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With today's economy is your money "disposable"? SAVE your $$$ and SAVE our planet while making the HEALTHY choice of cloth diapering your baby!
What are the components of a disposable diaper?
Most disposable diapers are made with these basic components:
1) Polyethylene or cloth-like Film: This is used as back sheet, and it helps to stop the liquids from leaking out of the diaper. The back-sheet can also be made to look as a cloth like back sheet, by adding a polypropylene non-woven to the film using either hot melts or heat and pressure. Contrary to popular belief, the cloth-like back sheet is made of plastics. Breathable cloth-like can also be used instead of film, even when the fact of the matter is that a breathable diaper with 200 ml of urine will lose less than 2.5% of its weight after 24 hours, however this is enough the cool the diaper due to evaporation.
2) Tissue: This is used to help the manufacturing process, it is used as a carrier for the pad (the pad is the absorbent core of the diaper). The tissue paper helps during the pad knife process, specially for machines equipped with continuous drum forming systems. Tissue helps the diaper by adding integrity and reducing the pin holes associated to the superabsorbent particles damaging the inner plastic film. Tissue comes from the Kraft paper process. A difference between this material and regular bathroom tissue is its higher elasticity and wet strength. Tissue can be replaced with low gage carrier SMS nonwoven but only when it is used near the back sheet.
3) Hot Melts: They are used to glue the different components of the diaper, such as the pad and the elastics. They are made of a mixture of resins, oils and tackifiers. The hot melt adhesive is applied melted and when it cools down provides the bonding force to glue the materials. Most times two types of adhesives are used: a construction adhesive, for the back sheet and nonwovens, and an elastomeric adhesive, for the leg and waist foam elastics. The elastomeric adhesive has a more elastic nature to hold the materials as they are being stretched, it also has a higher bonding strength and it is generally more expensive than construction adhesives. When the diaper pad is very thin, another specialty adhesive known as "pad integrity adhesive" is also used to add strength to the diaper core when it is wet. This integrity adhesive is specially useful when SAP loadings exceed 20% from the total pad weight.
4) Hydrophobic Non-woven: It is used as a top sheet for the leg cuffs, it will not allow water to pass through. It is made of polypropylene resin without any added surface surfactants. The phobic nonwoven is used to make the leg cuffs that prevent leakage to the outside of the diaper. It is also possible to make a roll of nonwoven only partially philic applying surfactant to a restricted area (called the Zebra process)
5) Hydrophilic Non-woven: It is the main top sheet, the top surface that is in contact with the baby's skin allowing the liquids to flow into the diaper core. The difference between the two non-wovens (philic and phobic) is the surfactant treatment used in the process. The surfactant treatment reduces the surface tension of the nonwoven, reducing the contact angle with the water and allowing it to pass. Flow dynamics within the diaper core prevent liquids from returning to the surface. Most nonwovens used in diapers are made with the spunbond process, however it is also possible to use thermal bonded nonwovens, which are softer but with lower resistance, and Trough Air Bonded which are more lofty.
6) Elastics: Used to improve the fit of the diaper, usually made of polyurethane foam, rubber or lycra (spandex). They are used for the waist and also for the legs, they can also be used as lateral side panels and in tape construction. Most gasketing cuffs use spandex to provide a seal with baby's legs. One foot of spandex can stretch as much as 400% before it breaks. New generations of softer and stronger elastic materials are coming out, this is probably the raw material area of more attention in diaper research and development.
7) Lateral Tapes: In premium diapers, VelcroR type materials have been used to provide mechanical means, it is also known as the "hook tape". In more economic diapers, adhesive tapes made of polypropylene are used. There are new versions of elasticized Nonwoven Velcro Tapes. I believe in a few years baby diapers will replace training pants with the help of these new stretchable fastening systems, giving the same characteristics to the consumer but with a lower cost. Some adult incontinence diapers use what is called the "target tape" system, where the tape has two adhesive tabs to avoid the need for a frontal tape. This is a cheaper alternative for adult diapers but not as good as using a frontal tape which will not force you to reposition the tape on top of the target.
