CA2117142A1 - Process for the production of hollow bodies of thermoplastic polymer and hollow bodies produced thereby - Google Patents
Process for the production of hollow bodies of thermoplastic polymer and hollow bodies produced therebyInfo
- Publication number
- CA2117142A1 CA2117142A1 CA002117142A CA2117142A CA2117142A1 CA 2117142 A1 CA2117142 A1 CA 2117142A1 CA 002117142 A CA002117142 A CA 002117142A CA 2117142 A CA2117142 A CA 2117142A CA 2117142 A1 CA2117142 A1 CA 2117142A1
- Authority
- CA
- Canada
- Prior art keywords
- hollow body
- set forth
- layer
- gas mixture
- polymer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
- B29C49/22—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor using multilayered preforms or parisons
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
- B29C49/42—Component parts, details or accessories; Auxiliary operations
- B29C49/46—Component parts, details or accessories; Auxiliary operations characterised by using particular environment or blow fluids other than air
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2031/00—Other particular articles
- B29L2031/712—Containers; Packaging elements or accessories, Packages
- B29L2031/7172—Fuel tanks, jerry cans
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
- Containers Having Bodies Formed In One Piece (AREA)
- Laminated Bodies (AREA)
Abstract
In a process for the production of hollow bodies of thermoplastic material whose wall comprises a laminate, at least one of the layers of the laminate being a barrier layer to influence the permeation properties of the wall and at least one further layer being provided at the inward side of the at least one barrier layer, the inward surface of the wall is treated with a fluorine-bearing gas mixture or provided with a polymer cover layer by means of plasma polymerisation in order in that way to influence the permeation properties of the inner laminate layer or the surface thereof in relation to at least one component of the filling material which in use is contained in the hollow body.
Description
The invention concerns a process for the production of hollow bodies from a thermoplastic synthetic polymer and a hollow body such as more particularly a fuel tank comprising such a polymer.
The less expensive plastic materials, for example most polyolefins, which are usually employed for the production of hollow bodies such as more particularly containers, for example fuel tanks, for reasons of cost and also in consideration of their mechanical properties, are more or less permeable in relation to many substances, with the result that the content of the container or components of the material contained in the container can diffuse to the exterior through the container wall when it consists only of such plastic materials. Cn the other hand there is also the possibility that components from the atmosphere surrounding the container, for example the oxygen in the air, may diffuse into the container through the wall thereof, with the result that the material contained in the container experiences changes in its properties, which can give rise to a drop in the quality of the material contained in the container. In many situations such diffusion phenomena are lm~es;rable and possibly even unacceptable. A typical example in this respect is fuel tanks consisting of polyethylene (HDPE), the wall of which is permeable in relation to at least some hydrocarbons, unless it is subjected to an additional treatment. In that respect, as also in other situations, there is the possibility that a number of the components of the material contained in the container, in this case therefore being the fuel, co-operate to afford permeation values which are different from the permeation value of each co~ponent when considered individually.
Thus for example the permeation properties in regard to the wall of a polyethylene tank may change in ~eper~ence on the alcohol content of the fuel in the container.
Hollow bcdies which are produced by a co-extrusion blow molding process from thermoplastic material may be provided with a multi-layer laminate wall structure, wherein at least one of the layers of the laminate forming the wall provide the required mPchAnical stability for the hollow body or container, while at least one other layer of the laminate structure comprises a material which is not permeable or which is of only low permeability in relation to the material to be contained in the container, or at least one component thereof. As the materials employed for forming the barrier layer or layers generally do not form a strong bond to the material forming the other carrier layer or layers of the hollow body or container, and therefore cannot be welded thereto, it is normally necessary to provide an intermediate layer which can be referred to as a bonding layer and which essentially serves to join the barrier layer to a layer consisting of another material. In that respect attention is directed to US patent specification No 4 522 775 and EP-A-0 249 866 in which the above-discussed problems and aspects are considered. The barrier layer may also exhibit little or no p~rTPAhility in relation to the surrounding atmosphere or at least a component thereof, and can therefore reduce or prevent diffusion of substances into the container from the exterior thereof, for example to prevent oxygen from penetrating into the container.
In addition containers such as more particularly fuel tanks whose wall consists of a polyolefin may be treated preferably on the inside thereof with a fluorine-bearing gas mixture in order in that way to provide the inside surface of the wall of the container with a fluorinated interface layer which is not permeable or is permeable only to a slight degree in relation to the material to be contained in the container, for example the usual fuels when the container is a fuel tank.
Both of the previous methods discussed above suffer from various disadvantages. Thus it has been found that, when using the co-extrusion blow molding process, the barrier effect of the barrier layer consisting of the materials which nowadays are generally employed for that purpose markedly decreases in many cases after some time. That can be due inter alia to the fact that, at the temperatures which predominantly fall to be considered, the material forming the barrier layer of the laminate structure is substantially more brittle and thus less flexible than in p~rt;~ r polyethylene or another polyolefin. That property can result in the barrier layer being subjected to such damage, under detrimental conditions, that it can no longer fulfil the function to be attributed thereto, at any event to the required degree. Thus the barrier layer may suffer from a not inconsiderable amount of mechanical loading by virtue of the fact that the layer which is arranged at the inside of the wall of the container and which for ~x~mrle comprises polyethylene, to form the inside surface of the container, swells under the effect of the material contained in the container, for ~x~mple under the effect of fuel when the container is a fuel tank. That swelling ph~n~menon can result in considerable variations in the dimension of the internal layer, in parallel relationship with the wall of the container, with the consequence that the inner layer performs movements which are ~L~lbl"itted to the barrier layer, for e-x-ample by way of an interposed bonding layer as referred to above. The situation can then arise where the barrier layer is subjected to considerable stresses which in addition cannot be readily defined in respect of nature, direction and magnitude, and which accordingly cannot be predicted. In unfavourable circumstances the lo~i ng~ produced in such a situation can give rise to damage to the barrier layer, as the latter is normully not sufficiently flexible to follow the movements of the inner layer caused by the swelling phenamenon, or to alleviate the stresses resulting therefrom, by virtue of suitable deformation.
The above-described kind of loading generally occurs in the form of a continuous or fatigue loading which takes effect over prolonged periods of time. In many situations of use of containers having a multi-layer or laminate wall structure, in particular packaging items, that aspect is not of major significance as for example very many of the plastic hollow bodies which are used as packaging items involve only a very short period of use. In contrast, in the case of hollow bodies which involve a longer period of use, the period of time for which the barrier layer is effective, which period may be relatively short under some circumstances, can give rise to difficulties. As typical examples, consideration may be directed to fuel tanks which are to be fitted in motor v~h'~les and in respect of which it is generally expected that their service life is no shorter than the service life of the vehicle itself. It is however also possible to envisage other situations of use in which the above-mentioned problem may also arise, for example large-scale packaging articles such as stationary tanks, drums, barrels and the like.
