JP2002037900A - Polyester film containing void - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film containing voids having high reflectivity to visible light by improving the dispersion of voids, while the difference of reflectance between both sides is suppressed to the utmost, which is useful for a raw material of various reflectors. SOLUTION: The polyester film containing voids has an average spectral reflectance to an electromagnetic wave of 450 nm wave-length of 98.0% or more, and the difference of spectral reflectance to 450 nm electromagnetic wave for one side and the other side is less than 6.0% in absolute value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a void-containing film made of a polyester resin. More specifically,
The present invention relates to a void-containing polyester film having high reflectivity to visible light and suitable for various reflectors such as constituent members of a liquid crystal display.

[0002]

2. Description of the Related Art In recent years, as information processing apparatuses such as computers, word processors, and mobile phones have become higher in performance and smaller and lighter, liquid crystal displays have been used as display devices to replace cathode ray tubes and LED panels that have been frequently used. Displays are rapidly spreading. In these information processing devices, for miniaturization and improvement of portability,
Weight reduction is required for each component of each part, and studies are also being continued to realize smaller and lighter liquid crystal displays. In this trend, polyester films are used as reflectors and diffusers, which are components of backlights for liquid crystal panels, and are lightweight, durable, and highly processable materials not found in other materials such as glass and metal. Attention has been paid.

[0003] The role of a reflector in a liquid crystal backlight is to improve the brightness of a display, and plays this role by reflecting light guided from the side through a light guide plate forward. For this reason, the reflection plate is required to have high reflectance with respect to visible light, and is also required to provide uniform reflection light at all wavelengths, and various techniques have been studied.

In general, as a method for making a polyester-based film opaque and improving its reflectivity with respect to visible light, white inert particles are added and dispersed in the film. Many studies have been made on this method as a technique using a polyester film as a printing material or a display material, and various kinds of inorganic particles such as calcium carbonate, titanium dioxide, barium sulfate, and heat-resistant organic particles are used. Attempts have been made to include active particles in the film. At present, one having a certain degree of reflectivity has already been obtained by this technique and is used in the actual production of liquid crystal panels, but at present some problems remain as unsolved problems.

[0005] One of the unsolved problems is the problem of film density. Originally, the purpose of using a polyester film as a reflector is to reduce the size and weight, and there is a demand for obtaining a high reflectivity with a film that is as thin and light as possible. However, in many cases, the inert particles as described above are substances having a significantly higher density than the raw material resin of the film. Is increased. This impairs the advantage of lightness obtained by using a polyester-based film for the reflector, and is an important issue to be improved.

[0006] Another unsolved problem is productivity and cost. Generally, these inert particles are more expensive than the resin constituting the film, and including a large amount of the inert particles in the film increases the production cost of the film. Further, when producing a film containing inert particles, breakage during film formation and process contamination due to particles often occur, and the productivity generally tends to decrease. This is also a factor that increases the production cost of the film, and is another problem of a method for containing inert particles.

On the other hand, as a method of imparting reflectivity to a film by a method not depending on a method of containing inert particles, a method of including fine voids in the film is being studied.

[0008] As one of the typical methods for containing fine cavities in a film, a method is known in which a thermoplastic resin incompatible with the polyester constituting the base of the film is added. Regarding this method, many studies have already been made as a technique for using a polyester film as a printing material, a display material, or the like.

For example, the use of resins such as polystyrene, polypropylene, and polymethylpentene alone or in combination has been disclosed in Japanese Unexamined Patent Publication No. 49-1347.
No. 55, Japanese Patent Publication No. 54-29550,
Japanese Patent Application Laid-Open No. 296819/1996 and Japanese Patent Application Laid-Open No. 8-143692.

[0010] Among them, Japanese Patent Application Laid-Open No. H8-143892.
In the publications, a method of finely dispersing cavities by including two types of polyolefin-based and polystyrene-based resins in a polyester-based resin serving as a film base to prevent thermal wrinkles and thermal curls has been reported. Thereby, the dispersibility of the cavity is greatly improved as compared with the conventional case. However, even in the film obtained by the method shown here, the fine dispersion of the cavities is insufficient for use as a reflector material, and the cavity stacking number density required for improving the reflectivity to visible light has not been achieved. .

In the processing of a reflector for a liquid crystal backlight, which is a main use of the polyester film containing a cavity for a reflector, which of the inner and outer surfaces of the film roll is used as the reflecting surface depends on the design of the processing machine base. In the past, since the reflective surface having a high reflectivity was made to be an appropriate surface inside and outside the roll as necessary, the film was used after being rewound.

[0012] In particular, in the above-mentioned method in which the thermoplastic resin is contained in the film, the dispersion state of the contained resin in the film is not always uniform due to the shape of the melt line and the temperature distribution. It is difficult to control the reflectance to be equal,
Processing through such a rewinding step is essential.

However, this rewinding step not only complicates the processing step and increases the labor, but also causes a reduction in yield and processing cost due to processing loss. It has been desired to provide a film and a film roll that can be used.

