JP3367331B2 - Biaxially oriented polyamide resin film and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel polyamide-based biaxially oriented film and a method for producing the same, and in particular, it is a slippery and transparent film excellent in handling workability in a high humidity environment. A biaxially oriented polyamide resin that is tough and has excellent pinhole resistance when laminated with an olefin resin film such as polypropylene or polypropylene and used for packaging retort foods, and has excellent curl resistance during boiling water treatment. The present invention relates to a film and a manufacturing method thereof.

[0002]

2. Description of the Related Art Generally, a uniaxially stretched or biaxially stretched polyamide-based stretched film is excellent in mechanical properties and thermal properties and has a high gas barrier property. Therefore, soup, konjac, hamburger , Miso, ham,
It is widely used as liquid foods such as rice, aquatic foods, frozen foods, retort foods, pasty foods, livestock meat and marine foods, and packaging materials for heavy goods. These films mainly used for packaging are required to have good slipperiness and excellent workability in printing, vapor deposition, laminating, bag making, etc. The film has a drawback that it softens due to moisture absorption in a high-humidity environment and its slipperiness deteriorates. Therefore, in the rainy season, there are various problems caused by insufficient slipperiness during handling or processing. Therefore, as a means for improving the slipperiness of the polyamide resin film, (1) fine particles such as silica and kaolin are added to the resin, and these fine particles are projected on the film surface by a stretching treatment to form fine projections. , A method of reducing the contact area between films,
(2) A method of forming spherulites on the film to reduce the contact area between the film surfaces, (3) Addition of an organic lubricant such as a bisamide compound of a higher fatty acid to the polyamide resin, and interaction between the contacted portions of the films To reduce energy consumption, (4)
The film has a multi-layer structure by a method such as coating, laminating, and co-extrusion, and the above-mentioned (1)-
A method of forming a layer having improved slipperiness obtained by the method (3) has been proposed.

[0003]

However, in order for the polyamide resin film obtained by the above method (1) or (2) to secure satisfactory workability even under high humidity,
It is necessary to increase the amount of fine particles added to form protrusions on the film surface and the amount of spherulites, and the transparency of the film decreases accordingly, which is a fatal defect for packaging applications where a beautiful appearance is required. Become. Further, the polyamide-based resin film obtained by the above method (3) has a slight decrease in transparency as compared with the polyamide-based resin film obtained by the methods (1) and (2), and may have improved slipperiness. I can, but
Increasing the amount of organic lubricant added to obtain sufficient lubricity will result in poor adhesion and wettability with other materials when the film is laminated or laminated with other materials, resulting in printing, vapor deposition, or lamination. There was a drawback that it adversely affected processing such as.

On the other hand, as a method for producing a biaxially oriented film, a longitudinal / transverse sequential biaxial stretching method is known, and it is also used in a polyamide resin. However, due to the inherent properties of polyamide-based resins, that is, the high crystallization rate and the formation of hydrogen bonds between and within molecules due to the arrangement of molecules, increasing the longitudinal stretching ratio significantly increases the stress during transverse stretching. However, breakage easily occurs, and the longitudinal stretching ratio has to be lowered. Reducing the longitudinal stretching ratio reduces productivity, which is an industrial problem.

The present invention solves the problems of the conventional biaxially oriented polyamide resin film and the method for producing the same, and can be used in packaging applications without impairing the excellent properties of the biaxially oriented polyamide resin film. To provide a biaxially oriented polyamide resin film capable of satisfying various processing suitability and satisfying both transparency and slipperiness, particularly transparency and slipperiness under high humidity, and a method for producing the same. To aim.

[0006]

In order to achieve the above object, the biaxially oriented polyamide resin film of the present invention comprises a polyamide resin containing 0.03 to 0.80% by weight of fine particles for forming surface protrusions. A biaxially oriented film, the protrusion density of protrusions having a surface height of 0.27 μm or more is 200 / mm ² or more, and the area ratio of microvoids contained in the surface layer is 0.1% or less. It is characterized by being.

The biaxially oriented polyamide resin film of the present invention having the above-mentioned constitution has a good slidability, has a slidability capable of obtaining an excellent workability even in an environment of high humidity, and is excellent in transparency. It is a stretched polyamide resin film.

Further, the biaxially oriented polyamide resin film of the present invention is a surface protrusion in which protrusions having a height of 0.27 μm or more on the film surface are contained in the polyamide resin in an amount of 0.03 to 0.80% by weight. It is characterized in that it is mainly formed by forming fine particles.

