JPH0341335B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides T-
The present invention relates to a method for manufacturing a die-cast film, and more particularly to a method for manufacturing a T-die-cast film made of a polypropylene resin that has excellent film strength, particularly low-temperature impact resistance and heat sealability, and has good transparency. [Prior art and problems to be solved by the invention] The characteristics of polypropylene T-die cast film are already well known, but when used as a packaging material at low temperatures, especially at temperatures below 0°C. The disadvantage is that the 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 the T-die casting method is used, the problem arises that transparency is not achieved. In addition, it had the disadvantage that its heat sealability at low temperatures was significantly inferior to that of high-pressure polyethylene and linear low-density polyethylene. As described above, no polypropylene resin has been known that provides a film that is excellent in impact strength at low temperatures, heat sealability, and transparency. Therefore, an object of the present invention is to provide a method for producing a T-die cast film that has excellent strength, particularly film strength at low temperatures, transparency, and low-temperature heat sealability. [Means for solving the problems and their effects] According to the present invention, MFI (230°C, load 2.16Kg)
The following properties (a) to (d) were obtained by reducing the molecular weight of a propylene-ethylene random copolymer at a rate of 0.01 to 0.3 g/10 min.
A polypropylene resin T- consisting of a resin having
Manufactures die-cast film. (a) Ethylene content determined by C ¹³ −NMR method: 8.4~
15 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 50 g/
10min (d) MLMFI (230℃, load 10.0Kg) and MFI (230
°C, load 2.16Kg) ratio MLMFI/MFI: 10~
16 The term "block index" as used herein refers to the monomer sequence determined in triads by the C ¹³ -NMR method, and the fraction of ethylene added in a block manner, i.e., propylene unit: 1, ethylene unit: 0 [ (100) + (000)],
Sum of all triad fractions including ethylene [(101) +
The percentage divided by (100) + (000)] is [100-(100-
(Mole percentage of ethylene content) ^2/100 ]. Block index = (100) + (000) / (101) + (100) + (000) × 100
/100−[100−C _E (mol%)] ² /100 (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 8.4-15 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 contain 5 mol % or less of methyl-pentene-1, hexene-1, octene-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 8.4 to 15 mol%. Polypolymers and random copolymers with an ethylene content of less than 8.4 mol% are not preferred because they have poor cold resistance and low-temperature heat sealability even if other requirements are met. On the other hand, if the ethylene content exceeds 15 mol%, the blocking resistance of the film deteriorates, making it necessary to add a large amount of antiblocking agent (for example, silica, etc.), making it difficult to obtain a film with excellent transparency. This is not preferable as it will be difficult. 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 triads in C ¹³ -NMR, 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 (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 above-mentioned ethylene-propylene block copolymers and copolymers produced by low-temperature polymerization of high ethylene content copolymers or copolymers polymerized with special catalyst systems have block indexes larger than this value, and are called propylene-ethylene block copolymers. 3 for polymers
Takes a value greater than or equal to When the blocking index is greater than 1.1, the transparency and low-temperature heat sealing properties of the film decrease, and anti-blocking agents (such as silica)
Even if the amount of slip agent (for example, amide) is controlled, a good balance between transparency and anti-blocking property cannot be achieved, which is not preferable. The melt flow ratio of the copolymer used in the present invention, that is, MLMFI (230°C 10.0Kg load) and MFI
(230℃ 2.16Kg load) and 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, when a copolymer with an MFI of 0.09 g/10 min is subjected to molecular weight reduction by changing the amount of 1,3-bis(t-butylperoxyisopropyl)benzene used, the change in MLMFI/MFI after reduction is as follows. It 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 degradation is small, so that a desirable balance between transparency and low-temperature impact resistance is not achieved, and especially low-temperature impact resistance decreases. 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. MFI of the copolymer used in the present invention
