JPS5935348B2 - Method for manufacturing composite film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composite film having a laminate layer consisting of crystalline polypropylene, low density polyethylene and ethylene-1-butene random copolymer.

Biaxially oriented polypropylene film (OPP film) has superior properties compared to other polyolefin resins in terms of moisture resistance, transparency, oil resistance, heat resistance, stiffness, and physical strength, and has been in demand as a packaging material in recent years. However, it is extremely difficult to heat seal and its low-temperature impact strength is insufficient, so improvements are being made.

For example, a method is known in which OPP film is laminated with low density polyethylene, ethylene vinyl acetate copolymer petroleum resin, etc., but the transparency is poor. There were many disadvantages such as easy blocking. Further, JP-A-50-26886 discloses a method for producing an extrusion coated product by adding low density polyethylene and an amorphous ethylene-propylene copolymer to crystalline polypropylene. However, the composite film obtained by this method still has some unsatisfactory points, such as the adhesiveness of the laminate layer to the base film and the heat-sealability which deteriorate over time. The present inventors investigated a method for producing a composite film with less change over time in the adhesion between the base film and the laminate layer, low-temperature heat sealability, and surface unevenness. The present invention was achieved by discovering that a composite pool laminated with a composition containing a specific amount of density polyethylene and an ethylene-1-butene random copolymer consisting of a specific component satisfies these requirements and has very excellent properties. It is.

That is, the present invention provides melt index (230°C)
5 to 50 crystalline polypropylene (A) 65 to 94% by weight, melt index (1906C) 2 to 201 density 0.90 to 0.93 gA? Low density polyethylene (B) 3 to 15 weight? , and melt index (1
9 ``C) Ethylene-1-butene random copolymer which is a soft resin of 3 or more (C) 3 to 20 weight? This is a method for producing a composite film, which is characterized by melt-extruding a composition consisting of the following and applying extrusion coating or extrusion lamination to one side of a base film.

The materials of the base film to be laminated include polypropylene,
There are unstretched films and biaxially stretched films made of polyesters such as cellophane, polyethylene terephthalate, and nylon, and those coated with polyvinylidene chloride are preferably used.

In order to improve performance, heat stabilizers, ultraviolet absorbers, anti-blocking agents, slip agents, antistatic agents, etc. may be added to these base films as necessary. The crystalline polypropylene used in the present invention has a density of 0.89 to 0.92 g/CTill Melt Index (23
00C) 5 to 501 preferably 10 to 40,
Although a propylene homocopolymer may be used, crystalline polypropylene consisting of a random copolymer having an ethylene content of 4 to 15 mol % is preferably used in the present invention because of its good low-temperature heat sealability. The low density polyethylene has a melt index (at 190°C) of 2 to 201, preferably 5.
15 and a density of 0.90 to 0.93 g/.

The ethylene-1-butene random copolymer is a random copolymer with an ethylene content of 83 to 93 mol%,
It is a soft resin having a density of 0.85 to 0.92 g/CTill melt index (190C) of 3 or more, particularly preferably transparency of 4 to 25, and crystallinity by X-rays of 5 to 30%.

It is desirable that the copolymer does not contain a diene component, and even if it does contain it, it is desirable that it be in a very small amount. When the ethylene content of the ethylene-1-butene random copolymer is less than 83 mol%, it becomes rubbery, and when used as a composite film, unsuitable points such as poor slip properties and weak stiffness are observed.

When the ethylene content exceeds 93 mol%, no synergistic effect is observed when low density polyethylene and ethylene-1-butene random copolymer are used together, and surface unevenness is not eliminated.
Furthermore, even if a material with a very low melt index is used, surface unevenness cannot be eliminated. Furthermore, if a film with a too high melt index is used, a film with high impact strength cannot be obtained. Copolymers suitable for these purposes can be produced by various methods, but those produced using vanadium catalysts are particularly preferred. Is the blending amount of low density polyethylene 3 to 15 weight? , the amount of ethylene-1-butene random copolymer blended is 3 to 20% by weight? It is.

When the content of low density polyethylene is less than 3% by weight, the net-in becomes large and the molten film becomes unstable, so that the lamination speed is not improved. If it exceeds 15% by weight, unevenness will occur on the film surface and transparency will decrease.

