JP5220460B2 - Method for producing cast polyamide resin molded body - Google Patents

Description

  The present invention relates to a method for producing a cast polyamide resin molded body, and more particularly to a method for producing a cast polyamide having no upper layer having a polymerization defect or void defects such as bubbles.

  The method for producing a molded body made of cast polyamide resin is to heat a cylindrical mold until it reaches a predetermined temperature in a hot air oven or heat transfer oil, steam, etc., and then put a polymerizable lactam solution in the mold. The lactam was injected and polymerized.

  The cast polyamide resin moldings obtained are the most representative engineering plastics, and have excellent mechanical strength, impact resistance, heat resistance, chemical resistance, and good workability. It is used as many machine parts such as plates.

  However, according to this method, since the polymerizable lactam solution injected into the mold is in contact with the atmosphere, the difference in polymerization shrinkage due to the temperature difference between the inner layer and the upper layer, polymerization failure due to moisture in the atmosphere, or polymerization Oxidative degradation of the lactam solution causes cavities, deep depressions, and flow patterns to occur frequently at the upper part of the molded body, and the upper part of the molded body is inevitably cut to a predetermined length and shipped as a product.

  For this reason, conventionally, a method has been employed in which the atmospheric layer in contact with the polymerizable lactam solution injected into the mold is replaced with heated nitrogen.

  Furthermore, in Patent Document 1, liquid paraffin is poured into the surface of a polymerizable lactam solution cast into a mold to form a film, thereby blocking air and moisture in the atmosphere, and thereby forming a cavity or flow pattern above the molded body. A technique for preventing the occurrence of the above is disclosed.

  Further, Patent Document 2 discloses that a cavity is formed in the upper part of a molded body by allowing polymerization to proceed in a state where the polymerizable lactam liquid is blocked from the atmosphere by floating a float body on the surface of the polymerizable lactam liquid cast in the mold. Techniques for preventing the occurrence of defects and flow patterns are disclosed.

JP-A-10-67023 JP 2000-71261 A

  However, since the volume of the polymerizable lactam solution changes during the polymerization process, the lid of the mold cannot be sealed. Therefore, inflow of air cannot be avoided, and sufficient effect of nitrogen substitution cannot be obtained.

  In addition, a method has been proposed in which heated nitrogen is continuously fed into the mold during the polymerization process, but there is a problem in terms of economy because the equipment cost increases.

  The method of pouring liquid paraffin onto the surface of the polymerizable lactam solution has a problem that, if the liquid paraffin is not sufficiently heated and dried, internal defects are generated.

  Moreover, although the method of floating a float on the surface of a polymerizable lactam solution can be expected to have a certain effect on prevention of sink marks and flow patterns on the surface of the molded product, it is still insufficient and further improvement is required. .

  The present invention improves such problems, and by fully considering the characteristics of the polymerization process of the polymerizable lactam solution, there are no void defects such as bubbles, deep depressions and flow patterns in the upper layer. It is to provide a method for producing a cast polyamide.

In order to achieve the above object, in claim 1 of the present invention, a polymerizable lactam solution comprising at least an anionic polymerization catalyst and an anionic polymerization initiator is anionic polymerized in a mold in a substantially anhydrous ω-lactam. In the molding method of cast polyamide, the inner lid is floated on the surface of the polymerizable lactam liquid cast in the mold, and the polymerizable lactam is shielded from moisture in the atmosphere by pressurizing with an inert gas. When the polymerization proceeds , the inner lid used has a total projected area of 70% to 85% of the area of the inner diameter of the mold, has a concave bottom and a flat bottom surface, and has an upwardly inclined surface around it. It is dish-shaped, has a bottom area that occupies 50% or more of the total projected area, has a thickness of 0.01 to 0.20 mm, and is made of an aluminum thin film .

  By adopting the method as described in claim 1 above, it is possible to prevent the formation of a deep depression at the upper part of the inner lid floated on the surface of the lactam liquid, and further pressurize with an inert gas such as nitrogen gas. Can be more reliably blocked and polymerization failure can be almost completely prevented. Moreover, since pressurization with an inert gas is performed following the shrinkage accompanying polymerization and crystallization of the lactam solution, the mold is not in a reduced pressure state, and defects in the molded product can be prevented.

