JP5346682B2 - Method for producing stretched film with coating layer - Google Patents

Description

  The present invention relates to a method for producing a stretched film with a coating layer in which an uncured thermosetting resin coating solution is applied to a stretched film made of polyester and having voids, followed by drying and thermosetting.

  A white film that has been made white by including fine voids in the film is already known. This white film reflects light at the interface between the voids inside the film and the polyester, and has a high light reflectance due to the difference in refractive index.

  As a kind of polyester film, a white film containing fine voids inside the film is known (Patent Document 1), and light is reflected due to the refractive index difference at the interface between the voids inside the film and the polyester, As a result, it has a high light reflectance. As an application of this white film, there is a reflection film of a backlight unit of a liquid crystal display device (Patent Document 2).

JP 2008-036823 A Japanese Patent Laid-Open No. 11-291432

When a coating layer is provided on a polyester film having voids therein, voids are easily deformed or voids disappear, and in this case, the reflectivity of the film decreases.
This invention makes it a subject to provide the manufacturing method of the extending | stretching film with an application layer which can provide an application layer in the polyester extending | stretching film which has a void, without deforming a void.

That is, the present invention is made of a thermoplastic aromatic polyester having a glass transition temperature of 60 ° C. or more, and an uncured thermosetting resin coating solution is applied to a stretched film having voids in the polyester, followed by drying and thermosetting. In the manufacturing method of the stretched film with a coating layer which forms a coating layer on a stretched film by this, drying and thermosetting of a coating liquid are carried out in the temperature range of 40 degreeC or more and (the glass transition temperature of polyester-5 degreeC) or less. It is a manufacturing method of the stretched film with a coating layer characterized by performing in the state which applied the tension | tensile_strength of 100-200 N / m to the stretched film.
The present invention is also a stretched film with a coating layer produced by the above production method.

  According to the present invention, a stretched film made of polyester having voids can be provided with a coating layer on the stretched film surface without deforming the voids.

Hereinafter, the present invention will be described in detail.
[Stretched film with voids]
As the polyester of the stretched film having voids, a thermoplastic aromatic polyester having a glass transition temperature of 60 ° C. or higher is used. Examples of the thermoplastic aromatic polyester include polyethylene terephthalate and polyethylene naphthalene dicarboxylate.

  The polyester may be copolymerized with a copolymer component. In that case, in order to maintain the glass transition temperature at 60 ° C. or higher, the proportion of the copolymerization component should not be too large, for example, 20 mol% or less, preferably 12 mol% or less. As the copolymer component, for example, isophthalic acid can be used.

  As a stretched film having voids, an unstretched film of a polyester composition in which a void-forming substance is blended with polyester is stretched, and fine voids are formed inside the film by peeling at the interface between the void-forming substance and the polyester during stretching. A stretched film can be used. As the void forming substance, for example, inorganic particles, organic particles, and incompatible resin particles can be used.

  When an incompatible resin is used as the void-forming substance, examples of the incompatible resin include a polyolefin resin and a polystyrene resin, specifically, for example, poly-3-methylbutene-1, poly-4-methylpentene-1, polyethylene, Polypropylene, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polyfluorostyrene, cellulose acetate, cellulose propionate, polychlorotrifluoroethylene can be used. .

  When using an incompatible resin as the void-forming substance, for example, 5 to 30 parts by weight, preferably 8 to 25 parts by weight, more preferably 10 to 20 parts by weight per 100 parts by weight of the total of the polyester and the incompatible resin. Used in proportions. By using in this range, a stretched film containing a sufficient amount of voids can be obtained without breaking the film during stretching.

When inorganic particles are used as the void-forming substance, for example, titanium oxide, barium sulfate, calcium carbonate, or silicon dioxide particles can be used as the inorganic particles. The inorganic particles may be particles having a plate shape or a spherical shape.
When organic particles are used as the void-forming substance, for example, particles such as cross-linked polystyrene or resin particles exemplified as incompatible resins can be used.

