Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 96/00278 PCT/EP95/02293
w~~ 2189649
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PROCESS FOR STAMPING DETERGENT BARS
The present invention relates to a device, process and
apparatus for stamping a plastic material using a die to form
a shaped article. In particular, it relates to process for
stamping a detergent bar.
By "detergent bar" is meant a tablet, cake or bar in which
the level of surface active agent, which comprises soap,
synthetic detergent active or a mixture thereof, is at least
20wt~ based on the bar.
In the manufacture of detergent bars, preformed composition
comprising all components of the bar is typically extruded
from a nozzle to form a continuous "rod" which is cut into
smaller pieces of predetermined length, commonly referred to
as "billets". These "billets" are then fed to a stamper or,
alternatively, are given an imprint on one or more surfaces
using, for example, a die of the same dimensions as the bar
surface which is hit with force such as with a mallet or a
die in the shape of a roller.
Stampers typically have a die formed in two halves each with
a surface which contacts the billet during the stamping
operation. These surfaces are adapted to close to a preset
separation distance, thereby compressing the billet between
the die halves to give the bar its final shape and
appearance, and then separate. Excess composition is
squeezed out from the die halves as they close. This is
commonly referred to as "flash". The flash is then separated
from the soap bar by transferring the bar through holes in a
"deflashing plate".
Conventional die stamping machines include "pin die" shape
machines in which a pair of opposing die members or die
WO 96/00278 PCT/EP95/02293
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halves meet during a compaction step and a "box die" machine
in which a pair of opposing die members stamp a bar held
within a through-opening in a box frame but do not meet
during compaction, the peripheral face of the bar being
restrained by the box frame.
The die halves are often each provided with a die or ejector
insert. These are normally held closed within the die halve
by springs but can be pushed open by compressed air or
mechanical means to assist in the release of the bar from the
die. During closing of the die halves vacuum can be applied
to remove air trapped in the die cavity between the detergent
bar and die surface and, in the case of rotary dies, this
vacuum assists in retaining the bars in place during
rotation.
Stamping of detergent bars using a die is carried out to give
the bars a reproducible shape, smooth surface and/or to
imprint a design such as a logo, trade mark or similar onto
at least part of a surface of the bar.
However, as a result of die-blocking, i.e. amounts of
residual detergent left on die halves which builds up during
continued use of the dies, bars are often formed with visible
imperfections on their surfaces or they may not release from
the die surface.
Numerous solutions to these problems have been proposed. One
solution involves chilling the die halves during the stamping
operation.
Another solution is described in GB-A-746 769 which discloses
a die set which includes a die box and a pair of companion
die members made of plastic materials comprising polymers
with a specified modulus of elasticity. A disadvantage with
C3645
_ 3 _ 2 i X9649
this system is that die release agent is necessary to prevent
detergent from adhering to and building up on the dies and
marring the surfaces of subsequently pressed bars.
JP-A-56124237 and JP-A-06064054 disclose a use of an
elastomeric film on mating mould surfaces to absorb
irregularities in contact or in finish of the mould surfaces
to give a clean finish to the moulded product. It is not,
however, suggested that such elastomeric surfaces will assist
in de-moulding in the production of detergent bars. The film
may be very thin lJP-A-56124237 discloses a film thickness of
5-10 ~.un) .
Another solution is proposed in EP 276 971 which involves the
use of two die members, each comprising a non-elastomeric and
an elastomeric part. The elastomeric part, which contacts
the soap bar during the stamping process, comprises an
elastomer coating of at least 200 um and having a modulus of
elasticity within a specified range.
A disadvantage of thick coatings, such as those above 200 ~.un,
is that typically they need to be applied via a casting or
moulding process performed on the die. As an alternative,
separate parts are moulded which are then attached to the
die. The moulding process involves manufacturing dies in
which the cavities cut into the die are deeper than the final
intended depth of the bar. Furthermore, a separate coating
jig often needs to be employed to coat the ejectors.
