JPS6234529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing plate-shaped polyamide moldings by alkaline polymerization of lactams.

A method in which lactam is polymerized in the presence of an alkali catalyst and a cocatalyst in a mold maintained at a temperature above the melting point of the lactam and below the melting point of the resulting polyamide is well known as the monomer casting method. ing.

This method has the advantage that a molded product can be obtained directly from the raw material monomer, and the polymerization process can be completed in a short time, and the structure of the mold is significantly simpler than that of an injection mold. It is extremely advantageous in terms of mold cost, and has the advantage that there is no limit to the size of the molded product.

On the other hand, the disadvantage of the monomer casting method is that large volume shrinkage occurs during polymerization, and recesses are usually formed on the surface of the molded product, so the surface of the molded product must be cut or cut to smooth it after the polymerization is completed. As a result, the yield decreases, and the inside and surface of the molded product tend to contain bubbles called "su".

Several methods have been proposed to improve these drawbacks of the monomer casting method.

The method described in Japanese Patent Publication No. 39-25202 is an attempt to improve the heterogeneity of molded products and the occurrence of ``s'' caused by volumetric shrinkage during polymerization, and as a countermeasure to this, a lactam and a catalyst are used. The auxiliary container (raw material storage tank) containing the material is directly connected to the mold in an adiabatic manner, and the molten lactam in the material storage tank is maintained under pressure during polymerization by pressurized gas above the liquid surface. There is.

The purpose of the adiabatic connection between the reservoir and the mold in this method is to enable the temperature of the reservoir and the mold to be adjusted separately, thereby making it possible to control the temperature of the reservoir from the mold. This prevents heat transfer to the sides and prevents the reservoir from reaching polymerization temperatures.

In addition, the effect of pressurizing the molten lactam in the storage tank with pressurized gas is that the lactam corresponding to the volumetric contraction that occurs in the mold as polymerization progresses is injected from the storage tank, so the lactam is pressurized into the mold. It is possible to obtain a molded product with a volume that matches the voids in the mold, and at the same time, the occurrence of "s" is suppressed.

However, there is a difference between the quality of the polymer obtained from the lactam that is press-injected later and the quality of the polymer portion that was press-polymerized first, resulting in non-uniform quality of the entire molded product. If a molded article of uniform quality is to be obtained, the portion of the molded article containing the polymer from the lactam that was subsequently injected must be cut off, which reduces the yield accordingly.

The method described in Japanese Patent Publication No. 40-16153 is a method in which partial polymerization of the lactam in the mold occurs, and when the viscosity increases to a certain extent, press molding is performed to obtain a finished product in the desired shape. Since the die is forced down into the mold only after the viscosity increases, this method cannot eliminate air bubbles inside the molded product. Even when this method is applied to a monomer casting method for a plate-shaped body, air bubbles scattered inside the molded article and a collection of air bubbles near the upper surface of the molded article are still observed, resulting in an unsatisfactory result.

The present invention provides a method for manufacturing a plate-shaped polyamide molded article by a novel monomer casting method, which successfully solves the difficulties of the conventional methods as described above.

An object of the present invention is to provide a method for producing a plate-shaped polyamide molded product whose surface can be made smooth during polymerization.

Another object of the present invention is to provide a method for producing a plate-shaped polyamide molded article with high yield.

Still another object of the present invention is to provide a method for producing a plate-shaped polyamide molded product that is free of air bubbles inside and on the surface of the molded product.

That is, the present invention provides a method for polymerizing a molten lactam in the presence of an alkali catalyst and a cocatalyst in a polymerization molding machine that provides a plate-shaped molded product. It consists of a mold and a presser lid that is vertically slidable on the inner wall of the female mold, and a gap is formed between at least one arbitrary side surface of the presser lid and the inner wall of the female mold opposing thereto, The bottom surface of the presser cap is sloped upward toward the void, and (b) as the polymerization and solidification of the molten lactam progresses, the presser cap is pushed down to the extent that the contents do not overflow. This is a method for manufacturing a plate-shaped polyamide molded product.

According to the present invention, a plate-shaped polyamide molded product having a smooth surface without bubbles inside and on the surface can be obtained in high yield.

The lactam used in this invention is an ω-lactam having a five-membered ring or more, and specific examples thereof include γ-butyrolactam, δ-valerolactam,
ε-caprolactam, ω-enantlactam, ω
-capryllactam, ω-undecanolactam,
Examples include ω-laurin lactam. Among these lactams, ε-caprolactam and ω-laurinlactam are advantageously used industrially. Two or more lactams may be used in combination.

As the alkali catalyst, all the compounds used in the known alkaline polymerization method of lactam can be used, such as alkali metals, alkaline earth metals, their hydrides, oxides, hydroxides, carbonates, alkylated products, alkoxides,
Other examples include Grignard compounds, sodium naphthalene, and reaction products of these with lactams. As the reaction product of the metal or metal compound and lactam, potassium salt of lactam or sodium salt of lactam is preferably used.

The amount of alkaline catalyst used is
It is usually 0.1 to 5 mol%.

