JP2006077146A - Polyester film for protecting and releasing liquid crystal display plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for mold-releasing, usable for protecting a liquid crystal display plate such as a polarizing plate and a retardation plate, causing very little oligomer precipitation and having good transparency. <P>SOLUTION: The polyester film for protecting and releasing liquid crystal display plates has a polyester layer containing a titanium compound and a phosphorus compound simultaneously satisfying formula (1); 0<W<SB>Ti</SB>≤20, and formula (2); 1≤W<SB>p</SB>≤300. Wherein, W<SB>Ti</SB>is the titanium content (ppm) of the polyester layer; and W<SB>p</SB>is the phosphorus content (ppm) of the polyester layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyester film, and more particularly to a polyester film for protecting and releasing a liquid crystal display panel in which oligomer precipitation is small.

  Polyester films represented by polyethylene terephthalate and polyethylene naphthalate have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc. It is used in applications. However, as the uses diversify, the processing conditions and use conditions of the film diversify, and when the polyester film is heat-treated, there is a problem that the oligomer exuding from the inside is deposited on the film surface. . When oligomer deposition on the film surface is intense, various problems occur, such as oligomers adhering to the process during the film processing and becoming contaminated, or being unable to be used for applications requiring high transparency.

  Conventionally, as a method of preventing oligomer precipitation, the oligomer contained in the raw material is reduced by solid phase polymerization (Patent Document 1), and the hydrolysis resistance of the polyester film is improved by using a terminal blocker. And so on. However, even if it is a solid-phase polymerized raw material, depending on the film production conditions, the effect is not seen because the oligomer is produced as a by-product due to heating, etc. Has not reached. In addition, when a terminal blocking agent is used, there is a risk of the occurrence of foreign matters due to the terminal blocking agent, the coloring of the polymer, the deterioration of the solid phase polymerization property, and the like.

2. Description of the Related Art Conventionally, release films based on polyester films have been used for various applications such as liquid crystal display plate protection and ceramic release. As a problem in using the release film, oligomers that precipitate on the surface of the release layer or the surface on which the release layer is not provided at high temperatures may cause various problems in the production process.
When the release film is used, for example, for protecting a liquid crystal display panel, the production process includes a process in which the release film and the polarizing substrate are bonded to each other via a pressure-sensitive adhesive layer and wound into a roll shape. It is considered that the oligomer precipitates in the drying process after applying the agent. When the oligomer deposited on the surface of the release layer is transferred to the surface of the opposite adhesive layer to which it is bonded, and the polarizing substrate with the adhesive layer to which the oligomer is adhered is bonded to a glass substrate, the LCD of the resulting LCD There may be a problem such as a decrease in luminance.
In recent years, there is a tendency to increase the brightness of the display screen for the purpose of improving the visibility of the LCD, and the above problem has become a serious problem.

Furthermore, in the release film, transparency may be required for use, and examples thereof include a polarizing plate and an inspection process at the time of producing a retardation plate. In the inspection process, visual inspection or use of a magnifying glass is used. At present, measures are taken to prevent the outflow of defective products. However, if the release film is not sufficiently transparent, it is easy to overlook the foreign matter mixed in the product. The problem is that the rate will increase.
JP 2003-119271 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that it can be used for protecting a liquid crystal display panel such as a polarizing plate and a retardation plate. It is providing the polyester film for mold release.

  As a result of intensive investigations in view of the above problems, the present inventors have found that a polyester film having a specific configuration is a polyester film that is particularly suitable for liquid crystal display panel protective mold release applications without impairing excellent film properties. The present invention has been found out and can be completed.

That is, the gist of the present invention resides in a polyester film for protecting and releasing a liquid crystal display panel, characterized by having a polyester layer containing a titanium compound and a phosphorus compound in amounts satisfying the following formulas (1) and (2). .
0 <W _Ti ≦ 20 (1)
1 ≦ W _P ≦ 300 (2)
(In the _{formula, W Ti} is titanium element content of the polyester layer (ppm), _{W P} denotes phosphorus content of the polyester layers in (ppm))

Hereinafter, the present invention will be described in detail.
The polyester film referred to in the present invention is a film stretched as necessary after cooling a molten polyester sheet extruded by a so-called extrusion method that is melt-extruded from an extrusion die.

