Patent Application
20140154469
The present invention relates to an electromagnetic-wave-absorbing film having high electromagnetic wave absorbability as well as high thermal dissipation.
Electromagnetic-wave-absorbing sheets for preventing the leakage and intrusion of electromagnetic waves are used in communications apparatuses such as cell phones, smartphones, wireless LAN, etc., and electronic apparatuses such as computers, etc. Electromagnetic-wave-absorbing sheets now widely used are constituted by metal sheets or nets, and those having metal films vapor-deposited on plastic sheets have recently been proposed. For example, JP 9-148782 A proposes an electromagnetic-wave-absorbing sheet comprising a plastic film, and first and second aluminum films vapor-deposited on both sides thereof, the first vapor-deposited aluminum film being etched to a non-conductive linear pattern, and the second vapor-deposited aluminum film being etched to a conductive network pattern. However, because the electromagnetic-wave-absorbing sheet of JP 9-148782 A has regular linear and network patterns, it fails to efficiently absorb electromagnetic waves in a wide frequency range, and suffers large anisotropy in electromagnetic wave absorbability.
JP 11-40980 A proposes an electromagnetic wave shield having a copper layer and a nickel layer vapor-deposited in this order on a surface of a plastic film. However, the electromagnetic wave shield of JP 11-40980 A has insufficient electromagnetic wave absorbability with large anisotropy.
WO 2010/093027 discloses an electromagnetic-wave-absorbing film comprising a plastic film, and a single- or multi-layer thin metal film formed on at least one surface thereof, the thin metal film being provided with large numbers of substantially parallel, intermittent, linear scratches with irregular widths and irregular intervals in plural directions. The electromagnetic-wave-absorbing film of WO 2010/093027 has high electromagnetic wave absorbability with reduced anisotropy, because of linear scratches formed in plural directions. However, to solve the increasingly severer problems of electromagnetic wave noises, electromagnetic-wave-absorbing films having higher electromagnetic wave absorbability are desired. Further, because of linear scratches with irregular widths and irregular intervals, the division of electromagnetic-wave-absorbing films to smaller sizes is likely to cause unevenness in electromagnetic wave noise.
As electronic apparatuses and electronic communications apparatuses such as note-type, personal computers, ultrabooks, cell phones, smartphones, etc. have become smaller, electronic parts such as CPU, LSI, etc. have been highly integrated, resulting in larger heat generation. Because these electronic apparatuses and electronic communications apparatuses are mobile, waterproofness is also required, so that heat dissipation has become increasingly difficult.
In such circumstances, JP 2006-135118 A proposes an electromagnetic-wave-absorbing, heat-dissipating sheet comprising an electromagnetic-wave-absorbing layer having thermal conductivity of 0.7 W/mK or more, and a far-infrared-emitting layer formed directly or via at least one other layer on a surface of the electromagnetic-wave-absorbing layer. The electromagnetic-wave-absorbing layer is formed by an insulating polymer of silicone, acrylic rubbers, ethylene propylene rubbers, fluororubbers, chlorinated polyethylene, etc., in which powder of soft-magnetic metals such as carbonyl iron, electrolytic iron, Fe-Cr alloys, Fe-Si alloys, Fe-Ni alloys, Fe-Co alloys, Fe-Al-Si alloys, Fe-Cr-Si alloys, Fe-Cr-Al alloys, Fe-Si-Ni alloys, Fe-Si-Cr-Ni alloys, etc. is uniformly dispersed. The far-infrared-emitting layer is formed by a silicone resin, etc., in which far-infrared-emitting oxide ceramics such as silicon oxide, aluminum oxide, cordierite, etc. are dispersed.
However, the electromagnetic-wave-absorbing, heat-dissipating sheet of JP 2006-135118 A, in which both of the electromagnetic-wave-absorbing layer and the far-infrared-emitting layer are resin-based, cannot be sufficiently thin. In Example 1, for example, the electromagnetic-wave-absorbing layer is as thick as 0.1 mm, and the far-infrared-emitting layer is as thick as 80 μm.
Recently, graphite sheets having higher thermal conductivity than those of aluminum and copper have become used as thermal diffusion sheets. For example, Graphinity of Kaneka Corporation is as thick as 25-40 μm at thermal conductivity of 1500 W/mK. However, graphite sheets are disadvantageously expensive.
Accordingly, an object of the present invention is to provide a thin electromagnetic-wave-absorbing film having good absorbability to electromagnetic waves having various frequencies, together with high thermal diffusion (thermal dissipation), which can be produced at low cost.
