JPS63156541A - Production of absorptive sheet - Google Patents

Abstract

PURPOSE:To enhance the working characteristics, etc., of the title sheet, by adding a binder having ionicity opposite to the polarity of the zeta potential of an inorg. filler to an aq. dispersion slurry of cellulosic fibers, activated carbon powder, and the inorg. filler, and making the slurry into sheet by a wet process. CONSTITUTION:Cellulosic fibers, activated carbon powder, and an inorg. filler are added to water to prepare an aq. dispersion slurry. A binder having ionicity opposite to the polarity of the zeta potential of the inorg. filler is added to the aq. dispersion slurry or a fixing assistant having ionicity opposite to the polarity of the zeta potential of the inorg. filler is added, then a binder having the same ionicity as the polarity of the zeta potential of an inorg. filler is added, and the slurry is made into sheet by a wet process to obtain the adsorptive sheet. An SBR latex, an NBR latex, an acrylic resin emulsion, polyethyleneimine, colloidal silica, etc., are used as the binder.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for producing an adsorptive sheet, and more particularly to a method for producing an adsorptive sheet that is substantially free of asbestos, has processability, and has a high adsorption capacity.

BACKGROUND ART Conventionally, activated carbon powder, activated carbon fibers, etc. have been processed into sheets and used as adsorption materials.

These sheets may be used as they are as adsorbent sheets, but in most cases they are formed into honeycomb structures by corrugating, and used as adsorption devices for separation and recovery of organic solvents; or they are loaded with moisture absorbing agents for dehumidification. It is used as a device or total heat exchanger. In either form of utilization, high adsorption performance per unit volume is required, and for this purpose, first of all it is necessary to contain as much activated carbon as possible.

Other properties required of the sheet include high strength for post-processing such as the corrugating process, and excellent heat resistance. Among these types of sheets, sheets using activated carbon powder are usually dispersed in water together with natural fibers or chemical fibers, and are made using a wet papermaking method by adding a binder such as rubber latex to hold the activated carbon between the fibers. It had been made into paper. For example, JP-A No. 51-29388 describes a paper-making method using a strong cationic polymer electrolyte as a [method for producing activated carbon sheets], and JP-A-53-35712 describes a [method for producing activated carbon sheets]. '', a method of making paper using a combination of anionic polymer and cationic polymer has been disclosed, but in either case, the strength is not strong enough to withstand post-processing such as corrugating, and moreover, the paper does not have high adsorption capacity. No adsorbent sheet with these characteristics has been obtained. In other words, in the past, sheets that used a large amount of binder to increase their strength would have high strength and excellent processing suitability, but would have poor adsorption capacity. Even if we carefully examine the type of binder used, products with a small amount of carbon not only have low strength and lack suitability for processing, but also have a low activated carbon yield of less than 60%, making them difficult to use as adsorbent sheets. There was no sheet that met the two conditions.

In view of the above points, the present inventors have developed an adsorption method that uses a combination of cationic inorganic fibers such as asbestos fibers and anionic binders to provide processing suitability, high adsorption capacity, and a high yield of activated carbon powder. Invented a method for manufacturing adhesive sheets and applied for a patent application in December 1984.
The application was filed as No. 5117. However, in recent years, the use of asbestos has been restricted due to hygiene issues.

Problems to be Solved by the Invention The present inventors have conducted various studies to solve the above-mentioned problems. As a result, the inventors have developed a method to improve processing suitability by using an inorganic filler and combining it with a binder by utilizing its zeta potential. The present inventors have discovered that it is possible to make paper sheets that have high adsorption capacity and a high yield of activated carbon without containing asbestos, and have completed the present invention based on this fact.

Means for Solving the Problems The gist of the present invention is to adjust the zeta potential of the inorganic filler when dispersing cellulose fibers, activated carbon powder, inorganic filler, and binder in water so that the binder is significantly more concentrated in the inorganic filler than the activated carbon powder. The present invention relates to a method for producing an adsorbent sheet, which comprises producing unevenly distributed slurry and subjecting the slurry to wet paper making.

