13 March 2014
Raw Materials in Production of Stickers
The origins of the common sticker can be traced back to ancient Egyptians. Competition in busy markets forced people to develop new ways to attract customers to their stall. One method was to plaster or glue a piece of paper onto the wall. They would color the paper with dyes and write the price of the product on it. Thus the beginnings of the sticker were born. Over the years, this simple label was taken and modified, turning into the self-adhesive stickers that we use today. In 1839, a British citizen developed the first adhesive paper, introducing the product, stamps into the world (Jacob). People continued to improve upon the types of adhesives and materials used for the production of stickers. One of the greatest modification of the sticker occurred in North America during World War II. The new technology and findings during the war gave birth to the popular bumper sticker that is widely used today in the political and advertising world (Baker). Today, stickers play an enormously large role in our society. From advertising and supporting a political campaign, rewarding children for the effort in schoolwork and even mailing a letter or package across the country, stickers play an enormous role in our everyday life. This paper maps out the different components and raw materials within a sticker as well as some of the processes used during the production of stickers in order to understand the complexity of such a simple idea that has become integral in our society. The basic components of a sticker consist of three components, the release paper, adhesive and the bodystock.
There are many different types of adhesives that can be used for stickers, but the most commonly used is the pressure sensitive adhesive (PSA). Pressure sensitive adhesives are put on the common self-adhesive stickers that people purchase or print. The original as well as most common PSAs are made out of a combination of natural rubber and tackifier resin, also known as terpene. Terpene is produced from the terpene monomer. Terpene resins have been replaced due to economic reasons but are still considered excellent. Terpene resins may be replaced with solvent resins, in which case, the natural rubber will be replaced with thermoplastic rubbers. Natural rubber consists “of latex, collected from the sap of rubber tree” (Packham Pg 402). Over the years, natural rubber has been replaced with synthetic rubbers such as silicone rubber, butyl rubber, styrene block polymers etc. The rubber is applied to a strong backing, usually regenerated cellulose film otherwise known as cellophane.
The process of making cellophane is as follows: It “is first derivatized with carbon disulfide and sodium hydroxide to an alkali-soluable sodium cellulose xanthate…which is further dissolved in dilute sodium hydroxide” (Paunonen 3100). The liquid is then taken and placed inside a bath of sulfuric acid and sodium sulfate to turn it back into its solid state. Once back in its solid state, the product is called regenerate cellulose/cellophane. Unfortunately, this process produces hazardous byproducts. A new method to dissolve cellulose was developed using an alkali/urea/water mixture. “The films prepared from this…were found to have superior oxygen barrier properties compared to traditional cellophane” (Paunonen 3100). Another method which is more environmentally friendly is called N-methylmorpholine-N-oxide(NMMO)-technology. The pulp is first dissolved without pretreatment, in an NMMO water mixture. The solution is then taken to a precipitation bath for coagulation of cellulose. After this process is completed, NMMO is recovered. (Paunonen 3100).
Other alternative backings such as rigid PVC and polypropylene can be used in place of cellophane. These are used “extensively for general purpose pressure sensitive tapes and many other plastic films and papers are used in specialized products including tapes, labels and decals” (Packham 364). Once the paper or film is created, a permanent non-transferring coating called release agent is applied.
Release liner, typically the first thing you throw away, is the backing of a sticker that protects the adhesive on the sticker. Although release liners seem like a throw away item, it plays a large and important role in the production process of the stickers. Release liner has an impermeable surface and is coated with “material to prevent permanent adhesion to a dry or semi dry resin (Harper 482). This keeps the sticker intact during storage and transportation. The liner contains a property known as release. The release is the agent in which the force of separation between the face material and the release liner is measured (Trias 4). The release value becomes important in the application of labels in the machine. A high release value can cause breakage, stopping the machine from working during application to the sticker. A low release value prevents the sticker from adhering to the release paper, ruining the sticker.
Often times silicone,which is made out of the element silicon, is used to coat release paper/liners to protect transportation and storage of PSA. Silicon itself is the second most common element that is found in the Earth’s crust. The element is never found in its natural state but instead, in a “combination of oxygen and a silicate ion(SO4) in silica-rich rocks such as obsidian, granite, diorite, and sandstone”(Silicon). The application of silicone provides the “anti adhesive treatment” which prevents the liner from permanently adhering to the sticker. “Once silicone has been added to the release liner…(it)will enter a drying tunnel in which cross-linking and polymerization are produced at very high temperatures”(Trias 4).
