Surface Satisfaction: How Silicone Additives Keep Consumer Goods Looking Beautiful
Silicone additives are multi-tasking technologies.
In the aftermath of the 2008 recession, consumers are spending again, but not in the same way. According to Consumer Reports, “…we’re not the same old spendthrifts we used to be; this harrowing economic era has changed America’s buying habits, perhaps permanently.”1 One manifestation of this can be seen in consumers’ expectations of long-term quality and aesthetics from the big-ticket items they purchase. As noted by ForResidentialPros.com, “Though appliance upgrades are on the rise, that doesn’t mean consumers are buying blindly. They are still looking for high quality products and good value, manufacturers say.”2
Whether it’s a new dishwasher, the latest tablet device or even home medical equipment, consumers expect the item to retain its attractive appearance over a long period of time. With so many components of various consumer products made from plastics and composites, it is more important than ever to ensure these materials can resist scratches and marring, withstand exposure to ultraviolet (UV) radiation, avoid surface stickiness that attracts dust and dirt, retain texture and a consistently glossy or matte finish, and repel potentially damaging moisture.
Filling Plastics’ Performance Gaps
While many plastics offer some aesthetic attributes such as colorability, gloss and clarity, most can benefit from the enhancements provided by silicone additives. For example, resins such as polycarbonate (PC)—which are used for electronic device housings and touch screens—need protection against scratching that can dull their surfaces or affect their clarity and optical quality.
Another example is water repellency. A number of plastic resins, such as polyamide (PA) and polyester, tend to absorb water, and the incorporation of mineral fillers and/or glass fibers can make the situation worse. Water absorption can reduce mechanical properties, leading to accelerated aging. Further, moisture uptake can affect the appearance of the component. Parts made from PA can be over-engineered to counter the negative effects of water absorption; however, this translates into added costs.
Still another scenario is the development of surface tackiness that can attract dust and grime, dulling the product’s color and shine. In molded polypropylene (PP) containing organic slip additives, after exposure to UV light, the organics can migrate to the surface and exude an oily substance that collects dust and fingerprints, reduces gloss and causes yellowing.
Silicone Additives for Superior Surfaces
Silicone additive technologies offer many different ways to improve the surface aesthetics of plastics and composites used in appliances, electronics, medical equipment, automotive parts and more. Further, silicone technology helps to maintain these attributes over the long term.
A scratch mark is the result of two phenomena: a ductile failure that leaves an indentation, and a brittle failure that leaves a visible, white mark. These marks can be even more noticeable in talc-filled plastics when scratching exposes the white talc filler.
Silicone additives can prevent or minimize scratching and marring of polymer surfaces in applications ranging from electronic device covers to appliance handles, buttons and control panels. We have specifically designed silicone additives that migrate to the surface of the resin, self-level and anchor themselves to the plastic matrix during the melt phase of processing. This action decreases surface coefficient of friction (COF), so sharp or abrasive objects tend to slide off the part rather than catching on and penetrating the surface. Because they are soft, the silicone molecules absorb some of the stress and, as such, reduce the brittle failure.
As an added benefit, silicones can be used to improve surfaces by contributing a soft, silky feel that enhances haptics.
For polyolefins, such as polyethylene (PE) and PP, silicone master batches impart scratch resistance and improved processability at low loadings that avoid compromising mechanical properties of the resin.
Additives that prevent exudation
Migration of plastic additives to the exterior of the part surface can create a greasy or sticky film that acts as a dust magnet. In major household appliances, stickiness on door handles, grips, touch panels and screens can dull surface gloss, show fingerprints, cause an unpleasant tactile sensation and require constant cleaning. In small appliances such as irons and blenders, and in medical devices and equipment, a greasy surface on handles and grips can also be a safety hazard. The migration process, called exudation, is an undesirable side effect of organic waxes used to impart slip properties to plastic resins. In addition to attracting dirt and dust, exudation of waxes can create fogging and odors.
Unlike these organic slip additives, silicone technologies remain anchored in the resin matrix after migrating to the surface. In other words, they will not cause exudation. This property, together with the excellent slip performance of silicone additives, makes them a better choice for improving surface quality in appliance parts, electronic device cases and medical equipment housings, handles and controls.
With a few exceptions, such as acrylics and polyether ether ketone (PEEK), commonly used plastic resins are not inherently UV stable. Ultraviolet rays interact with a polymer’s chemical bonds to form free radicals, which then react further with oxygen in the atmosphere. As a result, exposed surfaces of products may discolor, fade or crack. Understandably, this degradation can be a great disappointment to consumers who expect their appliances, electronics and other products to maintain their original, attractive appearance.
