Apparatus for Stamping a Detergent Bar

Embodiments of the present invention will now be described by way of example only with reference to the accompanying figures; wherein:

FIGS. 1 to 5 are plots of adhesive force (F.sub.a) against a composite elastic modulus (E.sub.c) for Examples 1 to 5 respectively.

To illustrate the present process experiments were performed using a modified Instron Tensiometer. The modification comprised attaching a cylindrical punch having a flat end surface to the Instron Tensiometer. The arrangement was such that the punch moved downwardly so that its flat end surface contacted an area of a piece of firmly fixed detergent bar. In each experiment the temperature of the punch was maintained at 20.degree. C., the displacement velocity of punch was set at a constant 20 mm/min and the indentation depth into the detergent bar was selected as 3 mm. The type of detergent bar was varied and for each detergent bar tested at least two different types of punch having different moduli of elasticity were employed. The modulus of elasticity of each type of detergent bar and of each punch were measured. For each experiment the adhesive force between the punch and the detergent bar indentation was measured and a visual assessment was made of the surface of the punched indentation in the detergent bar.

The visual assessment of the bar surface was performed with respect to the following scale:

1 very smooth

2 smooth

3 relatively smooth

4 relatively rough

5 rough

6 very rough.

In Examples 1 to 5 below the results are presented in terms of plots of adhesive force (F.sub.a) against a composite elastic modulus (E.sub.c), wherein: ##EQU1## in which E.sub.s is the elastic modulus of the detergent bar being stamped and E.sub.d is the total elastic modulus of the punch. This presentation highlights the effect of the different types of punch employed.

Table I below lists the different punches employed and for each punch giveds it measured modulus of elasticity (E.sub.d) in Nm.sup.-2. For the punches coated with a layer of polyurethane, the thickness of the coated layer is given in mm and an identifying code number is given for each punch.

A commercially available personal washing soap bar was employed comprising a mixture of tallow and coconut soap in a proportion of tallow to coconut of 60:40, 7.5 wt % free fatty acid and 9.5 wt % water. Samples of the soap bar were equilibrated at 40.degree. C. Samples were tested by the Instron Tensiometer fitted with the stainless steel punch and a number of polyurethane coated punches. The modulus of elasticity of each sample of soap bar employed was measured and for each experiment a value for E.sub.c was calculated. The mean value for the modulus of elasticity of the soap bar samples was 2.times.10.sup.7 Nm.sup.2.

The results are illustrated graphically in FIG. 1 which is a plot of the adhesive force (F.sub.a) in N against the value of E.sub.c in Nm.sup.-2 calculated for each experiment. The open circles are the results using the polyurethane coated punches and the full circles are the results using the polished stainless steel punch. The numbers adjacent the open circles are the code numbers of the polyurethane punches employed. As can be seen from FIG. 1, use of the present elastomer coated punches not only produced reduced adhesive forces compared to the use of the stainless steel punch but the plotted points associated with use of the present elastomer coated punches tend to decreasing F.sub.a with decreasing E.sub.c, the spread in the points being due to the variation in E.sub.s among the different soap bar samples employed as well as the variation in E.sub.d between the punches.

Table II below includes for a representative number of experiments the values of the parameter E.sub.c and the score rating on the above scale with regard to the visual appearance of each soap sample. As can be seen, samples having acceptable scores were only achieved with the use of the present elastomer coated punch.

Experiments were performed on commercially available samples of household soap bar comprising by weight 86 parts tallow soap and 14 parts coconut soap, with a total fatty matter content of 63 wt %. The samples were maintained at 40.degree. C. and the Instron Tensiometer was operated under the conditions given above. Five different punch types were employed having a range of E.sub.d values. The punch types employed were polyurethane coated punches, the stainless steel punch, the perspex punch, the polyurethane punch and the polytetrafluoroethylene punch. The mean value of the modulus of elasticity of the soap bar samples employed was 1.times.10.sup.7 Nm.sup.-2.

