|
Архитектура Аудит Военная наука Иностранные языки Медицина Металлургия Метрология Образование Политология Производство Психология Стандартизация Технологии |
|
|
Архитектура Аудит Военная наука Иностранные языки Медицина Металлургия Метрология Образование Политология Производство Психология Стандартизация Технологии |
Intaglio, Gravure or Photogravure Printing
Gravure is a method of printing from a cylinder or plate in which the design is sunken below the surface as distinguished (в отличие) from relief printing. Intaglio printing is produced from copper cylinders and plates on sheet –fed and web rotary machines. The gravure processes which provide the printing surface on the cylinder or plate are almost completely photographic in technique.The sunken portions are cells which hold the ink for impression. We know the cells to be of constant width, which is determined by the screen (растр) used. Screen may be as fine as 300- line, but normal work requires a 150- line screen or approximately 22, 000 cells to the square inch. The deeper the etch (травление) the darker the tonal value. As gravure cylinder is ground and polished to close tolerance (малый допуск) no make- ready (приправка) is necessary. Therefore the first impression is as clear and sharp as the last one and the gravure process does not depend upon individual skill and experience as any other printing method. To make a printed impression, the cylinder or plate revolves in the ink container so that the cells will be filled with ink. Then the cylinder revolves further and the surplus (излишек) ink is mechanically wiped off by a steel scraper (скребок) leaving the non-printing surface clean but permitting the ink to remain in the cells. The cylinder now completes its revolution and the ink remaining in the cells is transferred to the moving web by pressure exerted by a rubber impression roller. This roller presses the web against the engraved cylinder and the web lifts the ink from the cells. Задание 2. Выберите утверждение, соответствующее содержанию текста. 1. The printing surface on the cylinder or plate is provided by: a. a printing methods b. almost photographic methods c. a scraper 2. The darker tonal value is made by: a. shallow etch b. inking c. deeper etch 3. The ink remaining in the cells is transferred: a. to the moving web b. to the cylinder c. to the ink container 4 Intaglio printing is produced from a cylinder or plate: a. in which the design is raised above the surface b. in which the design is on the plane c. n which the design is sunken below the surface Text 3C Задание 1. Прочтите текст, отыскивая в нём ответы на поставленные вопросы. 1. What is sheet- fed gravure? 2. What presses is sheet – fed gravure done on? 3. What presses is rotogravure done on? 4. What image carriers are used for sheet – fed gravure? 5. What image carriers are applied for rotogravure? Sheet – Fed Gravure and Rotogravure Sheet – fed gravure and rotogravure are based on photography and photo mechanics: both printing methods are capable of reproducing continuous tone pictures, and also line drawings together with type images. Sheet – fed gravure is often designated as photogravure in distinction from rotogravure. Unfortunately these two names do not indicate the true differences between the two intaglio methods to which they are applied. These differences lie neither in the use of photography on which both methods are based- nor in the rotary principle of printing, because this principle, too, is common to both. Technically speaking the main differences between the methods are two: first, that photogravure is done on sheet-fed presses, whereas rotogravure uses exclusively roll- fed equipment: and second, that the image carriers of photogravure are flat metal plates (in the USA mostly), whereas those for rotogravure are etched metal cylinders. (In Europe, sheet- fed gravure is often done with etched cylinders rather than flat plates as image-carriers). Text 3D Задание. Прочтите текст, пользуясь полиграфическим словарём для понимания всех деталей описания. Gravure Plates and Cylinders
Image carriers for gravure are either plates or cylinders. Plates are used for sheet- fed gravure, cylinders for rotogravure. Gravure plates consist of refined copper, have a highly polished surface, and are approximately 0.20 inch thick which makes it possible to wrap them around the plate cylinder of the press. Gravure plates need no particular preparation but should be free of surface defects. «If the plate has deep polishing marks or other defects, it should be polished with engraving coal, using kerosene, water or machine oil as a lubricant. To be effective, the polishing must be continued for a considerable time». It should be mentioned that gravure plates are much less used than gravure cylinders. Gravure plates are the image carriers for jobs printed by sheet-fed gravure and they are also used for the proofing of material which will finally be printed with cylinders, a technique widely used in advertising production. Cylinders can be made of iron, steel, copper, and aluminium. The image forming metal of gravure cylinders is copper. As the body of most gravure cylinders consists of other metals, they must be covered with copper before they can be used as image carriers. Copper deposition is done electrochemically in a plating tank. The thickness of the copper deposit varies greatly with the circumference, length and construction of the cylinder. The larger the cylinder, the greater the deposit. Photography and Retouching for Gravure
Essentially, photography for gravure does not differ from other kinds of graphic arts photography. The function of photography is the same in gravure as in all other printing processes: photography must provide intermediate records of the original images to be reproduced as required for the making of the printing-image carrier. But photography for gravure is more complex and can be executed in more variations than other branches of graphic arts photography. This is so for two main reasons: one is the necessity of providing the bearing surface for the doctor- blade; the other is the fact that gravure is capable of reproducing continuous-tone images in three principally different ways.
