FR3160713A1 - COMPOSITION FOR PAPER COATING SAUCE - Google Patents

Abstract

The invention relates to an aqueous composition for preparing a curtain coating papermaking color. This composition comprises a non-sulfonated surfactant compound, mineral particles, a binding agent, and a thickening agent. It does not contain any sulfosuccinate compounds. The invention also relates to a curtain coating method for preparing paper or board.

Description

COMPOSITION FOR PAPER COATING SAUCE

The invention relates to an aqueous composition for the preparation of a curtain coating papermaking slip. This composition comprises a non-sulfonated surfactant compound, mineral particles, a binding agent and a thickening agent. It does not comprise any sulfosuccinate compound. The invention also relates to a curtain coating method for the preparation of paper or cardboard.

There are many methods and techniques available for the production of paper or cardboard. Among these methods, curtain coating offers many advantages.

Curtain coating is a process for applying a thin liquid film to paper or cardboard. The liquid film is produced by a die to achieve a constant thickness; it is then subjected to a free fall before coming into contact with the surface to be coated. This process allows for very high-speed coating with high quality while allowing multiple layers to be applied in one application.

The applied layer is generally smooth and homogeneous, even when the substrate has a certain roughness or when it has an irregular surface. Curtain coating involves the free flow of the paper coating composition onto the substrate from a coating head.

A vertical curtain is formed with the coating composition on the substrate to be coated which is moved under the curtain. In the absence of a physical layer-producing element such as a blade, doctor blade, rod or bar, the curtain must inherently possess the properties allowing efficient deposition and retention on the substrate.

Thus, the coating results from the contact of the falling curtain on the moving substrate, the formation and stability of the coating sauce curtain are essential characteristics of these methods.

It is important to be able to control the stretching or elongation of the film for very different speeds both during its formation and when it comes into contact with the substrate. Also, the control of the dynamic surface tension is particularly important, especially when the flow rate during application is reduced. In particular, it is necessary to produce a minimum flow rate allowing the formation of a stable curtain.

A high pigment solids content of the coating composition is also an important property for these methods. Similarly, a high substrate velocity is sought upon contact with the coating slip curtain. Finally, the aim is generally to deposit a reduced amount of pigment evenly on the substrate. This can then reduce the weight of the coating on the substrate. Refining the curtain thickness without excessive dilution of the pigment is also a desirable property.

Furthermore, the compatibility of the different constituents of a paper coating sauce must also be taken into account, in particular to avoid destabilizing the curtain.

We are also seeking to limit or ban the use of substances that could lead to subsequent migration phenomena within the paper or cardboard, particularly when these substances pose health or regulatory problems, for example in the area of food packaging.

Furthermore, the curtain coating composition implemented should not alter the printability of the coated paper or coated board.

The various ingredients combined within a paper coating color do not always provide a satisfactory solution to these various problems. There is therefore a need for compositions for preparing curtain coating colors with improved properties. The aqueous composition for preparing a paper coating color according to the invention provides a solution to all or part of the problems of the compositions of the prior art.

Thus, the invention provides an aqueous composition, free of sulfosuccinate compound, for the preparation of a curtain coating papermaking sauce comprising:
* at least one non-sulfonated surfactant compound (a),
* at least one mineral material (b) in the form of particles,
* at least one binding agent (c),
* at least one thickening agent (d) and
* water.

The composition according to the invention does not comprise any sulfosuccinate compound, in particular any surfactant sulfosuccinate compound. It does not comprise any sulfonated surfactant compound. It therefore excludes the presence of a compound comprising an S(O)(O)OH group in this acid form or in a salified form or in the form of an ester. Furthermore, the aqueous composition according to the invention comprises the essential active ingredients (a), (b), (c) and (d) and no sulfosuccinate compound as an active ingredient directly influencing the curtain coating application. A sulfosuccinate compound could be used during the preparation of an ingredient of the composition according to the invention without this sulfosuccinate compound directly influencing the properties required for the curtain coating application.

According to the invention, the aqueous composition may comprise a single compound (a) or several different compounds (a), in particular in the form of a mixture of several compounds (a). Preferably, when using several compounds (a), the composition according to the invention comprises 2 or 3 different compounds (a), in particular in the form of a mixture of 2 or 3 compounds (a).