Under these circumstances, a void-containing polyester film suitable for use in various reflectors, which is the object of the present invention, has not yet been obtained, and a void-containing polyester in which the voids in the film have been finely dispersed has been obtained. System film is needed.

[0015]

That is, an object of the present invention is to solve the above-mentioned conventional problems, and to provide a void-containing polyester film which is lightweight, has high strength and is excellent in workability. It is an object of the present invention to provide a void-containing polyester film which has high reflectivity to visible light and minimizes the difference in reflectance between the two surfaces of the film and is suitable as a material for various reflectors.

[0016]

In the present invention, in a void-containing polyester film containing a polyester resin as a main raw material and having voids therein, the melt viscosity of a void developing agent dispersed in a base polyester is optimized. By setting the state, the average spectral reflectance with respect to an electromagnetic wave having a wavelength of 450 nm is significantly improved to 98.0% or more, and it has been found that high reflectance with respect to visible light can be exhibited. Absolute value is 6.
The above problem was solved when the content was less than 0%.

That is, the void-containing polyester film that can solve the above problems is as follows.

According to a first aspect of the present invention, there is provided a composition comprising a polyester resin and a thermoplastic resin incompatible with the polyester resin, wherein the thermoplastic resin is dispersed in the polyester resin in the form of particles. A void-containing polyester film containing voids caused by a resin inside the film, wherein the average spectral reflectance with respect to an electromagnetic wave having a wavelength of 450 nm is 98.0% or more, and the electromagnetic wave having a wavelength of 450 nm on one surface and the opposite surface of the film. Is a void-containing polyester film, wherein the absolute value of the difference in spectral reflectance with respect to is less than 6.0%.

A second aspect of the present invention is the void-containing polyester film according to the first aspect, wherein the number density of laminated voids defined by the following formula is not less than 0.20 / μm. Density of cavity stacking number (pieces / μm) = number of cavities in film thickness direction (pieces) / film thickness (μm)

A third invention is the void-containing polyester film according to the first or second invention, wherein the incompatible thermoplastic resin contains a polyolefin resin and a polystyrene resin.

A fourth invention is the void-containing polyester film according to the third invention, wherein the incompatible thermoplastic resin is a polyolefin resin and a polystyrene resin.

A fifth invention is characterized in that the melt viscosity η _o of the main component resin in the polyolefin resin and the melt viscosity η _S of the polystyrene resin satisfy the following formula (1). 4. A void-containing polyester film according to the invention of item 4. η _O / η _S ≦ 0.80 (1)

According to a sixth aspect of the present invention, there is provided the void-containing polyester film according to any one of the third, fourth and fifth aspects, wherein the main component resin in the polyolefin resin is a polymethylpentene resin. is there.

A seventh invention is directed to any one of the first, second, ^third , fourth, fifth and sixth inventions, wherein the apparent density of the film is 0.70 to 1.25 g / cm ^3. It is a void-containing polyester film described in the above.

The eighth invention is characterized in that the film has a tensile fracture strength of 1.0 to 4.0 MPa, wherein the film has a tensile fracture strength of 1.0 to 4.0 MPa. Is a polyester film containing cavities.

The ninth invention is characterized in that the ninth invention is used as a constituent member of a liquid crystal display.
A void-containing polyester film according to any one of 4, 5, 6, 7, and 8.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the void-containing polyester film of the present invention will be described in detail.

The polyester film containing cavities of the present invention has a wavelength of 450 nm as measured by the method described in the specification.
Is required to be 98.0% or more, preferably 99.0 to 108.0%, more preferably 100.0 to 105.0%. If the reflectance is less than 98.0%, it is not preferable because a film having high reflectivity to visible light, which is the object of the present invention, cannot be obtained.

In the polyester film containing cavities according to the present invention, in order to make it possible to use the film as a reflection surface regardless of the front and back surfaces thereof, a spectral reflection on one side of the film and an opposite side thereof with respect to an electromagnetic wave having a wavelength of 450 nm. It is necessary to design so that the absolute value of the difference between the rates is less than 6.0%, and it is preferable to be less than 3.0%.

In order to suppress the absolute value of the spectral reflectance difference and to set the difference in the above range, it is important to equalize the dispersion state of the cavities immediately below the surface layer on both surfaces of the film. The mixing can be achieved by a method in which the resin is stirred immediately before being extruded and solidified from the die, and the state of dispersion of the molten resin in the film is made uniform.

The void lamination number density of the void-containing polyester film of the present invention is defined by the following equation, and the void lamination number density measured by the method described in the specification is 0.20.
Particles / μm or more, preferably 0.25 to 0.4
More preferably, the number is 5 / μm, and 0.30 to 0.1.
It is particularly preferred that the number is 40 / μm. It is not preferred that the density of the number of laminated cavities is less than 0.20 / μm, because high reflectance to visible light, which is the object of the present invention, becomes difficult to be exhibited. Density of cavity stacking number (pieces / μm) = number of cavities in film thickness direction (pieces) / film thickness (μm)

The void-containing polyester film of the present invention preferably has an apparent density of 0.70 to 1.25 g / cm ^{3 as} measured by the method specified in the specification, and 0.80 to 1. more preferably 20 g / cm ^3, particularly preferably 0.85~1.15g / cm ^3. If the apparent density is less than 0.70 g / cm ³ , the mechanical strength of the film is lowered, and wrinkles are generated and the surface is cleaved. In addition, 1.25 g / cm ³
If it exceeds, the content of cavities is not sufficient, and it is difficult to obtain sufficient reflectivity for visible light, which is the object of the present invention, which is not preferable.

