JP7793171B2 - Industrial tubes and their manufacturing methods - Google Patents

Description

The present invention relates to industrial tubing with excellent heat resistance and flexibility, and a method for manufacturing the same.

Crystalline polyamides, such as nylon 6 and nylon 66, are widely used in clothing, industrial fiber materials, and general-purpose engineering plastics due to their excellent properties and ease of melt processing. However, problems such as oxidative degradation at high temperatures have been identified, and there is a growing demand for more heat-resistant, flexible polyamides.

Conventional industrial tubing has been made of metal, but resins are increasingly being used to reduce weight. Aliphatic resins such as PA11 and PA12 are widely used for their ability to inhibit permeation of liquids and gases and for their excellent mechanical properties. However, problems have been pointed out, such as insufficient heat resistance, due to their melting points below 200°C (Patent Document 1).

On the other hand, semi-aromatic polyamides containing aromatic dicarboxylic acids such as terephthalic acid are generally known to have better heat resistance than aliphatic polyamides. Because semi-aromatic polyamides are generally more rigid than aliphatic polyamides, it has been proposed to impart flexibility to them when used as tubes by alloying them with a flexibility-imparting agent such as an elastomer. However, when using semi-aromatic polyamides, a larger amount of flexibility-imparting agent such as an elastomer must be used to improve flexibility, making it difficult to achieve both flexibility and heat resistance (Patent Document 2). For example, industrial tubes containing flexibility-imparting agents suffer from bleed-out, where the flexibility-imparting agent seeps out to the surface, in high-temperature environments, resulting in poor surface properties.

Patent application 2011-237955 WO2020/175290

The inventors of the present invention discovered a new problem: when using conventional polyamides, it was not possible to obtain industrial tubing that was sufficiently excellent in both heat resistance and flexibility. Specifically, with regard to heat resistance, even if the melting point was relatively high, there was a problem with tensile strength retention, where the tensile strength decreased when heated.

The present invention aims to solve the above problems and provide industrial tubing with excellent heat resistance and flexibility.

The present invention also aims to provide industrial tubing that not only has excellent heat resistance and flexibility, but also has excellent rubber elasticity, mechanical properties, and surface properties.

The inventors discovered that the above objectives can be achieved by including a specific polyamide, and thus arrived at the present invention.

That is, the gist of the present invention is as follows.
<1> An industrial tube containing polyamide having a melting point of 240°C or higher and a flexural modulus of 100 to 1,300 MPa, which contains units consisting of an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms, units consisting of an aliphatic diamine (B) having 18 or more carbon atoms, units consisting of an aromatic dicarboxylic acid (C) having 12 or less carbon atoms, and units consisting of an aliphatic diamine (D) having 12 or less carbon atoms.
<2> The industrial tube according to <1>, wherein the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms is a dimer acid.
<3> The industrial tube according to <1> or <2>, wherein the aliphatic diamine (B) having 18 or more carbon atoms is a dimer diamine.
<4> The industrial tubing according to any one of <1> to <3>, wherein the aromatic dicarboxylic acid (C) having 12 or less carbon atoms is terephthalic acid.
<5> The industrial tube according to any one of <1> to <4>, wherein the aliphatic diamine (D) having 12 or less carbon atoms is 1,10-decanediamine.
<6> The industrial tubing according to any one of <1> to <5>, wherein the polyamide contains 15 to 70 mass% of units composed of an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms and units composed of an aliphatic diamine (B) having 18 or more carbon atoms, based on the total amount of all monomer components constituting the polyamide.
<7> The industrial tube according to any one of <1> to <6>, wherein the polyamide has a crystalline melting enthalpy of 20 J/g or more.
<8> The industrial tube according to any one of <1> to <7>, wherein the polyamide has an elongation recovery rate of 20% or more in a tensile test.
<9> The aliphatic dicarboxylic acid (A) having 18 or more carbon atoms has 20 to 40 carbon atoms,
the aliphatic diamine (B) having 18 or more carbon atoms has 20 to 40 carbon atoms,
the aromatic dicarboxylic acid (C) having 12 or less carbon atoms has 4 to 12 carbon atoms,
<9> The industrial tube according to any one of <1> to <8>, wherein the aliphatic diamine (D) having 12 or less carbon atoms has 4 to 12 carbon atoms.
<10> The content of units composed of the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms is 2 to 40 mass% based on all monomer components constituting the polyamide,
the content of units composed of the aliphatic diamine (B) having 18 or more carbon atoms is 5 to 45 mass% based on the total monomer components constituting the polyamide,
the content of units composed of the aromatic dicarboxylic acid (C) having 12 or less carbon atoms is 10 to 50 mass% based on all monomer components constituting the polyamide,
<1> The industrial tube according to any one of <1> to <9>, wherein the content of units consisting of the aliphatic diamine (D) having 12 or less carbon atoms is 10 to 50 mass% with respect to all monomer components constituting the polyamide.
<11> The industrial tubing according to any one of <1> to <10>, wherein the industrial tubing is a single-layer tubing containing the polyamide or a multi-layer tubing having a layer containing the polyamide.
<12> The industrial tubing according to any one of <1> to <11>, wherein the industrial tubing is an air tubing, a hydraulic tubing, a paint spray tubing, a high-pressure tubing, an automobile piping tubing, a cooling piping tubing, or a medical tubing.
<13> The industrial tube according to any one of <1> to <12>, wherein the outer diameter of the industrial tube is 3.0 mm to 20 mm and the wall thickness is 0.5 mm to 3.0 mm.
<14> A method for producing an industrial tube, comprising: obtaining a polyamide by the following batch polymerization method or split polymerization method:
a batch polymerization method in which an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms, an aliphatic diamine (B) having 18 or more carbon atoms, an aromatic dicarboxylic acid (C) having 12 or less carbon atoms, and an aliphatic diamine (D) having 12 or less carbon atoms are reacted together and polymerized; or a separate polymerization method in which an aromatic dicarboxylic acid (C) having 12 or less carbon atoms and an aliphatic diamine (D) having 12 or less carbon atoms are reacted separately from an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms and an aliphatic diamine (B) having 18 or more carbon atoms, and polymerized.
<15> The method for producing an industrial tubing according to <14>, wherein the polyamide is a polyamide contained in the industrial tubing according to any one of <1> to <13>.