Preferably for the composition according to the invention, compound (a) is a polyalkoxylated primary alcohol or a polyalkoxylated oxo alcohol. More preferably, compound (a) is a polyalkoxylated primary oxo alcohol chosen from a polyalkoxylated linear primary oxo alcohol, a polyalkoxylated branched primary oxo alcohol and combinations thereof. Compound (a) is more preferably a compound of formula I:
[chem I]
RCH ₂ (OE) _m (OP) _n OH
in which:
* R independently represents a C ₂ -C ₂₀ -alkyl group, preferably a C ₂ -C ₂₀ -alkyl group chosen from a linear C ₂ -C ₂₀ -alkyl group, a branched C ₃ -C ₂₀ -alkyl group and combinations thereof,
* m and n independently represent 0 or a number from 2 to 50, one of m and n is non-zero,
* OE represents an oxyethylene group and
* OP represents an oxypropylene group.

Preferably according to the invention, compound (a) is a compound of formula I in which R independently represents a branched C ₄ -C ₂₀ -alkyl group, preferably a branched C ₆ -C ₁₅ -alkyl group, more preferably a branched C ₈ -C ₁₂ -alkyl group or a 3-methyl-decenyl group.

Preferably according to the invention, compound (a) is chosen from polyalkoxylated primary oxo alcohols of formula I in which R represents a branched C ₉ -C ₁₀ -alkyl group or a combination of branched C ₉ -C ₁₀ -alkyl groups.

Preferably according to the invention, m represents a number ranging from 2 to 50, preferably from 2 to 30 or from 3 to 15, and n represents 0.

In addition to the surfactant compound (a), the composition according to the invention comprises particles of mineral material (b). Preferably according to the invention, the composition comprises a single mineral material (b) or two or three mineral materials (b). More preferably according to the invention, the composition comprises a single mineral material (b) or two mineral materials (b).

According to the invention, the mineral material (b) may be synthetic or of natural origin. Preferably, the mineral material (b) is chosen from alkaline earth metal carbonates, preferably calcium carbonate (natural calcium carbonate or precipitated calcium carbonate), strontium carbonate, magnesium carbonate, barium carbonate, dolomite, kaolin, titanium dioxide, talc, lime, calcium sulfate, barium sulfate, silicas, silicates and combinations thereof. More preferably, the material (b) is chosen from calcium carbonate (natural calcium carbonate or precipitated calcium carbonate), kaolin, titanium dioxide and combinations thereof.

The composition according to the invention makes it possible to produce a layer of particles of mineral material (b) on a substrate, in particular paper or cardboard, by curtain coating. According to the invention, the size of the particles of material (b) can be adapted. Preferably, the composition according to the invention uses particles of mineral material (b) having a size (d ₅₀ ) of less than 50 µm or a size of less than 20 µm, preferably of less than 10 µm.

Also preferably, the composition according to the invention uses particles of mineral material (b) having a size (d ₅₀ ) ranging from 0.05 µm to 50 µm or from 0.05 µm to 20 µm, preferably from 0.05 µm to 10 µm.

According to the invention, the characteristic d ₅₀ or median diameter is the value of the particle diameter of a population of particles for which 50% by volume of the particles have a size smaller than this value. In this case, 50% by volume of the particles have a size larger than this value. For a volume distribution, 50% of the total volume of the particle population corresponds to the volume of particles with diameters smaller than d ₅₀ . Graphically, the median size therefore corresponds to the diameter which divides the distribution into two parts of equal areas.

Preferably according to the invention, the equivalent spherical diameter of the particles of mineral material (b), for a size ranging from 0.05 µm to 50 µm or less than 50 µm, preferably for a size less than 10 µm, more preferably less than 5 µm or 2 µm, even more preferably less than 1 µm or less than 0.5 µm, is equal to 60% by dry weight or equal to 70% or even equal to 80% or even equal to 90%.

