JPH06226894A - White polyester film - Google Patents

Abstract

PURPOSE:To obtain a white polyester film which has excellent thermal dimensional stability, low specific gravity, flexibility, cushioning properties and thermal dimensions and in which folding wrinkle is scarcely formed. CONSTITUTION:A white polyester film comprises at least two layers, wherein one of them (named 'an A layer') is formed of a film formed of composition mixture of composition mixture of polyester (a), polymer (b) non-compatible with the polyester and polyester polyether copolymer (c), at least one side (named 'a B layer') is formed of polyester (a), and polyester polyether copolymer (d), fine bubbles are contained in the A layer to be whitened, and an apparent specific gravity is 0.5 to 1.1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white polyester film having a low specific gravity, good cushioning properties, flexibility, and excellent wrinkle resistance. Further, a coating layer may be provided on the surface layer of the white polyester film, or the white polyester film and the paper may be laminated and used.

In particular, printing substrates, packaging, cards, labels,
The present invention relates to a white polyester film used as a base material such as a receiving paper for a video printer, a printing paper, a display plate, a reflection plate base material for an area light source, an X-ray photographic film, and a release paper for ceramic molding.

[0003]

It is well known that white polyester is obtained by adding a large amount of titanium dioxide or calcium carbonate to polyester. It is also well known to add a polyolefin and an alkylene glycol or a polyalkylene polyester copolymer to polyester to obtain a white polyester film.

[0004]

However, a film obtained by adding a large amount of an inorganic substance such as titanium dioxide or calcium carbonate to polyester can impart whiteness,
There was a problem in applications where the specific gravity could not be reduced and the film became stiff and required cushioning properties.

When polypropylene is added,
Compared with the case where an inorganic substance is added, the hardness of the film itself is relaxed, but the thermal dimensional property is poor. In addition, when polymethylpentene is added, the thermal dimensional properties of the film are improved as compared with the case where polypropylene is added, but the flexibility is insufficient due to poor dispersibility, and creases are formed at some points. Cheap.

When polymethylpentene and polyalkylene glycol or polyalkylene glycol polyester copolymer are added, the dispersibility is improved, but the flexibility is still insufficient, so that wrinkles easily occur during handling. When this is used as a single layer, the interfacial tension of polyolefin is substantially lower than that of polyester,
There was a fatal defect that the surface tension of the film was lowered and the adhesiveness and printability were poor. In addition, since a film obtained by further laminating a polyester layer on the film in order to improve the adhesiveness and printability becomes poor in flexibility, the film is likely to be folded and wrinkled during handling.

That is, there has been no white polyester film having a low specific gravity, flexibility, cushioning property, thermal dimensional property, good polyester printability and adhesiveness, a high optical density, and little wrinkling.

[0008]

The present invention is excellent in thermal dimensional stability, low specific gravity, flexibility, cushioning property and thermal dimensional property,
Moreover, in order to obtain a white polyester film which is less likely to be wrinkled, at least two layers are formed, of which A layer is polyester (a), polyester incompatible polymer (b) and polyester polyether copolymer (c).
B is composed of a polyester (a) and a polyester-polyether copolymer (d).
A white polyester film having a apparent specific gravity of 0.5 or more and 1.1 or less, which is whitened by containing fine bubbles inside the layer A, and is a film made of a composition mixture containing

The polyester referred to in the present invention is a polymer obtained by polycondensation of a diol and a dicarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid phthalate, adipic acid,
It is represented by sebacic acid and the like. Also, with diol, ethylene glycol, trimethylene glycol,
Typical examples are tetramethylene glycol and cyclohexanedimethanol. Specifically, for example, polyethylene terephthalate (PET), polytetramethylene terephthalate (PBT), polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate (PCHDMT), polyethylene-2,6-naphthalene diene. Carboxylate (PEN)
And so on. In the case of the present invention, especially PET, PEN
Is preferred. Various known additives such as antioxidants and antistatic agents may be added to the polyester.

