KR100800971B1 - Melt-extrusion Optical Plastic Sheet of Improved Dimension Stability and Liquid Crystal Device Window Including the Same - Google Patents

Abstract

The present invention is a plastic sheet comprising a sheet substrate prepared by melt-extrusion of the optical polymer, and a hard coating layer added to both sides of the sheet substrate to enhance the surface hardness, wherein the sheet is bent in the inner surface direction In order to prevent the warpage phenomenon, an optical plastic sheet having an anisotropic structure with respect to the inner hard coat layer so that the outer hard coating layer resists the warpage phenomenon, and a liquid crystal having the optical plastic sheet attached thereto. Provide a device window.

The optical plastic sheet according to the present invention can significantly improve the dimensional stability of the sheet by suppressing the warpage phenomenon of the sheet base material produced by the melt extrusion method.

Description

METAL-EXtrusion Optical Plastic Sheet of Improved Dimension Stability and Liquid Crystal Device Window Including the Same}

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the warpage phenomenon which arises in the process of manufacturing an optical plastic sheet by the melt extrusion method;

2A and 2B are schematic diagrams of cross-sectional structures of an optical plastic sheet according to embodiments of the present invention;

3A and 3B are schematic views of cross-sectional structures of an optical plastic sheet according to still another embodiment of the present invention.

The present invention relates to an optical melt-extruded plastic sheet having an improved dimensional stability and a liquid crystal device window including the same, and more particularly, to a sheet substrate prepared by melt-extrusion of an optical polymer, and to enhance the surface hardness. A plastic sheet including a hard coating layer added to both sides of a sheet base material, wherein the outer surface hard coating layer (a) is used to prevent warping of the sheet in the inner surface direction (wapi development). An optical plastic sheet having an anisotropic structure with respect to the inner side hard coat layer (b) and a liquid crystal device window having the optical plastic sheet attached thereto so as to be resistant to the inner side.

As the usage of mobile phones, notebook computers, portable information communication terminals, and the like increases, the demand for optical plastic sheets for liquid crystal device windows used in these devices is also increasing. Conventionally, although a glass substrate is mainly used as a material of a liquid crystal device window, glass has a disadvantage in that its impact resistance is insufficient due to its characteristics, and glass is easily damaged by impact, and there is a limit in thinning and weight reduction. In order to solve such a problem, in recent years, the optical plastic sheet which is excellent in impact resistance and which can be reduced in weight is used as a material of a liquid crystal device window.

The optical plastic sheet may be prepared by a solution casting method, a blow molding method, a melt extrusion method, and the like. Most of the products currently commercialized are manufactured by a solution casting method.

The solution casting method is a batch production method in which a resin is dissolved in a solvent to form a solution, then applied to a caster and the solvent is evaporated to form a film or sheet. The sheet produced by the solution casting method has the advantages of excellent dimensional stability and impact strength, but the surface characteristics of the product is low, and the use of a large amount of solvents is essential, and the process hassle to evaporate these solvents. In addition, environmental problems such as air pollution in the workplace by the evaporated solvent is serious. In addition, there is a disadvantage in that the production cost is very high because the facility investment cost, the productivity is not high because it is a batch process.

On the other hand, the melt extrusion method, which is another method of manufacturing the optical plastic sheet, extrudes a sheet-shaped molding in a semi-melt (reaction) state by mounting a T-die, a coat hanger die, etc. in an extruder, and then cools the It is a method of producing continuously in the form of a sheet while cooling by. The melt extrusion method has no problem of process trouble to remove the solvent which is pointed out as a disadvantage of the solution casting method or environmental pollution by the solvent, and can be manufactured in a continuous process, which significantly lowers the production cost. have.

However, the sheet produced by the melt extrusion method has a serious problem that the warpage phenomenon occurs, especially in a high temperature / high humidity environment, the dimensional stability is relatively low.

