JP2008189939A - Method for solid phase polymerization of polyamide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for solid phase polymerization of polyamide, by which an increase in the yellowing degree is small upon the solid phase polymerization of the polyamide that comprises a diamine containing 70 mol% or more of xylylene diamine and a dicarboxylic acid containing 70 mol% or more of adipic acid. <P>SOLUTION: The method for the solid phase polymerization of the polyamide comprises obtaining a raw material polyamide by polycondensation of the diamine containing 70 mol% or more of xylylene diamine and the dicarboxylic acid containing 70 mol% or more of adipic acid via melt polymerization, storing the raw material polyamide once, and then further increasing the degree of polymerization of the polyamide by the solid phase polymerization, wherein the raw material polyamide is stored in air under conditions of relative humidity of 5%RH or less and a temperature less than Tg (the glass transition point of the raw material polyamide) while shielding light and the solid phase polymerization is performed within 20 days including days for storage after obtaining the raw material polyamide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for producing a solid phase polymer of polyamide. More particularly, the present invention relates to a method for obtaining a solid phase polymer of a polyamide having a small increase in yellowness in solid phase polymerization of a polyamide comprising a diamine containing 70 mol% or more of xylylenediamine and a dicarboxylic acid containing 70 mol% or more of adipic acid. Is.

Polyamide is a material excellent in heat resistance, chemical resistance, mechanical properties, and moldability, and is widely used as a molding material for synthetic fibers and automobile parts, and a packaging material for films. In recent years, products aimed at further enhancement of functionality have been developed in various fields where polyamides are deployed, and higher heat resistance, higher strength, higher gas barrier properties, and mechanical properties during water absorption will not deteriorate. Polyamide is desired.

In general, nylon MXD6 obtained by polycondensation of metaxylylenediamine and adipic acid is known as a polyamide having low water absorption, high strength, and high gas barrier properties. JP-A-6-192416 proposes a polyamide obtained by polycondensation of paraxylylenediamine, hexamethylenediamine and adipic acid as a polyamide having excellent moldability and mechanical properties upon water absorption. Polyamides obtained from these xylylenediamines are attracting attention as polyamides that do not deteriorate in high heat resistance, high strength, high gas barrier properties, and mechanical properties upon water absorption.

Polyamide is a water-absorbing thermoplastic resin that absorbs or absorbs moisture in a solid state in excess of the saturated moisture at the time of melting, and is therefore dried before molding. Alternatively, the dried product is filled in a moisture-proof packaging bag and then shipped as a product for use in molding. In the drying process, pellets obtained by melt polymerization are generally processed in a solid phase, and a melt drying method using an extruder or the like is disadvantageous in terms of productivity and coloring due to heat history.

Since the polyamide used for the molding material is molded by injection molding, it is required to have high fluidity at the time of melting, and a low-viscosity polyamide is used. On the other hand, polyamides used for bottles, sheets, films, fibers, etc. are molded not only by injection molding but also by extrusion molding. Middle, high viscosity polyamides are used. In order to obtain a medium or high viscosity polyamide by melt polymerization, it is necessary to continue the polymerization reaction in a molten state, and there is a high possibility that thermal decomposition will occur due to an increase in heat history accompanying the extension of the reaction time. In addition, a general stirring apparatus cannot provide sufficient power for maintaining the molten state of the polyamide in the polymerization tank uniformly, and a special polymerization apparatus is required. Moreover, it is difficult to remove the melted medium-viscosity or high-viscosity polyamide from the polymerization tank compared to the low-viscosity polyamide, and the amount of residual adhesion to the inner wall of the polymerization tank is also lower than that of the low-viscosity polyamide. And increase. For this reason, it is not preferable to produce a medium or high viscosity polyamide by melt polymerization.

For this reason, generally known as a method for obtaining a medium or high viscosity polyamide is so-called solid phase polymerization in which a low viscosity polyamide is polymerized by melt polymerization and then heat-treated in a solid phase. Solid-phase polymerization is advantageous over melt polymerization in that the degree of polymerization can be increased at a temperature below the melting point, so that there is no coloration due to thermal deterioration, and it is carried out in various forms.

