EP0704007A1

EP0704007A1 - Non-polluting process for increasing the wet strength of paper

Info

Publication number: EP0704007A1
Application number: EP94917691A
Authority: EP
Inventors: Jean Pierre Lallier; Jean François ARGILLIER; Stéphane Fouquay; Didier Vanhoye
Original assignee: Carbonisation et Charbons Actifs CECA SA
Current assignee: Carbonisation et Charbons Actifs CECA SA
Priority date: 1993-06-09
Filing date: 1994-05-27
Publication date: 1996-04-03
Anticipated expiration: 2014-05-27
Also published as: PL172968B1; WO1994029523A1; ATE160193T1; PL311873A1; DE69406787T2; AU6931394A; FR2706496A1; FR2706496B1; DE69406787D1; EP0704007B1; ES2110759T3

Abstract

Process for the manufacture of paper which provides a non-polluting method based on ionic lattices for giving wet strength. The process is characterized by successively adding to the fibrous composition a cationic polyelectrolyte, then a sulfonated anionic polyelectrolyte, for example, the acrylamide and acryloxyethyltrimethylammonium chloride copolymer and the acrylamide and 2-acrylamido-2-methylpropane sulfonate copolymer. The polyelectrolytes are used in an amount of 0.02 to 2.5 % by weight in relation to the dry weight mass of the cellulosic composition entering the head box. The process is non-polluting; and no AOX, formaldehyde or epichlorhydrine are produced when it is carried out. The paper formed is easily repulpable.

Description

NON-POLLUTANT PROCESS FOR INCREASING THE WET RESISTANCE OF PAPER.

The present invention relates to the manufacture of a sheet of paper, and more particularly to the addition of agents for improving the wet strength.

Wet strength is not a natural property of paper: untreated paper made from an assembly of cellulose fibers sees its strength decrease by 95% when it is saturated with water. It is however a sought-after property for many types of paper which will come into contact with water during their use, such as paper towels, handkerchiefs, "paper towels", disposable paper products used in hospitals, labels, etc.

The resistance of the paper is mainly attributed to the hydrogen fiber interfaces. Water destroys most of the hydrogen bonds, which results in a drop in wet strength. Historically, the improvement of the wet resistance of papers has been carried out according to two approaches. The first is to apply a hydrophobing layer on the surface of the paper which will prevent water from reaching and destroying the hydrogen bonds, which can be achieved, for example, by coating the paper. The other approach consists in adding to the pulp, at the headbox, that is to say at a point where the paper machine works in a humid zone, chemical agents capable of protecting the hydrogen bonds and / or creating water resistant connections. The present invention relates to the second approach.

Numerous solutions have been provided to the problem of increasing the dry strength of paper. We can cite on this subject the use of cationic polyacrylamides (US 2884057 - US 2884058), amphoteric polyacrylamides (JP 03227486 - JP 03227485 - JP 01085398 - JP 03227494 - JP 02145897 - JP 02112499). Mixed systems based on cationic polyacrylamides and sulfonates have also been proposed, in particular (EP 362770 - JP 01192899 - JP 52027807 - JP 03227482) of 2-acrylamido-2-methylpropane sulfonate (AMPS), or also of cationic polyacrylamides and of anionic polyacrylamides (JP 04057996 - JP 58060095 - JP 58060094 - FI 67735), the polymers being able to be introduced separately or after mixing leading to the formation of a polysel. In all these cases, the dry strength is improved without significantly increasing the wet strength, as is the case with the solutions proposed in CA 1,110,019, or at the expense of the appearance of the paper. The resulting increase in hardness is strictly acceptable for cartons; it becomes intolerable for papers, whose flexibility is an essential characteristic. More complex solutions by which we fight against the aggregation of fibers involve for example (JP 52027807) cationic resins, a cationic polyacrylamide, but also polyphosphates which the industry seeks today at all costs to avoid.

