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Customers do not ponder over production processes while buying diverse goods and commodities. They are more concerned about particular characteristics and properties of products they consume than about stages of their manufacturing process. However, infringements in production of even the simplest goods can result in their unsuitability and, consequently, customers’ financial losses.
Plastic bags are one of the most consumable goods; they are used to carry and store different things, package all kinds of purchases, preserve products, transport commodities, provide tightness or easy ingress to contents, line trashcans, and, thus, correspond to all consumers’ inquiries. Today, plastic bags are water resistant, persistent, not rumpled, and characterized by high mechanical durability. In addition, though plastic bags are basically produced translucent, today, the technological level of their manufacturing allows to make plastic bags of different colours including light yellow, bright pink, black, dark blue, grey, claret, etc. Their shapes and sizes can vary in a wide range. Handles of plastic bags can be made of such materials as rope, plastic, wood, cardboard, or even metal. Plastic bags can be decorated with diverse catching images, photos, pictures, companies’ logos, signs, and advertisements. Demands for plastic bags are constantly increasing; the rates of their sales are growing. Thus, plastic bags have been in high demand since the middle 1950s, the time when they first came to stay.
Plastic bags production should be performed in no less than 7-meter high premises due to specific characteristics of the equipment. The production of plastic bags does not require especial sanitary conditions; there is no necessity for separate engineering systems of water supply. However, power supplies and a favorable temperature mode are obligatory components of manufacturing plastic bags. These conditions “may affect properties such as the heat of fusion of a material and may also affect operations such as thermoforming operation and heat sealing” (Yam 2009). Spadework should precede production and involve working out and coordination of the breadboard model.
Although any kind of film or polyethylene are not toxic, their production can result in harmful consequences. If film is manufactured at the temperature exceeding that of polyethylene fusion, organic acids, aldehydes, hydrocarbons, and other harmful substances can be evolved. Thus, the determined thermal regime must be strictly kept.
The process of plastic bags production consists of the following stages:
1) Film manufacturing (extrusion);
2) Film printing or flexographic printing;
3) Finishing (cutting).
Film Manufacturing (Extrusion)
The initial substance for film production is utilized in the form of granules of various sizes and shapes; modern equipment does not depend on these characteristics of granules. However, properties of film are influenced by parameters of raw materials.
Film manufacturing occurs in the conditions of incessant extrusion. Extrusion is a process of transformation materials from granules to film in a specific shape such as polymeric pipes or sheets. Manufacture functions under the following scheme: granulated polymers are loaded into the bunker of an extrusion machine, and then they are pushed through the round section of the forming head designed according to established thickness and parameters in the conditions of high pressure and temperature. Using different additives and inks, manufacturers can paint originally colorless plastic materials in any colour.
Plastic materials are generally distinguished into thermoplastic (meltable) and thermoset (non-meltable) (Boedeker Plastics 2007). Plastic bags are usually fabricated from polyethylene or polythene (thermoplastic), which is “the most widely used mass-produced plastic” (Lajeunesse 2004; Piringer & Baner 2008). A wide spectrum of raw materials (the basic ones are petroleum and natural gas), solvents, additives, dyes, softeners, converters, inks, and other different chemicals are used in film production; they are heated, broken apart, and mixed with catalysts. Dyes should not exceed 3 % of a polymer’s weight.
Film for plastic bags should be manufactured in accordance with the official standards designed by the US Food and Drug Administration (FDA) in order to avoid its possible harmful impacts on products or other goods, and, thus, customers’ health.
The term “safe,” as it refers to food contact substances is defined as a “reasonable certainty in the minds of competent scientists that a substance is not harmful under the intended conditions of use.” The concept of safety used in this regulation involves the question of whether a substance is hazardous to the health of man or animal and considers the reality that it is impossible to establish with complete certainty the absolute harmlessness of the use of any substance (FDA 2007).