8) Frontal Tape: It is used to allow for multiple repositions of the lateral tape without tearing the back-sheet, it is made of polypropylene film and attached to the front of the diaper with adhesive. Its use has helped to reduce the thickness of the poly film without the risk of potential tears associated with the opening of the lateral tapes. In premium diapers, a special loop system has been developed in order to use Velcro type fasteners (also called the "hook and loop" system). A new generation of nonwoven materials will help to avoid the use of frontal tapes in a few years, as the whole backsheet will be used to reposition mechanical tapes.
9) Cellulose: Used in the construction of the pad, it gives integrity and absorbing capacity to the diaper. The capacity of pulp is around 10 cc of water per gram of pulp when the diaper is in "free swell" but less than 2 cc when subjected to 5 KPa of pressure, that is why superabsorbent is also needed to hold the liquids under pressure. Cellulose comes from pine trees from well managed forests. Liquids are absorbed due to the capillaries in the void spaces between the fibers and the surface tension angle between the fibers and the water. Typical fiber length used in diapers is about 2.6 mm. An alternative to pulp is to use air laid synthetic fibers, however it is still difficult for air laid to compete with pulp, unless it is in a special market niche where thickness is very important for the consumer (such as some sanitary napkins and the adult diapers used by active people).
10) Acquisition and Distribution Layer: A sub layer used between the top sheet and the absorbent core. This sub layer is specially needed when the absorbent core is very thin in order to quickly move liquids into the absorbent core and reduce potential leakage. It is made either of through air bond (TAB) nonwovens, "curly" fibers such as in P&G's pampers, or some kind of "high loft" nonwoven. Economic diapers sometimes use resin bonded nonwovens, but they do not work as well.
11) Sodium Polyacrylate: Also known as super-absorbent or "SAP" (super absorbent polymer). KC used to call it SAM (super absorbent material). It is typically used in granular form (like table salt). It helps to improve the capacity and retention of a disposable diaper, allowing for thinner products with improved performance and less usage of pine fluff pulp. The polyacrylate has sodium carboxylate groups hanging off the main chain. In contact with water the sodium detaches, leaving only carboxyl ions. Being negatively charged, these ions repel one another so that the polymer unwinds and absorbs water, which is attracted to the sodium atoms. The polymer also has cross-links, which effectively leads to a three-dimensional structure. In addition, it has molecular weights of more than a million; thus, it cannot dissolve but instead solidifies into a gel. The Hydrogen in the water (H-O-H) is trapped by the acrylate due to the atomic bonds associated with the polarity forces between the atoms. Electrolytes in solution, such as salt minerals (urine contains 0.9% of minerals), reduce the polarity, affecting the superabsorbent properties specially with regards to the superabsorbent capacity and liquid retention. This is the main reason why diapers containing SAP should never be tested with plain water. Linear molecular configurations will have less total capacity than non-linear molecules, but on the other hand, the retention in a linear molecule is higher than in a non-linear, due to improved polarity.
The superabsorbent can be designed to absorb higher amounts of liquids (with less retention) or very high retention's (but lower capacity). In addition, a surface cross linker can be added to the superabsorbent particle to help it move liquids while it is saturated, this helps to avoid the formation of "gel blocks", phenomena that describes the impossibility to move liquids once a SAP particle has saturated.
12) Top Sheet surface add-on lotions: In order to push the envelope in creating novelties for product differentiation, several topical lotions are added to the nonwoven top sheet, among others: Aloe Vera, Vitamin E, Petrolatum, etc. There is another trend to use Antibacterial lotions (such as tertiary ammonia or silver salt compounds), however many Pediatricians are against its use for obvious reasons.
13) Decorated Films and wettness indicators: For even more differentiation, some diapers use decorated films underneath the cloth-like backsheet, some use as many as 9 inks with all kind of well known characters such as Disney, Sesamo Street, Soccer teams, etc. Another option they use is for a wettness indicator. This is typically used for adult incontinence products but some baby diapers also use it.
