EP1197445B1 - Antistatic fabric for flexible intermediate bulk container - Google Patents

Abstract

Antistatic fabric for flexible containers for bulk material that includes electrically non-conducting threads and static dissipative, special permanent antistatic threads. The static dissipative, special permanent antistatic threads are made of a thermoplastic synthetic with an additive mixed in that increases the conductivity. The static dissipative, special permanent antistatic thread is shaped like a small band or tape with an approximately rectangular cross-section or a multifilament of very thin filaments.

Description

The invention relates to an antistatic flexible bulk container with the features of the preamble of the claim 1.

In the case of fabrics made of non-polar plastics, especially by friction, a charge separation instead, so that there is electrostatic charge on the surface of the Collect tissue and compress locally when in a dry Environment with low humidity does not have the Can drain air. In contact with earthed objects and / or people can then get these charges suddenly discharged, a spark igniting high energy, which may be suitable for dust / air or Ignite gas / air mixtures and trigger an explosion.

There is also a risk of an Charge accumulation. With this physical phenomenon can an electric field is formed between two bodies, in which a contactless charge transfer takes place. Consequently can cause electrical charges when filling one out Plastic fabric made container arise on neighboring Pass over bodies with greater capacity, e.g. B. Unearthed metal drums on wooden pallets. That is also a surrounding area of a container made of plastic fabric potentially explosive due to sparking.

In the applicant's patent DE 39 38 414 C2 Bulk container made of an electrically conductive fabric disclosed, that consists of synthetic fibers or plastic threads and has electrically non-conductive and electrically conductive threads, the electrically conductive threads made of a polyolefin exist and contain dispersed carbon black and / or graphite and woven into both the warp and the weft are.

A fabric of this type is for the high mechanical stresses, like when using the fabric for one flexible bulk container, well suited, and through the woven electrically conductive threads will be a safe discharge reached by electrostatic charge.

A fabric called "electrically conductive" has a resistance to earth of less than 10 ⁸ Ω. Such a leakage resistance is generally required for explosion protection measures based on various technical safety regulations, including flexible bulk material containers made of polypropylene tape type "C" in accordance with the classification of the German industrial working group "Combustible Dusts / Electrostatics".

However, it has been shown that such a low leakage resistance paradoxically, the fabric has an adverse effect entails: due to the low resistance can charges become very fast and with a high charge density move and move across the entire surface of the fabric then at a point where a touch by an opposing one charged charge carrier or for example a or grounded person, suddenly discharge. thats why always before the start of a filling process that separates the charge cause a connection to the earth, resulting charges immediately from the surface of the tissue can flow off against earth.

However, this earth connection has proven to be a hindrance there z. B. always a bulk container individually and manually a metal clamp and a metal cable are grounded before filling must be done and the earth connection then manually again must be solved. There is also a risk that Forget the earth connection due to carelessness becomes.

Furthermore, GB 21 01 559 A1 is a bulk container known, which is made of a fabric in the metal threads are incorporated over the electrostatic charges of the tissue can be derived.

The disadvantage of this solution is that the elongation behavior the metal fibers or threads very different from the elongation behavior of the rest of the tissue. This easily leads to Breakage of the metal threads and thus an interruption of the Dissipation.

Furthermore, there is a risk that metal threads, for. B. from Copper or iron or their alloys corrode in air. Such breakpoints will in the case of static charge the risk of sparking and explosion greatly increased.

In particular, however, occur because of the very good conductivity of the metal threads have the same problems that previously existed for the threads filled with soot have been described.

Tissues to which an antistatic is applied are also known is so that the finished fabric is electrical Can derive charges.

However, the fabric produced in this way only fulfills that as new goods Fire and explosion hazard requirements; the conductive antistatic coating according to the state the technology is not permanent, rather it is temporal is limited. Equipment with an applied antistatic Coating has been used in such applications proven unsuitable in which the fabric is strong mechanical Abrasion is subject to, even with bulk containers scrape together when stacking over large areas or over be ground. With the high strains one highly stressed plastic fabric tears the coating and / or flakes. In addition, these containers are on loan used several times. Then it is particularly dangerous that the loss of electrical conductivity caused by abrasion is not recognizable during the period of use, so that protection requirements are assumed for users, that are no longer there.

