In addition to the discussed fields of application, paraffin waxes are used in many branches of industry, such as the match industry, the rubber industry, PVC processing, precision casting of metals, manufacture of refractory ceramics, the electrical industry and building construction. Further consumers of para& waxes are the textile industry, dental profession, pencil manufacturers, pyrotechnic industry, etc.
(a) The match industry is one of the oldest consumers of paraffin waxes. Paraffin impregnation of the matches, usually made of wood, has the objective of ensuring rapid ignition of the matchwood after striking the matched. In addition, waxing improves adhesion of the matched to the matchwood and resistance to moisture. The latter is of particular importance for matches stored and used in high-moisture climates.
Previously, lower-melting micro crystalline paraffin waxes (42 to 46 “C m.p.) were preferred for match impregnation. At present higher-melting Paraffin waxes (m.p. 46 to 54 “C) are more wide-spread in use. Still higher-melting paraffin waxes could also be used, but are too expensive. The oil content of paraffin waxes for impregnation must not exceed 5 wt- %; the usual value is around 3 wt- %. Higher oil content paraffin wax leads to excessive flickering of the flame. Some match manufacturers use 1 to 2 wt- % paraffin wax in the match head, too, in addition with use Residue wax (Foots oil) in body of the match, resulting in more uniform burning.
(b) The rubber industry The rubber industry is also one of the most important paraffin wax consumers, using it for a variety of purposes. Paraffin wax, when used as an additive to rubber increases the stiffness of the product. This is of major importance in press-moulded rubber products. If the paraffin wax content in rubber exceeds 1 to 2 wt-%, it migrates to the surface and forms a continuous thin layer. This phenomenon is called efflorescence. The thin layer bends, without cracking, with the rubber products. Experience has shown that the layer of wax effectively inhibits the oxidative ageing processes accelerated by light. If it is desired to obtain low-friction surfaces, 3 to 5 wt-% paraffin wax is added to the rubber compounds. Paraffin waxes are often used with painted rubber goods to prevent decoloration. In rubber latices various paraffin waxes (I to 2 wt-%) are used as plasticize-rs to reduce toughness. Almost all types of paraffin waxes are in use in the rubber industry. In the manufacture of air tubes, macro crystalline paraffin waxes containing 2 to 5 wt- % oil are used to ease moulding and to achieve uniform surface resistance to abrasion in the Tyre. Blends of macro- and micro crystalline paraffin waxes are used in the manufacture of sealing rings for preserve jars and other types of sealing rbgs. For industrial-purpose rubber goods, e.g. hose, where requirements of color and odor are not so critical, less refined petrolatum of darker color are used.
(c) Precision casting, is a useful process for the economical manufacture of metal components and tools in small batches. Although the process is also used for components of mass greater than 100 kg, its most important field of application is with smaller components, with mass of the order of a kilogram. The process consists of the following steps: a die is made from a prototype, and paraffin wax is poured or pressed into the die. After cooling, the paraffin wax model is removed from the die, and a ceramic coating is applied onto the model. When the ceramic coating has solidified, the paraffin wax is melted and poured from the ceramic shell, which is subsequently baked in a kiln. The molten metal is usually cast into the ceramic moulds whilst the moulds are still hot. After solidification of the melt, the ceramic shell is broken to remove the casting. The most important components of casting paraffin waxes are lower-melting paraffin waxes, various natural waxes, e.g. carnauba wax, synthetic waxes, as well as higher melting fatty acids, e.g. stearic acid. Blends of around 50/50 wt-% macro crystalline paraffin wax and stearic acid are frequently used. In addition, some casting waxes contain bitumen. Studies carried out in the Hungarian Oil and Gas Research Institute demonstrated that low-contraction casting waxes can be produced from partially oxidized micro crystalline paraffin waxes and micro crystalline paraffin waxes containing wax esters.