In practice, it is known to obtain a suitable wet strength of the paper by adding either natural modified polymers (cationic starches) or synthetic polymers: urea-formaldehyde resins (UF), elamine-formaldehyde resins (MUF), polyamine-amide resins -epichlorohydrin (PAE), polyethyleneimines, or else by addition of glyoxylated cationic polyacrylamides (US 3556932 - JP 58156098) or copoly erized with monomers carrying an aldehyde or blocked aldehyde function (US 3709857). All of these systems have the major drawback today of generating either free formaldehyde which pollutes the atmosphere in work areas - this is the case for processes which use urea-formaldehyde resins or melamine-formaldehyde - or soluble organic halogen derivatives known as AOX (put for "adsorbable organically halogens") whose type is dichloropropanol and which are compounds considered as carcinogenic and which pass into effluents - this is the case of the processes in which are conventionally implemented EAPs.

The process according to the invention overcomes these drawbacks: it does not generate AOX, formaldehyde or epichlorohydrin. It consists in successively introducing into the suspension of cellulose fibers entering the headbox a cationic polyelectrolyte carrying a quaternary ammonium group, then an anionic polyelectrolyte carrying sulfonate groups. The overall amount of cationic and anionic polyelectrolytes used is between 0.02 and 2.5% by weight, relative to the cellulosic composition, counted by dry weight, entering in the headbox. The weight ratios between the cationic agent and the anionic agent are not indifferent. The development of wet resistance is a synergistic effect which is only fully manifested for ratios which obviously vary according to the polyelectrolyte systems chosen, even according to the pulp, but which are generally in a range of 0.5 to 10 ; in the case of the preferred system copolymer of acrylamide and acryloxyethyltrimethylammonium chloride and the copolymer of acrylamide and 2-acrylamido-

- 2-methylpropane sulfonate (see example 1 below), this ratio is close to 1 / 0.8.

The cationic polyelectrolytes necessary for the implementation of the invention are copolymers resulting from the copolymerization of n molecules of an uncharged vinyl monomer (A) and of m molecules of a vinyl monomer (B) carrying a group quaternary ammonium, the molar ratio n / m being between 25 and 0.2, preferably between 5 and 0.5, the mass molecular of the copolymer being between 40,000 and 2.10 ⁶ , preferably between 100,000 and 1.10 ⁶ .

These cationic polyelectrolytes can in particular result from the copolymerization of an uncharged monomer (A) consisting of acrylamide or methacrylamide

CH ₃

CH ₂ = CH ^CH 2 ^{= C} _\

CO ÇO ι ι

NH ₂ NH ₂

and of a monomer (B) of acrylic, vinyl or allylic type, carrying a quaternary ammonium group, corresponding to a general formula

ZR ₂ -NR ₃

R>

in which -Z- can be -CO-0-Rχ-, -CO-NR-Rχ-, -CH2 ~.

-CH2-O-R1-, -CH2-S-Rι-, -CH2-NR-R! -, -0-CO-Rχ-, where R is H- or CH3, where Ri is a C2 to Cn alkyl group , preferably ethylene or propylene, where R2 and R3 are alkyl groups, Ci to C4, preferably methyl, R2 and R3 which may constitute a ring with or without a nitrogenous or oxygenated heteroatom, where R4 is an alkyl group having 1-30 carbon atoms, or - [CH2 ~ CH (R) -0] pH [with p taking any statistical value between 1 and 3], or - CH2-CHOH-CH2OH, or -CH2COO, or -CH2-COOR5, R5 y being an alkyl group, Ci to C22 (linear or branched alkyl, saturated or unsaturated or alkylaryl), where X is an anion Cl ^" , Br ^" , I ^" , CH3S04 ^" , EtSθ4 ^~ , CH3PO4 ^"" /

OR CH3COO-. Other cationic polyelectrolytes according to the invention can result from the copolymerization of styrene as uncharged monomer (A) with as monomer

(B) carrying a quaternary ammonium group, substituted maleimides of formula "

CH = CH

CO CO

NOT

? ^ι

where RI, R2, R3, R4 and X have the previous meanings

In particular, the copolymers of acrylamide and of acryloxyethyltrimethylammonium chloride are cationic poly¬ electrolytes preferred for the invention. These products are obtained in a manner well known to those skilled in the art (see inter alia F. Mabire, POLYMER, September 1984, vol. 25, or FR 2390983 or US 4319013 or EP 150933).

