EP0501846A1 - Process for coating paper and cardboard, and its use to make paper having a good smoothness - Google Patents

Abstract

Process for coating paper and cardboard, in which the coating agent employed is water-insoluble crosslinked polymers containing, in molar proportions, in the polymerised state: … …  - from 50 to 99.995 % of acrylic acid of which at least 70 % is in the form of ammonium acrylate, …  - from 0.005 to 0.5 % of bisacrylamidoacetic acid containing approximately the same degree of neutralisation as the acrylic acid, and …  - the remainder to 100 % with acrylamide and application in paper coating. …

Description

The present invention relates to a process for coating paper and cardboard and its application to obtaining paper having good smoothness.

For certain uses, in particular for writing, printing and more particularly for gravure printing, non-rough papers are sought which have good smoothness possibly associated with good gloss. Of course, these particular properties must not be acquired to the detriment of other qualities of the paper such as, mechanical resistance in the dry or wet state allowing high production rates, good absorption of the inks without smearing, smudging or piercing, opacity, whiteness. It is known to give papers shine by calendering, associated with a judicious choice of pigments. As for smoothness, it is currently obtained by a difficult compromise between the costs and the industrial possibilities of the papermaker according to the surface state of the support and its thickness, the content and the nature of the solid materials of the coating. , the coating equipment used, the weight of the removal and the calendering conditions.

Consequently, from a given support, the papermaker wishing to obtain a paper having a good smoothness, is confronted with a problem which he attempts to solve by a compromise requiring numerous expensive tests.

However, the Applicant has surprisingly discovered a new process for coating papers with a view to giving them a good smoothness overcoming these drawbacks.

• 50 à 99,995 % d'acide acrylique dont au moins 70 % est sous la forme d'acrylate d'ammonium.
• 0,005 à 0,5 % d'acide bisacrylamidoacétique présentant environ le même taux de neutralisation que l'acide acrylique.
• et le complément à 100 % avec de l'acrylamide.

The process according to the invention is characterized by the use, as coating agent, of crosslinked polymers, insoluble in water, containing in molar proportions, in the polymerized state:

• 50 to 99.995% acrylic acid, at least 70% of which is in the form of ammonium acrylate.
• 0.005 to 0.5% bisacrylamidoacetic acid having about the same neutralization rate as acrylic acid.
• and the 100% complement with acrylamide.

• 65 à 95 % d'acide acrylique dont au moins 90 % à l'état d'acrylate d'ammonium,
• 0,005 à 0,5 % d'acide bisacrylamidoacétique dont au moins 90 % est à l'état de bisacrylamidoacétate d'ammonium,
• et le complément à 100 % d'acrylamide.

A more particular subject of the invention is the polymers as defined above, characterized in that they contain in molar proportions, in the polymerized state:

• 65 to 95% of acrylic acid, at least 90% of which is in the form of ammonium acrylate,
• 0.005 to 0.5% bisacrylamidoacetic acid of which at least 90% is in the form of ammonium bisacrylamidoacetate,
• and the complement to 100% acrylamide.

• environ 70 % d'acide acrylique neutralisé à pH = 6,2 avec de l'ammoniaque,
• 0,005 à 0,5 % d'acide bisacrylamidoacétique neutralisé à pH = 6,2 avec de l'ammoniaque,
• le complément à 100 % avec de l'acrylamide.

Among these latter polymers, there may be mentioned more particularly a crosslinked polymer insoluble in water containing in molar proportions:

• approximately 70% of acrylic acid neutralized at pH = 6.2 with ammonia,
• 0.005 to 0.5% of bisacrylamidoacetic acid neutralized at pH = 6.2 with ammonia,
• the 100% supplement with acrylamide.

The acrylic acid neutralized at pH = 6.2 corresponds to a neutralization rate greater than 90% and the acrylic acid neutralized at pH = 5.2 corresponds to a neutralization rate of approximately 70%. These neutralization rates are determined by potentiometry.

The present invention also relates to the compositions intended for coating paper containing, as active principle, one of the polymers defined above.

