Water-based latex of vinylidene chloride copolymer

Abstract

An aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)], wherein the copolymer (A) is - repeat units derived from vinylidene chloride (VDC) in an amount constituting 89.0 to 91.0% by weight of the copolymer; - repeat units derived from methacrylonitrile (MAN) in an amount constituting 2.00 to 5.50% by weight of the copolymer; - repeat units derived from at least one ionic comonomer (ICO) in an amount constituting 0.5 to 1.4% by weight of the copolymer (A), and - repeating units derived from methyl methacrylate (MMA) in an amount such that the sum of repeating units of VDC, MAN, ICO and MMA is 100% by weight and wherein the latex (L) comprises at least one surfactant [surfactant (S)] in an amount constituting 0.09 to 1.50% by weight of the copolymer (A). A process for producing an aqueous latex (L), a film produced therefrom, and a retort pouch prepared with such a film.

Description

[Technical Field]

[0001] This application claims priority to European Patent Application No. 19315171.9, filed December 20, 2019, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to aqueous latexes of vinylidene chloride copolymers, processes for making such latexes, films made therefrom, and retort pouches prepared with such films.

[0003] One of the main applications of aqueous latexes of vinylidene chloride copolymers (PVDC) is the preparation of films for food packaging in order to reach suitable water vapor and oxygen permeabilities.

[0004] Pasteurization and sterilization are often used to enhance food preservation. These processes involve the use of water or steam, and often, disappointingly, whitening is observed during pasteurization or sterilization of packaging containing PVDC film.

[0005] Therefore, there remains a need to provide aqueous PVDC latexes that can lead to the preparation of films that exhibit reduced whitening after pasteurization or sterilization. It is also important that these films are still characterized by adequate water vapor and oxygen permeabilities to provide a sufficient level of food protection.

[0006] One subject of the present invention is therefore an aqueous latex of vinylidene chloride copolymer that does not exhibit the disadvantages of the prior art latexes while retaining their advantages.

[0007] First, one subject of the present invention is an aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)], wherein the copolymer (A) is - repeat units derived from vinylidene chloride (VDC) in an amount constituting 89.0 to 91.0% by weight of the copolymer; - repeat units derived from methacrylonitrile (MAN) in an amount constituting 2.00 to 5.50% by weight of the copolymer; - repeat units derived from at least one ionic comonomer (ICO) in an amount constituting 0.5 to 1.4% by weight of the copolymer (A), and - repeating units derived from methyl methacrylate (MMA) in an amount such that the sum of repeating units of VDC, MAN, ICO and MMA is 100% by weight and the latex (L) contains at least one surfactant [surfactant (S)] in an amount constituting 0.09 to 1.50% by weight of the copolymer (A).

[0008] For the purposes of the present invention, the expression "aqueous latex [latex (L)] of vinylidene chloride copolymer [copolymer (A)]" is understood to mean an aqueous dispersion of copolymer (A) in water.

[0009] For the purposes of the present invention, the term "consisting essentially of" the above repeating units is understood to mean that any additional repeating units different from the above repeating units may be present in copolymer (A) in an amount advantageously of up to 1 mol %, preferably up to 0.25 mol %, and most preferably up to 0.5 mol %, compared to the total number of moles of repeating units in copolymer (A), and in such an amount as not to substantially alter the advantageous properties of copolymer (A).

[0010] If present in copolymer (A), the additional repeat units have the general formula: CH2=CR1R2 (wherein R1 is selected from hydrogen and a methyl group; R2 is selected from a -CN group and a -CO-R3 group; where R3 is selected from an OH group, an -O-R4 group; where R4 is selected from a linear or branched alkyl group containing 2 to 18 carbon atoms and optionally having one or more -OH groups, an epoxyalkyl group containing 2 to 10 carbon atoms, and an alkoxyalkyl group containing a total of 2 to 10 carbon atoms; and finally R3 is also selected from a -NR5R6 group; where R5 and R6, which may be the same or different, are selected from hydrogen and an alkyl group containing 1 to 10 carbon atoms and optionally having one or more -OH groups).

[0011] Preferably, if present in copolymer (A), the additional repeat units are those of methyl acrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, acrylamide and N-methylolacrylamide.

[0012] More preferably, if present in copolymer (A), the additional repeat units are of acrylonitrile, acrylic acid or n-butyl acrylate.

[0013] Copolymer (A) consists essentially of repeat units derived from vinylidene chloride (VDC) in particular in an amount constituting 89.0 to 91.0% by weight of copolymer (A).

[0014] Copolymer (A) consists essentially of repeat units derived from vinylidene chloride (VDC), in particular in an amount of at least 89.0% by weight of copolymer (A), preferably at least 89.2% by weight, more preferably at least 89.5% by weight, and most preferably at least 90.0% by weight.

[0015] Copolymer (A) consists essentially of repeat units derived from vinylidene chloride (VDC), in particular in an amount of at most 91.0%, preferably at most 90.8%, and more preferably at most 90.6% by weight of copolymer (A).

[0016] Copolymer (A) consists essentially of repeating units derived from methacrylonitrile (MAN) in particular in an amount constituting 2.00 to 5.50% by weight of the copolymer of copolymer (A).

[0017] Copolymer (A) consists essentially of repeat units derived from methacrylonitrile (MAN), in particular in an amount of at least 2.00%, preferably at least 2.20%, more preferably at least 2.50%, and most preferably at least 2.80% by weight of copolymer (A).

[0018] Copolymer (A) consists essentially of repeat units derived from methacrylonitrile (MAN), in particular in an amount of at most 5.50%, preferably at most 5.25%, more preferably at most 5.00% by weight of copolymer (A).

[0019] The copolymer (A) in particular consists essentially of repeat units derived from at least one ionic comonomer (ICO).

[0020] "At least" means, according to the invention, that the copolymer (A) consists essentially of repeat units derived in particular from one or more ionic comonomers (ICO). Preferably, the copolymer (A) consists essentially of repeat units derived in particular from one ionic comonomer (ICO).

[0021] The ionic comonomer (ICO) is advantageously chosen from 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt, 2-sulfoethyl sodium methacrylate, 4-vinylbenzenesulfonate sodium (also called styrene-4-sulfonic acid sodium salt) and mixtures thereof.

[0022] The ionic comonomer (ICO) is preferably selected from 2-acrylamido-2-methylpropanesulfonic acid sodium salt, 4-vinylbenzenesulfonic acid sodium salt (also called styrene-4-sulfonic acid sodium salt), and mixtures thereof.

[0023] The ionic comonomer (ICO) is more preferably selected from 2-acrylamido-2-methylpropanesulfonic acid sodium salt and 4-vinylbenzenesulfonic acid sodium salt (also called styrene-4-sulfonic acid sodium salt).

