Method for deinking recycled paper

Abstract

A method for deinking recycled paper, including a pulping step, and then a flotation step, which includes introduction of at least one dispersant of the polyacrylate type, representing from 0.05 to 3.5 wt % of the mineral fillers of the recycled paper. A specific dispersant is used during the flotation step of the method for deinking recycled paper.

Claims

1. A method for deinking recycled paper that comprises mineral filler, the method comprising: pulping by putting recycled paper into suspension with at least water to form a pulp, then performing a flotation by circulating air bubbles in at least one chamber receiving the pulp, diluted in aqueous solution, so as to constitute two adjacent phases, an upper phase comprising ink and intended to be removed, and introducing at least one deinking agent during the pulping and/or the flotation, the method further comprising introducing a water-soluble dispersant of the polyacrylate type that is not in the form of a polymer emulsion, in an amount of 0.05 to 3.5 wt % relative to the weight of mineral filler in the recycled paper, during said pulping and/or said flotation.

2. The method according to claim 1, wherein at least a part of the dispersant is introduced during the pulping.

3. The method according to claim 1, wherein the dispersant has a molecular weight between 2000 g.Math.mol.sup.1 and 100 000 g.Math.mol.sup.1, as determined by size exclusion chromatography.

4. The method according to claim 1, wherein the dispersant is introduced during the pulping in an amount of 0.25 to 3 wt % relative to the weight of the mineral filler of the recycled paper.

5. The method according to claim 1, further comprising the addition of soda and/or hydrogen peroxide during the pulping.

6. The method according to claim 1, wherein the dispersant is an acrylic acid homopolymer, optionally in neutralized form.

7. The method according to claim 1, wherein at least a part of the dispersant is introduced during the flotation.

8. The method according to claim 1, wherein the dispersant is a polymer consisting of acrylic acid, a polymer consisting of methacrylic acid, or a polymer consisting of a mixture of acrylic acid and methacrylic acid.

9. The method according to claim 8, wherein the dispersant is a polymer consisting of acrylic acid.

10. A method for deinking recycled paper that comprises mineral filler, the method comprising introducing a water-soluble dispersant of the polyacrylate type that is not in the form of a polymer emulsion to recycled paper, in an amount of 0.05 to 3.5 wt % relative to the weight of mineral filler in the recycled paper, wherein the method further comprises pulping, flotation, and introduction of at least one deinking agent, the dispersant being introduced during the pulping.

11. The method according to claim 10, wherein the dispersant is introduced in an amount of 0.25 to 3 wt % relative to the weight of the mineral filler in the recycled paper.

12. The method according to claim 10, wherein the dispersant is a polymer consisting of acrylic acid, a polymer consisting of methacrylic acid, or a polymer consisting of a mixture of acrylic acid and methacrylic acid.

13. The method according to claim 12, wherein the dispersant is a polymer consisting of acrylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Regarding the deinking agent, this consists of one or more foaming agents known by a person skilled in the art, for example a soap of fatty acid notably of the stearic or oleic type, a fatty acid or a mixture of fatty acids, a nonionic surfactant of the ethoxylated and/or propoxylated fatty alcohol type, a nonionic surfactant of the ethoxylated and/or propoxylated fatty acid type, various mixtures of surfactants and fatty acids, which may also be combined with enzymes, modified derivatives of the organosiloxane type.

(2) Regarding the dispersant used in the context of the invention, it comprises polymers obtained from acrylic monomers. The acrylic monomer is selected from acrylic acid, methacrylic acid and mixtures thereof. Thus, the polyacrylate polymer obtained could be a homopolymer or a copolymer. It is a water-soluble polymer, not a polymer emulsion.

(3) Homopolymer or copolymer of (meth)acrylic acid means either a polymer consisting exclusively of acrylic acid (acrylic acid homopolymer), or a polymer consisting exclusively of methacrylic acid (methacrylic acid homopolymer) or alternatively a polymer consisting of a mixture of acrylic acid and methacrylic acid (acrylic acid/methacrylic acid copolymer) and optionally of at least one other monomer unit. In the case of an acrylic acid/methacrylic acid copolymer, according to one aspect of the invention, the molar ratio of the monomers of acrylic acid to the monomers of methacrylic acid may vary between 1:100 and 100:1, for example between 1:1 and 100:1 or between 1:1 and 50:1.

(4) Said monomer may be partially neutralized. Thus, in one embodiment variant, 2 to 50 wt % of the monomer of (meth)acrylic acid, relative to the total weight of the monomer of (meth)acrylic acid introduced, is neutralized. This may be achieved using a single neutralizing agent or several neutralizing agents. The monomer may, for example, be partially neutralized using an alkali-metal or alkaline-earth hydroxide, an alkaline-earth oxide, and/or with an amine. We may mention, as examples, sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, calcium oxide, potassium oxide.

