JPS63189442A - Production of polyamide foam - Google Patents

Abstract

PURPOSE:To obtain a polyamide foam is good balance between such physical properties as strength, rigidity and surface appearance, by anionic polymerization of anhydrous lactam in the presence of an azo compound as the foaming agent having specific decomposition characteristics. CONSTITUTION:The objective polyamide foam can be obtained by anionic polymerization of (A) 100pts.wt. of anhydrous lactam, pref. epsilon-caprolactam or its mixture with minor amount of another omega-lactam in the presence of (B) 0.01-10(pref. 0.1-5)pts.wt. of an azo compound giving a half life 10hr with a decomposition temperature 50-170(pref. 66-160) deg.C [e.g., 2,2'-azobis(2,4-dimethyl valeronitrile), (1-phenylethyl)azo diphenylmethane] using 0.1-3mol. of a catalyst (e.g., lithium hydride) and 0.01-5mol. of an activator (e.g., acetyl caprolactam) (each based on the component A).

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention produces a polyamide with well-balanced physical properties such as strength, rigidity, and surface appearance by anionically polymerizing lactam in the presence of a specific blowing agent. The present invention relates to a method for producing a foam.

<Prior Art> Anionic polymerization of lactams using an alkali catalyst and an activator is already a well-known technique, and molded products are manufactured by various companies using this polymerization method.

Furthermore, many proposals have been made regarding methods for obtaining polyamide foams using anionic polymerization of lactams. The method for producing polyamide foam basically involves ionic polymerization of lactam in the presence of a blowing agent.
It has been reported that it is important to select the type of blowing agent and control the polymerization conditions depending on the purpose.

For example, a method for obtaining a polyamide foam using a gas such as air, nitrogen gas, or argon gas as a bubble source, or a method using a hydrocarbon volatile blowing agent such as benzene or toluene (such as Japanese Patent Publication No. 1463/1983) ), methods using halogenated hydrocarbons such as carbon tetrachloride and tetrachlorethylene as blowing agents (Japanese Patent Publication No. 1343/1983, Japanese Patent Application Laid-open No. 92894/1989, etc.), carboxylic acids such as formic acid and acetic acid, and anhydrous Method of using acid anhydrides such as maleic acid and phthalic anhydride as blowing agents (Japanese Patent Application Laid-Open No. 55-43125
JP-A No. 57-153031, etc.), methods using decomposable chemical blowing agents such as Azocica-bonamide, etc. are known.

However, all of the methods shown in these previous examples have advantages and disadvantages, and are not necessarily universal, and in reality, they can be used depending on the purpose, and there are still points that need to be improved before they can be put to practical use on an industrial scale. The current situation is that

<Problems to be Solved by the Invention> It has been found that the following problems exist in the above-mentioned prior art example in which a polyamide foam is obtained by anionic polymerization of lactam. That is, methods using gases such as air and nitrogen gas require a loading device to form bubbles, making it difficult to optimize conditions.

Methods in which compounds such as hydrocarbons and halogenated hydrocarbons are used as volatile blowing agents are undesirable because the bubbles in the foam often become large and mechanical properties such as strength and rigidity of the molded product deteriorate.

In the case of carboxylic acids or acid anhydrides, the foaming efficiency is low, the effect of compensating for sink marks in molded products is low, and the surface appearance is poor.

In addition, in the method of using azosicabonamide as a decomposable blowing agent, since the decomposition temperature of azosicabonamide is generally high, it does not cause foaming that is difficult to foam, but also generates gas that inhibits the anionic polymerization of lactam. This is not preferred because the polymerization rate decreases and a satisfactory molded product cannot be obtained.

As mentioned above, when producing polyamide foam by carrying out anionic polymerization of lactam in the presence of a blowing agent, the problems are that the blowing agent does not inhibit the polymerization, that the foaming efficiency is excellent, that there is no sinkage, and that the surface is free from sink marks. Molded products with excellent appearance can be obtained, the bubbles produced are uniform and fine, and the physical properties of the molded products are excellent. In other words, the purpose of the present invention is to find a foaming agent that is superior to the above-mentioned problems, and to establish a method for obtaining foam molded products with excellent mechanical properties such as strength and rigidity and a good surface appearance by optimizing polymerization conditions. It is to be.

