US 3622423 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent Inventor Thomas A. Hadley Hendersonville, N.C.
Appl. No. 30,842
Filed Apr. 22, 1970 Patented Nov. 23, I971 Assignee Kimberly-Clark Corporation Neenah, Wis.
PROCESS OF FORMING A REINFORCED NONWOVEN LAMINATE CONTAINING PLASTISOL ADHESIVE 10 Claims, 3 Drawing Figs.
US. Cl 156/309, 156/313, 156/324, 161/143, 161/156, 161/251 Int. Cl C09j 5/06 Field of Search 156/309,
 References Cited UNITED STATES PATENTS 3,186,889 6/1965 Boldrini etal. 161/251 X 3,249,482 5/1966 Gilfillan 1 161/251 X 3,327,708 6/1967 Sokolowski 161/143 X 3,536,563 10/1970 Brandts et a1 156/309 X Primar y Examiner-Reuben Epstein Allorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.
ABSTRACT: A process is described for forming a nonwoven laminate having outer plies of cellulose wadding and an inner reinforcing means having disposed on either side thereof a plastisol adhesive. Plastisol penetration into the cellulose wadding webs as well as plastisol fusion is accomplished by passing the laminate over the peripheral surface of a drum heated to a temperature above the fusion point of the plastisol adhesive, and subjecting the laminate to calendering while it is in contact with the heated drum.
PROCESS OF FORMING A REINFORCED NONWOVEN LAMINATE CONTAINING PLASTISOL ADHESIVE DESCRIPTION OF THE INVENTION Nonwoven materials are finding increasing use in applications where conventional woven fabrics have heretofore been employed. Such applications include wearing apparel, upholstery, bed sheets, pillow cases, and the like. A particularly useful class of nonwoven materials, contain creped cellulose wadding (i.e., tissue) as a primary constituent. The wadding is inexpensive, generally opaque, and has a fabric like hand." Thus, fabrics based on such nonwovens are inexpensive and pleasing in appearance and feel.
While the wadding has many desirable features, when used by itself it does not have sufficient strength for most applications. Thus, it has been the practice to reinforce the wadding with a nonwoven reinforcing means. Nonwoven reinforcing means which are generally used include scrims (i.e., cross sets of threads bonded at their points of intersection as described in Hirschy U.S. Pat. No. 2,841,202), drafted webs of staple length fibers such as described in Sokolowski U.S. Pat. No. 3,327,708, carded fiber webs and webs comprised of a plurality of randomly arranged, substantially continuous thermoplastic filaments such as described in Kinney U.S. Pat. Nos. 3,341,374 and 3,338,992. In use the nonwoven reinforcing means is generally between plies of cellulose wadding with at least one ply of wadding on either side of the reinforcing means. Preferred structures, especially when scrims are employed as the reinforcing means, include two plies of light weight wadding (e.g., each having dryer (i.e., before creping) basis weight of less than about g./yd. on either side of the scrim reinforcing means.
In the preparation of nonwoven material as above described, the. use of plastisol adhesives has been found to be particularly desirable in securing lamination of the reinforcing means to the wadding plies. The plastisol adhesive is easy to apply and is flexible, thus it does not adversely affect the characteristics of the material. Also, plastisols are inexpensrve.
As ordinarily accomplished, the plastisol adhesive is placed on the nonwoven reinforcing, means, usually on both sides, and then the wadding webs are brought into contact with the reinforcing means. Thereafter, the laminate is passed over a series of heated cans in order to fuse the plastisol adhesive, after which the laminate is passed through heated calenders in order to achieve plastisol penetration into all of the wadding lies.
p In order to achieve proper penetration, it has been the practice to use two separate heated calenders with opposite sides of the wadding successively in contact with the heated roll. Due to the temperature-viscosity characteristics of a plastisol it has been considered necessary to both fuse the plastisol prior to calendering and use two separate calendering operations. Moreover, heating during calendering is necessary in order to have the fused adhesive at a viscosity at which it will flow. The use of two separate heated calenders is necessary in order to achieve about the same penetration on both sides of the laminate since the fused adhesive will always flow more easily in the direction of the heated roll. While the use of such a procedure yields nonwoven materials which do not delaminate (evidencing good adhesive penetration) and are attractive (evidencing the absence of adhesive strike through"), it would be desirable to accomplish such without the use of multiple independent heating means for fusing and/or calendering.
Accordingly, it is a principal object of the present invention to provide a simplified method for preparing nonwoven materials as above described wherein fusing of the plastisol adhesive as well as securing ply attachment in the laminate can be accomplished with only a single-heating means.
A further object is to provide such a method which can be accomplished at high speeds and, thus, economically.
Other objects and advantages of the present invention will become apparent upon reading the following detailed description and with reference to the attached drawings in which:
FIG. 1 illustrates an embodiment of a laminate useful herein;
FIG. 2 illustrates an embodiment of a manner in which the present method can be accomplished; and
FIG. 3 illustrates the viscosityH-temperature characteristics of a plastisol adhesive.
