JP2011184512A - Rubber composition comprising rubber reinforcing agent and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition comprising a rubber reinforcing agent, which can be safely and economically manufactured due to high scorching safety at vulcanization and high vulcanization rate. <P>SOLUTION: The rubber composition comprising the rubber reinforcing agent comprises: 1-50 pts.wt. conjugated diene rubber (A) that is obtained by graft-modifying an acrylamide polymer by radical polymerization (NMP method) using a nitroxide compound, provided that the conjugated diene rubber (A) has a graft rate of 30-100%; 50-99 pts.wt. vulcanizable rubber (B) other than (A); and 30-70 pts.wt. rubber reinforcing agent (C). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber reinforcing agent-containing rubber composition containing a modified conjugated diene polymer obtained by graft-modifying 1,4-cis polybutadiene rubber with polyacrylamide and a method for producing the same.

  Industrially, due to its availability to most rubbers, there has been a strong demand for maintaining a good balance between sufficiently long scorch safety time and fast vulcanization time in the production of vulcanized rubber.

In general, the scorch safety is the length of time that a rubber compound can be held as a thermoplastic polymer even at elevated temperatures or vulcanization temperatures. Early in the scorch, the rubber component in the thermoplastic polymer begins to undergo a chemical change to a crosslinked network structure. That is, if the scorch occurs before the rubber component is formed into a desired shape, the rubber processing is not successful and the rubber cannot be used. Therefore, a longer scorch safety time is always preferred in the rubber processing process.

On the other hand, when the vulcanization of the rubber vulcanizate further proceeds after the scorch safety time has elapsed, the thermoplastic polymer changes to a crosslinked network structure at a high temperature. Also, the vulcanization rate is determined by how long it takes to reach the desired cross-linked or vulcanized state of the rubber vulcanizate. Therefore, a vulcanization speed is fast and a short vulcanization time is preferred in terms of production cost (Non-Patent Document 1).

In order to achieve a good balance between scorch safety time and vulcanization time, it has been sought to add additives to rubber compounds. Scorch inhibitors (PVI), such as N-cyclohexylthiophthalimide, have been used by adding small amounts in the rubber composition to increase the scorch safety time during processing. On the other hand, vulcanization accelerators such as sulfenamide, thiazole, and guanidine have generally been used to increase the vulcanization speed or shorten the vulcanization time (Non-patent Document 1).

Polar functionality similar to the functional groups contained in scorch inhibitors (vulcanization retarders) and vulcanization accelerators, which can be used without using scorch inhibitors (vulcanization retarders) and vulcanization accelerators Graft copolymerization techniques that modify the diene-based elastomers themselves that are used in rubber compositions with groups are one possible method that has recently received attention.

  The most well-known example that has been studied extensively in universities and companies is the free radical graft copolymer emulsion of methyl methacrylate (MMA) and styrene to obtain natural rubber latex particles with controlled morphology. Is a modification of natural rubber latex. The formed latex particle composite has been applied to a wide range of uses such as paints, rubber adhesives, gloves, organic opacifiers, biomolecule carriers, and thermoplastic resin impact modifiers (Non-Patent Documents 2 to 5 and Patent Document 1).

  Free radical grafting of the main chain of synthetic rubbers such as cis-butadiene rubber and vinyl-1,2-polybutadiene with polar monomers using common radical initiators such as organic peroxides and azo compounds Copolymers have also been reported. However, it is difficult to control the graft efficiency and the structure of polybutadiene after grafting. In particular, vinyl-1,2-polybutadiene is generally known to exhibit higher grafting efficiency. (Non-Patent Documents 6 and 7)

  Since the discovery of controlled radical polymers (abbreviated as CRP) by using compounds containing stable nitroxide free radicals, so-called nitroxide-mediated radical polymerization (abbreviated as NMP) (Non-Patent Documents 8 and 9), Application of NMP for the purpose of chemical modification to graft the side chain of the polymer is accompanied by control of molecular chain length and dispersibility on synthetic rubber, which is superior to conventional free radical graft copolymerization. It has become.

  For example, one of the researches disclosed at an early stage is the NMP method in which a polar monomer such as methyl acrylate is grafted onto the main chain of polybutadiene by extracting allyl hydrogen with a conventional radical initiator such as an organic peroxide. there were. The length of the molecular chain and the dispersibility of the grafted side chain are controlled by the action of a nitroxide such as di-tert-butyl nitroxide.

  However, in order to prevent a side reaction of hydrogen abstraction, there is a disadvantage that a toxic chlorinated hydrocarbon must be used as a solvent (Patent Document 2).

In recent years, grafting to a synthetic rubber using a compound having a stable free radical in a molecule such as 2,2,6,6-tetramethylpiperidine-1-oxyl (abbreviated as TEMPO) has been reported. .
The purpose is to improve the physical properties of rubber compounds such as processability and wear resistance (Patent Documents 3 and 4). Furthermore, research on grafting to rubber using multifunctional nitroxide in the presence of a conventional radical initiator intended for use as a reversible cross-linking agent has been reported.
However, there has been no report for the purpose of chemical modification that introduces a polar group into rubber (Patent Document 5).

More recently, studies on chemical modification of synthetic rubbers based on ethylene-propylene copolymers grafted with butyl rubber and nitroxide free radicals in a mixer without the use of solvents in the presence of conventional free radical initiators have been disclosed. Has been.
Although the introduction of polar groups into rubber was successful, the molecular weight of the grafted rubber gradually decreased, resulting in a problem that the grafting efficiency was lowered (Patent Document 6).

Therefore, as an improvement measure for suppressing the decrease in the molecular weight of the grafted rubber, it is effective to set the molar ratio of the functionalized nitroxide free radical to the radical initiator to 1.5 or more (Patent Document 7).
Furthermore, chemical modification of a synthetic rubber, which is a diene elastomer obtained by graft-copolymerizing a polar monomer capable of radical polymerization on the main chain of the rubber by the non-solvent system, has been reported.
In the silica-containing rubber composition containing the grafted rubber, the dispersibility of silica is improved, the hysteresis loss is further reduced, and the wear resistance is slightly improved (Patent Document 8).

