JPH0757525B2 - Manufacturing method of tubular film - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an improved process for producing tubular films. More specifically, the present invention is for producing a high-quality film showing balanced strength in the vertical direction and the lateral direction with high productivity when molding a tubular film of a polyolefin resin by an inflation method. It relates to an improved method.

[Conventional technology]

In recent years, the molecular orientation in the lateral direction has been increased by an inflation method such as an air-cooled inflation method, and a polyolefin resin, particularly a high-density high-density polyethylene film, in which the strength in the vertical direction and the strength in the lateral direction are balanced, It is widely used as so-called balance film for 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, The greater the position where the expansion starts, that is, the expansion start point, from the die surface, and the larger the expansion ratio (ratio of bubble diameter after expansion to die diameter), the higher the molecular orientation in the lateral direction and the strength in the lateral direction. It becomes balanced with the strength in the vertical direction. Therefore, in order to improve the balance of strength and increase the impact strength of the entire film, either increase the expansion ratio or
Alternatively, the expansion start point must be raised, but if this is done, the left and right swaying and up and down swaying of the bubble after expansion will be significant, causing wrinkles, sagging, and fluctuations in the width of the resulting film, which may cause quality deterioration. Become. In order to suppress the swaying of the bubble after such expansion and prevent the occurrence of the above troubles, a method in which the constricted portion of the bubble has hitherto been brought into contact with a mandrel having a diameter smaller than the diameter of the die (Japanese Patent Publication No. 55- 2180), a method of arranging a mandrel having a diameter larger than the diameter of the die at the position where the bubbles of the pillars standing upright in the center of the die begin to cool and solidify (JP-B-55-12367), the lower end and the upper end of the mandrel. The diameter of the part, the system of the circular base part that attaches this to the die is controlled, the bubble is raised along the circumferential side surface of the mandrel, and it is expanded rapidly before reaching the upper end (Japanese Patent Publication No. 59-5408). The die diameter is 1.01 to 1.2 times the diameter of the die and the length is sufficient, and the surface of the mandrel has a roughened metal hollow cylinder. Contact them before they happen, The method for starting the expansion on the tubular portion surface (JP-B
59-13964) and the like have been proposed.

[Problems to be solved by the invention]

However, in all of these methods, since the position of the stabilizer is fixed, various factors during long-term continuous operation, such as hunting of the extrusion amount, temperature fluctuation of the extruded resin, or feeding from a blower, are involved. The expansion start point is unavoidably moved upward or downward on the stabilizer due to temperature change of the air, etc., and finally it comes off the stabilizer, or the diameter of the stabilizer is smaller than the diameter of the expansion start point, or On the contrary, it causes an unfavorable situation such as being too large. Under such circumstances, the resin tubular body sways in the lateral direction, and further shakes up and down to significantly change the dimensions of the film, and to cause large wrinkles in the film, and further, the strength of the film is significantly reduced. And various problems such as scratches on the inner surface of the film may occur.

Therefore, in the above-mentioned method, in order to avoid such various inconveniences, the extruder or blower air volume must be manually adjusted, and as a result, the time and the time when the vertical movement of the expansion start point occurs. Before and after the work of adjusting, there is a problem that quality defects and product loss are inevitable.

On the other hand, in order to cope with the vertical movement of the expansion start point, there has been proposed a method in which a column on which a stabilizer is erected is moved up and down by an air cylinder or the like so that the position of the stabilizer can be varied (Japanese Patent Laid-Open Publication No. Sho. 58-42431), it is difficult to change steplessly and automatically in response to the rise and fall of the expansion start point, and it is artificially observed while monitoring the vertical movement of the expansion start point. However, there are drawbacks such as poor quality and easy product loss during adjustment work.

Further, in any of these known methods, there is a drawback that the physical properties of the obtained film are impaired by contact with a stabilizer whose expansion start point of the resin tubular body is fixed.

An object of the present invention is to overcome the drawbacks of the conventional inflation method and to provide a tubular film of a polyolefin resin which exhibits balanced strength in the vertical direction and the lateral direction at high speed and with poor quality. It is to provide a method that can be easily manufactured with low productivity such as low product loss.

[Means for solving problems]

As a result of various examinations on the operating conditions when producing a tubular film of a polyolefin resin by the inflation method, the inventors have found that the polyolefin resin tubular body extruded from an annular die has a diameter substantially equal to the die diameter. When it is inflated and molded into a tubular film,
By arranging a stabilizer (hereinafter referred to as a floating stabilizer) that is in contact with the tubular resin body at the expansion start point and is guided by the support column to float in accordance with the rise or fall of the expansion start point and automatically moves up and down. , The stabilizer can always keep in contact with the expansion start point of the resin tubular body to achieve the above-mentioned object, and the floating stabilizer is arranged as described above, and the fixed stability is provided between the annular die and the expansion start point. It was found that the object can be achieved more effectively by providing the body, and the present invention has been completed based on this finding.

