JP3422600B2 - White laminated polyester film - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white biaxially stretched polyester film which is highly improved in whiteness and weather resistance and can be produced at low cost. 2. Description of the Related Art Biaxially oriented polyester films represented by polyethylene terephthalate have excellent mechanical and electrical properties,
From the viewpoint of chemical resistance and dimensional stability, it is used as a base material in many fields such as information recording materials, capacitors, packaging, plate making, electrical discharge, and photographic films. In recent years, taking advantage of the excellent properties of such polyester films,
It is widely used for finance, communication, entertainment, transportation, etc. as a whiteboard for electronic whiteboards and for magnetic cards such as credit cards, telephone cards, JR cards, pachinko cards, etc. I have. In particular, prepaid cards and the like have an added value as a design product, such as a premium on the price displayed on the ticket depending on the design of the printing surface, etc., in combination with excellent printing technology. In this case, the whiteness of the white polyester film as the base material is particularly important in order to make the contrast of the design vivid and to produce a subtle cotton last. Further, the magnetic layer coated on the side opposite to the printed surface of the prepaid card is colored in the color of the constituent magnetic material, binder, etc., usually blackish brown, and this color is transmitted to the printed surface on the opposite side. The degree of hiding of the base film is extremely important so as not to lower the whiteness of the printed surface. However, in such applications, since it is used under the influence of temperature and humidity changes indoors and outdoors, or under the influence of sunlight or ultraviolet rays caused by indoor fluorescent lamps, etc., the polyester film used as a base material for a long time is concealed. However, there is a problem that the degree decreases over time and the degree of whiteness tends to decrease. It has been found that these problems are phenomena based on the deterioration reaction of titanium dioxide contained as a white hiding agent in a white polyester film due to ultraviolet rays and temperature and humidity. It is generally known that a white polyester film contains an ultraviolet absorber in order to prevent deterioration due to ultraviolet rays. This makes it possible to prevent the deterioration of the white polyester film to some extent. However, organic UV absorbers are generally easily thermally decomposed or oxidatively decomposed. For example, at a film formation temperature of 270 to 300 ° C. of polyethylene terephthalate, the UV absorber is thermally decomposed or sublimated, and its ultraviolet absorbing ability is reduced. Even if an organic ultraviolet absorber is incorporated into a white polyester film, it is very difficult to maintain sufficient weather resistance, for example, there is a problem of remarkable reduction. Meanwhile, as a method for improving the deterioration phenomenon, that is, the so-called weather resistance, of a white polyester film due to a change in ultraviolet light or temperature and humidity, as described in JP-B-7-5763 and JP-B-7-5564, It is known that anatase-type titanium dioxide containing a zinc compound, an aluminum compound, a silicon compound and the like may be used. However, titanium dioxide containing such a metal compound has the following problems. First, the inclusion of the metal compound has a problem that the b value increases and the whiteness decreases as compared with the untreated metal. Second
In addition, it is necessary to newly add processing equipment for processing with such a metal compound to the titanium dioxide particle manufacturing equipment, which increases the manufacturing cost of titanium dioxide and inevitably raises the cost of the final product film. Had occurred. That is, in order to suppress deterioration over time due to the deterioration phenomenon, anatase-type titanium dioxide containing the above metal compound is preferable, but the whiteness of the original anatase-type titanium dioxide is reduced, However, there is a problem that the manufacturing cost is worsened, and improvement is required. SUMMARY OF THE INVENTION The present inventor has made intensive studies to solve the above-mentioned problems in view of the strict requirements for weather resistance and whiteness maintenance of white polyester films. As a result, the anatase type titanium dioxide excellent in whiteness not treated with the metal compound as the outermost layer,
In the other layers, a co-extruded laminated biaxially stretched polyester having at least one layer containing anatase-type titanium dioxide treated with a metal compound to suppress the deterioration phenomenon achieves, for the first time, the hiding degree and whiteness maintenance of a white polyester film. And found that the production cost of the film could be reduced, and completed the present invention. That is, the gist of the present invention is that at least one layer containing the following white pigment b or c is used as at least one outermost layer (layer A) containing 2 to 40% by weight of the following white pigment a. (B layer) as a layer other than the outermost layer. White pigment a: anatase-type titanium dioxide white pigment having an average particle diameter of 0.1 to 1.0 μm substantially not containing a zinc compound and an aluminum compound b: containing an aluminum compound and having an average particle diameter of 0.1 to 1. 0 μm anatase type titanium dioxide white pigment c: containing zinc compound, average particle size 0.1 to
The present invention will be described in detail below. The polyester in the present invention is a generic name of a polymer containing an ester group obtained by polycondensation with a dicarboxylic acid, a diol or a hydroxycarboxylic acid. Dicarboxylic acids include terephthalic acid, isophthalic acid, adipic acid,
Azelaic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc., and diols such as ethylene glycol, 1,4-
There are butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, and the like, and the hydroxycarboxylic acid includes p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and the like. . Typical examples of such polymers include polyethylene terephthalate and polyethylene-2,6-naphthalate. These polymers may be homopolymers or copolymers of the third component. In the present invention, the polyester constituting the outermost layer contains substantially no aluminum compound (for example, the content is 0.01% in terms of aluminum element).
