JPS6250302B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene multilayer film with improved heat sealability. Plastic packaging films are used in many industrial fields to maintain and improve product value and streamline distribution processes. It is a well-known fact that heat sealability is one of the most important properties required for plastic films for packaging. Excellent heat-sealability requires that heat-sealing is possible at low temperatures and that the heat-sealed portion has high strength. Lower heat-sealing temperatures allow for faster packaging, which provides significant economic benefits. Polypropylene film, especially biaxially oriented polypropylene film, is used in various industrial fields, mainly in the food packaging field, due to its excellent transparency and rigidity, but it has the disadvantage of lacking heat sealability due to its inert surface. ing. In order to improve this drawback, various methods have been adopted to treat the film surface by physical or chemical means. One of these is a multilayer film coated with a resin having a heat sealing temperature lower than that of the polypropylene base material to form a so-called heat sealing layer, which is widely used industrially. As a resin with a low heat sealing temperature, ethylene containing 1 to 6% by weight of ethylene is used.
Although propylene copolymers are commonly used, they do not reduce heat sealing temperatures sufficiently. Recently, propylene-butene copolymers have been used in some cases, but even this resin is insufficient in lowering the heat-sealing temperature. The present inventors have conducted intensive studies on reducing the heat sealing temperature of polypropylene films, and have found that on the surface of the base layer made of polypropylene,
Mixture layer of 85-97 parts by weight of a propylene-butene copolymer with a butene-1 content of 10-25% by weight and 15-3 parts by weight of an ethylene-propylene elastomer with a propylene content of 20-60% by weight The inventors have discovered that by coating the film, the heat-sealing temperature is significantly lowered, the heat-sealing strength is high, and the other properties required of the film are not degraded in any way, leading to the present invention. Conventionally, it has been empirically known that the heat-sealing temperature of mixtures of the same type of resin has both additivity, but the mixture layer of the present invention shows an unexpected decrease in the heat-sealing temperature, and No decrease in heat seal strength was observed. Although the reason for this is not clear, it seems that some kind of interaction is present. The propylene-butene-1 copolymer used in the present invention is usually polymerized by a method widely used in industry, and the butene-1 content is
It is a 10-25% by weight random copolymer. When the butene-1 content is less than 10% by weight, the effect of lowering the heat sealing temperature is small, and when it is more than 25% by weight,
The slippage between the films worsens, making it impossible to put it to practical use. The ethylene-propylene elastomer used in the present invention has a propylene content of 20 to 60% by weight,
Preferably it is 25 to 50% by weight. This range of elastomers also includes so-called ethylene-propylene-diene elastomers which contain small amounts of third components. When the propylene content is less than 20% by weight or more than 60% by weight, the elastomer properties deteriorate and the effect of lowering the heat sealing temperature of the mixture layer is no longer recognized. In the present invention, the composition of the heat-sealing layer must be a ratio of 85 to 97 parts by weight of propylene-butene-1 copolymer and 15 to 3 parts by weight of ethylene-propylene elastomer, and as long as it is within this range, the adhesiveness is high. It is an interesting fact that even if the proportion of the ethylene-propylene elastomer increases, the slipperiness between the heat-sealed surfaces of the film hardly deteriorates, and may even improve in some cases. Although it is unclear whether this phenomenon is consistent with this, it is noteworthy that as long as the heat seal strength is within this range, no decrease is observed, and on the contrary, it is improved. If the proportion of the ethylene-propylene elastomer is 15 parts by weight or more, the slipperiness between the heat-sealed surfaces of the film will deteriorate significantly, making it impossible to put it to practical use. When the proportion of the ethylene-propylene elastomer is 3 parts by weight or less, the effect of lowering the heat-sealing temperature of the propylene-butene-1 copolymer is no longer recognized. There is no problem in adding to the mixture layer according to the present invention anti-deterioration agents, lubricants, anti-blocking agents, weathering agents, etc. which are commonly used in film applications. The present invention will be explained below with reference to Examples, but these are not intended to limit the present invention in any way. Heat-sealing temperature and strength measurement method: Using a heat-sealing tester manufactured by Toyo Seiki Co., Ltd., heat-seal the heat-sealed surfaces at several temperatures. A 180° peel strength test is performed on two heat-sealed film test pieces to determine the peel strength at each temperature. The temperature at which the peel strength was 300 g/25 mm width was determined from the graph and was determined as the heat sealing temperature. Since the peel strength reached a certain value at a certain temperature, the peel strength at that time was taken as the heat seal strength. Butene-1 content measurement method...N, J,
WEGEMERG'S METHODS (JOURNAL OF APPLIED POLYMER SCIENCE)
OF APPLIED POLYMER SCIENCE）vol 14
p573) using a Shimadzu spectrophotometer IR-27G. Propylene content measurement method...Method of Mr. P, E, WEI (ANALYTICAL CHEMISTRY) vol 33 p215
(61)) using a Shimadzu spectrophotometer IR-27G. Sliding property measurement method: Using a friction angle measuring device manufactured by Toyo Seiki Co., Ltd., a stainless steel block wrapped in film weighing 1 kg was placed on a plate covered with film, and the block was tilted at a speed of 2.7°/sec. The angle θ at which the vehicle started sliding is expressed as tanθ. Melt flow index measurement method: Measurement was carried out in accordance with JIS K-6758 using a melt inkser model MX-101 manufactured by Takara Kogyo Co., Ltd. Examples 1-3 Butene-1 content 21.0% by weight, melt flow index
11.0 propylene-butene-1 copolymer 97, 90,
For 85 parts by weight, 3 parts each of ethylene-propylene elastomer (propylene content 30% by weight),
10 and 15 parts by weight were mixed in a super mixer and melt-kneaded in a 40 mmφ extruder manufactured by Tanabe Plastics Co., Ltd. to obtain pellets. Next, using Sumitomo Noblen FA8011 (manufactured by Sumitomo Chemical) as the base layer and the above pellet as the heat-sealing layer on the surface, a two-layer film was obtained using an in-die adhesive type two-layer coextrusion die. The thickness of the base layer of this film was 41μ, and the thickness of the heat seal layer was 9μ. The heat-sealing temperature and heat-sealing strength between the heat-sealing surfaces of this film were measured and are shown in Table 1.
The results shown are obtained. Further, the results of measuring the slipperiness between the heat-sealed surfaces are also shown in Table 1. Comparative Examples 1, 2, 3 0, 20, and 100 parts by weight of the same ethylene-propylene elastomer as in Examples 1 to 3 to 100 and 80.0 parts by weight of the same propylene-butene-1 copolymer as in Examples 1 to 3, respectively. The mixture was mixed in a super mixer and melt-kneaded in a 40 mmφ extruder manufactured by Tanabe Plastics Co., Ltd. to obtain pellets. Two-layer films were obtained in the same manner as in Examples 1 to 3, and the heat-sealing temperature, heat-sealing strength, and slipperiness between the heat-sealing surfaces were measured. Table 1 shows the results.

