Supported three-dimensional arrangement of particles

(54) Description Process for the preparation of a particle-containing fibrous sheet product (56) Published publications: US 3,801,400

Other publications: Tappi Vol 56 no. 4 p 74-77 .11 Ι / -Γ lza ΙΝίΠΛηΗ Rokstav mom squeezes anaer tntema ^ unei. ' document code

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The present invention has its roots in the deficiencies of the prior art in presenting a mass of discrete particles for interaction with a medium. A particular example of these deficiencies is respirators. A current, commercial face mask for removing harmful vapors from the air includes a porous nonwoven sheet in which alumina particles are dispersed (the alumina particles have been introduced in the form of a cascade into a fluffy nonwoven web of staple fibers, which webs are made by rubbing web or the sheet is then compressed and cut into sheets of the desired shape, whereupon the edges of the cut sheets are heat sealed together). Although the mask is effective in removing the harmful vapors, the life of the mask is shorter than desired.

The short life span of this face mask has been found to be due to difficulties in achieving and maintaining a uniform distribution of particles. Initially, it is difficult to obtain a uniform distribution of particles by introducing them in the form of a cascade into a fluffy nonwoven web of staple fibers. In addition, it is believed that the particles inside the finished sheet migrate through the space of the fibrous web as a result

7500253-5 by normal operation or vibration of the mask or as a result of air flow through the mask. The result is that thin spots develop in the collection of particles. Eventually, a breakthrough of harmful vapors occurs at the thin spot, and the effective life of the mask is over. Although the weight of the alumina particles could be increased to extend the life of the mask, such a change would also increase the static pressure of the mask (ie the pressure drop through the mask), and breathing through the mask would be more difficult.

The described technique for supporting particles for interaction with a medium is only one example among many that have been proposed or used, but generally all of the previous solutions require some unsatisfactory compromise in properties. Some solutions require an undesirably high static pressure or pressure drop (such as in packed beds of the particles, which otherwise have maximum exposed surface area, or such as when particles are impregnated in or coated on fiber-containing paper; see U.S. Patents 328,947 and 3,158,532 ). Some solutions require too many constituents in addition to the particles themselves (such as binder materials, finishing agents and other additives), which limit the usefulness of the products due to the chemical or other properties of the added constituents (see U.S. Patents 2,369,462 and 3,745,060). Some solutions require that some of the reactive surface of the particles be covered and therefore reduce the efficiency of the particles, such as when binder materials are used to secure the particles in place in a floor or to each other (see U.S. Pat. Nos. 3,801,400, 3,745,060, 3,615,995, 2,988,469 and 3,474,600).

And some solutions require intricate and expensive supporting apparatus, such as in packed beds of the particles or in certain mixtures of fibers and particles (see U.S. Pat. No. 3,083,157). Although each of the solutions described has its own use and its own advantages, the deficiencies, including those stated above, lead to a need for a new, superior technique for supporting a particle mass.

The present invention provides a process for producing a porous sheet product containing a new, supported, three-dimensional arrangement of particles. This product, in which substantially the entire surface area of ​​the particles is available for interaction with a medium to which the sheet product is subjected, includes a

7500253-5 webs of melt-blown microfibers (very fine fibers made by extruding molten, fiber-forming material through fine openings in a nozzle into a high-velocity gas stream) and the particles themselves. No additional binder material is necessary to attach the particles to the fibers. Nor do the particles adhere to the fibers due to their tackiness.

More particularly, the invention relates to a process for producing a fibrous sheet product consisting essentially of a web of meltblown microfibers and solid particles dispersed in the web which are intended for chemical or physical interaction with a medium to which the product is subjected, e.g. polymer is extruded through fine nozzles into a nozzle into a high velocity gas stream and the solid particles are introduced into the gas stream; and the method is characterized in that the mixing of the particles into the gas stream without the addition of binder takes place at such a distance from the nozzle that the microfibers formed there have become tack-free so that the particles, which constitute at least 20% by volume of the solids content of the web, are retained in the floor. solely through point contacts between the microfibers and the particles so that substantially the entire surface of the particles is exposed for interaction with the medium.

Further features of the invention are apparent from the following, independent claims.

The particles are retained in the surface despite the fact that the melt-blown microfibers have no more than point contact with the particles (point contact occurs when preformed bodies bump into each other. This differs from surface contact obtained when a liquid material is deposited on a substrate, overflowing the substrate and then hardens into place). The full explanation of this retaining effect is not known. One factor is that the particles in a sheet product made according to the invention are usually large enough to be physically trapped in the space of the web. Because microfiber webs have small spaces and because the particles are introduced into a web during formation of the web, the particles are usually well trapped and enclosed by the microfibers.

