JPS63230722A - Reaction injection molding - Google Patents

Abstract

PURPOSE:To produce a void-free molding excellent in elongation, etc., by performing reaction injection molding of a feed component containing a high-MW active hydrogen compound and a specified chain extender and another feed component containing a polyisocyanate compound. CONSTITUTION:A synthetic resin molding is produced by reaction injection molding of at least two components, i.e., a feed component containing a high-MW active hydrogen compound (e.g., polyether polyol) and a chain extender and, optionally, a catalyst and a blowing agent and another feed component containing a polyisocyanate compound (e.g. 4,4'-diphenylmethane diisocyanate), by using a chain extender comprising an amino compound having a first amino group selected from prim. and sec. amino groups and a second amino group or a hydroxyl group less active than said first amino group [e.g., a polyamine of the formula (wherein R is a 1-4C alkyl, k is 0 or 1, X is a 1-12C alkyl or the like, and m is 0 or 1-4)] or a combination thereof with another chain extender. A molding having void-free surface and excellent elongation, etc. can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a reaction injection molding method for molding polyurethane urea elastomer molded articles.

[Prior art] Synthetic resin molded products using reaction injection molding method! IJ construction is well known, and its application to synthetic resins other than 9 polyurethane resins, which are widely used in the production of polyurethane resin molded products including polyurethane elastomers, is also known, such as polyamide resins, epoxy resins, etc. Applications to polyester-based resins, unsaturated polyester-based resins, etc. are being considered, and some have been put into practical use. In the reaction injection molding method, at least two fluid raw materials that rapidly react to form a synthetic resin are mixed immediately before a mold, and immediately injected into the mold, and the mixture is synthesized in the mold. This is a molding method that focuses on forming resin. Mixing of fluid raw material components is usually carried out by impingement mixing, and in order to achieve more uniform mixing, it is also common to inject the mixture into a mold through an after-mixing mechanism. Hereinafter, a mixture of at least two fluid raw material components will be referred to as a reactive mixture. In addition, although the present invention will be mainly described below with reference to the production of polyurethane elastomer molded articles by reaction injection molding, application to other polyurethane synthetic resins (e.g. semi-rigid foam) and polyurea resins is denied. isn't it.

By reaction injection molding using at least two components: a raw material component containing a high molecular weight active hydrogen compound such as a relatively high molecular weight polyol, a chain extender, and optionally a catalyst and a blowing agent, and a raw material component containing a polyisocyanate compound. Methods for producing polyurethane elastomers such as polyurethane elastomers and polyurethaneurea elastomers are known. Typical examples of high molecular weight active hydrogen compounds are relatively high molecular weight polyols, especially polyether polyols.

The chain extender is a relatively low molecular weight polyhydric alcohol or polyamine, which is also a type of active hydrogen-containing compound.

The use of a catalyst is usually essential and is usually added to the active hydrogen compound-containing raw material component, but it can also be added to the isocyanate compound-containing raw material component. The use of a small amount of a blowing agent such as a halogenated hydrocarbon blowing agent to produce a microcellular polyurethane elastomer is a commonly used means for improving moldability. The density of the microcellular polyurethane elastomer obtained using this small amount of blowing agent is normal Q,
[1 g/cm3 or more, especially about 0.9 g/cm” or more. Especially a large amount of reinforcing fiber.

Unless flaky fillers or powder fillers are added, the upper limit is usually 1.2 g/cm' or less, especially about 1.15 g.
/ Cll+" or less. The density of the non-foamed polyurethane elastomer is also normally within the above range. The active hydrogen-containing compound-containing raw material component is divided into two or more, and the isocyanate compound-containing raw material component and the isocyanate compound-containing raw material component are 3 in total. It is also known to carry out reaction injection molding using more than one component.

[Problems to be Solved by the Invention The copolyurethane elastomer does not have sufficient heat resistance, and improvements are desired. Generally, the heat resistance of polyurethane elastomers is improved.

l) Increase the amount of highly polar components such as isocyanate components to increase hardness.

2) Increased hardness by adding filler.

3) A trifunctional or higher functional active hydrogen component or an isocyanate component is blended to perform high-order crosslinking.

However, these methods all involve deterioration of elongation properties, and it is extremely difficult to achieve both heat resistance and elongation properties.

