Finishing of leather

Application of “Top Coat’’ the final coat
Top coat agents
Top coats are the final coats applied in the finishing process they serve several purposes depending on the type of leather.
1. Protection from soiling moisture, solvents and abrasives as well as damage caused by impacts and scratching furthermore they should be resistant to heat up to 100⁰ C and cold up to 30⁰ C if possible.
2. Imparting of the desired surface handle (dry, smooth, blunt, fatty, waxy or greasy).
3. Imparting of a matt or gloss effect with all possible intermediate stages.
Application of top coating agents
The products can be used alone or, if compatible, in combination according to the respective requirements as glossy, dull softness and feel. Except for patent leather the top coats should be sprayed in thin coats. However, they should not be sprayed too dry in order to ensure adequate film formation.
Casein products
The products used are non thermoplastic binders such as milk casein modified casein products and blood and egg albumen .a distancing is made between hart and soft products in general the harder products should be used for high gloss top coat thorough fixation of casein based top coats is required to achieve sufficient water resistance
In most cases products are applied in the water diluted compared to solvent diluted cellulose products they give the leather a pleasing handle. Dyed products are used for black leathers to avoid gray fog and to achieve brilliant black shade.
Nitrocellulose and CAB lacquers
Top coats on the basis of nitrocellulose lacquers are used less frequently. The cellulose aceto butyrate

Lacquers, which are more expensive but not inflammable and provide better fastness to amine and light are now increasingly employed both groups of products should never be applied as top coats on pure casein finishes because the casein films are not solubilized and adhesion is therefore not sufficient. Polyurethane products
Besides the solvent soluble polyurethane lacquers which are employed for production of mirror-bright patent leather and for easy-care finishes, the water-diluble one-component polyurethane dispersions are becoming more popular. These top coats are water-resistant fast to ageing and do not require additional fixation. Combined application is possible to improve the handle and fastness properties of the solvent-soluble or water-diluble nitrocellulose lacquers.
Polyamide lacquers
Polyamides are polymerized or polycondensed amino acids (textile raw material for nylon Perlon). Copolymers, which are soluble in mixture of alcohols and hydrocarbons, are obtained by additional condensation with dicarboxylic acids and diamines. In the leather industry they are used alone or with nitrocellulose lacquers. Such top coats increase water-resistance, improve flexing endurance and resistance; improve flexing endurance and fastness to rubbing. Furthermore they inhibit migration of brightening dyes, avoid damage to the finish during spraying of plastic soles in shoes production and improve the lightfastness of dyeing.

Basicity concept

Chromium salt basicity used in leather tanning
Chromium (+3) in a solution has a strong attraction for hydroxyl ions (OH-). The reaction of chromium with the OH may be written as a three steps reaction as it takes on the 1st, 2nd and the 3rd hydroxyl group. The tendency of the 1st step of reaction to take place is very strong, and even at pH 2(a concentration of OH- in the solution of 10-12) the chromium will hold the1st OH group. As the pH is raised (the concentration of OH- increase) the 2nd OH group enters into the reaction with chromium. This takes place between pH 3 and pH 4. Near pH 4 the 3rd oh enters into the reaction in order to complete the reaction with the 3rd OH group it is necessary to raise the pH to about 8 to 9 and to bring the temperature of the solution to the boiling point.
The percent of the primary valence bonds of the chromium in solution accompanied by OH groups is called the basicity of the solution.
[ Cr ]+3 + OH- <……> [ Cr- OH] ++ 33 % basicity
pH 2.0 and below – approximately
[ Cr- OH] ++ + OH- <………> [ Cr(OH)2]+ 66 %
pH 2.0 – 4.0 approximately
[ Cr(OH)2]+ + OH- <……> [ Cr(OH)3]0 ppt.
pH 4.0 – 8.0 or 10 may require heat
the chromium salt used in chrome tanning usually basicities between 33 % to 66 %.

Leather news source leather international.mag

Leather Mark promotion
South Africa
Published: 25 March, 2010


The South African Skin Hide and Leather Association (SHALC) have decided to resume the promotion of genuine leather. After a gap of almost twenty years, active generic promotion of genuine leather and the registered Leather Mark is back on the agenda, according to Colin Gerrans, SHALC chairman.

PR company Twins, which originated the successful ‘Beef-up’ campaign, will assist SHALC and both organisations have devised a communications strategy which was due to commence earlier this year. Limited funds dictate that furniture upholstery, footwear and leathergoods will receive the initial attention. The Red Meat Industry Forum is granting limited funding from statutory levies collected from hides and skins and dealers will be contributing towards the costs of point-of-sale stickers, tags etc.

Source: S&V African Leather
Leather news from England
New England tanners to host seminar
United States
Published: 17 March, 2010

The New England Tanners Club have announced that they will be hosting an education seminar, which will take place in Portsmouth, New Hampshire on April 30. They have speakers from Clarks North America, Environmental Resource Management and the United States Hide, Skin and Leather Association. The seminar will also include a discussion on the Leather Working Group and restricted substance legislation management. Drinks and a dinner will follow the event. Cost is $35 per head. More information will be posted on the club website www.newenglandtannersclub.com
Chinese authorities to close dirty tanneries
China
Published: 22 March, 2010

The China Leather Industry Association (CLIA) has clarified the position of the Chinese government towards the development of the nations tanning industry. There are approximately 700 tanneries operating in the country which are considered to be medium and large sized operations which have adequate pollution control and turn over more than 5 million RMB (US$732,000) a year.

