MXPA99005876A - Die and process for stamping plastic material - Google Patents

Abstract

A device for stamping a detergent bar, i.e. a bar comprising soap, a synthetic detergent active or a mixture thereof, includes a die. The die (11) has at least one bar stamping surface provided with at least one elastomeric coating (16) and includes a rim (30) having a rigidity greater than that of the elastomeric coating (16). Good release of the detergent bars from the die is possible without chilling of the dies. Use of the rigid rim increases the useful life of the coating.

Description

TROQUEL AND PROCESS TO PRINT PLASTIC MATERIAL FIELD OF THE INVENTION The present invention relates to a device, process and apparatus for embossing a plastic material using a die to form a shaped article. In particular, it relates to a process for stamping a detergent bar. By "detergent bar" is meant a tablet, cake or bar in which the concentration of the surfactant, which comprises soap, synthetic active detergent or a mixture thereof, is at least 20% by weight based on in the bar.

BACKGROUND OF THE INVENTION In the manufactures of detergent bars, a preformed composition comprising all the 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 "blocks" . These "blocks" are then fed to a stamping machine or alternatively, an impression is provided on one or more surfaces using, for example, a die of the same dimensions as a bar surface. The bar surface is hit hard, for example, with a mallet or a die in the form of a roller. The printers typically have a die formed in two halves, each with a surface which makes contact with the block during the stamping operation. These surfaces are adapted to close at a preset separation distance, so they compress the block between the die halves to provide the bar with its final shape and appearance, and then separate. The excess composition is removed by compression of the die halves as they close. This is commonly referred to as "burr". The burr is then removed from the bar of soap by transferring the bar through holes in a "burr removal plate". Conventional die-stamping machines include "pin die" shaped machines in which a pair of opposing die members or die halves coincide during a comparison step and a "box die" machine in which a pair of opposing die members stamp a bar which is held within a through opening in a box frame but which does not contact during compaction, the peripheral face of the bar is restricted by box frame. The die halves are often each provided with a die or an ejector insert. These are normally kept closed within the spring die half but can be pushed open by compressed air or a mechanical means to assist in the release of the die bar. During the closing of the die halves, vacuum can be applied to remove air trapped in the die cavity between the detergent bar and the die surface and, in the case of rotating dies, this vacuum helps keep the bars in place. place during the rotation. The stamping of detergent bars using a die is carried out to provide the bars with a reproducible shape, a uniform surface and / or to print a design such as a logo, trademark or the like on at least part of the surface of the bar. However, as a result of die blocking, that is, the amounts of residual detergent remaining in the die halves which accumulate during continuous use of the dies, the bars often form with visible imperfections on their surfaces. or can not be released from the die surface. Many solutions to these problems have been proposed.

One solution involves cooling the die halves during the stamping operation. Cooling uses valuable resources, particularly energy sources. Another solution is described in GB-A-746 769 which discloses a die assembly which includes a die box and a pair of accompanying die members made of plastic materials comprising polymers with a specified modulus of elasticity. A disadvantage of this system is that a die release agent is necessary to prevent the detergent from adhering and accumulating in the dies and scraping the surfaces of subsequently compressed bars. United States Patent No. 1, 817,157 for Lucko describes a frame for soap. United States Patent No. 3,127,457 for Pinto describes a fluorocarbon film used with a release agent for molding polyurethane articles. U.S. Patent No. 3,539,144 to Krugg discloses a mold useful for producing polyurethane foam, which includes a structural mold form and a hot vulcanized silicon rubber coating, placed on the structural mold as well as a rubber cold vulcanized silicon deposited on hot-vulcanized silicon rubber. U.S. Patent No. 3,889,919 to Ladney discloses a plastic vent insert for molding a chamber for molding plastic parts. The molding cavity 26 includes a peripheral lip 28. U.S. Patent No. 4,035,122 to Cavanugh discloses a device for saving soap by compressing the remaining soap bars.

