WO2004052986A1

WO2004052986A1 - Polymer composition and moulded articles made thereof

Info

Publication number: WO2004052986A1
Application number: PCT/NL2003/000882
Authority: WO
Inventors: Richard Seivert Henk Spit; Louis-Philippe Antoine Eugene Maria Reuvekamp; Jacobus Wilhelmus Maria Noordermeer
Original assignee: Stichting voor de Technische Wetenschappen STW
Current assignee: Stichting voor de Technische Wetenschappen STW
Priority date: 2002-12-12
Filing date: 2003-12-11
Publication date: 2004-06-24
Anticipated expiration: 2005-06-12
Also published as: NL1022150C2; AU2003295255A1

Abstract

Polymer composition that contains a copolymer and as a filler silica with a dibutyl phthalate value, measured according to ISO-4656/2, of at least 150g/100g, which copolymer contains monomer units of ethylene, an α-olefin and a non-conjugated diene, characterized in that the polymer composition contains 99-85 parts by weight of the copolymer and 1-15 parts by weight of natural rubber. The invention also relates to vulcanized rubber which is formed by vulcanization of the polymer composition and to moulded articles that consist wholly or partially of the vulcanized rubber, preferably engine mounts or exhaust suspension rubbers.

Description

POLYMER COMPOSITION AND MOULDED ARTICLES MADE THEREOF

The invention relates to polymer composition that contains a copolymer and as a filler silica with a dibutyl phthalate value, measured according to ISO-4656/2, of at least 150g/100g, which copolymer contains monomer units of ethylene, an α-olefin and a non-conjugated diene. The invention also relates to a vulcanized rubber that is formed by vulcanization of the composition and to moulded articles that consist wholly or partially of the vulcanized rubber

A polymer composition that contains a copolymer, which copolymer contains monomer units of ethylene, an α-olefin and a non-conjugated diene, is for example known from "Rubber Technology Handbook W. Hofmann"; Carl Hanser Verlag (1989), pages 93-100. A copolymer that contains ethylene, an α-olefin and a non- conjugated diene is referred to hereafter as EPDM. EPDM is blended in general with for example Plasticizers, reinforcing fillers and vulcanizers to form the polymer composition that contains the EPDM. Polymer compositions that contain EPDM are commonly used for the production of moulded articles. During the processing to form moulded articles the polymer composition is converted by vulcanization of the EPDM into the final vulcanized EPDM rubber. Examples of such moulded articles that consist wholly or partially of the vulcanized EPDM rubber are seal profiles for windows in cars and buildings, roofing film and conveyor belts.

The vulcanized EPDM rubber possesses good resistance to ozone, heat and oxidation. Vulcanized EPDM rubber further possesses good mechanical properties, although it is desirable that for some applications of EPDM rubber a higher tear strength is attained. Surprisingly a vulcanized rubber is obtained with not only good ozone heat and oxidation resistance, but also with good tear strength, if the rubber is formed by vulcanization of a polymer composition which polymer composition contains 99-85 parts by weight of the copolymer and 1-15 parts by weight of natural rubber Although natural rubber is to possess a high tear strength, it possesses precisely a poor resistance to ozone, heat and oxidation. It is further known that during blending of different elastomers often even an antagonistic effect occurs, so that the final rubber obtains the adverse properties of both components. Furthermore in "Rubber technology handbook W. Hofmann"; Carl Hanser Verlag (1989), page 22, last paragraph it is recommended not to manufacture a blend that contains EPDM and natural rubber. Very surprisingly, however, very good results are achieved with the composition according to the invention. For example, a very high tear strength is achieved despite the small natural rubber content in the composition. A further advantage of the composition according to the invention is that a vulcanized rubber with high tear propagation resistance is obtained. This means that after the first tear a high force must always be exerted to cause the tear to grow.

Still another advantage of the composition according to the invention is that a vulcanized rubber with a high tensile strength is obtained. Yet another advantage of the polymer composition according to the invention is that a vulcanized rubber with good resistance to cyclic loads is obtained.

The α-olefin that is applied in the EPDM is for example an α-olefin with 3- 10 carbon atoms.