There are also around 1000 small and medium sized businesses whose production capacity is less than 30,000 cattle hides per year. Most of these businesses have little or no pollution control and the government intends to forcibly close down these sites and has already begun the process.

However, if a tannery with a low production capacity (less than 30,000 pieces per annum) but they have acceptable waste treatment controls then they will be able to remain in business.

It the intended aim of the Chinese government to irradiate polluting tanneries and move towards a leather manufacturing sector focussed more on high quality as well as high output production.

Factors which influence the leather dyeing

Choice of dyestuff

The choice of dyestuff depends primarily on the demanded fastness for the types of leather to the produced, on the desired shade and on the respective main tanning method or the retanning agents used. Perfect combinability of the dyes is a further criterion. This depends on the build-up properties, on the absorption rate and chemical structure of the dyes. In principle, the dyer should adjust the desired shades by means of the smallest possible number of shading dyestuffs in order to restrict the possibility of introducing additional defects. Price is a further factor which influences the choice of dyestuff. However, when using low price dyestuff their fastness and intensity should be examined thoroughly. Often they have a high content of extenders or extremely different mixed suppliers’ sample cards should be considered when choosing dyes according to fastness
Solubility of dyes
Anionic readily soluble dyes are dissolved in water at 70-80 ⁰ C in a ratio of 1:10 to 1:20 briefly and if they are intended for high-quality aniline leathers filtered through a fine-meshed cloth to be on the safe side.
Cationic dyes are made into a paste by means of acetic acid with about half the weight of the dye, especially if hard water is used and dissolved in water at 80-90 ⁰ C. Boiling should be avoided anionic and cationic dyes should not be dissolved together as otherwise precipitation or Color Lake may occur. Liquid dyes have the advantage of being dust-free and better to handle because they are easily diluted.


Quantity of dyes
In the case of wet leathers the quantity is calculated in relation to the shaved weight of the leathers, in the case of intermediately dried leathers according to the dry weight. However, it would be more favorable to relate the calculation to the leather surface because the thinner a leather, the greater is its surface per kilogram. In this case better constancy of shade without significant variations is achieved for the subsequent lots.
Addition of dye
For high-quantity aniline leathers the addition of dyes in dissolved form and in several portions is always advantageous for an even and leveled absorption. Liquid dye should therefore also be added in diluted form. Powder dyes in short float processes mostly result in reduced depth and brilliance of color. With this form of application it is necessary to ensure that all dye components are evenly and are readily soluble.

Float ratio
A large of dye-liquor promotes the distribution of the dyes and auxiliary agents used. Furthermore, it prevents an excessive rate of absorption on the surface or reverses side. This should be considered especially when dyeing pastel shades which should therefore be dyed in larger quantities of dye-liquor. The quantities of dye-liquor commonly used are 100-250 % and up to 400 % for pastel shades.
The “dyeing without float” or “short-float dyeing methods” with floats of 0-30 % have to be performed at low temperatures in order to avoid unleveled dyeing because in short penetration rapidly increases but the leveling become uneven. Short floats should not be used for very thin leathers to avoid tearing or tangling of the leather material. These processes should be performed more gently in the automatic chamber or sector machine.

Theory of leather dye fixation

The dye woods, being closely related to the vegetable tannins, are similar to the vegetable tannins in this theory of fixation. The dyewoods are loss colloidal in nature and will penetrate more easily than the vegetable tanning but the same general principles are involved. Fixation is by hydrogen bonding and the lower the pH, the greater the fixation. Direct dyes are attracted to the leather fiber and will be absorbed on the surface of the leather by physical forces rather than by strong chemical and physical bonds. Direct dyes are not penetrating when used on chrome tanned leather; rather they will be absorbed on the surface. Acid dyes behave as weak acid, being absorbed by the hide the fixation and penetration of an acid dye follow the same general laws that apply in the acid syntans. The acid dyes are attracted to the leather through the positively charged groups of the hide; therefore the acid group will be attracted to the amino group on the hide and will be fixed by hydrogen bonding. At low pH the acid dyes will be fixed more readily than at high pH, but they will penetrate deeper into the skin as the pH values increases. Since dyestuffs vary in molecular size, in their degree of solubility and in their acid –base characteristic, fixation of the dye by the leather will depend on all these factors under given conditions the dye will vary in these characteristic from one dye to another.
The base dyes are attracted by negatively charged groups on the leather under acid condition leather, like untanned protein will absorb hydrogen ions and assume a positive charge the basic dye also positively charged will have little affinity for the leather. As the pH is raised the leather become more negatively charged and fixation of the basic dye is acided in addition to the pH factor in the fixation of dyes; the presence of the other materials on the leather fiber is important to the behavior of the dye in relation to the leather chrome tanned leather carries an additional positive charge due to the presence of cation reaction with the hide. The acid dyes, therefore will be more strongly attracted to chrome leather and will fix directly to it. Basic dyes on the other hand have little affinity for chrome leather. In order to fix a basic dye onto chrome leather this is done by mordanting chrome tanned leather by adding a vegetable tanning material or an anionic syntan. The basic dye than will very strongly attracted to the “mordanted” fiber and stable fixation will take place

