JPH0655433B2 - Inflation film, its manufacturing method and equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inflation film of ultra-high molecular weight polyethylene, a method for producing the same, and an apparatus for the same.

[Conventional technology]

Ultra high molecular weight polyethylene is
It has excellent impact resistance, abrasion resistance, chemical resistance, tensile strength, etc., and its application is expanding as an engineering plastic. However, it has a very high melt viscosity and poor flowability as compared with general-purpose polyethylene, so it is extremely difficult to mold it by conventional extrusion molding such as inflation molding or injection molding, and most of them are compression molded. The present situation is that some rods are extruded at a very low speed.

Further, as a method for producing an ultra high molecular weight polyethylene film, after sintering ultra high molecular weight polyethylene powder, it is heated to a temperature equal to or higher than the melting point of polyethylene, heated between two belts, pressure-bonded, and cooled. A method for producing a film (Japanese Patent Publication No. Sho 48-11576) or a method for orienting a sintered ultra high molecular weight polyethylene sheet with a pressure roll in a temperature range from the second transition point to below the melting point (JP-A-53).
-45376 gazette) is proposed. However, although the above method produces a film having a good appearance,
Ultrahigh molecular weight polyethylene has an extremely high melt viscosity and is not suitable for forming thinner films. Also in the latter method, since the ultrahigh molecular weight polyethylene has a higher viscosity at a temperature lower than the melting point, it has a drawback that a thin film cannot be obtained even by rolling with a pressure roll. As a method for forming a thin film, a stretching method can be considered. However, since ultra-high molecular weight polyethylene has a very large molecular weight, it cannot be stretched at all by itself. It is also conceivable to heat it to a temperature above the melting point during rolling with a pressure roll, but usually when crystalline polyolefin is heated above the melting point, the tackiness increases and the viscosity decreases and roll rolling becomes difficult. However, even in the case of ultra-high molecular weight polyethylene, the above-mentioned JP-A-53-
In the 45376 publication, it is also pointed out that if the melting point or higher, the molten resin sticks to the pressure roll and a film having a good appearance cannot be obtained.

On the other hand, as a method for producing a film by improving the extrusion moldability of ultra-high molecular weight polyethylene, the present applicant has a method of producing a biaxially stretched film by mixing a large amount of a plasticizer with ultra-high molecular weight polyolefin and extruding the mixture ( JP-A-59-227420) has been proposed. The biaxially stretched film obtained by such a method is remarkably excellent in mechanical strength such as tensile strength and impact strength, but since the moisture permeability is also better than that of a normal polyolefin film, it is not suitable for use depending on the application. I understand.

[Problems to be solved by the invention]

In view of such a situation, the present inventor has conducted various studies to develop a method for obtaining a thin film of ultra-high molecular weight polyethylene, and as a result, L / D was attached to the tip of an extruder equipped with a low compression screw.
Using a molding machine in which five or more tube dies are connected, and the tube die mandrel is directly connected to the screw tip of the extruder, the molten tube film extruded from the tube die is blown with air to be cooled while expanding. As a result, it was found that an inflation film made of ultra-high molecular weight polyethylene was obtained, and the present invention was completed.

[Means for solving problems]

That is, the present invention provides, as a first invention, an intrinsic viscosity [η].
There consist 5 dl / g or more ultra-high molecular weight polyethylene, and the longitudinal direction of the break tensile strength 800 kg / cm ² or more, laterally 700 kg / cm ² or more, impact strength 5000 kg · cm / cm or more,
Shrinkage at permeance is ^{0.45 g · mm / m 2 ·} 24hrs and less than 130 ° C. (lateral direction) and a thickness of 10% or more 10~1000μm
A second aspect of the present invention provides an inflation film of ultra-high molecular weight polyethylene, which has a limiting viscosity of 5 dl / g or more and is melted with a screen extruder. The mandrel then rotates with the rotation of the screw, at least L
After extruding from a tube die with a / D of 5, a blown gas is blown into the molten tube-shaped film to increase the expansion ratio from 1.1 to
A process for producing an inflation film, which is characterized in that the film is expanded by 20 times and cooled to form a film, and a third aspect of the invention is to provide a grooved cylinder and a compression ratio of 1 to 1 from the extruder side.
An extruder consisting of a screw in the range of 2.5, a mandrel connected to the end of the screw and rotating with the rotation of the screw, and an outer die, at least L /
D is 5, the ratio (S ₁ / S ₂ ) of the sectional area S _{1 at the} inlet of the tube die to the sectional area S ₂ at the middle portion of the tube die is in the range of 0.5 to 3.0, and the sectional area S _{2 at the} middle portion of the tube die and the outlet area of the tube die are Ratio of cross-sectional area S ₃ of resin flow path (S ₂ /
Device for manufacturing inflation film, characterized in that it comprises a tube die having S ₃ ) in the range of 1.0 to 3.0, a gas flow passage extending inside the screw and the mandrel of the tube die. Is provided.

