JP3314815B2 - Void-containing polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when used in labels, posters, recording paper, packaging materials, etc., contains a large amount of fine cavities inside a film with improved surface peel strength, opacity, whiteness, etc. The present invention relates to a polyester film for printing, particularly for thermal transfer, which has a small thermal deformation.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute made of synthetic resin as a main raw material, has a higher water resistance, a greater moisture absorption dimensional stability, and a higher stability than natural paper.
Excellent in surface stability, gloss and sharpness of printing, mechanical strength, etc. In recent years, application development utilizing these advantages has been promoted. As a method for obtaining a film having a function similar to paper made of polyester as a main raw material, a method of containing a large amount of fine cavities inside the film can provide a point that the film itself can be reduced in weight and impart appropriate flexibility. ,
There is an advantage that clear printing and transfer become possible. Conventionally, as a method to generate fine cavities inside the film,
A method is disclosed in which a polymer incompatible with polyester is melt-kneaded with an extruder, a sheet in which the polymer is dispersed in fine particles in polyester is obtained, and a cavity is generated around the fine particles by further stretching the sheet. I have. Examples of the polymer that is incompatible with the polyester used for the cavity (hereinafter, referred to as a cavity developing agent) include a polyolefin-based resin (for example, JP-A-49-134755) and a polystyrene-based resin (for example, JP-B-49-2016). And Japanese Patent Publication No. 54-29550) are preferred. Until now, the void-containing polyester film is lightweight,
Although it had excellent properties such as concealing property and strong stiffness, thermal deformation at high temperatures was large and curling due to heat was a problem.

[0003]

DISCLOSURE OF THE INVENTION The present invention has the above-mentioned drawbacks, namely, by optimizing the distribution of cavities, the surface strength is excellent , and printing, printing, copying, etc. are clear and durable.
It is an object of the present invention to provide a substrate which is excellent in concealing property and whiteness and does not curl due to heat.

[0004]

That is, the present invention provides a polyester layer containing fine cavities formed by at least uniaxially orienting a polymer mixture of a polyester and a thermoplastic resin incompatible with the polyester. A layer (B) made of a thermoplastic resin was provided on at least one surface of (A).
A laminated void-containing polyester film, wherein the layer A has a void content of not more than 8% by volume from the surface to 3 μm, and the laminated film has an average void content of 10%.
Or less vol% 50 vol%, and at least one direction of the heat shrinkage starting temperature of 180 ° C. or higher, the maximum shrinkage ratio of 1%
Polyester containing a laminated cavity characterized by the following
Related to a system film. The polymer mixture of the present invention obtained by mixing the polyester and the thermoplastic resin incompatible with the polyester is obtained, for example, by mixing chips of each resin, melt-kneading in an extruder, and extruding and solidifying. Method, a method in which both resins are kneaded in advance by a kneader and then further melt-extruded from an extruder and solidified,
In a polymerization step of the polyester, a chip obtained by adding an incompatible thermoplastic resin to the polyester and stirring and dispersing the resulting mixture is melt-extruded and solidified. To the polymer mixture, a coloring agent, a light-fast agent, a fluorescent agent, an antistatic agent, and the like can be added according to the application. The obtained polymer mixture is further stretched between rolls having different speeds (roll stretching), stretched by gripping and spreading with a clip (tenter stretching), or stretched by air pressure (inflation stretching). At least one axis orientation treatment is performed by such as. By the orientation treatment, peeling occurs at the interface between the polyester and the cavity developing agent, and cavities are developed. Therefore, the amount of the thermoplastic resin incompatible with the polyester to be mixed with the polyester varies depending on the amount of the target cavity, but is preferably 3% by weight to 35% by weight based on the entire polymer mixture. If the content is less than 3% by weight, there is a limit in increasing the amount of cavities formed, and the desired flexibility, lightness and drawing property cannot be obtained. Conversely, if 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 performed sequential biaxial stretching step, for example, taking a continuous sheet of the polymer mixture as a roll in the longitudinal direction and then stretching in the width direction. In the case of the sequential biaxial stretching method in which tenter stretching is performed, the following is performed. In the roll stretching, it is preferable that the temperature is not higher than the biaxial stretching temperature of the polyester + 30 ° C. and the magnification is 1.2 to 5 times in order to generate many cavities. In tenter stretching, the temperature is set to 80 to 140 for stable film formation without breaking.
It is preferable that the temperature and the magnification are 1.2 to 5 times. If the void-containing film subjected to the stretching orientation treatment is heat-set at 130 ° C. or more, preferably 180 ° or more, the dimensional stability at high temperatures can be improved. In the present invention, a so-called composite film in which a surface layer and a center layer are laminated must be used. The method is not particularly limited. However, in consideration of productivity, the so-called co-extrusion lamination is most preferable, in which the raw materials for the surface layer and the center layer are extruded from separate extruders, led to one die to obtain an unstretched sheet, and then oriented at least uniaxially. .