Efficiency of Carnot engine

The ratio between input and out is called efficiency. The work done on machine is input and the work done by machine is output. The input of Carnot is equal to the amount of heat Q1 supplied during isothermal process.
The output is equal to the difference of work done on the system and the work done by the system. During Carnot cycling engine work done in two steps. In final two steps to bring the engine in its initial stage the work is done on the system. At returning the engine in its initial stage its internal energy will be equal to zero.
ΔU = 0 therefore it observe Q1 heat in isothermal expansion process and release Q2 heat in isothermal compression and the resultant of absorb heat will be equal to the
ΔQ = Q1 – Q2
According to the 1st law of thermodynamic
ΔQ = ΔW + ΔU
Q1 – Q2 = ΔW (ΔU = 0)
Q1 = input
Q1 – Q2 = output
Efficiency = output/ input
E = ΔW/ Q1 > E = Q1 – Q2/ Q1
E = (Q1/Q1 – Q2/Q1)
E = (1 - Q2/Q1) *100 % or Q2/Q1= T2/T1
E = (1 - T2/T1) *100 %




Related problem
Efficiency of a heat engine is 20 % and does 20 joule work in each cycle find in each cycle
a. The amount of heat absorbs?
b. The amount of heat release?
Solution
Data
Work done in each cycle = output of each cycle ΔW = 200 J
Efficiency = 20 %
Amount of heat absorbs = Q1
Amount of heat release = Q2
Efficiency (E) = output/ input * 100
E = ΔW /Q1 * 100
20 = 200 / Q1 *100
Q1 = 200 * 100 /20
Q1= 1000 J heat absorbs in each cycle

Q1 – Q2 = ΔW
1000- Q2 = 200
Q2 = 1000-200
Q2 = 800 J

Leather fashion by Shafi Reso

The theater is the world,

                                The stage by excellence is fashion 

The  essence of leather industry lies in fashion the skin itself is nothing but it can transformed into gold if it has been treated with balanced combination of chemicals and projected according to the precise fashions requirement  Shafi  Reso  chem. There for always emphasizes on supplying of quality chemicals and keeping eyes on the forthcoming fashion trends. We have commitment to transfer our knowledge to our leather industry so that industry can go ahead in right direction. We organize seminars for in a year, both Continuous Technical Education and Fashion Forecast, aiming to share our knowledge with the leather industry of Pakistan.

Importance of fashion forecast

As “Globalization” marches ahead day b y day, it has made compulsory to obtain the knowledge of future trends for every business organization in this competitive environment. Just imagine if you have developed leather articles for an overcoat in black color whereas the fashion fall in the selling seasons is for overcoat in grey color, what would happen to your articles?

Colors

The colors that fall for next fashions are Egocentric (insensitive, selfish, and egotistic) Vanity (worthlessness, vain pride, unreal or idle thing) and Fragile (easily broken, brittle, perishable)

There are 09 shades of colors projected in Egocentric, 11 shades of colors in Vanity and 10 shades of colors Fragile.

Materials

What I See Is What I Feel

 Glossy is cold, Opaque is Warm and Powdery, Soft is Foaming

The resources and equipment will be focused in upcoming year are those that give natural look to leather showing as it really is like the warmth of vegetable leather raised grain new brush off leather sweet super soft feel weightlessness and soft with simplicity handing of glossy and transparent effects like wet look natural transparences, contrast of glossy and dim look, hand work and shadows. Engrave and scratches like shadows metal mix, discontinuous strips, summer effects, sectioning light and liquid metal. Other tools may be used are precious lining and inside, deeply printed patterns and laser-worked effects.

Stahl trend and technology show 2010

Stahl Pakistan (Pvt) Ltd.
Held
Stahl trend & technology show 2010 on Tuesday, 16 March 2010 at National Institute of Leather Technology Karachi.

Stahl a leading leather chemical supplier world wide introduce new and latest developed article by the company. The fashion fancy articles for garment leather attract many costumers. Fur leather made on cow hide was also attractive. Shoe upper leather stock with good design and high gloss effect was interesting one. But most interesting and attractive was drum dyed and low finishing article because the trend of low finishing or less finishing is becoming more popular these days. All type of Stahl latest product was attractive and interesting for visitors.

In trend and technology show by Stahl about all reputable company from Pakistan leather industry participated in 1st place Shafi company technical staff were attended this show MIMA leather industry,KHas (PVT)ltd. All technical information about each article made by Stahl was given to the visitors.

