JP2580270B2 - Ultra-high molecular weight polyethylene biaxially stretched film and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biaxially stretched film made of ultra-high molecular weight polyethylene and a method for producing the biaxially stretched film, and more particularly to mechanical strength, moisture permeability and sliding. The present invention relates to a thin biaxially stretched film excellent in dynamic characteristics and the like and a method for producing the biaxially stretched film.

Technical background of the invention and its problems Ultra-high molecular weight polyethylene is superior to conventional so-called general-purpose polyethylene in its properties such as impact resistance, abrasion resistance, chemical resistance, and tensile strength. The use as engineering plastics is expanding.

However, ultra-high molecular weight polyethylene has a very high melt viscosity and low fluidity as compared with general-purpose polyethylene, so when molding using such ultra-high molecular weight polyethylene, conventional inflation molding methods and the like are used. There is a problem that molding methods such as extrusion molding and injection molding are difficult to use. For this reason, compression molding is mainly employed as a method for molding ultra-high molecular weight polyethylene, and as another method, only a method of extruding a rod or the like at a very low speed has been proposed.

Also, as a method for producing an ultra-high molecular weight polyethylene film, after sintering ultra-high molecular weight polyethylene powder,
A method in which a film is produced by heating to a temperature equal to or higher than the melting point of the ultra-high molecular weight polyethylene used and heating, compressing and cooling between a pair of belts (see Japanese Patent Publication No. 48-11576); Of ultra high molecular weight polyethylene sheet obtained by sintering the powder of (1) using a pressure roll at a temperature within a range from the second transition temperature or higher to a temperature lower than the melting point (JP-A-53-45376). Publications) are proposed.

Although a film having a good appearance can be produced by the above-mentioned method, it is very difficult to keep the thickness of the obtained film below a certain value because the melt viscosity of ultrahigh molecular weight polyethylene is extremely large. In addition, particularly in the latter method, since the heating temperature is lower than the melting point, the viscosity of the ultra-high molecular weight polyethylene further increases, and even if rolling is performed using a pressure roll, a thin film cannot be obtained. Was.

As a method of producing a thin film, a method of stretching a thick sheet can be considered.However, since ultra-high molecular weight polyethylene has a very high molecular weight, even if ordinary stretching conditions are employed, the film is stretched during stretching. There has been a problem that stretching cannot be performed smoothly, such as frequent cutting.

Furthermore, a method of producing a thin film by rolling a sheet made of ultra-high molecular weight polyethylene using a pressure roll is also conceivable.However, when the crystalline polyethylene is heated to a melting point or higher, the viscosity increases and the viscosity decreases. , Roll rolling and the like tend to be difficult, in fact, even in ultra-high molecular weight polyethylene, the above-mentioned JP-A-53-45376, the melting point or higher, the resin melted on the pressure roll adheres, good It is described that a film having an appearance cannot be produced.

On the other hand, the present applicant has already applied for a method for producing a biaxially stretched film of ultrahigh molecular weight polyethylene by an extrusion molding method (see JP-A-59-227420). The method for producing a biaxially stretched film according to this application is a method in which a large amount of a plasticizer is mixed with ultra-high molecular weight polyethylene and extruded.

The biaxially stretched ultra-high molecular weight polyethylene obtained by this method has excellent mechanical properties such as tensile strength and impact strength, but a considerable amount of plasticizer remains in the obtained film, When the plasticizer is extracted and removed, voids are formed in the portion where the plasticizer was present, so that the resulting ultra-high molecular weight polyethylene film has high moisture permeability and is difficult to use in some applications. Was.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems associated with the prior art as described above, and has a low moisture permeability coefficient and a low dynamic friction coefficient, and also has an excellent high impact strength and tensile strength at break. It is an object to provide a film and a method for producing this film.

