JPH06234179A - White polyester film and thermal recording receive sheet using it - Google Patents

Abstract

PURPOSE:To obtain a film whose irregularity in thickness is improved, from which a white polyester film having excellent heat dimension stability, low specific gravity, softness, cushioning property, heat dimension property, and hardly having creasing can be obtained. CONSTITUTION:A white polyester film is a laminated film constituted of at least three layers: a layer A, a layer B and a layer C, wherein at least one utmost outer layer is made of the layer A and other utmost outer layer is made of the layer A or the layer C with an apparent specific gravity of 0.5 or more and 1.1 or less. The layer A contains a polyester whose melting point is 200 deg.C or more as a main component. The layer B is made of a soft polyester (d) containing a polyalkylene terephthalate as a main component. The layer C is made of a mixed composition consisting of the polyester (a), a polymer (b) incompatible with the polyester, and an additive (c) which substantially makes the polymer (b) scatter differentially, containing fine foams inside thereof so as to be whitened.

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, excellent flexibility and less wrinkles. 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,
Relating to white polyester film used as a base material for video printer receiving paper, photographic paper, display board, thermal recording receiving sheet, surface light source reflecting plate base material, X-ray photographic film, ceramic molding release paper, etc. Is.

[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 folds and wrinkles are formed due to insufficient flexibility due to poor dispersibility. Cheap.

When polymethylpentene and an alkylene glycol or a polyalkylene glycol polyester copolymer are added, dispersibility is improved, but flexibility is still insufficient, so that wrinkles are likely to occur during handling. When used in a layer, the interfacial tension of the polyolefin is substantially lower than that of polyester, so that the surface tension of the film is lowered and there is a fatal defect that the adhesiveness and printability are 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.
Further, when a flexible polymer is laminated on the outer layer, the flexibility is improved and it becomes difficult for creases to be formed during handling, but it causes sticking on the longitudinal stretching roll, which is a manufacturing problem.

That is, a white polyester film which has a low specific gravity, flexibility, cushioning property, thermal dimensional property, good printability and adhesiveness of polyester, high optical density, is less likely to be wrinkled, and has no problem in production. Did not exist.

[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 hard to be wrinkled, a laminated film of at least three layers consisting of the following A layer, B layer and C layer, wherein at least one outermost layer is A layer and the other outermost layer is The present invention relates to a white polyester film comprising an A layer or a C layer and having an apparent specific gravity of 0.5 or more and 1.1 or less.

Layer A: A layer mainly composed of polyester having a melting point of 200 ° C. or higher.

Layer B: A layer made of a flexible polyester (d) containing polyalkylene terephthalate as a main component.

Layer C: A mixed composition comprising a polyester (a), a polymer (b) incompatible with the polyester, and an additive (c) for substantially finely dispersing the polymer (b). A layer that is whitened by containing fine bubbles.

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

The incompatible polymer referred to in the present invention has the effect of being dispersed in polyester by melt extrusion molding and causing voids by causing interfacial peeling at the interface of the incompatible polymer dispersion in the stretching step which is a subsequent step. As an incompatible polymer, poly-3-
Methylbutene-1, poly-4-methylpentene-1, polyvinyl-t-butane, 1,4-trans-poly-2,
3-dimethylbutadiene, polyvinylcyclohexane,
Selected from polystyrene, polymethylstyrene, polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t-butyl ether, sululose triacetate, cellulose tripropionate, polyvinyl fluoride, polychlorotrifluoroethylene, etc. Polymers with a melting point of 200 ° C or higher can be raised. 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 when the melting point is less than 200 ° C., the dispersed shape of the incompatible polymer in the polyester film does not take a spherical shape but often takes a layered or flat shape, and a polyester film having a high cushioning property cannot be obtained. . Further, the melting point of the incompatible polymer is 300 ° C. or lower,
It is 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 C layer 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.