If the content of the ethylene-1-butene random copolymer is less than 3% by weight, the adhesive strength between each layer of the composite film and the bag-breaking strength will not improve, and surface unevenness will not be eliminated.

If it exceeds 20% by weight, the slip property will be poor, the elasticity will be weak, and the surface hardness will be low, which is not preferable.

A composition containing crystalline polypropylene, low density polyethylene, and ethylene-1-butene random copolymer contains a heat-resistant stabilizer to improve the performance of the film.
Ultraviolet absorbers, anti-blocking agents, slip agents, antistatic agents, etc. can be added as necessary. Further, in order to improve the overlapping packaging properties and the adhesion to metals, part or all of the ethylene-1-butene random copolymer may be modified with an unsaturated carboxylic acid or its anhydride. The above composition can be used, for example, in a tumbler, V
It can be adjusted by mixing with a mold blender, pen shell mixer, etc., extruding, and then kneading with a Banbury mixer, kneader, rolls, etc.

In addition, the method for laminating the above composition on a base film involves forming a base film that has been unstretched or biaxially stretched in advance, applying an anchor treatment to one side of the film if necessary, and extruding the above composition for coating. Or extrusion lamination method. A method in which a laminating film consisting of a base film and the above composition is formed in advance and then laminated. Alternatively, there are methods such as coextrusion, but extrusion coating or extrusion lamination is preferred in order to obtain a relatively thin laminate layer. A particularly preferred embodiment of the present invention is a method of manufacturing a composite film using biaxially oriented polypropylene as a base film and using the above composition by extrusion lamination.

Another preferred embodiment is a method of manufacturing a composite film by extrusion lamination of the above composition onto a base film made of biaxially oriented polypropylene coated with polyvinylidene chloride.

By the manufacturing method according to the present invention, it has become possible to stably produce a laminated film with less neck-in during film lamination.

Furthermore, when only low density polyethylene was blended, the surface of the resulting film was uneven and had poor transparency, but this was significantly improved by the combined use of ethylene-1-butene random copolymer. The composite film obtained according to the present invention can be produced by a method (Japanese Unexamined Patent Application Publication No. 5-111) that uses low-density polyethylene and an amorphous ethylene-propylene copolymer in combination.
It has transparency equal to or higher than that of the composite film obtained in Japanese Patent Publication No. 0-26886). Moreover, the adhesion between both layers is excellent and long-lasting. These effects can be seen not only when the base film is made of polypropylene, but also when the base film is made of polyester such as cellophane, polyethylene terephthalate, polybutylene terephthalate, and nylon. In particular, if a biaxially oriented polypropylene film or a biaxially oriented polypropylene film coated with polyvinylidene chloride is used as the base film, organic titanium compounds, polyethylene imine, or isocyanate adhesives, etc., which were conventionally applied during lamination, can be used as anchors. Even without coating, the laminate layer adheres well to the base film and is persistent.

The composite film produced by the method of the present invention has excellent transparency and low-temperature heat-sealing properties, has no surface unevenness, and has improved low-temperature impact strength, and is therefore widely used as a packaging film for food products. Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded. The evaluation methods were as follows. (1) Melt index: ASTM-D-1238-65T (2) Density: ASTM-D-1505-67 (3) Adhesion: A 15 mm wide composite film was peeled in a T-shape, and its adhesive strength was determined from the peel strength. was evaluated.

(4) Surface smoothness: Distortion of a distant view when viewed through the composite film was evaluated.

(5) Transparency (haze): ASTM-D-1003 (6) Surface hardness: The hardness was measured using a Shore hardness tester D type.

(7) Heat seal strength: When the surfaces of the laminate layers of the composite film are overlapped with each other 2
k9/01! After heat-sealing a width of 5 mm at 140° C. for 1 second under a pressure of 1 liter, a test piece of 15 mm width was cut from the sealed portion, and the peel strength of the heat-sealed portion was measured.

Examples 1 to 3 Crystalline polypropylene with a melt index (230°C) of 30, low-density polyethylene (Mirason 8M-11 manufactured by Mitsui Polychemical Co., Ltd.) with a melt index (1906.5), and melt index Tsukusu (19
The components of an ethylene-1-butene random copolymer (ethylene content: 88 mol? and crystallinity by X-rays: 10%), which is 10% (ethylene content: 88 mol? and X-ray crystallinity: 10%), were blended in the weight ratios shown in Table 1, and After pelletizing, the mixture was melt-extruded at a resin temperature of 28°C and extrusion laminated onto a biaxially stretched polypropylene film prepared in advance with a thickness of 20μ so that the thickness of the laminate layer was 20μ.

