JP5508501B2 - Method for producing biaxially stretched film - Google Patents

Description

  The present invention relates to a method for producing a biaxially stretched film made of a propylene-based polymer.

Biaxially stretched polypropylene films are widely used in various applications including packaging materials, taking advantage of their excellent transparency, mechanical strength, moisture resistance, rigidity, and the like. As a method for forming a biaxially stretched film of polypropylene, simultaneous biaxial stretching and sequential biaxial stretching are known. By biaxially stretching a polypropylene film, its strength, transparency, etc. can be improved and the product value can be increased, and it is expected to be used for a wider range of applications.
Although it has been proposed to add a stretching process between rolls to a biaxially stretched film of polypropylene, the strength of the resulting film is insufficient.

Japanese Patent Publication No.41-21790 Claims

  The object of the present invention is to improve the strength and heat resistance of the propylene-based polymer by stretching orientation, and to improve the heat resistance and strength of the simultaneous biaxially stretched polypropylene film.

  The present invention provides a method for producing a propylene-based biaxially stretched film, characterized in that the biaxially stretched film is further biaxially stretched after the scissors of the propylene-based film stretched in at least one direction are cut off.

  According to the method of the present invention, it is possible to obtain a biaxially stretched film having superior strength and heat resistance as compared with conventional biaxially stretched polypropylene films.

Propylene-based polymer In the method of the present invention, the propylene-based polymer as a raw material is a polymer mainly composed of propylene which is generally produced and sold under the name of polypropylene, and usually has a density of 0.890 to 0.930 g / cm ³ , MFR (ASTM D 1238 load 2160 g, temperature 230 ° C.) 0.001 to 60 g / 10 min, preferably 0.5 to 10 g / 10 min, more preferably 1 to 5 g / 10 min. It is a composition of a polymer or propylene and another small amount, for example, 1% by weight or less of an α-olefin, such as ethylene, butene, hexene-1, or the like, or a composition of a homopolymer and a copolymer. These propylene polymers may be two or more kinds of compositions having different molecular weights, and two or more kinds of compositions having different isotacticity may be used. Among these, polypropylene having high isotacticity (mesopentad of 98% or more) is preferable. These polypropylenes are blended with a hydrocarbon resin such as petroleum resin or a nucleating agent as necessary.
In particular, a composition in which high molecular weight polypropylene (MFR 0.01 or less) is further blended in an amount of 3 to 30% by weight in ordinary high isotacticity (mesopentad is 98% or more) polypropylene is also carried out.

In addition, a composition of polypropylene having a high isotacticity as polypropylene, for example, a polypropylene having a higher isotacticity and a polypropylene having a lower isotacticity, the ratio of the isotacticity values (higher pen Also suitable are compositions in which the difference between the tad isotacticity value and the lower pentad isotacticity value is 1 to 4 (unit%).
Among these, a homopolymer of propylene, or a polymer having a high isotacticity with a random copolymer of 1% by weight or less or a composition thereof is excellent in elastic modulus and heat resistance of the obtained biaxially stretched polypropylene film. Therefore, it is preferable.
The polypropylene according to the present invention is not limited to a Ziegler-Natta catalyst, and may be one polymerized using various known catalysts such as a single site catalyst (metallocene catalyst).

  Polypropylene also includes heat stabilizers, weathering stabilizers, UV absorbers, lubricants, slip agents, benzylidene sorbitol and other nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, inorganic or organic Various additives usually used for polyolefins such as a filler may be added within a range not to impair the object of the present invention.

