A description of different types of glass used in pharmaceutical packaging production and usage
Types of Glass:
- Type I - Borosilicate Glass
- Type II - Soda Lime Glass (surface treated)
- Type III - Soda Lime Glass
A specific combination of limestone, soda ash and other natural substances with approximately 70% of sand are used in the production of virgin glass quantities of these additives will vary depending on the required properties of the glass being made.
An additional component is required in the manufacture of soda lime glass, the addition of recycled crushed glass (known as cullet) is added to the mixture. The quantity of cullet varies with each production run. Cullet helps to decrease the melting temperature and therefore reduces the energy required and the materials required to manufacture glass.
Heat resistant glass known as Borosilicate glass is not used in the recycling process because it is heat resistant and therefore inappropriate, its melting temperature melts at different temperatures when compared with that of Soda lime glass and causes the viscosity of the liquid glass to change during melting.
Techniques for the Production Glass Containers:
Blowing and/or pressing glass is the method that is used to produce glass containers what we commonly referred to as moulded glass products. A moulding machine forces air in to globs of heated glass thereby creating a vessel with the general container shape. The tube shape (Parison) is then manipulated using additional processes to create the desired container shape from the parison.
These additional process are known as "Blow and Blow Press" for narrow containers the parison is formed using compressed air to form the neck finish and shape. The "Press & Blow Process" is used for forming containers with a larger diameter, this involves pressing the glass against a mould with the metal plunger, the plunder is inserted and then air is forced in afterwards.
With the introduction of the "Vacuum assist process", the "Press & Blow Process" is now also used for containers with a smaller mouth diameter. The advantages of this include the ability to manufacture strong lightweight containers.
The formation of tubing glass uses either the Vello of Danner process, this is used to ensure the desired diameter and thickness of the glass is archived by drawing the glass back and forth across rollers.
Conditioning the glass is a vital step, as glass is a super cooled liquid, (it always remains a liquid) when it is formed in to rigid containers it causes extreme stresses to build up within the glass. After the glass containers are created and formed the temperature of the glass needs to be raised once again to remove these stresses within the glass. The containers are placed in an Annealing Lehr, heated to around 1500℉, and slowly cooled to below 900℉. This process removes the stresses from the glass and stop it from shattering.
A tin oxide based mixture or polyethylene coating is applied to the surface of the glass to prevent breakage by abrasion. This mixture is sprayed on the hot surface (hot end treatment) of the glass, this causes a reaction and producing a resilient tin oxide coating. By applying this coating to the surface, the bottles do not stick together and thus preventing breakage. After the glass is treated to a "cold end treatment", whereby prior to application the glass containers temperature is reduced to between 225 to 275℉, this can be washed off from the surface, whereas the hot end treatment causes a reaction with the surface of the glass and therefore cannot be removed by washing.
Finally, an internal treatment known as "Internal Fluorination Treatment" (IFT), the process that makes Type III glass into Type II glass and is applied to the glass to prevent bloom.
Glass containers used in the pharmaceutical industry that use these process include Sirop Bottles (Blow and Blow) and (Press and Blow) Powder Jars Glass Containers.
What is Tubular Glass?
Tubular glass is manufactured in a variety of different diameters usually ranging from 1.6mm to 66.5mm,
A layer of glass is formed around the hollow shaft or blowpipe, it flows in a ribbon like fashion from the hearth and is wrapped around the tube forming a smooth layer of glass around the tube. This "tube" is then drawn over a row of rollers that draws the glass tubing out.