U.S. Patent No. 6423783 US Patent No. 4581429 Japanese Patent Laid-Open No. 10-182881 JP 2004-182926 A Japanese Patent Laid-Open No. 2003-524037 Japanese Patent No. 3993917 (US Pat. No. 7,282,542) Japanese Patent No. 4101242 JP 2008-297559 A Ignatz-Hoover, F., To, B.H., Rubber Compounding: Chemistry and Applications, Brendan Rodgers Edt., Marcel Dekker Inc., 2004, p. 505. Schneider, M., Pith, T. and Lambla, M., J. Appl. Polym. Sci., 62: 273 (1996). Schneider, M., Pith, T. and Lambla, M., Polym. Adv. Technol., 7: 577 (1996). Teng, G. and Soucek, M.D., Polymer, 42: 2849 (2001). Benny, G., Maiti, S.N., and Varma, I.K., J. Elastomers and Plastics, 38: 319 (2006). Huang, N.J., Sundberg, D.C., J. Polym. Sci., Part A: Polym. Chem., 33, 2571 (1995). Huang, N.J., Sundberg, D.C., J. Polym. Sci., Part A: Polym. Chem., 33, 2587 (1995). Georges, M. K .; Veregin, R. P. N .; Kazmaier, P. M .; Hamer, G. K., Macromolecules, 26, 2987-2988 (1993). Hawker, C. J .; Bosman, A. W .; Harth, E. Chem. Rev., 101, 3661-3688 (2001).

In the present invention, 1,4-cis-polybutadiene rubber having a 1,4-cis structure of 94 to 99% is controlled radical grafting via nitroxide using existing radical initiators such as organic peroxides and azo compounds. The graft ratio of the graft-modified conjugated diene rubber prepared by the copolymerization technique is 30 to 100% and 1 to 50 parts by weight. The vulcanizable rubber (B) other than (A) and the rubber reinforcing agent (C) By using a rubber composition blended with a rubber reinforcing agent characterized by the addition of the above, scorch safety at the time of vulcanization is high, and safe and economical production with a fast vulcanization speed can be achieved.
Furthermore, the manufactured rubber reinforcing agent-containing rubber composition has high 100% tensile elasticity and 300% tensile elasticity, and can create excellent tensile elasticity.

  In order to achieve the above object, the present invention provides a rubber obtained by graft-modifying 1,4-cis-polybutadiene rubber having a 1,4-cis structure of 94 to 99% with polyacrylamide by NMP method at a graft ratio of 30 to 100%. By using the rubber compound, the rubber compound exhibits a good balance between the function as a scorch inhibitor (vulcanization retarder) and the function as an accelerator, and achieves a long scorch safety time and a fast vulcanization rate.

Graft ratio of the conjugated diene rubber (A) obtained by graft modification of the acrylamide polymer by using radical polymerization (NMP method) using a nitroxide compound is 30 to 100% and 1 to 50 parts by weight ( The present invention relates to a rubber composition containing a rubber reinforcing agent, characterized in that the vulcanizable rubber (B) other than A) is 50 to 99 parts by weight, and further 30 to 70 parts by weight of a rubber reinforcing agent (C) is added.

The acrylamide polymer is polyacrylamide, and the rubber reinforcing agent-containing rubber composition is characterized.

The conjugated diene rubber has a 1,4-cis structure, and the ratio thereof is 94 to 99%.

Graft ratio of the conjugated diene rubber (A) obtained by graft modification of the acrylamide polymer by using radical polymerization (NMP method) using a nitroxide compound is 30 to 100% and 1 to 50 parts by weight ( A method for producing a rubber composition containing a rubber reinforcing agent, characterized in that the vulcanizable rubber (B) other than A) is 50 to 99 parts by weight, and further 30 to 70 parts by weight of a rubber reinforcing agent (C) is added. About.

  The rubber reinforcing agent (C) is a silica composition containing the rubber reinforcing agent described above, wherein the rubber reinforcing agent (C) is silica.

As described above, according to the present invention, an existing free radical initiator and a nitroxide free radical are allowed to coexist in a rubber solution dissolved in an aromatic hydrocarbon solvent, and radical polymerization that is an acrylamide is possible in the rubber molecule main chain. It is possible to provide a method for efficiently chemically modifying 1,4-polybutadiene obtained by graft-modifying various polar monomers.
In addition, by appropriately adjusting the polymerization conditions such as radical initiator, temperature, degree of polymerization, and molar ratio of nitroxide to radical initiator, graft modified 1,4-cis with controlled molecular weight of the grafted polyacrylamide side chain. -Polybutadiene can be produced.
Provided is a silica-containing rubber composition containing the graft-modified 1,4-cis-polybutadiene having a good balance between the function as a scorch inhibitor (vulcanization retarder) and the function as a vulcanization accelerator. be able to.

The conceptual diagram of the method of manufacturing the 1, 4-cis-polybutadiene graft-modified using polyacrylamide. 4 is an FT-IR spectrum of PMMA-grafted BR150L (graft rate: 14.16%) according to Reference Example A. 7 is an FT-IR spectrum of PDMA-grafted BR150L (graft rate 56.59%) according to Reference Example 8. A comparison of the vulcanization characteristics of the blends of PMMA grafted BR150L (Comparative Example 1) and PDMA grafted BR150L (Example 1) is shown. The comparison of the network density in the vulcanizate of PMMA grafting BR150L (comparative example 1) and PDMA grafting BR150L (example 1) is shown. The general mechanism of vulcanization with the aid of CZ, a vulcanization accelerator, is shown. 2 shows the proposed mechanism of vulcanization occurring in the presence of polyacrylamide.

Polybutadiene The polybutadiene used in the modified conjugated diene polymer according to the present invention is characterized in that high cis polybutadiene (1,4-cis structure 94-99.9 mol%) is applied. . According to the modified conjugated diene polymer according to the present invention, by applying high cis polybutadiene, the silica-rubber interaction is improved, and the high performance of the high cis structure compared to the molecular terminal modification and the polybutadiene main chain. The balance of the degree of denaturation can be maintained.

