JPH0952335A - White laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coextrusion laminated white biaxially oriented polyester film which has high whiteness and hiding property and moreover can maintain high degree of whiteness and hiking property even if it is exposed to ultraviolet rays or variations of temperature and humidity. SOLUTION: A coextrusion laminated biaxially oriented polyester film is provided, wherein a layer (layer A) containing a white pigment (a) of 2-40wt.% is disposed at least at the outermost layer and at least one layer (layer B) containing white pigment (b) or (c) is diposed at a layer other than the outermost layer. The pigment (a) is anatase type titanium dioxide having a mean particle diameter of 0.1-1.0μm and substantially containing no zinc compound nor aluminum compound and the pigment (b) is an anatase type titanium dioxide having a mean particle diameter of 0.1-1.0μm and containing an aluminum compound, and the pigment (c) is anatase type titanium dioxide having a mean diameter of 0.1-1.0μm and containing a zinc compound.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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.

[0002]

2. Description of the Related Art Biaxially oriented polyester films represented by polyethylene terephthalate have excellent mechanical properties, electrical properties,
From the standpoint 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 insulation and photographic films. Taking advantage of the excellent properties of such polyester films in recent years,
Widely used for electronic whiteboards and for magnetic cards such as credit cards, telephone cards, JR cards, and pachinko cards for finance, communications, entertainment, transportation, etc. There is.

Particularly in prepaid cards and the like, in combination with an excellent printing technique, the price displayed on the face of the printed sheet has a premium depending on the design or the like on the printed surface, so that it has an added value as a design product. 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 pattern vivid and to reveal the subtle shadow lasting.

Further, since the magnetic layer applied 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, this color is transmitted to the opposite printed surface. Therefore, the degree of hiding of the base film is extremely important so as not to reduce the whiteness of the printed surface. However, in such applications, since it is used while being affected by changes in temperature and humidity indoors and outdoors, or by ultraviolet rays such as sunlight and indoor fluorescent lamps, concealment of the polyester film used as the base material for a long time However, there is a problem in that the degree of whiteness is likely to decrease over time and the degree of whiteness is likely to decrease. It has been found that these problems are phenomena based on the deterioration reaction of titanium dioxide contained as a white masking agent in the white polyester film due to ultraviolet rays and temperature and humidity.

In order to prevent deterioration by ultraviolet rays, it is generally known that a white polyester film contains an ultraviolet absorber. This makes it possible to prevent deterioration of the white polyester film to some extent. However, since the organic ultraviolet absorber is generally easily decomposed by heat or oxidatively, for example, at a film forming temperature of polyethylene terephthalate of 270 to 300 ° C., the ultraviolet absorber is thermally decomposed or sublimated and its ultraviolet absorbing ability is reduced. It is very difficult to maintain sufficient weather resistance even if an organic UV absorber is blended with the white polyester film, such as a problem of marked reduction.

By the way, as a method for improving the deterioration phenomenon of white polyester film due to ultraviolet rays and changes in temperature and humidity, so-called weather resistance, as described in JP-B-7-5763 and JP-B-75764, It is known that anatase type titanium dioxide containing a zinc compound, an aluminum compound, a silicon compound or 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 is increased and the whiteness is decreased as compared with the untreated one. Second
In addition, since the treatment equipment for treating with such a metal compound has to be newly added to the titanium dioxide particle production equipment, the production cost of titanium dioxide increases, and the problem of the final product film cost increase is inevitable. Was happening to. That is, in order to suppress deterioration of quality due to deterioration over time, anatase-type titanium dioxide containing the above-mentioned metal compound is suitable, but the whiteness of the original anatase-type titanium dioxide is reduced, or a film is formed. However, there is a problem that the manufacturing cost of the product deteriorates, and improvement is required.

[0007]

Means for Solving the Problems In view of the situation where the requirements for weather resistance and whiteness maintenance of white polyester films are becoming strict, the present inventors have made diligent studies to solve the above problems, and as a result, Anatase type titanium dioxide excellent in whiteness not treated with metal compound is used as the outermost layer,
In the other layers, the coextrusion laminated biaxially oriented polyester having at least one layer containing anatase type titanium dioxide treated with a metal compound in order to suppress the deterioration phenomenon achieves the hiding power and whiteness maintenance of the white polyester film for the first time. In addition, they have found that the manufacturing cost of the film can be reduced, and have completed the present invention.

