Polyorganosiloxane-based composition intended for tyre moulding/stripping

Abstract

The present invention relates to compositions in the form of silicone oil emulsions intended to be applied to curing bladders as a mould-release agent during tyre production.

Claims

1. A mold release agent composition (I) in emulsion form, the composition comprising: (a) at least one reactive polyorganosiloxane (A) comprising at least two silanol groups ≡SiOH per molecule; (b) at least one crosslinking agent (B) having at least three ≡SiH units per molecule; (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 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; (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 water being sufficient to obtain an oil-in-water emulsion; wherein the composition of the glass beads (D) is as follows: the content of silicon expressed as SiO.sub.2 is less than 63% by weight, the content of calcium expressed as CaO is greater than 20% by weight, the content of sodium expressed as Na.sub.2O is less than 2.9% by weight, the content of aluminum expressed as Al.sub.2O.sub.3 is from 0.5% to 15% by weight, the content of boron expressed as B.sub.2O.sub.3 is from 0.2% to 2.5% by weight, the content of potassium expressed as K.sub.2O is from 0.35% to 1% by weight, and the content of magnesium expressed as MgO is from 1% to 4% by weight, relative to the total weight of SiO.sub.2, CaO, Na.sub.2O, Al.sub.2O.sub.3, B.sub.2O.sub.3, K.sub.2O and MgO.

2. The mold release agent composition (I) as claimed in claim 1, wherein that the amount of glass beads (D) is from 0.1% to 20% by weight relative to the total weight of the composition.

3. The mold release agent composition (I) as claimed in claim 1, wherein the reactive polyorganosiloxane (A) 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 identical or different radicals 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.

4. The mold release agent composition (I) as claimed in claim 3, wherein the radicals R.sup.2, R.sup.3 and R.sup.4 of the siloxy units of the reactive polyorganosiloxane (A) are methyl radicals.

5. The mold release agent composition (I) as claimed in claim 1, wherein the crosslinking agent (B) is a polyorganosiloxane having at least one unit of formula (II) and which is terminated by units of formula (III) or cyclic units consisting of units of formula (II) represented below: ##STR00004## in which: the symbols R.sup.1 are identical or different and represent: a linear or branched alkyl radical containing 1 to 8 carbon atoms, which is unsubstituted or which is substituted by at least one fluorine, a cycloalkyl radical containing from 5 to 8 cyclic carbon atoms, or an aryl radical containing from 6 to 12 carbon atoms, an aralkyl radical having an alkyl part containing from 5 to 14 carbon atoms and an aryl part containing from 6 to 12 carbon atoms, unsubstituted or substituted on the aryl part with halogens, alkyls and/or alkoxyls containing 1 to 3 carbon atoms, the symbols Z′ are identical or different and represent: a hydrogen radical, or a group corresponding to the same definition as that given above for R.sup.1, with at least three of the symbols Z′ per molecule representing H.

6. A process of lubricating an expandable rubber bladder during a vulcanization of a green tire within a metal press, the process comprising providing the bladder so that an outer surface of the bladder, intended to be in contact with an inner face of the green tire, is coated with a mold release agent composition (I) in the form of an oil-in-water emulsion, wherein the mold release agent composition comprises: (a) at least one reactive polyorganosiloxane (A) comprising at least two silanol groups ≡SiOH per molecule; (b) at least one crosslinking agent (B) having at least three ≡SiH units per molecule; (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 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; (d) glass beads (D) as spherical amorphous filler, the composition of which is as follows: the content of silicon expressed as SiO.sub.2 is less than 63% by weight, the content of calcium expressed as CaO is greater than 20% by weight, the content of sodium expressed as Na.sub.2O is less than 2.9% by weight, the content of aluminum expressed as Al.sub.2O.sub.3 is from 0.5% to 15% by weight, the content of boron expressed as B.sub.2O.sub.3 is from 0.2% to 2.5% by weight, the content of potassium expressed as K.sub.2O is from 0.35% to 1% by weight, and the content of magnesium expressed as MgO is from 1% to 4% by weight, relative to the total weight of SiO.sub.2, CaO, Na.sub.2O, Al.sub.2O.sub.3, B.sub.2O.sub.3, K.sub.2O and MgO; (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 water being sufficient to obtain an oil-in-water emulsion; the process thus making it possible to directly obtain an expandable rubber bladder lubricated on the outer surface thereof and leading to several cycles of green tire molding and of vulcanized tire demolding.