Film should not have cracks, wrinkles, folds, ruptures, and apertures. Therefore, technological requirements should be strictly supervised and controlled by workers involved in the process of film manufacturing.
Plastic bags can be made of polyethylene of low density (LDPE), high density (HDPE), or medium density (MDPE). Polyethylene is semi crystalline.
Those thick, glossy shopping bags from the mall are LLDPE, while grocery bags are HDPE, and garment bags from the dry cleaner are LDPE. The major difference between these three materials is the degree of branching of the polymer chain. HDPE and LLDPE are composed of linear, unbranched chains, while LDPE chains are branched (Lajeunesse 2004).
Density of all types of polyethylene depends on their ramifications and some other molecular properties.
Polyethylene of low density (LDPE) is produced by polymerization in suspension or in a gas phase in the presence of various catalysts and additives. These substances are utilized to create additional useful properties of film such as ultraviolet or frost resistance. For instance, metallocene polyethylene is made of ethylene and metallocene catalysts; it is characterized by perfect organoleptic properties. Its density is 0.926–0.940 g/cm3.
Polyethylene of medium density (MDPE) is created by adding such catalysts as Ziegler-Natta catalysts, chromium/silica catalysts, metallocene catalysts, and other homogeneous or heterogeneous catalysts. The density of MDPE is equal to roughly 0.926–0.940 g/cm3.
Polyethylene of high density (HDPE) is fabricated within the process of radical polymerization of ethylene at the temperature of approximately 320°?. Polymerization of HDPE is often initiated by a transition-metal catalyst; Ziegler-Natta catalysts and chromium catalysts are frequently added to HDPE. Polyethylene of high density can be produced in reactors of a tubular type. The density of HDPE comprises no less than 0.926–0.940 g/cm3. Density and thickness of film can fluctuate within the maximum and minimum thickness of each film type. Thus, maximum deviations should correspond to maximum deviations of the next nominal thickness.
Manufactured polyethylene is transported to plastic bags manufacturers. Film is spooled on plastic or cardboard plugs made in accordance with officially standardized specifications and technical documentation, and wrapped up in packing paper. It is supposed to apply other kind of paper to packing if its indicators correspond to the specified ones. The weight and width of rolls should correlate with standards, as well. Each packed roll should have a label with instructions and information concerning a name of a manufacturer and (or) his/her trade mark, raw materials, gross weight, net weight, a length of film in meters, a square of film in square meters, a date of production, results of undertaken tests on the quality of film, and a name of a packer or his/her number.
Film Printing (Flexographic Printing)
Diverse images, photos, pictures, logos, and fonts can be pressed on plastic bags. All pictures and patterns look impressive due to the faultlessly smooth and plain surface of plastic bags. Catching images attract potential consumers of commodities, thus, plastic bags have become an effective means of advertising.
The second stage of plastic bags production proceeds with operations on flexographic printing presses. Plastic bags can be multicoloured due to developed properties of new machines. They are produced by such companies as Cerutti Corporation, Star Flex International, Marsons Print-Craft Machines, HC Miller Press, and other business units. This equipment is available in various sizes according to manufacturers’ requirements for patterns and colours of plastic bags. There are five main types of flexographic printing presses such as a central impression cylinder (CIC), the stack type, an in-line unit, and a 4-, 5-, or 6-color unit. All of them are supplied with “a plate cylinder, a metering cylinder known as the anilox roll that applies ink to the plate, and an ink pan. Flexographic printing presses are specifically designed for printing on flexible polyethylene film with the maximum quality and productivity. Application of the modern microprocessor equipment provides the fast task of speed and exact positioning on signals of photogauges, and possibilities for automatic packing of plastic bags in a pile. Thus, it saves time and energy.
Some presses use “a third roller as a fountain roller and, in some cases, a doctor blade for improved ink distribution” (PNEAC).
