MXPA00011771A - Hybrid stamping die - Google Patents

Abstract

A stamping die includes a substrate stamping surface comprising a base matrix of open structure having a coating of elastomeric material applied thereon. The resulting surface is a composite comprising predominantly elastomer having matrix protruding through the elastomer in places.

Description

GIVEN OF HYBRID PRINTING The invention relates to stamping dies, and particularly soap stamping dies. In this context, with soap is meant a solid product containing soap, synthetic detergent, or a combination thereof, comprising at least 20 percent of the product. Soap stamping dies usually consist of of a pair of symmetrically opposed die halves, each • one having a cavity, which are put together towards the substrate, to form an embossed ingot of the substrate. A critical part of the stamping process involves the release of the stamped ingot from one half of the die, after the separation of the halves. Various methods have been proposed to facilitate the release of the die, including the use of die ejectors, the coating of the stamping surfaces of the substrate with talcum powder or a • release fluid, or coating the surfaces stamping with an elastomeric coating. For example, EP 285 722 discloses a composite coating for imparting an abrasion resistant release surface to a substrate, the coating comprising a thermal metal matrix having a silicone film impregnated therein.

The method of coating dies with elastomeric coatings has proven to be a particularly successful means of facilitating the release of the die; however, different problems have been found with this method. Firstly, elastomers, when used in printing machines, are continuously exposed to deformation by shear stress and deformation, due to the action of stamping the dice. This leads to elastomeric coatings being damaged over periods of time relatively short. When this happens, that in the case of • Stamping machines that operate continuously can be as frequently as every three weeks, the coatings on the dice have to be replaced, which involves stopping the machines for extended periods of time. 15 An additional problem with these coatings is that during application, some elastomers may hang and run down the non-horizontal faces of the die before healing, which results in a • uneven surface that is not uniform in thickness. Those faults in the stamping surface of the die generally result in faults in the stamped product. Another problem with some elastomers is that they require a binder to achieve adequate adhesion to the surface of the die, binding agents that generally comprise reactive chemicals, which are classified as high risk, and volatile organic compounds as carrier solvents. Modern legislation on health, safety and the environment imposes increasingly strict controls on the industrial use of these materials. It is a desirable object of the invention to provide a substrate embossing surface for embossing dies, which exceeds or improves upon at least some of the above problems. In a first aspect of the invention, there is provided a stamping die having a substrate stamping surface comprising a base matrix of open structure, having a coating of elastomeric material applied thereon. In this specification, the term "open structure" when applied to the matrix, is taken to mean that the surface of the matrix is non-uniform, and if viewed in cross section, it would include a multiplicity of depressions, peaks and plateaus. Typically the distance from peak to depression may be in the region of 50-200 micras, or 70-150 micras. When a matrix surface is applied to it, the elastomer fills the depressions and coats within the matrix such that it becomes strongly bound to the matrix, by virtue of the locked nature of the joint. In addition, the low viscosity elastomer compositions, when applied to those open matrix structures, are retained by the matrix until they are cured, and in this way the elastomers are less likely to drain or hang. • In a preferred embodiment of the invention, the stamping surface is a composite structure with the matrix protruding through the elastomeric coating in places. Ideally, the surface is predominantly an elastomer. Generally, the matrix comprises a material of ceramic or metal that, in one embodiment, is applied to the die by means of plasma or flame spray techniques. Alternatively, the matrix can be formed by laser or mechanical micromachining, chemical acid corrosion, anodization, spark erosion, plasma or ion beam treatment of the die material. However, the invention is not restricted to the above methods to form an open structure matrix. A full description of the term "elastomer" and specific examples of elastomers can be found suitable in the published European Patent Application Number 9592 4225 of the applicants, the content of which is incorporated herein by reference. In a preferred aspect of the invention, the elastomer comprises a silicone or fluorosilicon elastomer. The elastomers suitable for use in the dies according to the invention typically have a relatively low level of damping, and a low modulus. In accordance with a further preferred aspect the elastomers may typically contain carbon, and consequently may be of the "R", "M" or "U" classes, as classified by the American Society for Testing and Materials D1418. These classes are the unsaturated carbon chain elastomers, the saturated carbon chain elastomers, and the elastomers containing carbon, nitrogen and oxygen in the polymer chain. It has been found that • elastomers of this type are relatively easy to restore in the dies, for example, by completely burning the residue of the old elastomer coating. Suitable carbon-containing elastomers include polyurethane, acrylonitrile butadiene rubber, and hydrogenated acrylonitrile butadiene rubber, especially hydrogenated acrylonitrile butadiene rubber. The examples of • last include Therban (ex Bayer) and Zeptol (ex Zeon). The invention also relates to a process for making a stamping die, the process comprising the steps of: preparing a matrix surface of open structure on the surface of the die; and 25 - applying an elastomer coating on the matrix. Ideally, the process includes the subsequent step of curing the elastomer. • Typically, the array formation step includes the array formation methods referenced above. The invention also relates to the use of composite hybrid coatings of the type comprising a base matrix of open structure, which has a coating elastomeric applied on it, as surfaces of • Stamping of the substrate in the stamping dies. Ideally, the resulting hybrid coating includes matrix bags that protrude through the elastomeric coating. The invention also relates to a process for printing a product, such as for example a detergent bar, by employing a stamping die having a stamping surface comprising a matrix • open structure base, which has a coating of elastomeric material applied thereon, the process comprising the steps of: - - feeding a composition of the product to the stamping die; - stamping the composition on the die to form a stamped product; and - releasing the stamped product from the die. Ideally, the product being stamped will be a detergent composition, such as, for example, soap.

