JPH0214899B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene composite film, and more particularly to a polypropylene composite film that uses a resin with excellent low-temperature heat sealability and has excellent heat sealability and transparency. Crystalline polypropylene films, especially biaxially oriented films, are excellent in optical properties such as transparency and gloss, mechanical properties such as rigidity and tensile strength, and are odorless and non-toxic. It is especially widely used as a food packaging material. However, polypropylene film units have drawbacks in that the temperature at which heat sealing can be performed is high and sufficient sealing strength cannot be obtained. In order to improve these drawbacks, for example, (1) a method of coating one or both sides of a biaxially oriented polypropylene film with a resin having easy heat-sealability as a solution or emulsion; (2) a method of coating polypropylene on one or both sides of a biaxially oriented polypropylene film; A known method is to manufacture a bonded film by bonding easily heat-sealable resins to form a uniaxially or biaxially stretched film before stretching.
Among these, method (2) does not require coating, drying, or solvent recovery equipment unlike coated film (1), is low in cost, and has relatively high sealing strength. There are many cases where method (2) is adopted. The resin used in method (2) to improve heat-sealability must have an excellent balance of major properties such as low-temperature heat-sealability, transparency, and scratch resistance. Many resins have been proposed for various applications. For example, JP-A No. 52-11281 and JP-A No. 52-11281,
As seen in Publication No. 11282, such compositions can be obtained by mixing not only propylene-ethylene-butene terpolymer but also propylene-ethylene random copolymer or propylene-butene copolymer with polybutene-1. There are many attempts to do so. However, although a blend of a propylene copolymer and a different type of polymer (crystalline polyptene) may improve low-temperature heat sealability, it is not preferred in terms of transparency. Further, an example of using a propylene-ethylene random copolymer whose molecular weight has been reduced as a laminated film can be found in JP-A-55-133962. This has an ethylene content of 1-7% by weight and an MFI of 0.5-30g/
The copolymer was degraded for 10 min so that the melt flow ratio (ratio of flow rate between a load of 2160 g and a load of 325 g at 2.60°C) was 12 or less, and the heat of the laminated film obtained by this method The sealing temperature and heat sealing temperature are not necessarily fully satisfactory. On the other hand, JP-A-55-14223 reports that with regard to propylene-ethylene copolymers used as heat-sealing films, simply increasing the ethylene content deteriorates blocking resistance and does not improve transparency. There is. In fact, the inventors
A propylene-ethylene copolymer with an MFI of 10.3 g/10 min, an ethylene content of 11.7 mol%, and an MLMFI/MFI ratio of 19.6 was produced without directly reducing the molecular weight by polymerization (see Comparative Example 2), but the blocking resistance and In terms of transparency, it was significantly inferior to the propylene-ethylene random copolymer used in the present invention. The present inventors have demonstrated that they satisfy all the physical properties required for a heat-sealing laminated film made of biaxially oriented polypropylene (hereinafter sometimes referred to as OPP), including heat-sealing properties, blocking resistance, transparency, and high-speed moldability. As a result of careful study of the film that can be used, we found that the ethylene content measured by ^C13 -NMR
17 mol%, block index described below is 1.1 or less,
MLMFI/MFI ratio 10-16 and MFI 1-60
The present invention was achieved based on the recognition that a propylene-ethylene random copolymer film having a characteristic of g/10 min exhibits specific excellent performance in the above-mentioned desired physical properties. The polypropylene film according to the present invention is
It consists of a layer containing crystalline polypropylene and a propylene-ethylene random copolymer resin layer having the following properties (a) to (d) bonded to at least one side of the layer. (a) Ethylene content determined by C ¹³ −NMR method: 10~
17 mol% (b) Block index defined below calculated by C ¹³ -NMR method: 1.1 or less (c) MFI (230°C, load 2.16 kg): 1 to 60 g/min (d) MLMFI (230°C, load 10.0Kg) and MFI (230
°C, load 2.16Kg) ratio MLMFI/MFI: 10~
Consists of 16. The term "block index" used in the present invention refers to the monomer sequence determined in triads by the C ¹³ -NMR method, and the fraction of ethylene added in a block manner, that is, propylene unit: 1, ethylene unit: 0 [( 100) + (000)],
Sum of all triad fractions including ethylene [(101) +
(100) + (000)] divided by 100 - [100 - ethylene content molar percentage] ² . Block index = (100) + (000) / (101) + (100) +
(000)×100/100−[100−C _E (mol%)] ² 〓 However, C _E indicates the ethylene content (mol%). As described above, according to the present invention, since the propylene-ethylene random copolymer as described above is used as the heat-sealing layer, it has excellent heat-sealability, scratch resistance, blocking resistance, transparency, and high-speed moldability. A polypropylene-based composite film is provided. The copolymer used as the heat seal layer 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. It is obtained by obtaining a copolymer having a content of 10 to 17 mol % and an MFI of 0.01 to 0.3 g/10 min, and then reducing its molecular weight in the presence of a radical generator. Furthermore, in addition to ethylene, it is possible to contain 5 mol % or less of α-olefin having 4 or more carbon atoms, such as butene-1,4-methyl-pentene-1, hexene-1, octene-1, and the like. The copolymer used as the heat-sealing layer of the composite film of the present invention needs to have an ethylene content (hereinafter simply referred to as ethylene content) of 10 to 17 mol% as determined by ^C13 -NMR method.
