JPH059325A - Production of crosslinked foam of olefinic elastomer composition - Google Patents

Abstract

PURPOSE:To obtain the subject foam, containing a homogeneously dispersed foaming agent with hardly any pinholes, excellent in tensile strength and elongation and useful as an automotive interior trim material, etc., by molding a specific composition for a crosslinked foam, then crosslinking the molded product and subsequently expanding the crosslinked molded product. CONSTITUTION:With 100 pts.wt. resin composed of 10-50wt.% PP and 50-90wt.% ethylene-propylene-diene copolymer rubber, is kneaded 10-20 pts.wt. foaming agent such as azodicarbonamide at a temperature below the decomposition temperature of the aforementioned foaming agent. Thereby, a foaming agent- containing masterbatch is produced. With 10-80wt.% PP, are kneaded 20-90wt.% ethylene-propylene-diene copolymer rubber and 5-70wt.% above-mentioned masterbatch at a temperature below the decomposition temperature of the aforementioned foaming agent. As a result, a composition for a crosslinked foam is produced and molded. The obtained molded product is subsequently crosslinked and then expanded to afford the objective foam.

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 crosslinked foamed product of an olefin elastomer composition, and in particular, a foaming agent is evenly dispersed, the number of pinholes is small, and the tensile strength such as tensile breaking strength is excellent. The present invention relates to a method for producing a crosslinked foam of an olefin elastomer composition.

[0002]

BACKGROUND OF THE INVENTION Polyolefin foams are excellent in mechanical strength, flexibility, texture, heat resistance, chemical resistance, etc., and are used as interior materials for automobiles, heat insulating materials, sports goods and foods. It is widely used as a cushioning material for packaging, as well as as a sound deadening material and exterior material.

Among them, polyethylene foam is excellent in flexibility, texture, elongation and the like due to its low melting point. On the other hand, polypropylene foam has excellent mechanical strength such as tensile strength and bending strength and heat resistance, but due to its high melting point, molecular breakage considerably progresses during foaming, resulting in large and undeveloped foam cells. It tends to be uniform. Moreover, the usual foaming agent is about 170
Since it starts to decompose at about ℃, it is not very suitable for polypropylene resin with high melting point, and since the blowing agent with high decomposition temperature produces less gas, it is necessary to obtain a sufficiently high foaming ratio. Has a problem in that it requires a large amount of foaming agent and is not economical. Further, the above-mentioned polyolefin cross-linked foam has a problem that flexibility, elasticity, elongation and the like are not always sufficient.

Therefore, it is considered that the above-mentioned drawbacks can be solved by blending polypropylene with an ethylene-propylene-diene copolymer rubber having elasticity to some extent. The crosslinked foam of such an olefin elastomer composition is usually dry-blended with a foaming agent which is a powder, and is extruded to form a raw sheet, which is then subjected to radiation crosslinking and heat treatment. It is manufactured by

However, the above-mentioned method has a problem that it is difficult to sufficiently knead and to uniformly disperse the foaming agent in order to avoid decomposition of the foaming agent. If there is a poorly dispersed portion of the foaming agent in the unfoamed molded article, large bubbles or pinholes are likely to be present in the foamed article, and the mechanical properties of the foamed article are likely to deteriorate.

Therefore, it is an object of the present invention to provide a method for producing a foam of an olefinic elastomer composition in which a foaming agent is uniformly dispersed, the number of pinholes is small, and the tensile strength is excellent.

[0007]

As a result of earnest research in view of the above problems, the present inventors have found that polypropylene and ethylene
Propylene-diene copolymer rubber, when producing a foam from a composition comprising a blowing agent, polypropylene,
An ethylene-propylene-diene copolymer rubber and a foaming agent were kneaded in a significantly thickened state to prepare in advance, and the resin component and the resin component were mixed to obtain a desired foaming ratio. When the molded product obtained from the composition is crosslinked by radiation and then heated and foamed, the dispersed state of the foaming agent is improved, the number of pinholes is reduced, and the tensile elongation is significantly improved. And found the present invention.

