JPH0365260B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a film heat treatment apparatus that can heat a thermoplastic polymer film while continuously running the film without causing a bowing phenomenon (lag in the center of the film). Industrial heat treatment methods for thermoplastic polymer films are broadly divided into roll-type heat treatment methods in which the film is brought into contact with heated rolls, and tenter-type heat treatment methods in which both edges of the film are restrained and heated with hot air or the like. be. Disadvantages of the roll heat treatment method include transfer of scratches from the roll, uneven temperature in the width direction of the roll, resulting in uneven film quality in the width direction, and wrinkles (especially common when using Nitpro rolls). It was hot. In addition, the tenter heat treatment method does not cause wrinkles or scratches, but compared to the roll heat treatment method, there is a bowing phenomenon in which the center of the film lags behind the side edges in the width direction of the film, resulting in an arched shape. This tends to result in uneven molecular orientation in the width direction, resulting in uneven dimensional stability (thermal shrinkage), mechanical strength, and elongation, resulting in poor coating quality. It often causes problems in post-processing such as laminating, slitting, printing, and bag making, and also impairs the commercial value of the finished product. Since it is made into a product, it has the disadvantage of decreasing product yield. Various methods have been tried in the past to prevent such drawbacks, but all of them have drawbacks. For example, a heat treatment method in which a film is brought into contact with a heating roll having a nip roll (see Japanese Patent Publication No. 39-29214) has the disadvantage of neck-down due to not restraining both edges, as well as the drawbacks of the roll-type heat treatment method. In addition, heat treatment methods that apply a temperature difference in the width direction (see Japanese Patent Publication No. 42-9273) include:
The roll type has the above-mentioned drawbacks, and the tenter type has drawbacks such as complication of equipment and reduction in effective operating rate due to the time taken to adjust conditions. In addition, there is a heat treatment method (see Japanese Patent Application Laid-Open No. 1983-91973) that increases the wind speed at both side edges of the film to make the physical properties uniform in the width direction.
It has the same drawbacks as the tenter type in No.-9273. In addition, a method of heat-treating the film after horizontal stretching using a nip roll provided between the horizontal stretching process and the heat treatment process in a tenter (Japanese Patent Laid-Open No.
50-73978), the film comes into contact with the roll in a heated state, so scratches on the roll are easily transferred, and wrinkles occur due to the temperature difference between the surrounding atmosphere and the roll. Furthermore, the occurrence of the bowing phenomenon cannot be sufficiently prevented simply by cutting the film tension between the stretching process and the heat treatment process. The present inventors investigated in detail the occurrence of the bowing phenomenon in order to provide a tenter-type heat treatment apparatus that can take advantage of the advantages of the tenter system and perform film heat treatment without causing the bowing phenomenon. As a result, the following causes were found. First, an example of the implementation state of the conventional tenter type heat treatment method will be explained with reference to FIG. 1. The film 1 is made to run in the direction of arrow They are installed on both the front and back sides of the film 1, and blow hot air almost perpendicularly onto the film 1 for reasons of thermal efficiency. As a result, the hot air flows as shown by arrow Y, giving heat to film 1 and lowering its own temperature as it flows over the surface of film 1, but the hot air blowing direction is almost perpendicular to the surface of film 1. As a result, a considerable amount of it flows to the upstream side of the film 1 in the running direction (arrow That's what I'm going to do. Further, when a tenter-type heat treatment apparatus is provided with a preheating zone (not shown) having a certain size and a lower temperature atmosphere than the heat treatment zone, similar heating is performed on the unheated portion. According to research conducted by the present inventors, if there is a part of the film that is heated at a temperature slightly lower than that of the heat treatment zone, heat shrinkage occurs in this part and the film is stretched both vertically and horizontally, resulting in a high temperature. It has been found that bowing, or bowing, occurs with the largest delay in the center of the film, which is farthest from both side edges of the film where the restraining force is applied near the heat treatment zone. Furthermore, as a result