During the 1950s, shoemaking methods were changing and becoming more automated to keep up with faster production methods. Machines that exerted greater stress levels on both the crust leather and the finish began to replace operations that were earlier carried out by hand. Solvent-based adhesives were used to attach linings, stiffeners and sole units. Exposure to steam and heat enabled the mechanised lasting of the upper without cracking.

As a result, Stahl introduced new polymers to withstand the wear and tear of modern-day shoemaking methods. New acrylic resins were developed that improved the resistance of the finish film to water and eliminated swelling when exposed to solvents. A range of novel solvent-based top coats improved surface protection and provided different gloss levels and surface feels that could be further enhanced with the addition of unique handle modifiers.

Stahl’s Titekote was also born; an aliphatic solvent dilutable polyurethane designed for use as an impregnator for full grain and corrected grain leathers which does not harden the leather when compared with water-based alternatives.

Water-based finishes

In the 1970s, Stahl had already begun work on the development of water-based polyurethane finishing technology but the idea was slow to catch on because early water-based finishes did not match their solvent counterparts in terms of performance. However, the fuel crisis had pushed solvent prices sky high and new health and safety legislation began to appear in many countries.

A range of both aliphatic and aromatic Unires polyurethane resin emulsions was launched for base coat application and these new products provided unparalleled performance when compared with the more commonly used acrylics.

Polyurethane technology soon became one of Stahl’s core competencies. The company’s range of hybrid Superes polymers are neither polyurethane nor acrylic but a synthesis of both and offer the combined advantage of high levels of performance derived from the polyurethane with the natural character and economy of acrylics. The products are VOC-free and have excellent embossing retention, ideal for automotive and some furniture upholstery leathers.

Polymatte technology followed and this provided a breakthrough in the development of high-performance water-based top coats. Many finishing formulae now combine acrylic, Superes hybrid and Unires polyurethane resins, blended to enhance the performance properties of the finish.

Automation and machinery

Automation has replaced expensive manpower in many tannery operations with application techniques being adapted from other industries. In particular, the printing industry has led to the adoption of synchro and reverse rollercoating machines that have revolutionised the leather finishing process.

In recent years, there has been a growing demand for softer leathers that were difficult to feed through the early designs of rollercoating machines. Once again, the printing industry came to the rescue as machines based on the rotogravure process were able to cope very successfully with upgrading soft leathers and, in doing so, often permitted the use of thinner coats of finish.

Stahl have been closely involved with the machine manufacturers to develop an ideal combination of chemical and machine design. These new application methods now allow tanners to produce softer leathers and upgrade lower selections with a lighter finish.

To satisfy the industry requirements for simple processes and low product inventories that are easy to manage, Stahl now manufacture a complete range of Compact resin finishes for different types of leather. These consist of ready-to-use products that simply require the addition of pigment prior to application by rollercoater or spray.

The past 25 years

When fashion changed to require very soft feeling and natural looking leathers, Stahl introduced a completely new range of cationic products that, when formulated, maintain the natural character of the leather and enhance the surface upgrading. The advantage is that some of these cationic products may be used in combination with selected anionic products to retain a natural surface appearance, a soft touch and improvement in the final quality selection, especially when applied on garment and soft shoe upper leathers.

Stahl also developed a CFC-free foam finishing system that could be applied to low selection crust leather with the advantage that it flowed into the surface defects and camouflaged them. New research enabled Stahl to develop stable mechanical methods of foam application that resulted in a resurgence in interest in the technique both as a method of upgrading and, due to its low coating weight, as a sealer coat in preparation for more natural, softer covering finishes for upholstery and automotive applications.

Stahl introduced the Water Transfer System (WTS) in the mid-80s. This is a system whereby the finish is applied to a continuous roll of transfer release paper in reverse order, top coat first, and then intermediate and base coats, followed by an adhesive which glues the finish film to the leather. The paper usually has a print design embossed into its surface and can be reused a number of times. The machinery required for this system is fairly large and complex and is best suited to large-scale production of mainly split leathers.

Recent developments

Many tanners would agree that leather finishing begins in the beamhouse. Since the early 90s, Stahl have grown their Colours & Tanning (C & TP) wet-end product business and now have a complete range of products for retanning and dyeing in addition to selected beamhouse products. The ability to work on a customer’s new product development project from retanning, dyeing and fatliquoring through finishing is an important asset in ensuring that products used throughout the process are entirely compatible.

The acquisition of Salem Oil & Grease has helped to establish Stahl firmly in this product segment. Having combined application laboratories around the world has dramatically speeded up response times to problem solving and ensures that customer requirements are dealt with in a timely manner across the whole spectrum of leather processing and finishing.

Newly-introduced products for the wet-end range include a new generation of compact polymer based wet-finishing products (Corilene CPF).

And for the future

Following the management buy-out from Avecia a few years ago, Stahl have received strong financial support for investment in additional research and development facilities, application laboratories and production facilities in the key global leather producing regions around the world.

Acquisitions such as the Salem product range in the USA and Pielcolor in Spain have been made with a view to the future expansion of the wet-end and leather finish businesses.

Investment in new manufacturing plants in India and China is also seen as vital to securing the company’s planned business development into the future. Throughout the world, Stahl are using the latest reactors and blenders to manufacture their products. As recently as April last year, a new IR (in-line reaction) blending plant using state-of-the-art technology for the production of polyurethane emulsions was opened at the Waalwijk site. Other investments include the adoption of computer-automated production lines that ensure the highest accuracy in producing a high-quality range of products across the globe. This enables Stahl to achieve ‘right first time’ manufacture with ‘on-time’ delivery.

Reviewing the past fifty years, perhaps the most outstanding advances have been the change from solvent to water-based finishing products and the development of polyurethane related technology. The introduction and expansion of Stahl’s wet-end products and dyes range makes the whole process of leather production simpler and more cost effective and enables the company to apply a unique and total focus on the end requirements of the tannery customer.

Stahl have made an acknowledged contribution to helping their customers comply with health, safety and environmental challenges and will continue to provide a high level of both customer and technical service to the industries that they serve.