Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-01-07
2003-02-11
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S036910, C428S483000, C428S515000, C428S516000
Reexamination Certificate
active
06517918
ABSTRACT:
The present invention relates to a multilayer composite plastics material, containing at least one layer (A), which, based on the total weight of this layer, consists of at least 90 wt % of ethylene homopolymers or copolymers, at least one barrier layer (B), which substantially consists of polybutylene terephthalate and also, if desired, layers of adhesion promoter (C) serving to improve the adhesion between these layers.
The present invention also relates to a process for the preparation of such composite plastics materials, to hollow bodies and, in particular, plastic fuel cans made of such composite plastics materials and also to the use of polybutylene terephthalate as a barrier material in such multilayer composite plastics materials.
Polyethylene (PE), particularly high-density polyethylene (PE-HD), is highly suitable for extrusion blow molding of hollow bodies. Such hollow bodies are suitable for the storage and transport of liquid and solid materials. A special use of these hollow bodies is the storage and transport of hazardous liquid materials. Another usage is that of plastic fuel cans (PFC), such as are used in motorcars to provide a spare supply of liquid diesel fuel or fuel for Otto engines in a manner which saves space and weight. Its high degree of tenacity and rigidity and its good processibility, making it possible to produce even voluminous containers, are the reason for the widespread use of PE-HD as the material for said containers in said applications.
The main drawback of PE compared with conventional materials of which such containers are made, such as steel, is its high degree of permeability to non-polar liquids, such as hydrocarbons or halogenated hydrocarbons. In order to reduce hydrocarbon emissions from motorcars, PFCs of PE-HD are provided with an antipermeation barrier layer. This can be effected in a purely chemical way by treatment of the interior surface of the container with sulfur trioxide (sulfonization) or fluorine (fluorination) or by precipitation of the polymer in a plasma (plasma polymerization). Further known methods are the application of a layer of varnish or paint to the interior surface of the container or coextrusion of the polyethylene with a suitable barrier polymer.
Of these various processes, coextrusion has been increasingly adopted world wide. Suitable barrier polymers mainly used at present are polyamides (PA) or poly(ethylene-co-vinyl alcohol)s (EVOH) (cf W. Daubenbuechel, “Anwendung der Coextrusion beim Extrusionsblasformen”, in Kunststoffe, 81, 894 (1991) and “Coextrudierte Kunststoffkraftstoffbehälter”, ebenda, 82, 201 (1992)). Both types of material are suitable for use as barrier layers for the reduction of the permeation of non-polar stock material such as hydrocarbons, particularly diesel fuels and fuels for Otto engines not containing added alcohol. Polyamide has the advantage of being comparatively cheap, but it suffers from the drawback of showing an inadequate barrier effect to alcohol-containing, particularly methanol-containing, fuels when used in conjunction with PE as a composite. On the other hand, EVOH has a high barrier action to fuels containing or not containing alcohol, but the use of EVOH is less economical on account of the complicated process required for its manufacture.
It is an object of the present invention to provide a multilayer composite plastics material which no longer suffers from the above drawbacks and at the same time has a good barrier effect to fuels and is economical to produce.
Accordingly, we have found the above multilayer composite plastics materials, a process for the manufacture thereof, hollow bodies and plastic fuel cans made of such materials and the use of polybutylene terephthalate as a barrier material in such multilayer composite plastics materials.
The ethylene homopolymers or copolymers used for layer (A) are characterized by a melt flow rate MFR (190° C., 21.6 kg) of from 1 to 20 g/10 min, more preferably from 1 to 12 g/10 min and most preferably from 2 to 7 g/10 min. The density of these polymers is between 0.92 and 0.96 g/ccm, more preferably between 0.935 and 0.957 g/ccm and most preferably between 0.94 and 0.957 g/ccm. The polymers concerned are generally homopolymers of PE or poly(ethylene-co-&agr;-olefin)s. The total thickness of all of the PE layers is generally from 60 to 98.5% and preferably from 80 to 98% of the overall thickness of the composite. If the multilayer composite plastics material of the invention is in the particularly advantageous form of a 5-layer composite, which can be supplemented by a sixth reclaim layer if desired, the inside layer of PE usually has a thickness which is from 20 to 50%, preferably from 25 to 35%, of the overall thickness of the composite. The outer layer of PE usually has a thickness which is from 1 to 50%, preferably from 3 to 40%, of the overall thickness of the composite.
The multilayer composite plastics materials of the invention contain at least one barrier layer (B) substantially comprising polybutylene terephthalate. This polybutylene terephthalate preferably has a melt volume flow rate MVR (250° C./2, 16 kg) of from 3 to 60 mL/10 min, more preferably from 5 to 40 mL/10 min. Examples of suitable products have been found to be the various Ultradur® types (manufacturer: BASF AG).
The thickness of the barrier layer (B) is generally from 1 to 10% of the overall thickness of the composite material. Preferably it is from 1 to 5% and more preferably from 2 to 4%. The overall thickness of the composite, especially when used for containers, is usually between 1 and 20 mm, preferably between 1 and 10 mm and more preferably between 1.5 and 8 mm.
The composite plastics materials of the invention can exhibit various lamellar structures. Particularly advantageous is a 5-layer structure composed of a middle barrier layer (B) sandwiched between interior and exterior layers (A) with two layers of adhesion promoter (C) being located between the layers (A) and (B).
This 5-layer compound can be supplemented by a sixth reclaim layer in which the pinch-off material produced during the manufacture of the containers can be reused.
In such a 6-layer composite, the reclaim layer has a thickness which is from 10 to 60% of the overall thickness of the composite container material, preferably 15 to 50% and more preferably from 20 to 45%.
Furthermore, it is possible to make the inside and outside layers from polyethylene mixed with reclaim instead of pure PE. In such case the load-bearing inside and outside layers generally contain not more than 10%, preferably from 2 to 4%, of polybutylene terephthalate.
Multilayer compounds are conceivable, basically, in which a barrier layer (B) forms the inner or outer skin of a container.
In such cases the PE layer (A) and the barrier layer (B) are combined with an adhesion promoter layer (C) to form, preferably, a 3-layer compound. Particularly preferred are such 3-layer compound structures having an inner barrier layer (B) of polybutylene terephthalate.
In order to produce a permanent and stable bond between the layers (A) and (B), the presence of layers of adhesion promoter (C) between these layers (A) and (B) is advantageous. Preferably, these layers of adhesion promoter (C) substantially consist of polar-modified ethylene homopolymers or copolymers. By polar modification we mean here any introduction of polar groups into these polymers, achieved, for example, by copolymerization in the presence of polar comonomers, by graft polymerization with polar monomers or by a polymer-like reaction of polymers with polar modifying agents.
Suitable adhesion promoters are for example polar-modified polyethylenes based on low-density polyethylene (PE-LD), linear low-density polyethylene (PE-LLD) and PE-HD. Those layers of adhesion promoter (C) have been found to be advantageous which substantially consist of copolymers of ethylene and comonomers selected from the group comprising vinyl alcohol esters, acrylic acid and the esters thereof, methacrylic acid and the esters thereof, and the nitrites and amides of (m
Büschges Ulrich
Rohde Wolfgang
Springholz Bernhard
Basell Polyolefine GmbH
Keil & Weinkauf
Thibodeau Paul
Zacharia Ramsey
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