While the invention is susceptible of various modifications and alternative constructions, there is shown in the drawings and will herein be described in detail the preferred embodiments. It is to be understood, however, that it is not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.
Briefly, the process herein described involves the formation of a nonwoven laminate having outer plies of cellulose wadding and an inner reinforcing means having disposed on at least one surface thereof a plastisol adhesive. Plastisol penetration into the cellulose wadding webs as well as plastisol fusion is accomplished by passing the laminate over the peripheral surface of a drum heated to a temperature above the fusion point of the plastisol adhesive, and subjecting the laminate to calendering while it is in contact with the heated drum. By appropriately selecting the points of calendering as well as the degree of calendering at each point, plastisol fusion and a desirable degree of adhesive penetration can be achieved with the heated drum being the only heat source. Such is accomplished by employing the unusual viscosity-temperature characteristics of a plastisol adhesive in a unique way.
Turning now to the drawings, FIG. 1 illustrates a type of nonwoven material which can be prepared according to the process described herein. As shown, the material is a laminate 10 having two plies of cellulose wadding 12-18 on either side of a nonwoven scrim 20 having warp threads 21 and fill threads 23. Prior to forming the laminate 10, the scrim 20 has had applied to each of its surfaces a plastisol adhesive in an amount of about 3-10 g./yd. and, preferably, 4-6 g./yd.
In order to prepare a useful material from the laminate it is necessary that the plastisol adhesive applied to either side of the scrim 20 be caused to completely penetrate through the inner wadding layers 14 and 16 and into, but not through, the outer wadding layers 12 and 18. Such penetration is necessary in order to provide the nonwoven material with sufficient delamination resistance. Penetration through the outer layers 12 and 18, Le, strike through, is undesirable since such results in a material which is unattractive in appearance. Moreover, in order to be useful as an adhesive, the plastisol must be fused.
Referring to FIG. 2, appropriate plastisol penetration and fusion can be achieved by passing the laminate 10 over the adjustable prewrap roll 22 and into contact with the surface of a heated drum 24. Penetration of the plastisol adhesive into the upper layers of cellulose wadding (i.e., those layers on the side of the reinforcing means not next to the heated drum) is achieved by passing laminate 10 through the nip formed between the drum 24 and the calender roll 26. Plastisol penetration into the lower layers of cellulose wadding is achieved by passing the laminate through the nip formed between the drum 24 and the calender roll 28. Plastisol fusion is achieved while the laminate is in contact with the drum 24 at some point between its passage through the above mentioned two pins.
The position of the two nips described above is important in aCI-Iieving the advantages of the present process and, in order to better appreciate this, reference is directed to FIG. 3 which shows the general viscosity behavior of the plastisol adhesive as a function of temperature. As is evident, viscosity of the plastisol increases as temperature is increased from a point A up to a point C. Thereafter, the viscosity decreases as temperature is increased. Point C is designated as the fusion point of the plastisol and, as discussed in TAPPI 50, 7OA-84A, fusion corresponds to that state in which the plastisol exists as a continuous plastic phase. Prior to fusion, the plastisol is either a two phase system of resin particles distributed on plasticizer (termed the fluid state and designated as the region A to B in FIG. 3) or a discontinuous number of resin particles swelled with plasticizer (termed the gel state and designated as the region B to C in FIG. 3).
Ordinarily gelling occurs at about 140-220 F. with the plastisol having a viscosity of about 1O"10 centipoise. Fusion occurs at about 280-350 F. at a viscosity of about -10 centipoise. The gel point for a particular plastisol can be determined by the hot bench test method described in Plastics Technology Oct. 1960, pp. 43-47. The dotted line in FIG. 3 illustrates the viscosity-temperature characteristics of another plastisol. As is evident, this plastisol fuses faster than the one previously discussed, i.e., fusion can be obtained with a smaller temperature increase. Plasticizer selection can be used to establish an appropriate fusion rate. Vinyl chloride plastisols which contain vinyl chloride polymers or copolymers and organic phthalate, sebacate, adipate, or phosphate plasticizers are particularly suitable. In addition, useful plastisols can contain solvents or thinners in amounts up to about percent.
With respect to the present discussion, the important thing to note is that so long as the plastisol is either fluid or gel, an increase in temperature will result in an increase in viscosity. On the other hand, once the plastisol has been fused, a temperature increase results in a viscosity decrease. Furthermore, since plastisol fusion is irreversible, once fusion has occurred the plastisol viscosity will decrease with a temperature increase irrespective of whether the temperature is above or below the original fusion point.
Referring again to FIG. 2, the position of the roll 26 should be such that the amount of laminate prewrap 30 puts enough heat into the laminate to place the plastisol on the upper side of the scrim into its gel state or at least very close thereto. Being closer to the drum, the plastisol on the lower side of the scrim will be at a higher temperature. Thus, due to the difference in temperatures, the layers of plastisols will have different viscosities and, since under pressure a fluid will principally flow in the direction of lowest viscosity, the pressure from first nip will cause plastisol penetration into the upper layers of wadding with but little penetration into the lower layers. Having the penetrating plastisol at above its gel point on entering the first nip minimizes the tendency of the laminate to spring" apart after release of the nip pressure. On the other hand, the prewarp should not be so great as to result in plastisol fusion since such could result in plastisol flow toward the lower wadding layers rather than the upper.
