MXPA99009003A - Device for producing foamed shaped parts, method for the production of a form tool and method for the production of a shaped foamed parted - Google Patents

Abstract

The invention relates to a device for foaming foamed shaped parts in a form tool which can be opened and closed. Said tool is provided with a non-stick coating. The invention also relates to a method for the production of a form tool with a non-stick coating. Lastly, the invention relates to a method for producing a foamed shaped part. Foamed shaped parts stick to the form tools in which they are produced thereby making it difficult or even impossible to remove said parts therefrom. The invention provides a solution to this problem by creating a dense crystal-structure surface coating for said form tools. The molecules of the foaming systems are also excited by ionized air along the surfaces of said tools in such a way that the molecules cannot penetrate the crystal-structure coating. Molecular excitation of the foaming systems along the coating in the mold cavity occurs by means of a flat voltage potential which in turn obtains its impulsivity from the positive charged ionized gas that is blown in.

Description

PROCESS TO PRODUCE A MOLDED PIECE OF FOAM, APPARATUS FOR FOAMING MOLDED PIECES OF ESPUMA AND PROCESS TO PRODUCE A MOLD The invention relates to a process for producing a molded piece of foam in a mold as described in the characterizing part of claim 1, it relates to an apparatus for foaming molded pieces of foam in a mold which may be open or closed as described in the pre-characterizing part of claim 8 and to a process for producing such a mold as described in the pre-characterizing part of claim 10. The molded pieces of foam adhere to the molds in which they are produced, and it is therefore extremely difficult or impossible to remove the molded pieces of foam. There are several attempts to solve this problem, and these are briefly described below. It is known from JP-A-62 044 410 that, after the forming process, the plastic residues adhering to the surface of the external side of a "mold blowing ionized air on the surface can be removed in such a way that static electricity, which is generated on the outer side of the mold, is neutralized, and then the plastic debris can be easily removed, however, no statement is made about any method to avoid adhesion of the molded part of the mold. foam in the mold from the start.In addition, in "Polyurethane" [Polyurethanes], Kunststoff Handbuch 7, 3- edition 1993, pp. 362-363, Hanser Verlag, describes a chemical coating of nickel or other hard coatings of molds to improve their surface quality. It is also said that the use of molds made of electroplated nickel with an aluminum support layer or highly saturated cast resin is limited due to the different coefficients of expansion of the materials used. In "Taschenbuch für Galvanotechnik" [Electrodeposition Technology Manual], Vol. 1, pp. 222-259, LPW, it is said that by applying a sufficient thickness of intermediate coating made of nickel and excellent ductile before the real process of hard chrome plating, better protection against corrosion than can be obtained through the process can be achieved. hard chrome A further way to improve the release performance is to add an internal release agent to the components to form the foamed part. A process of this type is described, for example, in DE-C-38 37 351, where liquid polybutadiene is added to the polyol component and, respectively, to the polyamine component when articles made of polyurethane and, respectively, polyurea are produced. This procedure is also described in "Innere Trennmittel für Polyurethane Systems" [Internal Release Agents for Polyurethane Systems], P. Horn, H. -U. Schmidt and G. Ranlow, Kunststoffberater 19/1987, pp. 24-26. As an alternative to this method, a release agent can also be applied to the surface of the mold. This process is described, for example, in DE-A-1 131 873, where an excess of substances which react with isocyanate groups when producing articles made of polyurethane foam is applied to the mold. In DE-C-38 27 595, it is also said that the internal walls of the mold used can, if desired, be treated / coated with known external mold release agents to improve the demolding properties. The disadvantages of using internal or external release agents are that these release agents are damaging to health and the environment and increase the production costs for the molded pieces of foam and also that the introduction or application of the release agents retard The production process. In addition, the release agents can affect the properties of the foam molded parts. However, until now it has not been possible to distribute completely releasing agents. The object of the invention is therefore to provide a process and an apparatus for producing a foam molded part which allow to provide a hard release layer and which is excited in the simplest manner possible to reconstruct the potential of the release layer for cause the ejection effect. Another object of the present invention is to provide a process for producing a mold with which the mold can be provided with a hard release layer that can be excited in the simplest manner possible. The solution consists of a process for producing a molded piece of foam with the features described in claim 1, an apparatus for foaming a molded piece of foam with the features of claim 5 and a process for producing a mold with the features described in claim 10. Using the novel process to produce a foam molded part the potential of the release, and therefore the ejection effect, can be regenerated in a simple manner. The novel device has a particularly hard release layer whose potential can be easily regenerated. Using the novel process to produce a mold, this hard release layer can be obtained in a simple manner. Other advantages of the invention are that it allows the formation of a stable and controlled thin layer on the surface of the molded pieces of foam. Since release agents can be dispensed with, no technical equipment is required, such as spray systems and discharge systems or application systems. There are no residues of release agents on the surface of the foam moldings. In addition, application time is saved, costs are eliminated, and there is usually less risk to people and the environment. Advantageous embodiments are given in the dependent claims. For example, the used mixture of ionized gas can be positively charged air at from about 30 to 90 ° C which is injected into the mold at from about 4 to 6 bars. In addition, to facilitate the transfer of charge, the gas or, respectively, the gas mixture, or the components to form the foam molded part, can be enriched with a dielectric. An advantageous embodiment of the new apparatus stipulates that the electrodeposited layer is composed of chromium VI with traces of chromium III, ferrite and zinc. The thickness of the electrodeposited layer is preferably from 40 μm to 0.1 mm. The electrodeposited layer can advantageously be applied to a chemical transition layer made of nickel with a proportion of from 1 to 15% copper, where the thickness of the transition layer can be from 35 to 55 μm. An advantageous embodiment of the new process for producing a mold takes into account that, in the case of molds made of plastic, an electrically conductive supporting or support layer is first applied. Further practical examples of the invention are described below with reference to the drawings. Figure 1 shows a diagram of a novel apparatus with a closed mold. Figure 2 shows a diagram of a novel apparatus with an open mold. Figure 3 shows a diagram of the ejection effect. Figure 4 shows a diagram of the graph of electrode potential versus time for a foaming process. Figure 5 shows a diagram of the effect of surface tension.

