JP2018030901A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film that achieves both of excellent reflection performance and excellent glossy feeling by generating a controlled cavity inside.SOLUTION: A polyester film contains a cavity and satisfies the following formulas (1)(2): L1≥50 (1) and L3/L1≥0.04 (2), where L1: L(SCI), L2: L(SCE), L3: L(SCI)-L(SCE).SELECTED DRAWING: None

Description

The present invention relates to a polyester film that has excellent reflectivity and gloss and is suitably used as a light source reflecting member or a decorative member.

Conventionally, a film containing voids generally generates fine bubbles (voids) around the incompatible resin by stretching the incompatible resin dispersed in a matrix resin. These microbubble-containing films are excellent in reflectivity and concealment, provide softness and flexibility similar to paper, and can achieve low specific gravity, so labels and posters, thermal recording paper, sublimation thermal recording It is widely used for various applications such as paper and IC cards, and is particularly indispensable as a reflector base material for internally illuminated electric signs and liquid crystal displays (Patent Documents 1 and 2). In addition, in order to improve creases and further reflectivity, which are disadvantages of these fine bubble-containing films, it has also been proposed to alternately laminate layers containing fine bubbles and a resin layer separating the layers (Patent Literature). 3-5).

JP-A-2-81678 JP-A-10-286920 JP 2004-50479 A JP 2002-137350 A JP 2003-136619 A

  However, the microbubble-containing film shown in the patent literature has the following problems. Since the reflectivity of the film containing fine bubbles is caused by scattering at the interface between the fine bubbles and the resin, it depends on how small and many fine bubbles are made. On the other hand, the microbubble-containing film shown in the patent document is a film containing fine bubbles with the incompatible resin as the core by stretching after containing an incompatible resin in the resin constituting the film. However, since fine bubbles are not generated if the incompatible resin as a core is too finely dispersed, there is a limit to miniaturization of the fine bubbles. Further, since the fine bubbles are mainly diffused light, they do not have any gloss, and it is necessary to give them gloss by another means in order to use them for decoration.

  The present invention has been made in view of the above problems, and achieves both excellent reflection performance and glossiness.

The present invention for solving the above problems has the following configuration.
A polyester film containing a cavity and satisfying the following formulas (1) and (2).
L1 ≧ 50 (1)
L3 / L1 ≧ 0.04 (2)
L1: L (SCI)
L2: L (SCE)
L3: L (SCI) -L (SCE)

  The polyester film of the present invention is lightweight, has both reflection performance and glossiness, can be used for backlights such as liquid crystal displays, and can be used for decorative films due to its excellent glossiness.

It is a cross-sectional model of a film containing fine bubbles. It is a cross-sectional model of a multilayer film containing fine bubbles. 2 is a cross-sectional model of a film containing high aspect ratio cavities. 2 is a cross section of a multilayer film (17 layers) containing high aspect ratio cavities. It is a cross section of the multilayer film (401 layer) containing the cavity of a high aspect ratio. It is a schematic diagram which shows the ferret diameter of a cavity.

  Hereinafter, the present invention will be described in detail with specific examples.

  The present invention relates to a polyester film.

  The polyester here has a dicarboxylic acid component and a diol component. In addition, in this specification, a structural component shows the minimum unit which can be obtained by hydrolyzing polyester.

  The dicarboxylic acid component constituting the polyester used in the polyester film of the present invention includes malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimeline Aliphatic dicarboxylic acids such as acids, azelaic acid, methylmalonic acid, ethylmalonic acid, and the like, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalate Acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid Acid, 5- Examples include dicarboxylic acids such as thorium sulfoisophthalic acid, phenylendanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, and aromatic dicarboxylic acid such as 9,9′-bis (4-carboxyphenyl) fluorenic acid, or ester derivatives thereof. It is not limited to these.

