JP5533631B2 - Measuring device for measuring low molecular weight in heating oven and measuring method for measuring low molecular weight - Google Patents

Description

  The present invention relates to a method of continuously measuring a low molecular weight substance as a particle concentration in a heated air flow when an electrically insulating sheet is stretched while being heated.

  Among the electrical insulating sheets, the biaxially stretched polyester film is excellent in heat resistance and productivity, and is widely used in applications such as receiving paper, optical applications, and printer ribbons. In recent years, with the growth of the IT field, optical materials such as antireflection films for displays, diffusion plates for backlights for liquid crystals, base materials for touch panels, and optical papers such as optical displays and liquid crystal phase difference plates are used. Use for film applications is increasing.

  What is required for optical films is high transparency and reduction of foreign matter on the film surface and coating defects compared to other uses. For this reason, it is necessary to greatly reduce foreign matter adhesion defects and repelling defects that occur after the water-based resin or water-dispersed resin coating process.

  In the optical film forming process, the melted polyester resin is extruded into a sheet shape, quenched with a cooling drum, formed into a sheet, and then stretched 3 to 5 times in the film running direction while heating. Subsequently, the film is generally stretched 3 to 5 times in the transverse direction. This transverse stretching process is performed in an oven (or called a tenter or a stenter).

  The oven is a large device, and air heated by heated steam is circulated in the oven. In the oven, a heat exchanger and a circulation fan are arranged to circulate hot air having a constant temperature. In addition, there are an air supply pipe for sending fresh air into the oven and an exhaust pipe for exhausting a part of the air in the oven.

Patent Document 1 discloses using an oven in which the amount of dust is controlled in order to suppress the above-described foreign matter adhesion defect and application repelling defect. In Patent Document 1, the degree of dust in the oven is 5000 particles / ft ³ or less for dust of 0.3 μm or less, more preferably 3000 particles / ft ³ or less for dust of 0.3 μm or less, more preferably 0.3 μm. It is disclosed that the defects are greatly reduced by setting the following dust to 1000 pieces / ft ³ or less. In order to control the amount of dust, it is disclosed that an air supply and exhaust system is provided in each compartment of the oven so that the number of ventilations is increased while fresh air is taken in.

  Patent Document 2 discloses an oven having a dry electrostatic precipitator that collects suspended particles in the oven in order to keep the inside of the oven clean. A schematic diagram is shown in FIG. In the oven 1, the film 2 is gripped by the clip 3 and travels from the front to the back in FIG. 3. The heated air is conveyed to the surface of the film 2 by the air supply means 4 to heat the film 2. Hot air is collected by the circulation path 5, reheated by the heat exchanger 6, and sent again to the air supply means 4 by the fan 7. The dry electrostatic precipitator 8 is installed in the circulation path 5 of the heated air, and a part of the hot air is guided to the dry electrostatic precipitator 8. In the dry electrostatic precipitator 8, the floating particles are charged, and then an external electric field is applied to trap the particles with electrostatic force. The hot air that has passed through the dry electrostatic precipitator 8 is returned to the circulation path 5 by a pump (not shown).

  Patent Document 1 discloses a method using a particle counter as a method for measuring dust in an oven. In Patent Document 2, as a method for measuring the weight of suspended particles, a part of hot air is sucked for 100 minutes, passed through heat-resistant filter paper, and suspended particles having a size of 0.3 μm or more are captured. In summary, a method for measuring weight change is disclosed. In any method, it was necessary to measure dust and particles in the oven by sucking hot air from the oven for a long time.

Patent Document 1 discloses a method for measuring dust and suspended particles separately from oligomer particles. This method uses an oligomer sampling apparatus. An oligomer is a low molecular weight molecule deposited from, for example, a polyester film. Many oligomers have several ester molecules bonded to each other. The oligomer sampling apparatus sucks the air in the oven over 100 to 200 minutes and collects the oligomer in the snake tube. A method is disclosed in which collected oligomer particles are dissolved in methanol, the absorbance of ester groups is measured with an ultraviolet spectrophotometer, and the oligomer concentration (mg / m ³ ) is determined from a calibration curve. This method also requires 100 to 200 minutes for the measurement, and further requires post-treatment such as dissolving the collected oligomer with a solution, and cannot be measured continuously.