FIG. 2 illustrates the results graphically and is a plot of adhesive force (F.sub.a) in N against E.sub.c in Nm.sup.-2 for each sample. The identification of the symbols indicating which punch was employed is given in Table III below. The numbers adjacent the open circles are the code numbers given in Table I. As can be seen from FIG. 5, substantially reduced adhesive force is associated only with the present elastomer coated punch.

A representative range of samples was assessed visually and given a score according to the above scale. The results are given in Table III below. Also included in Table III is the E.sub.c value for each sample assessed and the E.sub.d value for the punch used.

Commercially available samples of a laundry soap bar were employed. The samples were each maintained at 40.degree. C. and a number of experiments with some of the present elastomer coated punches and the stainless steel punch were performed. The soap bar samples had a mean modulus of elasticity of 7.times.10.sup.6 Nm.sup.-2.

The results in terms of a plot of adhesive force (F.sub.a) against E.sub.c are given in FIG. 3. The open circles in the figure relate to the elastomer coated punches and the filled circles to the stainless steel punch. The numbers adjacent the open circles are the code numbers given in Table I identifying which elastomer coated punch was employed. As can be seen from the figure, reduced adhesive force is associated with the use of the present elastomer coated punches. Two representative samples were assessed for their visual appearance according to the above score. The results are given in Table IV below. Also given in Table IV are the E.sub.c values for each sample.

Experiments were performed on samples of detergent bar comprising an admixture of soap and sodium fatty acyl isethionate. The samples were each maintained at 40.degree. C. and a number of experiments were performed using some of the present elastomer coated punches and the stainless steel punch. The results are shown as a plot of F.sub.a against E.sub.c in FIG. 4 and show that reduced adhesive forces are achieved with the elastomer coated punch. In the Figure the filled circles relate to the stainless steel punch and the open circles to the polyurethane coated punches with the appropriate identifying code number adjacent each circle. The mean modulus of elasticity of the present detergent bar samples was 2.times.10.sup.7 Nm.sup.-2. Two representative samples were assessed visually and the scores are given in Table V below. The E.sub.c for each sample is also given in Table V, together with the E.sub.d value for the punch employed.

Experiments were performed on samples of detergent bars comprising 50 wt % sodium fatty acyl isethionate, 8 wt % soap 5 wt % sodium isethionate, 20 wt % stearic acid, 3 wt % coconut fatty acid, 5 wt % moisture and 7 wt % remainder. The samples were maintained at 40.degree. C. and a number of experiments were performed with some of the present elastomer coated punches and the stainless steel punch. The results are shown graphically in FIG. 5 which is a plot of F.sub.a against E.sub.c and shows that reduced adhesive forces were achieved with the elastomer coated punches. In the figure the filled circles relate to the use of the stainless steel punch and the open circles, with identifying code numbers adjacent, to the use of the polyurethane coated punches. The mean modulus of elasticity of the present detergent bars was 3.times.10.sup.-7 Nm.sup.-2.

Two representative samples were assessed visually according to the above score. The results are given in Table VI below. Also included in Table VI are the E.sub.c values.

A number of experiments were performed using samples of a personal washing soap bar which has the same as that for Example 1. The samples were each maintained at 40.degree. C. and a number of experiments were performed using the present elastomer coated punches nos. 1, 14, 16 and 2 having respectively different thicknesses of polyurethane coating. The results are given in Table VII which lists F.sub.a in N and the thickness of the polyurethane layer in mm. As can be seen the value of F.sub.a decreases with increasing elastomer layer thickness. The decrease in F.sub.a thus can be correlated with decreasing modulus of elasticity of the punch.

Each of the samples was assessed for its visual appearance according to the above score. The results are also given in Table VII below, together with the E.sub.c value for each sample and the E.sub.d value for each punch employed.

Elastomer coated pin dies were used to stamp bars of a soft sticky soap, which would tend to adhere strongly to metal dies, necessitating surface chilling to prevent die-blocking problems from becoming unmanagable.

Using the elastomer coated dies, satisfactory bars were produced without surface chilling and without serious die-blocking.