In the present invention, in order to set the cavity lamination density and the apparent density in the above ranges, for example, the content of a thermoplastic resin incompatible with the polyester resin shown below is adjusted to an appropriate value. And methods for adjusting the stretching temperature and stretching ratio of the film.

The void-containing polyester film of the present invention has a tensile breaking strength of 1.0 to 4.0 MPa.
It is more preferably 1.5 to 3.0 MPa, and particularly preferably 2.0 to 3.0 MPa. When the tensile breaking strength is less than 1.0 MPa, when processing the film into a reflection plate, the breakage in the process of passing through a processing machine (coater, cutting machine, etc.) increases,
Workability and yield tend to decrease. On the other hand, when the tensile breaking strength exceeds 4.0 MPa, the film becomes difficult to cut, and it tends to be difficult to cut the film into a predetermined size.

As methods for controlling the tensile breaking strength within the above-mentioned preferred ranges, there are methods such as adjusting the apparent specific gravity, adjusting the longitudinal and transverse stretching ratios and stretching temperatures, and adjusting the degree of polymerization of the raw polyester resin. Although a method is mentioned, it is not limited to this.

In the void-containing polyester film of the present invention, it is preferable that an incompatible thermoplastic resin containing a polyolefin resin and a polystyrene resin is dispersed in the polyester resin. Specifically, dispersed particles having a core-shell structure are formed around the polyolefin-based resin particles and covered with a phase made of a polystyrene-based resin, and the interface between the incompatible resins becomes more stable (the interface energy is small). It is preferable that the particles are dispersed in the polyester resin in the state as the cavity developing agent particles. The cavities contained in the film of the present invention are preferably developed at the interface between the dispersed particles and the polyester resin by stretching a melt-formed product containing the dispersed particles having the above structure in the polyester resin.

The polyester resin used in the void-containing polyester film of the present invention includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid or esters thereof with ethylene glycol, diethylene glycol, 1,3-propanediol, 1,
A polyester resin produced by subjecting a glycol such as 4-butanediol or neopentyl glycol to an esterification reaction or a transesterification reaction followed by a polycondensation reaction.

These polyester resins are prepared by directly esterifying an aromatic dicarboxylic acid and a glycol followed by a polycondensation reaction, or by subjecting an alkyl ester of an aromatic dicarboxylic acid to a transesterification reaction with a glycol followed by a polycondensation reaction. Or by a method such as a polycondensation reaction of a diglycol ester of an aromatic dicarboxylic acid.

Representative examples of such polyesters include polyethylene terephthalate, polytrimethylene terephthalate, polyethylene butylene terephthalate and polyethylene 2,6-naphthalate.
This polyester may be a homopolymer or a copolymer of the third component. In any case, in the present invention, 70 units of ethylene terephthalate unit, propylene terephthalate unit, butylene terephthalate unit or ethylene-2,6-naphthalate unit are used.
It is preferable to use a polyester having a mol% of at least 80 mol%, particularly preferably at least 90 mol%. The above-mentioned polyester resins may be used alone or as a blend of two or more.

The thermoplastic resin incompatible with the polyester resin which can be used in the void-containing polyester film of the present invention includes polyolefin resins and
Polystyrene resin, polyacrylic resin, polycarbonate resin, polysulfone resin, cellulose resin,
Examples include polyphenylene ether-based resins, but are not limited thereto. In addition, among the incompatible thermoplastic resins, it is preferable that a polyolefin resin and a polystyrene resin are included as essential components.

Examples of the polyolefin resin include polyethylene, polypropylene, polybutene and polymethylpentene. These are not necessarily limited to homopolymers, but may be copolymers obtained by polymerizing two or more olefin monomers,
A modified polyolefin resin obtained by copolymerizing an organic acid component or the like may be used. It is not necessary to use the polyolefin resin alone, and in addition to the main component (the polyolefin resin component having the largest content), other subcomponents (the polyolefin resin component having a smaller content relative to the main component) are used. You may mix and use.

In the present invention, a polymethylpentene resin is more preferable because it is hardly softened even at a high temperature and has excellent cavitation properties.

The content of the polyolefin resin is 2.0 to 1 with respect to the resin composition constituting the cavity-containing layer.
It is preferably 4.5% by weight, and 4.0 to 11.5.
It is particularly preferred that the amount is by weight. If the content is less than 2.0% by weight, the void content of the film becomes insufficient, and it becomes difficult to achieve the spectral reflectance specified in the present invention, which is not preferable. On the other hand, if it exceeds 14.5% by weight, the stretching step at the time of film formation tends to be unstable, which is not preferable.

