KR102467377B1 - Coextruded film and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a co-extruded film having excellent appearance quality by reducing the number of foreign matters and defects by applying a process for reducing foreign matters that may occur in an extrusion process, and a method for manufacturing the same.

Description

Coextruded film and its manufacturing method {COEXTRUDED FILM AND MANUFACTURING METHOD OF THE SAME}

The present invention relates to a coextruded film having excellent appearance quality by reducing the number of foreign matter and defects and a method for manufacturing the same.

Displays of various types and sizes exist, from small displays such as mobile phones to LCD or PDP TVs or billboards (PID, DID). In particular, since the LCD or PDP panel of a display is a key component, it must be protected from external impact or harsh conditions. Accordingly, most displays have a front plate. In addition, as the display itself becomes slimmer and larger, the importance of the front plate becomes even greater.

Conventionally, glass was used as such an optical transparent film. However, although glass has good transparency, it is easily damaged by impact due to its lack of impact resistance due to the nature of glass, and there is a limit to thinning, as well as a large weight per unit volume, so there is a limit to lightening. Therefore, in recent years, polymers that have good impact resistance and can be reduced in weight, such as polycarbonate (PC), polyimide (PI), polyethersulfone (PES), and polyarylate (which have excellent optical properties) Thermoplastic polymers such as polyarylate (PAR), poly(ethylene naphthalate) (PEN), polyethylene terephthalate (poly(ethylene terephthalate), PET), cycloolefin copolymer, acrylic resin, epoxy resin, A transparent film manufactured using a polymer obtained by curing a curable resin such as unsaturated polyester is gradually replacing glass.

However, it is also necessary to reinforce the mechanical properties of the transparent film for optical use formed of the above-mentioned polymers. As a method for reinforcing mechanical properties without deteriorating optical properties of a transparent film, a method of improving physical properties by laminating different types of transparent films has recently emerged. This is a method of supplementing insufficient physical properties of an optically transparent film formed of a single type of polymer by laminating films formed of different types of polymers. For example, polymethyl methacrylate has excellent chemical resistance and surface hardness, but is brittle and has poor thermal properties. In addition, polycarbonate has excellent thermal properties, but its chemical resistance and surface hardness are inferior to those of polymethyl methacrylate. On the other hand, polyethersulfone has excellent heat resistance and excellent high-temperature stability.

As a method of manufacturing a multilayer transparent film for optical use by laminating different types of transparent films, a co-extrusion method, a thermal laminating method, a film bonding method using an adhesive, and the like are used.

In the co-extrusion method, the thermal characteristics of the film to be laminated must be considered. That is, since the melting temperature of the polymer constituting each film is different, it is difficult to control the process temperature during processing, and optimal process temperature control is required to solve various problems such as deformation of the coextruded film or interfacial adhesion. In addition, if the difference in melting temperature of the polymer constituting each film is too large, there is a limit to using the co-extrusion method.

In order to overcome the limitations of manufacturing a film using such a co-extrusion method, the present invention aims to develop a co-extrusion film having excellent appearance quality by reducing the number of foreign substances and defects.

In order to solve the problems of the prior art as described above, the present invention provides a coextruded film having excellent appearance quality by applying a process for reducing foreign matter that may occur in the extrusion process, thereby reducing the number of foreign matter and defects, and a method for manufacturing the same. aims to do

A method for manufacturing a coextruded film according to an embodiment of the present invention includes melt-extruding a polycarbonate resin and an acrylic resin with an extruder, respectively; co-extruding the melt-extruded resin from a die; and manufacturing a coextruded film by cooling with first to third cooling rolls arranged in a horizontal direction, wherein the ratio of the speed of the first cooling roll to the speed of the second cooling roll is 1 to 1.1:1. can

At this time, a bank that is a molten resin projection may be formed on a contact surface between the molten resin discharged from the die and the second cooling roll.

In addition, the first cooling roll may be a shaft roll made of metal and an elastic roll in which a metal thin film is coated on an outer circumferential surface of the shaft roll.

In addition, the method for manufacturing a coextruded film according to the present invention may further include, after the step of preparing the coextruded film, forming a hard coating layer by applying and curing a hard coating solution on the acrylic resin layer.