U.S. Patent No. 4,076,207 to Austin discloses a food mold comprising a coating and a rigid support wherein the coating has a projection for immobilization to the support. United States Patent No. 4,809,945 for Roussel describes a mold cavity for use in molded articles such as soap bars. U.S. Patent No. 5,332,190 to atanabe discloses an elastic molding die made of a laminated elastomer film, the innermost layer of which does not contain filler materials. In U.S. Patent No. 5,269,997, it is proposed to provide each of two dies of a soap mold with an elastomeric septum tensioned across its surfaces. Such a system would be complex to use at the speed needed for commercial manufacturing and thin coverage would be susceptible to tearing and the reproduction of the logo would be expected to be poor. WO 96/00278 describes 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 thickness Total elastomeric coating is less than 200 micrometers. In a preferred embodiment, the elastomeric coating is the only elastomeric material of the bar embossing surface. Another solution is proposed in EP 276 971 and in U.S. Patent Nos. 4,793,959 and 4,822,273, which involve the use of two die members, each comprising a non-elastomeric and an elastomeric part. The elastomeric part, which makes contact with the soap bar during the stamping process, comprises an elastomeric coating of at least 200 microns and has a modulus of elasticity within a specified range. The manufacture of thick coated dies is a complex and expensive process. Therefore, it is highly desirable to maximize the working time of such coatings. GB-A-2276345 describes a process for the manufacture of articles such as soap bars using molds which have on at least a part of their surface a modulus of elasticity in a certain range. The exemplified mold r can have cutting edges in which the edge of the portion having a given modulus of elasticity and the base of the mold coincide. One difficulty which has been encountered with elastomeric coatings is that they tend to have brief useful durations, in the order of a few days or longer. The problems this causes are evident.

BRIEF DESCRIPTION OF THE INVENTION It has been found that the short life durations of the elastomeric die coatings result from the high stresses that are experienced by the edge of the die during the compression operation of the soap. This results from the high soap stamping cutting forces which tend to tear the elastomeric coating away from the metal base of the die. This problem tends to eliminate the advantages of using elastomer coated dies, for example, the ability to avoid the use of expensive chilled metal dies. It has been found that the tension to which elastomeric coatings are subjected can be reduced by the use of a protrusion or flange having a greater stiffness than that of the elastomeric coating of the die, especially one which itself is similarly coated with elastomer. . Preferably, the edge of the flange is made of a metal or other hard or rigid material. The use of a metallic edge results in a decreased tearing of the elastomer by decreasing the stresses to which it is subjected, preferably, the edge extends over the leading edge of the elastomer and therefore the stresses that are applied during stamping. This appreciably improves the life of the elastomer coated die and allows the advantages of the coated dies to be enjoyed without the disadvantage of an extremely short useful life. Although it may be easier to make the edge of the same material as the die, this is not necessary. The edge of the flange can be manufactured from a wide variety of materials including urethane plastics and composite materials. In a preferred embodiment, the edge is provided in a "T" or umbrella structure, wherein the elastomer is protected below the top of the umbrella. The invention is particularly useful for dies used to make detergent bars which have side walls which extend generally perpendicular to the longitudinal axis of the bar, that is, "strip bars". Elastomeric dies for web bars are considered to experience even higher stresses compared to elastomeric bar dies that lack a vertical side wall or for which the vertical side wall extends only a small percentage of the height of the bar . It is contemplated that the edge or flange of the invention can also be used on a die which itself is made of an elastomeric material, instead of only being coated with one. The edge is usually made of a harder material than the die. For a more complete understanding of the above characteristics and other features and advantages of the invention, reference is made to the following detailed description of the preferred embodiments and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of the dies according to the invention; Figure 2 is a cross-sectional side view of a die according to the invention; Figure 3 is a front cross-sectional view of a die according to the invention; and Figure 4 is a cross-sectional view of a die according to Figure 3, wherein the die has been coated with an elastomeric coating.

