JPH11320671A - Method and apparatus for producing stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing a plastic film, which improve the productivity of a coated film by improving a drying step of an aqueous coating agent. SOLUTION: In a method for producing a plastic sheet having a step of applying an aqueous coating agent on at least one surface of a traveling plastic film, after the applying step, the coating agent is dried using a near-infrared radiation heater and heated air. A method for producing a plastic film, which comprises a step, and an apparatus therefor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a stretched film, and more particularly, to a stretching method which comprises a step of applying (coating) an aqueous coating agent to a plastic film, and thereafter performing drying by a specific means. The present invention relates to a method and an apparatus for producing a film.

[0002]

2. Description of the Related Art In order to impart functions such as easy adhesion, easy slip, antistatic property, gas barrier property, concealing property, ink acceptability, optical antireflection property and antifogging property to a plastic film. It is widely practiced to coat a film with a function-imparting coating material. This coating material is usually applied in a solvent-free, solution or dispersion state, dried or cured, and integrated with a plastic film.

In the production of such a plastic film, in recent years, a demand for high productivity and the like has required a high-speed application of a coating agent, and a drying method after coating has sometimes been unsatisfactory with a conventional method. In particular, after coating the plastic film, in the manufacturing process having a step of stretching the plastic film in the width direction, or simultaneously stretching in the width direction and the running direction, the drying of the coating material can not catch up, the plastic film in the stretching step In some cases, stretching has become impossible due to a decrease in the temperature.

In order to cope with such inconveniences, in the prior art, the temperature of the air for heating is increased in response to a decrease in the temperature of the plastic film in the stretching step, the wind speed of the air is increased, and the heat transfer coefficient is improved. Measures such as reducing the thickness have been taken.

However, when the temperature of the air is increased,
As the thermal crystallization of the uncoated part of the plastic film progresses, the extensibility is reduced, and when the air velocity is increased, unevenness of coating or uneven coating due to the dance or wind of the plastic film is caused. When the thickness is reduced, uneven coating and coating defects occur due to a decrease in coating uniformity, and a predetermined coating function such as ink receptivity cannot be exhibited.

[0006] Thermal crystallization of the non-coated portion is particularly problematic, and a known technique is disclosed in Japanese Patent Application Laid-Open No. 60-42222.
Although there is a method disclosed in Japanese Patent Laid-Open No. 6 (1994), it is not always advantageous from the viewpoint of productivity. Also, JP-A-10-24
The method using dry air disclosed in Japanese Patent No. 261 is still not suitable for coating and manufacturing at a higher speed, or for forming a high-performance ink-receiving layer by increasing the coating thickness, and forming barrier properties and concealing properties. Not enough.

[0007]

As described above, in the prior art, even if an attempt is made to increase the production speed of a plastic film in order to improve productivity, the drying of a coating material, especially an aqueous coating material, cannot keep up. The drawbacks are that stretching cannot be performed, or the target quality cannot be obtained even if the drying is overtaken, and drying cannot be overtaken for the purpose of applying a high coating amount in order to improve the functional quality.

In view of such circumstances, the present inventors have studied a method for improving the speed of drying an aqueous coating composition. As a result, a combination of a near-infrared heater and heated air was used to dry the aqueous coating composition applied to a plastic film. It was found that it was effective and that excellent productivity could be obtained.

That is, water absorbs the near-infrared wavelength band well, but the plastic film has a characteristic that it is relatively hard to absorb near-infrared rays. The temperature of the part rises due to the absorption of near infrared rays of water, and drying is promoted,
It has been found that the portion of only the film in the non-applied portion has relatively little absorption of near-infrared rays and is difficult to be heated, and the rise in the film temperature in the non-applied portion is suppressed. In addition, subsequent to the drying step of the coating material, by simultaneously stretching in the horizontal direction or the vertical direction by the tenter method, the effect of the present invention is remarkably exhibited, that is, the coating part is started at the time of starting the stretching. If the temperature difference between the non-coated part and the non-coated part is large, stretching starts selectively from the high temperature part, or stretched unevenness, thick and thin unevenness due to thermal crystallization, and more particularly, breaks during stretching, which is an extremely undesirable state However, in order to avoid this, it was necessary to make the temperature difference between the coated part and the non-coated part less than a certain level, and it was found that heating by the near infrared heater was extremely effective. Furthermore, it is preferable to use a near-infrared heater and heated air for drying.This is because when the coating film is dried, the high-humidity air evaporated on the surface of the coating film stays and the drying speed is reduced, so that the heated air is used. The inventors have also found that the effect of removing the high humidity vapor is exerted, and that the coating film and the film by the heated air can be heated to contribute to the improvement of the drying ability.

