JPH02187431A - Polyamide-based biaxially oriented film - Google Patents

Abstract

PURPOSE:To obtain the subject film, containing a polyester resin having ionic groups in a polyamide resin, excellent in successive biaxial orienting properties and improved in slipperiness, transparency and flatness without impairing the mechanical characteristics of polyamide films. CONSTITUTION:The objective film obtained by containing (B) 0.5-50 pts.wt., preferably 3-25 pts.wt. polyester resin (preferably a polyester prepared by copolymerizing 0.5-30mol% dicarboxylic acid having preferably metal sulfonate groups) in (A) 100 pts.wt. polyamide resin.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is a polyamide film that has excellent sequential biaxial stretchability and improved smoothness, transparency, and flatness without impairing the excellent mechanical properties of polyamide film. The present invention relates to a polyamide biaxially stretched film.

[Prior art] Biaxially stretched films made of polyamides such as polyε-caprolactam and polyhexamethylene adipamide have excellent tensile strength, impact strength, pinhole resistance, heat resistance, cold resistance, and gas barrier properties against oxygen and other gases. It is widely used in food packaging and other applications.

Biaxial stretching methods for these films include the tubular method, simultaneous biaxial stretching method, and sequential biaxial stretching method under special conditions (JP-A No. 61-283527, JP-A-Sho 61-283527, 61-244527,
JP-A No. 61-177229, etc.).

[Problems to be Solved by the Invention] However, although polyamide film has excellent properties as described above, it has poor slipperiness, and when inorganic particles are added to improve this, the transparency may decrease or the inherent mechanical properties may deteriorate. This will result in deterioration of characteristics.

Furthermore, since polyamide films undergo large dimensional changes due to moisture absorption, they require moisture-proof packaging, and the film cannot be stored for a long period of time after opening, resulting in operational disadvantages and a decrease in yield.

Furthermore, in the sequential biaxial stretching method in which a polyamide film is stretched in the longitudinal direction and then in the transverse direction, the intermolecular hydrogen bonds are aligned parallel to the film surface, that is, oriented in the transverse direction. Stretching in this direction is extremely difficult.

The above-mentioned methods have been used to improve this problem, but the tubular method tends to cause thickness unevenness, and the simultaneous biaxial stretching method requires expensive equipment and is difficult to increase speed. Sexuality decreases.

Furthermore, the special sequential biaxial stretching method, ie, the method known in the above-mentioned JP-A-Sho, is inferior in terms of productivity because the stretching conditions are extremely restricted.

The present invention improves these drawbacks and provides a biaxially stretched polyamide film that has good slip transparency and flatness without impairing the excellent mechanical properties and thermal properties of the polyamide film, and is excellent in sequential biaxial stretching. The purpose is to provide

[Means for Solving the Problems] The present invention provides (1) a biaxially stretched polyamide film characterized by containing 0.5 to 50 parts by weight of an ionic polyester resin per 100 parts by weight of the polyamide resin; .

(2) The polyamide biaxially stretched film according to claim (1), wherein the ionic polyester resin is a polyester copolymer having a sulfonic acid metal base.

(3) The polyester copolymer having a sulfonic acid metal base has a dicarboxylic acid having a sulfonic acid metal base of 0.
The polyamide biaxially stretched film according to claim 2, which is a polyester copolymerized with 5 to 30 mol%.

(4) The polyamide biaxially stretched film according to any one of claims (1) to (3), wherein the polyamide biaxially stretched film has a haze of 2.0% or less at a thickness of 15 μm.

The main points are as follows.

The polyamide resin as used in the present invention is a general term for resins formed from polymeric compounds having amide bonds, and may be aliphatic polyamide or aromatic polyamide.

