KR20120045755A - A manufacturing method of transparent polyimide composite film for the use of display panel - Google Patents

Abstract

PURPOSE: A manufacturing method of a transparent polyimide composite film for a display panel is provided to use semi-solid phase polyimide film, thereby easily positioning a mat consisting of glass fiber inside a polyimide film. CONSTITUTION: A manufacturing method of a transparent polyimide composite film for a display panel comprises: a step of manufacturing polyimide liquid by dissolving polyimide resin into solvent; a step of spreading polyimide solution on a substrate; a step of forming a substrate, in which semisolid phase polyimide film is coated by evaporating a part of solvent in the polyimide solution; a step of positioning the semi-solid phase polyimide film(11) on the upper side and the lower side of a mat(13), respectively; a step of heating and pressing the substrate by passing between a pair of rollers maintaining gap-pressure; a step of forming the polyimide film laminated to one body; and a step of delaminating the substrate, and removing solvent from the polyimide film.

Description

A manufacturing method of transparent polyimide composite film for the use of display panel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a transparent film for a display panel such as a flexible display substrate that requires transparency, and more particularly, to a transparent composite film in which a reinforcing mat made of glass fibers is embedded in a polyimide film.

There are various types and sizes of displays ranging from small displays such as mobile phones to LCD or PDP TVs or outdoor billboards (PID and DID). In particular, as the society develops into the ubiquitous era, which is a highly knowledgeable and information society, the demand for portable devices with simple and mobility is exploding. As a result, flexible display technology that is thinner, lighter, easier to carry, folds like paper and sometimes rolled up, is being activated, and is emerging as a new growth engine business.

Conventionally, glass was used as such a transparent film for display panels. However, glass has good transparency but lacks impact resistance due to the characteristics of the glass, so it is easily broken by impact and has a limitation in thinning, and has a limitation in weight reduction due to its large weight per unit volume. Therefore, recently, resins having good impact resistance and light weight, such as polycarbonate (PC), polyimide (PI), polyethersulfone (PES), and polyarylate (excellent optical properties) thermoplastic resins such as polyarylate, PAR), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), cycloolefin copolymer, acrylic resin epoxy resin, Transparent films manufactured using curable resins such as unsaturated polyesters are gradually replacing glass.

However, since the above-mentioned plastic transparent film has a higher coefficient of thermal expansion than glass films, thermal expansion occurs largely at high temperatures, and thermal shrinkage greatly occurs when the temperature is lowered to room temperature. If the thermal expansion and thermal contraction is large during the display manufacturing, due to the difference in the coefficient of thermal expansion existing between the functional coating surface, such as hard coating, inorganic thin film and the transparent film, the coating surface is peeled off or cracks occur, and curling occurs. Due to such a phenomenon, the array of pixels constituting the screen is disturbed to cause screen distortion so that display performance cannot be properly expressed. Therefore, in order to apply the plastic transparent film for optics, it is very important to minimize the thermal contraction phenomenon by lowering the coefficient of thermal expansion. Moreover, it is also necessary to complement the mechanical strength of a transparent film.

As a method for lowering the coefficient of thermal expansion and reinforcing mechanical properties without substantially deteriorating the optical properties of the transparent film, a method of uniformly dispersing fine-sized glass fibers in the transparent film has been proposed. Glass fiber is a transparent inorganic material, has a low coefficient of thermal expansion, hardly shrinkage and expansion due to heat, and excellent mechanical properties. If glass fibers having a size smaller than the wavelength range of visible light to be transmitted are uniformly dispersed in the base resin forming the transparent film, transparency can be secured by minimizing the effects of scattering or reflection caused by particles.

However, nanoparticles tend to aggregate tens or hundreds of particles together due to electrostatic properties such as van der Waals attraction. As a result, reflection and scattering of visible light may be induced, thereby greatly hindering the transparency of the display panel film, and there is a limit in obtaining an effect of improving mechanical properties to a desired degree.

As an alternative to the reinforcement made of an organic-inorganic material having a size of such nano units, a method of using a woven fabric or a nonwoven fabric using a mat made of glass fibers, that is, a glass fiber having a refractive index similar to that of the base resin, has been attempted.