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However, particles that are not physically trapped in the space of the web are also physically retained in the web. This retention action obviously occurs due to the unique nature of the melt-blown microfibers. Their fine size allows a limited volume of fiber material to have a large number of contact points with the particles. Furthermore, the adaptability of the microfibers favors such contacts which produce strong surface attracting forces.

Whatever the explanation, stunning results are possible. Sheet products can be made according to the invention in which over 99% by volume of the solids content of the web are particles (by solids content is the proportion of the web which is physically occupied by a tangible object, such as microfibers or particles, and does not include voids between particles or fibers). Despite the high particle contents, the sheet products have low pressure drops and other useful floral properties, including good durability.

It has previously been proposed to incorporate particulate material into a microfibre web, but generally these proposals have required the fibers of the web to be sticky to hold the particles in place (see the aforementioned patents 3,801,400, 3,615,995 and 2,988 469). It has also been proposed to add probably small amounts of particles, which modify the properties of the microfiber flora (see RR Buntin and DR Lohkamp, ​​Melt-Blowing— A One-Step Web Process for New Nonwoven Products, TAPPI, vol. 56, no. 4, p 74-77, which was reportedly presented as a lecture on October 24-25, 1972 and which briefly proposes that powder or spray solutions which cannot be extruded, such as fire retardants or wetting agents, are added directly at the time of the floral formation ).

None of these known methods meets the need for improved kinds of supported three-dimensional arrangement of particles, as evidenced by the deficiencies of the known breathing apparatus described above. Prior to the time of the present invention, as far as is known, it is not known that large particle volumes can be introduced in a durable, uniform manner into a melt-blown microfibre web without adhering the particles to the microfibers using a binder material or using tacky fibers. with hardly any increase at all in the pressure drop as a result of the presence of the particles, and during retention

7500253-5 of other useful flora properties. The uniformity of the particle load is selected. is also obtained with small particles, which means large usable surface area, and because of the durable uniformity, thin sheet products according to the invention will also have a long useful life.

The uniformity of the particle distribution is indicated by a test for the removal of noxious vapors (the term uniformity used here means that adjacent cubic centimeters of continuous web have substantially the same number of particles and the term does not refer to the precise regularity of a crystal structure). When, for example, a 171 cm² sample of a sheet product consisting of a web, which per cm² contains 0.004 g of meltblown polypropylene microfibers having an average diameter of 5 µm and alumina particles having an average diameter of 120 µm, the alumina particles being about 25% by volume of the solids content of the flora, being exposed to dry air at an amount of 16 l / min, which air contains 33 million parts (ppm) of hydrofluoric acid, less than 5 ppm of hydrofluoric acid breakthrough is obtained until at least about 4 hours have elapsed. To achieve a corresponding breakthrough time using the above-described commercial face mask with its bed of alumina particles arranged on the inside of a nonwoven sheet, typically more than a two-fold increase in the number of particles would be required. This would increase the cost of the mask, result in less efficient use of the particles and increase the pressure drop across the mask.

Such uniformity in combination with the other useful properties of the sheet products produced in accordance with the invention results in a wide usefulness in addition to air purification. Nothing in the prior art has allowed for the increased utility of supported, three-dimensional arrangement of particles provided by the present invention.

In the drawings, Figure 1 shows a schematic view of an apparatus used to practice the present invention. Fig. 2 is a greatly enlarged cross-sectional view of a portion of a sheet product made in accordance with the invention. Fig. 3 is a diagram showing the results of tests of sheet product samples, the ordinate referring to ppm toluene vapor and the abscissa minutes.

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The appliances, soaps. used in the practice of the present invention, is shown schematically in Figure 1 and is generally in the form of the apparatus described in Wente, Van A., Superfine Thermoplastic Fibers in Industrial Engineering Chemistry, Vol. 48, ρ. 1342 et seq. (1956), or in Report No. 4364 of the Naval Research Laboratories, published May 25, 1954 entitled Manufacture of Superfine Organic Fibers of Wente, VA; Boone, CD; and Fluharty, EL The apparatus shown comprises two nozzles 10 and 11, which comprise a set of aligned parallel nozzle openings 12 through which the molten polymer is extruded, and co-operating air openings 13 through which heated air is forced at very high speed. The air draws out and dilutes the extruded polymer material and after moving a short distance in the gas stream, the extruded material solidifies into a mass of microfibers. In accordance with the present invention, preferably two nozzles are arranged which are arranged so that the streams 14 and 15 of microfibre exiting the nozzles intersect to form a stream 16 which proceeds to a collector 17. The latter may take the form of a fine perforated, cylindrical screen or drum, or a moving belt. The collected microfibre web 18 is then fed from the collector and wound into a bearing roll.

