JPH0588727B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides ethylene-
This invention relates to a method for producing sponge products made of α-olefin rubber. More specifically, a molded article of a sponge composition of ethylene-α-olefin rubber containing ethylene-α-olefin-dicyclopentadiene rubber as a main component is subjected to electron beam irradiation treatment, followed by vulcanization and foaming. This invention relates to a method for producing a sponge product with improved surface skin. Ethylene-α olefin rubber, represented by ethylene-propylene-nonconjugated diene copolymer, has excellent weather resistance, heat resistance, and ozone resistance, so it is used as insulation sponge, in the fields of automobiles, building materials, and industrial products. It is widely used in various sponge products such as protector sponges, sealing sponges, vibration-proofing and sound-proofing sponges. Incidentally, such sponge products are generally produced by preforming an uncrosslinked rubber composition containing a foaming agent and a crosslinking agent using an extruder, roll, press, etc., and then molding it in a hot air tank, fluidized bed tank, high frequency heating tank, or high frequency heating tank. It is manufactured by crosslinking and foaming in a heating tank such as a steam tank. Here, foaming generally proceeds by thermal decomposition of the foaming agent, but if foaming precedes crosslinking too much, problems such as roughness of the surface and low foaming ratio may occur due to bubble loss. Therefore, a high vulcanization rate is usually required to match the decomposition rate of the blowing agent. Therefore, when manufacturing sponge products, ethylene-α-olefin rubbers that vulcanize quickly, such as ethylene-α-olefin-ethylidenenorbornene rubber, are often used, and ethylene-α-olefin-dicyclopentadiene rubbers, such as ethylene-α-olefin-dicyclopentadiene rubber, are often used. Those with relatively slow vulcanization were only used as supplementary materials. Ethylene-α-olefin-
The amount of dicyclopentadiene rubber used in combination was 40% by weight or less, generally 10 to 30% by weight, based on the entire ethylene-α-olefin-nonconjugated diene rubber. When manufacturing sponge products using the conventional vulcanization process, if more ethylene-α-olefin-dicyclopentadiene rubber is used, it is impossible to obtain a highly foamed, low-density sponge product with a good sponge skin. Ta. Furthermore, it has been considered impossible to manufacture sponges using such a manufacturing method using ethylene-α-olefin-dicyclopentadiene rubber alone. However, ethylene-α-olefin-dicyclopentadiene rubber is more economical than ethylene-α-olefin-ethylidene norbornene rubber, and although it has a slow vulcanization rate, it also requires a long scorch time, resulting in poor thermal stability during kneading and molding processes, and sponge compounding. A major feature of the composition is that it has excellent storage stability. The present inventors took advantage of these excellent characteristics of ethylene-α-olefin-dicyclopentadiene rubber to create a rubber that is highly economical, has good thermal stability during processing, and has good storage stability of the composition. The present invention was developed through extensive research into a method for producing highly foamed, low-density sponges with excellent surface texture. The method of the present invention is to apply electron beam irradiation to a molded product of a sponge compound composition made of ethylene-α-olefin rubber containing ethylene-α-olefin-dicyclopentadiene rubber as a main component.
This method involves heat treatment, vulcanization, and foaming to produce sponge products with improved surface texture. The difference from conventional methods is that, prior to vulcanization and foaming, only the surface layer is crosslinked using an electron beam. After a smooth crosslinked layer is formed on the surface layer of the rubber molded article by electron beam crosslinking,
Since vulcanization and foaming of the inner layer progresses, it is thought that a sponge with a good surface texture and a high foaming ratio can be obtained. In the present invention, the ethylene-α-olefin rubber containing ethylene-α-olefin-dicyclopentadiene rubber as a main component is, for example, ethylene-α-olefin-dicyclopentadiene rubber containing at least 30% or more and preferably up to 100%. is 50%
Examples include ethylene-α-olefin-nonconjugated diene rubber mixtures containing up to 100%. The remaining components are not particularly limited, but ethylene-α-olefin-ethylidene norbornene rubber, which has a relatively fast vulcanization rate, is suitable, for example. The α-olefin referred to in the present invention is
Propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 8-methyl-1-pentene, 1-hexene, 1-octene, 1-decene,
Examples include 1-dodecene and 1-hexadene.
Further, as the ethylene-α-olefin rubber referred to in the present invention, ethylene-α-olefin non-conjugated diene rubber or a mixture thereof is exemplified, and the non-conjugated diene here includes 1,4-
Hexadiene, 1,7-octadiene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, 5-ethylene-2-norbornene,
Examples include dicyclopentadiene and the like, as well as a combination system of two or more selected from these. Particularly suitable compositions for the present invention include mixtures of ethylene-propylene-dicyclopentadiene rubber and ethylene-propylene-ethylidenenorbornene rubber, or mixtures of ethylene-1-butene-dicyclopentadiene rubber and ethylene-propylene-dicyclopentadiene rubber.
A mixture of 1-butene-ethylidene norbornene rubber is exemplified. The sponge compound composition referred to in the present invention contains the above-mentioned rubber as a main component, and also contains relatively small amounts of other synthetic rubbers, natural rubbers, or synthetic resins, and fillers such as carbon black, talc, clay, etc. Calcium carbonate, etc., and processing agents, softeners,
Processing oils and anti-aging agents can be added. Examples of the vulcanizing agent include, but are not limited to, sulfur, organic peroxides, etc., and vulcanization aids and vulcanization accelerators are also appropriately selected and used depending on each vulcanizing agent. As the blowing agent, ordinary blowing agents can be used. For example, orthobissulfonylhydrazine (OBSH), azodicarboxamide (AZC), dinitrosopentamethylenetetramine (DPT), etc., may be used alone or in combination. These rubbers and various materials are kneaded in required amounts using a kneading machine such as a Banbury mixer, kneader, roll, etc. to form a sponge composition.
The sponge composition is processed into an unvulcanized molded product using a calendar roll, extruder, etc., and then subjected to electron beam irradiation treatment. In electron beam irradiation treatment, the irradiation device and irradiation conditions are selected depending on the purpose. As the irradiation conditions, the accelerating voltage and the irradiation dose are determined, but to give an example of a range suitable for the present invention, the accelerating voltage is
100kv or 500kv, irradiation dose is 1Mrad
A range of 20 to 20 Mrad is used, and is adjusted up or down as necessary. The molded product subjected to electron beam irradiation treatment is then vulcanized and foamed in a hot air vulcanization tank, UHF vulcanization tank, fluidized bed vulcanization tank, or vulcanization can to achieve the desired improved surface texture. Completed as a sponge product with As sponge products, in addition to those made of a single sponge, so-called sponge solid composite products, which are composites of sponge and non-foamed rubber, are also suitable objects of the present invention. Examples are shown below, but the present invention is not limited thereto. Example 1, Comparative Example 1