When the glass fiber mat is used as the reinforcing material of the base resin, the glass fibers do not aggregate in the transparent base resin at all, and the glass fiber reinforcing material embedded in the mat form has greater mechanical properties than the glass reinforcing material added in the form of short fibers. It shows an improvement effect.

On the other hand, polyimide resin is a plastic that has been widely applied to electrical and electronic parts due to its excellent chemical resistance and heat resistance, attracting attention as a candidate that can be applied to the next-generation display panel of the base resin described above. Polyimide has strong heat resistance and chemical resistance due to imide groups in the molecule. However, the polyimide resin also needs to improve heat shrinkage characteristics in order to be applied as a display panel material, and there is a problem in that it is very difficult to embed the aforementioned fiberglass mat.

That is, if the glass fiber mat is immersed after casting the polyimide solution in which the polyimide resin is dissolved in the solvent according to a conventional method, the glass fiber mat is not immersed in the polyimide solution formed with high viscosity to form a transparent film for display panel. Without floating on the casting solution. The polyimide composite film thus formed is not embedded in the polyimide film and is located on the surface side, so that the function as a reinforcing material is not well expressed, and various problems may occur due to the glass fiber mat derived from the surface layer.

The problem to be solved by the present invention is to provide a method for manufacturing a polyimide transparent composite film for a display panel by improving the coefficient of thermal expansion by easily placing the mat made of glass fibers in a polyimide film to solve the above problems. .

The manufacturing method of the polyimide transparent composite film for display panels of this invention,

(S1) dissolving a polyimide resin in a solvent to prepare a polyimide solution;

(S2) applying the polyimide solution onto a substrate, and then evaporating a portion of the solvent in the polyimide solution to form a polyimide film on semi-solid;

(S3) placing the substrate coated with the polyimide film on the semi-solid on the upper and lower surfaces of the mat made of glass fibers, respectively, and heating and pressurizing while passing between the pair of rollers maintaining the gap pressure Integrating the mat and a polyimide film on a semi-solid stacked on top and bottom of the mat; And

(S4) desorbing the substrate, and then removing the solvent from the polyimide film on the semi-solid stacked on the upper and lower surfaces of the mat.

In the method for producing a polyimide transparent composite film for display panel of the present invention, it is preferable to use N, N-dimethylacetamide (DMAc) as the solvent for dissolving the polyimide, and the semi-solid The content of the solvent in the polyimide film on the)) is preferably 5 to 10% by weight based on the total weight of the polyimide film on the semi-solid.

In the manufacturing method of the polyimide transparent composite film for display panel of the present invention, the heating temperature of the step (S3) is preferably 80 ~ 120 ℃, the semi-solid polyimide film coated on the substrate It is preferable that the thickness of is 50-70 micrometers, and it is preferable that the thickness of the mat is 30-70 micrometers.

In the manufacturing method of the polyimide transparent composite film for display panel of this invention, it is preferable that the refractive index of the said polyimide resin and glass fiber is 1.54-1.56. As a mat of glass fiber, it is preferable to use a glass fiber fabric woven by weft and warp yarn made of glass fiber.

According to the manufacturing method of the present invention, by using a semi-solid polyimide film, a mat made of glass fibers can be easily positioned in the polyimide film.

Accordingly, the coefficient of thermal expansion is improved, it is possible to manufacture a polyimide transparent composite film for a display panel with improved mechanical properties.

1 is a schematic cross-sectional view of a polyimide transparent composite film for a display panel according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Hereinafter, a method of manufacturing a polyimide transparent composite film for display panel according to the present invention will be described in more detail.

First, the polyimide resin is dissolved in a solvent to prepare a polyimide solution (step S1).

As the polyimide resin, any polyimide suitable for use for a display panel can be used, but it is preferable to use a transparent and colorless polyimide resin. Methods for producing a colorless and transparent polyimide resin are disclosed in various documents, for example, Japanese Patent Publication Nos. 61-14173, 62-13436, 62-67421, 63-170420, etc. Publication Nos. 2007-106824, 2008-55531, 2009-25503, 2009-25504, 2009-21591, 2009-19306 and the like.