(d) The manufacture of refractory ceramics Paraffin wax casting of ceramics is a process being increasingly used in industry, mainly for porcelain, A1,0,, MgSiO,, ZnTiO,, TiO,, ZrO, and fireclay. Other materials for which the process has been used are CaO, MgO, MgA1,0,, Sic, Mo.Si,, Si,N,, Si, TiB,, TiN, ZrB, and other high-melting compounds. Clay cannot be used as binding material for shaping, since it reduces the melting point of refractories. Instead, the ground refractories are mixed with molten paraffin wax to yield a malleable mass, which is then cast into metal moulds or moulded at pressures of several hundred bars. Injection moulding is also used for mass production. The parts solidified in the water-cooled moulds are coated with a porous embedding material and introduced into the prefiguring kiln. The temperature is slowly raised to 400-60O0C, whereupon paraffin wax diffuses out into the embedding material where it evaporates and burns away. Depending on the composition of the ceramic, prefiguring is continued to 900- 1250°C. Subsequently the embedding material is removed and final firing at high temperature follows. Slack wax melting at 50-54 “C is used to prepare the slurry for casting.
(e)The electrical industry uses large amounts of different types of paraffin waxes for insulation at ambient temperature. Obviously, paraffin waxes alone cannot be used at higher temperatures, only in blends with synthetic waxes. In addition to high relative permitting, low dielectric loss and high resistance values, important requirements for paraffin waxes to be used in the electrical industry are flexibility, ductility and low thermal expansion coefficients. Direct paraffin wax coating is frequently used for the insulation of Wires, cables, flat or irregular-shaped metal surfaces. For such purposes only micro crystalline paraffin waxes which are flexible, adhere well to metals, and have only a slightly shrinkage on cooling are usable. Paraffin wax impregnation of other insulating materials, e.g. paper, textiles, asbestos, wood, is also frequently used in order to improve their insulating properties and moisture resistance. Paraffin waxes and paraffin waxes with additives are much used for building up blocking layers, e.g. for capacitors, for cable terminals and couplings, for impregnating cable-insulation paper, for filling the space between cables and around the coupling. The zinc casings of dry cells can be sealed with paraffin wax or paraffin wax impregnated paper. This will efficiently reduce desiccation of the cell. Paraffin waxes used for insulation usually have melting points above 55 “C and oil contents below 1 wt-%. Paraffin waxes are used to reduce the viscosity of bitumen used for impregnating linen tape. For this purpose the oil content may be as high as 2 to 4 wt-%. To impregnate paper for paper-insulated capacitors, the oil content must not exceed 0.5 to 1 wt-%, and the melting point should exceed 55 “C. In roll-type cylindrical or flat capacitor elements encased in metal or paper the empty space is usually filled with paraffin wax. For paper casings, blends of higher melting micro crystalline paraffin waxes and various resins are used. The melting point of cable waxes is in the range of 55 to 65 “C. Requirements are non-stickiness and absence of components with boiling points below 180 “C
Paraffin wax usage in the food industry is partly implied in paper industry applications, since a major part of paper products coated or impregnated with paraffin wax, and also laminated films and foils using paraffin waxes as adhesives are manufactured for food packaging. These applications have been discussed earlier. Paraffin wax is widely used in the poultry-processing industry for the wax picking of poultry, mainly for ducks and geese. After De-plumbing, the poultry is immersed in melted paraffin wax. When the wax coating has solidified, it is removed by a so-called whipping machine. The feather pins and small feathers left after depluming, embedded in the wax coat, will be removed together with it. Macro crystalline wax is unsuited for wax picking owing to its brittleness. The products used for this purpose consist of blends of macro- and micro crystalline paraffin waxes, together with additives, e.g. polyethylene wax. The micro crystalline wax increases flexibility, the additives serve to improve adhesion and toughness.
