Tablet Printing Machines
What is the best shape for precise positioning systems?
The best shape is a sphere. The more geometry a product has, the more difficult it becomes to manipulate it. The following shapes are listed in order of descending degree of difficulty for precise positioning:
- Simple Caplet
- Bi-convex Caplet
- Shapes (Squares, Rectangles, Triangles, Pentagons, etc.)
Is the product’s shape a determining factor?
A product’s physical appearance is usually described as being “dimensional”. A sphere being one dimension, a flattened sphere becomes a tablet with two dimensions, an elongated tablet now becomes a caplet with three dimensions, and so on. The more dimensions a product has, the more manipulation is required to orient or position it to perform the printing and packaging task. Score lines and debossing on caplet shapes requires an even number of characters, to “straddle” the score. Scored round tablet shaped products require special evaluation.
Compressed products all have straight sides due to the compressing of the granulation or compound within a set of punches and a die. These straight sides are normally referred to as the “belly band”. The thickness of the compressed product and the shape of the top and bottom surfaces determine the size of the “belly band” after compression. The wider this band becomes, the more difficult it becomes to determine if the product wants to lie down, or stand on its’ edge. It is to the designer’s advantage to design the tooling so as to minimize the possibility of the product standing on its edge, to eliminate “side printing”, which is not desirable. If minimizing this bandwidth cannot be implemented, it is strongly advised that there be an absolute minimum of .100″ inches (2.54mm) difference between the width and thickness of the compressed product. (The width should be larger than the thickness.) This will give the product an identity. The greater the width-to-thickness ratio, and the smaller the “belly band”, the greater the success rate of proper product positioning.
Can products have score lines or embossing and still be printed successfully?
Score lines and embossing WILL affect printing success. If the product has a score line, the printed logo will need to “straddle” the score lines eliminating the need to print “into” the depth of the score. Product MUST be evaluated prior to a decision to score or emboss.
What are the best curve radii for the product?
The selection of the curve radius is dependent on the proximity of one product to the next product. A high crowned product requires more wrapping area of the offset roller. A dense pattern of high crowned products tend to “steal” more available product contact area from the product next to it, as the offset roller wraps around the product surface. Evaluation is required.
Is it possible to print two sides?
Yes, it is possible to print on two sides.
Is it possible to print in more than one color?
Yes, it is possible to print in several colors. One and two-sided printing enables printing of one or more colors on each side. Tablet shape and color placement must be reviewed to determine optimum printer design.
What type of ink is used? (Composition)?
The ink to be used is the combined responsibility of the product and ink manufacturers. The composition of the inks needs to be “married” to the composition of the product and product surface, and is dependent on environment.
Who is the ink supplier? Is there more than one supplier?
There are several ink manufacturers. The choice is up to the purchaser. Ackley Machine would rather not be in the position to make any specific recommendations; therefore we leave the choice up to the purchaser. We DO recommend that inks chosen contain, even in trace amounts, all ingredients that may be required to “tailor” the ink performance as, or if, required by regulations. This will eliminate the need to re-submit to governing authorities if the need arises.
How does the ink quality compare between different ink suppliers?
Different ink suppliers may have different “recipes”, and they are usually proprietary. Ink quality can vary among ink suppliers. The “grind” (particulate size) and types of solvents or carriers can affect quality.
Which colorants are used in the printing inks?
The product manufacturing’s engineering or marketing departments, along with the manufacturer of the ink, determine the colorants used in the inks.
Are inks approved worldwide?
Some coloring materials and solvents are allowed and, not allowed in some countries. The ink manufacturer should know and supply this information.
What are the most important specifications of the ink to control performance?
The most important ingredients in a printing ink are the solvents, or additives that control the drying time of the ink, such as SDA 3A, I.P.A, Normal Butyl, Propylene Glycol, etc. As mentioned earlier, it is highly recommended that all important ingredients exist in the submitted inks.
Are room temperatures and humidity a factor in controlling print quality?
Temperature and humidity can definitely affect printing success and requirements for ingredients must be taken into account. Normal drying environments are generally 65-75°F and 45-55% R.H. There are exceptions. For example, Ackley has a customer whose product was extremely hydroscopic, and required the R.H. to be a maximum of 17%. Ackley also has customers in places such as Puerto Rico, Korea and China, where the R.H. sometimes approached 85-90%. If the inks are developed properly, all of these conditions can be dealt with easily. Another factor impacting dry time is air movement within an area. Direct exposure to heating, air conditioning and ventilation ducts will accelerate drying of the ink, and cause premature loss of critical solvents.
