JP2008030411A - Manufacturing method for polyamide resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a polyamide resin molding, which can eliminate an internal defect such as the formation of a vacuum void and an air bubble, because an amount reduced by shrinkage can be compensated for by supplying a polymerizable lactam fluid, even if a decompressed state is caused by the occurrence of the shrinkage during the progress of polymerization. <P>SOLUTION: A polymerization process is divided into two stages. In the first stage, a polymerization-suppressed state is caused by keeping the polymerizable lactam fluid 14 in the upper portion of a cavity 13 at a low temperature; and after that, the polymerization is progressed in a first molding portion except the upper portion of the cavity 13. Subsequently, in the second stage, the polymerization is performed by heating the polymerizable lactam fluid 14 in a second molding portion of the upper portion of the cavity 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a polyamide resin molded article by casting, and more specifically, a polyamide resin molded article that prevents generation of voids and sink marks on the bottom of the mold when molding rod-shaped and plate-shaped molded articles. Involved in the manufacturing method of the body.

  As a mold for producing a plate-shaped molded body with a polyamide resin, a cavity is formed between a pair of side plates made of aluminum, iron, or the like as shown in FIG. The mold is heated with a hot air oven or a heating plate using oil as a heating medium until the temperature reaches 180 to 190 ° C., a polymerizable lactam solution is poured into the mold at a predetermined temperature, and the mold is heated again. And polymerized.

JP 9-201832 A

  When a polymerizable lactam solution is cast and the polymerization starts to progress, the viscosity increases and shrinkage occurs due to polymerization and crystallization. There is no problem at the top of the mold because the amount of shrinkage caused by the drop of the polymerizable lactam solution is compensated for, but there is no problem at the bottom of the mold, and there is a reduced pressure at the bottom of the mold. In addition, sink marks (insufficient thickness) occur on the surface of the plate. When such voids, bubbles, and sink marks are generated, a product of a predetermined size cannot be obtained and becomes defective.

  Accordingly, the present invention provides a method and apparatus for producing a polyamide resin molded article that can solve such problems and prevent the occurrence of defects such as vacuum voids, bubbles, and surface sinks at the bottom of the mold. Objective.

  In order to achieve the above object, in claim 1 of the present invention, a lactam is polymerized by casting and heating a polymerizable lactam, an anionic polymerization catalyst and an anionic polymerization initiator in a cavity of a mold. In the method for producing a molded body comprising the polyamide resin, the polymerization is suppressed in the first step by maintaining the polymerizable lactam at the upper part of the cavity at a low temperature, and then polymerization in the first molded part other than the upper part of the cavity is performed. Then, as a second step, polymerization is performed by heating the polymerizable lactam in the second molding part at the upper part of the cavity.

  In Claim 2, As a manufacturing method of the polyamide resin molding of Claim 1 which suppresses superposition | polymerization by keeping the temperature of the polymerizable lactam in the 2nd shaping | molding part of a cavity upper part in the range of 70-130 degreeC in a 1st step. Yes.

  In Claim 3, the temperature is controlled by disposing a cooling tool on the cavity in the first stage to suppress the polymerization of the second molding part, and then the cooling is removed by removing the cooling tool in the second stage. It is set as the manufacturing method of the polyamide resin molding of Claims 1-2.

  In Claim 4, the range of the 2nd shaping | molding part which suppresses superposition | polymerization of a cavity upper part in a 1st step is a range of 10-50% of length from the top among the total height of a molded object. This is a method for producing a polyamide resin molded body.

  In claim 1, since the polymerization of the other first molding part in which the polymerization of the second molding part at the upper part of the cavity is suppressed, the lactam of the second molding part remains in a liquid state, and the first molding part Even when the polymerization of the central part and the lower part progresses and solidifies and shrinks, the amount of shrinkage is compensated by the lactam liquid remaining in the second molding part, so that the problem that voids or the like enter without being in a reduced pressure state is solved. be able to.

  In Claim 2, the temperature range at the time of suppressing superposition | polymerization in the cavity upper part in a 1st step is limited, By controlling to such a temperature range, superposition | polymerization can be suppressed reliably, As a result It is possible to prevent defects such as voids in the molded body.

