JPH05124099A - Method for preventing curling of multilayer film - Google Patents

Abstract

PURPOSE:To prevent curling of a film with a laminated polyolefine layer by keeping the multilayer film, after it was heat set and its saponified ethylene- vinyl acetate copolymer layer was allowed to absorb water, in the condition of a specified temperature and humidity until the absorbance ratio of the layer satisfies a specific equation. CONSTITUTION:A biaxial oriented multilayer film consisting of a surface layer of a saponified ethylene-vinyl acetate copolymer, an adhesive layer, and a polyolefine layer is heat set after stretching. The saponified ethylene-vinyl acetate copolymer layer is allowed to absorb water by contacting it with steam or hot water, and the film is kept in the condition of temperature 10-40 deg.C and RH 30-70% until the absorbance ratio of the saponified ethylene-vinyl acetate copolymer satisfies the equation of 25T-8alpha+10890<1000d/a<25T-8alpha+11390, where d is the absorbance at about 1141cm, a is the absorbance at about 1330 cm<-1>, T is a heat setting temperature ( deg.C), and (alpha is an ethylene content (mol%) in the saponified ethylene-vinyl acetate copolymer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a multilayer biaxially stretched film comprising a polyolefin resin layer, an ethylene-vinyl acetate copolymer saponified layer, and an adhesive resin layer present between these layers, and at least three layers. The present invention relates to a method for preventing curling that occurs when a film is produced and stretched and heat set.

[0002]

2. Description of the Related Art Plastic films used for food packaging and the like are selected by using a resin having characteristics most suitable for the purpose of use. It is becoming more and more difficult to meet such demands. Therefore, the mutual defects of single resin are compensated,
In addition, multilayer films are beginning to be developed one after another in order to bring out the characteristics of individual resins to have desired properties. Among them, the multilayer biaxially stretched film that we have developed, which is laminated with saponified ethylene-vinyl acetate copolymer via polyolefin resin layer via adhesive resin layer, has high oxygen barrier property, impact resistance, toughness, and easy incineration. Have sex.

[0003]

The multilayer biaxially stretched film having such a structure may cause a phenomenon of curling with one surface facing inward depending on the manufacturing conditions or the characteristics of the resin to be laminated. For example, polypropylene (inner layer)
The multilayer biaxially stretched film obtained by laminating the ethylene-vinyl acetate copolymer saponified resin layer (outer layer) via the adhesive resin layer has a property of curling with the polypropylene layer inside during heat setting. Therefore, troubles occurred during use and handling, and it was not satisfactory in practice.

As a method of preventing curling of a multilayer film, "a thermoplastic resin layer having a water absorption of 0.5 wt% or more,
It is composed of a thermoplastic resin layer having a water absorption rate of less than 0.5 wt% and is melt-bonded so that the free surface on one side is the former resin layer, and after cooling and solidifying the laminated body thus constituted, A method for producing a non-curling multilayer film characterized by being applied "(Japanese Patent Application Laid-Open No. 51-79192)," A curl-resistant laminated film obtained by laminating a polyolefin resin layer and a hygroscopic resin layer on the hygroscopic resin. Curling of a laminated film, characterized by absorbing 0.5% by weight or more of water based on the weight of the layer and curling the laminated film with the resin layer located inside the curling laminated film facing outside Method ”(Japanese Patent Laid-Open No. 58-33427) and the like. However, when one outer layer of the multilayer film is a saponified ethylene-vinyl acetate copolymer layer or a single-layer film of an saponified ethylene-vinyl acetate copolymer, the ethylene-vinyl acetate copolymer is When the saponified layer surface is subjected to steam or warm water treatment, the crystal structure of the ethylene-vinyl acetate copolymer saponified layer changes with the absorption of moisture or heat absorbed after the treatment, and the state of standing (particularly humidity)
In some cases, the water absorption of the layer also changes every moment, and finally the curling behavior of the multilayer film also changes.

