Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
2001-05-07
2002-09-24
El-Arini, Zeinab (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S010000, C134S026000, C134S036000, C134S061000, C134S111000, C134S186000
Reexamination Certificate
active
06454867
ABSTRACT:
The invention relates to a method and a machine for cleaning objects having the general form of plates, such as screens or stencils for screen printing, notably screen printing stencils used in the production of electronic circuits for depositing adhesives or solder pastes, and more particularly stencils for frames, so-called self-tensioning frames, which are simple flexible fragile thin metal foils.
So far, cleaning of such pieces is often realized in practice manually with the help of solvents on a duster for the glue, or with the help of machines (DE-A-4,010,679) spraying under pressure on the pieces either aqueous solutions with saponification agents or solvents (with all the technical strains imposed by the use of chemicals with an ignition point). Such devices are cumbersome, represent important investments, and do not allow to clean and separate in one step residues of various chemical compositions. However, modern regulations on environment impose to be able to separate residues to allow their recycling, their inerting, or their later destruction according to their chemical composition.
So, with these devices, it is necessary to provide a rinsing step and a residue sorting/separating step. Moreover, the cleansing solutions load with residues and must be regularly renewed, which is expensive and harmful to environment.
Further, these devices do not allow to clean the stencils for self-tensioning frames, which are too fragile for a manual rub cleaning or a pressure spray cleaning.
So, effective technical cleansing compositions are known such as VIGON® SC 200 marketed by the company Dr. O.K. WACK for spray cleaning of screen printing stencils, which has the advantage of eliminating at room temperature adhesives used for surface mounting of components (CMS) and solder pastes, and which is not inflammable. This composition based on water-dissolved alcoxypropanols forms a microphase at a temperature between 20 and 30° C. It is recommended by the manufacturer, after applying the fluid by spraying on objects to be cleaned, to rinse with water. With these compositions, it is noted that the spray-treatment time for each piece is in general more than 1 hour, drying included.
Document PATENT ABSTRACTS OF JAPAN, vol. 95, no. 8, Sep. 29
th
1995 & JP 07116617 describes a cleaning method and a cleaning machine in which an object is immersed in a cleansing liquid which flows from the bottom up in the treating vessel, spills over into a peripheral overflow vessel, carrying along residues in suspense, and is recycled, after filtering, in the treating vessel bottom part. Precipitated residues of high granularity are extracted because of a high flow rate from the bottom part of the treatment vessel, and then filtered and recycled. This device does not allow in practice to clean pieces and to separate residues of low density, of residues of average density and of residues of high density with an efficiency and a time compatible with industrial operating stresses. Particularly, this device does not allow to separate residues from successive or alternative treatments of pieces soiled with solder pastes (light and heavy residues), and then of pieces soiled with adhesive (residue of average density). Particularly, it is to be noted that the device according to this document does not particularly allow to separate residues of low density from other residues, notably from residues of average density in suspense. This separation is indeed the most difficult one to realize, but it is important, notably insomuch as residues of low density such as fluxes or fats have a chemical composition very different from that of residues of average density such as epoxy glue, and thus need later different treatments. Further, this device which does not comprise any heating means does not allow to use a liquid susceptible of forming a microphase. It works thus either as a solvent, or as a surfactant. Consequently, in such a device, the cleansing liquid dissolves residues, and must thus be regularly renewed, which is expensive and harmful to environment.
The invention aims thus to solve these drawbacks by providing a method and a machine for cleaning objects having the general form of plates, such as screen printing stencils, which can be soiled with residues of average density, notably of density of the order of 1, and/or with solid residues of high density, notably of density not less than 1, and/or with residues of low density, notably of density less than 1, and this under economical conditions compatible with an industrial use, and allowing to separate at least residues of low density.
More particularly, the invention aims to allow to automatically separate residues according to their density, after indifferently successive or alternative treatments of a number of different pieces soiled with residues of any density. Particularly, the invention aims to allow to alternatively treat pieces soiled with residues of low density and with residues of high density, such as screen printing stencils soiled with solder pastes (including fluxes of low density and metal alloy particles of high density), and pieces soiled with residues of average density such as screen printing stencils soiled with glue (residue of average density), and to separate these different residues according to their density at the time of each treatment, without maintenance between two treatments of distinct pieces.
The invention aims thus to allow to treat successively or alternatively pieces soiled with various residues (indifferently of low, high or average density), without any waiting time between pieces.
Particularly, the invention aims to allow to avoid to realize the distinct subsequent steps consisting in rinsing and separating residues, and permanently renewing the used cleansing composition.
The invention aims also to provide a method and a machine which has a low cost-investment, is simple and economical to use and provides a high cleansing efficiency. Particularly, the invention aims to enable a complete treatment (cleansing and drying) with a treatment time less than 1 hour, notably of the order of 0.5 hour, per object.
The invention aims to enable to clean any kind of objects, included fragile objects, such as stencils for self-tensioning frames, soiled with various very resistant residues adhering to the object such as metal particles (solder alloys), solder fluxes, fats, adhesives (epoxy glues, adhesives for CMS, . . . ).
For so doing, the invention relates to a method for cleaning objects having the general form of plates, such as screen printing stencils susceptible of being soiled with residues of average density such as adhesive particles, and/or with solid residues of high density such as metal particles, and/or with residues of low density such as solder fluxes or fats, in which at least one object to be cleaned is immersed in a vessel, so-called treating vessel, filled with a liquid cleansing composition, at least one of vertical walls of the treating vessel, so-called overflow wall, being adapted to form an overflow container into a second adjacent vessel, so-called overflow vessel, the overflow wall being common to the treating vessel and the overflow vessel, at least one flow Q
1
of cleansing composition is continuously extracted from the treating vessel and reintroduced into the treating vessel after a passage through filtering means for filtering residues, and a flow Q
2
of cleansing composition is continuously extracted from the overflow vessel and reintroduced into the treating vessel after a passage through filtering means for filtering residues, characterized in that:
it is used a cleansing composition formed of a liquid azeotropic solution of a density at least substantially equal to the density of residues of average density, adapted to loose residues from the object without solubilizing them,
at least one object is placed vertically into a treating vessel adapted to have at least substantially vertical walls, so-called vertical longitudinal walls, spaced by a distance less than 10cm, from the main faces, dis
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