Polyamide and industrial pipe

Abstract

Provided are: a polyamide which has excellent heat resistance and flexibility and which has a higher molecular weight; a method for producing the polyamide; and an industrial pipe which contains the polyamide. The present invention pertains to a polyamide containing a unit comprising an aliphatic dicarboxylic acid (A) having 18-48 carbon atoms, a unit comprising an aromatic / aliphatic dicarboxylic acid (C) having 4-12 carbon atoms, and a unit comprising an aliphatic diamine (D) having 4-16 carbon atoms, the polyamide has a melt flow rate (MFR) of 20 g / 10 minutes or less as measured by the method described in JIS-K7210-1 under conditions of a temperature of 340 DEG C and a load of 1.2 kg.

Description

Technical Field

[0001] The present invention relates to a flexible polyamide and an industrial pipe. Background Art

[0002] Industrial pipes have traditionally been made of metals such as SUS, but are now being made of resins to reduce weight. Aliphatic PA11 and PA12 resins are widely used for these resins due to their excellent visibility through liquids and gases and excellent mechanical properties (Patent Document 1).

[0003] However, industrial pipes made of PA11 and PA12 resins can bleed out plasticizers, such as toluenesulfonic acid alkylamides, benzenesulfonic acid alkylamides, and alkyl hydroxybenzoates, which act as softening ingredients, onto the pipe surface during use in high-temperature environments or over time. This plasticizer bleed can cause contamination of the transported fluid (e.g., air, pure water, solvents), solidification, and thinning (weight loss) of the pipe body. Furthermore, it has been reported that this plasticizer scattering can adversely affect electronic equipment within factories.

[0004] In recent years, polyamide resins that are excellent in heat resistance, flexibility, and chemical resistance (particularly solvent resistance) and do not contain a plasticizer have been disclosed (Patent Document 2: random polyamide, Patent Document 3: block polyamide).

[0005] However, the polyamide resin described in Patent Document 2 has the following problem: since an aliphatic dicarboxylic acid (36C) having 18 to 44 carbon atoms, an aliphatic diamine (36N) having 18 to 44 carbon atoms, or an aliphatic diamine (DDA) having 4 to 16 carbon atoms is almost simultaneously added to an aromatic dicarboxylic acid (TPA) having 4 to 12 carbon atoms as a raw material for polymerization, the aromatic dicarboxylic acid with a high specific gravity precipitates during the feeding stage, resulting in uneven distribution, which disrupts the molar balance and makes it impossible to control the molecular weight.

[0006] On the other hand, the polyamide resin described in Patent Document 3 first reacts an aromatic dicarboxylic acid with 4 to 12 carbon atoms as the hard segment with an aliphatic diamine with 4 to 16 carbon atoms to form a prepolymer (salt). Subsequently, an aliphatic dicarboxylic acid with 18 to 44 carbon atoms and an aliphatic diamine with 18 to 44 carbon atoms are added in a certain ratio to form the soft segment and polymerize. This method produces a highly segmented polyamide with good heat resistance and flexibility. However, due to the long soft segment, it flows easily when melted and has difficulty increasing the melt viscosity. Therefore, it is not suitable for industrial pipes requiring high melt viscosity. In addition, depending on the molar ratio of the aromatic dicarboxylic acid with 4 to 12 carbon atoms to the aliphatic diamine with 4 to 16 carbon atoms as the hard segment, the formation of the prepolymer (salt) may be difficult.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-95802

[0010] Patent Document 2: International Publication No. 2020 / 085360 Pamphlet

[0011] Patent Document 3: International Publication No. 2022 / 054944 Pamphlet Summary of the Invention

[0012] Therefore, an object of the present invention is to solve the above-mentioned problems and provide a polyamide having excellent heat resistance and flexibility and having a sufficiently high molecular weight, a method for producing the same, and an industrial pipe comprising the polyamide.

[0013] Another object of the present invention is to provide a polyamide having a sufficiently high molecular weight that is excellent not only in heat resistance and flexibility but also in bleed resistance and heat-resistant flexibility, a method for producing the same, and an industrial pipe comprising the polyamide.

[0014] The present inventors have conducted intensive studies to solve the above-mentioned problems and, as a result, have found that the above-mentioned object can be achieved, thereby completing the present invention.

[0015] The gist of the present invention is as follows.

[0016] <1> A polyamide comprising: units consisting of an aliphatic dicarboxylic acid (A) having 18 to 48 carbon atoms, units consisting of an aromatic / aliphatic dicarboxylic acid (C) having 4 to 12 carbon atoms, and units consisting of an aliphatic diamine (D) having 4 to 16 carbon atoms,

[0017] The polyamide has a melt flow rate (MFR) of 20 g / 10 min or less as measured by the method described in JIS-K7210-1 under the conditions of a temperature of 340° C. and a load of 1.2 kg.

[0018] <2> The polyamide according to <1>, further comprising or not comprising a unit composed of an aliphatic diamine (B) having 18 to 48 carbon atoms,

[0019] The content of the unit composed of the aliphatic diamine (B) having 18 to 48 carbon atoms is 0 to 20% by mass based on the total monomer components constituting the polyamide.

[0020] <3> The polyamide according to <1> or <2>, wherein the polyamide has a flexural modulus at 23°C in accordance with ISO 178 of 100 to 600 MPa.

[0021] <4> The polyamide according to any one of <1> to <3>, wherein the content of the units composed of the aliphatic dicarboxylic acid (A) having 18 to 48 carbon atoms is 40 to 80% by mass based on the total monomer components constituting the polyamide.

[0022] The content of the unit composed of the aromatic / aliphatic dicarboxylic acid (C) having 4 to 12 carbon atoms is 5 to 50% by mass relative to the total monomer components constituting the polyamide.

[0023] The content of the unit composed of the aliphatic diamine (D) having 4 to 16 carbon atoms is 10 to 50% by mass based on the total monomer components constituting the polyamide.

[0024] <5> The polyamide according to any one of <1> to <4>, wherein the aromatic / aliphatic dicarboxylic acid (C) is one or more dicarboxylic acids selected from sebacic acid, azelaic acid, adipic acid, and aromatic dicarboxylic acids.

[0025] <6> The polyamide according to <2>, wherein the content of the units composed of the aliphatic dicarboxylic acid (A) is 42 to 56% by mass based on the total monomer components constituting the polyamide.

[0026] The content of the unit composed of the aliphatic diamine (B) is 0 to 15% by mass based on the total monomer components constituting the polyamide.

[0027] The content of the units composed of the aromatic / aliphatic dicarboxylic acid (C) is 9.5 to 20% by mass based on the total monomer components constituting the polyamide.

[0028] <7> The polyamide according to <6>, wherein the content of the units composed of the aliphatic dicarboxylic acid (A) is 45 to 55% by mass based on all monomer components constituting the polyamide.

