JP4783779B2 - Magnetite-containing silicone rubber composition - Google Patents

Description

  The present invention relates to an elastomer composition that enables artificial control of externally applied energy such as heat and electromagnetic waves. Specifically, as an added value to the elastomer composition, electromagnetic wave shielding properties, radio wave absorption characteristics, etc. The present invention relates to a magnetite-containing silicone rubber composition that can control the physical properties of the magnetite with high efficiency by means of compounding design.

In recent years, social development such as mobile communication and ETC system has progressed, and the demand for rubber products having radio wave absorption has increased. Conventionally, soft magnetic powder and ferrite have been frequently used to improve the radio wave absorption of rubber products made of elastomer. However, even when these fillers are blended into rubber products, effective radio wave absorption with respect to high frequencies is essentially difficult. For this reason, in order to correspond to a frequency of the gigahertz band or higher, filling up to the filling limit blending amount into the elastomer has become a precondition for being recognized as a radio wave absorber. However, it was still difficult to obtain a good absorption capacity.

Accordingly, the applicant of the present application has proposed a magnetite-containing elastomer composition that exhibits high efficiency in radio wave absorption performance by blending a specific magnetite with an elastomer in a patent application according to Patent Document 1.
JP 2007-45975

In such an elastomer composition, the above-mentioned drawbacks of the prior art were solved, and an elastomer composition with a wide application range having a broadband type radio wave absorption performance capable of supporting a high frequency band without losing flexibility was obtained. However, subsequent studies have revealed that when the elastomer composition is exposed to a high temperature state for a long time, the surface of the composition is discolored and the discoloration proceeds to the inside.

In particular, when silicone rubber is employed as the elastomer component, the elastomer composition is often crosslinked at a high temperature or used in a high temperature environment, and the magnetite-containing silicone rubber composition is used in a temperature range of 200 ° C. or higher. Subsequent cross-linking or use would change the color from black to brown or reddish brown, resulting in a problem in appearance.

Accordingly, an object of the present invention is to provide a magnetite-containing silicone rubber composition having an excellent broadband wave absorbing performance without losing flexibility, and to prevent discoloration of the silicone rubber composition in a high temperature environment. It is what.

As a result of intensive studies, the inventors have changed the color change of black magnetite (Fe ₃ O ₄ ) to brown gamma ferric oxide (Fe ₂ O ₃ ) at 180 to 400 ° C. (oxidation). I found out that it was due to that. And, when zinc oxide (ZnO) powder was added to the magnetite-containing silicone rubber composition, it was found that the oxidation discoloration reaction of the magnetite can be prevented, and discoloration of the magnetite-containing silicone rubber composition in a high temperature environment can be prevented. The present invention has been completed.

The present invention, a magnetite powder 100 parts by weight of the silicone rubber blended with 100 to 1000 parts by weight, further zinc oxide powder were blended to 100 parts by weight were kneaded, magnetite content, characterized in that to prevent discoloration A silicone rubber composition (claim 1) . The magnetite powder may be a magnetite powder excluding magnetite whose surface is treated with 1 to 10% by weight of alumina or silica-alumina (claim 2).

In addition, the present invention provides a magnetite-containing silicone rubber composition in which 100 to 1000 parts by weight of magnetite powder is blended with 100 parts by weight of silicone rubber, and 1 to 100 parts by weight of zinc oxide powder is blended and kneaded. This is a method for preventing discoloration of the silicone rubber composition.

ADVANTAGE OF THE INVENTION According to this invention, even if it uses the rubber product which consists of the said magnetite containing silicone rubber composition in a high temperature environment, it can prevent that a rubber product discolors and the effect that the external appearance quality of a product is not impaired is acquired. .

Embodiments of the present invention will be described below.
Various silicone rubber compositions can be preferably used in the present invention. The silicone rubber composition is a polyorganosiloxane, and a dimethyl type siloxane or a phenyl type siloxane called a millable type is particularly suitable, and one or a combination of two or more of these silicone rubbers can be used. . Liquid silicone rubber can also be used as the silicone rubber of the present invention.