Photomechanics for Gravure Photomechanics for gravure often appear to the beginner to be complex and a little confusing. But if you keep firmly in mind what functions photomechanics have in the production of gravure image-carriers, you will not find the subject too difficult. You want to remember that gravure can obtain tonal reproductions either bу depositing ink films of varying thickness in different areas of the printed image or by varying the size of intaglio halftone dots, or, finally, by combining both techniques. Technically, this is achieved either by varying the depth of cells, or by varying the area of cells, or by varying both cell depth and area. Close control of both depth and area of gravure cells is therefore essential for all gravure methods. Treating the image carrier with an etchant removes the required amounts of metal where it should be removed and thereby produces the gravure cells. Photomechanics provide the guide and control for the etching operation. Both the cell areas and their depth can be decisively influenced by the photomechanical image which is either formed on the surface of the image carrier or transferred to this surface after having been formed independently. We distinguish two kinds of photomechanical images: stencils and continuous photomechanical layers of varying hardnesses and thicknesses. Stencils serve for the making of intaglio halftone image carriers, whereas images of varying hardness and thickness serve as resists in the etching of gravure cells of varying depth. A firm grasp of the difference between these two photomechanical products is a prerequisite for the understanding of photomechanics for gravure. In photomechanical stencils, the light-sensitive coating is either completely hardened or not hardened at all, with no significant variations between these two extremes. During development of the photoprinted coating, all hardened areas remain on the supporting surface and all unhardened areas are washed away. In continuous photomechanical layers of varying hardness and thickness, the light-sensitive coating is variably hardened throughout and changed in its solubility to various degrees in various areas. In some areas the coating is harder; in others it is less so. After development, such a coating still presents a continuous uninterrupted film, but it is a film of varying hardness and thickness. The hardness and thickness variations of this film depend on the amount of light to which a given area is exposed; areas exposed to more light are more hardened than areas exposed to less light. These variations in the physical properties of the resist influence the extend to which a given etchant can pass though it or permeate and etch the metal underneath. The hardness and thickness of the developed photomechanical coating plays a decisive role in the etching of gravure image carriers with cells of varying depth. As a simplified generalizations, it can be said that the depth of cells is inversely related to the hardness and thickness of the photomechanical film. The photomechanical film serves as a resist during the etching of the intaglio image carrier. In gravure methods the resist protects various metal areas not uniformly but to varying degrees from the etchant, depending on its own hardness and thickness in any given area. The harder and thicker the resist, the more an area is protected from the action of the etchant; the more an area is protected, the less it will be etched. Conversely, the less an area is protected from the etchant the deeper will the cells be etched. The lands, bridges, or posts, as the metal areas between cells are called, must consequently be completely protected, whereas the deep shadows, which require the deepest etched calls, are least protected from the etchant.
Lesson 4 Грамматика: Цепочка определений. Основной текст A: Paper: beneath the surface. Цепочка определений Если между артиклем (или другим определителем) и существительным, к которому он относится, стоит несколько существительных, они образуют цепочку определений, а существительное, к которому относится артикль, является по отношению к ним опорным. С него рекомендуется начинать перевод цепочки определений. ink properties – свойства краски; the car speed calculation problem – проблема вычисления скорости автомобиля. Некоторые существительные – определения могут переводиться прилагательными, например: bar – стержень, magnet – магнит; bar magnet – стержневой магнит; machine building industry – машиностроительная промышленность. Однако подобный способ перевода не всегда возможен, часто такие определения приходится переводить существительными в косвенных падежах или предложными оборотами, при этом целесообразно пользоваться " правилом ряда". Порядок перевода обуславливается смысловыми связями между определениями и определяемым словом. Перевод следует начинать справа налево с последнего существительного, а существительные, стоящие перед ним в роли определения, нужно переводить на русский язык существительными в косвенных падежах (чаще родительном) или предложным оборотом. Например: 1 2 3 3 2 1 products price decrease – уменьшение цен на изделие. Исходя из контекста, устанавливается связь между определениями, например: 3 1-2 the electric equipment supply – питание электрооборудования. В данном случае первое слово (electric) является определением второго (equipment). Часто в подобную атрибутивную группу слов входят прилагательные, причастия, например: hard – won freedom – с трудом завоеванная свободa; stainless steel top cover – верхняя крышка из нержавеющей стали; fixed contact – неподвижный контакт. Упражнение 1. Переведите на русский язык: the control system; the measuring unit; semiconductor industry; measuring equipment; life time; effective life time; power consumption; first-class quality; room temperature; power supply line; normal operation conditions; rubber industry; control desk; print quality; average coating weight; high speed wet-on-wet sheet-fed rotary letterpress printing.