As a characteristic of polyamide, since it is easy to be colored yellow due to oxidative degradation and thermal degradation during molding processing, it is desirable that the raw material polyamide used in the molding processing is not colored as much as possible. Therefore, in order to suppress coloring due to oxidative degradation during solid-phase drying and solid-phase polymerization, treatment is performed by heating from the heat transfer surface of the apparatus under reduced pressure, or in an inert gas atmosphere such as heated dry nitrogen. The method is known. Generally, after the polyamide as a raw material is obtained by melt polymerization or the like, it is subjected to solid phase drying or solid phase polymerization treatment relatively quickly (without long-term storage). It should be noted that oxygen is excluded during solid-phase drying and solid-state polymerization. However, after the production of a polyamide as a raw material due to problems with solid-phase drying or solid-state polymerization equipment, etc., if solid-phase drying or solid-phase polymerization cannot be performed quickly, solidification again after solid-phase drying or solid-phase polymerization for reasons such as moisture absorption. When performing phase drying, when performing solid phase polymerization in order to further increase the molecular weight after solid phase drying or solid phase polymerization, or manufacturing sites such as melt polymerization of polyamide as a raw material, and solid phase drying or solid phase polymerization sites When the polyamide as the raw material has to be stored for a long period of time, such as when they are separated from each other, it is difficult to sufficiently suppress the oxidative degradation only by the above measures.

Japanese Patent Application Laid-Open No. 2000-129119 discloses a method of spraying water on the surface of polyamide obtained by melt polymerization. This is intended to prevent excess moisture from covering the polyamide surface and coming into contact with air by increasing the moisture content. However, in order to maintain the effect, it is necessary to maintain a water film, and it is necessary to provide the polyamide with water above the saturated moisture of the polyamide, which is not practical for long-term storage. In addition, such excessive water imposes a very high heat load and an extended process time in the subsequent solid-phase drying or solid-state polymerization process, which is an industrially disadvantageous operation.

It is also known to add phosphoric acid, phosphorous acid, hypophosphorous acid, and salts and compounds thereof as stabilizers to polyamide in order to suppress thermal deterioration and oxidative deterioration (Japanese Patent Publication No. 48-23199). ). However, even when these stabilizers are added, coloring during solid phase drying or solid phase polymerization cannot be sufficiently suppressed. Further, since these stabilizers also act as a polymerization accelerator for polyamide, it is not preferable to add an amount of stabilizer more than necessary for controlling the degree of polymerization.

An object of the present invention is to provide a solid phase polymerization method of polyamide with little increase in yellowness.

As a result of diligent investigations to solve the above problems, the inventors of the present invention have increased the yellowness by solid-phase polymerization after the raw material polyamide obtained by polycondensation by melt polymerization is stored under specific conditions. The inventors have found that a small amount of solid phase polymerized polyamide can be obtained, and completed the present invention.

That is, the present invention is a method in which a raw material polyamide obtained by polycondensation by melt polymerization of a diamine containing 70 mol% or more of xylylenediamine and a dicarboxylic acid containing 70 mol% or more of adipic acid is once stored and then further solidified by solid phase polymerization. In the method of increasing the degree of polymerization, the raw material polyamide is stored in air, in a light-shielded state, at a relative humidity of 5% RH or less and at a temperature less than Tg (the glass transition point of the raw material polyamide) and stored after obtaining the raw material polyamide. The invention relates to a solid phase polymerization method for polyamide, characterized in that solid phase polymerization is carried out within 20 days including the number of days.

By the solid phase polymerization method of polyamide according to the present invention, a solid phase polymerized polyamide having a low yellowness can be produced.

The present invention is described in detail below. The polyamide used as a raw material for solid phase drying or solid phase polymerization in the present invention is a polyamide obtained from a diamine containing 70 mol% or more of xylylenediamine and a dicarboxylic acid containing 70 mol% or more of adipic acid. In addition to using the polyamide obtained by melt polymerization as a raw material, there may be a case where a polyamide solid-phase dried or solid-phase polymerized after melt polymerization is used as a raw material for the purpose of re-drying or further increasing the molecular weight. Examples of xylylenediamine include metaxylylenediamine, paraxylylenediamine, and orthoxylylenediamine, which may include one or more of these.

