JPH0261963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polypropylene resin film for shrink wrapping, and more specifically to shrink wrapping which has extremely excellent shrink properties, excellent film strength, especially impact resistance at low temperatures, and good transparency. The present invention relates to a polypropylene resin film for use. As is already well known, polypropylene shrink wrapping film has excellent transparency,
It has characteristics such as the contents look beautiful, the film has excellent surface gloss, and the appearance is not affected by scratches, but it has poor low-temperature shrinkability, making shrink-wrapping at low temperatures difficult and requiring shrink-wrapping at high temperatures. Therefore, there is a drawback that the influence of heat on the contents cannot be avoided. The inventors of the present invention have conducted intensive studies to develop a polypropylene resin film for shrink wrapping that can be shrink wrapped at low temperatures and has excellent ^transparency and anti-blocking properties.
~14 mol%, block index described below is 1.1 or less,
MLMFI/MFI ratio 16-10 and MFI 0.5-15
Shrink wrapping film manufactured using a propylene-ethylene random copolymer with a property of Having recognized this fact, we have arrived at the present invention. The polypropylene resin film for shrink wrapping according to the present invention is made by melt-extruding a propylene-ethylene random copolymer resin having the following properties (a) to (d) into a tube shape, and then biaxially stretching the film. (a) Ethylene content determined by ^C13 -NMR method: 8~
14 mol% (b) Block index defined below calculated by C ¹³ -NMR method: 1.1 or less (c) MFI (230°C, load 2.16 kg): 0.5 to 15 g/min (d) MLMFI (230°C, load 10.0Kg) and MFI (230
℃, load 2.16 kg) MLMFI/MFI: 10 to 16 The term "block index" used herein refers to the monomer sequence determined in triads by the ^C13 -NMR method, and the ratio of ethylene to the monomer sequence measured in triads by the C13-NMR method. The fraction, that is, propylene unit: 1, ethylene unit: 0, [(100) + (000)],
The percentage divided by the sum of all triad fractions including ethylene [(101) + (100) + (000)] is 100
−[100−C _E (mol%)] Refers to the value divided by ² . Block index = (100) + (000) / (101)
+(100)+(000)×100100−[100−C _E (mol%)] ^{2
(Note) However, C _E indicates the ethylene content (mol%). The copolymer used in the present invention is C 13 −
It is necessary that the ethylene content (hereinafter simply referred to as ethylene content) determined by NMR method is 8 to 14 mol%. Homopolymers and random copolymers with an ethylene content of less than 8 mol % are not preferred because they have poor shrinkage properties even if other requirements are met. On the other hand, when the ethylene content exceeds 14 mol%,
This is not preferred because the blocking resistance of the film deteriorates and it becomes necessary to add a large amount of an antiblocking agent (eg, silica), making it difficult to obtain a film with excellent transparency. Furthermore, as will be described later, it is important that the above-mentioned content of ethylene is more uniformly distributed in the copolymer, and the block index must be 1.1 or less. When the blocking index exceeds 1.1, transparency is particularly deteriorated, which is undesirable. So-called propylene-ethylene block copolymers are unsuitable for use in the present invention. The previously defined block index was measured and used as a means of determining the distribution of ethylene in the copolymer. Looking at the C 13 -NMR triads, the ratio of the fraction of triads containing ethylene in block form to the sum of the fractions of all triads containing ethylene is almost 0 at low ethylene contents (less than 3 mol%); The value increases as the ethylene content increases. Therefore, the block index expresses the blockiness of the distribution of copolymerized ethylene, and in the present invention, it is necessary that this index is 1.1 or less. The previously mentioned ethylene propylene block copolymers, copolymers with high ethylene content polymerized at low temperatures, or copolymers polymerized with special catalyst systems have block indexes larger than this value, and block copolymers have a block index of 3. Takes a value greater than or equal to When the blocking index is greater than 1.1, the transparency of the film decreases, and even if the amount of anti-blocking agent (e.g. silica) or slip agent (e.g. amide) is controlled, a good balance between transparency and anti-blocking property cannot be maintained. It is not desirable because it does not reach the range. The melt flow ratio of the copolymer used in the present invention, that is, MLMFI (230°C 10.0 kg load) and MFI
(230℃, 2.16Kg load) Outflow ratio MLMFI/MFI
It is important that the value is between 10 and 16. MLMFI/MFI of commercially available ordinary propylene-ethylene copolymer
The ratio is 18-25. Therefore, MLMFI/MFI can be considered to represent the degree of molecular weight reduction. For example, a copolymer with an MFI of 0.09 g/min is
The change in MLMFI/MFI after molecular weight reduction when changing the amount of bis(t-butylperoxyisopropyl)benzene used is as follows. MFI MLMFI/MFI 0.09 20.1 (before degradation) 0.13 18.6 0.56 15.8 1.8 13.1 3.4 12.8 8.2 12.6 12.3 12.3 28.6 11.6 That is, the copolymer used in the present invention
MLMFI/MFI is in the range of 10 to 16, but a more preferable range is MLMFI/MFI of the degraded copolymer.