As the 1,4-cis-polybutadiene rubber, commercially available Ube Industries (UBEPOL BR150L) or specially synthesized 1,4-cis-polybutadiene rubber can be used, but is not limited thereto.
The proportion of 1,4-cis structure of the 1,4-cis-polybutadiene rubber is preferably 94-99.9%, more preferably 94.5-99%, most preferably 95-98%. .

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) is preferably 37 to 48, more preferably 39 to 46, and particularly preferably 42 to 44. Furthermore, the 5 wt% toluene solution viscosity (Tcp cps), which is an index of rubber linearity (linearity), is preferably 98 to 110, more preferably 100 to 108, and particularly preferably 103 to 107.
When the ratio of the 1,4-cis structure is lower than 94%, or when the Tcp is lower than 98, the wear resistance is inferior as well as the viscoelastic properties of rubber, which is not preferable.

In addition, as applicable rubber, vulcanizable rubber can be used. For example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), acrylonitrile-chloroprene rubber, acrylonitrile-isoprene rubber , Ethylene-α- such as diene rubber such as styrene-chloroprene rubber, styrene-isoprene rubber, ethylene-propylene rubber, ethylene-butene rubber, ethylene-vinyl acetate copolymer (EVA), ethylene-propylene-diene rubber (EPDM) Examples include olefin copolymer rubber. These may be used alone or in combination.

A rubber component having a high cis structure, which is also an aim of the present invention, is preferable, and natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and the like are more preferable.
High cis-butadiene rubber (BR) is particularly preferable.

Radical initiator The radical initiator used in the present invention generates carbon radicals on the 1,4-cis-polybutadiene main chain through thermal decomposition in order to obtain free radicals. As the radical initiator, organic peroxides and azo compounds can be used.

For example, dibenzoyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, di-n-octanoyl peroxide, tert-butyl peroxybenzoate, dicumyl peroxide, tert-butylcumyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxy-3-hexyne, 2,4-dichlorodibenzoyl peroxide, di-tert-butylperoxy-diisopropylbenzene, 1, 1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, n-butyl-4,4-bis (tert-butylperoxy) valerate, 2,2-bis (tert-butylperoxy) butyl , Diisobutyl peroxide, cumyl peroxyneodecanate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butylperoxydicarbonate, 1,1,3,3-tetramethylbutylperoxyneodecanate , Di (4-tert-butylcyclohexyl) peroxydicarbonate, 1-cyclohexyldicarbonate, tert-hexylperoxyneodecanate, dimethoxybutylperoxycarbonate, tert-butylperoxyneodecanate, tert-hexylperoxyneocarbonate, dimethoxybutyl There are peroxycarbonates, di- (3,5,5-trimethylhexanoyl) peroxide. Furthermore, azo compounds can also be used.
For example, 1,1′-azobis (cyanocyclohexane), 2,2′-azobis (2-methylpropane), 2,2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis (iso Butyronitrile), 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4) -Dimethylvaleronitrile).

Among these radical initiators, dibenzoyl peroxide and 2,2'-azobis (isobutyronitrile) (abbreviated as AIBN) are more preferable. Furthermore, AIBN is particularly preferred.

Compound contained in stabilized nitroxide free radical As the compound contained in stabilized nitroxide free radical, commercially available TEMPO and TEMPO derivatives can be used. Here, TEMPO is 2,2,6,6-tetramethylpiperidine-1-oxyl, and the TEMPO derivative is 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (OH—). TEMPO) and 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (OXO-TEMPO). The use of TEMPO is particularly preferable.

Polar monomer capable of radical polymerization The polar monomer capable of radical polymerization is not particularly limited, but acrylamides are preferably used. Acrylamides include acrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N-butylacrylamide, N-hexylacrylamide, N- (iso-butoxymethyl) acrylamide, N-butoxymethylacrylamide, N- Methylolacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide, N, N-diisopropylacrylamide, N, N-di-n-butylacrylamide, N, N-dihexylacrylamide, N-methyl-N-ethylacrylamide N-ethyl-N-hexylacrylamide and 4-acryloylmorpholine, N, N-dimethylaminoethylacrylamide, methacrylamide, N-methylmethacrylamide, N, N Dimethylmethacrylamide, N, N-diethylmethacrylamide, N, N-diisopropylmethacrylamide, N, N-di-n-butylmethacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, diacetone acrylamide, N- ( 2-hydroxypropyl) methacrylamide, iso-butoxymethacrylamide, dimethylaminoethylmethacrylamide. You may use these individually or in combination of 2 or more.

Solvent When the controlled radical graft copolymerization is carried out in the present invention, the solvent for dissolving 1,4-cis-polybutadiene is preferably an aromatic hydrocarbon, particularly preferably benzene, toluene and xylene. Preferably it is toluene.

FIG. 1 shows a method for producing 1,4-cis-polybutadiene which is graft-modified using polyacrylamide which does not crosslink main chains of 1,4-cis-polybutadiene and whose molecular chain length is controlled. Show. The operation procedure is shown below.

(Reaction operation method)
(1) Dissolve 1,4-cis-polybutadiene in an aromatic hydrocarbon solvent until a uniform rubber solution is obtained.
(2) A carbon radical is generated on the 1,4-cis-polybutadiene main chain via hydrogen abstraction by the above-described thermally decomposable radical initiator at a desired graft-modified copolymerization temperature.
At this stage, a compound containing a molecular stable nitroxide free radical or a TEMPO derivative attacks the carbon radical on the 1,4-cis-polybutadiene main chain in order to extinguish the carbon radical by a reversible reaction.
(3) Add acrylamide monomer to graft copolymerize 1,4-cis-polybutadiene main chain in rubber solution at desired polymerization time.
(4) A rubber solution containing 1,4-cis-polybutadiene grafted with a desired polyacrylamide homopolymer is precipitated using a large volume of methanol. It is filtered and dried.
(5) A polyacrylamide homopolymer is easily extracted from 1,4-cis-polybutadiene grafted by stirring in a large volume of methanol at room temperature.
The obtained grafted 1,4-cis-polybutadiene product was evaluated for various physical properties such as polyacrylamide content, graft ratio, molecular weight, molecular weight distribution, and gel amount.