• However, the process and device of the invention are is intended to be used in the stamping of various different products such as, for example, tablets and food. The coatings and stamping surfaces of the substrate prepared in accordance with the invention give an excellent inter-layer bond strength of elastomeric metal. In many cases, the bonding strength makes • obviates the need for the use of separate bonding agents. Accordingly, in a further aspect of the invention there is provided an elastomer coated die that is absent from a binding agent or primer between the die metal and elastomer layer. In addition, the matrix of the invention provides a support surface with multiple contact points for the elastomer applicator, such that the elastomer can be pushed deep into the matrix, moistening the texture and giving as result an excellent mechanical locking and adhesion of elastomer base. The coating is of uniform and optimum thickness, controlled by the maximum peak height of the texture of the matrix. With the coatings of the invention, the coating of functional elastomer is protected from accidental damage by means of hard matrix bags, which protrude through the elastomer coating in modalities where this is the case. In this way, improved resistance to physical damage can be achieved even when relatively soft and brittle elastomers are used. The shear deformation occurring in the elastomer at key locations on the die surface is minimized, since the elastomer zones are restricted by means of matrix islands, and they are prevented from contributing to the shear stresses of the elastomer at gross, and wear processes. These factors contribute to providing more robust factory equipment, and a significant increase in the life time of the hybrid die. Careful control of the roughness of the matrix allows for a composite final surface topography to be imparted to the hybrid coated die. This can help reduce friction on the elastomer surface of the product, and reduce the incidence of showy surface marks on the soap bar. In addition, a preferred surface texture can be applied to the soap bar, by controlling the texture of the hybrid coated die. The invention will be understood more clearly by the following description of some embodiments thereof, given by way of example only. 1. MODALITY OF THE HYBRID DICE THAT INCLUDES A MANUFACTURING ELEMENT The hybrid die consists of the following components, • one die of metal soap; a hard open matrix, wear-resistant; and an upper elastomer coating. The hybrid die manufacturing examples are as follows. (a) A die of metal soap is machined from aluminum, then a hybrid coating is applied commercially available, for example, PlasmaCoat 1915/11, from Impreglon UK Ltd, comprising a base layer of tungsten carbide and a silicone elastomer. (b) A hard, wear resistant matrix of nickel / aluminum powder is applied to the surface formed of the die, by means of thermal spray techniques. An elastomer of choice is then coated on the die as follows. Then an elastomer [eg, Silastic 9050/50 silicone from Dow Corning] is coated on the die formed surface, prepared as recommended by the manufacturer. manufacturer, with a clean, soft brush, at a coating thickness where the nickel / aluminum texture is completely covered over. The die coated with the elastomer is placed in an oven at 160 ° C for 2 hours, to cure the elastomer. 25 2. DESCRIPTION OF THE USE OF HYBRID DICES WITH SOAP This section demonstrates that the convenient reduction in adhesion between printed products and surfaces • embossing, which is achieved using elastomeric coatings (as demonstrated in European Patent Application Number 95924225), is inherent in using the hybrid coatings of the present invention. Laboratory measurements were made, using aluminum punches in which the extreme face had been coated by means of flame spraying Ni / Al powder, in • a range of narrow particle size distributions, between 38 and 280 μm. A silicone elastomer was then applied by spraying from a solvent solution. Before curing the elastomer, additional layers were applied [1, 2 and 3], to give a range of final coating thickness [not quantified]. The final surface roughness of this hybrid coating was 1-15 μm Ra, and it was found to be dependent on both the particle size of the metal and • the thickness of the elastomer coating. 20 Each punch was split into a soap formulation that had previously been heated to 40 ° C. The depth of the slit was 3 millimeters, and during the slit the punch was turned at 12 revolutions per minute. The punch was then pulled away from the soap, and the force required for separate the punch and the soap. The adhesive strengths developed were in the range of 10-45 N for all coated punches, or 10-25 N if the punches coated with a single layer of elastomer were excluded. Everybody • the elastomer-coated punches showed a markedly reduced adhesive force, compared with a polished stainless steel [100 N] control punch. 3. DEMONSTRATION OF ADVANTAGES OF HYBRID DIATIONS ON CONVENTIONAL ELASTOMER COATED DIE 10 • 3.1 Bonding Metal-Elas omero Without Chemical Primer Experiments have shown that the mechanical wedging of the elastomer within the hybrid base coat can give excellent interfacial bond strength or metal-elastomer fracture energy, to a degree that it is no longer necessary to use a binder or chemical primer, as required with conventional metal-elastomer bonding. Consequently, the use of, and the • exposure to hazardous chemicals frequently contained in the reactive primers. Chemical primers have been essential to achieve sufficient adhesion between many soap die materials, eg, silicone elastomer and bronze, and in the worst case there is in effect zero interfacial bond strength without its use. However, as in many other rubber-metal bonding applications, a further significant increase in interfacial adhesion can be obtained by the use of chemical binding agents. These can be found beneficial for particular hybrid-base-elastomer combinations in terms of interfacial adhesion or durability and long-term stabilization of the interface against corrosion. In this case, the hybrid texture gives a greatly increased and intricate interface, which must be mechanically interrupted or chemically attacked before any interfacial failure. • These characteristics, (a) sufficient interfacial strength without a primer, and (b) improvement of the hybrid base with primer, have been exemplified using two silicone elastomers of different cohesive strength and a test of 180 ° detachment [BS 3712, part 4, 1991]. This test consists of a laminate, where a fine stainless steel wire mesh is embedded in the elastomer, and a rigid metal substrate is detached. An energy is calculated • of fracture (G) from the resistance to detachment [P, the detachment force per unit width ()], using the equation G = 2P / w. Substrates were (i) bronze that had been fired with glass globules, (ii) bronze as before, then primed with S2260 [this is a reference for metal dice conventional elastomer coated; no primer resulted in almost zero fracture energy and no useful bonding strength], (iii) aluminum that had been sprayed by flame with Ni / Al powder and (iv) aluminum that was • had sprayed by flame with Ni / Al, and then primed with S2260. The primer and the elastomers were supplied and used as recommended by Dow Corning.

