EP1379579A1

EP1379579A1 - Foamed moulded bodies made from silicon and use of said produced products

Info

Publication number: EP1379579A1
Application number: EP02716810A
Authority: EP
Inventors: Rolf Siegel
Original assignee: Stuemed GmbH
Current assignee: Stuemed GmbH
Priority date: 2001-02-27
Filing date: 2002-02-26
Publication date: 2004-01-14
Also published as: US6855740B2; US20040157943A1; WO2002072679A1

Abstract

The invention relates to foamed moulded bodies made from silicon which can be produced in large quantities by means of injection moulding machines for known per se for liquid silicon. The invention is characterised in that mixtures of the powdery ammonium carbonate and/or ammonium carbaminate and/or ammonium hydrogen carbonate and at least one of the two liquid-paste components are produced from liquid silicon. Both of the liquid silicon components are subsequently treated in a known manner with the proviso that the casting mould is not completely filled with the dispersion.

Description

Foamed molded body made of silicone and use of the manufacturing products

description

The invention relates to a method for producing foamed molded articles made of silicone, in particular silicone rubber, and the use of the manufactured products.

Silicones can be divided into oils, resins and rubbers according to their areas of application. Silicone oils that are processed into emulsions, anti-show agents, pastes, fats and the like are linear polydimethylsiloxanes. Silicone resins are more or less cross-linked polymethyl- or polymethylphenylsiloxanes, whose elasticity and heat resistance increase with the content of phenyl groups. Silicone resins are used, for example, to manufacture paints, to coat household appliances and laminates. Silicone rubbers are masses which can be converted into the rubber-elastic state and which, as base polymers, contain polydiorganosiloxanes which have groups accessible to crosslinking reactions. Silicone rubbers differ from the other types of rubber in that they are not purely organic compounds. Their structure gives the silicone rubbers their unique properties. A general distinction is made between hot-vulcanizing (HTV) silicone rubbers and cold-curing (RTV) silicone rubbers. One can differentiate between one and two component systems for the cold-curing RTV silicone rubber compounds. In the case of one-component silicone rubber (RTV-1), the mass polymerizes slowly at room temperature under the influence of atmospheric humidity, the crosslinking taking place through condensation of SiOH groups with formation of Si-O bonds. The SiOH groups are formed by hydrolysis of SiX groups of an intermediate species formed from a polymer with terminal OH groups and a crosslinker. In the case of two-component rubbers (RTV-2), mixtures of silicic acid esters and organotin compound, for example, are used as crosslinking agents.

HTV silicone rubbers are usually plastically deformable materials that contain highly disperse silica and organic peroxides as cross-linking catalysts and, after vulcanization at temperatures of more than 100 ° C, result in heat-resistant elastic silicone elastomers (silicone rubber). Another crosslinking mechanism consists in the addition of Si-H groups to Si-bonded vinyl groups, both of which are built into the polymer chains or at the end thereof. Radiation crosslinking is also known for HTV silicone rubbers. Since 1980, a liquid rubber technology (LSR Liquid Silicone Rubber) has been established, are vulcanized in which two liquid silicone rubber components via ^'addition crosslinking in injection molding machines. ■

Liquid silicones (LSR) open up new applications due to their ^• special ^' material properties. rich in elastomer processing. In this way, new types of elastomer-thermoplastic composites can expand the range of previous silicone rubbers.

The technology for large-scale production of solid molded parts made of silicone rubber using liquid silicone is known as injection molding (Liquid injection molding, LIM). The liquid injection molding process offers the advantage that complex parts can be designed flexibly, that preheating is not necessary, that the molded articles do not shrink after solidification and that less material is required.

On (fully automatic) injection molding machines, two liquid-pasty silicone prepolymers are first mixed intimately with one another using a static mixer at room temperature and then pressed into a mold under high pressure. By heating the mold, an additive reaction between the two components leads to a three-dimensional crosslinking of the silicone prepolymers to form a solid, molded silicone polymer, to the molded body made of silicone (cf. company brochures from Wacker Burghausen regarding ELASTOSIL® LR or from GE BAYER Silicones Leverkusen regarding SILOPREN ^® LSR or from Battenfeld Meinerzhagen regarding injection molding machines for liquid silicone). Often these injection molding machines also have metering devices for the homogeneous admixing of colors or other additives to the two liquid-pasty silicone prepolymers, so-called multi-component metering systems. Foamed molded articles made of silicone, for example silicone rubber, such as profiles or sealing plugs for bacteria culture bottles and processes for their production are known.

Japanese patent application Sho 44-461 (461/1969) describes moldable sponge-like silicone rubber compositions which contain a thermally degradable blowing agent, in particular azobisisobutyronitrile. By breaking down the blowing agent, however, substances are produced which are harmful to humans and are therefore problematic from the point of view of environmental pollution.