[Table] Examples 4 and 5 Butene-1 content is 12.3% by weight, melt flow index
6.5 propylene-butene-1 copolymer, 95, 90
5 and 10 parts by weight of ethylene-propylene elastomer (propylene content: 31% by weight) were mixed in a super mixer and melt-kneaded in a 40 mmφ extruder manufactured by Tanabe Plastics Co., Ltd. to obtain pellets. Next, using Sumitomo Noblen FS2011 (manufactured by Sumitomo Chemical) as the base layer and the above pellet as the heat-sealing layer on the surface, a two-layer film was obtained using an in-die adhesive type two-layer coextrusion die. The thickness of the base layer of this film was 230μ, and the thickness of the heat seal layer was 20μ. This film was stretched 3 times in length and width at 130°C using a research polymer film biaxial stretching apparatus manufactured by Iwamoto Seisakusho, and then heat set at 120°C. Table 2 shows the results of measuring the heat-sealing temperature, heat-sealing strength, and slipperiness between the heat-sealing surfaces of the multilayer biaxially stretched film obtained as described above. Comparative Examples 4 and 5 To 100 and 80 parts by weight of the same propylene-butene-1 copolymer as in Examples 4 and 5, 0 and 20 parts by weight of ethylene-propylene elastomer, respectively, as in Examples 4 and 5 were added to a super mixer. and melt-kneaded using a 40 mmφ extruder manufactured by Tanabe Plastics Co., Ltd. to obtain pellets. A multilayer biaxially stretched film was obtained in the same manner as in Examples 4 and 5, and the heat-sealing temperature, heat-sealing strength, and slipperiness between the heat-sealing surfaces were measured. Table 2 shows the results.

