JP3127462B2 - Cavity-containing polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a paper containing fine cavities inside a film, having cushioning properties and drawing properties, and having low light transmittance and excellent concealing properties. The present invention relates to a polyester film having a similar function.

(Prior art) Synthetic paper, which is a paper substitute made of synthetic resin as a main raw material, is more water-resistant, has greater moisture absorption dimensional stability, better surface smoothness than natural paper.
Excellent printing gloss, sharpness, mechanical strength, etc.

In recent years, application development utilizing these advantages has been promoted.

Polyethylene, polypropylene, polyester, etc. are used as the main raw materials for synthetic paper, and among these, polyester flakes, such as polyethylene terephthalate, are excellent in terms of high heat resistance and strong rigidity. Application development is possible.

As a method for obtaining a film having a function similar to that of paper using polyester as a main raw material, there have been conventionally (1) a method in which fine cavities are contained in a large amount in the film, or (2) sandblasting of a normal flat polyester film. Treatment, (2-2) chemical etching treatment, and (2-3) matting treatment (method of laminating a matting agent together with a binder)
For example, a method of roughening the surface by the method is disclosed.

Among them, the method of (1), in which a large amount of fine cavities are contained in the film, allows the film itself to be reduced in weight and imparts appropriate flexibility, thereby enabling clear printing and transfer. There is an advantage.

As a method to generate fine cavities inside the film,
Conventionally, a polymer or inorganic fine particles (hereinafter, referred to as a void generating agent) incompatible with polyester are melt-kneaded by an extruder to obtain a sheet in which the polymer is dispersed in fine particles in polyester, and the sheet is further stretched. Discloses a method for generating a cavity around fine particles.

Examples of the polymer which is incompatible with polyester used for generating cavities include polyolefin resins (for example, JP-A-49-134755) and polystyrene-based resins (for example, JP-B-49-2016 and JP-B-54-29550). ) And polyarylate resins (for example, Japanese Patent Publication No. 58-28097).

In addition, as the inorganic fine particles, calcium carbonate
43-12013) and barium sulfate (Japanese Patent Publication No. 60-30930).

These inorganic fine particles are preferable because they are inexpensive compared to the case of using a polymer, and are excellent in heat resistance and do not cause a problem of reduced surface wettability caused by by-products due to thermal decomposition of the polymer. .

Opacity is a major characteristic of a film having a function similar to that of paper. The concealing property can be imparted by using the above-mentioned cavity-forming agent, but its level is not sufficient.
The use of titanium dioxide to improve concealment,
A method which is suitable and used in combination with a cavity-forming agent has been proposed. Among them, a method in which calcium carbonate and titanium dioxide are used in combination is proposed (Japanese Patent Application Laid-Open No. 1-29041). However, in this method, it is necessary to add a large amount of calcium carbonate or titanium dioxide in order to obtain a polyester film having an intended void content and opacity. If a large amount of these fine particles is added, the stretchability of the polyester will be reduced, making it difficult to economically produce a film having satisfactory mechanical properties. There has been a demand for the development of a compounding agent that can enhance both the opacity and the opacity.

(Problems to be Solved by the Invention) The present invention is directed to a formulation of an inorganic fine particle system in which the above-mentioned drawbacks, that is, the need to add a large amount of inorganic fine particles to increase both the void content and the opacity, are improved. It is intended to provide a polyester film that contains fine voids inside the film, has cushioning properties and drawing properties, has a low light transmittance, and has a function similar to that of paper with excellent concealment properties. .

(Means for Solving the Problems) That is, the above objects can be achieved by a void-containing polyester film containing at least composite fine particles containing titanium dioxide and calcium carbonate.

The polyester in the present invention is a thermoplastic polyester containing preferably at least 70 mol% of ethylene terephthalate repeating units obtained by a polymerization reaction of terephthalic acid or a derivative thereof and ethylene glycol. The polyester, other dicarboxylic acid component,
An embodiment in which at least one of the diol component and the oxycarboxylic acid component is copolymerized, and the polyester is a polyester such as polybutylene terephthalate and / or polyethylene 2,6-naphthalate and / or polycyclohexylene dimethylene terephthalate. Is also included.

