JPS6031811A - Filter cloth for solid-liquid separation - Google Patents

Abstract

PURPOSE:To attain to enhance solid-liquid separation efficiency or transfer property, by raising the surface of a fabric or a knitted fabric to cover the same with an extremely fine fiber with a thickness of 0.1-10mum having directionality. CONSTITUTION:The surface of a base material such as a fabric or a knitted fabric made of a synthetic fiber is raised to cover the surface thereof with an extremely fine fiber with a thickness of 0.1-10mum and a filter layer is formed of said raised fiber. As the fabric, a satin fabric is pref. and a weft yarn is raised to a warp yarn direction. As the knitted fabric base material, a circular knitted fabric base material, a circular knitting fabric or a warp knitting fabric is used and a half-knitting tricot fabric is pref. Raising is formed of needle cloth. A directionality index shown as the ratio of peeling force in a cellophane easily peeling direction and a cellophane hardly peeling direction requires 1.2-10. The base material is used as endless filter cloth wherein filter cloth is formed into an endless state and perforated belts 2, 3 are stitched thereto and this endless filter cloth is used in a belt press type dehydrator.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a filter cloth for solid-liquid separation, and more particularly to a filter cloth used when dewatering or filtration is performed while rotating an endless filter cloth carrying solid-liquid.

Conventionally, an endless filter cloth loaded with a solid liquid is run through a pressing section consisting of a transfer drum and a press roll, and the liquid component is squeezed out by the pressing section, and the so-called solid components remaining on the filter cloth are transferred to the transfer drum. A belt press type dehydrator that transfers the liquid and collects it by scraping it with a scraper, or a belt press type dehydrator that uses gravity to filter the liquid component without squeezing the solid liquid on the filter cloth, and removes the remaining solid component with a water nozzle. So-called solid-liquid separators, such as filtration machines that collect liquid with a scraper, are used in various fields. In these solid-liquid separators, especially in filters, a pressure reduction part is provided near the solid-liquid supply part and opposite the back surface of the filter cloth to suck out liquid components and improve separation efficiency. Some did. The filter cloth of this invention is
It is used in such a solid-liquid separation device.

As the filter cloth used in the solid-liquid separator as mentioned above,
Conventionally, (1) Thick short fibers with a thickness of 30 to 100 μm were flocked on the surface of a textile base material using an adhesive to form raised naps that were tilted in one direction, and (2) The base material was raised on the surface of a textile base material. It is known that there are thick piloere formations with a thickness of several tens of microns.

These conventional filter cloths obtain the necessary strength as a filter cloth through the use of a textile base material, and at the same time, the naps on the surface prevent solid components from entering the cloth. In other words, the raised piloeres form a filter layer. That's why. However, all such conventional filter cloths have the drawbacks of low solid-liquid separation efficiency and poor transferability.

In other words, in the conventional filter cloth (2) mentioned above, the naps are formed by flocking with an adhesive, and in order to prevent the holes in the base material from being buried by the adhesive, the density of the naps cannot be made very high, and the thickness of the naps cannot be made very high. Since it is very thick with a diameter of 30 to 100 μm, the gaps formed between the nape, that is, the eyes, are quite large, and fine solid components can easily pass through the gaps.

Therefore, when using this conventional filter cloth (2), it is essential to coarsen the solid component by using a flocculant, which not only increases running costs but also poses a problem of toxicity depending on the type of flocculant.

The use of flocculants also increases the amount of solid components.

In addition, - V conventional cloth ■ has a nape thickness of 30 to 100 μm.
Because it is very thick, it is rigid and difficult to lie on the surface of the base material.

Therefore, the gaps that form between the nape are very deep, and if solid ingredients get into those gaps, it will be difficult to remove them.
The filter cloth becomes clogged. This tendency is very remarkable, partly because the raised pils are rigid and easily pierce solid components. Furthermore, the fact that the piloerection is difficult to lie down also means that the cline formed by the piloerection is bulky. Therefore, airtightness is poor when vacuum suction is performed. Further, since the gaps between the naps are deep, the surface has large irregularities, and the thickness of the solid component on the filter cloth becomes uneven, so that pressure at the pressing part is not uniformly applied.

