JPS6315132B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a laminated stretched film,
Specifically, the present invention relates to a method for producing a laminated stretched film with good interlayer adhesion and heat sealability without impairing the optical properties and mechanical properties that are the original characteristics of a polyester stretched film. In recent years, the demand for films in the packaging field, including the food industry, and various industrial fields has increased significantly, and their uses are becoming increasingly diverse. As a result, commercially available single films are no longer able to meet the demands of multiple branches. Therefore, efforts have been made to create a composite film by combining two or more types of materials with different properties to meet the required characteristics while compensating for the shortcomings of the individual films. By the way, polyester stretched film has excellent optical and mechanical properties, but due to its high melting point, it has poor heat-sealing properties, which is a major problem, especially in the packaging field. For this reason, the following suggestions have been made regarding improvement measures. That is, a dry lamination method in which an isocyanate-based, ethyleneimine-based, organic titanate-based adhesive, etc. is applied to a stretched polyester film, and an unstretched film of polyolefin having heat sealability is laminated thereon; Heat-sealability has been improved by an extrusion lamination method in which a polyolefin resin is melt-extruded onto a stretched film and then heated and pressed between rolls. However, these methods are expensive due to the large number of steps required to obtain the final product, are difficult to handle because the adhesive used is toxic, and furthermore pose the risk of ignition and pollution due to organic solvents. Problems will also arise. The present inventors focused on the above-mentioned circumstances, and developed a polyester stretched film with good heat sealability and interlayer adhesion through a simple manufacturing process without sacrificing its original characteristics such as excellent optical properties and mechanical properties. We have been conducting research to establish a manufacturing method for laminated stretched films that can impart properties. The present invention was completed as a result of such research, and its structure is that when producing a laminated film having a polyolefin layer on at least one side of a polyester film, vinyl acetate is placed between the polyester film and the polyolefin film. 70 mol% or less of the acetoxyl groups in the ethylene-vinyl acetate copolymer containing 15 to 70% by weight are saponified, and the copolymer is added with an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride.
A laminated unstretched film is produced by interposing an adhesive resin layer made of a modified ethylene-vinyl acetate copolymer (hereinafter referred to as modified EVA copolymer) which is graft-modified to contain 0.05 to 5% by weight, and then The gist is that this film is stretched at 80 to 150°C in the longitudinal and/or transverse directions at an area stretching ratio of 4 to 20 times. In the present invention, a modified EVA copolymer that has adhesive properties for both polyester film and polyolefin film is used as an adhesive resin layer, and after forming a composite film using a normal lamination method, it is stretched at a predetermined temperature and a predetermined stretching ratio. This method significantly simplifies the manufacturing process compared to the method using adhesives as described above, and eliminates the dangers associated with the use of hazardous substances.
There is no risk of problems such as ignition, explosion, and pollution caused by the use of organic solvents. Furthermore, the modified EVA copolymer has the composition described below and has excellent adhesion to both polyester film and polyolefin film, so that it can be used between the layers of the final composite stretched film. Adhesion is also extremely high. In this way, it has become possible to inexpensively produce a high-performance composite film that can exhibit both the optical and mechanical properties of a polyester film and the heat-sealing properties of a polyolefin film. The polyester used in the present invention refers to a substantially linear aliphatic or aromatic polyester obtained by polycondensation of dibasic dicarboxylic acid and dihydric alcohol, such as polyethylene terephthalate, polyethylene terephthalate-iso Phthalate copolymer, polyethylene 2.6 naphthalate, polytetramethylene terephthalate,
Examples include polyethylene sebacate, copolymers and mixtures of two or more thereof, and among them, polyethylene terephthalate is one of the most preferred. The following graft modified product is used as the modified EVA copolymer constituting the adhesive resin layer, and this modified product has excellent adhesion to both polyester and polyolefin. That is, the content of vinyl acetate, which is the base polymer, is 15 to 70%.
(Hereinafter, the weight percentage is shown unless otherwise specified), more preferably 20 to 50%, and 70 mol% of the acetoxyl group.
Hereinafter, preferably using a partially saponified ethylene-vinyl acetate copolymer in which 50 mol% or less is saponified,
0.05 to 5%, more preferably 0.2%, of unsaturated carboxylic acid or its anhydride is added to this by a graft reaction.
The modified product containing up to 2% is extremely excellent in terms of adhesiveness and formability of laminated films. If the content of vinyl acetate is less than 15%, adhesion to polyester will be poor, while if it exceeds 70%, extrusion moldability will be poor. The degree of saponification of acetoxyl groups is closely related to interlayer adhesion and gas barrier properties of the final product; increasing the saponification degree improves gas barrier properties but lowers interlayer adhesion. Therefore, the degree of saponification should be determined based on the balance between the two, but when emphasis is placed on interlayer adhesion, it is best to set the degree of saponification to 70 mol% or less, and when particularly strong interlayer adhesion is required, It should be about 50 mol% or less. In addition, monomers used for graft modification of the partially saponified product include various unsaturated carboxylic acids or modified products thereof,