[0005]

Means for Solving the Problems As a result of intensive studies on the curl prevention method of the above-mentioned multilayer biaxially stretched film, the present inventors have found that a stable crystal structure can be obtained by storing the film in a predetermined humidity controlled atmosphere. The present invention has been completed and the present invention has been completed. The gist of the present invention is an ethylene-vinyl acetate copolymer saponified material layer as a surface layer, at least an ethylene-vinyl acetate copolymer saponified material layer, an adhesive layer,
In manufacturing a multilayer biaxially stretched film having three layers of polyolefin resin layers, heat setting is performed after the stretching step in the manufacturing process of the multilayer biaxially stretched film, and then a saponified ethylene-vinyl acetate copolymer layer. Water is absorbed by bringing it into contact with steam or warm water, and the film is heated at a temperature of 10 to 4 until the absorbance ratio of the saponified product of the ethylene-vinyl acetate copolymer satisfies the following formula [I].
A method for preventing curling of a multilayer film is characterized by placing under conditions of 0 ° C. and humidity of 30 to 70% RH.

[0006]

## EQU00002 ## 25T-8.alpha. + 10890 <1000d / a <25T-8.alpha. + 11390 ... [I] [wherein d is the absorbance around 1141 cm.sup.- ¹ a is the absorbance around 1330 cm.sup.- ¹ T is the temperature at the time of heat setting (° C.) α is It is the ethylene content (mol%) in the saponified product of the ethylene-vinyl acetate copolymer]

In the present invention, as the polyolefin resin, polypropylene (MFI: 0.5 to 15) alone or a mixture of polypropylene and another polyolefin resin is preferably used. Other polyolefin resins include ethylene, propylene, homopolymers of α-olefins such as butene-1, copolymers of α-olefins with other α-olefins, α-olefins with a small amount of vinyl acetate, acrylic acid, Examples thereof include copolymers with polar monomers such as maleic acid. The adhesive resin is polypropylene (usually MF
0.01 to 5.0% by weight of unsaturated carboxylic acid such as maleic acid and acrylic acid, an anhydride of the unsaturated carboxylic acid, or an ester of the unsaturated carboxylic acid, What was graft-copolymerized in the ratio of is preferable. As the saponified product of the ethylene-vinyl acetate copolymer, one having an ethylene content of 25 to 50 mol% and a saponification degree of 90% or more is particularly preferable.

The multilayer biaxially stretched film to which the method of the present invention can be applied includes the above-mentioned polyolefin resin layer, adhesive resin layer,
It is a multilayer biaxially stretched film having curling properties, which is composed of at least three saponified ethylene-vinyl acetate copolymer layers. The multilayer biaxially stretched film may be obtained by any method. For example, it is applied to a sequential or simultaneous biaxially stretched film by a tenter method and a simultaneous biaxially stretched film by a tubular method. Among them, the thickness ratio of polyolefin resin layer: adhesive resin layer: ethylene-vinyl acetate copolymer saponified material layer is 8.8 to 5.5: 0.2 to.
A coextrusion multilayer water-cooled blown film of 3: 1 to 1.5 was stretched at MD × TD = 2.5 to 5.0 × 2.5.
-5.0 (the product of the longitudinal stretching ratio and the lateral stretching ratio is 9 to 25, and the ratio of the longitudinal stretching ratio to the lateral stretching ratio is preferably 1: 1 to 1.2: 1), and then the tubular biaxial stretching is performed to make a total. Thickness 10-40
μm, heat treatment temperature 140 to 160 ° C., relaxation rate 0 to 1
A multilayer biaxially stretched film heat set at 0% is especially preferred.

In the present invention, the operation of bringing steam into contact with the saponified layer of the ethylene-vinyl acetate copolymer of the above-mentioned multilayer biaxially stretched film is carried out by heat setting after
Directly or indirectly apply steam of a predetermined temperature and a predetermined humidity to the film from a blowing nozzle provided on the surface side of the saponified vinyl acetate copolymer layer. It can be achieved by passing it through a damp space, and using together. On the other hand, the operation of bringing hot water into contact is achieved by passing through a circulating hot water bath adjusted to a predetermined temperature. At this time, if the steam temperature, the humidity, or the hot water temperature is too low, that is, if there is not enough heat and water to induce stretching relaxation, the water absorption (hydrated) state may not occur and the curl may not disappear. In the case of hot water treatment, it is preferable to immediately remove excess water droplets attached to the film with a water absorbing roll or the like. After steam treatment or hot water treatment, store in a humidity-controlled atmosphere. The temperature of the atmosphere is 10 to 40 ° C., preferably 20 to 25 ° C., and the humidity is 30 to 70% RH, preferably 40 to 60% RH.

By aging the multilayer film in such a specific atmosphere, the crystalline state of the saponified ethylene-vinyl acetate copolymer constituting the multilayer film is made specific. The crystalline state is a crystalline state represented by the following formula [I].

