Water based paints: Standardisation of bases in plant level

Excerpt: Standardisation is a process by which the bases are to be matched with any reference sample along with some specified tests which are usually followed in the industry.

HAVING manufactured the bases it is very important to standardise the bases. Standardisation is a process by which the bases are to be matched with any reference sample along with some specified tests which are usually followed in the industry. This is a very important step after the bases are made. Unless standardisation is done the bases cannot be tinted as one may get a lighter shade or darker shade or the shade after tinting is no way near to the colour card. It must be understood clearly that the colour and strength are controlled to the system standard and to which colorants are added to get desired colour. Tinting Bases are White, Clear and Coloured for the Water-based Decorative Paints. In other words Standardisation of Bases has to be done first in R&D & then in production. Standardisation means Properties such as Weight/Litre, Viscosity, Reducing Strength, Colour Difference (DE), Opacity, Gloss, Fill Volumes etc has to be defined with their Acceptance Range in the Specification of each Base and then approve each batch of base as per the Specifications.

For the benefit of the readers' continuity I reproduce the concept of Bases as follows:

White Bases can be three in number depending on the percentage of Titanium Dioxide in it. Mid Base will have some calculated percentage of Titanium Dioxide in it. However, it will have a standardised amount of Extenders (Clay, Talc, Calcite, Barytes etc) in it. Clear Base will have zero percentage of Titanium Dioxide in it. However, it will have a standardised amount of Extenders (Clay, Calcite, Talc, Barytes etc) in it. Coloured Bases are either Organic (has standardised amount Organic pigment or Inorganic Pigment (has standardised amount of Yellow Oxide or Red Oxide pigment etc)

Now let me take on the laboratory standardisation of bases. It is clear that unless the bases are standardised, when tinted, they will not yield the correct shade, hence it has to be matched with a base which already possesses all such properties. When a manufacturer starts to manufacture the bases for the first time he may not have the ready standard bases nor are such standardised bases available ready in the market to buy and compare by conducting various standardisation procedures. It therefore has become an accepted practice in the paint industry either to theoretically define such parameters governing the bases or take any other base that is already been marketed by any other manufacturer which are well accepted and that can be tinted in the factory end or at the point of sales. Now let us examine both the possibilities:

1) In the case of a already available bases which are freely marketed and can be tinted without any problem to get the desired shade, the manufacturer must have done enough home work in this regard. Which means in the R & D Laboratory, they have to prepare several samples of the bases containing varying percentage of Rutile, Emulsion and Extender pigments apart from the additives? These base samples will be subjected to tinting with one tinter or multiple tinters depending on the bases. Finally the base nearest to the shade should be arrived at. But this is very laborious process may take lots of time and also variations will be observed depending on the extender pigments.

2) The second and the fool proof and easy method is to start making the bases with the guideline formulations. Then they should be compared with any accepted market sample so that post tinting they may not pose a problem. The process of this standardisation is known as Green Reduction Technique. One may think or question what green reduction technique is and why GREEN Tinter is chosen for this purpose? The principle behind will be explained now. Green meant "caution" at first. Green's role in lights has actually changed dramatically over time. Its wavelength is next to (and shorter than) yellow's on the visible spectrum, meaning it's still easier to see than any colour other than red and yellow. This is an adaptation based on humans interacting in the natural world, where green are predominant. The reason our eyes see more shades of green than any other colour has to do with the sensitivity of the three different types of cones to different wavelengths (colours) of light. Our eyes have three types of photoreceptor cells called cones -- which contain photo-pigments -- that are designed to sense wavelengths. Together, the cones work to communicate to the brain the colours we see. During the day, our eyes are most easily able to pick up green light, followed by yellow and blue. This is one reason traffic lights are green. Red is also used in traffic lights because it stands out against all the green in nature -- even though red is actually the least visible colour at a distance. The following illustration can explain it more effectively.

From the above explanations and illustarions one can now understand why is GREEN prefered over other colours for the reduction test comparison of bases. I shall now proceed to expalain how the green reduction test is carried out and how the comparisons are made to arrive at the right standardisation of bases.

Green reduction standardisation of bases

Lets us take a classic case of a low end emulsion paint for which all the bases were made in the R & D Laboratory. First weigh out 50 gms of the market sample Base I in a wax coated paper cup and add 250 mgs of GREEN tinter accurately. It is highly advised that a very accurate electronic balance with four decimal accuracy is used, otherwise a very few milligram of tinter added can lead to wrong results and inaccurate interpretation of such results. Now the Base I made in the Lab shall also be subject to similar process. Both the samples are stirred well and thoroughly so that no green tinter is left over in the bottom or the sides of the paper cup. Now both the paint mix shall be placed in a draw down paper side by side (Left side always the standard sample) and draw down is made. The card is completely dried for comparison. Sun drying can be done or in a hot air over set at 60 Deg.C. From the above illustration one can see clearly how a green reduction comparison is done. It can be observed that the standard is slightly darker than the trial; hence the trial batch needs correction to have an accurate matching. Usually the formulation is looked into and minor variations are carried out in the extender pigments without disturbing the Rutile content since the deviation is very much on the lower side. With few trials the base will match, if so, it can be construed to be matched and that the base is capable of producing all pastel shades.

Once this standardisation by green reduction is carried out it is essential to check the bases with Red and Blue tinters to see how it is matched. In a similar way the bases are subjected to Red and Blue reduction, quantity of base and tinters remain same ie: 50 gms base and 250 mgs of Tinter. The drawdown is made with the standard and compared to ensure the level of matching. Invariably the matching will take place, however if any deviations are observed the same may be corrected by minor modifications in the trial batch pertaining to that bases. Likewise all the white bases are matched with the standard.

In case of D Base the standardisation process is slightly different. In addition to green reduction the Base is subjected to Black reduction also. In this reduction process both the standard and the trials are subjected to black reduction. The procedure is simple, in 45mgm of the base and add 5 gms of Black tinter and mixed well. Draw downs are made side by side and after complete drying they are compared. One should observe that there are no deviations in the black colour and the jet blackness is seen on both the cards. Moreover there shall not be any light whitish transparent coating observed on the trial. If observed it means there is a scope of reducing some of the extender pigments and replacing the same preferably with Talc or Barytes to eliminate this phenomenon and at the same time the Wt/ltr is well maintained compared to the standard. It must be borne in mind that invariably D-Bases are filled at the rate of 900 ml in each can of one litre and the balance 100 ml of tinters are added to get dark shades. Few trials in this regard will standardise the D-Bases. The process of standardisation described above is known as manual method and if done carefully one can match near to the standard with very little deviations.

References

https://www.google.com/search?ei=y46sXMbbHIyymAXN5T4BQ&q=why+green+is+visible+better+than+other+colours%3F&oq=why+green+is+visible+better+than+other+colours%3F&gsl=psy-ab.12...0.0..5508...0.0..0.0.0.......0......gws-wiz.Bpip7zCxBtQ

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https://www.google.com/search?ei=3SsXPfVC4XZhwOckYPQBA&q=paint+drawdown&oq=paint+drawdon&gsl=psyab.1.2.0i13l5j0i13i30l5.9540.16144..24312...6.0..0.270.2126.18j2j1......0....1..gws-wiz.....0..0i71j33i21j0i67j0j0i131j

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0i10j0i22i30.0V1Za2bMZIA - To be continued

Author Details

Veeramani