As a result of intensive research in view of the above object, the inventor has found that the formation of a thin carbon nanotube layer on a thin-metal-film-side surface of an electromagnetic-wave-absorbing film comprising a thin metal film formed on a plastic film, the thin metal film being provided with large numbers of substantially parallel, intermittent, linear scratches with irregular widths and irregular intervals in plural directions, improves (a) electromagnetic wave absorbability with little unevenness even when divided to small pieces, and (b) thermal diffusion (thermal dissipation). The present invention has been found based on such finding.
Thus, the electromagnetic-wave-absorbing film of the present invention having high thermal dissipation comprises a plastic film, and a single- or multi-layer thin metal film formed on at least one surface of the plastic film; the thin metal film being provided with large numbers of substantially parallel, intermittent, linear scratches with irregular widths and irregular intervals in plural directions, and coated with a thin carbon nanotube layer; the linear scratches having widths in a range of 0.1-100 μm for 90% or more and 1-50 μm on average, and transverse intervals in a range of 1-500 μm and 1-200 μm on average; and the carbon nanotube having average length of 2 μm or more.
The linear scratches are preferably oriented in two directions with a crossing angle of 30-90°.
The thin metal film is preferably made of at least one metal selected from the group consisting of aluminum, copper, silver, tin, nickel, cobalt, chromium and these alloys.
The thickness of the thin carbon nanotube layer is preferably 0.01-0.5 g/m2 when expressed by the mass of carbon nanotube coated per a unit area.
The carbon nanotube is preferably multi-layer carbon nanotube. The carbon nanotube preferably has average length of 3 μm or more.
The thin carbon nanotube layer preferably contains a binder resin.
A plastic film is preferably heat-laminated on the thin carbon nanotube layer.
a) is a cross-sectional view showing an electromagnetic-wave-absorbing film according to one embodiment of the present invention.
b) is a partial plan view showing the details of linear scratches in the electromagnetic-wave-absorbing film of
c) is a cross-sectional view (a thin carbon nanotube layer omitted) taken along the line A-A in
d) is an enlarged cross-sectional view showing a portion A′ in
e) is a cross-sectional view showing an electromagnetic-wave-absorbing film according to another embodiment of the present invention.
f) is an enlarged cross-sectional view showing a portion B (a thin carbon nanotube layer omitted) in
a) is a partial plan view showing the details of linear scratches in an electromagnetic-wave-absorbing film according to a further embodiment of the present invention.
b) is a partial plan view showing the details of linear scratches in an electromagnetic-wave-absorbing film according to a still further embodiment of the present invention.
c) is a partial plan view showing the details of linear scratches in an electromagnetic-wave-absorbing film according to a still further embodiment of the present invention.
a) is a partial plan view showing the details of linear scratches and fine pores in an electromagnetic-wave-absorbing film according to a still further embodiment of the present invention.
b) is a cross-sectional view (a thin carbon nanotube layer omitted) taken along the line C-C in
a) is a perspective view showing one example of apparatuses for forming linear scratches.
b) is a plan view showing the apparatus of
c) is a cross-sectional view taken along the line D-D in
d) is a partial, enlarged plan view for explaining the principle of forming linear scratches inclined from the moving direction of a composite film.
e) is a partial plan view showing the inclination angles of a pattern roll and a push roll from a composite film in the apparatus of
a) is a plan view showing a system for evaluating the electromagnetic wave absorbability of an electromagnetic-wave-absorbing film.
b) is a partially cross-sectional front view showing a system for evaluating the electromagnetic wave absorbability of an electromagnetic-wave-absorbing film.
a) is a plan view showing a sample and an acrylic support plate used for the evaluation of thermal diffusion (thermal dissipation).
b) is a plan view showing a sample fixed to an acrylic support plate.
c) is a cross-sectional view showing a sample fixed to an acrylic support plate.
d) is a partial, enlarged cross-sectional view showing a sample.
The embodiments of the present invention will be explained referring to the attached drawings, and it should be noted that explanation concerning one embodiment is applicable to other embodiments unless otherwise mentioned. Also, the following explanation is not restrictive, and various modifications may be made within the scope of the present invention.
