JPS5912469B2 - Thick polypropylene stretched film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a thick polypropylene (hereinafter abbreviated as PP) stretched film that is difficult to cleave, has excellent electrical properties and heat sealability, and can be used for film edge recycling.

In order to biaxially stretch PP to produce a film with excellent physical properties and a uniform thickness, an unstretched PP film must be stretched 40 to 60 times its original area. Therefore 6
In order to obtain a thick film of 0μ or more, it is necessary to cast an unstretched sheet with a thickness of 2.4 m or more. Because thick sheets cannot be rapidly cooled uniformly in the thickness direction, differences in spherulite growth occur in the thickness direction, and the growth of spherulites becomes more pronounced in the center of the thickness, making it difficult to stretch and causing film tearing. Conventionally, it has not been possible to industrially stably and continuously produce biaxially stretched films with a thickness of 60 μm or more because the transparency of the film may be lost. Therefore, various efforts have been made to create thick films. 10 Examples include (1) Thin single PP films that have been molded and cast separately in advance, and multiple sheets of PP and adhesive films are stacked alternately as necessary, and stretched to form a single film. Make thick film.

(2) A method of laminating biaxially stretched PP films using an adhesive. (3) A method of making a thick film by heat-sealing a plurality of biaxially stretched PP films using an adhesive film such as polyethylene or ethylene vinyl acetate copolymer. However, thick films made by these conventional methods have the following drawbacks. (a) Although it is true that a thick film made by (1) is superficially integrated, the adhesive force between each layer is weak, so it is difficult to bend repeatedly and be subjected to impact during actual use. , it easily splits open when subjected to effects such as rubbing. Furthermore, when an adhesive film is sandwiched between PP and integrated, wrinkles and air bubbles tend to form, which not only deteriorates the appearance but also deteriorates electrical properties such as withstand voltage. (b) The thick film of (2) is (1
Although the cleavability is improved compared to the film of ), the film becomes white and its adhesive strength decreases when subjected to hot water treatment. Also, electrical properties generally deteriorate. (c) The thick film produced by (3) is prone to wrinkles and air bubbles during heat-sealing, and the mechanical properties are deteriorated due to orientation relaxation caused by heat. Therefore, the present inventors conducted repeated research in order to obtain a thick film that overcomes these drawbacks, and as a result, a laminated film coextruded with PP using a modified polyolefin having carboxyl or hydroxyl groups (hereinafter abbreviated as Polymer B) was developed. The inventors have discovered that by employing the following, it is possible to obtain a thick stretched film that solves all of the above-mentioned drawbacks, and have arrived at the present invention. That is, in a biaxially stretched laminated film consisting of PP layer/polymer B layer/PP layer, the total thickness composition ratio of the PP layer and polymer B layer is 1:0.15 or less (preferably 1:0).
．． 10), and the total film thickness is 60μ or more. Further, other films or polymer B layers may be laminated above and below the basic structure within a range that does not impair the characteristic values.

Alternatively, two or more PP/polymer B laminated films may be stacked one on top of the other. Even in such a case, the thickness ratio of the entire PP layer to the polymer B layer must be kept within the above range. Compared to thick films made by laminating Polymer B within specific conditions, the product of the present invention does not have wrinkles or air bubbles during lamination, so it has a good appearance and transparency, is difficult to cleave, and has excellent heat sealability. . Even though it is a laminated film with an adhesive layer, the electrical properties (particularly the dielectric strength) do not deteriorate, and it has excellent electrical properties similar to a single PP film. Another great advantage is that film scraps such as film edges can be recycled. In particular, the combination in which Polymer B is on the surface layer significantly improves printability and lamination properties. When a thick stretched film is made by combining a polymer other than Polymer B with PP, even if it becomes difficult to cleave, the electrical properties may deteriorate, transparency may be impaired, or biaxial stretchability may deteriorate. This method has a major disadvantage in that the film scraps cannot be reused.
The thickness composition ratio of PP and polymer B must be 1:0.15 or less (preferably 1:0.10 or less).

When the ratio exceeds 1:0.15, polymer B occupies a large amount in the finished biaxially stretched film, resulting in loss of heat resistance, increased heat shrinkage rate, and decreased mechanical strength.

In addition, the dielectric strength decreases and the properties of the PP stretched film are lost. Furthermore, when the film scraps are recycled and used, the film becomes less transparent, making it impossible to collect the scraps. In the present invention, PP refers to polypropylene homopolymers and copolymers with other α-olefins (especially ethylene, butene, etc.).