Patent leather highly fashionable leather

The history of patent leather begins in the early 19th century and owes its invention to Seth Boyden of Newark, New Jersey. During the year 1818, Boyden began to investigate the possibility of creating a version of leather that was treated in such a way that the material retained its desirable qualities of protection and durability. At the same time, this new type of leather would also have an appearance that would be decidedly more dressy than work boots and similar leather goods.
Using a formula that was based on a series of treatments using layers of linseed oil based coats, the new shiny leather began commercial production on 20 September 1819. Boyden’s efforts resulted in the production of glossy leather that quickly caught on the perfect compliment for formal dress. Almost two centuries later, patent leather still maintains the status of being part of a formal look for men and women alike.
Patent leather begins life as a superior grade of fine grain leather that undergoes a process to achieve the glossy look that is considered sophisticated. Originally, this was accomplished by applying layers of a linseed oil finish to the leather, gradually creating the sleek appearance. As time went on, the invention of plastics impacted the methods for producing patent leather.
Plastic finishes were able to produce effects similar to the application of several treatments with linseed oil, with the advantage of considerably less monetary investment on the part of the producer. Over time, the development of synthetic resins further simplified the process and cut production costs even further, making the mass production of patent leather possible.
Characterized by a glass like finish that catches the light, the typical patent leather accessory is a solid black. In addition to the mirror like finish, patent leather is also virtually waterproof, while still retaining a very flexible texture. The visual elements of patent leather have made it a sought after material for all sorts of formal accessories. Just about all men’s footwear produced to be worn with tuxedos are patent leather shoes. Many formal types of heels for women are also produced using patent leather. Clutches and small handbags for women are also made using patent leather, as well as some formal wallets and cigarette cases. Essentially, patent leather is always considered an integral part of formal wear.
With almost two centuries of history, patent leather is one type of material that seems to keep going no matter what current fashion trends dictate. It seems that as long as there is a need to dress up for an occasion, patent leather will be found in closets and tuxedo shops across the country.
Patent leather research by B LC leather

Patent leather highly fashion able leather  

BLC Leather Technology Centre present an overview of patent and metallic fashion finishing effects that can be seen on more and more leathers these days. Every few years patent and other highly fashionable finishes applied by foils such as metallic become heavily demanded but often present a range of technical difficulties to the tanner or finisher

Leather is a fashion item subject to the seasonal and annual variations that occur in the fashion industry. As a result, every few years there is a demand on the leather industry to produce patent and metallic leathers. These trends certainly add sparkle to a wardrobe either in the form of shoes, handbags, belts or even full garments.
The potential downside of fashion trends being imposed on a traditional industry such as leather is that new products and effects will invariably have their own unique problems and technical issues. The recent metallic trend has imposed the development of metallic finishes on leather suppliers resulting in an increasing number of technical problems and complaints within the industry.
Patent leathers are also currently highly fashionable, but tanners, retailers and end users need to take care to avoid the many potential problems and issues with the manufacture of this type of leather. It is important to ensure good practice is employed in the coating system used. Patent leathers were traditionally produced in black or white for evening wear and children’s footwear, but increasing fashion trends have led to the production of patent in a myriad of colours. New patent leathers are also being developed to provide two tone, metallic and pull-up patent finishes.

History
During the year 1818, Seth Boyden of Newark, New Jersey, began to investigate the possibility of creating a version of leather that would retain its desirable qualities of protection and durability whilst at the same time having a more dressy appearance.
Originally, this was accomplished by applying layers of a linseed oil finish to fine grain leather, gradually creating the sleek appearance which resulted in the production of glossy leather that was quickly adopted as a complement to formal dress.
Coating with linseed oil required considerable time and effort. Many individual applications were needed with a long drying period for each coat, which meant that it could take up to four weeks of production time. As time went on, the invention of plastics impacted the methods for producing patent leather.
Plastic finishes were able to produce effects similar to the application of several treatments with linseed oil, with the advantage of considerably less monetary investment on the part of the producer. The original methods of production as well as being time consuming also had poor fastness properties. Technology has moved on considerably and genuine patent leathers are produced by a solvent based polyester/isocyanate cross-linking system. There are also water based finishes to produce the same patent ‘wet look’ which are easier to produce with greatly reduced problems and hazards.
The standard method of finishing, which applies to the majority of patent leathers, is outlined in the next section. However, it is also possible to use transfer papers to produce the patent effect. Great care needs to be taken when using these papers, which can either be the ‘whole’ finish including base coats or simply the patent top coat. The papers are applied using a conventional tannery press at 125°C for 3 to 5 seconds at 100 bar pressure.

Standard method of production for patent leathers
Leather preparation
It is the final coat applied that gives the required gloss, but the base coats and leather preparation also have a profound impact on the final properties.
Most patent leathers are produced on corrected grain. Careful preparation is required and the leather needs to have good buffing properties and a tight flat grain. One of the main reasons for the grain correction is that the production of such a high gloss finish needs a surface free from blemishes. The surface is then heavily impregnated, covered with pigment coats prior to the application of the final gloss. Vegetable retannages are used to enhance the deep buffing and often the final surface deposition of an acrylic resin to enhance the tightness. It is also important to ensure that the fatliquors used penetrate to ensure the surface is free from grease.
Dust is a major enemy of patent leathers so it is good practice to spray the flesh side of the leather with a light seal to avoid subsequent cross-contamination.

Finishing system
The finishing sequence comprises of various coats and it is essential that the formulae promote good inter-coat adhesion. The normal sequence is impregnation, base coat, intermediate coat and patent top coat.

