Ever since the inception of “Denim Jeans” in the 1870s as workwear for miners and cowboys, these iconic garments have evolved to become a popular item of casual wear throughout the world today. Coming in various fits to suit different tastes and fashions an important part of their appeal is the distressed look, visibly aged and worn, but still intact and functional. The process of washing improves the fastness properties of indigo-dyed denim jeanswear and in addition by altering the types of washes, various fashion looks are achieved.
In this technical bulletin we will explain how denim apparel is wet processed and highlight the parameters associated which need to be controlled in denim manufacturing and subsequent wash processes.
Over the past few decades, different denim washing techniques have been developed and used on different materials to create a large variety of designs for trendy denim garments and jeans. Special color effects and washed/vintage looks are often achieved in denim garments. The hand feel of the washed goods is relatively superior, which makes them suitable for leisure wear. These effects are difficult to achieve through other processing techniques.
The results obtained from denim washing represent a combined effect of color dissolution, destruction of the dye and mechanical abrasion, which sometimes causes the removal of surface fibers from the materials. Thus surface dyed (ring dyed effect) colors in denim garments are more easily washed down during the washing processes.
Traditionally denim is a 3/1 warp faced twill fabric made from yarn dyed warp and undyed weft yarn. Typical construction of the fabric is 32 × 19; 45 × 54 tex; 310 g/m2. More recently, other weaves have been used with lighter constructions’. Jeans are defined as ‘A 2/1 or 3/1 warp faced twill fabric used chiefly for overalls or casual wear with a typical construction of 35 × 24; 32 × 21 tex cotton’. Although by definition, denim and jeans refer to different things, they now mean the same thing in the market. Conventionally, warp yarn in denim fabric is dyed with indigo with a ring dyed effect. As a result, the washing technique and effect described in this chapter are based on indigo dyed fabric.
Several types of garment washing for denim fabric are carried out to create varied effects in denim garments to meet the needs of today’s denim fashion trends. However each washing technique has its own advantages and limitations. Denim is either rubbed or worn with stones and other abrasive materials, called mechanical washing, or treated with bleach and other kinds of colour-altering substances, known as chemical washing.
Denim Jeans Washing Techniques
Mechanical washes include:
- Rinse wash
- Water jet fading
- Stone wash
- Microsanding including sandblasting
- Mechanical abrasion
- Laser treatment
Chemical washing includes:
- Acid wash, ice or snow wash
- Hydrogen peroxide wash or Bleach washing
- Enzyme wash
- Ozone fading
- Spray techniques
- Overdyeing and tinting
The effects desired for denim goods change every year owing to fashion. Various washing effects have been popularly obtained by laser, sandblasting and enzymatic washing processes. In addition to these processes, hypochlorite bleaching (acid wash) is often preferred, especially for summer denims.
General finishing sequence of denim:
There are almost countless variations of processing techniques used by designers and textile chemists to achieve fashionable looks that are distinctive and desirable. Only the basic treatment conditions are addressed in this chapter; the number of variations is very large and the evolution of chemical and mechanical techniques is continuing. There often are some secretive and proprietary methods. Regardless of the specific look and name chosen, the following are the process steps normally used to attain the desired results.
Flow Chart of Denim Finishing
Hand Scraping/Hand Brush:
- Garments are wearing on a dummy or pattern board.
- Hand scraping is done on specific area of garments by emery paper according to approve sample.
- Different type of emery paper is used like 220, 320,400,600.
- Most common used grade no of emery paper is 320.
- Then sent for further processing.
- This process is done manually by destroy machine.
- Glass pencil/blade is used in this process.
- Destroy is done on specific area of garments.
- Destroying warp yarn by blade gives new outlook.
- Garments sent for further processing.
- Tagging is done on garments for fashion and value added fashion wear.
- In this process tag pin is used.
- At first garments are clipped with tag pin by tagging machine.
- After wash upper portion of garment occurs crease marks & inside of tagging occurs dark shade.
- At first design is produced on pattern board according to buyer requirement.
- Then pattern board is placed inside the garments.
- Then hand rubbing is done by emery paper on Specific area.
- By using different types of emery paper (220,320,400,600) design is produced on surface of garments.
- Most common used grade no emery paper is 320.
- Then sent for further processing.
Potassium Permanganate (P.P) Spray:
- At first a solution is made by potassium permanganate & water.
- Sometimes CH3COOH (acetic acid) is used for solution preparation.
- A spray gun machine is used for spraying the P.P solution.
- Spray gun m/c spray the solution as per requirement.
- A few minutes later reddish color is found on the surface of garments.
- Then garments sent for further processing.
Permanent crinkle given on denim surface are known as crinkle effect. Resin application is done on denim to retain crinkle by using iron machine or pressing crinkle machine and even after wash.
