JP2002046171A - Method for manufacturing polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyester film having a smooth surface free from a surface defect such as a slip scratch or the like. SOLUTION: In the method for manufacturing the polyester film having a process for longitudinally stretching the polyester film between a heating roll and a cooling roll, as the cooling roll of at least a stretching part, a ceramic roll having surface roughness satisfying conditions such that (1) Ra is 0.1 μm>=Ra, (2) the maximum height of parts projected from a center line is 0.5 μm or less, (3) the maximum depth of parts depressed from the center line is 1.0 μm or less (wherein, Ra is center line average roughness and the center line is a line formed by embedding ridges and troughs in a roughness cross-sectional curved line).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester film, and more particularly, to a method for producing a polyester film which achieves a good surface state free from scratch defects caused by a longitudinal stretching roll.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, polyester films have been used for optical applications such as antireflection films, reflection sheets and display screens, and high transparency and quality against surface defects have become important.

[0003] In order to make the film highly transparent, the film is inevitably added with no particles or only a small amount or minute particles, and it is necessary to stretch the film with a very smooth surface state.
The rolls in the longitudinal stretching process caused scratches, and the quality of surface defects could not be satisfied.

Conventionally, as a method for producing a polyester film, an unstretched film is stretched in the longitudinal direction by a peripheral speed difference between a plurality of sets of rolls, and then stretched in a transverse direction by a stenter using a clip. The axial stretching method is generally employed.

[0005] Rolls that are stretched in the longitudinal direction are required to have excellent anti-adhesive properties, anti-slip properties, and durability with the recent increase in speed and temperature of the film forming process. In order to achieve such performance, a surface treatment roll having a surface coated (sprayed) with a ceramic such as alumina oxide or chromium oxide is considered to be useful.

Heretofore, it has been considered preferable that the surface be appropriately roughened in order to achieve both the purpose of preventing sticking and preventing scratches caused by slipping, and it has been considered that Ra ≦ 0.1 μm makes the surface sticky.

[0007] However, when a film having substantially no projection is stretched, a scratch due to slippage has been generated although the scratch depth is very small.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a method for producing a polyester film having a smooth surface without surface defects such as sliding scratches.

[0009]

According to the present invention, there is provided a method for producing a polyester film comprising a step of stretching a polyester film in a longitudinal direction between a heating roll and a cooling roll. A method for producing a polyester film, comprising using a ceramic roll having a surface roughness satisfying the following conditions.

(1) 0.1 μm ≧ Ra (2) The maximum height of the portion that is convex from the center line is 0.5 μm or less. (3) The maximum depth of the portion that is concave from the center line is 1.0 μm or less. , Ra are the center line average roughness, and the center line is a line formed by filling peaks and valleys in the roughness sectional curve.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The center line average roughness Ra of a ceramic roll used in the present invention needs to be 0.10 μm or less, and preferably 0.06 μm or less.

Until now, when the Ra was 0.10 μm or less, it has been considered that the film is sticky due to the high temperature in the cooling roll of the stretching part. It turns out.
Conversely, when the film was stretched using a roll having a Ra larger than 0.10 μm, generation of scratches was observed.
The reason for this has not been clarified yet, but when the film itself becomes very smooth, the contact area with the roll becomes large, so that the high-temperature film immediately after stretching is also rapidly cooled near the very vicinity of the surface in contact with the roll. On the contrary, it is considered that a roll having a large Ra makes it slippery without causing sticking, and that the scratches are caused by the unevenness.

On the other hand, in the case of a conventional film having a certain degree of protrusions, the contact area with the roll is small, and the surface of the high-temperature film immediately after being stretched and coming into contact with the roll is peeled off without being sufficiently cooled. It is considered that the stickiness was caused by this.

Although it is considered that reducing Ra in this way is effective for surface defects, it is extremely difficult to reduce Ra to less than 0.03 μm in current ceramic roll coating (spraying) and polishing techniques. It was difficult to evaluate.

The maximum height of the portion of the ceramic roll used in the present invention that is convex from the center line must be 0.5 μm or less. When the film is stretched in the longitudinal direction, the film causes a neck down in the width direction.If this neck down also occurs on the cooling roll surface of the stretched section, the film will slide in the width direction on the roll surface while moving in the vertical direction. If the roll has coarse projections, it will cause diagonal scratches. This flaw often occurs near the edge where the amount of neck down is large, and decreases near the center. If the maximum height of the portion that is convex from the center line is higher than 0.5 μm, neck-down is likely to occur even on the cooling roll, and this convex portion triggers an oblique scratch. Although there is no particular lower limit for the maximum height, it is usually about 0.1 μm.