Упражнение 2. Проанализируйте и переведите следующие словосочета-ния на русский язык: the traffic speed; the traffic speed increase; the railway bridge; the railway bridge reconstruction; the London underground; the London underground problem; the thermoelectric generator development; the energy accumulation process; the modern house ventilation facilities; the car speed calculation; the arch bridge construction site; the research program result; the Moscow region newspaper; the temperature limit determination; the household goods store; the steam engine invention; the deep sea current measuring device. Упражнение 3. Переведите на русский язык следующие словосочетания: internal combustion engine; George Washington Bridge bus terminal station; current events; cylinder wall; English Channel coast; supersonic vertical take-off bomber; fourteen bird and animal stories and plays; wooden house advantages; automatic flight control equipment; essential research programme; beginning college student; improved traffic flow; free school bus service; two-page story; two-bed hotel room, life-long hobby; class words and expressions; federal highway office; Dynamo versus Spartak football match; National Coal Research Institute; Electronic Research and Engineering Laboratory. Vocabulary Notes
Задание. Переведите следующие предложения. 1. rags – тряпьё, ветошь At first paper industry relied on the use of rags. 2. linen – льняная ткань In the West it was linen that was used for papermaking until the mid-1800s. 3. cotton – хлопок Cotton was introduced later for papermaking. 4. to treat – обрабатывать Both linen and cotton were treated to turn them into papermaking fibre. treatment – обработка Linen and cotton were used for papermaking because of minimum treatment required. 5. fibre – волокно Developments of non-cellulosic fibre from plastic are already on the market. 6. pulp – древесная масса; волокнистая масса, целлюлоза Different techniques are used for making pulps of woods. 7. softwood – мягкая древесина Spruce and pine are considered to be softwoods. 8. hardwood – твердая древесина Hardwoods are reaching the limit of their present economic exploitation. 9. binder – связующее вещество; слой; покрытие бумаги Lignin is a binder for forming a matrix of fibres. 10. damage – ущерб, повреждение Damage to the fibre results in a weakened fibre. 11. to weaken – ослаблять Weakening the fibre is not taken into account with mechanical pulp. 12. bark – кора The tree is ground after bark removal. 13. to grind (ground, ground) – перемалывать For making mechanical pulp the tree is ground to produce small chips of wood. 14. resin – смола Small chips of wood contain all the lignin and resins after mechanical treatment. 15. formation (of paper) – направление волокна Formation of paper means the distribution of fibres. 16. density – плотность The thickness of the fibre cell wall is related to the sheet density. 17. bulk – объем; пухлость, рыхлость (бумаги) The hardwood pulps improve bulk. 18. opacity – непрозрачность Filters increase the opacity of the paper. 19. absorbency – впитываемость The hardwood pulps give better absorbency to paper. 20. tear – сопротивление бумаги надрыву Thicker walled fibres give high tear. 21. tensile – растяжимый; растяжение Lower tensile is due to thicker walled fibres. 22. burst – сопротивление (бумаги) продавливанию; разрыв кромки The thickness of the fibre cell affects burst of paper. 23. smoothness – гладкость Smoothness, whiteness and gloss may affect print quality. 24. beating – размол бумажной массы Sulphate pulps require more beating than sulphite pulps. 25. acid – кислота Sulphite process is an acid system. 26. alkaline – щелочной Sulphate process is an alkaline system. 27. to alter – изменять The quality of pulp can be altered in sulphite process. alteration – изменение Alteration of the pulping conditions has no influence on the quality of pulp in the sulphate process. 28. shrinkage – усадка (бумажного листа) Sulphate pulps produce lower shrinkage at the same strength. 29. bleaching – отбеливание; обесцвечивание Special bleaching chemicals and equipment are used to produce good coloured mechanical pulps. 30. permanence – стойкость (краски) Mechanical pulps have little permanence. 31. waste paper – макулатура, отходы бумаги Waste paper is a good fibre source. 32. coated (body stock) paper – мелованная бумага Better grades of waste paper can be used to make coated papers. 33. impregnation – пропитывание; пропитка Impregnation of papers is often used to produce laminated surfaces.