Release liners are extremely susceptible to heat and humidity and may crease or wrinkle, during production. This is known as cockling. “Eighty five percent of PSA(Pressure sensitive adhesives) are made from wood pulp derived paper” (Thyberg 56) making release papers highly susceptible to cockling, costing manufacturers money and materials. Any liner exposed to cockling must be thrown away because it could damage not only the quality of the liner, but the pressure sensitive adhesive. By using different materials and coatings for release liners, cockling may be prevented. “The first step in handling off cockling is the selection of material of silicon coated release liners” (Thyberg 58). Densified kraft paper is the cheapest and therefore most commonly used material for release paper. Unfortunately, it is also highly susceptible to cockling. By sealing release paper with polyolefin coating, it encapsulates and protects the paper from drawing in moisture. “Polyolefin are thermoplastic resins polymerized from petroleum-based gases” (Guide 2). The basic elements that polyolefin is derived from are hydrogen and carbon atoms (Guide 2). Carbon and hydrogen atoms are bonded together to form high-purity ethylene and propylene gas. These gasses “can be a petroleum factory by-product or they can be extracted from ethane-propane liquefied gas mixtures…from gas fields” (Guide 6). The weight and toughness of the resin depends upon the molecular weight of the atom. As the average molecular weight increases, so does the resins toughness. Alternatives to using polyolefin coating include plastic film liners made of polyester, polyethyleneterphthalate, and other polymers which all absorb less moisture than paper.
As mentioned earlier, bodystock or facestock of a sticker is the material in which the design is printed on. Depending on the type of finish that is desired, different materials can be used. Material used for the facestock may also change the quality of the printed product. Most stickers alternate between the use of paper or PVC. In the case of paper, a varnish or lacquer is applied. Some things to consider when using paper is the weight of the paper; Stickers made with heavier paper are more durable than those made with lighter paper. The weight of the paper determines the paper’s thickness. There are several disadvantages of using paper. According to Boxin Zhao and Robert Pelton, “The paper structural properties, such as surface roughness and porosity, seemed more important than surface chemistry”. They conducted an experiment to “understand how paper properties influence PSA peeling from paper surfaces” (Zhao 861). From their study I found the components of filter paper. Filer paper is composed of “pure cellulose which has a relatively high surface energy” and newsprint from “mechanical pulp which contains about 30 wt% lignin instead of 100% cellulose in filter paper” (Zhao 828). Different coated paper such as semi-gloss or glossy paper can affect the quality as well. Polyvinyl chloride(PVC) is used multiple times in the production process of stickers and in the production of secondary materials used to make stickers such as making PSA. PVC is a common type of plastic that is either rigid or plasticized. Rigid PVC is an unmodified polymer and is used for the facestock. No information was found on the specific type of PVC used in PSA. PVC is made form the vinyl chloride monomer(VCM) which consists of 1, 2-dichloreothylene (ethylene+chlorine from the electrolysis of brine). It goes through the process of polymerization where vinyl chloride monomer is dispersed in water with protective colloid and monomer soluble initiator. Types of dispersing agents include, gelatin, soaps, glycols, pentaerythritol (Andrady 96-97). During the production process of PVC, HCL is removed making it flame resistance due as well as an “… excellent resistance to acids vases alcohol oil and other hydrocarbons” (Harper pg 452).
The cheapest method in printing stickers is the screen printing method. “Screenprinting is characterized by large, solid blocks of opaque color, often with shiny ink surfaces” (Baker 254). Common machinery used in industrial screen printing includes a desk with a screen holder, washing machines, binding and finishing equipment and some prepress equipment1. Other materials involved in screen printing include printing ink, adhesives, coatings, and cleaning solvents. Organic solvents are used to clean excess ink off the screens after use. A porous mesh is often used with a piece of fabric stretched out on top. When the process was initially used, people used silk but people now replace it with other synthetic fabric. This is the reason why screen printing may also be called silk screen printing. DIY methods of screen printing involve the use of squeegee, stencils, pourous mesh, metal frame, paper, cardboard, textile, screen emulsion, screen printing ink, solvent and adhesive, pvc, leather, adhesive and cleaning solution.