Typical polyamides include nylon 6 and nylon 66.
, nylon 610, nylon 11, nylon 12, polyethylene isophthalamide, polymethaxylylene adipamide, poly(hexamethylene isophthalamide/terephthalamide), poly(hexamethylene isophthalamide/monomethyl terephthalamide), hexamethylene isophthalamide Copolymer of phthalamide/terephthalamide and ε-force prolactam,
A copolymer of hexamethylene terephthalamide and hexamethylene adipamide can be used. Of course, these may be used alone or in a mixture of two or more components. In the present invention, a case will be described in which nylon 6 is used as a representative example of polyamide resin. The viscosity of the polyamide resin used in the present invention is determined by the relative viscosity in 98% sulfuric acid [η
r] is 2 to 5, preferably 2.5 to 4. If the relative viscosity is lower than this range, the impact resistance of the biaxially stretched film will be poor, while if it is higher than this range, film formability will deteriorate, fish eyes will increase, etc.
Alternatively, this is not preferable since it may cause a decrease in dimensional stability.

Next, the polyester resin used in combination with the polyamide resin must have ionic properties. Due to the ionic nature of polyester resin, it can be mixed extremely homogeneously with polyamide resin, which improves transparency compared to polyamide resin alone, provides smoothness, improves flatness due to moisture absorption, and improves sequential biaxial stretchability. Improvements will be made. When a polyester that does not have ionicity is contained in a polyamide resin, the effect of improving slipperiness is observed, but the transparency is reduced and there is no effect of improving flatness.

Furthermore, during sequential biaxial stretching, particularly when stretching in the longitudinal direction and then in the width direction, necking and tearing are likely to occur, and the mechanical strength is also reduced.

Here, the ionic polyester resin is a polyester resin having a functional group that ionizes in water and exhibits ionic properties, and specific examples include carboxylates, phosphate ester salts, quaternary ammonium salts, and sulfate ester salts. It is a polyester copolymer into which one or more types of salts such as , sulfonate, etc. are introduced.

Among these, typical polyester copolymers having the following compositions are useful. i.e. aromatic dicarboxylic acid,
A polycondensate of an ester-forming sulfonic acid metal salt compound and a glycol can be preferably used. Specifically, aromatic dicarboxylic acid components include, for example, terephthalic acid, isophthalic acid, phthalic acid, 2.5-dimethylterephthalic acid, 2.
Examples include 6-naphthalene dicarboxylic acid, biphenyl dicarboxylic acid, 1,2-bis(phenoxy)ethane-p, p'-dicarboxylic acid, and ester-forming derivatives thereof.

In addition to aromatic dicarboxylic acids, non-aromatic dicarboxylic acids described below may also be used as part of the copolymerization component. Examples of non-aromatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, geltaric acid, adipic acid, sebacic acid, 12-
Examples thereof include cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, and ester-forming derivatives thereof. Among these, when the aromatic dicarboxylic acid and/or its ester-forming derivative accounts for 70 mol% or more, preferably 80 mol% or more of the total dicarboxylic acid component, film forming properties are improved.
This is preferable in terms of maintaining mechanical strength.

In addition, as ester-forming sulfonic acid metal salt compounds,
For example, sulfoterephthalic acid, 5-sulfoisophthalic acid,
4-sulfoisophthalic acid, 4-sulfonaphthalene-2,
Examples include alkali metal salts (alkali metal salts of sulfonic acids) such as 7-dicarboxylic acid, sulfo-p-xylylene glycol, and 2-sulfo-1,4-bis(hydroxyethoxy)benzene, and ester-forming derivatives thereof. . Among these, 5-sulfoisophthalic acid, sodium salt of sulfoterephthalic acid, and copolymers of these ester-forming derivatives have excellent homogeneous dispersibility with polyamide resin,
It is preferable in terms of biaxial stretchability and easy transparency.

Next, the glycol component is an aliphatic glycol having 2 to 8 carbon atoms or a ring glycol having 6 to 12 carbon atoms, and specific examples include ethylene glycol, 1.3-
Propanediol, 1,4-butanediol, l,2-
propylene glycol, neopentyl glycol, l,
4-Cyclohexane dimetatool, 1.6-hexanediol, 1.3-cyclohexane dimetatool, 1.2
-Cyclohexane dimetatool, p-xylylene glycol, diethylene glycol, triethylene glycol and the like are preferably used.

