JP7809569B2 - Polyamide resin composition and polyamide molded article - Google Patents

Description

The present invention relates to a polyamide resin composition and a polyamide molded article.

Polyamide resin compositions have long been known as molding materials. They are widely used as materials for a variety of components, including automotive parts and electrical and electronic parts, and are known to produce molded articles with excellent mechanical strength and heat resistance.

For example, Patent Document 1 discloses a polyamide resin composition formed from a diamine component including 1,3-bis(aminomethyl)cyclohexane or the like, a dicarboxylic acid component including terephthalic acid or the like, and a lactam and/or ω-amino acid component, in which the diamine component and the dicarboxylic acid component are used in equimolar amounts. Patent Document 1 claims that the polyamide resin composition has an increased glass transition temperature, thereby improving mechanical properties such as tensile strength at high temperatures.

Japanese Patent Application Laid-Open No. 2017-075303

As mentioned above, polyamide resin compositions can be used as materials for automotive parts. For example, they can be used as materials for automotive exterior parts such as sunroofs and back doors. Such automotive exterior parts are painted before being attached to the vehicle body. During painting, the paint may be heated to a temperature of approximately 130°C to 200°C to cure more quickly and improve productivity. In this case, the exterior parts are required to have discoloration resistance so that they do not discolor even when heated at high temperatures (so that their visible light reflectance does not decrease). This is because discoloration of the exterior parts due to heating would result in poor appearance.

The inventors' investigations revealed that the polyamide resin composition described in Patent Document 1 discolored when molded products were heated at high temperatures, and the decrease in visible light reflectance could not be suppressed.

The present invention was made in consideration of the above circumstances, and aims to provide a polyamide resin composition and a polyamide molded article that can suppress a decrease in visible light reflectance even after the molded article is heated.

The present invention relates to the following polyamide resin composition and molded article thereof.

The polyamide resin composition of the present invention comprises a polyamide resin containing component units (a) derived from a dicarboxylic acid and component units (b) derived from a diamine, wherein the dicarboxylic acid-derived component units (a) include component units derived from an aromatic dicarboxylic acid or an alicyclic dicarboxylic acid, and the diamine-derived component units (b) include component units (b1) derived from an alkylene diamine having from 4 to 18 carbon atoms, which account for more than 50 mol % and not more than 90 mol % of the total number of moles of the diamine-derived component units (b), and component units (b2) derived from 1,3-bis(aminomethyl)cyclohexane, which account for from 10 mol % to less than 50 mol % of the total number of moles of the diamine-derived component units (b), and the molar ratio ((b)/(a)) of the content of the diamine-derived component units (b) to the content of the dicarboxylic acid-derived component units (a) is 1.005 or greater.

The molded article of the present invention is obtained by molding the above-mentioned polyamide resin composition.

The present invention provides a polyamide resin composition and a polyamide molded article that can suppress a decrease in visible light reflectance even after the molded article is heated.

Embodiments of the present invention are described in detail below. Note that the present invention is not limited to the following embodiments.

In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified.

1. Polyamide Resin Composition The polyamide resin composition of the present invention comprises a polyamide resin containing component units (a) derived from a dicarboxylic acid and component units (b) derived from a diamine, wherein the molar ratio ((b)/(a)) of the content of component units (b) derived from the diamine to the content of component units (a) derived from the dicarboxylic acid is 1.005 or more.

The inventors have discovered that by adjusting the content of component unit (a) derived from dicarboxylic acid contained in a polyamide resin and component unit (b) derived from a diamine including component unit (b2) derived from 1,3-bis(aminomethyl)cyclohexane to a predetermined molar ratio ((b)/(a)), it is possible to suppress a decrease in the visible light reflectance of a molded product of the polyamide resin (hereinafter simply referred to as the molded product) even after it has been heated.

When polymeric compounds such as resins are exposed to energy such as heat, their molecular chains are scissed, generating radicals. Oxygen in the air adds to these radicals, generating peroxide radicals (ROO.). These peroxide radicals then scisse other molecular chains, which in turn generate more radicals. This chain reaction of molecular chain scission causes the resin to oxidize and deteriorate, or form conjugated structures, resulting in discoloration of the molded product.

In contrast, the 1,3-bis(aminomethyl)cyclohexane used in the present invention has a bent structure, which increases the glass transition temperature (Tg) of the polyamide resin and raises the temperature at which the mobility of the polyamide resin's molecular chains (particularly the amorphous portions) becomes active. This limits the permeation of oxygen and radicals into the resin (particularly permeation through the amorphous portions) even at high temperatures, thereby suppressing oxidative degradation within the resin. This is thought to make the resin less susceptible to oxidative degradation and less likely to form a conjugated structure.

From the above, it is believed that by increasing the content of component unit (b) derived from diamine containing component unit (b2), oxidative degradation of the polyamide resin can be suppressed even when the molded body is heated, and the formation of a conjugated structure can be suppressed, thereby suppressing discoloration of the molded body due to heating (a decrease in the reflectance of visible light).

1-1. Polyamide Resin In the present invention, the polyamide resin contains a component unit (a) derived from a dicarboxylic acid and a component unit (b) derived from a diamine.

(Component unit (a1) derived from dicarboxylic acid)
The dicarboxylic acid-derived component unit (a1) includes a component unit derived from an aromatic dicarboxylic acid or an alicyclic dicarboxylic acid. This can increase the melting point (Tm) and crystallinity of the polyamide resin. When the melting point (Tm) of the polyamide resin is increased, the heat resistance of the molded body tends to be increased, and when the crystallinity of the polyamide resin is increased, the mechanical strength (tensile strength) of the molded body tends to be increased. Furthermore, since the component unit derived from an aromatic dicarboxylic acid or an alicyclic dicarboxylic acid has a cyclic structure, it is thought that molecular cleavage is less likely to occur when the molded body is heated.

Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalenedicarboxylic acid, and their esters. Examples of alicyclic dicarboxylic acids include cyclohexanedicarboxylic acid and its esters. From the viewpoint of enhancing the crystallinity of the polyamide resin, it is preferable that the dicarboxylic acid-derived component unit (a) contains a component unit derived from terephthalic acid, naphthalenedicarboxylic acid, or cyclohexanedicarboxylic acid. From the viewpoint of further suppressing molecular chain scission when the molded body is heated, it is more preferable that the component unit (a) contains a component unit derived from terephthalic acid or naphthalenedicarboxylic acid, and even more preferable that it contains a component unit derived from terephthalic acid. These component units have a resonance structure, which is thought to make molecular chain scission less likely to occur.

The content of component units derived from aromatic dicarboxylic acids or alicyclic dicarboxylic acids is preferably 50 mol% or more and 100 mol% or less, and more preferably 70 mol% or more and 100 mol% or less, relative to the total number of moles of component units (a) derived from dicarboxylic acids. A content of 50 mol% or more can further enhance the crystallinity of the polyamide resin.

When the dicarboxylic acid-derived component units (a) include component units (a1) derived from terephthalic acid, naphthalenedicarboxylic acid, or cyclohexanedicarboxylic acid, the content of these component units can be greater than 20 mol% and less than 100 mol%, preferably 45 mol% to 100 mol%, more preferably 50 mol% to 99 mol%, even more preferably 80 mol% to 99 mol%, and particularly preferably greater than 90 mol% to 99 mol%. Having the content within the above ranges can further enhance the crystallinity of the polyamide resin.