That is, the method for producing a crosslinked foamed product of the olefin elastomer composition of the present invention comprises (A) 10 to 50% by weight of polypropylene and 50 to 90% by weight of ethylene-propylene-diene copolymer rubber. A foaming agent-containing master batch is produced by kneading 10 to 200 parts by weight of a foaming agent with respect to 100 parts by weight of a resin component at a temperature lower than the decomposition temperature of the foaming agent, and (B) (a) polypropylene 10 to 80% by weight, and (b) ethylene-propylene-diene copolymer rubber
20 to 90% by weight, (c) the masterbatch 5 containing the foaming agent
~ 70 wt% and to produce a composition for crosslinked foam by kneading at a temperature below the decomposition temperature of the foaming agent, (C) the composition is molded and then crosslinked, and then foamed. Characterize.

The present invention will be described in detail below. First, various components as raw materials will be described. In the method of the present invention, polypropylene is a crystalline polymer obtained by polymerizing a propylene monomer as a main component, and is not limited to a homopolymer but includes a block copolymer or a random copolymer of propylene and another α-olefin such as ethylene.
Also, a propylene random copolymer containing a non-conjugated diene comonomer may be used. For copolymers,
As will be described later, it is preferable to use a propylene-ethylene block copolymer for the foaming agent-containing masterbatch, and it is preferable to use a propylene-ethylene random copolymer for the base resin of the foam. In the case of a propylene-ethylene random copolymer, the content of ethylene is preferably 5% by weight or less, more preferably 0.4 to
It is 4.0% by weight. In the case of a propylene-ethylene block copolymer, the content of ethylene is preferably 1-10% by weight, more preferably 2-8% by weight. Such polypropylene is usually 1 to 50 g / 10 minutes, preferably 3 to
It has a melt flow rate of 30g / 10 minutes (MFR, JISK7210, load 2.16kg, 230 ° C).

As explained above, the term "polypropylene" used in the present specification is not limited to a homopolymer of propylene, and it should be understood to include each copolymer as described above.

In the method of the present invention, the ethylene-propylene-diene copolymer rubber (EPDM) is a low crystalline polymer composed of ethylene, propylene and diene, and has an ethylene content of 40 to 70 mol%. The propylene content is preferably 30 to 60 mol%, and the diene content is preferably 1 to 10 mol%. More preferred ranges are 50 to 60 mol% ethylene, 40 to 50 mol% propylene, and 3 to 6 mol% diene.

Examples of the diene component include non-conjugated dienes such as dicyclopentadiene, 1,4-hexadiene, cyclooctadiene and methylenenorbornene, or butadiene,
Conjugated dienes such as isoprene can be used.

The Mooney viscosity ML _{1 + 4} (100 ° C.) is 10 to 10
It is preferably in the range of 0, more preferably 20 to 90.
Is. Further the density is preferably in the 0.84~0.90g / cm ^3, more preferably 0.85~0.88g / cm ^3.

The above ethylene-propylene-diene copolymer (EPDM) basically comprises the above repeating unit, but within a range not impairing the characteristics of these copolymers, for example, butene-1. Or 4-methylpentene-
Other α-olefins such as 1 may be included up to a proportion of 10 mol% or less.

In the method of the present invention, the foaming agent is a compound which is liquid or solid at room temperature but decomposes or vaporizes when heated to a temperature higher than the melting point of polypropylene. Anything can be used as long as it does not interfere with the
It is preferably in the range of to 270 ° C. Specific examples thereof include azodicarbonamide, azodicarboxylic acid metal salt, dinitrosopentamethylenetetramine, hydrazodicarbonamide, p-toluenesulfonyl semicarbazide and s-trihydrazinotriazine.

Next, a method for producing a crosslinked foamed product of the olefinic elastomer composition of the present invention using each of the above components will be described.

First, a blowing agent-containing masterbatch is manufactured by the following procedure. The masterbatch is produced by adding a blowing agent to a resin component composed of polypropylene and an ethylene-propylene-diene copolymer rubber at a high concentration and kneading the resin component.

When a propylene-ethylene block copolymer is used as the polypropylene component, the resulting masterbatch has a resin component, particularly ethylene-propylene-
It is preferable because it is well dispersed in the diene copolymer rubber.

The blending ratio of the above polypropylene and the ethylene-propylene-diene copolymer rubber is 10 to 50% by weight of polypropylene, preferably 10 to 30% by weight,
The ethylene-propylene-diene copolymer rubber is 50 to 90% by weight, preferably 70 to 80% by weight. If the polypropylene content is less than 10% by weight (ethylene-propylene-diene copolymer rubber content exceeds 90% by weight), the mechanical strength of the resulting foam is lowered, and if the polypropylene content exceeds 50% by weight (ethylene- If the propylene-diene copolymer rubber is less than 50% by weight), the elasticity and tensile elongation of the resulting foam will be insufficient.

