Calendering bonding

The formaldehyde approach is stiU used by Futamura Chemical (Japan). They make spun-laid viscose nonwovens where the hydroxymethylceUulose xanthate derivative formed from formaldehyde ia the spia bath allows the fibers to bond after layiag. This process was originally developed by Mitsubishi Rayon (30), who later found that the derivative was thermoplastic, and the web could be calender-bonded (120°C) prior to regeneration (31). 

Three physical properties that may improve field performance are tensile strength, tear strength, and abrasion resistance. In case of SB, both tear and abrasion properties are controlled by the amount of thermal calender bonding imparted to the fabric. To increase tear strength, the amount of thermal calender bonding is decreased via reduced temperature and/or pressure. On the other hand, abrasion resistance is normally only improved if the amount of thermal calender bonding is increased (Avril, 2001). 

Production carded cotton/PP web on one or both sides of spun bond calender. Bonding Thermally into two or three layers. 

Fusion technology bonds the thermoplastic PP nonwoven top sheet, barrier cuffs, and PE film outer cover. Thick constructions usually use ultrasonic bonding and thin constructions use pattern calender bonding. 

Thermobonding calender bonds the web selectively by thermal bonding. 

In the calendering method, a PVC compound which contains plasticizers (qv) (60—120 phr), pigments (qv) (0—10 phr), fillers (qv) (20—60 phr), stabilizers (10—30 phr), and other additives, is kneaded with calender roUs at 150—200°C, followed by extmsion between clearance-adjusted roUs for bonding onto the substrate. This method is employed for products with thick PVC layers, ie, of 0.05—0.75 mm thickness. The main plasticizer used is di-2-ethylhexyl phthalate (DOP). For filler to reduce cost, calcium carbonate is mainly used. A woven or knit fabric made of cotton, rayon, nylon, polyester, and their blend fiber is used as substrate. For foamed vinyl-coated fabrics, the bonded materials are heated in an oven to decompose the foam-blowing... 

Smooth surfaces are normally estabflshed by calendering, a process which subjects the fabric at the nip point(s) of two or more roUs to the influence of controlled time, temperature, and pressure. When calendering is used as a thermal-bonding process, the roUs are of the same dimension and composition and are independently driven. However, when calendering is used as a fabric finishing operation, the roUs are frequently of different dimensions and composition and are not always independently driven. 

Further, no really high bond adhesive was found for it, so that the surface gradually disbonded from the adhesive over a period of time. Efforts to improve the bond included calendering fabric into the face of the rigid material, but this was largely abandoned because, in a number of cases, the fabric pulled out of the sheet so that the sheet still disbonded. 

The most successful method to provide an unplasticized PVC face to the corrosives was found to be a laminate, calendering a plasticized sheet to the underside (or back side) of the unplasticized sheet to provide a good surface for bonding to the substrate, leaving the rigid side exposed to the harsh chemicals. For many years, this laminate sheet was manufactured in Trenton, NJ, and readily available. Domestic manufacture was discontinued a decade ago, but currently, the material is available on import from Europe, and is stocked in northern New Jersey. 

Compounding alters the chemical and thermal resistances of the basic ma-terials-almost invariably reducing it, so that the finished sheet has less chemical resistance and often a lower thermal limit than the resin before compounding. But the principle reasons for selecting these materials in the first place are based on these same or better chemical resistances and higher thermal limits. Therefore, in a few cases, some of these materials, in the uncompounded state, are calendered or molded in a composite layer on the exposed side of the sheet or molded part, so that the compounded side may be used for bond to anchor the lining to the substrate while the side with better resistance is exposed to the corrosive environment. 

Special methods of incorporation processing history has an essential effect on conductivity shear imposed during mixing causes a fracture of secondary carbon aggregates increased temperature during mixing may preferentially form rubber-carbon bonds rather than the carbon-carbon bonds required for conductivity vulcanization temperature may affect recovery of broken connections between carbon-carbon bonds talc reduces melt viscosity which results in a smooth surface of extruded and calendered products as well as reduced wear of equipment ... 

Paper is used extensively in laminations where it is bonded, usually by heat and/or adhesive, to other films, notably plastics and aluminium, e.g. LDPE/adhesive/aluminium/adhesive/calendered paper. This type of lamination can be used for form fill and seal work, e.g. sachet packs of deliquescent powders. 

Extrusion, lay flat tubing, calendering, casting, solvent or aqueous dispersion coating, etc. for single layer materials. Multilayer processes—wet or dry bonding (lamination), extrusion coating, coextrusion, etc. 

The smaller the fiber diameter used in the prefilter, the greater the surface area for adsorption of particles and the better the retention of small particles. In the sixties, asbestos fibers were recognized as the best prefilter media. The individual fibrils were smaller than 0.01 ju and they had a positive zeta potential. However, when it was suspected that asbestos fibers presented a health hazard, fine diameter glass and synthetic polymer fibers were substituted. Unfortunately, neither media equals the performance of asbestos. Glass fibers are available in the finest diameters, but some users are fearful they may represent a similar health hazard. The trend has been to use polypropylene or polyester fiber prefilters. Melt blown or spun-bonded fibers are available in diameters near 1 ju. Multilayers of these media with appropriate calendering have resulted in surprisingly efficient prefilters. 

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