The present invention makes it possible to provide polyamide-containing industrial tubing that has excellent heat resistance and flexibility.

The polyamide contained in the industrial tubing of the present invention contains units of aliphatic dicarboxylic acid (A) having 18 or more carbon atoms (hereinafter sometimes referred to as component (A)), units of aliphatic diamine (B) having 18 or more carbon atoms (hereinafter sometimes referred to as component (B)), units of aromatic dicarboxylic acid (C) having 12 or less carbon atoms (hereinafter sometimes referred to as component (C)), and units of aliphatic diamine (D) having 12 or less carbon atoms (hereinafter sometimes referred to as component (D)). Components (A) to (D) are contained in the polyamide as monomer components (or monomer residues). Therefore, "units of aliphatic dicarboxylic acid (A) having 18 or more carbon atoms" may be simply expressed as "aliphatic dicarboxylic acid (A) monomer having 18 or more carbon atoms" or its residue. "Units of aliphatic diamine (B) having 18 or more carbon atoms" may be simply expressed as "aliphatic diamine (B) monomer having 18 or more carbon atoms" or its residue. "Units consisting of aromatic dicarboxylic acid (C) having 12 or less carbon atoms" may be simply expressed as "aromatic dicarboxylic acid (C) monomer having 12 or less carbon atoms" or its residue. "Units consisting of aliphatic diamine (D) having 12 or less carbon atoms" may be simply expressed as "aliphatic diamine (D) monomer having 12 or less carbon atoms" or its residue.

The aliphatic dicarboxylic acid (A) having 18 or more carbon atoms used in the polyamide of the present invention is preferably an aliphatic dicarboxylic acid consisting entirely of hydrocarbons except for the carboxyl group, such as hexadecanedicarboxylic acid (18 carbon atoms), octadecanedicarboxylic acid (20 carbon atoms), or dimer acid (36 carbon atoms). Among these, aliphatic dicarboxylic acids having 20 or more carbon atoms are preferred, and dimer acid is more preferred, due to their enhanced flexibility. Dimer acid may be obtained by the addition reaction of two molecules selected from unsaturated fatty acids such as oleic acid and linoleic acid. The two molecules may be the same or different. The dimer acid may be a dicarboxylic acid having unsaturated bonds; however, hydrogenated dicarboxylic acids in which all bonds are saturated are preferred because they are less susceptible to discoloration. (A) may be one of the above, or two or more may be used in combination.

From the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides, the carbon number of component (A) is preferably 20 to 40, more preferably 30 to 40, and even more preferably 34 to 38.

From the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides, the content of component (A) is preferably 2 to 40% by mass, more preferably 5 to 35% by mass, particularly preferably 5 to 17% by mass, and even more preferably 12 to 17% by mass. This content is the content of residues of component (A) and is the ratio to all monomer components constituting the polyamide (or the total amount of their residues). When the polyamide contains two or more types of component (A), the total amount of these components should be within the above range.

The aliphatic diamine (B) having 18 or more carbon atoms used in the polyamide of the present invention is preferably an aliphatic dicarboxylic acid consisting entirely of hydrocarbons except for the amino group, such as octadecanediamine (18 carbon atoms), eicosanediamine (20 carbon atoms), and dimer diamine (36 carbon atoms). Among these, dimer diamine is preferred. By using dimer diamine, the flexibility of the entire polymer can be effectively improved even with a resin composition containing less dimer diamine than other monomers. Dimer diamine is typically produced by reacting dimer acid with ammonia, followed by dehydration, nitrification, and reduction. While dimer diamine may be a diamine containing unsaturated bonds, hydrogenated diamines in which all bonds are saturated are preferred because they are less likely to discolor. Component (B) may be one of the above, or two or more may be used in combination.

The carbon number of component (B) is preferably 20 to 40, more preferably 30 to 40, and even more preferably 34 to 38, from the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides.

From the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides, the content of component (B) is preferably 5 to 45% by mass, more preferably 5 to 35% by mass, particularly preferably 5 to 25% by mass, and even more preferably 13 to 20% by mass. This content is the content of residues of component (B) and is the ratio to all monomer components (or the total amount of their residues) that make up the polyamide. If the polyamide contains two or more types of component (B), the total amount of these components should be within the above range.

Examples of aromatic dicarboxylic acids (C) having 12 or less carbon atoms used in the polyamide of the present invention include sebacic acid (10 carbon atoms), azelaic acid (9 carbon atoms), adipic acid (6 carbon atoms), terephthalic acid (8 carbon atoms), isophthalic acid (8 carbon atoms), and orthophthalic acid (8 carbon atoms). Among these, aromatic dicarboxylic acids having 8 or more carbon atoms are preferred, and terephthalic acid is more preferred, as they tend to further improve heat resistance, flexibility, and rubber elasticity. Component (C) may be used alone or in combination of two or more of the above.

The carbon number of component (C) is preferably 4 to 12, more preferably 6 to 12, and even more preferably 6 to 10, from the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides.

From the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides, the content of component (C) is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, particularly preferably 25 to 40% by mass, and even more preferably 25 to 35% by mass. This content is the content of residues of component (C) and is the ratio to all monomer components (or the total amount of their residues) that make up the polyamide. If the polyamide contains two or more types of component (C), the total amount of these components should be within the above range.

Examples of aliphatic diamines (D) having 12 or fewer carbon atoms used in the polyamide of the present invention include 1,12-dodecanediamine (12 carbon atoms), 1,10-decanediamine (10 carbon atoms), 1,9-nonanediamine (9 carbon atoms), 1,8-octanediamine (8 carbon atoms), and 1,6-hexanediamine (6 carbon atoms). Among these, diamines having 6 or more carbon atoms are preferred, diamines having 8 or more carbon atoms are more preferred, and 1,10-decanediamine is even more preferred, as they tend to further improve heat resistance, flexibility, and rubber elasticity. Component (D) may be used alone or in combination of two or more of the above.

The carbon number of component (D) is preferably 4 to 12, more preferably 6 to 12, and even more preferably 8 to 12, from the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides.