The incompatible polymer referred to in the present invention has the effect of being dispersed in the polyester by melt extrusion molding and causing interfacial peeling at the interface of the incompatible polymer dispersion in the subsequent stretching step to form voids. As an incompatible polymer, poly-3-
Methylbutene-1, poly-4-methylpentene-1, polyvinyl-t-butane, 1,4-trans-poly-2,
3-dimethylbutadiene, polyvinylcyclohexane,
Melting point selected from polystyrene, polymethylstyrene, polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t-butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride, polychlorotrifluoroethylene, etc. It is possible to raise the polymer above 200 ℃. In the case of the present invention, poly-4-methylpentene-1, cellulose triacetate and modified products thereof are particularly preferable in terms of price, heat stability, dispersibility with polyester and the like. Of course, the melting point of the incompatible polymer needs to be 200 ° C. or higher, preferably 210 ° C. or higher, more preferably 220 ° C. or higher. This is because if the melting point is less than 200 ° C., the dispersed shape of the incompatible polymer in the polyester film does not have a spherical shape, but often takes a layered or flat shape, and a polyester film having high cushioning properties cannot be obtained. Further, the melting point of the incompatible polymer is 300 ° C. or lower, preferably 280 ° C. or lower, and more preferably 260 ° C. or lower. This is because the incompatible polymer does not melt unless it is lower than the melt extrusion temperature of polyester.

The amount of the incompatible polymer used in the layer A is 2 to 25% by weight, preferably 4 to 15% by weight.
Is. When the added amount is less than 2%, it is difficult to obtain a white polyester film of the present invention having an apparent specific gravity of 1.1 or less, and also a high cushioning white polyester having a cushion ratio of 10% or more is obtained. Is difficult. On the contrary, when the amount of the incompatible polymer added exceeds 25% by weight, not only the mechanical properties of the polyester film of the present invention are inferior but also the thermal dimensional stability is inferior and the heat shrinkage rate at 150 ° C. Will increase to 5% or more.

In the polyester polyether copolymer used in the present invention, the dispersion diameter of the incompatible polymer in the polyester is made small in the A layer so that the voids formed by stretching become fine and uniform, thereby imparting flexibility to the film and eventually breaking it. It has the effect of making wrinkles less likely to occur, and imparts the flexibility of polyester in the B layer, and has the effect of making it less likely to fold wrinkles. In addition, since it is a copolymer with polyester, it does not bleed out (precipitate) and has good printability and adhesiveness. For example, polyester used as a polyester-polyether copolymer is polyethylene terephthalate (PE
T), polytetramethylene terephthalate (PBT),
Polyethylene-p-oxybenzoate, poly-1,4
-Cyclohexylene dimethylene terephthalate (PCH
DMT), polyethylene-2,6-naphthalene dicarboxylate (PEN) and the like. The polyether used for copolymerization preferably has a molecular weight of 300 to 20,000, such as polyethylene glycol (PEG),
There are methoxy polyethylene glycol, polytetramethylene glycol (PTMG), polypropylene glycol (PPG) and the like. Preferred polyester polyether copolymers are PET-PEG, PBT-PTMG,
There is PCT-PPG. The copolymerization ratio of the polyester and the polyether is preferably 1: 9 to 9: 1 by weight, more preferably 4: 6 to 9: 1, further preferably 4: 6 to 6: 4. As a production method, a polyester-polyether copolymer can be produced by adding a polyether at an arbitrary stage when producing a polyester composed of an acid component and a glycol component.
The molecular weight of the polyether used is 400 to 20.
000 is desirable. It is preferably 1,000 to 10,000.

The amount of the polyester-polyether copolymer used in the layer A is 0.5 to 20% by weight, preferably 1 to 5% by weight. Addition amount is 0.5
If it is less than wt%, the incompatible polymer is not finely dispersed, the voids generated are large, and wrinkles are likely to occur in the film. On the other hand, when it exceeds 20% by weight, voids are less likely to be formed and the cushioning property becomes insufficient.

The amount of the polyester-polyether copolymer used in the layer B is 0.5 to 50% by weight, preferably 10 to 40% by weight. When the amount added is less than 0.5% by weight, the outer layer polyester is not sufficiently flexible and wrinkles easily occur. On the other hand, if it exceeds 50% by weight, roll stickiness occurs during stretching, and film formability deteriorates.