Therefore, there is a high need for the development of an optical plastic sheet manufacturing method that exhibits excellent dimensional stability while compensating for the disadvantages of the solution casting method by manufacturing by melt extrusion.

In this regard, the present invention proposes an optical plastic sheet made of an anisotropic structure of a hard coating layer laminated in order to impart surface hardness to both surfaces of the optical plastic substrate produced by the melt extrusion method, as described below. have.

On the other hand, there are some known techniques for additionally forming a polymer resin layer on the optical plastic film produced by the melt extrusion method. For example, in Japanese Patent Application Laid-Open No. 1997-123275 and Japanese Patent No. 3040512, an organic material layer is coated on at least one surface of the heat-resistant optical film obtained by the melt extrusion method, and the surface of the crosslinked film is rolled. As a heat-resistant optical film polished by, a technique aimed at improving the smoothness by polishing the surface of an ultraviolet curable organic material layer has been proposed.

However, even if the optical plastic sheet having a predetermined thickness is manufactured on the basis of the above techniques, it was confirmed that the warpage phenomenon cannot be prevented. That is, the technique of manufacturing the sheet which improved the dimensional stability by prevention of the warpage phenomenon based on the melt extrusion method is not confirmed yet.

In addition, Korean Patent Application Publication No. 2004-38689 includes a methacrylic resin layer containing rubber particles to secure scratch resistance, and has a cured layer containing a curable paint on at least one surface of the film. A film having a thickness of 1,800 μm is disclosed. However, the cured layer may be formed only on one side of the film as to secure scratch resistance, and thus it is not possible to prevent the warpage phenomenon, and as described below, the degree of curing of the upper and lower hard coating layers may be reduced. There is a difference from the present invention for preventing the warpage phenomenon by configuring the anisotropic structure in a different way.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After various experiments and in-depth studies, the inventors of the present application have a bending direction during warpage development among hard coating layers added on both sides of sheet substrates prepared by melt-extrusion of an optical polymer to enhance surface hardness. By specifically configuring the hard coating layer on the opposite side to, it has been confirmed that when the hard coating layer having the anisotropic structure as a whole is formed, it is possible to fundamentally prevent occurrence of the warpage phenomenon, and thus the present invention has been completed.

Accordingly, the optical plastic sheet according to the present invention is a plastic sheet including a sheet substrate prepared by melt-extrusion of an optical polymer, and a hard coating layer added to both sides of the sheet substrate to enhance surface hardness. Anisotropic structure with respect to the inner side hard coating layer (b) so that the outer side hard coating layer (a) can resist the warpage phenomenon so as to prevent the sheet from warping in the inner side direction (" waji phenomenon "). Consists of

In the optical plastic sheet of the present invention, since the hard coating layer has an anisotropic structure, the warpage phenomenon can be suppressed and the dimensional stability of the sheet can be greatly improved. For example, the sheet base material manufactured by the melt-extrusion method is manufactured by adjusting the thickness, hardening degree, etc. of a hard coating layer, such as making the thickness of the hard coating layer of an inner side direction thicker than the hard coating layer of an outer side direction, or increasing hardening degree. Preventing the appearance of the warpage phenomenon near the glass transition temperature (Tg) temperature during the process improves the dimensional stability of the sheet.

In general, the sheet substrate is very weak to surface scratches, thereby improving the stretch resistance by additionally adding a hard coating layer on both sides of the sheet substrate to maintain the surface hardness of the sheet to a certain degree.

The hard coating layer may be formed by various methods, such as a flow coating method, a spin coating method, a dip coating method, a bar coating method, and the like. The process of drying the hard coating layer is very important because a crosslinking process should be included. The coating solution may be coated on a substrate and then thermally cured at a predetermined temperature, or may be photocured to irradiate ultraviolet rays.