During curing of the coating shrinkage often occurs and,
although the volume may be insignificant, the shape change
may result in gaps between the die and the ejector insert.
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218964,
Thus, the manufacture of thick coated dies is a complex and
expensive process. Furthermore, although it is possible to
recoat the dies, there are many difficulties~associated with
the process, namely specialist equipment is required for
compounding and mixing the coating, air can become entrapped
within the elastomer during the recoating process and it is
necessary to bleed out excess elastomer. In view of these
difficulties, in many cases it is necessary to use expensive
specialist equipment generally only available at a location
remote from the detergent bar manufacturing facility.
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~ 18964-9
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In US Patent 5 269 997 it is proposed to provide each of two
dies of a soap mould with elastomeric septum stretched across
their surface. Such a system would be complex to use at the
speed required for commercial manufacture and a thin covering
S would be prone to tearing and logo reproduction would be
expected to be poor.
we have now found an alternative device that can be used to
produce bars such that surface decoration can be achieved in
an easy reproducible manner.
Hereinafter "surface decoration" is meant a uniform shape,
smooth surface, a design such as a logo, trade mark or
similar.
Thus, according to the invention there is provided a device
for stamping a detergent bar comprising a die, the die having
at least one bar stamping~surface wherein the bar stamping
surface is provided with an elastomeric coating, the total
thickness of the elastomeric coating being less than 200 um.
In a preferred embodiment, the elastomeric coating is the
sole elastomeric material of the bar stamping surface.
By "elastomeric" according to the invention is meant a
material as defined in ISO (International Standard Organis-
ation) 1382 as an °elastomer", or a "rubber". Also included
in the definition of "elastomeric" materials according to the
invention are thermoplastic elastomers and copolymers and
blends of elastomers, thermoplastic elastomers and rubbers.
Elastomers are defined as polymers with long flexible chains,
independent in the raw material and transformed via
vulcanising or crosslinking agents which introduce crosslinks
and form a crosslinked network structure. The network
CA 02189649 1999-09-21
WO 96/00278 PCT/EP95/02293
- S -
and form a crosslinked network structure. The network
structure retains the movement of the macro-molecular chain
molecules and as a result returns rapidly to approximately
its initial dimension and shape after deformation by a force
and release of the force.
With increasing temperature an elastomer goes thro~igh a
rubbery phase after softening and retains its elasticity and
elastic modulus until its decomposition temperature is
reached.
Thermoplastic elastomers consist of amorphous and crystalline
phases. The amorphous phase has a softening range below
ambient temperature and thus acts as an elastic spring whilst
~ the crystalline segments whose softening range is above
ambient temperature, act as crosslinking sites
Preferably the elastomeric material according to the
invention is selected from those classes described in
American Society for Testing and Materials D1418 which
include .
1. Unsaturated carbon chain elastomers (R Class) including
natural rubbers e.g. Standard Malaysian Rubber;
2 S butadi ene a . g . "BLJNATM" type ex Bunawerke Huls; and
butadiene acrylonitrile copolymer e.g. "PerbunanTM" ex
Bayer.
2. Saturated carbon chain elastomers (M Class) including
ethylene-propylene types a . g . "NordelTM" ex DuPont and
fluorine containing types a . g . "VitonTM" ex DuPont.
3. Substituted silicone elastomers (Q Class) including
liquid silicone rubbers e.g. SilasticTM 9050/50 P (A + B)
ex Dow Corning. -
CA 02189649 1999-09-21
WO 96/00278 PCT/EP95/02293
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4. Elastomers containing carbon, nitrogen and oxygen in the
polymer chain (U Class) including polyurethanes e.g.
polyurethanes ex BelzOnarM.
Suitable elastomeric coatings can be obtained from materials
such as liquid silicone rubbers such as Silastic 9050/50 P
A+B (ex Dow Corning) which after curing has a modulus of
elasticity about 2-3 MPa; and polyurethanes, for example
Belzona PU2221, as hereinafter defined, which after curing
has a modulus of elasticity of about 9MPa, and Belzona 2131
(MP Fluid Elastomer), a 2 part product based on a
diphenylmethane 4,4'-diisocyanate (MDI) system with a
phenylmercuric neodecanoate catalyst.