For example, around 1g/10min, it is 12 to 16, 10g/
It can be said that it is 10 to 14 around 10 min. When the MLMFI/MFI ratio exceeds 16, the degree of molecular weight reduction is small, resulting in poor stretchability during film molding and loss of surface gloss.
On the other hand, if it is less than 10, the degree of molecular weight deterioration is very large, and a large amount of radical generator is required, causing problems with color, odor, etc. The MFI (230°C, load 2.16 kg) of the molecular weight reduced copolymer used in the present invention is 0.5 to 15
g/10 min, preferably 1 to 10 g/10 min. If the MFI of the copolymer is outside the above range, it will be difficult to form a film, which is not preferred. The MFI of the copolymer before degradation is generally 0.5.
g/10min is used, especially 0.01
~0.3g/10min is suitable. normal
Rather than producing a copolymer in the MFI range (MFI = 0.5 to 60 g/10 min) by direct polymerization, the molecular weight of a high molecular weight copolymer (MFI = approximately 0.01 to 0.3 g/10 min) is reduced.
Although it is not clear why a film with an MLMFI/MFI ratio of 10 to 16 is effective in the present invention, it is speculated as follows. When we tested the isobutyl alcohol-soluble content and hexane-soluble content of various polymers and powders produced by changing the MFI of propylene-ethylene copolymer with an ethylene content of 12.3 mol%, we found that the alcohol-soluble content was generally low. It was confirmed that hexane is extracted in proportion to the amount of molecular weight, and in hexane, it is extracted in accordance with crystallinity (ethylene content) in addition to low molecular weight. That is, the hexane soluble content is
It decreases rapidly at MFI of 0.3 g/10 min or less, but this degree cannot be explained only by the effect of increased molecular weight in comparison with the isobutyl alcohol soluble content. It is reasonable to assume that the amount of low crystallinity areas has been significantly reduced. For high molecular weight copolymers (MFI: 0.01-0.3), normal MFI (1-20)
Compared to the copolymers of 1 and 2, the distribution of the comonomer ethylene in the polymer is considered to be uniform even with the same ethylene content. Furthermore, it is thought that the maximum molecular weight in the high molecular weight region decreases due to molecular weight reduction, and the stretchability during film molding increases. The copolymer used in the present invention can be produced, for example, by the following method. Random copolymerization of propylene and ethylene is carried out in the presence of a Ziegler-type catalyst (for example, a catalyst system consisting of a solid catalyst component mainly composed of titanium trichloride, an organoaluminum compound, and an electron-donating compound as necessary) to produce ethylene. The content is 8 to 14 mol% and
It is obtained by obtaining a copolymer having an MFI of 0.01 to 0.3 g/10 min and reducing its molecular weight in the presence of a radical generator. Furthermore, in addition to ethylene, α-olefins having 4 or more carbon atoms, such as butene-1, 4-
It is possible to include up to 2 mol % of methyl-pentene-1, hexane-1, octene-1, etc. Organic or inorganic free radical generators used for molecular weight reduction include peroxides, hydroperoxides, peracides, metal alkyls, which are commonly used as radical polymerization initiators.
