WO2010000734A1

WO2010000734A1 - Liquid thermal pvc stabilizers

Info

Publication number: WO2010000734A1
Application number: PCT/EP2009/058174
Authority: WO
Inventors: Stefano Romagnano; Giuseppe Li Bassi
Original assignee: Lamberti Spa
Priority date: 2008-06-30
Filing date: 2009-06-30
Publication date: 2010-01-07
Also published as: EP2294122A1; RU2010151127A; ITVA20080038A1; CN102076753A

Abstract

PVC thermal liquid stabilizers having no toxicological impact comprising: a) mixed barium and zinc salts of one or more linear or branched aliphatic saturated or unsaturated carboxylic acids containing from 6 to 20 carbon atoms and of one or more aromatic carboxylic acid containing from 8 to 10 carbon atoms, not classified as CRM, wherein the weight ratio of aliphatic acids salts to aromatic acids salts is higher than 3:1; b) one or more organic phosphites of the formula R₁OP(OR₂)OR₃ wherein R₁, R₂ and R₃ are the same or different and each is alkyl containing from 6 to 15 carbon atoms or phenyl or C₁₀-C₂₀ alkylaryl.

Description

LIQUID THERMAL PVC STABILIZERS FIELD OF THE INVENTION

The present invention relates to PVC thermal liquid stabilizers having no toxicological impact and having stabilizing characteristics on plasticized PVC that are similar to those obtained using stabilizers based on components with intrinsic risk of carcinogenicity, reprotoxicity and mutagenicity (CRM). The formulation of a thermal liquid stabilizer for plasticized PVC entails the use of specific mixtures of Ba and Zn salts with lipophilic acids that are compatible with the physico-chemical properties of PVC; the formulation must also give suitable lu brication, when mixed with PVC, to allow its processability by the main technologies which are commonly used (calendaring, injection molding, extrusion and so on) and require the contact between fluid or softened PVC and hot metal devices of the machines. 4-tert-butyl benzoic acid is the main component of these formulations. This acid is now classified as CRM (reprotoxic category: 2). Therefore, the acid and the corresponding salts should not be used in thermal stabilizer formulations, because the PVC finished products containing these chemicals could release them, causing potential serious risks for the public health.

Moreover, the workers involved in preparation of stabilizers and PVC finished products could be chronically exposed to the above mentioned chemicals with potential risks to their health. Therefore, in conventional formulations of PVC liquid thermal stabilizers, the industrial need exists to substitute 4-tert-butyl benzoic acid with acids having α safer profile and suitable characteristics that give similar performance of stability and processability to plasticized PVC. BACKGROUND OF THE ART

The most advanced formulations of thermal liquid stabilizer for plasticized PVC are mainly based on mixtures of salts of Ba/Zn or Ca/Zn based on combinations of long chain aliphatic and aromatic carboxylic acids, organic derivatives of phosphorous and, optionally, high boiling point hydrocarbons and plasticizers used as diluents. Co-stabilizers and other additives, such as antioxidants, lubricants, plasticizers, are added to these mixtures to improve the performances.

The presence of aromatic carboxylic acids is very important because their salts improve the initial colour of the PVC formulations during processing without affecting transparency. Benzoic acid, the simplest aromatic carboxylic acid, can give plate-out problems, mainly in calendaring, due to the poor lipophilicity of its inorganic salts.

On the contrary, 4-tert-butyl benzoic acid has the best physico-chemical characteristics to satisfy the requirements of the technology. U.S. Pat. No 5,880,189 refers to thermal stabilizer compositions that give to PVC films good wettability and adherence to water based inks applied to such films. It discloses that Ba/Zn thermal liquid stabilizers can have good performance when the Ba/Zn salts are based on Cs-Co aromatic carboxylic acids and the weight ratio of the aliphatic carboxylate to the aromatic carboxylate is in the range 3:1 to 1 :3 and preferentially is about 1 :1. Unexpectedly, we have found that even ratios between aliphatic carboxylate and Cs-Co aromatic carboxylate exceeding 3:1 can give to the thermal stabilizer a performance that allow the elimination of 4-tert- butylbenzoic acid from the formulation, without interfering with the thermal stabilizing capacity of the stabilizer and with the PVC processability. SUMMARY OF THE INVENTION One aspect of the present invention is a composition of Ba/Zn liquid stabilizers that does not contain 4-tert-butylbenzoic acid and imparts very good heat stability and processability to PVC, without the drawbacks of benzoic acid and its salts.

