WO2006035112A1

WO2006035112A1 - Coated fibrous web and process for the production thereof

Info

Publication number: WO2006035112A1
Application number: PCT/FI2005/000417
Authority: WO
Inventors: Jukka Perento; Soili Peltonen; Kirsi Immonen; Hannu Mikkonen
Original assignee: Panipol Oy
Priority date: 2004-09-30
Filing date: 2005-09-30
Publication date: 2006-04-06
Also published as: EP1794364A1; FI20041272A0; FI20041272A

Abstract

Coated fibrous product and method for the production thereof. The product comprises a web which is formed by cellulosic or lignocellulosic fibres, and on the top of the web a coating layer which comprises a binding agent and light scattering pigments. The coating layer comprises a synthetic, electrically conductive polymer which is mixed with the binder and at least partially attached to the pigments and, as a result, the coating layer can be rendered electrically conductive. By means of the present invention it is possible to apply an electrically conductive polymer onto the surface of paper or cardboard using a conventional coating technique and, as a result, additional process stages, for instance in the production of antistatic package materials, can be avoided.

Description

Coated Fibrous Web and Process for the Production thereof

The present invention relates to a coated fibrous web in accordance with the preamble of Claim 1

A fibrous web such as this usually comprises a base web, at least one surface of which comprises a pigment-bearing coating layer.

The present invention also relates to a method of manufacturing coated fibrous web, according to the preamble of Claim 13.

According to certain estimates, electrostatic phenomena cost the electronics industry several billion euros every year. As components increase their speeds and their sizes decrease, their vulnerability to electrostatic charging and discharging (hereafter also abbreviated as "ESD") increases, too. Moreover, these ESD phenomena affect the productivity and the functionality of products in almost all fields of the electronic industry. Managing ESD is important in clean room applications and in the graphics industry, too.

One way to decrease ESD is to incorporate electrically conductive components in the packages of electronic products, in floor coverings or underlay coatings. Examples of conductive components are metal powders, graphite and electrically conductive polymers. These polymers are arousing more and more interest because, among other things, it is possible to flexibly modify their properties and in turn, for example, adjust the electrical conductivity to a desired level depending on whether ESD protection or antistatic properties are desired. This has led to electrically conductive polymers being used, among other things, in antistatic packages and in products which protect against electromagnetic radiation. Due to their properties these polymers are also suitable for use as electrodes of primary or secondary batteries and also for security paper application.

Package applications have been presented in US Patent Specification 5,421,959 and security papers in the DE Published Patent Application 19826800. Microwave packages comprising electrically conductive polymers, in turn, are known from US Patent Specification 5,211,810. Electrically conductive polymers have been incorporated in the above-mentioned products which comprise cellulosic fibres, by mixing the polymers with the fibres or by polymerizing the polymers onto the surface of the fibres.

There are considerable disadvantages associated with known solutions. Accordingly, in paper products the polymers are generally loosely attached to the fibre matrix. When the polymer is mechanically mixed with the fibres, the polymer is weakly fastened to the fibres because the polymer is generally hydrophobic and the fibres are hydrophilic. By polymerizing the prepolymer which has been absorbed into the paper the polymer is primarily precipitated onto the fibres because the prepolymer only slightly penetrates into the finished fibre network of the paper, thus the polymerization takes place on the top of the fibre network. According to US Patent Specification 5,211,810 the polymerization is carried out in situ in the presence of a strong mineral acid, namely IN hydrochloric acid. The acid modifies for instance the amorphous areas of the cellulose, lowers the strength, keratinizes the fibre and decreases the water retention capacity of the fibre. Keratinized fibre also demands considerably more grinding energy. The effect of a low pH-treatment is almost equivalent to drying the cellulose.

In solutions related to practical applications, a large part of the electrically conductive polymer is situated, with regard to the paper or fibre products, in places where it does not contribute to generating the electrical conductivity of the product surface. Because the electrically conductive polymer is incorporated in the paper body, a lot of electrically conductive polymer is needed, which increases the price of the product. Moreover, in cases where the polymer is only loosely attached, part of the polymer ends up in the circulating water and complicates the achieving of a closed system process.

A method of manufacturing wallpaper which protects against electromagnetic radiation is also known. In this method, ordinary wallpaper is coated with a mixture that comprises a matrix polymer, an electrically conductive polymer and additives mixed with these (EP Published Patent Application 1,139,710). In this case the affixing of the electrically conductive polymer onto the paper surface represents an additional treatment step, one that is intended to create a separate surface layer which otherwise would not exist in the structure of the paper. In addition, in order to produce a homogeneous electrically conductive surface, it is necessary to use large quantities the electrically conductive polymer, which is the most expensive component of the composition.

It is an aim of the present invention is to eliminate the disadvantages associated with the known technology and to generate a new fibre web comprising an electrically conductive polymer and a method for its production.

The present invention is based on the idea that a paper or cardboard product, the production costs of which are competitive, and which comprises electrically conductive polymer, is produced most suitably in such a way that the electrically conductive polymer is brought onto the surface of the fibre web in association with an ordinary coating process. In that case, the electrically conductive polymer-bearing layer is spread, i.e. applied onto the surface of the paper or cardboard surface, to form a coating layer.

According to the present invention, a coated fibrous web is produced which has at least a first layer comprising cellulosic and/or lignocellulosic fibres, and a second layer comprising a coating layer which is on the top of the fibrous web and which comprises synthetic electrically conductive polymer mixed into a binding agent and light scattering pigments. Most suitably the electrically conductive polymer is brought onto the surface of the pigments and at least partially attached to them. The coating layer on the surface of the fibrous web is conductive or it must be made conductive at least in part of the coating layer.

More specifically, the product according to the present invention is characterized by what is stated in the characterizing part of Claim 1.

The method according to the invention is, again, characterized by what is stated in the characterizing part of Claim 13.

