JP3623549B2 - Extrusion film forming method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for extrusion film formation of a thermoplastic resin that prevents a neck-in phenomenon during extrusion film formation and has a small variation in thickness and enables a long run operation.
[0002]
[Prior art]
Conventionally, various methods for forming a sheet by forming a film by extruding a thermoplastic resin from a T die have characteristics, but in any case, from the lip port 2 of the T die 1 toward the vertical direction. It is ideal to extrude. However, in reality, it does not go as ideal, and as shown in FIG. 3, the angle (b) between the vertical direction (a) and the extruded molten sheet 10, the so-called pulling angle (b) is to some extent. Was needed. In general, when pulling down from the lip port 2 of the T die 1, it is pulled down on the normally cooled chill roll 3, and is brought into close contact with the surface of the chill roll 3 by the air knife 4. This chill roll 3 has line speed and cooling capacity. Therefore, it is quite difficult to draw the molten sheet 10 vertically onto the chill roll 3. This is because the tangential direction of the chill roll 3 is preferable for the pull-down, and for this reason, the distance between the lip port 2 and the contact point where the molten sheet 10 contacts the chill roll 3, the so-called air gap, requires that the diameter of the chill roll 3 increases. It gets bigger. In this regard, the distance between the lip port 2 and the contact point where the molten sheet 10 contacts the chill roll 3 is preferably as small as possible. If this distance is large, the molten sheet 10 is pulled and tapered as the chill roll 3 rotates. This is because the so-called neck-in phenomenon in which both ears are thick and the central part is thin increases. Normally, this distance is not specified because it varies depending on the rotational freezing degree of the surface of the chill roll 3, that is, the line speed, but it is supposed that the smaller the better. However, even if it is considered that the production speed increases as the chill roll 3 increases in line speed, it is also true that the distance cannot be made as small as necessary when pulling down vertically.
[0003]
Considering these points, if the distance is reduced to prevent neck-in, it is difficult to pull the lip from the lip mouth to the chill roll at the above-mentioned pulling angle of 0 ° at this normal line speed. Therefore, unless the pulling angle is increased to some extent, the distance cannot be set within a range in which neck-in can be prevented. However, if the pulling angle is increased, the molten sheet will be discharged from the lip port in a tilted state, so that the molten resin flow is disturbed near the lip port, the weight of the resin, etc. (This point is uncertain ...), or the thickness of the molten sheet varies widely, so-called uneven thickness is likely to occur. Drops of resin spilled into both ears and adhered to the extruded molten sheet, resulting in poor quality, resulting in problems with long-run operation. These points were also pointed out as problems. .
[0004]
[Problems to be solved by the invention]
In order to solve such a conventional problem, the present inventors have set a condition for allowing the molten sheet to be drawn with a reduced pulling angle when the molten sheet is extruded from the lip opening of the T die. Various studies were conducted. That is, when it is assumed that the size of the chill roll is not changed, each item necessary for reducing the pulling angle and shortening the distance between the lip opening and the contact point where the molten sheet contacts the chill roll is investigated. As a result of comprehensive investigation of the survey items, it was found that the above-mentioned conventional problems could be solved by pulling at least both ears of the molten sheet from the lip mouth and with the angle being reduced. The invention has been completed.
[0005]
[Means for Solving the Problems]
When forming a sheet by extruding a thermoplastic resin from a lip opening of a T-die onto a chill roll, a drop between the both ears and the center of the molten sheet is formed between the lip opening and the chill roll. The angle difference is 1 to 17 °, and the pull-down angle at both ears is within 20 °, and a roll member is provided at a portion that contacts both ears of the molten sheet. .
[0006]
Next, means for solving the problem will be described in further detail.
Examples of the thermoplastic resin in the present invention include polyethylene, polypropylene, butene, and appropriate copolymers thereof, polyolefin resins such as modified polyolefin, ethylene-vinyl acetate copolymer, nylon-6, nylon-66, and copolymers thereof. Examples thereof include polyamide resins such as amorphous nylon such as coalescence and hexamethylenediamine-tereisophthalamide, and there is no particular limitation, and a mixture thereof may be used. Further, it may be a thermoplastic resin necessary for constituting a multilayer film formed by co-extrusion using a plurality of these resins and other appropriate resins, and in particular how to use the thermoplastic resin. There is no limit. Accordingly, examples of the film formed by the method of the present invention include a polypropylene film, a composite film thereof, and a polyamide-based coextruded multilayer film.
Here, the polypropylene composite film can be exemplified by “polypropylene resin layer / appropriate copolymer layer selected from ethylene, propylene and butene”, and the polyamide coextruded multilayer film can be exemplified by “polyamide resin”. Layer / ethylene-vinyl acetate copolymer saponified layer / polyamide resin layer ”,“ polyamide resin layer / ethylene-vinyl acetate copolymer saponified layer / polyamide resin layer / modified polyolefin layer / polyolefin resin layer ” The thing of the structure of can be illustrated.