In particular, the fundamental components of the formulation of liquid thermal stabilizers are: a) mixed barium and zinc salts of one or more linear or branched aliphatic saturated or unsaturated carboxylic acids containing from 6 to 20 carbon atoms and of one or more aromatic carboxylic acid containing from 8 to 10 carbon atoms, not classified as CRM, wherein the weight ratio of aliphatic acids salts to aromatic acids salts is higher than 3:1 ; b) one or more organic phosphites of the formula RiOP(OR2)OR3 wherein Ri, R2 and R3 are the same or different and each is alkyl containing from 6 to 15 carbon atoms or phenyl or C10-C20 alkylaryl.

DETAILED DESCRIPTION

One of the most important aspects of the liquid thermal stabilizers of the present invention is that they allow the operators and end-users of plasticized PVC to avoid any contact with chemicals having toxicological issues, such as reprotoxic products (category 2). As α matter of fact the liquid stabilizers of the present invention are devoid of acid salts belonging to the above mentioned toxicological category. The liquid stabilizers are prepared by reaction of barium and zinc hydroxides or oxides with mixtures of C6-C20 aliphatic carboxylic acids and Cs-Ci 0 aromatic carboxylic acids; this salification reaction is optionally carried out in the presence of organic phosphites of the formula RiOP(OR2)OR3 and of solvents of the class of Cs-Ci 6 alkyl alcohols, glycols or glycol ethers or of hydrocarbons having low volatility. Alternatively, the organic phosphites of the formula RiOP(OR2)OR3 and the above-mentioned solvents can be added at the end of the salification reaction.

Optionally, one or more co-stabilizers, such as β-diketones and dihydropyridines, solutions of barium carboxylate/barium carbonate (overbased barium), zinc salts of C6-C20 aliphatic carboxylic acids (to have more flexibility in the ratio Ba/Zn), can be added to the thermal liquid stabilizers prepared as described above. Advantageously, acid phosphites are not added to the thermal liquid stabilizers of the present invention. The salt mixtures comprises cations of Ba and Zn. The Ba/Zn weight ratio in the salt mixture is in the range of about 1 :1 to about 10:1 and preferably of about 3:1 to about 8:1 , more preferably of about 3.5:1 and 4:1. The salt mixture contains as well an anionic component comprising two different types of anions. One of the types consists of one or more anions selected from the group of linear or branched, saturated or unsaturated aliphatic carboxylic acids containing from 6 to 20 carbon atoms; the preferred acids are carboxylic acids with from 0 to 3 carbon-carbon double bonds in the molecule. The most preferred carboxylic acids are oleic acid (or olive oil fatty acids), πeodecaπoic acid and isomers of octaπoic acid, such as 2-ethyl hexaπoate. The second type of anions consists of one or more aromatic carboxylic acids containing from 8 to 10 carbon atoms. The aromatic carboxylic acids are molecules containing a phenyl ring to which the carboxylic moiety is directly or indirectly bonded through a saturated or unsaturated alkylene bridge; the phenyl ring can be additionally substituted with one or more alkyl groups. The preferred aromatic carboxylic acids are substituted derivatives of benzoic acid; the most preferred aromatic carboxylic acids are acids not classified as CRM, and in particular A- isopropyl benzoic acid, 4-ethyl benzoic acid, 2-methyl benzoic acid, 3- methylbenzoic acid, 4-methylbenzoic acid, 3,4-dimethyl benzoic acid and 2,4, 6-trimethyl benzoic acid.

The weight ratio of the aliphatic carboxylate salts to the Cs-Co aromatic carboxylate salts is higher than 3:1 and preferably is in the range of about 3.5:1 to 7:1.