However even the fact that the permeation properties of a wall comprising a polyolefin or another polymer are influenced by fluorination does not afford any guarantee that certain permeation properties which are attained by virtue of the treatment with fluorine remain effective over prolonged periods of time and under all circumstances which may arise in the course of use. That is not least to be attributed to the fact that the permeation properties of the fluorinated interface layers of a hollow body may be subjected to changes and modifications, depending on the cGmposition of the material contained in the hollow body. At least in the case of fluorinated polyolefins, there is a clear ~pPr~e~cy in respect of the permeation properties on the alcohol content and in particular the methanol content of the material contained in the hollow body, for example the fuel in the case of a fuel tank. Thus for example the permeability of such walls which are provided with a fluorinated interface layer, when certain proportions of methanol are present in the fuel, increases noticeably at least within certain ranges of such proportions, with the result that the limit values which are prescribed in most countries in regard to fuel evaporation due to permeation frequently cannot be met. Another oonsideration which makes 21171~2 the situation more difficult is that the composition of the fuel must be reckoned to fluctuate, over prolonged periods of time, for example in such a way that fuels of different compositions, including in respect of the ~lcohol content, are put into the tank during the service life of a normal vehicle and the tank fitted therein.
In accordance with the present invention, in a first aspect, there is provided a process for the production of a hollow body which at least predominantly comprises a thermoplastic polymer by blow molding of a preform having a wall of which at least a portion is formed as a laminate, the layers thereof comprising at least three different materials and at least one thereof ccmprising a material which at least for certain substances has a markedly lower level of permeability than at least one other layer in the laminate, wherein the inward layer of the wall of the hollow body comprises a polymer of ethylene or propylene and the surface of said inward layer is exposed to the action of a fluorine-bearing gas mixture.
In accordance with another aspect of the invention there is provided a process for the production of a hollow body which at least predominantly comprises a thermoplastic synthetic polymer by blow molding of a preform having a wall of which at least a portion is formed as a laminate, the layers thereof comprising at least three different materials and at least one thereof comprising a material which at least for certain substances has a markedly lower level of permeability than at least one other layer in the laminate, wherein the inward layer of the wall of the hollow body comprises a polymer and the surface thereof is provided with at least one polymer cover layer produced by plasma polymerisation fram at least one starting substance which is polymerisable under the respective plasma conditions.
As will be seen in greater detail from the following description of preferred embodiments of the invention, the present invention can accordingly provide a process for the production of a hollow body, which at least considerably reduces the above-discussed disadvantages of the prior operating procedures.
More specifically the present invention can provide a process for the production of hollow bodies such as tanks for fuels, which makes it possible to achieve low permeation values, even in respect of ~lc~hol-bearing fuels and even with different compositions in respect of commercially available fuels, in partic~ r in regard to the alcohol content, such that the permeation values achieved ccmply with present or expected requirements and can be maintained over prolonged periods of time. m e process according to the present invention for the production of hollow bodies at least pre~min~ntly camprisinga thenm~plastic polymer of a laminate wall structure, can afford reduced wall permeation values by the attainment of a barrier effect without a significant increase in cost, using a blow molding method employing readily usable means and procedures, with the resulting hollow body not being substantially different from known hollow bodies employed for the specified purposes, apart from the improved permeation properties over prolonged periods of time. In consequence the hollow body such as a fuel tank which is prcduced by the process of the invention enjoys at least a markedly lower level of permeability through the wall thereof and is produced by a procedure that is simple to carry into effect.
It will be more specifically seen hereinafter that the process according to the invention in the first aspect set forth above thus provides that a hollow body, for example a fuel tank, is firstly produced, using for example a co-extrusion blow molding procedure. The inside surface of the hollow body is then treated with a fluorine-bearing gas mixture in order thereby to produce a fluorinated 21171~2 interface layer at the inward surface of the container, that fluorinated layer exhibiting different permeation properties and in particular a lower degree of permeab;l~ty, than in the untreated condition. In that respect the procedure may be such that the fluorinating treatment of the inward surface of the hollow body is carried out while the hollow body is still within the blow mol~'~g mold. That is advantageous in particular when the fluorination operation is carried out when the hollow body is at an elevated temperature, for example at a temperature above the crystallite fusion temperature of the layer which is exposed to the effect of the fluorine.
It will generally be sufficient to carFy out the usual treatment with fluorine in which the inward surface of the hollow body is ex~osed to the action of a fluorine-bearing gas mixture for a given period of time. However, to achieve an improved effect, it is also possible for the treatment with fluorine to be carried out in first and second steps. In that respect it is advantageous to operate in such a way that in a first treatment step the inward surface of the hollow body is treated with a gas mixture containing fluorine and oxygen while in a second step the surface is exposed to the action of a gas mixture which contains fluorine but no oxygen. It has been found that such a procedure provides for particularly stable permeation values in the fluorinated interface layer, more specifically in partic~ r such that, in the event of a varying c~mpos;tion in respect of the material to be contained in the hollow body when in the form of a container such as a fuel tank, more specifically in regard to the alcohol content thereof, the fluctuations in respect of the permeation values of the wall of the container or tank lie within naFrow limits.
In regard to the process as set forth above in accordance with the second aspect of the invention, wherein the inward layer of the wall of the hollow body is treated by a polymer cover layer being produced on the inward surface of the wall of the hollow body using plasma polymerisation and more part;~l~rly low-pressure plasma 21171~2 polymerisation, the permeation properties of the cover layer produced in that way can be influenced in the desired fashion by virtue of suitable selection of the starting substance or substances, for example.
It may be noted at this point that processes for plasma polymerisation to produce a barrier layer are described for example in German patent specification No 3 632 748 and German laid-open ~plic~tion (DE-OS) No 39 08 418, to which attention may therefore be directed.
The invention further affords the possibility of the laminate having at least first and second layers comprising a barrier material, between which there is disposed at least one layer comprising another material, wherein the thickness of the individual barrier layers is so selected that it would not produce an adequate barrier effect without the presence of at least one further barrier layer. Such an arrangement takes account of the fact already mentioned above that the materials used nowadays for the barrier layer, at the temperatures encountered in practical use, are substantially more brittle and thus less flexible than the materials used for the at least one support or carrier layer, more particularly a polyolefin. The fact that the barrier material is divided between at least first and second layers provides that the individual layer portions exhibit a substantially lower level of brittleness than a single layer of double the layer thickness, so that it is possible to achieve a higher degree of flexibility and thus better elastic deformability in respect of the material constituting the barrier layer. In general terms there is a linear dependency between the thickness of a barrier layer and the permPability thereof so that, when the barrier layer is fonmed by first and second layer portions, each thereof is of for example about 50% of the overall thickness required to give the desired total barrier effect.