[0024] When the latex (L) is used to prepare a film or a retort pouch used for packaging food that is subjected to pasteurization, a latex (L) of a copolymer (A) consisting essentially of repeating units derived from 2-acrylamido-2-methylpropanesulfonic acid sodium salt is more particularly preferred.

[0025] More particularly preferred are latexes (L) of copolymers (A) consisting essentially of repeating units derived from ionic comonomers selected from 2-acrylamido-2-methylpropanesulfonic acid sodium salt and sodium 4-vinylbenzenesulfonate (also called styrene-4-sulfonic acid sodium salt), especially when the latex (L) is used to prepare films or retort pouches used for food packaging that undergo sterilization.

[0026] The copolymer (A) consists essentially of repeat units derived from at least one ionic comonomer (ICO) in an amount that constitutes, in particular, 0.5 to 1.4% by weight of the copolymer (A).

[0027] The copolymer (A) consists essentially of repeat units derived from at least one ionic comonomer (ICO), in particular in an amount of at least 0.5%, preferably at least 0.6%, more preferably at least 0.7% and most preferably at most 0.8% by weight of the copolymer (A).

[0028] The copolymer (A) consists essentially of repeat units derived from at least one ionic comonomer (ICO), in particular in an amount of at most 1.4%, preferably at most 1.2%, and more preferably at most 1.1% by weight of the copolymer (A).

[0029] Copolymer (A) consists essentially of repeating units derived in particular from methyl methacrylate (MMA) in an amount such that the sum of the repeating units of VDC, MAN, ICO and MMA is 100% by weight.

[0030] The latex (L) contains at least one surfactant [surfactant (S)] in an amount constituting 0.09 to 1.50% by weight of the copolymer (A).

[0031] "At least one surfactant (S)" means that the latex can contain one or more surfactants (S).

[0032] In the remainder of this specification, unless expressly stated otherwise, the expression "surfactant (S)" used in the singular or plural shall be understood to refer to one or more surfactants (S).

[0033] The surfactant (S) can be an anionic surfactant or a nonionic surfactant.

[0034] Among the anionic surfactants, but not limited to, are alkyl sulfates, such as sodium lauryl sulfate; alkyl sulfonates, such as n-alkyl-(C 10 ~C 13 ) Sodium benzenesulfonate and sodium 1-hexadecanesulfonate in their pure form, also known as paraffin sulfonates C 12 ~C 20 In the form of a mixture of alkyl sulfonates; alkylaryl monosulfonates or disulfonates; alkylaryloxide disulfonates, for example, branched alkyl-(C 12 ) sodium diphenyloxide disulfate; and dialkyl sulfosuccinates such as sodium diethylhexyl sulfosuccinate and sodium dihexyl sulfosuccinate.

[0035] Among the nonionic surfactants, mention may be made, but is not limited to, alkyl or alkylaryl ethoxylated derivatives, alkyl or alkylaryl propoxylated derivatives, and sugar esters or sugar ethers.

[0036] The surfactant (S) is preferably an anionic surfactant, optionally in a mixture with one or more nonionic emulsifiers. Anionic surfactants are particularly preferred.

[0037] The latex (L) comprises at least one surfactant [surfactant (S)] in an amount of at least 0.09% by weight of the copolymer (A), preferably at least 0.10% by weight, more preferably at least 0.12% by weight, especially more preferably at least 0.15% by weight, most preferably at least 0.17% by weight, and especially most preferably at least 0.20% by weight.

[0038] The latex (L) comprises at least one surfactant [surfactant (S)] in an amount of at most 1.50% by weight of the copolymer (A), preferably at most 1.40% by weight, more preferably at most 1.30% by weight, especially more preferably at most 1.20% by weight, most preferably at most 1.10% by weight, and especially most preferably at most 1.00% by weight.

[0039] The latex (L) advantageously comprises two surfactants, preferably two anionic surfactants, more preferably an alkyl sulfonate and an alkylaryloxydisulfonate, most preferably an n-alkyl-(C 10 ~C 13 ) Sodium benzenesulfonate and branched alkyl-(C 12 ) Sodium diphenyloxide disulfate.

[0040] First, one subject of the present invention is an aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)], wherein the copolymer (A) is - repeat units derived from vinylidene chloride (VDC) in an amount constituting 89.2 to 90.8% by weight of the copolymer; - repeat units derived from methacrylonitrile (MAN) in an amount constituting 2.20 to 5.25% by weight of the copolymer; - repeat units derived from at least one ionic comonomer (ICO) in an amount constituting 0.6 to 1.2% by weight of the copolymer (A), and - repeating units derived from methyl methacrylate (MMA) in an amount such that the sum of repeating units of VDC, MAN, ICO and MMA is 100% by weight and the latex (L) contains at least one surfactant [surfactant (S)] in an amount constituting 0.10 to 1.40% by weight of the copolymer (A).

[0041] The aqueous latex [latex (L)] of the vinylidene chloride copolymer [copolymer (A)] according to the invention, wherein the copolymer (A) is advantageously - repeat units derived from vinylidene chloride (VDC) in an amount constituting 89.0 to 91.0% by weight of the copolymer; - repeat units derived from methacrylonitrile (MAN) in an amount constituting 2.00 to 5.50% by weight of the copolymer; - repeat units derived from at least one ionic comonomer (ICO) in an amount constituting 0.5 to 1.4% by weight of the copolymer (A), and - repeating units derived from methyl methacrylate (MMA) in an amount such that the sum of repeating units of VDC, MAN, ICO and MMA is 100% by weight and the latex (L) contains at least one surfactant [surfactant (S)] in an amount constituting 0.09 to 1.50% by weight of the copolymer (A).

[0042] For the purposes of the present invention, it is understood that the term "consisting of" the above repeating units means that no additional repeating units different from the above repeating units can be present in the copolymer (A).

[0043] The preferences defined above when copolymer (A) consists essentially of repeating units as defined above also apply when copolymer (A) consists of repeating units as defined above.

[0044] The aqueous latex according to the invention [latex (L)] is advantageously characterized by a solids content of at least 40% by weight, and preferably at least 42% by weight. The aqueous latex [latex (L)] is advantageously characterized by a solids content of at most 50% by weight, and preferably at most 48% by weight. The aqueous latex according to the invention [latex (L)] is more preferably characterized by a solids content of 44 to 46% by weight.

[0045] The individual polymer particles in the aqueous latex [latex (L)] advantageously have a z-average particle diameter (D) of at least 120 nm, preferably at least 130 nm, and more preferably at least 140 nm, measured by Dynamic Light Scattering (DLS) as described in the experimental section. z They advantageously have an average diameter of at most 300 nm, preferably at most 200 nm, more preferably at most 160 nm.

[0046] The aqueous latexes according to the invention [latex (L)] are advantageously characterized by a surface tension of at least 48 mN / m, preferably at least 49 mN / m and more preferably at least 50 mN / m, measured by the Wilhelmy rate method as described in the experimental section. They advantageously have a surface tension of at most 65 mN / m, preferably at most 63 mN / m, more preferably at most 60 mN / m and most preferably at most 55 mN / m.

