JPH03222719A - Manufacture of laminated biaxially oriented film - Google Patents

Abstract

PURPOSE:To obtain a laminated biaxially oriented film superior in oxygen barrier properties and mechanical strength, by a method wherein an ethylene-vinyl acetate copolymer saponified matter and polyamide are quenched by laminating within an annular die and tubular biaxial orientation is performed under a specific orientation condition. CONSTITUTION:A matter (EVOH) whose ethylene content is 25-45mol% and saponification proof is 98% or higher is used as an ethylene-vinyl acetate copolymer saponification matter. A laminated sheet extruded through an annular die lip and comprised of polyamide, EVOH and the polyamide is quenched by a liquid whose temperature is, for example, 40 deg.C or lower, fed to two pairs of nip roll groups which are positioned at the top and bottom and having different peripheral speeds and biaxially oriented both in length and width simultaneously by pressure of gas enclosed on the inside and adjustment of peripheral speeds of the nip rolls. An annular film is heated at 45-100 deg.C by an annular heter and oriented immediately by 2-5 times within respective ranges of mean deformation rates of 2000-10000%/min. in a flowing direction and a direction meeting at right angles with the flowing direction. Then heat-treated within a temperature range extending from 190 deg.C to a temperature lower by 10 deg.C than the melting point of the polyamide.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a laminated double layer comprising at least one layer of saponified ethylene-vinyl acetate copolymer and at least one layer of polyamide. The present invention relates to a method for producing an axially stretched film.

Specifically, the present invention relates to a method for producing the above-mentioned film, which has excellent oxygen gas barrier properties, mechanical strength such as pinhole resistance, thickness accuracy, and dimensional stability.

The oxygen gas barrier property and pinhole resistance strength of the film of the present invention are, for example, as in foods, medical products, drugs, etc.
This is an important property for packaging films for contents where deterioration due to oxygen is a problem, and thickness accuracy and dimensional stability are important properties during printing and laminating.

[Prior art]

A biaxially stretched film made of a saponified ethylene vinyl acetate copolymer exhibits extremely excellent oxygen gas barrier properties, as well as excellent transparency and oil resistance. It is inferior in quality, and its uses are limited.

On the other hand, although polyamide films have excellent mechanical properties such as tensile strength and pinhole resistance, they do not have sufficient oxygen gas barrier properties when used for packaging foods, medical products, drugs, etc.

Therefore, a laminated biaxially stretched film, which is a composite of each of the above-mentioned films, has been attracting attention, and several manufacturing methods have been proposed.

For example, JP-A-52-115880 describes a method in which a saponified ethylene-vinyl acetate copolymer film and a polyamide film are closely laminated and then the laminated film is biaxially stretched. Japanese Patent Publication No. 55-8
No. 2650 proposes a method for producing a composite film in which an unstretched or l-axis stretched polyamide film is composited with an ethylene-vinyl acetate copolymer saponified film and then stretched, and a sequential biaxial stretching method is proposed. There is also a description of Furthermore, Japanese Patent Publication No. 6i22613 discloses that a laminated tubular film made of a saponified ethylene-vinyl acetate copolymer and polyamide is coextruded, the moisture content is maintained at 2 wt% or less, and then heated and A tubular method has been proposed in which simultaneous biaxial stretching is performed using internal gas pressure.

[Problems to be Solved by the Invention] However, the method described in JP-A-52-115880 is a method in which a saponified ethylene-vinyl acetate copolymer film and a polyamide film are produced separately and then laminated in close contact with each other. However, this method involves complicated steps such as film production, lamination, and stretching, and cannot be said to be an industrially advantageous method. In addition, the method described in Japanese Patent Application Laid-open No. 55-82650 not only requires expensive manufacturing equipment but also requires complicated operating conditions, so it cannot be said to be an industrially advantageous method.

Further, although the method described in Japanese Patent Publication No. 61-22613 is a relatively advantageous method, as a result of additional tests by the present inventors, a film with excellent dimensional stability could not be obtained.

