JP2002001810A - Method for relaxation heat treating biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for relaxation heat treating to efficiently obtain a biaxially oriented polyester film having excellent thermally dimensional stability and low thermal shrinkage capable of correcting a heat shrinkage factor of the film even when there is a small distribution in the factor. SOLUTION: In the method for relaxation heat treating of the biaxially oriented polyester film comprising the step of relaxation heat treating the biaxially oriented polyester film while running the film from a preheating roll toward a cooling roll in a state in which the film is suspended, a means for locally heating and/or cooling at least one position of the film in a width direction and/or a longitudinal direction of the film is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat-treating a biaxially stretched polyester film, and more particularly to a method for relaxing heat treatment of a biaxially stretched polyester film.

[0002]

2. Description of the Related Art A biaxially stretched polyester film represented by a polyethylene terephthalate film has been widely used as a base film of a photographic photosensitive film. In particular, in the case of heat-sensitive photographic materials, the film is often heat-developed at a temperature of 80 to 150 ° C. in a use stage, and a low heat-shrinkable film that can be superposed and developed without dimensional deviation even under a heat load is demanded. Have been.

[0003] In response to this demand, the crystallinity is increased by setting the heat setting temperature high during the production process of the biaxially stretched polyester film, or the film is subjected to relaxation treatment in the longitudinal and transverse directions to reduce the heat shrinkage. A plan is being made. However, a desired low heat shrink film cannot be obtained only by the treatment during the film forming process, and a biaxially stretched polyester film has been subjected to relaxation heat treatment offline.

There are various methods for relaxation heat treatment. For example, a method has been proposed in which a film continuously run in a suspended state is relaxed under a specific temperature condition to reduce the heat shrinkage to 0.1% or less. (Japanese Patent No. 1891172). However, in the film manufacturing process, there is a temperature distribution in the heat setting zone, or because the running tension of the film is not uniform, the film is formed with the heat shrinkage ratio having a distribution in the width direction. There is a problem in that the desired low heat shrinkage cannot be realized over the entire width of the product simply by treating the film with the relaxation heat treatment method of the related art.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to correct even a small distribution of the heat shrinkage of a film, thereby achieving a low heat shrinkage with excellent thermal dimensional stability. An object of the present invention is to provide a relaxation heat treatment method for efficiently obtaining a biaxially stretched polyester film.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for performing a relaxation heat treatment while a biaxially stretched polyester film is suspended and run from a preheating roll toward a cooling roll. Alternatively, the problem can be solved by a method of heat treatment for relaxing a biaxially stretched polyester film, wherein a means for locally heating and / or cooling at least one portion in the longitudinal direction is provided.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a side view showing an example of a relaxation heat treatment apparatus representing one embodiment of the present invention. In FIG. 1, 1 is a preheating roll, 2 is a cooling roll, 3 is a biaxially stretched polyester film, 4a to 4c are infrared heaters for local heating, 5
Denotes an oven, 6 denotes an infrared heater, and a denotes a running direction of the film 3. FIG. 2 shows the local heaters 4a to 4c.
It is a partial front view showing 4c.

In the present invention, running the film in a suspended state means moving the film 3 in the direction of gravity from the preheating roll 1 to the cooling roll 2 as shown in FIG. Since the direction of gravity and the running direction of the film coincide, the film can be transported and heat-relaxed relatively stably even under low tension while maintaining the flatness of the film. The tension of the suspended film is preferably 0.04 to 0.5 MPa,
When the value is below the lower limit, the film meanders. When the value exceeds the upper limit, the residual stress of the film cannot be alleviated, and it is difficult to obtain a sufficiently low heat shrinkable film. The tension of the suspended film is more preferably 0.08 to 0.40 Mpa.

A preferred feature of the present invention is that the maximum temperature of the film at the time of the relaxation heat treatment can be adjusted at a specific position in the width direction of the film and, at the very least, the amount of heat shrinkage after the relaxation heat treatment can be adjusted. 4c (infrared heater for local heating).

The maximum temperature of the film is (Tg + 50)
To (Tg + 150) ° C. (where Tg is the glass transition temperature of the polyester). The temperature is adjusted to this temperature range by the infrared heater 6 and the preheating roll 1 provided in the oven 5. At this time, if the heat shrinkage ratio of the film before the heat relaxation treatment is substantially constant in the width direction, it is possible to reduce the heat shrinkage while maintaining uniformity by maintaining the uniform temperature or tension in the oven. become.

