How are Latex balloons imprinted?

Most Latex balloons manufactured today are imprinted using one of three popular methods, depending upon the quantity, balloon size, delivery date, quality of the imprinting desired and/or other factors involved in the order. Contrary to popular belief, most imprinted Latex balloons manufactured these days are not hand stamped in a deflated condition as they once were! Rather, most are usually imprinted in an inflated state and are either sprayed, offset or screen printed.
When balloons are inflated for printing, they are only inflated to approximately 75 to 80 percent of the total capacity. This gives the proper tension to the surface of the balloon for the ink to successfully transfer. Specialized "balloon friendly" inks must also be used that will penetrate (and adhere) to the surface of the balloon but yet not penetrate completely through the Latex into the interior, causing holes. Once placed on the balloon, the ink is then allowed to dry and the balloons are then deflated, drummed in rotating industrial dryers (to shrink them back to their "like new" condition) and then packaged.
One popular method of imprinting creates what the Pioneer Balloon Company (makers of the popular Qualatex® line of balloons) calls a spray balloon. In this process, balloon ink in various colours is simply sprayed onto balloons by a machine after automatically inflating them. The inflated balloons are rotated as the ink is sprayed on, usually in some form of recurring, all around pattern. The more popular Qualatex patterns include multi-colored polka dots, squiggles, stripes, stars, music notes, candles, etc. These sprayed-on patterns result in an image that is not nearly as sharp as other, more labor intensive imprinting methods when the balloon is fully inflated for use. So, while this form of imprinting is a bit less expensive than the more labor intensive forms of imprinting, it also results in a less "bold" imprint on the balloon.
The next imprinting method is a form of offset printing. In this process, balloon ink is applied to a plate which reads right, the plate then transfers the ink to a printing drum, and the image reads wrong. The inflated balloon is then rolled across the printing drum transferring the image to the balloon. The image once again reads right.
A third, and increasingly popular method of printing (but probably the most labor-intensive) is called silk screening. In this process, a silk screen (onto which an image has been etched) is laid over an inflated balloon and balloon ink is then forced through the image area mesh in the screen and onto the balloon. The silk screening is usually done by using a holding device for the balloon that looks very much like a ordinary wooden box. A worker manually places an inflated balloon into the box and then slightly compresses the surface of the printing area of the screen onto the balloon prior to applying the ink with a roller-like device. This process may be repeated multiple times for a single balloon depending on how much of the balloon is to be imprinted (front, back, top, all around, etc.) This type of screening can also be done with an automatic machine on small to medium size balloons. Once the image(s) are placed on the balloons, the balloon is released and deflation begins. However, by the time the balloon is deflated, the ink must be dry in order to prevent offsetting it onto other balloons in close proximity. To speed this process along, newly imprinted balloons are sometimes placed (neck first) into a conveyor belt device that moves the balloons beside a line of heaters to help dry the ink as the balloons deflate.
As you can see, the process of imprinting balloons is a laborious, often manual (human-tended) activity. This is why imprinted printed latex balloons are so much more expensive than unprinted balloons to produce.