JP2013079339A - Modified natural rubber latex as well as manufacturing method thereof, modified natural rubber, rubber composition, and tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modified natural rubber latex, as well as a manufacturing method thereof, capable of obtaining a modified natural rubber that can improve the low heat generation property (low loss property) of a rubber composition compared with a normal natural rubber, a modified natural rubber contained in the modified natural rubber latex, and a rubber composition that contains the modified natural rubber, and a tire using the rubber composition.SOLUTION: The modified natural rubber latex, consisting of natural rubber molecules and a bridge region obtained by crosslinking between the natural rubber molecules, and containing the modified natural rubber whose number average molecular weight is 150,000-450,000, is obtained by a radical graft polymerization of a compound that has two or more polymerizable functional groups and one or more polar group in a molecular to the natural rubber latex containing the natural rubber molecules.

Description

  The present invention relates to a modified natural rubber latex and a method for producing the same, and to a modified natural rubber, a rubber composition, and a tire, and in particular, the low exothermic property (low loss) of the rubber composition as compared with ordinary natural rubber. Modified natural rubber latex capable of improving modified natural rubber and method for producing the same, modified natural rubber contained in the modified natural rubber latex, rubber composition containing the modified natural rubber, and the rubber The present invention relates to a tire using the composition.

  As a rubber modification method, a monomer (monomer) is graft-copolymerized to a rubber molecule. For example, acrylonitrile is used for the purpose of increasing oil resistance and reinforcing effect against natural rubber latex. , Methyl methacrylate, styrene, and the like are graft copolymerized to obtain a latex polymerization product.

  Furthermore, by synthesizing a syndiotactic 1,2-polybutadiene and a diene rubber having a network structure, the thermoplastic elastomer composition is excellent in resin processing molding, in particular, excellent in abrasion resistance and scratch resistance. (For example, refer to Patent Document 1) or by reacting a rubber latex with a reactive monomer having two or more vinyl groups to form a cross-linked structure between rubber molecules and improving the film forming property. A rubber product that has strength and has a very small amount of ash during incineration and can be easily disposed of is obtained (see, for example, Patent Document 2).

  However, modifying the natural rubber to improve the low exothermic property (low loss property) of the rubber composition has not been made yet, and improving the low exothermic property (low loss property) of the rubber composition. There is a strong demand for the development of modified natural rubber that can be used.

Japanese Patent Laid-Open No. 7-118446 JP 2003-12736 A

  An object of the present invention is to provide a modified natural rubber latex capable of obtaining a modified natural rubber capable of improving the low heat build-up (low loss) of a rubber composition as compared with ordinary natural rubber, and a method for producing the same. Another object of the present invention is to provide a modified natural rubber contained in the modified natural rubber latex, a rubber composition containing the modified natural rubber, and a tire using the rubber composition.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have radical grafted a compound (only) having two or more polymerizable functional groups and one or more polar groups in the natural rubber latex. As a result of the polymerization reaction (emulsion polymerization reaction), it has been found that a modified natural rubber having an advanced network structure, a polar group, and a large molecular weight can be obtained compared to a normal natural rubber. The low exothermic property (low loss property) of the rubber composition can be improved, and the present invention has been completed.

  That is, the modified natural rubber latex of the present invention is a modified natural rubber latex containing a modified natural rubber having a number average molecular weight of 150,000 to 450,000, which is composed of a natural rubber molecule and a crosslinked portion formed by crosslinking between the natural rubber molecules. The natural rubber latex containing the natural rubber molecule is subjected to radical graft polymerization reaction with a compound having two or more polymerizable functional groups and one or more polar groups in the molecule.

  In the modified natural rubber latex of the present invention, the polar group is an amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, sulfide group, disulfide group, sulfonyl group, Selected from the group consisting of sulfinyl group, thiocarbonyl group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group, tin-containing group, and alkoxysilyl group It is preferable that there is at least one.

  The method for producing a modified natural rubber latex of the present invention comprises a modified natural rubber latex comprising a modified natural rubber having a number average molecular weight of 150,000 to 450,000, comprising a natural rubber molecule and a crosslinked portion formed by crosslinking between the natural rubber molecules. The natural rubber latex containing the natural rubber molecule is a radical graft polymerization reaction of a compound having two or more polymerizable functional groups and one or more polar groups in the molecule. And

  The method for producing a modified natural rubber latex according to the present invention comprises adding 0.01 parts by mass to 10.0 parts by mass of the compound with respect to 100 parts by mass of natural rubber molecules (solid rubber content) in the natural rubber latex. It is preferable.

