JPH06322141A - Production of thermoplastic elastomer composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition, excellent in fluidity, thin film- forming properties in molding a sheet and tensile strength by previously decompressing a specific olefinic plastic, then adding a specified copolymer rubber and a peroxide thereto and carrying out the dynamic heat treatment. CONSTITUTION:The objective composition is obtained by previously decompressing (A) 7-50 pts.wt. peroxide decomposition type olefinic plastic, then directly adding (B) 50-93 pts.wt. peroxide crosslinkable type olefinic copolymer rubber and (C) an organic peroxide thereto and carrying out the dynamic heat treatment. Furthermore, (D) 5-300 pts.wt. mineral oil-based softening agent is preferably added after carrying out the dynamic heat treatment and completing the partial crosslinking reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic elastomer composition, and more specifically, a peroxide-crosslinkable olefin copolymer rubber, a peroxide-decomposable olefin plastic, an organic peroxide, and if necessary. Automotive interior and exterior parts, civil engineering and construction materials, industrial machine parts, medical equipment, housings, OA parts, and miscellaneous goods, which are obtained by dynamically heat-treating a composition consisting of a mineral oil-based softening agent and a crosslinking assistant The present invention relates to a method for producing a thermoplastic elastomer composition which is excellent in thin-film moldability and can be extrusion-molded or injection-molded.

[0002]

2. Description of the Related Art For injection molding of ordinary rubber, a vulcanization step is required after compounding and kneading additives into the rubber and molding in a mold. However, there is a problem that it is long and the process is complicated, and there is a similar problem in extrusion molding, which has been an obstacle to mass production of rubber products. Therefore, there has been a strong demand for a thermoplastic elastomer composition which can be molded without vulcanization and has rubber-like performance.

A composition comprising a crosslinking agent such as a peroxide-crosslinking olefin copolymer rubber, a peroxide-decomposing olefin plastic, or an organic peroxide is thermally treated in a molten state to partially crosslink with an olefin resin. A composition comprising the above-mentioned rubber is already known as an olefinic thermoplastic elastomer composition.

However, in the thermoplastic elastomer composition, the organic peroxide-decomposing olefin-based plastic and the organic peroxide cross-linking olefin-based copolymer rubber are charged into a continuous or batch-type kneading machine almost at the same time to obtain an organic peroxide. It is manufactured by heat treatment in the presence of oxide, and although it has excellent performance as a thermoplastic elastomer, its fluidity is significantly inferior to general-purpose plastics, and when extruded or injection molded, It has a drawback that flow marks are generated and a product having a good appearance cannot be obtained.

In order to improve the fluidity of the thermoplastic elastomer composition and the thin-film formability during sheet molding, (a)
There are methods such as increasing the melt flow ratio (MFR) of the olefin-based plastic used, (b) decreasing the degree of crosslinking of the rubber portion in the thermoplastic elastomer composition, and the like, but using the method (a). There is a problem that the strength of the thermoplastic elastomer composition decreases due to the decrease in the strength of the olefin plastic due to the decrease in the molecular weight of the olefin plastic, and the decrease in the adhesive force between the olefin plastic and rubber. The method (1) has a problem that the strength of the thermoplastic elastomer composition decreases when the degree of crosslinking of the rubber portion decreases.

Mineral oil-based softening agents are added to these thermoplastic elastomer compositions in order to improve fluidity without substantially impairing the heat resistance, tensile properties, flexibility and impact resilience of these compositions. However, it is also possible to perform the heat treatment dynamically in the presence of an organic peroxide, for example, as described in JP-B-56-15.
It is known as described in Japanese Patent Publication No. 741.

[0007]

SUMMARY OF THE INVENTION By the way, the present inventors, when producing a thermoplastic elastomer composition,
As a result of investigating the peroxide-decomposing olefin-based plastics, the peroxide-decomposing olefin-based plastics were immediately decomposed in the presence of organic peroxide or under the heat and shearing force, and immediately after the peroxide-decomposing olefin-based plastics were decomposed. A thermoplastic elastomer composition obtained by adding a peroxide-crosslinking olefin-based copolymer rubber to a plastic and subjecting it to a crosslinking reaction in the presence of an organic peroxide is a peroxide-decomposing type in which MFR is increased to the same extent by previously decomposing. It was found that the tensile strength is improved as compared with a thermoplastic elastomer composition obtained by simultaneously adding an olefin-based plastic and a peroxide-crosslinking olefin-based copolymer rubber and crosslinking the same in the presence of an organic peroxide. The invention of claim 1 was completed.