Inorganic particles may be added to the layer B in order to improve the winding property during film formation and to improve the optical characteristics of the surface. As the inorganic particles used in the B layer, those usually added to polyester can be used. Examples include calcium carbonate, titanium dioxide, barium sulfate, silica, alumina and the like. Although not limiting the present invention, the amount added is 0.01 to 30% by weight, preferably 0.01 to 20% by weight. When the amount added is less than 0.01% by weight, the film has poor slipperiness and poor handling. On the other hand, if it exceeds 30% by weight, the inorganic particles are scraped off during the stretching, and the roll is soiled. Without limiting the invention, the average particle size is about 0.1 to 10 μm, preferably about 0.5 to 5 μm.

The main component polyester in the layer A is 70
Weight% or more is good. If it is less than 70% by weight, it becomes difficult to exhibit the mechanical strength and heat resistance, which are advantages of the polyester film.

The amount of the incompatible polymer is larger than that of the polyester polyether copolymer. The addition amount is preferably twice or more. If the amount of incompatible polymer is less than the amount of polyester polyether copolymer added,
Voids are less likely to occur from the interface of incompatible polymer particles, and it becomes difficult to obtain a white polyester film having low specific gravity and high optical density.

Next, although not limiting the present invention, the whiteness of the present invention is 55% or more, preferably 80% or more,
More preferably, 90% or more is desirable. Whiteness is 55%
Below the range, it is difficult to take advantage of the special features of the white film.

Although the whiteness is changed by the addition of the above-mentioned incompatible polymer or polyester polyether copolymer, a fluorescent whitening agent containing an inorganic fluorescent agent may be added if necessary. The fluorescent whitening agents are trade names "Ubitech" OB,
MD (made by Ciba-Geigy), "OB-1" (made by Eastman), etc. are mentioned.

Although not limiting the present invention, the cushion ratio of the present invention is 10% or more, preferably 15% or more,
More preferably, it is 20% or more. Cushion rate is 10
When it is less than%, when it is used as a receiving paper for a video printer, for example, when the pressure of the thermal recording head is lowered, the contact with the head is hard and dots are missing, and a clear image cannot be transferred. Feels bad when you touch.

Although not limiting the present invention, the optical density of the white polyester film of the present invention in terms of 150 μm is preferably 0.7 or more and 1.6 or less, more preferably 0.8 or more and 1.6 or less, More preferably 1.0
The above is 1.6 or less. When the optical density is less than 0.7, the hiding property of the film is insufficient and the back side is transparent, which is not preferable.

As the laminated constitution of the white polyester film of the present invention, for example, two-layer constitution of A layer / B layer, B layer / A
It has a three-layer structure of layer / B layer and C layer / A layer / B layer. In this case, the layer A is a layer containing fine bubbles,
Layer B is a composition mixture layer composed of polyester (a) and polyester-polyether copolymer (d). Further, inorganic particles may be further added to the B layer. The C layer is a normal polyester resin layer. With such a configuration, while obtaining the target high whiteness and concealability by the layer A,
By the layers B and C, the wetting tension and adhesiveness on at least one side can be maintained at the same level as polyester. Further, by adding the polyester polyether copolymer (c) to the layer B, the flexibility of the layer B is improved, and as a result, folding wrinkles are less likely to occur and the appearance is improved.

Next, although not limiting the invention,
In the present invention, the incompatible polymer has a shape close to a sphere in the white polyester, that is, the shape factor is 1 to 4
It is desirable to be within the range. That is, when the shape of the immiscible polymer is close to a sphere, not only the specific gravity can be reduced as compared with the case where the incompatible polymer is dispersed in a layered shape or a flat shape, but also a film having a high cushion rate and good thermal dimension can be obtained.
The shape close to a sphere means the shape factor of the incompatible polymer dispersed in the film, that is, the ratio of the major axis to the minor axis is 1 to 4,
It is preferably 1 to 2.

The shape of the voids in the film is also correlated with the physical properties of the film, particularly the cushion rate, the hiding power, the whiteness and the occurrence of wrinkles. That is, the void lengths of the film in the machine axis direction and in the direction perpendicular to the machine axis are x (μ
m) and y (μm), the dispersion diameter of the incompatible polymer is a (μ)
m), it is desirable to satisfy the following and equations.

