JP3022987B2 - Hollow molded body made of polyacetal resin - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyacetal resin hollow molded article. More specifically, the present invention relates to a polyacetal resin hollow molded article having excellent impact strength, which is molded by an injection blow molding method.

[Conventional technology]

Polyacetal resin is widely used as an engineering plastic having well-balanced mechanical properties in electric / electronic parts, automobile parts, and the like.

However, most of them are so-called molds formed by an injection molding method, and there are almost no hollow molded bodies formed by a blow molding method. This is because the melt flow characteristics of the polyacetal resin are close to Newtonian flow, the parison at the time of molding is easy to draw down, and due to the draw down, uneven thickness occurs in the molded body, the impact strength of the thin part is extremely weak, This is because there is a disadvantage that the strength required as a container for holding the liquid is insufficient.

As a method for increasing the impact strength as a hollow molded body, a method for producing a hollow molded body from a composition obtained by blending an elastomer such as polyurethane with a polyacetal resin is known, but the polyacetal produced by the above-described conventional technique is known. Although the hollow molded article manufactured from the resin composition as a raw material has an improved impact strength, the impact strength is insufficient because the thickness deviation of the hollow molded article is not completely improved, and further improvement is desired. I have.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyacetal resin hollow molded article having a sufficient impact strength as a container for holding a liquid or the like, overcoming the above-mentioned problems of the prior art.

[Means for solving the problem]

The inventors of the present invention have studied to solve the above-mentioned problems, and as a result, a hollow molded body obtained by molding a polyacetal resin having a specific melt index at a specific resin temperature by an injection blow molding method has a disadvantage. It has been found that a hollow molded article made of a polyacetal resin having a very small degree of meat and having extremely excellent impact performance can be obtained, and the present invention has been achieved.

That is, the present invention is a hollow molded article made of a polyacetal resin obtained by molding a polyacetal resin having a melt index of 0.05 to 10 at a resin temperature of 180 to 240 ° C by an injection blow molding method.

In the present invention, the melt index (hereinafter abbreviated as MI),
A polyacetal resin in the range of 0.05 to 10, preferably 0.5 to 3, is used as a raw material.

Here, MI of the present invention refers to a value measured by ASTM D-1238. When the MI is less than 0.05, it is extremely difficult to form a parison by injection molding because the melt viscosity is high.
On the other hand, if the MI is more than 10, the melt strength will be low, causing drawdown in the process of blowing up the parison, and a molded article having good impact strength cannot be obtained.

In the present invention, the resin temperature needs to be in the range of 180 to 240 ° C. Preferably it is 185-220 degreeC. If the resin temperature is lower than 180 ° C., a molded article having a good shape cannot be obtained. On the other hand, when the resin temperature is higher than 240 ° C., the melt strength of the resin is low, which causes drawdown, resulting in uneven thickness of the molded product, making it impossible to obtain a molded product having a desired impact strength.

As for the polyacetal resin used as a raw material of the hollow molded article of the present invention, as long as the MI of the polyacetal resin is in the range of 0.05 to 10, the polyacetal may have any molecular structure of linear, branched or crosslinked. Among these molecular structures, a branched or crosslinked molecular structure is more preferable from the viewpoint of the appearance of the molded article, that is, from the viewpoint of the surface finish of the molded article and the viewpoint of preventing drawdown.

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

Polyacetals having a branched molecular structure can be obtained by homopolymerizing formaldehyde or trioxane 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, or formaldehyde. Alternatively, it can be obtained by copolymerizing trioxane and a cyclic ether.

The polyacetal having a crosslinked molecular structure is obtained by homopolymerizing formaldehyde or trioxane in the presence of a polyfunctional glycidyl ether containing two or more epoxy groups in one molecule, or forming formaldehyde or trioxane with a cyclic ether. Obtained by copolymerization.

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 the obtained hollow molded article, it is preferable to use a polymer for improving impact resistance, which is mainly composed of a vinyl polymer or an elastomer, mixed with 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,
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,
The impact resistance of the hollow molded article obtained by the injection blow molding method may be insufficient. On the other hand, if the blending of the polymer, the reaction amount exceeds 50 parts, the solvent resistance of the hollow molded body becomes insufficient, which may be a practical problem as a container used as a raw material of the hollow molded body of the present invention The resulting polyacetal resin may contain known stabilizers and additives such as heat stabilizers, antioxidants, light stabilizers, lubricants, flame retardants, crystal nucleating agents, and coloring agents.

Although the hollow molded article of the present invention is molded by a known injection blow molding machine, it is preferably produced by a general injection blow molding machine usually used when producing molded articles of polyolefin, polystyrene and the like.

