Chapter 13 433 through pH maintenance, but is dependent on the amount of water contained and the other ingredients within the system. Inhibitors such as sodium benzoate, ammonium benzoate, cyclohexylamine ammonium benzoate, and combinations of borates and ammonium hydroxide are often employed.23,24 Can corrosion screening methods are available to assist in determining the potential for a system to be corrosive and can be very useful in the selection of polymers, inhibitors and additives, and resultant use levels.25,26 Long-term stability of the final system should be performed over a series of time intervals and temperatures. Additional package considerations include the valve material and gasket, and the wall thickness of the can used. Generally, it is good practice to use the same metal content for the valve as for the can type. The gasket material of the valve should also be checked for compatibility with the propellants and solvents within the system to avoid possible clogging and/or leakage due to swelling, shrinking, or other potential issues. The pressure of the finished system at 54.5°C (130°F) must also be known in order to choose the appropriate can. The delivery of the product is an important attribute both aesthetically and functionally. Valve selection in combination with the finished system needs to address sprayability, clogging, and evacuation. In general, for 55% VOC hair spray, there is usually 35-40% propellant, based on hydrofluorocarbon 152a low water or anhydrous, or dimethyl ether hydroalcoholic based systems propellant blends are used as well. Based on these propellant ratios, the viscosity of the concentrate of the formulation should generally not exceed 25 cP to provide for adequate breakup upon actuation. The polymer or polymers chosen will have a direct impact depending on the molecular weight and use levels. The use of surface active ingredients may aid in lower solution viscosity as well as improve the wetting of the polymer film once applied to the hair. There are many variables within the valve and actuator mechanism that can be varied to optimize the overall aesthetics of a spray, including such attributes as output, spray pattern, particle size distribution, force, and even the sound.
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Chapter  13  433  through  pH  maintenance,  but  is  dependent  on  the  amount  of  water  contained  and  the  other  ingredients  within  the  system.  Inhibitors  such  as  sodium  benzoate,  ammonium  benzoate,  cyclohexylamine  ammonium  benzoate,  and  combinations  of  borates  and  ammonium  hydroxide  are  often  employed.23,24  Can  corrosion  screening  methods  are  available  to  assist  in  determining  the  potential  for  a  system  to  be  corrosive  and  can  be  very  useful  in  the  selection  of  polymers,  inhibitors  and  additives,  and  resultant  use  levels.25,26  Long-term  stability  of  the  final  system  should  be  performed  over  a  series  of  time  intervals  and  temperatures.  Additional  package  considerations  include  the  valve  material  and  gasket,  and  the  wall  thickness  of  the  can  used.  Generally,  it  is  good  practice  to  use  the  same  metal  content  for  the  valve  as  for  the  can  type.  The  gasket  material  of  the  valve  should  also  be  checked  for  compatibility  with  the  propellants  and  solvents  within  the  system  to  avoid  possible  clogging  and/or  leakage  due  to  swelling,  shrinking,  or  other  potential  issues.  The  pressure  of  the  finished  system  at  54.5°C  (130°F)  must  also  be  known  in  order  to  choose  the  appropriate  can.  The  delivery  of  the  product  is  an  important  attribute  both  aesthetically  and  functionally.  Valve  selection  in  combination  with  the  finished  system  needs  to  address  sprayability,  clogging,  and  evacuation.  In  general,  for  55%  VOC  hair  spray,  there  is  usually  35-40%  propellant,  based  on  hydrofluorocarbon  152a  low  water  or  anhydrous,  or  dimethyl  ether  hydroalcoholic  based  systems  propellant  blends  are  used  as  well.  Based  on  these  propellant  ratios,  the  viscosity  of  the  concentrate  of  the  formulation  should  generally  not  exceed  25  cP  to  provide  for  adequate  breakup  upon  actuation.  The  polymer  or  polymers  chosen  will  have  a  direct  impact  depending  on  the  molecular  weight  and  use  levels.  The  use  of  surface  active  ingredients  may  aid  in  lower  solution  viscosity  as  well  as  improve  the  wetting  of  the  polymer  film  once  applied  to  the  hair.  There  are  many  variables  within  the  valve  and  actuator  mechanism  that  can  be  varied  to  optimize  the  overall  aesthetics  of  a  spray,  including  such  attributes  as  output,  spray  pattern,  particle  size  distribution,  force,  and  even  the  sound.  

                
        

     


                
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