Читать книгу Plastics Process Analysis, Instrumentation, and Control - Группа авторов - Страница 42

A polymer molded product with a fine structure has been increasingly utilized in various fields such as electronic devices, optical devices, recording media, and medical devices (58). Various methods for manufacturing such a molded product with fine structure have been proposed but attention has been attracted to a UV and thermal nanoimprint method owing to high economic efficiency and productivity. In the case of nanoimprint methods, there is a hot embossing, i.e., a thermal nanoimprint method, in which a stamper mold is pressed to a polymer substrate softened under heating to cause plastic deformation, thereby transfer-molding a pattern of the stamper mold. The hot embossing method shows a high productivity and has advantages such as the capability of fabrication of fine patterns of various thermoplastic polymer substrates.

However, the thermal nanoimprint method has a problem as, in the filling stage of a fine structure of a high aspect ratio, the fluidity of the polymer is insufficient or a high pressure is needed. Also, the hot embossing method has a problem that, when the polymer is heated to the melting temperature, the fluidity of the polymer exceedingly increases and the polymer substrate only undergoes deformation of extending in a plane direction even when pressed, and thus the polymer is not filled into a deep groove portion of the fine structure in which flow resistance is large.

To address this problem, a method of manufacturing a molded product with a nanostructure and a microstructure has been proposed, which includes (59, 60):

1 A step of placing a powdery polymer on the surface of an original plate,

2 A step of heating the original plate and the polymer to a temperature equal to or higher than the glass transition temperature of the polymer and equal to or lower than the melting temperature,

3 A step of pressing the polymer to the original plate, and

4 A step of removing the original plate after cooling the polymer to a temperature equal to or lower than the glass transition temperature so as to form a reverse structure of the nanostructure and microstructure of the original plate.

On the other hand, besides the hot embossing method, there is a UV optical nanoimprint method in which, after a liquid photocurable polymer is coated on a substrate at room temperature, an optically transparent stamper mold is pressed to the polymer and the polymer is irradiated with a light through the stamper mold to cure the polymer, thereby transcribing a pattern onto the polymer substrate. The advantages of the UV optical nanoimprint method are that processing can be performed at room temperature, transcribed pressure is low, and a highly accurate pattern can be molded (58).

However, in the UV optical nanoimprint method, although the pressure for transcription is low, a photocurable polymer generally exhibits a small amount of shrinkage at curing and has properties resembling an adhesive, so that it is difficult to release the imprinted film polymer from the stamper mold and thus there is a concern that a fine structure of the stamper mold will be broken through releasing the imprinted film (58).

To adddress this problem, a manufacture method has been proposed in which a replica is formed based on the stamper mold original plate (61). The replica is used as a stamper mold in the UV optical nanoimprint step.

This method for manufacturing a polymer-made imprinted film with a fine structure having a minimum processing size of 1,000 nm or less includes (61):

1 A step of forming a coating film on the surface of a fine structure having a fine concavo-convex pattern of 1,000 nm or less and being composed of a polymer formed by polymerization,

2 A step of pressing the imprinted film with fine structure to a polymer precursor monomer or a composition of a polymer precursor monomer and polymerizing the polymer precursor monomer or the composition of a polymer precursor monomer, and

3 A step of releasing the imprinted film with fine structure from the polymer of the polymer precursor monomer or the composition of a polymer precursor monomer to transfer the fine concavo-convex pattern on the surface of the imprinted film with fine patterns to the polymer.

The above-described methods (59–61) for manufacturing a molded product with fine pattern are methods of performing a transfer-molding by pressing a heated polymer substrate or a molten polymer to a stamper mold having a fine structure. Such methods require the pressurization of a stamper mold having a nanoscale fine structure. A high degree of concern exists of breaking the stamper mold.

On the other hand, in electronic devices, optical devices, recording media, and biodevices, an attempt has been made to further improve their functionality by a molded product with a fine nanostructure, so there is a demand for a manufacturing method capable of manufacturing a molded product with fine nanostructure stably using various materials (58).

A method for manufacturing a molded product with a fine structure consists of the following steps (58):

1 In a temperature-controlled stamper mold having a fine structure containing a concavo-convex pattern having a width of 10 nm to 1 µm, forming a thermoplastic molten polymer layer to be in contact with the fine structure of the stamper mold which was kept at a predetermined temperature,

2 Holding the thermoplastic molten polymer layer for a predetermined time so as to transcribe the fine structure of the stamper mold to the thermoplastic molten polymer layer under gravity,

3 Cooling and solidifying the transcribed thermoplastic molten polymer layer, and

4 Subsequently releasing the solidified thermoplastic molten polymer layer from the stamper mold.

This method for manufacturing a molded product with a fine structure can economically manufacture a molded product with fine structure containing a concavo-convex pattern in high productivity without requiring pressurization (58). Moreover, it is possible to manufacture a molded product with fine structure which has a large area, which is rich in homogeneity, and which does not have internal strain, birefringence, and orientation. Furthermore, it is possible to manufacture such a molded product with a fine structure having a width of about 10 nm and a high aspect ratio. Since it is possible to perform the molding without any pressurization, damages such as abrasion and breakage of the fine structure of a stamper mold should be low, so that the life of the stamper mold can be lengthened.