[1] Electromagnetic-Wave-Absorbing Film
As shown in
(1) Plastic Film
Resins forming the plastic film 10 are not particularly restrictive as long as they have sufficient strength, flexibility and workability in addition to insulation, and they may be, for instance, polyesters (polyethylene terephthalate, etc.), polyarylene sulfide (polyphenylene sulfide, etc.), polyamides, polyimides, polyamideimides, polyether sulfone, polyetheretherketone, polycarbonates, acrylic resins, polystyrenes, polyolefins (polyethylene, polypropylene, etc.), etc. From the aspect of strength and cost, polyethylene terephthalate is preferable. The thickness of the plastic film 10 may be about 10-100 μm.
(2) Thin Metal Film
Metals forming the thin metal film 11 are not particularly restrictive as long as they have conductivity, and they are preferably aluminum, copper, silver, tin, nickel, cobalt, chromium and their alloys, particularly aluminum, copper, nickel and their alloys, from the aspect of corrosion resistance and cost. The thickness of the thin metal film is preferably 0.01 μm or more. Though not restrictive, the upper limit of the thickness may be practically about 10 μm. Of course, the thin metal film may be thicker than 10 μm, with substantially no change in the absorbability of high-frequency electromagnetic waves. The thickness of the thin metal film is more preferably 0.01-5 μm, most preferably 0.01-1 μm. The thin metal film 11 can be formed by vapor deposition methods (physical vapor deposition methods such as a vacuum vapor deposition method, a sputtering method and an ion plating method, or chemical vapor deposition methods such as a plasma CVD method, a thermal CVD method and a photo CVD method), plating methods, or foil-bonding methods.
When the thin metal film 11 is a single layer, the thin metal film 11 is preferably made of aluminum or nickel from the aspect of conductivity, corrosion resistance and cost. When the thin metal film 11 has a multi-layer structure, one layer may be formed by a non-magnetic metal, while the other layer may be formed by a magnetic metal. The non-magnetic metals include aluminum, copper, silver, tin and these alloys, and the magnetic metals include nickel, cobalt, chromium and these alloys. The thickness of the magnetic thin metal film is preferably 0.01 μm or more, and the thickness of the non-magnetic thin metal film is preferably 0.1 μm or more. Though not restrictive, the upper limits of their thickness may be practically about 10 μm. More preferably, the thickness of the magnetic thin metal film is 0.01-5 μm, and the thickness of the non-magnetic thin metal film is 0.1-5 μm.
(3) Linear Scratches
As shown in
90% or more of the widths W of the linear scratches 12 are preferably in a range of 0.1-100 μm, more preferably in a range of 0.1-50 μm, most preferably in a range of 0.5-20 μm. The average width Way of the linear scratches 12 is preferably 1-50 μm, more preferably 1-10 μm, most preferably 1-5 μm.
The transverse intervals I of the linear scratches 12 are preferably in a range of 1-500 μm, more preferably in a range of 1-100 μm, most preferably in a range of 1-50 μm, particularly in a range of 1-30 μm. The average transverse interval Iav of the linear scratches 12 is preferably 1-200 μm, more preferably 5-50 μm, most preferably 5-30 μm.
Because the lengths L of the linear scratches 12 are determined by sliding conditions (mainly relative peripheral speeds of a roll and a film, and the angle of the composite film wound around the roll), they are substantially the same (substantially equal to the average length) unless the sliding conditions are changed. The lengths of the linear scratches 12 may be practically about 1-100 mm, preferably 2-10 mm, though not particularly restrictive.
The acute crossing angle (hereinafter referred to simply as “crossing angle” unless otherwise mentioned) Os of the linear scratches 12a, 12b are preferably 10-90°, more preferably 30-90°. With sliding conditions (sliding direction, peripheral speed ratio, etc.) between the composite film and the pattern roll adjusted, linear scratches 12 with various crossing angles Os can be formed as shown in
(4) Fine Pores
As shown in
(5) Thin Carbon Nanotube Layer
A thin carbon nanotube layer 14 is formed on the thin metal film 11 having linear scratches 12. The carbon nanotube may have a single-layer structure or a multi-layer structure. Multi-layer carbon nanotube is preferable, because it has a diameter of about 10 nm to several tens of nm, is easily formed into a uniform, thin layer without aggregation, and has excellent conductivity.
Carbon nanotube coated on the thin metal film 11 having linear scratches 12 should have an average length of 2 μm or more. The carbon nanotube intrudes into the linear scratches 12 on the thin metal film 11, resulting in electric conduction not only between the carbon nanotube and the thin metal film 11, but also between the carbon nanotubes themselves. Accordingly, too short carbon nanotube provides insufficient electric conduction, resulting in low electromagnetic wave absorbability and low thermal diffusion (thermal dissipation). The average length of carbon nanotube can be determined by image-analyzing a photomicrograph of a glass plate coated with a dilute carbon nanotube dispersion. The upper limit of the average length of carbon nanotube is not particularly restricted, but may be determined taking into consideration the dispersibility of carbon nanotube.