Considerable advantages are obtained by means of the invention. Thus, the invention can be used to bring the conductive polymer onto the surface of the paper or cardboard using a conventional coating technique, hi this way, additional process steps can be avoided. When the conductive polymer is placed on the surface of the base paper and being completely incorporated in the coating layer, it does not disturb the existing main functions of the paper. Rather, the surface of the paper or cardboard can, for example, be used as a surface for printing and at the same time the cellulosic or lignocellulosic matrix of the base paper gives the product the desired strength properties.

The polymer can be incorporated into one or several coating layers. If it is added only in the precoating layer, it is possible to hide the conductive layer under the surface coating. This is advantageous if it is desired to hide the colour of the polymer in the product surface, such as the green colour in the case of polyaniline. Correspondingly, the electrically conductive polymer can be used in one single or in several surface coating layers, if it is desirable that the conductive layer is as close to the surface as possible. The place at which the polymer is added can also be chosen according to the pigment. As described in more detail below, an acidic pH-value is advantageous for the conductivity of the polymer, in which case an acid-stable pigment is preferably chosen as the pigment for a layer which comprises electrically conductive polymer. In a way which is known per se the pigments of the coating used in the precoating can be different from those in the surface coating, in which case a less acid-stable pigment can be used in the layer containing no electrically conductive polymer.

An electrically conductive polymer in the coating layer can provide several different functions; also, it is not directly visible to the consumer. The conductive polymer can be utilized for example for equipping the product with additional information or for checking the authenticity of the product. No contact is needed for measuring conductivity. Non- contact measurement, for instance capacitive measurement, can be carried out at a short distance.

By adjusting the amount of the electrically conductive polymer it is possible to reach a selected conductivity level, which is, for example, 10⁴-10^π ohm/square, typically approximately 10 -10 ohm/square. When the sheet resistance is 10 ohm or lower, the product can easily be distinguished from non-conductive products. By incorporating a conductive network into the paper or cardboard it is possible to provide the surface with several different functions which, depending on the conductivity level, are associated with antistatic applications, storage of identification data, security marks, etc. The present invention provides a novel fibrous product having an electrical conductivity, one which is maintained over extended periods of time. When attached to the pigment which, in turn, is mixed into the binder, the polymer is evenly and homogeneously distributed throughout the whole web surface. The advantage of this is that good conductivity is reached with small amounts of polymer. As the examples below show, even an amount of 10 % by weight polyaniline gives a good electrical conductivity, one which is of the order of 10⁴ ohm. A smaller amount of the electrically conductive polymer which is attached to the pigment is needed than if the electrically conductive polymer were only dispersed in the binder. Because the pigment particles have a large surface they easily form a continuous network in the dried coating. Spherical pigments are more preferable especially if they are hollow or if their inner part has a lower density than their surface layer, because in that case they are flattened due to the compression and the calendering and form a homogeneous surface.

Another special advantage which is attained with pigment coating is that it is easy to adjust the amount of the electrically conductive polymers by changing the amount of the coating to be applied.

In the following, the present invention will be examined more closely with the aid of a detailed description and some working embodiments.

Mineral materials and compounds of electrically conductive polymers are already known. Accordingly, the EP Published Patent Application 298,746 discloses a material which comprises an inorganic powdery or granular material, is suitable for coatings and which is coated with an electrically conductive polymer such as polyaniline, in a non-aqueous or aqueous dispersion. Among the materials to be coated are talc, mica, wollastonite, calcium carbonate, aluminium hydroxide, aluminium oxide and hydroxyapatite.

The EP Published Patent Application 1,010,733 describes a polymer composition which is suitable for coatings and which has a good refractivity, conductivity and translucency. The composition comprises mainly C₁-C₃ alcohol and amide with dissolved polytiophene-based conductive polymer, high refractivity inorganic sol, resin binders and dopant comprising a sulphonic acid group. A composition such as this can be used to coat the outer surface of a CRT tube by means of spin or spray coating. The references disclose no statements about the fact that the described compositions would be used to coat fibrous webs. In known solutions, no references to usability of products generated in this way, for instance in the production of security products, can be found either.

For the sake of completeness, it should also be mentioned that US Patent Publications 4,007,148 and 3,887,496 disclose compositions which comprise quaternary methylammonium-cloride based polymers and pigments and which are used for example for the coating of paper. In those publications, there is no reference to the fact that the polymers in question would be attached to the surface of the pigments, which means that these known solutions cannot be used to prevent the polymer from ending up in the circulating waters.

In a fibrous web, according to the present invention, there are always at least two layers, conventionally at least three. First, the fibrous web comprises a base paper or corresponding uncoated web which consists of cellulosic or lignocellulosic fibres. The cellulosic or lignocellulosic fibres can be sourced from mechanical, chemi-mechanical or chemical pulp which is produced from plant fibres (one-year or perennial fibres). Typically, the fibrous web comprises a conventional paper or cardboard web which is produced from paper or cardboard pulp made of wood based fibres.

According to the present invention, non-woven products and fabrics can be coated, too. The latter can be made of natural fibres or synthetic fibres, or combinations of these.

In that case, on the base paper or base cardboard that is in general the substrate - at least on one of its surfaces - there is a coating layer comprising a synthetic electrically conductive polymer which is mixed into the binder that forms the binder matrix. In addition, there are light scattering pigments in the coating layer.

By "matrix" is meant a polymer network or layer, one which is at least partially continuous in such a way that it is capable of forming continuous surfaces and layers. Due to the electrically conductive polymer, the second layer is at least partially electrically conductive or it can be rendered electrically conductive. Typically, the surface resistivity of a second layer is in the electrically conductive form approximately 10²-10ⁿ ohm, preferably approximately 10³-10¹⁰ ohm, in particular approximately 10⁴-10⁹ ohm. In the examples below, a surface resistivity of 10⁵-10⁹ ohm was reached.

The grammage of the web to be coated is generally approximately 5-700 g/m², typically approximately 20-500 g/m², for instance approximately 30-150 g/m² in the case of paper, and 80-300 g/m² with cardboard. The total grammage of the product is generally 10-1500 g/m², typically approximately 40-1000 g/m².

The bottom web can comprise one layer or comprise a two or more layer web which is made using for instance a "layer webbing technique" - for example as used with a multilayer headbox - or by laminating.

