FI58874B - SAETT ATT FRAMSTAELLA FIBERGRANULAT - Google Patents

Description

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France-France (FR) 7226U26 (71) Societe d'Exploitatiandes Brevets Granofibre SEBREG, "Le Verenay", 69I20 Ampuis, France-France (FR) (72) Guy Jacquelin, Grenoble, Jean Fournet, Saint-Romain-en-Gal , France-Frankrike (FR) (7 ^) Oy Kolster Ab (5 ^) The way to make fiber granules - Sätt att framställa fibergranulat

The present invention relates to a process for the preparation of fibrous granules by first bringing natural or synthetic non-wetting fibers, but possibly up to 55% by weight of the fibers, into a loosely cohesive fibrous aggregate.

As starting materials in the process according to the invention, relatively inexpensive fibers can be used, examples of which are: natural fibers: vegetable fibers: wood fibers, annual plant (straw) fibers, cotton lint fibers, etc.

animal fibers such as wool and various kinds of hair, mineral fibers: asbestos, various fibrous crystals, - artificial fibers: organic fibers, eg viscose and rayon fibers, mineral fibers such as glass and rock wool fibers, etc.

- synthetic fibers made of polyvinyl chlorides, poly-58874 olefins, polyamides, polyesters, polycarbonates, various copolymers.

According to a known process of this type of treatment, the following are carried out sequentially: - dry treatment, in which the individual fibers fed loosely into the horizontal tunnel are circulated by rotating the tunnel so as to promote the grouping of fibers to form aggregates which are poorly cohesive, by means of a stream of liquid during the treatment of which the fibrous compositions are suspended in a liquid, this liquid either simply subjecting them to a swirling motion or a swirling motion combined with a pulsating motion so that these fibrous compositions solidify and form granules with the above properties.

Hereinafter, the term "composition" refers to the groups of fibers obtained during dry processing, and the term "granule" refers to those spherical formations obtained by solidifying these compositions.

The object of the invention is to reduce the time required for this second treatment as well as the power consumed in carrying it out and to remove the water contained in the obtained granules, so that the manufacturing costs of these granules can be considerably reduced.

It is also an object of the invention to simplify the equipment required for manufacturing, which on the one hand can significantly reduce investment costs and their effect on granule manufacturing costs and on the other hand connect equipment of reasonable capacity and cost-effectiveness close to where the fibrous granules are converted for use as such or semi-finished products.

The method according to the invention is characterized in that water or a liquid which wets the fiber aggregates is sprayed on the surface of the fiber aggregates in order to increase their tightness. fibers so much that the average moisture content of the whole pulp is between 50-85% *, whereby liquid flakes are formed between the fibers on the surface of each aggregate, which increase the attraction between the fibers, and that the liquid is then evaporated, thereby strengthening the compression of the fibers.

In some cases, where the final product to be manufactured has to be assembled from fibrous granules only, the pulp obtained from the dry treatment is classified as separating fiber compositions of suitable length from other pulp components such as powdered products, free fibers, 3 58874 unsuitable diameter these fibrous components are decomposed to completely release the fibers they contain, after which the free fibers recovered during separation and the fibers released as a result of the decomposition are mixed with new fibers to dry treat all of these fibers, taking into account only the classified fiber compositions.

According to a particularly interesting embodiment of the invention, the fiber compositions separated from the pulp obtained as a result of the dry treatment are applied in an evenly thick layer and a liquid is sprayed on this layer while the compositions are vibrated.

The liquid used may be water, possibly containing a surfactant and / or a binder.

Finally, the fibrous granules can be suitably dried after wetting.

In order to illustrate the invention, an embodiment of the invention will now be described by way of example, and at the same time some specific examples are presented, which, however, do not limit the invention.

In order to carry out the method according to the invention, said separately shaped fibers are used. This definition means that:. the fibers are completely separated from each other and that the pulp to be treated from the vegetable fibers contains few lumps, i.e. thick bundles in which the numerous parallel fibers are joined together into combinations which are no longer fibrous in shape.

