JPH0523938B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a biaxially stretched polyolefin film for adhesive tape that can be easily cut by hand or with a dispenser. [Prior Art] Conventionally, biaxially oriented polyolefine films (for example Japanese Unexamined Patent Publication 1983-
136418, etc.) have been proposed. [Problems to be solved by the invention] However, the above film had the following drawbacks. In other words, low-molecular-weight polyolefins with an intrinsic viscosity of around 1.0 have extremely low viscosity and fast crystallinity, so they can be used to remove polymerization catalyst residues and lubricants, which did not cause any particular problems with conventional intrinsic viscosities of about 1.8 to 2.2. , anti-blocking agents, crystal nucleating agents, etc. may be unevenly dispersed in the film and become foreign matter, or these foreign matter may be used as nuclei to form voids in the stretched film, resulting in a film with poor appearance. Furthermore, when cutting by hand or with a dispenser, the cut surface has the disadvantage that irregularities are formed due to foreign matter or voids, and the cut edges propagate randomly in multiple directions. In addition, when used for coating material such as adhesive tape, it may cause poor appearance due to surface unevenness.
It also had drawbacks such as uneven coating. [Object of the Invention] The present invention eliminates the above-mentioned drawbacks, such as poor appearance, unevenness and random propagation of the cut surface when cutting the film, and uneven coating of the coating agent.
To provide a biaxially stretched polyolefin film for adhesive tape that can be easily cut by hand or with a dispenser and has practical strength. [Means for Solving the Problems] In order to achieve the above object, the present invention provides a crystalline low molecular weight polyolefin film having the following configuration, that is, an intrinsic viscosity of 0.5 to 1.5, and the film has (1) Ash content is less than 100ppm (2) Shapey impact strength in the width direction is 0.5 to 5.0
(Kg・cm/cm) Biaxially stretched polyolefin film. It is necessary that the intrinsic viscosity of the film of the present invention is in the range of 0.5 to 1.5, preferably 0.8 to 1.2, and more preferably 0.9 to 1.05. If the intrinsic viscosity is lower than this range, the film will not only become brittle and lack practical strength, but also have significantly poor film formability. Conversely, if the intrinsic viscosity is higher than this range, it will not be easy to cut by hand or with a dispenser. In addition, the film of the present invention has an ash content of less than 100 ppm.
Preferably it should be less than 40 ppm. When the ash concentration exceeds 100ppm, the amount of foreign matter increases significantly.
In addition, voids caused by foreign matter may cause poor appearance, the cut surface may become uneven when the film is cut, random propagation cuts may occur, and uneven coating of the coating agent may occur due to surface unevenness. Further, the film of the present invention has a shear peace impact strength in the width direction of 0.5 to 5.0, preferably 1.5 to 5.0.
Must be within the range of 3.0 (Kg・cm/cm). If the value is lower than this range, the film will become too brittle and will lack practical strength. Conversely, if the value is higher than this range, it will not be possible to cut it by hand or with a dispenser. Note that the film of the present invention is a biaxially stretched film. The crystalline low molecular weight polyolefin used in the film of the present invention is a homopolymer of propylene, ethylene, butene-1,4-methylpentene-1, etc., or a copolymer of the above monomers with another olefin having 2 to 10 carbon atoms. Polymer (however, the copolymerization rate is 30
It is a crystalline substance represented by (weight% or less),
In the case of the film of the present invention, propylene-based copolymers, especially propylene/ethylene random copolymers (ethylene content 1 to 5% by weight) are preferred. Of course, amorphous polyolefins such as polystyrene and polymethyl methacrylate are heat resistant and
It is insufficient in terms of chemical resistance and practical strength, and is not preferred as a raw material for the film of the present invention. In order to reduce the ash content, the crystalline low molecular weight polyolefin used in the film of the present invention is prepared by adding alcohol (particularly ethanol,
By washing with isopropanol, etc.),
The ash content can be reduced to less than 100 ppm. The ash content can be further reduced by increasing the number of washings, but the lower limit that can be achieved is approximately 30 ppm. Furthermore, the film of the present invention may contain antioxidants, antistatic agents, ultraviolet absorbers, crystal nucleating agents, and the like, as necessary, to the extent that the effects of the present invention are not impaired. In addition, in the case of the film of the present invention, since a low molecular weight polymer is used, the crystallization rate is very fast, and large spherulites grow, resulting in poor transparency.