In addition, the present invention provides a coextruded film manufactured by the above-described manufacturing method, having a defect number of 20 or less per 1 m ² and a birefringence of 30 nm or less.

In the method for manufacturing a coextruded film according to the present invention, as a process for reducing foreign matter that may occur during the extrusion process is applied, a coextruded film having excellent appearance quality can be provided by reducing the number of foreign matter and defects.

In addition, the coextruded film according to the present invention has not only appearance quality but also high transparency and excellent surface properties, so that it can be suitably used for display cover windows and the like.

Figure 1 is a schematic diagram showing the flow of molten resin on an extrusion process according to the prior art.
Figure 2 is a schematic diagram showing the flow of molten resin in the extrusion process according to an embodiment of the present invention.

Since the present invention can have various changes and various forms, specific embodiments will be described in detail in the text. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. In addition, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where another part is present in the middle. Conversely, when a part such as a layer, film, region, plate, etc. is said to be "under" another part, this includes not only the case where it is "directly under" the other part, but also the case where there is another part in between. In addition, in the present application, being disposed "on" may include the case of being disposed not only on the top but also on the bottom.

Hereinafter, embodiments of the present invention will be described in more detail.

The present invention relates to a co-extruded film having excellent appearance quality by reducing the number of foreign matters and defects by applying a process for reducing foreign matters that may occur in an extrusion process, and a method for manufacturing the same.

A method of manufacturing a coextruded film according to an embodiment includes melt-extruding a polycarbonate resin and an acrylic resin with an extruder, respectively; co-extruding the melt-extruded resin from a die; and manufacturing a coextruded film by cooling with first to third cooling rolls arranged in a horizontal direction.

First, in the melt-extruding step, flowability is imparted to the polycarbonate resin and the acrylic resin through heat and pressure using separate extruders. Here, the polycarbonate resin may use a main extruder, and the acrylic resin may use a sub extruder. The temperature of the extruder is not particularly limited as long as it can impart flowability to the resin, but the temperature of the main extruder is preferably 230 to 260 ° C and the temperature of the sub extruder is 220 to 240 ° C.

Here, the polycarbonate resin is a material having transparency and excellent heat resistance, strength and flexural modulus. In addition, the polycarbonate resin is composed of carbonate ester (-O-(C=O)-O-) between monomer units, and can be easily processed and thermoformed. There are two methods for producing such a polycarbonate resin: a solvent method using phosgene and a melting method. First, the solvent method is a method of dissolving BPA (bisphenol A) in an aqueous phase layer and phosgene in an organic solvent layer, respectively, and then reacting at the interface in the presence of an acid binder and a solvent to synthesize them. As the acid binder, there are a method using pyridine and a method using an alkaline aqueous solution. In addition, the melting method is a reaction in which polycarbonate is polymerized by separating phenol as a by-product in a high vacuum in a transesterification reaction by a bulk polymer of bisphenol A and diphenyl carbonate. The polycarbonate resin used in the present invention may be a highly heat-resistant polycarbonate having a melt index (MI) in the range of 5 to 15 g/10 min.

On the other hand, since the polycarbonate resin has a disadvantage of low hardness, in order to improve this, the present invention is characterized in that an acrylic resin layer having excellent surface hardness is formed on the polycarbonate resin layer to provide a multi-layered coextruded film.

At this time, the acrylic resin constituting the acrylic resin layer may be a methacrylic resin. The methacrylic resin may be a homopolymer of methyl methacrylate with 100% by weight of methyl methacrylate units, or a copolymer of methyl methacrylate and one or more monomers copolymerizable therewith.

In addition, each of the polycarbonate resin layer and the acrylic resin layer may contain at least one additive selected from, for example, a light stabilizer, an ultraviolet absorber, an antioxidant, a release agent, a flame retardant, and an antistatic agent.

Then, the molten resin passes through a screen changer. The screen changer filters internal and external foreign substances and non-melted substances contained in the molten resin and serves to protect the machine at the later stage.

The molten resin that has passed through the screen changer passes through a T-die that makes a film shape. At this time, the molten polycarbonate resin and the acrylic resin are extruded from the T-die and laminated and integrated. The temperature of the T-die is preferably 280 to 300°C. If the temperature of the T-die is too low, stretching orientation occurs due to the drawing of the cooling rolls, resulting in increased birefringence. If the temperature is too high, extremely fine cooling wrinkles are generated on the cooling rolls, resulting in non-uniformity in optical birefringence.