The amount of the foaming agent added is 1 total of the above polypropylene and ethylene-propylene-diene copolymer rubber.
10 to 200 parts by weight, preferably 20 to 10 parts by weight, relative to 00 parts by weight
0 parts by weight. If the content of the foaming agent is less than 10 parts by weight, foaming will be insufficient, while if it exceeds 200 parts by weight, uniform mixing will be difficult.

The content of the foaming agent in the masterbatch may be appropriately set depending on the desired expansion ratio and the total amount of the resin components in the composition for crosslinked foam described later, but usually the resin components are used. The total amount of 100 parts by weight, 1-30
It is used in a range such that it is part by weight, and the mixing amount can be arbitrarily changed according to each type and foaming ratio.

Next, the masterbatch thus obtained, polypropylene, and ethylene-propylene-diene copolymer rubber are kneaded to produce a composition for crosslinked foam. At this time, the melt-kneading temperature needs to be lower than the decomposition temperature of the foaming agent. The preferred melt-kneading temperature is
165-175 ° C.

In the above kneading, the mixing ratio of various components is
(a) Polypropylene 10 to 80% by weight, preferably 20 to 70
% By weight, (b) the ethylene-propylene-diene copolymer rubber is 20 to 90% by weight, preferably 30 to 80% by weight, and (c) the blowing agent-containing masterbatch is 5 to 70% by weight, preferably Is 10 to 60% by weight.

In the present invention, a peroxide may be added in addition to the above components during the kneading in order to carry out a crosslinking reaction. However, when the crosslinking reaction is carried out by ionizing radiation, the organic peroxide may not be used. When an organic peroxide is used, it preferably has a decomposition temperature of about 150 ° C or higher, and specific examples include methyl ethyl ketone peroxide (182 ° C), t-butylperoxyisopropyl carbonate (153 ° C), dicumylperoxide. Oxide (171 ℃),
Cumene hydroperoxide (255 ℃), 2,5-dimethyl-2,5
-Di (t-butylperoxy) hexane (179 ° C), 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 (193
℃), di-t-butyl peroxyphthalate (159 ℃). These organic peroxides are 0.01 to 1.0 part by weight, preferably 0.05 to 0.
Use at a ratio of 5 parts by weight.

In order to carry out the crosslinking reaction smoothly and efficiently, it is preferable to add a crosslinking aid. Examples of the crosslinking aid that can be used in the present invention include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol pentaacrylate,
Examples include diallyl phthalate and diallyl maleate. The amount of the above-mentioned crosslinking aid added is 0.5 to 5.0 parts by weight, preferably 1.0 to 3.0 parts by weight, based on 100 parts by weight of the total amount of the resin components.
Parts by weight.

In addition, for the purpose of improving the properties of the crosslinked foam of the elastomer composition, various other compounding agents, specifically rubbery substances, other resins, pigments, various fillers, flame retardant substances, etc. , An antioxidant and the like can be appropriately mixed.

Next, a method for producing a crosslinked foam of an elastomer composition using the composition for crosslinked foam comprising each of the above components will be described. First, the kneaded product of the masterbatch having the above composition is extruded from a die such as an extruder. In this case, set the kneading temperature to prevent decomposition of the foaming agent.
165 to 175 ℃ Next, the masterbatch is blended with polypropylene + ethylene-propylene-diene copolymer rubber in a predetermined amount and kneading is performed again. At this time, the temperature of the die
Control in the range of 165 to 175 ℃. The extrusion is performed using a T-die or the like so that a sheet-shaped molded body can be obtained.

Crosslinking is performed on the thus obtained molded body. As a method for forming a crosslinked structure, in addition to the method using an organic peroxide as described above, α rays, β rays (electron rays), γ
A conventionally used method such as a method of irradiating ionizing radiation such as a ray or a method of heating can be adopted.
Among these methods, the method by irradiation of ionizing radiation is preferable, and the crosslinking by electron beam irradiation is most preferable. The radiation dose varies depending on the type and amount of the crosslinking aid, the degree of crosslinking, etc., but is generally 0.1 to 50 Mrad, preferably 1
~ 30 Mrad.

