Mass_Pigmentation

TABLE OF CONTENTS 1.0 Introduction 2.0 Mass pigmentation 3.1 Definition 3.2.1.1 Features of a pigment 3.2.1.2 Aplication of pigments. 3.2 Mass pigmentation application characteristics. 3.0 Textile spin finishers and finishes 4.3 Definiton 4.4 Classification of finishes 4.5 Pre-treatment processes 4.6 Important finishes 1.0 INTRODUCTION This is a research assignment on mass pigmentation, being a part of Textile raw materials MIT 221. 2.0 MASS PIGMENTATION 2.1 DEFINITION Mass pigmentation is the incorporation of the pigment in a molten polymer mass during processing into a compound or molten batch or when the end user or converter prepares a finished article e.g. an injection moulding. Pigments are generally coloured, organic or inorganic solid powder, and usually are insoluble. They are not affected physically or chemically in the substrate in which they are incorporated. Pigments can give a full range of colours. Pigments have a variety of applications that includes plastics, ink, and coating applications. 2.1.1Features of the Pigments The pigments are versatile coloring agents that come with all round features to give credence to its suitability in a variety of mediums. Some of the striking features are given here: * Excellent light and weather fastness * Easily dispersible * Consistency and uniqueness of shades * A good baking stability that makes them suitable for automotive and other industrial paints * High tinting strength * Good spray fastness when applied in paints * Gives good heat stability of around 300° C in the case of Polyolefin’s Plastics * Displays good solvent resistance properties 2.1.2 Application of Pigments Pigments find regular application in the following sectors: * Electronics industry * Inkjet Inks * Paints Industry * Plastics * Construction Industry * Wood working * Cement Industry 2.2 MASS PIGMENTATION APPLICATION CHARACTERISTICS The term mass pigmentation encompasses al the processes by which metal flakes are combed with polymer to ultimately form a finished article. Of these methods injection moulding is the most technically challenging because it has the most variables requiring control. They include; i. Colour Colour in the context of pigments generally means brilliance/brightness. It broadly corresponds to cleanliness in organic pigments. Metallic colour is influenced by the surface finish of the pifgment,its tint strength and its concentration. The specific case of alluminium pigments, improved colour equates to increased whiteness. These properties are in turn dependant on the particle size distribution and the surface brightness of the flake. ii. Dispersability The process of dispersion starts with a combination of metal flakes and polymer in dry state. Masterbatch preblending is used here. Masterbatch in this context covers the metal flake pigment damped or carried by any suitable organic material such as a plasticizer or a polymer. A short period of dry tumbling erg in a double can blender should be sufficient for most commonly available alluminium pigment masterbatches. High speed powder blenders are not recommended for two reasons: a) There is a danger that the high shear will break down the masterbatch, releasing single flakes with a consequent danger of explosion. b) The same high shear can bend or break the flakes leading to a loss of metallic brightness. Most metal flake pigments are very resistant to heat. The flakes themselves remain stable well above the highest polymer processing temperatures. In practice, the maximum processing temperature is often dictated by the polymer. iii. Opacity and tint strength Opacity or hiding power is a function of flake diameter, thickness and density of the metal. At constant thickness and density, opacity is roughly proportional to the inverse square of the diameter. The smaller the diameter or thickness, the higher the total surface area. With more surface area available to obliterate the substrate, opacity is higher. Tint strength refers to the ability of a metal pigment to modify the colour depth of a colourant with which it is incorporated. Thus a deep blue metallic effect will become paler if further metal flake pigment is added to the formulation. A finer particle size flake will create a greater colour shift than the same weight of a courser flake. Increasing flake thickness i.e. reducing the aspect ratio is practiced to improve degradation resistance. It is at the expense of opacity. Folded and bent flakes have an ambivalent effect on opacity. Folded and bent flakes have reduced effective surface area. Alternatively if the focus becomes thinned and breaks, surface area is increased. This is however accompanied by loss of brightness due to both increased concentration of fine particles and the disruption of uniform orientation caused by bent and folded flakes. Loss of opacity becomes very marked at large particle diameters. Because of this, very large aluminium flakes are generally used to provide a random sparkle effect in combination with other colorants. The large density range of metal flakes influences opacity. iv. Orientation For a metal