  Examples of the diol component constituting the polyester used in the polyester film of the present invention include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and 1,2-butanediol. Aliphatic diols such as 1,3-butanediol, cycloaliphatic diols such as cyclohexanedimethanol and spiroglycol, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9 Examples include, but are not limited to, diols such as' -bis (4-hydroxyphenyl) fluorene and aromatic diols, and a plurality of the aforementioned diols linked together.

In the polyester film of the present invention, among the polyesters described above, a polyester mainly composed of polyethylene terephthalate or polyethylene naphthalate is preferable. In this invention, a main component means that it is 60 mass% or more in the resin composition which comprises a polyester film. Further, it may be a copolymer of polyethylene terephthalate or polyethylene naphthalate, a knitted body, or a blend with another polymer. In particular, a polyester mainly composed of polyethylene terephthalate (hereinafter sometimes referred to as PET) is preferable from the viewpoint of mechanical strength, heat resistance, chemical resistance, durability, and the like. Various additives such as an antioxidant, a heat stabilizer, a slipping agent, an antiblocking agent, an antistatic agent, inorganic particles, and organic particles may be added to the polyester.
The polyester film of the present invention is a polyester film containing cavities and satisfies the following formulas (1) and (2).
L1 ≧ 50 (1)
L3 / L1 ≧ 0.04 (2)
L1: L (SCI)
L2: L (SCE)
L3: L (SCI) -L (SCE)
L1 and L2 calculated | required here are the values measured by the spectrophotometer CM-3600A or CM-3700A made from Konica Minolta. L (SCI) represents the brightness of the specularly reflected light (total reflected light) measured by the SCI method, L (SCE) represents the lightness excluding the specularly reflected light measured by the SCE method, and L (SCI) −L (SCE) represents the brightness of specularly reflected light. That is, (L (SCI) −L (SCE)) / L (SCI) in the expression (2) represents the ratio of regular reflection light to total reflection light. When this value is 0.04 or more, glossiness is exhibited. More preferably, it is 0.1 or more, More preferably, it is 0.2 or more. As this value approaches 1, it becomes a mirror body, which is preferable. However, in the manufacturing method of the present invention, it is difficult to set all reflected light to regular reflection only, and 0.6 is the upper limit. L (SCI) needs to be 50 or more. When L (SCI) is less than 50, the reflection performance and glossiness are inferior. More preferably, L (SCI) is 80 or more.

  As for the polyester film of this invention, it is preferable that the A layer and the B layer are laminated | stacked 30 layers or more alternately by the thickness direction. It is only necessary to have at least a part of a laminated film having a total of 30 or more layers. For example, there may be a layer that does not correspond to each of the above layers as the outermost layer. Moreover, since the reflectance improves as the number of layers increases, it is preferably 200 layers or more. However, if the number is too large, flow marks tend to appear on the film surface, and each layer becomes unstable and a beautiful film is obtained. It is preferable that it is 1000 layers or less because it becomes impossible to do so.

  In the polyester film of the present invention, when 30 layers or more of the A layer and the B layer are alternately laminated in the thickness direction, the value of L (SCI) increases because at least one layer (for example, the B layer) has a cavity. In addition, it is preferable because the film can be lightened. Further, by alternately laminating layers having cavities and resin layers, stress concentration at the time of stretching is alleviated, so that it is difficult to break even when stretched at a high magnification, and film forming stability is improved.

In particular, the shape of the cavity included in the B layer preferably has an average aspect ratio (plane direction / thickness direction) of 15 or more and 1000 or less. More preferably, it is 20 or more, More preferably, it is 30 or more. When the cavity has a high aspect ratio, the ratio of L3 is increased and the glossiness is obtained. The higher the average aspect ratio, the higher the glossiness and the better. However, if the average aspect ratio is too high, the shape of the cavity cannot be maintained and the cavity is crushed. Therefore, the upper limit of the average aspect ratio of the cavity is more preferably 150 or less.
Here, the average aspect ratio of the cavity is derived from the SEM or TEM cross-sectional image of the film obtained by cutting the film with a microtome. Also, in order to prevent the cross-sectional shape of the cavity from changing depending on the cutting method, the sample was embedded in an acrylic resin or an epoxy resin mainly composed of methyl methacrylate (MMA) or butyl methacrylate (BMA), and then liquid nitrogen. The cross-sectional shape is cut out in steps of 1 μm after freezing in step 1, whereby a clean cross-sectional shape can be obtained. The plane direction is not particularly limited as long as it is in the range of 70 to 110 ° with respect to the thickness direction. The average aspect ratio is represented by an average value when at least 100 independent cavities are measured.

