Method for producing electrostatically non-chargeable and/or electric charge-draining plastic containers and a plastic container produced according to the method

Abstract

The invention relates to a method for producing multi-layered containers from a thermoplastic material ( 10 ), said containers being used to store and transport liquid fillers, especially combustible or explosive fillers, and a plastic container produced using said method. The inventive containers are provided with a thin, permanently electrostatically non-chargeable or electric charge-draining outer layer. According to the invention, the permanently electrostatically non-chargeable or electric charge-draining properties of the outer layer are created by adding a defined quantity of a specific compound based on a polymer to the base plastic material of the outer layer and incorporating the same into the plastic material, and the outer layer is thin so that the transparency or translucency of the compounded outer layer is either not affected, or only slightly affected, such that the filling level of a liquid poured into the container remains optically identifiable without taking any other measures.

1 .- 13 . (canceled)  
   
   
       14 . A method for producing a multi-layer container of thermoplastic material by a blow-molding technique, for storing and transporting liquid fill material, said method comprising the steps of: 
 applying to the container an exterior layer incapable of permanently retaining an electrostatic charge by allowing electric charges to drain, and    adjusting a charge-retaining characteristic of the exterior layer by adding and admixing to the plastic material a limited quantity of a polymer-based compound and reducing a layer thickness of the compounded exterior layer so as to have a substantially unchanged transparency or translucency, thereby allowing easy optical detection of a fill level of the liquid fill material in the container.    
   
   
       15 . The method of  claim 14 , further comprising the steps of adding and admixing a limited quantity of color pigments to the plastic material of the exterior layer for coloring the plastic material of the exterior layer to allow visualization and evaluation of an area distribution and a layer thickness distribution of the exterior layer, while leaving the transparency or translucency substantially unchanged so as to allow easy optical detection of the fill level of the liquid fill material in the container.  
   
   
       16 . The method of  claim 14 , further comprising the steps of adding and admixing a limited quantity of optical brightening agents to the plastic material of the exterior layer, said optical brightening agents producing no recognizable coloration under ambient light, and illuminating the exterior layer with a wavelength other than ambient light to detect a response from optical brightening agents for visualization and evaluation of an area and layer thickness distribution of the exterior layer.  
   
   
       17 . The method of  claim 14 , wherein the exterior layer comprises a fusible, easily stretchable thermoplastic material selected from the group consisting of LLDPE (Linear Low Density PolyEthylene(New) and LDPE (Low Density PolyEthylene(New), and wherein at least one of a center layer and an interior layer of the multi-layer container comprises a cold-impact-resistant HDPE material (High Density PolyEthylene(New) with a high molecular weight.  
   
   
       18 . The method of  claim 14 , wherein the layer thickness of the exterior layer of the multi-layer container is adjusted to a thickness of approximately 0.25% to 5% of a wall thickness of the plastic container.  
   
   
       19 . The method of  claim 14 , wherein the multi-layer container is a pallet container having an average wall thickness of approximately 2 mm to 2.5 mm and a capacity of approximately 1000 liters, and wherein the thickness of the exterior layer is adjusted to approximately 0.05 mm to 0.2 mm.  
   
   
       20 . The method of  claim 14 , wherein the multi-layer container is adapted for storing and transporting flammable or potentially explosive fill materials.  
   
   
       21 . The method of  claim 16 , wherein the wavelength other than ambient light comprises black light.  
   
   
       22 . The method of  claim 18 , wherein the layer thickness of the exterior layer of the multi-layer container is adjusted to a thickness of approximately 2.0% of the wall thickness of the plastic container.  
   
   
       23 . The method of  claim 18 , wherein the thickness of the exterior layer is adjusted to approximately 0.1 mm.  
   
   
       24 . A container made of thermoplastic material by a blow-molding technique, for storing and transporting liquid fill material, comprising: 
 at least one gas-tight and fluid-tight closable fill and/or drain opening disposed in a top wall or in a cover of the container, and    an exterior layer incapable of permanently retaining an electrostatic charge by allowing electric charges to be drained, said exterior layer including a limited quantity of a polymer-based compound which does not or only insubstantially change a transparency or translucency of the external layer, allowing easy optical detection of a fill level of the liquid fill material in the container.    
   
   
       25 . The container of  claim 24 , wherein the exterior layer comprises a limited quantity of color pigments which slightly color the plastic material of the exterior layer, but allow visualization and evaluation of an area distribution and a layer thickness distribution of the exterior layer.  
   
   
       26 . The container of  claim 24 , wherein the exterior layer comprises a limited quantity of optical brightening agents, which produce no recognizable coloration under ambient light, but allow visualization and evaluation of an area distribution and a layer thickness distribution of the exterior layer under illumination with light having a wavelength other than ambient light.  
   
   
       27 . The container of  claim 24 , wherein a layer thickness of the exterior layer is adjusted to a thickness of approximately 0.25% to 5% of a wall thickness of the plastic container.  
   
   
       28 . The container of  claim 24 , wherein the multi-layer container is a pallet container having an average wall thickness of approximately 2 mm to 2.5 mm and a capacity of approximately 1000 liters, and wherein the thickness of the exterior layer is adjusted to approximately 0.05 mm to 0.2 mm.  
   
   
       29 . The container of  claim 24 , wherein the exterior layer comprises a fusible, easily stretchable thermoplastic material selected from the group consisting of LLDPE (Linear Low Density PolyEthylene(New) and LDPE (Low Density PolyEthylene(New), and wherein at least one of a center layer and an interior layer of the multi-layer container comprises a cold-impact-resistant HDPE material (High Density PolyEthylene(New) with a high molecular weight.  
   
   
       30 . The container of  claim 26 , wherein the wavelength other than ambient light comprises black light.  
   
   
       31 . The container of  claim 27 , wherein the layer thickness of the exterior layer is adjusted to a thickness of approximately 2.0% of the wall thickness of the plastic container.  
   
   
       32 . The container of  claim 28 , wherein the thickness of the exterior layer is adjusted to approximately 0.1 mm.  
   
   
       33 . The container of  claim 24 , wherein the multi-layer container is a pallet container having a thin-wall cuboid interior container with a fill port in a top wall and a drain port on a lower side, and an extraction fitting made of a permanent antistatic or electric charge-draining plastic material and attached to the drain port.