The void-containing polyester film thus obtained has a void content of not more than 8% by volume in the layer from the surface of the layer A to a depth of 3 μm and an average void content of the entire layer of 10% by volume. It is necessary to be above. When the thermoplastic resin B layer is not provided, or when the surface layer from the surface of the layer A to the depth of 3 μm contains more than 8% by volume of cavities, a material having particularly good surface strength cannot be obtained. The thickness of the surface layer portion of the cavity ratio A layer be not more than 8% by volume 3
Even when the thickness is smaller than μm, particularly good surface strength cannot be obtained. Therefore, in the present invention, A having less cavities than the central portion
The surface portion of the layer should have a depth of at least 3 μm and the void content contained therein should be 8 % by volume. Further, as the entire layer, the average content of the cavities needs to be 10% by volume or more. If the average porosity of the entire layer is less than 10% by volume, the flexibility inherent in the void-containing polyester film becomes insufficient, and the drawing properties and cushioning properties also become insufficient. In order to reduce the amount of cavities only in the surface layer of layer A,
It is effective to make the dispersed particles of the thermoplastic resin in the polymer mixture finer near the surface layer of the layer A than near the center, and the melt viscosity characteristics of the polyester and the thermoplastic resin and the meltability from the extruder are improved. It can be obtained by selecting the conditions for pushing. Void containing film stretched orientation treatment, and at 220 ° C. or higher, preferably 235 ° C. or higher vertical high heat shrinkage starting temperature by laterally to relax 2% to 8% while heat-set, according to high heat because the amount of shrinkage is small A void-containing film with less curl is obtained.

[0007]

In the present invention, polyester is used for
This is for satisfying the heat resistance and mechanical strength of the void-containing polyester film. In the present invention, mixing a thermoplastic resin incompatible with the polyester to the polyester, to obtain a polymer mixture, by dispersing fine particles of the thermoplastic resin incompatible with the polyester in the polyester, This is because the nuclei of the cavities generated by the next alignment treatment are formed. In the present invention, the reason why the thermoplastic resin B layer is provided and the amount of cavities included in the surface layer portion 3 μm of the A layer is set to 8% by volume or less is to increase the surface strength. On the other hand, the reason why the average void content of the entire layer is set to 10% by volume or more is to provide appropriate drawing properties and cushioning properties. In the present invention, the heat shrinkage initiation temperature is 180 ° C. or more,
The reason why the maximum deformation amount is set to 1% or less is to eliminate curling due to high heat in the thermal transfer machine.

[0008]

Next, examples of the present invention will be described. 1) Intrinsic viscosity of polyester The 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) Apparent specific gravity of the film The film was accurately cut into a square of 5.00 cm × 5.00 cm, the thickness was measured at 50 points, and the average thickness was tμ.
m, its weight is measured to 0.1 mg and wg,
The apparent density of the film was calculated by the following equation. Apparent density (g / cm ³ ) = w / (5 × 5 × t) × 10000 The specific gravity of the solid is the density of the solid and the density of water at 4 ° C.
(0.999973 g / cm ³ ) and generally defined as
It is the density of water and substantially 1.00 g / cm ³ Minaseruko
From the apparent density of the film divided by the density of water
And the apparent specific gravity of the film is calculated as follows.

Apparent specific gravity (−) = w / (5 × 5 × t) × 10000

4) Average porosity of film Calculated by the following equation. Cavity content (vol%) = 100 × (1−true specific volume / apparent specific volume) where true specific volume = x1 / d1 + x2 / d2 + x3 / d3 +... + Xi / di +.

Apparent specific volume = 1 / apparent specific gravity of film 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 the true specific gravity used in the calculations in the examples are polyethylene terephthalate 1.40, general-purpose polystyrene 1.05 , anatase type titanium dioxide 3.9.
Was used.

