WO2023149547A1

WO2023149547A1 - Polyamide resin composition and film thereof

Info

Publication number: WO2023149547A1
Application number: PCT/JP2023/003576
Authority: WO
Inventors: 敦志山下; 恵太郎小野; 剛中村
Original assignee: Ｕｂｅ株式会社
Priority date: 2022-02-03
Filing date: 2023-02-03
Publication date: 2023-08-10

Abstract

This polyamide resin composition is obtained by blending, in 100 mass% of the polyamide resin composition: 70.00-95.00 mass% of an aliphatic homopolyamide resin (A) having relative viscosity of 3.40-4.50; 1.00-25.00 mass% of an aliphatic homopolyamide resin (B) having relative viscosity of 2.00-2.60; 0-15.00 mass% of an aliphatic copolymerized polyamide resin (C); 0.01-0.50 mass% of an anti-blocking agent (D); and 0.02-0.20 mass% of a lubricant (E).

Description

Polyamide resin composition and its film

The present invention relates to polyamide resin compositions and films thereof.

Polyamide resins have excellent mechanical strength, thermal properties, chemical properties, and molding processability, so they are widely used in various parts in the automotive field, electronic and electrical fields, as well as films, fibers, and monofilaments. .
Among these uses, polyamide resin films are widely used due to their excellent gas barrier properties and mechanical properties. A polyamide resin film is made of a composition containing a polyamide resin, a lubricant, and other additives.

As a method for producing a polyamide resin containing such additives, Patent Document 1 describes adding a masterbatch of inorganic particles and a part of the lubricant to the polyamide resin. Patent Literature 2 describes that a film is produced by a specific method from a polyamide resin using different masterbatches for each type of additive. Patent Document 3 describes that inorganic particles are made into a masterbatch, a lubricant is added to a polyamide resin as a main component, and the two are mixed to obtain a film. In Patent Document 4, a polyamide resin having a specific relative viscosity is used as the main component, and a masterbatch obtained by blending a lubricant with a polyamide having a lower relative viscosity than the main component is mixed with the main component polyamide resin to form a film. It is stated to obtain

JP-A-2006-131891 Japanese Patent Application Laid-Open No. 2021-88190 JP 2017-171741 A JP 2011-126937 A

Polyamide resin films are required to be transparent and glossy because they are used for food packaging applications. In addition, it is also required that it should not be easily cut by contact with the contents or the outside. On the other hand, it is also required that the pressure of the resin composition is such that excessive pressure is not applied to the apparatus during film production, and that the resin composition is free from burden during stretching.

Although the transparency and gloss have been confirmed in Patent Documents 1 to 4, there is still room for investigation, and furthermore, the strength against puncture and the polyamide resin composition that does not have a burden on production have not been studied. rice field.

Therefore, in the present invention, the resin pressure during molding of the polyamide resin composition is moderate, and the stretching stress during molding is suppressed, resulting in excellent moldability, and when made into a film, the strength against piercing is high. An object of the present invention is to provide a polyamide resin composition which is excellent in slipperiness, transparency and gloss of a film.

The present invention is, for example, the following [1] to [12].
[1] In 100% by mass of the polyamide resin composition, 70 to 95% by mass of an aliphatic homopolyamide resin (A) having a relative viscosity of 3.40 to 4.50, and an aliphatic homo having a relative viscosity of 2.00 to 2.60 Polyamide resin (B) 1 to 25% by mass, aliphatic copolymerized polyamide resin (C) 0 to 15% by mass, antiblocking agent (D) 0.01 to 0.50% by mass, and lubricant (E) 0.02 A polyamide resin composition containing 0.20% by mass.
[2] The polyamide resin composition of [1], wherein the aliphatic homopolyamide resin (A) has a terminal amino group concentration of 30 to 39 μmol/g.
[3] The polyamide resin composition according to [1] or [2], wherein the aliphatic homopolyamide resin (B) has a terminal amino group concentration of 30 to 100 µmol/g.
[4] The aliphatic homopolyamide resin (A) is at least one selected from the group consisting of polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyamide 611 and polyamide 612. A polyamide resin composition according to any one of [1] to [3].
[5] At least aliphatic homopolyamide resin (B) is independently selected from the group consisting of polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyamide 611 and polyamide 612 The polyamide resin composition according to any one of [1] to [4].
[6] The polyamide resin composition of any one of [1] to [5], wherein the content of the aliphatic copolyamide resin (C) is 2 to 11% by mass.
[7] The polyamide resin composition of any one of [1] to [6], wherein the lubricant (E) is a combination of two or more lubricants.
[8] Lubricant (E) includes polyalkylene glycol terminal-modified products, phosphates, phosphites, higher fatty acid monoesters, higher fatty acids, higher fatty acid metal salts, carboxylic acid amides, magnesium silicate, The polyamide resin composition of any one of [1] to [7], which is at least one selected from the group consisting of dibenzylidene sorbitols and polyolefin waxes.
[9] The polyamide resin composition of any one of [1] to [8], wherein the lubricant (E) contains a higher fatty acid metal salt and a carboxylic acid amide.
[10] The polyamide resin composition of any one of [1] to [9], wherein the antiblocking agent (D) is at least one selected from the group consisting of mica, kaolin, zeolite, talc and silica.
[11] A film made of the polyamide resin composition according to any one of [1] to [10].
[12] The film of [11] having a thickness of 3 to 15 μm.

The polyamide resin composition of the present invention has an appropriate resin pressure during molding, and excellent moldability due to the suppression of stretching stress during stretching, and when formed into a film, has excellent strength against piercing and a film. Excellent lubricity, transparency and gloss.

The present invention comprises 70.00 to 95.00% by mass of an aliphatic homopolyamide resin (A) having a relative viscosity of 3.40 to 4.50 and a relative viscosity of 2.00 to 2.00% in 100% by mass of a polyamide resin composition. 60 aliphatic homopolyamide resin (B) 1.00 to 25.00% by mass, aliphatic copolyamide resin (C) 0 to 15.00% by mass, antiblocking agent (D) 0.01 to 0.50 A polyamide resin composition containing 0.02 to 0.20% by mass of a lubricant (E).
In this specification, the content of each component is a value rounded to the third decimal place. However, when described as 0% by mass, it means that it is not contained.