  In the polyester film of the present invention, the porosity of the A layer is preferably less than 2% by volume, and the porosity of the B layer is preferably from 50 to 90% by volume. Since the reflection efficiency of the A layer and the B layer increases as the porosity in the B layer increases, L1 can be increased. The porosity of the A layer is more preferably less than 1% by volume, and still more preferably substantially free of voids.

  The polyester film of the present invention preferably has a maximum thickness per layer of the A layer of 0.05 μm or more and less than 2 μm. As the thickness of the A layer is reduced, the ratio of the B layer in the film, and hence the ratio of the cavities, is increased, so that L1 can be increased. On the other hand, if it is less than 0.05 μm, it is difficult to maintain the shape of the cavity, which is not preferable.

As a method for generating cavities, a high melting point incompatible resin is finely dispersed in the B-layer resin and stretched to form cavities around the incompatible resin particles. Stretching is preferably biaxial stretching. A film containing conventional fine bubbles is also produced in this way (FIG. 1). However, since the cavity created in this way is generated using particles as a fulcrum, the cavity has an elliptical shape and a low aspect ratio. Moreover, since the length of the cavity in the thickness direction depends on the particle diameter, even if the thickness of each layer is reduced, there is essentially no change (FIG. 2).
In the case of generating a high aspect ratio cavity which is a preferred embodiment of the present invention, 50% by weight or more and 99% by weight or less of the resin of the B layer is the resin (C) having low stretchability, which is incompatible with the resin. The resin (D) is preferably contained in an amount of 1% by weight to 50% by weight. More preferably, the resin C is 65% by weight or more and 95% by weight or less. By adopting such a configuration, the film after melt extrusion exists as resin C as sea and resin D as islands. When biaxial stretching is performed on this film, after peeling at the interface between the resin C and the resin D, the layer B does not follow the biaxial stretching, and thus the layer is cut off (FIG. 3). The ratio of the cavities generated at this time is larger than that of the fine bubbles in FIG. Further, since the cavity is generated by the tearing between layers, the thickness of the cavity substantially depends on the thickness of the B layer. As a result, if the layer thickness is controlled by the number of layers, the aspect ratio can be increased, and ultimately, a multi-layer structure having an amida pattern can be created (FIGS. 4 and 5). Further, when the number of layers is increased, interference reflection at the interface is also generated, and an appearance like pearly luster is exhibited.
On the other hand, when the number of layers is increased and the thickness per layer becomes 2 μm or less, even if the resin has low stretchability, it becomes difficult to generate cavities. Therefore, it is preferable because the cavity is easily extended by setting the draw plane magnification to 16 to 39 times. The stretching plane magnification is not limited to both sequential biaxial and simultaneous biaxial, but it is preferable to perform multi-stage stretching because high-stretching tends to be broken at once.
With the resin (C) having low stretchability, the glass transition temperature Tg (A) of the A-layer polyester resin (A) and the glass transition temperature Tg (C) of the resin C preferably satisfy the following formula.
Tg (C) −Tg (A) ≧ 25 (3)
More preferably, Tg (C) −Tg (A) ≧ 50 is preferable. With such a configuration, in the stretching step, the A layer is stretched but the B layer is not stretched, so that a cavity as shown in FIG. 3 is more likely to occur. In the present invention, engineering plastic resins such as polyethylene naphthalate, polymethylpentene, cycloolefin, polyacetal, polycarbonate, polyacrylonitrile, and modified polyphenylene ether, and super engineering plastic resins such as polyarylate, liquid crystal polymer, and polysulfone are exemplified. Of these, polymethylpentene is most preferable from the viewpoint of cost and handleability.
Further, even when the resin C does not satisfy the above formula (3), for example, a PET resin (GF reinforced PET) blended with glass fiber, a resin in which rigid particles are dispersed at a high concentration, and when cast Resins that cold-crystallize 40% or more (PBT, MXD6) and resins containing a large amount of a crystal nucleating agent and a crystal facilitator are also applicable because biaxial stretching is difficult. Crystal nucleating agents include talc, aliphatic carboxylic acid amides, aliphatic carboxylates, aliphatic alcohols, aliphatic carboxylic acid esters, aliphatic / aromatic carboxylic acid hydrazides, sorbitol compounds, and organic phosphoric acid compounds. It can be selected preferably.