Other methods of printing stickers include lithography, and digital inkjet printing. “Offset lithography uses a rubber blanket cylinder as an immediate transfer ink from the plate to the stock” (Baker 255). The inks that are normally used with offset lithography dry quickly and allow “for photorealistic images” because of its four color separation (Baker 256). Digital inkjet printing is currently the most popular way to not only print stickers but also to simply print. The printers are commercially affordable and are used on a day to day basis by companies, students and adults. The inks used in digital inkjet printing are dispersed in a solvent and place within a chamber. “A chamber ﬁlled with liquid is contracted in response to application of an external voltage. This sudden reduction sets up a shockwave in the liquid, which causes a liquid drop to eject from the nozzle” (Singh 673). The force of gravity and expulsion of the ink droplet causes it to soak into the substrate and dries through solvent evaporation. Most digitial inkjet printers use UV ink.
During the early screen printing processes of stickers, solvent based inks were used. When bumper stickers were introduced, daylight fluorescent inks became popular to use. Daylight fluorescent inks are now used in street signs, fire trucks, police cars, ambulances… due
to its reflective properties. For a while, people switched to using water based inks because they were easier to clean and did not cause as much pollution. “Water-based ink utilizes either dyes or pigments in a suspension with water as the solvent” (Plastisol). In the present day, ultraviolet(UV) cured inks are becoming popular. There are two main types of UV curable ink, free radical and catatonic. The difference between the two types, is based on the drying method of the ink. UV cured ink contains conventional pigments in polymeric vehicle and use medium pressure mercury arc lamps. The polymeric vehicle is usually comprised of six materials (Emmett):
1. Various polyfunctional methylol propane triacrylate/ pentaerythritol triacrylate.
2. UV reactive unsaturated polymer such as acrylated urethane polyester oligomer, acrylated epoxy resin oligomer.
3. Photoinitiators such as benzophenone
4. Alcohols or phthalates
5. Hydrogen transfer agents such as triethanolamine
6.misc agents (stabilizers, surgactants, fillers, flattening agents and polymerization inhibitors
The invention of the sticker has changed human life dramatically from the way we organize to the way we decorate. Such a simple idea has created an entire industry devoted to it. From the production of bodystock, release liners and adhesives, stickers are composed of many secondary materials such as synthetic rubber, silicone, PVC etc. The amount of different materials brought together to make a sticker is highly complex and shocking for a simple product that we use on a daily basis.
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12 March 2014
Embodied Energy in the Life of a Sticker
Many people these days use stickers to promote something that they believe in. Based on www.stickerpalace.com, stickers dated back in the European days. It is believed that in the 1880s, most European merchants need to catch customers’ attention to buy goods (stickerpalace.com). These labels then evolved into many type of stickers including bumper stickers, commercial stickers, products labels, and more. At first people used gum paste and then evolve into postage stamps and many other personal preferences. In making stickers, there are several processes of production and the energy that is put into making stickers. There are many forms of energy embodied into the making materials of stickers, distribution process, and waste and management. The major energy embodied within each step of a life cycle of a sticker is electrical, chemical, and thermal energy.
Energy embodied in the production process
Stickers go through many production processes. Many stickers can be produced from individual companies to larger companies. The production process is different due to the fact that these individual companies are more based on human powered and these larger companies are based on machine-powered. Based on the video, “How It’s Made Stickers”, the early stage of making a sticker is the design which is usually being done on a computer. The energy being input to using the computer is electricity. Electricity comes from transforming heat energy released from fossil fuels (energyeducation.tx.gov). These fossil fuels may come in gas, natural oil or gas (energyeducation.tx.gov). The design is now taken to the printing press to be exposed in UV violet light, and then goes through the printing press. Most of these works is done by machines, which run by some forms of energy. This energy are run by electricity as well. According to www.eia.gov, it needs three units of primary energy to generate a unit of electricity. These are coal, nuclear, and natural gas. Fossil fuels and electricity are used in the manufacturing process. Based on the chart from eia.gov, machinery delivered around 18% of energy. This means that the rest of energy is not being used into the production process. The fossil fuels are used to “drive turbines, reciprocating engines, and other prime movers that provide mechanical power for rotating machinery”. This means that the production process of a sticker requires not only electricity, but also man power to help running these machines and other activities that machines cannot do.