Paraffin wax products are frequently used for direct coating of food. The most important of such applications are coatings for cheese and fruit. The paraffin wax coat on the surface of the cheese prevents its desiccation, reduces loss in flavor substances, and protects the surface of the cheese from undesired moulding. The main requirements for paraffin waxes used for coating cheese are melting points between 55 and 75 “C, melt viscosity in the range of 5 to 15 mm2/s at 100°C, high flexibility and good adhesion. Flexibility is of importance from two viewpoints: it ensures that no cracking will occur under the effect of mechanical impact, and it allows the preparation of peel able coatings. Consequently macro crystalline slab waxes cannot be used by themselves for cheese coating, the formulation must always contain substantial amounts (60 to 80 wt- %) of micro crystalline paraffin wax and polymer additives. Among the types of micro crystalline paraffin waxes, those with melting points of 55 to 60 “C, manufactured from residual oil or from the paraffin wax by-product of residual oil by fractional crystallization, are particularly suited for high-grade cheese waxes. The additives used are synthetic rubbers, polyisobutene, polyethylene waxes and various co-polymers.
Paraffin wax coatings are applied to fruit and other agricultural produces whose peel will not be consumed, and to those transported to long distances, for example to lemons, oranges, tangerines, melons, egg-fruit. In some countries apples, tomatoes and fodder beet are also being waxed. Fodder beet is waxed by immersion in melted paraffin wax at 120 to 130°C. For citrus fruits, a widely used process is to spray the fruit, as it passes on a conveyor belt, with a solution of paraffin wax in white oil. After coating, uniform thickness of the coat is achieved by brushing. In another process the wax is dissolved in gasoline and sprayed on the fruit. Melons, egg-fruit and tomatoes are coated by immersion in cold wax emulsions, after being washed with cold water. Main requirements for the emulsions are low surface tension, good wetting power and rapid drying after coating. The melting point of paraffin waxes used for emulsions is around 52 to 60 “C. The emulsifying agent is usually a soap-type product. For coating fruit and other agricultural produces, colourless, odourless and tasteless macro crystalline slab waxes are preferred. In agriculture, saplings, shrubs and grafts are frequently protected during storage against desiccation and plant diseases by coating with paraffin wax. The coating is carried out by immersion in melted paraffin or by spraying with a paraffin emulsion. For these purposes, mainly for immersion, blends of macro- and micro crystalline paraffin waxes are used. Coating waxes made with micro crystalline paraffin waxes yield impact-resistant, flexible coatings.
Paraffin waxes in cosmetics industry are using in the last century. Initially raw materials of cosmetics were vegetable or animal origin were solely used for such purposes. Only later did petroleum products make their entrance into the cosmetics industry and find general acceptance. The following petroleum products are in use for cosmetic purposes : Vaseline oil, Vaseline, macro- and micro crystalline paraffin waxes. Macro- and Micro crystalline paraffin waxes make a significant difference to the resistance to mechanical impact, hardness and softening point properties of cosmetic preparations. Micro crystalline paraffin waxes are tougher than macro crystalline waxes, they exhibit plastic flow under the effect of compression, while macro crystalline waxes have higher compression strength. Since the solvent and oil uptake capacity of micro crystalline paraffin waxes are very high, increasing oil content usually results in higher plasticity.
Vaselines are important constituents in a large sector of cosmetic products. With regard to their origin, Vaselines are natural Vaselines, so-called slack wax Vaselines or artificial Vaselines. Natural Vaselines are obtained from the distillation residues of petroleum by direct treatment with bleaching earth, or by refining with sulfuric acid and bleaching earth. Alternative processes are De-asphalting of the residue followed by bleaching, or refining with sulfuric acid and bleaching. Slack wax Vaselines are manufactured from paraffin slack waxes or petrolatum. Artificial Vaselines are blends of Vaseline oils and macro- or micro crystalline paraffin waxes. The use of Vaselines can be regarded as an indirect use of macro crystalline, and, especially intermediate and micro crystalline paraffin waxes.
Paraffin waxes are used in the manufacture of fatty solid perfumes. Solid perfumes are used to scent the surface of the skin. Those having a higher alcohol content also have a refreshing effect that can be increased by menthol. The two main types of solid perfumes are fatty and alcoholic perfumes, the latter containing more than 75 wt- % alcohol.