For the reasons mentioned above, the conventional filter cloth (3) has a very low solid-liquid separation efficiency. If the solid-liquid separation efficiency is low, not only will a large amount of solid components be included in the liquid component, but also the amount of water in the recovered solid component will increase, requiring a large amount of energy for post-processing such as incineration. Become.

Furthermore, with the conventional filter cloth (2), as mentioned above, the solid components trapped between the naps are difficult to remove.

Therefore, when the filter cloth is separated from the transfer drum, the solid components are drawn back to the filter cloth by the raised fluff, resulting in poor transferability.

On the other hand, although the conventional filter cloth ■ mentioned above is not the same as the conventional filter cloth ■,
As expected, the gaps between the piloerections are quite large and deep. Therefore, this conventional filter cloth (2) also has low solid-liquid separation efficiency and poor transferability.

On the other hand, the inventors of this invention previously filed a patent application in
No. 591 and Japanese Patent Application No. 57-226384@, a new type of filter cloth was proposed. These filter cloths are
The so-called cline layer on the surface of the base material is formed of raised microfibers with a thickness of 0.1 to 10 μm.

Since the above-mentioned filter cloth has a filter layer formed of ultra-fine naps with a thickness of 0.1 to 10 μm, the gaps formed between the naps are very small, and even fine solid components can be blocked. In addition, the raised fibers of the polar is fibers are very flexible and lie easily, so the gaps between the raised fibers are shallow, and solid components do not get into the gaps while deforming and become difficult to pull out, making it difficult to cause clogging. The fact that the piloere is easy to lie down also means that the cline formed by it does not become bulky and the filling rate of the piloere is high, so that airtightness can be maintained highly when vacuum suction is performed. For these reasons, the filter cloth has very high solid-liquid separation efficiency.

In addition, the transferability is also high because the gaps between the raised fluffs are small, making it difficult for solid components to fit into the gaps, and because the raised fluffs are flexible and are prevented from digging into the solid components.

In this way, the i11 cloth proposed in both of the above applications is an excellent product that does not have the drawbacks of the conventional filter cloths (2) and (3) mentioned above. Another problem is that the solid-liquid separation performance is unstable due to the fibers being pushed into the grooves of the base material, making it difficult to stand up again, and the raised fibers becoming entangled.

This invention was made in view of such stability problems, and its purpose is to provide a filter cloth for solid-liquid separation that is stable and has high performance such as solid-liquid separation efficiency and transferability. There is something to do.

In order to achieve the above object, in the present invention, the surface of a base material made of a woven or knitted fabric is covered with raised ultrafine fibers of 6-string with a thickness of 0.1 to 10 μm made by raising the base material. There is provided a filter cloth for solid-liquid separation, characterized in that the raised naps have directionality and have a directional index of 1.2 to 10.

To explain one embodiment of the filter cloth of the present invention, in FIG. 1, a filter cloth 1 is sewn together along dotted lines and processed into an endless shape. At both ends of the filter cloth 1, there are belts 2 with holes for stretching the filter cloth 1 and running it without meandering.
．． 3 are sutured. The belt 2.3 preferably has some elasticity so that it can be stretched without causing wrinkles in the filter cloth 1. Therefore, belt 2.3
It is preferable that the core material is a synthetic fiber fabric, and the core material is a composite of the core material and rubber.

The above-mentioned filter cloth is obtained by raising the surface of a base material made of woven or knitted synthetic fibers, and has a thickness of 0°1 to 10μ, preferably 0.3 to 7μ, more preferably 0.3μ. ~5μ
It is covered with raised piloes made of ultra-fine sewn strings, and these piloes form a cline.

The above-mentioned woven fabric has 200 to 50,000 single weft yarns made of twin yarns of ultrafine fibers, egg spun yarns, or multifilament yarns having a thickness of 0.1 to 10 μm, and preferably 3 to 8 weft yarns to the warp yarns. It is made of woven, preferably satin fabric. The weft yarns are arranged at a density of 20 to 100 pieces/Cl1 in the width direction of the filter cloth, the warp yarns are arranged in the longitudinal direction, and the weft yarns are mainly raised in the warp direction. In addition, the warp threads are made of 10 to 15 fibers with a thickness of 10 to 30μ.
A bundle of 0 yarns is arranged at a density of 0.7 to 3 times the density of the weft yarns. The floating structure is used because it reduces the number of intersections between the weft and warp yarns, reduces the unevenness of the fabric, and provides a filter cloth with less surface unevenness. Also,
The reason why the weft yarns are mainly raised is that since a large tension is applied to the warp yarns, raising them will reduce the strength of the filter cloth.

