 
resins are of non-polymeric type and the waxes and resins are so selected 
as to be compatible with each other and to produce a melting point of 
between 60.degree. and 80.degree. C. and a melt viscosity of between 50 
and 1000 cps. 
These and other features of the invention will be more clearly apparent 
from the following description of some preferred embodiments which are 
given by way of non-limiting example.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The ribbon comprises a thermoplastic material base carrier which is covered 
on one side by a thin layer of solid ink which is thermotransferable to a 
printing carrier of paper and/or thermoplastic nature. The printing 
process provides for the simultaneous application of pressure and heat by 
means of the printing head to the inked ribbon, to produce the effect of 
transfering the ink from the ribbon to the printing carrier. 
The ribbon must permit printing at a high printing rate, with a medium 
quality of printing, in terms of good character definition, sufficient 
resistance to rubbing and good penetration into the fibres of the paper 
carrier, with limited surface roughness. It is prepared in various forms, 
in black or in colours, and is generally used in high-speed printers 
and/or digital copiers of B/W and colour type, for example of the type 
described in our U.S. patent application Ser. No. 577,341, filed on Feb. 
6, 1984, entitled `Method and Apparatus for Reproducing Colour Images`. 
The inking mixture comprises a binder of non-polymeric type which 
accordingly, when heated, melts and flows rapidly from the carrier to the 
paper, penetrating into the fibres of the paper. The binder is so 
formulated as to give a low melting point, for example 60.degree. to 
80.degree. C., and a melt viscosity of 50 to 1000 cps. The ribbon is 
produced by spreading an inking mixture or ink over a carrier comprising 
mylar, kapton, polythene, or capacitor paper, from 5 to 15.mu. in 
thickness. The spreading is effected in a machine with a spreading station 
in which the carrier receives the ink in the form of a thin layer of 15 to 
30.mu. in thickness, which, after drying, becomes solid and adheres to the 
substrate in a thickness of from 2 to 6.mu.. The ribbon can also be 
prepared by spreading the mixture in bands of alternate colours for 
3-colour printing, for example of the type described in the applicants' 
above-identified patent application. 
The ribbon when prepared in this manner makes it possible to print with 
heads with a vertical row of printing elements and with a definition of 
eight to ten dot/mm at high printing rates (40-120 characters/sec), with 
good quality of printing, over a range of papers with roughness of 10 to 
100 mil/min. 
For that reason, the roughness of a wide range of office papers which are 
available on the market was measured using an instrument from Bendtsen & 
Wattre (Stockholm), using the Scan-Test Standard Method Scan-P 21:67 
procedure. 
The results obtained fall in a range of values of from 10 to 100 ml/min. 
The binder consists of a mixture of natural or synthetic waxes with a 
melting point of from 60.degree. to 80.degree. C., and microcrystalline 
and synthetic paraffins prepared according to the Fischer-Tropsch process, 
with a melting point of from 60.degree. to 70.degree. C., with particular 
non-polymeric resins of the colophonies, modified colphonies, hydrocarbons 
and modified rosins type. 
The following were found to be particularly attractive, among the various 
waxes tried: beeswax, Japan wax, having melting points of 60.degree. to 
65.degree. C., microcrystalline paraffinic wax such as Paraffin Wax 
(manufactured by Pergamon Wax), S 45 Wax (trademark of S.P.A. Tillmans), 
Micro 60/63 Wax (trademark of Spica S.P.A.) having melting points of from 
60.degree. to 65.degree. C., esterified and partially esterified waxes 
with a melting point of between 70.degree. and 80.degree. C. of the 
Hostalub We 4, Hostalub WE2, trademarks of Hostalub TMWE 14 (Hoechst) 
type, synthetic waxes of the type of fatty acid esters with glycerin, 
glycols or higher alcohols, fatty acid amides and stearic and oleic 
amines, the hydrogenated tallow amines commercialized as Armeen 2HT and 
the H-tallow amineacetate commercialized as Armac HT (trademarks of 
Akzo-Chemie). 
