The shoe, clothing and furniture industries are the main customers for leather materials. There, bonding of the popular and hard-wearing material is a widespread and proven joining technique. Today, there are suitable adhesives for almost every conceivable surface and application.
Today, textiles are also increasingly being glued industrially - in the meantime, the market share of glued textiles has already reached almost ten percent. But with the abundance of different fabrics and a wide range of different textile properties, it all comes down to the right adhesive: spray adhesives, hot melt adhesives or solvent adhesives have proven their worth here, depending on the application as "liquid thread from the bottle".
Bonding leather is usually done using dispersion or solvent adhesives based on polyurethane or polychloroprene.
The latter are usually applied using the contact bonding method but can also be applied using the heat activation method. This method can also be used for 2-component polychloroprene or polyurethane adhesives with special polyisocyanates as a second component - especially when a particularly high adhesion to the sole material is required.
This is ideal for bonding decorative foils in combination with leather. The highest strength is achieved after heat activation. One example is 3M Scotch-Weld 1099.
Cyanoacrylate adhesives are also suitable for bonding leather material to hard substrates such as wood, metal or solid plastics.
Self-adhesive tapes, film or foil materials etc. are particularly suitable for bonding or laminating flat leather material to hard substrates such as metal, wood and plastic. The component geometry hardly changes. Some products, such as the adhesive films from the 3M range, are only 0.025 to 0.13 millimeters thin. However, the performance characteristics of the adhesive formulations - strong/weak adhesive - differ on the two sides of the carrier material due to their chemical structure.
Characteristics: excellent final adhesive strength with extremely high ageing, UV, temperature, and chemical resistance.
Characteristics: as with acrylate, but better adhesion to low-energy materials such as leather as well as better immediate adhesion.
Characteristics: excellent instant adhesion combined with good shear strength on most materials with low-energy surfaces (PP, PE).
Leather is an animal skin (usually from cattle, horses, buffalo, or pigs) that has been chemically preserved by tanning with a natural fibre structure that has been preserved. It's divided into the finer papillary layer on the outside, which gives the leather surface its smooth appearance. Below this is the coarsefibred reticular layer, which is decisive for the mechanical strength.
Leather is characterised by its supple, tough, relatively strong, durable, and versatile properties. It's relatively impermeable to water, yet it is breathable, i.e. sufficiently permeable to air and water vapour. This hardwearing material is widely used for shoes, clothing, belts, handbags, textiles and seating furniture such as sofas or car seats.
The largest consumers of leather adhesives in terms of volume are undoubtedly the shoe industry and craftsmen, but also the furniture industry. Here, bonding leather is a widespread joining technique.
Basically, a wide range of adhesives are suitable for leather. However, their selection depends on the respective substrate and intended use.
Leather is inherently elastic and flexible, which means that if leather is to be bonded to leather or a similar material, the adhesive must also remain elastic. This means that furniture and leathers should be glued with a flexible adhesive.
Less flexible adhesives such as superglues are only suitable if the leather is to be glued to a hard or rigid surface such as wood or metal.
Natural materials like leather will often react differently to the adhesive used due to its formulation and the natural variation in fats or tannic acids used in the manufacturing process.
Before application, it is therefore necessary to check the material over a small area for discoloration on contact with the adhesive
Contact adhesive is particularly suitable for bonding flexible materials such as leather (e.g. with shoe soles) over large areas. Such materials are often hardly permeable to the solvent. Therefore, the solvent must be allowed to evaporate or flash off before the parts are joined. (Rule of thumb: wait a quarter of an hour until the surface just no longer feels sticky. Then press together with a force of about 50 Newtons per square centimeter, i.e. about 5 kg).
Gluing at the touch of a button - Spray adhesives are almost perfect for gluing leather; either to itself or to solid surfaces such as wood or metal. The adhesive is simply applied from the aerosol can without any tools such as brushes, squeegees, etc. On the market are spray adhesives based on synthetic elastomers (polychloroprene) such as 3M Scotch-Weld 80, which are characterised by a short flash-off time with a long adhesive spread.
Solvent adhesives, as so-called "all-purpose adhesives", bond leather with a wide variety of materials such as metals, plastics, and rubber.
However, it's essential to test coloured leather beforehand to see whether the adhesive changes the colour of the leather. This is because adhesives containing solvents can, under certain circumstances, "bleed through" the leather and possibly remain as ugly stains. This is a problem that occurs mainly with thin, dyed leather, such as suede or aniline leather.
Dispersion adhesives based on acrylate and polychloroprene have similar characteristics and fields of application as solvent-based adhesives, but the adhesives are dispersed in water.
The flash-off time can usually be shortened by heat (infrared, hot air). This category includes, for example, the polychloroprene-based dispersion adhesive 30 from 3M's Scotch-Weld range, which has good water resistance and high flexibility.
Dispersion adhesives based on plastic polymers are suitable, for example, for bonding in the interior of shoes.
Sewing leather is common, especially in the clothing or shoe industry. For thick leather, there are usually special leather needles for the sewing machine.
Thin leather can even be sewn with normal 80-90-gauge needles. However, seam allowances and hems of leather are often glued afterwards. Seam allowances do not need to be serged.
Repairs to shoes can often be done yourself using suitable adhesives. As a rule, you need an adhesive that is waterproof. Especially when gluing footwear, there's also the problem of sweat and heat. Ordinary all-purpose glue is usually not sufficient for use on footwear.
Procedure: First clean the footwear thoroughly and lit it dry. Apply a suitable glue (see above). Then check whether an adhesive film has formed on the surface/s. To do this test with a gloved finger or suitable alternative tapping lightly on the adhesive surface, if ready the surface should not stick.