of intensive studies by the present inventors on how to prevent this bowing phenomenon, the inventors of the present invention have found that a hot air blowing device that blows hot air onto the film 1, which is forced to run continuously with both side edges restrained, is equipped with a hot air blowing device that blows hot air at least in the running direction of the film 1. By providing the hot air blowing device located at the most upstream side so that the hot air blowing direction is inclined from diagonally upward on the upstream side to diagonally downward on the downstream side in the running direction of the film 1 with respect to the surface of the film 1, The present invention was completed by investigating that the above object can be achieved. That is, the present invention provides a heat treatment apparatus equipped with a hot air blowing device that blows hot air onto a film that is forced to run continuously with both side edges restrained. A hot air blowing device located on the side is provided so that the hot air blowing direction thereof is inclined from diagonally upward on the upstream side to diagonally downward on the downstream side in the running direction of the film with respect to the surface of the film. The present invention relates to a film heat treatment apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus of the present invention will be explained in detail below with reference to drawings showing main parts of embodiments thereof. FIGS. 2, 3, and 4 are cross-sectional explanatory views showing the main parts of three embodiments of the film heat treatment apparatus according to the present invention. In the drawings, the meanings of numbers 1 and 2 and arrows X and Y are the same as in FIG. 1 above. In the apparatus of the present invention, both side edges 1a of the film 1 (not shown in FIGS. 2, 3, and 4)
Heat treatment is carried out by blowing hot air onto the film 1 at the beginning of the heat treatment zone where the hot air is restrained and allowed to travel continuously while substantially preventing the hot air from flowing upstream in the traveling direction (arrow X) of the film 1. This is what we do. The bowing phenomenon occurs in the film 1 due to the hot air flowing upstream in the running direction of the film 1 when the hot air flows to the unheated part upstream of the heat treatment zone, and the film 1 is heated to some extent. There is no problem in the hot air flowing upstream in the heat treatment zone where the heat treatment zone is in such a state that it is necessary to prevent the hot air from flowing upstream after hitting the film 1 at the beginning of the heat treatment zone. Further, the flow of hot air to the upstream side can be prevented if, for example, a small amount of hot air to the upstream side or hot air at a temperature lower than the glass transition point of the film 1 to be heat treated is allowed to flow to the upstream side. If there is a radiant heat source other than hot air that can heat the film 1 above the glass transition point, it is natural that the radiant heat must be prevented. In the apparatus of the present invention, one or more rows of hot air blowing devices 2 blow hot air onto the film 1 which is continuously run with both side edges 1a restrained (restraint devices not shown). The hot air blowing device 2 in at least the most upstream row is installed on one side or both sides so that the hot air blowing on the film 1 does not substantially flow upstream in the running direction of the film 1. This film heat treatment apparatus is installed so that the direction (arrow Y') is inclined with respect to the surface of the film 1 from diagonally upward on the upstream side to diagonally downward on the downstream side in the running direction of the film 1. If the hot air blowing direction is inclined as shown above,
In other words, the angle formed by the hot air blowing direction (arrow Y') and the running direction of the film 1 (arrow X) (θ in Fig. 2, hereinafter referred to as the blowing angle) is 180°>θ>
If the angle is 90°, there is an effect of preventing the occurrence of bowing reduction, which is the object of the present invention, but the effect is even greater when the angle is preferably 135°>θ>105°. In FIG. 2, the hot air blowing device 2 itself is installed at an angle, but in FIG. 3, the hot air blowing direction from the hot air blowing device 2 itself is perpendicular to the film 1.
The hot air direction plate 4 provided at the hot air outlet of the hot air blowing device 2 regulates the direction of hot air blowing. It is also effective as a hot air blocking plate that prevents hot air from flowing upstream in the traveling direction. The reason why it is not necessary to restrict the direction of hot air blowing in this way for all of the hot air blowing devices 2, and it is sufficient if it is done for at least the most upstream row as shown in FIG. The hot air blown onto film 1 travels on the surface of film 1 in the traveling direction of film 1 (arrow X).