The activated carbon powder used in the present invention not only has high adsorption capacity but also has performance as a carrier for catalysts and catalysts, and usually has an average particle diameter of less than 100 mesh.
Particularly favorable results are obtained with those having an average particle diameter of 50 to 325 meshes. Activated carbon powder with an average particle size larger than 80 mesh tends to sink to the bottom in the slurry, making it impossible to form a uniform sheet.
The activated carbon powder may also fall off the sheet.

On the other hand, if the particle size becomes too small, the yield in the sheet will be poor, and the activated carbon surface will be more likely to be clogged with binders and impurities, resulting in a decrease in the adsorption performance of the sheet.

The cellulose fiber used in the present invention is KP.

Examples include wood bulbs such as SP and GP, and Vi physical fibers such as hemp and cotton linter regenerated cellulose short fibers. In order to increase the yield of activated carbon powder etc. during paper making, the above 1.
! It is preferable to use the fiber after beating it with a beater or the like. If beating is not performed, it is preferable to use a fiber having a short length such as LBKP.

In the present invention, examples of inorganic fillers include kaolinite, kaolin, kaolin clay, and calcined clay.

Halloysite, sericite, shirasu, waxite, gicrite, vermiculite, perlite, diatomaceous earth, talc-7wolastonite, bentonite, cristobalite, gypsum, calcium carbonate.

Magnesium carbonate, titanium dioxide (rutile, anatase), zinc sulfide, zinc white, aluminum silicate, calcium silicate, magnesium silicate, fibrous magnesium silicate, fibrous potassium titanate, aluminum hydroxide,
One or more natural or synthetic inorganic fillers such as magnesium hydroxide are used.

Any of these inorganic fillers can be selected and used as appropriate, but if the inorganic filler and activated carbon powder have the same zeta potential when using only the binder or when adding a fixing aid to the binder, the result will be the desired one. This may cause uneven distribution of the binder, resulting in poor adsorption performance of the sheet. In this case, it is generally necessary to adjust the zeta potential of the inorganic filler by adjusting the pH, and since activated carbon powder usually has a negative zeta potential, the zeta potential of the inorganic filler is more than 10 mV more negative than the activated carbon. Preferably, the voltage is at a potential. Note that the zeta potential of activated carbon powder differs depending on the raw material and pH before carbonization treatment, so care must be taken when adjusting.

Furthermore, if an inorganic filler with a fibrous or acicular crystal structure, such as fibrous potassium titanate, fibrous magnesium silicate, or acicular calcium silicate, is used, the suitability of the slurry for papermaking will increase, and the strength of the sheet will increase. Improves processing suitability.

As the binder in the present invention, SBR latex, N
Liquid materials include organic polymer emulsions such as BR latex and acrylic resin emulsions, organic polymer electrolytes such as polyethyleneimine, polyacrylamide, and polyurea polyamide condensed metals, and inorganic colloidal liquids such as colloidal silica and colloidal alumina. .

Powdered organic binders such as starch and polyvinyl alcohol powder, and heat-melting fibrous binders such as vinylon fibers and polyethylene fibers can also be used as long as the purpose is not impaired.

Example Next, the present invention will be explained in detail.

In the production method of the present invention, cellulose fibers, activated carbon powder, and inorganic filler are dispersed in water to create a slurry (hereinafter referred to as base material dispersion slurry), and the polarity of the zeta potential of the inorganic filler is changed to the opposite ionicity. or by adding a fixing aid having an ionicity opposite to the polar zeta potential of the inorganic filler, and then adding a binder having an ionicity of the same polarity as the zeta potential of the inorganic filler. This is a method for producing an adsorbent sheet using a wet papermaking method, and this method can be divided into the following two methods depending on the polarity of the inorganic filler.

(a) In the normal case where the cellulose fibers, activated carbon and inorganic filler in the base material dispersion slurry all have negative zeta potential,
The inorganic filler is preferably adjusted to have a zeta potential of 10 mV or more more negative than the zeta potential of activated carbon, and then a cationic binder is added thereto, or a cationic fixing aid is added, and then an anionic zeta potential of the anion is added. A method of adding a binder and making paper using a wet papermaking method.

(b) If the cellulose fibers, activated carbon, and inorganic filler in the base material dispersion slurry all have a positive zeta potential, the inorganic filler is adjusted to have a potential of +5 mV or more than the others, and then the anion is added to the inorganic filler. A method in which an anionic binder is added, or an anionic fixing aid is added, and then a cationic binder is added, and the paper is made using a wet papermaking method.