Still in accordance with the present invention in a further aspect there is provided a hollow body produced by a co-extrusion blow molding process and at least predominantly comprising a thermoplastic synthetic polymer, the hollow body having a wall of which at least a portion is formed as a laminate comprising layers made from at least three different materials, at least one thereof comprising a material which at least for certain substances is of a markedly lower level of permeability than at least one Other layer in the laminate, the inward layer of the laminate comprising a polymer of ethylene or propylene and having a surface of a nature produced by treatment with a fluorine-bearing gas mixture.
In another form of the hollow body such as a container and more particularly for example a fuel tank which is produced by a co-extrusion blow molding process and which at least predominantly comprises a thermoplastic polymer, the hollow body having a wall of which at least a portion is formed as a laminate comprising layers made from at least three different materials, at least one thereof comprising a material which at least for certain substances exhibits a markedly lower level of pen~e~h;l~ty than at least one other layer in the laminate, the inward layer of the laminate which comprises a polymer, preferably of ethylene or propylene, is provided with at least one polymer cover layer which is produced by means of plasma polymerisation, preferably low-pressure plasma polymerisation, from at least one starting substance which is polymerisable under the respective plasma conditions.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 shows a portion of a wall of a container comprising a five-layer laminate, and 30Figure 2 shows a portion of a wall of a container comprising an eight-layer laminate.
Referring firstly to the drawings in general, it will be -noted that the structure shown involves the wall for ~x~mrle of a fuel tank for a motor vehicle, the tank being produced by a co-extrusion blow molding process from a preferably t~lbulAr preform whose wall is fonmed as a laminate at least in portions thereof.
Looking now at Figure 1, in the structure ill~sLlaLed therein the wall 10 is in the form of a laminate having five substantially parallel layers of which the tw~ outer layers 12 and 14 ccmprise a polyolefin, for ~x~m~le HDPE, and impart to the wall 10 the required mP~h~n;cAl ~LlenyLh and inherent st;ffn~ss. The wall 10 is provided with a barrier layer 18 dlldil9ed substantially ~y~ ~Llically relative to the central plane 16. The laminate further ;ncll~c first and second bonding layers 24 and 26 of which the bonding layer 24 produces the join ~etween the polyolefin layer 12 and the barrier layer 18 and the bon~;ng layer 26 provides the join between the polyolefin layer 14 and the barrier layer 18.
If the polyolefin layer 12 of the wall of the container is arranged on the inward side of the container wall, the surface of that layer thus represents the inward bolln~Ary or interface surface of the container. It would thus be in contact with the material contained in the container and would possibly experience a variation in its form under the effect of the material contained in the container, for example due to swelling or other ;nfl~l~n~s. That could result in the above-mentioned stressing of the barrier layer 18, that the invention seeks to avoid. For that reason ffl surface of the polyolefin layer 12 has been subjected to a treatment with a gas contA;n;ng fluorine so that a fluorinated interface layer 30 is formed at the inward surface of the wall of the container. The fluorinated layer 30 influ~nces the permeation properties of the surface of the wall of the container, to the effect that it bec~mps very much less pPrmeAhl~ in relation to the material contained in the container, for ~XAmrl ~ fuel in a fuel tank.
In that respect the tw~-step treatment already referred to above can be carried out in ~p~n~Pn~e on the respective requirements involved.
It will be appreciated that the thickness of the fluorinated interface - layer 30 and the barrier layer 18 as well as the two bonding layers 24 and 26 is shcwn in greatly ~xAyy~Led fARh;on in the drawing, for the sake of enhAnce~ clarity thereof. In actual fact the thickness of the fluorinated layer 30 is in the region of a few ~m, possibly in the m~lecular range, whereas the thickness of the barrier layer 18 and the ~n~ g layers 24 and 26 can be for ~XA~rl e between about 0.05 mm and 2 mm.
When the plasma polymerisation operation, more part;~ rly low-pressure plasma polymerisation, is used, as referred to above, the interface layer 30 would then be formed by a polymer cover layer which is produced by plasma polymerisation from at least one starting substance which is polymerisable under the respective plasma conditions employed.
Reference will now be made to Figure 2 in which the layers are once again shown in ~x~y~raLed thicknesses for the sake of enhanced clarity. The ~m~c~imp-nt shown in Figure 2 differs fram that shawn in Figure 1 in that the wall 10 is provided with first and second barrier layers 18 and 20 which are joined together by a thin layer 22 which is disposed therebetween and which camprises for example bonding material, being for example between about 0.05 mm and 2 mm in thickness. m e wall 10 in this ~mho~;~ent also has first and second bonding layers 24 and 26 of which the bonding layer 24 provides the join between the polyolefin layer 12 and the barrier layer 18 and the bonding layer 26 provides the join between the barrier layer 20 and an additional layer 28 which camprises recycled material. The recycled material may be the waste material which had been squeezed off in the operation of shAri~g the hollow body fram a preferably tllblllAr preform in the blow molding process. In that case the waste material is camposed of all components of the wall laminate structure.
The provision of the additional layer 28 for making use of the recycled material represents a further difference in relation to the 21171~2 -~mho~l~pnt shcwn in Figure 1.
On the outside the additional layer 28 is covered with a layer 14 of new material, for P~m~le a polyolefin. As inevitably the major part of the material forming the layer 28 comprises polyolefins or same other material which forms the load-bearing layers, it is readily possible to produce a welded join between the layer 28 and the layer 14, without the interposition of a bonding agent.
The two barrier layers 18 and 20 of the laminate shown in Figure 2 are each of approximately half the thickness which is required to produce the barrier effect to be afforded by the barrier material. Dividing the overall barrier layer structure into two barrier layers affords the advantage that the individual layers, that is to say for exdll~le each of the t~o layers 18 and 20 illustrated in Figure 2, is less brittle and thus more flexible than would be the case if the barrier material nPcPss~ry to produce the required barrier effect were to be arranged as a single layer.