5) Porosity of the surface layer of the void-containing film A photograph of the vicinity of the surface of the cross section of the film taken with a scanning electron microscope, and then the cavities in the region from the surface to a depth of 3 μm are traced and painted on the tracing film. Was subjected to image processing by an image analyzer, and the porosity was obtained as an area ratio, and this value was directly displayed as volume%. -Scanning electron microscope used: Hitachi S-510
Type-Image analysis processing device used: Luzex IID manufactured by Nireco Corporation

6) Light transmittance According to JIS-K6714, a Poick integrating sphere formula T.
The light transmittance of the film was measured using an R meter (manufactured by Nippon Seimitsu Kogaku). The smaller the value, the higher the concealment property. 7) Surface Peeling Strength Using a cellophane tape (18 mm width, made by Nichiban), the surface peeling strength was evaluated by a cellophane tape peeling test. The peel angle was performed in the direction of about 150 degrees while the cavity-containing film was kept flat. The area was differentiated from the area of the peeled void-containing film as follows. Class 5: The whole has peeled off Class 4: Almost peeled off Class 3 ... About half the peeled off Class 2 ... Almost no peeling Class 1 ... No peeling off at all

Example 1 As a raw material, a melt flow index of 2.0 was added to 80% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62.
g / 10 minutes Polystyrene for general use 15% by weight, 5% by weight of anatase type titanium dioxide having an average particle diameter of 0.3 μm is used as a raw material of the layer A, and 95% by weight of a polyethylene terephthalate resin and an average particle diameter of 0.3 μm are used as a raw material of the layer B. 5 wt% of rutile-type titanium dioxide is melt-extruded from a T-die at 290 ° C. by another twin screw extruder, and solidified electrostatically on a cooling rotary roll, and each layer is B / A / B
= 30/440/30 µm to obtain an unstretched sheet of a polymer mixture. At this time, the T-die slit interval is 1.0 mm
The average flow rate of the melt of the polymer mixture in that portion is 8.
8 m / sec. Subsequently, the unstretched sheet was longitudinally stretched 3.5 times at 83 ° C. in a roll stretching machine , and subsequently stretched 3.5 times at 130 ° C. in a tenter .
Relax 5% laterally at 30 ° C and roll at 237 ° C
And heat-set while relaxing by 4% to obtain a polyester film containing a large number of cavities inside . Thickness is B / A / B
= 3/44/3 μm. The porosity of the surface layer of layer A of the obtained film was 2% by volume, and the whole was 21% by volume. In addition, a portion with few cavities was present from the surface to a depth of about 3 μm. The surface strength of the void-containing film obtained in this example was class 1. In addition, when the cross section of the unstretched sheet of the polymer mixture of this example was observed with a scanning electron microscope, the dispersed particle diameter of polystyrene at the center was 5.0 μm on average, while the dispersed particle diameter near the surface layer was The average was 0.7 μm. The apparent specific gravity was 1.11, the porosity of the surface layer portion of the A layer was 2% by volume, the overall average porosity was 19% by volume, the light transmittance was 13%, and the thickness was 50 μm. The thermal shrinkage onset temperature of this film was 190 ° C., and the maximum shrinkage was 0.6%. The measuring device is a thermal stress tester (SSC-5000 manufactured by Seiko Denshi Kogyo), sample width 4 mm, length 15 mm, heating rate 5 ° C./min, heating start temperature 20
C. The thermal shrinkage onset temperature was defined by the intersection of the low temperature side baseline and the high temperature side baseline as shown in FIG. A color printer (VY-150,
When thermal transfer recording was carried out using Hitachi (manufactured by Hitachi, Ltd.), it was good with little curl.

Comparative Example A void-containing film was obtained in exactly the same manner except that the film of the example was heat set at 200 ° C. while relaxing only 4% in the horizontal direction. When this film was subjected to thermal recording in exactly the same manner as in the examples, curling occurred. The heat shrinkage starting temperature of this film is 152
C., the maximum shrinkage in the machine direction was 3%.

[0016]

The void-containing polyester film of the present invention has the same light weight, flexibility, concealing properties, matting properties, and drawing properties as the conventional void-containing polyester film obtained using polystyrene or polyolefin as a void-generating agent. It has excellent properties such as specific gravity, whiteness and surface strength compared to conventional void-containing polyester films, and has less curl at high temperatures.It is inexpensive for labels, posters, Recording paper,
It is particularly suitable for thermal transfer, such as packaging-like materials.

[Brief description of the drawings]

FIG. 1 is a chart showing the relationship between the temperature of a thermal stress tester and the amount of elongation / shrinkage.

[Explanation of symbols]

 1. Measurement result 2. Baseline on low temperature side 3. Baseline on high temperature side 4. Shrinkage onset temperature 5. Maximum shrinkage (rate)

Claims (1)

(57) [Claims] At least one surface of a polyester layer (A) containing fine cavities formed by at least uniaxially orienting a polymer mixture of a polyester and a thermoplastic resin incompatible with the polyester. , Polyester containing laminated cavities provided with layer (B) made of thermoplastic resin
The layer A has a void content of not more than 8% by volume from the surface thereof to 3 μm, and the laminated film has an average void content of not less than 10% by volume and not more than 50% by volume. less and, and at least one direction of the heat shrinkage starting temperature 1
80 ° C. or higher, laminated void-containing polyester film, wherein a maximum shrinkage rate is 1% or less.