flake pigment, orientation influences brightness and to some extent opacity. Flakes that reflect more light from the full area of their faces appear very much brighter than flakes presenting their edges. In mass pigmented articles, orientation is determined by the polymer flow characteristics. Flakes tend to align themselves to reduce their resistance to flow. v. Mechanical properties Metal flakes in polymers tend to cause an increase in viscosity if added as dry flake. This is attributed to poor wetting of the flake surface. Low loadings of metal flake pigments in polymers generally cause a very little change in tensile and impact strength. Indeed in certain polymers, these properties may be enhanced. The table below shows the effects of including glanular alluminium flake pigment in a range of common polymers at loadings between 0.5% and 6% by weight of polymer. Percentage change in mechanical properties as a result of pigmentation of PP by aluminium flake pigment granules Metal particle size | Metal% | Tensile break | elongation | 10 micro meters | 0.71.42.85.6 | -4-5-5-5 | -42-47-63-86 | 30 micro meters | 0.71.42.85.6 | -1-2-3-4 | -38-65-67-79 | Table 1 Source Metallic pigments in polymers - Google Books.htm#v=onepage&q=wh Percentage change in mechanical properties as a result of pigmentation of elastomer modified PP by alluminium flake pigment granules{NC=No Change} Table 2 Source: Metallic pigments in polymers - Google Books.htm#v=onepage&q=wh Metal particle size | Metal% | Impact strength | Tensile break | elongation | 10 micro meters | 1.01.52.5 | 152429 | NCNC4 | -23-64-76 | 30 micro meters | 0.51.01.52.0 | -5-4-5NC | 41-1-2 | -63-51-61-59 | 75 micro meters | 1.01.52.03.04.0 | -20-26-34-36-30 | 13414 | -59-69-74-75-74 | Continuation. Table 2 Source: Metallic pigments in polymers - Google Books.htm#v=onepage&q=wh Conclusions drawn; The degree of mechanical strength loss is broadly proportional to the metal flake loading. Larger flake particle sizes are less prone to strength loss, whilst the more polar polymers such as polyamide show the greatest percentage of loss at higher loadings. vi. Cost The cost of a metal pigment in a formulation depends upon the metal concentration in the pigment, the loading and the unit price e.g. aluminium is cheaper than gold pigments 2.0TEXTILE SPIN FINISHING 2.1Definition Finishing is the general term for a multitude of chemical processes and treatments which a fabric may undergo after it has been made (woven or knitted) and colored (dyed or printed). It is the final processing of the cloth and its purpose is to make the fabric suitable for its intended end use. That may mean for example, making the fabric shrink proof, softer, stiffer, water repellent and crease resistant or a combination of these properties. 2.2 CLASSIFICATION OF FINISHES Textile finishes and finishing are classified in several ways. Persons concerned with end products (designers, merchandisers and sales personnel) usually categorize finishes as aesthetic finishes and functional finishes. The former modify the appearance and/or hand (feel) of fabrics, while the latter improve the performance of a fabric under specific end use conditions. Persons concerned with textile processing (chemists and finishers) categorize finishes into chemical finishes and mechanical finishes. These are also called wet finishing and dry finishing, respectively. Finishes are also categorized by their degree of permanence. These finishes are called permanent, durable, semi-durable and temporary. 1. Permanent finishes usually involve a chemical change in fibre structure and will not change or alter throughout the life of a fabric. 2. Durable finishes usually last throughout the life of the article, but effectiveness becomes diminished after each cleaning and near the end of the normal use life of the article, the finish is nearly removed. 3. Semi-durable finishes last through several launderings or dry cleanings and many are renewable in home laundering or dry cleaning. 4. Temporary finishes are removed or substantially diminished the first time an article is laundered or dry cleaned. 2.3PRE-TREATMENT PROCESSES Pre-treatment processes consist of cleaning operations to rid the fabric of all soil and additives used during the weaving or knitting process. These processes are usually the first treatments a fabric undergoes after leaving the loom or knitting machine and are required before any dyeing, printing or finishing can be accomplished. The processes consist of various types of cleaning actions, depending upon the fibre, the impurities present and the fabric construction. In cottons, cotton blend, silk and man-made fibres, the processes are, known generally as the boil-off. In woolens and worsteds, it is called a scour or scouring. RESINS Resins are the chemical group used in many of the finishes. Resins are the most widely used chemicals in the textile industry. They are used for many purposes, primarily on cellulosic and cellulosic blend fabrics. Resins have a profound effect on and cause changes in the hand (feel), drapability and physical characteristics of