[Work]

The ultrahigh molecular weight polyethylene used in the present invention has an intrinsic viscosity [η] of 5 dl / g or more measured at 135 ° C. in a decalin solvent,
Ethylene homopolymers or ethylene and other .alpha.-olefins such as propylene, 1-butene, 1-hexene preferably having a melt flow rate (MFR: ASTM D1238, F) of 0.01 g / 10 min or less at 8 to 25 dl / g. It is a copolymer mainly composed of ethylene with 1-octene, 4-methyl-1-pentene and the like and is crystalline.

The inflation film of ultra-high molecular weight polyethylene of the present invention is produced by the method described below for the ultra-high molecular weight polyethylene and has an intrinsic viscosity [η] of 5 dl / g.
Above, preferably 8 to 25 dl / g, MFR 0.01 g /
Ten minutes or less, longitudinal tensile strength at break (TS-M) is 800
kg / cm ² or more, preferably 1000 kg / cm ² or more, transverse direction (TS-T) is 700 kg / cm ² or more, preferably 800 kg / c
m ² or more, impact strength of 5000 kg · cm / cm or more, preferably 80
Moisture permeability of less than 0.45 g · mm / m ² · 24hrs under the conditions of 00 kg · cm / cm or more, temperature of 40 ° C and humidity of 90%, preferably 0.
Shrinkage rate (lateral direction) at 40 g · mm / m ² · 24 hrs or less and at 130 ° C is 10% or more, preferably 50% or more and the thickness is 10 to
The film has a thickness of 1000 μm, preferably 10 to 500 μm.

Those with an intrinsic viscosity [η] of less than 5 dl / g have tensile strength at break,
It cannot be used as a shrink film because it has insufficient mechanical strength such as impact strength and when it is shrunk by heating, the film softens and loses its shape as a film. The upper limit of the intrinsic viscosity [η] is not particularly limited, but those having a viscosity of more than 25 dl / g tend to have an excessively high melt viscosity and inferior extrusion moldability.

The method for producing an inflation film of the present invention comprises melting the above-described ultra high molecular weight polyethylene in a screw extruder, preferably a screw extruder having a grooved cylinder (barrel), and then heating the mandrel with the rotation of the screw. Rotate at least L / D is 5 or more, preferably
After extruding from a tube die of 10 or more, more preferably 20 to 70, the gas is blown into the molten tube-like film to expand it to a expansion ratio of 1.1 to 20 times, preferably 1.5 to 12 times, and then cool the film. It is a method of making.

If the intrinsic viscosity [η] is less than 5 dl / g, the melt viscosity is low, so twisting due to co-rotation of the melt of the ultrahigh molecular weight polyethylene and the mandrel in the tube die and uneven thickness due to bending of the mandrel are likely to occur. It is difficult to obtain a film and moldability is poor.

Since the melt of ultra-high molecular weight polyethylene is a rubber-like lump unlike the melt of general-purpose polyethylene, in a tube die with an L / D of less than 5, the melt is completely homogeneously fused before being extruded from the die. Therefore, when the gas is blown into the tube-shaped film extruded from the die, the tube does not swell evenly or breaks, so that a good film cannot be obtained. On the other hand, the upper limit of L / D is not particularly limited, but it is preferably 70 or less for practical use. The L / D of the tube die is correlated with the productivity, and the larger the L / D is, the higher the molding speed can be.

Also, the tube die mandrel must be rotated with the rotation of the extruder screw. The rotation speed of the mandrel does not necessarily have to be the same as the rotation speed of the screw, and the object of the present invention can be achieved only by rotating the rotation speed. If the mandrel does not rotate, the mandrel will be eccentric and a tube-shaped film of uniform thickness cannot be obtained. The mandrel can be attached to the tip of the screw by directly fixing, screwing, fitting or inserting the mandrel on the tip of the screw, or by interposing a joint, etc., but directly attaching the mandrel to the tip of the screw. The method is simple and can be removed, so there are advantages that the extruder and tube die can be disassembled and cleaned, and the inner diameter can be easily changed.