That is, the gist of the present invention is to use at least one outermost layer (A layer) containing 2 to 40% by weight of the following white pigment a and at least one layer containing the following white pigment b or c ( It exists in a coextrusion laminated biaxially stretched polyester film having layer B) as a layer other than the outermost layer. White pigment a: Anatase-type titanium dioxide having an average particle size of 0.1 to 1.0 μm and substantially free of zinc compound and aluminum compound White pigment b: An aluminum compound containing an average particle size of 0.1 to 1. 0 μm anatase type titanium dioxide white pigment c: containing zinc compound, average particle size 0.1
1.0 μm anatase type titanium dioxide

Hereinafter, the present invention will be described in detail. The polyester referred to in the present invention is a general term for polymers containing ester groups obtained by polycondensation with dicarboxylic acids, diols or hydroxycarboxylic acids. Examples of dicarboxylic acids include terephthalic acid, isophthalic acid, adipic acid,
There are azelaic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and the like, and diols include ethylene glycol and 1,4-
There are butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol and the like, and examples of hydroxycarboxylic acid include p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. . Typical examples of such polymers include polyethylene terephthalate and polyethylene-2,6-naphthalate. These polymers may be homopolymers or may be copolymers of a third component.

In the present invention, substantially no aluminum compound is contained in the polyester constituting the outermost layer (for example, the content is 0.01 in terms of aluminum element).
Anatase titanium dioxide (hereinafter, about 0.1% by weight or less) and substantially not containing a zinc compound (for example, the content is about 0.1% by weight in terms of zinc element) (hereinafter,
A specific amount of white pigment a) is blended with the polyester. For 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 referred to as white pigment) Pigment c) is blended with the polyester.

The content of the white pigment a is 2.0 to 40% by weight based on the polyester constituting the outermost layer, and is 5.0
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 increases 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 is lowered and problems such as film breakage during film formation may occur, which is not preferable.

The white pigments a, b and c used in the present invention have an average particle diameter of 0.1 to 1.0 μm and 0.2 to 0.5.
It is preferably μm. If 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. On the other hand, if the average particle size exceeds 1.0 μm, the original whiteness of the anatase type titanium dioxide decreases, which is not preferable. The thickness of the polyester layer forming the outermost layer of the coextrusion laminated white biaxially stretched polyester of the present invention is preferably 0.1 to 50 μm, more preferably 0.2 to 40 μm. When the layer thickness is less than 0.1 μm, the outermost layer thickness becomes smaller than the particle diameter of titanium dioxide used for the outermost layer,
Titanium dioxide particles tend to fall off the surface of the film, and as a result, whiteness tends to deteriorate. When 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 layer other than the outermost layer is usually 0.01 to 2.0% by weight in terms of aluminum element, and 0.1 to 1%. It is preferably 0.0% by weight. When 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 weather resistance improving effect of the film tends to be insufficient. On the contrary, when 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 content of the white pigment b is 2.0 to 30% by weight, preferably 5.0 to 20% by weight, based on the polyester. This amount is 2.0% by weight
If it is less than 1, the light transmittance tends to increase, and the hiding effect may be insufficient. Also, this amount is 30% by weight
If it exceeds, the mechanical strength of the film may decrease, and 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 converted to anatase type titanium dioxide by 1.0 in terms of silicon element.
By containing the content of the titanium dioxide in an amount of not more than about wt%, the dispersibility of titanium dioxide in the polyester can be improved. As a method for incorporating such an aluminum compound and silicon dioxide into anatase titanium dioxide, a predetermined amount of aluminum compound such as aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum chloride and silicon dioxide are added and blended during the production of anatase 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, zinc nitrate. However, the present invention is not limited to these. Among these, zinc compounds having good heat resistance are preferable.

The amount of zinc compound contained in the white pigment c is
It is usually 0.1 to 2.0% by weight in terms of zinc element, and is 0.1.
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 1, the weather resistance improving effect 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 be lowered, and problems such as film breakage during film formation may occur. There is.