Furthermore, it is known that one of the problems in one-reaction injection molding is that defects such as voids are likely to occur in the molded product. A void is a relatively large air bubble that exists inside a molded product. A molded product having such voids has extremely non-uniform physical properties and is likely to have a recess formed on one surface, which poses a problem in terms of appearance. Additionally, if voids exist on the surface of the molded product,
The appearance becomes extremely poor due to depressions and missing parts.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. In a method for producing a synthetic resin molded article by reaction injection molding using at least two components, a raw material component containing a polyisocyanate compound and a raw material component containing a polyisocyanate compound, a high molecular weight active hydrogen compound and a chain extender are used as a chain extender. In a method for producing a synthetic resin molded article by reaction injection molding using at least two components: a raw material component containing an optionally mixed catalyst and a blowing agent, and a raw material component containing a polyisocyanate compound, as a chain extender, An amino compound having a first amine group selected from a primary amine group and a secondary amino group, and a second amine group or hydroxyl group with lower activity than the first amino group, or an amino compound containing the same and other chain elongation groups. The present invention provides a reaction injection molding method characterized by using a chain extender or a reaction injection molding method characterized by using the same and another chain extender.

In the following description of the chain extender, the amino group means both a primary amino group and a secondary amine group. The activity of amino groups (reactivity toward isocyanate groups) is greater for primary amino groups than for secondary amino groups, and for primary amino groups, amino groups bonded to aliphatic carbon atoms (aliphatic amino An amino group (
aromatic amino group). Furthermore, the reactivity of a primary aromatic amino group decreases if a substituent such as an alkyl group or an electron-withdrawing group is present on the aromatic nucleus to which the amine group is bonded. When the same substituent is present, the reactivity is lower when the substituent is in the ortho position than in the rose position. Although it depends on the type of substituent, electron-withdrawing groups are generally more effective in reducing reactivity than alkyl groups. However, when an alkyl group is present at the ortho position, the activity of the amino group may be further reduced due to steric hindrance of the alkyl group. And hydroxyl groups usually have lower activity than any amine groups.

The present invention is characterized by focusing on the reactivity of these active hydrogen-containing functional groups and selecting and combining the most appropriate chain extenders.

The first chain extender in the present invention is an amino compound (hereinafter referred to as an amino compound (A
). The amino compound (A) has at least 1
amine groups, which are more active than any of the other active hydrogen-containing functional groups. There may be two or more first amino groups having approximately the same activity, but there is usually only one first amino group. This first amine group is the first
It is preferable that it is a class amino group, but in some cases,
It may also be a secondary amino group. When this first amino group is a secondary amino group, the second activated water described below.

The element-containing functional group is preferably a hydroxyl group.

Hereinafter, in the description of the amino compound (A), it is assumed that the first amine group is a primary amine group.

The activity of the first amino group requires high activity toward the active hydrogen-containing functional group of cylinder 2, which will be described later, and as long as this is the case,
It may itself be an amino group with suppressed reactivity as described above. However, preferably, the first amino group is an aliphatic amino group or an aromatic amino group having no alkyl group or electron-withdrawing group at its ortho position. From the viewpoint of heat resistance of the molded article, the chain extender is preferably a compound having an aromatic nucleus. Therefore, also in the case of aliphatic amine groups, aliphatic amino groups in aromatic compounds such as aminoalkyl groups bonded to aromatic nuclei are preferred.

The amino compound (A) further has an active hydrogen-containing functional group that is less active than the first amino group, which is a second amino group that is relatively less reactive than the first amino group. It is an amino group or a hydroxyl group. This hydroxyl group needs to be an alcoholic hydroxyl group, and a phenolic hydroxyl group causes a decrease in the heat resistance of the molded article. This second amino group is preferably a secondary amine group or a primary amino group with suppressed reactivity, especially having at least one alkyl group or electron-withdrawing group in the ortho position. Aromatic primary amino groups are preferred.

The amino compound (A) will be further explained using a chemical formula, but the amine compound (A) is not limited to the following three compounds.

(11 Polyamine Attractive group (however, if m and n are 2 or more, they may be both an alkyl group and an electron-attracting group) m, n: O or an integer of 1 to 4 A: 2 Only a few linking groups, or none However, in (l-i), when k=0, m is 1 to 2
is an integer, and X must be located at one or both of the two ortho positions of one amino group.