In some cases, polyether may be copolymerized for the purpose of imparting flexibility. The term "polyether" as used herein refers to a polymer having an ether bond as a main bond chain, such as polyethylene glycol, polypropylene glycol, glycerin ether, polytetramethylene glycol, and polyethylene glycol ether.

Particularly preferred examples of the ionic polyester resin produced from the above-mentioned aromatic dicarboxylic acids, ester-forming sulfonic acid metal salt compounds, and glycol include terephthalic acid and its ester-forming derivatives, and ester-forming aromatic dicarboxylic acids. This is a case where 5-sulfoisophthalic acid and its ester-forming derivatives are used as the sulfonic acid metal salt compound, and ethylene glycol is used as the glycol component.

The copolymerization ratio of terephthalic acid and 5-sulfoisophthalic acid metal salt is not particularly limited, but the molar ratio of terephthalic acid and 15-sulfoisophthalic acid is 99.510.5 to 70/30, preferably 99/1 to 75/25, More preferably 98/
It is desirable that the ratio is 2 to 80/20.

If the copolymerization ratio of 5-sulfoisophthalic acid is less than 0.5 mol%, the effect of improving the properties of the present invention is not clear, and if it exceeds 30 mol%, the handling properties of the resin are poor and film formation is difficult. Sexuality also tends to worsen.

Intrinsic viscosity of the above ionic polyester resin (
(measured in orthochlorophenol at 25°C) is 0.40
-1.20, preferably 0.50-0.90, more preferably 0.55-0.85 dl/g.

Polyester resins with such ionic properties are usually
It can be manufactured using conventional polyester manufacturing techniques.

That is, it can be obtained by melt polycondensation of the acid component and glycol component described above using a reaction catalyst such as esterification or transesterification catalyst or polymerization catalyst.

In the present invention, the mixing ratio of the ionic polyester resin and polyamide resin is 0.5 to 50 parts by weight, preferably 2 to 35 parts by weight, of the ionic polyester resin to 100 parts by weight of the polyamide resin. parts, more preferably 3 to 25 parts by weight.

The mixing ratio of ionic polyester resin is 0.5
If the amount is less than 1 part by weight, there will be no effect of improving biaxial stretching and only a film with poor thickness unevenness will be obtained, and there will be no effect of improving lubricity and flatness.

If the amount exceeds 50 parts by weight, the mechanical strength and cold resistance, which are inherent characteristics of polyamide films, will deteriorate, making it impossible to achieve the object of the present invention.

In the present invention, transparency refers to a biaxially stretched film thickness of 15 μm.
Haze at m is 2.0% or less, preferably 1.8%
The following is preferable because the beautiful appearance of the printing and the gloss of the AI vapor-deposited film when observed through the film surface are good.

In the above mixed resin, known additives may be added to the extent that they do not impede the effects of the present invention, such as heat stabilizers, oxidation stabilizers, weather stabilizers, ultraviolet absorbers, antistatic agents, organic lubricants, organic or Inorganic fine particles, pigments, dyes, nucleating agents, etc. may be added.

The thickness of the polyamide biaxially stretched film of the present invention is not particularly limited, and the thickness can be appropriately selected depending on the intended use. Usually 3-300μm1 preferably 5-300μm
The thickness is preferably 200 μm, more preferably 10 to 150 μm.

Next, the method for producing the biaxially stretched polyamide film of the present invention will be described, but the method is not limited thereto.

