Friday 21 June 2013

Diaper Design Optimisation

Carlos Richer of Richer Investments (USA) dominated the opening day of this year's INDA VIsion Conference in Orlando with a first-class workshop on diaper design and production for new entrants, especially those in the developing economies.  He commenced with the biology resulting in the production of urine and how the quantities produced vary with fluid intake, age and climate.  He  moved on to practical  diaper designs and factors affecting absorbency, retention and leakage before considering skin irritation, comfort and the ways to optimise diaper design for different markets.  He concluded with a tour of the latest constructions and some speculation about future products. Noteworthy points follow:

·         Whereas on a normal day 62% of fluid is lost as urine, 18% as sweat, 16% as respiration and 4% as faeces, on a hot day sweat increases to 30% at the expense of urine. This reduction in urine output is more pronounced and more important for design in the under-developed markets.
·         Disposable diaper sales decrease in hot sunny weather due mothers preferring to use washables when they can be line dried – at least in markets where disposables penetration is lower than in the USA.
·         Most new diaper producers define their absorbency for a medium size and then adjust the capacity for other sizes in proportion to baby’s weight.  However, a 2kg baby produces about 200mls urine/day and a 26kg baby produces 1650 ml/day from a much larger bladder.  Mls/kg/hour of urine should be considered and this goes down as baby grows.
·         Diapers are worn for 4.5 hours on average before changing but this increases to 6.5 hours as baby grows and varies dramatically with culture.  Japan and Korea change much more frequently.
·         Probability of diaper leakage decreases as the amount of urine absorbed increases.  This is because leakage failure is usually occurs on first urination through the cuffs due to poor construction.
·         Leakage through cuffs is higher for thermally bonded cuffs than for glue-line bonded.  This is because thermal bonding causes topsheet surfactant to migrate to the cuff thereby destroying some cuff hydrophobicity.
·         The problem with glue is that if it is not applied precisely the cuffs can stick down when the diaper is opened.
·         Producers who base their design on Pampers often have leakage problems because their topsheets can’t match Pampers for rapid strikethrough. (Pampers= 15 secs, Clones= 40 secs.)
·         The smell of faecal matter is the signal for change in most markets.  However in Japan and Korea mothers want highly breathable diapers so that the smell is detected early.  Other markets want low breathability to extend the diaper life.  (Low MVTR = 1500: High MVTR = 10,000)
·         To minimise skin irritation, diaper topsheet must stay as dry as possible throughout use.  Ammonia is not the problem, its wetness.
·         Topically applied lotions can cause problems, as can the practice of spraying water on the hammer-milled pulp to kill static in hot climates.  The water can be a source of spores and infections.
·         Comfort is improved by using bulky ADL’s which not only improve dryness but also provide good thermal insulation.  Wet diapers tend to feel cold so air trapped in the ADL is good for comfort.
·         Highly breathable diapers tend to be less comfortable, especially at night, so “heat transfer” is becoming a new key design parameter.
·         The three basic measurements for diaper design are still strikethrough, rewet and maximum absorbency in use.  These need balancing to suit each market.  More SAP helps the last 2 but as it increases relative to the pulp content, other components such as ADL need to be added to maintain strikethrough.
·         SAP is best uniformly dispersed in the pulp.   Targeting or layering fails.
·         Diaper SAP is not the same as the best SAP for adult incontinence products, and the permeability of both needs to be matched to the ADL.
With regard to future trends Mr Richer thought the increasing elasticisation of diapers was the key story.  Pulp-free cores using SAP on elastic nonwovens are now possible and are being tested by DryLock in the EU.  K-C too is extruding elastomers directly into diapers during manufacture, and P&G has an elastic backsheet. 
·         The core composition, now about 50/50 pulp/SAP is likely to move to 33/67 Pulp/SAP on average in the developed markets by 2015. 
·         Perforated films are being used instead of nonwovens for the ADL in adult incontinence pads,
·         SCA has developed a diaper which is clone of the best features of K-C and P&G technology.  It has the best ever 3rd insult rewet results in Mr Richer’s testing.
·         The “Toujours” diaper from DryLock Technologies uses a 100% SAP core sandwiched between nonwovens and ultrasonic welded.  It is made in the Czech Republic on Zuiko machines running at half capacity (400dpm) and launched recently in Germany.  It has a 156 gsm 2-layer ADL and a very low strikethrough time.  Mr Richer believes this is over-engineered and cannot survive in its present form.  They are buying market share with a super product which will have to be cheapened if money is to be made.
·         Private Label diapers will also move to high SAP and this may be an opportunity for air-laid pre-formed cores to get into the market.
·         Diapers made in China are on sale in Target in the USA.  Consumers prefer them to Walmart’s own label.  However the supply chain is a logistical nightmare and might hit problems.
Who, apart from P&G will gain from K-C’s withdrawal from diapers in the EU?  DryLock, Ontex and Abena.

    Why are elastic cores important?  Because elasticity allows better fit, and better fit means better function.

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