JPS6145000B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an adsorbent sheet having high adsorption capacity, high degree of homogeneity, substantially no shedding of carbonaceous material, and excellent corrugation processability. Conventionally, sheets with adsorption properties have been known in which powdered or granular activated carbon is contained in paper, nonwoven fabric, etc.; It is hard to get wet and easy to fall off. For this reason, the effective life of the adsorbent sheet is short, and the activated carbon that falls off pollutes the surrounding area and closes the passage for gas, liquid, etc. Furthermore, such a sheet can be shaped into a zigzag shape, for example,
When processing such as processing into corrugated cardboard, the powdered activated carbon has the disadvantage that it becomes even more difficult to fall off. On the other hand, absorbent papers made of activated carbon fibers and other fibrous materials have been proposed as packaging materials for products that emit odors, such as fish, vegetables, or garbage. However, it is only disclosed that when activated carbon fiber is used as an adsorbent, a paper without the adsorbent falling off is obtained due to the intertwining of the fibers, and the applicant of the present application has developed an activated carbon fiber based on the disclosed invention. Adsorbent paper was produced by mixing it with other fiber materials, but the resulting paper was not very homogeneous and did not have excellent workability when it was shaped into a zigzag shape or processed into corrugated board. Moreover, only a paper with a low density can be obtained, and the adsorption capacity of the paper is small, causing problems in use in cases where it is desired to restrict air flow through the paper. In view of the above-mentioned problems, the inventors of the present application have conducted extensive research to obtain an activated carbon fiber sheet that has a high degree of homogeneity, excellent shaping processability, and high density, and as a result has arrived at the present invention. Diameter is 15μ or less, elongation at break (hereinafter referred to as elongation)
(%)/diameter (μ) ratio is 0.1 or more and the average length is
By dispersing activated carbon fibers and other fiber materials in the range of 0.1 to 5 mm in weight ratio in water at a ratio of 1:0.25 to 1:1 and making paper, the activated carbon fibers with excellent shaping processability as the object of the present invention can be obtained. We were able to obtain a carbon fiber sheet. The phenomenon in which carbonaceous material falls off from a sheet containing activated carbon fibers can be broadly classified into the following two types. The first is activated carbon fiber comrades,
Or, because the intertwining with other fibers for mixing is insufficient, carbonaceous material is easily removed from the sheet when the sheet is shaken, gas is passed through it, or the sheet surface is rubbed. This is a case where it falls off. The second case is when the sheet is folded or subjected to strong friction, the activated carbon fibers break and extremely short activated carbon fibers fall off. One way to make such a sheet without shedding of carbonaceous material was to add a large amount of a so-called binder to strengthen the bond between activated carbon fibers or with mixed fibers, but this method According to the method, most of the surface of the activated carbon fibers was covered with the binder, making it impossible to obtain a sheet with the high adsorption capacity aimed at in the present application. Therefore, in order to make a sheet with good adsorption capacity retention and no carbon shedding, activated carbon fibers should be selected so that homogeneous intertwining of activated carbon fibers will occur sufficiently, and the activated carbon fibers should be It has been found that it is essential to choose activated carbon fibers that are resistant to deformation and breakage. In order to ensure that the activated carbon fibers are sufficiently homogeneously intertwined to prevent the first shedding, the fibers must first be easily deformed, and unlike activated carbon fibers, For materials with greater rigidity than raw material pulp,
It has been found that it is particularly important to pay attention to this point. In other words, the diameter and elongation of the activated carbon fibers have a large influence on the appearance of homogeneous entanglement with other activated carbon fibers or mixed fibers, and the smaller the diameter of the activated carbon fibers and the greater the elongation, the more likely entanglement will occur. As a result, carbonaceous material is less likely to fall off from the resulting adsorbent sheet. Next, in order to prevent the second dropout from occurring,
It is preferable that activated carbon fibers are difficult to break when subjected to large deformations, and it has been found that in this case, the ratio of elongation to diameter of activated carbon fibers has a large effect. That is, the smaller the ratio of elongation (%)/diameter (μ), the easier it is to break due to large elongation deformation or bending deformation, and as a result, it becomes difficult to produce a sheet without shedding of carbonaceous material. As a result of various studies, the diameter of activated carbon fibers is 15μ or less, preferably 10μ or less, which is a much smaller value than the natural or synthetic pulp that is the raw material for general paper, and the elongation (%) / diameter (μ) Activated carbon fibers with a ratio of 0.1 or more were required. The elongation of the activated carbon fiber varies depending on the type of raw material and the conditions of the manufacturing process, and can be made up to a maximum of about 3%, but in the present invention, it is preferable to use an elongation of 1 to 2%. The next requirement concerns the average length of the activated carbon fibers. In other words, the longer the average length of the activated carbon fibers, the more intertwining the fibers will have, which may seem advantageous at first glance, but if the average length is too long, the fibers will become entangled with each other, creating a pill-like appearance. As a result, a sheet with a high degree of homogeneity and good texture cannot be obtained. If such pill-like aggregates are present in the sheet, spots of various properties will become extremely large.