(230° C., load 2.16 kg) must be 0.5 to 50 g/10 min, and if the MFI of the copolymer is outside the above range, it will be difficult to mold a T-die cast film. A particularly preferred MFI is 2 to 15 g/10 min. The MFI of the copolymer before degradation is generally 0.5.
g/10min is used, especially 0.01
~0.3g/10min is suitable. preferable
Instead of producing a copolymer in the MFI range (MFI = 0.5 to 50 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 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 peroxys such as 2,5-dimethyl 2,5-di(t-butylperoxy)hexane, 2,5-dimethyl 2,5-di(t-butylperoxy)hexane-3, lauroyl peroxide,
Examples include diacyl peroxides such as benzoyl peroxide, peroxy esters such as t-butyl peroxyacetate and t-butyl peroxylaurate, methyl ethyl ketone peroxide, and methyl isobutyl ketone peroxide. Furthermore, peroxides of polymers such as those produced by air oxidation, hydrogen peroxide,
Lithium peroxide or alkali or alkaline earth metal peroxides are also useful in the present invention if heated. 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 Therefore, in reality, the amount added is adjusted taking into account the MFI before and after degradation. 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 T-die cast film can be manufactured by a general manufacturing method.
It was melt-extruded at 250°C through a 0.7mm T-die onto a cooling roll at 25°C, and a film with a thickness of 60μ could be processed. T made of polypropylene resin according to the present invention
−Die-cast film has low-temperature heat sealability,
It has excellent low-temperature impact resistance and transparency, and is suitable for use as packaging materials, especially packaging materials for low-temperature preservation 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 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 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. (e) Heat-sealing strength A 15-mm-wide test piece was cut from a sample that was heat-sealed using a 5-mm-wide heat-sealing bar at 110°C under heat-sealing conditions of a heat-sealing pressure of 1 Kg/cm ² and a heat-sealing time of 1 second. The peel strength was measured at room temperature using a run tester at a tensile speed of 300 mm/min. 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) 39 g/H was placed in a 290 continuous ring reactor.
Et ₂ AlCl in heptane solution (2mol/) 0.30/
H, propylene 90 kg/H, ethylene 4 kg/H and hydrogen 4.0 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 0.07 g/10 min, and ethylene content was 12.4 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 form pellets.
The MFI of this pellet was 9.5 g/min. At this time, the MLMFI/MFI was 12.3, the block index in C ¹³ -NMR was 0.92, and the melting point was 126.3°C. This pellet contains 0.40% synthetic silica (anti-blocking agent) and oleic acid amide (slip agent).
0.25% was added and melt-extruded at 250°C on a cooling roll at 25°C through a commonly used extruder with a diameter of 40mm and a T-die with a slit gap of 0.7mm to obtain a film with a thickness of 60μ. 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 and 3 and Comparative Examples 1 to 5 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 anti-blocking agent and a slip agent were added to reduce the molecular weight, and a T-die film with a thickness of 60 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 4 A copolymer was produced in the same manner as in Example 1, except that in addition to the ethylene supply amount of 4 kg/hr, butene-1 was also supplied at 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 T-die 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 also 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 T-di film was obtained after molecular weight reduction. The results obtained are shown in Table 1. Comparative example 6 Ethylene content is 7.4 mol%, MFI is 5.1 g/
10min, block index 3.7, MLMFI/MFI
A T-die 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). The results obtained are shown in Table 1 below.

[Table] * Comparison when adding the minimum amount of silica and amide to make opening easier

Claims (1)

[Claims] 1 MFI (230℃, load 2.16Kg) is 0.01 to 0.3g/
Polypropylene-based resin T-
A method for producing a T-die cast film, the method comprising producing a die cast film. (a) Ethylene content determined by C ¹³ −NMR method: 8.4~
15 mol% (b) Block index defined in the text produced by C ¹³ -NMR method: 1.1 or less (c) MFI (230°C, load 2.16 kg): 0.5 to 50 g/
10min (d) MLMFI (230℃, load 10.0Kg) and MFI (230
°C, load 2.16Kg) ratio MLMFI/MFI: 10~
16