7 ≦ (xy / a ² ) ≦ 12 2 ≦ (x / a) ≦ 4 2 ≦ (y / a) ≦ 4

Next, a method for producing the white polyester film of the present invention will be described, but the method is not limited to such a method.

Polymethylpentene as the incompatible polymer and polytetramethylene terephthalate (PBT) -tetramethylene glycol (PTMG) copolymer as the polyester polyether copolymer were mixed with polyethylene terephthalate, and the mixture was thoroughly mixed, Let it dry, 2
It is supplied to the extruder A heated to a temperature of 70 to 300 ° C. Polytetramethylene terephthalate (PBT) -tetramethylene glycol (PTMG) copolymer as a polyester polyether copolymer and CaCO ₃ or the like as inorganic particles are mixed with polyethylene terephthalate and fed to the extruder B by a conventional method. In a T-die two-layer or three-layer die, a composition of A / B or B / A / B is provided so that the polymer of the B layer of the extruder is on one or both surfaces of the A layer.
It may be laminated in layers or three layers. Here, the polymer mixture can be extruded with a vented twin-screw extruder to remove water during extrusion.

The melted sheet is electrostatically adhered to the drum cooled at a drum surface temperature of 10 to 60 ° C. to be solidified by cooling, and the unstretched film is guided to a roll group heated at 75 to 120 ° C. The film is longitudinally stretched in the machine direction by 2.0 to 5.0 and cooled by a roll group at 20 to 50 ° C. At this time, the film has a structure containing fine bubbles. In order to obtain a white polyester film having the desired cushion ratio, it is better to generate voids in this process. The uniaxially stretched film obtained at this time may be subjected to corona discharge treatment for coating. Then, while holding both ends of this uniaxially stretched film with clips, it is guided to a tenter and 90 to 1
The film is transversely stretched in a direction perpendicular to the machine direction in an atmosphere heated to 40 ° C. The stretching ratio is 2 to 5 times in each of the length and width, and the area ratio is preferably 6 to 15 times. If the area magnification is less than 6 times, the whiteness is insufficient, and conversely, if it exceeds 15 times, tearing tends to occur during stretching and the film-forming paper tends to be defective.

In order to impart the flatness and the dimensional stability of the biaxially stretched film in this manner, the film thickness of 150 to 150
It is heat-set at 230 ° C., uniformly cooled slowly, then cooled to room temperature and wound. At the time of heat setting, it is possible to add a relaxation of 10% or less in order to reduce the heat shrinkage rate. Thus, the white polyester film of the present invention is obtained.

Alternatively, the white polyester film may be first produced under the above conditions as described above, and the coating layer may be laminated thereon by melt extrusion or coating.

The white polyester film of the present invention comprises:
Fine particles of calcium carbonate, amorphous zeolite particles, anatase type titanium dioxide, calcium phosphate, silica, kaolin, talc, clay and the like may be used in combination. The addition amount of these is preferably 0.005 to 1 part by weight with respect to 100 parts by weight of the polyester composition. In addition to such fine particles, fine particles precipitated by the reaction of the catalyst residue and the phosphorus compound in the polyester polycondensation reaction system can be used in combination. Examples of the deposited particles include those composed of calcium, lithium and phosphorus compounds, those composed of calcium, magnesium and phosphorus compounds, and the like, and the content of these particles in the polyester is 100 parts by weight of the polyester. 0.05 ~
It is preferably 1 part by weight.

[0032]

[Measurement of physical properties and evaluation method of effect]

1. Specific gravity The film is cut into 100 x 100 mm square and the dial gauge (Mitoyo Seisakusho No. 2109-10) has a diameter of 10 m.
The thickness of a minimum of 10 points is measured with the one to which the m measuring element (No. 7002) is attached, and the average value d (μm) of the thickness is calculated. In addition, this film is weighed with a direct balance and the weight w (g) is read to the unit of 10 ⁻⁴ g. At this time, specific gravity = w / d × 100.