Impregnation
The formula needs to be carefully controlled and includes:

• Impregnating resin of the correct particle size
• Wetting agent to reduce the surface tension without creating poor wet adhesion
• Strict control of the balance of the resin to penetrator (typically 10% penetrator by volume).
• Controlled and consistent deposition of the resin at the grain corium junction (typically between 3-5g/sq ft).

Base coat
This is the main fully pigmented covering coat. Selection of resins is important and must reflect the final properties required in the final leather, such as resistance to cracking and solvents, good ironing properties plus wet and dry adhesion.
Adhesion problems can be minimised by avoiding waxes, oils and silicones. The base coat needs to be applied at levels of between 14-16g/sq ft and is usually applied by several rollercoater applications with an intermediate ironing.

Intermediate coat
On conventional leathers this would be called the top coat. This is a heavy coat of nitrocellulose lacquer which provides a bond between the base coat and the patent top coat, improving adhesion. It is usually applied by spraying. Within this coat it is possible to produce ‘effects’, eg antique, two-tone, tips, by the addition of dyes and pigments.

Patent top coat
The application must be carried out in dust free conditions with up to 20g/sq ft (lower amounts for soft leathers). It is important to ensure that there are no air bubbles in the finish, resulting in the application methods being airless spray or curtain coater. Solvent selection is crucial and any solvents that contain water will give a tendency to bloom. The drying can take longer than 12 hours and it is essential to use an isolated room. The area used must be sealed to prevent airborne dust contamination in the surface finish. The drying is usually 2 hours at 25°C followed by around 10 hours at 50°C. Great care is required in handling the final product to prevent the flesh coming into contact with the grain surface.

What can go wrong?

• Tacky feel and fingermarking

This is probably caused by insufficient crosslinker in the top coat, resulting in a soft surface. To clean, wipe the whole surface with a cloth impregnated with a silicone-based cleaner.

• Creasing

This can be caused by the combination of adding a ‘thick’ finish to a thin loose leather. The finish accentuates the looseness problem resulting in creasing.

• Cloudy dull appearance can be caused if the patent coat is contaminated with water. Consider changing solvents.
• Air bubbles in the finish. This can be caused either by dirt on the surface prior to the patent top coat or incorrect viscosity of the patent top coat, affecting the flow out.
• Poor flex resistance. Check the failure to determine which coat has failed. It may be that there is too much crosslinker in the patent coat.
• Problems with transfer papers. Peeling or lifting due to poor bond with leather. Defects in transfer papers allowing humidity to penetrate and lift the transfer papers.

Production of foiled leathers
There are many types of foils and transfers that can be applied to leathers including:

• printed effects
• metallic foils
• crackle foils
• multilayer foils
• lacquer/coated films
• holographic films etc

The production of metallic foiled leathers can be split into a series of stages which are summarised below.

Pre-application checks
Before the foil is applied the following considerations must be made:

• The leather should be clean and dry crust (can be dyed) without any type of finish.
• The leather should be free from dust and with a dry, non-greasy surface. Regular checks at the tannery are recommended.
• The leather should be flat before application with pleats or folds removed by trimming.
• The plate of the press should be pre-heated to the required temperature before transfer.
• The felt in the press should be covered with a sheet of Teflon to improve handing and efficiency.

Application of the adhesive

• The amount of adhesive applied is important and should only be sufficient to ensure good adhesion without peeling. This may initially require development and the amount applied should be monitored for consistency during production. Too much adhesive can result in the whole film peeling off with the foil, this is particularly likely under wet conditions. Too little adhesive can mean low film strength, resulting in low adhesion and ‘powdering off’ of the foil particles.

• The adhesive is usually applied by spray although rollercoaters can also be used. The absorption to the surface is important and must be consistent from pack to pack. Unfortunately, a process of trial and error is required to find the optimum amount for each particular type of crust.

• The choice of adhesive is important and is determined by the type and absorption of the crust. The adhesive is  usually an aqueous polyurethane, which may need diluting slightly for spray application or thickening if applied by rollercoater.

• Usually the adhesive is dried prior to application so it is tacky. Sometimes the foil is applied without the adhesive being dried (wet application). The best route for individual tanners depends on their leathers, circumstances and preferences. Trials should always be carried out to determine the best method and control checks to be used within the tannery. This is to ensure that processing

conditions are maintained. The conditions of manufacture of the end product should also be taken into account, including processes such as moulding, lasting in shoe manufacture and even shipping. Changes in heat and humidity can affect the adhesion of the leather/ adhesive/ foil bonds.

Transfer
Typically, the foil is cut to the approximate size of the leather ensuring a slight overlap
without too much wastage. The first step is to place a Teflon sheet on the felt and then add the leather followed by the cut piece of foil. The latter two are often assembled in advance and placed into the opening on the hydraulic press. Application temperatures and pressure vary but table 1 shows an example of normal settings.

Post transfer
After the foil has been applied it is advisable to leave the leather to mature for around 4 hours to achieve the best results in terms of adhesion, scuff and gloss. The backing carrier paper from the foil should be removed in one constant movement. Further operations such as staking, milling and ironing can be carried out on the foiled leathers to achieve the required handle.

Common problems
As with other leather types, foiled leathers are subject to their own unique series of problems. Some of these are described here with the potential causes.