The dicarboxylic acid-derived component unit (a) may contain component units derived from dicarboxylic acids other than the above-mentioned component unit (a1), provided that the effects of the present invention are not impaired. Examples of such other dicarboxylic acids include component units (a2) derived from aromatic dicarboxylic acids other than the above-mentioned component unit (a1), and component units (a3) derived from aliphatic dicarboxylic acids having from 4 to 20 carbon atoms.

Examples of the other aromatic dicarboxylic acids include isophthalic acid and 2-methylterephthalic acid. Of these, isophthalic acid is preferred.

When the dicarboxylic acid-derived component unit (a) contains the other aromatic dicarboxylic acid-derived component unit (a2), the content of the component unit (a2) is preferably 1 mol % or more and 50 mol % or less, more preferably 1 mol % or more and 20 mol % or less, even more preferably 1 mol % or more and 10 mol % or less, and particularly preferably 1 mol % or more and 5 mol % or less, relative to the total number of moles of the dicarboxylic acid-derived component unit (a). Keeping the content below a certain level can further enhance the crystallinity of the polyamide resin.

The aliphatic dicarboxylic acid has 4 to 20 carbon atoms, preferably 6 to 12. Examples of such aliphatic dicarboxylic acids include adipic acid, 2-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, sebacic acid, and suberic acid. Of these, adipic acid and sebacic acid are preferred.

When the dicarboxylic acid-derived component unit (a) includes the aliphatic dicarboxylic acid-derived component unit (a3) having from 4 to 20 carbon atoms, the content of the component unit (a3) is preferably from 0 mol% to 40 mol% of the total number of moles of the dicarboxylic acid-derived component unit (a), more preferably from 0 mol% to 20 mol%, even more preferably from 0 mol% to 10 mol%, and particularly preferably from 0 mol% to 5 mol%. Keeping the content below a certain level further enhances the crystallinity of the polyamide resin.

In addition to the dicarboxylic acid-derived component units (a1), the polyamide resin of the present invention may further contain component units derived from tribasic or higher polycarboxylic acids, such as trimellitic acid or pyromellitic acid. The content of such polycarboxylic acid-derived component units can be 0 mol % or more and 5 mol % or less, based on the total number of moles of dicarboxylic acid-derived component units (a).

(Diamine-derived component unit (b))
The diamine-derived component unit (b) includes a component unit (b1) derived from an alkylenediamine having from 4 to 18 carbon atoms and a component unit (b2) derived from 1,3-bis(aminomethyl)cyclohexane.

When the polyamide resin contains component units (b1) derived from an alkylenediamine having from 4 to 18 carbon atoms, the crystallinity of the polyamide resin tends to be increased, and the flowability of the polyamide resin composition during injection molding and the tensile strength of the molded article tend to be improved.

Furthermore, the component unit (b2) derived from 1,3-bis(aminomethyl)cyclohexane reduces the mobility of the molecular chains of the polyamide resin. Therefore, by including the component unit (b2) in a polyamide resin, the glass transition temperature (Tg) of the polyamide resin can be made higher than that of a polyamide resin that does not contain the component unit (b2). Furthermore, because the component unit (b2) has a cyclic structure, scission of the molecular chains of the resin is less likely to occur even when the polyamide resin is left in a high-temperature environment for a long period of time, thereby improving the long-term heat resistance of the polyamide resin. For these reasons, it is believed that by including the component unit (b2) in a polyamide resin, the tensile strength of a molded article heated at high temperatures for a long period of time can be increased and that high tensile strength can be maintained for a long period of time.

Furthermore, as described above, the component unit (b2) is resistant to oxidative degradation and is resistant to the formation of conjugated structures, so that even after the molded body is heated, discoloration of the resin due to oxidative degradation can be suppressed, thereby suppressing a decrease in the reflectance of visible light. Furthermore, the component unit (b2) can increase the glass transition temperature, further suppressing the discoloration.

Furthermore, by including the component unit (b2) derived from 1,3-bis(aminomethyl)cyclohexane in the polyamide resin, the melting point (Tm) of the polyamide resin can be appropriately lowered compared to polyamide resins that do not contain the component unit (b2). As a result, polyamide resins that contain the component unit (b2) tend to have improved fluidity and moldability during injection molding.

The alkylenediamine has 4 or more and 18 or less carbon atoms, but from the viewpoint of suppressing a decrease in the glass transition temperature (Tg) of the polyamide resin, it preferably has 4 or more and 10 or less carbon atoms.

The component units (b1) derived from alkylenediamines having 4 to 18 carbon atoms preferably include component units derived from linear alkylenediamines or component units derived from branched alkylenediamines (alkylenediamines having side chains).

Examples of linear alkylenediamines include 1,4-diaminobutane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, and 1,12-diaminododecane. Only one type of linear alkylenediamine may be included, or two or more types may be included.

Examples of branched alkylenediamines include 2-methyl-1,5-diaminopentane, 2-methyl-1,6-diaminohexane, 2-methyl-1,7-diaminoheptane, 2-methyl-1,8-diaminooctane, 2-methyl-1,9-diaminononane, 2-methyl-1,10-diaminodecane, 2-methyl-1,11-diaminoundecane, etc. Only one type of branched alkylenediamine may be included, or two or more types may be included.

Of these, preferred linear or branched alkylenediamines are 1,4-diaminobutane, 1,6-diaminohexane, 1,9-diaminononane, 1,10-diaminodecane, 2-methyl-1,5-diaminopentane, and 2-methyl-1,8-diaminooctane, with 1,6-diaminohexane and 1,10-diaminodecane being more preferred.

From the viewpoint of enhancing the crystallinity of the resin, it is preferable that the above-mentioned component unit (b1) contains a component unit derived from a linear alkylenediamine.

The content of component units derived from linear alkylenediamine is preferably 30 mol% to 100 mol%, and more preferably 50 mol% to 80 mol%, relative to the total number of moles of component units (b1) derived from alkylenediamine having from 4 to 18 carbon atoms. When the content is above a certain level, the crystallinity of the polyamide resin is more likely to be enhanced.

The content of component units derived from branched alkylenediamine is preferably 0 mol % or more and 80 mol % or less, and more preferably 0 mol % or more and 50 mol % or less, relative to the total number of moles of component units (b1) derived from alkylenediamine having from 4 to 18 carbon atoms. When the content is within the above range, the crystallinity of the polyamide resin is more likely to be enhanced.

The content of component units (b1) derived from alkylenediamines having 4 to 18 carbon atoms is preferably greater than 50 mol% and less than 90 mol% of the total number of moles of component units (b) derived from diamines. A content greater than 50 mol% further increases the crystallinity of the polyamide resin, thereby improving the flowability of the resin during injection molding and the tensile strength of the molded article. A content of 90 mol% or less increases the content of component units (b2) derived from 1,3-bis(aminomethyl)cyclohexane. This increases the glass transition temperature (Tg) of the polyamide resin, thereby increasing and maintaining the tensile strength of the molded article after prolonged heating at high temperatures. Furthermore, the melting point (Tm) of the polyamide resin can be appropriately lowered, improving moldability and further suppressing the decrease in visible light reflectance after heating the molded article.

