EP1572799A1

EP1572799A1 - Method for vulcanizing a rubber compound, and rubber articles manufactured from a vulcanized rubber compound as obtained with the method

Info

Publication number: EP1572799A1
Application number: EP03789645A
Authority: EP
Inventors: Bernard Van Baarle; Geert Heideman; Jacobus Wilhelmus Maria Noordermeer
Original assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 2002-12-11
Filing date: 2003-12-11
Publication date: 2005-09-14
Also published as: WO2004052981A1; AU2003294184A1; NL1022146C2

Abstract

The invention relates to a method for vulcanizing a rubber compound, wherein the rubber compound, under heating, in the presence of sulfur or a sulfur-containing compound, and a vulcanization accelerator, is contacted with an activator comprising a support material loaded with Ba, Pd, Cd, Ca, Mg and/or Zn ions provided on the support material through an ion exchange process with a metal ion-containing solution. The invention also relates to rubber articles manufactured from a vulcanized rubber compound as obtained with the method according to the invention.

Description

Title: Method for vulcanizing a rubber compound, and rubber articles manufactured from a vulcanized rubber compound as obtained with the method

The invention relates to a method for vulcanizing a rubber compound, and rubber articles manufactured from a vulcanized compound as obtained with the method according to the invention.

Rubber compounds normally need to be vulcanized with sulfur or a sulfur-containing compound to ensure that they have the proper physical properties that are needed for the various applications. The vulcanization is usually carried out at elevated temperature and in the presence of a vulcanization accelerator because the vulcanization as such proceeds slowly. To further improve the physical properties of the rubber vulcanisates to be obtained, the vulcanization is normally carried out in the presence of a vulcanization catalyst or activator. Typically, zinc oxide is used as activator, often in combination with stearic acid in compounds containing sulfur. As a most important application, zinc oxide is used in the preparation of rubber compounds that are used in tires. In tire treads, zinc has the drawback that through wear of the car tires, tire grindings end up in the surface water. Given the fact that zinc is a heavy metal unfortunately having a harmful effect on microorganisms, it will be clear that a reduction of the zinc concentration in tires for transport purposes, for instance car tires, would be very favorable to the environment. Surprisingly, it has now been found that rubber compounds can be vulcanized utilizing a specific activator that contains no zinc or substantially less zinc, which is highly favorable to the environment.

Accordingly, the invention relates to a method for vulcanizing a rubber compound, wherein the rubber compound, under heating, in the presence of sulfur or a sulfur-containing compound, and a vulcanization accelerator, is contacted with an activator comprising a support material loaded with Ba, Pd, Cd, Ca, Mg and/or Zn ions provided on the support material through an ion exchange process with a metal ion-containing solution. Preferably, the support material is loaded with zinc ions.

The rubber compounds that can be used according to the invention are generally known and can be selected from the group of polymers such as natural rubber, styrene butadiene rubber, polyisoprene rubber, nitrile butadiene rubber and ethylene propylene diene rubber.

Preferably, the support material of the activator is a clay, though not limited to the groups mentioned. Suitable clays can be selected from the group of the halloysite, illite, kaolinite, bentonite, phyllosilicate, and/or paly gorskite -like clays. Halloysite -like clays can be suitably selected from the group of allophane, endellite, halloysite, indianite, metahalloysite and schrotterrite. Suitable illite-like clays can be selected from the group of brammallite, bravaisite, glimmerton, hydromica and sercicite. Suitable ^■ kaolinite-like clays can be selected from the group of anauxite or ionite, collyrite, dickite, ferrikaolinite, nacrite, neokaolin, metakaolin, metanacrite and severite. Suitable montmorillonite-like clays can be selected from the group of beidellite, bentonite, chloropal, erinite, ferrimontmorillonite, hectorite, metabentonite, montmorillonite, nontronite, otaylite and saponite. A suitable phyllosilicate-like clay is vermiculite. Paly gorskite -like clays can be suitably chosen from the group of attapulgite, calciopaly gorskite, lassalite, palygorskite, paramontmorillonite, parasepiolite and sepiolite.

Such support materials can be suitably used in the method according to the invention because they contain (relatively) large amounts of exchangeable ions (Ca, Mg, Na).

Preferably, according to the invention, a clay is used from the group of bentonite and phyllosilicate. Particularly suitable supports herein are bentonite, montmorillonite and vermiculite.

These support materials are further described in U.S. Patent 3,902,886. The metal loading of the activator is generally 0.1-30 wt.%, calculated on the support material. In a suitable embodiment, the metal loading is 1-15 wt.%, calculated on support material. Preferably, the metal loading is 3-7wt.%, and more preferably 4-6 wt.%, calculated on support material. In a suitable embodiment, the amount of activator is 0.1-20 wt.%, calculated on the rubber compound. Preferably, the amount of activator is 1-7 wt.%, calculated on the rubber compound, and more preferably the amount of activator is 2.5-5 wt.%, calculated on the rubber compound.