Furthermore, blends with already known polymers (for example, polyethylene, polybutene, polybutadiene, polystyrene, polyterpene,
hydrogenated petroleum resin, Polymer B, etc.). What is Polymer B? (1) At least one polyolefin selected from α, β monoethylenically unsaturated dibasic acids such as maleic acid, fumaric acid, and itaconic acid, and their esters, amides, imides, and anhydrides thereof. A product obtained by graft polymerization of monomers. (2) Copolymers of ethylene and α,β monounsaturated carboxylic acids (and/or metal salts thereof) such as acrylic acid and methacrylic acid. (3) Polyolefins obtained by graft polymerization of α,β monounsaturated carboxylic acids (and/or the alkyl esters and metal salts). (4) Ethylene・
Saponified product of vinyl acetate copolymer. (5) A polymer obtained by graft polymerizing the graft monomers described in (1) and (3) above to the polymer of (4) above. (6) A blend of the required amount of the polymers (1) to (5) above with PP or polyethylene. Among these, especially (1), (3), (5)
, (6) are preferred. Depending on the purpose, these PPl polymers B may contain antioxidants, antistatic agents, inorganic fine particles, pigments, etc.
It goes without saying that various additives such as plasticizers and organic lubricants can be added.

An example of a method for industrially and continuously manufacturing the thick PP stretched film of the present invention will be described below, but the present invention is not limited to this method.

For example, a laminated film of PP and polymer B is produced by supplying each polymer to a separate extruder, laminating them in a polymer tube leading to a die or in a die, and forming a laminate of PP/polymer B or polymer B/PP/polymer B. Extrude the film. In this case, the thickness composition ratio of PP and polymer B is PP:polymer B-1:
The ratio is 0.15 or less, preferably 1:0.10 or less. The method for continuously manufacturing two laminated films of PP and polymer B is as follows: (1) Using a wide mouthpiece, divide the discharge section into two, and simultaneously extrude and cast the two laminated films. Method (Figure 1).

(2) A method in which two laminated films are each extruded from a single die having two discharge portions parallel to each other and cast onto separate cast drums (Fig. 2).

(3) A method of extruding laminated films separately using two ferrules and two cast drums (Figure 3).

(4) Using two ferrules, place two casters on a common cast drum.
A method of casting two sheets of laminated film (Fig. 4).

(5) After casting a wide film using a wide nozzle,
A method such as dividing an unstretched film into two at the center can be carried out.

In the present invention, methods (1) and (5) are particularly preferred from the viewpoint of die precision, ease of extrusion, and economic efficiency.

The laminated films can be subjected to various surface treatments such as various electric discharge treatments and flame treatments on the surfaces to be laminated.

It is best to stack the laminated films in an unstretched state because this prevents the films from being cleaved, wrinkles, and air bubbles. When stretching the stacked films, it is particularly preferable that the films are adhered or fused to each other in advance, but it is also possible to stretch the films to adhere them to each other without causing any adhesion between the films. In the case of sequential biaxial stretching, a press roll with an elastomer surface that can freely move in the circumferential direction of a low-speed introduction roll is provided for longitudinal stretching, the film is nipped, and the film is stretched between a free pass with a high-speed output roll. Longitudinal stretching is carried out by a method such as a stretching method or a method of stretching with a group of closely spaced rolls. 110-16'C (preferably 1
20-15'C) 3-10 times (preferably 4-7 times)
Stretch.

When the polymer B is on the surface layer, it is particularly preferable to use non-adhesive rolls as the longitudinal stretching rolls and to locally heat the rolls with a radiation heater or the like immediately before stretching. The longitudinally stretched film thus integrated is fed into the tenter 13.
5 to 17"C (preferably 140 to 1601C)
Stretch horizontally by 15 times (preferably 7 to 12 times). Next, heat treatment is performed as necessary. Lateral stretching and heat treatment further improve the adhesion between each film layer. The thick PP film according to the present invention can be subjected to various known surface treatments, such as corona discharge treatment, fire treatment, or a combination thereof, as with conventional PP films.

The product of the present invention can be used as an electrical insulation material, especially for cable wrapping, interlayer insulation, albums, stationery, etc.
Higher quality than conventional thick film. This will be explained below with reference to examples.

Example 1 Isotactic index (1.I.) 97%
, 2.3 PP measured in tetralin at 135° C. and the following polymer B were prepared.

Polymer B: 72.3, PP with ethylene content 2.0 wt%
A copolymer grafted with 0.5 wt% maleic anhydride.

The above PP was supplied to an extruder with a diameter of 65 mmφ and heated at 285°C.
It melted.

On the other hand, polymer B was supplied to an extruder with a diameter of 30 m1Lφ,
It melted at 275°C. Both are merged in a polymer tube leading to the base, and the total width is 600m77! extruded through a nozzle split in two in the center (Fig. 1) and cast at 30°C to a thickness of 2 m.
A two-layer film with a width of 270 mm was made at 7x. Two films with different composition ratios were continuously cast by changing the discharge rates of the two extruders, and the films were stacked so that the polymer B sides overlapped each other.

This was stretched 5 times in the longitudinal direction at 140°C while adhering the polymer B side to each other at 135°C in the preheating process for longitudinal stretching, then stretched 8 times in the transverse direction at 165°C with a tenter, and then stretched to 8% at 150°C. A biaxially stretched film with a thickness of 100 μm was prepared by performing a relaxation heat treatment. Table 1 shows the thickness composition ratio and film physical properties. f). 1 and 2 are transparent and have good withstand voltage and are difficult to cleave. On the other hand, in case 3, the layer of polymer B is too large, which increases the opacity and reduces the withstand voltage. It was confirmed that black 1 and 2 films could be made into flakes using a crusher, re-extruded at a flake mixing ratio of 10 to 50%, and the scraps could be recovered and reused. Evaluation method> Dielectric breakdown voltage: Measured according to JISC23l8.