[0047] The subject of the present invention is then a process for the preparation of an aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)] according to the invention, characterized in that VDC, MAN, at least one ICO and MMA are polymerized by radical polymerization in aqueous emulsion in the presence of at least one surfactant (S) to obtain a latex (L) of copolymer (A).

[0048] The expression "radical polymerization in aqueous emulsion" is understood according to the present invention to mean any radical polymerization process carried out in an aqueous medium in the presence of at least one surfactant and at least one radical generator. This definition includes in particular the so-called "conventional" polymerization in aqueous emulsion, in which a water-soluble radical generator is used, and also polymerization in microsuspension, also called polymerization in homogenized aqueous dispersion, in which an oil-soluble radical generator is used and an emulsion of monomer droplets is prepared by vigorous mechanical stirring and in the presence of a surfactant.

[0049] The present invention is particularly suitable for so-called "conventional" polymerizations in aqueous emulsion carried out under conditions known to those skilled in the art, i.e., polymerizations carried out with the intervention of surfactants and water-soluble radical generators.

[0050] The process for producing the latex (L) according to the invention advantageously uses at least one radical generator and at least one surfactant (S).

[0051] The expression "at least one radical generator" is understood to mean that, according to the present invention, the manufacturing process of the latex (L) may use one or more radical generators.

[0052] In the remainder of the text, the expression "radical generators" used in the singular or plural should be understood to refer to one or more radical generators, unless otherwise indicated.

[0053] The radical generator is advantageously water-soluble. The expression "water-soluble radical generator" is understood according to the invention to mean a radical generator that is soluble in water.

[0054] The radical generator is advantageously selected from water-soluble diazo compounds, water-soluble peroxides, and redox systems combining a water-soluble peroxide with a reducing agent.

[0055] Examples of water-soluble diazo compounds may include: - 2-(azocarbamoyl)isobutyronitrile; - 4,4'-azobis(4-cyanovaleric acid); - ammonium 4,4'-azobis(4-cyanovalerate); - sodium 4,4'-azobis(4-cyanovalerate); - potassium 4,4'-azobis(4-cyanovalerate); - 2,2'-azobis(N,N'-dimethyleneisobutylamidine); - 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride; - 2,2'-azobis(2-amidinopropane) dihydrochloride; - 2,2'-azobis[2-methyl-N-(1,1-bis(hydroxymethyl)-2-hydroxyethyl)propionamide]; - 2,2'-azobis[2-methyl-N-(1,1-bis(hydroxymethyl)ethyl)propionamide]; 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]; and - 2,2'-Azobis(isobutyramide) dihydrate.

[0056] 4,4'-Azobis(4-cyanovaleric acid), ammonium 4,4'-azobis(4-cyanovalerate), sodium 4,4'-azobis(4-cyanovalerate) and potassium 4,4'-azobis(4-cyanovalerate) are preferred.

[0057] Examples of oil-soluble peroxides may include: inorganic peroxides, such as sodium, potassium and ammonium persulfates; - tert-butyl hydroperoxide; - hydrogen peroxide; and - Perborate.

[0058] Water-soluble peroxides are preferred. Among these, alkali metal persulfates such as sodium persulfate and potassium persulfate, ammonium persulfate, and hydrogen peroxide are particularly preferred. Alkali metal persulfates and ammonium persulfate are even more particularly preferred.

[0059] Examples of the water-soluble peroxide that constitutes the redox system may include the water-soluble peroxides described above. Examples of the reducing agent that constitutes the redox system may include alkali metal sulfites, alkali metal metabisulfites, ascorbic acid, and sodium salts of organic sulfinic acid derivatives, such as the disodium salt of 2-hydroxy-2-sulfinato-acetic acid, or mixtures containing the same (e.g., the products BRUGGOLITE® FF7 and BRUGGOLITE® FF6M).

[0060] Preferred redox systems are alkali metal or ammonium persulfate / alkali metal sulfite, alkali metal or ammonium persulfate / alkali metal metabisulfite, alkali metal or ammonium persulfate / ascorbic acid, alkali metal or ammonium persulfate / disodium salt of 2-hydroxy-2-sulfinato-acetic acid, hydrogen peroxide / ascorbic acid, hydrogen peroxide / ferrous sulfate, hydrogen peroxide / disodium salt of 2-hydroxy-2-sulfinato-acetic acid, and t-butyl hydroperoxide / sulfoxylate systems. Sodium sulfite and sodium metabisulfite are particularly preferred among the alkali metal sulfites and alkali metal metabisulfites, respectively.

[0061] Particularly preferably, the process for producing latex (L) according to the invention uses a single water-soluble radical generator, which is particularly preferably selected from alkali metal persulfates, ammonium persulfates, hydrogen peroxide, and the alkali metal or ammonium persulfates / sodium sulfite, alkali metal or ammonium persulfates / sodium metabisulfite, alkali metal or ammonium persulfates / ascorbic acid, alkali metal or ammonium persulfates / disodium salt of 2-hydroxy-2-sulfinato-acetic acid, hydrogen peroxide / disodium salt of 2-hydroxy-2-sulfinato-acetic acid, and hydrogen peroxide / ascorbic acid redox systems.

[0062] Optionally, at the end of the polymerization, an oil-soluble radical generator (soluble in the monomer) may also be added.

[0063] Preferably, one portion of the radical generator is introduced at the beginning and the other portion at a later point in time.

[0064] If the introduction occurs at a later time point, it can be done continuously or as a single infusion.

[0065] The expression "continuous introduction" is understood to mean that the introduction is carried out over a specific period of time rather than in a single injection at a given time, preferably at a specific rate, particularly preferably at a constant specific rate.

[0066] The process for producing an aqueous latex [latex (L)] according to the present invention is characterized in that VDC, MAN, at least one ICO and MMA are polymerized by radical polymerization in an aqueous emulsion in the presence of at least one surfactant (S).

[0067] The expression "at least one surfactant (S)" is understood to mean that, according to the present invention, the manufacturing process of the latex (L) may use one or more surfactants (S).

[0068] Preferably, one part of the surfactant (S) is introduced at the beginning and the other part at a later point in time.

[0069] If the introduction is carried out at a later time point, it is preferably carried out sequentially, according to sequential introduction as defined above.

[0070] According to the process for preparing the latex (L) according to the invention, the monomers (ie VDC, MAN, ICO and MMA) may be introduced into the polymerization medium in several different ways and in different forms.

[0071] Thus, according to a first variant, some monomers are introduced in one go at the beginning and other monomers are introduced at a later point in time, either in one go or successively.

[0072] According to a second variant, the monomers are introduced all at once at the start.

[0073] According to a third variant, the monomers are all introduced successively at a later point in time.

[0074] According to a fourth variant, a portion of the total monomer is introduced at the beginning and the remainder at a later time, either once or continuously.

