JPH072851B2 - Polyester film and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a white polyester film having excellent thermal dimensional stability and low specific gravity, which can be used as a substitute for paper, and a method for producing the same. More specifically, receiving papers for video printers, receiving papers for bar code printers, receiving papers for match printing, copying papers, printing papers, posters, labels, stickers, cards, slips, display boards, white boards, maps, The present invention relates to a white polyester film having a high cushioning property, which is used as a base material such as dust-free paper, a reflector such as a surface light emitter, a backing material such as a marking film, and a method for manufacturing the same.

[Prior Art] The plastic film used for the above-mentioned applications as a substitute for paper is required to be white and opaque. Conventionally,
Known polyolefin-based resins, such as those obtained by adding a large amount of inorganic particles such as calcium carbonate to polyolefin resin (Japanese Patent Publication No. 63-64310).

There is also a film obtained by adding a large amount of an inorganic substance such as calcium carbonate or titanium dioxide to polyester.
Further, there is a polyester film having fine cells formed by adding an incompatible polymer to a polyester such as polypropylene based on the polyester (see, for example, Japanese Patent Application Laid-Open No. S60-12065).
63-168441 etc.).

[Problems to be Solved by the Invention] However, when polypropylene is used as a base, there are problems that the film is vulnerable to heat and mechanical strength is weak.

Further, the white film based on polyester has the following problems.

A film obtained by adding inorganic particles to polyester cannot be made to have a low specific gravity, and the film itself becomes hard, which may cause a problem depending on the use.

The film in which polypropylene is added to polyester has a low specific gravity, and the hardness of the film is somewhat relaxed, but the thermal dimensional stability is poor and the film is inferior in flexibility and whiteness to paper.

To add incompatible polymer such as polyolefin to polyester, improve dispersion of incompatible polymer,
In addition, when a compound is added to accelerate the formation of voids, the strength, humidity dimensional stability, whiteness, etc. of the polyester deteriorate.

An object of the present invention is to solve such conventional problems, to provide a white film excellent in thermal dimensional stability, low in specific gravity and rich in flexibility, and without deterioration of characteristics of the polyester itself due to addition of a low specific gravity agent. Is.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention has the following constitution, that is, a composition A containing a low specific gravity agent in a polymer incompatible with polyester, A polyester film characterized by being dispersed and mixed in polyester, and a master chip in which a low-density agent is premixed in a polymer incompatible with polyester, and the master chip is added to polyester and then melted. The method for producing the polyester film is characterized in that the polyester film is extruded.

The polyester referred to 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-1,
Examples thereof include 4-cyclohexylene dimethylene terephthalate and polyethylene-2.6-naphthalene dicarboxylate. Of course, these polyesters may be homopolyesters or copolyesters, and examples of the copolymerization component include diol components such as diethylene glycol, neopentyl glycol, polyalkylene glycol, adipic acid, sebacic acid, and fulleric acid. , Isophthalic acid, 2.6-naphthalenedicarboxylic acid,
Examples include dicarboxylic acid components such as 5-sodium sulfoisophthalic acid.

Also, in this polyester, various known additives,
For example, an antioxidant, an antistatic agent, an ultraviolet absorber or the like may be added. Polyethylene terephthalate is preferable as the polyester used in the present invention.
Polyethylene terephthalate film is excellent in water resistance, durability and chemical resistance.

