JPS5913323B2 - Cooling method for thermoplastic resin film or sheet - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for cooling a thermoplastic resin film.

5 The purpose of the present invention is to cool and solidify a thermoplastic resin film extruded from a die in a molten state by contacting the surface of a rotating cooling roll, and to cool and solidify a thermoplastic resin film extruded from a die in a molten state. It's called a mask.

) side, and also significantly reduces the accumulation of volatile low polymers that tend to adhere to the cooling air nozzle and its surroundings, thereby almost eliminating the adhesion of foreign matter to the film. The present invention aims to provide a method for producing high-quality films with few surface defects.
15 Conventionally, the method usually employed to cool and solidify a thermoplastic resin film extruded from a die in a molten state is to cast the film on a rotating cooling roll with a cooling liquid circulating inside. .

In this method, usually only one cooling roll is used, and most of the heat transfer for cooling the film on the cooling roll relies on heat transfer on the side of the cooling roll of the film. In this method, for example, about 1000μ
When producing thick films of 25 or more, or when the diameter of the cooling roll is relatively small and the production speed of the film is high, even if the cooling capacity of the cooling roll is improved, the temperature of the film, especially on the A side. The disadvantage is that the temperature cannot be lowered to or below the desired temperature. This is mainly caused by the low thermal conductivity of the thermoplastic resin itself.As a result, after the cooling process, crystallization occurs in areas where cooling is insufficient, and the film is subsequently stretched and heat treated. The film often breaks when doing this,
It is impossible to consistently and continuously produce films of excellent quality. 35 As a method to improve such drawbacks,
Although a method of increasing the diameter of the cooling roll may be considered, this method is not a preferable method because it causes various restrictions, for example, because the equipment becomes too large.

Furthermore, as another improvement method, a method has been proposed in which the A side is cooled using liquid or gas.

For example, when side A is forcedly cooled using a gas such as air, a cooling air blowing nozzle (hereinafter referred to as CK There is a method in which a high-speed air flow is blown onto the film surface from a retouching nozzle to promote cooling of the film. In this method, one CK or two or more CKs can be used as required. Thermoplastic resins, especially thermoplastic resins obtained by polycondensation, contain low molecular weight components.

This low molecular weight component vaporizes into the air from the moment it is extruded from the melt extrusion die lip, and condenses and adheres to a part of the film manufacturing equipment again in the form of a white powder. Additionally, some additives contained in the resin, such as lubricants, stabilizers, matting agents, etc., similarly evaporate into white powder and condense and adhere. The white powdery substance generally tends to adhere to areas that are cooler than surrounding objects, such as the surface of the cooling roll and its surroundings. Therefore, when using CK placed on side A,
Since the inside of the CK device is mostly cooled by air, the CK tends to become a place where white powdery substances adhere and accumulate. This is particularly noticeable in the CK portion close to the film that is being cooled. If such white powdery substances adhere or accumulate near the film that has not yet been completely cooled and solidified,
In particular, in the case of the method of cooling the A side with CK, various serious problems occur as shown below. The first problem is that, for example, white powdery substances that sometimes peel off from the CK adhere to the surface of the film that has not been completely cooled and solidified, significantly impairing the flatness of the film in that area.

Second, to avoid this phenomenon, sometimes CK
In some cases, the manufacturing process line has to be temporarily stopped to remove white powdery substances that have accumulated on the surface of the product, resulting in a decrease in yield. Furthermore, in the conventional method of using CK to promote cooling of the film from the A side of the film, there is a problem with the influence of the heated air (hereinafter referred to as exhaust air) that has undergone heat exchange with the film. be.

That is, the exhaust air disturbs the flow of the surrounding atmosphere and stirs up dust, which adheres to the film and impairs the uniformity of the film surface in that area. The influence of this exhaust air also has a negative effect on the cooling process and subsequent steps. For example, the exhaust air may lower the temperature of the heated roll in the next step, resulting in various defects that are critical to film quality. As a result of intensive research into a film cooling method that does not have such drawbacks, the present inventor discovered that two or more Cs on the A side, which had conventionally been randomly arranged,
By arranging K in a specific manner depending on the opening degree of the RITSU PRO and the wind speed of the air flow in the RITSUPRO, the adhesion of white powdery substances to CK can be significantly reduced, and the exhaust air from these Ck can be placed in a specific position. The inventors have discovered that it is possible to prevent foreign matter such as dust from adhering to the film by discharging from the exhaust port, and have arrived at the present invention.