In the above, 4 to 15 times/Cll1 for weft and warp
It is preferable to use a material having a certain degree of twist, since it is possible to secure a flow path for the base material even if the weaving density is high, and in the case of weft yarns, the retention of the napped yarn is improved and it becomes difficult to come off.

As the knitting base material, circular knitting such as rib knitting and double-sided knitting, warp knitting such as half knitting, Queen's cord knitting, etc. can be used. Among these, a half-knit fabric, also known as 1-ricotta fabric, is preferable because it is relatively less prone to forming naps.

Synthetic materials that make up woven and knitted fabrics [f is mainly for durability, polyamide fibers, polyester fibers, polyvinyl alcohol! Preferably, the fibers are polyethylene fibers, polyfluoroethylene fibers, polypropylene fibers, polyacrylonitrile fibers, or the like. Depending on the type of solid-liquid, it is preferable to use these fibers that have been subjected to hydrophilic or hydrophobic processing.

The thickness of the raised fluff needs to be 0.1 to 10 μm as described above. That is, if it is thinner than 0.1μ, even if it is possible to increase the density of the naps, the strength will be low and will break easily, making it impossible to obtain a filter cloth that can withstand practical use. In addition, the channel resistance of the cline increases significantly, which not only greatly reduces efficiency but also reduces solid-liquid separation efficiency. On the other hand, if it is thicker than 10 μm, the piloe become rigid and stand up, making it impossible to form a single-layer cline, and the gaps between the piloe become large, causing fine solid components to form. As a result, the solid-liquid separation efficiency is greatly reduced. In addition, the surface irregularities become large, and the solid components stuck in the depths become difficult to come out, combined with the piercing of the rigid raised hairs, causing clogging and greatly reducing transferability.

Figure 2 shows the results using a belt press type dehydrator, which will be described later, and using pond water containing about 100 mo of Microcystis per liter, which has a particle size of 1 to several tens of microns, and is commonly called blue-green algae. , the relationship between the thickness d (μ) of the raised pils and the rejection rate K (%) of solid components was investigated. The rejection rate 1 is expressed as a percentage of the weight of the recovered solid component to the weight of the solid component contained in the solid liquid, and the weight of each solid component is measured after heating and evaporating water. From FIG. 2, it can be seen that when the thickness of the raised fluff exceeds 10 Il, the rejection rate decreases significantly and it no longer functions as a filter cloth for fine solid components such as blue-green algae. The upper limit of the thickness of the nap is preferably 7μ, more preferably 5μ. On the other hand, if the thickness of the raised fluff is less than 0.1μ, it is theoretically thought that the rejection rate will be high, but if it is too thin, the damage to the wire layer will be severe and the durability will be lost, as well as the flow path of the wire layer. The resistance increases extremely, and the solid-liquid separation efficiency decreases significantly, as shown in FIG. 3 by the relationship between the thickness d (μ) of the nap and the solid component concentration C (wt%). Note that the directional index of the filter cloth used in this experiment was approximately 2.

Another advantage of forming ultra-fine napped fibers with a thickness of 0.1 to 10 μm is that the flexibility of the II string is inversely proportional to the fourth power of the thickness, so the napped fibers are very flexible and can be easily transferred to the transfer drum. During transfer, the fluffs are smoothly caused one after another and are rubbed off the solid components by 1iI, and the force that pulls the solid components back toward the filter cloth becomes weaker, thereby improving transferability.

The length of the nap is preferably such that it bridges 2 to 6 wefts of the base material, since it becomes impossible to sufficiently cover the surface of the base material. If the nap length is set as above, the number of naps per 1 m of base material is 10.
It is possible to form a very favorable series of 0 to 4,000 fibers.

Methods for forming raised naps include sewing cloth, 1Nando paper,
There are sand cloths, lean nets, whetstones, steel brushes, polishing brushes, sand rolls, garnets, sand honing, etc. Among these, it is most preferable to use clothing.

Now, in this invention, it is necessary that the above-mentioned nap has directionality and its directional index is 1.2 to 1o. A preferred directionality index is 1.3-5. Here, the directional index is measured as follows.

