JPH0688591B2 - Multi-layer plastic fuel tank - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multi-layer plastic fuel tank having impact resistance at low temperature equivalent to or higher than that of a single-layer high-density polyethylene tank and having low fuel permeability. Is.

(Prior art) Regarding the plastic fuel tank, the single-layer type is the most popular, and the fuel tank for automobiles has already been accumulated for more than 10 years mainly in Europe, but it shows a large fuel permeability. ing. On the other hand, a multi-layer plastic fuel tank has been conventionally researched and developed, and a fuel tank 1 of three kinds and three layers structure using a polyamide resin layer 2, a modified polyethylene layer 3, and a high-density polyethylene layer 4 as shown in FIG. It has been known. A fuel tank of three types and five layers is also known from JP-A-58-181642. Such a fuel tank can be formed into a three-kind five-layer molding by utilizing a three-kind five-layer blow molding machine. For example, a polyamide resin layer 2, a modified polyethylene layer 3 and a high-density polyethylene layer as shown in FIG. A three-kind five-layer tank 1 using No. 4 is also known.

(Problems to be Solved by the Invention) Plastic fuel tanks of three kinds of three layers or three kinds of five layers formed by multi-layer molding have an advantage of excellent fuel permeation preventive ability, but in the case of three layers, weather resistance In terms of performance, when a polyamide resin layer is used on the inside, a modified polyethylene layer is used in the middle, and a high-density polyethylene is used on the outermost layer, the impact strength of the pinch-off part is improved in the single-layer pinch-off shape. Due to the shortage, a special pinch-off shape is required.

Further, in the case of three kinds and five layers, the structure is as shown in FIG. 2, the shape of the pinch-off part does not matter, and at room temperature, it can have almost the same drop strength as the single layer. When a drop impact is performed at a low temperature of around ℃, when the overall thickness is set to be the same as a single layer or three layers, the high-density polyethylene layer that shares rigidity is divided into two parts, Since the thickness of the polyethylene layer in the case of a single layer or three layers is about half, it was found that a drop test at -40 ° C or lower may cause cracking to be weaker than that of a single layer under extreme conditions.

(Means for Solving the Problem) As a result of microanalyzing the factors of the above cracks, the inventors found that the low temperature embrittlement temperature of polyamide was -40 ° C among the constituent elements.
It was found that there is a so-called notch effect and the fact that the fracture of polyamide causes cracks in the vicinity, and paying attention to the fact that the drop strength of a single-layer tank is excellent, and high density polyethylene, which is a constituent material, and modified Considering that the mechanical and physical properties of polyethylene and polyamide should be close to each other in temperature dependence, and by using a modified polyamide with high impact resistance as the polyamide, it is possible to obtain an impact equivalent to that of a single-layer tank at -40 ° C. We have developed a multi-layer plastic fuel tank that exhibits strength.

As the high density polyethylene used in the fuel tank of the present invention, it is preferable to use a high molecular weight polyethylene having a molecular weight of about 200,000 to 300,000 in consideration of gasoline resistance. The temperature dependence of the physical properties of typical polyethylene is as follows, and the low temperature embrittlement temperature is usually -80 ° C or lower, and the impact resistance is extremely excellent.
Here, the low temperature embrittlement temperature means the temperature at which 50% of the samples are broken by the low temperature embrittlement temperature test method of ASTM D-746-57.

Next, there are two types of modified polyethylene, one based on high-density polyethylene and the other based on low-density polyethylene. To soften the impact with a modified polyethylene layer sandwiched in the middle, select a soft low-density polyethylene. Although there is an idea, in the present invention, from the idea that it is desirable to match the rigidity with high density polyethylene, based on high density polyethylene, maleic anhydride or the like is added and polymerized to a part thereof to introduce a polar group such as a carboxyl group. Use the one that you made.

For polyamide, nylon 6,66,610,11,12
As a result of studying the above, as a grade capable of blow molding, 5 to 40% polyolefin-modified polyamide, which is a modified polyamide having high impact resistance, is used.

In addition, with the recent advances in polymer alloy and polymer blend technologies, the use of modified polyolefins having a polar group introduced as a polyamide alloy is an important point for improvement. For example, in the case of blending with an acidic olefin copolymer having a carboxylic acid group, a reaction occurs between the acidic group and the amine terminal of the polyamide to increase the solution viscosity, improve the extrusion moldability, and at the same time significantly improve the impact strength. Kosho 42
-12546). It has also been shown that impact strength can be improved by alloying with a modified polyolefin having a hydroxyl group as a polar group (Japanese Patent Publication No. Sho 48-11221) and by using a modified polyethylene having an epoxy group introduced by copolymerization. .
Also, a reactive polymer alloy obtained by polymerizing caprolactam in the presence of ethylene-ethyl acrylate copolymer (EEA) and grafting caplactam on the EEA main chain (Japanese Patent Publication No.
44-29262) is also attracting attention as a method for producing high quality polymer alloys, but the specific contents of each marketed modified polyamide produced by these methods are not disclosed due to commercial practice. However, those skilled in the art can appropriately select an advantageous material through experiments.

