JPH0651348B2 - Method for producing tube-shaped biaxially stretched film - Google Patents

Description

The present invention relates to a tube-shaped uniaxially stretched film obtained by melt-casting a polyolefin resin containing an inorganic filler and stretching it in the machine direction. And a tube-shaped biaxially stretched film.

[Conventional technology and its problems]

Conventionally, as a method for producing a tube-shaped biaxially stretched film, an unstretched tube-shaped film is introduced between two sets of nitro rolls, allowed to reach a stretching temperature, and laterally stretched by the pressure of gas blown into the tube, almost simultaneously. Stretching in the machine direction is carried out due to the difference in peripheral speed between the nickel rolls.

The most important point in the production of the tube-shaped biaxially stretched film is how to reduce the fluctuation of the stretching start position, that is, the position where the expansion of the tube starts, and there are some improved methods for heating the tube. Proposed, but still insufficient to get good quality products. In particular, in the production of a tube-shaped biaxially stretched film of a polyolefin resin containing a large amount of an inorganic filler, the stretching start position is liable to vary, and the variation of the tube diameter during stretching, and eventually the rupture of the tube, makes stretching difficult. Further, even when the film is stretched relatively stably, unevenness in thickness and unevenness in stretching, so-called stretching unevenness occur, and a good quality film cannot be obtained. These phenomena become more prominent as the line speed during stretching increases.

[Structure of Invention]

The present inventors have completed the present invention as a result of diligent studies in order to obtain a stable and good quality product with little variation in the stretching start position in the production of a tube-shaped biaxially stretched film of a polyolefin resin containing an inorganic filler. It came to do.

That is, the gist of the present invention is that a tube-shaped uniaxially stretched film obtained by melt-forming a polyolefin resin containing an inorganic filler and stretching it in the machine direction is stretched in the machine direction and the transverse direction by a tuber stretching method. In producing the axially stretched film, a heating air ring, a shielding plate, and a cooling air ring are fed between two sets of nip rolls, and the tube-shaped uniaxially stretched film is fed to the tuber stretching device sequentially arranged from the nip roll side. It is continuously supplied through a nickel roll, and hot air having a velocity vector in the direction opposite to the direction of travel of the tube is blown out toward the tube from the heating air ring to heat it to the stretching temperature and the pressure of the gas introduced into the tube After stretching the tube in the transverse direction, it immediately has a velocity vector in the same direction as the traveling direction of the tube. The 却風 blown from the air ring for the cooling, resides in the production method of Chiyubu like biaxially oriented film, characterized by cooling the Chiyubu.

Hereinafter, the present invention will be described in detail.

The tube-shaped unstretched film used in the present invention is obtained by an ordinary inflation method using a circular die. The unstretched tube-shaped film thus obtained is pre-stretched in the machine direction before stretching in the biaxial direction (machine direction and machine direction).

The apparatus for pre-stretching in the machine direction is not particularly limited, and a roll type uniaxial stretching machine may be used, or an unstretched tube may be simply introduced between two sets of nip rolls and stretched depending on the peripheral speed difference.

The pre-stretch ratio in the machine direction is preferably 1.1 to 5 times. If it is less than 1.1, it is difficult to stretch in the lateral direction in the post process, and if it is 5 times or more, the tube easily expands at low gas pressure, so it is easily affected by slight temperature unevenness and film thickness unevenness. It becomes difficult to perform uniform drawing on the sheet.

The stretching temperature may be below the melting point and above room temperature.

The tube-shaped film pre-stretched in the machine direction is then
It is biaxially stretched by the tumbler method. Next, the method will be described with reference to the drawings.

FIG. 1 is an explanatory view showing an example of a tubular stretching apparatus used in the method of the present invention.

In the figure, 1 is a tube-shaped uniaxially stretched (pre-stretched) film, 2
Is a feeding nip roll, 3 is a take-up nip roll, 4 is a heating air ring, 5 is a cooling air ring, 6 is a preheating cylinder,
7 is a partition plate, 8 is a gas blowing tube, 9 is a biaxially stretched film, 10 and 10 'are guide rolls, 11 is a slitting device, 12 and 12' are slit biaxially stretched films,
Reference numerals 13 and 13 'denote a winding portion, 14 a valve, and 15 a shield plate.

First, the outline will be described. The pre-stretched tube-shaped uniaxially stretched film 1 is fed from a feeding nip roll 2,
It is heated to the stretching temperature by the hot air from the heating air ring, expanded (stretched) by the gas pressure from the gas blowing pipe 8, and stretched in the longitudinal direction by the difference in the peripheral speed between the feeding nip roll 2 and the take-up nip roll 3. Be wound up.