  The modified natural rubber of the present invention is characterized by coagulating and drying the modified natural rubber latex of the present invention.

  The rubber composition of the present invention includes the modified natural rubber of the present invention.

  The rubber composition of the present invention preferably contains 15% by mass or more of the modified natural rubber of the present invention in the rubber composition.

  The tire of the present invention is characterized by using the rubber composition of the present invention.

  According to the present invention, a modified natural rubber latex capable of obtaining a modified natural rubber capable of improving the low heat build-up (low loss) of the rubber composition as compared with normal natural rubber, and a method for producing the same. In addition, a modified natural rubber contained in the modified natural rubber latex, a rubber composition containing the modified natural rubber, and a tire using the rubber composition can be provided.

(Modified natural rubber)
The modified natural rubber of the present invention comprises a natural rubber molecule and a crosslinked part formed by crosslinking the natural rubber molecule.
In addition, the modified natural rubber of the present invention coagulates the modified natural rubber latex of the present invention, which will be described later, and after drying, is dried using a normal dryer such as a vacuum dryer, an air dryer, a drum dryer, or a thin film distillation. Is obtained.

<Natural rubber molecule>
There is no restriction | limiting in particular as a number average molecular weight of the said natural rubber molecule, Although it can select suitably according to the objective, 150,000-450,000 are preferable and 250,000-450,000 are more preferable.
When the number average molecular weight of the natural rubber molecule is less than 150,000, exothermic deterioration due to a low molecular weight component may occur, and when it exceeds 450,000, the viscosity becomes high and blending workability may deteriorate. On the other hand, when the number average molecular weight of the natural rubber molecule is within the more preferable range, it is advantageous in terms of the balance of molecular weight, exothermic property, and compounding workability.
The number average molecular weight of the natural rubber molecule can be measured, for example, by gel permeation chromatography (GPC) of the natural rubber molecule obtained by dissolving it in tetrahydrofuran.

<Bridge part>
The crosslinking part is not particularly limited as long as it is derived from a compound having two or more polymerizable functional groups and one or more polar groups in the molecule, and can be appropriately selected according to the purpose.

-Compound-
The compound is not particularly limited as long as it has two or more polymerizable functional groups and one or more polar groups in the molecule, and can be appropriately selected according to the purpose. And the like.

  There is no restriction | limiting in particular as a commercial item of the said compound, Although it can select suitably according to the objective, For example, diallylamine, N, N '-(1,2-dihydroxyethylene) bisacrylamide, 3,9-divinyl -2,4,8,10-tetraoxaspiro [5.5] undecane, triallylamine, bis (vinylsulfonyl) methane, 1,3-bis (vinylsulfonyl) -2-propanol, 1,3-divinyl-1 , 1,3,3-tetramethyldisilazane, 1,3-divinyltetramethyldisiloxane, 1,6-bis (acryloyloxy) hexane, N, N′-bis (acryloyl) cystamine, bis (vinylsulfonyl) methane 1,3-bis (vinylsulfonyl) -2-propanol, N, N'-bis (vinylsulfonylacetyl) ethylene Amine, diallyl adipate, vinyl 10-undecenoate, trans, cis-2,6-nonadienal, divinyl adipate, cis-3-hexenyl cis-3-hexenoate, 2-isopropenyl-5-methyl-5-vinyl Tetrahydrofuran, (2,7-octadien-1-yl) succinic anhydride, diallyl 1,4-cyclohexanedicarboxylate (cis-, trans-mixture) (above, manufactured by Tokyo Chemical Industry Co., Ltd.); divinyl glycol, divinyl sulfone , Divinyl adipate, divinyl sebacate, diethylene glycol divinyl ether, triethylene glycol divinyl ether, diethylene glycol diacrylate, ethylene glycol diacrylate, 1,4-phenylene bisacrylate, polyethylene diacrylate Recall, N, N′-Diacryloylethylenediamine, N, N′-hexamethylenebisacrylamide, N, N′-methylenebisacrylamide (manufactured by Wako Pure Chemical Industries, Ltd.); 1,4-butanediol diacrylate ( Merck Co., Ltd.);

--Polymerizable functional group--
There is no restriction | limiting in particular as said polymeric functional group, According to the objective, it can select suitably, For example, a vinyl group, an acryl group, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.
Among these, an acrylic group is preferable in terms of polymerization reactivity.