Just as many resins themselves are sensitive to UV light, additives used to enhance the properties and processing of these plastics can also exhibit instability under UV exposure. In particular, organic waxes such as erucamide, which enhance slip performance, are highly sensitive to sunlight. For instance, traditional talc-filled PP compounds containing organic slip additives can develop undesirable stickiness or tackiness after just a few months of UV exposure.
In contrast, silicone-based slip additives are stable when exposed to UV radiation, helping to prevent surface aging. For example, in a Kalahari-type test protocol on the surface of a talc-filled PP copolymer, our siloxane additive showed no exudation, delivering higher UV stability compared to two types of organic additives: erucamide and oleamide.
Water absorption by plastic components can affect part dimensions and mechanical properties, accelerate aging and degrade performance of the end application. Besides the fact that some resins such as PA, polyester and PC absorb significant moisture, many inorganic fillers used in compounds are also highly hydrophilic.
When PA absorbs water, the results are swelling of the polymer and a reduction in modulus. In polyester, the initial impact is swelling, but then, as soluble materials leach out, the resin shrinks. In either case, water absorption can change the dimensions of parts whose fit is critical. Because silicone is a highly hydrophobic species, silicone-based additives can prevent moisture uptake as they are blended or reacted with both the filler and the resin matrix.
In mineral-filled polymers, water can affect the interface between the two materials, causing stress cracking or corrosion. This process can accelerate degradation of the part surface. In filled compounds, next-generation silicone additives can impart hydrophobicity by competing with water molecules for the mineral surface. This prevents water from clustering in droplets or forming a film at the interface.3
The plastic components of appliances and equipment that are exposed to moisture— whether for a range, washer, dishwasher or a home medical device used in the bathroom—need to be enhanced with hydrophobicity agents. Silicone additives not only inhibit water absorption, they also improve the dispersion and de-agglomeration of inorganic fillers.
Silicone additives are multi-tasking technologies. In addition to improving surface appearance in many different ways—including imparting smoothness and silkiness—these additives deliver extra value. First, they enhance processability by avoiding die build-up and lowering screw torque in extrusion, and by increasing flowability and mold release in injection molding. The benefits include faster throughput, fewer interruptions for maintenance, reduced scrap, lower energy costs and higher productivity.
Second, they often enhance other resin properties besides surface quality. Silicone additives can add flame retardancy, modify impact performance and control light diffusion in optical applications. They can also reinforce materials by optimizing dispersion of compounds and improving compatibility between inorganic fillers and organic polymers.
Silicone additives are also well known for their high performance at low loadings, which minimizes negative impact on the mechanical properties of the resin and helps boost cost-effectiveness.
As consumers resume spending following the 2008 recession, they are placing greater emphasis on the long-term value of major purchases such as appliances and electronics. The best way to maintain the surface quality of plastics used in these applications is to incorporate silicone-based additives. These versatile agents can prevent or minimize scratching, combat water absorption and increase resistance to UV degradation. Unlike organics, silicone additives do not cause surface exudation that attracts dust and dulls the finish of plastics. Further, these additives boost surface aesthetics by contributing a silky, soft tactile feel.
How American consumers shop now. Consumer Reports. September 2014. http://www.consumerreports.org/cro/magazine/2014/11/how-america-shops-now/index.htm
Elizabeth Richards. Appliances Favor Flexible Designs, Smart Technology. ForResidentialPros.com. October 9, 2013. http://www.forresidentialpros.com/inspiration/product-trends/article/11149454/kitchen-appliance-trends-favor-flexibility-energy-efficiency-and-smart-technology
Interfaces in Polymer Matrix Composites: Composite Materials, Volume 6. Edwin P. Plueddemann, ed. https://books.google.com/books?id=6KRmDAAAQBAJ&pg=PA200&lpg=PA200&dq=how+do+silicones+prevent+water+absorption+in+plastics&source=bl&ots=Sr13geMjm7&sig=G1cMLOPG2zuoPWVt4w8FSsBpJF4&hl=en&sa=X&ved=0ahUKEwi8xZDkh9jNAhXNzCYKHbJyAe04ChDoAQgbMAA#v=onepage&q=how%20do%20silicones%20prevent%20water%20absorption%20in%20plastics&f=false