The resins considered must satisfy certain requirements such as perfect 
compatibility with the waxes, low melting point and a high level of 
fluidity in the molten state. The following commercially available rosin 
based resins gave optimum results: Unirez 221, Unirez 6012, Unirez 3300, 
Unitol NCY (trademarks of Union-Camp Corp.), the synthetic rosin ester 12 
B 715 (manufactured by Lawter Chemicals N.V.), the colophane based resins 
having a melting point of between 68.degree. and 80.degree. C. such as 
Colophane-Dismutee, Dertomal 4, Dertoline S.G (trademarks of Derives 
Resiniques Et Terpeniques), Resinall 585 (trademark of Carolina Processing 
Co) and alicyclic H-saturation trademark of National Ink Co.). 
The formulation of the ink requires perfect compatibility of the two main 
components (resins and wax) in various ratios for the purposes of having 
an appropriate melting point (MP) and suitable fluidity in the molten 
state. Added to that mixture is a colouring agent and/or pigment to 
produce a black or coloured ink. Having regard to the particular nature of 
the basic components of the ink, wax and resin, the colour must be 
suitably selected in order to satisfy the requirements in regard to 
compatibility with the binder, stability with respect to light, 
temperature and the ambient air. 
The selection in respect of the colouring agent or pigment of complementary 
colour, cyan, magenta and yellow, to prepare a ribbon which is envisaged 
for use in printers or copiers for producing colour printing, must take 
account of the shade of the colour required for producing colour printing 
in three colours. 
The most significant colours are Sandorin 2 GLS Blue, Graftolo BP Ruby, 
Graftolo GXS Yellow, Graftolo WTP Ruby, Sandorin 5 BL Brilliant Red 
(trademarks of Sandoz) and Fat Black HT (trademark of Hoechst). 
In the case of an inked element which is produced by sequentially coating 
the inks which are coloured with the colouring agents or pigments, cyan, 
magenta and yellow, over carriers comprising mylar, kapton, etc., it is 
possible to produce a ribbon for use in colour printers and copiers, which 
print by superpositioning of the cyan, magenta and yellow in successive 
printing steps. By varying the composition of the thermotransferable 
coating and the thickness of the carrier, it is possible to transfer the 
coating and thus to produce the printing by applying an energy of from 1 
to 10 Joule/cm.sup.2, with any type of thermal head which is known in the 
art. 
Such characteristics in respect of the ribbon permit normal speeds of feed 
movement of the head or the sheet of paper of up to 20 cm/sec. In the case 
of parallel heads, it is therefore possible to achieve a theoretical 
printing rate of up to 30 pages per minute. In practice however, that 
potential on the part of the ribbon is conditioned by the known 
limitations with the thermal inertia of the head, the power of the power 
supply available, and the mechanics of the process. For that reason 
optimised planning and projection of those components could make it 
possible to achieve printing rates which are comparable to those of 
xerographic copiers. 
In the case of three-colour printing, the printing rates are reduced by a 
factor of 3 or 4 by virtue of the fact that three or four printing passes 
with the printing head are required. 
As already stated, the composition and choice of the carrier for the ribbon 
may be optimised and adapted in dependence on the type of head used, 
insofar as each type of head requires a ribbon with specific features. 
In particular, in the case of parallel heads, the speed of feed motion is 
relatively modest and therefore the ribbon is not subjected to excessive 
mechanical stresses. Under those conditions, it is possible for the 
thermotransferable coating to be formulated in such a way as to give the 
maximum definition of dots transferred. In the case of a series-parallel 
head in which the movement is an oscillatory movement and the printing 
step takes place in a serial mode, in contrast, increased mechanical 
strength is required from the carrier of the ribbon, and increased 
sensitivity to heat on the part of the thermotransferable coating, so as 
to guarantee adequate printing rates. Those limitations are further 
accentuated in the case of serial heads. 