2. Average Diameter (a) and Shape Factor of Dispersion A cross section of the unstretched film cut in the machine direction (MD) or its vertical direction (TD) was measured by a scanning electron microscope.
A photograph magnified up to 5000 times is taken, and at least 100 or more incompatible polymer dispersions in the specified thickness range are subjected to an image analyzer to obtain a distribution of diameters of circles corresponding to the areas of the dispersions. The area average diameter of this distribution was defined as the average diameter (dispersion diameter) of the dispersion. The ratio of 100 major axis / minor axis was used as the shape factor of the dispersion.

4. Heat shrinkage rate The film is cut in MD direction or TD direction to a width of 10 mm and a length of 300 mm, marked at 200 mm intervals, fixed to a support plate under constant tension (5 g), and then the original length a (mm) of the marking interval is measured. . Next, a load is applied using a clip of 3 g and the treatment is performed for 30 minutes while rotating in a hot air oven at 150 ° C., and the marking interval b (mm) is measured in the same manner as the measurement of the original length. The heat shrinkage rate was calculated by the following formula, and the average value of 5 was used.

Thermal shrinkage (%) = (ab) / a 5. Optical Density One or several sheets of film are stacked and an optical densitometer (TR9
27, manufactured by Macbeth Co.) is used to measure the transmission density. The thickness of the film and the optical density were plotted, and the optical density corresponding to the thickness of 150 μm was determined by the interpolation method or the extrapolation method.

6. Cushion rate (%) Dial gauge No. of Mitoyo Manufacturing Co., Ltd. 2109-10
The standard gauge head 900030 is used for the dial gauge stand No. It was calculated from the following formulas from the film thicknesses d ₅₀ and d ₅₀₀ when a dial gauge pressing partial load of 50 g and 500 g was applied using 7001DGS-M.

Cushion rate = 100 × (d ₅₀ −d ₅₀₀ ).
/ D ₅₀

7. MIT Flex Resistance Test According to JIS-P-8115, the test was performed until the film was broken, and the number of times was measured.

8. Flexibility and creasing property About 1 part of acrylic acid ester type adhesives KP-1405 and CK-102 (crosslinking agent) manufactured by Nippon Carbide Industry Co., Ltd.
The mixture was mixed in a ratio of 00 to 1, and one side of the film was coated with the pressure-sensitive adhesive mixture solution in a dry state so as to have a thickness of 25 μm, and left for one week to be cured. When the adhesion is strong, the amount of the curing agent is increased, and when the adhesion is weak, the amount of the curing agent is decreased to adjust the adhesion.

(1) Flexibility A film made of stainless steel (SUS304, SUS304,
Stick it on the mirror surface and bend it up to 180 °. At this time, the angle at which wrinkles start to develop is measured. The flexibility was judged as follows. ○ and ◎ were passed.

Bending wrinkles were observed within the range of 0 ° or more and less than 60 °. Bending wrinkles were observed in the range of 60 ° or more and less than 120 °. Bending wrinkles were observed within the range of 120 ° or more and less than 180 °. ◎

(2) Folding wrinkle As described above, the 180 ° peel strength with stainless steel (SUS304, mirror surface) was adjusted to 200 ± 20 g / 25 mm, and the film was peeled at a peeling speed of 300 mm / min.
The peeling angle was 180 °. The determination of the crease property was performed as follows. ○ and ◎ were passed.

When 10 or more wrinkles were observed per 10 cm of the peeled portion × When 1 to 9 wrinkles were observed per 10 cm of the peeled portion ○ There was no wrinkle per 10 cm of the peeled portion ◎

9. Void length after stretching (x) The cross section of the stretched film is observed by SEM and the length of the void is read. At this time, the cross section cut in the MD direction was taken as the MD cross section, and the cross section cut in the TD direction was taken as the TD cross section. The void length read from each cross-section observation photograph was defined as x (μm) and y (μm).

10. Whiteness U manufactured by Shimadzu Corporation according to JIS-L-1015
When using V-260, the reflectance at wavelengths 450 nm and 550 nm is B% and G%, respectively.

Whiteness (%) = 4B + 3G.

11. Glossiness Using Nippon Denshoku Industries Co., Ltd. gloss meter VG-107,
According to JIS-Z-8741, the incident angle and the light receiving angle were measured according to specified angles.

