EP2176302A2

EP2176302A2 - Copolymer(s) latex, method for preparing same and use thereof for coating paper and carton

Info

Publication number: EP2176302A2
Application number: EP08826710A
Authority: EP
Inventors: Laurence Couvreur
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2007-07-25
Filing date: 2008-07-24
Publication date: 2010-04-21
Also published as: US20100255329A1; FR2919290A1; FR2919290B1; WO2009016320A3; WO2009016320A2; JP2010534264A

Abstract

The invention relates to copolymer(s) latexes prepared from vinylic monomers, non-conjugated dienes and optionally comonomers, particularly acrylic ones, in the presence of at least one chain transfer agent of the following formula. These latexes are particularly well-suited for coating paper and cardboard.

Description

COPOLYMER LATEX (S), PROCESS FOR PREPARING SAME AND USE THEREOF FOR COATING PAPER AND CARDBOARD

The present invention relates to copolymer latexes (s) made using halogen-free molecular weight chain transfer agents or regulators that can be used for paper coating applications, particularly in the field of odor-sensitive applications (eg food packaging).

Latexes that can be used for the coating of paper and board must have good mechanical properties (printability, resistance to tearing of the coating). For this purpose, it is necessary to control the molecular weight of the copolymer latex (s) during the polymerization using regulators or chain transfer agents (CTA).

In the past, organohalogen compounds have been widely used as chain transfer agents (eg carbon tetrachloride, carbon tetrabromide) and have been banned for some years for ecological reasons and replaced by sulfur transfer agents. of the mercaptan type, and in particular by tert-dodecyl mercaptan (TDM). Mercaptans perform very well their role in action on the control of the molecular weight of the chains in the copolymer latex (s) and make it possible to obtain latexes which have good resistance to tearing in the dry state or wet. However, the major disadvantage of mercaptans is their undesirable and very marked odor which persists not only in the latex but also in paper and / or cardboard made with such latexes, which is a brake on their use and development. in the field of paper and cardboard.

Other technical solutions have been proposed:

No. 5,837,762 discloses the use of chain transfer agents derived from rosin for the manufacture of the copolymer latex (s). However, the regulation efficiency of rosin is much lower than that of mercaptans. It is therefore necessary to use up to 9% of rosin during the polymerization of the latex to reach acceptable values of resistance to dry tearing of coated paper. On the other hand, rosin is a natural product whose quality varies greatly depending on the source. Finally, it should be mentioned that rosin has a strong clean color (yellow to brown), which can be a drawback in coated paper, given the amounts of rosin that are implemented.

FR 2,665,450 discloses a very broad family of organosulfide transfer agents which are substituted diphenyl disulfides and are used as transfer agents for the preparation of low-odor latex since they have little or no undesirable residual odor. Or ₁ this patent discloses that diphenyl disulfide alone is not sufficiently effective as a CTA and other organic disulfides, known as molecular weight regulators, such as thiuram disulfide, diethyl xanthogen disulfide and diphenyl substituted with amines. These additives are rather known as retarders and produce undesirable odors. The amounts of transfer agent recommended in the patent for the polymerization are between 0.5% and 10%, with an optimum between 0.5% and 5% to obtain a paper having satisfactory properties (printability, resistance to abrasion). removal of the coating) close to the treated paper with obtained with TDM. JP 7166496, JP 7278213 and JP 2001/003298 disclose the use of alpha-methylstyrene dimer alone or in admixture as a transfer agent for latices for coated paper applications. However, because of the low efficiency of these products, quantities much higher than those usually used must be implemented to arrive at good final properties of the materials.

EP 1 380 597 describes the use of several types of peroxides used as chain transfer agents (such as di-tert-butyl peroxide, cumol hydroperoxide, or di-tert-butyl, etc.). However, the amount of peroxides used must be twice as great as that of TDM in order to obtain quasi-similar performances (particle size, glass transition temperature (Tg), gel ratio and intrinsic properties of the coated paper). Nothing is indicated on the smell of the product. US 6,369,158 claims the use of dibenzyl trithiocarbonate (DBTTC) for the synthesis of SBR type latex ("styrene-butadiene rubber") of high molecular weight which is mainly in pneumatic applications. It is well known that these elastomeric type products are characterized by low glass transition temperatures, incompatible with applications in which the elastomeric type products are not sought.

The problem is to look for variants of regulatory systems that do not contain halogen, do not present an odor as undesirable and marked as that of mercaptans while being suitable for making copolymer latexes (s) having a strength of sufficient bonding (i.e. tear resistance) and thus can be used in the area of odor-sensitive applications for coating paper and board.