These compositions are characterized by the fact that they are self-reversible dispersions, the average particle size of which is less than 20 μm, consisting on the one hand, of an aqueous phase, containing one of the polymers defined above, dispersed in a phase oil, and on the other hand, by at least two emulsifying agents having an overall HLB value greater than 10, at least one of these emulsifying agents having an HLB value less than 5.

The oily phase of the dispersion consists, for example, of one or more hydrophobic hydrocarbons such as hexane, cyclohexane, straight or branched C les-C₁₃ mineral gasoline cuts such as paraffinic or paraffinic oils / Commercial naphthenics sold under the name of SHELL white oil, ISOPAR or SOLPAR.

The dispersed aqueous phase represents approximately 30 to 75% of the total weight of the emulsion and it contains in solution from 20 to 40% by weight of a polymer defined above.

The emulsifying agent with an HLB value of less than 5 is chosen from known emulsifying agents, soluble in oils, such as sorbitan monostearate, monooleate or sesquioleate, and it is contained in the dispersion in proportions of 2 to 8% by weight relative to the total weight of the dispersed aqueous dispersion.

The emulsifying agents present in the dispersion must have an overall HLB value greater than 10, it is therefore necessary to use one or more emulsifying agents having an HLB value greater than 10, so as to compensate for the HLB value less than 5 d '. at least one of the emulsifying agents. These emulsifying agents with an HLB value greater than 10 are chosen from known emulsifying agents, soluble in water, such as ethoxylated alkylphenols, sodium dialkylsulfosuccinates, soaps derived from C₁₀-C₂₂ fatty acids.

The polymers defined above and the abovementioned compositions containing them, which are not known, can be prepared by methods analogous to those described for the preparation of the polymers and the compositions containing them known.

The polymers defined above and the aforementioned compositions can be prepared in particular by radical polymerization within a water-in-oil emulsion. This type of polymerization is widely described in the literature and it consists in preparing, in the presence of one or more emulsifiers soluble in oils, a water-in-oil emulsion whose particles have a size of less than 20 μm and containing in solution in the aqueous phase dispersed the monomers, then after careful deoxygenation of this emulsion, to carry out the polymerization reaction with an initiation using one or more free radical generators, then finally to cool the dispersion obtained to room temperature after having introduced a sufficient quantity of water-soluble surfactant (s) therein to make it self-reversible.

The starting water in oil emulsion is prepared using water in oil emulsifying agents known for this purpose such as monostearate, monooleate, sorbitan sesquioleate. These emulsifying agents must have an HLB value of less than 5 and they are contained in the emulsion in proportions of 2 to 8% by weight relative to the total weight of the aqueous phase.

The oily phase of the dispersion consists, for example, of one or more hydrophobic hydrocarbons such as hexane, cyclohexane, straight or branched chain C d'ess-C₁₃ mineral spirits such as commercial paraffinic or paraffinic / naphthenic oils. sold under the name of SHELL white oil, ISOPAR or SOLPAR.

The dispersed aqueous phase represents approximately 30 to 75% of the total weight of the emulsion and it contains in solution from 20 to 40% by weight of monomers.

The polymerization reaction is initiated by one or more free radical generating agents such as redox couples, azo such as azo-bis acid 4.4 ′ (4-cyano pentanoic). Advantageously, as redox couple, it is possible to use the couple described in French patent n ° 2529895. The polymerization temperature depends on the polymerization initiator chosen and can vary within wide limits, from 5 ° C to 100 ° C for example, but in general the polymerization is carried out at normal pressure at temperatures of 10 to 80 ° C.

At the end of polymerization, one or more surfactants whose HLB value is greater than 10 are introduced into the dispersion obtained. These are essentially hydrophilic and water-soluble products such as ethoxylated alkylphenols, sodium dialkylsulfosuccinates, soaps derived from C₁₀-C₂₂ fatty acids. Advantageously, nonylphenols ethoxylated with 6 to 12 moles of ethylene oxide are used. In the final dispersion, 2 to 8% by weight are incorporated relative to the total weight of the dispersion of several surfactants having an HLB value greater than 10 so that the overall HLB value of the surfactants present in the dispersion is greater to 10.