For example, there may be unevenness in adsorption capacity, unevenness in ventilation resistance, unevenness in thickness, etc., resulting in various inconveniences. This fluff-like aggregate is generated during the preparation stage of the papermaking stock solution during the wet papermaking process. Once generated, it does not easily disappear and cannot be homogenized even during the dilution process of the papermaking stock solution immediately before papermaking. The occurrence of such fluff-like aggregates is particularly likely to occur in the case of activated carbon fibers, which are the subject of this application, compared to other general fibers or carbon fibers that do not have substantial adsorption ability. This is due to the strong affinity between activated carbon fiber surfaces in an aqueous dispersion system. The occurrence of this fluff-like aggregate of activated carbon fibers is influenced to some extent by the concentration in the paper stock raw material liquid. That is, the lower the concentration, the longer the maximum allowable average length of activated carbon fibers for preventing the formation of pill-like aggregates tends to become longer. Furthermore, the larger the diameter of the activated carbon fibers, the smaller the elongation/diameter, and therefore the harder it is to deform, the longer the allowable maximum average length becomes. In the case of activated carbon fibers having the diameter and elongation/diameter ratio as described above, the average length must be was found to be less than 5 mm. On the other hand, if the length of the activated carbon fibers becomes too short, it becomes difficult to form intertwining between the fibers that is effective in preventing carbonaceous material from falling off, and the escape of activated carbon fibers from the screen during wet paper making becomes difficult. This tends to lead to a decrease in the weight yield of activated carbon fibers, contamination of white water, and a decrease in the strength of the obtained sheet. As a result of the study, it was determined that the average length of the activated carbon fibers should be 0.1 mm or more. Next, the processability of the mixed sheet will be explained.
The mixed sheet, which mainly contains activated carbon with adsorption ability, can be used not only as is, but also by processing it into single-sided corrugated cardboard or shaping it into a zigzag waveform, to further expand its range of applications. known to expand. When this type of shaping operation that is performed on ordinary paper is performed on a mixed sheet mainly made of activated carbon fibers,
In addition to the possibility of shedding of the carbonaceous material, activated carbon fibers are generally highly rigid, so even if the sheet is creased, the mixed sheet will bounce off, for example, once it exits an embossing roller. It becomes difficult to form creases and, as a result, tends to have poor shape retention during shaping. Naturally, the higher the content of the blending fibers, the better the processability, but it was found that at the same content, the shorter the average length of the activated carbon fibers, the better the processability. did. Although it was a secondary benefit, the smaller the diameter of the activated carbon fiber, the more advantageous it was. In the case of a mixed sheet with high adsorption capacity, which is the object of this application, the main component is activated carbon fibers, and the average length of the activated carbon fibers must be 5 mm or less. Regarding the improvement of the processability, in addition to the method proposed in this patent, there is a method in which a thermoplastic binder is mixed, the mixed sheet is heated above the softening point of the binder, and the sheet is forcibly pressed. An attempt was made to obtain a sheet with improved properties, but this method resulted in an extremely low adsorption capacity, making it impossible to obtain a sheet with high adsorption capacity and high processability as the aim of this application. Ta. Another major object of the present invention is to provide a sheet with high density. The density decreases as the ratio of activated carbon fiber increases, and when the ratio of activated carbon fiber and other fibers for mixing is greater than 1:0.25, the density becomes 0.1 g/cc or less, and the adsorption capacity per