Polymers incompatible with the polyester referred to in the present invention (hereinafter,
Sometimes referred to simply as an incompatible polymer) means poly-
3-methylbutene-1, poly-4-methylpentene-
1, polyvinyl-t-butane, 1,4-trans-poly-
2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polymethylstyrene, polydimethylstyrene, polyfluorostyrene, poly-2-methyl-
It is a polymer having a melting point of 200 ° C. or higher selected from 4-fluorostyrene, polyvinyl-t-butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride, polychlorotrifluoroethylene and the like. In the present invention, poly-4-methylpentene-1, cellulose triacetate and modified products thereof are particularly preferable in terms of cost, heat stability, dispersibility in polyester and the like. The melting point of the incompatible polymer is 200 ° C. or higher, preferably 210 ° C. or higher, more preferably 220 ° C. or higher. When the temperature is lower than 200 ° C., the dispersed shape of the incompatible polymer in the polyester film does not become spherical, and the layered flat shape is likely to be obtained, and the polyester film having high cushioning property cannot be obtained. The melting point of the incompatible polymer is 300 ° C or lower, preferably 280 ° C or lower, and more preferably 260 ° C or lower. This is because the incompatible polymer does not dissolve and disperse unless it is lower than the melt extrusion temperature of the polyester. The amount of the incompatible polymer added is preferably 3 to 30% by weight. More preferably 5 to 20% by weight
Is. When the added amount is less than 3% by weight, the specific gravity of the polyester film of the present invention is less likely to be 0.95 or less, and the whiteness of the film is less than 80%, and it is difficult to obtain whiteness.
In addition, it is difficult to obtain a film with a high cushioning property with a cushion rate of 10% or more. Further, if the amount of the incompatible polymer added exceeds 30% by weight, the mechanical strength of the polyester film of the present invention will be poor and the thermal dimensional stability will also be poor.

The low specific gravity agent in the present invention is added to the polyester together with the incompatible polymer, good dispersion of the incompatible polymer, promotes peeling of the interface between the polyester and the incompatible polymer when the film is stretched, It refers to a compound that has the effect of promoting void formation and reducing the specific gravity of the film.

As the low-density agent, polyethylene glycol, methoxy polyethylene glycol, polytetramethylene glycol, polyalkylene glycol such as polypropylene glycol, ethylene oxide / propylene oxide copolymer, sodium dodecylbenzene sulfonate,
Alkyl sulfonate sodium salt, glycerin monostearate, tetrabutylphosphonium paraaminobenzene sulfonate, etc. are typical. In the present invention, polyethylene glycol is particularly preferable. Further, the addition of this low specific gravity agent improves the whiteness of the polyester film, smoothes the surface, improves the cleavage resistance, and improves the stretchability of the film, thereby improving the productivity. The addition amount of the low specific gravity agent in the present invention,
0.05 to 3% by weight is preferable. More preferably 0.1 to 2
% By weight. If the addition amount is less than 0.05% by weight, the effect of adding the low specific gravity agent does not appear. On the contrary, if the addition amount exceeds 3% by weight, the effect of reducing the low specific gravity is not observed and the whiteness of the film decreases. However, the humidity stability of the film deteriorates.

In the polyester film of the present invention, it is necessary that the composition A in which the low specific gravity agent is contained in the incompatible polymer is dispersed and mixed in the polyester. This is because the low specific gravity agent acts on the interface between the polyester and the incompatible polymer, so the amount of the low specific gravity agent added in the incompatible polymer is small, and in the base polymer This is because the characteristics of a certain polyester are not impaired.
The state in which the specific gravity reducing agent is contained can be confirmed by dyeing the cross section of the film with a selective dyeing agent such as osmic acid. At this time, even if the specific gravity reducing agent is transferred from the incompatible polymer into the polyester, it can be confirmed because the dye is stronger in the incompatible polymer. As described above, in order to allow the low specific gravity agent to be contained in the composition A and to be dispersed and mixed in the film, the low specific gravity agent is previously mixed with the incompatible polymer, and then the incompatible polymer is mixed with the polyester. Need to be mixed.

The thermal dimensional stability of the film is a preferable condition because the film does not deform in a heat-sensitive process such as thermal transfer, printing or drying. In particular, it is often judged by the heat shrinkage rate at 150 ° C. Therefore, in the present invention, 15
The heat shrinkage at 0 ° C is preferably less than 2%, more preferably less than 1.5%. For this reason, it is preferable that the polyester film is heat-treated at 200 ° C. or higher, preferably 220 ° C. or higher. You may relax.

The specific gravity of the polyester film is 0.95 or less, preferably
It is preferably 0.90 or less, more preferably 0.80 or less. This is because if it is larger than 0.95, the film is not imparted with softness and flexibility. The flexibility is a necessary item in order to be able to transfer an image clearly even when the pressure of the thermal recording head is reduced when it is used as a receiving paper for a video printer or the like. In addition, it is necessary for the feel when touched with the hands. From these factors, the film cushion rate is preferably 10% or more.