Vaseline and Vaseline oil are main ingredient of Cosmetic creams. They are paste-like preparations used for skin care of the face and hands. The types so-called dry, semi-fatty and fatty creams. They are usually prepared on a stearate base. In addition to stearic acid derivatives they contain relatively high amounts of petroleum products (Vaseline, Vaseline oil), fatty alcohols (e.g. acetyl alcohol) and multi functional alcohols (e.g. glycerol). Fatty creams contain less water and more fatty substances, waxes, fatty alcohols and petroleum products. In summer and winter varieties of these creams also exist: within a given formulation these varieties are prepared by changing the oil content (e.g. Vaseline oil) and the content of solid or semi-solid components (e.g. Vaseline, paraffin wax). Cleansing creams belong to the group of fatty creams. They are primarily intended for persons with sensitive skins, to cleanse the facial skin. Anhydrous cleansing creams contain higher amounts of paraffin waxes, Vaseline and Vaseline oil. Homogeneous creams can be prepared best by using micro crystalline paraffin micro crystalline, since they retain oil at the temperature of application. Cold creams belong to the fatty or semi-fatty type, depending on fat content. These are aqueous emulsions with a cooling effect on the skin. Of the petroleum products, cold creams use greater quantities of Vaseline oil and Vaseline, but lesser amounts of paraffin waxes, with a substantially higher water content than that of the fatty creams. In contrast to fatty creams they do not leave behind an oily, fatty film on the skin. They can readily be removed from the skin with pure water.
Baby creams also contain substantial amounts of Vaseline and Vaseline oil. Their composition resembles that of cleansing creams. Sport creams belong to the semi-fatty group. They are aqueous emulsions containing substantial amounts of petroleum products.
The main objective of beauty masks is to relax the tissues of the face and enhance blood circulation.
Protective creams are being used in many branches of industry, especially to protect the skin on the hands and arms of the workers against harm caused by various chemical and physical effects. Most of the protective creams are based on Vaseline, but some of them also contain macro crystalline paraffin waxes.
Cosmetic preparations for facial care, e.g. to soften dry, parched lips are made of natural and synthetic waxes, fats, fatty alcohols, Vaseline and sincerer. The most important starting materials for the manufacture of lipsticks are various natural and synthetic waxes, fats, fatty alcohols, Vaselines, paraffin waxes and dyes. Mechanical strength of the lipstick is achieved by using waxes and
Micro crystalline paraffin waxes with higher melting points. Among natural waxes, bees-wax is typical of the kind used in almost all types of lipstick, owing to its plasticity. Among petroleum products, high-melting micro crystalline paraffin waxes raise the strength and softening point of the lipstick, but are rarely used in amounts exceeding 15 wt-%, because they tarnish the gloss of the surface. The use for macro crystalline paraffin waxes is limited, due to their causing a granular structure. Vaseline increases gloss and is of importance for the consistency of the product. It is, however, easily wiped off from the lips. Vaseline is usually present in concentrations of 20 to 35 wt-%. The effect of vaseline oil is very similar to that of Vaseline. In addition, it improves uniform spreading of the lipstick. Excess amounts of both Vaseline and Vaseline oil result in low-melting, soft lipsticks. The melting point of lipsticks varies between 45 and 65 “C. Lower-melting types spread better, while contours are easier to draw with the higher-melting lipsticks.This particular one is characterized by its high paraffin wax content. Face make-up is manufactured from the same raw materials as lipsticks. The main requirement is easy and uniform spreading, so that they contain higher
Among cosmetic preparations for hair, solid brilliantine and hair pomades utilize significant amounts of paraffin waxes and Vaseline, the higher percentages being found in the latter.
A perspiration-reducing and deodorant product containing relatively high percentages of paraffin wax and Vaseline
Various grades of macro- and micro crystalline paraffin waxes are used in household chemicals. The main consumers for paraffin waxes are polishes and candles. Paraffin waxes are used as additives in many polishes, and a substantial part of candle material is paraffin wax.
