Compositions based on silicone resin, processes for their preparation and their applications

Abstract

Composition comprising: - 3 to 30 wt.% silicone resin, wherein the silicone resin is a thermosetting silicone resin having a three-dimensional lattice with a high degree of crosslinking and the formula R n Six m O y has, whereby - R, identical or different, represents a methyl or a phenyl, - X, identical or different, represents hydrogen, chlorine, a hydroxy, a methoxy or a phenyloxy group, - y, n and m are such that the molecule reaches a molecular mass in the order of 2000 to 6000, - 5 to 50 wt.% nitrile butadiene rubber (NBR) and / or derivatives thereof, wherein the derivatives of NBR are carboxylated NBR (XNBR) and / or hydrogenated NBR (HNBR), - at least one yarn.

Description

[0001] The present invention relates to silicone resin-based compositions, the processes for their preparation and their applications as friction material, in particular their use in friction rings for clutch friction discs or brake linings.

[0002] A friction ring is generally made from at least one yarn, which ensures centrifugal force resistance, and a binder (also called "cement"), which provides cohesion. Most binders are made from organic resins such as phenolic or melamine resins. These binders offer high thermal stability. However, recent developments in the binder field (reduction of thermal mass in double-damped flywheels and self-adjusting clutches, increased performance and energy, etc.) have led to a need for binders with higher thermal resistance.

[0003] It is known from the prior art, and in particular from patent application EP 0 637 698 A1, that the incorporation of silicone resin into a binder comprising a phenolic resin makes it possible to increase the thermal resistance of this binder. However, "silicone resins" in this document actually refer to silicone elastomers. However, there are three major families of silicones: fluids, elastomers, and resins, the latter two being chemically distinct. Furthermore, the combination of a phenolic resin with a silicone elastomer described in this patent application does not allow the production of a binder with an acceptable coefficient of friction above a temperature of 350°C.

[0004] EP 1 505 114 A1 discloses a composition with improved flowability which contains at least one hydrogenated nitrile rubber.

[0005] From JP 2006-096830 A a composition with NBR, polysiloxanes and fillers and possibly other polymers is known.

[0006] The inventors' work has made it possible to identify a composition that can be used as a binder, this binder having an improved behavior of the friction coefficient as a function of temperature, in particular above 350°C.

[0007] The invention is a composition as defined in claim 1, a method as defined in claim 10 and a use as defined in claims 13 and 14.

[0008] The present invention therefore relates to a composition comprising: - 3 to 30 wt% silicone resin, preferably 5 to 15%, - 5 to 50 wt.% NBR rubber and / or derivatives thereof, preferably 10 to 25%.

[0009] "Silicone resin," also called "polysiloxane resin," refers to thermosetting silicone resins that have a three-dimensional lattice with a high degree of cross-linking. They generally have the formula R n Six m O y , where - R, identical or different, represents a methyl or a phenyl, - X, identical or different, represents hydrogen, chlorine, a hydroxy, a methoxy or a phenyloxy group, - y, n and m are such that the molecule reaches a molecular mass in the order of 2000 to 6000.

[0010] These resins have a glass transition temperature that is higher than the ambient temperature (18-21°C).

[0011] According to the invention, these are in particular and preferably silicone resins of the polymethylsiloxane, polyphenylmethylsiloxane and / or polyphenylsiloxane type.

[0012] "NBR" refers to nitrile butadiene rubber. NBR derivatives include carboxylated NBR (XNBR) and hydrogenated NBR (HNBR). "NBR and / or its derivatives" refers to each of these compounds, considered individually or in a blend.

[0013] Advantageously, the composition according to the invention can comprise at least one further resin, the percentage of the total weight of all the resins present in the composition being from 10 to 50%, preferably from 15 to 30%. This at least one further resin can be selected from the group consisting of melamine-formaldehyde resins, phenolic resins (novolac resins, resole resins), resorcinol resins, epoxy resins, etc. The incorporation of a melamine or phenolic resin into the composition is then advantageously carried out in a weight proportion of from 5 to 30% or from 0 to 20%, respectively, of the total weight of the composition. Preferably, the weight proportions of melamine or phenolic resin are from 10 to 20% or from 0 to 10%, respectively. Thus, it is possible for a melamine resin to be present without a phenolic resin being present.