The cocatalysts used in this invention are aliphatic, cycloaliphatic and aromatic mono- or polyisocyanates, specific examples being stearyl isocyanate, phenyl isocyanate, cyclohexyl isocyanate, toluene diisocyanate, diphenylmethane diisocyanate, Naphthalene diisocyanate, hexamethylene diisocyanate, metaxylylene diisocyanate,
Examples include hydrogenated diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate, hydrogenated metaxylylene diisocyanate, phenylene diisocyanate, cyclohexene diisocyanate, isophorone diisocyanate, and the like. Furthermore, reaction products of lactams and the above-mentioned isocyanates can also be used as isocyanates in this invention. These isocyanates may be used alone or in combination of two or more.

The amount of isocyanate used is usually 0.05 to 5 mol% based on the lactam.

The polymerization molding machine used in this invention will be explained with reference to the drawings.

FIG. 1 is a vertical sectional view of one specific example of a polymerization molding machine used in the present invention.

The polymerization molding machine 1 consists of a female mold 2 installed horizontally and a presser lid 3 that is vertically slidable on the inner wall of the female mold 2.

The female mold 2 has a cavity 16 in which the opposing large surfaces of the plate-shaped polyamide molded product obtained by polymerization molding are positioned above and below. The female mold 2 may be fixed or may be attached to a hydraulic cylinder (not shown) so that it can move vertically.

The presser cover 3 is attached to a presser 4 and is movable in the vertical direction.

Preferably, a heater 5 is attached to the female mold 2 and the presser lid 3 so that their temperatures can be adjusted.

A gap 8 is formed between at least one arbitrary side surface 6 of the presser lid and an inner wall 7 of the female mold 2 facing thereto. The size of the void 8 is preferably 0.1 to 1 mm.

It is preferable that an injection port 10 for filling the cavity 16 of the female mold 2 with a molten lactam (hereinafter referred to as a monomer mixture) containing an alkali catalyst and a co-catalyst is provided through the side wall 9 of the female mold 2 . This injection port 10 is connected to the cavity 16 described above.
It can also be used as an inert gas inlet when replacing air with inert gas.

The bottom surface 11 of the holding lid 3 is sloped upward toward the gap 8. Its scent is 1/1000~2
Preferably it is 0/1000.

The bottom surface 11 of the presser lid 3 is also attached to the inner bottom surface 12 with the female mold 2.
It is preferable to form an inclination parallel to the inclination of , from the viewpoint of obtaining a plate-shaped polyamide molded product having a uniform thickness.

The bottom wall 13 of the female mold 2 is preferably provided with a through hole 15 through which a knockout pin 14 for ejecting the plate-shaped polyamide molded product from the female mold 2 passes.

Next, the polymerized form of lactam in this invention will be explained.

The female mold 2 and the presser lid 3 are heated by a heater 5 to a temperature that is higher than the melting point of the lactam and lower than the melting point of the produced polyamide. After this, the monomer mixture is immediately poured into the cavity 16 of the female mold 2.
However, prior to filling with the monomer mixture, the presser lid 3 is placed so that its side wall 6 is in the female mold 2.
The female mold 2 is pressed down until it comes close to the upper part of the inner wall 7 of the mold, and then an inert gas such as nitrogen gas is blown into the female mold 2 through the injection port 10 to replace the air inside the female mold 2. Thereafter, the monomer mixture can be filled through the injection port 10. preferable.

In this invention, the polymerization induction period of the lactam is
It is preferable to set the type and amount of the alkali catalyst and co-catalyst, and the polymerization temperature so that the polymerization time is within the range of 0.5 to 5 minutes. This is because if the polymerization induction period of lactam is too short, when the monomer mixture is filled into the cavity 16 of the female mold 2, the air bubbles trapped in the monomer mixture will not be able to form a polymerization system before they float to the surface of the monomer mixture. As the viscosity of the molded product increases, only molded products containing bubbles can be obtained. Furthermore, if the polymerization induction period of the lactam is too long, the polymerization cycle will become long, which is industrially disadvantageous.

Pour the monomer mixture into cavity 1 of female mold 2.
After the lactam is filled in the container 6, the polymerization and solidification of the lactam progresses, and in this invention, as the polymerization and solidification of the lactam progresses, it is necessary to press down the presser lid 3 to an extent that the contents do not overflow.

In this invention, pushing down the presser cover 3 means that the female die 2 is fixed and only the presser cover 3 is pushed down, and the female die 2 is pushed up while the presser cover 3 is fixed and the female die 2 is pushed up. This means that the presser cover 3 is pushed down relative to the mold 2, and that the female mold 2 is pushed up at the same time as the presser cover 3 is pushed down.

Preferably, the presser lid 3 is pressed down so that the monomer mixture or the polymerization product mixture does not overflow from the void 8. At the initial stage of polymerization, the polymerization product mixture also flows, so it is preferable to calculate in advance a pressing down speed commensurate with the volumetric shrinkage from the relationship between polymerization time and volumetric shrinkage rate, and press down at a speed that is equal to or slightly higher than this.

