Lubrication method

Abstract

A method of lubricating an expandable rubber bladder is described for use during a vulcanization of a green tire within a metal press. The method can include applying compositions in the form of emulsions of silicone oils to the inner surface of the green tires and/or to the outer surface of the vulcanization bladders to facilitate the molding-demolding thereof during the manufacture of the tires.

Claims

1. A method of lubricating an expandable rubber bladder for use during a vulcanization of a green tire within a metal press, the method comprising coating the outer surface of the bladder, brought to be in contact with the inner face of the green tire, with a mold release agent composition (I) in the form of an oil-in-water emulsion, wherein the composition (I) comprises: (a) at least one reactive polyorganosiloxane (A) comprising, per molecule, at least two SiOH silanol groups; (b) at least one crosslinking agent (B) having, per molecule, at least three SiH units; (c) at least one non-reactive linear polyorganosiloxane oil (C) which is a linear homopolymer or copolymer which has, per molecule, monovalent organic substituents, which are identical to or different from one another, bonded to the silicon atoms, and which are selected from the group consisting of C.sub.1-C.sub.6 alkyl, C.sub.3-C.sub.8 cycloalkyl, C.sub.6-C.sub.10 aryl and C.sub.7-C.sub.15 alkylaryl radicals; (d) glass beads (D) as spherical amorphous filler; (e) at least one surfactant (E); (f) optionally at least one additive (F) selected from the group consisting of: a film-forming polymer, a complementary lubricant, an antifriction agent, a coalescence agent, a wetting or dispersing agent, a mineral filler, an antifoam agent, a thickener, a stabilizer, an acidifying agent, a biocide and an antifungal agent; (g) optionally at least one dehydrogenation-condensation catalyst (G), and (h) water (H), the amounts of surfactant(s) and of water being sufficient to obtain an oil-in-water emulsion; with the proviso that the composition (I) does not comprise a mica-type filler to evacuate air; the method making it possible to obtain an expandable rubber bladder that is lubricated on its outer surface and resulting in several green tire molding and vulcanized tire demolding cycles.

2. The method as claimed in claim 1, wherein the glass beads (D) of the mold release agent composition (I) have the following features: a mean diameter of particles measured according to ISO 13320 standard of from 0.1 m to 150 m, a bulk density measured according to ASTM D 3101-78 of from 1000 kg/m.sup.3 to 2000 kg/m.sup.3, and an oil absorption measured according to ASTM D-1483 of from 10 g to 30 g of oil per 100 g of spheres.

3. The method as claimed in claim 1, wherein the glass beads (D) of the mold release agent composition (I) have the following features: a mean diameter of the particles measured according to the ISO 13320 standard of from 0.5 m to 100 m, a bulk density according to ASTM D 3101-78 of from 1200 kg/m.sup.3 to 1800 kg/m.sup.3, and an oil absorption according to ASTM D-1483 of from 15 g to 25 g of oil per 100 g of spheres.

4. The method as claimed in claim 1, wherein the reactive polyorganosiloxane (A) of the mold release agent composition (I) comprises the following siloxy units:
M.sup.OH=[(OH)(R.sup.2).sub.2SiO.sub.1/2] and D=[R.sup.3R.sup.4SiO.sub.2/2] wherein: R.sup.2, R.sup.3 and R.sup.4 are radicals, which are identical or different, selected from the group consisting of: linear or branched C.sub.1-C.sub.6 alkyl radicals, C.sub.3-C.sub.8 cycloalkyl radicals, C.sub.6-C.sub.10 aryl radicals, and C.sub.7-C.sub.15 alkylaryl radicals.

5. The method as claimed in claim 1, wherein the reactive polyorganosiloxane (A) of the mold release agent composition (I) is an ,-bis(hydroxy)polydimethylsiloxane.

6. The method as claimed in claim 1, wherein the crosslinking agent (B) of the mold release agent composition (I) is selected from those that have at least one unit of formula (II) and that are terminated by units of formula (Ill) or that are cyclic having units of formula (II) represented below: ##STR00002## wherein: the R.sup.1 symbols are identical or different and represent: a linear or branched alkyl radical having 1 to 8 carbon atoms, which is unsubstituted or which is substituted by at least one fluorine, a cycloalkyl radical having 5 to 8 cyclic carbon atoms, or an aryl radical having 6 to 12 carbon atoms, an aralkyl radical having an alkyl part having 5 to 14 carbon atoms and an aryl part having 6 to 12 carbon atoms, which is unsubstituted or which is substituted on the aryl part by halogens, alkyls and/or alkoxyls having 1 to 3 carbon atoms, the Z symbols are similar or different and represent a hydrogen radical, or a group corresponding to the same definition as that given above for R.sup.1, with, per molecule, at least three of the Z symbols representing H.