In Figure 2 also the inward layer 12 of the wall 10 is subjected to fluorination treatment using a fluorine-bearing gas mixture, to form a fluorinated interface layer 30. Alternatively the inward layer of the laminate may be subjected to plasma polymerisation to produce at least one polymer cover layer 30 fram at least one starting substance which is polymerisable under the respective plasma conditions, the polymer cover layer 30 at least reducing the diffusion of material contained in a container formed by the wall 10 into the layer 12, at any event to such an extent that significant ~Pf~r~Ation and ~h~gPS in dimension of the layer 10 due to swelling or other influ~nc;ng factors are avoided. That provides that little or no stresses occur within the wall 10, which could result in an adverse effect in particular on the functional cAF~h;l;ty of the barrier layer or layers.
It will be seen therefore that, in the pr,ocess according to the invention for the production of hollow bodies at least predominantly comprising a thermoplastic synthetic polymer, by blow 21171~2 molding of a preferably t~lhl~lAr preform having a wall m the form of a laminate structure at least in portions thereof, the layers of which comprise at least three different materials and at least one layer being made of a material which at least in relation to certain substances has a markedly lower level of perT~Ah,; 1 ty than at least one other layer in the laminate, the inward layer of the wall of the hollow body camprises a polymer, preferably of ethylene or propylene, wherein the surface of that layer is exposed to the action of a fluorine-bearing gas mixture or is provided with at least one polymer cover layer produced by plasma polymerisation. The hollow body being produced fram the preform by expansion of the latter within the blow molding mold until it bears against the internal contour of the blow molding mold, expansion is effected using a fluorine-free gaseous pressure agent such as an inert gas. The treatment of the internal surface of the hollow body with a fluorine-bearing gas mixture can be effected within the blow n~l~;ng mold, and the gas mixture can be an oxygen-free gas mixture containing fluorine, or a gas mixture containing both fluorine and oxygen. The gas mixture containing fluorine and oxygen can be used in a first treatment step for treating the internal surface of the hollow body, while the oxygen-free but fluorine-bearing gas mixture can be used in a second treatment step.
The first and second steps can be carried out in l~nf~;Ate succession.
The hollow body can be fl~l~he~ or purged with an inert gas for removing at least oxygen the~eL~u,l, between the first and second treatment steps, while the fluorine content in the treatment gas may be higher during the second step than the first step. The period of action of the gas mixture during the second step may be longer than during the first step. The treatment with a gas mixture containing fluorine and oxygen may be effected at a ~l~eL~L~re above the crystallite fusion temperature of the polymer forming the inward layer of the wall of the hollaw body, while treatment with an oxygen-free but fluorine-bearing gas mixture may be effected at a t~"~e~ re 21171~2 beneath the crystallite fusion L~l,~e.a~re.
It will be appreciated that the foregoing laminate structures and procefis~s for the production of the hollow body have been set forth solely by way of example and illustration of the principles of the present invention and that various other modifications and alterations may be made therein without thereby departing fm m the spirit and scope of the invention. Thus the recycled material may also be distributed to form first and second barrier layers. It is also p~fi~lhle for the layers which preferably consist of a polyolefin to be so arranged that the layer 14 is disposed on the inside and the layer 12 is disposed on the outside. It would also be poss~ble to envisage a structure in which the above-mentioned layer consisting of recycled material represents the inward layer and would thus be fluorinated or treated by means of low-pressure plasma polymerisation. In general terms however it is preferred that the layer of recycled material does not come into contact with the material to be contained in the hollow bcdy or container so that under nonmal circumstances the layer of recycled material is covered by a possibly thin layer of fresh material.
The less expensive plastic materials, for example most polyolefins, which are usually employed for the production of hollow bodies such as more particularly containers, for example fuel tanks, for reasons of cost and also in consideration of their mechanical properties, are more or less permeable in relation to many substances, with the result that the content of the container or components of the material contained in the container can diffuse to the exterior through the container wall when it consists only of such plastic materials. Cn the other hand there is also the possibility that components from the atmosphere surrounding the container, for example the oxygen in the air, may diffuse into the container through the wall thereof, with the result that the material contained in the container experiences changes in its properties, which can give rise to a drop in the quality of the material contained in the container. In many situations such diffusion phenomena are lm~es;rable and possibly even unacceptable. A typical example in this respect is fuel tanks consisting of polyethylene (HDPE), the wall of which is permeable in relation to at least some hydrocarbons, unless it is subjected to an additional treatment. In that respect, as also in other situations, there is the possibility that a number of the components of the material contained in the container, in this case therefore being the fuel, co-operate to afford permeation values which are different from the permeation value of each co~ponent when considered individually.
Thus for example the permeation properties in regard to the wall of a polyethylene tank may change in ~eper~ence on the alcohol content of the fuel in the container.
Hollow bcdies which are produced by a co-extrusion blow molding process from thermoplastic material may be provided with a multi-layer laminate wall structure, wherein at least one of the layers of the laminate forming the wall provide the required mPchAnical stability for the hollow body or container, while at least one other layer of the laminate structure comprises a material which is not permeable or which is of only low permeability in relation to the material to be contained in the container, or at least one component thereof. As the materials employed for forming the barrier layer or layers generally do not form a strong bond to the material forming the other carrier layer or layers of the hollow body or container, and therefore cannot be welded thereto, it is normally necessary to provide an intermediate layer which can be referred to as a bonding layer and which essentially serves to join the barrier layer to a layer consisting of another material. In that respect attention is directed to US patent specification No 4 522 775 and EP-A-0 249 866 in which the above-discussed problems and aspects are considered. The barrier layer may also exhibit little or no p~rTPAhility in relation to the surrounding atmosphere or at least a component thereof, and can therefore reduce or prevent diffusion of substances into the container from the exterior thereof, for example to prevent oxygen from penetrating into the container.
In addition containers such as more particularly fuel tanks whose wall consists of a polyolefin may be treated preferably on the inside thereof with a fluorine-bearing gas mixture in order in that way to provide the inside surface of the wall of the container with a fluorinated interface layer which is not permeable or is permeable only to a slight degree in relation to the material to be contained in the container, for example the usual fuels when the container is a fuel tank.