If the expansion ratio of the tube-shaped film extruded from the tube die is less than 1.1 times, a thin inflation film with a thickness of 200 μm or less cannot be obtained, and since the oriented crystal in the lateral direction is small, the tensile strength at break, impact strength, Mechanical properties such as tear strength cannot be improved. Further, it is impossible to impart the performance as a shrink film. On the other hand, when the expansion ratio exceeds 20 times, the film becomes cloudy or bursts. Therefore, the expansion ratio of 20 times is the limit. The expansion ratio in the present invention means the ratio of the circumferential length of the tube at the die exit to the circumferential length of the expanded tube.

The gas blown into the tube-shaped film is usually air, but nitrogen or the like may be used.

Cooling of the expanded film should be done either by air blown out uniformly from the air ring equipped with a blower on the outside of the film, or by a water-cooled or air-cooled cooling ring that is in close contact with the film. You can also

After cooling, the film is folded in a conventional manner, i.e. a stabilizer. Then, using a pinch roll, a flat film composed of two sheets is formed and wound up by a product winding machine.

In the present invention, the extrusion molding temperature of ultra-high molecular weight polyethylene is usually not lower than the melting point and not higher than 350 ° C, preferably 140 to 330 ° C.
It is preferable to extrude at a temperature of. If the extrusion molding temperature is lower than the melting point, the resin is likely to be clogged in the die, which causes equipment damage. If the extruder temperature is 200 to 330 ° C, the temperature of the tube die inlet to the middle is 180 to 310 ° C, and the temperature of the tube die middle to the outlet is 136 to 170 ° C, the molding temperature in the tube die is This is preferable because no land melt fracture occurs.

The apparatus for producing the inflation film of ultra-high molecular weight polyethylene of the present invention has a grooved cylinder 2 and a compression ratio of 1 to 2.5, preferably 1.3 to 1.8, from the extruder 1 side as shown in FIG. An extruder 1 consisting of a screw 3, a mandrel 5 connected to a screw tip 4 and rotating with the rotation of the screw, and an outer die 6 have at least L / D of 5, preferably 10, more preferably 20 to 70, and a tube die inlet. The ratio (S ₁ / S ₂ ) of the cross-sectional area S ₁ of the resin flow path of the portion 71 and the cross-sectional area S ₂ of the resin flow path of the tube die middle portion 72 is 0.5 to 3.0, preferably 1.0 to 2.0 and the above S ₂ . it the ratio of the sectional area S ₃ of the resin flow path Chiyubudai inlet 73 _(S 2 _/ S ₃₎ is 1.0 to 3.0, Chiyubudai 7 preferably is in the range of from 1.1 2.0, of Sukuriyu 3 And formed by and a gas flow passage 8 formed by extending the inside of the mandrel 5 Chiyubudai.

The groove portion 21 of the grooved cylinder 2 stably supplies the ultra high molecular weight polyethylene powder to the pressure bonding portion 22. If the compression ratio of the screen 3 is less than 1.0, the compression stress of the resin against the wall surface of the cylinder is small and the extrusion amount becomes unstable, and the appearance of the film tends to be poor due to the surging phenomenon or degassing failure.
On the other hand, when it exceeds 2.5, the resin temperature abnormally rises due to the blockage phenomenon or frictional heat in the compression section 22, the molecular weight of the resin is significantly decreased by thermal decomposition, and the mechanical strength of the film may decrease, which is preferable. Absent.

Although the mandrel 5 is screwed to the tip of the screw 3 in the figure, it may be fixed, fitted or inserted as described above.

When the L / D of the tube die is less than 5, the molten resin is not completely fused, and a good inflation film cannot be obtained. The L / D of the tube die is the tube die entrance.
Length from 71 to Chubudai exit 73 and Chubudai exit
The ratio is 73 to the inner diameter of the outer die 6. Also S ₁ / S
_There is no particular problem if ₂ is in the range of 0.5 to 3.0,
If the S ₂ / S ₃ ratio is less than 1.0, the molten resin will not be completely fused, while if it exceeds 3.0, the resin pressure will be excessive and it will be difficult to extrude the tube-shaped film.

As described above, the flow channel area of the tube die is basically narrowed toward the outlet of the tube die. That is, although it is a taper die, it is preferable that the tip portion 74 of the tube die is a so-called straight shape in which the flow passage area does not change, because the dimensional accuracy can be highly maintained. The straight part usually has an L / D of about 5 to 10.