The salt mixture can be prepared reacting basic Zn and Ba compounds, such as zinc oxide and barium hydroxide, with an aliphatic carboxylic acid or with a mixture of C6-C20 aliphatic carboxylic acid (such as, for example, oleic acid, neodecanoic acid or 2-ethylhexoic acid) and with an aromatic acid such as 4-isopropyl benzoic acid, 4-ethyl benzoic acid, 2-methylbenzoic acid, 3-methylbenzoic acid, 4-methylbenzoic acid, 3,4-dimethylbenzoic acid and 2,4, 6-trimethyl benzoic acid or mixtures thereof, in the presence of organic phosphites. The reaction is carried out under vigorous stirring to obtain a homogeneous mixture of barium and zinc salts of organic acids. The preparation of the thermal stabilizer can also entail the use of solvents, such as high boiling point hydrocarbons (by way of example a mixture of isoparaffins and hydrogenated naphthenic hydrocarbons of the Exxsol class), Ci2-Ci5 θxoalcohols, glycols, glycol-ethers, mixtures of linear or branched C15- C40 alkyl benzenes and mixtures thereof.

The organic phosphites of the formula RiOP(OR2)OR3 wherein Ri, R2, R3 are the same or different and each is alkyl containing from 6 to 15 carbon atoms, or phenyl or C10-C20 alkylaryl are fundamental compounds in the thermal liquid stabilizers of the present invention; preferably the organic p h os p h ites a re tri a l kyl p h os p h i tes , d i p h e nyl a l kyl p h os p h ites , phenyldialkyl phosphites, triphenyl phosphites, trial kylaryl phosphites, dialkylaryl alkylphosphites, monoalkylaryl dialkylphosphites, or mixture thereof; the most preferred organic phosphites are trisnonylphenylphosphite, decyldiphenylphosphite and tristridecylphosphite. The organic phosphites can also be added after the above described salification reaction. Preferably the organic phosphites are added after the reaction and are decyldiphenylphosphite and/or tristridecylphosphite and/or a mixture of trial kyl phosphite (5-9%), dialkylnonilphenylphosphite (42- 43%) and monoalkyldinonylphenylphosphite+trinonylphenylphosphite (53- 48%) wherein the alkyl group is a linear or monobranched alkyl group containing 12-15 carbon atoms.

The weight ratio of the total quantity of phosphites (expressed as P) to the quantity of Ba and Zn mixed salts is between 0.04 and 0.07 and more preferably between 0.05 and 0.06. One or more co-stαbilizers, such as β-diketoπes or dihydropyridiπes, and more preferably dibeπzoylmethaπe, stearoylbenzoylmethane, dehydroacetic acid or mixture thereof, can be added under stirring at moderate temperature to the thus obtained mixture. The co-stabilizer is dosed at a weight percentage between 0.1 and 8% on the total weight of the stabilizer and preferably between 0.2 and 5% and more preferably between 0.4 and 3%.

Additional components that can be added to the thermal stabilizer formulation are: overbased barium, zinc salts of C6-C20 aliphatic carboxylic acids and other additives such as antioxidants, plasticizers, lubricants, flame retardants, fillers, pigments and the like, in relative amounts to fulfill the desired functions of each additional ingredient. These ingredients can be added after the preparation of the mixture of salts and phosphites. The stabilizer systems of the present invention are effective in enhancing the resistance to heat-mediated deterioration of PVC resins, that is to deterioration which is due to exposure to excessive heat, as well as deterioration which is initiated or accelerated by exposure to heat. The term "PVC" as used herein is inclusive of any polymer formed at least in part of the recurring group (-CHCI-CX2-)n and having a chlorine content in excess of 40%. In this formula, each of the X groups can be either hydrogen or chlorine and n is the number of units in the polymer chain. In PVC homopolymers, each of the X groups is hydrogen. Thus , the term includes not only polyvinyl chloride homopolimers, but also post-chlorinated polyvinyl chlorides, as well as copolymers of vinyl chloride in a major proportion with other copolymerizable monomers, such as copolymer of vinyl chloride and vinyl acetate, vinyl chloride and maleic or fumaric acids or esters, and copolymers of vinyl chloride with styrene.

The stabilizer compositions of the present invention are effective also with mixtures of PVC containing PVC in major portion and minor portions of other synthetic resins, such as chlorinated polyethylene or acrylonitrile, butadiene and styrene copolymers.