(5) Moreover, the copolymer according to the invention may also further comprise one or more other ethylenically unsaturated monomer(s) selected from the group consisting of 2-acrylamido-2-methylpropane sulfonic acid (AMPS), maleic acid, fumaric acid, crotonic acid, itaconic acid, the unsaturated telomers of acrylic acid, the monomers of formula (I):

(6) ##STR00001##

(7) in which: R.sub.a, R.sub.b and R.sub.c represent, independently of one another, H or CH.sub.3, n is an integer varying between 0 and 2 (i.e. 0, 1 or 2).

(8) In particular, the monomer may be allyl alcohol (n=1), methallyl alcohol (n=1), isoprenol (n=2). Advantageously, isoprenol is used.

(9) Unsaturated telomers of acrylic acid means oligomers of acrylic acid or of acryloxypropionic acid, of formula (II):

(10) ##STR00002##

(11) where n is an integer in the range from 1 to 10. These various oligomers may be mixed. When n=1, the oligomer is an acrylic acid dimer.

(12) In the presence of other unsaturated monomer(s), according to one aspect of the invention, the molar ratio of the monomers of (meth)acrylic acid to the other unsaturated monomer(s) may vary between 1:1 and 100:1, for example between 1:1 and 75:1 or between 1:1 and 50:1.

(13) Other chemical constituents may be added during the method for deinking, such as soda, hydrogen peroxide, sodium silicate and soap.

(14) Apart from the use of a specific dispersant, in particular proportions during a step of the method for deinking, the method according to the invention is known by a person skilled in the art. More particularly, the recycled paper passes through a pulper, a plurality of purifiers and classifier stations, arranged at different places along the deinking chain, having the respective function of removing the heavy and large particles, as well as at least oneconventionally a pluralityflotation cell or chamber. Thus, the method for deinking according to the invention uses the stations and materials that are usually employed, without modifying them, but the invention is suitable for the flotation technique and not for the washing technique.

EXAMPLES

(15) A plurality of tests that have demonstrated the invention relative to the prior art as well as its various particular features are presented below. For brevity and clarity, only a few results are presented, but of course the applicant has carried out many other tests and analyses in order to comprehend and evaluate the context of the invention as defined here.

(16) Compounds Used in the Tests:

(17) XP 1831 (according to the invention): dispersant of the polyacrylate type consisting of 100% of acrylic acid, with a molecular weight of 4000 g/mol (as determined by SEC), obtained by conventional methods of radical polymerization.

(18) ET.sub.1 (outside the invention): polymer of the comb type consisting of hanging chains of the poly(ethylene glycol) type with a molecular weight of about 50 000 g.Math.mol.sup.1.

(19) ET.sub.2 (outside the invention): polymer of the comb type consisting of hanging chains of the poly(ethylene glycol) type with a molecular weight of about 100 000 g.Math.mol.sup.1.

(20) ET.sub.3 (outside the invention): Potassium tripolyphosphate (KTPP).

(21) Liptol S100: deinking agent consisting of a surfactant of the ethoxylated/propoxylated fatty alcohol type marketed by the company CECA.

(22) Molecular Mass (or Molecular Weight) Mw of the Dispersant of the Polyacrylate Type According to the Invention:

(23) A technique of this kind employs liquid chromatography apparatus made by WATERS, equipped with a detector. This detector is a detector of refractometric concentration made by WATERS.

(24) This liquid chromatography equipment is equipped with a size exclusion column suitably selected by a person skilled in the art for separating the different molecular weights of the polymers under investigation. The liquid phase for elution is an aqueous phase adjusted to pH 9 with 1N soda containing 0.05M of NaHCO.sub.3, 0.1M of NaNO.sub.3, 0.02M of triethanolamine and 0.03% of NaN.sub.3.

(25) In detail, according to a first step, the polymerization solution is diluted at 0.9% dry in the dissolution solvent for SEC, which corresponds to the liquid phase for elution for SEC, to which 0.04% of dimethylformamide is added, which performs the role of marker of flow rate or internal standard. Then it is filtered at 0.2 m. 100 L are then injected into the chromatography apparatus (eluent: an aqueous phase adjusted to pH 9.00 with 1N soda containing 0.05M of NaHCO.sub.3, 0.1M of NaNO.sub.3, 0.02M of triethanolamine and 0.03% of NaN.sub.3).

(26) The liquid chromatography apparatus contains an isocratic pump (WATERS 515), the flow rate of which is set at 0.8 ml/min. The chromatography apparatus also comprises a furnace, which in its turn comprises the following system of columns in series: a precolumn of the GUARD COLUMN ULTRAHYDROGEL WATERS type with a length of 6 cm and an inside diameter of 40 mm, and a linear column of the ULTRAHYDROGEL WATERS type with a length of 30 cm and an inside diameter of 7.8 mm. The detection system consists of a refractometric detector of the RI WATERS 410 type. The furnace is heated to a temperature of 60 C., and the refractometer is heated to a temperature of 45 C.

