When silk-screened marks start failing in the field, it's rarely the ink that gets blamed first. Production teams troubleshoot pre-treatment processes, adjust cure times, and experiment with different ink formulations. But for manufacturers marking polypropylene and other low-surface-energy plastics, the problem often isn't execution. It's the marking method itself.
AFM Engineering discovered this firsthand when one of their customers kept rejecting entire lots of polypropylene parts because the silk-screened markings were coming off. The solution wasn't better ink or more consistent pre-treatment. It was switching to hot stamping with steel dies from Durable Technologies.
Why Does Silk Screening Fail on Polypropylene and Low-Surface-Energy Plastics?
Silk screening relies on ink adhesion to the substrate surface. For that adhesion to work, the surface needs adequate surface energy to allow the ink to wet and bond properly. Polypropylene, polyethylene, and similar plastics have inherently low surface energy, which means ink wants to bead up rather than spread and adhere.
Manufacturers try to compensate for this through surface pre-treatment processes like corona treatment, flame treatment, or plasma treatment. These methods temporarily raise the surface energy so ink can bond. The problem is that pre-treatment effectiveness varies based on treatment intensity, time elapsed between treatment and printing, environmental conditions, and the specific resin formulation of the plastic being marked.
Even small variations in any of these factors can produce inconsistent results. A part that passes inspection on Monday might fail on Thursday because humidity levels changed or the pre-treatment equipment drifted slightly out of specification. When you're marking safety warnings, child hazard labels, or regulatory compliance information, "usually works" isn't good enough.
The ink itself also presents challenges. Silk screen inks for low-surface-energy plastics require precise formulation and application. Too thin, and coverage suffers. Too thick, and the ink may crack or peel during part handling or end use. Cure times and temperatures must be tightly controlled, adding another set of variables that can introduce defects.
What Are the Real Costs of Inconsistent Part Marking?
Rejected parts are the most visible cost of marking failures, but they're rarely the full picture. When a customer rejects an entire lot because markings are coming off, the direct costs include scrapped inventory, expedited replacement production, and premium shipping to meet delivery commitments. These costs add up quickly on high-volume production runs.
The indirect costs often exceed the direct ones. Quality teams spend hours investigating root causes and implementing corrective actions. Production schedules get disrupted as resources shift to rework or replacement orders. Customer relationships suffer when quality issues repeat, even if each individual incident gets resolved.
For manufacturers serving regulated industries, marking failures create compliance risk. Child warning labels on consumer products must remain legible throughout the product's useful life. Medical device markings must withstand sterilization and handling. Automotive component identification must survive under-hood temperatures and chemical exposure. When marks fail in these applications, the consequences extend beyond customer complaints to potential regulatory action and liability exposure.
There's also the hidden cost of process complexity. Silk screening low-surface-energy plastics requires maintaining pre-treatment equipment, training operators on proper procedures, storing and handling specialized inks, and running quality checks at multiple process stages. Each of these adds labor, equipment, and consumable costs that accumulate over time.
How Does Hot Stamping Create Permanent Marks on Difficult Plastics?
Hot stamping works through a fundamentally different mechanism than silk screening. Instead of relying on ink adhesion to an unprepared surface, hot stamping uses heat and pressure to transfer pigmented foil onto the substrate. The combination of temperature and mechanical force creates a bond that doesn't depend on surface energy characteristics.
When a heated die contacts the plastic surface through hot stamping foil, several things happen simultaneously. The heat softens the plastic surface slightly, making it receptive to the foil's adhesive layer. The pressure forces intimate contact between the foil and substrate. The pigment layer transfers from the foil carrier to the part, creating a permanent mark that's embedded in the surface rather than sitting on top of it.
This process eliminates the pre-treatment step entirely. Polypropylene parts can go directly from molding to hot stamping without corona treatment, flame treatment, or any other surface preparation. The heat and pressure of the stamping process handle surface oxidation and create the conditions needed for permanent marking in a single operation.
The resulting marks are significantly more durable than silk-screened printing. Because the pigment is transferred under heat and pressure rather than simply deposited on the surface, it resists abrasion, chemical exposure, and environmental degradation. Parts can be handled, packaged, and shipped without concern that markings will rub off or fade.
How AFM Engineering Solved a Silk Screening Quality Problem
AFM Engineering, located in Santa Ana, CA, specializes in refurbishing, rebuilding, and selling hot stamping and other manufacturing processing equipment. When their long-time hot stamping steel die supplier no longer met their quality and professional requirements, they searched the market and found Durable Technologies.
