LAYER
Tlie present i~i\rention relates to a paper, intended in particular for
5 printing an electroconductive layer, as well as to its production process.
Papennaking techniques which are known to the person skilled in the
art may be enlployed in order to produce a paper in accordance with the in~~ention.
A known process cotisists of preparing a homogeneous pulp in a pulper by mixing
cellulose fibres arid water. The pulper allows stirring and shearing the fibres so as to
10 separate them arid isolate the111 witli a view to fortii~iga fibrous suspension.
The pulp then passes tlxough a refiner. This comnl~risesa stator and a
mtor turning at high speed, equipped with teeth or radial serratiotis. Tlie pulp moves
between tlie rotor and the stator of the refiner in a manner such as to modify the
structure of the wdl of tlie fibres in order to introduce water into the ir~terioro f the
-
15 fibres with a view to cutting the fibres and/or increasing fibril formation and, as a
consequence, the potential for bonding between fibres.
Tlie composition of the pulp map then be adjusted before being sent to the
head box of a paper tnachine.
Tlie head box can be used to uniformly distribute the pulp over a moving
20 wire of a drainage table (in the case of a Fourdrinier maclu~ie), where it is drained
through the mesh of the wire under gravity and by suction with the aid of suction
boxes witli a view to producing a slieet. A felt is generally applied to the sheet,
opposite to the wire. At the outlet from the drainage table, tlie sheet still contains a
*
large quantity of water.
25 / During this step, tile fibres are orientated mainly in tlie direction of
displace~nerit of tlie wire, termed the machine direction. The tenii "cross-machine
direction" defuies the direction perpendicular to tlie machine direction. Fultliermore,
tlie side of the sheet which is applied against the wire (wvire side) generally has a
greater rouglmness than the opposite side (felt side).
Papcr niachines luio~v~asl twin wire paper n~aclli~leasls o exist; tliey
comprise two opposing wires applied to either side of tlie sheet. Water tnay be
evacuated by suction through each of the wires.
Once the sheet of paper is formed, it passes through the press section of
5 the paper machine in order to remove more water. To t11is end, the slieet passes
between a series of cylinders compressing the sheet in order to extract water from it:
During this step, the sheet of paper is also sandwicl~edb etween absorbent felts in the
form of contir~uous belts, suctiou boxes enabling the water absorbed by the felts to be
withdrawn upon conlpletion of pressing of the sheet, before the felts are applied
10 against the sheet once more,
The sheet then passes thmug11 a dryer composed of a series of cylinder
heated with steam, on which the sheet is passed. The temperature of the mlls
increases gradually, fiom upstream to downstreatn with respect to the direction of
displacement of the sheet.
- -
15 Tlle wet section of the paper machine is defmed as the set of eleniet~tos f
the machine (head box, d~ainageta ble) located upstrean1 of the d~yer.
Once the t~loisture content of the sheet has bee11 substantialtp rednced,
and is, for example, of the order of 5%, the sheet may undergo a surface sizing
treatment by being passed t111ough a size press. The size press is generally formed by
20 two rolls disposed side by side in a manner such as to for111 a uip supplied with a
sizing solution or bath wit11 a specific compositiot~. The sheet passes between the
rolls it1 a 111antler such as to coat, for example, one or both of its opposed sides with
the solution in order to fonn a layer.
The sheet then passes into a section known as the calel~der section in
25 which it is again applied against one or more steam-heated roils.
At the end of these various steps, the sheet is in the form of a co~lti~l~~ous
web comprisi~iga n inner zone or core foorniit~ga fibrous substrate or mat, at least one
outer side or surface of 1vliic11 is covered with a layer or coating.
This sheet may optionally undergo fmishing operatio~ls such as, for
30 example, calendering or stnoothi~igin order to inlprove tlie surface co~lditiolio f the
A paper intended for printing an electroco~lductive layer is pa~ticularly
appropriate, but not exclusively so, for use in electronics applications such as in
printed electronics.
Printed electronics consists of depositing an electroconductive layer
5 onto a supple and flexible support, such as a plastic fill11 nsitlg k ~ l o t~ecnlu liques,
with a view to producing electronic components such as electronic chips, of the
RFlD type for example.
However, although plastic films (such as those made fro111 PEN and
from PET) have a lo\v surface rouglu~ess wvhich is particularly advantageoos for
10 printed electronics, these plastic films are not very ther~llally stable and are
relatively expensive (the cost of these films being greater than or equal to
approximately 4 euros/m2).
The Applicant's patent application WO 2013/104520 discloses a process
for the production of a sheet comprising at least one electroconductive layer, this
-
15 sheet comprising a paper substrate, at least one side of which is at least partially
covered with a layer or with several superimposed layers including said
electroconductive layer, the nlethod eo~nprisingth e steps consisting oE:
a/ preparing or providing a multi-layer structure comprising at least, or constih~ted
by, a plastic film, an anti-adhesive coating, and a base layel; the anti-adhesive
20 coating being inserted between a side of the plastic film and the base layer,
b/ applying glue to a side of the substrate and/or the side of the multi-layer structure
located on the opposite side to the plastic film, and applying said side of the
substrate against said side of the multi-layer structure, so as to cross-laminate the
multi-layer stroch~rea nd the substrate,
25 c/ removing the plastic film and the anti-adhesive coating fro~om the base layer, the
process being characterised in that the base layer is covered with an
electroconductive layer by means of an additional step consisting of:
dl/ depositiiig an electroeondocti\~ef ilrn on the base layer; or
d2/ printing tlie base layer with at least one ink having electrical properties, the
30 base layer being a printable layer based on a binder in a ratio of more than 15% in
subjecting the printed sheet to an annealing heat treattue~lst o as to forin a layer of
electmconductive ink.