[0008]
The extrusion film forming apparatus for carrying out the method of the present invention may be basically the one described in FIG. 3, for example, which is conventionally used, and is not particularly limited, but is further shown in FIGS. As described above, the portion between the lip port 2 and the chill roll 3 of the T-die 1 that is in contact with both ears of the molten sheet immediately after being extruded from the lip port 2 is pushed in a direction in which the pulling angle decreases. It is essential to provide the roll member 5 for taking out. Both the ears of the molten sheet in contact with such a roll member 5 are pulled down in a direction in which the angle is reduced compared to the central part thereof, for example, a direction close to 0 °. Neck-in can be prevented and uneven thickness can be prevented. The reason why uneven thickness can be prevented is not clear, but as described above, the roll member 5 is placed so that the both ears of the molten sheet have a smaller pulling angle than the central part. Even if the roll member 5 is provided, the effect of the present invention is not exhibited if the pull-down angle is the same in both ears and the center. Here, the difference in the pulling angle between the both ears and the central part of the molten sheet is not particularly limited, but usually 1 to 17 °, preferably about 3 to 12 ° can be exemplified. The angle is not particularly limited, but is preferably close to 0 °, and is usually within 20 °, preferably within 10 °.
[0009]
Examples of such a roll member 5 include metal rolls, ceramic rolls, rubber rolls such as silicon, and the like. Preferably, the roll member 5 is preferably a fluororesin roll, a roll whose surface is covered with a fluororesin or its tube, etc. The roll which consists of a fluorine resin can be mentioned. Since these have good slip properties and poor adhesiveness, the molten sheet does not adhere to them and can be exemplified as preferable ones, but there are no particular restrictions on the roll members. The width and diameter of the roll member may be appropriately set depending on various factors such as the thickness of the molten sheet, the state of the ear portion, the line speed, and the roll member may be cooled through water or the like. Further, the roll member holding mechanism 6 preferably has a structure capable of adjusting a pulling angle when the roll member abuts the molten sheet, and the shaft 7 is arranged so as to be movable in the width direction of the molten sheet. It is good also as a structure which can slide with the holding mechanism 6. FIG.
[0010]
At this time, the pulling angle will be described. The direction of 0 ° is normally the vertical direction at the present time because of the structure of the extrusion film forming apparatus. However, this is not particularly limited, and the direction with a pulling angle of 0 ° may be the horizontal direction (lateral direction), the reverse vertical direction (upward direction), or the oblique direction. Good. In this case, the diagonal direction means that the slit openings 2 of the die 1 are arranged obliquely, and even with such an arrangement, the pulling angle can be set to a direction of 0 °.
Further, the distance from the lip port 2 to the roll member 5 is preferably as small as possible without considering the structure of the apparatus. However, in consideration of the size of the chill roll, the line speed, etc., the distance is usually about 30 to 100 mm.
[0011]
The present invention has been described above by way of example, and the present invention is of course not limited to such description.
【Example】
Hereinafter, the present invention will be described in more detail by way of examples together with comparative examples.
Example 1
1 and 2 (the air knife as shown in FIG. 3 is also attached), the pulling angle at both ears of the molten sheet 10 is 3 °, and that at the center is 13 °. The distance between the lip port 2 of the T die 1 and the fluorine roll 5 is set to 70 mm, the distance between the fluorine roll 5 and the chill roll 3 is set to 80 mm, and extrusion is performed so that the thickness is 1.25 mm and the width is 86 cm. A film was formed to obtain a sheet. At this time, the temperature of the T die is 200 ° C., the slit width of the lip mouth is 2 mm, the width of the lip mouth is 90 cm, the diameter of the fluorine roll is 5.4 cm, the width is 15 cm, the diameter of the chill roll is 100 cm, and the temperature of the chill roll is 35 The line speed (rotational speed of the chill roll surface) was 30 m / min. The fluorine roll was made of Teflon and no drive was provided. Here, the air knife 4 is provided in order to make the extruded molten sheet 10 adhere to the surface of the chill roll 3. In the sheet thus formed by extrusion, there was almost no variation in thickness between the center portion and both ear portions.
Subsequently, the sheet was stretched 5 times in the longitudinal direction and 10 times in the transverse direction to obtain a film having a thickness of 25 microns and a width of 6.5 m. The thickness was good with almost no variation in thickness between the center and both ears. At this time, the difference between the maximum thickness and the minimum thickness, so-called uneven thickness difference, was 0.9 microns.