Energy embodied in the materials
There are many materials put into making stickers which are essential. The major materials are plastic, adhesives, and ink. The part of the sticker that is being printed on is plastic, but often made out of PVC. PVC is also known as polyvinyl chloride and there are many process of making polyvinyl chloride. Polyvinyl chloride is made out of Vinyl Chloride Monomer. PVC is linked together by “monomer molecules together in the polymerization process”(pvc.org). According to the same source, PVC is made out of ethylene and chlorine, which makes ethylene dichloride, which is the basic of Vinyl Chloride monomer. According to the “Proceedings of the Royal Society of Medicine” by A.W. Barnes, Vinyl chlorides also went through a lot of process to produce PVC to such a solid material. The polymerization is an exothermic process because it requires 60-80 degrees Celsius for it to be heated (Harper and M. Petrie). This process releases HCl, which is Hydrochloric Acid. These polymers that are produced only 70% conversion when being precipitated. It is also believed by Barnes that at this point, the “rate of reaction correspondingly diminishes until at about 92-95% total conversion the speed of polymerization becomes uneconomically slow” which means that the energy that was put to make PVCs are most lost when making the PVC itself (277). Barnes also claims that the polymerization process needs to be above the boiling point, and therefore the “industrial process must be carried out in pressure vessels (at 50oC the vapor pressure of vinyl chloride is ~7 atmospheres)” (Barnes 278). These process is an exothermic reaction, which means that heat energy is being released. As the polymerization progresses, eventually, PVC forms as a powdery product and being added to different additives which will becomes a PVC product. These PVC materials then can be used in many different ways, one of them is to make bumper sticker (pvc.org). The website, thebumpersticker.com claims that bumpers stickers need to be waterproof, so that it will lasts. This water proof material make it easy for bumper stickers to not easily decays.
Adhesives are the most important part when it comes to making the sticker; it is what stickers are called stickers. The production process of making adhesives is divided into four steps. They are: “The application of silicone, the application of adhesives, conditioning, and formation of the adhesive complex” (torraspaper.com). The application of silicone is necessary so that it is possible to apply the actual adhesives, and to protect the adhesives that are being used and for the face materials to be removed from the liner. First we want to know where these silicons come from. Silicons are chemical compounds which are made out of different elements. Silicon is extracted from the earth’s crust such as the sand, which is a primary energy (eoearth.org). Silicon dioxide, which is SiO2, is called quartz, and it is known to be the most pure sand. The other source that can be found in silicon is tac and mica. Sand can be found mostly all over the world, including the United States. To make sand into silicon powder, there are many steps applied to it. According to Grey, Silica powder can be made by burning silica that is made into silicon by heating with coke, which is some sort of coal (popsci.com). Coal comes from the earth as well. This energy being put in into burning the silica is a chemical process because it transforms the chemical form of the product.
The energy required into making adhesives varies from human energy, physical energy, and chemical energy. The adhesives that making it possible to stick is a pressure sensitive adhesive which comes from natural rubber, resins, synthetic raw materials, and additives (Benedect 367-370). Natural rubber comes from Havea Brasiliencis trees that can be found in many Asian countries. The energy embodied making natural rubber into adhesives is mostly man power and kinetic energy. One of the most common adhesives that is used for stickers is the Pressure sensitive adhesives. Pressure sensitive adhesives consist of natural rubber, blended with tackier resin and antioxidant. Natural rubber came from a tree that can be found in many Asian countries such as Malaysia and Indonesia. The trees, which are Havea Brasiliencis Trees which are mostly from Asian countries, are cut in a 20-30 degree angle so that these rubbers can come out of the trees (azom.com). The making of the pressure sensitive adhesives is that by “blending hard resin with “a lower Tg elastomer provides a desirable formulating latitude” (Benedek 367). This mixing includes tackification, cohesion regulation, detackification, and polymer degradation. I have not found the energy being put into the tackification process but it can be viewed as chemical process due to the blending of all sorts of materials to make the pressure-sensitive adhesives. The adhesive itself, however, has a binding force of adhesion and cohesion. Benjamin E. Russ claimed that, “‘when two materials are brought into contact with each other, the surface molecules interact, and rise to attractive forces that may be physical’” (scientificamerican.com). This means, that the bonding itself may be a physical force but the making of these adhesives may be a chemical force.
One of the most common ink on making stickers is Ultraviolet based ink. According to fashionuv.com, UV cured ink is from Ultraviolet radiation, which comes from the sun. This UV cured ink goes through a photochemical process which is energy in a form of light (britannica.com). These molecules absorbing light is called transient excited states. In this process, these molecules transform to another chemical species. These chemical species can combine or transfer with other molecules such s hydrogen atoms and protons. After this chemical process are proceeded, liquid monomers and oligomers are mixed with a portion of photo initiators, and then being exposed to UV energy, Finally, the product hardens in a few seconds.