The foaming of the composition for crosslinked foams thus crosslinked is carried out at a temperature higher than the melting point of the resin component, preferably
It can be carried out by heating to a temperature of 230 ° C or higher, more preferably 250 to 270 ° C. The heating time required for foaming is usually 1 to 3 minutes.

[0030]

In the present invention, first, polypropylene and
A composition (masterbatch) is prepared by adding a blowing agent at a high concentration to a resin component composed of an ethylene-propylene-diene copolymer rubber, and then the masterbatch is further mixed with polypropylene and ethylene- A propylene-diene copolymer rubber is blended in such a manner that the content of the foaming agent will be a desired ratio with respect to the resin component, whereby a cross-linking foaming composition is obtained, and a radiation-crosslinked molded article obtained from this composition is obtained. After that, the foam is produced by heating and foaming. The foam obtained by such a method of the present invention has few pinholes and is excellent in physical properties such as tensile strength and tensile elongation.

The reason why such an effect is obtained is that in a resin system comprising polypropylene and ethylene-propylene-diene copolymer rubber (EPDM), first, a high-concentration foaming agent-containing composition is prepared, and then, It is considered that this is because the blowing agent is extremely well dispersed in the entire composition because it is blended with polypropylene and the ethylene-propylene-diene copolymer rubber.

[0032]

The present invention will be described in more detail by the following specific examples. The following raw material resins were used. [1] Polypropylene RPP: Propylene-ethylene random copolymer [melt flow rate (MFR, 230 ° C, 2.16 kg load) 14 g / 10
Min, ethylene content 0.4% by weight] BPP: propylene-ethylene block copolymer [melt flow rate (MFR, 230 ° C, 2.16 kg load) 15 g / 10
Min, ethylene content 7.5% by weight, density 0.900 g / cm ³ ] [2] ethylene-propylene-diene copolymer rubber / EPDM [Moonie viscosity ML _{1 + 4} (100 ° C) 40, density 0.
86 g / cm ³ )

Synthesis Example 1 Production of Masterbatch Containing Blowing Agent 25 parts by weight of propylene-ethylene block copolymer (BPP) and ethylene-propylene-diene copolymer rubber (EPD
M) 100 parts by weight of a thermoplastic olefin elastomer consisting of 75 parts by weight and 10 parts by weight or 50 parts by weight of a foaming agent (azodicarbonamide: ADCA) are kneaded by an extruder at 170 ° C. for 3 minutes. , Masterbatch containing blowing agent (MB-1 and MB-2) was produced.

Examples 1 to 6 and Comparative Examples 1 to 4 Propylene-ethylene random copolymer (RPP) or propylene-ethylene block copolymer (BPP) and ethylene-propylene-diene copolymer rubber (EPDM). The proportion of the blowing agent-containing masterbatch (MB-1 or MB-2) obtained as described above is shown in Table 1, and the crosslinking aid (triad) was added to 100 parts by weight of the above components. 3 parts by weight of methylolpropane trimethacrylate and neopentyl glycol and 0.5 parts by weight of antioxidant were added and mixed by a Henschel mixer for 2 minutes at 500 rpm, and then an extruder (50 mmφ, L / D = 28, with T-die) ) And extruded at an extrusion temperature of 170 ° C. to form a sheet having a thickness of 1.0 mm.

Next, this sheet was irradiated with an electron beam having a dose of 750 kV and 4 Mrad to perform crosslinking. The gel fraction of the crosslinked sheet was about 40% by weight. Then, the mixture was placed in an air oven at 250 ° C. for 2 minutes to decompose the foaming agent and foam it.

For each crosslinked foamed sheet thus obtained, the expansion ratio, tensile strength at break, tensile elongation at break and pinhole number were measured. The results are shown in Table 2.

For comparison, a thermoplastic olefin comprising a propylene-ethylene random copolymer (RPP) or a propylene-ethylene block copolymer (BPP) and an ethylene-propylene-diene copolymer rubber (EPDM). For each foamed sheet produced from a crosslinked foam composition obtained by adding 10 parts by weight or 4 parts by weight of a foaming agent to 100 parts by weight of the elastomeric composition, mixing them all at once, and melt-kneading the mixture. Similarly, foaming ratio, tensile breaking strength,
The tensile elongation at break and the number of pinholes were measured. The results are shown in Table 2 together with the content of the foaming agent.

