SK288314B6 - Use of polyvinyl alcohol for manufacturing of the friction ring for the friction disk clutch and the friction ring for the disc clutch - Google Patents

Abstract

Described is use of polyvinyl alcohol for manufacturing of the friction material especially of the friction ring for the friction disk clutch. The friction ring includes at least one strand on the base fibres first of all mineral as are glass fibres, organic fibres, fibres of polyacrylonitrile or derivate, wherein an aqueous impregnation cement contains fillers, phenol resin and/or latex and polyvinyl alcohol.

Description

Technical field

The present invention relates to the use of polyvinyl alcohol for the production of a friction material and in particular a friction ring for a clutch friction disk as well as a friction ring. More specifically, the friction ring for the clutch friction disc is a friction ring with dry friction.

BACKGROUND OF THE INVENTION

Such a friction ring is usually made from at least one strand, which mainly contains mineral fibers, such as glass fibers, which provide resistance to centrifugal force, rubber to achieve the correct coefficient of friction at different loads, and a binder, in practice phenolic resin to make the whole cohesive. Most often, said fiber-based strand is comprised of fibers. Such a ring must actually withstand the centrifugal force load in the coupling, but it must also withstand high temperatures during repeated maneuvers or difficult driving conditions.

During the production of the ring, organic solvents, in particular chlorinated solvents, are usually used, in particular for dissolving rubber.

The problem that arises with the use of these solvents is their harmful aspect, which consequently requires the application of restrictions and recovery in order to prevent any contact with workers and any escape into the atmosphere.

In order to overcome these problems, these chlorine solvents are usually replaced with water. This requires the use of latex instead of dry rubber. In practice, an aqueous mastic is produced, which usually results from the mixing of filler phenolic resins, especially in the form of powder, and latex in water.

This putty is then used to impregnate a strand, which is primarily mineral fibers, and serves to form a blank which is then fired under pressure to form a friction ring. The Applicant has found that the water-based sealant has a viscosity which increases rapidly over time. This results, on the one hand, in a short time during which the sealant is usable and, on the other hand, in changes in the frictional properties and wear resistance of the friction rings, which are then produced. The addition of the phenolic resin powder to the latex-containing composition causes the absorption of the water present in the latex structure, leading to a rapid increase in viscosity, and the sealant becomes unsuitable for impregnation of the strand.

In GB-A-2 054 626, an aqueous impregnating sealant comprises at least one surfactant type component.

In EP-B1-1 088 176, the aqueous impregnating sealant comprises an anionic-type aqueous surfactant such as sodium polyphosphate, which makes it possible to stabilize the aqueous sealant.

However, the problem of cementing the mastic particles is a problem that requires continuous improvement, especially when the aqueous mastic is complex type with fillers and contains a large proportion of phenolic resin and / or NBR latex and / or XNBR (carboxylated NBR latex). One object of the present invention is to solve this problem.

SUMMARY OF THE INVENTION

Therefore, the present invention proposes to use at least one surfactant component which is polyvinyl alcohol. Such use is primarily intended to stabilize the aqueous mixtures for the clutch rings, in particular containing mixtures of latex, phenolic resins, melanin-formaldehyde and various organic and mineral powders.

More particularly, the present invention provides the use of polyvinyl alcohol for the production of a friction material and in particular a friction ring for a clutch friction disc as well as a friction ring, using at least one impregnation operation of at least one strand containing mineral fibers such as glass fibers by at least one aqueous impregnation a sealant in which the aqueous sealant comprises at least one surfactant-type component and a filler, characterized in that the surfactant-type component comprises polyvinyl alcohol (or PVA).

Generally, the PVA of the present invention is used pre-dissolved in water, most often in 15% to 30% solutions, then diluted to the percentage of desired stabilization in the aqueous suspension.

The present invention stabilizes the aqueous sealant especially in the presence of many other ingredients in the sealant, such as high molecular weight formaldehyde resins, such as novolak (a generic name that refers to a group of phenolic resins marketed by multiple manufacturers), for example in the presence of rubber carboxylated (XNBR) or non-carboxylated (NBR) latex Nitrile Butadiene Rubber. Without intending to limit the invention, the Applicant believes that there is some association between this effect and the very nonionic steric nature (protective colloid) of PVA.

It will be appreciated by those skilled in the art that in the presence of latex, a basic pH of the sealant must be formed so that the latex does not lose its stability. According to the present invention, when latex is used, ammonia is usually added for quenching.

