JPH0698681B2 - 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 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.

2. Description of the Related Art In recent years, polyolefin-based resins, particularly high-molecular-weight high-density polyethylene, have been used to increase the lateral molecular orientation by an inflation method such as an air-cooled inflation method and balance the strength in the vertical direction and the lateral direction. The film is widely used as a 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 the bubble diameter after expansion to the 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 increased, 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 part 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 columns erected in the center of the die start to cool and solidify (JP-B-55-12367), the lower end and the upper end of the mandrel. The diameter of the part, the diameter of the circular base that attaches this to the die is regulated, 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 has a sufficient length, and the surface of the mandrel has a roughened metal hollow cylinder. Contact before it happens, cylindrical The method for starting the expansion on the surface (JP-B
59-13964) and the like have been proposed.

DISCLOSURE OF THE INVENTION 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 rate and extruded resin The expansion start point is inevitably moved upward or downward on the stabilizer due to temperature fluctuations or temperature change of the air sent from the blower, and finally it comes off the stabilizer or the diameter of the stabilizer is the expansion start point. If the diameter is smaller than the diameter or is too large on the contrary, an unfavorable situation is brought about. 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 method, in order to avoid such various inconveniences, it is necessary to manually adjust the extruder or blower air flow rate, and as a result, the vertical movement of the expansion start point and 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 to make the position of the stabilizer variable. 58-42431 gazette), it is difficult for this method to automatically and steplessly change in response to rise and fall of the expansion start point, and it is artificially monitored 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 manufactured with high productivity such as less product loss.

Means for Solving the Problems The present inventors have variously studied the operating conditions when producing a tubular film of a polyolefin resin by an inflation method, and as a result, have examined a polyolefin resin tubular extruded from an annular die. When raising the body with a diameter almost equal to the die diameter and then expanding it to form a tubular film,
By arranging a stabilizer (hereinafter referred to as a floating stabilizer) which is guided by the support column and floats up and down automatically following the rising or falling of the expansion start point in the expansion region above the expansion start point, The stabilizer always keeps contacting the portion of the same shape in the expansion region above the expansion start point of the resin tubular body,
It is possible to achieve the above-mentioned object, and it is possible to achieve the above-mentioned object more effectively by disposing the floating stabilizer as described above and providing a fixed stabilizer between the annular die and the expansion start point. 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 this case, the resin tubular body can move up and down along a column provided coaxially with the annular die, which is arranged at a proper position in the expansion region above the expansion start point, and the stability of the resin tubular body at the contact position. At least 1 having a weight less than or equal to body support
The present invention provides a method for producing a tubular film, characterized in that the individual floating stabilizers are always in contact with and follow the position of a resin tubular body having a diameter equal to the diameter of the floating stabilizer, and the resin tubular body is expanded.

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 being in contact with a stabilizer provided coaxially with the annular die. An annular ring disposed at a proper position in the expansion region above the expansion start point by contacting at least one fixed stabilizer provided at a proper position between the die and the expansion start point with the resin tubular body. At least one floating stabilizer, which is movable up and down along a column provided coaxially with the die and has a weight equal to or lower than the stabilizer supporting force of the resin tubular body at the contact position, is always The method for producing a tubular film is characterized in that the resin tubular body is expanded while making contact with the position of the resin tubular body having a diameter equal to.

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 start point here means that when the molten resin tubular body extruded from the annular die has a diameter substantially equal to the die diameter, or when the molten resin tubular body is slightly expanded or contracted while being expanded, the tubular body is The point at which the diameter suddenly increases.

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 appears to float in this expansion region while being in contact with the resin tubular body. It should be noted that the diameter of the expansion start point of the resin tubular body is not forcedly expanded by the floating stabilizer, and the stability of the entire tubular body is not impaired. In response to the vertical movement of the expansion start point that occurs as a result, the floating stabilizer continuously moves up and down rapidly, so that it is of good quality in terms of strength and appearance during long-term operation. The film can be produced.

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 column 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 column. 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 1.0 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. The floating stabilizer 10 is located above the expansion starting point 13 and one or more floating stabilizers are attached. 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 first floating stabilizer (the one closest to the die) if multiple floating stabilizers are used
Should be above the position of the expansion start point 13 of the tubular body when the film is started up.

