JP2792123B2 - White polyester film - Google Patents

Description

The present invention relates to a polyester film having high whiteness. More specifically, cards, labels, courier slips, video printer receiving paper, barcode printer receiving paper, match print receiving paper, posters, maps, dust-free paper, display boards, white boards, photographic paper, copy paper, etc. The present invention relates to a white polyester film used as a substrate.

[Related Art] It is well known that a white polyester film is obtained by adding a large amount of titanium dioxide or calcium carbonate to a polyester film.

[Problems to be Solved by the Invention] However, when a large amount of calcium carbonate is added to the polyester, the polyester is colored yellow because of the decomposition of calcium carbonate or the interaction with the polyester, and the polyester film has high whiteness. Cannot be obtained. Such films can be used on cards, labels,
When used for applications such as receiving paper and photographic paper, the white background of the printed surface looks yellowish.

Of course, in order to improve the whiteness, it has been proposed to add a large amount of a fluorescent whitening agent. It often causes surface defects such as gels, which is not practical.

[Means for Solving the Problems] The present invention provides the following constitution in order to obtain a polyester film having high whiteness, that is, 7 to 30 parts by weight of calcium carbonate, a strontium compound and / or a barium compound per 100 parts by weight of polyester. The present invention relates to a white polyester film containing 0.001 to 5 parts by weight.

The polyester referred to in the present invention is a polymer obtained by condensation polymerization of a diol and a dicarboxylic acid. Representative examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid, and the like. And diols include ethylene glycol, trimethylene glycol,
And those represented by tetramethylene glycol, cyclohexanedimethanol and the like. Specific examples include polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene 2,6-naphthalenedicarboxylate. In the case of the present invention, polyethylene terephthalate and polyethylene naphthalate are particularly preferred.

Of course, these polyesters may be homopolyesters or copolyesters. Examples of the copolymerization components include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, and phthalic acid. And dicarboxylic acid components such as isophthalic acid, 2,6-naphthalenedicarboxylic acid and 5-sodium sulfoisophthalic acid.

Further, various known additives such as an antioxidant and an antistatic agent may be added to the polyester. Polyethylene terephthalate is preferred as the polyester used in the present invention. The polyethylene terephthalate film is excellent in water resistance, durability, chemical resistance and the like.

On the other hand, calcium carbonate may be natural or synthetic, but natural is obtained by repeating operations such as pulverization and classification, and has a wide particle size distribution and contains coarse particles. Many of them are not preferable as particles added to the film of the present invention, and synthetic calcium carbonate is more preferable. On the other hand, as the synthetic calcium carbonate, those synthesized by the carbonation reaction of milk of lime, or a method of adding an aqueous solution of sodium carbonate or ammonium carbonate to an aqueous solution of calcium chloride, such as calcium carbonate synthesized by the so-called calcium chloride method, etc. However, in the case of the present invention, calcium carbonate having a calcite structure synthesized by a reaction method between a suspension of calcium hydroxide and carbon dioxide, that is, a so-called carbon dioxide combination method is preferable.

The addition amount of the inorganic calcium carbonate particles is 7 to 30 parts by weight based on 100 parts by weight of the polyester. Preferably it is in the range of 8 to 20 parts by weight. If the added amount is less than 7 parts by weight, it is not possible to improve characteristics such as optical density and whiteness of the film. Conversely, if the amount exceeds 30 parts by weight, the film tends to break during stretching. In this case, the average particle diameter of the inorganic calcium carbonate particles is preferably 0.3 to 5 μm. More preferably, it is 0.4 to 3 μm. 0.3
When the particle size is less than 5 μm,
When the ratio exceeds, no improvement in characteristics is observed.

As the strontium compound and / or barium compound, their carbonates, sulfates, chlorides, hydroxides,
Oxides and the like can be mentioned. These compounds may simply be allowed to coexist with calcium carbonate, but are preferably added during the synthesis of calcium carbonate. For example, a form in which a predetermined amount of a strontium compound or a barium compound is added before or during the carbonation reaction, the reaction is performed, and the form is adsorbed on calcium carbonate is more preferable.

The strontium compound, the barium compound, or both are added in an amount of 0.0
The amount is from 01 to 5 parts by weight, preferably from 0.005 to 5 parts by weight, more preferably from 0.01 to 4 parts by weight. When the addition amount is less than 0.001 part by weight, the whiteness of the polyester film is not improved, the color tone is poor, and the film is only yellowish. On the other hand, when the amount exceeds 5 parts by weight, not only the effect of improving whiteness is not recognized, but also defects such as agglomeration of the particles and surface defects are caused.

In the polyester film of the present invention, in addition to calcium carbonate, amorphous zeolite particles, anatase type titanium dioxide, calcium phosphate, silica, kaolin, talc,
Fine particles such as clay may be used in combination. The amount of these additives is preferably 0.005 to 1 part by weight based on 100 parts by weight of the polyester composition. In addition to the fine particles, fine particles precipitated by the reaction between the catalyst residue and the phosphorus compound in the polyester polycondensation reaction system can be used in combination.
Examples of the precipitated fine particles include calcium, lithium and phosphorus compounds, calcium and phosphorus compounds, or calcium, magnesium and phosphorus compounds, and the like. Content is polyester 100
It is preferably 0.05 to 1 part by weight based on part by weight.

