FR2780992A1 - Improving resistance of paper in dry and humid conditions - Google Patents

Abstract

Method for improving resistance of paper in dry and humid conditions involves simultaneous but separate application of either a cationic resin or a latex containing acid functions; or a previously prepared stable mixture containing said resin and a latex stabilized with a nonionic surfactant. Method (1) for treating paper consists of applying cationic resin and aqueous dispersion of polymer dispersed in form of particles of diameter = 30-500 nm stabilized by an optionally polymeric surfactant; said dispersion containing 0.5-10wt.% at least one monomer (A) which has at least one acid function; and 90-99.5wt.% at least one monomer (B) which is polymerizable in emulsion and copolymerizable with (A) such as vinyl, (meth)acrylic, styrene and diene monomers. Independent claims are also included for a composition used for said application; and a method (2) for improving the resistance of paper in humid conditions.

Description

NEW ADDITIVES TO IMPROVE RESISTANCE

WET AND DRY OF PAPER

  The invention relates to the manufacture of paper and in particular to the

  manufacture of paper having good wet strength.

  For certain applications in particular absorbent papers, wallpapers, paper for bottle labels, paper money, the paper is asked to keep in the wet state part of its mechanical resistance to dryness. The wet strength of the paper, hereinafter referred to as REH, generally expressed in% is calculated from the relation LR wet REH - xl00 LR dry o: LR wet is the breaking length of a strip of paper wet,

  LR dry is the breaking length of a strip of dry paper.

  Generally, a paper is qualified as resistant to the state

  wet as soon as its WER exceeds 5%.

  A person skilled in the art has long known how to improve the WER of paper.

  Generally, it proceeds by incorporating, into the mass of the cellulosic pulp (also called fibrous suspension or paper pulp), resins which can react with the cellulosic fibers such as the cationic resins which are spontaneously crosslinkable on the fiber at neutral pH. As for example resins of the polyamidopolyamine-epichlorohydrin type, designated below by PAE, of low weight

  well known to those skilled in the art.

  However, it is known that the improvement in WER due to PAE presents a saturation with the level of PAE introduced into the pulp because the amount of PAE which can adsorb on the cellulosic fibers is limited. This is all the more true as the fibers have a surface density of

  low negative charges, as is the case for cotton pulp, for example.

  Thus the optimal WERs conventionally obtained in a chemical pulp are of the order of 20 to 25%, while in certain specific applications a

REH of 40% is requested.

  We then tried to improve the wet resistance by associating with the PAE resin various substances known as wet resistance promoters, generally polymers of natural origin or derived from natural polymers, of more or less pronounced anionic or amphoteric nature, among others, sodium carboxymethylcellulose (H. Espy, 1983 Papermakers Research J., pp. 191-195 or E. Strazdins 1994, Wet Strength Resins and their applications, Ed by L. Chan, TAPPI Press pp. 78-79) and guar gum modified (patents CA 808,531 or US 5,318,669). These products are marketed in powder form. Placing them in aqueous solution is a long and delicate operation which must be carried out prior to their use in the wet part of the paper machine. These solutions are very sensitive to bacterial degradation and cannot be stored under the conditions of

  ambient temperature of production workshops.

  US 5,200,036 proposes a solution based on the use of a PAE modified by reaction with the acid function carried by a monomer polymerizable by the radical route. The free double bond of the monomer is

  then copolymerized with a mixture of monomers to form a mono-

  crosslinked compound. This solution may not be effective because the PAE crosslinks at neutral pH and at room temperature and all the faster the higher the temperature. See for example the book "Applications of Wet End Paper Chemistry", 0. Au, I. Thorn, Ed: Blackie Academic and Professional. It is therefore probable that the PAE crosslinks at the time of the copolymerization and is therefore not

  more fully reactive to react with cellulosic fibers.