The hard coating layer may be preferably formed by applying a coating liquid containing a UV curable material to the sheet substrate by a flow coating method and then irradiating UV. Here, the "flow coating" means the coating liquid is applied to the sheet substrate in the form of a liquid film. In addition, considering that the warpage phenomenon of the sheet base material occurs near the Tg temperature, it is preferable to perform UV curing rather than thermosetting.

The hard coat layer needs to have a predetermined surface hardness. In such aspect, the UV curable material as the material of the hard coating layer, for example, a composition comprising a urethane (urethane) material, an acrylic (acryl) material, a thermoplastic elastomer (elastomer) and the like, Preferably it is a composition comprising a urethane-based material.

If the thickness of the hard coating layer is too thin, the wear resistance of the coating layer is reduced to exhibit a synergistic effect of the surface hardness, on the contrary, if the thickness is too thick, there is a risk of peeling or cracking due to the stress of the coating layer, the thickness of the hard coating layer Preferably it can be formed in 2-20 micrometers. In this case, since the thickness of the hard coating layer is different depending on the coating method, when the thickness is thin, the coating may be performed several times.

As described above, the sheet substrate produced by the melt extrusion method causes warpage phenomenon near the Tg temperature. This warpage phenomenon is a phenomenon in which the sheet passing through the T-die and the cooling roll is simultaneously bent in the direction of the contact surface of the cooling roll and the MD direction of the sheet.

In this regard, FIG. 1 schematically illustrates a process in which a sheet substrate made while passing through a T-die by a melt extrusion method passes through a cooling roll. For convenience of description, in FIG. 1, the hard coating layers are added to both surfaces of the sheet substrate.

Referring to FIG. 1, the sheet substrate 110 made by passing through the T-die is solidified by the cooling roll 200. Although not shown in FIG. 1, the process is repeatedly performed in alternating manner on both sides of the sheet substrate 110 using a plurality of cooling rolls 200.

On both sides of the sheet substrate 110, hard coating layers 120 and 130 are added to increase the surface hardness in a subsequent process, thereby manufacturing the plastic sheet 100.

When defining the contact surface direction of the cooling roll 200 in the inner surface direction, such a plastic sheet 100, more specifically, the sheet substrate 110 is subjected to the warpage phenomenon bent in its inner surface direction. That is, the phenomenon (B) of bending in the contact surface direction of the cooling roll 200 and the phenomenon (B) of bending in the MD direction of the sheet base material 100 appear simultaneously.

This warpage phenomenon may be a very serious problem in manufacturing the plastic sheet 100 used for the optical substrate by melt extrusion.

Therefore, in order to prevent such warpage phenomenon, the optical plastic sheet of the present invention is made of an anisotropic structure as a whole. In one preferred example of such an anisotropic structure, the thickness of the outer hard coating layer (a) may be made thicker than the thickness of the inner hard coating layer (b).

Since the physical properties of the hard coating layer are more flex-resistant than the sheet base material, if the thickness of the outer hard coating layer, which is the opposite surface of the cooling roll contact surface, is thicker than the inner hard coating layer, it exhibits high resistance to deformation in proportion to such increase in thickness. The warpage phenomenon can be prevented. Adjusting the thickness of the hard coating layer may be possible, for example, by adjusting the amount of coating liquid or controlling the number of coating processes.

When the thickness of the outer surface hard coating layer (a) and the thickness of the inner surface hard coating layer (b) are expressed as a thickness ratio, it may be preferably from 1: 1 to 1:10. If the thickness ratio of the hard coating layer is too small, the resistance to deformation of the sheet may not be sufficient, and thus, the desired warpage prevention effect may not be exerted. On the contrary, if the thickness ratio is too large, the outer surface hard coating layer is unnecessarily thick and total sheets. It is not preferable because the thickness becomes thick.