  The polyester film of the present invention has various additives such as antioxidants, heat stabilizers, weathering stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, antistatic agents. Further, a nucleating agent or the like may be added to such an extent that the characteristics are not deteriorated.

  Next, the preferable manufacturing method of the biaxially-oriented polyester film of this invention is demonstrated below. The present invention should not be construed as being limited to such examples.

  The biaxially oriented polyester film of the present invention uses a method (melt cast method) in which a dried raw material is heated and melted in an extruder as necessary and extruded from a die onto a cast drum cooled to be processed into a sheet shape. Can do.

  The polyester A used for the A layer and the resin B used for the B layer are supplied to separate extruders and melt extruded. At this time, it is preferable to control the resin temperature to 265 ° C. to 295 ° C. under an atmosphere of flowing nitrogen in the extruder, with an oxygen concentration of 0.7% by volume or less. In the present invention, it is preferable that the resin A and the resin B are laminated in multiple layers, and are laminated using a composite device such as a multilayer feed block, a square mixer, or a multilayer die. Foreign matter is removed and the amount of extrusion is leveled through a filter and a gear pump, respectively, and discharged from a T-die onto a cooling drum in a sheet form. At that time, an electrostatic application method in which a cooling drum and the resin are brought into close contact with each other by static electricity using an electrode applied with a high voltage, a casting method in which a water film is provided between the casting drum and the extruded polymer sheet, The sheet-like polymer is brought into close contact with the casting drum, cooled and solidified by a method of sticking the extruded polymer at a glass transition point to (glass transition point−20 ° C.) or a combination of these methods, and unstretched. Get a film. Among these casting methods, when using polyester, a method of applying an electrostatic force is preferably used from the viewpoint of productivity and flatness.

  The biaxially oriented polyester film of the present invention is obtained by stretching an unstretched film in the longitudinal direction and then stretching in the width direction, or by stretching in the width direction and then stretching in the longitudinal direction, or It can be obtained by stretching by a simultaneous biaxial stretching method in which the longitudinal direction and the width direction of the film are stretched almost simultaneously.

  The stretching ratio in such a stretching method depends on the number of layers, but in order to obtain an ideal cavity, it is preferably 3.5 times or more and 7.0 times or less, more preferably 3.8 times or more in the longitudinal direction. 6 times or less is adopted. The stretching speed is preferably 1,000% / min or more and 200,000% / min or less. The stretching temperature is preferably from the glass transition temperature of the A layer resin to the glass transition temperature + 40 ° C. Further, the stretching ratio in the width direction is 80% or more and 120% or less with respect to the stretching ratio in the longitudinal direction. The stretching speed in the width direction and the stretching temperature are the same. Moreover, it is not necessary to stretch | stretch each draw ratio at once, and after extending | stretching longitudinal direction and width direction extending | stretching, you may re-extend longitudinal direction extension and width direction extending | stretching further.

  Furthermore, the film is heat-treated after biaxial stretching. The heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. This heat treatment needs to be performed at a stretching temperature or higher and −10 ° C. or lower than the melting point of the main component resin of the B layer. Here, the preferable heat treatment temperature indicates the highest temperature among the heat treatment temperatures performed after biaxial stretching. The heat treatment time can be arbitrarily set within a range not deteriorating the characteristics, and is preferably 5 seconds to 60 seconds, more preferably 10 seconds to 40 seconds, and most preferably 15 seconds to 30 seconds. Good.

