JP2000085008A - Production of biaxially stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily adjust the width of an unstretched sheet without replacing a T-die with respect to the fluctuations of the width of the unstretched sheet due to the fluctuations of conditions. SOLUTION: A thermoplastic resin is extruded from a T-die in a molten state to obtain an unstretched sheet which is, in turn, brought into close contact with a cooling drum to be quenched and, next, both end parts of the unstretched film are grasped by clips and this film is simultaneously biaxially stretched biaxially by 2.0 times or more at stretching temp. of [glass transition point to (m.p. -15)] deg.C to produce a bizalially stretched film. In this method, a seal material is inserted in at least one of end parts of the slit part 2 of the T-die to be melted and extruded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for improving the productivity of a simultaneously biaxially stretched film made of a thermoplastic resin.

[0002]

2. Description of the Related Art A large amount of packaging bags made of plastic films are used for packaging foods, medicines, miscellaneous goods, etc., and films made of various thermoplastic resins such as polyamide and polyester are used. Above all, biaxially stretched polyamide films are excellent in transparency, tensile strength, pinhole resistance, gas barrier properties, and dimensional stability, and are used in a wide range of applications including food packaging. As a method for producing a biaxially stretched film, a simultaneous biaxial stretching method, a sequential biaxial stretching method, a tubular method, and the like are used.

In these production methods, a film obtained by a sequential biaxial stretching method has a strong orientation anisotropy in a machine direction (MD direction) and a direction perpendicular to the machine direction (MD direction) of the film. However, there is a problem that the uniformity of the film thickness is poor. On the other hand, in the simultaneous biaxial stretching method, the above-mentioned problems are small, and when a highly crystalline thermoplastic resin such as polyamide is used, cutting during stretching is difficult to occur. The method is particularly preferably used.

However, in the case of the simultaneous biaxial stretching method, the width of the left and right clips in the width direction for gripping both ends of the unstretched sheet is set constant in the stretching step.
Difference in the shrinkage rate of molten resin during cooling depending on the type of raw material,
The width of the unstretched sheet varies depending on the heating and drying treatment before stretching after various coating treatments on the surface of the unstretched sheet, or the manufacturing conditions before stretching. If the width of the unstretched sheet is too large, the clip may cause the sheet edge to be gripped or the sheet edge may be broken and two sheets may be gripped. On the other hand, if the width of the unstretched sheet is too narrow, the clip cannot grip the unstretched sheet sufficiently, and ear jumps may occur which may come off the clip during stretching. In either case, cutting of the film at the time of stretching is caused, and the operability is significantly impaired.

As described above, when the width of the unstretched sheet fluctuates, there is a problem that in order to hold both ends of the unstretched sheet normally, T dies having different widths must be replaced. , Significantly impaired operability.

[0006]

An object of the present invention is to solve the above-mentioned problems and to provide a method for producing a biaxially stretched film with good operability by a simultaneous biaxial stretching method.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve such a problem, and as a result, by inserting a sealing material into at least one end of the slit portion of the T-die, We found that the problem was solved.

That is, the gist of the present invention is that an unstretched sheet obtained by melt-extruding a thermoplastic resin from a T-die is brought into close contact with a cooling drum and rapidly cooled, and then both ends of the unstretched sheet are gripped with clips. , [Glass dislocation point to (melting point -1)
5)] In a method for producing a biaxially stretched film by simultaneously biaxially stretching the film at a stretching temperature of 2.0 ° C. or more at a stretching ratio of 2.0 ° C. or more at a stretching temperature of at least one end of a slit portion of a T-die. A method for producing a biaxially stretched film, comprising inserting a material and performing melt extrusion.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. As the thermoplastic resin used in the present invention,
For example, various resins such as polyamide, polyester, and ethylene-vinyl alcohol can be used.