The anionic polyelectrolytes carrying sulfonate groups which constitute the other associated chemical means of the invention are copolymers resulting from the copolymerization of m 'molecules of an uncharged vinyl monomer (A') and n 'molecules of a monomer vinyl (B ') carrying a sulfonate group, the m' / n 'molar ratio being between 25 and 0.2, preferably between 5 and 0.5, the molecular weight of the copolymer being between 40,000 and 2.10 ⁶ , preferably between 100,000 and 1.10 ⁶ .

These anionic polyelectrolytes can in particular result from the copolymerization of an uncharged monomer

(A ') consisting of acrylamide, methacrylamide or maleic anhydride

_{/ C} H ₃

CH = CH CH ₂ = C CH -, = CH co ÇO CO CO

N ¹ H ₂ N'H ₂ ^" \ ₀ /

of 2-acrylamido-2-methylpropane sulfonate (AMPS), or of an anionic monomer (B ¹ )

CH ₂ = CH

where R 'is a benzene sulfonate, naphthalene sulfonate, ethylene sulfonate or propene sulfonate residue.

When the monomer (B ') is a styrene sulfonate, the monomer (A') can simply be styrene.

These anionic polyelectrolytes in a manner known to those skilled in the art according to the same general methods as those which have been reported above for cationic polyelectrolytes. Preferred copolymers for the invention are copolymers of acrylamide and 2-acrylamido-2-methylpropane sulfonate (AMPS).

The sharp increase in wet strength which results from the combination of the cationic and anionic polymers according to the invention in the same treatment of the cellulose pulp is unexpected. It must be assumed that the cellulose fibers being naturally negatively charged spontaneously adsorb the cationic polyelectrolyte and that the subsequent addition of the anionic copolymer corresponds to the establishment of an ion network by strong electrostatic interactions between the ionized quaternary ammonium groups for the cationic and sulfonate group for the anionic. The best results have been obtained when the two cationic and anionic copolymers are formed from acrylamide as an uncharged monomer. Acrylamide is capable of giving hydrogen bonds with the groups carried by the cellulose fibers. It may be thought that these hydrogen bonds are "protected" during the soaking of the paper by ionic interactions of high affinity and thus contribute, in addition to the electrostatic interactions, to the overall resistance of the paper.

The implementation of the invention offers no major difficulty, since it consists simply in the process well known to those skilled in the art skilled in the manufacture of paper, to be added successively to the fibrous composition entering the headbox the cationic agent, then the anionic agent as defined above.

The papers which are obtained by using these polyelectrolytes readily offer a wet resistance of 50%, as will be shown in the examples which are given to illustrate and better understand the invention. They also have the significant advantage of being easily plumpable.

EXAMPLES

The following examples are borrowed from the laboratory. Their transposition on an industrial scale is immediate for those skilled in the art.

The formulas were produced on a FRANCK device from a Kraft type chemical paste (ALICEL), unless otherwise indicated. The dough is refined to 27 degrees Shopper. (For the Shopper degree, see the book by Pierre Valette and Christian de Choudens: Wood, Pulp, Paper, p.84). Unless otherwise indicated, the pH of the fiber suspension is adjusted to 8.3 with dilute sodium hydroxide. The reagents are added to the suspension of cellulose fibers maintained with stirring. The contact time between an agent and the fibers is 3 minutes. The average grammage obtained is of the order of 80 g / m ^. The formulas are conditioned for at least 24 hours in a room thermostatically controlled at 22 ° C with a humidity level of 50% before the tensile tests are carried out.

The tensile strength tests are carried out in accordance with standard NF Q 03-056. Strips (test pieces) of paper 180 mm long and 15 mm wide are cut from the formettes. The tensile tests are carried out with an ADAMEL Lhomargy device, set to a speed of 50 mm / min. These tensile tests are carried out according to standard NF Q03-056. Unless otherwise indicated, the paper is immersed for one hour in tap water at a constant temperature of 25 ° C. the paper strips are then wrung out according to a rigorous procedure described in the standard. Ten tensile tests are carried out on 10 wet specimens. The tensile strength F is measured in Newtons. The wet break length or LRH is the limit length expressed in meters beyond which a paper strip of any width suspended by a extremity breaks under the action of its own weight. The LRH is calculated in meters from the expression:

LRH (m) = 1/98. F. width 1. weight ^-1

in which the width is taken in meters and the grammage in kilograms per square meter.

