KR100829397B1 - Melt-extrusion Optical Plastic Sheet Having Resin Layer of High Molecular Weight and Liquid Crystal Device Window Including the Same - Google Patents

Abstract

The present invention comprises a sheet substrate prepared by melt-extruding a polymer having a predetermined molecular weight, and a high-strength resin layer is coated on both sides of the sheet substrate while having a higher molecular weight than the polymer to enhance mechanical properties A liquid crystal device window comprising a plastic sheet and the optical plastic sheet is provided.

Such an optical plastic sheet has a mechanical property comparable to that of a plastic sheet manufactured by a solution casting method by compensating for the weakness of mechanical properties such as impact strength of the plastic sheet manufactured by a melt extrusion method, Economical and excellent surface properties.

Description

Melt-extrusion Optical Plastic Sheet Having Resin Layer of High Molecular Weight and Liquid Crystal Device Window Including the Same}

1 is a schematic diagram showing a process in which a sheet substrate made while passing through a T-die by a melt extrusion method passes through a cooling roll according to one embodiment of the present invention;

2 is a schematic diagram showing a cross-sectional structure of an optical plastic sheet according to an embodiment of the present invention;

3 is a schematic cross-sectional view of an optical plastic sheet according to another embodiment of the present invention.

The present invention relates to an optical melt-extruded plastic sheet containing a high molecular weight resin layer and a liquid crystal device window comprising the same, and more particularly, a sheet base material manufactured by melt-extruding a polymer having a predetermined molecular weight, and Optical plastic sheet composed of a high-strength resin layer coated on both sides of the sheet substrate while having a higher molecular weight than the polymer for strengthening the mechanical properties, and a liquid crystal device window comprising the optical plastic sheet will be.

The optical plastic sheet according to the present invention has a mechanical property comparable to that of the plastic sheet manufactured by the solution casting method by supplementing the vulnerability of mechanical properties such as impact resistance of the plastic sheet manufactured by the melt extrusion method, Economical and surface characteristics are very excellent.

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 also serious. In addition, since the method is a batch process, the investment cost of the facility is high, and the productivity is not high.

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 melt extrusion method has a problem in that mechanical properties such as dimensional safety and impact strength are relatively low. Since mechanical properties have a close relationship with the molecular weight of the plastic resin, a method of using a polymer having a high molecular weight may be considered as a method for improving such mechanical properties. However, due to the torque applied to the extruder, there is a limitation that a polymer having a high molecular weight as in the solution casting method cannot be used.

Therefore, there is a high demand for the development of an optical plastic sheet having excellent mechanical properties while being manufactured by the melt extrusion method.

In this regard, the present invention proposes an optical plastic sheet in which a polymer resin layer having a high molecular weight is formed on both surfaces of an optical plastic substrate produced by a melt extrusion method as described below.

On the other hand, there are some known techniques for additionally forming a polymer resin layer in the optical plastic sheet produced by the melt extrusion method. For example, Japanese Patent No. 3463968 forms an organic resin layer containing a silane coupling agent on at least one surface of a transparent plastic substrate, and on which tetraalkoxy silane comprises at least one of metal alkoxides or phosphate esters. As a transparent conductive film coated with a hydrolysis solution to form an inorganic cured layer, and then further laminated a thin transparent conductive film thereon, and coated with a UV curable acrylate resin cured layer to improve adhesion between the inorganic cured layer and the thin film, The technique regarding the transparent conductive film for liquid crystal display elements which has the gas barrier property which is substantially not dependent on temperature or humidity is proposed.

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 a heat-resistant optical film obtained by melt extrusion, and the surface of the crosslinked film is polished by a rolling roll. As a heat resistant optical film, the technique aimed at improving the smoothness by grinding the surface of an ultraviolet curable organic material layer is proposed.

However, even when manufacturing an optical plastic sheet having a predetermined thickness based on the above techniques, it was confirmed that it is difficult to exert predetermined mechanical properties such as excellent impact resistance. That is, a technique for producing a sheet based on the melt extrusion method and showing excellent mechanical properties has not been confirmed yet.

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 applied a high-strength resin layer having a higher molecular weight than the polymer on both sides of the sheet substrate to a sheet substrate prepared by melt extrusion of a polymer having a predetermined molecular weight. In the case of the plastic sheet for use, it was confirmed that it had very excellent mechanical properties comparable to that of the optical plastic sheet produced by the solution casting method, and the present invention was completed.

The optical plastic sheet according to the present invention is a sheet substrate prepared by melt-extruding a polymer having a predetermined molecular weight, and a high strength resin layer coated on both sides of the sheet substrate while having a higher molecular weight than the polymer for enhancing mechanical properties. It is configured to include.