-Polar group-
The polar group is not particularly limited as long as it has high affinity with the filler described later, and can be appropriately selected according to the purpose. For example, an amino group, imino group, nitrile group, ammonium group , Imide group, amide group, hydrazo group, azo group, diazo group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, nitrogen-containing Heterocyclic groups, oxygen-containing heterocyclic groups, tin-containing groups, alkoxysilyl groups, and the like. These may be used individually by 1 type and may use 2 or more types together.
Among these, an amino group is preferable in that a modified natural rubber having high affinity with a filler and low loss (low rolling resistance) can be obtained.
The nitrogen-containing heterocyclic ring in the nitrogen-containing heterocyclic group is not particularly limited and can be appropriately selected depending on the purpose. For example, pyrrole, histidine, imidazole, triazolidine, triazole, triazine, pyridine, pyrimidine, pyrazine, Indole, quinoline, purine, phenazine, pteridine, melamine, and the like. The nitrogen-containing heterocycle may contain other heteroatoms in the ring.
There is no restriction | limiting in particular as an oxygen-containing heterocyclic ring in the said oxygen-containing heterocyclic group, According to the objective, it can select suitably. The oxygen-containing heterocycle may contain other heteroatoms in the ring.
There is no restriction | limiting in particular as said tin containing group, According to the objective, it can select suitably, For example, a tributyl vinyl tin etc. are mentioned.

<Number average molecular weight of modified natural rubber>
The number average molecular weight of the modified natural rubber is not particularly limited as long as it is 150,000 to 450,000, and can be appropriately selected according to the purpose, but is preferably 250,000 to 450,000.
When the number average molecular weight of the modified natural rubber is less than 150,000, the heat build-up may be deteriorated due to the low molecular weight component, and when it exceeds 450,000, the viscosity becomes high and the blending workability may be deteriorated. On the other hand, when the molecular weight of the modified natural rubber is within the preferred range, it is advantageous in terms of the balance of molecular weight, heat build-up, and compounding workability.
The number average molecular weight of the modified natural rubber can be measured, for example, by gel permeation chromatography (GPC).

<Coagulation>
The coagulation method is not particularly limited and can be appropriately selected depending on the purpose. For example, a method of adjusting pH to 4.7 by adding formic acid to the modified natural rubber latex of the present invention described later, Etc.

<Dry>
The drying conditions are not particularly limited and can be appropriately selected according to the purpose.
It is preferable to heat at a temperature condition of 60 to 150 ° C. for 0.5 to 72 hours.

(Modified natural rubber latex)
The modified natural rubber latex of the present invention includes at least a modified natural rubber, and may include an unmodified natural rubber, an unmodified natural rubber, a surfactant, and the like as components other than the modified natural rubber.

There is no restriction | limiting in particular as content of the said modified natural rubber in the said modified natural rubber latex, Although it can select suitably according to the objective, 10 mass parts-60 with respect to 100 mass parts of said modified natural rubber latex. Mass parts are preferred, and 15 to 30 parts by mass are more preferred.
If the content of the modified natural rubber is less than 10 parts by mass, the coagulation rate and the uptake of non-rubber components may be affected. If it exceeds 60 parts by mass, there is a concern that non-uniform coagulation occurs. On the other hand, when the content of the modified natural rubber is within the more preferable range, it is advantageous in terms of uniform coagulation reaction.

(Method for producing modified natural rubber latex)
As a method for producing the modified natural rubber latex of the present invention, a radical graft containing a compound (only) having two or more polymerizable functional groups and one or more polar groups in the molecule is added to natural rubber latex containing natural rubber molecules. As long as the method is a polymerization reaction, there is no particular limitation, and it can be appropriately selected according to the purpose.