The concentration of 1,4-cis-polybutadiene rubber in the toluene solution is an important factor that greatly affects controlled graft copolymerization. The preferred rubber concentration is 0.015 to 0.07 g / ml, more preferably 0.02 to 0.06 g / ml, and most preferably 0.025 to 0.045 g / ml.
A rubber concentration of 0.07 g / ml or more is not preferable because the viscosity is too high, resulting in a non-uniform polymerization solution. This can cause uncontrollable graft copolymers and too high gel content.
On the other hand, if it is 0.015 g / ml or less, the rubber concentration is too low, the grafting rate becomes low, or the reaction rate of the monomer grafted onto the rubber in the solution becomes lower than the uniform polymerization rate, which is not preferable.

The temperature of the graft copolymerization is theoretically a temperature (T (° C.) 1−h t _1/2 ) at which half of the initial amount decomposes in 1 hour for the radical initiator to generate free radicals. In this invention, the preferable temperature of graft copolymerization is 70-100 degreeC, More preferably, it is 75-95 degreeC, Most preferably, it is 80-90 degreeC.
If the temperature is 100 ° C. or higher, it is not preferable because it is close to the boiling point of the aromatic hydrocarbon solvent used in the polymerization, which causes bumping in the glass reactor and pressure increase. On the other hand, when the temperature is too lower than 70 ° C., the number of generated radicals is too small, and the efficiency of graft copolymerization is lowered.

The number of graft sites on the 1,4-cis-polybutadiene main chain is preferably 1 to 5 mol%, more preferably 2 to 4 mol%, and particularly preferably 2.5 to 3 mol%. When the number of graft sites is less than 1 mol%, the effect of graft copolymerization is low, and the amount of polyacrylamide grafted to 1,4-cis-polybutadiene is reduced. Therefore, an increase in polarity in the rubber cannot be expected. On the other hand, if the number of graft sites is more than 5 mol%, uncontrollable gelation occurs between the rubber main chains, and as a result, a large amount of gel is generated, which is not preferable.

The molar ratio of the radical initiator to the graft site (initiator / graft site) is usually preferably from 0.5 to 1.5, particularly preferably from 0.7 to 1.2.

The molar ratio of TEMPO or TEMPO derivative to the radical initiator (TEMPO / initiator) is preferably 0.7 to 1.5, particularly preferably 1.0 to 1.2. Optimum balance between TEMPO / initiator molar ratio of 1.0-1.2, copolymerization rate (acrylamide monomer conversion) and controllability of graft copolymerization with living polymerization properties It becomes a condition.

The molar ratio of acrylamide to graft site or degree of polymerization (DPn) is a theoretical value for the desired molecular length of polyacrylamide grafted to the 1,4-cis-polybutadiene backbone.
In the present invention, the structure of the short chain of polyacrylamide grafted on the 1,4-cis-polybutadiene main chain may have the number of branched chains or the dispersibility of the branched chains relatively close to the number of graft sites. preferable.
Furthermore, the molar ratio (DPn) of the monomer to the preferred graft site is in the range of 20 to 150, more preferably 40 to 120, and particularly preferably 50 to 100.

If the value of DPn is less than 20, the short chain of the grafted polyacrylamide is too short, and the effect of increasing the polarity in the 1,4-cis-polybutadiene main chain is reduced, which is not preferable.
On the other hand, if the value of DPn is larger than 150, the short chain of the grafted polyacrylamide is too long, and as a result, the graft side chain becomes hard, which becomes an obstacle in the vulcanization process. Also, too hard graft side chains can cause loss of important properties of the elastomer and are not preferred.

Specific examples of graft copolymerization using AIBN as a radical initiator are shown in Table 1.

In Table 1, from the results of graft copolymerization using AIBN, poly (N, N-dimethylacrylamide) (PDMA) grafted 1,4-cis-polybutadiene (PDMA-grafted BR150L) under the aforementioned graft copolymerization conditions Was a well-controlled graft copolymer. As a result, the number average molecular weight (Mn) of the grafted BR150L increases in the range of 4,800 to 52,000. The weight average molecular weight (Mw) increases in the range of 2,000 to 273,000. Furthermore, the molecular weight distribution (MWD) is in the range of 2.0 to 2.9.

Under the condition that the gel amount is 0.2 wt% or less, the maximum content of poly (N, N-dimethylacrylamide) grafted to 1,4-cis-polybutadiene is 48.67%, the graft ratio (Percent Grafting, PG) was 94.82%, which was considerably more efficient than the poly (methyl methacrylate) grafted 1,4-cis-polybutadiene (PMMA-grafted BR150L) of Reference Example A. For well-controlled graft copolymers, a decrease in gel amount is obtained with an increase in the TEMPO / initiator molar ratio. The graft ratio (PG) of poly (N, N-dimethylacrylamide) increases with the increase in the number of graft sites and the molar ratio of DMA / graft sites (DPn), but the increase in the molar ratio of TEMPO / AIBN. Along with this, it shows a sharp decrease.

The preferred graft ratio (Percent Grafting, PG) in the present invention is 30 to 100%, more preferably 40 to 80%, and particularly preferably 50 to 70%.
By using a modified rubber in the above PG range, a vulcanization behavior showing ideal scorch safety can be obtained.
However, if PG is lower than 30%, the vulcanization speed at the initial stage of vulcanization is too fast, so that the safety of the scorch is inferior, and the vulcanization speed at the late stage of vulcanization is slowed down. It is difficult to create.
On the other hand, if PG is higher than 100%, it may be a cause of losing important properties of the elastomer such as elasticity and wear resistance, which is not preferable.

When the gel amount is 0.02 wt% or less, the maximum content of poly (N, N-dimethylacrylamide) grafted on 1,4-cis-polybutadiene is 48.67%, and the maximum graft ratio is 94.82%. is there.

FIG. 2 shows poly (methyl methacrylate) grafted 1,4-cis-polybutadiene (PMMA-grafted BR150L) and unmodified 1,4-cis-polybutadiene (BR150L) in Reference Example A (graft rate 14.16%). 2 shows a comparison of FT-IR spectra.
The C = O stretching vibration of the grafted polymethylmethacrylate is observed at 1734 cm- ¹ .