The examples of inking mixtures described hereinafter are not to be 
interpreted as limiting the invention but as being broadly representative 
thereof whenever pigments and/or colouring agents used are replaced by 
pigments and/or colouring agents set forth in the example, not being a 
departure from the scope of the invention. 
EXAMPLE 1 
120 g of Aliciclica H-satura resin is dissolved in 400 g of toluene, 80 g 
of Armeen HT is added, in total solution, and 550 g of ligroin (boiling 
point (BP) 75.degree. to 100.degree. C.) is added. The solution is poured 
into a 1500 ml steel bowl with 500 ml of glass marbles. 
50 g of Fat Black Ht, 6 g of Sandorin 2 GLS Blue, 16 g of Graftolo BP Ruby 
and 6 g of Graftolo GXS Yellow are added to the bowl. The addition of the 
three primary colours imparts a more intense shade to the black, by virtue 
of the synthesis of the three colours. 
The bowl is set milling for 76 hours. After the milling operation, the 
glass marbles are separated and the ink is coated in a spreading machine 
over a mylar carrier which is 8.mu. in thickness. 
The ribbon produced permits good quality printing at 80 characters/sec. 
EXAMPLE 2 
112 g of Unirez 3300 and 98 g of paraffin (MP 60.degree. C.) are dissolved 
in 500 g of toluene and 550 g of ligron (BP 75.degree. to 100.degree. C.) 
in the hot state (50.degree. C.). 
The solution produced is poured into a 1500 ml steel bowl with 500 ml of 
glass marbles, and 50 g of Fat Black and 20 g of Carbon Black Raven 1200 
(trademark of Cabot Co.) is added to the bowl. The bowl is set milling for 
76 hours. After the milling operation, the glass marbles are separated off 
and 4.mu. of ink is spread over a mylar carrier which is 8.mu. in 
thickness. The black ribbon produced permits good quality printing at up 
to 70 characters/sec. 
EXAMPLE 3 
120 g of Dertoline SG, 40 g of Pergamon wax and 40 g of beeswax are 
dissolved in 500 g of toluene and 550 g of ligroin (BP 75.degree. to 
100.degree. C.) in a hot state at about 50.degree. C. The hot solution is 
poured into a 1500 ml steel bowl with 500 ml of glass marbles. 70 g of 
Graftolo BP Ruby is added to the bowl. 
The bowl is set grinding for 76 hours. After the grinding operation, the 
glass marbles are separated off and the ink is spread over mylar which is 
8.mu. in thickness. The red ribbon produced permits good quality printing 
at up to 90 characters/sec. 
EXAMPLE 4 
120 g of resin 12B715 (Lawter Chemicals N.V.) and 80 g of Micro 60/63 are 
dissolved in 500 g of toluene and 550 g of ligroin (BP 75.degree. to 
100.degree. C.) in a hot condition (about 50.degree. C.). The solution is 
poured into a 1500 ml steel bowl with 50 ml of glass marbles. 70 g of 
Sandorin 2GLS Blue is added. The contents of the bowl are milled for 76 
hours, at the end of which the ink is separated, to be spread over a mylar 
carrier which is 8.mu. in thickness. The blue ribbon which is produced in 
that way has similar qualities to those of the ribbon described in Example 
3. 
EXAMPLE 5 
120 g of normal ester rosin, 40 g of beeswax and 40 g of paraffin (MP 
60.degree. C.) are dissolved in 500 g of toluene and 550 g of ligroin (BP 
75.degree. to 100.degree. C.) in a hot condition (at about 50.degree. C.). 
The solution is then poured into a 1500 ml bowl, with 500 ml of glass 
marbles. 70 g of Graftolo GXS Yellow is then added to the bowl. The 
contents of the bowl are milled for 76 hours. At the end of that 
operation, the ink produced is separated and spread in a spreading machine 
on a mylar carrier which is 8.mu. in thickness, in the form of a layer of 
dry ink which is 4.mu. in thickness. The ribbon has similar 
characteristics to those of Examples 3 and 4.