According to the invention, a stream of particulate material is introduced into the stream of microfibers prior to the collection of the microfibers on the collector. Preferably, a single stream 20 of particles is arranged between the two nozzles 10 and 11, as shown in Fig. 1, and the particle stream 20 intersects the two streams of microfibers at the intersection of the latter. Such an arrangement is assumed to give maximum particle load in a microfiber floor. Alternatively, a solitary nozzle may be used, whereby one or more particle streams are arranged to cut the stream of microfibre exiting the nozzle. The streams of microfibers and particulate matter may move in horizontal paths, as shown in Fig. 1, or may move vertically so as to be substantially parallel to gravity.

Once the particles have been enclosed in the microfibre streams, the process of the invention for making sheet products is substantially the same as the process for producing other microfibre webs, and the collectors, the methods of collection and methods.

The means for maintaining the collected web are generally the same as those used to produce non-particle laden, melt-blown microfibre webs. Maximum order of magnitude and uniformity with respect to particle loading or content is generally obtained by multilayer deposition methods, especially when the layers are laterally displaced relative to each other. In one embodiment of the invention, for example, the nozzles 10 and 11 and the nozzle 27 are moved perpendicularly to the width of the collecting drum to form a helical or helical deposit on the drum. The transverse movement is slow enough that successive layers of fibers and particles deposited during different rotational turns of the drum are partially overlapped.

According to the invention, the layer of fibers and particles formed at one turn as well as the complete sheet product can vary in thickness within wide limits. According to the invention, a thickness of 0.05-3 cm is used for most uses for the sheet products. In the case of respirators according to face masks, the thickness is generally about 0.05-1.5 cm, and when particularly low pressure drops are of importance, the thickness is preferably less than about 0.3 cm. For some applications, two or more, separately formed, particle-loaded webs may be assembled into a thicker sheet product.

In the embodiment shown in Fig. 1, the apparatus for feeding particles into the stream of microfibers comprises a funnel 22 for storing the particles, a measuring device 23, such as a solenoid valve or a measuring device according to US Patent 3,661,302, which feeds particles. in a conduit 24 in a predetermined flow, an air fan 25 which forces air through a second conduit 21 and thereby draws particles from conduit 24 into the second conduit 26, and a nozzle 27 through which the particles are ejected as a particle stream 20. The nozzle 27 may be formed by, for example, flattening the end of a cylindrical tube to create a wide, thin opening. The amount of particles in the particle stream 20 is controlled by the Juft flow through the conduit 26 and by the particle flow discharged by the measuring device 23.

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The invention is useful for generally supporting any kind of solid particle which can be dispersed in an air stream (the term solid particle used herein refers to particles in which at least one outer shell is solid, as opposed to liquid or gaseous). A wide variety of particles have utility in a three-dimensional arrangement in which they can interact with (e.g., chemically or physically react with or bring into physical contact with and modify or modify by) a medium to which the particles are exposed. According to the invention, more than one kind of particles is used in certain sheet products either in blending or in different layers. Air purification devices, such as breathing apparatus, in which the particles are intended for filtration or purification purposes, constitute a major and important use of the sheet products made according to the invention. Typical particles for use in filtration or purification devices, including activated carbon, alumina, sodium bicarbonate and silver particles, which remove a constituent from a fluid by adsorption, chemical reaction or amalgamation; or such particulate catalytic agents as aggregate, which catalyze the conversion of a noxious gas into a harmless form and thus remove the noxious constituent. In other embodiments of the invention, the particles supply rather than remove a component with respect to the medium to which the particles are exposed.

The particles can vary in size, at least from 5 µm to 5 mm in average diameter. Most often the particles are between 50 microns and 2 microns in average diameter. For respirators, the average diameter of the particles is generally less than 1 mm. When the average diameter of particles incorporated into a sheet product made according to the invention is at least as large as the gap between the microfibers in the microfiber floor (which gap in a non-particle web generally amounts to about 4 or 5 times the average diameter of the microfibers), the web is opened by the presence of the particles so that a greater volume between the fibers is obtained. This opening creates a potential for more contact between fibers and particles, so that a larger volume of particles can be incorporated into the floor. In addition, the fact that the particles are, on average, as large as the gap contributes to improved physical trapping of the particles. In most webs prepared according to the invention, the particles are the means

7500253-5 diameter at least 5 times the average diameter of the microfibers and preferably at least 10 times the average diameter of the microfibers.

Fine particles having an average diameter smaller than the average gap between the microfibers and ultrafine particles having an average diameter smaller than the average diameter of the microfibers can also be incorporated into the sheet products of the invention. Smaller particles generally open a web into which they are introduced, smaller than large particles, and fine and ultrafine particles are generally incorporated into a web at smaller levels than larger particles. Fine and ultrafine particles are sometimes incorporated into batches of large particles, either intentionally to obtain a desired mixture of particle sizes or because they are supported on larger particles as a result of particle-particle interaction. Microphotograms of some sheet products made according to the invention show how ultra-fine particles cover the microfibers. These particles obviously adhere to the microfibers due to Van der Waalska forces and the like. Upon tearing the sheet product and vigorously washing the fibers, the particles are removed. After removal, there are no marks in the fibers, which indicates that the particles are not wetted by the fibers.

