JP3561919B2 - Method for producing polyester film having good tearability and twistability - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a stretched polyester film. More specifically, a film or tape for packaging that maintains practical properties without losing the excellent properties of the stretched polyester film, such as heat resistance, fragrance retention, and water resistance, and has good tearing and twisting properties. The present invention relates to a stretched polyester film useful as an application film.
[0002]
[Prior art]
Conventionally, cellophane has been known as a film having excellent cuttability. Cellophane is widely used for various packaging materials and adhesive tapes due to its excellent transparency, easy cutting properties, twist wrinkle fixing properties, and the like. However, on the other hand, since cellophane has hygroscopicity, its characteristics fluctuate depending on the season, and it has been difficult to always supply a cellophane having a constant quality. In addition, packaging bags and adhesive tapes using polyethylene terephthalate as a base film are used because of the excellent properties such as toughness, heat resistance, water resistance and transparency of the stretched polyethylene terephthalate phthalate film. Although it has these excellent properties, it is difficult to cut, it is difficult to tear the mouth of the packaging bag, the adhesive tape is hard to cut, and the twist fixability is poor, so it can be used for twist packaging. There were drawbacks such as inability to do so.
[0003]
As a method for solving the above-mentioned drawbacks, a polyester film oriented uniaxially (Japanese Patent Publication No. 55-8551), a copolymer obtained by copolymerizing a diethylene glycol component or the like (Japanese Patent Publication No. 56-50692), or a method using a polyester resin having a low molecular weight ( Japanese Patent Publication No. 55-20514) has been proposed.
[0004]
[Problems to be solved by the invention]
However, in the above-mentioned prior art, the method of uniaxially orienting is easy to cut linearly in the orientation direction, but hard to be cut in other than the orientation direction, and a method of copolymerizing a large amount of diethylene glycol components is by copolymerization. Polyethylene terephthalate has the disadvantage of losing its inherent properties. Furthermore, the method using a polyester resin having a low molecular weight is not practical because a trouble of film breakage in a stretching step is apt to occur.
[0005]
That is, the present invention pays particular attention to the easy cutting property and the twist fixing property among the properties of cellophane, and has these properties, and furthermore, the excellent properties of the polyester film, such as heat resistance, moisture resistance, transparency, and fragrance retention. The purpose of this study was to obtain a film having the same characteristics as described above.
[0006]
[Means for Solving the Problems]
The present invention, on both sides of the polyester resin layer (A), the polyester resin layer to have a high melting point 10 ° C. or higher than the melting point of the polyester resin layer (A) (B) is laminated, from the polyester resin layer (B) become the total thickness of both surface layers is 15% or more relative to the total thickness of the laminated film, an unstretched laminated film is 50% or less, above the melting point of the polyester resin layer (a) after biaxial stretching, and a polyester resin layer a method for producing a resultant tear resistance and twist of good polyester film and its by heat treatment at a temperature below the melting point of (B).
[0007]
That is, the present invention is carried out after stretching different polyester laminate film having a melting point, a heat treatment at a temperature below the melting point of the side of a polyester having a high and higher melting point than the melting point of the polyester (A) on the side having a low melting point (B) By doing so, the polyester (A) layer constitutes a layer having tearability and twist fixability while maintaining the properties of the polyester resin such as heat resistance, transparency, water resistance and fragrance retention while the orientation in the stretching step is lost. The polyester (B) layer is a laminated film having two kinds of different characteristics such that the polyester film has a layer having excellent characteristics such as heat resistance and the like which maintains the orientation of the polyester film. Polyester film with contradictory properties of having good tearability and twist fixability while having Heading the Rukoto, which resulted in the completion of the present invention.
[0008]
The polyester used in the polyester resin layer (B) of the present invention is not particularly limited, and examples thereof include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolymers containing these components as main components. . The polyester used in the polyester resin layer (A) is preferably a copolymer having a melting point lower than the melting point of the polyester used in the polyester resin layer (B) by 10 ° C. or more, preferably 20 ° C. or more.
[0009]
Further, the thickness of the polyester resin layer (B) is preferably from 15% to 50% of the total thickness . When the thickness of the polyester resin layer (B) is less than 15% of the total thickness, the strength of the obtained film is reduced, and there is a problem in practical use. If the thickness of the polyester resin layer (B) exceeds 50% of the total thickness, the desired tearing property and twisting property decrease. The lamination of the polyester resin layer (A) and the polyester resin layer (B) preferably has a three-layer (B / A / B) configuration. Furthermore, the thickness of the stretched film is from 12 μm to 30 μm for use in packaging bags, adhesive tapes, and the like, which are the intended applications of the present invention, but is not particularly limited.
[0010]
The polyester film of the present invention may contain various known additives such as a lubricant, a pigment, an antioxidant, and an antistatic agent, as long as the effects of the present invention are not impaired.
[0011]
The term “unstretched laminated film” as used herein refers to a method in which a plurality of extruders and the like are separately melted at a temperature equal to or higher than the melting point, and a method in which unstretched films formed by extrusion from a die outlet are laminated in a heated state. Can be As another method, there is a method in which the surface of one unstretched film is melt-laminated with the other molten film. As still another method, there is a method of forming an unstretched film by extruding from a die outlet in a state of being laminated by a co-extrusion method.
[0012]
Next, an example of a method for producing the film of the present invention will be described. The vacuum-dried polyester resin (A) and polyester resin (B) are supplied to two separate extruders, respectively, extruded at a temperature equal to or higher than their melting points, passed through a composite adapter, and subjected to two types and three layers (B). / A / B), extruded from a die, cooled and solidified to form an unstretched laminated film.