The polyester can be produced by melt polymerization in a conventional manner, but is not limited thereto, and may be a polyester obtained by another polymerization method. The polymerization degree of the polyester is 0.
Those with 3 to 1.2 are preferred.

The composite fine particles containing titanium dioxide and calcium carbonate used in the present invention are fine particles mainly composed of two components, titanium dioxide and calcium carbonate, in which titanium dioxide and calcium carbonate are uniformly compounded in the particles. Or a non-uniformly composite one. The non-uniform composite may be one in which the inner layer is titanium dioxide and the outer layer is calcium carbonate, or conversely, the inner layer is calcium carbonate and the outer layer is titanium dioxide, but the former is particularly preferred.

The fine particles in which the inner layer is titanium dioxide and the outer layer is calcium carbonate can be prepared by performing a carbonation reaction of a water-soluble calcium salt in a state where the titanium dioxide fine particles are dispersed in water. For example, a method of adding calcium chloride to an aqueous dispersion of titanium oxide, then adding aqueous ammonia, and further introducing carbon dioxide gas to carry out a carbonation reaction (JP-A-2-51419) is exemplified. It is not limited to this method.

There is no particular limitation on the crystal forms of titanium dioxide and calcium carbonate.In the case of titanium dioxide, either rutile type or anatase type may be used, and in the case of calcium carbonate, calcite type, argonite type, or vaterite type may be used. .

The composition ratio of titanium dioxide and calcium carbonate in the composite fine particles was 0.1 / weight ratio of titanium dioxide / calcium carbonate.
The range of 0.9 to 0.9 / 0.1 is preferred, and the range of 0.3 / 0.7 to 0.7 / 0.3 is particularly preferred. If it is less than 0.1 / 0.9, the concealing property decreases, which is not preferable. Conversely, if it exceeds 0.9 / 0.1, the void content decreases, which is not preferable. If the amount is small, other components such as calcium oxide, calcium hydroxide, strontium carbonate and barium carbonate may be contained.

The composite fine particles preferably have an average particle diameter of 0.05 to 5 μm, particularly preferably 0.2 to 3 μm. If the thickness is less than 0.05 μm, both the concealing property and the void content are undesirably reduced. Conversely, if the thickness exceeds 5 μm, the concealing property is reduced, and the film is broken during biaxial stretching, making it impossible to form a normal film.

The amount of polyester in the composite particles is preferably 1 to 30% by weight. 3-20% by weight is particularly preferred. If it is less than 1% by weight, both the concealing property and the void content are undesirably reduced. Conversely, if it exceeds 30% by weight, the stretchability decreases, and the film is easily broken during biaxial stretching, which makes film formation difficult, which is not preferred.

This problem can be solved by co-extrusion with a normal polyester resin.
It can also be used in the case of 30% by weight. Here, the ordinary polyester is the above-mentioned polyester, and may contain additives such as particles. Layer structure is two layers or three
More than layers are included. The compounding of the composite fine particles into the polyester may be carried out in the polyester polymerization step or by kneading with the polyester resin. When the kneading method is used, the kneading may be performed in an extruder or a kneaded product may be extruded. A method of kneading in an extruder using a so-called master chip kneaded at a high concentration in advance is particularly recommended.

In the present invention, an organic cavity developing agent made of a thermoplastic resin insoluble in polyester may be used in combination.
This combination method is a preferred embodiment because the compounding amount of the composite particles can be reduced.

Polyorganic resins such as polyethylene, polypropylene and polymethylpentene, ionomer resins, copolymerized polyolefin resins such as ethylene propylene rubber, polystyrene, styrene-
Examples thereof include polystyrene resins such as acrylonitrile copolymer and styrene-butadiene-acrylonitrile copolymer, polyarylate resins, polyacrylonitrile resins, and the like.

In the present invention, a pigment, a coloring agent, a light-fast agent, a fluorescent agent, an antistatic agent, and the like can be added as needed. In addition, polyalkylene glycol derivatives can be blended to improve the wettability and adhesion of inks and coating agents, and extruded sheets and biaxially stretched films can be subjected to corona treatment and plasma treatment. It is.