  According to the third aspect, since the cooling tool is arranged to control the temperature of the upper part of the cavity, it is possible to easily control the partial temperature range of only the second molding part in the entire cavity.

  The height of the second molded part that suppresses polymerization during molding is specified in claim 4, and the polymerization of other first molded parts is controlled by controlling the lactam temperature within this range to suppress polymerization. Volume reduction due to shrinkage can be sufficiently compensated, and generation of voids in the second molded part can be reduced.

  1 is a perspective view of a mold 1 for molding a polyamide resin molded body according to the present invention, FIG. 2 is a partially cutaway front view of a side plate 2 used in the mold 1 shown in FIG. 1, and FIG. It is.

  The method for producing a polyamide molded body of the present invention is performed by using a mold 1 having a cavity 4 having an open upper part formed by a side plate 2 and a spacer 3, and from the opened upper part in the mold 1 into the cavity 4. A polymerizable lactam solution is poured into The polymerizable lactam solution in the cavity 4 is polymerized by heating for about 20 to 100 minutes. Although not shown, the heating is performed by passing the heat transfer oil through the side plate 2 or the spacer 3 using a heat transfer oil circulating device or the like.

  In the present invention, the polymerization is divided into a first stage and a second stage. In the first stage, when the polymerization is performed by heating the mold, the polymerization lactam solution located above the cavity 4 is kept at a low temperature so that the polymerization is suppressed, and the other portions are heated to advance the polymerization. As the polymerization proceeds, shrinkage associated with crystallization occurs. Due to the shrinkage, internal defects such as voids, sink marks, and nests are generated inside the molded product, but as described above, unpolymerized lactam liquid remains in the portion where the polymerization is suppressed at the upper portion of the cavity 4, and the shrinkage portion Inflow. By doing so, the site polymerized in the first stage can be formed into a molded product having no internal defects.

The side plate 2 is a hollow body formed of a metal plate such as aluminum or iron as shown in FIG. 2, and a crosspiece 2a extending in the width direction is provided in the sealed interior at regular intervals. An oil passage 2b that communicates the oil is provided.

  The spacer 3 is a U-shaped frame with one side open as shown in FIG. 3, and there is an oil passage (not shown) through which the heat transfer oil passes inside the frame, and the heat transfer oil is on the lower side. The spacer 3 is heated by passing through the oil passage from the provided oil outlet and exiting the oil outlet provided at the upper part of the side. A cavity is formed by sandwiching the spacer 3 with the side plate 2. In order to enhance the sealing effect between the spacer 3 and the side plate 2, a packing 5 made of a rubber elastic body such as polytetrafluoroethylene or silicon rubber is attached to the spacer 3. It can also be attached to both sides of the frame.

  The temperature of the side plates 2 and 2 and the spacer 3 can be adjusted by the heat medium oil circulation device. Further, at least one or more middle plates (not shown) capable of adjusting the temperature are arranged between the pair of side plates 2 and 2 that can adjust the temperature, and the spacer 3 is interposed between the pair of side plates 2. The plurality of cavities 4 may be formed by moving one side plate 2 to the other side plate 2 and sandwiching and fixing each panel and the spacer 3 integrally. Furthermore, the side plates 2 and 3 themselves may be provided with a heat medium passage so that they can be heated.

  In the present invention, as described above, the polymerization is divided into the first stage and the second stage. In the first stage, polymerization is suppressed by keeping the upper part of the cavity 4 at a low temperature, but the temperature is preferably kept in the range of 70 to 130 ° C. If the temperature is lower than 70 ° C., the melting point is not reached, so that the liquid state cannot be maintained, and the contracted portion cannot be replenished with the lactam solution. If the temperature exceeds 130 ° C., the polymerization of the lactam proceeds and cures. Moreover, the following methods can be mentioned as a means for keeping at low temperature. As shown in FIG. 4, after casting the polymerizable lactam solution in the cavity 4, the cooling unit 6 a that reaches the depth of 10 to 50% from the top of the entire height of the cavity 4 along the mold wall surface and the polymerizable property A cap-like lid body 6 having a blocking portion 6b that blocks the surface of the lactam liquid from air is attached. By attaching the lid 6, the liquid level of the polymerizable lactam solution can be shielded from air. Further, the cooling part has a passage inside, and the temperature of the polymerizable lactam liquid can be kept low in the upper part of the cavity 7 where the cooling part 6a is located by passing cooling water through the passage.

