JP2965660B2 - Gas tank made of polyacetal resin - Google Patents

Description

The present invention relates to a polyacetal resin gasoline tank formed by blow molding.

[Conventional technology]

Conventionally, gasoline tanks have been manufactured exclusively from metal. In recent years, gasoline tanks mainly made of high-density polyethylene have been put into practical use for the purpose of reducing the weight of automobiles.

[Problems to be solved by the invention]

However, high density polyethylene has the inherent disadvantage of high gasoline permeability. For the purpose of overcoming this drawback, a method has been developed in which the inner surface of a high-density polyethylene gasoline tank is subjected to a chemical treatment such as fluorination or sulfonation. Alternatively, a method of laminating high-density polyethylene and polyamide has also been developed.

The method of chemical treatment not only complicates the manufacturing process but also has a defect of non-uniformity of chemical treatment.

Further, the method of laminating has a defect that a regenerated material cannot be used, so that the resin loss during molding is extremely large.

[Means for solving the problem]

The present inventors have conducted studies to solve the above-mentioned problems, and as a result, by molding a polyacetal resin having a certain melt index at a certain extrusion temperature by a blow molding method, extremely excellent performance has been obtained. To obtain a polyacetal gasoline tank.

That is, the present invention is a polyacetal resin gasoline tank formed by blow molding a polyacetal resin having a melt index of 0.005 to 1.0 at an extrusion resin temperature of 180 to 260 ° C.

The gasoline tank of the present invention has extremely low gasoline and methanol permeability, and can be formed into any shape by blow molding.

[Specific description of the invention]

In the present invention, the melt index (hereinafter abbreviated as MI),
Polyacetal resin in the range of 0.005 to 1.0 can be used as a raw material.

Here, MI of the present invention refers to a value measured according to ASTM D-1238 (E condition). When the MI is less than 0.005, the blow moldability becomes extremely poor. On the other hand, when MI exceeds 1.0, the drawdown of the parison during blow molding is large, and a good molded product (gasoline tank) cannot be obtained.

In the present invention, the extrusion temperature needs to be in the range of 180 to 260 ° C. If the extrusion temperature is lower than 180 ° C., a molded article having a good shape cannot be obtained. On the other hand, when the extrusion temperature exceeds 260 ° C., silver streaks (silver streaks) run on the surface of the molded body, which impairs the appearance.

As the polyacetal resin of the present invention, any of linear, branched and crosslinked molecular structures can be used as long as MI is a polyacetal in the range of 0.005 to 1.0. Among these molecular structures, from the viewpoint of the appearance of the molded body, that is, from the viewpoint of the surface finish of the molded body and from the viewpoint of preventing drawdown,
A branched or crosslinked molecular structure is more preferred.

Here, the polyacetal resin having a linear molecular structure can be obtained by homopolymerizing formaldehyde or trioxane or copolymerizing formaldehyde or trioxane with a cyclic ether.

In addition, polyacetal resin having a branched molecular structure,
Formaldehyde or trioxane is homopolymerized in the presence of a polyfunctional compound containing three or more functional groups such as a hydroxyl group, an amino group and a carboxyl group in one molecule,
It is obtained by copolymerizing formaldehyde or trioxane with a cyclic ether.

In addition, polyacetal resin having a crosslinked molecular structure,
It can be obtained by homopolymerizing formaldehyde or trioxane or copolymerizing formaldehyde or trioxane with a cyclic ether in the presence of a polyfunctional glycidyl ether containing two or more epoxy groups in one molecule.

In the present invention, a composition obtained by blending or reacting a polymer for improving impact resistance with a linear, branched, or crosslinked polyacetal may be used as a raw material, or a blend of these polymers may be used. Alternatively, the polyacetal alone may be used as a raw material without reacting.

However, from the viewpoint of improving the practical performance of gasoline tanks, it is preferable to use a polymer mainly composed of a vinyl polymer or an elastomer for improving impact resistance, which is blended or reacted with polyacetal.