That is, in the present invention, when a thermoplastic resin film (or sheet) extruded in a molten state is cast onto a cooling roll and cooled and solidified, at least two cooling air blowers are placed opposite to the cooling roll. The nozzles are installed, and the distance between two adjacent nozzles is determined by the following formula 20≦y≦0.
45v0-0.75d+44 (Formula 1) where, y: Distance between two adjacent air blowing nozzles (unit: CTL) VO: Among two adjacent air blowing nozzles, Wind speed at the outlet of the nozzle installed on the higher temperature side of the film to be cooled (unit: m/Sec) d: Of the two adjacent air blowing nozzles, the one installed on the higher temperature side of the film to be cooled The lip opening of the installed nozzles (unit: [1) is arranged sequentially in the roll rotation direction so as to satisfy the lip opening degree (unit [1]), and an exhaust port is provided near the point where the film (or sheet) leaves the cooling roll. This is a method for cooling a thermoplastic resin film or sheet.

The resin used in the method of the present invention may be any thermoplastic resin that can be melt-extruded into a film or sheet, but polyolefins, nylons, polyesters (including polycarbonates), etc. are preferably used.

．． l! ::V) In particular, polyethylene terephthalate and so-called crystalline or semi-crystalline resins having a half crystallization time comparable to or shorter than polyethylene terephthalate (about 1 minute or less at 180° C.) are preferably used. The method of the present invention will be specifically explained below with reference to the drawings.

In FIG. 1, a sheet or film F made of a thermoplastic resin melted by an extruder (not shown) and extruded through a die c is cast onto a rotating cooling roll B, and is cooled and solidified while moving with the surface of the roll. The film is then passed through a peeling roll D and sent to the next process. Here, Ck-A, A',
Alternatively, air is blown onto the film surface from the air outlet of A'' (the case where three are installed is shown as an example) at V. (The wind speed may be the same or different for all three. Cooling is also performed from the air surface, and the exhaust port E is arranged close to the cooling roll B.
The distance between '-A'' is maintained so as to satisfy Equation 1. Although the case where there are three Ck is shown in FIG. 1, the method of the present invention is not limited to such a case; Needless to say, it is preferable that there be two or more.By arranging the Ck and the exhaust ports in this way, the airflow blown out from the Ck Ritsupro will flow along the outer circumferential surface of the cooling roll while accompanying the surrounding air. During this time, heat exchange with the film takes place.

As can be seen from Equation 1, the greater the VO and the smaller the d, the greater the distance the fluid flows along the outer circumferential surface of the cooling roll. If y is set within this distance range (that is, if the next Ck is placed), the adhesion of white powder to that Ck will be significantly reduced, and cooling by the air flow will continue. Further, a Ck having a length of 0.8 times or more the width of the film on the cooling roll and having an opening in a direction perpendicular to the direction of film travel is placed on the side A facing the cooling roll, and the Ck It is preferable that the RITSUPRO be as close to the film surface as possible, but for operational reasons it is better to place it approximately 5 to 30 meters from the film surface.
The angle at which air is blown onto the film is desirably within 300, preferably within 100, from the tangential direction to the cooling roll in the rotational direction of the cooling roll. This is because if the air is blown beyond 300 degrees from the tangential direction, the air flow will flow toward the extrusion die, causing significant adverse effects such as cooling the extrusion die. On the other hand, if the film is oriented toward the air side rather than the tangential direction, the film cooling effect will be significantly reduced, which is not preferable. In the method of the present invention, even if a thick film, for example, a film (also referred to as a sheet) with a thickness of 1 m or more, is cooled from the A side as well, the thermoplastic resin forming the film can be cooled. The temperature range in which crystallization occurs relatively quickly (for example, for polyethylene terephthalate, about 220 to 13
C) It can be quickly cooled to a low temperature,
Therefore, even in such a thick film, crystallization of the unstretched film can be suppressed to a low level, and an unstretched film that is transparent and has excellent stretchability can be obtained.

This means that an oriented film having uniform surface properties, little thickness unevenness, excellent transparency, and high strength can be obtained from the unstretched film. On the other hand, if the distance y between the CKs is larger than the range shown in equation 1 above, the cooling effect of the film by air decreases, the cooling effect becomes insufficient, and the subsequent CKs (on the film traveling direction side) are exposed to white powdery substances. This is not preferable because the adhesion becomes noticeable and causes a decrease in yield.