The biaxially oriented polyamide resin film of the present invention having the above-mentioned constitution has a good slidability and has a slidability capable of obtaining an excellent workability even in an environment of high humidity, and has sufficient transparency. It is an excellent stretched polyamide resin film.

Further, in the biaxially oriented polyamide resin film of the present invention, the fine particles for forming surface protrusions have an average particle size of 0.
It is characterized by being 5 to 5 μm.

The biaxially oriented polyamide resin film of the present invention having the above-mentioned constitution has a good slipperiness and a slipperiness capable of obtaining excellent workability even in an environment of high humidity, and has sufficient transparency. It is an excellent stretched polyamide resin film.

Further, the method for producing a biaxially oriented polyamide resin film of the present invention is a sheet made of a polyamide resin containing 0.03 to 0.80% by weight of substantially non-oriented fine particles for forming surface protrusions. In the method for producing a polyamide-based resin film by the sequential biaxial stretching method in which the film is stretched in the longitudinal direction and then stretched in the transverse direction by 3 times or more, the longitudinal stretching is performed as the first stretching at a low temperature crystallization temperature (Tc) to Tc + 30 ° C. 1.
After stretching 2 to 3.0 times, the glass transition temperature (Tg) or higher is maintained, and then as the second stretching, Tg + 10 ° C. to Tc +.
It is characterized in that stretching is carried out at 20 ° C. so that the total longitudinal stretching ratio is 3.0 to 6.0 times.

According to the method for producing the biaxially oriented polyamide resin film of the present invention having the above-mentioned constitution, the protrusion density of the protrusions having a height of 0.27 μm or more on the surface thereof is 200 pieces / mm ^2.
The biaxially oriented polyamide resin film having the above-mentioned and having an area ratio of the microvoids contained in the surface layer of 0.1% or less and having excellent slipperiness and transparency can be obtained with high productivity.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the biaxially oriented polyamide resin film of the present invention and the method for producing the same will be described in detail.

The polyamide resin used in the present invention is a polymer having an amide group in the molecular chain, and specific examples thereof include nylon 6, nylon 7, nylon 11 and
Polyamide resins such as Nylon 12, Nylon 66, Nylon 6T, Nylon MXD6, Nylon 6I, Nylon 46, and their copolymers, blends, and alloys can be mentioned.

The fine particles for forming surface protrusions used in the present invention are appropriately selected from inorganic lubricants such as silica, kaolin and zeolite, and high molecular organic lubricants such as acrylic and polystyrene.

The fine particles for forming surface projections used in the present invention preferably have an average particle size of 0.5 to 5 μm, more preferably 1 to 3 μm, and an average particle size of 0.5 μm.
If it is less than 5 μm, a large amount is required to obtain good slipperiness, while if it exceeds 5 μm, the surface roughness of the film becomes too large to satisfy practical properties.

The content of the surface projection-forming fine particles used in the present invention in the biaxially oriented polyamide resin film is 0.03 to 0.80% by weight, more preferably 0.1.
It is in the range of 0 to 0.50% by weight. When the content is less than 0.03% by weight, the density of protrusions formed is insufficient and the slipperiness under high humidity conditions is not sufficiently improved, while the content is less than 0.
If it exceeds 50% by weight, the transparency of the film becomes unacceptably poor.

The biaxially oriented polyamide-based resin film of the present invention contains the polyamide-based resin and fine particles for forming surface protrusions as essential components, but various other additives such as, for example, various additives within the range not impairing the above-mentioned characteristics. Lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, light stabilizers,
It is also possible to contain an impact resistance improver and the like. In particular, it is preferable to add an organic lubricant having an effect of lowering the surface energy to such an extent that the adhesiveness and the wettability do not cause a problem, because the stretched film can have more excellent slipperiness and transparency.

On the surface of the biaxially oriented polyamide resin film of the present invention, the protrusion density of protrusions having a height of 0.27 μm or more needs to be 200 / mm ² or more, and the protrusion density is 200 / mm. ^When it is less than ² , the slipperiness under high humidity conditions is not sufficiently improved.

Furthermore, the area ratio of microvoids contained in the surface layer of the biaxially oriented polyamide resin film of the present invention must be 0.1% or less, more preferably 0.05% or less. If it exceeds 0.1%, the transparency cannot satisfy the requirements for packaging.