[0029] <8> The polyamide according to any one of <1> to <7>, wherein the polyamide has a melting point of 300°C or higher.

[0030] <9> The polyamide according to any one of <1> to <8>, wherein the content of the plasticizer component is 0.5% by mass or less based on the polyamide.

[0031] <10> The polyamide according to any one of <1> to <9>, wherein the mass reduction rate due to heat treatment at 120°C for 72 hours is 5% by mass or less.

[0032] <11> The polyamide according to any one of <1> to <10>, which has a flexural modulus of elasticity at 23° C. of 100 to 600 MPa based on ISO 178 and a Shore D hardness of 30 to 75 (before heat treatment).

[0033] <12> The polyamide according to any one of <1> to <11>, wherein the increase or decrease in Shore D hardness before and after heat treatment of the polyamide is ±3,

[0034] The heat treatment was performed at 120° C. for 72 hours.

[0035] <13> A method for producing polyamide, comprising:

[0036] a first polymerization step of reacting an aliphatic dicarboxylic acid having 18 to 48 carbon atoms (A) with an aliphatic diamine having 4 to 16 carbon atoms (D); and

[0037] The second polymerization step is to further add an aromatic / aliphatic dicarboxylic acid (C) having 4 to 12 carbon atoms to carry out a reaction after the first polymerization step.

[0038] In the first polymerization step, the reaction may be carried out by further adding an aliphatic diamine (B) having 18 to 48 carbon atoms, or the reaction may be carried out without adding the aliphatic diamine (B) having 18 to 48 carbon atoms.

[0039] <14> The polyamide according to any one of <1> to <12>, produced according to the method for producing a polyamide according to <13>.

[0040] <15> An industrial pipe comprising the polyamide according to any one of <1> to <12>.

[0041] The polyamide of the present invention is excellent in heat resistance and flexibility and has a sufficiently high molecular weight. DETAILED DESCRIPTION

[0042] The polyamide of the present invention contains a specific combination of units selected from the group consisting of aliphatic dicarboxylic acids (A) having 18 to 48 carbon atoms (hereinafter sometimes referred to as component (A)), aliphatic diamines (B) having 18 to 48 carbon atoms (hereinafter sometimes referred to as component (B)), aromatic / aliphatic dicarboxylic acids (C) having 4 to 12 carbon atoms (hereinafter sometimes referred to as component (C)), and aliphatic diamines (D) having 4 to 16 carbon atoms (hereinafter sometimes referred to as component (D)). Components (A) to (D) that can constitute the polyamide of the present invention are each contained in the polyamide as a monomer component (or monomer residue). Therefore, "units consisting of aliphatic dicarboxylic acids (A) having 18 to 48 carbon atoms" can also be simply expressed as "aliphatic dicarboxylic acid (A) monomers having 18 to 48 carbon atoms" or their residues. "Units composed of an aliphatic diamine (B) having 18 to 48 carbon atoms" can also be simply expressed as "an aliphatic diamine (B) monomer having 18 to 48 carbon atoms" or its residue. "Units composed of an aromatic / aliphatic dicarboxylic acid (C) having 4 to 12 carbon atoms" can also be simply expressed as "an aromatic / aliphatic dicarboxylic acid (C) monomer having 4 to 12 carbon atoms" or its residue. "Units composed of an aliphatic diamine (D) having 4 to 16 carbon atoms" can also be simply expressed as "an aliphatic diamine (D) monomer having 4 to 16 carbon atoms" or its residue.

[0043] The polyamide of the present invention comprises units consisting of component (A), units consisting of component (D), and units consisting of component (C), and may or may not further comprise units consisting of component (B). From the viewpoint of having excellent heat resistance, high molecular weight properties, bleed resistance, and heat-resistant flexibility, and further improved flexibility, the polyamide of the present invention preferably comprises units consisting of component (A), units consisting of component (B), units consisting of component (C), and units consisting of component (D).

[0044] As component (A), an aliphatic dicarboxylic acid composed entirely of hydrocarbons except for carboxyl groups is preferred, and examples thereof include hexadecanedicarboxylic acid (carbon number 18), octadecanedicarboxylic acid (carbon number 18), and dimer acid (carbon number 32 to 48 (particularly 36 to 44)). Aliphatic dicarboxylic acids are acyclic aliphatic compounds having two carboxyl groups in one molecule and not containing any aromatic rings such as a benzene ring or a naphthalene ring. Among them, aliphatic dicarboxylic acids having 20 or more carbon atoms are preferred from the perspective of high flexibility, and dimer acid is more preferred. For example, the dimer acid may be obtained by addition reaction of two molecules of unsaturated fatty acids having 18 to 22 carbon atoms selected from oleic acid, linoleic acid, erucic acid, etc. The two molecules may be of the same type or of different types. The dimer acid may be a dicarboxylic acid having an unsaturated bond, but from the perspective of being less likely to discolor, a dicarboxylic acid that has been hydrogenated so that all bonds are saturated is preferably used. Component (A) may be used alone or in combination of two or more. In this specification, C36 dimer acid refers to a dimer acid having 36 carbon atoms. For example, C36 dimer acid can be obtained by an addition reaction of two molecules selected from unsaturated fatty acids such as oleic acid and linoleic acid. C44 dimer acid refers to a dimer acid having 44 carbon atoms. For example, C44 dimer acid can be obtained by an addition reaction of two molecules selected from unsaturated fatty acids such as erucic acid.

[0045] From the viewpoint of further improving the heat resistance, flexibility, high molecular weight characteristics, bleed resistance and heat-resistant flexibility of the polyamide or a molded article of the polyamide (e.g., a test piece, an industrial pipe) (hereinafter referred to as "polyamide, etc."), the number of carbon atoms in component (A) is preferably 18 to 48, more preferably 18 to 44, further preferably 20 to 40, particularly preferably 30 to 40, and fully preferably 34 to 38.

[0046] The content of component (A) is not particularly limited. From the perspective of further improving the heat resistance, flexibility, high molecular weight characteristics, anti-bleeding and heat-resistant flexibility of polyamides, the content is preferably 40 to 80% by mass, more preferably 40 to 59% by mass, further preferably 42 to 56% by mass, and particularly preferably 45 to 55% by mass. This content is the content of the residues of component (A), which is the ratio relative to all monomer components (or the total amount of these residues) constituting the polyamide. When the polyamide contains two or more components (A), their total amount can be within the above range. When the polyamide does not contain component (A), at least one of the characteristics of softness, high molecular weight characteristics, and anti-bleeding is significantly reduced, greatly shortening the life of the polyamide.

[0047] In this specification, heat resistance refers to a property of polyamide or the like having a sufficiently high melting point.

[0048] Flexibility refers to a property in which the flexural modulus of polyamide or the like is within an appropriate range and the Shore hardness D (before heat treatment) of the polyamide is within an appropriate range.