  Furthermore, in order to improve the adhesive force with the object, at least one surface can be subjected to corona treatment or can be coated with an easy adhesion layer. As a method of providing the coating layer in-line in the film manufacturing process, at least uniaxially stretched film with a coating layer composition dispersed in water is uniformly applied using a metalling ring bar or gravure roll. Then, a method of drying the coating while stretching is preferable, and in this case, the thickness of the easy adhesion layer is preferably 0.01 μm or more and 1 μm or less. Also, various additives such as antioxidants, heat stabilizers, ultraviolet absorbers, infrared absorbers, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc. may be added to the easy-adhesion layer. Good. The resin preferably used for the easy-adhesion layer is preferably at least one resin selected from an acrylic resin, a polyester resin, and a urethane resin from the viewpoint of adhesiveness and handleability. Furthermore, off-annealing under conditions of 140 to 200 ° C. is also preferably used.

  The polyester film of the present invention can be used as a film for a light source reflecting member because it exhibits high-brightness reflection efficiency when mounted on a display device such as a large screen liquid crystal display. Moreover, since it has pearl luster, it can be suitably applied to decorative plates, packaging ribbons for gifts, etc., cases for gifts, etc., and decorative films for interior wall linings.

[Characteristic evaluation method]
1. The total film thickness and each layer thickness film were embedded in an epoxy resin, and the film cross section in the width direction was cut out with a microtome (Leica: RM2265). The conditions at this time were as follows: a diamond cutter was used for cutting and liquid nitrogen was used for cooling, and cutting was performed at a cutting step interval of 1 μm. The cross section was observed with a transmission electron microscope (TEM H7100, manufactured by Hitachi, Ltd.) at a magnification of 1000 to 5000 times according to the number of layers, and the total thickness of the film and the thickness of each polyester layer were determined.

2. L (SCI), L (SCE), L (SCI) -L (SCE)
A sample was cut out at 5 cm × 5 cm, and then the back surface of the sample was painted black with magic ink (name) and CM-3600A manufactured by Konica Minolta Co., Ltd. was used under the condition of a target mask (CM-A106) with a measuring diameter of 8 mm. The L value was measured by the method and the SCI method, and the average value of n number 3 was obtained. The white calibration plate was CM-A103, and the zero calibration box was CM-A104.

3. A cross-sectional photograph obtained with a porosity of layer B of 1 or a composite photograph thereof (1000 to 5000 times magnification) was captured with an image size measuring instrument (manufactured by Keyence: IM-6125). The portion sandwiched between the A layers is defined as the B layer, and the entire area (S1) of the B layer and the area of the void portion (S2) of the B layer are separated by binarization, and S2 / S1 × 100 is defined as the B layer. It was set as the porosity of. It is assumed that 100 voids whose entire shape is clear are averaged.

4). The image size was measured in the same manner as for the void aspect ratio of 3. The vertical ferret diameter (thickness direction) and horizontal ferret diameter (plane direction) are obtained for each gap, and the horizontal ferret diameter / vertical ferret diameter is taken as the aspect ratio (FIG. 6). It is assumed that 100 voids whose entire shape is clear are averaged.

5). Glass transition temperature, melting point In accordance with JIS K7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and a disk session “SSC / 5200” was used for data analysis. Perform the measurement in the manner described above.

  5 mg of a sample is weighed in a sample pan, and the sample is heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN), held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. Immediately after that, the temperature was increased again from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./min. Get. The temperature at the top of the endothermic peak obtained from the 2ndRUN DSC curve was taken as the melting point. In the case of a laminated film, the melting point of each layer alone can be measured by scraping each layer of the film according to the laminated thickness. In the present invention, in the case of a polyester film having a polyester A layer and a polyester B layer, the melting point of each layer was measured, and a layer having a higher melting point was a polyester A layer and a lower layer was a polyester B layer.