[0010] On the other hand, when drying is carried out with conventional hot air and dry air, the temperature of the coating portion rises slowly due to evaporation of water, and the temperature of the non-coating portion rises first, which tends to cause the above-mentioned stretching unevenness. However, there is no means for selectively heating the coated portion as in the present invention, resulting in insufficient drying ability.

Accordingly, an object of the present invention is to provide a method for producing a stretched film having excellent productivity and quality by improving the drying speed of an aqueous coating applied to a plastic film and exhibiting excellent stretchability. It is to provide the device.

[0012]

SUMMARY OF THE INVENTION The object of the present invention is to provide: Production of a stretched film in which a water-based coating agent is applied to at least one surface of a running plastic film and dried, and then stretched in a direction substantially perpendicular to the running direction of the film or simultaneously stretched in both directions of the perpendicular direction and the running direction. In the method, a method for producing a stretched film, wherein the drying is performed using a near-infrared radiation heater and heated air,
And 2. An application step of applying an aqueous coating agent to a traveling plastic film, a drying step of drying the applied coating film, and stretching the dried film in a direction substantially perpendicular to the traveling direction or in a direction perpendicular to the perpendicular direction and the traveling direction. In a stretched film manufacturing apparatus having a stretching step of stretching in both directions simultaneously,
The drying step is achieved by a stretched film manufacturing apparatus, which includes a drying unit using a near-infrared radiation heater and a drying unit using heated air.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An apparatus for producing a plastic film according to the present invention is an apparatus for producing a plastic film having means for applying an aqueous coating agent on at least one side of a running plastic film. And a drying step having means for drying the coating material by using both heating by a near-infrared heater and heating by heated air. This stretching step comprises a step of stretching in a direction substantially perpendicular to the running direction of the film, or a step of simultaneously stretching in the perpendicular direction and the running direction.

The near-infrared radiation heater according to the present invention comprises:
It is preferable to install it at a stage before the temperature of the plastic film substantially does not reach near the heated air temperature. Even after heating to the heated air temperature, heating with a near-infrared heater further increases the temperature of the film and causes crystallization,
It is wasteful on energy saving. The radiation effective width of the near-infrared heater is preferably the entire width of the film including the uncoated width. If the production application width is constant, irradiation may be performed only for the application width.

Examples of the near-infrared radiation heater include a Heraeus Twin-tube, a mid-wave infrared radiator with a gold reflective film, and a short-wave infrared radiator with a gold reflective film. These heaters can adjust the emission wavelength of the maximum energy from about 1 μm to about 4 μm depending on the temperature of the heating element. The temperature of the heating element is preferably in the range of 600 to 2000C.

In drying with heated air, it is preferable to blow heated air at a constant temperature substantially in the width direction over the entire width of the plastic film to dry the coating material.

In the drying with heated air in the present invention, the heated air is sent to the film as a circulating system in a drying oven, and a part of the circulating air is exhausted out of the oven, and an amount corresponding to the exhausted amount is used. It is preferable to include a means for supplying air having a lower humidity than the circulating air. The heating air in this drying step is preferably circulated in the oven in order to reduce the heating energy, but in a completely closed system, there is an increase in humidity, and the drying speed is reduced. It is preferable to take in and replace. This intake air may be at room temperature or may be heated.
When the amount to be taken in is large, it is preferable that the heating is performed from the viewpoint of adjusting the temperature in the oven.

In the step of drying the coating agent, the temperature of the plastic film is measured, and based on the measurement result,
It is preferable to control the production conditions so that the temperature of the film falls within the set range. Furthermore, at the end of drying of the coating,
The difference between the temperature of the plastic film in the coated part and the temperature of the plastic film in the non-coated part is 0 ° C to 20 ° C.
It is preferable to fit within the range.

To exemplify a more specific embodiment of the method and the apparatus of the present invention, the method and the apparatus of the present invention apply a water-based coating, dry the coating, and then move the plastic film in the running direction. In the drying step of the coating material in the method and the apparatus for manufacturing a stretched plastic film that is stretched in a direction substantially perpendicular to or at the same time in the running direction and the direction perpendicular thereto, the drying of the coating material and the temperature at which the plastic film can be stretched. It has a means for promoting drying of the applied coating material by using a near-infrared radiation heater and heating air at a constant temperature to raise the temperature.

Further, there is provided a plastic film production method and apparatus for controlling production conditions such that the temperature of the plastic film at a predetermined position in the film running direction does not fall below a set value in a drying and heating step of the plastic film.

In the present invention, a plastic is a thermoplastic plastic which crystallizes together with molecular orientation when stretched, such as polyester, polyamide, polypropylene, high-density polyethylene, polyvinyl alcohol, or a copolymer containing these as a main component. Or a mixture, and may contain an organic substance or an inorganic substance within a stretchable range.

