JP3314822B2 - Void-containing polyester film laminate - 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 laminate in which an adhesive layer is provided on a polyester film.

[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.

[0003] As a method of forming fine cavities inside a film, conventionally, a polymer incompatible with polyester is melt-kneaded with an extruder, and a sheet in which the polymer is dispersed in fine particles in polyester is obtained. A method of generating a cavity around fine particles by stretching is disclosed. Examples of the polymer incompatible with the polyester used for the cavity (hereinafter, referred to as a cavity developing agent) include polyolefin resins (for example, JP-A-49-13).
No. 4755) and polystyrene resins (for example, JP-B-49-2016 and JP-B-54-29550) are preferable.

[0004] The conventional void-containing polyester film has excellent properties such as light weight, concealing property and strong stiffness. However, since the surface strength is not good, it has been applied as a label with an adhesive. Later, when peeled off again, there was a problem that the surface layer part was peeled off.

[0005]

[SUMMARY OF THE INVENTION The present invention, the disadvantages, i.e., by suitability of the distribution cavity, printing or printing, copying, etc. There are vivid and durable, concealing property and whiteness, Excellent surface strength and labels, stickers,
It is an object of the present invention to provide a base material having an optimal adhesiveness for bookbinding base paper and the like.

[0006]

That is, the present invention relates to a method for forming a fine cavity produced by orienting at least one axis a polymer mixture comprising a polyester and a thermoplastic resin incompatible with the polyester. In the polyester film containing a large number, the content of voids contained in the surface layer from the surface to a depth of 3 μm is 4% by volume or less, and the average void content of the whole layer is 8% by volume or more and 50% by volume or less. The present invention relates to a void-containing polyester-based film laminate, wherein an adhesive layer is provided on at least one surface of a certain film.

The polyester of the present invention and a polymer mixture obtained by mixing the polyester with an incompatible thermoplastic resin may be obtained, for example, by mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. A method obtained by kneading both resins with a kneading machine in advance, and a method of solidifying by extruding the mixture further by an extruder, or adding a thermoplastic resin incompatible with polyester in a polyester polymerization step, stirring and dispersing. It can also be obtained by a method of melt-extruding the chips obtained and solidifying them.

[0008] To the polymer mixture, a coloring agent, a light-proofing agent, a fluorescent agent, an antistatic agent and the like can be added according to the use. 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 which is incompatible with the polyester and which is mixed with the polyester depends on the amount of the target cavity, but is preferably 3% by weight to 35% by weight based on the whole 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, 40
If the amount is more than the weight percentage, the heat resistance and strength of the polyester film are significantly impaired.

In order to reduce the amount of cavities only in the surface layer,
It is effective to make the dispersed particles of the thermoplastic resin in the polymer mixture finer near the surface layer than near the center,
It can be obtained by selecting the melt viscosity characteristics of the polyester and the thermoplastic resin and the conditions for melt extrusion from an extruder. 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.

[0011] The void-containing film subjected to the stretching orientation treatment is
When heat setting is performed at 30 degrees or more, preferably 180 degrees or more, dimensional stability at high temperatures can be improved. When the amount of cavities contained in the surface layer from the surface to a depth of 3 μm is more than 4% by volume, a material having particularly good surface strength cannot be obtained. In addition, when the thickness of the surface layer portion having a porosity of 4% by volume or less is less than 3 μm, particularly good surface strength cannot be obtained. Therefore, in the present invention, it is necessary that the surface layer portion having less cavities than the central portion has a depth of 3 μm or more, and the void content contained therein is 4% by volume. Furthermore, the average content of the cavities needs to be 8% by volume or more for the entire layer. If the average porosity of the entire layer is less than 8% by volume, the flexibility inherent in the void-containing polyester film becomes insufficient, and the drawing properties and cushioning properties also become insufficient.

The adhesive used for the void-containing polyester film includes natural rubber, chloroprene rubber,
Solvent-type adhesives such as NBR, butyl rubber, urethane rubber, vinyl acetate and its copolymer, acrylic acid and its copolymer, natural rubber latex, chloroprene latex, NBR latex, vinyl acetate and its copolymer, acrylic acid and Emulsion-type adhesives such as copolymers, water-soluble adhesives such as polyvinyl alcohol, starch, glue, thermosetting adhesives such as epoxy resin, polyester resin, urea and melamine resin, phenol resin, polyurethane resin, paraffin Hot melt adhesives such as wax, microcrystalline wax, asphalt and resin wax mixture, polyethylene, polypropylene, unsaturated polyester and the like are not particularly limited. These may be used alone or in combination, and a third component such as a curing agent or a filler may be mixed. These may be provided on the anchor coat layer.

