AU6549001A

AU6549001A - Rubber composition for belt and belt comprising same

Info

Publication number: AU6549001A
Application number: AU65490/01A
Authority: AU
Inventors: Kenji Sanpe
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 2000-08-28
Filing date: 2001-08-27
Publication date: 2002-03-07
Anticipated expiration: 2021-08-27
Also published as: JP4629199B2; AU776936B2; JP2002069241A

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Bridgestone Corporation Actual Inventor(s): Kenji Sanpe Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: RUBBER COMPOSITION FOR BELT AND BELT COMPRISING SAME Our Ref 651039 POF Code: 93170/352049 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1eoo6Q RUBBER COMPOSITION FOR BELT AND BELT COMPRISING SAME BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to a rubber composition for belts and a belt which comprises the rubber composition. More particularly, it pertains to such a rubber composition for belts that is capable of affording a belt which is excellent in energy saving performance, decreases belt driving energy owing to this energy saving, and in its turn can contribute to the improvement in environmental problems, when applied to a conveyor belt for the purpose of a long distance haul of an object of transport.

It is also concerned with a belt which comprises the aforesaid rubber composition.

2. Description of the Related Arts In the industrial fields of iron/steel, coal, Portland oo.. cement and the like, an object of transport has hitherto been conveyed with a belt conveyor for a long distance. In general, 0 the belt conveyor used for conveying an object of transport comprises a belt which is reinforced with canvas or steel cord.

In the case of a long distance haul of an object of transport by using a belt conveyor, the belt comes in contact with a large number of rollers with a result that loss of energy generated upon the contact increases the electric power consumption for driving the belt conveyor. Such being the case, in order to curtail the electric power consumption it has been required to develop an energy saving belt.

la It is known that most of the loss of energy generated upon the contact between a belt and a roller is attributable to the characteristics of rubber material which constitutes the belt.

There is available tand 3 2 as an index for loss of energy, where tan6 denotes loss tangent, and E'denotes dynamic modulus of elasticity (unit: N mm) The loss tangent tans is the ratio of dynamic loss E" to the dynamic modulus of elasticity E' when a specimen undergoes a stress. It is said that with regard to a rubber material, the energy loss is little in the case where the tan6 3 2 at 51C is set on at most 0.110.

There has heretofore been employed a belt comprising a rubber composition which is blended with carbon black of a low grade (FEF class or lower grade) or silica. In this connection, such problems are involved in that a belt comprising a rubber composition which is blended with carbon black of a low grade is 0 01% insufficient in anti-tear properties, a belt comprising a rubber composition which is blended with silica is insufficient in elongation, and a belt comprising a rubber composition which is blended with unmodified polybutadiene has an excessively large energy loss.

SUMMARY OF THE INVENTION ee* A general object of the present invention, which has been made in the light of the above-mentioned circumstances, is to provide a rubber composition for belts which is excellent in energy saving performance, when applied to a conveyor belt for the purpose of a long distance haul of an object of transport; and to provide a belt comprising said rubber composition.

-2- Other objects of the present invention will become obvious from the text of this specification hereinafter disclosed.

In view of the foregoing, intensive research and investigation were accumulated by the present inventors in order to achieve the above-mentioned objects. As a result, it has been found that the objects can be achieved by a rubber composition comprising a rubber component composed of natural rubber and terminal modified polybutadiene rubber at a specific ratio by weight, and specific carbon black blended with the foregoing rubber component in a specific amount. The present invention has been accomplished on the basis of the above-mentioned findings and information.

That is to say, the present invention provides a rubber composition which comprises 100 parts by weight of a rubber component composed of natural rubber and terminal modified polybutadiene rubber at a ratio by weight of 20 80 to 50 50, and to 50 parts by weight of carbon black having an iodine adsorption amount of at least 117 g/kg, a DBP(dibutyl phthalate) wow.

oil absorption amount of at least 85 cm 3 100g, a DBP oil absorption amount under compression of at least 82 cm 8 100g, a specific surface area by CTAB (cetyltrimethyl ammonium bromide) adsorption of at least 108 m 2 g and a specific surface area by nitrogen adsorption of at least 115 m 2 g.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The rubber composition according to the present invention comprises as polymers, natural rubber and terminal modified polybutadiene rubber. Examples of the terminal modified poly- -3butadiene rubber to be employed in the present invention include all polymers wherein the polybutadiene rubber has been subjected to a terminal modification. As a method for modifying a terminal of polybutadiene rubber, there is available a method comprising modifying an active terminal of polybutadiene rubber by the use of a modifying agent. Examples of the modifying agent include halogenated tin such as tin tetrachloride and tin tetrabromide; halogenated organotin compounds such as tributyltin chloride; silicon compounds such as silicon tetrachloride and chlorotriethylsilane; compounds containing an isocyanate group such as phenyl isocyanate; amide compounds; lactam compounds; urea compounds; isocyanuric acid derivatives; and the like.