[0049] The high molecular weight property refers to a property that polyamide or the like has a higher molecular weight, and in particular, a property that the melt flow rate (MFR) of polyamide or the like is sufficiently small.

[0050] Bleeding resistance refers to a property of more fully suppressing bleeding from polyamide or the like due to heat treatment, and in particular, a property of sufficiently reducing the mass loss rate of polyamide or the like due to heat treatment.

[0051] Heat-resistant flexibility refers to a property in which polyamide or the like maintains sufficient flexibility even after heat treatment, and in particular, a property in which the increase or decrease in Shore D hardness of polyamide or the like before and after heat treatment is sufficiently small.

[0052] As component (B), an aliphatic diamine composed entirely of hydrocarbons except for amino groups is preferred, for example, octadecanediamine (carbon number 18), eicosanediamine (carbon number 20), and dimerized diamine (carbon number 32 to 48 (especially 36 to 44)). Aliphatic diamines are non-cyclic aliphatic compounds having two amino groups in one molecule and not containing any aromatic rings such as a benzene ring or a naphthalene ring. Among them, dimerized diamine is preferred. By using dimerized diamine, the overall flexibility of the polymer can be effectively improved even with a resin composition that is less than that of other monomers. Generally, dimerized diamine is produced by reacting a dimer acid with ammonia, followed by dehydration, nitrilation, and reduction. Dimerized diamine may be a diamine having an unsaturated bond, but from the perspective of being less prone to coloring, it is preferred that a diamine having all saturated bonds be hydrogenated. Component (B) may be used alone or in combination of two or more. N36 dimerized diamine is a dimerized diamine having 36 carbon atoms. N36 dimer diamine can be produced by, for example, reacting C36 dimer acid with ammonia, followed by dehydration, nitrilation, and reduction.

[0053] From the viewpoint of further improving the heat resistance, flexibility, high molecular weight characteristics, bleed resistance, and heat-resistant flexibility of polyamides, the number of carbon atoms in component (B) is preferably 18 to 48, more preferably 18 to 44, further preferably 18 to 40, particularly preferably 18 to 38, and most preferably 34 to 38.

[0054] The content of component (B) is not particularly limited. From the perspective of further improving the heat resistance, flexibility, high molecular weight characteristics, anti-bleeding and heat-resistant flexibility of polyamide, etc., it is preferably 20% by mass or less (i.e., 0 to 20% by mass), more preferably 15% by mass or less (i.e., 0 to 15% by mass), further preferably 10% by mass or less (i.e., 0 to 10% by mass), and particularly preferably 9% by mass or less (i.e., 0 to 9% by mass). This content is the content of the residues of component (B), which is the ratio relative to all monomer components constituting the polyamide (or the total amount of these residues). When the polyamide contains two or more components (B), their total amount can be within the above range. It should be noted that a content of component (B) of 0% by mass means that the polyamide does not contain component (B). Therefore, component (B) is an arbitrary component. In detail, the polyamide may contain or not contain component (B). If it contains, it can be contained within the above range. From the viewpoint that the polyamide of the present invention has excellent heat resistance, high molecular weight characteristics, bleed resistance, and heat-resistant flexibility, and further improved flexibility, the content of component (B) is preferably 3 to 9 mass %, more preferably 5 to 9 mass %.

[0055] Component (C) is an aromatic / aliphatic dicarboxylic acid (i.e., an aromatic or aliphatic dicarboxylic acid), specifically, one or more dicarboxylic acids selected from aromatic dicarboxylic acids and aliphatic dicarboxylic acids. Aromatic dicarboxylic acids are cyclic aromatic compounds having two carboxyl groups and one or more aromatic rings such as benzene rings and naphthalene rings in one molecule. Aliphatic dicarboxylic acids are non-cyclic aliphatic compounds having two carboxyl groups and no aromatic rings such as benzene rings and naphthalene rings in one molecule. From the viewpoint of further improving the heat resistance, flexibility, high molecular weight characteristics, anti-bleeding and heat-resistant flexibility of polyamides, etc., aromatic / aliphatic dicarboxylic acids (C) are preferably aromatic dicarboxylic acids.

[0056] Examples of component (C) include aliphatic dicarboxylic acids such as sebacic acid (10 carbon atoms), azelaic acid (9 carbon atoms), and adipic acid (6 carbon atoms), and aromatic dicarboxylic acids such as terephthalic acid (8 carbon atoms) and isophthalic acid (8 carbon atoms). Of these, aromatic dicarboxylic acids having 8 or more carbon atoms are preferred, with terephthalic acid being more preferred, from the perspective of further improving heat resistance and flexibility. Component (C) may be used alone or in combination of two or more.

[0057] From the viewpoint of further improving the heat resistance, flexibility, high molecular weight characteristics, bleed resistance, and heat-resistant flexibility of polyamide, etc., the number of carbon atoms in component (C) is preferably 4 to 12, more preferably 6 to 12, and even more preferably 6 to 10.

[0058] The content of component (C) is not particularly limited. From the perspective of further improving the heat resistance, flexibility, high molecular weight characteristics, anti-bleeding and heat-resistant flexibility of polyamides, it is preferably 5 to 50% by mass, more preferably 9.5 to 20% by mass, and even more preferably 10 to 15% by mass. This content is the content of the residue of component (C), which is the ratio relative to all monomer components (or the total amount of these residues) constituting the polyamide. When the polyamide contains two or more components (C), their total amount is within the above range. When the polyamide does not contain component (C), at least one of the heat resistance, mechanical properties (flexural modulus), high molecular weight characteristics, anti-bleeding and heat-resistant flexibility is reduced. When the polyamide does not contain component (C), in detail, the heat resistance (melting point) and mechanical properties (flexural modulus) are significantly reduced, and the softness is excessively obtained (too soft), so it has no practical application as a pipe.

[0059] Component (D) is an aliphatic diamine, which is an acyclic aliphatic compound having two amino groups per molecule and containing no aromatic rings such as a benzene ring or a naphthalene ring. Examples of component (D) include 1,14-tetradecanediamine (14 carbon atoms), 1,13-tridecanediamine (13 carbon atoms), 1,12-dodecanediamine (12 carbon atoms), 1,11-undecanediamine (11 carbon atoms), 1,10-decanediamine (10 carbon atoms), 1,9-nonanediamine (9 carbon atoms), 1,8-octanediamine (8 carbon atoms), 1,6-hexanediamine (6 carbon atoms), and 1,4-butanediamine (4 carbon atoms). Among these, diamines having 6 or more carbon atoms are preferred, diamines having 8 or more carbon atoms are preferred, diamines having 10 or more carbon atoms are more preferred, and 1,10-decanediamine is even more preferred, from the perspective of easily improving heat resistance and flexibility. As the component (D), one of the above may be used alone, or two or more of them may be used in combination.

