JPS5833427A - Method of preventing curl in piled film - Google Patents

Abstract

PURPOSE:To extinguish permanently the curl generated in a piled film by causing the film in which a polyolefine resin layer and a moisture-absorbing resin layer are piled up to absorb specially determined ratio of water and to bend in a constant direction. CONSTITUTION:The polyolefine resin film obtained by 2-10 times drawing in one axial direction is extrusion-laminated with moisture absorbing resin (e.g. PVA), if necessary, by way of adhesive resin. The piled film with curl-property is obtained by drawing the resin film in the different direction from said drawing direction. Next, room temperature -80 deg.C water is sprayed on this piled film. After the water of 0.5-5wt% to the weight of the moisture absorbing layer is absorbed in the piled film, the curled inner side-resin layer of the piled sheet is caused to become outer side and is bent to form the curved surface with diameter less than 200cm and then it is kept in a curved state more than an hour.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing curling of a laminated layer having a curling property formed by laminating a polyolefin resin layer and a ridge-wetting resin layer.

Polyolefin films are widely used as packaging materials for foods and pharmaceuticals, but their use may be restricted depending on the field of use. For example, polyolefin films have poor gas barrier properties and are unsuitable as packaging materials for high-quality products, which tend to be modified by contact with oxygen gas.

In such cases, various laminated films have been proposed in which other specific resin layers are laminated on the polyolefin film in order to compensate for the drawbacks of the polyolefin film. However, depending on the manufacturing conditions or the characteristics of the laminated resin, wrinkled laminated films may curl due to internal pressure on one side1.For example, ethylene-acetic acid is used to impart gas barrier properties to polyolefin films. A method of laminating resin layers made of saponified vinyl copolymers is known, but the laminated film obtained by this method may have curling properties. That is, when obtaining a laminated film formed by laminating a polyolefin resin layer made of a biaxially stretched polyolefin film and a resin layer made of the saponified copolymer, the gas barrier properties of the resin layer made of the saponified copolymer, In order to improve water resistance and form a uniform fermentation layer, generally a uniaxially stretched polyolefin film is clarified with a resin layer made of the copolymer kenated product, and then stretched in a direction different from that of the -axially stretched polyolefin film. 1. The laminated film thus obtained has the property of curling the biaxially stretched polyolefin film on the inside ζ·r. Therefore, even if the laminated film with the above-mentioned curling property can compensate for the drawbacks of polyolefin film, it is not satisfactory for practical use because it often curls during use and handling. I couldn't say yes.

As a result of extensive research into methods for preventing curling of the laminated film, the present inventors have discovered a laminated film obtained by laminating a hygroscopic resin layer on a polyolef/f/resin layer made of a polyolefin film. The inventors have discovered that the curls that occur in the laminated film can be permanently eliminated by absorbing the moisture of a specific child into the laminated film and curving the laminated film in a certain direction, leading to the completion of the present invention. .

That is, the present invention allows a curlable laminated film formed by laminating a polyolefin resin layer and a hygroscopic resin layer to absorb moisture of 0.5% by weight or more based on the weight of the hygroscopic resin layer, and This method of preventing curling of a laminated film is characterized in that the laminated film is curved with the resin layer located inside the curled laminated film facing outward.

In the present invention, the polyolefin resin is a homopolymer of α-olefins such as ethylene, propylene, and butene-1; a copolymer of α-olefins and other α-olefins;
Copolymers of α-olefins and small amounts of polar monomers such as vinyl acetate, acrylic acid, and maleic acid; or mixtures thereof are commonly used. It is a general term for resins that have properties that can be used. In the present invention, a resin capable of absorbing moisture in an amount of O, S in an amount of at least 1% by weight based on the weight of the resin is preferably used. Typical hygroscopic resins include, for example, polyvinylfursol 9-ethylene-hinyl alfur copolymer, propylene-vinyl alcohol copolymer, polyacrylic acid, polyamide, and polyamino acid-containing resin.

The laminated film to which the method of the present invention can be applied is a laminated film having curling properties, which is formed by laminating a resin layer made of the polyolefin resin described above and a resin layer made of a hygroscopic resin. The skeleton laminate film may be obtained by any method. For example, films made of unstretched or stretched resins are bonded under pressure.