Polishes are materials which, on the one hand, increase the gloss of the treated surface or restore its initial gloss, and on the other hand, protect the surfaces against mechanical and chemical effects, and thus prolong the service life of the object. Solvent-containing, liquid polishes have a cleaning effect, too.
Polishes containing considerable amounts of paraffin waxes include floor, furniture, shoe and automobile polishes. Polishes usually contain several kinds of natural and synthetic waxes, paraffin waxes, resins, solvents, auxiliary agents and water. As well as the requirements of the consumer, cost of the components is an important factor in the formulations. This is one of the reasons for the tendency to replace a part of the relatively expensive natural and synthetic waxes by less expensive paraffin waxes. The origin of natural waxes is diversified: carnauba wax, for example, is obtained from a palm, bees-wax is produced by the insect, and crude montan wax is extracted from lignite. Refined montan wax, chemically transformed into acid esters or partly hydrolyzed, is widely used. The synthetic waxes include products obtained by esterification of fatty acid fractions from the oxidation of macro- and micro crystalline paraffin waxes, as well as polyethylenes. Suitably selected paraffin waxes improve gloss, but greater amounts may result in an opaque surface. Another important factor in the choice of the solid components and their ratios is the requirement to form a mechanically resistant film.
Paraffin wax is used for floor polish coatings as serve the purpose of preventing water, vapor and air penetrating into the floor and protecting the flooring against wear. Wood floors are usually coated first with a priming paraffin wax layer, and subsequently, if necessary, with a liquid polish. After evaporation of the solvent, the film remaining is rubbed to produce a gloss. Solid floor polishes are pastes or solvent-less polishes. Liquid polishes yield either surfaces requiring rubbing for gloss formation, or yield directly glossy surfaces after drying
Floor pastes are usually manufactured from carnauba or some corresponding wax, montan wax, macro crystalline paraffin wax and ceresin. The paraffin waxes, which are softer than the former waxes, ensure proper consistency of the paste and increase solvent retention capacity. The carnauba wax content seldom exceeds 12 wt-%. Since wood absorbs paraffin waxes readily, their content is kept around 10 wt-%. Within these general ranges the formulations for floor pastes vary widely.
An important characteristic of paraffin waxes in polishes is solvent uptake. Even if the structure of the product after manufacture is a perfect gel, cracks may be formed in the course of storage, and the spreading properties of the wax may deteriorate. This is the result of poor solvent retention of the waxes. ‘This disadvantage
hardness of the paraffin wax constituents and significantly improve gel formation even in small amounts. In turn, solvent uptake of paraffin waxes is low, but solvent retention is excellent. Thus, relatively high amounts of paraffin wax combined with small amounts of montan wax-based synthetic waxes yield readily gelling pastes with good solvent retention.
With liquid floor polishes a gloss is obtained by rubbing the film formed after applying the polish. The components of the polishes are the same as those of pastes, the only difference being the solvent content. The solids content of liquid floor polishes varies between 8 and 15 wt-%. The most widely used components of floor polish emulsions are bees-wax, carnauba wax, candelilla wax, japan wax, and macro- and micro crystalline paraffin waxes. An example of a formulation for a liquid emulsion floor.
The duty of furniture polishes is to remove dust and other dirt from the surface of the furniture and to increase its gloss. The five large groups of furniture polishes are furniture oils, oil-in-water type emulsions, wax emulsions, furniture pastes and silicone-containing furniture polishes. Paraffin waxes are used in two of these groups, in wax emulsions and in furniture pastes. The most widely used solid components of wax emulsions are carnauba wax, beeswax, macro- and micro crystalline paraffin waxes, stearic acid and various estersed synthetic waxes.
The duties of automobile polishes are manifold: they cleanse the car body and the metal decorating elements from dirt, e.g. dust, oil spots, etc., they restore the initial gloss and smoothness of the varnish, and form a thin continuous film that will protect the varnish coat against weathering for some time. In addition to the usual waxes, paraffin waxes, plasticizers, emulsifiers and solvents, automobile polishes also contain abrasive powders, which remove dust particles adhering strongly to the surface and cause roughness. Such strong adhesion is the result of paint and varnish softening by the heat of sun radiation or by the heat of the motor.