Homopolymers and random copolymers with an ethylene content of less than 10 mol% are not preferred because they have poor low-temperature heat sealability. Regarding low-temperature heat sealability, it mainly depends on the melting point of the resin used, but the melting point of homopolymers is approximately 160℃;
If the ethylene content is less than 10 mol%, the temperature will exceed 135℃,
Heat seal temperature improvement is insufficient. On the other hand, if the ethylene content exceeds 17 mol%, the films tend to stick together, making it necessary to add a large amount of anti-blocking agent, etc., making it difficult to obtain a film with excellent transparency, which is preferable. do not have. Furthermore, it is preferable for a heat-sealing film that the ethylene content shown above is more uniformly distributed in the copolymer. It is unsuitable as a heat seal film. 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 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, it is difficult to maintain a good balance between transparency and blocking resistance. This is not preferable because it does not reach . In the present invention, the MLMFI of the copolymer (230°C
It is important that the flow rate ratio MLMFI/MFI of 10.0Kg load) and MFI (230°C 2.16Kg load) is 10 to 16. The MLMFI/MFI ratio of commercially available common propylene-ethylene copolymers is 18-25. Accordingly
MLMFI/MFI can also be considered to represent the degree of molecular weight degradation. For example, MFI is 0.09g/
When the molecular weight of the copolymer was reduced for 10 minutes by changing the amount of 1.3bis(t-butylperoxyipropyl)benzene used, the changes in MLMFI/MFI after reduction are 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 of transparency, blocking resistance, heat sealability, etc. cannot be achieved.On the contrary, when the ratio is less than 10, the degree of molecular weight deterioration is small. It is very large and requires a large amount of radical generator,
Problems with color, odor, etc. occur. The MFI of the molecular weight reduced copolymer used as the heat seal layer is 1 to 60 g/10 min,
Preferably it is 5-20g/10min. The MFI of the copolymer before degradation is generally lower than 0.5 g/10 min, and particularly preferably 0.01 to 0.3 g/10 min. Normal MFI area (MFI0.5~
High molecular weight copolymer (MFI approx. 0.01-0.3g/10min) without directly polymerizing the copolymer (60g/10min)
Why does a film with a molecular weight reduction and an MLMFI/MFI ratio of 10 to 16 have good transparency, anti-blocking properties, and
Although it is not clear whether heat sealability or the like is superior, it is assumed as follows. When various polymers produced by changing the MFI of propylene-ethylene copolymer with an ethylene content of 12.3 mol% were tested for isobutyl alcohol-soluble content and hexane-soluble content in powder, the alcohol-soluble content was generally It was confirmed that it was extracted in proportion to the amount of low molecular weight, and in hexane, it was extracted in proportion to the crystallinity (ethylene content) in addition to the 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 would be reasonable to assume that the amount of low crystallinity areas was drastically reduced. In high molecular weight copolymers (MFI: 0.01 to 0.3), the distribution of the comonomer ethylene in the polymer is considered to be more uniform even with the same ethylene content compared to copolymers with normal MFI (1 to 60). 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, cyclomyl peroxide,
Dialkyl peroxides such as 2,5-dimethyl 2,5-di(t-butylperoxy)hexane, 2,5-dimethyl 2,5-di(t-butylperoxy)hexyne-(3), lauroylper oxide, diacyl peroxides such as benzoyl peroxide, t-butyl peroxyacetate, t
Examples include peroxy esters such as -butyl peroxylaurate, ketone peroxides such as methyl ethyl ketone peroxide, and methyl isobutyl ketone peroxide.
