JPS6097829A - Drawing method of plastic film - Google Patents

Abstract

PURPOSE:To prevent a drawing film to be contaminated by monomar or oil mist by a method wherein heated air in a drawing device or circulating ducts is contacted to an absorbing device and monomer or oil mist is absorbed. CONSTITUTION:In the biaxial drawing device which uses heated air as heating source, heated air is contacted with absorb agent and monomar, oligomer, and oil mist etc. in the heated air are absorbed and removed by the method heated air is flown in the circurating duct therein an absorb agent layer is arranged or absorb agent is placed at the part of a biaxial drawing device, for instance, on the floor surface, or on the surface of a tenter clip running cover. Because biaxially oriented film without contamination can be got through this method, the said film is useful for a food package material without printing defects or condenser material without defecting electric insulation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a stretched plastic film, and more particularly to a method for producing a stretched film whose surface is not contaminated with monomers, oligomers, oil mist, etc.

Biaxially stretched films such as polyamide and polyester have excellent strength, heat resistance, transparency, processability, etc., and are widely used for food packaging, gold and silver thread, condensers, magnetic tape, and other industrial applications.

After melt-forming, these films are generally biaxially stretched using a simultaneous biaxial stretching machine or a two-stage biaxial stretching machine that combines a roll-type longitudinal stretching machine and a tenter-equipped horizontal stretching machine. Furthermore, the most widely used simultaneous biaxial stretching machine or transverse stretching machine is a method in which hot air is used as a heating source to heat the film to a temperature for stretching and crystallizing the film. In this case, low-molecular-weight substances such as polymers and oligomers contained in the film sublimate from the film and float in the hot air, condensing and adhering in the low-temperature parts of the aircraft, or accompanying the traveling film and leaving the aircraft. Condensation and deposition on the cooled film often occurs. Furthermore, the lubricating oil supplied to the tenter clip traveling device of the stretching machine becomes oil mist that floats in the hot air, which may contaminate the film. Films coated with monomers, oligomers or oil mist cause various problems during use. In the case of food packaging films, there are problems with poor appearance such as printing defects, and when used in capacitors, it causes electrical insulation defects. Japanese Patent Publication No. 57-36851 proposes a method for preventing oligomers from adhering to a film by suctioning and discharging heated air flowing from the crystallization zone to the cooling zone or intermediate zone through an exhaust duct. . However, in order to obtain a substantial effect with this method, it is necessary to increase the displacement, and there is a problem of energy loss due to the exhaust of high-temperature air.Also, even in the high-temperature setting zone inside the stenter, there are local low-temperature parts such as the tenter clip running cover. When the oligomer condenses and adheres to the film and the hot air flow conditions change due to stretching and cutting, etc., the accumulated oligomer mass peels off and adheres to the film, leaving a problem. JP-A-58-65731 proposes a method in which hot air is passed through an oxidation catalyst layer to burn and remove oligomers. However, the oxidation catalyst is expensive and deteriorates due to the catalyst poison contained in the oil mist, so it has a short lifespan and is not a very economical method. This method is effective for polyester films, but when applied to resins 1, such as nylon 6, which have a lower melting point than polyester, nylon 6
The catalytic ability is small at the hot air temperature suitable for stretching and heat fixing. Therefore, when applying to resins with low melting points such as nylon 6, part of the circulating hot air is drawn out of the machine and heated to a temperature that increases the catalytic function. After that, it must be passed through an oxidation catalyst layer, cooled again, and then returned to the inside of the aircraft.

The inventors of the present invention have conducted intensive research on methods for removing foreign substances such as monomers, oligomers, and oil mist from circulating hot air, and have found that these foreign substances can be easily adsorbed and removed using inexpensive adsorbents such as activated carbon, alumina, and white clay. They discovered that there are few restrictions on hot air temperature and that regeneration is easy, and arrived at the present invention.

As the adsorption device used in the present invention, it is also possible to install a general adsorption device such as a two-rotation fluidized bed type or a moving bed type outside the machine and treat the hot air inside the machine with this device. Usually, a simple method is effective, such as providing an adsorbent layer in the circulation duct and blowing hot air through it, or spreading an adsorbent on a part of the interior of the machine, such as the floor or tenter clip travel cover.

