Method of producing a felted porous polychloroprene latex foam

Abstract: A method of felting porous polychloroprene latex foam to obtain desired properties. Such felting renders the finished foam suitable for controlled ink flow required for printing purposes. The felting is accomplished by reducing the volume of the porous polychloroprene latex foam and heating at a temperature of 400° to 460°F for five to ten minutes.

Description: This invention relates to a method of producing a felted porous polychloroprene latex foam, which may be used in an inking member. In the printing industry, there are generally two types of inks, dispersion inks and solution inks. Dispersion inks have been widely used throughout the years because they more easily can be formulated. The primary disadvantage of dispersion inks is that their components tend to settle and, as a result, the inks must be agitated on occasion. Although solution inks do not have a settling problem, they are more difficult to produce. Recently, strides have been made in the capability of producing solution inks, but such inks have been found to be incompatible with the systems that are used to apply such inks. For example, in the print head of a postage meter, an inking pad or roller, hereafter collectively referred to as an inking member, will contact the print head to transfer ink thereto and the inking member will be removed from the print head so that the inked print head can contact a mailpiece to print an indicia. There are also two general types of inking members, rechargeable inking members and self containing inking members. In developing solution inks, it has been found that inking members that are acceptable for use with dispersion inks simply are not efficient when used with solution inks. This is because inking members suitable for dispersion inks have pores that are too large. Such large pore sizes are required to allow dispersed particles to be distributed through the inking member. Additionally, typical inking members for dispersion inks were found to be incompatible with polyglycols, a component of contemporary solution inks. Consequently, it has become evident that if the benefits offered by solution inks are to be realized, inking members must be developed that will enhance the use of such inks. From US-A- 5,006,404 a replaceable ink pad which is capable of supplying ink in excess of 5,000 printing cycles is known. The pad includes a bottom layer that serves as an ink reservoir and is made of porous melamine foam that has a pore size of 140 to 180 µm. The melamine foam was felted by compressing with heat of 260 °C to 288 °C for a period of approximately five minutes and subjected to pressure to provide the necessary resiliency to recover from printing impacts with a printing dye and to assure the required amount of ink is released with each printing cycle. The pressure was created by reducing the thickness of the pad by approximately 1/3. A top layer is attached to the bottom layer by a fusible adhesive. An adhesive that has been found to be particularly useful is porous polyamide 0,2 mm thick, density of 20 g/ m² and a melting temperature of 112 to 120 °C. The web adhesive which allows the ink to flow and is compatible with ink is heat activated. The heat activation can be accomplished by either having the pad in an oven or in a press at 310 °C to 315 °C for three minutes. The top layer is foam material with relatively small pores such as polyethylene with a pore size of 10 to 20 µm that serves to dispense ink to a print dye by which it is contacted. The pad will have ink supplied thereto by a conventional manner. A rechargeable printing member has been formulated that is compatible with solution inks. The ink member consists of three layers: a first layer of microporous polyethylene that contacts a print head to transfer ink thereto, a second layer of fusible web adhesive, and a third layer of felted porous polychloroprene latex foam which serves as a reservoir layer for ink. With such an inking member, one obtains high quality indicia printing, excellent compatibility with solution inks, durability, and a high edge acuity. Having the layer of porous polychloroprene latex foam felted was thought to offer particular advantages; however, no prior method of felting such a material was known. In fact, felting of polychloroprene was deemed to be unavailable because of the high resiliency and lack of compression set. For this reason, a method was developed for felting porous polychloroprene latex foam which involves placing the material under pressure then heating between 400 to 460°F. (204 to 238°C) for a period of five to ten minutes. The invention will be better understood from the following non-limiting description of an example thereof given with reference to the accompanying drawings, in which:- Figure 1 is a perspective, partially exploded view of an inking member made in accordance with an example of the invention and the environment in which such an inking member is used; Figure 2 is a plan view of the inking member shown in Figure 1 taken along the lines 2-2; Figure 3 is a cross sectional view of the inking member shown in Figure 1; and Figure 4 is a cross sectioned view of a portion of an apparatus used to felt foam materials. A portion of an inking system in which the present invention can be used is shown generally at 10. It includes an inking member 12. A tray 14 receives the inking member as will be described in greater detail hereafter. Inking