From the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides, the content of component (D) is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, particularly preferably 30 to 45% by mass, and even more preferably 30 to 40% by mass. This content is the content of residues of component (D) and is the ratio to all monomer components (or the total amount of their residues) that make up the polyamide. If the polyamide contains two or more types of component (D), the total amount of all of them should be within the above range.

In the polyamide used in the present invention, it is preferable that units consisting of an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms and units consisting of an aliphatic diamine (B) having 18 or more carbon atoms form soft segments, while units consisting of an aromatic dicarboxylic acid (C) having 12 or less carbon atoms and units consisting of an aliphatic diamine (D) having 12 or less carbon atoms form hard segments. As a result, it is believed that the polyamide can have superior heat resistance while also having sufficiently excellent flexibility. Specifically, in the polyamide used in the present invention, the hard segments act as crosslinking points for the rubber, allowing the soft segments to freely expand and contract, thereby ensuring heat resistance while also exhibiting flexibility. Examples of combinations of components (C) and (D) include terephthalic acid and butanediamine, terephthalic acid and 1,9-nonanediamine, terephthalic acid and 1,10-decanediamine, and terephthalic acid and 1,12-dodecanediamine, with terephthalic acid and 1,10-decanediamine being preferred. The use of terephthalic acid and 1,10-decanediamine makes it easier for the hard segments to become highly crystalline, promoting the formation of a phase-separated structure between the hard and soft segments and resulting in superior flexibility. The term "rubber" is used to describe a substance that exhibits the property of being locally deformed by an external force but returning to its original shape when the force is removed.

The polyamide used in the present invention preferably does not contain polyether or polyester components, which are prone to decomposition during polymerization. Examples of polyether components include polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, and polyoxyethylene-polyoxypropylene glycol. Examples of polyester components include polyethylene adipate, polytetramethylene adipate, and polyethylene sebacate. When polyether or polyester components are used, high polymerization temperatures can cause decomposition.

From the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing said polyamides, the total content of the polyether component and 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 typically 0% by mass. This total content is the content of residues of the polyether component and polyester component, and is the ratio to all monomer components (or the total amount of their residues) that make up the polyamide. The polyether component and polyester component are components that constitute part of the polyamide through covalent bonds with the polyamide, and are not simply blended into the polyamide.

The polyamide used in the present invention may contain an end-capping agent to adjust the degree of polymerization and to inhibit product decomposition and discoloration. 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 above end-capping agents may be used alone, or two or more may be used in combination. The content of the end-capping agent is not particularly limited, but is typically 0 to 10 mol % based on the total molar amount of dicarboxylic acid and diamine.

The polyamide used in the present invention may contain additives. Examples of additives include fibrous reinforcing materials such as glass fiber and carbon fiber; fillers such as talc, swellable clay minerals, silica, alumina, glass beads, and graphite; pigments such as titanium oxide and carbon black; antioxidants; antistatic agents; flame retardants; and flame retardant assistants. Additives may be added during polymerization or by melt-kneading after polymerization.

The total content of units consisting of aliphatic dicarboxylic acid (A) having 18 or more carbon atoms and aliphatic diamine (B) having 18 or more carbon atoms in the polyamide is preferably 15 to 70% by mass, more preferably 15 to 65% by mass, particularly preferably 15 to 40% by mass, and even more preferably 25 to 35% by mass, based on the total monomer components constituting the polyamide.

The industrial tube of the present invention and the polyamide contained therein are sufficiently excellent in heat resistance and flexibility, and usually also have sufficiently excellent rubber elasticity, mechanical properties and surface properties.
In this specification, heat resistance refers to a characteristic in terms of melting point and heat aging resistance. Specifically, it refers to a characteristic of having a higher melting point and a higher tensile strength retention. The tensile strength retention refers to the tensile strength retention (%) after heat treatment at 150°C for 100 hours. For example, even if the melting point is relatively high, if the heat aging resistance is poor, the tensile strength retention after heat treatment will be low, resulting in the material being unable to withstand use at relatively high temperatures. Furthermore, even if the heat aging resistance is good, if the melting point is relatively low, the material will melt at a relatively low temperature, resulting in the material being unable to withstand use at relatively high temperatures.
Flexibility refers to a property related to flexural modulus, and more specifically refers to a property having a moderately small flexural modulus.
Rubber elasticity refers to a property related to elongation recovery rate, and more specifically refers to a property having a large elongation recovery rate.
The mechanical properties refer to properties related to tensile strength, and more specifically, to properties having a larger tensile strength.
The surface property refers to the property of the components leaching out to the surface, and more specifically, refers to the property of the components leaching out to the surface being sufficiently suppressed even when heat treated at 100° C. for 100 hours.

The melting point of polyamide, which is one indicator of heat resistance, must be 240°C or higher, and from the perspective of further improving heat resistance, it is preferably 300°C or higher, and more preferably 305°C or higher. There are no particular upper limits on the melting point, and for example, the melting point may usually be 350°C or lower, particularly 330°C or lower. If the melting point is too low, it will melt at a relatively low temperature and will not be able to withstand use at relatively high temperatures.

The melting point of the polyamide was determined using a differential scanning calorimeter DSC-7 (PerkinElmer) at a heating rate of 20°C/min, using the exothermic peak temperature.

Regarding the heat aging resistance of polyamides, which is one indicator of heat resistance, the tensile breaking strength retention rate is typically 70% or more, and from the perspective of further improving heat resistance, it is preferably 75% or more, and more preferably 80% or more.

The tensile strength retention rate of polyamide is a value expressed as the ratio of the tensile strength after heat treatment to the tensile strength before heat treatment, measured in accordance with ISO 178 before and after heat treatment at 150°C for 100 hours. The tensile strength before heat treatment is typically 10 MPa or more, and from the perspective of further improving mechanical properties, it is preferably 20 MPa or more, and more preferably 30 MPa or more. There is no particular upper limit for the tensile strength before heat treatment, and the tensile strength is typically 100 MPa or less.

The flexural modulus of polyamide, which is an indicator of flexibility, must be between 100 and 1300 MPa. From the perspective of further improving flexibility, it is preferably between 100 and 1200 MPa, and more preferably between 100 and 1000 MPa. If the flexural modulus is too high, flexibility will decrease. If the flexural modulus is too low, the overall material will be too soft and will not withstand use as industrial tubing.