7. A process of lubricating an expandable rubber bladder during a vulcanization of a green tire within a metal press, the process comprising in a first step outside the press, coating an inner surface of the green tire with a mold release agent composition (I) in the form of an oil-in-water emulsion that comprises: (a) at least one reactive polyorganosiloxane (A) comprising at least two ≡SiOH groups per molecule; (b) at least one crosslinking agent (B) having at least three ≡SiH units per molecule; (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 alkyls, C.sub.3-C.sub.8 cycloalkyls, C.sub.6-C.sub.10 aryls and C.sub.7-C.sub.15 alkylaryls; (d) glass beads (D) as spherical amorphous filler, the composition of which is as follows: the content of silicon expressed as SiO.sub.2 is less than 63% by weight, the content of calcium expressed as CaO is greater than 20% by weight, the content of sodium expressed as Na.sub.2O is less than 2.9% by weight, the content of aluminum expressed as Al.sub.2O.sub.3 is from 0.5% to 15% by weight, the content of boron expressed as B.sub.2O.sub.3 is from 0.2% to 2.5% by weight, the content of potassium expressed as K.sub.2O is from 0.35% to 1% by weight, and the content of magnesium expressed as MgO is from 1% to 4% by weight, relative to the total weight of SiO.sub.2, CaO, Na.sub.2O, Al.sub.2O.sub.3, B.sub.2O.sub.3, K.sub.2O and MgO; (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 water being sufficient to obtain an oil-in-water emulsion; the first 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, bringing the coated inner surface of the green tire into contact with an expandable rubber bladder; the process thus making it possible to obtain, by transfer, an expandable rubber bladder lubricated on the outer face thereof and leading to several cycles of green tire molding and of vulcanized tire demolding.

8. The process of claim 6, wherein the mold release agent composition (I) comprises: from 0.1 to 30 parts by weight of at least one constituent (A) comprising at least two silanol groups ≡SiOH per molecule, from 0.1 to 20 parts by weight of at least one constituent (B) having at least three ≡SiH units per molecule, 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 alkyls, C.sub.3-C.sub.8 cycloalkyls, C.sub.6-C.sub.10 aryls and C.sub.7-C.sub.15 alkylaryls, from 0.1 to 20 parts by weight of glass beads (D) as spherical amorphous filler, the composition of which is as follows: the content of silicon expressed as SiO.sub.2 is less than 63% by weight, the content of calcium expressed as CaO is greater than 20% by weight, the content of sodium expressed as Na.sub.2O is less than 2.9% by weight, the content of aluminum expressed as Al.sub.2O.sub.3 is from 0.5% to 15% by weight, the content of boron expressed as B.sub.2O.sub.3 is from 0.2% to 2.5% by weight, the content of potassium expressed as K.sub.2O is from 0.35% to 1% by weight, and the content of magnesium expressed as MgO is from 1% to 4% by weight, relative to the total weight of SiO.sub.2, CaO, Na.sub.2O, Al.sub.2O.sub.3, B.sub.2O.sub.3, K.sub.2O and MgO; 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); per 100 parts by weight of the sum of the constituents (A) to (H).

9. A lubricated bladder obtained by the process as described in claim 6.

10. A process of vulcanizing a green tire, the process comprising employing a lubricated bladder as described in claim 9.

11. The mold release agent composition (I) as claimed in claim 2, wherein the amount of glass beads (D) is from 0.1% to 15% by weight.

