JPH0757524B2 - Manufacturing method of tubular film - Google Patents

Description

FIELD OF THE INVENTION This invention relates to an improved process for making tubular films. More specifically, the present invention relates to an improved method for obtaining a film having a balanced strength in the vertical direction and the lateral direction when a tubular balance film of polyolefin resin is formed by an air-cooled inflation method. It is a thing.

2. Description of the Related Art In recent years, a polyolefin resin, in which the molecular orientation in the transverse direction is enhanced by the air-cooling inflation method to balance the strength in the longitudinal direction and the transverse direction, a film of high-density polyethylene with a high molecular weight is a so-called balance film. Is widely used as packaging, agricultural and industrial materials.
In this case, in order to enhance the molecular orientation in the lateral direction, the molten resin tubular body extruded from the annular die is raised while maintaining a diameter close to the diameter of the die and expanded at a predetermined height, As the position where the expansion starts, that is, the expansion start point is farther from the die surface, and the expansion ratio (the ratio of the bubble diameter after expansion to the die diameter) increases, the lateral molecular orientation increases, It comes to balance with the strength of the direction. Therefore, in order to improve the balance of strength and increase the impact strength of the entire film, it is necessary to increase the expansion ratio or increase the expansion start point. Shaking from side to side or up and down becomes significant, causing wrinkles, sagging, and fluctuations in the width of the obtained film, which causes quality deterioration. In order to suppress the shaking of the valve after such expansion and prevent the occurrence of the above-mentioned trouble, the constricted part of the bubble has been
A method in which a mandrel having a diameter smaller than the diameter of the die is contacted (Japanese Patent Publication No. 55-2180), and a mandrel with a diameter larger than the diameter of the die is placed at the position where the bubbles start to cool and solidify on the pillar erected in the center of the die. How to place
-12367 gazette), the diameters of the lower and upper ends of the mandrel and the diameter of the circular base part that attaches the mandrel to the die are regulated, the bubbles rise along the circumferential side surface of the mandrel, and the bubbles expand rapidly before reaching the upper end. Method (Japanese Patent Publication No. 59-5408), a mandrel having a metal hollow cylindrical portion having a roughened surface with a diameter 1.01 to 1.2 times the diameter of the die lip and a sufficient length. A method has been proposed in which a molten resin tube is brought into contact with the surface of the cylindrical portion before constriction occurs and expansion is started on the surface of the cylindrical portion (Japanese Patent Publication No. 59-13964).

Problems to be Solved by the Invention As described above, a number of air-cooled inflation methods for stabilizing bubbles and improving quality have been proposed so far by using a mandrel. Since the starting point of expansion or the constriction is in contact with the surface of the mandrel, that is, the stabilizer, the balance between the vertical strength and the lateral strength is unavoidable, and it is difficult to obtain a high-strength film. There was a drawback that the bubble stabilizing effect of itself was not fully exerted.

By the way, recently, due to the high performance of the inflation device, it has come to be produced with a high discharge amount, and the air blowout amount from the air cooling ring necessary for air cooling the molten resin tubular body is increased, so that the tubular body and the bubble are produced. There is a problem that the bubble is apt to sway due to an increase in the wind pressure with respect to, and the production cannot be performed with a high discharge amount. In particular, when forming a large expansion ratio, bubbles tend to roll due to an increase in the amount of air blown out, and the expansion start point tends to move up and down, and it is often impossible to manufacture a product that can be put to practical use. The roll of the bubble and the vertical movement of the expansion start point are caused by wrinkles, sagging, and fluctuation of the width of the film, and the atmospheric temperature of the bubble affects the quality of the film. In the daytime, when the position of the expansion start point is set and the atmospheric temperature is lowered in the middle of the night, the position is lowered, so that the folding width is reduced, the thickness is increased, and the quality is not constant.

The object of the present invention is to overcome the drawbacks of the conventional inflation method and stabilize the bubble in a short time with little fluctuation of the bubble when the film size is changed at the start of molding or during the molding. It is an object of the present invention to provide a method capable of producing a high-quality tubular film of a polyolefin resin, which has a large bubble stabilizing effect and has a well-balanced strength in the vertical direction and the lateral direction at high speed and with high productivity.

Means for Solving the Problems As a result of various examinations on operating conditions in the air-cooled inflation method, the present inventors raised the polyolefin resin tubular body extruded from the annular die at a diameter substantially equal to the die diameter. It is effective in stabilizing the bubble after expansion to use a mandrel that prevents the tubular body from swinging between the die and the expansion start point when the film is expanded and then formed into a balance film. The use of a mandrel with a structure that allows contact before and after the start point rather than contact at the starting point has a stabilizing effect on the bubble after expansion.Furthermore, if each mandrel is provided with a vent hole, the pressure of each part inside the bubble will be increased. Even when the film size is changed at the start of molding or during the molding process, bubbles do not sway and bubbling occurs in a short time. The present invention has been completed based on this finding.