In contrast to plastic films, papers and sheets based on paper are
cheaper and also have the advantage of being capable of being recycled and having
5 higher thermal stability. hl addition, the use of sheets or papers for printed
electronics allows very large printed surfaces to be produced, which are more difficult
to obtain with plastic films. Fntlhernlore, a sheet or a paper nlay be printed for an
electronics application directly after it has been fabricated, i.e. the printing machine
n1aj7 be disposed directly after the paper fabrication machine using a continuous
10 process (roll-to-roll process). In addition, it is easier to obtain a glossy white paper
than a glossy white plastic filn becanse the combination of the properties of
\vluteness and gloss is difficult to obtain with a plastic film, which is also more
dificult to cover with a coating composition in an aqueous medium than a paper
which has a hydrophilic nature.
-
15 Using the process described in patent application WO 2013/104520
allows producing a support wherein at least one side intended for printing is veq
smooth, with a roughness Ra it1 the range 1 to 30 nm, for exanlple, which allows
producing an electroconductive sheet by printing a layer of ink of vety low tl~ickness.
In cases where the inks used are relatively expensive, such as, for
20 example, inks using silver nanoparticles, the fact that a vely thin layer of ink is used
allows substantially reducing the cost of producing an electroconductive sheet of this
type.
However, the process cited above for producing a paper support is
relatively cotnplex and expensive. In cases where the inks used are cheaper or in
25 cases where printing techniques are to be used which necessitate depositing a thicker
layer, it is not necessaqr to use a support \vlvherein the side intended for printing is that
snlooth. Indeed, in the case of a screen printing process, the layer of ink whicl~is
deposited is typically in the range 10 to 15 pm, this layer being in the range I to 3 pm
in the case of a flexographic printing process. Thus, the inventors have determined
exalnple, in the range 0.1 to 3 pm could be sufficient to produce high quality
electroconductive sheets.
In addition, the highly pronounced sn~oothtless provided by the
aforenlentioned process means that the ~iiicroporosityo f the suppost is reduced, \vIiich
5 has a negative influence on tlie adhesion of the ink to the surface of the su~pport.
Tl~ust,h ere is a need for the provisiotl of a support, it1 pal-ticular fonned
fio~npa pel; which allows the use of the printing processes cited above with a view to
forniing an electroconductive sheet, and wvhich can be economically produced.
Furthermore, after printing the layer of ink, the support thus coated with
10 tlie layer of ink generally undergoes an annealing treatment which is carried out, for
example, in a tunnel filmace or an oven and during wvhich the paper and the layer of
ink are subjected to a high temperature for a given period.
By way of exatnple, patent application US 200910242019 describes the
~~p
productiot~ of solar cells by depositing silane onto a flexible plastic support,
~p
15 annealing at a temperature in tlie range 250°C to 40OoC allo\ving transforn~ingt he
silane into polycrystalline silicon.
It should be noted that such a plastic support of this type has a relatively
low heat resistance (with the exception of cettain expensive plastics such as
polyimide) compared with a paper support.
20 The use of a paper to produce an electroconductive product in the folm of
a sheet has the following disadvantages.
In the case in which an uncoated paper support is used onto \vllich an
electroconductive layer is produced by printing, it is observed that the conductivity of
the tracks formedis relatively low. Tllis can be explained by the vely substantial
25 roughness and porosity of the support, ~fliich cause a discontinuity in the
electroconductive tracks. By \\lay of exanlple, the resistance of the conductive tracks
printed by flexography with inks containing silver nanopat-ticles, with an annealing at
180°C for 5 minutes onto a BristolB type paper produced by Arjowiggins Creative
Papers, is of the order of 3100 Wsq. It \\rill be recalled that the higher this
In contrast, coated papers have pigment layers bonded with a sj~ntlietic
latex, so that thcir surface porosity arid roughlless are lower. If these coated papers
are printed with conductive inks, here again it is obsewed that the conductivity of the
tracks obtained is nlcdiocre, since a liigl~te mperature annealing cannot be carried out.
5 In fact, coated papers of illis type have poor dimensional stability (deformations or
dimensional shrinkage during a high temperature annealing). By way of exanlple, the
resistance of the conductive tracks printed by flexography with inks containing silver
nanopatticles wwith an runealing at 180°C for 5 minutes on a Sensation@ type paper
produced by Arjowiggins Creative Papers is of the order of 1700 Wsq.
10 Besides, it has been observed that papers of this type turn yellow above
140°C.
Thus, there is a need for the prow~ision of a paper which can act as a
support for a layer of electroconductive ink deposited by printing in particular, and
which is both inexpensive to produce, thernially resistant (low deformation or
-
15 diniensional shrinkage at high temperature, low yello\ving effect) and which allowing
producing conductive tracks with good conductivity (in particular due to the relatively
low porosity andlor low roughness of the sul-face of the paper which is to be printed).
The objective of the inventiori is, in particular, to provide a simple,
effective and economical solution to this problem.
20 To this end, it provides a paper cotnprising a fibrous substrate comprising
at least one side covered with at least one layer, said layer comprising or consisting of:
- 100 parts in dry weight of pigments,
- 5 to 50 parts in dry weight of one or Inore binders wvhich are
resistant to exposure to temperatnres in the range 140 OC to 200 OC and
having a glass transition temnperature of less than 20°C, in particular of
one or more acrylic binders the glass transition teniperature of which is
less than or equal to 20°C, preferably less than or equal to IO°C,
- 0 to 15 parts in dry weight of a viscosifying agent such as polyvinyl
alcohol, for example.
in contrast, it may cover a litnited zone, tlie surface area of which is smaller than the
surface area of each side of the substrate.
In accordance with a particular e~nbodilnent of the invention, the
fibrous substrate is colnpletely or partially covered with a single layer and this layer
5 is as defined above.
The use of binders which are heat resistant allows imnproving the heat
resistance of the paper during an optional thermal annealing step, i.e. reducing the
deformations or dimensional slwinkage as well as the effect of the yello\ving produced
during such an atitiealing step.
10 In a pat-ticular en~bodimento f the invention, the binder or the binders of
the layer deposited onto the surface of the substrate arid intended to be priiited is an
acrylic binder composed of aclylic ester and acrylonitrile with a glass transition
temperature which is below 10°C. By may of example, the binder coniprises or is
constituted by Acronal LN579S sold by BASF.