Composition A comprising a low specific gravity agent in an incompatible polymer
Preferably has a shape close to a sphere in the film, that is, the shape factor is in the range of 1 to 4. More preferably, it is in the range of 1 to 3. Even when the composition A is added to the polyester film, the film characteristics obtained depending on the shape of the composition A, particularly, the film specific gravity, the cushion rate, the thermal dimensional stability, the whiteness, and the surface roughness are different. come. That is, the composition A having a nearer spherical shape has a smaller specific gravity and a larger whiteness than a layered composition,
It is possible to obtain a film having excellent cushioning properties and good thermal dimensional stability.

The whiteness of the polyester film is preferably 80% or more, more preferably 90% or more. The higher the whiteness, the higher the whiteness of the film, giving a high-class feeling. If necessary, a fluorescent whitening agent may be added to change the color tone. Examples of optical brighteners include "Ubitech" OB, MD (Ciba Geigy), "OB-1" (Eastman).

The optical density of the polyester film is preferably 0.8 or higher, more preferably 0.9 or higher. The higher the optical density is, the more the hiding property of the film is increased, which is a preferable property in each application.

Calcium carbonate, inorganic particles such as anatase type titanium dioxide, calcium phosphate, amorphous zeolite particles, silica, kaolin, talc and clay may be added to the polyester film of the present invention. The addition amount of these is preferably 0.005 to 25 parts by weight with respect to 100 parts by weight of the polyester composition. In addition to these particles, fine particles precipitated by the reaction of the catalyst residue and the phosphorus compound in the polyester polycondensation reaction system may be used in combination.

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

Poly-4-methylpentene-1 as incompatible polymer
Then, polyethylene glycol, which is a specific gravity reducing agent, is added and pelletized in advance to prepare a master chip. Next, the master chip and a polyethylene terephthalate chip are mixed, vacuum dried at 180 ° C. for 3 hours, sufficiently mixed, supplied to the extruder A heated to 280 ° C., and molded into a sheet from a T die. To do. At this time, in order to emphasize the whiteness of the obtained film, the optical brightener may be added in the form of master chip or powder. If necessary, polyethylene terephthalate containing an inorganic additive such as titanium dioxide, silicon dioxide or calcium carbonate is supplied to the extruder B by a conventional method to prepare the extruder B in the T-die three-layer die or in the polymer tube. B / so that the polymer is on both surface layers
It may be laminated in three layers of A / B.

The surface temperature of the film extruded from this T-die is 10
The unstretched film is cooled and solidified by a cooling drum at -60 ° C, guided to a roll group heated to 80 to 120 ° C, longitudinally stretched in the longitudinal direction, and cooled at a roll group at 20-30 ° C.

Then, the both ends of the longitudinally stretched film are guided to a tenter while gripping both ends of the film with a clip, and transversely 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 in the longitudinal and transverse directions, but the area ratio (longitudinal stretching ratio × horizontal stretching ratio) needs to be 6 to 20 times. If the area ratio is less than 6 times, the whiteness of the obtained film becomes poor, while if it exceeds 20 times, the film tends to be broken during stretching and the film-forming property becomes poor.

In order to impart the flatness and dimensional stability of the biaxially stretched film in this way, heat setting is carried out at 150 to 230 ° C. in a tenter, and after uniform slow cooling, it is cooled to room temperature to obtain the film of the present invention. .

[Measurement of Physical Properties and Evaluation Method of Effect] (1) Specific Gravity Carbon tetrachloride-n-heptane density gradient tube at 25 ° C
It was measured at.

(2) Optical density films were stacked so as to have a thickness in the vicinity of 150 μm and measured with an optical densitometer (TR927 manufactured by Macbeth Co.). The thickness and the optical density were plotted, and the optical density corresponding to the thickness of 150 μm was taken as the optical density in terms of the thickness of 150 μm.