Since the optical plastic sheet of the present invention includes a high-strength resin layer, it is possible to fundamentally solve the problem of weak mechanical properties that may occur by being manufactured by the melt extrusion method as described above. Specifically, by coating a polymer having a higher molecular weight than the polymer of the sheet substrate on both sides of the sheet substrate, to improve the impact strength by supplementing the sheet substrate produced by the melt extrusion method that can not use a polymer having a high molecular weight Physical properties can be improved.

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.

In one preferred example, the high-strength resin layer may increase the molecular weight by applying a coating resin on both sides of the sheet substrate and then curing it. In the case where the high strength resin layer is formed on only one surface of the sheet base material, it is preferable to form it on both sides of the sheet base material because desired mechanical properties cannot be obtained or warpage may occur on the sheet base material.

As a method for curing the applied coating resin, preferably thermosetting or UV curing may be used. Since thermal curing or UV curing methods are known in the art, detailed descriptions thereof are omitted herein.

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) and 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, homopolymers, copolymers or blends selected from the group consisting of PMMA, PC, PES and ABS excellent in transparency and homogeneity can be used.

The weight average molecular weight of the sheet base 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 weight average molecular weight after curing is larger than the molecular weight of the sheet base polymer. However, the larger the molecular weight, the greater the attraction between the molecules, and therefore preferably has a weight average molecular weight of 150,000 or more.

When expressing the weight average molecular weight of the said sheet base polymer and the weight average molecular weight after hardening of the said high strength resin layer polymer as a ratio of molecular weight within the range of this molecular weight, Preferably it is the ratio of 120,000: 200,000-170,000: 250,000. Can be.

When the molecular weight ratio is too small, it means that the molecular weight after curing of the polymer for high strength resin layer is close to the molecular weight of the polymer for sheet base material, so that it is difficult to exert desired mechanical properties and impact strength, and on the contrary, when the molecular weight ratio is too large, Bonding may not be easy at the contact surface of the sheet base material and the high strength resin layer, surface properties may be degraded, and the curing time may be lengthened to produce a high molecular weight high strength resin layer, which may lower production yield. .

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. Can be.

In particular, the urethane-based resin has a UV curing functional group, and by increasing the resin elongation after curing, it can play a role in mitigating external impact, in one preferred embodiment, the coating resin is a urethane-based urethane acrylic monomer, oligomer And / or polymers of low polymerization degree.

Especially preferably, a high strength resin layer can be formed by apply | coating urethane acrylic oligomer of 500-5,000 degree of polymerization to both surfaces of a sheet | seat base material, and irradiating UV and 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 determined in 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 one preferred example, in order to increase the surface hardness of the optical plastic sheet, a hard coating layer may be further added to the outer surface of the high strength resin layer. Since the hard coating layer must have excellent resistance from the external environment, for example, scratch resistance, it is necessary to have a hardness and weather resistance of a predetermined or more. In such a aspect, the material of the hard coating layer may include, for example, a urethane-based material, an acrylic material, a composition including a thermoplastic elastomer, and the like. It is a composition containing urethane resin.

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. In addition, since the crosslinking reaction proceeds during the drying of the hard coating layer, 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.

Preferably, the hard coating layer may be formed by applying a coating liquid containing a UV curable material on a high strength resin layer of a sheet base material 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 consideration of the possibility of deformation of the sheet substrate by heat, it is preferable to perform UV curing rather than thermosetting.

The thickness of the hard coating layer is preferably in the range of 2 to 20 μm in consideration of wear resistance, surface hardness, peeling or cracking of the coating layer. Here, 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.

In addition, in order to improve adhesion to the surface of the high strength resin layer, the hard coating layer may further include a silicon-based material.

The present invention also provides a liquid crystal device window made of such an optical plastic sheet. 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.

FIG. 1 schematically illustrates a process of manufacturing an optical plastic sheet by a melt extrusion method according to an embodiment of the present invention, and FIG. 2 illustrates an optical plastic sheet according to an embodiment of the present invention. The cross-sectional structure is schematically shown.

Referring to these drawings, the sheet substrate 110 in the semi-melt (or semi-solidified) state made through the T-die (not shown) of the melt extruder 200 is solidified by the cooling roll 210. 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 210.

On both sides of the sheet substrate 110, through a subsequent process, high strength resin layers 120 and 130 for improving impact resistance are laminated and manufactured as the plastic sheet 100. Therefore, based on the contact surface direction of the cooling roll 210, the high strength resin layer 120, the sheet base material 110, and the high strength resin layer 130 are laminated one by one. That is, the optical plastic sheet 100 has a structure in which the high strength resin layers 120 and 130 are stacked on both surfaces of the sheet base 110.