For example, acrylic acid, methacrylic acid, maleic acid,
Cinnamic acid, crotonic acid, etc. or their anhydrides may be used alone or in combination of two or more, but maleic anhydride is most preferred. The graft modification rate is
The content should be selected from the range of 0.05 to 5%; if it is less than 0.05%, the modification effect will not be sufficient, and the adhesion to polyester film in particular will be insufficient. On the other hand 5
If it exceeds %, the modification effect will not be improved any further, but rather the extrusion moldability will deteriorate, which is not preferable. Any polyolefin film that has heat-sealability even after stretching can be used, but preferred are low-density polyethylene,
Examples include ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-butene-1 copolymer, etc. alone or in a mixture of two or more,
Among them, low-density polyethylene is optimal in terms of both cost and performance. Next, the lamination method is not particularly limited, but a preferred method is a method in which three types of films are separately formed, the modified EVA copolymer is used as an intermediate layer, the remaining two types are stacked, and the layers are pressed together using heated rolls. A modified EVA copolymer and polyolefin are simultaneously extruded from a two-layer die onto a pre-formed unstretched polyester film, and the three are pressed together using a roll (extrusion lamination method), using a multilayer extruder. A method of simultaneously extruding three types of resins with the modified EVA copolymer as an intermediate layer and forming them into a film using rolls (coextrusion method);
The most preferred method is one that takes into account interlayer adhesion, workability (number of steps), subsequent stretchability, etc. In this method, three types of resins are simultaneously extruded from a flat die or circular die of three types and three layers or three types and five layers, and metal rolls,
Although direct or indirect cooling is performed using water, air, etc., stretching, heat treatment, etc., which will be described later, can be performed continuously, thereby further simplifying the manufacturing process. Next, in the stretching process, it is necessary to set conditions such that the three types of resin films can be stretched uniformly, and the stretching temperature must be 80 to 150°C. If the stretching temperature is less than 80℃, uniform stretching will be difficult and partial delamination or cracks will occur during the stretching process;
If it exceeds the melting point of the polyolefin, it will stick to tenter clips, etc., reducing workability. However, uniform stretching can be achieved at a stretching temperature of 80 to 150°C, more preferably 90 to 150°C, especially 90 to 150°C.
At temperatures above 0.degree. C., the residual strain of the film is small, and the curling phenomenon that tends to occur when manufacturing asymmetric laminated films is also suppressed. The stretching ratio should be set so that the area stretching ratio when uniaxially or biaxially stretched in the longitudinal and/or transverse directions is 4 to 20 times. When the areal stretch ratio is 4 times or less, the optical properties, which are the characteristics of polyester film,
The mechanical properties become insufficient and it becomes difficult to stretch uniformly. On the other hand, if it becomes 20 times or more, it becomes easy to break during the stretching process. Whether to use uniaxial or biaxial stretching can be decided depending on the intended use and required properties of the final product, but biaxial stretching is preferred in order to ensure better optical and mechanical properties. is advantageous, and in this case either simultaneous biaxial stretching or sequential biaxial stretching may be employed. The thickness of each resin layer in the final product can be set according to the application, but in order to ensure sufficient heat sealability, it is necessary to
It is desirable that the total thickness of the EVA copolymer layer and the polyolefin layer be 10μ or more, preferably 20μ or more. After stretching, heat treatment can be performed if necessary, but the heat treatment temperature should be higher than the stretching temperature and lower than the melting point of the polyester so as not to impede the effects of stretching on improving optical and mechanical performance. As mentioned above, the laminated film of the present invention has a structure in which a modified EVA copolymer layer is interposed between a polyester layer and a polyolefin layer, and the number of combinations of each layer can be adjusted appropriately depending on the application and required performance. However, the most common are 3 types 3 layers (polyester/modified EVA/polyolefin) and 3 types 5 layers.
layer (polyolefin/modified EVA/polyester/modified EVA/polyolefin). Each resin used in the present invention may contain stabilizers, fillers, ultraviolet absorbers, dyes, pigments, lubricants,
It is of course possible to incorporate additives such as antistatic agents and flame retardants. Next, an experimental example will be shown. Experimental example 1 A layer, B layer each equipped with a screw of 20 mmφ,
Using a three-layer extrusion molding machine consisting of layer C, the resin shown in Table 1 was supplied to each layer, melted at the temperature shown in the table, and coextruded from the same nozzle at a die temperature of 285°C. An unstretched film was produced.
The film forming conditions were all extremely good.