From the above perspective, the content of component units (b1) derived from alkylenediamine having from 4 to 18 carbon atoms is more preferably from 55 mol% to 85 mol% and even more preferably from 60 mol% to 80 mol% of the total number of moles of component units (b) derived from diamine.

The content of component units (b2) derived from 1,3-bis(aminomethyl)cyclohexane is preferably 10 mol% or more and less than 50 mol% of the total number of moles of component units (b) derived from diamine. A content of 10 mol% or more increases the glass transition temperature (Tg) of the polyamide resin, increasing and maintaining the tensile strength of the molded product after heating at high temperatures for a long period of time. It also moderately reduces the Tm of the polyamide resin, improving moldability. Furthermore, a content of 10 mol% or more further suppresses the decrease in visible light reflectance after heating the molded product.

When the above content is less than 50 mol%, the content of component units (b1) derived from alkylenediamine having 4 to 18 carbon atoms can be increased. This further increases the crystallinity of the polyamide resin, thereby improving the flowability of the resin during injection molding and the tensile strength of the molded body.

Furthermore, from the above viewpoint, the content of component units (b2) derived from 1,3-bis(aminomethyl)cyclohexane is more preferably 15 mol% or more and less than 45 mol%, even more preferably 20 mol% or more and 40 mol% or less, even more preferably 20 mol% or more and 38 mol% or less, and particularly preferably 20 mol% or more and 33 mol% or less, relative to the total number of moles of component units (b) derived from diamine.

The diamine-derived component unit (b) may further include a component unit (b3) derived from a diamine other than the above-mentioned component units (b1) and (b2), as long as the effects of the present invention are not impaired. Examples of such other diamines include aromatic diamines and alicyclic diamines other than 1,3-bis(aminomethyl)cyclohexane.

Examples of the aromatic diamines include metaxylylenediamine. Examples of the other alicyclic diamines include 1,4-diaminocyclohexane and 1,3-diaminocyclohexane.

The content of the component units (b3) derived from the other diamine can be, for example, 50 mol % or less relative to the total number of moles of component units (b) derived from the diamine.

The constituent units of polyamide resin and their ratios can be calculated from the charge ratios used when preparing the polyamide resin, or can be measured using NMR spectroscopy.

When measuring using ^1H NMR spectrum, for example, 30 mg of polyamide resin is dissolved in 0.5 mL of deuterated hexafluoroisopropanol (HFIP) to prepare a sample for NMR measurement. NMR measurement of the prepared sample is performed using a nuclear magnetic resonance spectrometer (ECA-500, manufactured by JEOL Ltd.), and the respective structural units of the polyamide resin and their ratios are calculated from the peak areas derived from hydrogen of each component constituting the polyamide resin in the obtained spectrum.

(Polyamide Resin Composition)
In the polyamide resin composition of the present invention, the molar ratio ((b)/(a)) of the content of the component unit (b) derived from diamine to the content of the component unit (a) derived from dicarboxylic acid is 1.005 or more. As described above, by having this molar ratio of 1.005 or more, it is possible to suppress a decrease in the reflectance of visible light even after the molded article is heated.

In addition, when the molar ratio is 1.005 or higher, the effect of the component unit (b2) derived from 1,3-bis(aminomethyl)cyclohexane in increasing the glass transition temperature (Tg) of the polyamide resin is more pronounced, and it is believed that the tensile strength of the molded body can be increased even after it has been heated at high temperatures for a long period of time.

From these perspectives, the molar ratio is preferably 1.010 or greater, more preferably 1.025 or greater, more preferably greater than 1.030, and even more preferably 1.040 or greater. Furthermore, a molar ratio of 1.010 or greater makes it easier to adjust the amount of terminal amino groups, described below, to a preferred range. There are no particular limitations on the upper limit of the molar ratio, but it is preferably 1.1 or less.

The above molar ratio can be calculated from the charge ratio when preparing the polyamide resin, or can be measured by the NMR method. The NMR method can be performed in the same manner as described above.

The amount of terminal carboxyl groups in the polyamide resin is preferably 100 mmol/kg or less. By ensuring that the amount of terminal carboxyl groups is 100 mmol/kg or less, the amount of terminal amino groups in the polyamide resin can be further increased. It is believed that the terminal amino groups react with peroxide radicals generated during the process of molecular chain scission to produce hydroxyperoxide (ROOH), thereby terminating the chain scission of the molecular chain. Therefore, it is believed that an increase in the amount of terminal amino groups makes it more difficult for the reflectance of visible light to decrease even after the molded body has been heated.

Modified articles of the polyamide resin composition can also be used as automotive components, such as the housing of a water pump that pumps coolant to cool the engine. Water pumps sometimes use antifreeze, such as long-life coolant (LLC), as coolant. When the molded article is exposed to LLC, hydrolysis of the polyamide resin can occur, reducing the tensile strength (LLC resistance) of the molded article. In contrast, by ensuring that the amount of terminal carboxyl groups in the polyamide resin is 100 mmol/kg or less, the amount of carboxyl groups, which have higher water absorption than amino groups, can be reduced, suppressing the promotion of hydrolysis. This improves the hydrolysis resistance and LLC resistance of the molded article.

From these perspectives, the amount of terminal carboxyl groups in the polyamide resin is more preferably 70 mmol/kg or less, even more preferably 50 mmol/kg or less, and even more preferably 30 mmol/kg or less. There are no particular limitations on the lower limit of the amount of terminal carboxyl groups, but it is preferably 1 mmol/kg or more.

The amount of terminal carboxyl groups can be measured, for example, using the NMR method. For example, 30 mg of polyamide resin is dissolved in 0.5 mL of deuterated hexafluoroisopropanol (HFIP) to prepare a sample for NMR measurement. NMR measurement is performed on the prepared sample using a nuclear magnetic resonance spectrometer (ECA-500, manufactured by JEOL Ltd.). The molecular weight of the polyamide resin is calculated from the peak areas derived from hydrogen atoms of each component constituting the polyamide resin in the obtained spectrum. The amount of terminal carboxyl groups ([COOH], unit: mmol/kg) is then calculated using the peak areas derived from hydrogen atoms specific to the terminal carboxyl groups and the molecular weight value.

The amount of terminal amino groups in the polyamide resin is preferably 40 mmol/kg or more. Having a terminal amino group amount of 40 mmol/kg or more makes it easier to stop the chain scission of molecular chains that occurs when a molded body is heated, and can further suppress a decrease in visible light reflectance and a decrease in tensile strength after heating. From the above perspective, the amount of terminal amino groups is more preferably 60 mmol/kg or more, and even more preferably 80 mmol/kg or more. There is no particular upper limit to the amount of terminal amino groups, but it is preferably 200 mmol/kg or less.

The amount of terminal amino groups can be measured, for example, by the following method.

1 g of polyamide resin is dissolved in 35 mL of phenol and mixed with 2 mL of methanol to prepare a sample solution. Using thymol blue as an indicator, the sample solution is titrated with 0.01 N hydrochloric acid solution using a potentiometric titrator (Metrohm) until the solution turns from blue to yellow, and the amount of terminal amino groups ([NH ₂ ], unit: mmol/kg) is measured.