Shoe polishes are required to protect and shine the leather. They form flexible, glossy wax films resistant to water, dust and the effects of weather. As well as various natural waxes, paraffin waxes are also being used in the manufacture of shoe polishes. An accepted terminology is hard and soft shoe polishes. However, these attributes do not refer directly to the hardness of the waxes or paraffin waxes present, but to other properties, such as solvent uptake, solvent retention, consistency, film-forming properties, drying time, etc. The attribute “hard” refers, in this respect, to waxes such as carnauba wax, hard macro crystalline paraffin waxes and ceresins, candelilla wax, while “soft” applies to waxes such as crude montan wax, bees-wax, japan wax and various micro crystalline paraffin waxes. As a substitute for natural waxes, many synthetic waxes are being used at present.
In the formulation of shoe creams the proper proportion of hard and soft materials is of particular importance. Hard materials jn themselves are unsuitable for manufacturing shoe creams having paste-like consistencies. The soft waxes act as binders for the hard waxes and also as a binder between the paraffin waxes and solvent. On the other hand, hard waxes and hard paraffin waxes are imperative from the viewpoint of shine. In addition to the above solids, shoe creams that are aqueous emulsions contain oleic acid, stearic acid, borax and triethanolamine as well as sodium and potassium soaps.
One of the oldest fields of application for paraffin waxes is in the manufacture of candles. Paraffin waxes were first used for this purpose in the middle of the last century. The composition of candles is defined by their intended use, by climatic factors and by the specific demands of the consumers. The most important processes are : mechanized moulding using cylindrical moulds, dipping and pouring. The illumination power of pure paraffin wax candles per mass unit is higher, owing to the pure hydrocarbon composition, than that of candles containing other components besides paraffin waxes. However, pure paraffin wax candles have several disadvantages. Their low melt viscosity causes excessively high amounts of melt being picked up by the capillaries of the wick, and consequently the flame tends to soot. Candles made of macro crystalline paraffin waxes with low softening points may bend and adhere to one another under the effect of their own weight. Candles made of higher softening point waxes, on the other hand, will be difficult to light in cold weather, the flame will tend to blow out, and repeated lighting will again be difficult, because the heat of the igniting flame will not be satisfactory for easy melting of the candle material. For this reason, the majority of candles are manufactured from blends of macro crystalline paraffin waxes and stearic acid. Also, bees-wax, micro crystalline paraffin waxes (ceresins), vegetable and synthetic waxes are used. Macro crystalline paraffin waxes having melting point between 48 and 54 “C are suitable for candle manufacture. So-called composite candles made of paraffin wax and stearic acid contain 5 to 15 wt- % stearic acid, which can, however, be substantially higher in candles manufactured for hot climates. Even candles made of pure stearic acid are being manufactured.
The melting point of composite candles is around 50 “C. The melting point of commercial stearic acid is 55 to 60 “C. The melting point of the blend is lower over the total concentration range than that of the individual constituents. The melting point minimum is around the 50/50 wt- % ratio of the constituents and is lower by 6 to 9 “C than that of the pure paraffin wax. However, softening starts at a higher temperature than that of the pure paraffin wax. Church candles, in contrast to other candle types, contain a Paraffin wax and higher share of bees-wax, sometimes exceeding 50 wt-%.
Although the use of plastics steadily increases in packaging, cellulose-based papers, cardboard and corrugated paperboard still remain the most important packaging materials. Besides other additives, paraffin waxes and wax-containing auxiliary products are largely used for improving the properties of paper, cardboard and corrugated paperboard. The packaging industry is one of the most important consumers for direct applications of paraffin wax. This is due mainly to the following factors: – paraffin waxes are inexpensive, – they are available in practically unlimited quantities, – their grades do not vary. In fields where the paraffin waxes themselves are not capable of meeting the necessary requirements, their functional properties can readily be improved by the addition of natural or synthetic waxes or polymers. Such products can be utilized in the paper industry using simple and rapid operations. Paraffin waxes, with suitably selected plastics additives, have favorable properties : good adhesion, permanent gloss, impermeability to water and water vapor, broad ranges within which viscosity, plasticity and mechanical strength may be varied. Para& waxes are used in the paper industry especially for impregnation, coating and laminating. In addition, paraffin waxes are used as additives to paper sizes.