Flexographic printing presses are gearless, sleeve, and frequently equipped with automatic registration control and wash-up systems; they can consist of several printing sections and be manufactured in up to ten colours; facsimile drawing and photos can be printed on polyethylene film, as well. “As with Gravure and Lithographic printing, the various tones and shading are achieved by overlaying the 4 basic shades of ink. These are magenta, cyan, yellow, and black. Magenta being the red tones and cyan being the blue” (PNEAC). Modern flexographic printing presses can print on different materials including the thinnest film and foil.
Flexoprinting differs from traditional kinds of printing in inks and dyes utilized. Highly elastic liquid printing paints are used in manufacturing plastic bags. The main technological stage of flexoprinting is the transference of liquid and quick-drying inks, dyes, and diverse colouring matters on polyethylene through the soft polymeric forms fixed on cylinders by a sticky tape or by means of special glue. Rolls of polyethylene film move in flexographic printing presses where they are decorated with chosen images, pictures, or signs. Colours, brightness, and images are chosen and coordinated with customers. Flexing mechanisms print images according to the set periodicity and sizes of plastic bags.
Flexographic printing consists of the three obligatory phases which include the following operations:
1) Image preparation. Images are processed for printing on polyethylene by cameras, scanners, or computers. Components of images can be positioned and manually assembled according to customers’ requirements. A scanned copy or a digitally created image is set up using the special software. Position and accuracy of an image are strictly controlled. “When color is involved, a color proof is submitted to the customer for approval” (PNEAC).
2) Plate making. A relief type plate is used within this stage. Such plates are made of rubber, different polymers, plastics, or any other flexible materials. “There are three primary methods of making flexographic plates; photomechanical, photochemical and laser engraved plates” (PNEAC).
3) Printing. Inks are laid on polyethylene; solvents and other harmful substances are removed.
Design of plastic bags is chosen according to their specific utilization and in order to satisfy public tastes; it is inextricably linked with modern technological possibilities. People’s opinions concerning aesthetics make an essential impact on design of plastic bags. Today, translucent plastic bags painted in different colours or in silvery tones and strict one-color images are in high demand.
Colourful and catching images are printed more easily on polyethylene of low density (LDPE). Photographic images or intricate graphic drawings look worse on polyethylene of high density (HDPE).The external shape depends on imagination of a designer and possibilities of the printing equipment. However, polyethylene of low density (LDPE) is more susceptible to creasing, formation of wrinkles and blanks on images during flexographic printing than polyethylene of high density (HDPE), which is generally characterized by wrinkle recovery and resistance to creasing. Therefore, manufacturers recommend increasing density and thickness of polyethylene for plastic bags to provide consumers with reliable commodities.
The final stage of plastic bags manufacturing, cutting, is performed according to their sizes and shapes. In addition, this phase may include coating, folding, and binding. T-Shirt bags are widely used and the most frequently bought by customers because they are very capacious and suitable. T-Shirt plastic bags are supplied with handles. They can be manufactured in different sizes, colours, and thickness. Machines for their production are supplied with duplex knives and specific needles; the photocell catching drawing is necessary to cut plastic bags with printed images. This stage of manufacturing plastic bags is the shortest in their production process. However, the equipment should include a machine car cutting polyethylene film on pieces of the set size and soldering a final product in the necessary place. T-Shirts bags manufacturing can include utilization of a cutting press, as well.
Plastic bags are sold and distributed in rolls or piles depending on their size and type. All consignments of plastic bags should be provided with the quality certificate. This document should contain data on a name of a manufacturer and (or) its trade mark, a film specification, a lot number, a manufacturing date, a number of items, a type of polyethylene used for plastic bags manufacturing, net weight and gross, and results of tests conducted to estimate if plastic bags correspond to the official standardized requirements designed by the US Food and Drug Administration (FDA) or other authoritative bodies.
Plastic bags wholesales are widely promoted on the Internet and printed sources of information. An ultimate consumer can buy plastic bags in shops of all types independently of their specialization and location.