It is preferable that the tip 51 of the mandrel 5 is outside the outer die 6 because the meandering of the extruded molten resin is corrected. Inside the screw 3 and the mandrel 5 of the tube die, a gas flow passage 8 for applying an internal pressure to the inside of the tube-shaped film extruded from the tube die extends.

The apparatus for producing an inflation film of ultra-high molecular weight polyethylene according to the present invention is characterized by having the above-mentioned configuration. A tube-shaped film 9 extruded from the tube die is provided on the downstream side of the tube die through a gas flow passage 8 such as air. The thickness expanded by 1.1 to 20 times by the gas of 10 to 10
A stabilizer 32, a pinch roll 33, a take-up machine (not shown), etc., which folds the film after it has been cooled by a cooling ring 31 for cooling the 00 μm inflation film, and then takes it back,
It has a device provided in a known inflation film forming machine.

〔The invention's effect〕

The inflation film made of the ultrahigh molecular weight polyethylene of the present invention is not only high in productivity as compared with a film obtained by a conventional pressure press method or a skived film obtained by thinly peeling a rod or the like, but also has conventional characteristics. It has self-lubricating property, abrasion resistance, chemical resistance, and mechanical properties such as TS-M of 800 kg / cm ² or more, TS-T of 700 kg / cm ² or more, and impact strength of 5000 kg. c
It has excellent characteristics such as m / cm or more, a moisture permeability coefficient of less than 0.45g · mm / m ² · 24hrs and a shrinkage ratio (horizontal direction) at 130 ° C of 10% or more. The ultrahigh molecular weight polyethylene inflation film of the present invention takes advantage of such features to make use of such characteristics as a lining material for a transport line such as a cassette tape liner, shout, silo, and hopper, a shrink film for coating rolls, pipes, steel pipes, etc. , Packaging film for food packaging, packaging bag, and more,
The inflation film can be slit to be suitably used in various fields such as a packaging tape or a high strength drawn yarn.

The method and apparatus of the present invention can stably produce an inflation film of ultrahigh molecular weight polyethylene having the above-mentioned characteristics, which has been difficult to produce conventionally.

〔Example〕

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

Example 1 An inflation film made of ultra-high molecular weight polyethylene was produced using the apparatus for producing an inflation film shown in FIG.

Screen outer diameter 30mmφ, screen effective length (L / D)
34, flight pitch 20mm constant, screen compression ratio 1.8,
Adapter length 200 mm, tube die length 550 mm, tube die length (L / D) 25, die outlet outer die inner diameter
22 mmφ, die exit mandrel outer diameter 18 mmφ, S ₁ / S ₂ =
_{1.40, S 2 / S 3 =} 1.57, the gas flow path 6mmφ consisting extending inside Sukuriyu internal and Chi Yu parrot mandrel, cooling ring inner diameter 66 mm, stabilizer, pinch rolls and product winder provided. Ultra high molecular weight polyethylene [η]: 16.5
dl / g, MFR: less than 0.01 g / 10 min, melting point: 136 ° C., and bulk density: 0.45 g / cm ³ powdered resin (trade name: Heizex Million 240M, manufactured by Mitsui Petrochemical Industry Co., Ltd.),
The set temperatures of the extruder, the adapter (AD), the die base (D ₁ ) and the die end (D ₂ ) are 280 ° C, 270 ° C and 180 °, respectively.
℃ and 150 ℃, set the screw rotation speed to 15 rpm, while pulling with a pinch roll at a speed of 1.2 m / min,
Compressed air is blown from the gas flow passage of 6mmφ that extends inside the screw and mandrel of the tube die to expand the tube to the size that contacts the cooling ring inner diameter 66mmφ (expansion ratio = 3), folding width 104mm, thickness 200μm. An inflation film made of ultra-high molecular weight polyethylene was produced.

