JPH0519448B2 - - Google Patents

Description

[Detailed description of the invention]

[] Object of the Invention (Field of Industrial Application) The present invention relates to a low-temperature heat-shrinkable film that has large heat-shrinkability and shrinkage stress at low temperatures, excellent transparency, and good low-temperature heat-sealability. More specifically, the low-temperature product is obtained by molding a composition in which the two types of side chains are substantially alkyl groups having 1 to 10 carbon atoms and a low-density copolymer of ethylene and α-olefin. The present invention relates to a shrinkable film, and aims to provide a low-temperature heat-shrinkable film that has large heat-shrinkability and shrinkage stress, excellent transparency, and good low-temperature heat-sealability. [] Background of the invention (prior art) Conventional heat-shrinkable films, such as polyvinyl chloride and polypropylene, usually start shrinking at around 100°C and show a large shrinkage rate of 50 to 70% at around 130°C. It has its features. However, in general, high-pressure low-density polyethylene (LDPE) resin is used as a film raw material, and the melting point of this resin is 100 to 110°C.
It is impossible to obtain a large shrinkage stress at around the shrinkage temperature, and even if shrink wrapping is performed, there is a drawback that the tension is insufficient. Furthermore, as a low-temperature heat-shrinkable film, an attempt has been made to slightly stretch the above-mentioned high-pressure LDPE to a low magnification to give it low-temperature shrinkability. However, since the general high-pressure LDPE has many long chain branches, its stretchability is extremely poor, and as a result, stretch breakage occurs immediately, making it difficult to uniformly stretch the film at a high magnification. Therefore, since high-pressure LDPE is stretched non-uniformly at a low magnification (2 to 2.5 times), transparency, which is a very necessary element for packaging films, is also important in terms of haze value (cloudiness).
It was around 10%, which was not desirable. [] Structure of the Invention Based on the above, the present inventors have conducted various searches to obtain a low-temperature heat-shrinkable film that has improved these drawbacks ^. , and a copolymer (A) of ethylene and α-olefin in which the number of alkyl groups in the side chain having 1 to 10 carbon atoms is 3 to 30 per 1000 carbon atoms in the main chain (A), and ( B) Ethylene and α- having a density of 0.890 to 0.910 g/cm ³ and having substantially 1 to 10 carbon atoms and 10 to 60 alkyl groups in the side chain per 1000 carbon atoms in the main chain. It is a heat-shrinkable film formed by molding a composition consisting of a copolymer (B) with olefin, and the composition ratio of the copolymer (B) of ethylene and α-olefin in the composition is 10 to 10. 60
% by weight, the haze value of this film is 5% or less, the heat shrinkage rate in the M direction at a temperature of 90°C is 30% or more, and the shrinkage stress is 300/gmm ² or more. The film has greater heat shrinkability and shrinkability than the above-mentioned olefin-based polymer film, has good transparency, and has better low-temperature heat sealability than the above-mentioned olefin-based polymer film. The present invention has been developed based on these findings. [] Specific description of the invention (A) Copolymer of ethylene and α-olefin (A) The density of the copolymer of ethylene and α-olefin (A) used in the present invention is 0.915 to 0.935 g/
cm ³ , particularly preferably 0.915 to 0.930 g/cm ³ . If a copolymer having a density of less than 0.915 g/cm ³ is used as the copolymer (A) of ethylene and α-olefin, the shrinkage stress of the resulting heat-shrinkable film will be weakened. On the other hand, 0.935g/ ^cm3
If a copolymer exceeding this amount is used, the transparency of the film will deteriorate. In addition, the number of side chain alkyl groups having 1 to 10 carbon atoms per 1000 carbon atoms in the main chain of this copolymer is 3 to 30, preferably 3 to 15, and particularly preferably 5 to 15. It is. If a copolymer of ethylene and α-olefin having 1 to 10 carbon atoms per 1000 carbon atoms in the main chain and less than 3 alkyl groups in the side chain is used, the low-temperature shrinkability of the film will deteriorate. On the other hand, if a copolymer of ethylene and α-olefin containing more than 30 molecules is used, it becomes difficult to mold and process the film. The melt index (measured according to JIS K-7260 at a temperature of 190°C and a load of 2.16 kg, hereinafter referred to as "MI") of the copolymer is usually 0.05 to 50 g/10 minutes, and 0.1 to 50 g/10 minutes. 20
g/10 minutes is preferred, and 0.1 to 10 g/10 minutes is preferred. If a copolymer of ethylene and α-olefin with an MI of less than 0.05 g/10 minutes is used, the kneading properties and film formability described below will deteriorate. On the other hand, if the amount of ethylene copolymer exceeds 50 g/10 minutes, the resulting film will have low mechanical strength. (B) Copolymer of ethylene and α-olefin (B) Furthermore, the density of the copolymer of ethylene and α-olefin (B) used in the present invention is 0.890.
0.910 g/cm ³ to 0.910 g/cm 3 , particularly preferably 0.895 to 0.910 g/cm ³ . Density is 0.890g/