As noted earlier, a significant advantage of the invention is the ability to arrange quite small particles with large surface area in a useful pattern to obtain a high degree of reaction between the particles and a fluid to which the particles are exposed.

In general, a sheet product made according to the invention comprises at least 2 crn^z and preferably at least 10 cm of particle surface area per cm of floor area and per cm thickness of the floor. In addition to increase in surface area due to small size, the surface area may be large due to the use of porous or irregularly shaped particles, but the information given above refers only to surface area due to small size (and is calculated assuming the particles are perfect spheres).

The microfibers in the web can also vary in size and generally have an average diameter of about 1-25 µιη, preferably less than 10 µm. The length of the microfibers can also vary and the fibers can have a length of 10 cm or more. A variety of polymeric materials can be used, including polypropylene, polyethylene, polyamides and other polymers, as disclosed in the microfibre locking technique. Fibers of different polymers can be used in the same sheet product

In certain embodiments of the invention, either in admixture in one layer or in various layers. Likewise, preformed staple fibers may be included in admixture with the blown microfibers.

For <3e most sheet products made according to the invention, it is evident that the microfibers are substantially inert to the medium to which the particles are exposed, which means that the only active ingredient is the particles. However, in some embodiments of the invention, the microfibers have a function in addition to their physical support, such as a filter or sorbent.

As pointed out earlier, particles can be incorporated into a sheet product made according to the invention in a fairly large amount and they constitute at least 20 volumes? of the solids content of the flora. When the sheet product is used to purify air or some other fluid, the particle content also amounts to 20% by volume or more and preferably at least about 30% by volume. of the solids content of the flora. For many uses, higher particle loads or contents are needed, such as 50 volumes.

The unique nature of the particle retention action, in the sheet products prepared according to the invention, can be illustrated by considering the high particle contents or loads that can be achieved. When 75 volumes? of the web consists of particles, the particle volume is 3 times as large as the fiber volume. At 95 volumes? the particle volume is almost 20 times as large as the fiber volume. At 99 volumes? is the particle volume almost 100 times as large as the fiber volume, and at 99.5 volume? the particle volume is almost 200 times as large as the fiber volume. All of these particle loads or contents have been achieved without any use of binder or adhesive material which adheres the particles to the fibers, and without wetting the particles with the melt or sticky fibers.

The fact that the pressure drop across a sheet product made in accordance with the invention is not much greater than that of a comparable, with the particles unstressed, meltblown microfibre webs, is another significant advantage (with comparable here, the web includes the same microfibers which are collected under the same treatment conditions except that no particles were incorporated into the particle-delivering air stream).

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In many cases, the pressure drop over a particle-loaded sheet product made according to the invention is less than over a comparable, with particle-unloaded, melt-blown microfibre web, which is likely due to a certain opening of the web as a result of the presence of the particles. In other cases, the pressure drop across a sheet product made according to the invention is slightly greater than over a comparable meltblown microfibre web, although the pressure drop is generally not more than 200%, and preferably not more than 125% of the pressure drop across the comparable web.

The sheet products made according to the invention can be incorporated into breathing apparatus in the same way as conventional particle-loaded webs. In a suitable form, a sheet product made according to the invention is incorporated into a face mask of the general construction disclosed in U.S. Patent No. 3,333,585, generally together with a liner lying between the sheet product and the wearer of the face mask.

The invention will be further illustrated by the following examples, in which all pressure drops are measured at a surface velocity of 17 cm / s.

Examples 1-8

A series of products were prepared according to the invention using polypropylene microfibers having an average diameter of about 5 microns, as well as active carbon particles of various sizes and amounts. The sheet products were prepared with an apparatus according to Fig. 1, wherein the nozzle openings of the two nozzles were spaced 15 cm and the nozzles were arranged to direct the flowing fiber streams at an angle of 20 ° to the horizontal plant, the fiber streams cutting each other at a point about 20 cm from the mouthpiece. and then proceeded to a collection surface located 30 cm from the nozzle openings. The polymer was extruded through the nozzle openings at a flow of 0.07 kg / h / cm nozzle width and air heated to 415 ° C was forced through the hot air openings of the nozzles at a rate of 1980 l / min.

Three different samples of activated carbon particles were used in the Examples, one of which (Type A of Table 1) was Witco Brand Grade 249 activated carbon with a particle diameter of

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37-177 pm; Type Β in Table 1 was made up of Witcc Brand Grade 235 activated carbon particles having a diameter of 105-297 µm and Type C was made of Witco Brand Grade 360 ​​activated carbon having a particle diameter of 595-2000 µm. The carbon particles were uniformly fed to the air fan at flow rates of up to 0.45 kg / min. An air velocity through the supply line 26 of about 1500 m / min was used to provide a good particle / fiber mixture prior to collection.