DETAILED DESCRIPTION OF THE INVENTION The use of thick elastomeric coatings in the stamping of soap bars is described in EP 276971 and in US Pat. Nos. 4,793,959 and 4,822,273, the disclosures of which are incorporated herein by reference. Next, by "surface decoration" is meant a uniform shape, a smooth surface, a design such as a logo, trademark or the like. By the term "elastomeric" according to the invention, it is meant a material as defined in ISO (International Standards Organization) 1382 as a "elastomer" or a "rubber". Also included in the definition of "elastomeric" materials according to the invention are thermoplastic elastomers and copolymers and mixtures of - elastomers, thermoplastic elastomers and rubbers. Elastomers are defined as polymers with flexible long chains, independently of the untreated material and transformed via vulcanization or crosslinking agents which introduce crosslinks and form a crosslinked network structure. The network structure maintains the movement of the macromolecular chain molecules and as a result they return rapidly to approximately their initial dimension and shape after deformation by a force-releasing force. As the temperature increases, an elastomer passes through a rubber-like phase after softening and maintains its elasticity and elastic modulus until the decomposition temperature is reached.

The thermoplastic elastomers comprise amorphous and crystalline phases. The amorphous phase has a softening range lower than ambient temperature and therefore acts as an elastic spring, while 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 by the American Society for Testing and Materials D1418, which include: 1. Saturated chain elastomers (class R) which include natural rubbers, eg rubber from Malaysia standard; butadiene, for example, type "BUNA" from Buna eke Huís; and butadiene-acrylonitrile copolymer; for example "perbunan" of Bayer. 2. Saturated carbon chain elastomers (class M) include ethylene-propylene type, for example "Nordel" from DuPont and fluorine-containing types, for example "Viton" from DuPont. 3. Substituted silicone elastomers (class Q) including liquid silicone rubbers, for example Silastic 9050/50 P (A + B) from Dow Corning. 4. Elastomers containing carbon, nitrogen and oxygen in the polymer chain (class U) including polyurethanes, for example, Belzona polyurethanes.

As defined above, the "elastomeric" material can be pretreated, for example by forming a solution of a commercially available elastomer, before it is applied as a coating on the surface of the die. Elastomers, rubbers, and polymers as well as mixtures thereof are generally cured or cross-linked in situ on the surface of the die. For example, the components including the base elastomeric material, the crosslinking agents and other materials such as accelerators can be mixed before application as a coating. Once applied to the die, the coatings are cured in situ. This can be helped by the application of heat or other acceleration process, for example pressure; radiation or UV light. The elastomeric material can be applied either as a liquid or a semi-solid. For example, when applied as a liquid, the two halves of the die are kept spaced at a predetermined spacing to allow the elastomer to occupy the space between the two parts. Preferably, the die is filled with elastomer under pressure. In some cases, the materials can be dissolved with an appropriate solvent, applied to the die and the solvent subsequently removed.

