JPH0623892A - Cavity-containing polyester film laminate - Google Patents

Abstract

PURPOSE:To enhance lightweight properties, concealability and surface release strength and to eliminate inconvenience such that a surface layer is peeled off when re-peeled after lamination by arranging a self-adhesive layer to at least the single surface of a specific cavity-containing polyester film. CONSTITUTION:A cavity-containing polyester film laminate is constituted by arranging a self-adhesive layer to at least the single surface of a specific cavity- containing polyester film. At this time, the specific cavity-containing polyester film is constituted by arranging a thermoplastic resin layer (B) on at least the single surface of a polyester layer (A) having fine cavities formed by at least uniaxially orienting a polymer mixture consisting of polyester and a thermoplastic resin incompatible with this polyester. The content of cavities contained in the layer A up to the depth of 3mum from the surface thereof is set to 8vol.% and the average cavity content of the whole of the film is set to 10-50vol.%.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention, when used for labels, posters, recording papers, packaging materials, etc., contains a large amount of fine voids inside a film having improved surface peel strength, hiding power, whiteness and the like. The present invention relates to a laminate having a polyester film provided with an adhesive layer.

[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 using polyester as a main raw material, a method of containing a large amount of fine voids inside the film can give a point that the film itself can be made lightweight and appropriate flexibility. ,
There is an advantage that clear printing and transfer are possible.

As a method for forming fine cavities inside a film, conventionally, a polymer that is incompatible with polyester is melt-kneaded by an extruder to obtain a sheet in which the polymer is dispersed in fine particles to obtain a sheet. A method of forming voids around fine particles by stretching is disclosed. As a polymer which is incompatible with polyester used for cavities (hereinafter referred to as cavities expressing agent), a polyolefin resin (for example, JP-A-49-13)
4755) and polystyrene resins (for example, JP-B-49-2016 and JP-B-54-29550).

The conventional void-containing polyester films have excellent properties such as light weight, hiding power, and firmness, but since they have poor surface strength, they are attached as a label with an adhesive. After that, when peeled again, there was a problem that the surface layer portion was peeled off.

[0005]

DISCLOSURE OF THE INVENTION The present invention has the drawback of the previous term, namely, by optimizing the distribution of cavities, it is clear and durable for printing, printing, copying, etc., and has hiding power, whiteness, and surface. It is intended to provide a base material having an optimum adhesiveness for a label, a sticker, a base paper for binding, etc., which has excellent strength.

[0006]

That is, the present invention contains fine cavities formed by orienting at least uniaxially a polymer mixture in which a polyester and an incompatible thermoplastic resin are mixed with the polyester. The layer (B) made of a thermoplastic resin is provided on at least one surface of the polyester layer (A) to be formed, and the void content contained in the layer A from the surface to 3 μm is 8% by volume or less, and the average of the entire film. The void-containing polyester film composite is characterized in that an adhesive layer is provided on at least one side of a void-containing polyester film having a void content of 10% by volume or more and 50% by volume or less.

The polymer mixture obtained by mixing the polyester of the present invention and the 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.

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), stretching by gripping a clip and expanding (tenter stretching), or stretching by expanding by air pressure (inflation stretching) 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 is preferably 3% by weight to 35% by weight based on the total amount of the polymer mixture. . 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. Conversely, 40
If it is more than 10% by weight, 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 around the central portion.
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 the object of the present invention include, for example, the most commonly used sequential biaxial stretching step, in which a continuous sheet of the polymer mixture is roll-stretched in the longitudinal direction and then in the width direction. In the case of the sequential biaxial stretching method in which the tenter stretching is performed, it is as follows. In roll stretching, it is preferable to set the temperature to a biaxial stretching temperature of polyester + 30 ° C. or less and a draw ratio of 1.2 to 5 times in order to generate a large number of cavities. In the tenter stretching, the temperature is 80 to 140 for stable film formation without breaking.
It is preferable that the temperature and the magnification are 1.2 to 5 times.

