JP2001031928A - Thermally contact-bonding film and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally contact-bonding film capable of giving a very thin thermally contact-bonding layer without injuring the external appearance of the film. SOLUTION: There is provided a manufacturing method of a thermally contact-bonding film comprising a step of applying a thermoplastic resin composition on at least one surface of a transparent biaxially stretched plastic film followed by drying, wherein (1) an unstretched film is stretched in the direction of the flow and coated with a dispersion of the thermoplastic resin composition, dried, and subsequently stretched in the width-direction and (2) the coating weight of the thermoplastic resin composition is such that the apparent coating thickness calculated from the dry coating weight of the resin composition and the density of the resin particles in the dispersion of the resin composition is smaller than the average particle size of the resin particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermocompression-bondable biaxially stretched plastic film, particularly a biaxially stretched polypropylene film, which is suitably used for packaging foods, miscellaneous goods and the like, and for pseudo bonding such as concealed postcards.

[0002]

2. Description of the Related Art Biaxially stretched plastic films such as biaxially stretched polypropylene films (hereinafter referred to as OPP films) are excellent in transparency, gloss, mechanical strength, etc., and are used for packaging and printing of food and miscellaneous goods. Often used for laminating paper. In particular, when used in an automatic packaging machine equipped with a thermocompression bonding device, or when used for pseudo bonding such as concealed postcards by laminating on a substrate such as paper,
An OPP film provided with a thermocompression layer on the film surface in advance is used.

Conventionally, methods for providing a thermocompression bonding layer on an OPP film include, for example, (A) a method in which a polyolefin resin having a relatively low softening temperature is laminated on a polypropylene film before stretching, and (B) an OPP film. A method of applying and drying a solution or dispersion of a resin composition having thermoplasticity to the resin is often used.

[0004] However, the thermocompression bonding layer obtained by the method (A) is too thick to be used for pseudo-adhesion, so that the bonding strength becomes excessively high, and the press-bonded material can be peeled off cleanly. It tends to disappear. To solve this problem, a method of lowering the bonding strength by lowering the thermocompression bonding temperature is conceivable. However, it is necessary to control the thermocompression bonding temperature to an extremely narrow range, and it is not general because it requires advanced processing technology.

On the other hand, in the method (B), since a solution or dispersion of a resin composition having thermoplasticity is applied very thinly and dried, there is a problem that coating unevenness occurs and the appearance is impaired. To solve this problem, it is sufficient to increase the dry coating amount, but in this case, the same problem as in the method (A) occurs.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a thermocompression-bondable film which has a small temperature dependency in adhesive strength and is excellent in appearance, and which is suitably used for simulated bonding.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for producing a biaxially stretched plastic film provided with a thermocompression bonding layer, particularly an OPP film. After stretching, apply a dispersion of the thermoplastic resin composition under conditions that do not form a film,
It has been found that by drying and subsequently stretching in the width direction, the thickness of the thermocompression bonding layer can be extremely reduced without impairing the appearance of the film, and the present invention has been completed.

The first invention of the present invention relates to a method for producing a thermocompression-bondable film obtained by applying a thermoplastic resin composition to at least one surface of a transparent biaxially stretched plastic film and drying it. After stretching the film before stretching in the flow direction, a dispersion of the thermoplastic resin composition is applied and dried, and subsequently stretched in the width direction. (2) The coating amount of the thermoplastic resin composition is as follows. The present invention relates to a method for producing a thermocompression-bondable film, characterized in that an apparent coating thickness obtained from a dry coating amount and a density of resin particles in a resin composition dispersion liquid is smaller than an average particle diameter of the resin particles. It is. The second invention of the present invention provides a method for producing a thermocompression-bondable film obtained by applying a thermoplastic resin composition to at least one surface of a transparent biaxially stretched plastic film and drying the film, Thermostretchability characterized by applying a dispersion of a thermoplastic resin composition after stretching in the width direction, drying under a condition that the applied thermoplastic resin composition does not form a film, and subsequently stretching in the width direction. The present invention relates to a method for producing a film.