The coating can be performed as a single coating or as a double coating, in which case the coating pastes can be used either as a single coating paste or as a precoating paste and a surface coating paste. Triple coatings are possible, too. Generally, a coating colour according to the invention contains 10-100 parts by weight of at least one pigment or a mixture of pigments, 0.1-30 parts by weight of at least one binder, 0.1-50 parts by weight of an electrically conductive polymer and 1-10 parts by weight of other additives known per se. A more preferable coating mixture comprises a conventional pigment and a pigment coated with conductive polymer with a weight ratio of 100: 1...100:50.

Generally, a pigment coated with an electrically conductive polymer comprises an electrically conductive polymer which is 1-30 % by weight of the pigment weight.

The typical composition of a precoating mixture is as follows:

Coating pigment

(for example, coarse calcium carbonate) 100 parts by weight Electrically conductive polymer 1-20 parts by weight

Binder 1-20 % by weight of the pigment

Additives and auxiliary agents 0.1-10 % by weight of the pigment

Water balance Water is added to the precoating mixture so that the solids content is generally from 40 to 70 %.

According to the present invention, the composition of the surface-coat mixture or single coat mixture is for example as follows:

Coating pigment I

(for example fine carbonate) 10-90 parts by weight Coating pigment II

(for example fine kaolin) 10-90 parts by weight

Pigment total 100 parts by weight

Conductive polymer 1-30 parts by weight

Binder 1-20 parts by weight Additives and auxiliary agents 0.1-10 parts by weight

Water balance

Water is added to such a coating mixture so that the dry solids content is typically from 50 to 75 %.

According to the present invention, in the coating mixtures presented above it is possible to use pigments that have a steep particle size distribution, which means that a maximum of 35 % of the pigment particles are smaller than 0.5 μm, preferably at maximum 15 % are smaller than 0.2 μm.

The present invention can be applied to any pigment, particularly light-scattering pigments, and typically mineral or synthetic pigments. Examples of such pigments are precipitated calcium carbonate, ground calcium carbonate, calcium sulphate, calcium oxalate, aluminium silicate, kaolin (hydrous aluminium silicate), aluminium hydroxide, magnesium silicate, talc (hydrous magnesium silicate), titanium dioxide and barium sulphate, and mixtures of them. It is possible to use synthetic pigments, too. Of the pigments mentioned above, the main pigments are kaolin, calcium carbonate, precipitated calcium carbonate and gypsum, which in general constitute over 50 % of the dry solids in the coating mix. Calcined kaolin, titanium dioxide, satin white, aluminium hydroxide, sodium silicoaluminate and plastics pigments are additional pigments, and their amounts are in general less than 25 % of the dry solids in the mix. Of the special pigments, special-quality kaolins and calcium carbonates, as well as barium sulphate and zinc oxide, should be mentioned.

The present invention is applied, in particular, to mineral pigments selected from aluminium silicate and aluminium hydroxide, magnesium silicate, titanium dioxide and/or barium sulphate, as well as mixtures thereof.

Another pigment which is especially interesting is the spherical Hollow Pigment ("bubble particle") which is marketed by, among others, Roehm & Haas (e.g. under their brand name "Ropaque")- Dow Chemical has corresponding products, too (HS - Hollow Sphere Plastic Pigments). This pigment is synthetic and comprises a hollow latex ball approximately 0.1-10 μm in size; typically its average particle size is approximately 0.5-2 μm. The Ropaque product comprises styrene-acryl polymer, its void volume is over 50 % and density 1.02 g/cm³. Characteristically, therefore, it possesses a large surface in relation to its weight and, as a result, the surface weight of the coating can be decreased because the pigment gives a good coverage. At the same time, the amount of the electrically conductive polymer can be decreased. Because at least part of the pigment is flattened during the coating process, part of which is the IR drying and the following calendering, the conductive polymer that is attached to the surface of the pigment is able to form, even when used at low volumes, a continuous and conductive surface on the top of the fibrous web.

Additional advantages of the Hollow Pigment are, among others, its high glass transition point, tg, which is close to the tg of conductive polymer. The pigments are easy to use and it is possible to achieve a high conductivity even when using a pigment which is coated with 10-12 % by weight of electrically conductive polymer in the coating paste.

By using Hollow Pigment coated with conductive polymer in the coating paste, it is possible to produce a conductive/antistatic coating which is a fully organic material.

Hollow Pigment coated with conductive polymer can be used not only for coating paper and cardboard but also for modifying paints.

As binders in the coating mixture it is possible to use any known binders generally employed in paper production. Besides individual binders, it is also possible to use mixtures of binders. Examples of typical binders include synthetic latexes made of polymers or copolymers of ethylenically unsaturated compounds, for instance copolymers of the butadienestyrene type, which possibly also have a comonomer containing a carboxyl group, such as acrylic acid, itaconic acid or maleic acid, and polyvinyl acetate having comonomers that contain carboxyl groups. Together with the materials cited above, it is also possible to use as binders, for example, the water-soluble polymers, starch, CMC, hydroxyethyl cellulose and polyvinyl alcohol.

Furthermore, it is possible to use conventional additives and auxiliary agents, such as dispersants (e. g. sodium salt of polyacrylic acid), agents affecting the viscosity and water retention of the mix (e.g. CMC, hydroxyethyl cellulose, polyacrylates, alginates, benzoate), lubricants, hardeners used for improving water-resistance, optical auxiliary agents, anti- foaming agents, pH control agents, and preservatives, in the coating composition. Examples of lubricants include sulphonated oils, esters, amines, calcium or ammonium stearates; an example of agents improving water resistance is glyoxal; examples of optical auxiliary agents are diaminostilbene disulphonic acid derivatives; examples of anti- foaming agents are phosphate esters, silicones, alcohols, ethers, vegetable oils; examples of pH control agents are sodium hydroxide, ammonia, sulphuric acid, acetic acid and sulphonic acids; and finally examples of preservatives are formaldehyde, phenol, quaternary ammonium salts.