Both of the previous methods discussed above suffer from various disadvantages. Thus it has been found that, when using the co-extrusion blow molding process, the barrier effect of the barrier layer consisting of the materials which nowadays are generally employed for that purpose markedly decreases in many cases after some time. That can be due inter alia to the fact that, at the temperatures which predominantly fall to be considered, the material forming the barrier layer of the laminate structure is substantially more brittle and thus less flexible than in p~rt;~ r polyethylene or another polyolefin. That property can result in the barrier layer being subjected to such damage, under detrimental conditions, that it can no longer fulfil the function to be attributed thereto, at any event to the required degree. Thus the barrier layer may suffer from a not inconsiderable amount of mechanical loading by virtue of the fact that the layer which is arranged at the inside of the wall of the container and which for ~x~mrle comprises polyethylene, to form the inside surface of the container, swells under the effect of the material contained in the container, for ~x~mple under the effect of fuel when the container is a fuel tank. That swelling ph~n~menon can result in considerable variations in the dimension of the internal layer, in parallel relationship with the wall of the container, with the consequence that the inner layer performs movements which are ~L~lbl"itted to the barrier layer, for e-x-ample by way of an interposed bonding layer as referred to above. The situation can then arise where the barrier layer is subjected to considerable stresses which in addition cannot be readily defined in respect of nature, direction and magnitude, and which accordingly cannot be predicted. In unfavourable circumstances the lo~i ng~ produced in such a situation can give rise to damage to the barrier layer, as the latter is normully not sufficiently flexible to follow the movements of the inner layer caused by the swelling phenamenon, or to alleviate the stresses resulting therefrom, by virtue of suitable deformation.
The above-described kind of loading generally occurs in the form of a continuous or fatigue loading which takes effect over prolonged periods of time. In many situations of use of containers having a multi-layer or laminate wall structure, in particular packaging items, that aspect is not of major significance as for example very many of the plastic hollow bodies which are used as packaging items involve only a very short period of use. In contrast, in the case of hollow bodies which involve a longer period of use, the period of time for which the barrier layer is effective, which period may be relatively short under some circumstances, can give rise to difficulties. As typical examples, consideration may be directed to fuel tanks which are to be fitted in motor v~h'~les and in respect of which it is generally expected that their service life is no shorter than the service life of the vehicle itself. It is however also possible to envisage other situations of use in which the above-mentioned problem may also arise, for example large-scale packaging articles such as stationary tanks, drums, barrels and the like.
However even the fact that the permeation properties of a wall comprising a polyolefin or another polymer are influenced by fluorination does not afford any guarantee that certain permeation properties which are attained by virtue of the treatment with fluorine remain effective over prolonged periods of time and under all circumstances which may arise in the course of use. That is not least to be attributed to the fact that the permeation properties of the fluorinated interface layers of a hollow body may be subjected to changes and modifications, depending on the cGmposition of the material contained in the hollow body. At least in the case of fluorinated polyolefins, there is a clear ~pPr~e~cy in respect of the permeation properties on the alcohol content and in particular the methanol content of the material contained in the hollow body, for example the fuel in the case of a fuel tank. Thus for example the permeability of such walls which are provided with a fluorinated interface layer, when certain proportions of methanol are present in the fuel, increases noticeably at least within certain ranges of such proportions, with the result that the limit values which are prescribed in most countries in regard to fuel evaporation due to permeation frequently cannot be met. Another oonsideration which makes 21171~2 the situation more difficult is that the composition of the fuel must be reckoned to fluctuate, over prolonged periods of time, for example in such a way that fuels of different compositions, including in respect of the ~lcohol content, are put into the tank during the service life of a normal vehicle and the tank fitted therein.
In accordance with the present invention, in a first aspect, there is provided a process for the production of a hollow body which at least predominantly comprises a thermoplastic polymer by blow molding of a preform having a wall of which at least a portion is formed as a laminate, the layers thereof comprising at least three different materials and at least one thereof ccmprising a material which at least for certain substances has a markedly lower level of permeability than at least one other layer in the laminate, wherein the inward layer of the wall of the hollow body comprises a polymer of ethylene or propylene and the surface of said inward layer is exposed to the action of a fluorine-bearing gas mixture.
In accordance with another aspect of the invention there is provided a process for the production of a hollow body which at least predominantly comprises a thermoplastic synthetic polymer by blow molding of a preform having a wall of which at least a portion is formed as a laminate, the layers thereof comprising at least three different materials and at least one thereof comprising a material which at least for certain substances has a markedly lower level of permeability than at least one other layer in the laminate, wherein the inward layer of the wall of the hollow body comprises a polymer and the surface thereof is provided with at least one polymer cover layer produced by plasma polymerisation fram at least one starting substance which is polymerisable under the respective plasma conditions.
As will be seen in greater detail from the following description of preferred embodiments of the invention, the present invention can accordingly provide a process for the production of a hollow body, which at least considerably reduces the above-discussed disadvantages of the prior operating procedures.
More specifically the present invention can provide a process for the production of hollow bodies such as tanks for fuels, which makes it possible to achieve low permeation values, even in respect of ~lc~hol-bearing fuels and even with different compositions in respect of commercially available fuels, in partic~ r in regard to the alcohol content, such that the permeation values achieved ccmply with present or expected requirements and can be maintained over prolonged periods of time. m e process according to the present invention for the production of hollow bodies at least pre~min~ntly camprisinga thenm~plastic polymer of a laminate wall structure, can afford reduced wall permeation values by the attainment of a barrier effect without a significant increase in cost, using a blow molding method employing readily usable means and procedures, with the resulting hollow body not being substantially different from known hollow bodies employed for the specified purposes, apart from the improved permeation properties over prolonged periods of time. In consequence the hollow body such as a fuel tank which is prcduced by the process of the invention enjoys at least a markedly lower level of permeability through the wall thereof and is produced by a procedure that is simple to carry into effect.
It will be more specifically seen hereinafter that the process according to the invention in the first aspect set forth above thus provides that a hollow body, for example a fuel tank, is firstly produced, using for example a co-extrusion blow molding procedure. The inside surface of the hollow body is then treated with a fluorine-bearing gas mixture in order thereby to produce a fluorinated 21171~2 interface layer at the inward surface of the container, that fluorinated layer exhibiting different permeation properties and in particular a lower degree of permeab;l~ty, than in the untreated condition. In that respect the procedure may be such that the fluorinating treatment of the inward surface of the hollow body is carried out while the hollow body is still within the blow mol~'~g mold. That is advantageous in particular when the fluorination operation is carried out when the hollow body is at an elevated temperature, for example at a temperature above the crystallite fusion temperature of the layer which is exposed to the effect of the fluorine.
It will generally be sufficient to carFy out the usual treatment with fluorine in which the inward surface of the hollow body is ex~osed to the action of a fluorine-bearing gas mixture for a given period of time. However, to achieve an improved effect, it is also possible for the treatment with fluorine to be carried out in first and second steps. In that respect it is advantageous to operate in such a way that in a first treatment step the inward surface of the hollow body is treated with a gas mixture containing fluorine and oxygen while in a second step the surface is exposed to the action of a gas mixture which contains fluorine but no oxygen. It has been found that such a procedure provides for particularly stable permeation values in the fluorinated interface layer, more specifically in partic~ r such that, in the event of a varying c~mpos;tion in respect of the material to be contained in the hollow body when in the form of a container such as a fuel tank, more specifically in regard to the alcohol content thereof, the fluctuations in respect of the permeation values of the wall of the container or tank lie within naFrow limits.
