DE2236564A1 - FUEL TANK MADE OF THERMOPLASTIC PLASTIC - Google Patents

Description

·, FARBWERKE HOECHST AKTIENGESELLSCHAFT 2236564

¹ formerly Master Lucius & Brüning

File number: _{H0E 72} / f 220 u. H.

Date: July 18, 1972 'Dr.MD/CK

Thermoplastic fuel tanks

It is known that for the choice of material and the When designing fuel tanks, a number of recommendations must be followed. Regarding the choice of material for safety reasons it is required that the fuel tank has the chemical, mechanical and ' withstands thermal stresses that it is sufficiently impermeable to fuel and sufficient Has aging resistance. It must not be dangerously electrostatically charged and it must be built-in Prove that the condition is sufficiently fire-proof «With normal operational use, the accumulation of ignitable fuel-air mixtures in vehicle construction excluded be.

So far, fuel tanks have mainly been made from sheet steel. Due to the strength and conductivity of metallic materials meet this fuel. Sheet steel containers meet a number of the demands made satisfactory. However, the known susceptibility to corrosion, the deformation behavior and are disadvantageous the behavior in case of fire. For safety reasons, it is desirable that the fuel tank should not be used in the event of an accident the greatest possible crumple effect, suffers

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without tearing. Meet sheet steel fuel tanks this requirement is not satisfactory because they have only a limited impact and shock resistance. Even In terms of fire behavior, the sheet steel fuel tank may prove to be disadvantageous or even dangerous. The high strength means that the container will only tear when the fuel is already in use is under very high internal pressure. The fuel can burn down in the form of a dangerous fire lance.

Sheet steel fuel tanks are commonly used made from blanks by deep drawing and welding. This production method has the consequence that only geometrically simple designs can be produced economically. With the container made of sheet steel therefore, in many cases, optimal space utilization cannot be achieved.

Fuel tanks made from other materials are so far only for the engines of smaller machines and for Manufactured small series of automobiles and test vehicles.

In the foreground are thermoplastics, which are produced after the various thermoforming processes, e.g. B. Blow molding, pressing, rotary melting, injection molding and deep drawing can be processed. It is also known, plastic containers by polymerizing monomers, e.g. B. caprolactam to produce in a mold. For thermoplastic processing is mainly low pressure polyethylene and polyamide are used.

The plastics allow the geometry of the fuel tank as far as possible to adapt to that of the vehicle. This results in an optimal use of space and, consequently, the greatest possible Filling volume achieved. Other advantages of art

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-3-. 2236584

substances are the corrosion resistance under weather conditions, the favorable fire behavior and the good resilience to impact and shock loads. In case of fire the fuel tank melts in a temperature range in which there is not yet a very high internal pressure. Of the Fuel runs out and burns without deflagration. Furthermore, it is very important that when executing in plastic, the manufacturing costs, in particular the tooling costs, are comparatively low. Because of The low density of plastics, which is only about 1/7 that of ferrous materials, also results in considerable Weight savings.

In the case of the polyamides, which are characterized by a relatively low permeability for fuel, the known temperature and humidity dependence of the mechanical properties a disadvantageous factor, especially in the temperature range below freezing point. Low-pressure polyethylene has this disadvantage not on. However, it has a relatively high level of permeability for fuel, which makes the initially established Directives are not met.

Due to the known relationship between the diffusion rate and the wall thickness, it is possible that the Diffusion by increasing the wall thickness to a certain extent to slow down. However, for obvious reasons, a reduction by about one order of magnitude is not possible.

Attempts have been made to carch paint this disadvantage to eliminate. It was found that a layer of lacquer applied too thinly did not have a sufficient diffusion layer is and with sufficient thickness of the paint the impact and shock breaking strength disproportionately strong is decreased.

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It has now been found that fuel tanks made of low-pressure polyolefins are preferably made of low-pressure polyethylene, Polypropylene or copolymers of ethylene and propylene have excellent properties if you 75 to 100% of the surface of the fuel tank with a 10 to 100 µm thick plastic film, which is a Gas permeability for methane, measured according to DIN 53 380

3 "2 -1
no more than 150 cm. m, d, atm and fuel-resistant coated.

3 "2 -1 -I of at most 150 cm .m, d, atm, firmly adhering

The inspection of such fuel tanks showed that they are largely impermeable to fuel and that by Surprisingly, this composite also improves the impact and impact fracture behavior. After all it is possible to provide foils for the outer coating of the container that have an electrically conductive surface, e.g. B. a metal layer or an outer layer with a sufficient content of electrically conductive fillers, such as Graphite and / or certain types of carbon black. This creates a dangerous electrostatic charge on the Prevents fuel tank.

From the data in Table 1 it can be seen that, for example, films made of polyacetal, polyamide and polyterephthalic acid esters, preferably polyethylene glycol terephthalate, and in particular composite films made of these Plastics and polyvinylidene chloride are suitable, but not high-pressure polyethylene films. About a fuel-resistant composite To get between the plastic film and the container wall, you can use composite films on polyamide, polyacetal or use polyterephthalic acid esters with high pressure or low pressure polyethylene, being careful is that the polyethylene layer is arranged on the composite side.

