JP2008231272A - Block copolymer having urethane bond and rubber composition containing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the wear resistance of a rubber composition. <P>SOLUTION: The block copolymer including at least one polyisoprene block (A) and at least one polybutadiene block (B) has a urethane bond at a bonding site of the blocks (A) and (B). The rubber composition contains with respect to 100 pts.wt. of a diene rubber, 20-150 pts.wt. of a filler and 1-25 pts.wt. of the block copolymer. As the diene rubber, those made of a natural rubber, a synthetic rubber and a butadiene rubber are preferable. The wear resistance of the block copolymer is improved by alleviating the energy by generating reversible cutting or bonding for energy inputted from the outside by intermolecular hydrogen bond at the urethane bonding site. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a block copolymer comprising a polyisoprene block and a polybutadiene block, and a rubber composition containing the block copolymer.

  Conventionally, a blend of natural rubber and butadiene rubber has been widely used as a rubber raw material for pneumatic tires. In such a blend system of natural rubber and butadiene rubber, a method of blending an isoprene-butadiene block copolymer as a compatibilizing agent has been proposed for the purpose of improving mechanical strength (see Non-Patent Document 1 below). .

  For example, in the following Patent Document 1, a polybutadiene block and a polyisoprene block having a 1,4-cis bond content of 40% by weight or more with respect to 100 parts by weight of the total amount of polyisoprene rubber and polybutadiene rubber are described. It has been proposed to blend 0.5 to 25 parts by weight of the block copolymer.

On the other hand, the following Patent Document 2 discloses a modified polymer to be blended in a rubber composition, in which an organosilicon functional group such as an alkoxysilyl group is introduced into a terminal of polybutadiene or polyisoprene via a urethane bond. .
JP 2002-012702 A JP 2005-350603 A David J. Zanzig and 4 others, "IBR BLOCK COPOLYMERS AS COMPATIBILIZERS IN NR / BR BLENDS", RUBBER CHEMISTRY AND TECHNOLOGY, Vol.66, p538-549, 1993

  Patent Document 1 discloses that a copolymer composed of a polyisoprene block and a polybutadiene block is used as a compatibilizing agent. However, only the 1,4-cis bond content in the polybutadiene block is noticed, and the introduction of urethane bonds at the bonding sites of the polyisoprene block and the polybutadiene block is silent.

  On the other hand, Patent Document 2 discloses that a urethane bond is introduced into polybutadiene or polyisoprene. However, it is intended to improve the dispersibility of silica by introducing an organosilicon functional group via a urethane bond at the end of the polymer, and it has been disclosed to introduce a urethane bond inside the polymer. Absent. That is, in Patent Document 2, as described in paragraph 0014, polybutadiene or polyisoprene having a hydroxyl group at a terminal is reacted with a silane compound having an isocyanate group and an alkoxy group to cause a terminal to have a urethane bond. Introducing an alkoxysilyl group. Alternatively, a polybutadiene or polyisoprene having a hydroxyl group at the terminal is reacted with a compound having two or more isocyanate groups to obtain a urethane prepolymer having a urethane bond at the terminal, and this has a primary or secondary amine or a hydroxyl group. By reacting a silane compound having an alkoxysilyl group, an alkoxysilyl group is introduced into the terminal via a urethane bond. Thus, patent document 2 introduces a urethane bond to the terminal of a polymer to the last, and does not disclose any features of the present invention described later.

  The inventor of the present invention, in a block copolymer comprising a polyisoprene block and a polybutadiene block, introduces a urethane bond at a bonding site of both blocks, thereby to improve the wear resistance of the rubber composition containing the block copolymer. As a result, the present invention has been completed.

  That is, an object of the present invention is to provide a novel block copolymer that can improve the wear resistance of a rubber composition.

  The block copolymer according to the present invention is a block copolymer composed of at least one polyisoprene block and at least one polybutadiene block, and has a bonding site between the polyisoprene block and the polybutadiene block. It has a urethane bond.