Using a copolymer of ethylene and α-olefin with less than cm ³ reduces the shrinkage stress of the resulting film. On the other hand, if an ethylene copolymer exceeding 0.910 g/cm ³ is used, the low-temperature sealing properties of the resulting film will deteriorate. The number of alkyl groups in the side chain per 1000 carbon atoms in the main chain of the copolymer is 10 to 60, preferably 15 to 50, and particularly preferably 25 to 50. If an ethylene copolymer having less than 10 alkyl groups in the side chain per 1000 carbon atoms in the main chain is used, the resulting film will have poor low-temperature sealing properties. On the other hand, if an ethylene copolymer with a molecular weight exceeding 60 is used, the resulting film will have insufficient shrinkage stress. Furthermore, this copolymer of ethylene and α-olefin (B)
MI is generally from 0.05 to
50 g/10 minutes, preferably 0.1 to 20 g/10 minutes, most preferably 0.1 to 10 g/10 minutes. These copolymers of ethylene and α-olefin (A) and copolymers of ethylene and α-olefin (B) both contain ethylene and a large number of carbon atoms.
It can be produced by copolymerizing 12 α-olefins (for example, propylene, butene-1, hexene-1, 4-methylenepentene-1, octene-1) using the catalyst system described below. can. In these copolymers, "side chain alkyl group having substantially 1 to 10 carbon atoms" means that the alkyl group in the side chain mainly has 1 to 10 carbon atoms, and very little may have a side chain alkyl group having 11 or more carbon atoms. The catalyst systems used to produce these copolymers of ethylene and α-olefins are so-called Ziegler-Natsuta catalysts, which contain transition metal compounds (e.g. titanium-containing compounds) or supports (e.g. magnesium compounds) as the main catalyst. A carrier-supported catalyst is obtained by supporting a transition metal compound on a carrier-supported catalyst, and an organometallic compound (for example, an organoaluminum compound) is used as a co-catalyst.
These copolymers may be manufactured by any process such as slurry polymerization, solution polymerization, or gas phase polymerization, and the manufacturing method is well known. Furthermore, these copolymers are widely produced industrially and used in a wide range of applications. (C) Composition ratio In the composition for producing the low-temperature heat-shrinkable film of the present invention, a copolymer of ethylene and α-olefin (A) and a copolymer of ethylene and α-olefin (B) are combined. The composition ratio of the copolymer (B) of ethylene and α-olefin in the total amount is 10
~60% by weight, preferably 15-60% by weight,
Particularly preferred is 15 to 50% by weight. If the composition ratio of the copolymer (B) of ethylene and α-olefin in the composition is less than 10% by weight, moldability will be poor when producing a film from the composition. On the other hand, if it exceeds 60% by weight, the resulting film will have insufficient shrinkage stress. (D) Production of composition To produce the composition of the present invention, the above-mentioned copolymer of ethylene and α-olefin (A) and the copolymer of ethylene and α-olefin (B) They may be uniformly blended within the range of composition ratio (mixing ratio). In producing this composition, all the constituent components may be mixed at the same time, or a part of the constituent constituents may be mixed in advance to produce a so-called masterbatch, and this masterbatch and the remaining constituent components may be mixed to achieve the above-mentioned mixing ratio. The composition may be manufactured so that: Further, each compositional component may be used alone or in combination of two or more. The composition of the present invention may be composed of the copolymer of ethylene and α-olefin (A) and the copolymer of ethylene and α-olefin (B), but in addition to these components, an olefin-based copolymer may be added. Oxygen, heat and UV stabilizers, metal deterioration inhibitors, flame retardants, colorants, electrical property modifiers, antistatic agents, lubricants, processability modifiers and adhesives commonly used in the field of polymers. Additives such as property improvers may be added as long as they do not impair the properties of the composition obtained according to the present invention. This composition may be prepared by dry blending using mixers commonly used in the olefinic polymer industry such as Henschel mixers, Banbury mixers, kneaders, roll mills, and screw extruders. It can also be produced by melt-kneading using a mixer such as a mixer. At this time, a more uniform composition can be obtained by dry blending in advance and then melt-kneading the resulting mixture. (E) Production of film To produce the film of the present invention using the composition produced as described above, air is blown around the circumference of an extruded tube, and then the tube-shaped film is formed while cooling naturally. Although it is possible to do this using the conventional air-cooled inflation method, it is better to use a method that provides sufficient cooling.