Here, the polymer for improving impact resistance is -125 to 80
A vinyl polymer and / or an elastomer having a glass transition temperature of 0 ° C.

 Here, the vinyl polymer will be specifically described.

The first group of vinyl polymers is low density polyethylene (LD), high density polyethylene (HD), linear low density polyethylene (LL), low density polyethylene / styrene graft copolymer, low density polyethylene / acrylonitrile styrene graft It is a polyethylene polymer such as a copolymer or a modified low density polyethylene (modified with hydroxyl group).

The second group of vinyl polymers includes ethylene-propylene copolymers, ethylene-propylene-diene copolymers, modified ethylene-propylene-diene copolymers (modified with hydroxyl groups), ethylene-acrylic acid copolymers, and ethylene-propylene copolymers.
Ethylene polymers such as methacrylic acid / 2-hydroxylethyl methacrylic acid copolymer and modified ethylene / vinyl acetate copolymer (modified with hydroxyl group).

A third group of vinyl polymers is polybutadiene,
Modified hydrogenated polybutadiene (modified with hydroxyl group), isoprene
It is a butadiene-based polymer such as a butadiene copolymer.

In addition to these vinyl polymers, the glass transition temperature is -12.
It is also possible to use vinyl polymers between 5 and 80 ° C.

 Next, the elastomer will be specifically described.

The elastomer referred to in the present invention is a thermoplastic polymer, which is an amorphous segment having a low glass transition temperature (soft segment) and a segment having a high glass transition temperature for forming a thermoreversible crosslinked / bonded structure (hard segment). ).

In the present invention, it is possible to use an elastomer in which the glass transition temperature of the soft segment and the hard segment is between -125 and 80 ° C.

The first group of elastomers are polystyrene-based elastomers, in which polystyrene is a hard segment. Soft segments to be combined with polystyrene include diene systems such as polybutadiene and polyisoprene, and hydrogenated diene systems such as hydrogenated polybutadiene and hydrogenated polyisoprene. Among these polystyrene elastomers, a polystyrene-polybutadiene block copolymer and a polystyrene-hydrogenated polybutadiene block copolymer are particularly preferred.

The second group of elastomers are polyester-based elastomers, in which polyesters such as polyethylene terephthalate, polybutylene terephthalate, modified polyethylene terephthalate, and polyethylene butylene terephthalate have a hard segment. Soft segments to be combined with polyester include
There are polyethers such as polypropylene glycol and polytetramethylene glycol.

Among these polyester elastomers, a polybutylene terephthalate-polytetramethylene glycol block copolymer and a polyethylene / butylene terephthalate-polytetramethylene glycol block copolymer are particularly preferable.

The third group of the elastomer portion is a polyamide-based elastomer having a hard segment of polyamide such as nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12, or the like. Soft segments to be combined with the polyamide include polyethers such as polypropylene glycol and polytetramethylene glycol, and polyesters such as polyethylene adipate and polybutylene succinate. Among these polyamide-based elastomers, a nylon 6-polypropylene glycol block copolymer and a nylon 6-polytetramethylene glycol block copolymer are particularly preferred.

A fourth group of elastomers are polyurethane elastomers, with urethane as the hard segment.

Here, urethane is a diisocyanate such as 4,4'-diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate and ethylene glycol,
It is obtained by reacting with a glycol such as tetramethylene glycol.

Soft segments to be combined with urethane include polyester diols such as polyethylene adipate and polybutylene adipate, and polyether diols such as polypropylene glycol and polytetramethylene glycol.

Among these polyurethane elastomers, especially 4,
Polyurethanes synthesized from 4'-diphenylmethane diisocyanate, tetramethylene glycol and polytetramethylene glycol are preferred.

In addition to these elastomers, the glass transition temperature is -12
It is also possible to use an elastomer between 5 and 80 ° C.

The vinyl polymer and the elastomer are used by being blended with a linear, branched or crosslinked polyacetal or by reacting with the polyacetal via a binder such as diisocyanate.