12. Surface roughness (Ra) It was measured by a needle contact type surface roughness meter (ET-10 manufactured by Kosaka Laboratory) in accordance with JIS-B-0601.

[0049]

EXAMPLES The present invention will be described based on examples.

Example 1 PBT and polytetramethylene glycol (P
PBT produced by adding PTMG during the polymerization of PBT so that the weight ratio of TMG and molecular weight 4000) is 1: 1.
2% by weight of PTMG copolymer, 88% by weight of polyethylene terephthalate (PET) and 10% by weight of polymethylpentene (TPX, DX820 manufactured by Mitsui Petrochemical Co., Ltd.)
Are mixed and extruded from the extruder A with a twin-screw vent heated to 270 to 300 ° C. while degassing and drying with a vacuum pump so that the vent pressure becomes 10 (mmHg), and calcium carbonate particles (“Shiraishi Calcium Co., Ltd.” Softon 320
0 ") 14% by weight and PBT-P prepared as described above
18% PET chips added with 10% by weight of TMG copolymer
It was vacuum dried at 0 ° C. for 3 hours and extruded from extruder B. Extruder A co-extruded into a three-layer structure (B / A / B) of the inner layer and extruder B of the outer layer to form a sheet from a T die. . Further, this film was cooled and solidified by a cooling drum having a surface temperature of 25 ° C., led to a roll group heated to 80 to 100 ° C., longitudinally stretched 3 times in the machine axis direction, and cooled by a roll group of 25 ° C. Subsequently, both ends of the longitudinally stretched film were guided to a tenter while gripping both ends with clips, and transversely stretched 3.6 times in a direction perpendicular to the machine axis direction in an atmosphere heated to 115 ° C.
After that, heat setting was carried out at 220 ° C. in a tenter, and the film was slowly annealed and then cooled to room temperature to obtain a film having a winding thickness of 100 μm. The thickness configuration was 5/90/5. The gloss level is 2
The surface roughness was 0% and the surface roughness was 0.3 μm. The physical properties of the obtained film are shown in Table 1.

Comparative Example 1 A film was obtained in the same manner as in Example 1 except that PBT polymer was used in place of the polyester polyether copolymer in Example 1. The physical properties of the obtained film are shown in Table 3. The addition of PBT did not reduce the dispersion diameter of PMP used as an incompatible polymer, and the resulting film did not have excellent physical properties such as optical density, flexibility and wrinkles.

Example 2 PET and polyethylene glycol (PEG,
PE so that the weight ratio with the molecular weight 4000) is 6: 4.
0.5% by weight of a PET-PEG copolymer produced by adding PEG during the polymerization of T, polyethylene terephthalate (P
ET) 79.5% by weight and PP (Mitsui Toatsu Co., Ltd., Nobren, J3H) 20% by weight are mixed to give 270-300.
The PET-PEG manufactured as described above was extruded while being degassed and dried with a vacuum pump so that the vent pressure was 10 (mmHg) from the extruder A with a twin-screw vent heated to ℃.
PET chips to which 10% by weight of the copolymer and 0.05% by weight of silica were added were vacuum dried at 180 ° C. for 3 hours and extruded from extruder B. Extruder A was the inner layer and extruder B was the outer layer.
A layer structure (B / A / B) was coextruded to form a sheet from a T die, and a film was obtained in the same manner as in Example 1 below. The thickness was 50 μm, and the thickness constitution was 3/44/3. The physical properties of the obtained film are shown in Table 1.

Comparative Example 2 5% by weight of PEG (molecular weight 10000), 85% by weight of polyethylene terephthalate (PET) and 10% by weight of PP (Mitsui Toatsu Co., Nobrene, J3H) were mixed and mixed.
From the extruder A with a twin-screw vent heated to 70 to 300 ° C, extrude while degassing and drying with a vacuum pump so that the vent pressure becomes 10 (mmHg), and extrude PET chips vacuum dried at 180 ° C for 3 hours. Extruder from B, extruder A
Is an inner layer, and extruder B is an outer layer having a three-layer structure (B / A / B) and coextruded to form a sheet from a T die, and a film is obtained in the same manner as in Example 1 below. The thickness was 50 μm, and the thickness constitution was 3/44/3. The physical properties of the obtained film are shown in Table 3. Addition of PEG did not reduce the dispersion diameter of PP used as an incompatible polymer, and the resulting film did not have excellent physical properties such as optical density and wrinkles.