7. The method as claimed in claim 1, wherein the mold release agent composition (I) comprises: from 0.1 to 30 parts by weight of at least one constituent (A), from 0.1 to 20 parts by weight of at least one constituent (B), from 0.1 to 30 parts by weight of at least one constituent (C), from 0.1 to 20 parts by weight of at least one constituent (D), from 0.1 to 10 parts by weight of at least one constituent (E), from 0 to 5 parts by weight of the constituent (F), from 0 to 5 parts by weight of at least one constituent (G), from 20 to 90 parts by weight of the constituent (H); per 100 parts by weight of the sum of the constituents (A) to (H).

8. A lubricated expandable bladder obtained by the method as claimed in claim 1.

9. A method of vulcanizing a green tire, the method comprising using a lubricated bladder as described in claim 8.

10. A method of lubricating an expandable rubber bladder for use during a vulcanization of a green tire within a metal press, the method comprising in a first step outside of the press, coating the inner surface of the green tire with a mold release agent composition (I) in the form of an oil-in-water emulsion, wherein the composition (I) comprises: (a) at least one reactive polyorganosiloxane (A) comprising, per molecule, at least two SiOH groups; (b) at least one crosslinking agent (B) having. per molecule, at least three SiH units; (c) at least one non-reactive linear polyorganosiloxane oil (C) which is a linear homopolymer or copolymer which has, per molecule, monovalent organic substituents, which are identical to or different from one another, bonded to the silicon atoms, and which are selected from the group consisting of C.sub.1-C.sub.6 alkyl, C.sub.3-C.sub.8 cycloalkyl, C.sub.6-C.sub.10 aryl and C.sub.7-C.sub.15 alkylaryl radicals; (d) glass beads (D) as spherical amorphous filler; (e) at least one surfactant (E); (f) optionally at least one additive (F) selected from the group consisting of: a film-forming polymer, a complementary lubricant, an antifriction agent, a coalescence agent, a wetting or dispersing agent, a mineral filler, an antifoam agent, a thickener, a stabilizer, an acidifying agent, a biocide and an antifungal agent (g) optionally at least one dehydrogenation-condensation catalyst (G), and (h) water (H), the amounts of surfactant(s) and of water being sufficient to obtain an oil-in-water emulsion; the step thus making it possible to obtain a green tire, the inner surface of which is coated with the composition (I) and during a subsequent step within the metal press, the green tire, the inner surface of which is coated with said composition (I), is brought into contact with an expandable rubber bladder; with the proviso that the composition (I) does not comprise a mica-type filler to evacuate air; the method making it possible thus to obtain, by transfer, an expandable rubber bladder that is lubricated on its outer face and resulting in several green tire molding and vulcanized tire demolding cycles.

11. The method as claimed in claim 10, wherein the glass beads (D) of the mold release agent composition (I) have the following features: a mean diameter of particles measured according to ISO 13320 standard of from 0.1 m to 150 m, a bulk density measured according to ASTM D 3101-78 of from 1000 kg/m.sup.3to 2000 kg/m.sup.3, and an oil absorption measured according to ASTM D-1483 of from 10 g to 30 g of oil per 100 g of spheres.

12. The method as claimed in claim 10, wherein the glass beads (D) of the mold release agent composition (I) have the following features: a mean diameter of the particles measured according to the ISO 13320 standard of from 0.5 m to 100 m, a bulk density according to ASTM D 3101-78 of from 1200 kg/m.sup.3to 1800 kg/m.sup.3, and an oil absorption according to ASTM D-1483 of from 15 g to 25 g of oil per 100 g of spheres.

13. The method as claimed in claim 10, wherein the reactive polyorganosiloxane (A) of the mold release agent composition (I) comprises the following siloxy units:
M.sup.OH=[(OH)(R.sup.2).sub.2SiO.sub.1/2] and D=[R.sup.3R.sup.4SiO.sub.2/2] wherein: R.sup.2, R.sup.3 and R.sup.4 are radicals, which are identical or different, selected from the group consisting of: linear or branched C.sub.1-C.sub.6 alkyl radicals, C.sub.3-C.sub.8 cycloalkyl radicals, C.sub.6-C.sub.10 aryl radicals, and C.sub.7-C.sub.15 alkylaryl radicals.