The method for producing a biaxially oriented polyamide resin film according to the present invention comprises a sheet of a polyamide resin containing 0.03 to 0.80% by weight of substantially non-oriented fine particles for forming surface protrusions. In the method for producing a polyamide-based resin film by a sequential biaxial stretching method of stretching in the longitudinal direction and then stretching in the transverse direction by 3 times or more, the longitudinal stretching is the first stretching at a low temperature crystallization temperature (Tc) to Tc + 30 ° C. 1.2-
After being stretched 3.0 times, the glass transition temperature (Tg) or higher is maintained, and then as the second stretching, Tg + 10 ° C. to Tc + 20.
It is a method for producing a biaxially oriented polyamide resin film, which is stretched at 0 ° C. so that the total longitudinal stretching ratio is 3.0 to 6.0 times.

If the stretching temperature in the first stage of the longitudinal stretching is less than Tc, oriented crystallization proceeds and the stress during the second stretching increases, which is not preferable, and if it exceeds Tc + 20 ° C., thermal crystallization occurs. Although it is accelerated and the second stretching can be performed, whitening due to crystallization in the lateral stretching is not preferable. From this point, the temperature of the first stretching is preferably Tc + 5 to Tc + 20 ° C. Further, if the draw ratio during the first stretching is less than 0.2 times, the drawing tension becomes too low, resulting in instability, and it is insufficient to increase the total longitudinal drawing ratio. If it exceeds the above range, oriented crystallization proceeds too much, and the second stretching becomes difficult, which is not preferable. From this point, the first draw ratio is 1.5 to 2.5.
Double is preferred. Further, in order to achieve such a first stretching, it is preferable to reduce the stretching stress by slow stretching in which the deformation section of the film is lengthened rather than rapid stretching in a close gap in which the stretching roll gap is closely contacted, The first stretching may be performed in multiple stages.

Further, the film after the first stretching is kept at Tg or higher, and then in the machine direction at Tg + 10 to Tc + 20 ° C.,
The second stretching is performed so that the total longitudinal stretching ratio is 1.5 to 2.5 times and the total longitudinal stretching ratio is 3.0 to 6.0 times. Cooling after the first stretching accelerates crystallization and formation of hydrogen bonds in the reheating process to the second stretching, which makes it difficult to perform the second stretching, which is not preferable. From this point, the temperature between the first stretching and the second stretching is Tg + 1.
It is preferably 0 ° C or higher. Further, in industrial production, the residual heat after the first drawing can be used as it is in the field of high-speed drawing, which is very advantageous.

The temperature of the second stretching in the machine direction is Tg + 10 ° C.
If it is less than the above range, the orientation proceeds, and it is difficult to uniformly stretch the film in the lateral direction thereafter, resulting in large thickness unevenness, which is not preferable. Further, if the second stretching temperature in the longitudinal direction exceeds Tc + 20 ° C., it is not preferable because crystallization causes many breakages in the subsequent transverse stretching. From this point, the temperature of the second stretching is Tc.
-Tc + 15 degreeC is preferable. If the total longitudinal stretching ratio is less than 3 times, the purpose of high-speed film formation cannot be achieved, and if the total longitudinal stretching ratio exceeds 6 times, the orientation remarkably progresses and frequent breakage occurs in transverse stretching, which is not preferable because stable film formation cannot be achieved. From this point, the total longitudinal stretching ratio is 3.3 to 5.
5 times is preferable.

Subsequently, this film is stretched in the transverse direction 3 times or more, preferably 3.5 times or more, and further heat-fixed to obtain a biaxially oriented film.

In the heat setting step, heat treatment is carried out at a high temperature in order to improve the dimensional stability of the film, but heat treatment at a high temperature reduces the number of protrusions on the surface of the film, so avoid heat treatment more than necessary.

The thickness of the biaxially oriented polyamide resin film of the present invention can be set arbitrarily and is usually 5 to 250.
μm, 10 to 50 μm for general food packaging applications
Stuff is supplied.

The biaxially oriented polyamide resin film of the present invention may be further subjected to heat treatment or humidity control treatment in order to further improve dimensional stability depending on the use.
Depending on the application, corona treatment, coating treatment or flame treatment may be performed to improve the adhesiveness and wettability. Further, the biaxially oriented polyamide resin film of the present invention is generally subjected to processing such as printing, vapor deposition, laminating and the like depending on the application.