In another preferred example, the degree of cure of the outer surface hard coating layer (a) may be configured higher than that of the inner side hard coating layer (b). In other words, the greater the degree of curing, the higher the surface hardness, thereby preventing the sheet substrate from being deformed toward the inner hard coating layer (b) of relatively low degree of curing, thereby preventing occurrence of the warpage phenomenon. Control of the degree of curing, for example, by UV curing by adjusting the UV irradiation time, the longer the UV irradiation time, the higher the degree of curing.

The ratio of the curing degree of the outer surface hard coating layer (a) and the curing degree of the inner surface hard coating layer (b) may be preferably 1: 1 to 1:10. When the degree of cure of the hard coat layer is too small, the sheet base material cannot be sufficiently prevented from being deformed. On the contrary, when the degree of cure is too large, the curing time for increasing the degree of cure of the outer surface hard coat layer (a) is too long. It is not preferable because there are problems such as loss of productivity and lowered productivity.

The sheet-based polymer is preferably a polymer having an optical property of making transparency as a basic physical property. For example, polymethylmethacrylate (PMMA), polycarbonate (PC), polyimide (PI), polyethersulfone (PES), polyarylate (polyarylate) PAR), thermoplastic resins such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), thermosetting resins such as epoxy and unsaturated polyester, blends such as acryl-butadiene-styrene (ABS), and the like. Although it can be used, it is not limited to these, Preferably, the homopolymer, copolymer, or blend selected from the group which consists of PMMA, PC, PES, and ABS which are excellent in transparency and homogeneity can be used.

In one preferred example, a high strength resin layer having a higher molecular weight than the polymer of the sheet substrate may be further included between the sheet substrate and the hard coating layer to enhance mechanical properties.

The high-strength resin layer is a method of adding and solidifying a coating resin in a molten state, a method of removing a solvent after adding it as a composition dissolved in a solvent, adding a monomer having a predetermined viscosity, an oligomer, a low molecular weight polymer, and the like. It can be formed by a method such as crosslinking or curing afterwards. However, it should be understood that various methods other than the above methods are possible, and all of them are included in the scope of the present invention.

The coated resin for coating may preferably increase the molecular weight by thermal curing or UV curing. Since thermal curing or UV curing methods are known in the art, detailed descriptions thereof are omitted herein.

The molecular weight of the sheet-based polymer is in a range close to the limit of melt extrusion, and is 50,000 to 200,000. The high-strength resin layer polymer is not particularly limited as long as the molecular weight after curing is in a range larger than that of the sheet-based polymer. Since the larger the attraction between the molecules, the molecular weight is preferably 150,000 or more.

The coating resin for the high strength resin layer is not particularly limited as long as the resin has excellent impact resistance, thin film formability, flexibility, and the like, and for example, urethane acrylate or polyester acrylate may be used. have.

In particular, the urethane-based resin has a UV curing functional group, and may act to mitigate external impact by increasing the resin elongation after curing, in one preferred embodiment, the coating resin is a urethane-based urethane acrylic monomer, oligomer or Low polymerisation polymers may be included.

In one preferred example, a high strength resin layer may be formed by applying a urethane acrylic oligomer having a degree of polymerization of 500 to 5,000 to both surfaces of a sheet substrate and then irradiating with UV to photocuring. Of course, other coating materials such as a photoinitiator may be further added to the coating resin.

In the optical plastic sheet according to the present invention, the thickness of the sheet substrate may vary depending on the use of the optical plastic sheet, and the like, and preferably, the thickness may be 500 to 1,500 μm. When the thickness of the sheet base material is the same as the above range, the high strength resin layer may be a thickness of 1 to 300 ㎛. When the thicknesses are too thin, it is difficult to expect improvement in mechanical properties such as barrier properties and impact resistance to materials such as liquid crystals. On the contrary, when the thicknesses are too thick, workability is degraded and sheet thickness is increased.

In addition, in order to impart adhesion to the sheet substrate, the hard coating layer may further include a silicon-based material.

The present invention also provides a liquid crystal device window composed of the optical plastic sheet as described above. The liquid crystal device window according to the present invention may be in various forms depending on the form of the device, and is not particularly limited.