5 to 30 mol% of nylon obtained by a conventional polycondensation method to 6.100 parts by weight of nylon having a relative viscosity of 3.2.
- After thoroughly drying 0.5 to 50 parts by weight of sodium sulfoisophthalate copolyester resin under reduced pressure and heating, the mixture was mixed and fed to a known melt extruder.
It is melted at a temperature of °C, melted and extruded into a sheet through a slit-shaped die, and solidified by cooling to produce an unstretched sheet. In this case, the sheet is preferably cooled and solidified on a cooling drum at a temperature of 50° C. or lower, preferably 40° C. or lower. This unstretched sheet is heated at 40 to 90°C, preferably 50 to 80°C.
2.5-4 in the longitudinal direction at a stretching rate of 104-106%/min, preferably 5X10'-2X105%/min.
．． Stretch 5 times, preferably 3.0 to 3.5 times, and then quench as soon as possible to produce a -axially stretched film. This longitudinal stretching is preferably carried out between two pairs of nip rolls having different circumferential speeds in the heating zone. This -axially stretched film is stretched 3.0 to 5.0 times in the width direction while heating at 60 to 140°C, preferably 80 to 125°C. After that, heat treatment is performed at 180 to 220°C for 0.5 to 10 seconds, if necessary. Furthermore, if it is desired to increase the crystallinity of the film, the heat treatment time may be increased or a moist heat treatment may be performed. Further, if necessary, a relaxation treatment of 1 to 10% may be performed in the heat treatment step. The biaxially stretched film thus obtained may be subjected to known corona discharge treatment (in air, nitrogen, carbon dioxide, etc.), flame treatment, vapor deposition processing, etc.

The polyamide biaxially stretched film obtained in this way can be used as a variety of packaging films, especially packaging for water products such as konnyaku and pickles, packaging for frozen foods, solid packaging for snacks and ramen noodles, etc.
It is suitable for use in heavy packaging such as rice.

[Method for Measuring Characteristics and Evaluating Effects] Methods for measuring characteristics and evaluating effects in the present invention are as follows.

(1) Stretchability The thickness change in the width direction of the film after biaxial stretching was measured, and the stretchability was evaluated based on the degree of thickness unevenness as shown below.

When the thickness unevenness was 20% or less, the stretchability was evaluated as good "○", and when it exceeded it, the stretchability was evaluated as poor "x".

(2) Haze The haze per film was measured according to ASTM-D-1003-52.

(3) Friction coefficient 25℃65%R according to ASTM-D-1894-63
The static friction coefficient (μS) and dynamic friction coefficient (μd) at h were measured.

(4) Breaking strength and breaking elongation Measured at 25°C and 65% Rh using an Instron type tensile tester according to ASTM-D-882.

(5) Pinhole resistance strength Attach a circular frame with an inner diameter of 30 mm to the crosshead of the autograph, secure the sample film under tension to this frame, and attach the stainless steel tip to the load cell attached to one autograph head. Q. Attach a spherical needle with a diameter of 5 mm, raise the crosshead at a speed of 100 mm/min, and measure the strength when the needle breaks the film.
The value divided by the thickness of the film was defined as the pinhole resistance strength.

6) Cold resistance - Measured in accordance with JIS-6717 in an atmosphere of 10°C. The film is stretched in a circle with a diameter of 70 mm, and the steel ball falling onto the film weighs 535 g and falls at a height of 200 mm.
It was set to 0 mm.

(7) Flatness The flatness of the film after being left in a 65% Rh environment at 25° C. for 2 weeks was visually evaluated using the following criteria.

◎: Extremely good flatness.

○: Some seaweed-like wrinkles occur, but at a level that causes no practical problems.

△: Slightly wakame-like wrinkles are noticeable.

×: Significant seaweed-like wrinkles.

[Effects of the Invention] The present invention achieves the following excellent effects by mixing a specific polyester resin with a polyamide resin in a specific ratio.

(1) Superior successive biaxial stretchability compared to polyamide resin alone.

■ Excellent lubricity and transparency without sacrificing the mechanical strength, cold resistance, and other properties of polyamide resin films.

(3) Compared with a single polyamide resin film, the dimensional change under high humidity or oral change is smaller, and therefore the deterioration of flatness is smaller.

[Example] Next, embodiments of the present invention will be described based on Examples.

Example 1 (Production of ionic polyester resin) 90 parts of dimethyl terephthalate, 10 parts of 5-sodium dimethyl sulfoisophthalate (abbreviated as SSIA), 100 parts of ethylene glycol, 0.11 part of manganese acetate tetrahydrate, Mix 0.07 parts of calcium acetate dihydrate and stir under nitrogen stream for 14 days.
After distilling methanol and performing transesterification at 0 to 220°C, 0.09 part of trimethyl phosphate and 0.06 part of antimony dioxide are added, and the temperature is raised from 240°C to 280°C over 1 hour and 30 minutes. At the same time, the pressure in the system was gradually lowered from normal pressure to Q. A polyester copolymer having the following was obtained.