Comparative Example 3 PBT and polytetramethylene glycol (P
PBT produced by adding PTMG during the polymerization of PBT so that the weight ratio of TMG and molecular weight 4000) is 1: 1.
-2% by weight of PTMG copolymer, 97% by weight of polyethylene terephthalate (PET) and 1% by weight of polymethylpentene (TPX, DX820 manufactured by Mitsui Petrochemical Co., Ltd.) were mixed, and the biaxial vent heated to 270 to 300 ° C. Extruder A was used to extrude while being degassed and dried with a vacuum pump so that the vent pressure was 10 (mmHg), and PET containing 10% by weight of the PBT-PTMG copolymer produced above and 0.05% by weight of silica was added. 180 ° C for chips
Was vacuum-dried for 3 hours and extruded from extruder B. Extruder A co-extruded into a three-layer structure (B / A / B) of inner layer and extruder B of outer layer to form a sheet from a T-die. Further, this film is cooled and solidified by a cooling drum having a surface temperature of 25 ° C.,
It was led to a roll group heated to 80 to 100 ° C, longitudinally stretched twice in the machine axis direction, and cooled by a roll group at 25 ° C. Subsequently, both ends of this longitudinally stretched film were guided to a tenter while holding both ends with clips, and horizontally stretched 4 times in a direction perpendicular to the machine axis direction in an atmosphere heated to 115 ° C. After that, relax and heat set at 10% at 220 ° C in the tenter, and evenly cool slowly and then cool to room temperature and take-up thickness 50μ.
m film was obtained. The thickness configuration was 3/44/3. The physical properties of the obtained film are as shown in Table 4. In the film having a specific gravity of 1.22, optical scattering due to voids did not sufficiently occur and the physical properties such as optical density and whiteness of the film were not excellent.

Example 3 PHDMT (polycyclohexyldimethanol) and polytetramethylene glycol (PTMG, molecular weight 4000) were preliminarily adjusted so that the weight ratio was 8: 2.
PHDMT-P manufactured by adding PTMG during the polymerization of T
5% by weight of TMG copolymer, 85% by weight of polyethylene naphphthalate (PEN) and 10% by weight of polymethylpentene (TPX, DX820 manufactured by Mitsui Petrochemical Co., Ltd.) were mixed, and the biaxial vent heated to 270 to 300 ° C. Extruder A was extruded while being degassed and dried by a vacuum pump so that the vent pressure was 10 (mmHg), and 10% by weight of the PHDMT-PTMG copolymer produced above and calcium carbonate particles ("Softon" manufactured by Shiraishi Calcium Co., Ltd. 32
00 ″) added 14% by weight of polyethylene naphphthalate (PEN) chips under vacuum drying at 180 ° C. for 3 hours and extruded from extruder B. Extruder B contacts the drum, extruder A
Was coextruded into a two-layer structure (A / B) on the non-contact side of the drum to form a sheet from a T die. Further, this film is cooled and solidified by a cooling drum having a surface temperature of 25 ° C.
It was led to a roll group heated to ˜150 ° C., longitudinally stretched 4 times in the machine axis direction, and cooled with a roll group at 25 ° C. continue,
The both ends of this longitudinally stretched film were guided to a tenter while holding both ends with clips, and laterally stretched 3.6 times in a direction perpendicular to the machine axis direction in an atmosphere heated to 135 ° C. Then, heat setting was carried out at 220 ° C. in a tenter, and the film was gradually cooled and then cooled to room temperature to obtain a film having a winding thickness of 66 μm. The thickness configuration was 6/60. The physical properties of the obtained film are shown in Table 2.
Is the street.