The void-containing film stretch-oriented is 1
When heat setting is performed at 30 ° C. or higher, preferably 180 ° C. or higher, dimensional stability at high temperature can be improved. In the present invention, a so-called composite film in which the surface layer and the center layer are laminated must be used. The method is not particularly limited. However, in view of productivity, the raw materials for the surface layer and the central layer are extruded from different extruders, introduced into one die to obtain an unstretched sheet, and then oriented at least uniaxially,
The lamination by the so-called coextrusion method is most preferable.

The void-containing polyester film thus obtained has a void content of 8% by volume or less in the layer from the surface of the layer A to a depth of 3 μm, and the average void content of the entire layer is 10% by volume. It is necessary to be above. If the thermoplastic resin B layer is not provided, or if the surface layer of the layer A from the surface to a depth of 3 μm contains more than 8% by volume of cavities, particularly good surface strength cannot be obtained. Further, the thickness of the surface layer portion of the layer A having a porosity of 4% by volume or less is 3 μm.
If the thickness is smaller than that, it is not possible to obtain a particularly good surface strength. Therefore, in the present invention, the surface layer portion of the layer A having less voids than the central portion has a depth of 3 μm or more, and the void content contained therein needs to be 4% by volume. Further, the entire layer needs to have an average void content of 10% by volume or more. When the average porosity of the whole layer is less than 10% by volume, the flexibility peculiar to the void-containing polyester film becomes insufficient, and the drawing property and cushioning property also become insufficient.

In order to reduce the amount of voids only in the surface layer of the 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 central portion. It is obtained by selecting the melt viscosity characteristics of the polyester and the thermoplastic resin and the conditions for melt extrusion from the extruder. Examples of the pressure-sensitive adhesive used in the void-containing polyester film include solvent-based adhesives such as natural rubber, chloroprene rubber, NBR, butyl rubber, urethane rubber, vinyl acetate and its copolymers, acrylic acid and its copolymers, and natural Emulsion type adhesives such as rubber latex, chloroprene latex, NBR latex, vinyl acetate and its copolymers, acrylic acid and its copolymers, polyvinyl alcohol, starch, water-soluble adhesives such as glue, epoxy resin, polyester resin , Thermosetting adhesives such as urea and melamine resins, phenolic resins, polyurethane resins, heat-melting adhesives such as paraffin wax, microcrystalline wax, asphalt, resin wax mixture, polyethylene, polypropylene, unsaturated polyester It is not particularly limited like Le. These may be used alone or in combination, or a third component such as a curing agent or a filler may be mixed.

These may be provided on the anchor coat layer.

[0015]

In the present invention, the polyester is used
This is because the heat resistance and mechanical strength of the void-containing polyester film are satisfied. In the present invention, a polyester is mixed with an incompatible thermoplastic resin to the polyester to obtain a polymer mixture by dispersing fine particles of an incompatible thermoplastic resin in the polyester in the polyester, This is to form a nucleus of a cavity generated by the next alignment treatment.

In the present invention, the reason why the thermoplastic resin B layer is provided and the amount of the cavities contained in the surface layer portion 3 μm of the A layer is 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 10% by volume or more is to provide appropriate drawing properties and cushioning properties. The reason why the adhesive layer is provided in the present invention is to impart adhesiveness.

The void-containing polyester film laminate thus obtained has good surface strength required for applications such as labels, stickers, packaging materials, heat-sensitive recording paper, delivery slips, etc., and is adhesive. It was

[0018]

EXAMPLES Examples of 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-K7210. 3) Density The film was cut into a square of 5.00 cm × 5.00 cm and the thickness was measured at 50 points, and the average thickness was t μm.
The weight was calculated up to 0.1 mg to be wg, and the weight was calculated by the following formula.

[0019]

[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 were polyethylene terephthalate 1.40, general-purpose polystyrene 1.05, polypropylene 0.91, and anatase type titanium dioxide 3.9.