15 Although the conventional wisdom is that a binder with a high glass
transition teniperature is more thermally resistant, the Applicant has sulprisingly
discovered that, in contrast, using a binder with a low glass transition temperature, in
particular 20°C or less, preferably 10°C or less, allowvs considerably itnproving the
thermal iesistat~ce of the paper, in pal3icular in terms of defonnation. This is
20 illustrated in Exarnples 1 and 2 below.
Said layer may comprise 10 to 30 parts in dry weight of binder with a
glass transition temperature of 20°C or less, preferably 15 to 25 parts in dry weight,
even more preferably 19 parts in dry weight. Preferably, an actylic binder is used.
In a particular e~nbodiments, aid layer may comprise 0.05 to 15 parts in
25 dly weight of viscosifying agent, more preferably 0.05 to 5 pal-ts in dry weight, and
even more preferably 0.05 to 4 parts in tlly weight of such an agent.
In pa~ticular,s aid layer may comprise 5 to 10 pai-ts in d ~ ywe ight of
polyvinyl alcohol used as a viscosifying agent, more preferably 8 parts in dry weight.
Exaliiples of other viscosifying agents which may be cited include:
30 polyvinyl alcoho
galacto~iia~inatai, nanocellulosc, a polysaccharide, a cross-linked polyacrylatc, a
poly\ri~inylpyrrolidone, a hydrophobic ethoxylated urethane, and a hydrophobic
emulsion which is expandable in an alkaline medium.
By way of example, said layer may comprise 0.05 to 1 part in drp
5 weight of carboxymetliyl cellulose, or of liydroxytnetliyl cellulose, used as a
viscosifying agent.
The type of viscosifying agent is selected as a function of the coating
process used. In general, the greater the quantity of viscosifying agent(s), the less
the layer resists to high temperatures.
10 Preferably, the substrate comprises 70% to 90% in dl7 weight of short
cellulose fibres, with a mean length comprised in the range 0.5 to 1.5 111111, such as
wood fibres, in pa~ticularw vood fibres obtained from eucal~rptns.
The use of short fibres allows improving the thermal resistance of the
paper as regards the deformation or dimensional sh~inkageo f the paper. Such an
-
15 advantage is illustrated in Example 3.
Besides, it has been shown that the use of fibres coniprising a small
ratio of lignin such as wvood fibres obtained from a bleached chemical pulp of
eucalyptus, which are also short fibres, allows improving the thermal resistance of the
paper (in particular of the substrate) in terms of yellowving hi case of exposure to high
20 temperatures. This is illustrated in Example 4.
Preferably, the substrate comprises 80% dry weight of short cellulose
fibres, or more.
In a particular e~iibodinient of the inw~entiori, the substrate is obtained
from a fibrous pulp with a degree of refining of less than 50°SR, or less thai 40°SR,
25 preferably less than 35"SR.
Furthermore, the fibrous substrate cotnprises 10% to 30% of at least one
mineral filler, for exaniple calcium carbonate, kaolin or titanium dioxide.
Calcium carbonate, or any other mineral filler, allo\\ls reducing inter-fibre
bonds and thus i~iipuovingth e dimensional stability.
Advantageouslj: the paper has a whiteness in the range 70 to 90,
preferably in the range 75 to 85, in order to reduce the paper yellowing effect. This
corresponds to a cream shade.
Wlliteness is measured in accordance with IS0 statidard 2470.
5 Indeed, the Applicant has denionstrated that the difference in shade of tile
paper after an annealing step, conipared ~vithtl ie same paper before annealing, is
dependent on the colour of tlie paper before annealitig. Thus, the \vliiter tlie paper
before annealing, the more visible is the yellowing effect at high teniperature. Thus,
yellowing of a paper with a cream, vanilla or ivory colour is a lot less visible than in
10 the case of a white paper. Tlus is illustrated in Example 5.
Advantageously, tlie difference in shade Al3 of the paper, calculated om
the CIE LAB coordinates of the paper, after an annealing at 200°C for 5 mirit~tesi s
less that1 5, preferably less than 2, compared with said paper before annealing.
It should be noted that a difference in shade of 1 or Less is not visible to
-
15 the naked eye for a knowledgeable person. A difference in shade of 5 or less is
relatively small. In this manner, it is ensured that the annealing step has little
influence on the colour of the paper.
Besides, the layer covering the sobstrate of the paper in accordance
with the invention does not comprise, or comprises very little, optical brighteners,
20 i.e. fewer than 0.5 parts in dry weight per 100 parts in dry \i~eight of pigments,
preferably less than 0.1 parts in dry ~veighpt er 100 parts in dry weight of pigments,
Optical brighteners are used in the prior art in order to increase the
wvhitet~ess of paper. While optical brighteners of this type can increase the
whiteness at low te~iipetrltures,t hey are however destroyed wlien exposed to high
25 teniperatures, in particular during an annealing step. The resoltiag difference in
shade at the end of such an annealing step is consequently higher as tlie quantity of
optical brighteners is uicreased.
Fut-ther~iio~t~hee, layer covering at least one side may be printed over all
or a portion of the area of said layer \vitli a thickness of electroco~iductivei nk of 0.1 to
As was seen above, this printing may be carried out by screen p~inting,
flexograpl~o. r heliogaphy.
An electroconductive ink is an ink cotnprising conductive elements such
as nanopai-ticles and/or molecules, these eletnents endowing the paper printed with the
5 ink (and optionally having undergone an atlnealing step) with an electrical
conductivity.