textiles. While many benefits are achieved through these changes, there are also some shortcomings. Resins modify fabrics in the following ways: A. They add stiffness to fabrics and are thus used as stiffening agents or to create a firm hand. B. Resins stabilize fabrics in the same shape or configuration as when the resin was cured. Fabrics cured m a smooth, nonwrinkled condition will return to that shape after being wrinkled in wear, while fabrics cured with creases in garments will retain these creases. C. Yarns in fabric will be stabilized and will resist shrinkage in laundering. D. Fabrics will become less moisture absorbent, thus drying more rapidly. They will also be less comfortable in warm, humid weather. E. Resins combine chemically with cellulosic fibres (cotton, rayon, ete.) to cause significant reductions in abrasion resistance, breaking strength and tear strength. This reduction can be as high as 50%. F. Most resins produce an offensive "fish-like" or formaldehyde odour in fabric. This odour eventually disappears on exposure to air and/or laundering. G. Resins have an affinity for oily soils, creating a soiling problem. Soil release finishes help alleviate this objection. 2.4 IMPORTANT FINISHES * Anti-static Finishes Anti-static finishes are chemical substances applied at the textile finishing mill for the purpose of reducing or eliminating static. These chemicals are actually substances which absorb small amounts of moisture from the atmosphere, thus reducing the dryness of the fabric. Anti-static finishes are not a truly satisfactory method for coping with the problem of static in textiles because they are merely semi-durable. These finishes wash out or wear out in several launderings or dry cleanings. Permanent anti-static effects are obtainable, however, with the man-made fibres which have been especially modified for this purpose. Antiseptic Finishes Antiseptic finishes are chemical agents inhibiting the bacterial growths which cause irritation and odour in shoes, luggage, underwear fabrics and similar items. These finishes are low in cost, easily applied and are durable to laundering and dry cleaning. Calendering Calendering is not a single type of finish. There are various types of calender machinery, each producing different types of finished fabrics. Fundamentally, a calender is a mechanical device consisting of two or more large rotating cylindrical rollers stacked on top of each other and usually heated. The cylindrical rollers are in contact with each other under pressure. Fabric being calendered passes around and between these cylinders. The specific type of calendered finished fabric varies with the nature of the cylinder surface, the speed of the cylinders and the nature of the fabric being finished. The various types of calendering finishes include the following (a) Simple calendering (b) Glazing calendering (c) Embossed calendering (d) Moire calendering (e) Schreiner calendering Crease Resistant Finishes Crease resistant finishes are popularly known as CRF finishes. They are used on cotton, rayon and linen because these three fibres wrinkle easily. CKF finishes are resin finishes; the fabric is saturated with resin and then the resin is cured at temperatures of about 360°F. The fabric becomes stiffer, less absorbent and more resistant to wrinkling. Resin treatments also results in tensile strength loss and reduction of abrasion resistance in cellulosic fibres. Most CRF finishes are durable. Flame Resistant Finishes There are two systems to make fabrics flame resistant. The first is to use selective fibres which have characteristic flame resistant properties. The second is by the use of flame resistant finishes. All of the many types of flame retardant finishes now available suffer from at least one of the following shortcomings: (a) they cause stiffening and loss of fabric drapability; (b) they result in significant strength loss in fabric; (c) they are easily removed in laundering (nondurable); and (d) they become ineffective when laundered in household bleach, with soaps or with water softeners. Fulling Fulling is a permanent finish used on wool fabrics; it is also known as milling or felting. The process is a carefully controlled scouring or laundering process to induce felting shrinkage in wool fabrics. The resultant fulled fabric is smoother, more compact and has yarns more tightly embedded than an unfulled fabric. Woolens are frequently heavily fulled. Mercerization Mercerization is one of the most important of all cotton finishes. This finish imparts luster to the cotton, increases its strength by nearly 25% and improves dye affinity, producing brighter shades than unmercerized cotton. It also enhances the hand as well as uses less dye to achieve the same depth of shade. The finish consists of treating the material while under tension with cold, concentrated sodium hydroxide solution. Both fabrics and yarns can be mercerized, but fibres cannot. Mercerization is a permanent finish. Napping Napping is a mechanical finish in which woven or knitted fabrics are passed against rotating, bristled wire-covered brushes. This action