JPS62191121A - Manufacture of tubular biaxially stretched film - Google Patents

Abstract

PURPOSE:To highly efficiently manufacture a biaxially stretched film with high strength and without thickness ununiformity by a method wherein a tubular uniaxially stretched film is continuously supplied and heated up to a drawing temperature by hot air blasted in the direction opposite to the running direction of the tube so as to stretch laterally and then cooled down by cooling air blasted in the running direction of the tube. CONSTITUTION:A pre-stretched tubular uniaxially stretched film 1 is led-in by lead-in nip rolls 2, heated up to a drawing temperature by hot air blasted from a heating air ring 4, inflated by the pressure of gas supplied through a gas blowing pipe 8, longitudinally stretched by the difference between the peripheral speed of the lead-in nip rolls 2 and that of take-up nip rolls 3 and taken up. The tube is cooled down by cooling air, which has the velocity vector same in direction as the direction of the running of the tube and is blasted from a cooling air ring 5. The cooled biaxially stretched film 9 is taken up through guide rolls 10 and 10' to the take-up nip rolls 3 and biaxially stretched films 12 and 12', both edges of which are slitted off by a slitting device 11 in order to be taken up to take-up parts 13 and 13'.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to a tubular uniaxially stretched film formed by melt-forming a polyolefin resin containing an inorganic filler and stretching it in the machine direction. The present invention relates to a method for producing a tubular biaxially stretched film by stretching the film.

[Conventional technology and its problems]

Conventionally, as a method for producing a tubular biaxially stretched film, an unstretched tubular film is guided between two sets of nip rolls, the stretching temperature is reached, and the film is stretched in the transverse direction by the pressure of gas injected into the tube. At the same time, stretching in the longitudinal direction is carried out using a peripheral speed difference between nip rolls.

The most important point in the production of tubular biaxially stretched film is how to reduce the variation in the stretching start point, that is, the point at which tube expansion begins, and several improvements have been made to the tube heating method. has been proposed, but it is still insufficient to obtain good quality products. In particular, in the production of tubular biaxially stretched films of polyolefin resins containing multiple sources of inorganic fillers, the stretching start position tends to fluctuate, leading to fluctuations in the tube diameter during stretching, and even tube rupture, making stretching difficult. Become. Furthermore, even when the film is stretched relatively stably, uneven thickness and non-uniform stretching occur, so-called stretching unevenness, making it impossible to obtain a film of good quality. These phenomena become more pronounced as the line speed during stretching increases.

[Structure of the invention]

The inventors of the present invention have conducted intensive studies to obtain a stable, high-quality product with little variation in the stretching start point in the production of a tubular biaxially stretched film made of polyolefin resin containing an inorganic filler. It was completed.

That is, the gist of the present invention is to produce a tubular uniaxially stretched film by melt-forming a polyolefin resin containing an inorganic filler and stretching it in the longitudinal direction. When producing a biaxially stretched film, the tubular uniaxially stretched film is sent to a tubular stretching device in which a heating air ring, a shielding plate, and a cooling air ring are placed between two sets of nip rolls in order from the nip roll side. The pressure of the gas introduced into the tube is increased by continuously supplying hot air through the included nip rolls and blowing hot air having a velocity vector in the opposite direction to the tube's traveling direction from the heating air ring toward the tube to heat it to the stretching temperature. A tubular biaxial stretching method characterized in that after the tube is stretched in the lateral direction, cooling air having a velocity vector in the same direction as the tube's traveling direction is immediately blown out from the cooling air ring to cool the tube. The problem lies in the film manufacturing method.

The present invention will be explained in detail below.

The tubular unstretched film used in the present invention is obtained by a conventional inflation method using a circular die. The thus obtained unstretched tubular film is pre-stretched in the machine direction before being stretched in the biaxial directions (longitudinal and transverse directions).

The device for pre-stretching in the longitudinal direction is not particularly limited, and a roll-axial stretching machine may be used, or an unstretched tube may simply be introduced between two sets of nip rolls, and stretching may be effected by the difference in circumferential speed.

The preliminary stretching ratio in the longitudinal direction is preferably 5 times. /, 1
If it is less than 3 times, it will be difficult to stretch in the lateral direction in the post process, and if it is 3 times or more, the tube will easily expand with low gas pressure, so it will be easily affected by slight unevenness in AI degree or film thickness. It becomes difficult to perform uniform stretching in this direction.

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

The longitudinally prestretched tubular film is then
It is stretched biaxially by the tubular method. Next, the method will be explained using the drawings.