  Further, the rubber composition according to the present invention is obtained by blending the block copolymer. Specifically, the filler is 20 to 150 parts by weight with respect to 100 parts by weight of the diene rubber, and the block copolymer. It is preferable to contain 1-25 weight part. Further, as the diene rubber, those made of natural rubber or synthetic isoprene rubber and butadiene rubber are particularly suitable.

  When the block copolymer of the present invention is blended with a rubber composition, its wear resistance can be improved. This is considered to be due to the fact that the block copolymer has a urethane bond at the bonding site between the polyisoprene block and the polybutadiene block, and the urethane bonding site introduced inside the polymer has intermolecular hydrogen bonding. . That is, since the intermolecular hydrogen bond is a reversible physical bond, it can be considered that the intermolecular hydrogen bond can be reversibly cut and bonded to the energy input from the outside, thereby relaxing the energy.

  The block copolymer has a polyisoprene block and a polybutadiene block, and these blocks can be co-vulcanized together with the diene rubber in the rubber composition, so that the mechanical strength is easily maintained.

  In addition, when the rubber composition is composed of natural rubber or synthetic isoprene rubber and butadiene rubber, the block copolymer has a polyisoprene block and a polybutadiene block. It acts as a solubilizer, suppresses problems such as poor dispersion in the matrix rubber, and makes it easier to maintain mechanical strength.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  The block copolymer according to the present invention is an IR-BR block copolymer composed of a polyisoprene block (A) and a polybutadiene block (B), and a binding site of both blocks (A) and (B). Have a urethane bond.

  The polyisoprene block (A) is a block having isoprene (that is, 2-methyl-1,3-butadiene) unit as a main structural unit. The isoprene unit content in the block (A) is preferably 70% by weight or more, more preferably 90% by weight or more, and particularly preferably 100% by weight.

  Other monomer units that can constitute the polyisoprene block (A) are not particularly limited, and examples thereof include 1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, and the like. Examples include conjugated dienes other than isoprene, aromatic vinyls such as styrene, olefins such as ethylene, propylene, and isobutene, acrylonitrile, and methacrylonitrile. These monomer units are preferably bonded at random in the polyisoprene block (A).

  The number average molecular weight (Wn) measured by gel permeation chromatography (GPC) of the polyisoprene block (A) is preferably 1000 to 5000. More preferably, the number average molecular weight is 1500-3500. When the number average molecular weight is too small, the affinity with the diene rubber blended in the rubber composition is impaired. On the other hand, if it is too large, the molecular weight of the entire block copolymer becomes large, and it becomes difficult to obtain the effect of improving processability.

  The polybutadiene block (B) is a block having 1,3-butadiene units as main constituent units. The 1,3-butadiene unit content in the block (B) is preferably 70% by weight or more, more preferably 90% by weight or more, and particularly preferably 100% by weight.

  Although it does not specifically limit as another monomer unit which can comprise a polybutadiene type block (B), For example, 1 such as isoprene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene etc. Conjugated dienes other than 1,3-butadiene, aromatic vinyls such as styrene; olefins such as ethylene, propylene and isobutene, acrylonitrile, methacrylonitrile and the like. These monomer units are preferably bonded at random in the polybutadiene block (B).

  The number average molecular weight (Wn) measured by gel permeation chromatography (GPC) of the polybutadiene block (B) is preferably 1000 to 5000. More preferably, the number average molecular weight is 1500-3500. When the number average molecular weight is too small, the affinity with the diene rubber blended in the rubber composition is impaired. On the other hand, if it is too large, the molecular weight of the entire block copolymer becomes large, and it becomes difficult to obtain the effect of improving processability.