Furthermore, the present inventors have examined the timing of addition of the mineral oil-based softening agent when producing the thermoplastic elastomer composition, and as a result, the mineral oil-based softening agent was found to be a peroxide-crosslinking olefin-based copolymer rubber and a peroxide. In the process of dissolving in a resin composed of oxide-decomposable olefin plastics, a large viscosity unevenness occurs in the resin (the portion where the mineral oil-based softening agent is dissolved has a low viscosity, and the other is high viscosity), and the mineral oil-based softening agent dissolves in the resin When the crosslinking reaction is performed in the process,
The high-viscosity part is not kneaded (the high-viscosity part is difficult to be kneaded) and crosslinking occurs, which causes coarse particles of the crosslinked rubber to be generated. The coarse particles of the crosslinked rubber process the thermoplastic elastomer into a sheet or the like. In such a case, it was found that the fish eyes would be adversely affected by the appearance, physical properties and secondary workability of the product, and the invention of claim 2 of the present application was completed.

The present inventors have developed a peroxide-decomposable olefin-based plastic in the presence of organic peroxide.
Alternatively, when degradation treatment is carried out to decompose under heat and shearing force, a large number of radicals are present in the peroxide-decomposing olefin plastic, and the peroxide cross-linking olefin copolymer rubber is added to the olefin plastic. When the cross-linking reaction is performed in the presence of organic peroxide, the adhesive property at the interface between the peroxide-decomposing olefin-based plastic and the peroxide cross-linking olefin-based copolymer rubber is improved, thereby improving the tensile strength. It is estimated to be.

Further, it was found that the thermoplastic elastomer composition thus obtained has a large MFR of the entire composition and not only improves the fluidity but also the tensile strength.

[0011]

The first invention of the present application is
A mixture of (a) 50 to 93 parts by weight of a peroxide-crosslinking olefin-based copolymer rubber and (b) 7 to 50 parts by weight of a peroxide-decomposing olefin-based plastic is added (c).
In producing a thermoplastic elastomer composition obtained by dynamic heat treatment in the presence of organic peroxide to partially crosslink, (a) and (c) are added immediately after the degradation treatment of (b) in advance. And a method for producing a thermoplastic elastomer composition characterized by performing a dynamic heat treatment. The second invention also comprises (a) 50 to 93 parts by weight of a peroxide-crosslinking olefin-based copolymer rubber, (B)
Peroxide decomposition type olefin plastic 7-5
When 0 part by weight of the mixture was subjected to a dynamic heat treatment in the presence of (c) an organic peroxide to produce a thermoplastic elastomer composition partially crosslinked, immediately after (b) was pre-degraded ( (a) and (c) are added and dynamic heat treatment is performed to complete the partial crosslinking reaction. (d) Mineral oil softener 5
The method for producing a thermoplastic elastomer composition is characterized by adding ˜300 parts by weight.

The (a) peroxide-crosslinking olefin-based copolymer rubber used in the present invention is an amorphous random elastic copolymer containing an olefin as a main component and mixed with an organic peroxide and heated. A rubber which is crosslinked by being kneaded below to have reduced fluidity or which does not flow, for example, a rubber such as ethylene-propylene copolymer rubber, ethylene-propylene-non-conjugated diene rubber, ethylene-butadiene copolymer rubber. Of these, ethylene-propylene copolymer rubber and ethylene-propylene-non-conjugated diene rubber are preferable, and as the ethylene-propylene-non-conjugated diene copolymer rubber, as the diene monomer, those having 5 to 20 carbon atoms are preferable. Conjugated dienes such as 1,4-pentadiene, 1,4- and 1,5-hexadiene, 2, -Dimethyl-1,5-hexadiene and 1,4-octadiene, etc., cyclic dienes such as 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene, alkenylnorbornenes such as 5-ethylidene- and 5-butylidene-2- Norbornene, 2-methallyl- and 2-isopropenyl-5-
Examples thereof include those using norbornene, and among these, ethylene-propylene-ethylidene norbornene copolymer rubber is particularly preferable in that a composition excellent in heat resistance, tensile properties and impact resilience can be obtained.