The paper of tlie invention may be used for various types of application in
the field of printed electrotlics; of which six stand forward:
- printed circuits comprising conductive tracks, resistances, capacitances
10 and transistors;
- photovoltaic cells;
- displays (electrochromic or LCD);
- membrane keyboards; tlie sheet may then comprise a component or
undergo a particular treatment to render it flameproof; the sheet may, for example,
~p ~~~-
15 comprise flame retardants of the aluminium tril~ydroxide type, for example BACO
FRF408 from Alcan Chemicals (values of 30 % of BACO FRF408 in the bulk of
the sheet map allow obtaining a fire rating of MI or M2); it is also possible to add
products, in the size press, of the phosphol~~s/ammo~lisuamlt type with ratios of
50% with respect to starch; other products may also be used, for example based on
20 ammonium polyphosphate, antimony trioxide, arnmoniut~sl ulphamate etc.;
- OLEDs (organic electrolurninescent diodes) are electrolul~lit~escet~t
diodes the emitter material of which is an organic material; when a current passes
tl~rongtlh~i s material, it becomes a light source;
- "switcll" rnenlbranes (or membrane switches) can be used to make a
25 temporary comiection by contact; conductive irk is deposited on a flexible polyester
or polycarbouate type ssuppot-t; a dome is formed arid cotistih~testh e active element of
a button; under pressure, the dome is defortned and closes the circuit; this technology
is used in mobile telephoties, photographic cameras, control panels, toys etc.; and
- WID (Rr~dio Freqztet~cjI~D etztgficntion) labels, also known as
receive a radio signal atid return a different radio signal in response, containing
infonilation.
The invention thus concerns an ob-ject or product produced with at1
electroconductive printed paper in accordance wvith the invention, such as an object
5 selected from the above list.
The invention also concerns a process for tlie productio~i of a paper of
tlie type cited above, characterized in that it comprises the steps consisting of:
- forming a fibrous substrate with the aid of a fibrous pulp,
- at least partially covering at least one surface of the fibrous substrate
by coatitig with a layer comprising 100 parts in d ~wye ight of pigments, 5
to 50 parts in dry weight of one or tnore binders which are resistant to
exposure to temperatures comprised in the range 140 "C to 200 'C and
having a glass transition temperature of less than 20°C, in particular of
one or more acrylic binders, the glass transition temperature of which is
less than or equal to 20°C, preferably less than or equal to 10°C, and 0
to 15 paits in dry weiglit of a viscosifying agent, preferably 0.05 to 15
pa& of a viscosifying agent, for example polyvi~lyal lcohol.
As is ge~ierallyth e case in the papennaking field, tlie coating process
refers to a process for the direct deposition of a layer (or coating) wvhich is it1 an
20 aqueous medium. Examples of processes for depositing a layer in an aqueous
medium which may be cited are processes for deposition by a size press atid by at1 air
blade. I11 contrast to the process proposed hi docunient WO 2013/104520, the coating
processes used in the context of the inventio~ld o not irivolve trausfer of a d ~ lyay er
fiom an alternative support to the substrate.
25 Preferably, the degree of refining of the fibrous pulp is less than 50°SR,
preferably less than 40°SR, more preferably of the order of 35"SR. It should be noted
that for implementational reasons when carrying out tlie production process, it is in
fact preferable for the degree of refining to be 20°SR or higher.
The Applicant has also demoustrated that tlie degree of refilling of the
.. Indeed it has
been obsenred that the lolver the degree of refining, the less the paper will teud to
defomi. This phenomenon is illustrated it1 Example 6.
It should be noted that the tmeasurc~lleat of the degree of refiniug,
expressed in SchopperRicgler degrees, is ca~~ieoudt ui accordance with IS0 standard
5 5267-1:1999. This degree of refining represents the quantity of water in centilitres
drained tlwough a cake of pulp and flowing via an overflow. This is a drainability
index which can be used to measure the rate at which water can be extracted fiom a
suspension of diluted pulp.
Preferably, said layer covering all or a portion of the fibrous substrate is
10 applied by coating, using a size press of a paper machine for example, which rneans
that the production costs for a paper of tlus type can be reduced.
The invention also concerns a process for the production of an
electroconductive product, comprising the steps consisting of:
- covering, by printing using an electroconductive ink, at least one zone of
-
15 a suppoi-t produced fiom a paper of the type cited above,
- annealing the suppoi-t and the ink in a manner such as to fo~man
electroconductive layer or contitiuous track on the support.
In a particular embodiment, printing using electroconducti\~e ink is
carried out by flexogapliy or screen printing.
20 The inve~itiona lso conceins a paper as obtained by said process. TIie
paper in accordance with the invention or as obtained by this process is capable of
receiving and fixing, in a stable manner, an electroconductive ink because of its
surface condition, exhibiting a surface porosity which is low but sufficient to allow
the ink to penetrate the surface of the paper. Tlms, the porosity of the surface of a
25 paper in accordance \writ11 the invelltiou has, in a Microcontour test such as that
described in Example 8, an optical density value of Inore than 0 (at a wavelength
between 380 and 780 nm) and in pa~ticular an optical density in the rauge 0.2 to 1 or
in particular 0.2 to 0.8.
The amlealing duration may be co~i~priseind the range fiom less than one
Furthemiore, the layer of ilk deposited onto the support by printing may
be co~nprisedin the range 0.5 to 15 pm, preferably in the range 1 to 10 lun.
In addition, the electroconductive ink may be deposited nsing a screen
printing, flexographic or lieliograpliic printing process.
5 Besides, the imrention also concerns a paper conlprising a fibl.ous
substrate comprising a side covered with a layer onto wliicli an electroconductive ink
is printed, as obtained by xileans of steps consisting of:
- forming a fibrous substrate with tlie aid of a fibrous pulp,
- at least partially covering at least one surface of tlie fibrous substrate
10 by coating with a layer coniprising 100 parts in dl31 weight of pigments, 5 to 50 parts
in dry weight of one or more binders which are resistant to an exposure to
tenlperatures in the range 140 "C to 200 OC and having a glass transition
temperature of less than 2OoC, in particular of one or more acrylic binders, the
glass transition temperature of which is less than or equal to 20°C, preferably less
-
15 than or equal to 10°C, and 0.05 to 15 parts in dry weight of viscosifying agent;
- covering at least one zotle of the layer by printing using an
electroconductive ink;
- anriealitig the coated substrate and the ink in a manner such as to forni
an electroconductive layer or conti~iuoustr ack on the support.
