AQUEOUS LATEX OF VINYLIDENE CHLORIDE COPOLYMER

Abstract

Aqueous latex of vinylidene chloride copolymer An aqueous latex [latex (L)] of a vinylidene chloride copolymer [copolymer (A)], wherein the copolymer (A) consists essentially of recurring units derived from vinylidene chloride (VDC) in an amount comprised between 89.0 and 91.0 wt % of the copolymer, recurring units derived from methacrylonitrile (MAN) in an amount comprised between 2.00 and 5.50 wt % of the copolymer, recurring units derived from at least one ionic comonomer (ICO) in an amount comprised between 0.5 and 1.4 wt % of the copolymer (A), and recurring units derived from methylmethacrylate (MMA) in an amount such that the total of recurring units of VDC, MAN, ICO and MMA is 100 wt %, and wherein the latex (L) comprises at least one surfactant [surfactant (S)] in an amount comprised between 0.09 and 1.50 wt % of the copolymer (A).
Process for the manufacture of the aqueous latex (L), film made therefrom and retort pouch prepared with such film.

Claims

1. An aqueous latex (latex(L)) of a vinylidene chloride copolymer (copolymer (A)), wherein the copolymer (A) consists essentially of: recurring units derived from vinylidene chloride (VDC) in an amount comprised between 89.0 and 91.0 wt % of the copolymer(A), recurring units derived from methacrylonitrile (MAN) in an amount comprised between 2.00 and 5.50 wt % of the copolymer(A), recurring units derived from at least one ionic comonomer (ICO) in an amount comprised between 0.5 and 1.4 wt % of the copolymer (A), and recurring units derived from methylmethacrylate (MMA) in an amount such that the total of recurring units of VDC, MAN, ICO and MMA is 100 wt %, and wherein the latex (L) comprises at least one surfactant (surfactant (S)) in an amount comprised between 0.09 and 1.50 wt % of the copolymer (A).

2. The aqueous latex (L) according to claim 1, wherein the recurring units derived from vinylidene chloride (VDC) are present in an amount of at least 89.2 wt % of the copolymer (A), and of at most 90.8 wt % of the copolymer (A).

3. The aqueous latex (L) according to claim 1, wherein the recurring units derived from methacrylonitrile (MAN) are present in an amount of at least 2.20 wt %, of the copolymer (A), and of at most 5.25 wt % of the copolymer (A).

4. The aqueous latex (L) according to claim 1, wherein the recurring units derived from at least one ionic comonomer (ICO) are present in an amount of at least 0.6 wt % of at most 1.2 wt % of the copolymer (A).

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 wt % % of the copolymer (A), and in an amount of at most 1.40 wt % of the copolymer (A).

6. The aqueous latex (L) according to claim 1, wherein the copolymer (A) consists essentially of; recurring units derived from vinylidene chloride (VDC) in an amount comprised between 89.2 and 90.8 wt % of the copolymer, recurring units derived from methacrylonitrile (MAN) in an amount comprised between 2.20 and 5.25 wt % of the copolymer, recurring units derived from at least one ionic comonomer (ICO) in an amount comprised between 0.6 and 1.2 wt % of the copolymer (A), and recurring units derived from methylmethacrylate (MMA) in an amount such that the total of recurring units of VDC, MAN, ICO and MMA is 100 wt %, and wherein the latex (L) comprises at least one surfactant (surfactant (S)) in an amount comprised between 0.10 and 1.40 wt % of the copolymer (A).

7. The aqueous latex (L) according to claim 1, wherein the ionic comonomer is selected from the group consisting of 2-acrylamido-2-methyl-1-propane sulfonic acid sodium salt, sodium 2-sulfoethyl methacrylate, sodium 4-vinylbenzenesulfonate and mixtures thereof.

8. The aqueous latex (L) according to claim 1, wherein the ionic comonomer is selected from the group consisting of 2-acrylamido-2-methylpropane sulfonic acid sodium salt and sodium 4-vinylbenzenesulfonate.

