FR2662449A1 - Process and apparatus for adding thermoplastic fibres to cellulose fluff pulps - Google Patents

Abstract

In this process for adding thermoplastic fibres, such as polyethylene fibres, to a cellulose fluff pulp, the thermoplastic fibres and the cellulose fluff pulp are introduced into a device in which the fibres are disintegrated and the mixture homogenised. According to the invention the thermoplastic fibres are introduced into a receptacle (3) in which an environment whose moisture content is controlled is maintained and are then transferred in a wet state by an endless screw (6) in a pipe (4) as far as the mixer.

Description

METHOD AND APPARATUS FOR ADDING FIBERS

  THERMOPLASTICS WITH CELLULOSE FLUFF PASTA

  The present invention relates to a method for adding thermoplastic fibers, such as polyethylene fibers, to a kind of cellulose wad known in the art as "cellulose fluff pulp", a method in which a thermoplastic fiber and a cellulose fluff pulp are loaded into a mixer and transformed into paste therein and the mixture is homogenized The invention also relates to an apparatus

to implement this process.

  In a known process of the type mentioned above, the polyethylene is used in the form of sheets. The polyethylene sheets are coarsely pulped and are conveyed on a conveyor belt to a kneader into which is also introduced the cellulose fluff pulp transported pneumatically and in which the

  fibers are disaggregated and the mixture homogenized.

  The mixture of cellulose fluff pulp and thermoplastic fibers is used as an absorbent in absorbent bodies intended for disposable absorbent articles, such as disposable diapers, sanitary napkins and incontinence pads The role of thermoplastic fibers is to improve the mechanical resistance of the absorbent bodies and the proportion of mixed fibers is of the order of 15,

  20%, depending on the desired properties of the product concerned.

  Because thermoplastic fibers are 4 to 5 times more expensive than cellulose fibers, manufacturers are careful not to use a higher proportion of thermoplastic fibers than is absolutely necessary for this purpose, it is important to measure precisely the amounts of

  thermoplastic fibers introduced into the mixer.

  However, it has been found that it is difficult to accurately measure the amounts of thermoplastic fibers when practicing the known method, because the moisture content of the polyethylene used varies and because the irregular surface weight of the polyethylene sheets can influence the final result This is why it is difficult to determine the weight percentages of water and thermoplastic fibers introduced into the mixer when loading a

polyethylene of a given weight.

  The object of the present invention is to solve these problems by means of a method and an apparatus which, when thermoplastic fibers are added to cellulose fibers, makes it possible to precisely measure the quantity of thermoplastic fibers introduced into the mixer. in which a homogenization of the

mixture with formation of paste.

  The objective of the present invention is achieved by means of a method of the aforementioned type which is characterized by the introduction of a thermoplastic fibrous material into an environment whose moisture content is controlled and then by the introduction of said fibrous material into the mixer in a wet state Because the thermoplastic fibrous material tends to assume a state of equilibrium with its environment, the material absorbs moisture by capillary effect until this state is reached This allows equalization of variations in the moisture content of the fibrous material introduced into the atmosphere at controlled humidity content, so that the fibrous material leaving said humid environment has a constant moisture content The weight of the fibers of the fibrous material discharged from the humid environment can be easily determined, which makes it possible to load the fibrous material in quantity in which the weight is determined

in a specific way.

  An apparatus for carrying out the method according to the invention comprises an arrangement operating so as to create a humid environment, means for advancing the fibrous material and introducing it into said humid environment, and means for advancing the wet fibrous material from said humid environment

and introduce it into the mixer.

  A preferred embodiment of the invention will now be described in more detail with reference to the accompanying drawings, in which: FIG. 1 schematically shows an apparatus / installation for implementing the method according to the invention; and FIG. 2 shows a preferred embodiment of a device incorporated in the apparatus / installation of FIG. 1 and operating in such a way as to provide an environment with controlled humidity, as well as a device for transporting the fibrous material thermoplastic in a wet state from the humid environment to the mixer incorporated in

the installation.

  Figure 1 very schematically shows the components incorporated into the device for adding polyethylene fibers to a pulp cellulose fluff The cellulose "fluff" is loaded into a kneader via a pipe in which the pulp cellulose fluff is transported pneumatically and is discharged into the mixer The polyethylene is introduced into station A in the form of sheets which, at the time of manufacture, have a moisture content of approximately 50% but which, after storage and transport, have a variable moisture content due to the different environments to which the said sheets were subjected during storage and transport The polyethylene sheets are coarsely pulped at station A, by means of an apparatus suitable, such as a hammer mill The coarsely defibrated polyethylene is then dropped on a medium suitable conveyor, for example a belt conveyor, and the polyethylene is transported by this conveyor means to station B The polyethylene is exposed to a humid environment in station B The polyethylene absorbs water from the surrounding atmosphere up to that a state of equilibrium is reached with said atmosphere, the drier parts of the material absorbing more water than the wetter parts of the latter Consequently, all the parts of the polyethylene leaving station B have the same content mutually humidity and, therefore, it is possible to determine

  easily the weight of the fibers of said material.