The polystyrene resin is not particularly limited, but typical resins include a homopolymer obtained by polymerizing a styrene monomer and a modified polystyrene resin obtained by copolymerizing each main component such as an organic acid component.

The polystyrene resin has a function of stabilizing the phase structure of the immiscible resin as well as a function as a void developing agent. For this reason, the content of the polystyrene resin is, with respect to the resin composition constituting the cavity-containing layer,
It is preferably 0.5 to 7.0% by weight, and 1.0 to
More preferably, it is 5.0% by weight. Content is 0.
If the content is less than 5% by weight, the void-generating agent particles made of a resin incompatible with the polyester resin are coarsely dispersed and the voids become large, and physical properties such as reflectance and surface strength are easily deteriorated. On the other hand, if the content exceeds 7.0% by weight, the rigidity of the film tends to increase, and the flexibility tends to be impaired.

In the cavity-containing polyester film of the present invention, the total content of the thermoplastic resin containing the polyolefin resin and the polystyrene resin and being incompatible with the polyester resin is determined by the resin constituting the cavity-containing layer. It is preferably from 2.5 to 15.0% by weight, more preferably from 4.0 to 10.0% by weight, based on the composition. If the content is less than 2.5% by weight, the void content of the film is insufficient, and it is difficult to achieve the reflectance specified in the present invention, which is not preferable. On the other hand, when the content is 1
If it exceeds 5.0% by weight, the stretching step during film formation tends to be unstable, which is not preferable.

The melt viscosity η _O (poise) of the polyolefin resin and the melt viscosity η of the polystyrene resin
_{The S} (poise) ratio (η _O / η _S ) is preferably 0.80 or less, more preferably 0.50 or less. If the melt viscosity ratio exceeds 0.80, the distribution of the polystyrene resin becomes uneven, and the phase structure of the incompatible resin becomes unstable. As a result, the dispersion state of the cavity developing agent deteriorates, and it becomes difficult to obtain the dispersion state of the cavity defined in the present invention. When a mixture of two or more polyolefin resins is used, the melt viscosity of the polyolefin resin (main component) having the highest content is defined as η _O (poise) and the resin is required to satisfy the above-mentioned relationship of melt viscosity. It is preferable to set the viscosity.

When a polymethylpentene resin is used as a main component of the polyolefin resin, the melt viscosity η _O of the polymethylpentene resin is preferably 3,500 poise or less, more preferably 2,000 poise or less. preferable. Melt viscosity of polymethylpentene resin is 3,5
If it exceeds 00 poise, it is difficult to disperse the polymethylpentene resin in the step of kneading and extruding the film raw material, and it is difficult to obtain a dispersed state of cavities satisfying the spectral reflectance specified in the present invention. Absent.

Further, the melt viscosity of polystyrene resin η _S
Is preferably from 1,000 to 10,000 poise, and more preferably from 3,000 to 7,000 poise. The melt viscosity of polystyrene resin is 10,000
If the poise is exceeded, it becomes difficult to disperse the polystyrene resin in the step of kneading and extruding the film materials. Further, when the melt viscosity of the polystyrene resin is less than 1,000 poise, the void distribution of the polystyrene resin becomes non-uniform, and in any case, a dispersed state of cavities satisfying the spectral reflectance specified in the present invention is obtained. It is not preferable because it becomes difficult to be performed.

The void-containing polyester film of the present invention may contain inorganic and / or organic inert particles, if necessary, to improve the performance by improving the wavelength dependence of the reflectance. You may. Here, as the inert particles that can be added, titanium dioxide, silica, kaolinite, talc, calcium carbonate, zeolite, alumina,
In addition to inorganic particles such as barium sulfate, carbon black, zinc oxide, and zinc sulfide, generally used particles such as organic particles are assumed, but are not particularly limited. Also, the content of the inert particles is not particularly limited. However, in general, when inert particles are contained in a film, the reflectance is reduced due to scattering of light by the particles. Therefore, the type and content of the inert particles prevent the expression of a high reflectance which is the object of the present invention. Should not be set.

In the void-containing polyester film of the present invention, in order to improve the slipperiness and adhesiveness of the film and to impart other functions, at least one surface of the film is formed of a thermoplastic polyester resin layer or polyester resin. A layer made of a thermoplastic resin having adhesiveness may be laminated by a co-extrusion method.

Further, the thermoplastic resin to be laminated may contain a void-forming agent or inert particles of the same or different type as the void-containing polyester film of the present invention.
However, when a layer containing no voids is laminated, if the thickness ratio of this layer to the total thickness of the film is significantly increased, the reflectivity per unit thickness naturally decreases, which is not preferable.

Further, a coating layer may be provided on at least one side of the film of the present invention. By providing the coating layer, the adhesiveness and the antistatic property can be improved. As the compound constituting the coating layer, a copolymerized polyester resin is preferable. In addition, a polyurethane resin, a polyester urethane resin, an acrylic resin, and other means for improving the adhesiveness or antistatic property of a normal polyester film. And the like are applicable.

