JPH0229016B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite film for packaging, and more particularly, it is made by stretching a laminate of an isotactic polybutene-1 homopolymer or copolymer and a propylene homopolymer or copolymer in at least one direction. The present invention relates to a composite film having excellent properties required for a packaging film, particularly flexibility and punch hole strength. Packaging films are required to have many properties such as transparency, tensile strength, blocking resistance, flexibility, and punch hole strength, among which the demands on flexibility and punch hole strength have recently become particularly severe. In other words, as the types of products and packaging formats become more diverse, "flexibility" becomes an essential requirement in order to be compatible with all types of products and packaging formats.However, when transporting products over long distances,
Punch hole strength is also extremely important in preventing film damage during transportation. In particular, textile products such as clothing, bedding, interior products, etc. are soft products, so these products must be packaged in a soft manner, and are susceptible to holes due to external forces during handling and transportation. , it is necessary to prevent the progression of fracture starting from the opening, and the above two types of characteristics are important. On the other hand, many types of synthetic resin films are known as packaging materials, such as polyvinyl alcohol, polybutadiene, ethylene-vinyl acetate, polyethylene, soft vinyl chloride resin, and vinyldene chloride resin. The most widely used is soft polyvinyl alcohol. However, although polyvinyl alcohol film has excellent transparency, antistatic properties, and flexibility, it has serious problems in that it is sensitive to changes in humidity and loses flexibility and hardens during dry periods. However, many problems have been pointed out, such as poor workability during packaging due to stickiness on the film surface, and blocking occurring when packaged products are stacked. The present inventors paid attention to the above-mentioned circumstances and began research in order to provide a film particularly excellent in flexibility and punch hole strength. First, they focused on highly flexible isotactic polybutene-1 and attempted to modify it for use in packaging films. However, polybutene has a low softening point, has a sticky surface, and has poor punch hole strength, so it cannot be put to practical use as a packaging film as described above. It has been confirmed that the punch hole strength of films made of ordinary crystalline polymers is improved by stretching. However, although isotactic polybutene-1 has some crystallinity, it cannot be subjected to stretching treatment, so that stretching cannot be expected to improve punch hole strength. Therefore, rather than improving the physical properties of isotactic polybutene-1 itself, we thought that it would be possible to prevent the above-mentioned drawbacks by combining it with other film materials, and conducted further research. The present invention was completed as a result of these studies, and consists of a base layer made of an isotactic polybutene-1 homopolymer or copolymer with a butene content of 60 to 100% by weight, and one or both sides of the base layer. is laminated with a film made of a propylene homopolymer or copolymer having a propylene content of 70 to 100% by weight and stretched in at least one axis, and the thickness of the base layer is 50% or more of the total thickness. The key point is that the punch wheel strength (described later) is 1800 g or more. The base layer of the composite film according to the present invention is an isotactic polybutene-1 homopolymer or copolymer, and the butene content must be 60% by weight or more. The reason for this is that if the butene content is less than 60% by weight, the flexibility as a base layer will be poor, the flexibility will change significantly due to temperature differences, and furthermore, the film will have poor transparency. The most common copolymerization component is a-olefin ( _C2 to _C10 , excluding _C4 ), which can be copolymerized with butene-1, and the copolymerization forms include random copolymers and block copolymers. Although any copolymer may be used, a random copolymer is most suitable for improving transparency. In addition, the butene content in the material constituting the base layer is
It is also possible to blend an a-olefin polymer within a range that satisfies the requirement of 60% or more.
This homopolymer or copolymer is laminated with the propylene homopolymer or copolymer shown below to form a composite film, but the thickness of the base layer is the same as that of the entire thickness of the film.