It is desirable that the nip pressure at the first nip be comparatively low, on the order of about 30-100 pli. and, generally, about -60 pli. To this end, a roll 26 having a soft cover is preferably employed. The use of a soft nip achieves a more uniform adhesive penetration and minimizes the danger of adhesive strike through and buildup on the roll 26. In this respect, it should be noted that on entering the first nip, the adhesive is generally at a low viscosity where a high-nip pressure could easily result in strike through.
In order to achieve the advantages of the present invention, the adhesive must be fused to the time at which the laminate enters the second nip formed between the roll 28 and the drum 24. Thus, the position of the roll 28 is coordinated with the temperature of the drum and the speed of the laminate in order to assure that such plastisol fusion occurs.
In accordance with the above discussion concerning the viscosity behavior of a fused plastisol, laminate passage through the second nip causes the plastisol to flow in the direction of the lower layers of cellulose wadding (i.e., the higher temperature direction) since, in the fused state, such is the direction of lower viscosity. Moreover, since the viscosity of the plastisol is higher at this stage of the process then when the laminate entered the first nip, the second nip should be a hard nip in order to drive the plastisol into the lower layers of wadding to about the same extent as it was forced into the upper layers of wadding by the first nip. For this nip, pressures on the order of about 150-500 pli. and, generally, about 250-400 pli, are useful.
As is apparent from the above discussion, the important aspect of the illustrated process resides in accomplishing the calendering operations in a manner so as to utilize the unusual viscosity-temperature characteristics of a plastisol adhesive. Thus, the position of the rolls 26 and 28 is not especially critical so long as the roll 26 is located at a position prior to plastisol fusion and the roll 28 is located at a position after the plastisol fusion. Simple experimentation can be used to appropriately position the rolls and establish nip pressures for given conditions of drum temperature and laminate speed. As an example, a laminate such as illustrated in FIG. 1 wherein the cellulose wadding webs are each about 10 g./yd sheets and the plastisol adhesive parts polyvinyl chloride resin, 50 parts dioctyl phthalate, 10 parts mineral spirits) is applied to each side of the scrim in an amount of about 5 g./yd. can be prepared under the following conditions (referring to FIG. 2): Drum 24=60 inches in diameter at 360 F.
Calender roll 26 =15 inches in diameter, Viton" rubber cover, nip pressure of 50 pli.
Prewrap 30=30 inches.
Calender 28=l 5 inches diameter, nylon cover, nip pressure of 300 pli.
Wrap between roll 26 and roll 28=l 20 inches.
Web speed=600 feet per minute.
While the invention has been illustrated above with respect to creped cellulose wadding, other materials such as webs of cotton or rayon fibers can also be used. The principal requirement of the web is that it be porous so as to permit adhesive penetration. Similarly, reinforcing means other than scrims are also useful and examples of such have been given in the opening paragraphs hereof. Moreover, the process described herein is useful for preparing laminates wherein no reinforcing means is present. In such a case, the adhesive is simply placed between the plies to be laminated and the process herein described carried out.
The basis weight of the webs employed herein is not particularly important so long as heat transfer can be achieved through the laminate at a reasonable rate. In general, the tissue webs will individually have a weight of about 7-25, and preferably about 9-15, g./yd. The reinforcing web generally has a weight of about 2.5-10, preferably about 3-6, g./yd.
I claim as my invention:
1. The process of preparing an adhesively bonded nonwoven structure containing at least two plies of porous webs comprising forming an unsecured laminate comprised of two porous webs with a plastisol adhesive placed there between, bringing the laminate into contact with a rotating heated drum at a temperature above the plastisols fusion point, subjecting the laminate to a first calendering while the plastisol is below its fusion point, maintaining laminate contact with the drum until plastisol fusion is achieved, and, while still in drum contact, subjecting the laminate to a second calendering, said calenderings being sufficient to effect the desired degree of plastisol penetration into the plies of porous webs.
2. The process of claim 1 wherein the laminate contains an inner reinforcing means.
3. The process of claim 2 wherein the reinforcing means is a scrim.
4. The process of claim 1 wherein the porous webs are of cellulose wadding and the laminate contains at least four plies of wadding.
5. The process of claim 4 wherein the laminate contains an inner reinforcing means.
6. The process of claim 5 wherein the reinforcing means is a scrim.
7. The process of claim 1 wherein the first calendering is soft and the second calendaring is hard.
8. The process of claim 7 wherein the porous webs are of cellulose wadding and the laminate contains at least four plies of wadding.
9. The process of claim 8 wherein the laminate contains a inner reinforcing means. 5
The process of claim 9 wherein the reinforcing means is a scrim.