JPH025182B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polypropylene multilayer biaxially stretched film that has excellent tear resistance, particularly tear propagation resistance. Polypropylene film has excellent gloss and transparency, and has properties such as extremely high moisture resistance, moderate stiffness, and heat resistance that can withstand boiling, so it is used mainly in the light packaging field, such as food, It is used as a protective film in all fields such as textiles, industrial materials, and chemicals. Among these, biaxially oriented polypropylene film (hereinafter referred to as OPP) is the most commonly used polypropylene film these days because it has improved physical properties such as strength, cold resistance, and moisture resistance compared to unoriented film. however
OPP's tear resistance is excellent without notches, but once a notch or tear occurs, it tears easily. That is, it has the disadvantage of poor tear propagation resistance. A possible method for improving the tear propagation resistance of OPP is to add a rubbery substance such as an amorphous ethylene-propylene copolymer or polyisobutylene to polypropylene.
There is a risk that the original characteristics of OPP, such as transparency and rigidity, may be impaired. Another option is to attach polyethylene to OPP, but simply attaching OPP and polyethylene does not have adhesive properties, so there is a risk of them peeling off during use. Therefore, the present inventor investigated the development of a film that has excellent interlayer adhesion and tear propagation resistance, and also has the transparency, rigidity, and scratch resistance inherent to OPP, and as a result, arrived at the present invention. That is, in the present invention, the intermediate layer is made of ethylene having a density of 0.870 to 0.940 g/cm ³ , a melting point of 50 to 130°C, and an ethylene content of 75 to 97% by weight, and a carbon number of 4.
or 20 random copolymers with α-olefins
(A), or a propylene content of 55 to 80% by weight;
The heat of crystal fusion is 10 to 80 Joule/g and the melting point is 100 to 130℃ based on thermal analysis using a differential scanning calorimeter.
A random copolymer (B) of propylene and an α-olefin having 4 to 10 carbon atoms, and a copolymer with a lower melting point than the polypropylene resin (C) that is the surface layer, and the polypropylene resin that is the surface layer. The present invention provides a polypropylene multilayer biaxially stretched film, characterized in that (C) is biaxially stretched, and has excellent interlayer adhesion and tear propagation resistance, as well as transparency, rigidity, and scratch resistance. The ethylene/α-olefin random copolymer (A), which is one of the copolymers used for the intermediate layer of the multilayer biaxially stretched film of the present invention, has a density of 0.870 to
0.940g/cm ³ , preferably 0.880 to 0.930g/
cm ³ , melting point 50 to 130℃, preferably 60 to 130℃
125°C, an ethylene content of 75 to 97% by weight, preferably 78 to 95% by weight and a melt flow rate (ASTM D1238:E) of 0.5 to 20g/
Ethylene and α of 4 to 20 carbon atoms in the range of 10 min
- Random copolymers with olefins, preferably 4 to 18 α-olefins. density is
If it is less than 0.870 g/cm ³ , the interlayer adhesive strength is excellent, but the effect of improving tear propagation resistance is poor, and the rigidity of the multilayer biaxially stretched film decreases. Density is 0.940g/ ^cm3
If it exceeds the above, the interlayer adhesion will be poor and interfacial peeling will occur from the surface layer. Those with a melting point of less than 50°C have little effect on improving tear propagation resistance and are poor in heat resistance, while those with a melting point of more than 130°C have poor interlayer adhesion and cause interfacial peeling from the surface layer, which is undesirable. Ethylene content is correlated with density and melting point; ethylene content less than 75% by weight has little effect on improving tear propagation resistance, and more than 97% by weight has poor interlayer adhesion. Further, the ethylene/α-olefin copolymer (A) of the present invention preferably has a melt flow rate of 0.5 to 20 g/10 min. Those having a melt flow rate outside the above range tend to have poor moldability. Specifically, α-olefin having 4 to 20 carbon atoms includes, for example, 1-butene, 1-pentene,
1-hexene, 4-methyl-1-pentene, 1-
Octene, 1-decene, 1-hexadecene, 1-
octadecene or a mixture thereof,
Copolymers with propylene have little effect on improving tear propagation resistance. In the present invention, the melting point of the ethylene/α-olefin copolymer (A) is the highest temperature at the point showing the endothermic peak determined from the endothermic curve measured by a differential scanning calorimeter (DSC) at a heating rate of 10°C/min. It is about. Some of the ethylene/α-olefin random copolymers (A) used in the present invention have not only one but a plurality of endothermic peaks. The ethylene/α-olefin random copolymer (A) used in the present invention is prepared by mixing ethylene and α-olefin to the required density using a known method, that is, a so-called medium-low pressure method using a transition metal catalyst. It can be obtained by polymerizing at a certain ratio. In this case, a molecular weight regulator such as hydrogen may be used to obtain the desired melt flow rate. Polymerization can be carried out by various methods such as slurry polymerization, gas phase polymerization, and high temperature solution polymerization. Propylene/α-olefin random copolymer (B) is another copolymer used in the intermediate layer of the present invention.