[0060] From the viewpoint of further improving the heat resistance, flexibility, high molecular weight characteristics, bleed resistance, and heat-resistant flexibility of polyamide, etc., the number of carbon atoms in component (D) is preferably 4 to 16, more preferably 4 to 14, even more preferably 8 to 14, and even more preferably 8 to 12.

[0061] The content of component (D) is not particularly limited. From the perspective of further improving the heat resistance, flexibility, high molecular weight characteristics, anti-bleeding and heat-resistant flexibility of polyamides, the content is preferably 10 to 50% by mass, more preferably 18 to 45% by mass, and even more preferably 25 to 40% by mass. This content is the content of the residues of component (D), which is the ratio relative to all monomer components (or the total amount of these residues) constituting the polyamide. When the polyamide contains two or more components (D), their total amount can be within the above range. When the polyamide does not contain component (D), at least one of the heat resistance, high molecular weight characteristics, anti-bleeding and heat-resistant flexibility is reduced.

[0062] The polyamide of the present invention is excellent in heat resistance, flexibility, and high molecular weight characteristics, and more preferably, is also excellent in bleed-out resistance and heat-resistant flexibility.

[0063] The polyamide of the present invention preferably does not contain a plasticizer component. A plasticizer component refers to an additive doped in the polymer in order to reduce the melt viscosity of the polymer (i.e., increase in the MFR of the polymer) and / or improve the flexibility of the polymer. Such a plasticizer component can be all compounds used as plasticizers for polyamides in the past. As a specific example of a plasticizer component, for example, toluenesulfonic acid alkylamides, benzenesulfonic acid alkylamides, alkyl hydroxybenzoates, etc. can be cited. It should be noted that the present invention does not necessarily mean that the polyamide does not contain a plasticizer component. For example, the user can make the polyamide contain a plasticizer component in order to adjust the flexibility.

[0064] From the perspective of further improving the heat resistance, flexibility, high molecular weight characteristics, anti-bleeding and heat-resistant flexibility of polyamides, the content of the plasticizer component is preferably 5% by mass or less, more preferably 1% by mass or less, particularly preferably 0.5% by mass or less, and further preferably 0.1% by mass or less. The lower limit of this content range is usually 0% by mass. This content is a value relative to the polyamide and can be measured as the mass reduction rate caused by heat treatment at 120°C for 72 hours. The plasticizer component is an additive that is present between polyamide molecules by doping or mixing in the polyamide, and does not constitute a part of the polyamide by covalent bonding with the polyamide.

[0065] As used herein, the mass reduction rate after heat treatment can be measured by maintaining a 4 mm thick test piece in air at 120°C for 72 hours in a constant temperature dryer (DRV320DA, manufactured by ADVANTEC). Specifically, the mass reduction rate refers to the ratio of the mass difference (amount of mass reduction) before and after heat treatment to the mass before heat treatment.

[0066] The fact that the polyamide of the present invention contains no plasticizer components is one of the reasons why it is preferred for industrial pipe applications, as described below. Specifically, because the polyamide of the present invention maintains flexibility suitable for industrial pipes even without the presence of a plasticizer, there is no risk of plasticizer exudation during use in high-temperature environments or over time. Consequently, contamination of the transported fluid (e.g., air, pure water, solvents) and the solidification and thinning (weight loss) of the pipe body are eliminated. Because the polyamide of the present invention contains no plasticizer components, even with prolonged use in high-temperature environments, there is no weight loss due to the release of the plasticizer, and flexibility is not compromised.

[0067] The polyamide of the present invention preferably does not contain polyether or polyester components that are susceptible to decomposition during polymerization. Examples of polyether components include polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, and polyoxyethylene / polyoxypropylene glycol. Examples of polyester components include polyethylene adipate, polybutylene adipate, and polyethylene sebacate. When polyether or polyester components are used, decomposition may occur at high polymerization temperatures.

[0068] From the perspective of further improving the heat resistance, flexibility, high molecular weight properties, anti-bleeding and heat-resistant flexibility of polyamides, the total content of the polyether component and the polyester component is preferably 2% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.1% by mass or less. The lower limit of this total content range is usually 0% by mass. This total content is the content of the residues of the polyether component and the polyester component, and is the ratio relative to all monomer components (or the total amount of these residues) that constitute the polyamide. The polyether component and the polyester component are components that constitute a part of the polyamide by covalent bonding with the polyamide, and are not simply doped into the polyamide.

[0069] The polyamide of the present invention may contain an end-capping agent for purposes such as adjusting the degree of polymerization, inhibiting product decomposition, and inhibiting coloration. Examples of end-capping agents include monocarboxylic acids such as acetic acid, lauric acid, benzoic acid, and stearic acid, and monoamines such as octylamine, cyclohexylamine, aniline, and stearylamine. One of the end-capping agents listed above may be used alone, or two or more may be used in combination. The amount of the end-capping agent is not particularly limited, but is generally 0 to 10 mol % relative to the total molar amount of the dicarboxylic acid and diamine.

[0070] The polyamide of the present invention may contain additives. Examples of additives include fibrous reinforcements such as glass fiber and carbon fiber; fillers such as talc, expandable clay minerals, silica, alumina, glass beads, and graphite; pigments such as titanium dioxide and carbon black; antioxidants; antistatic agents; flame retardants; and flame retardant additives. These additives may be added during polymerization or after polymerization through melt kneading. These additives are incorporated into the polyamide.

[0071] The melting point of the polyamide is generally 200°C or higher, and from the perspective of further improving heat resistance, is preferably 280°C or higher, more preferably 300°C or higher, and even more preferably 310°C or higher. The upper limit of the melting point is not particularly limited; for example, the melting point is generally 400°C or lower, and particularly 380°C or lower. The melting point of the polyamide may be the melting point of the polyamide without any additives.

[0072] In this specification, the melting point is the value measured using a differential scanning calorimeter (DSC-6000, manufactured by PerkinElmer) under the following conditions: The temperature was raised to 350°C at a heating rate of 20°C / min, then held at 350°C for 5 minutes, then lowered to 25°C at a cooling rate of 20°C / min, then held at 25°C for 5 minutes, and then again raised at a heating rate of 20°C / min. The top of the endothermic peak during this measurement was defined as the melting point.

[0073] The melt viscosity of the polyamide of the present invention, measured in terms of melt flow rate (MFR), must be 20 g / 10 min or less. The melt viscosity of the polyamide of the present invention is preferably 10 g / 10 min or less, more preferably 5 g / 10 min or less. By achieving such a high viscosity, the polyamide becomes a material suitable for industrial pipes. If the MFR is too high, the molecular weight of the polyamide is insufficient. Therefore, it is difficult to use the polyamide for molding. For example, it is difficult to mold into a tube shape. The MFR of the polyamide can be the MFR of a polyamide that does not contain any additives.

