JPS626509B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyolefin laminated film with improved hand tearability. Conventionally, polyolefin films with excellent hand-cutting properties have been produced by laminating a uniaxially oriented film in the width direction on top of a biaxially oriented film (for example, Japanese Utility Model Publication No. 1983-44519), or by laminating a biaxially oriented film with an electronic film. There are known methods such as irradiation with radiation such as radiation (for example, Japanese Patent Application Laid-open No. 106779/1983), and a method of creating a laminated film in which a brittle polymer layer such as polystyrene is sandwiched between two polypropylene layers. They are used in applications that require hand-tearability, such as adhesive tapes and flower packaging. However, each of these conventional films has the following fatal flaws.
In other words, when a uniaxially oriented film is laminated on top of a biaxially oriented film, if it becomes cloudy or white when cut, if a part of the cut part remains, if the film is miscut, or if the temperature is raised to 40 to 50°C, Not only does it have little hand-cutting properties and the sample curls, but it also has the drawbacks of poor productivity. Furthermore, in the case of electron beam irradiation, not only the properties of manual tearability and toughness cannot be satisfied, but also the film surface layer easily cleaves if the film is easy to cut by hand. Furthermore, in the case of a three-layer film in which a layer of brittle polymer such as polystyrene is sandwiched between polypropylene layers, not only does the adhesion between the two layers be poor and cleave easily, but the transparency, chemical resistance, and heat resistance are also poor. Furthermore, it has the disadvantage that it is not possible to collect scraps during film production, resulting in poor productivity. An object of the present invention is to eliminate the above-mentioned drawbacks and provide a laminated film that has excellent hand-cutting properties and toughness, is free from curling, clouding, whitening, cleavage, etc., and has excellent productivity. In order to achieve the above object, the present invention has the following configuration: a layer () made of polyolefin A, a layer () made of propylene copolymer B,
()/()/(), and the laminated film has (i) a Charpy impact value (P) of 5 Kg-cm/cm or less (ii) a refractive index in the longitudinal direction (N _MD ) and the refractive index (N _TD ) in the width direction minus the birefringence (Δn), which is a value within the range of 0.002 to 0.02. The polyolefin A applied to the laminated film of the present invention is a polyolefin represented by polypropylene, propylene/ethylene copolymer, 4-methylpentene-1 polymer, 4-methylhexene-1 polymer, 5-methylhexene-1 polymer, polyethylene, etc. In particular, in the case of the film of the present invention,
Polypropylene is the most suitable raw material because it has excellent quality and productivity, such as hand-cutability, toughness, transparency, and interlayer adhesion. Further, the polypropylene copolymer B applied to the laminated film of the present invention is a copolymer of propylene with up to 50 mol% of monomers such as ethylene, butene, pentene, hexene, etc., and includes, for example,
Polyolefins represented by ethylene/propylene/butene terpolymer, ethylene/propylene binary copolymer, etc., and in the case of the film of the present invention, particularly ethylene/propylene copolymer, ethylene/propylene/butene copolymer, etc. Combined, propylene
Butene copolymers and propylene/hexene copolymers are preferred. As for the type of copolymer, random copolymers are particularly preferred over block copolymers. Of course, other polymers may be blended with the polyolefin A and propylene copolymer B as long as their properties are not significantly changed. In the case of the film of the present invention, in particular, the polyolefin The layer () is a blend of 10 to 60% by weight, preferably 20 to 50% by weight, of A, and 10 to 30% by weight, preferably 15 to 25%, of propylene copolymer B to polyolefin A.
By laminating a blend of weight percent as a layer (), it satisfies toughness and hand-cutability, further improves cleavage resistance, and allows for a wide range of temperature conditions during film formation, resulting in stable film formation. become Of course, you don't necessarily have to get the same effect by blending.