  The block copolymer has at least one polyisoprene block (A) and polybutadiene block (B). As the bonding form, (A)-(B), (A)-(B)-(A), (B)-(A)-(B), ((A)-(B)) n (however, n is 2 or more). Preferably, it is composed of at least three blocks. That is, (A)-(B)-(A), (B)-(A)-(B), or those obtained by further adding blocks (A) and / or (B) to these are suitable. . This is because by comprising three or more blocks, the number of urethane bonds in the block copolymer is increased, and the energy relaxation effect by the intermolecular hydrogen bond is increased.

  The ratio of the polyisoprene block (A) to the polybutadiene block (B) is preferably (A) :( B) = 10: 90 to 90:10, more preferably (A ) :( B) = 30: 70 to 70:30.

  In the block copolymer, the polyisoprene block (A) and the polybutadiene block (B) are bonded through a urethane bond. More preferably, the block (A) and the block (B) are bonded via a bonding group represented by the following general formula (1).

—O—CO—NH—R—NH—CO—O— (1)
In the formula (1), R is a divalent organic group, and specifically includes a deisocyanate residue of a diisocyanate compound.

  The block copolymer is preferably synthesized by bonding a polyisoprene polymer having a hydroxyl group at a terminal and a polybutadiene polymer having a hydroxyl group at a terminal via a diisocyanate compound. By using a diisocyanate compound, a urethane bond can be easily introduced into the bonding site between the polyisoprene block (A) and the polybutadiene block (B). In this case, since the hydroxyl group can be provided at the terminal of the block copolymer, the affinity with a filler having a polar group on the surface can be improved.

  More preferably, the above block copolymer is synthesized from a hydroxyl group-terminated liquid polyisoprene polymer having a number average molecular weight of 1000 to 5000, a hydroxyl group terminated liquid polybutadiene polymer having a number average molecular weight of 1000 to 5000, and a diisocyanate compound. It is to be.

  As a specific synthesis method, a diisocyanate compound is introduced by reacting a hydroxyl group at the end with a diisocyanate compound to form a urethane bond with either a hydroxyl-terminated polyisoprene polymer or a hydroxyl-terminated polybutadiene polymer. To do. Next, the other polymer is added to the one polymer in which the diisocyanate compound is introduced at the terminal to react the terminal hydroxyl group of the other polymer with the unreacted isocyanate group of the diisocyanate compound. Thereby, said one polymer and the other polymer can be couple | bonded through a diisocyanate compound.

  The block copolymer synthesized in this way is mainly composed of (A)-(B)-(A) or (B)-(A)-(B), depending on the reaction conditions and the like. Are synthesized in a state where other types of bonds such as (A)-(B) are also mixed, and such a mixture can also be used in the present invention.

  Specific examples of the diisocyanate compound include methylene diphenyl diisocyanate (MDI), tolylene diisocyanate (TDI), 1,6-hexamethylene diisocyanate (HMDI), trimethylhexamethylene diisocyanate (TMHMDI), isophorone diisocyanate. Narto (IPDI) and the like.

  The number average molecular weight (Wn) measured by gel permeation chromatography (GPC) of the block copolymer is preferably 2000 to 500,000, more preferably 3000 to 100,000, still more preferably 4000 to 20000, particularly preferably. 5,000 to 10,000. If the number average molecular weight is too small, it is difficult to ensure mechanical strength. Conversely, when too large, workability will be impaired. In particular, when the number average molecular weight of the block copolymer is 10,000 or less, the Mooney viscosity is lowered when blended with a rubber composition, and the processability is improved.

  The rubber composition according to the present invention contains the block copolymer together with a diene rubber and a filler.

  Examples of the diene rubber include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), and chloroprene rubber (CR). These may be used either alone or in combination of two or more.

  The diene rubber is preferably at least one selected from the group consisting of natural rubber, synthetic isoprene rubber, and butadiene rubber, and further, isoprene rubber of natural rubber or synthetic isoprene rubber, and butadiene rubber. And a blend (IR / BR blend). With such IR / BR blending, the block copolymer having a polyisoprene block (A) and a polybutadiene block (B) acts as a compatibilizing agent, so that the block copolymer is incorporated into the matrix rubber. The dispersion can be improved and the mechanical strength can be effectively maintained.