Because the carbon nanotube is formed in the presence of a metal catalyst such as Co, Ni, Fe, etc., it contains an unseparated catalyst. It has been found that particularly when the thin metal film 11 is made of aluminum, the aluminum is corroded by a reaction with the remaining catalyst. Accordingly, when the thin aluminum film 11 is coated with a catalyst-remaining carbon nanotube dispersion, the electromagnetic wave absorbability and the thermal diffusion (thermal dissipation) are deteriorated with time. To prevent this, the metal catalyst is preferably removed from the carbon nanotube. The removal of the metal catalyst can be conducted by adding an acid such as nitric acid, hydrochloric acid, etc. to an aqueous carbon nanotube dispersion.
The thickness (coated amount) of the thin carbon nanotube layer 14 is preferably 0.01-0.5 g/m2 when expressed by the mass of carbon nanotube. When the thin carbon nanotube layer 14 is thinner than 0.01 g/m2, a sufficient effect of improving electromagnetic wave absorbability with more uniformity cannot be obtained. On the other hand, when it is thicker than 0.5 g/m2, it is difficult to prevent the aggregation of carbon nanotube, resulting in an uneven thin carbon nanotube layer 14. The thickness of the thin carbon nanotube layer 14 is more preferably 0.02-0.2 g/m2, most preferably 0.04-0.1 g/m2, when expressed by the mass of carbon nanotube.
To prevent the detachment of carbon nanotube, the thin carbon nanotube layer preferably contains a binder resin. The binder resins include celluloses such as ethyl cellulose; acrylic resins; styrene polymers such as polystyrene, styrene-butadiene random copolymers and styrene-butadiene-styrene block copolymers; polyvinyl pyrrolidone; polyvinyl alcohol; polyethylene glycol; polypropylene glycol; polyvinyl butyral; polypropylene carbonate; polyvinyl chloride; etc. These binder resins may be used alone or in combination. Though not restrictive, the amount of the binder resin contained is preferably, for example, in a range of 0.01-10 g/m2. In addition to the binder resin, a known dispersant may be contained.
Because both linear scratches 12 and carbon nanotube have random sizes and distributions, they microscopically form an uneven electromagnetic-wave-absorbing structure, but the existence of numerous, different electromagnetic-wave-absorbing structures macroscopically exhibits uniform electromagnetic wave absorbability.
(6) Protective Layer
To protect the thin carbon nanotube layer 14, as shown in
[2] Production Method of Electromagnetic-Wave-Absorbing Film
(1) Formation of Linear Scratches
a) to 5(e) show one example of apparatuses for forming linear scratches in two directions. This apparatus comprises (a) a reel 21 from which a thin metal film-plastic composite film 100 is wound off, (b) a first pattern roll 2a arranged in a different direction from the transverse direction of the composite film 100 on the side of the thin metal film 11, (c) a first push roll 3a arranged upstream of the first pattern roll 2a on the opposite side to the thin metal film 11, (d) a second pattern roll 2b arranged in an opposite direction to the first pattern roll 2a with respect to the transverse direction of the composite film 100 on the side of the thin metal film 11, (e) a second push roll 3b arranged downstream of the second pattern roll 2b on the opposite side to the thin metal film 11, (f) an electric-resistance-measuring means 4a arranged on the side of the thin metal film 11 between the first and second pattern rolls 2a, 2b, (g) an electric-resistance-measuring means 4b arranged downstream of the second pattern roll 2b on the side of the thin metal film 11, and (h) a reel 24, around which the linearly scratched, thin metal film-plastic composite film 1 is wound. In addition, pluralities of guide rolls 22, 23 are arranged at predetermined positions. Each pattern roll 2a, 2b is supported by a backup roll (for instance, rubber roll) 5a, 5b to prevent bending.
As shown in
d) shows the principle that linear scratches 12a are formed on the composite film 100 with inclination from the moving direction thereof Because the pattern roll 2a is inclined from the moving direction of the composite film 100, the moving direction (rotation direction) a of fine, hard particles on the pattern roll 2a differs from the moving direction b of the composite film 100. After a fine, hard particle at a point A on the pattern roll 2a comes into contact with the thin metal film 11 to form a scratch B at an arbitrary time as shown by X, the fine, hard particle moves to a point A′, and the scratch B moves to a point B′, in a predetermined period of time. While the fine, hard particle moves from the point A to the point A′, the scratch is continuously formed, resulting in a linear scratch 12a extending from the point B′ to the point A′.