The (b) peroxide-decomposable olefin-based plastic used in the present invention contains a crystalline part which is degraded in the presence of organic peroxide or under heat and shearing force to increase the fluidity of the resin. Olefinic plastics, including, for example, crystalline high molecular weight solid products obtained from the polymerization of one or more monoolefins, examples of preferred olefins include propylene, 1-butene, 1- Pentene, 1-hexene, 2
-Methyl-1-propene, 3-methyl-1-pentene,
Homopolymers and copolymers of 4-methyl-1-pentene and 5-methyl-1-hexene and mixtures thereof, and particularly preferably polypropylene resin.

The polypropylene resin is isotactic polypropylene or a random or block copolymer of propylene and an α-olefin such as ethylene, butene-1, hexene-1 and the like, and the crystal portion of which is polypropylene. Is.

In the present invention, this peroxide-decomposable olefin-based plastic needs to be adjusted to a melt flow rate of 50 to 10000 g / 10 minutes by degradation treatment. As the method of degradation, decomposition treatment is carried out in the presence of organic peroxide or by heat and shearing force.

In the case of degrading with organic peroxide, it may be carried out by melting and kneading at 170 to 250 ° C. for 0.5 to 5 minutes in the presence of organic peroxide. The amount of the organic peroxide used is 2 parts by weight or less based on 100 parts by weight of the peroxide-decomposable olefin-based plastic, and can be appropriately changed and used depending on the target melt flow rate.

Decomposition of a peroxide-decomposable olefin-based plastic in the present invention under heat and shearing force means
Peroxide decomposition type olefin plastic 29
A time sufficient to decompose in the range 0-480 ° C, preferably 320-450 ° C, typically 1-10 minutes,
Preferably, the mixture is kneaded for 2 to 6 minutes to be decomposed.

In the present invention, the peroxide-decomposable olefin plastic contributes to the improvement of the fluidity and heat resistance of the composition, and the amount of the peroxide-decomposable olefin plastic is 100 parts by weight of the total composition. Is in the range of 7 to 50 parts by weight, preferably 10 to 40 parts by weight, and when it exceeds 50 parts by weight, the flexibility and impact resilience of the composition are impaired and a sink mark is produced in the product. When the amount of the oxide-decomposable olefin-based plastic is less than 7 parts by weight, the heat resistance and fluidity of the composition are impaired and the object of the present invention cannot be achieved.

The mineral oil-based softening agent (d) used in the present invention usually weakens the intermolecular action force of the rubber during the roll processing of the rubber to facilitate the processing, and at the same time, the carbon black, white carbon, etc. It is added to help dispersion and improve the fluidity and flexibility of the thermoplastic elastomer. Paraffin-based, naphthene-based, aromatic-based softening agents can be used, and paraffin-based and tephten-based softeners are particularly preferable. .

The blending amount of the mineral oil type softener in the present invention is
Total amount of peroxide-crosslinking olefin copolymer rubber and peroxide-decomposing olefin plastic 1
5 to 300 parts by weight with respect to 00 parts by weight, preferably 10 to 2
00 parts by weight, especially 10 to 100 parts by weight. If the amount is less than 5 parts by weight, there is no sufficient fluidity improving effect on the thermoplastic elastomer composition, and if it exceeds 300 parts by weight, the heat resistance of the composition is high. And the softening agent oozes out to impair the appearance.

The mineral oil-based softening agent may be present before the dynamic heat treatment, but it is preferably added after the dynamic heat treatment to complete the crosslinking reaction and melt-kneaded.

