KR0181095B1 - Method for manufacturing thermoplastic resin - Google Patents

Abstract

The present invention relates to a method for producing a biaxially oriented film by longitudinally stretching, transversely stretching and heat-treating a sheet made of a thermoplastic resin, wherein the transverse stretching apparatus gives 3 to 5% of lateral relaxation to the film during the preheating process, A process characterized in that at least 55% of the stretching is performed in the first half of the transverse stretching process, wherein the thermoplastic resin film obtained above is caused by the transverse stretching and heat setting process in the transverse stretching apparatus (tenter). The bowing phenomenon of the film is suppressed to have uniform physical properties in the transverse direction.

Description

Manufacturing method of thermoplastic resin film

FIG. 1 shows the bowing phenomenon that occurs during the transverse stretching and heat treatment process of the film.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic resin film having uniform physical properties in the transverse direction. In particular, the bowing of the film caused in the process of transverse stretching and heat setting in the transverse stretching apparatus (tenter) is avoided. It relates to a method for producing a thermoplastic resin film that is suppressed to have uniform physical, chemical or physicochemical properties in the transverse direction.

Thermoplastic films, especially homopolyesters, copolyesters or mixed polyesters, polyethylene terephthalates, polyethylene-2,6-2 naphthalates, polytetramethylene terephthalates, polytetramethylene-2,6-naphthalenecarboxylates, liquid crystals Polyester films such as polyester and other films such as polypropylene, polyvinyl chloride, nylon, polyamide, polycarbonate, polystyrene and polyphenylene sulfite are widely used for packaging, recording media, industrial, and other uses. If the physical properties of these films, i.e., heat shrinkage, mechanical strength, density, etc. are non-uniform in the transverse direction, it may cause deterioration during post-processing such as coating, vapor deposition, cutting, printing, etc., and the quality of the product is likely to be degraded. Therefore, there is an urgent need for a film having uniform physical properties in the transverse direction.

However, in the conventional manufacturing method, it is extremely difficult to equalize the lateral physical properties of the film. This is because both ends of the film are fixed by clips in the tenter (lateral stretching device), so that both ends of the film are deformed against the longitudinal stretching stress caused by the longitudinal stretching and transverse stretching processes and the shrinkage stress caused by the heat setting. While this is constrained, the central portion of the film is less influenced by the clip and thus the weaker the force for deformation. Due to the difference in the binding force between both ends and the center part in the transverse stretching device, the center part is pushed in the opposite direction of the film traveling direction, which causes bowing of the film, which is accompanied by biaxial stretching and heat setting process. It is a fundamental problem in the film forming process of a film, and causes a nonuniformity of the lateral physical property of a film.

Various methods have been tried to prevent this problem. For example, Japanese Unexamined Patent Publication No. 39-29214 discloses a heat treatment method using a heating roll, but this method has a disadvantage of causing width shrinkage because both ends are heat treated without being constrained by the heating roll. In addition, heat treatment methods such as a method of giving a temperature gradient in the transverse direction of the film (JP-A 42-9173) or a change in flow rate (or flow rate) and a forced heating method at both ends of the film (JP-A-62-183327 and 183328) However, these have disadvantages such as lowering the effective operation rate due to the complexity of the facility and the prolongation of the condition adjustment time. Moreover, the method of heat-processing the film after the end of transverse stretching by the nip roll provided between the transverse stretching process and the heat processing process in a transverse stretching apparatus (Japanese Unexamined-Japanese-Patent No. 50-73978), and forcibly advancing the center part of a film by a nip roll In the method (JP-A 63-24459), damage to the film due to contact with a roll at a high temperature is fatal. On the other hand, the heat treatment method (Japanese Patent Laid-Open Publication No. 3-130126, 130127, Japanese Patent Laid-Open Publication No. 4-142916, 142917) undergoes a cooling process after the transverse stretching process reduces the bowing of the film even though the cooling treatment is performed in a section longer than the full width. Not only has little effect, but also has the disadvantage of low productivity, such as increased equipment and waste of energy. In addition, the heat treatment method (Japanese Patent Laid-Open No. 61-8324, Japanese Patent Application Laid-Open No. 1-204723) that gives a temperature increase rate to the film width after the transverse stretching step in the transverse stretching apparatus is uniformly heat treated with respect to the full width of the film. There is a problem that can not be reduced.