Propylene content 55 to 80% by weight, preferably
60 to 75% by weight, heat of crystal fusion based on DSC of 10 to 80 Joule/g, preferably 20 to 80 Joule/g.
70Joule/g, melting point 100 to 130℃, preferably 105 to 125℃, and melt flow rate (ASTM D1238:L) 0.5 to 30g/10min
It is a random copolymer (B) of propylene in the range of If the propylene content is less than 55% by weight, the effect of improving tear propagation resistance will be small and the heat resistance will be poor. If the propylene content exceeds 80% by weight, the melting point of Since the difference is small, when biaxially stretched, the intermediate layer is also stretched, and the effect of improving tear propagation resistance becomes small. The heat of crystal fusion has a value that correlates with the degree of crystallinity of the copolymer, but the heat of crystal fusion is
Those exceeding 80 Joule/g are copolymerized components α
-The transparency is poor because the amount of olefin is small or α-olefin is copolymerized in a block manner. On the other hand, when the heat of crystal fusion is less than 10 Joule/g, the effect of improving tear propagation resistance is small and the heat resistance is also poor. There is almost a correlation between the melting point and the propylene content,
Those with a melting point of less than 100°C have a small effect of improving tear propagation resistance and are poor in heat resistance, and those with a melting point of over 130°C have a small effect of improving tear propagation resistance. The heat of crystal fusion of the propylene/α-olefin random copolymer (B) in the present invention is measured using the specific heat curve of the copolymer in a completely molten state obtained by DSC (preferably at a temperature of 160°C or higher and 240°C or lower). This is a value calculated using a straight line obtained by directly extrapolating the specific heat curve (shown) to the low temperature side as a baseline. The melting point and heat of crystal fusion are 2000 for the copolymer.
After leaving at ℃ for 5 minutes, cool to -40℃ at a rate of 10℃/min, leave at -40℃ for 5 minutes, and heat from -40℃ to 200℃ at a temperature increase rate of 20℃/min. These are the temperature and endothermic area of the endothermic peak determined from the endothermic curve obtained. Propylene/α-olefin random copolymer
(B) with a melt flow rate of less than 0.5/10 min has a high melt viscosity and poor moldability, and has a melt flow rate of 300 g/10 min.