Similarly, in (·l-mouth), when k=0, it is preferable that n=0. In that case, m is an integer between 1 and 2 and
must be present at one or both of the two ortho positions of the amino group. More preferably, in both (l-i) and (l-i), m is l or 2, regardless of the value of k, and X is present at the ortho position of the amino group. Further, in (1-mouth), n is preferably O regardless of the value of k. Furthermore, compounds such as the following (1-iii) can also be used as polyamines.

-12rl (R, X, m are the same as above) (2) Aromatic hydroxyamine R1, alkylene group R having 1 to 4 carbon atoms, X, X', A are the same as in formula (1) above. This (2-
b) In the case of (2-way), m and n do not have to be O, regardless of the value of , and the bonding positions of X and X' are also not limited.

However, preferably m and n are each O or an integer of 1 to 2.

(3) Compound having secondary amine R2: alkylene group having 1 to 8 carbon atoms, especially 2 to 4 carbon atoms R1, alkyl group having 1 to 4 carbon atoms p: 0 or an integer of 1 to 2 (4) Primary Hydroxyamine Ha N-R' -OH---(41R4: 2 carbon atoms) having an amino group
~10 alkylene groups In each of the above formulas, the alkyl group represented by X or X' is suitably an alkyl group having 1 to 12 carbon atoms;
The alkyl group of 8 is preferred.

Particularly preferred are alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and butyl. Examples of the electron-withdrawing group which is X or X' include a halogen atom, a nitro group (-NOal), a cyano group (-CN), and an alkoxycarbonyl group (-CDOR').

and an alkoxycarbonyl group (-SOsR'), etc. (R'-R" each has 1 to 8 carbon atoms, especially 1 to
4), particularly preferred are a chlorine atom, a nitro group, a cyano group, and an alkoxycarbonyl group. Eight represents a divalent group or a direct bond of an aromatic nucleus, especially the number of carbon atoms! -6 alkylene group or -R''-NIICO-
(R' represents an alkylene group or not) and includes an amide bond-containing bonding group. Particularly preferred A is a methylene group.

The above-mentioned amine compounds (A) in the present invention are particularly suitable for the formulas (1-i), (1-c), (2-i) and (
Compounds represented by (2) are preferred. Further, the amino compound (A) preferably has a molecular weight of 600 or less, particularly 400 or less. Of course, two or more of these amine compounds (A) can be used in combination.

The above amino compound (A) can be used in the entire amount of the chain extender, but is more preferably used in combination with one or more other chain extenders. Other chain extenders include amino compounds (
There are polyamines, hydroxyamines, polyols, etc. other than A). One of the features of the present invention is that it enables the use of compounds and substances that were previously too active to be used as chain extenders for reaction injection molding, and that could be used in special reaction injection equipment such as high-speed injection machines. The purpose of this method is to enable the use of highly active chain extenders, which have been difficult to mold using conventional reaction injection molding equipment, using more general equipment. Hitherto, aliphatic polyamines and aromatic polyamines whose activity has not been suppressed (or whose activity has not been sufficiently suppressed) could not be used as chain extenders. Such chain extenders (hereinafter referred to as
Examples of polyamines (referred to as B) include ethylenediamine, tetramethylenediamine, hexamethylenediamine, cyclohexylmethanediamine, isophoronediamine, 4,4'-dicyclohexylmethanediamine,
Examples include xylylene diamine, toluenediamine, and benzenediamine. these are.

Even if it is used in combination with ethylene glycol, 1,4-butanediol, etc., its activity is too high and the fluidity of the injected mixture is significantly reduced, and the difference in activity from diol is too large. Control was impossible and molded products with good physical properties could not be obtained. In the present invention, even if a highly active polyamine is used in combination with the amino compound (A) or further in combination with a chain extender such as another diol, molded products with good physical properties can be molded. It becomes possible to do so.

