JP2718172B2 - White polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a white polyester film which is rich in cushioning properties and whose surface is difficult to be cleaved. For more details, cards, labels, courier slips, video printer receiving paper, barcode printer receiving paper, match print receiving paper, posters, maps, dust-free paper, display boards,
The present invention relates to a white polyester film used as a base material of a white plate, photographic paper, copy paper, or the like.

[Prior Art] If paper is used for printed matter used outdoors, it cannot withstand the weather, and water-resistant paper or plastic film has conventionally been used. A typical plastic film used for such a purpose is a plastic film obtained by adding calcium carbonate to a polyolefin resin (for example, JP-B-63-64310). This has been considered to be weak to heat and to have a problem in mechanical strength because it is based on polyolefin.

On the other hand, in the case of a film based on polyester,
It is resistant to heat and mechanical strength, but has the disadvantage of being expensive.

When used as a substitute for paper, there are many uses for printing. In this case, if the surface is easily cleaved, the powder is wiped during printing, which causes printing trouble.

[Problems to be Solved by the Invention] It is an object of the present invention to provide an inexpensive white film that can solve the above-mentioned drawbacks, is resistant to heat, has high mechanical strength, and is printable.

[Means for Solving the Problems] The present invention relates to a method in which a polyolefin resin is added to a polyester.
The present invention relates to a white polyester film which is biaxially stretched and has a film density of 0.5 to 1.2 g / cm ³ and a cleavage index of the film surface of 15 or less. .

The polyester in the present invention may be any polyester as long as it can form a film. For example, polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-0-oxybenzoate, poly-
Examples thereof include 1,4-cyclohexylene dimethylene terephthalate and polyethylene 2,6-naphthalenedicarboxylate. 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. , Isophthalic acid, 2.6-naphthalenedicarboxylic acid,
And dicarboxylic acid components such as 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. Polyethylene terephthalate film is excellent in water resistance, durability, chemical resistance and the like.

The polyolefin resin referred to in the present invention may be any resin as long as it can be mixed with polyester to form a film, but at 280 ° C., a shear stress of 10 ⁵ dyn / cm ²
And the melt viscosity (βPOISE) at a shear stress of 10 ⁶ dyn / cm ² satisfies the following relationship: 3 ≦ logα ≦ 51 ≦ logβ ≦ 31 1 ≦ log (α / β) ≦ 3, and The polyolefin resin preferably has a critical surface tension of 10 to 30 dyn / cm. More preferably, 3.5 ≦ logα ≦ 4.52 ≦ logβ ≦ 31.5 ≦ log (α / β) ≦ 2.5, and the critical surface tension of the polyolefin resin is 15 to
25. It is the melt viscosity and the critical surface tension that determine the dispersion state of the polyolefin resin when extruded after being added to the polyester. If log α is less than 3, the formation of voids described later will be poor. If the log α exceeds 5, the voids become too large, and the strength of the film decreases. If the logβ is less than 1 or the critical surface tension exceeds 30 dyn / cm, the melt viscosity is low, or the compatibility with the polyester is good, so that the polyolefin-based resin easily gathers on the surface layer of the film and the surface is easily peeled. Therefore, the cleavage index cannot be reduced to 15 or less. Further, if the critical surface tension exceeds 30 dyn / cm, voids are less likely to be generated during stretching due to good compatibility with polyester,
The density cannot be reduced below 1.2 g / cm ³ . logβ is 3
If or exceeds, or if the critical surface tension is less than 10 dyn / cm, the melt viscosity is high, or because of poor compatibility with polyester, the dispersion of the polyolefin resin becomes poor, as a result, near the film surface layer The voids also increase, and the cleavage index cannot be reduced to 15 or less. Also, lo
When g (α / β) is less than 1, the difference in melt viscosity of the polyolefin resin becomes smaller than the difference in shear force between the vicinity of the wall and the center of the flow in the extruder. The state cannot be distributed, and as a result, the size of the void cannot be different between the film surface portion and the central portion, and the film density cannot be reduced to 1.2 g / cm ³ or less, or the cleavage index is 15 or less. You cannot do that. If the log (α / β) exceeds 3, the dispersion of the polyolefin resin becomes uneven, and the film-forming property deteriorates.