The crystallization behavior of the film can be confirmed by X-ray diffraction or differential thermal analysis. These plastics are characterized in that molecules are oriented by stretching and the crystallization start temperature is lowered, and crystallization easily proceeds when subjected to a heat history after stretching. Here, the crystallization start temperature is
This is the temperature at which crystallization starts due to heating, and the difference between the tangent line of the rising part of the exothermic peak first appearing in the differential thermal analysis curve measured while raising the plastic film from room temperature at a constant rate of 160 ° C./min, and the baseline. Let it be the temperature indicated by the intersection.

The drying by the near-infrared radiation heater in the present invention is preferably carried out by adjusting the temperature of the heating element to adjust the emission wavelength of the maximum energy to about 1 μm to 4 μm. The temperature of the heating element is 600
It is preferably in the range of ２０００2000 ° C.

The drying by the near-infrared radiation heater is as follows:
The drying is preferably performed before the drying with heated air, but is preferably performed in a range where the film temperature is equal to or lower than the heated air temperature. Furthermore, the film temperature is 30 ° C. lower than the heated air temperature,
It is preferred to carry out at a temperature that reaches a range of 0 ° C. lower.

In the present invention, the temperature of the heated air blown onto the plastic film is preferably substantially constant in the width direction over the entire width of the film. In addition, this temperature is preferably as low as possible within a range that does not affect the drying and stretching of the coating material in order to prevent thermal crystallization of the plastic film. It is preferable to set the range. This temperature adjustment can be performed by a heater in the oven.

Even when a plastic film is manufactured using this apparatus, a change in manufacturing conditions causes a decrease in the temperature of the film, thereby lowering the stretchability and possibly causing the film to break. In order to avoid this, at a predetermined position in the running direction of the plastic film,
The temperature of the film is measured, and the result is used to control the above process. Here, examples of the predetermined position include an end point of the drying step of the coating material and a starting point of stretching.In addition, in order to observe a temperature change of the plastic film in the drying step of the coating material, It is preferable to provide at least one measurement point in the process. In addition, the control here refers to adjusting the wind speed of the air, the temperature of the air, and the like in the drying process so as to match the film manufacturing conditions, that is, within a predetermined range. At this time, it is preferable that the temperature of the plastic film is controlled in a range in which stretchability is good. The temperature range to be controlled varies depending on the type of the plastic film to be produced.
It is preferable to control the temperature within the range of 0 ° C.

[0027] The coating agent used in the present invention is not particularly limited.
Suitable for vapor deposition, a polymer solution or a polymer dispersion for improving surface lubricity, for example, polyvinylidene-based resin,
Thermoplastic resins such as polyvinyl resin, polyolefin resin, ionomer resin, polyester resin, polyamide resin, polyvinyl alcohol resin, cellulose resin, polyacryl resin, polycarbonate resin, amino alkyd resin, amino acryl Resin,
Thermosetting resins such as melamine-based resins, urea-based resins, epoxy-based resins, polyurethane-based resins, and silicone-based resins, and mixed compositions of these resins can be used.

Various additives such as an emulsifier, an antistatic agent, an antiblocking agent, a leveling agent and a viscosity modifier can be appropriately added to the coating material according to the purpose.

The aqueous coating composition used in the present invention is a solvent containing water as a main component which dissolves an agent imparting a desired function and / or
Alternatively, it refers to a dispersion, and various additives can be appropriately added according to the purpose. The solid content concentration of the paint is 0.5
% By weight or more, more preferably 1% by weight or more,
Further, it is preferably at most 20% by weight, more preferably at most 15% by weight.

Next, one embodiment of the present invention will be described together with its operation. For example, an unstretched plastic film is cooled and solidified on a rotating cooling drum of a molten sheet extruded from a die to form a film, and then stretched in the longitudinal direction of the film in a longitudinal stretching machine. At this time, the orientation crystallization of the plastic film proceeds as the stretching ratio increases, and the crystallization start temperature decreases. As the orientation crystallization progresses, the stretchability in the lateral direction (width direction) at the subsequent stage decreases.

Subsequent to the stretching in the machine direction, at least one surface of the plastic film is coated (coated) with an aqueous coating material and sent to a transverse stretching machine such as a tenter. In a horizontal stretching machine, the coating material is dried and the temperature of the coated plastic film is increased to target horizontal stretching conditions. In the drying step, in the present invention, the plastic film is heated to a target transverse stretching condition using a near-infrared radiator and heated air. As a result, it is possible to produce a plastic film at a higher production speed than before by promoting drying of the coating material and increasing the coating thickness of the coating material without drastically changing the air temperature and the wind speed. Becomes possible.

The coating method is not particularly limited. For example, a gravure roll method, a reverse roll method, an air knife coating method, a metaling bar coating method, a die coating method, or various coating methods based on a combination thereof can be employed. It can be appropriately selected depending on the characteristics of the coating agent and the target coating thickness.