The blending or reaction amount of a polymer mainly composed of a vinyl polymer or an elastomer for improving impact resistance is preferably in the range of 0.5 to 50 parts based on 100 parts of polyacetal. When the blending of the polymer and the reaction amount are less than 0.5 part,
No effect of improving the impact resistance of gasoline tanks. On the other hand, if the blending and reaction amount of the polymer exceeds 50 parts, the permeation amount of gasoline and methanol increases, which may cause a practical problem.

After adding an antioxidant, a heat stabilizer, a flame retardant and the like to the polyacetal resin of the present invention, the polyacetal resin is shaped into a gasoline tank by a blow molding method. The gasoline tank of the present invention
It is used as a storage tank for hydrocarbons such as gasoline and kerosene, and alcohols such as methanol and ethanol.

Hereinafter, the present invention will be described specifically with reference to examples. The meanings of the terms in the examples are as follows.

MI: Melting index under standard load of 2.16 kg at 190 ° C (ASTM D-1238 E condition) Antioxidant: 2,2-methylenebis (4-methyl-6-t
-Butylphenol) Heat stabilizer: Nylon 3 Izod impact value: Polyacetal resin was made into a flat plate using an injection molding machine, and a test piece was cast from this flat plate using ASTM D-256.
Create and measure according to.

Example 1 (1) Method for producing polyacetal resin (branched) Anhydrous formaldehyde was blown into cyclohexane containing glycerin as a branching agent and tetrabutylammonium acetate as a polymerization catalyst, and polymerization was carried out at 50 ° C. After separating the polymer from cyclohexane by filtration, the terminal of the polymer was stabilized using acetic anhydride.

To 100 parts of stabilized polymer, polyurethane elastomer, (synthesized from 4,4'-diphenylmethane diisocyanate, tetramethylene glycol, polytetramethylene glycol, glass transition temperatures -48 ° C and 15 ° C)
12 parts, 0.5 parts antioxidant, 0.3 parts heat stabilizer, 65mm
The mixture was melt-mixed with a twin screw extruder to form pellets. The MI of the pellet was 0.08.

(2) Production method of gasoline tank Using the pellets, a gasoline tank having a content of 55 was molded at an extruded resin temperature of 215 ° C using a large blow molding machine equipped with a 90 mmφ single screw extruder. The moldability was good, and the molding time could be considerably shortened as compared with the case where high-density polyethylene was used. The appearance of the gasoline tank was glossy and had a good finish.

(3) Performance of gasoline tank Gasoline permeability of the polyacetal resin of this example at 25 ° C is 0.23 g · mm / m ² · day, and methanol permeability is 0.72 g ·
mm / m ² · day, which is a very low transmittance. The Izod impact value was a good value of 15 kg · cm / cm. Also, the pinch-off strength at the bottom of the gas tank was good.

Example 2 (4) Production method of polyacetal resin (crosslinked) Trioxane, ethylene oxide, 1,4 as a crosslinking agent
-Butanediol diglycidyl ether and boron trifluoride dibutyl etherate as a polymerization catalyst were added, and the mixture was polymerized at 85 ° C in a biaxial kneader. Triethylamine and water were added to the polymer, and the mixture was stabilized in a 65 mmφ twin screw extruder.
Next, with respect to 100 parts of the polymer, a polyester elastomer (terephthalic acid, adipic acid, isophthalic acid,
Synthesized from 1,4-butanediol, glass transition temperature -18
C) 5 parts, 0.4 parts of an antioxidant, 0.3 parts of a heat stabilizer and 0.3 part of a heat stabilizer were blended and melt-mixed with a 65 mmφ twin screw extruder to obtain pellets. The MI of the pellet was 0.2.