This is because it is sufficient to prevent the unheated portion of the film 1 from being heated to a temperature slightly lower than the temperature at the time of spraying, that is, the temperature of the heat treatment zone. The optimal gap between the hot air deflection plate 4 and the surface of the film 1 is about 0 to 5 mm, but it is preferable that the hot air deflection plate 4 and the film 1 do not come into contact with each other to avoid damaging the film 1. The objects to be treated with hot air by the apparatus of the present invention are polyethylene terephthalate, polyethylene-2,6
- Consists of thermoplastic polymers such as naphthalate, polytetramethylene terephthalate, polyhexamethylene adipamide, polycapramide, polyethylene, polypropylene, polyvinyl chloride, polyvinyl fluoride, copolymers based on these, or mixtures thereof. The present invention is particularly applicable to uniaxially stretched films and biaxially stretched films. According to the apparatus of the present invention having such a structure, unlike the conventional tenter type, thermal contraction of the film 1 on the upstream side of the heat treatment zone does not occur or is negligibly small, and as a result, the bowing phenomenon hardly occurs. For example, a straight line drawn in advance in the width direction of an untreated film hardly deforms into an arched shape with a delayed central part even after heat treatment. Depending on the conditions, it is also possible to correct the bowing caused by the lateral stretching of the tenter. Furthermore, since there is no need to vary the temperature or wind speed of the hot air in the width direction, the equipment is simple, and operation is easy and stable. Furthermore, the heat-treated film obtained by the apparatus of the present invention has almost no quality unevenness in the width direction, is difficult to break, and has excellent quality stability. Examples 1 to 2, Comparative Example 1 Polyethylene terephthalate was extruded from a die having a circular slit, rapidly cooled, heated, and stretched in a tube shape by 3.3 times in the machine direction (longitudinal direction) and 3.5 times in the circumferential direction (horizontal direction). A biaxially stretched film with a thickness of 20 μm was obtained. Next, using a tenter-type heat treatment apparatus similar to that shown in FIG. 3, hot air at 220° C. was passed along the hot air deflection plate 4 while running the stretched film at a speed of 20 m/min while keeping the stretched film in a stacked state with a width of 1300 mm. The stretched film was heated for 7 seconds while being sprayed at spray angles of 120° (Example 1) and 135° (Example 2) to obtain heat-treated films. The temperature of the hot air is a value measured on the surface of the film being blown onto it (the same applies to the following Examples and Comparative Examples). As a comparative example, a heat-treated film was obtained by removing the hot air deflection plate 4 from the heat treatment apparatus and performing the same heat treatment operation. In each of the above cases, a straight line was drawn in the width direction of the film surface before heat treatment, and the delay at the center of the film width was actually measured as an indicator of the amount of deformation (bowing phenomenon) after heat treatment. Further, the deviation of the principal axis of orientation from the reference value at each position a predetermined distance apart from one side edge in the width direction of the film was measured using a polarizing microscope. However, the standard orientation main axis is the horizontal direction, and the deviation of the orientation main axis is in the direction of travel of the film.If it deviates counterclockwise from the lateral direction when viewed from above the film, it is a + direction, and if it deviates clockwise, it is a - direction. direction. The above results are shown in Table 1.

[Table] Example 3, Comparative Example 2 A biaxially stretched polyethylene terephthalate film having a thickness of 15 μm was obtained in the same manner as in Examples 1 and 2.