[0074] In this specification, MFR refers to a value measured by the method described in JIS-K7210-1 under the conditions of a temperature of 340° C., a load of 1.2 kg, and preheating for 5 minutes.

[0075] The flexural modulus of polyamide, which is an indicator of flexibility, is generally 100 to 600 MPa. From the perspective of further improving flexibility, it is preferably 150 to 600 MPa, more preferably 150 to 500 MPa, and even more preferably 150 to 280 MPa. The flexural modulus of polyamide may be the flexural modulus of polyamide without any additives.

[0076] In this specification, the flexural modulus is a value measured at 23° C. using a 4 mm thick test piece in accordance with ISO 178.

[0077] The Shore D hardness (before heat treatment) of the polyamide, another indicator of flexibility, is generally 30 to 75. From the perspective of further improving flexibility, it is preferably 45 to 70, more preferably 50 to 65, and even more preferably 50 to 60. The Shore D hardness of the polyamide before heat treatment may be the Shore D hardness of the polyamide without any additives.

[0078] The Shore hardness D of the polyamide of the present invention after heat treatment is generally 30 to 75, and from the viewpoint of further improving heat-resistant flexibility, is preferably 45 to 70, more preferably 50 to 65, and even more preferably 50 to 60. The Shore hardness D of the polyamide after heat treatment may be the Shore hardness D of a polyamide after heat treatment that does not contain any additives.

[0079] The change in Shore D hardness before and after heat treatment of the polyamide of the present invention is generally ±10, preferably ±5, and more preferably ±3, from the perspective of further improving heat-resistant flexibility. For example, "±10" means "-10 to +10." The change in Shore D hardness before and after heat treatment of the polyamide can be the change in Shore D hardness before and after heat treatment of a polyamide without any additives.

[0080] In this specification, Shore hardness D is a value measured using a 4 mm thick test piece with a durometer according to JIS K 6253 (Type D). Heat treatment can be performed by maintaining the sample at 120° C. for 72 hours in air using a constant temperature dryer (DRV320DA, manufactured by ADVANTEC).

[0081] The polyamide of the present invention can be produced by a two-stage polymerization method. Specifically, the polyamide of the present invention can be produced by the following method, which comprises:

[0082] A first polymerization step of reacting component (A) and component (D); and

[0083] In the second polymerization step, after the first polymerization step, component (C) is further added to carry out the reaction.

[0084] In the first polymerization step, component (B) can be further added to carry out the reaction, or the reaction can be carried out without adding component (B). In more detail, in the preferred method for producing the polyamide of the present invention, at least one acid component and one amine component are selected from component (A), component (B) and component (D), and they are fully reacted at a polymerization temperature that is not easy to volatilize to make them highly viscous (first polymerization step), and then component (C) is further added to fully react (second polymerization step). If component (C) (such as TPA) is added in the first polymerization step, the component (C) will precipitate due to its high specific gravity and cannot be well dispersed in the system, resulting in segregation. In addition, at the stage of the first polymerization step, since the temperature at which component (C) reacts with other amine components in the system has not yet been reached, it is impossible to fully achieve a high molecular weight. In the first polymerization step, component (C) can be added all at once, or it can be added in batches. As mentioned above, both cannot achieve a high molecular weight due to the temperature range in which component (C) reacts.

[0085] In the first polymerization step, all components except component (C) of the monomer components constituting the pre-produced polyamide are generally used. For example, when producing a polyamide whose monomer components include dimer acid (36C), dimer diamine (36N), terephthalic acid, and 1,10-decanediamine as components (A) to (D), dimer acid (36C) is used as component (A), and dimer diamine (36N) and 1,10-decanediamine are used as components (B) and (D), respectively, in the first polymerization step. Alternatively, for example, when producing a polyamide whose monomer components include dimer acid (36C) as component (A), and terephthalic acid and 1,10-decanediamine as components (C) and (D), respectively, dimer acid (C36) is used as component (A), and 1,10-decanediamine is used as component (D) in the first polymerization step.

[0086] In the first polymerization step, an amino-terminated prepolymer is typically synthesized because the diamine component is used in excess. Therefore, the aforementioned two-stage polymerization method, which is the method for producing the polyamide of the present invention, can also be referred to as an "amino-terminated prepolymer synthesis-type two-stage polymerization method." While classified as a two-stage polymerization method, the "salt synthesis-type two-stage polymerization method" described in Patent Document 3 typically first reacts an aromatic dicarboxylic acid having 4 to 12 carbon atoms as a hard segment with an aliphatic diamine having 4 to 16 carbon atoms to form a prepolymer (salt). Subsequently, an aliphatic dicarboxylic acid having 18 to 44 carbon atoms and an aliphatic diamine having 18 to 44 carbon atoms are added in a predetermined ratio to form the soft segment and polymerize. This method produces a highly segmented polyamide with excellent heat resistance and flexibility. However, due to the long soft segment, the polyamide tends to flow easily during melting, making it difficult to increase the melt viscosity.

[0087] The polymerization temperature (reaction temperature) in the first polymerization step is preferably 100 to 190°C, more preferably 130 to 180°C, and even more preferably 160 to 180°C. If the polymerization temperature is lower than 100°C, the polymerization reaction will not proceed. On the other hand, when the polymerization temperature exceeds 190°C, component (D) (e.g., 1,10-decanediamine) volatilizes, disrupting the molar balance and making molecular weight control difficult. Specifically, sufficient molecular weight cannot be achieved.

[0088] By providing the first polymerization step in this manner, the melt viscosity of at least the reaction product (or oligomer or prepolymer) comprising components (A) and (D) is increased before the addition of component (C). Therefore, even when component (C) having a relatively high specific gravity is added in the subsequent second polymerization step, segregation due to precipitation is less likely to occur, allowing the reaction to proceed more uniformly, thereby achieving a higher molecular weight.

[0089] In the first polymerization step, the polymerization time is not particularly limited, and may be, for example, 0.5 to 5 hours, particularly 1 to 3 hours.

[0090] In the second polymerization step, component (C) may be added in portions or all at once, but from the perspective of further increasing the molecular weight, it is preferred to add component (C) in portions. By adding component (C) having a high specific gravity in portions, precipitation at the bottom of the polymerization reactor (e.g., a polymerization kettle) can be more effectively prevented, and a more sufficient molecular weight can be achieved without disrupting the molar balance within the polymerization system.