Means for Solving Problems〉 The present inventors mainly focused on azo compounds as decomposable blowing agents in a method for obtaining polyamide foam by anionic polymerization of lactam, and investigated the presence or absence of inhibition of lactam polymerization and the generation of bubbles. After conducting detailed studies on the state of the foam, the physical properties of foamed molded products, and the surface appearance, it was discovered that certain azo compounds did not give very good results as a foaming agent. reached.

That is, the present invention provides a polyamide foam characterized by anionically polymerizing a substantially anhydrous lactam in the presence of an azo compound having a half-life of 10 hours and a decomposition temperature within the range of 50 to 170°C. It provides a manufacturing method.

The azo compound used in the present invention decomposes quickly during anionic polymerization of lactam, and the decomposition temperature must be within a certain range so that the nitrogen gas and other gases generated become uniform and fine bubbles.

The decomposition behavior of an azo compound is expressed by the relationship between temperature and half-life time, and in the present invention, the decomposition temperature at which the half-life is 10 hours is 5.
It is necessary to use azo compounds within the range 0-170°C, preferably 66-160°C.

If the decomposition temperature, which indicates the 10-hour half-life of the azo compound, is less than 50°C, the decomposition will be too fast, causing air bubbles to escape, or the air bubbles will become large, reducing the strength and rigidity of the molded product, which is undesirable. . On the other hand, when the decomposition temperature exceeds 170°C,
It is unsuitable because sufficient foaming does not occur during anionic polymerization of the lactam, air bubbles are unevenly distributed within the molded product, and the effect of preventing sink marks on the surface of the molded product is small, resulting in only a poor surface appearance.

Examples of typical azo compounds include 2,2゛-azobis(2,4-dimethylvaleronitrile), (1-phenylethyl)azodiphenylmethane, 2,2゛-azobisisobutyronitrile, dimethyl-2 , 2°-azobisisobutyrate, 2,2′-azobis(2-methylbutyronitrile), 1,1°-azobis(1-cyclohexanecarbonitrile), 2-(carbomoylazo)-isobutyronitrile, 2,2゛-azobis(2,4,4-trimethylpentane), 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, 2,2゛-azobis(
2-methylpropane), 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2°-azobis(N
, N'-dimethyleneisobutyramidine), 4.4°-
azobis(4-cyanopentanoic acid), among others, 2,2°-azobisisobutyronitrile, 1゜1゛-
Azobis(1-cyclohexanecarbonitrile), 2.
2'-azobis(2,4,4-)limethylpenkune) and the like are preferably used.

In the present invention, the amount of the azo compound used is not particularly limited. The reason for this is that the azo compound itself decomposes and disappears, so the amount cannot be specified, but it is usually 0.01 to 10 parts by weight, preferably 0.0 parts by weight, per 100 parts by weight of lactam.
It is appropriate to use 5 to 7 parts by weight, more preferably 0.1 to 5 parts by weight.

The lactams used in the present invention include pyrrolidone, valerolactam, caprolactam, enantlactam, capryllactam, laurolactam, etc. Among them, ε-caprolactam or ε-caprolactam is the main component, and other ω-lactams are copolymerized. Preference is given to using mixtures of the components.

It is also possible to use further small amounts of polyols to copolymerize with the lactam, examples being polyethylene glycol, polypropylene glycol, polyoxyethylene/oxypropylene copolymer, polytetramethylene glycol, polycaprolactone diol, polybutadiene. Examples include diol, hydrogenated polybutadiene diol, and polyoxyethylene/dimethylsiloxane copolymer.

The lactam used in the present invention can be produced by any method, but it is required to be substantially anhydrous.

The anionic polymerization of lactams in the present invention is usually carried out using a catalyst and an activator.

The above catalysts include alkali metals, alkaline earth metals, hydrides, hydroxides, oxides, carbonates, alkoxy compounds, alkyl compounds, aryl compounds, Grignard reagents, aluminum compounds, and salts of these metals and lactams. At least one compound selected from the following is preferable, and particularly preferable metals include lithium, sodium, potassium,
Magnesium, calcium and aluminum.

