Title:
Method of forming liquid reservoirs
United States Patent 3895133


Abstract:
A precisely dimensioned liquid reservoir is formed by selecting an open-celled, porous form material, saturating the foam with a suitable liquid and thereafter cutting or shaping the foam into the particular form required.



Inventors:
Fleisig, David H. (Walnut Creek, CA)
Anderson, James D. (Kensington, CA)
Goop, Rune E. (Moraga, CA)
Application Number:
05/352913
Publication Date:
07/15/1975
Filing Date:
04/20/1973
Assignee:
FIBREBOARD CORPORATION
Primary Class:
Other Classes:
83/22, 141/20.5, 401/196, 427/289
International Classes:
B43K8/03; C08J9/36; C08J9/40; (IPC1-7): B44D1/06
Field of Search:
117/4,98,119,138.8D 26
View Patent Images:



Primary Examiner:
Fritsch, Daniel J.
Attorney, Agent or Firm:
Beck, Robert A.
Claims:
What is claimed is

1. A method for making an accurately dimensioned liquid reservoir comprising the steps of

2. The method of claim 1 further comprising the steps of

3. The method of claim 1 wherein said foam material is saturated with ink.

4. The method of claim 3 wherein said open celled, porous foam material is a compressed polyurethane foam.

5. The method of claim 3 wherein said cutting step comprises cutting from said saturated foam material a cylindrical ink roller having a longitudinal passage therethrough and suitable for mounting and use in an ink marking device.

Description:
BACKGROUND

The advent of individual item price marking in supermarkets has created a need for devices to mark such items quickly and economically. This need has been filled by the development of price markers which are now marketed by several companies. The typical price marker uses a roll of paper tape with adhesive on one side, a set of indicia wheels and an ink reservoir, conventionally in the form of a roller. In operation, the indicia wheels are set for the proper marking, usually the item price. Upon triggering the marker, these indicia pass over the roller to pick up a film of ink and then print it on the paper tape which is then ejected, cut off and pressed into adherence with the article to be marked.

The primary problem with these markers is in the ink reservoirs, or rollers. These rollers must be accurately dimensioned so that good contact is made with the indicia, should contain sufficient ink for several thousand impressions before replacement is required, but most hold the ink so that it will pass to the surface in quantities suitable for inking the indicia but not in quantities which will exude from the roller. Further, such rollers must not deform during continued use, and since replacement is required, must be reasonable in price. Rollers available on the market at the time of this invention were deficient in one or more of these criteria, while such rollers or other liquid reservoirs made by the methods described herein overcome these deficiencies.

PRIOR ART

A typical prior art method applicable to forming ink reservoirs of this type is disclosed in U.S. Pat. No. 2,777,824 in which such reservoirs may be formed by foaming a resin in a mold with ink or marking fluid added thereto prior to foaming and incorporated into the reservoir during the formation process. This process requires individual molds to form the reservoirs and since the resin must be foamed and cured in the mold, a large number of molds are required to mass produce such reservoirs. Further, it has been found that when this type of reservoir is in the form of an ink roller, it shrinks as the ink within it is used. Thus, as the ink supply is used up, contact between the marking indicia and the roller is gradually lost, the marks become indistinct and the roller must be replaced.

A second prior art method involves foaming and curing an open cell resin in molds approximately the size of the required roller or reservoir, removing the roller from the mold, milling the roller to the prescribed size and then saturating it with ink. As can be seen, this method is slow and laborious. A further problem arises in that saturation of such foams with liquids may cause expansion of the foam, and thus the rollers must be originally milled undersize to compensate for this expansion, creating problems in accuracy of the final dimensions of the rollers.

In addition, efforts to cut individual rollers or other shapes of reservoirs from dry foam and thereafter saturate such rollers with ink or the like have failed for several reasons. First, such dry foams are extremely difficult to cut by conventional means since friction with the cutting blades tends to rip and tear the foam apart. Further, in those instances where the cutting is successfully completed, heat created by the cutting friction fuses many of the cell openings and destroys the ability of the foam to permit migration of the ink or other liquid therethrough. Another serious problem arises with respect to those few rollers which can be successfully formed from the dry foam. When such rollers are saturated they may expand in volume up to as much as 20%, and this expansion is not always uniform. Thus, formation of accurately dimensioned saturated rollers by this method is virtually impossible.

It is therefore an object of the invention to provide a method for forming an accurately dimensioned reservoir made of open-celled foam containing a substantial amount of liquid which may be removed from the reservoir in thin films on objects brought into contact with the reservoir, and which will remain dimensionally stable during removal of the liquid.

It is a further object to provide a method for forming an ink roller for use in printing or marking devices or the like, said roller formed by saturating an open-celled piece of foam with ink and thereafter cutting rollers out of the saturated foam, such rollers being accurately dimensioned and capable of giving thousands of printing impressions throughout the course of which the roller remains dimensionally stable.

It is a further object to provide a method for accurately controlling the amount of ink or other liquid in such open-celled reservoir or roller.

