Depilatory paint thickener comprising an anylopectin starch

Details Depilatory paint thickener comprising an anylopectin starch Depilatory paint thickener comprising an anylopectin starch

2001-03-12

2003-07-08

Boyer, Charles (Department: 1751)

Bleaching and dyeing; fluid treatment and chemical modification

Treatment of hides, skins, feathers and animal tissues

Depilating

C008S09410R, C008S160000, C008S161000, C008S094150, C008S094320, C510S275000

Reexamination Certificate

active

06589293

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to the dehairing or dewooling (depilating) of animal pelts, hides or skins, more specifically to depilatory paint and depilatory paint (depilation paint) thickener used in the depilation process in for example fellmongeries.
Depilation is a process whereby a depilatory paint is applied to a (sometimes pre-shorn) hide or skin and let to soak for several hours during which chemicals act to de-hair the skin. During that time, the paint should remain in place to provide for continuous chemical action, for which a certain thickness or viscosity is required. After depilation, the skins or hides (now often called slats) are washed and cleaned for further processing. Depilated hair is in general not further useful, depilated wool (now often called slipe wool) sometimes finds further use.
Traditionally (see depilatory thickeners, S. M. Cooper, New Zealand Leather and Shoe Research Institute) hydrated lime has been used for thickening depilatory paint. It has a number of advantages. It works well as a thickener because of its low solubility. It provides an alkali reserve for the depilation processes to keep the pH high enough for hair or wool loosening. It is readily available, and best of all it is cheap. Lime is still used for paint thickening in quite a high proportion of fellmongeries. However lime does have disadvantages when used as a thickener. In general, it does not stay in suspension. Furthermore, pelts painted with a low lime-paint tend to have a brighter grain, and they require less washing out of lime and are easier to delime. A number of alternative thickeners have been tried. Among the most successful are pregelatinised potato starch ethers. Pregelatinised potato starch ethers give good thickening at low concentrations of 1.5 to 3 percent. They are reasonably easy to mix into the paint, at least compared to some of the alternative non-lime thickeners, and they do not require any heating. However, in general they are not as easy to mix as lime. Unlike some of the non-lime thickeners, they are not so tacky that they cause sticking problems, with pelts sticking to each other or the boards of the pulling machines. They do not tend to have drip problems, and paint thickened with these thickeners is stable when sprayed under pressure. With some thickeners thinning under pressure leads drip problems. By using some lime in the system to act as an alkali reserve, sodium hydroxide is not needed to increase the pH. However there have been some problems in production. Paints thickened with these thickeners not always have behaved completely consistently when sprayed onto pelts, and this has caused problems of too much or too little paint on the pelts, or uneven coverage. This can lead to difficult pulling or residual wool problems or in some cases pelt damage.
It is thought that these inconsistencies are due to small changes in the viscosity of the paint from day to day, due to slight changes in the proportion of ingredients or the method of mixing, or even the temperature during mixing or application of the paint. Small differences in viscosity could lead to differences in application rate because a spray system is very sensitive to viscosity changes.
The operation of the depilation process can be looked at in two ways;
a) The Processes Taking Place in the Fellmongery
These are the observable processes that are carried out in the fellmongery on the skin and are controlled by the fellmongery manager. The process-steps involved may consist of; Wash; pre-flesh; squeeze or spin dry; apply depilatory paint; hold skins; remove wool.
Each of these processes are controlled to give good clean hair or wool removal with minimal damage to the skin.
b) The Underlying Processes
This requires an understanding of what is occurring as the depilatory paint is penetrating the skin, i.e.
how do sulphide and hydroxide penetrate the skin;
how much hydroxide and sulphide bind to the collagen in the corium layer;
how the sulphide and hydroxide react with the wool roots; the equilibrium between sulphide and hydrosulphide.
To date, depilation research has looked at the processes carried out on the skin and their improvement without looking at the underlying processes that are occuring in the skin. Approaching depilation from the view of the underlying processes will enable the critical processes to be determined. These processes can then be optimised to give better depilation performance.
The optimisation and control of these critical processes depend on the ability to observe what is occurring, both on the underlying processes and the processes carried out. Factors which are of importance during depilation are:
thickness of skin; paint performance; paint application rate; rate of penetration of chemicals.
Current techniques for application of depilatory paint involve applying a larger amount of depilatory paint to the centre of the skin. This is to compensate for the assumed 2:1 ratio between the thick and thin regions of the skin. However the actual ratio between the thick and thin regions of the skin may be much larger than assumed. This may mean that the differential spraying technique may not deliver enough paint to the thicker areas of the skin.
If the correct amount of paint at the correct concentration is applied to the skin, there may still be problems with depilation if the spray pattern does not hold. Common starch thickeners are currently used in the industry to hold the spray pattern. However, even with the addition of common starch thickeners it is often found that when the skins are stacked or pole hung that the spray pattern will shift. A correctly thickened paint should not produce such paint migration.
To ensure that paint migration does not occur, a depilatory paint must be thickened correctly with a suitable thickener. The means of determining the suitability of a thickener for depilatory paints has not always been well understood. Often the thickener used has relied on suggestions from chemical companies. The selection of a thickener by this means may not always meet-the requirements of depilation. To determine the suitability of a thickener for a depilatory paint, the requirements of depilatory thickeners must be understood. These requirements can be put into four categories:
1) Viscosity Requirements
For a thickener to be considered suitable, the thickener must provide the required level of viscosity consistently and simply. Special handling requirements limit the use of the thickener in the fellmongery situation. To satisfy this the thickener should;
Thicken at normal temperatures (20-25° C.) without requiring heating.
easily disperse without lumping into sulphide solutions without the need for high speed agitators.
not be sensitive to shear.
2) Stability Requirements
Not only should a depilatory thickener provide the required level of viscosity, but it should also be stable, ie the thickener should not be broken down or form solid gels by process or chemical conditions. This can be satisfied if the thickener;
is not thinned excessively by mixing too long.
is stable under high NaOH and sulphide concentrations, e.g. does not gel or thin over time.
provides paints of consistent viscosity, e.g. will make the same paint again and again.
3) Tack Requirements
When two skins are placed together flesh to flesh after depilatory has been applied, there maybe some adhesion of the skins making pulling apart difficult. To be acceptable as a depilatory paint thickener, the thickener should not adhere skins when skins are placed together flesh to flesh for 2-3 hours.
4) Downstream Processing Requirements
The use of the thickener should not have any adverse effects on any further processing that may be carried out. The thickener;
should not affect the quality of the slats produced.
should not affect the quality of the slipe wool produced.
should not increase the waste treatment loading.
should easily be washed out.
SUMMARY OF THE INVENTION
The invention provides a depilatory paint thickener comprising a starch containing essentially only amylopectin

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