Patent Description:
A millimeter wave radar device used for the purpose of enabling automated driving and preventing collisions of automobiles is known. A millimeter wave radar device is mounted to various locations such as the front center, both sides, and both rear sides of a vehicle, and is provided with: a high frequency module with an antenna for transmitting and receiving radio waves installed, a control circuit for controlling the radio waves, a housing that houses the antenna and the control circuit, and a radome covering the transmission and reception of radio waves for the antenna (<CIT>). A millimeter wave radar device thus constituted transmits and receives millimeter waves using the antenna, and can thereby detect relative distances and relative velocities with respect to an obstacle. The antenna may also receive radio waves reflected from a road surface or other objects besides a target obstacle, and thus there is a risk that the detection accuracy of the device may be reduced. In order to solve this problem, the millimeter wave radar device according to <CIT> is provided with a shielding member that shields radio waves between the antenna and the control circuit.

As an invention for solving the problems of the invention of <CIT>, a thermoplastic resin composition containing long carbon fibers with a fiber length from <NUM> to <NUM>, and a molded article that is obtained therefrom and exhibits performance of shielding millimeter waves are proposed (<CIT>). In addition, an invention has been proposed with favorable electromagnetic wave shielding properties of a thermoplastic resin molded article containing carbon fibers having an average length from <NUM> to <NUM> (<CIT>). In addition, a thermoplastic resin molded article having favorable electromagnetic wave shielding properties has been disclosed in <CIT>.

An object of the present invention is to provide an electromagnetic wave shielding and absorbing molded article excelling in a shielding property and an absorbency for electromagnetic waves having a specific frequency.

The present invention provides an electromagnetic wave shielding and absorbing molded article according to appended claim <NUM>.

The electromagnetic wave shielding property according to the present invention exhibits a combined performance for both absorbency and reflectivity with respect to electromagnetic waves.

Furthermore, by using stainless steel fibers, the electromagnetic wave shielding and absorbing molded article according to the present invention can increase both the shielding property and the absorbency for electromagnetic waves having frequencies from <NUM> to <NUM>.

Preferred embodiments of the present invention are set forth in the dependent claims.

<FIG> is a schematic diagram of device that was used in the examples to measure the electromagnetic wave shielding property.

The thermoplastic resin composition used in the present invention contains stainless steel fibers, and as for the stainless steel fibers, stainless steel fiber itself can be used as is, and may also be used in the form of a master batch made from stainless steel fibers and a thermoplastic resin.

The outer diameter of the stainless steel fibers is preferably from <NUM> to <NUM>. Examples of the materials for the stainless steel fibers include, but are not limited to, SUS302, SUS304 and SUS316.

One or more thermoplastic resins selected from polypropylenes, propylene unit-containing copolymers and acid-modified polypropylenes is used, and the thermoplastic resin is preferably a polypropylene.

When the stainless steel fibers are used in the form of a master batch which contains stainless steel fibers and a thermoplastic resin, a form of a thermoplastic resin-bonded stainless steel fiber bundle (thermoplastic resin-bonded fiber bundle) having a length from <NUM> to <NUM>, in which stainless steel fibers aligned in a length direction being bundled and integrated with a thermoplastic resin is used.

The thermoplastic resin-bonded fiber bundle are those which include the following three forms depending on the bonding state of the thermoplastic resin.

The thermoplastic resin-bonded fiber bundle used in the present invention is preferably a thermoplastic resin-impregnated fiber bundle or a thermoplastic resin surface-coated fiber bundle, and is more preferably a thermoplastic resin-impregnated fiber bundle. The resin-bonded fiber bundles of the forms (I) to (III) can be produced by the method described in <CIT>.

The outer diameter of the thermoplastic resin-bonded fiber bundle is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and even more preferably from <NUM> to <NUM>, and the length is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and even more preferably from <NUM> to <NUM>.

The content ratio of the stainless steel fibers in the thermoplastic resin-bonded fiber bundle is from <NUM> to <NUM> mass%, preferably from <NUM> to <NUM> mass%, and even more preferably from <NUM> to <NUM> mass%.

For the thermoplastic resin-bonded fiber bundle, a number of the stainless steel fibers included in the bonded fiber bundle is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and even more preferably from <NUM> to <NUM>. The cross-sectional shape in the width direction of the thermoplastic resin-bonded fiber bundle is preferably circular or a shape similar thereto, but may also be an oval shape or a shape similar thereto or a polygonal shape or a similar shape.

The thermoplastic resin composition used in the present invention may be made from a master batch only (thermoplastic resin-bonded fiber bundle), which includes stainless steel fibers and a thermoplastic resin, or may be made from the master batch and a thermoplastic resin.

The thermoplastic resin composition used in the present invention can contain a known resin additive within a range at which the problem of the present invention can be solved. Examples of known resin additives include stabilizers with respect to heat, light, UV light, and the like, lubricants, nucleating agents, plasticizers, known inorganic and organic fillers (note that carbon fibers and carbon black are excluded), antistatic agents, release agents, flame retardants, softeners, dispersants, and antioxidants. The total content ratio of the abovementioned known resin additives in the composition (the electromagnetic wave shielding and absorbing molded article) is preferably <NUM> mass% or less, more preferably <NUM> mass% or less, and even more preferably <NUM> mass% or less.