[0091] The polymerization temperature (reaction temperature) in the second polymerization step is usually 230-340°C, preferably 230-300°C, more preferably 235-290°C, and even more preferably 235-285°C. From the viewpoint of further improving the high molecular weight characteristics, the second polymerization step is preferably carried out at a lower temperature within the above-mentioned polymerization temperature range, and then at a higher temperature. From the viewpoint of further improving the high molecular weight characteristics, the second polymerization step is preferably carried out at a lower temperature within the above-mentioned polymerization temperature range, and then at a relatively medium temperature and a relatively high temperature in sequence. Such a low temperature is preferably, for example, 230-250°C, and more preferably 235-245°C. Medium temperature refers to a temperature between low temperature and high temperature, for example, preferably 250-270°C, and more preferably 255-265°C. High temperature is preferably, for example, 270-290°C, and more preferably 275-285°C. At this time, the stepwise addition of component (C) is preferably completed in advance at the medium temperature polymerization reaction stage.

[0092] In the second polymerization step, the polymerization time is not particularly limited. For example, when the second polymerization step is carried out in one stage, in two stages of low temperature and high temperature, or in three stages of low temperature, medium temperature, and high temperature, the overall polymerization time can be, for example, 1 to 5 hours, particularly 1 to 3 hours. In particular, when the second polymerization step is carried out in three stages of low temperature, medium temperature, and high temperature, the polymerization time in each stage can be, for example, independently 0.1 to 3 hours, particularly 0.5 to 2 hours.

[0093] The polyamide of the present invention can be used in industrial pipes. For example, the polyamide of the present invention can be used in industrial pipes. Industrial pipes are pipes intended for use in industries such as industry, mining, and agriculture. Specific examples of industrial pipes include automotive fuel pipes, automotive cooling pipes, electronic equipment cooling pipes, and chemical liquid delivery pipes for semiconductor manufacturing equipment.

[0094] The industrial pipe of the present invention can be produced, for example, by subjecting the polyamide of the present invention to extrusion molding. The industrial pipe of the present invention is not particularly limited as long as it comprises the polyamide of the present invention. For example, in the case of a single-layer industrial pipe of the present invention, 50% or more by mass, preferably 70% or more by mass, more preferably 90% or more by mass, even more preferably 99% or more by mass, and particularly preferably 100% by mass of the constituent polymer components is composed of the polyamide of the present invention. The polymer component refers to a polymer having a weight-average molecular weight of 10,000 or more.

[0095] Example

[0096] The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0097] The physical properties of the polyamide resin composition were measured by the following methods.

[0098] (1) Melting point (heat resistance)

[0099] Using a differential scanning calorimeter DSC (DSC-6000, manufactured by PerkinElmer), the temperature was raised to 350°C at a heating rate of 20°C / min, then maintained at 350°C for 5 minutes, then cooled to 25°C at a cooling rate of 20°C / min, and further maintained at 25°C for 5 minutes. The temperature was then again increased at a heating rate of 20°C / min, and the top of the endothermic peak during the measurement was defined as the melting point.

[0100] ◎: 310℃ or above (optimal);

[0101] ○: 300°C or higher and less than 310°C (excellent);

[0102] △: 200°C or higher and less than 300°C (no practical problem);

[0103] ×: Less than 200°C (problematic in practice).

[0104] (2) Melt viscosity of resin (MFR (g / 10 minutes))

[0105] The polyamide resin of the present invention has high viscosity and is excellent in processability for industrial pipes.

[0106] Specifically, polyamide pellets were subjected to melt flow rate (MFR) measurement in accordance with JIS-K7210-1 at a temperature of 340°C and a test load of 1.2 kg. The MFR is preferably 20 g / 10 min or less (Δ: no practical problem), more preferably 10 g / 10 min or less (◯: excellent), and even more preferably 5 g / 10 min or less (⊚: excellent). The MFR is categorized into grades, and the best grade is adopted as the evaluation result.

[0107] Furthermore, a higher viscosity does not pose a practical problem unless the melt processability (fluidity) is impaired due to gelation or the like.

[0108] (3) Flexural modulus (flexibility)

[0109] The tube of the present invention has excellent flexibility.

[0110] Specifically, polyamide pellets are injection molded into 4 mm thick test pieces, and the bending modulus is measured at 23°C based on ISO178. The bending modulus is more preferably 600 MPa or less, and even more preferably 500 MPa or less. In addition, from the viewpoint of not damaging the function as a tube, the above-mentioned bending modulus must be 100 MPa or more, preferably 150 MPa or more. If the bending modulus exceeds 600 MPa or is less than 100 MPa, there will be problems in practical use. Therefore, the bending modulus (softness) is graded according to the following benchmarks, and the better grade among the classified grades is adopted as the evaluation result.

[0111] ◎: 150~500MPa (optimal);

[0112] ○: 150-600 MPa (excellent);

[0113] △: 100~600MPa (no problem in practice);

[0114] ×: Exceeds 600 MPa or is less than 100 MPa (problematic in practice).

[0115] (4) Shore D hardness before and after heat treatment (softness and heat-resistant softness)

[0116] The tube of the present invention has little change in mechanical properties due to heat treatment and maintains flexibility.

[0117] Specifically, polyamide pellets were injection molded into 4 mm thick test pieces, which were then heat treated in air at 120°C for 72 hours using a constant temperature dryer (DRV320DA, manufactured by ADVANTEC). The test pieces before and after the heat treatment were then measured using a durometer according to JIS K 6253 (Type D). To ensure that the flexible tube function is maintained, the Shore D hardness before and after the heat treatment is preferably in the range of 30 to 75 (Δ: no practical problem), more preferably 45 to 70 (◯: excellent), and even more preferably 50 to 65 (⊚: optimal). The Shore D hardness is graded, and the best grade is adopted as the evaluation result.

[0118] Furthermore, the change in Shore D hardness before and after heat treatment is preferably ±10 or less (Δ: no practical problem), more preferably ±5 (○: excellent), and even more preferably ±3 (◎: optimal). If the change in Shore D hardness before and after heat treatment is less than -10 or exceeds 10, the pipe is considered to be outside the design specifications and is considered to be practically problematic. The change in Shore D hardness is graded based on the change in Shore D hardness, and the better grade is selected as the evaluation result.

[0119] (5) Mass reduction after heat treatment (leakage resistance)

[0120] The tube of the present invention does not cause leakage of plasticizers due to heat treatment, and therefore does not pollute the use environment, and maintains flexibility.

[0121] Specifically, polyamide pellets are injection molded into 4 mm thick test pieces (dumbbell test pieces), and the test pieces are heat treated at 120 ° C for 72 hours in air using a constant temperature dryer (DRV320DA, manufactured by ADVANTEC). Next, the mass before and after heat treatment is measured and the mass difference is compared. The greater the mass reduction rate, the more plasticizer oozes out, and the more it will damage the flexibility function as a tube. Therefore, the mass reduction rate is preferably 5% by mass or less (△: no practical problem), preferably 3% by mass or less (○: excellent), and further preferably 1% by mass or less (optimal: ◎). Therefore, those with a mass reduction rate of 5% or more (poor: ×) have practical problems as tubes. Grades are divided according to the mass reduction rate, and the better grade is used as the evaluation result in the classified grade. The mass reduction rate specifically refers to the ratio of the mass difference (reduction amount) before and after heat treatment to the mass before heat treatment.