The content of the white pigment c is preferably 2.0 to 30% by weight, more preferably 5.0 to 20% by weight based on the polyester. The amount of white pigment c is 2.0
If it is less than wt%, the light transmittance tends to be high, and the white hiding effect tends to be insufficient. On the other hand, if this amount exceeds 30% by weight, the mechanical strength of the polyester may be lowered, and problems such as breakage of the film during film formation may occur. As a method for incorporating a zinc compound into anatase titanium dioxide, a predetermined amount of zinc compound such as zinc oxide, zinc hydroxide, zinc carbonate or zinc chloride may be added and blended at the time of producing anatase titanium dioxide, or commercially available. The anatase type titanium dioxide may be surface-treated with a zinc compound such as zinc oxide, zinc hydroxide, zinc carbonate or zinc chloride.

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 in the anatase type titanium dioxide or may be present on the surface, but the weather resistance is not limited. In order to improve the property or the initial whiteness, it is preferable that it is 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 manufacturing process.

In the present invention, if necessary, weather resistance and whiteness are not adversely affected, the number of coarse particles is not increased,
In addition, inactive particles other than the white pigments a, b, and c may be used in combination as long as the average particle diameter and 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, which are precipitated by the reaction of the catalyst residue and the phosphorus compound in the reaction system, can be used together. The outermost layer of the coextrusion laminated white biaxially oriented polyester of the present invention has a thickness of usually 0.1 to
It is selected from 50 μm. For example, since the thickness of the polyester base film of a pachinko card is usually 188 μm, if the outermost layer thickness is 20 μm, the total layer thickness other than the outermost layer is 148 μm.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing the film of the present invention will be specifically described below, but the invention is not particularly limited to the following examples as long as the requirements for the present invention are satisfied. A polyester containing a predetermined amount of the above white pigment a and a polyester containing a predetermined amount of the above white pigment b or c,
Separately dried and melt extruded from different extruders, then laminated and laminated in a laminar flow in the molten polymer channel pipe or in the extrusion die and discharged from the extrusion die to form an unstretched laminated film . For drying, it is preferable to use a hopper dryer, a vacuum dryer, a paddle dryer, an oven or the like. When the B layer is used as the main extruder and the sub extruder is used for the A layer, 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. Especially when switching production of films with different whiteness, there is little loss and it contributes to productivity improvement. It is also preferable to apply an electrostatic contact method at the time of casting and also use a liquid application method such as water.

The unstretched laminated film thus obtained is
First, the film is stretched in the longitudinal direction at 70 ° C. to 145 ° C. in a single step or in multiple steps at a rate of 2.0 to 6 times to obtain a longitudinally uniaxially stretched film, and then the coating liquid is sequentially applied to both surfaces of the film, and appropriate drying is performed, Alternatively, without drying, the coated uniaxially stretched film is gripped with a clip and guided to a tenter, and first stretched in the transverse direction at 90 to 160 ° C. to 2.0 to 6.0 times, and then to 150 to
It is preferable to perform heat treatment at 250 ° C. for 1 to 600 seconds. At this time, in the maximum temperature zone of the heat treatment and / or the cooling zone at the exit of the heat treatment, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the lateral direction is preferable. Further, it is also possible to add re-longitudinal stretching and re-transverse stretching if necessary.

[0022]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In addition, various physical properties,
Characteristics are measured or defined as follows. In the examples, “%” means “% by weight” and “part” means “part by weight”.

