A blooming problem

4 mins read

Blooming – that unwelcome haze that can occur after applying the wrong adhesive – can detract from the visual appearance of the bonded parts. Bob Orme, senior applications engineer at Loctite discusses why blooming occurs and how to avoid it.

We’ve likely all been there in our everyday lives, when making a simple repair on a picture frame or a table leg. We’ve applied the adhesive and bonded the parts together. But there’s that slight haze around the bondline. That doesn’t matter so much for small scale, one-off maintenance. But when professionals strive for the cleanest finish, blooming can go from a minuscule mishap to mass disappointment with product after product having an amateurish, home-repaired look.

The knock-on effects can be myriad and highly damaging for a customer; from increased time and financial expenditure to fix the problem, all the way to scrapping products that are unusable. However, the practical effects in comparison to the reputational harm caused by the effects of blooming can be just as damaging.

Blooming, in short, happens because of the chemistry within a cyanoacrylate adhesive (CA). When unreacted CA molecules become airborne, they can fall back to the substrate’s surface, react with surface moisture, and adhere to the substrate outside the bondline.

But fear not; the problem is manageable. There are several ways to mitigate the effect of blooming on bonded parts – and it can even be eliminated. Of course, there is no one-size-fits-all solution. The risk of blooming will depend on the root cause of the issue. But there are several steps everybody can take to minimise the chances of blooming.

Factors that can affect blooming

First and foremost, one of the vital steps to avoiding blooming is having a low bloom product which is in date. Older adhesives do not cure as quickly as fresh products, increasing the chances of blooming. Loctite specialises in low bloom bonds, with a range of products which consist of heavier cyanoacrylate particles with less tendency to become airborne, thus minimising the threat of blooming.

Time is very much of the essence when trying to curtail blooming. With the Loctite range of light curing CA products, which cure in seconds under UV light, customers can reduce bond times and, therefore, the chances of blooming. Customers can also shrink these times further by utilising post-assembly activators, accelerating any exposed adhesive to a complete cure.

 However, users can accelerate the curing process naturally by increasing the environment’s airflow. Cross ventilation is beneficial for carrying airborne CA particles away from the bond area – so avoid immediately placing the assembled parts in airtight conditions.

A suitable product that cures quickly in an appropriate setting is a great advantage. However, end users must be keenly aware of the environments they are applying the adhesives and the impact those environments can have on blooming. For example, extreme temperatures or vacuum environments will both cause a blooming effect: the former because it drives unreacted molecules from within the adhesive, the latter because it pulls unreacted molecules from the bond.

That also goes for relative humidity (RH). An ideal RH for bonding is between 40-80%. If the bonding environment has a low RH, the adhesive will remain uncured for longer – and that means increased time for CA molecules to become airborne and form blooming.

One must also know the surface the adhesive is being placed on. Acidic surfaces, for example, slow down the CA cure mechanism and keep the bond uncured for longer, increasing the time for CA molecules to become airborne and create the blooming effect. To avoid this issue, selecting a surface-insensitive product is vital. However, if one is unavailable, rinsing the surface to reduce its acidity is an alternative.

Issues of blooming are frustrating. A sloppy-looking product can do lasting harm to businesses over the long term, but many customers have turned to some of the solutions Loctite provides.

Case studies

One customer was packing premium devices into a plastic bag – a vacuum environment – to speed up logistics, but with the unfortunate side-effect that adhesives used to manufacture the products were not given the full recommended 24-hour curing time. That caused blooming to occur, and impacted upon time and cost, with extra cleaning, device scrap and warranty costing a triple-figure sum per device. More importantly, however, was the reputation the brand suffered due to end user complaints. Initially, the customer believed the product was causing the effect, but Loctite helped them to realise the assembly process was at fault. To better control the blooming effect, Loctite application engineers collaborated with the customer, adjusted the application method to needles, improved the application geometry, and improved the dosage amount.

Of course, the most appropriate solution to the problem may be using a different product which matches the specification of the environment and materials the customer uses. But this must also be carefully applied; otherwise the positive effect could be negligible.

A start-up company which manufactures high-end stands for tablets was experiencing unpredictable results due to bondline variation and cosmetic issues caused by blooming. Inconsistent product dosage veered from too little – which impacted assembly strength – to too much, which caused blooming.

These inconsistencies meant additional cleaning was required, resulting in the expenditure of extra time and costs. Furthermore, when the product failed the required drop test, reapplication of the adhesive was required – and in some cases part of production had to be scrapped.

With the help of Loctite experts, the application was reconsidered. A rubber-toughened adhesive (Loctite 410) was recommended to withstand the drop test requirements. Additionally, a digital syringe system was implemented to provide consistent application, and greater ventilation was recommended to eliminate the effects of blooming.

This was a perfect example of how a combination of small solutions created an overall resolution of the customer’s issue. With these changes implemented, the failure rate of drop tests was reduced to almost nil, thus providing a huge boon to the customer’s efficiency, costs and reputation.

For many end users, the first opinion they form of a product will be its appearance. A slick aesthetic is often the difference between a new sale and the customer moving on. Poor presentation can dent a customer’s confidence in the product and perhaps the company which provides the product. Blooming on a large scale can be more than a small annoyance, but with a combination of solutions companies can be confident they have the best advice possible to avoid it.