Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a method for
applying a composition to a substrate and to a composition
for use therein, notably to a method for applying
thermoplastic inks and to a novel thermoplastic ink
composition.
It has been proposed to apply inks through an ink
jet printing machine where the inks are in the form of wax
based compositions which are applied molten through the
nozzle of the printer~ In order to reduce problems which
would be expected in attempting to operate at elevated
temperatures (for example degradation of the composition),
the prior proposals have required the use of comparatively
low melting point compositions and low temperatures of
operation. Thus, for example, in USP No. 3653932 the
composition is required to have a melting point which does
not exceed 51C and contains a didodecyl sebacate which is
a highly viscous material. In order to overcome the
problems associated with that formulation, USP No. 4390369
proposes the use of a composition which comprises a natural
wax and has a melting point below about 75C. The use of
natural waxes i5 also proposed in published European
Application No. 097823, where the composition contains
mixtures of parafin and natural waxes, eg. carnauba wax,
and in published European Patent- Application No. 099682
where the composition comprises a mixture of paraffin wax
and
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stearic acid. However, such compositions do not adhere
satisfactorily to plastics substrates, suffer from
smudging, and problems are encountered due to the high
viscosity of the components where synthetic materlals are
used.
Contrary to the teaching of the prior proposals, we
have found that it is advantageous to operate a hot ~elt
ink jet printer at a temperature in excess of 10nC. At
such elevated temperatures, the waxes of the earlier
10 proposals would often decompose whereas in the pre~ent
lnvention they result in an image of improved definition,
which resist~ s~udging and has impro~ed adhesion to
plastics substrates, and also reduces the problems
associated with the use of high viscosity materials.
US Patent ~o 33692S3 discloses a number of
compositions for use in a pen type chart recorder in
which ink flows con~inuously from a no~zle onto a moving
substrate to draw lines ~hereon~ There is direct contact
beiween the nozzle and the substrate via the ink
20 compositlon and the composition mus~ ha~e a suficien~1y
high surface tension at the temperature of operation to
be pulled from ~he nozzle as a continuous stream and not
as ~a series of indlvidual droplets. S~ch requirements
are totally the reverse of what i8 re~uired in an ink jet
25 printer whese there is no direct contact between th~
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printer and the substrate and the ink issues as a serles
o~ discrete droplets. Fur~hermore, in the US Patent the
substrate has ~o be of a specified type with a mandatory
surface layer in order that the molten composition should
be not cause appreciable dimensional changes in the
substrate. The need for a special surface on the
substrate se~erely limits the possible fields of use of
this technique.
Accordingly, the present invention provides a process
10 for applying a thermoplas~ic composition through a
non-contact ink jet printing apparatus as a series of
discrete droplets onto a substrate moving relati~e to th~
apparatus, characterised in that the molten composition
is thermally stable at the temperature of application and
15 is applied at a temperature in excess of 100C~
The invention can be used to apply the molten
composition to a variety of substrates using on-de~and or
continuous non-contact ink jet application techniques.
However, the inven~ion is of especial use in the
20 application of thermoplastic inks to a .substrate uslng an
on-demand ink jet printer.
In an on-demand ink je~ printer, ink is fed under
pressure, typically 0.5 to 20 psi gauge, though higher
pressures may be used if desiredy from a reservoir to a
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series of nozzles via valve mean~ which control the flow
of the ink through each nozzleO The valve means is
typically an electro-magnetically ac~uated valve, notably
a solenoid val~e. The ink is discharqed throuqh the
nozzlesas discre~e droplets in the desired sequence to
form the required imaga on the substrate. usually, the
nozzles are arranged in one or more series transversely
to the line of movement of the substrate. ~ypically,
such printers have quick acting valves with an operating
10 cycle time of from 1 to 5 mi1liseconds feeding noz~les
with orifices ha~ing bore diameters of from 0.01 to 0.45
mms and an internal bore length to diameter ratio of from
3:1 to 1:2, notably ~rom 2:1 to 1:1.
The thermoplastic compositions for present use
15 comprise one or more image forming components, preferably
oil miscible or soluble, in a fusible carrier medium.
The image forming materlal can be one which forms a
visual image on the subs~rate, eg. it can b~ a dyestuff,
or one which is de~ected by other means, eg. it can be a
20 magnetic material to be scanned by a suitable reader, or
a fluorescent material, eg. one which is detected by an
ultra-violet or other radiation scanner. For
convenience, the present invention will be described in
terms of a composition contalning a visually detectable
25 dyestuff.
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The composition for present use is preferably a
solution or emulsion of the dyestuf in the carrier
medium, ie. it i8 subs~antially free from particles which
might block the nozzles through which the composition is
to be disch~ryed. If neces~ary, the composition can
contain a co-solvent or a bridging fluid ~o aid formation
of a substan~ially homogeneous composition.