The coating mix can be applied to the material web in a manner known per se. The method according to the present invention for coating paper and/or cardboard can be carried out with a conventional coating apparatus, i.e. by blade coating, or film coating or spray application or curtain coating.

The conductivity of the electrically conductive polymer is adjusted using an acid or, correspondingly, an alkali, as described in detail below. Because a high level of conductivity is usually achieved in a clearly acidic pH area, it is advisable to choose the components of the coating material mix in accordance with the above in order to allow the coating layer to function well in different conditions. This means that many of the binders mentioned above are alkaline, for example. They must be neutralized if it is desirable to bring the conductive polymer into the coating layer in a conductive form. Certainly it is possible to apply the layer comprising electrically conductive polymer in an alkaline form and change it to a conductive form after the coating, for example during the printing stage.

According to a preferable application of the present invention, an electrically conductive polymer is used which is an inherently electrically conductive polymer and which can be "doped" to generate charge carriers, and the polymer in question is attached to pigments.

In the present invention the term "Electrically conductive polymers" means inherently electrically conductive polymers (ICP), which are "doped" (furnished, processed) in order to generate charge carriers (holes and electrons). Common to all electrically conductive polymers are the conjugated double bonds of the backbone chain (alternate single and double bonds, delocalized silicon electron system), which enable the movement of the charge carriers. Electrically conductive polymers have both ionic and electronic conductivity, which can be utilized in various applications. The conductivity of electrically conductive polymers can fluctuate and be regulated within the whole conductivity range, from insulant to metallic conductor. Generally, a polymer is considered to be electrically conductive if its maximum resistance is 10¹¹ ohm (as surface resistivity).

An electrically conductive polymer can be present in the binding agent layer both in an electrically conductive and in an electrically non-conductive form. Consequently, the term "electrically conductive polymer" in the claims presented below also means a polymer that is non-conductive at the time of reference, but which, however, can be brought to an electrically conductive state, for instance by using a suitable doping agent treatment.

One of the advantages when using inherently conductive polymers is, among others, that by using doping the coated product can be equipped with desired electrically conductive patterns.

Polyaniline, polypyrrol, polyacetylene, polyparaphenyl or polytiophene, or derivatives or mixtures of them, are used as electrically conductive polymers. Among the derivatives, the alkyd and aryl derivatives and the chlorine and bromine-substituted derivatives of the polymers mentioned above are particularly worth mentioning. If needed, electrically conductive particles, such as graphite or carbon black can be added, too.

Polyaniline is more preferable in the present invention. The monomer in the aniline polymer is aniline or a derivative of that, and the nitrogen atom of the monomer is in most cases bonded to the para-position carbon of the benzene ring of the next unit. The unsubstituted polyaniline can be in different forms, among which the emeraldine form, which as a salt is characterized by a clear, emerald-green colour, hence its name, is generally used for conductive polymer applications.

By using doping, the electrically neutral polyaniline can be converted into a conductive polyaniline-complex. The doping agents used in the present invention can vary widely and they are generally employed when conjugated polymers are doped into an electrically conductive or semiconductive form.

Protonic acids are known doping agents in the field of inherent conductive polymers, as can be seen from the references by J. -C. Chiang and Alan G. MacDiarmid, and in the W. R. Salaneck citation: o Chiang et al., Synth. Metals (1986) 13: 193-205 o MacDiarmid et al., Papers from the 6th European Physical Society Industrial

Workshop Eur. Phys. Soc. o Salaneck et al., Synth. Metals (1986) 13:291-297 No Month Available.

Such doping agents comprise inorganic or organic acids, and their derivatives, among which mineral acids, sulphonic acids, picric acid, n-nitrobenzene acid, dichloric acetic acid and polymer acids are typical examples. If desired, more than one doping agent can be used.

Preferably, a functional acid is used for doping, such as a sulphonic acid, particularly an aromatic sulphonic acid, which comprises one aromatic ring, or two fused rings, in which case at least one ring may have a polar or a non-polar cyclic substituent, such as a functional group (for instance a hydroxyl group) or a hydrocarbon chain, such as an alkyl chain with 1-20 carbons. Examples of these are alkylbenzene sulphonic acids and dialkylbenzene sulphonic acids (where the alkyl comprises 1-20 carbon atoms), other branched benzene sulphonic acids, aromatic diesters of phosphoric acid, etc.

The following can be mentioned in particular:

MSAs (methylsulphonic acids),

Ethylsulphonic acids

BSAs (benzoic sulphonic acids)

TSAs (toluene sulphonic acids)

DBSAs (dodecylbenzene sulphonic acids) Ethylbenzene sulphonic acids

PSAs (phenol sulphonic acids or hydroxybenzene sulphonic acids)

CSAs (camphor sulphonic acids)

AMPSA (2-acrylamide-l-methyl-propanesulphonic acid)

Vinylsulphonic acids Isophthalic sulphonic acid and esters

PPA (phenyl phosphine acids)

Phosphone acetic acid,

DIOHP (bis(2-ethyl hexyl hydrogenphosphate))

Chlorobenzene sulphonic acids Pyridine sulphonic acids

Anisidine sulphonic acids

Aniline sulphonic acids

Quinoline sulphonic acids

Naphthalene sulphonic acids Sulphosalisylic acids

Phosphonic acids

Polymers which are functionalized at their ends? by sulphonic acid [polystyrene (PSSA), polyolefins, polyethylene oxide, polyvinyls], along with sulphonated polyparaphenylenes and sulphonated aromatic polyamides and similar substances, are noteworthy examples of polymeric acids.

Preferred acids are dodecylbenzene sulphonic acid (DBSA), camphor sulphonic acid, para- toluene sulphonic acid and phenol sulphonic acid. The preparation of polyaniline complexes are described in detail in, for instance, the EP Published Patent Applications Nos. 545,729 and 582,919 and in the FI Published Patent Applications Nos. 932557, 932578 and 940626, the contents of which are herewith incorporated by reference.