The total amount of terminal carboxyl groups and terminal amino groups in the polyamide resin is preferably 130 mmol/kg or less. When the total amount of terminal carboxyl groups and terminal amino groups is 130 mmol/kg or less, hydrolysis of the polyamide resin is less likely to occur, and hydrolysis resistance and LLC resistance can be further improved. From the above perspective, the total amount of terminal carboxyl groups and terminal amino groups is more preferably 120 mmol/kg or less, and even more preferably 115 mmol/kg or less. There are no particular restrictions on the lower limit of the total amount, but it is preferably 30 mmol/kg or more.

The ratio of the amount of terminal amino groups to the amount of terminal carboxyl groups in the polyamide resin is preferably greater than 1.0. A ratio greater than 1.0 increases the amount of terminal amino groups, making it easier to stop the chain scission of molecular chains that occurs when the molded body is heated, and further suppresses a decrease in visible light reflectance and a decrease in tensile strength after heating. From the above perspective, a ratio of 1.2 or greater is more preferable, and 3 or greater is even more preferable. There is no particular upper limit to the ratio, but 100 or less is preferred.

The amount of terminal carboxyl groups and the amount of terminal amino groups can be adjusted to fall within the above range by adjusting the molar ratio ((b)/(a)) or by using a terminal blocking agent during synthesis of the polyamide resin.

For example, if the molecular end is a carboxyl group, the end-capping agent is preferably a monoamine, and if the molecular end is an amino group, the end-capping agent is preferably a monocarboxylic acid.

Examples of monoamines include aliphatic monoamines such as methylamine, ethylamine, propylamine, and butylamine; alicyclic monoamines such as cyclohexylamine and dicyclohexylamine; and aromatic monoamines such as aniline and toluidine. Examples of monocarboxylic acids include aliphatic monocarboxylic acids having 2 to 30 carbon atoms such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecylic acid, myristic acid, palmitic acid, stearic acid, oleic acid, and linoleic acid; aromatic monocarboxylic acids such as benzoic acid, toluic acid, naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid, and phenylacetic acid; and alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid. Aromatic monocarboxylic acids and alicyclic monocarboxylic acids may have a substituent on the ring structure.

(Physical Properties)
The polyamide resin in the present invention can have a melting point (Tm) of 280°C or higher and 330°C or lower, as measured by a differential scanning calorimeter (DSC). When the melting point (Tm) is 280°C or higher, the heat resistance of the polyamide resin composition and the molded article is less likely to be impaired. Furthermore, when the melting point (Tm) is 330°C or lower, the polyamide resin composition can be easily molded without excessively increasing the molding temperature, thereby improving moldability. From the above viewpoint, the melting point (Tm) of the polyamide resin is more preferably 290°C or higher and 330°C or lower, and even more preferably 300°C or higher and 330°C or lower.

The polyamide resin may also have a glass transition temperature (Tg) of 135°C or higher and 180°C or lower, as measured by differential scanning calorimetry (DSC). A glass transition temperature (Tg) of 135°C or higher can increase the tensile strength of the polyamide resin composition and molded articles in high-temperature, high-humidity environments and maintain this strength for a longer period of time. A glass transition temperature (Tg) of 180°C or lower can improve the molding processability of the polyamide resin composition. From the above perspectives, it is more preferable that the glass transition temperature (Tg) of the polyamide resin be 140°C or higher and 170°C or lower.

The heat of fusion (ΔH) of the polyamide resin is preferably 10 mJ/mg or more. When the heat of fusion (ΔH) of the polyamide resin is 10 mJ/mg or more, the crystallinity is further enhanced, making it easier to improve the fluidity and tensile strength during injection molding. From this perspective, the heat of fusion (ΔH) is more preferably 15 mJ/mg or more, and even more preferably 20 mJ/mg or more. There is no particular upper limit for the heat of fusion (ΔH) of the crystalline polyamide resin, but it can be set to 90 mJ/mg or less in order to avoid impairing moldability.

The melting point (Tm), glass transition temperature (Tg), and heat of fusion (ΔH) of polyamide resin can be measured using a differential scanning calorimeter (DSC220C, manufactured by Seiko Instruments Inc.).

Specifically, approximately 5 mg of polyamide resin is sealed in a measuring aluminum pan and heated from room temperature to 350°C at 10°C/min. To completely melt the resin, it is held at 350°C for 3 minutes, then cooled to 30°C at 10°C/min. After leaving it at 30°C for 5 minutes, it is heated a second time to 350°C at 10°C/min. The temperature (°C) of the endothermic peak during this second heating is taken as the melting point (Tm) of the polyamide resin, and the inflection point corresponding to the glass transition is taken as the glass transition temperature (Tg). The heat of fusion (ΔH) is determined from the area of the endothermic peak during melting during the first heating process, in accordance with JIS K7122:2012.

The melting point (Tm), glass transition temperature (Tg), and heat of fusion (ΔH) of the polyamide resin can be adjusted by the composition and content of the dicarboxylic acid-derived component unit (a) and the composition and content of the diamine-derived component unit (b).

The intrinsic viscosity [η] of the polyamide resin, measured in concentrated sulfuric acid at 25°C, is preferably 0.7 dl/g or more and 1.3 dl/g or less, and more preferably 0.75 dl/g or more and 1.1 dl/g or less. When the intrinsic viscosity [η] of polyamide resin (A) is 0.8 dl/g or more, the tensile strength of the polyamide resin is likely to be sufficiently increased. When the intrinsic viscosity [η] is 1.1 dl/g or less, the fluidity of the polyamide resin composition during molding is less likely to be impaired.

The intrinsic viscosity [η] of a polyamide resin can be measured as follows: 0.5 g of semi-aromatic polyamide resin (A) is dissolved in 50 ml of 96.5% sulfuric acid solution to prepare a sample solution. The flow time of the obtained solution at 25°C ± 0.05°C is measured using an Ubbelohde viscometer, and the intrinsic viscosity [η] is calculated based on the following formula:
[η]=ηSP/(C*(1+0.205ηSP))
[η]: Intrinsic viscosity (dl/g)
ηSP: specific viscosity C: sample concentration (g/dl)
t: number of seconds for the sample solution to flow down (seconds)
t ₀ : Number of seconds (seconds) for blank sulfuric acid to flow
ηSP=(t−t ₀ )/t ₀

Polyamide resins can be produced using methods similar to those used to produce known polyamide resins. For example, they can be produced by polycondensing dicarboxylic acids and diamines in a homogeneous solution. Specifically, as described in WO 03/085029, dicarboxylic acids and diamines are heated in the presence of a catalyst to obtain a low-order condensation product, and then a melt of this low-order condensation product is subjected to shear stress to cause polycondensation.

1-2. Reinforcing Material The polyamide resin composition of the present invention may contain a reinforcing material.

Reinforcing materials can impart higher tensile strength to polyamide resin compositions. Examples of reinforcing materials include fibrous reinforcing materials such as glass fiber, wollastonite, potassium titanate whiskers, calcium carbonate whiskers, aluminum borate whiskers, magnesium sulfate whiskers, zinc oxide whiskers, milled fiber, and cut fiber, as well as granular reinforcing materials. These may be contained in the polyamide resin composition alone or in combination. Of these, wollastonite, glass fiber, and potassium titanate whiskers are preferred because they tend to increase the tensile strength of the molded product, with wollastonite or glass fiber being more preferred.