From US-PS 5,679,449 and US-PS 6,112,772 are flexible Bulk goods containers, so-called flexible intermediate bulk containers (FIBC), which consist of a fabric that contains quasi-conductive threads that are metallized.

The effect of the so-called corona discharge is used here. This occurs on a charge carrier with a very small one Radius of curvature, so also on thin woven threads or on Tips on. With the corona discharge a very arises weak, limited to the immediate vicinity of the tip Discharge to the air, which is continuous and over one longer period expires, so manual grounding over ground wire is not required.

However, the conductivity of the tissue is so great that a fast charge transfer when in contact with a large charge sink and an associated sudden discharge can occur with spark formation.

Another disadvantage is that the antistatic, quasi-conductive It is difficult to produce threads in the known fabric and are to be processed. Already applying one metallic surface on a plastic thread formed core is complex and expensive. The antistatic Sheathing is subject to mechanical wear as before has been described for full-area coatings.

In addition, the antistatic thread has a cross-sectional geometry, those of those commonly used for bulk containers Ribbon tissues deviate and thus in terms of Processability causes problems.

The diameter of the coated thread can for reasons of Processability and mechanical resilience too not be kept as small as it would be desirable to the effect of corona discharge over the length of the thread and not only at the ends - to be able to use. Therefore can still local charge fields in unfavorable conditions form on the tissue surface that is not due to corona discharge are degradable, but degrade suddenly can.

From WO 96/09629 is an antistatic additive for thermoplastic Known plastics made from a thermoplastic Polymer mass is an electrically conductive Includes network of non-metallic, microcrystalline needles. This network is fusible, so that it can the usual processing methods of plastics technology is processable and with cooling of a plastic melt crystallized again. The microcrystalline network is in the polymer mass is embedded and therefore wear-resistant because it not be abrasively removed from the surface of a component can.

The invention has for its object a bulk container of the type mentioned at the outset, the has permanent antistatic properties and thus in explosive and fire hazardous areas can be used and which, in particular, are not earthed in all applications got to.

According to the invention, the task with an antistatic flexible bulk container with the characteristics of the generic term of claim 1 in that the antistatic, quasi-conductive threads made of a thermoplastic Made of plastic in which the conductivity increases Is mixed in additive, which is a thermoplastic, thermosetting or cross-linked polymer that is electrically conductive network of microcrystalline needles is permeated as a means of forming current paths in the threads to enable a braked charge transport.

A fabric is called "antistatic, quasi-conductive" here, the surface resistance of which, measured according to DIN 53482, is greater than 10 ⁸ Ω and less than 10 ¹¹ Ω. The electron flow is strongly slowed down at this resistance, but is still possible.

Under "ribbons" are extruded or cut from foils Plastic tapes are understood to be in cross section have a large width in relation to their thickness and which can be processed using web technology.

By mixing the conductive additive into the polymer mass the thread is achieved on the one hand that an electron line is made possible within the thread. On the other hand is the specific electrical resistance of the obtained thermoplastic mixture however so high that the electron flow is possible only very slowly. This ensures that a constant flow of electrons and a constant Delivery of cargo to the environment is possible, however cannot flow as much charge in a short time, that there is a sudden high energy discharge can come under the formation of an ignition spark.

Due to the geometry of the quasi-conductive ribbon-shaped The thread has very narrow, sharp edges. On these edges Corona discharge can occur over the entire length of the ribbon take place through which constantly in controlled Wise charge from the surface of the tissue to the environment can drain off. In addition to the advantage of corona discharge to the Narrow edges gives the further advantage that the relative wide ribbons have a large surface and therefore one have a large capacity for receiving electrical charge. The charges are seen across the large surface of the fabric distributed, and local charge concentrations leading to sudden high energy discharges, are avoided.

In the case of a flexible bulk goods container, the aforementioned can be used Establish a manual earth connection via earth clamp and cable in most applications to be dispensed with, since contactless electrical derivation Charges to the environment is enabled.

To form "islands" of electrostatically insulating Fabric sections in the middle of the grid made of electrically conductive Avoiding threads is the distance between the threads not less than 1 cm and not more than 5 cm. Preferably a distance of 3 cm is selected.

The fabric advantageously has the warp threads, the weft threads and covering the antistatic, quasi-conductive threads antistatic plastic coating made from a thermoplastic consists of a conductivity increasing additive is mixed. Through this coating it is achieved that a load is large can spread over the fabric surface and local charge peaks can be broken down.