Examples of the organic peroxide used in the present invention for crosslinking the peroxide-crosslinking olefin-based copolymer rubber or decomposing the peroxide-decomposing olefin-based plastic include dicumyl peroxide and di-
t-butyl peroxide, 2,5-dimethyl-2,5-
Di- (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-
3,1,3-bis (t-butylperoxyisopropyl) benzene, 1,1-bis (t-butylperoxy)
-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate,
Benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t
-Butyl peroxybenzoate, t-butyl peroxy isopropyl carbonate, diacetyl peroxide, lauroyl peroxide, t-butyl cumyl peroxide and the like can be mentioned, and among these, 2,5
-Dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3,1,3-bis (t-butylperoxyisopropyl) benzene , 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane and n-butyl-4,4-bis (t-butylperoxy) valerate are preferable, and 2,5-dimethyl-2 is particularly preferable. , 5-di (t-butylperoxy) hexyne-
3 is the most preferable.

When the peroxide-crosslinking olefin-based copolymer rubber is subjected to a crosslinking reaction, it is preferably 0.05 to 2 parts by weight, and more preferably 0.
It should be selected to be in the range of 1 to 1 part by weight, and if the compounding amount is less than 0.05 part by weight, the crosslinking degree of the peroxide-crosslinking olefin-based copolymer rubber is too low, and as a result, the composition Insufficient rubber-like properties such as heat resistance, tensile properties, elastic recovery and impact resilience, while exceeding 2 parts by weight increases the degree of crosslinking of the peroxide-crosslinking olefin copolymer rubber, resulting in flow of the entire composition. Sex decreases.

In the present invention, it is possible to use a cross-linking auxiliary together with these cross-linking agents in the dynamic heat treatment, if necessary. The cross-linking auxiliary used in the present invention is a peroxide cross-linking type or a polyfunctional one. (Meth) acrylate monomers, polyfunctional vinyls and metal salts of α, β-unsaturated carboxylic acids, such as sulfur, p-quinone oxime, p, p′-dibenzoylquinone dioxime, N-methyl- N, 4-dinitrosoaniline, nitrobenzene,
Organic peroxide crosslinking aids such as vinyl butyrate, vinyl stearate, zinc acrylate, zinc methacrylate, diphenylguanidine, trimethylolpropane, N, N'-m-phenylenedimaleimide, or divinylbenzene (DVB), ethylene. Glycol dimethacrylate, pentaerythritol triacrylate,
1,3-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate (TMPT), triallyl cyanurate, triallyl isocyanurate,
Examples thereof include diallyl phthalate, diallyl terephthalate, polyethylene glycol dimethacrylate, 1,2-polybutadiene, maleic anhydride, neopentyl glycol diacrylate, and glycidyl methacrylate. Addition of such a compound causes a uniform and mild crosslinking reaction. Expected, especially when trimethylolpropane trimethacrylate is used in the present invention, it is easy to handle, and the phase of the peroxide-crosslinked olefin-based copolymer rubber and the peroxide-decomposable olefin-based plastic that are the main components of the object to be treated is improved. Since it has good solubility, has an organic peroxide solubilizing action, and acts as a dispersion aid for peroxides, a cross-linking effect by heat treatment is uniform, and a composition with a well-balanced fluidity and physical properties can be obtained. Most preferred There.

The amount of the crosslinking aid compounded is preferably 0.05 to 2% by weight, more preferably 0.1 to 1% by weight, based on 100 parts by weight of the resin component. When the blending amount of the peroxide is large, as a result of the crosslinking reaction, the fluidity of the composition is poor, while when the blending amount of the organic peroxide is small, as an unreacted monomer,
Excessive compounding should be avoided because it is present in the composition and changes in physical properties may occur due to thermal history during processing and molding of the composition.

In the present invention, in order to accelerate the decomposition of organic peroxide, tertiary amines such as triethylamine and tributylamine, and aluminum, cobalt, vanadium, copper, calcium, zirconium, manganese, magnesium, lead, mercury and the like are used. It is also possible to use a decomposition accelerator such as an organic metal carboxylate such as naphthenate or octanoate.

In the production method of the present invention, the above-mentioned peroxide-decomposable olefin-based plastic of each component is decomposed in advance in the presence of organic peroxide or under heat and shearing force to obtain a molten resin. Partial cross-linking reaction is carried out by dynamically adding the remaining components to heat treatment, or adding the components excluding the mineral oil-based softener from the remaining components,
The partial crosslinking reaction is terminated, and after that, a mineral oil-based softening agent is added and kneaded and dissolved.