It is obvious that it may be obtained by direct polymerization, for example, by polymerizing a polyolefin homopolymer in the early stage of polymerization and adding a comonomer in the late stage of polymerization to obtain a blended product of the homopolymer and copolymer. The melting point of polyolefin A is preferably higher than the melting point of propylene copolymer B, and in the case of the film of the present invention, it is convenient that the melting point is in the range of 5 to 50°C, preferably 10 to 30°C. . In addition, the intrinsic viscosity of propylene copolymer B is 0.8~
1.2, preferably in the range of 0.9 to 1.1, and the viscosity average molecular weight is preferably about 10 ⁴ to 10 ⁶ . Polyolefin A and propylene copolymer B contain antioxidants, antistatic agents, heat stabilizers, lubricants, ultraviolet absorbers, fillers, thickeners, and surface roughening agents, which are known as additives for polymers. Agents, peroxides, etc. may be added to the extent that the effects of the present invention are not impaired. As for the structure of the film of the present invention, the layer ( ) made of polyolefin A must be laminated on both surface layers of the layer ( ) made of propylene copolymer B. This is because the layer ( ) consisting of polyolefin A does not exist on the surface layer, and the layer consisting of propylene copolymer B
If the layer consisting of , not only will the product break more frequently and become less productive,
This is because the resulting laminated film does not have both toughness and hand-cutting properties, and the film ends up being severely curled. Of course, polyolefin A is laminated on both surface layers of the layer () made of polypropylene copolymer B.
It is preferable for both surface layers to have the same composition and the same thickness in terms of curling and productivity, but they do not necessarily have to have exactly the same composition and thickness, and can be freely modified depending on the use and purpose. It is clear from the gist of the present application that the layers ()' may be laminated. The layer () made of polyolefin A is preferably moderately biaxially oriented, and may have a strong orientation in one extreme direction,
If the sheet is strongly oriented in the thickness direction, it will become white or cloudy when cut, hairs will remain when dispenser cut, or it will cleave, making it unsuitable for practical use. Further, the orientation state of the layer () made of propylene copolymer B can be selected depending on the required performance, but in the case of the film of the present invention, weak biaxial orientation is preferred. Furthermore, this layer () suppresses the growth of spherulites as much as possible during casting of the melt, and even if the spherulites grow, the size of the spherulites is 2
Unless the spherulites are made as small as micrometers or less, the film of the present invention obtained by stretching and orienting the spherulites will easily cleave. The sea py impact value of the polyolefin film of the present invention is 5 (Kg-cm/cm) or less, preferably 3
(Kg-cm/cm) or less. This means that the Shalpy impact value is less than 5 (Kg-cm/cm),
Preferably, if it is less than 3 (Kg-cm/cm), it will not be possible to provide the cuttability by hand at all, or even if it can be given the cuttability by hand, there will be a high probability of mis-cutting, or the cut end surface will be deformed. This is because beautiful clean cuts cannot be made. In more detail, as shown in Table 1, there is a strong correlation between the Shalpy impact value and the hand tearability.

[Table] Also, from the absolute value △N of the difference between the refractive index in the width direction (TD) and the refractive index in the longitudinal direction (MD) of the film of the present invention, the long axis and short axis in the plane determined using a polarizing microscope. The value obtained by subtracting the birefringence △n, which is the difference between
It should be in the range 0.002-0.02, preferably 0.003-0.01. If the range is outside this range, not only will it not be possible to provide excellent hand-cutting properties and toughness, but the film will become cloudy or white when cut, or the film will curl or stretch at the edges, resulting in a film with a poor appearance. It is. The value of △N - △n is the birefringence △n ₁ of the layer () made of polyolefin A and the layer () made of polypropylene copolymer B.
There is a close correlation with the birefringence △n ₂ of , and there is a relationship expressed by the following equation. △N - △n = (△n ₁ - △n ₂ ) (t ₂ / t ₀ ) where t ₀ is the total thickness of the film t ₂ is the thickness of the layer () In other words, the orientation of the layer () is always It is necessary that the orientation is larger than that of the layer (2), and for convenience, when a cross section of the film of the present invention is observed under polarized light, there is a difference in color due to a difference in retardation, or
This can be determined from the linearity of interference fringes obtained using an Interphaco interference microscope (Carl Zeiss Jera). At this time, to prevent whitening when cutting,
It is preferable that the birefringence △n ₂ of the () layer is 0.002 or more, and therefore the birefringence △n ₁ of the () layer is △
It is preferable to have a balanced biaxial orientation which is larger than n ₂ and whose value Δn ₁ is in the range of 0.004 to 0.030. Of course, the thickness t ₀ of the film of the present invention
is particularly preferably in the range of 10 to 150 μm, and the ratio to the total thickness t ₀ of the layer () is 30 μm.