By adding a crystal nucleating agent that has good compatibility with low molecular weight polymers and excellent uniform dispersibility, the spherulite size is reduced and finely dispersed, resulting in a significant improvement in transparency. Next, an example of the method for manufacturing the film of the present invention will be described, but the method is not necessarily limited thereto. A crystalline low molecular weight polyolefin thoroughly washed with alcohol (ethanol) is supplied to an extruder and melt-extruded from a die. At this time, since the melt viscosity is lower than that of ordinary polyolefin due to its low molecular weight, it is melted at the lowest possible temperature and coarse foreign substances are removed using a high mesh filter. Next, this melt is grounded on a moving cooling support (cast drum) kept at 70 to 130°C,
The ground point is brought into close contact with an air knife with a lower wind speed than usual, and the film is peeled off from the cast drum while maintaining the film temperature at 70°C or higher. The intrinsic viscosity of the cast film thus obtained is in the range of 0.5 to 1.5. Next, the temperature of the cast film was set to 60℃.
While maintaining the stretching ratio above, the stretching ratio was increased to 4.5 in the longitudinal direction using a known simultaneous biaxial stretching method or sequential biaxial stretching method.
Stretched by ~10 times and 6 to 15 times in the width direction. The stretching temperature T _MD in the longitudinal direction at this time is preferably in a temperature range 10 to 30°C lower than the melting point T _n of the crystalline low molecular weight polyolefin, and the birefringence of the obtained longitudinally stretched film is 0.01 or less. Further, the stretching temperature _TTD in the width direction is preferably in a temperature range 10 to 50°C lower than _Tn . Next, the biaxially stretched film is heat-treated at a temperature of T _n or less, and if necessary, one or both sides of the film are subjected to a known surface activation treatment such as corona discharge treatment to increase the wetting tension to 35 to 35.
50dyne/cm. The thickness of the biaxially stretched film thus obtained is
The thickness is preferably in the range of 8 to 90 μm, preferably 15 to 50 μm. Further, the film may have a shear peace impact strength CH _TD in the width direction in a range of 0.5 to 5.0 (Kg·cm/cm). Further, the ash content of the film can be less than 100 ppm. By setting the stretching temperature to T _MD > T _TD , the birefringence in the width direction of the biaxially stretched film can be set to 0.013 or more, making the film easy to cut mainly in the width direction and not in the longitudinal direction. On the other hand, by setting the stretching temperature to T _MD ≦T _TD and making the birefringence less than 0.013, the film can be cut in any direction within the film plane. That is, the cutting direction can be freely controlled depending on the degree of birefringence in the width direction. Furthermore, in the case of the film of the present invention, since a highly crystalline and low molecular weight polymer is used as a raw material, the film can have excellent thermal dimensional stability even without intense heat treatment at high temperatures. [Effect of the invention] As described above, the present invention has an intrinsic viscosity of 0.5 to 1.5.
a crystalline low molecular weight polyolefin film having: (1) an ash content of less than 100 ppm; and (2) a shear py impact strength in the width direction of 0.5 to 5.0.
(Kg・cm/cm) By adopting the structure of a biaxially oriented polyolefin film for adhesive tape, the following excellent effects are produced. That is, (1) it can be cut by hand only in the width direction or in any direction within the film plane;
It also has practical strength. (2) Beautiful cuts can be made without uneven cut surfaces or random propagation of cut edges. (3) The appearance is clean and there are few surface irregularities. (4) Excellent solvent resistance and heat resistance. (5) Excellent dimensional stability due to low thermal shrinkage and no moisture absorption. (6) The film does not curl when heated or when external force is applied. (7) When this film is used as a base material for adhesive tape, it can be easily cut with a dispenser, and there is no uneven coating or surface unevenness caused by adhesive application. (8) Furthermore, when used as a base material for adhesive tapes or laminates, it is strong against external forces in the thickness direction and does not cause cleavage. Next, methods for measuring each characteristic value in the present invention will be summarized below. (1) Intrinsic viscosity Completely dissolve 0.1 g of polymer in 100 ml of tetralin at 135°C, measure this solution with a viscometer in a constant temperature bath at 135°C, and determine the intrinsic viscosity from the specific viscosity S according to the following formula. Intrinsic viscosity=S/0.1×(1+0.22S) (2) Melting point Scanning calorimeter (DSC-type: Perkin Elmer
5 mg of polymer was set in a tube (manufactured by Nippon Steel & Co., Ltd.), heated under a nitrogen atmosphere, and raised to 290°C at a rate of 20°C/min. After holding this temperature for 60 seconds, the sample is removed and immediately placed in liquid nitrogen for quenching. This sample was placed in the measurement cell again, and the temperature was raised at a rate of 20°C/min.