Examples of the polyolefin resin include polyethylene, polypropylene, polybutene, polymethylpentene, and the like. Further, the copolymer is not necessarily 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.

In the present invention, the addition amount of the polyolefin-based resin must be in the range of 5 to 30% by weight, preferably 5 to 20% by weight, and more preferably 8 to 15% by weight. If the addition amount is less than 5% by weight, the amount of voids formed is insufficient, resulting in lack of whiteness. On the other hand, if it exceeds 30% by weight, the film is likely to be broken during film formation, and the productivity is low.

The biaxially stretched film in the present invention is an unstretched film extruded into a sheet shape from a die and cooled and solidified by a cooling drum having a surface temperature of 10 to 60 ° C. After longitudinal stretching in the tenter
It is heated again in an atmosphere at 90 to 140 ° C., and is stretched 2 to 5 times in the direction perpendicular to the longitudinal direction. At this time, the area ratio (longitudinal stretching ratio × lateral stretching ratio) is preferably 6 to 20 times. If the temperature during longitudinal stretching is less than 80 ° C. or the temperature during transverse stretching is less than 90 ° C., the formed voids become brittle, and the cleavage index cannot be reduced to 15 or less. On the other hand, if the temperature during longitudinal stretching exceeds 120 ° C. or the temperature during transverse stretching exceeds 140 ° C., it becomes difficult to form voids, and the film density cannot be reduced to 1.2 g / cm ³ or less. If the area magnification is less than 6 times, the obtained film has poor whiteness, while if it exceeds 20 times, the film tends to be broken during stretching and the film-forming property tends to be poor. further,
Even when a film is formed, the size of the voids increases, and the cleavage index cannot be reduced to 15 or less.

In addition, the void referred to in the present invention refers to a space formed in the film, where the interface between the polyester and the additive substance is peeled off by stretching.

The equivalent spherical diameter of the void in the present invention is a diameter when the area of the void containing the polyolefin resin is equivalent to a circle in a cross section taken in the machine direction or the vertical direction of the film forming process.

In the present invention, it is preferable that the average sphere-equivalent diameter of the void existing between 5 μm in the thickness direction from at least one surface of the film is 0.1 to 3 μm. More preferably, it is 0.2 to 2 μm. In order for the average sphere equivalent diameter to be less than 0.1 μm, it is necessary to apply a large shearing force in the extruder, which causes a decrease in the intrinsic viscosity of the polyester and the like.
If it exceeds 3 μm, cleavage of the film surface is likely to occur.

Further, it is preferable that the average equivalent sphere diameter of the voids at the center of the film ± 2.5 μm is 1 to 100 μm. More preferably, it is 2 to 50 μm. If it is less than 1, the film density will not be reduced, and the whiteness and optical density of the film will be insufficient. If it exceeds 100 μm, the strength of the film becomes weak.

Further, it is preferable that the average equivalent sphere diameter of the void existing between at least one surface of the film and 5 μm in the thickness direction is smaller than the average equivalent sphere diameter of the void at the central portion ± 2.5 μm. If the average equivalent sphere diameter of the surface layer is greater than or equal to the average equivalent sphere diameter of the central portion, a film having a sufficiently low density and having no cleavage on the surface cannot be produced.

The density in the present invention needs to be 0.5 to 1.2 g / cm ³ . Preferably 0.6~1.0g / cm ^3, more preferably 0.6 to
0.9 g / cm ³ . Generates a large amount of voids in the film,
Reduce the apparent density of the film, reduce the amount of raw materials,
This is to reduce the cost of the film. 0.5g density
If it is less than / cm ³ , a film having too low strength will be formed with voids. If the density exceeds 1.2 g / cm ³ , the cost of the film will not be reduced.