[Table] The mixture shown in Table 1 was kneaded using a bumperley mixer and a mixing roll, and
An EPDM rubber composition was obtained. This rubber composition is processed using a 45mmφ extruder (dice 100℃).
After irradiating the surface of the extruded product with an electron beam, it was heated in a hot air bath at 280° C. for 5 minutes to perform vulcanization and foaming to obtain a rubber foam. Table 2 shows the evaluation of the surface texture of the obtained rubber foam and the specific gravity of the rubber foam.

[Table] ◎Excellent, ○Good, △Good, ×Not good As shown in Table 2, by applying electron beam irradiation, a highly foamed low specific gravity sponge with good sponge skin, which was previously considered impossible with dicyclopentadiene-based EPDM, was created. It is possible to obtain it easily. Examples 2 to 4, Comparative Examples 2 to 6 Examples of the present invention in sponge compositions using a combination of dicyclopentadiene-based EPDM and ethylidene norbornene-based EPDM are shown.

[Table] The compound shown in Table 8 was kneaded in the same manner as in Example 1, and the obtained rubber composition was extruded with a 45 mmφ extruder using a Garpey die at a die temperature of 100°C. After electron beam irradiation as in 1,
Vulcanized and foamed in a hot air bath. The results obtained are shown in Table 4.

[Table] From Table 4, by combining dicyclopentadiene-based EPDM with electron beam irradiation, extrudability,
It is clear that a sponge product with good sponge surface and skin texture can be obtained. When ethylidene norbornene-based EPDM is used, the scorch is short, so the surface texture is good even without electron beam irradiation, but scorch decreases during extrusion, making the extrusion state unstable.

Claims (1)

[Claims] 1. In a method for producing a sponge product by vulcanizing and foaming a molded product of a sponge composition composed of an ethylene-α olefin rubber containing ethylene-α olefin-dicyclopentadiene rubber as a main component, the molded product is A method for producing a sponge product with improved surface texture, characterized by performing vulcanization and foaming after radiation treatment.