As a method for providing a coating layer, a commonly used method such as a gravure coating method, a kiss coating method, a dip method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method, and a reverse roll coating method is applied. it can. As the step of applying, any method such as a method of applying before stretching the film, a method of applying after longitudinal stretching, and a method of applying to the surface of the film after the orientation treatment is possible.

The method of producing the void-containing polyester film of the present invention is arbitrary and not particularly limited. For example, a mixture having the above-described composition is melted and extruded into a sheet to form an unstretched film. Thereafter, a general method of stretching the unstretched film can be used.

In the step of melting and extruding the film raw material of the void-containing polyester film of the present invention, a thermoplastic resin incompatible with the polyester resin is dispersed in the polyester resin. In the present invention, the polyester resin and the thermoplastic resin incompatible with the polyester resin are those supplied in the form of pellets, but are not limited thereto.

Raw materials to be fed into an extruder for melt molding into a film were prepared by mixing these resins in pellets according to the desired composition. However, the specific gravity of the polyester resin and the polyolefin resin used in the present invention are generally greatly different from each other, and it is preferable to take measures to prevent the pellets once mixed from being separated again in the process of being supplied to the extruder. As a preferable example of the method for this, there is a method in which some or all of the raw material resins are combined in advance, kneaded and pelletized, and prepared as master batch pellets. Although this method was used in the present invention, it is not particularly limited as long as the effects of the present invention are not hindered.

Further, in the extrusion of a mixed system of these incompatible resins, even after being mixed and finely dispersed in a molten state, there is a property of reaggregating due to the function of reducing the interfacial energy of the resin. . This is a phenomenon that, when the unstretched film is extruded, the cavity developing agent is coarsely dispersed, which hinders the development of the desired physical properties.

In order to prevent this, when forming the film of the present invention, a twin-screw extruder having a higher mixing effect is used.
It is preferable that the cavity-forming agent is finely dispersed in advance. When this is difficult, it is also preferable to supply the raw resin from the extruder to the feed block or the die via a static mixer as an auxiliary means. As the static mixer used here, a static mixer, an orifice, or the like can be used. However, when these methods are employed, care must be taken because the resin that has been thermally degraded may stay in the melt line.

Since the reagglomeration of the incompatible resin in the molten state is considered to proceed with time in a low shear state, reducing the residence time in the melt line from the extruder to the die is a fundamental solution. Become. In the present invention, the residence time in the melt line is preferably 30 minutes or less, and more preferably 15 minutes or less.

The conditions for stretching and orienting the unstretched film obtained as described above are closely related to the physical properties of the film. Hereinafter, stretching and orientation conditions will be described by taking, as an example, the most general sequential biaxial stretching method, particularly a method of stretching an unstretched film in the longitudinal direction and then in the width direction.

In the longitudinal stretching step, stretching is performed between two or many rolls having different peripheral speeds. As a heating means at this time, a method using a heating roll, a method using a non-contact heating method may be used, or both may be used. Next, the uniaxially stretched film is introduced into a tenter, and (T
(m-10 ° C.) or less at a temperature of 2.5 to 5 times. Here, Tm means the melting point of the polyester.

The above-mentioned biaxially stretched film is subjected to a heat treatment as required. The heat treatment is preferably performed in a tenter, and is preferably performed in the range of (Tm−60 ° C.) to Tm.

The void-containing polyester film thus obtained is characterized in that the fine voids dispersed in the polyester resin exhibit high reflectivity to visible light.
It is suitable as a material for various reflection plates.

[0065]

Next, examples of the present invention and comparative examples will be described.
First, a method for evaluating characteristics used in the present invention will be described below.

(1) Number Density of Cavity Lamination Using a scanning electron microscope, a cross section parallel to the longitudinal stretching direction of the film and perpendicular to the film surface was observed at five different portions of the film sample. The fractured surface was observed at an appropriate magnification of 300 to 3,000 times, and a photograph was taken in which the distribution of cavities in the entire thickness of the film could be confirmed. A straight line was drawn perpendicular to the film surface at an arbitrary position on the photographic image, and the number N (the number of layers) of cavities intersecting the straight line was counted. Further, the total thickness T (μm) of the film is measured along this straight line, and the number N (number of cavities) of the cavity is divided by the total thickness T (μm) of the film to obtain a density N / T of the number of laminated cavities.
(Pieces / μm). In addition, the measurement is 5 per photograph.
It is carried out in the place, averages the density of the number of laminated layers in a total of 25 places,
The number of hollow layers of the sample was defined as the number density (pieces / μm).

(2) Number of Cavities The number of cavities observed in the cross section of the film was counted for the electron micrograph taken in the above (1). After dividing this by the area of the observation part and standardizing it, multiply it by 2,500 to 50 μm
It was converted to the number of cavities contained in all sides (2,500 μm ² ). Note that the measurement was performed using photographs of five different portions of the sample, and the average value was obtained as the number of cavities of the sample (pieces / 2,500 μm ² ).