■ The longitudinal direction of the filter cloth to be measured, that is, the warp direction if the base material is a woven fabric, or the warp direction if the base material is a knitted fabric.
-Length 25cIl11 Width 3cn
Make 4 + shredded pieces.

At the end of each shredded piece, mark the end that will become the leading edge when running as a filter cloth.

(2) Next, in order to remove the distortion in the wire layer, the above-mentioned shredded pieces were placed in a continuous layer on a 50-mesh wire mesh and submerged in water. After 24 hours, pull out the filter cloth along with the wire mesh,
After being air-dried, it is left in an atmosphere with a temperature of 25±2° C. and a relative humidity of 65±5% for 24 hours to maintain constant moisture absorption.

(2) Next, a glass plate having a length of 55 cn+ and a width of 3 Qci is prepared, and one longitudinal end of the glass plate is lifted by 2°5 CIll and tilted. Furthermore, place one of the shredded pieces prepared in step ① above on top of the glass plate so that its longitudinal direction is the longitudinal direction of the glass plate, and the edge of the mark is on the side of the slope of the glass plate. 7cm long and 3cm wide from the top edge to 7cm.

It is covered with a polyester film with a thickness of 75 μm, and on top of that, a cellophane tape with a length of 35 CI 111 and a width of 2.4 cm is placed so that both ends are 5 cm from the top and bottom ends of the filter cloth.
Protrude by +n and place it so that it touches the surface of the glass plate and the adhesive side is on the filter cloth side.

13-(2) Next, a SUS steel roll with a smooth surface having an outer diameter of 5 cm, a length of 15 cI, 111, and a weight of 2.3 Ko is rolled by gravity from the upper end of the cellophane tape to adhere the filter cloth and the cellophane tape. To reduce measurement errors, this rolling operation is performed twice. After adhesion, 5 cm of both ends of the cellophane tape are cut off to obtain a bonded product of the filter cloth and the cellophane tape.

(2) Next, the adhesive obtained in (1) above is subjected to a peel test between a filter cloth and cellophane tape. This test was carried out using a tensile testing machine, with the upper chuck holding the polyester film and the lower chuck holding the filter cloth, at a tensile speed of 30.
It is carried out continuously under the condition of 7 minutes. Then, the starting point is 30IIl from the peeling start end, and 9c from the starting end.
The peel force is measured as the average value between m. Hereinafter, the peeling force obtained by this measurement will be referred to as A.

(2) Next, perform exactly the same test on another cut piece of the glass, but this time with the other end corresponding to the edge of the 14-marker above being on the upper side of the slope of the glass plate. This measurement yields the peel force.

(2) Next, the third cut piece is subjected to the same tests as (1) to (3) above, but this time, a polyester film is placed on the lower end of the filter cloth. By this measurement, the peeling force B
get.

(2) Next, perform the same test as (2) above on the last test piece. However, in this case as well, place the polyester film on the lower end of the filter cloth, as in the above case. By this measurement, the peeling force C is obtained.

■ Next, from the above peeling forces A, B, and CXD, (B+D)
/(A10) is performed. The result of this calculation is the directional index referred to in the present invention.

As is clear from the above definition, the directional index is the ratio of the peeling force in the direction in which the cellophane tape is easy to peel and in the direction in which it is difficult to peel, and this indicates the stability of the direction of napping. A directional index of 1.2 to 10 can be obtained by appropriately selecting the number of times of raising, direction, type of raising, etc. In the above test, the cellophane tape used has an adhesive strength specified in JIS 21522-1982 and has a width of 24 rnm.

FIG. 4 is a graph showing the relationship between the directionality index T and the transfer rate P, which was investigated for 16 surplus sludge generated from an activated sludge treatment apparatus using a belt press type dehydrator. In this graph, the solid line is immediately after the start of use, and the dotted line is at 50
The relationship after 0 hours of use is shown. From FIG. 4, it can be seen that good transferability is obtained when the directionality index is in the range of 1.2 to 10, and that it does not deteriorate much even after 500 hours of use.

Figure 5 shows the relationship between the lower directional index and the inhibition rate when the above-mentioned blue-green algae was similarly tested. It is high, and there is little deterioration after 500 hours of use.