In regard to the process as set forth above in accordance with the second aspect of the invention, wherein the inward layer of the wall of the hollow body is treated by a polymer cover layer being produced on the inward surface of the wall of the hollow body using plasma polymerisation and more part;~l~rly low-pressure plasma 21171~2 polymerisation, the permeation properties of the cover layer produced in that way can be influenced in the desired fashion by virtue of suitable selection of the starting substance or substances, for example.
It may be noted at this point that processes for plasma polymerisation to produce a barrier layer are described for example in German patent specification No 3 632 748 and German laid-open ~plic~tion (DE-OS) No 39 08 418, to which attention may therefore be directed.
The invention further affords the possibility of the laminate having at least first and second layers comprising a barrier material, between which there is disposed at least one layer comprising another material, wherein the thickness of the individual barrier layers is so selected that it would not produce an adequate barrier effect without the presence of at least one further barrier layer. Such an arrangement takes account of the fact already mentioned above that the materials used nowadays for the barrier layer, at the temperatures encountered in practical use, are substantially more brittle and thus less flexible than the materials used for the at least one support or carrier layer, more particularly a polyolefin. The fact that the barrier material is divided between at least first and second layers provides that the individual layer portions exhibit a substantially lower level of brittleness than a single layer of double the layer thickness, so that it is possible to achieve a higher degree of flexibility and thus better elastic deformability in respect of the material constituting the barrier layer. In general terms there is a linear dependency between the thickness of a barrier layer and the permPability thereof so that, when the barrier layer is fonmed by first and second layer portions, each thereof is of for example about 50% of the overall thickness required to give the desired total barrier effect.
Still in accordance with the present invention in a further aspect there is provided a hollow body produced by a co-extrusion blow molding process and at least predominantly comprising a thermoplastic synthetic polymer, the hollow body having a wall of which at least a portion is formed as a laminate comprising layers made from at least three different materials, at least one thereof comprising a material which at least for certain substances is of a markedly lower level of permeability than at least one Other layer in the laminate, the inward layer of the laminate comprising a polymer of ethylene or propylene and having a surface of a nature produced by treatment with a fluorine-bearing gas mixture.
In another form of the hollow body such as a container and more particularly for example a fuel tank which is produced by a co-extrusion blow molding process and which at least predominantly comprises a thermoplastic polymer, the hollow body having a wall of which at least a portion is formed as a laminate comprising layers made from at least three different materials, at least one thereof comprising a material which at least for certain substances exhibits a markedly lower level of pen~e~h;l~ty than at least one other layer in the laminate, the inward layer of the laminate which comprises a polymer, preferably of ethylene or propylene, is provided with at least one polymer cover layer which is produced by means of plasma polymerisation, preferably low-pressure plasma polymerisation, from at least one starting substance which is polymerisable under the respective plasma conditions.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 shows a portion of a wall of a container comprising a five-layer laminate, and 30Figure 2 shows a portion of a wall of a container comprising an eight-layer laminate.
Referring firstly to the drawings in general, it will be -noted that the structure shown involves the wall for ~x~mrle of a fuel tank for a motor vehicle, the tank being produced by a co-extrusion blow molding process from a preferably t~lbulAr preform whose wall is fonmed as a laminate at least in portions thereof.
Looking now at Figure 1, in the structure ill~sLlaLed therein the wall 10 is in the form of a laminate having five substantially parallel layers of which the tw~ outer layers 12 and 14 ccmprise a polyolefin, for ~x~m~le HDPE, and impart to the wall 10 the required mP~h~n;cAl ~LlenyLh and inherent st;ffn~ss. The wall 10 is provided with a barrier layer 18 dlldil9ed substantially ~y~ ~Llically relative to the central plane 16. The laminate further ;ncll~c first and second bonding layers 24 and 26 of which the bonding layer 24 produces the join ~etween the polyolefin layer 12 and the barrier layer 18 and the bon~;ng layer 26 provides the join between the polyolefin layer 14 and the barrier layer 18.
If the polyolefin layer 12 of the wall of the container is arranged on the inward side of the container wall, the surface of that layer thus represents the inward bolln~Ary or interface surface of the container. It would thus be in contact with the material contained in the container and would possibly experience a variation in its form under the effect of the material contained in the container, for example due to swelling or other ;nfl~l~n~s. That could result in the above-mentioned stressing of the barrier layer 18, that the invention seeks to avoid. For that reason ffl surface of the polyolefin layer 12 has been subjected to a treatment with a gas contA;n;ng fluorine so that a fluorinated interface layer 30 is formed at the inward surface of the wall of the container. The fluorinated layer 30 influ~nces the permeation properties of the surface of the wall of the container, to the effect that it bec~mps very much less pPrmeAhl~ in relation to the material contained in the container, for ~XAmrl ~ fuel in a fuel tank.
In that respect the tw~-step treatment already referred to above can be carried out in ~p~n~Pn~e on the respective requirements involved.
It will be appreciated that the thickness of the fluorinated interface - layer 30 and the barrier layer 18 as well as the two bonding layers 24 and 26 is shcwn in greatly ~xAyy~Led fARh;on in the drawing, for the sake of enhAnce~ clarity thereof. In actual fact the thickness of the fluorinated layer 30 is in the region of a few ~m, possibly in the m~lecular range, whereas the thickness of the barrier layer 18 and the ~n~ g layers 24 and 26 can be for ~XA~rl e between about 0.05 mm and 2 mm.
When the plasma polymerisation operation, more part;~ rly low-pressure plasma polymerisation, is used, as referred to above, the interface layer 30 would then be formed by a polymer cover layer which is produced by plasma polymerisation from at least one starting substance which is polymerisable under the respective plasma conditions employed.
Reference will now be made to Figure 2 in which the layers are once again shown in ~x~y~raLed thicknesses for the sake of enhanced clarity. The ~m~c~imp-nt shown in Figure 2 differs fram that shawn in Figure 1 in that the wall 10 is provided with first and second barrier layers 18 and 20 which are joined together by a thin layer 22 which is disposed therebetween and which camprises for example bonding material, being for example between about 0.05 mm and 2 mm in thickness. m e wall 10 in this ~mho~;~ent also has first and second bonding layers 24 and 26 of which the bonding layer 24 provides the join between the polyolefin layer 12 and the barrier layer 18 and the bonding layer 26 provides the join between the barrier layer 20 and an additional layer 28 which camprises recycled material. The recycled material may be the waste material which had been squeezed off in the operation of shAri~g the hollow body fram a preferably tllblllAr preform in the blow molding process. In that case the waste material is camposed of all components of the wall laminate structure.