  When the polymerization of the lower part of the cavity 4 to be polymerized in the first stage is completed, the cooling unit 6a is then removed and the process proceeds to the second stage. In the second stage, the polymerization proceeds by contact of the unpolymerized lactam solution, whose progress has been suppressed by the cooling unit 6a, with the heated mold. The upper part in the cavity 4 which has not been polymerized is polymerized to complete the entire polymerization.

  After the polymerization is completed, the molded body is cooled, and demolding is performed when the temperature drops to near room temperature. Then, if necessary, the final target product can be obtained by performing annealing by putting it in an oven or performing a finishing process such as cutting or polishing.

  By performing the polymerization process in the first stage and the second stage as described above, even if shrinkage occurs during the polymerization of the lactam liquid in the first stage of the polymerization, it remains unpolymerized in the upper part of the cavity 4. Since the lactam solution flowing into the contracted portion does not generate a reduced pressure state due to the contraction, it is possible to prevent internal defects such as generation of voids and nests in the finished molded body.

  The part polymerized in the first stage becomes a molded body having no internal defects, and then the remaining part is polymerized in the second stage. However, the lactam solution is not replenished with respect to the shrinkage during the polymerization, and the lactam. For example, sinking may occur on the upper surface of the molded body by lowering the upper surface of the molding. However, when comparing the lower part of the cavity 4 polymerized in the first stage and the upper part of the polymerized part in the second stage, the lower part of the cavity 4 is the back side of the cavity sealed by the mold, and the polymerization proceeds to some extent and the resin hardens. When the pressure is reduced due to polymerization shrinkage, the lactam liquid is not supplied smoothly and internal defects are likely to occur. However, this is prevented by the present invention, and the molded body is surely free of defects at the bottom. In consideration of the fact that the defect portion collected at the upper portion can be easily removed by means such as polishing by collecting the defects at the upper portion, the occurrence of sink marks above the molded body is not a big problem.

Although the example which manufactures a round bar was given and demonstrated above, it is not restricted to a round bar, In addition, it can apply also in the case of manufacture of a flat plate etc. In the case of manufacturing a round bar, a polymerizable lactam solution 14 is poured into a cavity 13 of a mold composed of a cylindrical side mold 11 and a lower mold 12 as shown in FIG. The first-stage polymerization is performed in a state where the lid 15 having the cooling unit 15a and the blocking unit 15b that blocks the lactam solution 14 from the air is disposed. Polymerization is suppressed in the cooled portion, and an unpolymerized lactam solution is supplied along with the shrinkage generated during the polymerization of the uncooled portion, so that a molded body without internal defects is obtained. Then, the cooling unit 15a is removed, and the remaining unpolymerized lactam solution is heated, whereby the second-stage polymerization is performed, and the entire polymerization is completed. A molded body is obtained by removing the mold after cooling.

  The polymerizable lactam solution used in the present invention is obtained by adding an anionic polymerization catalyst and an anionic polymerization initiator to ω-lactam, and the ω-lactam is substantially anhydrous α-piperidone, ε-caprolactam, ω -Laurolactam, or a mixture of two or more of these, industrially preferred lactams are ε-caprolactam and ω-laurolactam.

  As the anionic polymerization catalyst, a known ω-lactam polymerization catalyst such as sodium hydride, lithium hydride, sodium, potassium and the like can be used, and the addition amount thereof is 0.1 to 2.0 with respect to ω-lactam. Mol%. Examples of the initiator for anionic polymerization include N-acetyl-ε-caprolactam, isocyanate, diisocyanate, urea derivative, urethane, isocyanurate derivative, and the addition amount thereof is 0.05 to 1. A range of 0 mol% is preferred.