[0014] The composition according to the invention can preferably contain 10 to 40% by weight of at least one filler. These are, in particular, friction additives such as barium sulfate or carbon black.

[0015] The composition may also comprise at least one surfactant and / or an adjuvant.

[0016] "Surfactant" refers in particular to polyvinyl alcohol (PVA) and anionic surfactants such as phosphates, polyphosphates, pyrophosphates, sulfates, sulfonates, or carboxylates linked to a cation (sodium, potassium, ammonium, calcium, or amines), and mixtures thereof. Preferably, the anionic surfactant is sodium polyphosphate and / or PVA. The use of PVA is particularly recommended in the case of a binder that simultaneously contains NBR and / or its derivatives in a mixture with a phenolic resin. Indeed, PVA makes it possible to stabilize the aqueous solution during the preparation of the composition according to the invention.

[0017] The term "adjuvant" essentially refers to so-called "manufacturability" adjuvants, such as catalysts (such as sulfur, particularly advantageous in cases where NBR is used), thickeners (cellulose or its derivatives) and adhesion-enhancing agents (rosin, petroleum resin).

[0018] The composition according to the invention also contains at least one yarn, preferably a yarn blend, which may be at least one textured glass yarn, one metal yarn, and one yarn based on mineral and / or organic fibers. Such a composition, especially when fillers are present, is particularly suitable for the production of a friction ring for a clutch friction disc operating with dry friction. The textured glass yarn preferably has a fineness of 600 to 5000 tex. The metal yarn is advantageously a copper yarn. The mineral and / or organic fibers are preferably glass fibers, polyacrylonitrile fibers, or fibers made from polyacrylonitrile derivatives.

[0019] The invention also relates to the processes for preparing the compositions described above.

[0020] The invention therefore proposes a first process for preparing a composition according to the invention, which comprises the following steps: - Preparation of an aqueous mixture containing NBR rubber and / or its derivatives, - Addition of the resin(s).

[0021] In the case of a composition which also comprises at least one filler and possibly surfactants and / or adjuvants, the process for preparing a composition according to the invention may comprise the following steps: - preparing a premix containing the resin(s) and the filler(s), optionally the surfactant(s) and / or the adjuvant(s) and water, and - Addition of NBR rubber and / or its derivatives to the premix.

[0022] Alternatively, the process for preparing this composition may comprise the following steps: - preparation of a premix containing NBR rubber and / or its derivatives, optionally the surfactant(s) and / or the adjuvant(s) and water, and - Addition of the resin(s) and filler(s) to the premix.

[0023] The preparation of the composition which also comprises at least one yarn is particularly preferred according to the invention and is carried out by impregnating the yarn or yarns with any of the compositions obtained by the three preparation processes according to the invention described above.

[0024] The applications of the compositions according to the invention are also within the scope of the invention. This particularly concerns the use of a composition according to the invention for producing a friction material, especially for producing a clutch lining. These compositions are particularly suitable for the production of friction rings for clutch friction discs operating with dry friction, as well as for brake linings.

[0025] The composition according to the invention can be used for a friction material such as a friction ring for a dry friction clutch friction disc or a brake pad.

[0026] The invention will be better understood by reading the following description, given solely by way of example and with reference to the drawings, in which: Fig.1 shows the variation of the friction coefficient as a function of temperature for compositions containing or not containing siloxane resin, Fig. 2 shows the variation of the friction coefficient as a function of temperature for compositions containing or not containing NBR, Fig. 3 shows the change in the coefficient of friction as a function of temperature for compositions containing or not containing polymethylphenylsiloxane resin and NBR, and Fig. Figure 4 shows the variation of the friction coefficient as a function of temperature for compositions containing or not containing polymethylsiloxane resin and NBR. Example 1: Example of a composition according to the invention material % by weight Yarn recipe : - acrylic fibers, 12,5 - glass fibers (roving), 12,5 - textured glass yarn, 14 - Copper yarn. 9,8 Putty recipe : - polymethylsiloxane resin, 7,6 - Melamine resin, 14,5 - NBR, 12,3 - Barium sulfate, 9,6 - soot, 5,5 - sulfur, 1,5 - Sodium polyphosphate. 0,2