Polyamide-forming compounds other than xylylenediamine and adipic acid are not particularly limited, but lactams such as caprolactam, valerolactam, laurolactam, undecalactam; 1,1-aminoundecanoic acid, 1,2-aminododecanoic acid, etc. An aminocarboxylic acid of trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1, Diamines such as 2- (bisaminomethyl) cyclohexane, 1,3-bis (bisaminomethyl) cyclohexane, 1,4-bis (bisaminomethyl) cyclohexane, orthophenylenediamine, metaphenylenediamine, paraphenylenediamine; Haq acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, phthalic acid, isophthalic acid, terephthalic acid, may be mentioned dicarboxylic acids such as 2,6-naphthalene dicarboxylic acid.

The present invention relates to a polyamide obtained by polycondensation of a polyamide having a structural part relatively susceptible to thermal decomposition such as benzylmethylene, that is, a diamine containing 70 mol% or more of xylylenediamine and a dicarboxylic acid containing 70 mol% or more of adipic acid. The effect can be recognized. In addition, a more remarkable effect is recognized with respect to a polyamide obtained by polycondensation of a diamine containing 70 mol% or more of xylylenediamine, which is at least 70 mol% or more of xylylenediamine, and a dicarboxylic acid containing 70 mol% or more of adipic acid. be able to. Further, the present invention is based on the knowledge about the sorption phenomenon of oxygen to polyamide, and 70% of diamine and adipic acid containing 70 mol% or more of xylylenediamine having low oxygen permeability, that is, slow diffusion / dissolution rate. The effect can be recognized particularly for polyamides obtained by polycondensation of dicarboxylic acids containing at least mol%. Since polyamides other than the present invention, such as nylon 6 and nylon 66, have high oxygen permeability, that is, high diffusion and dissolution rates, it is practically very difficult to control the oxygen sorption amount. With the polyamides other than the invention, it is also easy to exclude oxygen once entering the inside of the polymer, so that the effect of the present invention is not recognized so much.

In order to accelerate the polymerization reaction in the melting and solid phase polymerization steps, a phosphorus compound may be added to the polyamide. As the phosphorus compound, phosphoric acid, phosphorous acid, hypophosphorous acid, and salts or ester compounds thereof can be used. These phosphorus compounds may be used alone or in combination. The method for adding these phosphorus compounds includes, but is not limited to, the present invention including a method for adding to a polyamide salt raw material, an aqueous nylon salt solution, a diamine or dicarboxylic acid, a method for adding during melt polymerization, and the like. .

When industrially producing a solid phase dried product and solid phase polymer of polyamide, after obtaining the polyamide as a raw material by melt polymerization, etc., solid phase drying or solid phase polymerization at the same or close factory site relatively quickly It is processed. When the rapid transition from the production of the raw material polyamide to the next solid-phase drying or solid-state polymerization treatment is surely performed, the knowledge of the present invention relating to the storage conditions of the raw material polyamide is not so useful. . However, after manufacturing the polyamide as a raw material due to problems such as solid-phase drying or solid-phase polymerization equipment, if solid-phase drying or solid-phase polymerization cannot be carried out quickly, again after solid-phase drying or solid-phase polymerization for reasons such as moisture absorption In the case of performing solid phase drying, or in the case of performing solid phase polymerization to further increase the molecular weight after solid phase drying or solid phase polymerization, the present invention provides effective knowledge. In addition, if the production site for melt polymerization of polyamide, which is the raw material, is separated from the solid phase drying or solid phase polymerization site, the case where consignment production is performed, or additives etc. with special equipment not available at the polyamide production site Due to diversification of market needs in recent years, globalization of production sites, etc., such as when solid phase drying or solid phase polymerization is added, the present invention provides very useful knowledge. That is, the present invention provides a particularly remarkable effect when solid-phase drying or solid-phase polymerization is carried out after 20 days or more after polymerization of the raw material polyamide.

In the present invention, it is desirable that the polyamide as a raw material is stored under a light-shielding condition that is not exposed to direct sunlight and at a temperature lower than Tg (glass transition point of the raw material polyamide). When light is applied during storage of the raw material polyamide, the yellowness of the solid phase drying and the solid phase polymer often increases even if the yellowness of the raw material polyamide does not increase. Even if no visible change appears, it is easily assumed that light affects the polymer molecule, such as radical generation. The temperature is preferably stored at a temperature lower than Tg for the purpose of avoiding coloring due to oxidative deterioration during storage. Further, when storing an amorphous polyamide, blocking such as fusion of the polyamide during storage can be prevented at a temperature lower than Tg.