The flexural modulus of polyamide is measured at 23°C in accordance with ISO 178.

In the polyamide used in the present invention, the crystalline melting enthalpy, which is an indicator of the crystallinity of the hard segments, is preferably 20 J/g or more, more preferably 40 J/g or more, and even more preferably 60 J/g or more, from the viewpoint of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of the polyamide and industrial tubing containing said polyamide. The crystalline melting enthalpy is typically 120 J/g or less (particularly 90 J/g or less).

The crystalline melting enthalpy of polyamide was measured using a differential scanning calorimeter DSC-7 (PerkinElmer) at a heating rate of 20°C/min, using the heat quantity of the endothermic peak.

The elongation recovery rate of polyamide is typically 20% or more, and from the perspective of further improving rubber elasticity, it is preferably 30% or more, more preferably 50% or more, and even more preferably 55% or more.

The elongation recovery rate of polyamide is measured by pulling a dumbbell test piece (4 mm thick) prepared in accordance with ISO 178 at a tensile test speed of 5 mm/min in an environment of 23°C until it reaches an elongation of 11 mm, and then immediately returning it to its original state at the same speed.

The density of the polyamide is usually 0.90 to 1.10 g/cm ³ , and from the viewpoint of further improving rubber elasticity, it is preferably 0.95 to 1.05, and more preferably 0.98 to 1.01.

The density of polyamide is measured in accordance with JIS K 7112 using an ISO multipurpose test piece.

The polyamide used in the present invention can be produced by any method, including but not limited to, a method in which an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms, an aliphatic diamine (B) having 18 or more carbon atoms, an aromatic dicarboxylic acid (C) having 12 or less carbon atoms, and an aliphatic diamine (D) having 12 or less carbon atoms are reacted together (hereinafter sometimes referred to as a "batch polymerization method"), or a method in which components (C) and (D) are reacted separately from components (A) and (B) (hereinafter sometimes referred to as a "split polymerization method"). Polyamides are preferably produced by a split polymerization method from the perspective of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing such polyamides. By producing polyamides by a split polymerization method, the polyamides have a more favorable crystalline melting enthalpy, thereby further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing such polyamides.

In bulk polymerization, all of the specified components are mixed and polymerized. There are no particular limitations on the polymerization method, but examples include a method in which the mixture is heated to a temperature below the melting point of the resulting polyamide and polymerized by maintaining that temperature under a nitrogen stream while removing condensed water from the system. The "melting point of the resulting polyamide" refers to the "melting point of the desired polyamide," and may be, for example, the "melting point of the hard segment polymer" described in the separate polymerization method described below.

Therefore, when producing polyamide by bulk polymerization, for example, a hard segment polymer is first obtained by the production method described below in the section polymerization method. The melting point of the resulting hard segment polymer is then measured. The melting point can be measured using a differential scanning calorimeter, for example. The mixture containing the monomer (or prepolymer) is then subjected to a polymerization reaction at a temperature below the melting point (particularly, a temperature below the melting point) to produce polyamide. For example, when dimer acid, dimer diamine, terephthalic acid, and 1,10-decanediamine are used as components (A) to (D), respectively, the melting point of the "target polyamide" (e.g., the "melting point of the hard segment polymer") is 315°C, and the polymerization temperature in the bulk polymerization method may be 220 to 300°C (particularly, 240 to 280°C). In this case, the polymerization time in the bulk polymerization method is not particularly limited as long as sufficient polymerization is achieved, and may be, for example, 1 to 10 hours (particularly, 3 to 7 hours).

In the separate polymerization method, component (C) and component (D) are reacted separately from component (A) and component (B) to carry out polymerization. For example, component (C) is reacted with component (D) to obtain a reaction product, and then the reaction product is further reacted with component (A) and component (B) to carry out polymerization. More specifically,
Component (A),
Component (B),
a reaction product of component (C) and component (D);
react to polymerize.

In such a separate polymerization method, components (A) and (B) may be used in an unreacted state or in a reacted state (i.e., in the form of their reaction product). For example, the polyamide used in the present invention may be obtained by first reacting components (A) and (B), and then polymerizing the resulting reaction product of components (A) and (B) with the reaction product of components (C) and (D). More specifically, the polyamide used in the present invention may be obtained by reacting and polymerizing the reaction product of components (A) and (B) with the reaction product of components (C) and (D). From the perspective of further improving the heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties of polyamides and industrial tubing containing such polyamides, it is preferable that components (A) and (B) be used in a reacted state (i.e., in the form of their reaction product).

Polyamides polymerized by the segmental polymerization method differ from polyamides polymerized by the bulk polymerization method in that they are obtained as polyamides composed of hard segments consisting of components (C) and (D) and soft segments consisting of components (A) and (B). Therefore, while polyamides polymerized by the bulk polymerization method are "random polyamides," polyamides polymerized by the segmental polymerization method can be called "block polyamides" from the perspective of the hard and soft segments they contain.

In the segmental polymerization method, the chain length of the resulting reaction product can be controlled by adjusting the monomer ratio [(C)/(D)] of the aromatic dicarboxylic acid (C) having 12 or less carbon atoms and the aliphatic diamine (D) having 12 or less carbon atoms. As a result, the flexibility and rubber elasticity of the resulting polyamide can be controlled. To achieve more satisfactory improvements in flexibility and rubber elasticity, the molar ratio [(C)/(D)] is preferably 45/55 to 60/40, and more preferably 45/55 to 55/45.

In the segmental polymerization method, the method for producing a reaction product containing an aromatic dicarboxylic acid (C) having 12 or less carbon atoms and an aliphatic diamine (D) having 12 or less carbon atoms (hereinafter sometimes simply referred to as "reaction product production method X") is not particularly limited. For example, it may involve heating to a temperature above the melting point of component (D) and below the melting point of component (C), and adding component (D) so as to maintain component (C) in a powder state. For example, when terephthalic acid and 1,10-decanediamine are used as components (C) and (D), respectively, the heating temperature may be 100 to 240°C (particularly 140 to 200°C). Component (D) is preferably added continuously, for example, over a period of 1 to 10 hours (particularly 1 to 5 hours).

