JPH04307239A - Composite polyester type film - Google Patents

Abstract

PURPOSE:To impart heat sealability to a polyester type film without damaging the characteristics of said film by laminating a modified polyester resin layer to the polyester type film or laminating a polyolefin resin layer to the modified polyester resin layer through an adhesive resin layer. CONSTITUTION:A composite film is constituted of at least two layers composed of polyester resin/modified polyester type resin or at least four layers composed of polyester type resin/modified polyester type resin/adhesive resin/polylefinic resin. A polyester type film is pref. composed of a homopolymer of ethylene terephthalate. As the modified polyester type resin, for example, a copolymer consisting of an acid component whose 50-90mol% is terephthalic acid and a diol component composed of ethylene glycol and/or other diol is used. As the polyethylenic resin, polyethylene, an ethylene copolymer or an ionomer can be designated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an easily heat-sealable composite polyester film that has excellent lamination strength, heat-seal strength and transparency.

0002

[Prior Art] Films made of homopolyester resins whose main repeating unit is ethylene terephthalate have been known to have excellent strength, rigidity, transparency, heat resistance, gloss, chemical resistance, sanitary safety, etc. Although it is used for many purposes, it has rarely been used alone as a packaging film because of its poor heat sealability.

[0003] In order to impart heat-sealability to a homopolyester film, a coating method is employed in which a plastic resin having easy heat-sealability is coated with an adhesive prepared by dissolving it in an organic solvent, or a polyolefin resin is laminated or laminated. There are methods of imparting heat-sealing properties.

[0004] There are various methods for laminating or laminating polyolefin resins, but generally, dry lamination or a method of coextruding a polyolefin resin onto a homopolyester resin via an adhesive resin to form a composite is used. He had been hired.

[0005]

[Problem to be solved by the invention] However, residual solvent is a problem in coating, which requires expensive equipment investment such as advanced drying equipment and solvent recovery equipment, which has the disadvantage of increasing processing costs. .

[0006] In the case of adhesive sealing, there is a problem in that when the film is folded and sealed, the sealed portion tends to separate due to the repulsive action based on the elasticity of the film.

[0007] Laminating easily heat-sealable films by dry lamination or the like requires a large number of man-hours, is economically disadvantageous, and is also complicated to operate, and there is also the problem of environmental pollution due to solvents and the like.

A product in which easily heat-sealable resin layers are laminated by a coextrusion method has heat-sealability and can be used in some applications, but it can be used in applications that require even stronger lamination strength and heat-sealing strength, such as packaging bags for heavy items. However, it is not suitable for transporting packaged articles containing heavy items, and improvements in lamination strength and heat sealing strength are required.

[0009]

Means for Solving the Invention The present invention provides a composite film having at least a two-layer structure obtained by laminating a modified polyester resin on at least one side of a polyester film serving as a base layer, and a composite polyester film having a two-layer structure. The present invention relates to a composite polyester film having at least a four-layer structure in which a polyolefin resin is laminated on the modified polyester thread resin layer side of the film via an adhesive resin.

[0010] The polyester film serving as the base material layer in the present invention is intended to be one in which the main repeating unit is a homopolymer of ethylene terephthalate, but is not necessarily limited to this. % or more of terephthalic acid and less than 10 mol% of dicarboxylic acids other than terephthalic acid, such as aromatic dicarboxylic acids such as isophthalic acid and naphthalene dicarboxylic acid, alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexaisophthalic acid, and adipic acid. , aliphatic dicarboxylic acids such as sebacic acid, and one or more derivatives thereof, and the diol component is ethylene glycol and/or a diol component other than ethylene glycol, such as diethylene glycol, trimethylene glycol, tetramethylene glycol, Examples include a copolymer composed of 1,4 cyclohexanedimethanol and one or more derivatives thereof, and a mixture of a polyethylene terephthalate homopolymer and the copolymer.