On the other hand, polyamines whose activity has been sufficiently suppressed can be used as chain extenders for reaction injection molding. Such polyamine (hereinafter referred to as polyamine (C)) 2
There are aromatic polyamines that have an alkyl group or an electron-withdrawing group at the ortho position of each of the two amino groups. Specifically, diethyl toluene diamine, other ortho-alkyl-substituted toluene (or benzene) diamine substituted at the ortho position with an alkyl group such as t-butyl group, monochloro-p
- Benzenediamine, etc. However, although these can be molded using a high-speed injection machine, it is difficult to mold them using a general reaction injection molding machine because the activity is too high and the fluidity of the injected mixture becomes low.

By using such a chain extender in combination with the amino compound (A) of the present invention, it becomes applicable to general reaction injection molding equipment.

In the present invention, other chain extenders that can be used in combination include, in addition to the polyamine (B) and polyamine (C), commonly used polyols such as polyhydric alcohols. The most widely used polyols are, but are not limited to, ethylene glycol and 1,4-butanediol. These so-called chain extenders are usually compounds with a molecular weight of 400 or less, among which polyols are preferably compounds with a molecular weight of 200 or less.

In the present invention, 1 of the amine compound (A) with respect to the total chain extender is at least 10%, preferably 20 to 20%.
It is 100% by weight. When the amino compound (A) and another total extender are used together, the other chain extender is the polyamine (B).
) and/or polyamine (C), its proportion to the total chain extenders is at least 5% by weight, especially 10%.
~60 cities 1% is preferred. If the other chain extender is a polyol, its proportion to the total chain extender is at least 5
1% by weight, especially 10-80% by weight is preferred. In the present invention, the chain extender is particularly preferably an amino compound (A)
It consists of 1% by weight of 10-95% and 5-90% by weight of other chain extenders.

As the high molecular weight active hydrogen compound, a high molecular weight polyol having two or more hydroxyl groups is suitable. However, the use of high molecular weight active hydrogen compounds having two or more amine groups or an amino group and a hydroxyl group is also known. Oxyalkylene compounds (hereinafter referred to as aminated polyethers) can also be used. The average molecular weight per active hydrogen-containing group (i.e., hydroxyl group and/or amino group) of the high molecular weight active hydrogen compound is about 60
It is preferably between 0 and 4000, particularly between about 800 and 3000. The number of active hydrogen-containing groups per molecule is preferably 2.0 to 4.0 on average, particularly about 2.0 to 3.5. As the high molecular weight active hydrogen compound, polyether polyols, mixtures containing polyether polyols as a main component with other high molecular weight polyols, and polymer polyols based on polyether polyols are most preferred. Suitable polyether polyols include polyether polyols obtained by adding monoepoxides such as alkylene oxide or tetrahydrofuran to a polyvalent initiator. In particular, polyether polyols obtained by adding a monoepoxide such as alkylene oxide or tetrahydrofuran to a polyvalent initiator are suitable. Preferred are polyether polyols obtained by adding the same. For application to reaction injection molding, the presence of highly reactive hydroxyl groups, i.e., primary hydroxyl groups, is required, and in the case of polyether polyols using monoepoxides, there is usually a small amount (approximately 5
The presence of oxyethylene groups in weight percent is considered almost essential. The higher the proportion of terminal oxyethylene groups, the higher the proportion of primary hydroxyl groups and the higher the reactivity, but the higher the proportion of oxyethylene groups, the higher the hydrophilicity of the polyether polyol, which in turn increases the water absorption of the polyurethane elastomer. becomes high, causing a decrease in water absorption dimensional properties. Therefore,
The upper limit of the amount of oxyethylene groups present in the polyether polyol is suitably about 35% by weight, particularly about 25% by weight.
Weight percent is preferred. However, this is not the case when producing hydrophilic polyurethane. It is almost essential that at least 5% by weight of oxyethylene groups be present at the ends of the polyether chains, but they may also be present inside the polyether chains. The polyether polyol may be a mixture of two or more polyether polyols having different numbers of hydroxyl groups and molecular weights, and in particular, a mixture of two or more polyether polyols containing polyether diol or polyether triol as a main component or with other polyether polyols. Mixtures are preferred.