[0009] The third invention of the present invention is directed to the first or second invention.
In the invention, the dry coating amount of the resin composition is 5 to 100 mg / m per biaxially stretched plastic film after stretching.
^{The present} invention relates to a method for producing a thermocompression-bondable film in the range of ² . The fourth invention of the present invention relates to a method for producing a thermocompression-bondable film, wherein the transparent biaxially stretched plastic film in any one of the first to third inventions is a biaxially stretched polypropylene film. The fifth of the present invention
The invention relates to a thermocompression bonding layer of a thermocompression bonding film in which a thermocompression bonding layer made of a thermoplastic resin composition is laminated on at least one surface of a transparent biaxially stretched plastic film, and has a width of 0.5
The present invention relates to a thermocompression-bondable film having cracks or gaps at intervals of about 50 μm.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, after a film before stretching is stretched in the machine direction, a dispersion of a thermoplastic resin composition is applied and dried under conditions that do not form a film, and subsequently stretched in the width direction. Thus, a thermocompression-bonding film having a good appearance can be obtained while maintaining pseudo-adhesion. That is, coating unevenness is prevented by increasing the amount of dry coating by the stretch ratio as compared with the case where the dispersion of the thermoplastic resin composition is applied to the film after biaxial stretching.

When the dispersion of the thermoplastic resin composition is dried to form a film by a generally used method, the thermocompression bonding layer of the present invention is stretched in the width direction because the thickness is extremely small. In this case, a film crack occurs and the appearance is impaired. On the other hand, if the film is applied and dried under conditions that do not form a film as in the present invention, gaps are generated between particles of the adjacent thermoplastic resin composition when stretched in the width direction. These gaps are extremely fine and cannot be recognized by the naked eye, so that a thermocompression-bonding film having excellent appearance can be obtained. Therefore,
In the present invention, it is extremely important to apply and dry a dispersion of the thermoplastic resin composition under conditions that do not form a film.

Means for applying and drying the dispersion of the thermoplastic resin composition under conditions that do not form a film include a method of applying and drying the resin composition so that the particles of the thermoplastic resin composition do not cover the entire surface of the film. In other words, after stretching the biaxially stretched plastic film as the base material in the flow direction, and then applying and drying the dispersion of the thermoplastic resin composition, the dry application amount of the resin composition and the resin composition dispersion A method in which the apparent coating thickness determined from the density of the resin particles in the resin composition is smaller than the average particle diameter of the resin particles in the resin composition dispersion. In this case, even if the resin composition in the resin composition is dried at a temperature at which the resin particles can be fused together, the resin does not cover the entire surface of the film because the amount of the resin is small. Further, there is a method of drying under conditions that the applied thermoplastic resin composition does not form a film. To dry the applied thermoplastic resin composition without forming a film,
For example, drying may be performed at such a low temperature that the resin particles in the resin composition melt and do not form a film. In this case, as described above, it is not necessary to apply the apparent coating thickness smaller than the average particle diameter of the resin particles in the resin composition dispersion. The present invention may use any of these methods, but it is more preferable to combine the two methods.

When the thermocompression-bondable film obtained by the above method is observed with a microscope, cracks or gaps having an interval of 0.5 μm or more are present in the thermocompression layer on the surface, and the gap is less than 50 μm, most preferably less than 20 μm. If it is, it will be extremely excellent in appearance. On the other hand, as in the present invention, even when the film is stretched in the flow direction, and then the dispersion of the thermoplastic resin composition is applied and dried, even when the coating amount of the thermoplastic resin composition is large, or When the dispersion of the plastic resin composition is dried under the conditions for forming a film, no cracks or gaps having an interval of 0.5 μm or more are observed in the thermocompression-bonded layer of the film, but subsequently stretched in the width direction. When a biaxially stretched thermocompression-bondable film is formed, large cracks are formed as visually recognized and visually impair the appearance.

The dispersion liquid of the thermoplastic resin composition used in the present invention includes, for example, polyolefin resins such as polyethylene and polypropylene, polyester resins, acrylic resins, polyvinyl acetate resins, and copolymer resins thereof. And the like, various commonly known thermoplastic resin compositions dispersed in various solvents such as water and alcohol can be used. In addition, various additives such as surfactants such as dyes and pigments, defoamers and wetting agents, antiblocking agents, lubricants and thickeners are added to the dispersion of the thermoplastic resin composition as necessary. You can also.

The average particle size of the thermoplastic resin composition in the present invention can be measured by a laser diffraction / scattering method, a Coulter counter method, a sedimentation method, microscopic observation, etc. described in JIS K1150.

The method for applying and drying the dispersion of the thermoplastic resin composition in the present invention may be, for example, a combination of a known and official drying method with various coating apparatuses such as a roll coater, a bar coater, a gravure coater, and an air knife coater. Done. In addition, the dry coating amount of the thermoplastic resin composition dispersion liquid per biaxially stretched plastic film after stretching,
Preferably 5 to 100 mg / m ² , particularly preferably 10
５０50 mg / m ² . If the dry coating amount of the resin composition is too small, sufficient adhesive strength cannot be obtained, and if it is too large, the adhesive strength is too strong and it is difficult to peel off cleanly, so that it cannot be used as a pseudo-adhesive application.