After the polymerization of the lactam has progressed and the polymerization mixture no longer naturally flows, by applying a load to the presser cap 3, the presser cap 3 is increased to compensate for the volumetric contraction.
can be pushed down.

The effects of pressing down the presser cover 3 will be explained next.

When the presser lid 3 is pressed down and its bottom surface 11 comes into contact with the liquid level of the monomer mixture, the air bubbles existing at or near the liquid surface of the monomer mixture move toward the void 8 along the slope made on the bottom surface 11 of the presser lid 3. It is pushed out and discharged from the cavity 8. Therefore, according to the present invention, a plate-shaped polyamide molded product without air bubbles on the surface can be obtained.

Furthermore, by pressing down the presser lid 3 by an amount commensurate with the volumetric shrinkage caused by the polymerization and solidification of the lactam, a plate-shaped polyamide molded product without surface depressions called "sink marks" and internal "holes" can be obtained. I can do it. That is, taking ε-caprolactam as an example, the volumetric shrinkage rate due to polymerization and solidification of molten lactam is 14% at a polymerization temperature of 130°C, and 17% at a polymerization temperature of 170°C, and the presser lid 3 is not pressed down. A recess is formed on the surface of the plate-shaped polyamide molded product obtained by volumetric shrinkage, but by pressing down the presser lid 3 by an amount corresponding to the volumetric shrinkage due to polymerization and solidification of the lactam, the plate-shaped polyamide molded product without the recess is formed. can get.

Polymerization time varies depending on conditions, but is usually 5 to 15
It's a minute.

After the predetermined polymerization time has elapsed, the presser lid 3 is pulled up, and the obtained plate-shaped molded product is placed on the knockout pin 1.
4 to eject it from the female mold 2.

The method of the present invention can be suitably used for producing a long plate-shaped polyamide molded article.

Next, Examples and Comparative Examples will be shown.

EXAMPLE A monomer mixture consisting of 100 parts by weight of ε-caprolactam, 0.4 parts by weight of sodium salt of ε-caprolactam and 0.2 parts by weight of toluene diisocyanate was polymerized in a polymerization molding machine 1 shown in FIG.

The female mold 2 has a cavity 16 of 100 cm x 40 cm x (height) 10 cm, and the injection port 10 opens at a position 8 cm from the inner bottom surface 12 of the female mold 2.
Inner bottom surface 12 of female mold 2 and bottom surface 11 of presser lid 3
was sloped at a slope of 3/1000, and the size of the gap 8 was 0.1 mm.

The temperature of the presser lid 3 and the female mold 2 was heated to 160° C. by the heater 5. The presser lid 3 was pushed down until its side wall 6 came close to the upper part of the inner wall 7 of the female mold 2, and then nitrogen gas was blown into the female mold 2 through the injection port 10 to replace the air inside the female mold 2.

5 kg of the monomer mixture was injected into the cavity 16 of the female mold 2 from the injection port 10 in 5 seconds. about 10
After being allowed to stand still for a second, the presser cover 3 was pushed down until one end of its bottom surface 11 came into contact with the liquid level of the monomer mixture, and then the presser cover 3 was pushed down at an initial speed of 0.3 mm/min.

Polymerization and solidification of ε-caprolactam progresses, and approximately 6
After a few minutes, it became impossible to press down the presser foot lid 3. After this, apply a load of 20Kg/cm ² to the presser foot lid 3 and add 15
Polymerization was carried out for minutes.

Then, the presser lid 3 was pulled up, and the plate-shaped polyamide molded product was ejected from the female mold 2 using the knockout pin 14.

The size of the plate-shaped molded product was 100 cm x 40 cm x 1 cm, and the surface was extremely smooth with no depressions or bubbles observed. I cut the molded product and observed whether there was a "su" inside.
was not recognized. Molding yield is 98 excluding burrs
It was in weight%.

Comparative example: Inner bottom surface 12 of female mold 2 and bottom surface 1 of presser lid 3
The process was carried out in the same manner as in the example except that the polymerization molding machine 1 without a slope was used.

Many traces of air bubbles were observed on the surface of the obtained plate-shaped molded product.

[Brief explanation of the drawing]

Figure 1 shows one of the polymerization molding machines used in this invention.
FIG. 3 is a vertical cross-sectional view of a specific example. 2... Female mold, 3... Holder lid, 8... Gap, 1
0... Inlet, 11, 12... Inclined surface.

Claims (1)

[Scope of Claims] 1. A method of polymerizing a molten lactam in the presence of an alkali catalyst and a cocatalyst in a polymerization molding machine that gives a plate-shaped product, (a) The polymerization molding machine has a horizontally installed female It consists of a mold and a presser lid that can be slid vertically on the inner wall of the female mold, and a gap is formed between at least one arbitrary side surface of the presser lid and the inner wall of the female mold that faces it. , the bottom surface of the presser cap is sloped upward toward the void, and (b) as the polymerization and solidification of the molten lactam progresses, the presser cap is pushed down to the extent that the contents do not overflow. A method for manufacturing a plate-shaped polyamide molded product.