Heating air ring 4 for heating the pre-stretched film 1
Has an inner diameter of 1.01 to 1.5 times the tube diameter of the tube-shaped uniaxially stretched film 1 preliminarily stretched in the longitudinal direction. Further, the hot air blown from the heating air ring 4 toward the tube-shaped uniaxially stretched film 1 needs to have a velocity vector in the direction opposite to the traveling direction of the tube-shaped uniaxially stretched film 1, and the hot air blowing angle is preferable. Is 20 to the side surface of the tube-shaped uniaxially stretched film 1.
It is preferably 70 °.

When hot air is blown obliquely from the heating air ring 4 toward the traveling direction of the tube-shaped uniaxially stretched film 1 and is stretched in the lateral direction, the stretched tube is further heated, and the tube is further deformed to change the tube diameter. It causes a defect that it cannot be kept constant.

Also, if the inner diameter of the heating air ring 4 is smaller than 1.01 times the tube diameter of the tube-shaped uniaxially stretched film 1, it is not preferable because the tubular tube comes into contact with the hot air outlet due to the internal pressure. The stretching start position of (1) changes, which is not preferable.

Next, when the blowing angle of the hot air from the heating air ring 4 exceeds 70 ° with respect to the side surface of the tube, a part of the hot air also flows in the tube traveling direction, so that the tube stretched in the lateral direction is heated and the tube is further expanded. It may be deformed, and it is difficult to keep the tube diameter constant.
If it is less than °, the tube expands before passing through the hot air outlet, the stretching start position fluctuates, and further, the tube expands larger than the inner diameter of the hot air outlet and may contact the heating air ring 4, so it is recommended. Can not.

A preheating cylinder 6 formed of a tubular body in the front portion of the heating air ring 4, that is, in the direction in which the hot air of the heating air ring 4 faces.
It is good to provide. The preheating cylinder 6 is a tube-shaped uniaxially-stretched film 1 in which the heating air blown from the heating air ring 4 is heated.
It is intended to be held around and preheated, which serves to improve heating efficiency.

The inner diameter of the preheating cylinder is the same as that of the tube-shaped uniaxially stretched film 1.
It is about 1.05 to 2 times. If the inner diameter of the preheating cylinder 6 is less than 1.05 times the diameter of the tube-shaped uniaxially-stretched film 1, the gap is too narrow and the flow velocity of the hot air becomes too fast, causing a disturbance in the flow of the hot-air and making the tube-shaped uniaxially-stretched film 1 uniform. I can't preheat. If it is more than twice, the space formed by the tube-shaped uniaxially stretched film 1 and the preheating cylinder 6 is too large, so that the preheating heating by the hot air blown from the heating air ring 4 becomes insufficient, and the effect of providing the preheating cylinder 6 is sufficient. Can't get to.

The preheating cylinder 6 is provided with a structure through which the tube-shaped uniaxially stretched film 1 can pass and a small amount of hot air can pass, preferably a donut-shaped partition plate 7 having a gap between the tube and the tube of about 0.5 to 5 mm. Often, this further increases the preheating efficiency. Further, a plurality of partition plates 7 can be provided in the preheating cylinder 6.

As a preliminary heating for the tube-shaped uniaxially stretched film 1, an external heating device, for example, an infrared heater may be additionally provided in the preheating cylinder 6. It is also possible to introduce hot air from the outside into the preheating cylinder 6 for auxiliary heating.

The length of the preheating cylinder 6 and the gap between the partition plate 7 and the tube-shaped uniaxially stretched film 1 may be appropriately set depending on the stretching conditions and the like.

The tube-shaped uniaxially stretched film heated by the hot air from the heating air ring 4 is then laterally expanded (horizontally stretched) by the pressure of the gas introduced from the gas blowing pipe 8, and the feeding nip roll 2 and the take-up nip roll 3 The film is further stretched in the machine direction due to the difference in the peripheral speed between the film and the film to obtain a biaxially stretched film.

The stretching ratio is set by adjusting the pressure of the gas introduced into the tube. For example, a take-up Nipro roll 3 of a tube-shaped biaxially stretched film 9 stretched in the lateral direction is used as a grooved roll, and a gas blowing pipe 8 is inserted into the tube through the groove to continuously blow gas into the tube. Adjust to the tube diameter of. More preferably, the gas blowing pipe 8 inserted into the tube is a double pipe, and the gas is continuously blown into the tube from one side, and a part of the gas blown from the other side is exhausted to the outside of the tube. The diameter can be adjusted.

The stretching ratio in the longitudinal direction is preferably 1.1 to 5.0 times,
If it exceeds 5.0 times, if the tube diameter fluctuates or if there are pinholes in the film, the film is likely to tear during stretching, and the tube will puncture, making continuous stable stretching difficult.