The ultrahigh molecular weight polyethylene biaxially stretched film according to the present invention has an intrinsic viscosity [η] measured at 135 ° C. in a decalin solvent.
A skive sheet or an inflation film made of ultra-high molecular weight polyethylene that is 5 dl / g or more, a constant temperature within a temperature range of 10 ° C. lower than the melting point of the ultra-high molecular weight polyethylene and 15 ° C. higher than the melting point, and 30 mm / min. A film obtained by stretching at least 4 times in the machine direction and the transverse direction at the following stretching speed, and the film has a thickness of 0.5 to 500 μm and an impact strength of 5000 kgcm.
/ cm or more, the dynamic friction coefficient is 0.2 or less, the tensile strength at break is 700 kg / cm ² or more, and the moisture permeability coefficient is 0.45 gmm / m ²
・ It is characterized by being less than 24 hours.

Further, the method for producing a biaxially stretched ultrahigh molecular weight polyethylene film according to the present invention comprises a skive sheet or an inflation film made of ultrahigh molecular weight polyethylene having an intrinsic viscosity [η] of 5 dl / g or more measured in decalin solvent at 135 ° C. From the melting point of the ultra-high molecular weight polyethylene by 10
30 ° C in the temperature range 15 ° C higher than the melting point
/ Min in the machine direction and the machine direction
It is characterized in that it is stretched twice or more to a thickness of 0.5 to 500 μm.

According to the production method of the present invention, a thin biaxially stretched film can be produced using ultra-high molecular weight polyethylene having low moldability.

The biaxially stretched ultrahigh molecular weight polyethylene film thus produced is a thin film, and has characteristics such as a low moisture permeability coefficient and a low dynamic friction coefficient, and a high impact strength and a high tensile strength at break.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the biaxially stretched film of the ultrahigh molecular weight polyethylene of the present invention and the method for producing the ultrahigh molecular weight polyethylene film will be specifically described.

The ultrahigh molecular weight polyethylene biaxially stretched film of the present invention has an intrinsic viscosity [η] of 5 measured at 135 ° C. in a decalin solvent.
It is a biaxially stretched film made of ultra high molecular weight polyethylene of dl / g or more and having a thickness of 0.5 to 500 μm. In this biaxially stretched film, the stretching ratio in both the longitudinal and transverse directions is 4 times or more.

And the biaxially stretched film of the present invention has a dynamic friction coefficient.
And 0.2 or more, break tensile strength longitudinal and also the transverse direction 700 kg / cm ² or more, impact strength is at 5000 kg · cm / cm or more, and moisture permeation coefficient 0.45g · mm / m ² · 24 hours Is less than.

The biaxially stretched film according to the present invention, 13 in decalin solvent
It can be produced by biaxially stretching an inflation film or skive sheet made of ultrahigh molecular weight polyethylene having an intrinsic viscosity [η] of 5 dl / g or more measured at 5 ° C. at a specific temperature.

The ultrahigh molecular weight polyethylene used in the present invention is a polymer or a copolymer containing a structural unit derived from ethylene. In the present invention, when the ultrahigh molecular weight polyethylene is a copolymer, propylene, 1-butene, 1-hexene, 1-octene and 4
And a structural unit derived from an α-olefin such as -methyl-1-pentene.

The ultrahigh molecular weight polyethylene used in the present invention has an intrinsic viscosity [η] of 5 dl / g or more, preferably 8 to 25 dl / g, measured at 135 ° C. in a decalin solvent. Above intrinsic viscosity [η]
Is less than 5 dl / g, it is not possible to obtain a biaxially stretched film having excellent properties such as sufficient tensile strength at break. And the intrinsic viscosity is 8d
By using an ultrahigh molecular weight polyethylene of l / g or more, a biaxially stretched film having particularly excellent properties such as mechanical strength such as tensile strength at break can be obtained. The upper limit of the intrinsic viscosity [η] of the ultrahigh molecular weight polyethylene used in the present invention is not particularly limited. For example, when an ultrahigh molecular weight polyethylene having an intrinsic viscosity exceeding 25 dl / g is used, the melt viscosity is too high. Thus, it becomes difficult to produce an inflation film or skive sheet used in producing a biaxially stretched film.