<Aliphatic Homopolyamide Resin (A) and Aliphatic Homopolyamide Resin (B)>
The polyamide resin composition contains an aliphatic homopolyamide resin (A) with a relative viscosity of 3.40-4.50 and an aliphatic homopolyamide resin (B) with a relative viscosity of 2.00-2.60.
An aliphatic homopolyamide resin is a polyamide resin composed of one type of structural unit derived from an aliphatic monomer. The aliphatic homopolyamide resin may consist of at least one aminocarboxylic acid that is one type of lactam and a hydrolyzate of the lactam, and consists of a combination of one type of diamine and one type of dicarboxylic acid. can be anything. Here, the combination of diamine and dicarboxylic acid is regarded as one type of monomer in combination of one type of diamine and one type of dicarboxylic acid. Aliphatic also includes cycloaliphatic.

Lactams include ε-caprolactam, enantholactam, undecanelactam, dodecanelactam, α-pyrrolidone, α-piperidone and the like. Among these, one selected from the group consisting of ε-caprolactam, undecanelactam and dodecanelactam is preferable from the viewpoint of polymerization productivity.
Aminocarboxylic acids include 4-aminobutanoic acid, 5-aminopentanoic acid, 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid. Among these, one selected from the group consisting of 6-aminocaproic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid is preferred from the viewpoint of polymerization productivity.

Diamines include ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, peptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, tridecanediamine, and tetradecanediamine. , pentadecanediamine, hexadecanediamine, heptadecanediamine, octadecanediamine, nonadecanediamine, eicosanediamine, 2-methyl-1,8-octanediamine, 2,2,4/2,4,4-trimethylhexamethylenediamine, etc. 1,3-/1,4-cyclohexyldiamine, bis(4-aminocyclohexyl)methane, bis(4-aminocyclohexyl)propane, bis(3-methyl-4-aminocyclohexyl)methane, (3 -methyl-4-aminocyclohexyl)propane, 1,3-/1,4-bisaminomethylcyclohexane, 5-amino-2,2,4-trimethyl-1-cyclopentanemethylamine, 5-amino-1,3 , 3-trimethylcyclohexanemethylamine, bis(aminopropyl)piperazine, bis(aminoethyl)piperazine, norbornane dimethylenediamine and other alicyclic diamines.

Dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecane. Aliphatic dicarboxylic acids such as dioic acid, hexadecanedioic acid, octadecanedioic acid, eicosanedioic acid; 1,3-/1,4-cyclohexanedicarboxylic acid, dicyclohexanemethane-4,4'-dicarboxylic acid, norbornanedicarboxylic acid alicyclic dicarboxylic acids such as

Specific examples of the aliphatic homopolyamide resin (A) and the aliphatic homopolyamide resin (B) include polycaprolactam (polyamide 6), polyenantholactam (polyamide 7), polyundecanelactam (polyamide 11), polylauryl Lactam (polyamide 12), polyhexamethylene adipamide (polyamide 66), polytetramethylene adipamide (polyamide 46), polytetramethylene sebacamide (polyamide 410), polytetramethylene dodecamide (polyamide 412), poly Pentamethylene Adipamide (Polyamide 56), Polypentamethylene Azelamide (Polyamide 59), Polypentamethylene Sebacamide (Polyamide 510), Polypentamethylene Dodecamide (Polyamide 512), Polyhexamethylene Azelamide (Polyamide 69) , polyhexamethylene sebacamide (polyamide 610), polyhexamethylene dodecamide (polyamide 612), polynonamethylene adipamide (polyamide 96), polynonamethylene azelamide (polyamide 99), polynonamethylene sebacamide ( Polyamide 910), polynonamethylene dodecamide (polyamide 912), polydecamethylene adipamide (polyamide 106), polydecamethylene azelamide (polyamide 109), polydecamethylene decamide (polyamide 1010), polydecamethylene dodecamide (polyamide 1012), polydodecamethylene adipamide (polyamide 126), polydodecamethyleneazelamide (polyamide 129), polydodecamethylene sebacamide (polyamide 1210), polydodecamethylene dodecamide (polyamide 1212), polyamide 122, etc. is mentioned. These may be used individually by 1 type, or may be used in combination of 2 or more types. Among these, from the viewpoint of molding processability and gas barrier properties, the aliphatic homopolyamide resin (A) and the aliphatic homopolyamide resin (B) are independently polyamide 6, polyamide 10, polyamide 11, polyamide 12, and polyamide. 46, polyamide 66, polyamide 610, polyamide 611 and polyamide 612 are preferred.
The types of the above polyamides of the aliphatic homopolyamide resin (A) and the aliphatic homopolyamide resin (B) may be the same or different.

The aliphatic homopolyamide resin (A) has a relative viscosity of 3.40 to 4.50, preferably 3.40 to 4.20, preferably 3.60 to 4.20. When the relative viscosity is within the above range, moldability is improved.
The aliphatic homopolyamide resin (B) has a relative viscosity of 2.00 to 2.60, preferably 2.10 to 2.50, and preferably 2.10 to 2.40. When the relative viscosity is within the above range, moldability is improved. The relative viscosity is measured at 25° C. by dissolving 1 g of polyamide resin in 100 ml of 96% concentrated sulfuric acid according to JIS K-6920. The relative viscosity is a value rounded to the third decimal place.
By using the aliphatic homopolyamide resin (A) and the aliphatic homopolyamide resin (B) having different relative viscosities in this way, a melt viscosity suitable for molding can be obtained and a good resin pressure can be obtained. The moldability of the film is improved.

As long as the relative viscosity is satisfied, the aliphatic homopolyamide resin (A) may be used alone or in combination of two or more, and the aliphatic homopolyamide resin (B) may be used alone or two or more. They may be used in combination. When the aliphatic homopolyamide resin (A) contains two or more polyamide resins with different relative viscosities, it is preferable to measure the relative viscosity of the aliphatic homopolyamide resin (A), but each polyamide resin contained The relative viscosity of the aliphatic homopolyamide resin (A) may be the average value calculated by summing the values obtained by multiplying the relative viscosities of the mixture ratios. The same applies to the aliphatic homopolyamide resin (B).