Must be 50% or more. However, if the thickness of the base layer is less than 50%, the above-mentioned flexibility peculiar to the base layer will not be fully exhibited, making it impossible to achieve the purpose. Next, the propylene-based homopolymer or copolymer laminated on one or both sides of the base layer is extremely important for imparting stretchability to the composite film and mainly for increasing punch hole strength. That is, as mentioned above, it is extremely difficult to stretch an isotactic polyptene-1 polymer, and no improvement in punch hole strength can be expected by stretching, but when a propylene polymer film is laminated thereon, The entire composite film can be stretched, thereby increasing the punch hole strength. Furthermore, since the surface of the composite film is coated with a non-sticky propylene polymer film, the problem of blocking is also eliminated. Propylene polymers suitable for such purposes include propylene homopolymers or copolymers of propylene and a-olefins (preferably C ₂ to C ₁₀ , but excluding C ₃ ) such as ethylene, butene, and hexane. However, the propylene content must be at least 70% by weight. The reason for this is that if the propylene content is less than 70% by weight, the properties cannot be satisfied, and as in the present invention, isotactic polybutene-1, which is difficult to stretch,
When laminated with a composite film, the stretchability of the composite film as a whole may not be sufficiently improved. The propylene copolymer may be either a random polymer or a block polymer, but a random polymer is most suitable for improving transparency. However, it is not superior to propylene homopolymer. When selecting the above-mentioned isotactic polybutene-1 polymer and propylene polymer, the most suitable one should be selected depending on the physical properties of the other material to be combined, etc. After considering the selection criteria, we found that it is most practical to decide based on the difference in melting point between the two materials, and the melting point of the main polymer forming the base layer is 5 to 50°C higher than the melting point of the surface layer. It has been found that a high quality composite film can be obtained by selecting a material with a low value in the range of . The above-mentioned composite film can be manufactured, for example, by the following method. [1] The base layer and the covering layer are individually melt-extruded and then melt-laminated, or the base layer is melt-extruded and laminated onto a previously produced covering film, and then cooled and solidified. The cooling solidification temperature in this case depends on the melting point of the material, but is -20 to 100℃ (preferably -
20~70℃) is common. When taking off or applying tension, it is preferable to arrange the rolls so that the coated layer contacts the chill roll and the base layer contacts the hot roll. However, when coating layers are provided on both sides, such consideration is not necessary and is completely unnecessary. [2] The unstretched composite film obtained above is then stretched in a uniaxial direction (preferably biaxial direction) by a conventional method. The stretching ratio etc. is not particularly limited, but in order to obtain a punch hole strength of 1800 g or more, it is best to set it to about 1.5 to 20 times in the longitudinal direction and 1.5 to 16 times in the transverse direction, and the optimal stretching temperature in this case is 30-160 for longitudinal stretching
°C (more preferably 60 to 135 °C), and in the case of transverse stretching, 60 to 160 °C (more preferably 80 to 140 °C). This composite film exhibits sufficient punch hole strength even when stretched only uniaxially (generally about 2 to 20 times at 60 to 160°C), but the punch hole strength is further improved by biaxial stretching. At the same time, it is preferable that creep properties, transparency, blocking resistance, antistatic properties, etc. are further improved. The stretched film obtained in this way may be rolled up as it is and commercialized, or if necessary,
It is possible to perform aging treatment at about 50°C, and further to perform corona discharge treatment, electron beam treatment, flame treatment, etc. The present invention is roughly constructed as described above, and a packaging film is produced by laminating a propylene polymer on one or both sides of an isotactic polybutene-1 polymer film with excellent flexibility and stretching the film. It was possible to significantly improve the essential properties as a material, especially flexibility and punch hole strength. Therefore, this composite film is extremely useful for packaging soft products such as textile products, and can also be used with other thermoplastic films, cellophane,
By laminating paper, cloth, metal foil, etc., it can be applied to applications depending on the characteristics of each. Next, Examples and Comparative Examples will be shown, but prior to that, evaluation methods for various test items to be described later will be explained. (1) Melting point Measured using a Perkin-Elmer differential calorimeter at a heating rate of 20°C/min. (2) Blocking Measured in accordance with ASTM-D-1893-67, heating temperature was 50°C. (3) Coefficient of friction Measured according to ASTM-D-1894-63 method. (4) Haze Measured according to ASTM-D-103-52. (5) Gloss Measured according to ASTM-D-523-67. (6) Surface unevenness and ripple-like pattern Rating 5: Good with no defects Same 4: Slight presence of no problems in practical use Same 3: Slight presence of unevenness and can be used Same 2: Quite noticeable patterns observed and unusable Same 1: There are unevenness and ripples that stand out from each other on the entire surface, making it completely impractical.(7) Punch hole strength A 5mmφ round hole is punched in the film, and this hole is
Hook a hook made by bending a metal wire with a diameter of 3 mm with a radius of curvature of 10 mm, and pull the hook at a speed of 200 mm/min with one side of the film fixed.
The load when the hole ruptures is measured using a Tensilon tensile tester (manufactured by Orientek Co., Ltd.). Example 1 Mixture consisting of 80% by weight of isotactic polybutene-1-ethylene copolymer (ethylene content: 3.5% by weight), 10% by weight of propylene-butene-1 copolymer and 10% by weight of propylene-ethylene copolymer The composition is mixed with 1% by weight of an ethylene oxide adduct of an alkylamine as an antistatic agent to obtain a base layer film material (A). The film material (B) for the coating layer is a mixture of 50% by weight each of propylene-butene-1 copolymer (butene content 12% by weight) and propylene-ethylene copolymer (ethylene content 4.5% by weight). This mixture is mixed with 0.4% by weight of silicon dioxide (average particle size 3 to 4 μm). After melt-extruding the above materials (A) and (B), they are laminated in a molten state and then cooled with a cooling roll at 25℃ (B)
A laminated unstretched film was obtained in which the ratio of layer/(A) layer/(B) layer thickness was 15/75/15 (the total thickness was 40 μm).