  The Applicant has now found that it is possible to improve both the wet strength and the dry strength of the paper thanks to either a particular process for treating paper using a cationic resin and a wet strength promoter based on a aqueous dispersion of a polymer containing acid functions, or to a particular stable composition based on a cationic resin and a wet resistance promoter based on an aqueous dispersion of a polymer containing acid functions

  and stabilized with a nonionic surfactant.

  One of the objects of the invention is a process for treating paper consisting in the application to the paper of a cationic resin and an aqueous dispersion of polymer, said polymer contains from 0.5 to 10% by weight of units derivatives by polymerization of at least one monomer carrying an acid function, dispersed in the form of particles of diameter included

  between 30 and 500 nm, stabilized by a polymeric surfactant or not.

  The polymer concentration of the aqueous dispersion did not

influence on the process.

  The cationic resins used for the implementation of the invention are low molecular weight resins with azetidinium structure crosslinkable to

  neutral pH on the cellulosic fiber. Resins of polyamide structure

  polyamine-epichlorohydrin (PAE) constitute a typical example of cationic resins, and are moreover commonly used by a person skilled in the art. These resins (PAE) are obtained by the condensation of adipic acid and

  diethylenetriamine followed by condensation on epichlorohydrin.

  The aqueous dispersions, hereinafter referred to as latex, consist of a dispersion of particles with a diameter between 30 and 500 nm of thermoplastic polymers containing acid functions and stabilized by a surfactant. These latexes can be obtained by radical emulsion polymerization in the presence of at least one surfactant of a mixture of monomers containing: - from 0.5 to 10% by weight of at least one monomer A containing acid functions chosen from the group consisting of mono or dicarboxylic acids ao, unsaturated therein such as acrylic acid, methacrylic acid,

  Itaconic acid or maleic acid.

  - from 90 to 99.5% by weight of at least one monomer B chosen from the group consisting of vinyl, styrenic, (meth) acrylic monomers, or

  C1-C8 (meth) acrylic esters.

  According to a preferred form of the invention, the monomer A represents

0.5 to 5% by weight.

  The preferred monomer A of the invention is acrylic acid or methacrylic acid. The mixture of monomers generally represents from 5 to 60% by weight of the aqueous solution, however, as described above, the concentration of monomers has no influence on the treatment process.

paper.

  The monomer (s) A and the monomer (s) B are chosen and their respective quantities defined according to the properties and characteristics which it is desired to confer on the targeted polymer. For example, the glass transition (Tg) of a polymer can be estimated in advance by the following law 2T.T Tgi E wiTg i Tgi: is the glass transition temperature of the homopolymer obtained by polymerization of the monomer i

  wi: is the weight fraction of the monomer i.

  Thus, depending on the intended application, the Tg of the polymer is fixed and the

  monomers (i) chosen accordingly.

  The surfactant (s) is (are) chosen from the group made up

  ionic or nonionic micromolecular surfactants.

  The ionic surfactants can be anionic, cationic or amphoteric. Most often anionic surfactants are used such as

  sodium dodecylbenzene sulfonate or ethoxylated fatty alcohol sulfates ...

  The nonionic surfactants are chosen from the family of alkyls

  ethoxylated phenol or that of ethoxylated fatty alcohols.

  polymeric surfactants such as copolymers comprising on the one hand a monomer chosen from the family of acrylic acid, methacrylic acid or maleic anhydride, and on the other hand, a monomer chosen from the family of styrenic, vinyl or acrylic or methacrylic esters, for example and without limitation, a styrene / maleic anhydride copolymer, a styrene / acrylic acid copolymer, a methyl methacrylate and acrylic acid copolymer, a styrene copolymer and

butyl acrylate.

  Preferred forms of these latexes have been disclosed in the applications.

  of French patents FR-A-96 08226 and 96 08875 (Elf Atochem S.A.).