The polymer polyol is preferably a polymer polyol based on a polyether polyol as described above. Particularly preferred is a polymer polyol obtained by polymerizing at least one of acrylonitrile, styrene, and other vinyl monomers in a polyether polyol. others,
Polymer polyols obtained by laminating vinyl monomers in polyether polyols containing unsaturated groups, polyols containing condensates obtained by performing 1 filtration in polyether polyols, and polyols containing other polymer components may also be used. Vine. Other high molecular weight polyols that can be used in combination with polyether polyols include hydroxyl group-containing hydrocarbon polymers such as butadiene homopolymers and copolymers having two or more hydroxyl groups, and polyester polyols. is effective for the water absorption dimensional property 1- of polyurethane elastomers. The aminated polyether is a compound obtained by aminating some or all of the hydroxyl groups of the above polyether polyol or polyether polyol that does not have an oxyethylene group at the end, and can be used alone or as a polyether polyether. Can be used in combination with polyol, etc.

The amount of chain extender relative to the total of the high molecular weight active hydrogen compound and chain extender must be at least 3%. The greater the amount of chain extender, the harder the molded product obtained (assuming the high molecular weight active hydrogen compound is the same). In order to obtain a molded product with good heat resistance, a hard molded product using a large amount of chain extender is preferable. In the present invention, the amount of chain extender is 5 to 50
% by weight is preferred, in particular 10-45% by weight, and in order to obtain particularly hard molded products, 20-45% by weight is used.

Modified or unmodified aromatic polyisocyanates are suitable as the polyisocyanate compound, and in some cases, other polyisocyanate compounds may be used alone or in combination with aromatic polyisocyanates and the like. As the aromatic polyisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate, tolylene diisocyanate, etc. are suitable, and diphenylmethane diisocyanate consisting of 4,4'-diphenylmethane diisocyanate and its isomers is particularly suitable. These can be used as unmodified products, but modified products are generally used when applied to reaction injection molding methods. Modified products include, but are not limited to, prepolymer-type modified products and carbodiimide-type modified products. The amount of the polyisocyanate compound used is preferably about 90 to .120, particularly about 95 to +10, expressed as an isocyanate index.

The use of catalysts is usually essential in the production of polyurethane elastomers. As a catalyst, a tertiary amine catalyst or an organic tin compound is usually used, and a blowing agent is often used to improve the filling properties of the reactive mixture into a mold. Polyurethane elastomers obtained using relatively small amounts of blowing agents are microcellular (
It is called a polyurethane-based elastomer. Foaming agents include trichlorofluoroethane, methylene chloride, other halogenated hydrocarbon foaming agents, and water, and both are often used in combination. It is particularly preferable to use a halogenated hydrocarbon blowing agent, and the amount thereof is preferably about 15 parts by weight or less, particularly about 2 to 10 parts by weight, based on 100 parts by weight of the high molecular weight active hydrogen compound.

Polyurethane elastomers are produced by using arbitrary additives in addition to the above raw materials. Examples of optional additives include fillers, colorants, ultraviolet absorbers,
These include light stabilizers, antioxidants, and flame retardants. Examples of fillers include inorganic fibers such as glass fiber and wollastonite, organic fibers such as synthetic fibers, calcium carbonate, other powder fillers, mica, and other tabular fillers.

The amount of these fillers is about 30% for all synthetic resin raw materials because the larger the amount, the more problems arise with the viscosity and operability of the raw material components.
It is preferably less than 20% by weight, particularly 20% by weight or less. These additives are mainly blended into the active hydrogen compound-containing raw material component, but those that are non-reactive with isocyanate groups are also blended into the isocyanate compound-containing raw material component.

Synthetic resin molded articles obtained by the present invention, particularly polyurethane elastomer molded articles, can be used for various purposes.

It is particularly suitable for automobile exterior parts, such as bumper shells, fascias, fenders, and door panels. However, the application is not limited to this, and it can also be used for other automotive parts, electronic or electronic device housings, and other applications.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

(The downstream examples described below were conducted using the following raw material components and molding tests.

1) High molecular weight polyol A: Oxyethylene group content 25% by weight with an oxyethylene group at the end, hydroxyl value 28 using glycerin as an initiator
Uses polyoxypropylenoxyethylene triol.

2) Isocyanate C The amount of the prepolymer type modified diphenylmethane diisocyanate component having an isocyanate content of 26.01ffi% is such that the equivalent ratio is 1.05 to the active hydrogen component.

(Molding test) Using a reaction injection molding device (high pressure foaming machine), the discharge output was 15
Reaction injection molding was carried out under conditions such as 0 kg/cm'', discharge rate of 15±5 kg/min, and liquid temperature of each component at 30 to 40°C.