Some illustrative properties of the various sheet products according to the examples are given in Table 1 Table 1

<td rowspan="2">Example No</td><td rowspan="2">Microfibre weight A (mg / cm)</td><td colspan="2">Amount of carbon</td><td rowspan="2">Pressure drop over sheet product (mm water)</td>

<td>Weight (Mg / cm²)</td><td>Vol% of the solids content of the flora</td>

<td> 1</td><td> 6,13</td><td> 0,32</td><td> 2,5</td><td> 10</td>

<td> 2</td><td>hrs</td><td> 1,61</td><td> 11,7</td><td> 10</td>

<td> 3</td><td>Π</td><td> 2,58</td><td> 14,9</td><td> 10</td>

<td> 4</td><td>ft</td><td> 3,87</td><td> 24,2</td><td> 10</td>

<td> 5</td><td>Π</td><td> 6,13</td><td> 33,5</td><td> 10</td>

<td> 6</td><td>it</td><td> 23,9</td><td> 66,3</td><td> 13</td>

<td> 7</td><td>ff</td><td> 43,5</td><td> 78,2</td><td> 10</td>

<td> 8</td><td>tt</td><td> 77,4</td><td> 86,5</td><td> 8,5</td>

Type of carbon

A

A

A

AA

A

B

C

Comparison-

<td colspan="5">example</td>

<td> 1</td><td>ft</td><td> 0</td><td> 0</td><td> 12</td>

As can be seen by way of example, the sheet products according to the invention can be produced with very low levels of particles, as well as with very high levels. However, in this whole range of different particle contents, the pressure drop of the particle loaded sheet products of the invention remains very close to the pressure drop of the comparable microfiber web which does not contain particles.

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The above sheet products were tested for uniformity of carbon particle content by subjecting the sheet products to a dry air stream (equal to 32 l / min per 81 cm area), which contained an average concentration of 90 ppm toluene vapor, and the toluene concentration after airflow throughput of the sheet product was measured with a flame ionization detector. The results for two of the sheet products, Examples 6 and 7, are shown in Figure 3.

The curves in Fig. 3 show that although the sheet products have only a small total weight of carbon (1.9 g and 3.5 g per 81 cm sheet product respectively), they completely remove the toluene vapor until a rapid breakthrough occurs. The steep slope of the curves illustrates the lack of thin spots in the floor and indicates that substantially all of the carbon is saturated before breakthrough occurs.

Examples 9-10

A second series of sheet products according to the invention was prepared using the apparatus described in Examples 1-8. Polymer was extruded through the nozzle openings at a rate of 0.1 kg / h / cm nozzle width and air heated to 440 ° C was forced through the hot air openings at a rate of 1700 l (NTP) per minute. Witco Brand Grade 337 activated carbon with a diameter of 105-297 µm was charged in different flows for the various examples at a rate of the particle delivering air of 5400 m / min. The microfibers produced had an average diameter of 5 µm. The values ​​for the obtained sheet materials are given in Table 2.

Table 2

Amount of carbon

<td>Example No</td><td>Microfibre weight (Mg / cm²)</td><td>Weight (Mg / cm²)</td><td>Vo1% of the solids content of the flora</td><td>Pressure drop over sheet product (mm water)</td>

<td>Comparative Example 2</td><td> 6,45</td><td> 0</td><td> 0</td><td> 12</td>

<td> 9</td><td> 6,45</td><td> 24,5</td><td> 66</td><td> 11,8</td>

<td> 10</td><td> 6,45</td><td> 53,5</td><td> 81</td><td> 7,9</td>

The sheet product of Example 9 was tested for its ability to sorb toluene vapor using a 14 l / min dry air flow over an 81 cm area and an added concentration of 330 ppm toluene. At the beginning of the test, it contained filtered air

7500253-5 ppm toluene, which continued during the first 10 minutes of the test. Then, the sheet product rapidly lost filtration capacity until, after 17 minutes, the filtered air contained 90 ppm toluene vapor. Examples 11-14

A series of sheet products of the invention were prepared using the process variables of Examples 9 and 10, except that the hot air stream was reduced to 1130 L (NTP) per minute, resulting in the production of microfibers having a diameter of 10 µm. The same kind of carbon as in Examples 9 and 10 was used and fed into the floor in different flows to give different loads. The velocity of the particle delivering air stream was reduced to 2400 m / min.

The properties of the sheet material are shown in Table 3.