(5) Production method of gasoline tank Using these pellets, using a large blow molding machine with a 120 mmφ single screw extruder, at an extruded resin temperature of 240 ° C. and a capacity of 45
Molded gas tank. The moldability was good, and no parison drawdown was observed. In addition, the molding time was shorter than that of high-density polyethylene. The appearance of the gas tank was glossy.

(6) Gasoline tank performance The gasoline permeability of the polyacetal resin of this example at 25 ° C. is 0.28 g · mm / m ² · day The methanol permeability is 0.68 g · mm
/ m ² · day, a good value. The Izod impact value is
It showed a good value of 12 kg · cm / cm. The pinch-off strength at the bottom of the gasoline tank of this example was also excellent.

Example 3 (7) Preparation of Polyacetal Resin Trifluoroxane and 1,3-dioxolane were added with trifluoromethanesulfonic acid as a polymerization catalyst, and polymerized at 90 ° C. in a biaxial kneader. Tributylamine and water were added to the polymer, and the mixture was stabilized in a 65 mmφ twin screw extruder.
Next, 0.3 part of an antioxidant and 0.25 part of a heat stabilizer were blended with 100 parts of the polymer, and melt-mixed with a 65 mmφ twin screw extruder to obtain pellets. The MI of the pellet was 0.65.

(8) Gasoline tank production method Using the pellets, a large blow molding machine equipped with a 120 mmφ single screw extruder was used.
Molded gas tank. The moldability was good and the molding time could be shortened.

(9) Performance of gasoline tank The gasoline permeability of the polyacetal resin of this example at 40 ° C. is 0.30 g · mm / m ² · day, and the methanol permeability is 3.5 g.
・ It was a good value of mm / m ² · day. The Izod impact value was 9.0 kg · cm / cm. The pinch-off strength at the bottom of the gasoline tank of this example was excellent.

Example 4 (10) Production method of polyacetal resin Trifluoroxane and 1,3-dioxolane were added with trifluoromethanesulfonic acid as a polymerization catalyst and polymerized at 90 ° C. in a biaxial kneader. Triethylamine and water were added to the polymer, and the mixture was stabilized in a 45 mmφ twin screw extruder.
To 100 parts of this polymer, a polyester elastomer (synthesized from terephthalic acid, adipic acid, 1,4-butanediol, polytetramethylene glycol, glass transition temperature -68
15 ° C. and 45 ° C.) and 1 part of 4,4′-dicyclohexylmethane diisocyanate were added and reacted in a 65 mmφ extruder. Add 0.5 part of antioxidant and 0.3 part of heat stabilizer, add 50 parts
Pellets were formed using a mmφ single screw extruder. The MI of the pellet was 0.36.

(11) Production method of gasoline tank Using the pellets, a gasoline tank having an internal capacity of 80 was formed at a temperature of 230 ° C using an extruded resin at a large blow molding machine equipped with a 90 mmφ single screw extruder. The moldability was good.

(12) Gasoline tank performance The gas transmission rate of the polyacetal resin of this example at 25 ° C was 0.24 g · mm / m ² · day, and the methanol transmission rate was 0.70 g ·
mm / m ² · day, which was an extremely low transmittance. Also, the Izod impact value was as good as 23 kg · cm / cm, and the pinch-off strength of the tank bottom was also good.

Comparative Example 1 (Examples of other resins) (13) Manufacturing method of high-density polyethylene gasoline tank Using a high-density polyethylene of MI0.02 (ASTM D-1239 E condition), a large blow molding machine with a 90 mmφ single screw extruder was used. 20
A gasoline tank having a content of 55 was molded at an extruded resin temperature of 0 ° C. The molding time was longer than when a polyacetal resin was used, and the appearance of the gasoline tank was not glossy and the finish was not always good.

(14) Performance of high-density polyethylene gasoline tank The gasoline permeability of the high-density polyethylene of this comparative example at 40 ° C was 95 g · mm / m ² · day, which was poor. The methanol permeability was 2.8 g · mm / m ² · day. The Izod impact value was 15 kg · cm / cm, and the pinch-off strength on the lower surface of the tank was at a level without any problem.