Text 4A
Задание. Прочтите текст. Paper: beneath the surface From the invention of papermaking in China until the mid-1800s the industry relied on the use of rags. The exact composition of these rags depended on the origin of rag, but in the West it was mainly linen before the introduction of cotton. Their use was dictated by the basic requirement of minimum treatment to turn them into papermaking fibre. The slowness to develop alternative plant fibre sources was due to the lack of chemical technology to produce chemicals and materials resistant to chemical attack. The second major stage in fibre usage for papermaking began in the 1860s with the discovery of pulping techniques for straws, esparto and softwoods, such as spruce and pine, first by the soda process, then by the sulphite process, and finally by the sulphate process. At the moment it is wood that supplies the vast majority of papermaking fibre but the variety and quality of the pulps available to the papermaker have greatly increased - high white hardwood and softwood pulps, high-yield semi-chemicals and mechanicals. Each pulp has its own particular property and it is the skill of the papermaker which gives the customer such a wide range of papers with differing characteristics. The third stage in fibre development, if not with us now, is almost upon us. Both softwood and hardwoods are reaching the limit of their present economic exploitation, hence new methods of forestry, and more rapid growing species giving a better return on capital and land usage and improved pulping efficiencies are already under active research and development. Developments of non - cellulosic fibre from plastics, or even plastic papers are already on the market. All the cellulosic fibres used in papermaking have been part of a plant and the final characteristic of a fibre in a sheet of paper is the product of its construction and subsequent separation, purification and papermaking history. It is important, therefore, to have a basic understanding of fibre structure to appreciate the final influence that the fibre has on the paper surface. Fibre structure and behaviour is called fibre morphology. In the simplest form a fibre, or elongated plant cell, consists of a series of concentric tubes, each tube or layer having its own structure and function. The outer layer contains the least cellulose and most lignin, whereas the innermost layers contain the bulk of the cellulose. Each fibre in turn is bonded to its neighbour by lignin, or other binder, to form a matrix of fibres. The pulping operation leading to the chemical wood pulps must first remove this lignin and the lignin in the cellulose fibre with the least damage to the fibre structure. Damage to the cellulose fibre results in a weakened fibre. In the case of ground-wood, or mechanical pulp, such considerations do not apply because after bark removal the tree is ground to produce small chips of wood still containing all the lignin and resins. The ratio of the length of the fibre to its diameter and the thickness of its cell wall are of great importance. The difference between softwood and hardwood fibres is shown by such considerations. Softwood fibres average 2 to 5 mm in length and 30 to 40 microns in width, while hardwood fibres average 1.5 mm in length and 10 to 30 microns in width. The hardwood fibres are also lighter than the softwoods. Such factors indicate that one gramme of a bleached softwood pulp contains about ten million fibres while a similar bleached hardwood contains twenty-five million. This difference in the number of fibres in a given weight is sufficient to alter sheet characteristics, particularly the evenness of formation and smoothness. The thickness of the fibre cell wall and the ease with which it can collapse and bond with other fibres is related to the sheet density. Thicker walled fibres give high bulk, opacity, porosity, absorbency, tear, but lower tensile and burst, with thin-walled fibres giving dense, well-bonded sheets. The hardwood pulps not only improve formation but improve bulk, smoothness, opacity, absorbency, require less beating and are cheaper than the softwood pulps. One of the most important fibres in this group is eucalypt, a fast-growing species which gives a fibre of almost constant properties. It is now found in a large number of printing papers since its properties resemble those of esparto-the traditional fibre found in printing papers. The ever-rising cost of esparto, compared with the more stable cost of eucalypt, has forced papermakers to use eucalypt fibre. There are four different chemical pulping processes commonly used for treating plant fibres and these can reduce or reinforce the differences due to pulp-wood species. The two main pulping processes are sulphite - an acid system and sulphate (or kraft) - an alkaline system. As a rule the quality of pulp can be altered in the sulphite process by alteration of the pulping conditions such as temperature, pressures and concentration of cooking chemicals, but this is not easy for the sulphate process where it is the wood species which has the major influence on quality. Sulphate pulps, when compared with sulphite pulps, tend to have a higher tear, produce lower shrinkage at the same strength, have higher bulk, opacity, absorbency but require more beating to give a certain level of drainage, thus they generally allow the papermaker