Energy embodied in distribution process of stickers
The distribution process of sticker’s raw materials and the finished product are similar. The transportation of natural rubber that comes from the trees to many other countries requires ships, trucks, and railroads. These ships require bunker fuel in order for them to transport. Bunker fuel is a type of crude oil, and it needs to be heated in order to be used for ships. These heating process is a type of chemical energy because heat is being transport. It is also a part of a thermal energy because it requires different temperature. During this “fractional distillation, oil refineries can also use catalysts to ‘crack’ the hydrocarbon chains in the crude oil to create specific oil fractions”(wisegeek.com). Bunker oil is then used for ships for large transportations. Based on the information being found on the transportation being used for natural rubbers, it can be assumed that other raw materials may have a similar energy distribution process. The distribution process after these stickers are made is usually shipped to stores or companies are similar to the distribution process of the materials. Because they are numerous private and bigger companies there are, there are also numerous ways of distribution in each companies so the information. I have failed to find the major distribution process of whether the stickers are distributed as a blank stickers or if it is distributed when it is finished. Most of the common ways to distribute these stickers after they are made is through land transfer such as trucks or railroads if stickers are distributed within the country. For railroads and trucks, the fuel that they use is diesel fuel. Diessel fuel comes from crude oil, which is from the earth’s ground (science.howstuffworks.com). This black liquid is called petroleum. This black liquid has different chain lengths that have continuously higher boiling points which can be separated by distillation. The meaning of distillation is “technique of heating a liquid to create vapor which is collected when cooled separate from the original liquid” (chemistry.about). This distillation process is also known as the oil refinery process. During oil refinery process, the crude oil is heated, and the different chains are being pulled out by vaporization to make the different type of fuels. For diesel, it takes 12 or more carbon atoms and the boiling range is 250 to 350 degrees Celsius. Gasoline, on the other hand, is a mixed of alkanes and cycloalkanes and the boiling range is 40 to 205 degree celsius.
Energy embodied in waste and maintenance
The recycling process of stickers is included in all category due to the original purpose of a sticker itself, which is to being stick-on. According to iwanttoberecycled.org, we do not have to worry about recycling stickers because it is already going to be washed away in a heat process. For example, if the sticker is the label of a can, we should not tear it apart because it will be already dissolved in the melting process. The aluminum cans and glass bottles are what usually stickers are put on. The recycling process of aluminum cans and bottles are first they transport it into a recycling place. The energy put into the trucks are from fossil fuel, or oil. Although stickers cannot really be re-used, the great majority of the sticker itself is made out of the polyvinyl chloride which is managed in terms of waste and recycling.
One of the control waste management of PVC products is feedstock recycling. Based on pvc.org, feedstock recycling mixes plastics and packagings, which, 10 percent is from PVC. This feedstock recycling process includes a “thermal cracking” process, which “can be done via hydrogenation, pyrolysis, or gasification”. This “thermal cracking” is when the hydrocarbons are being conduct to “high heat and temperature to break the molecular bond” (wisegeek.org). This gasification process includes a pre-treatment which “consists of a sorting or separation step of the used input that allows adjusting the chlorine content the main waste stream”(pvc.org). Feedstock recycling involves chemical energy due to the thermal cracking process and heat and temperature being involved as well.
The gasification process consists of two sections such as reaction section and product collection (sciencedirect.com). The first section is the reaction section. In stage one, there are two different quartz tube which have different temperatures, “by means of electrical resistances’. There is also an apparatus in between the two stages in this stage. Then, the blend is put into the reactor at a “uniform volumetric rate supplied by an adjustable feed rate screw feeder”. The reactor then produced a charge which is from pyrolysed, which is a decomposition of a material or compound because of heat when there is no oxygen (dictionary.reference.com). This pyrolysis produced this char material which is goes to the end of stage one and combines with steam and oxygen that was also produced from stage one. This mixture, which consists of: “hydrogen, carbon monoxide, carbon dioxide, gaseous hydrocarbons” are all mixed in the package to have time to finish this gasification process.