(I) Propylene film stretched in at least one direction The propylene film stretched in at least one direction used in the present invention includes (i) a propylene film stretched uniaxially in the vertical direction, and (b) a horizontal direction. And (d) a biaxially stretched propylene film, or (d) a simultaneous biaxially stretched film.
(A) A conventionally known method can be adopted as a method of forming a propylene film uniaxially stretched in the vertical direction (MD direction). Generally, a method of stretching only the vertical direction of an unstretched film using a roll, a tenter or the like is employed. The draw ratio in the vertical direction (MD direction) is usually 2 to 6 times, and the thickness of the uniaxially stretched film is usually 20 to 800 microns (μm). Since this uniaxially stretched film is used for subsequent simultaneous biaxial stretching, it is desirable that the film thickness is particularly uniform. The temperature of the film when uniaxially stretching in the vertical direction is preferably in the range of about 110 to about 160 ° C.
(B) A conventionally known method can be adopted as a method of forming a propylene-based film uniaxially stretched in the horizontal direction (TD direction). In general, a method of stretching only the horizontal direction (TD direction) of an unstretched film using a tenter is employed. The stretch ratio in the horizontal direction (TD direction) is usually 1.5 to 15 times, and the thickness of the uniaxially stretched film is usually 20 to 800 microns (μm).
(C) The biaxially stretched film is formed by uniaxially stretching a propylene-based sheet in the vertical direction (MD direction) and then further stretching in the horizontal direction (TD direction).
A conventionally known method can be adopted as the forming method for successive biaxial stretching. Generally, the draw ratio in the vertical direction (MD direction) is 2 to 7 times, and the draw ratio in the horizontal direction (TD direction) is 3 to 13 times. The thickness of the successively biaxially stretched film is usually 20 to 500 microns (μm). Since this biaxially stretched film is used for subsequent simultaneous biaxial stretching, it is particularly desirable that the film thickness be uniform.
(D) The simultaneously biaxially stretched film can be formed by various conventionally known methods. The draw ratio is usually in the range of 7 to 12 times in the machine direction (MD), preferably 8 to 11 times, and 7 to 12 times in the transverse direction (TD), preferably 8 to 11 times. The temperature in the tenter during stretching is usually in the range of 140 to 200 ° C, preferably 150 to 190 ° C. The thickness of the simultaneous biaxially oriented propylene-based film is usually about 30 to 500 microns (μm).

(Ii) Further simultaneous biaxial stretching The propylene-based film stretched in at least one direction is further biaxially stretched.
Further simultaneous biaxial stretching may be carried out by employing various conventionally known methods, and may be carried out in the same manner as the above simultaneous biaxial stretching, and the molding is carried out by raising the respective stretching temperatures. Things are also done. The draw ratio is usually in the range of 1.5 to 12 times in the machine direction (MD), preferably 2 to 11 times, and 0.8 to 12 times in the transverse direction (TD), preferably 1.0 to 11 times. It is. The temperature in the tenter during stretching is usually in the range of 140 to 200 ° C, preferably 150 to 190 ° C. The thickness of the propylene-based film obtained by this further simultaneous biaxial stretching is usually about 30 to 200 microns (μm).

(Ii-a) Stretching in the vertical direction In the simultaneous biaxial stretching, the stretching conditions are mainly set so as to be stretched in the vertical direction. That is, as a condition for further simultaneous biaxial stretching, the stretching ratio in the vertical direction (MD direction) is 1.5 to 10 times, and the horizontal direction (TD direction) is in the range of 0.8 to 1.5 times. Is also done. The temperature of the film during stretching is preferably in the range of about 150 to about 180 ° C.
In addition, these further simultaneous biaxial stretchings may be carried out by cooling the film temperature to a room temperature when a propylene-based film previously stretched in at least a uniaxial direction is obtained by molding, and then heating again to stretch in the vertical direction. However, following these stretches, it is desirable to adjust the temperature of the film to a range of about 150 to about 180 ° C. and perform simultaneous biaxial stretching.

In the present invention, when the propylene-based film stretched in at least one direction is further biaxially stretched, it is preferable that the biaxial stretching is further performed after the scissors at both ends are cut off.
The term “mimi” refers to a portion of the end of the film or sheet that has not been stretched, and is usually a portion about 3 centimeters (cm) from the end in the width direction of the film.
Mimi portions at both ends remain weak because they are not sufficiently stretched during stretch molding. Even if tenter stretching such as simultaneous biaxial stretching is performed by gripping the mimetic part again with a tenter clip for the purpose of increasing the strength, if the stretching ratio increases, the mimetic part will have a higher strength than the part where the strength has increased due to the stretching orientation at the center. Since the strength is weak, the Mimi portion is extended and the tenter clip is easily detached.
Therefore, when further stretching the tenter, it is desirable to use a material obtained by cutting off the end portions in the longitudinal direction in advance. In this way, by cutting out the low-strength Mimi portion, the portion that has become high strength by stretching such as biaxial stretching can be gripped by the clip. Thereby, it can endure the high tension at the time of extending | stretching accompanying high elastic modulus.

However, the thickness of the film is the same at the stretched portion at the center and at both sides, and the difference in stretchability at the time of stretching becomes the same, the gripped portion extends, and the clip is liable to slip.
In this case, it is possible to enable high-stretching by providing an easy stretching difference by, for example, providing a temperature difference between the central part and both side parts in the width direction of the film.
The temperature at both ends of the stretched film after the cut off at both ends, including the portion gripped by the tenter clip, can be controlled to be lower than the temperature at the center of the film. desirable.