Impregnation is used both during paper manufacture and for the finishing of the paper. Paper has a capillary structure which causes it to absorb moisture. This property is often inconvenient and can be mitigated by impregnation with various additives, e.g. paraffin waxes. The formed paper web can also be impregnated by leading it, by means of guide rolls, through the solution or melt of the impregnating material. Shaped paper products, such as containers, etc., can also be subjected to impregnation. The impregnating substance uptake is defined by the above-cited conditions. It usually varies between 3 to 35 g/m2. The substances suitable for impregnation are macro- and micro crystalline paraffin waxes, their blends, and modified low melt-viscosity paraffin waxes containing a maximum of 10 wt-% polymer. The polymers used for this purpose are polyethylene, polyisobutylene, ethylene-vinyl acetate copolymer.
In coating, a film is formed directly on the surface of the paper, without applying an adhesive between the film and the paper. In addition, the film is an unbroken, glossy, flexible, smooth layer, it is waterproofing and impermeable to water vapor. The equipment developed for melt-coating is based on rollers, discharge devices or nozzles. For high-viscosity hot-melt coating special discharge slots, so-called curtain-coating equipment has been developed, forming a film curtain under which the shaped products pass and become coated. The melt uptake is controlled according to the viscosity of the melt and the porosity of the paper material; 10 to 20 g/m2 paraffin wax application yields a continuous layer. Three types of melt are used for coating : – paraffin waxes with a maximum 10 wt-% polymer content, with melting points only slightly higher than that of the paraffin wax, and with low melt viscosity ; – waxes and paraffin waxes with 20 to 35 wt-% polymer content (so-called hot-melts), having higher melting points than those of the former type, and medium melt viscosity values ; – extrusion coating materials with high melting points and high melt viscosity. For coating with paraffin wax products it is expedient to use suitable blends of macro- and micro crystalline waxes. The macro crystalline waxes lend gloss, light color, stiffness and transparency to the coating, the micro crystalline waxes provide low permeability to water vapor and fatty substances, adhesion and high flexibility. The particularly important duty of the micro crystalline wax components is to preserve impermeability to water vapor of packaging materials (corrugated paperboard for machines, instruments, food, containers, cups, etc.) under the effect of mechanical loads. The difference in water vapor permeability between macro- and micro crystalline paraffin waxes is scarcely detectable. However, the papers coated with these waxes show significant differences, since micro crystalline waxes, owing to their higher flexibility, form layers more resistant to mechanical effects. For this reason, paraffin wax products for the paper industry always contain micro crystalline waxes. According to whether their function is coating or increase of hardness, Rumberger stipulated the requirements listed in Table 111-2 for micro crystalline paraffin waxes. Waxes for coating originate from residual oils, and improve the melting point and the vapor proofing properties of the macro crystalline waxes. Micro crystalline waxes for improving the hardness and melting point of macro crystalline waxes are products obtained from tank waxes or petrolatum by DE-oiling. The surface gloss obtained with paraffin wax products can be increased with hard waxes as additives. The further advantages of these components consist (a) in their anti-blocking property, i.e. surfaces placed one on one another do not stick together; and (b) in their flexibility, ensuring that the film does not crack during use. The product ensures good mechanical strength for the raw paper. It improves resistance of the papers to cracking, and reduces their permeability to water and water vapor. Owing to the optimum oil content, the wax layer has a high flexibility and smooth surface. Due to the high drop melting point, packaging paper treated with the product can also be used in warm climates. The low viscosity of the melt allows simple processing. Among polymers containing paraffin wax products, the three-component products consisting of polyethylene, macro crystalline paraffin wax and micro crystalline paraffin wax are prominently good. Such polyethylene waxes mix readily with paraffin waxes at temperatures around 110-120 “C, and only slightly increase the melt viscosity of the paraffin waxes. Increased gloss can be observed with percentages of the additive as low as 2 wt-x, and the blocking temperature is also higher. To achieve the gloss, melting point, blocking temperature, abrasion resistance and flexibility required in specifications, 3 to 5 wt-% of the polyethylene additive must be used. Still higher gloss is obtained by 6 to 10 wt-%. and a suitably chosen polyethylene wax are presented. Macro- and micro crystalline paraffin waxes worked well for the safe sealing of flasks and containers used to pack goods sensitive to air and moisture.