[0075] The monomers may be introduced individually (neat or in the form of an emulsion) or after blending (the blend being introduced neat or in the form of an emulsion).

[0076] Preferably, after reaction of the contents of the reactor by heating the contents of the reactor until the degree of conversion of the monomers is advantageously at least 82%, preferably up to 100%, a latex (L) of copolymer (A) is advantageously obtained.

[0077] The temperature at which the contents of the reactor are reacted is advantageously at least 30° C., preferably at least 40° C. In addition, it is advantageously at most 200° C., preferably at most 120° C.

[0078] Before use, the resulting latex is then advantageously stripped of residual monomers. Stripping can be carried out by stripping under vacuum or by stripping under vacuum and simultaneously injecting steam into the latex. Preferably, stripping is carried out by stripping under vacuum and simultaneously injecting steam into the latex.

[0079] In the process according to the invention, the polymerization is advantageously carried out in the presence of a seed latex (seed latex (SL)).

[0080] The term "seed latex (SL)" is understood to mean, according to the invention, a latex characterized in that it can be used as a base for producing at least one other latex, and in particular that it is advantageously characterized by the fact that it absorbs the organic phase sufficiently and prevents the formation of parasitic particle clusters.

[0081] In the process according to the invention, the polymerization is preferably carried out in the presence of a methyl methacrylate polymer seed latex [PMMA seed latex].

[0082] The expression "in the presence" is understood to mean that a seed latex (SL), preferably a PMMA seed latex, is present in the polymerization medium when carrying out the polymerization according to the present invention. It is not excluded that a small amount of seed latex (SL), preferably a PMMA seed latex, may be added at a later time, but it is preferred that all of the seed latex (SL), preferably all of the PMMA seed latex, is present when the reactor contents are reacted. Particularly preferably, all of the seed latex (SL), preferably the PMMA seed latex, is introduced at the beginning and is therefore present when the reactor contents are reacted.

[0083] It is understood that the expression "at the start" means with the initial charge.

[0084] It is understood that the expression "later" means that the introduction begins after the initial charge has been introduced to initiate the polymerization reaction.

[0085] According to the process for producing the latex (L) according to the invention, the polymerization is carried out in the presence of advantageously at most 3% by weight, preferably at most 2.5% by weight, particularly preferably at most 2% by weight, more particularly preferably at most 1.5% by weight, and most particularly preferably at most 1.3% by weight of the dry matter of the seed latex (SL), preferably a PMMA seed latex, expressed relative to the total weight of the monomers (VDC, MAN, MMA and ICO).

[0086] The seed latex (SL), preferably a PMMA seed latex, can be prepared by any process.

[0087] Advantageously, the PMMA seed latex is prepared by radical polymerization in the presence of (a) an aqueous emulsion of methyl methacrylate (MMA) and optionally at least one comonomer, (b) at least one radical generator, (c) at least one surfactant [surfactant (S')] in a total amount of at least 4 wt. % relative to the total weight of (a), and (d) water, which comprises the following steps: (1) introducing at least a portion of (b), at least 2.5 wt. % of (c) based on the total weight of (a), at least a portion of (d), and optionally at least a portion of (a) into a reactor; and then (2) reacting the contents of the reactor while continuously introducing the remainder of (a), (b), (c), and (d) therein; and (3) PMMA seed latex is obtained and isolated.

[0088] The expression "radical polymerization in aqueous emulsion" is defined above, and the preferences defined above also apply to the process for preparing the PMMA seed latex.

[0089] The polymerization is preferably carried out by introducing into a reactor at least a portion of (b), at least 2.5% by weight of (c), based on the total weight of (a), at least a portion of (d), and optionally at least a portion of (a), and then reacting the contents of the reactor while successively introducing therein the remainders of (a), (b), (c), and (d), and then obtaining and isolating a PMMA seed latex.

[0090] The PMMA seed latex is advantageously characterized by a solids content of at least 25% by weight, preferably at least 30% by weight, and more preferably at least 32% by weight. The PMMA seed latex is advantageously characterized by a solids content of at most 40% by weight, and preferably at most 35% by weight.

[0091] The PMMA seed latex is more preferably characterized by a solids content of 32-35% by weight.

[0092] The individual polymer particles in the PMMA seed latex advantageously have a z-average particle diameter (D) as measured by Dynamic Light Scattering (DLS) as described in the Experimental Section of at least 25 nm, preferably at least 28 nm, and more preferably at least 30 nm. z They advantageously have an average diameter of at most 42 nm, preferably at most 40 nm and more preferably at most 38 nm.

[0093] The expression "methyl methacrylate polymer or PMMA" is understood to mean both the homopolymer of methyl methacrylate (MMA) and the copolymers which it forms as the main monomer with at least one comonomer which is copolymerizable with MMA.

[0094] The expression "major monomer" for an MMA polymer is understood to mean a monomer that is present in an amount of at least 100 / n% by weight of the monomer blend and that forms at least 100 / n% by weight of the monomer units of the resulting polymer, where n is the number of monomers in the monomer blend.

[0095] Particularly preferred MMA copolymers are those containing MMA in an amount of at least 100% by weight and, as copolymerizable monomers, vinyl chloride, vinylidene chloride and / or copolymers of the general formula: CH2=CR1R2 (wherein R1 is selected from hydrogen and a methyl group; R2 is selected from a -CN group and a -CO-R3 group; where R3 is selected from an OH group, an -O-R4 group; where R4 is selected from a linear or branched alkyl group containing 2 to 18 carbon atoms and optionally having one or more -OH groups, an epoxyalkyl group containing 2 to 10 carbon atoms, and an alkoxyalkyl group containing a total of 2 to 10 carbon atoms; and finally R3 is also selected from a -NR5R6 group; where R5 and R6, which may be the same or different, are selected from hydrogen and an alkyl group containing 1 to 10 carbon atoms and optionally having one or more -OH groups).

[0096] More particularly preferred MMA copolymers are those which contain as copolymerizable monomers vinyl chloride, vinylidene chloride, and / or the (meth)acrylic monomers methyl acrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, acrylamide and N-methylolacrylamide.

[0097] Comonomers copolymerizable with MMA are preferably not used. Therefore, the process for preparing PMMA seed latex by radical polymerization in aqueous emulsion preferably uses methyl methacrylate. Therefore, the PMMA seed latex is preferably a seed latex of MMA homopolymer.

[0098] According to step (1) of the process for preparing the PMMA seed latex, optionally at least a portion of (a) is introduced into a reactor.

[0099] When at least a portion of (a) is introduced in step (1), preferably at least 1% by weight of the total of (a), particularly preferably at least 2.5%, even more particularly preferably at least 5%, and most particularly preferably at least 8% is introduced in step (1).