The composition according to the invention comprises at least one binding agent (c) which makes it possible to hold the particles of mineral material (b) on the substrate. Preferably for the composition according to the invention, the binding agent (c) is a natural binding agent such as starch, carboxymethyl cellulose (CMC), hydroxyethyl celluloses, casein, proteins, alginates, or a synthetic binding agent such as a latex. More preferably, the binding agent (c) is chosen from a styrene-butadiene polymer, a styrene-acrylic polymer, a styrene-acetate polymer, a vinyl acetate polymer, more preferably a styrene-acrylic polymer or a styrene-butadiene polymer.

According to the invention, the rheology of the aqueous composition for the preparation of a curtain coating papermaking sauce is controlled by means of at least one thickening agent (d). Preferably for the composition according to the invention, the thickening agent (d) is chosen from a polyacrylamide polymer, an ASE polymer, a HASE polymer, a poly(ethylene oxide) polymer.

Within the composition according to the invention, the proportions of the different ingredients may vary. Preferably, the composition according to the invention comprises:
* from 0.2% by dry weight to 6% by dry weight of compound (a),
* from 60% dry weight to 90% dry weight of mineral material (b),
* from 2% dry weight to 20% dry weight of binding agent (c),
* from 0.5% dry weight to 5% dry weight of thickening agent (d) and
* from 7.3% by weight to 37.3% by weight of water.

More preferably, the composition according to the invention comprises:
* from 0.3% by dry weight to 6% by dry weight of compound (a),
* from 80% dry weight to 90% dry weight of mineral material (b),
* from 8% dry weight to 15% dry weight of binding agent (c),
* from 0.5% dry weight to 5% dry weight of thickening agent (d) and
* from 1.2% by weight to 12.2% by weight of water.

The composition according to the invention may comprise other ingredients in the form of adjuvants, in particular at least one adjuvant chosen from dispersing agents, anti-foaming agents, biocidal agents, coloring agents, lubricating agents, crosslinking agents and optical brightening agents.

Very advantageously according to the invention, the composition is prepared by mixing the different ingredients, preferably by adding these ingredients to water and with stirring.

The aqueous composition according to the invention for the preparation of a curtain coating papermaking sauce has very good properties and allows the coating of a substrate, in particular paper or cardboard. The invention therefore provides a method for preparing coated paper or coated cardboard comprising the use of an aqueous composition according to the invention. Preferably according to the invention, this composition is used during one or more curtain coating steps of the paper or cardboard.

For this preparation method according to the invention, the composition is deposited on the surface of the paper or cardboard during at least one curtain coating step with a deposit after drying of 1 g/m² to 15 g/m², preferably of 1 g/m² to 10 g/m² or of 1 g/m² to 6 g/m².

Advantageously, the method according to the invention makes it possible to effectively control the flow rate of the composition during its application in the form of a curtain which is generally produced by means of a die. The flow rate measures the volume quantity of composition which is applied per second as a function of the dimension of the die. Preferably for the method of preparing coated paper or coated board according to the invention, the flow rate of composition is less than 0.9 cm ² /s, preferably less than 0.8 cm ² /s.

Also preferably for this preparation method according to the invention, the composition has a dynamic surface tension, measured at 100 ms using a bubble pressure tensiometer, of less than 60 mN/m. More preferably, the composition has a dynamic surface tension of less than 58 mN/m or 56 mN/m.

Very advantageously for this preparation method according to the invention, the composition has a low shear viscosity (Brookfield viscosity at 100 rpm) which is sufficient and compatible with the curtain coating process. Preferably according to the invention, the composition has a low shear viscosity (Brookfield viscosity at 100 rpm) ranging from 100 mPa.s to 1000 mPa.s. More preferably, it ranges from 300 mPa.s to 700 mPa.s or from 300 mPa.s to 550 mPa.s.

The advantageous, particular or preferred characteristics of the composition according to the invention define methods of preparing this composition as well as methods of preparing coated paper or coated cardboard according to the invention which are also advantageous, particular or preferred.

The various aspects of the invention may be illustrated by examples.