<Natural rubber latex>
The natural rubber latex is not particularly limited as long as it contains natural rubber molecules, and can be appropriately selected according to the purpose. Examples thereof include field latex, ammonia-treated latex, centrifugal concentrated latex, surfactant and enzyme. Examples include treated deproteinized latex and combinations thereof.
The natural rubber latex may contain water, protein, lipid, mineral, carbohydrate, and the like as components other than natural rubber molecules.
In addition, for example, (i) a radical reaction is performed on the natural rubber latex by overheating in the presence of a peroxide or an azo compound, and (ii) a redox initiator having a persulfate as a component is used. (Iii) irradiation with X-rays, α rays, γ rays, etc., (iv) adding a carbonyl compound and oxidizing in the presence of a radical generator. It is also possible to use a depolymerized natural rubber latex as a starting material. The radical generator for promoting air oxidation is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a peroxide radical generator, an azo radical generator, a redox radical generator Agents, etc. There is no restriction | limiting in particular as said carbonyl compound, According to the objective, it can select suitably, For example, various aldehydes, ketones, etc. are mentioned.

There is no restriction | limiting in particular as content of the said natural rubber molecule in the said natural rubber latex, Although it can select suitably according to the objective, 10 mass parts-60 mass parts with respect to 100 mass parts of said natural rubber latex. Is preferable, and 15 to 30 parts by mass is more preferable.
If the content of the natural rubber molecule is less than 10 parts by mass, the reaction efficiency may be reduced, which may affect the coagulation rate and the incorporation of non-rubber components. If the content exceeds 60 parts by mass, the viscosity will increase. Therefore, there is a concern that the uniformity will deteriorate. On the other hand, when the content of the natural rubber molecule is within the more preferable range, it is advantageous in terms of uniform reaction of polar groups.

There is no restriction | limiting in particular as an addition amount of the said compound with respect to 100 mass parts of natural rubber molecules (solid rubber part) in the said natural rubber latex, Although it can select suitably according to the objective, 0.01 mass part-10 0.0 part by mass is preferable, and 0.1 part by mass to 5.0 parts by mass is more preferable.
When the addition amount of the compound is less than 0.01 parts by mass, the effect of improving the molecular weight may be small. When the addition amount exceeds 10.0 parts by mass, the natural rubber latex is excessively gelled. Dispersion of fillers (for example, fillers, etc.) in the rubber composition to be contained becomes difficult, and the influence on rubber physical properties may be increased. On the other hand, when the addition amount of the compound is within the more preferable range, it is advantageous in terms of balance between heat generation and other physical properties.

<Radical graft polymerization>
In the radical graft polymerization, the type and amount of the graft polymerization initiator, the polymerization temperature, and the like are not particularly limited and can be appropriately selected depending on the purpose.
Here, in the radical graft polymerization, when performing a depolymerization reaction by adding a radical initiator, the graft polymerization can be performed simultaneously. In addition, the above-mentioned compound is added to a natural rubber latex that has been depolymerized and water and an emulsifier are added as necessary, a graft polymerization initiator is added, and the mixture is stirred and polymerized at a predetermined temperature. Good. In addition, when adding the compound to the natural rubber latex, an emulsifier may be added to the natural rubber latex in advance, or after emulsifying the compound, it may be added to the natural rubber latex. There is no restriction | limiting in particular as an emulsifier, According to the objective, it can select suitably, For example, nonionic surfactants, such as polyoxyethylene lauryl ether, etc. are mentioned.

-Graft polymerization initiator-
There is no restriction | limiting in particular as said graft polymerization initiator, According to the objective, it can select suitably, Various initiators for emulsion polymerization can be used, and there is no restriction | limiting in particular also about the addition method.
The type of the graft polymerization initiator is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, and di-tert. -Butyl peroxide, 2,2-azobisisobutyronitrile, 2,2-azobis (2-diaminopropane) hydrochloride, 2,2-azobis (2-diaminopropane) dihydrochloride, 2,2-azobis ( 2,4-dimethylvaleronitrile), potassium persulfate, sodium persulfate, ammonium persulfate, and the like. In order to reduce the polymerization temperature, it is preferable to use a redox graft polymerization initiator.
The reducing agent combined with the peroxide used in the redox polymerization initiator is not particularly limited and can be appropriately selected depending on the purpose. For example, tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing property Examples include metal ions and ascorbic acid.
The redox initiator is not particularly limited and may be appropriately selected depending on the intended purpose. However, a combination of tert-butyl hydroperoxide and tetraethylenepentamine is preferable.
The addition amount of the graft polymerization initiator in the natural rubber latex is not particularly limited and may be appropriately selected depending on the intended purpose. However, when a filler (carbon black, silica) is blended, the workability is improved. From the viewpoint of improving the low-loss characteristics without reducing the content, the content of the polymerizable functional group-containing compound (polar group-containing compound) is preferably 1 mol% to 100 mol%, more preferably 10 mol% to 100 mol%.
If the addition amount of the graft polymerization initiator is less than 1 mol%, the effect of adding the graft polymerization initiator may not be obtained, and if it exceeds 100 mol%, it is uniformly polymerizable functional group in each natural rubber molecule. The containing compound (polar group-containing compound) may not be introduced. On the other hand, when the addition amount of the graft polymerization initiator is within the more preferable range, the polymerizable functional group-containing compound (polar group-containing compound) is introduced into each natural rubber molecule in a uniform and sufficient amount, thereby generating heat. This is advantageous in that the property is improved.