The modified polyester resin according to the present invention is not particularly limited, but has an acid component of 50 to 90 mol% of terephthalic acid and 10 to 50 mol% of isophthalic acid, adipic acid, sebacic acid, etc. The diol component is ethylene glycol and/or a diol component other than ethylene glycol,
For example, a copolymer composed of one or more of diethylene glycol, neopentyl glycol, 1,4 cyclohexanedimethanol, 1,4 butanediol, etc. and their derivatives, or a copolymer of these and the above-mentioned polyethylene terephthalate homopolymer. A mixture can be exemplified.

[0012] When the terephthalic acid component of the modified polyester resin exceeds 90 mol%, the heat sealing properties may deteriorate, and when the content falls below 50 mol%, the mechanical strength tends to decrease and the film forming properties tend to decrease significantly. , blocking, etc. often occur, but it can be used depending on the application.

Examples of the adhesive resin used in the four-layer composite polyester film according to the present invention include ethylene-propylene copolymer, propylene copolymer, propylene-butene copolymer, modified polyolefin resin, and ionomer. However, any other material may be used as long as it can bond the modified polyester resin layer and the polyolefin resin layer, and is not particularly limited.

Modified polyolefin resins include olefin homopolymers or copolymers, unsaturated carboxylic acids or acid anhydrides such as maleic acid, fumaric acid, acrylic acid, etc.
Typical examples include modified copolymers obtained by copolymerizing, for example graft polymerizing, ester or metal salt derivatives. The modified polyolefin resins include the modified copolymers described above alone or in mixtures with other components, such as polyolefin resins. In this case, polyolefin resins include low, medium, and high density polyethylene, linear low density polyethylene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-acrylate copolymer, and ethylene-vinyl acetate copolymer. Examples include merging.

The polyolefin resin laminated on the modified polyester resin layer via an adhesive resin is not particularly limited, but includes low, medium, and high density polyethylene, linear low density polyethylene, and ethylene-propylene copolymer. , ethylene-butene copolymer, ethylene-propylene-butene terpolymer, ethylene-acrylate copolymer, ethylene-vinyl acetate copolymer, and ionomer. In this case, a mixture of these is also included in the polyolefin resin.

The method for laminating the composite polyester film of the present invention is not particularly limited, but examples include coextrusion, dry lamination, extrusion lamination, thermocompression lamination, etc., with coextrusion being convenient. .

[0017] In the coextrusion method, when forming a two-layer film, at least two extruders are combined with a flat multilayer die or an annular multilayer die, and one extruder extrudes polyester. An example of a method is to supply a modified polyester resin to another extruder, introduce the resin into the heated multilayer die, join within or outside the multilayer die, and extrude.

[0018] When forming a composite polyester film having a four-layer structure, at least four extruders are used, one extruder extruding polyester resin, the other one extruding modified polyester resin, and the other extruder extruder extruder extruder. A method of supplying adhesive resin to one machine and polyolefin resin to the other machine, introducing them into a heated coextrusion multilayer die, joining them in a molten state inside or outside the multilayer die, and coextruding them. can be exemplified. Furthermore, if necessary, at least one extruder may be connected to the composite polyester film to laminate it on the surface or in the middle thereof, which is also included in the present invention.

There are no particular restrictions on how to stretch the composite polyester film of the present invention. For example, after being stretched in the longitudinal direction with heated rolls, the film is fed into a tenter and stretched in the transverse direction while holding both ends of the film, and then in the rear chamber of the tenter. An example is a sequential biaxial stretching method in which heat treatment is performed and heat setting is performed, but the method is not limited to this, and simultaneous biaxial stretching, uniaxial stretching, or a combination of these may be used, or stretching may be performed using a circular multilayer die. A tubular composite film may be formed and simultaneously biaxially stretched into a tubular shape without any particular limitation.

The stretching conditions are not particularly limited, but the stretching temperature in the longitudinal direction is 60 to 100°C, the stretching ratio is 2 to 6 times,
The stretching temperature in the transverse direction is 60 to 130°C, and the stretching ratio is 2 to 1.
For example, the heat setting temperature is 150 to 250°C for 3 to 10 seconds.

In the composite polyester film of the present invention, in the case of a composite film having a two-layer structure of a homopolyester film and a copolyester film, the homopolyester resin and the modified polyester resin are both in the category of polyester resins, so they are compatible with each other. It has good solubility, and the molten phases mix with each other, making it appear as if only the polyester resin is molten, and can often be considered as one layer of polyester resin, thus increasing the lamination strength between the phases. Peeling tends to be less likely to occur.