The thickness of the nap of the filter cloth used in the experiments shown in FIGS. 4 and 5 above is about 1.5 μm.

The filter cloth as described above has a basis weight of 100 to 400 (1/
Preferably it is tn2. In other words, the basis weight is 1000
If it is less than /rn', the filter cloth tends to stretch due to tension during running, resulting in poor running stability. Furthermore, a filter cloth with a basis weight exceeding 400 (J/1112) is not economical since it is necessary to increase the water pressure during washing.

Further, the filter cloth of this invention has a temperature of 20±2 on the surface of the filter cloth.
℃, relative humidity 65±5% 240g/cm
It is preferable that the porosity when a load of 2 is applied is 0.5 to 0.75. That is, when the porosity is less than 0.5,
This is not practical because the flow path resistance increases and the throughput decreases. On the other hand, if it exceeds 0°75, the filter cloth tends to contain a large amount of liquid component, which increases the time required for solid-liquid separation, making it necessary to use a long filter cloth, which is not preferable.

When the filter cloth of the present invention is used in a belt press type dehydrator, as shown in FIG. The endless filter cloth 1 carrying the filter cloth 6 is run, and the liquid component in the solid liquid 6 is squeezed out by the squeezing section, and the solid component remaining on the filter cloth 1 is transferred to the transfer drum 4.
Scrape and collect with scraper 7. In this case, filter cloth 1
The filter cloth 1 is mounted so that the surface having the nap, 1'', faces the surface of the transfer drum, and the direction of the inclination of the nap faces in the opposite direction to the running direction of the filter cloth 1. In addition,
In FIG. 6, numeral @8 is a water spray nozzle for washing the filter cloth from the front and back surfaces after transfer, and 9 is a vacuum suction tank for liquid components.

The filter does not have a transfer drum as described above, and the solid components remaining on the filter cloth are collected with a scraper or a water spray nozzle.

The filter fabric of this invention can be manufactured by various methods. Next, a preferable example will be shown.

That is, the weft is composed of an island component made of a polymeric material, preferably polyester, and a sea component made of a polymeric material, preferably polystyrene, and contains 35 to 75% of the island component. So-called multifilament composite mH or mixed spun fibers containing 80% or more of fibers that generate ultra-fine fibers, twin yarns or egg spun yarns or multifilament yarns are used as warp yarns, false twisted yarns or composite latent crimped yarns. Using this method, the weft and warp yarns are woven with satin so that they have a desired density and a desired floating structure.

Next, the sea component of the weft is removed with a suitable solvent, such as trichlorethylene, and after drying, the weft is raised to form a nape, forming a so-called cline.

Another method is to make a woven or knitted fabric using a composite fiber obtained by laminating and spinning different polymeric substances, peeling off the lamination, and raising the fibers to form a nap. The polymer material to be bonded together is preferably polyamide and polyester copolymer.

As for the peeling method, it is preferable to rub vigorously in hot water and then air dry.

The filter cloth of the present invention can stably separate extremely fine solid components, and therefore can be used for various purposes. For example, sludge, scum, etc. generated during wastewater treatment, such as so-called suspended sludge and so-called fixed sludge discharged from biofilm treatment equipment,
It can be used to concentrate and dehydrate flocs, wash water, concentrated sludge, etc. Specifically, for example, sludge generated from water and sewage treatment, excess sludge generated from septic tanks, sludge generated from urine treatment, scum generated from pressurized flotation operations, flocs generated from industrial wastewater treatment, and flocs formed by flocculation and sedimentation. , backwash water from various filtration devices such as sand filters, and sludge concentrated in screen devices. Furthermore, it can be used to recover solid components in various manufacturing industries, such as paper pulp manufacturing, food manufacturing, sake brewing, and miso brewing.

Furthermore, it can also be used to purify water in ponds and rivers.

As explained above, in the filter cloth of the present invention, the naps forming the so-called linear layer have directionality, and the directional index is 1.2 to 10, so that the filter cloth is easy to use during use. It is possible to prevent the nape from being pushed into the holes of the base material and making it difficult to stand up again, or from getting entangled with the nape, and stable solid-liquid separation efficiency can be obtained.