(3) Spectral Reflectance An integrating sphere was mounted on a spectrophotometer (Hitachi, Spectrophotometer U-3500), and the spectral reflectance with respect to an electromagnetic wave having a wavelength of 450 nm was measured. An alumina white plate (210-0740, manufactured by Hitachi Instrument Service Co., Ltd.) was used as a standard reflection plate, and the reflectance was set to 100%, and the spectral reflectance of the film sample was measured.

The measurement of the spectral reflectance was performed from one section of the film sample for each layer thickness while sequentially stacking the film samples such that one surface of the film and the other surface were opposed to each other, and measured 188.0 μm. This was performed until the thickness exceeded. The relationship between the thickness and the spectral reflectance was plotted on a graph, and the spectral reflectance at a thickness of 188.0 μm was determined by interpolation from the graph to determine the spectral reflectance of the sample. This measurement was performed on one side of the film and on the opposite side, and the average value was used as a representative value of the spectral reflectance. The higher this value, the higher the reflectivity to visible light was evaluated.

(4) Melt Viscosity (η _O , η _S ) The melt viscosity at a resin temperature of 285 ° C. and a shear rate of 100 / sec was measured using a flow tester (CFT-50, manufactured by Shimadzu Corporation).
0). In addition, it is difficult to measure the melt viscosity at a shear rate of 100 / sec while fixing the shear rate to 100 / sec.
The melt viscosity was measured at an arbitrary shear rate of less than / sec and at an arbitrary shear rate larger than the above-mentioned shear rate, the melt viscosity was plotted on the vertical axis, and the shear rate was plotted on the horizontal axis, and plotted on a log-log graph. The above two points are connected by a straight line, and a shear rate of 10
The melt viscosity at 0 / sec (η: poise) was determined.

(5) Film Thickness and Apparent Density Four samples of the film were cut into 5.00 cm squares to obtain samples. By stacking four of them, a film thickness gauge (manufactured by SONY Precision Technology Inc., DigitalMicrome
Using ter M-30), 10 points were measured with 4 significant figures, and the average value of the layer thickness was determined. The average value was divided by 4 and the fourth decimal place was rounded off, and the average film thickness per sheet (t: μm) was determined by the third decimal place. The weight (w: g) of the four samples was measured by an automatic precision balance to four significant figures, and the apparent density was determined by the following equation. The apparent density was rounded to three significant figures. Apparent density (g / cm ³ ) = w × 10 ⁴ /(5.00×
5.00 × t × 4)

(6) Intrinsic Viscosity of Polyester Resin The polyester material is dissolved in a mixed solvent of 60% by weight of phenol and 40% by weight of 1,1,2,2-tetrachloroethane, and the solid content is filtered through a glass filter. Measured at ° C.

(7) Tensile breaking strength According to JIS-K7113, the tensile test speed is 200 m
m / min, and measured at room temperature in the longitudinal stretching direction and the transverse stretching direction. The average value was used as the tensile breaking strength (MPa) of the film.

Next, examples of the present invention will be sequentially described, and the main conditions relating to the film production method are shown in Table 1, and the evaluation results of the obtained film are shown in Table 2.

Example 1 (Preparation of Master Pellet) Melt Viscosity (η _O ) of 1,3
00 poise polymethylpentene resin (manufactured by Mitsui Chemicals, Inc.
DX820) 60.0% by weight and a melt viscosity (η _S ) of 3,
900 poise polystyrene resin (Nippon Polysty Co., Ltd.
G797N) 20.0% by weight and a melt viscosity of 2,0
A pellet mixture of 20.0% by weight of a 00 poise polypropylene resin (manufactured by Grand Polymer Co., Ltd., J104WC) was supplied to a vented twin-screw extruder whose temperature was controlled at 285 ° C., and was pre-mixed. This molten resin is continuously supplied to a vent-type single-screw kneader, kneaded and extruded, and the obtained strand is cooled and cut to obtain a cavity developing agent master pellet (M
1) was adjusted.

(Production of polyester raw material) First, aggregated silica particles having a secondary aggregated particle diameter of 1.5 μm were mixed in ethylene glycol, and the slurry was subjected to 5 passes at 500 kg / cm ² using a high-pressure homogenous disperser. Time circulation processing,
Further, the solution was filtered through a filter made of viscose rayon having a 95% cut diameter of 30 μm, and the average particle diameter was 1.0%.
An ethylene glycol slurry of aggregated silica particles of μm was obtained. The slurry concentration was 140 g / L.

