JP2898861B2 - Hollow injection molded product made of polyacetal resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow molded article made of polyacetal resin having excellent dimensional stability after molding.

[0002]

2. Description of the Related Art Plastic has low specific gravity, good workability,
Due to its non-corrosive nature, its field of application has expanded in recent years,
Its use is increasing significantly. Accordingly, demands for plastics from users have also become more sophisticated, and engineering plastics having excellent heat resistance and mechanical properties have come to occupy a particularly important position.

[0003] Polyacetal resin is a known engineering plastic, and has mechanical strength, slidability, heat resistance,
Automobiles as resins with excellent chemical and creep resistance,
It is widely used as a mechanical component or an exterior component in various fields such as general machinery, precision machinery, and electric / electronics. Various demands for molded products made of polyacetal resin have been advanced in accordance with recent high-tech applications in various fields of application, and responding to these demands has become a technical issue.

[0004] Since polyacetal resin is a crystalline thermoplastic resin, it shrinks greatly when solidifying from a molten state during injection molding. For this reason, it is very difficult to reduce sink marks and warpage and obtain a molded product with high accuracy.
For this reason, attempts have been made to solve various problems from the viewpoints of mold design, molding method, resin characteristics and the like. For example, as an approach from a molding method, a hollow injection molding method has recently been used. The hollow injection molding method is a molding method in which a thermoplastic resin is injected into a mold cavity in injection molding, and then a gas is injected into the resin to obtain a hollow molded product. In the hollow injection molding method, a gas is supplied into the resin, and the shrinkage of the resin is compensated for by the hollow portion, so that good dimensional accuracy can be obtained. Although the shrinkage of the resin can be compensated by applying a resin holding pressure even in a normal injection molding method, the supply of the resin is stopped after the gate sealing because the resin is solidified at the gate portion. However, in the hollow injection molding method, the shrinkage of the resin is compensated by the gas even after the gate seal, so
Less warpage and good effect. A representative example of such a hollow molding method is disclosed in Japanese Patent Publication No. 57-14968.

[0005]

By the way, when additives such as a heat stabilizer and an antioxidant are added to the polyacetal resin, the crystallization speed of the compound is increased (the crystallization time is shortened), and after the molding, If left for a long time or left at a high temperature for a short time, dimensional change occurs due to shrinkage later, and there is a limitation in application to precision parts. As a method for improving the dimensional stability of the polyacetal resin, a method of blending an inorganic filler is conventionally known.

However, a polyacetal resin containing an inorganic filler has a great decrease in mechanical properties, particularly, elongation and impact resistance, and has a remarkable decrease in the strength of a weld portion, so that it is difficult to apply it to various parts. The present invention, without deteriorating the properties inherent in polyacetal resin,
An object of the present invention is to provide a hollow molded article made of a polyacetal resin having improved dimensional stability.

[0007]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to solve the above-mentioned problems, the use of a specific polyacetal resin molding material in the hollow injection molding method reduces sink marks and warpage. Moreover, they have found that a hollow molded article made of polyacetal resin having excellent dimensional stability can be obtained.

[0008] That is, the present invention relates to an additive of 0.01 to 5%.
Wt% and polyolefin 0.01-5% Ri name by blending, and hollow injection-molded article using a reportage <br/> Li acetal resin molding material having a crystallization time of formula (1) It is.

T1 ≧ T2 × 0.6 (1) T1: Crystallization time of polyacetal resin containing additive and polyolefin T2: Crystallization time of polyacetal resin containing no additive and polyolefin Will be described.

The polyacetal resin used in the molding material of the present invention refers to a substantially oxymethylene unit produced from a cyclic oligomer such as a formaldehyde monomer or its trimer (trioxane) or tetramer (tetraoxane). An oxymethylene homopolymer consisting of
And an oxyalkylene unit having 2 to 8 carbon atoms produced from the above raw material and a cyclic ether such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolan, glycol formal, or diglycol formal. An oxymethylene copolymer containing 20% by weight. The polyacetal resin of the present invention also includes an oxymethylene copolymer having a branched molecular chain, and an oxymethylene block copolymer containing 50% by weight or more of oxymethylene repeating units and less than 50% by weight of heterogeneous polymer units.