Table 1 Composition (parts by weight) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 RPP 20 15 23 --- BPP --- 20 15 23 EPDM 60 45 69 60 45 69 MB-1-40--40-MB-2 20-8 20-8 Content of foaming agent 10 4 4 10 4 4

Table 1 (continued) Composition (parts by weight) Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 RPP 25 25 --- BPP --- 25 25 EPDM 75 75 75 75 Blowing Agent 10 4 10 4

[0040] Table 2 Characteristics Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 expansion ratio ⁽¹⁾ 25 11 10 25 11 10 Tensile strength at break ⁽²⁾ 15.5 42.6 40.0 13.2 38.9 36.1 Tensile Elongation at break ⁽³⁾ 530 520 560 590 530 640 Number of pinholes ⁽⁴⁾ 2 0 1 1 0 1 Table 2 (continued) Characteristics Comparative example 1 Comparative example 2 Comparative example 1 Comparative example 2 Foaming ratio ⁽²⁾ 26 10 26 10 Tensile breaking strength ⁽³⁾ 13.0 37.0 10.8 32.8 Tensile breaking elongation ⁽⁴⁾ 400 380 510 470 Number of pinholes ⁽⁵⁾ 6 5 7 4

(1) The unit is double. (2) Measured value according to JIS K6767 (Unit: kg / cm
² ). (3) Measured value according to JIS K6767 (unit:%). (4) The number of pinholes (cells having a cell diameter 5 times or more the average cell diameter (about 100 μm)) per 1 m ^{2 of the} foamed sheet was counted (unit).

As is clear from Table 2, the crosslinked foams of the olefinic elastomers of Examples 1 to 6 according to the method of the present invention have the same tensile breaking strength and tensile breaking elongation. It was larger than that of the foamed product of No. 4, and the improvement in the value of tensile elongation at break was particularly remarkable. The number of pinholes was also greatly reduced. It is believed that this is because the method of the present invention disperses the blowing agent very well.

[0043]

As described above in detail, in the present invention,
First, a master batch prepared by blending a blowing agent at a high concentration with respect to a resin component composed of polypropylene and an ethylene-propylene-diene copolymer rubber is produced, and then this master batch is further supplemented with polypropylene and ethylene- A propylene-diene copolymer rubber is blended in such a manner that the content of the foaming agent will be a desired ratio with respect to the resin component, whereby a cross-linking foaming composition is obtained, and a radiation-crosslinked molded article obtained from this composition is obtained. After that, since the foam is produced by heat-foaming, the obtained foam has few pinholes and is excellent in physical properties such as tensile strength and tensile elongation.

The cross-linked foamed olefinic elastomer according to the method of the present invention is used as an interior material for automobiles, sports equipment, a cushioning material for food packaging, a heat insulating material, a sound deadening material, and other exterior materials. Suitable for

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Claims (3)

[Claims] 1. (A) 10 to 50% by weight of polypropylene and 50 to 90% by weight of ethylene-propylene-diene copolymer rubber.
With 100 parts by weight of the resin component consisting of
0 parts by weight, to produce a blowing agent-containing master batch by kneading at a temperature below the decomposition temperature of the blowing agent, (B)
(a) 10 to 80% by weight of polypropylene, (b) 20 to 90% by weight of ethylene-propylene-diene copolymer rubber, and (c) 5 to 70% by weight of the blowing agent-containing masterbatch of the blowing agent. A crosslinked foam composition is produced by kneading at a temperature lower than the decomposition temperature, and (C) crosslinking is performed after molding the composition, and then crosslinking of the olefinic elastomer composition is characterized by foaming. Method for producing foam. 2. The method for producing a crosslinked foam of an olefin elastomer composition according to claim 1, wherein the content of the foaming agent is 3.5 to 20% by weight based on 100% by weight of the entire composition for crosslinked foam. %, A method for producing a crosslinked foam of an olefinic elastomer composition. 3. The method for producing a crosslinked foamed olefin elastomer composition according to claim 1 or 2, wherein the polypropylene of the blowing agent-containing masterbatch is a propylene-ethylene block copolymer. A method for producing a crosslinked foam of an olefin elastomer composition.