[0013]

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 amount of cavities contained in the surface layer of 3 μm is set to a porosity of 4% by volume or less is to increase the surface strength, and to increase the cleavage strength by increasing the surface strength. is there. On the other hand, the reason why the average porosity of the entire layer is set to 8% by volume or more is to provide appropriate drawing properties and cushioning properties. The reason why the pressure-sensitive adhesive layer is provided in the invention is to impart tackiness.

The thus obtained void-containing polyester film laminate has good surface strength required for applications such as labels, stickers, packaging materials, thermal recording paper, and delivery slips, and has adhesiveness. Was.

[0016]

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 (volume%) = 100 × (1−true specific volume / apparent specific volume)

True specific volume = x1 / d1 + x2 / d2 + x3 / d3 +... + Xi / di +.

Apparent specific volume = 1 / apparent specific gravity of film

Xi in the above equation is the weight fraction of the i component, d
i represents the true specific gravity of the i component. The value of the true specific gravity used in the calculations in the examples was polyethylene terephthalate 1.4.
0, general-purpose polystyrene 1.05, and anatase-type titanium dioxide 3.9 were used. 5) Cavity ratio of the surface layer of the film containing cavities After photographing the vicinity of the surface layer of the cross section of the film with a scanning electron microscope, the cavities in the region from the surface layer to a depth of 3 μm were traced and painted on the tracing film to analyze the image. Image processing was performed by the apparatus, and the porosity was determined by the area ratio, and this value was directly used as the volume%.

-Scanning electron microscope used-S-510 scanning electron microscope manufactured by Hitachi-Image analysis processing equipment used Luzex IID (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: Completely peeled off Class 4: Almost peeled off Class 3 ... About half peeled off Class 2 ... Almost no peeling Class 1 ... No peeling off at all

EXAMPLE As a raw material, 86% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and a melt flow index of 3.0.
g / 10 minutes 10% by weight of polystyrene for general use and 4% by weight of anatase type titanium dioxide having an average particle size of 0.3 μm
It is melt-extruded at 290 ° C. from a T-die with an axial screw extruder, solidified electrostatically in close contact with a cooling rotating roll, and subsequently longitudinally stretched 3.5 times at 80 ° C. with a roll stretching machine, and subsequently at 130 ° C. with a tenter. Stretched 3.5 times, 220 ° C
And 3% relaxation to obtain a polyester film containing a large number of cavities inside. At this time, the average flow rate of the melt of the polymer mixture was 8.8 m / sec. The apparent specific gravity is 1.16, the porosity of the surface layer is 1% by volume, the average porosity of the whole is 16% by volume, the light transmittance is 15%, and the thickness is 5%.
It was 2 μm. In addition, the surface peel strength is extremely excellent,
It had class 2 performance. An acrylic emulsion adhesive (Boncoat PS-378 manufactured by Dainippon Ink and Chemicals, Inc.) was applied to this film, and release paper was attached to the surface of the adhesive to form a film laminate. When this laminate was stuck on a glass surface and peeled again after a few seconds, the substrate could be smoothly peeled with almost no substrate remaining on the glass surface.

Comparative Example A cavity-containing film was obtained in exactly the same manner as in Example except that the average flow rate of the melt was 4.4 m / sec.
An adhesive layer was provided. When this laminate was attached to a glass surface and peeled off again after a few seconds, the surface layer portion of the base material remained on the glass surface. At this time, the porosity of the surface layer was 14% by volume.

[0029]

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. In addition to having the properties, compared to the conventional void-containing polyester film , excellent opacity, whiteness, surface strength,
And it has adhesiveness. Accordingly, the void-containing polyester film of the present invention can be used for labels, posters, recording paper, packaging,
It can be used in a very wide range of fields such as materials for use , thermal recording materials, and photographic paper.

Claims (1)

(57) [Claims] 1. A polyester film containing a large number of fine cavities produced by at least uniaxially orienting a polymer mixture obtained by mixing a polyester with a thermoplastic resin incompatible with the polyester. The content of cavities in the surface layer up to a depth of 3 μm is 4% by volume
And the average void content of the entire layer is 8% by volume
A void-containing polyester film laminate, wherein an adhesive layer is provided on at least one surface of a film having a volume of 50% by volume or less.