Table 3

Amount of carbon

<td>Example No.</td><td>Microfibre weight (mg / cm²)</td><td>Weight (mg / cm)</td><td>Vol% of the solids content of the flora</td><td>Pressure drop over sheet product (mm water)</td>

<td>comparison Example</td><td></td><td></td><td></td><td></td>

<td> 3</td><td> 5,15</td><td> 0</td><td> 0</td><td> 4,5</td>

<td> 11</td><td> 5,15</td><td> 16,2</td><td> 61,2</td><td> 3,8</td>

<td> 12</td><td> 5,15</td><td> 28,4</td><td> 73,6</td><td> 4</td>

Comparison-

<td colspan="5">example</td>

<td> 4</td><td> 3,87</td><td> 0</td><td> 0</td><td> 2,5</td>

<td> 13</td><td> 3,87</td><td> 30,3</td><td> 79,8</td><td> 3,5</td>

<td> 14</td><td> 3,87</td><td> 22,6</td><td> 74,7</td><td> 3,0</td>

The porosity and the pore size distribution of the sheet products were measured by mercury penetration porosimetry. The results are given in Table 4 together with additional data for the sheet products.

Table 4 shows that the porosity of a sheet product decreases with increasing particle loading for the observed sheet products. The bulk density (ie, the weight of the web divided by its bulk volume) increases with the particle load, since the density of the carbon is approximately 2 times the density of the polypropylene base floor. From calculations made with respect to Example 13, it has been noted that the sheet product according to

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Sheet Product- Average size

Total tens of the sheet product's _______Weight____________

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In this example, the features approach the bed of carbon particles. This similarity obviously occurs because the sheet product includes a smaller amount of microfibers, although it contains the same proportion of particles to microfibers.

Examples 15-18

A further series of sheet products according to the invention were prepared using samples of different size particles. The apparatus and process variables were as described in Examples 11-14, except that the particle delivery system was set at an arbitrary feed rate of 1500 m / min and the particle addition flow varied. The microfibers produced had an average diameter of 10.pm. Witco Brand Grade 337 activated carbon was obtained in a size of 840-1680 µm and ground to 3 additional grain size distributions as follows:

Type 1

Type 2

Type 3

Type 4

<td> 800-1500</td><td>pm</td>

<td> 208-800</td><td>pm</td>

<td> 208-104</td><td>pm</td>

<td> 37-53</td><td>PRA</td>

The sheet products described in Table 4 were prepared using the different carbon types.

Table 5

Amount of carbon

microfibers

<td>Example No</td><td>weight (Mg / cnrj</td><td>Weight (Mg / cc)</td>

<td> 15</td><td> 3,87</td><td> 43,2</td>

<td> 16</td><td> 4,0</td><td> 39,2</td>

<td> 17</td><td> 4,2</td><td> 10,0</td>

<td> 18</td><td> 4,35</td><td> 6,65</td>

<td>comparison Example 5</td><td> 4,50</td><td> 0</td>

<td>Vo 17. of the solids content of the flora</td><td>Pressure drop over sheet product (mm water)</td><td>Keel type</td>

<td> 85</td><td> 2,5</td><td> 1</td>

<td> 83,2</td><td> 2,8</td><td> 2</td>

<td> 54,5</td><td> 3,3</td><td> 3</td>

<td> 43,3</td><td> 4,9</td><td> 4</td>

<td> 0</td><td> 3</td><td></td>

From the results in Table 5, it is generally seen that the lower the size of the particles in a web, the smaller the amount of particles can be introduced into the web for the same fiber size and the same fiber weight.

However, the reported results are not the maximum loads that can be achieved with the described particles and fibers.

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The conditions for feeding particles into the web (such as the air velocity through the supply line of the particles and the supplied particle flow) should be optimized for each particle size.

The pressure drop in Example 18 is remarkably higher than that in Comparative Example 5, probably due to the fact that the carbon with the grain size distribution of 37-53 µm corresponds closely to the pore size of the web and closes the pores rather than opening them.

In testing for the absorption of toluene vapor, the sheet products of these examples gave results similar to those of Example 9, taking into account the difference in carbon content of the sheet product. Examples 19-20

Although the present invention is particularly advantageous in covering a given area with a thin, uniform particle layer exhibiting low pressure drop, the invention is also useful in thicker layers. Seven layers of the sheet product of Example 13 were combined to give a sheet product (Example 19) having a carbon weight of 0.215 g / cm and a pressure drop of 20.8 mm of water at a surface velocity of 17.5 cm / s (the increased carbon weights obtained by laminating these webs can also be obtained directly by making thicker sheets in the sheet forming process). As a second example, four layers of the sheet product of Example 15 were combined and two layers of the sheet product of Example 13 to give a sheet product (Example 20) with a piston weight of 0.235 g / cm and a pressure drop of 14 mm of water at the same rate. The results of tests in which the composite sheet products were subjected to an air flow of 14 l / min over an 81 cm area, and the air flow contained 250 ppm toluene in Example 19 and 350 ppm toluene in Example 20 are given in Table 6.