The ~elastomeric' material, as hereinbefore defined, may be
pretreated, such as by forming a solution of a commercially
available elastomer, prior to it being applied as a coating
on the die surface. The elastomers, rubbers, and copolymers
and blends thereof are generally cured or crosslinked, in-
situ on the die surface. For example, the components
including the base elastomeric material, cross-linking agents
and other materials such as accelerators may be mixed prior
to application as a coating. Once applied to the die the
coatings are cured in-situ. This maybe aided by the
application of heat or other accelerating processes, for
example pressure; radiation or UV light.
In some cases, materials may be dissolved with an appropriate
solvent, applied to the die and the solvent subsequently
driven off.
In the case of themoplastic materials, they can be heated to
melt condition applied to the die, cooled and resolidified.
WO 96100278 218 9 6 4 9p~T~~5~02293
. . :,., _,.
Materials suitable as elastomeric coatings in the present
invention will preferably have a modulus of elasticity, in
the range 0.1 to 50 MPa, most preferably 1 to 35 MPa.
The modulus of elasticity of an elastomeric coating may be
measured by recording the force required to indent the
coating as a function of the indentation depth. Typically an
indentor with a spherical tip may be employed and the slope,
s, of the force as a function of the indentation depth to the
power 3/2 is determined. The indentation depth is the
movement of an indentor into the coating after it first
contacts the surface of the coating. In general, it is
necessary to correct the measured indentation depth for the
compliance of the measurement apparatus. That is, the actual
indentation depth, d, is related to the measured apparent
value d' by the following expression
d = d' -(F.G~
where F is the indentation force. The compliance C is
determined by compressing the indentor against a rigid
surface and recording the apparent displacement as a function
of the applied force which has a slope equal to C. The
modulus of elasticity E is calculated from the following
expression
E = 4.s. 1 . (1 - b2)
v~
where s = F / d3~2, R is the radius of the spherical tip of
the indenter and b is the Poisson's ratio of the coating
which is equal to about 0.5 for elastomers.
WO 96/00278 PCT/EP95/02293
.. ~~~.:~ t :v . ~ 189649
Under certain conditions to be described hereafter, the above
indentation method may give falsely large values of the
elastic modulus due to the influence of the rigid material
onto which the coating is applied. In order to safely avoid
this problem it is necessary to ensure that the contact
radius of the indentor with the coating does not exceed about
1/10 of the thickness of the coating. The contact radius, a,
is related to the indentation depth by the following
expression
For coatings less than 200 dun, it is recommended that a nano-
indenter is used which is capable of measuring indentation
forces at small indentation depths using indentors with tips
having a small radius. An example of such equipment is the
"NanoIndenter II" (Nano-instruments). The alternative is to
make thick (greater than 200 um) test coatings so that more
conventional measurement equipment such as an Instron tester,
(eg Model 5566) may be employed.
An advantage of the device according to the invention is that
the elastomeric coating being thin can easily be applied in a
factory to a conventional die with a built in logo. For
example it can be applied using a brush or spraying
techniques such as air assisted, airless or electrostatic
spraying. A combination of techniques may also be used, if
necessary. This may be so where it is necessary to apply
coatings of different thicknesses on different parts of the
die. For example, if a particular thickness is required in a
finely detailed region on the die, for example the logo, a
spray technique can be used with the logo ejector removed
from the main body of the die.
WO 96!00278 PCT/EP95/02293
y 21896
_9_ 9
The coating can be cured on the die at ambient temperature or
elevated temperatures depending on the type of elastomeric
material. Higher temperatures can be employed to drive off
solvent in solvent borne elastomers. Other methods such as
ultra violet light curing can be employed to hasten the
curing process.