The fuel tank of the present invention uses 5-40% of polyolefin-modified polyamide to form the polyamide layer in the tank shown in FIG. 2, and uses a maleic anhydride-modified high-density polyethylene layer as the modified polyethylene.
Like conventional tanks, it is usually made by blow molding. In the illustrated three-kind five-layer tank, the material is plasticized by three extruders and accumulated in the accumulator head to form five layers. In the case of three types and five layers, in addition to the fact that burrs are likely to occur in the blow molding method, the accumulator head is divided into two parts, which are the high-density polyethylene layer and the modified polyethylene layer sandwiching the modified polyamide layer, and then distributed. Since it is used and blow-molded, the amount of burr generated after molding is significantly increased. Therefore, reusing such burrs is important for cost reduction.
When using burrs, a blow molding machine with four extruders and five layers of accumulator pistons is used to
The tank innermost layer corresponding to the tank innermost layer high-density polyethylene 4 shown in FIG. (B) uses high-density polyethylene with a burr recovery material, and the tank outermost layer uses high-density polyethylene.
A modified polyethylene may be distributed on both sides in the middle to form a four-kind five-layer structure with a modified polyamide layer sandwiched therebetween. The above-mentioned burr material is usually mainly composed of high-density polyethylene, and contains a small amount of polyamide and a small amount of modified polyethylene. It is preferably used as the inner layer. Considering the recycling efficiency of materials, it is more cost effective to add the entire amount of Paris generated to new high-density polyethylene. Therefore, it is necessary to mix the burr material within the above range so as to reuse the entire amount of burr and not to lose the mechanical properties of the new polyethylene. Further, when the layer structure of the tank is considered symmetrically with respect to the polyamide, not only the load such as bending, tension and impact applied from the inside and outside of the tank becomes strong, but also the flowability and the moldability are improved, which is advantageous.

It is difficult to precisely set the thickness of each layer in blow molding, but the average thickness is 2.5 mm or more in total, the polyamide layer is 0.1 mm or more, and the modified polyethylene layer is 0.1 mm or more. Is desirable.

As a special example, the average thickness of high density polyethylene mixed with burr in the innermost layer is 0.1 to 0.2 mm, the average thickness of modified polyethylene adhesive layer is 0.1 to 0.2 mm, the average thickness of modified polyamide is 0.1 to 0.2 mm, and the modified polyethylene is If the average plate thickness of the adhesive layer is 0.1-0.2 mm, the average plate thickness of the new outermost high-density polyethylene layer is 2.2 mm or more, and the innermost layer of recycled polyethylene (high-density polyethylene mixed with collected burrs) is set to be thin Four
This is advantageous because only one of the extruder screws of this book needs to have a large capacity, and economically, only a small extruder needs to be added as compared with the three-kind three-layer and three-kind five-layer molding machine. Further, since the outermost layer is responsible for the structural strength, there is an advantage that even if the difference in the characteristics of the resin other than the outermost layer is considerably different, the mechanical properties are not affected.

(Example) This invention is demonstrated by the following example.

Example 1 As a high-density polyethylene (HDPE), Cyolex 4551
H (Showa Denko, product name), ADMER GT-1 (Mitsui Petrochemical, maleic anhydride modified high density polyethylene, product name) as modified polyethylene, Amilan CM1056 (Toray product, modified olefin) as polyamide Quantity 20-30
% By weight), and was molded by a three-kind five-layer blow molding machine to obtain a three-kind five-layer fuel tank (tank capacity 50) having the structure shown in FIG. Thickness of each layer HDPE 3.8mm, modified polyethylene 100μ, modified polyamide 100μ, total 4mm
It was.

The above-mentioned Amilan CM1056 has a thickened specification and is excellent in blow moldability.In addition, it is made by reacting polyolefin with polyamide to disperse it, and it has excellent adhesiveness with modified polyethylene and impact resistance. The low temperature embrittlement temperature is about 3 times better than the heat-resistant polyamide AMIRAN CM1046 for blowing.

Example 2 Hi-Zex 8200B (manufactured by Mitsui Petrochemical Co., Ltd.) as high-density polyethylene, and Admer as modified polyethylene
Blow molding was performed on GT-1 using Amilan CM1056 as a polyamide to obtain a three-kind five-layer plastic fuel tank similar to that of Example 1.