The invention also provides a mobile device comprising such a liquid crystal device window.

Representative examples of the mobile device may include a mobile phone, a notebook computer, a portable information communication terminal, and the like, and more detailed structures and manufacturing methods thereof are known in the art, and a detailed description thereof will be provided herein. Omit.

Hereinafter, the present invention will be further described with reference to the drawings according to embodiments of the present invention, but the scope of the present invention is not limited thereto.

2A and 2B schematically illustrate cross-sectional structures of an optical plastic sheet according to embodiments of the present invention.

Referring to these drawings, the optical plastic sheets 300 and 301 have a structure in which hard coating layers 320, 330/321, and 331 are stacked on both sides of the sheet substrates 310 and 311. That is, the inner hard coat layers 320 and 321, the sheet substrates 310 and 311, and the outer hard coat layers 330 and 331 are sequentially stacked on the basis of the contact surfaces of the cooling rolls (not shown).

As sheet substrates 310 and 311, PMMA (polymethylmethacrylate) having excellent optical transparency and homogeneity is generally used, and is manufactured by melt extrusion. Therefore, in manufacturing the sheet substrates 310 and 311 by the melt extrusion method, there is a limit to melt extrusion of a polymer having a high molecular weight due to the torque applied to the extruder.

The hard coat layers 320, 330/321, 331 are added to maintain the surface hardness of the sheet to some extent because the sheet substrates 310, 311 are very weak to surface scratches. The hard coating layers 320, 330/321, and 331 are formed by applying a coating liquid containing a UV curable material to the sheet substrates 310 and 311 by a flow coating method, and then irradiating UV and polymerizing the UV cured material. can do. The UV curable material is generally a urethane-based material, and a small amount of silicon-based material may be included to improve adhesion to the sheet substrates 310 and 311.

In particular, in order to prevent the warpage phenomenon of the sheet substrates 310 and 311 manufactured by the melt extrusion method, as shown in Figure 2a, the thickness of the outer surface hard coating layer 330 is the thickness of the inner surface hard coating layer 320 It is formed thicker. Alternatively, as shown in FIG. 2B, the degree of curing of the outer side coating layer 331 is higher than that of the inner side coating layer 321. As described above, the outer surface coating layers 330 and 331 having a relatively thick or high degree of hardening cause a large resistance in the process of bending the sheet substrates 310 and 311 in the inner surface direction, thereby preventing the warpage phenomenon.

3A and 3B schematically illustrate cross-sectional structures of an optical plastic sheet according to still another embodiment of the present invention.

Referring to these drawings, the optical plastic sheets 302 and 303 may be selectively stacked on both sides or one surface of the sheet substrate 312 and 313, whereby a high strength resin layer 342, 352/343 and 353 may be laminated. The hard coating layers 322, 332/323, and 333 are laminated on both surfaces and one surface of the substrates 312 and 313, or on the outer surfaces of the high strength resin layers 342, 352/343, and 353. That is, the inner surface hard coating layers 322 and 323, optionally the high strength resin layers 342 and 343, the sheet base materials 312 and 313, optionally the high strength resin layers 352 and 353 based on the contact surfaces of the cooling rolls. Side hard coating layers 332 and 333 are stacked in this order.

The high strength resin layers 342, 352/343, and 353 have a molecular weight greater than the molecular weight of the sheet substrates 312 and 313 to compensate for mechanical properties such as impact resistance of the sheet substrates 312 and 313 manufactured by melt extrusion. To be required.

In order to make the high strength resin layers 342, 352/343 and 353 have a high molecular weight, a coating resin containing urethane acrylate monomer, oligomer and the like is applied to the sheet substrates 312 and 313 and then polymerized by UV curing. Can be.

