Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-06-01
2001-01-09
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S210000, C156S472000
Reexamination Certificate
active
06171427
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the manufacturing of corrugated paperboard, and more particularly to the use of steam injection to allow higher production speeds without sacrificing adhesive bonding quality.
BACKGROUND OF THE INVENTION
In the manufacturing of corrugated paperboard, a single facer apparatus is used to flute the medium web, to apply adhesive (e.g. starch adhesives) to the flute tips on one of the faces of the medium web, and to bring a liner web into contact with glue lines on the flute tips of the medium web with the application of heat downstream to form the initial bond. Many manufacturers in the art use high-pressure (e.g. 20,000 lbs. of force) at the bonding nip where the liner web is introduced to the flute tips on the medium web. Others use less pressure at the bonding nip. The assignee of this application produces a single facer in which the liner roll introducing the liner web to the fluted medium web is spaced apart from the fluted surface of the bonding roll. The present invention involves the use of steam injection at the convergence of the webs to improve the formation of adhesive bonds between the liner web and the flute tips on the medium web, especially at relatively high production speeds (e.g. 1300 feet per minute). It is particularly useful on single facers that do not have a high pressure bonding nip.
When applied to the flute tips on the medium web, the starch adhesive consists of a slurry of starch granules in water (e.g. an aqueous-based starch adhesive). In order to achieve optimum bond strength, it is desirable that the water and starch granule slurry first gelatinize into a viscous gel. In order to gelatinize the starch adhesive, the adhesive slurry must be heated to a temperature of at least 150° F. for a sufficient amount of time. It is therefore known in the art to preheat the liner web to promote gelatinization of the adhesive, preferably to about 180° to 212° F. The viscous gel does not have significant bond strength until dehydration occurs. However, if dehydration occurs prematurely before gelatinization, the resulting bond will be poor.
It is important that the initial green bonds formed on the single facer between the liner web and the flute tips of the medium web have sufficient strength to withstand further processing downstream in the corrugator. Although green bond formation begins immediately at about 200° F., substantial dehydration of the glue line and adjoining web surfaces must occur before adequate green bond strength is realized. The medium web is heated on the bonding roll preferably to about 215° F. to facilitate dehydration and formation of the green bond. In order to achieve sufficient heat transfer, the bonding roll surface temperature should be at about 375° F. or more. As more heat is added to evaporate moisture, the bond strength continues to increase. A fully cured bond is finally obtained when most of the water is evaporated (e.g. approximately 80%).
As production speed increases, exposure times for gelatinization and green bond formation are proportionally reduced at the same time that the level of mechanical stress imposed on the freshly bonded corrugated web are increased. Heretofore, it has been difficult to increase production speeds above, for example, 1,000 feet per minute without sacrificing bond quality.
SUMMARY OF THE INVENTION
The invention promotes high speed corrugator production without sacrificing adhesive quality by injecting a steam cloud between the fluted medium web on a single facer bonding roll and the liner web directly at the line along which the webs converge. The direct application of the steam cloud provides additional heat to the glue lines on the flute tips without causing premature dehydration to facilitate appropriate gelatinization of the adhesive, and also promote sufficient green bond formation between the flute tips on the medium web and the liner web as the composite single face web is carried downstream on the bonding roll. Steam injection is a particularly effective means for additional heat because of the latent heat associated with the phase change of steam upon condensation. In addition, injected steam heating can be controlled virtually instantaneously.
The invention is preferably implemented using an elongated steam shower tube that extends generally parallel with the bonding roll and the liner roll. The elongated tube has a plurality of aligned steam discharge openings configured to produce a steam cloud that is directed at the line at which the webs converge. Preferably, the aligned steam discharge holes are located approximately 2 to 3 inches from the convergence line, thus allowing the steam cloud discharged from the aligned openings to be accurately directed at the convergence line. It has been found that applying the steam upstream of the convergence line significantly deteriorates the strength of the resulting green bond.
In many applications of the invention, it may be particularly desirable that the steam cloud consist of dry steam. Dry steam is steam in which the ratio by weight of water vapor in the steam to the combination of water vapor and suspended liquid droplets together is substantially high. By applying dry steam, excess moisture (which is present in wet steam from suspended liquid droplets) does not need to evaporate in order to achieve sufficient dehydration for initial green bond formation.
The preferred construction for a dry steam shower includes an elongated outer tube that receives the steam from the steam source, and an inner tube mounted within the outer tube. The inner tube includes steam inlet openings to allow the flow of steam into the inner tube. The dimensions of the steam inlet openings is limited, however, to restrict the flow of steam into the inner tube such that the steam pressure within the inner tube is lower than the steam pressure in the outer tube. The inner tube contains the aligned steam discharge openings that are directed at the web convergence line. In the embodiment shown in the drawings, the aligned steam discharge openings on the inner tube are exposed through a slot on the outer tube. The temperature of the steam within the inner tube is lower than the temperature of the steam within the outer tube because the pressure of the steam within the inner tube is lower than the pressure of the steam within the outer tube. The steam within the outer tube therefore heats the wall of the inner tube to a temperature greater than the temperature of the steam located within the inner tube. Because the wall of the inner tube has a temperature greater than the temperature of the steam within the inner tube, little or no condensation occurs within the inner tube and the amount of suspended liquid droplets in steam discharged from the shower is insignificant.
In another aspect, it is preferred that steam shower have an outlet that is located downstream of the aligned steam discharge openings. A normally closed valve is located at the outlet which is closed during normal operation so that steam flows through the aligned steam discharge openings. Upon system start-up, the valve is opened such that steam provided to the tube clears the tube of condensed water. This is important upon start-up so that a slug of condensed water does not blast against the webs and tear or otherwise damage the webs.
In the preferred embodiment of the invention, the liner roll does not apply pressure against the bonding roll at the convergence of the two webs. Such a single facer is disclosed in U.S. patent application Ser. No. 08/740,726, by Carl Marschke, filed on Nov. 1, 1996, and entitled “Low Pressure Single Facer” (See, e.g., page 10). However, the invention is likely to be useful in single facers having a low-pressure bonding nip or other configurations in which additional heat at the web convergence line are desired. In some aspects, the invention may be useful to promote bonding on other corrugator components, such as injecting dry steam on a double backer.
Subsequent to the web convergence line on the bonding roll, the liner web
Hess David W.
Hoyer Gale G.
Kornuth Keith R.
Marschke Carl R.
Andrus Sceales, Starke & Sawall
Ball Michael W.
Marquip Inc.
Piazza Gladys
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