JP5571014B2 - Electromagnetic wave suppression sheet - Google Patents

Description

  The present invention relates to a sheet for suppressing electromagnetic noise.

In recent years, various electronic devices such as personal computers (hereinafter referred to as PCs) have become more sophisticated and mobile communication devices represented by mobile phones have been widely used. However, in these electronic devices and communication devices, electronic components are mounted at a high density in order to achieve high performance, so that electromagnetic interference occurs inside the electronic devices, or electromagnetic noise radiated from these devices. There are also dangers that cause malfunctions in other devices and affect the human body.
In addition, for example, MPUs operating in the GHz band are becoming mainstream in PCs, so the frequency of generated electromagnetic noise tends to increase, and radiated electromagnetic noise exceeding 1 GHz has become a problem.

  Basically, such electromagnetic noise is sufficiently considered in circuit design, but if it cannot be prevented by any means, a sheet generally called “noise suppression sheet” is used.

  As the noise suppression sheet, a sheet obtained by mixing a magnetic metal piece with a resin, a sheet obtained by mixing a soft magnetic powder and a synthetic rubber, and the like are known. In recent years, the demand for a flame retardant type and a halogen-free type has been increased, and various proposals have been made. In various electronic devices and communication devices, there is a flow of customer needs for downsizing and weight reduction. In particular, in the noise suppression sheet as described above, a large amount of magnetic metal pieces and soft magnetic powder are put in large quantities. In order to express the functions, there are problems in terms of thickness and weight in terms of customer needs, such as downsizing and weight reduction of various electronic devices.

  In order to solve these problems, for example, as described in Patent Document 1 (JP-A 63-288298), Patent Document 2 (JP-A 2009-277736), and Patent Document 3 (JP-A 2010-40730), cellulose fibers, etc. A paper-based noise suppression sheet in which fibrous carbon is internally added has been proposed. Paper base substrates are preferred not only in terms of thickness and weight, but also from the viewpoint of carbon neutral. However, since such a paper-based noise suppression sheet contains combustible cellulose, it is easy to burn, and there is a problem in that a falling matter such as paper dust is generated when cutting. .

For imparting flame retardancy, methods of internally adding a flame retardant or post-processing such as impregnation are described in Patent Document 2, Patent Document 3, and Patent Document 4 (Japanese Patent Laid-Open No. 2009-194341). Yes. However, there is no description in Patent Documents 1 to 4 regarding a fallen matter that becomes a problem when handling or cutting these sheets. In order to prevent this fallout, for example, a method for producing dust-free paper is helpful. For example, Patent Document 5 (Japanese Patent Publication No. 60-167996) suppresses dust by impregnating paper with a specific polymer substance.
As described above, in the noise suppression sheet mainly composed of cellulose fibers, it is necessary to impart flame retardancy and prevent foreign matter from falling off. To that end, post-processing such as resin impregnation is required as a measure against flame retardancy and falling off foreign matter. Required.

  In order to impart post-processing properties such as impregnation to a sheet base paper mainly composed of cellulose fibers, it is necessary to provide the sheet base paper with sufficient wet strength. Methods include melamine formaldehyde, urea formaldehyde, polyamide polyamine epitaxy. A method of internally adding a chlorohydrin-based wet paper strength agent is common. However, in recent years, melamine formaldehyde-based and urea formaldehyde-based wet paper strength agents generate free formaldehyde and cause deterioration of the working environment. Switch to (Yes) is progressing. In addition, PAE is excellent in terms of functionality, such as being able to exhibit effects in a wide pH range, and in the current situation where neutral paper is mainly produced, 85% of wet paper strength agents used in Japan. Is said to be PAE (Non-Patent Document 1).

However, since this PAE contains chlorine (halogen), it is not preferable to use it for a halogen-free noise suppression sheet that will become increasingly demanded in the future as described above. There is a need to give wet strength necessary for post-processing without using PAE.