The compositions comprise a fusible carrier medium
which is rendered molten at the temperatures encountered
10 in the method of the invention. ~he fusible carrier
media for present use are thermally stable at the
temperature of application and satisfy the surface
tension and viscosity require~ents of the ink jet printer
they are to be applied through. In general, the carrier
15 should not be thermally degraded or decomposed at
temperatures of up to 160C and should have a viscosity
of less than 120 Cps at the temperature of application.
They should have a surface tension which is sufficiently
low at the operating tempera~ure for the ink ~o form
20 discrete droplets rather than a continuous jet which
forms a bridge bewteen the nozzle and the substrate. In
view of the dlfficulties in meas~ring surface tensions at
elevated temperatures, the most convenient te~t of
suitability for present use is to run the composition
25 throuqh the ink jet printer in which it is to be used to
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ascertain whether it forms a continuous jet or discrete
droplets at the operating temperature. In many cases
mPa-~urement of surface tension at 25C will give a prima
facie indication as to the suitabili~y or otherwise of a
composition ~or present use. The surface tension is
determined by establishing whether a sample of the
composition is wet or not by a ~eries of ~luids o~ known
surface tension. Where the solid composition is wet, it
has a higher surface tension than the fluid, where the
10 fluid forms a stable droplet on the surface of the
composition the composition has a lower surface tension.
In general, where the composition has a surface tension
of 50 dynes per cm or less in the abo~e test, it will be
suitable for present use.
The carrier media for present use can be selected
from amonst natural waxes having ~he desired porperties,
but we prefer to use synthetic materials. We have ~ound
that microcxystalline waxes, notably the synthetic forms
o~ such waxes, and/or hydrocarhon resins provide
20 particularly advantageous carrier media, in tha~ they can
provlde highly mobile molten compositions with reduced
risk of degr~dation at high operating temperatures, which
will typically be at from 110 to 160~C, notably at from
125 to 150~C~ Moreover, where the composition has a
25 softening point grea~er than 60C, the xapid cooling of
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the droplets of the composition as they ætrike the
substra~e and the partial fusing of the substrate below
the hot droplet in the case of plastics substrates gives
an image which resis~s smudging.
The in~ention therefore also provides a fusible ink
composition comprising one or more oil soluble or
miscible indicator materials, notably a dyestuff, in a
carrier medium comprising a synthetic microcrystalline
wax and/or a hydrocarbon res~n, the composition having a
10 viscosity of less than 120 Cps, a surface tension (as
determined by the test method descibed above) of less
than 50 dynes per cm at 25~C and a softening point of
from 60 to llO~C.
The microcrystalline waxes for present use can be
15 selected from a wide range of such waxes which are
available commercially. Typically, the wax will be a
synthetic hydrocarbon wax obtained from the processing of
petroleum or naphthas, notably the naphthenic,
polyethylene or polypropylene waxes which have softening
20 points in the range 60 to 110C, notably 70 to 90~C.
Other s~itable waxes include those obtained by the
Fischer Tropsch process, typically those comprisln9 long
chain linear parafins with molec~lar weights of from 300
to 1500 and softening points in the range 80 to 110C.
25 Preferred synthetic microcrys~alline waxe~ for present
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use include Slack Wax* and the polyethylene waxes obtained
from the lighter fractions of the cracking of naphtha and
petroleum. If desired, the microcyrstalline wax may be
used in the form of a derivative thereof, eg. as an
oxidised or maleinised derivative.
The hydrocarbon resins for present use are preferably
crystalline resins, notably C5 or Cg chain length aliphatic
waxes or polyolefins with softening points greater than
90C, typically 90 to 110C, and melting points greater
than 110C, preferably in the range 140 to 160DC.
rrypically, the polyethylene resins will have a mean
molecular weight of less than 1500, eg. 500 to 1200 and
an acid number of less than 1 (expressad as mg KOH/g.)~
Suitable hydrocarbon resins for present use thus include
polyolefins, notably polyethylene, polypropylene or
polybutylene; C5 to Cg chain aliphatic resins, eg. those
obtained by the steam cracking of naphthas; polyterpenes,
notably wood rosins, tall oil or balsam resins, which can
be esterified or hydrogenated if desired; and aromatic
compounds, eg. styrenes such as methyl styrenes.
Whilst the hydrocarbon resin may often be a
microcrystalline material, we have found that the use of a
mixture of both an hydrocarbon resin and a synthetic
microcrystalline wax as described above is of especial
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TIP/126/9 ~9~
advantage, since the hydrocarbon resin enhances the
adhesion of the wax based composition to non-porous
substrates, notably to plastics sheet substrates.