Japanese patent application Hei 10-36544 (36,544 / 1998) describes a moldable sponge-like silicone rubber composition which comprises hollow thermoplastic silicone resin particles which are mixed into the liquid silicone composition, during which gases develop during the polymerization and in this way produce pores in the molded body , However, the silicone rubber sponge produced in this way has only a low mechanical strength, so the uses of this sponge are limited.

US 6,299,952 describes a moldable silicone rubber sponge composition which also comprises a gas-containing thermoplastic resin bead.

A ^'method, in which initially low-boiling liquids to non-crosslinked - is also ten silicone prepolymers are added. These liquids are, for example, methylene chloride, HALON® (polytetrafluoroethylene), heptane and trichlorethylene. The mixture obtained is then filled into a mold in such a way that the filling quantity is only a percentage of the mold volume. The mold is then exposed to elevated temperatures. The liquid evaporates, causing the silicone prepolymer to swell and fill the mold completely. Due to the increase in temperature, the silicone prepolymer increasingly crosslinks to form the silicone polymer, so that a foamed molded body is formed that has the contours of the shape. So far, this technology has not established itself for the large-scale production of foamed moldings, since the mixing of liquids with a low boiling point to silicone prepolymers is disadvantageous. Either the liquids that can be mixed with silicone prepolymers are easily flammable, so that work must be carried out under explosion protection ■ conditions, or they are environmentally harmful, such as chlorinated or fluorinated chain hydrocarbons, CFCs.

The of the present invention underlying technical problem of providing means and methods for producing foamed articles made of silicone, in particular silicone rubber to provide, with the mold body using known methods, in particular the Liquid Injec- tion molding process, in ^■ simple and inexpensive Way ^' can be produced and have sufficient mechanical stability, and ^' where the disadvantages known in the prior art are avoided during manufacture.

The present invention solves its underlying problem by providing a method for producing a foamed molded body of silicone rubber, whereby a two-component liquid silicone composition in the injection molding apparatus is thermally heated and vulcanized in a shaping cavity of the injection molding ^apparatus', wherein before the thermal treatment at least one liquid silicone component is mixed with an ammonium compound.

The problem is therefore solved according to the invention in that a mixture of an ammonium compound is produced in at least one of the two liquid-pasty components of liquid silicone, preferably an addition-crosslinking two-component silicone, and then processed with the aid of injection molding machines for liquid silicone. The thermal treatment of the liquid silicone sublimates the ammonium compound, which means that it changes from the solid state to the gaseous one. The resulting gas or the resulting gaseous reaction products act as blowing agents, so that ^• open and / or ^• closed cells are formed in the polymerizing silicone composition over the entire mass.

The ammonium compounds ammonium carbonate, ammonium carbaminate and ammonium hydrogen carbonate which are preferably used according to the invention are known and toxic see crystalline chemicals that are used in food technology as a blowing agent, for example baking powder. The preferably used solid ammonium hydrogen carbonate passes into the gas phase at about 108 ° C., for example, without becoming liquid. The resulting reaction products are carbon dioxide, ammonia and water vapor, which are reaction products that are often found in the environment. Ammonia, which occurs in higher concentrations and is characterized by the pungent smell, can easily be neutralized by suction and contact with hydrochloric acid. Surprisingly, it has also been shown that ammonium carbonate, ammonium carbamate and ammonium hydrogen carbonate or the reaction products formed at higher temperatures do not poison the (platinum) catalyst of the addition-crosslinking 2-component silicone.

According to the invention, a mixture of the above-mentioned ammonium compounds is produced in at least one of the two liquid-pasty components of the liquid silicone, for example the addition-crosslinking two-component silicone, in that a powder of these compounds, the particle size in the lower micrometer range, preferably less than 50 μm, is homogeneously stirred into at least one component of the two-component silicone.

If these powdery ammonium compounds are to be stirred homogeneously into a silicone component with a higher viscosity, e.g. over 150,000 mPa ^* s len, in a preferred embodiment of the invention they are predispersed in silicone oil, the viscosity of which is advantageously between 100 and 3000 mPa * s. The dispersion obtained in this way can then easily be admixed with the silicone components; it serves as an inert distribution aid for the ammonium compounds and can be easily removed later by annealing the foamed molding.

In a particularly advantageous and particularly preferred embodiment of the invention, foamed moldings can be produced using injection molding machines which are equipped with a metering device for adding colors or other additives to the two silicone components. Dispersing the ammonium compounds in silicone oil ^'and feeds the dosing device with this dispersion so that rather than coloring pigments, the ammonium compounds to the two liquid-pasty silicon konkomponenten of the addition-crosslinking 2-component silicone are admixed.

The concentration of the ammonium compounds in the liquid-pasty silicone components or in the silicone oil can be varied within a wide range and is between 0.1 and 50% by weight (based on the total mass of the silicone to be processed), particularly preferably between 2 and 8% by weight .-% and very particularly preferably at 10 wt .-%. In the particularly preferred use of a metering device, a "saturated" dispersion of the ammonium compounds in silicone oil is used, ie the ammonium compounds are dispersed in a certain volume for as long as lumen silicone oil until the ammonium compound and silicone oil form a homogeneous paste and no clear silicone oil can be seen.