Description

EXAMPLES

1) Raw Materials Used

(1) Bluesil® Emulsion 242 sold by Bluestar Silicones: emulsion of α, ω-bis(hydroxy)polydimethylsiloxane oil having a viscosity of approximately 135 000 mPa.Math.s at 25° C. (A) and comprising a surfactant (E). Bluesil® Emulsion 247G—Bluestar Silicones: emulsion of a mixture of αω-bis(hydroxy)polydimethylsiloxane (A) gum having a consistency of approximately 700 expressed in tenths of a millimeter at 25° C. and of polydimethylsiloxane oil (C) having a viscosity of approximately 50 mPa.Math.s at 25° C. and comprising a surfactant (E). Bluesil® Emulsion 269 sold by Bluestar Silicones: emulsion of polymethylhydrosiloxane oil having a viscosity of approximately 25 mm.sup.2/s at 25° C. (B) and comprising a surfactant (E) Spheriglass® 3000A CP00 sold by Potters: soda-lime glass beads non-surface-coated with a coupling agent, having a mean diameter of 12-26 μm (D) measured according to standard ISO 13320 (type A). Spheriglass® 3000E CP03 sold by Potters: borosilicate glass beads surface-coated with a coupling agent, having a mean diameter of 12-26 μm (D) measured according to standard ISO 13320 (type E). GlassyCoat® C3 SP 20-60 TO sold by Sovitec: non-surface-coated glass beads, D50 15-30 μm (type X). Rhodopol® 23 sold by Solvay Novecare: xanthan gum, thickener (F). Imbentin® T/050 sold by Dr Kolb; Isotrideceth 5, wetting agent (F). Silcolapse® 5001 sold by Bluestar Silicones: antifoam emulsion (F). Proxel® GXL sold by Arch Chemicals: 1,2-benzisothiazolin-3-one, biocide (F).

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

2) Preparation of the Examples

(3) In all the examples, the percentages (%) mentioned are expressed by weight relative to the total weight of all the constituents of the formulation.

Comparative Example 1 (C1): Formulation with Type A Glass Beads

(4) In a 2-liter beaker with a diameter of 120 mm, produce a first mixture (M1): introduce 47.46% of water (H) and stir at 100 rpm using a disperser equipped with a deflocculating impeller having a diameter of 100 mm; then introduce 0.62% Imbentin® T/050 (F), 1.8% Silcolapse® 5001 (F) and 3% Spheriglass® 3000A CP00; increase the speed to 600 rpm and introduce 0.26% Rhodopol® 23 (F); disperse for 10 min at 600 rpm and stop the disperser.

(5) At the same time, in a 1-liter beaker with a diameter of 90 mm, prepare a second mixture (M2): introduce 30% Bluesil® Emulsion 247G (A & C) and stir at 100 rpm using a disperser fitted with an anchor impeller having a diameter of 80 mm, then introduce 7.47% Bluesil® Emulsion 242 (A), 0.15% Proxel® GXL (F), 0.06% of phosphoric acid (F), and homogenize for 5 min, and finally introduce 9.15% Bluesil® Emulsion 269 (B). homogenize for 5 min.

(6) Finally, introduce the mixture (M2) into (M1) while stirring at 300 rpm using a disperser equipped with an anchor impeller having a diameter of 80 mm and homogenize for 30 min. After homogenization, the mold release agent composition (C1) is obtained.

Comparative Example 2 (C2): Formulation with Type E Glass Beads

(7) In a 2-liter beaker with a diameter of 120 mm, produce a first mixture (Q1): introduce 47.91% of water (H) and stir at 100 rpm using a disperser equipped with a deflocculating impeller having a diameter of 100 mm; then introduce 0.2% Imbentin® T/050 (F), 1.8% Silcolapse® 5001 (F) and 3% Spheriglass® 3000E CP03; increase the speed to 600 rpm and introduce 0.26% Rhodopol® 23 (F); disperse for 10 min at 600 rpm and stop the disperser.