Particularly in the case of a flexible bulk goods container according to the invention of the aforementioned type, in which at least one antistatic Plastic coating on the on the carrier bag applied to the outside facing surface of the antistatic fabric the possibility advantageously remains remains to make a manual grounding. This needs just clamped a ground clamp to a fold of the fabric become. The antistatic coating is not only a good charge distribution over the entire surface sure, but also that the earth clamp is electrically connected to the antistatic, quasi-conductive threads in weft and / or warp connected is.

Further advantageous embodiments are the subclaims and the following description of an embodiment refer to.

Fig. 1

einen Schüttgutbehälter in perspektivischer Ansicht;

Fig. 2

einen Ausschnitt von der Oberfläche eines antistatischen, quasi-leitfähigen Fadens in stark vergrößerter Draufsicht;

Fig. 3

ein erfindungsgemäßes Gewebe in Draufsicht; und

Fig. 4

eine schematische Entladungskurve bei dem Gewebe des erfindungsgemäßen Schüttgutbehälters.

The invention is explained in more detail using an example which is shown in the drawing. The figures show in detail:

Fig. 1

a bulk container in perspective view;

Fig. 2

a section of the surface of an antistatic, quasi-conductive thread in a greatly enlarged plan view;

Fig. 3

a fabric according to the invention in plan view; and

Fig. 4

a schematic discharge curve for the fabric of the bulk container according to the invention.

1 shows a flexible fabric made from a fabric 100 Bulk goods container 10 with a carrying bag 15 there is a carrying strap designed as transport loops 17, 17 '.

In its lid area 14, the carrying bag 15 has a filler neck 18 and in its bottom area 11 an outlet nozzle 19 on. The carrying bag 15 is made of the anti-static Fabric 100 of the invention made. In the collar area 16, in Lid area 14 and in the area of the filler 18 and outlet nozzle 19 can be used to optimize the discharge behavior Compaction of the grid 12 from antistatic, quasi-conductive Threads are provided. Likewise, in the material for the carrying straps 17, 17 'to ensure the derivation conductive material incorporated.

2 shows a schematic view of an antistatic, quasi-conductive warp 4 or weft 5 as they offers itself under the microscope. In this preferred embodiment are 20% by mass of an additive, as described in WO 96/09629 is described, in a base polymer, here polypropylene, mixed.

In a matrix 8 of the base polymer there are a large number of microcrystalline needles 6 embedded, which are meltable and which crystallize out on cooling. In order to the mixture is extrudable, sprayable and otherwise can be processed with the techniques of plastics processing.

The needles 6 are in such a density within the matrix 8 arranged so that they touch or overlap. Thus, the example of the detail shown here forms between any point 7.1 and another Point 7.2 at the other end of a thread section through the microcrystalline needles 6 a multiplicity of current paths 7 , one of which is shown here as thick Line is marked. Along such a current path 7 braked charge transport is possible.

About the dosage of the mass fraction of the additive from 5% to The density of the microcrystalline is 30% compared to the polypropylene matrix 6 needles and thus the number of training Current paths 7 varies, thus reducing the conductivity / specific resistance of the polymer mixture as a whole is influenced.

It can also be provided that in addition to the additive acicular metal particles of macroscopic size, so with about 0.1 to 2 mm in length, embedded in the matrix 8 are. These metal particles appear as fine tips on the Surfaces of the antistatic, quasi-conductive threads; on A corona spray discharge can take place at each of these tips.

In Fig. 3 is a portion of one made in accordance with the invention Fabric 100 shown. Both warp threads 3 and Weft threads 4 are tapes made of a thermoplastic material. Such tapes are easily obtained by that a film is made from the plastic, which is then cut into ribbons by a knife in the direction of the web becomes; the ribbons are then stretched. There standard plastics, especially polypropylene, are also suitable and the ribbons are one in comparison to textile yarns Large widths of approximately 0.5 to 5 mm can be inexpensive large-area fabrics are produced. In the tissue 100 are antistatic, quasi-conductive threads 4 woven into the here for better illustration schematically as a bold double line are drawn.