9. A process for the manufacture of the aqueous latex (L) according to claim 1, characterized in that vinylidene chloride (VDC), methacrylonitrile (MAN), at least one ionic comonomer (ICO) and methylmethacrylate (MMA) are polymerized by radical polymerization in aqueous emulsion in the presence of at least one surfactant (S) in order to obtain the latex (L) comprised of the copolymer (A).

10. The process according to claim 9, characterized in that the polymerization takes place in the presence of a seed latex (seed latex (SL).

11. The process according to claim 9, characterized in that the polymerization takes place in the presence of a methyl methacrylate polymer seed latex (PMMA seed latex).

12. A method comprising coating the aqueous latex (L) according to claim 1 on a substrate to produce a multilayer film.

13. A film comprising the aqueous latex (L) according to claim 1.

14. The film according to claim 13, characterized in that it is comprised in food packaging.

15. A retort pouch comprising the film according to claim 14.

16. The aqueous latex (L) according to claim 1, wherein the copolymer (A) consists essentially of recurring units derived from vinylidene chloride (VDC) in an amount of at least 89.5 wt % of the copolymer (A), and of at most 90.6 wt % of the copolymer (A).

17. The aqueous latex (L) according to claim 5, wherein the copolymer (A) consists essentially of recurring units derived from methacrylonitrile (MAN) in an amount of at least 2.50 wt % of the copolymer (A), and of at most 5.00 wt % of the copolymer (A).

18. The aqueous latex (L) according to claim 1, wherein the copolymer (A) consists essentially of recurring units derived from at least one ionic comonomer (ICO) in an amount of at least 0.7 wt % of the copolymer (A), and of at most 1.1 wt % of the copolymer (A).

19. 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 0.12 wt % of the copolymer (A), and in an amount of at most 1.30 wt % of the copolymer (A).

20. The aqueous latex (L) according to claim 1, wherein the aqueous latex (L) is in the form of particles, and wherein the particles have a z-average particle diameter (D.sub.z) of at least 120 nm and of at most 300 nm.

Description

Measurement of the Particle Size Distribution

[0183] The z-average particle diameter (D.sub.z) and the polydispersity of the PMMA seed latex and of the PVDC latexes were measured by Dynamic Light Scattering (DLS) with a Zetasizer Nano ZS (Malvern Instruments) at 20° C. Samples withdrawn from PMMA seed latex and from PVDC latexes for DLS measurements were highly diluted with deionised water (diluted approximatively to 1000 times) in order to avoid interferences between the particles that may happen at high concentration.

Surface Tension

[0184] The surface tension of the PVDC latexes was measured at 20° C. by the Wilhelmy plate method (Kruss device).

Measurement of pH

[0185] The pH of the PVDC latexes was measured with a pH-meter.

Production of films with the PVDC latexes

[0186] Films were produced with the PVDC latexes. In order to do this, a corona treatment was first applied on a PET film. One layer of about 5 pm thick of PVDC was coated on and after drying, the film was rewound.

[0187] This coating was carried out on a Kroenert line with the following characteristics: [0188] line speed: 100 m/min; [0189] corona treatment: 1.5 kW; [0190] “reverse” rotation (110%) of the etched roll; [0191] drying temperature=110° C.

[0192] The thickness of layer M of the film was measured before carrying out the measurement of the water vapour transmission rate and of the oxygen transmission rate.

[0193] After coating, the films were placed in a fridge.

Treatment of the films before measurement

[0194] The films have undergone an accelerated ageing for 2 days at 40° C. and then either a sterilisation or a pasteurisation, under the conditions defined below which are standard conditions in the field.

[0195] Sterilisation took place by placing the films in a vessel containing steam at 120° C. during 30 min.

[0196] Pasteurisation took place by placing the films in a vessel immerging them in water heated at 95° C. during 2 h.

[0197] After these treatments, the films were placed in the fridge until measurement.

[0198] Before measurement, the films were removed from the fridge and placed at 23° C. and 50% relative humidity for 24 h.