The present invention utilizes a conventional heat treatment method in the transverse stretching apparatus in order to solve the above problems, while providing the relaxation of the transverse direction in the preheating process and the majority of the total transverse stretching occurs in the first half of the transverse stretching film It was possible to minimize the bowing of to make the lateral physical properties uniform.

That is, an object of the present invention is to provide a method for producing a thermoplastic resin film having uniform physical properties in the transverse direction.

In order to achieve the above object, the present invention provides a method for producing a biaxially oriented film by longitudinally stretching, transversely stretching and heat-treating a sheet made of a thermoplastic resin, wherein in the transverse stretching apparatus, 3 to 5% of lateral relaxation is applied to the film during the preheating process. It provides a method characterized in that at least 55% of the total transverse stretching is performed in the first half when one lateral stretching process is divided into two parts at equal intervals in the film advancing direction.

The production of the thermoplastic resin film is usually performed by subjecting the chips produced by the polymerization reaction to a drying process and then melt extruding to form a sheet, followed by biaxial stretching in the longitudinal and transverse directions, and heat treatment.

In the production of the film as described above, bowing usually occurs in the transverse stretching and heat treatment processes. The bowing phenomenon occurring during the transverse stretching and heat treatment processes in the transverse stretching apparatus is illustrated in FIG. 1. In FIG. 1, A is a straight line marked at the tenter inlet, A 'is a bowing line in the tenter, and A ″ is a bowing line exiting the tenter outlet. Here, in the initial stage of lateral stretching, reverse bowing occurs before the center of both ends of the film due to the longitudinal shrinkage stress caused by the lateral stretching, and bowing occurs only at the later stage of lateral stretching. At this time, the bowing of a film becomes small, so that the reverse bowing of a lateral stretch initial stage is large.

According to the present invention, in manufacturing the thermoplastic resin film, during the pre-heating step in the transverse stretching device, by providing 3 to 5% of relaxation in the transverse direction, the transverse longitudinal direction of the film is imparted to the initial transverse stretching, and one transverse stretching process. By dividing the into two equally spaced sections in the film's advancing direction, 55% or more of the transverse stretching is performed in the first half, which promotes reverse bowing at the beginning of the transverse stretching process and reduces the transverse stretching stress at the end of the transverse stretching process. As a result, the bowing of the film is reduced. Here, when the lateral relaxation during the preheating process is less than 3%, the bowing improvement is insignificant, and when it exceeds 5%, the inner shrinkage margin of the film is exceeded in the latter part of the preheating process, so that wrinkles are generated in the transverse direction. Worsen the thickness deviation. In addition, when the lateral stretch ratio in the first half of the lateral stretch process is less than 55% of the total lateral stretch ratio, extreme bowing due to the lateral stretch stress generated in the second half of the lateral stretch process cannot be prevented. At this time, it is preferable that the transverse stretching ratio of the first half of the transverse stretching step is in the range of 60% to 70% of the total transverse stretching ratio due to the equipment limitation of the stretching angle of the transverse stretching step.

Examples of the thermoplastic resin to which the production method of the present invention may be applied include homopolyester, copolyester or mixed polyester, and polyethylene terephthalate, polyethylene-2,6-naphthalate, polytetramethylene terephthalate, and poly Particularly preferred are polyesters such as tetramethylene-2,6-naphthalene carboxylate and liquid crystalline polyester, polypropylene, polyvinyl chloride, nylon, polyamide, polycarbonate, polystyrene and polyphenylene sulfite.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

Example 1

Polyethylene terephthalate chip having an intrinsic viscosity of 0.64 dl / g was melt-extruded at 290 ° C. to produce an amorphous sheet having a thickness of 200 μm at a rate of 70 m / min on a cooling roll at which the coolant temperature was maintained at 20 ° C. Stretched 3.5 times in the longitudinal direction of the film at 100 ° C. The longitudinally stretched film was preheated for 3 seconds at 120 ° C in the tenter and at the same time given 3% transverse relaxation, then transversely stretched at 120 ° C for 2.5 times in the first half and 2.0 times for the second half, and at 220 ° C for 3 seconds. Heat-setting for a second gave a biaxially stretched polyentylene terephthalate film having a thickness of 14 μm.