The subject of the invention is a copolymer latex (s) intended to be used for coating paper and board, where the copolymer latex (s) has a glass transition temperature between -30 ^° C. and 70 ^° C. C, preferably between -20 ° C and 40 ° C, manufactured with at least one chain transfer agent and comprising in polymerized form: a) from 10% by weight to 80% by weight of one or more vinyl monomers ; b) from 20% by weight to 70% by weight of one or more conjugated diene monomers; c) and optionally up to 70% by weight of one or more monomers comprising at least one ethylenic unsaturation copolymerizable, chosen from acrylic monomers, ethylene-type unsaturated dicarboxylic acid monomers, monomers further bearing at least one nitrile function, the monomers of vinyl esters, the monomers of

(meth) acrylamide, characterized in that the at least one chain transfer agent can be represented by the formula: where R is selected from -CH ₂ RI, -CHR1 R'1 and -CR1 R'1 R "1, with R1, R'1 and R ¹¹ I ₁ identical or different, each independently represent each other , a group chosen from optionally substituted alkyl, a saturated, unsaturated or aromatic carbocyclic or heterocyclic ring, optionally substituted, optionally substituted alkylthio, optionally substituted alkoxy group, optionally substituted dialkylamino, organometallic group, acyl, acyloxy, carboxy (and its esters and / or salts), sulphonic acid (and its salts and or sulphonates), alkoxy- or aryloxycarbonyl, and polymer chain prepared by any polymerization mechanism, wherein Z is selected from hydrogen, halogen (chlorine, bromine, iodine), optionally substituted alkyl, optionally substituted aryl, optionally substituted heterocycle, optionally substituted alkylthio -SR (R being as defined above), optionally substituted alkoxycarbonyl optionally substituted aryloxycarbonyl (-COOR2), optionally substituted carboxy (-COOH), acyloxy (-OCOR2), optionally substituted carbamoyl (-CONHR2, -CONHR2R3), cyano (-CN), dialkyl- or diarylphosphonato [-P (= O) OR2 ₂ ], dialkyl- or diaryl-phosphinato [-P (= O) R2 ₂ ], polymer chain prepared by any polymerization mechanism, -OR2 group, and -NR2R3 group, where R2 and R3, same or different , are selected from the group consisting of Ci-Cis alkyl, alkenyl C ₂ Cis, Cis aryl it to, heterocyclyl, aralkyl, alkaryl, each of which groups may be optionally substituted and wherein the substituents are selected from epoxy, hydroxy, alkoxy, acyl, acyloxy, carboxy (and its esters and / or salts), sulfonic acid (and its salts and or sulfonates), alkoxy- or aryloxycarbonyl, isocyanato, cyano, silyl, halo and dialkylamino.

The group R as defined above can be released in the form of a radical R ^" , which initiates free radical polymerization. Among the chain transfer agents, there may be mentioned dithioesters (compounds comprising at least one -C (= S) S-) unit, dithiocarbonates or xanthates (compounds comprising at least one -OC (= S) S- ), dithiocarbamates (compounds having at least one -NC (= S) S- unit) and trithiocarbonates (compounds having at least one -SC (≈S) S-) unit.

Dithioesters which can be advantageously used in the context of the invention are those corresponding to the following formula (I):

(I)

in which Z represents a group chosen from -C ₆ H ₅ , -CH ₃ , a pyrrole group, -OC ₆ F ₅ , a pyrrolidinone group, -OC ₆ H ₅ , -OC ₂ H ₅ , -N (C ₂ H ₅ ) 2, and advantageously the group -S-CH ₂ -C ₆ H ₅ (dibenzyl trithiocarbonate or DBTTC) of formula (II) below:

(II)

Particularly preferred are the chain transfer agents as defined above which are fat-soluble, and of little or no water-soluble nature. The transfer agent of formula (II) responds particularly to these conditions. In the case of chain transfer agents, dibenzyl trithiocarbonate (DBTTC) and its derivatives are particularly suitable.

The quantities of chain transfer agents used generally range from 0.1 to 10% by weight, preferably from 0.1 to 5% by weight, particularly from 0.1 to 3% by weight, relative to to 100% by weight of monomer (s) a) to c).

The amounts of chain transfer agents above allow the synthesis of copolymer (s) copolymer (s) whose (s) copolymer (s) free (fractions extracted from the copolymer (s) isolated (s) at room temperature. ambient temperature with toluene for 24 hours) have the following characteristics: 5,000 <Mn <80,000, preferably 5,000 <Mn <50,000, and 10,000 <Mw <270,000, preferably 10,000 <Mw <200,000, where Mn and Mw respectively represent the molar masses in number and in weight.

Surprisingly, it has been found that the quantities used of the chain transfer agents defined above can be less than those used with conventionally used chain transfer agents (mercaptans, di- and trithiols, and others), while retaining the mechanical properties of the copolymers (such as bond strength, tear resistance, and others).

The vinyl monomers a) comprise, in particular, vinyl aromatic monomers such as styrene, α-methylstyrene, para-ethylstyrene, ter-butylstyrene and / or vinyltoluene. Mixtures of one or more vinyl monomers may also be used. The preferred monomers are styrene and α-methylstyrene. The monomer (s) a) are generally used in a range from 10% to 80% by weight, preferably from 25% to 75% by weight, most preferably 35% to 70% by weight, based on to the total weight of the monomers.