In addition, the aliphatic homopolyamide resin (A) and the aliphatic homopolyamide resin (B) are composed of monoamines, diamines, monocarboxylic acids and dicarboxylic acids as modifiers in consideration of their respective terminal group concentrations and relative viscosities. At least one selected from the group can be added in an appropriate combination. For example, aliphatic monoamines such as methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, decylamine, stearylamine, dimethylamine, diethylamine, dipropylamine and dibutylamine, and fatty acids such as cyclohexylamine and dicyclohexylamine. aromatic monoamines such as cyclic monoamines, aniline, toluidine, diphenylamine and naphthylamine; aliphatic diamines such as hexamethylenediamine, decamethylenediamine and dodecamethylenediamine; alicyclic diamines such as cyclohexanediamine, methylcyclohexanediamine and isophoronediamine; Aromatic diamines such as meta-phenylenediamine, para-phenylenediamine, meta-xylylenediamine, para-xylylenediamine, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecylic acid, myristic acid, palmitic acid acids, stearic acid, pivalic acid, aliphatic monocarboxylic acids such as isobutyric acid, alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid, benzoic acid, toluic acid, α-naphthalenecarboxylic acid, β-naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid acids, aromatic monocarboxylic acids such as phenylacetic acid, adipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and other aliphatic dicarboxylic acids, 1,3- Alicyclic dicarboxylic acids such as cyclopentanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids such as isophthalic acid and 1,4/2,6/2,7-naphthalenedicarboxylic acid; These can use 1 type(s) or 2 or more types. These are used in amounts within the range to achieve the above objectives.

From the viewpoint of film strength and moldability, the aliphatic homopolyamide resin (A) preferably has a terminal amino group concentration of 30 to 39 μmol/g, more preferably 32 to 39 μmol/g. The aliphatic homopolyamide resin (B) preferably has a terminal amino group concentration of 30 to 100 μmol/g, more preferably 35 to 95 μmol/g.
The terminal amino group concentration is obtained by dissolving in a mixed solvent of phenol and methanol and performing neutralization titration.
When the aliphatic homopolyamide resin (A) and the aliphatic homopolyamide resin (B) have a specific terminal amino group concentration, the strength and moldability of the film are more excellent.

When the aliphatic homopolyamide resin (A) contains two or more polyamide resins with different terminal amino group concentrations, it is preferable to measure the terminal amino group concentration of the aliphatic homopolyamide resin (A), but The terminal amino group concentration of the aliphatic homopolyamide resin (A) may be an average value calculated by summing the values obtained by multiplying the terminal amino group concentrations of the respective polyamide resins by their mixture ratios. The same applies to the aliphatic homopolyamide resin (B).

The content of the aliphatic homopolyamide resin (A) in 100% by mass of the polyamide resin composition is 70.00 to 95.00% by mass, preferably 72.00 to 95.00% by mass, more preferably 75.00% by mass. ~95.00% by mass, more preferably 80.00 to 95.00% by mass. When the content of the aliphatic homopolyamide resin (A) is within this range, the effects of the present invention can be exhibited.

In 100% by mass of the polyamide resin composition, the content of the aliphatic homopolyamide resin (B) is 1.00 to 25.00% by mass, preferably 2.00 to 23.00% by mass, more preferably 2.00 ~21.00% by mass, more preferably 2.00 to 17.00% by mass. When the content of the aliphatic homopolyamide resin (B) is within this range, the effects of the present invention can be exhibited.

<Aliphatic Copolyamide Resin (C)>
Preferably, the polyamide resin composition optionally contains an aliphatic copolyamide resin (C).
The aliphatic copolymerized polyamide resin (C) is a polyamide resin composed of two or more structural units derived from aliphatic monomers. The aliphatic copolyamide resin (C) is a copolymer of two or more monomers selected from the group consisting of combinations of diamines and dicarboxylic acids, lactams and aminocarboxylic acids. Here, the combination of diamine and dicarboxylic acid is regarded as one type of monomer in combination of one type of diamine and one type of dicarboxylic acid. Aliphatic also includes cycloaliphatic.

Examples of the diamine include those exemplified as raw materials for the aliphatic homopolyamide.

Examples of the dicarboxylic acid include those exemplified as raw materials for the aliphatic homopolyamide.

Examples of the lactam include those exemplified as starting materials for the aliphatic homopolyamide.
In addition, the same aminocarboxylic acids as exemplified as raw materials for the aliphatic homopolyamide can be used.

In addition, in consideration of the terminal group concentration and relative viscosity, the aliphatic copolymerized polyamide resin (C) is appropriately added with at least one selected from the group consisting of monoamines, diamines, monocarboxylic acids and dicarboxylic acids as a modifier. They can be added in combination. Specific examples include those exemplified in the section on aliphatic homopolyamides.

Specific examples of the aliphatic copolymerized polyamide resin (C) include caprolactam/tetramethylenediaminoadipic acid copolymer (polyamide 6/46), caprolactam/pentamethylenediaminoadipic acid copolymer (polyamide 6/56), caprolactam /Hexamethylenediaminoadipic Acid Copolymer (Polyamide 6/66), Caprolactam/Hexamethylenediaminoazelaic Acid Copolymer (Polyamide 6/69), Caprolactam/Tetramethylenediaminosebacic Acid (Polyamide 6/410), Caprolactam/Penta Methylenediaminosebacic Acid Copolymer (Polyamide 6/510), Caprolactam/Hexamethylenediaminosebacic Acid Copolymer (Polyamide 6/610), Caprolactam/Hexamethylenediaminoundecanedicarboxylic Acid Copolymer (Polyamide 6/611), Caprolactam /Hexamethylenediaminododecanedicarboxylic acid copolymer (polyamide 6/612), caprolactam/decamethylenediaminosebacic acid copolymer (polyamide 6/1010), caprolactam/aminoundecanoic acid copolymer (polyamide 6/11), caprolactam /lauryllactam copolymer (polyamide 6/12), caprolactam/hexamethylenediaminoadipic acid/lauryllactam copolymer (polyamide 6/66/12), caprolactam/hexamethylenediaminoadipic acid/hexamethylenediaminosebacic acid copolymer Aliphatic copolyamides such as coalescence (polyamide 6/66/610), caprolactam/hexamethylenediaminoadipic acid/hexamethylenediaminododecanedicarboxylic acid copolymer (polyamide 6/66/612).
The aliphatic copolyamide resin (C) may be used alone or in combination of two or more.
Among these aliphatic copolymerized polyamide resins (C), aliphatic copolymerized polyamide resins containing caprolactam as one of the monomers constituting the copolymer are preferable, and caprolactam/hexamethylenediaminoadipic acid copolymer (polyamide 6 /66), at least one selected from the group consisting of caprolactam/lauryllactam copolymer (polyamide 6/12), and caprolactam/hexamethylenediaminoadipic acid/lauryllactam copolymer (polyamide 6/66/12) is more preferred.