volume of the adsorption sheet is It becomes something small. The fiber length of the activated carbon fibers has a large effect on the density of the sheet, and even if the ratio of activated carbon fibers is less than 1:0.25, the density of the sheet decreases rapidly when the fiber length of the activated carbon fibers reaches 5 mm. . In order to obtain a sheet of 0.1 g/cc or more, the fiber length must be 5 mm or less. Regarding the adsorption capacity of the activated carbon fiber used in this application, it is preferable that the equilibrium adsorption amount of benzene is 300 mg/g or more. As a result, a mixed sheet with a much higher adsorption capacity than conventional adsorbent sheets, in which the equilibrium adsorption amount of benzene on the mixed sheet is 140 mg/g or more, can be obtained. Activated carbon fibers with such adsorption ability can be used to absorb raw material fibers such as cotton, hemp, wood pulp cellulose regenerated fibers, polyvinyl alcohol fibers, acrylic fibers, aromatic polyamide fibers, lignin fibers, and petroleum pitch fibers into suitable flame-resistant materials. It is manufactured by flame-retardant treatment with a chemical agent and then activated carbonization at a temperature of 500°C or higher. Cellulose fibers, particularly polynosic fibers, are preferred because the activated carbon fibers obtained as raw material fibers have high physical properties (such as elongation). Even if the activated carbon fiber is pre-adjusted to the length within the above range,
Further, a cutting step may be incorporated into the papermaking process. In the latter case, cutting of fibers whose average fiber length is larger than the above-mentioned range can be advantageously achieved, for example, with a beater capable of free beating. In this case, it is preferable to cut the activated carbon fibers in the absence of fibers to be mixed, from the viewpoint of homogeneous dispersion of the activated carbon fibers. Next, the fibers to be mixed with the activated carbon fibers include:
Examples include natural fibers, synthetic fibers, organic fibers, and inorganic fibers. That is, they include natural fibers such as wood pulp, hemp pulp, and liciter pulp, semi-synthetic fibers such as rayon, synthetic pulps such as polyacrylonitrile, polyethylene, and polypropylene, and inorganic fibers such as asbestos fibers. These may be used alone or in combination of two or more. These mixed fibers need to be mixed in a weight ratio of 0.25 to 1.0 times the weight of activated carbon fibers. If the amount of mixed fiber is larger than this, a sheet with the desired high adsorption capacity cannot be obtained, and if the amount of mixed fiber is smaller than this, the mechanical strength of the obtained sheet will be low, which is not practical. . Furthermore, in the papermaking process, various auxiliary agents are used to improve papermaking operability, such as binders to improve the strength of wet paper, polyvinyl alcohol fibers, etc. Adhesives such as polyethylene oxide or polyacrylamide to homogenize the dispersion of carbon fibers and mixed fibers, and fluorine-based auxiliaries to improve the separation of the sheet from the dryer can be added to the sheet raw material liquid. In some cases it may be preferable. A conventional wet papermaking method is applied to obtain the mixed sheet. For example, activated carbon fibers, which have been prepared in advance to the above average length using a Hollender type beater, are disintegrated using a pulper and placed in a mixing tank. Next, the mixed fibers are similarly disintegrated using a pulper and placed in a mixing tank. The concentration of fiber in the mixing tank is usually 0.5
~3%. After adding various auxiliary agents to this mixing tank, the mixture may be filtered through a normal paper-making wire mesh, such as a circular wire mesh or a fourdrinier, and then dried in a Yankee type or multi-barrel dryer. The terms used in the present invention will be explained below. Benzene equilibrium adsorption amount Measure the equilibrium adsorption amount according to JIS K-1412
JIS specifies benzene adsorption power (%),
Change the expression and display it in mg/g. However, the sample
Use 0.1-0.2g. Example 1 The average length is 2 mm, the diameter is 8 μ, the elongation (%)/diameter (μ) ratio is 0.25, and the equilibrium adsorption amount of benzene is 480.