If it is less than 1.1 times, the resistance that the film receives while running,
For example, contact resistance with the shield plate 15, guide rolls 10, 1
Due to the contact resistance with 0 ', the take-up nip roll 3 cannot smoothly take the film, and the surplus film is
Since it is supplied from the feeding nickel roll 2, there is excess film near the entrance of the preheating cylinder 6, sagging, and feeding nickel roll 2
It causes problems such as winding around.

The draw ratio in the transverse direction is preferably 5 times or less, and 5
If it exceeds twice, the film tends to be affected by temperature unevenness and thickness unevenness of the film, and it may be difficult to uniformly stretch in the transverse direction. If the stretching ratio in the transverse direction is too small, the effect of stretching cannot be obtained, so a stretching ratio of about 1.3 times or more is usually adopted.

Biaxial stretching is carried out in this manner, and then, in the present invention, cooling air having a velocity vector in the same direction as the traveling direction of the tube is blown from the cooling air ring 5 to cool the tube. When cooling air is blown obliquely in the direction opposite to the direction in which the tube travels, the temperature of the tube-shaped film during stretching in the transverse direction becomes uneven, which is not preferable. Further, it is preferable that the cooling is performed promptly, and the rapid cooling can suppress the variation of the stretching start position in the transverse direction and the tube diameter.

A shielding plate 15 is provided between the heating air ring 4 and the cooling air ring 5 in order to enable the quick cooling.

The shielding plate 15 is 0.8 to 1.5 times the diameter of the tube-shaped biaxially stretched film 9 immediately before passing through the shielding plate, preferably 0.9 to 1.3.
It is a donut-shaped plate with a double hole diameter.

If the hole diameter is smaller than 0.8 of the film diameter, the film largely digs into the shielding plate, the contact force becomes large, and there is a problem that the film is damaged or punctured.

If the hole diameter exceeds 1.5 times the bubble diameter, the same inconvenience as when there is no shielding plate, that is, if the film feed speed is increased, the hot air blown out from the heated air ring will accompany the traveling film. Flow downwards, the hot air and the cold air blown out from the cooling air ring at the bottom are mixed, and therefore, the ambient temperature around the film is not uniform and constant, and the stretching state fluctuates due to temperature unevenness, The film swings so much that continuous stable stretching cannot be performed.

The biaxially stretched film 9 cooled by the cooling air from the cooling air ring 5 is taken up by the take-up nip roll 3 via the guide rolls 10 and 10 ', and the slitting device 11 is used.
Biaxially stretched film 1 with slits in both ears
The windings 12, 12 'are wound on the winding portions 13, 13'.

The polyolefin used in the polyolefin resin containing the inorganic filler used in the present invention is polyethylene,
Polypropylene or the like, and the polyethylene is an ethylene homopolymer having a density of 0.91 g / cc or more obtained by the medium- and low-pressure method, or a copolymer of ethylene and another α-olefin, and the polypropylene has a crystalline property. It includes a propylene homopolymer, a copolymer of propylene and other α-olefin, a random copolymer and a block copolymer, and these can be used alone or as a mixture of two or more kinds.

As inorganic fillers, calcium carbonate, talc, clay,
Kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, aluminum hydroxide, zinc oxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, asbestos powder, glass powder , Shirasu balloon, zeolite, silicate clay and the like are used, and calcium carbonate, talc, clay, silica, diatomaceous earth, barium sulfate and the like are particularly preferable.

The average particle size of the inorganic filler is preferably 30 μm or less, more preferably 10 μm or less, most preferably 5 μm or less.

The surface treatment of the inorganic filler is preferably carried out from the viewpoints of dispersibility in a resin and further stretchability, and treatment with a fatty acid or a metal salt thereof gives preferable results.

In addition to the polyolefin resin and the inorganic filler, additives such as a plasticizer, a surfactant, a polymer that is liquid at room temperature such as liquid rubber or polyhydroxy saturated hydrocarbon may be added.

Examples of the liquid rubber include liquid polybutadiene, liquid polyisoprene, and liquid polybutene. The polyhydroxy saturated hydrocarbon is a hydrocarbon-based polymer in which the main chain having at least 1.5 hydroxyl groups per molecule is saturated or mostly saturated.

The blending ratio of the inorganic filler to 100 parts by weight of the polyolefin resin is usually 25 to 400 parts by weight, and when the above-mentioned additive is used, the blending ratio of the additive is preferably 100 parts by weight or less.

〔Example〕

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples.

Example 1 Ethylene-butene-1 copolymer (MI2.1, density 0.922)
100 parts by weight of heavy calcium carbonate (average particle size 1.
Polyhydroxy saturated hydrocarbon (liquid polybutadiene having a molecular weight of 2000 (manufactured by Nippon Soda Co., Ltd.,
G-2000) was obtained by hydrogenation) and 15 parts by weight were mixed with a Henschel mixer. Then, the mixture was kneaded and granulated with a twin-screw kneader DSMII / 65 (manufactured by Nippon Steel Co., Ltd.). This is 30φ
Inflation molding was carried out by an extruder under the following extrusion conditions to form a film having a thickness of 55 μm.