The production of the foamed molded body from silicone essentially corresponds to that of the injection molding of solid silicone molded bodies by means of injection molding machines, with the difference, however, that according to the invention the mold or the mold cavity is not completely filled with silicone in which the ammonium compounds are dispersed. The extent to which the mold is filled can be varied within a wide range using the metering technology available on the injection molding machines and adapted to the desired properties of the foamed molded article: low filling of the mold corresponds to foamed molded articles with lower hardness, fuller filling of the mold corresponds to molded articles with greater hardness ,

The process according to the invention for producing foamed moldings is preferably carried out using addition-crosslinking silicone rubber starting materials, in particular addition-crosslinking two-component liquid silicone compositions. In a particularly preferred embodiment of the. Invention are used in commercially available compositions such SILOPREN ^® LSR. In a further embodiment of the invention, the process according to the invention can also be carried out using peroxide-crosslinking silicone rubber starting materials. • Another preferred embodiment of the invention relates to the foamed molded articles made of silicone rubber produced using the method according to the invention. In connection with the present invention, “foamed moldings” are understood to mean moldings with open and / or closed cells or pores distributed over their entire mass. Foamed moldings have a bulk density which is lower than that of the silicone rubber framework substance Moldings are characterized by excellent mechanical stability.

According to the invention, moldings produced in this way can be used as insulation material against thermal or acoustic influences, as packaging material, as absorber material against shock and shock, as absorber material for absorbing liquids, in particular non-polar liquids, such as e.g. (Mineral) oil, as an absorber material for gases and / or solvent vapors, as a cushioning material, e.g. as a mattress, • mattress topper or pillow, as a medical device, e.g. can be used as a non-sticky nose, ear, anal, fistula, wound tamponade, as a stopper for bacterial culture bottles.

example

Ammonium hydrogen carbonate (from Fluka) with a particle size of <50 μm, which is obtained by grinding on a steel screen. appropriate mesh size is produced, is by admixing and stirring ^' dispersed in silicone oil with a viscosity of approx.1,000 mm ² * s ^_1 (Dow Corning® Dimeticone Fluid) until a homogeneous paste is formed. The paste is poured into the metering device of a multi-component metering system (2-component mechanical engineering, Marienheide-Rodt) intended for color mixing. The multi-component dosing system is an integral part of an injection molding machine for liquid silicone (Aarburg, Lossburg) on which liquid silicone from GE BAYER, Leverkusen, SILOPREN® LSR 4030 is processed to form solid moldings.

Foamed moldings are produced by mixing the dispersion of ammonium hydrogen carbonate in silicone oil into the liquid silicone by means of a metering system and at the same time reducing the filling volume of the mold to approx. 35%. The other process parameters are essentially identical to the process parameters that are used for the production of solid moldings. The properties of the foamed molded body - hardness, porosity, pore size - can be selected by suitable selection of the liquid silicone, the amount of dispersion added and the filling volume of the mold. adjust in wide ranges. The foamed moldings have a skin, the structure of the pores is mostly closed-celled.

Claims

Expectations

1. A process for the production of foamed moldings made of silicone rubber, wherein a two-component liquid silicone composition is thermally heated in an injection molding device and vulcanized in a shaping cavity, characterized in that at least one liquid silicone component is mixed with an ammonium compound before the thermal treatment becomes.

2. The method according to claim 1, characterized in that the ammonium compound is ground to a powder before mixing.

3. The method according to claim 1 or, 2, characterized in that the ammonium compound is dispersed in silicone oil before mixing.

4. The method according to claim 3, characterized in that the ammonium compound dispersed in silicone oil is mixed with the liquid silicone component using a metering device.

5. The method according to any one of claims 1 to 4, characterized in that the ammonium compound is selected from the group consisting of • ammonium carbaminate, ammonium carbonate and ammonium hydrogen carbonate.

6. The method according to any one of claims 1 to 5, wherein the two-component liquid silicone is an addition-crosslinking silicone.

7. The method according to any one of claims 1 to 5, wherein the two-component liquid silicone

Peroxide-curing silicone is.

8. The method according to any one of claims 1 to 7, wherein the molding cavity of the injection molding device is not completely filled with the thermally treated components of the liquid silicone.

9. Foamed molded article made of silicone rubber, producible by a process according to one of claims 1 to 8.

10. Use of a foamed molded body according to claim 9 or produced according to one of claims 1 to 8 as insulation material against thermal or acoustic effects, as packaging material as absorber material against shock and shock, as absorber material for absorbing liquids, in particular non-polar liquids, such as e.g. (Mineral) oil, as an absorber material for gases and / or solvent vapors, as upholstery material, e.g. as a mattress, mattress pad or pillow, as a medical device, e.g. as a non-sticky nose, ear, anal, fistula, wound tamponade, and as a stopper for bacterial culture bottle.