The additive in the present invention is a substance added for the purpose of improving the thermal stability, heat aging resistance, weather resistance and other durability of the polyacetal resin. The crystallization time of the polyacetal resin containing these substances is shorter than that of the non-compounded polyacetal resin. In particular, an additive present as a solid at a temperature higher than the melting point of the polyacetal resin has an effect as a nucleating agent, and the crystallization time of the polyacetal resin in which the additive is blended becomes extremely short, resulting in poor dimensional stability.

First, the following heat stabilizers are added to improve the above heat stability.
Polyamide resins such as nylon 4-6, nylon 6,
Nylon 6-6, Nylon 6-10, Nylon 6-1
2, nylon 12, etc., and nylon 6 / 6-6 / 6-6-10, nylon 6 / 6-12, etc., which are copolymers thereof. Other than this, poly-β-alanine copolymer obtained by polymerizing acrylamide and its derivative or acrylamide and its derivative and other vinyl monomer in the presence of metal alcoholate, acrylamide and its derivative or acrylamide and its There is a polymer obtained by polymerizing a derivative and another vinyl monomer in the presence of a radical polymerization catalyst. Also, amines, amides, ureas,
A polymer having a nitrogen-containing group such as urethane is also used as a heat stabilizer.

Next, examples of the heat aging resistance improving agent for improving the heat aging resistance include the following. As phenolic antioxidants, for example, triethylene glycol-bis [3- (t-butyl-5-methyl-4-hydroxyphenyl) propionate], 2,
4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3,5-
Triazine, 2,2-thio-diethylenebis [3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate], octadecyl-3- (3,5-di-
t-butyl-4-hydroxyphenyl) propionate, 1,6-hexanediol-bis [3- (3,5-
Di-tert-butyl-4-hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,
5-di-t-butyl-4-hydroxyphenyl) propionate], N, N'-hexamethylenebis (3,5-
Di-tert-butyl-4hydroxy-hydrocinnamamide,
3,5-di-t-butyl-4-hydroxybenzylphosphonate-diethyl ester, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-
4-hydroxybenzyl) benzene, tris- (3,5
-Di-t-butyl-4-hydroxybenzyl) -isocyanurate, N, N'-bis- [3- (3,5-di-t
-Butyl-4-hydroxyphenyl) propionyl] hydrazine, 4,4′-thiobis- (6-t-butyl-3
-Methylphenol), 4,4'-butylidenebis-
(6-t-butyl-3-methylphenol), 2,2 ′
-Methylenebis- (4-methyl-6-t-butylphenol), 2,2'-methylenebis- (4-ethyl-6-
t-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 2-tert-butyl-6- (3'-tert-butyl-5'-)
Methyl-2'-hydroxybenzyl) -4-methylphenyl acrylate, 4,4'-butylidene-bis- (3
-Methyl-6-t-butylphenol), 3,9-bis [2- [3- (3-t-butyl-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] 2,4. 8,10-tetraoxaspiro [5,
5] Undacan, dibutylhydroxytoluene and the like.

Further, examples of the weather resistance improving agent for improving the weather resistance include the following. As a benzotriazole-based ultraviolet absorber, for example, 2- (2′-hydroxy-
5′-methyl-phenyl) benzotriazole, 2-
(2′-hydroxy-3 ′, 5′-di-tert-butyl-phenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-isoamyl-phenyl) benzotriazole, 2- [2 '-Hydroxy-3', 5'-bis- (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- [2'-hydroxy-4'-octoxyphenyl) benzotriazole and the like. Examples of the oxalic acid anilide-based ultraviolet absorber include 2-ethoxy-2′-ethyloxalic acid bisanilide,
There are 2-ethoxy-5-t-butyl-2'-ethyloxalic acid bisanilide and 2-ethoxy-3'-dodecyloxalic acid bisanilide. As the hindered amine light stabilizer, for example, bis (2,2,
6,6-tetramethyl-4-piperidyl) -sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) -adipate, 4-benzoyloxy-2,2,
6,6-tetramethylpiperidine, 4- (phenylcarbamoyloxy) -2,2,6,6-tetramethylpiperidine and the like.