The reaction product of component (C) and component (D) may be in the form of a salt of component (C) and component (D), or in the form of a condensate (or oligomer or prepolymer) thereof, or in the form of a composite of these.

When components (A) and (B) are reacted in advance, the method for reacting the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms with the aliphatic diamine (B) having 18 or more carbon atoms is not particularly limited, but examples include a method in which the reaction is carried out at a temperature of 80 to 150°C (particularly 100 to 150°C) for 0.5 to 3 hours.

The reaction product of component (A) and component (B), like the reaction product of component (C) and component (D), may be in the form of a salt, a condensate thereof (or an oligomer or prepolymer), or a composite of these.

In the segmental polymerization method, the polymerization method is not particularly limited, but examples include polymerization at a temperature below (preferably below) the melting point of the hard segment polymer (i.e., polyamide composed only of components (C) and (D) that constitute the hard segments). Specifically, polymerization is carried out by heating to a temperature below the melting point of the hard segment polymer (i.e., polyamide composed only of components (C) and (D) that constitute the hard segments) and maintaining that temperature under a nitrogen stream while removing condensed water from the system. Polymerization in this manner allows polymerization to occur in a molten state, without melting the hard segments. Polymerization at a temperature below the melting point of the hard segment polymer is particularly effective for polymerizing high-melting polyamides of 280°C or higher, which tend to decompose due to the high polymerization temperature.

The "melting point of the hard segment polymer" refers to the melting point of a polyamide obtained by fully polymerizing only the hard segment components (C) and (D) as monomer components. The "melting point of the hard segment polymer" may be, for example, the melting point of a polyamide obtained by fully polymerizing only the components (C) and (D) as monomer components, using the method described in International Publication No. 2013/042541. Specifically, the "melting point of the hard segment polymer" refers to the melting point of a polyamide (hard segment polymer) obtained by a method including step (i) of obtaining a reaction product from components (C) and (D) and step (ii) of polymerizing the resulting reaction product. In the process of producing the hard segment polymer, step (i) involves heating components (C) and (D) to a temperature above the melting point of component (D) but below the melting point of component (C), and adding component (D) so as to maintain component (C) in a powder state, thereby obtaining a reaction product. In step (i), for example, when terephthalic acid and 1,10-decanediamine are used as components (C) and (D), respectively, the heating temperature may be 100 to 240°C (preferably 140 to 200°C, particularly 170°C). Component (D) is preferably added continuously, for example, over a period of 1 to 10 hours (preferably 1 to 5 hours, particularly 2.5 hours). In the process of producing the hard segment polymer, in step (ii), the solid-phase reaction product obtained in step (i) is sufficiently heated to maintain the solid phase, thereby carrying out polymerization (i.e., solid-phase polymerization). In step (ii), for example, when terephthalic acid and 1,10-decanediamine are used as components (C) and (D), respectively, the heating temperature (i.e., polymerization temperature) may be 220 to 300°C (preferably 240 to 280°C, particularly 260°C), and the heating time (i.e., polymerization time) may be 1 to 10 hours (preferably 3 to 7 hours, particularly 5 hours). Steps (i) and (ii) are preferably carried out in a stream of inert gas such as nitrogen. For example, when terephthalic acid and 1,10-decanediamine are used as components (C) and (D), respectively, the melting point of the "hard segment polymer" is typically 315°C.

Therefore, when producing polyamide by the segmental polymerization method, for example, the following method can be used. First, components (C) and (D) constituting the polyamide are sufficiently polymerized using the above-described steps (i) and (ii) to obtain a polyamide (i.e., a hard segment polymer). Next, the melting point of the resulting polyamide is measured. The melting point is measured in the same manner as in the bulk polymerization method. Subsequently, components (C) and (D) are reacted using the above-described reaction product production method X to obtain a reaction product. This reaction product is then further reacted with components (A) and (B) at a temperature below the "melting point of the hard segment polymer" to polymerize it, thereby producing a polyamide. When dimer acid, dimer diamine, terephthalic acid, and 1,10-decanediamine are used as components (A) to (D), respectively, the polymerization temperature in the segmental polymerization method may be 220 to 300°C (preferably 240 to 280°C, particularly 260°C). In this case, the polymerization time in the split polymerization method is not particularly limited as long as sufficient polymerization is carried out, and may be, for example, 1 to 10 hours (preferably 3 to 7 hours, particularly 5 hours).

In the bulk polymerization method and the segmental polymerization method (hereinafter sometimes simply referred to as the "polyamide production method used in the present invention"), a catalyst may be used if necessary. Examples of catalysts include phosphoric acid, phosphorous acid, hypophosphorous acid, and salts thereof. The catalyst content is not particularly limited, but is typically 0 to 2 mol % based on the total molar amount of dicarboxylic acid and diamine.

In the method for producing the polyamide used in the present invention, organic solvents or water may be added as needed.

In the method for producing polyamide used in the present invention, polymerization may be carried out in a closed system or at atmospheric pressure. When carried out in a closed system, pressure may increase due to the evaporation of monomers and the generation of condensed water, so it is preferable to control the pressure appropriately. On the other hand, if the boiling point of the monomers used is high and the monomers do not leak out of the system even without pressurization, polymerization can be carried out at atmospheric pressure. For example, a combination of dimer acid, dimer diamine, terephthalic acid, and decanediamine can be polymerized at atmospheric pressure.

In the method for producing the polyamide used in the present invention, it is preferable to carry out polymerization in a nitrogen atmosphere or under vacuum to prevent oxidative degradation.

The polymerized polyamide may be extruded into strands and pelletized, or may be hot-cut or underwater-cut into pellets.

In the method for producing polyamide used in the present invention, solid-state polymerization may be performed after polymerization to further increase the molecular weight. Solid-state polymerization is particularly effective when the viscosity during polymerization is high and operation becomes difficult. Solid-state polymerization is preferably performed by heating the resin composition at a temperature below the melting point of the resin composition under an inert gas flow or reduced pressure for 30 minutes or more, and more preferably for 1 hour or more. The melting point of the resin composition may be the same temperature as the "melting point of the hard segment polymer" described above.

The industrial tubing of the present invention can be obtained by extruding polyamide.