In the present invention, the magnetite mixed with the silicone rubber component is represented by the chemical formula Fe ₃ O ₄ , and several industrial production methods have been proposed and implemented. One of the methods is that the magnetite obtained as a raw material of hematite produced through a dry pyrolysis method has excellent specific radio wave absorption characteristics when blended with an elastomer. Proposed in Patent Document 1. That is, a magnetite obtained by reducing a hematite produced by a pyrolysis method as a magnetite, and the crystal long side cross-sectional size of the magnetite is in the range of 10 to 100 nm, and the crystal discontinuous surface in the cross-section Is preferably used in order to improve the electromagnetic wave absorption characteristics of the elastomer composition.

The size of the magnetite as the powder is preferably 0.1 to 2.0 μm as the primary particle diameter, and if it is less than 0.1 μm, the tendency of aggregation between the primary particle diameters increases, and as a result, magnetite having a large particle diameter is blended. It is not preferable because it shows a result that is not different from what it is. On the other hand, if the thickness exceeds 2.0 μm, the cross-sectional long side dimension inside the crystal varies, and this adversely affects the radio wave absorption ability.

Magnetite often takes the form of secondary particles in which primary particles are aggregated. When blending without breaking the secondary particle size, good dispersion can be expected when the secondary particle size range is 0.5 to 10 μm as D50 and 10 to 50 μm as D90. These particle size measurements are based on numerical values obtained by the laser method.

The number of blended parts of magnetite cannot be uniformly defined by the desired product characteristics and the polymer to be used, that is, the elastomer component. However, if the amount of magnetite is 100 parts by weight or less with respect to 100 parts by weight of the elastomer component, the radio wave absorption is effective. However, when the amount exceeds 1000 parts by weight, filling may be impossible depending on the blending design, and the product may lose its elasticity and flexibility. Generally, 400 to 700 parts by weight is a suitable blending number for imparting radio wave absorptivity.

  A silicone rubber composition with a wide application range that has a broadband electromagnetic wave absorption performance that can be applied to a high frequency band without losing flexibility by heat-molding a compound obtained by blending the above-mentioned magnetite with a silicone rubber composition. Is obtained.

Zinc oxide (ZnO) blended in the elastomer composition of the present invention is a compound of zinc (Zn) and oxygen (O), and is a substance having a white appearance. In general, zinc oxide is an ionic crystal formed by ionic bonding. Specifically, a zinc atom loses two electrons to become a zinc ion, and becomes an oxide ion together with an oxygen atom that has received two electrons. Yes. In the zinc oxide crystal, there is a large gap between ions, and other atoms easily enter. The crystal structure of zinc oxide belongs to a so-called wurtzite crystal structure formed by combining anions and cations at 1: 1. Due to the lattice structure, it has piezoelectric characteristics. Further, it becomes an n-type semiconductor by zinc ions or oxygen vacancies.

Zinc oxide is known as an additive for rubber, particularly as a vulcanization accelerating aid (activator) in the case of vulcanizing natural rubber, nitrile rubber, butyl rubber, etc. with sulfur. 5 parts by weight is blended. However, an elastomer that is crosslinked by addition crosslinking or peroxide crosslinking such as silicone rubber is not usually added as a vulcanization acceleration aid. Conventionally, zinc oxide used as a rubber vulcanization accelerating aid has been produced by a French method or an American method, and also includes a fine particle zinc oxide produced by a wet method. The zinc oxide used in the present invention may be produced by any production method.

In the present invention, by adding zinc oxide to a silicone rubber composition containing magnetite, a silicone rubber composition that hardly changes color even when exposed to a high-temperature state for a long time can be obtained. The blending amount of zinc oxide is preferably 1 to 100 parts by weight of zinc oxide when 100 to 1000 parts by weight of magnetite is blended with 100 parts by weight of silicone rubber.
When blended with metal oxides other than zinc oxide, specifically magnesium oxide, calcium hydroxide, titanium oxide, cerium oxide, cerium hydroxide, calcium carbonate, etc., a sufficient discoloration prevention effect cannot be obtained. It was.

