JPH0419928B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to an improved heat shrink film for use in coating glass bottles. More specifically, the present invention relates to a heat-shrinkable film that has the ability to prevent fragments from scattering when a glass bottle such as a carbonated beverage bottle with internal pressure ruptures. Recently, in the glass bottle industry, the production of non-recycled bottles has been rapidly increasing for the purpose of simplifying distribution. Once a non-recycled bottle is filled with contents and delivered to a consumer, it is not used again, and for this reason, efforts are being made to make the wall thickness of the bottle as thin as possible. On the other hand, users of non-recycled bottles that are filled with contents, especially carbonated beverage manufacturers that are subject to internal pressure,
Plastic film is shrink-wrapped around the entire circumference of the glass bottle to increase its commercial value, and the plastic film compensates for the decrease in strength due to the thinning of the glass bottle, but this is not yet sufficient. That is, when a carbonated beverage bottle with internal pressure is ruptured, there is a risk that fragments will be scattered in all directions, and a strong plastic film suitable for preventing the fragments from flying is desired. Conventionally, expanded polystyrene films and vinyl chloride films have been used as labels for non-recycled bottles, and these films are placed on glass bottles and then heat-shrinked to cover the glass bottles. Expanded polystyrene film is stiff and suitable for mechanical packaging, but on the other hand, the film's impact resistance is low, and its ability to prevent fragments from scattering when a glass bottle bursts is poor. On the other hand, vinyl chloride film has a high impact resistance and is excellent in preventing fragments from scattering, but it has problems in that it damages the walls of garbage incinerators and is weak, making it difficult to make the film into a cylindrical shape for mechanical packaging. It has been pointed out that when the glass bottle is placed over a glass bottle from above or below, the lower or upper end of the cylinder bends due to frictional resistance with the glass bottle, making it impossible to insert the glass bottle. Under these circumstances, the present inventors developed a heat-shrinkable film that has impact resistance, is strong, transparent, slippery, has good mechanical packaging properties, and does not damage incinerators when processing waste. As a result of extensive research, the inventors discovered that a specific nitrile resin film could be effectively used, and completed the present invention. That is, in the present invention, acrylonitrile/butadiene copolymer with an acrylonitrile content of 5 to 60% by weight is added to 3 to 30% by weight.
A sheet obtained by stretching in at least one direction a resin obtained by graft copolymerizing 97 to 70% by weight of a mixture having a weight ratio of methyl acrylate of 95/5 to 50/50. A heat shrinkable film having a heat shrinkage rate of 30 to 80% and a heat shrinkage rate in a direction perpendicular to the heat shrinkage rate of less than 15%. The present invention will be explained in detail below. The resin used in the present invention is an acrylonitrile-butadiene copolymer containing 5 to 60% by weight of acrylonitrile and 3 to 30% by weight, and a weight ratio of acrylonitrile/methyl acrylate of 95/5.
It is a high nitrile resin obtained by graft copolymerizing 97 to 70% by weight of a ~50/50 mixture. As a commercially available product
BAREX (trademark, manufactured by Standard Chemicals, USA) is available. If the composition ratio of the backbone polymer, acrylonitrile-butadiene copolymer, in the high nitrile resin is less than 3% by weight, the film will lack impact strength, and if it exceeds 30% by weight, the film will deteriorate. Rigidity decreases. If the acrylonitrile content in the acrylonitrile-butadiene copolymer that is the backbone polymer is 5% by weight or less, the impact strength as a graft copolymer of acrylonitrile/methyl acrylate is insufficient. Moreover, if it exceeds 60% by weight, sufficient grafting with acrylonitrile/methyl acrylate cannot be achieved. If the weight ratio of acrylonitrile in the acrylonitrile/methyl acrylate composition ratio is 95% or more, the extrudability of the resin will be poor and a good sheet will not be obtained.
Furthermore, if the weight ratio of acrylonitrile is less than 50%, grafting cannot be achieved sufficiently, resulting in insufficient impact strength. In the present invention, the resin includes a coloring agent, various stabilizers,
There is no problem in adding antiblocking agents, antistatic agents, lubricants, etc. The stretching treatment for obtaining the heat-shrinkable film of the present invention involves stretching at least uniaxially in the machine direction or in the transverse direction, preferably in the machine direction. When stretching in the longitudinal direction, a roll stretching machine is usually used, and the preheating is preferably carried out at a temperature range of 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is 1.2 to 120°C.
5.0, preferably 2.0-3.0 is selected. If the preheating temperature is less than 70°C, it may be difficult to obtain a homogeneous film due to uneven thickness or breakage of the film during stretching. In addition, it is difficult to stretch at temperatures above 120°C.