There is no specific limitation on the molecular weight of the terminal modified polybutadiene rubber to be used in the present invention. The ratio by weight of the natural rubber to 9 the terminal modified polybutadiene rubber (natural rubber terminal modified polybutadiene rubber)is in the range of 20/80 99o999 to 50/50, preferably 35/65 to 45/55. The content of the natural rubber in the component when exceeding 50% by weight, results in failure to assure useful effect on energy saving. On the contrary, the content of the terminal modified polybutadiene rubber in the component when exceeding 80% by weight, leads to incapability of bringing the physical properties under normal state (elongation, strength and the like) to a level required of the rubber composition for belts.

A polymer other than the polymer component may be used in combination therewith to the extent that the objects of the present invention are not impaired. Specific examples of such a -4polymer include polyisoprene rubber, polybutadiene rubber other than the terminal modified polybutadiene rubber, styrene/butadiene rubber, liquid rubber of any of the foregoing, and the like.

It is preferable to set the blending amount of the above-cited polymer on at most 20 parts by weight (20 phr) based on 100 parts by weight of the total polymer components.

The rubber composition according to the present invention is blended as a filler, with carbon black having an iodine adsorption amount of at least 117 g/kg, a DBP(dibutyl phthalate) oil absorption amount of at least 85 cm 3 100g, a DBP oil absorption amount under compression of at least 82 cm 3 100g, a specific surface area by CTAB (cetyltrimethyl ammonium bromide) adsorption of at least 108 m 2 g and a specific surface area by nitrogen adsorption of at least 115 m 2 g. The aforesaid properties are each a value measured in accordance with JIS K o* 6217. The DBP oil absorption amount under compression is the DBP oil absorption amount obtained by compressing carbon black in advance to destroy the structure thereof and then measuring the same. Such carbon black as satisfies the requisite physical properties is that having a ISAF grade or higher grade.

The blending amount of the component is in the range of 30 to 50 parts by weight, preferably 35 to 40 parts by weight based on 100 parts by weight of the component By setting the blending amount of the component in the range of 30 to parts by weight based thereon, it is made possible to bring the anti-tear properties of the rubber composition in a tear test using trouser type test pieces(in accordance with DIN 53507 to at least 10 N /mm which is required of a conveyor belt. The blending amount of the component when being less than parts by weight, often brings about a marked energy loss at a temperature of 20 9 C or lower, whereby the foregoing anti-tear properties fails to reach 10 N mm. On the other hand, the blending amount of the component when being more than parts by weight, results in an unreasonably large energy loss at a temperature of 10 0 C or higher.

It is possible in the rubber composition according to the present invention to blend therein any of the additives that are blended with an ordinary rubber composition and are other than the components and to the extent that the objects of the present invention are not impaired thereby. For instance, It is possible to blend a softening agent in an amount of at most parts by weight (5 phr) based on 100 parts by weight of the o r polymer components. As the softening agent, there is exemplified .o Sa process oil such as paraffin oil, naphthene oil, aroma oil and spindle oil. Moreover, it is possible to properly and optionally c o blend a vulcanizing agent such as sulfur, a vulcanization roo accelerator such as a thiazole based vulcanization accelerator, a vulcanization assistant such as zinc oxide and stearic acid, an antioxidant, an age resister, a vulcanization retardant and the like.

The rubber composition according to the present invention is obtainable by kneading the components and and the additives as mentioned above by the use of a kneading machine such as an open mixing type kneading roller or a closed mixing machine such as a Banbury mixer. In addition, the belt according to the present invention is obtainable by molding the rubber -6composition thus obtained into the form of a sheet by means of a calender, an extruder or the like;laminating the resultant sheet -like rubber molding with a canvas or steel cord to be used as a reinforcing agent and core material so that it is covered with the rubber molding; and thereafter vulcanizing the resultant laminate. It is made possible in the preparation of the belt to lessen the energy loss thereof by forming at least the belt surface in contact with a roller by using the rubber composition according to the present invention.