[0122] (6) Comprehensive evaluation

[0123] Among the evaluation results of melting point, melt viscosity, flexural modulus, mass reduction rate after heat treatment, and Shore D hardness before and after heat treatment and its increase or decrease, the lowest evaluation result was adopted as the result of comprehensive evaluation.

[0124] (7) Polymer composition

[0125] The resulting particles or powder were analyzed by 1H-NMR using a high-resolution nuclear magnetic resonance apparatus (ECA-500NMR manufactured by JEOL Ltd.), and the resin composition was determined from the peak intensities of the individual copolymer components. (Resolution: 500 MHz, solvent: a 4 / 5 volume ratio mixture of deuterated trifluoroacetic acid and deuterated chloroform, temperature: 23°C)

[0126] (8) Monomer materials

[0127] C36 dimer acid is an aliphatic dicarboxylic acid having 36 carbon atoms per molecule, and Pripol 1009 (manufactured by Cargill) which is a dimer of an unsaturated fatty acid having 18 carbon atoms was used.

[0128] C44 dimer acid is an aliphatic dicarboxylic acid having 44 carbon atoms per molecule, and Pripol 1004 (manufactured by Cargill) which is a dimer of an unsaturated fatty acid having 22 carbon atoms was used.

[0129] N36 dimer diamine is an aliphatic diamine having 36 carbon atoms per molecule and is a diamine derived from a dimer (dimer acid) of an unsaturated fatty acid having 18 carbon atoms. Priamine 1075 (manufactured by Cargill) was used.

[0130] 1,20-Eicosanediamine (N20)

[0131] 1,10-Decanediamine (N10)

[0132] 1,11-Undecanediamine (N11)

[0133] 1,4-Butanediamine (N4)

[0134] 1,6-Hexanediamine (N6)

[0135] Example 1 (Method C; Two-stage polymerization method for synthesizing amino-terminated prepolymers)

[0136] Into a 150-liter reaction vessel equipped with a heating mechanism, a stirring mechanism, a nitrogen inlet, a condensation water outlet, a pressure relief port, and a raw material inlet, 53.04 parts by mass of component (A) C36 dimer acid, 6.39 parts by mass of component (B) N36 dimer diamine, 27.85 parts by mass of component (D) 1,10-decanediamine, and 0.2 parts by mass of sodium hypophosphite monohydrate (adjusted to a 40% solids concentration aqueous solution) as a catalyst were added, totaling 43.64 kg. The reaction vessel was purged with 99.9999% pure nitrogen gas from the nitrogen inlet, replacing the interior of the reaction vessel with nitrogen.

[0137] First Polymerization Step: Next, the reaction vessel was heated to 170°C for approximately 2 hours while stirring under a nitrogen purge atmosphere. (At this time, the condensation water generated by the polycondensation reaction in the system turned into steam and was discharged to the outside of the system, so the temperature at the condensation water outlet was 100-110°C.)

[0138] Second polymerization step: After the polymerization reaction in the reaction vessel is terminated, the temperature at the condensation water outlet is lowered to 90°C, and the temperature of the reaction vessel is raised to 240°C at a heating rate of 10°C / 10 minutes. Immediately after the temperature in the reaction vessel system reaches 240°C, 12.72 parts by mass of component (C) terephthalic acid are added from the raw material inlet of the reaction vessel in 10 portions at a rate of one portion every 10 minutes to proceed with polymerization. (At this time, the temperature at the condensation water outlet is 95-105°C.) After the temperature at the condensation water outlet has dropped to approximately 90°C, the temperature of the reaction vessel is raised to 260°C at a heating rate of 10°C / 10 minutes for reaction for 30 minutes, and then raised to 280°C at a heating rate of 10°C / 10 minutes. Thereafter, polymerization is carried out at 280°C for 1.5 hours.

[0139] After the polymerization was completed, the strands were discharged, cooled, cut, and dried to obtain polyamide resin pellets. The obtained pellets were injection molded to obtain 4 mm thick test pieces.

[0140] Examples 2 to 10 (Method C; Two-stage polymerization method for synthesizing amino-terminated prepolymers)

[0141] Pellets were obtained by the same operation as in Example 1 except that the types and amounts of monomers charged into the reaction vessel were changed as shown in Table 1. The obtained pellets were injection molded to obtain test pieces having a thickness of 4 mm.

[0142] Comparative Example 1 (Method A: All monomers are added at once)

[0143] A 150-liter reaction vessel equipped with a heating mechanism, a stirring mechanism, a nitrogen inlet, a condensation water outlet, a pressure relief port, and a raw material inlet was charged with 53.04 parts by mass of component (A) C36 dimer acid, 6.39 parts by mass of component (B) N36 dimer diamine, 12.72 parts by mass of component (C) terephthalic acid, 27.85 parts by mass of component (D) 1,10-decanediamine, and 0.2 parts by mass of sodium hypophosphite monohydrate (adjusted to a 40% solids concentration aqueous solution) as a catalyst, to a total of 50.00 kg. Subsequently, nitrogen gas with a purity of 99.9999% was purged from the nitrogen inlet, replacing the interior of the reaction vessel with nitrogen.

[0144] Next, the temperature of the reaction vessel was raised to 170°C while stirring under a nitrogen purge atmosphere and heated for about 2 hours. (At this time, the condensation water generated by the polycondensation reaction in the system turned into water vapor and was discharged to the outside of the system, so the temperature of the condensation water outlet was 100-110°C.) Thereafter, the polymerization reaction in the reaction vessel was terminated, and after the temperature of the condensation water outlet dropped to 90°C, the temperature of the reaction vessel was raised to 240°C at a heating rate of 10°C / 30 minutes. Next, the temperature of the reaction vessel was raised to 260°C at a heating rate of 5°C / 10 minutes, and after the reaction for 30 minutes, the temperature was raised to 280°C at a heating rate of 10°C / 10 minutes. Thereafter, polymerization was carried out at 280°C for 1.5 hours.

[0145] After polymerization, the molten polymer was initially discharged as white granules, likely containing terephthalic acid (C), a large amount. Subsequently, it was discharged in the form of strands. The strands were cooled, cut, and dried to obtain polyamide resin pellets. The resulting pellets were injection molded into 4 mm thick test pieces.