14. The method as claimed in claim 10, wherein the reactive polyorganosiloxane (A) of the mold release agent composition (I) is an ,-bis(hydroxy)polydimethylsiloxane.

15. The method as claimed in claim 10, wherein the crosslinking agent (B) of the mold release agent composition (I) is selected from those that have at least one unit of formula (II) and that are terminated by units of formula (Ill) or that are cyclic having units of formula (II) represented below: ##STR00003## wherein: the R.sup.1 symbols are identical or different and represent: a linear or branched alkyl radical having 1 to 8 carbon atoms, which is unsubstituted or which is substituted by at least one fluorine, a cycloalkyl radical having 5 to 8 cyclic carbon atoms, or an aryl radical having 6 to 12 carbon atoms, an aralkyl radical having an alkyl part having 5 to 14 carbon atoms and an aryl part having 6 to 12 carbon atoms, which is unsubstituted or which is substituted on the aryl part by halogens, alkyls and/or alkoxyls having 1 to 3 carbon atoms, the Z symbols are similar or different and represent: a hydrogen radical, or a group corresponding to the same definition as that given above for R.sup.1, with, per molecule, at least three of the Z symbols representing H.

16. The method as claimed in claim 10, wherein the mold release agent composition (I) comprises: from 0.1 to 30 parts by weight of at least one constituent (A), from 0.1 to 20 parts by weight of at least one constituent (B), from 0.1 to 30 parts by weight of at least one constituent (C), from 0.1 to 20 parts by weight of at least one constituent (D), from 0.1 to 10 parts by weight of at least one constituent (E), from 0 to 5 parts by weight of the constituent (F), from 0 to 5 parts by weight of at least one constituent (G), from 20 to 90 parts by weight of the constituent (H); per 100 parts by weight of the sum of the constituents (A) to (H).

17. A lubricated expandable bladder obtained by the method as claimed in claim 10.

18. A method of vulcanizing a green tire, the method comprising using a lubricated bladder as described in claim 17.

19. A mold release agent composition (1), wherein the composition comprises: from 0.1 to 30 parts by weight of at least one constituent (A) comprising, per molecule, at least two SiOH silanol groups; from 0.1 to 20 parts by weight of at least one constituent (B) having, per molecule, at least three SiH units; from 0.1 to 30 parts by weight of at least one constituent (C) which is a linear homopolymer or copolymer which has, per molecule, monovalent organic substituents, which are identical to or different from one another, bonded to the silicon atoms, and which are selected from the group consisting of C.sub.1-C.sub.6 alkyl, C.sub.3-C.sub.8 cycloalkyl, C.sub.6-C.sub.10 aryl and C.sub.7-C.sub.15 alkylaryl radicals; from 0.1 to 20 parts by weight of at least one constituent (D) as spherical amorphous filler, wherein the at least one constituent (D) is a glass bead; from 0.1 to 10 parts by weight of at least one surfactant (E); from 0 to 5 parts by weight of at least one additive (F) selected from the group consisting of: a film-forming polymer, a complementary lubricant, an antifriction agent, a coalescence agent, a wetting or dispersing agent, a mineral filler, an antifoam agent, a thickener, a stabilizer, an acidifying agent, a biocide and an antifungal agent; from 0 to 5 parts by weight of at least one dehydrogenation-condensation catalyst (G); from 20 to 90 parts by weight of water (H); and per 100 parts by weight of the sum of the constituents (A) to (H); and with the proviso that the composition (I) does not comprise a mica-type filler to evacuate air.