  When the isoprene-based rubber (NR, IR) and butadiene rubber (BR) are used in combination, the diene rubber is preferably composed of 20 to 90% by weight of isoprene-based rubber and 80 to 10% by weight of butadiene rubber. Preferably, it is composed of 50 to 90% by weight of isoprene-based rubber and 50 to 10% by weight of butadiene rubber. In this case, if the main component is isoprene rubber and butadiene rubber (that is, 50% by weight or more in the diene rubber), the remainder is another diene rubber such as styrene-butadiene rubber (SBR). May be contained.

  As said filler, various inorganic fillers, such as carbon black, a silica, a clay, and a zeolite, can be used, These can be used individually or in combination of 2 or more types. Carbon black, silica, or a combination of carbon black and silica is preferable. Examples of the silica include wet silica, dry silica, colloidal silica, and the like.

  The filler is blended in an amount of 20 to 150 parts by weight, more preferably 20 to 100 parts by weight, based on 100 parts by weight of the diene rubber. The block copolymer is blended in an amount of 1 to 25 parts by weight, more preferably 2 to 10 parts by weight, based on 100 parts by weight of the diene rubber. When the blending amount of the block copolymer is less than 1 part by weight, the effect of improving the wear resistance is insufficient. On the contrary, when the blending amount of the block copolymer is 30 parts by weight or more, the mechanical strength and the heat generation tend to be deteriorated.

  In addition to the components described above, the rubber composition according to the present invention includes a softener, a silane coupling agent, stearic acid, a plasticizer, zinc white, an anti-aging agent, a vulcanizing agent, a vulcanization accelerator, and the like. These various additives can be blended.

  The rubber composition according to the present invention can be used for various rubbers such as tires, conveyor belts, and vibration-proof rubbers. In particular, since the rubber composition is excellent in abrasion resistance, it can be suitably used as a tread rubber for tires and further for a tread rubber for heavy duty tires such as trucks and buses.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Synthesis Example 1 (Synthesis of Block Copolymer 1)]
100 g of hydroxyl-terminated liquid polybutadiene having hydroxyl groups at both ends (“R-45HT” manufactured by Idemitsu Kosan Co., Ltd., number average molecular weight = 2800) and 41 g of methylene diphenyl diisocyanate (MDI, “Sumidur 44S” manufactured by Sumika Bayer Urethane) The mixture was placed in a container and reacted at 70 ° C. for 2 hours with stirring. As a result, hydroxyl groups at both ends of the liquid polybutadiene were reacted with isocyanate groups of MDI, and MDI was introduced into both ends of the liquid polybutadiene via urethane bonds.

  Next, 100 g of liquid polybutadiene having MDI introduced at the ends obtained above and 145 g of hydroxyl-terminated liquid polyisoprene having hydroxyl groups at both ends (“Poly ip” manufactured by Idemitsu Kosan, number average molecular weight = 2500) are placed in a container and stirred. After mixing, the mixture was reacted at 70 ° C. for 2 hours. As a result, an unreacted isocyanate group possessed by MDI at both ends of liquid polybutadiene and a hydroxyl group at the end of liquid polyisoprene are reacted to form polyisoprene block (A) via MDI at both ends of polybutadiene block (B). (That is, a block copolymer 1 having a bonding form of (A)-(B)-(A)) was synthesized.

About the obtained block copolymer 1, while performing a GPC analysis and measuring a number average molecular weight, performing a ¹³ C-NMR analysis, confirmation of presence of a urethane bond, and the ratio of (A) and (B) Asked.

  GPC analysis was performed using THF as an eluent, “PLgel-MIXED-E” manufactured by Polymer Laboratories as a column, and a differential refractive index detector (RI) as a detector. As a result, the number average molecular weight of the obtained block copolymer 1 was 8,000.