In the ceramic roll of the present invention, the maximum depth of the portion that is concave from the center line must be 1.0 μm or less. Ceramic rolls are essentially porous because they are made by spraying ceramic fine powder. After the thermal spraying, polishing is performed to obtain a desired surface roughness. If the bonding between the ceramic particles is weak at the time of this polishing, the polishing is lost and a concave portion is formed. On the other hand, when the film is stretched to a high temperature, low molecular weight substances such as oligomers are deposited on the surface.
When the maximum depth of the portion that is concave from the center line is larger than 1.0 μm, the degree of adhesion increases because of the smooth film and roll, and low molecular weight substances that have precipitated from the film are easily accumulated in the concave portion, The growth causes a slip and causes a scratch, and the low molecular weight material itself grown to a certain size falls off the roll and adheres to the film, resulting in a surface defect. Although there is no particular lower limit for the maximum depth, it is usually about 0.5 μm.

The polyester referred to in the present invention is a well-known polyester and may be any polyester which can form a uniaxially or biaxially stretched film. As the acid component, terephthalic acid, isophthalic acid, phthalic acid, Aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, resin dicarboxylic acids such as decanedicarboxylic acid, alicyclic dicarboxylic acids such as cyclohexanecarboxylic acid, and tricarboxylic acids such as trimellitic acid. As the alcohol component, ethylene glycol, diethylene glycol, polyethylene glycol, 1,4-butanediol, neopentyl glycol, cyclohexanedimethanol, polytetramethylene glycol, and the like can be used.
In addition, monomers and prepolymers may be copolymerized or blended with various polymers as long as they do not impair the film-forming properties.

As the transesterification catalyst for the polyester resin as described above, Ca, Li, Mn, Zn, Ti and the like can be used. Alternatively, terephthalic acid may be directly transesterified. As the polymerization catalyst, S
b ₂ O ₃ , germanium oxide, or the like can be used.

If necessary, known additives such as stabilizers, viscosity modifiers, antioxidants, antistatic agents, antiblocking agents, ultraviolet absorbers and infrared absorbers may be added to the above polyester. .

If necessary, the polyester film after longitudinal stretching may be subjected to a known surface treatment, for example, a glow discharge treatment or a coating treatment with various polymers.

By using the stretching roll of the present invention, a polyester film having a surface roughness Ra of 0.01 μm or less and an Rmax of 0.05 μm or less can be produced.

[Measurement Method] (1) Roll Surface Roughness Surface roughness meter (Surfcoder SE) manufactured by Kosaka Laboratory Co., Ltd.
-400) was used to measure the two-dimensional surface roughness. The measurement conditions were as follows: feed rate: 0.1 mm / s, measurement length: 5.0 mm, cut-off value: 0.8 mm, and measurement chart in the height direction: 50
The output was made at a magnification of 00 times, in the measurement length direction: 100 times, and the height of the projection and the depth of the recess from the center line were read.

(2) Film surface roughness Surface roughness meter (Surfcoder ET) manufactured by Kosaka Laboratory Co., Ltd.
-30HK) to measure the three-dimensional surface roughness. The measurement conditions were as follows: feed speed: 0.02 mm / s, measurement length: 0.1 mm,
The cut-off is 0.08 mm, the number of measurement lines is 100, and the feed pitch is 0.2 μm.

(3) Defects on the film surface In a dark room, a strong light was applied obliquely, and the film surface was observed to see the reflected light, and defects such as scratches were inspected.

[0025]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples without departing from the gist thereof.

Example 1 A polyethylene terephthalate (PET) resin containing almost no particles was extruded at 290 ° C. from a T-die of a melt extruder into a sheet, cooled by a cast drum, and cooled to a thickness of 1 mm.
A 200 μm sheet was obtained. Using the roll stretching apparatus shown in FIG. 1, roll stretching was performed in the machine direction under the conditions of a stretching temperature of 98 ° C., a stretching ratio of 3.3 times, and a cooling temperature of 21 ° C. In FIG. 1, (1) to (4) are preheating sections, (5) and (6) are stretching sections, (7) to (9) are cooling sections, and (1) to (5).
Is a heating roll, and (6) to (9) are cooling rolls. A ceramic roll with Ra = 0.5 μm was used for the heating-side roll (5) of the stretching section. Chromium oxide is coated (sprayed) on the two cooling rolls (6) and (7) that are wound first on the cast surface side and the non-cast surface side of the stretched film, and Ra = 0.05 μm, convex from the center line. A ceramic roll having a maximum height of 0.2 μm at a portion having a maximum height and a maximum depth of 0.8 μm at a portion recessed from the center line was used. As the preheating roll and the cooling roll before and after the stretching section, a 0.2S HCr roll was used. Next, the longitudinally stretched film is stretched in the transverse direction by a known transverse stretching apparatus (stenter) under the conditions of a stretching temperature of 105 ° C. and a stretching ratio of 3.6 times, and is subjected to a usual heat setting treatment to a thickness of 100 μm.
m of biaxially stretched polyester film was obtained. As a result of observing the surface state of the obtained film, it was found that the film surface had no defects due to scratches and adhesion and was in an extremely good state.