The molten resin coming out of the T-die is cooled by passing through a cooling roll to form a film with a desired thickness. The cooling rolls may be first to third cooling rolls arranged in a horizontal direction.

As shown in FIG. 1, the molten resin 11 passing through the conventional T-die 10 passes through the rotating first cooling roll 21 and the second cooling roll 22 to reach the glass transition temperature of the resin. It is pressed at a temperature below (Tg), and in this case, surface molding is performed. At this time, looking at part A shown in FIG. 1, the surface where the molten resin 11, which is one of both sides in the thickness direction of the molten resin 11, and the second cooling roll 22 are in contact is in surface contact, , the other side, the surface where the molten resin 11 and the first cooling roll 21 are in contact, is in line contact.

On the other hand, due to various factors in the raw material and the extrusion process, foreign matter may exist at any position in the thickness direction of the molten resin 11. In addition, if a foreign material of the same size is present on the surface of the molten resin 11, when surface molding is performed, bubbles are generated due to the difference in viscosity of the molten resin 11 caused by the foreign material, and the size of the actual foreign material due to the difference in roughness A problem arises in which the foreign body appears larger.

Therefore, as shown in FIG. 2, in the present invention, in order to stabilize the surface molding in the area where the molten resin 110 is in surface contact with the second cooling roll 220, to form a bank 120, which is a molten resin projection characterized by When the bank 120 is formed, the foreign matter generated at the corresponding position is moved to the inside rather than the surface by the direction of the rotating second cooling roll 220, which causes the foreign matter to appear small in size or difficult to check. Accordingly, the number of foreign materials and defects can be reduced to 20 or less per 1 m ² of the film.

At this time, by adjusting the ratio of the speed of the first cooling roll 210 and the speed of the second cooling roll 220 to 1 to 1.1:1, the molten resin protrusion on the part of the second cooling roll 220 that makes surface contact A bank 120 is formed.

In addition, it is preferable that the first cooling roll 210 use a shaft roll made of metal and an elastic roll in which a metal thin film is coated on an outer circumferential surface of the shaft roll. When an elastic roll is used as the first cooling roll 210, when looking at part A' shown in FIG. It is effective in reducing foreign matter.

On the other hand, the temperature of the first to third cooling rolls is preferably a temperature equal to or less than the glass transition temperature (Tg) of the resin. Specifically, the temperature of the first cooling roll 210 may be 100 to 130 ° C, the temperature of the second cooling roll 220 may be 100 to 130 ° C, and the temperature of the third cooling roll (not shown) may be 130 to 150 ° C. . At this time, if the temperature of the cooling roll is too high, the film adheres to the roll shape and causes appearance defects, and if it is too low, fine cooling wrinkles occur.

In addition, the speed range of the first to third cooling rolls may be adjusted in consideration of the desired film thickness and the above-described speed ratio of the first cooling roll 210 and the second cooling roll 220, and T- It is important to loosely feed the film coming out of the die onto the rolls so that the film does not stretch on the first chill roll 201 and the second chill roll 220.

The coextruded film prepared as described above includes a polycarbonate resin layer and an acrylic resin layer. The thickness of the coextruded film may be 1,000 μm or less, preferably 500 μm or less, and more preferably 300 μm or less. In addition, the thickness ratio of the polycarbonate resin layer and the acrylic resin layer is preferably 9:1 to 7:3.

In addition, the coextruded film of the present invention is characterized in that the number of defects is 20 or less per 1 m ² , and the appearance quality is excellent, and the birefringence is 30 nm or less. Due to this, there is an advantage in that rainbow mura due to birefringence change does not occur even when the display to which the coextruded film of the present invention is applied is worn and used while wearing polarized sunglasses. In addition, the coextruded film according to the present invention has not only appearance quality but also high transparency and excellent surface properties, so that it can be suitably used for display cover windows and the like.

On the other hand, by disposing the hard coating layer on the acrylic resin layer of the manufactured co-extrusion film, it is possible to improve the hardness, which is advantageous for application to a display cover window.

