Lubricant compositions for use in diecasting of metals and process

Abstract: Polypropylene is used as a component of a lubricant/release agent composition in diecasting of metals, with the composition containing the polypropylene finely dispersed in a liquid carrier, for example in an aqueous emulsion; and, a process of diecasting metal parts using said composition.

Description: This invention generally relates to lubricant compositions for use in diecasting of metals, having improved lubricant and release properties. Diecasting machines, which include the pressure diecasting and squeeze casting processes, operate under high pressures and temperatures. The faces of the dies must be lubricated and sealed so that the cast metal can flow efficiently and can be released cleanly. In addition, various moving parts must be lubricated. The basic requirements of lubricant compositions for diecasting are as follows: (1) Parting Ability -- it must be possible to release the castings from the die surface without distortion or undue stress. (2) Barrier Formation -- the lubricant must form a physical barrier between the cast metal and the face of the die in order to reduce adhesion of the cast metal to the die surface (referred to as "soldering" or "galvanizing", depending on the metal being cast). (3) Control of Surface Finish -- the lubricant composition must not leave undesirable residues on the die face which might corrode the steel or impair the surface of the casting and hinder or prevent subsequent finishing operations. (4) Soundness of Casting -- the lubricant composition must not give off excessive amounts of gas which might lead to porosity of the casting surface and affect the pressure tightness of the castings. (5) Health and Safety -- it is important that lubricants do not contain dangerous or toxic components or components which will react to form undesirable byproducts. In the early days of diecasting, various pastes, oils, greases, and waxes were used and these were applied to the die by various means including brushing. These materials often caused a severe fume problem as solvent and oil evaporated or burned off the hot die surface. Additives such as aluminium paste and finely divided graphite had been used, but tend to cause discolouration of the surface (graphite staining) which can be undesirable in many applications. Silicone oils in some instances can be effective release agents, however under most conditions the silicone oils lack sufficient lubricant properties, especially for moving parts. Still further, hydrocarbon oils or polyethylene can cause the buildup of degradation products on the die faces and on the exterior of the dies. Buildup on the die faces themselves leads to inferior casting and surface staining, and shortens the overall life of the die. Deposits on the outside of the die can be troublesome and difficult to remove, requiring mechanical abrasion in the absence of effective solvents. Build up on the mating surfaces of dies can prevent complete closure of the dies, leading to dimensional inaccuracies of the castings. USP 2,923,041 describes a method of casting a non-ferrous metal which comprises coating the metal face surfaces of a metal mould with a uniform thin coating of a hydrocarbon polymer of an unsubstituted, monoolefinic aliphatic monomer. The coating is said to prevent the adherence of non-ferrous metal to the mould surface. JP-A-01053727 describes a water-soluble mould release agent comprising (a) a maleic anhydride adduct obtained by reaction with a copolymer of ethylene and propylene, (b) a surfactant, e.g. an anionic or nonionic surfactant, and (c) water, a mineral oil, a vegetable oil, an animal oil, a synthetic lubricant, silicone oil or a low melting pure wax. CS-A-155847 describes a mould release agent for plastic and rubber moulding. The agent includes polypropylene and silicone oil. There has thus been a need in the art for an improved lubricant/release agent which has the appropriate surface active properties to "wet" the die surface, suitable viscosity ranges to flow evenly, but stay in place on the die surface during the casting operation, while at the same time being suitably fugitive or removable so as to provide clean castings and die surfaces. It has been discovered that the use of polypropylene fulfils the above requirements and that its usage as described in the invention herein provides unexpectedly unique results. The polypropylene is preferably applied as a finely divided dispersion in a liquid carrier. In general the polypropylene is desirably formulated as an aqueous emulsion which can be sprayed onto the die to leave a surface film of the polypropylene after evaporation of the aqueous carrier. Broadly stated, this invention involves a new die lubricant and release agent composition containing polypropylene in a liquid carrier. Thus, the present