The melt flow rate of the ultra-high molecular weight polyethylene used in the present invention (MFR: ASTM D1238, F) is
Usually, it is 0.01 g / 10 minutes or less.

The weight average molecular weight of such ultra high molecular weight polyethylene is usually in the range of 500,000 to 5,000,000.

Such ultra-high molecular weight polyethylene is usually crystalline.

In the present invention, ultra high molecular weight polyethylene,
Although they can be used alone, additives such as heat stabilizers, weather stabilizers, lubricants, nucleating agents, dyes, pigments and fillers may be further added within a range that does not impair the object of the present invention.

The biaxially stretched film according to the present invention is manufactured using an inflation film or skive sheet manufactured using the ultrahigh molecular weight polyethylene as described above.

Blown film is disclosed, for example, in Japanese Patent Application No. 60-17 / 1987.
It can be produced according to the method for producing an inflation film described in the specification of Japanese Patent No. 5792 or the like.

FIG. 1 shows an example of a production apparatus capable of producing an inflation film used when producing the biaxially stretched film of the present invention.

The blown film manufacturing apparatus preferably used in the present invention comprises an extruder 1 and a tube die 2 connected to the extruder 1.

The extruder 1 includes a cylindrical grooved cylinder 3 having a groove 31 therein, and a screw 4 rotatably mounted in the cylindrical shape of the grooved cylinder 3.

The tube die 2 is joined to a screw 4 and includes a mandrel 5 that rotates with the rotation of the screw 4 and an outer die 6 having a through hole into which the mandrel 5 is inserted.

Further, the screw 4 and the mandrel 5 are provided with a gas introduction pipe 7 for blowing gas for expanding the ultrahigh molecular weight polyethylene extruded from the tip of the tube die 2.

In order to produce an inflation film using ultrahigh molecular weight polyethylene, the compression ratio between the grooved cylinder 3 and the screw 4 is usually 1 to 2.5, preferably 1.3 to 1.
It is desirable to use equipment within the range of 8. The L / D value of the tube die 2 in such an apparatus is usually 5 or more, preferably 10 or more, and particularly preferably in the range of 20 to 70. In addition, tube die 2
The ratio of the inlet portion 21 of the cross-sectional area S ₁ and the tube second resin flow path of the intermediate portion 22 of the resin flow path of the sectional area _{S 2 (S 1 / S 2} ) is generally
0.5 to 3.0, preferably 1.0 to 2.0, and the ratio (S ₂ / S ₂₎ of the cross-sectional area S ₂ of the resin flow path in the intermediate section 22 to the cross-sectional area S ₃ of the resin flow path in the outlet section 23 of the tube die 2. ₃ ) is usually 1.0 to 3.0, preferably 1.1 to 2.0.

Ultra high molecular weight polyethylene is charged from the hopper 8 of the above apparatus. The charged ultrahigh molecular weight polyethylene is heated by a heating means provided in the extruder 1 to a temperature higher than the melting point of the ultrahigh molecular weight polyethylene, preferably 200 to 330 ° C., and becomes a molten state. The ultra high molecular weight polyethylene in the molten state in this way is sent in the direction of the tube die as the screw 4 rotates. The ultra-high molecular weight polyethylene sent to the tube die 2 moves in the gap formed by the mandrel 5 and the outer die 6 rotating together with the screw 4 toward the outlet 23 of the tube die.
In the present invention, the temperature from the inlet 21 to the middle 22 is preferably 180 to 330 ° C. Further, the temperature from the intermediate part 22 to the outlet part 23 is preferably 136 to 170 ° C. With such a temperature, it is possible to effectively prevent the occurrence of land melt fracture inside the tube die.

A compressed gas such as air is blown into the tube of the ultra-high molecular weight polyethylene extruded from the gas introduction pipe 7 so that the expansion ratio of the tubular film 9 becomes 1.1 to 20 times. In the present invention, the compressed gas is preferably air at 3 to 20 atmospheres. By blowing compressed gas in this way, the thickness of the tubular film 9 is usually
It is 10 to 1000 μm, preferably 30 to 800 μm. After the tube is expanded in this way, it is cooled by the cooling ring 101, the film is folded by the stabilizer 102, and the pinch roll 1
By inflation and winding at 03, an inflation film can be manufactured.

