JPH1177707A - Method for producing bucket-shaped cast polyamide resin molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a box-shaped cast polyamide resin molding which is easy of the temperature control of a mold, relatively thin, free from internal defects, like a bucket. SOLUTION: In a method for producing a bucket-shaped cast polyamide resin molding by a method in which after a polymerizable lactam liquid in which at least an anionic polymerization catalyst and an anionic polymerization initiator being added to a substantially anhydrous ω-lactam being cast into a mold, anionic polymerization is done, a lower mold 15 and an upper mold 1 which are heated by a circulating heating medium are prepared. The temperature of the upper mold 1 is controlled to be higher than that of the lower mold 15 by up to 7 deg.C, after the lactam liquid being cast into the lower mold, when the surface temperature of the lower mold 15 reached 163-165 deg.C by the polymerization heat of the lactam liquid, the polymerization of the lactam liquid is made to progress further while the upper mold 1 being allowed to fall by its own weight to finish the polymerization. After the upper mold 1 being separated from the lower mold 15, a molding is taken out.

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-shaped bucket-shaped polyamide resin molded article, and more particularly to a box-shaped cast polyamide resin molded article having a relatively small thickness without internal defects. And a method for producing the same.

[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 furnace, the mold is taken out of the furnace, and a polymerizable lactam liquid is poured into the mold. The mold is placed in a hot blast stove again for polymerization. But,
According to this method, the molded article has a disadvantage that air bubbles tend to be contained therein during the polymerization process. Usually, when an anionic polymerization of a polymerizable lactam is performed, a volume shrinkage of about 15% occurs. This volume shrinkage has been one of the causes of generating cavity defects inside the compact. In a conventional method for producing a cast polyamide molded article, it has been a technically important task to reduce the occurrence of the above-described internal defects.

[0003] In order to prevent the occurrence of such internal defects in a molded article, a method of polymerizing a polymerizable lactam solution under pressure has been conventionally known. For example, Japanese Patent Publication No. 40-1615
As disclosed in Japanese Unexamined Patent Publication No. 3, there is a method in which the polymerizable lactam liquid is subjected to pressure molding when the viscosity of the system is increased to a maximum by polymerization.

Further, Japanese Patent Publication No. 39-25202 discloses that a mold maintained at a temperature at which polymerization proceeds and an auxiliary container maintained at a temperature at which polymerization does not proceed is insulated.
A method is disclosed in which a polymerizable lactam liquid is sealed in the auxiliary container and is pressurized with an inert gas so that the polymerizable lactam liquid is constantly fed into a mold to press-mold a polyamide molded article.

[0005]

However, in a method of manufacturing a molded article such as a bucket having a relatively small thickness,
Therefore, if the polymerizable lactam liquid cast between the outer mold and the inner mold is constantly pressurized during polymerization, the height of the liquid will fluctuate due to the movement of the inner mold during the initial stage of the polymerization. Was substantially difficult to produce.

In the case of polymerization in an oven, it is difficult to control the temperature in the mold and the oven because the mold is taken in and out of the oven at the time of casting. Temperature control of the mold was very difficult with the method.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is intended to provide a box-shaped cast polyamide resin molded article such as a bucket having a relatively small thickness which is easy to control the temperature of the mold and has no internal defects. It is to provide a manufacturing method.

[0008]

That is, the invention according to claim 1 of the present application is a method for forming a polymerizable lactam liquid obtained by adding at least an anionic polymerization catalyst and an anionic polymerization initiator to substantially anhydrous ω-lactam. In the method of producing a bucket-shaped cast polyamide resin molded article by anionic polymerization after casting into a lower mold and an upper mold heated by a circulating heat medium, the temperature of the upper mold is lower than that of the lower mold. Up to 7 ° from temperature
C, the temperature was adjusted so as to increase to C, and after the polymerizable lactam liquid was cast into the lower mold, when the surface temperature of the lower mold reached 163 to 165 ° C. due to the polymerization heat of the polymerizable lactam liquid,
The polymerization of the polymerizable lactam liquid is further advanced while the upper mold is dropped by its own weight, and after the polymerization is completed, the upper mold and the lower mold are separated and the molded body is taken out to produce a bucket-shaped cast polyamide resin molded body. In the method, there is a difference between the upper and lower mold temperature,
Furthermore, when the surface temperature of the lower mold reaches a predetermined temperature due to the polymerization heat of the polymerizable lactam liquid, the polymerization is further advanced while the upper mold is dropped by its own weight, and a relatively thin bucket without internal defects is provided. Such a box-shaped cast polyamide resin molded article can be formed.

According to the invention of claim 2 of the present application, the upper mold temperature is 143 before the polymerizable lactam liquid is poured into the mold.
This is a method for producing a bucket-shaped cast polyamide resin molded product having a lower mold temperature of 150 to 170 ° C. at a temperature of 150 to 170 ° C.