-Polymerization temperature-
There is no restriction | limiting in particular as said superposition | polymerization temperature, Although it can select suitably according to the objective, It is preferable that it is the temperature of room temperature vicinity.
According to the production method of the present invention, natural rubber latex containing natural rubber molecules is mixed with a compound having two or more polymerizable functional groups and one or more polar groups in the molecule, so that dispersibility is improved. Thus, the polymerization temperature can be set to a temperature around room temperature.

(Rubber composition)
The rubber composition of the present invention is not particularly limited as long as it contains the modified natural rubber of the present invention, and can be appropriately selected according to the purpose, but rubber components other than the modified natural rubber of the present invention, fillers, It preferably contains a crosslinking agent, a vulcanization accelerator, an anti-aging agent, a softening agent and the like.

<Modified natural rubber>
There is no restriction | limiting in particular as content of the modified | denatured natural rubber of this invention in the said rubber composition, Although it can select suitably according to the objective, 15 mass% or more is preferable.
If the content of the modified natural rubber in the rubber composition is less than 15% by mass, the heat generation reducing effect may be small.

<Rubber component>
The rubber component is not particularly limited and can be appropriately selected according to the purpose. For example, the modified natural rubber, natural rubber, various butadiene rubbers, various styrene-butadiene copolymer rubbers, isoprene rubbers of the present invention, Butyl rubber, isobutylene and p-methylstyrene copolymer bromide, halogenated butyl rubber, acrylonitrile butadiene rubber, chloroprene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber, styrene-isoprene copolymer Polymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, chlorosulfonated polyethylene, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluorine rubber, urethane rubber, etc. . These may be used individually by 1 type and may use 2 or more types together.
There is no restriction | limiting in particular as content of the modified natural rubber of this invention in the said rubber component, Although it can select suitably according to the objective, 20 mass% or more is preferable.
If the content of the modified natural rubber in the rubber component is less than 20% by mass, the heat generation reducing effect may be small.

<Filler>
The filler is not particularly limited and may be appropriately selected depending on the intended purpose. For example, carbon black, silica, aluminum hydroxide, clay, alumina, talc, calcium carbonate, magnesium carbonate, magnesium hydroxide, oxidation Examples thereof include magnesium and titanium oxide. These may be used individually by 1 type and may use 2 or more types together.
The carbon black is not particularly limited and may be appropriately selected depending on the intended purpose. However, SAF, ISAF, HAF, FEF, and GPF grade carbon black are preferable.
Moreover, there is no restriction | limiting in particular as said silica, Although it can select suitably according to the objective, Wet silica, dry-type silica, and colloidal silica are preferable.

There is no restriction | limiting in particular as content of the said filler, Although it can select suitably according to the objective, 5 mass parts-100 mass parts are preferable with respect to 100 mass parts of rubber components, and 10 mass parts-70 mass parts. A range of parts is more preferred.
When the content of the filler is less than 5 parts by mass, the effect of adding the filler may not be seen so much. When the content exceeds 100 parts by mass, the rubber component tends not to be mixed. .

<Crosslinking agent>
There is no restriction | limiting in particular as said crosslinking agent, According to the objective, it can select suitably, For example, sulfur etc. are mentioned.

There is no restriction | limiting in particular as content of the said crosslinking agent, Although it can select suitably according to the objective, 0.1 mass part-20 mass parts are preferable with respect to 100 mass parts of rubber components.
If the content of the cross-linking agent is less than 0.1 parts by mass, the effect of adding the cross-linking agent tends not to be obtained. If the content exceeds 20 parts by mass, cross-linking proceeds during kneading with some cross-linking agents. There is a tendency to become.