The average fiber length of the fibrous reinforcing material can be, for example, 1 μm or more and 20 mm or less. From the perspective of further improving the moldability of the polyamide resin composition and the tensile strength and heat resistance of the resulting molded body, the average fiber length is preferably 5 μm or more and 10 mm or less. Furthermore, the aspect ratio of the fibrous reinforcing material can be, for example, 5 or more and 2000 or less, and preferably 30 or more and 600 or less.

The average fiber length and average fiber diameter of the fibrous reinforcing material can be measured by the following method.
1) The resin composition is dissolved in a hexafluoroisopropanol/chloroform solution (0.1/0.9% by volume), and then filtered to obtain a filtrate.
2) The filtered material obtained in 1) above is dispersed in water, and the fiber length (Li) and fiber diameter (di) of each of 300 randomly selected fibers are measured using an optical microscope (magnification: 50x). The number of fibers with a fiber length of Li is designated as qi, and the weight-average length (Lw) is calculated based on the following formula, which is the average fiber length of the fibrous reinforcing material.
Weight average length (Lw) = (Σqi × Li ² ) / (Σqi × Li)
Similarly, the number of fibers having a fiber diameter Di is defined as ri, and the weight average diameter (Dw) is calculated based on the following formula, and this is the average fiber diameter of the fibrous reinforcing material.
Weight average diameter (Dw) = (Σri×Di ² )/(Σri×Di)

1-3. Nucleating Agent The polyamide resin composition of the present invention may contain a nucleating agent.

Nucleating agents can further increase the crystallinity of the molded article. Examples of nucleating agents include metal salt compounds such as sodium 2,2-methylenebis(4,6-di-t-butylphenyl)phosphate, aluminum tris(p-t-butylbenzoate), and stearates; sorbitol compounds such as bis(p-methylbenzylidene)sorbitol and bis(4-ethylbenzylidene)sorbitol; and inorganic substances such as talc, calcium carbonate, and hydrotalcite. Of these, talc is preferred from the perspective of further increasing the crystallinity of the molded article. The polyamide resin composition may contain only one type of these nucleating agents, or two or more types.

1-4. Other Components The polyamide resin composition of the present invention may contain other known components as long as the effects of the present invention are not impaired. Examples of other components include lubricants, antioxidants, flame retardants, corrosion resistance improvers, anti-drip agents, ion scavengers, elastomers (rubbers), antistatic agents, mold release agents, heat stabilizers (lactone compounds, vitamin E compounds, hydroquinones, copper halides, iodine compounds, etc.), light stabilizers (benzotriazoles, triazines, benzophenones, benzoates, hindered amines, oxanilides, etc.), other polymers (polyolefins, olefin copolymers such as ethylene-propylene copolymers and ethylene-1-butene copolymers, olefin copolymers such as propylene-1-butene copolymers, polystyrene, polyamides, polycarbonates, polyacetals, polysulfones, polyphenylene oxides, fluororesins, silicone resins, and LCPs).

Examples of lubricants include metal salts of hydroxycarboxylic acids and metal salts of fatty acids, such as metal salts of higher fatty acids.

The hydroxycarboxylic acid constituting the hydroxycarboxylic acid metal salt may be an aliphatic hydroxycarboxylic acid or an aromatic hydroxycarboxylic acid. Examples of the aliphatic hydroxycarboxylic acid include aliphatic hydroxycarboxylic acids having 10 to 30 carbon atoms, such as α-hydroxymyristic acid, α-hydroxypalmitic acid, α-hydroxystearic acid, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid, α-hydroxytetraeicosanoic acid, α-hydroxyhexaeicosanoic acid, α-hydroxyoctaeicosanoic acid, α-hydroxytriacontanoic acid, β-hydroxymyristic acid, 10-hydroxydecanoic acid, 15-hydroxypentadecanoic acid, 16-hydroxyhexadecanoic acid, 12-hydroxystearic acid, and ricinoleic acid. Examples of the aromatic hydroxycarboxylic acid include salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, gallic acid, mandelic acid, and trovic acid.

Examples of metals that make up the above metal oxycarboxylic acid salts include alkali metals such as lithium, and alkaline earth metals such as magnesium, calcium, and barium.

Of these, the metal oxycarboxylic acid salt is preferably a metal salt of 12-hydroxystearic acid, with magnesium 12-hydroxystearate and calcium 12-hydroxystearate being more preferred.

Examples of higher fatty acids that make up the above-mentioned higher fatty acid metal salts include higher fatty acids having 15 to 30 carbon atoms, such as stearic acid, oleic acid, behenic acid, behenic acid, and montanic acid.

Examples of metals that make up the above higher fatty acid metal salts include calcium, magnesium, barium, lithium, aluminum, zinc, sodium, and potassium.

Of these, the higher fatty acid metal salts are preferably calcium stearate, magnesium stearate, barium stearate, calcium behenate, sodium montanate, calcium montanate, etc.

Examples of antioxidants include phosphorus-based antioxidants, phenol-based antioxidants, amine-based antioxidants, and sulfur-based antioxidants. By including an antioxidant in the polyamide resin composition, oxidative degradation during heating can be more adequately suppressed, and a decrease in visible light reflectance and tensile strength after heating can be more adequately suppressed.

Examples of phosphorus-based antioxidants include 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, triphenyl phosphite, 2-ethylhexyl acid phosphate, dilauryl phosphite, tri-iso-octyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite, trilauryl phosphite, trilauryl-di-thiophosphite, trilauryl-tri-thiophosphite, trisnonylphenyl phosphite, distearyl pentaerythritol diphosphite, tris(mononylphenyl) phosphite, tris(dinonylphenyl) phosphite, trioctadecyl phosphite, 1,1,3-tris(2-methyl-di-tridecylphosphite-5-tert-butylphenyl)butane, 4,4'-butylidene-bis(3-methyl-6-tert-butyl)tridecyl sil phosphite, 4,4'-butylidene-bis(3-methyl-6-tert-butyl-di-tridecyl)phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite, tetrakis(2,4-di-tert-butylphenyl)4,4'-bisphenylene diphosphite, distearyl pentaerythritol diphosphite, tridecyl phosphite, tristearyl phosphite, 2,2'-methylenebis(4,6-di-tert-butylphenyl)octyl phosphite, sorbitol-tris-phosphite-distearyl-mono-C30-diol ester and bis(2,4,6-tri-tert-butylphenyl)pentaerythritol diphosphite. Among these are pentaerythritol-diphosphite-based phosphorus antioxidants such as bis(2,4-di-tert-butylphenyl)pentaerythritol-diphosphite and bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-diphosphite, as well as tetrakis(2,4-di-tert-butylphenyl)4,4'-bisphenylene diphosphite.