When manufacturing the industrial tubing of the present invention, it is preferable to use polyamide (especially pellets) that have been thoroughly dried. If the polyamide pellets contain a high moisture content, they may foam inside the cylinder of the molding machine, making it difficult to obtain an optimal molded product. The moisture content of the pellets used for molding is preferably less than 0.3 parts by mass, and more preferably less than 0.1 parts by mass, per 100 parts by mass of polyamide.

The outer diameter of industrial tubing is designed taking into account the flow rate of the fluid flowing inside. It is also desirable that the wall thickness of the industrial tubing be designed to a thickness that does not increase the permeability of the contents inside, is thick enough to maintain the required burst pressure of the tubing, and maintains flexibility that allows for easy assembly. The outer diameter of industrial tubing is, for example, 3.0 to 20.0 mm (particularly 3.0 to 10.0 mm), and the wall thickness is preferably 0.5 to 3.0 mm.

The industrial tubing of the present invention only needs to contain at least one layer containing the polyamide of the present invention, and may have a single layer or two or more layers as needed. Specifically, the industrial tubing of the present invention may be a single-layer tubing containing the polyamide described above, or a multi-layer tubing having one or more layers containing the polyamide described above.

In addition to the polyamide, the single-layer tube may contain other thermoplastic resins and/or additives. Specific examples of other thermoplastic resins include polymers similar to the thermoplastic resins described below as materials constituting the "other layers" of the multi-layer tube. Additives that are traditionally added to industrial tubing can be used, including pigments, dyes, colorants, heat stabilizers, antioxidants, weathering agents, UV absorbers, light stabilizers, lubricants, crystal nucleating agents, crystallization accelerators, mold release agents, antistatic agents, plasticizers, stabilizers such as copper compounds, antistatic agents, flame retardants, glass fibers, lubricants, fillers, reinforcing fibers, reinforcing particles, and foaming agents. The content of the polyamide in the single-layer tube is not particularly limited, but is typically 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 99% by weight or more, and particularly preferably 100% by weight, based on the total weight of the single-layer tube.

When the industrial tube of the present invention is composed of two or more layers, the arrangement of the layer containing the polyamide (hereinafter sometimes referred to as the "polyamide-containing layer") is not particularly limited, but in order to reduce the flow path resistance of the fluid flowing inside and to reduce unnecessary residue, it is preferable that the polyamide-containing layer be the innermost layer of the tube.

In a multilayer tube, the polyamide-containing layer may contain, in addition to the polyamide described above, other thermoplastic resins and/or additives. The other thermoplastic resins and additives may be selected from the same materials as the other thermoplastic resins and additives in the single-layer tube. The content of the polyamide described above in the polyamide-containing layer is not particularly limited, and is usually 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 99% or more, and particularly preferably 100% of the total amount of the polyamide-containing layer.

When the industrial tubing of the present invention is a multilayer tubing, the materials constituting the "other layers" other than the polyamide-containing layer are not particularly limited. From the perspective of tubing moldability, thermoplastic resins are preferred. Such thermoplastic resins can be appropriately selected taking into account the tubing's intended use and adhesion to adjacent layers. Specific examples include polyester-based resins such as polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polyethylene isophthalate; fluororesins such as ethylene-tetrafluoroethylene copolymer (ETFE), vinylidene fluoride copolymer (PVDF), polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer; polyolefin-based resins such as polyethylene, polypropylene, polystyrene, and saponified ethylene-vinyl acetate copolymer (EVOH); polyether resins such as polyacetal and polyphenylene sulfide; and polyamides such as semi-aromatic polyamides and aliphatic polyamides. The "other layers" may contain additives. The additive may be selected from the same materials as the additive in the single-layer tube.

The present invention will be explained in detail below using examples, but the present invention is not limited to these examples.

The physical properties of the polyamide were measured by the following methods.
(1) Resin Composition The resulting pellets and 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 intensity of each copolymerization component (resolution: 500 MHz, solvent: a mixed solvent of deuterated trifluoroacetic acid and deuterated chloroform in a volume ratio of 4/5, temperature: 23°C). In Tables 1 to 3, the resin compositions are shown as final compositions in terms of mass ratio.

(2) Melting Point and Crystalline Melting Enthalpy A few milligrams of the obtained pellets or powder was taken and measured using a differential scanning calorimeter DSC-7 (manufactured by PerkinElmer) by heating the sample to 350°C at a heating rate of 20°C/min, then holding the sample at 350°C for 5 minutes, cooling the sample to 25°C at a cooling rate of 20°C/min, further holding the sample at 25°C for 5 minutes, and then heating the sample again at a heating rate of 20°C/min.
The melting point was determined as the top of the exothermic peak during the reheating, and the heat of the endothermic peak was determined as the crystalline melting enthalpy, which was calculated from the peak area in the temperature range from the start to the end of melting.

Melting point: ⊚: 305°C or higher (best).
○: 300°C or higher and lower than 305°C (good).
△: 240°C or higher and lower than 300°C (no practical problems).
×: Less than 240° C. (problems in practical use).
Crystal fusion enthalpy: 60 J/g or more (best).
○: 40 J/g or more and less than 60 J/g (good).
Δ: 20 J/g or more and less than 40 J/g (no problem in practical use).
×: Less than 20 J/g (problems in practical use).

(3) Flexural modulus (flexibility)
The tube of the present invention has excellent flexibility.
Specifically, when the polyamide pellets used for the tube are injection molded into a 4 mm thick test piece (dumbbell test piece), the flexural modulus at 23°C measured in accordance with ISO 178 is preferably 1300 MPa or less (△: no practical problem), more preferably 1200 MPa or less (○: good), and even more preferably 1000 MPa or less (◎: best). Furthermore, from the viewpoint of not impairing the function as a tube, the flexural modulus must be 100 MPa or more, and preferably 300 MPa or more. Therefore, when the flexural modulus (flexibility) is more than 1300 MPa or less than 100 MPa, it is evaluated as being problematic for practical use.