systems 10 of the type in which the invention can be practiced are generally known, see for example U.S. Patent No. 4,945,831, and will, therefore, not be described in detail. Although the invention is described as it applies to an inking pad, it will be appreciated that the invention applies equally as well as to inking rollers without departing from the invention and the term inking member is intended to include inking pads, inking rollers or any other convenient forms. The tray 14 has an ink distribution chamber 16 that has a plurality of laterally extending ribs 18 that form channels 20 therebetween. The tray 14 has an inlet nozzle 22 having a central opening 24 that is confluent with the ink distribution chamber 16 whereby ink can be supplied to the chamber by attaching a tube (not shown) to the nozzle 22 with the tube being attached to an ink supply (not shown). Optionally, an outlet ink nozzle 28 can be supplied to the tray 14 with the outlet ink nozzle having a central opening 30 therein that is confluent with the ink distribution chamber 16. A tube (not shown) can be attached to the outlet nozzle 28 thereby allowing ink to be circulated through the ink distribution chamber 16. Also, with the presence of the inlet nozzle 22 and outlet nozzle 28 the ink distribution chamber can be cleaned with any appropriate cleaning fluid as required. A pair of arms 34 located and attached to opposite ends of the tray 14 provides support for movement of the tray. A plate 38 having a central opening 40 therein is attached to the tray 14 and the central opening forms a part of the ink distribution chamber 16. A frame 41 is formed at the inner perimeter of the plate 38 and overhangs the ink distribution chamber 16 so that a portion of the inking member 12 is received between the frame and the chamber whereas the central portion of the inking member is exposed. Much of what has been shown and described thus far has been disclosed in U.S. Patent No. 4,945,831, which also discloses an inker module in which an inking member 12 according to the invention can be used. The manner in which the ink distribution chamber 16 is supplied ink and the manner in which the ink member 12 contacts a print head is described in U.S. Patent No. 4,945,831 and will not be described herein as the same does not form part of the present invention. The inking member 12 includes a first, or lower porous, layer 42 (Fig. 3), an upper, or second, porous layer 44 and an adhesive 46 therebetween to secure the first layer to the second layer. The adhesive 46 is applied in the form of filaments that accumulate and cross over one another to form openings between the filaments. The thusly applied adhesive 46 creates a random non-woven opening pattern that allows free flow of ink from the first layer 42 that serves as an ink reservoir to the second layer 44 that serves as a metering member. It will be noted that the first layer 42 is somewhat larger than the second layer 44 and that the frame 41 fits over the exposed portion of the first layer 42 and the second layer 44 is received in the opening 40 when the inking member 12 is received within the ink distribution chamber 16. The first, or lower, layer 42 is preferably made of porous, also referred to as open cell, polychloroprene latex foam material having a pore size of 200 to 500 microns and serves as a reservoir of ink. Preferably, the polychloroprene latex foam material is felted and a manner in which it can be felted will be described hereinafter. The adhesive material that binds the two layers 42, 44 is a fusible web adhesive such as polyamide that is available from Freudenberg Nonwovens, Limited Partnership of Germany under the trade name PELLON. The second layer is a microporous sintered polyethylene having a pore size of about 10 to 20 microns. This second layer serves to meter ink to a print head upon contact therewith. The inking member 12 was made in the following manner. To achieve the right balance between resilience, conformance and re-inking ability, the polychloroprene latex foam layer 42 was felted 2:1. Since felting had not been performed on this type of material previously, felting conditions were developed using a high temperature press shown generally at 46, available from Pasadena Hydraulics Inc., Model No. 950R18122S. The essential elements of a high temperature press is shown in Figure 4 and includes an upper movable platen 50 which is attached to a piston 48 and a lower stationary platen 52. A source of heat 56 is provided in the form of resistive heating to heat the platens 50, 52 with foam material 60 to be felted located between the upper platen 50 and lower platen 52. A shim 54 is shown located on the lower platen 52. A number of important parameters had to be considered when determining processing conditions and feasibility of felting. Included in the variables were initial foam 60 thickness, shim 54 thickness for control of pressure, felting ratio, initial density, press temperature and time. A foam of an initial thickness 60 was placed in the press and shims selected that would achieve the final felting ratio. Pressure was applied to the foam 60 with the initial thickness until contact was made between the upper platen 50 and the shim 54 resulting in the foam of reduced volume 60d. For example, for a felting ratio of 2:1 and a finished polychloroprene thickness of 0.145" (about 3.7 mm), a press temperature of 400-425°F (204-218°C), a time of 5-10 minutes, shim thickness of 0.15-0.140" (3.8 to 3.6 