70 kg of activated carbon fiber with a concentration of mg/g was disintegrated in a water dispersion state at a concentration of 1% using a conventional disintegrator and placed in a mixing tank. Next, 30 kg of bleached softwood kraft pulp, which had been previously beaten to a freeness of SR30°, was put into a mixing tank through a disintegrator. A small amount of 7 kg of polyvinyl alcohol fibers, a fluorine-based sizing agent, and a silicone-based antifoaming agent were added to this mixing tank to prepare a stock stock solution having a total fiber concentration of 1%. Next, according to a conventional method, paper was made using a circular steel wet paper machine using polyethylene oxide as a sticky agent to obtain a mixed sheet with a basis weight of 50 g/m ² . The equilibrium benzene adsorption amount of this mixed sheet is 270
Yield of mg/g activated carbon fiber to mixed sheet is 98%
It was hot. Furthermore, no fluff-like aggregates of activated carbon fibers were observed in this mixed sheet, and even when air was flowed through this sheet at a speed of, for example, 50 cm/sec, no carbonaceous material was observed to fall off. No drop-off of carbonaceous material was observed even after this process. The carbonaceous shedding test was evaluated as follows. That is, after attaching an adhesive tape to an adsorption sheet, it was peeled off and the amount of black activated carbon fibers attached to the tape was observed. Separate samples were prepared and the shedding properties were evaluated by comparing them with the test products. Examples 2 to 3, Comparative Examples 1 to 4 Various mixed sheets were obtained in the same manner as in Example 1, except that only the shape and elongation of the activated carbon fibers used in Example 1 were changed. For each mixed sheet, average number of pill-like aggregates present in an area of 10 cm x 10 cm, presence or absence of carbonaceous material falling off when air is flowed through the mixed sheet at a speed of 50 cm/sec, processing of ordinary single-sided corrugated cardboard. At this time, the presence or absence of carbonaceous material falling off and the weight yield of activated carbon fibers into the mixed sheet were measured. The results are shown in Table-1.

[Table] Comparative Example 5 A mixed sheet was obtained in the same manner as in Example 1 except that the shape and elongation of the activated carbon fibers used in Example 1 were changed as follows.

[Table] Regarding this mixed sheet, the average number of pill-like aggregates present in an area of 10 cm x 10 cm, presence or absence of carbonaceous matter falling off when air is flowed through the mixed sheet at a speed of 50 cm/sec, and normal single-sided corrugated cardboard. The presence or absence of shedding of carbonaceous material during processing and the weight yield of activated carbon fibers into the mixed sheet were measured. The results were as follows.

[Table] Example 5 In Example 1, instead of bleached softwood kraft pulp, polyethylene synthetic pulp (Zerapack SWP manufactured by Mitsui Zerapack KK) was used as the mixed fiber.
A mixed sheet was obtained by the same operation except that . In this case, the sheet had a fluff-like aggregate of activated carbon fibers with a homogeneous texture, and no carbonaceous matter was observed to come off. Example 6 Average length 1mm, diameter 8μ, elongation/diameter ratio 0.16
50 parts of activated carbon fiber with an equilibrium benzene adsorption amount of 500 mg/g and 50 parts of bleached softwood kraft pulp with a beating degree of 25°.
A mixed sheet having a basis weight of 30 g/m ² was obtained from the same portion by the wet paper making method as in Example 1. The concentration of fibers in the mixing tank at this time was 2%. In this mixed sheet, no fluff-like aggregates were generated, and there was substantially no shedding of carbonaceous matter. Comparative example 6 Average length 1mm, diameter 16μ, elongation/diameter ratio 0.07
A mixed sheet was obtained in the same manner as in Example 6, except that activated carbon with an equilibrium benzene adsorption amount of 500 mg/g was used. When this mixed sheet was used to process single-sided corrugated cardboard, severe shedding of carbonaceous material was observed.

Claims (1)

[Claims] 1. Activated carbon fibers and other fiber materials with a diameter of 15 μ or less, an elongation (%)/diameter (μ) ratio of 0.1 or more, and an average length of 0.1 to 5 mm in a weight ratio of 1:
A method for producing an adsorbent sheet, which comprises dispersing it in water at a ratio of 0.25 to 1:1 and making paper.