However, as described above, the thermal shrinkage of the film may have a distribution, and in this case, it is necessary to actively change the attainable temperature to control the thermal shrinkage. Specifically, if there is a portion having a high heat shrinkage rate in part, since the heat shrinkage of the corresponding portion becomes high even after the relaxation heat treatment,
The film is preheated to a high temperature in advance by using an infrared heater for local heating corresponding to the portion, the ultimate temperature is increased, and the holding time at a high temperature is increased, so that the heat shrinkage can be partially reduced.

The case where three infrared heaters for local heating are arranged at both ends and the center in total is illustrated. However, the infrared heaters may be arranged only near both ends to control the amount of heat shrinkage on the left and right.
Conversely, a large number of heaters may be arranged to adjust the heating amount stepwise. When the film is transported at a relatively high speed such as exceeding 20 m / min, the film is locally moved in the longitudinal direction of the film in order to compensate for the shortage of the heat received by the film or to increase the response of the preheating process. By arranging the heating means, the object of the present invention can be achieved.

The local heating means may be a means for heating the film by radiant heat, such as an infrared heater, or a means for arranging several individually controlled narrow width rolls against the film and heating the film by contact heat transfer. Means for arranging the heaters in a non-contact manner and arranging them in a non-contact manner can be exemplified. Further, the surface of the preheating roll may be partially heated to control the preheating temperature in the width direction.

Although the response is inferior, the object of the present invention can be achieved by using a cooling means instead of the local heating means. In this case, a portion of the film before the relaxation heat treatment that has a low heat shrinkage may be cooled in advance to lower the temperature reached by the film. Examples of the cooling unit include a unit that presses a narrow roll having circulated cooling water against the film and cools the film by contact heat transfer, and a unit that sends cool air from a slit nozzle to the film and cools the film by forced heat transfer.

Further, even if the heating means and the cooling means are mixed, the heat shrinkage can be adjusted more precisely. As these local heating and / or cooling means, means conventionally known and used besides those exemplified above can be used. These means can achieve the object of the present invention even in an oven. However, in the oven, not only the film but also the air is heated, and a partial ascending air current is generated to disturb the air flow, so that the temperature in the oven is not stable. Therefore, the adjustment amount may be restricted.

In the present invention, the heat shrinkage of the film before the relaxation heat treatment is measured at least at three or more points in the width direction, a target value is set based on the result, and the adjustment amount of the heating / cooling means is controlled. I do. The setting of the target value may be within the range of the heat shrinkage required after the relaxation heat treatment, but the following three examples can be exemplified. The maximum value of the measured heat shrinkage is Smax, and the minimum value is Sm.
and the heating / cooling amount is adjusted with (Smax−Smin) / 2 as the target value. The heating amount is adjusted with the minimum value of the measured heat shrinkage as a target value. The cooling amount is adjusted using the maximum value of the measured heat shrinkage as a target value.

In the film manufacturing process and the relaxation heat treatment process, the film is treated while applying tension to the film and transporting the film. Low heat shrinkage is relaxation of residual stress, and the heat shrinkage becomes sensitive to the distribution of running tension. Therefore, the target value of the heat shrinkage to be corrected is often a value in the longitudinal direction of the film.

The temperature difference of the film at the outlet of the oven (immediately before reaching the cooling roll) is preferably 12 ° C. or less in the width direction.
If it exceeds this, the heat treatment conditions in the oven and the rectification of the rising airflow due to the heated air and the descending airflow due to the accompanying flow of the film are not appropriate, and the object of the present invention such as uniform low heat shrinkage may not be achieved.

In the present invention, the polyester constituting the polyester film is a linear saturated polyester synthesized from an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof.
Specific examples of the polyester include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylene dimethylene terephthalate), and polyethylene-2,6-naphthalenedicarboxylate. Alternatively, a blend of these with a small proportion of another resin is also included. Of these polyesters, polyethylene terephthalate or polyethylene-2,6-naphthalenedicarboxylate is particularly preferred.

In the polyester, a lubricant such as calcium carbonate, kaolin, silica, titanium oxide, alumina, crosslinked polystyrene particles, silicon resin particles and the like, and / or a catalyst residue may be added to the polyester film in view of the slipperiness and processability of the film. It is preferable to include precipitated fine particles and the like.
Further, other additives such as a pigment, a stabilizer, an ultraviolet absorber and the like can be contained as required.