These additives are required to be present in an amount of 0.01 to 5% by weight, preferably 0.05 to 3% by weight, based on the total amount of the polyacetal resin molding material. If the amount is less than 0.01% by weight, the effect of adding the additive is not exhibited. If the amount exceeds 5% by weight, the appearance of a molded article is poor due to a bleeding phenomenon or an avatar. As the polyolefin used in the present invention, low density polyethylene, linear low density polyethylene,
Examples include medium-density polyethylene, high-density polyethylene, polypropylene, ethylene and vinyl monomers such as ethylene and vinyl acetate, ethylene and ethyl acrylate, copolymers of ethylene and methyl acrylate, and copolymers of ethylene and propylene. In particular, low density polyethylene is preferred.

Flow rate of polyolefin used in the present invention [ASTM D1238-86 (condition E)]
Is preferably 1 to 45 g / 10 minutes. The addition amount of the polyolefin used in the present invention is 0.01 to 5% by weight based on the total amount of the polyacetal resin molding material,
Preferably it is 0.02 to 2% by weight. 0.01% by weight
If it is less than 5%, the effect of addition is not recognized.

As described above, according to the present invention, the additive is added in an amount of 0.01%.
In 5% by weight, and polyolefin down 0. 01-5% by weight
While you added to the polyacetal resin molding composition total amount, near the upper limit of the addition amount range of additives (e.g., 5 wt%) near the lower limit of the addition amount of the polyolefin (e.g., 0.01 wt%) addition of the combination of The amount does not provide a better dimensional stability improvement effect.

In other words , in order to obtain an excellent effect of improving dimensional stability, the crystallization time (T1) of the polyacetal resin in which the additive and the polyolefin are blended is equal to the crystallization time of the polyacetal resin in which these are not blended (T1). The relationship of T1 ≧ T2 × 0.6 is necessary for T2), and preferably, T1 ≧ T2 × 0.7. T1 is less than T2 × 0.6, excellent dimensional stability improving effect is not observed.

The effect of improving the dimensional stability of a polyacetal resin is closely related to its crystallization time.
The longer the crystallization time (the longer the crystallization time), the better the effect of improving the dimensional stability (see Examples and Comparative Examples). The method for preparing the molding material of the present invention is not particularly limited, and the addition form of the polyolefin and other additives may be a powder or a molten state. The method of adding the polyolefin or the like is generally performed by blending and kneading the polyacetal resin and the polyolefin together with an extruder. The extruder may be single-screw or twin-screw, and may be added during the polymerization process.

The molding material of the present invention may contain a lubricant, a pigment, an inorganic filler and the like, which are usually used in polyacetal resins, alone or in combination as long as the effect is not impaired. In particular, the polyolefin of the present invention may be used as a pigment treating agent, and the treated pigment and an additive may be blended and used. The hollow injection molding method of the present invention is performed by a combination of a usual injection molding machine and a gas injection device. The gas injection device is a device that injects a gas into the resin through a pipe after the resin is injected, and keeps the gas pressure for a set time.
For this, the gas to be injected is compressed to a high pressure in advance, stored in an accumulator, and a high-pressure gas is introduced through a pipe at the time of gas injection, or a method in which a certain amount of gas is continuously fed by a pump and pressurized. Although it is conceivable, any method is possible as long as a gas can be fed into the resin after injection. At this time, a method such as using a nozzle of a molding machine cylinder, a mold sprue, a mold runner as a gas injection port, or directly injecting into a product part can be considered. Any method can be used as long as it can be injected. A typical hollow injection molding method is disclosed in Japanese Patent Publication No. 57-14968.