JP-A 63-288298 JP 2009-277736 A JP 2010-40730 A JP 2009-194341 A JP 60-167996 A

"Cutting-edge technology of wet-end chemistry and manufacturing chemicals" P161 (CMC Publishing)

  The present invention is a disadvantage of the conventional paper-based noise suppression sheet, which suppresses electromagnetic waves that improve wet strength and is halogen-free (in this configuration, it means that the amount of chlorine is reduced). It is an object to provide a sheet.

The present inventors have made intensive studies to solve such problems, when the electromagnetic wave suppressing sheet to wet paper making, carbon nanotube aqueous dispersions of water dispersed in the lignosulfonate sodium or partially desulfonated sodium lignosulfonate The present inventors have found that the problem can be solved by using a combination of polyvinylamine and polyvinylamine.

That is, according to this invention, the following electromagnetic wave suppression sheets and its manufacturing method are proposed.
(1) To a suspension of cellulosic fibers, and the carbon nanotube aqueous dispersions of water dispersed in 60 to 150% by weight of lignin sulfonate sodium or partially desulfonated sodium lignosulfonate of carbon nanotubes, based on the cellulose fibers An electromagnetic wave suppression sheet having a wet strength of 0.40 kN / m or more and a volume resistivity of 1.00 Ω · cm or less obtained by wet papermaking a slurry containing 0.5 to 3.0% by mass of polyvinylamine.
(2) The electromagnetic wave suppression sheet according to (1), which is obtained by wet papermaking a slurry in which the carbon nanotube aqueous dispersion is blended in an amount of 10% by mass or more as carbon nanotubes with respect to cellulose fibers.
(3) To a suspension of cellulosic fibers, and the carbon nanotube aqueous dispersions of water dispersed in 60 to 150% by weight of lignin sulfonate sodium or partially desulfonated sodium lignosulfonate of carbon nanotubes, based on the cellulose fibers A method for producing an electromagnetic wave suppression sheet, comprising wet-making paper slurry containing 0.5 to 3.0% by mass of polyvinylamine.

According to the present invention, it has sufficient wet strength is difficult to web breaks in processing steps after for imparting paper dust measures and flame retardancy, a halogen content of less electromagnetic wave suppressing sheet is provided.

Evaluation results of transmission attenuation factor (Examples 1 and 2 and Comparative Example 2) Evaluation results of transmission attenuation factor (Examples 3 to 7 and Comparative Example 4)

Hereinafter, the present invention will be described in detail in order.
Electromagnetic wave suppressing sheet of the present invention, cellulose fibers, carbon nanotubes (lignin sulfonic acid sodium or using partial sodium desulfonation ligninsulfonate those aqueous dispersion as a dispersant), the slurry containing, as essential components polyvinylamine Is obtained by wet papermaking.
The cellulose fiber used is not particularly limited, and various wood pulps (mechanical pulp, chemical pulp, semi-chemical pulp) and non-wood fibers can be used. NBKP and LBKP are preferable because of high sheet strength. Furthermore, the use of ECF (Elemental Chlorine Free) pulp or TCF (Total Chlorine Free) pulp is particularly preferable.
Further, synthetic fibers and semi-synthetic fibers may be used in combination as long as the physical properties are not impaired. The above cellulose fibers can be used in any combination as long as the physical properties are not impaired. These cellulose fibers are disaggregated with a pulper so that the solid content concentration is 3 to 5%. This pulp slurry is beaten to 650-300 ml with Canadian Standard Freeness (CSF) using a refiner or beater.

  Carbon nanotube (hereinafter referred to as CNT) production methods include CVD, laser evaporation, arc discharge, etc., and CNTs produced by any of these production methods can be used, but a multiwall was used commercially. Better. Also, the fiber diameter should be small and the aspect ratio should be large. When the drainage on the wire is remarkably deteriorated, carbon fiber or the like may be mixed.

CNT has a property of being easily aggregated, and even if a commercially available product is used as it is, an electromagnetic wave suppressing effect cannot be obtained. Therefore, it is necessary to obtain a CNT dispersion. Various dispersion methods have been proposed for dispersing CNTs in a dispersion medium. In this paper, a dispersing agent, lignin sulfonic acid sodium or using the partial sodium desulfonation ligninsulfonate, adjusts the dispersion of CNT in the dispersion apparatus such as an ultrasonic homogenizer.