Weight percent) and substantially no zinc compound (for example, the content is less than about 0.1 weight% in terms of zinc element) anatase-type titanium dioxide (hereinafter, referred to as
White pigment a) is blended with the polyester in a specific amount. For the polyester constituting at least one layer other than the outermost layer, anatase-type titanium dioxide containing an aluminum compound (hereinafter, referred to as white pigment b) or anatase-type titanium dioxide containing a zinc compound (hereinafter, white) Pigment c) is blended with the polyester. The compounding amount of the white pigment a is 2.0 to 40% by weight with respect to the polyester constituting the outermost layer, and is 5.0% by weight.
It is preferably about 30% by weight. If the blending amount of the white pigment a is less than 2.0% by weight, the light transmittance of the film becomes large and the hiding effect becomes insufficient, which is not preferable.
On the other hand, if the amount of the white pigment a exceeds 40% by weight, the mechanical strength of the film decreases, and for example, problems such as breakage of the film at the time of film formation occur, which is not preferable. The average particle size of the white pigments a, b and c used in the present invention is 0.1 to 1.0 μm, and 0.2 to 0.5 μm.
μm is preferred. When the average particle size is less than 0.1 μm, the light transmittance of the film becomes large, and the white hiding effect becomes insufficient, which is not preferable. Conversely, if the average particle size exceeds 1.0 μm, the inherent whiteness of the anatase type titanium dioxide decreases, which is not preferable. The thickness of the polyester layer constituting the outermost layer of the co-extruded laminated white biaxially stretched polyester of the present invention is preferably from 0.1 to 50 µm, more preferably from 0.2 to 40 µm. When the layer thickness is less than 0.1 μm, the outermost layer thickness is smaller than the particle diameter of titanium dioxide used for the outermost layer,
Titanium dioxide particles tend to fall off the film surface, resulting in poor whiteness. If the outermost layer thickness exceeds 50 μm, the whiteness of the film tends to be poor. The amount of the aluminum compound contained in the white pigment b used in at least one of the layers other than the outermost layer is usually 0.01 to 2.0% by weight in terms of aluminum element, and 0.1 to 1% by weight. It is preferably 0.0% by weight. If the amount of the aluminum compound contained in the white pigment b is less than 0.01% by weight in terms of aluminum element, the effect of improving the weather resistance of the film tends to be insufficient. Conversely, if the amount of the aluminum compound contained in the white pigment b exceeds 2.0% by weight in terms of aluminum element, the thermal stability of the film tends to decrease, and problems such as breakage of the film during film formation may occur. There is. The amount of the white pigment b is preferably 2.0 to 30% by weight, more preferably 5.0 to 20% by weight, based on the polyester. 2.0% by weight
If it is less than 3, the light transmittance tends to increase, and the concealing effect may be insufficient. In addition, this amount is 30% by weight.