Examples of α-olefins that can be applied in the EPDM are propylene, butene, hexene, octene and the like. Preferably propylene is used.

The weight ratio between ethylene and the α-olefin in the EPDM is preferably between 90/10 and 20/80, more preferably between 70/30 and 40/60.

Examples of non-conjugated dienes that can be applied in the EPDM are 5-ethylene-2-norbornene, 5-vinyl-2-norbornene, dicyclopentadiene and 1.4-hexadiene. It is also possible for a blend of two or more non-conjugated dienes to be applied in the EPDM, for example a blend of 5-ethylene-2-norbornene and 5-vinyl-2-norbornene.

EPDM can be prepared by for example polymerisation with the aid of a Ziegler-Natta catalyst or a metallocene catalyst.

Natural rubber, hereafter referred to as NR, is obtained from the rubber tree. For a description of NR, see "Rubber Technology Handbook W. Hofmann"; Carl Hanser Verlag (1989), pages 11-22. The polymer composition according to the invention further contains for example oil, fillers, such as carbon black , silica, talc, chalk and pigments, additives, such as vulcanizers, accelerators, processing aids, such as fatty acid esters and alcohols.

The polymer composition according to the invention contains 99-85 parts by weight of EPDM and 1-15 parts by weight of natural rubber, and preferably 98-88 parts by weight of EPDM and 2-12 parts by weight of natural rubber.

The polymer composition according to the invention contains a silica as filler. For a description of the silica the reader is referred to "Rubber Technology Handbook W. Hofmann"; Carl Hanser Verlag (1989), pages 287-290. The polymer composition according to the invention can contain for example 10 - 100 parts by weight of silica for every 100 parts by weight of the sum of EPDM and NR. Preferably the polymer composition according to the invention contains 15-80 parts by weight, more preferably 20-70 parts by weight, still more preferably 25-60 parts by weight of silica to 100 parts by weight of the sum of EPDM and NR. In addition to silica one or more other fillers can be present in the polymer composition according to the invention, such as carbon black, talc, chalk and calcium or aluminium silicates. Preferably in the composition according to the invention the fillers are at least 80%, preferably at least 90%, more preferably at least 95% silica.

Preferably a precipitated silica is used. This is a silica which has been prepared by precipitating the silica from silicate solution.

As silica a silica with a dibutyl phthalate value of at least 150 g/100g is used, more preferably 175 g/100g, still more preferably 190g/100g. The dibutyl phthalate value is measured according to ISO-4656/2. As a result very good tear strength and tensile strength are obtained. Such a silica preferably is prepared by spray drying. A process for the preparation of silica by spray drying is described in US-5587416. This describes a process in which silica is precipitated from a solution preferably consisting of sodium or potassium silicate by conditioned acid addition. The silica precipitate is separated by for example filtration. Next, the filtrate is dried using the spray drying technique. Preferably the silica is used in combination with a coupling agent. This ensures good distribution of the silica particles and good adhesion between the silica particles and the elastomeric matrix. Good results are obtained if as coupling agent a compound according to formula 1 is used:

(R3)y (R4)u

(R1 -O)_x -Si-C_p-S_n-C_m-Si-(O-R2) Formula 1

where:

n is 2-12, preferably 2-8. m and p are independently of each other 1-30, preferably 1-20, more preferably 1-10, still more preferably 1-5, x+y and z+u are 3. x and u are 1-3.

R1 , R2, R3 and R4 are alkyl groups with 1-25 carbon atoms, preferably 1-15 carbon atoms.

Most preferably m and p are both 3. Most preferably R1 , R2, R3 and R4 are an ethyl group.

Very good results are achieved if as a compound according to the formula 1 bis(triethoxysilylpropyl)tetrasulfide is used. It is also possible to use as coupling agent a compound according to formula 2:

(R4)u

I Formula 2.

H-S-C_m-Si-(O-R2)_z

It is also possible to use as coupling agent a compound according to formula 3:

(R4)u I Formula 3. C=C-Si-C_p-S_n-C_m-Si-(O-R2)_z The symbols in formulae 2 and 3 have the same meaning as above- - described for Formula 1.

Compounds according to formulae 1 and 2 are preferably used for a vulcanization system based on sulfur. Compounds according to formula 3 are preferably used for a vulcanization system based on peroxide.