Examples of phenolic antioxidants include 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyl]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, 2,6-di-tert-butyl-p-cresol, 2,4,6-tri-tert-butylphenol, n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenol)propionate, styrenated phenol, 4-hydroxy-methyl-2,6-di-tert-butyl ethylphenol, 2,5-di-tert-butyl-hydroquinone, cyclohexylphenol, butylhydroxyanisole, 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol), 2,2'-methylene-bis-(4-ethyl-6-tert-butylphenol), 4,4'-iso-propylidenebisphenol, 4,4'-butylidene-bis(3-methyl-6-tert-butylphenol), 1,1-bis-(4-hydroxy-phenyl)cyclohexane, 4,4'-methylene-bis-(2,6-di- tert-butylphenol), 2,6-bis(2'-hydroxy-3'-tert-butyl-5'-methylmethylbenzyl)4-methyl-phenol, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butyl-phenyl)butane, 1,3,5-tris-methyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxy-benzyl)benzene, tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-tert -butyl-4-hydroxyphenyl)isocyanurate, tris[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl-oxyethyl]isocyanate, 4,4'-thiobis(3-methyl-6-tert-butylphenol), 2,2'-thiobis(4-methyl-6-tert-butylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol), and N,N'-hexamethylenebis(3,5-di-tert-butylphenol-4-hydroxycinnamamide).

Examples of amine antioxidants include 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, phenyl-α-naphthylamine, phenyl-β-naphthylamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-β-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, aldol-α-naphthylamine, 2,2,4-trimethyl-1,2-dihydroquinone polymer, and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline.

Examples of sulfur-based antioxidants include thiobis(β-naphthol), thiobis(N-phenyl-β-naphthylamine), 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, dodecyl mercaptan, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, nickel dibutyldithiocarbamate, nickel isopropyl xanthate, dilauryl thiodipropionate, and distearyl thiodipropionate.

1-5. Composition of Polyamide Resin Composition The content of the above-described polyamide resin is preferably 20% by mass or more and 100% by mass or less, more preferably 20% by mass or more and 95% by mass or less, and even more preferably 30% by mass or more and 80% by mass or less, based on the total mass of the polyamide resin composition.

When the polyamide resin composition contains a reinforcing material, the content of the reinforcing material is not particularly limited, but can be, for example, from 15% to 70% by mass, and preferably from 20% to 50% by mass, relative to the total mass of the polyamide resin composition. When the content is within the above range, the tensile strength of the polyamide resin composition can be further increased.

When the polyamide resin composition contains a nucleating agent, the content of the nucleating agent is preferably 0.1 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.1 parts by mass or more and 3.0 parts by mass or less, relative to the total mass of the polyamide resin composition. When the content of the nucleating agent is within the above range, it is easy to sufficiently increase the crystallinity of the molded body, and the tensile strength of the molded body can be further increased.

1-6. Physical Properties of Polyamide Resin Composition The polyamide resin composition preferably exhibits a change in reflectance, expressed as the difference between the visible light reflectance of a molded article and the visible light reflectance of the molded article heated at 160°C for 2 hours, of 5% or less, more preferably 4% or less, and even more preferably 3% or less.

The above reflectance can be determined, for example, using a spectrophotometer (CM3500d, manufactured by Konica Minolta, Inc.) to measure the reflectance in the wavelength range of 360 nm to 740 nm, with the reflectance at a wavelength of 540 nm being used as a representative value.

The method for heating the molded body is not particularly limited, and it can be heated, for example, using an oven, etc.

The polyamide resin composition of the present invention can be produced by any method, for example, by a step of mixing the polyamide resin and, if necessary, other components, followed by melt-kneading, and, after the mixing and melt-kneading, a step of further granulating or pulverizing, if necessary.

The mixing method can be any known method, such as a Henschel mixer, V blender, ribbon blender, or tumbler blender.

The melt-kneading method can be any known method, such as using a single-screw extruder, multi-screw extruder, kneader, Banbury mixer, etc.

The granulation or pulverization method can be any known method, for example, granulation or pulverization can be performed using a pelletizer.

2. Polyamide Molded Article The polyamide molded article of the present invention is obtained by molding the polyamide resin composition of the present invention.

In other words, the polyamide resin composition prepared as described above can be used to produce molded articles of the desired shape by conventional melt molding methods, such as compression molding, injection molding, or extrusion molding.

For example, the polyamide resin composition of the present invention can be placed in a molten state in an injection molding machine whose cylinder temperature is adjusted to a temperature above the melting point of the polyamide resin, for example, approximately 300°C to 350°C, and then introduced into a mold of a predetermined shape to produce a molded article.

The shape of the molded article produced using the polyamide resin composition of the present invention is not particularly limited, and various shapes can be used depending on the application.

Molded articles of the polyamide resin composition of the present invention can be used in a variety of applications. Examples of such applications include automotive exterior parts such as radiator grilles, rear spoilers, wheel covers, hubcaps, cowl vent grilles, air outlet louvers, air scoops, hood bulges, sunroofs, sunroof rails, fenders, and tailgates; cylinder head covers, engine mounts, air intake manifolds, throttle bodies, air intake pipes, radiator tanks, radiator supports, water pump housings such as water pumps, water pump inlets, and water pump outlets; thermostat housings such as water jacket spacers and thermostat housings; automotive engine compartment parts such as cooling fans, fan shrouds, oil pans, oil filter housings, oil filler caps, oil level gauges, oil pumps, timing belts, timing belt covers, engine covers, and turbo-related parts; fuel caps, fuel filler tubes, automotive fuel tanks, fuel sender modules, fuel cut-off valves, quick connectors, and canisters. automotive fuel system parts such as fuel delivery pipes and fuel filler necks; automotive drive system parts such as shift lever housings and propeller shafts, automotive chassis parts such as stabilizer bar linkage rods and engine mount brackets; automotive functional parts such as window regulators, door locks, door handles, outside door mirror stays, wipers and parts, accelerator pedals, pedal modules, joints, plastic screws, nuts, bushings, seal rings, bearings, bearing retainers, gears and actuators; automotive electronic parts such as wire harness connectors, relay blocks, sensor housings, fuse parts, encapsulations, ignition coils and distributor caps, and high-voltage automotive electrical parts; general-purpose equipment fuel system parts such as fuel tanks for general-purpose equipment (brush cutters, lawn mowers and chainsaws), electrical and electronic parts such as connectors and LED reflectors; building materials, industrial equipment parts, and various housing or exterior parts such as small housings (including housings for personal computers and mobile phones) and exterior molded products.

In particular, the polyamide resin composition of the present invention can suppress a decrease in visible light reflectance and prevent discoloration even after the molded product is heated, making it suitable for use in automotive components, particularly automotive exterior parts such as back doors that require painting. In addition, the resin composition of the present invention can be suitable for use in automotive electronics parts, electrical and electronic parts, industrial equipment parts, and electrical equipment parts such as housings or exterior parts for electrical equipment.

The present invention will be specifically explained below with reference to examples, but the scope of the present invention is not limited to the description of the examples.

1. Constituent Materials 1-1. Synthesis of Polyamide Resin (Synthesis Example 1)
259.5 g (1562.0 mmol) of terephthalic acid, 123.2 g (1060.2 mmol) of 1,6-diaminohexane, 81.3 g (571.6 mmol) of 1,3-bis(aminomethyl)cyclohexane, 0.37 g (3.49 mmol) of sodium hypophosphite monohydrate as a catalyst, and 81.8 g of distilled water were placed in a 1 L autoclave and purged with nitrogen. Stirring was started at 190 ° C, and the internal temperature was raised to 250 ° C over 3 hours. At this time, the internal pressure of the autoclave was raised to 3.0 MPa. After continuing the reaction for 1 hour, the low-order condensate was discharged into the atmosphere from a spray nozzle installed at the bottom of the autoclave and extracted. Thereafter, the low-order condensate was cooled to room temperature, pulverized in a pulverizer to a particle size of 1.5 mm or less, and dried at 110 ° C for 24 hours.