As the kneading device, conventionally known devices such as an open type mixi roll, a non-open type Banbury mixer, an extruder, a kneader and a continuous mixer can be used. Among these, it is preferable to use a non-open type device, and it is preferable to carry out the kneading in an atmosphere of an inert gas such as nitrogen or carbon dioxide when carrying out the crosslinking reaction.

The kneading is carried out at a temperature at which the half-life of the organic peroxide used is less than 1 minute, usually 150 to 280 ° C., preferably 170 to 240 ° C., 1 to 20 minutes, preferably 3 to 10 minutes. Good.

The composition obtained by the production method of the present invention can be molded by an apparatus used for usual thermoplastics, is suitable for extrusion molding, calender molding, injection molding, and is also a peroxide-crosslinking olefin. Since the system copolymer rubber component is partially crosslinked, it has excellent rubber-like properties such as heat resistance, weather resistance, tensile properties, flexibility and impact resilience, and has good flowability, and therefore has good moldability. Are better.

The thermoplastic elastomer composition produced by the method of the present invention may contain a filler such as calcium carbonate, calcium silicate, clay, kaolin, talc, silica, diatom, within a range that does not impair the fluidity and rubber properties. soil,
Mica powder, asbestos, alumina, barium sulphate, aluminum sulphate, calcium sulphate, basic magnesium carbonate, molybdenum disulfide, graphite, glass fibers, glass spheres, shirasu balloons, carbon fibers, etc. or colorants such as carbon black, titanium oxide. , Zinc flower,
Bengara, ultramarine, navy blue, azo pigment, nitroso pigment, lake pigment, phthalocyanine pigment, etc. can be mixed,
Further, if necessary, it is usually used in stabilizers such as antioxidants, ultraviolet absorbers and metal deterioration inhibitors, lubricants, antistatic agents, electrical property improvers, flame retardants, processability improvers and other resins or rubbers. Additives to be blended can be blended.

Applications of the thermoplastic elastomer composition produced by the method of the present invention include body panels, bumper parts, side shields, automobile interior / exterior parts such as steering wheels, civil engineering and construction-related materials, and industrial machine parts such as gaskets. , Medical equipment, housings, wire coatings, connectors, OA parts such as cap plugs, leisure products,
It can be used for sundries such as garden hoses, belts and footwear.

[0033]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples without departing from the gist thereof.

In Examples and Comparative Examples of the present invention,
The following raw materials were used. 1. Peroxide cross-linking olefin copolymer rubber EPDM: ethylene-propylene-ethylidene norbornene copolymer rubber [Moonie viscosity ML 1 + 4 (100
℃) = 88, iodine value 15.0, propylene content 28
Wt%] 2. Peroxide-decomposable olefin-based plastic BPP-1: propylene-ethylene block copolymer (BPP) [density 0.90 g / cm ³ , melt flow rate (MFR, 230 ° C., 2.16 kg load) 40 g /
10 minutes, ethylene content 7% by weight] BPP-2: BPP-1 treated with organic peroxide M
BPP with FR of 70 g / 10 min BPP-3: BPP-1 treated with an organic peroxide to give M
BPP with FR of 200 g / 10 minutes 3. Mineral oil-based softener Oil: Paraffin-based softener [Density at 15 ° C. 0.870
0 g / cm ³ viscosity index 110] 4. 4. Organic peroxide POX: 2,5-dimethyl-2,5- (t-butylperoxy) hexyne-3, 5. Crosslinking aid TMPT: trimethylolpropane trimethacrylate, (Example 1) BPP-1: 25 parts by weight in the first hopper of a co-rotating twin-screw kneader TEX54 (manufactured by Japan Steel Works),
Add 0.05 parts by weight of POX, cylinder temperature 28
It decomposed in a decomposition zone of 0 ° C. The MFR of the obtained BPP was 210.