"Durable Technologies makes a first-class hot stamping steel die. We've used them for a few years, and they do it right; there has never been a problem with anything they have made for us", says Dick Olhoffer, Sales Manager at AFM Engineering.
One recent project illustrates the marking challenge that hot stamping solves. Durable Technologies manufactured steel hot stamp dies designed to be 12" long and 2.5" wide for marking unique polypropylene parts that were previously silk-screened.
The polypropylene parts needed to be pre-treated for silk screen printing, but this process was inconsistent, and the printing would come off. This defect was a major issue because the end customer would reject the entire lot if any markings came off the parts.
With hot stamping, heat and pressure take care of any oxidation on the surface, and the marks are permanent and much more consistent. The switch eliminated the pre-treatment process entirely while producing marks that the end customer could rely on throughout the product's service life.
AFM Engineering rebuilds and refurbishes hot stamping, pad printing, and ultrasonic machines for consumer goods, housewares, medical, and automotive markets. Hot-stamping steel dies are used to mark logos, text, child warning labels, part numbers, and just about any other form of direct part marking for product identification.
Why Choose Steel Hot Stamping Dies for Plastic Marking Applications?
Hot stamping dies can be manufactured from several materials, including magnesium, brass, and steel. For plastic marking applications involving production volumes beyond short prototype runs, steel offers significant advantages in durability and per-impression cost.
Steel dies are unmatched in durability and are ideal for marking harder plastics or long production runs. Durable Technologies' steel dies are made from hardened and tempered tool steel, which keeps replacement costs to a minimum by extending die life across hundreds of thousands of impressions.
The hardness of properly heat-treated steel maintains crisp character edges and fine detail throughout the die's service life. Where softer die materials might show wear after tens of thousands of impressions, steel dies maintain mark quality over much longer production cycles. For manufacturers running multiple shifts or high-volume production, this translates directly to lower tooling cost per part.
Steel also performs well across the temperature ranges used for marking different plastic formulations. Polypropylene typically stamps at temperatures between 350°F and 450°F, depending on the specific resin and foil combination. Steel dies handle these temperatures without dimensional distortion or surface degradation, maintaining consistent mark quality from the first impression to the last.
Custom logo dies can be produced with any wording or design, in brass or steel, for stamping applications where your text remains constant. Durable Technologies' logo dies are often made type high (.918" / 23.3 mm) but can also be machined to any size to fit your present type holder.
Which Industries Benefit Most from Switching to Hot Stamping?
Any manufacturer marking polypropylene, polyethylene, or other low-surface-energy plastics should evaluate hot stamping as an alternative to silk screening. The benefits are most pronounced in applications where marking durability is critical, and lot rejection creates significant cost exposure.
Consumer goods manufacturers use hot stamping to apply brand logos, product identification, and required safety markings to plastic housings, containers, and components. Child warning labels and hazard symbols must remain legible throughout product life, making the permanence of hot-stamped marks particularly valuable.
Housewares producers face similar requirements for product marking. Kitchen items, storage containers, and household products often require branding, material identification, and care instructions that must withstand regular use and cleaning. Hot stamping provides marks that won't wash off or fade over time.
Medical device manufacturers operate under strict regulatory requirements for device identification and traceability. Markings must survive sterilization processes, handling in clinical environments, and extended storage. Hot stamping's permanent marks meet these requirements without the consistency concerns associated with silk screening on medical-grade plastics.
Automotive suppliers mark plastic components with part numbers, date codes, supplier identification, and material specifications. Under-hood components face temperature extremes and chemical exposure that can degrade surface-applied markings. Hot-stamped marks embedded in the plastic surface maintain legibility throughout vehicle service life.
How Do You Get Started with Custom Hot Stamping Dies?
Durable Technologies manufactures and supplies an extensive array of brass and steel type and dies, printers' type, monogramming type, Kingsley® wire marking type, heat shrink sleeving type, type holders, magnesium dies, branding irons and dies, and much more.
Every custom die project starts with understanding your specific marking requirements. What information needs to be marked? What are the dimensions of the marking area? What plastic material are you marking, and what foil and temperature combination works best for your substrate? What production volumes do you anticipate, and how does that affect die material selection?
Our engineers work with customers to specify dies that match application requirements and integrate with existing equipment. If you're currently silk screening and considering a switch to hot stamping, we can help evaluate whether your current hot stamping equipment will handle the new application or whether modifications might be needed.
For manufacturers dealing with silk screening quality issues on polypropylene or other difficult plastics, the conversion to hot stamping often pays for itself quickly through reduced scrap, eliminated pre-treatment costs, and improved customer acceptance rates.
Contact us about your hot stamping die requirements.