Generally, the temperature in the vicinity of the center of the film at the time of stretching such as simultaneous biaxial stretching is usually in the range of 150 ° C. to 190 ° C., and the temperature at both ends of the film (the portion gripped by the tenter clip) is In a preferred embodiment of the present invention, it is desirable to control the temperature to be lower by about 1 ° C. to about 100 ° C. than the temperature. The strength of the portion gripped by the tenter clip is made stronger than the strength of the other portions, for example, simultaneous biaxial stretching as a multilayer structure.
For example, it is particularly preferable that both ends after the cut off portion are folded, and the folded portion is gripped by a tenter clip and simultaneously biaxially stretched.
Also in this case, the temperature of both ends of the simultaneous biaxially stretched film after the scissors at both ends including the portion gripped by the tenter clip is higher than the temperature of the central portion of the film. It is desirable to control to a low temperature.

Furthermore, a short width film having a tensile elastic modulus higher than the tensile elastic modulus of the end portion is pressed to both ends after the cut-off portion is not disturbed, and the pressing portion of the short width film is tenter clip. It is also preferable to hold and simultaneously biaxially stretch.
As the short width film, a stretchable film such as a Kapton film can be used in addition to a stretched film made of the same material as the propylene film.
Due to the presence of air layers that do not move at both ends due to these, when stretching in the vertical direction, the temperature of the film portion gripped by the tenter clip near both ends is surely lowered compared to the temperature of the film near the center. The film can be reliably held by the tenter clip.

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.
The physical property values were determined by the following evaluation methods.
(1) Elastic modulus (MPa)
A strip-shaped film piece (length: 150 mm, width: 15 mm) is cut out from the biaxially stretched polypropylene film in the machine direction (MD) and the transverse direction (TD), and a tensile tester [Tensilon universal tester manufactured by Orientec Co., Ltd.] RTC-1225] was used, and a tensile test was performed under the conditions of a distance between chucks: 100 mm and a crosshead speed: 5 mm / min to obtain an elastic modulus (MPa).

Example 1
Production of simultaneous biaxially stretched propylene film F113G manufactured by Mitsui Chemicals, Inc. [density: 0.91, MFR: 3.0 g / 10 min (230 ° C.), isotacticity (mesopentad) 98.0%] Used, melt-extruded with a screw extruder, using a simultaneous biaxially stretched film forming apparatus, tenter (preheating temperature: 185 ° C., stretching temperature: 160 ° C. and heat setting temperature: 180 ° C. and relaxation rate; longitudinal direction: 5% and transverse Direction: 5%) and stretched 8 times in the machine direction (MD) and 8 times in the transverse direction (TD) to obtain a simultaneous biaxially stretched polypropylene film having a thickness of 30 microns (μm).
Stretching in the vertical direction In this way, from the both ends of the biaxially stretched film thus obtained, cut off the widths of about 10 centimeters (cm) from each end, and then sequentially fold both ends to a width of 2.5 centimeters (cm). , And supplied to the process of stretching in the vertical direction.
In the step of stretching in the vertical direction, the temperature of the film excluding both ends was set higher than the temperature of the film during simultaneous biaxial stretching.
While holding the folded portions at both ends of the simultaneous biaxially stretched film with a tenter clip, while simultaneously gripping the film width so as to be 0.82 times the width of the simultaneously biaxially stretched film from which the mimetic portion has been removed, The film was stretched 1.5 times in the vertical direction to obtain a film having a thickness of 37 microns (μm).
One side (coated surface) of the obtained film was subjected to corona treatment.
The results are shown in Table 1.
Table 1

Example 2
Production of sequential biaxially oriented polypropylene film As propylene homopolymer, F113G manufactured by Mitsui Chemicals, Inc. [density: 0.91, MFR: 3.0 g / 10 min (230 ° C.) (mesopentad) 98.0%] Used, melt-extruded with a screw extruder, quenched with a cooling roll (temperature of 30 ° C.) to make a sheet with a thickness of 2.5 millimeters (mm), and then, by successive biaxial stretching, the vertical direction (MD direction) 5 times, A sequential biaxially stretched film (thickness 50 microns) stretched 10 times in the horizontal direction (MD direction) was obtained.
Manufacture of biaxially stretched polypropylene film This sequential biaxially stretched film is made into a raw fabric, and the width of each part is cut off by about 10 centimeters (cm) from both ends, and then both ends are each about 2.5 centimeters (cm) wide. The material was sequentially bent and supplied to the simultaneous biaxial stretching process.
Next, using a simultaneous biaxially stretched film forming apparatus, using a tenter (preheating temperature: 175 ° C., stretching temperature: 175 ° C., 2.5 times in the machine direction (MD) and 0.85 times in the transverse direction (TD) The film was stretched to obtain a biaxially stretched polypropylene film having a thickness of 20 μm.
The results are shown in Table 2.
Table 2