Furthermore, by varying the proportions of the resin and
wax it is possible to tailor make the properties of the
composikion, eg. the viscosity, to suit a wide range of
operating conditions.
The compositions of the in~ention may contain other
ingredients in addition to the microcrystalline wax,
10 resin and image forming material. Thus, the compositions
can contain thermal and/or UV stabilising materials to
reduce the degradation of the ingredients of the
composition; and minor proportions of one or more
solvents or co-solvents for the ingredients to aid
15 formulation of the composition as a substantially
homoyeneous mixture.
~ he compositions for present use preferably have a
viscosity of from 2 to 120, notably 3 to 20, Cps at the
temperature of operation of the printer, typically 120 to
20 160C; and a ~urface tension of less than 40 dynes per
cm, notably less than 30 dynes per cm, at 25C using the
test metbod described above.
It may be desired to incl~lde one or more viscosity
and/or surface tension modifying agents in ~he
25 composition to achieve the desired viscosity and/or
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surface tension at the actual operating temperature3 for
optimum operation of a particular printer. Howe~er, as
indicated above, we have found that the viscosity and the
surface tension are affected by the relative proportions
of the microcrystalline wax and the hydrocarbon resin in
the composition and that the viscosity and surface
tension can often be adjusted to the desired value4
merely by varying the relative proportions of these two
ingredients.
Where the compositions are to be applied using a
continuous jet ink printer, it is necessary that the
composltion be one which can accep~ an electrical
charge. This is conveniently achieved by including one
or more ionic or polar materials in the composition,
15 e.g. potassium isothiocyanate. In order to reduce the
rlsk of segregation of these materials from the
composition, it may be desired to incorporate a bridging
compound, e.g. a wetting agent of the alkyl ether
sulphate or sulphonate or of the alkyl benzene su~phon~te
20 type, into the composition~ Typically, the composition
for applicatior. through a continuous jet printer will
have a conductivity of at leas~ 1000, preferably 1500 to
2500, microSiemens.
The compositions of the invention comprise the
25 microcrystalline wax, the hydrocarbon resin and the image
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TIP~126/11
forming material in any suitable proportion having regard
to the nature of the ingredients, the nat~lxe of the
substrate it is to be applied to and the operating
conditions under which it is applied. Typically, the
composi~ion comprises at least one selected from a
microcrystalline wax or an hydrocarbon resin, the
mlcrocryRtzlline wax being present in up to 99~9~,
notably from 40 to 99.5%; the hydrocarbon res~n being
presen~ in from 0 to 65%, notably 25 to 55~; and ~he
10 image forming material being present in from 0.05 to 5~,
preferably 0.1 to 2~: all percentages being of the active
material and by weight on the weight of the total
composition.
A particularly preferred composit~on for present use
15 comprises from 40 to 99 parts by weigh~ of a
micro-crystalline polye~hylene wax, from 0 to 60 parts by
weight of a polyethylene or styrene hydrocarbon resin of
molecular wsight Prom 500 to 1200 and 0.1 to 1~5 parts by
weight of an oil soluble dyestuff.
The compositions of the invention can be ~ade by any
sui~able technique, e.g. by melting the wax and/or rQsin
components ther~into.
The compositions can be put up in the form of powders
or granules by spraying the mol~en mixtures of the
25 components into a void vessel. Alternatively, they can
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TIP/126/12 -12-
be extruded through a suitable die to form moulded plugs
of the compo,~i~ion for insertion into a suitable shaped
receptacle in the printer for melting and use.
As stated above, the compositions of -the invention
are applied to a substrate by pas~ing them through the
nozzle or array of nozzle~ of an ink jet printer
appara~us at an elevated temperatur~. The apparatus can
be of conventional design, except that those parts of the
apparatus thxough which the molten composition is to flow
10 are heated or insulated so as to reduce the risk of the
composition solidifying within the appara~us. Such
heating can be achieved by any suitable means, e.g. by
electrical heating elements around the appropriate ducts
or vessels or by infra red or other radiant heaters
15 playing on the apparatus. Typically, the apparatus is
operated with the composition flowing therethrough at
temperatures of from 125 to 150C, e.g. about 140C.
The composition is fed to the apparatus in solid
form, e.g. as chips or granules or the shaped plugs
~0 described abo~e, and is melted in a suitable vessel
attached to or ~orming an integral part of the printer
apparatus. If desired~ the compositions can be held in a
separate heated reservoir and fed ~o one or more
individual printer3 through heated or insulated lines.
