Monthly Archives: April 2013

Types of Glass Used for Glass Vials

Types of Glass Used for Glass Vials

The types of glass used in containers can be determined by USP (United States Pharmacopoeia) criteria but, on it’s own, is generally not enough to choose the appropriate vial.  This means that the end user will have to look at the choices and then determine the characteristics of each vial on offer as these can vary between manufacturers.  However, the UPS criteria is a pretty good place to start.

USP Type I Borosilicate Glass

This is the least reactive type of glass available for containers.  All lab glass apparatus is generally Type I borosilicate glass.

In most cases Type I glass is used to package products which are alkaline or will become alkaline over a period of time. Care must be taken in selecting containers for applications where the pH is very low or very high, as even Type I glass can be subject to a reaction under certain conditions. Although Type I has the highest pH stability of any glass, some substances could still cause the glass to become unstable and contaminate the contents.

Many manufacturers now offer vials which have added surface treatments in order to improve the stability of the glass even further.

USP Type II De-alkalized Soda-Lime Glass

This type of glass has higher levels of sodium hydroxide and calcium oxide than type I.  Although it is still quite stable and safe to use with products that remain below pH7, it is not as stable as type I.

USP Type III Soda-Lime Glass

This type of glass could be used for storing dry powder and also liquids which are insensitive to alkali. Type III glass should not be used for products that are to be autoclaved, but is suitable for dry heat sterilization.

USP Type NP soda-lime glass is a general purpose glass and is used for non-parenteral products (to be taken orally or by inhalation) as the vial will not typically  be in contact with chemicals or heat. These vials are often used for storing medicines in tablet form.

What else should you consider when choosing a container?

  1. If light sensitivity of the product is an issue, you may wish to consider using an amber glass container.
  2. If a product is sensitive to certain chemicals within the glass, you could experience a leakage of these substances into the liquid product and cause contamination.
  3. The filling and processing stages that the container will have to withstand are important. If you require the container to have minimal thermal expansion, there are a few options open to you. A typical tubular container with thinner and more uniform walls will withstand thermal shock better than a moulded glass container within the same expansion range. The physical design of the container can also be important with regards to the amount of thermal and mechanical shock resistance it shows. You will often be required to make a compromise between resistance to mechanical shock and thermal shock in order to decide on the correct container to use.
  4. The interaction of glass and liquid solutions is incredibly complex. You will need to consider the risk of corrosion and reaction of the glass when used with certain products.

Please use this information purely as a guide to choosing the appropriate container for your application as each requirement will need evaluating separately.

If you would like advice or assistance in choosing the correct glass vial for your application, please contact us.

Stuart Marshall
Sales Director
Laboratory Precision Ltd. ©


Crimp Sealing Metal Caps on Vials and Containers

Sealing aluminium caps over a rubberised stopper or septa has been and still is the preferred way to seal a vial.  I have tested crimp seals to a pressure of well over 15 bar without leakage in a test rig, you would be surprised how big a bubble you can create from the seal bulging through the centre hole in the cap.  “Don’t try this as it was done in controlled conditions”. When fitted properly once a crimp seal is on, that is where it stays and it doesn’t have to be crushed tight to make a good seal.  Many people over-crimp a cap which puts unnecessary pressure on the tooling and can distort the seal.

Crimp cap materials
Historically over-seals (caps) have been made from aluminium because it is light, easy to cut and easy to form, plus when the correct grade of material is used there is less spring back than with steel.  Spring back is and has always been a problem in metal forming.  You need to break down the structure somewhat to make it stay where you put it and where possible you can over bend it to make it stay where you want it to, however when you push against a solid object this is not possible. That is why a rubberised stopper or septa of a reasonable thickness is so important, the seal must be able to cope with the spring back of the aluminium when formed under the head of the container and still maintain a tight seal between the septa/stopper and the container.

Preperation and inspection of parts to be used
The viability of a good seal is also determined by the surface the seal sits on.  There must not be any irregularities such as mould joints or marks that lead across the joint where leakage could flow.  This is often found on plastic bottles when the top has not been properly finished and in some cases there is misalignment between the two halves of the bottle where the mould has been misaligned.

Crimp cap sealing methods
There are a number of ways to form an aluminium cap under the head of the vial or container. The word “crimp” is perhaps what most people will know as what the hairdresser will do to your hair.  However, this relates to the corrugated effect used by metalworkers to reduce available metal.  You can only push so much metal into itself before it gets very hard and thick; so the crimp affect is another way to reduce the amount of available metal especially with steel caps such as beer bottle tops. The serrations are also found on spray cosmetics pump caps where the metal is pushed inwards where it either has to be pressed into itself or corrugated.

This term crimp or crimping although not entirely accurate has passed over to sealing by the hand tool method where the finished crimp is smooth and not corrugated i.e. shrinking the metal by pushing it into itself. Using aluminium makes it easier to do this and the finished product looks cleaner and is smoother.

The above is based on my 50 years experience of metal manipulation of which 25 years has involved the manufacture of crimping tools.  Please contact us for advice on which of our vial crimping tools is most suitable for your application.

Ken Marshall
Director of Engineering
Laboratory Precision Ltd. ©