Description

EXAMPLES

1) Raw materials used

(1) Bluesil Emulsion 242 sold by the company Bluestar Silicones: emulsion of ,-bis(hydroxy)polydimethylsiloxane oil having a viscosity approximately of 135 000 mPa.Math.s at 25 C. (A) and comprising a surfactant (E). Bluesil Emulsion 244company Bluestar Silicones: emulsion of a mixture of ,-bis(hydroxy)polydimethylsiloxane rubber (A) having a consistency approximately of 700 expressed in tenths of a millimetre at 25 C. and of polydimethylsiloxane oil (C) having a viscosity approximately of 50 mPa.Math.s at 25C and comprising a surfactant (E). Bluesil Emulsion 269 sold by the company Bluestar Silicones: emulsion of polymethyl-hydrosiloxane oil having a viscosity approximately of 25 mm.sup.2/s at 25 C. (B) and comprising a surfactant (E). Spheriglass 2530A CP01 sold by the company Potters: soda-lime glass beads surface-coated with a coupling agent, having a mean diameter of 56-70 m (D) measured according to the ISO 13320 standard. Spheriglass 2000A CP01 sold by the company Potters: soda-lime glass beads surface-coated with a coupling agent, having a mean diameter of 27-36 m (D) measured according to the ISO 13320 standard. Spheriglass 3000A CP01 sold by the company Potters: soda-lime glass beads surface-coated with a coupling agent, having a mean diameter of 12-26 m (D) measured according to the ISO 13320 standard. Spheriglass 3000E CP03 sold by the company Potters: borosilicate glass beads surface-coated with a coupling agent, having a mean diameter of 12-26 m (D) measured according to the ISO 13320 standard. Rhodopol 23 sold by the company Solvay Novecare: xanthan gum, thickener (F). Rheozan sold by the company Solvay Novecare: succinoglycan gum, thickener (F). Imbentin T/050 sold by the company Dr Kolb: Isotrideceth 5, wetting agent (F). Geropon SDS sold by the company Solvay Novecare: Sodium dioctyl sulfosuccinate, wetting agent (F). PEG 400 sold by the company Sigma-Aldrich: Polyethylene Glycol 400, wetting agent (F). Silcolapse 5001 sold by the company Bluestar Silicones: antifoam emulsion (F). Silcolapse 140 sold by the company Bluestar Silicones: antifoam emulsion (F). Sodium citrate: pH regulator (F). Proxel GXL sold by the company Arch Chemicals: 1,2-benzisothiazolin-3-one, biocide (F). Axilat Ultra Green DS2800 sold by the company Hexion Chemicals: dispersion of film-forming polymer (F) Alsibronz 39 sold by the company Engelhard: mica, platy filler.

(2) The % indicated below are by weight relative to the total weight of the composition.

2) Preparations of the examples

Comparative Example 1 (C1)

Formulation Without Glass Beads

(3) In a 2-liter beaker with a diameter of 120 mm, produce a first mixture (P1): introduce 52.22% water (H) and stir at 100 rpm using a disperser equipped with a deflocculating impeller having a diameter of 100 mm; then introduce 0.03% Geropon SDS (F), 0.9% PEG400 (F), 0.5% Silcolapse 140 (F); increase the speed to 600 rpm and introduce 0.23% Rheozan (F) steeped in 0.69% Imbentin T/050 (F); disperse for 10 min at 600 rpm and stop the disperser.

(4) At the same time, in a 1-liter beaker with a diameter of 90 mm, prepare a second mixture (P2): introduce 22% Bluesil Emulsion 244 (A & C) and stir at 100 rpm using a disperser equipped with an anchor impeller having a diameter of 80 mm, then introduce 11.2% Bluesil Emulsion 242 (A), 0.15% Proxel GXL (F), 0.08% phosphoric acid (F), and homogenize for 5 min, and introduce 5% Axilat Ultragreen DS2800 (F) and homogenize for 5 min, and finally introduce 7% Bluesil Emulsion 269 (B), homogenize for 5 min.

(5) Finally, introduce the mixture (P2) into (P1) while stirring at 300 rpm with the aid of a disperser equipped with an anchor impeller having a diameter of 80 mm and homogenize for 30 min.

(6) After homogenization, the mold release agent composition (C1) is thus obtained.

Comparative Example 2 (C2)

Formulation With Mica

(7) The procedure of comparative example 1 is followed but 10% water are replaced by 10% Alsibronz 39.

Example according to the invention (E1)

(8) The procedure of comparative example 1 is followed but 10% water are replaced by 10% Spheriglass 2530A CP01 (D).

Example according to the invention (E2)

(9) The procedure of the example (El) is followed but only 3% water are replaced by 3% Spheriglass 2530A CP01 (D).

Example according to the invention (E3)

(10) The procedure of the example (E1) is followed but Spheriglass 2000A CP01 glass beads are used as a replacement for Spheriglass 2530A CP01 (D).

Example according to the invention (E4)

(11) The procedure of the example (E1) is followed but Spheriglass 3000A CP01 glass beads are used as a replacement for Spheriglass 2530A CP01 (D).

Example according to the invention (E5)

(12) The procedure of the example (E1) is followed but only 3% water are replaced by 3% Spheriglass 3000A CP01 (D).