[0100] When at least a portion of (a) is introduced in step (1), preferably up to 30% by weight of the total of (a), particularly preferably up to 25%, even more particularly preferably up to 20%, and most particularly preferably up to 15% is introduced in step (1).

[0101] Good results were obtained by not introducing a portion of (a) in step (1) and continuously introducing the entirety of (a) in step (2), or by introducing about 10% by weight of the total amount of (a) in step (1) and the remainder in step (2).

[0102] The process for preparing the PMMA seed latex advantageously uses at least one radical generator.

[0103] It is understood that the expression "at least one radical generator" means that one or more radical generators may be used in the process of preparing the PMMA seed latex.

[0104] Preferably, a single radical generator is used. In the remainder of the text, the expression "radical generator" used in the singular or plural is understood to mean one or more radical generators, unless otherwise indicated.

[0105] The radical generator is advantageously water-soluble, as defined above.

[0106] The radical generator is advantageously chosen from water-soluble diazo compounds and water-soluble peroxides, examples of which are given above.

[0107] Water-soluble peroxides are preferred. Among these, alkali metal persulfates such as sodium persulfate and potassium persulfate, ammonium persulfate, and hydrogen peroxide are particularly preferred. Alkali metal persulfates and ammonium persulfate are even more particularly preferred.

[0108] In a particularly preferred manner, the process for preparing a PMMA seed latex by radical polymerization in aqueous emulsion uses a single radical generator (b), which is selected from alkali metal persulfates and ammonium persulfate.

[0109] According to step (1) of the process for preparing the PMMA seed latex, at least a portion of (b) is introduced into a reactor.

[0110] Preferably at least 50% by weight of the total of (a) is introduced in step (1), particularly preferably at least 60%, further particularly preferably at least 65%, and most particularly preferably at least 70%.

[0111] The process for preparing the PMMA seed latex advantageously uses at least 4% by weight of at least one surfactant (S') in total, relative to the total weight of (c)(a).

[0112] It is understood that the expression "at least one surfactant (S')" means that one or more surfactants (S') may be used in the preparation process of the PMMA seed latex.

[0113] Preferably, a single surfactant (S') is used. In the remainder of the text, the expression "surfactant (S')" used in the singular or plural form should be understood to mean one or more surfactants (S'), unless otherwise indicated.

[0114] The surfactant (S') can be an anionic surfactant or a nonionic surfactant. Examples of anionic and nonionic surfactants are the same as those given above for the surfactant (S).

[0115] The surfactant (S') is preferably an anionic surfactant, optionally in a mixture with one or more nonionic surfactants. The surfactant (S') is more preferably an anionic surfactant.

[0116] In the process for preparing the PMMA seed latex, advantageously at least 4% by weight, preferably at least 5% by weight, more preferably at least 7% by weight, and most preferably at least 8% by weight of at least one surfactant (S'), preferably a single surfactant (S'), is used in total relative to the total weight of (a).

[0117] In the process for preparing the PMMA seed latex, advantageously at most 20 wt. %, preferably at most 15 wt. %, and most preferably at most 12 wt. % of at least one surfactant (S'), preferably a single surfactant (S'), is used in total relative to the total weight of (a).

[0118] According to step (1) of the process for preparing the PMMA seed latex, at least 2.5% by weight of (c) relative to the total weight of (a) is introduced into the reactor.

[0119] Preferably, at least 3% by weight, more preferably at least 5% by weight, most preferably at least 7% by weight of (c) is introduced in step (1) relative to the total weight of (a).

[0120] Preferably, at most 20% by weight, more preferably at most 15% by weight, most preferably at most 12% by weight of (c) is introduced in step (1), relative to the total weight of (a).

[0121] Preferably, at most 5% by weight, more preferably at most 2.5% by weight of (c) relative to the total weight of (a) is introduced in step (2).

[0122] Good results have been obtained by incorporating all of (c) in step (1), preferably about 10% by weight of (c) relative to the total weight of (a), or by incorporating about 8% by weight of (c) in step (1) relative to the total weight of (a) and about 2% by weight of (c) in step (2) relative to the total weight of (a).

[0123] According to step (1) of the process for preparing the PMMA seed latex, at least a portion of (d) is introduced into a reactor.

[0124] Preferably, at least 70% by weight of all of (d), more preferably at least 75% by weight of all of (d), and most preferably at least 80% by weight of all of (d) is introduced in step (1).

[0125] Thus, advantageously, no reaction occurs during step (1).

[0126] The contents of the reactor are reacted according to step (2) of the process for preparing the PMMA seed latex.

[0127] It is understood that the expression "reacting the reactor contents" means that it is step (2) that initiates the polymerization reaction.

[0128] To react the contents of the reactor according to step (2), a means for generating radicals therein is used. For this purpose, it is particularly possible to heat the contents of the reactor or to expose them to intense light radiation, such as UV or visible light. Preferably, the contents of the reactor are heated.

[0129] The temperature at which the contents of the reactor are reacted is advantageously at least 30° C., preferably at least 40° C. In addition, it is advantageously at most 200° C., preferably at most 120° C.

[0130] The process for preparing the PMMA seed latex is advantageously a continuous process, the expression "continuous process" being understood to mean that at least a portion of one of (a), (b), (c) or (d) is introduced during step (2), as opposed to a batch or discontinuous process in which all of (a), (b), (c) and (d) are introduced in step (1).

[0131] According to step (2), the contents of the reactor are reacted while the remainder of (a), (b), (c) and (d) are continuously introduced thereto, the expression "continuous introduction" being defined above.

[0132] The remainder of (a), (b), (c), and (d) may be introduced singly or as a mixture. Preferably, the remainder of (a), (c), and (d) are introduced as a mixture, and the remainder of (b) is introduced separately from this mixture.

[0133] The process for preparing the PMMA seed latex is preferably carried out in the absence of viscosity reducing agents such as ionic electrolytes.

[0134] Advantageously, step (2) is continued until the MMA and optionally other comonomers have reacted to a certain extent, preferably until the degree of conversion of the MMA and optionally other comonomers is at least 82% and up to 100%.

[0135] According to step (3) of the PMMA seed latex preparation process, a methyl methacrylate polymer seed latex is obtained and isolated.

[0136] Thus, according to step (3), the PMMA seed latex is isolated from the reactor in which it was prepared. The process for preparing the PMMA seed latex is therefore advantageously an ex situ process, i.e. a process in which the seed latex is finally isolated, as opposed to an in situ process in which the seed latex is synthesized in a reactor and then used there for subsequent polymerization.

[0137] The PMMA seed latex may or may not then be stripped of residual monomers prior to use. If stripping is performed, this may be done by stripping under vacuum or by injecting steam into the latex while stripping under vacuum. Preferably, if stripping is performed, it is done by stripping under vacuum.