It is also possible to use as a coupling agent a compound that contains besides a silane group a group that serves as an accelerator in the vulcanization process. A suitable weight ratio between coupling agent and silica is between 1 to 5 and 1 to 20, preferably 1 to 8 to 1 to 12, most preferably 1 to 10. The invention also relates to a vulcanized rubber that is formed by vulcanization of the polymer composition according to the invention.

Although not preferable, it is possible for the polymer composition according to the invention to contain besides EPDM and NR a third elastomer. Examples of such elastomers are polybutadiene rubber, styrene-butadiene rubber. Preferably the polymer composition according to the invention contains 0-

20 parts by weight of a third elastomer, more preferably 0-10 parts by weight, still more preferably 0-5 parts by weight, even more preferably 0-2 parts by weight, still more preferably 0-1 part by weight. Most preferably the polymer composition according to the invention contains no third elastomer at all. As vulcanization systems for the polymer composition according to the invention the vulcanization systems for EPDM and the vulcanization systems for NR can be used. It is also possible by so-called Y-blending to prepare a blend of NR with a suitable vulcanization system, a blend of EPDM with a suitable vulcanization system and then to blend both blends with each other. The invention also relates to moulded articles that consist wholly or partially of the vulcanized rubber. Very good results are achieved with moulded articles that are subjected in their application to cyclic loads or with moulded articles for which the tear properties are important.

Cyclic loading is understood to be the subjection to a force of a varying magnitude, whether or not with a regular pattern. Preferably the vulcanized rubber according to the invention possesses a tear strength of at least 4 N/mm, more preferably 5 N/mm, more preferably 6 N/mm, more preferably 7N/mm, still more preferably 8 N/mm.

Very good results are obtained if the moulded articles are roofing material, conveyor belts, drive belts, door seal profiles, preferably door seal profiles that consist at least partially of the rubber in a sponge-like form. Most preferably engine mounts and exhaust suspension rubbers are chosen as moulded articles. These moulded articles must be capable of withstanding cyclic loads, possess a good tear and tear propagation strength and must also be capable of withstanding high temperatures. The invention is elucidated on the basis of the examples, without being limited thereto.

Materials used in the examples and comparative experiments:

EPDM: Keltan ™ 7441, supplied by DSM Elastomers B.V., a copolymer of ethylene, propylene and 5-ethylene-2-norbornene. The Keltan contains per 100 parts by weight of EPDM 75 parts by weight of paraffinic oil.

Natural rubber (NR): SIR 20.

Silica: Zeosil ™ 1165 MP, supplied by Rhodia silices.

Coupling agent: TESPT Silquest ™ A-1289, supplied by OSI Specialties Group/Crompton Corporation.

Zinc oxide, supplied by Merck

Stearic acid, supplied by Merck

Sulfur, supplied by J.A.Baker.

Teramethyl thiuramdisulfide (TMTD), supplied by Aldrich. Dipentamethylene thiuram terasulphide (DPTT), supplied by Flexsys BN.

Ν-cyclohexylbenzthiazole-2-sulphenamide (CBS), Santocure ™ CBS,), supplied by

Flexsys BN.

Mercaptobenzothiazole (MBT), supplied by Merck.

Diphenyl guanidine (DPG), Perkacit ™ DPG, supplied by Flexsys BN. Compound recipes of the compounds used in the examples and comparative experiments are given in Table 1. Table 1

This means that use was made of 0-175 parts by weight of Keltan partly consisting of the paraffinic oil as indicated above.

The EPDM and NR vulcanization systems used in compounds are given in table 2.

Table 2 Component NR system EPDM system

Parts by weight Parts by weight sulfur 0.3 1

TMTD 0.8

DPTT 0.8

MBT 1.5

CBS 3

DPG 1.5 1.5

Preparation of the compounds and the test samples.

The compounds were prepared by metering the components to a Brabender Plasticorder Labstation 390 ml internal blender. The degree of filling of the blender was 70%. The total blending time amounted to 6 minutes and 30 seconds. After 1 minute and 20 seconds' blending time the silica, the zinc oxide and the stearic acid were added. The temperature of the blender was 50 °C. A compound, upon being released from the blender, was rolled out to a sheet using a Schwabenthan 100 ml. roller.

