JPH07118432A - Polyester film - Google Patents

Abstract

PURPOSE:To obtain the title polyester which is useful as a label, poster, recording paper or the like because it has excellent opacity, drawability, productivity and film-forming properties, even when it is thin, by extruding a mixture of polyester and inorganic particles. CONSTITUTION:The objective polyester film which is produced by mixing and extruding (A) polyester, (B) less than 3wt.%, based on the component A, of inorganic particles, thus has less than 40mum thickness and preferably less than 30% light transmission. Or the polyester of component A is mixed with a non- compatible thermoplastic resin and melt-extruded to give a pores-containing polyester film which is oriented at least in one direction, has a number of fine pores with 10-40vol.% average porosity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film which is thin but has good concealing properties and drawing properties and is excellent in productivity and film-forming property.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute mainly made of synthetic resin, has a higher water resistance, a higher dimensional stability in moisture absorption, and a higher dimensional stability than natural paper.
It has excellent surface stability, gloss and clarity of printing, and mechanical strength. In recent years, application development has been promoted by making use of these advantages. As a method of obtaining a film having a function similar to paper mainly made of polyester, polypropylene, polyethylene, etc., a method of containing a large amount of fine voids inside the film is a point that the film itself can be made lightweight and an appropriate flexibility. It has the advantage that it is possible to impart the property and enables clear printing and transfer. As a method for forming fine voids inside the film, for example, a polymer incompatible with polyester is melt-kneaded with an extruder to obtain a sheet in which the polymer is dispersed in fine particles to further stretch the sheet. A method for generating cavities around the fine particles is disclosed. The conventional void-containing films have a problem that the properties such as hiding property and film strength and film-forming properties are deteriorated as they become thinner.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a base material which is excellent in concealing property, film strength, film-forming property, productivity and the like, which is free from the above-mentioned drawbacks.

[0004]

Means for Solving the Problems That is, the present invention provides a polyester film prepared by mixing a polyester with a thermoplastic resin incompatible with the polyester and inorganic particles, wherein the inorganic particles account for 3% by weight of the polyester. The present invention relates to a polyester film having a thickness of 40 μm or less.

The polyester in the present invention means an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid or an ester thereof and a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol. It is a polyester produced by condensation. These polyesters may be obtained by directly reacting an aromatic dicarboxylic acid with a glycol, and then transesterifying an alkyl ester of an aromatic dicarboxylic acid with a glycol, followed by polycondensation, or a diglycol ester of an aromatic dicarboxylic acid. Is produced by a method such as polycondensation. Typical examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate or polyethylene-2,6-naphthalate. This polyester may be a homopolymer or a copolymer of a third component. In any case, in the present invention, ethylene terephthalate units, butylene terephthalate units or ethylene-
A polyester having a 2,6-naphthalate unit content of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable.

In the present invention, a particularly important point is that the thickness can be reduced to 40 μm or less even though the inorganic particles are present in the polyester. Usually, as a means for imparting concealing property to a plastic film, that is, a means for lowering the light transmittance, a method of expressing a large number of internal cavities, applying a pigment or a dye to the surface layer of the film, or containing a large number of inorganic particles inside is used. There is. However, if the content of cavities or inorganic particles is further increased in order to further improve the hiding property, there is a problem in that the strength of the film is reduced and stable film formation cannot be performed. Further, when the coating amount of the pigment is increased, there is a problem that the pigment comes off. Therefore, as a method for improving the hiding property so as not to cause these problems, it is possible to secure the stretchability even if a large number of inorganic particles are contained inside the film.

In the case of ordinary void-containing polyester film, the added inorganic particles such as titanium dioxide, calcium carbonate, silicon dioxide, barium sulfate are all present in the matrix polyester. Therefore, when the addition amount of the inorganic particles is increased, the interface generated between the polyester and the inorganic particles is increased, and the tensile strength and film formability of the film are likely to decrease. This is 40μ thick
This is a particularly serious problem with a film having a thickness of m or less.