  According to the knowledge of the present inventors, the method disclosed in Patent Document 1 and Patent Document 2 that suppresses the concentration of dust and particles in the hot air to a certain level or less in the oven reduces the adhered foreign matter and coating defects on the film surface. Although it was effective, it was not enough. If the dust and particles in the hot air deteriorate in a short time, for example, they are averaged over 120 minutes and cannot be detected. Moreover, even if it was able to be detected, many product defects were generated.

  According to the knowledge of the present inventors, in addition to suspended particles and dust in the hot air, organic compound components such as oligomers and coating materials are vaporized or sublimated in the hot air and contained in a very small amount in the steam in the oven. Is also a drawback. The oligomer or organic compound vapor contained in the hot air exceeds the saturated vapor pressure in the vapor at a place where the temperature in the oven is low, and the vapor changes into liquid or solid particles and precipitates in the oven. It was found that the precipitated oligomer particles adhere to the film and cause foreign matter adhesion and coating defects.

  Here, since the concentration and weight of the oligomer particles precipitated from the vapor to the liquid or solid vary depending on the temperature of the hot air, it is necessary to measure the concentration and weight of the oligomer vapor contained in the hot air. However, there was no method for measuring the amount of oligomer particles from the concentration of oligomer vapor in hot air.

  For the measurement of oligomer vapor, the above-described oligomer sampling device disclosed in Patent Document 1 can be measured by cooling it, but the post-treatment is performed by sucking the air in the oven over several hours. It was necessary to measure, and it was not possible to measure continuously.

  In other words, there is no simple method for continuous measurement of particle concentration with regard to cleanliness in the oven, including oligomer particles generated from the oligomer vapor in the oven. It was not enough.

JP 2009-12242 A JP 2006-212805 A

  The object of the present invention is to solve the above-mentioned problems of the prior art described above, and to provide a method for continuously measuring cleanliness in an oven in a simple manner, including oligomer vapor in the oven.

  Another object of the present invention is to improve the cleanliness in the oven and to reduce the adhered foreign matter and coating defects on the film surface, thereby realizing a high quality film for optical members, for example.

  In order to achieve the above object, according to the present invention, in an oven for heating and stretching a sheet in hot air, a low molecular weight measuring device that continuously measures dust and low molecular weight materials contained in the hot air in a hot air circulation conveyance path. An oven having a detection unit for detecting a charge having a polarity opposite to that of a charged low molecular weight substance by electrostatic induction, and having a cooling means for cooling hot air upstream of the flow channel of the detection unit. Provided is a measuring device for measuring low molecular weight substances. Further, the detection unit provides a measuring device installed in an exhaust pipe for exhausting heated air from the oven to the outside of the system. Further, the present invention provides a measuring apparatus for measuring a low molecular weight substance in an oven, wherein the cooling means is a means for spraying cooling fins or water-based droplets.

  Furthermore, in an oven for heating and stretching the sheet in hot air, a method for measuring dust contained in the hot air and low molecular weight substances deposited from the sheet, a) a temperature that is 20 ° C. or more lower than the hot air temperature for heating the sheet A frictional charge amount of dust and a low molecular weight substance is detected in the hot air circulation and conveyance path of b), and b) an electric signal based on the frictional charge amount and a unit of a low molecular weight substance deposited from the dust and the sheet which has been calibrated A measurement method for measuring dust and low molecular weight materials in an oven characterized by measuring the concentration per unit volume of dust and low molecular weight materials contained in the hot air in the oven using a relational expression with concentration per volume I will provide a.