Examples of the solvent for dissolving the polyimide may include N, N-dimethylacetamide (DMAc), but are not limited thereto, and any solvent may be used as long as it dissolves the polyimide.

Subsequently, the polyimide solution is applied onto the substrate, and then a part of the solvent in the polyimide solution is evaporated to form a polyimide film on a semi-solid (S2 step).

In the present invention, the solvent is removed from the polyimide solution by a method such as heat drying, but only a part of the solvent is evaporated to form a semi-solid polyimide film and combined with the mat described below. In the present invention, the term "semisolid phase" does not mean that the solvent is completely removed to become a hard solid state, but a state in which a large amount of solvent remains as it is commonly used, and is soft and loose. Thus, the polyimide film on the semi-solid (semisolid) is maintained in appearance unlike the liquid, but can be easily changed in shape by the external force, such as pressure is applied. In addition, the polyimide film on semi-solid becomes gradually liquid phase with increasing temperature. Such a polyimide film of semi-solid phase is obtained by changing the liquid solution into a semi-solid phase by removing the solvent in the polyimide solution. Any solvent can be used as long as it can dry the solvent, such as hot air drying or IR drying. The content of the solvent in the polyimide film on the semi-solid is preferably 5 to 10% by weight based on the total weight of the polyimide film on the semi-solid.

The substrate for applying the polyimide solution includes a substrate made of a plastic film, a substrate made of a metal plate, and a ceramic plate provided that the polyimide film on the semi-solid formed by evaporation of a part of the solvent can be easily detached. Both substrates and the like can be used.

Then, (S3) place the substrate coated with the polyimide film on the semi-solid on the upper and lower surfaces of the mat made of glass fibers, respectively, and heat it while passing through one or more pairs of rollers maintaining a gap pressure. And pressing to integrate the mat and the polyimide film on the semi-solid layer stacked on the upper and lower surfaces of the mat (step S3).

Examples of the mat made of glass fibers include woven fabrics and nonwoven fabrics made of glass fibers having a refractive index similar to that of polyimide resins. When the glass fiber mat is used as the reinforcing material of the base resin, the glass fibers do not aggregate in the transparent base resin at all, and the glass fiber reinforcing material embedded in the mat form has greater mechanical properties than the glass reinforcing material added in the form of short fibers. It shows an improvement effect. For example, it is preferable to use a glass fiber fabric in which wefts of warp yarns and warp yarns of glass fibers of 0.5 to 20 µm in diameter are interwoven up and down. Fiberglass wefts and warp yarns can be alternately crossed one by one, but several wefts and warp yarns can be alternately crossed up and down, and patterns can also be woven in patterns such as plain weave, twill weave, and handwoven weave. have. Two or more glass fiber fabrics may be laminated.

Since the refractive index of the glass fiber is usually 1.54 to 1.56, it is preferable to use a polyimide resin having such a refractive index, and more preferably to use the same refractive index of the glass fiber and the polyimide resin. The thickness of the mat of the glass fiber is preferably 30 to 70 ㎛, but is not limited thereto.

On the upper and lower surfaces of the mat made of glass fibers, the polyimide film on the semi-solid separated from the substrate is placed, respectively, and heated and pressed while passing through a pair of rollers maintaining a gap pressure. By means of the gap pressure between the rollers, polyimide films on semi-solids positioned above and below the mat penetrate the mat and are integrated with each other. As described above, the polyimide film on the semi-solid is changed in shape by the gap pressure between the rollers and penetrates between the pores of the mat, and its fluidity is increased by the heated atmosphere to remove cracks and the like. In addition, bubbles that may occur in this process are mostly removed as they pass between the rollers. Thus, the upper and lower semi-solid polyimide films and the mat are integrated with each other without empty space therein. Of course, by further passing the result through one or more pairs of rollers can be further improved bubble removal and integration.

