JPH06313095A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain a biaxially oriented polyester film having high transparency and excel lent slipperiness and sui table as a general packaging film. CONSTITUTION:This biaxially oriented polyester film comprises a polyester containing 50-75ppm of silica particles and inner particles containing calcium element and phosphorus element, the content of the calcium element being 0.01-0.1wt.%, and the content of the phosphorus element being 0.5-2 times moles that of the calcium element, has projections having the maximum diameter of <=5mum in a rate of 20-60 projections/mum<2> on the surface of the film, and further preferably has a Haze of <=2%/10mum and a dynamic friction coefficient of <=0.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched polyester film used in various packaging materials and the like, and more particularly to a biaxially stretched polyester film having excellent slipperiness and transparency.

[0002]

2. Description of the Related Art Biaxially stretched films made of polyester typified by polyethylene terephthalate have excellent physical properties such as transparency, mechanical strength and dimensional stability, and chemical properties such as chemical resistance. Widely used in various applications such as magnetic tapes, capacitors, and food packaging. In particular, in the case of a film for magnetic tape, when sufficient slipperiness is not obtained, running stability, deterioration of tape life due to abrasion, and deterioration of quality due to surface scratches are greatly promoted, so running stability is improved. In terms of wear resistance, high slipperiness is required. Also, in general packaging films such as food packaging films, it is necessary to have a certain level of slipperiness in the manufacturing process or processing process, and if sufficient slipperiness is not obtained, in the winding process. Problems such as wrinkles, deterioration of winding shape, and deterioration of quality are likely to occur.

However, the polyester film is
Although it is excellent in its physical properties and chemical properties, it has a high friction coefficient due to the resin properties and is not sufficient in terms of slipperiness. Therefore, for the purpose of improving the slipperiness of the polyester film, a method of appropriately roughening the film surface is used. As a method of surface roughening, an external particle method of adding inorganic fine particles having a refractive index similar to that of polyester during the polymerization step of polyester, and an internal particle method of precipitating particles in the polymer during the condensation step of polyester have been proposed. There is.

[0004]

The external particle method is to add inorganic fine particles inactive to polyester such as calcium carbonate, titanium dioxide, calcium phosphate, etc., and the polyester film added with these inorganic fine particles is stretched. As a result, the inorganic fine particles are not destroyed or deformed, and relatively sharp protrusions are formed on the film surface to obtain high slipperiness. However, since these inorganic fine particles have a poor affinity with polyester, due to the generation of voids around the particles during stretching of the film, the inorganic fine particles are easily separated from the film surface, and a white powder substance is generated on the film surface. I have a problem. The external particle method also has a problem that the transparency of the film is impaired even when a small amount of inorganic fine particles is added.

Therefore, attempts have been made to solve these problems by using silica particles having a relatively good affinity with polyester, but the silica particles have poor dispersibility in polyester, There is a problem that particles are easily aggregated during the production of polyester, a large number of coarse particles are formed on the film surface, and the transparency of the film is deteriorated. On the other hand, the internal particle method is an application of the catalyst residue or the like that precipitates during polyester production, and it is difficult to control the amount of particles that precipitate and the particle size, and it is also difficult to suppress the formation of coarse particles. Have Also, by stretching the film,
In some cases, the internal particles are easily broken, so that sufficient slip properties cannot be obtained. An object of the present invention is to provide a biaxially stretched polyester film having transparency, which has sufficient slipperiness and can also be used as a general packaging film that requires high transparency. is there.

[0006]

In view of such circumstances, the inventors of the present invention have earnestly studied a method for imparting high slipperiness without impairing the transparency of the polyester film, and as a result, have reached the present invention. Is. That is, the biaxially stretched polyester film of the present invention contains 50 to 750 pp of internal particles containing calcium element and phosphorus element.
m of silica particles, the content of calcium element is 0.01 to 0.1% by weight, and the content of phosphorus element is 0.5 to 2 times equivalent in terms of element amount ratio to calcium element. The projections having a maximum diameter of 5 μm or less are present on the film surface at a density of 20 to 60 / μm ² .

The polyester resin used in the biaxially stretched polyester film of the present invention is a dicarboxylic acid component containing at least one aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid or an ester-forming derivative thereof. And a diol component containing at least one of ethylene glycol, butanediol, cyclohexanedimethanol, diethylene glycol, propylene glycol, triethylene glycol, neopentyl glycol, an ethylene oxide adduct of a bisphenol compound or its derivative as a main component. A polyester resin in which 80% or more of the repeating units are ethylene terephthalate is preferable. In addition,
Examples of the ester-forming derivative of aromatic dicarboxylic acid include dialkyl ester and diaryl ester of aromatic dicarboxylic acid. Further, in the present invention, a third component other than the above, such as an aliphatic dicarboxylic acid such as glutaric acid, adipic acid, sebacic acid, oxalic acid or succinic acid, may be contained.