The conditions under which the raw material polyamide is stored, that is, the conditions under which it is exposed, are closely dependent on the oxygen concentration sorbed to the raw material polyamide. Oxygen sorbed on the surface diffuses and dissolves toward the central part where the oxygen concentration is lower. It is not easy to eliminate oxygen introduced into the polymer or replace it with another gas. Therefore, in order to suppress an increase in yellowness due to oxidative degradation during solid phase drying or solid phase polymerization, it is necessary to suppress the amount of oxygen sorbed onto the polyamide as a raw material. The diffusion and dissolution phenomenon of low molecular weight substances such as oxygen molecules into the polymer is caused by the oxygen concentration, time and temperature, as well as the state of the polymer molecules, the degree of crystallinity, the moisture dissolved in the polymer, that is, the atmosphere exposed to the polyamide. It is affected by relative humidity. Therefore, after polymerizing a polyamide as a raw material for a solid phase dried body or a solid phase polymer, it is desirable to store under conditions satisfying the formula (A). Naturally, the storage conditions such as temperature and humidity are not constant and are expected to vary during the storage period, but the conditions can be defined by inputting an average value in the equation (A). In addition, when the average temperature of the day is 5 ° C or higher and the average humidity is 20% RH or more during the storage period, the average temperature is less than 5 ° C and the average humidity is less than 20% RH. It is preferable that the average temperature and the average humidity are input to the equation (A), values obtained from the equation (A) are added, and the cumulative value is determined.
0.8 × 10 ⁻⁹ ≧ P × D ^0.5 × exp {−6002 / T + (1-2 × C / 100) × (a × (h / 100−0.6) ² +0.62)} ... (A) Formula P: Oxygen partial pressure (MPa) of the atmosphere to which the polyamide is exposed
h: Relative humidity (% RH) of the atmosphere to which the polyamide is exposed
D: Storage time (days)
T: Temperature of the atmosphere to which the polyamide is exposed (K)
C: Crystallinity of raw material polyamide (%)
a: When h is less than 60% RH, 2.9 When h is 60% RH or more, 18.8

The temperature (T) of the atmosphere to which the polyamide used as the raw material is exposed is closely related to other storage conditions as can be seen from the formula (A). Storage at 50 ° C. or lower is desirable, more preferably 40 ° C. or lower.

The oxygen partial pressure (P) of the atmosphere to which the polyamide as the raw material is exposed is not related to other storage conditions as can be seen from the formula (A). In order to suppress, it is desirable to suppress to 0.01 MPa or less. In particular, in the case of solid phase drying or solid phase polymerization after polymerizing the polyamide as a raw material after several months or more, it is more desirable to suppress it to 0.001 MPa or less, and storage or storage container in a nitrogen atmosphere Treatment such as the presence of an oxygen scavenger is desirable.

As can be seen from the formula (A), the crystallinity (C) of the polyamide used as a raw material is closely related to other storage conditions, so it cannot be said unconditionally, but oxygen diffusion / dissolution does not occur in the crystalline region, Since it can be regarded as a barrier against oxygen diffusion / dissolution, the crystallinity is preferably 20% or more. More preferably, it is 25% or more. The degree of crystallinity is obtained from an exothermic peak caused by crystallization during measurement and an endothermic peak caused by melting, which are recognized in DSC measurement (differential scanning calorimetry).

Although the humidity (h) of the atmosphere to which the polyamide as the raw material is exposed is closely related to other storage conditions as can be seen from the formula (A), it cannot be generally stated, but oxygen diffusion in the polyamide of the present invention -Since the dissolution rate increases as the humidity approaches 100% RH and also approaches 0% RH, storage at 20% RH or more and 80% RH or less is desirable, more preferably 30% RH or more and 70%. RH or less.

The storage time (D) of the polyamide used as a raw material is not generally known because it is closely related to other storage conditions as can be seen from the formula (A), but within one year from the polymerization of the polyamide used as a raw material. Desirably, more preferably, within 3 months.