The temperature at the peak of the endothermic peak accompanying the melting of the crystal is defined as the melting point of the polymer. (3) Charpy impact strength The energy E (Kg・
cm) divided by the sample width (cm). E
The calculation method is as follows. 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 weight of the hammer after cutting the specimen. It is the swing-up angle. The shear peace impact strength in the width direction (longitudinal direction) is measured by taking a long sample in the longitudinal direction (width direction), attaching it to test clamps at the top and bottom of its long axis, and hammering it in the direction perpendicular to the long axis, that is, in the width direction (longitudinal direction). This is the value obtained by dividing the energy value E at which the film was cut by the width of the film sample. (4) Ash content Accurately weigh 100g of the sample (film), place it in a magnetic crucible, and heat it with a gas flame to ash it. This was heated in an electric furnace at 850°C ± 25°C for 2 hours, cooled in a desiccator for 30 minutes, and then weighed accurately.
Calculated using the following formula. Ash content (ppm) = Amount of ash content (g) / Sample (g) x 10 ⁶ (5) Number of foreign objects (Fish eyes) Observe foreign objects in the film with an optical microscope (normal transmitted light), and measure 100 μm in 10 cm ² of the film. The number of foreign substances shown above is as follows. (6) Whitening If the film is stretched by 5% in the longitudinal direction (width direction) and the haze value increases by 3% or less before and after stretching, it is determined that there is no whitening. (7) Curling A sample with a width of 10 mm and a length of 150 mm was suspended in a hot air oven at 120°C for 15 minutes under free load, and a sample that did not curl at all and maintained its flatness was defined as having no curl. (8) Cleavage Sellotape (Sekisui Chemical No. 1150,
Width 24mm), tape crimping roll machine (Toyo Seiki Co., Ltd.)
JIS-C2107) with a linear pressure of 1 Kg/cm, prepare more than 50 samples so that the pasted area is 24 x 200 mm square, and manually paste them at 1.5 m/cm.
The sample and cellophane tape were peeled 180° at a high speed of seconds, and judgment was made based on the presence or absence of cleavage on the surface layer of the film. (9) Birefringence Using the Na-D line as transmitted light, the retardation was determined using a compensator, and the value obtained by dividing it by the film thickness was used. Next, embodiments of the present invention will be described based on Examples. Example 1 As a raw material for crystalline low molecular weight polyolefin, an ethylene/propylene random copolymer containing 2.2% by weight of ethylene (intrinsic viscosity 1.05, melt index
(81g/10 minutes, melting point: 153°C) was thoroughly washed twice with a 50% methanol aqueous solution. 0.1% by weight of 2,6-di-tert-butyl-para-cresol as an antioxidant, and 0.005% by weight of calcium stearate as an extruder internal lubricant.
A crystal nucleating agent containing 0.15% by weight of a dibenzylidene sorbitol derivative was used. The raw material is fed to an extruder and melted at 200°C,
It was extruded through a flat die through a 25 micron cut porous metal filter. The melt was grounded on a drum kept at 75°C, and the ground point was brought into close contact with an air knife to obtain a cast film. The cast film was introduced into a longitudinal stretching machine without being cooled to below 60°C. A hot air oven type stretching machine was used as the longitudinal stretching device, and the film was stretched 6 times in the longitudinal direction at a hot air temperature of 137°C.
