JP2001010002A - White laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film suitable as an information recording and printing material, which is excellent in hiding property and whiteness and the whiteness of which is hard to lower even under the state exposed to ultraviolet rays and high temperature and humidity for a long period of time. SOLUTION: This film is a polyester film having a structure having two or more layers, the layer A forming at least one side of the film contains an anatase type titanium dioxide particles having the average particle size of 0.1 to 1.0 μm and benzoxazole fluorescent brightener, in which the content (a wt.%) of the titanium dioxide particles and the content (b wt.%) of the fluorescent brightener satisfy the relationships: 0.005×a<b<0.005×a+0.4, and 6<=a<=45.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a white film made of a polyester resin. More specifically, the present invention relates to a white polyester film having excellent concealing properties and whiteness and having good weather resistance and suitable as an information recording / printing material.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute using synthetic resin as a main raw material, is superior to natural paper in terms of water resistance, moisture absorption dimensional stability, surface stability, mechanical strength and the like. In recent years, applications that take advantage of these advantages have been developed. Polypropylene, polyester, polystyrene, etc. are used as the main raw materials for synthetic paper. Among them, polyester films represented by polyethylene terephthalate have high heat resistance, gloss and sharpness of printing, It is excellent in strength, and its use as printing materials and information recording materials is expanding.

[0003] When using this polyester film as a paper substitute, methods for dispersing fine voids in the film and a method for adding a white pigment have been studied as methods for imparting the required whiteness and concealing properties. Have been. For example, it has been studied to use a film having a high concealing property by imparting a concealing property by dispersing fine cavities and optimizing the dispersion state as a heat-sensitive recording material (Japanese Patent Laid-Open No. 9-31229).
Have been. However, when microvoids are contained in a film, the performance of the film itself such as a decrease in strength and the generation of wrinkles is inevitable with an increase in the content, and the upper limit is limited to the content. For this reason, in order to secure a sufficient hiding power for use in the above-mentioned applications, the addition of a white pigment must be used in combination.

A film to which calcium carbonate, barium sulfate, titanium dioxide or the like has been added has been studied as a film having improved concealing properties by adding white pigment particles (JP-A-8-244188).
Etc.). Titanium dioxide has a high refractive index,
Since it is possible to develop a high masking property with a small amount, its use has been widely studied. In general, the use of anatase type and rutile type particles having different crystal systems has been studied.
However, since anatase-type titanium dioxide itself has a strong photocatalytic action, there is an unavoidable problem that, in addition to an increase in the amount added for the purpose of improving whiteness, the denaturation and coloring of the film constituting material are promoted. At present, the surface treatment of titanium dioxide particles with other inorganic particles and the like has been attempted to reduce the photocatalytic effect, but there are problems such as a decrease in whiteness due to this treatment, and those that still have sufficient performance Not obtained.

Further, rutile type titanium dioxide has a unique property of lowering the spectral reflectance in a short wavelength region of 450 nm or less, and is a UV-absorbing type fluorescent whitening agent which is often added to improve whiteness. There is a problem that the effect is significantly impaired. If the method of increasing the amount of the optical brightener is used to compensate for the performance decrease, coloring due to light / heat deterioration of the optical brightener itself becomes remarkable, and as a result, deterioration of weather resistance is avoided. I didn't get it. In addition, addition of calcium carbonate and barium sulfate particles has a smaller refractive index than titanium dioxide, so it is necessary to add a large amount of particles to exhibit sufficient hiding power, which leads to an increase in cost and film. It has been difficult to solve problems such as a decrease in strength. Thus, in the prior art, a white polyester film having sufficient whiteness and concealed surname as an information recording material and having excellent weather resistance has not been obtained.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a white color suitable for use as an information recording / printing material which has excellent concealing properties and whiteness and has good weatherability. The object is to provide a polyester film.

[0007]

As a means for solving the above problems, at least one of the outermost layers of the co-extruded laminated polyester film contains an anatase type titanium dioxide pigment and a benzoxazole-based fluorescent whitening agent. The present inventors have found a method of optimizing the amount of addition and exhibiting the maximum weather resistance, and have completed the present invention. That is, the present invention relates to a layer (A
Layer) containing anatase type titanium dioxide particles having an average particle size of 0.1 to 1.0 μm and a benzoxazole-based fluorescent whitening agent, a polyester film having a layer structure of two or more layers, containing the titanium dioxide particles. Amount (a weight%)
And the content of the optical brightener (b wt%) is 0.005 × a <b <
A white laminated polyester film that satisfies the relationship of 0.005 × a + 0.4,6 ≦ a ≦ 45.

