US 3806405 A
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April 23, 1974 A. P. L. HEIDWEILLER 3,306,405
METHOD OF APPLYING A BINDER TO A WET"LAID FIBROUS WLB Original Filed Sept. 8. 1969 ATTCIRN EYS United States Patent Int. Cl. D21d 3/00 US. Cl. 162-186 8 Claims ABSTRACT OF THE DISCLOSURE Fibrous webs are made by bringing loose synthetic, organic or inorganic fibers, in the form of a suspension but without a binder, on to a moving porous carrier, and passing the fibers through a binder dispersion on the same carrier in covered condition. Preferably, the fibers are sandwiched between two porous belts and so run through a tank containing binder dispersion.
This is a continuation of application Ser. No. 856,118, filed Sept. 8, 1969, now abandoned.
This invention relates to a method of, and apparatus for, producing fibrous webs, which comprises bringing loose synthetic organic or inorganic fibers, or mixtures thereof in the form of a suspension in water or in a watermiscible solvent on a porous, moving carrier, providing the fibers with a binder, removing the Water or solvent from the carrier, and drying the resulting moist fibrous web.
There are many known processes for producing fibrous webs by the wet method. In most cases, a homogeneous suspension ofsynthetic, organic, or inorganic fibers and the binder in water is applied to a porous carrier, the water is withdrawn by suction, followed by drying, whereafter the fibrous web thus formed is removed from the carrier. The disadvantage of this process is that a high percentage of the binder is withdrawn and removed along with the water. Consequently, either the amount of binder which is left in the web is insufficient, or a large excess is used, in which latter case the great losses in binder represent a considerable cost item. Moreover, it is impossible to transfer the impregnated, Wet web in a self-supporting manner from the carrier on which it is de-watered to a next carrier which carries the web through the dry ing and hardening furnace, since the webs coherence and strength are insufficient for the purpose. To remedy this drawback, it would of course be possible to carry out impregnation, drying and hardening on one and the same porous belt. This, however, has the drawback that when the carrier or belt becomes fouled with binder, this can no longer be removed in a simple way after it has dried and hardened. In this way various pores of the carrier become clogged. During the next cycle of the carrier no de-watering takes place at these clogged positions, so that no fibers are deposited either. This results in thin spots or holes in the ready web.
3,806,405 Patented Apr. 23, 1974 ICC According to the invention, the fiber suspension is brought on to a moving, porous carrier without a binder, and passed through a binder dispersion on the same carrier in covered condition, whereafter the fiber suspension, soaked with binder, is freed of excess binder dispersion while still being on the same carrier, and ultimately dried separately from the carrier in separate drying apparatus.
The advantage of the subject method is that a homogeneous distribution of the binder throughout the fibers is ensured, without incurring the risk that the homogeneous layer of loose fibers is deformed, or inhomogeneities arise due to clogging of the pores of the carrier.
The fact that satisfactory fibrous webs can be produced in this way is more or less surprising, because it was unexpectable that, without drying and possibly hardening the binder, the web would be sutficiently self-supporting for it to be taken over by the moving belt of the drying apparatus without being damaged.
In a preferred embodiment of the invention, the carrier with the fiber suspension, into the binder dispersion in more or less tensioned conditioned around a roller while being covered with a belt passed between the roller and the layer of fibers. This belt need not be driven separately, but is adequately taken along by the moving carrier for it to run fully along with the latter.
Because of the fact that, in rounding the roller, the fiber suspension or layer of fibers is compressed between the carrier and the belt, the quantity of water or solvent that may still be present is largely squeezed out of the layer of fibers; since this compression is soon released again, the binder dispersion is subsequently absorbed into the suspension or layer of fibers.
This embodiment has been found to be very satisfactory in practice. This was by no means obvious, for the two belts necessarily have a difference in velocity in rounding the roller in the binder dispersion (owing to the difference in length of trajectory) so that the suspension or layer of fibers between the belt is subjected to shearing forces. Unexpectedly, however, a web thus produced turned out to be extremely free of blemishes and of excellent strength.
