JPH0369925B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a water-cooled blown film, and more specifically to a water-cooled blown film using a propylene-ethylene copolymer that has excellent film strength, particularly low-temperature impact resistance, and good transparency. This invention relates to a film manufacturing method. The characteristics of polypropylene water-cooled inflation film are already well known;
When used as a packaging material at low temperatures, particularly below 0° C., it has the disadvantage that impact strength is significantly reduced.
A method of copolymerizing different types of comonomers in the form of a block has been proposed as a method for improving this drawback, but when a water-cooled inflation method is used, the problem arises that transparency is not achieved. What is more important is that the opening property of blown film, which is inversely correlated with transparency, is sufficient for practical use. ) No polypropylene resin has been known that provides a film that is excellent in all of the above. The inventors of the present invention have conducted intensive studies to develop a water-cooled blown film with excellent strength, particularly film strength ^at low temperatures, transparency, and anti-blocking properties. 17 mol%, block index described below is 1.1 or less,
MLMFI/MFI ratio 10-16 and MFI 1-30
The water-cooled blown film produced using a propylene-ethylene random copolymer with the property of Compared to,
The present invention was achieved by recognizing that the film strength is particularly excellent at low temperatures. In the method for producing a water-cooled blown film according to the present invention, the ethylene unit content obtained by random copolymerization in the presence of a Ziegler type catalyst is 6 to 17 mol%, and the propylene unit content is 6 to 17 mol%, as determined by C ¹³ -NMR method. 83 to 94 mol% and α- having 4 or more carbon atoms
Olefin unit content is 0-5 mol%, MFI is
A propylene-ethylene random copolymer (hereinafter referred to as "propylene-ethylene random copolymer") having the properties (a) to (d) below, which is obtained by reducing the molecular weight of a propylene-ethylene copolymer with a yield of less than 0.5 g/10 min in the presence of a radical generator (sometimes simply called a copolymer) is formed by water-cooled inflation molding. (a) Ethylene unit content determined by C ¹³ −NMR method:
6 to 17 mol%, propylene unit content 83 to 94 mol%, and α-olefin unit content having 4 or more carbon atoms 0 to 5 mol% (b) Block index defined below calculated by C ¹³ -NMR method: 1.1 Below Block index = (100) + (000) / (101) + (100) + (000) × 1
00/100 - [(100 - C _E ) ² /100] [In the formula, 0 is ethylene unit, 1 is propylene unit, C _E indicates ethylene content (mol%)] (c) MFI (230℃, load 2.16Kg): 1 to 30g/min (d) MLMFI (230℃, load 10.0Kg) and MFI (230
℃, load 2.16 kg) MLMFI/MFI: 10 to 16 The term "block index" used in this specification refers to the monomer sequence determined in triads by ^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-ethylene content molar percentage] Refers to the value divided by ² . Block index = (100) + (000) / (101) + (100) + (000) × 1
00/100-[100-C _E (mol%)] ² (Note) However, C _E indicates the ethylene content (mol%). 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 6-17 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. In addition to ethylene, the propylene-ethylene random copolymer referred to in the present invention includes α-olefins having 4 or more carbon atoms, such as butene-1,4-methyl-pentene-1, hexene-1, octene-1, It is also possible to contain 5 mol% or less of 1 etc. 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 6 to 17 mol%. Homopolymers and random copolymers with an ethylene content of less than 6 mol % are not preferred because they have poor cold resistance even if other requirements are met. On the other hand, when the ethylene content exceeds 17 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 block 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 as a block to the sum of the fractions of all triads containing ethylene is almost 0 at low ethylene contents (3 mol% or less); 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 propylene-ethylene block copolymers and copolymers with high ethylene content that are polymerized at low temperatures or polymerized using special catalyst systems have block indexes larger than this value, resulting in block copolymers. Then it takes a value of 3 or more. 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 is
It is important that it is between 10 and 16. The MLMFI/MFI ratio of commercially available common propylene-ethylene copolymers 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 0.09g/10min is 1.3
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/
10 to 14 around 10min, 10 around 50g/10min
It can be said that it is ~12. When the MLMFI/MFI ratio exceeds 16, the degree of molecular weight deterioration is small, and a desirable balance between transparency, low-temperature impact resistance, and blocking resistance cannot be achieved.On the other hand, when the ratio is less than 10, the degree of molecular weight deterioration is very small. , a large amount of radical generator is required, and color,
This causes problems such as odor. The MFI (230°C, load 2.16 kg) of the molecular weight reduced copolymer used in the present invention is 1 to 30
g/10min, and the copolymer
If the MFI is outside the above range, it will be difficult to form a water-cooled inflation film. The preferred MFI is 2
~15g/10min. 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 (1-60)
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. 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 the same 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)hexine-3, lauroyl peroxide, 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. Furthermore, polymeric peroxides such as those produced by air oxidation, hydrogen peroxide, lithium peroxide, or alkali or alkaline earth metal peroxides are also effective in the present invention if heated. Others, for example,
Azo compounds such as α,α'-azobis-(isobutyronitrile) are also used as free radical generators. The amount of the radical generator added is an important factor in determining the MFI of the composition of the present invention, and the amount added is 0.001 to 2% by weight based on the polyolefin.
Preferably, the amount is 0.01 to 0.5% by weight; if it is too small, the effect of the addition will not be exhibited, and if it is too large, the degree of decomposition will be excessive, which is not preferable. Therefore, in reality, considering MFI before and after decline,
Adjust the amount added. 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. The manufacturing method of water-cooled inflation film is as follows:
Can be made using a general manufacturing method, for example, a commonly used extruder with a diameter of 40 mm and a die diameter
A water-cooled inflation molding machine with a diameter of 100 mm and a lip width of 0.8 mm has a cooling water temperature of 25°C.
At 220°C, a tubular film with a thickness of 30 μm and a folded diameter of 190 mm could be obtained. The water-cooled inflation film made of the polypropylene resin according to the present invention has excellent blocking resistance, low-temperature impact resistance, and transparency, and is suitable for use as packaging materials, especially packaging materials for low-temperature storage of foods 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, impact strength, and openness 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 10.0
The value of Kg is called MLMFI. (b) Film haze Measured using a haze meter according to ASTM-D-1003-61. (c) Ethylene content Measured using JEOL'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 count 10000 or more Temperature: 100℃ The 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) Impact strength Impact strength was measured in a constant temperature room at -5°C using a TTS impact tester manufactured by Toyo Seiki Co., Ltd. (d) Openability The amount of silica added was adjusted so that the cut end of the film could easily open after 5 minutes of molding. 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 kg of γ-butyrolactone) was placed in a 290 continuous ring reactor at 39 g/H.
Et ₂ AlCl in heptane solution (2mol/) 0.30/
H, propylene 91 kg/H, ethylene 4 kg/H and hydrogen 4.1 Nl/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 using a Henschel mixer, and then extruded using an extruder at a temperature of 240°C to produce 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 30 μm. , fold diameter is
A 190 mm tube-shaped film was obtained. The haze, ethylene content, and impact strength of this sample were measured using the methods described above. The results are shown in Table 1 below. Examples 2 to 4 and Comparative Examples 1 to 4 High molecular weight copolymer powders having 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 a water-cooled blown film having a thickness of 30 μm was obtained. 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 in which MLMFI/MFI exceeds the upper limit is shown, and Comparative Example 4 has a small degree of molecular weight degradation and MLMFI/MFI
Here is an example where exceeds the upper limit. Example 5 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 water-cooled inflation film was formed. The results are shown in Table 1 below. Example 6 The same procedure as in Example 1 was carried out except that the ethylene supply rate 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 water-cooled blown film was obtained after molecular weight reduction. The results obtained are shown in Table 1. Comparative Example 5 Ethylene content is 7.4 mol%, MFI is 5.1 g/
10min, block index 3.7, MLMFI/MFI
A water-cooled blown film was formed in the same manner as in Example 1 using a propylene-ethylene block copolymer of 19.6 (Showa Denko Co., Ltd. Showa Allomer MK311C). The results obtained are shown in Table 1 below. Compared to the case with low ethylene content (Comparative Example 2),
It is clear that very high low-temperature impact strength is obtained in Example 3 according to the present invention. Furthermore, when compared at the same ethylene content, the block index and MLMFI/
The material having MFI (Example 3) has significantly improved low-temperature impact impact strength compared to Comparative Example 2.