That is, the first aspect of the present invention is to form a tubular film by expanding a polyolefin resin tubular body melt-extruded from an annular die by an inflation method while being in contact with a stabilizer provided coaxially with the annular die. In doing so, the weight of the resin annular body at the contact position which is movable up and down along the column provided coaxially with the annular die and is equal to or less than the stable body supporting force of the resin annular body, and the tapered side surface that expands upward are provided. It is intended to provide a method for producing a tubular film, which comprises expanding the resin tubular body while always keeping the floating stabilizer in contact with the expansion start point of the resin tubular body.

The second invention is to form a tubular film by expanding a polyolefin resin tubular body melt-extruded from an annular die by an inflation method while bringing it into contact with a stabilizer provided coaxially with the annular die. , The resin tubular body is brought into contact with at least one fixed stabilizer provided in a proper position between the die and the expansion start point, and can be vertically moved along a column provided coaxially with the annular die. And a floating stabilizer having a weight equal to or less than the stabilizer supporting force of the resin tubular body at the contact position and a tapered side surface that expands upward is always set as the expansion start point of the resin tubular body having a diameter equal to its diameter. It is intended to provide a method for producing a tubular film, which comprises expanding the resin tubular body while following the contact.

The supporting force of the resin stabilizer as used herein means that when the resin tubular body supports the floating stabilizer, it does not substantially change the shape of the resin tubular body at that position and supports the floating stabilizer. It is the power to do. Further, the expansion starting point here means a diameter of the molten resin tubular body 8 extruded from the annular die as shown by 12 'in FIG. 2 which is almost equal to the diameter of the die, or slightly expanded or reduced. On the other hand, when the tubular body is taken up and inflated, it means a position where the tubular body suddenly starts to expand its diameter like 13.

Further, the expansion region is a region from the expansion start point to the expansion of the tubular body, the diameter of which expands until it reaches a certain diameter, that is, the region where the tubular body continues to expand. That is.

The floating stabilizer arranged in the present invention looks as if floating while contacting the resin tubular body at this expansion start point. The diameter of the expansion start point of the resin tubular body is not expanded by the floating stabilizer, and the stability of the entire tubular body is not impaired. Therefore, in response to the vertical movement of the expansion start point that occurs, the floating stabilizer continuously and rapidly moves up and down.
It is possible to produce a film with good appearance.

The fixed stabilizer is a stabilizer that is moved to an arbitrary position on the column and then fixed by a lock screw or the like.

Next, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an essential part showing an example of an embodiment of the present invention, in which the annular die 1 connected to the extruder is coaxially used for air blowing and circulation near the upper end and the lower end. A hollow pillar 3 having openings 5 and 11 and communicating with the air blowing pipe 2 is erected by screw fitting, and a first mandrel 4 as a fixed stabilizer is attached to the pillar. The first mandrel 4 attached here has an outer diameter large enough to contact the resin tubular body 8 extruded from the annular die 1, and its shape is cylindrical, disk-shaped, bobbin-shaped, or frustum-conical. It is selected from the shape. The mandrel 4 preferably has a vent hole 6. The main function of the first mandrel is to prevent the resin tubular body from being dented inward by the pressure of the air from the air ring 7 to impair its stability. The size and shape of the first mandrel 4 is such that the friction between the resin tubular body 8 and the mandrel becomes too large, which does not hinder the film starting operation or the movement of the tubular body to rise during operation. In general, the outer diameter is preferably 1.0 to 1.5 times the diameter of the tubular body.

Next, above the first mandrel 4, that is, the resin tubular body 8
A second mandrel 9, which is a fixed stabilizer, is provided between the expansion start point and the first mandrel 4. Both the first mandrel and the second mandrel can move up and down on the hollow column 3, but they are fixed to the column by a method such as screwing during operation. The number of the second mandrel 9 is not limited to one, and two or more mandrels can be used if necessary, and various shapes can be appropriately selected as in the case of the first mandrel. In addition, it is preferable to have the vent hole 6 as in the first mandrel.
The main action of this second mandrel is to support the resin tubular body 8 in the middle, and, like the first mandrel 4, its size and shape are such that the friction between the resin tubular body 8 and the second mandrel 9 is increased. Is too large to prevent the start-up work of the film and the movement of the tubular body trying to rise during operation, and its outer diameter is usually 0.8 to 1.5 times the diameter of the tubular body. Is preferred.