The plastic film used as the substrate in the present invention includes a propylene film, a polyester film, a nylon film and the like, and among them, a propylene film is preferable. The propylene film is mainly composed of polypropylene and / or a polypropylene resin having an olefin content of less than 2% by weight (hereinafter, simply referred to as a polypropylene resin). 2% by weight of olefins other than propylene
Above this, it is difficult to obtain the original quality of the OPP film, and the practicality is poor. The melt index of the polypropylene resin is not particularly limited, but is preferably in the range of 1 to 10 g / 10 minutes in order to provide good film moldability.

The method for producing a biaxially stretched plastic film of the present invention is exemplified by the method for producing an OPP film. A polypropylene resin is melted and kneaded.
It is extruded onto a cooling roll by a mold die and cooled and solidified into a sheet shape. The obtained sheet is stretched about 5 times in the longitudinal direction by a longitudinal stretching machine, and after performing corona treatment as needed, a dispersion of the thermoplastic resin composition is applied and dried under the condition that a film is not formed. . Subsequently, the horizontal stretching machine
The film is stretched to about 0 times and wound up as an OPP film. Thereafter, a corona treatment or the like may be further performed as necessary.

The biaxially stretched plastic film of the present invention contains, as additives, an antistatic agent, an antioxidant, a lubricant,
An anti-blocking agent, a filler, a petroleum resin, a terpene resin, or the like may be appropriately used. When extruding the polypropylene resin, various polyolefin resins may be laminated.

[0020]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[Preparation of Coating Liquid] Coating Liquid A An aqueous dispersion of a polyolefin resin (trade name “Chemipearl S-200” manufactured by Mitsui Chemicals, Inc .; 5μm, density 0.95g
/ Cc) to obtain a coating solution A having a solid content of 10%. Coating liquid B Water dispersion of polyolefin resin (trade name “Chemipearl S-659” manufactured by Mitsui Chemicals, Inc., average particle diameter <0.1 μm, density 0.95 as a dispersion of the thermoplastic resin composition)
g / cc) to obtain a coating liquid B having a solid content of 10%.

Example 1 A molten polypropylene resin was extruded onto a cooling roll by a T-die extruder, stretched 5 times in the longitudinal direction, corona treated, and then coated with a coating solution A with a bar coater. 0.0g
/ M ^{2 and} dried at 80 ° C. so as not to form a film.
The dry weight of the coating layer of the obtained film was about 0.40 g /
m ² , and the apparent coating thickness was 0.42 μm. (The average particle size of the resin in the thermoplastic resin composition is 0.1.
5 μm. Next, the film was stretched 10 times in the transverse direction to obtain a thermocompression-bondable film of the present invention. When the surface of the coating layer of the biaxially stretched film was observed with a microscope, cracks were observed in a streak shape at intervals of about 8 μm.

Example 2 Instead of using the coating liquid A, the coating liquid B was added at 2.0 g / m
A thermocompression-bondable film of the present invention was obtained in the same manner as in Example 1 except that the ^two coatings were performed and dried at 60 ° C. so as not to form a film. The dry weight of the coating layer before stretching in the width direction is about 0.2
0 g / m ² , and the apparent coating thickness was 0.21 μm. (The average particle diameter of the resin in the thermoplastic resin composition is less than 0.1 μm.) When the surface of the coating layer of the film after biaxial stretching was observed with a microscope, cracks were observed in a streak shape at intervals of about 3 μm. .

Example 3 A thermocompression-bondable film of the present invention was obtained in the same manner as in Example 1 except that the coating solution A was applied at 2.0 g / m ² and dried at 120 ° C. The dry weight of the coating layer was about 0.20 g / m ² and the apparent coating thickness was 0.21 μm. (The average particle diameter of the resin in the thermoplastic resin composition is 0.5 μm.) Observing the surface of the coating layer of the film after biaxial stretching with a microscope, an elliptic thermoplastic having a major axis of about 30 μm and a minor axis of about 3 μm. The resin composition was confirmed in an island shape.

Example 4 A thermocompression-bondable film of the present invention was obtained in the same manner as in Example 1, except that 8.0 g / m ^{2 of the} coating solution A was applied and dried at 60 ° C. so as not to form a film. The dry weight of the coating layer before stretching in the width direction was about 0.80 g / m ² , and the apparent coating thickness was 0.84 μm. (The average particle size of the resin in the thermoplastic resin composition is 0.5 μm.) When the surface of the coating layer of the biaxially stretched film was observed under a microscope, cracks were observed at intervals of about 8 μm.