From the second hopper, 75 parts by weight of EPDM, 0.12 parts by weight of POX and T were added to the BPP decomposed in the decomposition zone.
0.12 parts by weight of MPT was added, and dynamic heat treatment was performed in a heat treatment zone with a cylinder temperature of 200 ° C. in a nitrogen atmosphere to terminate the crosslinking reaction, and Oil: 37 was applied from a nozzle provided at the position.
The thermoplastic elastomer composition was manufactured by injecting parts by weight and kneading the oil in a zone of a cylinder temperature of 200 ° C.

A sheet was formed from this thermoplastic elastomer composition using an extrusion molding machine with a T die, and the thin film formed body was evaluated. The results are shown in Table 1 together with the tensile strength.

Example 2 A thermoplastic elastomer composition was produced in the same manner as in Example 1 except that the amount of POX added in the decomposition zone was 0.2 part by weight.

Table 1 shows the evaluation results of the obtained composition.

(Example 3) BPP-1: 25 parts by weight was added to the first hopper of the kneading machine without adding POX to the decomposition zone, and decomposition was carried out in the decomposition zone at a cylinder temperature of 400 ° C. A thermoplastic elastomer composition was produced in the same manner as in 1.

Table 1 shows the evaluation results of the obtained composition.

(Comparative Example 1) BPP-1: 25 parts by weight, E
PDM: 75 parts by weight, POX: 0.12 parts by weight, TMP
T: 0.12 parts by weight of the material composition was charged into the hopper of the kneader, and the cylinder temperature was 200 ° C. under a nitrogen atmosphere.
Dynamic heat treatment to terminate the crosslinking reaction in the heat treatment zone, oil: 37 parts by weight is injected from a nozzle provided at that position, and oil is kneaded in a zone of a cylinder temperature of 200 ° C.
A thermoplastic elastomer composition was produced.

Table 1 shows the evaluation results of the obtained composition.

Comparative Example 2 BPP-2 instead of BPP-1
A thermoplastic elastomer composition was produced in the same manner as in Comparative Example 1 except that was used.

Table 1 shows the evaluation results of the obtained composition.

(Comparative Example 3) BPP-3 instead of BPP-1
A thermoplastic elastomer composition was produced in the same manner as in Comparative Example 1 except that was used.

Table 1 shows the evaluation results of the obtained composition.

[0047]

[Table 1] From Table 1, BPP-1 was decomposed with organic peroxide,
The compositions of Examples 1 to 3 in which the remaining components were added to the material which was still in the molten state, the heat treatment was performed dynamically, and the crosslinking reaction was partially carried out were the undecomposed or pre-decomposed BPP. In comparison with the compositions of Comparative Examples 1 to 3 in which No. 1 is used, the tensile strength and the moldability are excellent, and in particular, Example 1 and Comparative Example 3 have a large difference in tensile strength even though the MFR is about the same. I know there is.

[0048]

As described above, according to the production method of the present invention, the fluidity and the thin-film formability during sheet forming are improved, and a large amount of radicals are present in the peroxide-decomposable olefin-based plastic. Since the crosslinking reaction with the olefin-based copolymer rubber is carried out, the adhesive property at the interface between the two is improved, and the thermoplastic elastomer composition obtained by the production method has remarkably improved tensile strength.

Claims (2)

[Claims] 1. A mixture of (a) 50 to 93 parts by weight of a peroxide-crosslinking olefin-based copolymer rubber and (b) 7 to 50 parts by weight of a peroxide-decomposing olefin-based plastic is added to (c) an organic peroxide. In producing a thermoplastic elastomer composition which is dynamically heat-treated underneath to be partially crosslinked, (a) and (c) are added immediately after the degradation treatment of (b), and then the dynamic heat treatment is performed. A method for producing a thermoplastic elastomer composition, comprising: 2. A mixture of (a) 50 to 93 parts by weight of a peroxide-crosslinking olefin-based copolymer rubber and (b) 7 to 50 parts by weight of a peroxide-decomposing olefin-based plastic is added to (c) an organic peroxide. In producing a thermoplastic elastomer composition which is dynamically heat treated below and partially crosslinked, (a) and (c) are added immediately after the degradation treatment of (b) and the dynamic heat treatment is performed. A method for producing a thermoplastic elastomer composition, which comprises adding (d) 5 to 300 parts by weight of a mineral oil-based softening agent after the completion of the partial crosslinking reaction.