The above film was transferred to a tenter type apparatus equipped with a hot air blowing apparatus having the same structure as that shown in FIG. Using a heat treatment device, the film was heat-treated for 5 seconds by blowing hot air at 210° C. while keeping the width of two films stacked at 1300 mm and traveling at a speed of 35 m/min to obtain a heat-treated film (denoted as film A). As a comparative example, a conventional tenter type heat treatment apparatus is different from the apparatus of the present invention in that the hot air blowing apparatus on the most upstream side does not have a hot air deflection plate 4. The film was heat-treated for 5 seconds by blowing hot air at 0.degree. C. to obtain a heat-treated film (referred to as film B). Various physical properties of the thus obtained films A and B were measured at predetermined locations in the width direction of the film, namely the amount of bowing (delay), thickness variation before and after heat treatment, density, thermal shrinkage rate, orientation principal axis direction, and birefringence. The measurement methods for the main measurement items were as follows. Density: Measured at 25°C using an n-hebutane-carbon tetrachloride density gradient tube. Heat shrinkage rate: 150℃, 2 in an open hot air circulation type
The shrinkage rate after heating for a period of time was measured. Birefringence and orientation principal axis direction: The optical path difference was measured using a Berek compensator with a polarizing microscope, and calculated as optical path/thickness. Note that birefringence here refers to the difference in refractive index when passing light in the direction of the alignment axis within a plane and in the direction perpendicular thereto. The measurement results are shown in FIG. Example 4, Comparative Example 3 A biaxially stretched film of polyhexamethylene adipamide with a thickness of 14 μm was obtained in the same manner as in Examples 1 and 2 except that polyhexamethylene adipamide was used instead of polyethylene terephthalate. Ta. The above films were stacked in two layers using a tenter-type heat treatment device having a structure similar to that shown in Fig. 3 and equipped with a hot air blowing device whose hot air blowing angle was adjusted to 120° using a hot air deflection plate 4. Keep width 1300mm at speed 30
Heat treatment was performed for 5 seconds while blowing hot air at 235° C. while running at a speed of m/min. Regarding the obtained heat-treated film, the delay at the center of the film and the deviation of the main axis of orientation were measured in the same manner as in Examples 1 and 2.
As a comparative example, a conventional tenter-type heat treatment apparatus, which differs from the above-mentioned apparatus of the present invention in that the hot air blowing apparatus does not have a hot air deflection plate 4, is used to heat the film at 235°C with hot air also flowing upstream in the film running direction. A film obtained by blowing hot air onto the film and performing heat treatment for 5 seconds was also measured in the same manner. The above results are shown in Table 2.

[Table] From the comparison between the above Examples and Comparative Examples, it can be seen that the film heat-treated by the apparatus of the present invention has extremely excellent uniformity of quality in the width direction. In addition, because there is extremely little unevenness in the width direction in properties related to mechanical properties such as dimensional stability (heat shrinkage rate), thickness, and density, it is possible to use it in subsequent processing steps such as coating, laminating, slitting, printing, and bag making. No problems occur, and the finished product is of excellent quality. Therefore, according to the apparatus of the present invention, it is possible to produce films suitable for applications requiring high precision, such as magnetic tapes for video and audio, base films for aerial photography, and electrical applications such as capacitors. Moreover, since the quality is excellent in uniformity in the width direction, the front width of the film can be effectively converted into products, resulting in a high product yield and extremely high industrial value.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of the implementation state of the conventional tenter type heat treatment method, Fig. 2, Fig. 3, and Fig. 4
The figures are explanatory cross-sectional views showing the main parts of three embodiments of the device of the present invention, and FIG. 5 is a diagram showing the measurement results of the fourth embodiment and the second comparative example. In the drawings, 1...film, 1a...side edge, 2
...Hot air blowing device, 4...Hot air deflection plate, X...
Film running direction, Y...Hot air flow direction,
Y′...Spraying direction.

Claims (1)

[Claims] 1. In a heat treatment apparatus equipped with a hot air blowing device that blows hot air onto a film that is forced to run continuously with both side edges restrained, the hot air blowing device is located at least on the most upstream side in the running direction of the film. A hot air blowing device is installed so that the hot air blowing direction is inclined from diagonally upward on the upstream side to diagonally downward on the downstream side in the running direction of the film with respect to the surface of the film. Heat treatment equipment.