Further, the sheet is biaxially oriented polyester film, provides a method for measuring low molecular weight substance to be measured to measure dust and low molecular weight of the oven is a oligomer having a terephthalic data Le acid structure.

  In the present invention, “charging of a low molecular weight substance” is as follows. A low molecular weight substance is a low molecular weight compound such as an oligomer deposited from a film that is heated and stretched in an oven or a coating component on the film surface. “Charging” refers to a state in which an electrostatic charge is applied. The triboelectric charge generated when a low molecular weight material collides with the inner wall of an oven or the wall of an air supply / exhaust pipe, and the charge generated by an electrostatic charge generated by a temperature change. State.

  In the present invention, the “low molecular weight product” is a compound having a molecular weight lower than that of a polymer. For example, it is a linear oligomer and a cyclic oligomer that are likely to precipitate in the case of a polyester film. Examples of the linear oligomer include terephthalic acid monohydroxyethyl terephthalate and bis-β-hydroxyethyl terephthalate. Cyclic oligomers include cyclic trimers and cyclic dimers. Further, it is a polyester or acrylic compound contained in the coating liquid.

  In the present invention, “electrostatic induction” is a charge induction phenomenon of a conductor that occurs when charged particles collide with a detection unit or pass through a very close vicinity. An inductive charge having a polarity opposite to that of the charged particles is generated in a conductor that is not grounded.

  According to the present invention, as will be apparent from the examples described later, it is possible to continuously measure the dust and particle concentration in the oven including particles generated from the oligomer vapor in the oven by a simple method.

  By this measurement, it is possible to further suppress the coating defect of the film as compared with the case where only the dust amount is controlled. For this reason, since a film can be manufactured while controlling the cleanliness of hot air in the oven, a high-quality film can be obtained stably.

It is a schematic explanatory drawing which shows the measuring method of particle | grains and vapor | steam in the oven of this invention. It is an enlarged view of the measuring method of particle | grains and vapor | steam in the oven of this invention shown in FIG. It is a schematic explanatory drawing which shows collection of the floating particle | grains in oven by the prior art.

Hereinafter, an example of the best embodiment of the present invention will be described with reference to the drawings, taking as an example a case where a plastic film (hereinafter simply referred to as a film) is used as an electrically insulating sheet. The present invention is not limited to these examples.
Examples of the film to which the present invention is applied include polyethylene terephthalate film, polyethylene naphthalate film, polypropylene film, polystyrene film, polycarbonate film, polyimide film, polyphenylene sulfide film, nylon film, aramid film, and polyethylene film.

  In particular, specific examples of polyesters that can be suitably used include polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate and poly-1,4-cyclohexanedimethylene terephthalate. In particular, polyethylene terephthalate and polyethylene-2,6-naphthalate are particularly preferably used because they are excellent in physical properties such as mechanical strength and dimensional stability and also in productivity. In addition, the polyesters used in the present invention may be one kind of those listed above, a copolymer of two or more polyesters, a mixture of two or more polyesters, or the like. Various additives can be added to these polyesters depending on the purpose. For example, inert particles such as colloidal silica, alumina, calcium carbonate, organic silicone, and polydivinylbenzenesulfonic acid can be added to impart easy slipping. Further, an antistatic agent or an antioxidant may be added.

  Next, a film forming method will be briefly described.

  For the film, sufficiently dried resin pellets are supplied to an extruder, the pellets melted from a die having a slit-like discharge port are extruded into a sheet shape, and cooled on a cooling roll to obtain an unstretched film. Next, a method for biaxially stretching an unstretched film will be described. As a biaxial stretching method, unstretched polyester is stretched in the longitudinal direction or the width direction, followed by sequential biaxial stretching in which stretching is performed in a direction perpendicular to the previous stretching direction, or in the longitudinal direction and the width direction at once. A method such as simultaneous biaxial stretching for stretching may also be used. Stretching may be performed in one step or stepwise in two or more steps, but it is difficult to cause defects such as scratches on the surface of the film and adhesive marks on the roll, and the stretching required for optical use is obtained. The method is preferred.