If it exceeds 10 min, the mechanical strength is low and the effect of improving tear propagation resistance is small. The propylene/α-olefin random copolymer (B) used in the present invention is, for example, (a) a composite containing at least magnesium, titanium, and halogen, (b) an organic compound containing metals from Groups 1 to 3 of the periodic table. It is obtained by random copolymerization of propylene and α-olefin using a catalyst formed from a metal compound and (c) an electron donor. Part or all of the electron donor (c) may be immobilized to part or all of the complex (a), or may be pre-contacted with the organometallic compound (b) prior to use. Good too. Particularly preferred is an embodiment in which a part of the electron donor (c) is immobilized on the complex (a), and the remainder is added to the polymerization system as it is or is used after being brought into preliminary contact with the organometallic compound (b). be. In this case, the electron donor immobilized on the complex (a) and the electron donor used by directly adding it to the polymerization system or by pre-contacting it with (b) may be the same or different. It's okay. The polypropylene resin (C) used in the surface layer of the multilayer biaxially stretched film of the present invention is a propylene homopolymer or a propylene-based polymer containing propylene and other α-olefins, such as ethylene, 1-
It is a random copolymer with butene, 4-methyl-1-pentene, 1-hexene, etc., containing 60% by weight or more, preferably 90% by weight or more of propylene, and is a crystalline resin. Among these, a propylene homopolymer is preferred because it has excellent transparency, scratch resistance, and rigidity. The multilayer biaxially stretched film of the present invention is characterized in that the melting point of the ethylene/α-olefin random copolymer (A) or the propylene/α-olefin random copolymer (B) that is the intermediate layer is the polypropylene base layer that is the surface layer. It is necessary to select and combine copolymers whose melting point is lower than that of the resin (C), preferably by 30°C or more. If copolymers (A) and (B) that form the intermediate layer have the same melting point or higher than the melting point of the polypropylene resin (C) that forms the surface layer, when biaxially stretched by the method described below, the intermediate layer Even the layers are oriented, and tear propagation resistance is not improved. The ethylene/α-olefin random copolymer (A), propylene/α-olefin random copolymer (B) and polypropylene resin used in the present invention
For (C), weather-resistant stabilizers, heat-resistant stabilizers, antistatic agents, slip agents, anti-blocking agents, lubricants, pigments, dyes, antifogging agents, etc. are added to ordinary polyolefins, either individually or in whole. Various compounding agents may be added within the range that does not impair the purpose of the present invention. In order to obtain the multilayer biaxially stretched film of the present invention, the ethylene/α-olefin random copolymer (A)
Alternatively, the propylene/α-olefin random copolymer (B) and polypropylene resin are each melted in separate extruders and coextruded by feeding them into a three-layer die so that (A) or (B) forms the middle layer. There are two methods: biaxial stretching of a three-layer film, extrusion lamination of (A) or (B) on a pre-obtained polypropylene resin film, and sandwich lamination. Biaxial stretching may be performed before lamination, or biaxial stretching may be performed after lamination. Among these, the coextrusion method is preferred because the process is simple and a multilayer biaxially stretched film with excellent interlayer adhesive strength can be obtained.
The biaxial stretching method may be either sequential stretching or simultaneous stretching at the temperature at which polypropylene resins are normally stretched, for example, 140 to 160°C. The multilayer biaxially stretched film of the present invention has transparency, scratch resistance, rigidity, etc., which are characteristics of polypropylene resin, and has excellent tear propagation resistance, so it is suitable for use in high-grade fiber packaging, food packaging, and heavy miscellaneous goods packaging. It is. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples as long as the gist of the present invention is not exceeded. Example 1 Polypropylene with a melt flow rate of 7.5 g/10 min (ASTM D1238: L) and a melting point of 161°C as a polypropylene resin (C) (trade name: Mitsui Petrochemical Polypro F600 manufactured by Mitsui Petrochemical Industries KK: hereinafter abbreviated as PP-) is an ethylene α-olefin random copolymer (A) with a melt flow rate of 4.0 g/10 min, a density of 0.886 g/cm ³ , a melting point of 69°C, and an ethylene content of 80.2% by weight.
Butene random copolymer (hereinafter abbreviated as EBC-)
Using a 60mmφ extruder (setting temperature: 270
°C) and EBC- are melted in a 45 mmφ extruder (set temperature: 240 °C) and then fed to a three-layer T-die with EBC- as an intermediate layer to form PP-/EBC-/PP-.