Foil peeling
There are several reasons for foil peeling:

• If the surface of the leather is not correctly prepared, (for example too oily or dusty) the foil may not adhere correctly to the surface
• Incorrect application of foil, for example too high temperatures or pressure
• Poorly made foil
• Foil damage during product manufacture: high temperatures/pressures and solvents from glues
• High temperature and humidity during transport
• Leather with too much stretch, which causes the foil to crack when pulled out
• Cleaning of leather with a product which is not suitable

Damage, during one part of leather or product manufacture can make the foil become more susceptible to damage during subsequent operations. These problems can be observed under magnification as small cracks. This allows moisture (or other contaminants) to penetrate the foil leading to further breakdown and loss of adhesion.
Foil can fail in several ways. Foils are usually an aluminium layer with a coloured coating to produce a gold or silver ‘colour’. Failure can occur between the leather and the foil (caused by one of the reasons above) and the indication for this will be the base leather colour showing. The other area can be the foil itself, where there is failure between the aluminium and coloured coating on the foil, this shows as silver colour with the coloured component being removed.

Foil flaking
Often foils can be ‘rubbed away’ from the leather and this can be caused by failure of the leather/adhesive/foil bond as outlined before. Another potential problem may, however, be related to over finishing (re-finishing) the foil to create fashion effects. It is important that the adhesion properties of the foil are tested to ensure suitability in wear.
In one example observed by BLC a foil had been sprayed with a nitrocellulose top coat followed by a coloured wax coat. The leather was then buffed to allow the silver foil to show through on the raised areas of the leather producing a worn antique look. A final protective nitrocellulose coat was then applied. Finish loss was observed and was caused by a failure in adhesion between the layers of the foil used. The foil was sensitive to the heat and humidity conditions that occurred during the over finishing and this resulted in a deterioration of the finish.
Application of any extra finish to a foil needs caution. It is important to ensure sufficient adhesion between coats to prevent layers from separating. To get good adhesion between layers it is necessary to get penetration of one layer into another. This in itself can cause a problem as migration of water/ humidity and solvent can affect the adhesion bond already in place. If the finish layer being applied to the foil is penetrating, then it may also be causing some damage. This then makes the finish more sensitive to further changes in conditions and more likely to show finish problems.

Conclusion
Fashion demands made on the tanner will always create situations where normal rules and standards are not applied. It is important that the tanner installs rigorous checks in their production processing to ensure that for metallic leathers the bonds between leather/adhesive/ foil are consistent. Once leather is foiled, care needs to be taken in subsequent processing as over-sprays and after treatments can affect the original bonds that have been formed. These problems may not surface until the leathers are subjected to variable heat and humidity situations, such as shipping or shoe manufacture. The tanner needs to implement sufficient safeguards and tests to account for this and BLC can provide advice on the areas of testing that should be considered.
BLC can help to identify the cause of problems experienced in the production of specialised leathers and offer technical advice and support to improve production procedures and ensure that appropriate product performance characteristics are achieved. For further information contact Stuart Booth on stuart@blcleathertech.com or +44 (0) 1604 679956.n

What is Physics?

Thursday, December 3, 2009

What is Physics?

A typical event studied and described by the science of physics: a magnet levitating above a superconductor demonstrates the Meissner effect.Physics (Greek: physis – φύσις meaning "nature") is a natural science; it is the study of matter[1] and its motion through spacetime and all that derives from these, such as energy and force.[2] More broadly, it is the general analysis of nature, conducted in order to understand how the world and universe behave.[3][4]

Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.[5] Over the last two millennia, physics had been considered synonymous with philosophy, chemistry, and certain branches of mathematics and biology, but during the Scientific Revolution in the 16th century, it emerged to become a unique modern science in its own right.[6] However, in some subject areas such as in mathematical physics and quantum chemistry, the boundaries of physics remain difficult to distinguish.

Physics is both significant and influential, in part because advances in its understanding have often translated into new technologies, but also because new ideas in physics often resonate with the other sciences, mathematics and philosophy.
Apple iPod touch 32 GB (3rd Generation) NEWEST MODEL