These polyester resins can be produced by a known direct polymerization method, transesterification method or the like, and the degree of polymerization thereof is not particularly limited, but the intrinsic viscosity (phenol / Measured in a mixed solution of tetrachloroethane and the like at 25 ° C) is 0.5 to
It is preferably about 1.2 dl / g. In the present invention, the polyester contains internal particles containing calcium element and phosphorus element and silica particles, the particles containing calcium element and phosphorus element is a calcium compound added to the reaction system during the production of polyester It is an internal particle deposited by a phosphorus compound.

The calcium compound added to the reaction system includes inorganic compounds such as hydroxides, oxides, carbonates and hydrogen carbonates, and organic acid salts such as acetates, propionates, butyrates and stearates. Can be used. Calcium becomes a core of internal particle formation by reacting with phosphorus, and if the addition amount is increased, the slip property of the film is improved, but since calcium accelerates thermal decomposition of the polymer,
These calcium compounds are added so that the content of the calcium element is 0.01 to 0.1% by weight. This is because when the content of the elemental calcium exceeds 0.1% by weight, the polymer is likely to be thermally decomposed in the polymerization step, a polymer having a high degree of polymerization cannot be obtained, and the polymer is colored. This is because if the element content is less than 0.01% by weight, a film having sufficient slipperiness cannot be obtained.

The phosphorus compound used in the present invention includes
Phosphoric acid, phosphorous acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite and the like can be mentioned, and these can be used alone or in combination of two or more kinds. Can be used. Since the internal particles are formed through the reaction between calcium and phosphorus, addition of a certain amount or more of phosphorus compound relative to the amount of calcium element causes excess phosphorus to react with the metal oxide added as the condensation polymerization catalyst. Therefore, the phosphorus compound is added so that the amount of the phosphorus element becomes 0.5 to 2 times the equivalent amount with respect to the calcium element. This is because if the element amount ratio to the calcium element is less than 0.5 times the equivalent amount, internal particles corresponding to the added calcium element are not formed and the unreacted calcium element causes thermal decomposition of the polymer. Becomes
This is because a polymer having a high degree of polymerization cannot be obtained and the polymer is colored. In addition, when the elemental ratio of phosphorus element to the elemental calcium exceeds twice, the excess phosphorus also reacts with the metal oxide added as the condensation polymerization catalyst to inhibit the polymerization, resulting in a polymer having a high degree of polymerization. Is not obtained, or the polymerization time becomes extremely long, which accelerates oxidative decomposition and thermal decomposition of the polymer, resulting in deterioration of quality.

Although silica particles having different hardness and refractive index can be obtained depending on the manufacturing method, in the present invention, those having a refractive index close to that of polyester are preferable, and in order to prevent the particles from falling off from the film surface, Preference is given to silica particles prepared by the wet method, which have a high affinity with polyester. Further, the silica particles are 50 to 750 pp.
added in the range of m, preferably 100 to 300 ppm
Is the range. This is because if the silica particles are less than 50 ppm, sufficient slidability cannot be obtained.
This is because when it exceeds, the transparency of the film is deteriorated due to the formation of coarse particles. In the present invention, by incorporating silica particles together with the internal particles, it is possible to maintain sufficient slipperiness even when a high load is applied, without impairing the transparency of the film.

The biaxially stretched polyester film of the present invention is formed, for example, by the following method. First, after drying the polyester resin, 270 to 300
The raw film is formed by melt-extrusion at about 0 ° C. and by a casting method or a calendering method. Next, this raw film is stretched in the machine direction and the transverse direction at a temperature of about 80 to 120 ° C. The film is stretched by a method such as simultaneous biaxial stretching or sequential biaxial stretching, and either the longitudinal direction or the transverse direction may be stretched first. If necessary, the biaxially stretched polyester film can be heat-treated at a temperature of 200 to 240 ° C. to fix the orientation by crystallization and improve the dimensional stability.

It is important that the biaxially stretched polyester film thus obtained has protrusions having a maximum diameter of 5 μm or less at a density of 20 to 60 protrusions / μm ^{2 on} the surface thereof. Here, the projections present on the film surface are projections caused by particles protruding on the film surface, and the particles themselves are covered with a thin resin layer without being exposed on the film surface. This is because the maximum diameter of the protrusions is 5 μm or less, and when the maximum diameter exceeds 5 μm, the appearance of the film is impaired and the slipperiness is reduced, which may cause the particles to fall off. Further, it is important that the density of the protrusions is in the range of 20 to 60 protrusions / μm ^{2 in} order to exhibit good transparency and dynamic friction. This has a density of 20 pieces / μm ²
Less protrusion distance becomes long in is because the slip properties when a strong force as such winding work in the film-forming process is applied is extremely lowered, 60 to reverse / [mu] m ² by weight, the film This reduces the transparency.