Conjugated diene monomers b) suitable for the manufacture of latices include conjugated diene monomers such as ^ι j

1,3-butadiene, isoprene and 2,3-dimethyl-1,3-butadiene. 1,3-butadiene is preferred in the present invention. Typically, the amount of conjugated diene monomer (s) present in the polymer phase ranges from 20% to 70% by weight, preferably from 20% to 65% by weight, more preferably from 20% to 70% by weight. % to 55% by weight, more preferably 30% to 50% by weight, most of the time 30% to 45% by weight, based on the total weight of the monomers.

The acrylic monomers c) usable in the present invention as copolymerizable comonomers include in particular acrylic acid, methacrylic acid, alkyl (meth) acrylates, hydroxyalkyl and / or alkoxyalkyl (meth) acrylates, where the alkyl group (n-alkyl, / -sat-alkyl or terf-alkyl) has 1 to 20 carbon atoms of alkyl and is optionally substituted by at least one epoxy group, amide, and / or at least one amino group; the reaction product of (meth) acrylic acid with the glycidyl ester of a neoacid such as versatic acids, neodecanoic acids or pivalic acid and mixtures thereof.

The preferred acrylic monomers are acrylic, methacrylic, alkyl and / or hydroxyalkyl and / or alkoxyalkyl (meth) acrylates, wherein the alkyl group is C1-C10, preferably

Ci-Cs. As examples of preferred acrylic monomers, mention may be made especially of acrylic acid, methacrylic acid, n-butyl acrylate, sec-butyl acrylate, ethyl acrylate and hexyl acrylate. tert-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate,

4-methyl-2-pentyl, 2-methylbutyl acrylate, methyl methacrylate, butyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, ethyl methacrylate, isopropyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, cetyl methacrylate, methoxyethyl methacrylate, ethoxyethyl acrylate, butoxyethyl methacrylate, methoxybutyl acrylate, methoxyethoxyethyl acrylate, hydroxyethyl acrylate , hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and / or hydroxybutyl acrylate

The most preferred acrylic monomers are acrylic acid, methacrylic acid, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate.

Typically, the amount of acrylic monomer (s) optionally present in the polymer phase depends on the monomer or monomers chosen; however, the typical range can be up to 70% by weight, preferably from 1 to 70% by weight, preferably from 1 to 60% by weight, most preferably from 0 to 51% by weight, by weight. relative to the total weight of the monomers.

The unsaturated dicarboxylic acid monomers of the ethylene type that can be used as copolymerizable comonomers c) within the scope of the present invention comprise, in addition to the ethylenically unsaturated dicarboxylic acids, their monoesters and / or their anhydrides. As monomeric examples of unsaturated dicarboxylic acid of ethylene type, mention may be made of fumaric acid, crotonic acid, maleic acid and maleic anhydride.

The nitrile monomers usable as copolymerizable comonomers c) in the context of the present invention comprise polymerizable unsaturated aliphatic nitrile monomers which contain from 2 to 4 carbon atoms in a linear or branched arrangement and which may be optionally substituted by acetyl or additional nitrile groups. These nitrile monomers include, for example, acrylonitrile, methacrylonitrile and fumaronitrile, with acrylonitrile being preferred. These nitrile monomers (if used) can be included up to about 25 parts by weight, preferably from 0 to 15 parts by weight, based on 100 parts by weight of monomers. The vinyl ester monomers useful as the coolymerizable monomers c) include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, vinyl 2-ethylhexanoate, vinyl stearate and vinyl esters. versatic acid. The preferred vinyl ester monomer for use in the present invention is vinyl acetate. Typically, the amount of vinyl ester monomer (if used), which is present in the polymer phase, ranges from 0 to 45% by weight, preferably from 0 to 35% by weight, based on the total weight monomers.

The monomers of (meth) acrylamide that can be used as coolmeasurable monomers c) include the α, β-olefin unsaturated carboxylic acid amides, such as, for example, acrylamide, methacrylamide and diacetone-acrylamide. The preferred (meth) acrylamide monomer is acrylamide. Typically, the amount of (meth) acrylamide monomer (if used), which is present in the polymer phase, depends on the monomer chosen, but the typical range is from 0 to 10% by weight, preferably from 0 to 5% by weight, most preferably from 0 to 2% by weight relative to the total weight of the monomers.

Another subject of the invention is a process for producing a copolymer latex (s) as defined above from:

A / from 10% by weight to 80% by weight of one or more vinyl monomers a);

B / from 20% by weight to 70% by weight of one or more conjugated diene monomers b);

C / optionally up to 70% by weight of one or more copolymerizable monomers c) chosen from acrylic monomers, ethylene-type unsaturated dicarboxylic acid monomers, nitrile monomers, vinyl ester monomers, monomers of (meth) acrylamide, and

D / at least one chain transfer agent (CTA) represented by the formula: where R and Z are as defined above, at temperatures of 0 ^° C to 130 ^° C, preferably 20 ^° C to 130 ^° C, more preferably 60 ^° C to 130 ^° C, particularly 60 ° C at 100 ° C and especially from 75 ° C to 100 ° C, in the presence of one or more emulsifiers or surfactants and / or a plurality of initiators and / or one or more protective colloids and / or a or several agents such as antifoam agents, wetting agents, thickeners, plasticizers, fillers, pigments, crosslinking agents, antioxidants and metal chelating agents.