Further, the skive sheet used in the present invention, for example, to produce a rod-shaped body, preferably a cylindrical body made of ultra-high molecular weight polyethylene having the intrinsic viscosity as described above,
The rod-shaped or cylindrical body can be manufactured by cutting the sheet into a sheet shape such that the sheet thickness is usually 10 to 1000 μm, preferably 30 to 800 μm by a cutting blade while rotating.

The blown film or skive sheet thus obtained is stretched at least four times in the longitudinal and transverse directions, respectively. In particular, in the present invention, 4 to 20 in the vertical direction
It is preferable that the film is stretched in the transverse direction at a stretching ratio of 4 to 20 times.

In the present invention, the stretching of the blown film or the skive sheet as described above is performed at a temperature range of 10 ° C. lower than the melting point of the ultrahigh molecular weight polyethylene constituting the film or sheet to 15 ° C. higher than the melting point. Alternatively, the heating is performed by heating the skive sheet. By heating the blown film or the skive sheet to the above temperature range, it is possible to stretch four times or more in the longitudinal direction and the transverse direction, respectively. In particular, in the present invention, the heating temperature of the blown film or skive sheet is preferably from 10 ° C. lower than the melting point to 15 ° C. higher than the melting point.

Specifically, the melting point of ultra-high molecular weight polyethylene is usually
Since it is in the range of 125 to 145 ° C., in the method for producing a biaxially stretched polyethylene film according to the present invention, an inflation film or a skive sheet is usually used.
The biaxial stretching is performed by heating to a temperature in the range of 115 to 160 ° C, preferably 120 to 150 ° C.

Further, the stretching under the temperature conditions as described above, 30
It is performed at a speed of less than mm / min. If the stretching speed is higher than 30 mm / min, the film may be cut during stretching. In particular, in the present invention, the stretching speed is preferably in the range of 1 to 30 mm / min.

As the biaxial stretching method of the inflation film or skive sheet as described above, various methods can be adopted.Specifically, after stretching in the vertical axis direction,
Furthermore, a method of stretching in the horizontal axis direction, a method of simultaneously stretching in the vertical axis direction and the horizontal axis direction, a method of repeating biaxial stretching, and a method of sequentially repeating stretching in any one direction, and further biaxially stretching, further in both directions A stretching method, a so-called vacuum forming method of stretching by reducing the pressure of a space formed by an inflation film or a skive sheet and a mold, and the like can be given.

Biaxial stretching as described above can be performed using a known device.

In the present invention, the inflation film or the skive film may contain a plasticizer such as a hydrocarbon compound as long as the properties of the obtained biaxially stretched film are not changed. The content of the system plasticizer and the like should be 15% by weight or less.

The biaxially stretched film according to the present invention thus obtained has an impact strength of 5,000 kgcm / cm or more, preferably 5,000
~ 40000 kgcm / cm, the coefficient of dynamic friction is 0.2 or less, preferably 0.05 to 0.2, and the tensile strength at break is 700 kg / c.
m ² or more, preferably 700~5000kg / cm ^2, and less than permeance is 0.45g · mm / m ² · 24 hours, preferably 0.05 to
0.45 g · mm / m ² · 24 hours.

As described above, the biaxially stretched film according to the present invention has excellent mechanical strength, a low friction coefficient, and a low moisture permeability coefficient.

That is, the biaxially stretched film according to the present invention has excellent properties not found in the conventional polyethylene film, and has low moisture permeability as compared with the ultrahigh molecular weight polyethylene film obtained by the conventional method.

The biaxially stretched film according to the present invention requires high strength, low moisture permeability, thinning, and high wettability in addition to the conventional use of a polyethylene film such as a packaging material by utilizing such properties. It can be used in the field, for example, as a capacitor film, an insulating film and the like.

The biaxially stretched film according to the present invention may be used alone, or may be subjected to a corona discharge treatment or an anchor treatment as necessary, and may be used by being laminated with another resin, paper, metal foil, or the like. You can also.

