Patent Publication Number: US-2002003319-A1

Title: Die and process especially for stamping detergent bars

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a device and process for stamping a plastic material using a die to form a shaped article. In particular, it relates to process for stamping detergent bars and foods such as frozen dessert bars.  
       [0002] 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.  
       BACKGROUND OF THE INVENTION  
       [0003] 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.” 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. The bar surface is hit with force by, eg., a mallet or a die in the shape of a roller.  
       [0004] 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.” 
       [0005] Conventional die stamping machines include “pin die” shaped 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.  
       [0006] 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 a 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.  
       [0007] 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, a problem with the ejectors is that they tend to apply higher pressure to a small area of the bar, which can cause problems for soft soap formulations.  
       [0008] Moreover, 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. Chilling uses valuable resources, particularly energy sources.  
       [0009] 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 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.  
       [0010] 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 microns and having a modulus of elasticity within a specified range.  
       [0011] A disadvantage of thick coatings, such as those above 200 microns, is that typically they need to be applied via a casting or molding process performed on the die. As an alternative, separate parts are molded which are then attached to the die. The molding 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.  
       [0012] 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. Another difficulty which has been encountered with elastomeric coatings is that they tend to have short useful lives, on the order of a few days or more.  
       [0013] Roussel, U.S. Pat. No. 4,809,945 discloses a mold cavity for use in molding articles such as soap bars.  
       [0014] A porous die called Metapor has been used for vacuum molding applications in which a vacuum is pulled through the pores to form a shape over the die.  
       [0015] Fluid release agents are commonly applied in soap stamping to aid bar release. These fluids are sprayed or applied to the dies or billets prior to stamping. Unfortunately, this often results in excess release agent transferring to the stamping apparatus, to the transfer belts or to other machinery. Such transfer can cause operational difficulties such as coveyor belt slippage and the release fluid can be corrosive to the stamping machine metallic part (eg. brine). Undesirable products of corrosion can also be transferred to the product. Moreover, release agent can be wasted.  
       SUMMARY OF THE INVENTION  
       [0016] The invention is directed to the discovery that of a new way to provide release agents to dies. In accordance with the invention, porous or otherwise permeable dies are utilized and the release agents are bled through the pores in the die so that they can be accurately applied to the die/product interface only.  
       [0017] In the case of stamping of soap bars, the invention permits application of the release agent to the bar rather than to the billet, with attendant accuracy in application. Excess fluid is eliminated and the die is repleneshed, eg by capillary action or from a fluid reservoir head.  
       [0018] In accordance with the present invention, release agent is applied evenly across the bar or other product being stamped due to the fact that it is distributed through the micropores of the die.  
       [0019] The invention encompasses the die/fluid feeding apparatus, as well as the process for stamping articles.  
       [0020] For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments and the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0021]FIG. 1 is a cross section of a of one half of a soap stamping die taken along its transverse axis, in accordance with the invention . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0022] Hereinafter by “surface decoration” is meant a uniform shape, smooth surface, a design such as a logo, trademark or the like.  
     [0023] The die of the invention is a porous die. The pores are within the range of from 2 to 500 microns in diameter, preferably from 5 to 50 microns, especially from 10 to 20 microns. By porous material herein is meant a material having pores within the range of from 2 to 500 microns in diameter. Preferably, the pores extend throughout the total soap-die contact area. Preferably the pores will constitute at least 15% of the available surface area of the total soap die contact area.  
     [0024] A preferred porous material of which the die can be constructed is Metapor F100 AL, a microporous, air permeable, aluminum available from Portec, North America, a division of NEST Technologies or from Portec, Ltd. a Swiss company. Another porous die material may be Porcerax II, a porous steel available from Mold Steel, Inc., of Erlanger, Ky., USA.  
     [0025] Preferably the die comprises a material selected from metals and their alloys, for example aluminum, brass and other copper alloys, steels including carbon and stainless steel and sintered forms of metals or metal composites, non-metallic materials such as ceramics, composites, thermosetting and thermoplastics in porous or foamed form.  