What is the shelf life of inks, and are there tests to prove the shelf life of inks?
The ink manufacturer should provide shelf life information and tests to prove shelf life.
Is ink used batch-wise, or is it discarded after each run?
Generally inks are produced in single, segregated lots, in an amount suggested by the ink manufacturer or established by the requirements of his customer. Each product batch should be printed with a procured amount of ink, and any excess (opened) ink discarded to avoid any cross contamination to subsequent product batches. This way any problems that may arise will be segregated and can be quarantined.
What is the cost of printing inks?
The ink manufacturer determines the cost of printing ink. Some colorants are commonplace, and some are very expensive. A container of ink goes a LONG way, as demonstrated by the study below:
There was a study done in cooperation with a pharmaceutical manufacturer and an ink manufacturer to determine the average weight amount of the dry solids remaining on the surface of a printed product. Inductively coupled, plasma atomic emission spectroscopy (ICP-AES) was used to quantify the amount of ink transferred to printed tablets.
The reported values are the average of five replicated samples, of 15 samplings each, which provides an estimate of the error of the method. The test results of the study determined that deposits on a single product were:
- 17.86 µgr (micro grams) – low limit
- 29.47 µgr – high limit
- 23.69 µgr – average
A previous calculation, performed at Ackley Machine Corporation, in January of 1994, was prompted by an inquiry from an Australian confectionary manufacturer, regarding a sugarcoated lentil shaped product. Their request was for the amount of remaining ink residuals in parts per million. Result of this calculation revealed:
- Colorant, .0000136gr =14 PPM.
- Food Grade Shellac, or methocel, (the binder) .0000319gr = 32 PPM.
These values, when incorporating average, common size print windows, can comfortably be quoted as realistic approximations for average printing applications.
Printing & Coating
Is there a relation between surface roughness and print quality?
Surface finish does affect print ability. A smooth surface is preferable. An offset roller may not always be able to print into pitted or eroded areas. See the previous discussion under Tablet Shape “Score lines and embossing.”
Should product surface be coated?
Product should be coated to increase lubricity, improve fill rates and most importantly, prevent the possibility of “dusting” and fouling equipment, printing roller and ink. Dusty product WILL shorten effective, productive printing sessions because of the need for more frequent cleaning breaks.
Is there a relation between coating color and ink color?
Surface color and ink color is a marketing call. Things that may be so obvious that they are overlooked, such as lighting conditions (fluorescent, incandescent, daylight, etc.) and even color blindness can play a very important part in determining if the print is even visible to the viewer!
Is there a quality impact if the wrong coating is used?
There is an impact if the wrong coating is used. Ink and product surface MUST be compatible. Certain inks may attack an incompatible surface causing breakdown and premature dissolution. Adhesion may be affected, fading may occur and chemical reaction may change the integrity of the drug.
We would like to use our own “homemade” coating. Will it be compatible?
The “homemade” coating should be discussed with the ink manufacturer.
Is product printing a reliable process?
Tablet printing can be reliable if the process is thoroughly and properly planned and executed.
What are the critical parameters to control to reduce the frequency of operator intervention?
Same as above. Critical parameters would be the performance of the ink; the integrity of the coating and the quality of the product; absence of broken pieces, lumped and twinned, etc.
Can printing be a continuous process, without maintenance of ink or rollers?
The extent of starting and stopping must be defined. Ink transferred from the printing cylinder to the offset roller must be transferred to the product continuously, or the ink will build up on the offset roller and it will require cleaning. If the printing cylinder is stopped and allowed to remain in ink in the tray, the ink will dry and require vigorous cleaning to remove the ink.
What actions are required when leaving, or stopping – starting the printing operation?
If stopping the printing operation for any considerable length of time, the offset roller should be thoroughly cleaned, and the printing roller speed reduced to a low, idling speed. Depending on the drying time and the viscosity stability of the ink, an amount of solvent may need to be added to the ink pan so the ink will not dry up or over-thicken during the operator’s absence. Insure that the rollers are separated so as to discontinue the transfer of ink for print roller to offset roller. If the printer is stopped with ink in the pan, the ink will dry and harden on the roller and be difficult and time consuming to remove. If the rollers are left in contact for any length of time without rotating, an irreversible flat spot may develop. This will greatly affect print and quality.
Are stability tests conducted to insure the integrity of the product and ink?
The product manufacturer’s S.O.P.’s address this issue.