JPH02153851A - Cement composite material having electromagnetic wave shielding property - Google Patents

Abstract

PURPOSE:To provide a composite material having high electromagnetic shielding properties and strength by mixing carbon fiber paper in a specific amount or more with cement. CONSTITUTION:The above-mentioned cement material is obtained by mixing >=0.7vol.% carbon fiber paper with cement. The aforementioned carbon fiber paper refers to carbon fiber having a two-dimensional extent and includes nonwoven fabric-like paper, paper produced by a sheet forming method, woven fabric-like paper, etc. The above-mentioned cement composite material has the following advantages. Lightweight and high electromagnetic wave shielding properties and strength relative to a low carbon fiber content, good dispersion of the carbon fiber and moldability, excellent in corrosion resistance and high deformability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cement composite material (CFRC) having electromagnetic wave shielding properties and used for structural members of external walls of intelligent buildings, computer rooms, etc.

(Prior Art) With the development of an advanced information society, various communication devices and electronic devices are being installed not only in workplaces and factories but also in each home.

These electronic devices generate various kinds of artificial noise (noise), and in recent years, the need for noise countermeasures has become extremely important in relation to atmospheric noise.

Furthermore, in recent years, many intelligent buildings have been constructed, and it has become necessary to protect the entire building from external noise such as harmful electromagnetic waves, and there is a desire to develop exterior wall materials that have radio wave shielding properties.

Cement and concrete, which are widely used as building materials, have a specific resistance of 1010 Ω・C or more, and are not conductive or have radio wave shielding properties. Therefore, they are generally used as materials with shielding properties, i.e. It is made of conductive metals (iron, zinc, copper, aluminum, stainless steel) in the form of a plate or box, and is multi-layered with cement and concrete building materials, or mixed with conductive fillers (metal fibers, carbon fibers). The reality is that it has shielding properties.

Among these, cement concrete building materials (CFR) using carbon fiber (hereinafter abbreviated as CF) as a shielding material.
C) is attracting attention as a material with potential as a shield building material that also serves as a structural material due to the excellent mechanical and chemical properties of CF. Recently, CFRC has been researched in various fields, and in some cases, it has even been possible to put it into practical use as a curtain wall. In addition, the shielding characteristics of CFRC have been studied, but currently the resistivity is several tens of Ω・σ or more, and sufficient shielding effect has not yet been obtained.Therefore, CFRC, which has a higher shielding effect, is It is hoped that construction materials will emerge.

(Problems to be solved by the invention) CFs that are currently being researched and developed or put into practical use in various fields
All RCs are systems in which chopped fibers CF are dispersed in a cement matrix, and their reinforcing effects naturally have limits in terms of their content and -dimensional reinforcement.

On the other hand, CFR reinforced with these chopped fibers
In C, the conductivity of CF itself is cut between the fibers, and the conductivity of the entire CFRC, that is, the specific resistance, is determined by the contact points of the fibers, considering the dispersibility of the fiber itself and the limit of the content. and these existing CFRs.
It is unavoidable that C has a certain limit in its radio wave shielding properties, that is, its conductivity.

In view of these points, as a result of intensive research, the present invention has solved the above problems by using carbon fiber paper as the reinforcing CF.

(Carbon fiber paper here refers to carbon fiber with a two-dimensional spread, such as non-woven fabric,
Including those made by papermaking method or woven ones,
So-called vapor, felt.

Including everything commonly called mat, sheet, cloth, etc.) Furthermore, fI & fiber length used in carbon fiber paper,
The technical challenge is to achieve a high t magnetic wave shielding effect by controlling the diameter, properties, paper properties, structure, etc.

(Means for Solving the Problems) The technical means for solving the above problems is to obtain a cement composite material having magnetic wave shielding properties by mixing Q, 7 VO 1% or more of returned fiber A-fiber paper into cement. More specifically, the fiber length of the carbon fiber paper is at least 6 mm or more, and a part of the binder used in the carbon fa fiber paper is made of a conductive carbonaceous binder, so that electromagnetic waves can be suppressed. The goal is to improve shielding performance.

(Function) According to the cement composite material having the above structure, the carbon fiber paper mixed into the cement produces electromagnetic wave shielding properties, and the carbon fiber paper makes it possible to reduce the weight and increase the strength of the building material.