A further advantage of the invention is that the elastomeric
coating can be applied to conventional dies. Consequently,
new dies need not be manufactured as is generally the case
when thick coatings are used. Typically with thick coatings
when the elastomeric part becomes worn or damaged through use
resulting in, for example, marking of the stamped detergent
bar the coating has to be removed; the die cleaned and the
new coating prepared and remoulded to the die surface using
specialist equipment. By contrast, the device of the present
invention can easily be recoated on site simply by removing,
for example, by mechanical means the old coating with the aid
of an appropriate chemical treatment (e. g. using a solution
of potassium hydroxide in a mixture of ethanol and toluene in
the case of silicone coatings and ethanol and/or methanol in
the case of polyurethane coatings), treating the die surface
and replacing the old coating with new material. This
results in considerable savings both in terms of the loss of
production time and the cost of recoating.
Preferably the die comprises a rigid material selected from
metals and their alloys, for example brass and other copper
alloys and steels including carbon and stainless steel; and
other non-elastomeric materials such as thermosetting and
thermoplastic resins, for example polyester, epoxy resins,
furan resins; hard cast polyurethanes; ceramics; composites
and laminates.
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Additional materials, for example fillers, can be added to
the elastomeric material to modify its mechanical and
processing properties. The effects of filler addition
depends on the mechanical and chemical interaction between
S the elastomeric material and the filler.
Fillers can be used to modify the elastomeric material such
that desirable properties, for example tear resistance, is
achieved. Suitable fillers include carbon blacks; silicas;
silicates; and organic fillers such as styrene or phenolic
resins
Other optional additives include friction modifiers and
antioxidants.
Preferably, the elastomeric coating has a thickness within
the range 1 to less than 200 ~zm, preferably at least 10 to
150 um, most preferably at 15 to 100 Vim. At thicknesses
below 1 um uniform coverage of the elastomeric coating on the
die surface may not be obtained. At thicknesses above 200 um
it may be difficult to apply the elastomeric coating by
simple application techniques such as application by a brush
and the resulting logo reproduction may be less distinct.
An advantage of the present invention is that the thickness
and hardness of the elastomeric coating can be varied
according to the detergent bar composition, processing
temperature and/or process parameters such as the shape of
the cavity in the die halves, speed of the stamping equipment
and separation distance of the die halves, in order to
achieve the desired result, for example, good release of the
detergent bar from the die. It has been found that for a
particular bar composition in combination with a simple logo
free die, elastomeric coatings at the lower end of the
C3645
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thickness range as defined and the upper end of modulus range
can achieve acceptable die release. However, for the same
composition with a complex logo bearing die or a complex die
shape acceptable die release is achieved with a coating
closer to the upper end of the thickness range and with a
lower modulus. Similarily, for a bar composition which is
inherently more difficult to stamp acceptable die release may
be achieved with an elastomeric coating closer to the upper
end of the thickness range and a lower modulus of elasticity.
Therefore, the invention allows for coatings of varying
thicknesses and moduli within the defined range whilst
maintaining the advantages of using thin coatings in the
manufacture of detergent bars.
The device according to the invention can be used to stamp a
detergent bar comprising a surface active agent which
comprises substantially soap or a synthetic detergent or a
mixture of soap and synthetic detergent. It finds particular
application in the stamping of soft and/or tacky detergent
bars which contain synthetic surfactants, translucent and
transparent soap bars having a reduced fatty matter content,
for example, in the range 63-78~wt with respect to the total
bar weight and those bars containing skin beneficial agents
such as humectants, polyols, oils, fatty acids and fatty
alcohols.
According to a further aspect of the invention there is
provided a process for stamping a detergent bar comprising
i) forming an elastomeric coating of less than 200 ~,un on at
least one bar stamping surface of a die;
ii) feeding a detergent bar composition to the die of step
i;
C3645 - -
2189b49
- 12 -
iii) stamping the composition in the die to form a stamped
bar; and
iv) releasing the bar from the die such that a surface
decoration is applied to the bar in an easily
reproducible manner.