It goes without saying that if the zeta potential of the inorganic filler satisfies each of the above conditions at the stage of adjusting the base material dispersion slurry, no further adjustment operation is required.

Examples of the anionic binder used in this production method include anionic organic polymer emulsions such as SBR latex, NBR latex, natural rubber latex, anionic acrylic resin emulsion, and vinyl acetate resin emulsion;
Examples include anionic inorganic colloidal liquids such as colloidal silica, anionic organic polymer electrolytes such as polyacrylamide, polyamide, and sodium polyacrylate.

The cationic binder is a cationic organic polymer emulsion such as an acrylic resin emulsion.

Examples include polyurea polyamide condensates, cationic organic polymer electrolytes such as polyethyleneimine, and cationic inorganic colloidal liquids such as colloidal alumina. When used alone as an anionic binder or a cationic binder, an emulsion type binder is preferably used. Furthermore, at present, there are more types of anionic binders than cationic binders, and the range of selection is wider.

Examples of the anionic fixing aid used in the production method of the present invention include the above-mentioned anionic inorganic colloidal liquids such as colloidal silica, the above-mentioned anionic organic polymer electrolytes such as polyacrylamide, and the like. As the cationic fixing aid, fjiER ferric iron is used.

Polyvalent metal salts such as ferric chloride, Fifr, acid aluminum, aluminum chloride, polyaluminum chloride.

Examples include the above-mentioned cationic organic polymer electrolytes such as polyurea polyamide condensates, the above-mentioned cationic organic polymer emulsions such as cationic acrylic resin emulsions, and the above-mentioned cationic inorganic colloidal liquids such as alumina sol. Note that it is preferable that the fixing aid has a high charge density.

Although the mechanism of binding and aggregation of the binder in the present invention has not been completely elucidated, it is presumed as follows. In other words, when a binder with an opposite charge to the inorganic filler is added,
As mentioned above, since the zeta potential of the activated carbon and the inorganic filler is large, more of the binder is electrostatically attracted to the inorganic filler, and the electric double layer of the two is neutralized and fixed. In other words, it is considered that the larger the absolute value of the zeta potential of the base material dispersed slurry, the more the binder will be fixed, and therefore the binder will be unevenly distributed as desired.

For example, the zeta potential of an inorganic filler is -30 mV.

If a cationic binder is added to the slurry adjusted so that the zeta potential of the valve is -25 mV and the zeta potential of activated carbon is -15 mV, the largest amount of the binder will settle on the inorganic filler, and the zeta potential of the valve and activated carbon will be 15 mV. More binder is fixed in this order.

Since the absolute value of the zeta potential of activated carbon is smaller than that of inorganic fillers and cellulose fibers, the charge is neutralized by fixation of a small amount of binder, and no further binder is fixed, resulting in no bonding on the activated carbon surface. With only small amounts of binder fixed, these substrates form aggregates sufficient for papermaking. Although the adsorption capacity of activated carbon is slightly reduced due to the fixation of the binder, since the amount of fixation is small, the purpose of the adsorption sheet is not impaired.

In other words, by appropriately stirring the slurry when adding the binder, the inorganic filler, activated carbon, and cellulose fibers are physically attached to each other by the fixed binder, and are bonded more strongly than before to form aggregates suitable for paper making. Therefore, the amount of activated carbon flowing out through the paper screen during paper making is small, and the yield is improved. Furthermore, it has the strength of wet paper necessary for continuous production using a paper machine, so continuous productivity is high.

In addition, in the manufacturing method using a fixing aid, as mentioned above, when the charge on the particles is neutralized, the concentration of the fixing aid is higher in the surrounding areas, even though the absolute value of the zeta potential is large, so the fixing aid added afterwards The binder, which has an opposite charge to the auxiliary agent, is attracted to the inorganic filler and cellulose fibers, and is fixed by the action of the fixing auxiliary agent. As a result, an adsorbent sheet with processability and high adsorption capacity can be produced at a high yield, similar to the production method that does not use a fixing aid.