The stabilizer compositions of the present invention can preferably be used in the stabilization of plasticized PVC in its different manufacturing processes, such as calendaring, injection molding, extrusion and the like, being particularly effective in calendaring.

They are used in small amount, but suitable to be effective to impart the desired stability to heat-mediated deterioration of PVC. Effective heat stability can be afforded by adding about 1 to about 5 phr (parts by weight per hundred parts of weight resin) of the thermal stabilizer of the present invention to the PVC resins. Preferred amounts of the stabilizer are in the range of about 1.5 to about 3 phr.

The following examples illustrate preparations and uses of the stabilizers according to the present invention. The examples are included for purposes of illustration and not to limit the scope of what the applicant considers to be the invention.

Example 1 - Use of 4-ethyl benzoic acid.

97.5 g of oleic acid, 17.5 g of 4-ethylhexoic acid , 44.5 g of oxoalcohol C12- C15, 5.9 g of linear alkylbenzene C15-C40 and 67.0 g of trinonylphenylphosphite were mixed together in an heated round bottom flask and stirred with a mechanical stirrer. The mixture was heated at 60°C and 12.0 g of zinc oxide were added in portion. The temperature was raised to 100⁰C. After 1 h, 33.1 g of 4- ethylbenzoic acid and 36 g of barium hydroxide monohydrate were added . The temperature was raised to 140⁰C and left to this temperature for two hours. 300 g of a clear mixture of Ba an d Zinc salts were obtained, with a Ba/Zn ratio of 2.7:1 w/w.

94.7 g of decyldiphenylphosphite , 63.2 g of an overbased barium salt (barium content 17.7 g), 26.3 g of a solution of zinc salts of oleic acid and neodecanoic acid ( Zn content 2.1 g) in decyldiphenylphosphite (13.8 g), 22.1 g of a mixture of linear alkylbenzenes Cl 5-C40 , 10 g of dibenzoylmethane and 10 g of an antioxidant were added to this mixture at 60⁰C under stirring.

526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3.7:1 and a ratio between aliphatic carboxylic acids and 4-ethyl benzoic acid 4.16:1 are obtained . The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.051.

Example 2 - Use of 4-isopropyl benzoic acid

The procedure of Example 1 was repeated, but 4-ethyl benzoic acid was substituted by 36.2 g of 4-isopropyl benzoic acid, reducing the quantity of linear alkylbenzene C15-C40 to 2.8 g.

526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3.7:1 and a ratio between aliphatic carboxylic acids and 4-isopropyl benzoic acid 3.8:1 are obtained . The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.051. Example 3 (use of 4-methyl benzoic acid)

The procedure of Example 1 was repeated, but 4-ethyl benzoic acid was substituted by 30.0 g of 4-methyl benzoic acid, increasing the quantity of linear alkylbenzene C15-C40 to 9.0 g. 526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3.7:1 and a ratio between aliphatic carboxylic acids and 4-methyl benzoic acid 4.6:1 are obtained . The ratio between total phosphorus content and the weight of Ba and Zn salts is

0.052.

Example 4 (use of 3-methyl benzoic acid) The procedure of Example 1 was repeated, but 4-ethyl benzoic acid was substituted by 30.0 g of 3-methyl benzoic acid, increasing the quantity of linear alkylbenzene C15-C40 to 9.0 g.

526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3.7:1 and a ratio between aliphatic carboxylic acids and 3-methyl benzoic acid 4.6:1 are obtained . The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.052.

Example 5 (use of 2-methyl benzoic acid)

The procedure of Example 1 was repeated, but 2-ethyl benzoic acid was substituted by 30 g of 2-methyl benzoic acid, increasing the quantity of linear alkylbenzene C15-C40 to 9.0 g.

526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3,7:1 and a ratio between aliphatic carboxylic acids and 2-methyl benzoic acid 4.6:1 are obtained . The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.052. Example 6 (use of 3,4-dimethylbeπzoic acid)

The procedure of Example 1 was repeated, but 4-ethyl benzoic acid was substituted by 33.1 g of 3,4-dimethylbenzoic acid.