When the oxygen concentration in the atmosphere to which the polyamide is exposed is higher than the oxygen concentration inside the polyamide, the oxygen is absorbed by the polyamide, and the oxygen diffuses and dissolves toward the central portion where the oxygen concentration is low. On the other hand, when the oxygen concentration in the atmosphere to which the polyamide is exposed is lower than the oxygen concentration inside the polyamide, the oxygen sorbed on the polyamide surface desorbs from the polyamide and diffuses into the atmosphere. Further, oxygen diffused and dissolved in the polyamide also diffuses and dissolves toward the polyamide surface having a low concentration. Oxygen sorbed inside the polymer can be easily removed and replaced with other gases, but the oxygen sorbed on the surface can be decompressed, or can be relatively removed with other gases such as nitrogen and water. Can be easily replaced. Therefore, before solid-phase drying and solid-state polymerization, the oxygen concentration in the atmosphere to which the polyamide is exposed is made lower than the inside of the polyamide, so that the sorbed oxygen can be removed during storage and the solidity with low yellowness can be removed. Phase dried and solid state polymers can be obtained. This desorption is basically affected by the same factors as sorption. In other words, the oxygen concentration of the atmosphere to which the polyamide is exposed is lower than that inside the polyamide, and the time is increased, the temperature is increased, the crystallinity is decreased, and the relative humidity of the atmosphere to which the polyamide is exposed is 20% RH or less. Alternatively, by setting it to 80% RH or more, oxygen sorbed during storage can be efficiently removed. However, when the purpose is to desorb oxygen substantially sorbed on the surface, the influence of the polymer molecule state, that is, the crystallinity, and the relative humidity of the atmosphere to which the polyamide is exposed is negligible, and the temperature and time are controlled. Is effective. That is, when the polyamide is solid-phase dried or solid-phase polymerized, it is desirable to start the dehydration operation after exposing the polyamide to an atmosphere having an oxygen partial pressure of 1 kPa or less at a temperature of 120 ° C. or less for 2 hours or more. The oxygen partial pressure is more preferably an atmosphere of 0.5 kPa or less. When the temperature exceeds 120 ° C., the oxidative deterioration becomes severe, and therefore treatment at 120 ° C. or lower is desirable. It is efficient and desirable to perform this operation in the same apparatus that performs solid-phase drying or solid-state polymerization before performing solid-phase drying or solid-state polymerization. Excluding oxygen in the apparatus before solid-phase drying or solid-state polymerization is conventionally performed. However, oxidative degradation during solid-phase drying or solid-state polymerization is eliminated only by removing oxygen in the atmosphere. It is carried out from the viewpoint of prevention, and is not performed for the purpose of eliminating oxygen sorbed on the polyamide as in the present invention.

The solid-phase drying and solid-state polymerization apparatus used in the present invention is not particularly limited and can be performed batchwise or continuously as long as it has a structure that can be used as a heating apparatus. In the case of using a batch heating device, heating is generally performed from the heat transfer surface of the device and an inert gas such as nitrogen is circulated or processed under reduced pressure. Examples thereof include a rotating drum type heating device called a tumble dryer, a conical dryer, a rotary dryer and the like, and a conical heating device having a rotary blade inside called a nauta mixer. Also, when using a continuous heating device, it is called a vertical airflow dryer called a hopper dryer that processes under the flow of heated dry nitrogen, or a paddle dryer that heats from the heat transfer surface and distributes nitrogen. Horizontal heat transfer dryers.

The solid-phase drying conditions are preferably selected from the temperature and time conditions at which the water present in the polyamide is sufficiently removed at a temperature at which the polymerization reaction of the polyamide does not proceed. Is done. In order to suppress oxidative deterioration during drying, it is desirable to perform solid phase drying under a dry inert gas stream such as nitrogen or under reduced pressure. When performing under reduced pressure, it selects from the pressure reduction conditions of 40 kPa or less. The drying time is set so that the moisture in the polyamide reaches the target moisture content, but is preferably at least 30 minutes in the above temperature range and reduced pressure conditions.