Examples include metal allyls and combinations thereof with inorganic complex salts. The organic peroxide may be in a liquid, solid, or solidified form with an inorganic filler, and is mixed and diffused with the polyolefin at a temperature at which the organic peroxide does not substantially decompose. The organic peroxide that can be used in the present invention is preferably selected from those having a half-life of 1 minute at a temperature of 70 to 300°C. For example, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, dicumyl peroxide,
Dialkyl peroxides such as 2,5-dimethyl 2,5-di(t-butylperoxy)hexane, 2,5-dimethyl 2,5-di(t-butylperoxy)hexyne-(3), lauroylperoxide oxide, diacyl peroxides such as benzoyl peroxide, t-butyl peroxyacetate, t
Examples include peroxy esters such as -butyl peroxylaurate, methyl ethyl ketone peroxide, and methyl isobutyl ketone peroxide. Others, such as α, α
Azo compounds such as -azobis-(isobutyronitrile) are also used as free radical generators. The amount of the radical generator added is based on the composition of the present invention.
It is an important factor in determining MFI, and the amount added is 0.001 to 2% by weight, preferably 0.01 to 0.5% by weight, based on the polyolefin. This is not desirable as the degree of The amount added is adjusted in consideration of the MFI of both main components and the MFI of the composition. The copolymer and the radical generator are blended in a predetermined ratio, dry blended using a super mixer, and the propylene polymer can be extruded under normal conditions.
For example, mixing and depolymerization can be easily achieved by melt-kneading at a temperature between 170°C and 300°C. Alternatively, a method of directly adding and mixing and melt-kneading can also be applied. In addition to the radical generator, the copolymer according to the present invention contains various auxiliary components that are normally blended, such as antioxidants, ultraviolet deterioration inhibitors, antiblocking agents, slip agents, antistatic agents, colorants, etc. It can contain. According to the present invention, the method for producing a shrink wrapping film from a propylene-ethylene random copolymer resin having the above-mentioned properties (a) to (d) is not particularly limited, and the method is not particularly limited. It can depend on the method of manufacturing the film. For example, the resin is heated to 200 to 280°C, preferably 210 to 250°C, by a general method.
It is produced by melt-extruding into a tube shape at a temperature of 120 to 140 degrees Celsius, cooling it to a temperature of about 10 to 30 degrees Celsius, and simultaneously biaxially stretching the obtained tube-shaped film in both length and width directions at a temperature of 120 to 140 degrees Celsius. be able to. The stretching ratio in the longitudinal and lateral directions is usually about 3 to 5 times, respectively. The obtained biaxially stretched film may be subjected to surface treatments such as corona discharge treatment and fire treatment, which are commonly used in industry. In this way, a propylene-based resin film for shrink packaging that is excellent in low-temperature shrinkability and strength at low temperatures can be produced, and can be suitably used for individual packaging, collective packaging, and the like. Hereinafter, the content of the present invention will be explained with reference to Examples, but it goes without saying that the present invention is not limited to these Examples. MFI and MLMFI, haze, ethylene content, shrinkage rate, and blocking in the following Examples and Comparative Examples were measured by the following methods. a Melt flow index (MFI) Measured by the method of JIS K-6758. However, temperature
The temperature was 230℃ and the load was 2.16Kg. Also, load 10.0Kg
The value of is called MLMFI. b Film haze Measured using a haze meter according to ASTM-D-1003-61. c Ethylene content JEOL Ltd.'s FT nuclear magnetic resonance absorption analyzer (FX
-100) under the following conditions: Observation width 1800Hz Pulse width 6μs (45° pulse) Pulse interval 3s Integration number 10000 or more Measurement temperature 100℃ Sample was mixed with 1,2,4-trichlorobenzene.
It was measured by dissolving it in a mixed solution of C ₆ D ₆ and calculated from the area of each peak. d Shrinkage rate The shrinkage rate of the film was measured according to JIS-Z-1709-1976. e. Blocking A load of 100 g/cm 2 was applied in an atmosphere at 40° C., and after 48 hours, the degree of adhesion between the films and the platyness were ranked using an index of 1 to 5. An index of 1 indicates the best condition. Example 1 A titanium trichloride composition (a powder obtained by co-pulverizing 5.0 kg of commercially available AA type titanium trichloride and 0.75 g of γ-butyrolactone) was placed in a 290 continuous ring reactor at 39 g/H.