The directions and crossing angle Os of the first and second linear scratch groups 12A, 12B formed by the first and second pattern rolls 2a, 2b can be adjusted by changing the angle of each pattern roll 2a, 2b to the composite film 100, and/or the peripheral speed of each pattern roll 2a, 2b relative to the moving speed of the composite film 100. For instance, when the peripheral speed a of the pattern roll 2a relative to the moving speed b of the composite film 100 increases, the linear scratches 12a can be inclined 45° from the moving direction of the composite film 100 like a line C′D′ as shown by Y in
Because each pattern roll 2a, 2b is inclined from the composite film 100, sliding with each pattern roll 2a, 2b provides the composite film 100 with a force in a transverse direction. Accordingly, to prevent the lateral movement of the composite film 100, the longitudinal position and/or angle of each push roll 3a, 3b to each pattern roll 2a, 2b are preferably adjusted. For instance, the proper adjustment of a crossing angle θ3 between the axis of the pattern roll 2a and the axis of the push roll 3a provides pressing power with such a transverse distribution as to cancel transverse force components, thereby preventing the lateral movement. The adjustment of a distance between the pattern roll 2a and the push roll 3a also contributes to the prevention of the lateral movement. To prevent the lateral movement and breakage of the composite film 100, the rotation directions of the first and second pattern rolls 2a, 2b inclined from the transverse direction of the composite film 100 are preferably the same as the moving direction of the composite film 100.
As shown in
To increase the power of the pattern rolls 2a, 2b pressing the composite film 100, a third push roll 3c may be provided between the pattern rolls 2a, 2b as shown in
Operation conditions determining not only the inclination angles and crossing angles of linear scratches but also their depths, widths, lengths and intervals are the moving speed of the composite film 100, the rotation speeds and inclination angles and pressing powers of the pattern rolls, etc. The moving speed of the composite film is preferably 5-200 m/minute, and the peripheral speed of the pattern roll is preferably 10-2,000 m/minute. The inclination angles θ2 of the pattern rolls are preferably 20-60°, particularly about 45°. The tension (in parallel to the pressing power) of the composite film 100 is preferably 0.05-5 kgf/cm width.
The pattern roll used in the apparatus for forming linear scratches is preferably a roll having fine particles with sharp edges and Mohs hardness of 5 or more on the surface, for instance, the diamond roll described in JP 2002-59487 A. Because the widths of linear scratches are determined by the sizes of fine particles, 90% or more of fine diamond particles have sizes preferably in a range of 1-1,000 μm, more preferably in a range of 10-200 μm. The fine diamond particles are attached to the roll surface preferably in an area ratio of 50% or more.
The thin metal film 11 having linear scratches 12 may be provided with large numbers of fine pores 13 by the method described in Japanese Patent 2063411. A roll per se for forming fine pores 13 may be the same as the roll for forming linear scratches. Fine pores 13 can be formed by causing the composite film 100 to pass between a roll having large numbers of fine particles with sharp edges and Mohs hardness of 5 or more on the surface like the roll for forming linear scratches and a roll having a smooth surface at the same peripheral speed.
(2) Formation of Thin Carbon Nanotube Layer
The thin metal film 11 having linear scratches 12, which is formed on at least one surface of the electromagnetic-wave-absorbing film 1, is coated with a carbon nanotube dispersion, and spontaneously dried to form a thin carbon nanotube layer 14. The carbon nanotube dispersion comprises (a) carbon nanotube and if necessary, a dispersant, or (b) carbon nanotube, a binder resin, and if necessary, a dispersant, in an organic solvent. The concentration of carbon nanotube in the dispersion is preferably 0.01-2% by mass. When the concentration of carbon nanotube is less than 0.1% by mass, a sufficient amount of carbon nanotube is not coated. On the other hand, when it is more than 2% by mass, carbon nanotube is likely aggregated in the dispersion, failing to form a uniform, thin carbon nanotube layer. The concentration of carbon nanotube is more preferably 0.01-1% by mass, most preferably 0.1-0.5% by mass.
When the binder resin is contained, its concentration in the carbon nanotube dispersion is preferably 0.1-10% by mass, more preferably 1-5% by mass, from the aspect of the viscosity of the dispersion and the uniform dispersibility of carbon nanotube.