  The polyester constituting the film of the present invention is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. The polyester used may be a homopolyester or a copolyester. In the case of a copolyester, it may be a copolymer containing 30 mol% or less of the third component. The dicarboxylic acid component of the copolymer polyester is selected from isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, P-oxybenzoic acid, etc.) and the like. The glycol component includes one or more selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

  At least one layer of the polyester film of the present invention needs to contain both a titanium compound and a phosphorus compound. The titanium element content in at least one layer of the film of the present invention needs to be 20 ppm or less, preferably 10 ppm or less, and the lower limit is usually 1 ppm, preferably 2 ppm. When there is too much content of a titanium compound, an oligomer is by-produced in the process of melt-extruding polyester, and a film having high transparency with a low oligomer cannot be obtained. Further, when no titanium element is contained, the productivity at the time of production of the polyester raw material is inferior, and the polyester raw material reaching the target degree of polymerization cannot be obtained. On the other hand, the amount of phosphorus element needs to be 1 ppm or more, preferably 5 ppm or more, and the upper limit is 300 ppm, preferably 200 ppm, more preferably 100 ppm. By containing a specific amount of the above-described titanium compound and containing a phosphorus compound, it is possible to exert a remarkable effect on the reduction of the contained oligomer. When there is too much content of a phosphorus compound, gelatinization will occur and it may become a foreign material and cause the quality of a film to fall. In the present invention, when the titanium compound and the phosphorus compound are contained in the above-described range, the by-product of the oligomer can be prevented, and the effect of the present invention is highly obtained.

  Further, the layer containing the titanium compound and the phosphorus compound preferably contains no antimony element, usually 100 ppm or less, preferably 60 ppm or less, and most preferably substantially free, ie 10 ppm or less. If the amount of the antimony element is too large, it may be reduced by the phosphorus compound during melt extrusion and aggregate to cause foreign matters, or the film may become dark and the transparency may be impaired.

  In the polyester film of the present invention, the polyester constituting the layer containing the titanium compound and the phosphorus compound within the above-mentioned range may be obtained by a melt polymerization reaction. If the raw material obtained by solid phase polymerization is used, the amount of oligomers contained in the raw material can be reduced, so that it is preferably used.

  In the polyester film of the present invention, the amount of the oligomer contained in the layer containing the titanium compound and the phosphorus compound within the aforementioned range is preferably 0.7% by weight or less, more preferably 0.5% by weight or less, particularly preferably. 0.3 wt% or less. When the amount of oligomer in the polyester layer is small, the amount of oligomer contained in the polyester film of the present invention is reduced and the effect of preventing oligomer precipitation on the film surface is particularly high.

  In the present invention, it may be a film having a structure obtained by coextrusion laminating a polyester having a low oligomer content on the surface of at least one side of a layer composed of a polyester having a normal oligomer content. The effect of suppressing oligomer precipitation obtained in the present invention can be exhibited to a high degree.

In the present invention, when the film is heat-treated at 180 ° C. for 10 minutes, the oligomer precipitation amount on the film surface is usually 5.0 mg / m ² or less, preferably 3.0 mg / m ² or less, more preferably Is 1.0 mg / m ² or less. In the present invention, the amount of oligomer on the film surface after applying methyl ethyl ketone to the film, drying and heat-treating at 180 ° C. for 10 minutes is 5.0 mg / m ² or less, preferably 3.0 mg / m ^2. Hereinafter, it is more preferably 1.0 mg / m ² or less. The amount of oligomer here refers to the amount of cyclic trimer (polyester-derived oligomer) measured by the method described later. When the amount of oligomer deposition on the film surface exceeds 5.0 mg / m ² , problems such as deterioration in film haze and adhesion and deposition of oligomers on a transport roll that comes into contact with the film in the coating process occur.

The difference (ΔH) between the film haze (H) after heat-treating the film of the present invention at 180 ° C. for 60 minutes and the film haze (H ₀ ) before heat treatment is preferably 5.0% or less, more preferably 3 0.0% or less, particularly preferably 1.0% or less. When ΔH exceeds 5.0%, there is a risk that the application may be limited, for example, it cannot be used in a field requiring high transparency.

  In the polyester obtained by the present invention, a weathering agent, a light-proofing agent, an antistatic agent, a lubricant, a light-shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, and a heat-stabilizing agent as long as the gist of the present invention is not impaired. You may mix | blend an agent and coloring agents, such as dye and a pigment. In addition, for the purpose of improving the slipperiness and abrasion resistance of the film, inert inorganic or organic fine particles can be blended with the polyester as necessary.