526.3 g of a Ba/Zπ stabilizer with a Ba/Zπ ratio of 3.7:1 and a ratio between aliphatic carboxylic acids and 3,4-dimethylbenzoic acid 4,16:1 are obtained.

The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.051.

Example 7 (use of 2,4,6-trimethylbenzoic acid)

The procedure of Example 1 was repeated, but 4-ethyl benzoic acid was substituted by 36.2 g of 2,4, 6-methyl benzoic acid, reducing the quantity of linear alkylbenzene C15-C40 to 2.8 g.

526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3.7:1 and a ratio between aliphatic carboxylic acids and 2,4,6-trimethylbenzoic acid 3.8:1 are obtained. The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.051.

Example 8 (use of benzoic acid as reference product)

The procedure of Example 1 was repeated, but 4-ethyl benzoic acid was substituted by 26.9 g of benzoic acid, increasing the quantity of linear alkylbenzene C15-C40 to 12.1 g. 526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3.7:1 and a ratio between aliphatic carboxylic acids and benzoic acid 5.1 :1 are obtained . The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.053.

Example 9 (use of 4-tert-butyl benzoic acid as reference product)

The procedure of Example 1 was repeated, but 4-ethyl benzoic acid was substituted by 39.3 g of 4-tertbutyl benzoic acid, eliminating linear αlkylbenzene C15-C40 and reducing the quantity of oxoalcohols C12-C15 to 44.2 g.

526.3 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3,7:1 and a ratio between aliphatic carboxylic acids and benzoic acid 3.5:1 are obtained . The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.050. Example 10 (use of 3-methyl benzoic and higher ratio between aliphatic carboxylic acids and 3-methylbenzoic acid).

20 g of oleic acid, 1.8 g of neodecanoic acid , 7.2 g of oxoalcohols C12-C15, 10.8 g of trinonylphenylphosphite are mixed together in an heated round bottom flask and stirred with a mechanical stirrer.

The mixture was heated at 60°C and 2.4 g of zinc oxide were added in portion. The temperature was raised to 100°C under stirring. After 1 h, 5.1 g of 3-methylbenzoic acid and 5.8 g of barium hydroxide monohydrate were added to the clear mixture . The temperature was slowly raised to 140°C and left to this temperature for two hours. 50 g of a clear mixture of Ba and Zinc salts were obtained, with a Ba/Zn ratio of 2.2:1 w/w.

26 g of decyldiphenylphosphite , 30 g of an overbased barium salt (barium content 8.4 g), 20 g of a solution of zinc salts of oleic acid and neodecanoic acid ( Zn content 1.6 g) in decyldiphenylphosphite (10.5 g), 57 g of a mixture of isoparaffines and hydrogenated naphthenic hydrocarbons, 10 g of butylcarbitol, 4 g of dibenzoylmethane and 3 g of a phenolic antioxidant were added to this mixture at 60°C under stirring.

200 g of a Ba/Zn stabilizer with a Ba/Zn ratio of 3.6:1 and a ratio between aliphatic carboxylic acids and 3-methylbenzoic acid 6.8:1 are obtained. The ratio between total phosphorus content and the weight of Ba and Zn salts is 0.059. Example 1 1

The evaluation tests on the performances of the stabilizers of Examples 1 -10 are reported: a) Static heat stability

To perform the static heat stability test, the formulations of the stabilizers reported in the preceding examples, have been incorporated in PVC resins having the formulations reported in Table 1 :

Table 1

2.5 phr of the stabilizers of the Examples 1 -4, 6, 10 and 9 (as reference) were added to an intimate mixture of these components; after the addition of the stabilizer every mixture has been processed with an heated two rolls mill ( temperature 180°C, friction 1 -1 .5). After 3 minutes of mixing, a thin film of PVC was obtained, and, after cooling at room temperature, some strips of 2x20 cm were cut from this film. These strips were introduced in α Werner Mαthis oven at a temperature of 200°C, base time 4 minutes, 20 mm every 4 min.

At the end of the cycle the samples were taken from the oven and the distance (mm) from the starting point of the strip to the beginning of the burning is noted.

The longer the distance between the starting point of the strip and the beginning of the burning, the more efficient is the stabilizer (Table 2).