Additionally, polymeric peroxides such as those produced by air oxidation, hydrogen peroxide, lithium peroxide, or alkali or alkaline earth peroxides are useful in the process of the present invention if heated. In addition, azo compounds such as α,α-azobis-(isobutyronitrile) can also be 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, preferably 0.01 to 0.5% by weight, based on the polyolefin. The effect of addition is not exerted, and too much of it increases the degree of decomposition, which is not preferable. 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 copolymer and radical generator according to the present invention, various auxiliary components that are commonly blended, such as antioxidants, ultraviolet deterioration inhibitors, antiblocking agents, slip agents, antistatic agents, colorants, etc. It can contain. Crystalline polypropylene as a substrate forming the film to which the above copolymers are to be bonded has a density of
0.89-0.92g/cc, 0.1-50 as MFI, boiling n-
It is a homopolymer with a heptane insoluble content of 85 to 99.5% or a copolymer with a small amount of ethylenically unsaturated monoolefin. Antioxidants, ultraviolet absorbers, antiblocking agents, slip agents, antistatic agents, etc. may be added to the crystalline polypropylene as necessary to improve its performance as a film. Furthermore, a small amount of different polymers may be mixed to the extent that the transparency of the film is not impaired. Examples of such polymers include low-density polyethylene, high-density polyethylene, ethylene-propylene copolymer rubber, polybutene, petroleum resin, etc. These polymers contain, for example, 1 to 10% by weight of polypropylene. can be incorporated into a containing layer. Next, a composite film consisting of the above-mentioned base material and a copolymer as a heat-sealing layer can be produced using a conventional method. For example, the copolymer is bonded in a molten state to one or both sides of a crystalline polypropylene film. After bonding, it may be unstretched or uniaxially or biaxially stretched. Further, the crystalline polypropylene film layer which is the base material layer has a thickness in the range of 5 to 200μ, preferably 5 to 70μ, and the heat seal layer has a thickness in the range of 0.1 to 200μ.
100μ, preferably in the range of 0.3 to 0μ. In some cases, it can also be produced by a method of co-extruding crystalline polypropylene and a heat-sealing layer. The polypropylene composite film according to the present invention has superior high-speed moldability and can be laminated extremely uniformly compared to conventional films, and maintains high heat sealability and transparency of the film. The polypropylene composite film of the present invention is suitable for uses such as food packaging, clothing packaging, and textile packaging. 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. Heat sealability, haze, MFI and
MLMFI was measured by the following method. (a) Heat-sealability A 25-mm-wide test piece was taken from a sample that was heat-sealed using a heat-sealing bar with a width of 5 mm under heat-sealing conditions of a heat-sealing pressure of 1 Kg/cm ² and a heat-sealing time of 1 second at each set temperature. Peeling strength was measured at room temperature using an Instron testing machine at a tensile speed of 50 mm/min. The intensity at each temperature was plotted and expressed as (A) the temperature at which the curve reached 500 g and (B) the temperature at which the curve reached 300 g. (b) Film haze Measured using a haze meter according to ASTM-D-1003-61. (c) 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. (d) 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. 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, add the radical generator 2,5-dimethyl-
2,5-di(t-butylperoxy)hexane (Perhexa 2,5B-40 manufactured by NOF Corporation), tetrakis[methylene-3-(3',5'-di-t-butyl-4'- Hydroxyphenyl propionate] 0.15 parts by weight of methane, calcium stearate
Add 0.1 part by weight of oleic acid amide in the amount listed in Table 1 and fine powder silica in the amount listed in Table 1, mix with a Henschel mixer, and then heat to 240°C with an extruder.