(1) Average particle size Centrifugal sedimentation type particle size distribution measuring device (SA-CP manufactured by Shimadzu Corporation)
The value of the integrated (weight basis) 50% in the equivalent spherical distribution measured by Type 3) is used. (2) Whiteness of film It was measured using a color difference meter manufactured by Tokyo Denshoku. The whiteness of the film is represented by the b value, and the smaller the value, the higher the whiteness. In addition, the larger the b value, the stronger the yellowish color, which indicates yellowing. (3) Concealment Degree The density of transmitted light 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 resistance to moist heat 17 days after exposing the film in an environment of 85 ° C. and 98% RH in a moist heat oven, the Macbeth densitometer (T) of the above (4) was used.
The transmission density (OD value) was measured using D-904 type. Ratio of initial OD value and OD value after 17 days (OD '), O
The larger D ′ / OD% indicates the better wet heat resistance. (5) Evaluation of UV resistance UV long life fade meter (F
AL-3 type) was used, and after irradiating with ultraviolet rays at 63 ° C. ± 3 ° C. for 300 hours, the b value was measured using the color difference meter (TC-5D type) of (2) above. The larger the difference (Δb = b′−b) between the initial b value and the b value (b ′) after 300 hours, the poorer the weather resistance. (6) Zinc and aluminum quantification method Zinc and aluminum were quantified using an SPS1500VR ICP emission spectroscopy analyzer 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 starting the reaction, it took about 4 and a half hours to heat up to 230 ° C,
The transesterification reaction was substantially completed. Then 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 raised to 280 ° C., while the pressure was gradually reduced to 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 Masterbatch Chip) 60 parts of the obtained polyester (A) and titanium dioxide (titanium dioxide a, titanium dioxide b-1, b-2, dioxide) produced by a conventional method and having an average particle diameter of 0.3 μm. Titanium c-1, c-
2), 40 parts are melt-mixed in a twin-screw extruder according to a conventional method,
Master-batch chips (Aa, Ab-1, respectively)
Ab-2, Ac-1, Ac-2) were obtained. The characteristics of the titanium dioxide used here are shown in Table 2 below.

(Film Forming Method) The above masterbatches Aa, A
-B-1 was blended with polyester A separately so that the blending amount of titanium dioxide was 7%, and then 180
After drying at 5 ° C for 5 hours, it is coextruded and rapidly solidified to form a sheet, which is biaxially stretched longitudinally and laterally at 83 ° C 3.1 times and 125 ° C 3.6 times respectively, and then heat treated at 230 ° C. As a result, a white biaxial polyester film of 188 μm was obtained. The layer structure of the obtained film was such that the outermost layer was a polyester layer containing 7% of titanium dioxide a, the thickness thereof was 15 μm, and the polyester layer containing 7% of titanium dioxide b was an intermediate layer.
Its thickness was 158 μm. The characteristics 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 White biaxial was prepared in the same manner as in Example 1 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.
The characteristics of the obtained white polyester film are shown in Table 1. 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 the 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 the titanium dioxide b-1 used in the intermediate layer of the film was changed to titanium dioxide a. Comparative Example 2 In Example 2, titanium dioxide b was used instead of titanium dioxide a.
A white biaxially stretched film was obtained by the same method as in Example 2 except that -1 was used as the outermost layer of the film. Comparative Example 3 A white biaxially stretched film was prepared in the same manner as in Example 3, except that titanium dioxide a was used for the intermediate layer of the film in place 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 the polymer was frequently broken, so that a biaxially stretched film could not be obtained. Comparative Example 5 A white biaxially stretched film was obtained in the same manner as in Example 3 except that titanium dioxide c-1 used in the intermediate layer of the film was changed to titanium dioxide c-2. However, the thermal stability of the polymer was poor and breakage occurred frequently, and a biaxially stretched film could not be obtained. The results obtained above are shown in Table 1 below.

[0031]

[Table 1] In Table 1, * represents a set value.

[0032]

[Table 2] In Table 2, * represents an Al element conversion and ** represents a Zn element conversion value.

[0033]

EFFECT OF THE INVENTION The film of the present invention has a high degree of whiteness and hiding power, and is a coextrusion laminated white biaxially stretched film that maintains a high degree of whiteness and hiding power even when exposed to ultraviolet rays and changes in temperature and humidity. Polyester film, yet productivity,
It is excellent in terms of cost and has a great industrial value.

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Claims (1)

[Claims] 1. A layer (A layer) containing 2 to 40% by weight of the following white pigment as at least one outermost layer, and at least one layer (B layer) containing the following white pigment b or c.
A coextrusion laminated biaxially stretched polyester film having as a layer other than the outermost layer. White pigment a: Anatase-type titanium dioxide having an average particle size of 0.1 to 1.0 μm and substantially free of zinc compound and aluminum compound White pigment b: An aluminum compound containing an average particle size of 0.1 to 1. 0 μm anatase type titanium dioxide white pigment c: containing zinc compound, average particle size 0.1
1.0 μm anatase type titanium dioxide