(8) At the same time, in a 1-liter beaker with a diameter of 90 mm, prepare a second mixture (Q2): introduce 30% Bluesil® Emulsion 247G (A & C) and stir at 100 rpm using a disperser fitted with an anchor impeller having a diameter of 80 mm, then introduce 7.48% Bluesil® Emulsion 242 (A), 0.15% Proxel® GXL (F), 0.06% of phosphoric acid (F), and homogenize for 5 min, and finally introduce 9.15% Bluesil® Emulsion 269 (B). homogenize for 5 min.

(9) Finally, introduce the mixture (Q2) into (Q1) while stirring at 300 rpm using a disperser equipped with an anchor impeller having a diameter of 80 mm and homogenize for 30 min. After homogenization, the mold release agent composition (C2) is obtained.

Example According to the Invention (E1): Formulation with Type X Glass Beads

(10) The procedure of comparative example 2 is followed but the type E glass beads are replaced with type X glass beads, GlassyCoat® C3 SP 20-60 TO batch 1.

Example According to the Invention (E2): Formulation with Type X Glass Beads

(11) The procedure of comparative example 2 is followed but the type E glass beads are replaced with type X glass beads, GlassyCoat® C3 SP 20-60 TO batch 2.

Example According to the Invention (E3): Formulation with Type X Glass Beads

(12) The procedure of comparative example 2 is followed but the type E glass beads are replaced with type X glass beads, GlassyCoat® C3 SP 20-60 TO batch 3.

3) Characterization Tests

Elemental Analysis of the Batches of Glass Beads (D)

(13) The elemental analysis of the batches of glass beads is carried out by plasma torch atomic emission spectrometry according to standard ISO 21587 (2007). Mention may be made, as an example of apparatus which can be used, of: ICP Varian Vista Pro or ICP Jobin Yvon Ultima 2.

Measuring the pH of the Formulations

(14) The pH of the formulations is measured using a pH meter equipped with a glass electrode and a reference electrode. The apparatus is calibrated every week with buffer solutions of pH=4, 7 and 11. The measurements are carried out at the ambient temperature of the laboratory. The apparatus automatically compensates the temperature variations of the measurement.

Measuring the Hydrogen Release of the Formulations

(15) The measurement of the hydrogen release on compositions stored at 50° C. is carried out by gas chromatography equipped with katharometric detection.

(16) The results of the analysis are expressed as ml/kg/day.

(17) The properties of the mold release agent compositions (I) are measured by evaluating the coefficients of friction and the number of demolding operations earned out without defects.

(18) A low coefficient of friction reflects good slip properties.

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

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

Slip Test

(21) The aim 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.

(22) This test is carried out by sliding a metal block of predetermined weight, under which a tire casing film (50×75 mm) is attached, over a rubber surface, the composition of which is that of the expandable bladder.

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

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

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

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

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

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

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

Demolding Test

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

(31) For this purpose, an expandable bladder film, pro-coaled 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.

(32) In detail, a sheet of rubber, having a composition identical to that of the bladder and having a size of 2 mm×80 mm×80 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.

(33) 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 μm is deposited. After drying in air, the assembly is cured at 170° C. for at least 10 minutes.

(34) 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.

(35) 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.

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

4) Elemental Analysis of the Different Types of Glass Bead

(37) TABLE-US-00001 Composition Glass Glass Glass beads of the glass beads beads type X % by weight type A type E Batch 1 Batch 2 Batch 3 SiO.sub.2 (%) 74.5 64.2 61.4 62.1 57.9 Na.sub.2O (%) 12.4 3.2 0.5 2.5 2.2 CaO (%) 9.2 18 22.5 22.5 24.4 MgO (%) 2.6 2.4 2.6 3.0 3.0 Al.sub.2O.sub.3 (%) 0.9 9 12.3 9.2 11.2 B.sub.2O.sub.3 (%) 0.1 3 0.4 0.3 0.8 K.sub.2O (%) 0.3 0.2 0.4 0.5 0.6 TOTAL 100 100 100 100 100