SUMMARY OF THE INVENTION

In its broadest aspect, the invention comprises selection of a suitable open-celled foam material, saturating pieces of the foam with a liquid and, thereafter, cutting individual liquid reservoirs from the foam. In one adaptation, the liquid may be a combination of a volatile solvent with a relatively non-volatile liquid and, after saturation, suitable means may be used to remove the volatile solvent leaving a reservoir containing a controlled amount of the relatively non-volatile liquid.

PREFERRED EMBODIMENTS

Although it may be used to make numerous types of liquid reservoirs, this invention is particularly suited to the manufacture of ink rollers for use in price markers, postage meters, computer printout devices and the like. These rollers are normally cylindrical in shape with a hollow passageway through the center. In use, the rollers are rotatably mounted within the marking device upon a shaft so that marking indicia may contact the outer surface of the roller to pick up a film of ink which is thereafter deposited on a paper tape which, in turn, is ejected from the device and attached to the article to be marked.

As hereinbefore noted, these rollers must be accurately dimensioned. If rollers are too large or too small the marking indicia will pick up either too much or too little ink, resulting in blurred or indistinct printing.

The foam used to form the rollers must be open-celled; that is, it must be such that passages exist throughout the foam so that the ink may flow to the roller surface from the interior, from cell to cell. Further, the cell size must be large enough to permit uninterrupted flow yet small enough so that the ink will be retained without exudation. In practice, it has been discovered that a wide range of cell sizes may be used, depending in part on the viscosity of the ink involved and whether or not the ink is pigmented. With pigmented inks, the cell size must be large enough so that individual pigment particles will not plug the cells and block passage of ink. For highly viscous or pigmented inks, cell size may be as large as 0.4 mm. in diameter, or about 4,000 cells per square inch of surface area of the roller. For relatively thin, unpigmented inks, cell sizes may be as small as 0.09 mm. in diameter, or about 80,000 cells per square inch.

A preferred foam for use in forming ink rollers by this method is a compressed, open-celled polyurethane foam manufactured by Scott Paper Company and sold under the tradename "SCOTT FELT." This material has a density in the range 30 to 40 pounds per cubic foot, a hardness of about 30 when measured on the Shore B Durometer, and has about 8,100 cells per square inch of surface area. The material is normally available in large sheets of 52 inches by 72 inches and of varying thicknesses.

The preferred inks for use in this method are those based on high boiling oils, plasticizers, high boiling glycols, glycol ethers or similar materials, although more conventional inks may be used if they are suitable for the end use desired.

To practice the method, the foam must first be saturated with the liquid involved. A preferred way to saturate the foam is by exposing the foam to the liquid in a vacuum. A quantity of ink substantially in excess of that required to saturate the foam is placed in a vacuum chamber. A sheet of Scott Felt is placed within the chamber in contact with the ink. The chamber is then closed and a vacuum of about 28 inches of mercury is applied. After about 30 minutes, the vacuum is released and the foam, now saturated with ink is removed from the chamber. At saturation this material will have absorbed an amount of ink equal to about 300% of its original weight. Further, during saturation, the foam may expand substantially. Although such expansion is not uniform from sheet to sheet of foam, it may amount to as much as a 20% increase in volume. It is believed that saturation with certain liquid relieves stresses originally created when the foam is formed to cause this expansion.

When removed from the vacuum chamber, the saturated sheets are ready to be cut into individual ink rollers. Cutting of the rollers may be accomplished by any suitable means but the preferred method is by use of conventional cylindrical cutters, well known in the art. Such cutters comprise an inner cylindrical knife blade and an exterior cylindrical knife blade. The interior blade forms the passageway through the interior of the roller while the exterior blade forms the outer surface of the roller. In operation, the cutter is mounted in a drill press or the like with the saturated sheet of foam beneath it. The cutter is then set into rotation and lowered to and through the foam, cutting out the precisely dimensioned cylindrical roller which is then ready for use in a suitable marking device.

It is apparent that the liquid retained in the foam tends to lubricate the cutting blades and thus prevents tearing of the foam, so that individual rollers may be cut out in this fashion without substantial losses from defective cutting. Ink rollers made by the above method have furnished over 50,000 impressions in price markers without exhaustion of the ink supply or substantial change in dimension of the rollers.

In certain applications it has been found that a roller fully saturated with ink is "overloaded" and it is preferred to have a smaller, controlled amount of ink present therein. This can be accomplished by a second embodiment of the method wherein prior to saturation of the foam, the ink is mixed with a calculated amount of volatile solvent. After saturation the volatile solvent may be removed by any suitable means. If a highly volatile solvent is used, removal may be accomplished by exposure to the air and consequent evaporation. In instances where less volatile solvents are used, a heat source may be required. As an example, to form a reservoir or roller which contains 70% of its saturated capacity of ink or the like, a mixture is made of 70% ink and 30% volatile solvent, the foam is saturated with this mixture and the solvent is then removed as noted above. Rollers formed from this foam will contain the requisite amount of ink. The solvent may be removed either before or after cutting of the individual rollers, as desired.

As can be readily comprehended from the above, this method may be applied to form accurately dimensioned liquid reservoirs of other shapes than cylindrical rollers and for other liquids than ink. Virtually any desired shape is possible. Other liquids which might be used are lubricants, perfumes, unguents and the like. In each instance the reservoir will deliver thousands of impressions of the liquid on a contacting surface without substantial change in the volume of the reservoir.