EP0551346B1

EP0551346B1 - Apparatus for washing-down serigraphical frames and filterpart for the apparatus

Info

Publication number: EP0551346B1
Application number: EP91917383A
Authority: EP
Inventors: Claus Hjorth Madsen
Original assignee: Cps - Chemical Products & Services AS; Cps Chem Prod & Service
Current assignee: Cps - Chemical Products & Services AS
Priority date: 1990-10-01
Filing date: 1991-09-30
Publication date: 1997-12-03
Anticipated expiration: 2011-09-30
Also published as: DE69128355T2; DK0551346T3; ATE160728T1; EP0551346A1; DK236390D0; WO1992005961A1; DE69128355D1

Abstract

Apparatus for washing-down serigraphical frames by means of a cleaning liquid comprises a sink-like tank unit (1) having V or U shaped ends, in which unit the serigraphical frames are placed, a scavenging hose (11) with affixed brush (12), a filter section (3, 4), a circulation pump (10), a sludge discharge system (7) and a recirculation system for liquid. The filter section comprises a filter tray (3) having V or U shaped cross-sections and a loosely fitted removable filter mat (4) of a chemically resistant material, preferably a polyester coated glass fibre material or polypropylene, with optimum surface. The collected sludge is discharged at intervals through the bottom (5) of the tank unit, the used cleaning liquid is recirculated continuously after filtration and added with fresh cleaning liquid. The apparatus is equipped with a double-acting suction system for vapours from the cleaning liquid and involves substantial advantages to the working environment.

Description

The present invention relates to an apparatus for washing-down serigraphical frames by means of a cleaning liquid, the apparatus comprising a sink-like tank unit having V or U shaped ends, in which tank unit the serigraphical frames are placed, a scavenging hose with affixed brush, a filter section, a circulation pump, a sludge discharge system and a recirculation system for filtered cleaning liquid. The apparatus according to the invention is characterized in what is stated in the characterizing portion of claim 1.
In US-A-4 808 237 there is disclosed a method of cleaning a silk screen including the steps of: providing a cleaning cabinet having an open front; supporting a removable silk screen in said cabinet; providing a water supply system; and spraying through said silk screen in said cabinet through said open front with solely water only from said system, essentially free of soaps, detergents, and hydrocarbons, as a water spray under pressure from 2700 to 3300 psi to thereby remove from said silk screen contaminants including inks, dyes and emulsions whereby said contaminants flow to a drain structure operatively connected to said cabinet.
Cleaning-off printing inks or serigraphical dyes from stencils, printing plates, serigraphical frames, rollers or the like has for many years been performed by means of cleaning liquids either containing substances which according to the definitions of the National Agency of Environmental Protection must be classified "hazardous substances" or containing low-boiling aromatic solvents. Such cleaning liquids involve considerable health hazards to the persons working with the liquids.
Recently the applicant has developed a group of efficient and versatile cleaning liquids for the serigraphical industry. The liquids, which do not contain hazardous substances, have proved to be at least as efficient as the cleaning liquids previously used, and they are significantly less health hazardous.
A group of similar cleaning liquids, which additionally may contain as much as 25% (v/v) highboiling aromatic compounds, has also been developed by the applicant. These liquids are also at least as efficient as the cleaning liquids previously used and considerably less health hazardous.
Even though these newly developed groups of cleaning liquids have made possible a considerable - and much needed - improvement of the working environment within the serigraphical industry, there is still need for further improvements, not least because washing-down serigraphical frames is traditionally performed manually with entailing large risk of breathing-in vapours from the cleaning liquids.
Consequently, it is an object of the present invention to provide an apparatus for washing-down serigraphical frames, which apparatus in particular is suited for use together with the abovementioned newly developed cleaning liquids with reduced health hazard. An efficient washing-down apparatus of the kind in question will be able to further lower this health hazard.
This is achieved with the apparatus according to the invention which is characterized in what is stated in the characterizing portion of claim 1.
In the following the apparatus according to the invention will be described in more detail, reference being made to the drawing in which

Fig. 1: is a schematical diagram illustrating the construction of the apparatus according to the invention; and
Fig. 2 and 3: show in detail the construction of the apparatus according to a preferred embodiment.