invention provides a liquid carrier based die lubricant and release agent composition, comprising in percent by weight: (a) 0.01% to 40% of polypropylene homopolymer having an average molecular weight between 500 and 300,000, (b) 0.1% to 50% of silicone oil, (c) 0.01% to 8% of an emulsifying agent to assist in maintaining the components of the composition in an emulsified form, and (d) up to 5% of an anti-corrosion agent, and the balance liquid carrier. From a process aspect, the invention concerns a process of die-casting metal parts or metal products including the steps of: treating the die with the die lubricant and release agent composition of the present invention, die-casting the metal product, and removing the product from the die. The polypropylene suitable for this invention has an average molecular weight between 500 and 300,000; and preferably between 2500 and 10,000; with most preferred results being obtained using polypropylene having an average molecular weight of between about 4000 and about 5000. The polypropylene may be in solids form. So called crystalline polypropylene is ideal, for example having a relatively sharp melting point (for example in the range of approximately 120-180°C). Typically the polypropylene is used in the composition in the form of an aqueous emulsion such as Emrel 7 (40% solids) obtained from Hickson and Welch Ltd. Other types of polypropylene may also be used, such as polypropylene particulate material or powdered material; for example, Eltex HY-P or Eltex RP-P products (obtained from Solvay Chemical Co.). The polypropylene used whether in aqueous emulsion form or solid powder form, in either event, is dispersed in the composition. As will be seen from the examples given herein the molecular weight of the polypropylene is sometimes specified with the letter "D" being used. This stands for the Dalton technique or methodology of describing or delineating the molecular weight. By the term polypropylene as used herein it is meant polypropylene homopolymers. The polypropylene in the composition is present within the range of 0.01% to 40% by weight of the composition, with preferred results being obtained when the polypropylene is present within the range of about 0.02% to about 20% by weight of the composition; and with best results being obtained when the polypropylene is present within the range of about 0.1% to about 15% by weight of the composition. As referred to, polypropylene or polypropylene emulsions used herein contain appropriate emulsifying agents or suspending agents, and particularly useful for this purpose are the non-ionic surfactants such as ethoxylated alcohols discussed below. The lubricant compositions in accordance with this invention may also suitably contain other components, such as mineral oils and anti-corrosion agents, as will be discussed hereinafter. The lubricant compositions described herein may be formulated as end usage compositions, or as concentrates which are diluted shortly before usage. The concentrates are typically diluted in a ratio of about 1:10 to about 1:100 by volume. It has been discovered that the use of polypropylene as described in this invention provides distinct and surprising advantages over the use of past lubricant/release agents. The polypropylene provides far fewer deposits of degradation products while also degrading cleanly and, most importantly, without causing porosity of the casting. The castings are cleaner and brighter, making them more suitable for subsequent processing such as plating; and, the dies and die faces remain cleaner and truer. The silicone oil used in the lubricant compositions of the invention, can be any one of a number of different commercially available materials. Typical examples of such silicone oils are Union Carbide L-42, Dow Corning 203, General Electric SF-1080 and the silicone oil product known as Wacker TN. These same silicone oils are available in aqueous emulsified form by product designations known as, for example, Wacker TNE; Union Carbide LE-420/HS; General Electric SM-2154; and Dow Corning No. 290. The silicone oils used are preferably an organo modified polysiloxane silicone oil. The silicone oil is present within the range of 0.1% to 50% by weight of the composition, with more preferred results being obtained when the silicone oil is present within the range of 0.1% to 23% by weight; and with best results being obtained when the silicone oil or silicone fluid is present within the range of 0.5% to 13% by weight of the composition. The emulsifying agent for use in the composition serves the function of maintaining the ingredients of the composition in an emulsified form within the liquid carrier system, and are generally referred to as non-ionic emulsifying agents. The emulsifying agent is present within the range of 0.01% to 8% by weight of the composition. Preferred results are