On the other hand, when y becomes 20 (unit/CTL) or less, the amount of blown air increases and the cooling effect per unit air amount decreases,
This is not desirable as it results in a lot of waste. In addition, if the exhaust port is not placed close to the point where the film leaves the cooling roll, the air warmed by cooling the film will disperse around the cooling roll, disturbing the surrounding atmosphere from the set conditions, and causing the film to drop. This is not preferable because it deteriorates the quality of the product. Under the cooling conditions employed in the method of the present invention, the lip opening degree d of Ck is usually 1 to 30,100 m, preferably 3 to 15 m, and the wind speed VO at the nozzle is 5 to 50 m.
It is preferable to set it to m/See. Therefore, the distance y between Ck in the method of the present invention is 24 to 66? The most preferred range is . Further, the temperature of the cooling air used in the method of the present invention is preferably as low as possible, but it is sufficient if the temperature does not cause dew condensation around the Ck. Although it is preferable to install the exhaust port so that the distance y from the final Ck satisfies the above formula 1, it is not necessary to do so, and it is necessary to install the exhaust port so that the distance y from the final Ck satisfies the above formula 1. It can be installed between. It is preferable that the amount of air discharged from the exhaust port be equal to or greater than the amount of air blown out from all CKs so as not to disturb the surrounding atmosphere. In the method of the present invention, the film is extremely effectively cooled by air blowing from the A side, and the adhesion of white powdery substances to the CK is extremely small. Since it is difficult to disperse, defects on the film surface caused by adhesion of foreign substances to the film can be significantly reduced, and a film with excellent uniformity can be obtained.

Moreover, since the film is also cooled by the cooling roll, the structural difference between the front and back sides of the film is significantly reduced.
The strength, base value, thickness unevenness, etc. of the film are improved.
Therefore, the film obtained by the method of the present invention can be used in applications that require small differences in physical properties between the front and back sides, such as electrical insulation and magnetic cards, and applications that require particularly strict film surface uniformity, such as It is particularly preferably used for photography and the like. The method of the present invention is particularly effective for thick films with a film thickness of 1 m or more on the cooling roll. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 When cooling a polyethylene terephthalate sheet having a thickness of 2[01n] melt-extruded at 280°C and having a diameter of 600m, a circulating water temperature of 20°C, and the surface of a cooling roll rotating at 4m/[001m], The air flow of the Rippuro was set at a wind speed of 30 m/Sec, and two cooling air blowing nozzles with a lip opening of 100 m were placed on the air surface side with various intervals between them, and the air was exhausted at the same position as in Figure 1. A vent was arranged to exhaust the air at an exhaust speed of 6 m/sec, and a film having a final product thickness of 175 μm was continuously produced.

Table 1 shows the surface temperature of the film on the air side when the cooling roll was separated and the cleaning frequency of the second-stage cooling air blowing nozzle. In this case, the distance y between the air blowing nozzles defined by Equation 1 is 20 to 50 CTrL. Example 2 A polyethylene terephthalate sheet with a thickness of 2.50 m melted and extruded at 280°C was extruded onto a cooling roll under the same conditions as in Example 1, and a cooling air blowing nozzle (d210, v0 = 20 m /Sec), the distance between each of the three units is 40? Or placed at 60cTrL.

Further, in each case, exhaust ports were arranged as shown in FIG. 1, and continuous production was carried out with and without exhaust, and films with a final thickness of 250 μm were obtained in both cases. In each production, 1000 products are produced on the second day after the start of production.
Table 2 shows the results of visually inspecting the film surface for m length. Example 3 A polyethylene terephthalate film with a thickness of 2 m melt-extruded at 280°C was heated to a diameter of 600 [001 mm and a circulating water temperature of 3.
The mixture was casted onto the surface of a cooling roll rotating at 0° C. and 4 m/Nml to cool and solidify.

At that time, while changing the air flow speed and lip opening degree of the Ritupro, the two air blowing nozzles were placed on the air surface side with different intervals, and the exhaust port was placed close to the cooling roll. , final film thickness 175μ width 2500111 [n
films were continuously produced. At that time, as in Example 2, the product length of 1000 m was visually inspected on the second day of production, and the number of defects on the film surface was checked. The results are shown in Table 3.
Shown below.

[Brief explanation of the drawing]

The drawing shows an example of an embodiment of the present invention, and is a schematic cross-sectional view of the vicinity of a cooling roll.

Claims (1)

[Claims] 1. When a thermoplastic resin film (or sheet) extruded in a molten state is cast onto a cooling roll and cooled and solidified, at least two pieces of cooling air are provided opposite to the cooling roll. The spray nozzles are installed, and the distance between two adjacent nozzles is determined by the following formula 20≦y≦0.45v_o-
0.75d+44 (Formula 1) where y: distance between two adjacent air blowing nozzles (unit/cm) v
_o: Wind speed at the outlet of two adjacent air blowing nozzles installed on the higher temperature side of the film to be cooled (unit: m/sec) d: Air blowing speed of two adjacent air blowing nozzles Among the nozzles, the nozzles are placed in the roll rotation direction in order to satisfy the lip opening degree (unit: mm) of the nozzle installed on the higher temperature side of the film to be cooled, and the film (or sheet) is placed on the higher temperature side of the film to be cooled. A method for cooling a thermoplastic resin film (or sheet) characterized by providing an exhaust port close to the point where it leaves the roll.