By adding the additive (c) for substantially finely dispersing the polymer (b) used in the present invention, the average dispersion diameter of the incompatible polymer can be reduced as compared with the case where this additive is not added. It is an additive having the effect of This has the effect of reducing the dispersion diameter of the incompatible polymer in the polyester in the C layer, making the voids formed by stretching fine and uniform, and imparting flexibility to the film, and thus making it difficult to cause wrinkles. For example, polyester-polyether copolymers and the like are preferably used. Polyester used as a polyester polyether copolymer is polyethylene terephthalate (PET), polytetramethylene terephthalate (PBT), polyethylene-
p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate (PCHDMT), polyethylene-2,6-naphthalene dicarboxylate (P
EN) and the like. The polyether used for copolymerization preferably has a molecular weight of 300 to 20,000, for example, polyethylene glycol (PEG), methoxy polyethylene glycol, polytetramethylene glycol (P
TMG), polypropylene glycol (PPG) and the like. Preferred polyester polyether copolymers include PET-PEG, PBT-PTMG, and 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. Further, the molecular weight of the polyether used is preferably 400 to 20,000. It is preferably 1,000 to 10,000.

The amount of the polyester-polyether copolymer preferably used in the C layer is 0.5 to 20% by weight, preferably 1 to 5% by weight. If the addition amount is less than 0.5% by weight, the incompatible polymer is not finely dispersed, the generated voids 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 main component polyester in the C layer 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.

Further, the amount of the incompatible polymer is added in an amount larger than the amount of the additive for substantially finely dispersing. Preferably 2
More than double the amount. When the amount of the incompatible polymer is less than the amount of the additive for substantially finely dispersing, voids are less likely to occur at the interface of the incompatible polymer particles, and it is difficult to obtain a white polyester film having low specific gravity and high optical density. Become.

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 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 air leakage index of the surface of the present invention is preferably 1000 to 30000 seconds, but preferably 5000 to 28000 seconds. When the air leakage index is 1000 seconds or less, the surface is rough and dot omission in printing is likely to occur. In addition, the adhesion to the head is poor and sufficient heat is not transferred, resulting in poor color development. 300
When the time is 00 seconds or more, slippage is poor, handleability such as winding is poor, and running performance in the printer is poor.

Although not limiting the present invention, the cushion ratio of the present invention is 10% or more, preferably 15% or more, more preferably 20% or more. When the cushion ratio is less than 10%, when used as a receiving paper for a video printer, for example, when the pressure of the thermal recording head is lowered, the head hits hard and missing dots occur and a clear image can be transferred. And the feeling when touched by the hand becomes worse.

Although not limiting the present invention, the optical density of the white polyester film in 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. , And most preferably 1.
It is 0 or more and 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.

The Young's modulus of the B layer is substantially lower than the Young's modulus of the A layer and the C layer, respectively, under the same film forming conditions.
When the layers, B layer and C layer are formed and the Young's modulus of each film is Ea, Eb and Ec, it means that Ea> Eb and Ec> Eb. Preferably 0.67 Ea>
Eb and / or 0.67Ec> Eb, and more preferably 0.5Ea> Eb and / or 0.5Ec> Eb.

As a method for making the Young's modulus of the B layer substantially lower than the Young's modulus of the A layer and the C layer under the same film forming conditions, for example, as the polymer component of the B layer, a non-oriented thermocrystalline polymer and / or a heat There are a method of using a polymer in which a soft component copolymerizing component such as a plastic elastomer is copolymerized, and a method of increasing the void amount in the B layer more than the void amount in the A layer and / or the C layer.

The non-oriented thermocrystalline polymer is a polymer which is hard to be thermally crystallized even when it is substantially oriented, and examples thereof include polycarbonate and polyarylate. The polymer copolymerized with the soft component copolymer component such as a thermoplastic elastomer is preferably polyester. For example, examples of the dicarboxylic acid component constituting this polyester include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, and aliphatic dicarboxylic acids.
Aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid and their derivatives, and alicyclic dicarboxylic acids include 1,
4-cyclohexanedicarboxylic acid and derivatives thereof, and the like, and aliphatic dicarboxylic acids include adipic acid, sebacic acid, dodecanedioic acid, eicoic acid, dimer acid, and derivatives thereof. As the alcohol component, ethylene glycol, trimethylene glycol,
Typical examples are tetramethylene glycol and cyclohexanedimethanol. Here, the dimer acid is a general term for a mixture of a chain branched structure obtained by dimerizing an unsaturated dicarboxylic acid such as methyl oleate and a hydrogenation reaction, and having a methylene chain having 20 to 80, 30 carbon atoms.
~ 60. In this case, the flexible component to be copolymerized is an alicyclic dicarboxylic acid, an aliphatic dicarboxylic acid, or the like. The copolymerization amount of the alicyclic dicarboxylic acid and the aliphatic dicarboxylic acid is 1 to 40 mol%, preferably 5 to 20 mol% with respect to the acid component. Furthermore, polyester polyethers obtained by copolymerizing this polyester with polyethers such as polyethylene glycol polytetramethylene glycol, polyester amide copolymers obtained by copolymerizing polyamides, block copolymers with aliphatic polyesters such as polycaprolactone, and the like are also included. .