(4) Elongation recovery rate (rubber elasticity)
Dumbbell test pieces were prepared in the same manner as in (3) above, and the elongation recovery rate was measured using a 2020 model testing machine manufactured by INTESCO Corp. The test pieces were stretched to an elongation of 11 mm under conditions of a chuck distance of 55 mm and a tensile test speed of 5 mm/min in an environment of 23°C, and then immediately returned to their original state at the same speed, and the residual strain A (mm) was determined when the stress became zero.
The elongation recovery rate was calculated using the residual strain A according to the following formula.
Elongation recovery rate (%) = (11-A)/11×100
◎: 50% or more (best).
○: 30% or more and less than 50% (good).
△: 20% or more and less than 30% (no problem in practical use).
×: Less than 20% (problems in practical use).

(5) Density The obtained polyamide pellets were thoroughly dried and then injection-molded using an injection molding machine (FANUC Corporation, S2000i-100B model) under the conditions of a cylinder temperature of "melting point of polyamide + 15°C" and a residence time in the cylinder of 10 seconds to prepare test specimens (ISO multipurpose test specimens). Measurements were carried out using these test specimens in accordance with JIS K 7112.

(6) Tensile strength (mechanical properties) and heat aging resistance Test pieces (ISO multipurpose test pieces) were prepared by injection molding the polyamide pellets using an injection molding machine S2000i-100B (manufactured by Fanuc Corporation) under the following conditions: a cylinder temperature of "melting point of polyamide + 15°C", a mold temperature of "melting point of polyamide - 175°C", and a residence time in the cylinder of "10 seconds".
Using the test pieces prepared by the above method, the tensile strength was measured in accordance with ISO178.
Further, the test specimens were heat-treated in a heating furnace under an atmospheric atmosphere at 150°C for 100 hours to prepare test specimens, and the tensile breaking strength retention (%) of the test specimens was determined to evaluate the heat aging resistance at 150°C. The tensile breaking strength retention is a value expressed as the ratio of the tensile breaking strength after heat treatment to the tensile breaking strength before heat treatment.

Tensile strength: Excellent: 30 MPa or more (best).
○: 20 MPa or more and less than 30 MPa (good).
△: 10 MPa or more and less than 20 MPa (no problem in practical use).
×: Less than 10 MPa (problems in practical use).

Heat aging resistance ⊚: The retention of tensile strength at break after heat treatment at 150°C for 500 hours was 80% or more (best).
Good: The retention of tensile strength at break after heat treatment at 150° C. for 500 hours was 75% or more and less than 80% (good).
Δ: The retention of tensile strength at break after heat treatment at 150° C. for 500 hours was 70% or more but less than 75% (no problem in practical use).
×: The retention of tensile breaking strength after heat treatment at 150° C. for 500 hours was less than 70% (problems in practical use).

(7) Surface Properties After Heat Treatment The tubes manufactured in each of the Examples and Comparative Examples were heat treated in a heating furnace in the air at 100°C for 100 hours, and the surface condition of the tube was visually observed. If no bleeding was observed compared to the surface condition of the tube immediately after manufacture, the surface was judged to be good.
⊚: The surface condition of the tube after the heat treatment was unchanged from the surface condition of the tube immediately after production (best).
◯: The amount of bleed-out on the tube surface after heat treatment was only slightly increased compared to the amount of bleed-out on the tube surface immediately after production, and the surface condition of the tube after heat treatment was good (good).
Δ: The amount of bleed-out on the tube surface after heat treatment was greater than the amount of bleed-out on the tube surface immediately after production, but the surface condition of the tube after heat treatment was practically acceptable.
x: The amount of bleed-out on the tube surface after heat treatment was significantly greater than the amount of bleed-out on the tube surface immediately after production, and the surface condition of the tube after heat treatment was problematic for practical use.

Example 1 (Reference Example) (One-step method = batch polymerization method)
A reaction vessel equipped with a heating mechanism and a stirring mechanism was charged with 26.7 parts by mass of dimer acid, 25.3 parts by mass of dimer diamine, 23.5 parts by mass of terephthalic acid, 24.4 parts by mass of 1,10-decanediamine, and 0.10 parts by mass of sodium hypophosphite monohydrate. The amount of sodium hypophosphite monohydrate was 0.24 mol % based on the total molar amount of the dicarboxylic acid and the diamine.
Thereafter, the mixture was heated to 260° C. with stirring, and polymerization was carried out for 5 hours at 260° C. under normal pressure in a nitrogen stream while removing condensed water from the system. During the polymerization, the system was in a suspended state.
After the polymerization was completed, the mixture was removed, cut, and dried to obtain polyamide pellets.

Examples 2 and 3 (Reference Examples) and Comparative Examples 1 to 3
Pellets were obtained in the same manner as in Example 1, except that the monomers charged into the reaction vessel were changed as shown in Table 1.

Example 4 (Two-step method = separate polymerization method)
Preparation of Reaction Product 26.8 parts by mass of terephthalic acid and 0.10 parts by mass of sodium hypophosphite monohydrate were charged into a ribbon blender-type reactor and heated to 170°C while stirring at 30 rpm under a sealed nitrogen atmosphere. Thereafter, while maintaining the temperature at 170°C and the rotation speed at 30 rpm, 23.4 parts by mass of 1,10-decanediamine heated to 100°C was continuously added (continuous injection method) using a liquid injection device over 2.5 hours to obtain a reaction product. The molar ratio of raw material monomers was terephthalic acid:1,10-decanediamine = 54.2:45.8.
Preparation of Polyamide: 18.6 parts by mass of dimer acid and 31.1 parts by mass of dimer diamine were placed in a reaction vessel equipped with a heating mechanism and a stirring mechanism. After stirring at 100°C for 1 hour, 50.2 parts by mass of the reaction product was added thereto while stirring.
Thereafter, the mixture was heated to 260° C. with stirring, and polymerization was carried out for 5 hours at 260° C. under a nitrogen stream at atmospheric pressure while removing condensed water from the system. During the polymerization, the system was in the state of a suspended solution.
After the polymerization was completed, the product was discharged, cut, and dried to obtain pellets. The amount of sodium hypophosphite monohydrate was 0.33 mol % based on the total molar amount of the dicarboxylic acid and the diamine.

Examples 5 to 7 and Comparative Examples 4 to 6, 10 and 11
Pellets were obtained by the same procedure as in Example 4, except that the type and/or amount of the monomers charged into the reaction vessel was changed as shown in Tables 1 to 3.

