JPH10100167A - Production of cast polyamide resin molded object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a box-shaped cast polyamide resin molded object such as a bucket having no internal flaw and relatively thin in thickness. SOLUTION: A polymerizable lactam soln. prepared by adding at least an anion polymerization catalyst and an anion polymerization initiator to substantially anhydrous ω-lactam is cast in a mold and subjected to anion polymerization to produce a cast polyamide resin molded object. In this method, an inner mold is arranged in an outer mold 1 in which the polymerizable lactam soln. is cast to cast the polymerizable lactam soln. and, after 5-15min is elapsed, one mold is moved by predetermined quantity so as to reduce the vol. in the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cast polyamide resin molded article, and more particularly to a method for producing a box-shaped cast polyamide resin molded article having a relatively thin thickness without internal defects. Things.

[0002]

2. Description of the Related Art In a method for producing a cast polyamide molded article, a mold is heated to a predetermined temperature in a hot blast stove, the mold is taken out of the furnace, a lactam polymerization solution is poured into the mold, and the mold is again heated. The lactam is polymerized by placing the mold in a hot blast stove. However, according to this method, there is a drawback that the molded body tends to contain bubbles in the polymerization process. Usually, volumetric shrinkage of about 15% occurs when the lactam polymerization solution is subjected to anionic polymerization molding. This volume shrinkage has been one of the causes of generating cavity defects inside the compact. In the conventional method for producing a cast rod-shaped molded article, it has been a technically important task to reduce the occurrence of the above-mentioned internal defects.

[0003] In order to prevent the occurrence of such internal defects in a molded article, a method of polymerizing a lactam polymerization solution under pressure has been conventionally known. For example, Japanese Patent Publication No. 40-16153
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, there is a method in which a lactam polymerization solution is subjected to pressure molding when the viscosity of the system is increased to a maximum by polymerization. In addition, Japanese Patent Publication No. 39-252
No. 02, insulated connection between a mold maintained at a temperature at which polymerization proceeds and an auxiliary container maintained at a temperature at which polymerization does not proceed, encloses the lactam polymerization solution in the auxiliary container There is disclosed a method of press-molding a polyamide molded article by pressurizing with an inert gas so that a lactam polymerization solution is always fed into a mold.

[0004]

However, in the method of manufacturing a molded article such as a bucket having a relatively small thickness, the outer mold and the inner mold are used.
Since the height of the polymerizable lactam liquid cast between the outer mold and the inner mold fluctuates due to the movement of the inner mold during the initial stage of polymerization, it is substantially difficult to manufacture buckets with good dimensional stability in thickness etc. Met.

An object of the present invention is to provide a method for producing a box-shaped cast polyamide resin molded article such as a bucket having a relatively thin thickness and having no internal defects.

[0006]

That is, the invention according to claim 1 of the present application provides a polymerizable lactam solution obtained by adding at least an anionic polymerization catalyst and an anionic polymerization initiator to substantially anhydrous ω-lactam. In the method for producing a cast polyamide resin molded article by anionic polymerization after casting into the mold, the polymerizable lactam liquid is poured into the mold after 5 to 15 minutes have elapsed after casting the polymerizable lactam liquid into the mold. In order to reduce the volume inside the mold, the occurrence of cavity defects inside the molded body is prevented.

[0007] The invention according to claim 2 of the present application is a more specific example of the invention of claim 1, wherein the inner mold is installed in the outer mold in which the polymerizable lactam liquid is cast, and the polymerizable lactam liquid is poured. After 5 to 15 minutes have passed from the mold, one of the molds is moved by a predetermined amount so as to reduce the volume in the mold. A molded article can be obtained.

[0008] The invention according to claim 3 of the present application is that the polymerizable lactam liquid is poured into the mold, and after 5 to 15 minutes have passed, the upper mold is moved to the inside of the mold containing the polymerizable lactam liquid. The volume is reduced, and the upper mold is brought into contact with the molded body during polymerization, and the amount of movement of the upper mold is limited.The pressurization of the molded body during polymerization causes cavity defects inside the molded body. And a molded article having a more stable thickness can be obtained.

[0009]

FIG. 1 is a sectional view showing an initial step of a method for producing a cast polyamide resin molded article according to the present invention. FIG. 2 is a method for producing a cast polyamide resin molded article according to the present invention. 3 is a cross-sectional view of the mold when the volume in the mold is reduced, and FIG. 3 is a graph showing a model of a relationship between the polymerization time of the polymerizable lactam liquid and the volume shrinkage.

In general, the relationship between the polymerization time of the polymerizable lactam solution and the volume shrinkage is shown in FIG. It consists of stages. In the thermal expansion time, there is a time when the volume expands due to thermal expansion of the polymerizable lactam liquid,
Thereafter, there is a stage in which the viscosity increases due to the polymerization of the polymerizable lactam solution, and the volume shrinks sharply, and the shrinkage progresses slowly due to crystallization. The volume shrinkage curve at the time of polymerization shrinkage is a downward convex curve, while the volume shrinkage curve at the time of crystallization shrinkage is an upwardly convex curve, and the inflection point of these curves is a polymerizable lactam liquid. And between 5 and 15 minutes. It became clear that reducing the volume in the mold at this time would prevent the generation of the internal space that would occur during the subsequent crystallization shrinkage period.