to run his paper machine faster at any given condition. The mechanical or groundwood pulp process is simple and consists of grinding a log, from which the bark has been removed, in the presence of water against a grindstone to produce a wood flour or a suspension of small wood chips. Traditionally only softwood species were used but now hardwood species are used. The quality of the pulp depends on the fineness of grind and the design of the grinding equipment. Normal chlorine bleaching techniques employed for chemical wood pulps cannot be used and special bleaching chemicals and equipment are required to give good coloured mechanical pulps; no high white mechanical pulps are made. Mechanical pulps are cheap, low-coloured, have poor strength, little permanence, discolour in sunlight, have good dimensional stability but are cheap and are used as a filler pulp. They are used in newsprint, cheap mechanical printings and cheap banks. With the current emphasis on pollution and the recovery of wastes, it is timely to consider the importance of waste paper as a fibre source. The use of waste paper is already well established in the UK for board making, but a higher recovery of waste could enable a major economic contribution to be made to a better sorting of waste. In this way better grades could be re-cycled after de-inking to make cheap printings, newsprint and the coated body stock papers as happens in Austria and certain other European countries where de-inking is more firmly established than in Britain. In a discussion on papermaking's future the word “plastics” is bound to occur. The word means one of four processes: the use of synthetic fibres, the impregnation of fibre material with polymer, plastics paper or films, or grafting. Papermakers already use rayon and nylon for making speciality papers such as filters, so their development for other uses is possible if the economics are right. The impregnation of papers is often used to produce such products as the inner soles of shoes, imitation leather and laminated surfaces. Japan, fearing a shortage of wood pulp, developed the use of plastics papers - some of which are only plastics films - when the price of oil products fell and the price of wood products was rising. However, oil is rapidly rising in price and subject to political discrimination, which makes such a source of raw material unattractive to industrialists. Упражнение 4. Переведите следующие словосочетания на русский язык: type matter; land transport; magazine paper; gravure printing quality; excessive ink tack; press speed; plant fibre sources; hardwood pulp; softwood pulp; fibre structure; surface sizing; waste paper; coated body stock papers; plastics paper; speciality papers; imitation leather; wood pulp; plastics films; oil resistance; tear resistance; improved strength properties; hand correction; full-page newspaper plates; reproduction processes; standard thickness gauge; light source; water rate bill; halftone screen formation; sidewall protection; image areas; bath replenishment; full range screen negatives; powder additive; a modified copper powderless etch chemistry. Упражнение 5. Переведите предложения согласно данным моделям. it is necessary – необходимо, нужно it is possible – можно, возможно it is evident – очевидно, ясно it is clear – ясно, понятно it is important – важно, необходимо 1. It is important to have a basic understanding of fibre structure to appreciate the final influence that the fibre has on the paper surface. 2. It is evident that the most important paper properties that influence printability are: smoothness, absorption, surface strength, optical properties, moisture content and dimensional stability. 3. It is possible to use waste paper as a fibre source. 4. It is necessary to differ web papers and paper for sheet-fed printing. 5. It is clear that paper is a product of a complex manufacturing process. 6. It is very difficult to explain such terms as " printability" and " runnability" of paper. 7. It is necessary to remember that the two sides of uncoated papers have different surface characteristics. 8. It is quite clear that the profession of an engineer is very difficult but interesting. 9. It is important to use different kinds of paper for different printing presses and processes. 10. It is evident that if paper with a coloured coating is required, colour pigments are used in the coating mixture. Упражнение 6. Переведите следующие предложения, обращая внимание на усилительную конструкцию. 1. It is the lack of chemical technology that explains the slowness of the development of alternative plant fibre sources. 2. It is wood that supplies the vast majority of papermaking fibre. 3. It is the skill of the papermaker which gives the customer such a wide range of paper with different characteristics. 4. It is the wood species which has the major influence on quality for the sulphate process. 5. It is because of the shortage of wood pulp that plastics papers were developed. 6. It is fillers that increase the opacity of the paper. 7. It is cellulose fibres alone that readily soak water and other liquids. 8. It is only better grades of paper that are made of rags. 9. It is tensile strength, flatness and ink receptivity that influence runnability and printability of papers. 10. It is the basic size and the basic weight of paper that are essential when paper is ordered by Print Shop.