Examples of the polyolefin resin include polyethylene, polypropylene, polybutene, polymethylpentene, and polystyrene. Also, not necessarily
The copolymer is not limited to a homopolymer, and may be a copolymer thereof. Among them, polymethylpentene is preferred. This is because polymethylpentene has good releasability from polyester and easily forms voids.

Here, the polyolefin-based resin, may be any such thing as long as it can form a film is mixed with the polyester, but at the time of 280 ° C., a melt viscosity at剪段stress 10 ⁵ dyn / cm ² (αPOISE ), The melt viscosity (βPOISE) at a shear stress of 10 ⁶ dyn / cm ² satisfies 3 ≦ logα ≦ 51 ≦ logβ ≦ 31 1 ≦ log (α / β) ≦ 3, and the polyolefin resin Has a critical surface tension of 10 to 30 dyn / cm.

The melting point of the polyolefin resin in the present invention is 200 to 2
Preferably it is 80 ° C. More preferably 220 ° C ~ 2
60 ° C. If the temperature is lower than 200 ° C., the film is melted by the heat treatment after stretching the film, and the void is reduced. Also
If it exceeds 280 ° C, it cannot be added to polyester and extruded.

In the present invention, the addition amount of the polyolefin resin is 5 to 30 parts by weight based on 100 parts by weight of the polyester,
Preferably, it is in the range of 5 to 20 parts by weight, more preferably 8 to 15 parts by weight. If the addition amount is less than 5 parts by weight, the amount of voids generated is insufficient and the cushioning property is lacking. If the addition amount exceeds 30 parts by weight, the film tends to be broken at the time of film formation and the productivity tends to be lacking. .

The specific gravity of the white polyester film in the present invention is 1.
Less than 20 is good. Preferably it is 0.50 to 0.95, more preferably 0.60 to 0.90. This is because a large amount of voids are generated in the film, the apparent specific gravity of the film is reduced, the cushioning property is improved, the amount of raw materials is reduced, and the cost of the film is reduced. When the specific gravity is less than 0.5, voids are excessively formed, resulting in a film having low strength. On the other hand, when the specific gravity is 1.2 or more, not only the cushioning property does not come out but also the cost of the film does not decrease.

The whiteness of the film of the present invention is preferably 90 or more, more preferably 95 or more in terms of whiteness. The color tone L value is 88 or more, a
Those having a value of -2 to 1.0 and a b value of -5 to 2 are preferred.

In the present invention, the optical density when the film thickness is converted to 150 μm is preferably 0.8 to 1.6. When the optical density is less than 0.8, the concealing rate of the film is poor, which is not preferable as a white film. In order to exceed 1.6, it is necessary to increase the stretching ratio of the film, and the film forming property is deteriorated.

Next, a method for producing the film of the present invention will be described.
It is not limited to such an example.

After sufficiently vacuum-drying the polyester chips containing calcium carbonate and strontium (barium) compound, if necessary, the polyolefin resin chips are mixed and supplied to an extruder heated to 270 to 300 ° C.
Extrude into a sheet from a T-die. Of course, it can be added in the form of a master chip or a powder to impart other properties. Further, the mixed chips may be previously kneaded with a pelletizer or the like. Further, the extruded film was brought into close contact with a cooling drum having a surface temperature of 10 to 60 ° C. by electrostatic force and cooled and solidified. Cool with a group of rolls.

Subsequently, the longitudinally stretched film is guided to a tenter while gripping both ends of the film with clips, and is horizontally stretched in a direction perpendicular to the longitudinal direction in an atmosphere heated to 90 to 140 ° C.

The stretching ratio is 2 to 5 times each in the vertical and horizontal directions, and the area ratio (longitudinal stretching ratio × lateral stretching ratio) is preferably 6 to 20 times. If the area magnification is less than 6 times, the whiteness of the obtained film becomes poor, and if it exceeds 20 times, the film tends to be broken at the time of stretching and the film forming property tends to be poor.

In order to impart the planarity and the dimensional stability of the biaxially stretched film in this manner, the film is heat-set at 150 to 230 ° C. in a tenter, uniformly cooled, and then cooled to room temperature to obtain a film of the present invention. .

[Measurement of Physical Properties and Method of Evaluating Effect] Methods of evaluating physical properties and effects of the present invention are as follows.

(1) Melt viscosity A polymer chip is converted to an advanced flow tester (Shimadzu Corporation)
(CFT type). The preheating time is 5 minutes and the measurement temperature is 280 ° C.