In Figures 1 and 2 there is a closed mold 1. { figure 1) or an open mold 1 (figure 2). An air processing unit 2 is connected to produce ionized gas, in this case ionized air, to the mold 1 by means of an injection probe 3, so that the ionized air and, if desired, also a dielectric can be conducted inside. of the mold 1 by means of the injection probe 3. The positive pole of a high-voltage unit 4 is connected, in figure 1, to the interior of the mold 1, and in figure 2 to the end of the injection probe 3. The negative pole of the high voltage unit 4 is grounded, and the mold 1 in each case has a ground 5. The mold of figure 1 also has ventilation devices 6. In the case of molds made of metal materials, the coating of According to the invention, it is applied as follows: After cleaning the surface of the mold and, if necessary, smoothing the surface of the mold in the glass range or, respectively, in the micro range, which can be effected by polishing, but without polishers chemicals, qualities of the surface are as follows: • bright (mechanically polished without polishing) • matt (electrolytically polished with subsequent blowing with glass balls) • structure (electropolished). The parts that are not to be coated in the article must then be covered with a specific surface coating material. Subsequently the mold is chemically or electrochemically treated or - in particular if the silicon content of the mold is high - is subjected to mechanical operations. For example, a chemical transition layer made of nickel with a proportion from 0 to 15% copper is applied in an acid bath by immersion. The thickness of the chemical transition layer is preferably from about 35 to 55 μm. An electrodeposition layer that can also be called a chemical service layer is then applied to the transition layer in an acid bath, for example in a bath of 2% concentrated sulfuric acid. The electrodeposited layer is preferably composed of chromium VI with traces of chromium III, ferrite in approximately 0.5% and zinc. This has a global thickness from approximately 40 μm to 0.1 mm. This can be composed, for example, of three sublayers, where a grounding layer of approximately 30 μm is first applied by means of fluidization with low current density. A carrier layer of thickness from about 5 to 50 μm is applied to this grounding layer, operating at a higher current density than the base layer, but controlling the crystallization rate by faster anodic advance. Finally, on the carrier layer a finished service layer or vector layer is constructed by changing the direction of the axis of the main crystalline structures or zones in the range from 15 to 60 ° (orientation) with respect to the normal surface vector layer. The thickness of the vector layer is from 5 to 15 μm. This is applied, as a passivated final layer, by means of polarity reversals +/- and by means of a reduction in the current density, for which the following preconditions must have been met: • microporous crystalline structure • layer thickness uniform in the directions of the derivatives of the main surface +/- 10 m • the additional anode in the direction of the electrodeposition must be dimensioned with respect to the dynamics of the fluids (the electrode spacing of 12 mm must be maintained as a grid dimension for the lead network electrode). The current density, the voltage, the quality of the direct current and the quality of the electrolyte must, as for the hard chromium, be calculated as required by regulation. All crystalline residues that may be present are subsequently removed by grinding the surface and the mold can be assembled. A high surface hardness of approximately 12 0 Vickers is achieved, as a result of which the life that can be achieved is practically unlimited. In the case of molds made of plastics (eg epoxy resin) the process is in principle identical with the exception that in this case a support layer is first applied to the mold which is electrically conductive and can be composed, for example, of lacquer epoxy or metallic lacquer and has a thickness of, for example, 0.2 mm. The coating offers a very dense crystal structure on the surface. In addition, the molecules of the foam through the surfaces of the mold are excited so that they can not penetrate the crystalline structure of the coating. This excitement must be maintained as much as possible as long as the chemical reactions that take place during the foaming process have been completed. The energy is dissipated by deferring pH values and differing volumes of water from the different systems of foaming. The cause of this dissipation are the polyurethane molecules in the cavity wall which are fixed in vibration during the course of the chemical process to cure the polyurethane. This energy dissipated gradually in the mold during chemical reactions must be continuously replaced if problems are to be avoided during the foaming operation. A controllable "ejection effect" on the surface of the mold is achieved by means of surface tension. With a temperature on the surface of the mold of 25 ° C an electrode potential as low as -0.7 E volts in the initial phase is effective including the injected air used. To ensure easy demolding of the foamed parts in series production it is important that the potential E be maintained in the mold cavity. The original potential of the coating in the mold cavity is desirably, but not necessarily, reduced after the first foaming process. This reduction represents a loss of energy. If the loss reaches a certain level, the reduced energy must be complemented to maintain the ejection effect. Figure 3 shows the function of the ejection effect and Figure 4 shows the graph of the potential E against time for a foaming procedure, in which each foaming procedure has been divided into individual phases. In phase 1 (0-1 in figure 4) the liquid polyurethane components 7 are injected into a mold 1 with a coating 8, in step 2 (1-2 in figure 4) the chemical process is carried out (the reaction), in phase 3 (2-3 in figure 4) the foamed part 9 is removed and then (not shown in figure 3, 3-4 in figure, 4) there is an external addition of the potential E of the coating , for example by means of friction or ionized air and the following definitions apply: Emax minus Ei = Eoss or EL; and Emax - Emin = [A] Ei: electropotential after the first foaming procedure E minus Emi = EreVerse or Er; Ei = Er + Ep E - En (Er + En where Emin: dissipation of the potential E by means of the foaming process chemical PU Er: addition of potential E by removal of the part (addition of internal potential E) therefore: if the limit Ed (t) »A and Ed = [ A] 2, 3 or Er = Ema? ~ Emin, then phase 3-4 waives After the chemical reaction has proceeded it is possible to apply an electrostatic charge to the outer thin layer of the polyurethane part. When the foamed part is demolded, a negative E potential is produced through the coating of the mold. This potential E in turn is transferred to the outer thin layer of the foamed part by means of the kinetic energy introduced when the part is removed. Immediately after separation of the coating from the mold cavity, the surface of the foamed part is positively charged and, in parallel, its negative E potential is supplemented by further separation of the coating. It can be seen that the foamed part has a certain electrical charge during the demolding; however, with a release agent this charge could be even greater (spark formation). It is also important to know that the operations of potential E only take into account those components that affect the so-called surface tensions. These operators are always the derivatives for which the direction of the normal vector runs parallel to and in the opposite direction to the main direction in the chemical reaction of the polyurethane content. This particular direction is mainly towards the center of gravity of the part. According to Poisson, the potential relationship can be described by; Eu here later U (r) as potential V (r) = the vector layer in the mold cavity and so r du du dx .. -._,, Y = -, y = -, V, = -7-,? potential U (r) dx and dy dz for V (r) Vdr = (grad U) dr - dU And so Vdr = dU U (b) - U (a), if a = a (ro) and b = b (r) a- b a- > b then U (r) - U (ro) = Vdr? U (r) = U (ró) + Vdr Simplified for a straight line: U (x, y.z) = [U (x0, y0, zo) + Vx (x, y0, z0) dy + Vy (x, y, z0) dy + Vx (x y, z) dz] * (- l) -The surface tension is given in this case in N / m. Only two-dimensional surface tension is therefore accepted through the coating of the mold. The potential E (volts) U (x, y, z) therefore acts as the motor that drives the surface tension between the cavity coating of the mold and the polyurethane content (approximately 0.03 N / m), as, for example, between mercury and oil, as a result of which this value gives the expression for a defined separation. In this example the mercury represents the coating of the mold and the oil represents the polyurethane system. The electrophysical parameters can therefore be easily compared.