[0138] According to one particularly preferred variant, the process for preparing the PMMA seed latex is characterized in that it comprises the following steps: (1) introducing into a reactor at least a portion of (b), at least 7 wt. % of (c) based on the total weight of (a), at least 80 wt. % of all of (d), and up to 15 wt. % of all of (a); and (2) reacting the contents of the reactor while continuously introducing the remainder of (a), (b), (c), and (d) therein; and (3) PMMA seed latex is obtained and isolated.

[0139] The aqueous latexes [latexes (L)] of the vinylidene chloride copolymers [copolymers (A)] according to the invention are advantageously applied as coatings on substrates for producing multilayer films.

[0140] Another object of the present invention is therefore the use of an aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)] according to the invention as a coating on a substrate for producing a multilayer film, preferably to be used for food packaging.

[0141] Any process can be used to coat the aqueous latex (L) on the substrate. Non-limiting examples of coating processes are air knife coating and engraved roll coating.

[0142] The substrate can be a polymer substrate, a paper substrate or a regenerated cellulose substrate. The substrate is preferably a polymer substrate.

[0143] Polymer substrates which can be coated with the latex (L) according to the invention are, for example, polyvinyl chloride, polyester (preferably polyethylene terephthalate), polyamide and polypropylene. Polyethylene terephthalate is particularly preferred as the polymer substrate.

[0144] Another object of the present invention is a film, preferably a packaging film, more preferably a food packaging film, and most preferably a flexible food packaging film, prepared with an aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)] according to the present invention.

[0145] The films according to the present invention are preferably used for food packaging, more preferably for retortable food packaging. The films according to the present invention are most preferably used to prepare retort pouches.

[0146] Another object of the invention is a retort pouch prepared with a film according to the invention.

[0147] "Retort pouch", also known as "retortable pouch", refers, in accordance with the present invention, to a type of food packaging that allows for the sterile packaging of a wide range of foods and beverages handled by an aseptic process, and is used as an alternative to traditional industrial canning methods.

[0148] When the film according to the invention is used to prepare a retort pouch, polyethylene terephthalate is particularly preferred as the polymer substrate.

[0149] Retort pouches are generally subjected to pasteurization or sterilization.

[0150] To the extent that the disclosure of any of the patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that a term may become unclear, the statements of this application shall control.

[0151] The present invention will now be described in more detail with reference to the following examples, the purposes of which are merely illustrative and are not intended to limit the scope of the invention.

[0152] Measurement of particle size distribution The z-average particle diameter (D z The particle size and polydispersity were measured by dynamic light scattering (DLS) using a Zetasizer Nano ZS (Malvern Instruments) at 20 °C. To avoid potential particle-particle interference at high concentrations, samples extracted from PMMA seed latex and PVDC latex for DLS measurements were highly diluted (approximately 1000 times diluted) with deionized water.

[0153] surface tension The surface tension of the PVDC latex was measured at 20°C by the Wilhelmy plate method (Kruess device).

[0154] pH measurement The pH of the PVDC latex was measured using a pH meter.

[0155] PVDC Latex Film Production Films were produced using PVDC latex. To do this, a corona treatment was first applied to a PET film. A layer of PVDC approximately 5 μm thick was then coated. After drying, the film was wound up.

[0156] This coating was carried out on a Kroenert line featuring: - Line speed: 100m / min - Corona treatment: 1.5kW; - "reverse" rotation of the etching roll (110%); - Drying temperature=110℃.

[0157] After measuring the thickness of the layer M of the film, measurements of water vapor permeability and oxygen permeability were carried out.

[0158] After coating, the films were placed in the refrigerator.

[0159] Film processing before measurement The films were subjected to accelerated ageing at 40° C. for 2 days and then sterilized or pasteurized under standard field conditions as defined below.

[0160] Sterilization was performed by placing the film in a container containing steam at 120°C for 30 minutes.

[0161] Pasteurization was performed by placing the films in a vessel and immersing them in water heated to 95°C for 2 hours.

[0162] After these treatments, the films were placed in a refrigerator until measurements were taken.

[0163] Prior to measurement, the films were removed from the refrigerator and placed at 23°C and 50% relative humidity for 24 hours.

[0164] Measuring the water vapor permeability of films The water vapor transmission rate (WVTr) of the films prepared as described above was measured according to standard ASTM F-1249 on a Permatran W 3 / 31 machine from Mocon at 38° C. and 90% relative humidity.

[0165] Water vapor permeability is g.μm / m 2 Expressed in .days.

[0166] Water vapor transmission rates were measured on films that had been subjected to accelerated aging at 40°C for 2 days (2D40) and then further sterilized (sterilized) or pasteurized (pasteurized) before measurement.

[0167] Measurement of oxygen permeability of films The principle of the method consists in determining the amount of oxygen that passes through a film made from a vinylidene chloride copolymer latex per unit time and per unit area for a given temperature and relative humidity.

[0168] The machine used was an OX-TRAN1000-H HUMIDICON (Mocon) machine conditioned to either 23°C and 0% relative humidity or 23°C and 85% relative humidity.

[0169] Oxygen permeability (OTr) is cm 3 .μm / m 2 .day.expressed in bars.

[0170] Oxygen permeability was measured on films that had been subjected to accelerated aging at 40°C for 2 days (2D40) and then further sterilized (sterilized) or pasteurized (pasteurized) before measurement.

[0171] Measurement of transparency and haze Clarity and haze were measured according to standard ASTM D 1003, which applies to transparent samples with haze values of 30% or less.

[0172] The principle is that the strength I O The light beam passes through a flat surface of the sample to be analyzed and then enters the integrating sphere. The light is uniformly distributed by the matte white coating on the sphere wall and measured by a detector.

[0173] Haze (H) is a measure of the dispersion of light at large angles and is the light intensity (I) transmitted through a sample outside a solid angle of 5°. H ) and the total light intensity transmitted through the solid (I T) is defined as the ratio between

[0174] Clarity is a measure of the small angle dispersion of light, The light intensity at the center of the annular sensor (I circ ) is subtracted from the light intensity (I center )and, The light intensity at the center of the annular sensor (I circ ) is the light intensity (I center ) is defined as the ratio between

[0175] The equipment used was the HAZE-GARD PLUS 4725 (Type C Illuminant) from BYK GARDNER. This device complies with standard ASTM D 1003.

[0176] Example 1 (according to the invention) - Preparation of PMMA seed latex 8.7 m (agitated at 20 rpm) with cooling circuit 3 A polymerization autoclave was charged with 3908 liters of demineralized water, 14 kg (6.7 g active material per kg of monomer) of powdered ammonium persulfate solution, and 814 liters (100 g active material per kg of monomer of the seed latex) of n-alkyl-(C 10 ~C 13 The autoclave was closed and then subjected to two vacuum operations at an absolute pressure of 140 mbar.

[0177] The stirring speed was then increased to 60 rpm while the mixture was brought to 85° C. Once the temperature reached 84° C., 151 kg (2.87 g activator wax per kg monomer) of a 40 g / L ammonium persulfate solution was added at a constant rate over 3 hours, while 2100 kg of methyl methacrylate was added at a constant rate also over 3 hours.