Although the mechanism by which the discoloration of the magnetite-containing elastomer composition in the high-temperature environment, that is, the oxidation of the magnetite is prevented by blending zinc oxide is not clear, as described above, zinc oxide is an ion having a unique crystal structure. Since it is a crystal, an electrical change occurs in zinc oxide in a high-temperature environment, and it is presumed that this may have contributed effectively to preventing the oxidation of magnetite.

  The elastomer composition containing the magnetite of the present invention can be prepared by blending the components in an arbitrary order and thoroughly mixing them. Mixing can be performed using a kneader, two rolls, a twin-screw kneading extruder, various mixers, and other kneaders.

  A conventionally well-known method can be widely employ | adopted for the method for manufacturing the silicone rubber composition containing the magnetite of this invention. For example, the rubber composition containing the obtained magnetite can be crosslinked by heating to obtain a rubber molding. Crosslinking can be carried out in an arbitrary mold to form a rubber molded body having a desired shape, and after extrusion molding of the rubber composition, it is continuously strip-shaped by passing through a heating tank as necessary. It is also possible to obtain a rubber molded body. Further, the heating can be performed in two or more stages, and various methods such as hot air heating and dielectric heating can be applied as the heating method.

In the description of the above embodiment, the case where silicone rubber is used as an elastomer component has been described. However, the effect of zinc oxide to prevent discoloration of magnetite is not limited to when blended with silicone rubber. It can also be obtained when blended with these elastomers. That is, an elastomer such as fluorine rubber or a thermoplastic elastomer can be used as the elastomer component. When used in a high temperature environment, fluororubber can be particularly preferably used.

EXAMPLES Next, although an Example demonstrates this invention in detail, this invention is not limited at all by these examples. All parts in the text mean parts by weight. Table 1 shows the composition and test results of Examples and Comparative Examples.

(Example) As silicone rubber, 100 parts of polydimethylsiloxane (Momentive Performance Materials Japan G.K.) containing 0.12 mol% of a methylvinylsiloxane unit whose end is blocked with a trimethylsilyl group, magnetite, D50 of 4 μm, D90 Magnetite (Nippon Heavy Chemical Co., Ltd.), which is obtained by reduction treatment of hematite produced by the pyrolysis method at 21 μm, has a crystal long side dimension range of 29 to 66 nm, and has at least one discontinuous surface in the crystal part. Kogyo Co., Ltd., trade name “MGR-22”) is blended in 400 parts, and zinc oxide is blended in 20 parts of type 2 ZnO (manufactured by Shodo Chemical Industry Co., Ltd.) and compounded using a pressure kneader. Got. To this, 0.6 parts of 2,5-dimethyl-2,5-ditertiary butyl peroxyhexane was added with an open roll, and dispensed into a sheet. Perform press-crosslinking at 160 ° C for 10 minutes using the prescribed mold, and then put the rubber in a constant temperature bath at 200 ° C for 4 hours to complete the secondary cross-linking, which is 600 mm x 600 mm x 3 mm and 200 mm x 200 mm x 1 mm. A sheet-like rubber sample piece was obtained.

(Comparative Example 1) As Comparative Example 1, a sheet-like rubber sample piece was obtained through the same blending and kneading / crosslinking steps as in the Examples, except that zinc oxide was not blended.

(Comparative Example 2) As Comparative Example 2, the same mixing and kneading / crosslinking steps as in Examples were performed except that 20 parts of titanium oxide (A-100: manufactured by Ishihara Sangyo Co., Ltd.) was used instead of 20 parts of zinc oxide. A sheet rubber sample piece was obtained.

Using the rubber sample pieces obtained as examples and comparative examples, the electromagnetic wave absorptivity and discoloration in a high temperature environment were evaluated.

