The invention relates to a method of producing a multi-layer composite material composed of low-density polyethylene (LDPE) and fiberglass reinforcement and intended for the manufacture of roadside safety barriers, the equipment for implementing the said method, and the multi-layer composite material produced by it.

Roadside restraints serve an important function in traffic safety by preventing vehicles from leaving the roadway or crossing over to the wrong lane. Until now steel or reinforced concrete has been used extensively to manufacture roadside safety barriers. However the durability of these materials is limited and in the event of collision they inflict additional damage to vehicles.

The advantage of using polymer materials in manufacturing roadside safety barriers is that polymer materials have a low friction rate and therefore do not cause additional damage to vehicles in the event of collision. Polymer materials are lighter, cheaper to produce and less prone to degradation via environmental factors

There is a number of patents pertaining to polymer materials, as well as methods of improving the mechanical properties of the polyethylene used for manufacturing roadside restraints or their parts. For instance, patent EP1409793B1 describes a specific structure of polyethylene, which is technologically challenging to produce.

A widely used method for improving the mechanical properties of polymer materials is reinforcing it with various materials, including fiberglass (for example, as described in patent US7743567). However the known methods fail to provide the composite material with mechanical properties that would comply with the requirements of the European standard EN 1317.

Methods for manufacturing composite materials are known wherein the reinforcing layer, such as fiberglass fabric, is glued to the layer of polymer material by means of another adhesive material (for example, as described in patent application US2006121805). However such a method is technologically unsuitable for continuous production. Furthermore, in the event of impact the composite material may disintegrate, as the deformative properties of each layer are different.

The present invention solves this technical problem by introducing a simple, resource- and cost-effective technology of producing composite material intended for the manufacture of roadside barriers, which is suitable for use within temperatures ranging from -50 to +40 °C.

In the method of producing multi-layer composite material for roadside safety barriers, which involves reinforcing LDPE with fiberglass, according to the present invention the middle sheet of LDPE, its thickness being 1 to 3 mm, is fed downward via the first pair of rollers and heated to the point of melting temperature, fiberglass fabric and the outer sheet of low-density polyethylene, its thickness being 1 to 3 mm, is applied to one side of the middle sheet of LDPE and braided fiberglass bundles and the other outer sheet of LDPE, its thickness being 1 to 3 mm, is applied to the opposite side of the middle sheet of LDPE by the second pair of rollers, spaced at a distance from each other that corresponds to the preferred thickness of the composite material, the braided fiberglass bundles are composed of 10 to 20 braided glass fibers each and fed at a distance of 8 to 20 mm from the adjacent braided fiberglass bundles, and all layers are compressed by the third pair of rollers.

The equipment for implementing the present method of manufacturing multilayer composite material for roadside safety barriers includes three pairs of rollers positioned below each other and designed to rotate at an equal speed ensuring even linear movement of the processed material, whereby the first pair of rollers is intended to evenly transport the middle sheet of LDPE downward, the second pair of rollers, spaced at a distance from each other that corresponds to the preferred thickness of the composite material, is intended to evenly transport all layers of the composite material downward, and the third pair of rollers is intended for compressing all layers of the composite material by the required force, as well as two hot air generators positioned symmetrically below the first pair of rollers. The symmetrical placement of hot air generators on both sides of the middle sheet of LDPE ensures that it is evenly heated to the point of melting temperature.

The multi-layer composite material produced by the present method is composed of five layers: the middle low-density polyethylene layer that has been embedded with fiberglass fabric on one side and braided fiberglass bundles on the opposite side and has welded the outer layers of low-density polyethylene together.

LDPE is a material that exhibits good operational properties over a wide range of temperatures from -50 to +40 °C. It is especially important to the application of this composite material in manufacturing roadside safety barriers that LDPE does not become fragile and retains its cold flow properties even at low temperatures. In order to increase the tensile strength of the composite material produced, LDPE is reinforced by fiberglass and fiberglass fabric, its thickness being no less than 0.1 mm. The tensile strength of glass fibers with a diameter of 1 1 to 13 microns is no less than 200 N per fiber. It has been experimentally established that the longitudinal tensile strength of the multi-layer composite material is sufficient when one layer of fiberglass fabric and one layer of braided fiberglass bundles, applied along the longitudinal direction of the composite material, are used. Using fiberglass fabric alone requires several layers of fiberglass fabric to be embedded in the composite material, however such a method is technologically complicated, costly and needlessly increases the amount of raw materials consumed. Embedding unbraided glass fibers is technologically complicated. On the other hand, if only layers of fiberglass bundles are used to reinforce the composite material, the longitudinal tensile strength of the composite material is satisfactory, but in the event of impact the composite material develops cracks between the embedded braided fiberglass bundles. By adding one layer of fiberglass fabric to the multi-layer composite material such cracks are prevented. The middle layer of LDPE must be sufficient to ensure that the melted LDPE would penetrate through the fiberglass fabric and simultaneously allow each glass fiber in a bundle to be embedded so that a uniform layer (coating) of fiberglass is formed and each glass fiber is in contact with the melted LDPE. It has been experimentally established that the consumption of raw materials is optimal when 0 to 20 glass fibers are braided in each fiberglass bundle, the fiberglass bundles are spaced at a distance of 8 to 20 mm from each other in the layer of composite material, and the thickness of LDPE sheets ranges from 1 to 3 mm.

The figure shows the basic sequence of producing multi-layer composite material intended for the manufacture of roadside safety barriers.

The present invention is implemented in the following way.

The equipment for manufacturing multi-layer composite material for roadside safety barriers includes three pairs of rollers 1 , 4, 8 positioned below each other and designed to rotate at an equal speed ensuring even linear movement of the processed material. The first pair of rollers 1 is intended to evenly transport the middle sheet of LDPE (2) downward, the second pair of rollers 4 is intended to evenly transport all layers of the composite material downward, whereby the rollers are spaced at a distance from each other that corresponds to the preferred thickness of the composite material, and the third pair of rollers 8 is intended for compressing all layers of the composite material 9 by the required force, whereas two hot air generators 3 are symmetrically positioned below the first pair of rollers.

The middle sheet of LDPE 2, its thickness being 2 mm, is fed downward via the first pair of rollers 1 at an even speed of linear movement, the hot air generators 3 heat the middle sheet of LDPE 2 to the point of melting temperature by streams of hot air. Fiberglass fabric 5 and the outer sheet of LDPE (6), its thickness being 2 mm, is applied to one side (left side in the figure) of the middle sheet of LDPE 2 and braided fiberglass bundles 7 and the other outer sheet of LDPE 2, its thickness being 2 mm, is applied to the opposite side (right side in the figure) of the middle sheet of LDPE 2 by the second pair of rollers 4, spaced at a distance of 5.8 mm from each other. The braided fiberglass bundles 7, composed of 10 braided glass fibers each, are fed at a distance of 10 mm from the adjacent fiberglass bundles. All layers are compressed by the third pair of rollers 8 thus improving the adhesion between layers. The thickness of the multi-layer composite material 9 produced is 5.2-5.8 mm. By way of melting, the middle sheet of LDPE 2 has been embedded with fiberglass fabric 5 and the braided fiberglass bundles 7 and has welded the outer sheets of LDPE 6 together. The mechanical properties of the produced multi-layer composite material comply with the T2 containment level of the European standard EN 1317.