A polyethylene terephthalate resin containing silica particles was obtained by the following method. Raise the temperature of the esterification reactor,
When the temperature reached 200 ° C., a slurry composed of 86.4 parts by weight of terephthalic acid and 64.4 parts by weight of ethylene glycol was charged, and while stirring, 0.03 part by weight of antimony trioxide and magnesium acetate 4 water were used as a catalyst. 0.088 parts by weight of the hydrate and 0.16 parts by weight of triethylamine were added. Then, the temperature was increased by applying pressure and the gauge pressure was 0.34.
The pressure esterification reaction was performed under the conditions of 3 MPa and 240 ° C. Thereafter, the inside of the esterification reactor was returned to normal pressure, and 0.040 parts by weight of trimethyl phosphate was added. In addition, 2
The temperature was raised to 60 ° C., and 15 minutes after the addition of trimethyl phosphate, the ethylene glycol slurry of the silica particles was
500 ppm was added to the produced polyester. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction vessel, and a polycondensation reaction was performed at 280 ° C. under reduced pressure. After completion of the polycondensation reaction, a filtration treatment was performed with a NASLON filter having a 95% cut diameter of 28 μm to produce a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g.

(Preparation of film raw material) 91.0% by weight of the above polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g, which was subjected to vacuum drying at 140 ° C. for 8 hours, and 90 ° C.
The master pellets (M
1) 9.0 wt% of pellets were mixed to obtain a film raw material (C1).

(Preparation of Unstretched Film) The above-mentioned film raw material (C1) was supplied to a twin-screw extruder whose temperature was controlled at 285 ° C., and was melt-kneaded. This molten resin was extruded into a sheet shape from a T-die on a cooling roll adjusted to 25 ° C., and was adhered and solidified by an electrostatic application method to produce an unstretched film having a thickness of 480 μm. At this time, the time during which the molten resin stayed in the melt line was about 3 minutes, and the shear rate received from the T-die was about 100 / sec.

(Preparation of Biaxially Stretched Film) The obtained unstretched film was uniformly heated to 65 ° C. using a heating roll, and two pairs of nip rolls having different peripheral speeds (low speed roll: 2)
(m / min, high-speed roll: 6.8 m / min). At this time, as an auxiliary heating device for the film,
An infrared heater (rated output: 20 W / cm) having a gold reflection film in the middle of the nip roll was placed at a position 1 cm from the film surface opposite to both surfaces of the film and heated. The uniaxially stretched film thus obtained is guided to a tenter, heated to 150 ° C., stretched 3.7 times in a transverse direction, fixed in width, subjected to a heat treatment at 220 ° C. for 5 seconds, and further heated at 200 ° C. in the width direction. To give a void-containing polyester film having a thickness of about 47 μm.

Example 2 Intrinsic viscosity 0.62 after vacuum drying at 140 ° C. for 8 hours
dl / g of the polyethylene terephthalate resin 86.
0% by weight and 14.0% by weight of the master pellet (M1) vacuum-dried at 90 ° C. for 4 hours were mixed as a pellet to obtain a film raw material (C2). This film material (C
2) was supplied to a twin-screw extruder whose temperature was controlled at 285 ° C., and was melt-kneaded. The molten resin was extruded into a sheet shape from a T-die on a cooling roll adjusted to a temperature of 25 ° C. and solidified by an electrostatic application method to produce an unstretched film having a thickness of 620 μm. Other conditions were the same as in Example 1, and the thickness was about 7
A 4 μm void-containing polyester film was obtained.

Example 3 A void-containing polyester film having a thickness of about 151 μm was obtained in the same manner as in Example 2 except that the thickness of the unstretched film was changed to 1150 μm.

Example 4 The same polyethylene terephthalate resin (raw material II) as that used for the film raw material (C1) was used alone for 290 in a single screw extruder in which the above-mentioned film raw material (C1; raw material I) was adjusted to 285 ° C. The mixture was separately supplied to a twin-screw extruder adjusted to a temperature of ° C. The molten resin discharged from the single-screw extruder is led through an orifice, and the resin discharged from the twin-screw extruder is led to a feedbook via a static mixer. A layer made of a terephthalate resin (layer A) was laminated in the order of layer A / layer B / layer A. The discharge rate of each extruder was adjusted so that the thickness ratio of each layer was 1: 8: 1, and co-extruded from a T-die onto a cooling roll controlled at 25 ° C., and was tightly solidified by an electrostatic application method.
An unstretched film having a thickness of 580 μm was produced. On this occasion,
The time during which the molten resin of the film raw material (C1) stayed in the melt line was about 12 minutes, and the shear rate received from the T-die was about 150 / sec. Other conditions were the same as in Example 1 to obtain a void-containing polyester film having a thickness of about 58 μm.

Example 5 In Example 1, the polymethylpentene resin used for the master pellet was changed to a resin having a melt viscosity (η _O ) of 4,300 poise (DX845, manufactured by Mitsui Chemicals, Inc.). The other conditions were the same as in Example 1 to prepare and stretch an unstretched film having a thickness of 620 μm to obtain a void-containing polyester film having a thickness of about 53 μm.

Comparative Example 1 In Example 4, the resin discharged from the extruder was directly guided to the feed block without using a static mixer and laminated. The other conditions were the same as in Example 3, and an unstretched film having a thickness of about 650 μm was prepared and stretched to obtain a void-containing polyester film having a thickness of about 67 μm.