Means for Solving Problem S] In view of the above-mentioned circumstances, the present inventors have conducted extensive studies on the tubular biaxial stretching method in order to provide an industrially advantageous manufacturing method for the laminated biaxially stretched film. To produce a laminated biaxially oriented film with excellent oxygen gas barrier properties, mechanical strength, thickness accuracy, and dimensional stability from a saponified ethylene-vinyl acetate copolymer with an extremely fast crystallization rate and polyamide. In particular, it has been found that the stretching temperature, stretching ratio, deformation rate during stretching, and heat treatment temperature of the stretched film are important.

The present invention was completed as a result of further studies based on the above knowledge, and the gist thereof is (a) extruding a saponified ethylene-vinyl acetate copolymer and a polyamide from separate melt extruders. A first step in which the obtained molten annular film is rapidly cooled to obtain an unoriented annular laminated film. An unoriented annular laminated film is supplied and heated with a ring-shaped heater, and simultaneously in the vertical and horizontal directions by adjusting the pressure of the gas sealed inside the unoriented annular laminated film and the peripheral speed of the nip roll. A second step of biaxial stretching; (c) A third step of heat-treating the stretched film; In a method for producing a laminated biaxially stretched film by a tubular biaxial stretching method, the saponified copolymer as a raw material is: Ethylene content 25
A saponified ethylene-vinyl acetate copolymer with a saponification degree of 98% or more and a saponification degree of 98% or more is used, and the stretching temperature in the second step is 45 to 100' C1, 2,000 to 2,000 to
o, 2 to 5 times at an average deformation rate of ooo%/min, 2,000~looo in the lateral direction, 2 at an average deformation rate of ooo%/min
The heat treatment in the third step was performed at 190°C.
The method for producing a laminated biaxially stretched film is characterized in that the process is carried out under temperature conditions in which the lower limit is 10° C. lower than the melting point of the raw material polyamide and the upper limit is 10° C. lower than the melting point of the raw material polyamide.

The present invention will be explained in detail below.

In the present invention, the saponified ethylene-vinyl acetate copolymer, which is one of the raw material resins, has an ethylene content of 25
~45 mol%, saponification degree of 98% or more (hereinafter referred to as r
E, V OHJ) are used. When the ethylene content is less than 25 mo 1%, melt extrudability is poor and coloring is likely to occur. On the other hand, 45m.

If it exceeds 1%, physical properties such as oxygen barrier properties will deteriorate.

If the degree of saponification is less than 98 mo 1%, oxygen barrier properties and moisture resistance will decrease.

In addition, the above EVOH includes propylene, isobutyne, α-
α-olefins such as octene, α-dodecene, α-octadecene, partial or complete alkyl esters of unsaturated carboxylic acids or their salts, comonomers such as nitriles, amides, anhydrides, unsaturated sulfonic acids or their salts, etc. There is no problem even if it contains a small amount of. Furthermore, E
VOH may be mixed with a small amount of polyolefin resin, polyester resin, polyamide resin, etc.

In the present invention, the other raw material resin, polyamide, is
■ε-caprolactam homopolymer (homopolymer), ■
A copolymer containing ε-caprolactam as the main component and 2 to 10 mol% of other compounds; ■ 5 to 20% by weight of a polymer compatible with these homopolymers and/or copolymers; It means a mixture.

Other compounds that form the above homopolymer include nylon salts with aliphatic or aromatic diamines or dicarboxylic acids, and representative examples of diamines include ethylenediamine, tetramethylenediamine,
Typical examples of dicarboxylic acids include pentamethylene diamine, hexamethylene diamine, octamethylene diamine, decamethylene diamine, metaxylylene diamine, paraxylylene diamine, etc., and adipic acid, sebacic acid, corkic acid, geltaric acid, and azelaic acid. , β-methyladipic acid, terephthalic acid, isophthalic acid, decamethylene dicarboxylic acid, dodecamethylene dicarboxylic acid, pimelic acid, and the like.