The method according to the invention is particularly advantageous for improving the smoothness of paper supports. For this application the method according to the invention is implemented very simply on a conventional coating device such as, size-press, size-tub, calender sizing, etc., by incorporating into the coating sauce containing the pigments and the binders usual as well as possibly other conventional additives, the necessary quantity of polymer defined above, to obtain the desired smoothness.

The polymer is used in the form of the composition defined above. As soon as it is incorporated into the aqueous coating sauce containing the usual ingredients such as pigments, binders, at a dose of dry matter of between approximately 50 and 75% by weight, the composition containing the polymer defined above reverses immediately by releasing the polymer swollen with water but insoluble in water into the coating sauce. The doses of use expressed in grams of dry polymer relative to the weight of the dry paper medium vary from 0.05 to 0.5%.

• en supprimant le transpercement du papier par la sauce de couchage avec pour conséquence l'élimination du blanchiment du backing-roll,
• en lubrifiant la lame : le couchage s'effectue beaucoup plus silencieusement et le confort du poste de travail est, de ce fait, grandement amélioré,
• en améliorant la rétention d'eau dynamique sur le papier couché : la couche déposée sèche beaucoup plus lentement que dans les procédés classiques, ce qui entraîne un couchage plus régulier, sans masque ni bavure,
• en ne modifiant pratiquement pas la viscosité des sauces de couchage.

The method according to the present invention makes it possible to considerably improve the surface condition of the paper supports obtained both with a chemical pulp (wood-free pulp) and with a mechanical pulp (wood pulp). In addition to improving the surface condition and reducing the roughness of the paper, particularly for papers made from mechanical pulp, the method according to the invention makes it possible to improve the conditions for implementing the coating, in particular :

• by eliminating the piercing of the paper with the coating sauce, with the consequence of eliminating the whitening of the backing-roll,
• by lubricating the blade: the coating is carried out much quieter and the comfort of the work station is, therefore, greatly improved,
• by improving the dynamic water retention on the coated paper: the deposited layer dries much more slowly than in conventional methods, which results in a more regular coating, without mask or burr,
• by practically not changing the viscosity of the coating sauces.

It has been found that the improvement in the smoothness of a paper support is in particular a function of the crosslinking rate of the polymer used. For a crosslinking rate of less than 0.005 mol% of bisacrylamidoacetic acid, there is practically no improvement in the smoothness. Similarly, from a crosslinking rate greater than 0.5 mol% of bisacrylamidoacetic acid, no improvement in smoothness is observed.

The following examples illustrate the present invention without, however, limiting it.

EXAMPLE 1 - Comparison example

• 181,72 g (2,522 mole) d'acide acrylique pur
• 7 6, 82 g (1,081 mole) d'acrylamide pur puis on amène le pH de cette solution à pH = 6,2 par addition d'ammoniaque à 31 % en poids. On introduit ensuite dans cette solution, désignée par la suite S :

• 0,36 g de sel de sodium de l'acide diéthylènetriaminepentaacétique,
• 0,03 g d'acide azo-bis 4,4'-(cyano-4 pentanoïque),
• la quantité d'eau nécessaire pour obtenir un poids total de 709 g. On ajuste enfin le pH de cette solution à pH = 6,2. Le taux de neutralisation de l'acide acrylique déterminé par potentionmétrie est d'environ 92 %.

Dissolve in 200 g of water:

• 181.72 g (2.522 mole) of pure acrylic acid
• 7 6.82 g (1.081 mole) of pure acrylamide, then the pH of this solution is brought to pH = 6.2 by addition of ammonia at 31% by weight. Then introduced into this solution, hereinafter designated S:

• 0.36 g of sodium salt of diethylenetriaminepentaacetic acid,
• 0.03 g of azo-bis 4,4 '- (4-cyano-pentanoic) acid,
• the amount of water necessary to obtain a total weight of 709 g. Finally, the pH of this solution is adjusted to pH = 6.2. The neutralization rate of acrylic acid determined by potentiometer is approximately 92%.