Preferred organic synthetic fibers are polyamide and polyester fibers, but fibers of other kinds of polymers may be used. Suitable inorganic fibers are glass and asbestos fibers. In addition, mixtures of the fibers mentioned may be used.
The suspension medium for the fibers is preferably water, but water-miscible solvents may be used. The same applies to the dispersing agent for the binder. Examples of organic solvents are ethylene glycol, propylene glycol, methyl and ethyl Cellosolve, as well as dimethyl formamide.
As for the binder, any binder dispersible in water or in water-miscible solvents, and which imparts sufiicient coherent strength to the web after drying will be suFable for the purposes of the invention. If the binder is soluble in the dispersing agent used, the binder dispersions have the form of solutions, otherwise of emulsions or suspensions. Examples of soluble binders are: starch, starch derivatives, cellulose derivatives, phenolformaldehyde condensates, condensates of formaldehyde with amino compounds, polyamides, and many others, so long as they are soluble in water or in water-miscible solvents. Examples of the binder emulsions are latices of elastomers, such as butadiene-styrene copolymers.
If so desired, two or more binders may be used. In that case the suspension or layer of fibers is passed through two or more binder dispersions, in covered condition in the manner indicated, with intermediate extraction between the stages.
The carrier may be made of the porous materials, which in paper making machines are used for the so-called copper cloth. Preferably a carrier of synthetic material is used. The covering belt is preferably made of a similar porous material.
The diameter of the roller in the binder dispersion ranges from to 60 cm. If the diameter is unduly large, the webs formed will show inhomogeneities, first of a minor nature, and later more marked.
Suitable apparatus for carryig out the method according to the invention comprises an endless porous belt running over a number of rollers, means for supplying the fiber suspension, a plurality of suction devices, one or more tanks for binder dispersion including a substantially horizontal rotary roller therein, below which runs the belt carrying the fiber suspension or layer of fibers, a second belt running over a plurality of rollers and passing between said rotary roller in the binder solution and the first belt carrying the fiber suspension or layer of fibers, and a washing device which frees the first belt from residues of binder and fibers.
One embodiment of the apparatus according to the invention will :be described by way of example with reference to the accompanying diagrammatic drawing, which shows a vertical, longitudinal view of the apparatus.
Referring to the drawing, 1 is an endless porous belt web or screen, for example, as used in paper machines, passed over rollers 2, 3, 4 and 5. A dispenser for the fiber suspension is designated by 6, while 7 and 8 represent suction devices for removing as much excess of water or solvent and binder dispersion as possible. A belt or web 9 runs over rollers 10 and 11 and, just as the belt 1, under roller 12. in a tank 13 filled with binder dispersion. Washing devices 14 and 15 are provided for washing the two belts clean of binder.
In operation, the belt 1 rotates over rollers 2, 3, 4, 5, 16, 17 and, under a certain tension, around roller 12. At this latter point, the belt 1 acts as a means for driving the belt 9, passed between the belt 1 and the roller -12. A suspension of the desired fibers, for example, polyamide and/or glass fibers, is sprayed on to the belt 1 through the dispenser 6. This suspension is partly de-watered by the suction device 7, for example, down to a dry content of about 40%. Then the upper surface of the partly de-watered suspension, which at this point is not yet self-supporting, is contacted by the belt 9. The tripartite assembly: belt 1,
the partly de-watered suspension, which has here adopted the character of a layer of fibers, and the belt 9, next runs through the binder dispersion in the tank 13, around the roller 12, and back upwardly, where a suction device 8, provided with a small roller 16, provides for the belt 1 and the binder-containing layer of fibers to be released from the belt 9. The belt 9 runs via roller 10, washing device 15, and roller 11 back to the point where it comes again into contact with the partly de-watered fiber suspension on the belt 1.
The belt 1 with the binder-containing layer of fibers is freed from binder dispersion as much as possible by the suction device 8, whereafter the belt is passed via rollers 4 and 5, washing device 14, and rollers 2 and 3 back to the feeding device 6. The most web formed after the passage of the suction device 8 is taken from the belt 1 in selfsupporting condition at the roller 4, and transported further by a belt 18 circulating through drying apparatus, in
which the web is heat treated to dryness and the binder is possibly hardened.