Evaluation of electromagnetic wave absorptivity was performed by measuring complex relative permittivity, complex relative permeability, and radio wave reflection attenuation. The complex relative permittivity and complex relative permeability were measured by the coaxial waveguide method using a vector network analyzer. The sample holder in the coaxial waveguide was adjusted to the specified sample size, a terminal load was attached, radio waves were incident, and the return loss and phase angle were measured and calculated. The radio wave reflection attenuation was measured by an apparatus shown in FIG. 1 called the arch method, which is one of the free space methods. This device is installed in an anechoic chamber. The transmission and reception antennas were provided on the arch support, and the oblique incidence characteristics were measured using TE waves with the incidence angle of the sample being 45 degrees while changing the incident angle. Values measured at 1, 5, 10, and 15 GHz were recorded. A network analyzer was used to measure the return loss. As a calculation method, first, a stainless plate having the same area as the sample is placed, and this return loss is measured. In order for metal to completely reflect radio waves, this measured value was used as a reference value, and the return loss of the composition sample placed on the stainless steel plate was measured in the same manner, and the difference was taken as the radio wave absorption.

For comparison of discoloration, the sample sheet was put into a hot air dryer at 250 ° C. for 2 hours, and the color difference between the sample surfaces before and after that was measured. A color difference meter was used to indicate the degree of discoloration, and the measurement result was expressed as ΔE.
In addition, the surface state of the sample after the primary vulcanization (160 ° C.) and the sample after the secondary vulcanization (200 ° C.) is increased by 20 times with the power high scope (manufactured by Hilox Co., Ltd.). It was enlarged and photographed and observed for evaluation. The sample after the primary vulcanization of the example is shown in FIG. 2, and the sample after the secondary vulcanization is shown in FIG. The sample after the primary vulcanization of Comparative Example 1 is shown in FIG. 4, and the sample after the secondary vulcanization is shown in FIG. The sample after the primary vulcanization of Comparative Example 2 is shown in FIG. 6, and the sample after the secondary vulcanization is shown in FIG.

The evaluation results are described below. Regarding the electromagnetic wave absorptivity, all of the evaluation samples showed high electromagnetic wave absorption characteristics at 1, 5, 10, and 15 GHz. That is, no significant difference in electromagnetic wave absorption due to blending of zinc oxide or titanium oxide was observed.

Moreover, when the surface state of the sample sheet | seat after primary vulcanization and after secondary vulcanization is observed, about the Example which mix | blended zinc oxide, the hue remains black and it is hue before and after secondary vulcanization. There was not much change. On the other hand, about the sample sheet | seat of the comparative example 1 and the comparative example 2, it had changed color from black to brown before and after secondary vulcanization. Further, in the measurement result (ΔE) by the color difference meter, it was confirmed that the discoloration was considerably suppressed in the sheet of the example, the discoloration in Comparative Example 1 was severe, and the discoloration in Comparative Example 2 was also considerably discolored. did it.

According to the present invention, a magnetite-containing silicone rubber composition having excellent radio wave absorption performance can be provided, and discoloration of the silicone rubber composition can be prevented particularly in a high temperature environment, and the appearance quality is excellent. Can provide rubber products.

It is a conceptual diagram which shows the measuring method of the electromagnetic wave reflection attenuation amount by the arch method. It is a photograph of the surface after the primary vulcanization of the sheet sample of an example. It is a photograph of the surface after secondary vulcanization of the sheet sample of an example. 2 is a photograph of the surface of a sheet sample of Comparative Example 1 after primary vulcanization. 4 is a photograph of the surface after secondary vulcanization of the sheet sample of Comparative Example 1. 3 is a photograph of the surface of a sheet sample of Comparative Example 2 after primary vulcanization. 6 is a photograph of the surface after secondary vulcanization of a sheet sample of Comparative Example 2.

Claims (3)

100 parts by weight of magnetite powder is blended with 100 parts by weight of silicone rubber,
Furthermore, 1-100 weight part of zinc oxide powder is mix | blended and knead | mixed , The magnetite containing silicone rubber composition characterized by the above-mentioned. The magnetite-containing silicone rubber composition according to claim 1, wherein the magnetite powder is a magnetite powder excluding magnetite whose surface is treated with 1 to 10% by weight of alumina or silica-alumina. For magnetite-containing silicone rubber composition containing 100 to 1000 parts by weight of magnetite powder with respect to 100 parts by weight of silicone rubber,
By blending 1 to 100 parts by weight of zinc oxide powder and kneading ,
A method for preventing discoloration of a magnetite-containing silicone rubber composition.