FIG. 3 shows poly (N, N-dimethylacrylamide) grafted 1,4-cis-polybutadiene (PDMA-grafted BR150L) and unmodified 1,4-cis- in Reference Example 8 (graft rate 56.59%). The FT-IR spectrum of polybutadiene (BR150L) is shown in comparison.
The C = O stretching vibration of the grafted poly (N, N-dimethylacrylamide) is observed at 1635 cm ⁻¹ , but overlaps the peak of C = C stretching vibration of the main chain of 1,4-cis-polybutadiene. . However, the C—N—C stretching vibration of the grafted poly (N, N-dimethylacrylamide) is observed alone at 1155 cm ⁻¹ .

(Silica-containing rubber composition containing polyacrylamide grafted 1,4-cis-polybutadiene)
Table 2 shows the components and amounts of the silica-containing rubber composition. Here, “phr” is “part by weight” and is the ratio of the weight of the elastomer or rubber to 100 weight.

(A) The amount of polyacrylamide grafted 1,4-cis-polybutadiene is preferably 1 to 50 parts by weight, more preferably 5 to 30 parts by weight, and particularly preferably 8 to 25 parts by weight.
Less than 1 part by weight of polyacrylamide grafted 1,4-cis-polybutadiene has no effect on the polarity of acrylamide in the rubber composition. On the other hand, if it exceeds 50 parts by weight, it will cause the wear resistance to deteriorate.

(B) The vulcanizable rubber other than (A) is preferably natural rubber or 1,4-cis-polyisoprene, 1,4-cis-polybutadiene, and particularly natural rubber and 1,4-cis-polybutadiene. Is preferred. The amount of the mixture used is preferably 50 to 99 parts by weight, more preferably 70 to 95 parts by weight, and particularly preferably 75 to 92 parts by weight. The Mooney viscosity (ML _{1 + 4} , 100 ° C.) is preferably 40 to 100, more preferably 50 to 80, and particularly preferably 60 to 70.

The amount of 1,4-cis-polybutadiene contained in the mixture of natural rubber other than (A) described in (B) and 1,4-cis-polybutadiene is preferably 10 to 90 wt% with respect to the mixture. 20 to 70 wt% is more preferable, and 30 to 60 wt% is particularly preferable. Further, the 1,4-cis-polybutadiene microstructure is preferably 80-98% for the 1,4-cis structure and 1-19% for the 1,2-vinyl structure. Moreover, 10-70 are preferable and, as for Mooney viscosity (ML1 ₊ 4,100 degreeC), 30-60 are more preferable.
For example, 1,4-cis-polybutadiene is not limited to commercially available 1,4-cis-polybutadiene, but in the presence of a cobalt-based catalyst such as cobalt (II) octoate and an organoaluminum compound such as diethylaluminum chloride. , 3-Butadiene obtained by solution polymerization may be used.

(C) As a rubber reinforcing agent, any reinforcing material of an inorganic rubber reinforcing agent and an organic rubber reinforcing agent can be applied. Inorganic rubber reinforcing agents include precipitated silica, metal oxides, alkali metal salts, and carbon black. However, it is not limited to these. An example of the organic rubber reinforcing agent is fibrous 1,2-polybutadiene. However, it is not limited to this.

As the rubber reinforcing agent, two or more kinds may be combined in addition to the above-described reinforcing agents used alone. For example, silica and carbon black may be used in combination.

When the rubber reinforcing agent is silica, the use of precipitated silica is most preferred, particularly those obtained by acidification of soluble silicic acid such as sodium silicate. Furthermore, as described above, these silicas may be combined with carbon black.

When using precipitated silica, the amount used is preferably 20 to 80 parts by weight, and more preferably 30 to 70 parts by weight. The precipitated silica has a BET specific surface area of 100 to 300 m ² / g and preferably a particle size of 0.01 to 0.1 microns.
If the specific surface area of the precipitated silica is too high, aggregation is likely to occur in the rubber matrix after the processing step or vulcanization, which is not preferable.

The precipitated silica used in the present invention or the precipitated silica generally used in the industry as a rubber compound is preferably obtained by the oxidizability of a soluble silicate such as sodium silicate.
Various commercially available precipitated silicas are available, in particular PPG silica, Rhodia Z1165MP and Z165GR silica known under the Hi-Sil trademark, and Evonik (Degussa AG) VN2 and VN3 (trademark Nippon). Silica known from Tosoh Corporation VN3 known to

  The amount of the silane coupling agent having a polysulfide moiety having 2 to 6 reactive sulfur atoms in interacting with the elastomer and the silane moiety when forming a bond having a silanol group on the silica surface is 1 to 10 Part by weight is good, and 1 to 5 parts by weight is more preferable.

In this invention, there exists an advantage which can reduce the quantity of the silane coupling agent to be used compared with the case normally used for a silica compounding rubber composition.
On the other hand, if the amount of the silane coupling agent is more than 10 parts by weight, the crosslinking proceeds too much at the stage of compositing, resulting in enormous results. Furthermore, if the amount of the silane coupling agent is less than 1 part by weight, it becomes difficult to disperse the silica in the rubber matrix, which is not preferable.

A commercially available silane coupling agent can be generally used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylpropyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercapto Ethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide 2-triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate Examples thereof include, but are not limited to, monosulfide and 3-trimethoxysilylpropyl methacrylate monosulfide. These silane coupling agents may be used alone or in combination. Among these, the use of bis (3-triethoxysilylpropyl) tetrasulfide is particularly preferable.

As other materials to be used, those generally used in rubber compounding and vulcanization stages can be used. For example, vulcanizing agents such as process oil, zinc oxide, stearic acid, antioxidants, vulcanization accelerators and sulfur. As the process oil, paraffin oil, naphthenic oil or aroma oil is used, but is not limited thereto. Among these, aroma oil is most preferable for use, and excellent physical properties such as tensile strength and abrasion resistance of the rubber composition can be maintained.
Furthermore, the amount used is preferably 1 to 50 parts by weight, more preferably 5 to 30 parts by weight.