Comparative Example 2 In Comparative Example 1, the polymethylpentene resin used for the master pellet (M1) was melted at a viscosity (η _O ) of 4,300.
Poise (manufactured by Mitsui Chemicals, Inc., DX845) was used. Other conditions were the same as in Comparative Example 1, and the thickness was about 5
An unstretched film of 80 μm is prepared and stretched to a thickness of about 5
A 6 μm void-containing polyester film was obtained.

Comparative Example 3 An unstretched film having a thickness of about 580 μm was prepared in the same manner as in Comparative Example 2, except that the addition amount of the master pellet (M1) was changed to 23.0% by weight. This unstretched film was stretched under the same conditions as in Comparative Example 2 to obtain a void-containing polyester film having a thickness of about 90 μm.

[0088]

[Table 1]

[0089]

[Table 2]

In Examples 1 to 5, fine dispersion of the cavity was achieved by the effect of the melt viscosity of the optimized cavity developing agent and the effects of the twin-screw extruder and the static mixer, and the film was exposed to an electromagnetic wave having a wavelength of 450 nm. The film satisfying the requirements of the present invention, having an average spectral reflectance of 98.0% or more and an absolute value of the difference between the spectral reflectances on one side and the opposite side of the film of less than 6.0%, was obtained. As a result, in the film made of the polyester resin, a void-containing polyester film having high reflectivity was obtained. On the other hand, in the films of Comparative Examples 1 to 3, the spectral reflectance which is a requirement of the present invention is not obtained, and the film has sufficient reflectivity for visible light, and contains a cavity suitable as a material for various reflectors. No polyester-based film was obtained.

[0091]

As described above, since the void-containing polyester film of the present invention is excellent in the dispersion state of the voids in the film, the spectral reflectance to an electromagnetic wave having a wavelength of 450 nm is as high as 98.0% or more. Further, the absolute value of the difference between the spectral reflectances on one side and the opposite side of the film is as small as less than 6.0%. As a result, they have found that a void-containing polyester film having improved reflectivity with respect to visible light can be obtained. The void-containing polyester film of the present invention is suitable as a material for various reflectors, which is lightweight, has high strength, and is excellent in workability and productivity.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 101/00 C08L 101/00 G02F 1/1335 G02F 1/1335 // B29K 23:00 B29K 23:00 25 : 00 25:00 67:00 67:00 101: 12 101: 12 105: 04 105: 04 B29L 7:00 B29L 7:00 (72) Inventor Yasushi Sasaki 2-1-1 Katada, Otsu City, Shiga Prefecture TOYOBO F-term in the Research Institute, Inc. (Reference) 2H091 FA16Z FB02 LA16 LA18 4F071 AA02 AA14 AA21 AA22 AA43 AA88 AD02 AF15 AF15Y AF29 AF29Y AH16 BA01 BB06 BB08 BC01 BC11 BC12 BC13 4F210 AA03 AA12 AA13 AA12A03A03A03A01 BB032 BB052 BB122 BB142 BB152 BB172 BC002 BC032 BC042 CF001 CF051 CF061 CF071 CF081 FA082 FD202 GP00

Claims (9)

[Claims] 1. A composition comprising a polyester resin and a thermoplastic resin incompatible with the polyester resin,
A void-containing polyester film containing voids caused by an incompatible thermoplastic resin dispersed in a particle form in the polyester resin inside the film, and having a wavelength of 450 n
m is not less than 98.0%, and the wavelength 45 on one side and the opposite side of the film is not less than 98.0%.
5. The absolute value of the difference in spectral reflectance with respect to an electromagnetic wave of 0 nm is 6.
A void-containing polyester film having a content of less than 0%. 2. The cavity stacking number density defined by the following equation is not less than 0.20 / μm.
The void-containing polyester film as described in the above. Density of cavity stacking number (pieces / μm) = number of cavities in film thickness direction (pieces) / film thickness (μm) 3. The void-containing polyester film according to claim 1, wherein the incompatible thermoplastic resin contains a polyolefin resin and a polystyrene resin. 4. The void-containing polyester film according to claim 3, wherein the incompatible thermoplastic resin is a polyolefin resin and a polystyrene resin. 5. The method according to claim 3, wherein the melt viscosity η _o of the main component resin in the polyolefin resin and the melt viscosity η _S of the polystyrene resin satisfy the following formula (1). Void-containing polyester film. η _O / η _S ≦ 0.80 (1) 6. The void-containing polyester film according to claim 3, wherein a main component resin in the polyolefin resin is a polymethylpentene resin. 7. The film has an apparent density of 0.70 to 0.70.
2. The composition according to claim 1, wherein the weight is 1.25 g / cm ³ .
The void-containing polyester film according to any one of 2, 3, 4, 5, and 6. 8. The film having a tensile strength at break of 1.0 to 1.0.
3. The pressure is 4.0 MPa.
The void-containing polyester film according to any one of 3, 4, 5, 6, and 7. 9. The liquid crystal display according to claim 1, which is used as a constituent member of a liquid crystal display.
The void-containing polyester film according to any one of claims 7 and 8.