[0011]

## EQU00003 ## 25T-8.alpha. + 10890 <1000d / a <25T-8.alpha. + 11390 (I) (wherein d and a represent absorbance. That is, the humidity-controlled ethylene-vinyl acetate copolymer of the multilayer biaxially stretched film) in the spectrum measurement by the total reflection infrared spectroscopy saponified layer surface, the absorbance of the crystalline bands polyvinyl alcohol type near 1141cm ^-1 is d, the absorbance of the O-H bending vibration near 1330 cm ^-1 is at a T is the temperature at the time of heat setting (° C.), α is the ethylene content (mol%) of the saponified product of the ethylene-vinyl acetate copolymer.) By realizing such a crystalline state, a curl-free multilayer It becomes a film.

According to the method of the present invention, the polyolefin resin layer, the adhesive resin layer, the ethylene
Curling that occurs in a multilayer biaxially stretched film having at least three saponified vinyl acetate copolymer layers and one outer layer of the saponified ethylene-vinyl acetate copolymer layer can be permanently eliminated. And its industrial value is great.

[0013]

EXAMPLES The present invention will be specifically described below, but the present invention is not limited to these examples. In the examples and comparative examples, the curl rate and the absorbance ratio by total reflection infrared spectroscopy were measured by the following methods. (A) Curl Rate After heat setting under a predetermined condition, the steam-treated or hot-water treated film is left at 23 ° C. and 50% RH for 1 week. After this, 20 cm (MD direction) x 20 cm from the film
Cut out (TD direction) and stick with tape on a board with a grid-like scale. At this time, if curl occurs, the inner surface of the curl should be attached upward. Next, as shown in FIG. 1 (a), assuming a 10 cm × 10 cm square in the center of the film, two sides adjacent to the upper left corner are cut out with a cutter knife, and the length {xcm (TD direction), ycm (M
D direction)} (Fig. 1 (b)) and its height (hcm)
(FIG. 1 (c)) is measured and the curl rate is calculated from the following equation. The curl toward the polyolefin resin layer side is minus, and the curl toward the saponified ethylene-vinyl acetate copolymer layer side is plus.

[0014]

[Equation 4] Curl rate (%) = (Ratio of the area that has been turned up) x (Descent from the position where the corner is set up vertically) x
100 = (xy / 2) / (10 × 10/2) × [{xy
/ √ (x ² + y ² )}-h] / {xy / √ (x ² +
y ² )} × 100 = xy−h√ (x ² + y ² ). At this time, if the film is curled more than half a turn, the heights h ₁ cm and h ₂ cm at both ends of the curl are measured. , H = (h ₁ + h ₂ ) / 2.

(B) Absorbance ratio by total reflection infrared spectroscopy (d / a) As shown in FIG. 2, about 1 cm × 5 cm in a direction of about 45 ° from the corner of the film used for curl rate measurement.
Cut out the strips to be used as a sample for measurement. At this time,
It is preferable to pay close attention to the close contact between the sample and the high refractive index medium (using a KBr prism), and measure at least three times to obtain the average. Also, the absorbance ratio (d / a) is around 1141 cm ^-1 (d) on the chart as shown in Fig. 3.
And the absorbance around 1330 cm ^-1 (a) is measured by a scale.

Example 1 Polypropylene manufactured by Mitsubishi Kasei Co., Ltd. (trade name “Mitsubishi Polypro 1220F”; MFI (230 ° C.) 2.0, density 0.
90, melting point 165 ° C: Maleic anhydride graft-modified polypropylene (trade name "NOVATE" manufactured by Mitsubishi Kasei Co., Ltd.
C.AP196P "; MFI (230 ° C) 2.6, density 0.89, melting point 140 ° C: Saponified ethylene-vinyl acetate copolymer manufactured by Nippon Synthetic Company (trade name" Soarnol E
T ”; ethylene content: 38 mol%, degree of saponification: 99
% Or more; thickness ratio of MFI (230 ° C.) 4.0, melting point 173 ° C.) is 8: 1: 1, total thickness 20 μm, draw ratio 3.5 × 3.5, tubular biaxially stretched film is heat treated. After heat setting at 160 ° C. and a relaxation rate of 10% for 10 seconds, steam treatment was performed in a steam atmosphere at a temperature of 80 ° C. and a humidity of 90% RH for a time period during which the curl disappeared. 23 ° C, 5
After being left at 0% RH for 1 week, the curl rate of the film was measured, and then the absorbance ratio was measured by the ATR method. The results are shown in Table 1. In addition, the spectrum by the total reflection infrared spectroscopy was measured using an FTIR spectrometer 20DXB type manufactured by Nicolet, Inc. at an incident angle of 45 °.