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Table I.

plastic

Layer thickness

or

Film thickness

around

Gas permeability

for methane according to DIN 53 -380 3 -2.-1. -I

cm. m .d .atm

Polyacetal
polyamide

High pressure polyethylene density 0.92 g / cnT Polyethylene terephthalate composite film made of: polyvinylidene chloride, polyethylene terephthalate High pressure polyethyle n

40 40

40 40

.5 12 50

67

33 80

3500 22

The film coating, which acts as a diffusion barrier, is applied on most advantageous applied to the outer surface of the fuel tank. In principle, however, it is also possible to coat the inner surface of the container. The container should be coated as completely as possible, what however, it is not always feasible. By comparative provisions It has been shown that even with a surface coating of 85%, the fuel permeability is compared to the uncoated container can be reduced by almost an order of magnitude. The use of composite films with a

OUI

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High-pressure or low-pressure polyethylene layer enables the firmly adhering and fuel-resistant bond, as this Layer welded to the container during production under increased pressure and temperature in the mold. Corresponding composite films made of polyterephthalic acid ester and Polyethylene are commercially available and inexpensive.

It is of particular advantage that the usual tools for the production of the fuel tank according to the invention, z. B. blow molding, injection molding or deep drawing tools are used come. There are several possibilities for the surface coating according to the invention. So z. B. a contour of the same shape Foil with a polyethylene layer on the composite side in an injection molding or injection molding machine designed for the production of a container half-shell Deep-drawing tool inserted and attached by suction, Adhesive or held by electrostatic charges. The contour of the same film lets through Produce deep drawing in the same or a suitable tool.

Another possibility is to insert several foil blanks corresponding to the tool geometry with a composite-side polyethylene layer, which may also be profiled, in the tool. In this case, the surface of the fuel tank is not completely covered, but to the required extent (at least 75 %) , whereby the relative fuel permeability is correspondingly reduced. Container half-shells produced in this way, in which the filling, venting and removal openings are already formed, can be connected to one another, for example, by welding.

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For the production of fuel tanks according to the invention extrusion blow molding can also be used. Here, the film is bonded with a polyethylene layer or the cutting material is placed in the hollow mold and held on the tool as already described. The blow molding of the fuel tank then takes place in a manner known per se Way, whereby the calibration of the connecting pieces is possible at the same time. Unless one of extruded, ribbon-shaped Preforms running out can be inserted between the strips can also be formed into baffles using this process.

Figure 1 shows an example of an embodiment of the fuel tank according to the invention,

FIG. 2 shows a detail "Z" of FIG.

Reference number 1 indicates the wall made of thermoplastic material, reference number 2 the diffusion-inhibiting one Foil with adhesive layer on the composite side.

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example

From low-pressure polyethylene, density 0.95 g / cm, containers with a filling volume of

3 2

3100 cm and an outer surface of 1100 cm.

The mean wall thickness of the container was 0.35 cm. The outer coating according to the invention with a thickness of 62 μm Composite film made of polyethylene terephthalate (12yUm) and High-pressure polyethylene (50 µm) was made by placing blanks in the blow mold and blow molding in a manner known per se achieved. The result was an external surface coverage of 85%.

A test series of 5 containers was tested with 60% by volume Filled with super fuel, tightly closed and stored at 40 C in a circulating air cabinet. Your conscience The weight loss was determined at intervals. The information is contained in Table 2. The association proved proven to be stuck and fuel resistant.

Comparative experiment

For comparison, the containers described in the previous example were produced without an external coating and tested under the same conditions. The results are shown in Table 2.

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Table 2 Weight loss G ■ Super fuel G Storage time according to the invention 1 Comparative experiments 7th at 40 ° C im container 8th - 57 Circulating air cabinet 14th 109 Days 28 236 10 37 302 : 30 50 80 100

G Uf

Claims (7)

Protection claims Fuel tanks made from low-pressure polyolefins for ' Internal combustion engines, characterized in that 75-100% of the surface of the fuel tank with a 10 to 100 µm thick plastic film, which measured a gas permeability for methane ο O -I "· DIN 53 380, of a maximum of 150 cm. m ~. d. atm " has a firmly adhering and fuel-resistant coating is. 2. Fuel tank according to claim 1, characterized in that that at least 85% of the surface of the fuel tank is coated. 3. Fuel tank according to claim 1 and 2, characterized characterized in that the outer surface of the fuel tank is coated. 4. Fuel tank according to claim 1 and 2, characterized characterized in that the inner surface of the fuel tank is coated. 5. Fuel tank according to claim 1 to 4, characterized characterized in that the plastic film is a composite film made of polyethylene and polyterephthalic acid ester is. 6. Fuel tank according to claim 1 to 4, characterized in that the plastic film is a composite film made of polyethylene, polyterephthalic acid ester and polyvinylidene chloride. 7. Fuel tank according to claim 1 to 6, characterized in that it is an electrically conductive Has surface. 3Q9886 / 0U1