[0178] After the end of the injection of methyl methacrylate and ammonium persulfate, the polymerization was continued until a temperature difference of less than 5°C was obtained between the temperature of the reaction medium and that of the cooling circuit, followed by 1 hour of post-polymerization, the stirring speed was then reduced to 20 rpm and the latex was degassed and then stripped under vacuum at 65°C for 3 hours.

[0179] The solids content of the PMMA seed latex so polymerized was according to the specification, i.e., 32-35%. The mean diameter of the particles determined by DLS was according to the specification, i.e., 30-38 nm.

[0180] Example 2 (according to the invention) - Polymerization of VDC in aqueous emulsion in the presence of PMMA seed latex prepared in Example 1 A 65 L polymerization autoclave equipped with a cooling circuit was charged with 6.5 L of demineralized water. It was then charged with 793 ml of PMMA seed latex (32.75% solids content) (corresponding to 11 g of dry material per kg of monomer) prepared by the process defined in Example 1 and 135 ml of a 3.7 g / L ascorbic acid solution. The autoclave was subjected to two vacuum operations. The medium stirring speed was 110 rpm. The autoclave was heated to 23°C.

[0181] A 150 l autoclave equipped with a cooling circuit was used as a premixer, to which 18.3 l of demineralized water, 109 ml of branched alkyl-(C 12 ) diphenyloxide disulfate sodium solution, 84 ml of n-alkyl-(C 10 ~C 13) Sodium benzenesulfonate solution, 3.49 L of 30 g / L tetrasodium pyrophosphate solution, and 1.45 L of 180 g / L 2-acrylamido-2-methylpropanesulfonic acid sodium salt were continuously charged. The premixer was subjected to two vacuum operations. The stirring speed of the medium was set to 130 rpm. A mixture of 1.45 kg of methyl methacrylate and 0.785 kg of methacrylonitrile was introduced into the premixer, followed by 23.7 kg of vinylidene chloride. After stirring for 30 minutes, the stirring speed was reduced to 90 rpm.

[0182] The temperature of the reaction medium in the autoclave rose to 60° C. At T=59° C., 340 ml of a 71.3 g / l ammonium persulfate solution was added. The introduction of ammonium persulfate was considered as the start of the polymerization (T o ).

[0183] At To+1 minute, 47.2 kg of monomer emulsion was added from the premixer at a constant rate over 8 hours. o At +1 min, 962 ml of an 11.7 g / l ascorbic acid solution was added at a constant rate over 8 hours and 45 minutes. o At +2 min, 823 ml of a 41.0 g / l ammonium persulfate solution were added at a constant rate over 8 hours 15 minutes. Once a temperature difference of 2°C was obtained between the temperature of the reaction medium and the temperature of the cooling circuit, the latex was postpolymerized for 120 minutes.

[0184] The stirring speed was reduced to 110 rpm, and the latex was then heat degassed and then stripped under vacuum at 60°C (autoclave temperature) for 2 hours. The cooling system temperature was then brought to 60°C. After 2 hours at 60°C (cooling temperature), the stirring speed was increased to 110 rpm. After 6 hours of stripping, the latex was cooled to 20°C and then filtered through a 60 μm filtration pocket. The solids content of the latex was measured and, if necessary, adjusted to 44% to 46% by weight by adding water.

[0185] The properties of the PVDC latex obtained in Example 2 were measured in the manner previously described, and the results are shown in Table 1.

[0186] Films were prepared using the PVDC latex obtained in Example 2. The properties measured on these films in the manner described above are shown in Table 2.

[0187] Example 3 (according to the invention) - Polymerization of VDC in aqueous emulsion in the presence of PMMA seed latex prepared in Example 1 Example 2 was reproduced with the following exceptions. The amount of PMMA seed latex (33.2% solids content) prepared by the process defined in Example 1 was 781 ml (corresponding to 11 g of dry material per kg of monomer); The amount of demineralized water introduced into the premixer was 18.0 l; · 1.45 l of 180 g / l 2-acrylamido-2-methylpropanesulfonic acid sodium salt was replaced with 1.74 l of 150 g / l styrene-4-sulfonic acid sodium salt (also known as sodium 4-vinylbenzenesulfonate) solution; The amount of methyl methacrylate was 1.44 kg; and At To+1 min, 47.17 kg of monomer emulsion was added from the premixer at a constant rate over 8 hours.

[0188] The properties of the PVDC latex obtained in Example 3 were measured in the manner previously described, and the results are shown in Table 1.

[0189] Films were prepared using the PVDC latex obtained in Example 3. The properties measured on these films in the manner described above are shown in Table 2.

[0190] Example 4 (according to the invention) - Polymerization of VDC in aqueous emulsion in the presence of PMMA seed latex prepared in Example 1 Example 2 was reproduced with the following exceptions. The amount of demineralized water introduced into the polymerization autoclave was 6.6 l; The amount of PMMA seed latex (34.0% solids content) prepared by the process defined in Example 1 was 762 ml (corresponding to 11 g of dry material per kg of monomer); The amount of demineralized water introduced into the premixer was 18.5 l; Branched alkyl (C) containing 486 g / l of active ingredient 12 ) The volume of diphenyloxide sodium disulfate solution was 323 ml; n-Alkyl-(C) containing 250g / l of active ingredient 10 ~C 13 ) No sodium benzenesulfonate solution was added. · The amount of 180 g / l 2-acrylamido-2-methylpropanesulfonic acid sodium salt solution was 1.24 l; The amount of methyl methacrylate was 1.48 kg; and At To+1 min, 47.25 kg of monomer emulsion was added from the premixer at a constant rate over 8 hours.

[0191] The properties of the PVDC latex obtained in Example 4 were measured in the manner previously described, and the results are shown in Table 1.

[0192] Films were prepared using the PVDC latex obtained in Example 4. The properties measured on these films in the manner described above are shown in Table 2.

[0193] Example 5 - Polymerization of VDC in aqueous emulsion in the presence of PMMA seed latex prepared in Example 1 Example 2 was reproduced with the following exceptions. The amount of PMMA seed latex (34.0% solids content) prepared by the process defined in Example 1 was 762 ml (corresponding to 11 g of dry material per kg of monomer); The amount of demineralized water introduced into the premixer was 18.4 l; The amount of demineralized water introduced into the polymerization autoclave was 6.6 l; Branched alkyl (C) containing 486 g / l of active ingredient 12 ) The volume of the diphenyloxide sodium disulfate solution was 484 ml; n-Alkyl-(C) containing 250g / l of active ingredient 10 ~C 13 ) No sodium benzenesulfonate solution was added. · The amount of 180 g / l 2-acrylamido-2-methylpropanesulfonic acid sodium salt solution was 1.24 l; The amount of methyl methacrylate was 1.48 kg; and At To+1 min, 47.33 kg of monomer emulsion was added from the premixer at a constant rate over 8 hours.