Therefore, as one of means for solving these problems, a method of treating the surface of the inorganic particles with an inorganic material containing aluminum, silicon, zinc or the like to increase affinity with polyester, or a method of adding a large amount to the surface layer of the laminated film Have been disclosed so far. However, in these methods, it is not possible to maintain the film strength, the surface strength and the film-forming property by containing a large amount of inorganic particles so as to achieve a light transmittance of 30% or less at a thickness of 40 μm or less, preferably 30 μm or less. It is possible. This is because the inorganic particles have a high surface energy and thus have a higher affinity for the polyester having a higher surface energy than the cavity developing agent. Then, as a means to reach the present invention, it is possible to increase the addition amount of the inorganic particles in order to improve the hiding property and to mix the stretchability improving agent. As a result, even if the content of the inorganic particles is increased, problems such as film strength and film forming property are eliminated. Examples of the stretching improver include polyalkylene glycol such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and / or its derivative and / or copolymer. Examples of the derivative include those obtained by blocking the terminal group with another bond, those obtained by polyesterification by reaction with a dicarboxylic acid, and the like.
Among these, polyethylene glycol, polyethylene glycol copolymers and polyesters or copolymerized polyesters obtained by dioling these are particularly preferable. The polyethylene glycol and / or its derivative has a molecular weight of 200 to 200,000, preferably 1,000 to 50,000. In addition, the addition amount is based on the whole film,
The amount is 0.05 to 5% by weight, preferably 0.1 to 1% by weight. If it is less than 0.05% by weight, stretching becomes difficult, and if it exceeds 5% by weight, the film becomes stiff and the processability such as printing is deteriorated. In the present invention, the film thickness is 40μ.
m or less, preferably 30 μm or less, and containing inorganic particles in an amount of 3% by weight or more, preferably 6% by weight or more, and a light transmittance of 30% or less, the method is not limited to the above method, For example, when an incompatible thermoplastic resin is mixed with polyester, a method of incorporating inorganic particles into the thermoplastic resin can be used.

The inorganic particles used in the present invention are not particularly limited. Examples include titanium dioxide, calcium carbonate, barium sulfate, silicon dioxide, aluminum oxide, talc, kaolin and the like. Further, these inorganic particles may be surface-treated as necessary. Examples of the treating agent include, but are not limited to, aluminum oxide, silicon dioxide, zinc oxide, silicon-based resin, siloxane-based resin, fluorine-based resin, silane coupling agent or titanate coupling agent, polyol or polyvinyl pyridine. Not something. In the present invention, it preferably contains a large number of cavities inside.
The method of containing the cavities is not particularly limited, but preferably an unstretched sheet obtained by mixing, melting, and extruding an incompatible thermoplastic resin (cavity-developing agent) in the polyester is at least obtained. By orienting it uniaxially,
This is a method in which the interface between the polyester and the void-developing agent is peeled off to obtain a large number of voids inside. The cavity-developing agent must be incompatible with the polyester described above.
Specific examples include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, cellulose resins, polyamide resins, and the like. In particular, polystyrene resins, polyolefin resins such as polymethylpentene and polypropylene are preferable.

The polymer mixture obtained by mixing the polyester of the present invention and an incompatible thermoplastic resin with the polyester is prepared by, for example, mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. Method, or a method in which both resins are kneaded in advance by a kneader and further melt-extruded by an extruder to solidify, or an incompatible thermoplastic resin is added to the polyester in the polyester polymerization step and dispersed by stirring. It can also be obtained by a method of melt-extruding and solidifying the obtained chips. The polymer obtained by solidifying (unstretched sheet) is usually in a non-oriented state or a weakly oriented state. Further, the thermoplastic resin incompatible with the polyester is present in the polyester in a form dispersed in various shapes such as a spherical shape, an elliptic spherical shape, or a thread shape.

The polymer mixture obtained by mixing the polyester of the present invention and an incompatible thermoplastic resin to the polyester is prepared by, for example, mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. Method, or a method in which both resins are kneaded in advance by a kneader to be melt-extruded and solidified by an extruder, or an incompatible thermoplastic resin is added to the polyester in the polyester polymerization step and dispersed by stirring. It can also be obtained by a method of melt-extruding and solidifying the obtained chips. It is possible to add a colorant, a light-proofing agent, a fluorescent agent, an antistatic agent, etc. to the polymer mixture depending on the application. The obtained polymer mixture is further stretched between rolls having different speeds (roll stretching), stretched by gripping and expanding by a clip (tenter stretch), and stretched by expanding by air pressure (inflation stretch). At least one axis is subjected to orientation treatment by, for example, By the orientation treatment, peeling occurs at the interface between the polyester and the void-developing agent, and voids are developed.