Further , since the inner lid floated on the surface of the polymerizable lactam liquid serves as a mold and has an area smaller than the area of the inner diameter of the mold, a molded body free from constriction on the outer surface of the molded body can be obtained.

In addition , the concave shape follows the shrinkage accompanying the polymerization and crystallization of the lactam solution, so that the inner lid follows the molded body and deforms. Therefore, it is possible to obtain a molded body having no deep depression at the top.

In addition , this thickness is a preferable thickness for obtaining a molded body in which the inner lid is more easily attached to the molded body and does not have a deep depression at the top.

In addition , since the material of the inner lid is an aluminum thin film, it has excellent thermal conductivity and does not affect the polymerizable lactam solution so as not to inhibit polymerization. Even if polymerization shrinkage occurs, it can be closely adhered and sufficiently followed.

  FIG. 1 is a schematic view of a polymerization apparatus used in the method for producing a cast polyamide resin molded body according to the present invention.

  The apparatus 1 is divided into a storage tank 2 in which an anionic polymerization catalyst is put in a molten lactam and a storage tank 3 in which an anionic polymerization initiator is put in a molten lactam. Between the storage tanks 2 and 3 and the mixing 4, respectively. A tube 7 fitted with a valve 6 is connected. The molten lactam flowing out from the storage tanks 2 and 3 is mixed and stirred in the mixing unit 4 and then cast into a mold 5 having a relatively high thermal conductivity such as aluminum or iron heated to 150 ° C. to 180 ° C. Is done.

  Each storage tank 2, 3 is provided with a pipe 8 for supplying nitrogen as an inert gas and a pipe 9 for discharging it, so that the pressure in the tank is always constant. A metering pump (not shown) below the valve 6 provided in each storage tank 2, 3 can be installed.

  Immediately after casting the polymerizable lactam solution into the mold 5, the lid of the mold 5 is opened as shown in FIG. 2, and the inner lid 10 is placed so as to float on the surface of the polymerizable lactam solution. Then, nitrogen pressure is applied, the mold 5 is adjusted to 130 to 180 ° C., and the polymerization proceeds.

  The inner lid 10 used in the present invention is a substitute for a mold that floats on the polymerizable lactam solution in the mold 5 and causes the polymerization reaction to proceed rapidly. The inner lid 10 floats on the polymerizable lactam solution and is thermally conductive. It must be good and flexible enough to follow shrinkage during polymerization while closely contacting the lactam. Specifically, it can be a dish-shaped inner lid made of a thin film made of metal or synthetic resin, has good thermal conductivity and flexibility, and is excellent in aluminum because it easily follows polymerization shrinkage. However, it is not limited to aluminum, and other materials may be used. In terms of thermal conductivity, a metal material is preferable. If the flexibility is insufficient and the polymerization shrinkage cannot be sufficiently followed, sink marks on the upper part of the molded body will be increased, which is not preferable.

  Moreover, it is preferable that the inner lid 10 has such a size that the total projected area of the inner lid occupies 70% to 85% of the area of the inner diameter of the mold.

  If the total projected area of the inner lid exceeds 85% of the area of the inner diameter of the mold, the outer surface of the molded body is constricted, and in the case of a rod-shaped molded body, the outer diameter may be insufficient or may be elliptical. This replaces the mold with the inner lid closed, and the polymerization reaction starts simultaneously from the entire surface of the mold in contact with the polymerizable lactam solution. It is thought that constriction also occurs.

  If the inner lid is 85% or less of the area of the inner diameter of the mold, the surface area where the polymerizable lactam solution is exposed increases, and this causes a slight delay in the polymerization reaction near the inner lid. However, the constriction of the outer peripheral portion can be prevented.