  Here, the method will be described in which a uniaxially stretched polyester film stretched in the longitudinal direction is subsequently placed in an oven and stretched in the width direction.

  FIG. 1 is a schematic view of an oven 1 for heating and stretching the film 2 in the width direction.

  The film 2 is heated in the oven 1 while being gripped by the clip 3 running on the rail in the oven 1, and the film 2 is stretched in the width direction as the rail on which the clip 3 runs is expanded. The The stretching ratio in the width direction of the film 2 is about 2 to 5 times.

  In FIG. 1, one chamber of the oven 1 is shown. The oven 1 is composed of partitioned chambers for performing predetermined processing. Usually, it is composed of a heating chamber, a stretching chamber, a heat fixing chamber, a cooling chamber and the like from the upstream in the running direction of the film. A large amount of hot air heated by heating steam is circulated in the oven 1. In the oven 1, a heat exchanger 6 for maintaining a constant temperature and a circulation fan 7 for circulating warmed hot air are installed. Hot air is sent from the piping 4 of the air supply device and is ejected from the nozzle 10 near the traveling film 2. The jetted hot air heats the film 2 and the temperature of the film rises.

  The nozzle 10 may be slit-shaped or hole-shaped, and is devised and ejected so as not to cause temperature unevenness in the film 2.

  The hot air that has heated the film is returned to the heat exchanger 6 by the circulation device 5 and further circulated through the oven again by the circulation fan 7. Dust is removed by a filter or the like near the outlet of the heat exchanger 6, but if hot air in the oven is circulated as it is, dust and particles that could not be removed by the filter gradually increase. In the filter, since the low molecular weight vapor such as the oligomer and the coating solution dissolved in the hot air cannot be removed, the amount of the oligomer vapor increases.

  Therefore, in order to maintain the cleanliness of the hot air in the oven 1, fresh air is introduced into the oven 1 and part of the hot air is discharged out of the oven 1 system. In FIG. 1, a fresh air supply pipe 11 is piped before the heat exchanger 6 in order to introduce fresh air. The air from the fillet air supply pipe 11 is led to the heat exchanger 6 together with the circulating hot air, heated to a predetermined temperature, and circulated in the oven 1. On the other hand, a part of the hot air is exhausted out of the system from the exhaust pipe 12 (not shown) connected to a pump (exhaust pipe 12) for exhausting a part of the hot air on the wall or ceiling in the oven. The exhausted hot air is often released to the atmosphere.

  FIG. 2 is an enlarged view of the exhaust pipe 12 of FIG. As shown in FIG. 2, a cooling device 30 and a detector 20 are arranged in the exhaust pipe 12. There are one or more exhaust pipes 12 for each room, and several exhaust pipes 12 are finally gathered so that the exhaust in each room is collected. Each chamber is a heating chamber, a stretching chamber, a heat fixing chamber, or a cooling chamber, and each chamber is composed of a plurality of chambers (for example, one heat fixing chamber, two heat fixing chambers, three heat fixing chambers, etc.).

  1 and 2 show an exhaust pipe 12 installed on the ceiling of the oven 1. FIG. 2 shows a state in which sensors are installed in the three heat fixing chambers. The lower side of FIG. 2 is connected to three heat fixing chambers of the oven 1 in which the film 2 is stretched in the width direction. In FIG. 2, the exhaust pipe 12 is shown as exhausting from the top of the oven 1, but the exhaust pipe 12 may be connected from the side or the bottom of the oven 1. The exhaust pipe 12 sucks hot air in the oven 1 by a blower (not shown). The flow in the exhaust pipe is in the direction of arrow Y.

  The detector 20 is installed upstream of the exhaust pipe 12 in the order of the cooling means 30 and the detector 20.