obtained when the emulsifying agent is present within the range of 0.02% to 6% by weight; with best results being obtained when the emulsifying agent is present within the range of 0.1% to 5% by weight of the composition. Typical emulsifying agents or wetting and dispersing agents are: the ethoxylated alcohols, such as: Genapol X 060 and Genapol X 080 (available from Hoechst Chemicals); also usable are the Nonyl Phenol alcohols, such as, Antarox CO-530 and Antarox CO-630 (available from Rhone-Poulenc Chemicals Co.) [available in the U.S.A. as Igepal CO-530 or CO-630]; and ethoxylated castor oil, such as Emulan-EL (available from BASF). The anti-corrosion agent referred to herein is an optional ingredient in the composition, which may generally be present in an amount up to 5% by weight of the lubricant composition. Preferably the anti-corrosion agent is present within the range of 0.01% to 5% by weight of the composition, for example 0.01% to 4% by weight of the composition, and most suitable results are obtained when the anti-corrosion agent is present within the range of 0.1% to 3% by weight of the composition. Examples of suitable anti-corrosion agents are: sodium nitrite, sodium benzoate, triethanolamine salts, cheminite 10-01, and Becrosan BTO (available from Carl Becker GmBH). Other additives may also be used in the lubricant composition of this invention, such as, mineral oil, synthetic or natural oil, preservative agents, anti-foam agents, or bactericide agents. When these other additives are used they should generally be present within the range of 0.02% to 35% by weight of the composition, with preferred results being obtained when these additives are present within range of 0.1% to 30% by weight of the composition. The bactericide or preservative agents are for the purpose of preventing spoilage of the product. Suitable bactericide agents: Acticide BX (Thor Chemicals company, U.K.) which can be described as a synergistic blend of aromatic compounds, that is, a blend of isothiazilone and chloroacetamide with n-formal; or Emulcid (available from Thor Chemicals), or Grotan BK (available from Sterling Industrial Company), with both of these latter materials being Hexahydro-1,3,5 Tris(2-hydroxyethyl)-2-triazine. The liquid carrier for the composition is preferably water, however, it may also be selected from a number of other materials such as mineral oil or mineral spirits. According to a preferred embodiment, in the composition of the invention component (a) is present from 0.02% to 20%, component (b) is present from 0.1% to 23%, component (c) is present from 0.02% to 6%, and component (d) is present from 0.01% to 4%. In another preferred embodiment component (a) is present from 0.1% to 15%, component (b) is present from 0.5% to 13%, component (c) is present from 0.1% to 5%, and component (d) is present from 0.1% to 3% and said polypropylene has an average molecular weight between 4,000 and 5,000. In order to further illustrate the invention, the following examples are provided. In all the examples the materials used are specified in percentage by weight. EXAMPLE 1 (All In % By Weight) Emulsified Polypropylene: Oxidized Polypropylene Homopolymer of Average Molecular Weight 4,500D; As Present in Emrel 7, Polypropylene Aqueous Emulsion, (30% solids version) (Hickson and Welch Ldt.) - 1.65% Silicone Oil Aqueous Emulsion: (Dow Corning 290) Organo Modified Polysiloxane Silicone Fluid Aqueous Emulsion. 50% Solids content. - 15.30% Ethoxylated Alcohol Emulsifier - 0.20% Anti-corrosion Agent Becrosan BTO, (Carl Becker GmBH) - 2.00% Water - 80.85% 100.00% The above composition, for end usage, is diluted with water at a ratio of approximately 1:40 parts by volume water. The diluted composition is then sprayed on to the die surface for approximately 10-15 seconds, and the diecast parts are then formed, e.g., automotive engine parts such as manifolds, gear box casings, rocker covers etc. EXAMPLE 2 Emulsified Polypropylene: Oxidized Polypropylene Homopolymer of Average Molecular Weight 4,500D; As Present in Emrel 7 Polypropylene Aqueous Emulsion (40% solids version) (Hickson and Welch Ltd.) - 1.80% Silicone Oil Aqueous Emulsion: (Dow Corning 290) Organo Modified Polysiloxane Silicone Fluid Aqueous Emulsion. 