  Examples of the particles to be blended in the film include silicon oxide, alumina, calcium carbonate, kaolin, titanium oxide, and crosslinked polymer fine powder as described in JP-B-59-5216. These particles may be used alone or in combination of two or more components. And the content is 1 weight% or less normally, Preferably it is 0.01 to 1 weight%, More preferably, it is the range of 0.02 to 0.5 weight%. When the content of the particles is small, the film surface is flattened and the winding characteristics in the film production process tend to be inferior. Further, when the content of the particles exceeds 1% by weight, the degree of roughening of the film surface becomes too large, and the transparency may be impaired.

  Although the average particle diameter of the particle | grains contained in a polyester film is not specifically limited, Usually, 0.02-5 micrometers, Preferably it is 0.02-3 micrometers, More preferably, it is the range of 0.02-2 micrometers. . When the particle size is less than 0.02 μm, the film surface becomes flat and the winding properties in the film production process tend to be inferior. Moreover, when a particle size exceeds 5 micrometers, the degree of the roughening of the film surface becomes large too much, and the transparency of a film may be impaired. On the other hand, in order to improve the transparency of the film, when a laminated film of two or more layers is used, a method of blending particles only in the surface layer is also preferably employed. In this case, the front layer is at least one of the front and back layers, and of course, it is conceivable to mix particles in both the front and back layers.

  In the present invention, the method of blending the particles with the polyester is not particularly limited, and a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after the transesterification reaction. The condensation reaction may proceed. A method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder Etc.

  The thickness of the film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 4 to 50 μm, preferably 9 to 38 μm. Further, the thickness of the layer containing titanium element and phosphorus element is preferably 0.5 μm or more, more preferably 1 μm, and particularly preferably 2 μm or more.

  When the present invention is formed as a laminated film, the layer containing titanium element and phosphorus element is preferably at least the outermost layer, and there may be a case where either one side, both outermost layers, or the inner layer also has an approximate layer. .

Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.
First, although the preferable example of the manufacturing method of polyester used by this invention is demonstrated, this invention is not necessarily limited to this. Here, an example in which polyethylene terephthalate is used as the polyester is shown, but the production conditions differ depending on the polyester used. Bis-β-hydroxyethyl terephthalate (BHT) is obtained by esterification from terephthalic acid and ethylene glycol or transesterification of dimethyl terephthalate and ethylene glycol according to a conventional method. Next, it is transferred to this BHT polymerization tank, the temperature is raised while reducing the pressure, and finally the polymer is heated to 280 ° C. under vacuum to advance the polymerization reaction to obtain a polyester.

  The intrinsic viscosity of the polyester used in the present invention is usually in the range of 0.40 to 0.90, preferably 0.45 to 0.80, more preferably 0.50 to 0.70. When the intrinsic viscosity is less than 0.40, the mechanical strength of the film tends to be weakened. When the intrinsic viscosity is more than 0.90, the melt viscosity becomes high, the load on the extruder is increased, and the production cost is increased. Problems may occur.

  Next, for example, the polyester chip obtained as described above and dried by a known method is supplied to a melt-extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer and melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed. In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 2 to 90 to 160 ° C. in the lateral direction. It is preferable to perform ~ 6 times stretching and heat treatment at 150 to 240 ° C for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary. Furthermore, it is also possible to perform simultaneous biaxial stretching of the unstretched sheet so that the area magnification is 10 to 40 times.

  A so-called in-line coating, in which the film surface is treated during the stretching process, can also be applied. Although it is not limited to the following, for example, after the first stage of stretching, before the second stage of stretching, improvement of antistatic property, slipperiness, adhesion, etc., improvement of secondary workability, etc. For the purpose, a coating treatment with an aqueous solution, an aqueous emulsion, an aqueous slurry or the like can be performed.

  According to the present invention, it is possible to provide a particularly suitable polyester film, which is used for protecting a liquid crystal display panel such as a polarizing plate and a retardation plate, and is capable of providing a particularly suitable polyester film. The industrial value of the present invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. In the examples and comparative examples, “parts” means “parts by weight”. The measuring method used in the present invention is as follows.