(2) Equivalent sphere equivalent diameter of voids A cross section cut in the machine direction or its vertical direction in the film forming process is taken at a magnification of 1000 to 5000 times with a scanning electron microscope, and at least the specified thickness range Ten
Zero or more voids were applied to an image analyzer to determine the distribution of the diameter of a circle corresponding to the void area. The volume average diameter of this distribution is defined as the average sphere equivalent diameter of the voids.

(3) Specific gravity A carbon tetrachloride-n-heptane-based density gradient tube
The value at ° C was used.

(4) Overlay the optical density OD film to a thickness around 150 μm,
It is measured with an optical densitometer (TR927 manufactured by Macbeth). A plot of the thickness and the optical density was made, and the optical density corresponding to a thickness of 150 μm was defined as the optical density converted to a thickness of 150 μm.

(5) Whiteness The whiteness of magnesium oxide is defined as a comparison value by a whiteness meter (KETT C-1) when the whiteness is 100%.

(6) Color Tone The surface color of the film was measured using a color machine CM-20 (manufactured by Color Machine Co., Ltd.), and the L value, a value, and b value were determined. The color tone of the film judged to have excellent whiteness has the following value.

88 ≤ L value, -2 ≤ a value ≤ 1, -5 ≤ b value ≤ 2 (7) Stretchability When the film is continuously formed for 24 hours, a film having 1 or less breakage is "good", 2 times The above was defined as "torn."

(8) Slit chips When the film of the present invention is cut with a single-blade razor for 24 hours,
The case where white powder was adhered to the leather was defined as "generated".

[Effect of the present invention] When calcium carbonate is added to polyester, if a strontium (barium) compound is contained, 1. whiteness is improved.

2. Since it does not contain thermally unstable compounds such as fluorescent brighteners, a uniform white film without surface defects can be obtained.

3. When the film is slit, the loss of white powder of calcium carbonate is drastically reduced.

4. The stretching tension is reduced, and tearing during film formation is greatly reduced.

[Examples] The present invention will be described based on examples.

Example 1 A polyethylene terephthalate (IV 0.65) chip containing 16 parts by weight of calcium carbonate (average particle size: 1.0 μm) and 0.05 part by weight of strontium carbonate was vacuum-dried at 180 ° C. for 3 hours, and then heated to 285 ° C. The mixture was supplied to a heated extruder and extruded into a sheet from a T-die. Furthermore, the unstretched film cooled and solidified by a cooling drum having a surface temperature of 25 ° C. is guided to a roll group heated to 90 to 98 ° C.
The film was longitudinally stretched three times in the longitudinal direction and cooled with a roll group at 25 ° C.

Subsequently, the longitudinally stretched film was guided to a tenter while gripping both ends of the film with clips, and horizontally stretched three times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. Thereafter, the film was heat-set at 220 ° C. in a tenter, uniformly cooled, and then cooled to room temperature to obtain a film having a winding thickness of 50 μm.

 Table 1 shows the physical properties of the obtained film.

Comparative Example 1 A biaxially stretched film of 50 μm was obtained in exactly the same manner as in Example 1 except that the strontium carbonate compound used in Example 1 was not added.

Example 2, Comparative Example 2 To Example 1 and Comparative Example 1, only 10 parts by weight of 4-methylpentene-1 polymer was added, and only 10 parts by weight of calcium carbonate was added. And a biaxially stretched film having a thickness of 50 μm was obtained.

Thus, it is understood that a film having high whiteness can be obtained by adding the strontium compound. The stretchability was also good, and almost no chips were generated at the time of slitting.

Example 3 Example 1 was performed using a polyethylene terephthalate (intrinsic viscosity 0.71) chip containing 25 parts by weight of calcium carbonate (average particle size: 1.5 μm) and 0.1 part by weight of barium sulfate.
Extruded and cast as described above. After preheating the film on a roll heated to 105 ° C, stretched 3.2 times in the longitudinal direction,
Immediately cooled to 25 ° C. Subsequently, the film was guided into a tenter, heated to 125 ° C., stretched 3.3 times in the width direction, and then heat-treated at 230 ° C. for 10 seconds while relaxing 5% in the width direction.

The thickness of the obtained film was 125 μm, and had the following characteristics.

Whiteness (%) 121 Color tone L value 98 a value -1.5 b value -2.5 Optical density 1.2 Specific gravity 0.98 Stretchability Good Slit chip hardly observed

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-256558 (JP, A) JP-A-63-137927 (JP, A) JP-A-63-162755 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C08J 5/00-5/24 C08J 9/00-9/42

Claims (5)

(57) [Claims] A white polyester film comprising 100 parts by weight of polyester and 7 to 30 parts by weight of calcium carbonate and 0.001 to 5 parts by weight of a strontium compound and / or a barium compound. 2. A white polyester film characterized by further comprising 5 to 30 parts by weight of a polyolefin resin in the polyester of (1). 3. The white polyester film according to claim 1, wherein the specific gravity is less than 1.2. 4. The melting point of the polyolefin resin is 200 to 280 ° C.
The white polyester film according to (2) or (3), wherein 5. The white polyester film according to claim 2, wherein the polyolefin resin is polymethylpentene.