The hard coating layer may be formed by applying a hard coating solution on the acrylic resin layer of the coextruded film and performing heat or UV curing. At this time, the hard coating solution is preferably an acrylic hard coating solution, and more specifically, a (meth)acrylate monomer, a (meth)acrylate oligomer having an epoxy group and a weight average molecular weight of 500 to 10,000, and a curable coating solution containing silica particles. have.

The (meth)acrylate monomer functions to control the viscosity and curing density of the curable coating solution and to improve the adhesion of the coating layer. The (meth)acrylate monomers may be monofunctional or polyfunctional monomers. It may also exist in ethoxylated or propoxylated form. (Meth) acrylate monomers include 2 (2-ethoxyethoxy) ethyl acrylate, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, caprolactone acrylate, dicyclopentadienyl methacrylate rate, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, 1,3-butylene glycol diacrylate, 1,4 tandiol dimethacrylate, diethylene glycol diacrylate, ethoxylated bisphenol A Diacrylate, ethoxylated bisphenol A dimethacrylate, ethylene glycol dimethacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, propoxylated glyceryl triacrylate, propoxy Trimethylolpropane triacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tris(2-hydroxyethyl) isocyanurate triacrylate, etc. alone or in combination of two or more thereof and can be used.

The (meth)acrylate oligomer having an epoxy group and a weight average molecular weight of 500 to 10,000 is an oligomer having a (meth)acrylate group and an epoxy group, and contributes to good adhesion of the hard coating layer to the acrylic resin layer.

The silica particles may have an average particle diameter of 100 nm or less, or 40 to 90 nm, or 50 to 80 nm.

In addition, it is preferable that the curable coating solution further contains a silicon alkoxide having a (meth)acrylate group. In this specification, (meth)acrylate means acrylate or methacrylate. Examples of the (meth)acrylate group of silicon alkoxide include (3-acryloxypropyl)dimethylmethoxysilane, (3-acryloxypropyl)methyldimethoxysilane, (3-acryloxypropyl)trimethoxysilane, Cryloxymethyl) dimethylethoxysilane, methacryloxymethyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, methacryloxypropylmethyldimethoxysilane, (3-methacrylic Oxypropyl)triethoxysilane, (3-methacryloxypropyl)trimethoxysilane, etc. may be used alone or in combination of two or more thereof.

The thickness of the hard coating layer may be 0.5 to 10 μm, or 1 to 5 μm. When the thickness of the hard coating layer satisfies this range, physical properties and flexibility can be secured at the same time.

As described above, the coextruded film on which the hard coating layer is formed has excellent surface properties due to high transparency and reduced number of foreign substances and defects, so that it can be easily applied to a display cover window.

In order to apply the coextruded film on which the hard coating layer of the present invention is formed to the display cover window, in-mold labeling molding, thermal bending or thermoforming (thermoforming) is performed depending on the display size, molding size, and molding form. ) may be required. In order to prevent cracking of the hard coating layer during this forming process, the hard coating layer may be 2-step cured according to the forming depth (deep draw ratio). In the 2-step curing, pre-curing is performed during the first hard coating process, and post-curing may be performed after molding.

Hereinafter, the present invention will be described in detail through examples. However, the following examples are only to illustrate the present invention, and the present invention is not limited by the following examples.

[Examples 1 to 3]

PC/PMMA coextruded films were prepared using the coextrusion process conditions described in Tables 1 and 2 below, respectively. At this time, the polycarbonate resin was introduced into the main extruder (90 Pi), and the polymethyl methacrylate resin was introduced into the sub extruder (45 Pi). In addition, the polycarbonate resin used was Teijin PC with an MI of 9g/10min, and the polymethyl methacrylate resin was Lotte MCC VH grade with an MI of 2g/10min. When preparing the coextruded films of Examples 1 to 3, respectively, the extruder temperature and the roll temperature were equally controlled under the conditions shown in Table 1 below, and the roll speeds were respectively controlled under the conditions shown in Table 2 below. In addition, as the first cooling roll, an axis roll made of metal and an elastic roll in which a metal thin film is coated on an outer circumferential surface of the axis roll are applied.