Measurement of the water vapour transmission rate of the films

[0199] The water vapour transmission rate (WVTr) of the films prepared as described above, was measured according to the standard ASTM F-1249 on a Permatran W 3/31 machine from Mocon at 38° C. and 90% relative humidity.

[0200] The water vapor transmission rate is expressed in g.um/m.sup.2.day.

[0201] The water vapor transmission rate was measured on films having undergone an accelerated ageing for 2 days at 40° C. (2D40) and then on these films further submitted to a sterilisation (sterilized) or to a pasteurisation (pasteurized) before the measurement.

Measurement of the Oxygen Transmission Rate of the Films

[0202] The principle of the method consists in determining the amount of oxygen which passes through a film made of a vinylidene chloride copolymer latex, per unit time and unit area, for a defined temperature and relative humidity.

[0203] The machine used was an OX-TRAN 1000 - H HUMIDICON (Mocon) machine, conditioned either at 23° C. and 0% relative humidity or at 230 and 85% relative humidity.

[0204] The oxygen transmission rate (OTr) is expressed in cm.sup.3. mm.sup.2.day.bar.

[0205] The oxygen transmission rate was measured on films having undergone an accelerated ageing for 2 days at 40° C. (2D40) and then on these films further submitted to a sterilisation (sterilized) or to a pasteurisation (pasteurized) before the measurement.

Measurement of Clarity and Haze

[0206] The clarity and the haze were measured in conformity with standard ASTM D 1003 applied to transparent samples with a haze value of 30% or less.

[0207] The principle is that a light beam of intensity Io passes through the sample to be analyzed having a flat surface and then enters a sphere of integration. Light uniformly distributed by the matt white coating of the sphere wall is measured by a detector.

[0208] The haze (H) is a measure of the dispersion of the light at large angles and is defined as the ratio between the light intensity transmitted by the sample, outside a solid angle of 5° (IH) and the total light intensity transmitted by the solid (IT).

[0209] The clarity is a measure of the dispersion of the light at small angles and is defined as the ratio between [0210] the light intensity of the circular ring of the annular sensor (I.sub.center) (placed in the outlet orifice) subtracted from the light intensity at the center of the annular sensor (I.sub.circ); and [0211] the light intensity of the circular ring of the annular sensor (I.sub.center) added to the light intensity at the center of the annular sensor (I.sub.circ).

[0212] The equipment used wad apparatus HAZE-GARD PLUS 4725 (Type C Illuminant) from BYK GARDNER. This device is in accordance with standard ASTM D 1003.

Example 1 (According to the Invention) - Preparation of a PMMA Seed Latex

[0213] An 8.7 m.sup.3 polymerization autoclave (stirred at 20 rpm), equipped with a cooling circuit, was successively charged with 3908 1 of demineralized water, 14 kg (6.7 g of active material/kg of monomer) of a powdered ammonium persulfate solution and 8141 (100 g of active material/kg of monomer of the seed latex) of a sodium n-alkyl-(C.sub.10-C.sub.13) benzene sulfonate solution containing 25% of active material. The autoclave was closed then subjected to two vacuum operations at 140 mbar absolute pressure.

[0214] The stirring speed was then increased to 60 rpm while bringing the mixture to 85° C. When the temperature reached 84° C., 2100 kg of methyl methacrylate was added at a constant rate over 3 h while adding 151 kg (2.87 g of active material/kg of monomer) of a 40 g/l ammonium persulfate solution at a constant rate over the same 3 h duration.

[0215] After the end of the methyl methacrylate and ammonium persulfate injections, 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 a post-polymerization of 1 h. The stirring speed was then reduced to 20 rpm and the latex was degassed then stripped under vacuum at 65° C. for 3 h.

[0216] The solid content of the PMMA seed latex thus polymerized was according to the specification i.e. 32-35%. The average diameter of the particles, determined by DLS, was according to the specification i.e. 30-38 nm.