20 The invention will now be illustrated by, and other details,
characteristics and adval~tages of the invention will become apparent from, the
following description which i~icludesi mplementar~e~x amples of the invention,
made with reference to the figures in which:
- Figure 1 is a graph representing the humidity rate as a fi~nctiono f time
25 during a htunidity cycle;
- Figure 2 comprises a first graph representing the residual defor~iiationo f
a sheet of paper at the end of a humidity cycle, for four different types of fibres, and a
second graph representing the total ariiplitude of the defon~iationo f tlie paper during
said hunlidity cycle for the four types of fibres;
30 - Figure 3 is a graph illustrating the loss of ~~Iiitenesosr difference in
- Figure 4 is a graph illustrating, for four papers with different colours, the
difference in shade AE obtained after a~niealuig;
- Figure 5 is a graph illustrating, for different degrees of refining, the
residual defor~nation and total amplitude of the defomlation of paper during a
5 humidity cycle.
Example 1: Demonstrating the influence of the type of binder on the
thermal resistance of paper, in particular on the yellowing of paper.
In this exatnple, several papers each co~nprising a substrate
conlprising cellulosic wood fibres obtained from eucalyptus were produced, known
10 under the reference CenibraB, covered with a layel. in pa~ticularc omprising pigments
and a binder. For these different papers, the type of binder used in the layer was
varied arid for each type of binder used, the residual \~hitenesso f the coated paper
obtained was measnred after annealing for 5 minutes at 220°C.
The residual whiteness is the ratio of the whiteness measured after
-
15 annealing with respect to the whiteness measured before annealing, expressed as a
percentage. The whiteness values mentioned above were measured using IS0
standard 2470.
For each binder, its commercial denomination, the type of binder, the
glass transition temperature Tg of said bider and the residual whiteness measured
20 after annealuig are indicated.
The results obtained were as follows:
- Binder 1 : Styronal D 5 17; styrene-butadiene; Tg=O0C; measured residual
whiteness: 19%
- Binder 2: Acronal S 305 D; butyl-acrylate and styrene; Tg=2S°C; measured
25 residual ~vliitetiess:5 5 %
- Binder 3: PVA BF 17 H; polyvinyl alcohol; measured residual whiteness:
45 %
- Binder 4: Acronal S 728; butyl-acrylate and styrene; Tg=2S0C; measured
residual whiteness: 49 %
- Binder 6: Acronal S 888 S; acrylic ester, styrene and acrylonitrile;
Tg=3 1°C; measured residual whiteness: 47 %
- Biuder 7: Acronal DS 2416; acrylic ester and styrene; Tg=3S°C; measured
residual xvhiteness: 72 %
5 - Binder 8: Acronal S 996 S; acrylic ester and styrene; Tg=4G0C; measured
residual whiteness: 62 %
- Binder 9: Esacote PULPER 211s; aliphatic polyurethalle; measured residual
whiteness: 33 %
It should be noted that the binders offering the best the~mal resistance to
10 yellowitig, i.e. the best residual whiteness after annealing, are acrylic or ac~ylice ster
type binders such as the binders with references 5, 7 and 8, for example.
Example 2: Demnonstratiot~ of the influence of the glass transition
temperature, Tg, of a binder on tlie thermal resistance of a paper, in particular on the
-
15 deforn~ationo f the paper out of the plane of the sheet of paper.
The amplitude of these deformations was meastired by itnage analysis
using a triangulation method with the aid of two CCD cameras, the nieasurements
being carried out 60 tnii~utesa fter amiealit~g.A method of this type for measurement
by image analysis is known fiom the article "Stereo image correlation for fttll-field
20 measurement on composite femoral bones during compression tests", Remi Billard
et al., published on 21 March 2012.
In this example, several papers each comprising a substrate
comprising wood cellulose fibres obtained fiom eucalyptus were produced, known
under the reference CenibraR, covered with a layer comprising in pa1ticular
25 pigments and a binder. For these various papers, the type of binder used in the layer
was varied and for each type of binder used, the deformation of the sheet of paper
out of the plane of the sleet was measured. More particularly, for this comparative
esa~nple,a binder of the type Acronal LN 579 S (acrylic ester and acrylonitrile)
was used, the glass transition temperature Tg of which was 7OC (binder 6 in
I). ?'he paper obtained thereby underwent an annealing step at 120°C for 10
niinutes.
An out of plane defor~ilationo f 15 m111 was obtained for binder 6, the
glass transition temperature Tg of which was 7"C, and an out of plane defornlation
5 of 35 ninl was obtained for the binder 4, the glass transition temperature Tg of
which was 25°C.
It was thus observed tliat, the lower the glass transition temperature of
tlie binder, the higher is tlie thermal resistance of the paper in terms of defor~~ation.
10 Example 3: Demonstration of the influence of the type of fibres on the
deformation of said paper.
In this exatnple, several papers each comprising a fibrous substrate
were produced, covered with a layer comprising in particular pigments and a
bi~ider. For these various papers, the type of fibres used in tlie substlate was varied
-
15 and for each type of fibre used, the residual deformation of tile sheet of paper thus
produced after a humidity cycle as described below, as well as the total amplitude
of the deformation of said sheet during such a cycle were measured. In particular,
the defo~~natioinn the plane of the sheet of paper was measured.
To measure these defor~nations, a Variditn type inst~unient was used.
20 Furthermore, during a humidity cycle, the relative humidity rate of the sheet of
paper was varied with time in accordance with the rule illustrated in the graph of
Figure 1. This graph represents the relative hunlidity of the sheet, expressed as a
percentage, with respect to tulle, expressed in seconds. It should be noted that during
a cycle, the starting relative humidity is 50%, increasing slowly to 80% before
25 reducing to 20%, then increasing again slowly to 80% before again being gradually
reduced to 50%.
Figure 2 corilprises two diagrams, wherein a first graph represents the
residual deformation of the sheet of paper at the end of a humidity cycle, for four
different types of fibres, namely:
- Fibres A: short cellulosc wood fibres obtained from a bleached
chemical pulp of eucalyptus known under the reference CenibraB, with a mean
length cotllprised in the range 0.5 to 1.5 mtn,
- Fibres B: long cellulose wvood fibres obtained fi0111 sohvoods known
5 under the reference SodraB, wit11 a mean length conlprised in the range 1.5 to
3 mn1,
- Fibres C: short cotton fibres with a mean length comprised in the
range 0.5 to 2 mm,
- Fibres D: long bamboo fibres with a mean length comprised in the
10 range 0.8 to 1.8 mm.