[0008] The polyester in the present invention is obtained by mixing an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol. It is a polyester produced by condensation. These polyesters may be prepared by directly reacting an aromatic dicarboxylic acid and a glycol, or by subjecting an alkyl ester of the aromatic dicarboxylic acid to a transesterification reaction with a glycol followed by polycondensation, or a diglycol ester of an aromatic dicarboxylic acid. Can be produced by a method such as polycondensation. Representative examples of such polyesters include polyethylene 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, a polyester having ethylene terephthalate unit, butylene terephthalate unit or ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable. .

The amount of the titanium dioxide pigment particles used in the present invention is 6 to 45% by weight, preferably 25 to 35% by weight, based on the polyester constituting the layer (A layer) containing the titanium dioxide pigment particles. . If the amount of the particles is less than 6% by weight,
This is not preferable because the light transmittance of the film becomes large and a sufficient hiding effect cannot be obtained. The amount of the particles added is 45
If the amount is more than 10% by weight, the hiding effect of the fluorescent whitening agent blocks ultraviolet rays necessary for exhibiting the effect, and the whitening degree is reduced because the whitening effect cannot be obtained, which is not preferable.

The average particle size of the titanium dioxide pigment particles used in the present invention is 0.1 to 1.0 μm, preferably 0.2 to 0.5 μm. If the average particle size of the particles is less than 0.1 μm, the light scattering ability in the visible light region is reduced, the light transmittance of the film is increased, and both the whiteness and the concealing property are undesirably reduced. If the average particle size of the particles exceeds 1.0 μm, the inherent whiteness of the anatase type titanium dioxide decreases, which is not preferable.

[0011] In addition, inorganic or organic particles may be added to each layer in the laminated film as needed to further improve the concealing property and the like. However, when added to the titanium dioxide-containing layer (layer A), care must be taken not to impair the effects of the present invention. Particles that can be added include, in addition to the same or different titanium dioxide as the titanium dioxide,
Silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, carbon black,
Examples include zinc oxide, zinc sulfide, and organic white pigments, but are not particularly limited.

The amount (b wt%) of the fluorescent whitening agent used in the present invention with respect to the polyester constituting the layer containing the same (layer A) is based on the amount of the titanium dioxide particles in the layer A (a
Weight%), it is necessary to satisfy the relationship of 0.005 × a <b <0.005 × a + 0.4. If the amount of the fluorescent whitening agent is less than the specified amount, the amount of emitted fluorescent light is reduced and the bluish component of the reflected light is reduced, so that the film looks yellowish, which is not preferable. On the other hand, if the amount of the fluorescent whitening agent exceeds the above-specified amount, discoloration of the agent becomes remarkable under the condition of ultraviolet irradiation or high temperature and high humidity, and the weather resistance of the film is unfavorably reduced.

In the white film of the present invention, the whiteness determined by the addition amount of the titanium dioxide and the fluorescent whitening agent to be added to the layer A is -6.0 at the color difference b ₀ defined in the text.
≦ b ₀ ≦ −2.0, and more preferably −5.0 ≦ b ₀ ≦ −3.5. Whiteness b ₀ is strong blue is less than -6.0, undesirably color the expected can not be obtained when subjected to coloring by printing thereon. B ₀ is -2.
If it exceeds 0, the yellowing after the yellowing has progressed due to ultraviolet irradiation or use under high temperature and high humidity becomes strong, and similarly, the expected color development cannot be obtained.

In the white film of the present invention, the weather resistance determined by the addition amount of the titanium dioxide and the optical brightener added in the layer A is adjusted to Δb ≦ 3.5 at Δb defined in the text. There is a need. If Δb exceeds 3.5, it is not preferable because necessary weatherability cannot be obtained, for example, when the yellowing during use under ultraviolet irradiation or high temperature and high humidity progresses, the discoloration can be clearly identified by visual observation.

In the laminated film of the present invention, it is necessary that at least one of the layers except for the layer containing titanium dioxide (layer A) contains a cavity. The apparent specific gravity of the whole film needs to be adjusted to 0.7 to 1.3 g / cm ³ , and more preferably 0.8 to 1.1 g / cm ³ . If the apparent specific gravity is less than 0.7, the amount of cavities contained therein is remarkably increased, and the physical properties of the film such as a decrease in strength and generation of wrinkles are notably reduced, which is not preferable. The apparent specific gravity is 1.3 g /
If it exceeds cm ³ , the amount of cavities will be insufficient, and the light scattering effect of the cavities will be reduced, and the contribution to opacity and whiteness will be reduced, which is not preferable.