In the biaxially stretched polyester film of the present invention, it is preferable that the haze of the film is 2% / 10 μm or less and the dynamic friction coefficient between the same films is 0.5 or less. This is because in general packaging films, the back surface of the film is often printed, and in this case, the print is seen through the film, and when the haze of the film exceeds 2% / 10 μm, the film is printed. This is because the transparency of the image is reduced and the print cannot be seen clearly. Further, when the coefficient of dynamic friction is 0.5 or less, good manufacturing stability is exhibited, and no problem occurs in the processing step.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples. In the example, the protrusion diameter was measured by using a surface roughness meter manufactured by Kosaka Laboratory, by enlarging the longitudinal direction and the lateral direction by 200 times and the height direction by 20000 times, and based on the appearing convex portion. The line diameter was corrected to obtain the projection diameter. The density of the protrusions was measured by measuring the surface roughness per 1 μm ^{2 in} the same manner as the diameter of the protrusions to measure the number of protrusions, and was shown as an average value measured at 5 points.
As the haze, the haze of a film having a thickness of 10 μm was measured using a haze meter manufactured by Tokyo Denshoku Co., Ltd. The dynamic friction coefficient was measured using a surface tester manufactured by Shinto Kagaku Co., Ltd., with the same film attached to each of the fixed part and the movable part.

Example 1 Terephthalic acid and ethylene glycol were placed in a reaction vessel equipped with a rectification column and a stirrer and stirred while stirring 260
The temperature was gradually raised to ℃, the esterification was carried out while the distilled water was discharged to the outside of the system, and BHT (bis (2
-Hydroxyethyl terephthalate)) was obtained. The obtained BHT was transferred to a polycondensation reaction vessel, and a 2 wt% ethylene glycol solution of calcium acetate monohydrate was added so that the amount of calcium element in BHT was 225 ppm.
After a lapse of minutes, a 10 wt% ethylene glycol solution of trimethyl phosphate was added so that the amount of elemental phosphorus in BHT was 150 ppm. Then, after 10 minutes, an ethylene glycol solution of antimony trioxide was added by a conventional method,
After a lapse of 10 minutes, an ethylene glycol dispersion of silica particles synthesized by a wet method was added to silica in BHT for 20 minutes.
It was added so as to be 0 ppm. After 30 minutes, decompression and temperature increase were started, and polycondensation was performed at a vacuum degree of 1 mmHg or less and a temperature of 290 ° C. for 3 hours to obtain polyethylene terephthalate having an intrinsic viscosity of 0.672.

1 of the obtained polyethylene terephthalate was used.
After vacuum drying at 20 ° C. for 10 hours, a film having a thickness of 150 μm was formed using an extruder. The obtained sheet was stretched 3.5 times in the machine direction at a temperature of 90 ° C. using a stretching machine,
Then, it was stretched 3.5 times in the transverse direction to prepare a polyester film having a thickness of 12 μm. Table 1 shows the measured values of the content of calcium element, the content of phosphorus element, the ratio of the elemental ratio of phosphorus element to the calcium element, the content of silica particles, the maximum protrusion diameter, the protrusion density, the dynamic friction coefficient and the haze of the obtained film. It was shown to.

Examples 2 to 3 and Comparative Examples 1 to 4 Polyethylene terephthalate was obtained by carrying out polycondensation in the same manner as in Example 1 except that the addition amounts of calcium acetate, trimethyl phosphate and silica particles were changed. Using the obtained polyethylene terephthalate, film formation and stretching were performed in the same manner as in Example 1 to produce a 12 μm-thick polyester film. Content of calcium element of the obtained film, content of phosphorus element, elemental ratio of phosphorus element to calcium element, content of silica particles, maximum projection diameter,
Table 1 shows the measured values of the protrusion density, the coefficient of dynamic friction, and the haze.

[0019]

[Table 1]

[0020]

INDUSTRIAL APPLICABILITY The biaxially stretched polyester film of the present invention has high transparency and excellent slipperiness, and is excellent in practicality as a general packaging film, particularly a packaging film for printing. It is a thing.

Front page continuation (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C08K 5/51 KKD 7242-4J // B29K 67:00 B29L 7:00 4F

Claims (2)

[Claims] 1. Internal particles containing calcium and phosphorus elements and silica particles of 50 to 750 ppm are contained, and the content of calcium element is 0.01 to 0.1% by weight.
In addition, the content of the phosphorus element is 0.5 to 2 times equivalent of the element amount ratio with respect to the calcium element, and the projections having a maximum diameter of 5 μm or less are present on the film surface at a density of 20 to 60 pieces / μm ^2. A biaxially stretched polyester film characterized by being. 2. The biaxially stretched polyester film according to claim 1, which has a haze of 2% / 10 μm or less and a dynamic friction coefficient of 0.5 or less.