The process of plastic bags production undergoes considerable changes due to growing environmental contamination today. Therefore, production of biodegradable plastic bags is increasing. Biodegradable plastic bags are fabricated of materials which decay within several years under the influence of environment (air, humidity) and turn to organic substances. Biodegradable plastic bags do not make a negative impact on the nature and, consequently, demand for them is growing. Components utilized in the production of biodegradable plastic bags are determined by the authoritative bodies such as the Federal Trade Commission (the USA), the European Plastics Recyclers Association (the EU), and others.
The main types of biodegradable plastic bags are those made of polyethylene with starch or special solutions additives.Biodegradable plastic bagscontaining starch decompose far more rapidly than plastic bags made of ordinary polyethylene. However, it is possible to carry no more than 1 kilogram in such plastic bags due to their fragility. Moreover, their production is significantly more expensive because of additional machinery involved in manufacturing.
In order to decrease terms of plastic bags decomposition, their surface is covered by the special solution considerably accelerating process of decay. Their colours and shapes an do not differ from those of ordinary plastic bags. In addition, they are strong enough and convenient to use; changes in their production only include specific additives. Terms of their decomposition are approximately equal to terms of bags made of starch additives. Hence, such plastic bags manufacturing does not undergo practically any complicated or expensive modifications. Therefore, the rates of their production, supply, and demand are growing everywhere.
Specific additives used in the production of such biodegradable plastic bags are solutions added during film manufacturing. They accelerate the process of plastic bags decomposition under the influence of oxygen, ultraviolet, and water. When a plastic bag processed by the given solution is affected by the sunlight, air, and water, it turns in humus. Its term of decomposition does not exceed two years. However, if such a plastic bag is in other conditions, it cannot decay. Nevertheless, in case additives start acting and interacting with surroundings, the process will not stop any more. Thus, biodegradable plastic bags of this type can be identified as convenient, harmless, and inexpensive.
Advantages of biodegradable plastic bags include their following properties and specific characteristics:
1) they do not pollute environment;
2) they are suitable for storage of various goods and commodities, including foodstuff;
3) they are characterized by high durability and water resistance;
4) the process of decomposition can be supervised and regulated.
Disadvantages of biodegradable plastic bags production are comprised of the following facts:
1)costs of biodegradable plastic bags exceed costs of ordinary ones;
2)today, their production is not well developed to implement high-volume manufacturing due to the novelty of technology;
3)mistrust of consumers caused by their unawareness and insufficient advertising.
However, constantly conducted scientific researches and laboratory studies testify to effectiveness and profitability of biodegradable plastic bags manufacturing. Furthermore, all humans living on the Earth are greatly concerned about ecological problems and environmental pollution. Thus, higher prices of biodegradable plastic bags cannot significantly decelerate their distribution and production.
Today, new approaches to plastic bags production are developing. Spoilt plastic bags, films, and cardboard are recycled and processed to fabricate a new kind of an inexpensive polymer. Innovations designed by the Canadian Groupe RCM Inc. were supported by the government of the country. The Canadian governmental organization of Canada Economic Development invested $413,00 in the development of the new production of plastic bags in order to enable Groupe RCM “to acquire the equipment it needs to transform cardboard into pellets, shred plastics and operate and control the entire production line” (CEAP 2009).
The process of recycling involves utilization of knifes which work with high speed. They mill cardboard and plastic wastes and transform the mixture into a homogeneous material in the form of granules. A wide spectrum of plastic goods and commodities including bags can be made of these raw materials. The company’s innovations in plastic bags production, thus, allow manufacturers to produce inexpensive plastic bags and prevent contamination of the environment with different waste products.
To conclude, despite extremely wide utilization of plastic bags in humans’ everyday living, simplicity of their construction, blanket distribution, accessibility, and low prices, their production is a complicated process. Plastic bags manufacturing involves obligatory stages, which cannot be infringed or omitted in order to avoid harmful effects of plastic bags on customers’ health or their financial losses caused by the unsatisfactory quality of these goods.
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