50% Solids content. - 15.30% Ethoxylated Alcohol Emulsifier - 0.23% Anti-corrosion Additive Becrosan BTO, (Carl Becker GmBH) - 2.00% Water - 80.67% 100.00% The above composition, for end usage, is diluted with water at a ratio of approximately 1:40 parts by volume water. The diluted composition is then sprayed on to the die surface for approximately 10-15 seconds, and the diecast parts are then formed, e.g., automotive engine parts such as manifolds, gear box casings, rocker covers etc. EXAMPLE 3 Polypropylene Aqueous Emulsion PERMANOL 1111 (34% solids) - 11.00% Silicone Oil Aqueous Emulsion (50% solids) (DC-290) - 17.9% Water - 71.10% 100.00% EXAMPLE 4 Polypropylene Aqueous Emulsion (Emrel 7, 40% solids content) - 35.00% Silicone Oil Aqueous Emulsion (50% solids) (DC 290) - 10.00% Water - 55.00% 100.00% EXAMPLE 5 Polypropylene Dispersed Powder 0.2 to 2 microns average diameter particles Molecular weight 4,000 to 20,000 D. - 1.80% Silicone Oil Aqueous Emulsion (50% solids) (DC 290) - 15.30% Ethoxylated Alcohol Emulsifier Non ionic dispersing and wetting agent - 0.18% Anti-corrosion Agent (Becrosan BTO) Preservative - 0.20% Water - 80.52% 100.00% EXAMPLE 6 Polypropylene Aqueous Emulsion (40% solids) - 2.00% Silicone Oil Aqueous Emulsion (50% solids) - 2.70% Non-ionic Emulsifier - 4.90% Mineral Oil - 24.30% Preservative - .10% Water - 66.00% 100.00% EXAMPLE 7 Same as previous Example No. 2 but with polypropylene powder (0.2 to 2 microns average particle size diameter) used in place of the polypropylene emulsion in such proportion as to result in the same content of polypropylene in the product as was present due to the contribution of the polypropylene emulsion used in Example No. 2. EXAMPLE 8 Emulsified Polypropylene As Present in a 40% Solids Content Aqueous Emulsion (Emrel 7) - 1.80% Silicone Oil (DC-203) - 6.85% Ethoxylated Alcohol Emulsifiers Emulsifier (Genapol X-060) - 1.09% Anti-corrosion Agent (Becrosan BTO) - 2.00% Preservative - .10% Bactericide (Hexahydrotriazine) - 0.12% Anti-foam Agent (SAG 100) - 0.05% Water - 87.99% 100.00% In summary, the usage of polypropylene in the lubricant compositions as described herein for pressure diecasting and/or squeeze casting applications, with the polypropylene being either in the form of an aqueous emulsion or as a finely divided powder, will provide the following unique technical advantages and benefits: (1) cleaner, brighter castings with reduced staining, (2) reduced tendency for buildup of hard deposits on the dies, (3) markedly improved die lubrication and release properties, (4) improved economy in use of release agent products, (5) a reduced tendency for soldering to occur; and (6) applicant has also found that the lubricant compositions of the invention when applied (e.g., by spray treatment or other application to the die surface) provide excellent technical results in pressure diecasting due to: increased wetting temperatures which are possible relative to prior compositions (this improves cycle time and permits many more parts/hour to be produced), and a temperature plateau range also occurs which is very important (i.e., prior lubricants have a peak rather than a plateau) because the cooking of applicant's composition on the heat block or die surface permits heat to be taken out of the die in a very uniform manner, while leaving a continuous film of the lubricant intact.

Claims: A liquid carrier based diecasting lubricant and release agent composition, comprising in percent by weight: (a) 0.01% to 40% polypropylene homopolymer having an average molecular weight between 500 and 300,000, (b) 0.1% to 50% silicone oil, (c) 0.01% to 8% of emulsifying agent to assist in maintaining materials of the composition in an emulsified form, (d) up to 5% of an anti-corrosion agent, and the balance of a liquid carrier. The composition of claim 1 wherein said polypropylene homopolymer has an average molecular weight between 2,500 and 10,000. The composition of claim 1 or 2 wherein said polypropylene homopolymer is in solids form. The composition of claim 1, 2, or 3 wherein said polypropylene homopolymer is in finely divided dispersed form. The composition of any of claims 1 to 4 containing 0.01 to 5% of an anti-corrosion agent. The composition of any of claims 1 to 5 wherein, component (a) is present from 0.02% to 20%, component (b) is present from 0.1% to 23%, component (c) is present from 0.02% to 6%, and component (d) is present from 0.01% to 4%. The composition of claim 6 wherein, component (a) is present from 0.1% to 15%, component (b) is present from 0.5% to 13%, component (c) is present from 0.1% to 5%, component (d) is present from 0.1% to 3% and said polypropylene has an average molecular weight between 4,000 and 5,000. The composition of any one of claims 1 to 7 further comprising 0.02% to 35% of one or more additives selected from mineral oil, synthetic or natural oil, preservative agents, antifoam agents, and bactericide agents. The composition of claim 8 comprising 0.1% to 35% of said additive. A process of diecasting metal products including the steps of: treating the die with a die lubricant and release agent composition as claimed in any one of claims 1 to 9, diecasting the metal product, and removing the product from the die.

Inventors: WILLOUGHBY ANTHONY PETER, WILLOUGHBY, ANTHONY PETER
Applicants: ACHESON IND INC, ACHESON INDUSTRIES, INC.
Application year: 1993
Main classification: B22C3
IPC codes: B29C33, C08J3, C10N40, C10M173, C10N20, B22D17, C10N50, B22C3