Example 2 Screen outer diameter 20 mmφ, screen effective length (L / D)
22, flight pitch 12mm constant, screen compression ratio 1.8,
Adapter length 90 mm, tube die length 240 mm, tube die length (L / D) 40, die outlet outer die inner diameter 6
mmφ, die exit mandrel outer diameter 5 mmφ, S ₁ / S ₂ =
_{1.52, S 2 / S 3 =} 1.17, are provided gas flow passage of 2.5mmφ comprising extending a mandrel inside the Sukuriyu internal and Chiyubudai, cooling ring inner diameter 20 mm, stabilizer, pinch rolls and product winder Using the same powder resin as in Example 1, the extruder, the adapter (AD), the die base (D ₁ ), and the die end (D ₂ ) each had a preset temperature of 290.
℃, 290 ℃, 170 ℃ and 150 ℃, set the screw rotation speed to 13 rpm, while pulling with a pinch roll at a speed of 0.6 m / min, the gas flow of 2.5 mmφ extending inside the screw and mandrel. Compressed air was blown into the tube from the passage to expand the tube to a size that contacts the cooling ring inner diameter of 20 mmφ (expansion ratio = 3.3) to produce an ultra high molecular weight polyethylene inflation film having a folding width of 31 mm and a thickness of 75 μm.

Comparative Example 1 Under the conditions of Example 2 except that the expansion ratio was 1.0, the thickness of 260 μ
m ultra high molecular weight polyethylene film was produced.

Example 3 Under the conditions of Example 2 except that the expansion ratio was 1.2, the thickness was 200 μm.
m ultra high molecular weight polyethylene film was produced.

Example 4 An ultrahigh molecular weight polyethylene film having a thickness of 20 μm was produced under the conditions of Example 1 except that a cooling ring inner diameter of 220 mmφ was used to increase the expansion ratio by 10 while pulling with a pinch roll at a speed of 2.0 m / min. did.

Comparative Example 2 Commercially available [η]: 3.5 dl / g, MFR = 0.03, density: 0.95
A high density polyethylene film of 0 g / cm ³ and a thickness of 20 μm was used as a comparative example. Then, the physical properties of these films were evaluated by the following methods. The results are shown in Table 1.

Tensile test: Shape of test piece JIS K 6781 Chuck: 86 mm Tensile speed: 200 mm / min Temperature: 23 ° C. Under these conditions, tensile strength at break (TS: kg / cm ² ) was determined.

Impact strength: Film impact tester made by Toyo Seiki Capacity: 30 kg · cm Impact spherical surface: 1 inch φ was used to determine the fracture strength (kg · cm / cm).

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

Heat shrinkage: After heating in an air oven at 130 ° C for 1 hour, 23
The shrinkage rate after 24 hours at ℃ was obtained.

Moisture Permeability Coefficient: Based on JIS Z 0208, determine the moisture permeability (g / m ² · 24hrs) under the conditions of temperature 40 ° C and humidity 90%, 1 / thickness (m
m) to obtain the moisture permeability coefficient (g · mm / m ² · 24 hrs).

[Brief description of drawings]

FIG. 1 is a front sectional view of an inflation film forming apparatus according to the present invention. 1 ... Extruder, 5 ... Mandrel 7 ... Die

Claims (3)

[Claims] 1. An ultrahigh molecular weight polyethylene having an intrinsic viscosity [η] of 5 dl / g or more, and a tensile strength at break of 800 kg / cm ² or more in the longitudinal direction and 700 kg / c in the transverse direction.
m ² or more, impact strength of 5000 kg · cm / cm or more,
An inflation film having a moisture permeability coefficient of less than 0.45 g · mm / m ² · 24 hrs, a shrinkage ratio (lateral direction) at 130 ° C. of 10% or more, and a thickness of 10 to 1000 μm. . 2. An ultrahigh molecular weight polyethylene having an intrinsic viscosity [η] of 5 dl / g or more is melted by a screw extruder, and then a mandrel is rotated with rotation of a screw and extruded from a tube die having an L / D of 5 at least. After that, a blown gas is blown into the melted tubular film to expand it at a swelling ratio of 1.1 to 20 and then cooled to form a film. 3. An extruder comprising, from the extruder side, a grooved cylinder and a screw having a compression ratio of 1 to 2.5, a mandrel connected to the tip of the screw and rotating with the rotation of the screw, and an outer die. At least L / D is 5, the ratio (S ₁ / S ₂ ) of the cross-sectional area S ₁ of the tube die inlet portion to the cross-sectional area S ₂ of the tube die intermediate portion is in the range of 0.5 to 3.0, and the tube die Cross-sectional area S ₂ of the intermediate portion and cross-sectional area S ₃ of the resin flow path at the tube die outlet
A tube die having a ratio (S ₂ / S ₃ ) in the range of 1.0 to 3.0, a gas flow passage extending inside the screw, and inside the mandrel of the tube die. An apparatus for producing an inflation film, which is characterized in that