In the case of thermoplastic materials, they can be heated to the molten condition and can be applied to the die, cooled and re-solidified. Suitable materials as elastomeric coatings in the present invention will preferably have a modulus of elasticity in the range of 0.1 to 50 MPa, more preferably 1 to 35 MPa. The modulus of elasticity of an elastomeric coating can be measured by recording the force required to nick the coating as a function of the indentation depth. Typically a penetrator with a spherical tip can be used and the slope, s, of the force is determined as a function of the depth of indentation, # raised to 3/2. The indentation depth is the movement of a penetrator in the coating after it makes contact for the first time on the surface of the coating. In general, it is necessary to correct the indentation depth measured when considering the deformation of the measuring device. That is, the depth d of actual indentation is related to the apparent d 'value measured by the following expression d = d '(-F.C) Where F is the indentation force. The deformation C is determined by compressing the penetrator against a rigid surface and registering 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 = 3/4: s l / (R) h (l-b2) where s = F / d32, R is the radius of the spherical tip of the penetrator and b is the Poisson's ratio of the coating which is equal to approximately 0.5 for elastomers. Under certain conditions to be described later, the above indentation method can provide large false values of the elastic modulus due to the influence of the rigid material on which the coating is applied. In order to safely avoid this problem, it is necessary to ensure that the radius of contact of the penetrator with the coating does not exceed about 1/10 of the thickness of the coating. The radius of contact, a, is related to the depth of indentation by the following expression a = (dR) For coatings smaller than 200: m, it is recommended that a nanopenetrator be used which is capable of measuring the indentation forces of small depths of indentation using penetrators with tips that have a small radius. An example of such equipment is the "Nanolndenter II" (Nano-instruments). The alternative is to perform thick test coatings (greater than 200: m) so that more conventional measuring equipment such as an Instron determiner (eg model 5566) can be used. Preferably, the die comprises a rigid material that is selected from metals and their alloys, for example, bronze and other alloys of copper, aluminum and steels including carbon and stainless steel; and other non-elastomeric materials such as thermosetting and thermoplastic resin, for example polyesters, epoxies, furan resins; hard dump polyurethanes; Ceramic materials; composite and laminated materials. Aional materials, for example fillers, can be added to the elastomeric material to modify its mechanical and processing properties. The effect of the aion of filler materials depends on the mechanical and chemical interaction between the elastomeric material and the filler material. The fillers can be used to modify the elastomeric material so that desirable properties are obtained, for example tear strength. Suitable fillers include carbon black; silicas; silicate and organic fillers such as styrene or phenolic resins. Other aional aives include friction modifiers and antioxidants. The edge or flange should extend from the die wall to cover the thickness of the cavity coating and preferably the thickness of the coating outside the cavity. The dimensions of the edge for optimum performance are therefore determined by the desired coating thickness. The thickness and hardness of the elastomeric coating can be varied according to the detergent bar composition, the processing temperature and / or the process parameters such as the shape of the cavity in the die halves, the speed of stamping equipment and the separation distance of the die halves, in order to obtain the desired result , for example, a good release of the detergent bar from the die. For a die with a more complex logo or more complex die shapes, acceptable die release is favored by the use of thicker coatings and a smaller modulus. Similarly, for a stick composition which is inherently more difficult to stamp, an acceptable release of a die with a thicker elastomeric coating and / or one having a lower modulus of elasticity can be obtained.

The device according to the invention can be used to stamp a detergent stick comprising a surfactant which substantially comprises soap or a synthetic detergent or a mixture of soap and synthetic detergent. It finds particular application in the stamping of a mild and / or adherent detergent and / or soft bars which contain synthetic surfactants, translucent and transparent soap bars having a reduced fat content, for example, in the range of 63-78. % by weight with respect to the total weight of the bar, and those bars containing beneficial agents for the skin such as humectants, polyols, oils, fatty acids and fatty alcohols. According to a further aspect of the invention there is provided a process for printing a detergent bar comprising: i) forming an elastomeric coating on a die having an edge to retard tearing of the elastomeric coating; ii) feeding a detergent bar composition to the die of step i; iii) stamping the composition on the die to form a stamped bar; and iv) releasing the bar from the die, preferably in such a way that surface decoration is applied to the bar in a reproducible manner easily.