Example 4 PEN and polyethylene glycol (PEG,
PE so that the weight ratio with the molecular weight 4000) is 1: 1.
2% by weight of PEN-PEG copolymer produced by adding PEG during the polymerization of N, polyethylene terephthalate (PE
T) 90.5 wt% and polymethylpentene (manufactured by Mitsui Petrochemical Co., Ltd., TPX, DX820) 7.5 wt% were mixed, and the vent pressure from the extruder A with a twin-screw vent heated to 270 to 300 ° C. It was extruded while being degassed and dried by a vacuum pump so as to be 10 (mmHg), and 10% by weight of the PEN-PEG copolymer produced as described above and calcium carbonate particles (“Softon 320 manufactured by Shiraishi Calcium Co.
0 ") 14% by weight of PET chips is vacuum dried at 180 ° C. for 3 hours and extruded from extruder B. Extruder A is used as an inner layer and extruder B is used as a three-layer structure (B / A / B). Extrusion was performed to form a sheet from a T-die, and the film was cooled and solidified by a cooling drum having a surface temperature of 25 ° C.
It was introduced into a roll group heated to 80 to 100 ° C., longitudinally stretched 3.8 times in the machine axis direction, and cooled by a roll group at 25 ° C.
Subsequently, the both ends of the longitudinally stretched film were introduced into a tenter while gripping both ends with clips, and transversely stretched 4.0 times in a direction perpendicular to the machine axis direction in an atmosphere heated to 115 ° C. Then, heat setting was carried out at 220 ° C. in a tenter, and the film was slowly annealed and then cooled to room temperature to obtain a film having a winding thickness of 36 μm. The thickness composition was 3/30/3. The physical properties of the obtained film are as shown in Table 2.

[0057]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[0058]

The white polyester film of the present invention is
It has the following effects. By adding the polyester polyether copolymer, the dispersed diameter of the incompatible polymer becomes fine and the dispersed particles increase. As a result, the optical density of the white film is increased and the hiding property is improved. Further, since the void length inside the film is also reduced, the buckling strength of the film is increased, the flexibility is improved, and the creases are less likely to enter.
As a result, handling in the film processing process becomes easy.

Claims (13)

[Claims] 1. A composition mixture comprising at least two layers, of which one layer (referred to as A layer) comprises a polyester (a), a polyester-incompatible polymer (b) and a polyester polyether copolymer (c). A film made of a composition mixture having at least one side (referred to as layer B) of polyester (a) and polyester-polyether copolymer (d), which is whitened by containing fine air bubbles inside layer A. And a white polyester film having an apparent specific gravity of 0.5 or more and 1.1 or less. 2. The white polyester film according to claim 1, wherein the layer B is composed of a composition mixture consisting of polyester (a), polyester polyether copolymer (d) and inorganic particles. 3. The whiteness of the white polyester film is 5
It is 5% or more, The white polyester film of Claim 1 or Claim 2 characterized by the above-mentioned. 4. A white polyester film of 150 μm
The optical density per unit is 0.7 or more and 1.6 or less, The white polyester film according to claim 1 or 2, characterized in that. 5. The polymer incompatible with polyester is a polymer having a melting point of 200 ° C. or higher selected from methylpentene polymer, methylbutene polymer, styrene polymer, fluorine polymer, cellulose acetate and cellulose propionate polymer. The white polyester film according to claim 1 or 2. 6. The white polyester film according to claim 5, wherein the polymer incompatible with polyester is polymethylpentene. 7. The white polyester film according to claim 2, wherein the inorganic particles used in the layer B are calcium carbonate. 8. The polyester polyether copolymer (c) used in the A layer is of the same type as the polyester polyether copolymer (d) used in the B layer. The white polyester film according to 2. 9. The white polyester film according to claim 1, wherein the cushion ratio of the white polyester film is 10% or more. 10. By adding the polyester polyether copolymer (d) to the B layer, the crease when folded is more noticeable than the film in which the polyester polyether copolymer (d) is not added to the B layer. It does not exist, The white polyester film in any one of Claims 1-9. 11. By adding the polyester polyether copolymer (c) to the A layer, the crease when folded is more noticeable than the film in which the polyester polyether copolymer (c) is not added to the A layer. It does not exist, The white polyester film in any one of Claims 1-9. 12. The white polyester film according to claim 1, wherein the glossiness of the B layer is 60% or less. 13. The surface roughness of the B layer is 0.1 μm or more.
It is 0 micrometer or less, Claim 1- Claim 4 characterized by the above-mentioned.
The white polyester film according to any one of 1.