In this case, the most suitable adsorbent is an activated carbon pellet formed as strongly as possible. When an adsorbent layer is provided in the hot air circulation duct, for example, the cross-sectional area of the duct in this part is expanded, and the wind speed is preferably 1 m/sec or less, more preferably in order to reduce pressure loss and to prevent the fine powder remaining in the adsorbent pellet from being blown away. An effective method is to provide an activated carbon layer with an appropriate thickness sandwiched with gold and copper at a speed of 0.5 m/sec or less. It is also possible to adopt a method in which one circulation duct is provided with two sets of adsorbent-filled ducts whose flow paths can be selected by a switching damper, and continuous operation is performed while regenerating alternately. The lower the temperature, the stronger the effect of the adsorbent on separating low-molecular weight substances, but if it is used below the temperature at which monomers, oligomers, etc. sublimated from the film condense, the effect will be reduced due to the accumulation of coagulates on the surface of the adsorbent layer. There may be a sudden drop, and in order to prevent this, various measures may be required for the adsorption device. For nylon film, preheat stretching and heat treatment temperature.

In other words, it is effective over a wide range of about 150 to 200°C.

In the case of polyester film, the effect 5- is obtained at any temperature within the temperature range of the heat setting zone, that is, from 150 to 230'C. Activated carbon that has adsorbed nitrates, oligomers, oil mist, etc. may ignite if the ignition temperature decreases, and especially when the air flow is stopped, a localized high temperature area is generated in the activated carbon layer due to the heat of adsorption.

Therefore, it is desirable to provide the activated carbon layer with a water sprinkler device or a nitrogen purge device in case of an abnormality. Regeneration of the adsorbent can be carried out by desorption with hot steam, nitrogen or desorption under vacuum.

It is particularly important to remove m powder in the adsorbent pellet during regeneration and filling.

The plastic film to which the method of the present invention is applied is any film that can be stretched and oriented, but especially polyester films represented by polyethylene terephthalate and polyamide films represented by nylon 6 and nylon 66 produce monomers and oligomers in large quantities. Moreover, these stretched films are often used in applications where foreign matter adhering to the film is extremely disliked, so the method of the present invention is highly effective.

The method of the present invention will be specifically explained below using comparative examples and examples.

6- Comparative Example Simultaneous biaxial stretching machine during production of nylon 6 biaxially stretched film, catalyst layer coated with platinum catalyst on honeycomb-shaped ceramic upper material in hot air circulation duct of heat fixing zone (temperature 200°C) Set up.

An attempt was made to remove low molecular weight substances sublimated from the nylon 6 film and oil mist floating inside the machine by oxidative decomposition. Insert sampling pipes on both sides of the catalyst layer,
A small fan sucks out equal amounts of hot air before and after oxidation treatment in the catalyst layer.

The amount of low-molecular M substance and oil mist contained in two types of hot air was investigated by introducing it into a condenser. There was a clear difference between the white powder (low molecular weight substance) adhering to the capacitor before and after the treatment on the 10th test after the start of the test, but on the 20th test, the difference decreased to less than 1/2, and on the 33rd day it was completely different. The difference is gone. After quantifying the amount of oil mist that condenses in the condenser, iM has the following results. (Unit: g/day)
Therefore, when using an oxidation catalyst layer to remove low molecular weight substances and oil mist floating in hot air when producing nylon 6 film using a biaxial stretching machine in the first set of tenters, the effective period of the catalyst is too short to be practical. It has been found.

Example 1 The same device as in the comparative example was used, except that an activated carbon layer was used instead of the catalyst layer. The cross-sectional area of the hot air circulation duct in the heat fixation zone (temperature 200°C) was partially expanded to increase the superficial flow velocity of hot air to 0.5 m/sec.
Activated carbon pellets (manufactured by Narita Pharmaceutical Industries (tI)) sandwiched between stainless steel and gold steel.

Granular Shirasagi GX, size 6φ x 6-1 off) Ft was provided.

When a nylon film was manufactured under the same conditions as in the comparative example and the effect of the adsorption layer was investigated using the same method, it was found that the adsorption separation effect was good and continued for about one month.

Example 2 A polyethylene terephthalate biaxially stretched film was produced using the same equipment as in Example 1. In this case, we set the temperature of the heat fixation zone to 230°C and investigated the effect of the adsorption layer, and found that the adsorption separation effect was sufficiently strong even for oligomers that sublimed from the polyethylene terephthalate film.
It has been in effect for over a month.

Patent applicant: Unitika Co., Ltd. 9-

Claims (1)

[Claims] 1. When stretching a plastic film using a Tenku complete stretching device that uses hot air as a heating source, the hot air in the stretching device or circulation duct is brought into contact with an adsorption device to remove low molecular weight substances and oil in the hot air. Adsorbs mist. U3- A method for stretching a plastic film, characterized by i4I.