Among them, specific examples of catalysts particularly useful in the present invention include lithium hydride J1, methyl lithium 1, lithium methoxide, sodium, sodium hydride, sodium methoxide, sodium ethoxide, sodium hydroxide,
Sodium carbonate, sodium lactamate, potassium,
Potassium hydroxide, potassium methoxide, potassium ethoxide, potassium hydroxide, potassium carbonate, potassium lactamate, calcium hydroxide, ethylmagnesium bromide, butylmagnesium bromide, propylmagnesium bromide, phenylmagnesium bromide, ethylmagnesium chloride , propylmagnesium chloride,
Butylmagnesium chloride, phenylmagnesium chloride and reaction products of these Grignard reagents with ε-caprolactam, triethylaluminum, diethylchloroaluminum, ethyldichloroaluminum,
Examples include aluminum propoxide and reaction products of these aluminum compounds and ε-caprolactam.

The amount of the catalyst added is preferably 0.1 mol % or more based on ε-caprolactam from the viewpoint of polymerization activity, and 3 mol % or less from the viewpoint of the crystallinity of poly ε-caprolactam, particularly 0.3 to 2 mol %. A range of .5 mole % is preferred.

The activator is an acyllactam compound containing one or more structural units in the molecule in which the hydrogen atom on the nitrogen atom of ε-caprolactam is replaced with a carbonyl group, and ε-caprolactam to produce the above-mentioned acyllactam compound. Preferably, compounds are used.

Acyllactam compounds are broadly classified into those in which the acyllactam unit is directly bonded to a carbon atom and those in which the acyllactam unit is directly bonded to a heteroatom.

Examples of the former include acetylcaprolactam, adipoylbiscaprolactam, sebacoylbiscaprolactam,
Precursors of these acyllactam compounds include terephthaloyl biscaprolactam, 2-chloroterephthaloyl biscaprolactam, 2,5-dichloroterephthaloyl biscaprolactam, isophthaloyl biscaprolactam, and dibenzoyl biscaprolactam. Examples include corresponding carboxylic acids and halides thereof.

On the other hand, examples of the latter include hexamethylene-1,6-biscarbamide caprolactam, tolylene-2,4(2,6
)-biscarbamide caprolactam and the like. Examples of the precursor include hexamethylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, and polymethylene polyphenylisocyanate.

The amount of the activator to be added is 0.01 or more from the viewpoint of polymerization rate and polymerization rate, and 5 from the viewpoint of the degree of polymerization, relative to ε-caprolactam.
The content is preferably mol % or less, particularly preferably 0.05 to 4.0 mol %.

There are no particular restrictions on the anionic polymerization method of the present invention.
Conventionally known methods can be employed. For example, a method in which a lactam, a catalyst, an activator, and a blowing agent are melt-mixed all at once in one reaction vessel, and then the mixture is introduced into a molded mold and polymerized, or two lactams containing each of a catalyst and an activator are melt-mixed. prepare the product in two separate containers,
A so-called reaction injection molding method can be used in which the blowing agent is added and mixed in either container or both containers, and then the necessary amounts of both are mixed in a mixer and introduced into a mold.

Other methods such as centrifugal casting and rotational molding can also be used. The polymerization conditions can also be basically carried out under known conditions. For example, in the case of reaction injection molding, the stock lactam is heated and melted at 80 to 130°C,
After mixing both stock solutions, the mixture was heated to 120-180'
This can be carried out by injecting the mixture into a mold preheated to C and polymerizing for 0.5 to 30 minutes.

The purpose of the present invention is to produce a polyamide foam with excellent strength, rigidity, and surface appearance.Specifically, the specific gravity is preferably in the range of 0.30 to 1.12, particularly 0.30 to 1.12. The range of 40 to 1.10 is preferable. The foaming ratio calculated from this specific gravity is about 1.05 to 3.0 times, and low-foam foam wood is preferable. In order to exhibit this, it is preferable that the thickness is 10 μ or more, and from the viewpoint of strength and rigidity, it is 500 μ or less.

As described above, the production method of the present invention is characterized by anionically polymerizing lactam using a specific azo compound as a blowing agent, and the polyamide foam obtained by the present invention has the above-mentioned properties. The characteristics of this material are reflected in the strength, rigidity, surface appearance, etc., and the object of the present invention is achieved.

The foam of the present invention may contain other additives as long as they do not impair polymerizability and physical properties, such as pigments, dyes, heat-resistant agents, antioxidants, weathering agents, M-type agents, flame retardants, foam stabilizers, and antistatic agents. Agents and the like can be added and introduced.

The polyamide foam of the present invention is useful for mechanical parts, automobile parts, electrical/electronic parts, general miscellaneous goods, etc. of various manufacturers.