Oxidizing agents are generally used to polymerize a monomelic compound into a corresponding electrically conductive polymer. Preferred oxidizing agents are polyatomic metallic salts such as iron(πi) salts and per-compounds like peroxides, peracids, persulphates, perborates, permanganates, perchlorates and chlorates, nitrates and quinones. The amount of oxidizing agent in relation to the monomer is generally from 10: 1 to 1 : 1, more preferably from approximately 5:1 to 2:1 (parts by weight) or from 4:1 to 1:1 as mole fractions (oxidant/monomer).

The electrically conductive polymer is incorporated in the coating composition by mixing it with a binder, for example in dispersion form, or - preferably - by first polymerizing it on the surface of the pigment after which the pigment coated with the electrically conductive polymer is mixed in a way known per se with the other components of the binder and the coating mixture.

If the electrically conductive polymer is added in dispersion form into the binding agent, the most applicable way is to select a dispersion agent corresponding to the solvent of the binding agent. Hence, polyaniline can be used as a water paste in the case of aqueous binding agents. The concentration of polyaniline ranges, for instance, from 0.1 to 25 % by weight, preferably from approximately 0.5 to 20 % by weight and, particularly, from 5 to 17 % by weight. It is most suitable if the polyaniline is in a conductive form, in which case the previously mentioned concentration includes the amount of the doping agent. The amount of polyaniline (without the doping agent) ranges generally from approximately 0.1 to 15 % by weight. Where non-aqueous binders are used, polyaniline is added to organic solvents (for example toluene) in a dispersed state. The same concentrations, as described previously, are used.

According to a preferred embodiment of the present invention, the electrically conductive polymer is integrated into the compound already polymerized onto the surface of the pigment particles. The coated pigments are produced by bringing the pigments into close contact with the monomer which forms the electrically conductive polymer, in an intermediate agent, preferably an aqueous intermediate agent. Besides water and aqueous solutions it is possible to use organic, polar and non-polar solvents.

Here, "close contact" means that the pigments and the slurry comprising the monomeric pre-stage of polymer and/or the polymer doping agent are briskly mixed so that the monomer and/or the doping agent are well distributed among the pigments. It is possible to proceed as described in detail in the examples, that is by using the counter-ion and the monomer corresponding to the polymer to form a dispersion, to which the pigment to be coated is added and which is mixed to form a homogeneous dispersion, after which the oxidant is added in order to start the polymerization.

Here, "an aqueous intermediate agent" means both water and aqueous solutions in which the pigments are elutriated. Typically, the consistency of the aqueous slurry is 0.1-50 % (weight/weight), preferably approximately 0.5-30 and especially approximately 0.7-20 %. After that, the counter-ion of the electrically conductive material to be polymerized or a corresponding monomer can be dissolved in the aqueous phase. The quantity of the doping agent varies according to the amount of the monomers. Generally, the monomer percentage is approximately 0.1-200 % of the quantity of the doping agent/pigment, typically approximately 1-150 % by weight, preferably approximately 5-120 % by weight and especially approximately 10-100 % by weight. Generally, the amount of the counter-ions can be equimolar to the amount of the monomers, but it can also be approximately the same as the number of moles of the monomer ±30 %.

The temperature is generally above 0 ⁰C, but below room temperature. Typically, the temperature is approximately 1-18 °C, preferably approximately 2-15 ⁰C.

Generally, the counter-ion is acidic and in the pairing of the fibres and the polymer/monomer the pH-value of the aqueous phase is most suitably clearly acidic, preferably the pH is below 5, typically approximately 2 + 1.

The monomer amount (without the doping agent) is approximately 0.1-50 % by weight of the amount of pigment, most suitably approximately 1-30 % by weight, especially approximately 2-20 % by weight.

The coating of the pigment is described in the EP Published Patent Applications 298,746 and 1,010,733, the contents of which are herewith incorporated by reference.

The present invention provides a binding agent compound in which the percentage of the electrically conductive polymer (doping agent) is approximately 0.01-20 %, preferably approximately 0.05-15 %, most suitably approximately 0.1-10 % of the total weight of the compound. The percentage of the electrically conductive polymer of the coating layer formed by a compound like this is approximately 0.1-15 % by weight, preferably approximately 0.2-10 % by weight, typically approximately 0.5-7 % by weight, after the drying of the layer.

The electrically conductive polymer is at least partially bound to the binder, part of it can be dispersed or otherwise mixed into the binder, but typically at least 20 % by weight, preferably at least 50 % by weight, most suitably at least 75 % by weight of the electrically conductive polymer is attached to the surface of the pigment. The present invention also includes the case in which practically all the electrically conductive polymer is bound to the pigment.

It should be pointed out that in both of the forms of the application above, the pH value of the compound should preferably be kept on the acidic side, if the electrically conductive polymer is introduced (dispersed or attached to the pigment) in an electrically conductive form and there is no intention to change its electrical conductivity. A suitable pH value is 1-6.5, more preferebly approximately 1.5-5.

The coating mix can be applied to the material web in a manner known per se. The method according to the present invention to coat paper and/or cardboard can be carried out with a conventional coating apparatus, i.e. by blade coating, or film coating or spray application.

When the paper web is coated at least on one side, preferably both sides, a coating layer is formed having a grammage of 5 to 30 g/m². The uncoated side can be treated by, for example, surface sizing. The coated product in accordance with the present invention can be used to accommodate the introduction of electronic information as well as for communication and creating security symbols. In order to achieve these objectives, it is beneficial that the conductivity of the electrically conductive polymer in the coating layer has been changed locally to form an electrically conductive pattern or a non-conductive pattern, respectively.

The electric conductivity of the polymer is changed by means of doping a non-conductive polymer or dedoping an electrically conductive polymer, respectively. A non-conductive polymer is doped by treating the polymer layer with an acid solution, which is used to paint the desired pattern onto the surface of the paper or cardboard product. Or, the electrically conductive polymer is dedoped by treating the polymer layer with an alkali solution, which is used to paint the desired pattern on the surface of the paper or cardboard product. Doping or dedoping, respectively, can be achieved by printing the desired pattern on the surface of a paper or a cardboard product by using printing ink capable of doping or dedoping the electrically conductive polymer. If the layer comprising the electrically conductive polymer is coated with another, non-conductive layer, the doping/dedoping reaction can be generated through the non-conductive layer, too.