In the present invention, a molded article having a hollow portion is obtained, but the hollow portion here excludes a cavity (void) or a hollow portion caused by a foaming agent. Examples of the gas used in the present invention include an inert gas such as nitrogen, helium, neon, and argon. Any gas can be used as long as it is inert to the resin. When these gas bodies are used, impurities are usually contained. However, if there are too many impurity components, it is not preferable because resin may be decomposed or burnt during molding. In view of economy, nitrogen gas is more preferably used industrially.

Although the molded article of the present invention has a hollow portion, a preferable hollow ratio is 3 to 50%, and more preferably 5 to 4%.
0%. This is because a high hollow ratio deteriorates the surface appearance due to hesitation marks and the like, and a low hollow ratio impairs the effect on warpage and sink marks. The hollow ratio is defined by the following equation. Hollow ratio (%) = {(V × ρ−M) / (V × ρ)} × 10
In the above equation, V is the volume when the hollow portion is filled with the same resin, ρ is the specific gravity of the resin used, and M is the mass of the hollow molded product.

[0023]

The present invention will be described in more detail with reference to the following examples, which do not limit the present invention. The dimensional stability of the hollow molded article made of the polyacetal resin molding material of the present invention was evaluated according to the following method.

(Dimensional stability) Length x width x thickness 100 mm
A hollow molded article having a size of 15 mm x 10 mm is molded by a hollow injection molding method, and a longitudinal dimension (A) after leaving the molded article at 23 ° C for 48 hours, and further heating the molded article at 80 ° C for 6 hours. The length (B) in the longitudinal direction after standing at 48 ° C. for 48 hours was measured and calculated by the following equation.

Dimensional stability (%) = [{(A)-(B)}
/ 100] × 100 The hollow injection molding at this time was performed as follows.
The gate was provided at one point on one of the surfaces corresponding to 15 × 10 mm of the molded product, and the position was set at the center (center of gravity) of the surface. Also,
The mold temperature was 70 ° C., and the cylinder set temperature was 200 ° C. The hollow ratio was adjusted by changing the measured value.

Nitrogen gas was used as the gas to be injected into the resin, and the gas injection port was provided at the nozzle of the cylinder. At this time, a shut-off valve was provided on the screw side (hopper side) of the gas injection port in order to prevent gas from entering the cylinder (into the direction opposite to the mold). Nitrogen gas was introduced into the gas injection device, the pressure was increased to 100 kg / cm ² , the pressure was kept in the accumulator, and after the resin was injected, the gas was injected into the resin through a pipe. Gas was introduced from the nozzle through a sprue, runner and gate into a prismatic cavity. The conditions at this time were as follows: gas injection delay time (time from resin injection to gas injection) 0.5 seconds, gas injection time (gas injection time) 5 seconds, pressure holding time (gas injection The time for stopping the gas system and keeping the gas system closed and the time for gas injection) were set to 100 seconds. The mold was opened 5 seconds after the end of the pressure holding time, and the molded product was taken out.

According to the above method, a molded article having a hollow structure was obtained. FIG. 1 shows one embodiment of the hollow portion. (Crystallization time) The crystallization time was determined by Dikin manufactured by PerkinElmer.
It measured by the following method using fferential Scanning Calorimeter (DSC-7).

The measurement sample is placed on a sample table, and the temperature is set to 50 ° C. The temperature is increased to 200 ° C. at a rate of 320 ° C./min. Hold at this temperature for 1 minute for homopolymers and 2 minutes for copolymers. Thereafter, the temperature is lowered at a rate of 80 ° C./min to 156 ° C. for a homopolymer and to 150 ° C. for a copolymer.

The time from when the temperature dropped to a predetermined temperature to the peak of the exothermic peak due to crystallization was measured, and this time was defined as the crystallization time. The various additives used in the present invention are as follows. Heat stabilizer-IA: A batch type 30 liter kneader was used as a reactor, and acrylamide monomer 4.5 k was used.
g and N, N'-methylenebisacrylamide 0.5k
g of the monomer and 1.088 g of zirconium tetraisopropoxide in an amount of 1/20000 mol with respect to the monomer were added.
The reaction was performed at 0 ° C. for 4 hours. After the reaction, the solid was taken out and pulverized to an average particle size of 3.5 μm. This polymer was a poly-β-alanine copolymer having a primary amide content of 7.0 mmol / g of polymer. The primary amide content was determined by hydrolyzing the polymer with a 40% by weight potassium hydroxide solution and quantifying the amount of ammonia generated.