mm) and a pressure between 11,000 and 13,000lbs/in², (75.8 to 89.6 k Pa), with a foam starting thickness of 0.29" (7.4 mm.) was found advantageous. For higher felting ratios, higher press temperatures or pre-heating are useful, but it should be noted that volume reduction is paramount in determining the degree of felting. Shim thickness depends on the desired felting ratio as well as final pad thickness. The amount of felting achieved is proportional to the reduction of volume of the foam 60. If a 2:1 felting ratio is desired, the foam 60 originally placed in the press 46 will have its volume reduced by one half with heat applied for the periods above given. The felting of the polychloroprene open celled foam materials directly reduced the effect of pore size as well as increased the compression strength of the elastomeric foam material. As printing tests subsequently showed, by felting the bottom layer 42, the inking member 12 conformance was improved along with compressibility and ink pooling. Once a felted layer 42 of the proper dimension was produced, the same was laminated to the second layer 44. The goal of lamination is to assure intimate contact between the top layer 44 and the bottom layer 42 without impeding ink flow. Thus, an open web type of material was chosen. For example, a polyamide adhesive can be used to heat laminate the polychloroprene latex felted layer 42 to the polyethylene layer 44. A press temperature of 248°F (120°C) for a period of 3 minutes using appropriate shims is effective for lamination. The temperature for laminating can vary from 220 to 270°F (104 to 132°C) and the time can vary from 2 to 4 minutes and the pressure can vary between 4,500 and 5,500 lbs/in² (31027 to 37923 Pa). An inking member having a top layer 44 made of polyethylene foam, a bottom layer of porous polychloroprene latex foam and a fusible web adhesive for connecting the two has been shown to be quite advantageous. As opposed to prior materials, such as those discussed in U.S. Patent No. 4,945,831, superior inking properties were achieved with solution inks. The inking member 12 as disclosed herein yielded an estimated operating life of 1 to 2 years and a printing life cycle of 500,000 to one million when used with a solution ink. With a foam inking member made of polychloroprene, the volume of swell was found to be 1% as opposed to 5.9% for prior materials. In addition superior print quality was achieved that directly correlates to the smoothness of the surface of the top layer 44 in which pore size is a factor. The smooth top surface provides excellent undistorted ink transfer to the printing plate it contacts for subsequent transfer of ink to paper. In addition, for the purpose of constant print intensity over continuous printing cycles, a dual layer composite must be used which combines a small pore size metering surface 44 and an open pore size storage layer 42 for long term continuous printing. Good results can be accomplished with the arrangement disclosed. Attention is directed to U.S. patent number 5,136,968. The attention of the reader is also drawn to our EP-A-0,545,599 of the same priority date which contains subject matter also disclosed in this application.

Claims: A method of making a rechargeable inking member comprising the steps of: a) producing a first inking layer by placing a layer of open cell polychloroprene latex foam in a press, b) felting the first inking layer by reducing the volume of the first inking layer and subjecting it to a pressure of 11,000 to 13,000 lb/in² (75845 to 89635 Pa), and heating the first inking layer to a temperature of 400-425°F (204 to 218°C) for 5 to 10 minutes, c) removing the first inking layer from the press, and d) attaching the first inking layer to a second inking layer. The method of claim 1 wherein the step of attaching the first layer to the second layer is carried out by applying a polyamide between the first and second layers and heating at a temperature of 220 to 270°F (104 to 132°C) for a period of 2 to 4 minutes under a pressure of 4,500 to 5,500 lbs/in² (31027 to 37923 Pa). A method of felting open cell polychloroprene latex foam, comprising the steps of: a) placing a quantity of open cell polychloroprene latex foam in a press, b) reducing the volume of the open cell polychloroprene latex foam, c) heating the open cell polychloroprene latex foam to a temperature of about 400 to 425°F (204 to 218°C) for 5 to 10 minutes, and d) removing the open cell polychloroprene latex foam from the press. The method of claim 3 wherein the volume of the open cell polychloroprene latex foam is reduced by one half in step (b). An inking pad, comprising: a) a first layer of felted polychloroprene latex foam having a pore size of 200 to 500 microns, b) a second layer of mirco-porous sintered polyethylene having a pore size of 10 to 20 microns in registration with said first layer, and c) means for attaching said first layer to said second layer. The inking pad of claim 5 wherein said means for securing said first layer to said second layer is a polyimide adhesive. The inking pad of claim 6 wherein said means for securing said first layer to said second layer is a polyamide adhesive. An inking member when produced by a method according to claim 1 or 2. A latex foam when produced by a method according to claim 3 or 4.

Inventors: TERRY BETTY R, TERRY, BETTY R.
Applicants: PITNEY BOWES INC, PITNEY BOWES INC.
Application year: 1992
Main classification: B41N1
IPC codes: B41N7, B29C44, C08J9