Examples of the polyamide include nylon 6, nylon 610, nylon 11, nylon 12, polymethaxylylene adipamide (MX nylon), and copolymers thereof. Further, dicarboxylic acids such as terephthalic acid and isophthalic acid, hexamethylenediamine, metaxylylenediamine, 4,4′-diamino-3,3′-
Diamines such as dimethyl-dicyclohexylenemethane, various lactams, and isocyanates such as 4,4'-diphenylmethane diisocyanate may be copolymerized.

[0011] The monomer content in the polyamide is 0.1 to
Preferably, the content is 2.0 wt% and the water content is 5 to 50 ppm. If the monomer content or the water content is larger than the above-mentioned range, it causes foreign matters or the operability is reduced. If the content is less than the above-mentioned range, the production cost is increased, which is not economically preferable.

The relative viscosity of the polyamide is preferably 2.50 or more, particularly preferably in the range of 2.80 to 3.50. When the relative viscosity is less than 2.50, the mechanical strength of the film becomes insufficient. Further, even if the relative viscosity is larger than 3.50, not only the quality becomes excessive, but also the operability at the time of film production deteriorates, which is not economically preferable.

The crystalline polyamide has a melting point of 200.
The glass transition point is preferably in the range of 20 to 75 ° C for amorphous polyamide. If the melting point is lower than this range, heat resistance may be insufficient, which may be undesirable.

As the polyester, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PE)
N), polybutylene naphthalate (PBN) and the like.

PET has an intrinsic viscosity of 0.5 dl / g or more, preferably in the range of 0.6 to 1.2 dl / g. If the intrinsic viscosity is less than 0.5 dl / g, the mechanical strength of the film is insufficient, which is not preferable. Further, even if the intrinsic viscosity is increased beyond 1.2 dl / g, not only the quality becomes excessive, but also the operability at the time of film production deteriorates.

The crystalline polyester has a melting point of 200 to
The glass transition point is preferably in the range of 280 ° C and the amorphous polyester is in the range of 50 to 150 ° C. If the melting point is lower than this range, heat resistance may be insufficient, which may be undesirable.

The material of the sealing material used in the present invention is not particularly limited, and for example, a reinforced Teflon material can be cited as a material which does not have an effect of altering the resin and has excellent durability.

Next, a method for producing a film by the simultaneous biaxial stretching method in the present invention will be described in the order of steps using polyamide as an example.

First, after the polyamide is melted by an extruder, the polyamide is extruded from a T-die into a sheet, and the surface temperature is reduced to 0 to 2 mm.
The sheet is brought into close contact with a cooling drum (CR) adjusted to 5 ° C. and rapidly cooled to obtain an unstretched sheet. At this time, if the surface temperature is lower than 0 ° C., dew condensation occurs on the cooling drum, and if the surface temperature is higher than 25 ° C., the cooling becomes insufficient. The obtained unstretched sheet is
It is sent to a hot water tank whose temperature is controlled to 〜80 ° C., and is usually subjected to a humidity control treatment for 10 minutes or less. The humidity control is effective for preventing the film from being cut in the stretching process, and the humidity control can appropriately plasticize the resin and suppress crystallization. If the temperature of the hot water is lower than 20 ° C., the humidity control becomes insufficient,
If it is too high, not only does the humidity control effect saturate, but it also impairs economic efficiency. If necessary, in-line coating may be performed before stretching in order to further improve properties such as easy adhesion, antistatic properties, and gas barrier properties. Next, the end of the sheet is gripped by a clip of a simultaneous biaxial stretching machine, and at a stretching temperature of [glass transition point to (melting point -15)] ° C, the stretching ratio is 2.0 times or more in each of longitudinal and transverse directions.
Usually, after stretching to 2.0 to 4.0 times, the relaxation rate in the transverse direction is set to 2 to 8%, and [(glass dislocation point +50) to (melting point −
10)] Heat-treat at 1 ° C for 1 to 10 seconds to obtain a biaxially stretched film. The stretching ratio, the relaxation rate and the heat treatment temperature are appropriately adjusted within the above range according to the required physical properties of the film. Thereafter, the stretched film is cooled and wound up by a winder at a speed of 60 to 200 m / min, and the obtained raw roll is slit into a product roll.