Preferably, the elastomeric coating is bonded to the die
stamping surface by mechanical and/or chemical means to
increase the adhesion between the die and the coating.
The die surface may be subjected to a number of pre-
treatments prior to coating with the elastomeric material, to
improve the bond strength between the die surface and the
coating. These pre-treatments aim to remove weak boundary
layers for example weak oxides on metals; optimise the degree
of contact between surface and coating and/or alter the
surface topography such that the bondable surface area is
increased, and to protect the die surface before bonding.
Suitable techniques can be divided into three main groups:-
1. Mechanical Abrasion - techniques'include wire brushing
abrasion paper, blasting techniques such as water, grit,
sand and glass bead blasting, polishing such as diamond
polishing and spark erosion.
2. Chemical Treatment - including solvent cleaning, acidic
treatment, surface etching for example using acid,
anodising, application of a primer or application of an
adhesive bonding chemical for example a silane or
silicone, or combinations thereof.
3. Energetic Surface Pretreatment: More widely used with
non-metallic systems, techniques include corona
discharge, plasma, and laser techniques.
WO 96/00278 218 9 ~ 4 9 PCT/EP95I02293
' _ 13 _
In addition to being applied to the bar stamping surface of
the die, the elastomeric coating may advantageously be
applied to other parts of the stamping device and other
machinery in the soap processing line. For example, it may
be applied to the "deflashing plate", which separates the
stamped bar from the excess extruded bar composition, the
backing plate on which the die is mounted as well the non-
stamping surfaces of the die.
The invention is further illustrated with reference to the
accompanying figures and the following non-limiting examples.
Figure 1 is a cross-sectional view of a die with a detergent
bar.
Figure 2 is a cross-sectional view of the die in closed
position with the detergent bar stamped between the die
halves.
Figure 3 is a cross-sectional view of the die in its open
position after the stamping operation.
Figure 4 is a top elevation of the carbon steel die half used
in the following examples.
Figure 5 shows the logo borne by the die halves used in the
following examples.
Figure 6 is a cross section through the centre of a detergent
bar stamped with the die of figure 4 bearing the logo shown
in figure 5.
Referring to the figures in detail. Figure 1 shows a die 1
comprising two die halves. Each die halve comprises a rigid
member 2, 3. Each die half is provided, on the bar stamping
WO 96/00278 PCT/EP95102293
r~ r. .a
:'~ s't . 9
_ 14 - 2189649
surface 9, 12, with an elastomeric coating 5,6 respectively.
Elastomeric coating is also provided on the surfaces 8, 10,
11 and 13 of the die halves. One die half is provided with a
logo 14 on the bar stamping surface of the rigid member 3.
(In some cases both die halves will incorporate a logo).
This is also coated with elastomeric coating 6.
Figure 2 shows the die in the closed position where the logo
has been stamped onto the detergent bar 4.
Figure 3 shows the die in the open position after the
stamping has been completed. The billet is easily released
from the die half 2 because of the elastomer coating 5.
Removal of the billet from the second die half 3 is also easy
because of the coating 6.
Figure 4 shows a die half 15 with a die cavity 16 and pin
holes 17, 18 for aligning and securing the die half onto a
stamper. The cavity is provided with an opening 19 in which
an ejector bearing a logo is placed. The hole 20 represents
the passage through which vacuum can be applied during use of
the die half in the stamping operation.
Figure 5 shows the die cavity 16 complete with an ejector
bearing a logo 21.
The stamper used in the trials was a Binacchi USN 100.
A range of die halves were manufactured in carbon steel and
were spark eroded to a range of surface roughness values (Ra)
shown in the table, degreased with acetone, treated with a
primer and then coated with a range of elastomeric materials.
WO 96/00278 PCT/EP95/02293
2189649
:~ . - 15 -
A series of brass die halves were also used in the examples.
Similarly, these were degreased with acetone, treated with a
primer and then coated.