It is difficult to obtain a film with good shrinkage. If the stretching ratio is less than 1.2 times, a film with an appropriate shrinkage ratio cannot be obtained, whereas if it is more than 5.0 times, the film tends to tear in the stretching direction, and the impact strength of the film decreases. When stretching in the transverse direction, a tenter system is typically used, and the same preheating conditions and stretching ratio as in the longitudinal stretching are applied. Heat shrinkage rate of the film of the present invention (measurement conditions;
(Immersed in oil bath at 100℃ for 5 minutes) is 30 to 80 in the stretching direction.
%, preferably 50 to 70%, and less than 15%, preferably less than 5% in the direction perpendicular to it, and the tensile modulus in the direction perpendicular to the stretching direction is 10000
Kg/cm ² or more, preferably 15000 Kg/cm ² or more. If the shrinkage rate in the stretching direction is less than 30%, the shrinkage speed is slow, and when the film is made into a cylinder and is shrunk on a glass bottle, the top end of the cylinder does not stick to the glass bottle and bulges out, causing the product to deteriorate. This not only reduces the value but also reduces the ability to prevent scattering when the bottle is broken. On the other hand, if the shrinkage rate exceeds 80%, the rate of thermal deformation will increase, and when heat sealing the film into a cylindrical shape, there will be many joint defects, and if there is a scratch, it will easily tear from there, causing damage. The scattering prevention performance of the bottle deteriorates. Furthermore, if the heat shrinkage rate in the direction perpendicular to the stretching direction is 15% or more, the height of the film after shrink wrapping will be reduced, the pattern printed on the film will be deformed, and the product value will be impaired. The tensile modulus in the direction perpendicular to the stretching direction is
If it is less than 10,000 Kg/cm ² , when the uniaxially stretched film is made into a cylinder and inserted into a glass bottle to cover it, the film is weak and bends, resulting in a large amount of loss. The thickness of the film is preferably 10 to 200 μm. If the thickness of the film is less than 10 μm, loss and scattering prevention performance will decrease when inserted into a glass bottle.
Furthermore, if the thickness of the film exceeds 200 μm, there is a problem that even if the film is heated after being inserted into a glass bottle, it will not adhere uniformly. By using the heat-shrinkable film of the present invention, it becomes possible to coat a glass bottle with the film at high speed, and in particular, even if a glass bottle for beverages under internal pressure bursts, scattering of glass fragments can be suppressed. be able to. Furthermore, the film of the present invention not only has excellent transparency, allowing the contents to be easily seen, but also has good printability and can be used depending on the purpose. Next, the present invention will be explained using Examples and Comparative Examples. Examples 1 to 4 Comparative Examples 1 to 3 Using the resins shown in Table I as raw materials, a sheet was extruded from a 300 mm wide T die attached to a 50 mmφ extruder, and this sheet was stretched 2.5 times in the longitudinal direction to obtain a thickness.
A heat shrinkable film for labels of 70 μm was obtained. The performance of this film and the scattering retention rate of fragments when the bottle was broken were measured and are listed in Table I. Here, the scattering retention rate of fragments means that a glass bottle with an internal capacity of 315 c.c. (weight 170 g) is filled with 300 c.c. of a prescription liquid that generates carbon dioxide gas, and the internal pressure is 4 Kg/cm ² at a liquid temperature of 25°C.
The glass bottle was then dropped horizontally onto concrete from a height of 75cm to cause it to explode.The weight of the bottle fragments collected within a radius of 1m from the point of fall was measured, and that weight was added to the sample glass bottle. It is divided by the weight of , and shows the average of 60 pieces. Approximately 90% of the total weight of a glass bottle is covered with film, and a scattering retention rate lower than 90% means that pieces covered by the film will also scatter. , Conversely, a value greater than 90% means that the film has excellent scattering prevention performance. Comparative Examples 4 and 5 In Example 2, the stretching ratio was 1.1 and 6.0, respectively.
A film obtained in the same manner as in Example 2 except that the amount was doubled was used. The results are shown in Table-I. Comparative Examples 6 and 7 A uniaxially stretched film of vinyl chloride and a uniaxially stretched film of expanded polystyrene were used as the covering films. PVC film has poor workability,
Furthermore, expanded polystyrene film has poor scattering prevention properties when the bottle is broken.

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Claims (1)

[Scope of Claims] 1 Acrylonitrile-butadiene copolymer containing 5 to 60% by weight of acrylonitrile 3 to
Mixtures 97 to 30% by weight with a weight ratio of acrylonitrile/methyl acrylate of 95/5 to 50/50
A sheet obtained by stretching a resin obtained by graft copolymerizing 70% by weight in at least one axis, the sheet having a heat shrinkage rate of 30 to 30 in the stretching direction at 100°C.
80%, and the heating shrinkage rate in the direction perpendicular to it is 15%.
A heat shrinkable film characterized in that it is less than or equal to 2. The heat-shrinkable film according to claim 1, which is a uniaxially stretched film and has a tensile modulus of 10,000 Kg/cm ² or more in a direction perpendicular to the stretching direction.