The size or average diameter of the latex particles, measured by light scattering, is generally between 50 and 200 nm.

The copolymer latex composition (s) of the present invention can be manufactured according to polymerization processes which are known in the field of polymerization, and in particular according to the latex emulsion polymerization processes, in particular the latex polymerizations carried out. with seeding latexes. Representative methods include those described in US 4,478,974, US 4,751,111, US 4,968,740, US 3,563,946 and US 3,575,913 and DE-A-19 05 256. These methods may be suitable for the polymerization of the previously described monomers. The method of introducing monomers and other ingredients such as polymerization aids is not particularly critical. The polymerization is then carried out under customary conditions, until the desired degree of polymerization is obtained. Crosslinking agents and auxiliaries well known for latex polymerization such as initiators, surfactants and emulsifiers may be used depending on requirements. Primers useful in the context of the present invention include water-soluble and / or fat-soluble initiators, which are effective for the purpose of polymerization. Representative initiators are well known in the art and include, for example, azo compounds (such as AIBN) and persulfates (such as, for example, potassium persulfate, sodium persulfate and ammonium persulfate).

The initiator (s) are used in an amount sufficient to initiate the creation of polymerization at a desired rate; in general, an amount of initiator of 0.05 to 5% by weight, preferably 1 to 4% by weight, based on the weight of the total polymer, is sufficient. Advantageously, the amount of initiator reaches from 0.1 to 3% by weight, relative to the total weight of the polymer.

Among the suitable surfactants or emulsifiers, any type of usual surfactant known in the field of polymerization processes may be used. The surfactant (s) may be added to the aqueous phase and / or to the phase of the monomer (s). The amount of surfactant (s) is generally chosen to promote the stabilization of the particles in the form of colloid and / or to reduce the contact between the particles and / or prevent coagulation. In an uninoculated process, the amount of surfactant (s) is generally selected to influence particle size.

As examples of surfactants, mention may be made of ethylenically saturated and unsaturated sulphonic acids or their salts, including, for example, hydroxycarboxylic-sulphonic acids, such as vinylsulphonic acid, allylsulfonic acid and methallylsulphonic acid, and their salts. salts; aromatic hydroxycarboxylic acids, such as, for example, para-styrenesulfonic acid, naphthalenesulfonic acid and vinyloxybenzenesulphonic acid and their salts; sulfoalkyl esters of acrylic acid and methacrylic acid, such as, for example, sulfoethyl methacrylate and sulfopropyl methacrylate and their salts, and 2-acrylamido-2-methylpropanesulphonic acid and its salts; alkylated diphenyl oxide disulfonates, sodium dodecylbenzenesulfonates and esters sodium sulfosuccinic acid dihexyls, ethoxylated alkylphenols and ethoxylated alcohols; fatty alcohol (poly) ether sulphates.

The type and concentration of surfactant (s) typically depends on the content of solid polymers: a higher content of solid polymers generally increases the need for surfactant (s). Typically, the surfactant (s) are used at concentrations ranging from 0.05 to 20, preferably from 0.05 to 10, more preferably from 0.05 to 5 parts by weight, relative to the weight total monomers.

Various protective colloids may also be used instead of or in addition to the surfactants which have just been described. Suitable colloids include partially acetylated polyvinyl alcohol, casein, hydroxyethyl starch, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and gum arabic; the preferred protective colloids are carboxymethylcellulose, hydroxyethylcellulose and hydroxypropylcellulose. In general, these protective colloids are used at contents ranging from 0 to 10, preferably from 0 to 5, more preferably from 0 to 2 parts by weight, relative to the total weight of the monomers.

Various other additives, known to those skilled in the art of polymerization, can be incorporated to make the latex composition of the present invention. Such additives include, for example, antifoaming agents, wetting agents, thickeners, plasticizers, fillers, pigments, crosslinking agents, antioxidants and metal chelating agents. Known anti-foaming agents include silicone oils and acetylene glycols. Typical known wetting agents include alkyl phenol ethoxylates, alkali metal dialkyl sulfosuccinates, acetylene glycols and alkali metal alkyl sulfates. Typical thickeners include polyacrylates, polyacrylamides, xanthan gums, modified cells or particulate thickeners such as diatomaceous earths and clays. Typical plasticizers include mineral oil, liquid polybutenes, liquid polyacrylates and lanolin. Zinc oxide, titanium dioxide, aluminum hydrate, and calcium carbonate and clay are typically used fillers.

The object of the invention is also the use of the copolymer latices (s) defined above for the coating of paper and cardboard.

It has been found that the latexes of copolymer (s) comprising at least one unsaturated carboxylic acid monomer of the ethylene type, whether it is an acrylic monomer and / or that it is an unsaturated dicarboxylic acid monomer of the ethylene type, improves strongly. the stability of the latex and the adhesion of the latex films, which makes the latex particularly suitable for use in paper coating formulations. For the practical realization of the present invention, it is preferred to use the acid (s) or anhydride (s) of unsaturated aliphatic mono- or dicarboxylic acids of the ethylene type which contain from 3 to 5 carbon atoms. Examples of monocarboxylic acid monomers include, for example: acrylic acid, methacrylic acid and examples of dicarboxylic acid monomers include, for example: fumaric acid, crotonic acid, maleic acid and maleic anhydride.