Next, this low condensate was placed in a tray-type solid-state polymerization reactor, purged with nitrogen, and heated to 215°C over approximately 1 hour and 30 minutes. The reaction was then allowed to proceed for 1 hour and 30 minutes, after which the temperature was lowered to room temperature. The resulting prepolymer was melt-polymerized using a twin-screw extruder with a screw diameter of 30 mm and L/D = 36 at a barrel setting temperature of 330°C, a screw rotation speed of 200 rpm, and a resin feed rate of 6 kg/h to obtain polyamide resin 1. The resulting polyamide resin 1 had an intrinsic viscosity [η] of 0.9, a terminal amino group content of 70 mmol/kg, a terminal carboxylic acid content of 40 mmol/kg, a melting point (Tm) of 320°C, a glass transition temperature (Tg) of 156°C, and a heat of fusion ΔH of 48 J/g. The molar ratio of the content of diamine-derived component units (b) to the content of dicarboxylic acid-derived component units (a) was 1.045.

(Synthesis Example 2)
Polyamide resin 2 was obtained in the same manner as in Synthesis Example 1, except that the amount of terephthalic acid added to the autoclave was 259.5 g (1,562.0 mmol), the amount of 1,6-diaminohexane was 124.4 g (1,070.6 mmol), and the amount of 1,3-bis(aminomethyl)cyclohexane was 82.1 g (577.3 mmol). The intrinsic viscosity [η] of the resulting polyamide resin 2 was 0.9, the amount of terminal amino groups was 100 mmol/kg, and the amount of terminal carboxylic acid was less than 20 mmol/kg, making it unmeasurable. The melting point (Tm) was 320°C, the glass transition temperature (Tg) was 156°C, and the heat of fusion ΔH was 48 J/g. The molar ratio of the content of diamine-derived component units (b) to the content of dicarboxylic acid-derived component units (a) was 1.055.

(Synthesis Example 3)
Polyamide resin 3 was obtained in the same manner as in Synthesis Example 1, except that the amount of terephthalic acid added to the autoclave was 259.5 g (1,562.0 mmol), the amount of 1,6-diaminohexane was 118.9 g (1,023.2 mmol), and the amount of 1,3-bis(aminomethyl)cyclohexane was 78.4 g (551.3 mmol). The intrinsic viscosity [η] of the obtained polyamide resin 3 was 0.9, and the amount of terminal amino groups was less than 20 mmol/kg and therefore unmeasurable. The amount of terminal carboxylic acid was 100 mmol/kg, the melting point (Tm) was 320°C, the glass transition temperature (Tg) was 156°C, and the heat of fusion ΔH was 48 J/gJ/g. The molar ratio of the content of diamine-derived component units (b) to the content of dicarboxylic acid-derived component units (a) was 1.008.

(Synthesis Example 4)
Polyamide resin 4 was obtained in the same manner as in Synthesis Example 1, except that the amount of terephthalic acid added to the autoclave was 259.5 g (1,562.0 mmol), the amount of 1,6-diaminohexane was 118.0 g (1,015.5 mmol), and the amount of 1,3-bis(aminomethyl)cyclohexane was 77.8 g (547.1 mmol). The intrinsic viscosity [η] of the obtained polyamide resin 3 was 0.8, and the amount of terminal amino groups was less than 20 mmol/kg and therefore unmeasurable. The amount of terminal carboxylic acid was 120 mmol/kg, the melting point (Tm) was 320°C, the glass transition temperature (Tg) was 156°C, and the heat of fusion ΔH was 48 J/g. The molar ratio of the content of component units (b) derived from diamine to the content of component units (a) derived from dicarboxylic acid was 1.000.

(Polyamide resin 5)
Nylon 6 (Amilan CM1017, manufactured by Toray Industries, Inc.) was used. The melting point Tm of polyamide resin 5 was 225°C.

The intrinsic viscosity [η], terminal amino group content, terminal carboxyl group content, melting point (Tm), glass transition temperature (Tg), and heat of fusion ΔH of polyamide resins 1 to 4 were measured using the following methods.

(Intrinsic viscosity [η])
0.5 g of polyamide resin was dissolved in 50 ml of 96.5% sulfuric acid solution. The flow time of the obtained solution was measured using an Ubbelohde viscometer at 25°C ± 0.05°C. The intrinsic viscosity was then calculated based on the following formula:
[η]=ηSP/(C(1+0.205ηSP))
[η]: Intrinsic viscosity (dl/g)
ηSP: specific viscosity C: sample concentration (g/dl)
ηSP=(t−t ₀ )/t ₀
t: number of seconds for the sample solution to flow down (seconds)
t ₀ : Number of seconds (seconds) for blank sulfuric acid to flow

(Amount of terminal amino groups)
1 g of polyamide resin was dissolved in 35 mL of phenol and mixed with 2 mL of methanol to prepare a sample solution. Using thymol blue as an indicator, the sample solution was titrated with 0.01 N hydrochloric acid solution using a potentiometric titrator (Metrohm) from blue to yellow, and the amount of terminal amino groups ([NH ₂ ], unit: mmol/kg) was measured.

(Amount of terminal carboxyl groups)
30 mg of polyamide resin was dissolved in 0.5 mL of deuterated hexafluoroisopropanol (HFIP) to prepare a sample for NMR measurement. NMR measurement of the sample was performed using a nuclear magnetic resonance spectrometer (ECA-500, manufactured by JEOL Ltd.), and the molecular weight of the polymer was calculated from the peak areas derived from hydrogen atoms of each component constituting the polyamide resin in the obtained spectrum. The amount of terminal carboxyl groups ([COOH], units: mmol/kg or less) was then calculated using the peak areas derived from hydrogen atoms specific to the terminal carboxyl groups and the molecular weight obtained above.

(Melting point (Tm), glass transition temperature (Tg), heat of fusion ΔH)
The melting point Tm, glass transition temperature (Tg), and heat of fusion ΔH of the polyamide resin were measured using a differential scanning calorimeter (DSC220C, manufactured by Seiko Instruments Inc.) as follows.

Approximately 5 mg of polyamide resin was sealed in a measuring aluminum pan and heated from room temperature to 350°C at 10°C/min. To completely melt the resin, it was held at 350°C for 3 minutes and then cooled to 30°C at 10°C/min. After leaving it at 30°C for 5 minutes, it was heated a second time to 350°C at 10°C/min. The temperature (°C) of the endothermic peak during this second heating was taken as the melting point (Tm) of the polyamide resin, and the inflection point corresponding to the glass transition was taken as the glass transition temperature (Tg). The heat of fusion ΔH was calculated from the area of the endothermic peak during melting during the first heating process in accordance with JIS K7121:2012.

1-2. Crystal Nucleating Agent Talc (Hifiller #100, manufactured by Matsumura Sangyo Co., Ltd.) was used.