Example 2 (According to the Invention) - Polymerization of VDC in Aqueous Emulsion in the Presence of the PMMA Seed Latex Prepared in Example 1

[0217] A 65 1 polymerization autoclave equipped with a cooling circuit was charged with 6.5 1 of demineralized water. It was then charged with 793 ml of the PMMA seed latex (solid content of 32.75%) prepared according to the process as defined in Example 1 (corresponding to 11 g of dry matter/kg of monomers) and 135 ml of a 3.7 g/l ascorbic acid solution. The autoclave was subjected to two vacuum operations. The stirring speed of the medium was brought to 110 rpm. The autoclave was heated at 23° C.

[0218] A 150 1 autoclave used as premixer, equipped with a cooling circuit, was successively charged with 18.3 1 of demineralized water, 109 ml of a sodium branched alkyl-(C.sub.12) diphenyloxide disulfonate solution containing 486 g/l of active material, 84 ml of a sodium n-alkyl-(Cio-C.sub.13) benzene sulfonate solution containing 25% of active material. 3.49 1 of a tetrasodium pyrophosphate solution at 30 g/l and 1.45 1 of a 2-acrylamido-2-methylpropane sulfonic acid sodium salt solution at 180 g/l. The premixer was subjected to two vacuum operations. The stirring speed of the medium was brought to 130 rpm. A mixture of 1.45 kg of methylmethacrylate and 0.785 kg of methacrylonitrile, then 23.7 kg of vinylidene chloride were introduced in the premixer. After stirring for 30 min, the stirring rate was reduced to 90 rpm.

[0219] The temperature of the reaction medium in the autoclave was raised to 60° C. At T=59° C., 340 ml of a 71.3 g/l ammonium persulfate solution were added. The introduction of ammonium persulfate was taken as the beginning of the polymerization (To).

[0220] At T.sub.o+1 min, 47.2 kg of the monomers emulsion were added from the premixer at a constant rate over 8 h. At To+1 min, 962 ml of a 11.7 g/l ascorbic acid solution were added at a constant rate over 8 h 45 min. At T.sub.o+2 min, 823 ml of a 41.0 g/l ammonium persulfate solution were added at a constant rate over 8 h 15 min. When a temperature difference of 2° C. was obtained between the temperature of the reaction medium and that of the cooling circuit, the latex was post-polymerized for 120 min.

[0221] The stirring speed was reduced to 110 rpm and the latex was then hot-degassed then stripped under vacuum at 60° C. (autoclave temperature) during two hours. Then the temperature of the cooling system was brought to 60° C.

[0222] After two hours at 60° C. (cooling temperature), the stirring speed was increased to 110 rpm. After 6 h of stripping, the latex was cooled to 20° C. and then filtered through a 60 pm filtration pocket. The solid content of the latex was measured and if required adjusted, by addition of water, to be between 44 wt % and 46 wt %.

[0223] The properties of the PVDC latex obtained in Example 2 were measured in the manner described previously. The results are given in Table 1.

[0224] Films were made with the PVDC latex obtained in Example 2. The properties measured on these films in the manner described above, are given in Table 2.

Example 3 (According to the Invention) - Polymerization of VDC in Aqueous Emulsion in the Presence of the PMMA Seed Latex Prepared in Example 1

[0225] Example 2 was reproduced except that [0226] the quantity of a PMMA seed latex (solid content of 33.2%) prepared according to the process as defined in Example 1 was 781 ml (corresponding to 11 g of dry matter/kg of monomers); [0227] the quantity of demineralized water introduced into the premixer was 18.0 1; [0228] the 1.45 1 of a 2-acrylamido-2-methylpropane sulfonic acid sodium salt solution at 180 g/l was replaced by 1.74 1 of a styrene-4-sulfonic acid sodium salt (also called sodium 4-vinylbenzenesulfonate) solution at 150 g/l.; [0229] the quantity of methylmethacrylate was 1.44 kg; and [0230] at To+1 min, 47.17 kg of the monomers emulsion were added from the premixer at a constant rate over 8 h.

[0231] The properties of the PVDC latex obtained in Example 3 were measured in the manner described previously. The results are given in Table 1.

[0232] Films were made with the PVDC latex obtained in Example 3. The properties measured on these films in the manner described above, are given in Table 2.