[0013]
Comparative Example 1
The same polypropylene resin as in Example 1 was set using the apparatus shown in FIG. 3, the pulling angle was set to 10 °, the distance between the lip port 2 of the T die 1 and the chill roll 3 was set to 165 mm, the thickness was 1.25 mm, and the width was 84 cm. The film was formed by extrusion. At this time, other conditions were the same as in Example 1 except for the roll member.
Subsequently, this sheet was stretched 5 times in the machine direction and 10 times in the transverse direction to obtain a film having a thickness of 25 microns and a width of 6.4 m. Both ears were thicker than the central part by about 2.5 microns, and noticeable variation was observed. Also, the uneven thickness difference was 2.5 microns.
[0014]
Regarding the films of Example 1 and Comparative Example 1 thus obtained, the ratio of the central part excluding both ears treated as non-defective products was 94.24% for the former and 92.69% for the latter. From this, it can be seen that the present invention is useful. Here, also in Example 1, there is a portion that is not treated as a non-defective product to some extent because, as described above, when using the tenter for lateral stretching, both ear portions sandwiched by the clip must be cut.
[0015]
Example 2
Polyamide resin (blend of nylon-6 and amorphous nylon) / saponified ethylene-vinyl acetate copolymer / polyamide resin (same as above) / modified polyolefin resin / linear low density polyethylene resin Using the same apparatus (for coextrusion) as in Example 1, the pulling angle at both ears of the molten sheet 10 is set to 8 °, that at the center is set to 23 °, and the lip mouth 2 of the T die 1 The distance from the rubber roll 5 was set to 50 mm, the distance from the fluorine roll 5 to the chill roll 3 was set to 40 mm, and a polyamide-based five-layer sheet was coextruded to form a thickness of 0.96 mm and a width of 94 cm. At this time, the temperature of the T die is 250 ° C., the slit width of the lip mouth is 1.2 mm, the width of the lip mouth is 98 cm, the diameter of the rubber roll is 4.4 cm, the width is 7 cm, the diameter of the chill roll is 60 cm, and the temperature of the chill roll is The temperature was 4.4 ° C., and the line speed (chill roll rotation speed) was 30 m / min. The rubber roll was made of silicon and no drive was provided.
Subsequently, the sheet was stretched 3 times in the machine direction and 3 times in the transverse direction to obtain a film having a thickness of 40 microns and a width of 3.2 m. The thickness was good with almost no variation in thickness between the center and both ears. The uneven thickness difference was 1.7 microns.
[0016]
Comparative Example 2
Using the same resins as in Example 2, the apparatus shown in FIG. 3 sets the pulling angle at both ears of the molten sheet 10 to 10 ° and the distance between the lip port 2 of the T die 1 and the chill roll 3 to 90 mm. The film was coextruded to have a thickness of 0.36 mm and a width of 92 cm. At this time, other conditions were the same as in Example 2 except for the presence or absence of a rubber roll.
Subsequently, the sheet was stretched 3 times in the vertical direction and 3 times in the horizontal direction to obtain a film having a thickness of 40 microns and a width of 3 m. The uneven thickness difference of the portion excluding the tenter grip allowance during transverse stretching was 2.5 microns.
[0017]
Regarding the films of Example 2 and Comparative Example 2 thus obtained, the ratio of both ears treated as industrial waste was 11.90% for the former and 16.79% for the latter. From this, it can be seen that the present invention is useful. Here, in Example 2 as well, both ears must be cut to some extent because the portion sandwiched between the clips must be discarded when the tenter is used for lateral stretching.
[0018]
【The invention's effect】
The present invention has the above-described configuration, and prevents the neck-in phenomenon at the time of film formation when forming a thermoplastic resin by extrusion film formation, and also makes it difficult for thickness variation, so-called uneven thickness, to occur, and during continuous operation. In this case, a drop-like lump of molten resin called “eye” reduces leakage and enables long-run operation, and the effect is particularly remarkable.
[Brief description of the drawings]
FIG. 1 is a side view showing an example of a preferred apparatus for carrying out the method of the present invention.
FIG. 2 is a front view of the apparatus shown in FIG.
FIG. 3 is a side view showing an example of an apparatus for carrying out a conventional method.
[Explanation of symbols]
1, T dice 2, lip port 3, chill roll 4, air knife 5, control roll 10, molten sheet

Claims (3)

When forming a sheet by extruding a thermoplastic resin from a lip opening of a T-die onto a chill roll, a drop between both ears and the center of the molten sheet is formed between the lip opening and the chill roll. The difference between the two angles is 1 to 17 °, and the pull-down angle at both ears is within 20 °, and a roll member is provided in a portion that contacts both ears of the molten sheet. Extrusion film forming method. The method according to claim 1, wherein a polypropylene film or a polyamide-based multilayer coextruded film is formed by extrusion. The extrusion film-forming method according to any one of claims 1 to 4, wherein at least the surface of the roll is made of a fluororesin.

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