(3) Whiteness Based on JIS-L1015, spectrophotometer (Shimadzu UV-26
0) using an integrating sphere, the reflectance B (%) at a wavelength of 450 nm,
The reflectance G (%) at 550 nm was measured, and the whiteness was determined by the following formula.

Whiteness (%) = 4B-3G (4) Cushion ratio A standard gauge head (No.900030) is attached to a dial gauge (No.2109-10 manufactured by Mitoyo Seisakusho) and a dial gauge stand (No.7001DGS-M) is installed. To do. Assuming that the thickness of each film when a load of 50 g and a load of 500 g were applied to the dial gauge pressing portion was d ₅₀ and d ₅₀₀ , the cushion ratio was calculated from the following formula.

Cushion rate (%) = (d ₅₀ −d ₅₀₀ ) / d ₅₀ × 100 (5) Shape factor The cross section cut in the machine direction or the vertical direction of the film forming process of the film is 1000 to 5000 times enlarged with a scanning electron microscope. Take a magnified photograph, apply at least 100 or more incompatible polymer shapes to an image analyzer, and use the average of the major axis / minor axis ratios as the shape factor.

(6) Heat shrinkage The film was sampled in a width of 10 mm and a length of 250 mm, marks were made at intervals of 200 mm in the length direction, and the distance was measured (L
₀ mm). The sample was attached to a circular frame having a diameter of 33 cm, a 3 g weight was hung, and the sample was heat-treated while rotating in a hot air oven at 150 ° C. for 30 minutes. After cooling after heat treatment, the marked interval was measured (Lmm) and calculated from the following formula.

Thermal shrinkage (%) = (L ₀ −L) / L ₀ × 100 (7) Humidity expansion coefficient A sample with a width of 10 mm and a length of 150 mm is conditioned at 25 ° C and 40% RH for 25 hours, and then loaded with 20 g / 10 mm. Measure the equilibrium length (L ₀ mm) by leaving it in a thermo-hygrostat at 21 ° C and 40% RH for 12 hours. Next, the humidity was raised to 80% RH and left for 24 hours, the equilibrium length (Lmm) was measured, and it was determined by the following formula.

Humidity expansion coefficient (cm / cm /% RH) = (L−L ₀ ) / humidity difference / L ₀ [Effect of the present invention] The polyester film of the present invention has the following effects.

By including the low specific gravity agent in the incompatible polymer, the addition amount of the low specific gravity agent can be reduced, and the characteristics of polyester such as strength and humidity dimensional stability, and optical characteristics such as whiteness Does not deteriorate.

The specific gravity is as small as 0.95 or less, and it is possible to obtain a flexible film having high cushioning property, flexibility and high whiteness.

By using a polymer having a melting point of 200 ° C. or higher as the incompatible polymer, it is possible to obtain a film having excellent thermal dimensional stability despite having a low specific gravity.

By laminating a layer mainly composed of polyester on the surface, a film having a smooth surface and excellent adhesiveness in addition to the above-mentioned properties can be obtained.
It is possible to freely give characteristics such as drawing property and light shielding property.

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

Example 1 Poly-4-methylpentene-1 (TPX manufactured by Mitsui Petrochemical Co., Ltd.
DX820) polyethylene glycol (molecular weight 400
0) 0.5 part by weight was added, and the mixture was fed to an extruder at 280 ° C and pelletized. Polyethylene terephthalate (Intrinsic viscosity of 0.
65) 89.5% by weight, the above poly-4-methylpentene-1
The master chips were mixed at 10.5% by weight and vacuum dried at 180 ° C. for 3 hours. This raw material was supplied to the extruder A heated to 280 ° C. and introduced into the central layer of the T-die three-layer composite die.

On the other hand, 10% by weight of calcium carbonate (average particle diameter 1.0 μm) was added to 90% by weight of the above polyethylene terephthalate,
Furthermore, the raw material containing 0.03 parts by weight of the fluorescent whitening agent "OB-1" was added.
The mixture was supplied to an extruder B heated to 0 ° C., laminated on both surface layers of a T-die three-layer die, and the molten film was adhered and solidified on a cooling drum at 25 ° C. Then, the cooling film,
It was introduced into a roll group heated to 90 to 98 ° C, longitudinally stretched 3.5 times in the longitudinal direction, and cooled with a roll group at 25 ° C.