(27) The chromatography apparatus is calibrated using standards of sodium polyacrylate in powder form with different molecular weights certified by the supplier: POLYMER STANDARD SERVICE or AMERICAN POLYMER STANDARDS CORPORATION. The test protocol consisted of adding these products as a supplement in a reference recipe including a deinking agent and adding the dispersant, either in the pulper (concentrated medium at 27% of dry matter in water) or in a flotation cell/chamber (dilute medium at 1% of dry matter in water).

(28) A model HSM10 laboratory pulper made by Hobart and a Delta 25 flotation cell/chamber from the company Voith are used in the context of these tests.

(29) The raw materials considered are identical for all the tests in order to verify that this parameter (raw materials) does not affect the results. It is a mixture based on newspaper (45%) and weekly magazines (55%) in order to obtain a mixture with a fairly high level of mineral fillers, of the order of 28% of the dry matter (the paper contains conventionally 10% of water, the latter having been removed by drying the aforesaid mixture in a heat chamber).

(30) Similarly, chemical elements, of identical nature and amount for all the tests, were introduced in the pulper, namely: soda NaOH at a rate of 6 kg of pure product per tonne of recycled paper, sodium silicate at a rate of 18 kg of commercial product per tonne of recycled paper, hydrogen peroxide at a rate of 7 kg of pure product per tonne of recycled paper, Liptol S100 at a rate of 0.5 kg of commercial product per tonne of recycled paper.

(31) It should be pointed out that the tests were carried out with another deinking agent, namely a mixture of ethoxylated-propoxylated fatty alcohol and fatty acid of the oleic type, and showed results similarly to those observed with Liptol S100.

(32) Tests Carried Out:

(33) The method for deinking according to the invention is carried out, testing the various dispersants mentioned above, introducing them first in the pulping step, and in a second test in the flotation step. For all the tests, it is assumed that a whiteness of the recycled waste pulp of 56 and 59 must be obtained, and for each of these two levels of whiteness we determine the yield, i.e. the amount of recycled waste pulp (at the desired whiteness) relative to the initial amount of cellulose fibers present in the recycled paper dry matter (the result is expressed as a percentage).

(34) As a reminder, the dry matter corresponds essentially to the cellulose fibers and the mineral fillers (as well as the inks), i.e. to the weight of the recycled paper after removal of the water and all the other ancillary materials (plastics, staples etc.). The dry matter corresponds to the portion of the recycled paper that is put in the pulper.

(35) The tests are conducted in the laboratory, using 250 grams of recycled paper each time (i.e., assuming 10% of water present, 225 g of dry matter). In order to determine the time taken, in the flotation step, to obtain the desired level of whiteness (either 56, or 59), a preliminary analysis is carried out for each test, during which a sample is taken every minute, and its whiteness is measured. Once the flotation time has been determined for each of the tests, the test is repeated, leaving the flotation to continue until whiteness of 56 is obtained, and then a second time until whiteness of 59 is obtained. The yield is then found by determining the amount of matter recovered (recycled waste pulp) relative to the amount of dry matter initially present, i.e. of the order of 140 to 160 grams since the yields are of the order of about 60% to 70%.

(36) In the table given below, the amounts of dispersants are shown as percentage by weight of the mineral fillers of the recycled paper, as is the traditional practice for dosing the deinking agent.

(37) Results of the Tests Carried Out on the Test Specimens with the Various Formulations:

(38) Besides the tests presented in the following table, complementary tests demonstrated that the molecular weight of the dispersant according to the invention has an influence on its effectiveness. Thus, it was demonstrated that the dispersant according to the invention needed a molecular weight between 2000 g.Math.mol.sup.1 and 100 000 g.Math.mol.sup.1 (gram per mole) and preferably (gain in yield) between 3000 g.Math.mol.sup.1 and 10 000 g.Math.mol.sup.1.

(39) Moreover, in the method according to the invention, more than 35%, or even more than 40%, of the mineral fillers present in the recycled paper are preserved in the recycled waste pulp.

(40) TABLE-US-00001 Yield (white- ness Yield Yield Yield 56), (56), (59), (59), XP pulping flotation pulping flotation Tests 1831 ET.sub.1 ET.sub.2 ET.sub.3 step step step step 1 0.05 67.9 65.7 61.8 59.8 2 0.15 70.1 67.8 64.2 62.1 3 0.25 73 70.6 68.3 66.0 4 0.35 75.4 72.90 70.1 67.8 5 0.9 77.3 74.7 71.5 69.1 6 1.1 77.5 74.90 71.6 69.2 7 1.8 77.4 74.8 70.2 67.9 8 2.3 75.9 73.4 69.8 67.5 9 2.9 72.9 70.5 67.9 65.6 10 3.2 69.1 66.8 63 60.9 11 0.9 66.5 63.4 60.2 58.3 12 0.9 66.1 63.3 59.7 57.3 13 0.9 66.2 63.0 60.4 58.0 14 No dispersant 67.6 65.4 61.5 59.5