So e - U (^ x ^, yJ> z) '* _P_ = Ema_x * P E -, max = e * V xyz V (? Y, z) V Explanation: e: surface tension (N / m) U (x, y, z): potential E - in this case E ax volt or kg * qm A * sec electrical dipole moment [m * A * sec] V (x, y, z) volume of the space closed by the coating (3) For P, dielectric values are used for P: - A: not more than 30 [μA] (the value of the microampers parameter tested and determined in the foaming experiments) - m: approximately 0.5 [m] - sec: approximately 5 to 39 [sec) Figure 5 shows the effect of surface tension. Here a test fluid 10 which is the same in each case, for example oil, is shown on a coating 8 according to the invention with a different E potential, specifically in a.) E ax, b.) The and c .) Emin. The formation of the drop in Emax here is clearly recognizable and also reduces as the potential E is also reduced. The following describes ways to re-excite the potential E. The first way is to remove the electrodeposited layer by etching and then electrodepositing again, but this brings very high costs. The goal is to produce Emax again. A second way is to mechanically abrade the electrodeposited layer with a rotating and lubricating disc, using, for example, a rotating disc made of a textile or sheepskin (the potential El is increased to Emax by means of kinetic energy). The frequency of abrasion depends on the magnitude of the energy dissipation described above. Although the cost of material for this method is low, the method is difficult to automate and therefore requires labor. A third way is to re-excite the surface of the mold using ionized gases or mixtures of gases, in particular ionized air. Ionized air can be produced in a high-voltage system in which the air is charged, for example, positively while flowing through a high-voltage system of 50 kV and can be heated to about 30 to 90 ° C. The air treated in this way is applied to the mold or, respectively, to its surface at about 4 to 6 bars before injection of the foam. To facilitate the potential increase in the mold cavity, the air can be enriched with a dielectric (for example vegetable base, such as paraffin oil or castor oil, or any silicone oil) at a concentration of about 3%. This procedure can be easily automated completely, involves low energy consumption and provides easy detachment of the part. The only disadvantage is the need for installation in the system of foaming.