  When inorganic particles or organic particles are used as the void-forming substance, the average particle size of the particles is, for example, 0.3 to 3.0 μm, preferably 0.4 to 2.5 μm, and more preferably 0.5 to 2.0 μm. . By using a material having an average particle diameter in this range, the film can be stretched without breaking the film without causing aggregation of the particles.

  When inorganic particles or organic particles are used as the void-forming substance, for example, 31 to 60 parts by weight, preferably 35 to 55 parts by weight, more preferably 37 to 50 parts by weight per 100 parts by weight of the total of the polyester and the particles. Use. By using in this range, it is possible to obtain a void sufficient to make the film white without easily breaking the film.

  The stretched film having voids may be a single layer film composed of one layer or a multilayer film composed of a plurality of layers. In the case of a multilayer film, it is sufficient that there is at least one layer of polyester having voids, and the film having voids may be disposed on the surface layer of the multilayer film or may be disposed on the core layer.

  Voids in the polyester can be formed by stretching an unstretched film containing a void-forming substance in at least a uniaxial direction. Preferably, the voids are formed by stretching in a biaxial direction.

[Coating, drying and thermosetting]
In this invention, a coating layer is formed on a stretched film by apply | coating the coating liquid of an uncured thermosetting resin to the above-mentioned stretched film, and drying and thermosetting, and a stretched film with a coating layer is obtained.

  As a method for applying the coating liquid, a generally known method can be used. For example, a coating method such as gravure, roll, spin, reverse, bar, screen, dipping or the like can be used.

  In the present invention, the coating liquid is dried and thermally cured in a temperature range of 40 ° C. or higher and (polyester glass transition temperature −10 ° C.) or lower with a tension of 100 to 200 N / m applied to the stretched film. . This tension is a tension in the film transport direction, that is, in the machine axis direction.

  The temperature of drying and thermal curing of the coating liquid is 40 ° C. or higher and (polyester glass transition temperature −5 ° C.) or lower, preferably 40 ° C. or higher and (polyester glass transition temperature −10 ° C.). If it is lower than 40 ° C., the coating liquid is hard to be thermally cured and a strong coating film cannot be obtained. On the other hand, when the temperature is higher than (the glass transition temperature of polyester-5 ° C.), the voids of the stretched film are deformed by heat and tension.

  If the tension of the stretched film when the coating liquid is dried and thermally cured is less than 100 N / m, uneven coating occurs on the surface of the stretched film. On the other hand, if it exceeds 200 N / m, the film may break.

[Coating liquid for thermosetting resin]
As the thermosetting resin, for example, polyurethane, polyacrylate, polymethacrylate, polyisocyanate, a copolymer thereof, or a mixture of two or more thereof can be used. Among thermosetting resins, those that are thermoset at a relatively low temperature are preferred. In addition, for the purpose of forming a fast and strong coating layer, a mixture of a crosslinking agent is particularly preferable because adhesion of the thermosetting resin coating layer to the film is improved. As the crosslinking agent, isocyanate-based, melamine-based, and epoxy-based ones can be used.

  Whether the thermosetting resin contains a crosslinking agent or not, it is dissolved or dispersed in a solvent to form a coating solution. As the solvent, for example, butyl acetate or ethyl acetate can be used. For example, pigments, dyes, and fillers may be added to the coating liquid.

Hereinafter, the present invention will be described in detail by way of examples. Measurement and evaluation were performed by the following methods.
In Examples and Comparative Examples, Teijin Tetron UX02-225 (biaxially stretched film made of 12 mol% isophthalic acid copolymerized polyethylene terephthalate having a glass transition temperature of 72 ° C., thickness 225 μm, Teijin DuPont film was used as a stretched film having voids. Made).