(1) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Average particle diameter (d50)
The particle size was measured by a sedimentation method based on Stokes' resistance law using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 manufactured by Shimadzu Corporation.

(3) Oligomer (cyclic trimer) content in polyester film layer A predetermined amount of polyester layer is mixed with chloroform / 1,1,1,3,3,3-hexafluoro-2-propanol (mixing ratio: 3/2). ) After dissolving in the mixed solution, reprecipitated with chloroform / methanol (mixing ratio: 2/1) and filtered to remove linear polyethylene terephthalate, and then the solvent in the obtained filtrate was removed using an evaporator. After evaporation, the resulting precipitate was dissolved in a predetermined amount of DMF. The obtained DMF was supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer (cyclic trimer) contained in the polyester, and this value was divided by the amount of polyester used for measurement to obtain a polyester film. The amount of oligomer (cyclic trimer) contained therein. The amount of oligomer (cyclic trimer) determined by liquid chromatography was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by weighing a preliminarily collected oligomer (cyclic trimer) and dissolving it in a weighed DMF (dimethylformamide). The conditions for the liquid chromatograph were as follows.

Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: MCI GEL ODS 1HU manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(4) Amount of oligomer on film surface after solvent treatment After applying methyl ethyl ketone to the polyester film surface and drying in a hot air circulation oven at 120 ° C for 1 minute in a nitrogen atmosphere, this film was circulated in a hot air at 180 ° C in a nitrogen atmosphere. The polyester film was treated for 10 minutes in an oven. The surface of the polyester film after heat treatment was brought into contact with DMF for 3 minutes to dissolve the oligomer deposited on the surface. For this operation, for example, the method described in the elution apparatus used for the single-side elution method in the elution test can be adopted in the voluntary standard for food containers and packaging made of synthetic resin such as polyolefin. Next, the concentration of the obtained DMF was adjusted by a method such as dilution as necessary, and the resulting DMF was supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer in DMF, and this value was contacted with DMF. Divided by the film area, the amount of oligomer on the film surface (mg / m ² ) was obtained. The amount of oligomer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method).

  The standard sample was prepared by weighing a preliminarily collected oligomer (cyclic trimer) and dissolving it in a weighed DMF (dimethylformamide). The concentration of the standard sample is preferably in the range of 0.001 to 0.01 mg / ml. The conditions of the liquid chromatograph were as follows.

Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: MCI GEL ODS 1HU manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(5) Film haze (H)
In a nitrogen atmosphere, the polyester film was allowed to stand in an oven at 180 ° C. for 60 minutes and subjected to heat treatment according to JIS-K7105, using an integrating sphere turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. ) Was measured. The difference in film haze (ΔH) before and after the heat treatment was obtained by subtracting the turbidity (H ₀ ) of the polyester film before the heat treatment from (H).

(6) Determination of amount of metal element and phosphorus element in film Using a fluorescent X-ray analyzer (model “XRF-1500”, manufactured by Shimadzu Corporation), the film FP method was used. The amount of elements in the film was determined by sheet measurement, and the detection limit in this method is usually about 1 ppm.

<Production of polyester (A0) and (A1)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, adding tetrabutoxy titanate as a catalyst to the reactor, setting the reaction start temperature to 150 ° C., and gradually increasing the reaction temperature as methanol is distilled off. It was 230 degreeC after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. This reaction mixture was transferred to a polycondensation tank, and an ethylene glycol slurry of silica particles having an average particle size of 2.5 μm was added so that the content of the particles with respect to polyester was 0.06% by weight, and a polycondensation reaction was performed for 4 hours. went. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.55 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (A0). The intrinsic viscosity was 0.55. The obtained polyester chip was subjected to solid phase polymerization at 220 ° C. under vacuum to obtain polyester (A1) having an intrinsic viscosity of 0.65.

<Manufacture of polyester (B1)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate / tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is set to 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. Was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. This reaction mixture was transferred to a polycondensation tank, orthophosphoric acid was added, and germanium dioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester (B1) chip. The intrinsic viscosity of the polyester (B1) was 0.63.