This polyester copolymer was pulverized, dried under reduced pressure at 120° C. for 24 hours, and mixed with a polyamide resin.

As the polyamide resin to be mixed with the polyester resin, nylon 6 with a relative viscosity of 3.5 was mixed with nylon 6 under reduced pressure at 170°C.
The one that had been dried for a while was used.

10 parts by weight of the above polyester resin was mixed with 100 parts by weight of the above polyamide resin, fed to a melt extruder heated to 280°C, melt extruded from a T-shaped nozzle, and cooled to a cooling drum with a surface temperature of 20°C using an electrostatic application method. An unstretched sheet was prepared by winding the film around the film and cooling and solidifying it. This unstretched sheet is
It was stretched 3.2 times in the longitudinal direction between two pairs of nip rolls having different circumferential speeds under heating at 0°C, and then rapidly cooled with a group of cooling rolls at 15°C. This -axially stretched film was preheated at 60°C, stretched 3.8 times in the width direction at 110°C, and then heat treated at 200°C for 5 seconds while relaxing 2% in the width direction to obtain a biaxially stretched film with a thickness of 15 μm. Ta.

As shown in Table 1, this film had small thickness unevenness, good transparency, slipperiness, and flatness, and exhibited mechanical strength and cold impact strength equivalent to that of a single polyamide film. .

Comparative Example 1 A biaxially stretched film was produced in the same manner as in Example 1, except that a polyethylene terephthalate (intrinsic viscosity: 0.57) homopolymer was used in place of the ionic polyester resin of Example 1. This film had large thickness irregularities, poor transparency and flatness, and a decrease in pinhole resistance, which is a characteristic of polyamide films.

Examples 2 and 3, Comparative Examples 2 and 3 Biaxially stretched films were produced in the same manner as in Example 1 except that the mixing ratio of the ionic polyester resin and the polyamide resin was changed.

When the mixing ratio of the ionic polyester resin is lower than the range of the present invention (Comparative Example 2), the effect of improving stretchability is insufficient, resulting in large thickness unevenness, and both slipperiness and transparency are not improved. There wasn't.

In addition, if the mixture exceeds the scope of the present invention, the inherent mechanical properties, cold resistance, etc. of the polyamide film deteriorate, making it unsuitable for the purpose of the present invention. The object of the present invention could be achieved only when the mixing ratio was within the range of the present invention (Example 2.3).

Example 4 Dimethyl 2-potassium sulfoterephthalate (K
A copolymerized polyester having ionic properties and an intrinsic viscosity of 0.63 was obtained in the same manner as in Example 1 except that STA (abbreviated as STA) was used. This copolyester was mixed with nylon 6 in the same manner as in Example 1 to obtain a biaxially stretched film with a thickness of 15 μm. As shown in Table 1, the obtained film had good stretchability, transparency, slipperiness, and flatness, and maintained the same mechanical properties as nylon 6.

Comparative Example 4 A biaxially stretched film was produced in the same manner as in Example 1 using only nylon 6.

This film had poor stretchability, large thickness unevenness, and poor slipperiness, transparency, and flatness.

Claims (4)

[Claims] (1) A biaxially stretched polyamide film characterized by containing 0.5 to 50 parts by weight of an ionic polyester resin per 100 parts by weight of the polyamide resin. (2) The polyamide biaxially stretched film according to claim (1), wherein the ionic polyester resin is a polyester copolymer having a sulfonic acid metal base. (3) The polyester copolymer having a sulfonic acid metal base has a dicarboxylic acid having a sulfonic acid metal base of 0.5
3. The biaxially stretched polyamide film according to claim 2, which is a polyester copolymerized with ~30 mol%. (4) The polyamide biaxially stretched film according to any one of claims (1) to (3), wherein the polyamide biaxially stretched film has a haze of 2.0% or less at a thickness of 15 μm.