Chapter 11. HEAT 2ND YEAR PHYSICS COURSE SINDH FULL NOTES

Saturday, December 5, 2009

Chapter 11. HEAT 2ND YEAR PHYSICS COURSE SINDH FULL NOTES

Question: Define heat and its unit. Define temperature what the scale used to measure the temperature are.
Answer.
Heat
Heat is a form of energy which flow from hot body to cold body when they are in thermal contact.
Or heat is a form of energy which is related with the average movement of the molecule.
Unit
Heat is measured in Calorie (Calorie is the name of a scientist)
Definition of calorie
The amount of heat required to raise 1⁰C temperature of 1 gram water. In MKS system the unit of heat is joule 1 calorie =4.2 joule
Temperature
The degree of hotness or coldness of a body is called as temperature.
Unit: the unit of temperature is Kelvin it is measured by the help of thermometer.
There are three scale used to measure the temperature
1. Centigrade scale
On this scale the lower fixed point is at 0⁰C and upper fixed point is at 100⁰C where interval between these two points is divided in 100 equal scales. Each scale measures 1⁰C temperature
⁰C= 5/9 (⁰F -32)
2. Fahrenheit scale
On this scale the lower fixed point is at 32⁰F and upper fixed point is at 212 ⁰F where the interval between these two points is divided in 180 equal scales each scale measures 1⁰F temperature.
⁰F = 9/5 (⁰C +32)
3. Kelvin or absolute scale
On this scale the lower fixed point is at 273 k and upper fixed point is at 373 k where the interval between these points is divided in 100 equal scales each scale measure 1k temperature.
K =⁰C +273
Related problem conversation of temperature at different scale
Problem11.1
A normal body temperature is 98.4⁰F Find its temperature at ⁰C? And at K scale?
Sol. Data Fahrenheit temperature Tf = 98.4 ⁰F
Centigrade temperature Tc =?
Kelvin temperature K =?
We know that
Tc = 5/9 (F-32)
Tc = 5/9 (98.4-32)
Tc =5/9 (66.4)
Tc =36.89⁰C …………..1
K = 273 +⁰C
K = 273+ 36.89
K = 309.89⁰F …………..2
Question: What is thermal expansion explain linear expansion? Or prove that L’ = L (1 +αΔT)
Answer: Thermal expansion
If a body expand by gaining some heat from external source its dimension expands more due to the temperature difference the phenomena is called thermal expansion. The volume of body increases due to increasing movement of its molecule.

Linear expansion
The increase in length of a body due to heat is called as linear expansion for example if the length of a rod increases by supplying heat its expansion is linear expansion.
Explanation
Consider a thin rod of uniform cross section area
At temperature T1 ⁰C its length is L
At temperature T 2⁰C its length become L’
The increase in length ΔL of rod is directly proportional to the initial length of the rod L and to the change in temperature ΔT
Therefore
ΔL ∝ L …………..1 ΔL = L’-L change in length
ΔL ∝ Δ T ………………..2 ΔT= T2- T1 change in temperature
Combining 1 and 2

ΔL ∝ LΔT
ΔL= α LΔT ………….3
Where α is a sign of proportionality constant and is called coefficient of linear expansion it unit is 1/K.
The value of coefficient of linear expansion depend upon the nature of material the rate of expansion is different of different material
From eq. 3
ΔL= α LΔT
L’ - L= α LΔT
L’= L + α LΔT
L’ = L (1+ α ΔT) proved

Related problem
Question:
The length of a steel rod is 0.2 cm at 30⁰C what is its final length at 60⁰C?
Solution:
initial length L = 0.2cm
initial temperature T1 =30 ⁰C
final temperature T2 =60⁰C
value of coefficient of linear expansion α for steel = 11✕10 -6 /⁰C
final length L’ = ?
L’ = L (1+ α ΔT) ΔT= T2- T1 change in temperature
L’ = 0.2 ( 1+ 11✕10 -6✕ (60-30))
L’ = 0.2 ( 1+ 11✕10 -6✕30)
L’ = 0.2 ( 1+330 ✕10 -6)
L’ = 0.2 ✕1.000330
L’ =0.200066 cm the final length of the rod


Question: What is volume expansion prove that V’ = V (1 +βΔT)
Answer.
When the volume of a body increases by gaining heat it is called as volume expansion the body`s length, width and height increases.
Explanation
Consider a body of volume =V
At temperature =T1⁰C
Increasing temperature from T1⁰C
To T2⁰C at temperature T2⁰C volume become V’
The change in volume ΔV of the body is directly proportional to its initial volume V and change in temperature ΔT

ΔV ∝ V ……..1 → ΔV = V’ - V
ΔV ∝ΔT …………2 → ΔT = T2 –T1
Combining 1& 2
ΔV = constant vΔT
ΔV = β vΔT ……..3
where β is the constant of proportionality and is called coefficient of volume expansion its unit is 1/⁰C or 1/K
Coefficient of volume expansion depends upon the nature of material different materials expand at different rate and have different value of β
From 3 we know that
ΔV = β vΔT
V’ - V = β vΔT
V’ = V + β vΔT
V’ = V (1 +β ΔT) proved
Question: What is the Relationship between linear and volume expansion? or
Prove that β = 3α
To find the relation between α and β consider a box of rectangular shape. h
At temperature T1⁰ C its length is = l
Its width = b b
Its height = h l
The volume of the body at T1⁰ C V= l ✕ b ✕ h ……… A
When we increase its temperature from T1⁰ C to T2⁰ C thermal expansion takes place in the body it expands three dimensionally and its length, width and height increases so that its volume become larger
The length increases as l’ = l (1+ α ΔT) ……1 l’ is the final length
Width increases as b’ = b (1+ α ΔT) ……2 b’ is the final width
Height increases as h’=h (1+ α ΔT) …….3 h’ is the final height
Whereas the final volume at temperature T2⁰ C V’= l’ ✕ h’✕ b’ ….4
Putting the value of l’ ✕ h’✕ b’ from 1, 2 and 3 in 4
V’ =l (1+ α ΔT) ✕ h (1+ α ΔT) ✕ b (1+ α ΔT)
V’= l ✕ h✕ b (1+ α ΔT)3 but from A we know that V = l ✕ h✕ b
V’= V (1+ α ΔT)3 …………B
But the final volume expansion of the body(as the coefficient of volume expansion)
V’= V (1+ β ΔT) …………C
Comparing B and C we get
V (1+ β ΔT)= V (1+ α ΔT)3 canceling V from both sides
(1+ α ΔT)3 = 3 α ΔT + 3 α2 ΔT2+ α3 ΔT3
Neglecting the values of α3, α2 because these are the smallest values
(1+ α ΔT)3 = 1+ 3α ΔT
From C we know that (1+ α ΔT)3 = (1+ β ΔT)
(1+ β ΔT)= 1+ 3α ΔT
1- 1+ β ΔT-3α ΔT=0
ΔT (β -3α)=0
β -3α = 0
β = 3α proved


