The most important concern when buying diapers is breathability. Do you know what breathable film is?

Breathable film is an essential material for diapers, which are divided into three layers: surface cover layer, absorbent core layer, and bottom layer.

The surface of the diaper is made of non-woven fabric, and the absorbent core layer is made of water absorbing beads and fluff fibers. The bottom material is mainly made of PE film or PE film+non-woven fabric. The main purpose of the PE breathable bottom film is to prevent urine leakage.

What is breathable film

Breathable film generally refers to PE functional materials with environmentally friendly, waterproof and breathable properties. It is mainly used as the bottom film of women's sanitary napkins, cushion bottom film, baby diaper bottom film, etc. It is compounded with non-woven fabric and widely used in medical protective clothing, isolation clothing, medical mattresses, disposable beds, home textiles, etc. Whether the breathable bottom film is breathable depends not only on its material function, but also on the craftsmanship.

The principle of breathable membrane

The principle of breathable membrane is simple: inorganic material+stretching=micropores. In fact, the operation is very delicate, only micropores with appropriate size and uniform distribution are effective.

When the concentration of water vapor on one side of the film is higher than the environment on the other side of the film, a humidity gradient pressure difference is formed. This provides the basic conditions for gas (vapor) convection, as the formation of convection leads to a relatively balanced humidity environment on both sides of the film.

As a waterproof membrane, breathable film has a barrier effect on liquids because there are many pathways in the film, and the tortuous channels formed by it have a large "length to diameter ratio" (L/D) value, which can be understood as capillaries. So, under the same liquid (such as water) and pressure conditions, as long as the liquid column height of the capillary is less than the length of the capillary, it can ensure that the liquid will not leak out.

Therefore, the water resistance of the film directly depends on the pore size and channel length of the breathable membrane. This performance can usually be measured by water pressure resistance (Δ P), and when the water pressure exceeds the water pressure resistance value that the microporous membrane can withstand, water will leak out.

Production process of breathable film

1. Cast composite. This process involves melting plastic particles and then relying on the adhesive properties of the plastic itself to form a composite. The disadvantage is that it is almost not breathable. In 2014, there was no way to produce truly high breathability, high temperature resistance, waterproof and breathable membranes using this process worldwide.

2. Spray glue or scrape glue composite (hot melt adhesive composite). This process was first applied to sanitary napkins, diapers, and protective clothing. Currently, almost all domestic manufacturers use this process to produce highly breathable waterproof and breathable materials. The disadvantage is that the air permeability is relatively low because the micropores of the middle breathable film are actually blocked by hot melt adhesive. In addition, the most fatal disadvantage is that the temperature resistance is very low, only able to withstand temperatures of 60 degrees. Because this adhesive is actually a pressure-sensitive adhesive (sticker). A simple example is that in winter, double-sided tape has almost no stickiness and will layer, but in summer, the adhesive on the surface of the double-sided tape will melt. The quality of waterproof and breathable film made with this process can be imagined. During construction, as long as there is a certain temperature, non-woven fabric will peel and layer. Which construction company can guarantee that the roof will be covered immediately after the waterproof and breathable membrane is laid during construction? So, this waterproof breathable film can only be a counterfeit product of genuine waterproof breathable film, and there is no market in European and American countries.

3. Hot pressing composite. At present, the domestic market is mixed with good and bad products, and there are actually very few manufacturers that produce truly waterproof and breathable membranes. Many factories or sellers claim that their waterproof and breathable membranes are good, but almost the vast majority of users have never thought of it. Some manufacturers provide waterproof and breathable membranes that are not waterproof at all. For example, a domestic colleague deceived consumers by claiming it was an international company that used the technology and research and development achievements of a well-known international company. In fact, the static water pressure of the waterproof breathable membrane they produced was only about 750px. However, users did not know how to detect it. They only knew to splash water on the waterproof breathable membrane, which did not leak water. In fact, users did not know that water is under pressure and can penetrate. The only way is to randomly inspect each batch of waterproof breathable membrane, so that counterfeit and inferior products cannot hide. In fact, the real waterproof breathable film should be highly breathable, high temperature resistant, anti-aging, and hydrostatic pressure of more than 2 meters. The production process should be pure thermal composite technology, without glue, so it can achieve a temperature resistance of more than 110 degrees, high strength and anti-aging. This is a product that can really meet the EU standards in China at present, and is the latest technology in China.

Application of breathable film in diapers

The main factors determining the breathability are the number of breathable holes in the breathable base film and the manufacturing process. The main thing to note is colloids, including urinary gel and structural gel.

Due to the low usage of structural adhesive, many large enterprises tend to use cheaper products. This does not violate relevant national regulations, and there is no obvious evidence to indicate that it has harmful effects on the human body. However, there is a smell when smelled. Sometimes, if you smell diapers, it may be the smell produced by the breathable film. However, the smell of diapers is determined by multiple factors, not just the breathable film.

Finally, it is best to choose regular brands and large manufacturers when selecting diapers. The material is guaranteed and the breathable film will not be too hard, otherwise it is easy to scratch the baby's buttocks.