As indicated above, the use of ethylenically unsaturated carboxylic acid monomer (s) influences the properties of the polymer dispersion and the coatings produced therefrom, typically, when the amount of unsaturated carboxylic acid monomer (s) is present. Ethylenically ranges from 1 to 20% by weight, preferably from 1 to 10% by weight, relative to the total weight of the monomers.

According to a preferred embodiment, the copolymer latex composition (s) of the present invention prepared from styrene, butadiene, and acrylic acid, preferably copolymerized in the presence of DBTTC as a chain transfer agent.

The following examples illustrate the invention.

Unless otherwise indicated, the amounts, percentages, are expressed by weight. Example 1 (comparative) - styrene latex

Procedure for Batch Process Emulsion Polymerization (Batch Process) of Styrene at 65 ° C

- A solution is prepared containing 0.24 g of Na HCO ₃ (buffer), 8 g of surfactant SLS (Sodium Lauryl Sulfate) and 540 g of distilled water; the mixture is stirred and heated (approximately 50 ^° C.) until the surfactant is completely dissolved.

The transfer agent (DBTTC or TDM) / monomer (styrene) mixture is prepared, the CTA being introduced in the proportions indicated in Table 1 below; - Introduction of 2 mixtures above in a jacketed reactor of 1 L pre-vacuum, with stirring at 150 rpm and heated to 65 ⁰ C;

The medium is deoxygenated with 3 cycles of evacuation and then under nitrogen to inert the reactor, it is left under vacuum at 65 ° C. before introduction of the initiator;

A solution containing the initiator is prepared, ie 0.2 g of PRS in 15 g of water (ie 82.6 mol% of PRS relative to DBTTC);

This mixture is introduced into an airlock under nitrogen flushing and then injected into the reactor by nitrogen thrust; rinse the lock with 45 g of water still under nitrogen and injection into the reactor;

- The reactor pressure is then adjusted to 0.15 MPa with nitrogen. This moment is considered as the time T = O of beginning of polymerization. The conversion is followed by samples immediately cooled in the ice and control by dry extract with thermobalance at 140 ^° C. (Mettler Toledo HB43). The polymerization is stopped after 3 hours. The samples taken are dried in a ventilated oven overnight at 100 ^° C.

The dried polymers are analyzed by steric exclusion chromatography (SEC) in THF at 40 ^° C. at 1 g / l with a flow rate of 1 mL / min in a set of 2 Plgel MIXED B columns (30 cm) with a refractometric and UV detector. The results of the molar masses and distribution are expressed in polystyrene equivalent (PS)

- Particle sizes and final latex distribution are measured using a Malvern Zetameter (Zetasizer 5000) For each test, a latex of copolymer (s) is obtained for which is indicated in Table 1 below, the nature and amount of CTA implemented (in% relative to the monomers, the conversion rate (measured by dry extract), the number-average molecular weight measured by SEC with polystyrene calibration and the Mw / Mn polymolecularity index.

Table 1 Test ^! * CTA (%, J ^ *. ^ Mw / Mn '

1 - 0 0.95 1.100.000 »2.6 ^C

2 TDM 0.18 0.95 1 10.000 2.4

3 DBTTC 0.13 0.97 190.000 1, 8

4 DBTTC 0.26 0.94 150.000 1, 7 a: By dry extract, b: By SEC equivalent polystyrene, c: because of the presence of strong masses / gels

Example 2 - styrene-butadiene-acrylic acid-acrylate latex

Procedure for the semi-continuous emulsion synthesis of styrene-butadiene at 80 ° C. and 50% solids content. 300 g of butadiene originating from a bottle are prepared beforehand in a refrigerated capacity at -18 ^° C. 1,3-butadiene gas at room temperature. This so-called "distillation" stage makes it possible to obtain liquid butadiene by cooling.

- Introduced (just before starting the polymerization) in a vacuum capacity at room temperature, provided with a valve calibrated at 1, 2

MPa and placed on a balance the mixture of the following monomers (an excess of 50 g is expected):

303.3 g of styrene / 24.1 g of acrylic acid and chain transfer agent (DBTTC or TDM) in the amounts shown in Table 2 below

The vacuum is again made in the capacity and the capacity of liquid butadiene is pressurized with nitrogen (0.3 MPa). The scale is weighed under the capacity of the monomers and then 209.5 g of butadiene are introduced. This monomer capacity is then pressurized to 1 MPa with nitrogen.

- The butadiene capacity is degassed by nitrogen sweeping and stops cooling. - The following mixture is prepared that is introduced into the reactor 1 L provided with a jacket at 50 ⁰ C under vacuum and with stirring at 150 rpm:

205 g water / 0.03 g EDTA / 1, 55 g NaOH in 25 wt% aqueous solution / 3.97 g SLS at 29.7% by weight - The reactor is again evacuated and introduced into the reactor. then 30% of the monomers by weighing after calibration of the scale under capacity is the equivalent of 82.5 g of styrene / 57.1 g of butadiene / 6.6 g of acrylic acid / 1.21 g of DBTTC.