  When the inner lid is 70% or less of the area of the inner diameter of the mold, the area of the inner lid in contact with the polymerizable lactam solution is reduced, so that the upper polymerization reaction becomes too slow, resulting in the formation of deep dents in the upper part or polymerization reaction. This is not preferable because problems such as a flow pattern caused by unevenness occur.

  Furthermore, the shape of the inner lid 10 is concave, has a flat bottom surface, and has a dish shape having an upward inclined surface around the inner lid. The inner lid occupies 50% or more of the total projected area of the inner lid. I try to float. This concave shape makes it easy to float on the lactam solution, and the inner lid follows the molded body and deforms following the shrinkage caused by polymerization and crystallization, so that a molded body having no deep depression at the top can be obtained.

  If the bottom area of the inner lid 10 is less than 50% of the total projected area of the inner lid, it will tilt when it floats on the lactam, and the inner lid will follow the shrinkage associated with polymerization and crystallization of the lactam solution. In addition to reducing the area of the inner lid that comes into contact with the polymerizable lactam solution, the upper polymerization reaction becomes too slow, resulting in the formation of deep depressions in the upper part and the flow pattern associated with uneven polymerization reaction, etc. This is not preferable because of the above problems.

  Furthermore, the thickness of the inner lid 10 is preferably in the range of 0.01 to 0.20 mm. If it is less than 0.01 mm, it is easy to break, which is not preferable for handling. Further, if the thickness exceeds 0.20 mm, the rigidity increases, and even if the shape of the inner lid 10 is concave, the rigidity increases. Therefore, the inner lid follows the shrinkage due to polymerization and crystallization of the lactam solution, and the inner lid becomes a molded body. Since it becomes difficult to follow, it is not preferable.

  The polymerizable lactam used in the present invention, ω-lactam, is α-piperidone, ε-caprolactam, ω-laurolactam, or a mixture of two or more of these, and industrially advantageous lactams are ε-caprolactam and ω. -Laurolactam.

  The anionic polymerization catalyst used in the present invention may be a known ω-lactam polymerization catalyst such as sodium hydride, lithium hydride, sodium, potassium, etc. And 0.1 to 0.02 mol%.

  Examples of the initiator for anionic polymerization include N-acetyl-ε-caprolactam, isocyanate, and diisocyanate. Urea derivatives, urethanes, and isocyanurate derivatives can be used, and the addition amount is preferably in the range of 0.05 to 0.1 mol% with respect to ω-lactam.

  In the above production method, the anionic polymerization catalyst is added and dissolved in ω-lactam, and then an anionic polymerization initiator is added and mixed at the time of casting or after casting, or ω-lactam containing an anionic polymerization catalyst and anionic polymerization are used. It adjusts by the method of adding and mixing the omega-lactam containing an initiator at the time of casting or after casting.

  Moreover, although superposition | polymerization temperature of (omega) -lactam can be implemented at the temperature of 100-210 degreeC, Preferably it is the range of 130-180 degreeC.

  In carrying out the present invention, oils that do not inhibit polymerization other than the above components, lubricants such as wax, zinc stearate and calcium stearate, reinforcing materials such as carbon fiber and wollastonite, and colorants such as polyvinylidene chloride It is also possible to add.

  Hereinafter, the effect of the present invention was confirmed by giving examples and comparative examples of the present invention.

Example 1
14.2 kg of substantially anhydrous ε-caprolactam was heated and melted to 100 ° C., and 28.5 g of sodium hydride (63% oily) was added and dissolved by reaction. The lactam solution was heated to 125 ° C., and 12.5 g of trisphenyl isocyanurate was quickly mixed, and then poured into a cylindrical mold having an inner dimension φ120 and a depth of 1000 mm that had been heated to 140 ° C. in advance. . Thereafter, the inner lid of an aluminum thin film having an outer diameter of φ103 (80% of the inner diameter of the mold), a bottom area of φ75 (73% of the total projected area), a depth of 10 mm, and a thickness of 0.06 mm is used as a polymerizable lactam solution. After floating on the surface and capping the mold, the pressure was applied with nitrogen, the mold was adjusted to 160 ° C., and polymerization was performed.