Example 4 (According to the Invention) - Polymerization of VDC in Aqueous Emulsion in the Presence of the PMMA Seed Latex Prepared in Example 1

[0233] Example 2 was reproduced except that [0234] the quantity of demineralized water introduced into the polymerization autoclave was 6.6 1; [0235] the quantity of the PMMA seed latex (solid content of 34.0%) prepared according to the process as defined in Example 1 was 762 ml (corresponding to 11 g of dry matter/kg of monomers); [0236] the quantity of demineralized water introduced into the premixer was 18.5 1; [0237] the quantity of the sodium branched alkyl-(C.sub.12) diphenyloxide disulfonate solution containing 486 g/l of active material was 323 ml; [0238] no sodium n-alkyl-(C.sub.10-C.sub.13) benzene sulfonate solution containing 250 g/l of active material was added, [0239] the quantity of the 2-acrylamido-2-methylpropane sulfonic acid sodium salt solution at 180 g/l was 1.24 1; [0240] the quantity of methylmethacrylate was 1.48 kg; and [0241] at To+1 min, 47.25 kg of the monomers emulsion were added from the premixer at a constant rate over 8 h.

[0242] The properties of the PVDC latex obtained in Example 4 were measured in the manner described previously. The results are given in Table 1.

[0243] Films were made with the PVDC latex obtained in Example 4. The properties measured on these films in the manner described above, are given in Table 2.

Example 5—Polymerization of VDC in Aqueous Emulsion in the Presence of the PMMA Seed Latex Prepared in Example 1

[0244] Example 2 was reproduced except that [0245] the quantity of the PMMA seed latex (solid content of 34.0%) prepared according to the process as defined in Example 1 was 762 ml (corresponding to 11 g of dry matter/kg of monomers); [0246] the quantity of demineralized water introduced into the premixer was 18.4 1; [0247] the quantity of demineralized water introduced into the polymerization autoclave was 6.6 1; [0248] the quantity of the sodium branched alkyl-(C.sub.12) diphenyloxide disulfonate solution containing 486 g/l of active material was 484 ml; [0249] no sodium n-alkyl-(C.sub.10-C.sub.13) benzene sulfonate containing 250 g/l of active material was added, [0250] the quantity of the 2-acrylamido-2-methylpropane sulfonic acid sodium salt solution at 180 g/l was 1.24 1; [0251] the quantity of methylmethacrylate was 1.48 kg; and [0252] at To+1 min, 47.33 kg of the monomers emulsion were added from the premixer at a constant rate over 8 h.

[0253] The properties of the PVDC latex obtained in Example 5 were measured in the manner described previously. The results are given in Table 1.

[0254] Films were made with the PVDC latex obtained in Example 5. The properties measured on these films in the manner described above, are given in Table 2.

Example 6(C) (Comparative) - Polymerization of VDC in Aqueous Emulsion in the Presence of the PMMA Seed Latex Prepared in Example 1

[0255] Example 2 was reproduced except that [0256] the quantity of the PMMA seed latex (solid content of 33.2%) prepared according to the process as defined in Example 1 was 781 ml (corresponding to 11 g of dry matter/kg of monomers); [0257] the quantity of demineralized water introduced into the premixer was 17.6 1; [0258] the quantity of the sodium branched alkyl-(C.sub.12) diphenyloxide disulfonate solution containing 486 g/l of active material was 484 ml; [0259] no sodium n-alkyl-(Cio-C.sub.13) benzene sulfonate solution containing 250 g/l of active material was added, “the quantity of the 2-acrylamido-2-methylpropane sulfonic acid sodium salt solution at 180 g/l was 2.18 1; [0260] the quantity of methylmethacrylate was 1.31 kg; and [0261] at To+1 min, 47.33 kg of the monomers emulsion were added from the premixer at a constant rate over 8 h.

[0262] The properties of the PVDC latex obtained in Example 6 were measured in the manner described previously. The results are given in Table 1.

[0263] Films were made with the PVDC latex obtained in Example 6. The properties measured on these films in the manner described above, are given in Table 2.