Next, the floating stabilizer 10, which is an essential part of the present invention and is movable during film formation, will be described. One floating stabilizer 10 is attached to the expansion starting point 12. The floating stabilizer is not fixed to the column because it needs to be movable up and down along the column during film formation.

The shape of the floating stabilizer is required to have a tapered side surface that expands upward.For example, as shown in the figure, it is a truncated cone shape with a small radius at the lower end and a large radius at the upper end, and the inclination of the side surface is 0.05 to 0.8. , Preferably in the range of 0.1 to 0.4.

The floating stabilizer 10 will be
As shown in the drawing, the expansion start point of the resin tubular body 8 is in contact with the resin tubular body 8 and is supported by its supporting force.

The outer diameter of the upper end of the floating stabilizer is preferably larger than the diameter of the expansion start point 12 'of the resin tubular body when the floating stabilizer is not used, and the lower end thereof is preferably smaller than the diameter of the expansion start point 12'. On the other hand, the weight of the floating stabilizer is not more than the supporting force of the resin tubular body when the floating stabilizer contacts the resin tubular body. Therefore, the floating stabilizer is supported by contacting the resin tubular body without substantially changing the shape of the resin tubular body. However, it is preferred that the weight of the floating stabilizer does not become too light. This weight is appropriately selected according to various conditions such as film thickness, folding diameter and take-up speed in inflation molding.

The inventors of the present invention have proposed in the prior application a method for producing a tubular film in which the floating stabilizer is formed in a state where the floating stabilizer is in contact with the resin tubular body on the downstream side of the expansion region of the resin tubular body, that is, the expansion start point. However, according to this method, when the expansion ratio of the tubular body is large (for example, the expansion ratio is 4 or more) and the thickness of the film is thin (for example, 10 microns or less), the tubular body tends to shake sideways. I got it. The present application is intended to solve the above-mentioned inconvenience by bringing the floating stabilizer into direct contact with the position of the expansion start point of the tubular body.

On the other hand, it is preferable that the floating stabilizer has the air circulation hole 6 like the first and second mandrels. The floating stabilizer 10
As for the method of allowing the movable body to move along the support column 3, a method in which the cavity formed in the center of the floating stabilizer 10 or the support column 3 slides or a rotating body such as a ball bearing is used. A method usually considered such as a method of moving is used. A weight adjusting weight may be added depending on the case. In any case, the sliding portions or the rolling portions between the stabilizer and the weight and the column 3 should have a structure that does not hinder the vertical movement of the stabilizer and the weight and allows smooth movement. Therefore, there should be no significant gap between the support and the stabilizer or the sliding or rolling part of the weight. Further, in order to smooth the vertical movement of the stabilizer and the weight during operation, it is preferable to apply a lubricant such as oil or grease to the sliding or rolling portion with the hollow column 3. Furthermore, if necessary, it is preferable to attach a fastener 14 for fixing the vertical reciprocating range of the floating stabilizer 10 at an appropriate position by screwing or the like.

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. With polyethylene having a high melt viscosity and a high melt tension, preferable results can be obtained.

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 film of high-molecular-weight, high-density polyethylene that forms a film with an expansion ratio of 2 to 6.

EFFECTS OF THE INVENTION According to the present invention, by using a floating stabilizer capable of moving up and down, a film having a wide range of thicknesses and widths can be strengthened without being affected by outside temperature and other disturbances over a long period of time. Can be manufactured with good quality and high productivity without causing deterioration of wrinkles and meandering.

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 As a raw material, a melt index (190 ° C., 2.16 kg load)
Inflation film-forming material with a film diameter of 50 mm, extruder with a die diameter of 75 mm, and using film high-density polyethylene film with a density of 0.05 g / 10 minutes and a density of 0.954 g / cm ^3. It was used.

The extruder and die were set at a temperature of 200 ° C., the film thickness was 20 μm, and the film width was 350 mm (blow ratio 3.0).

The stabilizer has the structure shown in FIG. 1 and is as follows.

Stabilizer outer diameter Height from die 1st mandrel (fixed) 80mm 85mm 2nd mandrel (fixed) 80mm 300mm Floating stabilizer outer diameter 50-80mm Change from 80mm length to molding conditions First and second mandrels are made of steel With a thickness of about 20 mm,
A disc with a threaded stripe on the outer surface was used.

