Vulcanized rubber seals
The traditional red rubber stamp that everyone knows will have been made in a vulcanizing press. The first rubber stamp vulcanizing press was patented in 1890 by Charles Schultze in New Orleans, USA. Vulcanization is today one of the most cost-effective methods of making rubber stamps for mass-produced stamps. Each batch of stamps is produced using one mold. This manufacturing method is more suitable for making stamps where the same molds are used over and over again. Making custom seals with a vulcanizing press that requires ‘one time’ molds will significantly increase the cost of manufacturing.
Make the mold: Before a mold can be made, you must have a master plate made of metal or polymer, the master plate is embossed (the design is raised) to make an impression in the mold. Having a master plate made each time a mold is required is what increases the cost of manufacturing vulcanized seals. Pressing the master plate into a Matrix plate creates the mold that will accept the rubber. Heat and pressure are applied to the master plate and die within a vulcanizing press. The Matrix follows the shape of the relief provided by the master plate, which then hardens as it cools.
Rubber Stamp Making: Stamp creation is a simple process once the mold is made. The raw rubber stamp gum is placed on top of the mold and then placed inside the stamp press. Hydraulic pressure is applied to the rubber and mold from inside the stamp press, causing the rubber to melt in the areas of the mold containing the images and text, curing and hardening in about 10 minutes. Once cured, the rubber sheet is removed from the mold and cut into individual stamps to be attached to the supports.
The cost of a vulcanization system is approximately $12,000 AUD
Advantages – Low production cost for mass produced stamps, good ink transfer.
Disadvantages – Production cost of master plates and custom stamp molds.
Laser Engraved Rubber Stamps
The traditional raw rubber used to vulcanize stamp dies is quite unacceptable for the production of laser stamp dies, the laser process requires a very uniform thickness and blemish-free surface to produce an acceptable printed image from a stamp die. The rubber must also undergo a specific curing process before it can be exposed to the high temperature of a laser beam.
The depth of the engraving is determined by the speed of the laser, its power and the density of the rubber. For example, a 50 or 100W engraver will engrave rubber deeper and faster than a 25W machine, which may require a second pass to achieve a similar result. Usually supplied in the form of an A4 size sheet, a good quality laser rubber is required to engrave stamp dies and should also have adequate compressive strength and ink transfer properties.
To facilitate the engraving process, it is necessary to remove the excess dust that is constantly created by the laser cutting action with an efficient exhaust filtration system. Since very few, if any, CO2 laser engraving machines were initially designed to engrave and cut rubber, installing and maintaining an effective dust extraction system pays dividends in the long run. Mirrors, lenses, and any exposed contact surfaces should be thoroughly cleaned as part of a regular maintenance program. Any neglect in this area will be detrimental to the overall smooth operation of the laser, as the build-up of dust and debris will affect the efficiency of operation and the quality of the finished stamping die. The lasers are controlled directly from a computer, the software drivers supplied with the lasers work with many graphics programs such as CorelDraw.
The approximate cost of a 25-watt laser suitable for making stamps is $40,000.
Advantages: production is computer controlled, custom stamps can be made easily
Disadvantages: High capital investment, maintenance and running costs will be much higher than vulcanization or polymer manufacturing methods.
liquid polymer rubber stamps
Converting rubber stamp polymer from a liquid to a solid to make stamps is quite fascinating. Polymer stamps are made between two sheets of glass using precisely controlled ultraviolet light that passes through a negative containing the stamp design and solidifies the polymer. Negative production has been simplified with the introduction of water-based negative technology, photographic chemicals to produce negatives are now a thing of the past.
The first step in making polymer rubber stamps is to print your images, clipart, or text on Vellum, a nearly transparent, film-like paper.
To produce quality stamp designs you must use a laser printer, bubble jet printer inks are translucent and allow UV light to pass where it shouldn’t. Water-based negatives wash off easily after being exposed for a few minutes in a UV exposure stamp machine.
Polymer contained in a sachet is now replacing the old cumbersome method of using foam tape to create a dam and pouring rubber seal polymers. Sachets have also addressed the age-old problem of removing air bubbles from poured polymer.
The negative of your artwork and the polymer bag are sandwiched between two sheets of glass 2-3mm apart, which are then exposed in the machine for a few minutes. Once exposure is complete, it is a simple process of opening the envelope and washing off any excess unexposed polymer before returning the stamp to the machine for a 10 minute cure. Once the stamps are cured, they can be cut individually. Polymer envelopes are available in a variety of sizes up to A4 size.
Processing time is about 30 minutes for a batch of polymer stamps.
The cost of polymer stamp making machines ranges from $3,500 AUD for an Australian made unit designed specifically for stamp making to $15,000 AUD high-end imported units with computer controlled flushing.
Advantages: Lower capital investment, polymers make almost transparent stamps, making them ideal for scrapbooking and card making. The relief of the stamp can be easily controlled during exposure.
Disadvantages: Early polymers did not accept inks as well as polymers available today; this, in addition to being a new technology, caused initial resistance to polymer seals.
Summary
Most of the large stamp manufacturers have a combination of the above equipment. Unmounted rubber stamp dies produced by any of these manufacturing methods can be cut and affixed to simple hand stamps, date stamps, or self-inking stamps. Craft stamps are typically affixed to wood blocks or, in the case of polymer stamps, affixed to clear acrylic blocks with InstaGrip mounting mat or adhesives. Various manufacturers produce stamp holders. Astron Industries in Australia manufactures the ‘Vuestamp’ clear hand stamp and also distributes the Ideal range of self-inking mounts. Other brands of self-inking mounts are Trodat, Colop and Shiny.