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

In the figure, l is a tubular uniaxially stretched (pre-stretched) film, c is a feeding nip roll, 3 is a take-up nip roll, da is a heating air ring, j is a cooling air ring, 6 is a preheating cylinder,
7 is a partition plate, ε is a gas blowing pipe, 9 is a biaxially stretched film, 10 is a guide roll, // is a slitting device, lco, lco' are slit biaxially stretched films, /
3, /j' indicates the winding part, lda indicates the pulp, and ts indicates the shielding plate.

1 First, to explain the outline, a pre-stretched tubular uniaxially stretched film l is fed from an infeed nip rollco,
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, and transferred to the feeding Nippuro Rollco and the receiving nearer 7" o
- It is stretched in the longitudinal direction and wound up due to the difference in circumferential speed between A and J.

Heating air ring q for heating the pre-stretched film l
is 0/%/,! of the tube diameter of the tubular uniaxially stretched film l whose inner diameter has been pre-stretched in the longitudinal direction. It is said to be r times. Further, it is necessary that the hot air blown from the heating air ring l toward the tubular uniaxially stretched film l has a velocity vector in the opposite direction to the traveling direction of the tubular uniaxially stretched film l. The blowing angle is preferably 20 to 70' with respect to the vertical plane of the tubular uniaxially stretched film l.

Hot air is blown obliquely from the heated air ring toward the traveling direction of the tubular -JIlnlf=stretched film l.
When stretched in the transverse direction, the stretched tube is heated even after that, resulting in further deformation of the tube, resulting in a defect that the tube diameter cannot be kept constant.

In addition, the inner diameter of the heating air ring is tubular.
M' If it is smaller than x times the tube diameter of the stretched film l, the tube which has become cylindrical due to the internal pressure will come into contact with the hot air outlet, which is undesirable; if it is larger than 5 times, the horizontal stretching start position will be It fluctuates and is not desirable.

Next, when the blowing angle of the hot air from the heating air ring exceeds Oo to the side surface of the tube, a portion of the hot air also flows in the direction of tube movement, which causes the tube stretched in the lateral direction to continue to be heated, causing the tube to become even more elongated. It may have two shapes, making it difficult to maintain a constant tube diameter, and
If the tube is not vortexed at 0°, the tube expands before passing through the hot air outlet, causing fluctuations in the stretching start position.

This is not recommended because the tube may expand larger than the inner diameter of the hot air outlet and come into contact with the heated air ring.

It is preferable to provide a preheating cylinder 6 made of a cylindrical body in the front part of the heating air ring q, that is, in the direction toward which the hot air from the heating air ring q is directed. The preheating circular part 6 is for holding and preheating the heated air blown out from the heating air ring around the tubular uniaxially stretched film l, and serves to increase heating efficiency.

The inner diameter of the preheating cylinder is /,0! of the diameter of the tubular uniaxially stretched film l! -U times. The inner diameter of the preheating cylinder B is the diameter of the tubular uniaxially stretched film l, O! If it is less than r times, the gap is too narrow and the flow velocity of the hot air becomes too high, causing disturbance in the flow of the hot air and making it impossible to uniformly preheat the tubular uniaxially stretched film l. If the weight exceeds 21 g, the space formed between the tubular uniaxially stretched film 1 and the preheating cylinder 2 will be too large, resulting in insufficient preheating by the hot air blown out from the heating air ring, and the effect of the preheating cylinder 6 will not be sufficient. I can't.

The preheating cylinder 6 has a structure that allows the passage of the tubular uniaxially stretched film l and also allows a slight amount of hot air to pass through, preferably with a gap between the tube and the tube Q, j;--! A donut-shaped partition plate t of approximately rtllA may be provided, thereby further increasing the preheating efficiency.

Furthermore, a plurality of partition plates 7 may be provided within the preheating cylinder 6.

To preheat the tubular uniaxially stretched film 1, an external heating device such as an infrared heater may be provided to supplement the VC in the preheating cylinder 6.

Further, hot air can be introduced into the preheating cylinder 6 from the outside to perform supplementary heating.

The length of the preheating cylinder B and the gap between the partition plate and the tubular stretched film may be appropriately set depending on the stretching conditions and the like.

The tubular uniaxially stretched film heated by the hot air from the heating air ring is then expanded (stretched) in the transverse direction by the pressure of the gas introduced from the Tekas blowing pipe t, and then transferred to the feed nip roll and take-off nip roll. The film is further stretched in the longitudinal direction due to the difference in circumferential speed between the film and the film, resulting in a biaxially stretched film.

The stretching ratio is set by adjusting the pressure of the gas introduced into the tube.