Example according to the invention (E6)

(13) In a 2-liter beaker with a diameter of 120 mm, produce a first mixture (Q1): introduce 44.71% water (H) and stir at 100 rpm using a disperser equipped with a deflocculating impeller having a diameter of 100 mm; then introduce 0.1% Imbentin T/050 (F), 1.8% Silcolapse 5001 (F) and 3% Spheriglass 3000A CP01; increase the speed to 600 rpm and introduce 0.25% Rhodopol23 (F) steeped in 0.5% Imbentin T/050; disperse for 10 min at 600 rpm and stop the disperser.

(14) At the same time, in a 1-liter beaker with a diameter of 90 mm, prepare a second mixture (Q2): introduce 30% Bluesil Emulsion 244 (A & C) and stir at 100 rpm using a disperser equipped with an anchor impeller having a diameter of 80 mm, then introduce 7.47% Bluesil Emulsion 242 (A), 0.04% sodium citrate (F), 0.15% Proxel GXL (F), 0.07% phosphoric acid (F), and homogenize for 5 min, and finally introduce 11.91% Bluesil Emulsion 269 (B), homogenize for 5 min.

(15) Finally, introduce the mixture (Q2) into (Q1) while stirring at 300 rpm with the aid of a disperser equipped with an anchor impeller having a diameter of 80 mm and homogenize for 30 min.

(16) After homogenization, the mold release agent composition (E6) is obtained.

Example according to the invention (E7)

(17) In a 2-liter beaker with a diameter of 120 mm, produce a first mixture (Q3): introduce 47.45% water (H) and stir at 100 rpm using a disperser equipped with a deflocculating impeller having a diameter of 100 mm; then introduce 0.1% Imbentin T/050 (F), 1.8% Silcolapse 5001 (F) and 3% Spheriglass 3000E CP03; increase the speed to 600 rpm and introduce 0.26% Rhodopol23 (F) steeped in 0.52% Imbentin T/050; disperse for 10 min at 600 rpm and stop the disperser.

(18) At the same time, in a 1-liter beaker with a diameter of 90 mm, prepare a second mixture (Q4): introduce 30% Bluesil Emulsion 244 (A & C) and stir at 100 rpm using a disperser equipped with an anchor impeller having a diameter of 80 mm, then introduce 7.47% Bluesil Emulsion 242 (A), 0.04% sodium citrate (F), 0.15% Proxel GXL (F), 0.07% phosphoric acid (F), and homogenize for 5 min, and finally introduce 9.14% Bluesil Emulsion 269 (B), homogenize for 5 min.

(19) Finally, introduce the mixture (Q4) into (Q3) while stirring at 300 rpm with the aid of a disperser equipped with an anchor impeller having a diameter of 80 mm and homogenize for 30 min.

(20) After homogenization, the mold release agent composition (E7) is obtained.

Example according to the invention (E8)

(21) In a 2-liter beaker with a diameter of 120 mm, produce a first mixture (Q5): introduce 47.45% water (H) and stir at 100 rpm using a disperser equipped with a deflocculating impeller having a diameter of 100 mm; then introduce 0.1% Imbentin T/050 (F), 1.8% Silcolapse 5001 (F) and 3% Spheriglass 3000A CP03; increase the speed to 600 rpm and introduce 0.26% Rhodopol23 (F) steeped in 0.52% Imbentin T/050; disperse for 10 min at 600 rpm and stop the disperser.

(22) At the same time, in a 1-liter beaker with a diameter of 90 mm, prepare a second mixture (Q6): introduce 30% Bluesil Emulsion 244 (A & C) and stir at 100 rpm using a disperser equipped with an anchor impeller having a diameter of 80 mm, then introduce 7.47% Bluesil Emulsion 242 (A), 0.04% sodium citrate (F), 0.15% Proxel GXL (F), 0.07% phosphoric acid (F), and homogenize for 5 min, and finally introduce 9.14% Bluesil Emulsion 269 (B), homogenize for 5 min.

(23) Finally, introduce the mixture (Q6) into (Q5) while stirring at 300 rpm with the aid of a disperser equipped with an anchor impeller having a diameter of 80 mm and homogenize for 30 min.

(24) After homogenization, the mold release agent composition (E8) is obtained.

3) Characterization Tests

(25) The properties of the compositions are measured by evaluating the friction coefficients and the number of demolding operations carried out without failure.

(26) A low friction coefficient reflects good slip properties.

(27) A high number of demolding operations reflects a high durability of the lubrication of the bladder.

(28) The test for measuring the coefficients of friction and the durability were adapted to the application of the lubricating composition to an expandable rubber bladder.

(29) Slip Test

(30) The objective of this test is to assess the slip ability of a mold release agent composition placed at the interface between the expandable bladder and the inner surface of the casing of a tire.