(1) Amount of coating layer formed on surface of stretched film A stretched film with a coating layer was cut into a size of 10 × 10 cm and the weight was measured. Next, the surface of the stretched film with a coating layer was rubbed with gauze soaked with butyl acetate to remove the coating layer, and the weight of the stretched film after removal of the coating layer was measured. The amount of the coating layer was calculated by the following formula.
Amount of coating layer (g / m ² )
= (Weight of stretched film with coating layer (g)-Weight of stretched film after removal of coating layer (g))
÷ (0.1 (m) x 0.1 (m))

(2) Luminance (2-1) Creation of Evaluation Backlight Unit The built-in direct type backlight unit (32 inches) was taken out from the liquid crystal television (Sony Bravia KDL-32F1) prepared for evaluation. . The reflection sheet originally incorporated in the backlight unit was replaced with a film to be measured, and a backlight unit for evaluation was created.
(2-2) Luminance Measuring Method Using a luminance meter (Otsuka Electronics, instantaneous multi-photometry system MCPD-7700), the light receiving portion of the optical fiber for light reception is perpendicular to the optical sheet surface of the backlight unit (0 ° And fixed at a position where the distance from the optical sheet surface is 50 cm, the viewing angle was 2 °, and the luminance was measured 1 hour after the backlight was turned on.
(2-3) Brightness improvement rate In order to evaluate the brightness improvement rate of the backlight unit by providing the coating layer on the stretched film, the brightness improvement rate was calculated by the following formula.
Brightness improvement rate (%)
= (Brightness when using stretched film with coating layer)
/ (Luminance when using a stretched film before providing a coating layer)
× 100

(3) Glass transition temperature The film sample was measured using a differential scanning calorimeter (TA Instruments 2100 DSC) at a heating rate of 20 m / min.

[Example 1]
17 parts by weight of Udouble S2740 (uncured thermosetting resin, made by Nippon Shokubai, acrylic), 3 parts by weight of Coronate HL (crosslinking agent, made by Nippon Polyurethane Industry Co., Ltd., isocyanate), butyl acetate (organic solvent, sum) 20 parts by weight (manufactured by Kojun Pharmaceutical Co., Ltd.) was mixed to obtain a coating solution.
This coating solution was supplied on a void-containing layer of Teijin Tetron UX02-225 to which a tension of 150 N / m was applied in the machine axis direction with a gravure roll coater (number of lines 70), and then dried at 60 ° C. for 2 minutes. And heat-cured to obtain a stretched film with a coating layer. The evaluation results of the obtained stretched film with a coating layer are shown in Table 2.

[Examples 2 to 6]
A film with a coating layer was obtained in the same manner as in Example 1 except that the composition of the coating liquid was changed as shown in Table 1 and the drying and thermosetting conditions were changed as shown in Table 1. The evaluation results are shown in Table 2.

[Comparative Example 1]
A stretched film with a tension of 150 N / m applied in the machine axis direction was allowed to pass through at 60 ° C. for 2 minutes. Table 2 shows the evaluation results of the stretched film after passing through.

[Comparative Example 2]
A stretched film with a tension of 150 N / m applied in the machine axis direction was allowed to pass through at 100 ° C. for 2 minutes. Table 2 shows the evaluation results of the stretched film after passing through.

  The method for producing a stretched film with a coating layer of the present invention is useful for providing a coating layer on a polyester film having voids therein. The stretched film with a coating layer obtained by this method can be suitably used as, for example, a reflective film of a liquid crystal display device having a coating layer on the surface.

Claims (1)

  The stretched film is made of a thermoplastic aromatic polyester having a glass transition temperature of 60 ° C. or more, and a stretched film having voids in the polyester is coated with an uncured thermosetting resin coating solution and dried and thermally cured. In the method for producing a stretched film with a coating layer on which a coating layer is formed, the coating liquid is dried and thermally cured at a temperature of 40 ° C. or more and (polyester glass transition temperature −5 ° C.) or less in a stretched film. A method for producing a stretched film with a coating layer, which is performed in a state where a tension of ˜200 N / m is applied.