Different kinds of acid or alkali solutions, respectively, are suitable for doping or dedoping. In acid solutions, the same acids as in the doping of the electrically conductive polymer can be used (see above) or, alternatively, different acids can be used. Conventional hydroxides and carbonates (alkali metal and alkali earth metal hydroxides and carbonates) and different kinds of amines can be used as alkalis. Sodium hydroxide, potassium hydroxide and sodium carbonate are common alkalis. Generally, acids and alkalis are used as relatively dilute solutions (approximately 0.01 to 5 N, for example approximately 0.1 to 1 N solutions) to avoid brittleness of the fibre matrix.

The surface of the coating layer can be provided with a visual mark indicating the layer which contains the electrically conductive polymer. This mark discloses what kind of information is contained in the layered product. Thus, for example, the surface of the paper or cardboard product is provided with a printed pattern, which indicates how the electrical conductivity of the second layer can be detected.

Another preferred embodiment of the present invention is the ESD packages, which are especially suitable for the needs of the electronics industry. However, packages made of coated cardboard blanks can be used in any application where for instance a dust-free surface or a safety mark is technically or economically advantageous. Such applications are packaging for food and similar products (in these instances, it is preferable that a barrier sheet such as a polyethylene sheet) is fitted between the coated surface and the contents.

The following examples clarify the present invention. They also describe more closely the details of the preferred embodiments of the present invention:

Example 1

Polymerization of aniline in the presence of titanium dioxide

Material quantities and reaction conditions used in the reaction are described in Table 1.

Table 1

DBSA = Uf acid K = Dodecylbenzene-sulphonic acid APS = Ammonium persulphate p-TSA = Para-toluenesulphonic acid FDA = Phenylene diamine The polymerization was carried out as follows. The acid used was added to the quantity of water described in the table. Mixing was carried out for approximately 10 minutes. The aniline was added (over a period of 5 minutes) and in some cases phenylene diamine and mixing was carried out for a period of 15 minutes. Next, the titanium dioxide powder was added followed by a mixing for a period of 15 minutes. The APS was dissolved in water and this APS solution was added to the reactor over the period and at the temperature shown in the table. After the addition of the APS solution, the reaction continued according to the time shown in the table. The reaction mixture was then allowed to settle over night. If it was impossible to decant the solution, the reaction mixture was centrifuged and washed with water until the pH was > 3. The product was then either air-dried or freeze- dried.

Table 2 shows the material quantities and the reaction conditions for the bench-scale tests. The polymerizations were carried out by using five different counter-ions in the reaction.

DBSA = Uf acid K = Dodecylbenzene-sulphonic acid

APS = Ammonium persulphate p-TS A = Para-toluene sulphonic acid

PSA = Sulphocarbolic acid

CSA = Camphor sulphonic acid

FDA = Phenylene diamine

The polymerization was carried out as described in tests 1-4. In tests 5, 8, 9 and 10, the separation of the product was carried out by letting the product settle and decanting water from the surface, after which the product was washed with water and left to settle. In the test 7 the product was separated and the water was washed by suction filtering. In test 6, the reaction mixture was left to settle using an ethanol-water mixture (1:1), then suction filtered and washed with water. Before drying, the pH of the products was 2.5-3.5. The powder preparation in tests 5 and 6 was carried out by drying the product in a heating chamber (37 ⁰C) and grinding it to powder using a mill. In tests 7, 8, 9 and 10 the product was dried to a powder using a spray-dryer.

hi order to measure the surface resistivity of the reaction mixture, a sheet was prepared on cardboard by applying the reaction mixture using a metallic spiral rod (rod number 4), after which the sheet was dried in a heating chamber at 105 ⁰C for 10 minutes. To measure the resistivity of the product a sample was prepared by first mixing the powdery product with the binder, namely a polyvinyl alcohol-water solution (dry solids 10 %), and then applying the mixture onto the cardboard surface using a metallic rod, and, finally, drying the cardboard in a heating chamber at 105 ⁰C for 10 minutes. Following that, the surface resistivity of the dry sheet on the cardboard surface was measured by using an instrument which measures the electric resistance between two parallel 6.5 cm metal bars placed on the surface of the sample. The distance between the bars is 4 cm. The measurement voltage is 10 V in the conductive area <10⁵ ohm and 100 V in the area >10⁵ ohm.

Example 2

Polymerization of aniline in the presence of titanium dioxide and separation out of the product by ethanol precipitation

Material quantities and reaction conditions used in the reaction are described in Table 3.

Table 3.

DBSA = Ufacid K = Dodecylbenzene-sulphonic acid APS = Ammonium persulphate

The polymerization was carried out in the same way as in Example 1 above and using material quantities, reaction temperature and reaction times described in Table 3. The product was separated by ethanol precipitation (ethanol 1/3 of the reaction mixture quantity) and followed by filtering the sediment generated. The sediment was washed twice with an ethanol- water solution (1:1 v/v), then dried first at room temperature and finally in a heating chamber at 30⁰C.

Example 3

Polymerizing at laboratory scale of aniline in the presence of Hollow Pigment

Hollow Pigment latex (200 g) was diluted with water by adding a volume of water equivalent to half of the weight of the latex. The pH of the diluted latex was adjusted with 0.1 M sulphuric acid (22 ml) to pH 7 and the reaction mixture was diluted to 500 ml. 3.0 g of aniline was added over a period of 15 minutes and thereafter 10.5 g of DBSA over a period of approximately 0.5 h. The reaction mixture was cooled to approximately 10 ⁰C and the APS solution (15 g APS in 25 g of water) was added over a period of approximately 0.5 h. After that, the temperature of the reaction mixture was kept below 10 ⁰C for approximately 2 h and thereafter it was allowed to warm up to room temperature over a period of approximately 4 h. The resulting product was a homogeneous dispersion.

Example 4 Polymerization of aniline in the presence of Hollow Pigment; the effect of the quantity of the aniline and the reaction condition

Initial material quantities and reaction conditions used in the polymerization are described in Table 4.