Heat stabilizer-IB: Nylon 6-6 produced by a known condensation polymerization reaction is pulverized to an average particle size of 5.0 μm. Heat aging resistance improver-IIA: triethylene glycol-bis [3- (t-butyl-5)
-Methyl-4-hydroxyphenyl) propionate] Heat aging resistance improver-IIB: 1,3,5-trimethyl-2,4,6-tris (3,5
-Di-t-butyl-4-hydroxybenzyl) benzene Heat aging resistance improver-IIC: N, N'-bis- [3- (3,5-di-t-butyl-4)
-Hydroxyphenyl) propionyl] hydrazine weathering improver-IIIA: 2- [2'-hydroxy-3 ', 5'-bis- (α, α
-Dimethylbenzyl) phenyl] -2H-benzotriazole Weathering improver-IIIB: 2-Ethoxy-2'-ethyloxalic acid bisanilide Weatherability improver-IIIC: Bis (2,2,6,6-tetra Methyl-4-piperidyl) -sebacate polyolefin-IVA: low-density polyethylene flow rate manufactured by Asahi Kasei Corporation;
6.5 Polyolefin-IVB: Low density polyethylene flow rate manufactured by Asahi Kasei Corporation;
2.0 Polyolefin-IVC: Low-density polyethylene flow rate manufactured by Asahi Kasei Corporation;
10.0 Polyolefin-IVD: low-density polyethylene flow rate manufactured by Asahi Kasei Corporation;
20.0 Polyolefin-IVE: Linear low-density polyethylene flow rate manufactured by Asahi Kasei Corporation; 20.0 Polyolefin-IVF: High-density polyethylene flow rate manufactured by Asahi Kasei Corporation;
7.0 Polyolefin-IVG: High-density polyethylene flow rate manufactured by Asahi Kasei Corporation;
12.0 Polyolefin-IVH: high density polyethylene flow rate manufactured by Asahi Kasei Corporation;
40.0 Polyolefin-IVI: polypropylene flow rate manufactured by Asahi Kasei Corporation;
0 Polyolefin-IVJ: Asahi Kasei Corporation polypropylene flow rate; 1
4.0

[0031]

EXAMPLES 1-3 AND COMPARATIVE EXAMPLES 1-3 Polyoxymethylene copolymers containing 2.8% ethylene oxide were prepared by the known method described in U.S. Pat. No. 3,027,352. This had an intrinsic viscosity of 1.1 (intrinsic viscosity was measured at 60 ° C. by dissolving 0.1% by weight of the polymer in a p-chlorophenol solution containing 2% by weight of α-pinene). The flow rate according to ASTM D1238-86 (E condition) was 10.0 g / 10 minutes. The crystallization time of this polymer was 400 seconds.

Using this polymer as a base polymer, 0.3% by weight of heat stabilizer-IA and polyolefin-IVA
Was melt-kneaded with a twin-screw extruder in which the cylinder temperature was set to 200 ° C., and granulated and commercialized. Table 1 shows the results of measuring the crystallization time of the pellet and the dimensional stability of the hollow molded product as Examples 1 to 3. In addition, as a comparison, the measurement result of a material without addition of polyolefin is also shown in Comparative Example 1.
The results are shown in Table 1 below.

[0033]

Examples 4 to 12 and Comparative Example 4 In place of the polyolefin-IVA of Example 1, other various polyolefins were used, and a molding material was produced in the same manner except that the hollow ratio was 30%. The dimensional stability of the molded article was measured.
The results are shown in Table 2 as Examples 4 to 12. As a comparison, Table 2 also shows the measurement results of a material to which no polyolefin was added as Comparative Example 4.