A laminated film obtained by laminating by melt-pressing, adhesion with an adhesive resin, etc. and stretching if necessary, a polyolefin resin film obtained by unstretched or stretched, and a hygroscopic resin alone or adhesive. Umine Oshida through resin
After that, it is suitably applied to a laminated film etc. obtained by stretching this. In particular, extrusion laminate 1-1 with a hygroscopic resin alone or via an adhesive resin on a polyolefin resin film obtained by -axial stretching is applied to a laminated film obtained by stretching this in a direction different from the stretching direction. Therefore, the method of the present invention is particularly effective. In addition, the laminated film may further have an adhesive resin layer laminated on the surface of the hygroscopic resin layer. Note that the stretching ratio in the above-mentioned stretching operation is not particularly limited. Generally, uniaxial 2-1 in the direction
A range of 0 times, preferably 3 to 7 times is appropriate. Also,
The adhesive resin may be a polyolefin resin containing an unsaturated carboxylic acid such as maleic acid or acrylic #; an anhydride of the unsaturated carboxylic acid, or an esral of the unsaturated carboxylic acid in an amount of 0, 1 to 5. A resin containing a resin graft copolymerized in a proportion of % of Ofi is preferably used.

The method of the present invention allows the laminated film to absorb moisture in an amount of 0.5.3i [amount 3 or more, preferably 1% by weight or more] based on the weight of the hygroscopic resin layer, and It is characterized in that the laminated film is curved with the resin layer located on the outside. If the amount of moisture absorbed by the laminated film is lower than the above range, the curl of the core laminated film will not completely disappear even if the operation of curving the laminated film described later is performed. Also, if the amount of moisture is too high, the curl of the core laminated film will not disappear. There is a tendency for the quality or physical properties of the laminated film to deteriorate, such as hygroscopicity and surface roughening of the resin layer.
The upper limit of the water content is preferably 5% by weight or less, preferably 3% by weight or less.

In the present invention, the method for making the laminated film absorb moisture is not particularly limited. Examples of suitable methods include generally spraying water on the laminated film, spraying water vapor on the laminated film, and leaving the laminated film in a high humidity atmosphere for a certain period of time. Further, the above-mentioned treatment temperature is generally in the range of room temperature to 80°C, preferably 30 to 60°C. In the present invention, in order to achieve the intended purpose of the present invention, it is necessary to curve the laminated film that has absorbed moisture as described above with the resin layer located inside the curled laminated film facing outward. The degree to which the laminated film is curved is not particularly limited, but in order to fully exhibit the effects of the present invention, the degree to which K is curved is large (the more preferable).

Generally, it is preferred that the laminated film be curved so as to form a curved surface with a diameter of 2001 mm or less, preferably 1001 mm or less. An example of a suitable bending method is generally a method of winding the laminated film into a roll shape with the resin layer located inside the curled laminated film facing outward. Further, it is preferable that the curved laminated film is maintained in the curved shape for a certain period of time, for example, 1 hour or more, preferably 10 hours or more, since the curl of the laminated film can be completely eliminated.

In the present invention, the order of the operation of absorbing moisture into the laminated film and the operation of bending are not limited to % as long as the backing film contains moisture within the above range at the time of bending the wrinkled laminated film. That is, there are no particular restrictions on the mode in which the laminated film is curved after absorbing moisture, the mode in which the laminated film is curved while absorbing moisture, the mode in which the laminated film is curved and moisture is absorbed in this state, etc. Implemented.

According to the method of the present invention, it is possible to permanently eliminate curls that occur in a laminated film obtained by laminating a polyolefin resin layer Vce and a wet resin layer by a simple treatment, and its industrial value is extremely high. big.

The present invention will be specifically explained below, but the present invention is not limited to these Examples ().

In addition, in the Examples and Comparative Examples, the curl rate and water absorption rate were measured by the following method.

(a) A sample film cut to a size of 120I x 12Cm in curl rate was sandwiched between two glass plates, a load of 59/Cd was applied,
Leave for 24 hours at 50% RH. Thereafter, the film is cut into a size of 30w x 40u+ (in this case, cut so that the curl direction is 30mK) and placed on a glass plate with the curled inner surface facing down. At this time, the projected length t of the short side was measured and calculated using the following formula.

0 (b) Water absorption determined from the change in weight of the film. Sample film at 60℃
Example 1 Polypropylene film 2 stretched 5 times in the MD length direction
On top of 50 μnL, anhydride-maleic acid graft modified polypropylene (maleic anhydride content 0.06 mol%) 2
After bath melt extrusion lamination of 0 μm, saponified ethylene-vinyl acetate copolymer (ethylene content 45
Mol%, degree of saponification of 99.9% or more) 40 μm was melt-extruded and laminated to obtain a three-layer laminated film.

The three-layer laminated film was stretched 10 times in the TD force direction to obtain a laminated film. After the core films were left in a 40"C290%RH atmosphere for different periods of time to change the water absorption rate to the ratio shown in Cloth-1, each laminated film was placed inside the curl of the core laminated film. The polypropylene layer was wound into a rule shape so that the polypropylene layer was on the outside.The roll diameter was outside #&80α.