Example 2

A biaxially stretched polyethylene terephthalate film was obtained under the same conditions as in Example 1 except that 5% of lateral relaxation was imparted in the preheating process of the tenter.

Example 3

A biaxially stretched polyethylene terephthalate film was obtained under the same conditions as in Example 1 except that the first half transverse stretching ratio was 3.0 times and the second half transverse stretching ratio was 1.5 times.

Comparative Example 1

A biaxially stretched polyethylene terephthalate film was obtained under the same conditions as in Example 1 except that no transverse relaxation was imparted in the preheating process in the tenter.

Comparative Example 2

A biaxially stretched polyethylene terephthalate film was obtained under the same conditions as in Example 1 except that 7% of lateral relaxation was imparted in the tenter preheating process.

Comparative Example 3

A biaxially stretched polyethylene terephthalate film was obtained under the same conditions as in Example 1 except that the first half transverse stretching ratio was 2.25 times and the second half transverse stretching ratio was 2.25 times.

Table 1 shows the measurement results of the process conditions of the respective examples and the comparative examples, the amount of bowing of the obtained film, and the transverse physical properties.

In the tenter preheating step, the relaxation rate in the transverse direction was defined as follows.

In the tenter transverse stretching step, the front and rear transverse stretching ratios were defined as follows.

The amount of bowing (B) was defined as follows:

Where b is the distance from the reference straight line to the arcuate vertex, and W is the full width length of the film (see FIG. 1).

The change rate of the specific gravity of the transverse direction of the film was calculated by the following equation by measuring the specific gravity according to the conditions of ASTMD1505 in understanding the density gradient pipe method.

The rate of change of the transverse thickness of the film was calculated from the following equation by measuring the film thickness in the transverse direction of the film using a thickness gauge (manufactured by Winzen, USA).

As can be seen from Table 1, in the tenter preheating process, the present invention provides the transverse relaxation in the range of 3 to 5% and the transverse stretching ratio in the first half of the transverse stretching process to be 55% or more of the total transverse stretching ratio. The prepared films of Examples 1 to 3 facilitated reverse bowing early in the transverse stretching process, resulting in a reduced amount of bowing.

The film of Comparative Example 1 did not impart relaxation in the preheating process as usual, and the stretching stress in the early transverse stretching process was large and was not significantly affected by the longitudinal shrinkage force in the late transverse stretching process. Falling, which is inefficient in the bowing amount of the film. In the film of Comparative Example 2, the bowing of the film was minimized by increasing the reverse bowing at the beginning of the transverse stretching process, but the transverse thickness variation was increased due to excessive reverse bowing at the beginning of the transverse stretching process, so that the uniformity of the transverse quality of the film was increased. This resulted in a deterioration. The film of the comparative example 3 lacked the lateral stretch in the front part of a lateral stretch process, and could not prevent severe bowing by the lateral stretch stress produced in the late part of a lateral stretch process.

Claims (2)

In the method for producing a biaxially oriented film by longitudinally stretching, transversely stretching and heat-treating a sheet made of a thermoplastic resin, the transverse stretching apparatus gives a transverse relaxation of 3 to 5% in the transverse direction during the preheating process, At least 55% of the stretching is performed in the first half of the transverse stretching process. The method of claim 1, wherein the thermoplastic resin is polyethylene terephthalate, polyethylene-2,6-naphthalate, polytetramethylene terephthalate, polytetramethylene-2,6-naphthalene carboxylate, liquid crystal polyester, polypropylene, polyvinyl Process selected from the group consisting of chloride, nylon, polyamide, polycarbonate, polystyrene and polyphenylene sulfite.