Text 4В Задание 1. Прочтите текст, стараясь понять основное содержание. (Этот текст надо прочесть за 5 минут). There are many kinds and grades of paper, but most of them come under the five general classes such as: newsprint, book papers, writing papers covers and cardboards. While papermaking is a separate industry, its product is so essential to printing that in order to obtain the best results in a job, a printer must have a thorough knowledge of the materials and processes used in the production of paper. A printed product consists in reality of two things: a printed impression and the paper upon which the form is printed. Both are equally important. A careful selection of paper is required for each job in order that the finished product may be harmonious and suited to its particular purpose. Possibly no other substance is used so extensively as paper. That indispensable medium bears and preserves the printed word. The most important part of paper is the fibre which forms the body and gives it strength. The fibre is always a vegetable product. Almost any kind of vegetable fibre can be used in paper-making, but those fibres which are strongest and most plentiful are commonly used. Generally speaking, printing papers may be classified into two main groups: wood-pulp papers and rag papers. Many papers are also formed by a combination of these two basic fibres and are known as rag content papers. Cheap printing papers such as newsprint, most book papers, cardboards and cheaper grades of writing papers are made from wood pulp. Pulp is produced by two methods: the mechanical process and the sulphite process. In the mechanical process the logs are ground into fine sawdust, while in the sulphite process the wood is cut into small chips, and then the fibres are separated by cooking them in large kettles known as digesters. The latter process is used more extensively because of the superior quality of the pulp for printing and writing purposes. Notes: 1. cardboard – картон 2. digester – котел 3. log – бревно 4. preserve – сохранять 5. sawdust – опилки 6. vegetable – растительный Задание 2. Выберите утверждение, соответствующее содержанию текста. 1. The most important part of paper is: a) sizing; b) the fibre; c) sulphite. 2. Cheap printing papers are made of: a) wood pulp; b) rags; c) chemicals. 3. Pulp is produced by: a) one process; b) two ргоcessеs; c) by three processes. 4.Sulphite process is used more extensively because of a) its simplicity; b) its cheapness; c) the superior quality of the pulp for printing and writing purposes. Задание 3. Ответьте на следующие вопросы. 1. What forms the body and gives strength to paper? 2. By what method is pulp produced? 3. What kinds of printing paper are made of wood pulp? 4. How is pulp produced in the mechanical process? 5. Why is the sulphite process used more extensively? 6. How are the fibres separated in this process? Задание 4. Переведите на английский язык. 1. Волокно является основной частью бумаги. 2. Бумага изготавливается из тряпья и дерева. 3. Любой вид растительного волокна может быть использован в производстве бумаги. 4. Древесную массу получают либо механическим, либо сульфитным процесс-сами. 5. Сульфитный процесс даёт бумагу высокого качества. 6. Печатник должен знать, как изготавливается бумага. 7. Бумага сохраняет бумажное слово. Text 4С Задание 1. Прочтите текст. Printability of paper cannot be measured by one property alone. The individual properties that together constitute printability will depend upon the process used, the quality, and the rate of production required. Nevertheless, almost all printing processes put ink on to paper under pressure. Therefore there must be some underlying principles that are common to all processes. The most important of them is the penetration of inks into paper. Fundamental work on printability being carried out at various printing research associations has been directed to a study of this property. The problem of printability is to find the necessary paper requirements to enable a particular type of job of the required quality to be printed by a particular process at an economic speed. Because of demands (требования) made for certain properties in the paper by reason (причина) of its end usage it is often the case that it is not ideal from the point of view (точка зрения) of printing. It is then necessary to find the conditions, the process and the ink that enable the best possible result to be obtained from the paper. When papers are to be compared (сравнивать) for suitability (пригодность) for particular work, it is usually possible by means of testing to predict (предсказать) whether specific defects are likely to occur. Printability research, however, is a comparatively recent science and has not yet reached the stage where it would be possible to state (утверждать) definitely that one paper will give a better print on all counts than another. One of the difficulties at the present time is that there is no established method of assessing (определение) the factors that together make up print quality.