  The invention is implemented by introducing the cationic resin and the latex into the aqueous suspension of cellulose fibers often referred to as paper pulp. The resin and the latex can be introduced successively in no particular order, or else at the same time, which considerably simplifies the installation. The useful quantities according to the invention are, with regard to the resin, from 0.25 to 3% by weight of dry matter of resin relative to the mass of

  dry fibers and from 0.25 to 3% in the case of latex.

  It is preferable according to the invention to keep a dry matter ratio of

  latex / resin dry matter from 0.5 to 2.

  Thus we obtain wet resistances expressed in WER from 25 to%. The dry resistance of the papers obtained by this process is also

  increased by 10 to 40% compared to untreated paper.

  To simplify the paper processing methods such as that described above, an attempt has been made to reduce the number of operations by carrying out a single introduction into the paper machine of a mixture containing PAE and a latex. However, the PAE is unstable in an acid medium and such a mixture is not

not possible industrially.

  The Applicant has also discovered that it is possible, under certain conditions, to prepare a stable and ready-to-use mixture containing PAE and a latex. Indeed, the Applicant has discovered that when the latex is stabilized by a nonionic surfactant or by a predominantly nonionic mixture, consisting of ionic surfactants and nonionic surfactants, it is possible to mix it with the cationic resin without the composition

  obtained evolves or destabilizes during storage.

  Another object of the invention is an aqueous composition for improving the wet and dry resistance of paper containing: - 5 to 15% by weight of a cationic resin as defined above and in particular PAE - from 5 to 15% by weight of a thermoplastic polymer dispersed in the form of particles with a diameter between 30 and 500 nm characterized in that said polymer contains acid functions and that the particles are stabilized by 0.5% by weight of at least one cationic or amphoteric nonionic surfactant or a mixture of surfactants

mostly non-ionic.

  The cationic resins used for the implementation of the invention are low molecular weight resins with azetidinium structure crosslinkable to

  neutral pH on the cellulosic fiber. Resins of polyamide structure

  polyamine-epichlorohydrin constitute a typical example of cationic resins, and are moreover commonly used by a person skilled in the art. These resins (PAE) are obtained by the condensation of adipic acid and

  diethylenetriamine followed by condensation on epichlorohydrin.

  The aqueous dispersions, hereinafter referred to as latex, consist of a dispersion of particles with a diameter between 30 and 500 nm of thermoplastic polymers containing acid functions and stabilized by a macromolecular surfactant or not. These latexes are obtained by radical emulsion polymerization in the presence of at least one ionic or nonionic surfactant or else of a mixture of predominantly nonionic surfactants of a mixture of monomers containing from 0.5 to 10%. by weight and preferably from 0.5 to 5% of at least one monomer A containing acid functions chosen from the group consisting of mono or ca, unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, Il 'itaconic acid or maleic acid - from 90 to 99.5% by weight and preferably from 0.5 to 5% of at least one monomer B chosen from the group consisting of vinyl monomers,

  styrenic, (meth) acrylic, or (meth) acrylic esters of C1-C8.

  The preferred monomer A of the invention is acrylic acid.

  The mixture of monomers generally represents from 5 to 60% by weight of the aqueous solution, however the concentration of monomers has no influence on the stability of the composition or on the process for treating the

  paper using such a composition.

  The monomer (s) A and the monomer (s) B are chosen and their respective quantities defined according to the properties and characteristics

  that we want to give to the finished polymer.

  The nonionic surfactant is chosen from the group consisting of ethoxylated alkyl phenol such as ethoxylated nonyl phenol and / or ethoxylated fatty alcohols.

  The compositions described above are stable over time.

  They can be stored and used as is in a process

  improvement of the wet and dry resistance of the paper.

  One of the objects of the invention is a method for improving the wet and dry resistance of the paper consisting in the introduction of the stable aqueous composition described above into the aqueous suspension

cellulosic fibers.

  For the implementation of the invention, only the additive dry matter / fiber dry matter ratio counts. The concentration of the fibrous suspension is not known in advance, and whatever the initial dry extract of the mixture, a person skilled in the art knows how to dilute it in order to introduce the quantity

adequate in the dough.