Then the compound was blended again for 5 minutes in the blender and again brought onto the roller, after which the vulcanization agents were blended in on the roller.

Next the compounds were pressed to form sheets with a thickness of 2 mm and vulcanized at a temperature of 170 °C and a pressure of 100 bar.

Test samples were punched out of the sheets to measure the mechanical properties. Mechanical properties: The tear strength was measured with the aid of a

Zwick Z020 tension testing machine according to ISO-34, using the trouser model as the test sample.

Example 1 and comparative experiments A and B. Influence of NR on the tear strength and tear propagation strength.

The tensile strength was measured of compounds that contained 100 parts by weight of EPDM (comparative experiment A), 95/5 parts by weight of EPDM/NR (example 1) and 100 parts by weight of NR (comparative example B) ; after the first tear of the test samples the measurement was continued until the sample was completely torn through. The compounds were vulcanized with the NR system.

The results are shown in Fig. 1-3.

It is clear from Fig. 1 that the compound based on 100 parts by weight of EPDM (comparative experiment A) tears when subjected to a small force (7.4N) and continues to tear at approximately the same force. In Fig. 2 it can be seen that the compound based on 100 parts by weight of NR (comparative experiment B) tears at a much higher value (38N) and that after each tear a force must be built up. In Fig. 3 it can be seen that the compound based on 95/5 parts by weight of EPDM/NR possesses a very high tear strength and a very high and constant tear propagation strength (21 N), in view of the low natural rubber content. Furthermore, it can be seen that the elongation at full fracture in the case of the composition according to the invention is even higher than the elongation at full fracture of the NR Further examples and comparative experiments in which the tensile strength is determined as a function of the NR content.

Compounds with varying EPDM/NR ratios ranging from 100/0 to 0/100 were vulcanized to sheets as indicated above, after which the tensile strength was measured.

In Fig. 4 the thus measured tensile strength is given as a function of the NR content (NR + EPDM =100)

Examples and comparative experiments marked by a square were vulcanized with the EPDM system, those marked by a circle were vulcanized with the NR system and those marked by a triangle were vulcanized after Y-blending.

It is clear that the tensile strength is optimum for the polymer compositions according to the invention containing between 1-15 parts by weight of NR (and correspondingly 99-85 parts by weight of EPDM).

Claims

1. Polymer composition that contains a copolymer and as a filler silica with a dibutyl phthalate value, measured according to ISO-4656/2, of at least 150g/100g, which copolymer contains monomer units of ethylene, an α-olefin and a non-conjugated diene, characterized in that the polymer composition contains 99-85 parts by weight of the copolymer and 1-15 parts by weight of natural rubber.

2. Polymer composition according to claim 1 , characterized in that the copolymer contains propylene as α-olefin .

3. Polymer composition according to claim 1 or 2, characterized in that the polymer composition contains 10-100 parts by weight of silica for every 100 parts by weight of the sum of the copolymer and the natural rubber.

4. Polymer composition according to claims 1 to 3, characterized in that as silica a precipitated silica is used.

5. Polymer composition according to any one of claims 1 to 4, characterized in that as silica a silica is used with a dibutyl phthalate value, measured according to

ISO-4656/2, of at least 175g/100g

6. Polymer composition according to any one of claims 1 to 5, characterized in that the polymer composition contains a coupling agent.

7. Polymer composition according to any one of claims 1 to 6, characterized in that the polymer composition contains 0-20 parts by weight of a third elastomer.

8. Polymer composition according to any one of claims 1 to 7, characterized in that the polymer composition contains 0-10 parts by weight of a third elastomer.

9. Vulcanized rubber that is formed by vulcanization of the polymer composition according to any one of claims 1 to 8.

10. Vulcanized rubber according to claim 9, characterized in that the rubber possesses a tear strength of at least 4 N/mm.

11. Moulded articles that consist wholly or partially of the vulcanized rubber according to claim 9 or 10.

12. Moulded articles according to claim 11, characterized in that as moulded articles engine mounts or exhaust suspension rubbers are chosen.