[0146] Comparative Example 2 (Method A: All monomers are added at once)

[0147] The same procedures as in Comparative Example 1 were followed, except that the types and amounts of monomers charged to the reaction vessel were changed as shown in Table 2. Initially after completion of polymerization, a molten polymer was discharged as a white fluid containing a large amount of terephthalic acid, presumably component (C). Subsequently, the polymer was discharged in the form of strands. The strands were cooled, cut, and dried to obtain polyamide resin pellets. The resulting pellets were injection molded to produce 4 mm thick test pieces.

[0148] Comparative Example 3 (Method B: Salt Synthesis Type Two-Stage Polymerization Method)

[0149] Production of reaction products (salt synthesis)

[0150] 23.52 parts by mass of terephthalic acid and 0.2 parts by mass of sodium hypophosphite monohydrate were placed in a ribbon mixer-type reactor and heated to 170°C while stirring at 30 rpm under a nitrogen atmosphere. Subsequently, while maintaining the temperature at 170°C and the rotation speed at 30 rpm, 24.39 parts by mass of 1,10-decanediamine heated to 100°C was continuously added (continuous injection method) over 2.5 hours using a liquid injection device to obtain a reaction product.

[0151] Production of polyamide

[0152] In a reaction vessel equipped with a heating mechanism and a stirring mechanism, 26.75 parts by mass of dimer acid and 25.34 parts by mass of dimer diamine were added, and after stirring at 100° C. for 1 hour, 47.94 parts by mass of the reaction product was added while stirring.

[0153] Thereafter, the mixture was heated to 260° C. while stirring, and polymerization was carried out under a nitrogen stream at normal pressure and 260° C. for 5 hours while removing condensation water from the system. During the polymerization, the system was in a state of a suspension solution.

[0154] After the polymerization was completed, the pellets were discharged, cut, and dried to obtain polyamide pellets. The MFR of the obtained pellets was measured under the conditions of a set temperature of 340°C, a load of 1.2 kg, and a preheating time of 5 minutes. The result was 125 g / 10 minutes.

[0155] Comparative Example 4 (Method C; Two-stage polymerization method for synthesizing amino-terminated prepolymers, with one-time addition of component (C))

[0156] Except that the types and amounts of monomers introduced into the reaction container were changed as shown in Table 2, the same operation as in Example 1 was carried out, followed by drying to obtain pellets.

[0157] Comparative Example 5 (Additional Test)

[0158] The operation of Example 4 described in Patent Document 1 was carried out to obtain a polyamide.

[0159] Comparative Example 6 (Existing product)

[0160] Polyamide 12: Pellets manufactured by DAICEL EVONIK (L2121) were injection molded to obtain test pieces having a thickness of 4 mm.

[0161]

[0162]

[0163] The polyamide resins of Examples 1 to 10 satisfy the requirements specified in the present invention and are therefore sufficiently excellent in heat resistance, flexibility, high molecular weight characteristics, bleed resistance, and heat-resistant flexibility.

[0164] Industrial applicability

[0165] The polyamide of the present invention is mainly used in applications requiring heat resistance, flexibility, and high molecular weight properties (preferably further requiring bleed resistance and heat-resistant flexibility). Examples of such applications include industrial pipes.

Claims

1. A polyamide comprising: a unit consisting of an aliphatic dicarboxylic acid A having 18 to 48 carbon atoms, a unit consisting of an aromatic / aliphatic dicarboxylic acid C having 4 to 12 carbon atoms, and a unit consisting of an aliphatic diamine D having 4 to 16 carbon atoms, The polyamide has a melt flow rate (MFR) of 20 g / 10 min or less as measured by the method described in JIS-K7210-1 under the conditions of a temperature of 340° C. and a load of 1.2 kg.

2. The polyamide according to claim 1, wherein The polyamide further contains or does not contain units composed of an aliphatic diamine B having 18 to 48 carbon atoms, The content of the unit composed of the aliphatic diamine B having 18 to 48 carbon atoms is 0 to 20% by mass based on the total monomer components constituting the polyamide.

3. The polyamide according to claim 1, wherein The flexural modulus at 23°C based on ISO 178 is 100 to 600 MPa.

4. The polyamide according to claim 1, wherein The content of the unit composed of the aliphatic dicarboxylic acid A having 18 to 48 carbon atoms is 40 to 80% by mass based on the total monomer components constituting the polyamide. The content of the unit composed of the aromatic / aliphatic dicarboxylic acid C having 4 to 12 carbon atoms is 5 to 50% by mass relative to the total monomer components constituting the polyamide. The content of the unit composed of the aliphatic diamine D having 4 to 16 carbon atoms is 10 to 50% by mass based on the total monomer components constituting the polyamide.

5. The polyamide according to claim 1, wherein The aromatic / aliphatic dicarboxylic acid C is one or more dicarboxylic acids selected from the group consisting of sebacic acid, azelaic acid, adipic acid, and aromatic dicarboxylic acids.

6. The polyamide according to claim 2, wherein The content of the unit composed of the aliphatic dicarboxylic acid A is 42 to 56% by mass relative to the total monomer components constituting the polyamide. The content of the unit composed of the aliphatic diamine B is 0 to 15% by mass relative to the total monomer components constituting the polyamide. The content of the units composed of the aromatic / aliphatic dicarboxylic acid C is 9.5 to 20% by mass based on the total monomer components constituting the polyamide.

7. The polyamide according to claim 6, wherein The content of the units composed of the aliphatic dicarboxylic acid A is 45 to 55% by mass based on the total monomer components constituting the polyamide.

8. The polyamide according to claim 1, wherein The polyamide has a melting point of 300° C. or higher.

9. The polyamide according to claim 1, wherein The content of the plasticizer component is 0.5% by mass or less based on the polyamide.

10. The polyamide according to claim 1, wherein The mass reduction rate caused by heat treatment at 120° C. for 72 hours is 5 mass % or less.

11. The polyamide according to claim 1, wherein The polyamide has a flexural elastic modulus at 23° C. of 100 to 600 MPa based on ISO 178 and a Shore D hardness before heat treatment of 30 to 75.

12. The polyamide according to claim 1, wherein The increase or decrease of the Shore hardness D of the polyamide before and after the heat treatment is ±3, The heat treatment is performed at 120° C. for 72 hours.

13. A method for producing polyamide, comprising: In the first polymerization step, an aliphatic dicarboxylic acid A having 18 to 48 carbon atoms is reacted with an aliphatic diamine D having 4 to 16 carbon atoms; as well as The second polymerization step is to further add an aromatic / aliphatic dicarboxylic acid C having 4 to 12 carbon atoms to react after the first polymerization step. In the first polymerization step, the reaction may be carried out by further adding an aliphatic diamine B having 18 to 48 carbon atoms, or the reaction may be carried out without adding the aliphatic diamine B having 18 to 48 carbon atoms. 14 . The method for producing a polyamide according to claim 13 , which produces the polyamide according to claim 1 .

15. An industrial pipe comprising the polyamide according to any one of claims 1 to 12.

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