When CNTs are dispersed with a dispersing device, if too much time is taken, CNTs are torn off or structural damage is caused, which may reduce the electromagnetic wave suppression effect. In addition, when CNT is used in wet papermaking, if the CNT is dispersed too much, the yield of the CNT on the wire is lowered and the electromagnetic wave suppressing effect is hindered. Furthermore, if a chemical such as a retention agent is added excessively in order to increase the yield of CNTs, the CNTs aggregate, and eventually sufficient electromagnetic wave control cannot be obtained. Therefore, it is necessary to maintain an appropriate dispersion state.
For example, when a laser diffraction / scattering particle size measuring apparatus (LA-950V2; manufactured by HORIBA, Ltd.) as described in Example 1 is used, the median diameter is preferably about 0.2 to 80 μm.

  The amount of the dispersant used is preferably 60 to 150% with respect to CNT. If it is less than 60%, CNTs are not sufficiently dispersed and the volume resistance value becomes high. On the other hand, if it exceeds 150%, the volume resistance value becomes high and the wet strength becomes low. If the volume resistance value becomes high, the electromagnetic wave suppressing ability is not sufficiently exhibited.

In the present invention , polyvinylamines that are chlorine-free are further used. Thereby, an electromagnetic wave suppression sheet having sufficient wet strength and a low halogen content can be obtained. As usage-amount of polyvinylamine, 0.5%-3.0% are preferable with respect to a cellulose fiber. If it is less than 0.5%, sufficient wet strength cannot be obtained. On the other hand, if the content is more than 3.0%, the CNTs are excessively aggregated and the volume resistance value is increased.
The sufficient wet strength of the present invention refers to wet strength that does not hinder the provision of flame retardancy and resin impregnation in the post-treatment process. When measured by the method described in the examples, it is 0.40 kN / m or more.

  The chlorine content was measured according to the sample combustion-ion chromatography method (BS EN 14582). The chlorine content in the sheet is preferably as low as possible, but is 300 ppm or less, preferably 200 ppm or less, and more preferably 150 ppm or less.

  In the present application, a coagulant can be used as necessary. As the coagulant, an inorganic coagulant such as sulfuric acid band, aluminum chloride, polyaluminum chloride or an organic coagulant is used. These chemicals have the effect of neutralizing the charge of cellulose fibers (fine fibers), CNTs, and other chemicals, condensing them, and retaining them in the sheet to prevent stains such as wires and rolls.

  As the pH adjuster, sodium aluminate, sodium hydroxide, or the like is used.

The beating solution of cellulose fibers, CNT aqueous dispersion dispersed in water is lignosulfonate sodium or part de sodium lignosulfonate, and polyvinyl amines, the slurry obtained by mixing a coagulant according required, solids 0 After being diluted to about 0.02 to 2.0%, paper is made by a wet paper making method. At this time, a flocculant can also be used. The flocculant is preferably added after the slurry is diluted to about 0.02 to 2.0%. Examples of the aggregating agent include polyacrylamide and polyethylene oxide.

  Evaluation methods in the examples of the present invention are as follows.

(1) Wet tensile strength Measurement was performed according to the general method of JIS P8135. The wet tensile strength of the sheet is preferably 0.40 kN / m or more.

(2) Dry tensile strength Measurement was performed according to the general method of JIS P8113.

(3) Measurement was carried out in accordance with the general method of JIS P8124.

(4) Thickness Measurement was performed according to the general method of JIS P8118.

(5) Chlorine content in sheet The measurement was performed according to the sample combustion-ion chromatograph method (BS EN 14582).

(6) Volume resistivity
A sample is cut to a width of 1.5 cm and a length of 15 cm, and one end of the tester leads (two) is brought into contact with the surface of the sample using a digital multimeter 73302 (manufactured by Yokogawa Meter & Instruments). The tip of the other tester lead was brought into contact with the back surface of the sample, the distance between the two tester leads was 10 cm, and the resistance value was measured. From this resistance value, the volume resistivity was calculated using the following equation.