The provision of the additional layer 28 for making use of the recycled material represents a further difference in relation to the 21171~2 -~mho~l~pnt shcwn in Figure 1.
On the outside the additional layer 28 is covered with a layer 14 of new material, for P~m~le a polyolefin. As inevitably the major part of the material forming the layer 28 comprises polyolefins or same other material which forms the load-bearing layers, it is readily possible to produce a welded join between the layer 28 and the layer 14, without the interposition of a bonding agent.
The two barrier layers 18 and 20 of the laminate shown in Figure 2 are each of approximately half the thickness which is required to produce the barrier effect to be afforded by the barrier material. Dividing the overall barrier layer structure into two barrier layers affords the advantage that the individual layers, that is to say for exdll~le each of the t~o layers 18 and 20 illustrated in Figure 2, is less brittle and thus more flexible than would be the case if the barrier material nPcPss~ry to produce the required barrier effect were to be arranged as a single layer.
In Figure 2 also the inward layer 12 of the wall 10 is subjected to fluorination treatment using a fluorine-bearing gas mixture, to form a fluorinated interface layer 30. Alternatively the inward layer of the laminate may be subjected to plasma polymerisation to produce at least one polymer cover layer 30 fram at least one starting substance which is polymerisable under the respective plasma conditions, the polymer cover layer 30 at least reducing the diffusion of material contained in a container formed by the wall 10 into the layer 12, at any event to such an extent that significant ~Pf~r~Ation and ~h~gPS in dimension of the layer 10 due to swelling or other influ~nc;ng factors are avoided. That provides that little or no stresses occur within the wall 10, which could result in an adverse effect in particular on the functional cAF~h;l;ty of the barrier layer or layers.
It will be seen therefore that, in the pr,ocess according to the invention for the production of hollow bodies at least predominantly comprising a thermoplastic synthetic polymer, by blow 21171~2 molding of a preferably t~lhl~lAr preform having a wall m the form of a laminate structure at least in portions thereof, the layers of which comprise at least three different materials and at least one layer being made of a material which at least in relation to certain substances has a markedly lower level of perT~Ah,; 1 ty than at least one other layer in the laminate, the inward layer of the wall of the hollow body camprises a polymer, preferably of ethylene or propylene, wherein the surface of that layer is exposed to the action of a fluorine-bearing gas mixture or is provided with at least one polymer cover layer produced by plasma polymerisation. The hollow body being produced fram the preform by expansion of the latter within the blow molding mold until it bears against the internal contour of the blow molding mold, expansion is effected using a fluorine-free gaseous pressure agent such as an inert gas. The treatment of the internal surface of the hollow body with a fluorine-bearing gas mixture can be effected within the blow n~l~;ng mold, and the gas mixture can be an oxygen-free gas mixture containing fluorine, or a gas mixture containing both fluorine and oxygen. The gas mixture containing fluorine and oxygen can be used in a first treatment step for treating the internal surface of the hollow body, while the oxygen-free but fluorine-bearing gas mixture can be used in a second treatment step.
The first and second steps can be carried out in l~nf~;Ate succession.
The hollow body can be fl~l~he~ or purged with an inert gas for removing at least oxygen the~eL~u,l, between the first and second treatment steps, while the fluorine content in the treatment gas may be higher during the second step than the first step. The period of action of the gas mixture during the second step may be longer than during the first step. The treatment with a gas mixture containing fluorine and oxygen may be effected at a ~l~eL~L~re above the crystallite fusion temperature of the polymer forming the inward layer of the wall of the hollaw body, while treatment with an oxygen-free but fluorine-bearing gas mixture may be effected at a t~"~e~ re 21171~2 beneath the crystallite fusion L~l,~e.a~re.
It will be appreciated that the foregoing laminate structures and procefis~s for the production of the hollow body have been set forth solely by way of example and illustration of the principles of the present invention and that various other modifications and alterations may be made therein without thereby departing fm m the spirit and scope of the invention. Thus the recycled material may also be distributed to form first and second barrier layers. It is also p~fi~lhle for the layers which preferably consist of a polyolefin to be so arranged that the layer 14 is disposed on the inside and the layer 12 is disposed on the outside. It would also be poss~ble to envisage a structure in which the above-mentioned layer consisting of recycled material represents the inward layer and would thus be fluorinated or treated by means of low-pressure plasma polymerisation. In general terms however it is preferred that the layer of recycled material does not come into contact with the material to be contained in the hollow bcdy or container so that under nonmal circumstances the layer of recycled material is covered by a possibly thin layer of fresh material.
Claims (28)
1. A process for the production of a hollow body which at least predominantly comprises a thermoplastic polymer by blow molding of a preform having a wall of which at least a portion is formed as a laminate, the layers thereof comprising at least three different materials and at least one thereof comprising a material which at least for certain substances has a markedly lower level of permeability than at least one other layer in the laminate, wherein the inward layer of the wall of the hollow body comprises a polymer of ethylene or propylene and the surface of said inward layer is exposed to the action of a fluorine-bearing gas mixture.
2. A process as set forth in claim 1 wherein the hollow body is produced from the preform by expansion of the preform within a blow molding mold until it bears against the internal contour of the blow molding mold, expansion being effected using a fluorine-free gaseous pressure agent.
3. A process as set forth in claim 2 wherein the preform is expanded within the blow molding mold using an inert gaseous pressure agent.
4. A process as set forth in claim 1 wherein the treatment of the internal surface of the hollow body with a fluorine-bearing gas mixture is effected within a blow molding mold.
5. A process as set forth in claim 1 wherein the internal surface of the hollow body is treated with an oxygen-free gas mixture which contains fluorine.
6. A process as set forth in claim 1 wherein the internal surface of the hollow body is treated with a gas mixture containing fluorine and oxygen.
7. A process as set forth in claim 1 including a first treatment step in which the internal surface of the hollow body is treated with a gas mixture which contains fluorine and oxygen and thereafter a second treatment step in which the internal surface of the hollow body is treated with an oxygen-free gas mixture which contains fluorine.
8. A process as set forth in claim 7 wherein the first and second treatment steps are carried out in immediate succession.
9. A process as set forth in claim 7 wherein between the first treatment step and the second treatment step the hollow body is purged with an inert gas for removing at least oxygen from the hollow body.
10. A process as set forth in claim 7 wherein the fluorine content in the treatment gas is higher during the second treatment step than during the first treatment step.