The method of including voids in the laminated film of the present invention is not particularly limited. For example, a thermoplastic resin incompatible with polyester may be used to form a layer containing titanium dioxide among the layers constituting the film. It is formed by mixing and dispersing in at least one layer of polyester excluding (A layer) and stretching. Examples of the thermoplastic resin incompatible with the polyester used for forming the cavity include a polystyrene-based resin, a polyphenylene ether-based resin, and a polyolefin-based resin, but the present invention is not limited thereto.

The white laminated polyester film of the present invention may have a coating layer on at least one of the surfaces. Here, by providing a coating layer, the wettability and adhesion of ink, a coating agent, and the like can be improved. As the compound constituting the coating layer, a polyester resin is preferable, and in addition, a compound disclosed as a means for improving the adhesiveness of a normal polyester film, such as a polyurethane resin, a polyester urethane resin, and an acrylic resin. Etc. are applicable.

As the method for providing the 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 white laminated polyester film thus obtained has high whiteness / hiding property and good weather resistance derived from the optimized amount of the titanium dioxide and the amount of the fluorescent brightener.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing a white laminated polyester film of the present invention is arbitrary and not particularly limited. For example, a mixture having the above-mentioned composition is melted and co-extruded into a film. After forming a stretched laminated film, a general method of stretching the unstretched laminated film can be used. The conditions for stretching and orienting the unstretched film are closely related to the formation of cavities. In the following, the stretching and orientation conditions will be described by taking as an example a sequential biaxial stretching method most preferably used, particularly a method of stretching an unstretched sheet in the longitudinal direction and then in the width direction. First, in the first 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. However, in order to develop a large number of cavities at the interface of the incompatible resin, the stretching is performed 3 to 5 times at a stretching temperature of the polyester glass transition temperature T _g + 50 ° C. or lower. Next, the uniaxially stretched film is introduced into a tenter,
The melting point of the polyester in the width direction _Tm
Stretch up to 5 times. The biaxially stretched film thus obtained is subjected to a heat treatment as necessary. Heat treatment is preferably carried out in a tenter, the polyester melting point T _m -
It is preferable to carry out in the range of 50 ° C. to _Tm .

Next, examples of the present invention and comparative examples will be described. First, a measurement / evaluation method used in the present invention will be described below.

(1) Intrinsic Viscosity of Polyester The polyester was dissolved in a mixed solvent of 60% by weight of phenol and 40% by weight of tetrachloroethane, and measured at 30 ° C.

(2) Apparent Specific Gravity The film was cut into four squares of 5.00 cm square to obtain samples. The thickness was measured at four significant figures at 10 points per sheet, and the average value of a total of 40 points was determined to be the thickness (t μm). The mass (wg) of the same four samples was measured using an automatic precision balance with four significant figures. The apparent specific gravity was calculated by the following equation. The smaller the value, the more voids in the film. Apparent specific gravity (g / cm ³ ) = (w × 10 ⁴ ) / (5.00 × 5.00
× t × 4)

(3) Whiteness The color difference was measured using a color difference meter (Z-1001DP) manufactured by Nippon Denshoku. The whiteness of the film was evaluated using the b value (b ₀ ).
A larger value indicates a stronger yellow tint.

(4) Opacity The total light transmittance of a film having a thickness of 100 μm was measured using a turbidimeter (NDH-1001DP) manufactured by Nippon Denshoku. The smaller the value, the higher the concealing property.

(5) Weather resistance Using an acceleration tester Atlas Yubucon UC-1 manufactured by Toyo Seiki,
UV irradiation at 63 ° C ± 3 ° C for 4 hours and heating at room temperature for 4 hours
Acceleration treatment was performed by performing three cycles of wet. After acceleration processing
The b value (b₁) Was measured.
Whiteness after processing (b ₁) To whiteness before processing (b₀) Difference
The value of (Δb) is determined as the yellowing degree by the acceleration test, and the value of Δb
The smaller the value, the higher the weather resistance.

