What is breathable film? Why do sanitary napkins and diapers all use it?

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.

Today's dry goods guide is as follows:

✔  What is breathable film

✔  The principle of breathable membrane

✔  Principles of using breathable film

✔  Application of breathable film in diapers

What is breathable film

Breathable membrane is an environmentally friendly functional material that is breathable (vapor) and water-resistant (liquid, bacteria, dust). The emergence of microporous breathable membranes has a history of more than 20 years and has rapidly developed in the past 10 years. China is still in the early stages of technology, market, and application.

Polyolefin breathable membrane is made by adding inert fillers to PE or PP carriers, and then forming and stretching the membrane. During the film formation process, the product generates pores due to high magnification stretching, thus possessing the functions of breathability and moisture conductivity. In short, the function of breathable film is to block water and allow air (moisture) to pass through. The most commonly used breathable film is based on PE as the carrier.

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.

Principles of using breathable film

The manufacturing of microporous breathable membranes can be divided into blown film method and cast film method according to different membrane making processes; According to different stretching techniques, it can be divided into uniaxial stretching method, biaxial stretching method, and local stretching method. Compared with ordinary PE cast embossed film, the manufacturing of breathable film has higher technical requirements, raw material selection requirements, processing requirements, and so on.

The ultimate manifestation of the breathable effect of the breathable membrane depends on the structural design, and the safety (water resistance) of the breathable membrane is a prerequisite. Only when the safety is ensured can the breathability be discussed.

Compared with ordinary PE embossed film, breathable film has its inherent shortcomings, so the design of products should be good at avoiding shortcomings and leveraging strengths. For example, breathable membranes have low lateral strength (CD), monotonous colors, poor thermal stability, and so on.

The final breathable effect of the breathable membrane is directly proportional to the actual breathable area of the breathable membrane. When designing a product, it is important to cherish and protect the effective breathable area. The final product design should consider the convection of the small environment, and the effectiveness of breathable products on the user's body may have a time lag.

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.