The coating is performed, for example, while leaving the both ends of the longitudinally stretched plastic film. This is because, when the coating is performed on the entire surface, the tenter clip is easily stained in the transverse stretching step, and stretching and cutting are easily caused. In addition, it is difficult to obtain a plastic film of the same properties as the central part from both ends of the longitudinally stretched plastic film as well as the tenter clip gripping part, and it is not finally the target of the product, so trim that part It is not advisable to coat parts that are not covered by the product in order to recycle the raw materials, that is, for so-called recycling.

[0034]

Next, the present invention will be described in detail based on examples, but the present invention is not limited to these examples.

Example 1 Dried polyethylene terephthalate was melt-extruded at 290 ° C. by an extruder, and a molten sheet discharged from a die into a sheet was brought into close contact with a rotating cooling drum using an electrostatic application device. After cooling and solidification, an unstretched sheet was prepared.

Next, the unstretched sheet is stretched about four times in the running direction (longitudinal direction) of the film by a longitudinal stretching machine including a plurality of heating rollers having different peripheral speeds to form a uniaxially stretched film. A coating solution having a concentration of 8% by weight of a polyester-based water emulsion was applied to the lower surface of the film using a die coater having a uniform slit in the width direction to form a coating film having an average coating thickness of 10 μm.
This coated uniaxially stretched film is subjected to pre-stage drying by a near-infrared heater with a horizontal stretching machine, and then heated to 95 ° C. in a drying zone (composed of a zone having an air temperature of 90 ° C. and a zone of 120 ° C.). After that, 9
While elevating the temperature from 5 ° C. to 130 ° C., the film was stretched 3.6 times in the width direction of the film, and then heat-set to produce a biaxially stretched polyester film having a thickness of 50 μm. At that time, a part of the heated air in the drying zone was discharged to the outside, and the same amount of low-humidity air as the discharged amount was supplied to the drying zone along with the film from the entrance of the oven. In this example, in the conventional drying and temperature raising means without using the drying acceleration means of the near-infrared heater, the film is frequently broken in the horizontal stretching machine.
It was possible to produce a coating film at a high speed of 0 m / min.

Example 2 The same procedure as in Example 1 was carried out, except that an in-line coater was used to form a coating film having an average coating thickness of 10 μm on both surfaces of the film. In this case, the conditions other than the double-sided coating are the same as those in Example 1. In this example, in the conventional drying and temperature raising means without using the drying promotion means of the near-infrared heater, the film is frequently broken in the horizontal stretching machine, and the coating amount is about twice as large as the coating amount considered as the upper limit of the production speed. Was possible to produce a coating film.

[0038]

According to the present invention, the near-infrared heater and the heated air are used in the drying step of the aqueous coating composition after coating, so that the conventional drying conditions such as air temperature, air velocity and coating thickness can be obtained. It is possible to produce plastic films with higher productivity without changing the quality, etc., and by improving the drying ability, it is possible to produce without causing coating unevenness and coating defects, and high performance Can be thickened, which can contribute to high quality.

Claims (7)

[Claims] An aqueous coating is applied to at least one side of a running plastic film and, after drying, is stretched in a direction substantially perpendicular to the running direction of the film or is simultaneously stretched in both directions of the perpendicular direction and the running direction. A method for producing a stretched film, wherein the drying is performed using a near-infrared radiation heater and heated air. 2. The method for producing a stretched film according to claim 1, wherein the heating and drying with a near-infrared radiation heater is performed before the heating and drying with heated air. 3. The method for producing a stretched film according to claim 2, wherein the heating and drying by the near-infrared radiation heater is performed until the film temperature substantially reaches the temperature of the heated air. 4. Heat drying with heated air is performed by circulating the heated air in a drying oven to blow the film, and evacuating a part of the circulating air to the outside of the oven, and matching the amount of exhaust to the oven. The method for producing a stretched film according to any one of claims 1 to 3, wherein the method is performed by supplying an amount of air having a lower humidity than circulating air. 5. A coating step of applying a water-based coating agent to a running plastic film, a drying step of drying a coated film after the application, and stretching the dried film in a direction substantially perpendicular to the running direction. An apparatus for producing a stretched film having a stretching step of simultaneously stretching in both the direction and the running direction, wherein the drying step includes a drying unit using a near-infrared radiation heater and a drying unit using heated air. Manufacturing equipment. 6. The method according to claim 5, wherein drying means using a near-infrared radiation heater is provided before the drying means using heated air, and drying by the heater is performed substantially until the film temperature reaches the heated air temperature. An apparatus for producing the stretched film according to the above. 7. A means for drying with heated air blows the heated air into the drying oven as a circulating system to the film, and a part of the circulating air is exhausted out of the oven, and an amount corresponding to the exhausted amount is provided. The apparatus for producing a stretched film according to claim 5 or 6, comprising means for supplying air having a lower humidity than circulating air.