On the surface of the biaxially oriented film thus obtained, protrusions having a height of 0.27 μm or more and a protrusion density of 200 / mm ² or more are formed. In this method, which performs low stress longitudinal stretching in two stages at high temperature, the deformation (flattening) of fine particles due to the stress during stretching can be made smaller than that of the film obtained by using the normal one longitudinal stretching method. It is considered that the formation of the protrusions based on the fine particles thus made was made more effective. Further, when the longitudinal stretching with low stress is performed, it is possible to suppress the microvoids generated around the fine particles (it is considered that the stretching stress causes the interface between the fine particles and the resin as the matrix to be peeled off).
As a result, the transparency can be maintained high even if the protrusion density is increased (the slipperiness is improved). The height is 0.27
It is preferable that the protrusions with a size of μm or more are mainly formed by the fine particles for forming surface protrusions, preferably 50% or more, and particularly 90% or more by the fine particles for forming surface protrusions. In this case, as another method of forming the protrusions, an arbitrary method such as spherulite is conceivable.

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and changes may be made within the scope of the gist of the present invention. It can be carried out, and all of them are included in the technical scope of the present invention. The evaluation method of the physical property test adopted in the present invention is as follows.

(Sliding property of film under high humidity conditions) 20
The dynamic friction coefficient at ℃, 75RH%, ASTM-D1
It was measured according to 894. A film having a dynamic friction coefficient of 1.2 or less has good slipperiness under high humidity and can be evaluated as having excellent workability.

(Protrusion Density on Film Surface) A single ring (protrusion height: 0.27 μm) observed by depositing aluminum on the film surface under vacuum and mounting a filter with a wavelength of 0.54 μm on a two-beam interference microscope. The above rings are measured over 1.3 mm ² and displayed as the number (density) per unit area.

(Area Ratio of Microvoids Included in Surface Layer of Film) The film surface was observed under a reflection metallographic microscope,
The image was observed using a Luzex II-D type image processing device manufactured by Nireco Co., Ltd., and the observed area of microvoids (0.15 m
Calculate and display the ratio to m ² ).

(Glass transition temperature (Tg) and low temperature crystallization temperature (Tc)) An unoriented polyamide resin sheet is frozen in liquid nitrogen, decompressed and thawed, and then manufactured by Seiko Denshi KK
The measurement was performed using SC at a heating rate of 10 ° C./min.

(Film Temperature) The temperature in the longitudinal stretching is
The temperature of the film was measured using a radiation thermometer IR-004 manufactured by Minolta Co., Ltd.

(Thickness unevenness) The film is cut into a strip shape having a width of 50 mm, the thickness shape of the film is measured by a thickness meter K306C manufactured by Anritsu Electric Co., Ltd., and the thickness unevenness is calculated by the following formula. Thickness unevenness = {(maximum thickness-minimum thickness) / average thickness} × 10
0 (%)

(Situation of film formation) Biaxial stretching was successively carried out under the same conditions (operating time: 2 hours), and the number of film breaks was examined. Within this time, it is practically necessary that there is no breakage.

Example 1 Nylon 6 obtained by ring-opening polymerization of ε-caprolactam was used as a polyamide resin in a 100 liter batch type polymerization kettle. The nylon 6 chips were extracted with hot water using a batch-type polymerization kettle to reduce the content of monomers and oligomers to 1% by weight, and then dried to a water content of 0.1% by weight. used. The relative viscosities of the raw material nylon 6 and the stretched film are about 3. When measured at 20 ° C. using a 96% concentrated sulfuric acid solution.
It was 0. The fine particles for forming surface protrusions (0.
15% by weight) is a silica fine particle having a pore volume of 1.3 cc / g and an average particle diameter of 2.5 μm, which is polymerized by dispersing it in an aqueous solution of ε-caprolactam, which is a raw material of nylon 6, by a light flux stirrer. And then dispersed in nylon 6 in the polymerization step. Furthermore, after blending 0.15% by weight of N, N'-ethylenebisstearylamide, 2 with an extruder from a T-die.
Melt extruded at 60 ℃, load DC high voltage at 30 ℃
Was electrostatically brought into close contact with the above cooling roll to cool and solidify to obtain a substantially unoriented sheet having a thickness of 200 μm. The Tg and Tc of this sheet were 40 ° C. and 69 ° C., respectively. This sheet is first stretched 1.7 times in the machine direction at a stretching temperature of 75 ° C. and then second stretched while maintaining the temperature at 70 ° C. and a total longitudinal stretching ratio of 3.4 times at a stretching temperature of 70 ° C. Then, this sheet was continuously introduced into a stenter, horizontally stretched 4 times at 130 ° C., heat-set at 210 ° C. and subjected to 5% lateral relaxation treatment, and then cooled, and both edges were cut and removed. A biaxially oriented polyamide resin film was obtained. The film characteristics at this time are shown in Table 1.