The second section, which is the product collection, is to be cooled in a water-cooled exchanger. This process is basically to eliminate the chlorine that might have been left in this gasification process. The gas that is being put through two sodium hydroxide gathers these chlorine and the chlorine will be dried with a calcium chloride trap. This calcium chloride trap will sample the gas that and determined the balance of the carbon and the chlorine content. Oxygen is then later introduced into the mixture so that when the mixture is released, we know it is safe for the atmosphere.
The full life cycle of a sticker varies due to the fact that there are enormously many companies that produce their own individual process of making these stickers. The energy that is most being used on is mostly fossil fuels to generate these machineries. For those stickers that are produced by smaller companies, the production process mostly comes from human labor. Crude oil is the primary material for making diesel fuel for the distribution process after these stickers are made. Finally, because of stickers are usually attached to a can or a bottle, people do not re-use stickers or recycle them. Instead, they are being recycled along with the products that they are attached to as well. The life cycle of a sticker is interesting due to the fact that there are many energy being input into making them that you would have never have thought of before.
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March 13, 2014
Pressure Sensitive Adhesives: Waste and Emissions
Stickers are popular because they can spread simple, yet powerful messages, and are available in all sorts of forms, shapes, sizes, and colors. More importantly, they can adhere to multiple types of surfaces. Many companies take this to their advantage to promote and advertise their business, and mass-produce stickers to literally place their logo everywhere. When people buy these stickers, they pay relatively cheaply for them, or not even at all. This goes to say that stickers are readily available and cheaply made. However, an in-depth look into the manufacture process of stickers, or more technically known as “pressure-sensitive adhesives,” will tell a different story. The acquisition, transportation, manufacture, application, maintenance, recycling and disposal of the materials needed to make stickers prove that they challenge environmental demands quite harshly, although several ecologically friendly trends are aiming to fix this.
The manufacture of PSAs refer more to the manufacture of the rubber-like and liquid-like PSA components. Realistically, this manufacture is more of a “chemical and physical modification” to the materials, as these modifications merely allow the use of these materials in a “suitable state,” such as “in solution or dispersion” (Benedek 366). Manufacturing PSAs involves dissolution of natural rubber, and further milling for better solubility (Benedek 367). Resins must be modified chemically to be stabilized, so they are subject to “disproportionation and hydrogenation” (Benedek 367). Synthetic raw materials for PSAs only need to be synthesized and polymerized by special monomers, such as acrylic acid (Benedek 369). The formulation of PSAs means just changing the “adhesive composition, by addition of different macro or micro molecular compounds,” which often don’t require much machinery or high temperatures. Thus, the actual formation of PSAs does not leave much of an ecological footprint.
The maintenance of PSAs, however, are not so fortunate as they require certain conditions in order to remain stable for further production. Polyolefin resins, one of the primary components of PSAs, must be kept cleaned or else they produce poor products. They are shipped to processors “in rail cars, hopper trucks, 1000-and 1,500 pound polyethylene lined corrugated boxes and 50-pound bags” (“A Guide to Polyolefin Extrusion Coating” 8). Additionally, the transportation and storage of adhesives’ liners also present cockling problems. The storage units for release liners must be able to withstand high heats and humidity, because otherwise they would wrinkle and buckle, thus ruining substrates and wasting the plastic and paper materials (Thyberg 1). The transportation and maintenance of these materials show to be quite costly.
A majority of the waste that is left from the manufacture of stickers comes mainly from the printing process. This is largely due to the maintenance required for screen-printing materials, especially solvents and inks. These materials pose as a serious threat to the environment and community due to their physical and chemical characteristics, commonly placing them in the list of hazardous wastes. Hazardous wastes exhibit characteristics of “reactivity, ignitability, toxicity, and corrosiveness” (Andrady 635). Unfortunately, many of these wastes find their way into storm water and freshwater systems and eventually into streams, rivers, and lakes. If these products are placed in municipal solid waste landfills or disposed of on landfills, then there is a possibility of “leachability and groundwater contamination” (Andrady 635). If these hazardous materials are incinerated, they will contribute to hazardous emissions from stack and ash. Therefore, screen printers worldwide are taking on measures in order to preserve and reuse their solvents and inks as much as possible to reduce the amount of waste they leave in the environment.