Aliphatic copolyamide resin (C) conforms to JIS K-6920, 1 g of polyamide resin is dissolved in 100 ml of 96% concentrated sulfuric acid, and the relative viscosity measured at 25° C. is It is preferably 2.90 to 4.70, more preferably 3.00 to 4.50, even more preferably 3.00 to 4.30.

When the aliphatic copolyamide resin (C) contains two or more types of polyamide resins with different relative viscosities, the relative viscosity is obtained by the same method as described in the section on the aliphatic homopolyamide resin (A).

The terminal amino group concentration of the aliphatic copolymerized polyamide resin (C) is preferably 25 to 40 μmol / g as the terminal amino group concentration obtained by neutralization titration by dissolving in a mixed solvent of phenol and methanol, and 28 to 40 μmol/g is more preferable, and 30 to 40 μmol/g is even more preferable.

When the aliphatic copolyamide resin (C) contains two or more polyamide resins with different terminal amino group concentrations, terminal amino group concentrations are adjusted in the same manner as described in the section for the aliphatic homopolyamide resin (A). is required.

In 100% by mass of the polyamide resin composition, the content of the aliphatic copolymerized polyamide resin (C) is 0 to 15.00% by mass, preferably 0 to 13.00% by mass, more preferably 0 to 11.00% by mass %, more preferably 2.00 to 11.00 mass %. When the content of the aliphatic copolymerized polyamide resin (C) is within the above range, the effects of the present invention can be exhibited, and it is particularly desirable from the viewpoint of strength against puncture and stretchability.

<Polyamide resin>
Examples of polyamide resin production equipment include batch-type reactors, single-vessel or multi-vessel continuous reactors, tubular continuous reactors, single-screw kneading extruders, twin-screw kneading extruders, and other kneading reaction extruders. A known polyamide manufacturing apparatus can be used. As a polymerization method, known methods such as melt polymerization, solution polymerization, and solid phase polymerization can be used, and polymerization can be performed by repeating normal pressure, reduced pressure, and pressurization operations. These polymerization methods can be used alone or in combination as appropriate.

<Anti-blocking agent (D)>
The polyamide resin composition contains an antiblocking agent (D).
An antiblocking agent is a substance added to suppress adhesion between films by imparting unevenness to the surface of the film. The shape of the anti-blocking agent is not particularly limited as long as it can form surface protrusions on the film surface and can impart lubricity to the film, and can be powdery, particulate, flake-like, plate-like, fiber-like. It may have any shape such as shape, needle shape, cloth shape, mat shape, etc., but particle shape and plate shape are preferable. The antiblocking agent (D) includes those that also function as crystal nucleating agents.

The average particle size of the antiblocking agent is preferably 0.1 to 20 μm, more preferably 0.3 to 15 μm, even more preferably 0.5 to 10 μm. Desirably, it is substantially free of particles having a particle size greater than 20 μm. If a large amount of particles having a particle size of more than 20 μm is contained, fisheye gel may occur and the appearance of the film may be impaired. Moreover, even if the effect of improving slipperiness is exhibited, the transparency of the film may be deteriorated. On the other hand, when the average particle size is less than 0.1 μm, secondary aggregation tends to occur, which may conversely cause fish eye gels. Moreover, even if the aggregation can be prevented, it is difficult to obtain an uneven effect on the film surface, and the slipperiness may not be improved. Therefore, if the particle size of the antiblocking agent does not meet the requirements of the present invention, it is desirable to perform pulverization or classification in advance.
In addition, in this specification, an average particle diameter is the value measured by the laser diffraction method. Alternatively, in the case of commercial products, catalog values may be used.

Specific examples of these antiblocking agents include silica such as gel-type silica, precipitated-type silica, dry silica, colloidal silica, talc, kaolin, montmorillonite, zeolite, mica, glass flakes, wollastonite, potassium titanate, and magnesium sulfate. , sepiolite, xonolite, aluminum borate, glass beads, calcium silicate, calcium carbonate, titanium oxide, barium sulfate, zinc oxide, magnesium hydroxide and the like. These can use 1 type(s) or 2 or more types. Among these, mica, kaolin, zeolite, talc and silica are preferred from the standpoint of easy dispersibility. These may be used individually by 1 type, or may be used in combination of 2 or more type.

In particular, it is more preferable to use silica as the anti-blocking agent, since the obtained film is excellent in transparency and slipperiness. Silica is mainly composed of silicon dioxide represented by SiO ₂ ·nH ₂ O, and is roughly divided into two types, wet-process silica and dry-process silica, depending on the production method, but both can be used. can be done. In particular, silica preferably has an average particle size of 0.1 to 20 μm, more preferably 0.3 to 15 μm, even more preferably 0.5 to 10 μm.
The primary particles of silica have a particle size of the so-called submicron order, but the commonly used silica is soft silica (gel-type silica, precipitated silica) in which these primary particles aggregate to form secondary or tertiary particles. type silica, dry silica) and hard silica (colloidal silica) having a primary particle size of 1 μm or more, and soft silica is more preferable when the film is stretched. The average particle size of silica is the value of soft silica and hard silica, not the value of primary particles.