~98%, preferably in the range of 50-85%,
It is preferable because it satisfies various properties such as hand-cutability and toughness. In addition, the refractive index value _NTD in the width direction obtained with a refractometer such as Abbe is 1.525 ~
A value of 1.505, preferably in the range of 1.515 to 1.508, is effective in improving manual tearability and preventing whitening during cutting. Next, a method for manufacturing the film of the present invention will be described, but the method is not necessarily limited thereto.
Supplying polyolefin A and propylene copolymer B to two or three extruders, respectively,
After the polymer is melted, it is passed through a three-layer composite adapter or cap, ()/
Extrude a three-layer melt consisting of ()/(),
It was cooled and solidified on a cooling drum by a known method such as an electrostatic application method or an air knife method. The cast film is stretched 4 to 10 times in the longitudinal direction using a stretching machine, and then stretched 4 to 12 times in the width direction using a stenter, followed by heat treatment. The heat treatment temperature varies depending on the quality required, but if you want to give it easy hand-tearability like paper, heat treat it at a temperature of 10℃ or more above the melting point of the propylene copolymer to make the () layer non-oriented. If it is desired to impart toughness, it is preferable to perform heat treatment at a temperature near the melting point to leave a weak biaxial orientation. The laminated film of the present invention is made of propylene copolymer B.
By setting the orientation state and the Shapey impact strength to specific values in a three-layered film containing
It has the following excellent effects. (1) From films that are extremely easy to cut by hand, like paper, to films that are tough and easy to cut by hand, like acetate and cellophane.
The film can be made according to the purpose and quality. (2) When cutting the film, there are no problems such as the formation of "whiskers", whitening/cloudiness, curling, or miscuts at high temperatures. (3) The film forming process is simple because coextrusion is possible, and stable and highly efficient film forming is possible. (4) The obtained film has excellent thermal dimensional stability;
The heat shrinkage rate after 15 minutes at 120℃ is less than 1% on both axes, and that after 15 minutes at 100℃ is almost 0%, so high heating and drying temperatures can be used for printing and coating. Not only can high-speed processing be performed, but also printing and coating with high accuracy can be achieved with small dimensional changes during heating. Therefore, the film of the present invention can be used as raw material for adhesive tapes, as paper such as tracing paper, for general packaging such as flowers, and as a backing sheet for PTP (Press Through Pack) packaging by vapor-depositing Al. It is effective for such things. The methods for measuring the Charpy impact value, refractive index, birefringence, etc. used in the present invention will be explained. (1) The Charpy impact value is a value obtained using a Charpy impact tester, and is calculated by dividing the energy E (Kg-cm) required to cut the test piece by the sample width (cm). The method is based on the following equation. E=WR (Cosβ−Cosα) W is the weight of the hammer (Kg), R is the distance from the center of rotation of the hammer to the center of gravity (cm), α is the lifting angle of the hammer, and β is the vibration of the hammer after cutting the specimen. It is the top corner. (2) To measure the refractive index, use an Abbe refractometer, use Na-D rays as the light source, use methyl salicylate as the mounting liquid, change the direction of the polarizing plate, and measure the refractive index in a specific direction using the total internal reflection method. . (3) For birefringence, the retardation was determined using a compensator using the Na-D line as transmitted light, and the value was calculated by dividing the retardation by the film thickness. (4) Intrinsic viscosity is the viscosity when a polymer is dissolved in tetralin at 135°C and extrapolated to a concentration of 0. Next, in order to make it easier to understand the effects of the present invention, embodiments will be described using Examples and Comparative Examples, but the present invention is not limited thereto. Comparative Examples 1 and 2, Examples 1 and 2 Polypropylene (melting point 165°C, intrinsic viscosity 1.0) was used as polyolefin A, and ethylene propylene random copolymer (melting point 145°C, ethylene copolymerization amount 3.7) was used as propylene copolymer B. % by weight, intrinsic viscosity 1.0), and 20% by weight of propylene copolymer B and polyolefin A are blended on both surfaces of the layer (2), which is a blend of 40% by weight of propylene copolymer B and polyolefin A. % blended layer () by coextrusion method ()/
A cast film consisting of ()/() was obtained. The temperature at which the cast film is stretched in the longitudinal direction
Stretched 7 times at 140℃ and further stretched at 150℃ in the width direction.
