Natural leather product

Natural leather product production technology

Technology: Items needed to start producing a leather product

  1. Template or mannequin
  2. Idea and design or model
  3. Raw materials such as natural leather, all kinds of adhesives, all kinds of yarns, layers, liners, fittings and….
  4. Types of production tools such as cutting, sewing and styling tools and…

Template or mannequin

The mold is a three-dimensional shape of the body or part of the body that we want to cover with our leather product. The template can be a physical object or a three-dimensional image. The template determines the different sizes of the template. Physical mold is required in the production of some natural leather products such as shoes and clothing. In addition to determining the different sizes, the physical mold is also used to shape the cut leather parts. The quality of the mold is very effective in the comfort and satisfaction of the consumer.

We even need molds in the production of bags and accessories covers. In these cases, the accessory covered or the dimensions of the banknote or checkbook are considered as a template. Mold is extremely important in making shoes. The different sizes used in the pattern are extracted from the mannequin. In making shoes and clothes, a special mold is required for each standard size. Standard design of molds requires sufficient knowledge of body anatomy and mastery of ergonomics in design.

Research has shown that the size of the foot and other limbs varies on different continents and countries. That is why there are all kinds of sizes in the world. By doing research, standard sizes suitable for a community can be extracted and used as the basis for mold design. This significantly increases the convenience of the product. For example, a study in India found that the shape of the foot in this country is different from the standard shape of shoes in Europe. The difference in ankle height was the amount of arch of the foot and the width or width of the chest.

 

Basic Design Idea or Design

The word Design in English has the meaning of verb and noun and is a kind of process and its leather product that leads to creating beauty and thus human admiration. Man is a creature who looks at his surroundings and sees and admires its beauties. The ability to understand and admire the beauty of things that make humans different from other animals. Beauty can be divided into two types of natural beauty (blue sky, sea, trees…) and art beauty. Art can be divided into two types of applied and beautiful art. What is considered in the design of a natural leather product is more than the type of applied arts.

Elements of the design

The main elements of the design are: line, shape or form, value, color and texture.

Line

It arises from the joining of line points. Line types are straight and curved. Also straight line types are vertical, horizontal, scattered, broken, with jagged and diagonal edges. Types of curved lines also include gentle curvature, full rotation, compound rotation, and infinite rotation.

Lines function

  • Separation and specification of spaces and areas
  • Transmitting meaning or emotional or psychological significance

1- Eye movement control: Straight lines convey concepts such as strength and masculinity and direction and simplicity, and curved lines convey concepts such as softness, freedom, femininity and diversity. Each type of straight line and curve conveys its own concepts. For example, diagonal lines convey the concept of movement and action and scattered lines convey the concept of conflict.

  1. Shape or form: Shapes or forms are obtained by connecting straight lines or curves. Square, triangle and rectangle are created by joining straight lines, and circles and ellips are created by joining curved lines. From the combination of curved and straight lines, three-dimensional shapes such as cubes, cones, cylinders and pyramids are obtained.
  2. Value: means the amount of darkness and brightness. The amount of opacity and brightness is defined on a gray scale and in shades. Using value, concepts such as solidity and uniformity, distance and depth, and mode can be conveyed. All kinds of mental and emotional states can be transferred using value.
  3. Color: It is a feeling that is created by stimulating the optic nerves in us. Color has three main dimensions that are often defined as shade, value and intensity. The color of objects has a psychological effect on human perception. For example, large objects with cool colors look smaller, and the use of warm colors such as red makes objects appear larger. Different types of color matching and harmony are defined and used. For example, using different shades of one color (monochromatic accompaniment) or using contrasting colors. Each color conveys concepts and emotions to the viewer. For example, red represents violence and danger and is reminiscent of blood, fire and anger, and yellow is motivating, warm and joyful and reminiscent of sunshine.
  4. Texture: The surface quality of an object is called its texture. The texture of the surface leads to a different appearance and as a result creates different emotions in humans. For example, textures leading to a glossy appearance make the surface feel uniform, and textures leading to opaque levels create a feeling of surface strength.