Subsequently, while holding both ends of the longitudinally stretched film with clips, the film was introduced into a tenter and laterally stretched 3.5 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. After that, heat setting was carried out at 230 ° C. in a tenter, and after uniform uniform cooling, it was cooled to room temperature to obtain a film having a winding thickness of 100 μm. The thickness of the film was 5 μm on the surface layer and 90 μm on the central layer.

The cross section of the center layer of the obtained film was dyed with osmic acid and observed with a transmission electron microscope to find that poly-4
It was found that the inside of methylpentene-1 and the interface with polyester were strongly stained, and polyethylene glycol was dispersed and mixed in poly-4-methylpentene-1.

Table 1 shows the physical properties of the obtained film.

The film thus obtained has excellent thermal dimensional stability,
It can be seen that the cushioning property is a polyester film having a high whiteness and a low specific gravity.

Comparative Examples 1 and 2 Comparative Example 1 was carried out in the same manner as in Example 1 except that the polyethylene glycol of Example 1 was added to polyethylene terephthalate in advance, and Comparative Example 2 was one in which polyethylene glycol was not added at all.

When a cross section dyed with osmic acid was observed in the same manner as in Example 1, Comparative Example 1 strongly stained the interface in polyethylene terephthalate and poly-4-methylpentene-1, and Comparative Example 2 hardly dyed. It was

The physical properties of the obtained film are as shown in Table 1.

As described above, by adding polyethylene glycol to polyethylene terephthalate, the amount of polyethylene glycol present at the interface is relatively reduced, so that the specific gravity is increased and the whiteness is deteriorated. Further, the thermal dimensional stability also deteriorates. The same applies when polyethylene glycol is not added.

Examples 2 and 3 The amount of polyethylene glycol added to poly-4-methylpentene-1 in Example 1 was 0.1 parts by weight, and Example 2 was 1.0 parts by weight.

When the cross section dyed with osmotic acid was observed in the same manner as in Example 1, the interfaces in poly-4-methylpentene-1 and polyethylene terephthalate were strongly dyed in both Examples 2 and 3.

As shown in Table 1, the amount of polyethylene glycol added is 0.5
It can be seen that the weight% is sufficient, and the physical properties obtained by adding more than that amount remain unchanged.

Comparative Example 3 Instead of the incompatible polymer poly-4-methylpentene-1 used in Example 1, polypropylene (Noblene J4H, manufactured by Mitsui Toatsu Co., Ltd.) was used, and the other operations were performed in the same manner as in Example 1.

The physical properties obtained are as shown in Table 1. It can be seen that when polypropylene is used, a low specific gravity film excellent in dimensional stability cannot be obtained.

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Claims (6)

[Claims] 1. A polyester film in which a composition A comprising a polymer which is incompatible with polyester and a specific gravity reducing agent is dispersed and mixed in the polyester. 2. The heat shrinkage ratio at 150 ° C. is less than 2% and the specific gravity is 0.95.
The polyester film according to claim 1, which is as follows. 3. The shape factor of the composition A in the film is 1.
The polyester film according to claim 1 or 2, wherein the polyester film is 4. The incompatible polymer has a melting point of 200 ° C. selected from methylbutene polymer, methylpentene polymer, styrene polymer, fluorine polymer, cellulose acetate polymer and cellulose propionate polymer.
The polyester film according to any one of claims 1 to 3, which is the above polymer. 5. The low specific gravity agent is at least one selected from polyalkylene glycols, ethylene oxide / propylene oxide copolymers, alkylbenzene sulfonates, alkyl sulfonates, and modified products thereof. The polyester film according to any one of claims 1 to 4, which is characterized. 6. A master chip prepared by premixing a low specific gravity agent in a polymer incompatible with polyester,
The method for producing a polyester film according to any one of claims 1 to 5, wherein the master chip is added to polyester and then melt-extruded.