  FIG. 2 schematically shows a preferred embodiment of station B to which the coarsely pulped polyethylene is brought from station A using a conveyor 1 with a belt. The discharge end of this conveyor is located above above a feed funnel 2 which, in turn, is in the center of the opening of a container 3 which has an inclined bottom 4 The container 3 is also provided with an outlet tube 5 which s extends laterally and is

  extends obliquely upwards parallel to the bottom 4.

  The outlet tube is in the form of an oblique truncated cone and, therefore, decreases in section in the upward direction An endless transport screw 6 extends along the bottom of the container and somewhat in the outlet tube 5, this screw being supported for its rotation in a suitable manner Spray nozzles 7 are arranged around the opening

of the container.

  The container 3 is mounted inside a tank 8 into which water can be supplied via a conduit 9 The delivery side of a pump P is connected to the nozzles, while the suction side of the pump is connected to the tank 8 A row of holes or slots 10 formed in the side wall of the container 3 form an overflow passage

for tank 8.

  The apparatus illustrated in FIG. 2 operates from

the following way.

  When the apparatus starts, the container 3 is empty so as to avoid the presence of a surface of water on which the polyethylene, falling, can collect,

  this polyethylene being lighter than water.

  The container 3 is first emptied, if necessary, after which the polyethylene is introduced into the container 3, from the conveyor 1 and via the funnel 2, until the entire bottom 4 is covered The pump P which can be a variable displacement pump, is then put into action The pump is driven so that a relatively small quantity of water per unit of time is delivered by the nozzles 7 The polyethylene falling from the funnel 2 therefore crosses a rain of water before falling into the container and on top of the polyethylene previously supplied When the polyethylene has been supplied in such a quantity that it fills the container 3 up to the level of the rows of holes 10 from the container wall, the polyethylene supply is

  interrupted although water spraying continues.

  After a given period of time, the polyethylene present in the container has absorbed an amount of water such that the saturation point is reached and the water then sprayed on the material is discharged by the

row of holes 10.

  This ends the start-up phase of the treatment and the transport worm 6 and the conveyor belt 1 are then set in motion. A continuous length of polyethylene, or polyethylene rod, is then evacuated by the outlet tube 5 and falls under the effect of gravity on a transporter,

  or, if preferred, directly in the mixer.

  As will be understood, the supply of material into the container 3 must be adjusted appropriately so as to correspond to the discharge of the material through the tube 5 This can be achieved, for example, by adjusting the speed of the conveyor using a level sensor mounted in the funnel 2 and operating so as to indicate the level of the material

in the funnel.

  Water is delivered for a relatively long period during the start-up phase in order to allow the polyethylene absorption mechanism to act completely, this absorption, or aspiration, taking place mainly due to capillary forces After the capacity absorption has been used entirely, which is evidenced by the fact that the water then flows through the holes 10, the material no longer floats but has essentially the same density as water while having a consistency similar to a cereal porridge The bonding forces in this cereal porridge material are strong enough to maintain the cohesion of the material, even if a surface of water should form on top of this material When the start-up phase is completed, the flow of water formed by the nozzle 7 is increased so that an excess of water is obtained However, this excess of water must not be greater than the amount of water that can be drained

  through the holes 10 in the wall of the container.

  As mentioned previously, the outlet tube 5 decreases in cross section towards its outer end. The outer part of the tube 5 has perforations II arranged along its lower surface. The polyethylene is therefore compressed and its water expressed in the outlet tube, and the water extracted by compression is evacuated through the perforations 11 Consequently, the moisture content of the polyethylene leaving the tube 5 is lower than that which it

was in container 3.

  When mixing a fluff pulp of cellulose and polyethylene in the mixer, it is necessary that the mixture has a given moisture content in order to avoid the problems caused by static electricity. Consequently, there is an advantage when the polyethylene, as is the case in the process of the invention, introduced into the mixer, has a higher moisture content than in the case of the previously known process, in which it is necessary to add water in the mixer to counteract the static electricity which appears It may be mentioned, in this connection, that the homogeneous mixture of cellulose fibers and fibers forming a binder which leaves the mixer has, in general, a moisture content

between 7 and 15%.