• With the weakest elastomer [9050/50], discounting the substrate (i), the other three substrates resulted in the cohesive failure of the elastomer, that is, the energy of • interfacial fracture exceeded the fracture energy of the elastomer [2.3 KJ / m2]. (a) Therefore, the resistance of The interfacial junction that provides the hybrid base is adequate, even without a primer, (b) Since the failure remains cohesive, no additional information was obtained when the primer was added to the hybrid base. With the strongest elastomer [9280/50], all substrates resulted in an interfacial failure between the base and the elastomer, that is, the interface strength was less than the internal resistance of the elastomer. From this it can be concluded that (a) the interfacial binding strength provided by the hybrid base alone [3.5 KJ / m2] was similar to the bronze fired with primed globules [4.0 KJ / m2], and (b) if it was used primer with the hybrid base, the fracture energy was improved [4.6 KJ / m2]. 3.2 Elastomer Application Ease • 3. 2.1 Retention of a low viscosity elastomer by means of a textured hybrid surface The low viscosity elastomer coatings are can be applied with a brush, immersed or sprayed on the matrix, and the texture of the matrix retains the elastomer until healing. These are less likely to drain from non-horizontal surfaces, and this results in a • more uniform thickness of the elastomer. This prevents the The coating is hung or drained in dies with thin elastomeric coatings, as would happen under certain conditions with the coatings described in European Patent Application Number 9592 4225.6 of the applicants. 25 An example of this effect was shown when metal surfaces were coated, either bronze or aluminum as received, coated with Ni / Al sprayed by flame, with a low viscosity elastomer [Silastic 9050/50] and • then they were maintained at a 90 ° angle (vertical), both during a 15-minute stand-by time at room temperature, and then during the recommended 2-hour cure at 160 ° C. A thin coating, approximately 100 μm, was applied as was done for the thin coating dice, the full description of which is given in the f 10 EP 95924225.6. No control was applied to reproduce the same coating thickness between panels. The thickness of the coating was measured in a series of locations from the top of each panel, using laser profilometry through the boundary formed by a gold film, which had been deposited by steam to a thickness of a few nanometers on one half of the surface of the elastomer. The laser is reflected from gold, but f passes through the transparent elastomer and is reflected back out of the base. In this way, a step in the edge of the gold film, which allows the thickness to be calculated. Figure 1 shows the results obtained for the bronze and hybrid coated plates. This example and the data show the drainage that occurs with a thin coating bronze plate when held vertically for 15 minutes at room temperature after coating, and for an additional 2 hours during cure at a temperature • elevated. In comparison, the data for hybrid plate No. 5 showed no evidence of drainage, but gave a coating thickness of 100 +/- 20 microns. Therefore, for thin coatings, the hybrid surface reduces the sudden drop of low viscosity elastomer coatings on angled surfaces. • 3. 2.2 Coating of a textured hybrid surface with a high viscosity elastomer Elastomers with high viscosity or consistency similar to paste before curing are difficult to apply directly as a thin, even, crack-free coating. These can be applied from organic solvent, but this involves the use of hazardous organic solvents and potential degradation in the final mechanical properties of the elastomer. Spreading with an applicator directly on the metal die results in an uneven coating thickness. However, the matrix of a hybrid base can provide a support surface with multiple contact points for the applicator, in such a way that the paste can be pushed deep into the die. With care and experience, an effective even surface can be made for contact with the soap. The coating is of uniform and optimum thickness, controlled by the maximum peak height of the texture of the matrix. The texture of the hybrid base layer is completely wetted with the uncured elastomer, and this results in excellent mechanical locking and elastomer-base adhesion. To exemplify this benefit, interfacial fracture energies were obtained with the 180 ° detachment test described above, and with the Silastic 9280/50 elastomer in the hybrid Ni / Al base. A thin layer of elastomer, sufficient for die coating, was applied using a soft plastic applicator as described above, then a release test laminate was constructed with more uncured elastomer, and cured at 160 ° C for 2 hours . The fracture energy of this assembly was 3.6 KJ / m2 and the failure mode was interfacial. In comparison, when the initial elastomer layer was applied from a solution diluted in an organic solvent, such as toluene, this gave a very similar interfacial fracture energy of 3.5 KJ / m2. Therefore, the direct application method results in an equally high interfacial bond strength, but avoids the risks or problems of solvent application. 