Example 1 (Preparation of Master Pellets)
70% by weight of polyethylene terephthalate resin in polystyrene resin (TOPOLEX G797 manufactured by Nippon Polysty Co., Ltd.)
N) 6% by weight, 6% by weight of polypropylene resin (Noblen FO-50F manufactured by Mitsui Toatsu Co., Ltd.) and 18% by weight of polymethylpentene resin (TPX, DX-845 manufactured by Mitsui Petrochemical Co., Ltd.) The mixture was supplied to a twin-screw extruder, kneaded sufficiently, and the strand was cooled and cut to prepare a master pellet (A) containing a cavity-forming agent. Next, a mixture of 50% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 50% by weight of anatase type titanium dioxide particles (TA-300 manufactured by Fuji Titanium Co., Ltd.) having an average particle size of 0.3 μm is supplied to a vented twin screw extruder. After the preliminary kneading, the molten resin was continuously supplied to a vent-type single-screw kneader and kneaded to prepare a titanium dioxide-containing master pellet (B). Next, a mixture of 95% by weight of a polyethylene terephthalate resin having an inherent propensity of 0.62% and 5% by weight of a benzoxazole-based fluorescent brightener (OB-1 manufactured by Eastman Chemical Company) was supplied to a vented twin-screw extruder to be prepared. After kneading, the molten resin was continuously supplied to a vent-type single-screw kneader and kneaded to prepare a master pellet (C) containing a fluorescent whitening agent.

(Preparation of film raw material) 60% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, vacuum-dried at 140 ° C. for 6 hours, 35% by weight of the above-mentioned cavity-forming agent-containing master pellet (A), and titanium dioxide-containing 5% by weight of the master pellet (B) was pellet-mixed to obtain a film raw material (I). Also dried under the same conditions, intrinsic viscosity of 0.
The film raw material (II) was obtained by mixing 76% by weight of the 62 polyethylene terephthalate resin, 20% by weight of the above-mentioned titanium dioxide-containing master pellet (B), and 4% by weight of the fluorescent brightener-containing pellet (C).

(Preparation of unstretched film) These film raw materials are supplied to different extruders, respectively, and are fed from a T-die using a feed block so that the layers of the raw materials I and II have a thickness ratio of 95: 5. Extrusion produced an unstretched film having a thickness of about 440 μm.

(Preparation of Biaxially Stretched Film) The obtained unstretched film is uniformly heated to 65 ° C. using a heating roll,
Two pairs of nip rolls with 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 having a gold reflection film in the middle of the nip roll (rated output 20
W / cm) 1 c from the film surface facing both sides of the film
m and heated. The uniaxially stretched film thus obtained is guided to a tenter and heated to 150 ° C. 3.
The film was horizontally stretched 7 times, fixed in width, subjected to a heat treatment at 220 ° C. for 5 seconds, and relaxed at 210 ° C. in the width direction by 4% to obtain a white laminated polyester film containing voids.
In this film, the amount of titanium dioxide added to layer A is 10%,
The amount of the optical brightener added is 0.2%.

Example 2 In Example 1, 52% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 subjected to vacuum drying and 40% by weight of the above titanium dioxide-containing master pellet (B) were used as the film raw material (II), and the fluorescent whitening was carried out. 8% by weight of pellet containing agent (C)
Was obtained in the same manner as in Example 1 except that a mixture of pellets was used to obtain a white laminated polyester film containing voids. In this film, the addition amount of titanium dioxide to the layer A is 20%, and the addition amount of the optical brightener is 0.4%.

Example 3 In Example 1, 26% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 60% by weight of the above-mentioned titanium dioxide-containing master pellet (B) were vacuum-dried as the film raw material (II), and the fluorescent whitening was carried out. Agent-containing pellet (C) 4% by weight
Was obtained in the same manner as in Example 1 except that a mixture of pellets was used to obtain a white laminated polyester film containing voids. In this film, the addition amount of titanium dioxide to the layer A is 35%, and the addition amount of the optical brightener is 0.2%.

Example 4 In Example 1, 22% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 60% by weight of the above-mentioned titanium dioxide-containing master pellet (B) were vacuum-dried as the film raw material (II), and the fluorescent whitening was carried out. 8% by weight of pellet containing agent (C)
Was obtained in the same manner as in Example 1 except that a mixture of pellets was used to obtain a white laminated polyester film containing voids. In this film, the addition amount of titanium dioxide to the layer A is 35%, and the addition amount of the optical brightener is 0.4%.