After stretching 8 times at ℃, the heat treatment temperature was increased from 100℃.
The temperature was changed to 160°C, and heat treatment was performed for 13 seconds while allowing 5% relaxation in the width direction to obtain a laminated film with a thickness of 35 microns (3/29/3 microns).
The properties of this film were measured and are shown in Table 2. As shown in Table 2, if the difference between the refractive index difference △N and the birefringence △n is not within a certain range, whitening and turbidity will occur during cutting, even if it is easy to cut by hand. It can be seen that the quality of the film changes over time, which is not desirable.

[Table] Example 3 Polypropylene (intrinsic viscosity 1.2) was used as polyolefin A, and ethylene propylene random copolymer B ₁ (melting point 150) was used as propylene copolymer B.
°C, ethylene copolymerization amount 2.0% by weight, intrinsic viscosity 1.0)
and ethylene propylene random copolymer
Using propylene copolymer B ₁ (melting point 145°C, ethylene copolymerization amount 3.7% by weight, intrinsic viscosity 1.0), ₉₀ %
100 parts by weight of a composition containing 10% by weight of polyolefin A, 0.5 parts by weight of TPA5028 manufactured by Sanyo Chemical Co., Ltd. as an antistatic agent was blended into the layer (), 80% by weight of polyolefin A, 20% by weight of ethylene propylene random copolymer _B2
The mixed composition is supplied to the three-layer composite coextrusion die in the form of layers (), ()/()/().
A cast film with a three-layer structure consisting of The cast film is rolled in the longitudinal direction by a conventional method.
Stretched 7.3 times at 146℃, then stretched 9 times in the width direction at 153℃, heat treated at 160℃ for 12 seconds with 7% relaxation in the width direction, and treated with corona discharge on both sides to a thickness of 40 microns. (The composition of each layer is 2/36/
A laminated film with a thickness of 2 microns) was obtained. The properties of the thus obtained laminated film were measured and are shown in Table 3.

【table】

[Table] When we applied a release agent to one side of the laminated film and a pressure-sensitive adhesive to the other side, we checked various properties for use in adhesive tapes, and found that it had excellent hand tearability while maintaining toughness. Moreover, it could be easily and clearly cut without whitening, curling, or deformation of the end surface when cut by hand, and there were no miscuts or hairs when cut with a dispenser. Of course, at the time of manufacturing this tape, 50m/
Even after several minutes of high-speed unwinding, there were no problems such as cleavage or cutting, and it functioned normally. As described above, compared to cellophane-based cellophane tapes that have been used hitherto, the use of the polyolefin film of the present invention has low Γ water absorption and very little expansion and contraction of the tape. Γ Excellent leaf resistance and weather resistance. Γ It is easy to expose the edge of the adhesive tape. It was also found that there are other characteristics.

Claims (1)

[Claims] 1. A layer () made of polyolefin A and a layer () made of propylene copolymer B are ()/
A laminated film laminated in ()/(), and the laminated film has (i) a Shalpy impact value (P) of 5 Kg-cm/cm or less (ii) a longitudinal refractive index (N _MD ) and a width. A polyolefin laminated film characterized in that a value obtained by subtracting birefringence (Δn) from the absolute value of the difference with the refractive index ( _NTD ) in the direction is within the range of 0.002 to 0.02.