The zeta potential of the cellulose fibers, activated carbon, inorganic fillers, etc. used in the production method of the present invention varies depending on the measurement method, material, shape, and size, and also changes depending on the pH and the presence or absence of coexisting ions, but it is approximately as follows. It is as follows. -2mV to -40mV for activated carbon, 0 to -5 for bulb
0 mV, inorganic filler, for example, kaolin clay +3
0 to -40 mV, talc 30 to -30 rn V,
Aluminum hydroxide +10 to +2 mV, calcium carbonate -5 to -25 mV, aluminum silicate +40 to -4O
mV, calcium silicate +20 to -30 mV.

Titanium dioxide 0~-20mV, magnesium silicate +1
0 to +2 mV, magnesium carbonate +10 to -25 mV,
Zinc sulfide +30 to -25 mV, gypsum +5 to -10 mV,
Magnesium hydroxide is +15 to +2 mV. When implementing the present invention, the value of the zeta potential of each material may be measured under the actual conditions or a certain condition close thereto, and this value may be used.

Among these, there are some, such as kaolin clay, whose charge changes between positive and negative depending on the pH, but papermaking at extremely high or low pH is undesirable due to problems with wastewater treatment5) (Since paper is made at about 4 to PI (10), it is recommended to use the aforementioned zeta potential in that PH range,
Furthermore, when adjusting PHt, the relationship between zeta potential and PH changes depending on the type of PH preparation, so careful consideration is required. Furthermore, if necessary, it is also useful to adjust the pH again after adding the binder.

The blending ratio of each component in the present invention is that the essential components are 2 to 30 parts by weight of cellulose fiber, 90 to 30 parts by weight of activated carbon powder, and 5 to 68 parts by weight of inorganic filler, with a total of 100 parts by weight, and the liquid 2 to 25 parts by weight of the binder as a solid content, and 0.01 to 0.01 parts by weight as a solid content when using a fixing aid.
Use 15 parts by weight. At such a blending ratio, good processing suitability can be obtained. Although it depends on the use of the obtained sheet, it is preferable that the activated carbon powder is contained in the solid content of the sheet in an amount of 45% by weight or more, more preferably 60% by weight or more.

Further, other additives may be included within the range that does not impair the purpose of the present invention. For example, inorganic fibers such as glass fibers are used to improve the heat resistance and dimensional stability of sheets.
Depending on the temperature conditions, synthetic fibers may be used, or to increase strength, powdered organic binders such as starch or polyvinyl alcohol powder, or heat-melting fibrous binders such as vinylon fibers, polyethylene fibers, or acrylic fibers may be used. It is also effective. In addition, if flame retardancy is required for the sheet, flame retardancy can be improved by adding flame retardant synthetic fibers such as vinyl chloride or vinylidene chloride. If there is a process,
By blending heat-resistant synthetic fibers such as phenolic fibers, aromatic holamide fibers, and aromatic polyester fibers, the shape of the sheet after firing can be maintained and a good shape can be obtained.

Since the adsorbent sheet obtained as described above has high strength, post-processing such as corrugating is easy, and the productivity of honeycomb structures can be significantly increased. Utilizing its adsorption action, it is extremely effective as an adsorption device for the separation and recovery of organic solvents, as a carrier for various catalysts, and as an element in dehumidifiers and total heat exchangers, and is not sanitary. Because it does not contain any asbestos, it has a wide range of uses, including being used as elements in various air conditioning equipment such as air purification equipment and exhaust gas purification equipment, and does not generate asbestos dust when disposed of or incinerated after use. , has become very useful.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. In the Examples and Comparative Examples, parts refer to parts by weight of solid content unless otherwise specified, and the zeta potential of each substance was measured by microelectrophoresis.

Implementation Ml Cellulose fiber (LBKP valve) 15 parts, benzene adsorption amount 45g/100g, adsorption surface top 1700m"/g,
After dispersing 50 parts of coconut shell activated carbon with an average particle size of 7 μm and 35 parts of talc in water, the pH of the slurry was adjusted to 9.0 using sodium hydroxide, and LBKP was −15 mV and activated carbon −11 mV.

Talc was adjusted to have a zeta potential of 34 mV. Then aluminum sulfate 3.0 as a cationic fixing aid.
After that, 6.0 parts of SBR latex was added as an anionic binder and fixed, hand-sheeted using an 80-mesh mesh, and dried to obtain an absorbent sheet with a thickness of about 0.25 mm. .