Inorganic particles may be added to the layer A 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 layer A, 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 layer A is necessary for preventing roll tackiness and imparting slipperiness, and the layer A has a laminated thickness of 5 μm in order to keep the flexibility of the layer B and prevent creases from forming. The following is suitable, but preferably 1 μm or less,
More preferably, it is 0.1 μm. The lower limit will be 0.01 μm in terms of film forming technology. The layer A is a layer containing a polyester having a melting point of 200 ° C. or higher as a main component. Melting point 20
Polyester of 0 ° C. or less is not preferable because it causes roll adhesion. The upper limit of the melting point is 340 considering melt extrudability.
A temperature below ℃ may be appropriate.

As the laminated constitution of the white polyester film of the present invention, for example, three-layer constitution of A layer / B layer / C layer, five-layer constitution of A layer / B layer / C layer / B layer / A layer, A layer / Layer C / B
It has a four-layer structure of layer / A layer. In this case, C
The layer is a layer containing fine bubbles, and the B layer is a film layer having a lower Young's modulus than the A and C layers. Inorganic particles (d) may be further added to the B layer. With such a configuration, the C layer can obtain the target high whiteness and concealing property, and the flexibility of the B layer can prevent creases from forming easily, and the appearance can be improved. A white polyester film having good properties is obtained.

The present invention is not limited to the following.
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 abruptly close, not only the specific gravity can be reduced as compared with the case where the polymer is dispersed in a layered or 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 that 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, preferably 1 to 2.

The form of voids in the film is also related to the physical properties of the film, particularly the cushioning rate, the hiding power, the whiteness and the occurrence of wrinkles. That is, the void length in the machine axis direction of the film and in the direction perpendicular thereto is x (μm),
When y (μm) and the dispersion diameter of the incompatible polymer are a (μm), it is desirable to satisfy the following formula.

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

[0033] While the present invention is not necessarily a limitation, incident angle 60 ° and a light receiving angle of 60 ° glossiness G _1, incident angle 60 ° and the light-receiving angle of 45 ° glossiness G _2, the angle of incidence 6
Assuming that the glossiness G ₃ is 0 ° and the light receiving angle is 75 °, G ₁ ≤
60%, G ₂ / G ₁ ≧ 0.05, G ₃ / G ₁ ≧ 0.05
Is preferred. More preferably G ₁ ≦ 30%, G ₂ / G ₁
≧ 0.1, G ₃ / G ₁ ≧ 0.1, more preferably G ₁ ≦
15%, G ₂ / G ₁ ≧ 0.2 and G ₃ / G ₁ ≧ 0.2. When it is within the range of this glossiness, there is an effect that creases are less noticeable.

Although the present invention is not necessarily limited to this, the surface roughness Ra of the surface of the C layer is preferably 0.1 μm or more and 1.0 μm or less. More preferably, the surface roughness Ra of the surface of the C layer is 0.2 μm or more and 0.8 μm or less. More preferably, the surface roughness Ra of the C layer surface is 0.3 μm.
It is preferably m or more and 0.6 μm or less. When it is within the range of the surface roughness, there is an effect that creases are less noticeable.

Next, the 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) which is a polyester polyether copolymer as an additive for substantially finely dispersing the incompatible polymer. The copolymer is mixed with polyethylene terephthalate, thoroughly mixed and dried to form 270
Feed to extruder C heated to a temperature of ~ 300 ° C.
In addition, polyester polyether copolymer and CaCO
Inorganic particles such as ₃ are mixed and fed to the extruder B by a conventional method, and inorganic particles such as polyethylene terephthalate and CaCO ₃ are mixed and fed to the extruder A by a conventional method to form 4 or 5 layers of T-die. A / C / B / A or A / B so that the polymer of the extruder A layer is the outermost layer and the B layer is the inner layer in the die.
You may laminate to 4 layers or 5 layers of the structure of / C / B / A. Here, the polymer mixture can be extruded with a vented twin-screw extruder to remove water during extrusion.