According to other characteristics, which can be taken individually or in all possible combinations:

- the aqueous sealant additionally contains an anionic surfactant component,

- the anionic surfactant component is selected from the group of phosphates, polyphosphates, sulphates, sulphonates and carboxylates,

- the cation of the anionic surfactant component is selected from sodium +, potassium +, ammonium +, calcium ++ and amines,

the polyvinyl alcohol has a molecular weight of from 10 000 g / mol to 100 000 g / mol, preferably from 20 000 g / mol to 60 000 g / mol, for example 30 000 g / mol, and a hydrolysis rate of 70% to 90%, preferably from 80% to 90%,

the anionic surfactant component is a mixture of potassium and / or sodium polyphosphates and / or pyrophosphates, i.e. a mixture of potassium polyphosphates or a mixture of sodium pyrophosphates or a mixture of sodium pyrophosphates or a combination of these.

The degree of hydrolysis according to the invention is understood to mean the proportion, in molecular percent, of the acetate radicals replaced by hydroxyl radicals.

the aqueous sealant additionally contains at least one high molecular weight formaldehyde resin, according to the invention, i.e. usually from 2000 to 6000 g / mol, preferably in the presence of a rubber latex of nitrile butadiene (or Nitrile Butadiene Rubber, NBR), carboxylated (XNBR) or uncarboxylated (NBR), for example more than 80% by weight of said resin in said sealant;

the production of the impregnating sealant comprises either forming a premix comprising fillers, optionally at least one resin, or at least one anionic surfactant type component, PVA and water, and adding the latex to said premix, either, preferably, forming a premix which is substantially liquid and comprising water, PVA, optionally at least one anionic surfactant type, and latex, and adding a preformed composition comprising dry substances (ie, fillers and optionally at least one resin) to the masterbatch;

the latex is of the NBR or XNBR type;

the percentage by weight of PVA relative to the solids (dry extract) in the mastic (i.e. usually latex, fillers and one or several resins) is 0.4 to 3%, preferably 0.4 to 2.6%;

the strand comprises at least one basic textured glass fiber;

the texture of the textured glass fiber is from 600 to 5000 tex;

the strand comprises a metal fiber;

the friction ring for the clutch friction disk which operates dry comprises at least one strand formed of fibers, in particular mineral fibers, such as glass fibers, organic fibers, such as fibers of polyacrylonitrile or derivatives, the aqueous mastic comprising fillers, latex and PVA;

- the friction ring is obtained in the manner described above.

The aqueous sealant of the present invention may contain other ingredients known to the skilled person, such as thermoplastic melamine formaldehyde resins, but also water-soluble resorcinol resins, friction fillers such as barium sulfate and carbon black, and other additives such as ammonia. All of the preceding liquid substances are added at substantially the same time, preferably first.

It can be stated that, thanks to the present invention, the viscosity of the mixtures is lower, especially in the presence of stabilized NBR latexes, but also with SBR latex, which allows a higher concentration of aqueous sealant solutions and thus a shorter drying time.

Another advantage of the present invention is that the dried impregnated strand has better adhesive ability than the strands of the prior art, which facilitates further shaping for the manufacture of clutch lining materials.

In addition, it is possible to record the stability of the physicochemical properties of the sealant during the entire period of use, which preferably results in better and lasting quality of the final product, i.e. the friction ring.

Likewise, PVA, which acts as a specific surfactant, allows the strand to control the moisture level of the strand substantially from 2% to 7% when drying the strand, while maintaining the elastic nature of the strand, especially when the sealant contains a carboxylated NBR latex that is prone to cause solidification of the dried impregnated strand.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be shown in the description of exemplary embodiments of the invention, with reference to the accompanying drawings, in which:

- Figure 1 the evolution of viscosity (V) versus time (T) for sealants no. 1-1 (o), 1-2 (Δ) and 1-3 (□) of the invention;

2 shows the evolution of the viscosity (V) versus time (T) for the sealant no. 2-1 according to the invention for individual PVA contents;

3 shows the development of viscosity (V) versus time (T) for the sealant no. 2-2 of the present invention for individual PVA contents;

4 shows the development of viscosity (V) versus time (T) for the sealant no. 2-3 according to the invention for individual PVA contents;

5 shows the development of the viscosity (V) versus time (T) for the sealant no. 2-4 according to the invention for individual PVA contents;

6 shows the development of viscosity versus time for putty no. 3-1 according to the invention;

7 shows the evolution of the viscosity versus time for the sealant no. 3-2 of the present invention.