It is possible to use non-surface-treated silica, but it is also possible to use surface-treated silica. When an anti-blocking agent treated with a silane-based or titanium-based surface treating agent is used, the dispersibility is further improved, and the transparency of the resulting film is further improved. The surface treatment method is not particularly limited, and for example, a method described in JP-A-63-251460 is applied, in which a silane coupling agent diluted with water is added to fine silica under heating and stirring. can do

The antiblocking agent (D) may be used singly or in combination of two or more.
In 100% by mass of the polyamide resin composition, the content of the antiblocking agent (D) is 0.01 to 0.50% by mass, preferably 0.05 to 0.30% by mass, more preferably 0.10 to 0 .20% by weight. As a result, adhesion between the films can be effectively suppressed without impairing the properties of the obtained film.

<Lubricant (E)>
The polyamide resin composition contains a lubricant (E).
Lubricants are substances added to give lubricity between extruder screws and pellets during film formation, and between pellets, and to suppress adhesion between films.
Lubricants (E) include terminal-modified polyalkylene glycols, phosphates, phosphites, higher fatty acid monoesters, higher fatty acids, metal salts of higher fatty acids, carboxylic acid amides, magnesium silicate, and dibenzylidene. Compounds such as sorbitols and polyolefin waxes. Here, higher fatty acids refer to fatty acids having 6 to 24 carbon atoms. These may be used individually by 1 type, or may be used in combination of 2 or more type. Lubricants (E) include those that also function as crystal nucleating agents.

Examples of terminal-modified polyalkylene glycol include terminal-modified polyethylene glycol and terminal-modified polypropylene glycol.
More specific examples of phosphates and phosphites include aliphatic phosphates such as di(2-ethylhexyl)phosphate, tridecylphosphite, tris(tridecyl)phosphite, tristearylphosphite, and fatty and aromatic phosphites such as triphenylphosphite and diphenylmonodecylphosphite.

Higher fatty acid monoesters include myristyl myristate, stearyl stearate, behenyl behenate, oleyl oleate, and hexyldecyl myristate.
Examples of higher fatty acids include myristic acid, palmitic acid, behenic acid, oleic acid, and aragidic acid.
Metal salts of higher fatty acids include metal salts of higher fatty acids such as magnesium stearate, zinc stearate, lithium stearate, calcium stearate, and aluminum palmitate.

Examples of carboxylic acid amides include lauric acid amide, palmitic acid amide, oleic acid amide, stearic acid amide, erucic acid amide, behenic acid amide, ricinoleic acid amide, 12-hydroxystearic acid amide, and the like. aliphatic monocarboxylic acid amide, N-lauryllauric acid amide, N-palmityl palmitic acid amide, N-oleyl palmitic acid amide, N-oleyl oleic acid amide, N-oleyl stearic acid amide, N-stearyl stearic acid amide, N-stearyloleic acid amide, N-stearylerucic acid amide, N-stearyl-12-hydroxystearic acid amide, N-oleyl-12-hydroxystearic acid amide, methylolstearic acid amide, methylolbehenic acid amide, 12-hydroxystearin N-substituted aliphatic monocarboxylic acid amides such as acid monoethanolamide, methylenebisstearic acid amide, methylenebislauric acid amide, methylenebis-12-hydroxystearic acid amide, ethylenebiscapric acid amide, ethylenebislauric acid amide, ethylene Bisoleic acid amide, ethylene bis stearic acid amide, ethylene bis erucic acid amide, ethylene bis behenic acid amide, ethylene bis isostearic acid amide, ethylene bis-12-hydroxystearic acid amide, butylene bis stearic acid amide, hexamethylene bis oleic acid Amide, hexamethylenebisstearic acid amide, hexamethylenebisbehenic acid amide, hexamethylenebis-12-hydroxystearic acid amide, N,N'-dioleylsebacic acid amide, N,N'-dioleyladipate Aliphatic carboxylic acid bisamides such as amides, N,N'-distearyladipamide, N,N'-distearylsebacamide, N,N'-dicyclohexanecarbonyl-1,4-diaminocyclohexane, 1, 4-cyclohexanedicarbamide, 1,4-cyclohexanedicarboxylic acid diaminocyclohexane, 1,2,3,4-butanetetracarboxylic acid tetracyclohexylamide, N,N'-bis(3-hydroxypropyl)-1,4- cycloaliphatic carboxylic acid amides such as cuban dicarbamide, N,N'-(1,4-cyclohexanediyl)bis(acetamide), tris(methylcyclohexyl)propanetricarboxamide, 1,4-cyclohexanedicarboxylic acid dianilides, 1,4-cyclohexanedicarboxylic acid dibenzylamide, trimesic acid tris(t-butylamide), trimesic acid tricyclohexylamide, trimesic acid tri(2-methylcyclohexylamide), trimesic acid tri(4-cyclohexylamide), 2,6 -naphthalene dicarboxylic acid dicyclohexylamide, N,N'-dibenzylcyclohexane-1,4-dicarbamide, N,N'-distearylisophthalamide, N,N'-distearylterephthalamide, m-xylylenebis Aromatic carboxylic acid amides such as stearic acid amide and m-xylylenebis-12-hydroxystearic acid amide are included. Among these, aliphatic carboxylic acid amides selected from the group consisting of aliphatic monocarboxylic acid amides, N-substituted aliphatic monocarboxylic acid amides and aliphatic carboxylic acid bisamides are preferred, and aliphatic carboxylic acid bisamides are more preferred.
Examples of magnesium silicate include those having an average particle size of 1 to 10 μm. The method for measuring the average particle size is as described above.

Dibenzylidene sorbitols include dibenzylidene sorbitol synthesized by dehydration condensation of sorbitol and substituted benzaldehyde under an acid catalyst.

Polyolefin waxes include unmodified polyolefin waxes and modified polyolefin waxes.
Examples of unmodified polyolefin wax include unmodified polyethylene wax composed mainly of ethylene and unmodified polypropylene wax composed mainly of propylene.