The birefringence of the uniaxially stretched film thus obtained is
It was 0.008. Next, the uniaxially stretched film was introduced into a tenter and stretched in the width direction at a stretching temperature of 142°C and a stretching ratio of 9 times,
Immediately heat treatment was performed at 142°C for 7 seconds while allowing 5% relaxation in the width direction. thus obtained
Both sides of a 35 μm biaxially stretched film were subjected to corona discharge treatment to increase the surface wetting tension to 38 dyne/cm (JIS method). Table 1 shows the properties of the obtained film. The ash content of this film was 40 ppm, and it had a clean appearance with few foreign substances. In addition, when cutting the film by hand, the cut surface did not become uneven or randomly propagated. In addition, the film's shear py impact strength in the width direction is
2.9 (Kg cm/cm), the birefringence was 0.010, and it could be easily cut by hand in both the longitudinal and width directions. Further, one side of the film was coated with an acrylic pressure-sensitive adhesive and the other side was coated with a release agent to make an adhesive tape with a width of 12 mm. This adhesive tape has excellent transparency with no uneven adhesive application and no surface irregularities, and is easy to cut with a dispenser or by hand, and does not cause uneven cut surfaces or random propagation cuts. There was no whitening, clouding, or fibrillation in the dispenser. Of course, even when the adhesive tape was adhered to an adherend such as glass and then peeled off at high speed, the tape did not break or cleave. Thus, it can be seen that the film of the present invention has excellent cutting properties, has a clean appearance with few foreign substances, and has practical strength, and is particularly suitable as a base material for adhesive tapes. . Comparative Example 1 As a raw material for crystalline low molecular weight polyolefin, an ethylene/propylene random copolymer containing 2.2% by weight of ethylene (intrinsic viscosity 1.05, melt index
81 g/10 minutes (melting point 153°C), 0.05% by weight of 2,6-di-tert-butyl-para-cresol as an antioxidant, 0.2% by weight of calcium stearate as an extruder internal lubricant, and a crystal nucleating agent. A solution containing 0.15% by weight of a dibenzylidene sorbitol derivative was used. The raw material was fed into an extruder, melted at 200°C, passed through a 150-mesh wire mesh filter, and extruded from a flat die in the same manner as in Example 1 to form a biaxially stretched film with a thickness of 35 μm, and a film with a thickness of 35 μm was prepared on both sides. Corona discharge treatment was performed to give a surface wetting tension of 38 dyne/cm (JIS method). Table 1 shows the physical properties of the film thus obtained. The ash content of this film was 240 ppm, there was a large amount of foreign matter, and the film surface was lumpy and uneven, giving it a poor appearance. Furthermore, when the film was cut by hand, the cut surface often became uneven, and the cut edges often propagated randomly in multiple directions. Furthermore, when one side of the film was coated with an acrylic pressure-sensitive adhesive, the coating was uneven and the transparency and appearance were poor. Comparative Example 2 An ethylene/propylene random copolymer (ethylene/propylene random copolymer with an intrinsic viscosity of 2.2) was used as a polyolefin raw material.
A biaxially stretched film with a thickness of 35 μm was prepared in the same manner as in Comparative Example 1, except that 2.2% by weight, melt index 1.4 g/10 minutes, melting point 153°C) was used, and both sides were subjected to corona discharge treatment. The wetting tension was set to 38 dyne/cm (JIS method). Table 1 shows the physical properties of the film thus obtained. The ash content of this film was 245 ppm,
There were few foreign substances and the appearance was clean. However, the shear py impact strength of the film is 8.0/9.3 (Kg・cm/cm) in the longitudinal direction/width direction.
Therefore, it could not be cut by hand in either the longitudinal direction or the width direction. Example 2 The uniaxially stretched film obtained in Example 1 was stretched at a widthwise stretching temperature different from that in Example 1, that is,
Stretched 9 times in the width direction at 120℃, immediately heat treated at 135℃ for 7 seconds while allowing 5% relaxation in the width direction, and then corona discharge treated on the surface to reduce the thickness.
A biaxially stretched film of 35 μm was obtained, and the physical properties of the film are shown in Table 2. The resulting film had a shear pie impact strength in the width direction of 3.0 (Kg·cm/cm) and a birefringence of 0.022. Although this film cannot be cut by hand in the longitudinal direction, it can be easily cut by hand in the width direction.Moreover, the cutting direction coincides with the width direction, and it is cut in a straight line in the width direction. It was cut off. Further, the ash content of the film was 40 ppm, and the film had a clean appearance with few foreign substances. By coating this kind of film with adhesive,
It is excellent in cuttability with a dispenser or by hand, and also has the characteristics necessary for adhesive tapes, so it can be used as an excellent raw material for adhesive tapes.

【table】

[Table] (Note) In the table above, the molecules in the shaded areas are in the longitudinal direction,
The denominator indicates the value in the width direction.

【table】

[Table] The direction and denominator indicate the value in the width direction, respectively.

Claims (1)

[Scope of Claims] 1. A crystalline low molecular weight polyolefin film having an intrinsic viscosity of 0.5 to 1.5, the film having (1) an ash content of less than 100 ppm, and (2) a shear peace impact strength in the width direction of 0.5 to 5.5.
(Kg・cm/cm) Biaxially stretched polyolefin film for adhesive tape.