In the examples, the elastomeric coatings were formed from
polyurethanes or silicone materials.
The polyurethanes used were:-
PU - Polyurethane - Belzona 2221 (MP Fluid Elastomer) a two
part product based on a toluene diisocyanate (TDI) and
polyol/Phenylmercuric neodecanoate catalyst. Xylene was
added to reduce the viscosity of the TDI component.
The resultant mixture was then mixed with the polyol and
catalyst and applied to the dies. The coatings were
allowed to cure on the dies at ambient temperature.
PUA- Belzona 2221 modified by xylene as above and by the
addition of polypropylene glycol to reduce the modulus
of elasticity of the coating. The three components,
i.e. the TDI/xylene, Polyol/catalyst and polypropylene
glycol were mixed and the resulting material was applied
to the die surface and allowed to cure.
KE - Kemira Durelast, a one part system composed of a
isocyanate tipped polyurethane prepolymer based on
diphenylmethane 4,4~diisocyanate (MDI). The coating was
applied to the die surface and allowed to cure,
following exposure to atmospheric moisture, at ambient
temperature.
The primer used for the polyurethanes was Belzona 2921
(Elastomer GP Conditioner) based on a MDI/dichloromethane
solution.
WO 96/00278 _ PCT/EP95/02293
Z~89649
- 16 -
The silicone based materials used as elastomeric coatings
were:-
Si - liquid silicone rubber Silastic 9050-50P Parts A and B,
ex Dow Corning. In order to prepare the coating the two
parts were mixed at room temperature. The resulting
mixture was then brushed onto the die surface and cured
at 200°C.
HS - Silastic HS 500 ex Dow Corning, a peroxide cured
silicone elastomer. The premixed silicone elastomer and
peroxide were dissolved in white spirit. This was then
brushed onto the die surface. Heat was then applied to
accelerate the curing system.
The primer used for the silicone elastomers (Dow Corning 3-
6060) comprised 95~ methyl isobutyl ketone, 2o ethyl
polysilicate, 1~ isopropoxybis(acetylacetonate) titanium and
2o dimethyl, methyvinyl siloxane, acetoxy-terminated) was
diluted with white spirit.
The bar compositions used in the examples were as follows:-
Formulation A cwt
Anhydrous tallow soap 52.3
Anhydrous coconut soap 29.9
Coconut fatty acid 5.2
Water and minors to 100
WO 96/00278 218 9 6 4 9 PCT/EP95/02293
,,
- 17 -
Formulation B cwt
Sodium cocyl isethionate 27.00
Cocoamidopropyl betaine 5.00
Polyethylene glycol, M.Wt 33.12
Fatty acid 11.00
Filler 10.00
Sodium stearate 5.00
Water + minors to 100
Formulation C %wt
Sodium cocyl isethionate 49.78
82/18 Soap 8.31
Sodium Stearate 2.98
Alkyl Benzene sulphonate 2.02
Stearic acid 20.15
Coco fatty acid 3.08
Sodium Isethionate 4.68
Water + minors to 100
C3645 218 964
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WO 96100278 . ~ ~ ~ ~ ,~ CT/EP95/02293
For examples 1 to 7 carbon steel die halves were used. In
example 8 and comparative examples 1* and 2* brass die halves
were used. In 1* and 2* no elastomeric coating was applied
to the surface of the die.
For all examples, die block/release and logo reproduction was
assessed.
Die Block/Release was assessed visually and scored according
to a scale on which 1 indicates the bar released freely from
the die and 5 where the bar sticks to the die.
Logo Reproduction was assessed visually on detergent bars
released from the die and scored according to a scale on
which 1 indicated reproduction of all the detail of the logo
and 5 indicates poorly defined logo where at least some of
the detail is missing.
The results demonstrate thin coatings can be used on dies to
stamp a variety of product formulations and obtain good die
block/release and logo reproduction. In the absence of an
elastomeric coating detergent bars did not release from the
die.