That is, the present invention is to form a tubular film by contacting the resin tubular body with a stabilizer in which a polyolefin resin is arranged by an air-cooling inflation method so as to be coaxial with the tubular die. Between the first mandrel having a ventilation hole and the tubular body with an outer diameter of 1.0 to 1.5 times the diameter of the die provided in a suitable place between the first mandrel and the take-up side. The provided tubular body has an outer edge portion that contacts only before and after the expansion start point and does not contact at the expansion start point, and the outer diameter of the outer edge portion before the expansion start point is the diameter of the die. 1.0 times or more, has a ventilation hole, and the outer diameter of the outer edge after the expansion start point is
It is intended to provide a method for forming a tubular film, which comprises expanding the tubular body while contacting it with a second mandrel having a vent hole and having a diameter of 1.0 times or more of the die.

The expansion start point here means that when the molten resin tubular body extruded from the tubular die has a diameter approximately equal to the die diameter, or when the molten resin tubular body is expanded by slightly expanding or contracting the tubular body, the tubular body expands rapidly. The point at which the diameter starts.

Next, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a main part showing an example of an embodiment of the present invention, in which an annular die 1 connected to an extruder is coaxially provided with openings for air circulation near the upper end and the lower end. Have,
In addition, the hollow mandrel 6 communicating with the air blowing pipe 2 is erected upright by screwing, and the first mandrel 4 is vertically movable on the mandrel.
Install. The first mandrel 4 attached here has an outer diameter of 1.0 to 1.5 times the diameter of the die, has a cylindrical, columnar, conical, or disk-like structure, and has a vent hole 15. The closer the mounting position is to the die, the greater the bubble stabilizing effect and the less adverse effect on the balance of physical properties of the film, but the work of pulling up the molten resin tubular body from the die exit can be done easily, and the central part of the mandrel can be installed. The position where the center of the cooling air flow hits the air cooling ring is preferable. The first mandrel contacts the molten resin tubular body between the die and the expansion start point 9 and eliminates the sway, thereby effectively stabilizing the bubble after expansion. The larger the outer diameter of the first mandrel 4, the greater the bubble stabilizing effect. However, if the outer diameter of the first mandrel 4 exceeds 1.5 times the diameter of the forming die, stable film formation becomes difficult and the physical property balance of the film is deteriorated. The preferred outer diameter is 1.05 to 1.3 times the die diameter. It should be noted that the present invention is not limited to the combination of the support column 6 and the first mandrel 4 as shown in FIG. 1, and a combination of the two may be used. Also, the number of first mandrels need not be singular, and multiple mandrels can be used. Stanchion 6
Has a structure that communicates with the air blowing pipe 2 and can inject air into the bubble.

Next, the second mandrel 5 is attached to the upper column of the first mandrel so that the non-contact portion comes to the position of the predetermined expansion start point. The second mandrel is composed of parts 13 and 14 that come into contact before and after the expansion start point and parts that do not come into contact with the expansion start point 9. The outer diameter of the contacting parts 13 and 14 is 1.
It is a mandrel which is 0 times or more and has a vent hole 16.
The vent holes of each mandrel have only to be capable of equalizing the pressure of each part in the bubble, and the number and size of the holes are not particularly limited. The gas in the bubble easily flows through the vent holes, and the pressure in each part of the bubble becomes uniform, so at the beginning of molding,
When the dimensions of the film are changed during molding, the bubbles do not sway, and the bubbles are stabilized in a short time.

2 to 4 are side views showing different shapes of the second mandrel used in the present invention, and FIG. 5 is a side view of a conventional example. These are all integrated, but a plurality of mandrels may be combined.

The outer diameter of the contact portions 13 and 14 before and after the expansion start point of the second mandrel is 1.0 times or more the die diameter, but the contact passage of the tubular body is smoothly performed, the stability of molding, the stabilization of bubbles and From the viewpoint of the vertical movement suppression effect at the expansion start point, it is preferable that the outer diameter of the contact portion 14 after the expansion start point is equal to or larger than the outer diameter of the contact portion 13 before the expansion start.