m). On the other hand, an unstretched film was obtained in the same manner as above except that materials (A) and (B) were melt-extruded so that the thickness in the unstretched state was 720 μm, and then heated to 125°C and 4.0 times larger in the longitudinal direction. A biaxially stretched film having a thickness of approximately 40 μm was obtained by simultaneously biaxially stretching the film in the transverse direction by a factor of 4.5. One side of the unstretched or biaxially stretched film obtained above was subjected to a corona discharge treatment to adjust the surface wetting tension to 41 dynes/cm, and then subjected to the physical property tests shown in Table 1 below. Comparative Example 1 1.0% by weight of the same antistatic agent as in Example 1 was mixed with isotactic polypropylene and then melt-extruded, followed by the same procedure as in Example 1 to obtain an unstretched film and a biaxially stretched film with a thickness of 40 μm, Furthermore, a similar corona discharge treatment was performed to adjust the surface wetting tension to 40 dynes/cm. Comparative Example 2 An unstretched filter and a biaxially stretched film with a surface wetting tension of 40 dynes/cm were obtained in the same manner as in Comparative Example 1, except that low-density polyethylene (density 0.915 g/cm ³ ) was used instead of polypropylene. Ta. Comparative Example 3 The same isotactic polypropylene used in Comparative Example 1 (containing 1.0% by weight of antistatic agent) was used as the film material for the base layer, and propylene-ethylene copolymer (ethylene content: 4.0% by weight) was used for the coating layer. The film material was used in the same manner as in Example 1, with a surface wetting tension of 40 dynes/cm and a thickness of 40μ.
An unstretched film and a biaxially stretched film of m were obtained. Comparative Example 4 Polybutene 1 mixed with 1.0% by weight of antistatic agent
An unstretched film with a surface wetting tension of 40 dynes/cm and a thickness of 40 μm was prepared in the same manner as in Example 1, except that the low density polyethylene used in Comparative Example 2 was used as the film material for the base layer and the low density polyethylene used in Comparative Example 2 was used as the film material for the covering layer. A film and a biaxially stretched film were obtained. Comparative Example 5 The same isotactic polybutene-1 used in Example 1 was melt-extruded alone, and the thickness
An unstretched sheet of 720 μm was obtained. In this case, film formation was extremely difficult because the extruded sheet adhered to the chill roll, but productivity and appearance were completely ignored, and melt extrusion was carried out at a low speed of about 0.5 m/min. This unstretched sheet was biaxially stretched in the same manner as in Example 1 to obtain a film with a thickness of 40 μm. However, 125℃
Since it was not possible to perform stretching, the stretching temperature was set at 100°C. One side was then subjected to corona discharge treatment and the surface wetting tension was adjusted to 41 dynes/cm. Comparative Example 6 An unstretched film with a thickness of 720 μm obtained in the same manner as in Example 1 was simultaneously biaxially stretched by 4.0 times in the longitudinal direction and 4.5 times in the transverse direction at 32° C., resulting in biaxial stretching to a thickness of about 40 μm. I got the film. One side of this film was subjected to corona discharge treatment, and the surface wetting tension was adjusted to 41 dynes/cm. Table 1 shows the properties of each unstretched film and biaxially stretched film obtained in the above Examples and Comparative Examples.

[Table] ×)
As is clear from Table 1, the biaxially stretched film of Example 1 (the film of the present invention) is different from the unstretched film of Example 1 and the unstretched or biaxially stretched films of Comparative Examples 1 to 5 (both comparative It has superior punch hole strength compared to film. In addition, the film of the present invention showed comprehensively superior values in other properties compared to comparative films, and in particular, Young's modulus, which is a measure of flexibility, was inferior to that of isotactic polybutene-1 alone. In addition, the blocking and friction coefficient values are comparable to those of a polypropylene film alone. That is, the composite film of the present invention can be said to be a film that has both the features of isotactic polybutene-1 and the features of polypropylene, and has significantly improved punch hole strength.

Claims (1)

[Scope of Claims] 1. A base layer made of an isotactic polybutene-1 homopolymer or copolymer having a butene content of 60 to 100% by weight, on one or both sides of which the propylene content is 70 to 100% by weight. Films made of propylene homopolymers or copolymers are laminated and stretched in at least one axis, and the base layer has a wall thickness of 50% or more of the total wall thickness and a punch hole strength determined by the method below. A composite film characterized by a weight of 1800g or more. (Punch hole strength measurement method) A round hole of 5 mmφ is made in the film, and a hook made by bending a metal wire of 3 mm in diameter with a radius of curvature of 10 mm is hung in the hole, and one side of the film is fixed and the hook is fixed. It is determined by pulling the hook at a speed of 200 mm/min and calculating the load at the moment the hole begins to tear.