Plastic and nonmetallic article shaping or treating: processes – With step of making mold or mold shaping – per se
Reexamination Certificate
1997-09-12
2003-11-25
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of making mold or mold shaping, per se
C264S313000, C264S320000, C425S102000, C425S385000, C425SDIG004, C427S133000, C427S135000
Reexamination Certificate
active
06652792
ABSTRACT:
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 20 wt % based on the bar.
In the manufacture of detergent bars, a 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”. The “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 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 halves 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 the like 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 this system is that a 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.
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 having a modulus of elasticity within a specified range.
International patent application WO96/00278 describes a method and apparatus of stamping a detergent bar in which die members comprising a non-elastomeric part and an elastomeric part of thickness less than 200 microns are used. This is found to be particularly easy to maintain, as the thin elastomeric layer is readily applied and replaced.
Problems have been experienced with elastomeric coatings applied to non-elastomeric dies over long periods of use. It has been found that some elastomeric layers tend to separate from the non-elastomeric die. It has been found difficult to provide an elastomeric layer which has good adhesion to the non-elastomeric die but which has good release characteristics as well.
It is an object of this invention to overcome at least some of the above problems.
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.
The present inventors have discovered that the use of a plurality of separately formulated and polymerized elastomeric layers can be used to optimise adhesion to the non-elastomeric die or similar structure and release properties of the layer contacting the detergent.
Accordingly, the present invention provides a process for forming an elastomeric coating on a device for stamping or handling a plastic material comprising the steps of:
treating the device by chemical and/or mechanical means to form a bonding surface for said elastomeric coating;
forming on said bonding surface a first solidified elastomeric coating of selected composition under selected conditions; and
forming on said first solidified elastomeric coating at least one second solidified elastomeric coating of separately selected composition under separately selected conditions. With the invention, the properties and composition of each elastomeric coating can be tailored to give the desired properties. For example, the first solidified elastomeric coating can be made to have good adhesion to the bonding surface and resistance to forces involved in stamping and release. This would tend to give it poor release properties. However, the solidified elastomeric coating for contacting the plastic material can be tailored to have good adhesion to the underlying elastomeric coating (which is an easier bond to form than the bond to the bonding surface) and good release properties.
If necessary, a plurality of solidified elastomeric coatings of graded composition and/or properties (such as hardness, or adhesiveness) can be provided, each having the desired good adhesion to the underlying elastomeric coating and the final elastomeric coating having good release properties with the plastic material.
The present invention further provides a device for stamping or handling a plastic material, which device includes at least one contact surface which will contact the plastic mass, wherein at least one contact surface is provided with an elastomeric layer comprising at least two elastomeric coatings, the elastomeric coatings being of different composition and/or properties.
Each elastomeric coating must be able to withstand the conditions under which subsequent coatings are solidified.
By “elastomeric” according to the invention is meant a material as defined in ISO (International Standard Organisation) 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 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 through 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 whils
Klein Oliver
Neuhof Mario Peter
Solert Hans-Juergen
Lever & Brothers Company, division of Conopco, Inc.
McGowan, Jr. Gerard J.
Poe Michael I.
Silbaugh Jan H.
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