Volume resistivity = resistance value × sample width × sample thickness / tester lead interval

The volume resistivity is preferably 1.00 cm · Ω or less.

(7) Transmission attenuation rate For the evaluation of the electromagnetic wave suppression ability, the transmission attenuation rate (= Rtp) based on the microstrip line method was measured (IEC 62333-2 4.3).

Example 1
A 2.0% aqueous solution of sodium lignin sulfonate (Sun Extract P252; manufactured by Nippon Paper Chemicals Co., Ltd.) was prepared, and carbon nanotubes (hereinafter referred to as CNT): VGCF-X (manufactured by Showa Denko) were added thereto. 0.0% solution was obtained. This CNT 2.0% solution was treated with an ultrasonic homogenizer (US-600FCAT; manufactured by Nippon Seiki Co., Ltd.) for 90 min (amplitude 40 μm) to obtain a CNT dispersion. When this dispersion was measured with a laser diffraction / scattering particle size measuring device (LA-950V2; manufactured by Horiba, Ltd.), the median diameter of CNT was 0.35 μm.
As a cellulose fiber, LBKP (ECF pulp) having a beating degree of 487 ml was made into a 4.0% suspension, and the suspension was mixed with 10 parts by weight of CNT with respect to 100 parts by weight of the CNT dispersion. It was added to become. Furthermore, after adding 1.0 part by weight of polyvinylamine (Cathiofast VFH; manufactured by BASF) and 6 parts by weight of a sulfuric acid band, sodium aluminate was added to prepare a slurry of pH 7.3.
After the slurry was diluted to 0.5% with water, 0.03 part by weight of an anionic acrylamide-based flocculant (FA-230; manufactured by Hymo Co., Ltd.) was added, and the paper was quickly hand-drawn by square hand-drawing. To obtain a sheet having a weight of 85.3 g / m ² and a thickness of 0.120 mm.

Example 2
The same procedure as in Example 1 was used, except that high-purity partially desulfurized sodium lignin sulfonate (Vanilex N; manufactured by Nippon Paper Chemicals Co., Ltd.) was used instead of sodium lignin sulfonate in Example 1. A sheet having a thickness of 0.6 g / m ² and a thickness of 0.126 mm was obtained.

Comparative Example 1
The same procedure as in Example 1 was conducted except that sodium naphthalene sulfonate formalin condensate (Demol N; manufactured by Kao Corporation) was used in place of sodium lignin sulfonate in Example 1, and 88.3 g / m 2 ^2. A sheet having a thickness of 0.127 mm was obtained. The wet strength was insufficient.

Comparative Example 2
The same procedure as in Example 1 was performed except that sodium polystyrene sulfonate (PS-50; manufactured by Tosoh Organic Chemical Co., Ltd.) was used instead of sodium lignin sulfonate in Example 1, and 84.3 g / m ^{2 of} rice tsubo. An electromagnetic wave suppressing material having a thickness of 0.132 mm was obtained. The wet strength and volume resistance value were insufficient.

Comparative Example 3
The same procedure as in Example 1 was performed except that a polyamide polyamine epichlorohydrin resin-based wet paper strength agent (SR-6615; manufactured by Taoka Chemical Industries) was used instead of polyvinylamine in Example 1, and 90.7 g of rice tsubo A sheet having a thickness of 0.135 mm / m ² was obtained. The wet strength was insufficient and the amount of chlorine was large.

  Table 1 shows the evaluation results for Examples 1-2 and Comparative Examples 1-3.

The evaluation results of the transmission attenuation factor at 0.1 to 3.0 GHz of the sheets of Examples 1 and 2 and Comparative Example 2 are shown in FIG.
In particular, it was confirmed that Examples 1 and 2 showed good transmission attenuation factors in the region of 1 GHz or more.