Organic solvents used in the carbon nanotube dispersion include low-boiling-point solvents such as methanol, ethanol, isopropyl alcohol, benzene, toluene, methyl ethyl ketone, etc.; alkylene glycols such as ethylene glycol, propylene glycol, etc.; alkyl ethers of alkylene glycols such as propylene glycol monomethyl ether, dipropylene glycol monoethyl ether, etc.; alkyl ether acetates of alkylene glycols such as propylene glycol monoethyl ether acetate, dipropylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, etc.; terpenes such as terpineol, etc.
To form the thin carbon nanotube layer 14 having a thickness of 0.01-0.5 g/m2 when expressed by the mass of carbon nanotube, the amount of the carbon nanotube dispersion coated is determined depending on its concentration. Though not restrictive, the coating method of the carbon nanotube dispersion is preferably an inkjet printing method, etc. to form a uniform thin layer 14. The carbon nanotube dispersion need not be coated by one application, but may be coated by pluralities of application steps to form as uniform a thin carbon nanotube layer 14 as possible.
(3) Protective Plastic Layer
To protect the thin carbon nanotube layer 14, a protective plastic layer 15 formed by a plastic film is preferably heat-laminated. In the case of a PET film, the heat lamination temperature may be 110-150° C.
[3] Performance of Electromagnetic-Wave-Absorbing Film
(1) Evaluation of Electromagnetic Wave Absorbability
(a) Transmission Attenuation Power Ratio
Using a system shown in
Rtp=−10×log[10S21/10/(1−10S11/10)]. . . (1).
(b) Noise Absorption Ratio
In the system shown in
(2) Evaluation of Thermal Dissipation
The thermal dissipation of the electromagnetic-wave-absorbing film 1 is evaluated by the speed of heat given to a part of the film 1 diffusing to an entire region of the film. Specifically, a rectangular sample 200 (100 mm×50 mm) of the electromagnetic-wave-absorbing film 1 and an acrylic support plate 201 (200 mm×100 mm×2 mm) having a rectangular opening 202 of the same size as the sample 200 of the electromagnetic-wave-absorbing film 1 are prepared as shown in
As shown in
The present invention will be explained in more detail referring to Examples below without intention of restricting the present invention thereto.
Using an apparatus having the structure shown in
A carbon nanotube dispersion comprising 1% by mass of multi-layer carbon nanotube (catalyst removed) having diameters of 10-15 nm and an average length of 3 μm and 1% by mass of a dispersant in methyl ethyl ketone was coated on the linearly scratched, thin aluminum film 11 by an air brush, and spontaneously dried. The resultant thin carbon nanotube layer 14 was as thick as 0.064 g/m2 (coated amount). Thereafter, a 16-μm-thick PET film was heat-laminated to the thin aluminum film 11 at 120° C. to obtain a sample of an electromagnetic-wave-absorbing film 1.
Each test piece TP (55.2 mm×4.7 mm) cut out of the above electromagnetic-wave-absorbing film sample was adhered to the microstripline MSL in the system shown in
An electromagnetic-wave-absorbing film 1 having a linearly scratched, thin aluminum film 11 was produced in the same manner as in Example 1, without coating the thin aluminum film 11 with a carbon nanotube dispersion, and a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin were determined by the same methods as in Example 1 on a test piece TP cut out of the electromagnetic-wave-absorbing film 1. The results are shown in
As is clear from
The thermal diffusion (thermal dissipation) of the electromagnetic-wave-absorbing films 1 of Example 1 and Comparative Example 1 was evaluated at 22° C. and at humidity of 34% by the method described in [3] (2) referring to
Electromagnetic-wave-absorbing films 1 were produced in the same manner as in Example 1 and Comparative Example 1 except for forming a thin nickel film 11, and a test piece TP was cut out of each electromagnetic-wave-absorbing film 1 to determine a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin by the same methods as in Example 1. The results are shown in
An electromagnetic-wave-absorbing film 1 was produced in the same manner as in Example 1 except for changing the crossing angle θs of linear scratches to 30°, 60° and 90°, respectively, and the transmission attenuation power ratio Rtp and the noise absorption ratio Ploss/Pin were determined by the same methods as in Example 1 on a test piece TP cut out of each electromagnetic-wave-absorbing film 1. The transmission attenuation power ratios Rtp and the noise absorption ratios Ploss/Pin to the incident wave having a frequency of 6 GHz are shown in Table 1. As is clear from Table 1, high transmission attenuation power ratio Rtp and noise absorption ratio Ploss/Pin were obtained at any crossing angle θs of 30°-90°.