Both EVOH and polyamide are highly hygroscopic, but if you use one that has absorbed moisture, water vapor and oligomers are generated when the raw materials are melted and extruded, which tends to inhibit film formation. Preferably, less than 0.1% by weight of substantially anhydrous raw materials are used.

Furthermore, various additives such as lubricants, antistatic agents, antioxidants, anti-blocking agents, stabilizers, dyes, pigments, and inorganic fine particles may be added to the above raw resin to the extent that they do not impair the properties of the film. Can be added.

First, in the method of the present invention, in the first step, a substantially amorphous, unoriented, unstretched annular laminated film (hereinafter referred to as "annular laminated unstretched film J") is produced using EVOH and polyamide as raw material resins. .

To produce an annular laminated unstretched film, polyamide in a molten state guided by two spirals and EVOH in a molten state guided by another spiral are mixed from the inside with polyamide, EVOH, and polyamide. The laminated sheets in a molten state are extruded from the die lip and then brought into contact with a liquid at a temperature of 40° C. or less to be rapidly cooled to form an annular laminated unstretched film. get. In addition, the thickness structure of these laminated unstretched films is such that the total thickness of the polyamide layer is E V
It is preferable that the thickness be at least 1.3 times the thickness of the OH layer, since the subsequent stretching operation can be performed more stably.

Next, in the method of the present invention, in the second step, the annular laminated unstretched film obtained as described above is stretched using a specific stretching temperature, deformation rate, and magnification.

In the second step, the above-mentioned annular laminated unstretched film is continuously supplied to two pairs of nip rolls located at the top and bottom and having different circumferential speeds, and the pressure of the gas sealed inside and the circumferential speed of the nip rolls are adjusted. Biaxially stretched both vertically and horizontally at the same time.

In the above-mentioned stretching, the annular film is heated to a temperature range of 45 to 100°C by a ring-shaped heater, and immediately the average deformation rate in the machine direction is 2,000 to 1o, and the flow rate is increased by 2 to 5 times in the range of ooo%/min. Stretching is carried out 2 to 5 times at an average deformation rate of 2,000 to 10,00096/min in the direction perpendicular to the direction.

If the temperature of the unstretched film is lower than 45° C., the film will not soften due to temperature, and therefore the stretching stress will be high and stretching will not be possible. On the other hand, when the temperature exceeds 100°C, the stretching stress becomes weak, the stretching bubbles shake, and the stretching becomes extremely unstable. Moreover, as time passes after heating, the film rapidly crystallizes, causing stretching unevenness and making the film easy to tear during stretching. Therefore, it is necessary to stretch the film immediately after heating it to 45-100°C.

The average stretching deformation speed in the machine direction and the direction perpendicular thereto needs to be 2000%/min or more and 10000% or less. Here, the average deformation speed refers to a value calculated by the following equation.

In the above formula, each symbol has the following meaning.

V ]+1, , average longitudinal deformation rate of the film (%/min) (m) UL: Linear speed of low speed side nip roll (m/min) UH:
Linear speed of high-speed side nip roll (m/min) VTD: Average lateral deformation speed of film (%/min) Y: Lateral stretching ratio (times)
and is determined by R/2r. r is the width of the folded film at the exit of the nip roll on the low speed side, and R is the outer circumference length of the bubble when the bubble is at its maximum.

1. The average deformation speed in the vertical and horizontal directions is 2°000 each.
If it is lower than %/min, the film tends to tear easily during stretching, which is not preferable. Moreover, if it is greater than 10,000 per minute, stretching unevenness tends to occur, which is not preferable.

The stretching ratio is 2 in the machine direction and in the direction perpendicular to it.
If it is less than 5 times, the desired orientation effect cannot be imparted to the final film, and if it is more than 5 times, the film tends to tear during stretching, which is undesirable.

In the third step of the present invention, the film stretched simultaneously in the longitudinal and transverse directions through the second step is heat-treated in a temperature range with a lower limit of 190'C and an upper limit of 10'C lower than the melting point of the raw material polyamide.