EXAMPLES

Example 1: Preparation of aqueous compositions according to the invention and compa r ative

Mix with stirring using a “VMI Turbotest” dispersion device:
- 60 parts by mass of particles of a first material (b) (calcium carbonate at 78% by weight in water, d50 = 0.7 µm),
- 40 parts by mass of particles of a second material (b) (delaminated kaolin at 69% by weight in water, d50 = 0.5 µm),
- 10 parts of a binding agent (c) (carboxylated styrene-butadiene latex at 50% by weight in water, Tg 0°C),
- 0.15 parts of a thickening agent (d) (commercial anionic water-in-oil polyacrylamide-acrylate emulsion),
to the quantity of water allowing to obtain a mixture having a dry extract of 62% by mass and a pH of 8.8 by addition of sodium hydroxide in aqueous solution at 20% by weight.

Then, 0.15 parts by mass of compound (a) of formula I, in which R represents a branched C ₁₁ -alkyl group, m represents 8, n represents 0 and OE represents an oxyethylene group, are added with stirring using a stirrer equipped with a deflocculating blade, to obtain composition C1 according to the invention, the Brookfield viscosity of which at 100 rpm and at 25°C, measured using a Brookfield DV-I viscometer equipped with a module No. 3, is 505 mPa.s and the dynamic surface tension at 100 ms, measured using a BPT-mobile “Krüss” type bubble pressure tensiometer, is 58 mN/m.

Similarly, comparative composition CC1 is prepared and characterized by replacing compound (a) with 0.15 parts by mass of a sodium octylsulfosuccinate surfactant compound. In the same way as for composition C1, the Brookfield viscosity of composition CC1 is measured, which is 490 mPa.s, and its dynamic surface tension, which is 51 mN/m.

Example 2 – P repair and characterization of paper coating curtains or cardboard

From composition C1 according to the invention, a coating curtain is produced by means of a curtain head with an inclined flow surface of 26 cm width and a die gap of 300 µm which is fed by an eccentric screw pump equipped with a frequency inverter and a suction deaerator, a pulsation damper and a mass flow meter. The curtain coating head is equipped with non-stick inclined edge guides. A curtain is formed which is stable up to a minimum flow rate of 0.74 cm²/s.

In a similar manner, a coating curtain prepared using the comparative composition CC1 is prepared and characterized. It is stable up to a minimum flow rate of 0.8 cm²/s.

It is found that the composition according to the invention comprising the non-sulfonated compound (a) makes it possible to prepare a paper or cardboard coating curtain which is more stable than the curtain obtained using the comparative composition based on the sulfosuccinate compound.

Claims (14)