As mentioned hereinbefore, there is available tan6 32 as an index for energy loss, where tanS denotes loss tangent, and E' stands for dynamic modulus of elasticity unit: N/mm).

The loss tangent tanS is the ratio of dynamic loss E" to the dynamic modulus of elasticity E' when a specimen undergoes a stress. The energy loss of the belt according to the present invention is lessened by setting the tan6 8 2 at 5 0 C of the vulcanized rubber on at most 0.110. Judging from the aspect of energy saving for the belt, the tand 3 2 at 59C is preferably at most 0.080.

Since it is one of the objects of the belt according to the 9 present invention to impart thereto energy saving performance in a wide range of temperature region, it is the design concept for the belt to set the tan5 32 at 5C of the vulcanized rubber on at most 0.110 and at the same time, to decrease the temperature dependence of the energy loss in the range of low to ordinary temperatures. In addition, it is possible to set the tan 3 2 at 30C low temperature) thereof on at most 0.200 and to set the tan6 3 2 at 209C (ordinary temperature) -7thereof on at most 0.080. Consequently, the belt according to the present invention is minimized in the dependence of the energy loss upon temperature, and is enhanced in energy saving performance at temperatures of 400C and higher.

To summarize the advantages and the working effects of the rubber composition according to the present invention, it is capable of affording a belt which is excellent in energy saving performance in particular, and is imparted with sufficient antitear properties, when applied to a conveyor belt for the purpose of a long distance haul of an object of transport.

In the following, the present invention will be described in more detail with reference to comparative examples and working examples, which however shall not limit the present invention thereto. Therein, evaluations were made of physical properties of the rubber composition for a belt according to the following procedure.

Loss tangent tan6 and dynamic modulus of elasticity E'O. 32) By the use of a viscoelastic spectrometer manufactured by Toyo Seiki Manufacturing Co.,Ltd., measurements were made of the tan 6 and 2 in the range of 40"C to 600C under such conditions as a strain ratio of 2% and a frequency of 10 Hz, whereby the tan6 2 was obtained.

Anti-tear properties Test for anti-tear properties was carried out by the use of testing samples of type A (trouser type test pieces) from among the tear testing method for vulcanized rubber in accordance with DIN 53507.

-8- Examples 1 to 5 and Comparative Examples 1 to 8 Various vulcanized rubber compositions were prepared by blending natural rubber (RSS 4) terminal modified polybutadiene rubber (BR) (manufactured by Nippon Zeon Co., Ltd. under the trade name "NIPOL 1250N") high cis polybutadiene rubber (BR) (manufactured by JSR Corporation under the trade name "BR01"), carbon black of grade ISAF having such characteristics as given in Table 1 (manufactured by Tokai Carbon Co.,Ltd.), carbon black of grade FEF having such characteristics as given in Table 1 manufactured by Tokai Carbon Co.,Ltd.), stearic acid, zinc oxide age resister (manufactured by Ouchi Shinko Chemical Industrial Co.,Ltd. under the trade name "NOCRAC 6C") sulfur and vulcanization accelerator manufactured by Ouchi Shinko Chemical Industrial Co.,Ltd. under the trade name "NOCCELER NS") each at a blending proportion as given in Table 2. Subsequently the resultant rubber compositions were subjected to the foregoing tests. The results thereof are given in Table 1. In Example 1, the tand E'° 0 2 at 409C was 0.114.

ft -9- Table 1 Preferred FEF ISAF value Iodine adsorption amount (g/kg) 117 43 121 DBP oil adsorption amount (cm 3 /1O0g) 85 121 114 DBP oil adsorption amount under compression (cm 3 /lO0g) 82 88 100 Specific surface area by CTAB adsorption (m 2 108 42 ill Specific surface area by nitrogen adsorption (M 2 115 42 119 e.