With respect to a test piece TP cut out of each electromagnetic-wave-absorbing film 1 produced in the same manner as in Example 1 except for changing the amount of the carbon nanotube dispersion coated as shown in Table 2 below, the transmission attenuation power ratio Rtp and the noise absorption ratio Ploss/Pin were determined by the same methods as in Example 1. The transmission attenuation power ratios Rtp and the noise absorption ratios Ploss/Pin to the incident wave having a frequency of 6 GHz are shown in Table 2. As is clear from Table 2, when the thin carbon nanotube layer 14 had thickness in a range of 0.01-0.1 g/m2, high transmission attenuation power ratio Rtp and noise absorption ratio Ploss/Pin were obtained, but outside the above thickness range, there were insufficient effects of improving the transmission attenuation power ratio Rtp and the noise absorption ratio Ploss/Pin.
(1)Multi-layer carbon nanotube.
With respect to a test piece TP cut out of an electromagnetic-wave-absorbing film 1 produced in the same manner as in Example 1 except for changing the thickness of the thin aluminum film 11 to 0.08 μm, the transmission attenuation power ratio Rtp and the noise absorption ratio Ploss/Pin were measured. The results are shown in
With respect to a test piece TP cut out of an electromagnetic-wave-absorbing film 1 produced in the same manner as in Example 1, except for using a two-layer, thin metal film comprising a 50-nm-thick Ni layer and a 100-nm-thick Cu layer in this order from below, the transmission attenuation power ratio Rtp and the noise absorption ratio Ploss/Pin were measured. The results are shown in
A 0.05-μm-thick, thin nickel film 11 vacuum-vapor-deposited on a biaxially stretched PET film was coated with a thin carbon nanotube layer 14 as thick as 0.060 g/m2 by the same method as in Example 1, without forming linear scratches. A test piece TP cut out of the resultant sample was measured with respect to a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin. The results are shown in
A thin carbon nanotube layer 14 as thick as 0.061 g/m2 was formed in the same manner as in Example 1 on a 16-μm-thick, biaxially stretched PET film free of a thin metal film. A test piece TP cut out of the resultant sample was measured with respect to a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin. The results are shown in
A sample of a 16-μm-thick, biaxially stretched PET film provided with a linearly scratched thin aluminum film 11 and a thin carbon nanotube layer 14 in the same manner as in Example 1 was divided to 10 pieces having the size shown in Table 3 below, and each piece was measured with respect to a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin at 6 GHz. The results are shown in Table 3. Small values of Rtp and Ploss/Pin were obtained because each piece had a smaller area than that of the test piece TP (55.2 mm×4.7 mm). As is clear from Table 3, the electromagnetic-wave-absorbing film 1 of the present invention had small unevenness in a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin even when divided to small pieces. This appears to be due to the fact that the unevenness of randomly formed linear scratches was averaged by the thin carbon nanotube layer 14.
A sample of a 16-μm-thick, biaxially stretched PET film provided with a linearly scratched, thin aluminum film 11 in the same manner as in Example 1 (free of a thin carbon nanotube layer 14) was divided to 10 pieces having the size shown in Table 4 below, and each piece was measured with respect to a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin were measured. The results are shown in Table 4. As is clear from Table 4, when the electromagnetic-wave-absorbing film free of a thin carbon nanotube layer 14 was divided to small pieces, the unevenness of the transmission attenuation power ratio Rtp and the noise absorption ratio Ploss/Pin became larger than that of Example 7 having the thin carbon nanotube layer 14.