Maintenance of materials used to print stickers are integral to both the sustainability of the business and the materials themselves. This is done by cleaning, moisturizing, and restoring all the inks and solvents used with each job. Instead of disposing ink after applying them, printers scrape off ink from their screens back into the ink containers. All ink is basically re-usable. No ink should ever be disposed “unless it is on the screen and it is being reclaimed,” but even then, all excess ink should be restored for the next job (“Preventing Pollution in Screen Printing,” 26). Additionally, waste solvents used in cleaning, ironically, make up a big part of the hazardous wastes from screen printers. Maintenance of the print shop proves to take an environmental toll everyday.
Many inks and cleaning solvents used in the printing industry contain hazardous chemicals called volatile organic compounds (VOCs) or hazardous air pollutants (HAPs). VOCs are chemicals that evaporate into the air, then react with sunlight to form urban ozone (smog), which has serious health effects on humans’ lungs. HAPs are chemicals that can cause cancer, “birth defects, nerve disorders, and other chronic and acute diseases” (“Preventing Pollution in Screen Printing” 45). VOCs are the primary air pollutants for which the printing industry is regulated. Regulated air emissions come from virtually every piece of equipment in the printing process - inks, cleanup solvents, adhesives, coatings, and paints. More specifically, benzene, methylene chloride, chlorofluorocarbons, chlorocarbons, formaldehyde, aliphatic hydrocarbons, ethyl acetate, glycol ethers, and acetone are all VOCs that screen printers come into daily use with. Benzene is a known human carcinogen, a chemical frequently used to make chemicals to produce resins and plastics in stickers (Andrady 364). Methylene chloride in adhesive removers and aerosol spray paints is another VOC that is detrimental to human health. Waste aerosol cans challenge businesses also, for they become waste when they are empty and product “can no longer be expelled, or the product has exceeded the useful shelf life” (“Aerosol Cans” 1). Methylene chloride is converted to carbon monoxide within the human body, and these cause symptoms similar to those caused by exposure to carbon monoxide (EPA). Formaldehyde can be found in paints and adhesives as well, and irritates the “nerve endings in the cornea,” causing severe discomfort (Wolkoff, Kjaergaard 851). Needless to say, these VOCs are detrimental to human health, and improper disposal of these commonplace screen printing supplies will contaminate the environment with carcinogens.
The application of certain types of inks also pose as a serious threat to the environment because many inks contain VOCs. The traditional solvent-based and water-based inks are “formulated with petroleum-based oils and metal-based pigments” (“Preventing Pollution in Screen Printing” 41). There is a growing concern over petroleum-based inks because they emit VOCs while curing and drying. Therefore, UV-curable inks are taking the stage for the screen printing world as the primary type of printing ink for several reasons. Using light instead of heat, UV curing is based on a photochemical reaction. UV-curables include six main advantages over traditional inks: “decreased or eliminated VOC emissions;” “less press cleaning and solvent usage;” “reduction in required floor space,” and “reduced health and safety hazards associated with common solvents” (Jendrucko, Coleman, Thomas 41). However, several disadvantages prevent UV-curables from taking the industry by storm, namely their hefty prices, possible toxicity, and links to worker safety issues due to exposure to UV light and certain chemicals in the inks (Jendrucko, Coleman, Thomas 41). Despite these setbacks, the adoption of UV-curable inks would benefit screen printers and the environment in the long run.
Aside from the inks and solvents themselves, maintaining the rest of the supplies is important to business and the environment as well, for these supplies can pose as hazardous wastes if not properly cleaned or disposed of. For example, cleaning the floor can have an environmental impact depending on the cleaning method(s) used. Spilling inks, which contain heavy metals such as chromium, and then mixing them with floor sweepings contaminate sweepings with chromium. Dry sweeping is ideal over hosing off the floor because hosing uses a great deal of water, which then creates a greater risk of pollution, especially since it is “not effective for cleaning oils or oil-based inks” (“Preventing Pollution in Screen Printing,” 17). Furthermore, parts washers also tend to use solvents for cleaning. This poses another problem because they “evaporate readily and can cause air pollution problems,” thus creating more hazardous waste (“Preventing Pollution in Screen Printing,” 27). Some businesses use solvent-distillation units called ‘stills’, which remove contaminants to recycle the solvent. Reclaiming screens is also an important step in sustaining the business. Screen reclamation chemicals is hazardous because of the ink in the screen, as inks contain heavy concentrations of metals, such as cadmium, lead, chromium, silver, and barium (“Preventing Pollution in Screen Printing” 31). The contamination of these metals with screen reclamation chemicals willl create more hazardous waste.