The antistatic, quasi-conductive threads 4 are preferably in woven into a chain at a distance of about 3 cm from each other. Around especially in the event of breakage of the antistatic, quasi-conductive thread a derivative of the electrical charge ensure even at greater intervals of preferably 30 cm antistatic, quasi-conductive threads 5 in Weft to be woven. About these weft threads 5 can Interruption of a quasi-conductive warp thread 4 a diversion of the electrical charge flow until the next intact Warp thread 4 can be reached.

Whether the antistatic, quasi-conductive threads 4 mainly to be woven as weft or warp threads is for the electrical Properties of the fabric according to the invention irrelevant and can be chosen according to the needs of the weaver.

Since the geometry of non-conductive threads 2, 3 and antistatic, quasi-conductive threads 4, 5 is preferably the same, there are no weaving difficulties, when the antistatic, quasi-conductive threads are woven together in the weft become.

However, round threads with mixed additives can also be used Use if they are very thin and therefore the possibility a good corona discharge.

Fig. 4 shows the discharge of the tissue. The voltage drop is plotted over time. Starting from a high potential U _H , the charge supply is interrupted at time t ₁ . As the solid, upper line shows, the charge continuously degrades due to continuous corona discharge at the edges of the ribbon, the thread ends and any macroscopic metal particle tips that have been mixed in, until it reaches a minimum at the level of U _L1 at time t ₂ . Grounding was not carried out here.

If the same tissue is grounded with a ground cable, the charge - as indicated by the dashed line - degrades faster and to an even lower level U _L2 , but both times the levels of the residual potentials U _L1 and U _{L2 are} so low that at contact with people, metallic objects etc. no longer jumps a spark.

Claims (9)

1. An antistatic flexible bulk goods container (10), consisting of a flexible carrier bag and, fixed thereon, carrying means such as carrying loops (17, 17'), a carrying ring, carrying strap or the like, wherein at least the carrier bag consists of an antistatic woven fabric (100) which has electrically nonconductive (2,3) and antistatic quasi-conductive filaments (4), the antistatic quasi-conductive filament being in the form of a ribbon of approximately rectangular cross-section and with a narrow sharp edge, or is a thin round filament, characterised in that the antistatic quasi-conductive filaments (4) consist of a thermoplastic material in which there is mixed an additive which increases the conductivity and which is a thermoplastic, thermosetting or cross-linked polymer which is interspersed with an electrically conductive network of microcrystalline needles (5) as a means of forming current paths (7) in the filaments (4) in order to allow braked charge transport.
2. A flexible bulk goods container (10) according to claim 1, characterised in that the additive is mixed in with the thermoplastic material of the antistatic quasi-conductive filaments (4) in a proportion of 5% to 30% by weight.
3. A flexible bulk goods container (10) according to claim 1 to 2, characterised in that in addition to the additive there are embedded in the thermoplastic material of the antistatic quasi-conductive filaments (4) metal particles in the form of needles which are insulated from one another and which permit a corona discharge.
4. A flexible bulk goods container (10) according to any one of claims 1 to 3, characterised in that the filament in the form of a ribbon has a thickness of 100 µ to 500 µm and the width is 10 to 100 times the thickness.
5. A flexible bulk goods container (10) according to any one of claims 1 to 4, characterised in that the distance between the antistatic quasi-conductive filaments (4) in the warp direction (3) is 1 to 5 cm, preferably 3 cm.
6. A flexible bulk goods container (10) according to any one of claims 1 to 5, characterised in that the distance between the antistatic quasi-conductive filaments (4) in the weft direction is 10 cm to 60 cm, preferably 30 cm.
7. A flexible bulk goods container (10) according to any one of claims 1 to 6, characterised by an antistatic plastic coating which covers the warp filaments (2), the weft filaments (3) and the antistatic quasi-conductive filaments (4) and which consists of a thermoplastic material in which there is mixed an additive which increases the conductivity.
8. A flexible bulk goods container (10) according to any one of claims 1 to 6, characterised in that an antistatic plastic coating is applied to that surface of the antistatic woven fabric which faces the exterior on the carrier bag.
9. A flexible bulk goods container (10) according to any one of claims 1 to 8, characterised in that the antistatic woven fabric (100) of the bulk goods container has, in its lid (14) and collar zone (16), a number of antistatic quasi-conductive filaments (4) which is greater than the rest of the woven fabric of the carrier bag.

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