First have to do spray resin on the specific area we want to create 3D effect. Without resin spray 3D effect is not possible. A garment is in metal plate. Crease is made in required place. Then two times pressing is done. The temperature is 1900c. Light temp is 1000 watt, it deep the resin and then it send to the curing to make wrinkle. Then it set to the dummy and makes 3D effect by the help of hand of workers manually.
- This is very first & basic step but most important step of washing.
- This process removes impurities, starch & stains during handling of fabric.
Methods of Removing Sizes from Denim Jeans
- Washing with High Alkaline agents ( i.e. Soda ash )
- Washing with High Acidic agents (i.e. Acetic acid )
- Washing with Oxidative chemicals ( i.e. Hydrogen Peroxide )
To remove the size materials from the garments enzyme wash is applied. Enzyme wash is done on garments made from denim & jeans fabric, twill fabric garments. Sometimes knit items are also subjected for Enzyme wash. Garments made from indigo, vat, direct etc dyed fabric can be enzyme washed. Enzyme works chemically not mechanically for this reason it provide less damage/wastage then stone wash. It improves improve the color fastness & rubbing fastness. Enzyme improves the anti-pilling properties and decrease the hairiness hence it gives a very smooth surface of the garments.
Garments made from indigo, vat, reactive, direct etc dyed fabric can be bleach washed. It is a discoloration process by oxidation action. Color can be removed uniformly from the garment and removal of color done as per requirement. In general there are three categories such as light bleach (where maximum color is removed), medium bleach and bleach. All types of garment can be washed. Such as: woven knit garments. In case of woven fabric a pretreatment (Desizing) process is required. Dust, dirt, oil spot, impurities etc. are removed that may come from during process i.e. cut- ting, stitching and the back process.
- Calcium hypo chlorite
- Sodium hypo chlorite
- Hydrogen peroxide
- Potassium permanganate
Effect of Denim after Dry Process:
Hand Scraping/Hand Brush:
Scraping can be done on inflated rubber balloons for better effect (horizontal or vertical it’s up to operator’s convenience), even it can done plain wooden board of garment size & hand pressure should be uniform in order to get better results.
One of the most popular distressing effects currently, ‘Destruction’ is an art which make denim look unique & used.
This effect can be designed anywhere on the garment in different styles. Most favorite areas for tacking are on waistband, bottom hems, back pocket and front pocket corners etc. On front or back sides of garment, tacking can also designed horizontal of vertical patterns on full length panel.
Whiskers are one of the most important design of a used look garment. The idea of whiskers is taken from the worn out lines and impression patterns generated by natural wearing on hips and front thigh area.
Potassium Permanganate Spray:
PP Spray is being done on denim garments to achieve local abraded area to appear whiter than back ground indigo color shade.
Permanent wrinkles given on denim surface are known as crinkle effect. Resin application is done on denim to retain crinkle.
First have to do spray resin on the specific area we want to create 3D effect. Without resin spray 3D effect is not possible.
Function of Chemical Used in Washing:
- It is used to remove mainly starches, waxes, fats, pectin’s, minerals & Indigo dye from denim, twills, poplin &canvass fabrics etc.
- The action of enzyme during enzyme wash it hydrolysis the cellulose.
- At first it attacks the having projecting fibers & hydrolyzed them.
- Then it attacks the yarn portion & partly hydrolyzed them.
- As a result color comes out from yarn portion & faded effect is produced.
Sodium Meta Bi-Sulphite (Na2S2O5):
- It is used for neutralizing the activity of KMnO4 on fabric/solute.
Bleaching Powder (CaOCl2):
- Bleaching agent is an oxidizing agent.
- It is used for color out from denim garments.
- We can achieve different shade (dark, medium, light) from garments by this agent.
Soda Ash (Na2CO3):
- Soda ash create alkaline medium in wash bath.
- It helps to uniform bleaching action in bleach bath.
- It has cleaning power &help color fading affect of garments.
- It is used for color fixing in dye bath.
- It is also used for maintaining pH of wash bath.
Potassium Permanganate (KMnO4):
- It is used for discolorations of fabric.
Softener (Cationic, nonionic):
- It is used to make the garments soft.
- It also provides excellent lubricating properties.
Sodium Chloride (NaCl):
- It helps to exhaust dye in to the fiber.
Hydrogen Per Oxide (H2O₂):
- H2O₂ creates the prime role in bleach wash technique.
- In alkaline medium H2O2 breaks up and gives some perhydroxhyle ion.
- Hydrogen per oxide is used in scouring, bleaching bath to occur bleaching action for white/ready for dyeing of gray fabric garments.
- It is also used for neutralizing the garments from alkaline condition.
- Resin is used for semi permanent creases in denim.
- Binder is a film former consisting various polymer.
- Polymer contains reactive group & it forms crosslink during curing.
Acetic Acid (CH3COOH):
- To neutralize the alkaline condition of garment.
- To control pH value in wash bath.