The second gap11 represents the total amplitude of the deformation of
the paper, in the plane of the sheet and during a humidity cycle, for each of the
types of fibres A to D cited above.
It was observed t11at using short fibres (CenibraB, cotton) allows
-
15 reducing the total and residual defo~lnations of the paper undergoing a humidity
cycle compared with a substrate comprising long fibres (Sodram, banlboo).
Exarnple 4: Demonstration of the influence of the type of fibres on the
yellowitig of paper.
In this example, several papers each comprising a fibrous substrate
20 covered with a layer coinprising in particular pignlents and a binder were produced.
For these various papers, the type of fibres used in the substrate was varied arid for
each type of fibres used, the differences in shade of the paper between the paper
obtained after annealing relatively to the same paper before annealing was
measured. The paper was white in colour before annealing.
25 More particularly, the annealing was carried out in an oven at a
temperature of 20OoC for 5 minutes. The difference in shade, also known as the loss
of whiteness, is generally denoted AE and is calculated f i o ~ ith~e CIE LAB
coordinates for paper using the followving forn~ulaA: E = (LZ+ AZ+ B~)'.', as is well
known per se.
- Fibres A: short cellulose \\rood fibres obtained fro111 a bleachcd
chemical pulp of eucalyptus, knowvn under the reference CenibraO, with a lnean
length cotnprised in the range 0.5 to 1.5 mm,
- Fibres B: long cellulose \vood fibres obtained from soflwoods, knowvn
5 under the reference SodraB, with a tneall length co~npriscd in the range 1.5 to
3 mm,
- Fibres C: short cotton fibres with a mean length conlprised in the
range 0.5 to 2 111111,
- Fibres D: long banlboo fibres with a mean length con~prised in the
10 range 0.8 to 1.8 tnm.
It was obse~vedth at this difference in shade is all the more reduced as
the lignit~ content of the fibres is lower. In particolar, this difference in shade is
relatively slnall for cotton fibres, for batnboo fibres and for wood fibres obtained
from e~~calypt(uCs enibraa). In contrast, this difference in shade is relatively large
-
15 for \\rood fibres obtained from softwoods (Sodra@).
Exatnple 5: Demonstration of the influence of the colonr of the
substrate before atlnealing on the jlellowing of the paper after annealing.
In this example, different papers each conlprising a fibrous substrate
covered with a layer comprising in particular pigtnet~tsa nd a binder were produced.
20 For these various papers, the colour of the substrate (and thus of the paper) was
varied by adding a colorant to the pulp, for example in the pulper, during the
production of the paper. In particular, this example cotnprised six papers with
different shades, before annealing, respectively \vhite, ivory, vanilla, beige, brow11
and black papers. The above colours are listed in the reverse order of thei~
25 \vI~iteness.
These various papers then unde~~\petaint annealing step at 220°C for 5
minutes.
Figure 4 is a graph illustrating, for each paper, the difference in shade
AE obtained after atmealing, by conlpariso~lw ith the same paper before annealing.
shade is almost zero for a paper with a starting colour whic11 is the colour black, the
difference in shade vaiying progressively from one extretne to the otl~er as a
function of the starting colot~or f the paper.
5 Example 6: De~nonstration of the influence of degree of refining
(~neasured in degrees Schopper-Riegler or "SR) of the fibrous pulp 011 the
deformation of said paper.
In this example, several papers each connprising a fibrous substrate
covered with a layer comnprising in pa~ticularp igments and a binder \Yere produced.
10 in pal-ticulal; the substrate had a filler content of 15%.
For these various papers, the degree of refining (measured in degrees
Schopper-Riegler, denoted "SR) of the fibrous pulp was varied and for each paper,
the residual defo~~natioonf the sheet of paper thus obtained was measured after a
humidity cycle identical to that described above with reference to Figure I. The total
-
15 amplitude of the defo~lnatioto~f the sheet during a cycle was also measured. These
deformations correspond to the defo~mationso f the sheet of paper in its plane. As
described above, to measure these defo~lnationsa, Varidim type instrument was used.
Figure 5 is a graph illustrating, for each paper, and thus for different
degrees of refining, said residual deformation (curve Cl) and said total amplitude of
20 the deformation (curve C2). It can be seen] that these deformations are all the more
low as the degree of refining is lo~ver.
Similarlj~t,h e influence of the degree of refining on the defol~natioo~f ~
the sheet of paper out of its plane \vas studied.
To this end, two papers were prepared, one produced from a fibrous
25 pulp with a degree of refining of 40°SR and one produced fioin a fibrous pulp with a
degree of refining of 35"SR. The deformations were measured using the triangulation
image analysis method described above.
It was observed that the out of platle deformation for the paper prepared
from a pulp wvith a degree of refining of 40°SR \vas 4.8 mtn, \vhile it was ot~lp3 .2 tntn
30 for the paper
As a consequence, it has been established that defonnatio~~ofs this type
are all the more low as the degree of refining of the pulp is smaller.
Exatnple 7: Example of a paper in accordance with one en~boditnent
5 of the invention.
111 this etnbodiment, a homogeneous fibrous pulp was prepared in a
pulper. The pulp con~prised water, a yellow colo~ant (with a negligible dl31 weight
content) in order to obtain a crean shade for the substrate, approximately 80% in dry
weight of wood cellulose fibres obtained from eucalyptus of the CenibraO type and
10 approximately 20% in dry weight of calcium carbonate (CaC03) knowvn by the
reference OmyacarbB.
The pulp then passed through a refiner where its degree of refining
was adjusted to appmxitnately 35"SR.
The co~llpositiotio f the pulp was then adjusted in the head box of a
-
15 paper macline by adding a Hi-cat 1134A type cationic starch, in a proportion of 1%
by weight with respect to the d ~tyna tter content in the pulp.