(Example) Experimental examples and examples of the present invention will be described below.

According to Chelkunoff's theory, the electromagnetic shielding effect SE is the sum of the attenuated breathing loss A due to propagation within the sample, the reflection loss RE between the sample surface and the air, and the multiple reflection loss M due to repeated reflections on the sample plate, and is expressed by the following formula. .

5E=A+RE+M [dB] t [CT11]: Thickness of sample, p [Ω1cm]: Specific resistance f' [MHz Koni frequency, μ,: Relative permeability.

S: Radio wave penetration depth However, k = Z s / Xω
According to the above equation, it can be seen that the electromagnetic shielding effect of the sample (CFRC) becomes higher as the resistivity becomes smaller and the thickness becomes thicker.

Each experiment to obtain a cement composite material with high electromagnetic shielding properties will be described below.

1. Experimental method (1) Two types of PAN-based high-performance carbon fiber (HPCF) and two types of general-purpose grade pitch-based carbon fiber (GPCF) were used as the CF paper (carbon fiber paper). In all of these, the binder is organic. In addition, in order to make a CF prepreg sheet with continuous long fibers, PAN
High performance fiber (HPCF) and high modulus carbon a fiber (
HMCF), pitch-based high performance carbon 4tA fiber (HPCF)
) and high modulus carbon fiber (HMCF) were used, respectively.

Moreover, ordinary Portland cement was used as the cement.

(2) Production and measurement method Various CF papers (15cm x 15cm) are
/C ratio (40%) and thoroughly impregnated by hand.
The sheets were stacked. In addition, the long fiber CF prepreg sheet is
It was produced by arranging 28 CF tows of No. 6 in one direction at 5 cm intervals in a mold (15 cm x 15 cm). Cement paste (W) is applied to this CF prepreg sheet.
/C ratio, 40%), and this was laminated in two layers or 4B. These specimens were cured in water for two weeks to produce CFRC boards with a thickness of 3B.

Next, for each sample 100MHz ~ 1000MHz
The electromagnetic shielding properties (electric field shielding and magnetic field shielding) in the frequency range up to were measured using the Atopan test method. In addition, both ends of the CFRC board were shaved to expose the CF part, each surface was coated with silver paste, and the electrical resistance was measured.

2. Experimental results and ideas (1) Shadow depending on the type of CF paper and the number of stacked sheets
.

Table 1 shows the electric field and magnetic field shielding characteristics of CFRC made from Portland cement using various CF papers.
Shown below.

The shielding performance of CFRC was slightly attenuated as the frequency range increased in both cases. The electric field shielding effect of a CFRC using one CF vapor at 500 MHz was 6 to 17 dB. Moreover, the magnetic field shielding effect was also at the same level. However, in the case of 50a11, which has a long fiber length, the shielding effect was as high as 20 dB, showing an electric field and magnetic field shielding effect that was said to be 'slightly good'. With cement coagulum alone,
The shielding effect is 0.6~ compared to "not at all"
It can be seen that the effect is high despite the low CF content of about 0.7 vol.

Next, when 6 sheets of CF paper are stacked, PAN
In both systems and pitch systems, the shielding effect of CFRC increased by about 3-4 times to 22-29 dB for both electric and magnetic fields, showing a moderately good shielding effect to an average shielding effect. Furthermore, the electrical resistance of CFRC is shown on the right side of the table. These values were widely distributed from several Ω, Cm to 100 Ω, and CTn, and the lower the electrical resistivity, the higher the shielding effect.

Also, when the bending strength at this time was measured, it was 12~
It is in the range of 35 MPa, and the elastic modulus is about 6 GPa,
It also showed excellent mechanical properties as a building material.

By the way, 100 parts of ordinary Portland cement, 150 parts of silica sand, 70 parts of water, and 2 parts of CF were mixed in a mixer, and a 150 x 150 x 3 (1 ml) specimen was made by casting, and the shielding properties were measured. (500MH2) was a low value of about 10 dB.

Table 1 Effect of type of CF paper and number of layers on electric field and dust field shielding characteristics Electric field shield Magnetic field CF Lamination σ content Frequency (M&)
Resistivity shield.