***Article from "The Diaper Industry Source" http://www.richernet.com/FAQ.htm#how
1) Polyethylene or cloth-like Film: This is used as back sheet, and it helps to stop the liquids from leaking out of the diaper. The back-sheet can also be made to look as a cloth like back sheet, by adding a polypropylene non-woven to the film using either hot melts or heat and pressure. Contrary to popular belief, the cloth-like back sheet is made of plastics. Breathable cloth-like can also be used instead of film, even when the fact of the matter is that a breathable diaper with 200 ml of urine will lose less than 2.5% of its weight after 24 hours, however this is enough the cool the diaper due to evaporation.
2) Tissue: This is used to help the manufacturing process, it is used as a carrier for the pad (the pad is the absorbent core of the diaper). The tissue paper helps during the pad knife process, specially for machines equipped with continuous drum forming systems. Tissue helps the diaper by adding integrity and reducing the pin holes associated to the superabsorbent particles damaging the inner plastic film. Tissue comes from the Kraft paper process. A difference between this material and regular bathroom tissue is its higher elasticity and wet strength. Tissue can be replaced with low gage carrier SMS nonwoven but only when it is used near the back sheet.
3) Hot Melts: They are used to glue the different components of the diaper, such as the pad and the elastics. They are made of a mixture of resins, oils and tackifiers. The hot melt adhesive is applied melted and when it cools down provides the bonding force to glue the materials. Most times two types of adhesives are used: a construction adhesive, for the back sheet and nonwovens, and an elastomeric adhesive, for the leg and waist foam elastics. The elastomeric adhesive has a more elastic nature to hold the materials as they are being stretched, it also has a higher bonding strength and it is generally more expensive than construction adhesives. When the diaper pad is very thin, another specialty adhesive known as "pad integrity adhesive" is also used to add strength to the diaper core when it is wet. This integrity adhesive is specially useful when SAP loadings exceed 20% from the total pad weight.
4) Hydrophobic Non-woven: It is used as a top sheet for the leg cuffs, it will not allow water to pass through. It is made of polypropylene resin without any added surface surfactants. The phobic nonwoven is used to make the leg cuffs that prevent leakage to the outside of the diaper. It is also possible to make a roll of nonwoven only partially philic applying surfactant to a restricted area (called the Zebra process)
5) Hydrophilic Non-woven: It is the main top sheet, the top surface that is in contact with the baby's skin allowing the liquids to flow into the diaper core. The difference between the two non-wovens (philic and phobic) is the surfactant treatment used in the process. The surfactant treatment reduces the surface tension of the nonwoven, reducing the contact angle with the water and allowing it to pass. Flow dynamics within the diaper core prevent liquids from returning to the surface. Most nonwovens used in diapers are made with the spunbond process, however it is also possible to use thermal bonded nonwovens, which are softer but with lower resistance, and Trough Air Bonded which are more lofty.
6) Elastics: Used to improve the fit of the diaper, usually made of polyurethane foam, rubber or lycra (spandex). They are used for the waist and also for the legs, they can also be used as lateral side panels and in tape construction. Most gasketing cuffs use spandex to provide a seal with baby's legs. One foot of spandex can stretch as much as 400% before it breaks. New generations of softer and stronger elastic materials are coming out, this is probably the raw material area of more attention in diaper research and development.
7) Lateral Tapes: In premium diapers, VelcroR type materials have been used to provide mechanical means, it is also known as the "hook tape". In more economic diapers, adhesive tapes made of polypropylene are used. There are new versions of elasticized Nonwoven Velcro Tapes. I believe in a few years baby diapers will replace training pants with the help of these new stretchable fastening systems, giving the same characteristics to the consumer but with a lower cost. Some adult incontinence diapers use what is called the "target tape" system, where the tape has two adhesive tabs to avoid the need for a frontal tape. This is a cheaper alternative for adult diapers but not as good as using a frontal tape which will not force you to reposition the tape on top of the target.