[0027] The percentages are given in weight percentages based on the total weight of the composition. Example 2: Method for producing a friction ring

[0028] The mixture is prepared in an aqueous phase. Polysiloxane resin and any other resins are introduced in powder form into an aqueous mixture containing the NBR rubber latex and the other fillers or components of the mixture (dispersions). The water content is adjusted so that the viscosity is between 8 and 18 poise. The dry extract of the mixtures varies between 50 and 90%. To optimize the dispersions, thickeners can be added in an amount of 0.1 to 5% by weight of the mixture (for example, 0.3% hydroxyethylcellulose), surfactants in an amount of 0.1 to 1% by weight of the mixture (for example, 0.3% sodium polyphosphates, potassium oleate), or adhesion-enhancing agents in an amount of 0.1 to 5% by weight of the mixture (for example, 1.5 or 3% rosin).

[0029] A filament yarn composed of several types of fibers, such as glass fibers, polyacrylonitrile (PAN) fibers, and copper fibers, is then impregnated and dried. The water is evaporated to a relative humidity of 0.5 to 3%.

[0030] The friction rings (yarn blanks) are then formed into lobe-shaped pieces ("en lobage"). The following steps are thermocompression at 170-200 °C under 0.5 to 40 MPa and deburring of the rings.

[0031] The post-firing step varies from 2 to 6 hours, at temperatures that increase continuously or gradually from 200 to 330 °C. This step can also be omitted if no phenolic resin is present in the composition.

[0032] This is followed by the steps of sanding and drilling the parts and dust sealing.

[0033] In the following examples, the compositions are designated as follows: "Formulation X (Resin Type + Rubber Type)". Formulation 1, when containing phenolic resin and SBR, corresponds exactly to the reference formulation, while Formulation 2 is a variant of this formulation (identical to Formulation 1 except for the absence of copper). In the comparisons of the following formulations, only the type of resin (phenolic resin, PMPS = polymethylphenylsiloxane or PMS = polymethylsiloxane) and / or rubber (NBR or SBR) is changed, without changing the weight percentages or the rest of the formulation (1 or 2). For immediate identification of the compositions, the type of formulation is therefore indicated first by "Formulation 1" or "Formulation 2", followed by the type of resin and rubber in parentheses. Example 3: Change in the coefficient of friction as a function of temperature when simulating starting on an incline for compositions containing or not containing siloxane resin

[0034] This example aims to compare two compositions containing siloxane resins with a reference composition containing a phenolic resin, named “Formulation 1 (Phenol + SBR)”.

[0035] The reference composition is given below: material % by weight Yarn recipe : - acrylic fibers, 12,5 - glass fibers (roving), 12,5 - textured glass yarn, 14 - Copper yarn. 9,8 Putty recipe : - Phenolic resin, 7,6 - Melamine resin, 14,5 - SBR, 12,3 - Barium sulfate, 9,6 - soot, 5,5 - sulfur, 1,5 - Sodium polyphosphate. 0,2

[0036] The other two compositions are similar to the reference composition except for one modification: - The composition “Formulation 1 (PMS + SBR)” contains a polymethylsiloxane resin instead of the phenolic resin contained in the reference composition, - the composition ‘Formulation 1 (PMPS + SBR)’ contains a polymethylphenylsiloxane resin instead of the phenolic resin contained in the reference composition.

[0037] These compositions are compared in a gradient start test to determine the change in the friction coefficient as a function of temperature.

[0038] The test aims to track the change in the coefficient of friction as a function of temperature. The measurement is performed in a clutch on a brake test bench.

[0039] In Fig. 1 are indicated: - a solid thick line representing the minimum permissible friction coefficient, - a continuous thin curve representing the friction coefficient of the reference composition, - a uniformly dashed curve representing the friction coefficient of the composition “Formulation 1 (PMS + SBR)”, - a dot-dash curve representing the friction coefficient of the composition “Formulation 1 (PMPS + SBR)”.