As in FIGS. 2A and 2B, the outer hard coating layers 332 and 333 are configured to have a higher or higher degree of curing than the inner hard coating layers 322 and 323, so that the sheet substrates 312 and 313 are in the inner surface direction. The warpage phenomenon can be prevented.

Although the embodiments of the present invention have been described above with reference to the drawings, those skilled in the art will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

As described above, the optical plastic sheet according to the present invention is formed by the melt extrusion method by forming a hard coating layer added on both sides of the sheet substrate prepared by melt extrusion of the optical polymer to enhance the hardness of the surface in an anisotropic structure. The warpage phenomenon of the sheet base material manufactured can be suppressed, and the dimensional stability of a sheet can be improved significantly.

Claims (19)

A plastic sheet comprising a sheet substrate prepared by melt extrusion of an optical polymer, and a hard coating layer added to both sides of the sheet substrate to enhance surface hardness, wherein the sheet is warped in an inner surface direction ("wapi"). Paper sheet having an anisotropic structure with respect to the inner hard coating layer (b) so that the outer hard coating layer (a) can resist the warpage phenomenon. The optical plastic sheet of claim 1, wherein the hard coating layer is formed by applying a coating liquid containing a UV curable material by a flow coating method and then irradiating UV. 3. The optical plastic sheet according to claim 2, wherein the UV curable material comprises a urethane-based material. The optical plastic sheet of claim 1, wherein the hard coating layer has a thickness of 2 to 20 µm. The optical plastic sheet according to claim 1, wherein the thickness of the outer hard coating layer (a) is thicker than the thickness of the inner hard coating layer (b) to form the anisotropic structure. The optical plastic sheet according to claim 5, wherein the thickness ratio of the outer hard coating layer (a) and the inner hard coating layer (b) is in the range of 1: 1 to 1:10. The optical plastic sheet according to claim 1, wherein the degree of cure of the outer side hard coat layer (a) is higher than that of the inner side hard coat layer (b) to form the anisotropic structure. 8. The optical plastic sheet according to claim 7, wherein the ratio of the degree of cure of the outer side hard coat layer (a) and the degree of cure of the inner side hard coat layer (b) is 1: 1 to 1:10. The optical plastic sheet according to claim 1, wherein the sheet-based polymer is a polymer having an optical property of making transparency as a basic physical property. 10. The optical plastic sheet according to claim 9, wherein the polymer is a homopolymer, copolymer or blend selected from the group consisting of PMMA, PC, PES and ABS. The optical plastic sheet according to claim 1, further comprising a high strength resin layer having a higher molecular weight than the polymer of the sheet base material between the sheet base material and the hard coating layer to enhance mechanical properties. 12. The optical plastic sheet according to claim 11, wherein the high-strength resin layer increases molecular weight by thermal curing or UV curing after applying the coating resin to both surfaces of the sheet substrate. The method of claim 11, wherein the molecular weight of the sheet-based polymer is in the range close to the limit of melt extrusion is 50,000 to 200,000, the high-strength resin layer polymer is 150,000 in the range where the molecular weight after curing is greater than the molecular weight of the polymer for the sheet base material. The optical plastic sheet characterized by the above. 12. The optical plastic sheet according to claim 11, wherein the coating resin for high strength resin layer comprises a urethane acrylic monomer, oligomer or low polymer. 15. The optical plastic sheet according to claim 14, wherein a urethane acrylic oligomer having a degree of polymerization of 500 to 5,000 is applied to both surfaces of the resin substrate as the coating resin, and then a high strength resin layer is formed by irradiating and curing UV. 12. The optical plastic sheet according to claim 11, wherein the sheet substrate has a thickness of 500 to 1,500 µm, and the high strength resin layer has a thickness of 1 to 300 µm. 17. The optical plastic sheet of claim 16, wherein the hard coating layer further comprises a silicon-based material to impart adhesion to the sheet substrate. A liquid crystal device window made of the plastic sheet according to claim 1. A mobile device, comprising a liquid crystal device window according to claim 18.

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