Examples 5 to 10 Polyacetals having a linear, branched, or crosslinked structure shown in Table 1, polymers for improving impact resistance shown in Table 1,
From the antioxidant and the heat stabilizer, 55 gasoline tanks were molded at the extruded resin temperatures shown in Table 1. The moldability and the finished condition of the gasoline tank were all good.

Further, the gasoline permeability, methanol permeability, and Izod impact value of the polyacetal resin of each example were good, and the gasoline tanks molded from these polyacetal resins all had excellent performance.

Comparative Example 2 (Example of Extruded Resin Temperature) The polyacetal resin used in Example 1 was replaced with the polyacetal resin of Example 1.
An attempt was made to blow-mold at a resin temperature of 178 ° C using a large blow molding machine with a 90 mmφ single-screw extruder, but the shape of the gasoline tank was incomplete and a good molded product could not be obtained.

In addition, molding was attempted with the extruded resin temperature raised to 263 ° C., but countless silver streaks were observed on the surface of the gasoline tank, and the appearance was remarkably poor.

Comparative Example 3 (Example of MI) An anhydrous formaldehyde was polymerized to synthesize a polyacetal having a linear structure of MI1.5. An antioxidant and a heat stabilizer were added to this polyacetal to obtain a polyacetal resin. Using this polyacetal resin, blow molding was attempted on a large blow molding machine equipped with a 90 mmφ single screw extruder. However, the drawdown of the parison was so severe that blow molding was not possible.

On the other hand, a polyacetal having a branched structure having an MI of 0.004 was synthesized from anhydrous formaldehyde and glycerin as a branching agent. This polyacetal has an antioxidant,
A heat stabilizer was added to obtain a polyacetal resin. Using this polyacetal resin, blow molding was attempted on a large blow molding machine with a 90 mmφ single screw extruder, but no gasoline tank could be obtained due to insufficient fluidity of the resin.

Example 11 The amount of the modified ethylene / propylene / diene copolymer used in Example 10 (the amount of the ethylene / propylene / diene copolymer subjected to the coupling reaction using methylene diisocyanate) was increased to 55 parts. Others are all examples
Using the same polyacetal as in Example 10, the same operation as in Example 10 was performed. The MI of the polyacetal resin was 0.17.

When blow molding was performed using this polyacetal resin, the moldability of the gasoline tank was good,
Gasoline permeability tended to increase up to 35 g · mm / m ² · day. Further, the reaction amount of the modified ethylene / propylene / diene copolymer was reduced to 0.4 part, and a gasoline tank was formed. MI of polyacetal resin is 0.13,
The moldability was good. Gasoline tank permeability is 0.
25g · mm / m ² · day and it was the good Izod impact value 9
kg / cm / cm was slightly lower. The Izod impact value of the polyacetal resin to which no modified ethylene / propylene / diene copolymer had been added (and thus had not been reacted) was 9 kg · cm / cm.

〔The invention's effect〕

Gasoline tank made of polyacetal resin of the present invention,
The moldability during blow molding is good, and the gasoline permeability and methanol permeability are extremely small. A gasoline tank made of a polyacetal resin obtained by compounding or reacting a polymer for improving impact resistance with polyacetal has good impact resistance.

Claims (3)

(57) [Claims] 1. A polyacetal resin having a melt index of 0.005 to 1.0 at an extrusion resin temperature of 180 to 260 ° C.
A gas tank made of polyacetal resin, which is formed by blow molding. 2. The gasoline tank according to claim 1, wherein the polyacetal resin is a polyacetal having a branched or crosslinked molecular structure. 3. The polyacetal resin is polyacetal 10
A composition obtained by mixing or reacting 0.5 to 50 parts of a polymer for improving impact resistance, which is mainly composed of a vinyl polymer having a glass transition temperature of -125 to 80 ° C. and / or an elastomer with respect to 0 parts. The gasoline tank according to claim 1, which is a product.