6). Appearance Appearance was evaluated below.
A: Very excellent in reflection performance and glossiness.
B: Excellent reflection performance and gloss.
C: Low reflection performance but excellent gloss D: Excellent reflection performance but no gloss Film forming property The film forming property of the film was evaluated according to the following criteria.
A: Film breakage does not occur and stable film formation is possible.
B: Film tearing occurs, but film formation is possible.
C: Many film tears occur and continuous film formation is difficult.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

Example 1
As the main raw material, polyethylene terephthalate (hereinafter also referred to as PET) having an intrinsic viscosity of 0.65 was used. Also, a raw material to which 70% by weight of polymethylpentene (manufactured by Mitsui Chemicals: DX820, also referred to as PMP) is added as an auxiliary material, 22% by weight of PET, and 3% by weight of polyethylene glycol having a molecular weight of 4000 (hereinafter also referred to as PEG) is added as a dispersant. Was used. Each material was dehydrated by vacuum drying at 180 ° C. and melted and heated to 280 ° C. in each extruder. The raw materials were laminated in multiple layers in a feed block in which 17 layers of each material were alternately laminated. It was extruded into a guiding sheet to obtain a molten sheet. In addition, it laminated | stacked so that both surface layers might become a main raw material in this case. The molten sheet was tightly cooled by an electrostatic charge method on a cooling drum maintained at a surface temperature of 25 ° C. to obtain an unstretched film.
Subsequently, the unstretched film was stretched 3.2 times in the longitudinal direction using a roll group heated to 98 ° C. according to a conventional method, and cooled with a roll group at 25 ° C. Further, the stretched film was led to a tenter and stretched 3.4 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 125 ° C. Thereafter, it was heat-set at 220 ° C. in a tenter and uniformly cooled and wound up to obtain a polyester film having a thickness of 100 μm. The properties of the film thus obtained are as shown in Table 1, and a film excellent in glossiness was obtained although the reflection performance was not high. Since PMP used as an auxiliary material was crystallized at the time of an unstretched film, it was not stretched by biaxial stretching, and the cavity had a shape as shown in FIG.

(Example 2)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the feed block was changed to 201 layers, the stretch ratio was 3.3 times in length and 3.54 in width. While the reflection performance was greatly increased by increasing the number of layers, the glossiness was not improved much. This is presumably due to the fact that cavities are less likely to occur and the porosity of the B layer has decreased.

(Example 3)
A biaxially stretched polyester film was obtained in the same manner as in Example 2 except that the stretch ratio was 4.0 times in length and 4.7 in width. Glossiness was slightly improved by improving the surface magnification.

Example 4
A biaxially stretched polyester was produced in the same manner as in Example 2 except that the draw ratio was 4.0 times in the longitudinal direction and 4.7 times in the transverse direction, and then again stretched 1.1 times in the longitudinal direction and 1.1 times in the transverse direction. A film was obtained. Glossiness was greatly improved by increasing the surface magnification, and the appearance was pearly.

(Example 5)
A biaxially stretched polyester film was obtained in the same manner as in Example 2 except that the film was stretched 1.1 times in the transverse direction and stretched 1.1 times. Glossiness was greatly improved by increasing the surface magnification, and the appearance was pearly.

(Example 6)
As the auxiliary material 2, polycyclohexane terephthalate (hereinafter also referred to as PCT / I) in which 10 mol% of isophthalic acid was copolymerized was used. A third extruder was introduced and laminated so as to be on both surface layers of a multi-layered film with a feed block. At this time, the discharge ratio of (A + B) / C was set to 5. Otherwise, a biaxially stretched polyester film was formed in the same manner as in Example 5, and when wound up, the PCT / I layers on both surface layers were peeled off to obtain a 100 μm thick polyester film. The performance was almost the same as in Example 5, but the breakage was greatly reduced by the support layers being laminated on both surface layers.