  The detector 20 includes a probe 21, an insulation holder 25, a ground terminal 26, a processing circuit 22, and a detector main body 23. The detector body 23 is connected to the processing circuit 22 by a cable. The length of the cable is 10 to 20 m, and the detection level can be confirmed at a place away from the oven.

  The detector 20 is inserted almost vertically into the exhaust pipe 12 and is inserted into the flow of hot air in the exhaust pipe 12. The probe 21 is electrically insulated from the exhaust pipe 12 by an insulating holder 25. The exhaust pipe 12 and the ground terminal 26 are electrically grounded to 0V. Data detected by the probe 21 is sent to the detector main body 23 via the processing circuit 22.

  In the present invention, in order to measure the oligomer concentration in the hot air, it is important to lower the temperature of the hot air by cooling and precipitate the oligomer vapor as droplet particles. Therefore, a cooling device 30 is installed in front of the detector 20. The cooling device 30 is disposed so as to cool the hot air in the exhaust pipe 12. The distance between the detector 20 and the cooling device 30 is approximately 1 to 2 m. However, the distance from the detector 20 is not limited as long as the hot air can be cooled to a predetermined temperature.

  The cooling device 30 may be provided with a cooling member (for example, cooling fins) in which cooling water is flowed, or may be cooled around the tube wall. In order to efficiently deposit the oligomer vapor in the hot air as droplet particles, a method of discharging the minute mist together with the cooling air from the tip of the cooling device 30 to cool the hot air is also preferable. In this case, the liquid for forming the mist is preferably distilled water at room temperature. The minute mist has a large surface area and a high effect of cooling the hot air, and can also become a nucleus when the oligomer vapor dissolved in the hot air is precipitated, and has an effect of facilitating the precipitation of particles. At the same time, the cooling effect is enhanced by introducing cooled air.

  In FIG. 2, the cooling means 30 is installed. However, if the temperature of the hot air in the exhaust pipe is 20 ° C. or more lower than the control temperature of the hot air circulating in the oven 1, the cooling means 30 is not necessary. good. This is because the temperature of the hot air in the oven is naturally cooled before reaching the detection unit 20 of the exhaust pipe 12. If the detection part 20 is a place 20 degreeC or more lower than the control temperature of the circulating hot air, an attachment place will not be chosen. The case where the temperature is lower by 20 ° C. or more than the control temperature of the hot air circulating in the oven 1 originates from the fact that the temperature difference between the hottest heat fixing chamber and the cooling chamber entrance in the oven 1 is approximately 20 ° C.

  The present inventors have found that the upper part of the exhaust pipe 12 is 30 ° C. lower than the control temperature of the circulating hot air, and that the measurement at the upper part of the exhaust pipe 12 is preferable. Further, it is preferable to advance cooling because low molecular weight substances such as oligomers are likely to be precipitated, and the detection sensitivity is increased. If the hot air is exhausted out of the system of the exhaust pipe 12, there is an advantage that, even if the hot air is further cooled, it is not necessary to be reheated in order to monitor the concentration of the oligomer vapor, and no reheating energy is applied. The amount of oligomer in the exhaust pipe 12 is substantially the same as the amount of oligomer contained in the heated air in the circulation device 5. This is because the entire oven spreads between the film 2 and the air supply nozzle 10.

  On the other hand, the temperature of the heated air in the circulation device 5 is not lower than that in the oven, and the oligomer is difficult to precipitate and the sensitivity is low. Therefore, a part of the hot air circulating in the oven 1 may be branched from the circulation device 5 to be branched hot air and measured through the cooling device.

  Next, the operation of the detector 20 will be described.