This value is a characteristic of paper. To characterize an additive, you need a relative characteristic. We chose it, not compared to a paper obtained without additives, because the L.R.H. is in this case, both too weak and very poorly reproducible. It is evaluated with respect to the standard which corresponds to the addition of 1% of active material with respect to the fiber in PAE. The PAE used is a commercial product (R4944 from CECA S.A.) formulated at 12.5% in active ingredient. With the conditions defined above, we measure when using PAE at 1% in M.. (i.e. around 8% in commercial solution) a wet breaking length L.R.H of the order of 600 m. In all the series of tests a test is carried out with this PAE at 1% in M.A. and the results will be expressed as a percentage compared to those obtained with the PAE at 1% in M.A. under the same conditions. We therefore define a percentage of (relative) wet resistance PRH defined as:

PRH (%) = L.R.H. / L.R.H. (PAE 1%)

A PRH of 100% corresponds to the performance of the PAE at 1% in MA This is an ordinary result, but obtained with a polluting product. PRH> 50% are already considered acceptable, provided that they are obtained with clean products; 85% of HRPs are regarded as very interesting. The results are given at more or less 10%. Example 1 (best combination)

To the suspension of cellulose fibers with stirring is added 1% by weight of active material relative to the dry fiber of a cationic acrylic copolymer composed of acrylamide (54% by moles, or approximately 30% by weight) and chloride of acryloxyethyltrimethylammonium (46 mol%, or approximately 70% by weight) of high molecular mass (Mw greater than 500,000). After 3 minutes of stirring to allow time for the cationic copolymer to adsorb on the anionic fibers and fines, 0.8% by weight of active material is added relative to the dry fiber of an anionic sulfonated acrylic copolymer composed of acrylamide (76 mol%) and 2-acrylamido-2-methylpropane sulfonate (AMPS) (24 mol%) of high molecular mass (Mw greater than 100,000). The mixture is left stirring for 3 minutes before making the paper form.

According to the procedure described above, a PRH of 85% is obtained.

Example 2 (witness without agent)

By way of comparison, when no agent is added to the suspension of cellulose fibers, the untreated paper has a PRH of the order of 10%.

• Example 3 (cationic copolymer only)

Only the cationic copolymer (the same as that used in Example 1) is added to the cellulose fiber suspension at different% by weight of active material relative to the dry fiber. The suspension is left stirring for 3 minutes before making the form. The following PRH are obtained: cationic copolymer PRH (%:% in MA

0.5% 24%

1% 30%

1.5% 30%

2% 29%

5% 25%

It is interesting to note, by comparison with Example 1, that the use of the cationic copolymer alone, even at doses as high as 5%, does not allow access to acceptable wet strengths.

Example 4 (anionic copolymer alone)

Only the sulfonated anionic copolymer (the same as that used in Example 1) is added to the cellulose fiber suspension at a dosage of 0.8% by weight of active material relative to the dry fiber. The suspension is left stirring for 3 minutes before making the form. A PRH of the order of 20% is obtained. This result clearly shows the inability of the only anionic copolymer to raise the wet strength.

Example 5 (influence of the cation / anionic concentration ratio)

The same procedure and the same products are used as in Example 1. The cationic copolymer is added at 1% of active material relative to the fiber. The sulfonated anionic copolymer is then added at different dosages. The results are collated in the following table. The results corresponding to Example 1 and Example 3 were recalled there. anionic cationic copolymer copolymer PRH (%)

% in M.A.% in M.A.