The cleavage index of the film surface in the present invention, when the peel load of 1 kg / cm ² bond the cellophane tape to the film and vertically mixture was irradiated for 10 seconds on the film surface was divided into a grid of 1mm spacing 100 This is the number of areas with a film surface on the cellophane tape side. In the present invention, the cleavage index needs to be 15 or less. Preferably it is 5 or less. If it exceeds 15, it may cause paper dust trouble during printing.

In the present invention, the surface roughness Ra is preferably in the range of 0.1 to 1.0 μm. More preferably, it is 0.2 to 0.7 μm. To be less than 0.1 μm, it is necessary to finely disperse the polyolefin resin, it is necessary to apply a large shearing force in the extruder, and the intrinsic viscosity of the polyester is lowered. On the other hand, if it exceeds 1.0 μm, the smoothness of the film is poor, and the printability is lowered.

In the present invention, the optical density when the film thickness is converted to 150 μm is preferably 0.8 to 1.6. If the optical density is less than 0.8, the concealability 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.

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 the stretching of the film, and the void is reduced. If it exceeds 280 ° C, it cannot be added to polyester and extruded.

In the present invention, properties such as optical density and whiteness can be improved by adding inorganic particles together. In this case, the average particle diameter of the inorganic particles is 0.3 to 5 μm.
It is preferred that More preferably, 0.4 to 3 μm
It is. If it is less than 0.3 μm, dispersion in the polymer will be poor, and if it exceeds 5 μm, no improvement in properties will be observed. Further, the addition amount of the inorganic particles is preferably 2 to 25% by weight. More preferably, it is in the range of 5 to 20% by weight.
If the addition amount is less than 2% by weight, the characteristics such as optical density and whiteness of the film are not improved. Conversely, the addition amount is 25
If the content is more than 10% by weight, the film is likely to be broken during stretching. Also, any inorganic particles may be used, but calcium carbonate is preferred. The calcium carbonate may be either synthetic calcium carbonate or natural calcium carbonate.

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

After thoroughly vacuum drying the polyester chips,
The polyolefin resin chips are mixed, supplied to an extruder heated to 270 to 300 ° C., and formed into a sheet from a T-die. At this time, a fluorescent whitening agent may be added in the form of a master chip or a powder to enhance the whiteness of the obtained film. Further, the mixed chips may be previously kneaded with a pelletizer or the like. Further, the unstretched film cooled and solidified by a cooling drum having a surface temperature of 10 to 60 ° C. is led to a roll group heated to 80 to 120 ° C.
The film is stretched longitudinally in the longitudinal direction, and cooled with a group of rolls at 20 to 30 ° C.

Subsequently, the longitudinally stretched film is guided to a tenter while holding 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. When the area magnification is less than 6 times, the whiteness of the obtained film becomes poor, and when it exceeds 20 times, the film tends to be broken at the time of stretching and the film production tends to be poor.

In order to impart the planarity and dimensional stability of the biaxially stretched film in this manner, heat fix at 150 to 230 ° C. in a tenter, uniformly cool, and then cool 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 a Koka type flow tester (Shimadzu Corporation)
(CFT type). The preheating time is 5 minutes and the measurement temperature is 280 ° C.

(2) Average equivalent sphere diameter of voids Take a photograph of a cross section cut in the machine direction or the vertical direction of the film forming process with a scanning electron microscope at a magnification of 1000 to 5000 times, and take a photograph of 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) Density A density gradient tube based on carbon tetrachloride-n-heptane was used.

(4) Cleavage index Cellophane tape (manufactured by Nichiban) was applied to the film surface, a load of 1 kg / cm ² was applied to the entire film for 10 seconds, and then peeled off vertically from the film. 1
Of the 00 areas, the number of cellophane tapes on the film surface.