As indicated above, the head box allowed the pulp to be distributed
unifo~n~olyv er a wise where a sheet was formed before passing through the press
section then the d~yeorf the paper maclutle.
20 The sheet then underwent a surface coating treatment by passage
through a size press in order to form at least one layer. During this step, the sheet
passed tl~roagha bath the composition of \vlich is sutrunarized in the following table:
I Product used 1 1 1
( Water
I I l o
I I
Kaolin type pigment I Capim@ RG 1 70
I I
Anti-foarnitig agent ( Nopcomaste~@M PE 847 I 0.1
CaC03 type pignlent
Total pigment
Carbitaim 95
I I
30
-100
Ca~tabondBM ZI 0.5
( Sod~u~hynd roxide 1 l 1 7
I I
PVA 1 MowiolB 4-98 18
The sheet then passed into the section termed the calendering section.
At the end of these various steps, the sheet was in the for111 of a
continuous web coniprising an inner zone or core forniing a substrate or a fibrous mat,
5 the coniposition of wvhich was defined by the fibrous pulp, and at least one outer '
surface of which was covered \vith a layer, the conlposition of ~vluchw as defined by
the bath of the size press.
This sheet of paper may optionally undergo finishing operations.
A paper of this type has a relatively low surface porosity, a veiy low
10 yellowing in the case of annealing (a AE of less than 3 for an annealing of 5 minutes
at 18O0C), a very low dimensional shrinkage (less than 0.25% for an annealing of 5
minutes at 180°C) and allows obtaining a lugh thermal conductivity for the printed -
electroconductive tracks.
By way of example, the table below presents comnparative examples
15 between such a paper in accordance with the invention and other com~nercially
available papers, respectively a paper suitable for printing photographs (hel-einafter
ternied photographic paper), a coated paper sold by Arjowiggins Creative Paper with
the reference Sensation@, and a glossy coated paper sold by Arjowiggins Creative
Paper with the reference Main Gloss@
20 These comparative examples slow the different values for the
differences in shade AE for different temperatures and for different annealing
durations. The values for said shade differences AE are indicated in the table
below.
It will thus be observed that in the case of the paper of the invention
in accordance with Example 7 described above, the difference in shade obtained
after atulealing was very small by comparison with the other papers.
5 The table below presents other conlparative examples comparing the
paper in accordance with the invention, in accordance with Example 7, and the
Sensation@ and Main Gloss@ papers mentioned above. In these comparative
exanlples, the resistance R of the conductive tracks printed by screen printing or by
flexography, having then undergone an annealing treatment, was measured for each of
10 the papers metltioned above. The values for said resistances are indicated in the table
below.
- -
I Type of 1Paper 1 1
It can thus be seen that using paper in accordance with Exanlple 7 of
15 the invention allows reducing the resistance of the printed conductive tracks, and
thus improving their electrical conductivity, by compa~.isonw ith other co~mnercially
printing
Screen
printing
Dupont 5064
silver ink
Flexogaphy
Agfa
silver ink
Flexography
Agfa silver
ink
available papers.
Exatnple 8: Detllo~lstratio~olf the influence of the process for
annealing
150°C / 5 min
--
180°C / 5 mi11
150°C 190 s
according to
Example 7
R = 39 Rlsq
Paper
R = 45 Rlsq
Paper
R = 53 Q/sq
R = 1700 Rlsq
--
-
more ' than
90 000 Q/sq
more than
90 000 O/sq
and as a consequence on the adhesion of tlie elcctroconductive ink.
A support (powercoat HD 230) obtained by the proccss described in
patent application WO 20131104520 cited in the introduction to the present
docunient was compared with the support of the present iavention.
5 Firstly, a Scotch 3M paper tape test for the adhesion of ink was
carried out. The following were used:
a Scotch 3M 2525 paper tape, used in the known tear test for paints
and varnishes,
an Agfa Orgacon SI-P1000x ink, printed using screen printing,
10 three different supports.
By means of the support of patent application WO 20131104520 as
printed in this ii~am~ear ,p ortion of the ink was torn off using the Scotch paper
tape. With the support of the present invention, no pai-ticles of ink were found on
the Scotch paper tape. Starting from a PET film, few particles of ink remained
-
15 attached to the Scotch paper tape.
Secondly, an adhesion test was carried out during a photonic
annealing. A Novacentrix ICI-021 copper ink was used on a DEK horizon 03i
press, and open air drying was canied out, followed by a photoriic annealing using
light pulsed with a Xenon Sinteron 2000.
20 With the support of patent application WO 2013/104520, poor
adhesion of the copper during the annealing was observed. It was impossible to find
satisfactory parametels. Using the support of the present invention, good adhesion of
the copper was observed. On the PET support, copper adhesion was poor and the
temperature for the reduction of copper (approximately 500°C) ran the risk of
25 defornlation of the PET.
These differences can be explained by tlie variation in microporosity of
the pigment layer at the surface of the support between the patent application WO
20131104520 and the present invention. Indeed, using a plastic film to deposit the
pigment layer at the surface of the support as described in patent application WO
30 2013/104520, induces a vely high surface smootlu~ess of the support, along with a
present illvention induces a sufficient microporosity to allow inks to adhere to the
pigment layer.
In ordcr to characterize tlie micropomsity of the support surface, a
Microcontou~@te st was carried out:
5 The Microcontour test was carried out in order to evaluate, in a simple
manner, tlie surface state of samples by application of a blue Microcontour Test@
ink, Lorilleax (ref. 381 1). After covering the two supports mentioned above (in
accordance with WO 20131104520 and in accordance with the invention) using an
inked roll, the two surfaces Itrere wiped. This step allows visual detection of
10 irregularities on the surface or coating defects. After d~ying, optical density
measurements were carried out at a wavelengt11 in the visible (380-780 nm) in
order to quantify the ink remaining on the support.
This is a simple way of providing an idea of the roughness and/or
porosity of a support. In fact, the special ink contains pigments which are fairly
- -
15 coarse in size which can only become attached to very rough and/or porous
surfaces.