  The following examples illustrate the invention without limiting its scope

Examples

  a- preparation of a latex In a glass reactor heated by a double jacket and stirred using a mechanical stirrer, 438 g of water and 3.3 g of sodium dodecyl benzene sulfonate are introduced. This mixture is brought to 82 ° C. and 5% is introduced.

  of the preemulsion and 10% of the batch catalytic solution.

  After 30 minutes of reaction, the rest of the pre-emulsion and the catalytic solution are added in 4 hours using metering pumps so as to keep the flow constant. The reaction medium is then left

  1 hour at 82 C in order to lower the level of residual monomers.

  Catalytic solution 68.20 g of water 3.30 g of sodium persulfate Pre-emulsion 554 g of water 13.2 g of sodium dodecylbenzene sulfonate 641.3 g of butyl acrylate 425.7 g of methyl methacrylate

33 g methacrylic acid.

  Under these conditions, a dispersion (DAF 25) is obtained, the physicochemical characteristics of which are as follows E.S (dry extract) = 49.2% pH = 2.6

Particle size = 105 nm.

  The DAF 36 dispersion is obtained under analogous conditions by substituting the dodecylbenzene with a C12-C14 fatty alcohol ethoxylated for 30 moles of ethylene oxide in amounts sufficient to obtain a stable dispersion without coagulum. The characteristics of this dispersion are as follows:

E.S = 50.6%

pH = 2.3

Particle size = 350 nm.

  b- treatment of the paper In these examples, the papers are obtained according to the general process which consists in producing formettes on a FRANCK apparatus from a pulp refined to a certain degree Shopper (for the degree Shopper-Riegler - "SR- , see standard NF Q 50-003, determination of drainability, Schopper-Riegler method.) To the fibrous suspension consisting of 10 g / I of fibers in water whose pH, if necessary, is adjusted to 8.0 with dilute sulfuric acid or sodium hydroxide, the composition of wet-strength agents is added with stirring, that is to say in a first mode the latex, then approximately one minute later, the PAE (the order of introduction is unimportant: you can invert the order of introduction of the PAE and the latex, or introduce them simultaneously), either according to

  a second mode the stable aqueous composition containing the latex and the PAE.

  Whichever mode is used, agitation is continued for approximately three minutes. The form is then produced at an average grammage of the order of 65 g / m2, by draining the suspension on a metal grid, it is wrung, and the form is dried for 5 minutes at 95 C. The PAE resin is crosslinked putting

  the formettes for 7 minutes in an oven at a temperature of 105 C.

  In each form, two strips of paper, 180 mm long and 15 mm wide, were cut. The first is used to determine the resistance of dry paper. The tests used are tensile strength tests, carried out in accordance with standard NF Q 03-004. The tensile tests are carried out with an ADAMEL Lhomargy device, set to a speed of 50 mm / min. The force F expressed in Newtons which had to be applied to break the strip makes it possible to evaluate the length of break, calculated in meters from the expression: L.R. (m) = 1 / 9.81. F. width'1. grammage-1 in which the width is taken in meters

  and the grammage in kilograms per square meter.

  The displayed LR measurements by which the REH value is calculated are means of five tensile tests carried out on five test pieces,

  each from these five separate formulas.

  Tensile tests on a dry paper strip are carried out after a minimum of 24 hours of conditioning, at 23 C and 50% humidity. The tensile tests on the wet paper strip are carried out according to standard NF Q 03-056 on strips which, unless otherwise indicated, have been immersed for 1 hour in tap water at a constant temperature of 25 C, wrung out

  then tested according to a rigorous procedure described in the standard.

  The water absorption capacity of the paper is estimated according to the Cobb test, standard TAPPI T441-OM90, which consists in measuring the quantity of water absorbed by the paper during a time of 60 seconds. The result, called Cobb60, is

  expressed in grams of water per m2 of paper.