Resistance to cleavage: A cellophane tape with a width of 201171L is attached to the film surface, and both ends of the tape and the film are gripped by clamps with a separation angle of 180 degrees.

Next, the distance between the clamps was widened at 2 m/sec to break the bond between the film and the tape, and it was determined to what extent the film layers were cleaved. ◎: No cleavage occurs between film layers.

○: The cleavage occurring at 〃 〃 is less than 10% of the total.

Δ: Cleavage occurring between film layers accounts for 10 to 50% of the total.

X: Cleavage occurring between film layers accounts for 50% or more of the total.

Comparative Example 1 A single unstretched sheet with a thickness of 211 mm was made using the PP and equipment used in Example 1 (30111Lφ extruder was stopped), and two sheets were superimposed as in Example 1 and stretched in the same manner.
A film (black 4) with a thickness of 100 μm was produced under heat treatment conditions.

In addition, one sheet of 10PP with a thickness of 27 m was biaxially stretched under the same conditions to produce a film with a thickness of 50 μm. One side of the film was treated with corona discharge, and two sheets were bonded together using an organic titanate adhesive to make a 100μ thick film (black 5).
And so. Next, in order to measure the heat seal
, 4, 5 were subjected to corona discharge treatment, coated with a urethane adhesive, and then extruded and laminated with low density polyethylene at 330° C. to a thickness of 40 μm.

The polyethylene surfaces of the laminate films were stacked on top of each other and heat sealed at 125° C. using a foot-operated heat sealer, and the sealant was measured. As is clear from Table 2, Black 4 does not use Polymer B, so it is easy to cleave and the sealer is small. Black 5 loses its transparency and has a low withstand voltage. On the other hand, Black 1 has a large seal. Example 2 Polymer B was prepared by hydrolyzing an ethylene-vinyl acetate copolymer with a vinyl acetate content of 10 wt% (degree of saponification 90%), and graft-polymerizing 10 wt% of acrylic acid thereto. A mixture of 10 wt% of PP with a resistance of Ω2.0 was used.

Using the apparatus used in Example 1, PP with an ethylene content of 0.7 wt%, 1.1.96%, and C77l2.4 was supplied to a 65 mmφ extruder and melted at 280°C. 30n at 270℃
Polymer B was supplied to a φ extruder, and the two were combined in a polymer tube to obtain two unstretched sheets with a thickness of 1.6 m and 71 L.

The thickness composition was PP: Polymer B-1: 0.053.
These two sheets were stacked to form PP/Polymer B/PP/Polymer B, and biaxially stretched under the same stretching and heat treatment conditions as in Example 1 to obtain a film (Ya 6) with a thickness of 80 μm. For comparison, 1.52m1L (7) PP single film and 8
0μ polymer B single film and X). A stretched film black 7 having a thickness of 80 mm was made by superimposing the same structure as 6 and stretching it. Inventive product f). Film No. 6 had good transparency, voltage resistance, and cleavage resistance, and the polymer B side could be clearly printed with cellophane printing ink, which cannot be used with ordinary PP films because of their lack of adhesive properties.

On the other hand, Film No. 7 contained air bubbles, wrinkled in places and easily cracked open, and had a low withstand voltage, resulting in a poor-quality film.
Comparative Example 2 Using low density polyethylene (melt index 7.01 density 0.92) and ethylene vinyl acetate copolymer (vinyl acetate content 10 wt%, melt index 1.5) in place of Polymer B, Example 1 Under the same conditions as Noya 2,
When stretching was carried out to make a thick biaxially stretched film, the stretchability of the laminated film was very poor, and the film frequently broke when using a tenter, making it impossible to obtain a satisfactory stretched film.

When we conducted a film scrap collection experiment, we found that when polyethylene was used, the transparency of the film decreased, and ethylene
In the case of using vinyl acetate copolymer, there was an odor of acetic acid due to thermal decomposition of the polymer, making it impossible to reuse it. Example
3 Polymer B used in Example 1 was changed to various polymers shown in Table 4, and 3071L7! A biaxially stretched film with a thickness of 1001 tm was prepared in exactly the same manner as Sample 1 of Example 1, except that the temperature of the Lφ extruder was lowered to 250°C, and the transparency, cleavage, and dielectric breakdown of the film were evaluated. The voltage was measured and the results shown in Table 4 were obtained.

Claims (1)

[Claims] 1. In a biaxially stretched laminate film consisting of a polypropylene layer/a modified polyolefin layer having a carboxyl group or a hydroxyl group/a polypropylene layer, the total thickness composition ratio of the polypropylene layer and the modified polyolefin layer is 1:0.1.
A polypropylene thick stretched film having a thickness of 5 or less and a thickness of 60μ or more.