In the above manufacturing process, for example, when the unstretched sheet is subjected to humidity control in a hot water tank, warm water enters between the roll and the unstretched sheet, and the film meanders in the hot water tank. The width of the unstretched sheet varies by adjusting the peripheral speed of the roll at the front and rear portions of the hot water tank in order to prevent this meandering. In the above case, the width of the unstretched sheet can be easily adjusted by using the method of the present invention without replacing the T-die.

Next, FIG. 1 shows an example of inserting a sealing material into the end of the slit portion of the T-die according to the present invention. In FIG. 1, a sealing material 1 is inserted into a die slit 2 and fixed to a side block 4 of a T-die by bolts 3.

Example 1 Nylon 6 was melt-extruded using a T-die having a T-die slit having a width in the horizontal direction of 1500 mm, and a rotation speed was 50 m / min.
And then immersed in hot water at a temperature of 60 ° C. for 1 minute to form an unstretched sheet having a width of 1400 mm and a thickness of 150 μm. Next, both ends of the unstretched sheet were gripped with clips and simultaneously biaxially stretched to produce a biaxially stretched nylon film having a thickness of 15 μm. About one hour after the start of production, the rotation speed of the rubber roll inside the hot water tank changed due to expansion, and wrinkles were generated intermittently in the unstretched sheet. Therefore, the occurrence of wrinkles was corrected by adjusting the rotation speed of the rubber roll inside the hot water tank. However, the width of the unstretched sheet was widened by about 5 mm, so that buttoning occurred with clips. Thus, a film was formed by inserting a sealing material having a width of 5 mm into one end of the T-die slit and adjusting the width of the unstretched sheet. As a result, stable production could be continued.

Example 2 A T-die having a width of 1500 mm in the lateral direction of the T-die slit was used.
Is melted and extruded, closely cooled to a cooling drum having a rotation speed of 50 m / min, and then immersed in warm water at a temperature of 60 ° C. for 1 minute.
An unstretched sheet having a width of 1400 mm and a thickness of 150 μm was formed. Next, both ends of the unstretched sheet were gripped with clips and simultaneously biaxially stretched to produce a biaxially stretched nylon film having a thickness of 15 μm. Next, the unstretched sheet was subjected to an easy-adhesion coating treatment to change the brand, and then dried in a furnace having a furnace length of 10 m and a furnace temperature of 150 ° C. Was released. Therefore, as a result of removing the sealing material at one end of the T-die slit and adjusting the width of the unstretched sheet to form a film, stable production could be continued.

[0024]

According to the present invention, when a biaxially stretched film such as polyamide is produced by the simultaneous biaxial stretching method, the T-die is exchanged for a change in the unstretched sheet width due to a change in conditions. In addition, since the width of the unstretched sheet can be easily adjusted, productivity can be significantly increased, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an example in which a sealing material is inserted into an end of a slit portion of a T-die.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Seal material 2 Die slit 3 Bolt 4 T-die side block

Claims (2)

[Claims] 1. An unstretched sheet obtained by melt-extruding a thermoplastic resin from a T-die is stuck on a cooling drum and quenched, and then both ends of the unstretched sheet are gripped with clips.
[Glass transition point to (melting point -15)] In a method of producing a biaxially stretched film by simultaneously biaxially stretching the film at a stretching temperature of 2.0 ° or more in the longitudinal and transverse directions at a stretching temperature of ° C, the slit portion of the T-die is used. 2. A method for producing a biaxially stretched film, comprising: inserting a sealing material into at least one end of the film; 2. The method for producing a biaxially stretched film according to claim 1, wherein the thermoplastic resin is a polyamide resin.