The present apparatus comprises a tank unit (1), having in its longitudinal direction a "crib-like" shape with V or U shaped end faces. At the top of the tank there is mounted a lid (2) being weakly V shaped (e.g. 160°). At the bottom of the V shape the lid is provided with a row of holes, so that liquid may drain down along the entire length of the lid.
The washed-down cleaning liquid from the washing process drains through the row of holes down onto the centre of a similar underlying V or U shaped filter tray (3) (sieve filter). On the filter tray a loose filter mat (4) has been rolled out, which mat is easily removable.
After filtration of the liquid through the filter (4) the liquid drains to the lower part of the tank from where it is discharged through the liquid outlet (14) and recirculated for renewed use.
In the lowermost V or U shaped tip (6) of the tank which e.g. forms an angle of 60° a pumping-out system (7) for sludge is provided along the entire length of the tank. This system, which can be dismantled in view of cleaning the apparatus, comprises a suction pipe positioned in the longitudinal direction and having downwardly directed suction holes or an angle section positioned on support means with its tip pointing upwardly, and with two suction gaps in the bottom of the tank unit which gaps are adjusted according to the sludge thickness. The pipe or the angle section are preferably positioned at a distance of 4-8 mm from the sides and bottom of the tank.
The apparatus according to the invention operates in accordance with two setting possibilities:

(1) Recirculation/operation setting
(2) Pumping-out of sludge/emptying

The two setting possibilities are controlled by two ball valves (8,9). A circulation pump (10) is inserted between the ball valves, which are of the three-way-type. Activation of the ball valves can be automatized.
When the apparatus has been set for operation by means of the two valves, the filtered cleaning liquid is recirculated, as described above, and passed through the hose (11) out into the brush (12) which is used manually for the washing-down frames.
For sludge discharge the two ball valves are activated to the second setting possibility whereby the sludge settled in the tank is discharged by means of the circulation pump into the tank unit (13) for destruction.
The apparatus according to the invention is provided with a double-acting suction system for efficient removal of solvent vapours. The systems operates simultaneously according to an air curtain principle in front and a rim suction principle at the back.
The air curtain is provided by means of a blow-system with a plurality of holes positioned in the front edge of the sink. A correspondingly wide suction gap provided in the upper front edge of the apparatus ensures the required venting.
The rim suction of the apparatus functions by means of a suction duct provided in the rear wall, which duct encircles the light face positioned in the rear wall for illuminating the serigraphical frames. This double-acting suction system has proved to give an optimum degree of efficiency, as the air curtain in an efficient way supplements the rim suction. The latter is very efficient along the circumference of the light face, but not as efficient in the centre thereof. This lacking effect can be fully compensated for by the air curtain which at the same time shields the operator from solvent vapours during the washing-down process.
During the washing-down process the air curtain is thus only intersected by the tube or handle carrying the brush with which the washing-down is performed.
Fig. 2 is a perspective sketch of the appearance of the apparatus according to a typical embodiment. Typically, the apparatus has a width of about 2.7 m, a depth of 0.8 m and a height of 2.2 m, but these dimensions are only intended for guidance, as the apparatus may of course be dimensioned according to need. A and B show blowing-in and vent providing the air curtain.
The removable filter employed in the apparatus according to the invention is primarily of a chemically resistant fibre type, preferably a special chemically resistant glass fibre type, and secondarily a polypropylene filter cloth. Both types have surprisingly been found to be able to retain an optimum surface throughout the entire calculated life. Hereby large uniform through-flow velocity can be obtained without dirt cloggings.
The primary filter type which has proved to be particularly suited for the object of the invention, is supplied by the German company Glaswerk Sculler GmbH, Wertheim/Main. The filter is called "C-Glas-Vlies für Spezialbereiche, type S 5041 Sac 50/2-S-H6" and weighs as much as 100 g per m². This filter type has been developed for completely different purposes than the one intended according to the invention, viz. for use as reinforcement tissue, in particular in the boat industry, and for special air filtration purposes.
The basis material is a woven glass fibre material provided with a special polyester coating. This special combination of materials exhibits large durability and is well suited for filtration of both the cleaning liquids described above and strongly alkaline water-based solvents (pH 13 and above).
The secondary filter type which has proved suited for the purpose, is supplied from the American company Consler Corporation, Homeoye Falls, New York. It is a polypropylene sheet filtration material with pore sizes of as much as 100 µm. The filter type has been developed for use in the supplier's own production of filter cartridges and for this purpose it is delivered from the factory in rolls for sheet cutting. The material has not previously been used for filtration purposes of the kind to which the present invention relates.
The polypropylene cloth is woven from 100% clean polypropylene fibres. Such a filter exhibits long durability and is also well suited for filtration of both the cleaning liquids mentioned and strongly alkaline water-based solvents (pH 13 and above).
As is seen from Fig. 3, the filter unit retains its effect at a continous filling from the V shaped tip of the filter towards the sides. Hereby a long life is obtained.
According to a preferred embodiment the filter is supplied in a carton along with a polyethylene disposal bag, a closing strip and throw-away gloves. The used (sludge filled) filter is rolled up and placed in the disposal bag together with the throw-away gloves used when removing the filter. The bag is closed, put into the carton and sent for destruction. When the new filter has been positioned in the filter section of the apparatus the apparatus is ready again for operation.
The oils, resins and particles which are dissolved in the cleaning liquid when the apparatus is in operation and having a particle size of less than 5 µm, slowly precipitate along the inclined, smooth side walls of the tank and form a sludge-containing substance which at intervals (e.g. weekly) is pumped out and destructed.
As regards environment and safety the "layer-divided" drain, filtration and chemical sump provide a number of secondary advantages:
The drain holes in the lid (2) and the underlying sealing of the sieve-filter (3) make evaporations from the sump during standstill minimal. During standstill any evaporation from the chemical sump must thus pass both filter mat and lid with row of holes. This provides a braking effect as regards emission of vapours.
In the uppermost front edge of the washing chamber there may additionally be provided a "roller curtain" with a special coating, which curtain after finished washing-down is rolled down. The remaining vapours will subsequently - according to the rim suction principle - be passed towards the suction ducts situated at the back, which ducts are connected to a central suction apparatus.
By the apparatus according to the invention it has become possible to a very significant extent to eliminate the emission of vapours from the solvent to the surroundings, so that the staff performing washing-down of serigraphical frames by means of the apparatus, essentially avoid breathing in the vapours. As the staff at the same time avoid physical contact with the cleaning liquids - both when pumping out sludge and during the washing process - the users of the apparatus gain very substantial advantages in their working environment.