Table 4

DBSA = Ufacid K = Dodecylbenzene-sulphonic acid APS = Ammonium persulphate Hollow Pigment = plastic pigment, Rohm&Haas AG, (dry solids 32 %)

The polymerization was carried out by using material amounts described in Table 4. The Hollow Pigment latex was diluted with water by adding a volume of water equivalent to half of the weight of the latex. The pH of the diluted latex was adjusted with 0.1 M sulphuric acid to pH 7. The aniline was mixed in water and DBSA was added to the mixture over a period of approximately 1 h and the mixing was continued until the emulsion was homogeneous. The aniline/DBSA emulsion was added into the latex over a period of approximately 1 h and the reaction mixture was cooled to approximately 10⁰C. The APS solution was added over the period of time described in the table and the reaction continued after the addition for a period of time shown in the table. The temperature was allowed to increase to the temperature described in the table. The resulting product was a homogeneous dispersion.

The product was cleaned by centrifuging and washing the sediment several times with water until the pH of the washing solution had increased to > pH 3. Example 5

Cleaning of polyaniline dispersion prepared in the presence of Hollow Pigment

The aniline was polymerized onto the surface of Hollow Pigment as follows. 1.6 kg of Hollow Pigment latex (dry solids 32 %) were diluted by adding 1.4 kg of water to it. The pH of the latex was adjusted with 0.1 M sulphuric acid to pH 7. The aniline was mixed into 4 kg of water and DBSA was added while briskly stirring the solution for approximately 1 h. The emulsion generated continued to be mixed for a further 1 h, after which it was added to the Hollow Pigment latex over a period of approximately 1 h. The reaction mixture was then cooled to < 10 ⁰C. APS (120 g) was dissolved into 200 g of water and added to the reaction mixture over a period of 3 h, keeping the temperature at 8-10 ⁰C. After the addition, the cooling was stopped and the mixture continued to be mixed for another 2 h, and the temperature was allowed to increase to 16 ⁰C. The resulting product was a homogeneous green dispersion, the conductivity of which was at the level of E+5, measured as surface resistivity.

The dispersion can be cleaned by centrifuging the sediment and washing it with water, until the pH of the washing solution has increased to the desired level.

Alternatively, it can be cleaned with ethanol precipitation, too, using methods described below.

1 kg of uncleaned dispersion was mixed with 1 kg of ethanol (ETAX B, Primalco Oy). The mixture was allowed to rest over night, and, as a result, the polymeric material had settled onto the bottom of the vessel. The liquid phase was decanted and another 1 kg of ethanol was added to it. A new decanting was carried out after 4 months. The ethanol-bearing dispersion was diluted with 1 kg of water and the product was filtered using suction filtration. When almost all of the solution was filtered, another 1 kg of water was added to the product and suction filtration was carried out anew. The resulting product was a paste- like dispersion, of which dry solids made up approximately 18 %. The product is dried at 23 ⁰C. The total yield of dry pigment is 84 g / 1 kg of raw dispersion. Example 6

Polymerization of aniline in the presence of Hollow Pigment; scaled test

15 kg of water, which was cooled to 12 ⁰C, was added to 208.3 g of DBSA and mixed for approximately 15 minutes. After that, aniline (59.5 g) was added for approximately 15 minutes and the mixing was continued for another 15 minutes.

1700 g of Hollow Pigment latex (Ropaque Bright, dry solids 35 %), from Rohm & Haas, the pH of which was adjusted with 0.2 M sulphuric acid to neutral, was added to the mixture. When all the latex had been added and the product was demonstrated to be a homogeneous dispersion (approximately 45 min from the beginning of the addition of the latex), the feeding of the oxidant was started. APS (146 g) was dissolved in 1300 g of water. The time during which the oxidant was added was 4.5 h and the temperature was 9- 11 ⁰C. After the addition, the reaction mixture was mixed for approximately another 2 h at the said temperature. The colour of the dispersion was dark green and the conductivity of the reaction mixture, measured as surface resistivity, was E+5 ohm/square. The product was cleaned by adding to the reaction mixture ethanol 1/3 of the amount of the reaction mixture (ETAX A 10, Primalco Oy) and, as a result, the product was precipitated. The product was then filtered, i.e. washed with water using the filter?, until the pH of the filtrate was > 4. The product was then dried in a heating chamber at 50 ⁰C. The amount of dry product was 749 g.

Example 7

Treatment of cotton fabric with polyaniline dispersion attached to Hollow Pigment

Cotton fabric was treated according to the dispersion described in Example 4, Test 1. The fabrics were dried either at room temperature or at 130⁰C. The conductivities of the fabrics, measured as surface resistivity were 0.9 x E+6 and 0.5 x E+6 when the amount of dispersion applied during the treatment was 7.5 % of the amount of fabric. The electrically conductive pigment can be attached to the surface of the fabric using different binding agents, too, to improve the coating's resistance to wear. Example 8

Coating of paper using a dried polyaniline product which is attached to Hollow

Pigment

Test 1

A paper coating paste was prepared at the KCL laboratory as follows. The components of the paste were: 88.7 parts of basic pigment (SPS), 11.3 parts of electrically conductive polymer product bonded to Hollow Pigment, 10 parts of latex (DOW-966) and 0.8 parts of carboxy-methyl cellulose (CMC-10). The paste was prepared using 60 % dry solids. The paste was applied to the cardboard surface and dried. Surface resistivity was used to measure the electrical conductivity of the coating. The coating was not conductive. When a conductive pigment was added as a supplementary addition to the said paste, a conductive pigment percentage of 20 % generated a coating the surface resistivity value of which was E+6...E+7 ohm/square.

Test 2

Paper was coated with a 6.5 % mixture dispersion, comprising 90.4 % of the product according to Example 4, Test 2 above and 9.6 % of Acram ALW binder latex. The mixture was applied to a cardboard surface and the cardboard was dried at 130⁰C. The surface resistivity measured from the coating was E+5 ohm/square.