Irrespective of the origin of the fibers, that is to say, whether they are fibers obtained from flora or fauna or mineral or synthetic fibers, these fibers are always dried. The fibers are not superficially wetted, but may contain internal moisture. In the special case of treating wood fibers, their moisture content can be 3 ~ 55% of the total weight of the wet fibers, without still feeling wet when touched.

For dry processing, such separately shaped and dried fibers are fed into a tunnel rotating about a horizontal axis, possibly with partitions. The degree of filling of the tunnel is important: it must be greater than half its internal volume. No liquid is fed into this tunnel, so the processing of the fibers is really dry.

The fibers are mainly subjected to mechanical felting effects as the tunnel rotates. The fibers then flexibly deform slightly and their entanglement solidifies due to the shrinkages caused by these elastic forces 11 58874. Thus, fibrous compositions are formed in the moving mass of the fibers to be treated.

It is noted that the dimensions of the most cohesive spherical compositions approximately correspond to the average length of the fibers, and that these dimensions vary only slightly even if the treatment is extended. On the other hand, the formed fiber compositions are cohesive only if their dimensions do not very much exceed the average length of the fibers. You see, the largest compositions tend to break as the fiber layers slide along each other and as they fall through the tunnel.

The efficiency of the dry treatment depends on the degree of filling of the tunnel, because the effective transfer surface must be small compared to the treated volume. The efficiency also depends on the rotation speed of the tunnel. The best results are obtained if the filling level is between 2/3 and 1 + / 5 of the tunnel volume.

By way of example, 850 kg of wood fibers can be dry-dried in a tunnel with a diameter of 2.5 m and a length of 8 m, which corresponds to 63%. the degree of filling. The tunnel is rotated so that its circumferential speed is about 80 m / min.

After 2 hours of treatment, 80% of the pulp has been converted into compositions. Once the granularity of these compositions has stabilized, the dry treatment is stopped and the wet treatment can begin.

The pulp to be dry-treated may, before wet treatment, be classified in such a way as to distinguish: - fibrous compositions of suitable dimensions, - free fibers, - pulps of inappropriate or non-cohesive dimensions, - powdered components, etc.

Classification can be performed by screening to remove compositions that are too weakly sized from a pair of fiber compositions of suitable length. The latter do not withstand the stresses of screening but decompose.

However, such a distinction into different categories is not always necessary.

Pulps of inappropriate or non-cohesive dimensions, as well as waste of compositions decomposed during screening, are decomposed, e.g., by carding, to completely separate the fibers they contain. These fibers, as well as the free fibers, are mixed with new amounts of fibers, after which they are subjected to a new dry treatment, so that, in fact, fibers which have not joined together or have formed weak compositions are recycled.

5 58874 However, the fiber compositions of the same size thus obtained cannot be used as such because they remain too weak in size. It is thus necessary to solidify these compositions, which is done by the wet treatment described below.

It should first be noted that this wet treatment is suitably applied to fiber compositions that have already been separated from the rest of the dry-treated pulp. However, wet treatment may also be applied to the whole of this pulp in the event that the product for the manufacture of which the granules are used requires or permits the presence of free fibers or non-cohesive pulps and also provided that the fiber compositions account for a sufficient proportion.

Wet treatment is based on applying a liquid to the surface of the fiber compositions in an amount just sufficient to form liquid strands between the superficial fibers. These meniscus compresses the fibers together, and this compression is promoted by the evaporation of the liquid.

According to a particularly preferred embodiment of the method according to the invention, the fiber compositions are divided into an evenly thick layer on the moving surface, and the liquid is fed by spraying. To equalize the wetting, the moving surface is suitably vibrated. Whether this movable surface is horizontal, or upward or downwardly sloping, or flat, cylindrical, helical, or otherwise shaped, this surface directs suitably wetted fiber compositions toward a dryer in which the liquid forming the aforementioned menisci is completely and rapidly removed.