If the ratio exceeds the above range, the mechanical strength of the film decreases, and for example, problems such as breakage of the film during film formation may occur. Further, the white pigment b used in the present invention preferably contains silicon dioxide. For example, silicon dioxide is added to anatase type titanium dioxide in an amount of 1.0 as silicon element.
When the content is about 10% by weight or less, the dispersibility of titanium dioxide in the polyester can be improved. As a method of including such an aluminum compound and silicon dioxide in anatase-type titanium dioxide, a predetermined amount of an aluminum compound such as aluminum oxide, aluminum hydroxide, aluminum carbonate, and aluminum chloride and silicon dioxide are added and mixed during the production of anatase-type titanium dioxide. Alternatively, commercially available anatase-type titanium dioxide may be surface-treated with an aluminum compound such as aluminum oxide, aluminum hydroxide, aluminum carbonate, and aluminum chloride, and silicon dioxide. Examples of the zinc compound contained in the white pigment c used in the other outermost layer include zinc acetate, zinc benzoate, zinc oxide, zinc carbonate, zinc chloride, zinc hydroxide, zinc lactate, zinc phosphate, zinc sulfate, and zinc nitrate. And the like, but are not limited to these. Among them, zinc compounds having good heat resistance are preferable. The amount of the zinc compound contained in the white pigment c is
Usually 0.1 to 2.0% by weight in terms of zinc element;
It is preferably from 5 to 1.0% by weight. The amount of the zinc compound contained in the white pigment c is 0.1% by weight in terms of zinc element.
If it is less than 3, the effect of improving the weather resistance tends to be insufficient.
When the amount of the zinc compound contained in the white pigment c exceeds 2.0% by weight in terms of zinc element, the thermal stability of the polyester tends to decrease, and a problem such as film breakage during film formation may occur. There is. The amount of white pigment c is preferably 2.0 to 30% by weight, more preferably 5.0 to 20% by weight, based on polyester. When the blending amount of the white pigment c is 2.0
If the amount is less than 10% by weight, the light transmittance tends to increase and the white hiding effect tends to be insufficient. On the other hand, if the amount exceeds 30% by weight, the mechanical strength of the polyester is reduced, and for example, a problem such as breakage of the film during film formation may occur. As a method of causing the zinc compound to be contained in the anatase type titanium dioxide, a predetermined amount of zinc oxide, zinc hydroxide, zinc carbonate, zinc compound such as zinc chloride may be added and blended during the production of the anatase type titanium dioxide, or a commercially available zinc compound may be used. The anatase type titanium dioxide may be surface-treated with a zinc compound such as zinc oxide, zinc hydroxide, zinc carbonate, zinc chloride and the like. The aluminum compound and the silicon dioxide or zinc compound of the white pigments b and c used in the present invention may be contained inside the anatase type titanium dioxide or present on the surface. In order to improve the properties or the initial whiteness, it is preferably present on the surface. White pigments a and b used in the present invention
And c can be blended at any stage of the polyester film production process. In the present invention, if necessary, the weather resistance and the whiteness are not adversely affected, and the number of coarse particles is not increased.
In addition, inert particles other than the white pigments a, b and c may be used in combination as long as the average particle size and the content are such that the smoothness of the polyester film surface is not adversely affected. In addition to the above-mentioned inert particles, so-called precipitation-type fine particles precipitated by the reaction of a catalyst residue and a phosphorus compound in a reaction system can be used in combination. The thickness of the outermost layer of the co-extruded laminated white biaxially stretched polyester of the present invention is usually 0.1 to
It is selected from 50 μm. For example, since the thickness of the polyester base film of the pachinko card is usually 188 μm, if the outermost layer thicknesses are each 20 μm, the total thickness of the layers other than the outermost layer is 148 μm. Next, the method for producing a film of the present invention will be described in detail, but is not particularly limited to the following examples as long as the constitutional requirements of the present invention are satisfied. Polyester containing a predetermined amount of the above white pigment a, and polyester containing a predetermined amount of the above white pigment b or c,
After being separately dried and melt-extruded from separate extruders, they are joined and laminated in a laminar flow form in a molten polymer channel tube or an extrusion die, and discharged from the extrusion die to form an unstretched laminated film. . Drying is preferably performed using a hopper dryer, a vacuum dryer, a paddle dryer, an oven, or the like. When the layer B is used as the main extruder and the sub-extruder is used for the layer A, the sub-extruder is used as a twin-screw vent extruder.