The floating stabilizer is a truncated cone shape made of aluminum and having a thickness of about 3 mm.
The ambient temperature changes to 20-35 ℃. 30kg / hr in the room
The film was continuously formed for 24 hours with the discharge amount of. The height of the expansion starting point from the die at the start of molding was 540 mm, and under this condition, the diameter of the expansion starting point was 58 mm when the stabilizer was not used. The expansion start point varied from a minimum of 440 mm to a maximum of 610 mm during 24 hours of molding. During molding, the floating stabilizer moved up and down following the upward and downward movement of the expansion start point, and reached the same position in the expanded region of the tubular body. During this period, the film was sampled and the dart impact strength was measured, and it was stable at a high strength of 220 g at minimum and 270 g at maximum.

Comparative Example 1 In Example 1, as a stabilizer, as shown in FIG.
Stabilizer in which the surface of the aluminum cylinder is covered with felt (the outermost one has an outer diameter of 65 mmφ, and the outermost one has an outer diameter of 80 mmφ, a length of 300 mm, and a taber) A film was formed in the same manner as in Example 1 except that the film was fixed and used.

The height at which the tubular body contacts the stabilizer is 600 mm at the maximum, 450 mm at the minimum
However, when the height of the contact point was 490 mm or less, the film became unstable, wrinkles were generated, and the film appearance was poor. Also, the dart impact strength of the film is at least 150g,
The maximum was 220 g, which was low and varied greatly.

This is because the diameter of the expansion start point of the tubular body is forcibly expanded by the fixed stabilizer, and when the position of the expansion start point becomes higher, it is expanded by the part with the larger outer diameter of the stabilizer. This is because the strength becomes lower.

Example 2 Under the same equipment and conditions as in Example 1, the film was shaped to have a thickness of 13 μ and a width of 650 mm (blow ratio 5.5). When molding was carried out for 24 hours at a discharge rate of 27 kg / Hr at an outside air temperature of 18 to 30 ° C, the height of the expansion start point at the start of molding was 540 mm, but the maximum height was 580 mm during molding. The minimum was 410. During molding, as the expansion start point goes up and down,
The floating stabilizer automatically follows the top and bottom to stabilize the film,
The appearance was good. The dart impact strength was measured by sampling the film accompanying the vertical movement of the expansion start point, and it was stable at 120 to 150 g.

The diameter of the expansion starting point was 64 mm when the stabilizer was not used at the start under these film forming conditions.

Comparative Example 2 In Example 2, the stabilizer is a cylindrical stabilizer as shown in FIG. 2 (the surface is felt and the one on the most die side has an outer diameter of 70 mm).
φ, the outermost side has an outer diameter of 80 mmφ and a length of 300 mm). The other conditions are the same as in Example 2. During molding,
The height at which the tubular body contacts the stabilizer is 570 mm maximum and 410 mm minimum
It was. During this period, the film has a minimum dart impact strength of 70.
It was low at g, up to 130g, and had wide variations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an essential part of the tubular film forming method of the present invention. In the figure, reference numeral 1 is an annular die, 2 is an air blowing pipe, 3 is a hollow column, 4 is a first mandrel, 5 and 11 are openings for air blowing and circulation, 6 is a vent hole, 7 is an air cooling ring, 8 Is a tubular body, 9 is a second mandrel, 10 and 11 'are floating stabilizers, 12 is an expansion starting point, 13 is an expansion region, and 15 is a fastener for determining the reciprocating range of the floating stabilizer. FIG. 2 shows a film forming method using a known tubular stabilizer, and 15 is a tubular stabilizer. FIG. 3 shows a film forming method in the case where no mandrel, floating stabilizer, etc. are provided inside the tubular body 8.
12 'indicates the expansion start point at that time.

Claims (2)

[Claims] 1. A ring die for forming a tubular film by expanding a polyolefin resin tubular body melt-extruded from an annular die by an inflation method while contacting a stabilizer provided coaxially with the annular die to form a tubular film. A floating stabilizer that is movable up and down along a column provided coaxially with the resin and that has a weight less than the stabilizer support force of the resin tubular body at the contact position and a tapered side surface that expands upward is made of resin. A method for producing a tubular film, characterized in that the resin tubular body is expanded while making contact with the expansion start point of the tubular body. 2. A die for molding a tubular film by expanding a polyolefin resin tubular body melt-extruded from an annular die by an inflation method while contacting a stabilizer provided coaxially with the annular die to form a tubular film. Between the resin tubular body and at least one fixed stabilizer provided in a proper position between the expansion die and the expansion start point, and further movable up and down along a column provided coaxially with the annular die. A tubular body characterized in that the resin tubular body is inflated while the floating stabilizer having a weight equal to or less than the supporting force of the resin tubular body at the contact position is made to follow the expansion start point of the resin tubular body in contact therewith. How to make a film