In the method for producing a polyimide transparent composite film for display panel of the present invention, the heating temperature of the step (S3) is It is preferable that it is 80-120 degreeC, and it is preferable that the thickness of the polyimide film on the semi-solid coated on the said substrate is 50-70 micrometers.

Finally, the substrates located above and below the mat are each detached from the polyimide film on the semi-solid and then the solvent is removed from the polyimide film on the semi-solid stacked on the top and bottom of the mat. As the method of removing the solvent, any method can be used as long as it can dry the solvent, such as hot air drying or IR drying.

As shown in FIG. 1, the polyimide transparent composite film 20 for a display panel obtained according to the manufacturing method is a structure in which the polyimide film 11 completely surrounds a mat 13 made of glass fiber with a top and bottom surface. The mat 13 and the polyimide film 11 are completely integrated without empty space.

Hereinafter, examples will be described in detail to help understand the present invention. However, embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the following examples. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Example 1

A polyimide solution was prepared by dissolving a polyimide resin in a DMAc solvent. The polyimide resin was purchased from Kolon Co. with a refractive index of 1.547, and the concentration of the solution was prepared at 18 wt%.

The polyimide solution was uniformly coated on a PET film having a thickness of 50 μm and then dried using a hot air dryer. Drying was performed for 10 minutes at 100 degrees to produce a film in a semi-solid state. Two semi-solid polyimide films (solvent content of 7 wt% based on the total weight of the polyimide film on the semi-solid) were each detached from the PET film, followed by a plain weave glass mat having a thickness of 33 microns. (Nittobo, Japan, refractive index 1.546) was disposed so as to be centered. Thereafter, a glass mat film impregnated with polyimide resin was prepared while applying heat and pressure using a roll to roll lamination apparatus while being careful not to enter bubbles. At this time, the temperature of the pressing roll was 120 degrees, and the pressure was 5 kgf. After removing the PET film used as a carrier and further drying. The first drying was carried out for 30 minutes at 100 degrees, the second drying was carried out for 30 minutes at 230 degrees. CTE (thermal expansion coefficient) value of the prepared film was 17PPM, and the total light transmittance was 85%.

Example 2

Except for using a 43 micron glass mat was prepared in the same manner as in Example 1.

Claims (7)

(S1) dissolving a polyimide resin in a solvent to prepare a polyimide solution;
(S2) applying the polyimide solution onto the substrate and then evaporating a portion of the solvent in the polyimide solution to form a substrate coated with a polyimide film on a semi-solid;
(S3) placing the substrate coated with the polyimide film on the semi-solid on the upper and lower surfaces of the mat made of glass fibers, respectively, and heating and pressurizing while passing between the pair of rollers maintaining the gap pressure Integrating the mat and a polyimide film on a semi-solid stacked on top and bottom of the mat; And
(S4) A method for producing a polyimide transparent composite film for a display panel, comprising the step of removing the substrate and then removing the solvent from the semi-solid polyimide film laminated on the upper and lower surfaces of the mat. The method of claim 1,
The solvent is a manufacturing method of a polyimide transparent composite film for display panel, characterized in that N, N-dimethylacetamide (DMAc). The method according to claim 1 or 2,
The content of the solvent in the polyimide film on the semi-solid (semisolid) is 5 to 10% by weight based on the total weight of the polyimide film on the semi-solid (semisolid) of the polyimide transparent composite film for display panels Manufacturing method. The method according to claim 1 or 2,
The heating temperature of the step (S3) Method for producing a polyimide transparent composite film for a display panel, characterized in that 80 ~ 120 ℃. The method of claim 1,
A method of manufacturing a polyimide transparent composite film for display panel, characterized in that the thickness of the polyimide film on the semi-solid (semisolid) coated on the substrate is 50 to 70 ㎛, the thickness of the mat is 30 to 70 ㎛. The method of claim 1,
The refractive index of the polyimide resin and the glass fiber is 1.54 to 1.56 method for producing a polyimide transparent composite film for a display panel. The method of claim 1,
The mat is a manufacturing method of a polyimide transparent composite film for a display panel, characterized in that the glass fiber weaving interweaving the weft and warp made of glass fibers up and down.

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