3. 3 Improved life time • The functional elastomer coating is protected from accidental damage by the protruding hard matrix. Improved resistance to physical damage can be achieved even when relatively soft and brittle elastomers are used. The deformation by shear stress that occurs in the elastomer at key locations on the surface of the die is minimized, since the zones of the elastomer are restricted by • islands of the matrix, and they are prevented from contributing to shear deformations of the raw elastomer, and to wear processes. These factors contribute to a more robust factory equipment and a significant increase in the life time of the hybrid die, as shown in the following example. The end face of a copper punch was coated with a layer sprayed with tungsten carbide flame. After • it was covered with an elastomer [SiLastic 9050/50 of silicone from Dow Corning] to make the hybrid coating. A similar copper punch was primed with Dow Corning S2260 primer and coated with the same elastomer. The punches were mounted in turn on a machine designed to accelerate the wear caused by friction about soap. It has been found that this test in practice imitates the life of the die in factory situations. The punch is repeatedly driven into a test soap that is slowly extruded through an opening. The • Pressures exerted on the punch are designed to correspond with those that would occur during stamping. The test continues until the soap begins to adhere to the surface of the punch, and the number of cycles of slits needed for this to occur is recorded. The punch is then cleaned with ethanol and the place in the machine. The process is repeated until it • Adhere the soap to the surface of the punch. These are referred to as the first and second paste values. The stickiness is caused by micro-damage to the surface of the elastomer, and is indicative of the start of the wear. The elastomer coated punch was stuck after the first 70,000 and the second 72,000 cycles, while the hybrid coated punch continued to operate until the • first 100,000 and the second 110,000 cycles. He The hybrid coating of this invention resulted in a life time improvement of about 40 percent. 3. 4 Topography, Friction and Texture 25 By carefully controlling the roughness of the matrix it is possible to impart a final composite surface topography to the hybrid coated die. This can help reduce the friction on the soap's elastomer surface, • and reduce the incidence of unpleasant-looking surface marks on the soap bar. In addition, a preferred surface texture can be applied to the soap bar, by controlling the texture of the hybrid coated die. 3.4.1 Friction • Flat sheets of aluminum were coated in a similar manner, with metal and elastomer sprayed by flame, to the punches described above in section 2. The frictional force developed by sliding a piece of steel was measured. soap through the surface of the leaves, at a range of sliding speeds [7-30 millimeters / second] and normal loads applied. The coefficients of friction were calculated from the inclinations of the friction force / normal force points. They were also obtained values using a thick layer of 3 mm silicone, which can be considered as raw elastomer. The thick elastomer had a very high coefficient of friction with the soap [1.9-2.4], caused by the rough deformation of the elastomer. By restricting the elastomer in the matrix, friction is considerably reduced [0.4-0.8]. 3. 4.2 Texture The roughness of the coated punches was measured • Hybrids and soap surfaces, after the adhesion experiment 5 described in section 2, using a non-contact laser profilometer. There is a strong and direct correlation [-1: 1] between the roughness of the punch and the resulting roughness of the surface of the soap, both measured in Ra (μm). The invention is not limited to the embodiments described hereinabove, which can be changed both in construction and in detail.