  Sulfur is used as the vulcanizing agent, but is not limited to sulfur, and other vulcanizing agents can be used. As a usage-amount, it is 0.1-10 weight part, More preferably, it is 1-5 weight part. If the amount of the vulcanizing agent is more than 10 parts by weight, the vulcanization proceeds too much and the elasticity of the rubber is lost. On the other hand, if the amount of the vulcanizing agent is less than 0.1 parts by weight, physical properties such as tensile strength and wear resistance due to insufficient vulcanization cannot be obtained, which is not good.

Examples of the vulcanization accelerator include 2-mercaptobenzothiozole (abbreviated as M), dibenzylzothiazyl disulfide (abbreviated as DM), N-cyclohexyl-2-benzothiazylsulfenamide (abbreviated as CZ) and diphenyl. Examples include, but are not limited to, guanidine (abbreviated as D). Of these, the use of N-cyclohexyl-2-benzothiazylsulfenamide (CZ) and diphenylguanidine (D) is particularly preferred.
The amount used is preferably 0.1 to 5 parts by weight, and more preferably 1 to 3 parts by weight.

  FIG. 5 shows a generally known mechanism of rubber vulcanization that occurs in the presence of zinc oxide / stearic acid as a vulcanization accelerator and CZ / D as a vulcanization accelerator (non- Patent Document 1). An important step in controlling the overall vulcanization rate is the process of producing (a) and (b). Generally, since this stage relates to the scorch safety time, it is preferable that the generation rate of (a) at this stage is as slow as possible. On the other hand, the production rate of (b) at this stage is preferably as fast as possible because it is related to the vulcanization rate. Overall, fast vulcanization speeds lead to high productivity.

(I) Mixing step (first rubber composition)
In the mixing step, all components except the vulcanizing agent and the vulcanization accelerator are mixed within 90 minutes at 90 ° C. in a closed mixer such as plastmill. Immediately thereafter, the mixture is formed into a sheet shape after cooling in a temperature range of 30 to 60 ° C. using a mixing roll. The Mooney viscosity is measured using a sheet-like rubber composition sample.
The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the silica-containing rubber composition is preferably 110 to 150, more preferably 120 to 135.

(II) Vulcanization preliminary process (second rubber composition)
The sheet | seat of the silica compounding rubber composition obtained from the mixing process mentioned above mixes with a vulcanizing agent and a vulcanization accelerator like sulfur using a mixing roll in the temperature range of 30-60 degreeC. . The rubber composition in the vulcanization preliminary process is drawn into a sheet, and the sample is Mooney viscosity (ML _{1 + 4} , 100 ° C.), the optimal vulcanization point at 150 ° C. in RPA-2000 (2%, 5%, 10%) , 50%, 90% vulcanization time) and tan δ during vulcanization.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the second rubber composition in the preliminary vulcanization process is smaller than the Mooney viscosity of the first compound obtained from the mixing process, and its value is 60 to 110, more preferably 70. ~ 100. The time (t ₉₀ ) for 90% vulcanization at 150 ° C. of the second rubber composition in the vulcanization preliminary step is preferably 5 to 15 minutes, more preferably 7 to 12 minutes.

From the results shown in Table 3 and FIG. 4, the rubber composition (Example 1) containing PDMA-g-BR150L which is Reference Example 8 is 2 in comparison with BR150L (Comparative Example 2) which is the reference value. %, 5% and 10% vulcanization times were obviously slow, 50% and 90% vulcanization times were relatively fast and showed very good vulcanization characteristics. This suggests a good balance between long scorch safety time and fast overall vulcanization rate. It can be seen that the rubber composition containing PDMA-g-BR150L in the present invention retains both functions as a scorch inhibitor (vulcanization retarder) and a vulcanization accelerator.
On the other hand, the rubber composition containing PMMA-g-BR150L (Comparative Example 1), which is Reference Example A, exhibited vulcanization characteristics opposite to this. Compared with the vulcanization characteristics of BR150L as a reference example, the vulcanization time was slightly faster by 2%, 5%, and 10%, but obviously slow vulcanization time was confirmed at 50% and 90%. This is usually a vulcanization characteristic that is not desirable in the rubber processing industry.

   FIG. 6 shows the proposed mechanism of rubber vulcanization occurring in the presence of PDMA-g-BR150L with vulcanization accelerators zinc oxide / stearic acid and vulcanization accelerator CZ / D. ing. The amide group of PDMA is likely to be coordinated to zinc oxide, suggesting that it interferes with or slows down the formation of (a). In the meantime, however, after the formation of (a) is completed, the amide group of PDMA increases the formation rate of (b) and stabilizes the zinc complex of (b), resulting in an allyl hydrogen abstraction action from the diene-based rubber. The vulcanization stage further proceeds, functions similarly to the functional group of cyclohexylamine of CZ, and shows the effect of increasing the vulcanization speed.

(III) Vulcanization Step and Physical Properties of Silica Compound Rubber Vulcanized Material Table 3 shows the physical properties of the silica compound rubber composition containing PDMA-g-BR150L.

The 2nd rubber composition by a vulcanization preliminary process is press-molded at 150 degreeC which measured the vulcanization time. The rubber added material sample thus produced is measured for physical properties such as temperature sweep, tensile tension, network density, and viscoelastic properties.

  FIG. 5 shows rubber vulcanization containing PDMA-g-BR150L in the present invention (Example 1) compared with rubber vulcanizates of BR150L (Comparative Example 2) and PMMA-g-BR150L (Comparative Example 1). The result of the mesh density of the object is shown.

  The network density of the rubber vulcanizate containing PDMA-g-BR150L (Example 1) was higher than that of BR150L as Comparative Example 2 (about 29% higher). This result is consistent with the overall fast vulcanization rate as described above. Both in the same rubber composition, a high network density clearly indicates a high degree of cross-linking network, which is also believed to be a short chain of polysulfide (Sx), probably as described above. This is the effect of the vulcanization acceleration function of the amide group of PDMA.

  On the other hand, the network density of the rubber vulcanizate containing PMMA-g-BR150L (Comparative Example 1) was slightly lower than that of BR150L (Comparative Example 2). Therefore, the degree of the crosslinked network and the length of the polysulfide chain are almost similar to the rubber vulcanizates of both Comparative Example 1 and Comparative Example 2.