The solid-phase polymerization temperature is preferably selected from a temperature range in which the polyamide polymerization reaction proceeds easily and lower than the melting point, and 140 ° C. or higher and 20 ° C. or lower than the melting point. In order to suppress oxidative degradation, it is desirable to perform solid phase polymerization under an inert gas stream such as nitrogen or under reduced pressure. When performing under reduced pressure, the pressure which can remove rapidly the condensed water produced | generated by a polymerization reaction is desirable, and it selects from the pressure reduction conditions of 40 kPa or less. The polymerization reaction time is set so that the polyamide reaches the target molecular weight, but at least 30 minutes or more is desirable in the above temperature range and reduced pressure conditions.

The present invention will be specifically described below with reference to examples and comparative examples. In addition, the measurement for evaluation in this invention was based on the following method.

(I) Yellowness (YI)
Using a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., Σ80 type), tristimulus values X, Y, and Z of the XYZ color system due to reflection of the sample were measured according to JIS-K7103 and determined from the following equation.
YI = 100 (1.28X-1.06Z) / Y
(B) Crystallinity degree DSC measurement (differential scanning calorimetry) was performed under a nitrogen stream at a temperature increase rate of 10 ° C./min using a DSC (3100 type) manufactured by Mac Science Co., Ltd. It was determined based on the heat of crystal fusion from the exothermic peak due to melting and the endothermic peak due to melting.

Example Pellets (crystallinity 5%) of polymetaxylylene adipamide (hereinafter referred to as nylon MXD6) synthesized by melt polymerization were placed in a constant temperature and humidity chamber at 5% RH and 23 ° C. in the light-shielded state. Stored for 3 to 45 days. Then, it was put into a batch type solid phase polymerization apparatus, the inside air was replaced with nitrogen, and the polymerization apparatus was heated from room temperature to start solid phase polymerization. When the pellet temperature reached 135 ° C., the pressure reduction operation was started and the pressure was reduced to 1.33 kPa or less. When the temperature was further increased and the pellet temperature reached 200 ° C., the temperature of the polymerization apparatus was stopped and the inside was cooled to normal pressure with nitrogen. After the pellet temperature dropped to 80 ° C., the solid phase polymer was taken out from the polymerization apparatus, and the yellowness (YI) was measured. The thermal history during these solid phase polymerizations was constant. Moreover, after obtaining melt-polymerized pellets, the difference from the YI of the solid phase polymer obtained by rapid solid phase polymerization as a reference is shown as FIG. 1 as ΔYI.

As is apparent from FIG. 1, when stored under conditions other than the storage conditions of the present invention, ΔYI increases from the time when the storage days exceed 20 days, and the yellowness of the resulting solid phase polymer rapidly deteriorates. I understand that.

Reference Examples 1-2, Comparative Examples 1-2
Nylon MXD6 pellets (crystallinity of 5%) synthesized by the same melt polymerization as in the examples were placed in a light and temperature controlled humidity chamber and stored under the conditions shown in Table 1. Thereafter, solid phase polymerization was performed in the same manner as in Examples, and the yellowness (YI) of the obtained solid phase polymer was measured. The results are shown in Table 1.

Reference example 3
Nylon MXD6 pellets synthesized by the same melt polymerization as in the examples were placed in a stainless steel sealed container together with an oxygen scavenger (manufactured by Mitsubishi Gas Chemical Co., Ltd .: Ageless SA) to keep the interior in an oxygen-free state. After storing under the conditions shown in Table 1, solid phase polymerization was performed in the same manner as in the Examples, and the yellowness (YI) of the obtained solid phase polymer was measured. The humidity in Table 1 is a value measured in a stainless steel sealed container at the end of storage. The results are shown in Table 1.

Reference example 4
Nylon MXD6 pellets synthesized by the same melt polymerization as in Examples were immediately heated to 140 ° C. under reduced pressure for 6 hours after melt polymerization to crystallize to obtain pellets having a crystallinity of 33%. After putting it in a thermostatic and humidity chamber in a light-shielded state and storing it under the conditions shown in Table 1, solid phase polymerization was performed in the same manner as in Reference Example 1, and the yellowness (YI) of the obtained solid phase polymer was measured. . Table 1 shows the difference from the YI of the solid phase polymer obtained by rapidly solid-phase polymerization after crystallizing the pellet as a reference, and ΔYI.

As is clear from Table 1, by controlling the oxygen partial pressure, temperature, relative humidity, storage time, and crystallinity of the pellet in the atmosphere to which nylon MXD6 is exposed, the yellowness of the resulting solid phase polymer is controlled. It can be seen that it can be lowered.