This aqueous solution is then introduced with stirring, at room temperature, into a solution of 226.8 g of white Shell oil 2748 and 21.6 g of sorbitan sesquioleate. The emulsion obtained is then homogenized using a turbine and then it is carefully deoxygenated for one hour by bubbling nitrogen through it. The polymerization reaction is then started with stirring, at 10 ° C, by the addition of 0.0136 g of cumene hydroperoxide and 0.024 g of thionyl chloride. The temperature of the reaction medium reaches 80 ° C in 20 minutes. This temperature is maintained for one hour, then the mixture is cooled to 50 ° C. and 10 g of ethoxylated nonylphenol with 8 moles of ethylene oxide and 10 g of ethoxylated nonylphenol with 10 moles of ethylene oxide are incorporated. The dispersion thus obtained is cooled to the room temperature then it is filtered. The characteristics of this dispersion are given in Table 1.

EXAMPLE 2-6

• Exemple 2 : 0,01 g (0,05 mmole)
• Exemple 3 : 0,07 g (0,35 mmole)
• Exemple 4 : 0,285 g (1,44 mmole)
• Exemple 5 : 0,57 g (2,87 mmoles)
• Exemple 6 : 1,14 g (5,75 mmoles)

Example 1 is reproduced by incorporating into the aqueous phase S the following amounts of bisacrylamidoacetic acid, designated ABAA:

• Example 2: 0.01 g (0.05 mmol)
• Example 3: 0.07 g (0.35 mmol)
• Example 4: 0.285 g (1.44 mmol)
• Example 5: 0.57 g (2.87 mmol)
• Example 6: 1.14 g (5.75 mmol)

The physical characteristics of these different dispersions are given in Table I.

EXAMPLE 7

• 258,78 g (3,59 moles) d'acide acrylique pur
• 12,76 g (0,18 mole) d'acrylamide pur,
• 0,052 g (0,26 mmole) d'acide bisacrylamidoacétique.

Dissolve in 200 g of water:

• 258.78 g (3.59 moles) of pure acrylic acid
• 12.76 g (0.18 mole) of pure acrylamide,
• 0.052 g (0.26 mmol) bisacrylamidoacetic acid.

• 0,36 g de sel de sodium de l'acide diéthylènetriaminepentaacétique,
• 0,052 g d'acide azo-bis 4,4′-(cyano-4 pentanoïque),
• la quantité d'eau nécessaire pour obtenir un poids total de 709 g. On ajuste enfin le pH de cette solution à pH = 5, 2 avec de l'ammoniaque à 31 % en poids. Le taux de neutralisation de l'acide acrylique déterminé par potentionmétrie est d'environ 70 %.

Then we introduce into this solution:

• 0.36 g of sodium salt of diethylenetriaminepentaacetic acid,
• 0.052 g of azo-bis 4,4 ′ acid (4-cyano-pentanoic acid),
• the amount of water necessary to obtain a total weight of 709 g. Finally, the pH of this solution is adjusted to pH = 5.2 with ammonia at 31% by weight. The neutralization rate of acrylic acid determined by potentiometer is approximately 70%.

This aqueous solution is then subjected to a water-in-oil emulsion polymerization reaction according to the process described in Example 1. Then, at the end of polymerization, the dispersion obtained is treated as in Example 1. A dispersion is thus obtained, the characteristics of which are given in Table I.

In column A of Table I, the molar concentrations in ppm of bisacrylamidoacetic acid present in the polymer are mentioned. In column B are indicated the Brookfield viscosities determined at 20 ° C., with a Brookfield RVT apparatus, at speed 20, of the various dispersions at 1% by weight in water. In column C are indicated the Brookfield viscosities determined at 20 ° C., with a Brookfield RVT apparatus at the speed of the various dispersions at 1% by weight in water containing 0.1% by weight of sodium chloride. All viscosities are expressed in Pa.s. All the dispersions have a rate of 30% by weight of active materials and they have excellent stability to sedimentation: no deposit or salting out after one month of storage at 20 ° C.