A three-layer sheet consisting of Next, it was stretched 5 times in the longitudinal direction with a stretching roll (set temperature: 120°C),
Continue to tenter horizontally (set temperature: 155℃)
The film was stretched 8 times to obtain a multilayer biaxially stretched film. The physical properties were evaluated using the following method. Haze (%): ASTM D1003 Tensile test: ASTM D638 Tear strength (Kg/cm): JIS Z1702 Heat seal strength (g/15mm): Layer the film surfaces together and test at 150℃, 160℃, 170℃, 180℃ After sealing for 1 second at a pressure of 2 kg/cm ² using a seal bar with a width of 5 mm, the sample was allowed to cool. A 15 mm wide test piece was cut from this and the heat sealed part was peeled off at a crosshead speed of 200 mm/min.
The strength after that was defined as the peel strength. Example 2 Polypropylene (trade name: Mitsui Petrochemical Polypropylene) with a melt flow rate of 7.0 g/10 min and a melting point of 143°C was used instead of the PP- used in Example 1.
F630 manufactured by Mitsui Petrochemical Industries KK: hereinafter abbreviated as PP-) was used instead of EBC-, with a melt flow rate of 7.0 g/10 min, a propylene content of 65.0% by weight, a heat of crystal fusion of 50 Joule/g, and a melting point of 110°C. 1-butene random copolymer (hereinafter referred to as
The same procedure as in Example 1 was carried out except that PBC-) was used. The results are shown in Table 1. Example 3 Polypropylene (trade name: Mitsui Petrochemical Polypropylene) with a melt flow rate of 2.5 g/10 min and a melting point of 162°C was used instead of the PP- used in Example 1.
F301 manufactured by Mitsui Petrochemical Industries KK: hereinafter abbreviated as PP-) was used instead of EBC- at a melt flow rate of 2.5 g/10 min, a density of 0.923 g/cm ³ , and a melting point of 13°C.
(There are also peaks at 119℃ and 104℃) and ethylene 4-methyl-1 with an ethylene content of 91.4% by weight.
The same procedure as in Example 1 was carried out except that -pentene random copolymer (hereinafter abbreviated as EMC-) was used.
The results are shown in Table 1. Example 4 Example 2 was used instead of PP- used in Example 1.
The same procedure as in Example 1 was carried out except that PBC- used in Example 1 was used. The results are shown in Table 1. Comparative Example 1 ~ Instead of the EBC- used in Example 1, high-pressure low-density polyethylene (trade name: Mirason 24H manufactured by Mitsui Polychemicals KK; hereinafter abbreviated as LDPE) with a melt flow rate of 4.8 g/10 min, and a melt flow rate of 3.5 g/10min ethylene/vinyl acetate copolymer (product name: Evaflex P-1405
Made by Mitsui Polychemicals KK: High-density polyethylene (hereinafter abbreviated as EVA), melt flow rate 0.90g/10min, density 0.954 (product name Hi-Zex)
The same procedure as in Example 1 was carried out except that 3300F (manufactured by Mitsui Petrochemical Industries KK: hereinafter abbreviated as HDPE) was used. The results are shown in Table 1. 【table】

Claims (1)

[Claims] 1. The intermediate layer has a density of 0.870 to 0.940 g/cm ³ , a melting point of 50 to 130°C, and an ethylene content of 75 to 97.
Random copolymer (A) of ethylene and α-olefin having 4 to 20 carbon atoms (wt%), or propylene content of 55 to 80 wt%, heat of crystal fusion of 10 to 10% by weight based on thermal analysis using a differential scanning calorimeter.
From a random copolymer (B) of propylene and α-olefin having 4 to 10 carbon atoms and a melting point of 80 Joule/g and a melting point of 100 to 130°C and lower than that of the surface layer polypropylene resin (C). A polypropylene multilayer biaxially stretched film, characterized in that the surface layer of the polypropylene resin (C) is biaxially stretched.