With respect to the conventional zinc oxide activator, the proposed activator allows the zinc content to be reduced by a factor of 20 if the activator is loaded with zinc, or allows the zinc to be actually replaced with other metals. The activator that is used according to the invention can be suitably prepared by subjecting the support material to an ion exchange process with a metal ion-containing solution. Preferably, a zinc ion- containing solution is used. Suitable zinc ion-containing solutions can be selected from the group of zinc chloride, zinc nitrate and zinc acetate. Preferably, in the ion exchange process, use is made of a metal chloride solution and more preferably of a zinc chloride solution.

In a suitable embodiment of the invention, the ion exchange process is carried out at a temperature of 15-30° C for 10-24 hours at a pH of 6-8. Preferably, the ion exchange process is carried out at a temperature of 20-25° C for 12-18 hours, and at a pH of 6.5-7.5. The support material can be contacted under movement, for instance with shaking, with a metal ion- containing solution, preferably zinc chloride solution (for instance a 1M zinc chloride solution) for 2-8 hours. Next, the slurry obtained can be suitably dialyzed with, for instance, demineralized water until it is essentially anion- free. The thus obtained slurry can then be dried for 8-16 hours at a temperature of 65-70°C. Next, the thus obtained support material can, if desired, be ground and screened, whereby a particle size of less than 38 microns can be obtained. Preferably, the support material is treated with an acid before being subjected to the ion exchange process. Suitable acids can be selected from the group of hydrogen chloride and hydrogen sulfide acid. More preferably, as an acid, hydrogen chloride is used, for instance a solution of 20% hydrogen chloride.

The treatment with acid is suitably carried out at a temperature of 15-30°C for 2-8 hours, and at a pH of 1-4. Preferably, the treatment with acid is carried out at a temperature of 20-25°C for 3-5 hours, and at a pH of 1-2. Next, the obtained slurry can be neutralized with an alkaline solution, for instance a NaOH solution, until it has acquired a pH of 6.5-7. Next, the neutralized slurry can be suitably dialyzed, with, for instance, demineralized water, until the compound is substantially free of anions. Then, the slurry can be dried, for 8-16 hours at a temperature of 65-70°C, after which the obtained support material can be ground and screened, whereby a particle size of less than 38 microns can be obtained.

In the method according to the invention, preferably sulfur is used as vulcanizing agent. The amount of sulfur can be 0.5-3 wt.%, calculated on the rubber compound. Preferably, the amount of sulfur is 1-2 wt.%, calculated on the rubber compound. In the method according to the invention, use can be made of generally known vulcanization accelerators. Suitable vulcanization accelerators can be selected from the group of xanthates, carbamates, thiazoles, sulfenamides, thiurams, and guanidines, as described in Dutch patent specification 185670. Preferably, a vulcanization accelerator is selected from the group of sulfenamides.

The vulcanization accelerator can be present in an amount of 1-5 wt.%, calculated on the rubber compound. Preferably, the vulcanization accelerator is present in an amount of 2-4 wt.%, calculated on the rubber compound. It will be clear to the skilled person that the choice of the vulcanization accelerator will depend on the conditions under which the vulcanization process will be carried out.

Depending on the type of accelerator and vulcanization temperature, the vulcanization can be suitably carried out between 20-210°C, while for compression molding generally a temperature of 140-180°C is selected and for injection molding a temperature of 170-210°C. Continuous vulcanization can be carried out in a salt bath or hot air tunnels, with and without UHF with temperatures of 140°C to ca. 500°C. The invention further relates to rubber articles manufactured with a vulcanized rubber compound as obtained with the method according to the invention. Such rubber articles can be products such as tires for transport purposes such as car tires, airplane tires and tires for motorcycles, conveyor belts, (heating) hoses, driving belts, roller covering, electrical insulations, etc. In addition, the rubber articles can be sealing profiles for automobiles, radiator hoses, roof foil and membranes. Preferably, the invention furthermore relates to a tire for transport purposes, and more preferably a car tire, that is manufactured from the vulcanized rubber compound as obtained with the method according to the invention. Further, customary additives may be added to the rubber compound, such as black, plasticizers, clay, silica, pigments, antioxidants, antiozonants, delaying agents, and processing aids such as, for instance, fatty acids and process oils.