Comparative Example 1 In Example 1, 86% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, which had been vacuum-dried as the film raw material (II), 10% by weight of the above titanium dioxide-containing master pellet (B), and fluorescent brightening Agent-containing pellet (C) 4% by weight
Was obtained in the same manner as in Example 1 except that a mixture of pellets was used to obtain a white laminated polyester film containing voids. In this film, the addition amount of titanium dioxide to the layer A is 5%, and the addition amount of the optical brightener is 0.2%.

Comparative Example 2 In Example 1, as the film raw material (II), a mixture of 92 wt% of the above-mentioned master pellet containing titanium dioxide (B) and 8 wt% of a pellet (C) containing a fluorescent brightener was used. A white laminated polyester film containing cavities was obtained in exactly the same manner as in Example 1 except for the difference. In this film, the addition amount of titanium dioxide to the layer A is 46%, and the addition amount of the optical brightener is 0.4%.

Comparative Example 3 In Example 1, 59% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, which had been vacuum-dried, and 40% by weight of the above-mentioned titanium dioxide-containing master pellet (B) as the film raw material (II), and fluorescent brightening Agent-containing pellet (C) 1% by weight
Was obtained in the same manner as in Example 1 except that a mixture of pellets was used to obtain a white laminated polyester film containing voids. In this film, the addition amount of titanium dioxide to the layer A is 20%, and the addition amount of the optical brightener is 0.05%.

Comparative Example 4 In Example 1, 14% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 70% by weight of the above-mentioned master pellet (B) containing titanium dioxide, which had been vacuum-dried, as the film raw material (II), Agent-containing pellet (C) 16% by weight
Was obtained in the same manner as in Example 1 except that a mixture of pellets was used to obtain a white laminated polyester film containing voids. In this film, the addition amount of titanium dioxide to the layer A is 35%, and the addition amount of the optical brightener is 0.8%.

[0037]

[Table 1]

[0038]

[Table 2] Tables 1 and 2 show a list of the measurement results of the white laminated polyester film obtained by the above method. From the measurement results in Tables 1 and 2, the following can be considered. Since the films of Examples 1 to 4 satisfy the requirements specified in the present invention, high whiteness / hiding property and good qualities can be obtained by optimizing the added amount of titanium dioxide and the added amount of fluorescent whitening agent. It can be seen that a white laminated polyester film having a good balance of weather resistance is obtained. On the other hand, in Comparative Example 1 in which the amount of titanium dioxide added is less than the requirement specified in the present invention, the concealing property is low. Similarly, in Comparative Example 2 in which the amount of titanium dioxide exceeds the requirement specified in the present invention, white color is used. It can be seen that the excellent properties derived from the appropriate amounts of titanium dioxide and fluorescent brightener were impaired. In Comparative Example 3, in which the amount of the fluorescent brightener was less than the requirement specified in the present invention, the whiteness was low, and similarly, Comparative Example 4 in which the amount of the fluorescent brightener exceeded the requirement defined in the present invention. It can be seen that the weather resistance is low, and the excellent properties derived from the addition amount of titanium dioxide and the addition amount of the fluorescent whitening agent are impaired.

[0039]

It can be seen that the white laminated polyester film of the present invention is extremely useful as an information recording or printing material having excellent concealing properties and whiteness and good weather resistance.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasushi Sasaki 1-1-1, Katata 2-chome, Otsu-shi, Shiga F-term in Toyobo Co., Ltd. Research Laboratory 4F100 AA21A AA21C AH07A AH07C AH07H AK07 AK08 AK12 AK41B AK42 BA02 BA03 BA03 BA06 BA10A BA10C CA13A CA13C DC11A DC11B DC11C DE01A DE01C EH20 EJ38 GB90 JA13 JL09 JN28 YY00 YY00A YY00C

Claims (3)

[Claims] 1. A polyester film having a layer (A layer) containing anatase type titanium dioxide particles having an average particle size of 0.1 to 1.0 μm and a benzoxazole-based fluorescent whitening agent on at least one surface, A white laminated polyester film, wherein the content of the titanium dioxide particles (a wt%) and the content of the fluorescent whitening agent (b wt%) satisfy the following relationship. 0.005 × a <b <0.005 × a + 0.4 6 ≦ a ≦ 45 2. A white laminated polyester film, wherein whiteness (b ₀ ) and weather resistance (Δb) defined in the text satisfy the following relationship. −6.0 ≦ b ₀ ≦ −2.0 Δb ≦ 3.5 3. The laminated film according to claim 1, wherein at least one layer contains cavities and has an apparent specific gravity of 0.1.
A white laminated polyester film having a weight of 7 to 1.3 g / cm ³ .