Example 2 Two cooling-side rolls (6) and (7) wound first on the cast side and the non-cast side of the stretched film were as follows.
Coating (spraying) chromium oxide, Ra = 0.04
μm, the maximum height of the part convex from the center line is 0.3μ
m, the maximum depth of the concave portion from the center line is 0.95 μm
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the ceramic roll was used.
As a result, as in Example 1, the film surface was in a good state.

Example 3 The two cooling rolls (6) and (7) wound first on the cast side and the non-cast side of the stretched film were as follows.
Coating (spraying) chromium oxide, Ra = 0.03
μm, the maximum height of the part convex from the center line is 0.2μ
m, the maximum depth of the portion that is concave from the center line is 0.55 μm
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the ceramic roll was used.
As a result, as in Examples 1 and 2, the film surface was in a good state.

Example 4 The two cooling rolls (6) and (7) wound first on the cast side and the non-cast side of the stretched film were as follows.
Coating (spraying) chromium oxide, Ra = 0.09
μm, the maximum height of the part convex from the center line is 0.5μ
m, the maximum depth of the concave portion from the center line is 0.95 μm
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the ceramic roll was used.
As a result, as in Examples 1, 2, and 3, the film surface was in a good state.

COMPARATIVE EXAMPLE 1 Two cooling rolls (6) and (7) wound first around the cast side and the non-cast side of the stretched film were as follows.
Coating (spraying) chromium oxide, Ra = 0.05
μm, the maximum height of the part convex from the center line is 1.0 μm
m, a polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that a ceramic roll having a maximum depth of 0.8 μm in a portion concave from the center line was used. Observation of the surface condition of the obtained film revealed that the film had a very shallow depth but diagonal scratches near both ends in the film width direction.

COMPARATIVE EXAMPLE 2 The two cooling rolls (6) and (7) wound first on the cast side and the non-cast side of the stretched film were as follows.
Coating (spraying) chromium oxide, Ra = 0.05
μm, the maximum height of the part convex from the center line is 0.2μ
m, a polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1, except that a ceramic roll having a maximum depth of 2.0 μm in a portion concave from the center line was used. Observation of the surface condition of the obtained film showed that no defects such as scratches were found in the film immediately after the start of film formation. However, in the film 48 hours after the start of film formation, Comparative Example 1 was found near both ends in the width direction. Many similar oblique scratches were seen.

COMPARATIVE EXAMPLE 3 Two cooling rolls (6) and (7) wound first on the cast side and the non-cast side of the stretched film were as follows:
Coating (spraying) chromium oxide, Ra = 0.15
μm, the maximum height of the part convex from the center line is 0.5μ
m, the maximum depth of the concave portion from the center line is 2.35 μm
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the ceramic roll described above was used.
Observation of the surface condition of the obtained film revealed that a number of scratch defects were observed over almost the entire width of the film.

COMPARATIVE EXAMPLE 4 The two cooling rolls (6) and (7) wound first on the cast side and the non-cast side of the stretched film were as follows.
Coating (spraying) chromium oxide, Ra = 0.13
μm, the maximum height of the part convex from the center line is 0.4μ
m, the maximum depth of the concave portion from the center line is 0.95 μm
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the ceramic roll was used.
Observation of the surface state of the obtained film revealed that although it was thinner than that of Comparative Example 3, many scratch defects were found on almost the entire surface of the film.

Table 1 summarizes the results of Examples and Comparative Examples.
Shown in

[0035]

[Table 1]

[0036]

According to the present invention described above, a method for producing a polyester film having a very smooth surface and free from surface defects such as scratches is provided, and the industrial value of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of a roll stretching apparatus used in the present invention.

[Explanation of symbols]

 1-5: Heating roll 6-9: Cooling roll

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 7:00 B29L 7:00

Claims (1)

[Claims] 1. A method for producing a polyester film comprising a step of stretching a polyester film in a longitudinal direction between a heating roll and a cooling roll, wherein at least a cooling roll in a stretched portion has a surface roughness satisfying the following conditions. A method for producing a polyester film, comprising using a ceramic roll. (1) 0.1 μm ≧ Ra (2) The maximum height of the part that is convex from the center line is 0.5 μm or less. (3) The maximum depth of the part that is concave from the center line is 1.0 μm or less. The center line average roughness and the center line are lines formed by filling peaks and valleys in the roughness profile curve.