The content ratio of stainless steel fibers in the thermoplastic resin composition (electromagnetic wave shielding and absorbing molded article) used in the present invention is from <NUM> to <NUM> mass%, preferably from <NUM> to <NUM> mass%, more preferably from <NUM> to <NUM> mass%, and even more preferably from <NUM> to <NUM> mass%.

When the thermoplastic resin composition (electromagnetic wave shielding and absorbing molded article) used in the present invention is formed from a thermoplastic resin and a master batch (thermoplastic resin-bonded fiber bundle) which includes stainless steel fibers and a thermoplastic resin, from the perspective of dispersibility of the stainless steel fibers, the content ratio of the master batch (thermoplastic resin-bonded fiber bundle) in the thermoplastic resin composition (electromagnetic wave shielding and absorbing molded article) used according to the present invention is preferably from <NUM> to <NUM> mass%, more preferably from <NUM> to <NUM> mass%, and even more preferably from <NUM> to <NUM> mass%.

The electromagnetic wave shielding and absorbing molded article according to an embodiment of the present invention is obtained by molding the thermoplastic resin composition described above through application of a known resin molding method such as injection molding. The size and shape of the electromagnetic wave shielding and absorbing molded article according to an embodiment of the present invention can be appropriately adjusted, according to the application, within a range that satisfies the following thickness requirement.

The length of the stainless steel fibers in the electromagnetic wave shielding and absorbing molded article according to an embodiment of the present invention is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, even more preferably from <NUM> to <NUM>, and yet even more preferably from <NUM> to <NUM>. Note that because the stainless steel fibers are not prone to breakage during the molding process, the length of the stainless steel fibers in the composition and the length of the stainless steel fibers in the electromagnetic wave shielding and absorbing molded article are approximately the same.

The electromagnetic wave shielding and absorbing molded article according to the present invention has a thickness from <NUM> to <NUM>, preferably from <NUM> to <NUM>, and even more preferably from <NUM> to <NUM>. The thickness is measured by the method described in the examples.

With the electromagnetic wave shielding and absorbing molded article according to the present invention, the shielding property for electromagnetic waves having any frequency in a frequency domain from <NUM> to <NUM> can be set to <NUM> dB or greater, more preferably to <NUM> dB or greater, even more preferably to <NUM> dB or greater, and yet even more preferably to <NUM> dB or greater. The shielding property is preferably the shielding property for the entire frequency domain from <NUM> to <NUM>.

Furthermore, with the electromagnetic wave shielding and absorbing molded article according to the present invention, the electromagnetic wave absorbency for any frequency in a frequency domain from <NUM> to <NUM> can be set to <NUM>% or greater, and preferably <NUM>% or greater. The absorbency is preferably the absorbency for the entire frequency domain from <NUM> to <NUM>.

The electromagnetic wave shielding property and the electromagnetic wave absorbency of the electromagnetic wave shielding and absorbing molded article according to an embodiment of the present invention can be adjusted by adjusting (R) which is the content ratio and (T) which is the thickness of the stainless steel fibers.

When (R-T) which is the product of the content ratio (R) of stainless steel fibers in the electromagnetic wave shielding and absorbing molded article (composition) and the thickness (T) of the molded article ranges from <NUM> to less than <NUM>, the electromagnetic wave shielding property in the entire range of frequencies from <NUM> to <NUM> can be set to <NUM> dB or greater, and the electromagnetic wave absorbency can be set to <NUM>% or greater.

When the range of (R·T), which is the product of the content ratio (R) of stainless steel fibers in the electromagnetic wave shielding and absorbing molded article (composition) and the thickness (T) of the molded article is <NUM> or greater, and preferably from <NUM> to <NUM>, the electromagnetic wave shielding property in the entire range of frequencies from <NUM> to <NUM> can be set to <NUM> dB or greater, and the electromagnetic wave absorbency can be set to <NUM>% or greater.

A fiber bundle made from stainless steel fibers (diameter of <NUM> to <NUM>, approximately <NUM> bundlings) was heated at <NUM> using a pre-heating device and passed through a crosshead die. At that time, molten polypropylene (<NUM>:<NUM> (weight ratio) mixture of SunAllomer PMB60A (block PP available from SunAllomer Ltd. ] and MODIC P908 (acid-modified PP available from Mitsubishi Chemical Corporation)) was supplied to the crosshead die from a twin screw extruder (cylinder temperature: <NUM>), and the fiber bundles were impregnated with the polypropylene. Next, the material was shaped with a shaping nozzle at the outlet of the crosshead die, and the shape was further refined with a shape refining roll, after which the sample was cut to a predetermined length using a pelletizer to obtain pellets (cylindrical molded articles) with a length of <NUM>. The length of the stainless steel fibers was the same as the pellet length. In the pellets obtained in this manner, the stainless steel fibers were substantially parallel in the length direction.