〔Example〕

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 at 190 ° C under standard load of 2.16 kg (AS
TM D-1238E) Antioxidant: 2,2-methylenebis (4-methyl-6-t-
(Butyl phenol) Heat stabilizer: Nylon 3 Further, various physical properties of the obtained hollow molded article were measured according to the methods described below.

Thickness and unevenness degree: A cylindrical container was blow-molded by a downward blowing method, and the thickness of the side surface was measured by a commercially available micrometer. Thickness T ₁ (mm) of the side part 10mm higher than the bottom
And the thickness T ₂ (mm) of the side surface at a height corresponding to exactly half the height of the entire container, and the ratio (T ₁
/ T ₂ ). It is preferable that the value of T ₁ / T ₂ obtained by this measurement method is closer to 1, more preferably, the value of T ₁ / T ₂ is 0.9 or more and 1.
A hollow molded body in the range of 1 or less is suitably used as a container for holding a liquid or the like.

Impact resistance: Pure water equivalent to 80% of the internal volume of the hollow molded body is put into the obtained hollow molded body, plugged and sealed, and then placed on concrete floor from a height of 1m above the ground. The molded product was dropped and the state of destruction was measured. Any part of the molded body other than the plug is broken or scratched, etc., and any water leaked outside is judged to be unacceptable. Impact resistance performance was measured as an index.

The impact strength index measured by this measurement method is 10 (pieces / 1000 pieces)
Hereinafter, preferably, 5 (pieces / 1000 pieces) or less hollow molded articles are suitably used as a container for holding a liquid or the like.

Example 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 to carry out polymerization at 50 ° C. After the polymer was separated 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 0.13.

Method of manufacturing hollow molded body and physical properties of hollow molded body Using the above pellets, using a modified IB150 injection blow molding machine manufactured by Toshiba Machine Co., at a resin temperature of 210 ℃, diameter 50mmφ,
A cylindrical container having a height of 100 mm and an internal volume of 200 ml was formed by a downward blowing method. The moldability was good, and the obtained molded article had excellent glossy surface properties. Further, the thickness of the hollow molded body is _{T 1 = 1.01mm, T 2 =} 1.03mm, the thickness deviation degree T ₁
/ T ₂ was 0.98, and the degree of deviation in wall thickness was extremely small. Further, the impact strength index of this hollow molded article is 2 (pieces / 1000
) And had good impact resistance.

Example 2 Method for producing polyacetal resin (crosslinked) Trioxane and ethylene oxide were used as crosslinking agents in 1,4
-Butanediol glycidyl 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, polyester elastomers (terephthalic acid, adipic acid, isophthalic acid,
Synthesized from 4-butanediol, glass transition temperature -18 ℃
5 parts, 0.4 parts of antioxidant, 0.3 parts of heat stabilizer, 65 parts
The mixture was melt-mixed with a mmφ twin screw extruder to obtain pellets. The MI of the pellet was 2.2.

Manufacturing Method of Hollow Molded Article and Physical Properties of Hollow Molded Article Using the above-mentioned pellets, a cylindrical container having a diameter of 40 mmφ, a height of 50 mm and an inner volume of 60 ml at a resin temperature of 190 ° C. using the same molding machine as in Example 1. Was molded by a down-blowing method. This hollow molded article had the following physical properties.

Wall thickness: T ₁ = 0.99 mm, T ₂ = 1.00 mm Deflection degree (T ₁ / T ₂ ): 0.99 Impact strength index: 1 (pieces / 1000 pieces) As described above, this hollow molded article has excellent impact properties Had.

Example 3 Method for Producing 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 4.2.

Manufacturing Method of Hollow Molded Article and Physical Properties of Hollow Molded Article Using the above-mentioned pellets, a cylindrical container having a diameter of 50 mmφ, a height of 50 mm and an internal volume of 100 ml at a resin temperature of 205 ° C. using the same molding machine as in Example 1. Was molded by the downward blowing method. This hollow molded article had the following physical properties and was excellent in impact resistance.

Thickness: T ₁ = 1.02 mm, T ₂ = 1.09 mm Deflection degree (T ₁ / T ₂ ): 0.94 Impact strength index: 5 (pieces / 1000 pieces) Comparative Example 1 (Example of extrusion blow molding method) Extrusion blow Manufacturing method of hollow molded body by molding method and physical properties of hollow molded body The polyacetal resin used in Example 1 was blow-molded with a 50 mmφ single screw extruder at an extruded resin temperature of 210 ° C., a diameter of 50 mmφ, a height of 100 mm, A cylindrical container having an inner volume of 200 ml was formed by a downward blowing method. At the time of molding, the parison was drawn down, and the moldability was poor. The thickness of the obtained hollow molded body was T ₁ = 0.67 mm, T ₂ = 1.07 mm, and the thickness deviation T ₁ / T ₂
Was 0.63, which was a large degree. Further, the impact strength index of this hollow molded article was 174 (pieces / 1000 pieces), and did not have sufficient impact strength as a container.