Number of sheets (volX) 100 250 500 7
50 1000 (Ω・cm) 500MHz unit (dB) PANAI O,61886560763,733
-44312422189,020B 1 0.6
32-42 24 17 13 9 60
106 3.5 35-47 32 27 2
2 16 8.0 20 pits fc1 1 0.7
2111 32 18 6 6 4 15
．． 0 56 4.2 33-45 30 22
20 15 8.4 15C210,732-3
72820151021,01964,22g-523
52924195,727A: PAN (HPCF, thickness 0.3 Irrn, basis weight 33 g/m", fiber length 5 nv
n) B: PAN (HPCF, 30g/n", 10m)
C1: Pitch (GPCF, 0.3nn, 4011./
m”, 6+m+)C2:Pi fCGPCF, 0.7MB
, 40gJ is 50mm) (2) C of carbonaceous binder
When using F paper.

The electric field shielding effect of CFRC was found to be related to electrical conductivity from the experimental results in (1) above, so we made graphitized carbon fibers with low resistivity using a carbonaceous binder. CF paper (pitch type G'P
CF, 0.3in, 40g/m", 10
m1) was used.

CF paper contains polyethylene resin, epoxy resin, P
Organic binders such as VA resin, phenol resin, and pitch are used.

The carbonaceous binder refers to a CF paper made of this organic binder that is carbonized by treating it at a high temperature of 1000° C. or higher.

In this experiment, CF paper was used in which pitch-based GPCF was treated at 1,500 to 2,000°C to form a carbonaceous binder. 1 sheet, 6 sheets, or C of the organic binder in Table 1.
Used in combination with F paper at the same time, thickness t31m
A CFRC board was produced. Table 2 shows the relationship between the shielding characteristics and specific resistance of these CFRCs.

The number of laminated sheets of CF paper with R quality binder is 1 or 2.
．． As the number of sheets increases to 6, the electrical resistivity decreases from 3.3Ω to 1.4Ω, and the electric field shielding effect decreases from 19dB to 40dB, and the magnetic field shielding effect decreases by 2dB.
B to 46 dB, demonstrating "good shielding performance."

Furthermore, in order to lower the electrical resistivity of CFRC, 1% of fine graphite powder (average particle size 2 μm) was added to the cement paste, and this was added to the carbonaceous binder paper, which also showed a high shielding effect during the above experiment. Impregnated into 6 sheets, C
An FRC board was produced.

By adding graphite powder, the electrical resistivity decreased from 1.4 Ω·■ to 0.8 Ω·s, and both the electric field and magnetic field shielding properties increased to 48 dB and 52 dB. In particular, the magnetic field shielding property was the highest value in this experiment.

Table 2 Effect of carbonaceous binder CF paper on electric field and magnetic field shielding characteristics (dB) Number of laminated sheets Electric field shielding frequency (dB) Resistivity magnetic field shielding pitch system CF paper, Portland cement (W/C)
=40X)×)Using Portland cement paste (W/C=40%) with 1% graphite powder added (3) Effect of a-fiber length on CF.

Since reducing the specific resistance of CFRC was extremely effective for the shielding effect, Table 3 shows the electric field and magnetic field shielding effect and specific resistance of CFRC in which continuous filament-like CF tows are arranged. show.

CF receipt made from PAN-based HPCF filament CFRC with two layers (CF content 2.2 o 1%)
), the electric field shielding characteristic at 500MHz is 41dB,
The magnetic field shielding characteristic was 24 dB. On the other hand, when pitch-based HPCF is used (CF content 1, 3
volX) is 1.1Ω.

It showed a specific resistivity, an electric field shielding characteristic of 40 dB, and a magnetic field shielding characteristic of 27 dB. Furthermore, PAN-based HPC
CFRC with 4 layers of F (CF content 4, 4v
olX), the specific resistance of cTrI is 0.7Ω, and 57
dB (500MHz> electric field shielding characteristics and 34dB
It exhibited magnetic field shielding properties of ``shielding properties equivalent to those of metals''.

Furthermore, in order to lower the electrical resistivity of CFRC, we use continuous filaments of two types of high-modulus R fibers that have been heat-treated at a high temperature of 2000°C or higher, which has a low electrical resistivity of the carbon fiber itself. Had made. Their electrical resistivity and shielding characteristics are shown at the bottom of Table 3.