<Manufacture of film>
A raw material in which the polyester (A1) chip and the polyester (B1) chip are blended at a ratio of 95 parts by weight and 5 parts by weight, respectively, is melt-extruded at 290 ° C. with a vented twin-screw extruder, and an electrostatic application adhesion method is used Then, it was cooled and solidified on a cooling roll whose surface temperature was set to 40 ° C. to obtain an unstretched sheet. Next, the film was stretched 3.7 times in the longitudinal direction at 83 ° C., then led to a tenter, stretched 3.9 times in the lateral direction at 110 ° C., and further heat treated at 220 ° C. to obtain a polyester film having a thickness of 25 μm. . The amount of oligomer in the obtained film was 0.64% by weight, and the contents of antimony, titanium and phosphorus were 0 ppm (below the lower limit of detection), 5 ppm and 50 ppm, respectively. Hereinafter, the oligomer amounts, antimony, titanium, and phosphorus element contents in the films obtained in the respective Examples and Comparative Examples are shown in Table 2 below.

  In Example 1, a polyester (A2) chip having an intrinsic viscosity of 0.67 was obtained by changing the solid-state polymerization time for the obtained polyester (A0) chip in the same manner as the polyester (A1) chip. . In Example 1, a polyester film was obtained in the same manner as in Example 1 except that a polyester (A2) chip was used instead of the polyester (A1) chip used.

  In Example 1, a polyester (A3) chip having an intrinsic viscosity of 0.68 was obtained by changing the solid phase polymerization time of the obtained polyester (A0) chip in the same manner as the polyester (A1) chip. . In Example 1, a polyester film was obtained in the same manner as in Example 1 except that a polyester (A3) chip was used instead of the polyester (A1) chip used.

  In Example 1, except that the polyester (A1) chip and the polyester (B1) chip used were blended at a ratio of 95 parts by weight and 5 parts by weight, in place of the polyester (A1) chip only. A polyester film was obtained in the same manner as in 1.

  In Example 3, a polyester film was obtained in the same manner as in Example 3 except that a polyester (A2) chip was used instead of the polyester (A1) chip used.

(Comparative Example 1)
In the production of polyester (B1), a polyester (B2) chip having an intrinsic viscosity of 0.62 was obtained in the same manner as in the general production method except that the addition amount of normal phosphoric acid was changed. In Example 1, a polyester film was prepared in the same manner as in Example 1 except that the polyester (A2) chip and the polyester (B2) chip were used instead of the polyester (A1) chip and the polyester (B1) chip used. Obtained. In the obtained film, a foreign substance that was thought to be caused by a gelled product was generated, and the quality of the film was somewhat inferior, so that it could not be used for limited advanced applications.

(Comparative Example 2)
A polyester (A3) chip having an intrinsic viscosity of 0.56 was obtained in the same manner as in the general production method except that the amount of tetrabutoxy titanate was changed in the production of the polyester (A0). In Example 1, a polyester film was obtained in the same manner as in Example 1 except that a polyester (A3) chip was used instead of the polyester (A1) chip used.

(Comparative Example 3)
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding ethyl acid phosphate to this reaction mixture, it was transferred to a polycondensation tank, and an ethylene glycol slurry of silica particles having an average particle diameter of 2.5 μm was added so that the content of the particles with respect to polyester was 0.06 wt%. Then, antimony trioxide was added and a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester chip. The intrinsic viscosity of this polyester was 0.63. The obtained polyester chip was subjected to solid phase polymerization at 220 ° C. under vacuum to obtain a polyester (C) having an intrinsic viscosity of 0.67.

  Polyester (C) was melt-extruded at 290 ° C with a vented twin-screw extruder, and cooled and solidified on a cooling roll having a surface temperature set to 40 ° C using an electrostatic application adhesion method to obtain an unstretched sheet. . Next, the film was stretched 3.7 times in the longitudinal direction at 83 ° C., then led to a tenter, stretched 3.9 times in the lateral direction at 110 ° C., and further heat treated at 220 ° C. to obtain a polyester film having a thickness of 25 μm. .

  The film of the present invention can be suitably used, for example, as a liquid crystal display panel protective release film.

Claims (1)

A polyester film for protecting and releasing a liquid crystal display panel, comprising a polyester layer containing a titanium compound and a phosphorus compound in amounts satisfying the following formulas (1) and (2) simultaneously.
0 <W _Ti ≦ 20 (1)
1 ≦ W _P ≦ 300 (2)
(In the _{formula, W Ti} is titanium element content of the polyester layer (ppm), _{W P} denotes phosphorus content of the polyester layers in (ppm))