results in fibres actually being raised from the fabric. The overall effect is a fabric with raised fibre surface. Napped fabrics have a softer hand and provide better insulation than the same materials unnapped because they can entrap more air; hence, their wide use in blankets, sleepwear and winter clothing. However, the insulating value of cotton and rayon napped fabrics is not long lasting. The low resilience of these fibres causes premature flattening of the fibre nap. The nap can partially be restored by frequent brushing. Plisse Plisse is the name of a finish as well as the name of a fabric treated with this finish. It is a permanent finish, produced on cotton by the action of sodium hydroxide; but unlike mercerizing, no tension is used. The sodium hydroxide is printed on the fabric in the form of a paste. The fabric shrinks only where the sodium hydroxide is applied, producing a puckered effect. Shearing Shearing is a process used to cut off surface fibres on fabrics. It makes uniform the surface of napped fabrics. Most cut pile fabrics are also sheared to provide uniform pile height. Soil Release Finishes Soil release finishes in fabrics permit relatively easy removal of soils (especially oily soils) with ordinary home laundering. There are several types of soil release finishes. All of them accomplish the end result of making the fibre more absorbent (hydrophilic), thus permitting better “wetability" for improved soil removal. Most soil release finishes are applied at the same time that the resins are applied to textiles. Most are durable through 40 to 50 launderings and are routinely applied to fabrics for work clothes and table cloths. They are also often applied to fabrics for slacks and skirts. Several other benefits arise from the use of soil release finishes in durable press fabrics because of their increased absorbency. These include: improved antistatic properties, improved fabric drapability and somewhat greater comfort in hot weather. The challenges and effects of chemical spin finishing Proper formulation of chemical finishes requires consideration of several important factors such as: * The type of textile being treated(fibre and construction) * The performance requirements of the finish(extent of effect and durability) * Cost to benefit ratio * Restrictions imposed on the process by availability of machinery, procedure requirements and environmental considerations * Compatibility of different formula components as well as the interaction of the finishing effect A challenge to chemical finishing is the compatibility of primary and secondary effects of the different types of finishes that are being combined: * Some effects are similar or assist each other, for example silicone elastomers cause water repellency, softeners bring about antistatic effects and antistatic finishes can be softening. * Some effects are contradicting, for example hydrophobic finishes and hydrophilic antistatic finishes, or stiffening and elastomeric finishes, or stiffening and softening finishes. General requirements of chemical finishes Primary effects of finishes * High effect level at low cost for products and application * Possible effect design, adaptation to customer wishes, article demands and favored use Desired secondary effects * Usable for all kinds of fibres and all textile forms, as yarn, woven or knit fabric, garment, nonwovens * High permanence for washing and dry cleaning for garments and most household textiles * No loss of important textile qualities such as tear strength and abrasion resistance, comfort, appearance, hand * No yellowing of undyed fabrics, no shade change of coloured ones, no reduced colour fastness * Easy and safe handling, non-flammable * Simple application, preferably with several standard methods and equipment at low cost * High stability under storage and application conditions (temperature, pH, mechanical stress) * Even distribution, either on the fibre or fabric surface or inside the fabric * Compatibility with other finishes * Synergistic effects, no reduction of effect of other finishes * Easy correction of finishing faults such as removal of finish or stains * No environmental problems, non-toxic, biodegradable, no volatile organic compounds * * Other types of finishes reduce the main effect of a finish type, for example the flame retardant effect is decreased by nearly all other types of chemical finishes as they add flammable components to the fabric. * True antagonistic effects are rare, but true synergistic effects are also rare, where the resulting effects of a combination is greater than the sum of the single effects of the combined products. Examples of both cases are different types of flame retardants. REFERENCES a) www.gogle.com/Metallic pigments in polymers by Ian wheeler,Rapra Technology limited - Google Books.htm#v=onepage&q=wh b) WWW. Google Books My textile notes on google.com c) www.gogle.com/ Google Books Chemical finishing of textiles by Wolfgang D. Schindler, Peter J. Hauser, of Textile institute(Manchester United) d) WWW.googlebooks/HANDBOOK ON TEXTILESMan-made fibre manufacture by W. Klein