The dried coating could be recoated. When a polymeric coating was applied onto the first coating using a 5 % Mowital BH 45 ethanol solution, the conductivity remained at the level of E+5 ohm/square.

When a polymeric film was applied onto the first coating using Acram ALW, the conductivity dropped and fell into an antistatic range (surface resistivity E+7 ohm/square). However, the alkaline durability of the coating clearly increased. It could endure 0.2 N NaOH-treatments for short periods of time. The discharging of the conductive state could be seen as violet spots at the microholes in the thin polymer sheet.

Test 3

A 26 % mixed dispersion was prepared comprising 12.7 % of the product according to

Example 4, Test 2 and 87.3 % of starch polymer. The mixed dispersion was applied onto a paper surface and the coated paper was dried at 130⁰C. The surface resistivity measured from the coating was E+6 ohm/square.

When testing the alkaline durability of the sheet it was discovered that the green colour which is characteristic of conductive polymer changed to violet under the influence of a strong alkali, but the green colour returned after a period of time. This phenomenon can be explained by the fact that the pH of a starch-based binder is appriximately 4, thus it can have a buffer effect against the alkaline solution.

The results show that by using electrically conductive polyaniline bonded to Hollow Pigment as components of the coating, different conductive and antistatic paper and cardboard products can be produced.

Example 9 Polymerization of aniline in the presence of kaolin

Table 5.

a) Measured from a sheet which is applied onto the cardboard, and which is prepared from a starch dispersion (dry solids 50 %) and a product according to Test 2 (Pan 5 % of the total dry solids). Application was made with rod 4. b) Conductivity of the reaction mixture c) Measured from a sheet applied on the cardboard surface by using an approximately 7.5 % aqueous solution of Elvanol 75-30 comprising 3 % polyaniline as a binder. Application was made with rod 4.

Example 10

Polymerization of aniline in the presence of talc

Table 6.

a) Measured from a sheet which is applied on the cardboard, and which is prepared from a starch dispersion (dry solids 50 %) and a product according to Test 2 (Pan 5 % of the total dry solids). Application was made with rod 4. b) Resistivity of the reaction mixture Example 11

Polymerization of aniline in the presence of different carriers

Table 7.

a) Measured from, a sheet which is applied on the cardboard, and which is prepared from a starch dispersion (dry solids 50 %) and the whole product according to Example 4 (Pan 5 % of the total dry solids). Application was made with rod 4. b) Surface resistivity of the reaction mixture

Claims

Claims:

1. Coated fibrous product comprising

- a web formed by cellulosic or lignocellulosic fibres, and - on the top of the web a coating layer, one which comprises a binding agent and light scattering pigments, characterized in that

- the coating layer comprises a synthetic, electrically conductive polymer, one which is mixed with a binder and at least partially attached to the pigments, whereby the coating layer can be rendered electrically conductive.

2. The fibrous product according to claim 1, characterized in that at least approximately 20 % by weight of the electrically conductive polymer, most suitably approximately 50 % by weight, especially at least approximately 75 % by weight is bonded to the pigment.

3. The fibrous product according to Claim 1, characterized in that the amount of the electrically conductive polymer in the coating layer is approximately 0.1-30 % by weight of the amount of pigment.

4. The fibrous product according to Claim 1 or 2, characterized in that the electrically conductive polymer comprises an inherently electrically conductive polymer, which can be doped to generate charge carriers.

5. The product according to any of Claims 1-3.characterized in that the electrically conductive polymer is polyaniline, polypyrrol or polytiophene.

6. The fibrous web according to any of the preceding claims, characterized in that the coating layer comprises calcium carbonate, gypsum, silicoaluminate, kaolin, aluminium hydroxide, magnesium silicate, talc, titanium dioxide, barium sulphate, zinc oxide, synthetic pigment or mixtures thereof, as light scattering pigment.

7. The fibrous web according to Claim 6, characterized in that the coating layer comprises spherical Hollow particles as pigments.

8. The fibrous product according to any of the preceding claims, characterized in that it forms an authenticity product equipped with a security symbol, wherein, in order to form the security symbol, the electrical conductivity of the electrically conductive polymer in the coating layer has been locally changed in order to form either an electrically conductive or, respectively, an electrically non-conductive pattern.

9. The fibrous product according to Claim 8, characterized in that a pattern referring to the security symbol is fitted on the surface of the coating layer.

10. The product according to Claim 8 or 9, characterized in that the layer comprising electrically conductive polymer has been made locally non-conductive by dedoping the polymer with an alkaline solution or, respectively, locally conductive by doping the polymer with an acidic solution comprising the doping agent.

11. The product according to any of Claims 8-10, characterized in that the layer comprising the electrically conductive polymer can be identified on the basis of its electrical conductivity or the colour of the layer or combinations thereof , or on the basis of changes thereof.

12. The product according to any of the preceding claims, characterized by producing a product, which comprises 10-100 parts by weight of at least one pigment or pigment mixture, 0.1-30 parts by weight of at least one binder, 0.1-50 parts by weight of electrically conductive polymer, and 1-10 parts by weight of other additives which are known per se.

13. Method for producing a coated fibrous web product, according to which method

- at least one side of the fibrous web is coated with a coating composition comprising light scattering pigments and binder characterized by - using a coating composition, which comprises a synthetic, electrically conductive polymer, and

- forming on the surface of the fibrous web a coating layer, which can be rendered at least partially electrically conductive.

14. The method according to Claim 13, characterized in that the fibrous web is coated with a composition, one which comprises pigments with electrically conductive polymers attached to their surface.

15. The fibrous web according to Claim 14, characterized in that at least approximately 20 % by weight of the electrically conductive polymer, most suitably at least approximately 50 % by weight, especially at least approximately 75 % by weight, is attached to the pigment.

16. The fibrous web according to any of Claims 13-15, c h a r a c t e r i z e d in that the coating layer comprises calcium carbonate, gypsum, silicoaluminate, kaolin, aluminium hydroxide, magnesium silicate, talc, titanium dioxide, barium sulphate, zinc oxide, synthetic pigment, or spherical Hollow particles, or mixtures thereof, as light scattering pigment.