[0013]
The unstretched laminated film thus obtained is uniaxially stretched or biaxially stretched at a temperature higher than the second transition point of the polyester resin (A) and the polyester resin (B) and lower than the melting point of the polyester resin (A). Perform axial stretching. In the case of uniaxial stretching, it is at least 1.5 times or more, preferably 3 to 5 times, and in the case of biaxial stretching, the stretching area is 2 to 30 times, preferably 9 to 16 times. In the case of biaxial stretching, sequential stretching or simultaneous stretching may be used.
[0014]
This stretched film is heat-treated at a temperature higher than the melting point of the polyester resin layer (A) and lower than the melting point of the polyester resin layer (B). In this heat treatment, it goes without saying that a relaxation treatment may be performed as necessary.
[0015]
[Action]
Due to the heat treatment, the molecular orientation of the polyester resin layer (A) is almost destroyed by stretching, and the tearing and twisting properties of the present invention are obtained. The polyester resin layer (B) maintains the molecular orientation. It is believed that a film having the properties of the present invention is obtained.
[0016]
As described above, the present invention provides a target film by balancing a layer that imparts tearing and twisting properties, in which the molecular orientation is almost collapsed by heat treatment in a film-forming line, and a layer that has the original properties of polyester while maintaining the molecular orientation. In addition to the advantage that the characteristics can be freely set, there is an advantage that the layer having the molecular orientation is maintained, so that a trouble such as breakage in film formation can be prevented.
[0017]
Examples The present invention will be described below with reference to examples. Evaluation methods in Examples and Comparative Examples were performed by the methods (a) to (c).
[0018]
(A) Tear resistance: Evaluated by an average value measured according to JIS C2318-1975.
[0019]
(B) Hand-cutting property: Performed by a sensory test. When a tape-shaped sample having a width of 15 mm was cut by hand, a sample that could be easily cut by hand was evaluated as ○, and a sample that was not easily cut by hand was evaluated as ×.
[0020]
(C) Twistability: Performed in a sensory test. When a 30-mm wide tape-like sample was twisted by hand, it was evaluated as ○ when the twisted state did not return to its original state, and x when the twisted state could not be maintained.
[0021]
Example 1
Polyethylene isophthalate (A) having a melting point of 200 ° C. and polyethylene terephthalate (B) having a melting point of 260 ° C. are each melted at a temperature of 285 ° C. by a separate extruder. It was extruded and rapidly cooled with a cooling drum to obtain a three-layer unstretched laminated film having a (B / A / B) configuration.
[0022]
The unstretched laminated film is first stretched 3.5 times at 90 ° C. in the longitudinal direction and then 3.8 times at 110 ° C. in the transverse direction, and then heat-treated at a temperature of 230 ° C. while relaxing 3% to 25 μm. Was obtained. The thickness ratio of each B / A / B layer of this film was 2/21/2.
[0023]
The film thus obtained could be easily cut in any direction by applying a nail, and when the film was twisted, the twisted state could be maintained. In addition, this film was free from troubles such as breakage during film formation and slitting, and had good productivity.
[0024]
Example 2
Using the same raw material and method as in Example 1, a 25 μm film was obtained in which only the thickness ratio of each B / A / B layer was changed to 4/17/4.
The film thus obtained also had good twist fixability, except that a film having a little resistance than that of Example 1 and a hand-cutting property was obtained.
[0025]
Comparative Example 1
Using the same raw material and method as in Example 1, a 25 μm film was obtained in which only the thickness ratio of each layer of B / A / B was changed to 10/5/10.
The film thus obtained had no hand-cutting property, and even if the film was twisted, it returned to its original state and had no twist fixing property.
[0026]
Comparative Example 2
Except that the melting point of polyethylene isophthalate (A) was changed to 245 ° C., a film having a thickness of 25 μ was obtained in the same manner, conditions and thickness ratio as in Example 1.
The film thus obtained had no hand-cutting property, and even if the film was twisted, it returned to its original state and had no twist fixing property.
[0027]
Table 1 shows the evaluation results of the films obtained in the examples.
[0028]
【The invention's effect】
As described above, a polyester film having good hand-cutting properties and twisting properties was obtained, which proved to be effective for packaging.
[0029]
[Table 1]

Claims (3)

On both surfaces of the polyester resin layer (A), the polyester resin layer to have a high melting point 10 ° C. or higher than the melting point of the polyester resin layer (A) (B) is laminated, the two surface layers made of the polyester resin layer (B) Is higher than the melting point of the polyester resin layer (A) after biaxially stretching an unstretched laminated film having a total thickness of 15% or more and 50% or less with respect to the total thickness of the laminated film. obtained by heat treatment at a temperature lower than the melting point, polyester film arm for packaging or adhesive tape thickness 12～30Myuemu. On both sides of the polyester resin layer (A), a polyester resin layer (B) having a melting point higher than the melting point of the polyester resin layer (A) by 10 ° C. or more is laminated. The melting point of the polyester resin layer (B) is higher than the melting point of the polyester resin layer (A) after biaxially stretching an unstretched laminated film having a total thickness of 15% or more and 50% or less based on the total thickness of the laminated film. A method for producing a polyester film for packaging or pressure-sensitive adhesive tape, wherein the polyester film is heat-treated at a temperature of less than . The method for producing a polyester film for packaging or pressure-sensitive adhesive tape according to claim 2, wherein a polyester film having a film thickness of 12 to 30 µm is produced .