1-3. Reinforcing material Glass fiber (FT756D, manufactured by Owens Corning) was used.

2. Preparation of Polyamide Resin Composition The above materials were mixed in a tumbler blender in the composition ratios (units: parts by mass) shown in Table 1, and melt-kneaded using a 30 mmφ vented twin-screw extruder at a cylinder temperature of 300 to 335°C. The kneaded mixture was then extruded into strands and cooled in a water tank. The strands were then taken up in a pelletizer and cut to obtain pellets of a polyamide resin composition.

3. Evaluation The obtained polyamide resin compositions were evaluated according to the following criteria.

(Tensile strength (before high temperature treatment))
Each polyamide resin composition was injection molded under the following conditions to prepare a 3.2 mm thick ASTM-1 (dumbbell) test piece.
Molding machine: SG50M3, manufactured by Sumitomo Heavy Industries, Ltd.
Molding machine cylinder temperature: Melting point of polyamide resin + 10°C
Mold temperature: 120°C
The prepared test piece was left to stand for 24 hours in a nitrogen atmosphere at a temperature of 23°C in accordance with ASTM D638. Then, a tensile test was carried out in accordance with ASTM D638 in an atmosphere at a temperature of 23°C and a relative humidity of 50%, and the tensile strength was measured.

(Tensile strength (after high temperature treatment))
The test piece was left in an air circulating oven (temperature: 180° C.) for 1000 hours, then allowed to cool to 23° C., and subjected to a tensile test in accordance with ASTM D638 under an atmosphere of 23° C. and 50% relative humidity to measure the tensile strength.

(Tensile strength retention rate)
The tensile strength before the high-temperature treatment and the tensile strength after the high-temperature treatment were compared to calculate the ratio of the tensile strength after the high-temperature treatment to the tensile strength before the high-temperature treatment (tensile strength retention).

(Initial reflectance)
The obtained polyamide resin composition was injection molded using the molding machine described below under the molding conditions described below to prepare test pieces having a length of 30 mm, a width of 30 mm and a thickness of 0.5 mm.
Molding machine: SE50DU, manufactured by Sumitomo Heavy Industries, Ltd.
Molding machine cylinder temperature: Melting point (Tm) of polyamide resin + 10°C
Mold temperature: 150°C
The reflectance of the prepared test piece in the wavelength region of 360 nm to 740 nm was measured using a spectrophotometer (CM3500d, manufactured by Konica Minolta, Inc.) The reflectance at a wavelength of 540 nm was used as a representative value and was taken as the initial reflectance.

(Reflectance after heating)
The test piece whose initial reflectance had been measured was heated in an oven at 160° C. for 2 hours, and then the reflectance of the test piece was measured in the same manner as for the initial reflectance, and this was taken as the reflectance after heating.

(Change in reflectance)
The difference between the initial reflectance and the reflectance after heating (change in reflectance) was determined.

The evaluation results are shown in Table 1. Note that the composition values in Table 1 represent parts by mass.

As shown in Table 1, in Examples 1 to 3, in which the molar ratio of the content of diamine-derived component units (b) to the content of dicarboxylic acid-derived component units (a) was 1.005 or higher and the diamine component units (b) included component units (b2) derived from 1,3-bis(aminomethyl)cyclohexane, the change in visible light reflectance before and after heating the molded body was low, indicating that the decrease in visible light reflectance of the molded body after heating was suppressed. This is thought to be because the high content of diamine component units (b) including component units (b2) derived from 1,3-bis(aminomethyl)cyclohexane suppressed oxidative degradation and made it more difficult for conjugated structures to form.

In addition, in Examples 1 to 3, the tensile strength retention rate before and after high-temperature treatment was also good. This is thought to be because the component unit (b2) derived from 1,3-bis(aminomethyl)cyclohexane increased the glass transition temperature (Tg) of the polyamide resin, and because the content of the diamine component unit (b) was high, oxidative degradation of the polyamide resin was suppressed.

The polyamide resin composition of the present invention can suppress a decrease in the reflectance of visible light even after the molded product is heated. This is expected to improve the heat-induced discoloration resistance of molded products of the polyamide resin composition, broaden its applicability to various housings, in-vehicle components, and other applications, thereby contributing to the further spread of polyamide resin compositions.

Claims (12)

A polyamide resin composition comprising a polyamide resin containing a component unit (a) derived from a dicarboxylic acid and a component unit (b) derived from a diamine,
the component units (a) derived from the dicarboxylic acid contain component units derived from terephthalic acid in an amount of 70 mol % or more and 100 mol % or less, based on the total number of moles of the component units (a) derived from the dicarboxylic acid,
The diamine-derived component unit (b) is
component units (b1) derived from alkylenediamine having from 4 to 18 carbon atoms, in an amount of from 50 mol % to 90 mol % of the total number of moles of component units (b) derived from the diamine;
component units (b2) derived from 1,3-bis(aminomethyl)cyclohexane in an amount of 10 mol % or more and less than 50 mol % relative to the total number of moles of component units (b) derived from the diamine;
Including,
the molar ratio ((b)/(a)) of the content of the component unit (b) derived from the diamine to the content of the component unit (a) derived from the dicarboxylic acid is 1.005 or more;
Polyamide resin composition. the molar ratio ((b)/(a)) of the content of the component unit (b) derived from the diamine to the content of the component unit (a) derived from the dicarboxylic acid is greater than 1.030;
The polyamide resin composition according to claim 1. The amount of terminal carboxyl groups in the polyamide resin is 100 mmol/kg or less.
The polyamide resin composition according to claim 1 or 2. The amount of terminal amino groups in the polyamide resin is 40 mmol/kg or more.
The polyamide resin composition according to any one of claims 1 to 3. The ratio of the amount of terminal amino groups to the amount of terminal carboxyl groups of the polyamide resin is greater than 1.0.
The polyamide resin composition according to any one of claims 1 to 4. The polyamide resin composition has a reflectance change of 5% or less, which is expressed as the difference between the reflectance of a molded article of the polyamide resin composition at a wavelength of 540 nm and the reflectance of the molded article heated at 160°C for 2 hours.
The polyamide resin composition according to any one of claims 1 to 5. the content of the component units (b2) derived from the 1,3-bis(aminomethyl)cyclohexane is 15 mol % or more and less than 45 mol % based on the total number of moles of the component units (b) derived from the diamine;
The polyamide resin composition according to any one of claims 1 to 6. The component unit (b1) derived from an alkylenediamine having from 4 to 18 carbon atoms includes a component unit derived from a linear alkylenediamine or a branched alkylenediamine.
The polyamide resin composition according to any one of claims 1 to 7. The linear or branched alkylenediamine is a diamine selected from the group consisting of 1,4-diaminobutane, 1,6-diaminohexane, 1,9-diaminononane, 1,10-diaminodecane, 2-methyl-1,5-diaminopentane, and 2-methyl-1,8-diaminooctane.
The polyamide resin composition according to claim 8. The polyamide resin composition according to any one of claims 1 to 9 , which is a resin composition for an in-vehicle member. A molded product obtained by molding the polyamide resin composition according to any one of claims 1 to 10 .
Polyamide molding. Automotive components,
The polyamide molding according to claim 11 .