Biaxially oriented film consisting of ultra high molecular weight polyethylene of the effect the present invention relates to the impact strength is at 5000 kg · cm / cm or more, a coefficient of dynamic friction 0.2 or less, a break tensile strength 700 kg / cm ² or more, permeance of less than 0.45g · mm / m ² · 24 hours,
Moreover, it has a thickness of 0.5 to 500 μm and is excellent in properties such as mechanical strength and lubricity, and also excellent in various properties such as low moisture permeability.

The biaxially stretched ultrahigh molecular weight polyethylene film having such excellent properties can be produced by using an inflation film or skive sheet made of ultrahigh molecular weight polyethylene under specific stretching conditions and stretching.

[Examples] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist thereof.

Example 1 An inflation film made of ultrahigh molecular weight polyethylene was produced using the inflation film production apparatus shown in FIG.

The production conditions for the blown film are as follows.

That is, screw outer diameter 30mm, screw effective length (L / D) 34, flat pitch 20mm (constant), screw compression ratio 1.8, adapter length 200mm, tube die length 55
0 mm, tube die effective length (L / D) 25, die exit outer die inner diameter 22 mm, the mandrel outer diameter _{18mm, S 1 / S 2 =} 1.40, S
₂ / S ₃ = 1.57, and tube die length (L / D) 25, die exit outer die inner diameter 22mm, die exit mandrel outer diameter 18
mm, S ₁ / S ₂ = 1.40, S ₂ / S ₃ = 1.57, and an apparatus for producing a blown film having a gas introduction pipe with a diameter of 6 mm provided inside the screw and inside the tube timer handle was used. This manufacturing apparatus further includes a cooling ring having an inner diameter of 66 mm, a stabilizer, a pinch roll, and a film winder.

Ultra high molecular weight polyethylene [intrinsic viscosity [η] measured at 135 ° C. in decalin solvent = 16.5 dl / g, MFR: less than 0.01 g / 10 min,
Melting point: 136 ° C and bulk density: 0.45 g / cm ² ] powder resin (trade name: HIZEX MILLION 240M, Mitsui Petrochemical Industries, Ltd.)
The temperature of the press was set to 280 ° C, the temperature of the adapter was set to 270 ° C, the temperature of the die base was set to 180 ° C, and the temperature of the die end was set to 150 ° C, and the screw rotation speed was set to 15 rpm. While taking up at a speed of 1.2 m / min with a pinch roll, compressed air is blown from a gas introduction pipe with a diameter of 6 mm provided inside the screw and inside the mandrel of the tube die to bring the tube into contact with the cooling ring inner diameter 66 mm. Inflated (expansion ratio = 3), fold width 104mm, thickness 200μm
Of ultra-high molecular weight polyethylene blown film.

Table 1 shows the thickness, tensile strength at break (TS), impact strength, moisture permeability coefficient and friction coefficient of this blown film (sample 1). The intrinsic viscosity and MFR of the ultra-high molecular weight polyethylene used are also described.

From the blown film obtained as described above, a sample was cut out to a size of 90 × 90 mm, a biaxial stretching machine (manufactured by Toyo Seiki Seisaku-sho, Ltd.) was used, and the blown film was heated to 140 ° C. The stretching ratio in the transverse direction was set to 4 times and the stretching ratio in the transverse direction was set to 4 times, and the film was biaxially stretched at a stretching speed of 20 mm / min to produce the biaxially stretched ultrahigh molecular weight polyethylene film of the present invention.

Table 1 shows the thickness, TS, impact strength, moisture permeability coefficient and friction coefficient of the obtained biaxially stretched ultrahigh molecular weight polyethylene film.

In the present invention, TS, impact strength, moisture permeability coefficient and friction coefficient are values measured by the methods described below.

Tensile strength at break: Specimen shape JIS K 6781 Between chucks: 86 mm Peeling speed: 200 mm / min Temperature: 23 ° C A tensile test is performed under these conditions. From this value, tensile strength at break (TS: kg / cm ² ) and Young's modulus (E) was determined.