Example 3 BZ80 (manufactured by Mitsubishi Yuka, trade name) was added to high density polyethylene.
Modet H100F as modified polyethylene (manufactured by Mitsubishi Yuka, maleic anhydride modified high density polyethylene, trade name)
As a polyamide, Amilan UTM21 (high impact nylon, manufactured by Toray, trade name, modified olefin content 20-25% by weight)
Was molded by a multi-layer blow molding machine to obtain the same multi-layer plastic fuel tank as in Example 1.

Comparative Example 1 A single-layer fuel tank having a capacity of 50 was obtained by blow molding using high-density polyethylene and Schyolex 4551H.

Comparative Example 2 A three-kind five-layer plastic fuel tank was used in the same manner as in Example 1, except that the high-density polyethylene was Cyolex 4551H, the modified polyethylene was Admer GT-1, and the polyamide was Amian CM1046 (Toray, nylon 6, trade name). Got

Comparative Example 3 A three-kind three-layer plastic fuel tank was obtained in the same manner as in Example 4, except that Cyolex 4551H was used as the high-density polyethylene, Admer GT-1 was used as the modified polyethylene, and Amylan CM1046 was used as the polyamide.

The fuel tanks of Examples 1 to 5 and Comparative Examples 1 to 3 all have a total wall thickness of 4 mm and a capacity of 50, and the following tests were conducted on these fuel tanks. The results obtained are shown in Table 1.

(A) Measurement of fuel permeation prevention performance (permeation coefficient) (b) Low temperature impact test (drop test) (c) Low temperature impact test (square pyramid impact) The above test is ECE regulation 34 and Ministry of Transport Auto No. 1327 Showa It is based on the fuel permeation measurement method stipulated on December 27, 1952, "Technical Standard of Plastic Fuel Tanks for Passenger Cars", and is based on a low temperature impact test (square pyramid impact) 15 kgf square pyramid. 3.1kg ・ f ・ m (-40 ℃ ± 2 ℃)
Is.

From Table 1, the tanks of Examples 1 to 3 can remarkably reduce the amount of permeation as compared with the single-layer tank of Comparative Example 1, and also have an original standard value for impact strength at low temperature. However, even if an amount of energy that is five times the specified amount is applied, only the perforated mode occurs as in the single-layer tank, and there is little leakage of gasoline.

(Effects of the Invention) As described above, the multi-layer plastic fuel tank of the present invention has a polyolefin-modified polyamide layer having a high impact resistance of 5 to 40% as an intermediate layer of the tank, and therefore the conventional tank of this type However, there is a large difference in impact properties at low temperature between polyamide and polyethylene, and it approaches the low temperature embrittlement temperature of polyamide, especially under extreme conditions such as −40 °.
When the polyamide layer was damaged due to sharp changes in the physical properties of the polyamide due to abrupt changes in physical properties, it was sensitive to the so-called edge effect. When the energy was increased to 5 times the temperature, the fracture mode fracture occurred, but without such fracture, -40 ℃
It has the advantages of improved mechanical properties, especially impact resistance, excellent gasoline permeation prevention performance, stability, and light weight, which makes it very suitable for mounting on vehicles. Further, when the burr generated by blow molding is reused, the cost can be reduced, and a well-balanced multi-layer tank can be obtained with a minimum increase in cost. It is expected that the diversification tendency of the energy source will intensify this time, but special measures will be taken against alcohol fuels such as methanol and ethanol and gasoline fuel in the four-layer five-layer tank where the polyethylene layer exists in the innermost layer. The advantage is that there is no need.

[Brief description of drawings]

FIG. 1 (a) is a sectional view of a three-kind three-layer plastic fuel tank, FIG. 1 (b) is an enlarged view of part A of FIG. 1 (a), and FIG. 2 (a) is a three-kind five-layer plastic tank. A sectional view of the fuel tank, and FIG. 2 (b) is an enlarged view of a portion B in FIG. 2 (a). 1 ... Tank, 2 ... Polyamide layer 3 ... Modified polyethylene layer 4 ... High-density polyethylene layer

Claims (2)

[Claims] 1. A 5-40% polyolefin-modified polyamide layer is used as an intermediate layer, and a maleic anhydride-modified high-density polyethylene layer and a high-density polyethylene layer are laminated in this order on both sides of the intermediate layer. A multi-layered plastic fuel tank. 2. A multi-layer plastic fuel tank according to claim 1, wherein the innermost high-density polyethylene layer contains 10-40% by weight of burrs.