It is also a preferred embodiment to use a method of directly adding a white pigment or the like. In particular, when switching and producing films having different whiteness levels, loss is small and contributes to productivity improvement. It is also preferable to apply an electrostatic adhesion method at the time of casting and to use a liquid coating method such as water. The unstretched laminated film thus obtained is
First, stretched 2.0 to 6 times in one or multiple stages at 70 ° C. to 145 ° C. in a longitudinal direction to form a longitudinally uniaxially stretched film, and then sequentially apply a coating solution to both sides of the film and perform appropriate drying. Alternatively, without drying, the coated uniaxially stretched film is then gripped with a clip and guided to a tenter. First, the film is stretched 2.0 to 6.0 times in the horizontal direction at 90 to 160 ° C.
It is preferable to perform heat treatment at 250 ° C. for 1 to 600 seconds. At this time, a method of relaxing 0.1 to 20% in the vertical direction and / or the horizontal direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, re-longitudinal stretching and re-lateral stretching can be added as necessary. EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In addition, various physical properties,
Characteristics are measured or defined as follows. In the examples, “%” means “% by weight” and “parts” means “parts by weight”. (1) Average particle size A centrifugal sedimentation type particle size distribution analyzer (SA-CP manufactured by Shimadzu Corporation)
The value of 50% of the integrated (weight basis) in the equivalent spherical distribution measured in (Type 3) is used. (2) Whiteness of Film Measured using a color difference meter manufactured by Tokyo Denshoku. The whiteness of a film is represented by the b value, and the smaller the value, the higher the whiteness. In addition, the larger the b value, the more yellowish and yellowish. (3) Opacity The transmitted light density under the G filter was measured using a Macbeth densitometer (TD-904 type). The larger this value is, the higher the hiding power is. (4) Evaluation of Moisture and Heat Resistance The film was exposed in an environment of 85 ° C. and 98% RH in a moist heat oven, and 17 days after exposure, the Macbeth densitometer (T) described in (4) above.
D-904) was used to measure the transmission density (OD value). The ratio of the initial OD value to the OD value after 17 days (OD '), O
The greater the D '/ OD%, the better the moist heat resistance. (5) UV resistance evaluation Suga Test Instruments UV Long Life Fade Meter (F
After irradiating ultraviolet rays at 63 ° C. ± 3 ° C. for 300 hours using an AL-3 type), the b value was measured using the color difference meter (TC-5D type) of the above (2). An increase in the difference (Δb = b′−b) between the initial b value and the b value (b ′) after 300 hours indicates that the weather resistance is poor. (6) Method for quantifying zinc and aluminum Zinc and aluminum were quantified using an SPS 1500 VR ICP emission spectrometer manufactured by Seiko Denshi Kogyo. Example 1 (Production method of polyester chip) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol and 0.07 part of calcium acetate-hydrate were placed in a reactor, heated and heated, and methanol was distilled off to carry out a transesterification reaction. ,
After the start of the reaction, it took about 4.5 hours to raise the temperature to 230 ° C,
The transesterification was substantially completed. Next, phosphoric acid 0.0
4 parts and 0.035 part of antimony trioxide were added and polymerized according to a conventional method. That is, the reaction temperature was gradually increased to finally 280 ° C., while the pressure was gradually decreased to finally 0.05 mmHg. After 4 hours, the reaction was terminated, and the mixture was formed into chips according to a conventional method to obtain a polyester (A). (Production of master batch chip) Titanium dioxide (titanium dioxide a, titanium dioxide b-1, b-2, titanium dioxide a) having a mean particle size of 0.3 μm produced according to a conventional method with 60 parts of the obtained polyester (A). Titanium c-1, c-
2) 40 parts were melt-mixed in a twin-screw extruder according to a conventional method,
Master batch chip (A-a, A-b-1, respectively)
Ab-2, Ac-1 and Ac-2) were obtained. The properties of the titanium dioxide used here are shown in Table 2 below. (Film forming method) The above master batches A-a, A
-B-1 was separately blended with polyester A so that the blending amount of titanium dioxide was 7%, and then 180%.