The electromagnetic-wave-absorbing film 1 of Example 8 was produced in the same manner as in Example 1, except for using a carbon nanotube dispersion comprising 0.5% by mass of multi-layer carbon nanotube having diameters of 10-15 nm and an average length of 3 μm (a catalyst removed), which was uniformly dispersed in 98% by mass of a mixed solvent (xylene/isopropyl alcohol (IPA)=6/4), and further 1.5% by mass of polymethylmethacrylate (PMMA) dissolved in the mixed solvent. A test piece
TP cut out of this electromagnetic-wave-absorbing film 1 was measured with respect to a noise absorption ratio Ploss/Pin by the same method as in Example 1, and a sample cut out of this electromagnetic-wave-absorbing film 1 was evaluated with respect to thermal diffusion (thermal dissipation) by the same method as in Example 1. The noise absorption ratio Ploss/Pin measured is shown in
The electromagnetic-wave-absorbing film sample of Comparative Example 6 was produced in the same manner as in Example 8 except that a catalyst was not removed from the carbon nanotube dispersion of Example 8, and measured with respect to a noise absorption ratio Ploss/Pin. The results are shown in
As is clear from
An electromagnetic-wave-absorbing film was produced in the same manner as in Example 1, except for using a carbon nanotube dispersion comprising 1.0% by mass of multi-layer carbon nanotube having an average length of 1 μm and 1.0% by mass of PMMA, and a test piece TP cut out thereof was measured with respect to a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin by the same methods as in Example 1. The results are shown in
An electromagnetic-wave-absorbing film 1 was produced in the same manner as in Example 8 except for changing the concentration of carbon nanotube to 1.3% by mass, and measured with respect to a noise absorption ratio Ploss/Pin and thermal diffusion (thermal dissipation) by the same methods as in Example 1. The results are shown in
A sample obtained by coating a 16-μm-thick PET film free of a thin aluminum film 11 with the same carbon nanotube dispersion as in Example 8 was measured with respect to a noise absorption ratio Ploss/Pin and thermal diffusion (thermal dissipation) by the same methods as in Example 1. The results are shown in
A sample of a 16-μm-thick PET film having a 0.05-μm-thick, thin aluminum film 11 free of linear scratches was coated with the same carbon nanotube dispersion as in Example 8, and measured with respect to a noise absorption ratio Ploss/Pin and thermal diffusion (thermal dissipation) by the same methods as in Example 1. The results are shown in
Comparative Example 10
A sample having only a 0.05-μm-thick thin aluminum film 11 formed on a surface of a 16-μm-thick PET film was evaluated with respect to thermal diffusion (thermal dissipation) by the same method as in Example 1. The results are shown in
As is clear from
The comparison of the electromagnetic-wave-absorbing film of Comparative Example 1, in which the linearly scratched, thin aluminum film 11 was not coated with a thin carbon nanotube layer 14, with the electromagnetic-wave-absorbing film 1 of Example 8, in which the linearly scratched, thin aluminum film 11 was coated with a thin carbon nanotube layer 14, revealed extremely improved thermal diffusion (thermal dissipation). This indicates that a combination of the linearly scratched, thin aluminum film 11 with the thin carbon nanotube layer 14 provides remarkably improved thermal diffusion (thermal dissipation) as compared with a case where they are used alone.
A PGS graphite sheet (thickness: 17 μm) available from Panasonic Corporation was evaluated with respect to thermal diffusion by the same method as in Example 1. The results are shown in
An electromagnetic-wave-absorbing film was produced in the same manner as in Example 1, except for forming only linear scratches on a biaxially stretched PET film in one direction (longitudinal direction of the PET film), and a first test piece TP with linear scratches extending along its longitudinal direction and a second test piece TP with linear scratches extending along its transverse direction were cut out of the electromagnetic-wave-absorbing film to measure a transmission attenuation power ratio Rtp and a noise absorption ratio Ploss/Pin by the same methods as in Example 1. Their transmission attenuation power ratios Rtp and noise absorption ratios Ploss/Pin at 6 GHz are shown in Table 5. As is clear from Table 5, the electromagnetic-wave-absorbing film having the thin carbon nanotube layer 14 formed on the thin aluminum film 11 with mono-directional linear scratches had high electromagnetic wave absorbability, but its anisotropy was large.
Because the electromagnetic-wave-absorbing film of the present invention have linear scratches formed in plural directions on a thin metal film, and further a thin carbon nanotube layer formed thereon, it has excellent absorbability to electromagnetic waves of various frequencies with low anisotropy, and suffers little unevenness in electromagnetic wave absorbability even when divided to small pieces. In addition, the electromagnetic-wave-absorbing film of the present invention has higher thermal diffusion (thermal dissipation) than that of an expensive graphite sheet. The electromagnetic-wave-absorbing film of the present invention having such features can be suitably used as a heat-dissipating noise suppression sheet in electronic communications apparatuses such as cell phones, smartphones, note-type, personal computers, ultrabooks, etc., electronic apparatuses such as note-type, personal computers, ultrabooks, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-163755 | Jul 2011 | JP | national |
| 2011-166020 | Jul 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/068516 | 7/20/2012 | WO | 00 | 1/24/2014 |