[0194] The properties of the PVDC latex obtained in Example 5 were measured in the manner previously described, and the results are shown in Table 1.

[0195] Films were prepared using the PVDC latex obtained in Example 5. The properties measured on these films in the manner described above are shown in Table 2.

[0196] Example 6(C) (Comparative) - Polymerization of VDC in Aqueous Emulsion in the Presence of PMMA Seed Latex Prepared in Example 1 Example 2 was reproduced with the following exceptions. The amount of PMMA seed latex (33.2% solids content) prepared by the process defined in Example 1 was 781 ml (corresponding to 11 g of dry material per kg of monomer); The amount of demineralized water introduced into the premixer was 17.6 l; Branched alkyl (C) containing 486 g / l of active ingredient 12 ) The volume of the diphenyloxide sodium disulfate solution was 484 ml; n-Alkyl-(C) containing 250g / l of active ingredient 10 ~C 13) No sodium benzenesulfonate solution was added. · The amount of 180 g / l 2-acrylamido-2-methylpropanesulfonic acid sodium salt was 2.18 l; The amount of methyl methacrylate was 1.3 l; and At To+1 min, 47.33 kg of monomer emulsion was added from the premixer at a constant rate over 8 hours.

[0197] The properties of the PVDC latex obtained in Example 6 were measured in the manner previously described, and the results are shown in Table 1.

[0198] Films were prepared using the PVDC latex obtained in Example 6. The properties measured on these films in the manner described above are shown in Table 2.

[0199] Example 7(C) (Comparative) - Polymerization of VDC in Aqueous Emulsion in the Presence of PMMA Seed Latex Prepared in Example 1 Example 2 was reproduced with the following exceptions. The amount of PMMA seed latex (33.2% solids content) prepared by the process defined in Example 1 was 781 ml (corresponding to 11 g of dry material per kg of monomer); The amount of demineralized water introduced into the premixer was 19.1 l; Branched alkyl (C) containing 486 g / l of active ingredient 12 ) The volume of the diphenyloxide sodium disulfate solution was 1.08 l; n-Alkyl-(C) containing 250g / l of active ingredient 10 ~C 13 ) No sodium benzenesulfonate solution was added. · 180 g / l 2-acrylamido-2-methylpropanesulfonic acid sodium salt solution was not added; · The amount of methyl methacrylate was 1.24 kg; · The amount of methacrylonitrile was 1.29 kg; · The amount of vinylidene chloride was 23.6 kg; · The temperature of the reaction medium increased to 65 ° C; The addition of 340 ml of a 71.3 g / l ammonium persulfate solution was carried out at T=64°C; and At To+1 min, 47.60 kg of monomer emulsion was added from the premixer at a constant rate over 8 hours.

[0200] The properties of the PVDC latex obtained in Example 7 were measured in the manner previously described, and the results are shown in Table 1.

[0201] Films were prepared using the PVDC latex obtained in Example 7. The properties measured on these films in the manner described above are shown in Table 2.

[0202] [Table 1]

[0203] [Table 2]

[0204] Analysis of Table 2 shows that films made with latex according to the present invention exhibit low whitening after pasteurization or sterilization and still feature adequate water vapor and oxygen transmission rates to provide a sufficient level of food protection.

Claims

1. An aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)], The copolymer (A) is repeat units derived from vinylidene chloride (VDC) in an amount constituting 89.0 to 91.0% by weight of said copolymer; repeat units derived from methacrylonitrile (MAN) in an amount constituting from 2.00 to 5.50% by weight of said copolymer; repeat units derived from at least one ionic comonomer (ICO) in an amount constituting from 0.5 to 1.4% by weight of said copolymer (A), and repeating units derived from methyl methacrylate (MMA) in an amount such that the sum of the repeating units VDC, MAN, ICO and MMA is 100% by weight; and the latex (L) comprises at least one surfactant [surfactant (S)] in an amount constituting 0.09 to 1.50% by weight of the copolymer (A), and the ionic comonomer is selected from 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt, 2-sulfoethyl methacrylate sodium, 4-vinylbenzenesulfonate sodium, and mixtures thereof.

2. 2. The aqueous latex (L) according to claim 1, wherein the copolymer (A) consists essentially of repeating units derived from vinylidene chloride (VDC) in an amount of at least 89.2% by weight of the copolymer (A) and at most 90.8% by weight of the copolymer (A).

3. The aqueous latex (L) according to claim 1 or 2, wherein the copolymer (A) essentially consists of repeating units derived from methacrylonitrile (MAN) in an amount of at least 2.20% by weight of the copolymer (A) and at most 5.25% by weight of the copolymer (A).

4. The aqueous latex (L) according to any one of claims 1 to 3, wherein the copolymer (A) consists essentially of repeat units derived from at least one ionic comonomer (ICO) in an amount of at least 0.6% by weight of the copolymer (A) and at most 1.2% by weight of the copolymer (A).

5. 5. The aqueous latex (L) according to claim 1, wherein the latex (L) comprises at least one surfactant [surfactant (S)] in an amount of at least 0.10% by weight of the copolymer (A) and at most 1.40% by weight of the copolymer (A).

6. The copolymer (A) is repeat units derived from vinylidene chloride (VDC) in an amount constituting 89.2 to 90.8% by weight of said copolymer; repeat units derived from methacrylonitrile (MAN) in an amount constituting from 2.20 to 5.25% by weight of said copolymer; repeat units derived from at least one ionic comonomer (ICO) in an amount constituting from 0.6 to 1.2% by weight of said copolymer (A), and repeating units derived from methyl methacrylate (MMA) in an amount such that the sum of the repeating units VDC, MAN, ICO and MMA is 100% by weight; and wherein the latex (L) comprises at least one surfactant [surfactant (S)] in an amount constituting 0.10 to 1.40% by weight of the copolymer (A).

7. 7. A method for producing an aqueous latex (L) according to any one of claims 1 to 6, characterized in that vinylidene chloride (VDC), methacrylonitrile (MAN), at least one ionic comonomer (ICO) and methyl methacrylate (MMA) are polymerized by radical polymerization in aqueous emulsion in the presence of at least one surfactant (S) to obtain the latex (L) of the copolymer (A).

8. 8. The process according to claim 7, characterized in that the polymerization is carried out in the presence of a seed latex [seed latex (SL)].

9. 9. A process according to claim 7 or 8, characterized in that the polymerization is carried out in the presence of a methyl methacrylate polymer seed latex [PMMA seed latex].

10. Use of an aqueous latex (L) according to any one of claims 1 to 6 as a coating on a substrate for producing a multilayer film.

11. A film prepared with the aqueous latex (L) according to any one of claims 1 to 6.

12. The film of claim 11, characterized in that it is used for food packaging.

13. 13. A retort pouch prepared with the film of claim 12.

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