<Example> The present invention will be explained in more detail by giving examples below. The characteristics described in the following examples were measured by the following method.

(1) Specific gravity: A small piece of the molded product was placed in a density gradient tube prepared using a toluene/carbon tetrachloride mixture as a solvent, and the temperature was 25°C.
It was measured with

(2) Condition of bubbles: The cross section of the molded product was observed under a microscope.

(3) Tensile properties: ASTM D638 (4) Bending properties: ASTM D790 (5) Izot impact strength: A
STM D256 (6) Surface Appearance: Visual Judgment Example 1 To 113 g (1.0 mol) of substantially anhydrous ε-caprolactam, 2.4 mol % of sodium prolactamate was added and dissolved uniformly. (A) Component. On the other hand, 113 g of substantially anhydrous ε-caprolactam (1,
0 mol), 2 g of 1,1°-azobis(1-cyclohexanecarbonitrile) and 3.2 mol% of adipoyl biscaprolactam were added and uniformly dissolved (B
) component. Component (A) and component (9) are stored in separate containers and the melted liquid heated to 80°C is transferred using a pump,
After mixing equal amounts of components (8) and (8) in a mixer, the mixture was introduced into a mold heated to 150° C. to perform polymerization. When the mold was opened after 5 minutes, a foam molded piece with a good surface appearance was obtained, the specific gravity of this piece was 0.88, and the average diameter of the cells was 80 μm. Further, the physical properties of the test piece obtained here are as shown in Table 1, and it was found that the test piece had excellent balance in strength, rigidity, and impact resistance, and had high practical value.

Comparative Example 1 A molded piece was obtained by carrying out exactly the same operation as in Example 1 without using 1,1''-azobis(1-cyclohexanecarbonitrile) as a blowing agent, but there were large sink marks on the surface of the molded product and the appearance was poor. It was bad.

Comparative Example 2 Azocabonamide (
When anionic polymerization of caprolactam was carried out in the same manner as in Example 1 except that a decomposition temperature of 172°C (172°C with a half-life of 10 hours) was used, polymerization was inhibited and a large amount of unpolymerized caprolactam remained, making it difficult to put into practical use. A molded piece with high properties was not obtained.

Comparative Example 3 2,2゛- with a decomposition temperature of 30°C showing a half-life of 10 hours
Azobis(4-methoxy-2,4-dimethylvaleroni 1
A molded piece was obtained by carrying out the same operation as in Example 1 using . It was found that both rigidity and impact resistance were low.

Examples 2 to 5 The physical properties of test pieces obtained by performing the same operations as in Example 1 were measured by changing the types, amounts added, polymerization conditions, etc. of the blowing agent, lactam, catalyst, and activator. The results shown in the table were obtained. In all cases shown in Table 1, materials with excellent performance could be obtained.

a) CL: ε-caprolactam, LL: ω-laurolactam b) Na-CL: Sodium prolactamate, Et
HgBr: Ethylmagnesium bromide, K: Potassium C) AC Niasiboyl biscaprolactam, TC: Terephthaloyl biscaprolactam, HMDI: Hexamethylene diisocyanate d) ACHN: 1,1°-azobis(1-cyclohexanecarbonitrile), AMDV: 2,2'-azobis(4-methoxy-2
,4-dimethylvaleronitrile), ATMP: 2,
2'-azobis(2,4,4-)limethylpenkune>, A113N:2,2°-azobisisobutyronitrile<
Effects of the Invention> As described above, by using an azo compound having specific decomposition characteristics as a blowing agent during cationic polymerization of lactam, it has become possible to produce a polyamide foam having the following characteristics.

(a) It has a small specific gravity and is lightweight.

(b) The bubble diameter is appropriate and the foaming state is uniform.

It is particularly suitable for anionic polymerization conditions for lactams, and there is no air bubble loss or uneven distribution of air bubbles in the molded product.

(c) Does not inhibit anionic polymerization of lactam.

(d) A foam with excellent balanced physical properties such as strength, rigidity, and impact resistance can be obtained.

(E) Foaming suppresses sink marks on the surface of the molded product, resulting in a good surface appearance.

Claims (1)

[Claims] 1. A method for producing a polyamide foam, characterized in that a substantially anhydrous lactam is anionically polymerized in the presence of an azo compound having a half-life of 10 hours and a decomposition temperature in the range of 50 to 170°C.