CFRC made from PAN-based HMCD filament
exhibited an electrical resistivity of 0.7 Ωm, an electric field shielding characteristic of 44 dB, and a magnetic field shielding characteristic of 45 dB. or,
CFRC made from pitch-based HMCF filament
(CF content 5.0vo1%) showed an electrical resistivity of 0.6 Ω, an electric field shielding property of 60 dB, and a magnetic field shielding property of 45 dB. These values were the highest values during this experiment.

From these facts, the organization, structure, and
1 to 4v by adjusting i fiber length etc.

Despite having a low CF content of about 1%, extremely high electric field shielding and magnetic field shielding properties could be imparted. In addition, the mechanical properties of using the next elementary binder are as follows:
It was about the same level as CFRC using a normal organic binder.

Table 3 Effect of continuous filamentary CF on electric field and magnetic field shielding characteristics (a) F F content (volX) Electric field shielding frequency (MHz) Unit (dB) PAN system (Pσ) 2.2 4.4 Pitch system ( Pσ) 18 PAN system (HMG”) 5.0 Pitch system (■σ) 3.6 5.0 Portland cement (W/C=40%) magnetic field resistivity Tort.

As is clear from the experimental results such as 1000 (Ω-clTl) (500 MHz) or more, CFRC mixed with carbon fiber paper exhibits excellent electromagnetic shielding properties. In this case, the cement used may be ordinary Portland cement, alumina cement, blast furnace cement, etc., and aggregate may also be mixed. By mixing conductive aggregates and fibers such as graphite fine powder,
The electromagnetic shielding properties can be made even higher.

In addition, carbon fiber paper preferably has long fiber length, preferably 5 mm or more, preferably 10 m or more. Incidentally, a continuous filament-like material exhibits the most excellent properties. The amount of carbon fiber paper mixed is not particularly limited, but preferably 0.7 vol% or more.
The carbon a-fiber paper may be either PAN-based or pitch-based, and high-performance returned fibers, high-modulus carbon fibers, and other carbon fibers do not affect electromagnetic shielding, but they must be heat-treated at high temperatures, etc. Carbon lI with reduced electrical resistivity
By using CF paper made of #& fiber,
The electromagnetic shielding effect can be further enhanced. moreover,
Higher electromagnetic shielding can be achieved by using CF paper, which is treated with carbon fa fiber paper at a high temperature of 1000°C or higher, preferably 1500°C or higher, to carbonize or graphitize the organic binder and use it as a carbonaceous binder. produce an effect.

The reason why the resistivity is lowered and the electromagnetic shielding property is improved by the above-mentioned factors is that the number of contact points of the carbon fibers is increased by making the carbon fibers paper-like, and the number of cutting points is decreased due to the length of the fibers. Experimental examples also prove that electromagnetic shielding properties can be improved by imparting conductivity to the carbon fibers and the binder used.

(Effects of the Invention) As described above, according to the present invention, by mixing carbon a-fiber paper into cement,! A cement composite material with high magnetic shielding properties can be obtained.

In addition, by using CF paper as a reinforcing material, CF
The following advantages not available with chopped fiber CFRC can be obtained.

(1) It is strong and lightweight despite its content of /J\.

(2) Good dispersion of CF and good moldability.

(3) Excellent corrosion resistance.

(The deformability is large.

As described above, the CFRC according to the present invention has excellent mechanical properties, which are the most important physical properties as a building material.

As explained above, the CFRC according to the present invention makes it possible to obtain a completely new functional building material. Therefore, the effect can be applied to an extremely wide range of areas such as the external walls of intelligent buildings, structural members of computer rooms, clean rooms, operating rooms, etc., flooring of power plants, substations, power transmission stations, and underground structures of high-voltage transmission towers. have

Claims (4)

[Claims] (1) A cement composite material having electromagnetic wave shielding properties, which is obtained by mixing 0.7 vol% or more of carbon fiber paper with cement. (2) The cement composite material having electromagnetic wave shielding properties according to claim 1, wherein the carbon fiber paper is made of carbon fibers having a length of at least 6 mm or more. (3) The cement composite material having electromagnetic wave shielding properties according to claim 1 or claim 2, wherein the carbon fiber paper is heat-treated at a temperature of 1000° C. or higher. (4) Having electromagnetic wave shielding properties as set forth in claim 1, claim 2, or claim 3, characterized in that conductive aggregate is mixed into cement such as graphite or carbon black. Cement composite.