In order that the squeezing and absorbing elfect occurring around the roller 12 be as great as possible, the downcomings and the rising part of the belt 9 are preferably disposed at an acute angle relative to each other. A minimum value is 10, however. Also, it is recommendable that the two belts 1 and 9 are not firmly pressed together for the entire length that they are in contact with each other. It is better to have the two belts converge in the downcoming part from about 5 mm. to practically 0, and diverge in the rising part back to about 5 mm. In this way it is achieved that the binder is properly and highly homogeneously distributed over the fibers.
As defined in the claims the phrase in-going path portion refers to the portion 20 of the webs 1, 9, the phrase out-going path portion refers to the portion 21 of the webs 1, 9, and the phrase apex path portion refers to the portion 22 of the webs 1, 9 partially entrained about the roller 12. More specifically, the apex path portion is that portion of the Web 9 from its first contact with the roller 12 to a point at which it loses contact with the roller 12.
The above apparatus affords continuous and undistributed production of a fibrous web for a week or longer. The product is homogeneously provided with binder, and shows no holes or other inhomogenieties even after operation for many days. The most widely dilferent kinds of fibers and binders can be used. Finally, the apparatus is subject the minimum wear, because residues of binder are removed from the belts while still in moist and/or unhardened condition.
1. In a method of making fibrous Webs comprising the steps of admixin loose fibers in a liquid to form a suspen sion, depositing the suspension on a moving porous carrier, conveying the liquid-fiber suspension along an acute angle path of travel defined by in-going and out-going path portions joined together by an apex path portion, said apex path portion being immersed in a liquid binder, compressing the liquid-fiber suspension prior to its immersion into the liquid binder and during its immersion in the liquid binder while moving along said in-going path portion at least to said apex path portion, reducing the compression of the liquid-fiber suspension While moving along said out-going path portion when both in and out of the liquid binder whereby the liquid-fiber suspension is at least partially deliquified during its movement along the in-going path portion and the thereafter deliquified liquidfiber suspension expands during movement along the outgoing path creating a suction effect to draw thereinto the liquid binder, the improvement comprising confining the liquid-fiber suspension between porous moving webs during the conveying thereof along said acute angle path of travel, performing the compressing step by converging the webs along the in-going path portion, and later performing the reducing step by diverging the webs during movement thereof along the out-going path portion.
2. The method as defined in claim 1 including the step of partially dewatering the liquid-fiber suspension prior to movement thereof along said in-going path portion.
3. The method as defined in claim 1 wherein said apex path portion is in part defined by a roller totally immersed in said liquid binder about which said webs are at least partially entrained.
4. The method as defined in claim 1 including the step of partially dewatering the liquid-fiber suspension after movement thereof along said out-going path portion.
5. The method as defined in claim 1 wherein one of said porous moving webs is of a generally triangular configuration having two path ,portions disposed at an angle corresponding to the acute angle defined by the ingoing and out-going path portions, and said last-mentioned web includes another portion between said in-going and out-going path portions remote from said apex path portion along which a cleaning step is performed during the movement of the last-mentioned web.
6. The method as defined in claim 3 including the step of partially dewatering the liquid fiber suspension prior to movement thereof along said in-going path portion.
7. The method as defined in claim 3 including the step of partially dewatering the liquid fiber suspension after movement thereof along said out-going path portion.
8. The method as defined in claim 3 wherein one of said porous moving webs is of a generally triangular configuration having two path portions disposed at an angle corresponding to the acute angle defined by the in-going and out-going path portions, and said last-mentioned web includes another portion between said in-going and outgoing path portions remote from said apex path portion along which a cleaning step is performed during the movement of the last-mentioned web.
References Cited UNITED STATES PATENTS 7/1961 Krumsiek, Jr., et a1.
162165 X 2,104,052 '1/ 1938 Novak 162-265 ROBERT L. LINDSAY, 111., Primary Examiner W. F. SMITH, Assistant Examiner US. Cl. X.R.