For example, the nip roll 3 for taking up a biaxially stretched tubular film stretched in the transverse direction is a grooved roll, a gas blowing pipe S is inserted into the tube through the groove, and gas is continuously blown into the tube to achieve a predetermined value. Adjust to the tube diameter. More preferably, the gas blowing tube inserted into the tube is a double tube, and while gas is continuously blown into the tube from one side, a part of the gas blown from the other side is exhausted to the tube tube 1. The diameter can be adjusted to 2.

The stretching ratio in the longitudinal direction is 1-%! r is preferably 0 times; if it exceeds S, O times, if the tube diameter changes or there are pinholes in the film, the film will easily tear during stretching, the tube will become punctured, and continuous stable stretching will be impossible. It becomes difficult.

In addition, /, if it is less than 1 time, the resistance that the film receives during running, for example, the contact resistance with the shielding plate IS, the guide roll 10%
Due to the contact resistance with lθ', the film cannot be taken up smoothly by the take-up nip roll 3, and the excess film is fed to the feed nip roll, so there is an excess of film near the entrance of the preheating cylinder B. , causing problems such as sagging, wrapping around the feed nip rollco, etc.

The stretching ratio in the transverse direction is preferably 5 times or less, and 5 times or less.
If it exceeds twice that, the film becomes more susceptible to temperature and thickness unevenness, and it may become difficult to stretch it uniformly in the lateral direction. Note that if the stretching ratio in the lateral direction is too small, the stretching effect cannot be obtained. , a stretching ratio of about 3 times or higher is employed.

Biaxial stretching is performed in this way, and then, in the present invention, cooling air ring! Cooling air with a velocity vector in the same direction as the direction of travel of the tube is blown out to cool the tube. If the cooling air is blown in the direction VC opposite to the direction in which the tube travels, the temperature of the tubular film becomes uneven when it is stretched in the transverse direction, which is undesirable. Further, it is preferable to perform the cooling quickly, and by cooling quickly, it is possible to suppress fluctuations in the lateral stretching start position and the tube diameter.

A shielding plate 15 is provided between the heating air ring and the cooling air ring S in order to achieve this rapid cooling RIJ function.

The g bottom plate tS is 00g to 1.0g of the diameter of the tubular biaxially stretched film just before passing through the shielding plate. S times preferably 0
．． It is a donut-shaped plate with a hole diameter of 9 to 1.5 times.

If the hole diameter is smaller than 0%g of the film diameter, the film will dig into the shielding plate, the contact force will be large, the film will be damaged, or the film will be punctured, causing the same problem as when there is no plate. When the feeding speed is increased, the hot air blown out from the heating air ring flows downward along with the running film, and this hot air mixes with the cold air blown out from the cooling air ring at the bottom. For this reason, the ambient temperature around the film is not uniform and constant, resulting in temperature irregularities that cause the stretching state to fluctuate, resulting in large oscillations of the film, making continuous and stable stretching impossible.

The biaxially stretched film 9 cooled by the cooling air from the cooling air ring j passes through the guide rolls 10 and 10' and is taken up by the take-up nip roll 3, and then sent to the slitting device//
Biaxially stretched film with both sides slit by /
U, l-' are wound up by the winding section 13, /3'.

The polyolefin used in the polyolefin resin containing an inorganic filler used in the present invention is polyethylene,
Polypropylene, etc., and polyethylene is an ethylene homopolymer with a density o, q i f-/cc or more obtained by a medium-low pressure method, or a copolymer of ethylene and other α-olefins, Polypropylene includes crystalline propylene homopolymers, copolymers of propylene and other α-olefins, random copolymers, and block copolymers, which may be used alone or as a mixture of more than one olefin. is also used.

Inorganic fillers include 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, clay silicate, etc. are used, especially calcium carbonate, talc, tI clay, silica, diatomaceous earth,
Barium sulfate is preferred.

The average particle size of the inorganic filler is preferably 30μ or less, more preferably ioμ or less, and most preferably Sμ or less.

It is preferable that the surface treatment of the inorganic filler is carried out in terms of dispersibility in 11 fat and further stretchability.
Treatment with fatty acids or their bullion salts gives favorable results.

In addition to the polyolefin resin and inorganic filler, additives such as plasticizers, surfactants, normally liquid polymers such as liquid rubber or polyhydroxy saturated hydrocarbons may be added.

Liquid rubbers include liquid polybutadiene, liquid polyisoprene, and liquid polybutene.

Polyhydroxy saturated hydrocarbons are hydrocarbon polymers whose main chain is saturated or mostly saturated and has at least S hydroxyl groups per molecule.