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Table 2- 1 Blending Formulation (part/s Nos. of Example by weight) 1 2 3 4 Natural rubber 20 20 35 50 Terminal modified BR 80 80 65 50 Carbon black ISAF 40 50 40 35 Stearic acid 3 3 3 3 3 Zinc oxide 3.5 3.5 3.5 3.5 Age resister 2 2 2 2 2 Sulfur 2 2 2 2 2 Vulcanization accelerator 0.8 0.8 0.8 0.8 0.8 Evaluation of physical properties tan&~ /E' 0 32 0.108 0.097 0.158 0.172 0.178 tan 6 /E' 0 8 2 -5 0 C) 0.069 0.074 0.086 0.098 0.090 tan6 0 3 2 (20 0 C 0.043 0.054 0.069 0.079 0.060 Tear test according to DIN (N/mm) 10.8 12.5 13.4 13.8 11.8 a.

a. a a a.

a a a a a..

a a a a.

a a. a a a a a as -11- Table 2-2 Blending Formulation(part/s Nos. of Comparative Example by weight) 1 2 3 4 Natural rubber 10 50 20 Terminal modified BR 90 50 50 High cis BR Carbon black FEF Carbon black ISAF 50 55 25 Stearic acid 3 3 3 3 Zinc oxide 3.5 3.5 3.5 Age resister 2 2 2 2 Sulfur 2 2 2 2 Vulcanization accelerator 0.8 0.8 -0.8 0.8 Evaluation of physical properties tanc6 /E 0 O 32 (-309C) 0.061 0.160 0.232 0.090 tan 6 /E 0 O- 3 2 -5 0 C) 0.056 0.111 0.088 0.072

/E'

0 32 C20T) 0.053 0.102 0.065 0.060 Tear test according to DIN (N/mm) 8.0 16.9 11.3 a a.

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a -12- Table 2-3 Blending Formulation(part/s Nos. of Comparative Example by weight) 5 6 7 8 Natural rubber 50 60 55 Terminal modified BR 50 40 High cis BR Carbon black FEF 40 Carbon black ISAF 35 Stearic acid 3 3 3 3 Zinc oxide 3.5 3.5 3.5 Age resister 2 2 2 2 Sulfur 2 2 2 2 Vulcanization accelerator 0.8 0.8 0.8 0.8 Evaluation of physical properties tan6 /E 0 2 30C 0.213 0.232 0.218 0.172 tan 6 /E' 0 3 2 5C 0.070 0.084 0.098 0.106 tan6 /E' 0 32 20C 0.053 0.055 0.082 0.088 Tear test according to DIN (N/mm) 3.0 3.0 14.2 18.3 4 4* 0 0* -13- It is clearly understandable from the results as pointed out in Table 2, that unreasonably large blending amount of natural rubber gives rise to a large energy loss at 309C (Comparative Examples 6 7 whereas unreasonably small blending amount thereof gives rise to poor anti-tear properties (Comparative Example blend of carbon black FEF leads to poor anti-tear properties (Comparative Examples 5 6 and carbon black ISAF, even if blended, of an unreasonably large blending amount brings about a large energy loss at 20 0 C (Comparative Example 2) or poor anti-tear properties (Comparative Example 4), whereas unreasonably small blending amount thereof brings about a large energy loss at 30 0 C (Comparative Example 3).

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-14-

Claims

2. The rubber composition according to Claim 1, wherein the ratio by weight of the natural rubber to the terminal modified polybutadiene rubber is 35 65 to 45 :6 3. The rubber composition according to Claim 1, wherein the carbon black is contained therein in an amount of 35 to 40 parts by weight based on 100 parts by weight the component 4 The rubber composition according to Claim 1, wherein the tan6 E'0- 82 at 5C of said composition is at most 0.110, in which the tand is loss tangent, and E' is dynamic modulus of elasticity (N mm
5. The rubber composition according to Claim 1, wherein the tan6 E' 0 32 at 309C of said composition is at most 0.02, and the tan6 32 at 209C thereof is at most 0.080.
6. The rubber composition according to Claim 1, wherein the anti-tear properties of said composition as measured according to DIN 53507 is at least 10 N mm. c- 7 A belt which comprises the rubber composition as set forth in Claim 1
8. A belt which comprises the rubber composition as set forth in Claim 2.
9. A belt which comprises the rubber composition as set forth in Claim 3. 1 0 A belt which comprises the rubber composition as set forth in Claim 4. 1 1 A belt which comprises the rubber composition as set forth in Claim 1 2. A belt which comprises the rubber composition as set forth in Claim 6. 1 3. The belt according to Claim 7, which is a conveyor belt. Daed 4t ugs PHLIS...DE&FTZARC Atony for BRDGSTN COPRTO S9 coos% :9090 -16-