Polyurethane, latex or viscoelastic foams are present in our lives in different ways, normally related to rest or comfort: mattresses, sofas, car or motorcycle seats…

These foams have different manufacturing processes depending on their final use:

  • In the manufacture of mattresses, we may have to bond different types of foam to each other (dual density mattresses, for example). Also, parts of a mattress usually have to be assembled in order to insert springs inside.
  • In the manufacture of car seats, polyurethane foam is subject to a demolding process. In this process small flaws sometimes occur, which lead to breaks in the foam of the part that must be repaired.
  • Likewise, in the manufacture of seats, it is usually necessary to glue on the surface pieces of various plastics to facilitate the subsequent bond of the fabric that will cover the seat (or other parts that need to be attached to it).

Historically, to facilitate bonding in all these cases, solvent-based contact glues have been used for their quickness of bond and possibility of early handling. Currently, the global trend is to eliminate or minimize organic solvents released to the environment, gradually moving to products with VOC = 0 (volatile organic compounds). Solvent-based products are harmful to health, create explosive atmospheres, and hazardous (flammable and toxic) and unpleasant work environments.

The main polymer used in these solvent-based contact glues is polychloroprene (2-chlorobuta-1,3-diene), also known as neoprene. This polymer is a derivative of chloroprene and was invented by the company DuPont in 1930. It has great flexibility and maintains it in a very wide range of temperatures. This same polymer is the one that is usually used in the form of aqueous dispersion for the aqueous contact glues object of this article.

For decades in Concentrol we have accumulated experience in the development of adhesives for different applications working together with clients to understand in detail their specific needs to be able to provide customized solutions. For this reason, our specialization in different areas of the chemical industry, such as foams and adhesives, makes us a supplier of high technical reliability in adhesive solutions such as aqueous contact glues with excellent results on polyurethane, latex or viscoelastic foams.

Types of aqueous contact adhesives

We mainly have two types of adhesives:

  • Single component: No mixing prior to application is necessary to obtain the expected results.
  • Two-component: It is necessary to mix the adhesive with an activator to obtain the required adhesion. For these adhesives, the application is usually by spray gun specially prepared for this type of products, and the mixture is produced in the spray cloud, by the simultaneous release of both products through separate nozzles of the gun.

Composition

The basic composition of this type of glues usually consists of:

●      50-70% dispersion of polychloroprene

●      0-30% tackifying dispersions

●      0-5% of additives (biocides, antioxidants, thickeners …)

●      10-40% dispersions of other synthetic polymers

Through formulation and the types of polymers and additives used, the final properties of the adhesive can be varied, such as viscosity, open time, quickness of bond…

One of the major difficulties that the formulators of this type of adhesives come across is to find the balance between stability of the packaged product and speed of wet gluing, especially with single-component adhesives. This is because the mechanism of adhesion in this type of glues is through the destabilization of the product during its application. The product must remain unchanged in the container and be destabilized as quickly as possible during use.

Application

The two most common types of application systems are by spray gun or by roller. In the spray gun application, the destabilization is produced by the spraying air pressure. This method of application is used basically in the repair of breakages in demolding processes. These are applications in which the surface to be glued is not very large, usually a few centimetres.

In the application by roller, the destabilization occurs once the product is applied, when proceeding to apply pressure between the two surfaces to be glued. The process of gluing by roller is usually carried out in the manufacture of mattresses, as it is on large areas that need a very homogeneous application.

Considerations of aqueous contact glues

As we have discussed, these glues (especially the single-component ones) are products that are at the limit of their stability, so they must be treated as if they were considered “fragile”, not being advisable to stir prior to use.

Although their quickness of bond allows the practically immediate handling of the parts assembled or repaired, being water-based products, it is necessary to allow for a certain waiting time to allow the evaporation of the water and to assume a complete development of properties. Being foams (porous support), this evaporation is relatively easy, although it must be understood that environmental conditions influence the drying time: at higher environmental humidity or lower temperatures, the drying time increases.

The amount of product applied is not proportional to the speed of gluing, so an excess of product may be harmful, not only economically, but also in terms of properties. An excess causes longer drying time, unnecessary waste of adhesive, excessive hardness in the joint …

The spray application technique is also a determining factor to optimize the properties. Thus, a good regulation of the flow of product, air pressure, distance and angle of application are fundamental to obtain satisfactory results.

In spite of the higher economic cost compared to solvent-based adhesives, the ecological and work environment advantages, plus a better performance in terms of applied quantities, comparatively, aqueous contact adhesives end up being of a greater benefit to companies.

When dealing with water-based products, we must take into account what materials are used in the application to avoid corrosion (stainless steel, plastic, Teflon…). Likewise, it is necessary to protect the adhesive from frost or high temperatures.

Our product range

Our main adhesives product lines currently are:

  • TACKTROL CCA-514 D, single-component (colourless) for spray application, mainly for repairs on demolding lines. Adhesive of very high speed of bond, with application only on one side and it allows good gluing of foams to each other or to other supports usual in the sector (felts, carpets, EPDM, plastic grafts). Numerous groups in the automotive sector have it as a reference in their demolding lines.
  • TACKTROL CCA-48 C, single-component (colourless) for roller application in the manufacture of mattresses. It has very good mechanical stability and a rheology suitable for roller application, without any lumps or product spills on the roller that may stain the mattress. Good bond speed, which allows the immediate manipulation of large size mattresses, improving the effective work times on the line.
  • TACKTROL CCA-51 CR-2K, two-component (pink), for spray application, together with the activator TACKTROL CT-4. By varying the proportions of adhesive / activator, you can control parameters such as open time, speed…

At Concentrol we study each case to adapt our solutions according to the technical requirements of each client and ensure the best possible solution to their needs. Contact our experts.

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