According to a third aspect of the present invention, at least one partition plate for forming a flow path of a heat medium is provided in the heat medium chambers provided in the upper mold and the lower mold. By preventing the stagnation, the temperature of the upper mold and the lower mold can be further adjusted.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view of an upper die used in a method for producing a bucket-shaped cast polyamide resin molded article of the present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. FIG. 4 is a plan view of a lower mold used in the method for producing a bucket-shaped cast polyamide resin molded product of FIG.

The upper mold 1 has a main body 2 made of aluminum, iron or the like having a relatively high thermal conductivity, and a molded portion 3 projecting outward from the main body 2.
A closed heat medium chamber 5 in which a heat medium such as oil flows by fixing the upper plate 4 to the main body 2 with screws or the like is provided inside the molded portion 3. The heat medium chamber 5 is provided with a partition plate 6 therein to improve the flow of the heat medium. In the embodiment, the heat medium chamber 5 is divided into four chambers 7 by a cross plate 6 provided in a cross shape, and is discharged from the inlet 8. The heat medium is circulated to the outlet 9 by a pump (not shown) to accurately control the temperature.

When measuring the temperature of the upper mold 1, the upper mold 1
Is measured by contacting the surface thermometer with the surface of the upper mold 1 before fitting the lower mold 15 into the lower mold 15.

The lower mold 15 has a recessed accommodation portion 17 into which the protruding molded portion 3 of the upper mold 1 is fitted, and a closed heat medium chamber 18 through which a heat medium flows is formed by an outer wall 19 outside. . A heat insulating material (not shown) is attached to the outer wall 19. A partition plate 20 is also provided in the heat medium chamber 18, and the heat medium flowing from the inlet 21 flows smoothly without stagnation, flows out of the outlet 22, and circulates again to flow to the inlet 21. It has become. As shown in FIG. 4, a temperature sensor 24 is attached to the outer wall of the housing 17 in order to accurately control the temperature of the lower mold 15. The temperature sensor 24 is housed in a shielding room 25 so as not to directly touch the heat medium. The temperature sensor 24 is not limited to one location, and may be provided at two or more locations.

FIG. 5 shows a state in which the upper mold 1 and the lower mold 15 are respectively set in a molding machine 40. In this molding machine 40, four guide rods 42 are fixed on a base 51 in an upright state, and a support table 41 on which the lower mold 15 is installed and fixed is inserted into the four guide rods 42. It is moved up and down by a lifting device 43 installed at the center of the lower surface of the. The lifting device 43 rotates the ball screw 46 supported by the support member 45 by driving the motor 44 to reciprocate the lower die 15 in the vertical direction. The upper limit can be stopped by a limit switch. The polymerizable lactam liquid is introduced at the lowest position of the lower mold 15.

On the other hand, the upper die 1 is provided with the four guide rods 42 described above.
An air cylinder 49 is installed at the center of a support 48 fixed to the movable plate 51, and is stably hung on a movable plate 51 fixed to a rod 50 of the air cylinder 49 via four connecting rods 52. Accordingly, the position of the piston in the air cylinder 49 can be held by the compressed air to fix the upper mold 1, or the compressed air in the cylinder can be released to drop the upper mold 1 downward by its own weight.

FIG. 6 shows a state in which the lower mold 15 is raised along the guide rod 42 by operating the elevating device 44 and fitted to the upper mold 1 to polymerize the charged polymerizable lactam liquid.
FIG. 7 shows a state in which the lower mold 15 is lowered and the superimposed bucket-shaped molded body 30 is removed from the upper mold 1.

Thus, 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 dehydration tank is weighed into two casting tanks, and then a predetermined amount of an anion polymerization catalyst is added to the ω-lactam.
One casting tank containing lactam and a predetermined amount of an anionic polymerization initiator are charged into the other casting tank containing ω-lactam. And the upper mold 1 for forming the bucket
And the lower mold 15 are prepared, and the upper mold 1 and the lower mold 15 are respectively set at predetermined positions of the molding machine 40 as described above.

After the polymerizable lactam liquid discharged from each casting tank is mixed and stirred in the mixing section, the polymerizable lactam liquid is cast into a lower mold 15 whose temperature has been adjusted to 150 to 170 ° C. as shown in FIG. After that, the lower mold 15 is raised by the operation of the motor 44 and is fitted to the upper mold 1 whose temperature is adjusted to 143 to 163 ° C., so that the cavity 32 is formed between the lower mold 15 and the upper mold 1. This state is shown in FIG.
A gap 33 of about 2 to 5 mm is provided between the lower mold 15 and the upper mold 1. This gap 33 can be freely adjusted by a motor 44.