Since the transparency of the homopolyester resin and the modified polyester resin are considered to be substantially the same and are good, the transparency of the melt-laminated composite polyester film according to the present invention is often excellent.

Furthermore, homopolyester films have poor heat-sealability when crystallized, but modified polyester films contain amorphous components and components that lower the glass transition point (Tg), so they are heat-sealable. Heat sealability is imparted to a composite polyester film in which a homopolyester resin layer and a modified polyester resin layer are laminated. Due to the above-mentioned reasons, this composite polyester film has a strong lamination strength, and thus tends to have a strong heat seal strength as well.

In the composite polyester film having a four-layer structure according to the present invention, the polyester resin and the modified polyester resin are both polyester resins, so they have good compatibility, and when melt-laminated, the interface melts and mixes, as if it were It looks like one layer of polyester resin. Therefore, even if it has a four-layer structure, it can be considered as a three-layer structure of polyester resin layer/adhesive resin layer/polyolefin resin layer, and the lamination strength of the polyester resin layer and modified polyester resin layer is strong. In many cases.

Generally, the adhesive strength between the modified polyester resin layer and the adhesive resin layer tends to be stronger than the adhesive strength between the homopolyester resin layer and the adhesive resin layer. The film tends to have stronger lamination strength and heat seal strength than a conventional composite polyester film having a homopolyester resin layer/adhesive resin layer/polyolefin resin layer structure.

Moreover, the composite polyester film of the present invention has the excellent physical properties of polyester films such as mechanical properties, dimensional stability, heat resistance, chemical stability, transparency, gloss, and hygienic stability. It maintains excellent lamination strength and heat seal strength.

[0027] The thickness of the composite polyester film of the present invention may be set appropriately depending on the application, but generally, the thickness of the polyester film of the base layer is 7 to 20 μm, and the thickness of the modified polyester copolymer layer is 2 to 2 μm. For example, the adhesive resin layer may have a thickness of 15μ, the adhesive resin layer may have a thickness of 2 to 5μ, and the polyolefin resin layer may have a thickness of 10 to 70μ.

When the composite polyester film of the present invention is printed as necessary, it may be printed on the front side, the back side, etc. using an appropriate method such as a gravure printing machine.
A particularly preferred example is a method of printing on another film and laminating it by an appropriate method so that the printed surface is in contact with the composite polyester, but there is no particular restriction on this method.

If necessary, corona discharge treatment, coating with a solution of a resin etc. dissolved in an organic solvent, etc., extrusion lamination, dry lamination, etc. of a resin or film of the same or different type as the polyester resin or polyolefin resin may be performed. There is no particular restriction on this.

[0030] If necessary, resins, anti-blocking agents, lubricants, pigments, surfactants, ultraviolet inhibitors, stabilizers,
Fillers and the like may be added, and there are no particular restrictions on this.

Although the composite polyester film of the present invention is not particularly limited, it can be used as packaging for various foods, machine parts, heavy items, bags for stacking and transporting packages of heavy items (for example, water items), or in particular, Suitable for packaging products that require transparency.

[0032]

[Example] Examples will be described in detail below. Example 1 A homopolyester resin (A) consisting of 100 mol% of terephthalic acid as a dicarboxylic acid component and 100 mol% of ethylene glycol as a diol component was placed in an extruder with a barrel inner diameter of 40 mm, and terephthal was added as an acid component in another extruder with a barrel inner diameter of 40 mm. Acid 85 mol%, Isophthalic acid 15 mol%
and 85 mol% ethylene glycol as glycol component
, diethylene glycol and 15 mol % of the modified polyester resin (B) was fed into a flat coextrusion die heated to 250°C, and (A) and (B) were mixed in the die.
were laminated to extrude two layers of molten flat film. In this film, the interface between the homopolymer layer and the copolymer layer was melt-mixed and became as if they were one layer. Next, a cooling roll (30°C) where cooling water circulates through the film.
After being cooled and solidified, the film is stretched 3 times in the longitudinal direction with rolls heated to 85°C between a slow (front) drive roll and a fast (rear) drive roll, then entered into a tenter and heated to 100°C while holding both ends of the film, and then stretched in the transverse direction. Stretched to 4 times, then 240
A biaxially stretched composite polyester film was obtained which was heat-treated at ℃ for 5 seconds.