     [0026] It is expected that release agents already known for soap bar stamping may be employed in the present invention, subject to the need to apply the agent through the die pores. Examples of agents expected to be useful include brine, sodium isethionate solution, propylene glycol solution, isopropyl alcohol, moisturizing silicone oils and water. If desired, a release agent could be employed which also provides useful product characteristics to the soap, eg. a moisturizing agent.  
     [0027] 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 and/or mild 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.  
     [0028] According to a further aspect of the invention there is provided a process for stamping a detergent bar or other product comprising  
     [0029] i) feeding a detergent bar (or other) composition to a porous die;  
     [0030] ii) stamping the composition in the die to form a stamped product; and  
     [0031] iii) releasing the product from the die by introducing release agent to the bar surface through the pores of the die.  
     [0032] The invention may be used with conventional stamping equipment, such as Binacchi USN 100.  
     [0033] Referring to FIG. 1, die half  10  comprises bar stamping surface  12  and side walls  16 . Die  10  is made of a porous material. Side walls  16  are sealed to prevent passage of release fluid therethrough, whereas bar stamping surface  12  and generally parallel inner die wall  13  are not sealed and permit release fluid to pass through. Optional ejector  14  may be provided centrally within the die. Ejectors are well known in the art. Side walls  16  rest on base  18 .  
     [0034] A release fluid supply mechanism supplies fluid to the die. This can be, eg, via low pressure fluid supply system or reservoir head. The required pressure can be selected by one of ordinary skill depending on factors such as fluid viscosity, pore size, stamping rate, and the volume of fluid required for release of each bar. Since walls  16  are sealed and walls  12  and  13  are not, any fluid supplied passes through walls  12  and  13  and will contact any soap or other product resting on or in close proximity to die wall  12 .  
     [0035] The operation will be described particularly with respect to soap bars. In operation, a soap billet is conveyed to a position intermediate two halves  10  of the die. The halves are conveyed to points proximate, or even in contact with, each other whereby surfaces  12  each contact the soap so that it assumes the desired shape and surface indicia. Release fluid  23  is present on the stamping surface  12  which it enters through the pores in the die. When it is desired to remove the soap from the die, due to the presence of the release fluid, the soap is cleanly removed from the die halves. The ejector, if used, assists in removing the soap from the die.  
     [0036] The release fluid may be fed through existing cooling channel systems in the case of rotating dies. For reciprocating dies, existing systems of external reservoir may be used.  
     [0037] It can be expected that use of the porous die will result in distribution of the soap bar release fluid across the whole surface of the bar. This may eliminate the need for the ejector mechanism and the force concentration which usually attends its use. Thus, a very soft soap and high liquid fraction formulations can be released without deformation. It is preferred that the micropores are distributed evenly through a large percentage of the bar contacting surfaces of the die. Preferably the pores constitute at least 15% of the surface area of the bar contacting surface of the die half.  
     [0038] Good release of the detergent bars from the die is expected without the expensive chilling of dies, which may otherwise need to be employed. Alternatively, reduced chilling of dies may be used.  
     [0039] “Die half” is understood to comprise one stamping surface of a die, even if a second, similar surface is not utilized.  
     [0040] The sealant used may be an adhesive resin or sealant such as an epoxy or acrylic resin. For example Loctite ShadowCurve® type AR—an aerosol applied clear acrylic. The coating is spray applied and dries in air. The resin could be liquid applied via brush or even dipped.  
     EXAMPLE (PROPHETIC)  
     [0041] A range of die halves are manufactured from Metapor F100 AL, a microporous, air permeable, aluminum. The die halves are supplied with release fluid comprising brine.  
     [0042] The die halves are used to stamp the following soap formulations.  
     [0043] The bar compositions used in the examples are as follows:  
                                               % wt.                                                    Formulation A               Anhydrous tallow soap   52.3           Anhydrous coconut soap   29.9           Coconut fatty acid   5.2           Water and minors   to 100           Formulation B           Sodium cocyl isethionate   27.00           Cocoamidopropyl betaine   5.00           Polyethylene glycol, M.Wt.   33.12           Fatty acid   11.00           Sodium stearate   5.00           Water + minors   to 100           Formulation C           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                      
 
     [0044] After stamping, the soap releases cleanly from the die halves without the use of an ejector.  
     [0045] It should be understood, of course, that the specific forms of the invention herein illustrated and described are intended to be representative only as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.