After drying at 5 ° C. for 5 hours, co-extrusion, quenching and solidification are performed to form a sheet, and the sheet is sequentially and biaxially stretched at 83 ° C. 3.1 times and 125 ° C. 3.6 times, and then heat-treated at 230 ° C. To obtain a 188 μm white biaxial polyester film. The layer structure of the obtained film was such that the outermost layer was a polyester layer containing 7% titanium dioxide a, the thickness was 15 μm, and the middle layer was a polyester layer containing 7% titanium dioxide b.
Its thickness was 158 μm. The properties of the obtained white polyester film are shown in Table 1 below. The whiteness and weather resistance of the obtained polyester film were very good. Example 2 The same procedure as in Example 1 was carried out except that the amount of titanium dioxide a used in Example 1 was 20% and the amount of titanium dioxide b-1 was 5%. A stretched film was obtained.
Table 1 shows the properties of the obtained white polyester film. The obtained white polyester film had extremely satisfactory properties as in Example 1. Example 3 A white biaxially stretched film was obtained in the same manner as in Example 2, except that titanium dioxide b-1 used in Example 2 was changed to titanium dioxide c-1. The obtained white polyester film had extremely satisfactory properties as in Example 2. Comparative Example 1 A white biaxially stretched film was obtained in the same manner as in Example 1 except that titanium dioxide a-1 was used instead of titanium dioxide b-1 used for the intermediate layer of the film. Comparative Example 2 In Example 2, titanium dioxide b was used instead of titanium dioxide a.
A white biaxially stretched film was obtained in the same manner as in Example 2, except that -1 was used as the outermost layer of the film. Comparative Example 3 In Example 3, a white biaxially stretched film was produced in the same manner as in Example 3, except that titanium dioxide a was used for the intermediate layer of the film instead of titanium dioxide c-1. Obtained. Comparative Example 4 A white biaxially stretched film was obtained in the same manner as in Example 1 except that titanium dioxide b-1 used in the intermediate layer of the film was changed to titanium dioxide b-2. However, the thermal stability of the polymer was poor, and rupture occurred frequently, so that a biaxially stretched film could not be obtained. Comparative Example 5 In Example 3, a white biaxially stretched film was obtained in the same manner as in Example 3, except that titanium dioxide c-1 used for the intermediate layer of the film was changed to titanium dioxide c-2. However, the thermal stability of the polymer was poor, and rupture occurred frequently, and a biaxially stretched film could not be obtained. The results obtained above are shown in Table 1 below. [Table 1] In Table 1, * indicates a set value. [Table 2] In Table 2, * represents an Al element conversion, and ** represents a Zn element conversion value. The film of the present invention has a high degree of whiteness and hiding power, and maintains a high degree of whiteness and hiding degree even when exposed to ultraviolet rays or changes in temperature and humidity. It is a biaxially stretched polyester film, yet has productivity,
It is excellent in cost, and its industrial value is very large.

Claims (1)

(57) Claims 1. A layer (A layer) containing the following white pigment a in an amount of 2 to 40% by weight as at least one outermost layer, and at least one layer containing the following white pigment b or c. One layer (layer B)
And a co-extruded laminated biaxially oriented polyester film having a layer other than the outermost layer. White pigment a: anatase-type titanium dioxide white pigment having an average particle diameter of 0.1 to 1.0 μm substantially not containing a zinc compound and an aluminum compound b: containing an aluminum compound and having an average particle diameter of 0.1 to 1. 0 μm anatase type titanium dioxide white pigment c: containing zinc compound, average particle size 0.1 to
1.0 μm anatase type titanium dioxide