[0040] It can be seen that the reduction in the friction coefficients of the two siloxane resin-based compositions occurs at temperatures that are approximately 50 °C (“Formulation 1 (PMS + SBR)”) to approximately 130 °C (“Formulation 1 (PMPS + SBR)”) higher than that of the reference composition (i.e., approximately 450 °C and approximately 530 °C, respectively, compared to approximately 400 °C).

[0041] Conclusion: Compared to the reference composition, the compositions containing siloxane resins show a significantly better behavior of the friction coefficient as a function of temperature. Example 4: Change in the coefficient of friction as a function of temperature when simulating starting on an incline for compositions containing NBR or SBR

[0042] This example aims to compare two phenolic resin-based compositions whose formulation is essentially similar to that of the reference composition and which contain NBR ("Formulation 2 (Phenol + NBR)") and SBR ("Formulation 2 (Phenol + SBR)"), respectively. These two compositions are identical, only the type of rubber differs.

[0043] The test conditions are identical to those of Example 3.

[0044] The two compositions tested in this example are therefore identical except for the type of rubber incorporated into the composition.

[0045] In Fig. 2 are indicated: - a solid thick line representing the minimum permissible friction coefficient, - a uniformly dashed curve representing the friction coefficient of the composition containing SBR, - a dot-dash curve representing the friction coefficient of the same composition but containing NBR instead of SBR.

[0046] It can be seen that the change in the friction coefficients of the two compositions is similar.

[0047] Conclusion: If the resin present in the composition is a phenolic resin, the type of rubber incorporated in this composition has no influence on the temperature behavior of the friction coefficient. Example 5: Change in the coefficient of friction as a function of temperature when simulating starting on an incline for compositions containing polymethylphenylsiloxane silicone resin in combination with NBR or SBR, compared to the reference composition

[0048] The test conditions are identical to those of Example 3.

[0049] The composition named “Formulation 1 (Phenol + SBR)” corresponds to the reference composition described in Example 3.

[0050] This reference composition is compared with two other compositions: - ‘Formulation 1 (PMPS + SBR)’, which corresponds to the reference composition containing polymethylphenylsiloxane resin instead of phenolic resin, and - "Formulation 1 (PMPS + NBR)", which corresponds to the reference composition containing polymethylphenylsiloxane resin instead of phenolic resin and NBR instead of SBR. This latter composition is within the scope of the invention.

[0051] In Fig. 3 are indicated: - a solid thick line representing the minimum permissible friction coefficient, - a continuous thin curve representing the friction coefficient of the reference composition, - a uniformly dashed curve representing the friction coefficient of “Formulation 1 (PMPS + SBR)”, and - a dot-dash curve representing the friction coefficient of “Formulation 1 (PMPS + NBR)”.

[0052] It can be seen that the reduction in the friction coefficients of the compositions containing silicone and NBR occurs at temperatures that are approximately 50 °C (PMPS + SBR) to approximately 140 °C (PMPS + NBR) higher than that of the reference composition (ie approximately 450 °C and approximately 540 °C, respectively, versus approximately 400 °C).

[0053] Conclusion: Surprisingly, replacing SBR with NBR has an impact on the composition. Combining polymethylphenylsiloxane resin with NBR allows for significantly improved results in terms of the temperature behavior of the friction coefficient. Example 6: Change in the coefficient of friction as a function of temperature when simulating starting on an incline for compositions containing polymethylsiloxane silicone resin in combination with NBR or SBR, compared to the reference composition

[0054] The composition named “Formulation 1 (Phenol + SBR)” corresponds to the reference composition described in Example 3.

[0055] This reference composition is compared with two other compositions: - ‘Formulation 1 (PMS + SBR)’, which corresponds to the reference composition containing polymethylsiloxane resin instead of phenolic resin, and - "Formulation 1 (PMS + NBR)", which corresponds to the reference composition containing polymethylsiloxane resin instead of phenolic resin and NBR instead of SBR. This latter composition is within the scope of the invention.