Pellets were prepared by extrusion at ℃. The MFI of this pellet was 11.0 g/10 min. At this time
The MLMFI/MFI was 12.1, the block index in ^C13 -NMR was 0.92, and the melting point was 127.1°C. MFI2.3g/10min and boiling heptane extractor 97.6
% polypropylene sheet was subjected to short stretch stretching of substantially 5 times at a temperature of 140° C. between two sets of nip rolls having different circumferential speeds. The resin described above was then laminated onto the uniaxially stretched isotactic polypropylene sheet at a resin temperature of 250° C. using a small extruder. The two-layer sheet thus obtained was stretched in the transverse direction at a tenter temperature of 160°C to an effective magnification of 8 times, and subjected to tension heat treatment at 120°C for 3 seconds to obtain a two-layer biaxially stretched film. . The thickness of the base material layer of the obtained composite film was 30μ, and the thickness of the heat seal layer was 2μ. The heat-sealing temperature, heat-sealing strength, and haze of this sample were measured using the methods described above. The results are shown in Table 1 below. Comparative Example 1 Example 1 except that the ethylene feed amount was changed
Similarly, when the ethylene content is 8.0 mol% and the MFI is
A purified white powder of 0.08g/10min was obtained. Example 1
Similarly, by mixing and extruding the radical initiator,
Pellets having an MFI of 10.9/10 min, an MLMFI/MFI of 12.3, and a block index of 0.94 were obtained, laminated onto a polypropylene sheet in the same manner as in Example 1, and stretched to obtain a biaxially stretched film. The results are shown in Table 1 below. Comparative Example 2 82g/H of titanium trichloride composition and ethylene
MFI was 10.3 g/H in the same manner as in Example 1 except that hydrogen was 132 Nl/H and continuous polymerization was carried out at 40°C.
After 10 min, a white powder with an ethylene content of 10.7 mol% (partially attached) was obtained. No radical generator is added to this product. Other additives were added in the same manner as in Example 1, and pelletized to give an MFI of 10.6 g/10 min.
Pellets with MLMFI/MFI of 19.6 and block index of 1.21 were obtained. A composite film was produced from this pellet in the same manner as in Example 1, and its performance was evaluated. The results were as shown in Table 1 below. Comparative Example 3 Propylene-ethylene block copolymer (Showa Denko Shoromer SK711, ethylene content = 12.2
0.12% by weight of the same radical generator as in Example 1 was added to mol%, MFI = 0.83g/10min), and Example 1
I pushed it out in the same way. MFI of pellets is 12.4
g/10min, MLMFI/MFI was 14.6, and block index was 4.1. A composite film was produced from this pellet in the same manner as in Example 1, and its performance was evaluated. The results were as shown in Table 1 below. Comparative example 4 Without supplying ethylene, hydrogen supply amount was 130Nl/H
A propylene homopolymer having an MFI of 13.0 was obtained in the same manner as in Example 1 except that Next, a composite film was produced in the same manner as in Example 1, and its performance was evaluated. The results were as shown in Table 1 below. Comparative Example 5 A copolymer having an MFI of 24, an ethylene content of 6.5 mol%, and a block index of 0.90 was obtained in the same manner as in Example 1, except that ethylene was changed to 2 kg/H and hydrogen was changed to 290 Nl/H. Next, a composite film was produced in the same manner as in Example 1, and its performance was evaluated. The results were as shown in Table 1 below. Example 2 A copolymer having an MFI of 0.15, an ethylene content of 10.8 mol%, and a block index of 0.90 was obtained in the same manner as in Example 1, except that the ethylene content was 3.5 Kg/H and the hydrogen content was 5.7 Nl/H. Next, a composite film was produced in the same manner as in Example 1, and its performance was evaluated. The results were as shown in Table 1 below. Example 3 A copolymer having an MFI of 0.04, an ethylene content of 14.2 mol%, and a block index of 0.96 was obtained in the same manner as in Example 1, except that the ethylene content was 4.8 Kg/H and the hydrogen content was 2.5 Nl/H. Next, a composite film was produced in the same manner as in Example 1, and its performance was evaluated. The results were as shown in Table 1 below. Example 4 In the same manner as in Example 1 except that 6 kg/h of butene-1 was further supplied as a comonomer in addition to the ethylene supply, MFI was 0.10, ethylene content was 11.5 mol%, blocking index was 0.91, and butene content was A copolymer with a concentration of 2.8 mol % and a melting point of 124°C was obtained. Next, a composite film was produced in the same manner as in Example 1, and its performance was evaluated. The results were as shown in Table 1 below.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A polypropylene-based composite film comprising a layer containing crystalline polypropylene and a propylene-ethylene random copolymer resin layer having the following properties (a) to (d) bonded to at least one side of the layer. (a) Ethylene content determined by C ¹³ −NMR method: 10~
17 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): 1 to 60 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