The unmodified polyethylene wax may be composed of an ethylene homopolymer or an ethylene-α-olefin copolymer. α-olefins include propylene, 1-butene, isobutylene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadecene, 1-octadecene, 4-methyl- Examples include α-olefins having 3 to 20 carbon atoms such as 1-pentene. The content of ethylene units in the ethylene-α-olefin copolymer wax preferably exceeds 50 mol %. Examples of unmodified polyethylene waxes include Licowax (registered trademark) PE520, Clariant PE130, Clariant PE190; Licocene (registered trademark) PE3101TP, Clariant PE4201, Clariant PE5301; Ceridust (registered trademark) 3620, Clariant 3610, etc. be done.

The unmodified polypropylene wax may be composed of a propylene homopolymer or a propylene-α-olefin copolymer. α-olefins include 1-butene, isobutylene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadecene, 1-octadecene, 4-methyl-1- Examples include α-olefins having 3 to 20 carbon atoms such as pentene. The propylene unit content in the propylene-α-olefin copolymer wax preferably exceeds 50 mol %. Examples of unmodified polypropylene wax include Licocene (registered trademark) PP6102, PP6502, PP7502, PP1302, PP1502, PP1602, PP2602, and PP3602 manufactured by Clariant Chemicals; Ceridust (registered trademark) 6050M. .

The modified polyolefin wax is obtained by modifying the above-described unmodified polyolefin wax, and examples of the modified polyolefin wax include vinyl ester-modified polyolefin wax, acid-modified polyolefin wax, and oxidized polyolefin wax.

The vinyl ester-modified polyolefin wax can be obtained by copolymerizing a monomer constituting the polyolefin wax and a vinyl ester such as vinyl acetate or vinyl propionate.

The acid-modified polyolefin wax can be obtained by acid-modifying a polyolefin wax with an unsaturated carboxylic acid or its acid anhydride. Specific examples of unsaturated carboxylic acids or acid anhydrides thereof include maleic acid, fumaric acid, itaconic acid, acrylic acid, methacrylic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, maleic anhydride and itaconic anhydride. , cis-4-cyclohexene-1,2-dicarboxylic anhydride and the like, but maleic anhydride is preferred. Derivatives such as acid amides and acid esters can also be used instead of unsaturated carboxylic acid anhydrides. Examples of the maleic anhydride-modified polypropylene wax include Licocene (registered trademark) PP MA 1332, PP MA 6252, PP MA 6452, and PP MA 7452 manufactured by Clariant Chemicals.

Oxidized polyolefin wax can be obtained by oxidizing polyolefin wax.
Among the above lubricants (E), higher fatty acids, higher fatty acid metal salts, higher fatty acid monoesters, carboxylic acid amides and polyolefin waxes are preferred, higher fatty acids, higher fatty acid metal salts and carboxylic acid amides are more preferred, and aliphatic Carboxamides are more preferred.

The lubricant (E) may be used singly or in combination of two or more, but a combination of two or more is preferred from the viewpoint of improving slipperiness. "Two or more" means at least two or more different components as compounds, and does not necessarily mean only two or more in a broader concept such as "higher fatty acid".
As a combination of two or more, a combination of a higher fatty acid or a metal salt thereof and a carboxylic acid amide is preferred, a combination of a higher fatty acid metal salt and a carboxylic acid amide is more preferred, and a higher fatty acid metal salt and an aliphatic carboxylic acid are preferred. A combination with bisamide is more preferable from the viewpoint of improving slipperiness.

In 100% by mass of the polyamide resin composition, the content of the lubricant (E) is 0.02 to 0.20% by mass, preferably 0.05 to 0.15% by mass, more preferably 0.05 to 0.10 % by mass. As a result, the load on the screw of the extruder during film formation can be reduced, and adhesion between the films can be effectively suppressed without impairing the properties of the resulting film.

<Additive>
Depending on the purpose, the polyamide resin composition may contain optional components such as dyes, pigments, fibrous reinforcing materials, particulate reinforcing materials, plasticizers, antioxidants, heat-resistant agents, foaming agents, weathering agents, crystallization accelerators, A crystal nucleating agent, an antistatic agent, a flame retardant, a flame retardant auxiliary, a colorant, and other function-imparting agents may be contained as appropriate. Among these, substances that also function as antiblocking agents (D) or lubricants (E) are included in the content of antiblocking agents (D) or lubricants (E).
The optional additive may be contained in an amount of preferably 1.00% by mass or less, more preferably 0.50% by mass or less, based on 100% by mass of the polyamide resin composition.

The polyamide resin composition may contain thermoplastic resins other than polyamide resins. Thermoplastic resins other than polyamide resins are preferably 2.00% by mass or less, more preferably less than 0.10% by mass, based on 100% by mass of the polyamide resin composition, from the viewpoint of mechanical properties and moldability. is more preferred.

[Method for producing polyamide resin composition]
The method for producing the polyamide resin composition is not particularly limited, and for example, the following method can be applied.
For mixing raw materials of each component, a commonly known melt-kneader such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader, and a mixing roll is used. The melt-kneading temperature is not particularly limited as long as it melts the polyamide resin, but is preferably 190°C to 280°C.
For example, when using a twin-screw extruder, a method of melt-kneading after blending all the raw materials, a method of melt-kneading after blending some of the raw materials, and a method of blending and melt-kneading the remaining raw materials, or one Any method may be used, such as a method of mixing the remaining raw materials using a side feeder during melt-kneading after blending the raw materials of the part, but a method of melt-kneading after blending all the raw materials is preferable.

When mixing, each component may be blended individually, multiple types may be blended in advance, and then blended, or a masterbatch may be used. In addition, the order of blending can be appropriately selected according to the method and conditions of melt-kneading.

(Method for producing film of polyamide resin composition)
A polyamide resin composition is preferably used as a film.
A film comprising a polyamide resin composition can be produced by a known method. For example, after producing a polyamide resin composition, it is melt-kneaded with an extruder, extruded into a flat film with a T-die or a coat hanger die, cast on a casting roll surface, and cooled to produce a film. , a tubular method of manufacturing a film by air-cooling or water-cooling a tubular material melt-extruded into a cylindrical shape using a ring-shaped die. The produced film may be in a substantially non-oriented, unstretched state or in a stretched state.