Films with further improved transparency can be obtained by employing known quenching methods such as the water-cooled inflation method in which the tube is cooled by directly contacting it with water, and the chill roll method using a cooling roll (chill roll). be able to. The stretching temperature for producing the low-temperature heat-shrinkable film of the present invention is not particularly limited, but it exhibits excellent low-temperature heat-shrinkable properties at around 90°C, preferably from 80 to 100°C. [] Effects of the Invention The low-temperature heat-shrinkable film obtained in the present invention exhibits the following effects, including the composition used. By using the composition produced as described above, it is possible to increase the stretching ratio of the film to as high as 3.0 to 6.0 times, and by uniform stretching, a uniform film with no uneven thickness can be obtained. Since the stretching ratio can be as high as 3 times or more, a film with rapidly improved transparency, with a haze value (ASTM D-1003) of 5% or less, can be obtained. Further, the heat shrinkage rate (JIS Z-1709) in the M direction at 90° C. is 30% or more, and the shrinkage stress is 300 g/mm ² or more, so it has large heat shrinkability and shrinkage stress. In this case, if the stretching ratio is less than 3.0 times, there will be problems such as uneven stretching and uneven thickness, and the transparency will also be poor, and if the stretching ratio exceeds 6.0 times, stretch breakage will easily occur and stable production will be difficult. , it is difficult to obtain a film having the desired film properties of the present invention. Conventionally, films with outstanding transparency and low-temperature shrinkability have been made of polyvinyl chloride (PVC) or oriented polypropylene (PP), rather than polyethylene resin. However, the film of the present invention retains the excellent properties of polyethylene (low-temperature heat sealability, flexibility, food safety, etc.), has excellent transparency comparable to PVC or stretched PP film, and has excellent thermal properties. It is a film that has shrinkage properties. [] Examples and Comparative Examples The present invention will be explained in more detail below using Examples. In addition, in Examples and Comparative Examples, haze was measured according to ASTM D-1003. The heat shrinkage rate is according to JIS Z-1709, and the temperature
Measurements were made at 90°C and 100°C. In addition, the heat sealability was measured using tanzak-shaped test pieces (width
15mm) was cut out and heat-sealed at a sealing pressure of 2Kg/ ^cm2 and a sealing time of 1 second.The specimen was then heat-sealed using a tensile test specimen at a speed of 300mm/min.
The heat seal strength increases when peeled in the direction of
Shows the seal bar temperature when the weight exceeds 1.5Kg. Further, the shrinkage stress was measured using a Tensilon (equipped with a temperature riser/cooler) at 90°C while increasing the temperature by 3°C per minute. The physical properties of the copolymer of ethylene and α-olefin (A), the copolymer of ethylene and α-olefin (B), and other olefin-based polymers used in the Examples and Comparative Examples are shown below. . [(A) Copolymer of ethylene and α-olefin
(A)] As a copolymer of ethylene and α-olefin (A), ethylene has a density of 0.920 g/cm ³ and has an average of 12 ethyl groups as side chains per 1000 carbon atoms in the main chain. and butene-1 copolymer [MI
0.8 g/10 minutes, hereinafter referred to as "PE(1)"] was used. [(B) Copolymer of ethylene and α-olefin
(B)] A copolymer of ethylene and α-olefin (B) with a density of 0.890 g/cm ³ and an average of 45 ethyl groups as side chains per 1000 carbon atoms in the main chain. A copolymer of ethylene and butene-1 [MI 1.0 g/10 min, hereinafter referred to as "PE(2)"] was used. [(C) Other olefin-based polymers] As other olefin-based polymers, low-density ethylene homopolymer [MI 3.1 g/10 min, hereinafter referred to as "PE(3)"] manufactured by the so-called high-pressure method is used. ] was used. Examples 1 to 3, Comparative Examples 1 to 4 PE (1) and PE (2) whose blending amounts are shown in Table 1 were previously dry blended for 5 minutes using a Henschel mixer. Each of the obtained mixtures is melted and kneaded using a twin-screw extruder (diameter 50 mm, resin temperature 160°C) to form pellets (composition).
(Examples 1 to 3, Comparative Examples 3 and 4). Each composition and PE obtained as above
(3) was produced by an air-cooled inflation method while each composition or PE (3) was sufficiently cooled to produce a film. Each obtained film was removed at a film pull-out speed of 10 m/min and a take-up speed of 10 m/min.
A stretched film (30 microns thick, 600 mm wide) was produced by stretching at 40 m/min (22 m/min in Comparative Example 2) and a stretching temperature of 90°C. Table 2 shows the physical properties of each film obtained.

【table】

【table】

[Table] From the results of the above Examples and Comparative Examples, it is clear that the films obtained by the present invention not only have excellent heat shrinkability at relatively low temperatures, but also have good transparency. It is clear that the heat sealability is also excellent.

Claims (1)

[Claims] 1 (A) The density is 0.915 to 0.935 g/cm ³ ,
and a copolymer of ethylene and α-olefin in which the number of alkyl groups in the side chain having 1 to 10 carbon atoms is 3 to 30 per 1000 carbon atoms in the main chain.
(A) and (B) The density is 0.890 to 0.910 g/cm ³ and the number of alkyl groups in the side chain having substantially 1 to 10 carbon atoms is 10 to 60 per 1000 carbon atoms in the main chain. A heat-shrinkable film formed by molding a composition consisting of a copolymer of ethylene and α-olefin (B), which is a copolymer of ethylene and α-olefin (B). ) composition ratio is 10 to 60
% by weight, the film has a haze value of 5% or less, a heat shrinkage rate in the M direction at a temperature of 90°C of 30% or more, and a shrinkage stress of 300 g/mm ² or more. .