Design Principles

  • Equilibrium
  • Ratio
  • Repetition
  • Rhythm
  • Emphasis

Balance

Ratio: The accompaniment of different parts of the design together.

Rhythm: tells how to repeat the components of a whole.

Repetition: Reconsidering the constituent units of the plan in different dimensions and repetitions.

Emphasis: Visual valuation in such a way that a different mental weight is created when seen.

Types of design methods are defined in the world, the main category of design types can be seen in the figure below:

A change in design method is in fact a change in the method of observation or a change in the method of translating observations. For example, the natural method seeks a one-to-one image that is completely identical to the original nature or object, but the geometric method seeks to translate the resulting original image using geometric shapes.

Perspective

Perspective is how to give depth to a plan. Using perspective, a two-dimensional 3D design can be seen or a three-dimensional object can be depicted on a two-dimensional screen. Perspective also helps determine how an object looks when viewed from different angles. Different types of perspectives are used in design, including one-, two-, and three-point perspectives.

Text, handwriting, font

In industrial design, textless design will not have the ability to convey the message intended by the designer and there is a need to write the brand, title and object information. Hence the handwriting or font and dimensions and prominence or flatness of the text and…. It has a great impact on the quality of design.

The text is designed or used in a design according to the extent of the letters and the amount of emphasis on the letters, as well as according to the handwriting or font used.

 

Specifications of a good design in the production of natural leather product
  1. It must be appropriate to the intended use
  2. It must be appropriate to the material in which the object is used
  3. It must be suitable for the production method in which the object is used.

Achieving these three characteristics requires that the designer has sufficient knowledge of production methods and materials used in production and human needs in the object. This is why the best designs are often done by design teams that consist of a collection of people with expertise in each of the fields mentioned or by people with experience in the required fields.

 

Tips for achieving a good plan

Pay attention to nature to find ideas. Keep things simple and let the application guide the changes needed to the appearance of the object.

Do not overuse the decorations. As much as possible, let the materials used in the production show their natural appearance and create a natural decoration on the work. Do not cover the components with paint and avoid using a large number of different materials in one object.

Convert design to template

In many cases, production design is done by depicting a three-dimensional object. After designing, it is necessary to convert the three-dimensional image to a flat two-dimensional image so that it can be cut. Converting a 3D design to a 2D image is also called pattern design. Today, the process of converting a three-dimensional design to a two-dimensional model has become a series of standard calculations and pattern design is a science that can be learned easily.

Cut

After preparing the leather product production pattern, the pattern is divided into different parts and each part is placed on the desired material and cut. The quality of the cutting stage determines the quality of all subsequent stages and the mistakes made in this stage cannot be corrected in the next stages. Accuracy in cutting, having uniform lines without fringes, considering additional edges for joints and stitches, maintaining fit between different parts of the cut are some of the things that should be considered in the cutting process.

Various tools are used to cut leather products, which are selected depending on the method and scale of production and the type of product produced. For example, in manual production and a small number of scissors and cutters and in industrial production, various types of cutting tables with automatic suction and blade and laser cutting machines are used.

Leather cutting tools are different from other textile cutting tools, which are related to the greater thickness and strength of leather. Therefore, care must be taken in choosing the appropriate cutting tool according to the type of material to be cut.

Connecting leather product pattern parts

After cutting different parts of the production pattern of a leather product, these different parts must be connected to each other. The use of adhesives, stitching and welding or welding to connect different parts is common and practical. In the production of leather products, the connection process is often done in such a way that at first, the parts are joined together using glue so that they do not move relative to each other. Then two or more pieces are sewn or welded to each other. For example, in the production of a wallet, first the different parts and layers are fixed on each other using glue, and then the sewing of these connections is stronger and also creates a decorative aspect.

Adhesives

An adhesive is a material that has the ability to hold two materials together without reusing the connection of two surfaces. The word adhesive is a general term and includes concrete, adhesives and pastes. Adhesives have many applications in industry and are important auxiliary materials.