  From the results of the tensile properties shown in Table 3, the rubber vulcanizate (Example 1) containing PDMA-g-BR150L of the present invention has a tensile modulus at 300% elongation compared with BR150L (Comparative Example 2). It can be seen that it is extremely high, about 45% higher. However, the breaking strength was slightly lower and the breaking elongation was lower than expected due to the high degree of formation of the crosslinked network.

INDUSTRIAL APPLICABILITY Silica compounded rubber composition comprising natural rubber, UBEPOL BR150L and polyacrylamide grafted BR150L used in the present invention is polyacrylamide grafted to the main chain of 1,4-polybutadiene. By introducing a polar functional group such as a chain,
It is possible to provide a rubber vulcanizate that shows a good balance between a long scorch safety time and a fast vulcanization time.
As a result, it can be expected to realize an easy processing step and high productivity of rubber as in the present invention.
These rubber vulcanizates have a high possibility of being used as rubber components in combination with natural rubber and diene synthetic rubber for many purposes. Although not particularly limited to the following, specific applications include industrial belts, hoses, and other industrial elastomers including sealing materials.

The analysis contents of the rubber prepared in the present invention are shown below.
(Grafted poly (N, N-dimethylacrylamide) content in modified rubber)
The content of grafted poly (N, N-dimethylacrylamide) in the modified rubber was measured by measuring an FT-IR spectrum using Shimadzu-8700 manufactured by Shimadzu Corporation using a standard KBr method.
Poly (N, N-dimethylacrylamide) synthesized by radical polymerization in toluene solution in the presence of AIBN and TEMPO (TEMPO / AIBN molar ratio = 0.3) at 90 ° C. for 6 hours (Mn = 8) , 560, MWD = 2.06) and a blend of BR150L, the calibration curve was plotted by the ratio of the peak area of C—N—C stretching vibration (wave number ˜1150 cm ⁻¹ ) to the total peak area.
The result of the ratio of the peak area of C—N—C stretching vibration (wave number˜1150 cm ⁻¹ ) to the total peak area of each grafted sample rubber was determined using a calibration curve to determine the graft content in the rubber. To be compared.

(Grafting ratio in modified rubber (Percent Grafting, PG))
The graft ratio (PG) is expressed in% by weight and can be obtained from the result of the content of the grafted polymer obtained from the FT-IR measurement described above by the following calculation formula.

(Molecular weight and molecular weight distribution of rubber)
The molecular weight and molecular weight distribution were calculated using a standard polystyrene calibration curve using two columns in series using HLC-8220 GPC manufactured by Tosoh Corporation. The column used was Shodex GPC KF-805L columns, and the column temperature in THF was measured at 40 ° C.

(Rubber gel content)
The gel content was measured by dissolving 1 g of a rubber sample in 50 ml of toluene and stirring at room temperature for 24 hours.
The toluene solution of rubber was previously measured for No. After filtration using a 250 mesh filter, the product was washed several times with toluene. The filter obtained by filtering the swollen gel is dried in a vacuum state at 100 ° C. for 30 minutes, stored in a desiccator, and then the weight is measured.
The gel content (%) is calculated by the following formula.

(Mooney viscosity)
The Mooney viscosity (ML _{1 + 4} , 100 ° C.) was measured according to JIS K-6300.

(Measurement of vulcanization time)
The vulcanization time of rubber was measured as the time (t ₉₀ ) when the vulcanized state of the rubber composition progressed 90%. The measuring device is RPA-2000 manufactured by Alpha Technologies, measured at a temperature of 150 ° C. with a frequency fixed at 1 Hz and an angle of 0.5 degree, and is performed in accordance with JIS K-6300-2. It was.

(Fracture properties (tensile properties))
Measurement of tensile strength and tensile elongation in the fracture characteristics was performed using a TENSILON RTG-1310 tensiometer (manufactured by A & D) in accordance with JIS K-6251.

(Measurement of network density of vulcanizate)
A sheet having a thickness of 2 mm was cut into an appropriate size and immersed in toluene at 30 ° C. for 72 hours in accordance with JIS K 6258. The density of toluene was 0.8716 (g / cm ³ ) and the density of silica was 1.9. The rubber network density was calculated by the swelling method as (g / cm ³ ).

The synthesis method of poly (N, N-dimethylacrylamide) -grafted BR150L (PDMA-g-BR150L) is shown below.
(Reference Example 1)
In a nitrogen atmosphere, a 1 liter glass reactor with a stirring blade, a reflux condenser, and a thermocouple was installed in an oil bath, in which it was bubbled with nitrogen for 1 hour before use and dehydrated with molecular sieves. 350 ml of toluene solvent was added, and then 15 g (0.278 mol) of 1,4-cis-polybutadiene (BR150L) small pieces cut with nitrogen under pressure were added. BR150L was dissolved in a toluene solution at room temperature for 1.5 to 2 hours at a stirring speed of 350 to 400 (times / minute). Thereafter, 1.09 g (so that the molar ratio of TEMPO to AIBN = 1.0) of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was added under a nitrogen atmosphere. Thereafter, 1.14 g, ie, azobisisobutyronitrile (AIBN) corresponding to 0.278 mol (2.5% number of graft sites) was added under a nitrogen atmosphere.
The temperature was raised to 80 ° C., and the mixture was aged at a stirring speed of 350 (times / minute) for 30 minutes. Then, N, N-dimethylacrylamide (DMA) distilled under reduced pressure on 35.5 ml of CaH ₂ (so that the molar ratio of DMA to graft site or DPn = 50) is made to penetrate through the rubber membrane from the syringe. Added to the vessel. A sample of 0.25 ml of toluene solution collected with a gas tight syringe was immediately put into 10 ml of a mixed refrigerant of methanol and isopropanol (1 ml) to cause precipitation.
The graft copolymerization reaction was performed for 4 hours at a temperature of 80 ° C. and a stirring speed of 350 (times / minute). After 4 hours, a 0.25 ml toluene solution sample was again extracted with a gas tight syringe, and immediately poured into 10 ml of a mixed refrigerant of methanol and isopropanol (1 ml) to cause precipitation. The alcohol solution before and after polymerization was filtered to remove the precipitated rubber and then injected into a gas chromatograph to determine the conversion of DMA.
The reactor was cooled to 40 ° C. or lower, and immediately, the toluene solution in the reactor was poured into a large volume of cooled methanol for precipitation, and left overnight with stirring.
After filtration, the precipitated rubber was vacuum dried at 50 ° C. for 4 hours until the weight was constant.
The filtrate produced during filtration is evaporated with an evaporator, dissolved in toluene, precipitated in n-hexane, filtered, dried at 50 ° C. until the weight is constant, and poly (N, N-dimethyl). Acrylamide) (PDMA) oligomers were obtained.
PDMA grafted BR150L was measured for FT-IR, GPC and gel amount. Similarly, a sample of PDMA oligomer was measured by GPC.