[0034]

Examples 13 to 19 and Comparative Examples 5 to 11 A molding material was produced in the same manner as in Example 1 except that the heat stabilizer-IA was replaced with various additives and the hollow ratio was 30%. The crystallization time and the dimensional stability of the hollow molded article were measured. The results are shown in Table 3 as Examples 13 to 19. In addition, as a comparison, the measurement results of a material to which polyolefin was not added were also shown in Comparative Examples 5-1.
1 is shown in Table 3.

[0035]

Examples 20 to 22 and Comparative Examples 12 to 14 A molding material was produced in the same manner as in Example 1 except that the combination of additives was used, the amount of addition was changed, and the hollow ratio was changed. The properties were measured. The results are shown in Table 4 as Examples 20 to 22. In addition, Table 4 also shows the measurement results of materials without polyolefin as Comparative Examples 12 to 14 for comparison.

[0036]

Example 23 and Comparative Example 15 Instead of the polyoxymethylene copolymer of Example 1 and Comparative Example 1, a polyoxymethylene homopolymer (prepared by the method described in US Pat. No. 2,998,409; intrinsic viscosity 1.2, flow rate 9) 0.0 g / 10 min), and a molding material was produced in the same manner except that the hollow ratio was 30%, and the crystallization time and the dimensional stability of the hollow molded product were measured. The crystallization time of the unblended polymer was 300 seconds. The results are shown in Example 23 and Comparative Example 15
As shown in Table 4.

[0037]

Comparative Example 16 A molding was produced in the same manner as in Example 2 except that the heat stabilizer-IA was 7.0% by weight and the polyolefin-IVA was 7.0% by weight, to obtain a hollow molded product.
The appearance was poor and peeling was remarkable and could not be put to practical use.

[0038]

Comparative Example 17 A molding material was produced in the same manner as in Example 2 except that a normal injection molding method was used in place of the hollow injection molding method, and a molded product was obtained. Did not.

[0039]

Comparative Examples 18 to 20 A molding material was produced in the same manner as in Example 1 except that the amounts of the heat stabilizer-IA and polyolefin-IVA were changed to 5.0% by weight and 0.05% by weight, respectively. The crystallization time and the dimensional stability of the hollow injection molded article were measured. Table 4 shows the results. This comparative example is an example when the upper limit of the addition amount of the heat stabilizer is 5.0% by weight and the lower limit of the addition amount of the polyolefin is 0.05% by weight. The crystallization time in this example is out of the range of T1 ≧ T2 × 0.6, that is, the crystallization time is 230 seconds or less at the critical value of T1 of 240 seconds (= 400 × 0.6), and the dimensional stability is also 0. .1
6 to 0.17 and the value of the superior dimensional stability of the present invention 0.08
~ 0.11 is inferior.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

As shown in Tables 1 to 4, in Examples, hollow injection molded articles having better dimensional stability than Comparative Examples were obtained. In the present invention, since the hollow injection molding method is used, sink and warp are less, and since the additive and the polyolefin are blended in the polyacetal resin, the dimensional change after molding is small, and a highly accurate molded product can be provided. Therefore, it is very useful as various industrial parts such as automobiles, general machines, precision machines, and electric and electronic devices.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a hollow molded product obtained in Example 2.

[Explanation of symbols]

 1 Hollow part (hatched part) 2 Gate position

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-170526 (JP, A) JP-A-5-138678 (JP, A) JP-A-57-20974 (JP, A) JP-A-63-1988 22817 (JP, A) JP-A-6-32912 (JP, A) JP-A-6-157777 (JP, A) JP-A-6-329812 (JP, A) JP-A-7-90161 (JP, A) JP-A-57-14968 (JP, A) JP-A-7-70349 (JP, A) Patent 2741648 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 45/00

Claims (1)

(57) [Claims] 1. A hollow hollow body made of a polyacetal resin molding material containing an additive of 0.01 to 5% by weight and a polyolefin of 0.01 to 5% by weight and having a crystallization time represented by the formula (1). Injection molded products. T1 ≧ T2 × 0.6 (1) T1: Crystallizing time of polyacetal resin containing additive and polyolefin T2: Crystallizing time of polyacetal resin containing no additive and polyolefin