EXAMPLES 8-24 and comparison examples C1-C7

In these examples, a paper support obtained is treated, either with a chemical pulp B1, or with a mechanical pulp B2, with a coating sauce whose dry matter composition expressed in g is given in Table II, on a MK IV Heliocoater from the Charlestown Engineering Company. The weight of the deposit, as well as the pH and the viscosity of the coating sauce are also mentioned in Table II. The coated paper is then subjected to drying by hot air at 200 ° C. for 20 seconds, then its smoothness is determined with a BEKK measuring device according to French standard NF Q 03-012 of February 1974, and the results are expressed in second. The smoothness is better the longer the time.

In Table II, the weights are expressed in grams and the viscosities, determined on a Brookfield RVT device at 20 ° C, at the speed and with the axis recommended for the value indicated, are expressed in mPa.s. The rheology modifiers of the coating sauce are either the products described in the examples, or carboxymethylcellulose, designated CMC, and sold by the applicant under the reference TYLOSE ^R VCLL. The binders L1 and L2 are binders commonly used in the coating of paper; the binder L1 is an SBR latex marketed by the company DOW FRANCE under the reference DL 675 SBR and the binder L2 is an acrylic latex marketed by the applicant under the reference MOWILIT DM 595. The pH of the coating sauce is adjusted to the value indicated with 10% sodium hydroxide. The angle of the coating device blade is expressed in degrees. In Examples 8, 9 and CI for comparison, the smoothness is determined visually by a visual examination of the coated paper; for these three examples, example 9 gives an excellent smoothness, example 8 gives a smoothness slightly lower than that of example 9, and example CI gives a poor smoothness.

Examples 8-10 and C1, C2 of comparison show the advantage of the process according to the invention. With the weight of an identical deposit on an identical paper support, the method according to the invention allows a significant improvement. smoothness (58 against 46), which represents a savings of 0.75 g / m² for the same smoothness.

Examples 11-14 and C3, C4 and C5 for comparison confirm the advantage of the process according to the invention. With the same dry extract, the viscosity of the baths using the process according to the invention is higher, but this does not constitute an obstacle to their application on the supports; the deposits obtained are homogeneous and of the same order. In addition, at substantially identical viscosity (680 +20 mPa.s), with a different dry extract 62.2% against 52.8%, the smoothness is better when using the process of the invention.

Comparison examples 15-17 and C6 also confirm the advantage of the process according to the invention.

Examples 18-21 and C7 for comparison make it possible to demonstrate the advantage of the process according to the invention: compared with a carboxymethylcellulose, the process according to the invention makes it possible to obtain a smoothness greater by about 40%.

In Examples 22-24, for comparable deposits, a slight decrease in smoothness is observed due to an increase in the rate of crosslinking of the polymer.

Claims (6)

Process for coating paper and cardboard, characterized in that crosslinked polymers insoluble in water are used as coating agent, containing in molar proportions in the polymerized state: - from 50 to 99.995% of acrylic acid, at least 70% of which is in the form of ammonium acrylate, - from 0.005 to 0.5% of bisacrylamidoacetic acid having approximately the same neutralization rate as acrylic acid and, - the 100% supplement with acrylamide. Process according to Claim 1, characterized in that the polymers contain in molar proportions, in the polymerized state: - from 65 to 95% of acrylic acid, at least 90% of which is in the form of ammonium acrylate, - from 0.005 to 0.5% of bisacrylamidoacetic acid of which at least 90% is in the state of ammonium bisacrylamidoacetate and, - the complement to 100% acrylamide. Process according to either of Claims 1 and 2, characterized in that the polymers contain in molar proportions, in the polymerized state: - approximately 70% of acrylic acid neutralized at pH = 6.2 with ammonia, - from 0.005 to 0.5% of bisacrylamidoacetic acid neutralized at pH = 6.2 with ammonia and, - the 100% supplement with acrylamide. Process according to any one of Claims 1 to 3, characterized in that the polymers used are contained in a water-in-oil dispersion autoreversible with an average particle size of less than 20 µm. Application of the method according to any one of claims 1 to 4 in the coating of paper and cardboard. Application of the method according to claim 5, characterized in that 0.05 to 100% of dry polymers as defined in claim 1 are used by weight relative to the weight of dry materials present in the coating sauce.