Then press the two surfaces together firmly and accurately. The final adhesive strength of the glue can be up to one day after the bond is made. With the sensitivity of leather it is advisable to test the adhesive to be used on a small area first.
Important: Soles must be chemically roughened before gluing. Make sure there is a supply of fresh air!
If seams come loose on a sofa after a long period of use, it's usually quite easy to glue the detached leather areas back onto the sofa.
However, the area to be glued must be dry, clean and free of grease. Only pull the open area together so far ensuring no folds appear in the leather. Then apply superglue to one side only. The less glue applied, the stronger the bond. Press on for approx. 10-80 seconds depending on the amount of adhesive used.
Please note: With very thin leather covers, the adhesive tends to soak into the fibres of the leather and discolour the leather.
Different processes are commonly used in textile production:
In the case of textiles, the variety of manufacturing processes, combined with a broad spectrum of specific textile materials and fabrics, results in a large number of very different properties, which are optimally matched to the requirements of the application area.
These include mechanical properties such as strength and elongation under static and dynamic stress, as well as resistance to cleaning or creasing. Compared to structures made of compact materials such as metals and ceramics, all textiles have in common a high porosity that ensures air entrapment, thermal insulation, air transparency and good sweat absorption in garments.
Generally, textiles and textile connections are sewn with needle and thread. However, not least for economic reasons, bonding is increasingly gaining acceptance in the textile industry as an innovative joining technique - also as a helpful supplement to the classic sewing seam.
Gluing is mainly used in niche areas of the textile industry, i.e. rather for premium products, where the price sensitivity of the clientele is not quite so pronounced: for water-repellent functional textiles such as outdoor or sports clothing, for lingerie or more special designer creations. Adhesive seams are also common in the orthopedic sector (prosthetic stockings, support and wound dressings). According to experts, the market share of bonded textiles has now reached almost ten percent.
Rough, absorbent surfaces such as those of textiles offer the advantage of good mechanical anchorage when it comes to bonding: the adhesive penetrates well into fibres or settles in interstices.
However, to avoid incorrect bonding and discolouration when bonding textiles, the right adhesive must be chosen with care. In textile bonding, for example, different adhesives are suitable for larger areas than for small, punctual glued joints. Especially with cotton fabrics, the finish or dyeing, for example, must be considered.
This is because the adhesive surface of textiles that have been treated accordingly is no longer a pure cotton surface and thus has completely different adhesive properties. In addition, bonding is not always unproblematic when the textiles are later put into the washing machine.
Spray adhesive is an all-rounder. Thanks to the thin, fine spray application stains on the reverse side of the fabric are minimised unlike liquid textile adhesives. Before application the spray adhesive must be shaken and the textile surface should be clean and free of dust and grease.
Spraying from a distance of 25-30cm in a well ventilated area often gives an even coverage. Allow the adhesive to dry briefly (according to the manufacturer's instructions) and then press the surfaces together.
It is also possible to correct the bond for a short time by pulling apart the surfaces and pressing them back together in the correct orientation.
When using a spray adhesive it is no longer necessary to baste or pin the quilt layers (in a quilted fabric). The spray adhesive temporarily holds the layers together for hand or machine quilting. Simply spray the adhesive onto the batting, place the fabric, smooth it out and the sandwich is ready for quilting. Spray adhesives are also ideal for fixing sand, glitter or tinsel to fabric.
Spray adhesives that can be used include 3M Rubber and Vinyl 80 Spray Adhesive a synthetic elastomer based adhesive featuring a short flash-off time with a long bonding range.
3M Rubber and Vinyl 80 Spray Adhesive will bond textiles to each other or to wood, metals, rubber, cork and leather as well as foam and plastics such as rigid and flexible PVC.
Alternatively 3M Foam Fast 74 Spray Adhesive will give a soft, flexible adhesive seam allowing textiles to be bonded well to flexible foams.
3M Display Mount Adhesive is ideal for decorative and studio applications. It bonds textiles with polystyrene, cardboard and plastic immediately and permanently, is moisture resistant and does not bleed through the surface.
A hot glue is ideal for fibrous surfaces of fabrics and textiles. Because it is more liquid than many normal adhesives when applied to the desired fabric, it penetrates a little deeper into the fabric before it cools down. Hot glue is therefore particularly suitable for thick, sturdier textiles (such as for handicrafts), as there is no danger of seeing the glue from the back of the fabric.
Professional tip: When hot gluing to fabrics, it's also important to cover the surrounding areas with a strip of paper or cardboard so that the glue does not accidentally drip onto the fabric.
On the market here are, for example, the 3M hot-melt adhesives of the low-melt and hot-melt technology. These hot-melt adhesives with one hundred percent solids content are based on solvent-free thermoplastic hot-melt resins. Their advantage is that they are wettable in the molten state and develop good strengths to numerous materials such as textiles, felt, leather, cork, plastics and foams, rubber as well as glass, ceramics, and metals without chemical conversion.
Solvent adhesives also have good wetting properties on textiles in combination with, for example, felt, leather, cork, cardboard, wood, glass, ceramics, plastics, rubber, laminates, hardboard and decorative panels, veneers, etc. This adhesive is usually applied to both bonding surfaces and both parts are joined with a little pressure after a short flash-off time (also called bonding span). A one-sided application (i.e. wet bonding) can be done if at least one of the two surfaces is porous. One example is Scotch-Weld solvent adhesive 10, a contact adhesive based on polychloroprene with a short flash-off time and a long bonding span.
In practice, double-sided adhesive tapes such as the 3M 9088 with PET backing are suitable in addition to liquid adhesives. This not only bonds textiles to each other, but also to wood, paper, plastic, metal, glass. Double-sided adhesive films without a backing can also be used for this purpose.