Example 3
A 1.2% aqueous solution of sodium lignin sulfonate (Sun Extract P252; manufactured by Nippon Paper Chemicals Co., Ltd.) was prepared, and CNT: VGCF-X (manufactured by Showa Denko) was added to it, and a 2.0% solution of CNT and did. This CNT 2.0% solution was treated with an ultrasonic homogenizer (US-600FCAT; manufactured by Nippon Seiki Co., Ltd.) for 90 min (amplitude 40 μm) to obtain a CNT dispersion. As a cellulose fiber, a beating degree of 487 ml LBKP (ECF pulp) is made into a 4.0% suspension, and the CNT dispersion is added to this suspension so that the amount of CNT becomes 10 parts by weight with respect to 100 parts by weight of LBKP. Added to. Further, 1.0 part by weight of polyvinylamine (Cathiofast VFH; manufactured by BASF) was added, 6 parts by weight of sulfuric acid band was added, and then sodium aluminate was added to prepare a slurry having a pH of 7.3.
After the slurry was diluted to 0.5% with water, 0.03 part by weight of an anionic acrylamide-based flocculant (FA-230; manufactured by Hymo Co., Ltd.) was added, and the paper was quickly hand-drawn by square hand-drawing. To obtain a sheet having a weight of 90.1 g / m ² and a thickness of 0.132 mm.

Example 4
The same procedure as in Example 3 was conducted, except that the aqueous sodium lignin sulfonate solution to be adjusted was 3.0%, to obtain a sheet having a weight of 88.8 g / m ² and a thickness of 0.130 mm.

Comparative Example 4
The same procedure as in Example 3 was conducted, except that the aqueous sodium lignin sulfonate solution to be adjusted was 4.0%, to obtain a sheet having a basis weight of 91.2 g / m ² and a thickness of 0.138 mm. The wet strength was insufficient and the volume resistance value was high.

Example 5
Except that the addition amount of polyvinylamine was 0.5 parts by weight, the same procedure as in Example 3 was performed to obtain a sheet having a basis weight of 92.7 g / m ² and a thickness of 0.125 mm.

Example 6
Except that the addition amount of polyvinylamine was 2.0 parts by weight, the same procedure as in Example 3 was performed to obtain a sheet having a basis weight of 91.2 g / m ² and a thickness of 0.132 mm.

Example 7
The same procedure as in Example 3 was conducted, except that the addition amount of polyvinylamine was changed to 3.0 parts by weight, and a sheet having a basis weight of 92.0 g / m ² and a thickness of 0.135 mm was obtained.

Table 2 shows the evaluation results for Examples 3 to 7 and Comparative Example 4 described above.

FIG. 2 shows the evaluation results of the transmission attenuation factor at 0.1 to 3.0 GHz of the sheets of Examples 3 to 7 and Comparative Example 4 described above.
In particular, it was confirmed that Examples 3 to 7 showed good transmission attenuation factors in the region of 1 GHz or more.

The electromagnetic wave suppression sheet according to the present invention is particularly applicable to communication devices and electronic devices such as computers and mobile phones because it has a sufficient electromagnetic wave absorption performance at 1 GHz or more and is lightweight.

Claims (3)

0 To a suspension of cellulosic fibers, and the carbon nanotube aqueous dispersions of water dispersed in 60 to 150% by weight of lignin sulfonate sodium or partially desulfonated sodium lignosulfonate of carbon nanotubes, the cellulose fibers. An electromagnetic wave suppression sheet having a wet strength of 0.40 kN / m or more and a volume resistivity of 1.00 Ω · cm or less obtained by wet papermaking a slurry containing 5 to 3.0% by mass of polyvinylamine.   The electromagnetic wave suppression sheet according to claim 1, wherein a slurry in which the carbon nanotube aqueous dispersion is blended in an amount of 10% by mass or more with respect to cellulose fibers as a carbon nanotube is subjected to wet papermaking. 0 To a suspension of cellulosic fibers, and the carbon nanotube aqueous dispersions of water dispersed in 60 to 150% by weight of lignin sulfonate sodium or partially desulfonated sodium lignosulfonate of carbon nanotubes, the cellulose fibers. A method for producing an electromagnetic wave suppression sheet, comprising wet-making a slurry containing 5 to 3.0% by mass of polyvinylamine.

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