Example 7(C) (Comparative) - Polymerization of VDC in Aqueous Emulsion in the Presence of the PMMA Seed Latex Prepared in Example 1

[0264] Example 2 was reproduced except that the quantity of the PMMA seed latex (solid content of 33.2%) prepared according to the process as defined in Example 1 was 781 ml (corresponding to 11 g of dry matter/kg of monomers); [0265] the quantity of demineralized water introduced into the premixer was 19.11; [0266] the quantity of the sodium branched alkyl-(C.sub.12) diphenyloxide disulfonate solution containing 486 g/l of active material was 1.08 1; [0267] no sodium n-alkyl-(Cio-C.sub.13) benzene sulfonate solution containing 250 g/l of active material was added, [0268] no 2-acrylamido-2-methylpropane sulfonic acid sodium salt solution at 180 g/l was added [0269] the quantity of methylmethacrylate was 1.24 kg; [0270] the quantity of methacrylonitrile was 1.29 kg; [0271] the quantity of vinylidene chloride was 23.6 kg; [0272] the temperature of the reaction medium was raised to 65° C.; [0273] the addition of the 340 ml of the 71.3 g/l ammonium persulfate solution was made at T=64° C.; and [0274] at To+1 min, 47.60 kg of the monomers emulsion were added from the premixer at a constant rate over 8 h.

[0275] The properties of the PVDC latex obtained in Example 7 were measured in the manner described previously. The results are given in Table 1.

[0276] Films were made with the PVDC latex obtained in Example 7. The properties measured on these films in the manner described above, are given in Table 2.

TABLE-US-00001 TABLE 1 Solid content z-average after particle diameter Surface Exam- adjustment if D.sub.z (nm)/ tension ples required (%) polydispersity (mN/m) pH 2 45.03 146/0.022 50.5 2.2 3 44.98 144/0.033 50.4 2.65 4 44.95 144/0.033 54.4 2.3 5 44.91 144/0.065 53.0 2.3  .sub. 6(C) 45.09 155/0.004 51.7 2.3  .sub. 7(C) 44.89 142/0.014 43.1 2.2

TABLE-US-00002 TABLE 2 Treatment before Example Example Example Example Example Example measurement 2 3 4 5 6(C) 7(C) WVTr 2D40 9.2 10.5 8.9 8.2 8.5 8.1 (g .Math. μm/m.sup.2 .Math. day) 2D40 + pasteurized 10.5 11.6 7.8 7.9 9.9 8.7 2D40 + sterilized 9.8 11.4 9.4 9.1 13.2 9.4 OTr 2D40 8.5 8.2 7.7 7.8 8.5 8.4 23° C., 0% HR 2D40 + pasteurized 9.5 10.8 8.1 8.1 11.3 22.2 (cm.sup.3 .Math. μm/m.sup.2 .Math. day .Math. bar) 2D40 + sterilized 8.8 9.9 8.2 8.3 11.7 10.4 OTr 2D40 9.5 15.4 9.3 9.1 12.1 9.9 23° C., 85% HR 2D40 + pasteurized 11.5 21.1 9.2 9.1 16.6 20.5 (cm.sup.3 .Math. μm/m.sup.2 .Math. day .Math. bar) 2D40 + sterilized 12.3 17.8 9.9 9.5 17.7 25.1 Clarity 2D40 n.d. 91.7 93.1 93.2 93.1 90.5 (%) 2D40 + pasteurized n.d. 86.6 92.8 92.5 91.4 89.8 2D40 + sterilized n.d. 90.9 92.4 92.6 90.8 78.3 Haze 2D40 n.d. 5.7 5.4 5.6 5.7 7.2 (%) 2D40 + pasteurized n.d. >30 17.1 19.5 >30 17.1 2D40 + sterilized n.d. 9.6 16.0 17.9 26.4 >30 n.d.: non determined

[0277] From analysis of Table 2, it appears that the films made with latex according to the invention present less whitening after pasteurization or sterilisation and remain characterized by appropriate water vapor permeability and oxygen permeability to provide suffisant level of food protection.