Web formation methods

The web formation in nonwoven production is a critical part of end-use product performance. Three basic methods used to form a web are dry laid wet laid and polymer laid (spunlaid and melt blown). Webs, other than spunlaid, have little strength in their unbonded form. The web must therefore be consolidated in some way. There are three basic types of bonding chemical thermal and mechanical. The nonwoven formation methods are summarized in Fig. 10.6. 

In the dry laid process, the conventional staple fibers are used, which are usually 12 to 200 mm or longer. The fibrous web is prepared using the classical textile carding machine or air laying machine to separate and orient 

Worldwide production of nonwovens by process 10.6 Nonwoven web formation methods (from ref. 3). 

Feed hopper Extruder Gear pump Spinneret Cooling air Draw roll Air gun Porous belt Bonding oven Vacuum exhaust Fabric inspection Wind up 

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The web bonding techniques can be generally classified into three categories, mechanical, chemical, and thermal bonding, depending on the ultimate fabric applications and/or on the web formation method. Sometimes, in order to achieve products with certain properties, a combination of different bonding methods is applied. 

Nonwoven filter media are usually produced by using one of six major types of nonwoven web formation methods air-laid, wet-laid, spunbonding, melt blowing,... 

Other techniques include a group of specialized technologies in which the fiber production, web structure and bonding usually occur at the same time and in the same place, as melt-blown and flash spun web formation methods. 

J and M Laboratories has designed equipment to obtain additional quenching by three different methods. These methods provide substantially improved productivity and modified web formation to obtain improved filtration. 

The characteristics of the fibrous web are a key determinant of the physical properties of the final product. Fibre length determines the choice of methods for forming webs. Initially, the methods for the formation of webs from staple-length fibres were based on the textile carding process, whereas web formation from short fibres was based on a wet laid process similar to papermaking. These technologies are stiU in use, but... 

Binders. Latices are used as fiber binders by the paper and textile industries. The two principal methods of appHcation are (/) wet-end addition, wherein the ionic latex is added to a fiber slurry and then coagulated in the slurry prior to sheet formation, and (2) saturation of the latex into a formed fiber web wherein the latex is coagulated by dehydration. Latices are also used as binders for particulate matter such as mbber scrap. 

Lower-density E-plastomers have found alternate use in cast film processes to make elastic film laminates with good breathability which contain laminates of liquid impermeable extensible polymeric films with extensible-thermoplastic-polymer-fiber nonwovens and nonwoven webs of polyethylene-elastomer fibers as the intermediate layers. The development relates to a breathable film including an E-plastomer and filler that contributes to pore formation after fabrication and distension of the film. The method and extent of distension is designed to produce a breathable film by stretching the film to form micropores by separation of the film of the E-plastomer from the particulate solids. This film is useful for manufacture of absorbent personal-care articles, such as disposable diapers and sanitary napkins and medical garments. In detail, these constructions comprise a liquid impermeable extensible film comprising polyolefins. The outer layer contains extensible-thermoplastic-polymer-fiber nonwovens, and an elastic intermediate layer contains nonwoven webs of fiber E-plastomers. The intermediate layer is bonded to the film layer and the outer... 

An agrochemical company provided four submission formats to PMRA the CADDY specification, the PDF format, the PDF viewed in a Web browser, and paper. PMRA reviewers compared these formats in a methodical and unbiased manner. PMRA determined that the PDF format gave evaluators a 23% gain in efficiency over paper. They felt that the results clearly demonstrated that the PDF format provided evaluators with sufficient desktop functionality and improved efficiency. 

Web server This tier forwards appropriate requests to a servelet, a request handler that uses a standard API to plug in to the Web server. It translates CGI-encoded requests into proper method calls using distributed object invocations on an enterprise component. Then it formats and returns the results to the client. 

Techniques commonly used to produce fibrous webs include the wet laid, dry laid carded, and meltblown processes. The wet laid or paper making process is the predominant method for several reasons. The wet laid process, configured properly, allows for the blending of cellulosic and polymeric components. Also, the ability to use short cut length and fine denier fiber provides for consistent blending, uniform formation, and controlled pore structure. 

Because derivations are an important part of the curriculum, it is important to present here our method of dealing with them. We present derivations in electronic format in class and make the same derivations available on the web, allowing students to spend time in class thinking rather than copying. Our method is not specific to our choice of the order of topics, but it is important for the reader to know the details of our implementation. We encourage students to focus on the following points in dealing with derivations ... 

Once the value-added service has been designed, fees established, and the method(s) for compensation selected, the pharmacist must learn how to submit claims. When providers submit claims to Medicare, Medicaid, or any other third-party payers, the claim typically is submitted on the CMS Form 1500. One exception to this is the hospital outpatient clinic, which uses CMS Form 1450. On CMS Form 1500, information regarding the submitting entity, referring physician, type of services offered, and related health condition is included. To convey this type of information, CPT codes and ICD-9-CM codes are used. These coding systems provide detailed information regarding the types of services provided and the specific health condition in a numerical format. Example CMS 1500 and 1450 forms are available on the CMS Web site (www.CMS.hhs.gov). 

Taking, for instance, Al, with a melting point of 660 °C and a web substrate temperature of 50 °C, zone I formations will be created (porous structure, pointed crystallites, large voids) and up to 250 °C, formations in the transitional area (densely packed fibers) will appear. Up to 450 °C zone II (pillar-shaped crystallites), and above this temperature zone III (conglomerate-type crystallites) formations will be seen. Because of the relatively low maximum thermal stress that may be applied to polymer webs, the growth in metallized layers on polymer webs mainly occurs in Zone I or in the transitional zone. The different growth is also evident from comparison of cooling drum and free-span coater methods. 

Photoreceptors are prepared by the sequential application of the various layers onto a web or drum substrate. Vapor-deposition methods can be used for some pigments. Most layers, however, are coated from solution or dispersions in organic solvents. Wicks (1986) has reviewed film formation from polymer solutions. The choice of solvent is determined by such factors as solubility, evaporation rates, surface tension, toxicity, as well as environmental... 

This entry will be divided into sections covering the classification of ceramics, a brief history of ceramics, raw materials for ceramics, properties and applications of ceramics, processing of ceramics, and a brief commentary on future trends. The field of ceramics is very broad and encompasses not only well-known, conventionally used materials and technology but also much newer compositions, processing methods, and applications. More detailed information on all of these sections is available in printed format and on the web.[ °- "l... 

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