The outer diameter of the contact portion before the expansion start point must be selected according to the raw material resin and molding conditions. As a method of selection, the diameter of the tubular body at the expansion start point when molded excluding the second mandrel can be determined to be 1.2 times that diameter as the outer diameter of the contact portion before the expansion start point of the second mandrel. preferable. When the tubular body comes into contact with the second mandrel at the start of inflation molding, the tubular body is rapidly cooled, and the bubble becomes unstable.However, as the temperature of the mandrel itself rises and approaches the temperature of the tubular body, the bubble is generated. Stabilize. Therefore, it is preferable that both the first mandrel and the second mandrel have a reduced thickness or a meat cut to reduce the weight so that the heat capacity becomes small.

Next, a method of forming the film will be described. The upper end opening of the column 6 is closed, air is supplied into the space 11 from the air blowing pipe 2 which is open to the hole 7, and the molten resin tubular body 8 is extruded from the annular die 1. The tubular body 8 is cooled by the air flow blown from the air-cooling ring 3 and is expanded by the air pressure supplied from the hole 7 while passing through the first mandrel and the second mandrel, and then the pillar 6 The upper end opening is opened, and the air supplied from the air blowing pipe is blown into the spaces 11 and 12 to expand the diameter. Pinch the expanded tubular body with a pulling machine pinch roll. Next, the position of the expansion start point is moved to the center of the second mandrel while adjusting the amount of air cooling air from the air cooling ring 3. Then the tubular body is the first mandrel 4
Before and after the expansion start point is in contact with the second mandrel, and the expansion start point is expanded without contacting the second mandrel. By allowing the tubular body to pass through the first mandrel and the second mandrel in this manner, the swaying of the bubble after expansion suddenly disappears, and extremely stable molding becomes possible. Further, even if the discharge amount is increased, it becomes possible to suppress the sway of bubbles due to the increase in the amount of cooling air from the air cooling ring 3, and the productivity can be improved.

Also, in order to increase the film size during molding,
When air is supplied to the spaces 11 and 12 from the blow-in pipe 2, the pressure of each part inside the bubble is made uniform in an extremely short time after passing through the ventilation holes 15 and 16 of each mandrel, and therefore almost no shaking occurs. On the contrary, in order to reduce the film size during molding, even when holes are made in the film 10 to remove air, the air holes 15, 16 of each mandrel make the pressure in each part of the bubble uniform in an extremely short time. , And almost no bubble swaying, productivity can be increased.

Examples of the polyolefin resin used in the present invention include low density, medium density or high density polyethylene, homopolymers such as polypropylene, copolymers of ethylene or propylene with other monomers, and the like. Among them, polyethylene is preferable because a resin having a higher viscosity when melted and a higher melt tension gives a more preferable result.

The method of the present invention is applied over a wide range from a thin film of about 3μ to a thick film of 150μ. Particularly effective is a thin film having a small folding diameter, and a high-density polyethylene or a plastic film mainly composed of high-density polyethylene having an expansion ratio of 3.8 or less and a thickness of about 20 μ or less.

EFFECTS OF THE INVENTION According to the present invention, by using a plurality of mandrels having a specific shape and size and having vent holes, the swaying of bubbles after expansion is reduced and stabilized, and the discharge amount is also improved. Even if the number of air bubbles is increased, it is possible to suppress the fluctuation of bubbles due to an increase in the amount of cooling air from the air cooling ring, and the fluctuation of bubbles is reduced even when the film size is changed at the start of molding or during the molding. Since the bubbles can be stabilized in a short time, a high quality film can be produced with a high production amount.

EXAMPLES Next, the present invention will be described in more detail with reference to examples.

Example 1 A die diameter of 75 mmφ and a gear tape of 1.2 m connected to an extruder of 50 mmφ
The mandrel shown in Fig. 1 was erected in the center of the m die.
The first mandrel is an aluminum mandrel with an outer diameter of 80 mmφ, a length of 80 mm, a circumferential depth of 1.2 mm in the outer circumferential surface, and grooves with 2.0 mm intervals.The second mandrel has a contact part before the expansion start point. 3.0 mm thick, 2 aluminum discs with an outer diameter of 78 mmφ and the contact area after the expansion start point is 3.0 mm thick and an outer diameter of 95 mmφ
A mandrel having one aluminum disc and a 60 mm space attached thereto was used. Each mandrel has three vent holes with a diameter of 15 mm. A high-density polyethylene SANTEK HD F180 (MI: 0.06 density: 0.952) was used as a raw material and molded under the following molding conditions. Resin temperature: 215 ℃, film thickness: 1
8μ, expansion ratio: 3.6 (film folding width 424mm), height of expansion starting point: 650mm from die surface.

The extrusion rate started from 25 kg / H, gradually increased, and the maximum extrusion rate with which bubbles were stabilized and a high-quality film was obtained was 45.5 kg / H.