Comparative Example 3
Polyamide (hereinafter referred to as nylon 1,3BAC6) synthesized by melt polymerization from 1,3-bisaminomethylcyclohexane and adipic acid (hereinafter referred to as nylon 1,3BAC6) is placed in a thermostatic and humidity chamber in a light-shielded state. After storage under the conditions shown, solid phase polymerization was performed in the same manner as in the Examples, and the yellowness (YI) of the obtained solid phase polymer was measured. Table 2 shows the difference from the YI of the solid phase polymer obtained by melt polymerization to obtain pellets and then rapidly solid phase polymerization, and ΔYI.

As is clear from Table 2, it can be seen that the yellowness of the solid phase polymer of nylon 1,3BAC6 does not depend on the storage conditions of the raw material pellets. That is, the present invention works effectively in a polyamide having a diamine mainly composed of xylylenediamine as a constituent component.

Reference Example 5 and Comparative Example 4
Nylon MXD6 pellets (crystallinity = 5%) synthesized by the same method as in the examples were placed in a light-and-temperature-controlled constant temperature and humidity chamber, storage days = 36 days, oxygen partial pressure = 0.02 MPa, temperature = 23 ° C. , And humidity = 5% RH. Then, it put into the batch type solid phase polymerization apparatus, and the inside air was substituted with nitrogen (oxygen partial pressure = 0.5 kPa). Thereafter, the polymerization apparatus was heated from room temperature to initiate solid phase polymerization. When the pellet temperature reached 135 ° C., the pressure reduction operation was started and the pressure was reduced to 1.33 kPa or less. When the temperature was further increased and the pellet temperature reached 200 ° C., the temperature of the polymerization apparatus was stopped and the inside was cooled to normal pressure with nitrogen. After the pellet temperature dropped to 80 ° C., the solid phase polymer was taken out from the polymerization apparatus, and the yellowness (YI) was measured. In the above operation, the temperature rising time from putting the pellet into the solid phase polymerization apparatus and replacing the inside with nitrogen until the internal temperature reaches 120 ° C. is 2.5 hours (Reference Example 5), 30 minutes (comparison) The procedure was changed to Example 4). YI of the obtained solid phase polymer is shown in Table 3.

As is clear from Table 3, before solid-phase polymerization of nylon MXD6 pellets, the yellowness of the resulting solid-phase polymerization can be reduced by removing oxygen sorbed on the pellets under predetermined conditions. I understand.

FIG. 1 is a graph showing the relationship between ΔYI and the number of days until solid-phase polymerization (the number of storage days from polyamide production to solid-phase polymerization) in the examples.

Claims (7)

A method in which a raw material polyamide obtained by polycondensation of a diamine containing 70 mol% or more of xylylenediamine and a dicarboxylic acid containing 70 mol% or more of adipic acid by melt polymerization is once stored and then further increased in the degree of polymerization by solid phase polymerization The raw material polyamide is stored in air, in a light-shielded state, at a relative humidity of 5% RH or less and at a temperature lower than Tg (the glass transition point of the raw material polyamide), and 20 days including the storage days after obtaining the raw material polyamide. Solid phase polymerization of polyamide, characterized in that solid phase polymerization is carried out within. 2. The method for solid phase polymerization of polyamide according to claim 1, wherein at least 70 mol% of xylylenediamine is metaxylylenediamine. 3. The method for solid phase polymerization of polyamide according to claim 1 or 2, wherein the raw material polyamide has a crystallinity of 5% or less. The method for solid-phase polymerization of polyamide according to any one of claims 1 to 3, wherein a temperature lower than Tg (glass transition point of the starting polyamide) for storing the starting polyamide is room temperature. The method for solid phase polymerization of polyamide according to any one of claims 1 to 4, wherein the solid phase polymerization apparatus is a batch heating apparatus. The method for solid phase polymerization of polyamide according to any one of claims 1 to 4, wherein the solid phase polymerization apparatus is a continuous heating apparatus. The method for solid-phase polymerization of polyamide according to any one of claims 1 to 4, wherein the solid-phase polymerization is carried out under reduced pressure or / and nitrogen flow and at a temperature of 135 ° C or higher and 200 ° C or lower.

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