Example 2 20 parts of cellulose fiber (NBKP bulb), 60 parts of the same activated carbon as used in Example 1, and 20 parts of kaolin clay were dispersed in water. The pH of the slurry is 8.6
The zeta potentials were respectively -14 mV for NBKP, -10 mV for activated carbon, and 44 mV for kaolin clay.

After adding 2.0 parts of cationic epoxidized polyamide resin as a cationic fixing aid, 8.0 parts of anionic acrylic resin emulsion was added as an anionic binder.
The mixture was fixed by adding a portion of the mixture, hand-sheeted using an 80-mesh mesh, and dried to obtain an absorbent sheet.

Example 1'M3 10 parts of cellulose fiber (LBKP), 75 parts of the same activated carbon used in Example 1, 15 parts of talc, and in addition to these essential components, glass fiber (6μx6mm'>3 parts,
After adding 8 parts of flame-retardant acrylic fiber and dispersing it in water, the pH of the slurry was adjusted to 9.5 using sodium hydroxide, and the zeta potential of the slurry was adjusted to LBKP-16mV, activated carbon-13mV, and talc-37mV. It was adjusted. after that,
1.6 parts of aluminum sulfate and 1.1 parts of colloidal alumina were added as cationic fixing aids, and then 7.5 parts of NBR latex was added as an anionic binder for fixing. It was made into a paper using a paper machine and dried to obtain an absorbent sheet.

Example 4 7 parts of cellulose fiber (LBKP), 75 parts of the same activated carbon as used in Example 1, 18 parts of fibrous potassium titanate, and in addition to these essential components, glass fiber &i (6 μX
6mm) 3 parts, phenolic synthetic fiber (2dX6mm)
After adding 8 parts of the slurry and dispersing it in water, the pH of the slurry was adjusted to 9.0 using sodium hydroxide, and LBKP-15mV
, activated carbon was adjusted to have a zeta potential of 11 mV, and potassium titanate was adjusted to have a zeta potential of 25 mV. To it was added 4.4 parts of etherified starch as a powdered organic binder, then 2.2 parts of aluminum sulfate and 1.5 parts of colloidal alumina as a cationic fixing aid, and then anionic acrylic as an anionic binder. Resin emulsion7.
7 parts were added and fixed, and paper was made using a cylinder paper machine using a 60-mesh mesh, and dried to obtain an adsorption sheet.

Example 5 7 parts of cellulose fiber (LBKP), 50 parts of the same activated carbon as used in Example 1, 40 parts of m-male magnesium silicate, and in addition to these essential components, glass fiber (6 μx
6mm>3 parts were added and dispersed in water. PH of slurry
is 8.8 and the zeta potential is LBKP-14m, respectively.
V, activated carbon -11mV, fibrous magnesium silicate +4
It was mV. Thereafter, 4.5 parts of anionic acrylic resin emulsion was added as an anionic binder, the pH was adjusted to 5.1 using colloidal alumina, the paper was made using a Fourdrinier paper machine using a 60-mesh mesh, and dried to obtain an adsorbent property. Got a sheet.

Comparative Example 1 50 parts of the same activated carbon used in Example 1 and 50 parts of cellulose fiber (NBKP and LBKP mixed in a ratio of 1=1) were dispersed in water, and 1.0 part of cationic epoxidized polyamide resin and polyamide were dispersed in water. 1.0 part of acrylamide resin was added, and the mixture was hand-sheeted using an 80-mesh screen and dried to obtain an absorbent sheet.

Comparative Example 2 After dispersing 15 parts of natural cellulose fiber (LBKP), 50 parts of the same activated carbon as used in Example 1, and 35 parts of calcium sulfate in water, the pH of the slurry was adjusted to 8.5 using sodium hydroxide. The zeta potential was LB K P -14 mV and activated carbon -10 mV, respectively.
V, calcium sulfate - 7 mV. 3.0 parts of aluminum sulfate was added as a cationic fixing aid, and then 7.0 parts of SBR latex was added as an anionic binder for fixation, and a net of 80 mesh was formed. An absorbent sheet was obtained by hand-sheeting and drying.