The biaxially stretched and heat-set polyester film used in the present invention can be produced by a conventionally known method. For example, after drying the above polyester, it is melted at a polymer melting point of Tm to (Tm + 70) ° C., extruded from a die to a cooling drum, quenched, and cooled to an intrinsic viscosity of 0.35.
To 0.9 dl / g of an unstretched film, and the unstretched film is vertically stretched at a temperature of (Tg-10) to (Tg + 70) ° C (where Tg is the glass transition temperature of the polyester). The film is stretched at a magnification of 5 to 5.0 times, and then transversely stretched with a tenter at a temperature of Tg to (Tg + 70) ° C at a temperature of 2.5 to 2.5.
Stretched at a magnification of 5.0 times, and then (Tg + 70) to Tm ° C.
It can be manufactured by heat-setting at a temperature of For polyethylene terephthalate film, 1
It is preferable to heat set at 90 to 240 ° C. The heat setting time is preferably 1 to 60 seconds.

[0022]

The present invention will be further described with reference to the following examples. In addition, each characteristic or evaluation of the product film was measured by the following method, or a defined one was employed.

(1) Heat shrinkage at 120 ° C.
Cut to mm. Two holes are formed at intervals of 200 mm, the humidity is adjusted at 25 ° C. and 60% RH for 12 hours or more, and the distance between the holes is measured using a pin gauge (this length is defined as L ₁ (m
m)). Then, it is pressed on a stainless steel plate heated to 120 ° C. for 20 seconds. Then, at 25 ° C and 60% RH,
After the humidity control for 2 hours or more, the distance between the holes is measured again using a pin gauge (this length is defined as L ₂ (mm)). Then, the thermal dimensional change rate was determined based on the following equation.

[0024]

## EQU1 ## Heat shrinkage (%) at 120 ° C. = 100 × (L ₁ −
L ₂ ) / L _{1 The} heat shrinkage was determined by measuring the values of the film in the MD direction (longitudinal direction) and TD direction (lateral direction) at the center (C) in the width direction and near both ends (F, B). In addition, the heat shrinkage ratio is positive,
Negative values indicate elongation.

(2) Heat shrinkage at 150 ° C. A sample having a length of 350 mm and a width of 50 mm in a measuring direction was cut out, and marked points were placed at intervals of 300 mm near both ends in the longitudinal direction of the sample, and one end was fixed to an oven adjusted to a temperature of 150 ° C. Leave the other end free for 30 minutes. This is taken out and the distance between the gauges is measured at room temperature (this length is defined as L ₃ (mm)), and the heat shrinkage is calculated by the following equation.

[0026]

## EQU2 ## Thermal shrinkage at 150 ° C. (%) = 100 × (300−
L ₃ ) / 300 The heat shrinkage was measured in the MD (longitudinal) and TD (transverse) directions of the film at the center (C) in the width direction and near both ends (F, B). In addition, the heat shrinkage ratio is positive,
Negative values indicate elongation.

(3) Film temperature at the outlet The film temperature at 100 mm after exiting the oven is measured at equal intervals in the width direction at 10 points using a radiation thermometer, and the difference between the maximum value and the minimum value is determined as the film temperature difference. did.

(4) Glass transition temperature (Tg) A sample (10 mg) was set in a DSC device (differential scanning calorimeter) manufactured by PerkinElmer, and the sample was melted at a temperature of 300 ° C. for 5 minutes and then quenched in liquid nitrogen. Then, this quenched sample is
The temperature was raised at 0 ° C./min, and the glass transition temperature (Tg) was measured.

(5) Uniformity of heat shrinkage rate The production control range of the heat shrinkage rate after the relaxation heat treatment is 120 ° C.
The heat shrinkage for 20 seconds is 0.02-0.08 in the MD direction, T
-0.05 to -0.01 in the D direction. ：: All the heat shrinkage rates were within the control range. Δ: The heat shrinkage ratios are all within the control range, but one or more of them are the standard border values and are at the warning level. X: One or more of the thermal shrinkage rates are out of the control range.

Example 1 A pellet of polyethylene terephthalate (Tg: 70 ° C.) having an intrinsic viscosity (o-chlorophenol solution, 35 ° C.) of 0.65 was dried at 180 ° C. for 5 hours, and then dried at 270 to 300 ° C. The mixture was fed to a heated extruder and formed into a sheet by an extrusion die.
Further, this film was adhered and solidified by static electricity on a cooling drum having a surface temperature of 25 ° C. to obtain an unstretched film.