At this time, the temperature of the upper mold 1 and the lower mold 15 is
The temperature of the upper mold 1 is lower than the temperature of the lower mold 15, up to 7 ° C.
Preferably, a difference of about 3 to 6 ° C. needs to be provided. If the temperature of the lower mold 15 is increased, it is considered that the reaction from the lower side is promoted to make it difficult for bubbles to be generated inside. The molded article 3 having no internal defects is further reduced by dropping the upper mold by its own weight.
0 can be obtained. If the temperature difference between the upper mold 1 and the lower mold 15 exceeds a maximum of 7 ° C., the polymerization balance will be lost, and the surface of the molded body in contact with the upper mold surface will have irregularities, resulting in poor appearance. Conversely, when the temperature of the upper mold 1 is increased, the reaction proceeds from the upper side, making it difficult for air to escape during casting and leaving air bubbles inside the product.

The lower mold 15 in which the temperature of the polymerizable lactam solution is controlled.
When the casting is performed, the surface temperature of the lower mold is increased to 163 to 165 ° C. due to an increase in the temperature of the system due to polymerization heat of the polymerizable lactam liquid.
When the air cylinder 49 is activated, the upper die 1
Is released and dropped by its own weight to give a weight to the polymerizable lactam liquid. At this time, the molded body 30 is in a state of being pressed by the upper mold 1, and when crystallization proceeds further, the molded body 30 is pressed.
Since the volume of the material gradually shrinks, it is possible to finish the molded body 30 having a uniform thickness without any void defect inside.

The temperature of the lower mold 15 is 163 to 165 ° C.
When the upper mold 1 is dropped downward by its own weight before reaching, the polymerizable lactam liquid flows because the viscosity has not sufficiently increased at the initial stage of polymerization, and the thickness of the molded article becomes insufficient, or the crystallization is accompanied by crystallization. When the lower mold 15 and the upper mold 1 were brought into close contact with each other after the temperature of the system after the heat generation began to decrease, the crystallization of the polymerizable lactam liquid had already proceeded, and the pressure was insufficient during volume shrinkage. 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. In the present invention, the temperature of the upper mold 1 is lower than the temperature of the lower mold 15, and the difference is set to a maximum of 7 ° C., and at the same time, the temperature of the lower mold 15 is 163〜.
Due to two factors that cause the upper mold 1 to fall downward by its own weight before the temperature reaches 165 ° C., a box-shaped cast polyamide resin molded article such as a relatively thin bucket having no internal defects can be formed. .

In general, the relationship between the polymerization time of the polymerizable lactam liquid and the temperature of the system consists of two stages, namely, the first stage of exothermic polymerization and the second stage of exothermic crystallization. First, the temperature of the system rises due to the heat generated by polymerization of the polymerizable lactam liquid, and after a certain period of time, the temperature rise of the system reaches almost equilibrium. After that, the exothermic curve falls, but instead rises again due to the appearance of the exotherm accompanying the crystallization of the polymerizable lactam liquid, and then starts to fall smoothly. From the time when the temperature rise of the system reaches equilibrium to the time when the temperature of the system after heat generation accompanying crystallization starts to decrease, it is possible to reduce the volume in the mold in the subsequent crystallization shrinkage period. It became clear that the generation of the internal space that would occur would be prevented.

The ω-lactam used in the present invention is substantially anhydrous α-piperidone, ε-caprolactam, ω-lactam.
Laurolactam, ω-enament lactam, ω-caprylactam, ω-laurolactam, ω-decanolactam, ω-undecanolactam, etc. or a mixture of two or more thereof, and an industrially advantageous lactam is ε- Caprolactam and ω-laurolactam.

The anionic polymerization catalyst used in the present invention may be 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 production method, the anion polymerization catalyst
A method of adding and mixing an anionic polymerization initiator at or after casting after adding and dissolving to a lactam, or injecting ω-lactam containing an anionic polymerization catalyst and 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, oils, waxes, lubricants such as zinc stearate, calcium stearate and the like, and reinforcing materials such as carbon fiber and wollastonite may be added in addition to the above components. It is possible.

[0028]

The present invention will be described in more detail with reference to the following examples. Examples 1-2, Comparative Examples 1-4 After dehydration, ε-caprolactam in the dehydration tank was weighed and put into two casting tanks, 1,250 g into one casting tank and the other casting tank. After adding 1,250 g to the casting tank, 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.

An upper mold and a lower mold made of aluminum (length 200 mm, width 305 mm, depth 160 mm) were set in a molding machine and heated to a predetermined temperature with oil. The temperature of the upper mold was measured with a surface thermometer, and the temperature of the lower mold was measured with a temperature sensor attached to the outer wall. Then, after pouring the mixed polymerizable lactam liquid into the lower mold, the lower mold is raised and fitted to the upper mold heated to a predetermined temperature with oil, and about 8 mm between the upper mold and the lower mold. Was polymerized in a state where a gap was provided. Then, after the polymerizable lactam liquid was cast and the temperature sensors provided on the lower mold each reached a predetermined temperature, the position of the upper mold was released to give the polymerizable lactam liquid its own weight. When the polymerization was completed, the lower mold was lowered, and a 6 mm-thick bucket molded body was taken out.