Table 6

Example No.

Time (min)

Concentration by sheet product (PPm)

100

110

120

130

140

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The values ​​in Table 6 are very favorable compared to a packed bed of carbon, but the sheet products of the invention have a substantially lower pressure drop than a packed bed. The sheet products of the invention can be readily adapted to other methods to increase the exposed surface area and weight of reactive particulate material per unit cross-sectional area, such as by folding the sheet products into accordion patterns.

Example 21

A comparison of the grain size distribution was made between the carbon starting material used in Example 10 (i.e., the carbon placed in the hopper 22) having a diameter of 105-297 µm and the carbon removed from a sample of the finished sheet product. The charcoal was removed from the sheet product by tearing the floor, washing it and subjecting the floor to an ultrasonic bath in a water bath with wetting agent. Both grain size distributions were determined by random count using a light microscope. The results are given in Table 7.

Table 7

Percentage of particles larger than particle size (pm)

<td>given size</td><td>Flor</td><td>Precursor</td>

<td> 5</td><td> 235</td><td> 248</td>

<td> 10</td><td> 215</td><td> 230</td>

<td> 20</td><td> 188</td><td> 203</td>

<td> 30</td><td> 170</td><td> 188</td>

<td> 40</td><td> 160</td><td> 175</td>

<td> 50</td><td> 148</td><td> 159</td>

<td> 60</td><td> 135</td><td> 140</td>

<td> 70</td><td> 121</td><td> 128</td>

<td> 80</td><td> 108</td><td> 110</td>

<td> 90</td><td> 85</td><td> 85</td>

<td> 95</td><td> 30</td><td> 20</td>

<td>Example 22</td><td></td><td></td>

The tensile strength of strips is measured for the sheet products according to some examples and compared with the tensile strength of the corresponding webs without carbon particles. The results are given in Table 8.

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Table 8

<td>Example No.</td><td>Tensile strength (kp / cm width)</td><td>Weight ratio carbon: fibers</td>

<td>comparison Example</td><td></td><td></td>

<td> 2</td><td> 1</td><td> —</td>

<td> 9</td><td> 0,9</td><td> 3,8:1</td>

<td>Jämförelseexempe1</td><td></td><td></td>

<td> 4</td><td> 0,5</td><td> —</td>

<td> 13</td><td> 0,36</td><td> 8:1</td>

<td> 15</td><td> 0,44</td><td> 11:1</td>

comparison Example

0,5

The values ​​in Table 8 show that there is a decrease in the strip tensile strength of less than 25% even for those webs whose final weight to more than 90% is particles.

Example 23

Several layers of sheet product according to the invention, prepared in accordance with Example 13, were layered to form a thicker sheet product according to the invention, this thicker product was compared to beds of carbon packed in a tin box containing the same kind and amount of carbon used in sheet product. The particles had a diameter of 105-297 µm, the beds had a thickness of 0.75 cm, the composite sheet product was 1.75 cm thick. both the beds and the sheet product had a surface area of ​​81 cm, and both the beds and the sheet product contained 25.5 g of activated carbon.

It is difficult to prepare and maintain such thin beds, and the examples illustrate the superiority of sheet products according to the invention as compared to such beds. The first two attempts to test such a bed of carbon were unsuccessful because the beds immediately transmitted high percentages of the toluene passage to which the beds were exposed. The early failure and passage of toluene vapor probably occurred as a result of relocation of the particles into the bed during both experiments, and, at least with respect to the first experiment, in which the bed was compressed between two foam layers, by migration of the particles into the foam rubber ( The second and third attempts were placed on carpets

7500253-5 of blown microfibers between the layers of foam rubber and the bed). In the third experiment, the bed was not moved after preparation.

The beds and sheet product were exposed to 32 l / min of a dry air stream containing about 400 ppm toluene vapor. In the third test, the bed passed about 1 or 2 ppm of toluene during the first 40 minutes of the test, whereupon a rapid deterioration occurred to 10 ppm at 70 minutes, 30 ppm at 90 minutes and 65 ppm at 100 minutes. The sheet product according to the invention essentially did not pass through toluene during the first 70 min of the test, 8 ppm after 87 min and 60 ppm after 100 min: The pressure drops across each of the three packed beds at a flow rate of 42 l / min were more than twice that large as the pressure drop 'over the sheet product of the invention.

Examples 24-28

A sheet product according to the invention containing alumina particles having a diameter of 37-149 µm, was compared for its ability to remove fluorine hydrogen vapor with a known, nonwoven sheet containing the same alumina particles. The nonwoven web contained a mixture of polyethylene terephthalate fibers with denier numbers 16, 8 and

6th The alumina was applied to the fluffy web in the form of a cascade, after rando-weaving of the fibers, and the web was then compressed and the edges heat-sealed. The sheet product according to the invention: was manufactured with the apparatus generally shown in Fig. 1, except that only one nozzle was used. The nonwoven polyester flora contained 0.008 g of particles per: cm, while the sheet product of the invention

It contained only 0.004 g of particles per cm.