I Optical density I WO 20131104520 support I Support of the invention 1
Mean
Standard deviation
The results of this test confirn~ the apparent differences for the
20 support in accordance with patent application WO 20131104520 and the support of
the invention: tlie values for the optical densities between the two supports are very
different: the smooth closed paper of application WO 20131104520 has a vely low
optical density because the ink has not resisted being \\riped. In contrast, the support
of the invention has an optical density n~hich is norn~al, because the ink has
25 imnlediately penetrated the surface due to the n~icroporosity.
I I
0.04
0.01
Coefft of variation
0.61
0.061
25.0 10.0

CLAIMS
1. A paper con~prising a fibrous substrate comprising at least one side co\1ercd
5 wit11 at least one layer, said layer con~psisingo r consisting of:
- 100 parts in dry weight of pigments,
- 5 to 50 parts in dry weight of one or more binders which are
resistant to an exposure to teniperatures comprised in the range 140 "C
to 200 OC and having a glass transition temperature of less than 20°C,
in particular of one or more acrylic binders, the glass transition
temperature of which is less than or equal to 20°C, preferably less than
or equal to 1O0C,
- 0 to 15 pasts in dry weight of a viscosifying agent such as polyvinyl
alcohol, for example.
15 2. The paper as claimed in claim 1, characterized in that said layer conlprises
10 to 30 parts in dry weight of ac~ylic binder with a glass tlilnsition
temperature of 20°C or less, preferably 15 to 25 parts in dry weight, even
more preferably 19 pat-ts in dl37 weight.
3. The paper as clainled in claim 1 or claiin 2, characterized in that said layer
20 comprises 5 to 10 parts in dl31 weight of polyvit1~~a1lc ohol, Inore preferably
8 pasts in dry wveight.
4. The paper as claimed in one of claims 1 to 3, characterized in that the
fibrous substrate comprises 70% to 90% in dry weight of short cellulose fibres
with a mean length in the range 0.5 to 1.5 null, such as wvood fibres, in
25 particular wood fibres obtained from a bleached chemical pulp of eucalyptus.
5. The paper as claimed in claim 4, characterized in that the substrate
comprises 80% in dty wveigllt of shoi-t cellulose fibres.
6. The paper as claimed in one of claims 1 to 5, characterized in that the
fibrous substrate conlprises 10% to 30% by weight of at least one mineral
30 fillel; preferably calciunl carbonate, kaolin or titanium dioxide.
has a w\fl~itencscso mprised in the range of 70 to 90, preferably conlprised in
the range of 75 to 85.
8. The paper as clainled in one of clairns 1 to 7, cliaracterized in that the
difference in sliadc, AE, of the paper, calculated fronl the CIE LAB
5 coordinates of the paper, after an annealing at 200°C for 5 minutes is less than
5, preferably less than 2, compared with said paper before annealing.
9. The paper as claimed in one of claims 1 to 8, characterized in that the layer
covering at least one side is printed over all or a portion of the surface of
said layer with a layer of electroconductive ink of 0.5 to 15 pm thick.
10 10. A process for tlie production of a paper as clainled in one of claims 1 to 8,
characterized in that it comprises the steps consisting of:
- forming a fibrous substrate with the aid of a fibrous pulp,
- at least pat-tially coveringat least one surface of the fibmus substrate
by coating \vitli a layer cotnpris-in g 100 palls in dry wveight of pigments, 5 to
15 50 pasts in dry weight of one or more biders ~vluch are resistant to an
exposure and to teniperaturcs comprised in the range of 140 "C to 200 OC
and having a glass transition temperature of less than 2OoC, in particular of
one or more acrylic binders, the glass transition temperature of which is less
than or equal to 20°C, preferably less than or equal to 10°C, and 0 to 15
20 paits in dry weight of a viscosifj4ng agent
11. The process as claimed in claim 10, characterized in that the degree of
refining of the fibrous pulp is less than 50°SR, preferably less than 40°SR,
even more preferably of the order of 35"SR.
12. The process as claimed in clainl 10 or claitn 11, cliaracterized in that said
25 layer is applied by coating \vith the aid of a size press of a paper machine.
13. A process for tlie production of an electrocondoctive product, comprising the
steps consisting of:
- covering, by printing using an electroconductive ink, at least one zone of a
support produced fronl a paper as claimed in one of claims 1 to 8,
- tr~i~icnlintgl~ csu pport 21ntl [hc ink so ;is to Ii)t.111;I II c I ~ c t n ~ ~ ~ n dI ~uI ~~c It0.i 1\.' ~
contitiuous track on tlie support.
14. Tl~e process as claimed in claim 13, characterized in that the annealing
temperature is comprised in the rauge of 100°C to 300°C, preferably of 180°C
to 220°C.
15. The process as claimed in clainl 13 or claim 14, characterized in that the layer
5 of ink deposited by printhg on the support is comprised in the range of 0.5 to
15 pm, preferably of 1 to 10 pm.
16. The process as claimed in one of claims 13 to 15, characterized in that the
electroconductive ink is deposited using a screen printing, flexographic or
heliographic type printing process.
10 17. A paper comprising a fibrous substrate comprising a side covered wvitlt a layer
onto which an electroconductive ink is printed, as obtained by means of steps
consisting of:
- forming a fibrous substrate with the aid of a fibrous pulp,
- at least partially covering at least one surface of the fibrous substrate
-
15 by coating with a layer comprising 100 parts in d q weight of pigments, 5 to
50 parts in dly weight of one or more binders which are resistant to an
exposure and to temperatures comprised in the range of 140 "C to 200 OC
and having a glass transition temperature of less than 20°C, in particular of
one or more acrylic binders, the glass transition temperature of which is less
20 than or equal to 20°C, preferably is less than or equal to 10°C, and from 0 to
15 parts in dry weight of a viscosi6ing agent;
- covering at least one zone of the layer by printing using an
electrocoilductive ink;
- annealing the coated substrate and the ink so as to form an
25 electrocoi~ductivel ayer or continuous track on the suppol?,