[Table] Example 6 Butene-1 content is 23.9% by weight, melt flow index
An ethylene-propylene-diene elastomer (propylene content 45% by weight, Mooney viscosity 45, iodine value 1.3) containing a small amount of diene component was added to 92 parts by weight of the propylene-butene-1 copolymer of 15.2. 8 parts by weight were mixed in a super mixer and melt-kneaded in a 40 mmφ extruder manufactured by Tanabe Plastics Co., Ltd. to obtain pellets. A two-layer film was obtained in the same manner as in Examples 1 to 3 using Sumitomo Noblen FA8112 (manufactured by Sumitomo Chemical) as the base layer. Table 3 shows the results of measuring the heat-sealing temperature, heat-sealing strength, and slipperiness between the heat-sealing surfaces of this film. Comparative Examples 6 and 7 To 100 and 80 parts by weight of the same propylene-butene-1 copolymer as in Example 6, respectively 0.20 parts by weight of the same ethylene-propylene-diene elastomer as in Example 6.
The mixture was mixed in a weight part super mixer and melt-kneaded in a 40 mmφ extruder manufactured by Tanabe Plastics Co., Ltd. to obtain pellets. A two-layer film was obtained in the same manner as in Example 6,
Table 3 shows the results of measuring the heat-sealing temperature, heat-sealing strength, and slipperiness between the heat-sealing surfaces.

[Table] Comparative Examples 8 and 9 Butene-1 content is 8.5% by weight, melt flow index
To 100 and 90 parts by weight of the propylene-butene-1 copolymer of 8.8, 0.10 parts by weight of each of the same ethylene-propylene elastomers as in Examples 1 to 3 were mixed in a super mixer, and a 40 mmφ manufactured by Tanabe Plastics Co., Ltd.
The mixture was melt-kneaded using an extruder to obtain pellets. A two-layer film was obtained in the same manner as in Examples 1 to 3 using Sumitomo Noblen FA8011 as the base layer. Table 4 shows the results of measuring the heat-sealing temperature, heat-sealing strength, and slipperiness between the heat-sealing surfaces of this film. Comparative Examples 10, 11 Butene-1 content is 27.2% by weight, melt flow index
0 and 10 parts by weight of the same ethylene-propylene elastomer as in Examples 1 to 3 were mixed with 100 and 90 parts by weight of the propylene-butene-1 copolymer No. 13 in a super mixer, and a 40 mm product manufactured by Tanabe Plastics Co., Ltd.
The mixture was melt-kneaded using a φ extruder to obtain pellets. A two-layer film was obtained in the same manner as in Examples 1 to 3 using Sumitomo Noblen FA8011 as the base layer. Table 4 shows the results of measuring the heat-sealing temperature, heat-sealing strength, and slipperiness between the heat-sealing surfaces of this film.

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Claims (1)

[Claims] 1. 85 to 97 parts by weight of a propylene-butene-1 copolymer having a butene-1 content of 10 to 25% by weight and a propylene content of 20 to 60% by weight on at least one surface of a base layer made of polypropylene. A polypropylene multilayer film formed by forming a mixture layer with 15 to 3 parts by weight of ethylene-propylene elastomer.