1% 0% 30%

1% 0.2% 41%

1% 0.4% 55%

1% 0.6% 70%

1% 0.8% 85%

1% 1% 77%

1% 1.2% 50%

1% 1.4% 34%

The example illustrates the fact that, for given conditions (type of paste, pH, etc.), there is an optimum of the concentrations of the two products to be used, in the present case, between 1/0, 6 and 1/1 , with a fairly pronounced maximum around 1 / 0.8. An overdose of anionic agent reduces the gain in wet strength.

Example 6 (influence of the immersion time on the PRH)

The form is produced under the same conditions as that described in Example 1. Before carrying out the tensile test, the paper test pieces are immersed in the same water bath, for half for 5 minutes, for the other half for 1 hour (standard duration). The results are as follows:

5 minutes of immersion PRH = 84%. 1 hour immersion PRH = 85%

Example 7 (acrylamide-acryloxyethyltrimethylammonium chloride copolymer system / styrene-sulfonate-maleic anhydride copolymer)

To the suspension of cellulose fibers with stirring is added 1% by weight of active material relative to the dry fiber of a cationic acrylic copolymer composed of acrylamide (54 mol%) and acryloxyethyltrimethylammonium chloride (46 mol%) of high molecular weight (Mw greater than 500,000). After 3 minutes of stirring to allow time for the cationic copolymer to adsorb on the anionic fibers and fines, 0.25% by weight of active material is added relative to the dry fiber of an anionic sulfonated copolymer composed of styrene sulfonate ( 50 mol%) and maleic anhydride (50 mol%) of low molecular weight (Mw less than 5,000). The mixture is left stirring for 3 minutes before making the paper form. From the procedure described above, a PRH of 45% is obtained.

Example 8 (acrylamide-acryloxyethyltrimethylammonium chloride / polystyrenesulfonate copolymer system)

To the suspension of cellulose fibers with stirring, 1% by weight of active material is added relative to the dry fiber of a cationic acrylic copolymer composed of acrylamide (54% by moles) and of acryloxyethyltrimethylammonium chloride (46% in moles) of high molecular mass (Mw greater than 500,000). After 3 minutes of stirring to give the cationic copolymer time to adsorb on the anionic fibers and fines, 0.15% by weight of active material is added relative to the dry fiber of a sulfonated anionic polymer composed of styrene (20 mol%) and styrene sulfonate (80 mol%). The mixture is left stirring for 3 minutes before making the paper form. From the procedure described above, a PRH of 60% is obtained.

Example 9 (against example: acrylamide-acryloxyethyltrimethylammonium chloride / polyacrylate copolymer system) To the suspension of cellulose fibers with stirring is added 1% by weight of active material relative to the dry fiber of a cationic acrylic copolymer composed of acrylamide (54% by moles) and of acryloxyethyltrimethylammonium chloride (46% in moles) of high molecular mass (Mw greater than 500,000). After 3 minutes of stirring to allow time for the cationic copolymer to adsorb on the anionic fibers and fines, 0.8% by weight of active material is added relative to the dry fiber of an anionic acrylic copolymer composed of acrylamide ( 50 mol%) and sodium acrylate (50 mol%) of high molecular mass (Mw greater than 100,000). The mixture is left stirring for 3 minutes before making the paper form. From the procedure described above, a PRH of 28% is obtained. The addition of the anionic polyelectrolyte, the ionic groups of which are carboxylates and not sulfonates, does not provide any improvement compared to the addition of the cationic alone.

Claims

1. A method of manufacturing paper, making it possible to significantly improve and non-polluting its wet strength, comprising the successive addition to the suspension of cellulose fibers entering the headbox of a cationic polyelectrolyte carrying a quaternary ammonium group and an anionic polyelectrolyte carrying sulfonate groups, characterized in that - the cationic polyelectrolyte is a copolymer resulting from the copolymerization of n molecules of uncharged vinyl monomer (A) and m molecules of a vinyl monomer

(B) carrying a quaternary ammonium group, the n / m molar ratio being between 25 and 0.2, preferably between 5 and 0.5, the molecular weight of the copolymer being between 40,000 and 2.10 ^, preferably between 100,000 and 1.10 ⁶ 'the anionic polyelectrolyte is a copolymer resulting from the copolymerization of m' molecules of uncharged vinyl monomer (A ') and of n' molecules of a vinyl monomer (B ') carrying a sulfonate group, the ratio molar m '/ n' being between 25 and 0.2, preferably between 5 and 0.5, the molecular weight of the copolymer being between 40,000 and 2.10 ^, preferably between 100,000 and 1.10 ⁶ . the cationic polyelectrolyte and the anionic polyelectrolyte are in an effective weight ratio whose range is between approximately 0.5 and 10.