As the sheet substrate 110, PMMA (polymethylmethacrylate) having excellent optical transparency and homogeneity is generally used. However, as described above, in order to manufacture such a polymer in a sheet form by melt extrusion, an extruder torque due to a melt must be considered. The molecular weight of the polymer cannot be increased above a predetermined range.

On the other hand, according to the present invention, a coating resin containing a polymer of low polymerization degree (eg, urethane acrylic monomer, oligomer, etc.) is applied to one or both sides of the sheet substrate 110 and then UV cured, The high strength resin layers 120 and 130 having a higher molecular weight than the polymer of the sheet base 110 may be formed. The high strength resin layers 120 and 130 may complement the mechanical properties of the sheet substrate 110 having a limited molecular weight due to the manufacture by the melt extrusion method, and preferably the sheet substrate manufactured by the melt extrusion method ( The distortion phenomena, so-called warpage phenomenon, which are generally shown in 110, can be suppressed as much as possible.

3 is a schematic view showing a cross-sectional structure of an optical plastic sheet according to another embodiment of the present invention.

Referring to FIG. 3, in the optical plastic sheet 101, high strength resin layers 120 and 130 are laminated on both sides of the sheet base 110, and the hard coating layer 140 is formed on the outer surfaces of the high strength resin layers 120 and 130. , 150) is laminated. That is, the hard coating layer 140, the high strength resin layer 120, the sheet substrate 110, the high strength resin layer 130, and the hard coating layer 150 are sequentially stacked based on one side.

Therefore, in the optical plastic sheet 101, since the hard coating layers 140 and 150 are located at the outermost layer, the surface hardness thereof is very high. The hard coating layers 140 and 150 have excellent barrier properties and moldability to block gas, moisture, and the like including air, and require tensile strength and weather resistance to stably protect the liquid crystal device against an external environment. It is preferable that it is made from urethane resin from a side. In addition, a small amount of the silicon-based material may be included to improve adhesion to the high strength resin layers 120 and 130.

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 by adding a high-strength resin layer having a higher molecular weight than the polymer for strengthening mechanical properties on both sides of the sheet substrate prepared by melt extrusion of a polymer having a predetermined molecular weight, Complement the weak mechanical properties of the sheet which can be brought about by manufacturing by the melt extrusion method, to provide a good mechanical properties comparable to that produced by the solution casting method.

Claims (15)

An optical plastic sheet comprising a sheet substrate prepared by melt extruding a polymer, and a resin layer coated on both sides of the sheet substrate while having a higher molecular weight than the polymer for enhancing mechanical properties. The optical plastic sheet according to claim 1, wherein the resin layer increases the molecular weight by applying a coating resin to both surfaces of the sheet substrate and curing the coating resin. The optical plastic sheet according to claim 2, wherein the curing is achieved by thermal curing or UV curing. 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. The optical plastic sheet according to claim 4, wherein the polymer is a homopolymer, copolymer or blend selected from the group consisting of PMMA, PC, PES and ABS. According to claim 1, wherein the weight average 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 weight average molecular weight of the resin layer polymer after curing the weight average molecular weight of the polymer for the sheet base material Optical plastic sheet, characterized in that more than 150,000 in a larger range. The optical plastic sheet according to claim 1, wherein the weight average molecular weight of the sheet-based polymer and the weight average molecular weight after curing of the polymer for the resin layer are 140,000: 200,000 to 170,000: 250,000. The optical plastic sheet according to claim 2, wherein the resin coating resin is one or more selected from the group consisting of urethane acrylic monomers, oligomers, and polymers. The optical plastic sheet according to claim 8, 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 resin layer is formed by irradiating and curing UV. The optical plastic sheet according to claim 1, wherein the sheet substrate has a thickness of 500 to 1,500 µm, and the resin layer has a thickness of 1 to 300 µm. The optical plastic sheet according to claim 1, wherein a hard coating layer for increasing surface hardness is added to an outer surface of the resin layer. 12. The optical plastic sheet according to claim 11, wherein the hard coating layer is made of urethane resin. 13. The optical plastic sheet according to claim 12, wherein the hard coating layer further comprises a silicone-based material to impart adhesion to the sheet substrate. A liquid crystal device window made of the optical plastic sheet according to any one of claims 1 to 13. A mobile device selected from the group consisting of a cell phone, a notebook computer and a portable telecommunication terminal, comprising a liquid crystal device window according to claim 14.

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