Задание 2. Ответьте на вопросы по тексту 4С. 1. What does printability depend upon? 2. What is the most important principle of all printing processes? 3. How can the best possible result be obtained from the paper? 4. What is the problem of printability? 5. Is printability research a new or an old science? 6. What is one of the difficulties at the present time? Задание 3. Озаглавьте текст. Text 4D Задание 1. Прочтите текст. Paper Properties There are few papers which are suitable for all processes and most paper mills therefore depart from standard grades and develop papers specifically for individual processes. Certain paper properties affect all printing processes since they concern runnability and the visual impact of the finished work. Most printers, whether dealing with sheets or reels, demand good runnability first, while their customers look for quality of reproduction. In many cases it is simple for a paper mill to satisfy one or the other but the difficulty comes in meeting both requirements simultaneously. This is due to the fact that nearly all desirable printing properties of paper conflict with each other. By altering one property, one or more other properties are also changed. Thus to improve the printing quality of newsprint by increasing the finish, also compresses the sheet and renders it less porous to the black news ink, increasing second impression set-off, ink piling on turner bars and smeared copies. Similarly, to improve the gravure printing quality of a magazine paper by increasing its moisture content to make super - calendering more effective, sometimes leads to difficulties of level on reels, with subsequent bad runnability on the rotogravure press. Consistency of quality is most important and a printer expects this of every sheet or reel of a delivery, since variations within sheets, reams or reels cause far more trouble than a paper which, though it may be slightly below standard is a similar quality throughout the order. Colour and whiteness of paper are of prime importance to the paper buyer, the printer and the inkmaker, since they affect the appearance of the finished job. Colour, unfortunately, is so much a matter of individual preference that there is no such thing as the " best" paper in this respect. What is important is that the inks, plates, and paper combine to produce the most satisfactory result. Obviously, the whiter the paper, the better the printing result. Opacity is also of great importance, since paper of low opacity detracts from the appearance of the print in several ways. First, the printing onthe reverse side of a sheet shows through; secondly the effect of ink penetration is greater than on a more opaque paper and thirdly it reduces the apparent printing contrast, giving the impression of low print density. Papermakers have many methods of improving opacity but these usually increase costs, lower the brightness, or change other desirable properties of a paper. Flatness of a sheeted paper is important in all printing processes, particularly in litho and gravure due to the fact that the paper is in contact with the printing nip over its entire width. In these circumstances, any surplus paper in the form of a wave or cockle must form into a crease or cause misregister. Lack of flatness can appear in several ways, i.e. tight-edges, wavy, cockled, or curled sheets and except for the latter two, the reasons may not be the same on all occasions, and the cause may be impossible to ascertain. Wavy and tight edges are the most common and fully understood flatness defects since paper can pick up or release moisture according to the relative humidity of its surroundings with corresponding expansion or contraction. Only the fibrous portion of the paper is thus affected, so it follows that heavily loaded imitation art papers will change less than those without loading. If paper is brought into а warm pressroom from a cold atmosphere and immediately unwrapped, moisture from the warm pressroom air will condense on the exposed edges of the stack causing swelling of the fibres and wavy edges. Stacks should therefore be left wrapped to come to equilibrium with the pressroom temperature. Unwrapped sheeted paper with a moisture content higher than that at which it would be in equilibrium with the relative humidity of the pressroom will release moisture from exposed edges and leave the stacks with surplus paper in the centure (a defect known as tight edges). From the above, it will be seen that paper should not only be allowed to stand until in equilibrium with temperature, but should be left unwrapped until just before printing. Between workings, covering the stacks with polythene or other waterproof material, keeps dimensional change to a minimum, but these measures only apply to unconditioned pressrooms. Various instruments are available for checking the condition of paper before printing and these are discussed later. Paper which is not flat causes difficulty in feeding and delivery and introduces the troubles of creasing and misregister. Paper expands or contracts considerably more in the cross than in the machine direction due to the method of manufacture and the properties of individual fibres. This is why litho printers and high quality letterpress colour printers, normally require long grain paper which implies that the machine direction of the paper is parallel to the axis of the printing cylinder. Although very limited in the amount of change he can mаkе, the printer can often compensate for stretch or shrinkage of paper when it occurs round the cylinder by altering the circumference of cylinders with packing. Formation. - Another property affecting all printing processes is formation. This term means the distribution of fibres within the sheet as seen when holding the paper up to the light. Thus, a good formation is one that appears even and clear, while a bad formation exhibits point-to-point variations in translucency due to fibres coagulating in clumps, instead of being evenly distributed. It affects printing since variation in fibre density results in uneven ink vehicle absorption. In cases of bad formation, the effect shows particularly in solids