Disposable masks keep on evolving

January 9, 2013

TOKYO – Amid the cold of winter, many people use face masks to protect themselves from cold germs, pollen or yellow sand.

Nonwoven, disposable masks have largely replaced regular gauze masks over the past decade.

Relatively recent additions to the market include better-fitting protruding masks, the centre of which protrude to allow wearers to breathe easily, and masks that combine powerful filters and breathability.

In January 2003, Unicharm Corp. launched the first nonwoven, protruding mask, aimed at protecting users from pollen.

Disposable masks had previously been used by medical and industrial workers, but they were not common among the general public at the time. Also, many people initially disliked the shape of such masks, according to the Tokyo-based company.

However, disposable masks quickly became widespread after about 2009, due partly to an epidemic of new types of influenza. The main attractions of disposable masks are cleanliness and fine filters.

Their nonwoven fabric is made not by weaving fibers, but by blowing high-velocity air of about 200 C on artificial fibers thinner than human hair to arrange them in a flat, clothlike shape.

According to Unicharm, the method is called melt-blown technology. “It’s similar to the technique used in candy floss machines at festivals,” an official at the firm said.

The fineness of the filter is clearly visible in a picture magnified 50 times.

While gauze masks are made by weaving rope-like strings in a reticular pattern, there are no major hollows in nonwoven masks as the thin fibers intricately cross each other.

The diameter of a flu virus is about 0.1 micrometer, or one ten-thousandth of one millimeter, while an airborne droplet containing the flu virus measures about 5 micrometers.

Nonwoven masks can block these droplets and prevent wearers from spraying them out when they sneeze or cough.

The artificial fibers used in nonwoven masks are made from polyolefin or polyester, both of which are believed to be less conducive to the growth of bacteria than the cotton gauze used for making traditional masks.

Despite this fine filter, however, particles can enter a wearer’s body through the gap between the mask and the wearer’s face. Protruding masks were developed to solve this problem.

Unicharm made more than 1,000 trial products before launching its anti-pollen mask. Furthermore, it used lasers to measure the gap between models’ faces and the mask, and conducted wind tunnel tests in which it sprayed particles that were the same size as pollen at masks.

Based on data including the sizes of faces – the distance from the area between the eyebrows to the chin, and from the area between the eyebrows to the ears -taken from more than 40,000 children and adults, the firm developed a mask that matched the average Japanese face.

The gap between the face and the mask is 1,360 square millimeters for a regular gauze mask, but just 74 square millimeters for a protruding mask, according to the company.

Sixty-six per cent of exhaled air can be filtered by passing through a protruding mask, but only 15 per cent can be filtered by passing through a regular gauze mask, the firm said.

Letting more air through

The N95 is one of the most efficient masks in the world. It is at least 95 per cent efficient against particles that are 0.3 micrometer in diameter, according to the industrial standards of the US National Institute for Occupational Safety and Health.

However, some people may have trouble breathing while wearing such high-efficiency masks because the better their filters function, the less air permeability they have.

Therefore major chemical fiber maker Teijin Ltd. is developing a new mask that filters out the same percentage of particles but makes breathing twice as easy and is half the thickness of current masks. The Osaka-based firm aims to market the new mask this year.

Its new product is made of Teijin’s original ultrafine polyester fiber named Nanofront, which is 0.7 micrometer in diameter.

By irregularly and three-dimensionally combining Nanofront and other fibers about 10 micrometers in diameter, Teijin aims to make both large holes, through which people can breathe easily, and small holes to prevent particles from entering.

The new mask is being produced through “wet processing,” in which the fibers are put under high temperatures after being soaked in water, scooped onto a screen and shaken in a process similar to making Japanese washi paper.

This processing helps create a more precise fiber structure, thereby producing a flat, thinner sheet. Because the fibers are very thin, the mask is smooth to the touch, Teijin said.

The Japan Hygiene Products Industry Association stipulates in its voluntary standards that products called masks should be able to reduce the invasion of such things as pollen and the spread of droplets when a person coughs or sneezes.

Though masks cannot completely prevent colds and flu, “they can be more effective if people use them with less space [between their faces and masks],” said Kazunori Oishi, chief of the National Institute of Infectious Diseases’ Infectious Disease Surveillance Center.

“It’s also important to be careful about hygiene. The masks should be disposable in principle, and people should not wear them too long,” Oishi said.

Gauze masks are still popular in cold areas as they can be washed, are smooth to the skin, and provide warmth and a moisturizing effect. To better utilize these advantages, improved gauze masks are on the market. Some have in-between filters, while others involve multiple layers.

Source: The Yomiuri Shimbun/Asia News Network

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