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Micro-shape Formation Technology - Microhoneycomb

Ricoh uses a bubble inflation mechanism to form a large-surface, minute microhoneycomb structure.

Characteristics and Applications of Microhoneycomb Structure

A honeycomb structure is an array of regular hexagonal prisms without any gaps between them (in a broader sense, it is an array of hollow prisms of any shape). The structure is basically hollow, so it is used to make material that is lightweight and yet strong.

While the honeycomb structure is typically used for structural and interior materials in aircraft today, Ricoh has developed a technology to expand its use to other microscopic applications. The microhoneycomb formation technology produces micron-sized honeycomb structures.

A versatile technology to process material in many ways

The microhoneycomb formation method developed by Ricoh involves simple equipment and methods. It has capabilities at least equivalent to those of X-ray lithography which requires extremely expensive equipment or dry etching, which involves many processes. The principal capabilities of this microhoneycomb formation method are described below.

  1. Variable aspect ratio (cell height/wall thickness: 50 to 500)
  2. Variable pitch (from 5 to 150 µm or greater)
  3. Wide processing area (φ100 mm or greater)
  4. High processing speed (from a few seconds to a few minutes)

Figure 1: Ricoh technology enabling versatile processing

Figure 2: Shape comparison of the Ricoh method and dry etching

Principle of Microhoneycomb Structure Formation

Figure 3 shows how this method produces a microhoneycomb structure.

  1. A template with regularly arrayed holes is coated with material, which then becomes the base of the microhoneycomb, covering the holes.
  2. Air bubbles formed in the holes are inflated by air pressure to change the shape and harden the microhoneycomb material. The air bubbles in the holes are simultaneously inflated by lowering the air pressure around them from atmospheric pressure to a vacuum state.
  3. The solidified microhoneycomb shape is peeled off the template.

This process resembles the method of producing soap bubbles using a drinking straw. Although soap bubbles are usually spherical, when they attach to each other they form hexagons or squares. This technology makes use of that principle.

Figure 3: Microhoneycomb formation process

Figure 4: Microhoneycomb formed using this process

Expanding Applications for Microhoneycombs

Ricoh believes the ability to manufacture minute microhoneycombs with high aspect ratios and at a low cost will greatly expand honeycomb applications. Examples include absorption materials with large surface areas, anisotropic materials inducing heat or light in only one direction, and multifunctional materials combining hydrophilic and hydrophobic properties on a single surface.


Figure 5: Expansion of honeycomb applications

Ricoh has successfully applied this method to produce an array of hollow microneedles (needles with a microscopic conduit) and a homogeneous membrane filter with countless microscopic pores of the same size (for precision filtration).

The technology has great potential in the medical and pharmaceutical areas. Prospective applications are cell culture mediums for regenerative medicine (the membrane filter shown in the figure) and a poultice with a microhoneycomb backing.

Figure 6: An array of hollow microneedles

Figure 7: A homogeneous membrane filter with 5 µm pores

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