Milk cartons, butter and ice-cream cartons, containers for deep-frozen food, etc. require coatings allowing the filling of the containers at higher temperatures, and, therefore, higher melting points of the product used for coating. The characteristics of such products, also used for coating packaging materials for bread, meat, candies, etc., are listed . The paraffin wax products contain polyethylene wax.
plastics products are stronger than those obtained with paraffin wax-based products. However, in many cases the latter are preferable for this very reason, because the lower seal strengths allow the package to be opened without also destroying the whole packaging material. This is an important advantage when the content of the package is not consumed all at once, e.g. for bread packages. The strength of the seal depends both on the adhesion forces between the paper and the paraffin wax, and on the cohesion forces within the paper and the paraffin wax. These forces can be controlled by the temperature and time of the sealing operation, by the amount of wax applied, by the cooling speed after hot sealing, by the composition of the wax product and by the grade of the paper.
Lamination is the bonding operation of two or more webs, films or foils made of the same or of different materials (paper, metal foils, plastics films, etc.). Lamination allows the combination of the advantages of different types of packaging materials and the minimizing of their disadvantages. They are suited for strong, transparent packaging materials impermeable to fatty substances, gases and aromas. The adhesives are varnish resins, rubbers, etc.; – hot-melt lamination eliminating any use of solvents. The adhesives are paraffin waxes, micro crystalline waxes, paraffin waxes with polymer additives. The adhesive is applied from a heated tank onto one web, which is then joined with the other web, and finally the adhesive is solidified by passing over cooling rollers. This lamination procedure allows high speeds. Excellent packaging materials for e.g. macaroni, biscuits, cakes can be manufactured; – so-called stretch-lamination, in which paper is laminated with heat-plasticized, considerably stretched plastics film. Among hot-melt adhesives, waxes and paraffin waxes alone yield only low bond strengths, but this can substantially be improved by adding synthetic thermoplastic adhesives. The viscosity of the melt is controlled by temperature. Compositions whose viscosity are suitable within the 120 to 200 “C temperature range lend themselves readily to processing. The most widely used laminates manufactured by the hot-melt process are combinations of paper with aluminum foil, paper with cellophane and paper with plastics films. The grade of the micro crystalline paraffin waxes used as components of hot melt adhesives depends on the area of application. For instance, if porous layers are to be bonded, micro crystalline wax with good cohesive properties is required, with low oil content and no low-melting fractions. Such wax will not cause stains on the surface of the packaging material, and the low-melting fractions will not exude.
Paraffin waxes are used for sizing to reduce the moisture absorption of paper. Paraffin waxes or their emulsions used as additives promote the uniform distribution of the size in the fibrous structure of the paper, since the wax particles separate the resin adhesive particles from one another, thus preventing their agglomeration. Another advantage of adding paraffin wax is that it compensates the effect of the resin adhesives to mix with the various pigments. Thereby print ability is improved and efficiency of printing is increased. Also, the addition of 1 to 5 wt-% paraffin wax results in a substantial moisture repellent effect, owing to an increase of the surface tension of the adhesive. It is preferable to introduce the paraffin waxes into the system as emulsions containing usually 35 to 50 wt-% of solids. Particle size in the emulsion varies between 0.5 and 5 pm. Micro crystalline paraffin waxes or blends of micro- and macro crystalline waxes with melting points between 50 and 65 “C are used for these emulsions.