[0056] In Fig. 4 are indicated: - a solid thick line representing the minimum permissible friction coefficient, - a continuous thin curve representing the friction coefficient of the reference composition, - a uniformly dashed curve representing the friction coefficient of “Formulation 1 (PMS + SBR)”, and - a dot-dash curve representing the friction coefficient of “Formulation 1 (PMS + NBR)”.

[0057] It can be seen that the reduction in the friction coefficients of the compositions containing polymethylsiloxane resin and SBR occurs at temperatures approximately 120 °C higher than those of the reference composition. Regarding the composition "Formulation 1 (PMS + NBR)", no reduction in the friction coefficient was observed during this test.

[0058] Conclusion: Surprisingly, replacing SBR with NBR has an impact on the composition. Combining polymethylsiloxane resin with NBR allows for significantly improved results in terms of the temperature behavior of the friction coefficient.

Claims

[1] Composition comprising: - 3 to 30 wt.% silicone resin, wherein the silicone resin is a thermosetting silicone resin having a three-dimensional lattice with a high degree of crosslinking and the formula R n Six m O y has, whereby - R, identical or different, represents a methyl or a phenyl, - X, identical or different, represents hydrogen, chlorine, a hydroxy, a methoxy or a phenyloxy group, - y, n and m are such that the molecule reaches a molecular mass in the order of 2000 to 6000, - 5 to 50 wt.% nitrile butadiene rubber (NBR) and / or derivatives thereof, wherein the derivatives of NBR are carboxylated NBR (XNBR) and / or hydrogenated NBR (HNBR), - at least one yarn. [2] A composition according to claim 1, comprising 5 to 15 wt% silicone resin. [3] Composition according to claim 1 or 2, characterized by that the silicone resin is a silicone resin of the type polymethylsiloxane, polyphenylmethylsiloxane and / or polyphenylsiloxane. [4] Composition according to any one of claims 1 to 3, comprising 10 to 25 wt% NBR rubber and / or derivatives thereof. [5] Composition according to any one of claims 1 to 4, comprising a yarn mixture containing at least one textured glass yarn, one metal yarn and one yarn based on mineral and / or organic fibers. [6] Composition according to any one of the preceding claims, further comprising at least one further resin, the percentage of the resins present in the composition being from 10 to 50%, preferably from 15 to 30%, of the total weight. [7] Composition according to the preceding claim, comprising 5 to 30 wt%, preferably 10 to 20 wt%, of melamine resin and 0 to 20 wt%, preferably 0 to 10 wt%, of phenolic resin. [8] Composition according to any one of the preceding claims, comprising 10 to 40 wt.% of at least one filler. [9] Composition according to any one of the preceding claims, further comprising at least one anionic surfactant and / or an adjuvant, wherein the anionic surfactant is preferably sodium polyphosphate and / or PVA. [10] A process for producing a composition according to any one of the preceding claims, which contains at least one yarn, comprising the following steps: - Preparation of an aqueous mixture containing NBR rubber and / or its derivatives, - Addition of the resin(s), then - Impregnation of the yarn or yarns with the composition thus obtained. [11] A process for preparing a composition according to any one of claims 1 to 9, which contains at least one yarn, comprising the following steps: - preparing a premix containing the resin(s) and filler(s), optionally the surfactant(s) and / or adjuvant(s) and water, and - Addition of NBR rubber and / or its derivatives to the premix, then - Impregnation of the yarn or yarns with the composition thus obtained. [12] A process for preparing a composition according to any one of claims 1 to 9, which contains at least one yarn, comprising the following steps: - preparation of a premix containing NBR rubber and / or its derivatives, optionally the surfactant(s) and / or the adjuvant(s) and water, and - Addition of the resin (s) and filler (s) to the premix, then - Impregnation of the yarn or yarns with the composition thus obtained. [13] Use of the composition according to any one of claims 1 to 9 as a friction material. [14] Use of the composition according to any one of claims 1 to 9 as a friction ring for a clutch friction disc operating with dry friction or as a brake lining.

Images