The figures serve to illustrate the examples below and are explained in the examples below.

DETAILED DESCRIPTION OF THE INVENTION

A few examples of the composition of sealants for clutch friction materials are given. In the following, the components are expressed in percent by weight, based on the total solid dry material in the sealant.

The PVA used, the concentration of which can be varied, is a commercial product with a degree of hydrolysis of 88%, a pH of 6.8 to 8.2, a solution concentration of 18%, a Brookfield viscosity of 10 Po and a molecular weight of 30,000 g / mol.

1) Example of putty no. 1; a suspension of insoluble thermoplastic organic resins

We have a suspension with 100% novolak phenol-formaldehyde resin in water (dry extract from 58 to 60%), which is unstable without the addition of a stabilizer or the addition of a thickening agent (carboxylmethylcellulose); surfactants such as PPNa (sodium polyphosphate) and as fatty alcohol polyglycol ether (HLB or Balance Lipophile Hydrophile - from 9 to 16) are difficult to stabilize with classical anionic surfactants. The addition of a water-soluble resin, such as melamine-formaldehyde, makes it possible to obtain a stable emulsion, but to a limited extent up to 50% by weight to 50% by weight of the insoluble phenolic resin in suspension.

The sealant is made. Its basic composition is defined as follows;

a water-insoluble phenol-formaldehyde novolak resin; from 70 to 100% by weight; and

- soluble, melamine-formaldehyde resin; from 30 to 0% by weight.

This sealant is stabilized by the addition of PVA. There are three types of sealant compositions. 1, namely putty no. 1-1, putty no. 1-2 and putty no. 1-3 containing PVA, the composition of which is given in Table 1.

Table 1

mark composition Dry sealant extract (% by weight) % By weight of novolak % Melamine % PVA by weight % By weight stabilizers Tmel č. 1-1 58-60 100 0 1.4-1.5 0.03 * Tmel č. 1-2 58-60 80 20 1.4-1.5 - Tmel č. 1-3 58-60 70 30 1,3-1,4 -

* thickener = carboxylmethylcellulose

Picture no. 1 represents for each of the sealants no. 1-1, 1-2 and 1-3 reaction in terms of the kinetic stability of the dispersion shown in Example 1. 1 in the presence of PVA.

The vertical axis is the viscosity V (in Po) and the horizontal axis is the time T (in minutes).

It is possible to state a stabilization, which can be explained by the steric effect of the polymer on the interface between the insoluble phenol-formaldehyde resin particles and the continuous phase (water).

2) Example of putty no. 2; suspension of insoluble thermoplastic organic resins / carboxylated and non-carboxylated latex nitrile butadiene

We have a phenol-rich suspension that contains latex nitrile butadiene with or without a carboxylated surface function. The anionic surfactant-containing latex is pH sensitive and stable only in the pH range of 8.2 to 9. The novolak-type phenolic resin releases acidic functions into the water that can destabilize the NBR and XNBR latices (solidification, bonding of the particles together); such a suspension is usually not stable because;

pH stabilization by the addition of a chemical buffer alone is not sufficient to ensure the kinetic stability of the dispersion, and

anionic surfactants such as PPNa, and nonionic surfactants such as polyglycol ether of fatty alcohol (HLB from 9 to 16) do not improve the stability of this type of aqueous suspensions.

The sealant is made. Its basic composition is defined as follows;

a water-insoluble phenol-formaldehyde novolak resin; 80 to 90% by weight

carboxylated latex nitrile butadiene (XNBR) (A) or non-carboxylated (NBR) (B): 20 to 10% by weight;

- other substances: 1 to 5% (example: 2% resorcinol, pH regulator, rubber vulcanization activator)

This sealant is stabilized by the addition of PVA. Four sealant compositions are realized. 2, namely putty no. 21, putty no. 2-2, putty no. 2-3 and putty no. 2-4, containing PVA whose composition is shown in Table 2.

Table 5

mark composition Dry mastic extract (% by weight) Weight. % novolak Weight. % XNBR Weight. % NBR Weight. % PVA % By weight of other ingredients Tmel č. 2-1 60-63 90 10 - 0.7 to 2.6 2 to 3 Tmel č. 2-2 60-63 90 10 - 0.7 to 2.6 - Tmel č. 2-3 60-63 90 - 20 0.7 to 2.6 2 to 3 Tmel č.2-4 60-63 80 20 - 0.7 to 2.6 2 to 3

Figures no. 2 (2 sources of carboxylated NBR, latex A and latex B), 3 (carboxylated NBR), 4 (carboxylated NBR) and 5 (uncarboxylated NBR) respectively represent, for each of the sealants no. 2-1, 2-2, 2-4 and 2-3, the reaction in terms of the kinetic stability of the dispersion cited in Example 2. 2, in the presence of PVA, the content of which varies. The vertical axis is the viscosity V (in Po) and the horizontal axis is the time T (in minutes).