(tire)
The tire of the present invention is not particularly limited as long as the rubber composition of the present invention is used, and can be appropriately selected according to the purpose, but a pneumatic tire is preferable.
As a method for manufacturing the tire, a conventional method can be used. For example, normal tire manufacturing members such as a carcass layer, a belt layer, and a tread layer made of unvulcanized rubber are sequentially laminated on a tire molding drum, and the drum is removed to obtain a green tire. Next, the desired tire can be manufactured by heat vulcanizing the green tire according to a conventional method.
There is no restriction | limiting in particular as conditions for the said heat vulcanization, Although it can select suitably according to the objective, Temperature 100 to 200 degreeC and heating time 10 minutes-15 hours are preferable.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Production Example 1: Method for producing modified natural rubber A)
Clone species GT-1, 0.4 wt% NH ₃ treated natural rubber latex was centrifuged at a rotational speed of 7500 rpm using a latex separator (manufactured by Saito Centrifugal Co., Ltd.) to obtain a concentrated latex having a dry rubber concentration of 60% by mass. . 1000 g of this concentrated latex was put into a stainless steel reaction vessel equipped with a stirrer and a temperature control jacket, and 10 ml of water and 90 mg of emulsifier (Emulgen 1108, manufactured by Kao Corporation) were added in advance to 1.6 g of diallylamine and emulsified. Were added with 990 ml of water and stirred for 30 minutes while purging with nitrogen. Next, 1.2 g of tert-butyl hydroperoxide and 1.2 g of tetraethylenepentamine were added as polymerization initiators and reacted at 40 ° C. for 30 minutes to obtain a modified natural rubber latex.
Next, the modified natural rubber latex was coagulated by adding formic acid to adjust the pH to 4.7. The solid thus obtained was treated 5 times with a creper, crushed by passing through a shredder, and dried at 110 ° C. for 210 minutes with a hot air dryer to obtain modified natural rubber A (Table 1).

(Production Example 2: Method for producing modified natural rubber B)
Modified natural rubber B in the same manner as in Production Example 1 except that 3.3 g of N, N ′-(1,2-dihydroxyethylene) bisacrylamide was added instead of adding 1.6 g of diallylamine in Production Example 1. (Table 1).

(Production Example 3: Production Method of Modified Natural Rubber C)
A modified natural rubber C was obtained in the same manner as in Production Example 1 except that 2.5 g of N, N′-methylenebisacrylamide was added instead of adding 1.6 g of diallylamine in Production Example 1 (Table 1). .

(Production Example 4: Production Method of Modified Natural Rubber D)
Modified natural rubber D was obtained in the same manner as in Production Example 1 except that 3.6 g of N, N′-hexamethylenebisacrylamide was added instead of adding 1.6 g of diallylamine in Production Example 1 (Table 1). ).

(Production Example 5: Method for producing modified natural rubber E)
A modified natural rubber E was obtained in the same manner as in Production Example 1 except that 3.2 g of diacrylic acid 1,4-butanediol was added instead of adding 1.6 g of diallylamine in Production Example 1 (Table 1). .

(Production Example 6: Method for producing modified natural rubber a)
Clone species GT-1, 0.4 wt% NH ₃ treated natural rubber latex was centrifuged at a rotational speed of 7500 rpm using a latex separator (manufactured by Saito Centrifugal Co., Ltd.) to obtain a concentrated latex having a dry rubber concentration of 60% by mass. .
The natural rubber latex was then coagulated by adding formic acid and adjusting the pH to 4.7. The solid material thus obtained was treated 5 times with a creper, passed through a shredder to crumb, and dried at 110 ° C. for 210 minutes with a hot air dryer to obtain natural rubber a (Table 1).

(Production Example 7: Method for producing natural rubber b)
In Production Example 1, instead of adding 1.6 g of diallylamine, 2.1 g of divinylbenzene was added, and the others were produced under the same conditions to obtain modified natural rubber b.