^{For 13} C-NMR analysis, “DPX400” manufactured by BRUKER was used, and the deuterated chloroform solution of the sample was measured at room temperature. As a result, the presence of the urethane bond at the block binding site was confirmed by the carbonyl carbon signal (153.5 ppm). Further, the ratio of (A) in the block copolymer calculated from the ¹³ C-NMR spectrum was 65% by weight.

  As described above, the block copolymer 1 mainly has a bond form of (A)-(B)-(A), and the polyisoprene block (A) and the polybutadiene block (B) are represented by the above formula (1). It was confirmed that the terminal is a urethane bond-containing block polymer having a hydroxyl group at the end and bonded by a linking group containing a urethane bond.

[Synthesis Example 2 (Synthesis of Block Copolymer 2)]
100 g of hydroxyl-terminated liquid polyisoprene having hydroxyl groups at both ends (“Poly ip” manufactured by Idemitsu Kosan Co., Ltd., number average molecular weight = 2500) and 41 g of methylene diphenyl diisocyanate (MDI, “Sumidur 44S” manufactured by Sumika Bayer Urethane) The mixture was placed in a container and reacted at 70 ° C. for 2 hours with stirring. As a result, the hydroxyl groups at both ends of the liquid polyisoprene were reacted with the isocyanate groups of MDI, and MDI was introduced into both ends of the liquid polyisoprene via urethane bonds.

  Next, 100 g of liquid polyisoprene obtained by introducing MDI at the terminal obtained above and 150 g of hydroxyl-terminated liquid polybutadiene having hydroxyl groups at both terminals (“R-45HT” manufactured by Idemitsu Kosan Co., Ltd., number average molecular weight = 2800) are put in a container. After stirring and mixing, the mixture was reacted at 70 ° C. for 2 hours. As a result, the unreacted isocyanate group of the MDI at both ends of the liquid polyisoprene reacts with the hydroxyl group at the end of the liquid polybutadiene, and the polybutadiene block (B) is passed through both ends of the polyisoprene block (A) via MDI. (That is, a block copolymer 2 having a bonding form of (B)-(A)-(B)) was synthesized.

The obtained block copolymer 2 was subjected to GPC analysis and ¹³ C-NMR analysis in the same manner as described above. As a result, the number average molecular weight by GPC was 8,000. In ¹³ C-NMR analysis, the presence of a urethane bond at the block bond site was confirmed by a carbonyl carbon signal (153.5 ppm). The ratio of (A) in the block copolymer was 40% by weight.

  From the above, the block copolymer 2 mainly has a bond form of (B)-(A)-(B), and the polyisoprene block (A) and the polybutadiene block (B) are represented by the above formula (1). It was confirmed that the terminal is a urethane bond-containing block polymer having a hydroxyl group at the end and bonded by a linking group containing a urethane bond.

[Preparation and evaluation of rubber composition]
Using a Banbury mixer, according to the formulation shown in Table 1 below, rubber compositions for tire treads of Examples and Comparative Examples were prepared. Each component in Table 1 is as follows.

NR: natural rubber (RSS # 3),
・ BR: “BR01” manufactured by JSR,
・ Carbon black: ISAF grade, "Seast 6" made by Tokai Carbon,
Liquid polybutadiene: “R-45HT” (number average molecular weight = 2800) manufactured by Idemitsu Kosan Co., Ltd.
Liquid polyisoprene: “Poly ip” (number average molecular weight = 2500) manufactured by Idemitsu Kosan Co., Ltd.