Classification of extruder main serve Extruder temperature (℃) extruder 245 230 screen changer 270 225 adapter 270 225 melt pump 270 225 die 290 245 Roll temperature (℃) 1st roll 115 2nd roll 115 3rd roll 140

Example 1 Example 2 Example 3 Comparative Example 1 roll speed
(m/min) 1st roll 5.842 12.62 15.25 5.75 2nd roll 5.83 12.5 15.1 5.83 3rd roll 5.835 12.5 15.1 5.835

[Comparative Example 1]

A coextruded film was prepared through the same process as in Example 1, except that the first to third roll speeds were adjusted to the conditions described in Table 2 above.

[Experimental Example 1]

The physical properties of the coextruded films prepared in Examples and Comparative Examples were measured by the following method, and the results are shown in Table 3 below.

1) Number of defects: The number of defects was evaluated using the data of a foreign object detector installed in the extrusion line capable of detecting more than 100 μm, and the number of foreign objects per 1 m ² was measured.

2) Total light transmittance: When light passes through the film, the ratio of the transmitted (straight, scattered) light through the film is shown using an integrating sphere.

3) Haze: The haze of the film was evaluated using a total light transmittance meter according to the ASTM D1003 standard, and the measuring equipment was NDH5000 and was evaluated with equipment equivalent thereto.

4) Birefringence: Measured by multiplying the thickness of the refractive index difference in directions orthogonal to each other of the film. R = (n - n⊥) x d (thickness in nm) At this time, the equipment was measured with equipment conforming to Axoscan MMSP (FSVM).

5) Pencil Hardness: The presence or absence of scratches on the surface of the film was evaluated by a method for measuring pencil hardness according to the ASTM D3363-05 standard.

Example 1 Example 2 Example 3 Comparative Example 1 Thickness (㎛) 640 300 250 640 Number of defects (number per 1 m ² ) 8 12 15 39 Total light transmittance (%) 90.8 91.1 91.2 90.4 Haze (%) 0.12 0.10 0.08 0.13 Birefringence (nm) 28 20 18 34 pencil hardness H F F H

As can be seen from Table 3, it can be seen that the coextruded films according to Examples 1 to 3 have excellent appearance quality with less than 20 defects per 1 m ² . In addition, it can be seen that the coextruded films according to Examples 1 to 3 have high transmission optical properties with a total light transmittance of 90% or more, haze of 0.2% or less, and pencil hardness of F or more. In addition, the coextruded film of the present invention has a birefringence of 30 nm or less, and there is an advantage in that rainbow mura due to birefringence change does not occur even when a display using the coextruded film is worn with polarized sunglasses.

On the other hand, in the case of Comparative Example 1, as the ratio of the speed of the first cooling roll to the speed of the second cooling roll was out of the range of 1 to 1.1:1, it was confirmed that the number of defects of the coextruded film was significantly higher than that of Example. .

Therefore, the coextruded film according to the present invention has not only appearance quality but also high transparency and excellent surface properties, so that it can be suitably used for display cover windows and the like.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art or those having ordinary knowledge in the art do not deviate from the spirit and technical scope of the present invention described in the claims to be described later. It will be understood that the present invention can be variously modified and changed within the scope not specified.

Therefore, the technical scope of the present invention is not limited to the contents described in the detailed description of the specification, but should be defined by the claims.

10, 100: T-die
11, 110: molten resin
21, 210: first cooling roll
22, 220: second cooling roll
120: bank

Claims (5)

Melt-extruding a polycarbonate resin and an acrylic resin with an extruder, respectively;
co-extruding the melt-extruded resin from a die; and
Cooling with first to third cooling rolls disposed in the horizontal direction to produce a coextruded film,
Banks, which are molten resin projections, are formed on the contact surface between the molten resin discharged from the die and the second cooling roll,
The ratio of the speed of the first cooling roll to the speed of the second cooling roll is 1 to 1.1:1,
The method of manufacturing a co-extruded film, characterized in that the first cooling roll is a shaft roll made of metal and an elastic roll in which a metal thin film is coated on an outer circumferential surface of the shaft roll.
delete delete According to claim 1,
After the step of preparing the coextruded film, the method of manufacturing a coextruded film further comprising the step of applying a hard coating solution on the acrylic resin layer and curing to form a hard coating layer. A coextruded film produced by the manufacturing method according to claim 1, wherein the number of defects is 20 or less per 1 m ² and the birefringence is 30 nm or less.

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