Surprisingly, the presence of the microcrystalline
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TIP/126/13 -13-
wax or hydrocarbon resin, notably the combination
thereof, does not have the deleterious effect oE
radically increasing ~he viscosity of the composition RS
is the case with the sebecate waxes propos~d hitherto.
The printlng appara~us can therefore be operated under
similar pressures and flow rates as with a converitional
ink forrnulation and using nozzle orifices in the range 10
to 450 microns diameter.
The compositions of this invention can be applied to
10 a wide range of porous and non-porous substrates, e.g.
paper, metal, wood, plas~ics or glass without the need to
form any special surface layer on the -substrate.
However, the invention is of especial use in forming
images on non-porous materials, e.g. plastics, plastics
15 coated materials, glass and ~etalsO The high temperature
of the composition as it is desposited on a plastics
substrate causes enhanced adhesion of the composition due
to partial fusion with the substrate. In the case of
porous substrates the compositions penetrate lnto ~he
20 substrate as they cool. In both cases, the compositions
of the invention solidify rapidly on the substra~e to
give a sharp image resistant to smudging,
The invention has been described above in ter~s of
the application of an ink-type composition. However r it
25 can also be applied to adhesive composition, for example
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TIP/126/14 -14-
those containing polyacrylamide or similar polymers.
Whilst it is known to apply hot melt adhesives from a gun
or other applicator which extrudas the molten adhesive
onto a substrate, we believe ~hat it is novel to apply
ho~ melt adhesives as droplets emit~ed from an ink jet
printer where the droplets are emmitted at a frequency of
more than 100 drops per second from a nozzle.
~ he invention therefore also provides a method for
applying a molten adhesive composition to a substrate
10 characterised in that the adhesive composition is
dispensed at a temperature in excess of 100C through a
noz~le to form a serles of droplets which are applied to
the substrate, the droplets being formed at the nozzle at
a rate of more than 100 per second.
The invention will now be illustrated by the
following Examples in which all parts and percentages are
glven by weight:
Example 1
An ink formulation ~as prepared by melting the
~0 microcrystalline polyethylene wax commercially available
under the trade name Shell Microcrystalline wax MMP (54
part~) in a heated vessel fitted with a stirrer. To the
molten Wax were added the oll soluble dyestuff Ceres Blue
(1 part) and 45 parts of the hydrocarbon resin sold under
25 the trade name Escorez 5300. The resultant mixture had a
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TIP/126/15 -15-
softening point of 85C and a melting point of 90C, both
as determined by Brookfield thermoset viscometer, and
surface tension of less than 40 dynes per cm as
determinad by the test method described earlierO
The composition was fed ~o a drop-on-demand ink jet
prin~er having electrical heating coils to maintain the
ink reservoir, ink lines and printing head at 140C i
5C. The reservoir was pressurised to 2 psi gauge and
the molten composition printed khrough the print head
10 using a 0.225 mms bore orifice to produce a series of
separate droplets which formed discrete dot i~ages on a
paper or polyethylene sheet target placed below the
printing head. The dots were sharply defined, vell
anchored to the substrate and resistant to smudging.
By way of contrast, when natural car~uba wax was used
in place of the microcrystalline wax and hydrocarbon
resin, the composition had a melting point of 50C and
began to degrade when held ak 120C for 1 hour, as
evidenced by charring. When this composition was applied
20 to a paper substrate at 80C, the image was soft and
susceptible to smudging. Where a polyethylene sheet was
used as the substrate, the image did not adhere to the
sheet and was readily wiped off.
EXAMPLE 2
25 The process of Example 1 was repeated with a range of
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different resins and waxes being applied onto different
target substrates including gla~s, metal, polyethylene,
polypropylene, PVC, polystyrene, wax and plastics coated
paper and card. The compositions are set out below as
formulations A, B and C and in all cases the compositions
were applied as in Example 1 and gave good dot image~0
When the compositions were replaced by con~entional
sovent based formulations or low temperature wax
form-ulations and applied ~o a non-porous ~ubstrate, the
10 resultant dots either did not dry rapidly and gave a
runny image (in ~he case of a solvent ink) or were soft
and readily smudged ~in the case of the low temperature
waxes).
15 Formulation A
54.7~ wood rosin hydrocarhon resin
45.0~ low melting point microcrystalline polyethylene wax
0.3% oil soluble dyestuff
20 Formulation B
70.0% medium melting point microcrystalline polyethylene
wax
29.5% commercially available C5 - Cg aliphatic
hydrocarbon re~in
25 05% oil soluble dyestuf~
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Formulation C
55% commercially availahle water white grade alpha methyl
styrene hydrocarbon resin
44.9~ of a commercially available mixture of
microcrystalline and paraffin waxes
o.1% oil soluble dyestuff
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