(Examples 1-5 and Comparative Examples 1 and 2)
Next, rubber compositions 1 to 7 containing the modified natural rubbers A to E and (modified) natural rubbers a and b obtained in Production Examples 1 to 7 in the formulation shown in Table 2 were prepared by kneading with a plastmill. For each of the rubber compositions 1 to 7, “raw material Mooney (ML _{1 + 4} , 100 ° C.)”, “number average molecular weight (Mn)”, “compounding Mooney (ML _{1 + 4} , 130 ° C.)” and “tan δ” are as follows: It measured by the measuring method shown. The measurement results are shown in Table 3-1 and Table 3-2.

<Measuring method of raw material Mooney (ML _{1 + 4} , 100 ° C.)>
The Mooney viscosity ML _{1 + 4} (100 ° C.) of the (modified) natural rubber was measured at 100 ° C. in accordance with JIS K6300-1994.

<Measuring method of number average molecular weight (Mn)>
Gel permeation chromatography [GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two in series), detector: differential refractometer (RI)], each based on monodisperse polystyrene (modified) The number average molecular weight (Mn) of natural rubber in terms of polystyrene was determined.

<Measuring method of blended Mooney (ML _{1 + 4} , 130 ° C)>
The Mooney viscosity ML _{1 + 4} (130 ° C.) of the rubber composition was measured at 130 ° C. in accordance with JIS K6300-1994.

<Measurement method of tan δ>
For the vulcanized rubber obtained by vulcanizing the rubber composition at 145 ° C. for 33 minutes, a loss tangent (tan δ) at a temperature of 50 ° C., a strain of 5%, and a frequency of 15 Hz using a viscoelasticity measuring device (manufactured by Rheometrics). ) Was measured. It shows that it is excellent in low-loss property, so that tan-delta is small.

カーボンブラックＮ３３９：東海カーボン社製「シーストＫＨ」
老化防止剤６Ｃ：Ｎ−（１，３−ジメチルブチル）−Ｎ´−フェニル−ｐ−フェニレンジアミン
加硫促進剤ＤＺ：Ｎ，Ｎ´−ジシクロヘキシル−２−ベンゾチアゾリルスルフェンアミド

Carbon Black N339: “Seast KH” manufactured by Tokai Carbon
Anti-aging agent 6C: N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine vulcanization accelerator DZ: N, N′-dicyclohexyl-2-benzothiazolylsulfenamide

  As mentioned above, the modification | denaturation whose number average molecular weights are obtained by carrying out radical graft polymerization of the compound which has a 2 or more polymerizable functional group and a 1 or more polar group in a molecule | numerator in natural rubber latex is 150,000-450,000. It has been found that natural rubber can improve the low heat build-up (low loss) of the rubber composition (the sine loss (tan δ) of the compounded rubber is low) compared to normal natural rubber.

  The modified natural rubber of the present invention can be used for elastomer products in general, particularly for tire members.

Claims (8)

A modified natural rubber latex comprising a modified natural rubber having a natural rubber molecule and a crosslinked part formed by crosslinking between the natural rubber molecules, and having a number average molecular weight of 150,000 to 450,000,
A modified natural rubber latex obtained by subjecting a natural rubber latex containing a natural rubber molecule to a radical graft polymerization reaction with a compound having two or more polymerizable functional groups and one or more polar groups in the molecule.   The polar group is an amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, hydroxyl group And at least one selected from the group consisting of a carboxyl group, a carbonyl group, an epoxy group, an oxycarbonyl group, a nitrogen-containing heterocyclic group, an oxygen-containing heterocyclic group, a tin-containing group, and an alkoxysilyl group. The modified natural rubber latex according to claim 1. A method for producing a modified natural rubber latex comprising a natural rubber molecule and a crosslinked part formed by crosslinking between the natural rubber molecules, including a modified natural rubber having a number average molecular weight of 150,000 to 450,000,
A modified natural rubber latex obtained by subjecting a natural rubber latex containing a natural rubber molecule to a radical graft polymerization reaction with a compound having two or more polymerizable functional groups and one or more polar groups in the molecule. Production method.   The modified natural rubber latex according to claim 3, wherein 0.01 to 10.0 parts by mass of the compound is added to 100 parts by mass of the natural rubber molecule in the natural rubber latex. Method.   A modified natural rubber obtained by coagulating and drying the modified natural rubber latex according to claim 1.   A rubber composition comprising the modified natural rubber according to claim 5.   The rubber composition according to claim 6, wherein the content of the modified natural rubber in the rubber composition is 15% by mass or more.   A tire comprising the rubber composition according to claim 6.