Table 1 shows the maximum lamination speed at which a film can be stably obtained in this case and the evaluation results of the composite film obtained. Comparative Example 1 Table 1 shows the results of molding and evaluation in the same manner as in Example 1 in the case where the ethylene-1-butene random copolymer was not blended.

The composite film provided by the method of the present invention has better transparency and improved adhesive strength than conventional films, and has an especially smooth surface with no unevenness.

These effects cannot be seen when only low density polyethylene is blended with crystalline polypropylene.
Comparative Example 2 Table 1 shows the results of molding and evaluation of a composite film in the same manner as in Example 1 except that 30 parts by weight of the ethylene-1-butene random copolymer was added.

The blending amount of ethylene-1-butene random copolymer is 20
If the weight percentage is exceeded, the maximum lamination speed will decrease and the surface hardness will be poor, making it unsuitable for practical use. Comparative example 3 Ethylene content is 70 moles? and X-ray crystallinity 0
Table 1 shows the results of molding and evaluation of a composite film in the same manner as in Example 1 except for using the ethylene-1-butene random copolymer with %.

The ethylene-1-butene copolymer used in the present invention has an ethylene content of 83 to 93 moles? It must be.

If the ethylene content is less than 83 mol%, the surface hardness decreases, making it unsuitable for practical use. Examples 4-6 Melt index of ethylene-1-butene random copolymer (190°C)
Table 1 shows the results of molding and evaluation in the same manner as in Example 1, except that 18.

Composite films provided by the method of this example also include Examples 1-
Similar to No. 3, it has excellent performance, with no surface unevenness and excellent smoothness.

Example 7 Table 2 shows the results of testing the adhesive strength and heat seal strength of the composite film molded in Example 4 in an oven at 50°C over time.

Example 8 Table 2 shows the results of a test similar to Example 7 in which a biaxially oriented polypropylene film coated with polyvinylidene chloride was similarly laminated with the laminating composition used in Example 4. .

Comparative Example 4 The composite film molded in Comparative Example 1 was tested in the same manner as in Example 7 for changes in adhesive strength and heat seal strength over time, and the results are shown in Table 2.

Comparative Example 5 Ethylene-propylene copolymer (ethylene content 80 moles?) instead of ethylene-1-butene random copolymer.
Table 2 shows the results of a test for changes over time in the same manner as in Example 7 using a laminate composition containing a laminate composition containing 0% crystallinity and 0% x-ray crystallinity.

Comparative Example 2 shows that the adhesive strength and heat seal strength can be maintained for a long time even without the addition of laminated 1-butene random copolymer, but the comparative example shows that the surface smoothness is inferior. It is clearer than 1.

Furthermore, it is clear from Comparative Example 5 that when an ethylene-propylene copolymer is blended into the laminate layer, the adhesive force and heat seal strength cannot be maintained for a long time.

Claims (1)

[Claims] 1. 65 to 94% by weight of crystalline polypropylene (A) with a melt index (230°C) of 5 to 50, a density of 0.9 with a melt index (190°C) of 2 to 20.
0 to 0.93 g/cm^3 low density polyethylene (
B) Ethylene-1-butene random which is a soft resin with an X-ray crystallinity of 3 to 15% by weight and an ethylene content of 83 to 93 mol% and a melt index (190°C) of 3 or more. Polymer 3 to 20
1. A method for producing a composite film, comprising melt-extruding a composition consisting of % by weight and extrusion coating or extrusion lamination on one side of a base film. 2. The method for producing a composite film according to claim 1, wherein the ethylene-1-butene random copolymer (C) is an ethylene-1-butene random copolymer having a melt index of 4 to 25. 3. The method for producing a composite film according to claim 1, wherein the crystalline polypropylene (A) is a copolymer containing 4 to 15 mol% of an ethylene component. 4 Biaxially stretched polypropylene film or polyvinylidene chloride coated 2 as a base film
A method for producing a composite film according to claim 1, using an axially stretched polypropylene film.