and to a lesser extent in the mid-tones of half-tone prints. Paper gloss frequently has a considerable influence on the appearance of printing and with transparent inks the reflection from a paper with a high gloss noticeably enhances the printing result. Having dealt with paper properties which concern all printing processes, it is now necessary to consider those relating to specific ones. Letterpress printing is influenced by numerous paper properties apart from those mentioned above. Of these, smoothness is very important, since lack of it results in incomplete ink transfer. Lack of smoothness may be tolerated if the paper has sufficient compressibility enabling it to become smooth under printing pressure. Pick Resistance. - There are three types of pick, all of which are troublesome to printers, and these are: coating pick occuring within the coating layer itself, due to insufficient and/or unsuitable binder (adhesive); coating pick occuring at the interface between the coating layer and the base paper due to poor bonding of the two; and body pick occuring within the substrate of the base paper due to its physical weakness. Picking of any kind can be due to factors other than weakness of the paper, for example, excessive ink tack and printing pressure. In letterpress printing the demands on paper are less critical in this respect than for offset lithography. Nevertheless, with increasing press speeds the greater use of colour and wet-on-wet printing, severe demands are made on the pick strength of paper. The absorptive properties of paper for letterpress printing influence numerous print characteristics. Liquid is absorbed into paper by capillary attraction into the interfibre spaces. It follows, therefore, that the absorptive properties of paper are altered most by supercalendering. But the type of fibre, loading, surface treatment (Pigmented or otherwise) and the amount of beating all have significant effects on absorption. These factors are particularly important in newspaper and similar types of printing which rely entirely on the high absorption of the paper for " drying". Surface treating paper at the size press, being film forming, also lowers its absorptive capacity, as does roll-coating which relies on heavy supercalendering to obtain the requisite smoothness. Both types of treatment resulted in problems of ink-setting until modified inks were developed. High speed wet-on-wet sheet-fed rotary letterpress printing has also caused problems for both paper- making and ink manufacture. The absorptive properties of coated papers which were satisfactory on slower presses were insufficient in some cases causing set-off and sticking in the delivery stacks. A paper which is too absorbent can cause chalking or powdering by the vehicle of the ink being absorbed into paper too rapidly leaving pigment on the surface with insufficient binding medium. It is well known that coating paper with a layer of pigment and binder is one of the most effective ways of improving its surface for letterpress printing end generally speaking, printing qualities improve as coating weight increases. Thus, the best art papers have up to 30 g.s.m. of coating on each side while the lowest weight applied to cheaper papers may be as little as 5 g.s.m. on each side. An average coating weight for good results is about 16 g.s.m. per side. Coating, being principally china clay or other finely ground pigment accepts ink more readily than a fibrous surface and results in higher print density and when supercalendered gives higher print gloss. Type of body paper, method of coating and the formation itself all have a considerable bearing on the printing quality. Web-fed paper troubles. - Apart from any of the above properties which affect either sheet-fed or rotary letterpress printing, there are those which can cause trouble in web fed work only. The common faults are those or piping, stretched edges, generally bad level and uneven tension through the reel. It is a mistake view that web breaks are caused by weak paper, that is, paper of low tensile or other strength properties. The " pull" on a reeler in the paper mill is higher than on any printing machine and paper which continuously breaks on a reeler could not be sent out. Breaks are almost invariably caused by faults in paper, for example, edge tears, incorrect printing press tension, out-of-line reel stands or too much printing pressure. Overdry paper can cause breaks due to its rather brittle nature but, more serious, dry paper is prone to the generation of static electricity which often causes troubles on newspaper and magazine presses, especially at the folder. Static troubles can also be a dry pressroom atmosphere.
Задание 2. Сделайте доклады в соответствии с прочитанным текстом: 1. Важнейшие свойства бумаги. 2. Свойства бумаги, оказывающие влияние на высокую печать. 3. Способы улучшения поверхности бумаги для высокой печати. 4. Преодоление трудностей, связанных с бумагой, при рулонной подаче. Lesson 5 Грамматика: Словообразование. Основной текст A: General Characteristics of Inks. Словообразование В английском языке имеется несколько типов словообразования: аффиксация, т.е. прибавление к корню суффикса или префикса; конверсия и словосложение.
Основные префиксы и их значение
Основные суффиксы существительных
Основные суффиксы прилагательных
Основные суффиксы наречий
Основные суффиксы глаголов
Упражнение 1. Образуйте с помощью суффикса -еr (-or) существительные от данных глаголов; переведите их на русский язык: sail, act, write, read, visit, speak, sleep, found, lead, direct. Упражнение 2. Образуйте при помощи суффиксов -er, -or, или -istсуществительные от нижеприведённых слов: burn – гореть receive – получать compose – сочинять музыку drive – вести машину regulate – регулировать accumulate – аккумулировать special – специальный social – социальный. Упражнение 3. Образуйте с помощью суффикса -ian существительные от данных слов, переведите их на русский язык. Обратите внимание на изменения в произношении: technic, mathematics, statistics, politics, music. Популярное:
|
Последнее изменение этой страницы: 2017-03-11; Просмотров: 757; Нарушение авторского права страницы