The mold cavity had a size of 350 mm x 350 mm, a wall thickness of 3 mm, and a temperature adjusted to 60 to 70°C. The mold was removed 30 seconds after injection, and the density, tensile strength, and heat sag of the molded product were measured.

(Tensile test) 50% modulus (kg/cm"), tensile strength (kg/cm")
cm"l, elongation (%), No. 2 dumbbell, tensile speed 25
Measurement was carried out under the condition of 0 mm/min.

(Heat sag (thermal sag)) A sample of 25 x 125 x 3 mm was
Leave it in an overhang state at 120℃ for 1 hour.
After cooling for 30 minutes at room temperature, the sagging distance was measured.

Example 1 8 parts of ethylene glycol 1m-xylylene diamine 5.
9 parts of dibutyltin dilaurate and 2.1 parts of monoethanol were dissolved in 84 parts of high molecular weight polyol A, and 0.1 parts of dibutyltin dilaurate was dissolved.
1 part and 0.12 parts of triethylenediamine are mixed to form an active hydrogen component.

The equivalent ratio of isocyanate C to this active hydrogen component is 0.
Molding was carried out using an amount of 5, and a sheet with no molding defects was obtained in an injection time of 2.0 seconds.

After heat treatment at 120℃, 50% tensile modulus 134kg
/cm", tensile strength 295 kg/am", E B 2
It became 90%. Further, the heat sag was 16.5 mm.

Comparative Example 1 4 parts of m-xylylenediamine and 12 parts of ethylene glycol are dissolved in 84 parts of high molecular weight polyol A, and 0.1 part of dibutyltin dilaurate and 0.12 parts of triethylenediamine are mixed to form an active hydrogen component.

The equivalent ratio of isocyanate C to this active hydrogen component is 1.0.
Molding was performed using an amount of 5, and a defect occurred in which 30% of the mold cavity was unfilled at an injection time of 2.0 seconds.

Example 2 165 parts of ethyl aminobenzoate and 136 parts of m-xylyrezidiamine were placed in a reaction vessel, heated to 140°C while stirring, and ethanol was distilled off in a N gas stream, followed by reaction for about 6 hours. Ta. This reactant opening is dissolved in 80 parts of high molecular weight polyol A and 10 parts of ethylene glycol, and 0.1 part of dibutyltin dilaurate and 0.12 part of triethylenediamine are mixed to form an active hydrogen component.

The equivalent ratio of isocyanate C to this active hydrogen component is 1.0.
5 was used for molding, and the tensile strength was measured after Ihr heat treatment at 120°C. The 50% tensile modulus was 141 kg/cm" and the tensile strength was 310 kg/cm.
cm”, elongation was 305%. Also, heat sag was 1
It was 3 mm.

Procedural amendment (method) % formula % 1. Indication of the case Patent Application No. 64250 of 1988 2. Name of the invention Reaction injection molding method 3. Relationship with the person making the amendment Patent applicant address Chiyoda-ku, Tokyo Marunouchi 2-chome 1-2 name
(004) Asahi Glass Co., Ltd. Toranomon Chiyoda Building (1) "Reaction injection molding method" in the title of the invention column on page 1 of the specification is amended to "reaction injection molding method."

Claims (1)

[Scope of Claims] 1. Using at least two components: a raw material component containing a high molecular weight active hydrogen compound and a chain extender and optionally containing a catalyst and a blowing agent, and a raw material component containing a polyisocyanate compound, In a method for producing synthetic resin molded products by reaction injection molding, the chain extender is a first amino group selected from a primary amino group and a secondary amino group, and a first amino group with lower activity than the first amino group. A reaction injection molding method characterized by using an amino compound having a second amino group or a hydroxyl group, or the same and another chain extender. 2. The method according to claim 1, wherein the amino compound is an aromatic compound having a primary amino group whose reactivity is not suppressed and a primary amino group whose reactivity is suppressed. 3. The method according to claim 1, wherein the amino compound is an aromatic compound having a primary amino group and a hydroxyl group whose reactivity is not suppressed. 4. The method according to claim 1, wherein the other chain extender is a polyamine having a primary amino group. 5. The method of claim 1, wherein the other chain extender is a polyol.