Claims

Apparatus for washing-down serigraphical frames by means of a cleaning liquid, the apparatus comprising a sink-like tank unit (1) having V or U shaped end faces, above which tank unit the serigraphical frames are placed, a scavenging hose (11) with affixed brush (12), a filter section (3 and 4), a circulation pump (10), a sludge discharge system (7, 8, 10 and 9) and a recirculation system for liquid (14, 8, 10, 9, 11 and 12), characterized in that the filter section comprises a filter tray (3) having a V or U shaped cross-section with a loosely fitted removable filter mat (4) of a chemically resistant material, that the sludge discharge system consists of means (7, 8, 10 and 9) for intermittent discharge of the collected sludge through the bottom of the tank unit, that the recirculation system for liquid consists of means (14, 8, 10, 9, 11 and 12) for continuous recirculation during operation of the used cleaning liquid after filtration, and that the apparatus further comprises
- means for addition of fresh cleaning liquid; and

- a suction system for removal of vapours from the cleaning liquid comprising a system acting according to an air curtain principle arranged at the front side facing the operator and a system acting according to a rim suction principle arranged at the opposite back side.
Apparatus according to claim 1, characterized in that the chemically resistant material is a glass fibre material.
Apparatus according to claim 2, characterized in that the glass fibre material is a woven material weighing as much as 100 g/m², preferably 50 g/m², and that it is provided with a polyester coating.
Apparatus according to claim 1, characterized in that the chemically resistant material is polypropylene having a pore size of as much as 100 µm.
Apparatus according to claim 1, characterized in that the sludge discharge system (7, 8, 10 and 9) comprises a pumping-out system (7) for sludge which is positioned at the bottom of the tank unit (1) and comprises a suction pipe positioned in the longitudinal direction and having downwardly directed holes or an angle section positioned on support means with its tip pointing upwardly, and with two suction gaps in the bottom of the tank unit which gaps are adjusted according to the sludge thickness.