Next, when the film was extruded at an extrusion rate of 43 kg / H for 24 hours continuously, there was almost no change in the quality of the film. Also,
The time from the start of molding until the bubble became stable and a high quality film was obtained was 5 minutes.

Comparative Example 1 The mandrel used in Example 1 was removed, and the conical aluminum mandrel shown in FIG. 5 was erected so that the expansion starting point was at the center thereof. The outer diameter of the lower end of this mandrel is 57 mmφ and the outer diameter of the upper end is 82 mmφ. When molding was carried out under the same molding conditions as in the example, after molding was started,
It took 15 minutes to stabilize the bubble and obtain a high quality film. And the maximum extrusion rate that can obtain high quality film was 40.8 kg / H. After 24-hour continuous molding, the variation in folding width was ▲ 424 mm ⁺²¹ _-5 ▼, and the variation in average thickness was ▲ 18 μ ⁺² _-5 ▼.

Example 2 Extrusion rate using the raw material, film forming machine and stabilizer used in Example 1
A film with a thickness of 18μ and a folding width of 424 mm was molded for 1 hour at an extrusion rate of 25 kg / Hr, and then a predetermined amount of air with a pressure of 5 kg / cm ² was introduced into the bubble to form a film with a thickness of 14 μ and a folding diameter of 550 mm. , The bubble almost shook when the air flowed in. Further, even after the air flow was stopped, the film could be formed extremely stably, and no defective product was generated.

Comparative Example 2 Extrusion rate using the raw material, film forming machine and stabilizer used in Comparative Example 1.
A film with a thickness of 18μ and a folding width of 424 mm was molded for 1 hour at an extrusion rate of 25 kg / Hr, and then a predetermined amount of air with a pressure of 5 kg / cm ² was flowed into the bubble to form a film with a thickness of 14 μ and a folding width of 550 mm. The bubble shook when the air flowed in, and became stable about 1 minute after the air flow stopped. Therefore, the desired product was not obtained for about 3 minutes.

Example 3 In the same manner as in Example 2, after forming a film having a thickness of 14 μ and a folding diameter of 550 mm for 1 hour, a bubble having a length of about 20 mm was punched in a bubble with a knife to allow air to flow out to obtain a thickness of 18 μ and a folding diameter of 424 mm. The film was formed, but the bubbles hardly swayed when the air was introduced. Further, even after the air outflow was stopped, the film could be formed extremely stably, and no defective product was generated.

Comparative Example 3 In the same manner as in Comparative Example 2, after forming a film having a thickness of 14 μ and a folding diameter of 550 mm for 1 hour, a bubble having a length of about 20 mm was punched in a bubble with a knife to let out air, and a thickness of 18 μ and a folding diameter of 424 mm were prepared. The film was molded, but the bubbles shook when the air flowed in, and became stable about 30 seconds after the air flow stopped. Therefore, the desired product could not be obtained for about 2 minutes.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a tubular film manufacturing apparatus of the present invention, and FIGS. 2, 3, and 4 are side views of different examples of a second mandrel used in the present invention, and FIG. FIG. 4 is a side view of a conventional metal mandrel. In the figure, reference numeral 1 is an annular die, 2 is an air blowing tube, 3 is an air cooling ring, 4 is a first mandrel, 5 is a second mandrel, 6 is a hollow column, 8 is a tubular body, 9 is an expansion starting point, 13, Reference numeral 14 is a portion that contacts before and after the expansion start point of the second mandrel, and 15 and 16 are ventilation holes of each mandrel.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-18226 (JP, A) JP-A-58-183223 (JP, A) JP-A-62-149417 (JP, A) JP-A 61- 286117 (JP, A) Japanese Patent Publication Sho 55-12367 (JP, B2)

Claims (1)

[Claims] 1. When molding a tubular film while contacting a resin tubular body with a stabilizer in which a polyolefin resin is arranged by an air-cooled inflation method so as to be coaxial with the tubular die, the die and an expansion starting point are formed. Was set up in the right place,
An outer diameter of 1.0 to 1.5 times the diameter of the die, a first mandrel having a vent and the tubular body are brought into contact with each other, and the tubular body and the tubular body are provided closer to the take-up side than the first mandrel. It has an outer edge part that is in contact only before and after the expansion start point and is not in contact with the expansion start point, and the outer diameter of the outer edge part before the expansion start point is 1.0 times or more the caliber of the die, and the vent hole is formed. The outer diameter of the outer edge portion after having the expansion start point is 1.0 times or more the diameter of the die, and the tubular body is inflated while being brought into contact with a second mandrel having a ventilation hole. Manufacturing method of tubular film.