  The mold was adjusted to 50 ° C. while the molded body was kept in the mold when the mold surface temperature dropped by 1 ° C. after the mold surface temperature had been raised by the reaction heat by the temperature sensor attached to the mold surface. . After 30 minutes, the compact was removed from the mold. Table 1 shows the results of observing the upper part of the molded body after the molded body was sufficiently cooled.

( Comparative Example 1 )
A round bar-shaped polyamide resin molded body was molded in the same manner as in Example 1 except that the aluminum thin film inner lid was molded by floating an inner lid in which the total projected area was substantially equal to the area of the inner diameter of the mold. Table 1 shows the results of observation of the upper layer of the molded body.

( Comparative Example 2 )
The inner lid shape is concave and the outer diameter is the same as φ103, but it is the same as in Example 1 except that it is molded by floating the inner lid with a bottom area diameter of φ30 (29% of the total projected area) and a depth of 10 mm. A resin molded body was molded. Table 1 shows the results of observation of the upper layer of the molded body.

( Comparative Example 3 )
The aluminum thin film inner lid was formed with a thickness of 0.25 mm. Otherwise, the same conditions as in Example 1 were used to obtain a round bar-shaped polyamide resin molded body. Table 1 shows the results of observation of the upper layer of the molded body.

(Comparative Example 4 )
After casting the polymerizable lactam solution, it was molded without using the inner lid. Otherwise, the same conditions as in Example 1 were used to obtain a round bar-shaped polyamide resin molded body. Table 1 shows the results of observation of the upper layer of the molded body.

As can be seen from the results shown in Table 1 above, in Comparative Example 4 , a flow pattern accompanying a deep depression and uneven polymerization occurred in the upper part of the molded body despite being pressurized with nitrogen and shielded from the atmosphere. I understand that. In Comparative Example 1 , there is no uneven polymerization at the upper part of the molded body, but constriction occurs at the outer peripheral part. Further, in Comparative Example 2 , although the inner lid is used, the bottom area is less than 50% of the total projected area of the inner lid. It can be seen that the inner lid hardly adheres to the molded body following the shrinkage caused by this, and as a result, a deep depression is formed, and a flow pattern due to unevenness of the polymerization reaction is also generated. In Comparative Example 3 , the inner lid was difficult to follow the molded body due to the rigidity of the inner lid, and the same result as in Comparative Example 2 was obtained. Comparative Examples 1 to 3 are inferior to Example 1 although they are within the scope of the present invention.

  The polymerizable lactam solution can be used in the production of a monomer casting nylon for producing a plate-like molded body by polymerizing in a mold.

It is the schematic of the superposition | polymerization apparatus used for the manufacturing method of a cast polyamide resin molding. It is sectional drawing which shows the state where the inner lid is floated and pressurized with nitrogen after casting the polymerizable lactam solution in the mold. The surface portion of the polymerizable lactam liquid which shows the state where the inner lid is deformed along with the molded body following the shrinkage accompanying polymerization / crystallization of the lactam liquid after casting the polymerizable lactam liquid into the mold. FIG.

DESCRIPTION OF SYMBOLS 1 Polymerization apparatus 2 Storage tank 3 Storage tank 4 Mixing 5 Mold 6 Valve 10 Inner lid

Claims (1)

In a casting polyamide molding method in which a polymerizable lactam solution comprising at least an anionic polymerization catalyst and an anionic polymerization initiator is anionically polymerized in a mold to a substantially anhydrous ω-lactam, the polymerizability cast into the mold When the polymerization is allowed to proceed while the polymerizable lactam is shielded from the atmosphere by floating the inner lid on the surface of the lactam liquid and then pressurizing with an inert gas , the inner lid used is an area whose total projected area is the inner diameter of the mold. 70% to 85%, and the shape is a dish shape having a concave and flat bottom surface, and an upward inclined surface around the bottom, the bottom area occupies 50% or more of the total projected area, and the thickness is A method for producing a cast polyamide resin molded body having a thickness of 0.01 to 0.20 mm and comprising an aluminum thin film .

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