In the present invention, the above-described compound is melt-extruded into a sheet, and then stretched between rolls having different speeds (roll stretch), stretched by gripping and expanding with a clip (tenter stretch), or spread by air pressure. The film is oriented at least uniaxially by stretching (inflation stretching) or the like. At this time, delamination occurs at the interface between the dispersed void developing agent and the polyester, and many voids are generated in the polymer mixture. The conditions for the alignment treatment are also closely related to the formation of cavities. For example, taking the most commonly performed sequential biaxial stretching step as an example, a sequential biaxial stretching method in which a continuous sheet of the polymer mixture is roll-stretched in the longitudinal direction and then tenter-stretched in the width direction is generally used. The roll stretching temperature is preferably 50 to 140 ° C. and the magnification is 1.2 to 5 times. The tenter stretching temperature is preferably 60 to 150 ° C. and the magnification is preferably 1.2 to 5 times. Further, the stretch-orientated film containing cavities is 130 ° C.
When the heat-setting treatment is performed at a temperature of preferably 180 ° C. or more, the dimensional stability at a high temperature can be improved.

In addition, the film containing cavities oriented only in the uniaxial direction,
It is useful for shrinkable films and easily tearable films.

Since the present invention relates to a void-containing polyester film in which voids are generated by an orientation treatment, it is necessary to orient at least one axis.

In the present invention, a method for improving the wettability and adhesiveness of an ink or a coating agent by providing a coating amount on at least one surface of the void-containing polyester film of the present invention is recommended.

As a compound constituting the coating layer, a polyester-based resin is preferable, and in addition, a polyurethane-based resin,
Compounds disclosed as means for improving the adhesiveness of ordinary polyester films, such as polyester urethane resins and acrylic resins, can be applied. As the method for providing the coating layer, a method generally used such as a gravure coating method, a kiss coating method, a dip method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method, a reverse roll coating method, or the like can be applied. . As a step of applying, a method of applying in advance to the surface of the mixed polymer before performing the orientation treatment, 1
Any method such as a method in which the film is applied to the surface of the cavity-containing film that is oriented in the axial direction, and then the film is oriented in the perpendicular direction, or a method in which the film is applied to the surface of the film that has been subjected to the orientation treatment and the like, can be used.

 Next, examples of the present invention and comparative examples will be described.

 The measurement / evaluation method used in the present invention will be described below.

1) Intrinsic viscosity of polyester Polyester was dissolved in a mixed solvent of phenol (6 parts by weight) and tetrachloroethane (4 parts by weight) and measured at 30 ° C.

2) Melt flow index of polystyrene resin Measured at 200 ° C under a load of 5 kg according to JIS K-7210.

3) Melt flow index of crystalline polypropylene resin Measured at 230 ° C under a load of 2.16 kg according to JI K-6758.

4) Apparent specific gravity of the film The film is accurately cut out into a square of 5.00 cm × 5.00 cm, its thickness is measured at 50 points, the average thickness is tμm, the weight is measured up to 0.1 mg, and the weight is defined as wg. Calculated.

 Apparent specific gravity (−) = W / 5 × 5 × t × 10000 5) Cavity content of film Film was calculated by the following equation.

Cavity content (volume%) = 100 × (1−true specific volume / apparent specific volume) where true specific volume = x ₁ / d ₁ + x ₂ / d ₂ + x ₃ / d ₃ + ... + x ₁ / d ₁ + ... x ₁ in the apparent specific gravity above equation apparent specific volume = 1 / film is the weight fraction of i component, d ₁ represents the true specific gravity of component i.

The value of the true specific gravity used in the calculations in the examples is polyethylene terephthalate 1.40, anatase type titanium dioxide.
3.90, a general-purpose polystyrene resin 1.05, and a crystalline polypropylene resin 0.91 were used. The true specific gravity of the composite particles of calcium carbonate and titanium dioxide was calculated using the above-mentioned value of the true specific gravity of calcium carbonate and titanium dioxide, and calculated and used as a weighted average.

6) Concealment of Film The light transmittance of the film was measured using a Poic integrating sphere HTR meter (manufactured by Nippon Seimitsu Kogaku) in accordance with JIS K6714. The smaller this value is, the higher the concealment property is. The pulp paper for electrostatic copying which is usually used was measured and found to be 27%.