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

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

7) Surface Peel Strength Using cellophane tape (18 mm width, made by Nichiban), the surface peel strength was evaluated by a cellophane tape peel test. The peeling angle was in the direction of about 150 degrees while keeping the void-containing film flat. The area of the peeled void-containing film was differentiated as follows. Class 5 ... Peeled off entirely Class 4 ... Almost peeled off Class 3 ... Around half peeled off Class 2 ... Almost peeled off Class 1 ... No peeled off at all

Example As a raw material, 80% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 was added to a melt flow index of 2.0.
g / 10 minutes 15% by weight of general-purpose polystyrene, 5% by weight of anatase type titanium dioxide having an average particle size of 0.3 μm as a raw material for the A layer, and 95% by weight of polyethylene terephthalate resin as a raw material for the B layer, 0.3 μm average particle diameter 5% by weight of rutile type titanium dioxide is melt-extruded at 290 ° C. from a T-die by separate twin-screw extruders, electrostatically adhered and solidified on a cooling rotary roll, and each layer is B / A / B.
= 30/440/30 μm of an unstretched sheet of the polymer mixture was obtained. At this time, the T-die slit interval is 1.0 mm
Then, the average flow velocity of the melt of the polymer mixture in that portion is 8.
It was 8 m / sec. Subsequently, the unstretched sheet was longitudinally stretched 3.5 times with a roll stretching machine at 83 ° C., and then horizontally stretched 3.5 times with a tenter at 130 ° C. and then 4% at 235 ° C.
Heat treatment was carried out while relaxing to obtain a polyester film containing a large number of cavities inside. Thickness is B / A / B = 3 /
It was 44/3 μm. The porosity of the surface layer of the layer A of the obtained film was 2% by volume, and the whole was 21% by volume. The portion with few cavities was present from the surface layer to a depth of about 3 μm. The surface strength of the void-containing film obtained in this example was class 1. When the cross section of the unstretched sheet of the polymer mixture of this example was observed by a scanning electron microscope, the average dispersed polystyrene particle size of polystyrene was 5.
The average particle size of the dispersed particles near the surface layer is 0.
It was 7 μm. The apparent specific gravity is 1.10, the porosity of the surface layer of layer A is 2% by volume, and the average porosity of the whole is 21% by volume.
The light transmittance was 13% and the thickness was 50 μm. An acrylic emulsion adhesive (Bond Coat PS-378 manufactured by Dainippon Ink and Chemicals, Inc.) was applied to this film, and release paper was attached to the adhesive surface to form a film laminate. When this laminate was attached to the glass surface and peeled again after a few seconds, the substrate could be peeled off smoothly without leaving any residue on the glass surface.

Comparative Example After obtaining a void-containing film in the same manner as in Example except that the average flow velocity of the melt was set to 4.4 m / sec,
An adhesive layer was provided. When this laminate was attached to the glass surface and peeled again after a few seconds, part of the surface layer of the substrate remained on the glass surface. At this time, the porosity of the surface layer of layer A is 17
It was% by volume.

[0028]

INDUSTRIAL APPLICABILITY The void-containing polyester film of the present invention, like the void-containing polyester film obtained by using a conventional polystyrene or polyolefin as a void-developing agent, is lightweight, flexible, hiding, matte, and drawable. In addition to the properties, it has excellent surface strength and adhesiveness as compared with the conventional void-containing polyester film. Therefore, the void-containing polyester film of the present invention can be used in an extremely wide range of fields such as labels, stickers, posters, recording papers, packaging materials, heat-sensitive recording materials and printing papers.

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Claims (1)

[Claims] 1. A polyester layer (A) containing fine cavities formed by orienting at least uniaxially a polymer mixture in which a polyester and an incompatible thermoplastic resin are mixed, on at least one surface of the polyester layer (A). , A layer (B) made of a thermoplastic resin is provided, and 3 μm from the surface of the A layer.
To 8% by volume or less, and the average void content of the entire film is 10% by volume or more and 50% by volume or less. A void-containing polyester film laminate, which is provided with a layer.