  The PAE resin used is a resin with 14% dry extract, stabilized at

pH 2.5 - 3.5 (ECSC, R4947D).

  The latexes used are - DAF 25; it is a dispersion at 50.9% in dry extract, based on a butyl acrylate (ABu) / methyl methacrylate (MAM) / methacrylic acid terpolymer of composition 58.3 / 38.7 / 3 glass transition

   C, stabilized by an anionic dispersant (dodecylbenzene sulfonate).

  - DAF 36; it is a dispersion at 50.6% in dry extract, based on an ABu / MAM / AA terpolymer of composition 58.3 / 38.7 / 3 having a Tg of 10 C stabilized by a non dispersant ionic (fatty alcohol C12- C14

  ethoxylated to 30 moles of ethylene oxide on average).

Example 1

  In this example the fibrous suspension was treated only with

1% EAP.

Example 2

  In this example the fibrous suspension was treated successively

  with 1% PAE and with 1% DAF 25 latex.

Example 3

  For this example, a stable composition of PAE and DAF 36 latex was first produced. The contribution of each compound in the dry matter is 50%. In a second step, the fibrous suspension was treated

with 2% of the stable composition.

  The results obtained are summarized in the following table: Example Cationic resin Latex wet LR (m) WER (%) dry LR (m)

1 1% PAE - 1810 23 7930

2 1% PAE 1% DAF 25 2830 36 8380

  3 (*) 1% PAE 1% DAF 36 2550 32 10080

  <*) In this example, the PAE / Latex mixture was carried out before

  treatment of the fibrous suspension.

Claims (10)

  1. A process for treating paper consisting in the application to the paper of a cationic resin and an aqueous dispersion of a dispersed polymer in the form of particles with a diameter ranging from 30 to 500 nm, stabilized by a surfactant characterized in that said polymer consists: of 0.5 to 10% by weight of units derived by polymerization of at least one monomer (A) carrying an acid function, and from 90 to 99.5% by weight of units derived by polymerization of at least one monomer chosen from the group containing vinyl, acrylic monomers. 2. Method according to claim 1 characterized in that the polymer   dispersed contains from 0.5 to 5% by weight of units derived from the monomer (A).   3. Method according to claim 1 or 2 characterized in that (A) is chosen from the group containing the mono or dicarboxylic acids a, 13 unsaturated such as acrylic acid, methacrylic acid or their derivatives such than maleic anhydride.   4. Method according to claim 1, 2 or 3 characterized in that (A) is acrylic acid.   5. Method according to any one of the preceding claims   characterized in that the surfactant is chosen from the group consisting of: - ionic surfactants such as sodium dodecylbenzene sulfonate or ethoxylated fatty alcohol sulfates, - nonionic surfactants such as ethoxylated fatty alcohols, and of - polymeric surfactants such as copolymers of monomers   vinyl and monomers having at least one acid function.   6. Aqueous composition containing from 5 to 15% by weight of a cationic resin such as PAE and, from 5 to 15% by weight of a thermoplastic polymer dispersed in the form of particles with a diameter between 30 and 500 nm characterized in that said polymer contains from 0.5 to 10% by weight of units derived by polymerization of at least one monomer containing an acid function and that the particles are stabilized by a nonionic surfactant or by a mixture   of ionic and nonionic surfactants but mainly nonionic.   7. Composition according to claim 6 characterized in that the monomer A is chosen from the group containing the mono or dicarboxylic acids a b unsaturated such as acrylic acid, methacrylic acid, maleic anhydride.   8 Composition according to claim 7 characterized in that the monomer A is acrylic acid.   9. Composition according to claim 6 or 7 characterized in that the nonionic surfactant is chosen from the group consisting of   ethoxylated nonylphenols or ethoxylated fatty alcohols.   10. paper treatment process consisting of application on the   paper of the composition of claims 6 to 9.