【table】

[Table] The obtained unstretched film was stretched using a pantograph type film stretcher under the conditions shown in Table 2, and the stretching conditions and the interlayer adhesive strength and heat sealability of the obtained stretched film were examined. The results are summarized in Table 2.

[Table] Based on the above results, the following can be devised. (1) Experiment No. 1 is a comparative example in which the stretching temperature is too low and cannot be stretched uniformly, whereas if the stretching temperature is too high (Experiment No. 11), it is easy to break during stretching and sticks to the clip significantly, making it difficult to work. Bad sex. (2) Experiment No. 4 is a comparative example where the stretching ratio is too small.
Stretching unevenness occurs in some areas and a uniform film cannot be obtained. On the other hand, if the stretching ratio is too large (Experiment No.
8) Easy to break during the stretching process. (3) In contrast, the Examples (Experimental Examples Nos. 2, 3, 5, 6, 7, 9, and 10) that meet the requirements of the present invention have uniform and extremely excellent interlayer adhesion and heat sealability. . Experimental Example 2 Using the same three-layer extrusion molding machine as in Experimental Example 1, the A and C layers also used the same polyethylene terephthalate and low density polyethylene as in Experimental Example 1, and the B layer was made of modified EVA resin (acetic acid) with a different degree of saponification. A three-layer film having the same thickness structure as in Experimental Example 1 was manufactured using the same vinyl content and graft ratio as in Experimental Example 1. The obtained film was stretched at a stretching temperature of 100° C. and a stretching ratio of 3.5 times in the MD direction and 3.5 times in the TD direction, and the interlayer adhesive strength was examined. The results are shown in Table 3.

[Table] As is clear from Table 3, if a modified EVA resin with a degree of saponification exceeding 70 mol % is used, the interlayer adhesive strength becomes extremely low, making it impossible to achieve the object of the present invention. On the other hand, if a resin with a saponification degree of 70 mol% or less is used as an adhesive resin, a composite film with excellent interlayer adhesive strength can be obtained.

Claims (1)

[Claims] 1. In producing a laminated stretched film having a polyolefin layer on at least one side of a polyester film, 15% of vinyl acetate is added between the two layers.
Up to 70 mol% of the acetoxyl groups in the ethylene-vinyl acetate copolymer containing ~70% by weight are saponified,
and at least a modified ethylene-vinyl acetate copolymer obtained by graft-modifying the copolymer so as to contain 0.05 to 5% by weight of an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride as an adhesive resin layer. A three-layer laminated film is formed, and then 80~
A method for producing a laminated stretched film, which comprises stretching at 150° C. in the longitudinal direction and/or the transverse direction at an area stretching ratio of 4 to 20 times. 2. The method for producing a laminated stretched film according to claim 1, using maleic anhydride as the unsaturated carboxylic acid or unsaturated carboxylic anhydride. 3. In claim 1 or 2, the polyolefin is one type selected from the group consisting of low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, and ethylene-butene-1 copolymer. The method for manufacturing a laminated stretched film as described above. 4. A method for producing a laminated stretched film according to any one of claims 1 to 3, wherein the total thickness of the modified ethylene-vinyl acetate copolymer layer and the polyolefin layer is 10 μm or more by stretching. 5. A method for producing a laminated stretched film according to any one of claims 1 to 4, in which lamination is performed by coextrusion. 6. A method for producing a laminated stretched film according to any one of claims 1 to 5, wherein stretching is performed by simultaneous biaxial stretching. 7. The method for producing a laminated stretched film according to any one of claims 1 to 6, which after stretching is heat-treated at a temperature higher than the stretching temperature and lower than the melting point of the polyester.