(5) Surface roughness Ra was measured with a stylus type surface roughness meter (ET-10, manufactured by Kosaka Laboratories) in accordance with Ra JIS-B-0601.

(6) Optical density The films are stacked so as to have 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.

(7) Average Particle Diameter of Inorganic Particles The inorganic particles were dispersed in ethanol and measured using a centrifugal sedimentation type particle size distribution analyzer (CAPA500 manufactured by Horiba, Ltd.), and the volume average diameter was calculated to be the average particle diameter.

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

Examples 1, 2, 3 and Comparative Examples 1, 2, 3, and 4 After polyester chips were vacuum-dried at 180 ° C. for 3 hours, the polyolefin resin chips shown in Table 1 were mixed in the proportions shown in Table 1. Then, the mixture was supplied to an extruder heated to 270 to 300 ° C., and formed into a sheet from a T-die. Further, the unstretched film cooled and solidified by a cooling drum having a surface temperature of 25 ° C. was guided to a group of rolls heated to 90 to 98 ° C., stretched three times in the longitudinal direction, and cooled by a group of rolls of 25 ° C.

Subsequently, the film was guided to a tenter while gripping both ends of the vertically stretched film with clips, and was 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.

The physical properties of the obtained film are as shown in Table 1. It can be seen that if the amount of the polyolefin-based resin exceeds 30% by weight, the film-forming properties deteriorate. Further, it can be seen that when the addition amount is less than 5% by weight, the density does not decrease and the optical density is low. In addition, it can be seen that the use of polymethylpentene as the polymer is advantageous for lowering the density and increasing the optical density. Also, it can be seen that if a> 3 μm when logβ> 3, cleavage becomes easier. It can also be seen that by using a polymer having a critical surface tension exceeding 30 dyn / cm, the density does not decrease, that is, no void is formed.

[Effects of the Invention] The present invention regulates the size of voids generated at the time of stretching by adding a polyolefin-based resin having a limited critical surface tension and melt viscosity to polyester, thereby defining the size of voids generated at the time of stretching. It is possible to provide a white film that is difficult and has a small apparent density, improve the characteristics of the white film, and reduce the cost of the film.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B29L 7:00 C08L 67:02

Claims (9)

(57) [Claims] 1. A polyester comprising a polyolefin resin and
A white polyester film which is biaxially stretched and has a film density of 0.5 to 1.2 g / cm ³ and a film surface cleavage index of / 5 or less. 2. The film has a surface roughness Ra of 0.1 to 1.0 μm.
2. The white polyester film according to claim 1, wherein the optical density is 0.8 to 1.6 when the film thickness is converted to 150 [mu] m. 3. An average sphere-equivalent diameter a of voids existing between 5 μm in the thickness direction from at least one surface of the film,
3. The white polyester film according to claim 1, wherein the average sphere-equivalent diameter b of the voids present in a range of ± 2.5 .mu.m in the center of the film has a relationship of a <b. 4. The film according to claim 1, wherein a is 0.1 to 3 μm.
4. The white polyester film according to claim 3, wherein m and b are 1 to 100 [mu] m. 5. The melt viscosity (αPOIS) of the polyolefin resin at a shear stress of 10 ⁵ dyn / cm ² at 280 ° C.
E), melt viscosity at 10 ⁶ dyn / cm ² shear stress (βPOISE)
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 white polyester film according to any one of claims 1 to 4. 6. The polyolefin resin having a melting point of 200 to 2
The white polyester film according to any one of claims 1 to 5, wherein the temperature is 80 ° C. 7. The method according to claim 1, wherein said polyolefin resin is polymethylpentene.
Item 7. The white polyester film according to any one of Items 6. 8. An inorganic particle having an average particle size of 0.3 to 5 μm
The white polyester film according to any one of claims 1 to 7, wherein the white polyester film is added in an amount of up to 25% by weight. 9. The white polyester film according to claim 8, wherein said inorganic particles are calcium carbonate.