Impact strength: Film impact tester manufactured by Toyo Seiki Co., Ltd. Capacity: 30 kg · cm Impact head sphere: 1 inch φ was used to determine the breaking strength (kg · cm / cm).

Tear strength: Tear strength (kg / cm) was determined using an Elmendorf tear tester manufactured by Toyo Seiki Co., Ltd.

Dynamic friction coefficient: The measurement of the dynamic friction coefficient was performed by the method specified in ASTM D 1894-63. That is, the films were brought into contact with each other under a constant load, and the resistance when the films were slid was measured to calculate the dynamic friction coefficient.

Moisture permeability coefficient: 1 / thickness (m), determined according to JIS Z 0208, under conditions of a temperature of 40 ° C and a humidity of 90% (g / m ² · 24 hours).
m) to obtain a moisture permeability coefficient (g · mm / m ² · 24 hours).

Comparative Example 1 The ultrahigh molecular weight polyethylene used in Example 1 and paraffin wax (melting point = 69 ° C., molecular weight = 460) were mixed at a weight ratio of 50:50.

 The MFR of this mixture was 0.037 g / 10 minutes.

Using this mixture, a biaxially stretched film was produced under the following conditions.

The mixture was melted with a screw extruder having a diameter of 30 mm and L / D = 25, extruded into a sheet using a coat hanger type T die having a die width of 30 cm (set temperature: 280 ° C.), and cooled with an extrusion roll. Thus, a sheet having a thickness of 200 μm was obtained.

Next, a sample of 90 mm × 90 mm was cut out from the sheet and biaxially stretched at a stretching temperature of 120 ° C. using a biaxial stretching apparatus (manufactured by Toyo Seiki Seisaku-sho, Ltd.) to produce a biaxially stretched film.

Table 1 shows the thickness, TS, impact strength, moisture permeability coefficient and friction coefficient of the obtained biaxially stretched ultrahigh molecular weight polyethylene film.

The biaxially stretched film contained 50% by weight of paraffin wax.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of a molding apparatus capable of producing an inflation film used for producing a biaxially stretched film of the present invention. DESCRIPTION OF SYMBOLS 1 ... Extruder 2 ... Tube die 3 ... Groove cylinder 4 ... Screw 5 ... Mandrel 6 ... Outer die 7 ... Gas introduction pipe

Claims (2)

(57) [Claims] 1. A skive sheet or an inflation film made of ultrahigh molecular weight polyethylene having an intrinsic viscosity [η] of 5 dl / g or more measured at 135 ° C. in decalin solvent at a temperature 10 ° C. lower than the melting point of the ultrahigh molecular weight polyethylene. A constant temperature within a temperature range 15 ° C. higher than the melting point, and 30
A film obtained by stretching at least 4 times in the machine direction and the transverse direction at a stretching speed of not more than mm / min. The film has a thickness of 0.5 to 500 μm and an impact strength of 5000 kg ·
cm / cm or more, tensile strength at break is 700 kg / cm ² or more, dynamic friction coefficient is 0.2 or less, moisture permeability coefficient is 0.45 gmm
/ m ² · 24 hours, biaxially stretched ultra-high molecular weight polyethylene film. 2. A skive sheet or an inflation film made of an ultrahigh molecular weight polyethylene having an intrinsic viscosity [η] of 5 dl / g or more measured at 135 ° C. in a decalin solvent at a temperature 10 ° C. lower than the melting point of the ultrahigh molecular weight polyethylene. A constant temperature within a temperature range 15 ° C. higher than the melting point, and 30
The film is stretched 4 times or more in the machine direction and the transverse direction at a stretching speed of not more than mm / min to a thickness of 0.5 to 500 μm, and has an impact strength of 5,000 kg · cm / cm or more and a tensile strength at break. Is 700 kg / cm ² or more, a coefficient of dynamic friction is 0.2 or less, and a moisture permeability coefficient is less than 0.45 g · mm / m ² · 24 hours.