The reactor is heated to 80 ^° C. and the initiator is prepared with 1.46 g of Na ₂ S ₂ O ₈ and 15 g of water.

At 80 ^° C., the boot is introduced through an airlock under N ₂ of the initiator and the airlock is then rinsed with 20 g of water also introduced into the medium. The pressure is then close to 0.57 MPa.

- The polymerization is allowed to start so as to have a "seed", there is a drop in pressure of 0.02 MPa for about 30 minutes.

The following 3 mixtures are then introduced simultaneously into the reactor for a semi-continuous over 2 hours: a) by means of a microllimite valve, with a flow rate of 2.9 g / min, in 2 hours 70% is introduced monomers of the capacity, ie 192.5 g styrene /

133 g butadiene / 15.3 g acrylic acid and 2.83 g DBTTC; b) by means of a valve pump, at a flow rate of 1, 08 mL / min, in 2 hours is also introduced a mixture containing 3.41 g of Na ₂ S ₂ Os supplemented with 120 g of water followed rinsing the line with 10 g of water; c) by means of a valve pump, at a flow rate of 1, 1 mL / min, in 2 hours the mixture containing 1 10 g of water / 3.73 g of aqueous NaOH is also introduced into the mixture. % by weight / 9.28 g of SLS at 29.7% by weight followed by rinsing the line with 10 g of water; - At the end of the semi-continuous addition, the pressure is 0.73 MPa, then take a sample (5 to 10 g) after rinsing the bottom valve of the reactor, in a bottle equipped with a septum and containing a "polymerization terminating agent is 0.1 to 0.2 g of a solution of sodium dithiocarbamate to 1, 5% by weight in water. The dry extract conversion is then checked with the Mettler Toledo HB43 thermobalance (conversion = 43%)

The polymerization is allowed to continue for 2 hours (P = 0.55 MPa) and the sampling is repeated as indicated above with also a measurement of the conversion (74%). After an additional 1 h 30 (P = 0.39). MPa), the same operation is repeated, the conversion is then 95%.

- The reaction is then stopped with introduction by the lock under N ₂ in the reactor, 10 g of sodium dithiocarbamate solution to 1, 5% in water. - The reactor is then degassed and the heating setpoint is lowered.

20 ^° C., mixing is continued for 15 to 30 minutes and then the latex is withdrawn under suction of the hood. The bottle is left open under suction overnight to degas the residual butadiene.

The reactor is cleaned with water at 70 ^° C. and then with THF at 50 ^° C., then dried and disassembled for manual cleaning. Residual monomer capacity is degassed and cleaned by rinsing with acetone.

Characterizations of the SBAA Latex obtained:

- Particle size The final latex distribution is measured using a Zetameter

Malvern (Zetasizer 5000) after dilution of the latex to adjust to the concentration required in the measuring cell of the device. They can also be measured by CHDF. Values of 171 nm measured with Zetasizer and 156 nm with CHDF are typically obtained.

- Preparation of the latex film

In polytetrafluoroethylene cups (diameter 70 mm), the final raw latex is placed so as to have 6 to 7 g of dry product: approximately 14 g of latex per dish, which is allowed to dry slowly by evaporation in a hood for 3 days. Then drying is continued in a ventilated oven at 50 ^° C. for 1 day. Carefully take off the film obtained which is put on the back for additional drying of a day still in an oven at 50 ^° C.

- Coagulation of cold latex

At -1O ⁰ C for 24 hours after having diluted to 1/5 ^th . 20 g of crude latex are taken and diluted with 80 g of water. Then it is thawed and then washed and decanted-filter to best recover the coagulated latex in a crystallizer. It is dried in an oven at 50 ^° C. for 24 hours, then "peeled off" from the crystallizer to turn it upside down and again dried for 24 hours at 50 ^° C.

- Measurement of the Tq (glass transition temperature)

From the film latex and coagulated latex using a Mettler DSC30. Sample taken from 60 to 70 mg in the crucible. Measurement of the Tg after 2 passages from -100 to + 150 ^° C. at a rate of 10 ° C./min. There is obtained a latex IFPMA Tg = 2.3 ° C and a coagulated latex Tg = -1, 6 ⁰ C. The glass transition temperature is indicated as a point of inflection in DSC curve.

- Free polymer rate

It corresponds to the amount of polymer dissolved in toluene after 24 hours of hot extraction in a soxhlet. About 3 g of film latex or coagulated latex are weighed accurately to 10 g and placed in a soxhlet cartridge (Durieux model for extractor size 37x130 mm). A 500 ml balloon of toluene is filled under the soxhlet. refluxed for 24 hours. The free polymer thus extracted is recovered in the flask containing toluene. The amount of free polymer is measured by difference in weight of the cartridge after having previously dried in an oven at 120 ^° C. overnight and left at room temperature for the day (recovery of humidity). for the latex film, a percentage of free polymer equal to 53% and for the 100% coagulated latex.