This melted sheet was 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 was guided to a roll group heated at 75 to 120 ° C. The film is longitudinally stretched in the direction of 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 a desired cushion ratio, it is preferable to generate voids in this step. 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
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, a white polyester film may be first produced under the above conditions as described above, and a coating layer may be laminated thereon by melt extrusion or coating.

The white polyester film of the present invention comprises
Fine particles such as calcium carbonate, amorphous zeolite particles, anatase type titanium dioxide, calcium phosphate, silica, kaolin, talc and clay 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.

The heat-sensitive receiving sheet used in the present invention can be obtained by forming a heat-sensitive receiving layer on the white polyester sheet obtained above by a known method.

[0042]

[Measurement of physical properties and evaluation method of effect]

1. Specific gravity Cut the film into 100 x 100 mm square, and use a dial gauge (No. 2109-10, manufactured by Mitoyo Seisakusho) with a diameter of 10 mm.
The thickness of at least 10 points is measured with the one with the stylus (No. 7002) 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 5,000 times was taken, and at least 100 or more incompatible polymer dispersions in the specified thickness range were applied 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.

3. Heat Shrinkage The film was cut in the MD or TD direction to have a width of 10 mm and a length of 300 mm, marked at 200 mm intervals, fixed on a support plate under constant tension (5 g), and then the original length a (mm) of the marking interval was measured. . Next, a load was applied using a clip of 3 g and the treatment was performed for 30 minutes while rotating in a hot air oven at 150 ° C., and the marking interval b (mm) was 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

4. Optical Density One or several sheets of film are stacked and an optical densitometer (TR9
27, manufactured by Macbeth Co.) was 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.

5. 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

6. 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.

7. 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. The adhesive strength was adjusted by increasing the amount of the curing agent when the adhesive strength was strong and decreasing the amount of the curing agent when the adhesive strength was weak.

(1) Flexibility A film made of stainless steel (SUS304, SUS304,
It was adhered to a mirror surface) and bent to 180 °. At this time, the angle at which wrinkles began to occur was 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 within the range of 60 ° or more and less than 120 ° ○ Within 120 ° or more and less than 180 ° Bending wrinkles were observed ◎

(2) Folding and wrinkling property 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 ○ No wrinkles were found per 10 cm of the peeled portion ◎

8. Void length after stretching (x) The cross section of the stretched film is observed with an SEM to read the length of the void. 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).

9. Whiteness U manufactured by Shimadzu Corporation according to JIS-L-1015
When V-260 was used and the reflectances at wavelengths of 450 nm and 550 nm were B% and G%, respectively, whiteness (%) = 4B + 3G.

10. Dye Adhesion A known thermal dye was applied and dried, and then a cellophane tape peeling test was performed.

No abnormality on the coating film. Part of the coating film peeled off.

11. Air Leakage Index It was measured using an Oken smoothness meter KT-5 (manufactured by Asahi Seiko Co., Ltd.).

12. 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.

13. 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.

[0062]

EXAMPLES The present invention will be described based on examples.

Example 1 Polyethylene glycol (PEG, molecular weight 4000) 2
% By weight, 88% by weight of polyethylene terephthalate (PET) and polymethylpentene (Mitsui Petrochemical Co., Ltd., T
PX, DX820) 10 wt% are mixed, and 270-30
From the extruder C with a twin-screw vent heated to 0 ° C., the mixture was extruded while being degassed and dried by a vacuum pump so that the vent pressure was 10 (mmHg), and 85 mol% of terephthalic acid and 15 mol of sebacic acid were previously prepared as dicarboxylic acid components. %, And 100 mol% of ethylene glycol as a diol component, a sebacic acid copolymerized PET (P
ET-S) chips are vacuum dried at 180 ° C for 3 hours and extruded from extruder B, and polyethylene terephthalate (PET) 90
1% by weight of a mixture of 10% by weight and calcium carbonate particles ("Softon 3200" manufactured by Shiraishi Calcium Co., Ltd.)
Vacuum-dry at 80 ° C. for 3 hours and extrude from extruder A. Extruder C is the innermost layer, extruder B is the intermediate layer, and extruder A is the outermost layer.
The layer structure (A / B / C / B / A) was coextruded 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.
The film was guided to a roll group heated to 1, longitudinally stretched 3 times in the machine axis direction, and cooled by a roll group at 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. 220 in the tenter
The film was heat-set at 0 ° C., uniformly cooled and then cooled to room temperature to obtain a film having a winding thickness of 100 μm. Thickness composition is 1 /
It was 4/65/4/1. The physical properties of the obtained film are shown in Table. It is as 1. 2% by weight of polyethylene glycol (PEG, molecular weight 4000) used in the C layer,
88% by weight of polyethylene terephthalate (PET) and polymethylpentene (manufactured by Mitsui Petrochemical Co., TPX, D
X820) 10% by weight mixed composition, 100 parts by weight of sebacic acid copolymerized PET (PET-S), 90% by weight of polyethylene terephthalate (PET) and calcium carbonate particles ("Softon 3200" manufactured by Shiraishi Calcium Co., Ltd.) 10
The mixture consisting of wt% was formed into a single film by an extruder D in the same manner as above. The glossiness was 40% and the surface roughness (Ra) was 0.2 μm. The Young's modulus of each film is as shown in Table 1.