Table 2

b) plate out: the formulations of the thermal stabilizers reported in the preceding Examples have been incorporated in PVC resins according to the formulations reported in Table 3.

Table 3

To απ intimate mixture of these components 2 phr of the stabilizers of exemplesl -7 and 8 (as reference) is added; once introduced the stabilizer, every mixture has been processed with an heated two rolls mill

(Cylinder temperature 180°C, friction 1 -1 .5) for 1 minute.

Then the sheet has been removed without cleaning the cylinders.

A cleaning mixture was prepared with the formulation of Table 4.

Table 4

This cleaning mixture has been gelled on the two roll mills and continuously mixed on the cylinders for 3 minutes at 180°C. At the end the sheet has been detached from the cylinders . More intense is the color of the sheet, higher is the quantity of material left from the previous formulation. The color of the cleaning sheet has been evaluated with a color meter, measuring the a* value, in this way it is possible to quantify the relative differences between the different products. The higher the a* value, the higher the plate out. Table 5

The preceding examples show that the stabilizers prepared using aromatic carboxylic acids Cs-Co have: a) at least identical stabilizing properties against PVC thermal degradation to that obtained using 4-tert-butyl benzoic acid, so that they can replace 4-tert-butyl benzoic acid, which is dangerous for the public health; b) reduced plate-out with respect to benzoic acid during PVC sheet processing, particularly for calendering application, an effect that is important for the industrial practice.

Claims

1. Liquid thermal PVC stabilizers comprising: a) mixed barium and zinc salts of one or more linear or branched aliphatic saturated or unsaturated carboxylic acids containing from 6 to 20 carbon atoms and of one or more aromatic carboxylic acid containing from 8 to 10 carbon atoms, not classified as CRM, wherein the weight ratio of aliphatic acids salts to aromatic acids salts is higher than 3:1 ; b) one or more organic phosphites of the formula RiOP(OR2)OR3 wherein Ri, R2 and R3 are the same or different and each is alkyl containing from 6 to 15 carbon atoms or phenyl or C10-C20 alkyl aryl.

2. Liquid thermal PVC stabilizers according to claim 1 further comprising one or more co-stabilizers, selected among β-diketones, dihydropyridines, solutions of barium carboxylate/barium carbonate (overbased barium), zinc salts of C6-C20 aliphatic carboxylic acids.

3. Liquid thermal PVC stabilizers according to any of the preceding claims in which the weight ratio of the aliphatic carboxylate salts to the aromatic carboxylate salts is in the range of about 3.5:1 to 7:1.

4. Liquid thermal PVC stabilizers according to any of the preceding claims in which the Ba/Zn weight ratio is the range of about 1 :1 to about 10:1.

5. Liquid thermal PVC stabilizers according to claim 4 in which the Ba/Zn weight ratio is from about 3:1 to about 8:1.

6. Liquid thermal PVC stabilizers according to claim 5 in which the Ba/Zn weight ratio is from about 3.5:1 and 4:1.

7. Liquid thermal PVC stabilizers according to claim 1 wherein the aliphatic carboxylic acids are selected among oleic acid (or olive oil fatty acids), neodecanoic acid or 2-ethylhexoic acid and the aromatic acids are selected among 4-isopropyl benzoic acid, A- ethylbenzoic acid, 2-methylbenzoic acid, 3-methylbenzoic acid, A- methylbenzoic acid, 3,4-dimethylbenzoic acid and 2,4,6- trimethyl benzoic acid.

8. Liquid thermal PVC stabilizers according to claim 7 in which the organic phosphites are selected among trial kyl phosphites, diphenylalkyl phosphites, phenyldial kyl phosphites, triphenyl phosphites, trial kylaryl phosphites, dialkylaryl al kyl phosphites, monoalkylaryl dialkylphosphites.

9. Liquid thermal PVC stabilizers according to claim 8 wherein the weight ratio of the total quantity of phosphites (expressed as P) to the quantity of Ba and Zn mixed salts is between 0.04 and 0.07.

10. Use of the liquid thermal PVC stabilizers according to any of the claims from 1 to 9 in calendaring of plasticized PVC.