In this embodiment, the ω-lactam is dehydrated in a dehydration tank under reduced pressure to make it substantially anhydrous, and then replaced with an inert gas such as nitrogen. The ω-lactam in the dewatering tank is weighed into two casting tanks. Thereafter, a predetermined amount of an anionic polymerization catalyst is charged into one casting tank containing ω-lactam, and a predetermined amount of anionic polymerization initiator is charged into the other casting tank containing ω-lactam. Then, an outer mold 1 and an inner mold 2 for forming a bucket having a relatively high thermal conductivity such as aluminum, iron or the like are prepared.

[0012] After the polymerizable lactam liquid discharged from each casting tank is mixed and stirred in the mixing section, it is cooled to 130 to 18
After casting into the outer mold 1 whose temperature has been adjusted to 0 ° C., the inner mold 2 smaller than the outer mold 1 is installed. At this time, the inner mold 2 is replaced with the outer mold 1
The cavity 4 is formed between the outer mold 1 and the inner mold 2 by being mounted on a plurality of protruding support portions 3 provided at the edge of the outer mold. The protrusion amount H of the support portion 3 can be freely adjusted by a motor or the like, and the protrusion amount H of each support portion 3 becomes constant.

When 5 to 15 minutes elapse after casting the polymerizable lactam liquid, the polymerizable lactam liquid crystallizes and largely shrinks in volume. By moving the inner mold 2 downward, the volume in the mold is reduced. At this time, the inner mold 2 is not in contact with the support portion 3, but is in contact with the molded body during polymerization.
As the polymerization proceeds, the volume of the molded body gradually shrinks, so that the inner mold 2 comes into contact with the support portion 3. Thereby, it is possible to finish a molded body having no cavity defect inside. The protrusion amount H ′ of the support portion 3 is basically set to the thickness of the final product. Since the inner mold 2 is in contact with the molded body during polymerization, it is pressurized, and it is possible to finish the molded body with no cavity defects inside. However, in the present invention,
Since the timing of reducing the volume in the mold is an important factor, the inner mold 2 may be brought into contact with the support portion 3 when the volume in the mold is reduced.

If the inner mold 2 is moved downward for less than 5 minutes outside the above-mentioned time range, the polymerizable lactam liquid flows because the crystallization is not crystallized, and the thickness of the molded article becomes insufficient.
If the time exceeds 5 minutes, the polymerizable lactam liquid crystallizes and largely shrinks in volume, so that the pressure is insufficient and not only a cavity defect is generated inside the molded body, but also a concave portion is easily generated in the appearance of the molded body. Become.

The ω-lactam is substantially anhydrous α-piperidone, ε-caprolactam, ω-laurolactam, or a mixture of two or more thereof. Industrially advantageous lactams are ε-caprolactam and ω-laurolactam. Lactam.

Further, the anionic polymerization catalyst used in the present invention includes sodium hydride, lithium hydride, sodium,
Known polymerization catalysts for ω-lactams such as potassium can be used, and the amount added is 0.1 to ω-lactam.
~ 2.0 mol%. And, as the initiator for anionic polymerization, for example, N-acetyl-ε-caprolactam,
Isocyanate, diisocyanate, urea derivative, urethane, isocyanurate derivative,
-A range of 0.05 to 1.0 mol% based on lactam is preferred.

In the above-mentioned production method, the anionic polymerization catalyst is ω
A method of adding and mixing an anionic polymerization initiator at or after casting after adding and dissolving to a lactam, or injecting an ω-lactam containing an anionic polymerization catalyst and an ω-lactam containing an anionic polymerization initiator. It is adjusted by a method of adding and mixing at the time of molding or after casting. Further, the polymerization temperature of ω-lactam can be carried out at a temperature of 100 to 210 ° C., preferably 130 to 180 ° C.

In carrying out the method of the present invention, other than the above components, lubricants such as oils, waxes, zinc stearate, calcium stearate and the like, which do not inhibit polymerization, and reinforcing materials such as carbon fiber and wollastonite may be added. It is possible.

[0019]

The present invention will be described in more detail with reference to the following examples. Examples 1-2 After dehydration, ε-caprolactam in the dehydration tank was weighed and put into two casting tanks, and 1,250 g was put into one casting tank and 1,250 g was put into the other casting tank. Then, 5 g of sodium hydride (6
(3% oil) was added and dissolved, and 7 g of trisphenyl isocyanurate was further added to the other casting tank.
During this time, the polymerizable lactam solution was mixed while the temperature was raised to 125 ° C. while flowing nitrogen in the casting tank under atmospheric pressure.