The main advantages of adhesives are the bonding of thin films, fibers and small particles that are not done well or not at all by other methods using adhesives quickly and easily. At surfaces bonded by adhesives, stresses extend across the surface (in connection with other methods, there is a concentration of stress at the point of connection.

Strength to weight consumption and dimensional stability of inhomogeneous materials are improved by the use of adhesives. Lines made of adhesives provide insulation against electricity, moisture and water vapor. Materials that do not resemble each other are bonded together using adhesives, and the properties that the combination of these layers exhibits are better than the properties of each layer when applied individually. Bonding with adhesives is faster and cheaper than other bonding methods.

Category of adhesives

Adhesives can be categorized in different ways, for example, chemical structure, how to make a connection, how to fix and…. In the shoe industry, the usual method for classifying adhesives is based on the transfer medium (solvent) of the adhesive and the origin of the material. In this method, many adhesives that have the same chemical structure are classified into several different categories.

Here is the classification of adhesives based on the transfer medium.

Liquid adhesives: Liquid adhesives have many uses and are used as a solution or emulsion and the rest of these materials are sensitive to water.

  1. Of animal origin: casein, skin glue, fish glue, egg white
  2. Of plant origin: sesame, flour paste, dextrin, glucose, vegetable resins, natural latex
  3. Of artificial or semi-artificial origin: cellulose and wood derivatives, cellulose nitrate, methyl cellulose oil based on polyurethane
  4. Man-made origin: resins, formaldehyde, melamine, phenols, some acrylics, butadiene, PVC, PVA…

Adhesives in organic solvents

  1. Rubbers: Natural rubber, derived from latex rubber, soluble in solvents such as carbon tetrachloride, trichlorethylene or benzene
  2. Synthetic adhesive rubbers, which include polychloroprene, polyurethanes, butyl and polyisobutyl rubbers, nitrile and acrylonitrile rubbers used for laminating. Styrene butadiene tires used as pressure sensitive adhesives and thermoplastic tires.
  3. Cellulosic Adhesives: Nitrocelluloses

Solid binders

  1. Materials that melt by heat: polyamides, polyesters, EVA

2- Bonding resins: epoxy and aminorzin

Basic concepts of sticking

Zygology is the science of bonding materials, which includes the study of a variety of bonding methods such as gluing, welding, and mechanical bonding. In the shoe industry, only two concepts of zygological knowledge are used: grip and mechanical grip.

  1. Adhesion: A chemical bond is formed between the bonded surface and the adhesive. Therefore, the binder does not need to penetrate the surface, but must be able to perform a chemical reaction.
  2. Mechanical connection: A physical connection is established in which the adhesive penetrates into the surface penetration structure and thus creates a connection between the two surfaces. Therefore, this bonding method can only be done on porous materials. Leather and textiles are among the porous materials. In this connection, the binder penetrates into the surfaces in the liquid state and creates a bond after the solvent evaporates. This connection will not be broken without breaking the surface structure or the structure of the solid binder. The more porous the surfaces, the more adhesive must be applied.

Properties of adhesives

Properties of adhesives that are important in production are:

Tack viscosity: An adhesive that has this property, when coated on one surface, in contact with another surface, creates a bond. It is a kind of desire and speed of adhesion.

Plasticity: The ability to accept deformation without tearing

Stringiness: The ability to produce filaments when two surfaces coated with an adhesive separate:

  • Infiltrate
  • Covering
  • Drying time
  • Time to set
  • Pot life
  • Maintenance time or shelf time
  • Activation temperature
  • Select the appropriate adhesive for production

The main points that should be considered when choosing an adhesive in the shoe industry are:

  • Price
  • Strength
  • Material fit for use with shoe material
  • Fits shoe making processes

General Product Leather Considerations

Price is an important factor, but it should not be the only factor in the decision, because the initial cost is not the only cost that should be considered in the production process of the leather product. The amount of material used, the size of the material and the type of tools and the amount of labor required are other factors that affect the cost of use.