(31) This test is carried out by sliding a metal block of predetermined weight, under which a tire casing film (5075 mm) is attached, over a rubber surface, the composition of which is that of the expandable bladder.

(32) The surface of the expandable bladder is pre-coated with the mold release agent composition.

(33) The friction coefficient is measured using a tensiometer (at a speed of 50 mm/min). Five successive passes are carried out on the same expandable bladder sample, the tire casing sample being changed each time.

(34) The friction coefficient (Kd) corresponds to:

(35) $\mathrm{Kd}\left(\mathrm{dimensionless}\right)=\frac{\mathrm{average}\mathrm{force}\mathrm{for}\mathrm{conveying}\mathrm{the}\mathrm{block}\left(\mathrm{in}N\right)}{\mathrm{Weight}\mathrm{of}\mathrm{the}\mathrm{block}\left(\mathrm{in}N\right)}$

(36) The value of Kd mentioned in table 1 corresponds to the average of values obtained during the 5 passes.

(37) The lower the friction coefficient values, the better the slip properties of the lubricating composition.

(38) This slip test is perfectly representative of the performance to be achieved on industrial tooling, and is a first selection criterion.

(39) Demolding Test:

(40) The durability of a lubricating composition corresponds to the number of tires produced without degradation of the surface of the expandable bladder.

(41) For this, an expandable bladder film, pre-coated with the mold release agent composition to be evaluated, is pressed into contact with an unvulcanised tire casing film in a series of pressure and temperature cycles that simulate the steps of manufacturing a tire on industrial tooling.

(42) In detail, a sheet of rubber, having a composition identical to that of the bladder and having a size of 2 mm80 mm80 mm is prepared in a heated press at 200 C. for 30 minutes. The sheet is surface-structured to simulate the surface of a bladder.

(43) This sheet is coated in a paint booth by spraying the mold release agent composition with a compressed air spray gun. A layer of around 20 m is deposited. After drying in air, the assembly is cured at 170 C. for at least 10 minutes.

(44) The coated sheet is placed in a metal mold in a press. The platens are heated at 170 C. The sheet is left to preheat for 5 minutes, then a piece of green ILR (inner liner rubber, i.e. rubber that forms the inner surface of a green tire) having a thickness of around 9 cm is deposited on the sheet coated with the mold release agent composition. The mold is closed, followed by the press, and the ILR is left to cure for 7 minutes at 170 C. The mold is opened and the thin molded ILR sheet is removed.

(45) In order for a demolding operation to be considered to be successful, the sheet must be separated without applying force and without sticking. Otherwise, the demolding operation is recorded as a failure.

(46) The number of demolding operations corresponds to the number of ILR sheets removed from the mold without sticking.

(47) TABLE-US-00001 TABLE 1 3) Results of the tests: Filler Number of Friction mean size Filler demolding coefficient Film Ref. Filler (m) [%] operations (Kd) appearance C1 No filler NC NC 8 0.38 Transparent C2 Mica 39 ~39 10 4 0.34 Translucent E1 Spheriglass 56-70 10 18 0.32 Transparent 2530A CP01 E2 Spheriglass 56-70 3 14 0.55 Transparent 2530A CP01 E3 Spheriglass 27-36 10 12 0.30 Transparent 2000A CP01 E4 Spheriglass 12-26 10 18 0.28 Transparent 3000A CP01 E5 Spheriglass 12-26 3 18 0.32 Transparent 3000A CP01 E6 Spheriglass 12-26 3 18 0.2 Transparent 3000A CP01 E7 Spheriglass 12-26 3 10 0.38 Transparent 3000E CP03 E8 Spheriglass 12-26 3 16 0.45 Transparent 3000A CP03

(48) Compared to the comparative example (C1) with no filler, the addition of mica to a mold release agent composition as described in patent application EP 1 899 447 (comparative example C2) degrades the number of demolding operations by 50%, and therefore degrades the durability of the bladder.

(49) On the other hand, the examples according to the invention (E1 to E8) unambiguously show that the addition of glass beads makes it possible to increase the number of demolding operations, and therefore the durability of the bladder, by 1.25 to 2.25 times relative to (C1) and by 2.5 to 4.5 times relative to (C2) and this being at the same time as good slip properties.

(50) In conclusion, the use of glass beads, unlike mica, does not degrade the durability of the bladder coated with the mold release agent composition according to the invention. Furthermore, unlike mica, the formulations based on glass beads result in transparent films.