Cylinder temperature: 160/190/200 ° C Head, die temperature: 200 ° C Take-off speed: 4 m / min The obtained unstretched tube-shaped film was introduced between two sets of nickel rolls and heated by hot air from a heating air ring, It is stretched only in the machine direction under the following stretching conditions, and the tube diameter is 1
The film was 00 mmφ.

Stretching speed: 10 m / min Longitudinal stretching ratio: 1.2 times Hot air temperature: 115 ° C. The above uniaxially stretched film was stretched in the transverse direction under the following stretching conditions using the tubular stretching apparatus shown in FIG.

Heated air ring (4) Inner diameter 102mm Hot air blowing angle 45 ° Preheated cylinder (6) Inner diameter 170mm 〃 Length 400mm Partition plate (7) Inner diameter 103mm Hot air temperature 115 ° C Longitudinal stretching ratio 2.0 times Horizontal stretching ratio 2.5 times Shielding plate (15) The stability of the tube when stretched with an inner diameter of 150 mm was evaluated according to the following criteria, and the results are shown in Table 1.

◯: Stable stretching can be performed without fluctuation in the stretching start position.

Δ: The stretching start position fluctuates slightly.

X: The stretching start position fluctuates and is not stable.

Biaxially stretched films were produced in exactly the same manner as in Example 1, except that the feed rates of Examples 2 and 3 were changed as shown in Table 1.

The results are shown in Table-1.

Comparative Examples 1 and 2 A biaxially stretched film was manufactured in exactly the same manner as in Example 1 except that the film feed rate was changed as shown in Table 1 without providing a shielding plate.

The results are shown in Table-1.

[Effects of the Invention] According to the method of the present invention, a relatively fragile film containing an inorganic filler can be satisfactorily stably stretched, and a biaxially stretched film having high strength and no thickness unevenness can be highly efficiently produced. It can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a tubular stretching apparatus used in the method of the present invention. In the figure, 1 ... Cube-shaped uniaxially stretched film stretched in the longitudinal direction 2 ... Feeding Niprol 3 ... Taking Niprol 4 ... Heating air ring 5 ... Cooling air ring 6 ... Preheating cylinder 7 ... Partitioning Plate 8 ... Gas blowing tube 9 ... Cube-shaped biaxially stretched film 10 stretched in the lateral direction 10 Guide roll 11 11 Slitting device 12 Slit stretched film 13 Rolled up stretch Film 14 …… Blown gas control valve 15 …… Shield plate

Front page continuation (72) Inventor Yu Suzuki, 1000 Kamoshida-cho, Midori-ku, Yokohama, Kanagawa Sanryo Chemical Industry Co., Ltd. (72) Inventor Yoshinori Hayakawa, Kamoshida-cho, Midori-ku, Yokohama, Kanagawa Sanryo Kasei Industrial Research Institute

Claims (5)

[Claims] 1. A tube-shaped uniaxially-stretched film obtained by melt-forming a polyolefin resin containing an inorganic filler and stretching it in the machine-direction. The tube-shaped biaxially-stretched film is stretched in the machine-direction and the transverse-direction by a tuber stretching method. In the production of the two nip rolls, a heating air ring, a shielding plate, and a cooling air ring are fed, and the tube-shaped uniaxially-stretched film is continuously fed into the tube-stretching device arranged in order from the nip roll side. Gas is supplied to the tube from the heating air ring toward the tube to heat it to the stretching temperature, and the temperature of the gas introduced into the tube causes the tube to traverse. After being stretched in the direction, the cooling air having a velocity vector in the same direction as the traveling direction of the tube is immediately cooled. Blown from the air ring, the production method of Chiyubu like biaxially oriented film, characterized by cooling the Chiyubu. 2. The method according to claim 1, wherein the heating air ring has an inner diameter of 1.01 to 1.5 times the tube diameter of the tube-shaped uniaxially stretched film. 3. A preheating cylinder having an inner diameter 1.05 to 2 times as large as the tube diameter of the tube-shaped uniaxially stretched film is provided in the front portion of the heating air ring. The method described in the section. 4. The hot air withdrawn from the heating air ring is blown at an angle of 20 to 70 ° with respect to the side surface of the tube-shaped uniaxially stretched film.
The method described in the section. 5. The inner diameter of the shield plate is 0.8 to 1.5 times the diameter of the tube-shaped biaxially stretched film immediately before passing through the shield plate, as set forth in claim 1. Method.