Example 1 As a raw material, (1) 60% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, and (2) composite fine particles of calcium carbonate and titanium dioxide having an average particle diameter of 0.7 μm [titanium dioxide as a core and calcium carbonate on the surface layer Coated with calcium carbonate / titanium dioxide = 0.5 / 0.
5 (weight ratio)] of 40% by weight of a polyethylene terephthalate resin containing 30% by weight is melt-extruded from a T-die at 285 ° C. with a twin screw extruder, and is electrostatically adhered to a cooling rotating roll and solidified. Subsequently, the film was longitudinally stretched 2.8 times at 80% with a roll stretching machine, further stretched 3.2 times at 130 ° C. with a tenter, and heat-set at 220 ° C. to obtain a white polyester film. Table 1 shows the properties of the obtained film.

The film obtained in this example had characteristics similar to paper having a high void content and a low light transmittance.

Comparative Examples 1 to 3 In the method of Example 1, each of the composite fine particles comprising calcium carbonate and titanium dioxide was replaced with an average particle diameter of 1.0.
Calcite-type calcium carbonate having a composition of 12% by weight in the final film of calcite-type calcium carbonate of 12 μm, and 12% by weight of anatase-type titanium dioxide having an average particle size of 0.3 μm in the final film. Table 1 shows the properties of the polyester film obtained in the same manner as in Example 1 except that calcium carbonate and anatase-type titanium dioxide having an average particle diameter of 0.3 μm were changed so as to be 6 wt% in the final film. Show.

The film obtained in Comparative Example 1 has a high light transmittance, the film obtained in Comparative Example 2 has a low void content, and the film obtained in Comparative Example 3 has an intermediate void content and light transmittance. In each case, the quality was inferior to that of the film of Example 1.

Example 2 (1) 71% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, (2) 15% by weight of a master chip containing the same composite fine particles used in Example 1, and (3) a melt flow index of 3.0 g / 10 minutes. Table 1 shows the properties of the polyester film obtained by the same method as in Example 1 except that a raw material containing 14% by weight of a certain general-purpose polystyrene was used.

The film obtained in this example had characteristics similar to paper having a high void content and a low light transmittance.

Comparative Examples 4 to 6 Table 1 shows the characteristics of the films obtained by the same method as in Example 2, except that the fine particles as shown in Table 1 were used instead of the composite fine particles in the method of Example 2.

The film obtained in Comparative Example 4 has a high light transmittance, the film obtained in Comparative Example 5 has a low void content, and the film obtained in Comparative Example 6 has an intermediate void content and light transmittance. In each case, the quality was inferior to that of the film of Example 2.

Comparative Example 7 In the method of Example 2, the compounding of the composite fine particles was stopped.
Table 1 shows polyester films obtained by the same method as in Example 2 except that the amount of the polyethylene terephthalate resin is increased accordingly.

The film obtained in this comparative example is inferior to the film of Example 2 in both the void content and the light transmittance.

Example 3 (1) 59.3% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62, and (2) composite particles of calcium carbonate and titanium dioxide having an average particle diameter of 0.5 μm [the surface layer of which is coated with calcium carbonate using titanium dioxide as a core. Calcium carbonate / titanium dioxide = 0.3 / 0.7 (weight ratio)], 26.7% by weight of a master chip made of polyethylene terephthalate resin containing 30% by weight, and (3) crystallinity with a melt flow index of 2.5 g / 10 minutes. Table 1 shows the properties of the polyester film obtained in the same manner as in Example 1 except that a raw material containing 14% by weight of a polypropylene resin was used.
Shown in

The film obtained in this example had characteristics similar to paper having a high void content and a low light transmittance.

Comparative Examples 8 to 9 Table 1 shows the properties of the polyester films obtained in the same manner as in Example 3, except that the raw material composition was changed as shown in Table 1.

The films obtained in these comparative examples were inferior to Example 3 in both the void content and the light transmittance.

(Effect of the Invention) The void-containing polyester film of the present invention has a high void content, a low light transmittance, and excellent opacity, and has lightness, flexibility, opacity, and properties similar to paper. It has matting and drawing properties. Therefore, the void-containing polyester film of the present invention is extremely useful in a very wide range of fields such as labels, posters, recording paper, and packaging materials.

Claims (1)

(57) [Claims] 1. A void-containing polyester film containing composite fine particles containing at least titanium dioxide and calcium carbonate.