8) Frontal Tape: It is used to allow for multiple repositions of the lateral tape without tearing the back-sheet, it is made of polypropylene film and attached to the front of the diaper with adhesive. Its use has helped to reduce the thickness of the poly film without the risk of potential tears associated with the opening of the lateral tapes. In premium diapers, a special loop system has been developed in order to use Velcro type fasteners (also called the "hook and loop" system). A new generation of nonwoven materials will help to avoid the use of frontal tapes in a few years, as the whole backsheet will be used to reposition mechanical tapes.
9) Cellulose: Used in the construction of the pad, it gives integrity and absorbing capacity to the diaper. The capacity of pulp is around 10 cc of water per gram of pulp when the diaper is in "free swell" but less than 2 cc when subjected to 5 KPa of pressure, that is why superabsorbent is also needed to hold the liquids under pressure. Cellulose comes from pine trees from well managed forests. Liquids are absorbed due to the capillaries in the void spaces between the fibers and the surface tension angle between the fibers and the water. Typical fiber length used in diapers is about 2.6 mm. An alternative to pulp is to use air laid synthetic fibers, however it is still difficult for air laid to compete with pulp, unless it is in a special market niche where thickness is very important for the consumer (such as some sanitary napkins and the adult diapers used by active people).
10) Acquisition and Distribution Layer: A sub layer used between the top sheet and the absorbent core. This sub layer is specially needed when the absorbent core is very thin in order to quickly move liquids into the absorbent core and reduce potential leakage. It is made either of through air bond (TAB) nonwovens, "curly" fibers such as in P&G's pampers, or some kind of "high loft" nonwoven. Economic diapers sometimes use resin bonded nonwovens, but they do not work as well.
11) Sodium Polyacrylate: Also known as super-absorbent or "SAP" (super absorbent polymer). KC used to call it SAM (super absorbent material). It is typically used in granular form (like table salt). It helps to improve the capacity and retention of a disposable diaper, allowing for thinner products with improved performance and less usage of pine fluff pulp. The polyacrylate has sodium carboxylate groups hanging off the main chain. In contact with water the sodium detaches, leaving only carboxyl ions. Being negatively charged, these ions repel one another so that the polymer unwinds and absorbs water, which is attracted to the sodium atoms. The polymer also has cross-links, which effectively leads to a three-dimensional structure. In addition, it has molecular weights of more than a million; thus, it cannot dissolve but instead solidifies into a gel. The Hydrogen in the water (H-O-H) is trapped by the acrylate due to the atomic bonds associated with the polarity forces between the atoms. Electrolytes in solution, such as salt minerals (urine contains 0.9% of minerals), reduce the polarity, affecting the superabsorbent properties specially with regards to the superabsorbent capacity and liquid retention. This is the main reason why diapers containing SAP should never be tested with plain water. Linear molecular configurations will have less total capacity than non-linear molecules, but on the other hand, the retention in a linear molecule is higher than in a non-linear, due to improved polarity.
The superabsorbent can be designed to absorb higher amounts of liquids (with less retention) or very high retention's (but lower capacity). In addition, a surface cross linker can be added to the superabsorbent particle to help it move liquids while it is saturated, this helps to avoid the formation of "gel blocks", phenomena that describes the impossibility to move liquids once a SAP particle has saturated.
12) Top Sheet surface add-on lotions: In order to push the envelope in creating novelties for product differentiation, several topical lotions are added to the nonwoven top sheet, among others: Aloe Vera, Vitamin E, Petrolatum, etc. There is another trend to use Antibacterial lotions (such as tertiary ammonia or silver salt compounds), however many Pediatricians are against its use for obvious reasons.
13) Decorated Films and wettness indicators: For even more differentiation, some diapers use decorated films underneath the cloth-like backsheet, some use as many as 9 inks with all kind of well known characters such as Disney, Sesamo Street, Soccer teams, etc. Another option they use is for a wettness indicator. This is typically used for adult incontinence products but some baby diapers also use it.
***Article from "The Diaper Industry Source" http://www.richernet.com/FAQ.htm#how