When stretching an unstretched film, a conventionally known industrial method can be used. The stretched film includes a uniaxially stretched film, a simultaneous biaxially stretched film, a sequentially biaxially stretched film, and the like. It is produced by a known drawing method such as a biaxial drawing method or a tubular drawing method. For example, a simultaneous biaxial stretching method in which an unstretched sheet produced by a casting method is stretched vertically and horizontally simultaneously with a tenter type simultaneous biaxial stretching machine, and an unstretched sheet melt-extruded from a T-die is stretched in the longitudinal direction with a roll stretching machine. Later, there are a sequential biaxial stretching method in which the sheet is stretched in the horizontal direction by a tenter type stretching machine, and a tubular stretching method in which a tubular sheet formed from an annular die is stretched longitudinally and laterally simultaneously by gas pressure. The stretching step may be carried out continuously after the production of the film, or the produced film may be wound once and the stretching may be carried out as a separate step.
The stretching temperature is usually 30 to 200°C, preferably 40 to 150°C. The draw ratio is usually 1.5 to 6 times, preferably 2 to 5 times in each direction.

When laminating, the film can be subjected to surface treatments such as corona discharge treatment, plasma treatment, flame treatment, and acid treatment in order to improve printability, lamination, and adhesive application. Further, if necessary, after lamination, secondary processing steps such as printing, lamination, adhesive application, heat sealing, etc. can be carried out, and the product can be used for its intended purpose.

The thickness of the film is preferably 3-15 μm, more preferably 5-15 μm. When the thickness of the film is within the above range, the transparency and glossiness are excellent. In the present invention, by blending a plurality of types of aliphatic homopolyamide resins with different relative viscosities, an antiblocking agent, and a lubricant, a polyamide resin composition is formed, so that a film having such a thin thickness can have sufficient strength against piercing. It made it possible to be a high-quality film.
Depending on the purpose and application, when the film is used with a thickness greater than this, a plurality of films may be laminated and used.

The film is not particularly limited, but can be suitably used for applications such as food packaging, industrial material packaging, and exterior film for lithium ion batteries.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
Physical properties of Examples and Comparative Examples were measured by the following methods.
In each evaluation, ◯ was set as a pass, and x was set as a fail.

<Relative viscosity>
Based on JIS K6920, 1 g of polyamide resin is dissolved in 100 ml of 96% concentrated sulfuric acid and measured at 25°C.

<Terminal amino group concentration>
Polyamide resin was dissolved in a mixed solvent of phenol and methanol, and neutralization titration was performed.

<Average particle size>
It was measured by a laser diffraction method.

<Haze>
Measurement was performed according to ASTM D-1003 using a Haze Meter manufactured by Nippon Denshoku Industries Co., Ltd.
Transparency was evaluated according to the following criteria.
Good: The haze value is 2.5% or less.
x: The haze value is over 2.5%.

<gross>
Measurement was performed according to ASTM D-523 using a digital variable angle gloss meter manufactured by Suga Test Instruments Co., Ltd.
Gloss was evaluated according to the following criteria.
Good: The gloss value is 142% or more.
x: The gloss value is less than 142%.

<Puncture Strength>
According to JAS (P-1019), a needle with a diameter of 1.0φ and a tip shape of 0.5R was used to measure the maximum point load and elongation.
The puncture strength was evaluated according to the following criteria.
○: The value of the maximum point load is over 8.2N.
x: The value of the maximum point load is 8.2N or less.

<Dynamic Friction Coefficient/Static Friction Coefficient>
At 23° C. and 50% relative humidity (RH) at 23° C., the static friction coefficient or dynamic friction coefficient between the film surfaces was measured five times in accordance with ASTM D-1894, and the average value was obtained.
The slipperiness was evaluated according to the following criteria.
○: static friction coefficient (μS) is 0.60 or less and dynamic friction coefficient (μD) is 0.58 or less ×: static friction coefficient (μS) is over 0.60 and/or dynamic friction coefficient (μD) is over 0.58

<Resin pressure>
The value detected from the pressure gauge installed at the tip of the extruder of the film forming apparatus was read.
Film formability was evaluated according to the following criteria.
◯: Resin pressure value is 2.6 to 4.5 MPa.
x: The resin pressure value is less than 2.6 Pa or more than 4.5 MPa.

<Maximum stretching stress>
A 100 μm unstretched film was preheated at a stretching temperature of 100° C. for 60 seconds using a batch-type biaxial stretching apparatus, and stretched 3.0 times in both the longitudinal and transverse directions, and the maximum stretching stress was measured.
From the force required for stretching, the ease of film production was evaluated according to the following criteria.
◯: The maximum value of stretching stress is 26 kg/cm ² or less.
x: The maximum value of stretching stress is over 26 kg/cm ² .

[Examples 1 to 8, Comparative Examples 1 to 5]
Each component described in Table 1 was individually blended, and a twin-screw kneader ZSK32mc twin-screw extruder (manufactured by Coperion), cylinder diameter 32 mm, L/D 48, cylinder temperature 250 ° C., screw rotation 200 rpm, Melt-kneading was carried out at a discharge rate of 50 kg/hrs to prepare pellets of the intended molding material. Using these pellets, an unstretched film was molded at a molding temperature of 260°C and a chill roll temperature of 30°C using a GT-40-A-400 manufactured by Plastic Engineering Laboratory. Next, this film was subjected to simultaneous biaxial stretching at a stretching rate of 140 mm/sec and a stretching temperature of 100°C at a stretching ratio of 3.0 × 3.0 times using a biaxial stretching device of Iwamoto Seisakusho BIX703, and then stretched at 200°C. to prepare a biaxially stretched film having a thickness of 12 μm, and the haze, gloss and puncture properties were measured. Resin pressure and maximum stretching stress were measured as described above.
The unit of composition in the table is % by mass, and the total polyamide resin composition is 100% by mass.