2. Method according to claim 1, characterized in that the cationic polyelectrolyte results from the copolymerization of an uncharged monomer (A) consisting of acrylamide or methacrylamide and of a monomer (B) of acrylic, vinyl, allyl type carrying a quaternary ammonium group, corresponding to a general formula CH ₂ = C (R)

Z

, +

R ₂ -N ^~ R ₃

R ₄ x ^"

in which -Z- can be -CO-0-Rι ~, -CO-NR-Ri-, -CH2 ~, -CH2-0-R! -, -CH ₂ -SR! -, -CH ₂ -NR- Rι-, -0-CO-Rι-,

where R is H or CH3, where Ri is a C2 to Cn alkyl group, preferably ethylene or propylene, where R2 and R3 are alkyl groups. Ci to C4, preferably methyl, R2 and R3 which may constitute a ring with or without a nitrogenous or oxygenated heteroatom, where R4 is an alkyl group having 1-30 carbon atoms, or - [CH2-CH (R) -0] pH [with taking any statistical value between 1 and 3], or - CH ₂ -CHOH-CH ₂ OH, or -CH2C00, or -CH2-COOR5, R5 being an alkyl group. Ci to C22 (linear or branched alkyl, saturated or unsaturated or alkylaryl), where X is a Cl-, Br-, I-, CH3SO4-, EtSθ4-, CH3PO4-, or CH3COO- anion.

3. Method according to claim 2, characterized in that the cationic polyelectrolyte results from the copolymerization of styrene as uncharged monomer (A) and as monomer (B) carrying quaternary ammonium group, substituted maleimides of formula

CH = CH

I I

CO CO

\ /

NOT

^{X "} where RI, R2, R3, R4 and X- have the same meanings as in claim 2.

4. Method according to claim 3, characterized in that the cationic polyelectrolyte is a copolymer of acrylamide and of acryloxyethyltrimethyl¬ ammonium chloride.

5. Method according to claim 2, characterized in that the anionic polyelectrolyte results from the copolymerization of an uncharged monomer (A ') consisting of acrylamide, methacrylamide or maleic anhydride and 2-acrylamido-2-methylpropane sulfonate (AMPS) or an anionic monomer (B ') of formula

CH ₂ = CH

where R 'is a remainder

- benzene sulfonate or - naphthalene sulfonate or

- ethylene sulfonate or

- propene sulfonate.

6. Method according to claim 5, characterized in that the anionic polyelectrolyte results from the copolymerization of an uncharged monomer (A ') consisting of styrene and styrene sulfonate as anionic monomer

(B ').

7. Method according to claim 5, characterized in that the anionic polyelectrolyte is a copolymer of acrylamide and 2-acrylamido-2-methylpropane sulfonate (AMPS).

8. Method according to claims 1 to 7, characterized in that the cationic polyelectrolytes and anionics are used at a rate of 0.02 to 2.5% by weight relative to the weight of the cellulosic composition entering the headbox.

9. Method according to claims 2 to 6, characterized in that the cationic polyelectrolyte is the copolymer of acrylamide and acryloxyethyl¬ trimethylammonium chloride and that the anionic copolymer is the copolymer of acrylamide and 2-acrylamido-2- methylpropane sulfonate.

10. Method according to claims 2 and 9, characterized in that the copolymer of acrylamide and acryloxyethyltrimethylammonium chloride and the copolymer of acrylamide and 2-acrylamido-2-methylpropane sulfonate are in a weight ratio of between approximately 1 / 0.6 and 1/1.

11. Paper with a wet strength greater than 50% and containing neither formalin nor AOX, as can be obtained according to the process of claims 1 to 10.