The above heat treatment can improve the dimensional stability of the biaxially stretched laminated film.

The melting point of EVOH is 180° C. with an Et content of 32 mol %, and therefore, at 190° C. or higher, it exceeds the melting point of EVOH, but there are no problems such as film breakage, and dimensional stability is improved.

In the case of heat treatment, the folded ends of the film, which has been stretched simultaneously in the vertical and horizontal directions through the second step, are held in tenter clips at the exit of the nip roll and heat treated in the tenter. A method of heat-treating in a tenter by attaching it to a tenter clip,
Conventional heat treatment methods, such as a method of heat treating the folded film as it is on a high-temperature roll, can be employed.

If the heat treatment temperature is lower than 190°C, the hot water shrinkage rate and dry heat shrinkage rate of the final film will increase, making it impossible to obtain a film with high dimensional stability as desired.

Furthermore, heat treatment at a temperature exceeding the upper limit is not preferable because the film may break, the surface of the obtained film may become white or devitrified, or the film may become brittle.

The film that has been sufficiently heat-set by the heat treatment in the third step is cooled and rolled up according to a conventional method.

[Examples] Next, the present invention will be explained in more detail based on Examples, and the present invention is not limited to the following examples unless the gist thereof is exceeded.

In the example below, the physical properties of the resulting film are:
Evaluation was made by the method described below.

■ Film thickness (μm) Measure the total thickness of the film at intervals of 30 mm in the width direction,
The average value is calculated and used as the thickness of the film.

The thickness was measured using a contact thickness gauge.

■ Film thickness unevenness (%) It means the value calculated from the following formula.

(If this thickness unevenness is 10% or less, it can be said that the thickness accuracy is good.) ■ Hot water shrinkage rate (%) First, the product film is conditioned in an atmosphere with a temperature of 23°C and a relative humidity of 50%. On the surface, a marked line of a square with a negative side length of 80 mm was drawn so that each side of the square was parallel to the vertical and horizontal directions of the film. Next, this sample was immersed in boiling water for 5 minutes, taken out, and then left again in an atmosphere at a temperature of 23° C. and a relative humidity of 50% for 24 hours. The dimensions of the square before and after immersion in boiling water were measured and calculated using the following formula.

Average hot water shrinkage rate - (longitudinal hot water shrinkage rate + transverse hot water shrinkage rate)/2 In the above formula, I Ml + I M2 is the length of the side along the longitudinal direction of the film before and after immersion, I 'TI+
IT2 means the length of the side of the film in the lateral direction before and after dipping, respectively.

Note that the hot water shrinkage rate in the longitudinal direction and the hot water shrinkage rate in the transverse direction are desirably about 4% or less in the case of a non-shrinkable film.

■ Oxygen permeability (cc/cnr-day) Oxygen permeability measuring device 0XY-TRANl 00 type (Mode
rn contro 1) at 25°C, 6
Measurement was performed under the condition of 5% RH.

Example 1 Poly-ε-caproamide (Tsubamitsudo 1022 manufactured by Mitsubishi Kasei Co., Ltd. (Kiyoshi)), ethylene content 32 mol%, saponification degree 9
Using 9.5 mol% or more EVOH (Nippon Gosei Kagaku Kogyo Co., Ltd., Soarnol DC) as a raw material, using three 40 mmφ extruders, and using an annular die for adhesion within the die, the outer layer is polyamide resin and the middle layer is EVOH. Extrude a molten annular laminated film whose inner layer is made of polyamide resin, and
A polyamide resin layer with an outer layer of 45μ, rapidly cooled in water at ℃,
A laminated annular unstretched film was obtained in which the intermediate layer was an EVOH resin layer with a thickness of 45μ and the inner layer was a polyamide resin layer with a thickness of 45μ.

The above film is introduced into a nip roll at a circumferential speed of 7 m/min, spread into a tube shape by air pressure sealed inside the film, heated to 80°C with a ring-shaped heater, and bubbles are immediately generated by the sealed air pressure. formed.