Related problem
An aluminum sphere of radius 0.4 m is heated from 0 ⁰C to 100 ⁰C what will be the change in its volume?
Solution
Radius of sphere r = 0.4m
Initial temperature T1= 0 ⁰C
Final temperature T2 = 100 ⁰C
Change in volume ΔV=?
Coefficient of linear expansion for aluminum α= 24✕ 10-6/⁰C
β = 3α
Therefore coefficient of volume expansion β will be= 3 ✕24✕ 10-6/⁰C
= 72 ✕ 10-6/⁰ Initial volume of the sphere V1= 4/3 π r3
V1= 4/3 π (0.4)3
V1 =0.268m3
Change in volume of sphere ΔV = β v1 ΔT
ΔV = 0.268✕72✕10-6 (100-0)
ΔV = 1.930 ✕10-3
ΔV = 0.00193 m-3
Therefore the change in volume of aluminum sphere is
0.00193 m-3
Uses of thermal expansion
Bimetallic strip
It is made by joining two different metal strip or alloys in length wise outer side is made of that metal which has higher value of linear expansion. Different type of metals expand at different rate (because the value of coefficient of linear expansion α is different for each metal) therefore when this bimetallic is heated one metal expand more than other. These two metals are joint together firmly therefore bimetallic turns in curve shape. The expansion of bimetallic in curve shape is used in different instrument as for temperature control bimetallic thermostat is commonly used. It is used electric iron aircondtionar, refrigerator, room heater, cars radiator fans, oven and fire alarm.

Heat capacity

The amount of heat require to increase the temperature 1 ⁰ C is called heat capacity

C = ΔQ/ ΔT the value of heat capacity depend upon the nature of material and mass greater the mass of material greater will be the heat capacity J/ ⁰ C

Specific heat capacity

The amount of heat require to increase the temperature 1⁰ C of unit mass of a substance is called specific heat capacity.

More heat energy is required to increase the temperature of a substance with high specific heat capacity than one with low specific heat capacity. For instance, eight times the heat energy is required to increase the temperature of an ingot of magnesium as is required for a lead ingot of the same mass. The specific heat of virtually any substance can be measured, including chemical elements, compounds, alloys, solutions, and composites

equations

• The equation relating heat energy to specific heat capacity, where the unit quantity is in terms of mass is:

where Q is the heat energy put into or taken out of the substance, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature.

• Where the unit quantity is in terms of moles, the equation relating heat energy to specific heat capacity (also known as molar heat capacity) is

where Q is the heat energy put into or taken out of the substance, n is the number of moles, c is the specific heat capacity, and ΔT is the change in temperature.

C` = ΔQ/ mΔT

It only depends on the nature of the material not on the mass of the material. Each material has different specific heat capacity. The specific heat capacity of water is 4200j/kg.

Gas laws
Boyle`s law
“The volume of a given mass gas is inversely proportional to its pressure at constant temperature”
P ∝ 1/ V when T = constant
PV = constant T = constant
If the pressure of a gas is increased from P1 to P2 at constant pressure it volume will increase from V1 to V2 then according to Boyle`s law
P1V1 = P2V2
Mass effect: at given temperature pressure of gas P and volume of gas V depend upon mass of gas. Therefore
PV ∝ m
PV/m = constant
P1V1 /m1=P2 V2 /m2 = CONSTANT at temperature constant .

Charles`s law

It states that

“The volume of a given mass gas is directly proportional to its absolute temperature at constant pressure”

V ∝ T when P (pressure)= constant

P/V= CONSTANT when P(pressure)= constant

P1v1 =P_2/ T₂ at P= CONSTANT

General gas equation
If at constant temperature T1 the pressure of the gas is changed from P1 to P2 so that its volume is changed from V1 to V than according to Boyle’s law
P1 V1 = P2 V
V = P1 V1/ P2 …….A
Now at constant pressure P2 changing its temperature from T1 to T2
Its pressure changed from V to V2 than according to Charles law
V/T1 = V2/T2 …………B
Putting the value of V from equation A in equation B
We have
P1V1/P2 /T1 = V2/T2

P1V1/T1 = P2 V2/T2
PV/T = Constant


Relation between heat capacity and molar heat capacity
Consider M is the molecular weight of a substance the mass of n mole is m
m = nM
Specific heat capacity of the substance
C` = ΔQ/ mΔT
C` = ΔQ/ nMΔT
MC`= ΔQ/ nΔT C = ΔQ/ nΔT
MC` = C