Et ₂ AICI in heptane solution (2mol/I) 0.30/
H, propylene 91 kg/H, ethylene 4 kg/H and hydrogen 4.1 NI/H were supplied, and continuous polymerization was carried out at 60°C. This crude polymer was washed with isobutanol, purified and dried to obtain a white powder. of the obtained polymer
MFI was 0.08 g/10 min, and ethylene content was 12.0 mol%. To 100 parts by weight of this random copolymer, the radical generator 2,5-dimethyl-2, in the amount shown in Table 1,
5-di(t-butylperoxy)hexane (Perhexa 2,5B-40 manufactured by NOF Corporation), tetrakis[methylene-3-(3',5'-di-t-butyl-4'-
hydroxyphenyl propionate methane
0.25 parts by weight and 0.1 parts by weight of calcium stearate were added, mixed in a Henschel mixer, and then extruded in an extruder at a temperature of 240°C to form pellets.
The MFI of this pellet was 5.1 g/10 min.
At this time, the MLMFI/MFI was 12.7, the block index in C 13 -NMR was 0.92, and the melting point was 126.8°C. This pellet contains 0.55% synthetic silica (anti-blocking agent) and oleic acid amide (slip agent).
0.30%, and a water-cooled inflation molding machine with a commonly used 40 mm diameter extruder, a die diameter of 100 mm, and a lip width of 0.8 mm, with a cooling water temperature of 25 °C, and a die temperature of 220 °C, and a thickness of 300 μm. , fold diameter is
A 190 mm tube-shaped film was obtained. This film was biaxially stretched by 3.5 times at 125° C. in a tubular form, and the resulting shrinkable film was evaluated. The results are shown in Table 1. Examples 2 and 3 and Comparative Examples 1 to 3 High molecular weight copolymer powders with different ethylene contents were produced in the same manner as in Example 1, except that the amount of ethylene supplied was changed. Thereafter, in exactly the same manner as in Example 1, an antiblocking agent and a slip agent were added to reduce the molecular weight, and then a shrink film was molded. The results are shown in Table 1. In addition, in Comparative Example 3, polymerization was carried out by changing the amount of hydrogen used,
Block index and undegraded molecular weight
An example where MLMFI/MFI exceeds the upper limit is shown. Example 4 A copolymer was produced in the same manner as in Example 1, except that in addition to ethylene being supplied at a rate of 4 kg/hr, butene-1 was also supplied at a rate of 4 kg/hr. The copolymer obtained had a butene content of 1.6 mol% and a melting point of 126°C. This copolymer was subjected to molecular weight reduction in the same manner as in Example 1, and a shrink film was formed. The results are shown in Table 1 below. Example 5 The same procedure as Example 1 was carried out except that the ethylene supply amount was changed to 3 kg/Hr and butene-1 was supplied at 3 kg/Hr, but the MFI was 0.08 g/10 min, the ethylene content was 9.6 mol%, and butene-1 was supplied at 3 kg/Hr. A polymer powder with a 1.3 mol % 1 content was obtained. In exactly the same manner as in Example 1, a shrink film was obtained after molecular weight reduction. The results obtained are shown in Table 1. Comparative example 4 Ethylene content is 7.4 mol%, MFI is 5.1 g/
10min, block index 3.7, MLMFI/MFI
A shrink film was obtained in the same manner as in Example 1 using a propylene-ethylene block copolymer of 19.6% (Showaromer MK311C, manufactured by Showa Denko K.K.). The results are shown in Table 1. [Table] * Comparison when adding the minimum amount of silica and amide to make the blocking index of the film 1}

Claims (1)

[Scope of Claims] 1. A polypropylene resin film for shrink wrapping, which is made by melt-extruding a propylene-ethylene random copolymer resin having the following properties (a) to (d) into a tube shape and biaxially stretching the resin. (a) Ethylene content determined by ^C13 -NMR method: 8~
14 mol% (b) Block index defined in the text calculated by C ¹³ -NMR method: 1.1 or less (c) MFI (230°C, load 2.16 kg): 0.5 to 15 g/min (d) MLMFI (230°C, load 2.16 kg): load 10.0Kg) and MFI (230
°C, load 2.16Kg) ratio MLMFI/MFI: 10~16