(Reference Example 2)
PDMA grafted BR150L of Reference Example 2 was synthesized in the same manner as Reference Example 1 except that the number of graft sites was 3.5.

(Reference Example 3)
PDMA grafted BR150L of Reference Example 3 was synthesized in the same manner as Reference Example 1 except that the number of graft sites was 4.5.

(Reference Example 4)
The PDMA grafted BR150L of Reference Example 4 was synthesized by the same method as Reference Example 1 except that the polymerization temperature was 90 ° C. and the TEMPO / AIBN molar ratio was 0.8.

(Reference Example 5)
The PDMA-grafted BR150L of Reference Example 5 was synthesized by the same method as Reference Example 1 except that the polymerization temperature was 90 ° C.

(Reference Example 6)
The PDMA grafted BR150L of Reference Example 6 was synthesized by the same method as Reference Example 1 except that the polymerization temperature was 90 ° C. and the TEMPO / AIBN molar ratio was 1.2.

(Reference Example 7)
PDMA grafted BR150L of Reference Example 7 was synthesized in the same manner as Reference Example 1 except that the polymerization temperature was 90 ° C. and the TEMPO / AIBN molar ratio was 1.4.

(Reference Example 8)
The PDMA-grafted BR150L of Reference Example 8 was the same as Reference Example 1 except that the polymerization temperature was 90 ° C., the TEMPO / AIBN molar ratio was 1.2, and the DMA / graft site molar ratio (DPn) was 75. Synthesized by the method.

(Reference Example 9)
The PDMA grafted BR150L of Reference Example 9 was the same as Reference Example 1 except that the polymerization temperature was 90 ° C., the TEMPO / AIBN molar ratio was 1.2, and the DMA / graft site molar ratio (DPn) was 100. Synthesized by the method.

(Reference Example 10)
The PDMA grafted BR150L of Reference Example 10 was synthesized by the same method as Reference Example 1 except that the polymerization time was 2.5 hours.

(Reference Example A)
PMMA grafted BR150L of Reference Example A uses methyl methacrylate (MMA) distilled under reduced pressure on CaH ₂ instead of DMA as a monomer, a polymerization temperature of 85 ° C., a TEMPO / AIBN molar ratio of 0.95, and acetone. The synthesis was performed in the same manner as in Reference Example 1 except that the PMMA oligomer was extracted by reflux.

Examples of the silica-containing rubber composition are as follows.
Table 2 shows details of Comparative Example 2, Example 1, and Comparative Example 1.
(Example 1 and Comparative Example 1)
Kneading in a lab plast mill manufactured by Toyo Seiki Co., Ltd. with a start temperature of 90 ° C., an end temperature of 150 ° C., and a mixing time of 5 minutes or less, and a commercial grade cis-1,4-polybutadiene. The diene rubber component (UBEPOL BR150L) is first blended with the poly (N, N-dimethylacrylamide) (PDMA) grafted BR150 of Reference Example 8 (PDMA-g-BR150L, 56.59% graft rate). It was.
Then, precipitated silica (Nipsil VN3) was added and blended with silane coupling agent (Si69) and premixing components silica, aroma oil, zinc oxide, stearic acid and antioxidant (6C).
The first rubber composition obtained from the mixing process was stretched at a temperature of 30 to 60 ° C. using a 6-inch mixing roll. The sample was subjected to Mooney viscosity measurements.
In the vulcanization preliminary step, the obtained first rubber composition sheet is added with sulfur and a vulcanization accelerator (CZ and D) at a temperature of 30 to 60 ° C. using a 6-inch mixing roll, It was drawn into a sheet. The sample of the obtained second rubber composition was subjected to vulcanization time (t ₉₀ ) measurement using Mooney viscosity measurement and RPA-2000 manufactured by Alpha Technologies.
The silica-containing rubber composition obtained from the vulcanization preliminary process was molded at a temperature of 150 ° C. for the actual vulcanization time (2t ₉₀ ). Various forms of rubber vulcanizate samples in the present invention were used to measure tensile strength and network density.

(Comparative Example 2)
The silica compounded rubber composition of Comparative Example 2 was prepared in the same manner as Example 1 and Comparative Example 1 except that PDMA grafted BR150L or PMMA grafted BR150L was not used.

Claims (5)

The graft ratio of the conjugated diene rubber (A) obtained by graft modification of the acrylamide polymer by using radical polymerization (NMP method) using a nitroxide compound is 30 to 100% and 1 to 50 parts by weight ( A rubber composition containing a rubber reinforcing agent, wherein 50 to 99 parts by weight of the vulcanizable rubber (B) other than A) is added, and 30 to 70 parts by weight of a rubber reinforcing agent (C) is further added. 2. The rubber reinforcing agent-containing rubber composition according to claim 1, wherein the acrylamide polymer is polyacrylamide. 3. The rubber reinforcing agent-containing rubber composition according to claim 1, wherein the conjugated diene rubber has a 1,4-cis structure and a ratio thereof is 94 to 99%. Graft ratio of the conjugated diene rubber (A) obtained by graft modification of the acrylamide polymer by using radical polymerization (NMP method) using a nitroxide compound is 30 to 100% and 1 to 50 parts by weight ( A method for producing a rubber composition containing a rubber reinforcing agent, characterized in that the vulcanizable rubber (B) other than A) is 50 to 99 parts by weight, and further 30 to 70 parts by weight of a rubber reinforcing agent (C) is added. .   The rubber reinforcing agent-containing rubber composition according to any one of claims 1 to 4, wherein the rubber reinforcing agent (C) is silica.

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