  In each rubber composition, 3 parts by weight of zinc white (“Zinc Hana 1” manufactured by Mitsui Kinzoku Mining Co., Ltd.) and stearic acid (“Lunac S” manufactured by Kao Co., Ltd.) per 100 parts by weight of diene rubber -20 ") 2 parts by weight, anti-aging agent 6C (" Nocrack 6C "manufactured by Ouchi Shinsei Chemical Co., Ltd.) 2 parts by weight, wax (" Sannok "manufactured by Ouchi Shinsei Chemical Co., Ltd.) 2 parts by weight, sulfur ( 2 parts by weight of “Sulfur powder for rubber 150 mesh” manufactured by Hosoi Chemical Co., Ltd., 1 part by weight of vulcanization accelerator CZ (“Noxeller CZ” manufactured by Ouchi Shinsei Chemical Co., Ltd.), and vulcanization accelerator D ( 1 part by weight of Ouchi Shinsei Chemical Co., Ltd. “Noxeller D”) was blended.

  Each rubber composition was measured and evaluated for Mooney viscosity, hardness, tensile strength, elongation at break, and abrasion resistance. Each measurement / evaluation method is as follows.

Mooney viscosity: Measured at a temperature of 100 ° C. in accordance with JIS K6300 (L-shaped rotor), preheating 1 minute, measurement 4 minutes.

・ Hardness: About a test piece (length x width x thickness = 45 mm x 45 mm x 12 mm) vulcanized at 150 ° C x 30 minutes, using a type A durometer (A type) according to JIS K-6253 Measure hardness at 23 ° C.

・ Tensile strength, elongation at break: Measured using “Autograph SES1000” manufactured by Shimadzu Corporation for a test piece (dumbbell No. 3 type) vulcanized at 150 ° C. for 30 minutes in accordance with JIS K-6251 It was.

Abrasion resistance: A test piece vulcanized at 150 ° C. for 30 minutes was measured using a Lambourn abrasion tester based on JIS K-6264, and displayed as an index with the value of Comparative Example 1 being 100. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.

  As shown in Table 1, in Examples 1 to 6 in which an IR-BR block copolymer containing a urethane bond inside a polymer was blended with a diene rubber composed of natural rubber and butadiene rubber, the hardness was maintained. In addition, the wear resistance was greatly improved without substantially impairing the tensile properties. In addition, it was found that by blending the block copolymer, the Mooney viscosity was lowered and the processability was improved. Despite the decrease in Mooney viscosity, the hardness was substantially maintained.

  On the other hand, in Comparative Example 2 in which liquid polyisoprene and liquid polybutadiene were simply mixed and added in the same composition as block copolymer 1 instead of the block copolymer, the Mooney viscosity decreased, but the hardness was also low. In addition, the effect of improving the wear resistance was not obtained. Further, as shown in Comparative Example 3 (however, Comparative Example with respect to Claim 3), if the amount of the block copolymer is too large, the hardness could not be maintained and the tensile properties were also deteriorated.

  The block copolymer according to the present invention can be used by blending it with various rubber compositions such as a tire, a conveyor belt and a vibration-proof rubber. Since the wear resistance of the rubber composition can be improved by blending the block copolymer, tire tread rubbers that require wear resistance, particularly heavy duty pneumatic tires such as trucks and buses. It can be suitably used for tread rubber.

Claims (5)

  A block copolymer comprising at least one polyisoprene block and at least one polybutadiene block, wherein the block copolymer has a urethane bond at a bonding site between the polyisoprene block and the polybutadiene block. The number average molecular weight of the polyisoprene block is 1000 to 5000, the number average molecular weight of the polybutadiene block is 1000 to 5000, and the polyisoprene block and the polybutadiene block are represented by the following general formula (1). The block copolymer of Claim 1 couple | bonded through the coupling | bonding group represented.
—O—CO—NH—R—NH—CO—O— (1)
(In the formula, R is a divalent organic group.)   A rubber composition comprising 20 to 150 parts by weight of a filler and 1 to 25 parts by weight of a block copolymer according to claim 1 with respect to 100 parts by weight of a diene rubber.   The rubber composition according to claim 3, wherein the diene rubber comprises natural rubber or synthetic isoprene rubber and butadiene rubber.   A tread rubber for a tire comprising the rubber composition according to claim 3 or 4.