Aqueous composition, free from sulfosuccinate compound, for the preparation of a curtain coating paper sauce comprising:
* at least one non-sulfonated surfactant compound (a),
* at least one mineral material (b) in the form of particles,
* at least one binding agent (c),
* at least one thickening agent (d) and
* water. Composition according to claim 1 comprising a single compound (a) or several different compounds (a), preferably 2 or 3 different compounds (a), in particular in the form of a mixture of several compounds (a), preferably in the form of a mixture of 2 or 3 compounds (a), or for which the compound (a) is a polyalkoxylated primary alcohol or a polyalkoxylated oxo alcohol, preferably a polyalkoxylated primary oxo alcohol chosen from a polyalkoxylated linear primary oxo alcohol, a polyalkoxylated branched primary oxo alcohol and combinations thereof, more preferably a compound of formula I:
[chem I]
RCH ₂ (OE) _m (OP) _n OH
in which:
* R independently represents a C ₂ -C ₂₀ -alkyl group, preferably a C ₂ -C ₂₀ -alkyl group chosen from a linear C ₂ -C ₂₀ -alkyl group, a branched C ₃ -C ₂₀ -alkyl group and combinations thereof,
* m and n independently represent 0 or a number from 2 to 50, one of m and n is non-zero,
* OE represents an oxyethylene group and
* OP represents an oxypropylene group. 3. Composition according to one of claims 1 or 2 for which compound (a) is a compound of formula I in which:
* R independently represents a branched C ₄ -C ₂₀ -alkyl group, preferably a branched C ₆ -C ₁₅ -alkyl group, more preferably a branched C ₈ -C ₁₂ -alkyl group or a 3-methyl-decenyl group, or
* m represents a number from 2 to 50, preferably from 2 to 30 or from 3 to 15, and n represents 0. Composition according to one of claims 1 to 3 for which:
* a single mineral material (b) or two or three mineral materials (b) are used or
* the mineral material (b) is synthetic or of natural origin, preferably the mineral material (b) is chosen from alkaline earth metal carbonates, preferably calcium carbonate (natural calcium carbonate or precipitated calcium carbonate), strontium carbonate, magnesium carbonate, barium carbonate, dolomite, kaolin, titanium dioxide, talc, lime, calcium sulfate, barium sulfate, silicas, silicates and combinations thereof, more preferably calcium carbonate (natural calcium carbonate or precipitated calcium carbonate), kaolin, titanium dioxide and combinations thereof. 5. Composition according to one of claims 1 to 4 for which:
- the particles of mineral material (b) have a size (d ₅₀ ) less than 50 µm or a size less than 20 µm, preferably less than 10 µm; or
- the particles of mineral material (b) have a size (d ₅₀ ) ranging from 0.05 µm to 50 µm or from 0.05 µm to 20 µm, preferably from 0.05 µm to 10 µm; or
- the equivalent spherical diameter of the particles of mineral material (b), for a size ranging from 0.05 µm to 50 µm or less than 50 µm, preferably for a size less than 10 µm, more preferably less than 5 µm or 2 µm, even more preferably less than 1 µm or less than 0.5 µm, is equal to 60% by dry weight or equal to 70% or even equal to 80% or even equal to 90%. 6. Composition according to one of claims 1 to 5 for which the binding agent (c) is a natural binding agent such as starch, carboxymethyl cellulose (CMC), hydroxyethyl celluloses, casein, proteins, alginates, or a synthetic binding agent such as a latex, preferably chosen from a styrene-butadiene polymer, a styrene-acrylic polymer, a styrene-acetate polymer, a vinyl acetate polymer, more preferably a styrene-acrylic polymer or a styrene-butadiene polymer. 7. Composition according to one of claims 1 to 6 for which the thickening agent (d) is chosen from a polyacrylamide polymer, an ASE polymer, a HASE polymer, a poly(ethylene oxide) polymer. 8. Composition according to one of claims 1 to 7 comprising:
* from 0.2% by dry weight to 6% by dry weight of compound (a),
* from 60% dry weight to 90% dry weight of mineral material (b),
* from 2% dry weight to 20% dry weight of binding agent (c),
* from 0.5% dry weight to 5% dry weight of thickening agent (d) and
* from 7.3% by weight to 37.3% by weight of water; preferably
* from 0.3% by dry weight to 6% by dry weight of compound (a),
* from 80% dry weight to 90% dry weight of mineral material (b),
* from 8% dry weight to 15% dry weight of binding agent (c),
* from 0.5% dry weight to 5% dry weight of thickening agent (d) and
* from 1.2% by weight to 12.2% by weight of water. 9. Composition according to one of claims 1 to 8 also comprising at least one adjuvant, in particular at least one adjuvant chosen from dispersing agents, anti-foaming agents, biocidal agents, coloring agents, lubricating agents, crosslinking agents and optical brightening agents. 10. Method for preparing coated paper or coated cardboard comprising the use of an aqueous composition according to one of claims 1 to 9, preferably this composition is used during one or more stages of curtain coating of the paper or cardboard. 11. Method according to claim 10 for which the flow rate of composition is less than 0.9 cm ² /s, preferably less than 0.8 cm ² /s. 12. Method according to one of claims 10 or 11 for which the composition has a dynamic surface tension, measured at 100 ms using a bubble pressure tensiometer, of less than 60 mN/m, preferably less than 58 mN/m or 56 mN/m. 13. Method according to one of claims 10 to 12 for which the composition has a low shear viscosity (Brookfield viscosity at 100 rpm) sufficient and compatible for the curtain coating process, preferably a low shear viscosity (Brookfield viscosity at 100 rpm) ranging from 100 mPa.s to 1000 mPa.s, preferably from 300 mPa.s to 700 mPa.s or from 300 mPa.s to 550 mPa.s. 14. Method according to one of claims 10 to 13 for which the composition is deposited on the surface of the paper or cardboard during at least one curtain coating step with a deposit after drying of 1 g/m² to 15 g/m², preferably of 1 g/m² to 10 g/m² or of 1 g/m² to 6 g/m².