Example 2 Instead of PEG used in the C layer in Example 1, polybutylene terephthalate (PBT) was used as a fine dispersant. PBT 2% by weight, polyethylene terephthalate (PET) 88% by weight and polymethylpentene (TPI, DX820 manufactured by Mitsui Petrochemical Co., Ltd.) 10% by weight were mixed, and the extruder C with a twin-screw vent was heated to 270 to 300 ° C. Extruded while being degassed and dried by a vacuum pump so that the vent pressure was 10 (mmHg), and 85 mol% of terephthalic acid and carbon 3 were previously used as dicarboxylic acid components.
The dimer acid-copolymerized PET (PET-DDM) chips produced by a known method using 15 mol% of hydrogenated dimer acid of 6 and 100 mol% of ethylene glycol as a diol component were vacuum dried at 180 ° C. for 3 hours to obtain an extruder B. More extruded, 100% by weight of PET chips are vacuum dried at 180 ° C. for 3 hours and extruded from extruder A. Extruder A has an outermost layer, extruder B has an intermediate layer, and extruder C has an innermost layer having a five-layer structure (A / B / C
/ B / A) was coextruded 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 90 ° C., longitudinally stretched 3 times in the machine axis direction, and cooled by a roll group of 25 ° C. Subsequently, both ends of this longitudinally stretched film were guided to a tenter while holding both ends with clips, and laterally stretched 3.0 times in a direction perpendicular to the machine axis direction in an atmosphere heated to 95 ° C. Then, heat setting was carried out at 180 ° 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. Thickness composition is 1/10/1000/10 /
It was 1. The physical properties of the obtained film are shown in Table 1. Further, 2 wt% of PBT used in the C layer, 88 wt% of polyethylene terephthalate (PET), and polymethylpentene (manufactured by Mitsui Petrochemical Co., TPX, DX82
0) 10 wt% of the mixed composition, 100 parts by weight of PET-DDM, and 100 parts by weight of PET were each formed into a single film by the extruder D by the same method as above. The Young's modulus of each film is as shown in Table 1.

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, 88% by weight of polyethylene terephthalate (PET) and 10% by weight of polymethylpentene (TPX, DX820 manufactured by Mitsui Petrochemical Co., Ltd.)
Was mixed and extruded from the extruder C with a twin-screw vent heated to 270 to 300 ° C. while degassing and drying with a vacuum pump so that the vent pressure was 10 (mmHg), and the PBT-PTMG co-weight used above The combined chips were vacuum dried at 180 ° C. for 3 hours, extruded from the extruder B, extruded from a mixed composition extruder A having 90% by weight of PET chips and 10% by weight of titanium dioxide particles, and formed into a film by the same method as in Example 1. . The Young's modulus of each film is shown in Table 2.

Comparative Example 1 In Example 1, extruder A was not used, extruder C was the inner layer,
Extruder B coextruded into a three-layer structure (B / C / B) of the outer layer to form a sheet from a T die. A film was obtained in the same manner as in Example 1 below. The physical properties of the obtained film are as shown in Table 2.

Without the outermost layer (referred to as the A layer) having a polyester having a melting point of 200 ° C. or more as the main component, roll sticking occurred, resulting in poor film formability. The obtained white polyester film had large unevenness in thickness due to roll adhesion.