[0033] This composite polyester film has a homopolyester layer and a modified polyester layer completely melted and laminated.
Lamination delamination did not occur because the layers appeared to be polyester films. Heat sealing strength is heat sealing temperature 180℃, sealing pressure 2kg/
cm2, 1.0-1.2Kg/ under the conditions of sealing time of 1 second
It was 15 mm. The transparency was 2.1% (Haze), which was superior to the transparency of the homopolyester film/polyolefin film composite film, 4.5% (Haze).

Example 2 A polyethylene terephthalate resin (A) consisting of 100 mol% of terephthalic acid as a dicarboxylic acid component and 100 mol% of ethylene glycol as a diol component was placed in three extruders with a barrel inner diameter of 40 mm. 70 mol% of terephthalic acid as an acid component,
A modified polyester resin (B) consisting of 30 mol% of isophthalic acid and 100 mol% of ethylene glycol as a glycol component, a modified polyethylene resin (C) obtained by graft polymerization of maleic acid, and a linear low-density polyethylene resin (D).
) was supplied, and a molten flat film laminated in A/B/C/D was extruded in a flat coextrusion multilayer die heated to 250°C. Next, the film is cooled and solidified using a cooling roll (30°C) where cooling water circulates, and stretched 3 times in the longitudinal direction using a slow (front) drive roll, a fast (rear) drive roll, and a 90°C heating roll, and then enters a tenter and both ends of the film are stretched. hold 12
The film was heated to 0° C. and stretched 4 times in the transverse direction, and then heat-treated at 240° C. for 5 seconds while holding both ends of the film in the rear chamber of a tenter to obtain a heat-set biaxially stretched composite polyester film.

The laminated strength of the modified polyester resin layer (B) and the adhesive resin layer (C) of this composite polyester film is 200 to 230 g/15 mm, and the heat seal strength of the linear low density polyethylene of the composite polyester film is 200 to 230 g/15 mm. was 1.3 to 1.5 Kg/15 mm under the conditions of a heat seal temperature of 180 DEG C., a heat seal pressure of 2 Kg/cm2, and a heat seal time of 1 second.

[0036]

[Comparative example] Homopolyester resin (A
), a polyethylene adhesive resin (C) graft-polymerized with maleic acid, and a linear low-density polyethylene resin (D) were used in the same manner as in Examples to obtain an A/C/D composite polyester film.

The lamination strength of the homopolyester resin layer and adhesive resin layer of this composite polyester film is 150 to 160 g/15 mm. The heat sealing strength of the linear low-density resins was 800 to 900 under the same conditions as in the example.
g/15mm.

As is clear from this, the composite polyester film of the present invention has a stronger bond between the polyester film and the adhesive resin layer than the composite polyester film of the comparative example consisting of a homopolyester film/adhesive resin layer/polyolefin resin layer. Its lamination strength and heat seal strength are strong, making it possible to package a wide range of items from light to heavy items.

[0039]

Effects of the Invention The present invention is as described above, and is a composite polyester in which heat sealability is imparted to a polyester film whose main repeating unit is ethylene terephthalate, which has poor heat sealability, without inhibiting the properties of the polyester film. It provides films based on the following.

[0040] The composite polyester film of the present invention is
In particular, it has excellent lamination strength and heat sealing strength, and can be used to package lightweight to heavy items, and is expected to have a wide range of applications in the future.

Claims (2)

[Claims] 1. A composite polyester film having at least a two-layer structure in which a modified polyester resin layer is laminated on at least one side of a polyester film as a base layer. Claim 2: A composite polyester film consisting of at least four layers, in which a polyolefin resin layer is laminated on the modified polyester resin layer side of a laminated film consisting of a polyester film and a modified polyester resin layer via an adhesive resin layer. .