All image processing materials should also be recycled after use. Exposed and spoiled photographic film and paper is commonly “sold or given to reclaimers by much of the printing industry” (Jendrucko, Coleman, Thomas, 33). Fortunately, recyclers that purchase discarded film can then sell this film at gold and silver refiners and dealers by way of a business telephone directory. Large companies that generate this type of waste film and paper will even make a revenue from selling these films to recyclers. However, if there are no recyclers nearby, the waste film is landfilled, and this poses a potential risk to the environment as film contains high contents of heavy materials.
Thermal destruction of waste, or incineration, as well as landfill, are harmful to the environment. The emission of dioxins and furans are “among the prime issues of concern from the thermal destruction of plastics” (Andrady 633). Energy recovery from wastes is not as much of a problem as the environmental issues involved. Any waste recovery or conversion of waste to another form of useful energy must be “environmentally benign” (Andrady 633). The main issue at hand is making this whole system environmentally acceptable at affordable costs so that energy is recovered and waste is disposed of permanently. Landfills are not a viable option for disposing municipal solid waste (MSW), yet they represent 83% of destinations for waste disposal, and also the most environmentally problematic (Andrady 656). Landfills “create problems of odor, methane, carbon dioxide, and toxic gases” (Andrady 656). Carbon monoxide, a poisonous gas, and acid gases NOx, CL2, and Sox , cause corrosion (Andrady 656). Emission of pollutants, such as “HCl, CO2, unburned hydrocarbons, soot, particulates, dioxins, furans, and volatile organic compounds and metals” also raise international concerns (Andrady 656). Concerns over these pollutants are common to all combustion sources. Fortunately, two main alternatives to landfill and incineration are gasification and pyrolysis.
Gasification and pyrolysis aim to convert municipal solid waste (plastics) into usable energy. Gasification is a “thermochemical process in which the organic substances are converted into combustible gases with the aid of some agent,” namely common gases such as oxygen and hydrogen (Andrady 637). Gasification’s advantage over pyrolysis is that it converts more residue into gas, reducing the amount of solid waste. Gasification offers lower heating value gases, but volumes of these gases are higher; these gases can then be used for further energy applications. Pyrolysis, on the other hand, is “controlled thermal decomposition of an organic material into one of more recoverable substances” by using heat in an oxygen-free environment (Andrady 637). This process decomposes cellulose, plastic, and other rubbers into chemical products that can be used, while energy is preserved. These two types are different from incineration, which only results in ash and metals left in landfills or construction. Pyrolysis helps to decompose materials into “pyro-gas, pyro-oil, and solid by-products,” which perform like natural gas and can then be processed “into thermoplastics and asphalt applications” (Andrady 637). Companies should strive to adopt these two processes because they preserve useful energy in materials that would have otherwise been disposed of and pollute the environment.
Polyvinyl chloride (PVC), a primary component that serves as the backing of stickers, demands as much attention as other plastics. However, the recycling and disposal of PVCs are not as problematic. PVC is very easy to recycle mechanically, according to PVC.org. Mechanical recycling is well suited for PVCs as it can be done repeatedly since it does not harm the “chain length of its molecules” (PVC). The main setback in recycling PVC is in “collecting suitable waste at an acceptable cost” (PVC). Next to mechanical recycling is a dissolution process called Vinyloop, developed to extract PVC from common products. The recovered product can then be used without further processing. This provides a much more sustainable alternative to landfill and incineration, as it is a closed system that uses solvent-based recycling technology. Vinyloop’s Primary Energy Demand is “47% lower, ” and the Global Warming Potential is “40% lower” than the conventional route (Vinyloop). However, this process does not account for all plastics, and can only help to extract PVC from common materials.
Although the steps that prepare and maintain the manufacture of stickers are manifold, tedious, and environmentally challenging, several alternatives prove to prioritize sustainability when printing stickers. The market price of a sticker definitely does not represent its true price. It should consider the careful formulation of the adhesive materials, the transportation and storage of the liners, the ongoing cleaning of the printing shop, and the multiple recycle and disposal processes that the chemicals and plastics undergo. While sitting in landfills, carcinogenic VOCs emit into the air, polluting the very atmosphere that humans breathe everyday. People buy stickers every hour, not knowing about the pollution that arises from manufacturing them. Stickers are powerful for spreading a message, but no message is worth destroying the Earth.
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