Preferably, the elastomeric coating is attached to the die stamping surface by a mechanical and / or chemical means to increase the adhesion between the die and the coating. It is particularly preferred that the edge used to release the tension of the elastomeric coating itself is also partially coated with the elastomeric coating. Advantageously, the coating on the edge is thinner than that on the stamping surface of the die bar. For example, it may vary from 1 to 200 microns, especially from 10 to 50 microns. With reference to the figures in detail, Figure 1 shows die halves 10 formed from individual dies 12. Each die half is provided, on the bar stamping surface 14, with an elastomeric coating 16 respectively (see FIG. 4). The elastomeric coating is also provided on the surface 18 without stamping the die halves. A die half is provided with a logo 20 on the stamping surface of the bar (in some cases both die halves will incorporate a logo). This is also coated with an elastomeric coating. The die 12 includes a metal edge 30 which projects into the upper periphery of the cavity 32 of the detergent bar. As seen in Figure 4, the edge 30 covers the upper edge of the generally vertical riser section of cover 16. Preferably, the surface 34 of the edge 30 which is oriented toward the cavity 32 is at least in the same plane with the surface 36 of the elastomer 16 which likewise faces the cavity 32. Even more preferably there is an arrangement in which the edge 34 of the metal edge 30 extends slightly beyond the surface 36 of the cover 16 By using the edge or flange of the invention, the die is constructed so that the soft elastomer near the cutting edge is not damaged when the die is cut into the soap. This is done by covering the soft elastomer near the edge of the die with a stiffer and stronger material. This coating acts like an umbrella around the edge of the die as the soft elastomer slightly overlaps, preferably by approximately 0.025 to 0.38 mm (0.001"to 0.15"). This protects the soft material from excessive cutting and tension forces which can accelerate the damage to the soft material and render the die unusable. Although the edge relieving stresses of the metal die has been described, this will generally depend on the material from which the die is made. Typically, the edge will be the same as the material from which the die is made. However, the edge will typically be very rigid to protect the elastomer. The invention can be used with conventional embossing equipment, such as Binacchi USN 100. Preferably, the edge is trimmed which provides greater mechanical guidance.

EXAMPLE A set of carbon steel die halves are fabricated and electroerosed to a range of surface roughness values (Ra), degreased with acetone, treated with sizing and then coated with a range of elastomeric materials. A series of bronze die halves is also used in the examples. Similarly, they are degreased with acetone, treated with a size and then coated. Elastomeric coatings are formed of polyurethane. The polyurethane is prepared from: a) Andur 80-5AP - liquid isocyanate-terminated prepolymer based on polyether. Supplied by: Anderson Development Co., 1415 E Michigan Street Adrian, MI 49221-3499; and cured using b) Voronal 234-630 healing - Triol supplied by: Dow Chemical Co. 2040 Dow Center Midland, MI 48674 The stick compositions used in the examples are the following: The dies contain metal edges as illustrated by number 34 in Figure 4. It is found that the metal edges release tension on the upper periphery of the cavity during embossing and result in a longer useful life for the coating. Of course, it should be understood that the specific forms of the invention illustrated and described herein are intended to be representative only as changes may be made therein without departing from the clear teachings of the description. Accordingly, reference should be made to the following appended claims to determine the full scope of the invention.

Claims (9)

1. A device for embossing a substrate, the device is characterized in that it comprises a die having at least one substrate embossing surface covered with an elastomeric coating, the substrate embossing surface has a protrusion with a greater rigidity than that of the elastomeric coating. , the device is characterized in that the projection forms a flange which is in the same plane with, or extends beyond, a leading edge of the elastomeric coating of the punch.

2. The device according to claim 1, characterized in that the projection is metallic.

3. The device according to claims 1 or 2, characterized in that the protrusion is formed from the die material.

4. The device in accordance with the claim 1, 2 or 3, characterized in that the projection comprises a thinner elastomeric coating than the coating of the die.

5. The device according to any of claims 1 to 4, characterized in that the elastomeric coating is selected from elastomers, rubbers, thermoplastic elastomers and copolymers, and mixtures thereof.

6. The device according to any of the preceding claims, characterized in that the die comprises a rigid material that is selected from metals and their alloys, thermoplastic and thermosetting resins, hard die-cut polyurethanes, ceramic materials, composite materials and laminates.

7. A process for constructing an elastomeric coating on a device, according to any of the preceding claims, the process is characterized in that it comprises the steps of: i) pre-treating the device by chemical and / or mechanical means to form a bonding surface for the elastomeric coating; and ii) applying the elastomeric coating to the device.

8. A process for stamping a detergent bar, characterized in that it comprises the steps of: i) providing a device according to any of claims 1 to 6 ii) feeding a detergent bar composition to the die; iii) stamping the composition in the die to form a stamped bar; and iv) release the die bar.

9. The use of a device according to any of claims 1 to 6 for stamping a detergent bar.