Therefore, the amount of the thermoplastic resin which is incompatible with the polyester and mixed with the polyester varies depending on the amount of the target voids, but it is preferably 3% by weight to 40% by weight, preferably about 40% by weight, based on the total amount of the polymer mixture. Is 8% by weight
It is 20% by weight. . If it is less than 3% by weight, there is a limit to increase the amount of cavities generated, and the desired flexibility, lightness, and drawability cannot be obtained. On the other hand, when it is 40% by weight or more, the heat resistance and strength of the polyester film are significantly impaired. The conditions for orienting the polymer mixture are closely related to the formation of cavities. Therefore, the conditions for achieving this object are, for example, the most commonly used sequential 2
Taking the axial 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 as follows. In the roll drawing, the temperature is set to be not more than the biaxial drawing temperature of polyester + 30 ° C. and the magnification is 1.2 in order to generate many cavities.
It is preferably ˜5 times. In the tenter stretching, the temperature is preferably 100 to 140 ° C. and the magnification is preferably 1.2 to 5 in order to stably form a film without breaking. It is desirable to carry out the heat treatment condition after stretching by the method described below. After the stretching, the heat treatment is performed at 200 ° C or higher, preferably 220 ° C.
As described above, more preferably at 230 ° C. or higher. Further, at this time, heat fixation must be performed while relaxing by 3 to 8%. If it is less than 200 ° C or less than 3%, the heat shrinkage ratio at 150 ° C is less than 2%, preferably 1.
A void containing film of less than 7%, more preferably less than 1.5% is not obtained. The average porosity of the whole is 40% by volume
Below, preferably 30% by volume or less is suitable, and a void-containing film having an average void content of 40% by volume or more is difficult to manufacture because it frequently breaks during the stretching process, and the resulting film also has surface strength and tensile strength. It is not preferable because the strength is insufficient.

The apparent specific gravity of the film of the present invention is preferably 0.7 to 1.3, more preferably 0.9 to 1.3, still more preferably 1.0 to 1.2. If it is less than 0.7, there is no rigidity and the workability such as printing is deteriorated. If it exceeds 1.3, the drawability becomes poor, and it becomes a problem depending on the application. The film of the present invention preferably has a light transmittance of 30% or less,
It is more preferably 25% or less, more preferably 20% or less, and particularly preferably 17% or less. This is because the back side can be seen through when it exceeds 30%. Especially this is 4
This can be said for a thin film having a thickness of 0 μm or less, preferably 30 μm or less, but a thickness of more than that may be used. The film of the present invention must have a whiteness of 75 or more, preferably 80 or more. If it is less than 75, the quality is poor.

In consideration of post-processing and the like, the film of the present invention preferably has a tensile strength of 11 kg / mm 2 or more in both the longitudinal and transverse directions. In the present invention, a so-called composite film in which a surface layer and a center layer are laminated may be used. The method is not particularly limited. However, considering productivity, the raw materials for the surface layer and the central layer are extruded from separate extruders and
At least 1 after leading to two dies and obtaining unstretched sheet
Most preferred is the so-called co-extrusion method of laminating in the axial direction. In this case, the thermoplastic resin provided in the B layer is not particularly limited, and specifically includes polystyrene resin, polyolefin resin, polyacrylic resin, polycarbonate resin, polysulfone resin, cellulose resin, polyamide resin, etc. Can be given. However, polyester resins are preferred in the present invention. Also,
Inorganic particles may be contained if necessary. Further, the polyalkylene glycol and / or its derivative can be added to only the A layer or the B layer or both the A layer and the B layer. In this case, addition to the layer A makes it possible to improve the surface adhesiveness, water wettability, and the like. Furthermore, by providing a coating layer on the film surface, the wettability and adhesiveness of ink, coating agent, etc. are improved. The compound constituting the coating layer,
Polyester resins are preferred, but in addition to these, compounds disclosed as means for improving the adhesiveness of ordinary polyester films such as polyurethane resins, polyester urethane resins and acrylic resins can be applied. As a method for providing the coating layer, a commonly used method 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, and a reverse roll coating method can be applied. As the step of applying, a method of previously applying to the surface of the mixed polymer before the orientation treatment, a method of applying to the surface of the uniaxially oriented cavity-containing film and further orienting it in the orthogonal direction, Any method such as coating on the finished film surface is possible. The thus-obtained film has good hiding power, is strong, and has excellent surface strength and resistance to cleavage even if it is thin, and therefore, when the void-containing polyester film of the present invention is used as a material, a label, a poster , Card, recording paper, packaging material, video printer image receiving paper, bar code label, bar code printer image receiving paper, thermal recording paper, map, dust-free paper, display board, white board, electronic white board, photographic paper, decorative paper, wallpaper, banknote , Release paper,
It can be used for origami, calendars, magnetic cards, tracing papers, slips, delivery slips, pressure-sensitive recording papers, copy papers, clinical test papers, parabolic antenna reflectors, handy printer papers, graph papers, drafting papers, and the like.

Examples Next, examples of the present invention will be described. 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-K7210.

3) Density The film was cut into a square of 5.00 cm × 5.00 cm, and its thickness was measured at 50 points to obtain an average thickness of t μm.
The weight was calculated up to 0.1 mg to be wg, and the weight was calculated by the following formula.