(38) The type X glass beads have the desired features, namely: the content of silicon expressed as SiO.sub.2 is less than 63% by weight, the content of calcium expressed as CaO is greater than 20% by weight, the content of sodium expressed as Na.sub.2O is less than 2.9% by weight, the content of aluminum expressed as Al.sub.2O.sub.3 is between 0.5% and 15% by weight, the content of boron expressed as B.sub.2O.sub.3 is between 0.2% and 2.5% by weight, the content of potassium expressed as K.sub.2O is between 0.35% and 1% by weight, and the content of magnesium expressed as MgO is between 1% and 4% by weight, relative to the total weight of SiO.sub.2, CaO, Na.sub.2O, Al.sub.2O, B.sub.2O.sub.3, K.sub.2O and MgO.

5) Monitoring the pH of the Compositions Formulated with the Different Glass Beads Stored at 50° C.

(39) TABLE-US-00002 Tests according to the Number of Comparative Comparative invention, type X glass days of test C1 test C2 beads storage at Type A Type E E1 E2 E3 50° C. glass beads glass beads Batch 1 Batch 2 Batch 3 0 4.7 4.2 4.2 4.7 4.3 11 7.0 6.2 4.5 4.9 4.5 15 7.1 6.5 4.4 4.8 4.5 30 7.2 6.8 4.2 4.8 4.5 45 7.2 7.6 4.3 4.7 4.5 60 7.3 — 3.7 5.0 4.4

(40) Compared to the comparative tests C1 and C2, the pH of which changes quickly and significantly at 50° C. (+49% in 11 days and +55% in 60 days for C1), the pH of the compositions according to the invention (E1, E2 and E3), namely in the presence of type X glass beads, virtually does not change at all (+4% in 11 days and 6.4% in 60 days for E2).

(41) The pH of the compositions according to the invention does not increase on storage by more than 10% relative during a period of 60 days at 50° C., equivalent to one year at ambient temperature.

6) Measurement of Hydrogen Release During Storage of the Compositions Formulated with the Different Glass Beads

(42) TABLE-US-00003 Hydrogen release expressed as ml/kg/day Storage at 50° C. for 50 days Comparative Comparative Tests according to the invention test C1 test C2 Type X glass beads Type A Type E glass E1 E2 E3 glass beads beads Batch 1 Batch 2 Batch 3 110 85 30 50 55

(43) The hydrogen release of a mold release agent compositor according to the invention is on average 45 ml/kg/day at 50° C., i.e. a reduction of 59% relative to the comparative example C1 and a reduction of 47% relative to the composition of the comparative example C2.

7) Measurement of the Coefficient of Friction of the Coatings Obtained with the Compositions Formulated with the Different Glass Beads

(44) TABLE-US-00004 Coefficient of friction (Kd) Tests according to Number of months Comparative the invention, type of storage at test C1 X glass beads ambient Type A glass E2 temperature beads Batch 2 1 0.33 0.29 2 0.37 0.31 3 0.36 0.33 4 0.39 0.3

(45) The composition according to the invention leads to a coefficient of friction Kd<0.7.

8) Measurement of the Number of Demolding Operations of the Compositions Formulated with the Different Glass Beads

(46) TABLE-US-00005 Number of demolding operations Number of months Comparative Tests according to the invention, of storage at test C1 type X glass beads ambient Type A glass E2 temperature beads Batch 2 1 10 14 2 8 12 3 6 12 4 6 8

(47) The use of type X glass beads in the composition according to the invention does not degrade the number of demolding operations.

(48) Compared to the comparative example (C1), the use of type X glass beads in a mold release agent composition does not degrade the number of demolding operations and therefore the durability of the bladder, with simultaneously good slip properties.

(49) In conclusion, the use of type X glass beads, unlike type A or E glass beads, makes it possible to stabilize the pH of the mold release agent compositions and to avoid the loss of SiH, and therefore the release of hydrogen, without degrading the application properties.