US 3681115 A
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United States Patent 01 Patented Aug. 1, 1972 lice ABSTRACT OF THE DISCLOSURE An improved process for hot pressing molded pulp items which comprises applying an aqueous emulsion of silicone oil to moisten a portion of the surface of a pulp molded item which is subsequently hot pressed. The concentration of silicone in the emulsion is at least about 0.0025% by weight. The process reduces the amount of foreign deposit build-up on the press molds normally associated with hot pressing operations.
BACKGROUND OF THE INVENTION Field of the invention The invention relates to improvements in the manufacture of molded pulp items and more particularly to the improvements of hot pressing operations by applying to the surface of the molded pulp item, which is to undergo hot pressing, a dilute aqueous emulsion containing an additive prior to pressing to thereby reduce sticking, buildup of foreign deposits on the finished portion of the pressed mold, and reduce the shutdown time associated with the process as practiced in the prior art.
Description of the prior art The hot pressing operation as it is customarily practiced in the molded paper pulp industry, involves the formation and drying of molded pulp items by conventional processing and thereafter moistening a portion of the item on which a finished surface is desired with water, followed by passing the item through a hot press in which one of the mold portions have heated smooth or shiny finish, which by virtue of the pressing or ironing operation, is imparted to the moistened portion of the molded pulp structure.
It is well known that molded pulp items have a generally rough surface texture which is not especially suitable for printing and furthermore, do not have the attractive smooth finish which the commercial and consumer markets require for this type of product. For example, in the field of molded pulp egg cartons, especially the type of carton known as a 2 x 6 egg carton, a container is provided which has cavities in the lower portion of the container for holding two rows of six eggs each. The cover for the container is connected to the bottom by means of an integrally formed hinge and conventionally has a smooth top surface having a substantial portion thereof planar and which is customarily used for printing the name of the food packager.
The use of water alone as a moistening agent for those portions of the molded pulp carton or other items which undergo hot pressing, results in some transfer of deposits of foreign materials from the pulp item to the smooth finished portion of the mold used in hot pressing operations. The smooth part of the mold is customarily made of metal, and is usually chrome plated and highly polished. The non-finished portion of the mold used in this operation is frequently made of dissimilar materials, and since it contacts a non-moistened portion of the carton, does not present any particular problem of build-up of foreign deposits which are associated with the smooth portion of the mold. The deposits which contain alum, rosin, wax, and other additives, are the result of a solubilization of components of the pulp composition which then transfer by virtue of the moisture from the pulp material to the mold surface. The foreign deposits as indicated above, result in sticking of the molded items in the hot press with consequent damage to the molded item, result in frequent shutdowns for cleaning, cause corrosion and produce imperfect surfaces. In the industry, it has not been uncommon to require cleaning at three hour intervals with a consequent shutdown and substantial loss of production time.
SUMMARY OF THE INVENTION The present invention comprises an improved process for hot pressing of molded pulp items which comprises applying a dilute aqueous emulsion of a silicone oil to a portion of the rough formed surface of the pulp molded item, and thereafter hot pressing the moistened surface.
The concentration of the silicone oil in the aqueous emulsion ranges upwards from at least about 0.0025 by weight to 2%. Amounts above 2% can also be used but no economic advantage is derived thereby. A preferred concentration of the silicone oil in the aqueous emulsion is from about .0075% to about 1%.
The emulsion is applied to the portion of the carton or pulp molded unit by means of spraying of the item to moisten the surface, it being understood that the portion of the surface to which the silicone emulsion is applied is that which is intended to undergo the hot pressing operation. Other means such as roll coating or the like, can also be used. The hot pressing occurs on a production basis generally immediately after the spraying, since the molded pulp items prior to treatment have been through the conventional drying operation. It is necessary that the hot pressing occur while the moisture from the spraying remains on the pulp surface to achieve the desired ironing or smoothing effect.
The amount of the silicone fluid deposited on the surface of the pulp molded item to be hot pressed is not critical, however, it is preferred that the same be applied at a rate of from about 0.003 to 0.100 ounce per 1,000 square feet.