  Since the moisture content of the cellulose fluff supplied to the mixer can also vary, it is preferred to configure the tube 5 in a way that allows the moisture content of the stream of polyethylene leaving the tube to be modified. end, the part of the tube 5 placed externally to the screw 6 can be formed of two mutually cooperating parts, a lower rigid part of semicircular cross section and an upper part of U-shaped cross section, this upper part being able to pivot in a vertical direction, for example using a hinge, so that the common cross-sectional shape of the two parts can be modified by placing a more or less large part of the branches of the U above the upper line of definition of the lower cross-section It will be understood that other construction arrangements are also possible for controlling the moisture content of the material. re delivered by the outlet tube For example, conical tubular extensions can be arranged in the free end of the

outlet tube.

  In a variant (not shown) of the device illustrated in FIG. 2, the container 3 has a horizontal bottom and the transport worm 6 as well as the

  outlet tube 5 also extend horizontally.

  To prevent the appearance of a free water surface in the container 3, the lower part of the container is perforated. To shorten the time taken to complete the start-up phase, the flow of water delivered by the nozzle is adjusted. 7 so that excess water is constantly supplied to the polyethylene Then, to fill the container 3 to a given level, it will be understood that the start-up phase ends when the quantity of water discharged from the container 3 per unit of time is equal to the quantity of water delivered per unit time by the nozzles 7 However, this comparison between the above quantities requires the presence of relatively complicated and expensive measuring equipment and, therefore, it is preferred, in the case of this variant, empirically determine the duration of the

start-up.

  The polyethylene is introduced into the apparatus described in an environment such that its intrinsic absorption capacity is used to the full. The advantage provided by the use of such an environment is that it is possible to determine the moment when the capacity material absorption was used, for example by comparing the quantities of water supplied to and discharged from the device per unit of time, or by letting the flow of water above the overflow indicate than

  the material is unable to absorb more water.

  However, it is not necessary for the environment to be such as to allow maximum absorption in order to obtain a polyethylene having a homogeneous moisture content. To achieve this state, it is sufficient that the moist environment has a moisture content greater than the moisture content of the incoming polyethylene and to maintain this material in said environment for a time sufficient for it to take, by absorption, in all its parts, a state of equilibrium with respect to the environment However, since the moisture contents of the incoming material initially vary, this material absorbs varying amounts of water per unit of time from the environment, which means that it is necessary to modify the quantities according to which the water is delivered by unit of time in a humid or moist environment, to maintain continuity in the moisture content of this environment It is therefore preferable to use an environment in which it is possible to work with an excess of water, this making it possible to ensure in a simple way the continuity of the moist or humid environment into which is introduced

polyethylene.

  It will be understood that it is possible to modify, within the framework of the invention, the embodiments described and shown, particularly as regards the arrangement making it possible to create the abovementioned moist environment. For example, the polyethylene can be sprayed with water while it is on the conveyor belt and, in this case, the conveyor belt is perforated In addition, one can also use exit devices other than worm feeders According to one of the system variants , the polyethylene can be advanced from the coarse paste forming station through a water bath, using an endless feed screw, a "worm-piston" pump, or other similar devices, then compressed in a conical discharge pipe Because this compression contributes to a homogenization of the moisture content of the outgoing material, when the arrangement has been dimensioned correctly, such an arrangement you may not

operated during the start-up phase.

  It will also be understood that it is possible to use thermoplastic fibers forming a binder other than

polyethylene fibers.

Claims (6)

  1 Process for adding thermoplastic fibers, such as polyethylene fibers, to a cellulose fluff pulp, process in which the thermoplastic fibrous material and the cellulose fluff pulp are introduced into a kneader in which the fibers are disintegrated and the mixture is homogenized, characterized by the introduction of a thermoplastic fibrous material into an environment whose moisture content is controlled and then by the introduction of the material into the mixer in a wet state.   2 Method according to claim 1, characterized by the creation of said humid environment by spraying water on the fibrous material   thermoplastic during its passage to the mixer.   3 Method according to claim 1, characterized by the creation of the humid environment by passing the   thermoplastic fibrous material through a water bath.   4 Method according to any one of   previous claims, characterized by   compression of the thermoplastic fibrous material leaving the humid environment before its introduction into said mixer, and by evacuation of the expressed water of said material.   5 Installation for implementing the method according to claim 1, this installation comprising a pneumatic transport device for transporting the cellulose fluff pulp to a mixer, characterized in that the installation comprises an arrangement (B ) operating to create a moist environment, means (1) for transporting the fibrous material to the arrangement (B) operating to create a moist environment, means (2) for introducing the fibrous material into said humid environment, and means (5, 6) for transferring the wetted fibrous material out of the environment   wet and introduce it into said mixer.   6 Installation according to claim 5, characterized in that the means for transferring the wetted fibrous material out of the humid environment comprises means for compressing the transferred material outside of said environment.