A disposable diaper consists of an absorbent pad sandwiched between two sheets of non-woven fabric. The pad is specially designed to absorb and retain body fluids, and the nonwoven fabric gives the diaper a comfortable shape and helps prevent leakage. These diapers are made by a multi-step process in which the absorbent pad is first vacuum-formed, then attached to a permeable top sheet and impermeable bottom sheet. The components are sealed together by application of heat or ultrasonic vibrations. Elastic fibers are attached to the sheets to gather the edges of the diaper into the proper shape so it fits snugly around a baby's legs and crotch. When properly fitted, the disposable diaper will retain body fluids which pass through the permeable top sheet and are absorbed into the pad.
Disposable diapers were developed to release moms'hands. The earliest disposables used wood pulp fluff, cellulose wadding, fluff cellulose, or cotton fibers as the absorbent material. These materials did not absorb very much moisture for their weight, however. Consequently, diapers made from these materials were extremely bulky. More efficient absorbent polymers were developed to address this issue.
The diaper manufacturer must use the diaper machine to product disposable diapers in quantity, the diaper making machine is a professional converting machine to combine the raw materials together, such as pulp, SAP, non woven fabric, elastic thread, hot melt adhesive and so on, the maker input these raw materials into the diaper production line, and waiting for finished diapers at output mouth, The full servo motor controlled diaper machine is the most efficient diaper production equipment at present. The full servo motor controlled diaper machine is equipped with PLC and HMI operation interface. It is a highly automated machine, which greatly improves the diaper production efficiency and quality.
Crucial raw materials of disposable diaper:
Absorbent pad / core (Pulp & SAP)
The single most important property of a diaper, is its ability to absorb and retain moisture. Cotton material used in cloth diapers is reasonably absorbent, but synthetic polymers far exceed the capacity of natural fibers. Today's best disposable diaper will absorb 20 times its weight in water. This phenomenal absorption capacity is due to the absorbent pad found in the core of the diaper. This pad is composed of two essential elements, a hydrophilic, or water-loving, polymer and a fibrous material such as wood pulp. The polymer is made of fine particles of an acrylic acid derivative, such as sodium acrylate, potassium acrylate, or an alkyl acrylate. These polymeric particles act as tiny sponges that retain many times their weight in water. Microscopically these polymer molecules resemble long chains or ropes. Portions of these chemical "ropes" are designed to interact with water molecules. Other parts of the polymer have the ability to chemically link with different polymer molecules in a process known as cross linking. When a large number of these polymeric chains are cross linked, they form a gel network that is not water soluble but that can absorb vast amounts of water. Polymers with this ability are referred to as hydro-gels, super absorbents, or hydro-colloids. Depending on the degree of cross linking, the strength of the gel network can be varied. This is an important property because gel strength is related to the tendency of the polymer to deform or flow under stress. If the strength is too high the polymer will not retain enough water. If it too low the polymer will deform too easily, and the outermost particles in the pad will absorb water too quickly, forming a gel that blocks water from reaching the inner pad particles. This problem, known as gel blocking, can be overcome by dispersing wood pulp fibers throughout the polymer matrix. These wood fibers act as thousands of tiny straws which suck up water faster and disperse it through the matrix more efficiently to avoid gel blocking. Manufacturers have optimized the combinations of polymer and fibrous material to yield the most efficient absorbency possible.The production of disposable hygiene products (Baby Diapers, Adult Incontinence Briefs, Feminine Hygiene Pads, etc.) begins with fiberized cellulose (wood pulp) conveyed in an air stream. Super absorbent particles are mixed into the air stream and the blend is pulled via a vacuum fan onto a rotating drum where the solids and air are separated by a permeable screen. We called that as core forming drum in diaper making machine.
The absorbent pad is at the core of the diaper. It is held in place by nonwoven fabric sheets that form the body of the diaper. Nonwoven fabrics are different from traditional fabrics because of the way they are made. Traditional fabrics are made by weaving together fibers of silk, cotton, polyester, wool, etc. to create an interlocking network of fiber loops. Nonwovens are typically made from plastic resins, such as nylon, polyester, polyethylene, or polypropylene, and are assembled by mechanically, chemically, or thermally interlocking the plastic fibers. There are two primary methods of assembling nonwovens, the wet laid process and the dry laid process. A dry laid process, such as the "meltblown" method, is typically used to make nonwoven diaper fabrics. In this method the plastic resin is melted and extruded, or forced, through tiny holes by air pressure. As the air-blown stream of fibers cools, the fibers condense onto a sheet. Heated rollers are then used to flatten the fibers and bond them together. Polypropylene is typically the material used for the permeable top sheet, while polyethylene is the resin of choice for the non-permeable back sheet.
Hot melt adhesive / glue
In manufacturing, the hot glue is called hot melt adhesive. The scientific term to describe hot melt adhesive is thermoplastic. This literally means “softer when heated,” and it is exactly what occurs. Hot melt adhesives melt into the surface of the layers or pieces they are applied to and form a grip as they cool down. They then harden and become solid again at room temperature.
Hot melt adhesives are able to repeat the heating and cooling process. This means you can separate two items that were bonded with a hot melt adhesive by reheating the hot melt to the temperature you used to apply it.
The equipment used for hot melts throughout the industry (and for disposable hygiene products in particular) is usually hotter and more complex than your at-home glue gun. This allows the hot melt adhesive to keep up with the speed of the production line. Unlike with a hot glue gun, hot melt adhesive is not simply applied as a thick bead. Instead, the equipment applies the hot melt adhesive in specific patterns in very precise parts of the diaper or pad. This creates a strong bond and helps with product performance.
(image: Hot melt adhesive machine is Nordson Altablue & hot melt adhesive is Henkel)
Over the last 20 years, many changes have taken place in diaper design and use of elastics for diaper leg cuff and standing leg cuff applications. In fact, most of today's diaper designers say that better form, fit and functionality will be achieved through elastics. While elastics can be supplied in many forms, here classic elastic thread for cuff application will be covered.
Over the last few years, as diapers have become thinner, it has become increasingly important to supply an elastic with a "flat" return curve. This will allow the elastic to perform at economically acceptable levels while still maintaining the necessary process and physical requirements. A flatter return curve will supply a more consistent fit over a broader range of sizes. Obviously a too flat return curve will make it difficult to adjust on-line tensions.
RCH diaper making machine has automatic elastic threads unwinding system and tension adjustment function, the operator can adjust elastic threads unwinding speed and tension by touch screen easily, this is a high automation unit in diaper machine.
To be continued...