  The detector 20 detects a minute charge of a droplet or particle and generates an electrical signal corresponding to the charge amount of all particles including hot air. That is, an electrical signal proportional to the particle concentration is generated. According to the knowledge of the present inventors, the particles in the hot air are in an electrostatically charged state in the following two processes. One is contact charging by collision with a wall surface, a film, or a piping structure. The other is a phenomenon in which particles are charged by temperature change. In particular, when particles are deposited from the oligomer vapor and cooled, the generated particles are easily charged. In either case, the particles contained in the hot air in the oven 1 are easily charged, and it has been found that this charge can be used to detect with high sensitivity.

  It is a probe 21 made of an ungrounded conductor arranged at the tip of the detector 20 that detects minute charging of particles in the hot air. The probe 21 has a rod-like shape, preferably has a diameter of 15 to 30 mmφ, a length of 100 to 200 mm, and a material having heat resistance, such as SUS. The probe 21 is set to be at least larger than the radius of the exhaust pipe 12 and about 0.9 times the diameter so that the charged particles passing through the pipe are easily detected when inserted into the exhaust pipe 12. .

  When the charged minute particles approach the vicinity of the probe 21, a charge having a polarity opposite to the charged polarity of the particles is induced at the tip of the probe 21 by electrostatic induction. Therefore, a current flows through the probe 21 and the particle concentration is measured by detecting this minute current. At this time, it is preferable that an alternating change in which charged particles approach or move away from the probe 21 is detected as a signal. This is because, when a low molecular weight substance such as an oligomer or a droplet is deposited on the probe 21, it is offset to the signal, but the influence on the detection level can be reduced by using only the AC signal.

For the conversion to the particle concentration, a method of obtaining a calibration curve obtained in advance from the intensity of the signal from the detector 20 is used. In the calibration curve, a predetermined amount of particles is flowed into the hot air in advance, and the correlation with the signal intensity is taken. The weight per unit time and unit flow rate can be calculated from the flow velocity of the exhaust pipe 12. As another method, the charge amount of the oligomer in the hot air may be obtained by the blow-off method, converted from the amount of current flowing per second, and the weight may be obtained. According to the knowledge of the present inventors, the charge amount of the oligomer of the polyester film is approximately 1 × 10 ⁻¹⁶ [C] when the particle size is 1 μmφ. .

When a calibration curve is obtained by flowing a known oligomer weight in hot air, it is preferable to create a calibration curve by creating three points of signal intensity and the weight [g] of particles ejected per unit flow rate [m ³ ]. In this case, the signal intensity is proportional to the particle weight per unit volume.

  It is also important to know the tendency of whether the cleanliness in the oven 1 is improved or worsened without calibrating the accurate value as described above. In this case, it is only necessary to monitor the rate of change of the obtained signal. In this case, the change in the signal depends on the flow rate and the charge amount of the particles, but generally increases in proportion to the flow rate, so it is preferable to convert the flow rate.

  Details of organic low molecular weight substances and oligomers dissolved as steam in the hot air in the oven 1 will be described below.

  Organic low molecular weight materials are primarily components of in-line coats that are dried in an oven. The polyester film may be stretched only in the longitudinal direction and then coated with various water-based resins or water-dispersed resins on one side or both sides for the purpose of imparting adhesiveness. Although it does not specifically limit as resin apply | coated to the surface of a polyester film, Aqueous solution or aqueous dispersions, such as polyester, an acrylic polymer, polyamide, and a polyurethane, are used suitably. After the coating liquid is applied thinly, it is stretched in the width direction to form a biaxially stretched film, but the oven may be used as a drying step for the water-based coating material. Therefore, the coating material component may melt out as steam in the hot air. The oligomer sublimates and dissolves in hot air when the polyester film is treated at a high temperature. It was found that when the vaporized low molecular weight substances, additives, and oligomers come into contact with the low temperature part of the oven 1, they become droplets or solids, and when these foreign substances adhere to the film, they become film defects.