PP1 pellets (pellets obtained in Production Example <NUM> containing <NUM> mass% of stainless steel fibers) and PP2 pellets (PMB60A, available from SunAllomer Ltd. ) were dry blended, and molded at a molding temperature of <NUM> and a mold temperature of <NUM> using an injection molding machine (α-150iA, available from Fanuc Corporation), and flat plate shaped electromagnetic wave shielding and absorbing molded articles (<NUM> × <NUM>) according to an embodiment of the present invention were obtained. The obtained electromagnetic wave shielding and absorbing molded articles were used, and the various measurements shown in Table <NUM> were performed.

The thickness at a center portion (portion of intersection of diagonal lines) of a flat electromagnetic wave shielding and absorbing molded article (<NUM> × <NUM>) was measured.

The measurement device (network analyzer) illustrated in <FIG> was used.

A molded article <NUM> (length of <NUM>, width of <NUM>, thickness shown in the table) to be measured was held between a pair of horizontally opposing antennas (corrugated horn antennas) <NUM>, <NUM>. The spacing between the antenna <NUM> and the molded article <NUM> was <NUM>, and the spacing between the molded article <NUM> and the antenna <NUM> was <NUM>. In this state, electromagnetic waves (<NUM> to <NUM>) were radiated from the lower antenna <NUM>, electromagnetic waves transmitted through the molded article <NUM> to be measured were received by the upper antenna <NUM>, the electromagnetic wave shielding property (the penetration inhibition of radiated waves) was calculated from Equations <NUM> and <NUM> below, and the electromagnetic wave absorbency was calculated from Equations <NUM> to <NUM> below. <MAT> <MAT> In Equation <NUM>, S<NUM> represents an S parameter (Equation (<NUM>)) showing a ratio of a transmitted electric field intensity to an incident electric field intensity, and can be measured using a network analyzer <NUM>.

In Equation <NUM>, the logarithm of the reciprocal of the S parameter was used to express the electromagnetic wave shielding property (dB) as a positive value. With the measurement device of <FIG>, a range of from <NUM> to approximately <NUM> dB can be measured. Cases in which the electromagnetic wave shielding property exceeded <NUM> dB are indicated in Table <NUM> by "><NUM> (dB)".

In Equation <NUM>, S<NUM> represent an S parameter showing a ratio of the reflected electric field intensity to the incident electric field intensity, and similar to S<NUM>, can be measured using the network analyzer.

The absorptivity was denoted as a percentage as expressed by the following formula on a basis of power. The absorptivity is shown in Table <NUM> as an electromagnetic wave absorbency. <MAT> <MAT> <MAT>.

As is clear from a comparison of the examples and the comparative example in Table <NUM>, containing a predetermined amount of stainless steel fibers resulted in an excellent electromagnetic wave shielding property in the frequency range from <NUM> to <NUM> as well as excellent absorbency for electromagnetic waves having the frequency range from <NUM> to <NUM>. Furthermore, the electromagnetic wave shielding property improved as the content ratio of stainless steel became larger, but the electromagnetic wave absorbency was better with less stainless steel content.

Claim 1:
An electromagnetic wave shielding and absorbing molded article having a thickness (T) from <NUM> to <NUM>, a content ratio (R) of the stainless steel fibers from <NUM> to <NUM> mass%, and a shielding property of <NUM> dB or greater and an absorbency of <NUM>% or greater for electromagnetic waves having any frequency in a frequency domain from <NUM> to <NUM> obtainable by molding a thermoplastic resin composition including stainless steel fibers,
wherein the thermoplastic resin composition includes a thermoplastic resin-bonded fiber bundle having a length from <NUM> to <NUM>, in which stainless steel fibers aligned in a length direction are bundled and integrated with a thermoplastic resin, wherein a content ratio of the stainless steel fibers in the thermoplastic resin-bonded fiber bundle is from <NUM> to <NUM> mass%, and
wherein the thermoplastic resin is selected from polypropylenes, propylene unit-containing copolymers and acid-modified polypropylenes,
with the proviso that the following absorbing molded articles are excluded:
an absorbing molded article comprising a thermoplastic resin composition comprising <NUM> parts by weight polypropylene, <NUM> parts by weight of scale-like graphite particles having an average particle size of <NUM>, and <NUM> parts by weight of stainless steel fiber masterbatch having a stainless steel fibers concentration of <NUM>%, stainless steel fibers diameter of <NUM> and stainless steel fibers length of <NUM>; and
an absorbing molded article comprising a thermoplastic resin composition comprising <NUM> parts by weight polypropylene, <NUM> parts by weight of scale-like graphite particles having an average particle size of <NUM>, and <NUM> parts by weight of stainless steel fiber masterbatch having a stainless steel fibers concentration of <NUM>%, stainless steel fibers diameter of <NUM> and stainless steel fibers length of <NUM>.