Water is used as the liquid in most cases, especially when the fibers used as starting material are natural fibers. The average moisture content of the whole mass must be in the range of 50-85% of the total weight of the wet compositions.

However, in some special cases, some other wetting fluid may be used. As an example, in the treatment of polyethylene fibers, a hydrocarbon or a solvent which wets the fibers can be used as the liquid.

To demonstrate the change resulting from the wet treatment, as a result of which the poorly cohesive fiber compositions become better cohesive fiber granules, two different types of experiments have been performed.

In the first set of experiments, the shrinkage of the diameter of the wet-treated fiber compositions was measured. Compositions formed of wood fibers were fitted to a stationary plate, and the diameter variations of the numerous compositions were measured using a catheter.

6 58874 In this case, it was found: - that crushing with water causes a shrinkage of the compositions of 5 to 10%, - that drying causes a new shrinkage of about 1%.

In the second set of experiments, the cohesiveness of the fiber compositions was measured. To this end, the protective needle was immersed diametrically in each of the formed granules, after which a force was applied by means of a dynamometer, which tended to separate the needles from each other until the granule under test disintegrated. The magnitude of the fracture force, which is said to be an arbitrary or freely definable cohesion force, is relevant and presented as a measure of criticism.

The following example shows a few test results:

Resin fibers, e.g., those consisting of a "defibrator pulp", were dry treated by applying the first step of the process of the invention. The cohesiveness of the obtained fiber compositions was low and the cohesive force was 10-12 g when the diameter is 8 mm.

These compositions were moistened 80- $ 5 with water, after which they were dried by applying the second step of the method of the invention. The cohesiveness of the fiber compositions thus obtained reached a cohesion value of 25 ~ 30 g.

In addition, it may be advantageous to enhance the wetting effect and to provide a physico-mechanical compression treatment of the compositions to the fibers by combining this wetting effect with a different fiber-binding effect.

The formation of reinforcing bonds can be effected by means of a wetting fluid. In this case, the liquid swells the fibers superficially, whereby in the event that the fibers are sufficiently close to each other under the influence of surface tension forces, bonds between the fibers are formed, which strengthen the obtained granules. As an example, when treating polymer fibers, an expanding agent can be used as the wetting liquid, which, when evaporated, causes the fibers to stick together.

According to another alternative, some thermoplastic granules are subjected to a heat treatment which considerably accelerates the evaporation of the wetting liquid and the drying of the granules, in order to soften the surface of the fibers and to make this surface sticky. The surface tension forces then cause local adhesion of the approaching fibers.

By way of example, granules made of polyvinyl chloride fibers with a diameter of 5 to 8 mm and a cohesive force of a few grams between the needles can achieve a cohesiveness of more than 1,58784,800 grams after heat treatment for a few minutes at 100 to 110 ° C: in.

The heat-shrinkable fiber granules can be subjected to a heat treatment which considerably accelerates the evaporation of the wetting liquid and the drying of the granules, as well as causes increased compression of the fibers.

A method in which the wetting liquid is mixed with a substance capable of solidifying the approaching fibers by forming adhesive-type bonds is suitable for all fibers.

For this purpose, starches, various polymers and, in general, all products which can cause interfiber adhesions as a result of drying and / or heat treatment can be used.

By way of example, the fiber compositions obtained as a result of the dry treatment of the resin fibers may be moistened with an aqueous suspension of pregelatinized starch used at an amount corresponding to 20 g / l corresponding to the weight of the compositions. After drying, the cohesiveness of the fiber granules reaches a value of 80-100 g.

The method according to the invention can be used in all cases where the fibrous granules used must be inexpensive and in which they are not subjected to tensile stresses or at least to higher tensile stresses.

Particularly interesting applications are the production of lightweight, porous and insulating fillers and the production of basic products for the production of molded or extruded articles consisting of different coating layers.