Comparative Example 2 2% by weight of PBT used in the C layer in Example 2, 88% by weight of polyethylene terephthalate (PET) and polymethylpentene (manufactured by Mitsui Petrochemical Co., Ltd., TPX, DX82)
0) 100 parts by weight of PET was extruded from the extruder C instead of the 10% by weight mixed composition, and a film was obtained in the same manner as in Example 2. The physical properties of the obtained film are shown in Table 3.

Without the incompatible polymer in the C layer, the whiteness was low and the specific gravity of the white polyester film was 1.1 or less.

Comparative Example 3 PET and polyethylene glycol (PEG, molecular weight 40
PET) -PEG copolymer produced by adding PEG during the polymerization of PET so that the weight ratio of the PET-PEG copolymer to the above is 0.004.
5% by weight, polyethylene terephthalate (PET) 7
9.5% by weight and PP (Mitsui Toatsu Co., Ltd., Noblen,
J3H) 20% by weight is mixed, and the vent pressure is 10 from the extruder C with a biaxial vent heated to 270 to 300 ° C.
(MmHg) is extruded while being degassed and dried by a vacuum pump, and a mixture of 90% by weight of PET and 10% by weight of calcium carbonate particles (“Softon 3200” manufactured by Shiraishi Calcium Co.) is vacuum dried at 180 ° C. for 3 hours and extruded. Extruder A, extruder C is the inner layer, extruder A is the outer layer
The layer structure (A / C / A) 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 75 μm, and the thickness constitution was 5/65/5. The physical properties of the obtained film are shown in Table 3.

Without the flexible layer of layer B, the flexibility was insufficient, and a white polyester film which was likely to be wrinkled was obtained.

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[Table 1]

[Table 2]

[Table 3]

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The white polyester film of the present invention is
It has the following effects.

The C layer provides the target high whiteness and concealing property, while the flexibility of the B layer makes it less likely to cause creases and improves the appearance. A film is obtained.

Claims (15)

[Claims] 1. A laminated film of at least three layers consisting of the following A layer, B layer and C layer, wherein at least one outermost layer is A layer and the other outermost layer is A layer or C layer, A white polyester film having an apparent specific gravity of 0.5 or more and 1.1 or less. Layer A: A layer mainly composed of polyester having a melting point of 200 ° C. or higher. Layer B: A layer made of a flexible polyester (d) containing polyalkylene terephthalate as a main component. Layer C: a mixed composition comprising a polyester (a), a polymer (b) incompatible with the polyester, and an additive (c) that substantially finely disperses the polymer (b), and has fine air bubbles inside. A layer which is whitened by containing. 2. The white polyester film according to claim 1, wherein the B layer is substantially a film layer having a lower Young's modulus than the A layer and the C layer. 3. The white polyester film according to claim 1, wherein the layer A is composed of a composition mixture comprising polyalkylene terephthalate (d) and inorganic particles. 4. The layer A has a laminated thickness of 0.01 to 0.1 μm.
The white polyester film according to any one of claims 1 to 3, wherein 5. The whiteness of the white polyester film is 5
It is 5% or more, The white polyester film according to any one of claims 1 to 4. 6. A white polyester film of 150 μm
The optical density per hit is 0.7 or more and 1.6 or less, and the white polyester film according to any one of claims 1 to 4. 7. A melting point of the polymer (b) incompatible with polyester selected from methylpentene polymer, methylbutene polymer, styrene polymer, fluorine polymer, cellulose acetate and cellulose propionate polymer.
A white polyester film according to any one of claims 1 to 4, which is a polymer having a temperature of ℃ or more. 8. The white polyester film according to claim 7, wherein the polymer (b) incompatible with polyester is polymethylpentene. 9. The white polyester film according to claim 3, wherein the inorganic particles used in the layer A are calcium carbonate. 10. Additive (c) is a polyester-polyether polyester, characterized in that
The white polyester film according to claim 4. 11. The white polyester film according to claim 1, wherein the polyester used in the A layer is the same type as the polyester (a) used in the C layer. 12. The white polyester film according to claim 1, wherein the cushion ratio of the white polyester film is 10% or more. 13. The white polyester film according to claim 1, wherein the glossiness of the C layer is 60% or less. 14. The surface roughness of the C 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. 15. A heat-sensitive recording receiving sheet comprising the white polyester film according to any one of claims 1 to 4 as a base material.