[Table] * Comparison when adding the minimum amount of silica and amide that makes opening easier.

Claims (1)

[Scope of Claims] 1. Obtained by random copolymerization in the presence of a Ziegler type catalyst, the ethylene unit content as determined by C ¹³ -NMR method is 6 to 17 mol%, and the propylene unit content is 83 to 94 mol%. , and the content of α-olefin units having 4 or more carbon atoms is 0 to 5 mol%, and the MFI is 0.5 g/
A propylene-ethylene random copolymer having the properties (a) to (d) below, which is obtained by reducing the molecular weight of a propylene-ethylene copolymer for less than 10 min in the presence of a radical generator, is water-cooled and inflation-produced. A method for producing a water-cooled inflation film, which is characterized by forming the film. (a) Ethylene unit content determined by C ¹³ −NMR method:
6 to 17 mol%, propylene unit content 83 to 94 mol%, and α-olefin unit content having 4 or more carbon atoms 0 to 5 mol% (b) Block index defined below calculated by C ¹³ -NMR method: 1.1 Below Block index = (100) + (000) / (101) + (100) + (000) × 1
00/100 - [(100 - C _E ) ² /100] [In the formula, 0 is ethylene unit, 1 is propylene unit, C _E indicates ethylene content (mol%)] (c) MFI (230℃, load 2.16Kg): 1 to 30g/min (d) MLMFI (230℃, load 10.0Kg) and MFI (230
°C, load 2.16Kg) MLMFI/MFI: 10 to 16