Example 1

A master batch was prepared, consisting of 100 parts of s-SBR Buna VSL 2525-0 (a solution SBR having a high content of polymer (98%); 50 parts N 375 (carbon black); and 5 parts of Enerflex 75 (aromatic oil). Using a laboratory roll, a vulcanization system was added to the master batch. The vulcanization system consisted of 2.5 parts of zinc clay; 2 parts of stearic acid; 1.75 parts of sulfur; and 1.50 parts of N-tert.butyl-benzothiazyl sulfenamide (accelerator), the parts being calculated on 100 parts of polymer (see also Table 1). Twenty-five grams of Montmorillonite were refluxed for 4 hours with an excess of HC1 (20%), and neutralized with a solution of 25% sodium hydroxide solution to pH 7. Next, the zinc clay was prepared by subjecting the acid-treated support material to an ion exchange process. The ion exchange was carried out with 12.5 grams of treated support material and 125 ml of a 1M zinc chloride solution, with shaking, at a temperature of 20°C, for 16 hours. Next, the obtained slurry was dialyzed with demineralized water until it was essentially anion-free. The thus obtained slurry was then dried for 12 hours at a temperature of 70°C. Next, the thus obtained zinc clay was ground and screened, whereby a particle size of 63 microns at a maximum was obtained. The zinc clay comprised 4.5 wt.% of zinc, calculated on .Montmorillonite. The obtained mixture of the master batch and the vulcanization system was vulcanized for 30 minutes at a temperature of 160°C and a pressure of ca. 10 Bar. The obtained vulcanisate was then stored for 16 hours at 23°C, after which mechanical and physical properties of the vulcanisate were determined (see Table 2).

Example 2

A vulcanization process as described in Example 1 was carried out, except that in the vulcanization system, instead of 2.5 parts of zinc clay, 5 parts of zinc oxide were used as zinc activator. The composition of the obtained compound of the master batch and the vulcanization system is shown in

Table 1. The mechanical and physical properties of the obtained vulcanisate are shown in Table 2.

Tables 1 and 2 clearly show that surprisingly good and comparable mechanical and physical product properties can be obtained using the vulcanization process according to the invention, while the zinc concentration used has been reduced by as much as a factor of 20 (from 2.42% to 0.12%).

Table 1

Compound Example 2 Example 1 composition (parts) (parts) s-SBR VSL 2525 100 100

Carbon Black N375 50 50

Enerflex 75

Sulfur 1.75 1.75

TBBS * 1.5 1.5

Stearic acid

Zinc clay (activator) 2.5

ZnO (activator)

Zn-conc. (wt. %) 2.42 0.12

Table 2

Examples 3 and 4 (latex variants)

Two aqueous dispersions were prepared in a small 0.25 liter-ball mill with ceramic balls of a diameter of 8 mm. The grinding time in the ball mill was 24 hours. The compositions of the prepared dispersions are shown in Table 3. The latex compounds were prepared according to the formulations in Table 4. The latex compounds were subsequently stored for five days at room temperature. Of the two qualities, small molded plates were manufactured in metal frames on a glass plate. The drying time was 24 hours. The plates were subsequently dried further for 1 hour at 70 °C. Of each rubber quality, two plates were vulcanized at 100°C for 1 hour. Of these plates, physicomechanical properties were determined, listed in Table 5.

Table 3: Dispersions of zinc oxide and Zinc clay

Table 4: Latex compounds

Table 5: Physicomechanical properties of vulcanized latex plates

The measured physicomechanical properties demonstrate that there are no great differences between the latex qualities examined. The values for the tensile strengths are high, the moduli are comparable. The permanent deformation after storage at 70°C of the compound with zinc clay is of equal ) value as the compound with zinc oxide. This is an indication that the compound with zinc clay has reached a good degree of vulcanization after 1 hour of vulcanization at 100°C.

Claims

1. A method for vulcanizing a rubber compound, wherein the rubber compound, under heating, in the presence of sulfur or a sulfur -containing compound, and a vulcanization accelerator, is contacted with an activator comprising a support material loaded with Ba, Pd, Cd, Ca, Mg and/or Zn ions provided on the support material through an ion exchange process with a metal ion-containing solution.

2. A method according to claim 1, wherein the support material of the activator is a clay.

3. A method according to claim 1 or 2, wherein the support material is loaded with Zn ions.

4. A method according to 2 or 3, wherein the clay is selected from the group of the halloysite-, illite-, kaolinite-, montmorillonite-, bentonite-, phyllosilicate- and/or paly gorskite -like clays.

5. A method according to claim 4, wherein the clay is selected from the group of montmorillonite, vermiculite and/or bentonite.

6. A method according to any one of claims 1-5, wherein the metal content is 0.1-30 wt.%, calculated on the, support material.

7. A method according to claim 6, wherein the metal content is 1-15 wt.%, calculated on the support material.

8. A method according to any one of claims 1-7, wherein the support material is treated with an acid before being subjected to the ion exchange process.

9. A metho according to any one of claims 1-8, wherein the ion exchange process is carried out with a metal chloride solution.

10. A method according to any one of claims 1-9, wherein the vulcanization accelerator is selected from the group of sulfenamides.

11. A method according to any one of claims 1-10, wherein the vulcanization is carried out at a temperature of 20-210°C.

12. A rubber article manufactured from a vulcanized rubber compound as obtained with the method according to any one of claims 1-11.

13. A rubber article according to claim 12, which article is a tire for transportation purposes.