Comparative Example 7
49.0 parts by mass of terephthalic acid and 0.10 parts by mass of sodium hypophosphite monohydrate were charged into a powder stirring device equipped with a heating mechanism. While heating to 170°C and stirring, 50.9 parts by mass of 1,10-decanediamine were added in small portions over 3 hours to obtain a nylon salt. The nylon salt was then heated to 250°C with stirring, and polymerization was carried out for 7 hours at 250°C under atmospheric pressure in a nitrogen stream while removing condensed water from the system. During the polymerization, the system was in a powder state.
After the polymerization was completed, the mixture was poured out to obtain a polyamide powder.

Comparative Example 8
Pellets were obtained in the same manner as in Comparative Example 7, except that the type and/or amount of the monomers charged into the reaction vessel was changed as shown in Table 2.

Comparative Example 9
Polyamide 12: Pellets of Ube Industries (UBESTA3030UFX1) were used.

Tube Production The polyamide pellets (or polyamide powder) described above were melted in a Plabor tube molding machine at a cylinder temperature of 300 to 340°C, and the extruded molten resin was cooled in a sizing die and taken up to produce a single-layer tube with an outer diameter of 10 mm and a wall thickness of 2 mm.

The polyamides of Examples 1 to 7 met the requirements of the present invention and therefore all had excellent heat resistance (melting point and heat aging resistance), flexibility, and rubber elasticity. Furthermore, the polyamides of Examples 1 to 7 maintained good surface properties even after heat treatment after the production of single-layer tubes.

The polyamides of Comparative Examples 1, 2, 4 and 5 had too low a flexural modulus and poor heat aging resistance.
The polyamides of Comparative Examples 3, 6, 7 and 8 had too high a flexural modulus and poor flexibility.
The polyamide of Comparative Example 9 had too low a melting point and poor flexibility.

The industrial tubing of the present invention includes all tubing used in fields such as manufacturing (or industry), mining, agriculture, fishing, transportation, and communications. Among the tubing used in these fields, the industrial tubing of the present invention is suitable as tubing that requires at least one of the following properties (e.g., all of these properties): heat resistance, flexibility, rubber elasticity, mechanical properties, and surface properties. Specific examples of uses for the industrial tubing of the present invention include air tubing, hydraulic tubing, paint spray tubing, high-pressure tubing, automotive piping tubing, cooling piping tubing, and medical tubing.

Claims (13)

The polyamide contains units consisting of an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms, units consisting of an aliphatic diamine (B) having 18 or more carbon atoms, units consisting of an aromatic dicarboxylic acid (C) having 12 or less carbon atoms, and units consisting of an aliphatic diamine (D) having 12 or less carbon atoms, and has a melting point of 240°C or higher, a flexural modulus of 100 to 1,300 MPa , and an elongation recovery rate in a tensile test of 50% or higher ,
an industrial tube, wherein the polyamide contains 15 to 70 mass% of units composed of the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms and units composed of the aliphatic diamine (B) having 18 or more carbon atoms, based on the total amount of monomer components constituting the polyamide . The industrial tubing described in claim 1, wherein the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms is a dimer acid. The industrial tubing described in claim 1 or 2, wherein the aliphatic diamine (B) having 18 or more carbon atoms is a dimer diamine. The industrial tubing described in any one of claims 1 to 3, wherein the aromatic dicarboxylic acid (C) having 12 or less carbon atoms is terephthalic acid. The industrial tubing described in any one of claims 1 to 4, wherein the aliphatic diamine (D) having 12 or less carbon atoms is 1,10-decanediamine. The industrial tubing according to any one of claims 1 to 5 , wherein the polyamide has a crystalline melting enthalpy of 20 J/g or more. The industrial tubing according to any one of claims 1 to 6, wherein the polyamide comprises a block polyamide comprising hard segments each comprising a unit consisting of the aromatic dicarboxylic acid (C) having 12 or less carbon atoms and a unit consisting of the aliphatic diamine (D) having 12 or less carbon atoms, and soft segments each comprising a unit consisting of the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms and aliphatic diamine (B) having 18 or more carbon atoms. the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms has 20 to 40 carbon atoms,
the aliphatic diamine (B) having 18 or more carbon atoms has 20 to 40 carbon atoms,
the aromatic dicarboxylic acid (C) having 12 or less carbon atoms has 4 to 12 carbon atoms,
The industrial tubing according to any one of claims 1 to 7 , wherein the aliphatic diamine (D) having 12 or less carbon atoms has 4 to 12 carbon atoms. the content of units composed of the aliphatic dicarboxylic acid (A) having 18 or more carbon atoms is 2 to 40 mass% based on the total monomer components constituting the polyamide,
the content of units composed of the aliphatic diamine (B) having 18 or more carbon atoms is 5 to 45 mass% based on the total monomer components constituting the polyamide,
the content of units composed of the aromatic dicarboxylic acid (C) having 12 or less carbon atoms is 10 to 50 mass% based on all monomer components constituting the polyamide,
The industrial tubing according to any one of claims 1 to 8 , wherein the content of units consisting of the aliphatic diamine (D) having 12 or less carbon atoms is 10 to 50 mass% based on the total monomer components constituting the polyamide. The industrial tubing according to any one of claims 1 to 9 , wherein the industrial tubing is a single-layer tubing containing the polyamide or a multi-layer tubing having a layer containing the polyamide. The industrial tubing according to any one of claims 1 to 10 , wherein the industrial tubing is an air tubing, a hydraulic tubing, a paint spray tubing, a high-pressure tubing, an automotive tubing, a cooling tubing or a medical tubing. The industrial tube according to any one of claims 1 to 11 , wherein the outer diameter of the industrial tube is 3.0 mm to 20 mm and the wall thickness is 0.5 mm to 3.0 mm. A method for producing an industrial tubing, comprising: carrying out polymerization by the following divided polymerization method to obtain a polyamide , wherein the polyamide is the polyamide contained in the industrial tubing according to any one of claims 1 to 12:
A separate polymerization method in which an aromatic dicarboxylic acid (C) having 12 or less carbon atoms and an aliphatic diamine (D) having 12 or less carbon atoms are reacted and polymerized separately from an aliphatic dicarboxylic acid (A) having 18 or more carbon atoms and an aliphatic diamine (B) having 18 or more carbon atoms.