Samples of both the polyester flora and the sheet product of the invention having a surface area of ​​171 cm² was subjected to a flow of 16 L / min of dry air containing a hydrofluorocarbon vapor concentration as set forth in Table 9. The concentrations before and after the test were measured by bubbling a portion of the air stream through water and measuring the fluorocarbon concentration change with a specific ion electrode for F ~. At low concentrations (less than 100 ppm), the voltage obtained from the ion electrode is directly proportional to the concentration. The tests were terminated when the concentration after the sample exceeded 5 ppm. The results obtained are given in Table 9.

An alumina-filled sheet product of the invention, as described in this example, was placed in a breathing apparatus and tested for hydrofluoric vapor. The respirator effectively reduced the concentration of: hydrogen fluoride in the inhaled air to a physiologically safe level.

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<td rowspan="2">Example No.</td><td colspan="3">Table 9</td>

<td>Average fluorine hydrogen added concentration (Ppm)</td><td>Time to&gt; 5ppm (hrs)</td><td>ppm x</td>

<td> 24</td><td> 17,5</td><td> 7</td><td> 122,5</td>

<td> 25</td><td> 17,5</td><td> 7</td><td> 122,5</td>

<td> 26</td><td> 22,4</td><td> 4,5</td><td> 100,8</td>

<td> 27</td><td> 22,4</td><td> 4,5</td><td> 100,8</td>

<td> 28</td><td> 33,1</td><td> 4,25</td><td> 140,7</td>

<td colspan="2">polyester floros as before</td><td>technique:</td><td></td>

<td>A</td><td> 32,4</td><td> 1,5</td><td> 48,6</td>

<td>B</td><td> 32,4</td><td> 1,75</td><td> 56,7</td>

<td>C</td><td> 31,2</td><td> 1,75</td><td> 54,6</td>

<td>D</td><td> 31,2</td><td> 2,25</td><td> 70,2</td>

Example 29

A sheet product according to the invention (as described in Example 16) was compared to a commercial carbon impregnated paper (containing 55% by weight carbon having an average grain size of about 40 µm, which is dispersed in wet laid paper and viscose fibers). Samples of each of the two products (with an area of ​​81 cm) were tested for pressure drop (using a surface velocity of 17.5 cm / s) and for the efficiency of toluene vapor removal (using dry air with a flow rate of 14 l / min, which contained an average of 40 ppm toluene vapor for the paper and an average of 360 ppm for the sheet product of the invention). The results are given in Table 10.

Table 10

Example No.

Load (mg / cm.)²)

Pressure drop (mm water)

Paper

38,8

10,5

Toluene vapor (ppm) transmitted at different time intervals in min

3 4 10 15 20

100 250 0 0

30 100 200

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Examples 30-34

A series of sheet products according to the invention were prepared using polypropylene microfibers having an average diameter of about 5 µm, and active carbon particles having a diameter of 800-1500 µm. An apparatus similar to that of Fig. 1 was used, except that the nozzles and particle delivery means were mounted above the collection surface, so that the particles fell vertically on the collection surface. The two nozzles were spaced apart at a distance of 15 cm and discharged fiber streams which cut at an angle of about 45 ° and at a distance of about 20 cm from the nozzle openings. The combined fiber and particle stream proceeded to a moving collector, located 30 cm from the nozzle openings. Polymer was extruded at a flow rate of about 1.2 g / min / cm nozzle width and air heated to 510 ° C was forced through the air openings at a rate of 2250 l (NTP) per minute. The carbon particles were fed to the mixing zone with flows varying from about 100 to 300 g / min / cm nozzle width. The collector speed was 7 m / min for Examples 30 and 31 and 9 m / min for Examples 32-34. Bulky, self-supporting sheet products were prepared which were loaded with from 98% by volume to over 99% by volume of particles (see Table 11). Although vigorous handling of the sheet products detached some particles from the sides of the web, the sheet products provided a useful support for the particles. Examples 35-3.8

A series of sheet products made of polypropylene microfibers and polypropylene pellets were prepared with the apparatus and conditions described in Examples 30-34 (the collector speed was 7 m / min for Examples 35 and 36 and 9 m / min for Examples 37 and 38). The polypropylene pellet had a somewhat flattened cylindrical shape and had a length of the order of 0.2 cm, a width of about 0.3 cm and a thickness of about 0.2 cm. The pellets were fed in amounts ranging from 200 to 300 g / min / cm nozzle width. Manageable, self-supporting webs were obtained with the compositions described in Table 12.

7500253-5 ______Col__

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