Comparative Example 1 The same film as in Example 1 was subjected to the same conditions as in Example 1 except that the steam treatment time was changed. The results at that time are shown in Table 1.

[0018]

[Table 1]

The same conditions as in Example 1 were used except that the heat treatment temperature was changed to 140 ° C. The results at that time are shown in Table 2.

Comparative Example 2 The same film as in Example 2 was processed under the same conditions as in Example 2 except that the steam treatment time was changed. The results at that time are shown in Table 2.

[0021]

[Table 2]

Example 3 The same conditions as in Example 1 were carried out except that the thickness ratio of polypropylene: maleic anhydride graft-modified polypropylene: ethylene-vinyl acetate copolymer saponified product was changed to 3: 1: 1 in order. The results at that time are shown in Table-3.

Comparative Example 3 The same film as in Example 3 was prepared under the same conditions as in Example 3 except that the steam treatment time was changed. The results at that time are shown in Table-3.

[0024]

[Table 3]

Example 4 The same conditions as in Example 1 were used except that a saponified ethylene-vinyl acetate copolymer having an ethylene content of 32 mol% was used. The results at that time are shown in Table 4.

Comparative Example 4 The same film as in Example 4 was prepared under the same conditions as in Example 4 except that the steam treatment time was changed. The results at that time are shown in Table 4.

[0027]

[Table 4]

Example 5 The same conditions as in Example 1 were used except that a saponified ethylene-vinyl acetate copolymer having an ethylene content of 44 mol% was used. The results at that time are shown in Table-5.

Comparative Example 5 The same film as in Example 5 was prepared under the same conditions as in Example 5 except that the steam treatment time was changed. The results at that time are shown in Table-5.

[0030]

[Table 5]

Example 6 The same conditions as in Example 1 were carried out except that after heat setting, the sample was immersed in warm water at 50 ° C. and was subjected to warm water treatment only for the time when the curl disappeared. The results at that time are shown in Table-6.

Comparative Example 6 The same film as in Example 6 was subjected to the same conditions as in Example 6 except that the hot water treatment time was changed. The results at that time are shown in Table-6.

[0033]

[Table 6]

[0034]

According to the method of the present invention, a good multilayer film having no curled portion can be obtained. It is simple in terms of method and operation and is very advantageous in practical use.

[Brief description of drawings]

FIG. 1 is an explanatory view of a method for measuring a curl rate of a film,

FIG. 2 is an explanatory diagram of a sample cutout position

FIG. 3 is an explanatory diagram of the measurement position of absorbance. “A” indicates the absorbance at 1330 cm ⁻¹ , “d” indicates the absorbance at 1141 cm ⁻³ , and “X” and “Y” indicate the turning-up length.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location // B29L 7:00 4F 9:00 4F (72) Inventor Yoshinori Hayakawa Kamoshida, Midori-ku, Yokohama-shi, Kanagawa 1000-cho, Sanritsu Kasei Co., Ltd.

Claims (1)

[Claims] 1. A multilayer biaxially stretched film having at least three layers of a saponified ethylene-vinyl acetate copolymer saponified layer, an adhesive layer, and a polyolefin resin layer, the saponified ethylene-vinyl acetate copolymer layer serving as a surface layer. When manufacturing
After the stretching step in the manufacturing process of the multilayer biaxially stretched film, heat setting is performed, and then steam or warm water is brought into contact with the saponified ethylene-vinyl acetate copolymer layer to absorb water, and this film is subjected to ethylene-vinyl acetate. The temperature is 10 to 40 ° C. and the humidity is 30 to 70% until the absorbance ratio of the saponified copolymer satisfies the following formula [I].
A method for preventing curling of a multilayer film, which is characterized in that it is placed under RH conditions. ## EQU1 ## 25T-8α + 10890 <1000d / a <25T-8α + 11390 ... [I] [wherein d is the absorbance around 1141 cm ^-1 a is the absorbance around 1330 cm ^-1 T is the temperature at the time of heat setting (° C) α is It is the ethylene content (mol%) in the saponified product of the ethylene-vinyl acetate copolymer]