  Also, a method in which an anionic polymerization catalyst is added to ω-lactam and dissolved, and then an anionic polymerization initiator is added and mixed at the time of casting, or ω-lactam containing an anionic polymerization catalyst and an anionic polymerization initiator Are adjusted by a method of adding and mixing at the time of casting.

  In carrying out the method of the present invention, it is also possible to add lubricants such as oils, waxes, zinc stearate, calcium stearate, etc. that do not inhibit polymerization, and reinforcing materials such as carbon fibers and glass fibers, in addition to the above components. is there.

  Next, the state of the internal defect of the molded body was compared between an example in which a cylindrical polyamide resin molded body was manufactured using the manufacturing apparatus according to the present invention and a comparative example that was not the present invention.

(Example)
In the examples, a polymerizable lactam solution was cast to a height of about 1,100 mm in a cylindrical mold having an inner diameter of 150 mm and a height of 1,200 mm adjusted to 150 ° C. Next, a ring-shaped lid having an outer diameter of 148 mm, an inner diameter of 118 mm, and a height of 200 mm, having a cavity inside and filled with water, was set on the upper part of the mold cavity. The lid body has a blocking portion at the top so that the liquid surface of the polymerizable lactam solution does not come into direct contact with air.

  In this state, the first stage polymerization was allowed to stand for 15 minutes, the lid was removed, and the polymerization was advanced by heating so that the upper lactam solution was in direct contact with the hot mold. After 1.5 hours from casting, the polymerized and solidified polyamide resin molded body (round bar) was released from the mold and cooled. Although the obtained round bar had slight sink marks on the upper surface, it was satisfactory in that no internal defects were found as a result of ultrasonic flaw detection.

(Comparative example)
Using the same mold as in the example, a polymerizable lactam solution was similarly cast and polymerized by heating to obtain a polyamide resin molded body. However, polymerization was carried out using a lid comprising only a blocking portion for preventing the liquid surface from being exposed to air, without using the lid having a cooling portion used in the examples.

  As a result of ultrasonic flaw detection on the obtained round bar, five internal defects having a size of 1 mm or less were found near the center.

  The present invention relates to a method for producing a polyamide resin molded body. Specifically, it can be used as a polyamide resin molded body in which voids generated at the bottom of the mold during molding and the occurrence of sink marks on the surface are prevented.

It is a perspective view of the mold used with the manufacturing method of this invention. It is a partially notched front view of the side plate used for the manufacturing apparatus shown in FIG. It is a front view of a spacer. It is sectional drawing of the place which has arrange | positioned the cover body to the mold. It is sectional drawing of the place which has arrange | positioned the cover body with the mold which shape | molds a round bar.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 2 Side plate 3 Spacer 4 Cavity 5 Packing 6 Lid 6a Cooling part 6b Shut off part

Claims (4)

  In the method for producing a molded body comprising a polyamide resin obtained by polymerizing lactam by pouring a polymerizable lactam, an anionic polymerization catalyst, and an anionic polymerization initiator into a cavity of a mold and heating, as a first step, Polymerization in the first molding part other than the upper part of the cavity is allowed to proceed after keeping the polymerization lactam on the upper part at a low temperature, and then polymerization in the second molding part on the upper part of the cavity is performed as the second stage. A method for producing a polyamide resin molded body, wherein the polymerization is performed by heating a functional lactam.   The manufacturing method of the polyamide resin molding of Claim 1 which suppresses superposition | polymerization by keeping the temperature of the polymerizable lactam in the 2nd shaping | molding part of the cavity upper part in the range of 70-130 degreeC at a 1st step.   The temperature is controlled by disposing a cooling tool at the upper part of the cavity in the first stage to suppress the polymerization of the second molding part, and then the polymerization is canceled by removing the cooling tool in the second stage. 2. A method for producing a polyamide resin molded article according to 2. 4. The polyamide resin molded body according to claim 1, wherein the range of the second molded portion that suppresses the polymerization at the upper part of the cavity in the first stage is in the range of 10 to 50% of the total height of the molded body. Manufacturing method.

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