The above-mentioned mixed polymerizable lactam liquid is preheated to 140 ° C. in an aluminum outer mold (200 m long).
m, width 305mm, depth 160mm)
The inner mold was set on a plurality of protruding supports provided at the edge of the outer mold. The protruding height of the support was 8 mm. This is 17
The polymerization was carried out in a furnace adjusted to 5 ° C. After 4 minutes, 12 minutes, 15 minutes, or 25 minutes have elapsed after casting the polymerizable lactam liquid, the protrusion height of the support was adjusted to 6 mm to complete the polymerization, the inner mold was removed, and the thickness was 6 mm. Was taken out.

After the molded body was sufficiently cooled, the inside was inspected with the naked eye, and the results of observation of cavity defects are shown in Table 1.

[0022]

[Table 1]

As a result, the polymerizable lactam solution was cast to obtain 1
When the volume in the mold was reduced after 2 minutes and 15 minutes, no internal cavity defects were observed in the molded body, but after 4 minutes from the injection of the polymerizable lactam solution, Has not risen sufficiently, overflowing the polymerizable lactam liquid,
Insufficient thickness of the compact and internal cavity defects were observed. In addition, after 25 minutes from the casting of the polymerizable lactam liquid, crystallization shrinkage has started, and the pressurization of the molded article during polymerization becomes insufficient, so that void defects occur inside the molded article. Not only that, a recess was formed on the appearance of the molded product.

COMPARATIVE EXAMPLE 3 The same polymerizable lactam solution as in Example 1 was previously prepared at 140 ° C.
Aluminum outer mold (200mm in height, 305 in width)
mm and a depth of 160 mm), and the inner mold was placed on a plurality of protruding supports provided on the edge of the outer mold. The protruding height of the support was 8 mm. This was transferred into a furnace adjusted to 175 ° C., but polymerized without adjusting the protruding height of the support in the polymerization process. Observation of cavity defects of the obtained molded body revealed that void defects were present in the entire inside of the molded body, and a concave portion was also generated in the appearance of the molded body.

[0025]

As described above, in the invention according to claim 1 of the present application, a polymerizable lactam liquid obtained by adding at least an anionic polymerization catalyst and an anionic polymerization initiator to substantially anhydrous ω-lactam is poured into a mold. After molding, in a method of producing a cast polyamide resin molded article by anionic polymerization,
After 5 to 15 minutes have elapsed after casting the polymerizable lactam liquid in the mold, there is a method for producing a cast polyamide resin molded article in which the volume in the mold containing the polymerizable lactam liquid has been reduced. Since the volume in the mold is reduced in accordance with the volume shrinkage of the polymerizable lactam liquid which occurs when 5 to 15 minutes have elapsed after casting, there is an effect of preventing generation of cavity defects inside the molded body.

In the invention according to claim 2 of the present application, claim 1
After embodying the invention of 5 to 15 minutes after installing the inner mold in the outer mold in which the polymerizable lactam liquid was cast and casting the polymerizable lactam liquid, the volume in the mold was increased. One mold is moved by a predetermined amount so as to make it smaller,
This has the effect of preventing the occurrence of cavity defects inside the molded body and obtaining a molded body having a stable thickness.

In the invention according to claim 3 of the present application, the polymerizable lactam liquid is cast into the mold, and after 5 to 15 minutes have passed, the upper mold is moved to the inside of the mold containing the polymerizable lactam liquid. The volume is reduced, and the upper mold is brought into contact with the molded body during polymerization, and the amount of movement of the upper mold is limited.The pressurization of the molded body during polymerization causes cavity defects inside the molded body. Is prevented, and a molded article having a more stable thickness can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an initial step of a method for producing a cast polyamide resin molded article according to the present invention.

FIG. 2 is a cross-sectional view of a method for producing a cast polyamide resin molded article according to the present invention when the volume in the mold is reduced.

FIG. 3 is a graph showing a model of a relationship between polymerization time and volume shrinkage of a polymerizable lactam liquid.

[Explanation of symbols]

 Reference Signs List 1 outer die 2 inner die 3 support part 4 cavity

Claims (3)

[Claims] 1. A castable polyamide resin is formed by casting a polymerizable lactam solution obtained by adding at least an anionic polymerization catalyst and an anionic polymerization initiator to a substantially anhydrous ω-lactam, followed by anionic polymerization. A method for producing a body, comprising: casting a polymerizable lactam solution into a mold, and after 5 to 15 minutes have elapsed, reducing the volume in the mold containing the polymerizable lactam solution. A method for manufacturing a resin molded body. 2. An inner mold is placed in an outer mold in which the polymerizable lactam liquid is cast, and after 5 to 15 minutes have passed since the polymerizable lactam liquid was cast, one of the molds is reduced so as to reduce the volume in the mold. The method for producing a cast polyamide resin molded article according to claim 1, wherein the mold is moved by a predetermined amount. 3. A polymerizable lactam liquid is poured into a mold to form a liquid.
After 15 minutes have passed, the upper mold was moved to reduce the volume in the mold containing the polymerizable lactam liquid, and the upper mold was brought into contact with the molded article being polymerized, and the amount of movement of the upper mold was limited. Item 3. A method for producing a cast polyamide resin molded article according to Item 2.