(Example 7)
A biaxially stretched polyester film was prepared in the same manner as in Example 5 except that a raw material to which 80% by weight of PMP and 20% by weight of cyclopolyolefin (Mitsui Chemicals Co., Ltd .: ZEONOR R1020R, hereinafter also referred to as COP) was added was used. Obtained. Since the diameter of the particles dispersed in the B layer was significantly reduced, the cavities were arranged in a more planar direction, and the glossiness was further improved.

(Example 8)
A biaxially stretched polyester film was obtained in the same manner as in Example 5 except that a raw material to which 70% by weight of a liquid crystal polymer (Ueno Pharmaceutical: 2030G, hereinafter also referred to as LCP) and 30% by weight of PET were added as an auxiliary material. It was. Since LCP belongs to Resin C, the cavities produced by stretching were the same as in FIG. On the other hand, the porosity of B layer was lower than Example 5, and the glossiness fell.

Example 9
A biaxially stretched polyester film was obtained in the same manner as in Example 3 except that polycarbonate (70% by weight, manufactured by Idemitsu Kosan Co., Ltd .: Taflon RLC 1500; hereinafter also referred to as PC) and 30% by weight of PMP was used as an auxiliary material. It was. Since the stretching temperature was considerably lower than the glass transition temperature of PC, the B layer did not follow the stretching, and the cavities produced by the stretching were the same as in FIG. On the other hand, the porosity of the draw ratio B layer was lower than that of Example 3, and the glossiness was slightly lowered.

(Comparative Example 1)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that a raw material to which 89% by weight of PET, 10% by weight of PMP and 1% by weight of PEG were added as auxiliary materials was used. The film had no glossiness due to the small aspect ratio of the cavities.

(Comparative Example 2)
As a secondary material, a raw material added with 50% by weight of polyethylene terephthalate (PET / I12) copolymerized with 12 mol% of isophthalic acid and 50% by weight of barium sulfate particles was used. Moreover, it carried out similarly to Example 4 except having made the vertical magnification 3.3 times, the horizontal magnification 3.3 times, and heat processing temperature 180 degreeC. There were almost no cavities in the B layer, and no glossiness was observed.

(Comparative Example 3)
A biaxially stretched polyester film was obtained in the same manner as in Comparative Example 1 except that the stretch ratio was 4.0 times in length and 4.7 in width. Even when the surface magnification was improved, the improvement in the aspect ratio was slight, and the glossiness was hardly changed.
(Comparative Example 4)
A biaxially stretched polyester film was obtained in the same manner as in Example 2 except that the stretch ratio was 3.0 times in length and 3.1 in width. Since the surface magnification was low, the cavity aspect ratio was low, and glossiness was hardly seen.

1 A layer 2 B layer 3 Cavity 4 Incompatible resin 5 Resin C
6 Horizontal ferret diameter 7 Vertical ferret diameter

It is a cross-sectional model of a film containing fine bubbles. It is a cross-sectional model of a multilayer film containing fine bubbles. 2 is a cross-sectional model of a film containing high aspect ratio cavities. 2 is a cross section of a multilayer film (17 layers) containing high aspect ratio cavities. It is a schematic diagram which shows the ferret diameter of a cavity.

Claims (6)

A polyester film containing cavities, which satisfies the following formulas (1) and (2).
L1 ≧ 50 (1)
L3 / L1 ≧ 0.04 (2)
L1: L (SCI)
L2: L (SCE)
L3: L (SCI) -L (SCE) The polyester film according to claim 1, wherein the A layer and the B layer are alternately laminated in the thickness direction by 30 or more layers, and at least the B layer contains a cavity. The polyester film according to claim 2, wherein the porosity of the A layer is less than 2% by volume, and the porosity of the B layer is 50 to 90% by volume. 4. The microbubble-containing film according to claim 2, wherein a maximum thickness of the A layer per layer is 0.05 μm or more and less than 2 μm. The film for light source reflective members using the polyester film in any one of Claims 1-4. The decorative film using the polyester film in any one of Claims 1-4.