Example 3
Production of sequential biaxially oriented polypropylene film The film was produced in the same manner as in Example 2.
Manufacture of biaxially stretched polypropylene film This sequential biaxially stretched film is made into a raw fabric, and the width of each part is cut off by about 10 centimeters (cm) from both ends, and then both ends are each about 2.5 centimeters (cm) wide. The film was sequentially bent, and a short-width sequential biaxial polypropylene film having a thickness of 40 micrometers (μm) and a width of 2.5 centimeters (cm) was sandwiched and supplied to the simultaneous biaxial stretching process.
Next, using a simultaneous biaxially stretched film forming apparatus, using a tenter (preheating temperature: 175 ° C., stretching temperature: 175 ° C.), 3.5 times in the machine direction (MD) and 0.85 in the transverse direction (TD). The film was stretched twice to obtain a biaxially stretched polypropylene film having a thickness of 14 μm.
The results are shown in Table 3.
Table 3

Example 4
Production of sequential biaxially oriented polypropylene film The film was produced in the same manner as in Example 2.
Manufacture of biaxially stretched polypropylene film Using this sequential biaxially stretched film as a raw material, cut off the width of each 10 cm portion from both ends, and then width is 50 micrometers (μm) at both ends. A 2.5 centimeter (cm) short-width sequential biaxial polypropylene film was pressed and supplied to the simultaneous biaxial stretching process.
Next, using a simultaneous biaxially stretched film forming apparatus, using a tenter (preheating temperature: 175 ° C., stretching temperature: 175 ° C.), the vertical direction (MD) is 2.5 times and the horizontal direction (TD) is 0.82 The film was stretched twice to obtain a biaxially stretched polypropylene film having a thickness of 20 μm.
The results are shown in Table 4.
Table 4

Comparative example
Production of sequential biaxially oriented polypropylene film The film was produced in the same manner as in Example 2.
Production of Biaxially Stretched Polypropylene Film This sequential biaxially stretched film was used as a raw fabric, and the width of each of the mimetic portions was cut about 10 centimeters (cm) from both ends and supplied to the simultaneous biaxial stretching process.
Next, using a simultaneous biaxially stretched film forming apparatus, using a tenter (preheating temperature: 175 ° C., stretching temperature: 175 ° C.), the vertical direction (MD) is 1.4 times and the horizontal direction (TD) is 0.80. The film was stretched twice to obtain a biaxially stretched polypropylene film having a thickness of 35 μm.
The results are shown in Table 5.
Table 5
In the biaxially stretched polypropylene film of the present invention, high strength stretching can be achieved and the elastic modulus can be increased by increasing the strength of the mimetic portion held by the clip. On the other hand, in the comparative example, since the strength of the mimetic portion was the same as the strength of the stretched portion, it was not possible to stretch at a high magnification, and the tensile modulus was insufficient.

According to the present invention, the strength and heat resistance of the propylene-based polymer due to the stretching orientation are improved, so that it can be used not only as a packaging material but also for various industrial materials such as a release film.

Claims (7)

  A method for producing a propylene-based biaxially stretched film, wherein a biaxially-stretched film is further stretched simultaneously after the cut portion of the propylene-based film stretched in at least one direction is cut off.   The method for producing a propylene-based biaxially stretched film according to claim 1, wherein the propylene-based film stretched in at least one direction is either a propylene-based film uniaxially stretched in the vertical direction or a propylene-based film stretched biaxially. .   The method for producing a propylene-based biaxially stretched film according to claim 2, wherein the propylene-based film stretched in at least one direction is either a propylene-based film that is sequentially biaxially stretched or a propylene-based film that is simultaneously biaxially stretched. .   The manufacturing method according to claim 1, wherein after the cut portion is cut off, both ends thereof are folded back, and the folded portion is gripped by a tenter clip and simultaneously biaxially stretched.   After the cut-out portion is cut off, a short film having a tensile modulus higher than the tensile modulus of the end is pressed to both ends of the short width film within a range that does not hinder stretching, and the tenter clip presses the pressed portion of the short film. The manufacturing method according to claim 1, wherein the film is held and simultaneously biaxially stretched.   After the cut-out portion is cut, a short film is sandwiched between the folded portions at both ends within a range that does not hinder stretching, and the tenter clip grips the folded folded portion and is simultaneously biaxially stretched. The manufacturing method according to claim 1. The propylene-based system according to any one of claims 1 to 6, wherein when the biaxial stretching is performed simultaneously, the stretching is performed 1.5 to 5 times in the vertical direction and 0.8 to 10 times in the horizontal direction. A method for producing a biaxially stretched film.