Strength: It should be suitable for the life of the product and the type of use of the leather product

General considerations:

  1. In general, the storage time should be long.
  2. It is better that the substance is non-toxic and non-flammable.
  3. The material should not shrink during drying because if it shrinks, it will cause wrinkles.
  4. The possibility of simple cleaning of the material is an advantage for cases where the adhesive is used incorrectly and needs to be removed without leaving a stain.
  5. The material should not cause discoloration or damage to the final finish of the procedure.
  6. The application of the material in a variety of applications is an advantage because it simplifies the purchase and storage processes and application instructions.

Adhesives used in the footwear and leather products industries

  1. Natural rubber latex: This material is obtained from a tree and contains 35% of solid material.
  2. Rubber adhesive: Natural rubber and latex is dried in an organic solvent such as carbon tetrachloride or trichloroethylene or benzene to produce a binder.
  3. Polycloprins: These base materials are one of the largest and most important classes of rubber binders.
  4. Polyurethanes: Polyurethanes are newer than other adhesives. The use of these substances is increasing due to their unique behaviors.
  5. Nitrocelluloses: They are produced from nitrocelluloses dissolved in a strong solvent with a ketone group. These materials were the first synthetic materials used in the footwear industry, but were gradually replaced by polycloperins and polyurethanes.
  6. Materials that melt by heat: These materials are normally solid. The raw material of this category is a plastic. Most are based on polyesters or polyamides and in some cases are based on EVA or PU.
  7. Two-component composite systems: Polychloroprene and polyurethane can be used in a two-component system with a reaction agent. It often binds to a polyisocyanate. These systems are used in cases where a strong connection and high heat resistance are required.

Application of adhesives

  1. Surface preparation: There are three types of surface preparation:

Mechanical: cutting the surface, sanding and polishing the surface

Chemical: Cleaning the surface using an organic solvent

Halogenation or surface chlorination

  1. Method of application: It varies depending on the solid or liquid of the material. In liquid materials, various tools such as brushes, sprays and coats are used. In the use of solids, special devices are used.
  2. Activation: If heat is needed to activate, infrared radiation or halogen lamps can be used. Pressing: A variety of pneumatic or hydraulic pressure devices can be used. The amount of pressure applied must be proportional to the type of material.

Textiles

The fibrous material is twisted and laminated from filaments or short fibers

Fabrics made from filaments, short fibers, or yarns that are produced as a nonwoven layer by weaving processes or fiber bonding and aggregation methods.

The main applications of textiles in the footwear industry are:

  • Connecting and putting together materials for:
  • Sewing, sewing, decorative sewing of leather products
  • Strengthen the leather product
  • Attach trinkets, buttons, and straps and…
  • Connecting the upper and the sole of the shoe
  • Lining for internal spraying, concealment, strengthening and styling
  • Shoe upper material
  • Underlayment of coatings
  • Substance of materials
  • Felt and non-woven materials

Fibers and yarns: yarn production

Threads are made up of fibers that are long enough together.

There are three types of fibers:

Natural fibers include animal and plant fibers

Synthetic fibers obtained from the reconstruction of natural fibers

Synthetic fibers made from synthetic polymers.

Spun yarns: Most common yarns are made from spinning fibers. During the spinning process, the fibers are arranged next to each other and then twisted.

In ricin yarns, the process of producing fibers and converting fibers into yarn is done simultaneously. Twisting is used to strengthen the yarn.

There are two types of swing clockwise and counterclockwise. The type of warp does not affect the amount of strength, but depending on the type of sewing machine, the type of warp is important.

Yarns are usually produced in two or three layers. Depending on the application, the number of layers of yarn and how they are wrapped varies.

To produce high-strength yarns, 2 and 3-layer yarns are rewound around each other. And produce 4, 6, or 9 layers of yarn.

Each layer of fibers is always twisted in the opposite direction to the multilayer twist of that layer.

Collector: Ms. Dr. Zeighami (Professor of Tehran Leather University)

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