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

[0031]

[Table 1]

As a result, a temperature difference between the upper mold and the lower mold is provided, and the surface temperature of the lower mold is adjusted to 163 by pouring a polymerizable lactam liquid.
When the temperature reaches １６165 ° C., the polymerization is further advanced while dropping the upper mold under its own weight so as to reduce the volume of the upper mold and the lower mold in which the polymerizable lactam liquid is contained, thereby reducing internal defects. A relatively thin bucket was obtained.

[0033]

As described above, according to the first and second aspects of the present invention, a lower mold and an upper mold heated by a circulating heat medium are prepared, and the temperature of the upper mold is at most 7 degrees lower than the temperature of the lower mold. ° C
After the polymerizable lactam liquid was cast into the lower mold, the upper mold was self-weighted when the surface temperature of the lower mold reached 163 to 165 ° C due to the polymerization heat of the polymerizable lactam liquid. After the polymerization of the polymerizable lactam liquid is further advanced while being dropped by the above, the polymerization is terminated, and then the upper mold and the lower mold are separated to take out the molded body. When the surface temperature of the lower mold reaches a predetermined temperature due to the heat generated by polymerization of the polymerizable lactam liquid, a difference is made in the mold temperature, and the polymerization is further advanced while dropping the upper mold by its own weight. In addition, a box-shaped cast polyamide resin molded article such as a bucket having a relatively small thickness without internal defects can be formed.

According to the invention of claim 3 of the present application, the heat medium chambers provided in the upper mold and the lower mold are provided with at least one partition plate for forming a flow path of the heat medium. By preventing the stagnation, the temperature of the upper mold and the lower mold can be further adjusted.

[Brief description of the drawings]

FIG. 1 is a plan view of an upper mold used in a method for producing a bucket-shaped cast polyamide resin molded article of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a plan view of a lower mold used in the method for producing a bucket-shaped cast polyamide resin molded article of the present invention.

FIG. 4 is a sectional view taken along line BB of FIG. 3;

FIG. 5 is a front view of a state where an upper mold and a lower mold are respectively installed in a molding machine.

FIG. 6 is a side view of FIG. 5 showing a state where the lower mold is raised and fitted to the upper mold.

FIG. 7 is a side view of FIG. 5 showing a state in which a lower die is lowered to take out a molded body.

FIG. 8 is a cross-sectional view showing a state where the lower mold and the upper mold are fitted to each other with a gap provided between them.

FIG. 9 is a cross-sectional view showing a state where polymerization is further advanced while the upper mold is dropped by its own weight.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper die 2 Main body 3 Molding part 4 Upper plate 5 Heat medium chamber 6 Partition plate 8 Inlet 9 Outlet 15 Lower die 17 Housing part 18 Heat medium chamber 19 Outer wall 20 Partition plate 21 Injection 22 Outlet 30 Molded body 40 Molding Machine 41 support base 42 guide rod 43 elevating device 44 motor 49 air cylinder 52 connecting rod

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B29L 22:00

Claims (3)

[Claims] 1. A bucket-shaped cast polyamide obtained by casting a polymerizable lactam liquid obtained by adding at least an anionic polymerization catalyst and an anionic polymerization initiator to substantially anhydrous ω-lactam, and then performing anionic polymerization. In the method for producing a resin molded body, a lower mold and an upper mold heated by a circulating heat medium are prepared, and the temperature of the upper mold is adjusted so that the temperature of the upper mold becomes a maximum of 7 ° C. higher than the temperature of the lower mold. After the castable lactam liquid is cast into the lower mold, the surface temperature of the lower mold is 163 to 165 ° due to the polymerization heat of the polymerizable lactam liquid.
C, when the upper mold is dropped by its own weight, the polymerization of the polymerizable lactam liquid is further promoted, and after the polymerization is completed, the upper mold and the lower mold are separated to take out the molded body. For producing a bucket-shaped cast polyamide resin molded article. 2. The bucket-like casting according to claim 1, wherein the upper mold temperature is 143 to 163 ° C. and the lower mold temperature is 150 to 170 ° C. before casting the polymerizable lactam liquid into the mold. A method for producing a polyamide resin molded article. 3. The bucket-shaped cast polyamide resin molded article according to claim 1, wherein at least one partition plate forming a flow path of the heat medium is provided in the heat medium chambers provided in the upper mold and the lower mold. Manufacturing method.