The process of the invention is preferable to hot pressing operations in which the finish or pressed portion of the molded item is obtained by the use of a highly finished or polished mold portion usually of chrome plated metal and having a smooth finish usually of polished chromium or similar alloy. The other portion of the mold used in the hot pressing operation is usually of a material which does not have a surface specially prepared to produce a smooth finish on the pressed item.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the present invention is most preferably applied to the hot pressing operation of egg cartons, and more particularly, to the hot pressing of the cover portions of 2 x 6 molded pulp egg cartons. In the most preferred form, the silicone material used is a dimethyl siloxane, represented by the structural formula:
wherein R and R are selected from the group consisting of aryl and lower alkyl. The lower alkyl groups preferably contain up to about 4 carbon atoms and methyl is the most preferred. The polymeric silicone material, of course, can be of variable molecular weight, but generally speaking, the integer n may have values from 83 to 2100 to produce silicones having viscosities of above about 50 centistokes and preferably from 10,000 to 100,000 centistokes. The characteristics of the silicone oil polymer notwithstanding the particular substituents which are employed in the silicone polymer precursor are desirably such as to provide a film which (a) is capable of wetting the metal in the mold to form a continuous relatively adherent film; (b) will withstand the heat and pressure conditions encountered during hot pressing operations; will be generally physically inert with respect to the dies and die surfaces; and (d) will not adversely effect the printability of the carton cover.
Conventionally, the emulsion is prepared using a nonionic emulsified, such as for example, trimethyl nonyl polyethylene glycol ethers which are sold under the trade name of Tergitol TMN (Union Carbide) or polyoxyethylene lauryl ethers sold under the trade names BRIJ 30 and 35 (Atlas Chemical). The following specific example will illustrate specific embodiments of the process of the present invention.
EXAMPLE An aqueous silicone oil emulsion having the trade designation LE 463, manufactured by Union Carbide, was diluted with from its original 35% concentration to a concentration of 0.346%. This dilute silicone oil emulsion was conveyed by means of mixing pumps and blended with water to produce a silicone emulsion spray at the spray head having a silicone oil concentration of about 0.0075
A fine spray of the diluted silicone emulsion was applied in a manner so as to moisten the total cover portion and the hinge area of a 2 x 6 molded pulp egg carton which was then passed through the hot pressing operation wherein the cover was hot pressed in a mold; the female portion of said mold was formed of chrome plated metal and the male portion of plastic. The following tables will illustrate the run time, the amount of time down for cleaning, and the percentage of production time lost for cleaning. For comparison purposes, a conventional water spray technique wherein water was sprayed on the carton surfaces instead of silicone is also shown.
TABLE II.HOT PRESS TRIALS-RUN NO. 2
Silicone Conditions spray Water spray Term of observation 30 hrs..." 29 hrs. 30 mins. No. of die c1eanings 9 Total time required for clear tin Non Percent production time loss for cleaning," 0. 00 7. 45
From the foregoing examples, it is readily apparent that the use of silicone oil emulsions on a treatment of molded pulp items in hot pressing operations results in very substantial savings in down time required for cleaning as compared to conventional hot pressing operations using water as the moistening agent. In the comparative runs described in Tables I and II above, the percentage of production time lost for cleaning in the water spray process is substantial. It should also be noted that in the runs of Table 11 using the silicone spray process, the cleaning of the mold surface did not require wire brushing but only water spray, indicating that the deposits formed were only lightly adhered to the mold surface.
What is claimed is:
1. An improved process for hot pressing the outer surface of a dried molded pulp container having a rough surface texture to provide a smooth printable surface thereon, said container having a substantially planar surface thereon, which comprises moistening a rough formed surface of the molded pulp container by spraying of an aqueous emulsion of silicone polymer oil having a strucwherein R and R are selected from the group consisting of aryl and lower alkyl containing up to about 4 carbon atoms and n having a value from 83 to 2100 on said surface, wherein the emulsion has a silicone polymer concentration of at least 0.025%, said silicone polymer having a viscosity of from about to about 100,000 centistokes, said emulsion being applied to the surface at a rate of from about 0.003 to 0.100 ounce of silicone polymer solids per 1000 square feet; and hot pressing the moistened portion in a die to impart a smooth surface thereto.
2. A process according to claim 1, wherein the emulsion has a silicone oil concentration of from about 0.0075 to about 1% by weight.
3. A process according to claim 1, wherein the silicone is a dimethyl polysiloxane.
References Cited UNITED STATES PATENTS 3,014,833 12/1961 Lee 11764 R 2,819,184 1/1958 Smith et al. 11764 R 2,950,502 8/1960 Weaver 11764 R 3,505,097 4/1970 Ratcliffe 11764 R 2,745,233 5/1956 Collings et a1. ll7-l39.5 A 3,190,791 6/1965 Potter 162-224 3,373,079 3/1968 Eastman et a1 162-224 3,468,755 9/1969 Culp 16 --224 WILLIAM D. MARTIN, Primary Examiner 5 W. R. TRENOR, Assistant Examiner US. Cl. X.R.
11764 C, 65.2, 139.5 A, R; 162-224