Raw materials used in the examples are as follows.
Polyamide resin (1): polyamide 6, relative viscosity 4.08, terminal amino group concentration 33 μmol / g, manufactured by UBE Corporation Polyamide resin (2): polyamide 6, relative viscosity 3.50, terminal amino group concentration 39 μmol / g, Polyamide resin manufactured by UBE Corporation (3): polyamide 6, relative viscosity 3.37, terminal amino group concentration 40 μmol / g, polyamide resin manufactured by UBE Corporation (4): polyamide 6, relative viscosity 2.47, terminal amino group concentration 95 μmol / g, UBE Corporation polyamide resin (5): polyamide 6, relative viscosity 2.47, terminal amino group concentration 45 μmol / g, UBE Corporation polyamide resin (6): polyamide 6, relative viscosity 2.20, Terminal amino group concentration 36 μmol / g, polyamide resin (7) manufactured by UBE Corporation: Polyamide 6/66, which is a copolymer of 85% by mass of polyamide 6 and 15% by mass of polyamide 66, relative viscosity 4.05, terminal amino group Concentration 33 μmol/g, silica manufactured by UBE Corporation: average particle size: 2.0 to 3.5 μm, surface treatment: γ-aminopropyltriethoxysilane, talc manufactured by Mizusawa Chemical Industry Co., Ltd.: average particle size: 5.0 μm, Product name Micro Ace L-1, manufactured by Nihon Talc Co., Ltd. Magnesium stearate: Product name Magnesium stearate, manufactured by NOF Corporation Ethylene bis stearamide: Product name EB-FF, manufactured by Kao Corporation

From Examples 1 to 8, the film obtained from the polyamide resin composition of the present invention has good transparency and gloss, has good slipperiness, and has strength against puncture, and the polyamide resin composition of the present invention Since the resin pressure when melted is moderate, the moldability of the unstretched film is excellent, and the maximum stretching stress during stretching is not high, so the stretchability is also excellent.
From Examples 3, 4, 7, and 8, when the polyamide resin composition contains the aliphatic copolymerized polyamide, the strength against puncture is high and the maximum stretching stress during stretching is low, so that excellent stretchability is exhibited. Haze is also suppressed.

When the aliphatic homopolyamide resin of Comparative Example 1 having a relative viscosity of 3.37 is included, the strength against puncture is low and the resin pressure is too low.
In Comparative Example 2, since the amount of the aliphatic homopolyamide resin (A) was larger than the range of the present invention, the pressure of the molten resin was high, making it difficult to form an unstretched film, resulting in poor formability. Furthermore, in Comparative Example 2, since the maximum stretching stress during stretching is high, there is a possibility that the machine will be burdened and the stretching will become difficult during film processing.
From Comparative Example 3, since the polyamide resin composition does not contain the aliphatic homopolyamide resin (B), the pressure of the molten resin is too high, making it difficult to form an unstretched film. Moreover, since the anti-blocking agent (D) is not contained, the coefficient of friction is large, and the sliding property between the films is poor, resulting in a problem in transportability of the film.

From Comparative Example 4, since the amount of the aliphatic homopolyamide resin (A) having a relative viscosity of 3.50 is larger than the range of the present invention, the strength against puncture is low. Moreover, since the anti-blocking agent (D) is not contained, the coefficient of friction is large, the slipperiness of the film is poor, and problems arise in transportability of the film.
From Comparative Example 5, although the amount of the aliphatic homopolyamide resin (A) having a relative viscosity of 4.08 is larger than the range of the present invention, the strength against puncture is high, but the stretching stress is high. In addition, since it does not contain a lubricant (E), the load on the screw of the extruder is large during film formation, making it difficult to form an unstretched film, and since the stretching stress is high, stretching is also difficult and the film formability is poor. Inferior. Moreover, when the lubricant (E) is not included, the value of the coefficient of friction is large, and the lubricity between the films is poor.

The polyamide resin composition of the present invention is suitably used as a film for packaging food and toiletry products, industrial products, heavy duty bags for commercial transportation, and pharmaceuticals.

Claims

In 100% by mass of the polyamide resin composition, an aliphatic homopolyamide resin (A) with a relative viscosity of 3.40 to 4.50 70.00 to 95.00% by mass, an aliphatic with a relative viscosity of 2.00 to 2.60 Homopolyamide resin (B) 1.00 to 25.00% by mass, aliphatic copolymerized polyamide resin (C) 0 to 15.00% by mass, antiblocking agent (D) 0.01 to 0.50% by mass, and A polyamide resin composition containing 0.02 to 0.20% by mass of a lubricant (E).
The polyamide resin composition according to claim 1, wherein the aliphatic homopolyamide resin (A) has a terminal amino group concentration of 30 to 39 μmol/g.
The polyamide resin composition according to claim 1 or 2, wherein the aliphatic homopolyamide resin (B) has a terminal amino group concentration of 30 to 100 µmol/g.
The aliphatic homopolyamide resin (A) is at least one selected from the group consisting of polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyamide 611 and polyamide 612. 3. The polyamide resin composition according to Item 1 or 2.
The aliphatic homopolyamide resin (B) is at least one selected from the group consisting of polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyamide 611 and polyamide 612. 3. The polyamide resin composition according to Item 1 or 2.
The polyamide resin composition according to claim 1 or 2, wherein the content of the aliphatic copolymerized polyamide resin (C) is 2.00 to 11.00% by mass.
The polyamide resin composition according to claim 1 or 2, wherein the lubricant (E) is a combination of two or more lubricants.
Lubricant (E) is terminal-modified polyalkylene glycol, phosphate, phosphite, higher fatty acid monoester, higher fatty acid, metal salt of higher fatty acid, carboxylic acid amide, magnesium silicate, dibenzylidene sorbitol 3. The polyamide resin composition according to claim 1 or 2, which is at least one selected from the group consisting of polyolefin waxes and polyolefin waxes.
The polyamide resin composition according to claim 1 or 2, wherein the lubricant (E) contains a higher fatty acid metal salt and a carboxylic acid amide.
The polyamide resin composition according to claim 1 or 2, wherein the antiblocking agent (D) is at least one selected from the group consisting of mica, kaolin, zeolite, talc and silica.
A film made of the polyamide resin composition according to claim 1 or 2.
The film according to claim 11, which has a thickness of 3 to 15 μm.