Comparative Example 2 (Example of Resin Temperature) An injection blow molding of the polyacetal resin used in Example 1 at a resin temperature of 178 ° C. was attempted using the same molding machine as in Example 1, but the obtained molded article was obtained. Is incomplete,
A good molded body could not be obtained.

Molding was attempted with the resin temperature raised to 243 ° C. The obtained molded article had the following physical properties, a large degree of uneven wall thickness, and did not have good impact resistance.

_{Thickness: T 1 = 0.62mm, T 2} = 1.10mm thickness deviation degree (T ₁ / T _2): 0.56 Impact Properties Index: 256 (pieces / 1000) Polymerization Comparative Example 3 (example MI) formaldehyde anhydrous Thus, a polyacetal having a linear structure with an MI of 10.8 was synthesized. An antioxidant and a heat stabilizer were added to this polyacetal to obtain a polyacetal resin. Injection blow molding was attempted using this polyacetal resin with the same molding machine as in Example 1, but the drawdown of the parison was severe and blow molding was impossible.

On the other hand, a polyacetal having a branched structure with an MI of 0.03 was synthesized from anhydrous formaldehyde and glycerin as a branching agent. An antioxidant and a heat stabilizer were added to this polyacetal to obtain a polyacetal resin. Using this polyacetal resin, injection blow molding was attempted using the same molding machine as in Example 1, but the flowability of the resin was so poor that parison could not be injection molded.

Examples 4 to 10, Comparative Examples 4 to 7 Polyacetals having a linear, branched, or crosslinked structure shown in Table 1, polymers for improving impact resistance shown in Table 1,
The same hollow molded body as in Example 1 was molded from the antioxidant and the heat stabilizer at the resin temperature shown in Table 1 using the same molding machine as in Example 1. The moldability was good in any of the examples.

In addition, the thickness, degree of uneven thickness, and impact characteristic index of the hollow molded article made of polyacetal resin of each example are also shown in Table 1, and in each of these examples, all were good and excellent. It had impact properties.

On the other hand, in each of the comparative examples, the degree of deflection of the obtained molded article was large, and the impact characteristics were insufficient.

[Effect of the Invention] The hollow molded article made of polyacetal resin of the present invention
By molding a polyacetal resin having MI at a specific resin temperature by an injection blow molding method, the degree of thickness deviation is significantly reduced, and the resin has excellent impact strength. The hollow molded article of the present invention forms a new market for applications such as containers for storing liquids or powders such as organic solvents and aqueous solutions.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B29C 49/00-49/80

Claims (8)

(57) [Claims] 1. A hollow molded article of a polyacetal resin obtained by molding a polyacetal resin having a melt index of 0.05 to 10 at a resin temperature of 180 to 240 ° C. by an injection blow molding method. 2. The polyacetal resin is polyacetal 10
A composition obtained by blending or reacting 0.5 to 50 parts of a polymer for improving impact resistance, which is mainly composed of a vinyl polymer or an elastomer having a glass transition temperature of -125 ° C to 80 ° C with respect to 0 parts. The hollow molded article made of a polyacetal resin according to claim 1, which is: 3. The hollow molded article made of a polyacetal resin according to claim 1 or 2, which is molded using a polyacetal resin having a melt index of 0.5 to 3. 4. A polyacetal comprising trioxane and 1,3-
The hollow molded article made of a polyacetal resin according to claim 1, 2 or 3, which is obtained by polymerizing dioxolane as a monomer. 5. The hollow molded article made of a polyacetal resin according to claim 2, wherein the polymer for improving impact resistance is a polyurethane elastomer. 6. The hollow molded article made of a polyacetal resin according to claim 5, wherein the polyurethane elastomer is a polyurethane synthesized from 4,4'-diphenylmethane diisocyanate, tetramethylene glycol and polytetramethylene glycol. 7. The polyacetal is obtained by homopolymerizing formaldehyde or trioxane in the presence of a polyfunctional compound containing three or more functional groups such as hydroxyl group, amino group, carboxyl group, etc. in one molecule, or cyclically reacting with formaldehyde or trioxane. The hollow molded article made of a polyacetal resin according to claim 1, which is a branched polyacetal obtained by copolymerizing with an ether. 8. A method of homopolymerizing formaldehyde or trioxane or copolymerizing formaldehyde or trioxane with a cyclic ether in the presence of a polyfunctional glycidyl ether in which the polyacetal contains two or more epoxy groups in one molecule. The hollow molded article made of a polyacetal resin according to claim 1, 2 or 3, which is a crosslinked polyacetal obtained by (1).