Esystem ^ ELOSS The ionized gas and, respectively, in this case the ionized air is injected into the mold for about 3 to 30 seconds, depending on the size of the mold, and this should be done after approximately every third shot. A fourth way is to mix the dielectric directly in component A of the foam system, for example in component A of a polyurethane system, as a constituent of the formulation. The mixture, limited to no more than 8%, reduces or stops the dissipation of energy by inhibiting the transfer of charge between the mold and the surface of the foamed part, and increases Ez. For trouble-free operation, 90 to 95% of the load transfer has to be prevented. The application is very easy, but low pH values and high water contents in the foaming systems reduce the effectiveness of the dielectric agents. The physical properties of the molded pieces of foam can be damaged. The very dense crystalline structure of the coating and the excitation of the surface of the mold effectively prevent the penetration of the foam components into the surface of the mold and any cross-linking that may occur there. Therefore, the removal of the molded pieces of foam presents no problem. The PU reactant molecules slip over the "microgrooves" of the crystalline structure of the coating surface. The present invention is particularly suitable for use when producing molded pieces of polyurethane foam with any of the currently known foaming systems, such as RIM, integral, flexible or rigid foam molded parts. The invention can also be used provided that the reaction media used has a tendency to bind homogeneously to a contact surface (e.g., carton production, etc.).