Next, this unstretched film is preheated to 75 ° C., heated by a group of heating rolls at 80 to 100 ° C., stretched 3.1 times in the machine direction, cooled by a group of rolls at 20 to 50 ° C. 2. While holding the film at both ends with clips, the film is moved laterally in a hot atmosphere at 120 ° C.
Stretched 9 times.

The film thus biaxially stretched is heat-set in a tenter as it is at 235 ° C. for 5 seconds, during which the width is relaxed by 1.5%.
After cooling the film, the edge of the film was cut off in a zone where hot air was not blown out, the film was relaxed by reducing the take-off speed by 1.5%, gradually cooled from 180 ° C to 110 ° C, taken out of the tenter, and cooled at room temperature to 90 ° C. The film cooled to 0 ° C. was taken up by a take-up roll at 75 ° C., and the film cooled to a region of room temperature to 50 ° C. was wound.

Further, the obtained roll of the biaxially stretched film having a thickness of 100 μm was slit into two rolls (A and B) having a width of 1500 mm and wound up. 1 of film roll A
Table 1 shows the heat shrinkage at 50 ° C.

The obtained film roll A was subjected to a suspension-type relaxation heat treatment according to the method of the present invention shown in FIGS. The temperature of the preheating roll 1 and the temperature of the infrared heater 6 were adjusted such that the length of the oven 5 was 4 m, the transport speed of the film 3 was 12 m / min, and the ultimate temperature of the film in the oven was about 150 ° C.

Furthermore, since the heat shrinkage in the MD direction at 150 ° C. measured in advance was such that the distribution became large at both ends of the film, the surface temperature of both ends 4a and 4c of the infrared heater for local heating was reduced. Heating was performed until the temperature reached 200 ° C., and relaxation heat treatment was performed. Table 1 shows the results.

Example 2 Table 1 shows the heat shrinkage at 150 ° C. of the biaxially stretched film roll B obtained in Example 1.
Since the heat shrinkage in the MD direction was distributed from one end to the other end of the film, the surface temperature of the center 4b and the end 4c of the infrared heater for local heating was 200 ° C., respectively. Heating was performed to 300 ° C., and the treatment was performed under the same relaxation heat treatment conditions as in Example 1 except for these conditions. Table 1 shows the results.

[Comparative Examples 1 and 2] Except that the local heating infrared heaters 4a to 4C were not heated, processing was carried out under the same film forming conditions and relaxation heat treatment conditions as in Examples 1 and 2, respectively. 1 and 2. Table 1 shows the results.

[0038]

[Table 1]

It is apparent from Table 1 that the present invention can produce a biaxially oriented polyester film having a uniform heat shrinkage and a low heat shrinkage.

[0040]

According to the relaxation heat treatment method of the present invention, a biaxially oriented polyester film having excellent heat shrinkage uniformity and low heat shrinkage can be efficiently obtained.

[Brief description of the drawings]

FIG. 1 is a side view of a relaxation heat treatment apparatus showing one embodiment of the present invention.

FIG. 2 is a partial front view showing heaters for local heating 4a to 4c.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Preheating roll 2 Cooling roll 3 Biaxially stretched polyester film 4a-4c Infrared heater for local heating 5 Oven 6 Infrared heater a Running direction of film 3

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yo Goto 3-37-19 Koyama, Sagamihara-shi, Kanagawa F-term in Sagamihara Research Center, Teijin Limited 4F210 AA24 AE01 AG01 AK01 AK04 QA02 QA03 QC06 QG01 QG18 QW09 QW12 RG43

Claims (4)

[Claims] 1. A method of performing a relaxation heat treatment while running a biaxially stretched polyester film in a suspended state from a preheating roll to a cooling roll, wherein at least one of the film in the width direction and / or the longitudinal direction before the relaxation heat treatment is applied. A method for relaxing heat treatment of a biaxially stretched polyester film, comprising providing means for locally heating and / or cooling a place. 2. The method according to claim 1, wherein the temperature difference in the width direction of the film immediately before reaching the cooling roll is 12 ° C. or less. 3. The heat shrinkage is measured at least at three or more locations in the width direction of the film before the relaxation heat treatment, and the heating amount and / or the cooling amount are adjusted based on the result.
Or the method of relaxing heat treatment of the biaxially stretched polyester film according to 2. 4. The method according to claim 1, wherein the heat shrinkage of the film measured before the relaxation heat treatment is a heat shrinkage in the longitudinal direction of the film. .