The bubbles were formed by controlling the air pressure and film temperature during stretching so that the bubbles reached their maximum diameter (3 times the diameter at the start of stretching) at a point 70 cm from the stretching start point. Next, while cooling the bubble and folding it with flat guide rolls, it was rolled for 21 m.
It was guided to a high-speed nip roll that rotates at a rate of 1/2 minutes.

Both ends of this folded film were held with tenter clips maintained at 40°C, and heat treatment was performed for 9 seconds while adjusting the film temperature to 200°C.

After the heat treatment, both edges of the film were cut out, and two films were wound up in a winder, and a polyamide resin layer of about 5 μm, an EVOH resin layer of about 5 μm, and a polyamide resin layer of about 5 μm were laminated in this order. Total thickness approx. 15
A laminated biaxially stretched film of μ was produced.

Film production was carried out continuously for 5 hours using the above method, and the operation was carried out smoothly without any abnormalities during the process.

Details of the operating conditions and conditions during stretching are shown in Table 1.

Examples 2 to 6 and Comparative Examples 1 to 8 Using the same raw materials as in Example 1 and following the same method, under each condition listed in Table 1, NY/EVOH/'N y was 7/7/ Laminated biaxially oriented films with layer configurations of 7 and 5/5/5 were produced.

Details of the operating conditions and conditions during stretching are shown in Table 1.

〔effect〕

The present invention has been explained in detail above, and the ethylene-
The present invention provides a method for easily, stably, and inexpensively producing a laminated biaxially oriented film made of saponified vinyl acetate copolymer and polyamide and extremely suitable for packaging foods, drugs, medical products, etc. , it produces the following particularly remarkable effects, and its industrial utility value is extremely great.

(1) When using the method of the present invention, particularly important stretching conditions in the biaxial stretching method have been established, so a laminated biaxially stretched film with stable quality can always be produced.

(2) When using the method of the present invention, a saponified ethylene-vinyl acetate copolymer with a specified composition is used, so a laminated biaxially stretched film with excellent oxygen gas barrier properties and mechanical strength can always be produced. be able to.

(3) When using the method of the present invention, specified heat treatment conditions are used, so a laminated biaxially stretched film with excellent dimensional stability can always be obtained.

Claims (2)

[Claims] (1) (a) Saponified ethylene-vinyl acetate copolymer and polyamide are extruded from separate melt extruders and laminated in an annular die.Then, the obtained annular film in the molten state is rapidly cooled and left unused. First step of obtaining an oriented annular laminate film; (b) The unoriented annular laminate film is supplied to two pairs of nip rolls positioned above and below and having different circumferential speeds and heated with a ring heater, and the unoriented annular laminate film is heated by a ring heater. a second step of simultaneously biaxially stretching the film in the longitudinal and transverse directions by adjusting the pressure of the gas sealed inside the film and the circumferential speed of the nip roll; (c) a third step of heat-treating the stretched film; In the method for producing a laminated biaxially stretched film using the biaxially stretched method, the saponified copolymer as a raw material has an ethylene content of 25%.
A saponified ethylene-vinyl acetate copolymer with a saponification degree of 98% or more and a saponification degree of 98% or more is used, and the stretching temperature in the second step is 45 to 100°C, and the longitudinal direction is 2,000 to 100°C.
,000%/min average deformation rate 2-5 times, lateral direction 2
,000-100,000%/min average deformation rate
Laminated biaxial stretching, characterized in that the heat treatment in the third step is carried out under temperature conditions with a lower limit of 190°C and an upper limit of 10°C lower than the melting point of the raw material polyamide. Film manufacturing method. (2) The layer structure of the laminated biaxially stretched film is a polyamide layer (A layer), a saponified ethylene-vinyl acetate copolymer (B
2. The method for producing a laminated biaxially stretched film according to claim 1, wherein the laminated biaxially stretched film has a layer structure in which the layers A/B/A are laminated in the order of A/B/A.