CS277065B6 - Process for press and injection moulds cleaning - Google Patents

Abstract

Prodn. of a heat-cured, filled, modified MF resin compsn. (I) with good flow properties comprises plasticising a mixt. of 20-70 wt.% MF resin, 20-79 wt.% mineral and/or fibre filler (ground to 0.001-0.1 mm), 0.1-15 wt.% glycols and urea and/or triazine derivs., and opt. dicyandiamide, by roll-milling for 1-30 mins. at 60-140 deg.C. Fillers are quartz powder, glass fibre and/or cellulose, amt. of MF resin is 30-60 wt.%, pref. glycol is ethylene glycol, and the mixt. is roll-milled at 80-110 deg.C.

Description

Technical field

The invention relates to a method of cleaning molds and injection molds using a cleaning composition comprising a thermosetting melamine-formaldehyde resin, mineral and / or fibrous binders and other additives which are introduced into the mold and, after solidification, removed therefrom together with the impurities contained in the mold.

BACKGROUND OF THE INVENTION

In the molding and injection molding of plastics, various contaminants remain on the contact surfaces of the mold, which come from the material and from auxiliaries, for example lubricants, which cause operating difficulties and which require periodic removal. The known cleaning methods are based on mechanical cleaning using special tools and special cleaning agents, which are labor-intensive operations. They require the mold to be opened and dismantled, thereby interrupting the manufacturing process. Known cleaning materials include chalk, ground dolomite and similar powdered minerals.

Also known are cleaning methods in which certain types of well-flowable melamine-formaldehyde molding compositions are used with cellulose as a filler, but which require high pressures, typically pressures above 30 MPa, to limit their use. These molding compositions each contain lubricants such as stearin and / or zinc stearate and / or magnesium stearate, the presence of which is intended to facilitate the separation of the moldings from the mold. Lubricants, however, can also settle on the surface of the moldings as an oily coating and make mold cleaning difficult. In addition, upon direct contact with the hot mold, these molding compounds release a considerable amount of free formaldehyde, which limits their use for health reasons.

Effective cleaning of the contact surface of the molds requires a material with a high flowability that allows extrusion at pressures of less than 20 MPa, while the material acts chemically and physically on impurities and releases at least formaldehyde. Workability at lower pressure is particularly important in the case of molds that are used to seal electronic components using epoxy molding compounds. Such molding compositions are generally processed at pressures below 3 to 12 MPa. In addition, the cleaning material used must maintain its good fluidity upon storage for several months.

Surprisingly, it has now been found that the process according to the invention successfully solves the problem of cleaning the injection molds and injection molds. The essence of the invention

According to the invention, the process of cleaning molds and injection molds consists in introducing into the molds a mixture containing by weight of the composition. 20 to 70% melamine formaldehyde resin, 28 to% mineral filler with a particle size of 0.001 to 0.1 mm and / or fibrous filler, 0.1 to 15.0% glycols and urea i

and / or triazine or dicyandiamide derivatives obtainable by plasticization at 60 to 140 ° C for 1 to 30 minutes, and cured in purified form at a pressure of less than 25 MPa, in particular at a pressure of 5 to 12 MPa, at a temperature of 130 to 200 ° C, preferably 165 to 185 ° C.

The cleaning composition used is produced by plasticizing on rollers, allowing the free formaldehyde residues contained in the melamine-formaldehyde resin and reactive with urea and triazine derivatives to flow out and / or react. As a result of this reaction, low-molecular products are formed which additionally plasticize the mass and increase its flowability. The mass used in the process of the invention is in the form of small granules and is pelletizable at ambient temperature.

The method according to the invention illustrates, but is not limited to, the following example of a practical embodiment.

DETAILED DESCRIPTION OF THE INVENTION

25 kg of solid melamine-formaldehyde resin, 27 kg of 50 μια silica flour, 0.5 kg of titanium dioxide, 1.5 kg of talc, 1 kg of glass fibers up to 6 mm in length and 1.2 kg of urea are introduced into a ball mill. . The mixture is worked for two hours and then the homogeneous mass is plasticized on rolls of 80-100 ° C for 10 minutes. The cooled film product is crushed in an impact mill to produce a finely granulated product. The granular product obtained has a flow rate of 76 cm, determined at a temperature of 177 ° C at a pressure of 7.0 MPa in an EMMI spiral.

The obtained material is used to clean the working surface of a mold for hermetizing electronic components.

The molds are contaminated with firmly adhering epoxy deposits as well as lubricants.

The granular products are pelletized at room temperature. Each pellet has a weight of 40 g. After pre-heating, the pellets are introduced into a press and kept in a mold at a pressure of 80 bar and a temperature of 170-180 ° C. The residence time in the mold is approximately 6 minutes. Then the mold is opened and the cured mass is removed together with the impurities that are visible on the surface. The cleaning process is repeated until the mold surface is completely clean, which is usually achieved after 3 to 6 operations.

No sharp odor of formaldehyde is observed at the workplace during cleaning.

Industrial applicability

The working surface of the molds and injection molds can be successfully cleaned by the method according to the invention.

Claims (1)

PATENT CLAIMS A process for cleaning molds and injection molds, wherein a cleaning composition comprising a melamine-formaldehyde resin is introduced into the mold, and the cured composition is then removed from the mold together with impurities, characterized in that a composition comprising a composition containing a composition is introduced into the mold. 20 to 70% melamine-formaldehyde resin, 20 to 79% mineral filler with a particle size of 0.001 to 0.1 mm and / or fibrous fillers, 0.1 to 15% glycols and urea and / or triazine or dicyandiamide derivatives, transportable by plasticization at 60 to 140 ° C over a period of 1 to 30 minutes, and cured in a purified form under a pressure below 25 MPa, preferably at a pressure of 5 to 12 MPa at a temperature of 130 to 200 ° C, preferably 165 to 185 ° C.