[0018]

[Equation 1]

4) Average Porosity of Film Calculated by the following formula.

[0020]

[Equation 2] However,

[0021]

[Equation 3]

[0022]

[Equation 4] In the above equation, xi represents the weight fraction of the i component, and di represents the true specific gravity of the i component. The values of true specific gravity used in the calculations in the examples are polyethylene terephthalate 1.40, general-purpose polystyrene 1.05, and anatase-type titanium dioxide 4.2.
Was used.

5) Light transmittance According to JIS-K6714, Poic integrating sphere type H.264. T.
The light transmittance of the film was measured using an R meter (manufactured by Nippon Seimitsu Optical Co., Ltd.). The smaller this value, the higher the concealing property.

6) Tensile Strength of Film The tensile strength of the film was measured according to JIS-C2318.

7) Whiteness It was measured according to JIS-L1015-1981-B method using Z-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.

8) Heat shrinkage rate A film having a width of 10 mm and a length of 250 mm is 200 m
Mark at m intervals and fix under a constant tension of 5 g, and mark intervals A
Measure Subsequently, the space B between the marks after being placed in an oven in an atmosphere of 150 ° C. for 30 minutes under no tension was determined, and the heat shrinkage rate was calculated by the following formula.

[0027]

[Equation 5]

9) Color Tones The appearance of white is shown as "white", and the appearance of yellow is shown as "yellow".

Example 1 71.5% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 as a raw material and 2.0 g of melt flow rate
15% by weight of general purpose polystyrene for 10 minutes, 13% by weight of anatase type titanium dioxide having an average particle size of 0.3 μm,
0.5 wt% polyethylene glycol with a molecular weight of 5000
Was mixed with a twin-screw extruder from T-die to 29
It was melt extruded at 0 ° C. and electrostatically adhered and solidified on a cooling rotary roll to obtain an unstretched sheet. Subsequently, the unstretched sheet was longitudinally stretched 3.5 times at 85 ° C. by a roll stretching machine, and then horizontally stretched 3.5 times at 130 ° C. by a tenter and then 235 ° C.
Was heat-treated while being relaxed by 4% to obtain a polyester film having a thickness of 25 μm and containing a large number of cavities therein.

Comparative Examples 1 and 2 In the same manner as in Example 1, except that the amounts of polyethylene glycol were 0 and 10% by weight, void-containing polyester films were obtained.

Example 2 A void-containing polyester film was prepared in the same manner as in Example 1 except that polyethylene terephthalate was used as a raw material in an amount of 79.5% by weight, polyethylene glycol was 0.5% by weight, and titanium dioxide was 20% by weight. Obtained.

Example 3 84.5% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 as raw material, 15% by weight of polystyrene for general use as melt flow index of 2.0 g / 10 minutes, and anatase type titanium dioxide having an average particle size of 0.3 μm 5% by weight of polyethylene glycol having a molecular weight of 5000 and 0.5
As a raw material for the A layer, 59.5 wt% of polyethylene terephthalate resin as the raw material of the B layer, 40 wt% of anatase-type titanium dioxide, and 0.5 wt% of polyethylene glycol having a molecular weight of 5000 are used as separate twin screws. A void-containing polyester film was obtained in the same manner as in Example 1 except that the film was placed in an extruder. The thickness was B / A / B = 2/21/2 μm.

[0033]

INDUSTRIAL APPLICABILITY The void-containing polyester film of the present invention has the same lightness, flexibility, matteness and drawability as the void-containing polyester film obtained by using conventional polystyrene or polyolefin as a void-developing agent. In addition to having the effect, it has the effect of having a high concealing property even if it is thin as compared with the conventional film. Therefore, the void-containing polyester film of the present invention can be used in a very wide range of fields such as labels, posters, recording papers, packaging materials, heat-sensitive recording materials and printing papers.

[0034]

[Table 1]

Claims (5)

[Claims] 1. A polyester film obtained by mixing and extruding polyester and inorganic particles, wherein the inorganic particles are present in an amount of 3% by weight or more based on the polyester, and the thickness is 40 μm.
Polyester film of m or less. 2. The polyester film according to claim 1, which has a light transmittance of 30% or less. 3. An incompatible thermoplastic resin is mixed with polyester, melted, extruded, and oriented at least uniaxially to contain a large number of fine voids therein, and the average void content is 10% by volume or more and 40% by volume. % Or less, and the polyester film according to claim 1 or 2. 4. The polyester film according to claim 1, wherein the polyester film is polyalkylene glycol and / or
Alternatively, a polyester film containing a derivative thereof. 5. A polyester film, comprising a layer (B) made of a thermoplastic resin laminated on at least one side of the film (A) according to any one of claims 1 to 4.