Claims (17)

1. CLAIMS 1- A stamping die having a substrate stamping surface comprising a base matrix of • open structure, which has a coating of elastomeric material 5 applied thereon, wherein the surface of the matrix, if seen in cross section, includes a multiplicity of depressions, peaks and plateaus.
2. 2. A stamping die according to claim 1, wherein the matrix has multiple points 10 contact for the elastomer. •
3. 3. A stamping die according to any of the preceding claims, characterized in that the elastomer can be pushed deep into the matrix.
4. 4. A stamping die according to any of the preceding claims, characterized in that it comprises a composite surface that is predominantly the elastomer, having the matrix projecting through the elastomer.
5. 5. A stamping die according to claim 4, wherein the matrix protrudes through the elastomer on islands.
6. 6. A stamping die according to any of the preceding claims, wherein the The die is absent from a binder or primer that adheres the elastomer to the matrix.
7. 7. A stamping die according to any of the preceding claims, wherein the • matrix comprises a ceramic or metal material.
8. 8. A stamping die according to claim 7, wherein the matrix is applied by means of plasma or flame spray.
9. 9. A stamping die as claimed in any of the preceding claims, wherein the The matrix is formed by means of laser micromachining or • Mechanical, corrosion by chemical acid, anodization, erosion by sparks, plasma or treatment with ion beam of die material.
10. 10. A stamping die as claimed in any one of the preceding claims, wherein the elastomer comprises a silicone or fluorosilicon elastomer.
11. 11. A stamping die as claimed in • any of claims 1-9, wherein the The elastomer comprises a die containing carbon.
12. 12. A stamping die according to claim 11, wherein the elastomer is selected from unsaturated carbon chain elastomers, saturated carbon chain elastomers, and elastomers containing 25 carbon, nitrogen and oxygen in the carbon chain.
13. 13. A stamping die according to claim 12, wherein the elastomer is polyurethane, acrylonitrile butadiene rubber, or acryl rubber. • Hydrogenated nitrilbutadiene.
14. 14. A stamping die as claimed in any of the preceding claims, for use for stamping soap.
15. 15. A process for making a stamping die, comprising the steps of: - preparing a matrix surface of open structure in • the surface of a die; and - applying an elastomer coating on the matrix.
16. 16. A process for stamping a product by using a stamping die in accordance with any 15 of claims 1-13, having a stamping surface comprising a base matrix of open structure, having a coating of elastomeric material applied thereon, the process comprising the steps of: - • feeding a composition of the product to given 20 stamping; - stamping the composition on the die to form a stamped product; and - releasing the stamped product from the die.
17. 17. A process according to claim 25, wherein the product is a bar of soap.