11. A process as set forth in claim 7 wherein the period of action of the gas mixture during the second treatment step is longer than during the first treatment step.
12. A process as set forth in claim 5 wherein the treatment with an oxygen-free gas mixture which contains fluorine is effected at a temperature beneath the crystallite fusion temperature of the ppolymer forming the inward layer.
13. A process as set forth in claim 7 wherein the treatment with an oxygen-free gas mixture which contains fluorine is effected at a temperature beneath the crystallite fusion temperature of the polymer forming the inward layer.
14. A process as set forth in claim 6 wherein the treatment with a gas mixture containing fluorine and oxygen is effected at a temperature above the crystallite fusion temperature of the polymer forming the inward layer.
15. A process as set forth in claim 7 wherein the treatment with a gas mixture containing fluorine and oxygen is effected at a temperature above the crystallite fusion temperature of the polymer forming the inward layer.
16. A process as set forth in claim 1 wherein the preform is a tubular preform.
17. A process for the production of a hollow body which at least predominantly comprises a thermoplastic synthetic polymer by blow molding of a preform having a wall of which at least a portion is formed as a laminate, the layers thereof comprising at least three different materials and at least one thereof comprising a material which at least for certain substances has a markedly lower level of permeability than at least one other layer in the laminate, wherein the inward layer of the wall of the hollow body comprises a polymer and the surface thereof is provided with at least one polymer cover layer produced by plasma polymerisation from at least one starting substance which is polymerisable under the respective plasma conditions.
18. A process as set forth in claim 17 wherein said polymer is of ethylene.
19. A process as set forth in claim 17 wherein said polymer is of propylene.
20. A hollow body produced by a co-extrusion blow molding process and at least predominantly comprising a thermoplastic synthetic polymer, the hollow body having a wall of which at least a portion is formed as a laminate comprising layers made from at least three different materials, at least one thereof comprising a material which at least for certain substances is of a markedly lower level of permeability than at least one other layer in the laminate, the inward layer of the laminate comprising a polymer of ethylene or propylene and having a surface of a nature produced by treatment with a fluorine-bearing gas mixture.
21. A hollow body as set forth in claim 20 wherein said surface of the inward layer has been treated with an oxygen-free fluorine-bearing gas mixture.
22. A hollow body as set forth in claim 20 wherein said surface of the inward layer has been treated with a gas mixture which contains fluorine and oxygen.
23. A hollow body as set forth in claim 20 wherein said surface of the inward layer has been treated initially with a gas mixture which contains fluorine and oxygen and thereafter in a second treatment step with an oxygen-free gas mixture which contains fluorine.
24. A hollow body as set forth in claim 20 in the form of a fuel tank.
25. A hollow body produced by a co-extrusion blow molding process and at least predominantly comprising a thermoplastic synthetic polymer, the hollow body having a wall of which at least a portion is formed as a laminate comprising layers made from at least three different materials, at least one thereof comprising a material which at least for certain substances is of a markedly lower level of permeability than at least one other layer in the laminate, the inward layer of the laminate which comprises a polymer being provided with at least one polymer cover layer produced by means of plasma polymerisation from at least one starting substance which is polymerisable under the respective plasma conditions.
26. A hollow body as set forth in claim 25 wherein said polymer is of ethylene.
27. A hollow body as set forth in claim 25 wherein said polymer is of propylene.
28. A hollow body as set forth in claim 25 wherein said plasma polymerisation operation is a low-pressure plasma polymerisation operation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4343002.3 | 1993-12-16 | ||
| DE4343002A DE4343002C2 (en) | 1993-12-16 | 1993-12-16 | Process for producing hollow bodies from a thermoplastic polymer |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2117142A1 true CA2117142A1 (en) | 1995-06-17 |
Family
ID=6505232
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002117142A Abandoned CA2117142A1 (en) | 1993-12-16 | 1994-03-07 | Process for the production of hollow bodies of thermoplastic polymer and hollow bodies produced thereby |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2117142A1 (en) |
| DE (1) | DE4343002C2 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19814314B4 (en) * | 1998-03-31 | 2016-07-28 | Volkswagen Ag | Process for the production of hollow bodies made of thermoplastic material and hollow body produced by this process |
| DE19946530B4 (en) * | 1999-09-28 | 2007-01-25 | Ti Automotive Technology Center Gmbh | Double-walled fuel tank |
| DE10018310B4 (en) * | 2000-04-13 | 2005-07-14 | Daimlerchrysler Ag | Plastic fuel tank and method for its production |
| EP1595913A1 (en) * | 2004-05-14 | 2005-11-16 | Inergy Automotive Systems Research (SA) | Method for preparing a hollow element of a fuel system |
| FR3038252B1 (en) * | 2015-06-30 | 2019-11-01 | Ipackchem Group | MULTILAYER CONTAINER IN PLASTIC MATERIAL. |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4522775A (en) * | 1982-03-04 | 1985-06-11 | American Can Company | Apparatus and method for producing multilayered laminates |
| DE3529870A1 (en) * | 1985-08-21 | 1987-02-26 | Basf Ag | METHOD FOR REDUCING THE PERMEATION OF BLOW-MOLDED HOLLOW BODIES MADE OF THERMOPLASTIC PLASTICS |
| DE3535602A1 (en) * | 1985-10-05 | 1987-04-09 | Hewing Gmbh & Co | Process for producing hollow articles fluorinated on the inner surface from thermoplastics by blow moulding |
| DE3620144A1 (en) * | 1986-06-14 | 1987-12-17 | Bekum Maschf Gmbh | STORAGE HEAD FOR THE MANUFACTURE OF MULTILAYER CO-EXTRUDED HOSES FROM PLASTIC |
| DE3632748A1 (en) * | 1986-09-26 | 1988-04-07 | Ver Foerderung Inst Kunststoff | Method of coating hollow bodies |
| EP0305740A2 (en) * | 1987-09-02 | 1989-03-08 | Messer Griesheim Gmbh | Method of blow-moulding and fluorinating hollow, thermoplastics articles |
| DE3908418C2 (en) * | 1989-03-15 | 1999-06-02 | Buck Chem Tech Werke | Process for the internal coating of plastic containers and device for coating |
-
1993
- 1993-12-16 DE DE4343002A patent/DE4343002C2/en not_active Expired - Fee Related
-
1994
- 1994-03-07 CA CA002117142A patent/CA2117142A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DE4343002A1 (en) | 1995-06-22 |
| DE4343002C2 (en) | 1998-02-19 |
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| EEER | Examination request | ||
| FZDE | Discontinued |