The blending ratio of the inorganic filler to 00 parts by weight of the polyolefin resin is usually -5-1lOO parts by weight, and when the above additives are used, the blending ratio of the additives is to
It is preferable that it is below the hit portion.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to the Examples.

Example 1 Ethylene-butene-1 conjugate (MI co, 11 density 0.
9 parts) 100 parts by weight, heavy calcium carbonate (average grain reverse L - 5μ, fatty acid treatment) / / 5 parts by weight iW and polyhydroxy saturated hydrocarbon (molecular 1000 parts by weight of liquid polybutadiene (obtained by hydrogenating G-co θ00, manufactured by Nippon Soda) were mixed in a Henschel mixer.

Next, a twin-screw kneader D8Mll/6j (Nippon Steel ■
(manufactured by) K was mixed and granulated. This was inflation-molded using a 30φ extruder under the same extrusion conditions to a thickness of SSμ.
It was formed into a film.

Cylinder temperature = 760/90-200℃ Head, die temperature: 100C Take-up speed [: 4'ttt/'' The obtained unstretched tubular film is guided between a set of nip rolls, and the Heated with hot air and stretched only in the longitudinal direction under the following stretching conditions to a tube diameter of 10
It was made into an OIHAφ film.

Stretching speed: lOm/- Longitudinal stretching ratio: Heko double Hot air temperature: ttsC The above-mentioned -axially stretched film was stretched in the transverse direction using the tubular stretching apparatus shown in FIG. 1 under the following stretching conditions.

Heating air ring (4) inner diameter l θλ1 Hot air blowing angle dS0 Preheating cylinder (6) inner diameter 1'79a Length dootrn Partition plate (inner diameter 103mm Hot air temperature 11jr °C Longitudinal stretching ratio
2.0x transverse stretching magnification 2.5x shielding plate (I9 inner diameter isOtrm) The stability of the tube during stretching was evaluated using the following criteria, and the results are shown in Table 7.

○: Stable stretching is possible without fluctuation in the stretching start position.

Δ: The stretching start position slightly fluctuates.

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

Examples C and J Biaxially stretched films were produced in exactly the same manner as in Example 1, except that the film feeding speed was changed as i-/.

The results are shown in Table-1.

Comparative example 1. A biaxially stretched film was produced in exactly the same manner as in Example 1, except that no shielding plate was provided and the film feeding speed was changed as shown in Table 1.

The results are shown in Table-/.

Table 7 [Effects of the Invention] According to the method of the present invention, a film containing an inorganic filler that is relatively easy to break can be stretched in a good and stable manner, and a biaxially stretched film with high strength and no unevenness can be obtained. can be manufactured with high efficiency.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a Tuupler stretching device used in the method of the present invention. In the figure, 7...Tubular uniaxially stretched film stretched in the longitudinal direction...Feeding nip roll J...Take-up nip rollder...Heating air ring S...Cooling air ring 6... Preheating cylinder...Partition plate...Gas blowing pipe 9...Tubular biaxially stretched film IO stretched in the transverse direction...Guide roll IT...Slitting device 12...Slitting Stretched film 13... Rolled stretched film/4 <... Blowing gas control valve, IS... Shielding plate, Figure 1

Claims (5)

[Claims] (1) A tubular uniaxially stretched film obtained by melt-forming a polyolefin resin containing an inorganic filler and stretching it in the longitudinal direction is stretched in the longitudinal and transverse directions by a tubular stretching method to produce a tubular biaxially stretched film. In manufacturing,
A heating air ring, a shielding plate, and a cooling air ring are arranged between two sets of nip rolls in order from the nip roll side. Hot air having a velocity vector in the opposite direction to the direction of travel is blown from the heating air ring toward the tube to heat it to the stretching temperature, and the tube is stretched laterally by the pressure of the gas introduced into the tube. . A method for producing a tubular biaxially stretched film, which comprises immediately blowing out cooling air having a velocity vector in the same direction as the traveling direction of the tube from the cooling air ring to cool the tube. (2) The method according to claim 1, wherein the heating air ring has an inner diameter that is 1.01 to 1.5 times the tube diameter of the tubular uniaxially stretched film. (3) A preheating tube having an inner diameter of 1.05 to 2 times the tube diameter of the tubular uniaxially stretched film is provided in the front portion of the heating air ring. The method described in section. (4) The method according to claim 1, wherein the hot air blown from the heating air ring is blown at an angle of 20 to 70 degrees with respect to the side surface of the tubular uniaxially stretched film. (5) According to claim 1, the inner diameter of the shielding plate is 0.8 to 1.5 times the diameter of the tubular biaxially stretched film immediately before passing through the shielding plate. Method described.