  Originally, it is necessary to measure the amount of steam in hot air, but it is difficult to continuously measure the concentration of steam. Therefore, the present inventors have found that when oligomer vapor is present, oligomer particles (solid) always exist, and the concentration of the fine oligomer particles is correlated with the vapor amount. Further, it has been found that the steam can be measured by forming droplet particles by efficiently lowering the temperature of the hot air in the oven 1. The means for efficiently reducing the temperature is, for example, cooling the temperature of the hot air circulating in the oven by spraying mist.

  And the minute charge which the above-mentioned droplet particle has is detected continuously using electrostatic induction, and is measured on-line. According to this method, it is possible to continuously measure low molecular weight substances contained in the hot air in the oven 1 that is in operation. At the same time, the amount of dust can be continuously measured.

  In general, the oven 1 is divided into a plurality of types including preheating, stretching, heat setting, and cooling, and reaches a maximum temperature in the heat setting zone. A contained component becomes easy to sublime, and it becomes a problem that a sublimation component precipitates and solidifies in the low-temperature part of a downstream, and adheres to the film 2 surface. Therefore, it is preferable to install at a downstream position following the maximum temperature portion of the heat setting zone.

  Here, the temperature of each adjacent chamber is often kept within a range of approximately 20 ° C. When the temperature is higher than 20 ° C., for example, an intermediate chamber may be provided between the heat fixing chamber and the cooling chamber to prevent movement of heat between the chambers and to enhance exhaust of the intermediate chamber. Therefore, it is also preferable to attach the detector 20 to the exhaust pipe 12 in the intermediate chamber and detect the amount of steam in the oven 1.

  Although the thickness of the film of this invention is not specifically limited, It is preferable that it is 30 micrometers or more and 360 micrometers or less suitably used for an optical use. When the thickness of the film is less than 30 μm or thicker than 360 μm, the productivity as a film may be unfavorable.

Polyethylene terephthalate having an intrinsic viscosity of 0.65 was dried under reduced pressure at a temperature of 180 ° C. for 5 hours, put into an extruder, melted at a temperature of 280 ° C., filtered through a filter, and then extruded into a sheet form from a die. .
The extruded sheet was brought into close contact with a cooling roll by an electrostatic application casting method and solidified by cooling to obtain an unstretched polyethylene terephthalate film. The unstretched polyethylene terephthalate film was stretched 2.5 times at a temperature of 90 ° C. with a longitudinal stretching machine composed of a roll group, and cooled to obtain a uniaxially stretched polyethylene terephthalate film.

  After applying a coating solution having the following composition on both sides of this uniaxially stretched polyethylene terephthalate film using a bar coater, the coating solution is stretched 3 times by an oven 1 and heat-set to perform biaxial stretching with a thickness of 100 μm. A polyethylene terephthalate film was obtained. The product number was 100U48.

  The coating liquid was prepared by adding 94 parts by weight of distilled water, 5 parts by weight of a polyester-based easy-adhesive material, and 1 part by weight of colloidal silica particles having an average particle size of 0.1 μm.

The detector 1 was installed in the exhaust pipe 12 of the third chamber from the upstream of the heat fixing chamber. The hot air temperature in the heat fixing three chambers was 220 ° C. The displacement of the three heat-fixed chambers was 30 m ³ / min. The size of the exhaust pipe 12 was 350 mm square in cross section. The detector 1 is installed in a straight pipe portion where the pipe rises to the ceiling in the ceiling portion of the oven 1. The distance from the oven 1 was about 3 m. A hole of 20 mmφ was made in the exhaust pipe 12 and the detector 1 was inserted vertically.

The temperature of the hot air in the detection part 1 was 175 degreeC. The cooling device 30 was installed 1.5 m away from the detection unit 1. The cooling device made cooling water flow from the wall surface of the exhaust pipe 12 together with air in a mist size of 10 to 20 μm. The flow rate was 0.2 × 10 ⁻³ m ³ per hour.