It can be stated that if the reaction can vary depending on the composition and complexity of the system from which the dispersion is to be obtained (when the number of individual components increases), usually from 1 to 2.6% PVA (weight fraction based on dry mastic extract) ) allows, for this type of dispersion composition, excellent stabilization, moreover, without observing colloidal colloid adhesion or flocculation in the system.

All results are satisfactory for managing the impregnation of the spring.

3) Example of sealant no. 3: complex suspension of insoluble thermoplastic organic resins / carboxylated latex nitrile butadiene and friction fillers and soluble resins

We have NBR rubbers, carboxylated or not, which are usually stable in the organic environment or in the aqueous phase with soluble phenol-formaldehyde resins (low molecular weight, usually less than 1000 g / mol). Conversely, in an aqueous environment and in the presence of high molecular weight novoloca phenol formaldehyde resin with simultaneous stabilizers (anionic surfactants such as sodium polyphosphates, and ammonia), the addition of these NBR rubbers makes the system metastable: solidification in less than 15 minutes of mixing.

The anionic surfactant latex is pH sensitive and stable only in the pH range of 8.2 to 9. The novolak phenolic resin releases acidic functions (protons) into the water that can destabilize the NBR (solidification, bonding of the particles together) because:

pH stabilization by the addition of a chemical buffer alone is not sufficient to ensure the kinetic stability of the dispersion, and

anionic surfactants such as PPNα, effective with SBR latexes, and nonionic surfactants such as polyglycol ether of fatty alcohol (HLB from 9 to 16), tested alone, do not improve the stability of this type of aqueous suspensions.

Due to the complexity of the system, in particular the presence of soluble resins and inorganic fillers which add further interactions to the dispersion, two different stabilization systems (anionic surfactants PPNa + PVA for sealant # 3-1 or separate PVA for sealant # 3-2) were tested. .

The sealant is made. Its basic composition is defined as follows:

- water-insoluble phenol-formaldehyde resin, novolak type: 27% by weight

carboxylated latex nitrile butadiene (XNBR): 19% by weight

- other organic constituents (melamine, dermulsen): 22%

- friction additives (BaSO ₄ , carbon black): 29%

- other (PPNa, ammonia, S): the 3% pH of the putty is in all cases maintained between 8.5 and 9 to avoid the latex being precipitated. This sealant is stabilized by the addition of PVA. There are two types of sealant compositions no. 3, namely putty no. 3-1 and putty no. 3-2 containing PVA whose composition is shown in Table 3.

Table 6

mark composition Dry mastic extract (% by weight) Weight. % novolak Weight. % XNBR Weight. % NBR Weight. % PVA Weight. % (other components) PPNa Weight % Tmel č. 3-1 64 27 19 - 0.4 - 0.6 54 0.4 Tmel č. 3-2 64 27 19 - 0.6 54 -

Figures no. 6 (source XNBR) and 7 represent for each of the sealants no. 3-1 and 3-2 of the reaction with respect to the 5 kinetic stability of the dispersion mentioned in Example 2. 3, in the presence of PVA. The vertical axis is the viscosity V (in Po) and the horizontal axis is the time T (in minutes).

Figure 6 shows the stability of NBR carboxylated latex. 3-1, for small amounts of PVA stabilizer combined with anionic stabilizer (PPNa).

Figure 7 shows the stability of the system without anionic surfactants (PPNa), but 10 only with the PVA stabilizer: carboxylated latex NBR: viscosity develops over time, but remains correct for impregnation with a 2 hour lifetime. (change 5 Mo). On the other hand, in Figure 7 there is no latex

SBR stabilized.

Claims (2)

Use of polyvinyl alcohol for the production of a friction material, in particular a friction ring, generally for a clutch friction disc. A friction ring for a clutch friction disk operating dry, comprising 20 at least one strand formed from fibers, in particular mineral fibers such as glass fibers, organic fibers such as fibers of polyacrylonitrile or derivatives, wherein the water-based sealant contains fillers , phenol resin and / or latex and polyvinyl alcohol.