Example 6 After dispersing 15 parts of cellulose fiber (NBKP), 50 parts of the same activated carbon used in Example 1, and 35 parts of talc in water, the pH of the slurry was adjusted to 9.0 using sodium hydroxide. NBKP-15mV, activated carbon-11
mV, talc was adjusted in the evening to have a zeta potential of -34 mV.

Thereafter, 4.0 parts of a cationic acrylic resin emulsion was added as a cationic binder and fixed, hand-sheeted using an 80-mesh mesh and dried to obtain an absorbent sheet.

Example 7 15 parts of cellulose fiber (NBKP), 50 parts of the same activated carbon as used in Example 1, and 35 parts of fibrous magnesium silicate were dispersed in water.

The pH of the slurry is 8.5, and the zeta potential is NBKP -14 mV and activated carbon -10 mV, respectively.

Fibrous magnesium silicate +4 mV. Thereafter, polyacrylamide resin 1.
After adding 5 parts, 5.0 parts of cationic acrylic resin emulsion was added as a cationic binder and fixed.
It was hand-sheeted using an 80-mesh mesh and dried to obtain an absorbent sheet.

Table 1 shows the results of measuring various physical properties for each of the adsorbent sheets obtained above.

(The following is a blank space) In Table 1, the shape retention after firing was determined as follows. That is, a cylinder with a diameter of 30 mm and a height of 30 mm was made from the absorbent sheet obtained above, the ends were slightly overlapped and stapled together, the pieces were placed upright on a table, and a 10 gr iron plate was placed on top of the cylinder. After placing it evenly, it is baked at 400°C for 20 minutes. Thereafter, the shape retention of the fired molded product is determined by the degree of deformation caused by the load. After firing, the degree to which the original shape of the molded product was retained was determined based on the following criteria.

◎...The molded product is not deformed.

O: The molded product is slightly deformed.

×...The molded product is completely deformed.

Furthermore, the strength of the honeycomb molded bodies in Table 1 was measured as follows. That is, the adsorbent sheets obtained in each of the Examples and Comparative Examples were processed into a single piece of cardboard with a flute diameter of 1.5 mm using a corrugated film forming machine, and this was formed into a cubic honeycomb in which the wave direction of the −50 mm side was the same. processed into the body.

As shown in the drawing, this honeycomb molded body is
Apply compressive force to the entire side surface in direction a) and direction b),
Find the pressure required for deformation to occur. Moreover, flammability is the result of placing the obtained adsorbent sheet in a flame and determining the degree of combustion.

[Brief explanation of the drawing]

The drawing is an explanatory view showing the compression direction when measuring the strength of a honeycomb molded body obtained by corrugating the adsorbent sheet of the present invention.

Claims (6)

[Claims] (1) Cellulose fibers, activated carbon powder, and inorganic filler are dispersed in water to make a slurry, and a binder having an ionicity opposite to the zeta potential polarity of the inorganic filler is added, or the zeta potential of the inorganic filler is A fixing aid having an ionicity opposite to the polarity of the electric potential is added, and then a binder having an ionicity having the same polarity as the zeta potential of the inorganic filler is added, and the paper is made by a wet papermaking method. A method for manufacturing an absorbent sheet. (2) Disperse natural cellulose fibers, activated carbon powder, and inorganic filler in water to make a slurry, adjust the inorganic filler to have a negative zeta potential, and then add a cationic binder to the slurry. Alternatively, the method for producing an adsorptive sheet according to claim 1, characterized in that after adding a cationic fixing aid, an anionic binder is added and the resulting paper is made by a wet papermaking method. (3) The method for producing an adsorptive sheet according to claim 2, wherein the paper is made so that the zeta potential of the inorganic filler is 10 mV or more more negative than that of activated carbon. (4) The method for producing an adsorptive sheet according to claim 1, wherein the inorganic filler is fibrous or acicular. (5) Cellulose fibers, activated carbon powder, and inorganic filler are dispersed in water to make a slurry, and after adjusting the inorganic filler to have a positive zeta potential, an anionic binder is added thereto or an anionic binder is added thereto. 2. The method for producing an adsorbent sheet according to claim 1, which comprises adding a cationic binder after adding a fixation aid, and then making the paper by a wet papermaking method. (6) The method for producing an adsorptive sheet according to claim 5, wherein the paper is made by adjusting the zeta potential of the inorganic filler to be at least +5 mV higher than that of activated carbon.