Claims (6)

1. A method for producing a foam molded part from foam components in a mold, wherein a mold is used and whose molding surfaces have a release coating in the form of an electrodeposited chrome base layer, which has been applied to a chemical transition layer, with the following steps: a stream of a gas or mixture of ionized gases is produced and, before the introduction of the foam components, it is injected into the mold; the reaction process leading to the molded piece of foam in the mold is carried out; the molded piece of finished foam is removed.

The method according to claim 1, further characterized in that the ionized gas mixture used is positively charged air at from about 30 to 90 ° C which is injected into the mold at from about 4 to 6 bars.

3. The method according to claim 1 or 2, further characterized in that, to facilitate charge transfer, the gas or gas mixture is enriched with a dielectric.

4. The method according to claim 1 or 2, further characterized in that, to facilitate load transfer, the components for forming the foam molded part are enriched with a dielectric.

A process for producing a mold for an apparatus for foaming molded pieces of foam in a mold which may be open or closed, wherein the mold molding surfaces have a release coating in the form of an electrodeposited chrome base layer, by the following steps: clean and polish the surface of the mold, use a specific material to coat a surface to cover the locations that are not to be coated in the article; apply a chemical transition layer made of nickel with a ratio of 1 to 15% copper, in an immersion bath apply an electrodeposited layer made of chromium VI with traces of chromium III, ferrite and zinc, in an immersion bath, where A grounding layer is first applied by nebulization with a low current density, then a carrier layer is applied by means of fluidization with a higher current density than that used for the grounding layer, where the speed of crystallization is controlled by relatively faster anodic advance, and finally a vector layer is applied in the form of a passivated final layer changing the direction of the axis of the main crystalline structures or zones in the range from 15 to 60 ° (orientation) with respect to to the surface normal vector layer by means of polarity reversals +/- and reduction in current density; if you want to rectify the surface to remove residual crystals.

6. The method according to claim 5, further characterized in that, in the case of molds made of plastic, an electrically conductive support layer is first applied. 7; An apparatus for foaming molded pieces of foam in a mold which may be open or closed, wherein the molding surfaces of the mold have a release coating in the form of an electrodeposited chrome base layer, further characterized in that the electrodeposited layer is obtained from according to the process of one of claims 5 and 6 and that there are means for producing a stream of an ionized gas or mixtures of ionized gases and means for injecting gas or gas mixtures into the mold. The method according to claim 7, further characterized in that the thickness of the electrodeposited layer is from 40 μm to 0.1 mm. The method according to claim 7 or 8, further characterized in that the thickness of the chemical transition layer is from 35 to 55 μm.