  As the detector 1, DT370 (manufactured by Kansai Automation Co., Ltd.) was used. The probe shape for taking a small amount of signal was set such that the length of the probe 21 was 150 mm, the diameter of the probe was 18 mmφ, the length of the insulating holder 25 was 50 mm, and the length of the installation terminal 26 was 50 mm (250 mm in total). More than the diameter of the exhaust pipe 12 can be covered.

  A signal generated by electrostatic induction was extracted from the measuring machine and amplified when the charged particles passed through the detector. Usually, the signal polarity is inverted when the particle approaches the detector and when the particle moves away from the detector. Therefore, a signal inversion circuit is attached. The measurement time was set to 1 second, and the average output value of charged particles for 10 seconds was continuously output to the recorder.

  As a result, when there was no film and the output when hot air was circulated (blank) was 1, an output value of 2.25 times was obtained during film formation. Moreover, in the polyethylene terephthalate raw material film formation which suppressed the oligomer, the output was small and was 1.8 times.

  Further, when the cooling device was operated and the hot air temperature was lowered to 120 ° C., an output value of 4.2 times was obtained. The film was formed by increasing the fan speed and the fresh air supply amount so as to maintain the output value of 4.2 times. Since the film can be produced while controlling the cleanliness of the hot air in the oven, a high-quality film could be obtained stably.

  When the fan rotation speed of the oven was decreased and the supply / exhaust amount was reduced by 20%, the output value started to increase, and after 5 minutes, the output value increased 5 times and could be detected. From the above, since the change in the supply / exhaust amount and the difference in film raw material can be read from the output value in a short time, the oligomer weight contained in the heated air in the oven could be continuously measured.

  In the present invention, the biaxially stretched thermoplastic resin polyester film of the present invention is not particularly limited, but is used for various applications such as films for optical applications such as plasma display and liquid crystal display members, surface protective materials, electrical insulating materials and mold release, In particular, it can be used effectively in applications that are severe in terms of defects such as optical applications and surface protective materials.

1: Oven 2: Film 3: Clip 4: Air supply pipe 5: Circulation pipe 6: Heat exchanger 7: Circulation fan 8: Electric dust collector 10: Air supply nozzle 11: Fresh air supply pipe 12: Exhaust pipe 20: Detector 21 : Probe 22: Processing circuit 23: Detector body 25: Insulating holder 26: Grounding terminal 27: Charged particles 30: Cooling device

Claims (5)

In an oven that heats and stretches a sheet in hot air, a low molecular weight measuring device that continuously measures dust and low molecular weight materials contained in the hot air in a hot air circulation conveyance path,
An oven having a detection unit for detecting a charge having a polarity opposite to that of a charged low molecular weight substance by electrostatic induction, and a cooling means for cooling hot air on the upstream side of the flow path of the detection unit. Measuring device for measuring low molecular weight substances inside. 2. The measuring apparatus for measuring low molecular weight materials in an oven according to claim 1, wherein the detection unit is installed in an exhaust pipe for exhausting heated air from the oven to the outside of the system. 3. The measuring apparatus for measuring low molecular weight substances in an oven according to claim 1, wherein the cooling means is a cooling fin or means for spraying water-based droplets. A method for measuring dust contained in hot air and low molecular weight substances deposited from the sheet in an oven that heats and stretches the sheet in hot air,
a) Detecting the triboelectric charge amount of dust and low molecular weight substances in the hot air circulation conveyance path at a temperature 20 ° C. or more lower than the hot air temperature for heating the sheet,
b) Using a relational expression between the electric signal based on the triboelectric charge amount and the concentration per unit volume of the low molecular weight substance deposited from the dust and the sheet, which is calibrated in advance,
A measuring method for measuring dust and a low molecular weight substance in an oven, wherein the concentration per unit volume of the dust and the low molecular weight substance contained in hot air in the oven is measured. Sheet is biaxially oriented polyester film, measuring the low molecular weight substance to be measured to measure dust and low molecular weight of the oven according to claim 4, characterized in that the oligomer having a terephthalic data Le acid structure Method.

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