Examples 2 to 4 and Comparative Examples 1 and 2 A biaxially oriented polyamide resin film was prepared under the same conditions as in Example 1 except that the pore volume and addition concentration of the surface projection forming fine particles used were changed. Obtained. The film properties are shown in Table 1.

Examples 5 to 8 Biaxially oriented polyamide films were obtained in the same manner as in Example 1 except that the longitudinal stretching conditions were changed as shown in Table 1.

Comparative Example 3 Except that the longitudinal stretching was carried out at a temperature of 65.degree.
A biaxially oriented polyamide film was obtained in the same manner as in Example 1.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the first longitudinal stretching was followed by rapid cooling to 35 ° C. and reheating for the second stretching. No film could be formed.

Comparative Examples 5 to 8 Biaxially oriented polyamide films were obtained in the same manner as in Example 1 except that the longitudinal stretching conditions were changed as shown in Table 1.

[0045]

[Table 1]

As is clear from Table 1, the film satisfying all the requirements of the present invention had good smoothness and transparency. On the other hand, in the case of the comparative example film which is out of the specified range of the present invention, a film satisfying easy sliding and transparency cannot be obtained, the thickness unevenness is large, and the stability of film formation (breakage)
However, it lacks practical use.

[0047]

EFFECT OF THE INVENTION The biaxially oriented polyamide resin film according to claim 1 satisfies both transparency and slipperiness, particularly transparency and slipperiness under high humidity. The biaxially oriented polyamide resin film according to the second aspect simultaneously satisfies transparency and slipperiness, particularly sufficient transparency and slipperiness under high humidity. The biaxially oriented polyamide resin film according to claim 3 simultaneously satisfies transparency and slipperiness, particularly sufficient transparency and slipperiness under high humidity. The method for producing the biaxially oriented polyamide-based resin film according to claim 4, comprises: transparency and slipperiness;
Satisfies transparency and slipperiness at the same time especially under high humidity 2
An axially oriented polyamide resin film can be obtained with high productivity.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI B29K 105: 16 B29K 105: 16 B29L 7:00 B29L 7:00 C08L 77:00 C08L 77:00 (56) References 7-290565 (JP, A) JP 3-192131 (JP, A) JP 2-133434 (JP, A) JP 62-112629 (JP, A) JP 5-212788 (JP, A) JP-A-5-212789 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08J 5/18

Claims (4)

(57) [Claims] 1. A fine particle for forming surface protrusions, comprising 0.03 to 0.
A biaxially oriented film made of a polyamide resin containing 80% by weight, the protrusion density of protrusions having a height of 0.27 μm or more on the surface thereof is 200 / mm ² or more, and included in the surface layer. Area ratio of micro voids is 0.1
% Or less, excellent in smoothness and transparency 2
Axial oriented polyamide resin film. 2. The projections having a height of 0.27 μm or more on the surface of the film are mainly formed by surface projection-forming fine particles contained in the polyamide resin in an amount of 0.03 to 0.80% by weight. The biaxially oriented polyamide resin film according to claim 1, which is excellent in slipperiness and transparency. 3. The average particle size of the surface projection-forming fine particles is 0.5 to 5 μm.
A biaxially oriented polyamide-based resin film having excellent slipperiness and transparency described above. 4. Easy sliding / transparency according to claim 1, 2 or 3.
With excellent manufacturing method of biaxially oriented polyamide resin film
Then, a substantially unoriented sheet made of a polyamide-based resin containing 0.03 to 0.80% by weight of surface projection-forming fine particles is stretched in the longitudinal direction and then stretched three times or more in the transverse direction. In the method for producing a polyamide-based resin film by the axial stretching method, the longitudinal stretching is performed as the first stretching at a low temperature crystallization temperature (Tc) to Tc + 30 ° C of 1.2 to 3.0.
After being double-stretched, kept at a glass transition temperature (Tg) or higher,
Then, the second stretching is performed at Tg + 10 ° C. to Tc + 20 ° C. such that the total longitudinal stretching ratio is 3.0 to 6.0 times, which is a method for producing a biaxially oriented polyamide resin film.