Comparative Example 1 A comparative thermocompression-bondable film was obtained in the same manner as in Example 2 except that the coating solution B was applied at 2.0 g / m ^{2 and} dried at 120 ° C. to form a film. The dry weight of the coating layer before stretching in the width direction was about 0.20 g / m ² , and the apparent coating thickness was 0.21 μm. (The average particle diameter of the resin in the thermoplastic resin composition is less than 0.1 μm.) Microscopic observation of the coating layer surface of the biaxially stretched film showed no cracks or gaps.

Comparative Example 2 A comparative thermocompression-bondable film was obtained in the same manner as in Example 4 except that coating liquid A was applied at 8.0 g / m ^{2 and} dried at 140 ° C. to form a film. The dry weight of the coating layer before stretching in the width direction was about 0.80 g / m ² , and the apparent coating thickness was 0.84 μm. (The average particle diameter of the resin in the thermoplastic resin composition is 0.5 μm.) No cracks or gaps were observed by microscopic observation of the coating layer surface of the film after biaxial stretching.

[Evaluation] The appearance and pseudo-adhesion suitability of the obtained thermocompression-bondable film after biaxial stretching were evaluated by the following methods.
The results are shown in Table 1. [Appearance] The appearance of the film was visually observed and judged according to the following criteria. ：: The coating layer is uniform and extremely excellent in appearance. Δ: Some film cracks occurred in the coating layer, and the appearance was slightly inferior. X: The film was severely cracked and could not be used. [Similar adhesion suitability] The thermocompression bonding surfaces of the thermocompression bonding film were overlapped with each other, and the area of 25 mm x 10 mm was thermocompression bonded at a pressure of 200 kPa for 1 second using a heat sealer set at 140 ° C. One hour later, the film was peeled off at a speed of 300 mm / min using a tensile tester, and the adhesive strength was measured. In addition, visually determine the presence or absence of abnormal appearance after peeling,
Pseudo-adhesion suitability was determined based on the following criteria. X: The adhesive strength is less than 0.1 N / 25 mm, and the adhesive strength is too weak to be used. ◎: Adhesive strength is 0.1 N / 25 mm to 0.5 N / 25 mm, and scars after peeling are scarcely left, which is extremely suitable for pseudo-adhesive use. ：: The adhesive strength is 0.5 mN / 25 mm to 2.0 mN / 25 mm,
It cannot be used for concealed postcards because it leaves traces of peeling, but it can be used for some pseudo adhesive applications. Δ: Adhesive strength exceeds 2.0 N / 25 mm, and it may not be able to be peeled off cleanly, so it cannot be used for pseudo-adhesive use.

[0029]

[Table 1]

As is clear from the table, Example 1 has a very good result because the coating amount is small and the drying temperature is low. Examples 2 and 4 have a large amount of application but a low drying temperature, and Example 3 has a small amount of application, so that good results can be obtained even at a high drying temperature.

[0031]

As is clear from the results shown in Table 1, the thermocompression-bonding film of the present invention has an extremely excellent appearance.
It is suitably used for pseudo bonding applications.

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Claims (5)

[Claims] A method for producing a thermocompression-bondable film obtained by applying a thermoplastic resin composition to at least one surface of a transparent biaxially stretched plastic film and drying the composition.
(1) After stretching the film before stretching in the flow direction, apply and dry the dispersion of the thermoplastic resin composition, and subsequently stretch in the width direction. (2) The amount of the thermoplastic resin composition applied is determined by the resin composition. A method for producing a thermocompression-bondable film, characterized in that the apparent coating thickness obtained from the dry coating amount of the product and the density of the resin particles in the resin composition dispersion liquid is smaller than the average particle size of the resin particles. . 2. A method for producing a thermocompression-bondable film obtained by applying and drying a thermoplastic resin composition on at least one surface of a transparent biaxially stretched plastic film, wherein the film before stretching is stretched in the flow direction. Thereafter, a method for producing a thermocompression-bondable film, comprising applying a dispersion of a thermoplastic resin composition, drying the applied thermoplastic resin composition under conditions that do not form a film, and subsequently stretching in the width direction. . 3. The dry coating amount of the resin composition is 5 to 100 mg / m ² per stretched biaxially stretched plastic film.
The method for producing a thermocompression-bondable film according to claim 1 or 2, wherein 4. The method for producing a thermocompression-bondable film according to claim 1, wherein the transparent biaxially stretched plastic film is a biaxially stretched polypropylene film. 5. A thermocompression-bondable film in which a thermocompression bonding layer made of a thermoplastic resin composition is laminated on at least one surface of a transparent biaxially stretched plastic film, wherein the thermocompression bonding layer has a width of 0.5 to 0.5 mm. A thermocompression-bondable film having cracks or gaps at intervals of 50 μm.