Sample calculation for testing with DBTTC:

Weighing Mass (g) Latex Coagulated Latex Film

Tare empty cartridge 13,536 12,4513

Mass latex (about 3 g) 3.0559 3.1286

Mass cartridge (Tare + dry latex) after extraction

14.9604 12.4557 24 h in toluene and drying 120 ⁰ C overnight

Dry mass: (cartridge mass - Tare cartridge) 1, 4244 0.0044

% free polymer: 100 x (m latex - dry m) / m latex 53.39 99.86

- Rate and Index of swelling

The measurement of the gel level serves to determine the insoluble fraction of a polymer in a specific solvent and the crosslinking of the copolymer latex (s). It corresponds to the gel portion of the polymer not solubilized in toluene after 24 hours in the cold. As a solvent, toluene is then used. The swelling is done on films that have been manufactured as described above. The toluene insoluble gel is filtered off, dried and weighed. The gel content is defined as the quotient of the weight of the dried gel divided by the weight of the original latex film (before swelling with toluene) and is indicated in%.

Weigh accurately with 10 ^"4 g in a metal basket of width 25 mm and height 60 mm with very fine mesh (opening 50 μm with a wire of 40 μm), 0.5 g of latex film or coagulated cut in very This basket is immersed in a 100 ml beaker containing 75 ml of toluene, this at room temperature under a bell in a toluene-saturated air, the polymer is left to swell for 24 hours, the basket is removed from the toluene and let it drain for one hour, weigh it and this measurement gives the swelling index, we obtain for the film latex an index of 26 and for the coagulated latex 17. Then dried in a ventilated oven at 120 ⁰ C, the basket overnight. The weighing of the dried basket gives the value of the gel level of the polymer which has not been solubilized in toluene. This gives the film latex a gel level of 37% and for the coagulated latex a rate of 1%.

Sample calculation for test with DBTTC

Weighing mass Latex film _{cpagu | é} n ° panier 1 2

P1 (empty basket tare) 22,496 22,5035 P2 (wet basket tare after 30 'in toluene) 22,8273 22,7444

P3 (tare + about 0.5 g latex) 22.9987 22.9969

P4 (after swelling 24 h in toluene and drained 1 h) 2277,, 55887788 22,821 P5 (dry basket after drying 120 ^° C overnight) 22,68 22,508 Swelling index: (P4-P2) / (P5-P1) 25 , 87 17.02% Gel rate: 100x (P5-P1) / (P3-P1) 36.60 0.91

- Molar masses and distribution by chromatoaplasia of steroid exclusion fSEQ

Using gel permeation chromatography (GPC) it is possible to determine the molar mass of the polymers provided that the polymers dissolve entirely in the solvent used (here THF)

The free polymer (previously extracted in toluene after 24 hours of reflux with Soxhlet) is recovered in PTFE cups by evaporation of toluene in a ventilated oven at 50 ^° C. for 2 days. The masses and distribution by steric exclusion chromatography (SEC) in THF at 40 ^° C. and at 1 g / L are determined with a flow rate of 1 mL / min over a set of 2 Plgel MIXED B columns (30 cm) with a refractometric and UV detector. The results of the molar masses and distribution are expressed in PS equivalents.

We obtain as follows:

For each test, a film is obtained for which the nature and the amount of CTA used (in% relative to the monomers), the conversion rate (measured by dry extract), glass transition temperature (Tg) the gel level, the number-average molecular weight Mn measured by SEC with polystyrene calibration and the Mw / Mn polymolecularity index

Table 2

Type ™ 7 "f ^ιa . ^{" X} 0 Rate

CTA assay Pjjj ^ J ^ particles Tg CC) de gel Mn ^b

Mvi / Mrf pj (9-mor ¹ )

(%) / (hh) ls _α i _ln on _n ? ^a ( ^nm )

CT

4.5 0.95 146 1, 5 69 8.800> 12.3 ^C (1, 14)

DBTTC

0.95 171 2.3 47 11.800 4.4 (0.82)

DRTTP

⁷ ^ 04-n ⁴ ' ⁵ ° ^{96 158 11} ' ⁷ ° ^{75 13} - ^{400 7> 6} a: By dry extract, b: By SEC equivalent polystyrene, c: because of the presence of heavy masses / gels

Claims

1. Latex copolymer (s) having a glass transition temperature between -30 ° C and 70 ^° C, preferably between -20 ^° C and 40 ° C, manufactured with at least one chain transfer agent and comprising in form polymerized: a) from 10% by weight to 80% by weight of one or more vinyl monomers; b) from 20% by weight to 70% by weight of one or more conjugated diene monomers; c) and optionally up to 70% by weight of one or more monomers comprising at least one ethylenic unsaturation copolymerizable, chosen from acrylic monomers, ethylene-type unsaturated dicarboxylic acid monomers, monomers further bearing at least one nitrile function, the monomers of vinyl esters, the monomers of

