Asphalt Laminates

When two sheets of Kraft paper are bonded together by a layer of asphalt, a packaging barrier is produced which has considerable strength and also excellent resistance to both moisture and moisture vapor. Asphalt, how­

ever, is a complex mixture of lighter oils and heavy waxes and insoluble resins. Under normal use in paper laminates, there is a gradual migration of the oily constituents of the asphalt through the paper to the outside.

This not only causes a considerable discoloration and unsightly appearance, but may contaminate an article next to it. As shown in Fig. 80, FC-805

FI G . 8 0 . Asphalt laminated seed corn bag. Bag on right has outer ply treated with F C - 8 0 5 ; bag on left has untreated kraft.

is used commercially for asphalt laminates to prevent the asphalt bleed.

In this case the fluorocarbon size is applied to one side of the paper as indicated earlier. In the manufacture of the laminate, the paper is laminated so as to apply the asphalt to the untreated side. As we have seen from earlier considerations, this one-sided treatment is effective in giving good adhesion to the asphalt and yet preventing the migration of the oils against the

FI G . 8 1 . S h o w s resistance of F C - 8 0 5 treated paper to asphalt bleed. Sample on left is treated with F C - 8 0 5 at 0 . 2 5 wt % ; one on left is untreated. Both were exposed to 1 2 5 ° C for 1 hr.

"wettability gradient.'' Such asphalt laminates are not only more useful at room temperatures, but also maintain freedom from staining even at elevated temperatures or in the presence of oily materials. Figure 81 shows an example of treated and untreated laminates which have been exposed for one hr at 125°C.

2. Waxed Papers and Boards

Large quantities of paraffin and microcrystalline waxes are used to coat paper to provide a moisture vapor barrier and also to give resistance to liquid water. Such coated products find extensive use in such items as bread wraps, frozen food packages, bakery boards, and the like. In addition, it is common practice in many package constructions, where moisture

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vapor barrier is required, to laminate two sheets of paper or a sheet of paper and a sheet of paper board together using a layer of mierocrystalline wax. Fluorocarbon treatments, such as FC-805, have been used quite extensively in conjunction with these molten wax coatings to prevent unnecessary wax penetration and yet permit the wax to form a continuous smooth film with good anchorage. Generally, it has been found advan­

tageous to use a one-sided treatment for maximum opacity. The molten wax is generally applied to the treated side. Besides the reduction in the absorption of the molten wax into the paper and hence, a saving, it is also possible to retain the opacity of the sheet. Figure 82 shows how the opacity of a bleached kraft treated with FC-805 and with no filler remains the same as the unwaxed sheet. On the other hand a normal waxed sheet must be filled with a titanium pigment to the extent of 5% to retain even 69%

of the original opacity; while the unfilled sheet retains only 45% of its original opacity.

3. Carbonizing Tissues

In the modern business world, in fact, in everyday living, the role of paper in transmitting information is extremely vital. Not only do the elec­

tronic computers grind out enormous volumes of data, many copies of which must be circulated, but the modern secretary is required to make many copies of information for general circulation. One of the growing uses for paper has been one-time carbon papers which are used to repro­

duce copies of the original impression at the same time the original is made. To maximize the number of copies which can be made, this paper must be as thin as possible, yet relatively strong. They must also resist penetration by the hot molten carbon dope which is coated on one side since the other side must be free of this dope. The application of fluorocarbon sizing, such as FC-805, to such sheets permits the application of the dope without strike-through, even when the sheet is very thin and relatively porous, thus effecting superior performance at lower cost than with conventional highly beaten and rather expensive carbonizing grades.

4. Polyethylene Laminates

Perhaps one of the most interesting developments involving these fluorocarbon sized papers is their use in the combination with polyethylene.

Large quantities of polyethylene coated papers are used for a variety of packaging problems where the strength and formability characteristics of the paper or paper board, combined with the moisture vapor and liquid barrier characteristics of the polyethylene, offer an excellent packaging material. In general, these combinations have been restricted to uses where

• 1 FIG. 82. Shows resistance to wax penetration by FC-805 treated paper, as measured by opacity retention. Sample on left is untreated paper; sample in middle is a paper containing TiC>2, and sample on right has been treated with 0.20% FC-805.

440 H. G. BRYCE

they are free from excessive exposure to oily or greasy materials. When the polyethylene coating is applied to paper, on the untreated side, and a fluorocarbon sizing is applied to the opposite side, a construction results which has excellent resistance to penetration of a wide variety of oils, greases, etc. The data in Table XLVI I illustrates this point quite clearly;

T A B L E X L V I I

whereas neither the FC-805 treatment alone, nor the polyethylene film of even 2 mils is effective for any long period of time in resisting the pene­

tration of the oils, the combination of 1/2 mil of polyethylene combined with 0.25 wt % solids of FC-805 achieves a very high level of resistance to oils and greases, even when folded or creased.

5. Corrugated Cartons

Treatment of either the inside or the outside liner of a corrugated carton has been found to greatly increase the serviceability of corrugated cartons. In particular, such cartons have given excellent performance in the packaging of many greasy items such as binder twine, spare parts, sweeping compound, etc.

It is anticipated that besides the present commercial usages described above, there will be many more uses for these fluorocarbon sizings.