The floating stabilizer 10 will be
As shown in the figure, the expanded region of the resin tubular body 8 is in contact with the resin tubular body and is supported by its supporting force. The diameter of the second floating stabilizer 10 is larger than the diameter of the first floating stabilizer 10. Therefore, its position is above the floating stabilizer 10. Further, it is possible to arrange those having successively larger diameters at the top. Also, the outer diameter of the portion of the floating stabilizer which comes into contact with the film of the lowermost stage (most die side) has an expansion start point 13 '(see FIG. 3) of the resin tubular body when the floating stabilizer is not used. ) Diameter of 1.
It is selected in the range of 02 to 1.8 times, preferably 1.05 to 1.5 times.
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. Also,
A weight such as a weight is placed on the stabilizer to adjust the weight.
It is convenient to put. The weight may be mounted on each floating stabilizer or on a particular floating stabilizer.

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 to the method of allowing the column to move along the support column 3, a method in which a cavity or a hole formed in the center of the floating stabilizer 10 and the support column 3 slide, or a rotating body such as a ball bearing is used. A commonly considered method such as a moving method is used. 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. Also, in order to facilitate the vertical movement of the stabilizer and the weight during operation, the hollow pillar 3
It is better to apply a lubricant such as oil or grease to the sliding or rolling portion with. Further, if necessary, a fastener 15 for determining the vertical reciprocating range of the stabilizer at appropriate positions below the lowermost one of the floating stabilizer 10 and above the uppermost one including the weight. May be attached 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. It is possible to manufacture with good quality and high productivity without causing deterioration of wrinkles and 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 film grade of high density polyethylene having a melt index (190 ° C., 2.16 Kg load) of 0.05 g / 10 minutes and a density of 0.954 g / cm ³ was used. As a film forming material, a screw diameter of 50 mm was used. An extruder and an inflation film-forming material having a die having a die diameter of 75 mm were used.

The extruder and die were set at a temperature of 200 ° C., the film thickness was 25 μm, and the film width was 450 mm (blow ratio 3.8).

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

The first and second mandrels were made of aluminum, and had a thickness of about 20 mm, and a disk with a thread-shaped stripe on the outer surface was used.

The first and second floating stabilizers were discs made of aluminum and having a thickness of about 3 mm, and weights were placed on the discs to adjust the weight so that the shape of the expansion region was not changed. The film was formed continuously at a discharge rate of 30 Kg / Hr for 24 hours in a room in which the temperature of the atmosphere changed from 20 to 35 ° C. 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 73 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, with a minimum of 250 g and a maximum of 290 g.
And it was stable with high strength.

Comparative Example 1 In Example 1, as a stabilizer, as shown in FIG.
Stabilizer with the surface of aluminum cylinder covered with felt (the outer diameter of the die side is 75 mmφ, the outermost side is 90 mmφ, the length is 300 mm, and is tapered) 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 film's dirt impact strength is at least 160g,
The maximum was 240 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 molded to have a thickness of 13 μm and a width of 640 mm (blow ratio 5.5). When molding was performed 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 from the die was 540 mm. It was 580 mm, with a minimum of 410 mm. During molding, the floating stabilizer automatically followed up and down as the expansion start point went up and down, and the stability and appearance of the film were 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 was a cylindrical stabilizer as shown in FIG. 2 (the surface was felt and the one on the most die side had 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 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 10 'are floating stabilizers, 12
Is a weight, 13 is an expansion starting point, 14 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 16 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.
13 'indicates the expansion start point at that time.

Claims (2)

[Claims] 1. When a tubular film is formed 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. Weight that is movable up and down along a column that is coaxial with the annular die and that is placed at a proper position in the expansion region above the point, and that is less than the stabilizer support force of the resin tubular body at the contact position. A process for producing a tubular film, wherein the resin tubular body is expanded while always contacting and following at least one floating stabilizer having a diameter equal to the diameter of the floating stabilizer. 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. And at least one fixed stabilizer provided in a proper position between the expansion start point and the resin tubular body are brought into contact with each other, and coaxial with an annular die arranged in a proper position in the expansion region above the expansion start point. At least one floating stabilizer that is movable up and down along a column provided in the and that has a weight equal to or less than the stabilizer supporting force of the resin tubular body at the contact position is always equal to its diameter. The method for producing a tubular film, wherein the resin tubular body is expanded while contacting and following the position of the resin tubular body.