(meth) acrylamide, characterized in that the at least one chain transfer agent can be represented by the formula: where R is selected from -CH ₂ RI, -CHR1 R'1 and -CR1 R'1 R "1, with R1, R'1 and R" 1, identical or different, each independently represent each other , a group chosen from optionally substituted alkyl, a saturated, unsaturated or aromatic carbocyclic or heterocyclic ring, optionally substituted, optionally substituted alkylthio, optionally substituted alkoxy group, optionally substituted dialkylamino, organometallic group, acyl, acyloxy, carboxy (and its esters and / or salts), sulfonic acid (and its salts and or sulfonates), alkoxy- or aryloxycarbonyl, and polymer chain prepared by any polymerization mechanism; where Z is selected from hydrogen, halogen (chlorine, bromine, iodine), optionally substituted alkyl, optionally substituted aryl, heterocycle OQ optionally substituted, optionally substituted alkylthio -SR (R being as defined above), optionally substituted alkoxycarbonyl, optionally substituted aryloxycarbonyl (-COOR2), optionally substituted carboxy (-COOH), acyloxy (-OCOR2), carbamoyl (-CONHR2) , -CONHR2R3) optionally substituted, cyano (-CN), dialkyl- or diarylphosphonato [-P (= O) OR2 ₂ ], dialkyl- or diaryl-phosphinato [-P (= O) R2 ₂ ], polymer chain prepared by a any polymerization mechanism, -OR2, and -NR2R3 group where R2 and R3, identical or different, are selected from the group consisting of alkyl to alkenyl, C ₂ to C _8, aryie This-is -C , heterocyclyl, aralkyl, alkaryl, each of which groups may be optionally substituted and wherein the substituents are selected from epoxy, hydroxy, alkoxy, acyl, acyloxy, carboxy (and its esters and / or salts), sulfonic acid (and its salts and or sulfonates), alkoxy- or aryloxycar bony, isocyanato, cyano, silyl, halo and dialkylamino.

2. Latex copolymer (s) according to claim 1, characterized in that the at least one chain transfer agent is chosen from dithioesters, dithiocarbonates or xanthates, dithiocarbamates and / or trithiocarbonates, and preferably comprises dibenzyl trithiocarbonate (DBTTC).

3. Latex copolymer (s) according to claim 1 or 2, characterized in that the amount of at least one chain transfer agent used is from 0.1 to 10% by weight, preferably from 0, 1 to 5% by weight, particularly from 0.1 to 3% by weight, relative to 100% by weight of monomer (s) a) to c).

4. Latex copolymer (s) according to any one of claims 1 to 3, the (s) copolymer (s) free (fractions extracted from the copolymer (s) isolated (s) at room temperature by the toluene for 24 hours) have the following characteristics:

5,000 <Mn <80,000, preferably 5,000 <Mn <50,000, and 10,000 <Mw <270,000, preferably 10,000 <Mw <200,000, where Mn and Mw respectively represent the molar masses in number and in weight.

5. Latex copolymer (s) according to any one of claims 1 to 4, characterized in that the vinyl monomer (s) a) are chosen from styrene, α-methylstyrene, para-ethylstyrene, butylstyrene and / or vinyltoluene, and preferably from styrene and / or α-methylstyrene.

6. Latex copolymer (s) according to any one of claims 1 to 5, characterized in that the diene monomer or conjugates b) are selected from 1,3-butadiene, isoprene and 2,3-butadiene. dimethyl-1,3-butadiene and preferably 1,3-butadiene.

7. Latex copolymer (s) according to any one of claims 1 to 6, characterized in that the acrylic monomer or monomers c) are selected from acrylic acid, methacrylic acid, (meth) acrylates. alkyl, hydroxyalkyl and / or alkoxyalkyl (meth) acrylates wherein the alkyl group (n-alkyl, / -sat-alkyl or alkyl-ferf) has from 1 to 20 carbon atoms of alkyl and is optionally substituted by at least one epoxy, amine, amide group, and / or at least one amino group; the reaction product of (meth) acrylic acid with glycidyl ester, a neoacid such as versatic acids, neodecanoic acids, pivalic acid and mixtures thereof, and preferably acrylic acid, methacrylic acid , butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate.

8. Latex copolymer (s) according to any one of claims 1 to 7, characterized in that the average diameter of the latex particles, measured by light scattering, is between 50 and 200 nm.

9. A method of manufacturing a copolymer latex (s) according to any one of the preceding claims, from:

A / from 10% by weight to 80% by weight of one or more vinyl monomers a); B / from 20% by weight to 70% by weight of one or more conjugated diene monomers b);

D / at least one chain transfer agent (CTA) represented by the formula: wherein R and Z are as defined in claim 1, at temperatures of 0 ^° C to 130 ^° C, preferably 20 ^° C to 130 ^° C, more preferably 60 ^° C to 130 ^° C, particularly preferably 60 ^° C. to 100 ° C. and more particularly from 75 ° C. to 100 ° C., in the presence of one or more emulsifiers or surfactants and / or of a plurality of initiators and / or of one or more protective colloids and / or one or more agents such as antifoaming agents, wetting agents, thickeners, plasticizers, fillers, pigments, crosslinking agents, antioxidants and metal chelating agents.

10. Use of the copolymer latex (s) as defined above for coating paper and paperboard, preferably comprising styrene, butadiene, acrylic acid and DBTTC as chain transfer agent.