In addition, since the filter cloth of this invention is made of ultrafine fibers with a thickness of 0.1 to 1011 and forms a so-called linear layer, the gaps formed between the naps are extremely small, and fine solid components are removed. can also be prevented. Therefore, it is not necessary to add a flocculant. In addition, since the raised fluff is flexible and easily lies on the surface of the base material, the gaps are shallow and the solid components are prevented from getting deformed into the gaps and becoming difficult to handle, and there is almost no fear of clogging. The fact that the nape is supple and easy to lie down means that the line layer formed by it does not become bulky and the filling rate of the nape is high, so the airtightness is also high when vacuum suction is performed. For these reasons, the filter cloth of the present invention has very high solid-liquid separation efficiency.

21-Furthermore, in the filter cloth of the present invention, as mentioned above, the gaps between the naps are very small, making it difficult for solid components to enter the gaps, and the naps are flexible and prevent them from digging into the solid components. Therefore, the transferability of solid components to the transfer drum is high.

Example A 20/28 spun yarn made by spinning a 16-core multicore composite tlaN<thickness 20μ) with polyester as the island component and polystyrene as the sea component was used as the weft, and polyester fibers with a thickness of 20μ were used as the weft. A 5-ply satin fabric having a warp of 30 wefts of 10 m and a warp of 40 warps/cn+ was obtained.

Next, the sea component of the weft is removed using trichlorethylene as a solvent, and the weft is made of ultrafine fibers with a thickness of about 2.5 μm.
A fabric consisting of 000 bundles was obtained.

Next, the above fabric is put through a napping machine, and the napping operation is carried out 20 times in the warp direction, and the napping operation is further carried out 10 times in the opposite direction to mainly nap the weft yarns, so that the number of naps is about 1000/ml.
A filter cloth of the invention was obtained with a volume of 1 liter and a directionality index of approximately 2°2.

-22= Next, the width of the filter cloth is 3 with the warp direction as the longitudinal direction.
Cut into pieces of 0cm and 2.5m in length, sew the cut ends together and
An endless filter cloth (not shown) was obtained.

Next, the endless filter cloth was applied to a belt press type dehydrator shown in Fig. 6, and the running speed of the filter cloth was 4 m/min, the degree of vacuum in the vacuum suction tank was approximately 90011III1 water column, and the pressing force against the transfer drum was approximately 60 KO. A dehydration test was conducted as follows. As the solid liquid, tap water and clay with an average particle size of about 20 μm were used.
The clay concentration is approximately 300a+.

The amount adjusted to be 40 liters/liter was supplied at a rate of about 40 liters/minute without adding a flocculant.

The particle size distribution of the clay in the -[2 solid-liquid as measured by a Coulter counter was approximately 1 to 50 microns, and was distributed over a fairly wide range.

As a result of the test, approximately 60% of the components recovered by scraping with a scraper were solids, which was about 2000 times more concentrated than the original content. Also, the transfer rate to the transfer drum is approximately 82%.
and was extremely high.

Furthermore, the particle size distribution of the clay in the solid component measured with a Coulter counter was about 1 to 10 microns, and most of the particles larger than 10 microns were removed. Further, even after running for about 500 r1, the above performance did not change at all, and no abnormality was observed in the filter cloth.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of a shelf showing an embodiment of the filter cloth of the present invention, and FIG. 2 is a relationship between the thickness of the nap d (μ) and the solid component inhibition rate K (%). FIG. 3 is a graph showing the relationship between the thickness d (μ) of the piloerection and the solid component aaic (wt%), and FIG.
5 is a graph showing the relationship between the directional index T of piloerection and the rejection rate K (%) of solid components, and FIG. FIG. 2 is a schematic front view showing a state in which a belt press type dehydrator is operated using cloth. 1: Filter cloth 2.3: Belt with holes 4: Transfer drum 5 Nibbles roll 6: Solid liquid 7: Scraper 8: Water spray nozzle 9: Decompression suction tank Patent applicant Toshi Co., Ltd. 25- Fig. 1 Fig. 2 Figure 3flJ-d? ) No. 4-1! I-1 5W1-1Y1 Figure 6

Claims (1)

[Claims] The surface of a base material made of a woven or knitted fabric is covered with napped microfibers with a thickness of 0.1 to 10 μm made by raising the base material, and the napped fibers have directionality, and A filter cloth for solid-liquid separation characterized by an index of 1.2 to 10.