After the armpit film was left for one day and night, the curl rate was measured. Table - IK results are shown.

Table 1 Note that A4 and A5 are comparative examples.

The laminated films obtained by methods /161 to 3 in Table 1 were then dried to reduce the water absorption to about 0.1% by weight K, but no curling properties were observed.

Example 2 A 300 μm maleic anhydride-modified polyethylene resin film (maleic anhydride grafting amount: 0.1 mol %) stretched 5 times in the MD force direction and 100 μm nylon-6 film were melt-pressed to obtain a two-layer laminated film. This film was stretched 4 times in the TD force direction to obtain a laminated film.

This laminated film was placed in an atmosphere of 40°C and 90% RH for 1
After being left for 0 minutes to reduce the water absorption to 0.8% by weight, the laminated film was wound up with a winding diameter of 80 cm with the polypropylene layer located inside the curl facing outward, and left to stand day and night.

The curl rate of the obtained film was 0.

Comparative Example 1 The laminated stretched film obtained in Example 2 was rolled up under pressure in the same manner as in Example 2, without absorbing moisture, and left for day and night. The resulting film had a nylon-6 layer curled outward and exhibited a curl percentage of 25%. In addition, the water absorption rate of the skeleton film was 0.1% or less.

Example 3 A saponified ethylene-vinyl acetate copolymer with an ethylene content of 35 mot% and a degree of saponification of 99% was used as the inner layer, and modified polypropylene grafted with 0.13 mot% of maleic anhydride was used as both outer layers, and two extruders were used. ℃ using a machine, 230℃
While melting and compounding the mixture into three layers in a die, the mixture was extruded onto 250 μm of uniaxially stretched polyppyrene that had been stretched 5 times in the MD force direction. Then, it was stretched 10 times in the TD force direction at 155° C. to form a biaxially stretched polyp-pyrene/maleic anhydride graft modified polyp-pyrene/saponified ethylene-vinyl acetate copolymer/maleic anhydride/acid graft-modified polyp-pyrene= A four-layer composite film of 25μ/2μ/4μ/2μ was obtained.

Maleic anhydride grafted plexus of this film
After spraying water vapor from the pyrene layer side without condensation on the film surface to achieve a water absorption of 1% by weight, roll it with a winding diameter of 800I so that the Volivp pyrene layer side located on the inside of the curling laminated film is on the outside. I wound it up. The curl rate of the obtained laminated film was measured and was 0%, and the oxygen permeability was 7 cc 7 m"・24 h r-a
tm at 20”C.

Comparative Example 2 In Example 3, the laminated film was wound up in the same manner without steam treatment and the curl rate was measured. The percentage was 56%. Note that the water absorption rate of the film was 0.1% or less. .

Example: On a 200μ uniaxially stretched polypropylene film stretched 5 times in the MD force direction, a lid of 0.13 mot% of maleic anhydride granide-modified polypropylene (maleic anhydride rice graph) was placed.
) and unmodified polybupylene at a ratio of 50:50 (weight ratio) is melt-extruded and laminated to a thickness of 20 μm, and a saponified ethylene-vinyl F acid copolymer (ethylene-containing M35 mol %) is added to the blended resin layer side. , degree of saponification 99.9%) was laminated by bath melt extrusion to obtain a three-layer film. Further, the film was stretched 10 times in the TD direction at 160''C to obtain a laminate film of biaxially stretched polypropylene/blend resin/saponified material (20μ/2μ/4μ).

This laminated film is made with the polypropylene layer side inside.
It showed a curl rate of 30% in the MD direction. The laminated film was wound with a diameter of 8 so that the polypropylene layer was on the outside.
After winding it up loosely at 01, it was aged at 40° C. and 905 RH for 3 days. The curl rate of the obtained laminated film was 0%. The water absorption rate at this time is 1.5]ii%
Met.

Comparative Feed 3 The biaxially oriented polypropylene layer of the laminated film obtained in Example 4 was internally pressed and wound into a roll, and heated at 40°C and 90% R.
It was aged for 3 days in an atmosphere of H. Curl rate is 27
% and was not resolved at all. Further, the water absorption rate of the film was 1.5% by weight.

patent applicant Tokuyama Ichitatsu Co., Ltd.

Claims (1)

[Claims] A laminated film having curling properties formed by laminating a polyolefin resin layer and a hygroscopic resin layer, M of the hygroscopic resin layer is added.
Curling of a laminated film characterized by absorbing moisture of 0.5 times more than thlt, and bending the laminated film with the resin layer located on the inside of the curling laminated film on the outside. How to prevent it.